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A dissertation submitted to the Faculty of Engineering and the Built Environment, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Masters of Science in Engineering. Johannesburg, 2017 / This dissertation presents the zinc recycling of tool grade cemented tungsten scrap material generated during commercial production at Pilot Tools Pty Ltd (South Africa), production of powders and alloys from the zinc recycled materials, and evaluation of the properties of the recycled and un-recycled powders and alloys. Tool grade cemented tungsten carbide inserts were subjected to the zinc recycled process under controlled conditions. Tungsten carbide, cubic (TiC, TaC, NbC, TiCN) carbides and Co were recovered from the recycled scrap material. Two recycled alloys, R and RA, and two un-recycled alloys NS and N were produced following the conventional powder metallurgy route. Alloy R was made from 100 % zinc recycled powder with stoichiometric adjustment of C only, and alloy RA was made from 100% zinc recycled powder with stoichiometric adjustment of C and Co. Alloy N was produced under the same conditions as the recycled alloys R and RA, while alloy NS was produced at commercial level at Pilot Tools Pty Ltd (South Africa) using un-recycled powders. The alloy properties were evaluated following standard procedures for hardmetals. When the zinc recycled material was mechanically disintegrated, about 70 % of the recycled material was recovered as fine powder, while 30% was recovered as coarse oversize particles. The oversize particles were quite tough due to a high Co content, and it was difficult to disintegrate them through milling or repeated zinc recycling. The recycled powders took twice as much time to mill to the desired size as the new un-recycled powders, and had predominantly angular particles, while the new powders had smaller more rounded particles. A cubic free layer (CFL) was formed in all the alloys during sintering, although the recycled alloys R and RA had a narrower CFL compared to the new alloys NS and N. The recycled alloys R and RA had carbide grain size, carbide contiguity, binder mean free path, hardness, fracture toughness and wear rate which were generally within the same ranges as the new un-recycled alloys. / MT2018

Dissertation (Ph.D.)--Auburn University, 2009. / Abstract. Includes bibliographic references (p.139-151).

The reflectivity of crystalline and radiation-damaged silicon carbide and silicon has been measured in the 2-12 eV spectral region. Measurements were made using a standard Seya-Namioka Monochrometer which was modified to compensate for the fluctuations of the light source and interfaced to a micro-computer to facilitate data collection. The reflectivities of crystalline silicon carbide polytypes 6H, 15R, and 4H were found to be similar and the reflectivity of 3C-SiC showed agreement with the predictions of published band structure calculations. The observed reflectivity of radiation damage SiC agreed with the prediction of a simple model which takes into account the breakdown of k(→) -conservation and uses a realistic Bethe-lattice Hamiltonian to calculate the amorphous valence density of electron states.

Thesis (Ph. D. in Interdisciplinary Materials Science)--Vanderbilt University, May 2008. / Title from title screen. Includes bibliographical references.

Thesis (M.S.)--University of Alabama at Birmingham, 2008. / Description based on contents viewed Feb. 11, 2009; title from PDF t.p. Includes bibliographical references (p. 49-50).

Measurements of the high temperature dielectric properties of ceramic materials at microwave frequencies have been made using two different experimental techniques.Data has been collected at frequencies from O.2GHz to 4.0GHz and for sample temperatures up to 1200°C. Detailed cross checking of the high temperature dielectric data obtained by the two techniques has been carried out with the help of other laboratories worldwide. An investigation of the applicability of dielectric mixture equations to practical measurement techniques is reported. The most reliabl~ estimates of permittivity were given by the Landau-Lifshitz, Looyenga equation or by a cube root extrapolation technique.Permittivity data obtained for a series of yttria stabilised zirconia samples, three differently processed silicon nitride samples and ten related glass compositions are presented. Analysis of the frequency and temperature dependence of both components of complex permittivity has been undertaken· in an attempt to identify the physical origins of the dielectric loss mechanisms. For the yttria doped zirconia samples results indicate two distinct loss mechanisms dominant over different temperature ranges. Below approximately 950K a hopping model involving short range motion of oxygen vacancies around fixed dopant ions is proposed. Above 950K thermally activated quantum mechanical tunneling of electrons is suggested as the dominant mechanism. A single loss mechanism for the entire temperature range involving the lattice loss of the silicon nitride network itself is indicated from the measurements of the hot pressed and pressureless sintered silicon nitride samples. For the reaction bonded silicon nitride samples there is evidence of a second loss mechanism due to additional ion impurities above 1410K. The measurements on the oxide glass systems add support to the belief that + 1 charged metal ions will dominate the dielectric properties of glass systems when present. The loss process has an increasing activation energy with increasing temperature which is seen to be consistent with ionic motion within the previously proposed random potential energy model. Differences in the complex permittivity with composition are attributed to variation in ionic size and metal ion-oxygen ion bond strength.

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