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#086 What is Anodizing (Anodic Oxidization Process)?

Category : Anodizing
July 8, 2011

Anodizing is also called Alumite processing for the name was a registered trade name for the process by Riken Chemical Labs a long time ago. Anodizing process and layer properties will be discussed below.

(1) Process

Refer to [Fig.1] below. The process uses the subject aluminum object as the anode (+ pole) and a carbon electrode as the opposing pole, and performs an electrolysis (applies a DC current) submerged in electrolyte baths. The surface aluminum of the subject dissolves and binds with oxygen to create a aluminum oxide surface layer. This layer is called anodic oxide layer (anodized layer).

[Fig.1] Anodize Process Diagram

(2) Layer Structure

When a acid solution is electrolysis processed, the anode normally emits oxygen but not in a case of aluminum anodes. The oxygen from the aluminum anode immediately binds before gasifying with dissolved surface layer metal and forms an aluminum oxide. The layer forming process is shown in [Fig.2] below.

A barrier layer forms during the initial phase of the electrolysis advancing to a formation of porous layer. As the process progresses, this porous layer grows to a certain thickness. As can be seen on the diagram, an anodized layer is made up of a electrically conductive but non-growing barrier layer, and isolating but growing porous layer.

[Fig.2] Layer Formation Model Diagram

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