Dissertations / Theses: 'Hematite'

1

Lu, Baiqing. "Surface Reactivity of Hematite Nanoparticles." Thesis, Umeå universitet, Kemiska institutionen, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-90523.

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2

Medeiros, Alleyrand Sergio Ramos. "Efeito do método de preparação nas propriedades catalíticas de óxidos de ferro contendo alumínio." reponame:Repositório Institucional da UFBA, 2011. http://www.repositorio.ufba.br/ri/handle/ri/11138.

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Foi estudado o efeito do método de preparação nas propriedades catalíticas de óxidos de ferro contendo potássio com o objetivo de obter sólidos eficientes para catalisar a desidrogenação do etilbenzeno em presença de vapor d´água, a principal rota comercial para a produção de estireno. Este monômero é um produto químico de alto valor comercial utilizado na manufatura de polímeros e resinas, entre outras aplicações. Devido à toxidez dos catalisadores comerciais, existe a necessidade de investigar sólidos alternativos. As amostras baseadas em óxido de ferro contendo alumínio (Fe/Al (molar)= 10), ou não, foram preparados por hidrólise de nitrato de ferro e de alumínio com hidróxido de potássio pela adição de soluções: (i) do agente precipitante sobre a solução dos sais metálicos; (ii) dos sais metálicos (separadas) sobre a solução de hidróxido de potássio; (iii) dos sais metálicos (misturadas) sobre a solução do agente precipitante; (iv) dos sais metálicos (misturadas) e da solução do agente precipitante sobre a água; (v) do nitrato de ferro e da solução de hidróxido de potássio sobre a água, seguida de impregnação do gel obtido com solução de nitrato de alumínio; (vi) do nitrato de ferro e da solução de hidróxido de potássio sobre a água, seguida da impregnação do gel com solução de nitrato de alumínio e (vii) do agente precipitante sobre a solução do sal de ferro, seguido da impregnação com solução de nitrato de alumínio. As amostras foram caracterizadas por análise química, espectroscopia de infravermelho com transformada de Fourier, medidas de área de superficial específica, difração de raios X, redução a temperatura programada e espectroscopia fotoeletrônica de raios X. Os catalisadores foram avaliados em um microreator de leito fixo, a 1 atm e 530 ° C, utilizando uma razão molar vapor d´água/ etilbenzeno de 10. Após a reação, os catalisadores foram caracterizados por medidas de área superficial específica e difração de raios-X. Em todos os casos, foi produzida hematita (-Fe2O3) e não foi detectada nenhuma fase contendo potássio ou alumínio. Observou-se que a ação do alumínio sobre a hematita depende amplamente do método de preparação. A área superficial específica pode variar, dependendo da forma de introdução de alumínio no sólido: ela pode aumentar ou diminuir, dependendo do emprego da impregnação ou da precipitação, respectivamente. A redutibilidade dos sólidos também varia com o alumínio, dependendo do método de preparação; a amostra mais redutível é obtida pela adição da solução de hidróxido de potássio sobre a solução de nitrato de ferro e de alumínio, enquanto a menos redutível é obtida pela adição dos reagentes sobre a água, na ausência de alumínio. O método de preparação também afeta a ação do alumínio sobre a atividade de hematita na desidrogenação do etilbenzeno em presença de vapor. Em geral, quando o alumínio é adicionado ao sólido por precipitação são obtidos catalisadores mais ativos, em relação ao método de impregnação. Em todos os casos, o papel de alumínio, bem como do método de preparação, em afetar a atividade catalítica está mais relacionado à atividade intrínseca do que à área superficial específica. Dentre os métodos estudados, aquele em que uma solução de hidróxido de potássio é adicionada a uma solução de nitrato de ferro e alumínio, produziu catalisadores mais ativos em presença ou não de alumínio. Estes materiais apresentaram elevado rendimento a estireno, mas também foram seletivos aos subprodutos. O catalisador mais promissor para a produção de estireno foi aquele preparado por adição de uma solução de nitrato de ferro e alumínio a uma solução de hidróxido de potássio. Este método produziu um catalisador que levou ao rendimento a estireno mais elevado, com baixa seletividade a benzeno e tolueno e alta estabilidade, alcançada após 5000 s de reação.
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3

Dang, Mei-Zhen. "Moessbauer study of synthetic hematite aggregates." Thesis, University of Ottawa (Canada), 1992. http://hdl.handle.net/10393/7942.

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Synthetic hematite aggregates that result from a process that may have industrial and environmental relevance are studied by Mossbauer spectroscopy at room temperature and liquid nitrogen temperature. The Mossbauer results are compared to measurements involving chemical analysis, scanning electron microscopy, and X-ray diffraction on the same samples. Factors such as the crystalline quality of the hematite and the overall sample purity (wt%Fe$\sb2$O$\sb3)$ are followed as functions of the known synthesis conditions. Pure bulk hematite (high quality $\alpha$-Fe$\sb2$O$\sb3$) serves as a reference throughout. Mossbauer spectroscopy is useful in two ways in this problem: (i) it can detect and identify iron-bearing impurities (i.e. non-hematite Fe-compounds), and (ii) it gives much detailed microscopic information on the intra-sample hematite. We find that all of the sulphur seen by chemical analysis probably resides in an iron-bearing compound which, most often, is probably a quenstetite-like material: Fe$\sb2$(SO$\sb4)\sb3\cdot$nH$\sb2$O (n = 9-11). The synthesis conditions are understood to determine both the hematite yield (or sample purity: wt%Fe$\sb2$O$\sb3$) and the intra-hematite crystalline quality, in that these two factors are correlated. Our interpretation of the room temperature Mossbauer spectra resolves coexisting bulk-like and high-defect-density regions whose relative amounts and sample-dependent Mossbauer characteristics can be quantified accurately. On going to liquid nitrogen temperature, a Morin transition is seen to have occurred in all regions of the most bulk-like samples, to have occurred in some regions of intermediate samples, or not to have occurred at all in the samples with the highest defect-density hematites. This illustrates the intricate interplay between microstructural details and cooperative magnetism in hematite materials.

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4

Helgeson, Maria Rose. "Fe(II)-catalyzed recrystallization of hematite." Thesis, University of Iowa, 2014. https://ir.uiowa.edu/etd/1466.

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Hematite (α-Fe2O3) is a common, naturally occurring iron oxide, found throughout the earth's crust and atmosphere. Hematite is of interest to the scientific community because it is able to incite a reaction that produces hydrogen gas (H2), which is a form of clean energy (Bora et al., 2013). The composition of hematite in nature is also used to make inferences about conditions on early earth's surface (Guo et al., 2013). Hematite is useful for clean energy production and as an environmental indicator partly because of its apparent stability. However, some evidence suggests that hematite might not be as stable as previously thought. Many iron oxides undergo Fe atom exchange when they come into contact with aqueous Fe(II), as often occurs in nature (Pedersen et al., 2005, Jones et al., 2009, Gorski et al., 2012, Handler et al., 2009). This atom exchange can result in elements and nutrients being taken up or released from the iron oxides as they recrystallize (Frierdich & Catalano, 2012, Cwiertny et al., 2008, Boland et al., 2014). Although atom exchange has not been directly shown in hematite, it has been demonstrated that trace metals are released from hematite in the presence of aqueous Fe(II), implying that exchange may be occurring (Frierdich et al., 2011). Here, we directly demonstrate Fe atom exchange between hematite and aqueous Fe(II). This work provides knowledge concerning the surface chemistry of hematite that has important implications for clean energy production and the environment.

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5

Silva, Caio Luis Santos. "Efeito do gadolínio nas propriedades catalíticas de óxidos de ferro na reação de WGS." reponame:Repositório Institucional da UFBA, 2012. http://www.repositorio.ufba.br/ri/handle/ri/11726.

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Devido à necessidade de garantir o suprimento de energia através de tecnologias de conversão de energia mais limpas e mais eficientes, reduzindo a emissão de gases causadores do efeito estufa, o interesse pela reação de deslocamento de monóxido de carbono com vapor d´água (WGSR, water gas shift reaction) tem aumentado, especialmente devido ao seu papel nas células a combustível. A fim de obter catalisadores alternativos para essa reação, foi estudado o efeito da adição e do teor de gadolínio nas propriedades de catalisadores de óxido de ferro. As amostras foram preparadas pela hidrólise de nitrato de ferro e de gadolínio, seguida da lavagem do gel com uma solução de acetato de amônio para obter magnetita e com água para obter hematita. As amostras foram caracterizadas por termogravimetria, calorimetria diferencial de varredura, espectroscopia no infravermelho com transformada de Fourier, difração de raios X, medida da área superficial específica (B.E.T.) e redução à temperatura programada. Os catalisadores foram avaliados na WGSR a 1 atm, na faixa de 250 a 400 ºC, usando uma razão molar vapor d´água/gás de processo (3,7% CO, 3,7% CO2, 22,2% H2, 70,4% N2) igual a 0,6. As fases hematita e ferrita de gadolínio foram detectadas em todos os sólidos lavados com água, enquanto magnetita e ferrita de gadolínio foram encontradas naqueles lavados com acetato de amônio. No primeiro caso, a área superficial específica aumentou devido ao gadolínio, independente do seu conteúdo, um fato que foi relacionado ao seu papel como espaçador e/ou a uma causa de tensões na rede, produzindo partículas menores. Entretanto, em todos os sólidos baseados em magnetita, o gadolínio conduziu a uma diminuição da área superficial específica, devido à predominância da perovskita (ferrita de gadolínio), que apresenta valores tipicamente baixos. A adição de gadolínio facilita a redução de espécies Fe3+, em todos os catalisadores, mas aumenta a atividade apenas naquelas aquecidas sob ar. O sólido com Gd/Fe=0,1, aquecido sob ar, mostrou a mais alta atividade, provavelmente devido à area superficial específica aumentada devido ao gadolínio, que também facilitou a redução do ferro, tornando o ciclo redox mais fácil durante a WGSR. Além disso, os catalisadores baseados em hematita mostraram as atividades mais elevadas. Isto pode ser atribuído à predominância de hematita nesses sólidos, quando comparados a outros nos quais a ferrita de gadolínio foi a fase predominante. Isto significa que as espécies Fe3+, no ambiente da hematita, são mais ativas na reação de WGS que as espécies Fe4+, no ambiente da perovskita
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6

Dunn, James Albert. "Single Molecule Characterization of Peptide/Hematite Binding." The Ohio State University, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=osu1494014864020062.

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7

Ghopry, Samar A. "Magnetic Properties of Hematite (α-Fe2O3) Nanorods." VCU Scholars Compass, 2014. http://scholarscompass.vcu.edu/etd/3662.

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At this study three samples of hematite nanorods were deposited on the silicon substrates with different varieties of glancing angle deposition techniques. One sample (S1) was prepared by using thermal deposition with partially ionized beam (PIB) and substrate rotation. The second sample (S2) was synthesized by using thermal deposition with PIB and no substrate rotation. The third sample (S3) was obtained by using E-beam deposition, PIB and rotating substrate. In addition, one sample of magnetite nanorods (S4) has been prepared in order to compare the magnetic properties of the two different iron oxides. S4 was prepared by using thermal deposition and fixed glancing angle deposition, but no PIB was applied. The hysteresis loop has been studied for all samples and the temperature dependent magnetic properties of one of the hematite samples and the magnetite been studied, too. The studies of the magnetic hysteresis for S1, S2, S3 and S4 showed that all of the samples have hysteresis loops but with dissimilar values of the saturation magnetization Ms, remanence MR, and coercivity HC. Furthermore, the hysteresis loops of all four samples showed different behaviors as the nanorods of the samples change the orientation with respect to the magnetic field. In addition to that fact, the hysteresis loop demonstrated that samples that have similar morphology have like behavior of the hysteresis loop. Also, it has found that S2 has the largest hysteresis loop of all hematite samples and it has large hysteresis loop in the perpendicular and parallel directions with the field as well. However, the magnetite hysteresis loops are significant larger than the ones of the hematite. Likewise, the studies of the temperature dependence magnetic properties of S2 and S4 showed that the ZFC and FC M-T curves of S1and S4 behaved differently when the direction of the nanorods changed from perpendicular to parallel with the field. In addition, the ZFC and FC M-T curves of hematite were different than the ZFC and FC M-T curves of magnetite.

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8

Kirwan, Luke J. "An investigation of polyacrylate adsorption onto hematite." Thesis, Curtin University, 2002. http://hdl.handle.net/20.500.11937/308.

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For the majority of tailings substrates, flocculant adsorption proceeds through hydrogen bonding of the amide functionalities with neutral surfaces. However, flocculation of Bayer process residue solids takes place in highly caustic liquors, typically using high molecular weight polyacrylates. This represents an almost unique situation, and implies a totally different adsorption mechanism. Direct examination of polyacrylate adsorption within the complex matrix of real liquors and a mixture of residue phases is difficult, making it necessary to focus on a model substrate (hematite) and synthetic liquors (pH 13 at high ionic strength). Previous spectral studies have used ex situ techniques, with sample drying potentially altering the adsorbed species, leading to inconclusive results. This study presents for the first time direct in situ evidence of polyacrylate adsorption onto hematite obtained by Fourier Transform Infrared-Attenuated Total Reflection (FTIR-ATR) Spectroscopy. Adsorption and hence concentration of dilute polyacrylate solutions onto hematite-coated zinc selenide optics has provided spectra of adsorbed polymer under a range of conditions, unbiased by any contribution from the bulk polymer solution. Analysis of the polyacrylate carbon-oxygen stretching frequencies established differing modes of adsorption at low and high pH conditions. At pH 2 adsorption proceeded through bidentate chelation of the carboxylate to a surface ferric ion, facilitated through deprotonation of a carboxylic acid group and removal of a hematite surface hydroxyl group, i.e. chemisorption. Unshifted carboxyl peaks in the spectrum enabled the unadsorbed 'loops' and 'tails' to be distinguished from the adsorbed polymer, and represented at least 70% of the total polymer chain length.In contrast, at pH 13 adsorption of polyacrylate occurs via physisorption and was only possible with the addition of electrolyte. This adsorption was enhanced with increasing electrolyte concentrations up to 1 M NaCl. The hematite surface charge was negative at high pH, however with increasing ionic strength the specific adsorption of Na+ ions decreased the negative surface charge, and at very high salt concentrations the surface became positively charged. For electrolyte with different monovalent cations, polymer adsorption increased in the order Li+ > Na+ > Cs+. The identity of the monovalent cation had no effect on the polymer solution dimensions but the ability to reduce the magnitude of the hematite surface charge followed the same trend. This finding is consistent with the 'structure making - structure breaking' model proposed by Berube and de Bruyn. At both high and low pH, polyacrylate exhibited adsorption isotherms that are best described by the Langmuir expression. Surface coverage was greatest at low pH due to more available surface sites and the adsorbed polymer conformation (a greater fraction of loops and tails). Adsorbed conformation and hence maximum adsorption was independent of molecular weight at low pH, however at high pH maximum adsorption increased with increased molecular weight, indicating an adsorbed polymer configuration exhibiting a greater degree of loops and tails. While the individual carboxylate-surface interaction was stronger at low pH than high pH, both were relatively weak. Despite this, none of the polymers could be removed by washing, demonstrating the strength and irreversibility of the multi-attached polymer molecules.The stronger individual carboxylate-surface interactions at low pH is indicative of a higher activation energy of formation, and may be a contributing factor to the slower rate of adsorption at low pH. The rate of polyacrylate adsorption was dominated by mass transport limitations in all cases. The initial rate of adsorption was greater at lower polymer molecular weight, consistent with the relative polymer diffusion coefficients. This rate of adsorption was much less dependent on polymer molecular weight at high pH than at low pH, suggesting significantly different polymer-solvent interactions. It was clearly demonstrated that the sodium ion concentration within the high ionic strength Bayer liquors is more than sufficient to facilitate polyacrylate adsorption on bauxite residue. There is no need to postulate calcium bridging between the polymer and surface, as has been suggested in previous studies. Improved settling and clarity associated with the presence of calcium on residue surfaces is more likely due to enhanced particle coagulation prior to flocculation. FTIR-ATR has been shown to be an excellent tool for the in situ examination of polyacrylate adsorption onto hematite, and will be a powerful technique for the characterisation and subsequent comparison of the adsorption behaviour of other systems.

