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An investigation of the penetration of thin aluminum oxide films by liquid bismuth Allday, William John

Abstract

The penetration of thin aluminum oxide films by liquid bismuth was studied between 350 and 500°C. A correlation was sought between the type and thickness of the oxide film, and the time and nature of the attack. Mechanical and electropolished, and anodized films of different thicknesses were exposed to liquid bismuth either by immersing a plate in the liquid and measuring the contact angle or by melting a drop of bismuth on a specific area of a plate. Electropolished surfaces had no resistance to attack by the bismuth. Pitting and edge attack occurred with all other surface preparations. The anodized films often separated from the aluminum under thermal stresses and allowed the bismuth to spread under the film, sometimes removing it entirely. Attempts were made to control the number and nature of defects in the oxide film, but the difficulty of this is shown by the scatter in the results. No attack on aluminum oxide itself is likely and no diffusion of bismuth through the oxide was found at the temperatures used. The conclusion was reached that the bismuth penetrated the oxide film only at points where there was a high concentration in the film of some impurity oxide (such as nickel or copper oxides) that reacts with bismuth.

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