Corrosion of alumina in aqueous hydrofluoric acid

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