Electrochemical Noise Overview

Noise in electrochemical corrosion measurements is common, showing up in both the current and voltage signals. It originates from several different sources, including:

  • Electronic and thermal noise in the instrument
  • Antenna pickup in the cell and cell leads
  • Digitization of analog signals
  • Turbulent mass-transport in the chemical cell
  • Stochastic processes at the electrode surface

Noise is often a nuisance degrading the signals you are trying to measure, but in some situations it can be a benefit to the corrosion engineer. In pitting corrosion, noise measurements can detect the onset of pitting. There is a background noise in uniform corrosion processes caused by the first four mechanisms in the above list. At the onset of pitting, however, the noise from electrode surface reactions can increase dramatically. This noise can show up in either the current signal or voltage signal, or both.

There are several ways to measure current noise and voltage noise. You can apply a constant I signal and measure E noise, or vice versa. You can also measure both current and voltage simultaneously on an electrochemical cell under control of a ZRA (zero-resistance ammeter).

The Electrochemical Noise system measures noise using potentiostatic, galvanostatic, or ZRA control modes..

  • In potentiostatic tests, a corrosion specimen is immersed in a solution and its potential is controlled using a Gamry Instruments, Inc. potentiostat/galvanostat/ZRA in its three-electrode potentiostat mode. The noise in the cell current is measured as a function of time.
  • Galvanostatic tests are also three-electrode experiments where a constant current is applied to the cell, and the noise in the cell voltage is measured as a function of time.
  • In ZRA tests, two identical corrosion specimens are immersed in the same solution. The same potentiostat/galvanostat/ZRA is used, but this time it is connected as a ZRA. Current is measured between the two working electrodes which are held at the same potential. Voltage is measured independently between the two specimens and a reference electrode.