To investigate the formation mechanism of calcium hexaluminate(CaAl_(12)O_(19), CA_6), the analytically pure alumina and calcia used as raw materials were mixed in CaO/Al_2O_3 ratio of 12.57:137.43 by mass. The raw materials were ball-milled and shaped into green specimens, and fired at 1300–1600°C. Then, the phase composition and microstructure evolution of the fired specimen were studied, and a first principle calculation was performed. The results show that in the reaction system of CaO and Al_2O_3, a small amount of CA_6 forms at 1300°C, and greater amounts are formed at 1400°C and higher temperatures. The reaction is as follows: CaO ·2Al_2O_3(CA_2) + 4Al_2O_3 → CA_6. The diffusions of Ca^(2+) in CA_2 towards Al_2O_3 and Al^(3+) in Al_2O_3 towards CA_2 change the structures in different degrees of difficulty. Compared with the difficulty of structural change and the corresponding lattice energy change, it is deduced that the main formation mechanism is the diffusion of Ca^(2+) in CA_2 towards Al_2O_3.
Jun-hong ChenHai-yang ChenMing-wei YanZheng CaoWen-jun Mi
