MULLITE FORMATION KINETICS OF A SINGLE-PHASE GEL

A reaction kinetic study of the formation of mullite from single‐phase aluminosilicate gels has been performed using dynamic X‐ray diffraction. In situ measurements of conversion and separate infrared spectra data indicate that the amorphous single‐phase precursors form crystalline mullite at temperatures as low as 1213 K. All of the data are consistent with a nucleation rate‐controlled mechanism, unlike previous work with diffusion‐limited powders and diphasic gels. At temperatures below 1400 K, the conversion data are adequately fit with a binary model that can approximate a uniform distribution of activation energies. At higher temperatures, evidence indicates that diffusion mechanisms become the rate‐limiting step. Copyright © 1990, Wiley Blackwell. All rights reserved