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9

Kirwan, Luke J. "An investigation of polyacrylate adsorption onto hematite." Curtin University of Technology, Department of Applied Chemistry, 2002. http://espace.library.curtin.edu.au:80/R/?func=dbin-jump-full&object_id=13689.

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For the majority of tailings substrates, flocculant adsorption proceeds through hydrogen bonding of the amide functionalities with neutral surfaces. However, flocculation of Bayer process residue solids takes place in highly caustic liquors, typically using high molecular weight polyacrylates. This represents an almost unique situation, and implies a totally different adsorption mechanism. Direct examination of polyacrylate adsorption within the complex matrix of real liquors and a mixture of residue phases is difficult, making it necessary to focus on a model substrate (hematite) and synthetic liquors (pH 13 at high ionic strength). Previous spectral studies have used ex situ techniques, with sample drying potentially altering the adsorbed species, leading to inconclusive results. This study presents for the first time direct in situ evidence of polyacrylate adsorption onto hematite obtained by Fourier Transform Infrared-Attenuated Total Reflection (FTIR-ATR) Spectroscopy. Adsorption and hence concentration of dilute polyacrylate solutions onto hematite-coated zinc selenide optics has provided spectra of adsorbed polymer under a range of conditions, unbiased by any contribution from the bulk polymer solution. Analysis of the polyacrylate carbon-oxygen stretching frequencies established differing modes of adsorption at low and high pH conditions. At pH 2 adsorption proceeded through bidentate chelation of the carboxylate to a surface ferric ion, facilitated through deprotonation of a carboxylic acid group and removal of a hematite surface hydroxyl group, i.e. chemisorption. Unshifted carboxyl peaks in the spectrum enabled the unadsorbed 'loops' and 'tails' to be distinguished from the adsorbed polymer, and represented at least 70% of the total polymer chain length.
In contrast, at pH 13 adsorption of polyacrylate occurs via physisorption and was only possible with the addition of electrolyte. This adsorption was enhanced with increasing electrolyte concentrations up to 1 M NaCl. The hematite surface charge was negative at high pH, however with increasing ionic strength the specific adsorption of Na+ ions decreased the negative surface charge, and at very high salt concentrations the surface became positively charged. For electrolyte with different monovalent cations, polymer adsorption increased in the order Li+ > Na+ > Cs+. The identity of the monovalent cation had no effect on the polymer solution dimensions but the ability to reduce the magnitude of the hematite surface charge followed the same trend. This finding is consistent with the 'structure making - structure breaking' model proposed by Berube and de Bruyn. At both high and low pH, polyacrylate exhibited adsorption isotherms that are best described by the Langmuir expression. Surface coverage was greatest at low pH due to more available surface sites and the adsorbed polymer conformation (a greater fraction of loops and tails). Adsorbed conformation and hence maximum adsorption was independent of molecular weight at low pH, however at high pH maximum adsorption increased with increased molecular weight, indicating an adsorbed polymer configuration exhibiting a greater degree of loops and tails. While the individual carboxylate-surface interaction was stronger at low pH than high pH, both were relatively weak. Despite this, none of the polymers could be removed by washing, demonstrating the strength and irreversibility of the multi-attached polymer molecules.
The stronger individual carboxylate-surface interactions at low pH is indicative of a higher activation energy of formation, and may be a contributing factor to the slower rate of adsorption at low pH. The rate of polyacrylate adsorption was dominated by mass transport limitations in all cases. The initial rate of adsorption was greater at lower polymer molecular weight, consistent with the relative polymer diffusion coefficients. This rate of adsorption was much less dependent on polymer molecular weight at high pH than at low pH, suggesting significantly different polymer-solvent interactions. It was clearly demonstrated that the sodium ion concentration within the high ionic strength Bayer liquors is more than sufficient to facilitate polyacrylate adsorption on bauxite residue. There is no need to postulate calcium bridging between the polymer and surface, as has been suggested in previous studies. Improved settling and clarity associated with the presence of calcium on residue surfaces is more likely due to enhanced particle coagulation prior to flocculation. FTIR-ATR has been shown to be an excellent tool for the in situ examination of polyacrylate adsorption onto hematite, and will be a powerful technique for the characterisation and subsequent comparison of the adsorption behaviour of other systems.

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10

Santos, Manuela de Santana. "Efeito do lantânio nas propriedades de catalisadores de ferro para a produção de estireno." Instituto de Química, 2007. http://repositorio.ufba.br/ri/handle/ri/20530.

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Entre os intermediários utilizados na indústria petroquímica, o estireno é um dos mais importantes. Este monômero é empregado na produção de diferentes materiais poliméricos, sendo o poliestireno o mais importante. Desde 1930, a desidrogenação catalítica do etilbenzeno em presença de vapor d’água é mais importante via de produção de estireno. O catalisador clássico, baseado em óxido de ferro contendo potássio e cromo, entretanto, rapidamente desativa com o tempo, causando a necessidade de troca do catalisador a cada um ou dois anos. Como conseqüência, vários estudos estão sendo conduzidos com o intuito de descobrir dopantes alternativos que possam tornar o catalisador mais estável. Com esse objetivo, investigou-se neste trabalho, o efeito do lantânio e do método de preparação sobre as propriedades catalíticas da hematita. Amostras com diferentes razões molares ferro/lantânio (5, 10, 15 e 20) foram preparadas através do método sol-gel a partir de nitrato de lantânio, nitrato de ferro e hidróxido de amônio. Os catalisadores foram caracterizados por difração de raios X, medida de área superficial específica e redução à temperatura programada e avaliados na desidrogenação do etilbenzeno em presença de vapor d’água. Foi observado que as amostras mais ricas em lantânio (Fe/La = 5 e 10) se mostraram amorfas aos raios X, mas as outras eram formadas por hematita. Após a reação, detectou-se magnetita, em todas as amostras, hematita e um óxido de ferro e lantânio (FeLaO3). O lantânio evitou a sinterização dos sólidos, mas apenas nos catalisadores novos. Os catalisadores dopados com lantânio se mostraram mais ativos do que a hematita pura e este efeito aumentou com a quantidade de lantânio até o valor de Fe/La = 10; quantidades maiores desse dopante diminuiu a atividade. Esta melhoria do catalisador foi atribuída ao papel do lantânio em elevar a atividade intrínseca, assim como em estabilizar as espécies Fe+3, consideradas como a fase ativa. A fim de promover uma melhoria ainda maior desse catalisador, o efeito do tipo do agente precipitante foi também investigado, através da preparação de amostras com carbonato de sódio e potássio e hidróxido de sódio e potássio. Os catalisadores foram caracterizados pelas mesmas técnicas e também por espectroscopia fotoeletrônica de raios X e espectroscopia Mössbauer. O emprego de carbonato de sódio e potássio e hidróxido de sódio e potássio favoreceu a cristalização e a produção de sólidos com baixos valores de área superficial específica; a resistência contra redução aumentou. Também foi observado que sódio e potássio atuaram como promotores estruturais, sendo o potássio o mais eficiente, especialmente quando associado a espécies hidroxilas. O catalisador preparado com carbonato de potássio foi o mais ativo, um fato que foi atribuído à produção de ferrita de potássio na superfície das partículas, responsáveis pelo aumento da atividade dos sítios. O mais eficiente método de preparação desse sólido é a adição dos reagentes sobre a água; através da adição de carbonato de potássio aos nitratos de ferro e lantânio ou vice-versa foram obtidos catalisadores menos ativos. O catalisador foi mais ativo com conversão de 13% quando comparado a uma amostra comercial, que apresentou conversão de 9,0%, então é promissor para aplicação industrial
Among the intermediates used in petrochemical industry, styrene is by far one of the most important. This monomer is used for the production of different polymeric materials, the most important being polystyrene. Since 1930, the catalytic dehydrogenation of ethylbenzene in the presence of steam is the most important route for styrene production. The classical catalyst, based on iron oxide containing potassium and chromium, however, fastly deactivates with time, causing the need of replacing the catalyst each one or two years. As a consequence, several studies have been carried out in recent years aiming to get alternative dopants which could make the catalysts more stable. With this goal in mind, the effect of lanthanum and of the preparation method on the catalytic properties of hematite was investigated in this work. Samples with different iron to lanthanum molar ratio (5, 10, 15 and 20) were prepared by sol-gel method from lanthanum nitrate, iron nitrate and ammonium hydroxide. The catalysts were characterized by X-ray diffraction, specific surface area measurements and temperature programmed reduction and evaluated in the dehydrogenation of ethylbenzene in the presence of steam. It was found that the samples richest in lanthanum (Fe/La = 5 and 10) were amorphous to X-ray but the other were made off hematite. After reaction, magnetite, hematite and an iron and lanthanum oxide (FeLaO3) were detected in all the samples. Lanthanum avoided sintering but only for the fresh catalysts. The lanthanum-doped catalysts were more active than pure hematite and this effect increased with lanthanum amount up to Fe/La = 10; higher amounts of this dopant decreased the activity. This improvement of the catalysts was assigned to the role of lanthanum in increasing the intrinsic activity as well as in stabilizing the Fe+3 species, wich are supposed to be the active phase. In order to improve this catalyst even more, the effect of the kind of the precipitant agent was also investigated, by preparing samples with sodium and potassium carbonate and sodium and potassium hydroxide. The catalysts were characterized by the same techniques and also by X-ray photoelectron spectroscopy and Mossabuer spectroscopy. The use of sodium and potassium carbonate and hydroxide makes the crystallization easier and favors the production of solids with low specific surface areas; the resistance against reduction increased. It was also found that sodium and potassium were structural promoters, being potassium the most effective one, especially when associated with hydroxide species. The catalyst prepared with potassium carbonate was the most active one and this was assigned to the production of potassium ferrite on the particle surface, responsible for the increase of active of the sites. The most efficient way to prepare this solid is by adding all reagents to water; by adding potassium carbonate to the iron and lanthanum nitrate or vice-versa less active catalysts were produced. The catalyst was more active (13% of conversion) when compared to the commercial sample which showed 9% of conversion and thus is promising for industrial applications.

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11

Cheng, Terry Chi-Ming 1968. "Production of hematite in acidic zinc sulphate media." Thesis, McGill University, 2002. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=38169.

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In this work, the kinetic and equilibrium profiles of each individual reaction step involved in the production of hematite at 200°C via oxydrolysis of ferrous sulphate in concentrated zinc sulphate media were established. Crystallization of ferrous sulphate was found to play a crucial role in the overall process due to its relatively low solubility and fast crystallization kinetics at elevated temperatures. In fact, the overall kinetics of the oxydrolysis process were found to be limited by the re-dissolution of ferrous sulphate. Pre-crystallization of ferrous sulphate prior to oxidation was found to result in enhanced overall kinetics, cutting down the required retention time from 3 to 2 hours. Enhanced kinetics were also achieved by performing oxydrolysis in two-temperature stages: a low temperature (T = 180°C) first stage with retention time >20 min and an elevated temperature (T = 200°C) second stage with retention time >100 min.
The typical composition of the hematite material produced in this work was 64.3% Fe, 1.3% S (as SO4), 0.6% Zn, and 4.6% H2O. The sulphur content was found to be predominantly (0.6--0.8%) due to formation of sodium jarosite with the remaining (0.3--0.5%) attributed to SO4 chemisorption, and (to less extent) basic ferric sulphate formation. In the absence of zinc sulphate, the majority of sulphate contamination was due to basic ferric sulphate formation. Hematite was found to form via a predominantly homogeneous nucleation mechanism with sub-micron crystallites clustered together as aggregates of 5--10 mum size and around 7 m 2/g specific surface area. In contrast, hematite produced by direct hydrolysis of ferric sulphate possessed one order of magnitude higher specific surface area. As for the industrial hematite product, its composition was found to be 52.6% Fe, 4.6% S, 1.0% Zn, and 8.8% H2O. The sulphur contamination in the industrial product was mainly due to co-precipitation of jarosite and basic ferric sulphate compounds. Hydrothermal trans-formation of the industrial hematite product at elevated temperatures (>200°C) and retention time of >60 min with solids loading as high as 16 wt.% proved to be effective in reducing the sulphur content to less than 1%.

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12

OLIVERA, CARLOS ALBERTO CASTANEDA. "BIOFLOTATION OF HEMATITE USING THE BACTERIA: RHODOCOCCUS ERYTHROPOLIS." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2014. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=25131@1.

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PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO
CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO
A crescente demanda mundial por matérias-primas minerais levou ao aumento da exploração mineral e paralelamente novas pesquisas estão sendo dirigidas para a produção de novos reagentes de flotação, a fim de que estes apresentem maior seletividade e não sejam agressivos ao meio ambiente. Nesta pesquisa teve-se como objetivo estudar os aspectos fundamentais da bioflotação da hematita, avaliando a cepa bacteriana Rhodococcus erythropolis como biocoletor. Entre os estudos efetuados estão análises química para determinar as proteínas e carboidratos presentes no concentrado bacteriano, estabelecendo-se que é constituída por macromoléculas com características anfipáticas. O balanço entre grupos catiônicos e aniônicos da bactéria atribui um ponto isoelétrico (PIE) equivalente de 2,2. O perfil de potencial zeta da amostra mineral de hematita após interação com a bactéria mostrou uma mudança, onde o PIE mudou de 5,3 para 2,1. Para o estudo dos ensaios de adesão e microflotação, a amostra foi condicionada com a biomassa por meio de agitação sob condições específicas, tais como os tamanho de partícula, a concentração de biomassa, o pH da solução e tempo de condicionamento. A adesão da biomassa na superfície do mineral foi maior em pH 2 e na concentração de 200 mg / L. Os testes de microflotação foram feitos num tubo de Hallimond e foi avaliado a formação de espuma para uma concentração bacteriana de 200 mg / L, onde foi observado que a tensão superficial da solução aumenta à medida que o pH se torna básico. Das três faixas granulométricas utilizadas, a maior flotabilidade (83.86 por cento) foi alcançada na fração granulométrica (53 - 38 um), num pH 6 e com um tempo de flotação de 10 min. A bioflotação do mineral hematita segue o modelo cinético de segunda ordem, observou-se que as constantes de taxa (K2) da flotação do mineral aumentam com reduções de tamanho de partícula, mudando de 0,16369 (g.min)(-1) para 0,51604 (g.min)(-1) quando o tamanho de particula passou de (150 - 106 um) para (53 - 38 um). Os resultados apresentados mostram que o estudo do comportamento da cepa bacteriana Rhodococcus erythropolis como bioreagente na flotação de hematita foi viável, demonstrando o seu potencial uso como bioreagente coletor de mineral hematita, e assim projetando-se para uma futura aplicação na indústria da flotação mineral.
The growing world demand for raw minerals has led to the increased mineral exploration and at the same time new research is being directed toward the production of new flotation reagents, so that they present higher selectivity and they are environmentally friendly. This research aimed to study the fundamental aspects of bioflotation of hematite, evaluating the bacterial strain Rhodococcus erythropolis as biocollector. Among the studies are conducted chemical analyzes to determine the proteins and carbohydrates present in the bacterial concentrate, it was established that is composed of macromolecules with amphipathic characteristics. The balance between cationic and anionic groups of the bacteria assigns an equivalent isoelectric point (IEP) of 2.2. The profile of zeta potential of the sample of hematite mineral after interaction with the bacteria showed a change, where the IEP has changed from 5.3 to 2.1. To study the adhesion and microflotation assays, the mineral sample was conditioned with the biomass by stirring under specific conditions, such as the particle sizes, biomass concentration, the pH of the solution and conditioning time. The biomass adhesion on mineral surface was higher at pH 2 and at the concentration of 200 mg / L. The microflotation tests were carried out in Hallimond tube and was evaluated the foam formation to a bacterial concentration of 200 mg / L, which was observed that the surface tension of the solution increases as the pH becomes basic. Of the three granulometric fractions used, the greatest floatability (83.86 percent) was achieved in the granulometric fraction (53 - 38 um), at pH 6 and with a flotation time of 10 min. The hematite mineral bioflotation follows the second-order kinetic model, was observed rate constant (K2) of the mineral flotation increase with reductions of particle size, moving from 0,16369 (g.min)(-1) for 0,51604 (g.min)(-1) when the particle size changed from (150 - 106 um) to (53 - 38 um). The results presented show that the study of the behavior of the bacterial 10 strain Rhodococcus erythropolis as bioreagent in the flotation of hematite was feasible, demonstrating its potential use as collector bioreagent of mineral hematite, and so projecting into a future application in the mineral flotation industry.

