SOL-GEL METHOD FOR PREPARATION OF LARGE-SIZE DRY GELS AND MODIFIED GLASSES Russian patent published in 2006 - IPC C03C1/00 

FIELD: silica materials.

SUBSTANCE: invention enables preparation of dry gels and corresponding dense glasslike compositions having larger size as compared to similar known methods. Sol-gel method for preparation of three-dimensional dry gels having dimensions along all three axes larger than about 2 cm includes following process operations: (i) preparation of composition A comprising pyrogenic silica and aqueous acid solution, molar ratio H₂O/SiO₂ in composition A being equal to or less than 20 and its pH equal to or less than 1.5; (ii) preparation of composition B comprising silica and aqueous solution of base containing no metal cations, molar ratio H₂O/SiO₂ in composition B being in the range of 6 to 40 and its pH ranging from 10.5 to 13; (iii) preparation of mixture C by mixing composition A and composition B at such a ratio, at which molar ratio of silica from composition A to silica from composition B is in the range between 1:1 and 3:1, pH of mixture C ranging from 1 to 5 and molar ratio H₂O/SiO₂ being in the range of about 5 to 15; (iv) gelation of mixture C; (v) replacement of water present in gel pores and in vessel with gel by an aprotonic liquid capable of being mixed with water; and (vi) drying of gel either by evaporating it or by performing supercritical extraction of aprotonic liquid.

EFFECT: increased size of produced dry gel.

23 cl