Transmission electron microscopy of leached Na2O·3SiO2 and K2O·3SiO2 glasses showed that the hydrated glass surface is a silica rich gel which phase separates during leaching. Phase separation is initiated when pockets of an aqueous phase nucleate and grow in the hydrated silica matrix. The aqueous pockets eventually become a network of interconnected pores with a pore diameter of ∼30 nm. In advanced stages of leaching, the remaining interconnected silica rich phase resembles an aggregation of colloidal silica particles. The observed phase separation is consistent with literature models concerning the chemistry of silica in aqueous solutions and in leached glass.
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Bunker, B.C., Headley, T.J. & Douglas, S.C. Gel Structures in Leached Alkali Silicate Glass. MRS Online Proceedings Library 32, 41 (1984). https://doi.org/10.1557/PROC-32-41