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Biodiesel is currently produced by homogeneous catalysis. More recently however, heterogeneous catalysis is being considered as a cheaper alternative to the homogeneous process. In this research project, heterogeneous catalysts of zirconium oxide were produced by impregnation. Zirconium oxide impregnation with sulfuric acid produced acidic solid catalysts. It was determined that impregnation and calcination at 550^oC (SO₄/ZrO₂-550^oC) produced the best catalyst for palmitic acid esterification with 10 wt % as the optimum concentration in esterification of palmitic acid. SO₄/ZrO₂-550^oC was successfully recycled for eight consecutive runs before permanent deactivation. Its sulfur content was 1.04 wt % using SEM-EDS and 2.05 wt % using XPS for characterization. BET surface area was 90.89 m2/g. The reaction mechanism over Brønsted acid (SO₄/ZrO₂-550^oC) and Lewis acid (Al₂O₃) catalysts obeyed Eley-Rideal kinetics with palmitic acid and methanol adsorbed on the active site respectively. Zirconium oxide was also impregnated with sodium hydroxide to produce basic catalysts. The best catalyst was produced when zirconium oxide was impregnated with 1.5 M NaOH and calcined at 600^oC. Soybean oil was completely converted to biodiesel with 10 wt % catalyst and 1:6 oil to methanol. A mixture of the base catalyst with 30 wt % SO₄/ZrO₂-550^oC effectively converted soybean oil containing 5% oleic acid indicating that this mixture could be used for waste oils. The reaction was first order with respect to triglyceride and second order with respect to methanol. The activation energy was 49.35 kJ/mol and the reaction mechanism obeyed Langmuir-Hinshelwood kinetics. / Master of Science

In the last decade new materials appeared that are candidates to be used as an electrolyte in a Solid Oxide Fuel Cell, SOFC. Some materials show high ionic conductivity but lack in important properties, such as mechanical stability or chemical compatibility with other materials in the fuel cell. Scandia Stabilised Zirconia, SSZ, became a possibility when the scandia price dropped with the opening of the Chinese and Russian markets. In the starting system Ce[subscript(x)]Y[subscript(0.2-x)]Sc₀.₆Zr₃.₂O[subscript(8-δ)], (0≤x≤0.2), scandia is introduced to improve conductivity and stabilise the cubic phase; yttria is introduced to fully stabilise the cubic phase and ceria to enhance conductivity lost with the introduction of yttria. The aim of this project is to develop a reliable new method to produce quality ceramics that are not strongly composition dependent, then to prepare a range of compositions and compare intrinsic properties without having to be concerned that poor sintering dominates conduction properties. This project can be divided in two sections, the first section the powder production method, the characteristics of the powders and its final products are in focus. In the second section the relation between electric characteristics and microstructure of the material is reported. In the first section, the effect of different compositions of the system Ce[subscript(x)]Y[subscript(0.2-x)]Sc₀.₆Zr₃.₂O[subscript(8-δ)], (0≤x≤0.2) is studied, in terms of structure, phase and microstructure. The nature, size and shape of the powders are discussed, and their effect on the final product. The sol-gel and combustion method gives the formation of hard agglomerates (shells), during the combustion, a wide range of grain sizes, between less than 1µm and 200 µm, and the formation of grains with non spherical shape. In this project, the sol-gel and combustion process and solid state method are also compared. In the second section of this project, AC Impedance measurements, as a function of temperature, oxygen partial pressure and time are discussed. The Arrhenius plot for all compositions shows two regions (high and low temperature) and the change of region occurs at 580 °C. At low temperatures there is a slight difference between compositions but this difference is less at high temperatures. The obtained ionic conductivity, at 350 °C, varies from 3.84×10⁻⁶ to 5.53×10⁻⁵ S/cm; at 700 °C, ionic conductivity from 0.013 to 0.044 S/cm. At low temperatures, the activation energy associated with bulk process is generally lower than grain boundary process; for example, the composition Ce₀.₁Y₀.₁Sc₀.₆Zr₃.₂O₇.₆₅ has an activation energy, for the bulk process, of 1.05 eV and an activation energy, for the grain boundary process, of 1.17 eV. For compositions with higher ceria content, activation energy, for bulk and grain boundary, have similar values. The AC impedance as function of oxygen partial pressure show that the amount of ceria introduced as an effect on the conductivity at low oxygen partial pressure. For the sample with no ceria in its composition, Y₀.₂Sc₀.₆Zr₃.₂O₇.₆₀, the conductivity does not vary significantly as the oxygen partial pressure is decreased; for oxygen partial of 0.21 atm, conductivity is 0.018 S/cm and when oxygen partial pressure is approximately 10⁻²⁴ atm conductivity is 0.018 S/cm. For the sample with a higher content of ceria, Ce₀.₁₂Y₀.₀₈Sc₀.₆Zr₃.₂O₇.₆₆, there is a decrease in conductivity while oxygen partial pressure decreases; and there is also the appearance of a semi-circle for lower oxygen partial pressures. For oxygen partial pressure approximately 0.21 atm, conductivity is 0.019 S/cm, but when oxygen partial pressure is decreased to 10⁻²⁴ atm conductivity decreases to 0.011 S/cm. AC impedance measurements as a function of annealing time at 600 °C were performed. Total conductivity is fairly stable, for all compositions, until 1800 hours but after this time, conductivity slowly decreases. Some compositions show a second semi-circle in the AC impedance spectra, either from the beginning, time equals 0 hours, or after some working hours. Here, the changes in conduction and conduction processes with time are discussed.

