Optical determination of the temperature of a laser heated industrial diamond
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Date
2008
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Abstract
Diamond has the highest thermal conductivity among known materials. In order to heat diamond to high temperature and measure the temperature, one needs to have a laser heating system with sufficiently good power stability, beam position and suitable wavelength for absorption. In this dissertation we heated, and measured the temperature of a diamond sample by using a CO2 laser. Temperatures are difficult to measure with the accuracy and stability required for many potential applications. Temperature sensors such as thermocouples that depend on attainment of thermal equilibrium with a surface via conductive or convective heat transfer are problematic because: (i) they require intimate contact with the surface which affects the local surface energy balance, especially when minute regions of the sample are to be probed, and (ii) they are limited to temperatures of <1500 °C. Similar restrictions apply to pyrometric, non-contact, temperature determination of hot-spots where the colour of a hot object is referenced against that of a heated tungsten filament. However these limitations do not apply in the case of non-contact infrared thermometry (spectro-radiometry), involving the grey-body (Planck) emission envelope emanating from a hot spot, which may even be well below sub-millimeter dimensions. A model of the surface temperature was successfully developed and qualitatively compared to the experimental results. CO2 and Nd: YAG laser heating was employed for heating two different industrial diamonds at extreme high power levels. The industrial diamonds were characterised using Raman spectroscopy, Scanning electron microscopy and X-ray diffraction. We show that there was some changing (physical and chemical) in the industrial diamond after heating.
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Submitted in partial fulfilment of the requirements for the degree of
Master of Science, University of Zululand, 2008.
Keywords
Industrial diamond