This project investigated the reactive formation of hafnium diboride (HfB2) in a variety of metallic environments, including blends with Bi, Cu, Ni, and Sb. HfB2 has garnered interest for a variety of applications due to its hardness, stability at elevated temperatures, as well as electrical and thermal conductivity. Experimental testing included differential scanning calorimetry (DSC) to reveal reaction initiation temperatures and enthalpies of reaction; and optical pyrometry to measure maximum reaction temperatures. Overall, DSC results indicated melting preceded reaction initiation; suggesting that the reaction initiation temperature for a certain blend occurred soon after melt formation, and could be broadly approximated by examination of binary phase diagrams. However, compositions containing bismuth ignited almost 200 ºC above the expected melting temperature. The maximum temperature measurement did not appear to correlate with reaction enthalpies as might be expected. This lack of correlation may be a result of an inability to capture the true maximum temperature due to the measurement frequency of the pyrometer, the disparity of heating rates between the two experimental methods, and/or to the influence of intermediate reactions on the temperature increase. / Master of Science

Phytosterols are major components of food and are structurally related to cholesterol, but differ from it by virtue of a carbon substituent at the C-24 position and in some cases, a double bond between C-22 and C-23 (Figure i). Furthermore, phytosterols are shown to have protective actions against colon, breast, and prostate cancer1; further investigation is required as their mode of action is unknown. Thus, reported herein is the design and synthetic implementation required to construct these naturally occurring compounds. Figure i : Cholesterol Construction towards a double bond flanked by two asymmetric carbon atoms, observed in the phytosterol side chain, will be synthesised using an asymmetric Horner-Wittig (H-W) reaction, involving a chiral α-substituted aldehyde and a chiral β-substituted phosphine oxide. In addition to the synthesis, the stereochemical outcomes of these H-W reactions were probed. The results demonstrated, that by varying the steric bulk, electronic nature, and aromatic properties of the groups β to the phosphorus and α to the aldehyde can control the cis/trans selectivity in alkene formation. Finally, to display the utility of this methodology, the phytosterol compounds will be synthesised and tested in MD-MBA-231 cancer cell lines, allowing further investigation into the phytosterol mechanism of action.

Phytosterols are major components of food and are structurally related to cholesterol, but differ from it by virtue of a carbon substituent at the C-24 position and in some cases, a double bond between C-22 and C-23 (Figure i). Furthermore, phytosterols are shown to have protective actions against colon, breast, and prostate cancer1; further investigation is required as their mode of action is unknown. Thus, reported herein is the design and synthetic implementation required to construct these naturally occurring compounds. Figure i : Cholesterol Construction towards a double bond flanked by two asymmetric carbon atoms, observed in the phytosterol side chain, will be synthesised using an asymmetric Horner-Wittig (H-W) reaction, involving a chiral α-substituted aldehyde and a chiral β-substituted phosphine oxide. In addition to the synthesis, the stereochemical outcomes of these H-W reactions were probed. The results demonstrated, that by varying the steric bulk, electronic nature, and aromatic properties of the groups β to the phosphorus and α to the aldehyde can control the cis/trans selectivity in alkene formation. Finally, to display the utility of this methodology, the phytosterol compounds will be synthesised and tested in MD-MBA-231 cancer cell lines, allowing further investigation into the phytosterol mechanism of action.

Reaction synthesis is a processing technique where the thermal activation energy needed to form a compound is provided by the exothermic heat of formation of the thermodynamically stable product. This type of synthesis has been used to form a variety of ceramics, intermetallics, and in-situ composites. In this work, the effects of changing the stoichiometry of the titanium aluminide matrix, and the effects of extrinsic reaction variables on the behavior of the reaction were studied and compared to theoretical predictions. It was shown that changing the stoichiometry of the titanium aluminide did have an effect on the measured heat of reaction; however this did not match the prediction. Changing the extrinsic variables of titanium and aluminum particle sizes also showed a significant effect on the behavior of the reaction. / Master of Science

The in-situ synthesis of piezoelectric-reinforced metal matrix composites has been attempted with a variety of target matrix and reinforcement materials using reaction synthesis and high energy ball milling. Zinc oxide (ZnO) and barium titanate (BaTiO₃) have been successfully synthesized within copper and iron matrices in a range of volume percentages using reaction synthesis. The microstructures of these composites have been analyzed and found to partially consist of an interpenetrating microstructure. After considering experimental findings and thermodynamic issues involved with synthesis, ideal reaction system parameters have been identified that promote the creation of a composite with ideal microstructure and formulated composition. Reactive high energy ball milling has been used to create copper matrix composites reinforced with zinc oxide and copper matrix composites reinforced with lead titanate (PbTiO₃). The microstructures and compositions of each volume percentage formulation of the composite powders have been analyzed. In this work, several promising piezoelectric-reinforced metal matrix composite systems have been identified as having potential to be synthesized in an in-situ manner. / Master of Science

