Influence of holding time on microstructures of mullite synthesized by spent FCC equilibrium catalyst

The influence of holding time on microstructures of mullite synthesized by spent FCC equilibrium catalyst were investigated by means of XRD and SEM techniques.The results showed that using spent FCC equilibrium catalyst and commercial Al2O3as the raw materials,mullite synthesized by solid phase reaction at high temperature was mainly Al4.59Si1.41O9.7,and secondary mullitizatioin took place at the temperature 1 450 ℃;the amount of mullite reached 94wt% within holding time 3 h,and mullite crystal exhibited column shapes.When the holding time was more than 4 h,transition metals integrated into the structural vacancy that increased due to the replacement of Si4 +by Al3 +,which resulted in reducing the melting point of mullite.Therefore,the holding time was proportional to liquid phase that bonded with mullite,which lead to decreasing the mechanical performance.The holding time had great influence on microstructures of the secondary mullite.