電化學等效電路中擴散元件對三價鉻化成膜耐蝕性分析之影響

The Corrosion Resistance for Cr (III) Conversion Coatings Analyze by Diffusion Elements of the Equivalent Circuit in Electrochemical Impedance Spectroscopy (EIS)

本研究分別採用傳統的單層擴散元件與修正的複層擴散元件進行比較探討改善電化學阻抗頻譜法（EIS, electrochemical impedance spectroscopy）中之等效電路的擴散元件，以應用於鍍鋅三價鉻化成膜的特性分析。分析結果顯示，使用修正的複層擴散元件，皮膜的極化阻抗降低約5 ~ 15倍，其結果與極化曲線計算的皮膜阻抗值較吻合。另由擬合結果顯示，三價鉻化成膜的皮膜極化阻抗，在成膜後及烘烤後，極化阻抗由2.91 KΩcm2增加到6.69 KΩcm2，皮膜結構由Nernstian diffusion結構變為Impermeable diffusion結構，此結果與TEM橫截面圖結果相符合。

The diffusion elements placed with a conventional single layer and a revised multilayer were used in this study to compare the accuracy of diffusion element arrangements that to amend diffusion elements of the equivalent circuit in electrochemical impedance spectroscopy (EIS), and employed the method in analyzing characteristics of Cr (III) conversion coatings on zinc-galvanized steels. The analysis results show that the polarization resistance of coating with multilayer diffusion elements is more in agreement with that of polarization analyses, and the resistance of coatings with multilayer diffusion elements is 5 ~ 15 times lower than that of a single layer diffusion element. Moreover, the polarization resistance of as-deposited Cr (III) coatings is 2.91 KΩcm2, and increase to 6.69 KΩcm2 after baking the coatings. The diffusion behaviour of the as-deposited Cr (III) coating is originally Nernstian mode, but transform into impermeable mode after baking. This result is conformity to the cross-section structures of coatings observed by transmission electron microscope (TEM).