Formation of BN films on carbon fibers by dip-coating

Turbostratic boron nitride (BN) films (amorphous with some microcrystallinity) were successfully deposited onto carbon fibers and graphite substrates by dip-coating in methanolic boric acid and urea solutions, followed by nitriding in an ammonia flow at 1000 °C. BN coatings exhibited an orange-peel or pebble-like structure. Surface morphology results indicated that the sizes of the grain-like particles increased with the concentration of the dipping solution. The thickness of the BN film exhibited parabolic relationships with the viscosity of the dipping solution and the withdrawal speed. With the homogeneous surface, the thickness of the BN film increased with the concentration of the reactant in the solution. However, stripping and cracking at the surface have been observed while the reactant concentration was higher than 0.9 M. The yield of BN increased with the nitriding temperature. The increasing trend was slowed down at 800 °C and attained a maximum at 1000 °C.