Green Anodizing

By Ken Sigsbury, Berkshire Anodizing, LLC

Hard to believe, but anodized aluminum is the greenest form of material used in manufacturing applications today. Aluminum itself is 100% recyclable, and actually uses less energy to convert and reuse than aluminum bauxite mined from the earths crust.

There are various finishes that can be used on aluminum for corrosion resistance and cosmetic reasons. Anodizing is unique in the fact that it can only be used on aluminum, titanium, magnesium, zinc and niobium.

Anodizing is an electrolytic passivation process used to increase the thickness of the natural oxide layer on the surface of metal parts. Anodizing increases corrosion resistance and wear resistance, and provides better adhesion for paint primers and glues than bare metal. Anodizing changes the microscopic texture of the surface and can change the crystal structure of metal near the surface. Anodic films are generally much stronger and more adherent than most types of paint and metal plating, making them less likely to crack and peel.

Anodizing was first used on an industrial scale in 1923 to protect Duralumin seaplane parts from corrosion. Variations of this process soon evolved, and the first sulfuric anodizing process was patented by Gower and O’Brien in 1927. Since that time it has become one of the most common finishes for all aluminum products.

Since Anodizing is a conversion coating that makes the aluminum oxidize upon itself, the finishing along with the aluminum is 100% recyclable.

The entire wastes from the process are sulfuric, sodium hydroxide and aluminum. The sulfuric (acid) and sodium hydroxide (base) neutralize each other. The only waste then is the aluminum itself. Aluminum is removed the anodizing process and it creates a solid in the waste stream. With the proper equipment the aluminum can be removed and resold as a product to the Alum Industry.

Alum is extensively used in municipal waste treatment plants to tie up solids from human waste. Basically the acid and base neutralize each other and the aluminum is recovered and sold as a marketable product. Ultimately there is no waste in the anodizing process.