Dissertations / Theses on the topic 'Cobalt'
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England, Craig Dennis. "Properties of cobalt/copper and cobalt/palladium multilayers." Diss., The University of Arizona, 1991. http://hdl.handle.net/10150/185707.
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The physical properties of Co/Cu and Co/Pd magnetic multilayers have been studied. The Co/Cu multilayers were prepared by sputtering, while the Co/Pd multilayers were made by sputtering and molecular beam epitaxy (MBE). Various x-ray diffraction techniques have been used to study the structure of the multilayers. Magnetometry techniques were used to study the magnetic properties. Various optical techniques have been used to investigate the magneto-optical properties. Brillouin light scattering spectroscopy was used to determine the effective elastic constants of the Co/Cu multilayers and the magnetic properties of the sputtered Co/Pd multilayers.
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Reinikainen, Matti. "Cobalt and ruthenium-cobalt catalysts in CO hydrogeneration and hydroformylation /." Espoo : Technical Research Centre of Finland, 1998. http://www.vtt.fi/inf/pdf/publications/1998/P363.pdf.
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Pigram, David Dennis. "The electronic structure of the ferromagnets cobalt and cobalt disulphide." Thesis, University of Cambridge, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.306516.
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Ballou, Rafik. "Anisotropies magnétiques du cobalt dans les composés intermétalliques lanthanide-cobalt." Grenoble 1, 1987. http://www.theses.fr/1987GRE10114.
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Analyse phénoménologique des processus d'aimantation des composes YCo5 et GDCo5 mettant en évidence une anisotropie des interactions d'échangé Ln-Co liée à l'anisotropie de polarisation des électrons 5d de l'atome Ln. Etude de l'incidence de l'instabilité du magnétisme de bande 3d sur l'anisotropie magnétique dans les phases Ln2Co7 et LnCo3. Etude de l'anisotropie des systèmes à empilement quasi-unidimensionnel LnCo(1-epsilon ). Analyse de la sélection orbitale induite par les intégrales de transfert
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Ballou, Rafik. "Anisotropies magnétiques du cobalt dans les composés intermétalliques lanthanide-cobalt." Grenoble 2 : ANRT, 1987. http://catalogue.bnf.fr/ark:/12148/cb37602561f.
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Pour, Asghar Tajali. "Electrocrystallisation of cobalt." Thesis, Coventry University, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.279419.
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Grant, Simon Jonathon. "Azamacrocyclic cobalt catalysts." Thesis, University of Warwick, 1991. http://wrap.warwick.ac.uk/109401/.
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Ten azamacrocyclic ligands were synthesised and characterised. The coordination chemistry of these ligands was evaluated by the study of their Ni(II), Cu(II) and Zn(II) complexes in the development of azamacrocyclic cobalt catalysts. Co(II) complexes of ligands L3 and L4 were evaluated as potential auto-oxidation catalysts for aqueous gloss paint systems. These compounds act as catalysts, producing through dry paint films in a shorter time than commercially available catalysts. This surprising result could indicate the presence of a different drying mechanism for these complexes when compared to the commercial catalysts. Ligands L5 and L6 were designed to activate dioxygen when coordinated to Co(II). The X-ray crystal structure of [Zn(L5)](BF4)2 and n.O.e. experiments on [Zn(L6)](BF4)2 prove that the correct theoretical geometry is adopted by the ligands on coordination to metals. The Co(II) complexes of ligands L5 and L6 were not isolated as a result of their high reactivity towards dioxygen. The products obtained were the u-peroxo- bridged dimer species - a result of a bimolecular reaction. The Co(II) compounds were considered too reactive to be used as auto-oxidation catalysts. Azamacrocyclic organocobalt(III) complexes have been shown to act as photopolymerisation catalysts in the polymerisation of alkenes. In water a free radical mechanism occurs. In t.h.f. a metal centred polymerisation is proposed. Diode array gel permeation chromatography of polymeric solutions shows the presence of dimeric and trimeric species which could react to form high molecular weight species. A novel hydridocobalt(III) complex of L8 was prepared by reaction of hydrogen with [Co(L8)]2+. The presence of the Co-H bond was established by chemical means. A similar reaction was attempted for [Co(L7)](BF4)2 but the compound was unstable in solution, reductively eliminating H2-.
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Sun, Lihui. "Synthesis and reactivity of some cobalt-, phosphorus-chiral cobalt(III) complexes." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp01/MQ34235.pdf.
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Zitoun, David. "Synthèse et magnétisme de nanoparticules de cobalt/rhodium et cobalt/ruthénium." Toulouse 3, 2003. http://www.theses.fr/2003TOU30078.
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Ullman, Andrew. "Polynuclear Cobalt Complexes as Models of a Cobalt Water Oxidation Catalyst." Thesis, Harvard University, 2015. http://nrs.harvard.edu/urn-3:HUL.InstRepos:23845429.
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The electrochemical oxidation of Co2+ ions in the presence of a buffering species such as phosphate (Pi), methyl phosphonate (MePi), and borate (Bi) leads to the formation of amorphous cobalt oxide thin films that are capable of catalyzing the four electron-four proton oxidation of water to dioxygen. These cobalt oxygen evolving catalysts (Co–OECs) have been extensively studied by electrochemical techniques; however, the amorphous nature of these films means that garnering insights at the molecular and atomic level is difficult because electronic and structural characterization methods rely on measurements of bulk material. To address this challenge, polynuclear cobalt hydroxide and cobalt oxide compounds have been employed as platforms for understanding Co–OECs at the molecular level.
In the first part of the thesis, we present the synthesis of a heptanuclear cobalt cluster in two different oxidation states, Co(II)7 and a mixed valence Co(III)Co(II)6. An anomalously slow self–exchange electron transfer rate as compared to that predicted from semiclassical Marcus theory was measured, supporting a charge transfer process that is accelerated by dissociation of the anion from the oxidized cluster. This mechanism sheds light on the inverse dependence of anions in the deposition mechanism of Co–OECs. Moreover, the results address a long-standing controversy surrounding the Co2+/3+ self–exchange electron transfer reaction of the hexaaqua complex.
In the second part of the thesis, we report the synthesis and characterization of a dinuclear cobalt complex, which we use as an edge sites mimic (ESM) of the Co-OEC. A comparative investigation of the Pi and Bi binding of buffers to this ESM is provided. We find that the binding to the boric acid component of borate buffer is rapid, while binding to K2HPO4 is much slower, taking days to equilibrate at room temperature. These studies are used to provide a model for the interaction of Pi and Bi species with the active site of the Co-OEC. An inverse dependence on [Bi] of the electrochemical driven water oxidation activity by Co-OECs is demonstrated, which provides validation for the model and indicates that dinuclear cobalt edge sites are necessary for water oxidation catalysis.
In the final chapter of the thesis, we use a series of spectroscopic and electrochemical methods to show that the observed water oxidation activity of the compound class Co4O4(OAc)4(py–X)4 emanates from a Co(II) impurity. This impurity is oxidized to produce Co-OEC, which is an active water oxidation catalyst. Differential electrochemical mass spectrometry (DEMS) is used to characterize the fate of glassy carbon at water oxidizing potentials, and demonstrate that such electrode materials should be used with caution for the study of water oxidation catalysis. We then investigate the electrochemical properties of Co4O4 cubanes in non-aqueous solvents, showing that the neutral cubanes may be oxidized by two electrons yielding a formal oxidation state of Co(IV)2Co(III)2. Finally, we show that these cubanes may be synthetically modified with tethered NMI photooxidants, which opens new avenues for exploring fixed-distance photoinduced ET using Co4O4 cubanes as the electron donor. Ultra-fast transient absorption experiments demonstrate that a charge separated state is formed following laser excitation.Chemistry and Chemical Biology
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Felippini, Ana Luiza de Carvalho. "Estudo de metais pesados comumente utilizados na reabilitação oral: efeitos do cobalto no epitélio adamantino, epitélio juncional, gengiva inserida e ligamento periodontal." Universidade de São Paulo, 2007. http://www.teses.usp.br/teses/disponiveis/58/58131/tde-13112007-084209/.
