A dissertation submitted to the Faculty of Engineering and the Built Environment, University of the Witwatersrand, Johannesburg, in partial fulfillment of the requirements for the degree of Master of Science in Engineering, School of Mechanical, Industrial & Aeronautical Engineering, 2017 / An investigation of polycrystalline diamond compact (PDC) cutter failures, which are industrially known as spalling, was conducted by exploring changes in the diamond layer architecture and edge geometry of the cutter. Layer architecture was investigated through the use of layered functionally graded (FG) structures. Twenty one FG variations were prepared by the tape casting method and sintered using a high-pressure, high-temperature press. The vertical borer test (VBX), a laboratory test method, was used to gauge the improvement in spall resistance of the FG specimens against the benchmarks. Due to cost constraints associated with VBX testing, of the 21 available specimens, only four variations were tested for spalling. Contrary to expectation, it was found that all four specimens spalled during VBX testing despite showing a slight improvement in the spall area. For this reason, this route was abandoned. It was concluded that the use of layered structures is not effective in resolving the spalling problem. The use of novel edge geometry was investigated by taking three standard products and creating new geometric profiles on the specimens using a spark erosion machine. Each profile comprised a depression on the front face of the cutter. The specimens with novel geometry were also tested on the VBX. The spall was found to be confined between the chamfer breach and the depression feature. The depression appeared to have stopped the spall from propagating beyond the allowable spall limit of 1.2mm. On the basis of this 3 finding, it was concluded that spalling was successfully resolved. It is recommended that further optimization of this solution should be explored in field testing. In addition, a cost-effective way to fabricate the geometric profiles on the cutters should be further investigated because creating specimens using the spark erosion machine was quite expensive. Therefore, it is not viable for fabrication of large production volumes / CK2018

Thesis (Ph. D.)--University of Missouri-Columbia, 2007. / The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file (viewed on October 16, 2007) Vita. Includes bibliographical references.

Thesis (Ph. D.)--University of Missouri-Columbia, 1997. / Typescript. Vita. Includes bibliographical references (leaves 91-94). Also available on the Internet.

Thesis (Ph. D.)--University of Missouri-Columbia, 1997. / Typescript. Vita. Includes bibliographical references (leaves 91-94). Also available on the Internet.

Thesis (Ph.D.)--Texas Christian University, 2009. / Title from dissertation title page (viewed Oct. 30, 2009). Includes abstract. Includes bibliographical references.

Thesis (M.Sc.(Chemistry))--University of Pretoria, 2003. / Summaries in Afrikaans and English. Includes bibliographical references.

Differential pulse voltammetry is one of the most widely used analytical polarographic techniques especially for trace inorganic analysis. Up to now mercury electrode and different types of carbon electrodes were used for such analysis. The emphasis of the present dissertation is on the design of a new class of electrodes, namely mono crystalline diamond paste based electrodes, to be used in differential pulse voltammetry for trace analysis of inorganic compounds. Monocrystalline diamond and boron doped polycrystalline diamond based electrodes exhibit several superior electrochemical properties that are significantly different from those of other carbon allotropes based electrodes, e.g., glassy carbon electrodes, highly oriented pyrolytic graphite based electrodes, which have been widely used for many years. The advantages are: (a) lower background currents and noise signals, which lead to improve SIB and SIN ratios, and lower detection limits; (b) good electrochemical activity ( pre-treatment is not necessary); (c) wide electrochemical potential window in aqueous media; (d) very low capacitance; ( e) extreme electrochemical stability; and (f) high reproducibility of analytical information. Furthermore, later studies shown the superiority of the mono crystalline diamond as electrode material due to high mobilities measured for electrons and holes. The design selected for the electrodes is simple, fast and reproducible. The diamond powder was mixed with paraffine oil to give the diamond paste used as electroactive material in the electrodes. The results obtained by employing the diamond paste based electrodes proved a high sensitivity, selectivity, accuracy and high reliability. These characteristics made them suitable to be used for the analysis of different cations (e.g., Fe(ll), Fe(Ill), Cr(Ill), Cr(VI), Pb(ll), Ag(I)) as well as of anions (e.g., iodide) in pharmaceutical, food and environmental matricies. / Dissertation (MSc (Chemistry))--University of Pretoria, 2006. / Chemistry / unrestricted