阴极保护电位对破损环氧涂层阴极剥离的影响
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摘要
采用电化学阻抗技术(EIS),并结合SEM,EDS和XRD研究了室温、静态模拟海水中不同保护电位对海洋平台研制钢在模拟海水中防腐涂料与阴极保护联合作用效果以及对破损环氧防腐涂层的阴极剥离机理。结果表明:在本实验选择的保护电位中,随着电位的负移,涂层剥离面积逐渐增大。-750 mV (vs SCE,下同)保护电位对于破损涂层的金属基体欠保护。-1050 mV电位极化下发生严重的析氢现象,破坏了钙质沉积层的完整性,界面碱化程度较大,涂层剥离面积最大;-850和-950 mV保护电位均能抑制破损处金属的腐蚀;-950 mV保护电位下生成的CaCO_3和Mg(OH)_2钙质沉积层完整致密,保护效果最佳。
The combined effectiveness of the cathodic protection and epoxy coating for a steel,which is newly developed for offshore platform, as well as the cathodic delamination behavior of the epoxy coating with damages in artificial seawater at room temperature were examined by means of electrochemical impedance spectroscopy(EIS), scanning electron microscope(SEM), energy dispersive spectrum(EDS) and X-ray diffractometer(XRD). Results indicated that as the potential goes down within the selected range of protection potentials of-750～-1050 mV(vs SEC), the delamination area of the coatings increases. The ordinary protection potential-750 mV(vs SEC) for epoxy coatings is no longer applicable for the damaged coatings, while the cathode potential-1050 mV leads to serious hydrogen evolution in the damaged area, resulting in the integrity destruction of the deposited film there, leading to the seriously interfacial alkalization and therewith, the cathodic delamination area increases. However, the protection potential of-850 or-950 mV can inhibit the corrosion of metal on the damaged site of coating.The deposited film formed under-950 m V on the damaged site is composed of Mg(OH)_2 and CaCO_3 which is of integrity and dense, leading to the best protective effect on the substrate.
The combined effectiveness of the cathodic protection and epoxy coating for a steel,which is newly developed for offshore platform, as well as the cathodic delamination behavior of the epoxy coating with damages in artificial seawater at room temperature were examined by means of electrochemical impedance spectroscopy(EIS), scanning electron microscope(SEM), energy dispersive spectrum(EDS) and X-ray diffractometer(XRD). Results indicated that as the potential goes down within the selected range of protection potentials of-750～-1050 mV(vs SEC), the delamination area of the coatings increases. The ordinary protection potential-750 mV(vs SEC) for epoxy coatings is no longer applicable for the damaged coatings, while the cathode potential-1050 mV leads to serious hydrogen evolution in the damaged area, resulting in the integrity destruction of the deposited film there, leading to the seriously interfacial alkalization and therewith, the cathodic delamination area increases. However, the protection potential of-850 or-950 mV can inhibit the corrosion of metal on the damaged site of coating.The deposited film formed under-950 m V on the damaged site is composed of Mg(OH)_2 and CaCO_3 which is of integrity and dense, leading to the best protective effect on the substrate.
引文
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[19] Rousseau C, Baraud F, Leleyter L, et al. Kaolinite influence on cal‐careous deposit formation[J]. Electrochim. Acta, 2009, 55:196
[20] Wroblowa H S, Qaderi S B. Mechanism and kinetics of oxygen re‐duction on steel[J]. J. Electroanal. Chem. Interfacial Electrochem.,1990, 279:231
[21] Barchiche C, Deslouis C, Festy D, et al. Characterization of calcare‐ous deposits in artificial seawater by impedance techniques:3—De‐posit of CaCO3in the presence of Mg(II)[J]. Electrochim. Acta,2003, 48:1645
[22] Gutjahr A, Dabringhaus H, Lacmann R. Studies of the growth and dissolution kinetics of the CaCO3polymorphs calcite and aragonite II. The influence of divalent cation additives on the growth and dis‐solution rates[J]. J. Cryst. Growth, 1996, 158:310
[2] Xu L K, Ma L, Xing S H, et al. Review on cathodic protection for ma‐rine structures[J]. Mater. China, 2014, 33:106(许立坤,马力,邢少华等.海洋工程阴极保护技术发展评述[J].中国材料进展, 2014, 33:106)
