Metastable immiscibility and microstructural development during sintering of a SiO2-Al2O3 plasma prepared powder

Abstract

The sintering characteristics of SiO2-36.6 wt % Al2O3 powder, prepared by condensation from high frequency plasma, have been studied and microstructural changes occurring during sintering followed by transmission electron microscopy The as-prepared amorphous powder showed evidence of spinodal decomposition into an Al2O3-rich and SiO2-rich glass consistent with the position of a previously reported metastable miscibility gap in the SiO2-Al2O3 system. Mullite crystallized on an extremely fine scale at 1000° C and gradually coarsened at higher temperatures. Sintering occurred above 1100° C by a viscous flow mechanism with activation energy 87 kcal mol−1 which corresponds to the activation energy for viscous flow of SiO2-Al2O3 glass containing approximately 17 wt % Al2O3.