Anodizing aluminum: Difference between revisions

[[File:Sulfuric_acid_vs_sodium_bisulfate.png|right|framethumb|350px|Samples comparing results of anodising aluminum with sulfuric acid against sodium bisulfate.]]Aluminum has an oxide barrier coating because of a reaction with the oxygen in air. By using an electrolytic process the metal can have additional protection. In general there are two types of barrier coatings. The first is a thin, hard coating that increases the hardness and insulation properties. The second is a porous cellular structure that allows a dye to fill in the cells and provides a decorative and protective coating - as used here. This is a variable process that may require some experiments to determine what is happening. Longer anodizing times, different concentrations and temperature, different grade of aluminum, different current draw or voltage, and patience are all helpful.<ref name="obs"/>

[[File:Anodisation.jpg|right|framethumb|350px|Idealised depiction of an anodized layer and schematic of the anodising process.]]Prepare the aluminum for anodizing by cleaning thoroughly using a fine steel wool to remove the surface contaminants and reduce imperfections. Take care not to cause micro metal contamination by pressing too hard. Note that the finish that goes into the tank is what comes out of the tank. Follow by a wash with a plastic scouring pad and washing up detergent (or 99.9% isopropyl alcohol). Rinse well and either proceed to the sodium hydroxide etch for 2 to 3 minutes and rinse again, or go directly to the anodizing solution. The etch step provides some bite for the solution and allows for slightly larger cell size. Aluminum alloys are highly variable so if possible experiment with scrap pieces.<ref name="obs"/>