To see the other types of publications on this topic, follow the link: Oxide.
Dissertations / Theses on the topic 'Oxide'
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 50 dissertations / theses for your research on the topic 'Oxide.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse dissertations / theses on a wide variety of disciplines and organise your bibliography correctly.
1
Gillispie, Meagen Anne. "Metal oxide-based transparent conducting oxides." [Ames, Iowa : Iowa State University], 2006.
Find full text
2
Field, Marianne Alice Louise. "Transition metal oxides and oxide-halides." Thesis, University of Southampton, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.401833.
Full text
3
Boltz, Janika [Verfasser]. "Sputtered tin oxide and titanium oxide thin films as alternative transparent conductive oxides / Janika Boltz." Aachen : Hochschulbibliothek der Rheinisch-Westfälischen Technischen Hochschule Aachen, 2012. http://d-nb.info/1019850485/34.
Full text
4
Messi, C. "Nanostructured catalytic metal oxides supported over oxide supports of various nature : the iron oxide system." Doctoral thesis, Università degli Studi di Milano, 2008. http://hdl.handle.net/2434/57081.
Full text
5
Sayle, D. C. "Computer simulation of heteroepitaxial oxide/oxide and metal/oxide interfaces." Thesis, University of Bath, 1992. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.317429.
Full text
6
Lockyer, D. M. "Adsorption and reaction of cyanogen with copper oxide, chromium oxide and copper oxide-chromium oxide surfaces." Thesis, University of Bath, 1988. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.383244.
Full text
7
Reeder, Askia Enrico. "STUDY OF THE STRUCTURE AND THE ELECTRONIC PROPERTIES OF THE OXIDE/OXIDE INTERFACES IN MIXED METAL OXIDES." Doctoral thesis, Università degli studi di Padova, 2014. http://hdl.handle.net/11577/3423844.
Full textAbstract:
A very important role is played by metal oxides in many areas of chemistry, physics, and materials science. Transition metal and rare-earth metal elements are able to form a large diversity of oxide compounds which can adopt an ample array of atomic structures and electronic properties that can exhibit metallic, semiconductor, or insulator characteristics. In technological applications, metal oxides are used in the fabrication of microelectronic components, sensors, fuel cells, coatings to protect surfaces against corrosion, and as catalysts. In this thesis we have decided to study two known catalytic materials Zirconia-Titania and Ceria-Titania mixed oxides. For both materials bibliography principally concerns powders thus in order to better study their interfaces, of which a deeper study is still lacking, we decided to deposit zirconia and ceria as thin films onto rutile TiO2(110).
We first studied the zirconia-titania system by depositing an ultra-thin film of zirconium oxide via a metal-organic precursor: Zirconium Tetra tert-Butoxide. The deposition was carried at three different substrate temperatures 677 K, 738 K, 773 K in five stages of a minute each and the results were traced by using XPS. The chemical characterization via XPS showed an interesting chemistry undergoing on the substrate’s surface and we have observed the formation of carbonaceous species at the interface. Zirconium appeared to be at its highest oxidation state while titanium was seen to undergo reduction with each successive deposited layer. The ratio of the Zr/Ti signals showed that zirconia didn’t completely wet the surface. Furthermore, no long range order was observed via LEED. XPD measurements showed that zirconia does not form a substitutional oxide with titania. However with the aid of computer simulation we deduced that very likely zirconia forms nanochains on the surface of TiO2(110). This surface was exposed to 100 L of pyridine to test its acidity.
In the case of ceria, we have deposited the oxide on a heated TiO2(110) substrate via metal evaporation from a Mo crucible since the process is rather easy and garners clean deposits. During deposition the substrate was kept at 677 K and in an O2 environment of 5.2•10-6mbar, and, in order to obtain an ordered homogeneous surface the sample was further annealed in the same environment at 900 K. Through LEED imaging different phases were observed and were dependent on sample history and film thickness. Via computer simulation these phases were then referred to the parent oxide in order to better comprehend the difference in respect to the bulk phase. All films showed cerium present at Ce(III). Ultra-violet Photoelectron Spectroscopy showed the electronic properties of the film showing a binding energy shift and the population of Ce4f states due to stabilization of Ce(III) by TiO2(110). The reactivity of the ceria-titania system was the probed by using methanol and ethanol. Results showed that the addition of ceria opened the dehydrogenation path from alcohol to aldehyde. We have observed that oxygen pre-oxidation of the CeOx-TiO2(110) system had an impact on its selectivity by opening also a dehydration path from methanol and ethanol to respectively, methane and ethylene. This alternative path was viable only for low cerium oxide coverages as interaction with the substrate was needed for dehydration to occur. Aldehyde formation was seen to occur at mild temperatures (330 K) and was independent of film thickness. Subsequently, ceria-titania mixed oxide powders were characterized via XPS and we have observed that for increasing amount of cerium the element gradually became present at its highest oxidation state Ce(IV). By XPS we have also determined the formation of a very intimate composite between the two oxides by observing the increasing the full width at half maximum of the Ti2p peak for increasing amounts of cerium. Furthermore, compositional calculation showed that cerium had the tendency to disperse within the titania particles. These data helped to uncover a possibly good recipe for the formation of cerium titanate a composite with good oxygen storage capacity.Un ruolo molto importante è svolto dagli ossidi metallici in molti settori della chimica, fisica e scienza dei materiali. I metalli di transizione e le terre rare sono in grado di formare una grande diversità di composti ossidici che possono adottare un'ampia gamma di strutture atomiche ed proprieta’ elettroniche che possono esibire caratteristiche metalliche, semiconduttrici o isolanti. In applicazioni tecnologiche, gli ossidi metallici sono impiegati nella fabbricazione di componenti microelettronici, sensori, celle a combustibile, rivestimenti per proteggere le superfici dalla corrosione, e come catalizzatori. In questa tesi abbiamo deciso di studiare due noti materiali catalitici: gli ossidi misti di Zirconia-Titania Ceria-Titania. Per entrambi i materiali la bibliografia riguarda principalmente le polveri quindi, al fine di studiare meglio le loro interfacce, di cui uno studio più approfondito e’ tuttora neccessario, abbiamo deciso di depositare film sottili di ossido di zirconio e ossido di cerio su rutilo TiO2(110). Abbiamo prima studiato il sistema zirconia-titania depositando un film ultra-sottile di ossido di zirconio mediante un precursore metallo-organico: Zirconio Tetra tert-butossido. La deposizione è stata effettuata a tre diverse temperature del substrato 677. K, 738 K, 773 K in cinque fasi di un minuto ciascuno. La caratterizzazione mediante XPS ha mostrato una chimica interessante sulla superficie del substrato e abbiamo osservato la formazione di specie carboniose all'interfaccia. Lo zirconio sembrava essere nel suo piu’ alto stato di ossidazione mentre il titanio è stato visto gradualmente ridursi con ogni successive strato di deposito. Il rapporto dei segnali Zr/Ti ha mostrato che la zirconia non ha completamente coperto la superficie. Inoltre,tramite LEED non si e’ osservato nessun ordine a lungo raggio. Misure XPD ha mostrato che la zirconia non forma un ossido di sostituzione con la titania. Tuttavia, con l'ausilio di simulazione al computer abbiamo dedotto che la zirconia forma, molto probabilmente nanocatene sulla superficie di TiO2(110). Questa superficie è stato esposta a 100 L di pyridinina per testarne la acidita’. Nel caso di ceria, abbiamo depositato l'ossido su un substrato riscaldato di TiO2 (110) tramite evaporazione del metallo da un crogiolo Mo poiché il processo è piuttosto facile e fornisce depositi puliti. Durante la deposizione il substrato è stata mantenuto a 677 K in un ambiente di 5,2 • 10 -6 mbar di O2, e, al fine di ottenere una superficie omogenea e ordinata il campione è stato ulteriormente sottoposto a trattamento termico nello stesso ambiente a 900 K. Tramite la tecnica LEED sono state osservate differenti fasi dipendenti dalla storia del campione e dallo spessore del film. Tramite simulazione al computer queste fasi sono stati poi riferite rispetto al biossido di cerio per meglio comprendere le differenze rispetto alla fase massiva. Tutti i film hanno mostrato cerio presenti come Ce(III). La Spettroscopia Fotoelettronica a Ultravioletti ha mostrato le proprietà elettroniche del film che mostra uno spostamento in energia di legame e un popolamento degli stati Ce4f. Questo e’ dovuto alla stabilizzazione di Ce (III) da parte di TiO2 (110). Si e’ volute osservare la reattività del sistema ceria-titania nei confronti di metanolo ed etanolo. I risultati hanno mostrato che l'aggiunta di ceria ha aperto il percorso della deidrogenazione degli alcoli ad aldeidi. Abbiamo osservato che la pre-ossidazione con ossigeno del sistema CeOx-TiO2(110) ha avuto un impatto sulla sua selettività aprendo anche un percorso di disidratazione di metanolo ed etanolo rispettivamente a metano ed etilene. Questa via alternativa era valida solo per basse coperture di ossido di cerio avendo osservato che l’interazione con il substrato è stato necessario perche’ avvenga la disidratazione. La formazione di aldeidi fu osservata avvenire a temperature piuttosto (330 K) ed essere indipendente dallo spessore del film. Successivamente sono state caratterizzate tramite XPS delle polveri di ossidi misti di ceria e titania. Abbiamo osservato che per quantità crescenti di cerio l'elemento diventa gradualmente sempre piu’ presente al suo stato di ossidazione più alto Ce (IV). Con XPS abbiamo anche determinato la formazione di un composito molto intimo tra i due ossidi osservando l'aumento della larghezza a metà altezza del picco Ti2p per quantità crescenti di cerio. Inoltre, la determinazione della composizione ha mostrato che il cerio ha la tendenza di disperdersi all'interno delle particelle di titania. Questi dati hanno contribuito a scoprire una possibile buona ricetta per la formazione di cerio titanato; un composito con buona capacità di stoccaggio di ossigeno.
8
Burkardt, Sven. "Oxide and oxide supported nanoclusters on quasicrystals." Berlin Logos-Verl, 2009. http://d-nb.info/999419471/04.
Full text
9
Zhang, Huichun. "Metal oxide-facilitated oxidation of antibacterial agents." Diss., Available online, Georgia Institute of Technology, 2004:, 2004. http://etd.gatech.edu/theses/available/etd-07072004-152317/unrestricted/zhang%5Fhuichun%5F200407%5Fphd.pdf.
Full textAbstract:
Thesis (Ph. D.)--School of Civil and Environmental Engineering, Georgia Institute of Technology, 2005. Directed by Ching-Hua Huang.Wine, Paul, Committee Member ; Pavlostathis, Spyros, Committee Member ; Mulholland, James, Committee Member ; Yiacoumi, Sotira, Committee Member ; Huang, Ching-Hua, Committee Chair. Includes bibliographical references.
10
Taujale, Saru. "INTERACTIONS BETWEEN METAL OXIDES AND/OR NATURAL ORGANIC MATTER AND THEIR INFLUENCE ON THE OXIDATIVE REACTIVITY OF MANGANESE DIOXIDE." Diss., Temple University Libraries, 2015. http://cdm16002.contentdm.oclc.org/cdm/ref/collection/p245801coll10/id/347169.
Full textAbstract:
Civil EngineeringPh.D.
