Testing Electrochemical Impedance

For the scratch test, electrochemical impedance spectroscopy (EIS) data were recorded for samples immersed in the corrosive solution for 5 days. Samples were... 

Electrochemical Impedance Spectroscopy (EIS) and AC Impedance Many direct-current test techniques assess the overall corrosion process occurring at a metal surface, but treat the metal/ solution interface as if it were a pure resistor. Problems of accuracy and reproducibility frequently encountered in the application of direct-current methods have led to increasing use of electrochemical impedance spectroscopy (EIS). 

A simplification of the polarization resistance technique is the linear polarization technique in which it is assumed that the relationship between E and i is linear in a narrow range around E . Usually only two points ( , 0 are measured and B is assumed to have a constant value of about 20 mV. This approach is used in field tests and forms the basis of commercial corrosion rate monitors. Rp can also be determined as the dc limit of the electrochemical impedance. Mansfeld et al. used the linear polarization technique to determine Rp for mild steel sensors embedded in concrete exposed to a sewer environment for about 9 months. One sensor was periodically flushed with sewage in an attempt to remove the sulfuric acid produced by sulfur-oxidizing bacteria within a biofilm another sensor was used as a control. A data logging system collected Rp at 10-min intervals simultaneously for the two corrosion sensors and two pH electrodes placed at the concrete surface. Figure 2 shows the cumulative corrosion loss (Z INT) obtained by integration of the MRp time curves as ... 

ENA was recently used for remote on-line corrosion monitoring of carbon steel electrodes in a test loop of a surge water tank at a gas storage field. An experimental design and system for remote ENA and collection of electrochemical impedance spectroscopy (EIS) data (Fig. 13) have been presented elsewhere. In the gas storage field, noise measurements were compared with electrode weight loss measurements. Noise resistance (R ) was defined as... 

Electrochemical impedance, weight loss, and potentiodyne techniques can be used to determine the corrosion rates of carbon steel and the activities of both sulfate-reducing bacteria and acid-producing bacteria in a water injection field test. A study revealed that the corrosion rates determined by the potentiodyne technique did not correlate with the bacterial activity, but those obtained by electrochemical impedance spectroscopy (EIS) were comparable with the rates obtained by weight loss measurements [545]. 

Comparisons of electrochemical impedance spectroscopy of freshly prepared electrodes and after accelerated life test can give us some information of the deactivation mechanism. 

It is preferable to carry out laboratory corrosion tests and to validate the data with service tests for the selection of materials. It is needless to note that the chosen test method be reliable and cost effective. Some of the test methods in use in industry are service tests, field tests, laboratory tests, and rapid electrochemical methods such as potentiodynamic polarization, linear polarization, electrochemical impedance and electrochemical noise. 

J. R. Scully, D. C. Silverman, and M. W. Kendig, eds.. Electrochemical Impedance Analysis and Interpretation, American Society for Testing and Materials, Philadelphia,. 1993. 

Air Product and Chemicals, Inc. (USA) have found out that (in the absence of any topcoat) while the doped electrically conductive form of PAni performed well as a corrosion-resistant coating for carbon steel, the undoped, nonconductive form of PAni performed better. This was determined by electrochemical impedance spectroscopy (EIS), immersion testing (3wt % NaCl) and salt fog testing. Perfect performance of undoped PAni could be understood as follows. From the high pore-resistance value observed (2-10 U) it can be concluded that PAni forms a dense, adherent, low porosity film on carbon steel. Such a film would restrict the access of components required for corrosion to occur ... 

The research of Mallouk and Smotkin [45] considered combinatorial catalyst development methods. In the combinatorial research, the tools of electrochemical analysis (steady-state and dynamic voltammetry, chronoamperometry, scanning electrochemical microscopy, spectroelec-trochemistry, complex impedance analysis) are used to test electrochemical cell. These tools allow the kinetic and mechanistic studies not readily available in nanoelectrochemistry. The research concentrated on improving the metallic catalyst, and also optimizing the interfacial contact and utilization. 

D.D. Macdonald, M.C.H. Me Kubre, Electrochemical impedance techniques in corrosion science, in F. Mansfeld, U. Bertocci (Eds.), Electrochemical Corrosion Testing, STP 272, ASTM International, Philadelphia, PA, 1981, pp. 110-149. 

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