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13

Madden, Andrew Stephen. "Nanoscience Meets Geochemistry: Size-Dependent Reactivity of Hematite." Diss., Virginia Tech, 2005. http://hdl.handle.net/10919/28033.

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Recent studies have demonstrated that nanoscale crystalline iron oxide minerals are common in natural systems. The discipline of nanoscience suggests that these particles in the size range of approximately 1-50 nm will have properties that deviate from the bulk properties of the same material and that these properties will change as a function of particle size. This study begins to fill the void of corresponding experimental investigations that apply the principles of nanoscience to the geochemical reactivity of nanominerals. The rate of Mn²⁺(aq) oxidation on hematite with average diameters of 7.3 nm and 37 nm was measured in the presence of O₂(aq). In the pH range of 7-8, the surface area normalized rate was one to two orders of magnitude greater on the 7.3 nm average diameter particles. Based on the application of electron transfer theory, it is hypothesized that the particles with diameters less than approximately 10 nm have surface crystal chemical environments which distort the symmetry of the MnMn²⁺ surface complex, reducing the energy required to reorganize the coordinated ligands after oxidation to Mn³⁺. Cu²⁺, an analog for Mn³⁺, was used to probe for the presence and nature of the proposed changes in surface structure. Cu²⁺ and Mn³⁺ show similar electronic structure changes in response to the surrounding crystal field due to their d-electron configurations and Jahn-Teller coordinative distortions. Batch sorption experiments on hematite nanoparticles revealed a shift in the pH-dependent adsorption of Cu²⁺(aq). Specifically, an affinity sequence of 7 nm > 25 nm = 88 nm was determined based on the shift of the 7 nm sorption edge to approximately 0.8 pH units lower than that for the 25 nm and 88 nm samples. These data support the hypothesis that unique binding sites exist on the 7 nm nanoparticles that are not significantly present on the larger particles. The National Nanotechnology Initiative stresses the need to address the broader societal impacts of nanoscale research. This dissertation embraces this viewpoint through the development and inclusion of "Nano2Earth: Introducing Nanotechnology Through Investigations of Groundwater," a curriculum which combines nanoscience with the Earth sciences for high school students.
Ph. D.

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Sadat, Nabi S. Hasan. "Microscopic origin of magnetism in the Hematite-Ilmenite system." Diss., lmu, 2010. http://nbn-resolving.de/urn:nbn:de:bvb:19-117570.

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15

Bose, Saumyaditya. "Bioreduction of Hematite Nanoparticles by Shewanella oneidensis MR-1." Diss., Virginia Tech, 2006. http://hdl.handle.net/10919/30189.

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A dissertation is presented on the bioreduction of hematite (α-Fe2O3) nanoparticles. The study shows that an alternative extracellular electron transfer mechanism other than the classical 'direct-contact' mechanism may be simultaneously employed by Shewanella oneidensis MR-1 during solid-phase metal reduction. This conclusion is supported by analysis of the bioreduction kinetics of hematite nanoparticles coupled with microscopic investigations of cell-mineral interactions. The reduction kinetics of metal-oxide nanoparticles were examined to determine how S. oneidensis utilizes these environmentally-relevant solid-phase electron acceptors. Nanoparticles involved in geochemical reactions show different properties relative to larger particles of the same phase, and their reactivity is predicted to change as a function of size. To demonstrate these size-dependent effects, the surface area normalized reduction rates of hematite nanoparticles by S. oneidensis MR-1 with lactate as the sole electron donor were measured. As evident from whole cell TEM analysis, the mode of nanoparticle adhesion to cells is different between the more aggregated, pseudo-hexagonal to irregular shaped 11 nm, 12 nm, 99 nm and the less aggregated 30 nm and 43 nm rhombohedral particles. The 11 nm, 12 nm and 99 nm particles show less cell contact and coverage than the 30 nm and 43 nm particles but still show significant rates of reduction. This leads to the provisional speculation that S. oneidensis MR-1 employs a pathway of indirect electron transfer in conjunction with the direct-contact pathway, and the relative importance of the mechanism employed depends upon aggregation level and the shape of the particles or crystal faces exposed. In accord with the proposed increase in electronic band-gap for hematite nanoparticles, the smallest particles (11 nm) exhibit one order of magnitude decrease in reduction when compared with larger (99 nm) particles, and the 12 nm rates fall in between these two. This effect may also be due to the passivation of the mineral and cell surfaces by Fe(II), or decreasing solubility due to decrease in size.
Ph. D.

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16

Von, Rudorff Guido Falk. "Structure and dynamics of the hematite/liquid water interface." Thesis, University College London (University of London), 2017. http://discovery.ucl.ac.uk/1574700/.

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The hematite/liquid water interface is of interest for a wide range of applications. This work investigates structural and dynamic properties of the interface for several experimentally relevant combinations of crystal cuts, termination and protonation schemes. To this end, molecular dynamics simulations at hybrid functional DFT level have been performed for both neutral and charged systems. For bulk hematite, this work shows that the commonly used GGA+U level of theory gives good results for geometric properties, but cannot capture electronic structure equally well. However, a modified hybrid functional based on HSE06 is able to describe both geometric and electronic properties with sufficient accuracy. The two most common crystal surfaces and their most common terminations have been investigated and compared to experiment where possible. The resulting structural information is in good agreement with experiment, but highlights the importance of dynamic equilibria for the solvation structure. This work also shows that classical force fields cannot readily describe the surface protonation structure and dynamics. Besides an atomistic view of the surface structure, protonation dynamics, surface restructuring mechanisms and interconversion of surface aquo groups to bulk solvent are discussed. Two new methods are suggested in this work: (i) a screening method for Hartree-Fock exchange forces that significantly accelerates hybrid functional-based molecular dynamics calculation and (ii) a guided thermodynamic integration scheme for free energy estimation from short trajectories. The implementation thereof is tested and benchmarked and applied to the hematite/liquid water interface. To accelerate the calculation of HFX forces in a molecular dynamics force screening scheme is proposed. For actual systems of interest, this can speed up the whole molecular dynamics run by a factor of three. The method is assessed on a wide range of materials and for various properties including energy conservation. Finally, the pKa value of a surface protonation is calculated. By means of thermodynamic integration, the free energy difference between a proton at the surface of hematite and a solvated proton in bulk water is quantified. Various integration schemes are evaluated and a new analysis method is proposed to reduce human bias in the analysis and to automatically detect convergence of the vertical energy gap time series.

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Pinto, Thiago César de Souza. "Modelagem da velocidade crítica de transporte de polpas minerais contendo partículas grossas." Universidade de São Paulo, 2012. http://www.teses.usp.br/teses/disponiveis/3/3134/tde-16102012-113925/.

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O dimensionamento de sistemas de transporte hidráulico de polpas minerais exige especial atenção à medida que partículas grossas apresentam um comportamento de sedimentação no interior dos tubos. Dentro desta situação, a velocidade de transporte da polpa mineral deve ter magnitude suficiente para suspender e transportar os sólidos, evitando que os mesmos se depositem na base da tubulação. O bombeamento de polpas minerais em tubos horizontais contendo partículas grossas constituiu o objeto desta tese. Um levantamento sobre a literatura corrente foi realizado e, através de procedimentos experimentais, obteve-se um banco de dados para o modelamento da velocidade crítica (VC), isto é, a velocidade mínima em que ocorre a formação de um leito móvel na base do tubo, apresentando magnitude ligeiramente superior à velocidade de deposição VD, caracterizada pelo início da deposição das partículas na base dos dutos. Para a realização dos ensaios, foram construídas duas unidades experimentais de bombeamento de polpa mineral, onde foram estudadas as seguintes variáveis: i) gradiente de pressão por metro de tubo horizontal (\'delta\'P/L), ii) velocidade média do fluxo (V), iii) perfil de concentração de sólidos ao longo da seção transversal, iv) fator de forma através da função de esfericidade das partículas (\'psi\'), v) densidade do sólido e do líquido, vi) concentração volumétrica dapolpa mineral, vii) granulometria dos sólidos e viii) diâmetro da tubulação. A primeira unidade experimental foi montada com tubulação em PVC transparente de diâmetro interno de 25,4mm e a segunda unidade foi construída em PVC branco com um trecho de 2m em acrílico transparente, apresentando diâmetro interno de 50,8mm. A velocidade critica (VC) para cada condição estudada foi determinada visualmente, através das seções transparentes da tubulação. As amostras utilizadas neste trabalho foram: concentrados de apatita e hematita e o mineral quartzo. As frações granulométricas estudadas foram inseridas em duas classes de tamanho, sendo a primeira classe passante em 297µm e retida em 249µm e a segunda classe passante em 149µm e retida em 105µm. Os resultados permitiram determinar um novo modelo semiempírico para VC, alcançando desvios menores que 10% para as velocidades preditas em relação aos valores de velocidades observadas experimentalmente.
The design of hydraulic systems of slurry transport demands a special attention due to coarse particles present a settling behavior inside the pipes. In this situation, the transport velocity should have order of magnitude sufficient to promote the suspension and the transport of particles, avoiding the solids deposition at the bottom of pipe. The transport of mineral slurries containing coarse particles was the primary goal of the thesis. A survey of the available literature was done and through the experimental tests could be possible to raise a data bank in order to develop a new best fit correlation for the critical velocity (VC) which included the particle shape effect, through the sphericity function. VC could be defined as the minimum velocity where a moving bed of particles takes place at the bottom of the horizontal pipe and it is slightly above the deposition velocity VD, which could be characterized by a bed of stationary particles at the bottom of pipe. The research was conducted using two recirculating pipe test rigs with transparent PVC pipe of 25.4mm and 50.8mm internal diameter with slurry concentrations from 8% up to 27% by volume. The material used was apatite and hematite concentrates and quartz mineral, clustered in two classes of size range (-0.297+0.210mm; -0.149+0.105mm), where the variables were: i) Head losses per meter of horizontal pipe (\'delta\'P/L), ii) Mean transport velocity (V), iii) solids distribution profile, iv) particle shape effect, through the sphericity function (\'psi\'), v) density of particles and liquid, vi) Volumetric concentration of slurries, vii) particles size and viii) pipe diameter. The critical velocity (VC), for each studied condition, was visually determined through the transparent sections of the pipes. The results have yielded a new semi empirical model to predict the critical velocity, yielding a deviation of less than 10% from the observed values of experimental data for VC.

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Molaei, Aysan. "Effect Of Carbonate Alkalinity On The Flocculation Behavior Of Hematite." Master's thesis, METU, 2012. http://etd.lib.metu.edu.tr/upload/12614506/index.pdf.

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As high grade iron ore deposits are rapidly depleted, the minerals industry is increasingly obliged to enrich their ores and process lower grade iron ores. Production of large quantities of fine ores as tailings or by-products in mining operations and mineral liberation at fine particle sizes have led to the development of concentration methods employed to fine ores. Selective flocculation is one of the beneficial methods which can be used in recovering of very fine particles It is obvious that process water chemistry has a significant influence on the flocculation efficiency, and the water chemistry is deeply affected by carbon dioxide dissolution. Carbonate content of natural waters regulated by CO2, carbonicacid and solid carbonatesis known as &lsquo
carbonate alkalinity&rsquo
whichmay be an important factor in flocculation especially at alkaline pH. Selective flocculation of iron ores is usually run at around pH 11 where carbonate alkalinity could be rather high. There have been no reports in literature regarding the effect of carbonate alkalinity on the flocculation behavior of iron oxides, mainly hematite. In this study, the flocculation behavior of iron ores with starch under different alkalinities has been investigated. The extent of flocculation has been assessed by settling rate and suspended solid content measurements at different starch doses and pH values. Zeta potential measurements and starch adsorption studies were carried out to explain these effects by carbonate alkalinity. According to the results, flocculation is enhanced by addition of low amount of carbonate alkalinity, less than 2.4 mEq/L. However, adding the higher amount of alkalinity adversely affected the flocculation of hematite. Similar behavior was also observed during the starch adsorption tests, larger amount of starch wasadsorbed by hematite in low alkalinity compared to high alkalinity. Zeta potential measurements indicate that, by increasing the carbonate alkalinity of suspension, zeta potential values of solids will become more negativeleading to an increase in the stability of suspension and then adversely affecting flocculation. Therefore, as carbonate alkalinity has a significant effect on the flocculation of hematite, it should be seriously taken into account to optimize the selective flocculation of hematite ores.

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PUELLES, JHONATAN GERARDO SOTO. "HEMATITE FLOTATION USING A CRUDE BIOSURFACTANT EXTRACTED FROM RHODOCOCCUS OPACUS." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2016. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=29688@1.

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PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO
COORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIOR
FUNDAÇÃO DE APOIO À PESQUISA DO ESTADO DO RIO DE JANEIRO
PROGRAMA DE SUPORTE À PÓS-GRADUAÇÃO DE INSTS. DE ENSINO
BOLSA NOTA 10
A bioflotação é definida como um processo de separação, através do qual o mineral de interesse é flotado ou deprimido seletivamente, utilizando os reagentes de origem biológica, também conhecidos como bioreagentes. Estas substâncias são caracterizadas por possuírem uma química verde, seletividade e potencial para tratar a partículas finas. Neste sentido, o objetivo principal da pesquisa é a avaliação de um biosurfactante não refinado extraído da bactéria Rhodococcus opacus na flotação de hematita. Na primeira fase, foi desenvolvido um protocolo para a extração dos biosurfactantes intracelulares e aqueles associados a parede celular da bactéria. Mediante extração com etanol a 121 graus celsius e 2 atm, as substâncias anfifílicas foram liberadas e solubilizadas. A recuperação média de biosurfactante não refinado foi de 0,3 g por dm cubico. A caracterização por FTIR identificou grupos álcool (menos OH), cetona (C igual O) e cadeias de carbono saturadas e insaturadas. Que podem compor os mycolatas e trehalolipideos que são encontrados na parede celular da bacteria. Por estudos eletroforéticos encontrou-se umPIE de 7,5 e um PZC em torno de 7,6. Aplicando o modelo Gouy-Chapman e o modelo misto de Gouy Chapman e o capacitor de placas, foi possível estudar o efeito do biosurfactante no comportamento eletrostático das partículas de hematita. Predizendo como elas foram se tornando hidrofóbicas em valores de pH ácido e como sua flotabilidade diminuía em pH básicos, após interação com o biosurfactante. Finalmente, foi testado o biosurfactante e a própria bactéria em ensaios de microflotação de hematita, resultando o primeiro na melhora na flotabilidade de hematita. Os resultados mostraram uma boa afinidade e baixo consumo de reagente.
Bioflotation is defined as a separation process by which the mineral of interest is floated or depressed selectively, using reagents of biologic origin also known as bioreagents. These substances are characterized by their green chemistry, selectivity and potential to treat fine particles. Currently they are been studied with the expectative of substitute the synthetic reagents used in the mineral flotation processes. Between the diverse microorganisms, the hydrophobic bacteria Rhodococcus opacus has been studied as biofrother and biocollector in hematite flotation. In that sense, the research s principal objective is the assessment of the hematite floatability using a crude biosurfactant extracted from the bacteria Rhodococcus opacus and consequently determine its potential as an alternative against synthetic reagents or the bacteria itself. In a first stage, it was developed a protocol for the extraction of cell associated and intracellular biosurfactants from the bacteria. Throughout ethanol extraction at 121 degrees centigrade and 2 atm, the cell associated substances where released and solubilized. The average crude biosurfactant recovery was around 0.3 g per L of broth. Characterization by FTIR identified alcohol (minus OH) and ketone (C equal O) groups as well as saturated and unsaturated carbon chains. Which may compose the mycolates and trehalolopids that are found in the cellular wall of the genera Rhodococci. Electrophoretic studies of the hematite sample, before BS interaction, found an IEP around a pH of 7.5 and a PZC at pH 7.6. Applying the Guoy-Chapman model and the mixed model of Guoy Chapman and the plate capacitor, it was possible to study the effect of the biosurfactant onto the electrostatic behavior of the hematite particles. The model predicted the hydrophobicity of the modified hematite at acid pH. Finally it was tested the crude biosurfactant against the bacteria itself in microflotation tests, resulting the first one in an improved hematite floatability. The results showed a high affinity of the crude biosurfactant for hematite particles and relatively low reagent consumption.

