Abstract:
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 HCl 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=57.3K/(b-b0)cos , the crystallite sizes of the wBN were estimated at 24 nm, It was also noted that the sizes of wBN transformed from abovementioned two kinds of the raw material were no obvious difference. The DTA result manifests that the wBN started endothermal reaction at 1 127 K and the absorptive peak of heat was at 1 260 K. This shows the wBN to be more thermostable than diamond but less than zBN.
点击查看大图
下载:
