Guarding Substrates Against Corrosion

June 14, 2010

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Corrosion is the chemical reaction between materials and their surroundings. It is a destructive process that causes structural disintegration. Knowing how surface materials corrode can help in protecting them against their corrosive environment. Corrosion-resistant coatings systems can be identified that are appropriate to the type of corrosion that the materials are vulnerable to.

Here are some of the known types of corrosion:

1. Rusting

Also known as electrochemical corrosion, rusting is the result of the reaction of metals when exposed to oxidizing agents such as oxygen. Oxidants attack the iron atoms in vulnerable metal surfaces. Parts of the metal surface became casualties of the process, turning into oxides of iron and salts. These new materials are visible as rust.

2. Galvanic corrosion

Different-type metals can take part in galvanic preferential corrosion when exposed to electrolytes. Metals have varying electrode potentials. A conducting path can be created that causes ionic migration from the anodic metal to the cathodic metal. The anodic metal corrodes at a faster speed than the “noble” cathodic metal. The latter may even stop corroding at some point. Corrosion-resistant coatings to prevent galvanic corrosion are of particular importance to the marine industry.

3. Microbial corrosion

Bacterial corrosion occurs with the aid of microorganisms. Feeding on oxygen, some microorganisms can directly oxidize iron materials. Biogenic sulfide corrosion is due to bacteria oxidizing sulfur to produce sulfuric acid. Bacterial concentration cells can also enhance galvanic corrosion by feeding on the by-products of the ongoing corrosion process.

4. Corrosion due to high temperatures

A high temperature environment, together with oxidizing agents like sulfur or oxygen, can trigger the oxidation process that corrodes the metal surface. This type of corrosion particularly concerns the power, aviation and automobile industries, where materials are often subjected to long periods of intense heat.

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