by Yeung, Lap Kun. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2002. / Includes bibliographical references (leaves 96-98). / Abstracts in English and Chinese. / Abstract --- p.ii / Acknowledgements --- p.iv / Table of Contents --- p.v / Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Emergence of LTCC Technology --- p.1 / Chapter 1.2 --- Overview of the Work --- p.2 / Chapter 1.3 --- Original Contributions --- p.3 / Chapter 1.4 --- Thesis Organization --- p.4 / Chapter 2 --- Fundamentals of Partial Element Equivalent Circuit Modeling --- p.5 / Chapter 2.1 --- Introduction --- p.5 / Chapter 2.2 --- PEEC Formulation --- p.6 / Chapter 2.2.1 --- Mixed potential integral equation --- p.6 / Chapter 2.2.2 --- Current discretization --- p.7 / Chapter 2.2.3 --- Charge discretization --- p.8 / Chapter 2.2.4 --- Galerkin matching --- p.9 / Chapter 2.3 --- Partial Inductance --- p.11 / Chapter 2.4 --- Partial Capacitance --- p.12 / Chapter 2.5 --- Meshing Scheme and Circuit Interpretation --- p.13 / Chapter 2.6 --- Summary --- p.15 / Chapter 3 --- PEEC Modeling of LTCC RF Circuits using Thin-film Approximation --- p.16 / Chapter 3.1 --- Introduction --- p.16 / Chapter 3.2 --- A Simple LTCC Band-pass Filter --- p.17 / Chapter 3.3 --- Discretization Scheme --- p.18 / Chapter 3.4 --- Quasi-static Green's Functions --- p.21 / Chapter 3.4.1 --- Free-space Green's function --- p.21 / Chapter 3.4.2 --- System with a single ground plane --- p.22 / Chapter 3.4.3 --- System with two ground planes --- p.25 / Chapter 3.5 --- Complex-Image Analysis --- p.25 / Chapter 3.6 --- Partial Inductance --- p.31 / Chapter 3.6.1 --- Strip-to-strip inductance --- p.31 / Chapter 3.6.2 --- System with one or more ground planes --- p.33 / Chapter 3.7 --- Partial Capacitance --- p.34 / Chapter 3.8 --- Numerical and Experimental Results --- p.37 / Chapter 3.9 --- Summary --- p.40 / Chapter 4 --- PEEC Modeling of LTCC RF Circuits using Thin-film Approximation (Via-hole Modeling) --- p.41 / Chapter 4.1 --- Introduction --- p.41 / Chapter 4.2 --- Via-hole Modeling --- p.42 / Chapter 4.2.1 --- Discretization scheme --- p.42 / Chapter 4.2.2 --- Inductance formulae --- p.43 / Chapter 4.2.3 --- Empirical formula --- p.46 / Chapter 4.2.4 --- Edge-effect compensation --- p.48 / Chapter 4.3 --- Numerical and Experimental Results --- p.49 / Chapter 4.4 --- Summary --- p.51 / Chapter 5 --- An Efficient PEEC Algorithm for Modeling of LTCC RF Circuits with Finite Metal Strip Thickness --- p.53 / Chapter 5.1 --- Introduction --- p.53 / Chapter 5.2 --- PEEC Modeling using Thin-film Approximation --- p.54 / Chapter 5.3 --- PEEC Modeling with Finite Metal Thickness --- p.55 / Chapter 5.4 --- Edge-effect Compensation in Inductance Calculation --- p.57 / Chapter 5.5 --- Numerical and Experimental Results --- p.61 / Chapter 5.6 --- Summary --- p.65 / Chapter 6 --- A Compact Second-order LTCC Band-pass Filter with Two Finite Transmission Zeros --- p.66 / Chapter 6.1 --- Introduction --- p.66 / Chapter 6.2 --- Features of the Filter --- p.67 / Chapter 6.3 --- Design Theory --- p.68 / Chapter 6.4 --- LTCC Filter Implementation --- p.70 / Chapter 6.4.1 --- Circuit model --- p.70 / Chapter 6.4.2 --- Physical layout --- p.73 / Chapter 6.5 --- Experimental Results --- p.75 / Chapter 6.6 --- Summary --- p.77 / Chapter 7 --- Concluding Remarks --- p.79 / Chapter 7.1 --- PEEC Modeling --- p.79 / Chapter 7.2 --- Limitations of the Algorithm --- p.80 / Chapter 7.3 --- Further Improvements --- p.81 / Appendix --- p.82 / References --- p.96 / Author's Publications --- p.98

