, 马力, 叶章基, 李相波
, MA Li, YE Zhangji, LI Xiangbo
采用海水压力罐模拟深海高压环境,利用电化学阻抗谱 (EIS)、三维视频显微镜和扫描电子显微镜 (SEM) 等手段,对比研究了改性环氧防腐涂层在常压海水环境和模拟深海高压环境 (6 MPa海水压力) 下的失效行为。结果表明,试样在深海高压环境下浸泡30 d后,涂层阻抗已降低到105 Ωcm2;而常压环境下,涂层阻抗仅降低到108 Ωcm2,深海高压环境促使涂层更快地吸水达到饱和状态,高压环境导致涂层下的金属腐蚀活性面积不断增大,基体金属腐蚀速率不断增加。SEM观察表明,高压导致环氧防腐涂层中的颜填料发生脱附,使涂层/金属基体界面弱化,腐蚀活性表面积增大,从而导致涂层破损和基体腐蚀。
The degradation behavior of a modified epoxy resin coating was comparatively studied in sea water at atmospheric pressure and in a simulated deep-sea environment with high hydrostatic pressure of 6 MPa by means of electrochemical impedance spectroscopy (EIS), 3D optical microscope and scanning electron microscope (SEM). The results showed that the resistance of the coating decreased to 105 Ωcm2 after 30 d immersion under high hydrostatic pressure, while that decreased to 108 Ωcm2 at atmospheric pressure. The deep-sea environment can induce the enlargement of the active area and shorten the water-saturation process of coatings, therewith, the corrosion rate of the substrate was instantly accelerated. SEM showed that the hydrostatic pressure can deteriorate the attachment of pigments with the epoxy and weaken the adhesion between the epoxy coatings and the metal substrate. In this case, the active area of corrosion was enlarged, whilst the degradation of coatings and the corrosion of the steel substrate simultaneously occurred.
本文采用海水压力罐模拟深海高压环境,采用电化学阻抗谱 (EIS)、三维视频显微镜、扫描电子显微镜 (SEM) 等手段对浸泡在常压海水环境和模拟深海高压环境 (6 MPa海水压力) 中的改性环氧防腐涂层性能进行了对比研究,分析探讨了深海高压环境对该涂层失效行为的影响以及作用机理,以期为环氧防腐涂层的工程化应用以及新型深海防腐涂层的开发和改进提供技术依据。
基体金属材料为Q235钢,试样尺寸为30 mm×30 mm×3 mm,将其表面进行喷砂处理达到Sa 2.5级,经丙酮除油、无水乙醇除水后干燥。然后,采用手工方式刷涂改性环氧防腐涂层,并将试样放置于恒温箱中,控制条件为：40 ℃/24 h+室温 (25 ℃,30%RH)/168 h (7 d),以获得厚度均匀一致的涂层。
本实验采用的改性环氧防锈漆 (H44-61G) 由七二五所厦门分部提供。该防锈漆拟用于深海钢结构物表面防腐,实际工程中通常采用重防腐涂层体系,由2~3道改性环氧防腐涂层组成,涂膜厚度达到300~500 μm。由于该厚膜涂层在实验室浸泡条件下短期内不会产生明显变化,为便于研究该涂层的失效行为,本研究工作采用了较薄的涂层试样,涂层干膜厚度控制在 (80±5) μm。实验前采用KL-8型数字式直流电火花检漏仪检测涂层完整性,并采用MiniTest 600涂层测厚仪测量涂层厚度,每个试样选取5个点测试,最后取平均值。
本实验包括常压海水环境和模拟深海高压海水环境 (模拟水深约600 m处海水压力)。深海环境中的压力、温度、溶解氧等因素都和表层海水存在较大差别,每种因素都会对带涂层钢的腐蚀行为产生影响。本文只对比研究了其他因素相同时,海水压力对涂层失效的影响。常压海水浸泡实验在装有海水的烧杯中进行。采用Cortest公司的SSRT/Constant load/Low Cycle Fatigue测试系统模拟高压海水环境,压力控制在 (6.0±0.1) MPa。腐蚀介质为青岛本地天然海水,介质温度为室温 (25±1) ℃。
将进行电化学测试的带涂层钢试样连接导线后,采用环氧树脂进行封装,预留20 mm×20 mm的工作面积,分别置于两种模拟环境中进行浸泡实验。浸泡期间,选取2,4,9,12,16和30 d等6个测试周期点,定期将常压海水环境和模拟高压海水环境下的带涂层钢试样取出进行EIS测试。测试使用Princeton PAR2273电化学工作站,采用三电极体系,工作电极为带涂层钢试样,辅助电极为Pt电极,参比电极为饱和KCl甘汞电极。测试在腐蚀电位下进行,扰动信号为幅值50 mV的正弦波,测试频率设定为105~10-2 Hz。测试结束后,采用ZSimpWin软件对EIS数据进行拟合分析。
