Elastic properties of mullite

Using ultrasonic methods, we determined the ambient-temperature elastic constants of dense (99.7%) hot-pressed polycrystalline 3:2 mullite (3A1(2)O(3) . 2SiO(2)). We report the usual polycrystal elastic constants: Young's, shear, and bulk moduli, and the Poisson's ratio (nu). The Poisson's ratio (nu = 0.280) suggests interatomic bonding that is very different from that of either alumina or silica, Temperature dependences of the elastic constants show a strong irregularity; for example, nu decreases as the temperature increases. This irregularity suggests an internal-state change that hs perhaps related to the incommensurate structural modulation.