Synthesis of calcium hexaboride powder via the reaction of calcium carbonate with boron carbide and carbon

The synthesis of calcium hexaboride (CaB6) powder via the reaction of calci um carbonate (CaCO3) with boron carbide (B4C) and carbon has been investiga ted systematically in the present study. The influences of heating temperat ure and holding time on the reaction products have been studied using X-ray diffractometry, and the morphologies of CaB6 obtained at various temperatu res and holding times have been investigated via scanning electron microsco py. The interaction in the CaCO3-B4C- carbon system by which CaB6 is formed is a solid-phase process that passes through the transition phases Ca3B2O6 and CaB2C2. The optimal conditions for CaB6 synthesis are a holding time o f 2.5 h at a temperature of 1673 K, under vacuum (a pressure of 10(-2) Pa). CaB6 powder has the same morphology as B4C, and the properties and the sha pe of CaB6 powders can be improved by choosing good-quality raw materials.