Fabrication of diamond-transition metal carbide composites

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The oxidation of powder ZrC samples was carried out at temperatures of 380 to 550ﾟC and oxygen partial pressures of 4 to 16 KPa. It was found that the partial oxidation of the ZrC samples at 400 to 500ﾟC produces cubic ZrO_2 as well as carbon containing a very small amount of hexagonal diamond. Since it is possible to fabricate a diamond-ZrC composite by utilizing this partial oxidation of ZrC, the oxidation mechanism of ZrC using the powder and single crystal samples was investigated to reveal the deposition process of carbon containing diamond. Furthermore, the oxidation of HfC, TiC and NbC was performed to clarify its mechanism and to examine whether the carbon is formed during their oxidation.It was found on the basis of the EPMA, SEM and XPS results that the crack-free. compact layer of the ZrO_2 oxide 1 - 3 um thick containing 30 - 100 mol % carbon, which adhered to ZrC, was formed inside the porous, cracked layer of the oxide. The thickness of the former layer is kept constant during oxidation, being time-independent, whereas that of the latter layer grew linearly with time. The results similar to those of ZrC were obtained on oxidation of HfC single crystals. The oxidation mechanism of TiC and NbC was discussed from a kinetic viewpoint in connection with crystallization of the oxide (anatase and Nb_2O_5) and cracking as well as the formation of titanium and niobium suboxide.