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O cobalto é um dos principais componentes das ligas metálicas fundidas amplamente utilizadas na odontologia. Ele é considerado o constituinte de 45 a 70% de inúmeros trabalhos protéticos. Há evidência de elementos metálicos causarem toxicidade sistêmica e local. Este trabalho teve como objetivo, avaliar os efeitos do cobalto no epitélio juncional, epitélio adamantino, epitélio da gengiva inserida e ligamento periodontal do 1° molar superior do rato, durante a lactação. Para tal, foram utilizados ratos com 1 dia de vida pós-natal, cujas mães receberam 300mg de cloreto de cobalto por litro de água destilada no bebedouro (grupo tratado -T) e ratos cujas mães não receberam CoCl2 (grupo controle - C), durante toda a lactação. Ao final de 21dias, os filhotes foram sacrificados com sobredosagem anestésica. As cabeças foram separadas e fixadas em solução de alfac (álcool 80%- 85ml, formalina 10ml e ácido acético 5ml) incluídas em parafina e os cortes frontais seriados foram corados com hematoxilina e eosina. Os cortes foram focalizados ao microscópio de luz (100X), munido de uma câmara clara. Os núcleos das células dos tecidos estudados foram projetados sobre o papel com aumento final de 1000X e 50 núcleos de cada estrutura foram contornados com lápis preto para posterior medição do diâmetros maior (D) e menor (d). Uma vez determinados os diâmetros, foram estimados os seguintes parâmetros cariométricos: diâmetro geométrico médio, relação entre D/d, perímetro, área, volume, relação entre volume e área, excentricidade, coeficiente de forma e índice de contorno. Neste trabalho também foi utilizada uma grade impressa sobre papel. As imagens obtidas foram desenhadas sobre a grade. A grade pode ser usada tanto para contar pontos sobre uma determinada estrutura histológica bem como para contar intersecções entre duas estruturas contíguas, bastando para isso, no primeiro caso, considerar o número de pontos que caem sobre a estrutura em estudo, ou, no segundo caso, o número de vezes em que as superfícies vizinhas cortam a linha curva. Com a finalidade de se avaliar o volume citoplasmático, o volume celular, a relação núcleo/citoplasma, a densidade numérica celular, a relação superfície externa/camada basal, a espessura das camadas epiteliais e a densidade de superfície, foi utilizada ora a contagem de pontos ora o número de intersecções e aplicados às equações estereológicas apropriadas para cada uma dessas variáveis. Todos os dados colhidos foram submetidos à estatística não paramétrica - Teste de Wilcoxon-Mann-Whitney. Os núcleos dos tecidos estudados mostraram valores diminuídos, após cariometria, para os diâmetros maior, menor e médio; volume, área, perímetro e relação volume/área. Estereologicamente foi possível observar, no epitélio juncional, epitélio adamantino e no epitélio da gengiva inserida, células menos volumosas com citoplasma mais escasso levando a um maior número de células por mm3 de tecido. O ligamento periodontal também se apresentou desorganizado e com fibras de menor tamanho. Neste estudo, o cobalto ocasionou um quadro de hipotrofia epitelial, indicando uma ação direta nos epitélios juncional e adamantino, epitélio da gengiva inserida bem como no ligamento periodontal.Cobalt is one of the main components of cast metal alloys broadly used in dentistry. It is the constituent of 45 to 70% of numerous prosthetic works. There is evidence that metal elements cause systemic and local toxicity. The purpose of the present study is to evaluate cobalt effects on the junctional epithelium, adamantine epithelium, inserted gum epithelium, and periodontal ligament of the superior first molar in rats, during lactation. To do this, 1-day old rats were used, whose mothers received 300mg of cobalt chloride per liter of distilled in the drinker (treated group T) and rats whose mothers did not receive CoCl2 (control group C), during lactation. After 21 days, the rat pups were killed with an anesthetic overdose. The heads were separated and fixed in an alfac solution (80% alcohol-85ml, formaline-10ml, and acetic acid-5ml), embedded in paraffin and stained with hematoxylin and eosin. The cuts were viewed under a light microscope (100X) with a clear chamber. The nucleus of the studied tissue cells were projected on paper with a final increase of 100X. Fifty nuclei from each structure were outlined with a black pencil so that the greater (D) and smaller (d) diameters could be measured. After determining the diameters, the following cariometric parameters were established: mean geometric diameter, D/d relation, perimeter, area, volume, volume/area relation, eccentricity, form coefficient, and contour index. This study also used a grid printed on paper. The images obtained were drawn over the grid, which was used to count points over a certain histological structure as well as to count intersections between two contiguous structures. All that was needed, in the first case, was to consider the number of points located over the studied structure, or, in the second case, the number of times that neighboring surfaces cut the curve line. With the aim to evaluate the cytoplasmic volume, cellular volume, cytoplasm/nucleus relation, cellular numeric density, external surface/basal layer relation, the thickness of epithelial layers, and surface density, point counting was used at times and, at others, the number of intersections was considered and applied to the appropriate stereological equations for each variable. All the collected data were subjected to non-parametric statistics Wilcoxon-Mann-Whitney Test. The nuclei of the studied tissues showed reduced values after cariometry for: greater, smaller, and mean diameter; volume; area; perimeter; and volume/area relation. Stereologically, it was observed, in the junctional epithelium, adamantine epithelium, and in the inserted gum epithelium, cells with less volume and with scarce cytoplasm, which caused a greater number of cells per mm3 of tissue. The periodontal ligament was also disorganized and with smaller fibers. In this study, cobalt caused epithelial hypertrophy symptoms, indicating a direct action on the junctional and adamantine epithelium, inserted gum epithelium, as well as on the periodontal ligament.
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Sakita, Alan Massayuki Perdizio [UNESP]. "Filmes de 'CO' obtidos por deslocamento galvânico e suas propriedades magnéticas." Universidade Estadual Paulista (UNESP), 2014. http://hdl.handle.net/11449/110710.
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000774014_20150625.pdf: 1019373 bytes, checksum: 653cd9b6f404483574e7bea6de40de53 (MD5)Este trabalho aborda a deposição de cobalto sobre zinco utilizando a técnica de deslocamento galvânico. Inicialmente foi feito um estudo detalhado do zinco nas diversas condições em que foram depositados os filmes de cobalto. Os filmes de cobalto foram sintetizados em banhos de cloreto e sulfato com e sem glicina em pH 3 e 5 e analisados por SEM, MO, EDXS, XDR e VSM. Durante o processo de deposição foi monitorado o potencial em circuito aberto e adicionalmente foram realizadas medições de espectroscopia de impedância eletroquímica com a finalidade de elucidar os possíveis processos que ocorrem durante a deposição. Os filmes de cobalto obtidos mostram que a adição de glicina resulta numa deposição mais homogênea e sem a formação de produtos secundários como Zn5(OH)8Cl2.2H2O e Zn4(SO4)(OH)6.4H2O. A adição da glicina ainda revela uma maior evolução de hidrogênio no sistema, possivelmente relacionada à desprotonação do íon glicinato. O estudo eletroquímico do processo de deposição através de medições de potencial em circuito aberto revela maior estabilidade de potencial com a utilização de glicina no banho. O monitoramento da deposição de cobalto utilizando EIS mostra que os íons Co2+ facilitam o processo de dissolução de Zn. Com o aumento da concentração de glicina e do tempo de deposição aumenta os valores de capacitância da dupla camada elétrica e diminui a resistência à transferência de carga, sugerindo que ambas variáveis induzem o crescimento da área do eletrodo. As medidas das propriedades magnéticas mostram uma maior deposição de material metálico magnético em pH 3 em cloreto e sem a utilização de glicina, sendo que com a adição da mesma foi observado maior quantidade de cobalto metálico depositado em pH 5. Já em sulfato observa-se maior deposição de cobalto metálico na presença e ausência de glicina ambos em pH 5.
This work comprises the cobalt deposition onto zinc by using the galvanic displacement technique. The cobalt films were prepared from chloride and sulfate baths with and without glycine, and at pH 3 and 5. The deposits were characterized by: SEM, OM, EDXS, XRD and VSM. During the deposition process, it was monitored the open circuit potential and subsequently were conducted electrochemical impedance spectroscopy (EIS) measurements in order to elucidate the possible processes that may occur during the galvanic deposition. The results showed that the glycine addition leads to a more homogeneous deposition and no byproducts, such as Zn5(OH)8Cl2.2H2O and Zn4(SO4)(OH)6.4H2O, are formed. Furthermore, the glycine addition to the bath revealed a higher hydrogen evolution during the deposition process, possibly related to the deprotonation of glycinate ion. The electrochemical study of the galvanic displacement process by measuring the open circuit potential revealed a higher potential stability when glycine was employed in the bath. The monitoring of cobalt deposition by EIS showed that the Co2+ ions facilitate the process of Zn dissolution. By increasing the glycine concentration and the deposition time, the capacitance values, related to the double electric layer, increase and the charge transfer resistance decreases, suggesting that both parameters induce an increase in the electrode area. The magnetic properties of the Co deposits, extracted from the VSM measurements, exhibited the highest saturation magnetization for the deposit obtained from chloride bath at pH 3 without the glycine addition, indicating the presence of a higher amount of metallic Co in this condition. In the case of the sulfate bath, the highest saturation magnetization was reached for the deposits obtained at pH 5 in the presence of glycine.
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Marcos, Francielle Candian Firmino. "Estudo de catalisadores de cobalto suportados em matrizes de La2O3-CeO2-SiO2 para a produção de hidrogênio a partir da reforma a vapor do etanol." Universidade de São Paulo, 2012. http://www.teses.usp.br/teses/disponiveis/75/75134/tde-10102012-142141/.
