ELECTROCHEMICAL NOISE ANALYSIS OF PURE ALUMINUM IN SODIUM CHLORIDE SOLUTION WITH WAVELET TRANSFORM TECHNIQUE

1．I口毗rodOCtlOOThe characterlzatlon and monltoringofcorroslon process usingelectrochemlcal noisetechnology has received considerable attention since 1968[1－41．One of*theion most imper－tant advantages offered by this electrochemlcal technique Is its l     

Wavelets analysis of electrochemical noise generated during corrosion processes of pure Al in NaCl solution

1　INTRODUCTIONElectrochemicalnoise(EN )recordscancaptureinformationaboutthecorrosionrateandthecorrosionmechanism[13] .Generally ,theamplitudeofthefluc tuationsinENrecordscanbecorrelatedwiththein tensityofthecorrosionprocessandtheshapeofthefluctuationswiththetypeof process[4 ] .ENdataanalysismaybeperformedinthetimedomainbyin vestigatingthefluctuationshape ,sizeandthedistri butionintermofthepotentialorcurrenttransientsobservedduringcorrosion processes[5] .However ,mostsystemsarecharacter…     

高纯铝在含Cl~-溶液中电化学噪声的小波包子带能量特征

建立了基于小波包分解的电化学噪声子带能量表征方法 ,测试了高纯铝在含Cl-溶液中不同条件下的电化学噪声 ,分析了所测电化学噪声信号的时域特征、PSD特征及小波包分解子带能量特征 .PSD分析显示 :随着浸泡时间的增加 ,当蚀孔开始生长后 ,孔核的生长期缩短 ,消亡期延长 ,而SO2 -4 对孔核的生长期及消亡期没有显著影响 .与PSD方法相比 ,子带能量特征向量可以刻画电化学噪声信号的高频“指纹”特征 ,对腐蚀体系、腐蚀类型及腐蚀状态有较强的敏感性 .通过对第一子带能量变化分析显示 ,SO2 -4 会降低高纯铝在含Cl-溶液中孔核的发生频数 .     

AZ31镁合金在中性NaCl溶液中的电化学噪声研究

采用电化学噪声技术研究了AZ31镁合金在0.1 mol/L中性NaCl溶液中的腐蚀电化学行为,并通过小波分析研究了该体系在腐蚀过程中的腐蚀特征及机理.结果表明:AZ31镁合金在腐蚀之初,由于电极表面覆盖有在空气中形成的离散氧化膜,导致EDP的高阶(低频)能量占据主导地位;同时由于侵蚀性粒子在原始离散氧化膜的缺陷处的攻击,导致与点蚀密切相关的低阶(高频)能量分量在EDP中也占据重要地位;在镁合金的整个腐蚀过程中重复地发生腐蚀产物膜生长、局部剥离和大面积剥离的现象.因此,EDP谱图的特征相应地发生规律性变化：产物膜比较完整时,低频能量分量占据主导地位;腐蚀产物膜局部剥离时,低频能量分量降低,高频能量分量增大;产物膜大面积剥离时,高频能量分量占据主导地位.     

电化学噪声在腐蚀领域中的研究进展

综述了电化学噪声的起源和分类、测量方法、时域和频域分析以及小波分析；重点讨论了电化学噪声在金属腐蚀类型的判断、局部腐蚀特征、应力腐蚀、涂层性能评价、缓蚀剂的筛选和生物腐蚀等腐蚀领域中的应用研究进展，并提出了今后的研究方向.     

Electrochemical noise monitoring of the atmospheric corrosion of steels: identifying corrosion form using wavelet analysis

The early stage atmospheric corrosion of T91 and Q235B steels exposed to Tianjin’s urban atmosphere over 20 days was studied using two electrochemical probes via an electrochemical noise (EN) technique. To identify the corrosion process and the corrosion form of the two steels, EN data were analysed by statistics and wavelet transform. The results revealed that the wavelet energy of decomposed EN mainly located at high-frequency level for Q235B steel, whereas it mainly located at the low-frequency level for T91 steel. Analyses of surface images confirmed that Q235B steel underwent uniform corrosion whereas T91 steel suffered from localised corrosion. The obtained noise resistance correlated well with weight loss data.     

混凝土中钢筋点蚀的电化学噪声特性研究

    采用Sym4小波分析氯离子环境下砂浆中碳钢电化学噪声的电流波动及电压波动信号,通过提取信号的小波能量,得到了信号的能量分布曲线.结果表明,电化学噪声的小波能量是点蚀监测信号解析的重要特征参数,根据能量分布曲线的变化可以判定点蚀的发生.     

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。     

采用聚类分析研究X70钢在库尔勒土壤中初期电化学噪声特征

采用电化学噪声（EN）技术研究了X70管线钢在库尔勒原土（含水量1.04%）中腐蚀初期（0 d~7 d）的腐蚀行为。通过时域谱分析、统计量分析和Q型聚类分析研究了电化学噪声特征以及相应的腐蚀状态信息,并与实际腐蚀状态和电化学阻抗谱（EIS）结果进行了对比。结果表明,基于EN统计量的谱系聚类分析法可用于解析土壤EN数据。聚类分析结果与时域分析、腐蚀形貌特征和EIS结果相吻合,且更加精确。根据聚类分析结果,可将研究体系中初期土壤局部腐蚀过程分为不稳定萌发期、快速发展期和稳定发展期三个阶段。     

Corrosion electrochemical behavior of brass tubes in circulating cooling seawater

Electrochemical impedance spectroscopy(EIS) and electrochemical noise(EN) were used to study the corrosion electrochemical behavior of brass tubes in circulating cooling seawater using the developed sensor. EIS study shows that the inhibitor can lead to the formation of corrosion products on metal surface, which will then inhibit the corrosion process. When the flow rate of the seawater increases, the diffusion of oxygen speeds up and the action of filming on HA177-2 tube accelerates, resulting in decrease of corrosion rate. EN analysis shows that the flow rate of the seawater has little effect on pitting susceptivity of HSn70-1 tube; however the pitting susceptivity of HA177-2 tube increases with increasing flow rate. Good agreement is observed between the spectral noise resistance R30(f) calculated from EN data and the modulus of impedance. It is shown that the electrochemical noise technique can be used in corrosion monitoring.     

