| 摘要 |
<p>PURPOSE: To increase the bulk density of silica gel powder to be charged into a crucible and prevent the development of fine bubbles in the resultant silica glass molded form by heat treating silica gel powder in fluidization in a rotary kiln with its maximum stack height at a specified level or higher. CONSTITUTION: First, dry silica gel 10-1000μm in particle diameter is obtained by drying at 50-200 deg.C and pulverizing wet silica gel powder obtained by a sol-gel process such as hydrolysis or gelation of e.g. a tetraalkoxysilane. Secondly, the dry silica gel powder is heat-treated under fluidization in a rotary kiln with the core pipe made of quartz. In this case, there occurs no slippage between the powder 1 and the contact surface 3 of the core pipe 2 wall, the powder 1 is raised along the wall as the core pipe 2 is rotated and then allowed to fall (as indicated by arrows) off the wall at an angle of repose or above. To stabilize the fluid state of the powder 1, the maximum stack height of the powder 1 defined below is kept at >=75mm and the powder 1 is heated at 900-1100 deg.C (The maximum stack height is the maximum length of perpendiculars drawn from the powder surface 5 in contact with the space 4 inside the core pipe 2 toward the contact surface 3).</p> |
