Summary
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1.
All the types of etch-resistant surface films studied are electropositive with respect to the underlying metal. The most electropositive potential was recorded for films of maximum thickness.
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2.
Adjacent steel surfaces with and without etch-resistant films form galvanic macro- and microcells in which the etch-resistant films act as cathodes.
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3.
The etch-resistant films can, under specified conditions, considerably reduce the corrosion rate of steel in acid media. For example, a 20% reduction in the corrosion rate for 40Kh steel specimens with type II surface films was recorded in tests in a 53% H2SO4 solution.
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4.
A tentative explanation (based on the results of X-ray diffraction and metallographic analyses) of the electrochemical and corrosion properties of etch-resistant films is offered.
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5.
An analogy is suggested between the action of etch-resistant surface films and porous cathodic coatings.
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Karpenko, I.V., Gutman, E.M. & Mindyuk, A.K. Electrochemical properties and chemical passivity of etch-resistant surface films on steel. Mater Sci 1, 115–121 (1966). https://doi.org/10.1007/BF00715898
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DOI: https://doi.org/10.1007/BF00715898