采用HIROXKH-8700三维视频显微镜对试样进行形貌观察,将浸泡实验前后试样的形貌进行对比分析。
依照ASTM D4541-2009 《用便携式附着力测试仪测定涂层拉脱强度》标准,选用PosiTest拉拔式附着力测试仪将浸泡后的涂层拉脱,锭子直径为20 mm,记录拉拔后涂层的破坏形式和拉拔强度的大小,将带有拉脱后涂层的锭子置于Philips XL30场发射扫描电子显微镜下 (FE-SEM) 进行形貌观察,操作电压为20 kV。
2.1.1 常压海水环境下的EIS
图1 常压海水环境下浸泡不同时间后改性环氧涂层的EIS谱 (散点为测量数据,实线为拟合结果)
Fig.1 Nyquist (a, b) and Bode (c, d) plots of the modified epoxy coating immersed in sea water for different time at atmospheric pressure (Scattered points: experimental data, solid lines: fitting results)
2.1.2 模拟深海高压海水环境下的EIS
2.1.3 常压和高压两种海水环境下涂层电化学参数的比较 低频阻抗模值可以比较直观地展现涂层性能随浸泡时间的变化,
图3 模拟深海高压海水环境下不同浸泡时间后改性环氧涂层的EIS谱 (散点为测量数据,实线为拟合结果)
Fig.3 Nyquist (a, b) and Bode (c, d) plots of the modified epoxy coating immersed in sea water for different time at 6 MPa (Scattered points: experimental data, solid lines: fitting results)
图4
等效电路
Fig.4
Equivalent circuit models of
图5 常压海水环境和高压海水环境下涂层在0.01 Hz时的阻抗随浸泡时间的变化
Fig.5 Impendences determined at 0.01 Hz for the epoxy coating after immersion for different periods in sea water at atmospheric pressure and 6 MPa pressure
为了对比分析涂层的性能变化,采用
图6 常压和高压海水环境中改性环氧涂层的电容和电阻随浸泡时间的变化
Fig.6
Capacitance (a) and pore resistance (b)
从
图7
模拟深海高压海水环境中浸泡9 d后涂层的
Fig.7
根据有机涂层吸水体积计算公式[18],可以依次计算出不同浸泡时间后有机涂层的吸水率：
式中,
图8 改性环氧涂层在常压和高压海水环境条件下吸水率随浸泡时间的变化
Fig.8 Evolutions of water absorption rates of the modified epoxy coating immersed in sea water under atmospheric and 6 MPa pressures
从改性环氧涂层吸水率的变化曲线可以看出,在常压海水环境条件下,涂层经历了逐渐吸水并达到饱和的过程,饱和吸水率约在7%;而在高压海水环境条件下,涂层更快地吸水并达到饱和。
图9 改性环氧涂层在两种模拟海水环境浸泡前的表面形貌
Fig.9 Surface morphologies of the modified epoxy coating before immersion test in sea water at atmo-spheric (a) and 6 MPa (b) pressures
将浸泡后的两种试样按照标准进行拉拔实验,拉拔结果均为涂层的内聚破坏,常压下浸泡后的涂层附着力为6.12 MPa,高压下浸泡后的涂层附着力为4.65 MPa,而未浸泡涂层试样的附着力为10.88 MPa (平行样测试的平均值,平行样涂层厚度80 μm)。从附着力测试的结果可以看出,高压下浸泡后的涂层附着力下降比常压下浸泡后的明显。将拉脱后涂层置于SEM下观察 (见
有机涂层的屏蔽作用同涂层中颜填料状态密切相关。理想情况下涂层颜填料应该是细小均匀地分布在涂层中,阻挡水等腐蚀性介质的渗透。颜填料脱附使得水的有效扩散路径相对缩短,水更易沿着颜填料脱附形成的界面通道渗透过涂层,到达涂层/基体界面处,导致腐蚀发生。
图10 改性环氧涂层在两种模拟环境中浸泡30 d后的形貌
Fig.10 Surface morphologies of the modified epoxy coating after immersion in sea water for 30 d at atmospheric (a) and 6 MPa (b) pressures
(1) 相比于常压海水环境,改性环氧涂层在模拟深海高压海水环境条件下更容易失效。涂层在常压海水中浸泡30 d后,阻抗仍维持在108 Ωcm2数量级,表明涂层仍处于完好状态;而在高压 (6 MPa) 海水中浸泡30 d后阻抗已降到105 Ωcm2数量级,表明涂层已失去保护作用,金属基体已发生腐蚀。
(2) 涂层吸水率随浸泡时间逐渐增大,并在后期吸水逐渐达到饱和。在模拟深海高压环境条件下,涂层在第9 d吸水达到饱和,而常压海水中这一过程需要16 d。涂层吸水率在模拟深海高压海水环境中的要比在常压海水中的更大,吸水更快。
(3) 深海海水的高压作用会使改性环氧树脂涂层中的颜填料更容易脱附,并且也会使涂层/金属基体界面弱化,腐蚀活性表面积增大,从而促进涂层破损和基体腐蚀。
The authors have declared that no competing interests exist.