Mn oxides have high redox potentials and are known to be very reactive, rendering many contaminants susceptible to degradation via oxidation. Although Mn oxides typically occur as mixtures with other metal oxides (e.g., Fe, Al, and Si oxides) and natural organic matter (NOM) in soils and aquatic environments, most studies to date have studied the reactivity of Mn oxides as a single oxide system. This study, for the first time, examined the effect of representative metal oxides (Al2O3, SiO2, TiO2, and Fe oxides) and NOM or NOM-model compounds (Aldrich humic acid (AHA), Leonardite humic acid (LHA), pyromellitic acid (PA) and alginate) on the oxidative reactivity of MnO2, as quantified by the oxidation kinetics of triclosan (a widely used phenolic antibacterial agent) as a probe compound. The study also examined the effect of soluble metal ions released from the oxide surfaces on MnO2 reactivity. In binary oxide mixtures, Al2O3 decreased the reactivity of MnO2 as a result of both heteroaggregation and complexation of soluble Al ions with MnO2. At pH 5, the surface charge of MnO2 is negative while that of Al2O3 is positive resulting in intensive heteroaggregation between the two oxides. Up to 3.15 mM of soluble Al ions were detected in the supernatant of 10 g/L of Al2O3 at pH 5.0 whereas the soluble Al concentration was 0.76 mM in the mixed Al2O3 + MnO2 system at the same pH. The lower amount of soluble Al in the latter system is the result of Al ion adsorption by MnO2. The experiments with the addition of 0.001 to 0.1 mM Al3+ to MnO2 suspension indicated the triclosan oxidation rate constant decreased from 0.24 to 0.03 h-1 due to surface complexation. Fe oxides which are also negatively charged at pH 5 inhibited the reactivity of MnO2 through heteroaggregation. The concentration of soluble Fe(III) ions ( 4 mg-TOC/L or [alginate/PA] > 10 mg/L, a lower extent of heteroaggregation was also observed due to the negatively charged surfaces for all oxides. Similar effects on aggregation and MnO2 reactivity as discussed above were observed for ternary MnO2‒Al2O3‒NOM systems. HAs, particularly at high concentrations (2.0 to 12.5 mg-C/L), alleviated the effect of soluble Al ions on MnO2 reactivity as a result of the formation of soluble Al-HA complexes. Alginate and PA, however, did not form soluble complexes with Al ions so they did not affect the effect of Al ions on MnO2 reactivity. Despite the above observations, the amount of Al ions dissolved in MnO2+Al2O3+NOM mixtures was too low, as a result of NOMs adsorption on the surface to passivate oxide dissolution, to have a major impact on MnO2 reactivity. In conclusion, this study provided, for the first time, a systematical understanding of the redox activity of MnO2 in complex model systems. With this new knowledge, the gap between single oxide systems and complex environmental systems is much narrower so that it is possible to have a more accurate prediction of the fate of contaminants in the environment.
Temple University--Theses
11
Heap, Richard John. "Synthesis and characterisation of K2NiF4-related oxides and oxide fluorides." Thesis, University of Surrey, 2006. http://epubs.surrey.ac.uk/843525/.
Full textAbstract:
In the work presented here, a synthetic and structural study of K2NiF4-related oxides and oxide fluorides is reported. Several ranges of oxides and oxide fluorides have been synthesised and structurally characterised by Rietveld refinement of X-ray and Neutron diffraction data. Many of these materials are novel, and show some interesting structural, chemical and physical properties. These materials were all prepared via the standard solid state technique. Because most of the oxide fluorides presented here are not stable at high temperatures, their synthesis involved a two stage process; production of an oxide precursor, followed by low temperature fluorination of this precursor. Throughout this study, the polymer-based fluorinating agent, PVDF, was shown to be effective for the production of a number of novel oxide fluorides. In addition, during the course of the work presented here, the new fluorinating agent, (PTFE) was discovered, and also shown to be effective for this purpose.
12
Andronic, Laura Simona. "Photochemical metal organic deposition of layered materials of chromium oxide and lead oxide and of uranium oxide and cobalt oxide." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2001. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/MQ61529.pdf.
Full text
13
Bamroongwongdee, Chanut. "Surface science studies of model oxide catalysts : molybdenum oxide on single crystal iron oxide." Thesis, Cardiff University, 2010. http://orca.cf.ac.uk/54989/.
Full textAbstract:
This thesis is concerned with the study of molybdenum oxide layer deposited on a single crystal iron oxide substrate. The surface structure of an iron oxide single crystal was investigated by X-ray photoelectron (XPS), low-energy He+-ion scattering (LEIS), low-energy electron diffraction (LEED), and scanning tunneling microscopy (STM). XPS measurement reveals the presence of both Fe2+ and Fe3* oxidation states. LEED and STM results obtained from this surface were consistent with a formation of an Fe304(III) surface termination. LEED pattern and STM images reveal an hexagonal array with a periodicity of 6 A and steps in multiples of 5 A. LEIS result shows the presence of both Fe and O in the topmost layer. Well ordered epitaxial molybdenum oxide films were grown on iron oxide single crystal substrates. Their surface structure, morphology and composition were characterized by XPS, LEIS, LEED, and STM. They were prepared by depositing molybdenum oxide onto the substrate and then oxidizing it in 10"7 mbar of oxygen. In the sub-monolayer regime, molybdenum oxide formed islands of ordered structure. XPS measurement yields a Mo 3dsn binding energy consistent with the presence of Mo6*. High resolution STM images reveal a large hexagonal lattice of protrusions with a 12 A periodicity. This pattern is consistent with a p(4x4) structure. At the monolayer coverage, a (23 x 23 )R30 surface structure is produced by annealing in oxygen (107 mbar) at 973 K. STM topographies show clear hexagonal distribution with the period of 1.1 nm corresponding to the pattern observed in LEED. These results suggest that molybdenum oxide may interact with Fe304(III) to form iron molybdate which is stable on the surface.
14
Hernández, Viezcas José Angel. "Toxicity of zinc oxide and cerium oxide nanoparticles to mesquite (Prosopis juliflora-velutina)." To access this resource online via ProQuest Dissertations and Theses @ UTEP, 2009. http://0-proquest.umi.com.lib.utep.edu/login?COPT=REJTPTU0YmImSU5UPTAmVkVSPTI=&clientId=2515.
Full text
15
Shukri, Rashid Jaber Asa'd. "Supported oxide catalysts : cobalt oxide and molybdena on titania." Thesis, Brunel University, 1989. http://bura.brunel.ac.uk/handle/2438/7385.
Full textAbstract:
TiO2 supported MoO3 catalysts were prepared by aqueous impregnation of low area anatase (10 m2g-1) with solutions of (NH4)6Mo7024,4H20 (MT/C series), and H2[Mo03(C204)].H20 (MOT /C series), Three series of CoOx/Ti02 catalysts were fabricated by aqueous impregnation of the same support with solutions of Co(N03)2,6H20 (CT/C series), and Co(CH3COO)2.4H20 (CAT/C series), and by homogeneous precipitation using Co(N03)2,6H20 (CT/HP series), CoO and Mo03 were deposited on Degussa P-25 (55 m2g-1) by aqueous impregnation using (NH4)6Mo7024,4H20 and Co(N03)2,6H20 in three ways: ( i) CoO impregnated first, Mo03 second (CMT series); (ii) Mo03 impregnated first, CoO second (MCT series); and (iii) CoO and Mo03 together (CMTg series). The catalysts were characterized by laser Raman spectroscopy (LRS) , temperature-programmed reduction (TPR) , X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM), Monolayer coverage by XPS was independent of the precursor for the MoOx/Ti02 catalysts, but a function of the method of preparat ion and the precursor for the CoOx /Ti02 catalysts. XPS results for the CMTg series differed from those for the CMT and MCT series, suggesting different surface species had been formed by varying the mode of impregnation, Phase diagrams relating semiquantitatively to the oxide contents are presented. 2-propanol decomposition was studied to probe the acid-base properties of the catalysts, Ti02 and Mo03 exhibi ted dehydration activity, whereas CoO showed dehydrogenation activity, All the supported catalysts gave activation energies for dehydration higher than dehydrogenation. In the sub-monolayer region, the catalytic activity for dehydration was in the order: MCT > CMTg > CMT > MT/C > CT/C, while the selectivity remained almost unchanged, In the monolayer region, the activity was: MT/C > CMT > CMTg > MCT > CT/C and the selectivity increased compared with the sub-monolayer region. In the four-monolayer reg ion, the activity decreased compared with the sub-monolayer and monolayer regions, but the selectivity increased relative to the previous two regimes. "Compensation effect 0, plots revealed different types of active centres responsible for dehydration and dehydrogenation processes in the MoOx /Ti02 and CoO-Mo03/Ti02 catalysts, while active centres were almost identical with the CoOx /Ti02 system.
16
Bailey, Craig. "Promoted tin(IV) oxide and cerium (IV) oxide catalysts." Thesis, University of Nottingham, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.262967.
Full text
17
Binks, David Jason. "Computational modelling of zinc oxide and related oxide ceramics." Thesis, University of Surrey, 1994. http://epubs.surrey.ac.uk/883/.
Full text
18
Simo, Frantisek. "Novel oxide materials for solid oxide fuel cells applications." Thesis, University of Liverpool, 2014. http://livrepository.liverpool.ac.uk/19353/.
Full textAbstract:
The work of this thesis focuses on three perovskite-based compounds: YSr2Cu3−xCoxO7+δ cuprates, Gd2BaCo2O5+δ related phases and Sr2SnO4 Ruddlesden-Popper structures. Both YSr2Cu3−xCoxO7+δ and Gd2BaCo2O5+δ are cathode material candidates for solid oxide fuel cells (SOFCs). Doping of Sr2SnO4 aims to enhance the ionic conductivity of the parent phase and explore the phases as a potential SOFCs electrolyte material. The cobalt content in the layered perovskite YSr2Cu3−xCoxO7+δ has been increased to a maximum of x = 1.3. A slight excess of strontium was required for phase purity in these phases, yielding the composition Y1−ySr2+yCu3−xCoxO7+δ (where y = 0.03 and 0.05). The potential of Y1−ySr2+yCu3−xCoxO7+δ (where x = 1 to 1.3) as a cathode material for a solid oxide fuel cell has been explored through optimisation of processing parameters, AC impedance spectroscopy and DC conductivity measurements. The stability of Y0.95Sr2.05Cu1.7Co1.3O7+δ with commercial electrolytes has been tested along with the stability under CO2. This material exhibits a significant improvement in properties compared to the parent member, Y0.97Sr2.03Cu2CoO7+δ, and is compatible with commercially available doped ceria electrolytes at 900 °C. Energetics of Ln2BaCo2O7 (Ln = Gd, Nd, Ce) materials consisting of a layer of LnBaCo2O5+δ (Ln = Gd, Nd) and a fluorite layer (CeO2 or Ln2O3, Ln = Gd, Nd) have been studied using DFT calculations. Various reactions including binary oxides and double perovskites were taken into an account for the formation energy calculations. Phases favourable in DFT calculations were observed also in PXRD patterns of the materials prepared by a solid state synthesis. DFT prediction has been also used in the work with Ruddlesden-Popper phases. The structures of experimentally prepared Nb- and Ta-doped Sr2SnO4 phases were investigated using high resolution diffraction methods. The conductivity of single phased materials was studied by AC impedance spectroscopy. A significant improvement in conductivity was observed in Sr2Sn1−xTaxO4 compounds with x = 0.03 and 0.04. The origin of the enhancement has been studied using different techniques such as solid state Sn-NMR, UV-vis and NIR spectroscopy methods and it tends to be explained by an ionic contribution.
19
Bernuy-Lopez, Carlos. "Novel mixed conducting oxides for sold oxide fuel cells (SOFC's) applications." Thesis, University of Liverpool, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.501713.
Full textAbstract:
This thesis describes the search for new mixed conductors as potential anodes and cathodes for applications in Solid Oxide Fuel Cells. Several compounds have been synthesised and characterised by means of different diffraction techniques (X-Rays, neutrons and electrons), high resolution electron microscopy and electrical measurements (AC Impedance Spectroscopy and DC resistivity measurements).
20
Liu, Dameng. "High-K gate oxides for future complementary metal-oxide-semiconductor transistors." Thesis, University of Cambridge, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.611517.
