Boron Nitride Composites By Chemical Vapor Deposition

Composites of boron nitride ( BN) have been made by the chemical vapor deposition ( CVD) of a BN matrix on a BN felt fiber substrate. Reactant gases were boron trifluoride and ammonia. The composites have a relatively high density (1.70 g/cm 3 ), a crystallite size L C = 150 A and an interlayer spacing d 002 = 3.35 A. Measurements of elastic modulus and thermal conductivity and expansion showed some anisotropy as a result of the preferred fiber orientation of the substrate.