(Electrochemical) corrosion testing

Potentiodynamic scan (PDS)

A potentiodynamic scan is an electrochemical measurement used to evaluate the corrosion behavior of a metal in a specific environment. In this test, the potential of the specimen is continuously scanned over a selected range while the current is measured. The resulting polarization curve can be used to determine the corrosion potential, corrosion current density, and anodic and cathodic Tafel slopes (indicative for anodic an cathodic reaction rates). It can also provide information about electrochemical processes such as active dissolution, passivation, and localized corrosion.

Cyclic voltammetry (CV)

Cyclic voltammetry is used to investigate the electrochemical behavior and reactions of materials in a specific environment. During the measurement, the electrode potential is swept over a defined range and then reversed, while the current is recorded. The resulting voltammogram can be used to identify oxidation and reduction reactions, determine their potential ranges, and study changes in the electrode surface during polarization.
Additionally, cyclic voltammetry can be used to evaluate repassivation properties, stable passive and metastable passive potential regions.

Electrochemical impedance spectroscopy (EIS)

Electrochemical impedance spectroscopy (EIS) is used to study the interfacial properties of electrochemical reactions at the electrode surface. During the measurement, a small sinusoidally alternating potential or current is applied over a range of frequencies, and the resulting current or potential response is measured. The impedance response can be used to characterize the electrode–electrolyte interface and evaluate processes such as charge transfer, double-layer capacitance, and surface film formation.

Mott-Schottky (M-S)

Mott–Schottky analysis is used to investigate the semiconducting properties of passive or oxide films formed on an electrode surface. During the measurement, the electrode capacitance is measured at different applied potentials. The resulting Mott–Schottky plot can be used to determine the type of semiconductor (n-type or p-type), defect density, and flat-band potential of the surface film.

Linear polarization resistance (LPR)

Linear polarization resistance (LPR) is a quick, non-destructive electrochemical technique used to evaluate the corrosion rate of metals. During the measurement, the metal is polarized by a small potential, typically around ±10 mV relative to the open-circuit potential. The resulting polarization resistance can be used to determine the corrosion rate using the Stern–Geary equation. Due to its non-destructive nature, LPR is often used as a corrosion monitoring technique.

Electrochemical frequency modulation (EFM)

Electrochemical frequency modulation (EFM) is a non-destructive corrosion monitoring technique, that relies on applying two sinusoidal signals with a different frequency and measuring their response to determine corrosion current density, anodic and cathodic tafel slopes. For this calculation, the technique assumes a Butler-Volmer response of the corroding system. Any deviations of this ideal response are also recorded in confidence factors. Deviations in confidence factors can imply pitting corrosion or passive layer formation.

Open circuit potential (OCP)

Open circuit potential (OCP) is an electrochemical measurement of the natural potential of a material in a specific environment, with no external current applied. OCP can be used to monitor changes in the electrochemical state and surface condition of the material over time.

Corrosion Inhibition efficiency (IE)

For corrosion inhibitor evaluation, determining their efficiency is a good way to separate the well-performing inhibitors from the ones that don’t work. A calculation of inhibition efficiency can be done based on input from multiple PDS, LPR, EFM or EIS measurements. When investigating inhibitor combinations, synergism parameters can be calculated to determine if there is any added value in blending corrosion inhibitors (I.e. if they interact in a synergistic way).

Salt spray

Salt spray testing is a corrosion test used to evaluate the corrosion resistance of materials and protective coatings in a controlled salt-containing environment. Specimens are exposed to a continuous or periodic spray of a saline solution for a specified period, and their corrosion performance and surface condition are evaluated after exposure.

Weight-loss testing

Weight-loss testing is used to evaluate uniform corrosion and corrosion rate. A pre-weighed specimen is immersed in a corrosive environment for a specified period, then cleaned and reweighed to determine the mass loss due to corrosion. The mass loss is used to calculate the average corrosion rate, typically expressed in mm/year (mm/y) or mils per year (mpy).