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[求助]
关于阳极计划曲线的理解
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关于气相沉积薄膜耐腐蚀性研究中，阳极极化曲线的问题： 本人日前阅读了一篇利用阳极极化试验来表征钢材表面改性CrN薄膜耐腐蚀性能的文献。由于对腐蚀电化学原理不是很懂，特此摘录如下，有几个问题请教各位大虾，多谢！ 原文如下（附图）： Typical anodic polarization curves of the CrN coatings are given in Fig. 6. The intermediate treated CrN coatings showed almost similar behavior in the passive region (almost constant current at potential of 0.35–0.95 V vs Ag/AgCl), which means that the coatings have similar defect density as they have the same composition and thickness. The passive area showed slight increase of the current density when the coating was intermediate treated by micro-blasting II. This may be due to the differences in defect density of the coatings [8]. Moreover, the anodic polarization curves showed different behaviors of the intermediate Ar etching treated and continuously deposited CrN coatings. The intermediate Ar etching treated coating showed early sharp increase of current density in the passive region due to the onset of pitting as a result of local corrosion at the substrate–coating interface. Likewise, continuously deposited CrN coating (without any intermediate removal of the droplets) showed some active peaks at the active dissolution region (at the vicinity of 0.3 V vs Ag/AgCl) indicating the early formation of pitting corrosion. The coating surfaces after the anodic polarization tests are shown in Fig. 7. SEM images of coating surfaces showed clear pitting and corroded pinholes at intermediate Ar etching and continuously deposited coatings (Fig. 7d,e). This is clear evidence of the formation of penetrated pathways between the electrolyte (at the surface) and the substrate–coating interface. Similarly, SEM images of the intermediate treated coating surfaces showed almost no penetrated pinholes or pores (Fig. 7a,b,c). Some local interactions occurred at the vicinity of the dropletswithout formation of corrosion pathways. It can be inferred that droplets and inclusion removal midway of the deposition process can help to block pinholes and defects; therefore, improving corrosion resistance of the overall combination of substrate and coating. 文献中说，依据试验结果（见附图）对于intermediate Ar etching treated coating，因为其发生了早期的pitting(点蚀)，所以其钝化区电流密度出现了显著上升。对于continuously deposited CrN coating, 因为发生了早期pitting, 所以在活化区则出现了一些活化峰。 我的问题是，（1）都是发生点蚀，为什么会分别从活化区和钝化区进行解释和理解。 （2）continuously deposited CrN coating的钝化区曲线几乎与作者认为的耐腐蚀性较好的The intermediate treated CrN coatings。这有怎么解释？  捕获.JPG |
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