Thesis (Ph. D.)--University of Wisconsin--Madison, 1944. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 47-48).

Thesis (MScAgric)--University of Stellenbosch, 2006. / Bibliography. Also available via the Internet.

Thesis (Ph. D.)--University of Texas at Austin, 2007. / Vita. Includes bibliographical references.

Thesis (Ph.D.)(Metallurgical Engineering)--University of Pretoria, 2006. / Includes summary. Includes bibliographical references. Available on the Internet via the World Wide Web.

Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1994. / Vita. Abstract. Includes bibliographical references (leaves 182A-196). Also available via the Internet.

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Ferrihydrite (FHYD), a nanocrystalline material has long been described as a poorly crystalline disordered mineral mainly due to its small crystal size which is typically 2−6 𝑛𝑚. The three-dimensional structure of the mineral has long been described by a multi-phase structural model that consists of Fe3+ only in octahedral (Oh) coordination. In this model ferrihydrite is described as a mixture of two major phases (akaganeite/goethite-like f-phase and feroxyhite-like d-phase) and a minor ultradispersed nanohematite phase. This model has been recently challenged and a new, single-phase model was proposed, having a basic structural motif closely related to the Baker-Figgs δ-Keggin cluster and is isostructural with the mineral akdalaite, Al10O14(OH)2. In its ideal form, the proposed new structure of FHYD consist of 80 % Oh and 20 % tetrahedral (Td) Fe3+ polyhedra which can be adequately described by a single-domain model with the hexagonal spacegroup 𝑃63𝑚𝑐 and unit cell dimensions 𝑎=5.95 Å and 𝑐=9.06 Å. In this study, nanoparticles of 2-line FHYD (FHYD2), 2-line FHYD deposited onto SiO2 (FHYD2/SiO2) and 6-line FHYD (FHYD6) synthesised using rapid hydrolysis of Fe(NO3)3.9H2O solutions were characterized using X-ray diffraction (XRD), Raman spectroscopy, transmission electron microscopy (TEM), Mössbauer spectroscopy (MS) as well as magnetization and magnetic susceptibility measurements. The coordination environment of iron atoms in the structure of FHYD was investigated using TEM and MS. The thermal transformation of FHYD nanoparticles was monitored through changes in the magnetization as a function of temperature and the reduction behaviour in hydrogen environment was studied using temperature programmed reduction (TPR), in-situ XRD and MS. Electron diffraction, TEM/ scanning TEM (STEM) imaging, and electron energy loss (EELS) measurements were carried out on three different microscopes viz. JEOL JEM-2100 LaB6 TEM, aberration corrected Schottky-FEG JEOL JEM-ARM200F HRTEM and cold-FEG Zeiss SESAM TEM. EELS studies were concentrated mainly on the iron 𝐿-edge of FHYD and iron oxides reference spectra with well known crystal structures. The iron oxide Fe 𝐿-edge is usually characterized by two intense sharp peaks termed “white lines”. The fine structures introduced by the crystal field effect on the 𝐿- edge contain information that is highly specific to the Fe3+ site symmetry.

Availability of six minerals (Ca, P, Mg, Mn, Zn, and Cu) in commercial wheat, triticale, corn and barley samples was estimated with three-week old growing chicks. Effects of soybean meal and wheat fed at different dietary concentration on availability of these minerals were studied. The availability of minerals from specific inorganic sources were also evaluated. Availability value was determined by a balance procedure corrected for endogenous minerals. Results indicated that the availability of calcium, phosphorus, magnesium, manganese, zinc, and copper was 71.0, 67.4, 53.5, 48.4, 49.6 and 78.5%, respectively for the wheat and triticale samples. Copper availability was the highest in corn (87.2%), followed by calcium (70.0%), phosphorus (60.9%), manganese (60.0%), zinc (57.5%) and magnesium (51.0%). The availability of Ca, P, Mg, Mn, Zn and Cu in barley was 68.9, 68.8, 54.9, 54.9, 49.1 and 77.5%, respectively. Significant variation (P ≤ 0.05) exists among the cereal grains tested. Results indicate that mineral availability is influenced by the origin of the samples obtained. Availability of minerals is affected by the concentration of ingredients in the test diet. Significant differences (P ≤ 0.05) were observed in availability for all the minerals tested when soybean meal and wheat were supplied in the test mixture at five levels. Calcium and phosphorus from calcium phosphate were highly available to growing chicks. However, the availability decreased rapidly when the mineral level was in excess of the dietary requirement. Six levels of magnesium (150, 300, 450, 600, 750, and 900 ppm) from magnesium carbonate were evaluated. Results showed that magnesium was highly available to growing chicks. The values ranged from 82.3 to 61.9%. Excess amounts of magnesium in the diet tended to reduce the availability value. Various levels (25, 50, 75, 100 and 125 ppm) of manganese from manganese sulfate were tested. Manganese appeared to be poorly available for the levels tested. Zinc availability from zinc oxide was highly available for the chick. The availability values/ranged from 84.4 to 93% for all the diets containing 25 to 125 ppm of zinc. The availability of copper from copper sulfate was moderate to high (72.1-80.2%) for the low dietary copper concentrations (2-32 ppm). However, the copper availability values (61.8-63.6%) tended to decrease at higher dietary concentration (50-250 ppm). / Land and Food Systems, Faculty of / Graduate

M.Tech. (Ceramics) / The research project attempts to fill a void by assembling data dealing with a comprehensive range of South African clay and glaze materials, suited to the needs of the studio potter, and recording test results. South African kaolins, ball clays, fireclays, miscellaneous clays, grogs, bentonites, felspathic materials, alkaline earths, silica, refractory materials (other than clays) and mineral pigments are dealt with. A limited selection of foreign materials, frequently referred to in studio-potter publications, was also used in comparative tests. The materials are recorded with reference to the ultimate analysis, seger formula, proximate analysis (where applicable), properties and results of trials using the materials in clay bodies and/or glazes. It was demonstrated that South African materials are largely of good quality e.g. kaolin, felspars and silica. Variability of clay supplies because of lack of stockpiling and blending practices, especially by small suppliers, is often a problem. When the composition of glaze materials and trials indicated that imported equivalents were superior because of variability of local supplies or poor grade material, then substitutes were tested using South African materials. Basic clay bodies and glazes covering a wide temperature range from Egyptian Paste, low-fired wares such as raku, terracotta-and-white-earthenwares, stoneware and soft-porcelain bodies and glazes are dealt with giving a brief outline of the requirements for each type. Suggestions of suitable South African materials for their composition are made. Trials and results are recorded. The knowledge gained of South African materials available and a study of the materials enables the studio potter to utilize local materials with awareness and confidence