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No presente trabalho, foram estudados catalisadores de Co10%SiO2, com adições de La2O3 e CeO2, para a reação de reforma a vapor do etanol (RVE), visando aumentar a atividade catalítica e reduzir a formação de carbono sobre o catalisador. O teor mássico de cobalto utilizado foi de 10%, enquanto que os teores de La e Ce seguiram as seguintes proporções em 10%CoLa2%Ce50%-xSi50%, onde X = 2%, 4% e 6%. Os suportes foram preparados pelos métodos de co-precipitação e impregnação a fim de avaliar o efeito do método de preparação sobre o comportamento catalítico, e a fase ativa foi incorporada através do método da impregnação. Todos os catalisadores obtidos foram submetidos à análise de Espectroscopia Dispersiva em Emissão de Raios X (EDX), Difratometria de Raios X (DRX), Redução à Temperatura Programada (RTP) e Área Superficial Específica pelo método BET. Os catalisadores preparados pelo método de co-precipitação do suporte também foram analisados por Difratometria de Raios X- H2 \"in Situ\". Em seguida os catalisadores foram aplicados na reação RVE, e dentre os catalisadores estudados o que apresentou a maior seletividade para o H2 em cada método foi selecionado para a realização de estudos referentes á variação do teor em massa da fase ativa (10% e 20%) e a variação da temperatura de reação. O desempenho destes catalisadores foi comparado com o obtido para os catalisadores sem aditivo no suporte. Após os testes catalíticos, o coque formado foi quantificado por Análise Elementar e caracterizado por Microscopia Eletrônica de Varredura (MEV) e Difratometria de Raios X. Ao analisar os resultados de DRX e RTP observou-se a formação da fase Co3O4 para todos os catalisadores. E para os catalisadores mistos Co/La-Ce-Si, cujos suportes foram co-precipitados e impregnados, identificou-se, através do DRX, a formação da solução sólida entre o óxido de cério e o óxido lantânio. Nos ensaios reacionais foi observado que os catalisadores com maiores teores de La3+, para ambos os métodos de preparação, foram mais seletivos para H2, e que a temperatura influenciou no desempenho catalítico da reação. Ao analisar o carbono após a RVE, somente os catalisadores suportados em La2O3 puro, para ambos os métodos, apresentaram a espécie La2O2CO3 identificada através da DRX, que minimiza a formação do coque, e através da analise por MEV do catalisador após a reação, verificou-se que o coque formado foi filamentoso, permitindo a exposição do cobalto metálico por um maior período de tempo.This research reports studies with Co/SiO2 catalysts modified with La2O3 and CeO2 by steam reforming of ethanol (SRE) in order to increase the catalytic activity and reduce the carbon formation on the catalyst. The amount of Co used was 10%, already of La and Ce were 10% CoLaxCe50-xSi50, where X = 2%, 4% and 6%. The supports were prepared according co-precipitation and impregnation methods in order to evaluate the effect on the catalytic performance. The active phase was incorporated by impregnation method. All were characterized by Energy Dispersive X Ray Spectroscopy (EDX), X Ray Diffraction (XRD), Temperature-Programmed Reduction (TPR) and Specific Surface Area (BET) and those prepared by co-precipitation were also analyzed by X Ray Diffraction in Situ. Thereafter, the catalysts were applied in the SRE and the highest selectivity against H2 in each method was selected for studies of variation of the mass content of active phase (10% and 20%) and temperature reaction. The performance was compared with catalysts without additive in the holder. After tests, the coke formed was determined by Elemental Analysis and characterized by Scanning Electron Microscopy (SEM) and XRD. From the XRD and TPR results was possible identify the presence of Co3O4 phase in all catalysts. In the mixed catalyst (Co/Ce-La-Si) was identified, by XRD, the formation of solid solutions between the cerium and lanthanum. Was observed that the catalyst with higher concentrations of La3+, in both methods of preparation, were more selective against H2, furthermore the temperature affected the performance of the catalysis. After characterization and quantification of the produced carbon during SRE, only catalysts supported in pure La2O3, for both methods, showed the formation of La2O2CO3, which minimizes coke formation and was identified by XRD. Through of SEM analysis of the catalyst after the reaction, it was found that coke formed a filamentous-like structure, allowing the exposure of the metallic cobalt for a longer period of time with the support.
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Sader, Ana Paula de Oliveira. "Estudo espectrofotométrico do sistema cobalto(II)/tiocianato e seu aproveitamento analítico." Universidade de São Paulo, 2002. http://www.teses.usp.br/teses/disponiveis/59/59138/tde-19102006-204125/.
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Estudos sobre a formação dos complexos de metais, seus equilíbrios e, também, o aproveitamento analítico desses diferentes sistemas constituem uma tradicional linha de pesquisa em Química. Mais especificamente, as espécies formadas entre os vários pseudo-haletos e outros ligantes, com muitos cátions dos metais de transição, vêm sendo sistematicamente investigadas em nossos laboratórios de Química Analítica. Nesta linha, o emprego do íon tiocianato como ligante tem se destacado dentre os métodos analíticos para a determinação de cobalto, cuja procura tem sido crescente à medida que o homem, ao longo de sua evolução, descobre e produz novos materiais contendo esse metal. Desta forma, tendo em vista algumas características típicas do sistema Co(II)/SCN-, tal como sua intensa coloração, objetivou-se, nesta oportunidade, explorá-lo espectrofotometricamente com maior profundidade. Conseqüentemente, diversos parâmetros envolvidos na complexação dos íons cobalto (II) pelo tiocianato, tais como: a acidez do meio, a concentração disponível de ligante e a presença de solventes orgânicos no sistema, tiveram seus efeitos avaliados individualmente. Com os resultados destes estudos, estabeleceram-se as condições experimentais otimizadas para a montagem do método analítico, visando a determinação de íons cobalto(II). São elas: C (HClO4) =0,050 mol L-1 C (SCN-)=0,203 mol L-1 C(THF)=60% (v/v) Através de estudos espectrofotométricos preliminares, observou-se que o sistema apresenta dois máximos de absorção nestas condições experimentais: 316 e 622 nm, sendo esta última banda, aquela normalmente utilizada neste tipo de trabalho. Estudos de calibração nos dois comprimentos de onda indicaram que as leituras obedecem fielmente à lei de Beer em ambos os casos, porém com sensibilidade significativamente maior na região ultravioleta (E(316nm)= 1,20 x 104 e E(622nm)= 1,95 x 103 L mol-1 cm-1). Outros estudos sobre estabilidade, repetibilidade (precisão) e de possíveis interferentes também foram realizados, sendo os resultados bastante satisfatórios para fins analíticos. Observou-se interferência das espécies: I-, Al3+, IO3-, Mn2+, NO2-, BrO3-, S2O32-, Hg2+, Cd2+, quando presentes em concentrações cem vezes superiores à de cobalto(II). Entretanto, tal efeito desaparece quando estes íons acham-se em concentrações dez vezes maior do que a do metal de interesse. Aplicações analíticas do método proposto foram testadas em um produto farmacêutico (vitamina B12) e em uma liga odontológica, com resultados plenamente satisfatórios, já que os erros percentuais obtidos ficaram dentro da faixa aceitável (< 5%). A técnica de espectroscopia de absorção atômica foi utilizada paralelamente nestas análises, para efeito comparativo, na qual a determinação de cobalto mostrou-se possível na liga odontológica, mas inadequada para o fármaco (erro da ordem de 20%), nas condições de abertura realizadas. A comparação dos resultados mostra a potencialidade do método proposto, tendo em conta a simplicidade, exatidão e custo das aparelhagens. Finalizando, a possível influência do níquel (presente naturalmente em diversas amostras reais) na determinação de cobalto foi avaliada sob as condições experimentais estabelecidas para o método espectrofotométrico proposto. Observou-se que este contaminante natural exibe um pico de absorção em 245 nm e, através dos estudos, confirmou-se a aditividade das absorbâncias dos respectivos complexos (Co e Ni). Testou-se a possibilidade de determinação espectrofotométrica simultânea destes dois metais, através de leituras nos respectivos máximos (245 e 316 nm), empregando-se um sistema algébrico com duas equações simples, cujos resultados foram plenamente satisfatórios. As faixas úteis de trabalho, em termos de concentrações de cobalto e níquel foram, respectivamente: 0,94 a 4,04 mg L-1 e 28,7 a 123,7 mg L-1, respectivamente.Studies about the formation of metallic complexes, their equilibria and also the analytical utilization of these different systems represent a traditional research line in Chemistry. More specifically, the species formed among the various pseudohalides and other ligands, with several cations of transition metals, have been systematically investigated in our Laboratories. The use of the thiocyanate ion as ligand has been intensive from among the analytical methods for cobalt(II) determination, of which interest has increased more recently, according to the man discovers and production of new materials containing this metal. Due some typical characteristics of the system Co(II)/SCN-, such as its colored complexes, the principal purpose of this study was to explore it more carefully by visible-ultraviolet spectrophotometry. Consequently, several parameters involved in the cobalt(II)/thiocyanate complexes formation, such as acidity level, concentration of free ligand, and the percentage of organic solvents in the system, had their respective effects evaluated individually. Through the results of these diverse studies, appropriate experimental conditions were established for the analytical methods, for the determination of the cobalt(II) ion. They are: C (HClO4)=0.050 mol L-1 C (SCN-)=0.203 mol L-1 C(THF)=60% (v/v) Preliminary spectrophotometry studies showed two absorption maxima (peaks) under these optimized experimental conditions: 316 and 622 nm, being this last visible band normally applied for this type of work (determination). Calibration studies at these two wavelengths showed that the Beers Law is obeyed in both cases, but a higher sensitivity was obtained in the ultraviolet region ( E(316nm)= 1.20 x 104 e E(622nm)= 1.95 x 103 L mol-1 cm-1). Other studies about stability, precision, accuracy and possible interferences were also performed, showing satisfactory results for the analytical purposes. It was observed some interference of the following species: I-, Al3+, IO3-, Mn2+, NO2-, BrO3-, S2O32-, Hg2+ and Cd2+, when present in concentrations one hundred times higher than the cobalt(II). However, this effect disappears when these ions are presented on concentration just ten times higher. Analytical applications of the proposed method were tested for a pharmaceutical product (B12 vitamin) and for an odontological alloy, with large success, since the percentage of error was within the tolerance range (<5%). Atomic absorption spectroscopy was also used in this analysis for comparision, in which the cobalt determination was possible for the alloy but inadequate for the pharmaceutical product (error about 20%). Comparison of the results shows the potentiality of this alternative spectrophotometric method, taking in account its simplicity, accuracy and equipments prices. Finally, the influence of nickel (naturally present in several real samples) on the spectrophotometric cobalt determination was evaluated, under the optimized experimental conditions. It was observed that this natural contaminating exhibits an absorption peak at 245 nm. Other confirmatory studies show the additivities of the respective absorbances (nickel and cobalt/thiocyanate complexes), allowing the simultaneous spectrophotometric determination of these these metals, using a matematical system with two equations (peaks 245 and 316 nm). This attempt was well satisfactory and the useful concentration ranges for cobalt and nickel were, respectively, 0.94 to 4.04 mg L-1 and 28.7 to 123.7 mg L-1.
