Influence Of Additives On Mullite Fibers Preparation Process

With the development of science and technology, new materials with special functions which can be used in high temperature oxidizing environment of long-term material has become an important research direction in the field of material. Mullite fiber is an excellent high-temperature inorganic structural materials with high melting point, low density, low thermal conductivity and thermal expansion coefficient, excellent high-temperature creep resistance and thermal shock resistance, oxidation resistance and other properties. Mullite fibers are widely used as high-temperature structural materials and attract more and more attention.In this article, mullite fibers were prepared from aqueous solution of aluminum nitrate, aluminum isopropoxide and tetraethylorthosilicate by sol-gel method based on optimized formulation and process which got from preliminary research. MgO and CuO were introduced in the fibers by adding Mg(NO3)2and Cu(NO3)2. The morphology of mullite fibers were studied using scanning electron microscope. The crystallization mechanism was investigated by integrated thermal analysis, X-ray diffraction, IR spectra.The viscosity of sol increased than that without CuO during concentration, but result was different when adding amount continue to increase. Results showed the viscous flow activation energy increased during concentration, but decreased with an increase amount of CuO. SEM showed the fibers had different degrees of surface cracks, the higher CuO content, the more cracks were. The TGA results showed that CuO had a great impact on the exothermic peak at low temperature area. When3%CuO were added, the peak of Al-Si high temperature spinel phase formation was reached at a temperature of944℃, whereas without CuO at a temperature of970℃Crystallization happened at temperatures between800-900℃and mullite formation at temperatures between800-1100℃with the presence of CuO.Both of the viscosity of the sol and the activation energy of viscous flow increased with an increase amount of MgO. and also increased during concentration. SEM showed the fibers had smooth surface and without obvious defects with a low amount of MgO, but showed different degrees of surface cracks when more MgO was added. TGA analysis showed no significant effect on the exothermic peak at low temperature area, but showed Al-Si spinel phase at a lower temperature compared with no MgO was added. Mullite crystallization temperature decreased from1000℃to900℃with the presence of MgO, and all converted to mullite temperature from1300℃to1100℃.Considering the effect of the additives on morphology of fibers, the spinnability of the sol, the crystallization process, MgO is more appropriate, and1%MgO could get good morphology mullite fibers at low temperature.