Improvement of the chemical resistance of zirconium fluoride glasses coated with a Tiron Ò modified tin oxide layer prepared by the sol–gel process P. Hammer * , A.P. Rizzato, C.V. Santilli, S.H. Pulcinelli Instituto de Quı ´mica/UNESP, P.O. Box 355, CEP 14801-970, Araraquara, SP, Brazil Available online 24 July 2006 Abstract In order to improve the chemical resistance of zirconium fluoride glass a protective transparent SnO 2 layer was deposited by the sol– gel dip-coating process in the presence of Tiron Ò as particle surface modifier agent. After water immersion for different periods of time, both coated and non-coated fluoride glasses were analyzed by scanning electron microscopy, mass loss evaluation, infrared spectroscopy and X-ray photoelectron spectroscopy. In contrast to the effects occurring for non-coated glass, where the surface undergoes a rapid selective dissolution of the most soluble species, the results for the SnO 2 -coated glass showed that the filling of the film nanopores by dissolved glass material results in a hermetic barrier protecting the glass surface. The selective glass dissolution was confirmed by liquid chromatography measurements of the etching solution after each exposure time. Ó 2006 Elsevier B.V. All rights reserved. PACS: 79.60.Ài; 61.43.Fs; 68.35.Àp; 68.55.Àa Keywords: Chemical durability; Corrosion; Flims and coatings; Infrared glasses; Fluorides; Scanning electron microscopy; Nanoparticles; FTIR meas- urements; Tin oxide; XPS 1. Introduction Tin oxide films exhibit a combination of unique charac- teristics, such as high conductivity, high optical transmit- tance, excellent adhesion to glass substrates, and chemical and thermal stability. For this reason SnO 2 is widely used in anti-static coatings, sensors and transparent electrical contacts in solar cells and flat panel liquid crystal displays [1,2]. Another important application is its use as transpar- ent corrosion resistant coating [1]. To satisfy the demand for these applications a growing effort has been made to synthesize SnO 2 films by the sol–gel route combined with the dip-coating process, representing an easy, low cost and efficient route for coating surfaces with complex shapes and large areas [3]. The sol–gel process is considered as the coating method of choice especially in the case of materials with low glass transition temperature, like heavy-metal fluoride glasses [4], where spray pyrolysis or plasma pro- cesses are inadequate due to the high processing tempera- ture (>400 °C). In this family, the fluorozirconate glasses (ZBLAN) are very interesting for applications such as infrared windows, optical fibers, sensors, waveguides and lasers [4]. This is due to their high optical transmittance (>90%) in the visible and infrared spectral region between 0.3 and 6 lm. The main obstacle, however, for the commer- cial exploitation of ZBLAN is the rapid surface degrada- tion upon exposure to aqueous media or humid atmospheric environments. The reasons for the high chem- ical reactivity are the weak bonding and the low lattice energy of the material. It is well-known that the water driven surface degrada- tion of ZBLAN glass is caused by a leaching process which 0022-3093/$ - see front matter Ó 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.jnoncrysol.2006.03.098 * Corresponding author. Tel.: +55 16 33016644; fax: +55 16 33227932. E-mail address: peter@iq.unesp.br (P. Hammer). www.elsevier.com/locate/jnoncrysol Journal of Non-Crystalline Solids 352 (2006) 3653–3658