Thesis (Ph. D.)--University of Pennsylvania.

Thesis (Masters) -- California Institute of Technology, 1938. / Title from home page (viewed 04/28/10). Includes bibliographic references.

Thesis (Ph. D.)--Virginia Polytechnic Institute and State University, 1993. / Vita. Abstract. Includes bibliographical references. Also available via the Internet.

Thesis (Ph. D.)--State University of New York at Binghamton, Department of Chemistry, 2005. / Includes bibliographical references.

Thesis (Ph. D.)--University of Delaware, 2007. / Principal faculty advisor: Douglas J. Doren, Dept. of Physics & Astronomy. Includes bibliographical references.

M.Tech. / A mixture of HfC and TiC powders and a (Hf,Ti)C powder have been hot pressed with 4wt% Ni. In the absence of Ni the hot pressed temperature was 2000 °C and in the presence of Ni 1650 °C. The pressure of 30 MPa was applied in both cases. The starting powders were substoichiometric, as deduced from XRD spectra analyses, and the (Hf,Ti)C powders consisted of a range of compositions, as indicated by the width of the XRD peaks. In the absence of Ni the powders sintered without the formation of a liquid phase. In the case of HfC and TiC mixture, high- energy dry milled HfC + TiC +C black powder sintering occurred with simultaneous formation of (Hf,Ti)C solid solution. On account of mutual solid solubility of two carbides vacancy interdiffusion controlled the solution as well as the sintering process, assisted by the high concentration of vacancies in the starting powders. In the case of (Hf,Ti)C powder diffusion was also the controlling process because t he solid solution was not h omogeneous a nd the system t ended to homogenization, as shown by t he narrowing of t he XRD peaks after sintering. Since the diffusion of HfC into TiC did not occur at the same rate as the diffusion of TiC into HfC (as expected, on account of the different melting points of the two materials) diffusional porosity was observed in some of the (Hf, Ti) C grains. Grain growth was substantial but uniform. In the presence of Ni, sintering occurred with the formation of a liquid phase. The volume fraction of the liquid phase formed was sufficient to yield a low porosity. Grain growth was less than in the case of material sintered without Ni, probably just on account of lower sintering temperature. In the case of high- energy dry milled the reduction in particle size was observed.

The decreasing solid solubility limit at the titanium-rich end of the titanium-copper constitutional diagram suggests the possibility that titanium-rich alloys may be age-hardenable. However, results obtained by previous investigators, using lump samples, show that after quenching from 790°C the age-hardening of an alloy containing 1,7 percent copper is very light while a 0.8 percent copper alloy decreases in hardness, during heat treatment at 400°C. It was believed possible that powder samples of alloys might show different results from the lump samples used by previous investigators. Consequently, a 1.90 percent copper alloy was made by the technique of levitation melting, checked for homogeneity, and filings of 48-65 Tyler screen size were cut from it for aging experiments. Hardness readings do show a hardness peak at aging temperatures of 400°C, 450°C, and 500°C and thus indicate that the titanium-copper alloy is susceptible to age-hardening treatments. Interest in the Mn₆₀A1xZn₂₀_ₓC₂₀ and Mn₆₀GaₓZn₂₀-ₓC₂₀ systems results from pregious studies of Mn-A1-C, Mn-Zn-C, and Mn-Ga-C systems; in particular the alloys near compositions Mn₆₀A1₂₀C₂₀, Mn₆₀Zn₂₀C₂₀ and Mn₆₀Ga₂₀C₂₀. The saturation magnetization (σ) versus temperature (T) curve for alloys near the compositions Mn₆₀A1₂₀C₂₀ and Mn₆₀Ga₂₀C₂₀ shows normal ferromagnetic behaviour from 0°K to the Curie points of the alloys. Alloys near the composition Mn₆₀Zn₂₀C₂₀, on the other hand, have abnormal behaviour as they experience a maximum in the σ-T curve in the neighbourhood of -40°C. Reasons for investigating the Mn₆₀A1Zn₂₀-xC₂₀ andMN₆₀GaₓZn₂₀-ₓC₂₀ systems were: 1. to provide further data regarding the presence of abnormal behaviour in Mn₆₀Zn₂₀C₂₀ and of normal behaviour in Mn₆₀A1₂₀C₂₀ and Mn₆₀Ga₂₀C₂₀. (i.e. alloys near these compositions). 2. to suggest how the valency of the cube-corner atom affects the normal ferromagnetic moment of these alloys. However, investigation of these systems has lead to even more complicated phenomena, and the above two items remain, to a large extent, unsolved. / Applied Science, Faculty of / Mining Engineering, Keevil Institute of / Graduate

Titanium oxidation was studied between 400 and 800°C with oxygen partial pressures over the range 760 to 10⁻⁵ mm Hg and times up to 20,000 minutes. Oxidation rates were measured with a Cahn electrobalance after sophisticated metal preparation and experimental procedures. Growth effects in the oxide film were thoroughly examined at time intervals by removing specimens for metallographic observation. Films were stripped from these specimens for transmission electron microscope examination. The morphology development was then related to the rate curves. In all cases the rate curves were complex functions of temperature, pressure, specimen preparation, and oxidation procedure. In spite of the numerous rate transitions with time, reproducibility under a specific set of conditions was excellent. As the oxide grows from a thin film to a thick scale, an intermediate period of peculiar network formation, most pronounced at 500°C, is observed. The networks consist of thousands of small crystallites, approximately 100 to 5000 Angstroms in size, and arranged in random and oriented patterns of accelerated and suppressed growth areas. Two different types of whisker formation were observed in addition to the network phenomena. The complex rate data associated with periods of network growth do not conform to any of the simple rate laws reported by previous investigators. Since the network structures violated all of the assumptions associated with current transport theories regarding planar homogeneous films, it was concluded that these theories were inadequate to describe the growth kinetics. Surface diffusion is probably the main growth mechanism during network formation although orientation and epitaxial effects may have some influence. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate

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