Localised extended (“vermiform”) features formed during glass dissolution

Studies on glass durability are important to our understanding of the likely long term behaviour of vitrified nuclear wastes, natural and archaeological glasses; there has, however, been little in the way of systematic reporting of features associated with localised chemical attack on such glasses. Durability experiments performed in water at 90 °C from 28 d to 672 d on glass monoliths of 5 different compositions: 3 basaltic compositions; an inactive version of the 25 wt% loaded UK mixture Windscale (MW25) glass and the International Simple Glass (ISG) all yielded locally extended or vermiform alteration features. Similar features are seen on all glasses at all dissolution times studied. The number of features and whether they were filled by alteration products or not was dependant on glass composition. The majority of features have quite simple geometries but lesser numbers of more complex morphologies are seen. The location of these features is thought to be most probably linked to residual damage arising from the monolith production providing sites for locally accelerated dissolution. Despite being sites of localised accelerated dissolution the impact of these features on the total surface area is calculated to be limited. Hence the surface area term used to calculate normalised mass losses and normalised loss rates will not be greatly in error as a result of these features.