Full text
21
Kim, Dong-Geun. "Experimental study and thermodynamic modelling of the calcium oxide - silicon oxide - aluminum oxide - calcium fluoride system." Thesis, McGill University, 2012. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=106562.
Full textAbstract:
Mould flux for the continuous casting process is a major concern for the steelmaking industry. Nowadays, more than 90 % of steel is being produced by the continuous casting process, which requires mould flux as an essential additive. The development of mould flux has been achieved by the conventional trial and error approach since it was first introduced in industry in the 1960s. Recently, the interest on the properties of fluorine has increased a lot since it is reported that fluorine has important functions such as playing a critical role on the crystallization behavior, and decreasing the melting point and viscosity of slag. However, the conventional way to find a suitable mould flux is not efficient to face the increasingly stringent requirements of the continuous casting process such as thin slab casting and higher casting speed. Therefore, fundamental phase diagram study on mould flux systems is clearly necessary, and thermodynamic modeling is the most effective way to design new mould flux in terms of time and money saving. The major components of mould flux, the CaO-SiO2-Al2O3-CaF2 system, are investigated in this study as these four constituents will mostly affect the largest numbers of properties. Unfortunately, fluorine has high volatility at high temperature and high reactivity with other materials. Therefore, the results of previous experiments on F-containing systems are characterized by large discrepancies due to composition alteration and unexpected reactions during the experiment. As literature data show inconsistent results between each other, key phase diagram experiments were performed in this study. The phase diagram experiments were conducted with the quenching method in sealed Pt capsules to prevent fluorine loss during the experiment. The analyses were performed using a FE-SEM equipped with an EDS system, and a newly developed technique which produces more precise quantitative results for the equilibrium phase composition. The CaO liquidus of the CaO-CaF2 binary system, which the literature data differ from each other by up to 50 mol %, was confirmed. The CaO solubility in solid CaF2 was found for the first time and reaches about 5 mol % at the eutectic temperature. The liquidus of the CaO-Al2O3-CaF2 and CaO-SiO2-CaF2 systems were carefully studied and the miscibility gap in the CaO-Al2O3-CaF2 system was proved to be much smaller than that reported in literature. Also, thermal analysis was performed using DSC in a Pt crucible. The eutectic temperatures of the CaO-CaF2 and CaAl2O4-CaF2 systems were successfully measured and the α to β-CaF2 polymorphic transition was confirmed. Based on the new experimental data and reliable literature data, thermodynamic modeling of the CaO-SiO2-Al2O3-CaF2 system was also carried out. The results of thermodynamic calculation can be very beneficial for new mould flux design.L'usage des poudres de coulée continue est une préoccupation majeure pour l'industrie sidérurgique. Actuellement, plus de 90% de l'acier est produit par le procédé de coulée continue, nécessitant impérativement l'emploi de poudres de coulée. Traditionnellement, le développement des poudres de coulée a été réalisé par la méthode d'essai et d'erreur depuis son introduction dans l'industrie dans les années 1960. Récemment, l'intérêt porté sur le fluor s'est accru car celui-ci présente d'importantes propriétés et fonctions pour le procédé de coulée continue, telles que son influence sur la cristallisation et la diminution du point de fusion et de la viscosité du laitier. Toutefois, la méthode conventionnelle de développement des poudres de coulée appropriées n'est pas efficace pour faire face aux exigences croissantes du procédé de coulée continue, telles qu'effectuer la coulée de brames minces et atteindre de plus grande vitesse de coulée. Par conséquent, l'étude fondamentale du diagramme de phase des systèmes de poudres de coulée est manifestement nécessaire, et la modélisation thermodynamique est le moyen le plus efficace pour concevoir de nouvelles poudres de coulée en termes d'économie de temps et d'argent. Les principaux composants des poudres de coulée, qui font partie du système CaO-SiO2-Al2O3-CaF2, sont examinés dans cette étude car ces quatre constituants affecteront le plus grand nombre de propriétés des poudres de coulée. Malheureusement, le fluor a une volatilité élevée à haute température et une réactivité élevée avec d'autres matériaux. Par conséquent, les résultats des expériences effectuées précédemment sur les systèmes contenant des fluorures sont caractérisés par des écarts importants en raison du changement de composition et de réactions inattendues lors des expériences. Comme les données disponibles dans la littérature rapportent des résultats contradictoires entre eux, des expériences ont été effectuées dans cette étude pour établir les diagrammes de phase. Ces expériences ont été menées avec la méthode de trempe dans des capsules de platine scellées pour empêcher la perte de fluor pendant les expériences. Les analyses ont été effectuées en utilisant un microscope électronique à balayage (MEB) équipé d'un système d'analyse dispersive en énergie de rayons X (EDS), et une technique nouvellement développée qui produit des résultats plus précis lors de la quantification de la composition des phases à l'équilibre. La courbe du liquidus du CaO du système binaire CaO-CaF2, dont les données dans la littérature diffèrent entre elles jusqu'à environ 50 % atomique, a été confirmée. La solubilité de CaO dans CaF2 à l'état solide a été trouvée pour la première fois et atteint environ 5 % atomique à la température eutectique. Les courbes de liquidus des systèmes CaO-Al2O3-CaF2 et CaO-SiO2-CaF2 ont été soigneusement étudiées et l'étendue de la lacune de miscibilité dans le système CaO-Al2O3-CaF2 a été prouvée être beaucoup plus petite que celle rapportée dans la littérature. En outre, une analyse thermique a été réalisée par calorimétrie différentielle à balayage (DSC) dans un creuset en platine. La température eutectique des systèmes CaO-CaF2 et CaAl2O4-CaF2 a été mesurée avec succès et la transition polymorphique de la forme α-CaF2 vers la forme β-CaF2 a été confirmée. Sur base des nouvelles données expérimentales et des données fiables de la littérature, la modélisation thermodynamique du système CaO-SiO2-Al2O3-CaF2 a également été réalisée. Les résultats de calcul thermodynamique peuvent être très bénéfiques pour la conception de nouvelles poudres de coulée.
22
Hao, Yalin. "Continuous Hydrothermal Production of Iron Oxide (Fe[subscript 2]0[subscript 3]) and Cobalt Oxide (Co[subscript 3]O[subscript 4])." Thesis, Georgia Institute of Technology, 2002. http://hdl.handle.net/1853/11217.
Full text
23
Nguyen, Thanh Dinh. "Metal oxide, Mixed oxide, and hybrid metal@oxide nanocrystals: size-and shape-controlled synthesis and catalytic applications." Thesis, Université Laval, 2011. http://www.theses.ulaval.ca/2011/28408/28408.pdf.
Full textAbstract:
Le contrôle de la taille et de la morphologie de nanocristaux d’oxydes métalliques simples, d’oxydes mixtes et d’oxydes métalliques hybrides est un sujet de grand intérêt. La dépendance de leur propriétés physio-chimiques avec leurs taille et morphologies, génèrent une variété de leur applications dans plusieurs domaines. Cependant, le dévellopement des nanocristaux en controllant la taille, la forme, l’assemblage et l’homogénéité de la composition chimique pour l’optimisation de propriété spécifiques demandent la combinaison de nombreux parametres de synthèse.
Les trois différentes approches ont été développées dans le cadre de la thèse pour la synthèse d’une variété de nouveaux nanomatériaux d’oxydes simples, d’oxydes mixtes et d’oxydes métalliques hybrides dont la taille et la forme ont été bien controllées. Ces méthodes ont été nommées comme des méthodes solvo-hydrothermiques assistées par des molécules structurantes à l’état monophasique (eau ou eau/éthanol) et à l’état biphasique (eau-toluène). Nos approches de synthèse ont permi de préparer des nanocristaux des oxydes de métaux de transition (V, Cr, Mn, Co, Ni, In), et des terres rares (Sm, Ce, La, Gd, Er, Ti, Y, Zr), ainsi que des oxydes métalliques mixtes (tungstate, orthovanadate, molybdate). Ces nanomatériaux sont sous forme colloïdale mono-dispersée qui présente une cristallinité élevée. La taille et la forme de tels nanocristaux peuvent facilement être contrôlées par une simple variation des paramètres de synthèse telle que la concentration de précurseurs, la nature de la molécule structurante, la température et le temps de réaction. A large variété de techniques a été utilisée pour la caracterisation de ces nanomatériaux telles que TEM/HRTEM, SEM, SAED, EDS, XRD, XPS, FTIR, TGA-DTA, UV-vis, photoluminescence, BET. Les propriétés catalytiques de ces matériaux ont aussi été étudiées.
Dans ce travail, le contrôle de la cinétique de croissance des nucléides ainsi que le mécanisme gouvernant la forme qui conduit à la taille et la morphologie finale du nanocrystal ont été proposé. L’effet de la taille et de la forme des nanoparticules d’oxyde métallique hybrides sur les propriétés catalytiques pour la réaction d’oxydation du CO et la photo-dégradation du bleue de méthylène a été aussi étudié. Car les catalyseurs existant actuellement à base de métaux nobles sont très couteux et en plus très sensibles à l’empoisonnement par le gas H2S ou les émissions polluantes de SOx. L’activité catalytique des nanocristaux d’oxydes métallique hybrides Cu@CeO2 de formes cubiques dans l’oxydation de CO et de Ag@TiO2 de formes de ceinture dans la photo dégradation du bleue de méthylène ont montré la dépendance de la taille et la forme des nanocristaux avec leur propriétés catalytiques.The ability to finely control the size and shape of metal oxide, mixed metal oxide, hybrid metal/oxide nanocrystals has become an area of great interest, as many of their physical and chemical properties are highly dependent on morphology, and the more technological applications will be possible for their use. Large-scale synthesis of such high-quality nanocrystals is the first and key step to this area of science. A tremendous effort has recently been spent in attempt to control these novel properties through manipulation of size, shape, structure, and composition. Flexibly nanocrystal size/shape control for both monodisperse single and multiple-oxide nanomaterial systems, however, remains largely empirical and still presents a great challenge. In this dissertation, new synthetic approaches have been developed and described for the synthetic design of a series of colloidal monodisperse metal oxide, mixed metal oxide, hybrid metal-oxide nanocrystals with controlled size and shape. These materials were generally characterized using TEM/HRTEM, SEM, SAED, EDS, XRD, XPS, FTIR, TGA-DTA, UV-vis, photoluminescence, BET techniques. Effect of the size and shape of these obtained hybrid metal-oxide nanocrystals on the catalytic properties is illustrated. We have developed three different new surfactant-assistant pathways for the large-scale synthesis of three types of nanomaterials including metal oxide, mixed metal oxide, hybrid noble-metal-oxide colloidal monodisperse nanocrystals. Namely, the solvo-hydrothermal surfactant-assisted methods in one-phase (water or water/ethanol) and two-phase (water-toluene) systems were used for the synthesis of metal oxide (transition metal-V, Cr, Mn, Co, Ni, In and rare earth-Sm, Ce, La, Gd, Er, Ti, Y, Zr) and mixed metal oxide (tungstate, orthovanadate, molybdate). The seed-media growth with the assistant of bifunctional surfactant was used for the synthesis of hybrid noble metal@oxide (Ag@TiO2, (Cu or Ag)@CeO2, Au/tungstate, Ag/molybdate, etc.) nanocrystals. A significant feature of our synthetic approaches was pointed out that most resulting nanocrystal products are monodisperse, high crystallinity, uniform shape, and narrow distribution. The size and shape of such nanocrystals can be controlled easily by simple tuning the reaction parameters such as the concentration of precursors and surfactants, the nature of surfactant, the temperature and time of synthetic reaction. The prepared nanocrystals with the functional surface were used as the building blocks for the self-assembly into hierarchical mesocrystal microspheres. The effective ways how to control the growth kinetics of the nuclei and the shape-guiding mechanisms leading to the manipulation of morphology of final products were proposed. Our current approaches have several conveniences including used nontoxic and inexpensive reagents (most using inorganic metal salts as starting precursors instead of expensive and toxic metallic alkoxides or organometallics), relatively mild conditions, high-yield, and large-scale production; in some causes, water or ethanol was used as environmentally benign reaction solvent. Catalytic activity and selectivity are governed by the nature of the catalyst surface, making shaped nanocrystals ideal substrates for understanding the influence of surface structure on heterogeneous catalysis at the nanoscale. Finally, this work was concentrated on demonstration of heterogeneous catalytic activity of hybrid metal-oxide nanomaterials (Cu@CeO2, Ag@TiO2) as a typical example. We synthesized the high-crystalline titanium oxide and cerium oxide nanocrystals with control over their shape and surface chemistry in high yield via the aqueous surfactant-assist method. The novel hybrid metal-oxide nanocrystals were produced by the depositing noble metal ion (Cu, Ag, Au) precursors on the pre-synthesized oxide seeds via seed-mediated growth. The catalytic activity of these metal-oxide nanohybrids of Cu@CeO2 nanocubes for CO oxidation conversion and Ag@TiO2 nanobelts for Methylene Blue photodegradation with size/shape-dependent properties were verified.
