| 摘要 |
PURPOSE: To obtain silica gel with abnormal particles detected as black spots at or fewer than a specific number by sol-gel process while heating at specified conditions under a flow of N2 gas, and to obtain synthetic silica glass powder with improved quality by baking the silica gel. CONSTITUTION: A reaction unit having its inner wall bearing a scale layer with a thickness not greater than debonding limit is charged with a silicon compound such as an alkoxysilane and about 10 equivalent times of water to conduct a hydrolyzing condensation reaction under agitation to obtain silica gel <=1000μm in particle diameter. The silica gel is then ground and heated to >=100 deg.C to remove the water and the alcohol, etc., formed during the hydrolysis, thus dry gel <=30wt.% in moisture content is obtained. Next, the dry gel is classified to bring its particle size distribution into about 100-200μm and then heated in an N2 gas atmosphere at 800 deg.C for 15min, thus obtaining the objective silica gel <=200 counts/10g in the number of abnormal particles detected as black spots. The dry gel after classification is baked by raising temperature from room temperature to about 1200 deg.C to obtain the objective synthetic silica glass powder each <=1ppm in Fe and Cr contents and each <=100ppb in Na and K contents.
|