A systematic and scientific approach has been applied to the study of codeformation processing. A series of composites having mechanically-dissimilar phases were developed in which the high temperature flow behavior of the reinforcement material could be varied independent of the matrix. This was accomplished through the use of a series of intermetallic matrix composites (IMCs) as discontinuous reinforcements in an otherwise conventional metal matrix composite. The IMCs are produced using an in-situ reaction synthesis technique, called the XD™ process. The temperature of the exothermic synthesis reaction, called the adiabatic temperature, has been calculated and shown to increase with increasing volume percentage of TiB2 reinforcement. Further, this temperature has been shown to effect the size and spacing of the TiB2, microstructural features which are often used in discontinuous composite strength models. Study of the high temperature flow behavior of the components of the metal/IMC composite is critical to the development of an understanding of codeformation. A series of compression tests performed at 1000° to 1200°C and strain-rates of 10-3 and 10-4 sec-1. Peak flow stresses were used to evaluate the influence of material properties and process conditions. These data were incorporated into phenomenologically-based constitutive equations that have been used to predict the flow behavior. It has been determined that plastic deformation of the IMCs occurs readily, and is largely TiB2 independent, at temperatures approaching the melting point of the intermetallic matrices. / Ph. D.

Al₃Ti, Al₅CuTi₂, and Al₆₆Mn₁₁Ti₂₃, intermetallic matrices reinforced with 30, 40, and 50 volume % TiB, have been produced by XD_™ processing and densified into bulk form by powder metallurgy techniques. The compressive flow behavior of the Al₃Ti and Al₅CuTi₂, composites have been evaluated at temperatures ranging from 1000°C to 1200°C and strain rates of 0.0001 and 0.001 sec⁻¹. The results have been analyzed by a correlation to the resulting microstructure, especially with regards to the intermetallic matrix composition, TiB₂ size, and interparticle spacing. The results of these analyses are applied to a constitutive equation based upon the flow stress equation. It has been shown that at in this temperature regime, all deformation occurs within the intermetallic matrix. This is substantiated by the lack of TiB₂-dependent behavior with variations in volume percentage of reinforcement. In all cases, the composites are readily deformed at relatively low loads. The average strain-rate sensitivity values were 0.349 for the Al₃Ti-based composites, and 0.247 for the Al₅CuTi₂, variants. The average activation energies were calculated to be 485 kJ/mol and 920 kJ/mol for the Al₃Ti-and Al₅CuTi₂-matrices, respectively. The structure constant was calculated based upon these values. The Zener-Hollomon parameter was used to plot the flow stress along lines of constant temperature and strain rate, and serves as one type of constitutive equation. In addition, the flow stress was evaluated as a function of the strain rate and temperature. These models were found to provide adequate correlation to the measured flow behavior. / Master of Science

