Sol–gel deposition of silica ﬁlms on silicate glasses: Inﬂuence of the presence of lead in the glass or in precursor solutions Renzo Bertoncello a,b, * , Laura Milanese a,b , Jean Claude Dran c , Anne Bouquillon c , Cinzia Sada d a Dipartimento di Scienze Chimiche, Universita ` di Padova, via Loredan 4, 35131 Padova, Italy b Consorzio Interuniversitario Nazionale per la Scienza e Tecnologia dei Materiali (INSTM), via Varchi 59, 50132 Firenze, Italy c Centre de Recherche et de Restauration des Muse ´es de France (CRRMF) CNRS UMR 171, 6, rue des Pyramides, 75041 Paris, France d Dipartimento di Fisica ‘Galileo Galilei’, Universita ` di Padova, via Marzolo 8, 35131 Padova, Italy Received 26 April 2005; received in revised form 25 November 2005 Available online 10 January 2006 Abstract Many lead silicate historical glasses suﬀer degradation phenomena often observed as color changes and iridescence caused by lead ions leaching from the outer layers of the glass. In order to repair and to prevent these phenomena, glasses with large amounts of lead (6.7 and 14.3 at.% of lead) have been coated with silica ﬁlms at neutral pH by dipping them in a precursor solution of TEOS (tetraethyl orthosilicate), ethyl alcohol and deionized water without any other acid or basic catalyst. Experiments with long dipping times (24 h) and temperatures around 20 °C have been performed to evaluate the role of lead ions of the glass as a catalyst. Silica ﬁlms of very good qual- ity and optical transparency have been also obtained on lead-free, soda-lime glasses by adding catalytic amounts of Pb(NO 3 ) 2 instead of HCl to the precursor solution. The ﬁlms have been characterized by optical microscopy, AFM (Atomic Force Microscopy), XPS (X-ray Photoelectron Spectroscopy) and SIMS (Secondary Ion Mass Spectrometry). Ó 2005 Elsevier B.V. All rights reserved. PACS: 81.20.Fw; 79.60.i; 82.80.Ms; 68.37.Ps Keywords: Catalysis; UPS/XPS; Films and Coatings; Atomic force and scanning tunneling microscopy; Silica; Sol–gel, aerogel and solution chemistry; Surfaces and interfaces; XPS 1. Introduction To protect historical soda-lime and potassium–magne- sium silicate glasses from degradation phenomena, recently room temperature sol–gel coatings of silica ﬁlms have been successfully adopted [1,2]. A standard acid catalyzed solu- tion of tetraethyl orthosilicate [Si(OC 2 H 5 ) 4 ] (TEOS) in ethyl alcohol and deionized water has been used [1,3]. This approach however proved to be inapplicable to lead silicate glasses, due to color changes and iridescence formation at the surface even when an undamaged lead silicate glass is immersed in an acid solution. The large charge-to-radius ratio of lead ions [4], is responsible for their large mobility in the glass network. When immersed in an acid solution the lead ions of the glass are favored to exchange with pro- tons; as a consequence a considerable migration of lead ions toward the solution can be observed. So, as described in the literature [5,6] and conﬁrmed in our laboratory, in an acid environment, a leached surface layer, up to several hundreds of nanometers thick, depleted in lead and alka- line ions, is formed on lead silicate glasses. Analogously, the presence of hydrochloric acid as a cat- alyst in a sol–gel solution (measured acidity: pH  2) results in a high ﬂux of lead ions from a lead silicate glass when dipped in the solution. It has been measured that 0022-3093/$ - see front matter Ó 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.jnoncrysol.2005.12.005 * Corresponding author. Address: Dipartimento di Scienze Chimiche, Universita ` di Padova, via Loredan 4, 35131 Padova, Italy. Tel.: +39 049 8275204; fax: +39 049 8275161. E-mail address: renzo.bertoncello@unipd.it (R. Bertoncello). www.elsevier.com/locate/jnoncrysol Journal of Non-Crystalline Solids 352 (2006) 315–321