| 摘要 |
PURPOSE:To produce a calcined high-purity and high-density alumina sheet having high smoothness by adding a specific amount of alpha-alumina powder which is hexagonal platy crystals as a seed powder to an alumina sol, forming the resultant mixture into a green sheet and calcining the formed green sheet. CONSTITUTION:alpha-Alumina powder which is hexagonal platy crystals in an amount of at least 0.5wt.% based on 100wt.% expressed in terms of alumina weight as seed powder is added to an alumina sol to prepare a slurry. The above-mentioned alpha-alumina powder which is the hexagonal platy crystals can be produced by adding 0.5-1.0wt.% calcium salt to 100wt.% NaOH solution at a high temperature by the Bayer process. The resultant slurry is then formed into a film and dried to form a green sheet. The forming is carried out by a doctor blade method, etc., and the crystal surface of the aforementioned hexagonal platy crystals is oriented parallel to the sheet surface. The green sheet is subsequently calcined. In the above-mentioned calcining, the green sheet is shrunk and calcined in a prescribed direction without causing deforming, cracking, warping, holes, etc., to afford the calcined high-purity and high-density alumina sheet having a prescribed shape. |
