Studies On The Synthesis Of High-purity Mullite

This paper studied on the utilizing soft burning kaolin in coal , high pure quartzte and industral alumina as main raw material to synthesize high-purity mullite. And the different additives were prepared, such as ZnO and zircon( ZrSiO₄ )etc , in order to increase the mullite phase content and volume density of the sample. This paper analysesed the factors of influence synthesis of mullite, such as purity and fineness of raw material, Al₂O₃/SiO₂ ratio, the kind of raw material and firing temperature and soaking time etc. The bulk density was measured. The minerial phase was characterized by X-ray diffraction (XRD) and the microstructure was observed by scanning electron microsocope (SEM). The mullite phase content of the sample was calculated by K calculating.The results show that: both utilizing the soft burning kaolin in coal and industral alumina as main raw material, and utilizing the high pure quartzte and industral alumina as raw material can synthesize the mullite which seems white. And the mullite phase content of the former sample is higher than the latter. If only using the soft burning kaolin in coal and industral alumina as main raw synthesize mullite, the mullite phase content of the sample which the alumina is 68% and 72% is higher than other samples. But the sample which alumina content is 72% was observed some corundum phase. The ZnO is densification sintering and increase the mullite phase. The optimum of the ZnO is 1%. The zircon influences the bulk density effectively. The opimum amount is≤ 3%.The glass phase was observed in the sample which content more than 3% zircon. So the bulk density of this sample is reducing. The two steps sintering is densification sintering, increase the mullite phase and enhance the bulk density. The sample of utilizing the soft burning kaolin in coal and industral alumina as main raw material and added 1%ZnO,1% ZrSiO₄,after two steps sintering in oxidation atmosphere ,the contentof mullite phase is 97%, and the bulk density reaches to 2.89 g ? cm"3.The bauxite ore has been used for the production of sintered bauxite. The high iron and calcium in the bauxite were decreased to low levels by hydrochloric acid leaching. Temperature and acid concentration significantly affected the level of iron extraction from bauxite. The aluminum dissolution during acid leaching at 6M and below 60°C was ^ 2%, iron and calcium dissolution was over 95%, and almost all of alkali. The surface of leaded bauxite sintered at 1320°C is white.