LC4铝合金在氯化钠溶液中的孔蚀特征

LC4铝合金在 2 .0 %NaCl溶液中发生局部腐蚀的过程中 ,电位噪声的谱功率密度 (SPD)曲线具有相同的特征 ,即在极低频下为白噪声 ,随着频率的升高逐渐转化为 1/fa 噪声 ,相应于一个噪声信号波 ,有一个腐蚀孔出现。在孔蚀诱导期 ,白噪声水平升高 ,截止频率增大 ,SPD曲线的倾斜段直线斜率小于 - 2 5dBv/Hz ,且趋于增大。孔蚀发生后 ,上述 3个参量则各自朝着上述方向的逆方向变化。实验发现 ,孔蚀参数SE 和SG 可以正确的表征孔蚀的发生、发展及材料的均匀腐蚀。阻抗测量结果表明 :孔电阻在刚开始浸泡时较大 ,随后减少渐趋于平稳 ,最后孔电阻又升高。这是因为随着浸泡时间的增加 ,孔面积渐渐增大 ,浸泡 6 5 0 0 0min时 ,孔电阻有所上升 ,可能是由于母孔内子孔的形成所致。产物电阻逐渐稳定上升 ,表明腐蚀产物逐渐增多。     

孔蚀过程中电流噪声特征研究

研究了钝化的纯铁在含 Cl~-的中性溶液中及304和321不锈钢在含 Cl~-的硫酸溶液中在低于孔蚀电位的恒电位条件下电流噪声的特征。结果表明,噪声电流峰具有线性上升而后按指数规律衰减的特征。在一定条件下噪声电流上升到最大值所需时间ιc 大致恒定,但ιc 随电位的升高而增大。功率密度谱(SPD)曲线的截止频率都低于20Hz,表明孔核的发生、成长与再钝化过程是相当缓慢的过程。所有 SPD 曲线在极低频率下具有白噪声的特征,即功率密度的水平不随频率改变。随着频率的升高,SPD 曲线显示噪声转变为1/f~n 噪声。视腐蚀体系和控制的电位之不同,测得的表观 n 值在2～4之间。实验结果征实了前一篇文章中导出的 SPD 方程式[1]是适用的。讨论了表砚 n 值落在2～4之间的原因。     

孔蚀过程中的电化学噪声特征

研究了几种钝态金属在合有活性离子的中性缓蚀剂体系及硫酸体系中发生局部腐蚀时的电化学噪声行为。结果表明:在研究的所有腐蚀体系中,饨态表面孔蚀过程中腐蚀电位波动噪声的功率密度谱(SPD)曲线都具有相同特征,即在极低频率下为白噪声,随频率升高,逐渐转变为1/f~n 噪声。视金属材料不同,测得的表观 n 值在2.2—3.4之间。SPD 曲线上最高频率 f_c 与溶液中 Cl~-浓度关系呈现三种类型。提出了一个解释实验结果的 SPD 的数学模型.     

NaCl溶液中LC4,LY12及纯铝腐蚀过程的电化学噪声特征

应用电化噪声（electrochemical noise)技术对航空铝合金结构材料LC4，LY12及纯铝在质量分数为2．0％的NaCl溶液中的腐蚀过程进行了研究，发现不同材料在发生点蚀时其电化学噪声的时域谱波形特征各不相同，电化学噪声的频域谱SPD（spectra power density)曲线的三个特征参数：白噪声水平W，截止频率fc和高频线性部分的斜率K均随浸泡时间的延长而变化，在发点蚀时三者均趋于极值，但三者都不能单独正确地表征点蚀的强度和趋势，实验结果时表明：点蚀时，从不同材料的SPD曲线获得的点蚀参数SE和SG的数值具有一致性，且与未点蚀时的参数值存在着明显的区别，一般在而，点蚀发生时，SE＞5且SG＜1；非点蚀时，二者的取值正好相反，因此，二者可以很好地表征点蚀的发生。     

304不锈钢点蚀的电化学噪声特征

使用电化学噪声技术,通过长期连续实时监测,对304不锈钢在0.5mol/L FeCl₃溶液中发生局部腐蚀的点蚀发展过程和腐蚀机理进行研究。综合谱图分析、时域统计分析、小波分析等诸多方法进行分析和论证。结果表明：电化学噪声的谱图可以明显地分为4个阶段,分别对应于点蚀发展过程中的钝态期、亚稳态点蚀期、稳态点蚀期及稳态点蚀后期。在时域分析时,先用3阶多项式拟合移除漂移,电流噪声标准偏差Si在亚稳蚀和稳态点蚀阶段发生明显的升高,噪声电阻(R_n)、点蚀指标(PI)在对应时间点表现出相应的降低或升高。小波分析表明,随着反应的进行,能量积累开始逐步增大;亚稳态点蚀期能量开始向d4~d6处累积,当进一步发展为稳态点蚀时d5~d8出现极大值。     

