Mullite Formation of Colloidal Matrix Hybrid Aluminosilicate Gel

A hybrid aluminosilicate gel composed of a relatively small amount of single-phase gel in a diphasic matrix forms when a diphasic gel of AlOOH and SiO2 is heated at 700°C for 7 h. The formation of mullite from this hybrid gel is a sequential conversion process, but not of two entirely independent processes of single-phase gel and diphasic gel. The high commencement temperature (>1250°C) of mullite formation from this hybrid gel indicates that the dominant component (diphasic component) strongly affects or controls the mullite transformation behavior of the hybrid gel. The apparent activation energy for mullitization from this hybrid gel is 846 kJ/mol, which is somewhat lower than that of pure diphasic gel but much higher than that of pure single-phase gel.