A solid oxide fuel cell (SOFC) is an energy conversion device that has the potential to efficiently generate electricity in an environmentally-friendly manner. In general, a SOFC operates between 750&deg;C and 1000&deg;C utilizing hydrogen or hydrocarbons as fuel and air as an oxidant. The three major components comprising a fuel cell are the electrolyte, the cathode, and the anode. At present, the state-of-the-art SOFC is made from a dense yttria-stabilized zirconia (YSZ) electrolyte, a porous lanthanum manganite cathode, and a porous nickel/YSZ composite anode. With the advent of the anode-supported SOFC and the increased interest in using a wider range of fuels, such as those containing sulphur, knowledge of the anode properties is becoming more important. <br /> The properties of the current anodes are limited due to the narrow range of nickel loadings imposed by the minimum nickel content for electrical conductivity and the maximum allowable nickel loading to avoid thermal mismatch with the YSZ electrolyte. In addition, there is little research presented in the literature regarding the use of nickel metal as a starting anode material, rather than the traditional nickel oxide powder, and how porosity may affect the anode properties. <br /> The purpose of this investigation is to determine the influence nickel morphology and porosity distribution have on the processing and properties of tape cast Ni/YSZ composites. Specifically, the sintering characteristics, electrical conductivity, and thermal expansion behaviour of tape cast composites created from YSZ, nickel, nickel oxide (NiO), nickel coated graphite (NiGr), and/or graphite (Gr) powders are investigated. In addition to samples made from 100% YSZ, 100% Ni, and 100% NiO powders, five composite types were created for this investigation: NiO/YSZ, NiO&Gr/YSZ, Ni/YSZ, NiGr/YSZ, and Ni&Gr/YSZ each with nickel loadings varying between 4 vol% Ni of total solids and 77 vol% Ni of total solids. Another set of composites with a fixed nickel loading of 27 vol% Ni and 47 vol% Ni of total solids and varying graphite loadings were also created. <br /> During the burnout stage, the composites made from nickel oxide powder shrink slightly while the composites made from nickel metal expand due to nickel oxidation. Graphite additions below 20 vol% of the green volume do not alter the dimensional changes of the composites during burnout, but graphite loadings greater than 25 vol% of the green volume cause significant expansion in the thickness of the composites. <br /> After sintering, the amount of volumetric sintering shrinkage decreases with higher nickel loadings and is greater for the composites made with nickel oxide compared to the composites made from nickel metal. The porosity generated in the composites containing graphite is slightly higher than the volume of graphite added to the composite and is much greater than the porosity contained in the graphite-free composites. <br /> Dimensional changes of the porous Ni/YSZ and NiO/YSZ composites during both burnout and sintering were analysed based on concepts of constrained sintering of composite powder mixtures. In some cases constrained sintering was evident, while in others, a more simple rule of mixtures behaviour for shrinkage as a function of YSZ content was observed. <br /> When nickel oxide is reduced to nickel metal during the reduction stage there is essentially no change in the composite volume for the composites containing YSZ because the YSZ prevents the composites from shrinking. After reduction the additional porosity generated in the composites is equivalent to the change in volume due to the reduction of nickel oxide to nickel metal. <br /> When measuring the electrical conductivity, each composite type demonstrated classic percolation behaviour. The NiGr/YSZ composites had the lowest percolation threshold, followed by the Ni/YSZ and NiO/YSZ composites. When graphite was added with a nickel coating, the added porosity did not disrupt the nickel percolation network and allowed the nickel to occupy a larger effective volume compared to a composite made with similar sized solid nickel particles. When graphite was added to the composites, the electrical conductivity was reduced and the percolation threshold increased. <br /> Generally, the coefficient of thermal expansion (CTE) for Ni/YSZ composites are expected to follow the rule of mixtures prediction since the elastic properties for nickel and YSZ are similar. However when porosity is distributed unevenly between the YSZ and nickel phases, the CTE prediction will deviate from the rule of mixtures. When cornstarch was added to the NiGr/YSZ composites, the CTE increased as the amount of porosity in the YSZ phase increased. The CTE of the NiGr/YSZ composites followed the rule of mixtures indicating that the porosity was evenly distributed between the nickel and YSZ phases. For the other composite types, the measured CTE was higher than the rule of mixtures prediction suggesting that more porosity was contained within the YSZ phase.