[3] Li X, Bailey S I. A laboratory technique for evaluating marine splash zone corrosion[J]. Adv. Mater. Res., 2012, 347-353:3345
[4] Bi H C, Sykes J. An investigation of cathodic oxygen reduction be‐neath an intact organic coating on mild steel and its relevance to ca‐thodic disbonding[J]. Prog. Org. Coat., 2015, 87:83
[5] Shi W, Lyon S B. Investigation using localised SVET into protection at defects in epoxy coated mild steel under intermittent cathodic pro‐tection simulating inter-tidal and splash zones[J]. Prog. Org. Coat.,2017, 102:66
[6] Eltai E O, Scantlebury J D, Koroleva E V. Protective properties of in‐tact unpigmented epoxy coated mild steel under cathodic protection[J]. Prog. Org. Coat., 2012, 73:8
[7] Li Y N. The research of the cathodic ptotection effect on broken or‐ganic coating[D]. Qingdao:Ocean University of China, 2011(李玉楠.阴极保护对破损有机涂层防护作用的研究[D].青岛:中国海洋大学, 2011)
[8] Zhang L. The influence of cathodic polarization on performance of Zinc-rich coatings on steel[D]. Beijing:Beijing University of Chemi‐cal Technology, 2013(张丽.外加电流阴极极化下环氧富锌涂层的失效行为研究[D].北京:北京化工大学, 2013)
[9] Pan D W, Gao X X, Ma L, et al. Cathodic protection criteria of high strength steel in simulated deep-sea environment[J]. Corros. Prot.,2016, 37:225(潘大伟,高心心,马力等.模拟深海环境中高强钢的阴极保护准则[J].腐蚀与防护, 2016, 37:225)
[10] Zhang M S, Yin P F, Ma C J. The impressed current cathodic protec‐tion technology of jacket platform[J]. Total Corros. Control, 2013,27(3):20(张脉松,尹鹏飞,马长江.海洋平台外加电流阴极保护技术[J].全面腐蚀控制, 2013, 27(3):20)
[11] Yan M C, Xu J, Yu L B, et al. EIS analysis on stress corrosion initia‐tion of pipeline steel under disbonded coating in near-neutral pH simulated soil electrolyte[J]. Corros. Sci., 2016, 110:23
[12] Huang Y C. Electrochemical protection and its applicationⅡThe principle of cathodic protection and its application[J]. Corros. Prot.,2000, 21:191(黄永昌.电化学保护技术及其应用第二讲阴极保护原理及其应用[J].腐蚀与防护, 2000, 21:191)
[13] Le Thu Q, Takenouti H, Touzain S. EIS characterization of thick flawed organic coatings aged under cathodic protection in seawater[J]. Electrochim. Acta, 2006, 51:2491
[14] Touzain S, Le Thu Q, Bonnet G. Evaluation of thick organic coat‐ings degradation in seawater using cathodic protection and thermal‐ly accelerated tests[J]. Prog. Org. Coat., 2005, 52:311
[15] Funke W. Toward a unified view of the mechanism responsible for paint defects by metallic corrosion[J]. Ind. Eng. Chem. Prod. Res.Dev., 1985, 24:343
[16] S?rensen P A, Dam-Johansen K, Weinell C E, et al. Cathodic delami‐nation:Quantification of ionic transport rates along coating–steel interfaces[J]. Prog. Org. Coat., 2010, 67:107
[17] Li C J, Du M, Li Y, et al. The influences of protection potentials on the formation of calcareous deposits in dynamic seawater[J]. Peri‐odical Ocean Univ. China, 2011, 41(Z2):149(李成杰,杜敏,李妍等.动态海水中保护电位对钙质沉积层形成的影响[J].中国海洋大学学报(自然科学版), 2011, 41(Z2):149)
[18] Li C J, Du M. Research and development of cathodic protection for steels in deep seawater[J]. J. Chin. Soc. Corros. Prot., 2013, 33:10(李成杰,杜敏.深海钢铁材料的阴极保护技术研究及发展[J].中国腐蚀与防护学报, 2013, 33:10)
[19] Rousseau C, Baraud F, Leleyter L, et al. Kaolinite influence on cal‐careous deposit formation[J]. Electrochim. Acta, 2009, 55:196
[20] Wroblowa H S, Qaderi S B. Mechanism and kinetics of oxygen re‐duction on steel[J]. J. Electroanal. Chem. Interfacial Electrochem.,1990, 279:231
[21] Barchiche C, Deslouis C, Festy D, et al. Characterization of calcare‐ous deposits in artificial seawater by impedance techniques:3—De‐posit of CaCO3in the presence of Mg(II)[J]. Electrochim. Acta,2003, 48:1645
[22] Gutjahr A, Dabringhaus H, Lacmann R. Studies of the growth and dissolution kinetics of the CaCO3polymorphs calcite and aragonite II. The influence of divalent cation additives on the growth and dis‐solution rates[J]. J. Cryst. Growth, 1996, 158:310