Combustion synthesis of CaB6 powder from calcium hexaborate and Mg

As one of the important metal-borides, calcium hexaboride (CaB₆) is applied in refractory materials, metal deoxidant, neutron absorbent, wear-resisting agent and functional ceramic materials. Generally, CaB₆ is produced from B₄C or B₂O₃ which is obtained at high temperature and high cost. In this study, the CaB₆ powder was prepared through combustion synthesis by using calcium hexaborate and magnesium as starting materials. The calculated adiabatic temperature of CaB₆O₁₀–Mg system reached 2406.69 K. The XRD analyses of combustion products showed that there existed a small amount of Mg₃B₂O₆ and Ca₃(BO₃)₂ besides CaB₆ and MgO. The XRD patterns of products leached by HCl indicated the major part of the leached sample is comprised by CaB₆, showing that MgO and by-products were efficiently leached out. In addition, the technological conditions for combustion synthesis were investigated. It is resulted that larger particle size of CaB₆O₁₀ and higher compacting pressure is beneficial to the production of CaB₆.