镁合金阳极氧化膜腐蚀过程的电化学阻抗谱研究

采用阳极氧化工艺对AZ91D镁合金进行表面处理，利用电化学阻抗谱（EIS）方法研究AZ91D镁合金阳极氧化膜层在3．5％NaCl溶液中的腐蚀过程。根据腐蚀过程阻抗谱的变化特点，分别采用R（RQ）（RQ）模型和R（Q（R（RQ）））模型的等效电路来拟合阳极氧化膜层在孔蚀诱导期和在孔蚀发展期的电化学阻抗谱图。结果表明：在孔蚀诱导期，随浸泡时间的延长，溶液电阻Rsol和多孔层的电容Yp有所增大，多孔层电阻琊和阻挡层电阻风逐渐减小，弥散效应指数np值基本不变，而阻挡层的电容Yb和弥散效应指数nb无明显的规律性；在孔蚀发展期，随浸泡时间的延长，溶液电阻Rsol，弥散效应指数n1和蚀孔内的反应电阻R2逐渐减小，电容Y1逐渐增大，而蚀孔内溶液电阻R1，蚀孔内阳极金属／介质界面的常相位角元件Q2的电容Y2及弥散效应指数n2无明显的规律性。     

腐蚀电化学中的频谱分析研究

简要介绍了我们实验室中进行的电化学阻抗频谱(EIS)与孔蚀诱导期中电化学噪声(EN)的谱功率密度(SPD)的研究进展。通过引入定态过程稳定性条件,导出了具有2和3个时间常数EIS的法拉第导纳公式,将它们应用于EIS数据分析的工作也正在进行中;发展了混合电位下的EIS理论并成功地应用于界面型缓蚀剂研究。证明了孔蚀诱导期中EN的SPD的特征是:极低频率下为“白噪声”,在较高频率下则转变为f~n噪声,n的数值在2至4之间。导出了相应的理论公式。     

腐蚀电化学中的频谱分析研究

简要介绍了我们实验室中进行的电化学阻抗频谱(EIS)与孔蚀诱导期中电化学噪声(EN)的谱功率密度(SPD)的研究进展。通过引入定态过程稳定性条件,导出了具有2和3个时间常数EIS的法拉第导纳公式,将它们应用于EIS数据分析的工作也正在进行中;发展了混合电位下的EIS理论并成功地应用于界面型缓蚀剂研究。证明了孔蚀诱导期中EN的SPD的特征是:极低频率下为“白噪声”,在较高频率下则转变为f~n噪声,n的数值在2至4之间。导出了相应的理论公式。     

静水压力对超纯Al/超纯Fe电偶中超纯Al腐蚀行为的影响

采用动电位极化和电化学噪声方法在3.5%NaCl中研究了静水压力对超纯Al/超纯Fe电偶中超纯Al腐蚀行为的影响。利用离散小波变换去除噪声信号的直流漂移,然后进行散粒噪声和随机分析;利用HilbertHuang变换对噪声信号做时频分析;用SEM观察腐蚀试样的表面形貌;用有限元方法模拟压力分布。结果表明,不同静水压力下超纯Al在3.5%NaCl溶液中皆自钝化,与超纯Fe偶合后发生点蚀。随静水压力的升高,超纯Al/超纯Fe的电偶电位逐渐降低,电偶电流逐渐增大。静水压力越高,经电偶腐蚀后超纯Al表面形成的点蚀坑尺寸越小且分布更加均匀。静水压力的提高加速了电偶腐蚀中超纯Al的点蚀孕育速率,但抑制了点蚀生长概率,降低了局部腐蚀倾向。静水压力为常压时,点蚀可沿水平、竖直方向扩展;在静水压力存在的条件下,点蚀更易于沿水平方向扩展。     

锆在含四丁基溴化铵异丙醇溶液中的腐蚀行为（英文）

采用循环伏安、线性扫描、计时电流和扫描电镜(SEM)方法研究锆在含四丁基溴化铵异丙醇溶液中的腐蚀行为。循环伏安曲线表明,在Br-击穿钝化膜诱发点蚀前,锆在异丙醇溶液中不发生活性溶解。扫描电子显微镜证实了点蚀的发生,且电位正移,点蚀加剧,深度增加,腐蚀面积增大。随着溶液温度升高,四丁基溴化铵的浓度增大,锆点蚀电位均下降;而随着扫描速度增大,锆点蚀电位升高。腐蚀电流密度随温度升高而增大,锆阳极溶解表观活化能为21.88 k J/mol。计时电流曲线表明,四丁基溴化铵浓度增大,点蚀诱导时间缩短,点蚀成核和生长速度均增大。该研究结果有利于获得电化学合成异丙醇锆的最佳工艺条件。     

Crevice corrosion and pitting detection on 304 stainless steel using electrochemical noise

Random fluctuations in current and voltage under free corroding conditions have been measured on austenitic steel 304 in sodium chloride solutions with different aggressiveness. The evolution of these fluctuations in time and frequency domains is analysed and related to the corrosion process on the surface electrode. When the metal is passive, the noise becomes white meanwhile during localised attack changes in the current and voltage can be found. Electrochemical noise (EN) measurements also showed the ability of the technique to distinguish between different corrosion processes such as pitting or crevice corrosion.     

