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[求助]
關(guān)于陽極計劃曲線的理解
關(guān)于氣相沉積薄膜耐腐蝕性研究中,陽極極化曲線的問題:
本人日前閱讀了一篇利用陽極極化試驗來表征鋼材表面改性CrN薄膜耐腐蝕性能的文獻。由于對腐蝕電化學原理不是很懂,特此摘錄如下,有幾個問題請教各位大蝦,多謝!
原文如下(附圖):
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.
文獻中說,依據(jù)試驗結(jié)果(見附圖)對于intermediate Ar etching treated coating,因為其發(fā)生了早期的pitting(點蝕),所以其鈍化區(qū)電流密度出現(xiàn)了顯著上升。對于continuously deposited CrN coating, 因為發(fā)生了早期pitting, 所以在活化區(qū)則出現(xiàn)了一些活化峰。
我的問題是,(1)都是發(fā)生點蝕,為什么會分別從活化區(qū)和鈍化區(qū)進行解釋和理解。
(2)continuously deposited CrN coating的鈍化區(qū)曲線幾乎與作者認為的耐腐蝕性較好的The intermediate treated CrN coatings。這有怎么解釋?
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