High-temperature corrosion of aluminium nitride ceramics by coal ashes

New high-efficiency gasification reactors with higher temperatures and pressures and with changed temperature cycles require new types of refractory linings. Besides the oxide materials currently in use, nonoxide materials such as SiC and AlN ceramics show great promise as refractories in the reducing atmospheres found in gasifiers. One of the main corrosion mechanisms occurring involves the interaction between the lining and the slag. Hence, AlN materials (without additives and with MgO or CaO additives) were tested in basic and acidic coal ashes at temperatures of 900-1300 °C in a tube furnace with an atmosphere containing H2, CO and H2O. After dwell times of up to 200 h the cross sections of the materials were analysed by SEM and EDS. The results showed the high stability of the materials in acidic ashes, but interaction with alkaline and calcium oxides along the grain boundaries in basic ashes.