CRYSTALLIZATION BEHAVIOR AND CHARACTERIZATION OF TURBOSTRATIC BORON-NITRIDE

X-ray diffraction studies of boron nitride powders synthesized from bo ric oxide and ammonia at 900 degrees C indicates a turbostratic struct ure which is characterized by the absence of ordering in the third dim ension. Turbostratic boron nitride (t-BN) powders are found to be unst able and decompose into ammonium berate compound (NH4 . B5O8 . 4H(2)O) after long storing periods. Thermal transformation of t-BN into the s table, hexagonal ordered layer lattice structure was promoted with hea t treatments at 1500-1800 degrees C for 15 min-5 h. The transformation and degree of crystallization was observed with Xray diffraction anal ysis. The effect of crystallization period and temperature on the part icle sizes and shapes of the powders was examined with transmission el ectron microscope. BET surface area measurements of the powders were a lso performed for the characterization of powder properties. (C) 1997 Elsevier Science Limited.