A cadeia produtiva da construção civil está associada a grandes consumos de matérias-primas e energia, além de ser uma das maiores geradoras de resíduo, sendo responsável por parcela significativa dos impactos ambientais a nível global. Embora seja vasta a disponibilidade de literatura internacional a respeito de impactos ambientais causados por materiais de construção, a bibliografia nacional ainda é limitada. Este fato constitui uma barreira na determinação dos impactos ambientais causados por materiais de construção locais, e conseqüentemente os impactos causados pelas edificações e pelo setor da construção. Os materiais cerâmicos estão entre os mais tradicionais empregados na construção civil no Brasil, onde existem aproximadamente 11.000 indústrias, principalmente de pequeno e médio porte. No entanto o setor enfrenta uma série de problemas ambientais, econômicos e de qualidade dos produtos fabricados. Em 2000, o Núcleo Orientado para a Inovação da Edificação (NORIE), pertencente ao Departamento de Engenharia Civil da Universidade Federal do Rio Grande do Sul (UFRGS), iniciou uma pesquisa visando identificar de forma qualitativa e quantitativa os impactos ambientais causados pelo processo produtivo de materiais de cerâmica vermelha, para o Estado do Rio Grande do Sul. Este trabalho analisa os dados coletados em uma pesquisa realizada em 40 indústrias de cerâmica vermelha de diferentes escalas (com produção de 20.000 a 1.500.000 peças/mês) e utiliza a metodologia de Análise do Ciclo de Vida para obter resultados relativos a recursos naturais, fontes energéticas, geração de resíduos sólidos e emissões gasosas, relacionados a cada fase do processo produtivo. Os resultados obtidos revelam os impactos causados pelas indústrias de cerâmica vermelha no Rio Grande do Sul, apontando os aspectos positivos e negativos do processo. São também obtidos dados quantitativos com relação à energia incorporada nos produtos, através de informações coletadas nas indústrias. / The Building Construction supply chain is characterized by a high consumption of raw materials and energy and a high production of waste; being responsible for a significant share in the global environmental impact. Although being large the availability of international literature on environmental impacts determined by building materials, the existing literature on such impacts in Brazil is very limited. This constitutes a barrier to determine the environmental impact of local building materials, and consequently the impact caused by buildings and the building sector. Ceramic products are in the roll of the most traditional construction materials used in Brazil, where there are about 11,000 industries, mostly small and medium sized. However, the sector is going through environmental, economic and product quality problems. In 2000, NORIE, a section of the Department of Civil Engineering Department at UFRGS (Federal University of Rio Grande do Sul), started a research project aiming at identifying quantitative and qualitative environmental impacts caused by ceramic bricks, blocks and tiles production, in the State of Rio Grande do Sul, south of Brazil. This research analyses the collected data on a survey performed at 40 ceramic industries, with different scales (producing from 20,000 to 1,500,000 bricks/month), and uses LCA methodology to obtain results related to material and energy consumption, as well as waste emissions in each process step. The obtained results reveal the environmental impacts caused by ceramic bricks, blocks and tiles industries in Rio Grande do Sul, pointing out positive and negative production aspects. In addition, it was possible to estimate the embodied energy of local ceramic materials through the collected data.

This paper studies the geometrically non-linear bending behavior of functionally graded beams subjected to buckling loads using the finite element method. The computational model is based on an improved first-order shear deformation theory for beams with five independent variables. The abstract finite element formulation is derived by means of the principle of virtual work. High-order nodal-spectral interpolation functions were utilized to approximate the field variables which minimizes the locking problem. The incremental/iterative solution technique of Newton's type is implemented to solve the nonlinear equations. The model is verified with benchmark problems available in the literature. The objective is to investigate the effect of volume fraction variation in the response of functionally graded beams made of ceramics and metals. As expected, the results show that transverse deflections vary significantly depending on the ceramic and metal combination. / Revisión por pares

