| 摘要 |
PROBLEM TO BE SOLVED: To obtain a hexagonal boron nitride powder with high crystallinity and high orientation by adding a Ca compd. to a mixture of boric acid and melamine with a specified B/N atomic ratio, producing melamine borate under conditions of temp., relative humidity and retention time satisfying a specified relation, calcining and crystallizing the obtd. melamine borate in a nonoxidative gas atmosphere. SOLUTION: A Ca compd. is added to a mixture of boric acid and melamine in 1/1 to 1/6 B/N atomic ratio in such a manner that a liquid phase of calcium borate is produced by 5 to 20 wt.% based on the hexagonal boron nitride produced by crystallization. Then melamine borate is produced by controlling the temp. T( deg.C), relative humidity ψ (%) and retention time (hr) to satisfy the relation of T>=-20 log10 (t/4)+ (ψ-100)/200+60, and then calcined and crystallized at 1800 to 2200 deg.C in a nonoxidative gas atmosphere. The obtd. hexagonal boron nitride powder has <=1.20 graphitizing degree and >=25.0 intensity ratio of diffraction lines (I102 /I100 ). |
