Effect of pH on the stability of passivating gel layers formed on International Simple Glass

Abstract : It is known for decades that silica saturated solutions allow borosilicate glass to dissolve much slower than in deionized water. The present study assesses this assertion in the specific case of the International Simple Glass, a 6-oxide borosilicate glass of nuclear interest, which we altered between pH = 1 and 10.7 at 90 DC. Depending on the stage of reaction, aqueous silica can promote either the formation of a passivating gel layer on the glass surface or the precipitation of certain secondary phases at the expense of the passivating gel. We demonstrate a negligible effect of aqueous silica at acidic pH and a marked effect beyond pH$_{90}$ DC = 7, ensuring a better glass chemical durability. At higher reaction progress and above pH$_{90}$ DC = 9.5, this effect becomes negative due to the formation of secondary phases such as hydroxides or zeolites.