Homogeneous distribution of mullite in the matrix of alumina can be obtained through sol-gel method. In this work, nanopowder of alumina-mullite composite was synthesized with high homogeneity and high purity. So aluminum chloride hexahydrate and tetraethyl orthosilicate were used instead of alumina or mullite nanopowder. Studying the simultaneouse thermal analysis (STA) of mullite precursor reveals two endothermic peaks at 145 and 240°C due to dehydration and removal of the molecular water and the chloride component. An exothermic peak is also detected at 855°C. According to the XRD patterns of alumina-15vol.% mullite precursors calcined at different temperatures, crystallization of transitional alumina phases (γ, κ) occurs approximately at 800°C. Then these phases transform to α alumina approximately at 1000°C. XRD patterns of alumina-15%vol. mullite which were calcined at different temperatures show peaks of mullite relating to 1000°C. The specific surface area of this nanopowder calcined at 900°C was calculated to be 120.9±0.5 m2/g. The nanopowder was observed by TEM. پرونده مقاله