一般的电化学交流阻抗技术只提供跟腐蚀过度成反比的极化电阻,其比例常数须在另外的实验中测定。而交流阻抗测量中同时出现的高次谐波,反映了被测体系的非线性的极化特性。通过谐波分析可以直接求得腐蚀电汽及塔菲尔斜率。本文讨论了通过幂级数展开处理谐波数据的基本关系式。然后选择0.5NH_2SO_4中的碳钢作了实验验证。用带有谐波选择开关的频率响应分析仪测量了前三个谐波成份。测得的数据都修正了溶液的IR降,并从一次谐波中扣去了电容电流。着重讨论了交流信号的频率和幅值的影响。结果表明,谐波分析得到的腐蚀速度跟交流阻抗和失重测量的结果相当符合,同时获得的塔菲尔斜率跟极化曲线塔菲尔区的结果也基本一致。
The conventional a.c.impedance technique only provides polarization resistance inversely proportional to the corrosion rate. The proportionality constant has to be determined in an independent experiment. However, the harmonic components appearing in a.c. impedance measurments reflect nonlinear polarization characteristics of the corrosion system under study. By means of barmonic analysis, corrosion current could be obtained directly and Tafel slopes could be determined simultaneously. In the present paper, the basic formulas based on power series expansion for manipulation of harmonic data are derired. Mild steel corroding in 0.5N H_2SO_4 was chosen for experimental verification. The first three harmonic components are measured by a frequency response analyzer with harmonic selector. The measured data have been corrected for IR drop due to solution resistance. The shunting effect of the double layer capacitance has also been eliminated by subtracting the capacitive current from the first harmonic component. The effect of frequency of a. c. signal is discussed. The results show that corrosion rate determined by harmonic analysis correlates well with those from a.c. impedance and weight loss measurements. Tafel slopes obtained are in good agreement with those measured from polarization curves.
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