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Wednesday, 18 September 2019
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Raw materials & technologies, Applications, Protective & Marine coatings

Sol-gel coatings: shelter for historical window glass

Tuesday, 18 June 2013

Medieval glass is commonly attacked by atmospheric pollutants conveyed by water, triggering the corrosion process. Current conservation strategies aim to maintain window glass in its original context, and so it is necessary to protect it from further degradation. Italian scientists have recently developed hybrid coatings meeting the requirements for the conservation of Cultural Heritage.

Sol-gel coatings meet the requirements for the conservation of historical glass / Source: Fotolia

Sol-gel coatings meet the requirements for the conservation of historical glass / Source: Fotolia

Sol-gel technology is very effective for the preparation of protective films, using Si-alkoxide precursors chemically similar to the substrate. This study discusses water-repellent hybrid sol-gel coatings made from tetra-ethyl-ortho-silicate with different quantities of Si-alkoxides, functionalised with various alkyl groups. The coatings were deposited using the dip-coating technique and characterised by UV-VIS and FTIR spectroscopy. Static and dynamic contact angle measurements showed an overall homogeneity of the coatings and indicated improved water-repellency when functionalised by long alkyl chains.

Tests and results

The coatings with best performance in terms of transparency and contact angle, and with the lowest organic content, were selected and applied to medieval-like glass samples. Colorimetric characterisation was carried out using a spectrophotometric scanner before and after application of the coatings and no significant colour changes were found.

The electron microscopy images revealed relatively even, crack-free coatings, especially with higher organic contents. Contact angle and colorimetric measurements were repeated after accelerated ageing by exposure to UV light and an SO2-saturated atmosphere.

A significant decrease in the contact angle was observed only for the samples treated at the highest SO2concentration. The silica-based materials did not give reaction by-products, were water-repellent, compatible with the substrate, colourless, transparent and stable under exposure to chemicals and light, thereby satisfying the main requirements for the conservation of Cultural Heritage.

The complete article "Hybrid sol-gel based coatings for the protection of historical window glass” appeared in Journal of Sol-Gel Science and Technology, volume 66, 2013, issue 2, pp. 253-263.

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