磁场对金属腐蚀影响的研究进展
Research Progress of Effect of Magnetic Field on Metal Corrosion
通讯作者: 蔡光义,E-mail:cgy54@sina.cn,研究方向为金属腐蚀与防护
收稿日期: 2023-11-29 修回日期: 2024-01-22
Corresponding authors: CAI Guangyi, E-mail:cgy54@sina.cn
Received: 2023-11-29 Revised: 2024-01-22
作者简介 About authors
朱立洋,男,1997年生,博士生
随着越来越多的电磁设备应用在腐蚀环境下,磁场对金属腐蚀的影响成为一个不可忽略的因素。已有相关研究表明,磁场对金属腐蚀的促进或者抑制作用取决于具体的工况环境。普遍认为磁场主要通过Lorentz力和磁场梯度力影响电化学过程中的粒子运动来影响金属的电化学腐蚀过程,具体表现在金属腐蚀过程中的传质、界面反应和腐蚀产物这3个方面。本文综述了磁场中Lorentz力和磁场梯度力对金属腐蚀过程的具体影响,指出了磁场对电化学腐蚀影响未来研究和应用的方向。
关键词:
With more and more electromagnetic equipment was applied in corrosion environment, the effect of magnetic field on metal corrosion has become a factor that cannot be ignored. It has been found that the promotion or inhibition effect of magnetic field on metal corrosion depends on the specific working environment. It is generally believed that the magnetic field affects the electrochemical process of particle movement mainly through the Lorentz force and magnetic field gradient force, so that to affect the electrochemical corrosion process of metal, specifically in the corrosion of metal in the process of mass transfer, interfacial reaction and corrosion products of these three aspects. This paper summarizes the specific effects of the Lorentz force and magnetic field gradient force on the metal corrosion process in the presence of magnetic fields, and puts forward the direction of the future research and application of the influence of magnetic field on the corrosion process of metallic materials.
Keywords:
本文引用格式
朱立洋, 陈俊全, 张欣欣, 董泽华, 蔡光义.
ZHU Liyang, CHEN Junquan, ZHANG Xinxin, DONG Zehua, CAI Guangyi.
目前,磁场对腐蚀过程的影响并没有统一的观点,已有研究中还存在相互矛盾的结果。其中,有研究表明磁场能抑制铜和铝箔在Cl-溶液中的腐蚀[6,7],抑制FeCl3溶液中AISI 303不锈钢的腐蚀[8],并且随着磁场强度的增大,磁场对金属腐蚀的抑制作用更明显。与此相反,还有研究表明磁场的存在促进了铁电极边缘的局部电化学腐蚀[9,10]。此外,有观点认为磁场对腐蚀电化学过程的影响主要体现在液相传质过程,对电荷转移步骤影响微乎其微,但也有研究认为磁场能促进镀锌钢[11]腐蚀电化学反应过程中的电荷转移步骤,抑制表面致密腐蚀产物的形成。因此,外加磁场对不同金属在不同溶液中的腐蚀程度和磁场产物影响不同,这可能取决于具体的实验条件,如电解质中离子的磁性、浓度,金属材质的磁性,磁场的大小和方向等[12,13]。
1 磁场对金属腐蚀的影响机理
其中,
当顺磁离子存在或在腐蚀过程中产生时,磁场梯度力的作用比较明显,顺磁离子将受到磁场梯度力的作用向磁场梯度较大的电极表面移动。有研究表明在H2SO4溶液中Fe会发生局部不均匀溶解,不均匀程度随磁通密度的增加而增大,这是由于Fe磁性铁电极上磁通密度的不均匀分布以及由此导致的局部界面膜传质速率的增强所致[10,32,33]。White等[34,35]研究表明Fe微电极在均匀磁场中磁化会产生局部磁场梯度,这种梯度足以改变耗尽层中氧化还原物种的分布,Fe微电极的梯度力在大小上与Lorentz力相当,甚至可能更大。因此,磁场梯度力也会对传质过程起到重要作用,Lorentz力和磁场梯度力共同决定了磁场对金属腐蚀过程的影响。
2 磁场对金属腐蚀过程的影响分析
表1 磁场对金属腐蚀过程的影响总结
Table 1
Influence factor | Research method | Main result |
---|---|---|
