Investigation of the role of Mg and Ca in the structure and durability of aluminoborosilicate glass

The structure and dissolution behaviour of Na2O∙CaO∙(15–x)Al2O3∙xB2O3∙SiO2 and Na2O∙MgO∙(15–x)Al2O3∙xB2O3∙SiO2 glasses, relevant to compositions of UK nuclear waste glass, have been investigated using nuclear magnetic resonance (NMR) spectroscopy and static dissolution experiments using the PCT protocol. Structural data from 11B, 27Al and 29Si NMR analyses show that increasing the Increasing the [B2O3]/([Al2O3]+[B2O3]) ratio of the alkali-alkaline-earth aluminoborosilicate glasses led to an overall decrease in the proportion of non-silicate tetrahedral species (IVAl + IVB) and a decrease in Si – O – X bonds (X = B, Al). The Mg-containing glasses exhibited lower IVB fractions than their Ca-containing counterparts, which is thought to be due to the presence of IVMg tetrahedra in the network. The measured corrosion rates were similar for both Ca and Mg-containing glasses although unexpectedly some Ca-containing glasses exhibited higher corrosion losses than the Mg-containing ones for time periods up to 112 d. However, there was evidence of a greater tendency to rate resumption in the Mg containing than the Ca containing ones. Alteration products were found to contain Ca, Si and Al with the Ca containing glasses and Ca, Mg, Si and Al with the Mg containing glasses; Na was not detected in the alteration products although its presence cannot be ruled out based on the data obtained.