用碳化硅合成的金刚石微晶的抗氧化性

Oxidation Resistivity of Diamond Micro-crystals Synthesized from Silicon Carbide

用碳化硅加Ni70 Mn2 5Co5合金体系在高温高压下合成出具有完好晶形的金刚石微晶。通过粒度分析和热重量分析对这种晶体的热稳定性进行了评价。作为比较 ,对工业上用石墨合成的六种不同粒度的金刚石微粉和微晶也作了热重量分析。结果表明 ,用石墨合成的四种普通金刚石微粉的氧化温度随粒度的减小而明显降低 ,当粒度为80～ 10 0 μm到 1～ 2 .5 μm时 ,其起始氧化温度为 770℃到 6 2 7℃ ;两种未经破碎的金刚石微晶的抗氧化性能明显较高 ,其粒度为 2 0～ 70 μm ,起始氧化温度为 80 6℃和 819℃。与它们相比 ,用碳化硅合成出的金刚石晶体的粒度分布在 10～ 5 0 μm范围 ,而起始氧化温度为 838℃ ,完全氧化温度为 110 1℃ ,比用石墨合成的未经破碎的金刚石微晶具有更高的抗氧化性能。本文定性地讨论了用碳化硅合成的金刚石具有高耐热性的原因 ,认为完好的表面和硅杂质的存在可能对这种晶体热稳定性起了重要作用。

Diamond micro crystals were synthesized by using a system of SiC and Ni 70Mn 25Co 5 alloy under high pressure and high temperature,which wear perfect shapes and clear-cut faces.Oxidation-resistivity of the crystals was appraised by a grain-size analysis and a thermogravimetric analysis.To compare the properties,six kinds of commercially available diamond powders with respective grain size grade were also tested by the thermogravimetric analysis.It was made clear that oxidation temperatures of the commercial diamonds synthesized from graphite decrease remarkably with the decrease of the grain size,the initial oxidation temperatures are from 770℃ to 627℃,when the grain sizes are from 80-100μm to 1-2.5μm.And then two kinds of diamond micro-crystals synthesized from graphite without fracture have higher thermo-stability,their initial oxidation temperatures are 806 and 819℃ when the grain sizes are 20-70μm.By contrast,grain sizes of diamond crystals synthesized from SiC distribute in the range of 10 to 50μm,the initial oxidation temperature is 838℃,and the final oxidation temperature is 1101℃,both temperatures are higher remarkably than those of the general diamond powders and micro-crystals synthesized from graphite.The reason for the high thermo- stability of diamond synthesized from SiC was discussed qualitatively.It is considered that the perfect surface and impurity of silicon in the diamond could improve the oxidation-resistivity of the crystals.