Recently, a property of diamond as a semiconductor is focused on by many researchers. For the mass production, it is important to develop the manufacturing process. As it is thought that the ionic milling process has limitations, the application of gasification reactions with oxidizing gases such as CO 2 , H 2 O and O 2 is the best option.In this study, reaction behaviors of diamond at temperatures of more than 1273 K were investigated under a wide range of oxygen potentials, and the crystallographic relationship from diamond to graphite was clarified.A graphite layer was formed on the surface of diamond under both Ar gas with an oxygen potential of less than 100 ppm, and a CO 2 -Ar mixture (30 vol%). The Raman spectrum consisted of the amorphous carbon and graphite. However, the graphite formed differed from ordinary graphite in the reactivity. Furthermore, the crystallographic relationship between diamond and graphite was determined to be ð111Þ D == ð002Þ G .
Diamond is the ultimate state of carbon crystal. However, a transformation from diamond to graphite during gasification occurs under oxidizing atmosphere. The gasification behaviors of diamond vary with the reaction gas composition and temperature.There has been no kinetic study on the diamond gasification. Most of the interest in this area has been related to diamond growth. The change of morphology of diamond surface and the crystallographic orientation between the diamond and the graphite formed was presented in a previous study.In this study, the gasification of natural diamond was investigated using TG-DTA. Kinetic analysis was performed on the basis of Langmuir-Hinshelwood type equation, in which some rate constant was modified from the previous study for coke gasification. SEM observations of the diamond surface were carried out in order to clarify the change in surface morphology. Moreover, the simultaneous gasification of diamond and graphite was carried out in order to clarify the difference in reactivity between ordinary graphite and graphite formed on the diamond during gasification.
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