| [1] |
[本文引用:1]
|
| [2] |
The interest in deep-sea environment is increasing both in the scientific and business community. In order to meet deep-sea challenges great performances for structure materials are requested, but in situ studies are difficult to be executed due to high experimental cost and technical problems. Indeed, they are quite uncommon in the available literature compared with the amount of research in shallow sea water. This paper reviews the scarce available literature about deep-sea environment studies on corrosion of metals and alloys, some outlines of investigations on sunk objects are given.
|
| [3] |
slightly alkaline-solutions; sea-water; protective ability; passive; film; carbon steel; mild-steel; layer; iron; environments; temperature
|
| [4] |
A potential-control circuit has been devised to measure passive-current (corrosion rate) on stainless alloys in conditions simulating the usual noble drift of the open-circuit corrosion potential in the presence of passivating dissolved oxidizers. Open-circuit corrosion potential and passive-current decay were measured with and without dissolved oxygen in dilute sulfuric acid solutions as a function of time on austenitic stainless steel and a Ni-base Cr–Mo–W alloy. The results confirm the long-standing assumption that constant-potential potentiostatic tests give a good approximation of passive-film growth kinetics in the presence of passivating dissolved oxidizers. Mott–Schottky measurements showed that passive films on each alloy have similar semiconducting properties whether formed potentiostatically or by dissolved oxygen. In both cases, the passive film on stainless steel seems to be composed of an inner n-type barrier layer covered with an outer p-type layer. The passive film on the nickel-base alloy is primarily n-type with only weak evidence of p-type behavior in an outer layer. Results are in general agreement with predictions of the point-defect passive-film model proposed by Macdonald and coworkers.
|
| [5] |
The effect of hydrostatic pressure on the pit corrosion behavior of Fe–20Cr alloy was investigated in 3.5% NaCl solution by means of potentiodynamic polarization and potentiostatic technology, and the experiment data was analyzed based on stochastic theory. With the increase of hydrostatic pressure, the pit corrosion resistance of Fe–20Cr alloy was deteriorated, which was distinguished by the decrease of critical pit potential () and the increase of passive current density. The results also demonstrated that there exist two effects of hydrostatic pressure on the corrosion behavior of Fe–20Cr alloy: (1) the pit generation rate was evidently increased compared to that under lower hydrostatic pressure, and the metastable pits become faster and larger. However, it seemed that pit generation mechanism shows no hydrostatic pressure dependence; (2) the probability of pit growth increased with the increase of hydrostatic pressure, which implied that the metastable pit on Fe–20Cr alloy exhibited higher probability to become larger pit cavity during shorter time interval than that under lower hydrostatic pressure.
|
| [6] |
61High tensile device was used to study SCC of X65 pipeline in deep sea.61The organization of weld joint was simulated and its behavior was studied in deep sea.61The effect of hydrogen in SCC was studied in deep sea.
|
| [7] |
[本文引用:]
本文介绍了国外铝合金深海腐蚀的研究进展,并与表层海水铝合金的腐蚀情况进行对比,讨论了点蚀、缝隙腐蚀、应力腐蚀等铝合金深海典型腐蚀特征及规律,同时进一步展望了铝合金在深海中的应用前景及发展方向.
