Glass-based foam from alkali activation: A review on effect of primary foaming parameters on microstructure and density

Alkali activation techniques (AATs) are utilized to produce glass-based foams (GBFs) including glass or glass ceramic foam, due to their eco-friendly process. Numerous studies have examined the factors affecting the microstructure and density of GBFs during foaming processes. While secondary foaming parameters such as the heating rate, sintering temperature, and holding time have been extensively investigated, primary foaming parameters have been given less attention thus leading to the suboptimal properties and sustainable utilization of GBFs. This study reviews the impact of primary foaming parameters on the microstructure and density of GBFs. Principles, mechanisms, and significance of alkali activators and precursors are discussed. Influential parameters, including particle size of precursor and foaming agents, foaming agent, and alkali activator composition, are analysed along with controllable measures like solid-loadings, surfactants, and gelation time. In addition, different routes of AATs that have the potential to produce optimum properties of GBFs are deliberated. This review provides valuable insight into the production of GBFs using AATs, particularly for sustainable lightweight or thermal insulation applications.