Anisotropic Grain Growth Mechanism of Mullite Derived from Cobalt Oxide Doped Diphasic-Gels

The anisotropic grain growth of mullite derived from cobalt oxide doped diphasic-gels was investigated. Results show that cobalt oxide can decrease the crystallization temperature and promote the anisotropic grain growth of the mullite. The aspect ratio of elongated mullite grains mainly depends on the sintering conditions. The crystallization temperature of the mullite derived from cobalt oxide-doped diphasic-gel is lowered to 1200°C. The anisotropic grain growth of the mullite follows the empirical equation Gn-G0n=kt with the growth exponents 3 and 3∼4 for the length and diametric directions, respectively, as 3wt% of cobalt oxide is added. The activation energies of grain growth are 978 kJ/mol for the length and 1125 kJ/mol for the diametric directions, and the growth rate constants at 1600°C are 3.4 and 1.0 for the length and the diametric directions, respectively. The growth mechanism of mullite grains obey the two-dimensional nucleation step growth mechanism.