| 摘要 |
PROBLEM TO BE SOLVED: To produce a large-sized silica body free of crack by subjecting silica sol containing an organic surfactant whose molecular weight is specified to gelling and heat-treating the formed gel body. SOLUTION: Silica sol containing an organic surfactant having <2,000, as necessary, <1,000 molecular weight and hardly containing an organic polymer substance having >10,000 molecular weight, containing <= about 5 wt.% surfactant based on sol weight and having about 40-65 wt.% silica content is fed. A gelling agent is added to the silica sol so as to lower pH and the silica sol is made to gel over < about 1 hr and aged over <= about 24 hr. Then, the resultant gel is dried until about 90 wt.% of water content is removed under relative mild condition (at about <40 deg.C and about >50% relative humidity). Further, heat treatment is carried out in order to carry out burning out of existing organic substance, dehydroxylation, removal of residual water content and sintering to provide sintered gel body suitable for overcladding tube. |
