LD2668 .T4 1949 P48 / Master of Science

A dissertation submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of the academic requirements for the Degree of Master of Science. March 2016. / Tungsten carbide (WC) is characterized by its high strength, toughness, hardness, its high resistance to wear and can also be employed at high temperatures. It is used mainly in the form of cemented tungsten carbides which are produced by combining grains of tungsten carbide into a binder matrix element, for example cobalt (Co). Tungsten carbide is commonly used in industrial machinery as cutting tools and abrasives. The primary aim of this project is to investigate the effects of iron (Fe) as an alternative/additional binder in a tungsten carbide system. Therefore, two samples WC-10wt%Co-6wt%TiC and WC-10wt%Co-6wt%TiC-20wt%Fe alloys were prepared by milling and followed by sintering. Several studies have been undertaken in this project to ascertain the effect of Fe on the structural, electronic, magnetic and physical properties of the as-milled and as-sintered samples. A number of different experimental methods were applied to give such information. Transmission Mössbauer spectroscopy and conversion electron Mössbauer spectroscopy were employed as the main techniques to determine the charge states of Fe, Fe phases and other complex phases in the WC-10wt%Co-6wt%TiC-20wt%Fe alloy from the hyperfine interaction parameters. In addition, applied Vickers hardness test, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD) and strain analysis were utilized as complementary characterization techniques. The Vickers hardness value of 1358±70 HV was measured for the WC-Co-TiC sample whilst a lower value of 820±41 HV was found for the WC-Co-TiC-Fe sample. The microstructure analysis (SEM/EDS) confirmed the presence of WC in the matrix, and Co, Ti, and Fe as the binder elements. XRD results show the formation of the FeCo alloy in the as-milled powder and as-sintered samples. The strain analysis was performed on the as-milled powder, and the as-sintered samples by adopting the method used in accordance with the Topas description, defined in the Topas manual. The WC-Co-TiC sample showed that the tungsten carbide phase appears to have little strain whilst the titanium carbide phase appeared to have no strain. In the WC-Co-TiC-Fe sample, all phases show no strain. The Mössbauer spectrum at room temperature acquired from transmission Mössbauer spectroscopy was fitted with one sextet S1 attributed to -Fe. Best fits to the data obtained from conversion electron Mössbauer spectroscopy required four spectral components: two sextets S1 and S2 assigned to FeCo, one doublet D1 assigned to FeWC and one single SL1 assigned to FeTi alloy. / LG2017

A thesis submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, South Africa, in fulfilment of the requirements for the Degree of Doctor of Philosophy. / Quantum chaos is associated with the phenomenon of avoided level crossings on a large scale which leads to a statistical behaviour similar to that of a Gaussian Orthogonal Ensemble (GOE) of matrices. (Abbreviation abstract) / Andrew Chakane 2019

