Effect of surface roughness on medieval-type glass alteration in aqueous medium

Abstract Determination of the glass alteration rate requires the knowledge of the reactive surface area that is a key parameter. Many studies have evaluated this parameter for glass monoliths or powders by using either geometrical or BET surface area, but few have focused on the impact of glass roughness on the reactive surface area and on the global alteration. The roughness can be expected to proportionally increase the reactive surface area and to modify local conditions of alteration. Therefore, the aim of this study is to evaluate the impact of surface roughness and asperities on the alteration of a model medieval-type glass. Experiments were performed in aqueous medium on samples with different initial surface roughness level. The results show that, for an initially smooth surface, the altered layer is continuous and tends to scale, whereas for an initially rough surface, the alteration is heterogeneous in morphology and composition and asperities are highly hollowed. Surprisingly, despite these differences, the quantity of altered glass is relatively similar, which shows that the roughness does not significantly increase the reactive surface area. This is explained by a fast solution saturation in asperities that minimizes their contribution to the global alteration.