Multiplexed Galvanic Corrosion Purpose

This experiment allows you to measure galvanic corrosion versus time on up to eight samples sequentially.

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. One metal generally becomes a cathode and the other an anode. The anode’s corrosion rate is accelerated over its uncoupled rate. The corrosion rate of the cathode is reduced.

The generic instrument used in galvanic corrosion measurements is called a Zero-resistance Ammeter (ZRA). It measures the current flow between the metal samples, while keeping them at the same potential. In laboratory ZRAs, provision is also made to measure the potential of the two metal samples versus a reference electrode.

Up to eight samples are connected to the Framework™ system via an ECM8 Electrochemical Multiplexer. The ECM8 is connected to the potentiostat, which is set in ZRA mode. The metal samples in cells whose channels are inactive are shorted by a relay in the ECM8. All cells thus undergo galvanic corrosion continuously even though the ZRA is connected to only one cell at a time.

The graphical output of the experiment is a plot of log(current) and potential versus time. Analysis of the curves may yield the following types of information:

• Extent of a galvanic coupling problem
• Predicted effectiveness of a cathodic protection scheme