Replacing organic liquid electrolytes with nonflammable solid electrolytes can improve safety, offer higher volumetric and gravimetric energy densities, and lower the cost of lithium-ion batteries. However, today’s all-solid-state batteries suffer from low Li-ion conductivity in the electrolyte, slow Li-ion transport across the electrolyte/electrode interface, and slow solid-state Li-ion diffusion within the electrode. Defect chemistry is critical to understanding ionic conductivity and predicting the charge transport through heterogeneous solid interfaces. The goal of this dissertation is to analyze and improve solid state materials for energy storage applications by understanding their defect structure and transport properties. I have investigated defect chemistry of cubic Li7La3Zr2O12 (c-LLZO), one of the most promising candidate solid electrolytes for all-solid-state lithium batteries. By combining conductivity measurements with defect modeling, I constructed a defect diagram of c-LLZO featuring the intrinsic formation of lithium vacancy-hole pairs. The findings provided insights into tailoring single-phase mixed lithium-ion/electron conducting materials for emerging ionic devices, i.e., composite cathodes requiring both fast electronic and ionic paths in solid-state batteries. I suggested that oxygen vacancies could increase the Li-ion conductivity by reducing the amount of electron holes bound with lithium vacancies. Using a simpler but also attractive solid electrolyte Li2ZrO3 (LZO) as an example, I significantly improved Li-ion conductivity by creating extra oxygen vacancies via cation doping. In particular, Fe-doped LZO shows the highest Li-ion conductivity reported for the family of LZO compounds, reaching 3.3 mS/cm at 300 °C. This study brought attentions to the long-neglected oxygen vacancy defects in lithium-ion conductors and revealed their critical role in promoting Li-ion transport. More importantly, it established a novel defect engineering strategy for designing Li-oxide based solid electrolytes for all-solid-state batteries. I surface-modified LiNi0.6Co0.2Mn0.2O2 cathode material with a LZO coating prepared under dry air and oxygen, and systematically investigated the effect of coating atmosphere on their transport properties and electrochemical behaviors. The LZO coating prepared in oxygen is largely amorphous. It not only provided surface protection against the electrolyte corrosion but also enabled faster lithium-ion transport. Additionally, oxygen atmosphere facilitated Zr diffusion from the surface coating to the bulk of LiNi0.6Co0.2Mn0.2O2, which stabilized the crystal structure and enhanced lithium ion diffusion. Consequently, LiNi0.6Co0.2Mn0.2O2 cathodes coated with Li2ZrO3 in oxygen achieved a significant improvement in high-voltage cycling stability and high-rate performance.

The efficacy of dispersed reduced graphene oxide (rGO) as a nucleation site for the growth of mesophase in an isotropic pitch was investigated and quantified in this study. Concentrations of rGO were systematically tested in an isotropic petroleum and coal-tar pitch during thermal treatments and compared to pitch without rGO. The mesophase content of each thermally treated pitch was quantified by polarized light point counting. Further characterization of softening temperature and insolubles were quantified. Additionally, the pitches with and without rGO were melt spun, graphitized, and tensile tested to determine the effects of rGO on graphitized fiber mechanical properties and fiber morphology.

A piezoelectric microspeaker device that could be used in a variety of acoustic applications was designed and fabricated using a thin film ZnO layer that was reactively DC sputtered onto a single crystalline n-type silicon substrate. When tested the microspeaker did not produce sound due to complications in the etching process, the thickness of the diaphragms, and clamping effects. Instead, a characterization approach was taken and the structural, optical, electrical, and piezoelectric properties of the ZnO were investigated. Scanning electron microscopy, x-ray diffraction, and atomic force microscopy were utilized to discover the ZnO’s structural properties. Using the XRD and SEM, the as-sputtered ZnO films were found to have highly c-axis oriented columnar crystals. Optical properties were determined from the reflectance spectrums obtained from a Filmetrics F20 reflectometer and were used to determine the film thickness, the optical constants, and the optical band gap of the ZnO thin films. Using a four-point probe, the as-sputtered ZnO films were found to be highly resistive and insulative, mainly due to voided growth boundaries between the crystals. To improve electrical conductivity and piezoelectric response, ZnO samples were annealed at varying temperatures in a nitrogen environment. The annealing process successfully increased the electrical conductivity and piezoelectric properties of the films. The local piezoelectric properties of the ZnO were discovered with an Asylum MFP-3D and a piezoresponse force microscopy (PFM) technique called DART-PFM. The ZnO films that were sputtered with 70 watts and an argon to oxygen gas ratio of 2:1 were found to have the highest d33 piezoelectric coefficients. The ZnO sample that was annealed at 600°C for 30 minutes had the highest overall d33 value of 4.0 pm/V, which means that the 600°C annealed ZnO films would have the best chance of making a functional microspeaker.

The dissertation is split into two parts. The first part will be focused on changes in material properties found at the nanoscale, as miscibility and electronic structure can change significantly with size. The formation of classically-immiscible bimetallic nanoparticles (BNPs) becomes favorable at the nanoscale and novel catalytic properties can emerge from the bimetallic alloying. The formation of alloyed and non-alloyed BNPs is achieved through pulse laser ablation (PLA) and a significant increase in catalytic activity is observed for both. Recently discovered, the increased activity in the non-alloyed BNPs, deemed multicomponent photocatalysis, is examined and the proposed mechanism discussed. The second part of the talk will focus on thermal barrier coatings (TBCs), which are advanced, multi-layered coatings used to protect materials in high temperature environments. MCrAlY (M=Ni, Co) bond coats deposited via atmospheric plasma spray (APS) are intrinsically rough and initially the roughness provides a high surface area platform for the mechanical interlocking of the yttria stabilized zirconia (YSZ) top coat, which provides the bulk of the thermal insulation. After high temperature exposure, a protective oxide scale forms at the top coat/bond coat interface however the convex asperities of the bond coat can grow non-α-Al2O3 type oxides that can be detrimental for coating lifetime. A surface modification technique that removes the asperities while leaving intact the concavities is used to examine the role that roughness distribution has on 1100°C APS coating lifetime. Lastly, recent work validating a modelling strategy for evaluating 900°C TBC lifetimes, which can typically surpass 25 kh, is presented. Differences in coating-substrate interdiffusion behavior over 5-20 kh of 900°C exposure are discussed and reproduced with Thermo- Calc/DICTRA for three superalloys (1483, 247, X4) deposited with high velocity oxy fuel (HVOF) NiCoCrAlY coatings.