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Sakita, Alan Massayuki Perdizio. "Filmes de 'CO' obtidos por deslocamento galvânico e suas propriedades magnéticas /." Araraquara, 2014. http://hdl.handle.net/11449/124433.
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Orientador: Assis Vicente BenedettiCo-orientador: Rodrigo Della Noce
Banca: Hercilio Gomes de Melo
Banca: Roberto Zenhei Nakazato
Resumo: Este trabalho aborda a deposição de cobalto sobre zinco utilizando a técnica de deslocamento galvânico. Inicialmente foi feito um estudo detalhado do zinco nas diversas condições em que foram depositados os filmes de cobalto. Os filmes de cobalto foram sintetizados em banhos de cloreto e sulfato com e sem glicina em pH 3 e 5 e analisados por SEM, MO, EDXS, XDR e VSM. Durante o processo de deposição foi monitorado o potencial em circuito aberto e adicionalmente foram realizadas medições de espectroscopia de impedância eletroquímica com a finalidade de elucidar os possíveis processos que ocorrem durante a deposição. Os filmes de cobalto obtidos mostram que a adição de glicina resulta numa deposição mais homogênea e sem a formação de produtos secundários como Zn5(OH)8Cl2.2H2O e Zn4(SO4)(OH)6.4H2O. A adição da glicina ainda revela uma maior evolução de hidrogênio no sistema, possivelmente relacionada à desprotonação do íon glicinato. O estudo eletroquímico do processo de deposição através de medições de potencial em circuito aberto revela maior estabilidade de potencial com a utilização de glicina no banho. O monitoramento da deposição de cobalto utilizando EIS mostra que os íons Co2+ facilitam o processo de dissolução de Zn. Com o aumento da concentração de glicina e do tempo de deposição aumenta os valores de capacitância da dupla camada elétrica e diminui a resistência à transferência de carga, sugerindo que ambas variáveis induzem o crescimento da área do eletrodo. As medidas das propriedades magnéticas mostram uma maior deposição de material metálico magnético em pH 3 em cloreto e sem a utilização de glicina, sendo que com a adição da mesma foi observado maior quantidade de cobalto metálico depositado em pH 5. Já em sulfato observa-se maior deposição de cobalto metálico na presença e ausência de glicina ambos em pH 5.
Abstract: This work comprises the cobalt deposition onto zinc by using the galvanic displacement technique. The cobalt films were prepared from chloride and sulfate baths with and without glycine, and at pH 3 and 5. The deposits were characterized by: SEM, OM, EDXS, XRD and VSM. During the deposition process, it was monitored the open circuit potential and subsequently were conducted electrochemical impedance spectroscopy (EIS) measurements in order to elucidate the possible processes that may occur during the galvanic deposition. The results showed that the glycine addition leads to a more homogeneous deposition and no byproducts, such as Zn5(OH)8Cl2.2H2O and Zn4(SO4)(OH)6.4H2O, are formed. Furthermore, the glycine addition to the bath revealed a higher hydrogen evolution during the deposition process, possibly related to the deprotonation of glycinate ion. The electrochemical study of the galvanic displacement process by measuring the open circuit potential revealed a higher potential stability when glycine was employed in the bath. The monitoring of cobalt deposition by EIS showed that the Co2+ ions facilitate the process of Zn dissolution. By increasing the glycine concentration and the deposition time, the capacitance values, related to the double electric layer, increase and the charge transfer resistance decreases, suggesting that both parameters induce an increase in the electrode area. The magnetic properties of the Co deposits, extracted from the VSM measurements, exhibited the highest saturation magnetization for the deposit obtained from chloride bath at pH 3 without the glycine addition, indicating the presence of a higher amount of metallic Co in this condition. In the case of the sulfate bath, the highest saturation magnetization was reached for the deposits obtained at pH 5 in the presence of glycine.
Mestre
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Nik, Mohd Masdek Nik Rozlin. "Electrodeposition and corrosion study of nanocrystalline cobalt and cobalt-iron alloy coatings." Thesis, University of British Columbia, 2014. http://hdl.handle.net/2429/49944.
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Nanocrystalline materials with grain sizes less than 100 nm, have attracted considerable attention due to their enhanced properties as compared to their polycrystalline counterparts. However, investigation on the corrosion resistance of these materials is still lacking. In order to further expand their future applications, their corrosion behaviour is of great importance. Hence, in this study, nanocrystalline Co and CoFe alloy coatings were prepared through the electrodeposition process and their electrochemical corrosion behaviour were investigated. Depending on the environment, the effect of the nanocrystaline grain sizes as well as Fe alloying resulted in different corrosion responses. A decrease in grain size was observed with an increase in iron concentration that also leads to a change in crystal structure from HCP to BCC phase structure. Meanwhile, microhardness was first seen to increase gradually with the increase in iron content before it decreases with higher iron concentration of more than 18 wt%Fe. The corrosion properties of these electrodeposited nanocrystalline Co and CoFe alloy coatings were also studied in solutions ranging from acidic to alkaline. Nanocrystalline Co and CoFe exhibit higher corrosion rates in 0.1 M H₂SO₄ than in an alkaline environment. In deaerated acidic solutions, both nanocrystalline Co and CoFe alloy coatings showed only active anodic dissolution without any transition to passivation. Meanwhile, two stages of passivation were present in the alkaline solution which is reported to be due to the formation of a duplex passive film.
The presence and absence of saccharin as an additive in the electrolyte both showed detrimental and beneficial effect on the corrosion behaviour of these nanostructured deposited coatings. By employing the electrochemical quartz crystal microbalance (EQCM), it was observed that the mass decrease was significant with an increase in saccharin concentration indicating an active dissolution. However, saccharin was observed to hinder the formation of a protective passive film on CoFe alloy coatings in alkaline solution. The presence of the sulphide ion also significantly decreased the corrosion resistance of deposited CoFe alloy coatings. The presence of sulphide accelerates markedly the anodic reaction. The dissolution rate was two times faster when S²− was added.Applied Science, Faculty of
Materials Engineering, Department of
Graduate
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Chen, Ming-Chou. "Metallacyclobutenes as reactive intermediates : conversion to cobalt diene and cobalt allene complexes /." Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 1998. http://wwwlib.umi.com/cr/ucsd/fullcit?p9834967.
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Foelske, Annette. "Oberflächenanalytische Untersuchungen zur anodischen Deckschichtbildung auf Kobalt- und Co(0001)-Einkristallelektroden." [S.l. : s.n.], 2004. http://deposit.ddb.de/cgi-bin/dokserv?idn=970112378.
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Önem-Siakou, Evgenia. "Cobalt(III)-Kohlenhydrat-Verbindungen." Diss., lmu, 2003. http://nbn-resolving.de/urn:nbn:de:bvb:19-33130.
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Kim, S. S. "Cobalt catalysed oxidation reactions." Thesis, University of East Anglia, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.376060.
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Lyu, Ye. "Cobalt-catalyzed Hydroelementation Reactions." Thesis, Sorbonne université, 2019. http://www.theses.fr/2019SORUS611.
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Cette thèse portait sur l’utilisation des complexes de cobalt de basse valence bien définis tel HCo(PMe3)4/HCoN2(PPh3)3 ainsi que les complexes haute valence de la famille des Cp*Co(III) stables à l’air, et leurs applications en activation de liaisons R–H (R = B, C, Si). Premièrement, nous avons utilisé avec succès le complexe HCo(PMe3)4 pour catalyser l'hydroboration et la diboration régio- et setéréosélective d’alcynes. De plus, nous avons étendu cela à la silaboration d'alcyne. Ensuite, nous avons démontré que les complexes HCo(PMe3)4 et HCoN2(PPh3)3 permettaient l’ hydrogénation stéréo-divergente d’alcynes and fonction du complexe utilisé . Enfin, nous avons exploré l'application des complexes de type Cp*Co(III) stables avec des additifs de type acides chiraux en fonctionnalisation asymétrique de liaisons C–H. De plus, nous avons commencé la synthèse du complexe chiraux de type Cp*Co(III), ou le Cp est cette fois chiralThis thesis was focused on well-defined low-valent cobalt complexes HCo(PMe3)4/HCoN2(PPh3)3, the bench stable family Cp*Co(III) of complexes and their applications in R–H activation (R = B, C, Si). First, we successfully used the HCo(PMe3)4 complex to catalyze regio- and stereo-selective hydroboration and diboration of alkynes. In addition, we exploited the HCo(PMe3)4 complex to catalyze silaboration of alkyne. Then, we demonstrated that the HCo(PMe3)4 complex and HCoN2(PPh3)3 complex were useful in the stereo-divergent hydrogenation of alkynes. Finally, we explored the application of the bench- stable Cp*Co(III) together with chiral additives in asymmetrical C–H bond functionalization. In addition, we conducted the elementary exploitation in synthesis of chiral Cp*Co(III) complexes
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Haffer, Stefanie [Verfasser]. "Mesoporous spinel-type cobalt oxide, cobalt ferrite and alumina by nanocasting / Stefanie Haffer." Paderborn : Universitätsbibliothek, 2014. http://d-nb.info/1046651994/34.
