高温高压合成金刚石用叶蜡石腔体热导率研究

Research on thermal conductivity of compressed pyrophyllite block during diamond synthesis at HT/HP

针对高温高压下叶蜡石热导率实时测试存在的问题,采用PPMS综合物性测量系统和LFA427激光热导仪,分别测试了金刚石合成前后合成块不同区域叶蜡石的热导率。测试结果表明,金刚石合成前粉压叶蜡石热导率为6.45 W/(m·K),合成后叶蜡石热导率为2.77 W(m·K),合成后叶蜡石块中间层热导率最大、内层次之、外层最小。通过XRD衍射分析结果发现,经高温高压作用后的叶蜡石晶面间距不但没有被压缩反而发生膨胀,叶蜡石合成块不同区域晶格膨胀率与其相应的热导率有明显的相关性。根据固态声子热导理论模型,解释了高温高压作用前后叶蜡石热导率不同的原因,并推算出在金刚石合成温度压力条件下叶蜡石块的平均热导率为10.13 W/(m·K)。

For the in situ testing problems of thermal conductivity of pyrophyllite at HT/HP,in the paper the thermal conductivity of compressed pyrophyllite block before and after diamond synthesis at HT/HP were tested by using the comprehensive property measurement system PPMS and laser conductometer LFA427. The results showed that the thermal conductivity of compressed pyrophyllite before diamond synthesis was about 6. 45 W/( m · K),which was 2. 77 W/( m · k) after diamond synthesis at HT/HP. It was found that the thermal conductivity in the intermediate layer of pyrophyllite block was the largest,followed by the inner,and the outer layer of pyrophyllite block was the minimum. XRD analysis results showed that the crystal plane distance of pyrophyllite block was expanded instead of compressed after HT/HP process with the biggest expansion ratio at the intermediate layer,then the inner layer and the minimum in the outer layer of the block. Therefore it seem that the decrease of the thermal conductivity was obviously related with interplanar spacing expansion of pyrophyllite after HT/HP process. According to the theoretical thermal conductivity model of the spring oscillator,the decrease of the thermal conductivity of the pyrophyllite block after HT/HP process was explained,and the thermal conductivity of compressed pyrophyllite block under HT/HP of diamond synthesis was deduced to be about 10. 13 W/( m·K).