Borides and carbides of tantalum and hafnium are of great interest due to their ultrahigh temperature applications. Properties of these ceramics including oxidation resistance and mechanical properties might be further improved through solid solution/composite formation. Synthesis of single-phase TaxHf1-xC and TaxHf1-xB2 solid solution powders including nanopowders via carbothermal reduction (CTR) is complicated due to noticeable difference in reactivity of parent oxides with carbon, and also the low solubility of those oxides in each other. Moreover, for TaC-HfC system the solid solution may go through phase separation due to the presence of a miscibility gap at temperatures below 887°C.In this study, a method of low-cost aqueous solution processing followed by CTR was used to synthesize TaxHf1-xC and TaxHf1-xB2 solid solution powders. In fact, method was first used to synthesize boron carbide (B4C) powders as it paves the way for a detailed study on the synthesis of TaxHf1-xC and TaxHf1-xB2 solid solutions powders considering the fact that B4C contains both carbon and boron in its structure. Particular emphasis was given to investigate the influences of starting compositions and processing conditions on phase separation during the formation of both carbide and boride phase(s). It was found that individual TaC-HfC and TaB2-HfB2 phases always form quickly but separately during the CTR process (e.g., at 1600 °C within a few minutes). Those carbides and borides remain phase-separated unless heated to much higher temperatures for long time due to the slow inter-diffusion between them. It was also found that for TaxHf1-xC applying a DC electric field through the use of spark plasma sintering (SPS) system significantly accelerates the inter-diffusion of Ta and Hf leading to formation of a single-phase TaxHf1-xC solid solution at 1600 °C for 15 minutes. On the other hand, for borides alkali metal reduction reaction (AMR) method appears to be an excellent alternative to CTR-based method for formation of a single-phase TaxHf1-xB2 solid solution. In this method, chlorides of tantalum and hafnium are directly reduced using sodium borohydride (NaBH4) giving rise to formation of a single-phase Ta0.5Hf0.5B2 solid solution nanopowders in one step at much lower temperatures (e.g., 700 °C) by avoiding the oxides formation and the associated phase separation of individual borides as observed in the CTR-based process.

Abstract not available

Nanoscale surfaces were examined in order to determine the influence of surface curvature on polymer behavior at polymer-ceramic interfaces, as well as the influence of nanoparticles in cellulosic media. Poly(methyl methacrylate) and block copolymers thereof were adsorbed onto porous alumina substrates of various pore sizes in order to determine how polymer and copolymer adsorption behavior at nanoscale surfaces differs from adsorption onto flat surfaces. It was determined that chain density on concave surfaces dramatically decreases as curvature increases in much the same way that it does on convex surfaces (e.g. on the surface of nanoparticles), and physical models are provided to explain this similarity. Diblock copolymer adsorption is observed to vary dramatically with solvent quality and block asymmetry and can be correlated with the surface curvature very similarly to the adsorptive behavior of homopolymers on those same surfaces. The addition of nanoparticles to cellulosic media was investigated as a means to significantly modify the properties of cellulosic composites with minimal additions of nanoparticles. Although cellulose is among the most abundant polymers on earth, its primary uses are limited to bulk commodity goods, such as paper and textiles. This work demonstrates a simple means to control cellulosic fluid viscosity, thereby increasing the versatility of these biopolymers in additional applications with higher value-added potential. The formation of iron-cellulosic nanocomposites by the in-situ thermolysis of metal carbonyls to form metallic nanoparticles was performed and was analyzed by viscometry among other techniques. It was determined that the nanocomposites that were formed exhibited significantly increased viscosity, up to the point of gelation. Additionally, an introduction to the expansive field of nanocomposites is provided, including how and why composite properties change abruptly as filler size approaches the nanoscale. An extensive background on this diverse field as it relates to the current work is provided with an emphasis on cellulosic nanocomposites and the dependence of curvature on polymer-surface interactions. A detailed account of the experimental work relevant to this work is provided, including materials and characterization methods. Future work is proposed for both cellulosic nanocomposites as well as for curvature-dependent polymer adsorption. Finally, conclusions are drawn from the entire work and its implications to the greater field of nanocomposites.