COMPOSITIONAL EFFECTS IN THE DISSOLUTION OF MULTICOMPONENT SILICATE-GLASSES IN AQUEOUS HF SOLUTIONS

The dissolution rate of multicomponent silicate glasses in a 2.9 M aqueous HF solution is investigated as a function of its composition. The glasses studied are composed of SiO2, B2O3, Al2O3, CaO, MgO, ZnO, Na2O and K2O, covering the compositions of most of the technologically important glasses. Unlike many physical properties, no linear relations are observed between the composition of the glass and its dissolution rate. The dissolution rate of a multicomponent silicate glass is found to be largely determined by two factors: The degree of linkage or connectivity of the silicate network and the concentration of SiO2 in the glass. It is proposed that the dissolution of the glasses is preceded by the leaching of alkali and alkaline earth components present in the glass, followed by the subsequent dissolution of the leached layer. Probably fluorine species will diffuse into the leached layer to enhance the dissolution rate. Analysis of the activation energy data indicates that in some corrosive glasses the leaching itself becomes rate determining.