| 摘要 |
PURPOSE:To obtain a stable alumina coating film high in insulation property by thermally spraying an alumina powder on a material to be thermally sprayed, which is heated and kept at a specific temp., and cooled slowly. CONSTITUTION:A metallic plate 10 to be worked is heated to 2000-3000 deg.C by applying a plasma flame 9 on the material 10 to be worked placed on a iron plate-made pedestal 11 heated and kept at 200-400 deg.C. After that, the metallic plate 10 is thermally sprayed with alpha-alumina powder introduced into a equipment with a carrier gas. Since the heat capacity of the pedestal 11 is large and is kept at the temp., the temp of the metallic plate 10 is kept at 200-400 deg.C even after the heat of the plasma flame 9 is out and, thereafter, is controlled to cool slowly. Then, alpha-alumina is changed to gamma-alumina by the heat of the plasma flame when thermally spraying and >80% of gamma-alumina thermally sprayed is changed to a trigonal alpha-alumina by cooling slowly for one or two hours and is coated on the metallic plate. |
