Thermal stability studies of zeolites A and X synthesized from South African coal fly ash

The thermal stability of zeolites A and X synthesized from coal fly ash was studied by evaluation of TGA-DTA curves obtained on increasing the temperature and by in-situ temperature-programmed XRD analysis. It was found that zeolites A and X were both stable up to approximately 800 A degrees C and retained their characteristic diffraction peaks up to 440 A degrees C, meaning the crystal structure was still stable. Of particular interest was that zeolite X, which has a unique hierarchical morphology, was thermally stable and was, hence, suitable for applications requiring elevated temperatures, for example catalysis and pollution control.