Surface Chemistry of Calcium Aluminosilicate Glasses

Abstract

The surface chemistry of synthetic calcium aluminosilicate glasses exposed to aqueous solutions of varying pH was described using zeta potential measurements and batch surface titrations. Element release and proton consumption were measured to characterize the reactions at the surface as a function of pH. It was found that proton-metal exchange or leaching was the dominant proton consumption process at low pH. The exchange reaction was observed to maintain charge balance, indicating that over the limited duration of the experiments no repolymerization of the silica-rich leached layer occurred. At high pH, dissolution and hydrolysis of aqueous ions controlled the proton mass balance, no evidence for the formation of leached layers was found. Silica-rich glasses were found to be more resistant to corrosion by either proton-metal exchange or dissolution than CaO-rich glasses. Glass basicity was found to be reflected in the establishment of a higher pH when immersing the glass in neutral aqueous solutions and in a reduced stability of the glass surface toward aqueous solutions. High pH, high surface charge and reduced glass network polymerization act together in enhancing the reaction of CaO-rich glasses with aqueous solutions.G. Scherer-contributing editor Manuscript No. 35263.

Effect of calcium on dissolution and precipitation reactions of amorphous silica at high alkalinity

“…Oka et al [36,37] reported an inhibitory effect of Ca, Zn and Al on corrosion rate of fused silica glass in 0.5 M and 1.5 M NaOH solutions, and attributed this to formation of a protective barrier layer. Snellings [10,34] studied dissolution of synthetic CaAl-Si glasses at 20°C and pH ≈ 13, and confirmed that Ca in the solution can significantly reduce the initial rate of glass corrosion. By studying borosilicate and nuclear glasses, Chave et al [31] reported that the passivating properties of PRI are enhanced when it contains calcium (originating either from the glass or the solution).…”

“…(1) [9]. Leaching becomes significant at lower (acidic) pH, and increases the pH of the solution [9][10][11].…”

Fly ash as an assemblage of model Ca–Mg–Na-aluminosilicate glasses

“…A significant reduction in dissolution speed above 90 μmol(Si)/L might indeed be associated with precipitation. Other factors behind the non-linear trends may include incongruent glass dissolution and protective layer formation, but these have been shown to be uncommon under alkaline conditions [15].…”

Alkali-activated slag cements produced with a blended sodium carbonate/sodium silicate activator

“…However, recent studies (Snellings, 2015;Snellings et al, 2014) evaluating the surface characteristics of synthetic glasses within the system Alkali-activated slag cements produced with a blended sodium carbonate/sodium silicate activator Bernal, San Nicolas, van Deventer and Provis Offprint provided courtesy of www.icevirtuallibrary.com Author copy for personal use, not for distribution CaO-Al 2 O 3 -MgO-SiO 2 demonstrated that these glasses dissolve congruently in alkaline media (pH above 11), independent of the content of magnesium oxide. The partial substitution of sodium carbonate by sodium silicate promoted a higher alkalinity (activator pH = 13·1) than is achievable in a sodium-carbonate-activating solution, and therefore congruent dissolution of the slag is more plausible in the system studied here.…”