Reaction mechanism and size control of CaB6 micron powder synthesized by the boroncarbide method

Reaction synthesis mechanism of Calcium hexaboride (CaB6) powder was investigated by using CaCO3-B4C-C system. Micron-scale CaCO3 and B4C powders were used as main raw materials. The synthesized powder was determined by X-ray diffraction, showing no left reactants if enough CaCO3 was added to compensate the evaporation of calcium atoms at high temperature. The powder morphology was observed through SEM. The synthesized CaB6 powder formed hard agglomerates which consisted of cubic CaB6 crystallites when the reaction completely finished. Reaction process was illustrated indicating it was a solid-state reaction occurred from B4C surface to the centre. The dry high-energy ball milling was used to investigate the influence of ball-milling time on the shape and size of powder particles. The particle granularity was measured by laser size analysis method. It is obvious that the particles were refined greatly after ball milling for 8 h. However, the CaB6 powder could not been refined markedly after 16 h. Finally, optimized parameters for size controlling were given in this paper.