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20

Rodriguez, Raúl D. "Dynamic atomic force microscopy on hematite nanoparticules : beyond topographic measurements." Paris 6, 2008. http://www.theses.fr/2008PA066505.

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In this thesis, atomic force microscopy studies in Tapping Mode have been performed on a system composed of hematite nanoparticles deposed on either a MoS2 (molybdenite) or SiO2 (silice) substrate. The nature of nanoparticles facets was determined combining both atomic force microscopy and transmission electron microscopy. Later on, this nanoparticles and substrates were used as a model system to deduce material properties of a SiO2 surface using force spectroscopy. From the determination of interactions between the AFM tip and the SiO2 surface, the Hamaker constant was deduced. Contact interactions as a function of humidity were evidenced which confirmed the hydrophobic character of hematite nanoparticles
Dans cette thèse, des études de microscopie à force atomique en mode tapping ont été effectuées sur un système de nano-particules d'hématites sur substrat de MoS2 (molybdénite) ou de SiO2 (silice). La nature des facettes des nano-particules a été déterminée en combinant à la microscopie à force atomique la microscopie électronique en transmission. Ensuite ces nano-particules et leurs substrats ont été utilisées comme système modèle pour sonder comment interroger les propriétés de surface par spectroscopie et microscopie à force atomique, au-delà de la simple information de topographie, à partir de la détermination des interactions entre la pointe d'AFM et la surface des échantillons. Les interactions de Van der Waals à longue distance et la constante de Hamaker ont été déterminées. Les interactions de contact en présence et en absence d'humidité ont été mises en évidence, menant, entre autres, à la détermination du caractère hydrophobe des nano-particules

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21

Pendlebury, Stephanie R. "Charge carrier dynamics in hematite photoanodes for solar water oxidation." Thesis, Imperial College London, 2012. http://hdl.handle.net/10044/1/9952.

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Although the field of solar water splitting is now forty years old, in recent years there has been an upsurge of research in this area, with the aim of using sunlight to produce hydrogen cheaply and efficiently. Hematite (α-Fe2O3) is of particular interest as a photoanode material for solar water splitting, due to its optimum band gap (2.0-2.2 eV) and visible light absorption and stability. Various modifications – including nanostructuring and doping – have been investigated as routes to improved efficiencies, thought to be limited by long visible light absorption depths, low charge carrier mobilities and slow hole-transfer kinetics. Additionally, an anodic applied bias is required for water oxidation to occur on hematite. Improved understanding of the role of applied bias and the processes limiting the performance of hematite photoanodes will lead to more directed routes to photoanode architectures with increased efficiencies. This Thesis describes the results of transient absorption spectroscopy studies, in conjunction with photoelectrochemical measurements, of hematite photoanodes. Transient absorption spectroscopy on microsecond-second timescales allows direct monitoring of the recombination, trapping and reaction of photogenerated holes, both in isolated hematite films, and in photoanodes in a fully functional photoelectrochemical cell. Transient photocurrent measurements probe electron extraction from the photoanode on microsecond-millisecond timescales. The charge carrier dynamics are found to be strongly dependent on the electron density, which is controlled by applied electrical bias. The photocurrent generated is found to correlate with the population of long-lived holes, determined by the kinetics of electron-hole recombination. Generally, effects which lower electron density result in retarded electron-hole recombination kinetics, increasing the population of long-lived holes and hence increasing the photocurrent. Following an introduction and review of the literature, the first results chapter reports that the effect of a positive applied bias is to retard the otherwise dominant electron-hole recombination, increasing the lifetime of photogenerated holes such that water oxidation can occur. The relative timescales of recombination, electron extraction and water oxidation as a function of applied bias are discussed in the following chapter, in conjunction with the results of excitation density studies. The third results chapter compares the charge carrier dynamics in photoanodes with different nanomorphologies. The fourth results chapter discusses the effect of an energetic trap state on charge carrier dynamics, while the effects of surface treatment with cobalt, which is shown to retard recombination at low applied bias, is reported in the final results chapter. Overall conclusions are drawn and the implications of these for photoelectrode design are discussed.

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22

OLIVARES, LESLIE YASMIN LÓPEZ. "FUNDAMENTAL ASPECTS OF HEMATITE FLOTATION USING THE BACTERIAL STRAIN RHODOCOCCUS RUBER." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2014. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=25500@1.

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PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO
COORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIOR
PROGRAMA DE SUPORTE À PÓS-GRADUAÇÃO DE INSTS. DE ENSINO
Nos últimos anos, vários estudos têm sido realizados na aplicação dos microrganismos na biotecnologia mineral, atuando como coletores, depressores ou espumantes amigáveis com o meio ambiente, e induzindo propriedades hidrofóbicas, uma vez que eles podem-se aderir seletivamente sobre a superfície do mineral. O objetivo deste trabalho é estudar e avaliar o comportamento da cepa Rhodococcus ruber com a hematita. Entre os estudos efetuados estão à adesão microbiana à superfície mineral, medida do potencial zeta e análise no infravermelho antes a após interação do biorreagente com a hematita, assim como o estudo dos ensaios de microflotação. A amostra foi condicionada com a suspensão de biomassa por meio de agitação sob condições específicas, tais como tamanho das partículas, concentração da biomassa, pH da solução e tempo de condicionamento. Os resultados mostraram uma mudança no perfil do potencial zeta da hematita após interação com a R.ruber, e sua adesão na superfície do mineral foi maior ao redor do pH 3, e na concentração de 0.60g.L(-1) (10(9) células). Estudos de flotação foram realizados na célula de flotação modificada Partridge-Smith de 0.23L, e a maior valor de flotabilidade (84 por cento) foi atingido na fração menos 53 mais 38 um. Estudos complementários de flotabilidade foram realizados utilizando o espumante comercial Flotanol D24 combinado com a biomassa R.ruber, encontrando resultados interessantes em função do tamanho de partícula. Assim esta pesquisa visa avaliar a eficiência da bioflotação de minerais, particularmente da hematita, e do uso potencial do Rhodococcus ruber como biocoletor, projetando-se a uma futura aplicação na indústria da flotação mineral.
In the recent years, research has been developed in the application of microorganisms in mineral technology, acting as environmental friendly collectors, depressors and/or frothers and inducing hydrophobic properties, since they can be selectively adhere onto the surface of the mineral. This research work deals with the fundamental aspects of hematite flotation using the bacterial strain Rhodococcus ruber. The aim of this research was to study and evaluate the behavior of Rhodococcus ruber strain before and after interaction with hematite particles. The sample was conditioned with the biomass suspension by stirring under specific conditions such as particle size, biomass concentration, pH solution and conditioning time. Among the studies conducted are the microbial adhesion to the mineral surface, zeta potential measurements and analysis of infrared spectra before and after interaction of Rhodococcus ruber with hematite, as well as microflotation studies. The results showed a change in hematite zeta potential profile after interaction with Rhodococcus ruber, and its adhesion onto the mineral surface was higher at pH 3 and at concentration of 0.60 g.L(-1) (10(9) cells). Flotation studies were carried out in a 0.23L modified Partridge-Smith flotation cell, and the highest floatability (84 percent) was achieved at size fraction any less 53 more 38 um. Also, floatability studies were performed using frother Flotanol D24 combined with the Rhodococcus ruber biomass, concluding with interesting results in function of the particle size range. This work aims to evaluate the efficiency of bioflotation of minerals, particularly hematite, and the potential use of Rhodococcus ruber as biocollector, projecting its future application in mineral flotation industry.

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23

Cooke, David J. "Atomistic simulation of segregation to the surfaces of hematite and goethite." Thesis, University of Bath, 2003. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.760832.

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24

Forster, M. "Time-resolved spectroscopic studies of hematite photoelectrodes for photoelectrochemical water splitting." Thesis, University of Liverpool, 2017. http://livrepository.liverpool.ac.uk/3009951/.

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Harnessing the large quantities of energy delivered to the earth by the sun is one of the most promising routes to a clean, inexhaustible energy supply. However, the diurnal nature of sunlight and its variation in intensity around the globe necessitates an efficient means of storing (and transporting) solar energy on a large scale. The production of solar fuels provides a potential solution by capturing and storing solar energy in the form of chemical bonds to yield fuels which can then be stored, transported and used, as and when required. The majority of the work in this thesis focuses on the development of the metal oxide semiconductor, α-Fe2O3 (hematite), and its application as a photoelectrode in photoelectrochemical (PEC) water splitting systems. α-Fe2O3 is a promising photoelectrode material due to its suitable bandgap, low toxicity, stability, abundance and low cost. However, current α-Fe2O3 materials are well below the maximum theoretical efficiency due to limiting factors including: poor conductivity, short electron–hole lifetimes, slow oxygen evolution reaction kinetics and short hole diffusion length (2–4 nm). Modifications to α-Fe2O3 such as doping, nanostructuring and surface treatments are known to significantly improve activity and it is vitally important that the mechanisms of improvement are fully rationalised. The work presented here uses transient absorption spectroscopy (TAS) and electrochemical measurements to probe the charge carrier dynamics and address the activity of a range of recently developed α-Fe2O3 photoelectrodes, including oxygen deficient hematite and acid treated hematite. The presence of trap states in α-Fe2O3 photoelectrodes is also addressed, and the effect surface treatments have on such trap states are explored. Finally, shell isolated nanoparticles for enhanced Raman spectroscopy (SHINERS) is explored as an in situ technique for probing the mechanism of water oxidation on a metal oxide surface.

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Hwang, Yu Sik. "Adsorption Of Naturally-Occurring Dicarboxylic Acids At The Hematite/Water Interface." The Ohio State University, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=osu1226256959.

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26

Alrobei, Hussein. "Synthesis and Characterization of Alpha-Hematite Nanomaterials for Water-Splitting Applications." Scholar Commons, 2018. https://scholarcommons.usf.edu/etd/7661.

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The recent momentum in energy research has simplified converting solar to electrical energy through photoelectrochemical (PEC) cells. There are numerous benefits to these PEC cells, such as the inexpensive fabrication of thin film, reduction in absorption loss (due to transparent electrolyte), and a substantial increase in the energy conversion efficiency. Alpha-hematite ([U+F061]-Fe2O3) has received considerable attention as a photoanode for water-splitting applications in photoelectrochemical (PEC) devices. The alpha-hematite ([U+F061]-Fe2O3) nanomaterial is attractive due to its bandgap of 2.1eV allowing it to absorb visible light. Other benefits of [U+F061]-Fe2O3 include low cost, chemical stability and availability in nature, and excellent photoelectrochemical (PEC) properties to split water into hydrogen and oxygen. However, [U+F061]-Fe2O3 suffers from low conductivity, slow surface kinetics, and low carrier diffusion that causes degradation of PEC device performance. The low carrier diffusion of [U+F061]-hematite is related to higher resistivity, slow surface kinetics, low electron mobility, and higher electro-hole combinations. All the drawbacks of [U+F061]-Fe2O3, such as low carrier mobility and electronic diffusion properties, can be enhanced by doping, which forms the nanocomposite and nanostructure films. In this study, all nanomaterials were synthesized utilizing the sol-gel technique and investigated using Scanning Electron Microscopy (SEM), X-ray Diffractometer (XRD), UV-Visible Spectrophotometer (UV-Vis), Fourier Transform Infrared Spectroscopy (FTIR), Raman techniques, Particle Analyzer, Cyclic Voltammetry (CV), and Chronoamperometry, respectively. The surface morphology is studied by SEM. X-Ray diffractometer (XRD) is used to identify the crystalline phase and to estimate the crystalline size. FTIR is used to identify the chemical bonds as well as functional groups in the compound. A UV-Vis absorption spectral study may assist in understanding electronic structure of the optical band gap of the material. Cyclic voltammetry and chronoamperometry were used to estimate the diffusion coefficient and study electrochemical activities at the electrode/electrolyte interface. In this investigation, the [U+F061]-Fe2O3 was doped with various materials such as metal oxide (aluminum, Al), dichalcogenide (molybdenum disulfide, MoS2), and co-catalyst (titanium dioxide, TiO2). By doping or composite formation with different percentage ratios (0.5, 10, 20, 30) of aluminum (Al) containing [U+F061]-Fe2O3, the mobility and carrier diffusion properties of [U+F061]-hematite ([U+F061]-Fe2O3) can be enhanced. The new composite, Al-[U+F061]-Fe2O3, improved charge transport properties through strain introduction in the lattice structure, thus increasing light absorption. The increase of Al contents in [U+F061]-Fe2O3 shows clustering due to the denser formation of the Al-[U+F061]-Fe2O3 particle. The presence of aluminum causes the change in structural and optical and morphological properties of Al-[U+F061]-Fe2O3 more than the properties of the [U+F061]-Fe2O3 photocatalyst. There is a marked variation in the bandgap from 2.1 to 2.4 eV. The structure of the composite formation Al-[U+F061]-Fe2O3, due to a high percentage of Al, shows a rhombohedra structure. The photocurrent (35 A/cm2) clearly distinguishes the enhanced hydrogen production of the Al-[U+F061]-Fe2O3 based photocatalyst. This work has been conducted with several percentages (0.1, 0.2, 0.5, 1, 2, 5) of molybdenum disulfide (MoS2) that has shown enhanced photocatalytic activity due to its bonding, chemical composition, and nanoparticle growth on the graphene films. The MoS2 material has a bandgap of 1.8 eV that works in visible light, responding as a photocatalyst. The photocurrent and electrode/electrolyte interface of MoS2-[U+F061]-Fe2O3 nanocomposite films were investigated using electrochemical techniques. The MoS2 material could help to play a central role in charge transfer with its slow recombination of electron-hole pairs created due to photo-energy with the charge transfer rate between surface and electrons. The bandgap of the MoS2 doped [U+F061]-Fe2O3 nanocomposite has been estimated to be vary from 1.94 to 2.17 eV. The nanocomposite MoS2-[U+F061]-Fe2O3 films confirmed to be rhombohedral structure with a lower band gap than Al-[U+F061]-Fe2O3 nanomaterial. The nanocomposite MoS2-[U+F061]-Fe2O3 films revealed a more enhanced photocurrent (180 μA/cm2) than pristine [U+F061]-Fe2O3 and other transition metal doped Al-[U+F061]-Fe2O3 nanostructured films. The p-n configuration has been used because MoS2 can remove the holes from the n-type semiconductor by making a p-n configuration. The photoelectrochemical properties of the p-n configuration of MoS2-α-Fe2O3 as the n-type and ND-RRPHTh as the p-type deposited on both n-type silicon and FTO-coated glass plates. The p-n photoelectrochemical cell is stable and allows for eliminating the photo-corrosion process. Nanomaterial-based electrodes [U+F061]-Fe2O3-MoS2 and ND-RRPHTh have shown an improved hydrogen release compared to [U+F061]-Fe2O3, Al-[U+F061]-Fe2O3 and MoS2-[U+F061]-Fe2O3 nanostructured films in PEC cells. By using p-n configuration, the chronoamperometry results showed that 1% MoS2 in MoS2-[U+F061]-Fe2O3 nanocomposite can be a suitable structure to obtain a higher photocurrent density. The photoelectrochemical properties of the p-n configuration of MoS2-α-Fe2O3 as n-type and ND-RRPHTh as p-type showed 3-4 times higher (450 A/cm2) in current density and energy conversion efficiencies than parent electrode materials in an electrolyte of 1M of NaOH in PEC cells. Titanium dioxide (TiO2) is known as one of the most explored electrode materials due to its physical and chemical stability in aqueous materials and its non-toxicity. TiO2 has been investigated because of the low cost for the fabrication of photoelectrochemical stability and inexpensive material. Incorporation of various percentages (2.5, 5, 16, 25, 50) of TiO2 in Fe2O3 could achieve better efficiencies as the photoanode by enhancing the electron concentration and low combination rate, and both materials can have a wide range of wavelength which could absorb light in both UV and visible spectrum ranges. TiO2 doped with [U+F061]-Fe2O3 film was shown as increasing contacting area with the electrolyte, reducing e-h recombination and shift light absorption along with visible region. The [U+F061]-Fe2O3-TiO2 nanomaterial has shown a more enhanced photocurrent (800 μA/cm2) than metal doped [U+F061]-Fe2O3 photoelectrochemical devices.

