Definition - What does Anodic Coating mean?
An anodic coating is a type of coating material that utilizes anodizing to provide increased thickness, color and protection to aluminum or any type of substrate. This coating consists of the oxide film that is created on metal through electrolysis, with the metal acting as an anode.
The natural coating that exists in aluminum as well as other ductile and soft metal can be very thin, making it easily damaged. Thus, building up the anodic coating offers very beneficial properties to the surface of the aluminum.
Corrosionpedia explains Anodic Coating
An anodic coating is produced through the process of anodizing, or reversed electroplating. In anodizing, the surface serves as the anode, or positive electrode, within the electrolytic cell. The aluminum is submerged in a water solution or acid electrolyte. The consistency of the coating will depend on the controlled temperature.
At 20°C, the coating will be clear and soft. When exposed to 50°C, the end result will be a dull, gray and dense coating or hard anodizing. A direct current is then applied between the cathode and the anode or aluminum. Once applied, the water molecules present in the solution split and release oxygen into the anode. The oxygen will then combine with aluminum to form oxide and create the oxide film that can be found on the surface.
The acid in the electrolyte attempts to dissolve this oxide, and creates a permeable film oxide on top of the aluminum. The recommended anodic coating thickness can be as many as 25 microns, especially when intended for exterior use.
When the necessary thickness of anodic film is achieved, the aluminum or anode is extracted from the electrolyte and undergoes thorough rinsing to eradicate the acids. At this stage, the anodic coating is suited for coloring when required.
The anodic coating can be very permeable and will trap or accept almost all materials that pass through its pores. This can be either advantageous or disadvantageous to the existing properties. In order to prevent this, the coatings or pores are sealed through hydrolyzing, or the addition of water to the oxide.
The resultant coating will become hard, smooth, transparent and homogeneous.