|
| [8] |
Fur TYPES of metals (mild steel. brass. alum! nium and stainless st~ el) were exposed during the I~ eriod Novemb~ r, 1987, to November, 1988, at depths exceedmg IOOOm In the Arabian Sea, m order to assess thezr behavIOur with respect to corrosion. The results
URL
[本文引用:]
|
| [9] |
Abstract: The deep sea corrosion of ferrous alloys that undergo uniform corrosion without forming a passive layer is related to the amount of dissolved oxygen available in the sea water. The preformance of some ferrous alloys at depths of 500, 1200, 3500, and 5100m in the Indian Ocean has been studied. The results of atomic absorption spectroscopy have revealed that the corrosion product present on mild steel coupons is FeOOH. The results of experiments in shallow water have shown that micro- and macrobiological growths play a significant role in the corrosion of ferrous materials. However, in deeper waters, the absence of macrofouling was evident, and corrosion was not related to any biological product but mainly to the electrochemical reaction of these alloys with sea water. The results of morphological studies by SEM on the surfaces of exposed specimens are also presented.
|
| [10] |
[本文引用:1]
|
| [11] |
The failure of organic coating (epoxy resin filled with 5 mass% nano-SiO 2 particles) on mild steel under high hydrostatic pressure (35 atm) has been studied compared with that under atmospheric pressure (1 atm), using impedance measurements, gravimetric testing, adhesion testing and scanning electron microscopy (SEM). The results show that high hydrostatic pressure accelerated the failure of the organic coating by promoting diffusion of water in the coating, which speeds up water spread and electrochemical reactions at the interface. The roughness of the coating and steel has been discussed from point of view of their respective fractal dimensions D fc and D fdl, as deduced from impedance measurements
|
| [12] |
[本文引用:1]
|
| [13] |
[本文引用:]
|
| [14] |
Model epoxy coatings on a steel substrate have been investigated whilst immersed in a 3% NaCl solution using electrochemical impedance spectroscopy (EIS). The impedance of these barrier coatings remained high for a very long time during exposure and a superficial evaluation of the Nyquist plots of the impedance gave no indication of any change. However, a more accurate study matching the impedance to equivalent circuits containing a constant phase element (CPE) has revealed changes in the dielectrical properties of the coatings during long exposure times. In this way it was possible to detect localised loss of adhesion and the start of the corrosion process at the interface. These results have been compared with those of an investigation of the impedance of a dielectric sensor coated with the same coatings. With the dielectric sensor, a qualitatively similar response was observed as for the coatings on the steel panels and a separate water phase has been detected under the coating after immersion. With these additional results, the response of the coating/steel system may best be explained in terms of areas in the coating with different dielectrical behaviour due to localised loss of adhesion and the formation of corrosion products under the coating.
|
| [15] |
[本文引用:1]
从开发海洋和军事应用前景等方面分析了材料深海环境腐蚀性能研究 的实际需求和必要性;介绍了深海环境因素的特点--压力大、温度低、氧含量低;综述了美国、苏联、印度、挪威等国进行深海腐蚀试验的情况、试验研究方法. 深海腐蚀试验的特点是困难、复杂、危险和昂贵.简述了我国进行深海试验的必要性和前景.
|
| [16] |
One of the major factors affecting the acceptability of novel coating in engineering applications is the degradation of the coating by the moistures that will affect the physical and mechanical performances and causing it to fail. Nanoscale reinforcement provides opportunities for enhancing the polymer system with unique properties and increases the performance. These advantages not only lead to an improvement in the mechanical properties but also act as a barrier to slow the water permeation. In this study, an organically modified montmorillonite (MMT) nanoclay and a further modified “X-treated supernanoclay” were used to reinforce an isophthalic unsaturated polyester gelcoat. Five gelcoat systems were prepared and characterised by using a boiling water absorption test (with a saturation time of 1202h) to characterise and quantify the degree of water absorption. All nanocomposite samples show a very convincing result in terms of the coefficient of moisture absorption and reduction in water ingress as a function of weight fraction of nanoclays. The “X-treated supernanoclay” reinforced systems show the greatest improvement compared to conventional nanoclay system.
|
| [17] |
In this paper, the ultrasonic methods were used to assess an adhesion between polymer composite and concrete substrate. The usability of indirect (surface) ultrasonic methods was evaluated on the example of commercial polymer coating. The relationships between pull-off strength and propagation of ultrasonic wave were established and analyzed. The effect of chemical composition and thickness of PC system was discussed. The results confirmed usefulness of indirect ultrasonic method for non-destructive mapping of adhesion between polymer composite and concrete substrate.
|
| [18] |
[本文引用:2]
介绍了研究涂层性能的电化学阻抗谱(EIS)实验方法以及该方法在研究、评价有机涂层方面的应用。由于涂层的种类很多,每种涂层的防护机制各不相同,其EIS的数学物理模型也各不相同,本文共建立了6种模型(等效电路)来分别处理不同有机涂层体系的电化学阻抗谱。介绍了EIS数据处理的快速方法——特殊频率法。
|
