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A series of Fe 2 O 3 -Cr 2 O 3 -MoO 2 artificial passivation films that analogize with passive films on Fe-Cr-Mo alloys were prepared on Pt substrates by ion beam sputter deposition. Thinning rates of the films were measured in 1 M HCl by in situ ellipsometry under potentiostatic polarization. The addition of MoO 2 to Fe 2 O 3 -Cr 2 O 3 films suppressed the reductive dissolution of the Fe 2 O 3 component of the films under cathodic polarization, but accelerated the oxidation dissolution of the films due to the transpassive dissolution of MoO 2 . The transpassive dissolution of MoO 2 was suppressed by increasing Cr 2 O 3 content of the films. An Fe 2 O 3 -Cr 2 O 3 -MoO 2 film with the same cationic fractions as those of passive film on an Fe-18Cr-10Mo alloy hardly dissolved in the potential range of Ϫ0.3 to 1.0 V. This potential range covers the stable passivity region of Fe-18Cr-10Mo alloy in the same solution. Pitting potentials of Fe-Cr-Mo alloys containing Cr and/or Mo less than the Fe-18Cr-10Mo alloy exist in the reduction dissolution region of the Fe 2 O 3 component of Fe 2 O 3 -Cr 2 O 3 -MoO 2 films. This suggests that the reductive dissolution of the Fe 2 O 3 component in the passive films on the alloys may participate in pitting on the alloys.

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