Mo-Si-B alloys are a leading candidate for the next generation of jet turbine engine blades and have the potential to raise operating temperatures by 300-400°C. The alloys of interest are a three-phase mixture of the molybdenum solid solution (Moss) and two intermetallic phases, Mo3Si (A15) and Mo5SiB2 (T2). A novel powder metallurgical method was developed which uses the reaction of molybdenum, silicon nitride (Si3N4) and boron nitride (BN) powders to synthesize a fine dispersion of intermetallics in a Moss matrix. The covalent nitrides are stable in oxidizing environments up to 1000ºC, allowing for fine particle processing. The process developed uses standard powder processing techniques to create Mo-Si-B alloys in a less complex and expensive manner than previously demonstrated. This powder metallurgy approach yields a fine dispersion of intermetallics in the Moss matrix with average grain sizes of 2-4μm. Densities up to 95% of theoretical were attained from pressureless sintering at 1600°C and full theoretical density was achieved by hot-isostatic pressing (HIP). Sintering and HIPing at 1300°C reduced the grain sizes of all three phases by over a factor of two. Microstructure examination by electron back-scatter diffraction imaging was used to precisely define the location of the phases and to measure the volume fractions and grain size distributions. Microstructural quantification techniques including two-point correlation functions were used to quantify microstructural features and correlate the BN reactant powder size and morphology to the distribution of the intermetallic phases. High-temperature tensile tests were conducted and yield strengths of 580MPa at 1100°C and 480MPa at 1200°C were measured for the Mo-2Si-1Bwt.% alloy. The yield strength of the Mo-3Si-1Bwt.% alloy was 680MPa at 1100°C and 420MPa at 1300°C. A review of the pertinent literature reveals that these are among the highest yield strengths measured for these compositions. The oxidation resistance in air at 1000 and 1100°C was examined. The protective borosilicate surface layer formed quickly due to the close spacing of intermetallic particles and pre-oxidation treatment was developed to further limit the transient oxidation behavior. An oxidation model was developed which factors in the different stages of oxidation to predict compositions that minimize oxidation.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Samples of Bi 2Fe4O9 mullite and ReFe 0.5M0.5O3 (Re = Nd, Sm, Eu, Gd, Dy; M = Mn, Al) complex perovskites were successfully synthesized by using the combustion synthesis method. While the mullite was obtained after thermal treatment at temperatures below 1000ºC, complex perovskites are produced after thermal treatments between 1250ºC and 1500ºC for at most 24 h. The X-ray diffraction data analysis suggests the formation of single phase orthorhombic structure, after suitable heat treatment. Scanning electron microscopy (SEM) revealed the formation of micrometric grain size, giving to the sample the relative density. EDS spectra confirmed the homogeneity and purity of complex perovskites. Magnetization measurements as a function of field and temperature showed the diversity of magnetic behavior of the samples. Among the behaviors we can highlight the reorientation of spin for ortoferritas ReFe0.5Mn0.5O3 (Re = Dy, Gd, Eu, Sm, Eu) and ReFe0.5Al0.5O3 (Re = Dy, Nd). Another interesting finding was the effect of magnetic reversal of the samples ReFe0.5Al0.5O3 (Re = Nd, Gd) and EuFe0.5Mn0.5O3. Raman spectra show anomalous bands of second order in the perovskite DyFe0.5Al0.5O3 with characteristics of resonant effects. The evolution of the band associated with the symmetric vibrational mode of the octahedron shows hardening at the temperature range of ordered magnetic phase, thus suggesting a possible spin-phonon coupling. Depolarization current measurements highlights a relaxation process due to charge carriers in the samples ReFe0.5Mn0.5O3 (Re = Dy, Gd). The application of magnetic field profoundly influences the depolarization current behavior of DyFe0.5Mn0.5O3. Dielectric permittivity measurements showed no anomalies between 10 K and 300 K, that could can be associated to a ferroelectric phase. / Amostras da mulita Bi2Fe4O9 e das perovskitas complexas ReFe0.5M0.5O3 (Re= Nd, Sm, Eu, Gd, Dy; M = Mn, Al) foram sintetizadas com sucesso utilizando o método de síntese por reação de combustão. Enquanto a mulita foi obtida após tratamento térmico com temperaturas abaixo de 1000ºC, as perovskitas complexas foram produzidas após tratamentos térmicos entre 1250ºC e 1500ºC por, no máximo, 24 h. A análise de dados de difração de raios X sugerem a formação de estruturas ortorrômbicas de fase única, após os tratamento térmico apropriado. Medidas de microscopia evidenciaram formação de grãos micrométricos conferindo às amostras relativa densidade. Os espectros EDS confirmaram a homogeneidade e pureza das perovskitas complexas. As medidas de magnetização em função do campo e da temperatura evidenciaram a diversidade de comportamentos magnéticos das amostras estudadas. Entre os comportamentos destacamos reorientação de spin para as ortoferritas ReFe0.5Mn0.5O3 (Re = Dy, Gd, Eu, Sm, Eu) e ReFe0.5Al0.5O3 (Re = Dy,Nd). Outro interessante achado foi o efeito de inversão magnética das amostras ReFe0.5Al0.5O3 (Re = Nd, Gd) e EuFe0.5Mn0.5O3. Espectros Raman demonstram bandas anômalas de segunda ordem na perovskita DyFe0.5Al0.5O3 com características de efeitos ressonantes. A evolução da banda associada ao modo vibracional simétrico do octaedro apresenta endurecimento em temperaturas na faixa da fase magnética ordenada, sugerindo assim, um possível acoplamento spin-f onon. Medidas de corrente de despolarização destaca um processo de relaxação devido aos portadores de cargas nas amostras ReFe0.5Mn0.5O3 (Re=Dy,Gd). A aplicação de campo magnético influencia profundamente o comportamento da corrente de despolarização do DyFe0.5Mn0.5O3. Medidas de permissividade dielétrica não exibiram anomalias entre 10 K e 300 K que possam a ser associadas a uma fase ferroelétrica.