Evidence of formation of an amorphous magnesium silicate (AMS) phase during alkali activation of (Na-Mg) aluminosilicate glasses

There is some ambiguity regarding the fate of Mg during the alkali activation of Mg-rich precursors within the broader field of alkali activated materials (AAMs). The present work addresses this issue by studying the reaction products in AAMs synthesized from (Na-Mg) aluminosilicate glasses. Here, instead of magnesium silicate hydrate (M-S-H) phase, Mg exclusively forms an amorphous magnesium silicate (AMS) phase. Compared to M-S-H, AMS is a more depolymerized phase, which has not previously been well documented. The formation of AMS seems to be driven by the high charge density of the Mg cation which effectively stabilizes the depolymerized silicate species. We also show that the lack of hydrotalcite-group phases is due to aluminum depletion by zeolite formation. This work highlights the need to consider the existence of the AMS phase in Mg-containing AAMs, especially in complex systems, where its identification may be difficult.

Automated summary

This study investigates the reaction products in alkali activated materials (AAMs) synthesized from (Na-Mg) aluminosilicate glasses, revealing the existence of an amorphous magnesium silicate (AMS) phase instead of magnesium silicate hydrate (M-S-H) in Mg-containing AAMs. The formation of AMS is driven by the high charge density of the Mg cation, while the absence of hydrotalcite-group phases is attributed to aluminum depletion caused by zeolite formation.