A mathematical model has been developed to predict the operating behaviour of an SL/RN direct reduction kiln from a knowledge of the main process variables. The model is based on steady state principles and is capable of quantitatively describing the complex chemical reactions in the kiln such as reduction, Boudouard reaction, coal volatilization and combustion in the freeboard together with the mass and heat flows. Output from the model is in the form of axial profiles of gas, solids and wall temperatures, and concentrations in both the gas and the solid phases. Results from the model are in good agreement with measurements made on the 100 ton per day pilot kiln at the Steel Company of Canada. The influence of important process variables such as the type of coal, ore, degree of reduction, throughput etc. has been examined and predictions made regarding the operation of large commercial SL/RN kilns for sponge iron production. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate

Solution density modelling is important in hydrometallurgical processes as accurate predictions of single and mixed electrolytes can be used in the design of equipment and their sizing, heat transfer calculations and choosing of materials for construction. This research project entails modeling of electrolyte solutions by extending the Laliberte and Cooper (compound level) model to ionic level where an electrolyte solution is modeled as a mixture of cations, anions and water molecules. This modeling predicts single and mixed electrolyte density as a function of electrolyte temperature in degrees Celsius; water, cation and anion apparent volumes in cubic centimeters; and their respective concentrations in the electrolyte as mass fractions. The model was developed by fitting single electrolyte density data reported in literature using the least squares method in Microsoft Excel®. The following 26 single electrolyte solutions were used in the fitting exercise: Al2(SO4)3, BaCl2, CaCl2, CdSO4, CoCl2, CuSO4, FeCl3, FeSO4, HCl, HCN, HNO3, K2CO3, LiCl, MgSO4, MnCl2, Na2SO3, NaF, NaI, NaOH, (NH4)2SO4, NiCl2, SrCl2, ZnCl2, ZnBr2, (NH4)2C2O4 and KNO2. The above electrolytes attributed to the following ions: Al3+, Ba2+, Ca2+ Cd2+, Co2+, Cu2+, Fe3+, Fe2+, H+1, K+1, Li+1, Mg2+, Mn+2, Na+1, NH4+1, Ni2+, Sr+2, Zn2+, SO42-, Cl-1, CN-1, NO3-1, CO32-, OH-1, SO32-, Br-1, F-1, I-1, C2O4-2 and NO2-1. This translated to a combination of at least 216 single electrolyte solutions which could be feasibly modeled, and a solution with at most 10 anions for mixed electrolytes, which is comparable with practical hydrometallurgical solutions. A database of volumetric parameters was generated comprising a total of 18 cations and 12 anions. The validation of the developed model was done by predicting densities for both single and mixed electrolytes not used in the fitting exercise. The average density error i.e. the difference between experimental and model density for the single electrolyte solutions was 22.62 kg m-3 with a standard deviation of 39.66 kg m-3. For the mixed electrolytes, the average density error was 12.34 kg m-3 with a standard deviation of 24.48 kg m-3. These calculated errors translated to a maximum percentage average error of less than 4% for single electrolyte solutions and maximum average percentage of less than 3% for mixed electrolyte solutions.

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Two-phase composites have been prepared by infiltrating sintered iron compacts with liquid copper. The effects have been studied of iron particle size, matrix mean free path, and the volume fraction and micro-hardness of the iron-rich constituent, on the tensile properties of composites. It has been found that the strength of the composites is related to the amount of solution hardening of the iron component during infiltration. The results of tensile tests have suggested that the hardness of the iron-rich constituent is the dominant factor controlling yield strength, ultimate tensile strength and elongation. However, the ultimate strength has been found to depend also on the volume fraction of the hard constituent, and elongation has also been found to be a function of the interface area. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate

M.Tech (Metallurgy) / Abrasive wear is a major factor in the production costs of the mining industry in South Africa (as is the case in the rest of the world). These costs arise from the need to replace consumables such as digger teeth, mill liners, screens and chutes. Some materials used in these areas have been used for years with little or no change to their properties such as Hadfields manganese steel; others have been significantly modified to improve their performance, as is the case with high chromium white cast iron. Some areas in the mining industry have made a complete chanlfe of material in order to reduce wear rates; the use of 9% Cr stainless steel ( ) is an example of this. In some applications metals have been successfully replaced by ceramics for example the use of alumina in combination with cemented tungsten carbides ash conditioner blades (2) at ESKOM power stations. Significant improvements in profitability (in the form of reduced consumable costs and increased productivity) can be realised by the development of new abrasion resistant materials; hence many organisations are constantly involved in such work. The fundamental property required to resist abrasive wear is hardness, however a degree of toughness is always required depending on the application. Composite materials have the best possibility of combining these properties, for example high chrome white iron can be regarded as a composite material on a microscopic scale with very hard carbides supported by a tough martensitic matrix. This material performs extremely well in many highly erosive environments; it is also relatively cheap as the "composite microstructure" forms directlJ: from casting with a heat treatment process providing a hardened matrix 3). Another example of a composite material is cemented tungsten carbide; this is manufactured as a true composite, i.e. discrete particles of tungsten carbide are sintered with cobalt particles to form a relatively tough extremely hard material. This combines the hard brittle WC with the relatively soft tough cobalt binder acting as a matrix. This material has the best resistance to abrasive wear of all metallic materials. Ceramics have higher hardness but are significantly more brittle hence their application is limited to erosive rather than abrasive environments. Cemented tungsten carbide inserts are brazed or shrunk into steel holders and used as drill tips for rock drilling; this can be regarded as a composite product, using the strong and tough steel to hold the hard tungsten carbide inserts in place.

Please read the abstract in the 00front part of this document / Dissertation (M Ing (Metallurgical Engineering))--University of Pretoria, 1998. / Materials Science and Metallurgical Engineering / unrestricted

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