A solid oxide fuel cell (SOFC) is an energy conversion device that has the potential to efficiently generate electricity in an environmentally-friendly manner. In general, a SOFC operates between 750&deg;C and 1000&deg;C utilizing hydrogen or hydrocarbons as fuel and air as an oxidant. The three major components comprising a fuel cell are the electrolyte, the cathode, and the anode. At present, the state-of-the-art SOFC is made from a dense yttria-stabilized zirconia (YSZ) electrolyte, a porous lanthanum manganite cathode, and a porous nickel/YSZ composite anode. With the advent of the anode-supported SOFC and the increased interest in using a wider range of fuels, such as those containing sulphur, knowledge of the anode properties is becoming more important. <br /> The properties of the current anodes are limited due to the narrow range of nickel loadings imposed by the minimum nickel content for electrical conductivity and the maximum allowable nickel loading to avoid thermal mismatch with the YSZ electrolyte. In addition, there is little research presented in the literature regarding the use of nickel metal as a starting anode material, rather than the traditional nickel oxide powder, and how porosity may affect the anode properties. <br /> The purpose of this investigation is to determine the influence nickel morphology and porosity distribution have on the processing and properties of tape cast Ni/YSZ composites. Specifically, the sintering characteristics, electrical conductivity, and thermal expansion behaviour of tape cast composites created from YSZ, nickel, nickel oxide (NiO), nickel coated graphite (NiGr), and/or graphite (Gr) powders are investigated. In addition to samples made from 100% YSZ, 100% Ni, and 100% NiO powders, five composite types were created for this investigation: NiO/YSZ, NiO&Gr/YSZ, Ni/YSZ, NiGr/YSZ, and Ni&Gr/YSZ each with nickel loadings varying between 4 vol% Ni of total solids and 77 vol% Ni of total solids. Another set of composites with a fixed nickel loading of 27 vol% Ni and 47 vol% Ni of total solids and varying graphite loadings were also created. <br /> During the burnout stage, the composites made from nickel oxide powder shrink slightly while the composites made from nickel metal expand due to nickel oxidation. Graphite additions below 20 vol% of the green volume do not alter the dimensional changes of the composites during burnout, but graphite loadings greater than 25 vol% of the green volume cause significant expansion in the thickness of the composites. <br /> After sintering, the amount of volumetric sintering shrinkage decreases with higher nickel loadings and is greater for the composites made with nickel oxide compared to the composites made from nickel metal. The porosity generated in the composites containing graphite is slightly higher than the volume of graphite added to the composite and is much greater than the porosity contained in the graphite-free composites. <br /> Dimensional changes of the porous Ni/YSZ and NiO/YSZ composites during both burnout and sintering were analysed based on concepts of constrained sintering of composite powder mixtures. In some cases constrained sintering was evident, while in others, a more simple rule of mixtures behaviour for shrinkage as a function of YSZ content was observed. <br /> When nickel oxide is reduced to nickel metal during the reduction stage there is essentially no change in the composite volume for the composites containing YSZ because the YSZ prevents the composites from shrinking. After reduction the additional porosity generated in the composites is equivalent to the change in volume due to the reduction of nickel oxide to nickel metal. <br /> When measuring the electrical conductivity, each composite type demonstrated classic percolation behaviour. The NiGr/YSZ composites had the lowest percolation threshold, followed by the Ni/YSZ and NiO/YSZ composites. When graphite was added with a nickel coating, the added porosity did not disrupt the nickel percolation network and allowed the nickel to occupy a larger effective volume compared to a composite made with similar sized solid nickel particles. When graphite was added to the composites, the electrical conductivity was reduced and the percolation threshold increased. <br /> Generally, the coefficient of thermal expansion (CTE) for Ni/YSZ composites are expected to follow the rule of mixtures prediction since the elastic properties for nickel and YSZ are similar. However when porosity is distributed unevenly between the YSZ and nickel phases, the CTE prediction will deviate from the rule of mixtures. When cornstarch was added to the NiGr/YSZ composites, the CTE increased as the amount of porosity in the YSZ phase increased. The CTE of the NiGr/YSZ composites followed the rule of mixtures indicating that the porosity was evenly distributed between the nickel and YSZ phases. For the other composite types, the measured CTE was higher than the rule of mixtures prediction suggesting that more porosity was contained within the YSZ phase.