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Ogrin, Feoder. "Ferromagnetic resonance studies of cobalt films and cobalt based multilayers produced by MOCVD." Thesis, Keele University, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.362165.
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Govender, Alisa. "Cobalt core-shell nanoparticles as precursors for cobalt-based Fischer-Tropsch synthesis catalysts." Doctoral thesis, Faculty of Engineering and the Built Environment, 2018. http://hdl.handle.net/11427/30007.
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Core-shell nanoparticles may have an economic advantage over traditional nanoparticles as a catalyst, since the expensive, catalytically active material, which is subsurface, may be replaced with a cheaper counterpart. Furthermore, core-shell nanoparticles may be tailored to have a specific structure and composition at the nanoscale, due to a mixing of electronic properties of each phase and/or geometric effects. In this study, nickel ferrite (NiFe2O4) and zinc ferrite (ZnFe2O4) were chosen as core materials around which a cobalt (II, III) oxide (Co3O4) shell was grown. These ferrites were chosen due to their structural similarity to Co3O4 as this was expected to allow an epitaxial growth of the Co3O4 shell onto the ferrite core. Additionally, the difference in the lattice parameter between each ferrite core and the Co3O4 shell was postulated to introduce a varying degree of strain onto the shell, particularly after reduction when metallic cobalt should be present. Core-shell nanoparticles with either a nickel ferrite (NiFe2O4) core or a zinc ferrite (ZnFe2O4) core and a cobalt (II, III) oxide (Co3O4) shell (NiFe2O4@Co3O4 and ZnFe2O4@Co3O4 respectively) were synthesized, characterized and tested for their performance in the Fischer-Tropsch synthesis. These core-shell systems were compared to each other to evaluate the influence of the core and the applicability of NiFe2O4 or ZnFe2O4 as core nanoparticles in a cobalt-based Fischer-Tropsch catalyst. NiFe2O4@Co3O4 core-shell nanoparticles were also supported on Stöber silica spheres to determine the effect of the support on its properties and performance. The influence of two different reduction conditions, viz. 180°C (1 hour) or 230°C (2 hours), on the structure and Fischer-Tropsch synthesis performance of unsupported and Stöber silica spheres supported NiFe2O4@Co3O4 core-shell nanoparticles was also studied. Prior to the preparation of the core-shell nanoparticles, each ferrite core was prepared using the citrate precursor method. A Fe/M mole % ratio (where M is Ni or Zn) of 2.3 and calcination temperature of 450°C yielded phase pure NiFe2O4 or ZnFe2O4 nanoparticles with an average size of 14 nm. Using nickel ferrite (NiFe2O4) nanoparticles as a core, the growth of cobalt (II, III) oxide (Co3O4) around the core was studied by following a homogeneous precipitation synthesis. It was established that a two-step synthesis route was needed to synthesize the core-shell material with a fairly uniform Co3O4 shell. It was found that for both NiFe2O4@Co3O4 and ZnFe2O4@Co3O4 core-shell nanoparticles, the assynthesized materials had a Co3O4 shell around the ferrite core with an average thickness of 2 nm. NiFe2O4@Co3O4 and ZnFe2O4@Co3O4 core-shell nanoparticles were compared to each other as precursors for Fischer-Tropsch synthesis catalysts. Here, the first report on the nanoscale restructuring during reduction of these core-shell nanoparticles in pure hydrogen at 230°C and 250°C, respectively, was observed. This resulted in the formation of small cobalt islands on the ferrite surface. Catalytic testing of the core-shell materials, NiFe2O4@Co3O4 and ZnFe2O4@Co3O4, after reduction showed a cobalt-time yield of 13.64 µmolCO .gCo -1.s -1 and 4.27 µmolCO .gCo -1.s -1 and a C5+ selectivity of 47 C-% and 68 C-%, respectively. The observed difference in cobalt-time yield and selectivity between NiFe2O4@Co3O4 and ZnFe2O4@Co3O4 core-shell nanoparticles was due to a combination of effects that included the presence of cobalt islands over the surface of the core and the difference in extent of reduction of each core under Fischer-Tropsch synthesis conditions. The core-shell structure in NiFe2O4@Co3O4 core-shell nanoparticles was found to be retained with the use of mild reduction conditions of 180°C (1 hour). Thus, the performance in the Fischer-Tropsch synthesis of a system with a true core-shell structure with a cobalt shell was established. The former has not been reported to date. Owing to the former, strain effects may have contributed to NiFe2O4@Co3O4 core-shell (reduced at 180°C, 1 hour) having a low cobalt-time yield of 8.40 µmolCO .gCo -1.s -1 and a C5+ selectivity of 38 C-% during the Fischer-Tropsch synthesis. It was also shown that NiFe2O4@Co3O4 core-shell nanoparticles reduced at 180 °C (1 hour) had a similar activity to unsupported Co3O4, however, the former had a higher C5+ selectivity. The differences in the performance between NiFe2O4@Co3O4 core-shell (reduced at 180°C, 1 hour) and unsupported Co3O4 may have been due to strain effects. The nanoscale structural and compositional differences induced by each reduction condition applied may have been the cause for the inferior Fischer-Tropsch synthesis performance of these core-shell nanoparticles after reduction at 180°C for 1 hour than 230°C for 2 hours. The effect of a Stöber silica spheres support on the characteristics and Fischer-Tropsch synthesis behavior of NiFe2O4@Co3O4 core-shell nanoparticles was also investigated. Prior to characterization and the Fischer-Tropsch synthesis, NiFe2O4@Co3O4/SiO2 was reduced at either 180°C for 1 hour or 230°C for 2 hours. A higher cobalt-time yield (23.80 µmolCO .gCo -1.s -1) with a lower C5+ selectivity (44 C-%) was obtained with reduction at 230°C (2 hours) than 180°C (1 hour). After reduction at 230°C (2 hours), the influence of the support was clearly seen due to the higher activity obtained with NiFe2O4@Co3O4/SiO2. However, the unsupported and supported NiFe2O4@Co3O4 nanoparticles had similar product selectivities. After reduction at 230°C for 2 hours and exposure to Fischer-Tropsch synthesis conditions, the core-shell structure was retained in NiFe2O4@Co3O4/SiO2 possibly due to reducing the contact between the individual core-shell nanoparticles due to the presence of the support. This would be enhanced by anchoring the core-shell nanoparticles onto the Stöber silica spheres support.
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Kiviaho, Jari. "Fischer-Tropsch synthesis catalysed by cobalt-rhodium and cobalt-ruthenium carbonyl clusters on silica /." Espoo : Technical Research Centre of Finland, 1996. http://www.vtt.fi/inf/pdf/publications/1996/P290.pdf.
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Åkre, Torjus. "Electrowinning of Cobalt from Chloride Solutions: Anodic Deposition of Cobalt Oxide on DSA®." Doctoral thesis, Norwegian University of Science and Technology, Department of Materials Technology, 2008. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-2200.
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Gourion, Louis. "Le cobalt en biologie humaine." Paris 5, 1988. http://www.theses.fr/1988PA05P080.
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Ng, Jesse B. "Mono- and binuclear cobalt hydrides." Thesis, University of British Columbia, 1990. http://hdl.handle.net/2429/30789.
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The homogeneous hydrogenation of arenes with functional groups was studied with allylcobalt complexes containing the bulky chelating diphosphines dippp (1,3-bis(diisopropylphosphino)propane and dippcyp (trans-(±)-l,2-bis(diisopropylphos-phino)cyclopentane). The results indicated that these catalyst precursors were unsuitable for the hydrogenation reactions, being too sensitive to the nature of the substrate. From these hydrogenation reactions, the intermediates (η⁵-cyclohexadienyl)Co(dippcyp) (10) and (η⁴-2-methoxynaphthalene)Co(H)(dippcyp) (11) were isolated and structurally characterized, thus providing some insight into the mechanism of the hydrogenation reaction.
The production of binuclear hydrides such as [(dippp)CoH₂]₂ (4) and [(dippcyp)CoH₂]₂ (9) was observed to lead to the end of the catalysis. An X-ray structural characterization of the blue hydride [(dippp)CoH₂]₂ (4) showed that in the solid state it is binuclear. Although the complex is diamagnetic in the solid state (6-280 K), in solution its paramagnetic behaviour could only be attributed to an equilibrium with a second species proposed to be mononuclear, (dippp)CoH₂. In addition, a cyclic voltammogram of the complex in solution indicated that the predominant species still was the binuclear compound [(dippp)CoH₂]₂ (4).
