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The surface compositions of two Nisingle bondCrsingle bondFe alloys [Nisingle bond21Crsingle bond8Fe (at%) single crystal and Nisingle bond17Crsingle bond10Fe] have been characterized by angle-resolved ESCA, after polarization in the passive state or in the active state in 0.05 M H₂SO₄. The passive layer formed on Nisingle bond21Crsingle bond8Fe(100) has a bilayer structure with an oxide film in the interior of the film and an hydroxide layer on the surface. The film is markedly enriched with chromium oxide and hydroxide. The inner oxide layer consists of 96% Cr₂O₃ and 4% Fe₂O₃. There is no detectable Ni²⁺. The outer hydroxide layer is ∼100% Cr(OH)₃. At 300 mV(SHE), the thickness of the passive film is 11Å, and the thickness of the inner oxide layer is 6.5Å. At higher potentials the film is thicker: the thickness of the inner oxide layer is 9Åat 600 mV(SHE). On the Nisingle bond17Crsingle bond10Fe …