Hot corrosion of cordierite/mullite composites by Na-salts

Cordierite/mullite (C/M) ceramic composites were corroded by NaCl and Na2SO4 at 1000 °C for 24 h. The predominant corrosion products in attack by the Na-salts were found to be nepheline and carnegieite for the cordierite and mullite component, respectively. NaCl attacked both components with different corrosion rates, producing corrosion layers consisting of two distinct regions where both cordierite and mullite were chemically attacked near the surface region and only the cordierite phase was damaged in the succeeding inner part. In the hot corrosion by Na2SO4, on the other hand, only the cordierite component was severely attacked in the composites, resulting in occurrence of selective corrosion. Thus, the corrosion of the C/M composites by the Na-salts proceeded through the path of the less resistive cordierite component at 1000 °C in air.