不同浓度比的硫酸根和氯离子溶液中钝化膜的半导体特性转变机制研究

800合金作为核电站蒸汽发生器的一种关键材料,服役环境下其表面钝化膜的特性一直是人们研究的热点.本文用Mott-Schottky方法研究了800合金在不同硫酸根离子和氯离子浓度比的溶液中钝化膜的半导体特性,并结合电化学阻抗谱(EIS)、扫描电镜(SEM)、扫描电化学显微镜(SECM)研究了钝化膜的耐蚀性和表面活性.Mott-Schottky结果表明,800合金表面钝化膜的半导体特性与溶液中硫酸根、氯离子的浓度比有关,随硫酸根与氯离子浓度比的降低,半导体特性发生转变.当硫酸根与氯离子的浓度比较高时,钝化膜为p型半导体;而当硫酸根与氯离子的浓度比较低时,钝化膜为n型半导体.EIS、SECM、SEM结果表明,随浓度比的降低钝化膜由过钝化溶解转为明显的点蚀特征,钝化膜表面活性增加.钝化膜特性的改变与其半导体类型的转变密切相关,而半导体特性的转变由氯离子、硫酸根离子在800合金钝化膜表面的竞争吸附所致,其在表面的竞争吸附直接影响钝化膜表面发生的化学反应,改变电极/溶液界面电势差,使钝化膜中的空位类型改变,最终决定半导体类型.     

扫描电化学显微镜原位表征pH值对核电蒸汽发生器合金腐蚀行为的影响(英文)

用扫描电化学显微镜(SECM)和电化学阻抗谱(EIS)原位表征了溶液pH值对核电蒸汽发生器800合金溶液中的腐蚀行为的影响.实验结果表明:在酸性氯化钠溶液中,SECM探针渐进曲线为正反馈,表明800合金为活化阳极溶解,腐蚀电位下的EIS图呈现完整的单容抗弧特征;而在中性或者碱性溶液中,SECM探针渐进曲线为负反馈,表明800合金为自钝化,不同阳极电位下的EIS图均呈现不完整的容抗弧特征,但随着阳极极化电位的增加,EIS谱容抗弧半径减小,表明钝化膜的耐蚀性下降;SECM二维扫描图像结果显示探针电流增加,表明电极表面活性增加,即钝化膜的溶解速度增加.而在中性或者碱性溶液中的SECM二维图像中均可观察到若干活性点,这可能与晶界或者金属夹杂物等有关.     

扫描电化学显微镜原位表征pH值对核电蒸汽发生器合金腐蚀行为的影响

用扫描电化学显微镜(SECM)和电化学阻抗谱(EIS)原位表征了溶液pH值对核电蒸汽发生器800 合金溶液中的腐蚀行为的影响. 实验结果表明：在酸性氯化钠溶液中,SECM探针渐进曲线为正反馈,表明800合金为活化阳极溶解,腐蚀电位下的EIS 图呈现完整的单容抗弧特征;而在中性或者碱性溶液中,SECM探针渐进曲线为负反馈,表明800 合金为自钝化,不同阳极电位下的EIS 图均呈现不完整的容抗弧特征,但随着阳极极化电位的增加,EIS 谱容抗弧半径减小,表明钝化膜的耐蚀性下降;SECM二维扫描图像结果显示探针电流增加,表明电极表面活性增加,即钝化膜的溶解速度增加. 而在中性或者碱性溶液中的SECM二维图像中均可观察到若干活性点,这可能与晶界或者金属夹杂物等有关.     

镁合金在含F~-的NaOH溶液中钝化行为的电化学研究

采用极化曲线、电容-电位曲线、Mott-Schottky分析以及电化学阻抗(EIS)等电化学方法研究了镁合金在含F-NaOH溶液中的阳极钝化行为.结果表明,在-1.2～1.8V的电位范围内,镁合金在含F-的NaOH溶液中发生阳极钝化.所形成的钝化膜表现出n型半导体的导电特性.在0.7～1.8V的电位范围内,随着F-浓度增大,镁合金的阳极极化电流密度呈现出随着电位升高而逐渐增大的趋势,随着F-浓度增大这一趋势逐渐减弱.并且F-浓度的增大使得镁合金表面空间电荷层电容和钝化膜的载流子密度都不断减小.通过极化曲线和电化学阻抗共同说明,在5%的Na2SO4溶液中,NaOH溶液中阳极钝化后的镁合金随着钝化体系中F-浓度的增加其耐蚀性逐渐减弱。     

