Leaching studies on naturally weathered potash-lime–silica glasses M. Melcher * , M. Schreiner Institute of Science and Technology in Art, Academy of Fine Arts, Schillerplatz 3, 1010 Vienna, Austria Institute of Chemical Technologies and Analytics, Getreidemarkt 9/164, 1060 Vienna, Austria Received 27 May 2005; received in revised form 28 December 2005 Available online 9 March 2006 Abstract Within the international, EU-supported research project MULTI-ASSESS more than 150 glass samples with a chemical composition similar to medieval stained glasses were exposed in six European cities (Athens, Krakow, London, Prague, Rome and Riga) to the local environmental and climatic conditions. After exposure periods of 6 or 12 months the samples were investigated in the scanning electron microscope with energy dispersive X-ray microanalysis (SEM/EDX). Surface analyses indicate that the main weathering products were sulphates such as syngenite (CaSO 4 Æ K 2 SO 4 Æ H 2 O) and gypsum (CaSO 4 Æ 2H 2 O). Chlorides, organic compounds and/or carbonates or nitrates of the elements K, Ca and Na were predominantly detected on the 6-months samples, whereas Si-containing compounds appeared particularly on the 12-months samples. Linescan measurements performed on the cross-sectioned glass samples allowed for the determination of leaching depths of the network modifier ions according to an evaluation procedure recently presented. The average leaching depths after 6 months of exposure were d(K) = 0.88 ± 0.43 lm, d(Ca) = 0.62 ± 0.37 lm, d(Na) = 0.34 ± 0.32 lm and d(Mg) = 0.16 ± 0.18 lm. After 12 months an average increase of the leaching depths between 38% (K) and 63% (Mg) is observed. No leaching could be determined for the network former elements Al and P. A clear influence of the environmental conditions at the atmospheric test sites on the degree of weathering was observed. In a first approximation, the leaching depths exhibit a linear dependence on a general pollution factor comprising the concentrations of the acidifying gases SO 2 , NO 2 and O 3 . Ó 2006 Elsevier B.V. All rights reserved. PACS: 81.65.K; 68.35.B Keywords: Chemical durability; Ion exchange; Silicates; Surfaces and interfaces 1. Introduction Glasses are known to be attacked by various chemicals in a two-stage process: at first, an ion-exchange between the network modifier ions in the glass (Na + ,K + , Ca 2+ and Mg 2+ ) and H + ,H 3 O + and/or H 2 O species from the solution can be observed, which is displayed for a mono- and bivalent network modifier in Eqs. (1) and (2). The ions are diffusing in opposite directions, leading to the forma- tion of a so-called leached or gel layer in the glass, which is depleted in alkali and alkaline earth elements and enriched in hydrogen bearing species [1–5]. The ratio c(M)/c(Si) measured in the solution is significantly higher than in the bulk glass, indicating a selective (preferential) leaching of the modifiers M. Hence, the effective surface area of the glass exposed to the attacking medium is increased as micro-pores are produced by the leaching pro- cess, which may cause an accelerated rate of glass dissolu- tion. Moreover, the pH of the solution increases, as hydroxyl ions remain in the solution [6]. ð1Þ ð2Þ 0022-3093/$ - see front matter Ó 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.jnoncrysol.2006.01.017 * Corresponding author. Address: Institute of Science and Technology in Art, Academy of Fine Arts, Schillerplatz 3, 1010 Vienna, Austria. Tel.: +43 1 58816 203; fax: +43 1 58816 121. E-mail address: michael.melcher@akbild.ac.at (M. Melcher). www.elsevier.com/locate/jnoncrysol Journal of Non-Crystalline Solids 352 (2006) 368–379