Research Of Photoelectrochemical Characterization Of Passive Films On Nickel Alloy

Nickel-based alloy materials had excellent corrosion resistance, for this reason, they were widely applied to the nuclear power plant construction. Passive films of the stainless steel and nickel-based alloy surface had semi-conductor properties obviously. Besides stress corrosion and pitting corrosion, metal corrosion rate was closely related with the semi-conductor properties of passive films. This paper aimed to explore its structure, composition and semiconductor properties by studying the electrochemical and photoelectric chemical properties of passive films on 316 stainless steel, 600 and 800 nickel-based alloy surface.The Mott-Schottky curves of 316,600 and 800 were measured after dc passivation in different anode potential to determine corrosion potential E_corr and corrosion current icorr .Plotted the M-S curves to analyze semiconductor characteristics of the surface passive films, such as: semiconductor type; donor/acceptor concentration; the flat band ; width of space charge layer. The (i_phhν/I₀)^1/2- photon energy curves were performed using the current method, to analyze of the surface passive film structure; semiconductor type and the band gap of compound layers.The results showed that, compared with in sulfuric acid solution, in borate buffer solution the capacitance was higher, an obvious negative shift had happened, the corrosion current was lower, predictably, in neutral solution, the passive films had better corrosion resistance. Compared electrochemical treated samples with untreated, the corrosion current of nickel-based alloy surface was obviously lower ;the corrosion potential was higher than the original potentials; the donor and recipient concentration was lower, the corrosion resistance was better. The photo-current of 316 samples was positive, and the passive films presented n - type semiconductor properties. According to the forbidden band width, composition of passive films were possible: inner layer Cr₂O₃,outer layer Fe₂O₃ and (Fe, Cr)₂O₃.The composition of passive films of 800: inner layer partly were Ni(OH)₂ and NiO; partly was Cr₂O₃,outer layer were Fe₂O₃, NiCr₂O₄ or NiFe₂O₄.