| 摘要 |
PURPOSE:To form a dense and hard oxide film which is free from exfoliation on the surface of a work by alternately repeating weak oxidative and strong oxidative atmospheres and specifying the range of a treatment temp. CONSTITUTION:An operator sets the air ratio of a gas governor 7 by regulating the opening degrees of flow rate control valves V2, V3 while visually observing flow meters M1 and M2. The heating period of the weak oxidative atmosphere when soot is adequately generated in the stage of incomplete combustion and the cooling period in the strong oxidative atmosphere when only the air is supplied are thereby alternately generated. The furnace temp. is fluctuated up and down in a 600-900 deg.C range during this time. The soot sticking to the work 4 in the weak oxidative atmosphere is completely burned and is gasified as CO2 in the strong oxidative atmosphere. The surface of the work 4 is thus maintained clean. The thin film of Fe2O3 is formed in such strong oxidative atmosphere. The Fe2O3 is reduced to Fe3O4 in the next weak oxidative atmosphere. The dense oxide films of the Fe2O3 are successively grown by the repetition of such operation.
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