Anisotropic grain growth in boria-doped diphasic mullite gels

Densification and anisotropic grain growth were investigated in sol-gel der ived boria-doped diphasic mullite. Boria enhanced viscous flow densificatio n by reducing the viscosity and also produced a fine grain microstructure. Whisker-like mullite grains evolved from the dense, equiaxed microstructure . The onset temperature was similar to 1500 degrees C. Chemical leaching wa s employed to characterize the anisotropic grains. Growth kinetics showed t hat anisotropic grains followed the empirical equation G(n)-G(o)(n) = Kt wi th n = 3 and n=4 for the length and thickness directions, respectively. The activation energies for grain growth were 660 kJ mol(-1) for elongation an d 800 kJ mol(-1) for thickening. (C) 1999 Elsevier Science Limited. All rig hts reserved.