局部腐蚀电池中阴极和“闭塞”阳极之间电位差及其组份的研究

从理论上分析了分别插在局部腐蚀电池阳极液和本底溶液中的两个饱和甘汞电极之间,以及局部腐蚀电池阴、阳极之间的电位差及其组份的性质,导出了一组定量关系式。采用铁与10~(-8)NNaCl溶液构成的模拟电池,实验证明了这些定量关系。结果表明,前一种电位差主要是由阳极液和本底溶液之间的扩散电位差和欧姆电位降两部份组成。在两种溶液之间一旦建立起稳定的扩散区以后,其间的扩散电位差就趋于一个定值;而欧姆电位降则主要随阴极电位的变化而变化。其最终的稳定值将不因同一局部腐蚀电池的内电阻而异,接近于模拟电池在阴、阳极处于断路状态时其间电位差的绝对值。而后一种电位差,还包含有第三个组份,即它们电极电位的差值。

A STUDY OF THE COMPONENTS OF THE POTENTIAL DIFFERENCE BETWEEN THE CATHODE AND THE OCCLUDED ANODE IN LOCALIZED CORROSION SYSTEM

The components of the potential difference between two SCEs dipped respectively into the bulk solution and the occluded anolyte, and those between the cathode and the anode in localized corrosion cell have been analyzed. A group of quantitative relationships among them are deduced. Then they are verified experimentally by a simulating cell of iron in 10~(-3)N NaCl solution at room temperature. The resuits Show that, the first potential difference mentioned above are mainly composed of the ohmic drop and the diffusion potential difference between the bulk solution and the anolyte in the cell. Once the steady diffusion region between two solutions sets up, the value of the diffusion potential, difference would tend to a constant, while the ohmic drop changes with the electrode potential of the cathode. The final stable value will not change with the internal resistance of the corrosion cell. But for the latter potential difference mentioned above, it also contains third component, i. e., the difference of the electrode potentials between cathode and anode vs. SCEs. On the basis of the results and the polarization measurements, the relationships between the electrode potentials of occluded anode, corresponding to its zero current potential, passivation potential or immunity potential, and the electrode potentials of local cathode could be quantitatively established.