Abstract
The corrosion behavior of mullite ceramics prepared from various starting powders in water was studied by the autoclave method at 300°C and 8.6MPa for times up to 10 days. The degradation of bending strength due to corrosion was also examined for selected specimens. The aqueous corrosion proceeded according to the reaction 3Al2O3⋅2SiO2+3H2O→6AlOOH+2SiO2 with weight loss by dissolution of SiO2 and formation of boehmite (AlOOH) residue layer. The extent of corrosion resistance was significantly dependent on the powder preparation method and chemical composition. Seventy four wt% Al2O3-mullite prepared from an alkoxide-derived powder showed the highest corrosion resistance. On the other hand, 75wt% Al2O3-mullite prepared from a sol-gel powder showed the lowest corrosion resistance under the experimental conditions studied. Mullite ceramics with high-corrosion resistance was found to be attained by homogeneous mixing SiO2 with Al2O3 in an alkoxide-derived or coprecipitation powder. The bending strength of the corroded specimens reduced to around 2/3 of the original values in the early stage of corrosion, and then remained almost constant up to 10 days. An understanding of this sort of corrosion behavior is important and useful for improvement of mullite ceramics.