24
Nguyen, Thanh-Dinh. "Metal oxide, Mixed oxide, and hybrid metal@oxide nanocrystals : size-and shape-controlled synthesis and catalytic applications." Doctoral thesis, Université Laval, 2011. http://hdl.handle.net/20.500.11794/22994.
Full textAbstract:
Le contrôle de la taille et de la morphologie de nanocristaux d’oxydes métalliques simples, d’oxydes mixtes et d’oxydes métalliques hybrides est un sujet de grand intérêt. La dépendance de leur propriétés physio-chimiques avec leurs taille et morphologies, génèrent une variété de leur applications dans plusieurs domaines. Cependant, le dévellopement des nanocristaux en controllant la taille, la forme, l’assemblage et l’homogénéité de la composition chimique pour l’optimisation de propriété spécifiques demandent la combinaison de nombreux parametres de synthèse. Les trois différentes approches ont été développées dans le cadre de la thèse pour la synthèse d’une variété de nouveaux nanomatériaux d’oxydes simples, d’oxydes mixtes et d’oxydes métalliques hybrides dont la taille et la forme ont été bien controllées. Ces méthodes ont été nommées comme des méthodes solvo-hydrothermiques assistées par des molécules structurantes à l’état monophasique (eau ou eau/éthanol) et à l’état biphasique (eau-toluène). Nos approches de synthèse ont permi de préparer des nanocristaux des oxydes de métaux de transition (V, Cr, Mn, Co, Ni, In), et des terres rares (Sm, Ce, La, Gd, Er, Ti, Y, Zr), ainsi que des oxydes métalliques mixtes (tungstate, orthovanadate, molybdate). Ces nanomatériaux sont sous forme colloïdale mono-dispersée qui présente une cristallinité élevée. La taille et la forme de tels nanocristaux peuvent facilement être contrôlées par une simple variation des paramètres de synthèse telle que la concentration de précurseurs, la nature de la molécule structurante, la température et le temps de réaction. A large variété de techniques a été utilisée pour la caracterisation de ces nanomatériaux telles que TEM/HRTEM, SEM, SAED, EDS, XRD, XPS, FTIR, TGA-DTA, UV-vis, photoluminescence, BET. Les propriétés catalytiques de ces matériaux ont aussi été étudiées. Dans ce travail, le contrôle de la cinétique de croissance des nucléides ainsi que le mécanisme gouvernant la forme qui conduit à la taille et la morphologie finale du nanocrystal ont été proposé. L’effet de la taille et de la forme des nanoparticules d’oxyde métallique hybrides sur les propriétés catalytiques pour la réaction d’oxydation du CO et la photo-dégradation du bleue de méthylène a été aussi étudié. Car les catalyseurs existant actuellement à base de métaux nobles sont très couteux et en plus très sensibles à l’empoisonnement par le gas H2S ou les émissions polluantes de SOx. L’activité catalytique des nanocristaux d’oxydes métallique hybrides Cu@CeO2 de formes cubiques dans l’oxydation de CO et de Ag@TiO2 de formes de ceinture dans la photo dégradation du bleue de méthylène ont montré la dépendance de la taille et la forme des nanocristaux avec leur propriétés catalytiques.The ability to finely control the size and shape of metal oxide, mixed metal oxide, hybrid metal/oxide nanocrystals has become an area of great interest, as many of their physical and chemical properties are highly dependent on morphology, and the more technological applications will be possible for their use. Large-scale synthesis of such high-quality nanocrystals is the first and key step to this area of science. A tremendous effort has recently been spent in attempt to control these novel properties through manipulation of size, shape, structure, and composition. Flexibly nanocrystal size/shape control for both monodisperse single and multiple-oxide nanomaterial systems, however, remains largely empirical and still presents a great challenge. In this dissertation, new synthetic approaches have been developed and described for the synthetic design of a series of colloidal monodisperse metal oxide, mixed metal oxide, hybrid metal-oxide nanocrystals with controlled size and shape. These materials were generally characterized using TEM/HRTEM, SEM, SAED, EDS, XRD, XPS, FTIR, TGA-DTA, UV-vis, photoluminescence, BET techniques. Effect of the size and shape of these obtained hybrid metal-oxide nanocrystals on the catalytic properties is illustrated. We have developed three different new surfactant-assistant pathways for the large-scale synthesis of three types of nanomaterials including metal oxide, mixed metal oxide, hybrid noble-metal-oxide colloidal monodisperse nanocrystals. Namely, the solvo-hydrothermal surfactant-assisted methods in one-phase (water or water/ethanol) and two-phase (water-toluene) systems were used for the synthesis of metal oxide (transition metal-V, Cr, Mn, Co, Ni, In and rare earth-Sm, Ce, La, Gd, Er, Ti, Y, Zr) and mixed metal oxide (tungstate, orthovanadate, molybdate). The seed-media growth with the assistant of bifunctional surfactant was used for the synthesis of hybrid noble metal@oxide (Ag@TiO2, (Cu or Ag)@CeO2, Au/tungstate, Ag/molybdate, etc.) nanocrystals. A significant feature of our synthetic approaches was pointed out that most resulting nanocrystal products are monodisperse, high crystallinity, uniform shape, and narrow distribution. The size and shape of such nanocrystals can be controlled easily by simple tuning the reaction parameters such as the concentration of precursors and surfactants, the nature of surfactant, the temperature and time of synthetic reaction. The prepared nanocrystals with the functional surface were used as the building blocks for the self-assembly into hierarchical mesocrystal microspheres. The effective ways how to control the growth kinetics of the nuclei and the shape-guiding mechanisms leading to the manipulation of morphology of final products were proposed. Our current approaches have several conveniences including used nontoxic and inexpensive reagents (most using inorganic metal salts as starting precursors instead of expensive and toxic metallic alkoxides or organometallics), relatively mild conditions, high-yield, and large-scale production; in some causes, water or ethanol was used as environmentally benign reaction solvent. Catalytic activity and selectivity are governed by the nature of the catalyst surface, making shaped nanocrystals ideal substrates for understanding the influence of surface structure on heterogeneous catalysis at the nanoscale. Finally, this work was concentrated on demonstration of heterogeneous catalytic activity of hybrid metal-oxide nanomaterials (Cu@CeO2, Ag@TiO2) as a typical example. We synthesized the high-crystalline titanium oxide and cerium oxide nanocrystals with control over their shape and surface chemistry in high yield via the aqueous surfactant-assist method. The novel hybrid metal-oxide nanocrystals were produced by the depositing noble metal ion (Cu, Ag, Au) precursors on the pre-synthesized oxide seeds via seed-mediated growth. The catalytic activity of these metal-oxide nanohybrids of Cu@CeO2 nanocubes for CO oxidation conversion and Ag@TiO2 nanobelts for Methylene Blue photodegradation with size/shape-dependent properties were verified.
25
Bae, Joong-Myeon. "Properties of selected oxide cathodes for solid oxide fuel cell." Thesis, Imperial College London, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.244213.
Full text
26
Ng, Yew Sun. "Studies of metal ion - Phosphine oxide and arsine oxide interactions." Thesis, University of Canterbury. Chemistry, 1997. http://hdl.handle.net/10092/7303.
Full textAbstract:
This thesis reports a study of metal complexes of trimethyl-phosphine and trimethylarsine oxides. X-ray crystal structure determinations and other physical studies, notably infrared and nmr, were used to assess the factors that influence the stereo-chemistries of these complexes.
It was observed that the compounds, (Mg(Me₃AsO)₅)(ClO₄)₂, (Ni(Me₃AsO)₅)(ClO₄)₂ and (Mg(Me₃PO)₅)(ClO₄)₂, readily adopt the square-pyramidal geometry. Two unusual features have been found in these complexes. The axial metal-oxygen bonds are consistently shorter than the corresponding basal metal-oxygen bonds, and the penultimate atoms (phosphorus and arsenic) of the basal ligands are coplanar with the square-base of the pyramid. This latter feature produces a large space in the region of the vacant sixth coordination site. The shorter axial metal-oxygen bond is discussed in terms of a stronger π interaction in the axial direction while the stability of the square-pyramidal geometry is explained in terms of electrostatic interactions between adjacent basal oxygen and arsenic atoms. Further evidence of this type of interaction was obtained from coulombic calculations.
The crystal structures of (Mg(Me₃PO)₅)(ClO₄)₂ and (Mg(Me₃PO)₅H₂O)(ClO₄)₂ enable the influence of a sixth ligand on the coordination geometry to be assessed. The significance of the formation of the five-coordinate square-pyramidal geometry and the stereochemical effects of the binding of a sixth ligand are discussed in relation to the possible importance of these geometrical features in the biological function of calcium and magnesium ions.
Comparisons between the donor powers of the phosphine oxide and arsine oxide are made. While arsine oxide has a greater σ donor strength, phosphine oxide is capable of a stronger π interaction.
An interesting dinuclear structure was determined for a calcium arsine oxide complex. This complex, (Ca₂(Me₃AsO)₉)(ClO₄)₄, was found to be bridged by arsine oxide ligands. The different donor capacities of the terminal and bridging ligands are discussed in relation to X-ray and nmr results.
27
Raisch, Christoph Werner [Verfasser], and Thomas [Akademischer Betreuer] Chassé. "Investigations of the electronic, magnetic and crystalline structure of perovskite oxides and an oxide-oxide interface / Christoph Werner Raisch ; Betreuer: Thomas Chassé." Tübingen : Universitätsbibliothek Tübingen, 2013. http://d-nb.info/1162844124/34.
Full text
28
Akbarian-Tefaghi, Sara. "Microwave-Assisted Topochemical Manipulation of Layered Oxide Perovskites: From Inorganic Layered Oxides to Inorganic-Organic Hybrid Perovskites and Functionalized Metal-Oxide Nanosheets." ScholarWorks@UNO, 2017. http://scholarworks.uno.edu/td/2287.
