Thermal expansion in a crystal may be completely described from a phenomenological point of view by a second rank tensor whose elements are defined by λ_ij=(∂l_ij/∂T)_σ Or ε_ij=(∂e_ij/∂T)_σ Where the l_ij and the e_ij are the elements of the linear Lagrangian and Eulerian strain tensors respectively. These λ_ij and ε_ij have been formulated in terms of crystal cell parameters. For example, for a monoclinic crystal the λ_ij are of the form: λ₁₁(T) = 1/a₀sinβ₀ d[a(T)sinβ(T)]/dT , λ₁₃(T) = ½ (1/a₀sinβ₀ d[a(T)cosβ(T)]/dT - cotβ₀/c₀ dc(T)/dT) , λ₂₂(T) = 1/b₀ db(T)/DT , and λ₃₃(T) = 1/c₀ dc(T)/dT where a₀, b₀, c₀, and β₀ are the crystal’s cell parameters at some reference temperature T₀. By expressing the crystal cell parameters as power series expansions in the temperature, thermal expansion coefficients have been computed for indialite (hexagonal cordierite), emerald and beryl and for the clinopyroxenes: diopside, hedenbergite, jadeite, ureyite, acmite, and spodumene. The extended Grüneisen equation has been used to further examine the nature of the thermal expansion in emerald, beryl, and diopside. The crystal structures of the synthetic clinopyroxenes CaCoSi₂O₆ (cobalt diopside) and CaNiSi₂O₆ (nickel diopside) have also been determined. / Doctor of Philosophy

Seal glass is essential and plays a crucial role in solid oxide fuel/electrolyzer cell performance and durability. A seal glass should have a combination of thermal, chemical, mechanical, and electrical properties in order to seal different cell components and stacks and prevent gas leakage. All the desired properties can simultaneously be obtained in a seal glass by suitable compositional design. In this dissertation, SrO-La₂O₃-A₂O₃-B₂O₃3-SiO₂ based seal glasses have been developed and composition-structure-property relationships have been investigated. B₂O₃ free SrO-La₂O₃-Al₂O₃-SiO₂ based seal glass is the most suitable and its compatibility with the metallic interconnects and sealing performances have been evaluated. A seal glass should be stable for 5,000-40,000 hrs in the oxidizing and reducing atmospheres at 600-900°C but both the thermal and chemical stability is a persistent problem. The effect of Al₂O₃ on a SrO-La₂O₃-Al₂O₃-B₂O₃-SiO₂ based seal glass has been studied to improve the thermal properties, such as glass transition temperature, softening temperature and thermal expansion coefficient, and the thermal stability. Al₂O₃ improves the thermal stability but does not significantly affect the thermal properties of the seal glass. Comprehensive understanding of composition-structure-property relationships is needed to design a suitable seal glass. The thermal properties and stability of a borosilicate seal glass depend on the B2O3:SiO2 ratio in the composition. The role of B₂O₃:SiO₂ ratio on the glass network structure of the SrO-La₂O₃-Al₂O₃-B₂O₃-SiO₂ based seal glasses has been studied using Raman spectroscopy and nuclear magneto resonance spectroscopy. The thermal properties and thermal stability were correlated with the glass network structure and the calculated network connectivity. This study shows that the thermal properties degrade with increasing B₂O₃:SiO₂ ratio due to increase in the non-bridging oxygen and decrease in the network connectivity. High B₂O₃:SiO₂ ratio induces BO4 and SiO4 structural unit ordering, increases micro-heterogeneity, and subsequently degrades thermal stability. B₂O₃ free SrO-La₂O₃-Al₂O₃-SiO₂ seal glass shows the best combination of the thermal properties and thermal stability among the studied glasses. Nickel or nickel oxide is added into a seal glass to modify the thermal properties depending on the specific composition. The role of nickel as a network former or modifier and its effect on the thermal properties and thermal stability of the SrO-La₂O₃-Al₂O₃-SiO₂ based seal glasses have been investigated. Nickel is a modifier in this glass system and does not improve the thermal properties but degrades thermal stability by decreasing network connectivity and inducing micro-heterogeneity. The interconnect-seal glass interface stability is the most crucial for solid oxide fuel/electrolyzer cell. Crofer 22 APU and AISI 441 alloys are the preferred interconnects. The interfacial stability of the SrO-La₂O₃-Al₂O₃-SiO₂ based seal glass with these alloys have been studied as a function of time (0-1000 hrs), temperature (700-850°C), atmospheres (air, argon, and H₂O/H₂) using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and X-ray diffraction analysis (XRD). Complementary analytical techniques such as wave length dispersive spectroscopy (WDS) and SEM of thin samples were also carried out for selected samples. This study shows good interfacial stability of the SrO-La₂O₃-Al₂O₃-SiO₂ based seal glass with these alloys for the studied conditions. A suitable seal glass should be hermetic and withstand 100-1000 thermal cycles for practical application. Sealing performances of the SrO-La2O3-Al2O3-SiO2 based seal glass have been evaluated by pressure-leakage method. The seal glass is hermetic for at least 2000 hrs and withstands 100 thermal cycles. Overall, present work shows that the SrO-La₂O₃-Al₂O₃-SiO₂ based glass has all the desired properties and suitable for solid oxide fuel/electrolyzer cell seal. / Ph. D.

