Abstract: Silica aerogels were prepared by sol-gel method with ambient pressure drying.The influences of pH and hydrolysis time on transmittance of silica aerogels were investigated.Through two-stage catalysis of acid（oxalic acid）-alkali （aqueous ammonia），hydrophobic mesoporous silica was firstly prepared by sol-gel method under ambient pressure drying with tetraethyl orthosilicate as raw material.Silica aerogels were finally prepared by keeping the amount-of-substance ratio of tetraethyl orthosilicate，ethanol，oxalic acid，and aqueous ammonia at 1∶4∶5∶0.2，concentrations of oxalic acid and aqueous ammonia fixed at 0.008 mol/L and 0.05 mol/L and with dichlorodimethylsilane（DMDCS） as the surface modification agent.The silica aerogels were analyzed by transmission electron microscopy and scanning electron microscopy.Results showed that silica aerogels had an amorphous nano-porous structure and the pore diameter was in the mesoporous range.Contact angle test showed that the contact angle was 148°.The results proved that the aerogels were hydrophobic.

Key words: silica aerogels, sol-gel method, ambient pressure drying, transmittance