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DELCOMPARE, RODRÍGUEZ PAOLA ANDREA. "A theoretical investigation of ultrathin space charge layers in hematite photoelectrodes." Doctoral thesis, Università degli Studi di Trieste, 2022. http://hdl.handle.net/11368/3014973.

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Many efforts have been devoted to understand the hematite-electrolyte interface due to its potential application in the photoelectrocatalytic oxidation of water. This interface usually extends over lengths ranging from tens of nanometers to micrometers under water splitting conditions, therefore its realistic simulation via ab-initio calculations has been considered challenging. However, recent experiments measured space charge layers smaller ~10 Angstroms in highly doped nanostructured hematite photoanodes, which also displayed high photocurrent densities in water splitting experiments. We used a set of continuous equations based on the Poisson-Boltzmann distribution and the Stern model to investigate under which experimental conditions the space charge layer in hematite becomes ultrathin. In this regime, a considerable fraction of the potential drop across the interface is located in the Helmholtz layer, therefore we reported corrections to the Mott-Schottky equation that should be taken into account under these conditions. Using the continuous equations, we also examined the effect of the macroscopic properties provided by experiments on the microscopic state of the interface: we got access to the width of the space charge layer and the distribution of the electrostatic potential across the interface a function of the experimental conditions. We then used density functional theory (DFT) to get an atomistic insight of the space charge layer in the semiconductor, in systems ranging from the pristine stoichiometric surface, a surface with adsorbed hydroxyls, to Ti-doped slabs with doping densities of the order of ~10^{21} cm^{-3}. According to our analysis, space charge layers around 10 Angstroms must have been present also in other water splitting experiments with some of highest photocurrents registered. We observed that at high doping densities the inverse of the square of the capacitance should have a quadratic behavior close to flat-band conditions and a sub-linear behavior due to square-root-like corrections far from the flat-band potential. We used density functional theory to compute the band bending of the proposed atomistic models. The pristine stoichiometric and the hydroxylated undoped surfaces displayed band bendings of ~0.14 eV and ~0.49 eV, respectively. In the doped case, we found band bendings of ~0.07 eV and ~0.01 eV for the pristine and OH-terminated slabs, respectively. The latter band bendings corresponded to space charge layers extending in the sub-nanometer regime, according to the continuous equations. In the presence of doping, we found a qualitative and quantitative correspondence between the results provided by density functional and the continuous model. Contrary to the common picture of the electrochemical interface of a semiconductor and an electrolyte in water splitting experiments, where large space charge layers are present, the latter results give an insight of an unexpected regime of high photoelectrocatalytic efficiency in ultrathin space charge layers. Which in principle, are amenable to quantum mechanical ab-initio simulations. In this work we were able to describe the space charge layer of thin hematite slabs using DFT at an atomistic level.
Many efforts have been devoted to understand the hematite-electrolyte interface due to its potential application in the photoelectrocatalytic oxidation of water. This interface usually extends over lengths ranging from tens of nanometers to micrometers under water splitting conditions, therefore its realistic simulation via ab-initio calculations has been considered challenging. However, recent experiments measured space charge layers smaller ~10 Angstroms in highly doped nanostructured hematite photoanodes, which also displayed high photocurrent densities in water splitting experiments. We used a set of continuous equations based on the Poisson-Boltzmann distribution and the Stern model to investigate under which experimental conditions the space charge layer in hematite becomes ultrathin. In this regime, a considerable fraction of the potential drop across the interface is located in the Helmholtz layer, therefore we reported corrections to the Mott-Schottky equation that should be taken into account under these conditions. Using the continuous equations, we also examined the effect of the macroscopic properties provided by experiments on the microscopic state of the interface: we got access to the width of the space charge layer and the distribution of the electrostatic potential across the interface a function of the experimental conditions. We then used density functional theory (DFT) to get an atomistic insight of the space charge layer in the semiconductor, in systems ranging from the pristine stoichiometric surface, a surface with adsorbed hydroxyls, to Ti-doped slabs with doping densities of the order of ~10^{21} cm^{-3}. According to our analysis, space charge layers around 10 Angstroms must have been present also in other water splitting experiments with some of highest photocurrents registered. We observed that at high doping densities the inverse of the square of the capacitance should have a quadratic behavior close to flat-band conditions and a sub-linear behavior due to square-root-like corrections far from the flat-band potential. We used density functional theory to compute the band bending of the proposed atomistic models. The pristine stoichiometric and the hydroxylated undoped surfaces displayed band bendings of ~0.14 eV and ~0.49 eV, respectively. In the doped case, we found band bendings of ~0.07 eV and ~0.01 eV for the pristine and OH-terminated slabs, respectively. The latter band bendings corresponded to space charge layers extending in the sub-nanometer regime, according to the continuous equations. In the presence of doping, we found a qualitative and quantitative correspondence between the results provided by density functional and the continuous model. Contrary to the common picture of the electrochemical interface of a semiconductor and an electrolyte in water splitting experiments, where large space charge layers are present, the latter results give an insight of an unexpected regime of high photoelectrocatalytic efficiency in ultrathin space charge layers. Which in principle, are amenable to quantum mechanical ab-initio simulations. In this work we were able to describe the space charge layer of thin hematite slabs using DFT at an atomistic level.

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28

DALLE, CARBONARE Nicola. "Surface and interface modification of nanostructured hematite for solar water splitting." Doctoral thesis, Università degli studi di Ferrara, 2016. http://hdl.handle.net/11392/2403264.

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La possibilità di produrre idrogeno dalla scissione fotoindotta dell’acqua imitando ciò che la natura fa in ogni istante attraverso la fotosintesi, senza la necessità quindi di utilizzare alcuna fonte aggiuntiva di energia esterna, ha suscitato enorme interesse nella comunità scientifica, stimolata dal sogno di poter sviluppare una società che utilizzi idrogeno come fonte energetica primaria. Negli ultimi quattro decenni abbiamo assistito ad una straordinaria accelerazione nella razionalizzazione delle proprietà chimico-fisiche di materiali semiconduttori su cui si basano sistemi foto-elettrochimici adibiti alla conversione della luce solare in energia chimica e non in corrente elettrica da utilizzare istantaneamente, come nei comuni dispositivi fotovoltaici. Sin dai primi esperimenti di fotolisi, gli ossidi metallici sono stati i protagonisti di tali dispostivi, grazie alla loro eccellente stabilità in soluzioni acquose e alla possibilità di ottenere facilmente morfologie nano-strutturate che hanno garantito un notevole incremento in termini di assorbimento della radiazione luminosa e di capacità catalitiche nei confronti delle reazioni di riduzione ed ossidazione dell’acqua. Nel corso del mio Dottorato di Ricerca ho studiato le dinamiche di trasferimento di carica di elettrodi di ossido ferrico modificati con strutture sia amorfe che cristalline a base di ferro utilizzando, per la caratterizzazione, principalmente tecniche elettrochimiche sia in corrente continua che alternata, affiancate da spettroscopie di superficie e laser per una completa descrizione delle proprietà catalitiche. L’ossido ferrico è un materiale notoriamente impiegato per la foto-ossidazione dell’acqua, anche se la sua scarsa capacità di condurre e trasferire carica richiedono l’applicazione di un potenziale esterno. Utilizzando materiali non nocivi ed economici e semplici procedure in soluzione per la preparazione dei campioni e per le successive modifiche, siamo stati in grado di migliorare le prestazioni degli elettrodi sia in termini di foto-correnti generate che di stabilità, razionalizzando al contempo aspetti meccanicistici coinvolti nei processi di trasferimento di carica responsabili dell’ossidazione dell’acqua.
Inspired by nature and pursuing the concrete option of an economy based on hydrogen as a fuel for the everyday energetic consumption, scientists from different fields have based their research activity on the possibility to decompose water in its elementary constituents using only sunlight as external energy supply. In the last four decades there has been an exciting growth of knowledge about semiconductor physico chemical properties with regard to their leading role in photo-electrochemical (PEC) device able to convert light into chemical energy stored in the bond between hydrogen atoms, in a more elegant and powerful way with respect to conventional photovoltaic technology. Metal oxides have been from the beginning the most examined materials for PEC application due to their great stability in aqueous solution and to the easy access to various nanostructured morphologies that guarantee good optical and catalytic properties. During my PhD I have investigated the charge transfer dynamics in hematite (α-Fe2O3) thin film electrodes modified with iron oxide-based structures by using mainly both AC/DC electrochemical techniques in combination with laser photolysis and spectroscopy for the morphological characterization. Hematite is a well known semiconductor able to drive the bias-assisted water oxidation reaction at its surface, although important drawbacks related to its poor charge transport properties have limited the overall efficiency achieved so far. Using cheap and environmentally safe starting materials and solution-based procedure for all the preparative and modification steps, we have been able to efficiently modify mesoporous iron oxide films achieving excellent performances in term of photocurrent generation and stability. Mechanistic and kinetic insights about the effect of an iron-based water oxidation catalyst and of a thin underlayer are fundamental to a deeper understanding of the photogenerated carriers fate for a more useful design of these electrodes. Besides electrochemical performance, the possibility to obtain efficient devices with common and simple procedures is a key point for a future and concrete implementation of this technology for a large scale application.

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Rioult, Maxime. "Hematite-based epitaxial thin films as photoanodes for solar water splitting." Palaiseau, Ecole polytechnique, 2015. https://theses.hal.science/tel-01220396/document.

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Utiliser l'hydrogène en tant que vecteur énergétique pour stocker l'énergie solaire et/ou remplacer le pétrole comme carburant est très attrayant, d'autant qu'il peut être produit de façon propre par photo-électrolyse de l'eau. Dans ce procédé, des paires électron-trou, générées par éclairement dans des semi-conducteurs immergés dans une solution aqueuse, réalisent les réactions d’oxydo-réduction de l’eau (production d'oxygène à la photo-anode et production d'hydrogène à la photo-cathode). Les oxydes de métaux de transition, en particulier l'hématite (α-Fe2O3) qui présente un gap quasi-idéal pour cette application, sont les matériaux de photo-anode les plus prometteurs. Des films minces d'hématite ont été déposés sur des monocristaux par épitaxie par jets moléculaires assistée par plasma d’oxygène. Ces échantillons modèles ainsi que l’utilisation de techniques de pointe, notamment utilisant le rayonnement synchrotron, rendent possible l’identification des paramètres pertinents influençant les propriétés de photo-électrolyse. Je me suis d'abord intéressé à l'impact de la structure cristallographique, de la stœchiométrie et de la morphologie de surface. Ensuite, les effets d'un dopage avec du titane ont été analysés, montrant l'existence d'un taux de dopage optimal et l'augmentation de la longueur de diffusion des porteurs de charges induisant un fort gain en photo-courant. J'ai également étudié la structure électronique et la dynamique des recombinaisons en surface d'hétérojonctions TiO2 - hématite dopée Ti, révélant une interface diffuse. Enfin, le champ électrique interne créé par un film mince ferroélectrique de BaTiO3/Nb:SrTiO3 a été considéré pour améliorer les propriétés des photo-anodes. Un premier pas vers la compréhension du lien entre polarisation ferroélectrique et photo-courant a été fait, mettant en évidence un champ électrique interne favorable pour séparer les charges
Using hydrogen as an energy carrier for solar energy storage and/or fuel alternative to oil is very appealing, especially as it can be cleanly produced by solar water splitting. In this process, electron-hole pairs, generated in illuminated semiconductors dipped in an aqueous solution, realize the water oxidoreduction reactions (oxygen production at the photoanode and hydrogen production at the photocathode). Transition metal oxides, in particular hematite (α-Fe2O3) which features a quasi ideal band-gap for this application, are the most promising photoanodes materials. Hematite thin films were deposited on single crystals by oxygen plasma assisted molecular beam epitaxy. These model samples along with the use of high-end techniques, in particular using synchrotron radiation, make possible the identification of the relevant parameters affecting the photoelectrochemical properties. I firstly focused on the impact of the crystallographic structure, the stoichiometry and the surface morphology. Then the effects of doping with titanium were investigated, demonstrating the existence of an optimal doping level and an increase of the charges diffusion length inducing a high photocurrent gain. In addition, I studied the electronic structure and the surface recombinations dynamics of TiO2 - Ti-doped hematite heterojunctions, revealing a diffuse interface. Lastly, the internal electric field created by a ferroelectric thin film of BaTiO3/Nb:SrTiO3 was considered in order to enhance the performances of photoanodes. A first step toward the comprehension of the link between ferroelectric polarization and photocurrent was achieved through the evidence of an internal electric field favourable for the separation of charges

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Melo, Edilailsa Janu?rio de. "Hematitas nanoparticuladas como fotocatalisadores potenciais para degrada??o qu?mica de contaminantes org?nicos em meio aquoso e a produ??o de hidrog?nio por fragmenta??o molecular da ?gua e da am?nia." UFVJM, 2017. http://acervo.ufvjm.edu.br/jspui/handle/1/1371.

