Long term weathering rate of stained glass windows using H and O isotopes
The understanding of glass alteration is a biogeochemical, industrial, societal (radioactive waste confinement) and cultural heritage issue. Studies have been mainly performed in aqueous conditions. However, glass reactivity under hydraulically unsaturated conditions may be more important than previously recognized. In this context, we evaluate here the role of the alteration layer formed on medieval stained glass windows on the ongoing alteration in unsaturated conditions. H2O adsorption isotherms were measured to study the relation between the vapor sorption and the relative humidity inside the alteration layer. From it, the average pore radius was calculated, yielding a water vapor diffusion coefficient of 7.8 x 10 7 m2 s 1 inside the pore network. Experiments using doped water vapor (D218O) confirm the vapor transport up to the alteration front via fractures and pore network. They also demonstrate that the alteration mainly progresses via an interdiffusion mechanism. The calculated interdiffusion coefficients at 20 degC are 3.6 x 10 20 m2 s 1 at 70% RH and 4.9 x 10 20 m2 s 1 at 90% RH, which is similar to the values measured on model stained glass samples altered in short durations (1 4 years) Therefore, this study highlights that, given its morphology, the alteration layer is not protective against vapor transport and interdiffusion.Glass alteration: Understanding unsaturated conditionsIsotopic studies of the glass from stained glass windows have determined the effects of water vapor on their weathering. Understanding how glasses react to their environment over time is important in contexts such as nuclear waste storage and artifact conservation. They are known to form an amorphous 'gel' layer on their surface and many studies aimed at improving its understanding are carried out in aqueous solution, however, stained glass windows are exposed to alternating saturated and unsaturated conditions, characterized by liquid water and water vapor respectively. Now a team of scientists based in France, led by Loryelle Sessegolo of the Universite Paris Est Creteil and Universite Paris Diderot, have studied how the gel layer present on the stained glass windows affects its on going alteration in unsaturated conditions; they find that the layer is not protective against vapor transport or interdiffusion.
npj Materials Degradation