Magnitude and direction of magnetic field | Chemical soaking | Lorentz force accelerates mass transfer |
Concentration and magnetism and of ions | Electrochemical techniques | The magnetic gradient force affects the distribution of paramagnetic particles |
Magnetism of metal | Surface analysis | The magnetic field affects the corrosion behavior of metals by influencing the electrochemical reaction process |
2.1 磁场对腐蚀介质迁移的影响
磁场可以影响腐蚀介质中金属材料的电化学反应过程,特别是对液相传质过程的影响,而对电荷转移过程几乎没有影响。目前研究普遍认为磁场通过诱导溶液产生对流,从而增加了极限扩散电流密度,加速了传质过程[39~41]。任佩云等[42]通过X射线衍射(XRD)分析外加磁场0.4 T对不同铜合金腐蚀产物的影响,结果表明磁场不影响腐蚀产物元素种类(图1),表明海洋大气环境下磁场并不影响金属的电化学反应机理,而是通过影响反应离子的浓度分布来影响反应速率。Lyu等[43~45]对磁场下Fe的腐蚀进行了大量的研究,结果表明外加磁场对由电子转移步骤(ETS)控制的阳极溶解速度几乎没有影响(图2 AB Tafel区域),但对部分或全部由传质步骤(MTS)控制的阳极溶解速度有显著影响(图2 BC和CD区域)。当电流方向垂直于外加磁场时,因受Lorentz力的影响溶液中带电粒子的运动速度随磁感应强度的增大而增大,从而导致溶液的对流,加速传质过程,促进表面膜的溶解速度。
图1
图2
图3
磁场的大小和方向等特性对溶液中金属阳极溶解有着特殊影响。有研究[13]认为离子的传质控制着点蚀坑的稳定性,磁场可能通过影响传质过程来影响点蚀。磁场可以通过高场梯度力和Lorentz力的作用使铁磁性金属(Fe、Co或Ni)中的点蚀坑附近产生局部搅拌。如图4a,磁场平行于铁磁电极表面的点蚀坑时会引发局部搅拌作用,有助于将腐蚀产物输送出腔体并用新鲜溶液补充腔体,从而增加传质极限电流。当磁场垂直于电极表面时(图4b),场梯度力会将顺磁腐蚀产物引向金属表面,因此靠近点蚀坑表面边缘的金属离子容易达到饱和,腐蚀产物的覆盖充当保护层从而抑制了点蚀溶解。Wang等[47]研究磁场对Ni在HNO3 + NaCl溶液中腐蚀的影响也得出一样的结论,施加平行磁场时Lorentz力加强了传质过程,而施加垂直磁场梯度磁力抑制了对流,增加了电极/电解液界面局部位置的腐蚀产物的浓度。
图4
2.2 磁场对相界面反应的影响
图5
文献[51,52]认为铝镁合金会在NaCl溶液中腐蚀最先形成顺磁性粒子Al+ad,在顺磁梯度力的作用下使Al+ad聚集在铝合金电极表面,造成铝电极表面Al+ad浓度升高,并阻碍Al向Al+ad转变的反应过程,进而降低反应过程中生成Al3+的浓度,因此外加磁场会降低扩散层Al3+密度,减缓合金的腐蚀速率,降低腐蚀倾向。然而对于文献中提到的Al+ad是否能够稳定存在,在顺磁梯度力的作用下聚集在铝合金表面,并造成铝电极表面Al+ad浓度升高可能是难以确定的,这可能需要进一步研究讨论并加以证实。因为文献中也有提到Al+ad是铝合金腐蚀过程中不稳定的活性中间离子,极易失去电子或与水反应变成Al3+和Al(OH)3。
2.3 磁场对腐蚀产物的影响
磁场可以改变离子的运动从而影响腐蚀产物膜的生成、成分、破裂、剥落以及致密度等,进而促进或抑制金属的腐蚀行为。
Zhao等[53]研究表明对于Fe83Ga17合金,沿不同方向施加磁场时,顺磁性物质的分布差异使得V型槽腐蚀被增强或抑制。垂直于V型槽(B1)施加磁场时从V型槽底部开始沿垂直轴方向的磁通密度逐渐下降并趋向稳定[54],因此会出现一个指向V型槽内部的MFGF,它可以将顺磁性的氧分子和FeCl2吸引到V型槽内部,促进V型槽内的腐蚀。当磁场平行于V型槽(B2)时,腐蚀过程将相反,指向V型槽外部的MFGF可以将氧分子和FeCl2吸引到V型槽外部,减弱V型槽内部的腐蚀。当磁场沿V型槽的法线(B3)时,MFGF指向远离V型槽的两个表面,影响V型槽的上半部,吸引V型槽外部的顺磁离子(氧分子和FeCl2),而对V型槽的下半部影响不大。因此,V型槽内部的腐蚀受到轻微抑制。
Li等[55]研究了Fe78Si9B13玻璃合金在磁场作用下的腐蚀行为,结合EIS、EDS和XPS分析表明在0.2 T磁场作用下,磁场增强了非保护性Fe2O3的形成,诱发了应力集中,从而促进了保护性氧化硅膜的开裂,导致了严重的腐蚀。Hu等[56]研究表明磁场改变了铍铜的表面形貌和腐蚀产物中氧的分布,在低NaCl浓度下(图6a),0.4 T磁场下样品表面可以看到立方体状的团簇,磁场下腐蚀产物中氧含量的增加表明磁场加速了腐蚀过程。而在高浓度NaCl情况下(图6b),在没有磁场的情况下,样品表面可以看到雪花状的腐蚀产物,0.4 T磁场作用下铜样品腐蚀产物中氧含量下降,表明磁场抑制了铍铜的腐蚀。Zhao等[29]研究表明磁场可以通过增强电荷转移电阻Rct和磁离子吸附引起的感抗电阻RL(图7),两种方式影响碳钢表面中间产物FeOOH的形成,增强碳钢表面腐蚀产物的致密性,从而有效抑制碳钢的腐蚀行为。
图6
图6
铍铜在0 T和0.4 T磁场下浸入1%和3.5% NaCl溶液中15 d后的SEM图像和腐蚀产物化学成分[56]
Fig.6
