Curing treatments of silica gel for fire-retardant glass by intumescence

Abstract Silica hydrogels are used as fire-retardant materials due to the occurrence of intumescence that limits heat and mass transfer. They act as heat-sink, through continuous endothermic condensation reactions, meantime shrinking to a more connected network, towards the correspondent crystalline compound. Which compositions and treatments amplify this phenomenon is still of interest. To this aim, two silica sols containing two different complexing agents: ethylene glycol and glycerol has been prepared and analyzed. The samples were subjected to different treatments to induce gelation and densification: exposure to ultraviolet or microwave or infrared irradiation. Thermogravimetric analysis coupled with differential scanning calorimetry (TG-DSC) and scanning electron microscopy analyses has been also carried out. Moreover, dynamic mechanical spectroscopy (DMS) let to evaluate simultaneously the mechanical and intumescence behavior of the gels at increasing curing times for each type of irradiation. Intumescence of gels occurs up to 200 °C and appears as an endothermal group of peaks visible on the heat-flux DSC curves. DMS analyses let to assess that a MW cured glycerol-containing gel (GL-0-MW 6d) shows a glass transition above 150 °C, measured as the maximum of damping peak. Accordingly, this sample is a good option for the application: a few bubbles nucleate and grow fast at high temperature. Article Highlights Transparent fire doors contain silica gel, which absorbs heat and releases water by foaming. Two different silica gels were synthetized using different chelating agents. The foaming depends on the reagents used to produce the gel, on the treatments for stabilizing it and also on ageing. Both foaming and consolidation of the gel were studied with thermogravimetric and dynamic-mechanical analysis.