Pattern Formation in Silicate Glass Corrosion Zones

Abstract

Alteration zones of archeological glasses often show intriguing lamellar patterns in backscattered electron images. Here, we report results of static glass corrosion experiments with two different silicate glasses that revealed laminar porosity and subordinately chemical patterns inside silica-based corrosion zones that resemble those seen in naturally altered, ancient glasses. Aside from common laminar patterns, more complex patterns were observed in corrosion zones that developed along a fracture network. The formation of such patterns cannot be explained by any of the existing glass corrosion models. We suggest that silica-based corrosion zones form by a process that involves the congruent dissolution of the glass network, which is spatially and temporally coupled to the deposition of amorphous silica at an inwardly moving reaction interface. The patterns likely form in response to fluctuations of the pH and salinity in the interfacial solution, which govern the silica solubility, deposition, and dissolution rate, and thus, its microstructure and porosity, and, in turn, are controlled by the dissolution rate of the glass and the transport properties of the silica reaction layers. However, the exact feedback mechanism producing pH fluctuations in the interfacial solution has not yet been identified and is an open question for future research.

The mechanism of borosilicate glass corrosion revisited

“…1), the presence of which is commonly observed in similar experiments (e.g., Bunker et al, 1986;Casey and Bunker, 1990;Jégou et al, 2000;Donzel et al 2003;Dohmen et al, 2014). Experiments with glass "M", reacted in isotopically unlabelled milliQ water (18.2 MΩ·cm at 25 °C) at 90°C, contained etch pits after 1 hour (Fig.…”

Corrosion of the International Simple Glass under acidic to hyperalkaline conditions

“…Geisler and co-workers have suggested that banding in the alteration layers on the surface of glass can be explained by a self-organisation process involving coupled dissolution-reprecipitation on the surface of glass. 39,40 They argue that the underlying glass dissolution is congruent throughout, but that after the initial stage of dissolution, a silica gel layer develops and as this ripens, glass dissolution continues at the interface behind a silica gel layer. This model suggests that local compositional and pH changes occur in the pore solution that is present between the silica gel layer and the glass surface, and that diffusion of the species from the pore solution to the bulk solution is limited by the silica gel layer.…”

Long-term alteration of basaltic glass: Mechanisms and rates

“…from the layers considered to be protective, and becomes a driving force that sustains glass dissolution. Another approach has been proposed these last years to revisit glass dissolution mechanisms (Geisler et al, 2010;Hellmann et al, 2012;Dohmen et al, 2013): the key processes are the congruent dissolution of the glass whatever the reaction progress and the leaching conditions and the in situ precipitation of the less soluble elements at the reaction front to form alteration products (gel, crystalline phases).…”