Patent ID: 7216509

Claim:
Sol-gel process for the production of tridimensional dry gels having all of the three lateral dimensions higher than about 2 cm, comprising the operations of: preparing a composition A comprising pyrogenic silica powder and an aqueous solution of an acid, such that the molar ratio H 2 O/SiO 2 in composition A is 20 or lower and its pH is equal to or lower than 1.5; preparing a composition B comprising silica powder and an aqueous solution of a base not containing metallic cations, such that the molar ratio H 2 O/SiO 2 in composition B is between about 6 and 40 and its pH is between 10.5 and 13; forming a homogeneous composition C by mixing composition A and composition B in such a ratio that the molar ratio between silica from composition A and silica from composition B is between about 1:2 and 3:1, and whereby the pH of composition C is between 1 and 5 and the molar ratio H 2 O/SiO 2 is between 5 and 15; allowing gelation of composition C to obtain a wet gel; substituting water present in pores of the gel with a non-protic liquid miscible with water; drying the gel by evaporation or supercritical extraction of the non-protic liquid.