<p>Due to the constantly decreasing dimensions of electronic devices, the conventional dielectric material in transistors and capacitors, SiO₂, has to be replaced by a material with higher dielectric constant. Some of the most promising candidates are tantalum oxide,Ta₂O₅, zirconium oxide, ZrO₂ and hafnium oxide, HfO₂.</p><p>This thesis describes new chemical vapour deposition (CVD) and atomic layer deposition (ALD) processes for deposition of Ta₂O₅, ZrO₂ and HfO₂ using the metal iodides as starting materials. The layer-by-layer growth in ALD was also studied in real time with a quartz crystal microbalance (QCM) to examine the process characteristics and to find suitable parameters for film deposition.</p><p>All the processes presented here produced high-purity films at low deposition temperatures. It was also found that films deposited on Pt substrates generally crystallise at lower temperature, or with lower thickness, than on silicon and single-crystalline oxide substrates. Films grown on MgO(001) and α-Al₂O₃(001) substrates were strongly textured or epitaxial. For example, monoclinic HfO₂ deposited on MgO(001) were epitaxial for deposition temperatures of 400-500 C in ALD and 500-600 C in CVD. Electrical characterisation showed that the crystallinity of the films had a strong effect on the dielectric constant, except in cases of very thin films, where the dielectric constant was more dependent on layer thickness.</p>

Due to the constantly decreasing dimensions of electronic devices, the conventional dielectric material in transistors and capacitors, SiO2, has to be replaced by a material with higher dielectric constant. Some of the most promising candidates are tantalum oxide,Ta2O5, zirconium oxide, ZrO2 and hafnium oxide, HfO2. This thesis describes new chemical vapour deposition (CVD) and atomic layer deposition (ALD) processes for deposition of Ta2O5, ZrO2 and HfO2 using the metal iodides as starting materials. The layer-by-layer growth in ALD was also studied in real time with a quartz crystal microbalance (QCM) to examine the process characteristics and to find suitable parameters for film deposition. All the processes presented here produced high-purity films at low deposition temperatures. It was also found that films deposited on Pt substrates generally crystallise at lower temperature, or with lower thickness, than on silicon and single-crystalline oxide substrates. Films grown on MgO(001) and α-Al2O3(001) substrates were strongly textured or epitaxial. For example, monoclinic HfO2 deposited on MgO(001) were epitaxial for deposition temperatures of 400-500 C in ALD and 500-600 C in CVD. Electrical characterisation showed that the crystallinity of the films had a strong effect on the dielectric constant, except in cases of very thin films, where the dielectric constant was more dependent on layer thickness.

M. Tech. Metallurgical Engineering. / StudIes the tribocorrosion behaviour of copper-nickel-titanium shape memory composite reinforced by zirconia,synthesized through powder metallurgy process. The research aims to achieve the following objectives: 1. Study the tribocorrosion mechanisms of the composites in NaCl solution (typical human body fluid). 2. Investigate the tribocorrosion mechanisms of the composites in other environments typical of some engineering applications.The proposed study on incorporating zirconia into the matrix NiTiCu through powder metallurgical process and investigations of the phenomenon of joint wear-corrosion synergism occurring in sodium chloride considered typical of human body system and sulphuric acid environment typical of wide range engineering applications is therefore very novel. It is therefore aimed that information on the tribocorrosion behaviour of NiTiCu as well as with zirconia incorporation will form basis for typical compositional formulation approaches for improved bio-tribocorrosion improvement in biomedical applications and actuators used in other engineering applications.

Thesis (M.S.) -- Mississippi State University. Dave C. Swalm School of Chemical Engineering. / Title from title screen. Includes bibliographical references.

