What Is Anodizing?

The structure of many metals is weakened by the oxidation process, but not aluminum. Aluminum can actually be made stronger and more durable through a process called "anodizing." Anodizing involves placing an aluminum sheet in a bath of chemical acid, usually acetone in laboratory experiments. The aluminum sheet becomes the positive pole of the chemical battery, and the acid bath becomes the negative pole. Electricity is passed through the acid, which causes the surface of the aluminum to oxidize (essentially rust). Aluminum oxide replaces the original aluminum on the surface, creating a strong coating. The result is an extremely hard substance called anodized aluminum.

With the right anodizing process, anodized aluminum can be almost as hard as diamond. Many modern buildings use anodized aluminum where the metal frame is exposed to the elements. Anodized aluminum is also a popular material for high-end cookware like frying pans and pots. Heat is evenly distributed across the anodized aluminum, and the anodizing process provides a natural protective finish. Another plating process can be used to make anodized aluminum looks like copper or brass or other metals. Specialty dyes are also available for coloring anodized aluminum for decorative purposes.

Due to its strength and durability, anodized aluminum is also used in many other applications. Many satellites orbiting Earth are protected from space debris by layers of anodized aluminum. The automotive industry relies heavily on anodized aluminum to decorate and expose the protective casing of components. Furniture designers often use anodized aluminum as the frame of outdoor furniture and as the base metal for lamps and other decorative items. Modern household appliances and computer systems can utilize anodized aluminum as protective housing.

Due to its non-conductive nature, anodized aluminum may not be suitable for all applications. Unlike other metals such as iron, the oxidation process does not appear to weaken aluminum's strength. The "aluminum rust" layer remains part of the original aluminum and will not transfer to food and will not flake off easily under pressure. This makes it especially popular in food service applications and industrial applications where durability is critical.