The Silver Silver Chloride Electrode

Basic Principles

The silver/silver chloride electrode is a reference electrode of the second kind where the metal (silver) is in contact with a slightly soluble salt (silver chloride) containing the metal, which in turn is in contact with a solution containing the common anion (chloride ion). The ions in the solid phase and those in the liquid phase are in equilibrium.
Ag solid  =   AgCl solid  =  Cl  solution

The potential of the electrode is dependent on the concentration of the chloride ions in solution and temperature as governed by the Nernst equation.
ET  = E0 - RT/nF  ln Cl-   (in moles/litre)  
ET = Electrode Potential measured in Volts between a metal electrode (steel structure) and a reference electrode
E0 = Electrode Standard Potential
R = Universal gas constant
F = Faraday constant
T = Temperature
n = Number of moles
Cl = Chloride ions
SILVION reference electrodes consist of an Acetal tube electrode body. The electrodes are manufactured using a "unique” advanced technique which results in a porous silver matrix being formed around a silver wire skeleton. This porous matrix increases the active area of the monitoring surface hundredfold and also enables the deposition of a larger quantity of silver chloride. The deposition is precisely controlled by electrolytic coating and provides high reliability, high stability, greater accuracy and increased life performance. A porous plug at one end of the assembly allows contact between the field environment and the silver chloride electrode via the electrolyte. An insulated lead wire connects the central silver wire which can be connected to a high input impedance voltmeter (10MOhm) when potentials are to be measured. For embedding in concrete or for use in soil or potable water the reference electrode contains either sodium chloride (NaCl) or potassium chloride (KCl) to stabilize the silver chloride concentration.

Potential relationships for several different Reference Electrodes

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