Corrosion of selected ceramic materials in hot gas environment

The temperature dependence of the hot gas corrosion behaviour of various ceramic materials (Al(sub 2)O(sub 3), ZrO(sub 2) (Y-TZP), mullite, ZrSiO(sub 4) and YAG) was investigated. The tests were performed in a high temperature burner rig at temperatures between 1200°C and 1500°C, a total pressure of 1atm with a water vapour partial pressure of 0.24atm, a gas flow velocity of 100m/s and test times of about 130-300h. ZrO(sub 2) (Y-TZP) showed absolutely no corrosion, however, a very high susceptibility to thermal shock and phase transformation was observed. The other materials suffered degradation above 1300°C. This was the consequence of the formation and evaporation of volatile hydroxides (e.g. Si(OH)(sub 4) and Al(OH)(sub 3)). YAG showed a low corrosion rate and the formation of a protective surface layer. The corrosion susceptibility of these materials was found to be higher with increasing temperature. Thermochemical calculations of the partial pressure of volatile species formed in reaction with water vapour, affirm the observed differences in corrosion behaviour.