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Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior (CAPES)
O desenvolvimento de novos semicondutores fotocatalisadores, em particular os ativos na produ??o de hidrog?nio por fragmenta??o molecular da ?gua e da am?nia (presente no lixiviado de biodigestores ou de aterros sanit?rios e em efluentes industriais), tem dominado a ordem priorit?ria de interesse nas tecnologias avan?adas para a gera??o de energia limpa. Este trabalho teve como objetivo principal avaliar a produ??o fotocatalisada de hidrog?nio gasoso, a partir da fragmenta??o molecular da ?gua ou da am?nia, por uso da hematita pura ou da hematita dopada com os c?tions met?licos cobalto, n?quel, cobre e zinco como materiais semicondutores. Os materiais preparados por coprecipita??o foram caracterizados pelas t?cnicas de EDX, MEV, DRX, espectroscopia M?ssbauer, FTIR, BET e XPS. A taxa da produ??o de hidrog?nio foi avaliada por medidas de densidade da corrente gerada pelo H2(g) evolu?do da fragmenta??o molecular da ?gua ou da am?nia, em c?lula fotoeletroqu?mica (PEC). Foram tamb?m realizados testes fotocatal?ticos, sob luz vis?vel, com as hematitas, pura e com dopantes, como fotocatalisadores para degrada??o do corante ?ndigo de carmim, utilizado como mol?cula modelo, simulando a decomposi??o de substrato org?nico poluente em ?gua presente em efluentes industriais. Os resultados dos testes de degrada??o do corante mostraram que as hematitas dopadas com cobre e zinco tiveram relativamente alta atividade na degrada??o do corante; os melhores resultados foram obtidos com a hematita com zinco. Na evolu??o do hidrog?nio da fotocat?lise da ?gua, a dopagem com c?tions met?licos n?o alterou significativamente a atividade fotoeletroqu?mica da hematita. Ainda assim, a amostra de hematita dopada com n?quel foi a que apresentou um discreto aumento da densidade de corrente, maior propor??o de hidrog?nio gasoso produzido, sob radia??o com comprimento de onda maior do que 450 nm. A densidade de corrente gerada da degrada??o da am?nia foi maior, se comparada ? fragmenta??o da ?gua. No entanto, a dopagem tamb?m n?o alterou de forma significativa a atividade PEC dos materiais. Das amostras de hematitas dopadas, a com cobre foi a que apresentou os melhores resultados fotoeletroqu?micos, ainda que abaixo da efici?ncia fotoeletroqu?mica da hematita pura.
Disserta??o (Mestrado) ? Programa de P?s-gradua??o em Biocombust?veis, Universidade Federal dos Vales do Jequitinhonha e Mucuri, 2017.
Technological developments of semiconductors to be used as photocatalysts for hydrogen production and for the degradation of organic pollutants in water in different circumstances, such as ammonia sluggishness from biodigesters and organic residues from industrial effluents, are strongly challenging the interest of the scientific community. The main objective of this work was to evaluate the molecular hydrogen production from the molecular fragmentation of water and ammonia using pure hematite and cobalt, nickel copper and zinc dopant prepared as co-precipitators as semiconductor materials. The materials prepared were characterized by EDX, MEV, XRD, M?ssbauer, FTIR, BET and XPS spectroscopy. The evaluation of the hydrogen production was carried out through measurements of current densities generated by the decomposition of water and ammonia in a photoelectrochemical cell (PEC). Photocatalytic tests were also carried out under visible light using pure hematite and with dopants as photocatalysts for the degradation of carmine indigo dye used as a model molecule. The results of the dye degradation tests showed that copper and zinc doped hematite increased dye degradation, and the best results were obtained for zinc hematite. In the evolution of hydrogen from water, the doping with metallic cations did not significantly alter photoelectrochemical activity of hematite, the hematite with nickel was the sample that presented a small increase in current density when in the presence of light. The current density generated by the ammonia degradation and consequent hydrogen production was higher when compared to water, however, doping also did not significantly alter the PEC activity of the materials, comparing the materials, the hematite with copper was the sample that presented the best results.

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Teixeira, Gabriel Kolbe. "Caracterização mineralógica do Caulim : aplicação em perfis dos depósitos do Rio Capim (PA)." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2014. http://hdl.handle.net/10183/128019.

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O caulim do Rio Capim na Amazônia Oriental se constitui num depósito importante para o Brasil, ocupando lugar de destaque na produção mundial desta matéria prima mineral. Os modelos estabelecem uma origem para a caulinita vinculada ao intemperismo em condições lateríticas (Paleogeno Inferior) a partir de um substrato formado por rochas sedimentares da Formação Ipixuna (Cretáceo Superior). No perfil, destacam-se em ordem de importância entre os compostos de ferro, a hematita e a goethita, minerais pouco estudados no caulim do Rio Capim. A partir dos fácies principais do caulim (fácies caulim macio na base e caulim duro no topo), foram separados e concentrados os minerais de interesse para estudos de detalhe, utilizando a difratometria de raios X (DRX) e a espectrometria de infravermelho por transformada de Fourier (FTIR). Entre os parâmetros determinados, obtiveram-se estimativas da dimensão, forma, área superficial e substituição isomórfica. A interpretação dos resultados evidencia o potencial de aplicação das informações na estimativa do comportamento destes minerais durante o processo de beneficiamento e para a discussão do modelo genético dos perfis de caulim. As goethitas e hematitas de ambos os fácies possuem propriedades muito semelhantes, reforçando o modelo que especula sobre uma origem comum para a fácies caulim macio e caulim duro do perfil. Entre as propriedades, destacam-se a elevada cristalinidade e a baixa participação do alumínio em sua composição, proporcionando a estes minerais um comportamento com resistência moderada a elevada nos processos de lixiviação ácida e a tendência de dissolução preferencial da hematita. O conjunto de características dos óxidos e oxihidróxidos de ferro são compatíveis com uma formação em ambientes hidromórficos, com baixa influência da matéria orgânica a partir de soluções com baixa atividade do ferro, moderadamente redutoras a fracamente ácidas. Dentro do modelo genético da formação do caulim, sua origem não está associada à zona de laterização do perfil, sendo compatível com um ambiente saprolítico e hidromórfico. As propriedades observadas permitem afirmar que os processos naturais que favoreceram a formação da caulinita na base do manto de alteração foram suficientemente longos e intensos para promover a retirada do ferro destas fácies num processo não dissociado no tempo. No modelo, o caulim é uma fácies da base do perfil formado abaixo do nível freático de um espesso perfil laterítico em condições moderadamente redutoras e ácidas com elevada atividade do Si e do Al, porém, com carência de Al disponível para a formação da hematita e da goethita. Neste ambiente, haveria uma lenta mobilização do Fe dentro do perfil sem a necessidade do estabelecimento de um evento excepcional com uma elevada atividade da matéria orgânica, como previsto em alguns modelos.
The Rio Capim Kaolin from the eastern Amazon is recognized as one of the largest deposits of Brazil with a quality and volume that place this area amongst the most important deposits in the world. Despite the importance and the significant amount of studies about kaolin, many questions remain unanswered and the genesis of this occurrence is not well understood. Perhaps, the consensus today is the acceptance of the Rio Capim kaolin origin to be related to a lateritic weathering process during the Early Paleogene, period with favorable geotectonic, duration and climatic conditions to originate a thick cover with the development of a complete weathering profile above a substrate composed by sedimentary rocks of the Ipixuna Formation (Cretaceous). The models consider kaolin to be a bottom facies of a thick lateritic profile, but nowadays the upper lateritic facies was destroyed (probably by erosion periods along the middle to upper Paleogene). The kaolin profile has two facies: the bottom one, which is called soft kaolin, and the upper, differentiated one forming the flint kaolin. Most controversial points are related to the way that the flint kaolin was formed and the mechanism in which the iron was mobilized from the kaolin profile as a whole. This study aims to get some insight about the Rio Capim kaolin development using some properties measured from the iron oxides and oxyhydroxides. The iron and titanium minerals from the kaolin represent the most important contaminants, and a large effort is made by the industry to eliminate their influence but, despite this negative reputation, those minerals also represent a source of valuable information about the environmental conditions of the profile. Among them, hematite is the most widespread in the entire kaolin profile, followed by goethite, whose importance increases in the direction of the flint kaolin facies. Representative samples of kaolin facies were selected from the kaolin profile and submitted to an approach that allowed concentrating the iron minerals and eliminating the influence of kaolinite. Using X-ray diffraction (XRD) and Fourier Transform Infrared (FTIR), a set of properties of the hematite and goethite were determined, including median crystal dimensions, shapes, specific surface area and mineral composition by estimating the isomorphous replacement of iron (Fe) by aluminum (Al). The results show that hematites and goethites do not have enough differences in their properties to support a genesis model with radical changes in their conditions . In terms of behavior to acid leaching, the observed variations were important to predict differences in the rate of mineral dissolution and possibilities of preferential dissolution of hematite in relation to goethite, promoting the increase of the yellow component with the leaching. Both hematite and goethite have high crystallinity and the isomorphous replacement of Fe by Al is low. Comparing the properties observed in synthetic and natural environments, the hematite and goethite from the Rio Capim kaolin profile have characteristics that relate these minerals to a formation environment in hydromorphic conditions where the influence of organic matter was low, with low iron activity, weakly reduced and acidic conditions. These conditions are found in a saprolitic domain in accordance with the bottom facies of a thick laterite profile. Despite agreeing with a laterite model, differences make it difficult to explain iron depletion by organic matter only (Pirabas Event) and the origin of flint kaolin facies by a subsequent and superimposed laterite period. With the hematite and goethite properties found in this study, it is possible to propose that the Rio Capim kaolin is the bottom facies of a laterite profile formed in the zone permanently below the water table. Contrasting with the upper laterite portion of the profile, the bottom zone is in hydromorphic conditions and allowed the fixation of Al and Si to form kaolinite by primary feldspar and mica minerals of the Ipixuna Formation. This environment promotes the slow depletion of iron without the need of an exceptional accumulation of organic matter. The flint kaolin facies was formed in the same period of the soft kaolin facies and the observed differences in the kaolinite morphology are only related to changes caused by the location of this facies in the intermediate zone characterized by the water table fluctuation, but again without the need of subsequent superimposed lateritic processes.

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Noerpel, Matthew Robet. "Surface Complexes Of Lead And Organic Acids At The Hematite / Water Interface." The Ohio State University, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=osu1439904226.

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Cots, Ainhoa. "Development of hematite and cupric oxide photoelectrodes for water splitting tandem cells." Doctoral thesis, Universidad de Alicante, 2019. http://hdl.handle.net/10045/110620.

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Since the beginning of the Industrial Revolution, the global energy consumption has been continuously increasing, supplied mainly by coal, oil and natural gases. Unfortunately, this consumption is linked to the emission of greenhouse gasses such as CO2 to the atmosphere. For this reason, it is extremely important to look for sustainable and renewable energy sources in order to replace the commonly used fossil fuels. Within the different types of renewable energy sources, solar energy holds by far the largest potential capacity. In this respect, artificial photosynthesis is a promising technology not only to harvest solar energy, but also as a means of storage by producing energy-rich chemical fuels such as H2 from water. The main components of photoelectrochemical water splitting devices are the semiconductor light absorber photoelectrodes and the electrolyte. Chapter 1 reviews the fundamental aspects of photoelectrochemical water splitting and overviews the physics and electrochemistry of semiconductor materials. The second chapter describes the methodologies and techniques employed throughout the thesis. The experimental results are reported from Chapter 3 to 8, focusing on the development and further optimization of two photoelectrodes, concretely hematite and cupric oxide, besides the design and fabrication of tandem cells for standalone water splitting. In the case of hematite photoanodes, the main efforts have focused on its doping to enhance carrier density and mobility as a way of diminishing recombination. The major drawback present in cupric oxide photoelectrodes is their instability against photocorrosion, for this reason, research has focused on protecting them, both by impregnation and adsorption methodologies. Finally, a tandem cell composed by a hematite photoanode and a cupric oxide photocathode was developed. It is worth noting that a polymer electrolyte membrane (PEM) was employed as to facilitate upscaling and diminish the corrosion observed employing the typical acidic or basic liquid electrolytes.

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Ha, Juyoung. "Interaction of hematite nanoparticles with naturally occurring organic compounds, metals, and microorganisms /." May be available electronically:, 2008. http://proquest.umi.com/login?COPT=REJTPTU1MTUmSU5UPTAmVkVSPTI=&clientId=12498.

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Vanlerberghe, Jason Francis. "Chamber studies of the heterogeneous reaction of sulfur dioxide with particulate hematite." Thesis, University of Iowa, 2010. https://ir.uiowa.edu/etd/756.

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The goal of this thesis is to investigate the kinetics and amount of SO2 uptake on hematite, which will act as a representative of mineral dust aerosol. The environmental reaction chamber used here will allow the variation of water vapor pressure to examine the effect of relative humidity (RH) on these parameters. The role of a common atmospheric oxidant, ozone, in the uptake process will also be investigated. The results will be presented with emphasis on the role of hematite in mineral dust aerosols as a sink of SO2, and the possible acidification of hematite particles through heterogeneous reaction pathways.

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Boscolo, Bibi Sara <1993&gt. "Nanostructured hematite photoelectrodes for photoelectrochemical organic reactions and all-oxide solar cells." Master's Degree Thesis, Università Ca' Foscari Venezia, 2018. http://hdl.handle.net/10579/13082.

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This thesis is concerned with the development of materials and devices in the field of renewable energies. Particular attention is devoted to the optimization of the semiconductor nanostructures and the possibility to build heterojunctions between different semiconductors for photocatalysis and solar cell applications. The activity comes within a worthwhile collaboration between the Experimental Physics research group of Luleå University of Technology and the Department of Molecular Sciences and Nanosystems of Ca’ Foscari University of Venice. The project focuses on two different semiconductors whose synthesis and characterization were performed in parallel. Different nanostructures were prepared to maximize the functional properties of the semiconductors, due to the enhancement of the optical and catalytic properties often observed in nanoscale confined materials, among enhanced light absorption, rapid light response, and elevated surface area. In the first part of the thesis is discussed hematite (α‐Fe2O3), which is a cheap and widely available n‐type semiconductor, extensively used in the last few years for water splitting and solar cell applications due to the low band‐gap and the elevated oxidation potential of the photoinduced holes. This material was studied as an oxidative photo‐catalyst and prepared on fluorine-doped tin oxide (FTO) substrates by a hydrothermal method in order to get nanorods. Hematite nanorods were characterized by means of a wide spectrum of techniques: scanning electron microscopy, UV-Vis spectroscopy, X-ray diffraction, cyclic voltammetry, Mott–Schottky plot and impedance spectroscopy. The photo‐electrochemical activities of the prepared electrodes were investigated towards the oxidation of benzylamine to n-benzylidene benzylamine, as a useful replacement of the oxygen evolution reaction, usually limiting the efficiency of the water splitting processes. The products were studied using gas chromatography and nuclear magnetic resonance spectroscopy in order to get an insight into the correlation between the structure of the prepared photoelectrodes and the photocatalytic activity. Under solar simulator irradiation, the hematite photoanodes allow for a drop of the onset potential for the oxidation process equal to 0.8V, with respect to the pure electrochemical process. At the same time, the hydrogen evolution reaction has been observed at the counterelectrode, applying an external bias as low as 0.3 V, under constant illumination. The second part of the thesis is concerned cuprous oxide (Cu2O), which is one of the few p‐type oxide semiconductors showing elevated reduction potential of photoinduced electrons and wide absorption in the visible spectrum. To date, the applications of Cu2O have mainly been in the field of environment and energy conversion, particularly catalysts, sensors and chemical templates. Some examples are degradation of pollutants, reduction of CO2 and detection of in flammable or toxic gases. In this project, cuprous oxide was studied as a reductive photo‐catalyst and produced by an electrodeposition process. The characterization was the same as hematite nanorods. The performances of Cu2O films in photoelectrochemical and photovoltaic devices were evaluated using an FTO/α‐Fe2O3/Cu2O electrode structure. This design provided a working heterojunction all-oxide solar cell, with limited photocurrent at 0V due to the poor electrical properties of the two oxide semiconductors. Nevertheless, this class of all-oxide solar cells is characterized by extremely cheap realization process and the lack of any encapsulation need due to the optimal stability, therefore we expect it to be the subject of further interest among the new generation photovoltaic devices.

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McDermott, Robert G., Alexis K. Ault, James P. Evans, and Peter W. Reiners. "Thermochronometric and textural evidence for seismicity via asperity flash heating on exhumed hematite fault mirrors, Wasatch fault zone, UT, USA." ELSEVIER SCIENCE BV, 2017. http://hdl.handle.net/10150/626016.

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Exhumed faults record the temperatures produced by earthquakes. We show that transient elevated fault surface temperatures preserved in the rock record are quantifiable through microtextural analysis, fault-rock thermochronometry, and thermomechanical modeling. We apply this approach to a network of mirrored, minor, hematite-coated fault surfaces in the exhumed, seismogenic Wasatch fault zone, UT, USA. Polygonal and lobate hematite crystal morphologies, coupled with hematite (U-Th)/He data patterns from these surfaces and host rock apatite (U-Th)The data, are best explained by friction-generated heat at slip interface geometric asperities. These observations inform thermomechanical simulations of flash heating at frictional contacts and resulting fractional He loss over generated fault surface time temperature histories. Temperatures of >similar to 700-1200 degrees C, depending on asperity size, are sufficient to induce 85-100% He loss from hematite within 200 pm of the fault surface. Spatially-isolated, high temperature microtextures imply spatially -variable heat generation and decay. Our results reveal that flash heating of asperities and associated frictional weakening likely promote small earthquakes (M-w approximate to -3 to 3) on Wasatch hematite fault mirrors. We suggest that similar thermal processes and resultant dynamic weakening may facilitate larger earthquakes. (C) 2017 Elsevier B.V. All rights reserved.

