电化学性能指标

A brief description of various electrochemical

techniques

1.Open Circuit Potential (OCP) Measurement

Open circuit potential, also called rest potential or corrosion potential, is the potential of a working electrode when it is at rest. OCP provides information on the trendency of a metal towards reactivity /corrosivity. A metal with more negative potential will always corrode preferentially. OCP information is useful in designing sacrificial galvanic protection. For example, zinc, which is electrochemically more negative compared to steel is used to protect steel galvanically. The information obtained from OCP measurements are however thermodynamic in nature and provides information only on the possibility but not provide information on the rate of reaction/corrosion.

2.Electrochemical Impedance Spectroscopy (EIS)

In EIS a small AC potential perturbation, typically a since wave of amplitude ~±10mv is applied on a system with respect to its open circuit potential over a wide range of frequency (typically from 105-10-2Hz) and the response of the current is measured at each frequency. Barrier properties, water uptake and volume fraction, diffusion rate in organic coating, or the various processes involved during corrosion can be obtained. Quantitative results are obtained. A three electrode configuration is normally used. The metal substrate acts as the working electrode. Platinum mesh, graphite rods, or any other noble metal can act as the counter electrode. A saturated calomel electrode such as silver/silver chloride or mercury/mercury sulfate can also be used as the reference electrode. Very often modeling of EIS data is performed to obtain quantitative information.

3.Potentiodynamic Polarization Scan(PDS)

In PDS, the potential of the working electrode is scanned at a selected rate over a relatively large potential range by applying a current through the electrolyte. The corrosion behavior is interpreted from the nature of the polarization plot. Corrosion rate, corrosion resistance, corrosion current, corrosion potential, passivity,pitting susceptibility, and corrosion mechanisms can be predicted. It is a very commonly used testing technique and find wide application for the corrosion study of metals and alloys.

4.Galvanic corrosion (GALCORR)

Galvanic corrosion measurement measures the galvanic current and potential between two electrodes. The experiment in the zero resistance ammeter(ZRA) mode ensures that the two working electrodes(WE-1 and WE-2) behave as if they were directly connected by a ‘zero-resistance’ wire, such that the galvanic current between cathode and anode, and the mixed potential between them can be measured/recorded.

5.Scanning Vibrating Electrode Technique(SVET)

SVET can be used for localized study of a surface behavior. In SVET a vibrating probe/electrode