One of the syntheses of [(dippp)CoH₂]₂ (4) gave a product identified as (dippp)CoH₃ (5). Based on variable-temperature spin-lattice relaxation time (T₁) measurements and an electrochemical study, this red hydride complex appeared to contain an η²-H₂ ligand. The relationship of this complex with the blue hydride apparently involves the mononuclear species, (dippp)CoH₂. Independent pathways led to the formation of both the blue and red hydrides, and these pathways are discussed in terms of possible mechanisms.Science, Faculty of
Chemistry, Department of
Graduate
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Numprasanthai, Apisit Chemical Sciences & Engineering Faculty of Engineering UNSW. "Binary skeletal copper-cobalt catalysts." Publisher:University of New South Wales. Chemical Sciences & Engineering, 2009. http://handle.unsw.edu.au/1959.4/43587.
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Binary skeletal metal catalysts were made by starting with a ternary alloy. The percursor alloys and catalysts were characterised using Optical Microscopy, X-ray Diffractometer, Scanning Electron Microscopy, Inductively Coupled Plasma (ICP) and BET surface area in term of morphologies, phase identification, surface area and pore structure. Skeletal copper catalyst presented high surface areas and consisted primarily of CuAl2 grains, with small well-dispersed areas of the Al-CuAl2 eutectic. The CuAl2 phase, which represented a tetragonal structure, showed large cell volumes resulted in a fine skeleton structure. Binary nickel-copper catalyst composed of three majority phases including Ni2Al3, Cu4NiAl7 and Al. The Cu4NiAl7 was found to be a caustic resistant phase which led to low surface area in the nickel-copper catalyst In terms of the selective removal of aluminium from the copper-cobalt-aluminium alloy to create the binary copper-cobalt catalyst, 11 alloy samples with various compositions were produced following the ternary phase diagram. The surface area and pore size of these catalysts was dependant on the crystal structure of the phases present and the amount of remaining Al. Electrochemical glucose oxidation and carbon dioxide reduction activity have been used for testing the catalyst performance. The electrochemical oxidation of glucose experiment using 11 samples of skeletal Cu-Co catalyst as an electrode showed the results that the significant oxidation peaks were observed in sample 1, 4, 8, 9 and the small oxidation humps were observed in other sample except sample 2. These small peaks resulted from that the glucose molecule had difficulty to absorb on the surface area of the skeletal Cu-Co catalysts electrode. The difficulty may results from very fine pore volume and pore size of the catalysts. In term of assessing the skeletal Cu-Co catalyst with electrochemical reduction of carbon dioxide experiment, the skeletal Cu-Co catalyst sample 7 which presented the highest surface area was selected as an electrode to compare with Cu foil electrode. The result of using skeletal Cu-Co as an electrode indicated significantly higher current. This results from that a skeletal Cu-Co catalyst electrode presented an actual high surface area which leads to more adsorbed regions.
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Guindy, Christina Irene. "Cobalt complexes of radical ligands." Thesis, University of Nottingham, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.408058.
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Saikoff, Elsa, Edvin Andersson, Felix Bengtsson, Christoffer Olausen, Monika Galstyan, David Vikström, and Byström Joseph Lazraq. "Cobalt in High Speed Steels." Thesis, Uppsala universitet, Institutionen för teknikvetenskaper, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-355124.
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One of the most important additives in High Speed Steels (HSS) is cobalt, mainly for its effect on the hot properties. Based on statistic data about the increased price of cobalt and its negative effect on human health, an ethical and financial barrier in the steel industry have occurred. In order to solve the problem, it is of great importance to examine the future cobalt price and accessibility, as well as examine the possibility of finding alternative substitutes to cobalt. The purpose of this project was therefore to examine alternatives to cobalt as an alloying element in HSS. A qualitative literature study was performed by analyzing the economy of cobalt, studying the main reasons for cobalts tendency to improve the hot properties of the steel and finding alternative elements to replace, or at least reduce, cobalt in HSS without degrading the hot properties. Cobalt is used both in the chemical and metallurgical business. But the demand of cobalt is largely driven by chemical purposes with the focus on its rechargeable battery applications. The analysis shows that there is nothing pointing at a significant decrease of the price of cobalt. Lithium ion batteries stands for about 50% of current cobalt supply, which is why the price has surged the recent years. The market for electric vehicles and rechargeable batteries has skyrocketed. To decrease the price of cobalt, a substitute for cobalt in rechargeable batteries would need to be found, which is not very likely for the time being. The effect of cobalt in HSS is mainly on the red hardness and tempering resistance. Cobalt increases the bonding strength in the steel matrix and changes the microstructure of the finer secondary carbides. Also the growth rate and coalescence rate of the carbides decreases. This causes the red hardness and the tempering resistance to increase. To replace cobalt, several alternative alloying elements have been researched. Among the most promising are niobium, nitrogen and aluminium, where niobium were found to be of most interest, due to the broad support of relevant articles in the field of powder metallurgical processing. The positive effect of niobium could be regarded as three-fold. The first contribution is the refinement of grain size and homogeneity of the primary carbides, which increases the overall hardness. The second effect is that the addition of niobium shifts the phase equilibria in such a way that the precipitation of primary carbides mainly will be in the form of hard and stable NbC. The majority of the other alloying elements will hence be precipitated as secondary carbides during tempering. The final effect is an increase in secondary hardness, as a consequence of the large amounts of vanadium and smaller amounts of niobium that is being precipitated during tempering to the secondary carbides. This enables a high matrix hardening potential in the optimal state of tempering.
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McCombs, Michelle. "A 59-Cobalt NMR Investigation of the Hydrogen/Deuterium Exchange Kinetics in Cobalt(III) Complexes." TopSCHOLAR®, 2003. http://digitalcommons.wku.edu/theses/554.
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Currently, the hydrogen/deuterium exchange kinetics in cobalt(III) complexes are being investigated. In the presence of deuterated solvents, (e.g. D2 0 and CH3CH20D) the amine hydrogens in the complexes are exchanged for deuteriums. For the hexaamminecobalt(III) ion, 19 isotopmers (H18D0 to HOD 18) are possible. For the tris(ethylenediammine)cobalt(III) ion, 13 isotopmers (HI 2D0 to HOD 12) are possible. Each hydrogen/deuteruim exchange causes a shift in the observed 59Co resonance of approximately 6 ppm. The rate constant of the hydrogen-deuterium exchange for the first H-D exchange has been determined as a function of solvent. When the chosen solvent is D20, the rate constant is 1.09 x 10° sec"1 for the hexaamminecobalt(III) ion. In methanol-d, the rate constant is 1.82 x 10"4 sec"'. Electronic effects of ligands have also been investigated. Experimental conditions (e.g., observation frequencies and solution parameters) and the representative NMR spectra are presented.
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N'Guessan, Gilbert Kouakou. "Réduction électrochimique du composé d'insertion graphite-chlorure de cobalt : étude du composé réduit graphite-cobalt." Grenoble INPG, 1989. http://www.theses.fr/1989INPG0082.
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Le compose d'insertion du graphite c#5cocl#2#,#1#0 est utilise en cathode d'une pile au lithium. La decharge d'une telle pile conduit a la reduction en deux etapes du chlorure de cobalt insere. Le compose ainsi reduit de formule chimique moyenne c#1#1co#0#,#6##0#,#8(co cl#2)#0#,#4##0#,#2(licl)#0#,#5 contient une phase dans laquelle le cobalt est insere en 1#e#r stade
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Araújo, Júnior Ildeu Bastos de. "Estudo da influência do resfriamento em revestimento de liga Stellite 6 aplicada pelo processo TIG /." Bauru :, 2009. http://hdl.handle.net/11449/96481.
