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
, 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.