Boron nitride prepn. contg. compact wurtzite-type and cubic phases - using double treatment at high pressure and temp., so polycrystalline prod. has high mechanical strength

摘要

Boron nitride with a hexagonal crystal structure (HBN) is pressed using 3-8 kbars to make a blank. The blank is subjected to 100-150 kbars at 290-1500 deg.K., so at least 15 wt% of the HBN is converted into the compact modification possessing a wurtzite-type crystal structure (WBN). The pressure is then reduced to 40-90 kbars while the temp. is increased to 1600-3200 deg.K., so the HBN is completely transformed into polycrystalline compact phases, viz. HBN and cubic boron nitride (CBN). The initial blank pref. contains by wt. 0.1-0.8% of addns., esp. Al, B, transition metals, or nitrides, carbides, borides or carbonitrides of transition metals. The polycrystalline prod. obtd. has a much higher strength than similar conventional material.