ELECTROCHEMICAL TESTING
Matergenics performs electrochemical test procedures to determine or predict the corrosion rates of metals in a wide range of environments. Among the electrochemical techniques are the ASTM / NACE techniques, Cyclic Polarization, Impedance Spectroscopy, linear polarization tests , electrochemical tests for hydrogen permeation, real-time corrosion predictions for materials, and others.
oxidation and reduction reactions
controlled electrochemical experimental methods can be used to characterize the corrosion properties of metals and metal components in combination with various electrolyte solutions or soil environments.
The following plot exhibits a case example for using electrochemical technique ASTM G61. All corrosion is an electrochemical process of oxidation and reduction reactions. As corrosion occurs, electrons are released by the metal (oxidation) and gained by elements (reduction) in the corroding solution. Because there is a flow of electrons (current) in the corrosion reaction, it can be measured and controlled electronically. Therefore, controlled electrochemical experimental methods can be used to characterize the corrosion properties of metals and metal components in combination with various electrolyte solutions. The corrosion characteristics are unique to each metal/solution system.) for selection of materials in acidic chlorides. The plot clearly indicates Type 304 stainless steel is not a proper material selection for acidic chloride environments
Two basic methods of electrochemical measurement for materials selection and evaluation:
- Applying external current to generate electrochemical data away from the free corrosion potential. These tests generally explore the relationship between electrochemical potential and current
- Electrochemical measurements at the free corrosion potential, without the application of an external current.
DIFFERENCES
corrosion characteristics are unique to each metal/solution system.
Electrochemical Corrosion Tests Include The Following Techniques:
- Linear polarization resistance (LPR) measurements
- Potentio-dynamic polarization curves
- Current vs time curves (at a given potential)
- Electrochemical potentio-kinetic reactivation (EPR) measurements for intergranular corrosion
- Harmonic analysis
- Electrochemical impedance spectroscopy (EIS)
- Electrochemical noise (EN) measurements
Samples for electrochemical corrosion testing must utilize electrical conductors and must be small enough to fit in the polarization cell. Components can be tested as a whole or as a smaller section. Metal coupons are specially prepared for some tests.
About EIS
EIS technique is used to evaluate materials and coatings in corrosive environments. EIS measures impedance of the coating at different frequencies. This is an indication of barrier effect of the coating. Barrier coating will exhibit high impedance in corrosive exposures. Changes in electrical properties determined by EIS experiments have been found to closely resemble long-term performance of coatings.This way EIS method can detect deterioration at metal/coating interfaces well before defects become visible, and with greater accuracy than artificial testing methods such as salt spray.
