Composites, though used in a variety of applications from chairs and office supplies to structures of U.S. Navy ships and aircrafts, are not all designed to hold up to extreme heat flux and high temperature. Fiber-reinforced polymeric composites (FRPC) have been proven to provide the much needed physical and mechanical properties under fire exposure. FRPC notable features are its combination of high specific tensile strength, low weight, along with good corrosion and fatigue resistance. However FRPC are susceptible to thermal degradation and decomposition, which yields flammable gas, and are thus highly combustible. This property restricts polymeric material usage. This study developed a numerical model that simulated the degradation rate and temperature profiles of a fiber-reinforced polyester resin composite exposed to a constant heat flux and hydrocarbon fire in a cone calorimeter. A numerical model is an essential tool because it gives the composite designer the ability to predict results in a time and cost efficient manner. The goal of this thesis is to develop a numerical model to simulate a zonal-layer polyester resin and fiberglass mat composite and then validate the model with experimental results from a cone calorimeter. By inputting the thermal properties of the layered composite of alternating polymer and polymer-infused glass fiber mat layers, the numerical model is one step closer to representing the experimental data from the cone calorimeter test. The final results are achieved through adding a simulated heat flux from the pilot ignition of the degraded gas of the polyester resin. The results can be coupled into a mechanical model, which may be separately constructed for future study on the mechanical strength of composites under fire conditions.

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

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 use of aluminum nitride as a substrate material for microelectronics is examined. A brief look at thermal, mechanical, and electrical properties of aluminum nitride show that it is a viable alternative material for this use. A study of the interfaces between aluminum nitride and several thick film pastes (palladium silver conductor, ruthenium oxide resistor, and gold conductor) was performed with optical microscopy, scanning electron microscopy, and energy dispersive spectroscopy. Results of this investigation showed that the contaminants in the substrate material that affect thermal conductivity do not affect the adhesion of the thick film pastes. However, it was found that the lack of certain elements in the binder of the thick film paste could lead to weaker adhesion, and severe degradation of the thick film's adhesion during thermal cycling.

The positive temperature coefficient of resistivity (PTCR) sensors is resistor materials that undergo a sharp change in resistivity at a designed Curie temperature due to its unique structure and chemical composition. This effect serves important control functions in a wide variety of electronic circuitry and similar applications. Conventional calcining of mixed oxides method (CMO) is used for fabricating lanthanum doped barium titanate (BaTiO3) for PTCR behaviour through solid-state-sintering route, at 1100°C, 1350°C. Two batches of samples were fabricated at low and high sintering temperatures of 1100°C, 1350°C respectively. The effect of different concentrations of donor dopant on BaTiO3 on the electrical properties of Ba(1-x)LaxTiO3 with x= 0.0005, 0.001, 0.002, 0.0025, 0.003 mol%, is investigated at low sintering temperature. The influence of lantanum doping with Al2O3+SiO2+TiO2 (AST) as sintering aids on the electrical properties of Ba(1-x)LaxTiO3 with x= 0.0005, 0.001, 0.003 mol%, is also investigated. The results of the electrical characterization for the first batch of samples showed an increase in room temperature resistance with increaisng donor concentration. Also the results of the electrical characterization for the second batch of samples also showed the same increase in room temperature resistance with increasing donor concentration. For first batch of sensors the high room temperature resistance keeps the jump small and these materials showed V-shaped NTCR-PTCR multifunctional cryogenic sensor behavior with a strong negative coefficient of resistance effect at room temperature.Where as the second batch of sensors showed few orders of magnitude rise in resistivity values. The La-doped BaTiO3 ceramics co-doped with Mn gives an enhanced PTCR effect which can be exploited for various sensor applications.

Non-dilute salt strength solutions occur in many near surface geologic environments. In order to better understand the occurrence and movement of the water and salt, mathematical models for this non-ideal fluid need to be developed. Initial boundary value problems may then be solved to predict behavior for comparison with observations. Using the principles of equilibrium reversible and irreversible thermodynamics, relationships describing the thermo-physics of non-dilute saline solutions in variably saturated porous media are investigated. Each of four central chapters investigates a particular aspect of the flow of saline solutions through porous media. The first chapter derives the general relationships describing the effects of salt on the vapor content in the gas phase and also on the liquid pressure. The second chapter summarizes an example using the new theory for sodium chloride (NaCl) from zero to saturated strength. Additional terms beyond the dilute approximation are shown to be more important in very dry, fine textured soils with significant salt content. The third chapter derives the salt corrections for Darcy-type flow laws for variably saturated porous media, and an example for NaCl is given. Agreement between theory and experimental data is good, though there appear to be some unaccounted for effects. These effects may be the result of ionic interaction of the salt with the loamy sand used, and/or the effect of hysteresis of the water content-pressure relationship. The final chapter investigates two fundamental assumptions commonly used in process thermodynamics when considering mixtures described by porous media, saline water, and moist air. The first assumption is that temperature is the generalized intensive variable associated with entropy. The second assumption is that the form of the differential of total energy is known a-priori. It is shown that the first assumption is suspect under some circumstances, and a generalized notion of how to select extensive variables for a given system is introduced for comparison with the second assumption. Examples comparing the "usual" and new theories are accomplished for ideal gases and for isotropic Newtonian liquids, with results being favorable except possibly for the Gibbs-Duhem Relation of the Newtonian liquid for the "usual" theory. / Graduation date: 2005

