Progress in Organic Coatings 76 (2013) 1075–1081 Contents lists available at SciVerse ScienceDirect Progress in Organic Coatings jou rn al hom ep age: www.elsevier.com/locate/porgcoat Studies of impedance models and water transport behaviours of epoxy coating at hydrostatic pressure of seawater Liu Jie a,b,∗ , Li Xiang-Bo c , Wang Jia d , Luo Tian-Yuan a , Wang Xiao-Ming b a Southwest Technology and Engineering Research Institute, Chongqing 400039, PR China b School of Mechanical Engineering, Nanjing University of Science and Technology, Nanjing 210094, PR China c State Key Laboratory for Marine Corrosion and Protection, Qingdao 266071, PR China d State Key Laboratory for Corrosion and Protection, Shenyang 110016, PR China a r t i c l e i n f o Article history: Received 29 May 2012 Received in revised form 13 January 2013 Accepted 7 March 2013 Available online 31 March 2013 Keywords: Epoxy coating Impedance models Water transport Hydrostatic pressure of seawater a b s t r a c t In simulated deep-sea environment, the evolution of impedance models and water transport behaviours of epoxy coating on 907A steel surface were studied by electrochemical impedance spectroscopy (EIS). By the fitting analysis of EIS, three equivalent electrical circuits (EEC) were proposed to the epoxy coating/907A steel system at 25 atm hydrostatic pressure for different immersion stages: good bar- rier property of the coating (Circuit A), active corrosion period at the beginning (Circuit B), and finally emergency of diffusion impedance (Circuit C). The evolution of coating capacitance indicated that water transport followed the Fickian diffusion behaviour during the initial stage at 25 atm hydrostatic pressure and at atmospheric pressure. High pressure accelerated diffusion rates of seawater into epoxy coatings, this shortened the period of water uptake of the coating that reached saturation. The similar chemical structures of epoxy coatings at two kinds of hydrostatic pressure were found from the Fourier transform infrared spectroscopy (FT-IR) – attenuated total reflection (ATR) measurements. High pressure of seawa- ter accelerated the coating physical failure, and chemical structures of the coating did not change during the experiment. © 2013 Elsevier B.V. All rights reserved. 1. Introduction The metallic structural equipments will be prone to be attacked by aggressive species such as water, oxygen and ions if they are not protected from the corrosive seawater environment. Organic coatings have been effectively used for the protection of metals due to their capacity to act as a physical barrier between the metal surface and the corrosive environment in which they perform their function [1,2]. In the previous works [3–6], the corrosion mecha- nism of organic coating with immersion time and water transport behaviours in organic coating at atmospheric pressure have been studied in detail. In deep-sea environment, the high pressure [7,8] of seawater is an important factor to affect the lifetime of organic coatings and probably conduces to synergistic effects with other ageing factors. To our best knowledge, however, not any studies on evolution of impedance models of organic coating and water transport behaviours in organic coating at hydrostatic pressure of seawater were reported up to now. Electrochemical impedance ∗ Corresponding author at: Southwest Technology and Engineering Research Institute, Chongqing 400039, PR China. Tel.: +86 2368792155; fax: +86 2368792118. E-mail address: liujie6573@163.com (L. Jie). spectroscopy (EIS) appears to be a widespread technique for the investigation of the degradation of polymer coated metals, because of its good ability to study high impedance system and to provide abundant information [9–13]. It is necessary to select appropriate equivalent circuits for analysis of measured impedance of coat- ing/metal system at different immersion stages. The objectives of this paper are, firstly, to investigate the EIS characteristics of the coating/steel system in simulated deep-sea environment, secondly, to evaluate the water transport behaviour in the epoxy coating on 907A steel at 25 atm hydrostatic pressure. 2. Experimental 2.1. Sample preparation 907A steel plates (10 mm × 10 mm × 5 mm) were used as sub- strates of the coating. The substrates were pretreated by abrasion with #800 SiC paper, degreasing in acetone and rinsing with methyl alcohol. And then the sample was coated with an epoxy coating and dried several days for experiment. The coating thickness was measured using the MINITEST 600 Coating Thickness Gauge, in the thickness range of the studied materials, of ±3 m. The thickness results were the mean value of 10 measurements. And the coating with 100 m was used in this paper. 0300-9440/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.porgcoat.2013.03.006