Improving the flame retardance of hydrophobic silica aerogels through a facile post-doping of magnesium hydroxide

A facile post-doping of magnesium hydroxide (MH) is proposed to improve the flame retardancy of hydrophobic silica aerogels (SA). The lower tap density (0.12 g/cm3) and thermal conductivity (26 mW/m/K) are still maintained at the largest MH content of 20%. Meanwhile, the gross calorific value of the SA/MH is reduced by 15% and the thermal stability is improved to over ~545 °C. The SA/MH pyrolysis process can be divided into four stages, while the hydrophobic SA is a two-stage pyrolysis process. Furthermore, the improved flame retardancy of SA/MH is mainly attributed to the thermal decomposition of MH, the pyrolysis products (MgO, SiO2 and H2O) and the reaction between MgO and SiO2. The research outcomes demonstrate the validity of using MH as dopant to improve the flame retardancy of hydrophobic SA by a facile post-doping, which is beneficial to the expansion of hydrophobic SA in their practical thermal insulation application.