γ_Ν相在3.5%NaCl溶液中钝化膜的半导体性能

Semiconductor Properties of Passive Film Formed on γ_Ν-phase Layer in 3.5%NaCl Solution

采用等离子体源渗氮技术在AISI 304L奥氏体不锈钢表面制备高氮面心结构的γΝ相层。运用电化学的方法测试了γΝ相层在3.5%(质量分数) NaCl溶液中的阳极极化曲线和Mott-Schottky曲线,并借助点缺陷模型(PDM)计算了γΝ相层钝化膜的施主浓度、受主浓度、平带电位和氧空位扩散系数。结果表明:γΝ相层钝化膜的阳极极化曲线呈现活化溶解-自钝化-过钝化溶解过程,自腐蚀电位Ecorr较原始不锈钢提高了323 mV (SCE),维钝电流密度Ip降低一个数量级,耐蚀性能明显提高。γΝ相层钝化膜具有双层结构,在负于平带电位区间内钝化膜呈p型半导体性质,在高于平带电位区间内钝化膜呈n型半导体性质,且相比原始不锈钢,γΝ相层钝化膜内施主浓度和受主浓度更低,平带电位负移。根据PDM模型计算出原始不锈钢和γΝ相层钝化膜内氧空位扩散系数分别为1.22×10-16和7.96×10-17cm2/s,说明γΝ相层钝化膜绝缘性和致密性更好。

A high-nitrogen face-centered-cubic phase（γΝ） layer was prepared on the AISI 304 L austenitic stainless steel surface via plasma source nitriding process. The anodic polarization curves and Mott-Schottky plots of the γN-phase layer in 3.5%（mass fraction） NaCl aqueous solution was assessed by electrochemical measurements. The donor and acceptor density, the flat band potential, the diffusivity of point defect in the passive film on the γNphase layer were calculated by point defect model（PDM）.The results show that the anodic polarization curves of the γΝ-phase layer underwent a typical spontaneous passivation-transpassive dissolution process, the free-corrosion potential of the γΝ-phase layer increases by 323 mV（SCE）, the passivation current density deduces one order of magnitude, in comparison with the original stainless steel. The passive film on the γΝ-phase layer exhibits p-type semi-conductive characters in the potential region lower than the flat band potential, and n-type semi-conductive characters in the potential region higher than the flat band potential. The passive film on γΝ-phase layer has much lower donor-and acceptor-density and more negative of the flat band potential. On the base of a point defect mode, the diffusivity of point defect, which is caused by oxygen vacancy, in original stainless steel and γΝ-phase layer were calculated to be of 1.22×10-16 and 7.96×10-17 cm2/s, respectively. So in contrast to the original stainless steel, the passive film of γΝphase layer presents higher insulativity.