纤锌矿型氮化硼及其应用的研究(Ⅰ)——纤锌矿型氮化硼的冲击波合成

STUDY OF WURTZITE TYPE BORON NITRIDE AND ITS APPLICATIONS (I) --SHOCK WAVE SYNTHESIS OF WURTZITE-TYPE BORON NITRIDE

用hBN(Ⅰ、Ⅱ型层状结构的六角氮化硼)作原料,在斜冲击波的高温高压作用下,实现了hBN向wBN(纤锌矿型氮化硼)的转变。X光结构分析表明,生成的超硬氮化硼全部为wBN,没有发现zBN(闪锌矿型氮化硼)生成的任何证据。X光荧光光谱分析结果,得到的wBN的纯度接近99％。差热分析显示,在空气中温度为1127K时,开始吸热反应,吸热峰位于1260K。这表明wBN的热稳定性介于zBN和金钢石之间。

Two kinds of hBN (hexagonal boron nitride) powder were used as raw material for synthesizing superhard BN by shock compression. Our explosive experimental assembly was similar to that of Japan Nippon Oil and Fast Company Ltd. .After shock treatment the recovered mixture of BN and iron powders was immersed in HC1 solution to dissolve the iron material. The residue was refined by caustic fusion. By observing X-ray diffraction pattern we found that all refined BN was wBN (wurtzite-type boron nitride) and that zBN (zinc blende-type boron nitride) did not exist in the refined BN. The purity of refined wBN approached 99% and the impurities were Cr, Fe,Ti,Mn and Ca. We think the impurities to come from the stainless steel capsule used in caustic fusion,except the Ca originated in the raw material hBN,Using Scherrer line-broadening equation D=57. 3λK/(b -bo)cosθ, the crystallite sizes of the wBN were estimated at 24nm. It was also noted that the sizes of wBN transformed from abovementiond two kinds of the raw material were no obvious difference.The DTA result manifests that the wBN started endothermal reaction at 1 127K and the absorptive peak of heat was at 1260K. This shows the wBN to be more thermostable than diamond but less than zBN.