不锈钢钝化膜耐蚀性与半导体特性的关联研究

通过极化曲线、交流阻抗谱和钝化膜半导体特性等电化学测量，研究了经电化学阳极氧化处理的不锈钢钝化膜在0.5 mol•L^-1 NaCl溶液中耐蚀性能与其半导体特性的关系，进一步探索电化学改性处理不锈钢钝化膜的耐蚀机理. 结果表明，不锈钢钝化膜在负于平带电位范围表现为p型半导体，在高于平带电位范围表现为n型半导体，这主要与组成钝化膜的Fe和Cr氧化物半导体性质有关. 与自然条件下形成的不锈钢钝化膜比较，发现经过电化学阳极氧化后不锈钢钝化膜具有较低的施主与受主浓度，平带电位负移，说明阴离子在钝化膜表面发生吸附. 低的施主与受主浓度及钝化膜表面负电荷的增强，可有效排斥侵蚀性Cl^－在钝化膜表面的特性吸附，有利于提高不锈钢的耐局部腐蚀性能.     

N80油套管钢钝化膜的光电化学性能

采用电容测试法研究了N80油套管钢在浓度为0.5 mol/L NaHCO3溶液中形成钝化膜的半导体性能,结合Mott-Schottky方程分析了测试频率,成膜电位和C l-浓度对钝化膜半导体性能的影响。电容测试结果表明,钝化膜呈n型半导体特性,Mott-Schottky曲线的斜率随着测试频率的增加、成膜电位的正移和溶液中氯离子浓度的增加而增加,相应地膜内的施主密度减小。光电化学实验结果表明,光电流强度随成膜电位的正移及成膜时间的延长而增加,这主要归功于高电位和长时间下所成的钝化膜具有比较均匀的组成,光激发所成的空位或电子在膜内的迁移率的增加。     

无锡钢电镀溶液中氟离子电化学行为的研究

采用交流伏安法、电化学阻抗谱(EIS)和Mott-Schottky分析技术研究了无锡钢电镀液中氟离子电化学行为.结果表明,在氧化还原过程中氟离子抑制铬离子化学状态转变,降低铅合金和铅氧化物阳极的氧化电流密度,改变铅合金和铅氧化物阳极的氧化还原历程.EIS结果表明电场作用下溶液中铬氧离子团发生聚合,在铅合金阳极表面形成感抗现象.含氟溶液中铬氧离子团在阳极表面的感抗现象消失,溶液导电性提高.Mott-Schottky曲线显示氟离子提高阳极材料的载流子密度,铅合金阳极和铅氧化物阳极均为n型半导体.     

温度对铅阳极膜电化学性能的影响

利用线性电位扫描法、交流伏安法、电化学阻抗谱(EIS)及Mott-Schottky方程, 研究了温度对纯铅在4.5 mol/L H₂SO₄溶液中形成的阳极腐蚀膜电性能的影响. 结果表明: 温度对膜电化学性能具有显著的影响, 随着温度的升高, 膜的电阻增加, 孔隙率增加, 传递电阻减小. EIS结果表明膜的生长遵循固相机理, Mott-Schottky曲线显示腐蚀膜呈现n型半导体特性, 随着溶液温度升高, 膜内的施主密度减小.     

铬对碳钢在NaHCO3/NaCO3缓冲溶液中所成钝化膜半导体性能的影响

应用电化学阻抗谱技术研究铬对碳钢钝化膜半导体性能的影响.实验表明,在碳酸氢钠/碳酸钠缓冲溶液中碳钢形成的钝化膜具n型半导体特性,而含有3%铬的碳钢钝化膜则呈n-p型半导体特性,随着成膜电位的增加,以上两种钝化膜之Mott-Schottky直线部分的斜率均呈增大的趋势,表明成膜电位升高,膜内的杂质密度减小,但铬的加入使得碳钢钝化膜的施主密度增加约一个数量级,从而增加了碳钢点蚀发生的趋势.EIS分析表明:铬的加入降低了钝化膜的传递电阻R1和膜电阻R2,特别是膜电阻R2下降达3个数量级,这就有可能增加碳钢在高pH值环境中的腐蚀.     

