Effect of Composition on Mullitization Behavior of α‐Alumina/Silica Microcomposite Powders

Abstract

The effect of composition on mullite formation was investigated using submicrometer composite particles that consisted of α‐alumina cores and amorphous silica coatings. Powders with varying alumina/silica ratios were prepared by varying the thickness of the silica coating. The mullitization behavior was monitored using differential thermal analysis, X‐ray diffractometry, and scanning electron microscopy. The results were consistent with previous studies that indicated that mullite forms initially by nucleation and growth within the siliceous phase, but also that chemical interdiffusion within the mullite grains is required to complete the reaction. The reaction rate in both stages was affected by the alumina/silica ratio. Available evidence has indicated that the first stage of the reaction is controlled by the dissolution of alumina in the siliceous phase. Results for the second stage suggested that alumina diffuses more rapidly through mullite than silica.