Thesis (M.E.) - University of Queensland, 2004. / Includes bibliography.

Thesis--University of Wisconsin--Madison. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 159-163).

A mechanism for vaporization of solid metals involving monatomic ledges on metal crystal surfaces is deduced, and an equation is derived for evaporation rate in terns of the dynamics of these ledges. It is shown that crystal edges are a ready source for monatomic ledges. The limiting expression for the vaporization coefficient of large, perfect crystals is given as a function of pressure and temperature by α = 2/3 (p/pe ) ≠ 1/3, where pe is the equilibrium vapor pressure. The effect of screw dislocation-surface intersections on the limiting expression is developed. An equation is derived giving the perturbation due to such intersections. It is found that experimental results for silver crystals confirm various predictions of the theory. Applications of the results are considered.

M.Tech. / The most commonly used route in the hydrometallurgical extraction of zinc and copper is the roast-leach-electrowin process. During the roasting process, the concentrate is subjected to either relatively low temperatures (partial roasting) or high temperatures (to achieve dead roasting) to produce a calcine that will be leacheable to extract zinc and copper. The resulting calcine contains zinc and copper in a form of oxides (ZnO, CuO), sulphates (ZnSO4, CuSO4) and ferrites ((Zn,Cu 1-x, Mx)0Fe203) or Zn,CuFe2O4) in the case of partial roasting. In the case of dead roasting, mostly the oxide forms are produced but in most cases ferrites will form as well. The means of avoiding the ferrites completely have not yet been achieved. Attempts in the past had only been focusing on either partial roasting or dead roasting without actually finding the optimum roasting conditions to minimise the ferrite formation. In this study the main objective was to identify optimised conditions for roasting, i.e. the possibility of producing these ferrites in minimum amounts as compared to the targeted zinc/copper oxides. Optimised roasting conditions were achieved in this study on a Zinc-copper ore from Maranda mine, where the sulphur removal test was used to ensure a dead roasting. This was done by analysing the amount of sulphur remaining after each roasting condition. Characterisation of the calcine has been done using the XRD and the Mossbauer spectroscopy. More zinc oxide than zinc ferrite was obtained at conditions of 800 °C for 3 hours as per the XRD analyses. The sulphur removal test however, showed a dead roasting at 900 °C (2% remaining sulphur) and this is attributed to the inadequate (not designed as in industry) supply of oxygen by the laboratory furnaces used. The precipitation of iron from the three acids (HCI, H2SO4 and HNO3) was done using NH4OH and NaOH. The Mossbauer and XRD characterisation techniques were used, where the XRD characterisation showed different spectra of the precipitate attributing to different compounds. The results of the precipitates from the optimised roasting conditions are those precipitates that are not commonly found in industry. The effect of the acids and the cations showed goethite to be formed from H2SO4 and HNO3, with NH4+ and Na+ respectively. The possibility of the selective leaching of the concentrate has been investigated. This eliminates the roasting process completely and thus provides a possibility of leaving the pyrite (FeS2) in the residue and thus minimising the amount of iron to be handled. Selective leaching has been done using Mn02 and Na2S208 in the presence of H2SO4. It was observed that starting with Mn02 as an oxidising agent does not achieve good selective leaching results between the sphalerite and the chalcopyrite. It was however possible to preferable leach sphalerite over chalcopyrite with the use of Na 2S2O8 as a starting oxidising agent. So the choice of the oxidising agent plays a role in selectively leaching different minerals. The optimised roasting conditions at high temperatures resulted in some type of precipitates, (mohrite, ferrihydrite and akaganeite) that are not commonly formed in industry. Jarosite, which is the most common precipitate formed in industry, could not be precipitated. Goethite was also fcund to be present.

Thesis (Sc.D.) Massachusetts Institute of Technology. Dept. of Metallurgy, 1953. / Vita. / Bibliography: leaves 82-84. / by David Vincent Ragone. / Thesis (Sc.D.) Massachusetts Institute of Technology. Dept. of Metallurgy, 1953.

Thesis: B.S., Massachusetts Institute of Technology, Dept. of Metallurgy, 1958 / Cataloged from PDF version of thesis. / Includes bibliographical references (leaf 18). / An investigation was made to determine the effects of various mold variables on the surface condition of CA-15 alloy steel castings. This alloy often suffers from a peculiar defect known as measles, and an attempt was made to determine what reactions at the old-metal interface cause this defect. To this end, small cylindrical pins were rammed in sand molds and heated or melted in a small induction furnace. The type of sand and clay used were held constant while various atmospheres were provided in the mold flask. It was found that samples heated to 50°C below the melting point in an oxidizing atmosphere showed the characteristic measles defect encountered in casting CA-15 alloy in green sand molds. Samples melted, cooled to 50°C below the melting point, and held at that temperature in an oxidizing atmosphere showed a combination of the two defects. It was found that the measles defect is due to a liquid state reaction in which the chromium in the melt is oxidized to Cr₂O₃·Fe₂O₃ and Cr₂O₃·FeO. The mechanism was found to be akin to a pitting form of corrosion. The oxidizing atmosphere is provided by moisture in the molding material and carbon dioxide formed by the combustion of organic binders. / by Harold G. Fraunhofer. / B.S. / B.S. Massachusetts Institute of Technology, Dept. of Metallurgy

Thesis: B.S., Massachusetts Institute of Technology, Department of Metallurgy, 1958 / Includes bibliographical references (leaf 32). / by Mark Michael D'Andrea, Jr. / B.S. / B.S. Massachusetts Institute of Technology, Department of Metallurgy

Thesis: B.S., Massachusetts Institute of Technology, Department of Metallurgy, 1958 / Includes bibliographical references (leaf 22). / by Thomas G. Decker. / B.S. / B.S. Massachusetts Institute of Technology, Department of Metallurgy

Thesis: Sc. D., Massachusetts Institute of Technology, Department of Metallurgy, 1941 / Vita. / Includes bibliographical references (leaves 222-231). / by Otto Zmeskal. / Sc. D. / Sc. D. Massachusetts Institute of Technology, Department of Metallurgy

Thesis (M.S.) Massachusetts Institute of Technology. Dept. of Metallurgy, 1953. / Bibliography: leaves 32-33. / by Robert Maurice Genevray. / Thesis (M.S.) Massachusetts Institute of Technology. Dept. of Metallurgy, 1953.