Study of impedance model and water transport behavior of modified solvent-free epoxy anticorrosion coating by EIS

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• 作者：Rui Ding ; Jianming Jiang ; Taijiang Gui
• 刊名：Journal of Coatings Technology and Research
• 出版年：2016
• 出版时间：May 2016
• 年：2016
• 卷：13
• 期：3
• 页码：501-515
• 全文大小：2,883 KB
• 刊物类别：Chemistry and Materials Science
• 刊物主题：Chemistry
  Tribology, Corrosion and Coatings
  Surfaces and Interfaces and Thin Films
  Polymer Sciences
  Materials Science
  
• 出版者：Springer US
• ISSN：1935-3804
• 卷排序：13

文摘

This paper studies the evolution of impedance model of 30 μm solvent-free epoxy coating on Q235 steel surface in 3.5% NaCl solution using electrochemical impedance spectroscopy. The electrochemical process of the system was divided into five stages. Water absorption occurred at the coating mainly during the early stage of immersion. In the meantime, coating resistance became smaller and coating impedance deviated from purely capacitive characteristics. After water permeated into the metal/coating interface, corrosion reaction began. During the middle stage of immersion, due to the barrier effect of the coating, the electrochemical reaction at the coating/metal interface was controlled by diffusion of corrosion products. Since the coating prepared was relatively thin, transport distance was short for water, which could easily reach the coating/metal interface. During the middle-late stage of immersion, coating peeled off from the metal surface, diffusion of water molecules gradually turned to a macroscopic infiltration process, and the coating lost its protective effect. A logarithm of coating capacitance and the square root of time showed a linear relationship in the early immersion stage, which was a typical characteristic of Fick’s diffusion. Water diffusion coefficient in the coating was calculated to be 8.23 × 10−11 cm2/s, while volume fraction and total water absorption at saturation of coating were 3.5% and 105 μg/cm2, respectively, indicating good water resistance and protective properties of the coating. By solving the Fick’s diffusion equation, the kinetic equation which described the diffusion of water in the coating and included time and location variables were obtained.KeywordsSolvent-free epoxy coatingWater transportEISKinetic equation