PYROLYTIC BORON NITRIDE AND METHOD FOR ITS PRODUCTION Russian patent published in 1995 - IPC

FIELD: production of refractories and coatings on graphite products. SUBSTANCE: pyrolytic BN has metal impurity in form of zirconium in amount not in excess of 1 mas.%: X-ray spectrum has bimodal profile curve of line for reflection plane 002 with maximum X-ray intensity between -35 and -37 deg. and maximum X-ray intensity between +35 and +37 deg. relative to angle corresponding to precipitation plane. In this case, each of two intensity maxima has half width of line 8-16 deg., and intensity of line of X-ray spectrum at zero angle amounts to 5-15% of maximum intensity of any of two lines. Desired product is produced by introduction of flow of gas mixture of boron-containing reagent and ammonia to evacuated reaction chamber. Temperature of precipitation of desired product and holding is 1890-1970 C. Nitrogen-to-boron atomic ratio in gas mixture is 2:(1-4):1. Introduced into flow of gas mixture is zirconium by evaporation of metallic zirconium or zirconium dioxide present in reaction chamber, or addition of gaseous zirconium tetrachloride. Used as boron-containing reagent is BCl₃,B₂H₆,BF₃,, or B₃H₃N₃Cl₃,B₃N₃H₆,B₁₀H₁₄(C₂H₅)₃B.. Density of product BN is 2.22-2.24 g/cu. cm; thermal coefficient of expansion is (1.10-1.79)x(1,10-1,79)×10^-61/^°C. EFFECT: higher efficiency. 4 cl, 7 dwg, 2 tbl