Since the industrialization of platinum group metals (PGMs), particularly platinum (Pt), palladium (Pd) and rhodium (Rh), the control of trace impurities in these metals has become vital. Reliable analysis of impurities in these metals is, however a difficult task. Nobel metals are difficult to dissolve quickly and quantitatively. Thus, analytical techniques which determine samples in liquid form have become less favourable. They require time consuming digestions and are prone to contamination both from the chemicals and equipment used for the preparation. Direct-analysis techniques are increasingly being used in the platinum group metal (PGM) industry for the determination of impurities in the final products. Spark-optical emission spectroscopy (Spark-OES) for the analysis of metals offers rapid turnaround times. Since the technique is almost non-destructive, little of the product is lost during analysis. The technique is also well established in the PGM industry. It is routinely used by two of the three largest platinum producing companies for the determination of impurities in their products. It is also used for the determination of PGMs after Fire Assay procedure by Anglo American Platinum. The greatest challenge for this technique remains the availability of certified reference materials (CRM) and calibration standards. This study investigates the use of the Spark-OES for the determination of impurities in PGMs (notably gold (Au), silver (Ag), iron (Fe), nickel (Ni), copper (Cu), lead (Pb), magnesium (Mg), manganese (Mn), silicon (Si), aluminium (Al), antimony (Sb), chromium (Cr), tin (Sn), titanium (Ti), zirconium (Zr), calcium (Ca), zinc (Zn), boron (B), cobalt (Co), vanadium (V), molybdenum (Mo), bismuth (Bi), arsenic (As), selenium (Se), tellurium (Te), cadmium (Cd) in refined platinum, palladium and rhodium metals). It is to be used at Anglo American Platinum’s final metal’s laboratory. A method to be used routinely in the laboratory is also developed. The concentration of the impurities determined is used to quantify the overall purity of the PGMs. PGMs, other than the matrix (the metal whose purity is being quantified), are also determined. The use of Spark-OES was evaluated as an alternative to inductively coupled plasma-optical emission spectroscopy (ICP-OES). Due to the lack of CRMs and calibration standards, the study included the preparation of in-house reference material (IRM) for calibration and quality control purposes. The standards were prepared by spiking pure PGM metal sponges (produced by Anglo Platinum) with the metal oxides of the elements of interest. These were melted together using a vacuum induction furnace to produce metal disks. The disks were ground and analysed after dissolution using ICP-OES. The metal disks, and the shavings, were distributed to three other independent laboratories and analyzed by ICP-OES, inductively coupled plasma-mass spectroscopy (ICP-MS) and Spark-OES. The assigned consensus values were used for the calibration of the Spark-OES. The method was validated for linearity, accuracy, precision, robustness, bias and the measurement uncertainty of the method. The metal disks were first tested for homogeneity. It was found that the bottom surface of the rhodium metal was not homogenous. Rapidly cooled moulds, will facilitate almost instantaneous cooling of the metal. This eliminates the migration of elements during cooling. This could assist with homogenizing the metal. Limits of detections (LODs) achieved for the methods ranged from 0.1 mg.kg-1 to 4 mg.kg-1. The highest LOD was for silicon, which was caused by contamination from the crucibles used. The precision for all impurity elements, except ruthenium (Ru), of the three methods (analysis of platinum, palladium and rhodium) was satisfactory. Ru showed poor precision in all the matrices due to the channel installed in the spectrometer. Due to the lack of CRMs, the traceability of the method could not be validated and the accuracy could only be validated by comparing it to in-house reference material. Although the method met the validation criteria, it cannot be used to certify the purity of the product as the traceability could not be validated. It suggests that the method be used for twin stream analysis in conjunction with a primary method. Because of its rapid turnaround time, and its non-destructive nature, the method can be used for plant control purposes, where the level of accuracy required is not as stringent as required on a certificate of analysis.

by Cham Pak-Meng. / Title also in Chinese. / Thesis (M.Ph.)--Chinese University of Hong Kong, 1989. / Bibliography: leaves 124-125.

Cheng Pui-kwan. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2003. / Includes bibliographical references (leaves 69-71). / Abstracts in English and Chinese. / TITLE PAGE --- p.i / THESIS COMMITTEE --- p.ii / ABSTRACT (ENGLISH) --- p.iii / ABSTRACT (CHINESE) --- p.iv / ACKNOWLEDGEMENTS --- p.v / TABLES OF CONTENTS --- p.vi / LIST OF FIGURES --- p.viii / LIST OF TABLES --- p.xi / Chapter Chapter 1 --- Introduction --- p.1 / Chapter Chapter 2 --- A High Resolution Near Infrared Laser Spectrometer: the Construction --- p.4 / Chapter Section 2A --- Basic Principle of LASER --- p.4 / Chapter Section 2B --- Properties of Laser Radiation --- p.7 / Chapter Section 2C --- Common Laser Sources --- p.11 / Chapter Section 2D --- The Construction of a New Infrared Spectrometer --- p.11 / Chapter Section 2E --- Frequency Calibration and Data Acquisition System --- p.19 / Chapter Section 2F --- Spectrometer Performance Tests --- p.26 / Chapter Section 2G --- Summary --- p.36 / Chapter Chapter 3 --- Study of Pressure Broadening of Water Using Cavity Enhanced Absorption Spectroscopy --- p.37 / Chapter Section 3A --- Background --- p.37 / Chapter Section 3B --- Experimental Apparatus --- p.43 / Chapter Section 3C --- Results and Discussion --- p.50 / Chapter Chapter 4 --- Concluding Remarks --- p.68 / REFERENCES --- p.69

Liao, Zhenwu. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2013. / Includes bibliographical references (leaves 86-91). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstracts also in Chinese.

Digitized by Kansas Correctional Industries

No description available.

Graduation date: 1994