Influence of Calcium-oxide and Sodium-oxide On the Microstructure of Cordierite Catalyst Supports

Abstract

Cordierite (Coming EX-66 100/25) catalyst support samples, contaminated by Na2O and CaO, have been studied in the temperature range 800-1200-degrees-C by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The experimental results suggest that in CaO-contaminated samples the behaviour is strongly influenced by the Ca2+ ion diffusion rate; additional crystalline phases and microstructures develop at different temperatures. At 1200-degrees-C, anorthite, a tectosilicate, forms in the same way as the crystalline phases carnegieite and nepheline form in the case of Na2O contamination at 800-1000-degrees-C. All these phases have similar composition; their formulae are 2CaO-2Al2O3-4SiO2 and 2Na2O-2Al2O3-4SiO2. For the Na2O-contaminated samples, the formation of a high-temperature liquid phase can explain the presence of the observed glassy phase. In earlier studies of CaO- and Na2O-contaminated samples, mechanical properties were obtained by four-point bending (modulus of rupture); these data can be correlated with the results obtained in the present investigation