Orientador: Cecilia Amelia de Carvalho Zavaglia / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia mecanica / Made available in DSpace on 2018-08-04T10:23:14Z (GMT). No. of bitstreams: 1 Gomide_VivianeSilva_M.pdf: 10916166 bytes, checksum: 3d319a5e8b56700e5844bc42e9b8d18f (MD5) Previous issue date: 2005 / Resumo: Existe uma crescente demanda de materiais que possibilitam a remodelação e reconstrução de partes ósseas. A indicação de biomateriais para reconstrução dos defeitos cranianos depois do trauma, tumor ou infecção, ocorre devido a razões estéticas e proteção de estruturas intracraniais. Várias técnicas cirúrgicas vários materiais já foram utilizados na confecção dessas próteses crâniomaxilofaciais, mas é importante avaliar o comportamento desse material quanto à estabilidade fisiológica e resistência mecânica. O objetivo principal deste trabalho é desenvolver biomateriais para uso em preenchimento de defeitos ósseos. A hidroxiapatita, cerâmica bioativa semelhante à parte mineral do tecido ósseo, é um material que poderia ser utilizado para essa finalidade. Porém, essa cerâmica possui baixas tenacidade à fratura e resistência mecânica à compressão. Com a finalidade de obter materiais mais adequados para restaurações ósseas e implantes crâniomaxilofaciais, foram associadas a hidroxiapatita obtida no laboratório de materiais cerâmicos do DEMA-FEM-UNICAMP, partículas de reforço de três cerâmicas: zircônia, alumina e titânia, nas proporções de 30,40 e 50% em peso para cada composição. Os compósitos obtidos e sinterizados foram caracterizados por medida de tamanho de partículas, Microscopia Eletrônica de Varredura, Difração de Raios X e Espectroscopia de Fluorescência de Raios X e tiveram suas densidades aparentes, densidades teóricas, absorção de água, volumes aparentes e porosidades aparentes determinadas pelo ensaio de Archimedes. Algumas propriedades mecânicas como resistência à compressão, dureza e tenacidade à fratura foram determinadas. Os compósitos que tiveram melhor comportamento geral foram escolhidos para continuidade do trabalho (ensaios ¿ in vitro" e ¿Hin vivo ") / Abstract: There is a growing demand of materiaIs that make the remodeling and reconstruction of bone parts possible. Reconstruction of defects of the skulI after trauma, tumor or infection is indicated for aesthetic reasons and for protection of internal structures. Different materiaIs have been used for this purpose and alI of them must be evaluated as for their stability in physiological environments and mechanical strength. The main objective of this work is to develop biomaterials for use in fulfilIing of bone defects. The hydroxyapatite, similar bioactive ceramics to the mineral part of the tissue bone, is a material that could be used for this purpose. However, this ceramics possess decreases tenacity to the breaking and resistance mechanics the compression. With the purpose to get more adequate materiaIs for bone restorations and craniomaxilofacials implantations associates had been hydroxyapatite gotten in the laboratory of ceramic materiaIs of the DEMA-FEM-UNICAMP, particles of three ceramics bioinert, zirconia, alumina and titania, in the ratios of 30%, 40% and 50% in weight for each composition. The composites obtained and sintered were characterized by particles size measure, Scanning Electronic Microscopy, X Rays Difratometry and Spectroscopy of Fluorescence of X Rays and had its apparent densities and apparent porosity determined by the assay of Archimedes. Some mechanical properties as compressive strength, hardness and tenacity to the breaking had been performanced. The composites that had general behavior had been better chosen for continuity ofthe work (assays "in vitro" and "in vivo") / Mestrado / Materiais e Processos de Fabricação / Mestre em Engenharia Mecânica

ABSTRACT De-bonding is the most common failure of resin-bonded fixed partial dentures. The aim was to determine if the shear bond strength (SBS) differed between a dental adhesive and a Co-Cr alloy and an yttria-stabilized zirconia (Y-TZP). Furthermore, to determine whether retention holes in the two materials and storage for 21 days in water affected the results. The hypothesis was that there are no significant differences between the compared groups. 10 embedded discs of Co-Cr alloy without and 10 with retentive holes, and 10 discs of Y-TZP without and 17 with retentive holes were sand- and steam blasted. A pillar of adhesive cement was bonded to the surface of the discs and stored in water at 37 °C for 24 hr and / or 21 days. An UltraTest machine with a crosshead speed of 1 mm/ min was used for SBS. The mean SBS after 24 hr / 21 days in water were recorded. The SBS of Co-Cr alloy without retentive hole was 16.3 MPa after 24 hr and 11.4 MPa after 21 days, the SBS of Y-TZP without retentive hole was 18.5 MPa after 24 hr and 12.6 MPa after 21 days. The SBS of Co-Cr alloy with retentive hole 13.9 MPa after 21 days and Y-TZP with retentive hole 16.9 MPa after 21 days. No statistically significant differences were found between the groups with or without retentive holes and after 24 hr or 21 days in water, p&gt; 0.05.

DMagister Scientiae - MSc / The proton exchange membrane is one key component of direct methanol fuel cells, which has double functions of conducting protons, separating fuels and oxidant. At present, the performance and price of sulfonic acid proton exchange membrane used in direct methanol fuel cells are deeply concerned. In order to reduce membrane 's cost and improve performance of Nafion membrane, three different kinds of membranes have been studied in this thesis. These membranes are SPEEK membranes, SPEEK/ZP composite membranes and Nafion/ZP composite membranes. / South Africa