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。     

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。     

Electrochemical noise analysis of PbSCC of Alloy 600 SG tube in caustic environments at high temperature

An electrochemical noise (EN) monitoring technique was applied to analyse an initiation and a propagation of Pb-assisted stress corrosion cracking (PbSCC) of Alloy 600 material in a simulated environment of steam generator (SG) sludge piles at high temperature. A typical electrochemical potential decrease concurrent with a current increase was observed during the EN measurements, indicating the occurrence of localized corrosion events. The EN data were analysed for the processes of a uniform corrosion, an initiation and a propagation of PbSCC using a stochastic theory and microscopy.     

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.     

Electrochemical noise characteristics in corrosion process of AZ91D magnesium alloy in neutral chloride solution

The corrosion process of AZ91D magnesium alloy in neutral 1% (mass fraction) sodium chloride aqueous solution was investigated by electrochemical noise(EN), SEM and EDX. Fractal theory was primarily used to depict the corrosion process of the alloy. The fast wavelet transform(FWT), as well as the fast Fourier transform(FFT), was employed to analyze the EN data. The results show that the overall corrosion process can be described by three stages. The first stage corresponds to the pit nucleation and growth; the second stage involves the growth of a passive oxide layer; and the third stage involves reactivation. With increasing immersion time, fractal dimension increases fast initially, fluctuates in the medium and increases again at last. Pitting corrosion and fractal dimension increase due to the initiation and formation of pits in the initial and the end of immersion, while depresses due to the passivation in the medium period. The results of SEM and EDX support the above conclusions.     

7A60铝合金点蚀行为的电化学噪声和电化学阻抗谱表征

采用电化学阻抗谱（EIS）和电化学噪声（EN）方法研究回归再时效（RRA）热处理状态下7A60铝合金的点蚀行为,通过扫描电子显微镜（SEM）和能谱仪（EDS）观察和分析合金的组织和第二相颗粒成分。结果表明,7A60铝合金在3.5%Na Cl溶液中存在两个腐蚀阶段,并且可以用EIS出现两个电容时间常数的时间和由EN计算出的小波分形维数D的变化来表征。SEM和EDS分析结果表明,在7A60铝合金中,严重的点蚀主要是由阳极相Mg Zn2引起的,其次是Al2MgC u和Mg2Si相,Al7Cu2Fe相对7A60铝合金点蚀行为的影响不大。     

敏化态304不锈钢慢速率拉伸腐蚀过程的电化学噪声检测

采用电化学噪声方法对敏化态304不锈钢在0．5mol／LNa2＆O3溶液的慢速率拉伸过程的腐蚀进行检测,同时得到腐蚀过程的电位与电流变化曲线,试验后试样表面出现了多处应力腐蚀裂纹。分别采用时域谱、频域谱及小波分解分析电流噪声数据,表明腐蚀过程经历了应力腐蚀裂纹萌生与裂纹扩展的过程。根据多种电化学噪声谱图及小波分解后的能...     

Identification of steel corrosion associated with sulfate-reducing bacteria by electrochemical noise technique

Deterioration of steel structures in natural waters can result from microbiologically influenced corrosion (MIC) such as that caused by sulfate-reducing bacteria (SRB). Corrosion pits associated with MIC have been recently observed in submerged steel bridge piles and there is renewed interest to assess their deterioration. Conventional electrochemical techniques to identify MIC have been complicated due to the effects of the surface films and the mechanism for charge transfer by the bacteria on the steel surface. An electrochemical noise (EN) technique to identify steel corrosion in an aqueous solution has been developed and the method ideally can identify the onset of local pitting, but complications and limitations relating to data acquisition, filtering, and interpretation exist. EN analysis was shown to differentiate SRB and corrosion activity including initial biofilm development, pitting corrosion development, and diminution of SRB activity. Electrochemical behavior, environmental characteristics, SRB activity, and corrosion modality provided consistent correlation to EN and localized corrosion development.     

ELECTROCHEMICAL NOISE ANALYSIS OF THE INFLUENCE OF THE Zn^2＋ IONS CONCENTRATION ON ZINC ELECTROPLATING

The influence of the concentration of Zn^2 ions on zinc electroplating process was investigated by means of electrochemical noise (EN) and cyclic voltammetry methods in conjunction with the scanning electron microscopy (SEM) technique. It was found that the EN generated during the electroplating of dentritic or large polymeric zinc deposit has large potential oscillation amplitude and positive potential drift while the compact zinc deposit possesses small noise amplitude and little potential drift. With the change of rate determining step from diffusion-control through mixed-contro! to activation-control, the maximum relative energy obtained from wavelet analysis defined from the region with larger scales to those with smaller scales, and the EDP (relative energy distribution plot) can be us, as “fingerprints” of EN to characterize the electroplating process and the deposit structure. The results also showed that electrochemical noise technique can give more information about the electrodeposit structure than other normal electrochemical measurements, such as linear potential sweep method and cyclic voltammetry, technique.