Mixed reactions: Glass durability and the mixed‐alkali effect

Abstract

Multiple‐component oxide silicate glasses possess a complex network backbone, which results in manifolded composition property relationships. The relation between the chemical composition and durability of silicate glasses is not linear, however, this relation has always been considered somewhat relevant. Several contradicting observations on the mixed‐alkali effect and its relation with their chemical alteration have been reported. Here, laboratory results and historical evidence show that the often good state of preservation of aged mixed modifier glasses is in good agreement with the influence of a mixed‐modifier cation effect (MMCE) such as had been observed for other mobility‐ and bulk‐related properties. This concordance supports the proposals made through this work concerning pore closure and lower diffusivity of mobile species under the MMCE.

Towards designing reactive glasses for alkali activation: Understanding the origins of alkaline reactivity of Na-Mg aluminosilicate glasses

“…The alkaline reactivity of the glasses studied in this work specifically concerns how chemical durability (higher chemical durability implies lower alkaline reactivity) was influenced when one network modifier was substituted for another while keeping the equivalent network modifier content the same. The substitution of network modifier in silicate glasses is known to cause non-linear variation of many physical properties, and this has been attributed to what is known as the mixed-modifier cation effect (MMCE) [ 68 ]. There have been controversial observations in the studies of the influence of MMCE on the chemical durability of silicate glasses.…”

The technology, trade, and degradation pathologies of late bronze age vitreous materials in the Eastern Mediterranean

“…However, the mixed-alkali sample had thicker corrosion (500 μm) than the natron glasses (>200 μm) (Silvestri et al 2005(Silvestri et al , 1345. The experimental glasses created by Rodrigues et al (2019) and the mixed-alkali archaeological glass analyzed by Silvestri et al (2005) did contain more potash and less soda than the mixed alkali glasses tested by Hench and Clark (1978). This is likely the reason why more corrosion was seen in these glasses as opposed to what Hench and Clark (1978) report in their experimental samples.…”

“…Mixed alkali glasses that contain both soda and potash have been found to be more durable than if the glass was made with just one alkali (Hench and Clark 1978;Rodrigues et al 2019). The combination of alkalis creates a "mixed alkali effect" that reduces the amount of leaching (Hench and Clark 1978, 96).…”

“…The combination of alkalis creates a "mixed alkali effect" that reduces the amount of leaching (Hench and Clark 1978, 96). Studies of mixed alkali glasses have found that the combination of alkali can reduce the mobility of the alkali cations within the glass structure when exposed to water resulting in slower dealkalization (Rodrigues et al 2019). Hench and Clark (1978) found that in experimental mixed alkali glasses with about 12% soda and 3% potash, there was less diffusion of ions.…”

“…Iridescence, discoloration, and the formation of laminae are observed on some mixed-alkali glasses. The changes to the surface have been considered minor or just occurring in very thin surface layers (Rodrigues et al 2019). SEM imaging of 2nd-14th c. AD mixed alkali and natron archaeological glasses from Vincenza, Italy, demonstrated that both sets of glasses were iridescent and had developed laminar deterioration.…”