Preparation of CaB_6 by Combustion Synthesis

CaB_6 powder was prepared by combustion synthesis with CaO,B_2O_3 and Mg as re- actants.The DTA curves of the different reaction systems were investigated.Combustion products and leached products were characterized by XRD,SEM and particle size distribution techniques.The results indicate that apparent activation energy(E) of the exothermic peak near 872~C for reaction Mg+3B_2O_3+CaO=CaB_6+10MgO is 15.71kJ·mol~(-1) and its reaction order(n) is 1.1.The apparent ac- tivation energy is lower,so the reaction occurs easily.Combustion products consist of MgO,CaB_6 and a little amount of Mg_3B_2O_6 and Ca_3B_2O_6,and no nitrides form during the combustion process in air. CaB6 powder purity is 92.5% after combustion products are leached with acid.CaB_6 particles become finer with the increasing of the preparing sample pressure.