Master of Science

With the increasing research on advanced reactors, molten salt reactors have been recognized for their potential. As with any advanced reactor concept, each component and material must be thoroughly investigated before any reactors of that type are created. One of the most pressing issues in MSR research is that of the salts themselves. Though there are a multitude of salts to choose from when designing such a reactor, many of these salts lack the extensive research required to fully understand them. Across the decades there have been many studies that have investigated select molten salts, but there are a few problems with many of those studies. Those problems are the following: prior papers use obsolete and less reliable methods for their measurements, the papers don't investigate the salts across a wide enough range of temperatures nor at varying compositions, and finally many of the salts that are seen as candidates today were not given as much attention when molten salt reactors were first conceptualized which has resulted in a lack of research on them. Indeed, the research into these salts is lacking in many ways. This study seeks to investigate a collection of promising coolant salts in depth with acknowledgment to those past studies. LiF-NaF-KF (46.5-11.5-42.0 mol%) will be used as a calibration standard and for the purpose of verifying our methodology. Specifically, FLiNaK was used in the development of volume-height curves as calibration for density measurements. NaOH-KOH of four different compositions ( 0.5-0.5mol%, 0.55-0.45mol%, 0.6-0.4mol%, and 0.65-0.35 mol%) will be evaluated for their densities and heat capacities. And finally, BeF2-NaF(43-57mol%) will be evaluated within the question of if the properties are desirable enough that the dangers posed by beryllium are an acceptable risk. BeF2-NaF will have melting point, heat capacity, density, and vapor pressure measurements performed. Additionally, extensive impurity analysis and removal (via an HF gas system) was done to our BeF2-NaF samples. The melting point and heat capacity were evaluated using dynamic scanning calorimetry (DSC), the vapor pressure was evaluated using thermogravimetric analysis (TGA), and the density was measured using a system similar to the Arrhenius method that measures height. / Master of Science / Decades have passed since the discussion of nuclear energy began. Although great progress has been made in the field, the nuclear reactors in use today consist mainly of boiling water reactors (BWRs) or pressurized water reactors (PWRs). As reliable as these reactors have become, one can no longer ignore the fact that there is a multitude of other options for how a reactor can be built and operated. Options that provide greater safety and more energy output. Many reactor concepts of the past were discounted for the extensive research that would be required to make use of them. However, as time has passed and technology has improved, that research has become more and more possible. Many advanced reactors are the result of that attention to the reactor concepts and materials of the past that couldn't be given the attention that they deserve until now. Molten salt reactors (MSRs) are one of those promising concepts. However, before they can be built every part of the reactor, from the structure to the materials, must be entirely understood. One of the most pressing issues in MSR research is the properties of the salts in consideration for use. Though there are a multitude of salts to choose from when designing such a reactor, many of these salts lack the extensive research required to fully understand them. Across the decades there have been many studies that have investigated select molten salts, but there are a few problems with many of those studies. Those problems are the following: the papers are so old that the methods that were used are now obsolete, the papers don't investigate the salts across a wide enough range of temperatures nor at varying compositions, and finally many of the salts that are seen as candidates today were not given as much attention when molten salt reactors were first conceptualized which has resulted in a lack of research on them. Indeed, the research into these salts is lacking in many ways. This study seeks to investigate a collection of promising coolant salts in depth with acknowledgment to those past studies. LiF-NaF-KF will be used as a calibration standard and for the purpose of verifying our methodology. A multitude of different compositions of NaOH-KOH will be evaluated for their densities and heat capacities. And finally, BeF2-NaF will be evaluated within the question of if the properties are desirable enough that the dangers posed by beryllium are an acceptable risk. BeF2-NaF will have melting point, heat capacity, density, and vapor pressure measurements performed. Additionally, extensive impurity analysis and removal was done to our BeF2-NaF samples.

This thesis documents research done in the development and the exploration of feasibility for a high-throughput method to measure local thermal properties. The present capabilities in the measurement of local thermophysical properties such as thermal conductivity, thermal diffusivity, and Kapitza resistance are very inefficient and impractical to fully understand and characterize heat transport through certain materials and features. This work follows up on past work in local thermal property measurement via the spatial domain thermoreflectance (SDTR) method, and explores the possibility of parallelizing the process. The parallelized SDTR (P-SDTR) method involves using laser projector sources to periodically heat and measure the changes of reflectivity of a sample surface at multiple locations simultaneously. These measurements are made possible by the development of a lock-in camera that can measure the characteristics of modulated light using lock-in amplification at several spots across an area with an advanced camera sensor. This method allows for the measurement of local thermal properties across features such as grain boundaries, or directional properties in anisotropic materials. An experimental setup is developed to determine at which heating and probing parameters a thermoreflectance signal can be measured. A finite element model is also made to simulate the P-SDTR process, and validate that the assumptions made in SDTR can be made in P-SDTR measurements. It is shown that at an appropriate separation of heating/measurement locations, the solutions from the simulation approach that of a single measurement spot. An initial device design is proposed and tested. Future work in the development of the P-SDTR device is also laid out.

