Carbothermic synthesis of boron carbide with low free carbon using catalytic amount of magnesium chloride

Microcrystalline boron carbide was synthesized from boric acid and carbon black in the presence of a small amount of magnesium chloride by carbothermal reduction method at 1600 degrees C. The presence of magnesium chloride in the mixture has a determining effect in increasing the yield of the reaction and lowering the residual free-carbon content of the resulting boron carbide. We have also shown that, compared to several reported carbothermal reduction methods, the present catalyst also considerably lowers the excess amount of boron compound precursor required to afford boron carbide with negligible free carbon. X-ray powder diffraction (XRD) pattern indicated that the product was rhombohedral B4C. No peak, corresponding to free carbon, was observed in the XRD diffraction pattern of the B4C product formed from H3BO3:C:MgCl2 in the molar ratio of 1.0:1.45:0.01. Scanning electron microscopy image also showed that the product is fully crystalline and consisted of uniformly sized particles.