FORMATION OF HEXAGONAL BN BY THERMAL-DECOMPOSITION OF MELAMINE DIBORATE

The formation of h-BN by thermal decomposition of melamine diborate was examined by XRD, IR and thermal analysis. The melamine diborate, which was precipitated as white powders by cooling a hot solution of melamine and boric acid, was presumed to have a monoclinic structure with a = 2.0259 nm, b =1.4180 nm, c = 0.3504 nm, beta = 92.40-degrees, and its solubility in 100 cm3 water was about 0.6 g at room temperature. On dehydration the crystalline diborate was converted to an amorphous solid at the temperature ranges from 100 to 200-degrees-C. The melamine component decomposed at about 300-degrees-C, and the formation of BN skeletons occurred above 600-degrees-C. Turbostatic BN with 60% purity, which was obtained at 900-degrees-C, was well crystallized by further heating at 2000-degrees-C, accompanied by grain growth and purification.