A diffusion-controlled mullite formation reaction model based on tracer diffusivity data for aluminium, silicon and oxygen

Abstract

This paper compiles all the data from our tracer diffusivity studies in single crystalline 2/1-mullite. As tracers we used the rare stable isotopes 18O and 30Si and the artificial pseudo-stable isotope 26Al. Secondary-ion mass spectrometry was applied to analyze the depth distribution of the tracer isotopes after the diffusion annealing. An essential result of our tracer diffusivity studies was the very low diffusivity of 30Si compared to the diffusivities of 26Al and 18O, which are almost equal. Based on this observation, we propose a reaction model for the diffusion-controlled formation of mullite in the solid state, which assumes that the growth kinetics of a mullite layer is mainly controlled by the diffusion of aluminium ions and oxygen ions.