Fabrication of diamond-transition metal carbide composites

粉末ZrC样品的氧化在380至550 ℃的温度和4至16 KPa的氧分压下进行。结果表明，ZrC样品在400 ~ 500 ℃的部分氧化过程中，除了生成含有少量六方金刚石的碳外，还生成了立方相ZrO_2。由于有可能通过利用ZrC的这种部分氧化来制备金刚石-ZrC复合材料，因此使用粉末和单晶样品来研究ZrC的氧化机理以揭示含碳金刚石的沉积过程。此外，还对HfC、TiC和NbC进行了氧化实验，以阐明其氧化机理，并考察它们在氧化过程中是否有碳生成。在多孔的、有裂纹的氧化物层内形成了一层致密的ZrO_2氧化物层，其厚度为1 - 3 μ m，含30 - 100mol%的碳，并与ZrC相结合。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TiC和NbC氧化物的晶化、开裂以及钛和铌的低价氧化物的生成等动力学观点讨论了TiC和NbC的氧化机理。

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.