Study Of Synthesis Of Mullite By Micro-crystal Muscovite From West Sichuan

Mullite(3Al₂O₃·2SiO₂) is also called andalusite, while its theoretical composition is: Al₂O₃ 71.8%, SiO₂ 28.2%. Mullite is an aluminosilicate mineral,bearing low density, good volume stability, high refractoriness, excellent high-resistance and aseismatic performance, resistance to chemical attack, anti-creep and so forth.Micro-crystal muscovite in west Sichuan is a infrequent supergiant sedimentary micro-crystal muscovite mineral deposit from home and aboard, which is composed of more than 10 mines. Sedimentary micro-crystal muscovite not only has excellent properties of muscovite group minerals, such as heat resistance, acid and alkali resistance, insulation, high strength, but also has properties of natural ultra–fine, easy processing, high whiteness and high activity, which are superior to the traditional muscovite minerals. So far, study on synthesis of mullite by muscovite, especially by micro-crystal muscovite, is rare. In this paper, we made experiments to make sure whether mullite can be made by calcining of micro-crystal muscovite. And based on this, we can get pure mullite materials by calcining the mixture of micro-crystal muscovite and industrial alumina.In the experiment, producing the mullite materials, the way is as follows: micro-crystal muscovite and industrial alumina as raw materials were mixed for grinding and calcining. We studied the mullitization mechanism of the composition and the change of microscopic structure by scanning electron microscopy (SEM) and X-Ray Diffraction (XRD), and other means. The results indicate:(1) Mullite material can be synthesized by micro-crystal muscovite minerals from west Sichuan at some better temperature of 1500℃and stay warm for three hours. The mullite grains-2^l0μm-of the sample are columnar. During the experiment, in which mullite was synthesized directly by micro-crystal muscovite, quartz in the raw material could not react to form mullite but amorphous substances because of excessive content. But, pure mullite can be made by purifying micro-crystal muscovite minerals.(2) Mullite with high purity can be made by the introduction of industrial alumina to increase the ratio of Al/Si. We calculated the better raw material proportion of micro-crystal muscovite and industrial alumina to synthesize mullite. And the proportion is 1:1.24.(3) Base on a certain proportion of 1:1.24, micro-crystal muscovite and industrial alumina were calcined to synthesize high purity mullite. The better temperature is 1450℃, and holding time is 3 hours. The synthesized mullite grains-columnar, 2⁵μm -of the sample had a good growth.(4) Reaction mechanism: When micro-crystal muscovite as raw materials are calcined directly, a series of physical chemistry changes took place. Micro-crystal muscovite have a dehydroxylation effect and its structure is destroyed and decomposed into corundum Al₂O₃ and SiO₂. Al₂O₃ and SiO₂ had high-temperature reaction and created mullite when it is heated at 1450℃. The further increases of calcination temperature promoted complete reaction of Al₂O₃ and SiO₂, and the growth of mullite. The excess SiO₂ exists in the form of vitreous. Bringing in industrial alumina, when the calcination temperature reaches about 1350℃, the decomposed and the introducted Al₂O₃ reacted to form mullite with SiO₂. With further increases in calcination temperature and the set Al / Si ratio condition, Al₂O₃ and SiO₂ responded fully, mullitization tend to be absolutely, the crystallization of mullite formation are promoted.