GRAIN-SIZE DISTRIBUTION AND MORPHOLOGIES OF NANOCRYSTALLINE BORON-NITRIDE DURING BALL-MILLING

The ball milling process of boron nitride powders has been investigate d by means of X-ray diffraction (XRD) and transmission electron micros copy (TEM). During the early stage of milling, the grain size of boron nitride decreases rapidly and reaches a stable value of about 10 simi lar to 15 nm after milling for 4 similar to 5 h. It has been found tha t crystalline boron nitride may be vitrified by extended milling, and that boron nitride grains exhibit a plate-like morphology during the w hole milling process. Rosin and Rommlar's equation y = exp[-(k/x)(n)] can be successfully applied to describe the grain size distribution of boron nitride during the last stage of milling. Parameters k and k(n) are extrapolated in terms of the R-R equation and call be used to cha racterize the variation of grain sizes during the milling process.