Characterisation of monophasic and diphasic mullite precursors by solid state reaction study

The characterisation by various spectroscopic techniques of amorphous mullite precursors formed front monophasic (SH) and diphasic (DG) gels is reviewed. In a new approach, both types of precursor have been heated with CaCO3 and the crystalline phases formed during solid state reaction monitored using an X-ray powder diffraction technique. The formation of a calcium aluminosilicate phase (gehlenite) rather than calcium aluminate suggests that both precursors consist of an amorphous aluminosilicate phase of composition close to that of 3:2 mullite.