The preparation and thermophysical properties of some In(I), Ga(I) and Ag(I) substituted NZP type materials were explored. Many compositions with the NZP framework show low and negative thermal expansion. Previously reported material, GaZr2(PO4(3, transforms from one NZP related phase into another NZP type phase due to oxidation under air above 300oC. In addition, it exhibits hysteresis under inert atmosphere; the cell parameters are different on heating and cooling cycles for a given temperature. The synthesis, and characterization of a new material, InZr2(PO4)3, is outlined. It crystallizes in space group R -3 c. In addition, as GaZr2(PO4)3, it oxidizes above 300oC under air and exhibits hysteresis under inert atmosphere. Furthermore, the synthesis of AgTixZr2-x(PO4)3 solid solution compositions, their ion exchange characteristics with Ga(I) and their thermophysical properties are described. Thermal expansion anisotropy (the difference between a and c ) of the solid solutions decreases as the bigger ion, Zr4+, is substituted by the smaller one, Ti4+. Thermal expansion characteristics of GaZr2(PO4)3, InZr2(PO4)3 and AgZr2(PO4)3 are compared with MZr2(PO4)3 ( M = Li, Na, K, Rb, Cs). Ionic radii for Ga(I) and In(I) in a six coordinate oxygen environment were proposed.

In this studing, application of the digital image correlation method (DIC) for determining the coefficient of thermal expansion (CTE) of Indium Tin Oxide/Polyethylene Terephthalate(ITO/PET) thin film/flexible substrate was proposed and the effects of thinkness variations of ITO and PET, respectively, on the CTE of the specimens was disscussed. The observation range of experimental temperature was chosen from room temperature to the glass transfer temperature of PET, 70¢J. A novel DIC experimental process for reducing the errors caused from the variations of the refractive index of the surrounding heated air was proposed. As a result, the experimental error of CTE measurement was reduced form 10~17% to less than 5%. The experimental results showed that the CTE of ITO/PET specimen is anisotropic. Futhermore, the CTE of an ITO/PET specimen will be increased by decreasing the thinkness of PET flexible substrate, and increased by increasing the thinkness of ITO film - which means decreasing the surface resistance of ITO film.

In this work , impurity free vacancy diffusion (IFVD) quantum well intermixing(QWI) technology by high thermal-expansion-induced stress is used to perform bandgap engineering. In this paper, 1530nm InGaAsP multiple QWs sandwiched by p-InP (2£gm thickeneess, top) and n-InP (bottom) material is used as testing material structure also laser fabrication material, where contact materials (InGaAs and InP) on p-InP are used for comparison. By the difference between thermal expansion coefficients of SiO2 on the different material (InGaAs, InP), large different behaviors of QWI are observed, while low different dependence on defects created by ion-implantation is found. Above 70nm photo luminance (PL) wavelength shift of InGaAsP MQW below 2£gm thick InP is realized in this method. Further more, CW in-plane laser structures are also successfully fabricated and demonstrated by such QWI, giving the same shift as PL. It shows that good qualify of material can be obtained in such QWI method. Using local deposition of SiO2 causes different bandgap materials, re-growth free processing for monolithic integration can be expected, offering a powerful scheme of QWI for bandgap engineering.

Zirconium tungstate (ZrW2O8) is a ceramic that shows large isotropic negative thermal expansion over a wide range of temperature. This unique property makes it an interesting candidate for applications where thermal expansion mismatch between components constitutes a problem. ZrW2O8 is typically produced by solid-state reaction between zirconium oxide and tungsten oxide at 1200oC. In some studies, ZrW2O8 precursors have been produced from relatively expensive zirconium and tungsten sources. While the origin of negative thermal expansion has been the main focus in the majority of publications, production of particles with controlled size, distribution and morphology has not been studied extensively. Electrospinning is a simple technique for producing micron/nano sized fibers from polymer solutions. The method can also be used for producing ceramic or polymer/ceramic composite fibers by electrospinning of a mixture of ceramic precursors or ceramic nanoparticles with suitable polymers. Ceramic precursors could be synthesized either by sol-gel or chemical precipitation routes before mixing them with polymer solutions and a final burnout step would be needed, in case the fiber is desired to be composed of the ceramic phase. Electrospinning technique has not been employed to the production of ZrW2O8 ceramic fibers. In this study a novel precursor for ZrW2O8 from relatively cheaper and abundant starting chemicals, namely zirconium acetate and tungstic acid were used. Experimental details of development of the precursor are presented with a discussion on the effects of solution parameters on the phase purity of the fired product. Besides the solution parameters investigated (i.e. solubility of tungstic acid, adjustment of the stoichiometry, final pH of the solution, ageing time), evolution of the heat treatment protocol was used in the production of phase pure ZrW2O8. Second, the suitability of the developed precursor for producing ZrW2O8 in fiber form was investigated. Preliminary studies involved the adjustment of the viscosity of precursor solution for electrospinning with poly (vinyl alcohol) (PVA). Optimum PVA concentration leading to bead-free nanofiber mats and a method to increase the fiber production rate were reported. The characterization of the products was achieved by SEM and XRD.

