FINE LOW-DENSITY SILICA POWDERS PREPARED BY SUPERCRITICAL DRYING OF GELS DERIVED FROM SILICON TETRACHLORIDE

Silica gels were prepared by the hydrolysis of silicon tetrachloride i n pure water or in a tetrahydrofuran/water solution; hydrolysis in an ammonia/water solution yielded precipitated silica, After solvent tran sfer in acetone followed by supercritical point drying using liquid ca rbon dioxide, aerogel powders with high surface areas (up to 900 m(2)/ g) and low tapping densities (down to 0.040 g/cm(3)) were produced. Th e powders were characterised by transmission electron microscopy, ther mogravimetric analysis and infrared spectroscopy.