A research report submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg in partial fulfilment of the requirements for the degree of Master of Science / The aim of this work was to evaluate the measurement of the optical properties as a means of obtaining information on the growth history of synthetic diamond. A suite of sample of known synthesis origin representing the different types of commercially produced synthetic diamond was analysed hy photoluminescence. The photoh.{fnmescence intensity was normalising by using the area of tbe Raman peak. This allowed a semi-quantitative comparison of the defect concentration. Three photoluminescent centres were identified, H3, 575 run and 1.945 eV (with zero-phonon lines at 2.463 eV, 2.156 eV, and 1.945 eV respectively). Differences between the intensities of the luminescence due to these centres were observed as a function of the type ot diamond The H3 amd the 1.945 eV intensity was found to increase with the proportion of cubic growth sector, In addition the 1.945 eV intensity was found to increase with heat treatment and was higher in (100) than in (111) growth sectors. As all three defects detected involve vacancies and nitrogen impurity, an analysis was done to quantify any correlation between the luminescent intensities from the different defects in the same SDA powder sample. The 1.945 eV and 575 run intensities were observed to be correlated .. An additional correlation 'was found between the 575 lim and the H3 intensities in the case of finer particle size samples. The luminescence intensity for all three defect types was observed to be a function of the particle size of the sample. The shapes and widths of zero-phonon lines were related to the types and concentration of lattice defects present in a crystal according to line broadening theory. An attempt was made to explain the results in the context of the known synthesis origin and growth conditions. / AC 2018

A research report submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg in partial fulfilment of the requirements for the degree of Master of Science / The aim of this work was to evaluate the measurement of the optical properties as a means of obtaining information on the growth history of synthetic diamond. A suite of sample! of known synthesis origin representing the different types of commercially produced synthetic diamond was analysed hy photoluminescence. The photoluminescence intensity was normalising by using the area of tbe Raman peak. This allowed a semi-quantitative comparison of the defect concentration. Three photoluminescent centres were identified, H3, 575 run and 1.945 eV (with zero-phonon lines at 2.463 eV, 2.156 eV, and 1.945 eV respectively). Differences between the intensities of the luminescence due to these centres were observed as a function of the type ot diamond. The H3 amd the 1.945 eV intensity was found to increase with the proporticn of cubic growth sector, In addition the 1.945 eV intensity was found to increase with heat treatment and was higher in {lOO}than in {111} growth sectors. as all three defects detected involve vacancies and nitrogen impurity, an analysis was done to quantify any correlation between the luminescent intensities from the different defects in the same SDA powder sample. The 1.945 eV and 575 nm intensities were observed to be correlated. An additional correlation was found between the 575 nm and the H3 intensities in the case of finer particle size samples. The luminescence intensity for all three defect types was observed to be a function of the particle size of the sample. The shapes and widths of zero-phonon lines were related to the types and concentration of lattice defects present in a crystal according to line broadening theory. An attempt was made to explain the results in the context of the known synthesis origin and growth conditions. / AC2018

This study investigated the photo-excitation and thermoluminescence properties of diamonds which were synthesised primarily for thermoluminescence dosimetry. For investigations of thermally stimulated processes occurring in these crystals an analysis of the thermoluminiscence & low spectra and the temperature dependent isothermal decay spectra was undertaken [Abbreviated abstract. Open document to view full version] / GR2016

A method was investigated to synthesize diamonds at atmospheric pressure without the use of diamond seed crystals. The method was first proposed by Burton in 1905 and appears to have been lost in the literature. The procedure is based on Ostwald's principle of the formation of metastable, intermediate crystals en route to a more-stable final product. Carbon was dissolved in a lead-calcium alloy and was later precipitated out of the melt by the removal of calcium with steam. The calcium was used to increase the solubility of carbon in lead. Reaction temperatures between 775 K and 1025 K were used. The resulting precipitate, analyzed by both chemical and physical means, was found to be well-crystallized graphite. No diamond formation was found to occur. / Master of Science