Full textAbstract:
Developing new materials with desired properties is a vital component of emerging technologies. Functional hybrid compounds make an important class of advanced materials that let us synergistically utilize the key features of the organic and inorganic counterparts in a single composite, providing a very strong tool to develop new materials with ”engineered” properties. The research presented here, summarizes efforts in the development of facile and efficient methods for the fabrication of three- and two-dimensional inorganic-organic hybrids based on layered oxide perovskites. Microwave radiation was exploited to rapidly fabricate and modify new and known materials. Despite the extensive utilization of microwaves in organic syntheses as well as the fabrication of the inorganic solids, the work herein was among the first reported that used microwaves in topochemical modification of the layered oxide perovskites. Our group specifically was the first to perform rapid microwave-assisted reactions in all of the modification steps including proton exchange, grafting, intercalation, and exfoliation, which decreased the duration of multi-step modification procedures from weeks to only a few hours. Microwave-assisted grafting and intercalation reactions with n-alkyl alcohols and n-alkylamines, respectively, were successfully applied on double-layered Dion-Jacobson and Ruddlesden-Popper phases (HLaNb2O7, HPrNb2O7, and H2CaTa2O7), and with somewhat more limited reactivity, applied to triple-layered perovskites (HCa2Nb3O10 and H2La2Ti3O10). Performing neutron diffraction on n-propoxy-LaNb2O7, structure refinement of a layered hybrid oxide perovskite was then tried for the first time. Furthermore, two-dimensional hybrid oxides were efficiently prepared from HLnNb2O7 (Ln = La, Pr), HCa2Nb3O10, HCa2Nb2FeO9, and HLaCaNb2MnO10, employing facile microwave-assisted exfoliation and post-exfoliation surface-modification reactions for the first time. A variety of surface groups, saturated or unsaturated linear and cyclic organics, were successfully anchored onto these oxide nanosheets. Properties of various functionalized metal-oxide nanosheets, as well as the polymerization of some monomer-grafted nanosheets, were then investigated for the two-dimensional hybrid systems.
29
Guo, Muyao, and 郭牧遥. "Metal oxide photocatalysis." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2013. http://hub.hku.hk/bib/B50434457.
Full textAbstract:
Photocatalysis has been attracting much research interest because of its wide applications in renewable energy and environmental remediation. Among the photocatalysts, metal oxide semiconductors are the best choice due to distinctive properties, durability and cost effectiveness. However, the mechanisms of photocatalysis are still not entirely clear and the photocatalytic activity of the metal oxide materials needs to be improved. Therefore, this thesis concentrates on the study of the photocatalytic mechanism and the factors affecting the photocatalytic activity.
The photocatalysis of different commercial metal oxide nanoparticles has been studied. Different photocatalytic experiments have been designed to find out the mechanisms of photocatalysis. It is found that the dominant mechanism of photocatalysis is direct charge transfer between metal oxide and organic compounds. Reactive oxygen species, such as hydroxyl radicals also play a minor role in the photocatalysis.
ZnO tetrapods were synthesized by evaporating Zn powder in the flow of Ar gas at high temperature in this study. They exhibit excellent photocatalytic activity. By the comparison between ZnO tetrapods and different ZnO nanoparticles, it is found that the photocatalytic activity of the metal oxide is strongly affected by the native defects, especially by the nonradiative defects.
1D TiO2 nanotubes and ZnO nanorods were synthesized by anodization and hydrothermal growth respectively. ZnO nanorods with alumina and titania shell were prepared by solution-based methods. These structures are interesting as supported catalysts, which is important for practical applications, since it enables simple removal of photocatalyst from treated water. The core shell structures are expected to improve the stability of ZnO. The results also imply that the photocatalytic avtivity of materials is affected by the native defects.
Two different solution based methods hydrothermal growth and electrodeposition to grow CuxO layer were used. The hydrothermal grown CuxO exhibit excellent photocatalytic activity and good photocorrosion resistance. It was also found that the photocatalytic activity of the CuxO prepared by hydrothermal methods can be recovered by simple immersion of the sample into the precursor solution.published_or_final_version
Physics
Master
Master of Philosophy
30
Machin, Sophie Elizabeth. "Metal oxide nanowires." Thesis, University of Cambridge, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.648214.
Full text
31
Garcia-Vazquez, Valentin. "Copper oxide superconductors." Diss., The University of Arizona, 1992. http://hdl.handle.net/10150/185961.
Full textAbstract:
The properties of superconducting YBa₂Cu₃O₇₋(δ) thin films have been studied. Films have been prepared by multilayer deposition followed by ex situ furnace annealing. Deposition consists of a combination of dc triode sputtering from metallic targets of Y and Cu and thermal evaporation from a BaF₂ source. Superconducting and structural properties of the films strongly depend on the annealing conditions. Several heat treatment cycles were investigated, as well as different compositions. Best results were obtained for films deposited on (100) SrTiO₃ substrates, exhibiting T(c)(onset) as high as 92 K and zero resistance by 85 K. The second part of this dissertation examines the properties of ceramic Nd₂₋ₓCeₓCuO₄₋(δ) and Nd₁ͺ₈₅Ce₀ͺ₁₅(Cu₁₋(y)Zn(y))O₄₋(δ) bulk samples. Superconducting properties are examined as a function of x and y. Accurate (± 0.001 Å) lattice parameter calculations are performed from experimental x-ray diffraction data. Comparisons with previous zinc-doping studies in the hole superconducting material La₁ͺ₈₅Sr₀ͺ₁₅CuO₄₋(δ) are made. Theoretical implications and the question of electron-hole symmetry in the copper oxide superconductors are also discussed.
32
Nylen, Nick. "The Oxide Incident." OpenSIUC, 2014. https://opensiuc.lib.siu.edu/theses/1492.
Full textAbstract:
My interest in sound-centric filmmaking and the literary genre of magical realism fostered the development of my thesis film, The Oxide Incident. The film is the story of Simon, a recent divorcee and sound archivist, who discovers a mysterious reel-to-reel-audio tape that he believes may help him heal his damaged relationship with Hannah, his teenage daughter. This paper examines the influence of magical realism on the film, some of its thematic, theoretical, and conceptual ideas such as its exploration of interpersonal communication and its implications in regard to gender, as well as some of its formal strategies. It concludes with a reflection on the process, a historical note, and a glimpse at my future trajectory as a filmmaker.
33
JASMIN, ALLADIN. "Oxide Memristive Devices." Doctoral thesis, Politecnico di Torino, 2016. http://hdl.handle.net/11583/2639136.
Full textAbstract:
Resistive switching in metal oxide materials has recently renewed the interest of many researchers due to the many application in non-volatile memory and neuromorphic computing. A memristor or a memristive device in general, is a device behaving as nonlinear resistor with memory which depends on the amount of charges that passes through it. A novel idea of combining the physical resistive switching phenomenon and the circuit-theoretic formalism of memristors was proposed in 2008. The physical mechanism on how resistive switching occurs is still under debate. A physical understanding of the switching phenomenon is of much importance in order to tailor specific properties for memory applications. To investigate the resistive switching in oxide materials, memristive devices were fabricated starting from materials processing: low-pressure chemical vapor deposition of ZnO nanowires (NWs), low-temperature atomic layer deposition (ALD) of TiO2 thin films and micro-pulse ALD of Fe2O3 thin films. The distinct geometry of ZnO NWs makes it possible to investigate the effect of the electrode material, surface states and compliance to the memristive properties. A simpler method of fabricating TiO2-based devices was explored using low-temperature atomic layer deposition. This approach is very promising for device application using photoresist and polymeric substrates without thermal degradation during and after device fabrication. ALD of pure phase Fe2O3 thin films was demonstrated using cyclic micro-pulses. Based on the performance of the fabricated devices, the oxide materials under this study have promising properties for the next-generation memory devices.
34
Nasr, Maryline. "Elaboration of oxides membranes by electrospinning for photocatalytic applications." Thesis, Montpellier, 2017. http://www.theses.fr/2017MONTT210/document.
Full textAbstract:
De nos jours, les produits chimiques toxiques industriels ne sont pas toujours traités proprement, et leurs contaminants peuvent directement affecter la sécurité de l'eau potable. La photocatalyse, «une technologie verte» est une approche efficace et économique qui joue un rôle important dans la conversion de l'énergie solaire et la dégradation des polluants organiques. Ce manuscrit de thèse rapporte sur le développement des matériaux avancés (basés sur TiO2 et ZnO) susceptibles d'exploiter l'énergie solaire renouvelable pour résoudre les problèmes de pollution environnementale. Une partie de ce travail a été consacrée pour l’amélioration de l’activité photocatalytique du TiO2 sous lumière UV et visible. Par conséquent, les nanofibres composites de rGO/TiO2, BN/TiO2 et BN-Ag/TiO2 ont été élaborées en utilisant la technique d'électrofilage (electrospinning). La deuxième partie porte sur le ZnO, ainsi que les nanotubes multi co-centriques de ZnO/ZnAl2O4 et les nanotubes de ZnO dopés Al2O3 qui ont été synthétisés en combinant les deux techniques : dépôt de couche atomique (ALD) et electrospinning. Les propriétés morphologiques, structurelles et optiques de toutes les nanostructures synthétisées ont été étudiées par différentes techniques de caractérisations. Les résultats ont montré que les propriétés chimiques et physiques ont un effet très important sur les propriétés photocatalytiques des matériaux synthétisés. En outre, il a été constaté que l'effet de dopage conduit à une séparation de charge efficace dans le photocatalyseur, ce qui rend l’activité photocatalytique plus efficace. De plus, le méthyle orange et le bleu de méthylène ont été utilisés comme modèle de référence. Une amélioration significative et une stabilité à long terme de l’activité photocatalytique ont été observées avec les matériaux dopés comparés aux matériaux non-dopés sous lumière UV et visible. Des tests antibactériens contre Escherichia coli ont été également effectués; les résultats indiquent que BN-Ag/TiO2 présente à la fois des propriétés photocatalytiques intéressantes pour la dégradation des composés organiques et pour l'élimination des bactériesNowadays, industrial toxic chemicals are still not properly treated and these contaminants may directly impact the safety of drinking water. Photocatalysis “a green technology” is an effective and economical approach and plays an important role in solar energy conversion and degradation of organic pollutants. This thesis manuscript reports on developing advanced materials (based on TiO2 and ZnO) being capable of exploiting renewable solar energy for solving the environmental pollution problems. A part of this work was dedicated to improve the UV and visible light TiO2 photoresponse. Therefore, rGO/TiO2, BN/TiO2 and BN-Ag/TiO2 composties nanofibers were successfully elaborated using the electrospinning technique. The second part focused on ZnO. Novel structures of ZnO/ZnAl2O4 multi co-centric nanotubes and Al2O3 doped ZnO nanotubes were designed by combining the two techniques of atomic layer deposition (ALD) and electrospinning. The morphological, structural and optical properties of all synthesized nanostructures were investigated by several characterization techniques. The results show that the chemical and physical properties have a high impact on the photocatalytic properties of the synthesized materials. Moreover, it was found that the doping effect lead to a more efficient charge separation in the photocatalyst, which is an advantage for photocatalytic activities. In addition, methyl orange and methylene blue were used as model reference. A significant enhancement and a long-term stability in the photocatalytic activity were observed with the doped materials compared to the non-doped ones under both UV and visible light. Antibacterial tests against Escherichia coli have also been performed; the results indicate that BN-Ag/TiO2 present interesting photocatalytic properties for both organic compound degradation and bacterial removal
35
Almar, Liante Laura. "Ordered mesoporous metal oxides for solid oxide fuel cells and gas sensors." Doctoral thesis, Universitat de Barcelona, 2014. http://hdl.handle.net/10803/283997.
Full textAbstract:
Nanomaterials have received increasing attention during the last decades in the solid state field since they play a major role as catalyst and catalyst supports for many applications including fuel cells or gas sensors. The interest is mainly due to their high specific surface area, which leads to an increase of performance and a cost-effective solution for expensive or rare materials. However, many studies have reported the collapse of nanostructures at high temperature as one of the main drawbacks for their implementation in real devices and therefore, routes to thermally stabilize these materials must be explored.
In this thesis, the unique features of ordered mesoporous materials fabricated by nanocasting are exploited to create quasi-universal thermal stabilization methodologies, allowing implementing and evaluating them in high temperature energy applications e.g. solid oxide fuel cells.