No description available.

The effects of in situ Ti0₂ whisker reinforcement on mechanical and thermal properties of glass-ceramics in the Li₂O-Al₂0₃-P₂0₆-Si0₂ system were investigated. When Ti0₂ whiskers, having an average aspect ratio of 28, are precipitated from the glass-ceramic matrix, (Li_0.4,Ca_0.05)AI(Si_0.75,P_0.5)_04.5, flexural strength is improved from 72 to 134 MPa. Fracture toughness, K_Ic, is increased from the 1.1 to 1.6 MPa·m^1/2 due to crack deflection by the Ti0₂ whiskers. In situ Ti0₂ whisker-reinforced glass-ceramic exhibits rising fracture resistance, K_R, with increasing crack extension. The fracture resistance, K_R, is increased from 1.89 to 2.5 MPa·m^1/2 over the crack extension range range of 40 to 200 μm. The composite shows a narrow failure strength distribution compared to the glass-ceramic without Ti0₂ whisker precipitation. The coefficient of thermal expansion (CTE) changes from -2.8x10⁻⁷/"C to -1.7xl0⁻⁷/°C due to the precipitation of Ti0₂ phase which has a positive CTE (7.3xl0⁻⁶/°C). With the matrix composition, (Li_0.41,Mg_0.035)AI(Si₀0.48</sub>,P_O.52)O₄, a three-fold increase in flexural strength was observed with a Ti0₂ content of 12 wt%. CTE value of the composite increases linearly from a negative to a positive value with increasing Ti0₂ content up to 12 wt%. The in situ composite containing 8-10 wt% Ti0₂ exhibits near zero CTE values up to l000°C. / Ph. D.

A process for fabricating particulate reinforced composites from dry powder-powder blends was developed. The process was designed to exploit the nature of fine powder constituent materials, such that the energy input during the molding process could be reduced. Polymer and reinforcement materials were chosen, characterized, and molded into composite plaques. These composites were characterized in terms of mechanical and thermo-mechanical properties. Stiffness, coefficient of thermal expansion, and overall dimensional stability were found to improve; and strength, strain-to-failure, and toughness were found to decrease to varying degrees. The results of these predictions were compared with simple micromechanics models to gain a better understanding of their physical behavior. / M.S.

The fundamental and quantitative study of heat and mass transfer processes in wood plays an important role for understanding many important production processes, such as wood drying and hot-pressing. It will help us improve the existing products and production techniques and develop new manufacturing technology. The most difficult aspect of the study is the complicated interactions of heat and mass transfer mechanisms. Extensive characterization of these physical processes using a strictly experimental approach is extremely difficult because of the excessively large number of variables that must be considered. However, mathematical modeling and numerical techniques serve as a powerful tool to help us understand the complicated physical processes. The goal of this research is to model the simultaneous heat and mass transfer in wood. The specific objectives of this research are: 1) develop a computer simulation program, implementing an existing one-dimensional mathematical drying model, using a finite difference approach, to numerically evaluate the mathematical model. 2) study sensitivity of the heat and mass transfer model to determine the effects of wood physical properties and environmental conditions on the drying processes. / Master of Science

A detailed design was developed of an apparatus to measure moisture transfer in porous materials. The apparatus is to be used to collect data to aid in the development of mathematical models which accurately describe this phenomena. The apparatus consists of dual environmental chambers between which a specimen material is sealed. The temperature of each chamber is controlled separately allowing nonisothermal test conditions. The relative humidity is maintained without the use of saturated salt solutions. The moisture transfer rate is measured by periodically weighing a desiccant column used to absorb moisture as result of diffusion across the specimen. The apparatus was built and used to verify a heat transfer model written to predict its thermal characteristics. The chamber temperature capabilities are 5°C to 60°C with up to a 20°C temperature difference across the specimen. The relative humidity limits are based on the heat transfer into or out of the system. High relative humidities (75 to 85 percent) are possible at chamber temperatures close to ambient, but decrease sharply at the extremely high or low temperatures and during nonisothermal operation. The apparatus maintains a constant temperature within ±0.4°C of the setpoint when subjected to varying ambient temperatures. The spatial temperature variation close to the sample (within 25 mm) is within approximately ​​​​±1°C of the average chamber temperature. The relative humidity can be manually controlled to within ±.7 percent RH. Automated control, complicated by a response lag, was within ±1 percent RH. / Master of Science