What Does Anodic Oxidation Mean?
Anodic oxidation is an electrochemical method for the production of an oxide film on a metallic substrate. It removes electrons from a substance and oxidizes the anode.
Anodic oxidation increases corrosion resistance and wear resistance, and provides better adhesion for paint primers and glues than does bare metal.
Anodic films can also be used for a number of cosmetic effects, either with thick, porous coatings that can absorb dyes or with thin, transparent coatings that add interference effects to reflected light.
Corrosionpedia Explains Anodic Oxidation
Anodic oxidation is an accelerated electrochemical oxidation process, which is intensified by the natural oxide skin of the metal. It involves the application of an electrical bias at relatively low currents while the substrate is immersed in an acid bath. The films can be very dense and stable, with a variety of microstructural characteristics. Normally anodic oxidation is done in an electrochemical cell containing ~0.4 L aqueous solutions of sulfuric acid, hydrogen peroxide and phosphoric acid at ~77°F (~25°C).
The microstructures and thicknesses of the films are characterized using X-ray diffraction (XRD), Raman microspectroscopy and field emission scanning electron microscopy (FESEM).
For example, anodic oxidation is used to modify the surfaces and properties of titanium and aluminum owing to:
- Resultant mechanical properties
- Biocompatible resultant mechanical properties
- Corrosion resistance
Titanium is always coated by an oxide surface layer of 1.5-10 nm thickness, which forms spontaneously upon exposure to air and atmospheric water vapor. Anodic oxidation of titanium allows the controlled production of a protective oxide surface layer much thicker than that formed naturally. These coatings may be dense/porous, amorphous or crystalline, depending on the conditions. The electrolytes most commonly used to anodize titanium are sulfuric and phosphoric acids.
In order to obtain satisfactory coating quality, the following must be considered:
- Appropriate electrolyte bath
- Power supply waveform
- Bath temperature
- Process time