By use of a bromine‐methanol solution the authors have been able to isolate passive films from electrolytic chromium, ferritic, and austenitic stainless steel, and from the alloys "Nichrome" V and "Inconel." The films were very thin and transparent and were found to be formed on initially film‐free (pickled) surfaces by air exposure and by passivation treatments in and in solutions. These passive films have been examined by both light microscopy and electron microscopy and by electron diffraction. Chemical analyses indicate that both chromium and iron are major constituents in the films from Type 430 and Type 317 stainless steel. It is believed that these are present together in solid solution, possibly in a spinel type of crystalline lattice. The films from chromium passivated in have been shown to contain a high percentage of chromium, probably as .
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Mahla et al. (1948) studied this question.