Both Alodine and Andodize are chemical processes used to create a protective oxide barrier on certain types of metal. This barrier, when applied to metals such as aluminum, niobium, tantalum, titanium, tungsten and zirconium protects the metals from corrosion. The difference between Alodine and Anodize lies mostly in the process of applying or creating the barrier and the cost.
Metals treated with Alodine must first be etched with acid. To prepare a surface for Anodizing, it must be clean of debris and placed in a tank of salt water.
Acid-etched metals can be dipped in a tank containing Alodine or painted with the chemical. Dipping produces the most even coating, but both methods should be dried with hot, forced air. Anodizing is a complicated electro-chemical process. Anodizing chemicals are added to the salt water tank and electrodes are inserted to create the reaction.
Alodine coats the surface of the metal with a thin surface barrier. Anodizing also coats the surface, but penetrates the metal further for a thicker barrier, and has the added effect of hardening the material.
Alodine is more affordable to purchase supplies for, and simpler to apply as it only requires painting the surface or having enough of the chemical to submerge the metal. Anodizing involves much more expensive chemicals and electro-chemical bath machinery. The process of Anodizing is more hazardous and requires more skill than Alodining.