Formation of hexagonal BN by thermal decomposition of melamine diborate

Abstract

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, β = 92.40°, 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 °C. The melamine component decomposed at about 300 °C, and the formation of BN skeletons occurred above 600 °C. Turbostatic BN with 60% purity, which was obtained at 900 °C, was well crystallized by further heating at 2000 °C, accompanied by grain growth and purification.