The work developed is divided into seven parts. The first chapter introduces the basics of mesoporous materials, solid oxide fuel cells, catalysis and gas sensors. The second chapter focuses on the experimental procedures and the characterization tools employed. In the third chapter, a novel route to thermally stabilize 3-D open mesoporous structures is presented. The next three chapters, show the fabrication and evaluation of thermal stable mesoporous materials as electrodes for solid oxide fuel cells. Finally, chapter seven presents the suitability of mesoporous ceramic oxides as functional materials in humidity sensors.Los nano-materiales han recibido especial atención durante estas últimas décadas en el campo del estado sólido dado el importante papel que desempeñan como catalizadores y/o soportes catalíticos en diversas aplicaciones, tales como las pilas de combustible o los sensores de gas. Este interés se debe principalmente a su elevada área específica, que da lugar a una mejora del rendimiento y es una solución efectiva para aquellas aplicaciones que requieran materiales de elevado coste. Sin embargo tal y como señalan muchos estudios, el colapso de estas nano-estructuras a elevadas temperaturas es uno de los mayores inconvenientes para su implementación en dispositivos reales, siendo por tanto necesario explorar nuevas rutas que consigan estabilizar estos materiales térmicamente. El objetivo de la presente tesis es desarrollar metodologías cuasi-universales de estabilización térmica, mediante la explotación de las características exclusivas que poseen los materiales mesoporosos ordenados fabricados a partir de un template. Lo cual nos permite implementarlos y evaluarlos en aplicaciones energéticas que operan a elevada temperatura p.ej. pilas de combustible de óxido sólido. El trabajo desarrollado se divide en siete partes. El primer capítulo introduce los fundamentos de los materiales mesoporosos, las pilas de combustible de óxido sólido, la catálisis y los sensores de gas. En el segundo capítulo se detallan los procedimientos experimentales y las técnicas de caracterización empleados. El tercer capítulo presenta una nueva metodología para estabilizar térmicamente los materiales mesoporosos de estructura 3-D abierta. Los siguientes tres capítulos, muestran la fabricación y el comportamiento electroquímico de materiales mesoporosos térmicamente estables trabajando como electrodos de pilas de combustible de óxido sólido. Por último, en el capítulo siete se demuestra la viabilidad de los óxidos cerámicos mesoporosos como materiales funcionales en sensores de humedad.
36
Jewmaidang, Jirasak. "Homogeneous sulfur tri-oxide formation in gas reburning for nitrogen oxides control." Ohio : Ohio University, 1999. http://www.ohiolink.edu/etd/view.cgi?ohiou1175801641.
Full text
37
Makgae, Mosidi Elizabeth. "Environmental electrochemistry of organic compounds at metal oxide electrodes." Thesis, Stellenbosch : Stellenbosch University, 2004. http://hdl.handle.net/10019.1/49947.
Full textAbstract:
Dissertation (PhD)--Stellenbosch University, 2004.ENGLISH ABSTRACT: This study investigates the electrochemical oxidation of phenol. Phenol is a major toxin and water pollutant. In addition, during water treatment it reacts with chlorine to produce carcinogenic chlorophenols. lts treatment down to trace levels is therefore of increasing concern. For this purpose, dynamically stable anodes for the breakdown of phenols to carbon dioxide or other less harmful substances were developed and characterized. The anodes were prepared from mixed oxides of tin (Sn) and the precious metals ruthenium (Ru), tantalum (Ta) and iridium (Ir), which in tum were prepared using sol-gel techniques. This involved dip-coating the aqueous salts of the respective metals onto titanium substrates and heating to temperatures of several hundreds of degree Celsius. The properties of these mixed oxide thin films were investigated and characterized using thermal gravimetric analysis (TGA), scanning electron microscopy (SEM), atomic force microscopy (AFM), elemental dispersive energy X-ray analysis (EDX), X-ray diffraction (XRD), Rutherford backscattering spectrometry (RBS), particle induced X-ray emission (PIXE) and electrochemical measurements. A variety of different electrode materials including Til Sn02-Ru02-Ir02, Ti/Ta20s-Ir02 and Ti/RhOx-Ir02 were developed and tested for their potential as oxidation catalysts for organic pollutants in wastewaters. Depending on the anode type, phenol was found to be electrochemically degraded, to different extents, on these surfaces during electrolysis. It was however found that the oxidation rate not only depended on the chemical composition but also on the oxide morphology revealed, resulting from the preparation procedure. The Ti/SnOz-Ru02-Ir02 film was found to be the most efficient surface for the electrolytic breakdown of phenol. This film oxidized phenol at a potential of 200 mV vs Ag/AgC!. The activity of the catalytic systems was evaluated both on the basis of phenol removal efficiency as well as the kinetics of these reactions. Phenol removal efficiency was more than 90% for all the film surfaces prepared and the rate of the reaction followed first order kinetics. A pathway for the electrochemical degradation of phenol was derived using techniques such as HPLC to identify the breakdown products. These pathway products included the formation of benzoquinone and the further oxidation of benzoquinone to the carboxylic acids malic, malonic and oxalic.
AFRIKAANSE OPSOMMING: Die onderwerp van hierdie studie is die elektrochemiese oksidasie van fenol deur nuwe gemengde-oksied elektrodes. Fenol is 'n belangrike gifstof en besoedelingsmiddel in water. Daarbenewens kan fenolook met chloor reageer tydens waterbehandeling om sodoende karsinogeniese chlorofenole te vorm. Dit is dus belangrik dat metodes ondersoek word wat die konsentrasie van fenol in water verminder. Hierdie studie behels die bereiding en karakterisering van nuwe dinamiese stabiele anodes (DSA) vir die afbreek van fenol tot koolstofdioksied en ander minder gevaarlike verbindings. Hierdie nuwe anodes is berei vanaf die gemengde-okside van die edelmetale tin (Sn), ruthenium (Ru), tantalum (Ta) en iridium (Ir), met behulp van sol-gel tegnieke. Die finale stap in die bereiding behels kalsinering van die oksides by temperature van "n paar honderd grade Celsius. Hierdie nuwe elektrodes is later gebruik om die oksidasie van fenol te evalueer. Die gemengde-oksied dunlae/anodes IS d.m.v. die volgende analitiesetegnieke gekarakteriseer: termiese-gravimetriese analise (TGA), skandeerelektronmikroskopie (SEM), atoomkragmikroskopie (AFM), elementverstrooiingsenergie- X-straalanalise (EDX), X-straaldiffraksie (XRD), Rutherford terug-verstrooiingspektroskopie (RBS), partikel-geinduseerde X-straal emissie (PIXE), en elektrochemiese metings. 'n Verskeidenheid elektrodes van verskillende materiale is berei en hul potensiaal as oksidasie-kataliste vir organiese besoedelingsmiddels in afloopwater bepaal. Hierdie elektrodes het die volgende ingesluit: Ti/Sn02-Ru02-Ir02, Ti/Ta20s-Ir02 en Ti/RhOx-Ir02. Gedurende elektrolise is fenol elektrochemies afgebreek tot verskillende vlakke, afhangende van die tipe elektrode. Die oksidasietempo het egter nie alleen van die chemiese samestelling van die elektrode afgehang nie, maar ook van die morfologie van die okside, wat op hulle beurt van die voorbereidingsprosedure afgehang het. Daar is bevind dat die Ti/Sn02-Ru02-Ir02 elektrode die mees effektiewe oppervlakke vir die afbreek van fenol is. Hier het die oksidasie van fenol by 'n potensiaal van 200 mV plaasgevind. Die aktiwiteite van die katalitiese sisteme IS bepaal op grond van hulle fenolverwyderingsdoeltreffendheid. Die kinetika van die reaksies is ook bepaal. Al die elektrodes het >90% fenolverwyderingsdoeltreffendheid getoon en die reaksietempos was van die eerste-orde. Deur van analitiese tegnieke soos hoëdrukvloeistofchromatografie (HPLC) gebruik te maak is die afbreekprodukte van fenol geïdentifiseer en 'n skema vir die elektrochemiese afbreek van fenol uitgewerk. Daar is bevind dat bensokinoon gevorm het, wat later oksidasie ondergaan het om karboksielsure te vorm.
38
Gu, Jingjing. "Ternary Oxide Structures for High Temperature Lubrication." Thesis, University of North Texas, 2015. https://digital.library.unt.edu/ark:/67531/metadc804963/.
Full textAbstract:
In this research, a temperature dependent tribological investigation of selected ternary oxides was undertaken. Based on the promising results of previous studies on silver based ternary oxides, copper based ternary oxides were selected to conduct a comparative study since both copper and silver are located in the same group in the periodic table of the elements. Two methods were used to create ternary oxides: (i) solid chemical synthesis to create powders and (ii) sputtering to produce thin films. X-ray diffraction was used to explore the evolution of phases, chemical properties, and structural properties of the coatings before and after tribotesting. Scanning electron microscopy, Auger scanning nanoprobe spectroscopy, and X-ray photoelectron spectroscopy were used to investigate the chemical and morphological properties of these materials after sliding tests. These techniques revealed that chameleon coatings of copper ternary oxides produce a friction coefficient of 0.23 when wear tested at 430 °C. The low friction is due to the formation of copper tantalate phase and copper in the coatings. All sputtering coatings showed similar tribological properties up to 430 °C.
39
Balestrieri, Matteo. "Transparent conductive oxides with photon converting properties in view of photovoltaic applications : the cases of rare earth-doped zinc oxide and cerium oxide." Thesis, Strasbourg, 2014. http://www.theses.fr/2014STRAE019/document.
Full textAbstract:
L’objectif de cette thèse était d’étudier les propriétés de conversion de photons des ions terres rares insérées dans des matrices d’oxydes transparents en vue d’application photovoltaïques. En particulier, le but était de fonctionnaliser des couches minces déjà utilisées dans les cellules solaires comme couches antireflet ou oxydes transparents conducteurs. Nous avons donc sélectionné deux matériaux (ZnO et CeO2) compatibles avec les cellules solaires au silicium.Ce travail a montré que les couches minces dopes aux terres rares peuvent être utilisées pour convertir les photons dans des applications photovoltaïques, mais qu’il n’est pas facile d’obtenir des rendements élevés.Cependant, nous avons obtenu des informations très importantes sur l’influence de la matrice sur les propriétés de conversion des terres rares et sur les mécanismes de transfert d’énergie entre la matrice et la terre rareThe objective of this thesis was to investigate the photon converting properties of rare earths (RE) ions embedded in transparent oxide hosts in view of potential application on silicon solar cells. In particular, the goal was to functionalize thin films that are already used in solar cells such as anti-Reflection coatings or transparent conductive oxides.Two host materials (ZnO and CeO2) have been selected, which are compatible with silicon solar cells.This work shows that RE-Doped transparent oxide films are a viable low-Cost solution for obtaining photon-Converting layers that can be applied on solar cells, but that achieving high efficiencies is much more difficult than it might appear in theory. Nevertheless, very valuable information has been obtained on the effect of the host material on the photon management properties and on the energy transfer mechanisms in these systems. In particular, the energy level diagram of some of the rare earth ions in the specific matrices has been reconstructed
40
Tang, Ling. "MODIFICATION OF SOLID OXIDE FUEL CELL ANODES WITH CERIUM OXIDE COATINGS." Case Western Reserve University School of Graduate Studies / OhioLINK, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=case1244252739.
Full text
41
Mirzababaei, Jelvehnaz. "Solid Oxide Fuel Cells with Methane and Fe/Ti Oxide Fuels." University of Akron / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=akron1415461807.
Full text
42
El-Mashri, Saleh M. "Structure of anodic-oxide and hydrated oxide films on pure aluminium." Thesis, University of Warwick, 1985. http://wrap.warwick.ac.uk/108759/.