This work focuses on the chemical substitution of cations and anions in the frameworks of materials that have been known to exhibit negative thermal expansion (NTE). Zr2(PO4)2(SO4) is a member of the A(2)M(3)O(12) family which has been known to exhibit NTE. We have shown that Zr2(PO4)2(SO4) exhibits anisotropic positive thermal expansion. We have also shown that this material has been characterized in the wrong space group. Hf2(PO4)2(SO4) behaves similarly to Zr2(PO4)2(SO4) and follows this trend. Under pressure, Hf2(PO4)2(SO4) appears to undergo a phase transition. We have still yet to determine what space group the materials transitions to. While many members of the AX(2)O(7) family of frameworks have been fully characterized, the thermal expansion of PbP2O7 has yet to be reported. We were unable to obtain a reproducible procedure for synthesis of PbP2O7 from its precursor. Finally, variable temperature and variable pressure studies were performed on ZrMo2O8 in an attempt to learn more about the local structure. We found that space groups P213 and Pa-3 gave poor fits of the local structure at low r. Behavior of the nearest neighbor Zr-Mo distance was very similar to the bulk CTE. On compression, pressure induced amorphization is observed in ZrMo2O8. All interatomic correlations above 4 angstroms are washed out. Zr-O-Mo linkages remain well defined and do not massively deform as the pressure is increased. Finally, we we observed that Zr-O-Mo linkages change geometry reversibly as the pressure is increased.

This thesis explores the thermal expansion and high pressure behavior of some materials with the ReO₃ structure type. This structure is simple and has, in principle, all of the features necessary for negative thermal expansion (NTE) arising from the transverse thermal motion of the bridging anions and the coupled rotation of rigid units; however, ReO₃ itself only exhibits mild NTE across a narrow temperature range at low temperatures. ReO₃ is metallic because of a delocalized d-electron, and this may contribute to the lack of NTE in this material. The materials examined in this thesis are all based on d⁰ metal ions so that the observed thermal expansion behavior should arise from vibrational, rather than electronic, effects. In Chapter 2, the thermal expansion of scandium fluoride, ScF₃, is examined using a combination of in situ synchrotron X-ray and neutron variable temperature diffraction. ScF₃ retains the cubic ReO₃ structure across the entire temperature range examined (10-1600 K) and exhibits pronounced negative thermal expansion at low temperatures. The magnitude of NTE in this material is comparable to that of cubic ZrW₂O₈, which is perhaps the most widely studied NTE material, at room temperature and below. This is the first report of NTE in an ReO₃ type structure across a wide temperature range. Chapter 3 presents a comparison between titanium oxyfluoride, TiOF₂, and a vacancy containing titanium hydroxyoxyfluoride, Tiₓ(O/OH/F)₃. TiOF₂ was originally reported to adopt the cubic ReO₃ structure type under ambient conditions, therefore the initial goal for this study was to examine the thermal expansion of this material and determine if it displayed interesting behavior such as NTE. During the course of the study, it was discovered that the original synthetic method resulted in Tiₓ(O/OH/F)₃, which does adopt the cubic ReO₃ structure type. The chemical composition of the hydroxyoxyfluoride is highly dependent upon synthesis conditions and subsequent heat treatments. This material readily pyrohydrolyizes at low temperatures (~350 K). It was also observed that TiOF₂ does not adopt the cubic ReO₃ structure; at room temperature it adopts a rhombohedrally distorted variant of the ReO₃ structure. Positive thermal expansion was observed for TiOF₂ from 120 K through decomposition into TiO₂. At ~400 K, TiOF₂ undergoes a structural phase transition from rhombohedral to cubic symmetry. High pressure diffraction studies revealed a cubic to rhombohedral phase transition for Tiₓ(O/OH/F)₃ between 0.5-1 GPa. No phase transitions were observed for TiOF₂ on compression. In Chapter 4, an in situ variable pressure{temperature diffraction experiment examining the effects of pressure on the coefficients of thermal expansion (CTE) for ScF₃ and TaO₂F is presented. In the manufacture and use of composites, which is a possible application for low and NTE materials, stresses may be experienced. Pressure was observed to have a negligible effect on cubic ScF₃'s CTE; however, for TaO₂F the application of modest pressures, such as those that might be experienced in the manufacture or use of composites, has a major effect on its CTE. This effect is associated with a pressure-induced phase transition from cubic to rhombohedral symmetry upon compression. TaO₂F was prepared from the direct reaction of Ta₂O₅ with TaF₅ and from the digestion of Ta₂O₅ in hot hydro uoric acid. The effects of pressure on the two samples of TaO₂F were qualitatively similar. The slightly different properties for the samples are likely due to differences in their thermal history leading to differing arrangements of oxide and uoride in these disordered materials. In Chapter 5, the local structures of TiOF₂ and TaO₂F are examined using pair distribution functions (PDFs) obtained from X-ray total scattering experiments. In these materials, the anions (O/F) are disordered over the available anion positions. While traditional X-ray diffraction provides detailed information about the average structures of these materials, it is not suffcient to fully understand their thermal expansion. Fits of simple structural models to the low r portions of PDFs for these materials indicate the presence of geometrically distinct M{X{M (M = Ti, Ta; X = O, F) linkages, and a simple analysis of the TaO₂F variable temperature PDFs indicates that these distinct links respond differently to temperature.

