High-temperature corrosion of silicon carbide ceramics by coal ashes

New high-efficiency gasification reactors with higher temperatures and pressures and with different temperature cycles than previously require new types of refractory linings. Besides the oxide materials currently in use, SiC ceramics show great promise as refractories in the reducing atmospheres found in gasifiers. The behaviour of RSiC and SSiC materials was investigated in a flowing CO/H2-containing Ar atmosphere with three different ashes (from basic to strongly acidic) in the temperature range between 1000 °C and 1300 °C. After dwell times of up to 100 h the cross sections of the materials were analysed by SEM and EDS. The results showed the high stability of the materials in all ashes. The porous RSiC materials showed small amounts of infiltration depending on the ash composition, but no destruction of the necks between the SiC grains was observed. Thermodynamic calculations simulating the conditions prevailing in a gasification reactor yielded similar phases to those obtained in the corrosive conditions used in the experiments. Due to the strongly reducing conditions the sulphates in the starting ashes reduced to sulphides of much lower corrosion activity