Pressing hexagonal boron nitride for refractory or electric use - using a moulding mixt. of boron nitride, urea, and boric acid

摘要

Prods. are made of hexagonal boron nitride, using a mixt. of finely-dispersed BN with an easily meltable compsn. (a) contg. boron and nitrogen. The mixt. is pressed at 80-160 degrees C. so the molten compsn. (a) fills all the pores in the blank. The pressing is then heated at 1000-1400 degrees C. in ammonia, followed by sintering at a high temp. Pref. mixt. contains by wt. 60-90% hexagonal boron nitride, and 10-40% compsn. (a); where compsn. (a) is boric acid and urea used in a ratio between 1:1 - 1:3; and this mixt. is pressed at 0.25-1.0 t/cm3. The initial BN powder employed pref. has a specific surface of 20-300 m2/g. Prods. are used for electric insulators resistant to fluctuating temps.; dielectrics in electronic appts.; as antifriction material and vessels for corrosive media.