Aluminum oxide is rated 9 out of 10 on the Mohs hardness scale, meaning second only to diamond. That will leave you with a hard, natural aluminum oxide coating, able to withstand chemical attack and very scratch resistant. Once this level is reached, and if no color is needed, the process is stopped and the surface can be sealed simply by rinsing in water. For typical non-hard coatings, the depth can be up to 10 microns. The longer the current is applied the greater the penetration of these columns. This is called a barrier layer, a defense against further chemical reactions at those spots.Ī regular pattern of surface porosity is created when electric current is applied. The aluminum at the surface combines with the negatively charged O 2 ions to create aluminum oxide.

These pores form a geometrically regular pattern and begin to erode down into the substrate. The electrochemical reaction causes pores to form on the surface of the aluminum as excess positive ions escape. The electric current in this circuit causes positive ions to be attracted to the negative plates, and negative ions to flock to the positive anode, the piece of aluminum. An electrolyte is an electrically conductive solution with lots of positive and negative ions that it wants to swap.Ī positive electric charge is applied to the aluminum, making it the “anode”, while a negative charge is applied to plates suspended in the electrolyte. To prepare aluminum for anodizing, the surface is first thoroughly cleaned and rinsed, and then placed into a bath of some electrolytic solution like sulfuric acid. Anodizing is one of the most durable surface treatments 1.

Does aluminium rust in water