Glass - Back to the Future!

Presenting Author:
Teresa Palomar

article posted 08 Feb 2016

Teresa Palomar is Doctor in Chemistry from the Autonoma University of Madrid, she has focused her research to the corrosion and conservation of inorganic materials from cultural heritage, especially on glass and metal. Currently, she is making a post-doc in the Centro do Vidro e da Cerâmica para as Artes (Lisbon, Portugal).

The role of marine ions in the aqueous alteration of silicate glasses

Teresa Palomar*, Marcia Vilarigues
Depto. de Conservação e Restauro and Research Unit VICARTE-Vidro e Cerâmica para as Artes, Campus de Caparica, FCT-UNL, Quinta da Torre, 2829-516 Caparica, Portugal

The degradation of silicate glasses in natural aquatic mediums has been study along with the archaeometrical characterizations of historical glass objects from shipwrecks. These few works have observed that the degradation rate on a marine synthetic medium depended on the glass composition and the temperature, and that the presence of neutral salts dissolved in pure water can increase the corrosion rate of quartz and durable commercial glasses.

The aim of this work is to study systematically the salt-induced alteration mechanism of soda-lime, potash-lime and lead silicate glasses to determine the specific influence of each ion in the degradation mechanism of silicate glasses. The glass samples were submerged during 100 days in aqueous solutions with NaCl, KCl, CaCl2, MgCl2, and NaBr. The alteration was characterized periodically and at the end of the experiment by Optical Microscopy, Micro-Infrared Spectrometry, Micro-Raman, Scanning Electron Microscopy - Energy Dispersive X-Ray Microanalysis and Atomic Force Microscopy.

The results of this induced alteration proved that the degradation mechanism is directly connected to the cations presented in the aqueous solution and the chemical composition of glass. Solutions with Na+ ion accelerate the alteration rate because it can produce the opening of glass network. Soda lime and lead silicate glasses formed pits, while potash-lime silicate glass, the least durable glass, formed stratified gel layers easily detached.