Fabrication of diamond-transition metal carbide composites

ZrC粉末样品的氧化温度为380 ~ 550ºC，氧分压为4 ~ 16 KPa。结果表明，ZrC样品在400 ~ 500℃的温度下部分氧化得到立方ZrO_2和含有极少量六方金刚石的碳。由于可以利用ZrC的部分氧化制备金刚石-ZrC复合材料，因此研究了ZrC在粉末和单晶样品上的氧化机理，揭示了含碳金刚石的沉积过程。此外，对HfC、TiC和NbC进行了氧化，以阐明其氧化机理，并检查碳是否在其氧化过程中形成。通过EPMA、SEM和XPS分析发现，材料无裂纹。在多孔裂纹的氧化层内部，形成了一层厚度为1 ~ 3um，碳含量为30 ~ 100 mol %的致密ZrO_2氧化层。前一层的厚度在氧化过程中保持恒定，与时间无关，而后一层的厚度随时间线性增长。对HfC单晶的氧化得到了与ZrC相似的结果。从动力学的角度讨论了TiC和NbC的氧化机理，包括氧化物（锐钛矿和Nb_2O_5）的结晶和裂解以及钛和亚氧化铌的形成。

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.