DC electrochemical characterisation of a corrosion system

Corrosion is an unwanted spontaneous electrochemical process leading to a structural degradation of a material. This process involves electrochemical reactions taking place at the interface material/electrolyte. The electrochemical characterization of a corrosion system (material+electrolyte) consists of the determination of certain parameters like corrosion potential, corrosion current, Tafel parameters, pitting and repassivation potentials (for passivable materials), etc. Two types of methods are used to carried out this characterization: the DC and AC method.

Tafel plot is one of the most commonly used DC method for the electrochemical characterization of a corrosion system. It directly provides the value of the corrosion current of the material and consequently, its corrosion rate.  Another commonly used DC technique is the Stern and Geary method (Linear Polarization Resistance). This method is less destructive than the Tafel method and easily allows the determination of the polarization resistance of the material. Both methods are applicable for a Tafelian system where the corrosion process is controlled by the electron transfer reaction (limiting reaction). For a real corrosion system, many processes on the material can impact on the kinetics of reactions involved in the corrosion of the material such as adsorption, diffusion (mass transport), and a high resistance of an electrolyte which generates an ohmic drop over the electrolyte during the measurement.  For the last example, an Ohmic drop compensation is needed for reliable measurement. The compensation can be done automatically using ZIR protocol available in EC-Lab software.

Read More …

• Tutorial I: Corrosion: theory and basics
• Tutorial II: Corrosion: Electrochemical characterization by EC-LAB techniques
• AN#10: Corrosion current measurement for an iron electrode in an acid solution
• AN#48: Inaccuracy of the corrosion current determination in presence of an ohmic drop: EC-Lab® solutions