【作者】 蔡超；

【导师】 高作宁；

【作者基本信息】 宁夏大学 ， 分析化学， 2005， 硕士

【摘要】 本论文分为两部分,第一部分用电化学阻抗谱(electrochemical impedance spectroscopy, EIS)技术结合扫描隧道显微镜(STM),扫描电镜(SEM)等现代测试手段对纯铝在中性氯化钠溶液中的腐蚀机理进行了研究。 EIS研究结果表明:在腐蚀反应进行的初试阶段,在低频率域(10mHz)得到的极化电阻(R_p)和双电层电容(C_dl)同时增加,符合纯铝腐蚀初期氧化膜生成过程的特征。随着时间的延续,电极电位与R_p分别达到最大值说明:在表面氧化膜不断生长的过程中,侵蚀性卤素离子已经开始进攻纯铝的表面并逐渐通过扩散达到其基体。同时,在整个的腐蚀过程中,该体系表现出两个时间常数,高频区域的时间常数代表包括氧化膜和反应产物在内的保护层,低频区域的时间常数代表腐蚀过程中的扩散以及腐蚀反应中的快速过程。大量的实验结果证明EIS特征与金属样品在腐蚀过程中表现的形貌特征有良好的对应关系,同时验证了点腐蚀的自加速过程以及腐蚀过程中局部阳极周围的区域在反应中得到了适当的保护。 论文的第二部分通过运用快速傅立叶(FFT)、小波分析(Wavelet)等非线性数据处理方法并结合SEM等测试手段研究了纯铝在中性NaCl溶液中的电化学噪声(electrochemical noise, EN)信号。FFT的分析结果表明:一方面电化学噪声频域曲线PSD(功率密度谱)的三个特征参数(W, f_c, k)不能单独正确的描述材料表面孔蚀的强度和趋势。另一方面,在基于因次分析法的基本原理和对材料腐蚀过程影响因素的分析发现:从电化学噪声频域曲线PSD的特征参数导出了能正确表征材料表面孔蚀强度和趋势的两个参数S_E和S_G,其中S_E与孔蚀的强度有比较好的规律性。而S_G在现阶段工作中只能确定其数值范围在5-20之间,其规律性在进一步研究之中。 对EN信号的小波分析结果表明:不同阶段的能量分布可以与腐蚀形貌进行良好的对应关系。对于非稳态腐蚀点的产生,可以利用D等级系列中较小等级的能量加以对应。同样,中间等级和较高等级分别对应于腐蚀点的生长和再钝化过程。与此同时,纯铝腐蚀样品在3.0wt%的NaCl溶液中的腐蚀形貌与EDP(能量分布谱)特征有较好的对应关系。更多还原

【Abstract】 This thesis consists of two parts. In part one, the corrosion of pure aluminum in 3.0wt% neutral sodium chloride solutions was studied by electrochemical impedance spectroscopy （EIS） techniques, combining the examination of scanning tunneling microscopy （STM） and scanning electron microscopy （SEM）. The results show that during the initial immersion segment, the polarization resistance （Rp） obtained at low frequency （10mHz） and the C_dl increase simultaneously, which coincides with the growth of oxide film on pure aluminum. While the discrepancy between the time when R_p and free potential arrived at their maximum respectively indicates that, during the growth process of oxide film, chloride ions have commenced their attacking to the pure aluminum substrate. And two times constant were confirmed, the high frequency one originates from the protective layer on the corroding substrate including the oxide film and the corrosion products, while the low frequency one comes from thediffusion process or the corrosion reaction and so on. Meanwhile, It is found that satisified relationship between the EIS features and the corroding morphologies has been observed, which has been interpreted according to the characteristics of corrosion process such as auto acceleration of pitting corrosion and the protection of local anodic reaction to the area around them.In part two, electrochemical noise （EN） measurements in conjunction with the scanning electron microscopy （SEM） technique have been used to study the corrosion behavior of pure aluminum in neutral 3.0wt% sodium chloride solution. The FFT analysis shows that none of the spectral power density plot’s （PSD）three parameters which including high frequency linear （k）, the white level （W） and the cut-off frequency （f_c） can properly describe the propensity and intensity of corrosion process respectively. Two new parameters （Se and Sg） were derived by using dimensional analysis method, and the value of S_E can characterize the severity of pitting corroding material. While the value of the other parameter （SG_） was confirmed into the range of 5-20 and it’s meaning remains for further investigationIn the other hand, the Wavelet analysis indicated that the energy distribution plot （EDP） can be used as fingerprints of EN signal and can be used to characterize the corrosion process. For metastable pitting, the relative energy mainly defined at the D crystals with small scales, while for pits propagation and pits growth, the relative energy mainly defined at the D crystals with middle and large scales respectively. Meanwhile, Good relationship between the EN features and the corroding morphologieshas been observed during the pitting corrosion process of pure aluminum in neutral 3.0wt% sodium chloride solution.更多还原