ELECTROCHEMICAL NOISE FEATURES OF PURE ALUMINUM DURING PITTING CORROSION IN NEUTRAL NaCl SOLUTION

Spontaneous electrochemical noise (EN) can be a rich source of information concerning the processes simultaneously occurring at a corroding interface. Potential noise fluctuations during the free corrosion of pure aluminum in different concentration of neutral sodium chloride solution are investigated, and the breakdown and restoration of passive metal's film are studied using potentiodynamic scanning (PDS) measurements and electrochemical impedance spectroscopy (EIS) technique. Two capacitance loops are observed in the Nyquist plots in two kinds of concentration, and the corrosion process is under activation control at first, then become diffusion control within the oxide film and corrosion products of (Al(OH)p-mCl-m) accumulated on the surface of the corroding electrode. It is suggested that the pitting corrosion is much easier to occur for pure aluminum in 7.0wt% than in 2.0wt% NaCl solution, and the high concentration of chloride ion in solution inhibits the repassivation of a metastable pit. The co     

Interpretation of electrochemical noise by wavelet transform and fractal analysis

Electrochemical noise(EN) was measured during pitting and stress corrosion tests in 3.5 % NaCl solutions for type 403 stainless steel tempered at 520 °C and 610 °C. The energy contributions of smooth crystal and detail crystals in three frequency divisions were analyzed after wavelet transform and compared with the change in the Hurst parameter based on the rescaled range analysis. The contribution of smooth crystal to the total energy is greater than that of low-frequency detail crystal in general corrosion and stable pit formation, but it is less in both meta-stable pitting and growth of stable pits. Crack growth rate can be estimated qualitatively by the evaluation of the energy contributions of smooth and detail crystals, and correlation was found between the change in the Hurst parameter and that in the energy contribution of smooth crystal or one of detail crystals in three frequency divisions.     

Evaluation of a fractal analysis technique for corrosion studies

Corrosion tests were performed to obtain electrochemical noise (EN) data during general and pitting corrosion in NaCl solutions for type 316 and 403 stainless steels. The data were analyzed by the Hurst parameter (HP) based on the rescaled range analysis. A correlation of the HP with the noise resistance was found in general corrosion, and the variability in published HP data is in part due to the difference in the value of noise resistance. The variability is also attributed to the difference in the amount of high frequency components in EN data. The HP is, however, a useful parameter for assessing the effectiveness of an inhibitor based on the characteristics of EN spectra, but not for identifying changes in the mode of corrosion in the case where the level of EN is low.     

基于Hilbert-Huang变换的电化学噪声解析及其应用

借助Hilbert-Huang变换 (HHT) 研究了Q345B碳钢在模拟混凝土孔隙液中的电化学噪声信号的时频谱,发现相比离散小波变换 (discretewavelet transform,DWT),HHT在噪声信号识别过程中具有更高的时频分辨率和稳定性,能够从本质上提高对电化学噪声中耦合的亚稳态点蚀信号的解析精度。针对Q345B碳钢处于钝化态、亚稳态点蚀萌发和稳态点蚀生长等不同阶段的噪声特点,提出了一套基于HHT边界谱的腐蚀状态量化指数与腐蚀特征识别方法。借助于在线电化学噪声监测装置,HHT算法将可用于诊断工业环境的腐蚀形态和腐蚀发展趋势。     

CORROSION MONITORING OF LY12 IN SODIUM CHLORIDE SOLUTION WITH ELECTROCHEMICAL NOISE TECHNIQUE

1. IntroductionThe study of spontaneous current or potential fluctuations, which has been designatedas electrochemical noise (EN), for the characterization of corrosion processes has receivedconsiderable attention since 196811--4]. The study of such fluctuations for the characterization of a corroding interface hajs an importal advantage over all the other electrochemicaltechniques since it is completely non-perturbative[4--7]. So far, the study of corrosion potential fluctuations was applied…     

Assessment of stress corrosion crack initiation and propagation in AISI type 316 stainless steel by electrochemical noise technique

Electrochemical noise (EN) analyses, using time domain, frequency domain and statistical parameters, were carried out on the potential and current data obtained on AISI type 316 stainless steel during (i) pitting corrosion in deaerated 0.5 M sodium chloride (NaCl) solution, and during (ii) stress corrosion cracking (SCC) in boiling acidified NaCl solution. Visual records and statistical analysis of the current and potential data alongwith the spectral estimation using maximum entropy method (MEM) gave useful informations on differentiating between these corrosion processes and on the effect of stress in accelerating pitting corrosion. The results correlated well with the optical microscopic observations.