Study On Mullization Of Sillimanite

Sillimanite is widely used in refractory field as its excellent heat resistance. This raw material is consumed within the refractory industry because of the ability to form mullite phase at calcining condition. It is significant for improving strength, toughness of lightweight refractory.Mullite and SiO2 glass phase is formed when heating sillimanite at high temperature. Quantitative analysis of the amount of mullization from sillimanite is a difficult task. And the analysis of sllimanite-mullite transformation has been not systematic studied.In this article, sillimanite was calcined at differernt conditions. By some methods of quantitative analysis, such as chemical analysis, HF dissolution, NaOH dissolution, calculation of the amount of mullite transformated from sillimanite exist deviation. By (220) diffraction peak of sillimanite and mullite, analysis result of the quantity is more reasonable. With the standard working curve, the amount of mullite was calculated. The amount of mullite reaches 97% when calcining sillimanite 4 hours at 1650℃.DTA, IR, SEM and TEM analysis method was used to study sillimanite-mullite transformation. The results show that the new mulite is parallel to the sillimanite growth direction(c-axis), the growth of the mullite crystals start at the outside particles, the formation of glass phase enriched in mullite grain interface and crystal ends, as the degree of mullization increase Si-O bond fracture raise, Si-O bond partly replace by Al-O bond and O vancancies formed in mullite crystals, crystal structure gradually transform to the ideal mullite.