Electrical impedance spectroscopy corrosion testing

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 veirious types of measurement technologies for assessment of corrosion may be summarized as shown in Tables 2 to 5. These techniques cover both laboratory Jind field use. However, many of the direct methods, particularly the electrochemical methods of potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) are generally more suited to laboratoiy evaluation. In the laboratory, test conditions are clean and more controlled. Consequently, more sophisticated measurement electrode systems can be used that take advantage of their more sophisticated measurements technologies. In the field, practicalities of changing process conditions, high flow rates, debris, electrical noise, and electrical safety limit their use. 

The electrical conductivity and resistivity of concrete is indirectly related to the degree of resistance offered by concrete to the passage of corrosive species to the steel reinforcement The concrete resistivity is very high (>4KS2) and it can be best measured by the EIS technique (Electrochemical Impedance Spectroscopy) described earlier. ASTM Test C1202-94 can be used to determine concrete resistivity (Fig. 12.37). 

Successful inhibitor tests require suitable corrosion measurement and analysis techniques that are able to correctly record and interpret corrosion rate data. Many testing and monitoring techniques that were developed initially for the diagnosis and prediction of corrosion have been successful employed in laboratory and field corrosion inhibitor testing and research. These techniques include the use of corrosion coupons, solution analysis, electrical resistance probe, polarization resistance, electrochemical impedance spectroscopy and many other physical, electrical and electrochemical methods. 

---