This previous article — Corrosion Part 1: What is it? — discussed why metallic materials corrode, and this article dives into the nitty gritty about how this corrosion takes place.
A good place to start with describing how corrosion takes place is to look at the 4 different parts of an electrochemical cell:
- Anode
- Cathode
- Electrolytic Path
- Driving Potential
An electrochemical cell
The anode is the scene of the crime. It’s the location within an electrochemical cell where the corrosion actually occurs. The anodic reaction is an oxidation reaction; the anode sheds metal atoms and electrons, thus becoming positive. This release of metal atoms and electrons is what we witness as corrosion. Like an anodic reaction occurs at the anode, a cathodic reaction occurs at the cathode. The cathode consumes the ions that the anode has shed in what is called a reduction reaction. Think of the anode as the quarterback, the cathode as the receiver, and the ions as the football.
Electrolytes aren’t just things in your Gatorade! In the corrosion cell, the electrolyte is the medium that facilitates the anodic and cathodic reactions. It is essentially a tunnel between the anode and the cathode; it’s the pass from the quarterback to the receiver. Ordinary water is the most common electrolyte associated with corrosion. This is detrimental because water is found everywhere, be it in the form of condensation, rainwater, soil water, etc. Corrosion, therefore, has the potential to be almost anywhere, as well.
The final requirement to complete the corrosion cell circuit is a driving potential. The driving potential can come from a variety of sources including inhomogeneous single metals and the pairing of dissimilar metals. Corrosion of a single metal is often unexpected because the metal is seemingly homogenous and in theory should not corrode. However, seemingly “homogeneous” metals often include stress gradients or other defects, which makes part of the metal anodic to the rest and corrosion ensues.
There are many different types of corrosion and just as many prevention and mitigation techniques. Other articles here cover corrosion types and prevention methods, and you can also find out about how our ProTek Wear Pads, ProTek Pipe Shoes and ProTek Flat Plates can help.
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