SEM-EDS, EPMA and MRS analysis of neo-crystallisations on weathered glasses

When a glass is exposed to the atmosphere the combined action of water and environmental elements leads to the weathering of the glass surface. Both the chemical composition of the glass and the environmental parameters influence the mechanism of glass weathering mainly consisting in the formation of a layer of hydrated leached glass and salt deposits. The study of these phenomena is very important for both industrial and cultural heritage applications. In order to study the weathering mechanism of glasses exposed outdoor the chemical composition of the glass and the chemical and mineralogical nature of the reaction products should be determined. X-ray micro-analytical techniques such as scanning electron microscopy and X-ray microanalysis (SEM-EDS) and electron probe microanalysis (WD-EPMA) are traditionally employed in this type of investigation. Nevertheless particular compounds are hardly detected with this technique (for ex. nitrates) and no direct information can be obtained on the mineralogical features of the reaction products. Moreover, X-ray diffractometry (XRD) cannot be successfully used because of the very low amounts of deposited material. This work reports the results of a combined complementary X-ray fluorescence spectrometry (WD-XRF), SEM-EDS, WD-EPMA and μ-Raman spectroscopy (MRS) investigation on the surfaces of an industrial float glass and a glass reproducing the low-durable glass of ancient stained windows exposed sheltered outdoor for 6 months. The investigation enabled the identification and characterisation of different reaction products (soluble salts) confirming the need of this analytical approach for the study of the glass weathering process.