Corrosion of steel reinforcement in concrete structures results in significant repair and rehabilitation costs. In the past several years, new fiber reinforced polymer (FRP) reinforcing bars have been introduced as an alternative to steel reinforcing bars. Several national and international organizations have recently developed standards based on preliminary test results. However, limited validation testing has been performed on the recommendations of these standards. High variability of the tensile properties, degradation of tensile strength, direct shear capacity, predicted deflections due to creep, cracking behavior of FRP-reinforced concrete flexural members, bond behavior and development length, and effects of thermal expansion on cracking of FRP reinforced concrete have all been reported, but are areas that need further investigation and validation. The objective of this study is to evaluate the characteristics of glass FRP reinforcing bars and provide recommendations on the design and construction of concrete structures containing these bar types with regard to the areas described. The recently developed ACI 440 design guidelines were analyzed and modifications proposed.

Turbine components operate under severe loading conditions and at high and varying temperatures that result in thermal stresses in the presence of temperature gradients created by hot gases and cooling air. Moreover, static and cyclic loads as well as the motion of rotating components create mechanical stresses. The combined effect of complex thermo-mechanical stresses promote nucleation and propagation of cracks that give rise to fatigue and creep failure of the turbine components. Therefore, the relationship between thermo-mechanical stresses, chemical composition, heat treatment, resulting microstructure, operating temperature, material damage, and potential failure modes, i.e. fatigue and/or creep, needs to be well understood and studied. Artificial neural networks are promising candidate tools for such studies. They are fast, flexible, efficient, and accurate tools to model highly non-linear multi-dimensional relationships and reduce the need for experimental work and time-consuming regression analysis. Therefore, separate neural network models for γ’ precipitate strengthened Ni based superalloys have been developed for predicting the γ’ precipitate size, thermal expansion coefficient, fatigue life, and hysteresis energy. The accumulated fatigue damage is then estimated as the product of hysteresis energy and fatigue life. The models for γ’ precipitate size, thermal expansion coefficient, and hysteresis energy converge very well and match experimental data accurately. The fatigue life proved to be the most challenging aspect to predict, and fracture mechanics proved to potentially be a necessary supplement to neural networks. The model for fatigue life converges well, but relatively large errors are observed partly due to the generally large statistical variations inherent to fatigue life. The deformation mechanism map for 1.23Cr-1.2Mo-0.26V rotor steel has been constructed using dislocation glide, grain boundary sliding, and power law creep rate equations. The constructed map is verified with experimental data points and neural network results. Although the existing set of experimental data points for neural network modeling is limited, there is an excellent match with boundaries constructed using rate equations which validates the deformation mechanism map.