Reaction study of various mixtures of tetra ethyl ortho silicate and aluminum nitrate

Several studies on the formation of amorphous aluminosilicate phase during heating slow hydrolysis (SH) or Type 1 mullite gel prior to formation of 2:1 mullite is briefly reviewed. Tetra ethyl ortho silicate (TEOS) and aluminum nitrate nonahydrate (ANN) are isothermally heated on water bath at 80 C. It has been shown that these react in an exothermic manner. The resultant isothermally heated gel (ISG) removes organics, moisture on heating and forms alumino silicate (A) precursor phase. Among the various mixtures of the two components, the batch composition corresponds to Al/Si ratio of 3/1 generates highest evolution of heat which suggests that precursor analogous to the composition of 3:2 mullite is most stable. Slow hydrolysis gels of different Al2O3:SiO2 ratios synthesized out of similar sources exhibit 980 C exotherm on DTA analysis which is a function of Al2O3 content. The highest exotherm is observed for the gel/ precursor analogous to the same composition of the batch synthesized above by isothermal condition. Corroborating heat evolution behavior of ISG gels with DTA analysis of SH gels, it is suggested that the various compositions of intermediate aluminosilicate (A) phase may form. The composition corresponds to 3:2 mullite may be most stable.