Corrosion is the deterioration of the properties of a material due to its interaction with the environment. Corrosion occurs everywhere from your teeth to your batteries. A common place that we want to control corrosion-besides our teeth-is in metal or ceramic materials. Metal typically corrodes due to the oxidation of iron atoms as they react with water or oxygen while ceramics typically corrode by exposure to the sun's ultraviolet light. Some metals better resist corrosion than others, which is why, for example, brass is frequently used in plumbing.
Under the right conditions, a very thin film of corrosion can actually protect the rest of an element from further corrosion. In air and water of moderate temperatures, aluminum, stainless steel, titanium and silicon will undergo this process, which is technically known as passivation. While in general, passivated materials are superior at resisting corrosion, if they do succumb, the corrosion tends to be less obvious than other types of corrosion, like, say, rust, thereby escaping notice. If you do decide to purchase passivated materials, beware of the following types of corrosion:
- Pitting Corrosion. Pitting corrosion appears as small pits that can continue to increase in size because the inside of the pit is deprived of oxygen.
- Fretting. Passivating oxides can also be abrasives when particles rub against the passivating film where two surfaces join.
- Weld Decay. Corrosion can occur near welding points. The special alloys that can prevent weld decay require a post-welding heat treatment so as to prevent knifeline attack, which is a similar form of corrosion that looks like it sounds (small and hard to detect).
- Microbial Corrosion. Also known as bacterial corrosion, microbial corrosion is caused by microorganisms.
- High Temperature Corrosion. Materials subjected to high temperatures in an environment containing corrosive products may yield to this type of corrosion.
For materials that are not specifically known to resist corrosion like, say, iron, here are some ways to control corrosion:
- Barrier. Barrier corrosion control consists of putting a corrosion-resistant material between the environment and the material you are trying to protect. This would include the application of enamel, as well as plating, galvanizing and painting.
- Coatings. In controlled environments, chemical agents that inhibit corrosion can be added to the environment. These agents range from salts to phosphates.
- Anodizing. At the end of the manufacturing process, aluminum alloys can be anodized by being put into a chemical wash, thereby creating a protective layer.
- Cathodic Protection (CP). Cathodic protection controls corrosion by making a metal surface into the cathode of an electrochemical cell.
That's the short lesson in corrosion control. Keep your eye out for corrosion in your home. One of the best ways to stay ahead of corrosion is to control it early on.