A thesis submitted to the Faculty of engineering. University of Witwatersrand. Johannesburg, in fulfilment of the requirements for the Degree of Doctor of Philosophy Pretoria, 1995 / This thesis describes a study of the friction and wear characteristics of a range of oxide and silicon-based ceramics sliding against AlSI 440C stainless steel, as well as various sliding combinations of two types of De Beers polycrystalline diamond (PCD), namely Syndite and Syndax, To facilitate the former work, a high-speed reciprocating sliding test machine with computerized data acquisition and control was developed. It was confirmed that under water-lubricated sliding, the oxide ceramics (alumina, PSZ, 3YTZP, and Ce-TZP) showed higher friction coefficients and Weal' rates than the silicon-based ceramics (Sialon and silicon nitride). This was related to different levels of adhesion and the formation of metallic transfer films. For the zirconia ceramics, increased transformation toughening was associated with increased surface fracture damage and metallic film formation. In general, the metallic transfer films were beneficial, protecting the underlying ceramic and dominating the friction and wear behaviour. The superior performance of the silicon-based ceramics was related to the formation of lubricious tribofilms containing silicon oxides and hydroxides. Experiments with synthetic mine water as lubricant demonstrated that the presence of significant amounts of chloride and sulphate in the water generally reduced friction and wear. This was tentatively explained in terms of reduced adhesion and the promotion of iron oxide and hydroxide formation. It is suggested that the influence of sulphate may be more important in thi'3 regard than that of chloride. The tribological behaviour of self-mated Syndite PCD sliding couples is dominated by the formation of Co-rich trlbofilms, which nrc associated with increased friction coefficients and reduced load carrying capacity (LCC). Syndax, which employs silicon as the binder phase, shows lower friction coefficients anti higher LCe under both dry and water-lubricated sliding conditions. Mixed Syndax/Syndite couples show superior performance to self-mated Synditc tinder dry sliding conditions, but 110 improvements in the presence of water. The former effect is related to the preferential removal of Co 11'0111 the Syndite surface to the Syndax / GR 2017

Thesis (M.Phil.)--City University of Hong Kong, 2006. / "Submitted to Department of Physics and Materials Science in partial fulfillment of the requirements for the degree of Master of Philosophy" Includes bibliographical references.

No description available.

Paramagnetic defects in free standing polycrystalline diamond films made by chemical vapour deposition (CVD) have been studied using electron paramagnetic resonance (EPR), electron-nuclear double resonance (ENDOR) and infrared absorption. EPR experiments at a range of frequencies (1-35 GHz) confirm the ¹H hyperfine parameters for the recently identified H1 defect (Zhou et al., Phys. Rev. B, 54:7881 (1996)). In the samples studied here, H1 is always accompanied by another defect at g=2.0028(1). Saturation recovery measurements are consistent with two defects centred on g=2.0028. The spin-lattice relaxation rate of H1 is a factor of 10-100 times more rapid than the single substitutional nitrogen centre (N⁰_S), which is known to be incorporated into the bulk diamond. ¹H matrix ENDOR measurements indicate that the H1 centre is in an environment with hydrogen atoms 2-10 A distant from the centre. The near neighbour hydrogen identified by the EPR was not detected in the ENDOR experiments. The concentration of H1 correlates with the total integrated C-H stretch absorption in the samples studied here. All the evidence is consistent with H1 being located at hydrogen decorated grain boundaries (or in intergranular material) rather than in the bulk diamond. The affect of annealing the films in vacuo up to 1900 K has been studied. On annealing at 1700 K it was found that some of the hydrogen on internal grain boundaries became mobile but was not lost from the sample, and the intensity of the EPR absorption at g=2.0028 decreased. Annealing at 1900 K severely degraded the optical properties of the samples, and a new defect with g=2.0035(2) was created. Infrared measurements show that hydrogen is lost from most CVD diamond samples when annealed to 1900 K for four hours. An EPR imaging (EPRI) probe was designed and built. This comprised a 3-loop, 2-gap loop-gap resonator and a pair of anti-Helmholtz coils providing a magnetic field gradient ∂B_z/∂z. Using this probe the distribution of N⁰_S was measured in the growth direction of four CVD diamonds to a resolution of 20 μm. The distribution of N⁰_S is shown to be different to the distribution of defects with g=2.0028. Two-dimensional images of the spin density of N⁰_S in single crystal type Ib diamonds made by the high temperature and pressure (HTP) method have been generated, demonstrating a resolution of 100 μm. A two-dimensional image of the spin density of g=2.0028 defects in a CVD sample is compared to a photograph of the same sample, showing the correlation between the distribution of the defects with the distribution of non-diamond material in the sample. The distribution of the [N-N]⁺ defect in a natural diamond has been examined using ∂B_z/∂B_ϰ field gradient coils.

Thesis (M.Eng.). / Written for the Dept. of Chemical Engineering. Title from title page of PDF (viewed 2008/07/29). Includes bibliographical references.

Thesis (M.S.)--Rochester Institute of Technology, 1990. / Typescript. Includes bibliographical references (leaves 92-97).