Comparative catalytic study on the carbothermic formation of hexagonal boron nitride with Li, Na, K and Ca carbonates

Catalytic effects of Li, Na, K and Ca carbonates on carbothermic formation of hexagonal boron nitride (hBN) were investigated. Experiments were conducted by keeping the plain and catalyst added B2O3 + C powder mixtures at 1400 degrees C in flowing nitrogen for 40-160 min. Products were subjected to quantitative and X-ray diffraction analyses, scanning and transmission electron microscopy examinations, and particle size measurements. Investigated catalysts increased the amount, particle size and crystallinity of the formed hBN. Average particle sizes of the obtained hBN powders were in 150-350 nm range. Catalytically, lithium and sodium carbonates were found to be the most effective, whereas calcium carbonate was the least effective. In the experiments conducted for 80 min, the quantity of the formed hBN increased 13-fold when 40 wt% Li2CO3 was used, as compared to plain mixture. The increases were ninefold and fourfold for the same duration when 40 wt% K2CO3 and 10 % CaCO3 were used, respectively.