Alkaline attack of boro-alumino-silicate glass: New insights of the molecular mechanism of cold consolidation and new applications

This paper focuses on the activation of boro-alumino-silicate glass from discarded pharmaceutical containers as fine powders suspended in relatively diluted alkaline solutions (2.5 M NaOH/KOH), followed by drying at 40°C for 7 days. A specific molecular mechanism of glass hardening is proposed. Unlike geopolymers, the hardening does not result from the condensation of products of extensive dissolution. Instead, condensation reactions occur in hydrated surface layers, leading to strong bonds (Si-O-Si, Al-O-Si, etc.) between individual glass particles. Silicates, borates, and aluminates from glass dissolution combine with alkaline ions, yielding additional soluble phases. This mechanism is supported by the results of solid-state NMR spectroscopy and elemental analysis using ICP-OES. Stable matrices prepared by direct foaming or by the inclusion of cenospheres or commercial expanded glass (Poraver®) can be exploited for the fabrication of lightweight components