Ultrafine pure mullite powder (3Al2O3·2SiO2) was prepared by the sol-gel method using silicon tetraethoxide and aluminum nitrate as starting materials. The phase transformation process and the effects of a catalyst on mullite gels were determined by differential thermal analysis (DTA) and X-ray diffraction (XRD). The results show that a pure mullite phase was obtained at 980°C in a nitric acid-catalyzed gel. In an ammonia-catalyzed gel, a pure mullite phase forms at 1200°C, while a spinel appears at 980°C. In an ammonium acetate-catalyzed gel, mullite and α-alumina form at 980°C and the main phase mullite appears at 1200°C. A pure mullite phase was obtained at 1300°C. The mean particle size of the mullite powder obtained from the nitric acid-catalyzed gel is <0.5 μm and its particle size distribution is narrow. Mullite ceramics hot-pressed at 1600°C under 25 MPa for 90 min have a density of 3.168 g/ml, and flexural strength at 1200°C of 280 MPa. © 1992 Elsevier Science Publishers B.V. All rights reserved.
Ge, M., Yang, H., Jiang, Z., Wang, Y., & Zhang, F. (1992). Ultrafine pure mullite powder prepared by sol-gel method. Journal of Non-Crystalline Solids, 147–148(C), 565–568. https://doi.org/10.1016/S0022-3093(05)80677-5