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Orientador: Yukio KobayashiBanca: Gilberto de Magalh B. Gonçalves
Banca: Rodolfo Libardi
Resumo: A indústria busca uma melhor otimização e performance de seus equipamentos, há muito notou-se a importância da contenção do desgaste para o aumento de vida útil dos componentes de máquinas. Em condições operacionais onde há o desgaste por abrasão, comumente faz-se o endurecimento da camada superficial ou a aplicação de uma liga mais nobre e de dureza mais elevada, visando conter este desgaste. A técnica também é chamada de revestimento. Entender melhor os parâmetros que influenciam nos resultados da aplicação destes revestimentos torna-se importante possibilitando menores perdas e uma maior economia, pois busca-se como alvo trabalhar com a melhor performance do revestimento. Objetivou-se neste trabalho o estudo das ligas a base de Cobalto que são aplicadas cada vez mais rotineiramente nas indústrias petroquímicas, onde os componentes e órgãos de máquinas estão expostos a condições severas de desgaste por abrasão e corrosão além da severidade dos trabalhos a altas temperaturas e pressão. Relacionando o desgaste, as ligas a base de Cobalto possuem uma posição destacada e a liga é conhecida comercialmente como "Stellite 6". Em alguns trabalhos é chamada também de liga coringa por sua versatilidade e destaque em especial. Neste trabalho procurou-se variar as velocidades de resfriamento em cinco patamares, analisou-se a influência da diluição na micro-dureza e os efeitos da variação da velocidade de resfriamento no mecanismo de endurecimento. A aplicação do revestimento ocorreu em três camadas através do processo TIG. Verificamos ainda a interferência da diluição na dureza em cada camada de revestimento. A terceira e última camada foi a que apresentou maior dureza devido à menor diluição com o metal base principalmente no corpo de prova que possuía à menor velocidade de resfriamento devido ao tempo para a formação de precipitados e carbonetos na liga metálica
Abstract: The industry searchs a better optimization and performance of their equipment, long noted the importance of containment to increase the wear life of components of machines. In operating conditions where there is wear by abrasion, usually it is the hardening of the surface layer or the application of a more noble alloy and high hardness, wear it to contain. The technique also called hardfacing. Better understand the parameters that influence the results of applying these coatings becomes important because it enables lower losses and greater economy as it seeks to target work with the best performance of the coating. The objective of this research is complements the study of cobalt-based alloys that are applied more routinely in petrochemical industries, where the component units and machines are exposed to severe conditions of wear by abrasion and corrosion than the severity of the work at high temperatures and pressure. Relating the wear, the cobalt-based alloys have a prominent position and the league is known commercially as "Stellite 6". Some work is also called the league wildcard for its versatility and highlight in particular. In this work we have tried to vary the speed of cooling in five steps, looked up the influence of dilution on micro hardness and the effects of variation in the rate of cooling in the hardening mechanism. The application of the coating occurred in three layers using the TIG process. We note also the interference of dilution in hardness in each layer of coating. The third and final layer was the one with higher hardness due to less dilution with the base metal mainly in the body of evidence that had the lowest rate of cooling due to the time for the formation of precipitates and carbides in the metal
Mestre
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Monteiro, Kristian. "Recycling of spent lithium nickel-cobalt batteries through leaching of nickel and cobalt from cathode material." Thesis, Monteiro, Kristian (2018) Recycling of spent lithium nickel-cobalt batteries through leaching of nickel and cobalt from cathode material. Honours thesis, Murdoch University, 2018. https://researchrepository.murdoch.edu.au/id/eprint/41912/.
Full textAbstract:
This research paper investigates a hydrometallurgical approach that includes the leaching of spent lithium-ion battery cathode material. The targeted elements to be recovered are cobalt and nickel which are identified to be the cost drivers in the lithium-ion battery to date. The observation of parameters surrounding the leaches give a brief but excellent understanding into the recovery mechanisms and extraction stages of nickel and cobalt in a sulphuric acid and hydrogen peroxide medium.
The recycling of lithium ion batteries is trending to become one of the major processes in the recycling industry heading forward. As more appliances and technologies look to lithium ion batteries for an energy storage system, it is crucial that the supply is not hindered with the increase in demand for the battery. The eventual commercialization of a hydrometallurgical process will most likely be based around the leaching of the spent lithium ion batteries and the recovery of valuable metals.
Although further test work is necessary to achieve credible and reliable results, this thesis demonstrates the effect of the change in parameters within the test work which leads to the recovery of nickel and cobalt from waste lithium ion batteries. 113.2 % cobalt and 98.6 % nickel were recovered with the leaching of cathode material while 109.6 % cobalt and 100.5 % nickel were extracted with the leaching of separator material. The increased recovery at a lower cost will generally lead to a commercialised process that will in the future be used to process all spent lithium- ion batteries.
This thesis looks at the broader scope of the energy storage system market, identifies the cost driver and looks to decrease that cost driver for a viable and cost effective process.
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Firriolo, Janet Marie. "Disposition and toxicity after oral and intravenous administration of cobalt naphthenate and cobalt chloride in rats." Diss., The University of Arizona, 1992. http://hdl.handle.net/10150/185760.
Full textAbstract:
The objective of this study was to determine the absorption and disposition in rats of two cobalt compounds: cobalt chloride, an aqueous-soluble compound, and cobalt naphthenate, an aqueous-insoluble compound. Their in vitro dissolution rates were investigated to determine whether they correlate with their toxicity. Dissolution of cobalt naphthenate was strongly media and pH dependent and showed increased dissolution in the presence of protein and at low pH. Cobalt oxide, an aqueous-insoluble cobalt compound, was unaffected by solution conditions. The in vitro alveolar macrophage results indicated that compounds added as particulates were more cytotoxic than those added in solution. Cobalt chloride was the most cytotoxic and cobalt oxide the least. These results suggest that the order of in vitro cytotoxicity to alveolar macrophages may be predicted from their in vitro dissolution behavior. When the in vitro dissolution of the cobalt compounds was tested at a pH of 2 to model the environment inside the stomach, the dissolution of cobalt naphthenate and cobalt chloride was identical. This indicated that oral exposure to cobalt naphthenate could result in essentially complete dissociation of cobalt at gastric pH. The distribution and elimination of cobalt naphthenate was identical to that of an equivalent Co(II) dose of cobalt chloride. The oral blood cobalt concentration curves were triphasic and exhibited similar pharmacokinetic parameters. Following intravenous administration, approximately 10% of the dose was found in the feces, indicating that cobalt can be secreted in the bile. The intravenous cobalt concentration curve was also triphasic with a terminal elimination half-life of 19.0 hr. Intestinal ring incubation experiments indicated that cobalt transport has both active and passive components. The finding that uptake was saturable may explain the small degree of absorption following oral dosing. The results of the heme oxygenase assays indicated that subcutaneous and intravenous administration resulted in increased activity over controls at an equivalent hepatic Co(II) content. Thus, these results demonstrated that the extent of cobalt absorption across the gastrointestinal tract is incomplete and that concentration and route of exposure may determine its systemic toxicity.
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Van, Leeuwen Robert Alan. "Structural and magnetic properties of cobalt/palladium superlattices, ultra-thin cobalt films and manganese antimony alloys." Diss., The University of Arizona, 1993. http://hdl.handle.net/10150/186431.
Full textAbstract:
Structural, magnetic, and magneto-optical properties of Co/Pd and Co/Pd/Cu superlattices, ultra-thin Co films and MnSb alloys have been studied. The superlattices and Co films were grown by molecular beam epitaxy (MBE) while the MnSb alloy films were made by sputtering techniques. Several x-ray diffraction techniques were used to analyze the physical structure of the superlattices and alloys. Magnetometry techniques were used to determine some of the room temperature and temperature dependent magnetic properties of the films. In situ and ex situ measurements of the magneto-optical properties of the ultra-thin Co films and alloys also were made.
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Lussier, Alexandre Francois. "Ferromagnetism in cobalt-doped titanium dioxide." Diss., Montana State University, 2005. http://etd.lib.montana.edu/etd/2005/lussier/LussierA1205.pdf.
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Ghaschghaie, Natascha. "Heteroleptische Cobalt(III)-Chelatkomplexe mit Bioliganden." Diss., lmu, 2010. http://nbn-resolving.de/urn:nbn:de:bvb:19-121266.
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Sims, Jeffrey J. "Formic Acid Decomposition on Cobalt Surfaces." Thesis, Université d'Ottawa / University of Ottawa, 2015. http://hdl.handle.net/10393/32592.
Full textAbstract:
The decomposition of formic acid proceeds via two principal reaction pathways: dehydration and dehydrogenation. Mechanisms and reaction ratios depend on the nature of the catalysts used. This work provides mechanistic insight into the decomposition of formic acid on Co(0001) and a highly stepped cobalt surface. The catalytic systems were studied in ultra-high vacuum by XPS and temperature programmed desorption. On both surfaces, an overall reaction (1) was observed:
2 HCOOH→H_2 O+CO+H_2+CO_2 (1)
The surfaces had differing reaction intermediates, reaction temperatures, and activation energies. On Co(0001), formate, carbon, and hydroxyl are intermediates and the reaction has an activation energy of 44.3 ± 0.6 kJ/mol, pre-exponential factor of 0.7 ± 0.05 mbar/s. On highly stepped cobalt, formate and formyl are intermediates and the reaction has an activation energy of 147.2 ± 2.0 kJ/mol and pre-exponential factor of 1011.3 ± 0.2 mbar/s. Desorption energies of observed species and mechanisms of observed reactions are reported.
A detailed description and proof of concept of a PM-IRRAS reactor designed for this thesis is also presented.
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Beard, Collen Alana. "Rubredoxin cobalt substitution and crystallization attempts." Thesis, Georgia Institute of Technology, 1989. http://hdl.handle.net/1853/29863.
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Kuyucak, Nural. "Algal biosorbents for gold and cobalt." Thesis, McGill University, 1987. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=75374.
