A copper part (C1100), used in an EGR-equipped engine, got corroded. This copper part was directly contacting an iron part (S45C), for which the iron part should have been corroded before the copper one began being corroded, because iron is less noble than copper. However, it was found that the corrosion had taken place only on the copper part. In order to clarify the reason, we investigated the phenomenon for substances related to the corrosion and tried to identify how the environments became corrosive and what mechanisms caused the corrosion, using a chemical method. As the result, we came up with the conclusion that a solution consisting of sulfuric acid and nitric acid might probably have worked on the corrosion, by verifying that copper becomes more corrosive than iron in a place where nitric acid is present.
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