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Chen, Chun-Wen. "Numerical Modeling of Dissimilatory Iron Reduction in Sediments at a Field Site." Master's thesis, University of Central Florida, 2005. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/4090.

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The primary purpose of this study is to identify the 'universal' rate formulations with scaled-dependent parameters for the biological reduction of hematite. Three possible rate formulations were proposed to describe the bioreduction rate of hematite, and two kinds of simulation were conducted to validate the formulations and parameters with both batch and column experimental data: a reaction-based biogeochemical (batch) modeling with BIOGEOCHEM 1.0 and a reactive biogeochemical transport (column) modeling via HYDROGEOCHEM 4.0. Based on the results of simulations, only the dual Monod kinetic with inhibition rate formulation with respect to the concentrations of lactate, ßFeOOH, and Fe2+ under certain initial concentration of dissimilatory metal-reducing bacterium could fit the experimental data well. Our results also revealed that the equilibrium reaction rate for the surface hydration of hematite may have to be substituted with the kinetic rate formulation.
M.S.Env.E.
Department of Civil and Environmental Engineering
Engineering and Computer Science
Environmental Engineering

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Muller, Katherine Charlotte. "Formation of iron-rimmed sandstone nodules on earth; terrestrial analogue for the formation of Martian blueberries?" Diss., Rolla, Mo. : Missouri University of Science and Technology, 2009. http://scholarsmine.mst.edu/thesis/pdf/Muller_2009_09007dcc8071b44c.pdf.

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Thesis (M.S.)--Missouri University of Science and Technology, 2009.
Vita. The entire thesis text is included in file. Title from title screen of thesis/dissertation PDF file (viewed November 11, 2009) Includes bibliographical references (p. 85-87).

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Lima, Tatiana Aparecida Fernandes de. "Estudo de inclusões fluidas em hematitas e em quartzo associado das formações ferríferas da Serra do Sapo, Conceição do Mato Dentro, MG." CNEN - Centro de Desenvolvimento da Tecnologia Nuclear, Belo Horizonte, 2009. http://www.bdtd.cdtn.br//tde_busca/arquivo.php?codArquivo=115.

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Neste trabalho foram estudados as inclusões fluidas associadas ao minério de ferro da Formação Serra do Sapo, Supergrupo Espinhaço, Conceição do Mato Dentro, MG. No setor foram diferenciadas três gerações de hematita, denominadas Hematita I, II e III. A Hematita I (mais antiga), de textura granoblástica, apresenta evidências de processos de recristalização parcial ou total, gerados durante um processo metamórfico, e não esta associada ao quartzo. Sob radiação infravermelha mostrou um bom grau de transparência. A Hematita II, ou tabular, apresenta morfologia micro lamelar precipitada no interstício associada aos cristais de quartzo, porém sem formar veios. Não se comporta como transparente sob a luz infravermelha. Por último, a Hematita III (mais nova, especularita) apresenta hábito especular e está associada aos veios de quartzo que cortam as gerações anteriores. Isto fortalece a tese de que essa geração teria crescido condicionada ao fluido do veio, precipitando-se por diminuição da pressão de confinamento do fluido nas fraturas. Os veios de quartzo/especularita envolvem ou estão associados a outros minerais (clorita, moscovita, calcita e granadas) que não aparecem nos corpos de minério. A microtermometria em inclusões fluidas (IF) indica, que o fluido que originou a Hematita I (granular) pertencia ao sistema aquo-salino H2O-NaCl-FeCl2, com temperaturas mínimas de 220-240C e com salinidade média de 17% p/p equiv. NaCl. Já a Hematita III (especularita) foi formada por soluções pertencentes ao sistema aquo-salino H2O-NaCl-KCl (provavelmente com MgCl2) a temperaturas entre 240-260C e salinidades de 10-12% p/p equiv. NaCl. Dados de LA-ICP-MS nos fluidos mostram, em termos de elementos traços, maior concentração de K, Ca, Ba, Mg, Mn, Cu, Pb, Sr e As nas soluções da Hematita I, quando comparados com os da especularita. Destaca-se que, esta última geração, apresenta maiores teores de Li e Sb. O cruzamento do geotermômetro clorita (255C) com as isócoras dos fluidos forneceu pressões de 0,56 Kbar e 0,26 Kbar para a formação das hematitas granulares e especularíticas respectivamente. Isto sugere que o minério de ferro foi originado entre 750m de profundidade (especularita) e 1500m (hematita granular). Interessante destacar que, embora os testes de esmagamento mostrem uma clara liberação de gases, sugerindo a presença de fases carbônicas nos fluidos dos veios de quartzo, não foi constatada a presença desses compostos moleculares nas soluções primárias através da espectroscopia Raman. A diferença de salinidade e de cátions entre os fluidos da hematita granular e os de quartzo-especularita indica a participação de diferentes fluidos durante essas fases específicas da mineralização. Os fluidos participantes do minério de ferro da Serra do Sapo, CMD, são diferentes de outros fluidos mineralizadores associados a depósitos de ferro do Quadrilátero Ferrífero estudados até agora. Uma comparação com as soluções que geraram hematitas granulares e especularitas da Mina Conceição evidenciam tendências de processos evolutivos inversos (em termos de salinidades e temperaturas de homogeneização), embora haja coincidências sobre a ausência de fases carbônicas na formação do minério ferrífero nas duas áreas.
Fuid inclusions associated with the iron ore from Serra do Sapo Formation, Espinhaço Supergroup, Conceição do Mato Dentro, in Minas Gerais, stak were studied. Three hematite generations, named hematite I, II and III were found in these ores. The Hematite I (earliest), with granoblastic texture shows. Partial or total recrystallization texture, was generated during the metamorphic process forming the Hematite I which is the oldesr and not associated with quartz. Under infrared radiation these hematite showed a good degree of transparency. The Hematite II or tabular with micro lamellar morphology was precipitated in the interstitium associated with quartz, but without forming veins and not being transparent under infrared light and also not behaving as transparent under infrared light. Finally, the Hematite III (latest, especularite) has a totally specular habit and is associated with quartz veins which cut the earlier generations. This supports the argument that this hematite generation would have grown subject to veins fluid, by the precipitation of fluid in fractures for decrease pressure confinament. The quartz/specularite veins involve or are associated with other minerals (chlorite, muscovite, calcite and garnet) that not appear in the ore bodies. Fluid inclusions (FI) microtermometry indicates that the fluid that has originated the Hematite I (granular) belonged to the aquo-salt system H2O-NaCl-FeCl2, with minimum temperatures of 220-240C and average salinity of 17 wt% NaCl eq. However, the Hematite III (specularite) was formed by solutions belonging to the aquo-salt H2O-NaCl-KCl (probably with MgCl2) at temperatures between 240-260C and salinities of 10-12 wt% NaCl eq. NaCl. LA-ICP-MS data in fluids, in terms of trace elements, show higher concentration of K, Ca, Ba, Mg, Mn, Cu, Pb, Sr and As in Hematite I solutions when compared to the specularite. This last generation has higher contents of Li and Sb. The geothermometry chlorite (255C) intersection with the fluid isochoric supplied pressure of 0.56 kbar and 0.26 kbar for the granular and specularitic hematite formation, respectively. This suggests that iron ore was produced from a depth of 750m (specularite) and 1500m (granular hematite). It is interesting to note that, although the crushing tests show an incontestable gases release suggesting the presence of carbon phase in the quartz veins fluid, these molecular compounds was not found in the primary solutions. The difference in salinity and ions between granular hematite and quartz-specularite fluids suggests the involvement of different fluids during specific mineralization stages. The ore-forming fluids of Serra do Sapo iron formation, CMD, are different from other mineralizing fluids associated with Iron Quadrangle deposits. The comparison with the Mine Conceição solutions, that generate granular hematite and specularite, evidence contrary evolutive trends (regarding salinity values and homogenization temperatures), although there are coincidences on the carbon phases absence in the ore ferriferous formation in both areas.

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41

Longbottom, Raymond James Materials Science &amp Engineering Faculty of Science UNSW. "The formation of cementite from hematite and titanomagnetite iron ore and its stability." Awarded by:University of New South Wales. Materials Science and Engineering, 2005. http://handle.unsw.edu.au/1959.4/22023.

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This project examined the reduction and formation of cementite from hematite and titanomagnetite ores and cementite stability. The aim of the project was to develop further understanding of cementite stability under conditions relevant to direct ironmaking and the mechanism of cementite decomposition. The reduction of hematite and ironsand by hydrogen-methane-argon gas mixtures was investigated from 600??C to 1100??C. Iron oxides were reduced by hydrogen to metallic iron, which was carburised by methane to form cementite. The hematite ore was reduced more quickly than the ironsand. Preoxidation of the ironsand accelerated its reduction. Hematite was converted to cementite faster than preoxidised ironsand. The decomposition of cementite formed from hematite was investigated from 500??C to 900??C. This cementite was most stable at temperatures 750-770??C. The decomposition rate increased with decreasing temperature between 750??C and 600??C and with increasing temperature above 770??C. The stability of cementite formed from pre-oxidised titanomagnetite was studied from 300??C to 1100??C. This cementite was most stable in the temperature range 700-900??C. The rate of decomposition of cementite increased with decreasing temperature between 700??C and 400??C and with increasing temperature above 900??C. Cementite formed from ironsand was more stable than cementite formed from hematite

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42

Zheng, Jennie Olivia. "Equilibrium configurations of oxygen bubbles on surfaces for applications in nanostructured hematite electrodes." Thesis, Massachusetts Institute of Technology, 2015. http://hdl.handle.net/1721.1/98668.

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Thesis: S.B., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2015.
Cataloged from PDF version of thesis.
Includes bibliographical references (page 32).
The variability of a nanostructured material's fundamental properties as compared to its bulk state has led to the rich field of nanotechnology and the quest to uncover unique properties of structures at the nanoscale. An active application for these materials is in the nanostructuring of [alpha]-Fe₂O₃ (hematite) for photoelectrochemical (PEC) splitting of water to generate hydrogen. A model of a bubble on a nanorod was developed in this work to facilitate the understanding of equilibrium configurations of oxygen bubbles on a nanostructured hematite electrode. The equilibrium configurations are computed using Surface Evolver, a program which models surfaces shaped by various constraints and forces. A nanorod with a top surface dimension of 100 by 100 nm was the subject of the bulk of this work. The energy of different starting configurations of the bubble and increasing volume of the bubble were compared to that of a free spherical bubble. The energy of the bubble approaches the total surface energy of a free spherical bubble, indicating that a bubble that has nucleated on the surface of a nanorod will approach a shape that has nearly the same energy as a detached spherical bubble. For applications in PEC splitting of water, this result indicates that from an equilibrium and lowest energy perspective, an oxygen bubble could nucleate on the surface of a nanorod, grow in volume, and detach or pinch-off from the nanorod.
by Jennie Olivia Zheng.
S.B.

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43

Ross, Andrew [Verfasser]. "Probing magnetostatic and magnetotransport properties of the antiferromagnetic iron oxide hematite / Andrew Ross." Mainz : Universitätsbibliothek der Johannes Gutenberg-Universität Mainz, 2021. http://d-nb.info/1230059962/34.

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44

Lanzl, Caylyn Ashley. "Size-dependent reactivity of hematite nanoparticles: environmental implications of dissolution mechanisms and aggregation." Diss., University of Iowa, 2013. https://ir.uiowa.edu/etd/2557.

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The interfacial reactivity of iron oxides such as hematite (Α-Fe2O3) has been extensively studied because they are naturally abundant materials that are also versatile in a range of engineering applications. A poorly understood determinate of iron oxide interfacial reactivity is their particle size, a factor that has received increasing scrutiny given the emergence of nanoscience and nanotechnology. In natural systems, size-dependent trends in dissolution may have a profound influence on the rate and extent of iron redox cycling, which will indirectly effect the numerous processes in which soluble ferric [Fe(III)] and ferrous [Fe(II)] iron subsequently participate. This work seeks to establish (i) the size-dependent dissolution of hematite nanoparticles across a range of dissolution mechanisms (e.g. proton-promoted, ligand-promoted, thermal reductive and photoreductive dissolution) and pH values, (ii) the extent to which nanoparticle aggregation effects the reactivity of hematite nanoparticles and trends observed in size-dependent reactivity of such aggregates, and (iii) how size-dependent dissolution activity of hematite impacts the production of environmentally relevant reactive oxygen species in sunlit surface waters via the photo-Fenton chemical reaction. Results herein reveal that size-dependent reactivity for two sizes of hematite nanoparticles, 8 and 40 nm, is observed throughout all dissolution processes and mechanisms investigated. Notably, this work is among the first where size-dependent reactivity is clearly observed into circumneutral and neutral pH values representative of most natural systems. Enhanced reactivity of the smaller 8 nm hematite is likely due to available reactive surface area compared to its larger analog. Under native aggregation of nanopowders (i.e., minimal ionic strength and no sonication) and induced aggregation of nanoparticle suspensions (i.e. high ionic strengths) mass normalized rates of reductive dissolution were greater for aggregates of 8 nm hematite, and aggregate size exhibited little influence on size-dependent reactivity. Finally, size-dependent reactivity also occurs in model surface water reactions, specifically the dissolved organic matter mediated photo-Fenton reaction. Smaller nanophase hematite exhibits greater rates of Fe(II) production, which in turn yields greater steady-state hydroxyl radical concentrations. Insights from this work advance current knowledge of size-dependent reactivity of natural nanomaterials and their implications for pollutant fate and elemental cycling in environmental systems.

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45

Dudchenko, N. O., A. B. Brik, and V. P. Ponomar. "Preparation of Magnetic Fine Particles for Different Applications by Reducing of Non-Magnetic Hematite and Goethite with Biomass." Thesis, Sumy State University, 2015. http://essuir.sumdu.edu.ua/handle/123456789/42631.

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Phase transformations of natural and synthetic hematite and goethite by reducing with starch at temperature range up to 650°C were investigated. The saturation magnetization of all initial samples was ~1 A*m2/kg, while the saturation magnetization of the samples after phase transformations increases greatly (up to 70 A*m2/kg for synthetic goethite sample). It was shown by X-Ray diffraction method that all phases transformed into magnetite. Rather high saturation magnetization of obtained magnetic particles makes them promising for different medical-biological applications (cells separation, DNA purification, targeted drug delivery, adsorbents of radioactive waste, etc.).

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46

Murphy, Riley Tomas. "Reactivity of Iron-Bearing Minerals Under Carbon Sequestration Conditions." Diss., Temple University Libraries, 2011. http://cdm16002.contentdm.oclc.org/cdm/ref/collection/p245801coll10/id/140596.

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Chemistry
Ph.D.
The rise in anthropogenic carbon dioxide in the atmosphere has caused the pursuit of adequate methods to alleviate the resulting strain on the world's ecosystem. A promising strategy is the geological sequestration of carbon dioxide, in which carbon dioxide emitted from large point sources is injected underground for storage. Under storage, carbon dioxide trapped as a carbonate mineral may be stable for geological time periods. Experiments were conducted to test the potential of ferric-bearing minerals to sequester carbon as a ferrous carbonate mineral (siderite). The formation of siderite requires the reduction of ferric ions which may be achieved by the co-injection of H2S or SO2 contaminants with CO2. Both ferrihydrite and hematite nanoparticles were exposed to an aqueous Na2S solution in the presence of supercritical CO2 (scCO2) and were analyzed in situ by attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR). In situ ATR-FTIR indicated that the formation of siderite occurred on the order of minutes for ferrihydrite and hematite nanoparticles. Particles were analyzed post-reaction with X-ray diffraction (XRD) and electron microscopy. XRD results indicated that ferrihydrite reacted completely to form siderite and elemental sulfur after 24 h at 100 °C, while hematite only partially reacted to form siderite and pyrite after 24 h at 70 °C. Additionally, hematite nanoparticles were exposed to H2S and scCO2 in a series of batch reactions, and the reaction products were determined by XRD as a function of CO2 and H2S partial pressures, alkalinity, salinity, time, and temperature.
Temple University--Theses

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47

Santos, Reginaldo da Silva. "TiO2 e TiO2 dopado com ferro = efeitos da inserção do dopante e da segregação de hematita nas propriedades e na atividade fotocatalítica para conversão de energia solar." [s.n.], 2011. http://repositorio.unicamp.br/jspui/handle/REPOSIP/250022.