SEM images (a1, a2, b1, b2) and chemical compositions (a3, b3) of the corrosion products formed on beryllium copper after immersion in 1% (a) and 3.5% (b) NaCl solutions for 15 d in 0 T (a1, a2) and 0.4 T (b1, b2) magnetic fields
图7
3 总结与展望
磁场对金属腐蚀过程的影响主要通过Lorentz力和磁场梯度力来实现。磁场强度和方向决定了带电粒子所受Lorentz力的大小,Lorentz力会影响极限扩散电流密度,引起对流从而增强传质过程。磁场梯度力会使顺磁性粒子在高磁通量的区域集中,进而影响电化学反应过程。磁场对金属腐蚀过程的影响具体表现在金属腐蚀过程中的传质、界面反应和腐蚀产物这3个方面。
目前,由于实验条件等因素的局限性,大多数研究是局限于静态均匀磁场,并且磁场强度较低(0.5 T及以下)。对于实际应用中电气设备引起的复杂磁场环境,如非均匀磁场、交变磁场、强磁场等条件下对金属的腐蚀影响还需进一步研究,从而更好的采取防护措施避免磁场加速金属腐蚀影响设备安全服役。
目前,磁场已被证明可以改变水的物理化学性质,对溶解、沉积、凝固等方面产生影响,有效防止和减少水垢、油垢、石蜡沉积等,在工业设备管路抑垢、缓蚀等方面应用前景广阔。其次,通过磁场增强传质和磁场梯度力促进零价铁(ZVI)的腐蚀可以有效促进污染水中零价铁对Se(IV)、As(V)和Cu2+等污染物的去除[9],磁场处理是污染水处理中一种很有前景的环保方法。此外,磁场引起的磁流体动力学效应已被证明可以引起电化学沉积时钴、锌镍合金等金属沉积物的表面形态、相成分、结构等变化,从而可以合理地调控合金成分和性质,提高其耐蚀能力。
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[J].通过扫描电子显微镜、能谱分析仪、电化学工作站研究了磁场对不同Mg含量Al-Mg合金腐蚀行为的影响;通过自制磁场装置对氯化钠溶液进行磁化处理,研究磁场对溶液性质的影响。探究磁场对带电粒子的作用和磁场对溶液性质的改变对铝镁合金腐蚀过程的影响差异。结果表明,溶液经过磁场处理后,pH和电导率增加,进而导致合金的腐蚀速率升高。在磁场的作用下,顺磁粒子Al<sub>ad</sub><sup>+</sup>被聚集在合金表面,抑制腐蚀进一步发展,从而降低了铝镁合金的腐蚀速率。磁场对带电粒子的作用大于溶液pH和电导率变化对合金腐蚀行为的影响,因此整体上导致合金腐蚀速率的降低。
Effect of a magnetic field on stress corrosion cracking of Fe83Ga17 alloy
[J].
Influence of high magnetic field on the corrosion of carbon steel
[J].
Severe corrosion behavior of Fe78Si9B13 glassy alloy under magnetic field
[J]. J.
Effects of applied magnetic field on corrosion of beryllium copper in NaCl solution
[J].<p>The effects of an applied magnetic field on the corrosion process of beryllium copper in NaCl solution have been investigated by electrochemical measurements, scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The results showed that a horizontal magnetic field with 0.4 T barely shifted the open circuit potentials (<em>E</em><sub>corr</sub>) of beryllium copper in NaCl solution with different concentrations. However, the horizontal magnetic field increased the limiting current density of beryllium copper in NaCl solution with low concentration, while decreased the limiting current density of beryllium copper in NaCl solution with high concentration. It was found that magnetic field accelerated the diffusion of CuCl<sup>2-</sup> away from the electrode surface and delayed the formation of Cu<sub>2</sub>O. The results of SEM and EDS showed that the influence of magnetic<br />field over the elements distribution of the corrosion products differed from the di®erent concentration of the immersion solution.</p>
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