The Galvanic Corrosion technique is used to study the electrochemical reactions that occur when two different metals, immersed in the same solution, are electrically coupled to each other. One metal generally becomes a cathode and the other an anode. The anode corrosion rate is accelerated over its uncoupled rate. The corrosion rate of the cathode is reduced.
In many cases, galvanic corrosion is a problem. The classic example is steel and copper pipes connected together in a water-delivery system.
Passive cathodic protection takes advantage of the galvanic corrosion reaction. It protects one metal by coupling it to a sacrificial anode. The Galvanic Corrosion technique can be used to perform laboratory studies of the protection process.
The instrument for galvanic corrosion measurements is a Zero-resistance Ammeter, or ZRA. It connects the two metals as though they were connected with a wire, while simultaneously measuring the current between the two. In laboratory ZRAs, provision is also made to measure the potential of the two metal samples (both must have the same potential) versus a reference electrode. A Gamry potentiostat can be configured as a very accurate ZRA.
The graphical output of the experiment is a plot of current and potential versus time. Analysis of the curves may yield the following types of information.