Full textAbstract:
The technique of electron yield-EXAFS has been used to derive information about the different structures of amorphous films, formed anodically on pure aluminium when various electrolyte solutions are used. It has been found that the uniform non-porous (barrier-type) oxide films which are formed in neutralised sodium tartrate or sodium borate electrolyte are amorphous and have an average Al-0 bond length of 0.190 nm. The amorphous oxide produced in neutralised sodium oxalate gives an average Al-0 separation of 0.185 nm, while the porous oxides formed in strong aggressive electrolytes, chromic acid and phosphoric acid, have an average Al-0 bond length of 0.183 nm and 0.180 nm respectively. Both the non-porous and the porous types of films have also been examined by high resolution scanning electron microscopy. The films formed in neutralised electrolytes show a structureless morphology, while the films prepared in strong acid are shown to have a porous morphology. All these oxide films become hydrated when exposed to hot water at 85°C. The time for complete hydration varies according to whether the film is porous or not. Electron yield-EXAFS analysis of these hydrated films yields two well defined Al-0 distances, 0.205 nm and 0.280 nm, which appear to be associated with the formation of an oxy-hydroxide similar in structure to boehmite. The SEM observation of these hydrated films shows a narked change in the micromorphology during hydration. A "cornflake" structure is developed which is related to the oxy-hydroxide structure (boehmite-like phase). These measured Al—O bond lengths derived from the EXAFS differ, depending on the nature of the anodising treatment, which suggests different states of aluminium-oxygen coordination. A possible model for the structure of amorphous alumina, based on this information, is proposed. These results are also discussed in relation to the structural chemistry of the hydration process.
43
Adeyemo, Adedunni D. "Interaction of Metal Oxides with Carbon Monoxide and Nitric Oxide for Gas Sensing Applications." The Ohio State University, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=osu1332475552.
Full text
44
LoStracco, Gregory 1960. "Furance and carbon dioxide laser densification of sol-gel derived silicon oxide-titanium oxide-aluminum oxide planar optical waveguides." Thesis, The University of Arizona, 1994. http://hdl.handle.net/10150/291388.
Full textAbstract:
An experimental investigation on the furnace and CO₂ laser densification of sol-gel derived SiO₂-TiO₂-Al₂O₃ planar optical waveguides was performed. Solutions containing equal mole fractions of tetraethoxysiline [Si(C₂H₅O)₄], titanium ethoxide [Ti(C₂H₅O)₄], aluminum tri-sec-butoxide [Al(C₄H₉O)₃] were used to spin films with a nominal 2:2:1 molar SiO₂-TiO₂-Al₂O₃ composition. Emphasis was placed on determining what effects the densification techniques had on film shrinkage, index change, crystallization and composition. Film shrinkage and refractive index change were found to be similar for both densification techniques. Fully dense, amorphous film were obtained with both methods. After densification, further heating caused titania crystalline phases to form with both processing techniques. However, anatase formed in the furnace fired films while rutile formed in the laser irradiated films.
45
Li, Zhisheng. "Surface Chemistry Studies of Transition Metal Oxides: Titanium Oxide and Iron Oxide." Thesis, 2015. https://doi.org/10.7916/D8R2109Z.
Full textAbstract:
Surface chemistry studies of two transition-metal oxides: titanium oxide and iron oxide are presented, which are focused on thermal induced chemistry using proximal probe imaging and spectroscopy. In the first, using single crystal of rutile TiO2 (110), arrays of nano-scale locally varying surface strain field were generated by introducing highly pressurized nanoscale argon clusters 4-11 layers below the surface. The characteristics of the argon clusters are explored through STM tip-assisted surface excavation, combining with a continuum mechanical model. This work experimentally demonstrates that surface elastic strain influences the adsorption energy of adsorbates significantly and, thus, can be used for applications of surface nanopatterning. As a comparison with work on nanoscale, two forms of titanium oxide in reduced dimensionalities are experimentally synthesized and investigated for their surface reactivity: 3D nano TiO2 crystals and monolayer TiO films, both of which are supported on single crystal Au(111) surface. This work demonstrates that both nano crystals and ultrathin films of titanium oxide exhibit distinctive surface structural and catalytic properties compared to the bulk surface terminations. In particular, TiO2 nano crystals are more catalytically active and provide a new dissociation channel for adsorbed 2-propanol, a probe molecule chosen for this study. In the process of undertaking this research, it was found that monolayer TiO film can be used to employ moire varied chemistry. In particular, a long range pinwheel-shaped surface moiré pattern due to gradual shift of atom registry on Au (111), was found to further influence the adsorption geometry of adsorbates and to cause thereby smoothly varying sites for reactions.
In the case, of the second transition metal oxide surface, Fe3O4 (111), a comparison was made with rutile TiO2 (110) surface, Fe3O4 (111) is a polar surface with apparent surface charge, and thus undergoes various surface reconstructions. Therefore, its surface structure is of great complexity. Our work shows that the reaction of methanol on this iron-oxide surface is highly sensitive to atomic-level surface reconstructions.
46
Konkena, Bharathi. "Aqueous Dispersions of Graphene Oxide, Reduced Graphene Oxide and Functionalized Graphene Oxide." Thesis, 2014. http://etd.iisc.ac.in/handle/2005/3035.
Full textAbstract:
Graphene sheets, one atom thick, two dimensional layers of carbon atoms, have gained enormous importance over the past few years due to their unique attributes - high electronic, thermal conductivities and exceptional mechanical strength. Chemical reduction of graphene oxide (GO) has been considered as a viable route for large scale production of graphene sheets. The reduced graphene oxide (r -GO) sheets although their conductivities are comparatively lower than that of graphene are nevertheless versatile material for applications in thin films and composites. An important consideration in the design of solution processing techniques for the preparation of processable graphene sheets is the dispersibility of GO and r -GO in different solvents, especially aqueous dispersibility. While GO is dispersible in water over a wide range of pH values, r -GO shows poor dispersibility and over a limited range of pH values.
Graphene oxide, the oxidized form of graphene, are single atomic layers with lateral dimension that can extend to hundreds of nanometers. The sheets contain a sizable fraction of carbons that are sp3 hybridized and covalently bonded to oxygen in the form of epoxy, carbonyls as well as ionizable hydroxyl and carboxylic functional groups located on the rim of the sheets. The remaining carbons form isolated sp2 graphene like networks. On reduction the oxygen functionalities are removed and the sp2 network partially restored. This thesis focuses on the aqueous dispersibility of GO and r -GO, and describes a strategy to enhance the dispersibility of r -GO by cyclodextrin functionalization. Chapter 1 of the thesis provides a brief review of the synthetic procedures and structure of GO and r -GO while Chapter 2 describes the experimental methods and characterization techniques used in the thesis.
The chemistry underlying the aqueous dispersibility of GO and r -GO at different
values of pH have been investigated by zeta potential measurements, pH titrations and
infrared spectroscopy (Chapter 3). These measurements show that r -GO sheets have
ionizable groups with a single pKa value (8.0) while GO sheets have groups that are
more acidic (pKa = 4.3), in addition to groups with pKa values of 6.6 and 9.0. Infrared spectroscopy has been used to follow the sequence of ionization events. In both GO and r -GO sheets, it is ionization of the carboxylic groups that is primarily responsible for the build up of charge, but on GO sheets, the presence of phenolic and hydroxyl groups in close proximity to the carboxylic groups lowers the pKa value by stabilizing the carboxylate anion, resulting in superior water dispersibility.
Till recently GO was primarily considered only as an easily available precursor for
chemical routes to r -GO but it has now been recognized as an interesting material in
its own right. Two such attributes that have attracted wide spread attention are the in-
trinsic and tunable fluorescence of GO as well as formation of liquid crystalline phases.
Aqueous dispersions of GO exhibit strong pH dependent fluorescence in the visible region
that originates, in part, from the oxygenated functionalities present. In Chapter 4, the
spectral migration on nanosecond timescales of the pH dependent features in the fluores-
cence spectra of GO is described. The changes in the steady state fluorescence spectra
with pH have been correlated with the sequence of dissociation events that occur in GO dispersions at different values of pH described in Chapter 3, from time resolved emission spectra (TRES) constructed from the wavelength dependent fluorescence decay curves, it is shown that the migration is associated with excited state proton transfer. Both ‘intramolecular’ and ‘intermolecular’ transfers involving the quasimolecular oxygenated aromatic fragments are observed.
Aqueous dispersions of GO constitute a distinctive class of 2D-anisotropic colloids with competing interactions - long range electrostatic repulsion, originating from ionized carboxylic groups located on the rim of the sheets and weak dispersive attractive interactions originating from the un-oxidized sp2 graphitic domains. In Chapter 5, it is shown that, colloidal dispersions of GO are intrinsically frustrated, exhibiting a range of arrested or metastable states, encompassing fluid, glass and gels that coexist with liquid crystalline
order. These states can be accessed by varying the relative magnitudes of the repulsive and attractive forces by changing the ionic strength of the medium, by addition of salt and/or the concentration of the dispersion. At low salt concentrations, where long range electrostatic repulsions dominates, the formation of a repulsive Wigner glass is observed while at high salt concentrations, when attractive forces dominate, the formation of gels that
exhibits a nematic to columnar liquid crystalline transition. These studies highlights how the chemical structure of GO - hydrophilic ionizable groups and hydrophobic graphitic domains coexisting on a single sheet - gives rise to a rich and complex phase diagram.
The poor dispersibility of r -GO in aqueous media limits its use in practical applica-
tions. To enhance the dispersibility, r -GO sheets have been functionalized by covalently
linking -cyclodextrin ( -CD) cavities to the sheets via an amide linkage (Chapter 6).
The functionalized -CD: rGO sheets, in contrast to r -GO, are dispersible over a wide range of pH values (2 - 13). Zeta potential measurements indicate that there is more than one factor responsible for the dispersibility. It is shown that planar aromatic molecules adsorbed on the r -GO sheet as well as nonplanar molecules included in the tethered -CD cavities have their fluorescence effectively quenched by the -CD: rGO sheets. The -CD: rGO sheets combine the hydrophobicity associated with r -GO along with the hydrophobicity of the cyclodextrin cavities in a single water dispersible material.
Resonance Raman spectroscopy is a powerful analytical tool for detecting and identi-
fying analytes, but the associated strong fluorescence background severely limits the use of the technique. In Chapter 7, it is shown that the cyclodextrin functionalized -CD: rGO sheets, described in Chapter 6, provides a versatile platform for resonance Raman detection. Planar aromatic and dye molecules that adsorb on the r -GO graphitic domains and non-planar molecules included within the tethered -CD cavities have their fluorescence effectively quenched. Using the water dispersible -CD: rGO sheets, it is possible to record the resonance Raman spectra of adsorbed and included organic chromophores directly in aqueous media without having to extract or deposit on a substrate. The Raman signal intensities show a linear dependence with the concentration of analyte present in water. This is significant, as it allows for the identification and estimation of organic
analytes present in water by resonance Raman spectroscopy.
47
Konkena, Bharathi. "Aqueous Dispersions of Graphene Oxide, Reduced Graphene Oxide and Functionalized Graphene Oxide." Thesis, 2014. http://hdl.handle.net/2005/3035.
Full textAbstract:
Graphene sheets, one atom thick, two dimensional layers of carbon atoms, have gained enormous importance over the past few years due to their unique attributes - high electronic, thermal conductivities and exceptional mechanical strength. Chemical reduction of graphene oxide (GO) has been considered as a viable route for large scale production of graphene sheets. The reduced graphene oxide (r -GO) sheets although their conductivities are comparatively lower than that of graphene are nevertheless versatile material for applications in thin films and composites. An important consideration in the design of solution processing techniques for the preparation of processable graphene sheets is the dispersibility of GO and r -GO in different solvents, especially aqueous dispersibility. While GO is dispersible in water over a wide range of pH values, r -GO shows poor dispersibility and over a limited range of pH values.
