Influence of calcium oxide and sodium oxide on the microstructure of cordierite catalyst supports

Abstract Cordierite (Corning EX-66 100/25) catalyst support samples, contaminated by Na 2 O and CaO, have been studied in the temperature range 800–1200°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 Ca 2+ ion diffusion rate; additional crystalline phases and microstructures develop at different temperatures. At 1200°C, anorthite, a tectosilicate, forms in the same way as the crystalline phases carnegieite and nepheline form in the case of Na 2 O contamination at 800–1000°C. All these phases have similar composition; their formulae are 2CaO2Al 2 O 3 4SiO 2 and 2Na 2 O2Al 2 O 3 4SiO 2 . For the Na 2 O-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 Na 2 O-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.