No description available.

No description available.

No description available.

Thesis (Ph. D.)--University of Washington, 1990. / Vita. Includes bibliographical references (leaves [231]-242).

Thesis (M.S.)--University of Michigan, 1979.

Thesis (M.S.)--University of Michigan, 1979.

This dissertation reports on the study of black molybdenum, a new cermet consisting of small Mo particles embedded in MoO₂. As with most two-phase materials, the optical properties of black molybdenum are significantly different from those of either constituent, and can be adjusted within wide limits through modifications of composition and microstructure due to variations of the fabrication process parameters. The subject of this work is to understand the exact relationships, to allow reproducible production of films with chosen optical properties. Theoretical interpretation of the optical properties of two-phase materials has in the past been hampered by insufficient microstructural characterization. Recent theoretical work by others has lifted the requirements of detailed microstructural knowledge, leaving only two required parameters for characterization of cermet reflectance: the optical properties of the constituent phases and their volume fractions in the cermet. Better characterization is obtained when structural considerations, such as film topology, surface texture and the presence of a possible amorphous phase, are taken into account. We adopted this approach to the study of black molybdenum, and accomplished satisfactory agreement between theoretical and observed reflectances. Black molybdenum films were prepared using two separate chemical vapor deposition (CVD) techniques, involving deposition from either Mo(CO)₆ or MoO₂Cl₂. We found the influence of composition through a comparison of films with different Mo:MoO₂ ratios, while the influence of structure on film reflectance was determined by comparing films from these two deposition techniques. During this investigation we produced black molybdenum films which display a spectrally selective profile--low visible reflectance combined with high infrared reflectance, and which may be applied to photothermal solar energy conversion. The versatility of CVD in adjusting film composition and structure resulted in another film of interest in photothermal conversion--black tungsten, a tungsten-tungsten oxide composite material. The black molybdenum and black tungsten systems studied here establish the utility of CVD for the production of high temperature thin film optical devices.

A thesis submitted to the Faculty of engineering. University of Witwatersrand. Johannesburg, in fulfilment of the requirements for the Degree of Doctor of Philosophy Pretoria, 1995 / This thesis describes a study of the friction and wear characteristics of a range of oxide and silicon-based ceramics sliding against AlSI 440C stainless steel, as well as various sliding combinations of two types of De Beers polycrystalline diamond (PCD), namely Syndite and Syndax, To facilitate the former work, a high-speed reciprocating sliding test machine with computerized data acquisition and control was developed. It was confirmed that under water-lubricated sliding, the oxide ceramics (alumina, PSZ, 3YTZP, and Ce-TZP) showed higher friction coefficients and Weal' rates than the silicon-based ceramics (Sialon and silicon nitride). This was related to different levels of adhesion and the formation of metallic transfer films. For the zirconia ceramics, increased transformation toughening was associated with increased surface fracture damage and metallic film formation. In general, the metallic transfer films were beneficial, protecting the underlying ceramic and dominating the friction and wear behaviour. The superior performance of the silicon-based ceramics was related to the formation of lubricious tribofilms containing silicon oxides and hydroxides. Experiments with synthetic mine water as lubricant demonstrated that the presence of significant amounts of chloride and sulphate in the water generally reduced friction and wear. This was tentatively explained in terms of reduced adhesion and the promotion of iron oxide and hydroxide formation. It is suggested that the influence of sulphate may be more important in thi'3 regard than that of chloride. The tribological behaviour of self-mated Syndite PCD sliding couples is dominated by the formation of Co-rich trlbofilms, which nrc associated with increased friction coefficients and reduced load carrying capacity (LCC). Syndax, which employs silicon as the binder phase, shows lower friction coefficients anti higher LCe under both dry and water-lubricated sliding conditions. Mixed Syndax/Syndite couples show superior performance to self-mated Synditc tinder dry sliding conditions, but 110 improvements in the presence of water. The former effect is related to the preferential removal of Co 11'0111 the Syndite surface to the Syndax / GR 2017

No description available.

Thesis (M.S.)--University of Michigan, 1965.