Abstract
The thermal oxidation of high pressure and high temperature (HPHT) diamond powders, of between 0.75 and 1.5 μm diameters, has been studied in dry oxygen. Under conditions of poor thermal transfer between the powders and the substrate extremely rapid oxidation has been observed. The onset temperature of the latter ‘explosions’ occurs between 514 and 576 °C, at 1 atm O 2 pressure, where bulk diamond is known to oxidise relatively slowly. A model has been developed in which the exothermicity of the surface oxidation reaction is not dissipated when the sample is in poor thermal contact with the support. A runaway ‘explosion’ occurs in samples of high surface area/volume particulate diamond arising from the high activation energy of the oxidation kinetics of diamond coupled with poor thermal contact. Improving the thermal contact allows diamond powders with the diameters of about 1 μm to be stable even at temperatures up to 700 °C.
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