Tetraethoxysilane was hydrolyzed with HCl and mixture of HF with the fumed silica was added and well—dispersed. By adding ammonia solution the pH value of sol was adjusted to 4. 5 and the sol was poured into a polypropylene mold and gelled

then the gel was dried into dry—gel and sintered into silica glass. Large—size silica glass tubes are obtained whose outside diameter is 20 mm

the wall thickness is 2. 5 mm and the length is 250 mm

the ratio of the volumes of wet gel to silica glass is 50%

Dry—gel is not easy to crack. The rate of finished products is about 90%.