For inorganic aerogels, silicon aerogel is the most aerogel studied at present. In sol-gel process, three dimensional network structure silicon aerogel was obtained by hydrolysis and condensation of silicon source material. Its reaction principle is
    Si(OR)4 +4H2O  → Si(OH)4 +4HOR     (hydrolysis)
   nSi(OH)4  → (SiO2)n +2nH2O  ( polycondensation )[7]