Corrosion of alumina in aqueous hydrofluoric acid

A variety of alumina-based ceramics were evaluated for dissolution in an azeotropic aqueous hydrofluoric acid test protocol at temperatures up to 200 degrees C. Weight change measurements and microstructure analysis showed that HF corrosion in polycrystalline aluminas generally occurred at grain boundaries by the dissolution of silicate-based, glass grain boundary films that segregate to grain boundaries. These materials often have useful service lifetimes even though thermodynamic calculations indicate high solubilities. It is proposed that corrosion rates are controlled by chemical reactions at the solid/liquid interface, the physical structure of the solid, and microstructure, The addition of MgO to alumina greatly increased corrosion resistance by removing silicate-based glassy grain boundary films.