双极性半导体钝化膜空间电荷电容分析

钝化膜的空间电荷电容的测量(Mott-Schottky(M-S)曲线)是研究其半导体性质的重要手段, 双极性半导体钝化膜在耗尽态电位区M-S曲线斜率往往会发生改变, 首先建立了半导体富集态、耗尽态以及反型态空间电荷电容的统一计算公式, 进而将双极性半导体钝化膜空间电荷电容等效为钝化膜/溶液界面处电容和内层钝化膜/外层钝化膜界面处的np结电容的串联, 模拟计算结果能够很好地解释M-S曲线斜率发生改变这一实验现象. 同时, 计算结果表明, 对于双极性半导体的M-S曲线, 利用其直线部分的斜率、直线与电位坐标轴的截距来确定钝化膜的载流子浓度以及平带电位会产生一定的误差.     

690合金在300 ℃含硫模拟碱性水化学中的腐蚀行为

Alloy 690 is one of the steam generator (SG) tubing materials in pressurized water reactors (PWR). The degradation of this alloy in alkaline solutions containing reduced sulfur is one of the main causes of stress corrosion cracking. In this study, the corrosion behavior of Alloy 690 in simulated alkaline crevice chemistry at 300 ℃ was investigated using polarization curves, scanning electron microscopy (SEM), Auger electron spectroscopy (AES), and time-of-flight secondary ion mass spectrometry (ToF-SIMS). Studying the effect of thiosulfate and sulfate on the properties of the passive film formed on Alloy 690 showed that the film formed at 300 ℃ was composed of an outer porous layer and an inner compact layer, and that the ion species presented in chloride solutions had a significant impact on the corrosion behavior of the alloy. The addition of thiosulfate increased the passive current density, decreased the transpassive potential, and therefore lowered the corrosion resistance. The presence of thiosulfate also led to a decrease in Cr levels and an increase in Ni levels in the passive layer. The thiosulfate can reduce sulfur at the film surface and enter into the film, causing an increased sulfide content in the film which decreases the corrosion resistance. However, experiments using sulfate had no obvious effect on film degradation as the ion had minimal interaction with the film.     

Electrochemical Behavior and Nonlinear Mott-Schottky Characterization of a Stainless Steel Passive Film

The electrochemical behavior of 304-stainless steel in solutions with different pH values and chloride concentrations was investigated by potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), and a nonlinear Mott-Schottky analysis method. The results showed that the corrosion behavior of 304-stainless steel was affected by various factors, such as pH, chloride ion concentration, and dissolved oxygen. The pit initiation and propagation stage were observed in EIS plots through the addition of sodium chloride. In addition, the effect of pH on the passive film dominated one of the film growth kinetic reactions. The effect of chloride ion concentration was caused by the generation of more cation vacancies, leading the passive film more susceptible to pitting, which was also demonstrated by X-ray Photoelectron Spectroscopy. The results are consistent with the point defect model.     

In-situ Study the Corrosion Degradation Mechanism of Tinplate in Salty Water by Scanning Electrochemical Microscopy

In this work, the corrosion degradation of tinplate in contact with salty water is investigated by scanning electrochemical microscopy (SECM) electrochemical impedance spectroscopy (EIS). Experimental results indicate tin maintains at passive state during the exposure; however, pores and defects existed in tin coating leads to an exposure of carbon steel substrate to the electrolyte, in which localized corrosion tends to occur within the pore. A phenomenological model is proposed to interpret corrosion mechanism of tinplate in contact with salty food based on the proposed electrochemical equivalent circuit.     

Investigation of stress-enhanced surface reactivity on Alloy 800 using scanning electrochemical microscopy

Scanning electrochemical microscopy (SECM) was used to simultaneously investigate the impact of tensile and compression stress on reactivity of the same Alloy 800 sample in ferrocenemethanol solution containing thiosulfate. Strong surface reactivity was observed on the stressed regions. Both tensile (the exterior edge) and compressed (inner edge) regions showed higher reactivity than the region between these. Hence both tensile stress and compression stress increased the localized surface reactivity, indicating potential for acceleration of corrosion susceptibility of Alloy 800 under stress in thiosulfate-contained chemistries.     