Graphene oxide, the oxidized form of graphene, are single atomic layers with lateral dimension that can extend to hundreds of nanometers. The sheets contain a sizable fraction of carbons that are sp3 hybridized and covalently bonded to oxygen in the form of epoxy, carbonyls as well as ionizable hydroxyl and carboxylic functional groups located on the rim of the sheets. The remaining carbons form isolated sp2 graphene like networks. On reduction the oxygen functionalities are removed and the sp2 network partially restored. This thesis focuses on the aqueous dispersibility of GO and r -GO, and describes a strategy to enhance the dispersibility of r -GO by cyclodextrin functionalization. Chapter 1 of the thesis provides a brief review of the synthetic procedures and structure of GO and r -GO while Chapter 2 describes the experimental methods and characterization techniques used in the thesis.
The chemistry underlying the aqueous dispersibility of GO and r -GO at different
values of pH have been investigated by zeta potential measurements, pH titrations and
infrared spectroscopy (Chapter 3). These measurements show that r -GO sheets have
ionizable groups with a single pKa value (8.0) while GO sheets have groups that are
more acidic (pKa = 4.3), in addition to groups with pKa values of 6.6 and 9.0. Infrared spectroscopy has been used to follow the sequence of ionization events. In both GO and r -GO sheets, it is ionization of the carboxylic groups that is primarily responsible for the build up of charge, but on GO sheets, the presence of phenolic and hydroxyl groups in close proximity to the carboxylic groups lowers the pKa value by stabilizing the carboxylate anion, resulting in superior water dispersibility.
Till recently GO was primarily considered only as an easily available precursor for
chemical routes to r -GO but it has now been recognized as an interesting material in
its own right. Two such attributes that have attracted wide spread attention are the in-
trinsic and tunable fluorescence of GO as well as formation of liquid crystalline phases.
Aqueous dispersions of GO exhibit strong pH dependent fluorescence in the visible region
that originates, in part, from the oxygenated functionalities present. In Chapter 4, the
spectral migration on nanosecond timescales of the pH dependent features in the fluores-
cence spectra of GO is described. The changes in the steady state fluorescence spectra
with pH have been correlated with the sequence of dissociation events that occur in GO dispersions at different values of pH described in Chapter 3, from time resolved emission spectra (TRES) constructed from the wavelength dependent fluorescence decay curves, it is shown that the migration is associated with excited state proton transfer. Both ‘intramolecular’ and ‘intermolecular’ transfers involving the quasimolecular oxygenated aromatic fragments are observed.
Aqueous dispersions of GO constitute a distinctive class of 2D-anisotropic colloids with competing interactions - long range electrostatic repulsion, originating from ionized carboxylic groups located on the rim of the sheets and weak dispersive attractive interactions originating from the un-oxidized sp2 graphitic domains. In Chapter 5, it is shown that, colloidal dispersions of GO are intrinsically frustrated, exhibiting a range of arrested or metastable states, encompassing fluid, glass and gels that coexist with liquid crystalline
order. These states can be accessed by varying the relative magnitudes of the repulsive and attractive forces by changing the ionic strength of the medium, by addition of salt and/or the concentration of the dispersion. At low salt concentrations, where long range electrostatic repulsions dominates, the formation of a repulsive Wigner glass is observed while at high salt concentrations, when attractive forces dominate, the formation of gels that
exhibits a nematic to columnar liquid crystalline transition. These studies highlights how the chemical structure of GO - hydrophilic ionizable groups and hydrophobic graphitic domains coexisting on a single sheet - gives rise to a rich and complex phase diagram.
The poor dispersibility of r -GO in aqueous media limits its use in practical applica-
tions. To enhance the dispersibility, r -GO sheets have been functionalized by covalently
linking -cyclodextrin ( -CD) cavities to the sheets via an amide linkage (Chapter 6).
The functionalized -CD: rGO sheets, in contrast to r -GO, are dispersible over a wide range of pH values (2 - 13). Zeta potential measurements indicate that there is more than one factor responsible for the dispersibility. It is shown that planar aromatic molecules adsorbed on the r -GO sheet as well as nonplanar molecules included in the tethered -CD cavities have their fluorescence effectively quenched by the -CD: rGO sheets. The -CD: rGO sheets combine the hydrophobicity associated with r -GO along with the hydrophobicity of the cyclodextrin cavities in a single water dispersible material.
Resonance Raman spectroscopy is a powerful analytical tool for detecting and identi-
fying analytes, but the associated strong fluorescence background severely limits the use of the technique. In Chapter 7, it is shown that the cyclodextrin functionalized -CD: rGO sheets, described in Chapter 6, provides a versatile platform for resonance Raman detection. Planar aromatic and dye molecules that adsorb on the r -GO graphitic domains and non-planar molecules included within the tethered -CD cavities have their fluorescence effectively quenched. Using the water dispersible -CD: rGO sheets, it is possible to record the resonance Raman spectra of adsorbed and included organic chromophores directly in aqueous media without having to extract or deposit on a substrate. The Raman signal intensities show a linear dependence with the concentration of analyte present in water. This is significant, as it allows for the identification and estimation of organic
analytes present in water by resonance Raman spectroscopy.
48
Chen, Hao, and 陳豪. "Characterization of III-V Compound Semiconductor MOSFETs with Titanium Oxide and Aluminum Oxide Stacked Layers as Gate Oxides." Thesis, 2014. http://ndltd.ncl.edu.tw/handle/ggp92v.
Full textAbstract:
碩士國立中山大學
電機工程學系研究所
102
Due to the high electron mobility compared with Si, much attention has been focused on III-V compound semiconductors (gallium arsenide (GaAs), indium phosphide (InP), indium gallium arsenide (InGaAs)) high-speed devices. The high-k material TiO2 not only has high dielectric constant (k =35-100) but also has well lattice match with GaAs, InP and InGaAs substrate. Therefore, titanium oxide (TiO2) was chosen to be the gate oxide in this study, and aluminum oxide (Al2O3) has high bandgap (Eg~9eV) and self-cleaning capability, we use TiO2 and Al2O3 stack layers to decrease leakage currents and increase capacitance. The major problem of III-V compound semiconductor is known to have poor native oxide on it leading to the Fermi level pinning at the interface of oxide and semiconductor. The C-V stretch-out phenomenon can be observed and the leakage current is high. Use atomic layer deposition (ALD) system to grow stack double layers ALD-TiO2 and ALD-Al2O3 films on III-V substrate by high-k of TiO2 and high bandgap and self-cleaning capability of Al2O3 to reduce only one layer’s defect. The surface passivation of III-V with (NH4)2S treatment (S-III-V) could prevent it from oxidizing after cleaning and improve the interface properties of MOSFET. The leakage current of sulfur passivation can be improved. The leakage current densities are 7.31 x 10-7, 3.11 x 10-6 and 7.40 x 10-7 A/cm2 at ±2.0MV/cm, respectively. The (NH4)2S is necessary to passivation III-V surface form S-thin film of fabrication of III-V devices.
49
Yen, Li Chen, and 嚴立丞. "The Electrical and Structural Properties of Thulium Oxide, Thulium Titanium Oxide, Ytterbium Titanium Oxide, and Holmium Titanium Oxide Gate Dielectrics." Thesis, 2009. http://ndltd.ncl.edu.tw/handle/13869296123658571908.
Full textAbstract:
碩士長庚大學
電子工程學研究所
97
In this thesis, we reported on structural and electrical characteristic of high-k thulium oxide (Tm2O3), tulium titanium oxide (Tm2Ti2O7), ytterbium titanium oxide (Yb2TiO5) and holmium titanium oxide (HoTiO5) the metal-oxide-semiconductor capacitance gate dielectrics by reactive RF sputtering. Effect of titanium content in thulium oxide, ytterbium oxide and holmium oxide of the gate dielectrics with post deposition O2 annealing treatment on the crystallization temperature, leakage current, dielectric constant, and interface trap density. Compared to Tm2O3, Tm2Ti2O7, Yb2TiO5, and HoTiO3 was found to exhibit excellent electrical property such as a high accumulation capacitance, low leakage current density and a thin interfacial layer. The superiority of Tm2Ti2O7, Yb2TiO5, and HoTiO3 can be attributed to the addition of titanium the thulium oxide and holmium oxide matrix. It is found that the capacitance value of Tm2Ti2O7, Yb2TiO5, and HoTiO3 gate dielectric annealed at 800°C is higher compared to the other annealing temperatures and exhibits a lower hysteresis voltage as well as interface trap density in C-V curves. They also show almost negligible charge trapping under high constant voltage stress. This phenomenon is attributed to an amorphous Tm2Ti2O7, Yb2TiO5, and HoTiO3 structure and the decrease of the interfacial layer and Tm and Ho silicate thickness observed by X-ray diffraction and X-ray photoelectron spectroscopy, respectively. In addition, we reported Tm2Ti2O7, Yb2TiO5, and HoTiO3 compound layers grown by PDA process should display a sufficiently high-k value to achieve very thin EOT values, combined with lower hysteresis voltage, interface trap density, low leakage current density, and good reliability. This is due to the formation of amorphous microstructure and the reduction of lower-k interfacial layer.
50
"Spectrophotometric determination of aluminium oxide, calcium oxide and iron (III) oxide in Portland cement." Chinese University of Hong Kong, 1993. http://library.cuhk.edu.hk/record=b5887734.
Full textAbstract:
Shu King-hung.Thesis (M.Phil.)--Chinese University of Hong Kong, 1993.
Includes bibliographical references (leaves 80-81).
ABSTRACT --- p.1
Chapter CHAPTER I. --- INTRODUCTION --- p.3
REFERENCES --- p.6
Chapter CHAPTER II. --- BRIEF REVIEW OF THE ANALYTICAL METHODS USED
Chapter 1. --- Spectrophotometry --- p.8
Chapter 2. --- Derivative spectrophotometry --- p.9
Chapter 3. --- Atomic absorption spectrometry --- p.12
Chapter 4. --- X - Ray fluorescence --- p.12
REFERENCES --- p.14
Chapter CHAPTER III. --- SIMULTANEOUS DETERMINATION OF ALUMINIUM OXIDE AND IRON (III) OXIDE
Chapter 1. --- Introduction
Review of the reported methods --- p.15
Determination of aluminium and iron with
8-hydroxyquinoline --- p.18
Chapter 2. --- Experimental --- p.21
Chapter 3. --- Results and discussion
Determination of iron --- p.28
Determination of aluminium --- p.38
Chapter 4. --- Conclusion --- p.52
REFERENCES --- p.53
Chapter CHAPTER IV. --- RAPID DETERMINATION OF CALCIUM OXIDE
Chapter 1. --- Introduction --- p.56
Chapter 2. --- Experimental --- p.62
Chapter 3. --- Results and discussion --- p.66
Chapter 4. --- Conclusion --- p.79
REFERENCES --- p.80
FIGURES
Chapter II-1 --- Attenuation of a beam of radiation by an absorbing solution --- p.8
Chapter II-2 --- Gaussian curve and its first to fourth derivatives --- p.11
Chapter III-l --- Effect of pH on the extraction of metals with8- hydroxyquinoline --- p.19
Chapter III-2 --- "Normal absorbance spectra of the metal - oxinates: A1 (5ppm), Fe (5ppm)" --- p.20
Chapter III-3 --- Effect of pH on the determination of iron (5ppm) --- p.29
Chapter III-4 --- Calibration curve for the determination of iron (III) by spectrophotometry at 580 nm --- p.33
Chapter III-5 --- "The first derivative spectra of metal-oxinates A1: 5ppm, Fe : 5ppm" --- p.39
Chapter III-6 --- "The second derivative spectra of metal-oxinates, A1: 5ppm, Fe : 5ppm" --- p.39
Chapter III-7 --- "Normal absorption spectra of the metal-oxinates : A1(5 ppm), Ti (5 ppm)" --- p.41
Chapter III-8 --- Effect of pH on the determination of aluminium --- p.43
Chapter III-9 --- Calibration curve for the determination of aluminium by second derivative spectrophotometry at 390 nm --- p.47
Chapter IV-1 --- "Effect of pH on the development of colour of Ca- GBHA complex. Ca : 1.2 ppm, wavelength : 530 nm" --- p.68