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Orientador: Claudia Longo
Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Química
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Resumo: Nanopartículas de TiO2 foram preparadas por método sol-gel a partir da hidrólise de isopropóxido de titânio, tratamento hidrotérmico (200 °C, 8 h) e calcinação (450 °C, 30 min); amostras de TiO2 dopado com ferro (Fe:TiO2) foram obtidas pela mesma metodologia incluindo nitrato férrico nos precursores (razão molar Fe/Ti de 1, 3 e 5%). Para comparação, investigou-se também uma mistura de a-Fe2O3/TiO2 (Fe/Ti = 4 %). O intervalo de banda proibida, de 3,2 eV para o TiO2, diminuiu de 3,0 para 2,7 eV com o aumento do teor de Fe. Análises por difração de raios X e refinamento Rietveld revelaram que o TiO2 é constituído por anatasa (82 %) e brookita (18 %); para Fe:TiO2, observou-se 30 % de brookita e identificou-se 0,5; 1,0 e 1,2 wt % de hematita nas amostras com Fe/Ti de 1; 3 e 5%. Filmes porosos, com espessura de 1,5 mm, foram depositados em eletrodos de vidro a partir de suspensões com polietilenoglicol e calcinação. Em solução aquosa, irradiados com um simulador solar, os eletrodos apresentaram comportamento de semicondutor tipo-n: para o TiO2, fotopotencial de -0,95 V em circuito aberto e fotocorrente de 0,34 mA cm em 0,8 V; valores muito menores foram observados para Fe:TiO2 e a-Fe2O3/TiO2. O TiO2 também apresentou maior atividade fotocatalítica para degradação de fenol e, quando utilizado como foto-anodo em célula de dois compartimentos, polarizado a + 0,7 V por 4 h, promoveu a oxidação de formiato e a produção de 18 mmol de H2 sobre contra-eletrodo de Pt. Os eletrodos de Fe:TiO2 e a-Fe2O3/TiO2 apresentaram valores menores de corrente, impossibilitando a obtenção de H2 no catodo. Embora as amostras de Fe:TiO2 tenham apresentado maior aproveitamento da luz visível, a inserção do ferro como dopante e a hematita segregada podem dificultar a separação das cargas fotogeradas e o transporte de elétrons através dos contornos de grãos, resultando em menor atividade fotocatalítica nas aplicações decorrentes da conversão de energia solar
Abstract: TiO2 nanoparticles were synthesized by sol-gel method from hydrolysis of titanium isopropoxide followed by hydrothermal treatment (200 °C, 8 h) and annealing (450 °C, 30 min). Fe doped TiO2 (Fe:TiO2) samples were synthesized by similar methodology adding ferric nitrate, with Fe/Ti atomic ratio corresponding to 1, 3 and 5 %. A mixture of a-Fe2O3/TiO2 (with Fe/Ti = 4 at %) was also investigated. The band gap energy, estimated as 3.2 eV for TiO2, gradually ranged from 3.0 to 2.7 eV with increasing iron content. Rietveld refinement of X ray diffraction data revealed that TiO2 consisted of 82 % anatase and 18 % brookite; for Fe:TiO2, brookite increased to 30 % and hematite was also identified (0.5; 1.0 and 1.2 wt % for samples prepared with 1; 3 and 5 % of Fe/Ti). Porous films, 1.5 mm thick, were deposited on transparent electrodes from aqueous suspension with polyethylene glycol and annealing. In aqueous solution, irradiated by a solar simulator, the electrodes exhibited n-type semiconductor behavior: for TiO2 electrode, -0,95 V of photo-potential at open circuit condition and 0,34 mA cm of photocurrent when biased at 0.8 V; much lower values were observed for Fe:TiO2 and a-Fe2O3/TiO2 electrodes. TiO2 film also exhibited higher photocatalytic activity for phenol oxidation than other samples. The electrodes were also used as photo-anodes in a two-compartment electrochemical cell with Pt counter-electrode and HCOONa as hole scavenger. The cell assembled with irradiated TiO2 anode biased at + 0.7 V for 4 h produced 18 mmol of H2 at the cathodic compartment. H2 evolution was not detected and very low currents were observed for Fe:TiO2 or a-Fe2O3/TiO2 photo- anodes. Although Fe:TiO2 samples exhibited higher sunlight harvesting, inserted iron and segregated hematite can hinder the separation of photogenerated charges, as well as the electron transport across the grain boundaries, resulting in lower photocatalytic activity for solar energy conversion
Doutorado
Físico-Química
Doutor em Ciências

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48

Gomes, Romário Pimenta [UNESP]. "Gênese, mineralogia e dinâmica do fósforo nos solos do Planalto Ocidental Paulista." Universidade Estadual Paulista (UNESP), 2017. http://hdl.handle.net/11449/151719.

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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)
Nos solos tropicais, o fenômeno de adsorção de fósforo é regido pela mineralogia da fração argila, que, por sua vez, é afetada pelo material de origem e intensidade de dissecação da paisagem. Desse modo, objetivou-se relacionar o fósforo total e adsorvido com principais minerais da fração argila dos solos do Planalto Ocidental Paulista, São Paulo, associando com a geologia e o grau de dissecação da paisagem. Foram selecionadas cinquenta e cinco amostras de solo representativas da variabilidade fisiográfica do Planalto Ocidental Paulista, na profundidade de 0,0 – 0,2 m, para a caracterização das formas de fósforo, mineralogia da argila por difração de raios-x (DRX) e espectroscopia de reflectância difusa (ERD); utilizou-se também calibração quimiométrica através da regressão de mínimos quadrados parciais (PLSR). Verificou-se que o P total e o P adsorvido são influenciados pela geologia e grau de dissecação da paisagem, e são covariativos dos óxidos de Fe e Al, sendo esses óxidos importantes indicadores de ambientes com maiores e menores potenciais de adsorção e com baixos e altos teores de P. A caracterização das curvas espectrais permite diferenciar o conteúdo de P total com base na mineralogia da fração argila. A análise por regressão de mínimos quadrados parciais (PLSR) dos dados espectrais evidencia a influência dos óxidos de ferro no conteúdo de P total e adsorvido, sendo a Hm ao P total e a Gt ao P adsorvido.
In tropical soils, the phenomenon of phosphorus adsorption is governed by the mineralogy of the clay fraction, which in turn is affected by the material of origin and intensity of dissection of the landscape. the objective was to relate the total phosphorus and adsorbed with the main minerals of the clay fraction of the soils of the Planalto Ocidental Paulista, associating with the geology and the degree of dissection of the landscape. Were selected fifty - five soil samples representative of the physiographic variability of the Planalto Ocidental Paulista, in the depth of 0.0 - 0.2 m, for the characterization of phosphorus forms, clay mineralogy by X - ray diffraction (XRD) and diffuse reflectance spectroscopy (DRS); it was also used chemometric calibration Through the partial least squares regression (PLSR). It was verified that the total P and adsorbed P are influenced by the geology and degree of dissection of the landscape, and are covariate of the Fe and Al oxides, and these oxides are important indicators of environments with higher and lower adsorption potentials and with low and high levels of P. The characterization of the spectral curves allows to differentiate the total P content based on the mineralogy of the clay fraction. Partial least squares regression analysis (PLSR) of the spectral data shows the influence of iron oxides on the total and adsorbed P content, with Hm at the total P and Gt at the adsorbed P.

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49

Braga, Cláudio Taranto Lima. "Efeito do agente precipitante nas propriedades de catalisadores de hematita contendo alumínio e cobre." Instituto de Química, 2014. http://repositorio.ufba.br/ri/handle/ri/16019.

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Considerando a busca por tecnologias mais limpas e sustentáveis, o hidrogênio surge como uma das fontes de energia mais práticas e sustentáveis do futuro. Esse combustível é obtido comercialmente pela reforma de gás natural, seguido de uma etapa de purificação, conhecida como conversão de monóxido a dióxido de carbono com vapor d’água (reação de HTS, High Temperature Shift). Os catalisadores comerciais empregados nessa reação são constituídos por hematita (-Fe2O3) contendo cromo hexavalente, um íon tóxico aos seres humanos e ao meio ambiente. Por essa razão, diversas pesquisas têm sido desenvolvidas visando a substituir o cromo nesses sólidos. Com o objetivo de otimizar as propriedades de catalisadores baseados em hematita contendo alumínio (Fe/Al=10) e cobre (Fe/Cu=10) para a reação de HTS, neste trabalho, estudou-se o efeito do agente precipitante sobre as propriedades desses sólidos. As amostras foram preparadas através do processo sol-gel, misturando-se soluções de nitrato férrico e nitrato de alumínio e usando diferentes agentes precipitantes (hidróxido de sódio e hidróxido de amônio), seguida de impregnação com solução alcoólica de cobre. Os sólidos foram caracterizados por termogravimetria, espectroscopia no infravermelho com transformada de Fourier, difração de raios X, medida de área superficial específica e de porosidade, redução à temperatura programada e espectroscopia Mössbauer. Os catalisadores foram avaliados na reação de HTS a 1 atm e 400 °C. Observou-se a formação da hematita e magnetita nos catalisadores antes e após a reação, respectivamente, não se detectando nenhuma outra fase. Os dopantes foram inseridos na rede do óxido de ferro, o que pode ser explicado pela similaridade dos raios iônicos das espécies Cu+2, Al+3 e Fe+3; esse processo foi facilitado pelo hidróxido de amônio. Quando presentes isoladamente, o alumínio e o cobre aumentaram a área superficial específica dos sólidos obtidos com hidróxido de amônio mas o hidróxido de sódio inibiu a ação textural do cobre e alumínio, juntos ou isoladamente. O hidróxido de amônio favoreceu o desenvolvimento de mesoporos interparticulares nos sólidos macroporosos obtidos. A redutibilidade da hematita foi alterada pela presença dos dopantes e pela natureza do agente precipitante; o alumínio dificultou a formação da magnetita (Fe3O4) e do ferro metálico enquanto o cobre e o hidróxido de amônio facilitaram esses processos. Dessa forma, a presença simultânea dos dopantes favoreceu a formação da fase ativa (magnetita) e a estabilidade do catalisador, retardando sua desativação pela formação de ferro metálico. Todos os catalisadores foram ativos na reação de HTS, mas aqueles contendo cobre, e obtidos com hidróxido de sódio, foram os mais ativos, devido a um aumento na atividade dos sítios ativos e à maior facilidade de formação da fase ativa (magnetita). O papel do alumínio foi relacionado ao aumento da resistência dos catalisadores à redução da fase ativa. O catalisador mais promissor foi aquele preparado com hidróxido de sódio, que apresentou elevada atividade (10,68 x 10-7 mol.s-1.g-1) e alta resistência à redução da fase ativa (magnetita), com a vantagem de não ser tóxico, podendo ser manuseado e descartado sem risco à saúde humana e ao meio ambiente.
Considering the search for cleaner and more sustainable technologies, hydrogen emerges as one of the most practical and sustainable energy source in the future. This fuel is commercially obtained by natural gas reforming, followed by a purification step known as the water gas shift reaction at high temperatures (HTS, High Temperature Shift). The commercial catalysts for this reaction are composed of hematite (-Fe2O3) containing hexavalent chromium, a toxic ion to humans and the environment. For this reason, many studies have been carried out aiming to replace chromium in these solids. In order to optimize the properties of catalysts based on hematite containing aluminum (Fe/Al= 10) and copper (Fe/Cu= 10) for the HTS reaction, the effect of precipitating agent on the properties of these solids was studied in this work. Samples were prepared by sol-gel process by mixing solutions of iron nitrate and aluminum nitrate and using different precipitating agents (sodium hydroxide and ammonium hydroxide) and impregnated with an alcoholic solution of copper. The solids were characterized by thermogravimetry, Fourier transform infrared spectroscopy, X-ray diffraction, specific surface area and porosity measurement, temperature programmed reduction and Mössbauer spectroscopy. The catalysts were evaluated in the HTS reaction at 1 atm and 400 °C. It was found hematite and magnetite in the catalysts before and after reaction, respectively and no other phase was detected. The dopants were found to be into the iron oxide lattice, a fact that was explained by the similarity of the ionic radii of Cu+2, Al+3 and Fe+3 species, this process being facilitated by ammonium hydroxide. Aluminum and copper alone increased the specific surface area of the solids obtained with ammonium hydroxide but sodium hydroxide inhibited the textural action of copper and aluminum, together or separately. Ammonium hydroxide favored the development of nterparticlemesopores in the macroporous solids obtained. The reducibility of hematite was changed by the dopants and by the kind of the precipitating agent, aluminum hindering the formation of magnetite (Fe3O4) and metallic iron while copper and ammonium hydroxide facilitated this process. Therefore, the dopants favored the formation of active phase (magnetite) and the catalyst stability, delaying its deactivation through the formation of metallic iron. All catalysts were active in HTS reaction, those containing copper and obtained with sodium hydroxide being the most active ones, due to increase in the activity of the active sites and the ease of formation of active phase (magnetite). The role of aluminum was related to increased resistance to reduction of the active phase. The most promising catalyst was the one prepared with sodium hydroxide, which showed high activity (10.68 x 10- 7 mol.s-1.g-1) and high resistance against the reduction of the active phase (magnetite), with the advantage of being non-toxic and can be handled and disposed without risk to human health and the environment.

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Engwayu, Jophat. "Aggregation and dispersion phenomena in the quartz-hematite system in the presence of polymers." Thesis, University of British Columbia, 2015. http://hdl.handle.net/2429/55112.

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Abstract:

Aggregation and dispersion phenomena in the quartz-hematite system in the presence of polymers were analyzed through the measurement of adsorption density of polymers, turbidity of mineral suspensions, and zeta potential distributions. All the tests were performed on single minerals as well as on their 1:1 mixtures (by volume). A procedure was developed to determine the composition of the tested supernatants using scanning electron microscopy in order to enhance interpretation of zeta potential distributions obtained for mineral mixtures. Two carboxymethyl celluloses and a sodium lignosulfonate were chosen as polymeric additives. It was found that carboxymethyl celluloses selectively adsorbed on hematite in mixtures with quartz and that the selectivity of adsorption was a result of a high affinity of the polysaccharides towards the hematite surface. Lignosulfonate exhibited low affinity type of adsorption on both minerals although preferential adsorption on hematite at pH 5.5 was also observed. At pH 5.5, carboxymethyl celluloses acted as flocculants towards hematite, while lignosulfonate functioned as a coagulant. The polymers strongly dispersed hematite at high pH. The polymers also showed dispersing capabilities towards quartz regardless of pH. Selective flocculation of residual hematite from mixtures with quartz was observed at low pH despite extensive heterocoagulation between the minerals. Lignosulfonate behaved as a selective dispersant of hematite at high pH despite similar adsorption densities of the polymer on the tested minerals. It was generally determined that conditions (pH, polymer concentration) leading to strong dispersion were associated with very narrow zeta potential distributions (10-20 mV), indicative of uniform surface charging characteristics of the tested particle population. In contrast, polymer-induced aggregation of mineral particles (flocculation or coagulation) was accompanied by broad zeta potential distributions (up to 70 mV) resulting from non-uniform adsorption of the polymers on mineral particles and surface charge heterogeneities. Such broad zeta potential distributions were also characteristic of heterocoagulated mixtures in the absence of polymers. Several recommendations were made regarding measurements of zeta potential distributions in mineral mixtures. In order to characterize the entire population of a mineral mixture, such measurements should be performed on very dilute samples of constant turbidity to limit the differential settling of aggregated components.
Applied Science, Faculty of
Mining Engineering, Keevil Institute of
Graduate

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