Anodizing is an electrolytic passivation process used to increase the thickness of the natural oxide layer on the surface of metal parts.
These carabiners have an anodized aluminium surface that has been dyed; they are made in many colours.
Colored anodized aluminium key blanks
Colored iPod Mini cases are dyed following anodizing and before thermal sealing.
Image: Aluminum Heatsink Case for Raspberry Pi 4 Blue 49317288727
In physical chemistry and engineering, passivation is coating a material so that it becomes "passive", that is, less readily affected or corroded by the environment. Passivation involves creation of an outer layer of shield material that is applied as a microcoating, created by chemical reaction with the base material, or allowed to build by spontaneous oxidation in the air. As a technique, passivation is the use of a light coat of a protective material, such as metal oxide, to create a shield against corrosion. Passivation of silicon is used during fabrication of microelectronic devices. Undesired passivation of electrodes, called "fouling", increases the circuit resistance so it interferes with some electrochemical applications such as electrocoagulation for wastewater treatment, amperometric chemical sensing, and electrochemical synthesis.
Tempering colors are produced when steel is heated and a thin film of iron oxide forms on the surface. The color indicates the temperature the steel reached, which made this one of the earliest practical uses of thin-film interference.
Relation between voltage and color for anodized titanium.
