Reducing the flammability of hydrophobic silica aerogels by doping with hydroxides

In this work, we utilized Al(OH)3 (AH) and Mg(OH)2 (MH) as dopants to reduce the flammability of hydrophobic silica aerogels (SA) and the related thermal properties and flame retardance were investigated detailedly. The TG-DSC analyses showed the thermostability of SA in MH/SA reached 512.4 °C and that for AH/SA was just 426.1 °C, both of which were higher than that of pure SA, 399.5 °C. It was known from cone calorimeter tests that the heat release rate, peak heat release rate and total heat release of AH/SA and MH/SA decreased significantly compared to that of pure SA. The time to ignition (TTI) of MH/SA was dramatically extended, reaching 20˜38 s, which was far longer than those of pure SA (˜6 s) and AH/SA (3˜8 s). The reduction in CO concentration, CO production rate and cumulative CO production verified the decreased smoke toxicity of AH/SA and MH/SA. It was further indicated that the flame-retardant effect of AH and MH correlated with their inhibitory effect on the pyrolysis of SA, while MH showed much better flame-retardant performance than that of AH. The research outcomes provide an inspiration to reduce the flammability of SA and benefit their expansion in thermal insulation field.