Co-W合金镀层表面氧化膜在碱性体系中的电化学研究

Study on Electrochemistry of Oxide Films Formed on the Surface of Cobalt-tungsten Alloy Coatings in Alkali Solution

采用电化学手段以及Mott-Schottky理论,并结合氧化膜点缺陷模型(PDM)分析研究了Co-W合金镀层在1 mol·L-1 NaOH溶液中表面氧化膜的半导体性质,并分别计算出了不同W含量的Co-W合金镀层在-0.15,-0.25和-0.35 V三个不同电位下阳极氧化后氧化膜的供体密度、平带电位及氧空穴扩散系数.结果表明,Co-W合金镀层在1 mol·L-1 NaOH溶液中表面氧化膜的Mott-Schottky曲线线性区斜率为正,表现出N型半导体性质;随着阳极氧化电位的升高或合金镀层W含量的降低,氧化膜供体密度ND逐渐增大,导致氧化膜被破坏或发生点蚀的几率升高;随着阳极氧化电位的降低或合金镀层W含量的降低,氧化膜平带电位呈降低趋势,说明其耐蚀性升高;不同W含量的Co-W合金镀层在三个不同电位下阳极氧化后的氧化膜的氧空穴扩散系数为(1.543～8.533)×10-14 cm2·s-1.

Electrochemical methods and Mott-Schottky analysis in conjunction with the point defect model（PDM） for oxide films have been used to investigate the semiconductor properties of the oxide films formed on the surface of cobalt-tungsten alloy coatings in 1 mol·L-1 NaOH electrolyte.The donor density（ND）,the flatband potential（Ufb） and the oxygen vacancy diffusion coefficient（D0） of the oxide films on the coatings with different tungsten contents under three different anodization potentials were calculated from the Mott-Schottky plots,respectively.The results indicated that the Mott-Schottky plots of the oxide films were linear with a positive slop,and showed behaviour of the N-type semiconductor.The donor density（ND） of the oxide films increased with the rising of anodization potential or with the decrease of the tungsten content in the alloy coatings,therefore,the chances of oxide films breakdown and pitting initiation increased.The flatband potential of the oxide films dropped with the decrease of anodization potential or with the decrease of the tungsten content in the alloy coatings.Therefore,the corrosion resistance of the anodic oxidation films enhanced.The oxygen vacancy diffusion coefficient（D0） of the anodic oxidation films which formed on the surface of cobalt-tungsten alloy coatings with different tungsten contents at three different anodization po-tentials were（1.543～8.533）×10-14 cm2·s-1.