Full textAbstract:
Different types of biomass samples including fungi and algae were treated for their gold and cobalt uptake capacity. The performance of activated carbon and ion-exchange resins were compared with the metal uptake capacity of the biosorbents. Sargassum natans, a brown seaweed, exhibited a high gold uptake capacity outperforming the ion-exchange resin and equalling activated carbon. Algal biomass of Ascophyllum nodosum proved to be a very potent biosorbent for cobalt. While the temperature, agitation and biomass particle size did not affect the metal uptake process, the effect of pH was significant for both gold and cobalt uptakes. The optimum pH for gold uptake was 2.5 and for cobalt, was 4-5. The kinetics of cobalt biosorption was relatively rapid (5 min) at the initial concentration of the metal in solution, 100 mg/L. The biosorptive uptake of gold required 2 h to reach equilibrium when the initial concentration of gold was 100 mg/L. None of the tested cations, such as K$ sp+$, Ca$ sp{2+}$, Fe$ sp{2+}$, Cr$ sp{3+}$, UO$ sbsp{2}{2+}$, Ni$ sp{2+}$, Zn$ sp{2+}$, Ag$ sp+$, affected the gold uptake capacity of S. natans biomass under the optimum conditions. Anions, such as NO$ sbsp{3}{-}$, SO$ sbsp{4}{2-}$, CO$ sbsp{3}{2-}$, PO$ sbsp{4}{3-}$, and Pb$ sp{2+}$ suppressed the gold uptake somewhat. Under the optimum process conditions cations, except K$ sp+$ and Fe$ sp{2+}$, and anions, NO$ sbsp{3}{-}$ in particular, exhibited a pronounced negative effect on the cobalt uptake by A. nodosum biomass.Sequestered gold was eluted with a mixture of thiourea and ferric ammonium sulphate solution. Approximately 98% of sequestered gold was eluted with 17 h in a batch contacting system at the optimum solids (biomass)-to-liquid ratio of 5 and pH of 5. At increased temperatures, the gold elution rate increased only slightly. Efficient desorption of cobalt was achieved using CaCl$ sb2$/HCL solution at pH 3. Cobalt elution time was quite short. Temperature affected neither desorption rate nor the equilibrium. The optimum solid-to-liquid ratio was 12 for desorption of cobalt from A. nodosum biomass.
The gold taken up by the biosorbent was deposited in its elemental form.
Available mathematical models, including the REDEQL2 chemical equilibrium model, were tested for theoretical predictions of co-ion competition in attempt to better understand the biosorption mechanism. (Abstract shortened with permission of author.)
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Jane, Reuben Thomas. "Cobalt(III) Complexes For Surface Engineering." Thesis, University of Canterbury. Chemistry, 2010. http://hdl.handle.net/10092/4424.
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This thesis addresses the potential for use of cobalt(III) complexes for functionalisation of lightly oxidised iron surfaces.
In Chapter 2 the preparation of cobalt(III) complexes of a series of ligands based on 1,1,1-tris(aminomethyl)ethane is described. The synthesis was approached in two ways. Firstly, preparation of functionalised triol molecules as precursors to functionalised triamine ligands was investigated. This approach utilised the Tollens condensation of aldehydes with formaldehyde. In a second approach, the functionalisation of tetrakis(aminomethyl)methane in which one amine arm has been differentiated was used. The tetraamine was reacted with benzaldehyde and reduced with borohydride ion to give a secondary amine molecule that was then functionalised using alkyl or aryl sulfonyl chloride molecules.
Chapter 3 describes the measurement of the binding of some cobalt(III) complexes to the surface of high surface area goethite. It was observed that complexes that have three exchangeable ligands bind more strongly than those with two exchangeable ligands. This is rationalised as being due to there being more bonds to the surface formed by complexes with three exchangeable ligands. It was also observed that complexes with three exchangeable ligands give greater surface coverage than those with two. This is likely due to the larger cross sectional area of the complexes with two exchangeable ligands in comparison to that of those with three, which blocks potential adjacent sites.
Preliminary experiments on the use of the contact angle, SEM, EDS and QCM to characterise complex binding are explored in Chapter 4 . The results from the EDS and QCM experiments show that these may be valuable tools for measuring this binding and the subsequent surface properties, but have not yielded detailed results at this point.
In Chapter 5 the use of cobalt(III) complexes as inhibitors of corrosion of iron in hydrochloric acid is investigated. All the complexes tested, even those that showed no binding to goethite surfaces, inhibit the corrosion to some degree. The level of inhibition is dependent on the complex, with [Co(tren)Cl2]Cl showing maximum inhibition of 81% and [Co(tame)Cl3] showing maximum inhibition of 53%. For some of the complexes, their concentration in solution over the course of the experiment was monitored by UV-vis. It was found that the complex disappears in a zero order reaction, the rate of which is dependent on the complex. However, the exact nature of this reaction is unknown. Furthermore, it was observed that inhibition of corrosion continues after the complex is no longer observed in solution. There is a difficulty in rationalising the inhibition being dependent on the complex identity, but not its continued presence in solution. Consequently, the mechanism of corrosion inhibition that explains all of these observations is still not known.
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Patel, V. F. "Cobalt-medicated radical reactions in synthesis." Thesis, University of Nottingham, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.380160.
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Beaumont, Ian R. "The chemistry of cyclopentadienyl cobalt complexes." Thesis, University of Nottingham, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.291970.
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Medforth, C. J. "Cobalt (III) porphyrin N.M.R. shift reagents." Thesis, University of Liverpool, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.384368.
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Papageorgiou, Iraklis. "The genotoxicity of cobalt-chrome particles." Thesis, University of Bristol, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.431833.
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Cracknell, R. B. "Agostic interactions at a cobalt centre." Thesis, University of Bristol, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.371994.
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LARRUDE, DUNIESKYS ROBERTO GONZALEZ. "CARBON NANOTUBES DECORATED WITH COBALT PARTICLES." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2007. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=10465@1.
Full textAbstract:
CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOOs nanotubos de carbono desde seu descobrimento têm atraído crescentemente a atenção devido a sua estrutura original e propriedades eletrônicas únicas. Encontrando muitas possíveis aplicações, como na área de materiais suportes para catálise, dada sua grande área superficial e boa condutividade elétrica quando comparado aos materiais convencionais à base de carbono. Essas características favorecem uma maior dispersão e estabilização de nanopartículas metálicas o que propicia o acceso a um número maior de átomos cataliticamente ativos. Neste trabalho foram produzidos nanotubos de carbono de paredes múltiplas de uma boa qualidade estrutural utilizando o método de Spray Pyrolysis. Foram encontrados os parâmetros de crescimento ideais de nosso sistema tais como fluxo de gás e faixa de valores para a concentração da solução precursora, 1800 sccm e 2,0-2,9% em peso, respectivamente. Os nanotubos foram decorados com partículas de cobalto através de uma rota química sendo o processo mais eficiente o que envolve a dissolução do nitrato de cobalto em acetona para a formação de um pó homogêneo de nanotubos-oxido de cobalto para sua posterior redução em atmosfera de H2 a 573 K. A qualidade estrutural dos nanotubos produzidos bem como do material decorado foi avaliado através de diferentes técnicas de caracterização tais como espectroscopia Raman, microscopia eletrônica de varredura e de transmissão, e difração de raios-X.
Carbon nanotubes since they are observed for the first time have been attracted attention due to their structure and unique electronic properties. Many applications, as support materials for catalysts, are proposed because of their aspect ration and good electrical conductivity. These properties favor a better dispersion and stabilization of the metallic nanoparticles, increasing the number of catalytic active atoms. In this work, we produced multi- walled carbon nanotubes (MWNT) with good structural properties using the Spray Pyrolysis method. We found the optimum parameters for the growth of high quality MWNT, namely, the gas flux and the concentration of the precursor solution, 1800 sccm and 2,0-2,9 wt %, respectively. The nanotubes were decorated via a chemical route, being the most efficient process the one where the cobalt nitrate was diluted in acetone with the formation of a homogeneous cobalt oxide particles-MWNT powder, with a subsequent reduction in H2 atmosphere at 573K. The structural characterization was performed by a multitechnique approach, including Raman spectroscopy, transmission and scanning electron microscopes (TEM and SEM) and x-ray diffraction (XRD).
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McAulay, Kate. "Cobalt rhenium catalysts for ammonia synthesis." Thesis, University of Glasgow, 2017. http://theses.gla.ac.uk/8421/.
Full textAbstract:
Cobalt rhenium ammonia synthesis catalysts which are highly active at ambient pressure and 400°C under N2/H2 (1:3) have been prepared without an ammonolysis step. For all highly active cobalt rhenium materials the post-reaction powder XRD patterns reveal there is a shift of their Re reflections to a slightly higher 2θ angle. This shift is due to mixing of cobalt and rhenium within the material and this interaction was confirmed via XAS analysis. The XRD patterns of cobalt rhenium materials with minimum ammonia synthesis activity resemble the reference pattern for metallic rhenium and show no signs of bimetallic mixing. Cobalt rhenium materials have been benchmarked against CsNO3 doped Ru/Al2O3 materials. Pre-treatments under N2/H2 (1:3), Ar/H2 (1:3), N2 and Ar gas mixtures have been shown to influence catalytic performance, with the first resulting in an instantly active material, whereas, the others lead to a 20 minute induction period prior to the development of activity upon switching to an ammonia synthesis feedstream. Also, pre-treatment in N2/H2 (1:3) resulted in a material with higher catalytic activity. CoRe4 was studied via in situ XAS/XRD to elucidate the reducibility and local environment of the two metals during reaction conditions. The phases present in the CoRe4 catalyst during ammonia production are largely bimetallic Co-Re and also monometallic Co and Re species formed during both pre-treatments. It was found the presence of nitrogen during the pre-treatment strongly promotes the mixing of the both Co and Re. Preliminary tests were also conducted on cobalt rhenium catalysts for ammonia decomposition and the materials were found to have high activity. To the author's knowledge this is the first report of low surface area materials being particularly active for this reaction.