| 摘要 |
PURPOSE:To produce transparent, high-purity boron nitride of cubic system having excellent heat resistance under a high-temperature condition by sintering boron nitride of hexagonal system having oxygen content of <= a specific amount under static extra-high pressure not using a sintering auxiliary. CONSTITUTION:Boron nitride of hexagonal system (e.g. one obtained by treating high-purity powder or sintered body of boron nitride of hexagonal system sold on the market in vacuum at 1,600 deg.C for 2 hours and in N2 gas at 2,100 deg.C for 2 hours) having <=0.06wt.% oxygen content is treated under high pressure at high temperature under >=7 GPa under thermodynamically stable condition of cubic-system at >=2,100 deg.C without using a sintering auxiliary to give a transparent, high-purity sintered body of boron nitride of cubic system suitable for window material of specific use, cutting tool of material to be hardly cut, etc. |
