Journal Spherical Mullite Particles Prepared by Hydrolysis of Aerosols

Nonhollow spherical particles were prepared by hydrolysis of liquid aerosols consisting of mixtures of silicon methoxide and aluminum sec‐butoxide. In order to obtain particles with mullite composition, some chloroform had to be added to the alkoxides mixture. TEM microanalyses carried out in single particles revealed a rather narrow distribution in composition around the mullite nominal value. The particles, as prepared, were amorphous. Their thermal evolution was studied by thermal analyses, X‐ray diffraction, and infrared and 27 A1, 29 Si NMR spectroscopies. Crystallization of pseudo‐tetragonal mullite was detected at 950°C, suggesting a high degree of Al‐Si mixing in the original particles. At the same time, some silica segregation was also observed. Between 1200°‐1400°C, the pseudo‐tetragonal/ orthorhombic mullite transformation took place, accompanied by the incorporation of segregated silica into the originally formed mullite.