Oxygen self-diffusion in a cordierite glass

Oxygen self-diffusion measurements determined below and above the glass tra nsition temperature in a cordierite glass are reported. The diffusion exper iments were performed by the solid-gas isotope exchange method using O-18 a s a tracer in H-2-(H2O)-O-18 and Ar/O-18(2) atmospheres. The O-18 diffusion profiles were established by secondary ion mass spectrometry (SIMS) after appropriate diffusion annealing. The oxygen diffusion coefficients changed at the glass transition temperature as expected. The atmosphere affected th e oxygen diffusivity in agreement with other studies. The diffusion data we re useful for comparisons with diffusion controlled process in the same gla ss. There is a difference between the activation enthalpies for crystal gro wth, viscous flow, and oxygen self-diffusion. Hence, bond-breaking and mole cular reorientation required for crystallization and the atomic transport m echanism involved in viscous flow are not correlated in any obvious way to oxygen diffusion in cordierite glass. (C) 1998 Elsevier Science B.V. All ri ghts reserved.