电解液添加剂硫酸亚乙酯对锂离子电池性能的影响

在1mol/LLiPF6/碳酸乙烯酯+碳酸二甲酯+碳酸甲乙酯(体积比1∶1∶1)电解液中,采用恒流充放电测试、循环伏安法(CV)、扫描电子显微镜(SEM)、能量散射光谱(EDS)、电化学阻抗谱(EIS)等测试技术,研究了添加剂硫酸亚乙酯(DTD)对锂离子电池性能及石墨化中间相碳微球(MCMB)电极/电解液界面性质的影响。结果表明,在电解液中引入体积分数0.01%DTD后,MCMB/Li电池可逆放电容量从300mA.h/g提高至350mA.h/g,电池总阻抗降低,循环稳定性提高。CV测试发现,在首次还原过程中,DTD在电极电位1.4V左右(vsLi/Li+)发生电化学还原,参与了MCMB电极表面固体电解质相界面膜(SEI膜)的形成过程。同时,DTD对LiMn2O4电极性能无不良影响。     

Application of scanning electrochemical microscopy and scanning electron microscopy for the characterization of carbon-spray modified electrodes

Different gold surfaces modified by carbon-spray have been investigated by scanning electron microscopy (SEM) and scanning electrochemical microscopy (SECM). A transformation of the SECM image to a distance-location profile is proposed which assists the correlation of both images. The structures found in the transformed SECM images of carbon-spray layers on gold substrates can be explained by the topographic features visible in the SEM pictures. Tempering the carbon spray results in an increased density of electrochemically reactive carbon particles which could be confirmed by cyclic voltammetric investigations. Gold minigrids modified with carbon spray expose some areas of especially large currents which could not be predicted from their SEM images. This effect may result from particles located at the edge of a wire intersection having relatively large active surfaces per particle. They contribute significantly to the total current of the minigrid.     

The local electrochemical behavior of the AA2098-T351 and surface preparation effects investigated by scanning electrochemical microscopy

In this work, scanning electrochemical microscopy (SECM) measurements were employed to characterize the electrochemical activities on polished and as-received surfaces of the 2098-T351 aluminum alloy (AA2098-T351). The effects of the near surface deformed layer (NSDL) and its removal by polishing on the electrochemical activities of the alloy surface were evaluated and compared by the use of different modes of SECM. Confocal laser scanning microscopy (CLSM) and scanning electron microscopy (SEM) were also employed to characterize the morphology of the surfaces. The surface chemistry was analyzed by X-ray photoelectron spectroscopy (XPS). The surface generation/tip collection (SG/TC) and competition modes of the SECM were used to study hydrogen gas (H₂) evolution and oxygen reduction reactions, respectively. H₂ evolution and oxygen reduction were more pronounced on the polished surfaces. The feedback mode of SECM was adopted to characterize the electrochemical activity of the polished surface that was previously corroded by immersion in a chloride-containing solution, in order to investigate the influence of the products formed on the active/passive domains. The precorroded surface and as-received surfaces revealed lower electrochemical activities compared with the polished surface showing that either the NSDL or corrosion products largely decreased the local electrochemical activities at the AA2098-T351 surfaces.     

Development of Solid Contact Micropipette Zn-Ion Selective Electrode for Corrosion Studies

Micron-size ion selective micropipettes can be used in scanning electrochemical microscopy (SECM). They can provide excellent spatial resolution. Unfortunately the resistance of these small sensors is high. Their application needs special shielding and slow scanning rates. Usually their lifetime hardly exceeds a few days.

Zinc layer or dispersed zinc particles containing films are often used for providing cathodic protection against corrosion in case of metal surfaces. Therefore, in corrosion studies, measurements of local zinc ion concentration can give important information about the nature of the process. For corrosion studies we needed SECM measuring tips for imaging concentration profiles of Zn²⁺ions involved in surface processes. Based on our earlier experience, solid contact micropipettes for selective measurements of Zn²⁺ion concentration were prepared with a tip size of a few micrometers. The properties of the micropipettes were investigated. They were also used in SECM imaging. In this paper, details of Zn²⁺ion selective microelectrode preparation are described. Data about their properties, lifetime, resistance, and ion activity response are shown. Preliminary findings in SECM imaging of zinc ion concentration profiles are shown. The improvement of the scanning rate achieved by lowering tip resistance is a main advantage in potentiometric SECM.