HIGH-PRESSURE PHASE-TRANSFORMATIONS IN TURBOSTRATIC BORON-NITRIDE USING MAGNESIUM BORON-NITRIDE AS THE CATALYST

Results of high pressure phase transformations in turbostratic boron n itride (tBN) using magnesium boron nitride as the catalyst-solvent are described. It was observed that turbostratic boron nitride undergoes various structural changes accompanied with the formation of hexagonal , cubic and wurtzitic modifications of boron nitride at high pressures and high temperatures. It was also found that the formation of these phases is sensitive to the pressures and temperatures prevailing in th e reaction zone. At higher pressure (> 40 kbar) and temperatures (> 13 00 degrees C), cubic boron nitride (CBN) was observed as the predomina nt phase, whereas at lower pressure (less than or equal to 40 kbar) an d 1300 degrees C, the predominant phase was that of wurtzitic boron ni tride (WBN). The tBN - WBN phase transformation under static high P-T conditions with the use of catalyst-solvent process is reported for th e first time.