LOW TEMPERATURE SYNTHESIS AND CHARACTERIZATION OF SOME LOW POSITIVE AND NEGATIVE THERMAL EXPANSION MATERIALS Kathleen Madara White 151 pages Directed by Dr. Angus P. Wilkinson Low temperature non-hydrolytic sol-gel synthesis was used to explore the possibility of lowering the crystallization temperatures of some known AIVMV2O7 compounds. Crystallization temperatures for ZrP2O7 and ZrP2O7 were unaffected by the use of non-hydrolytic sol-gel methods; however, successful synthesis of these compounds broadens the range of materials that can be produced using this method and suggests the possibility of synthesizing solid solutions (or composites) including ZrP2O7 or ZrV2O7. This research presents for the first time the direct synthesis of ZrP2O7 from separate zirconium and phosphorus starting materials using mild autoclave methods. Characterization of some AIVMV2O7 compounds, using lab and high resolution synchrotron powder XRD, led to the assignment of a new symmetry for CeP2O7 and to the suggestion that the reported structure for PbP2O7 was inadequate. Studies using in situ high temperature lab and synchrotron powder XRD for PbP2O7 and CeP2O7 provided the opportunity to report their thermal properties for the first time, and to compare their behavior to that of some other AIVMV2O7. High pressure diffraction measurements on CeP2O7 provided data for the estimation of bulk moduli and suggested two possible pressure-induced phase transitions. A broad range of MIIIMVP4O14 compounds were prepared using low temperature hydrolytic sol-gel synthesis. Thermal studies revealed nearly linear trends in CTEs and lattice constants with respect to the sizes of MIIIMV cations. Some lower ionic radii compounds had CTEs comparable to that of ZrP2O7 at low temperature, suggesting a similar superstructure. Three compounds were found to exhibit temperature-induced phase transitions.

Nanoenergetic composite materials have been synthesized by a sol-gel chemical process where the addition of a weak base molecule induces the gelation of a hydrated metal salt solution. A proposed proton scavenging mechanism, where a weak base molecule extracts a proton from the coordination sphere of the hydrated iron (III) complex in the gelation process to form iron (III) oxide/hydroxide, FeIIIxOyHz, has been confirmed for the weak base propylene oxide (PO), a 1,2 epoxide, as well as for the weak bases tetrahydrofuran (THF), a 1,4 epoxide, and pyridine, a heterocyclic nitrogen-containing compound. THF follows a similar mechanism as PO; the epoxide extracts a proton from the coordination sphere of the hydrated iron complex forming a protonated epoxide which then undergoes irreversible ring-opening after reaction with a nucleophile in solution. Pyridine also extracts a proton from the hydrated metal complex, however, the stable six-membered molecule has low associated ring strain and does not endure ring-opening. Fe2O3/Al energetic systems were synthesized from the epoxides PO, trimethylene oxide (TMO) and 3,3 dimethyl oxetane (DMO). Surface area analysis of the synthesized matrices shows a direct correlation between the surface area of the iron (III) oxide matrix and the quantified exothermic heat of reaction of the nano-scaled aluminum-containing energetic material due to the magnitude of the interfacial surface area contact between the iron (III) oxide matrix and the aluminum particles. The Fe2O3(PO)/Al systems possess the highest heat of reaction values due to the oxide interfacial surface area available for contact with the aluminum particles. Also, reactions containing nano-scale aluminum react differently than those containing micron-scale aluminum. RuO2/Al energetic systems behave differently dependent on the atmosphere the sample is heated. Heating the RuO2/Al samples in an inert atmosphere results in the complete reduction of the ruthenium oxide matrix to Ru(0) before reaction with the aluminum particles, resulting in the exothermic formation of RuxAly intermetallics, with the stoichiometry dependent on the initial Ru:Al concentration. However, heating the samples in an oxygen-rich atmosphere results in an exothermic reaction between RuO2 and Al.

The positive temperature coefficient of resistivity (PTCR) sensors is resistor materials that undergo a sharp change in resistivity at a designed Curie temperature due to its unique structure and chemical composition. This effect serves important control functions in a wide variety of electronic circuitry and similar applications. Conventional calcining of mixed oxides method (CMO) is used for fabricating lanthanum doped barium titanate (BaTiO3) for PTCR behaviour through solid-state-sintering route, at 1100°C, 1350°C. Two batches of samples were fabricated at low and high sintering temperatures of 1100°C, 1350°C respectively. The effect of different concentrations of donor dopant on BaTiO3 on the electrical properties of Ba(1-x)LaxTiO3 with x= 0.0005, 0.001, 0.002, 0.0025, 0.003 mol%, is investigated at low sintering temperature. The influence of lantanum doping with Al2O3+SiO2+TiO2 (AST) as sintering aids on the electrical properties of Ba(1-x)LaxTiO3 with x= 0.0005, 0.001, 0.003 mol%, is also investigated. The results of the electrical characterization for the first batch of samples showed an increase in room temperature resistance with increaisng donor concentration. Also the results of the electrical characterization for the second batch of samples also showed the same increase in room temperature resistance with increasing donor concentration. For first batch of sensors the high room temperature resistance keeps the jump small and these materials showed V-shaped NTCR-PTCR multifunctional cryogenic sensor behavior with a strong negative coefficient of resistance effect at room temperature.Where as the second batch of sensors showed few orders of magnitude rise in resistivity values. The La-doped BaTiO3 ceramics co-doped with Mn gives an enhanced PTCR effect which can be exploited for various sensor applications.