Decay processes of silicate glasses in river and marine aquatic environments

To characterize the degradation mechanisms of silicate glasses in river and marine aquatic environments, soda-lime silicate, potash-lime silicate and lead silicate glasses were submerged during 300 days in synthetic marine and river solutions. The alteration was characterized through optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive X-ray microanalysis (EDS) and atomic force microscopy (AFM). The results of this induced alteration showed that the degradation mechanism is directly connected to the chemical composition of glass. In soda-lime silicate glasses the degradation proceeds in a two-step mechanism: firstly hydration and fissure development occurs, and secondly fissures grow and pits are formed. Lead silicate glass forms simultaneously pits and a recurrent alteration layer. Potash-lime silicate glasses forms stratified gel layers, which are easily detached. The potash-lime silicate glass was the least durable under aquatic conditions. Samples submerged in simulated marine water were altered faster than those submitted to river water.The authors kindly thank M. Oujja (IQFR-CSIC) and the components of the CERVITRUM Research group (CCHS-CSIC) for their help during the experiments. This work has been partially funded by the Fundação do Ministério de Ciência e Tecnologia de Portugal (Project ref. UID/EAT/00729/2013 and Post-doctoral grant ref. SFRH/BPD/108403/2015) and GEOMATERIALES 2-CM Program Ref. S2013/MIT-2914. Professional support from Techno-Heritage (Network on Science and Technology for the Conservation of Cultural Heritage) is also acknowledged.Peer Reviewe