MagpuLoverBoy, on 01 January 2010 - 09:52 AM, said:
, or anodising
in British English, is an electrolytic passivation
process used to increase the thickness of the natural oxide
layer on the surface of metal parts. The process is called "anodizing" because the part to be treated forms the anode
electrode of an electrical circuit
. Anodizing increases corrosion
resistance and wear resistance, and provides better adhesion for paint primers and glues than 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. Anodizing is also used to prevent galling
of threaded components and to make dielectric films for electrolytic capacitors
. Anodic films are most commonly applied to protect aluminium alloys
, although processes also exist for titanium
, and tantalum
. This process is not a useful treatment for iron or carbon steel
because these metals exfoliate when oxidized; i.e. the iron oxide
(also known as rust
) flakes off, constantly exposing the underlying metal to corrosion.
Anodization changes the microscopic texture of the surface and changes the crystal structure
of the metal near the surface. Thick coatings are normally porous, so a sealing process is often needed to achieve corrosion resistance. Anodized aluminium surfaces, for example, are harder than aluminium but have low to moderate wear resistance that can be improved with increasing thickness or by applying suitable sealing substances. Anodic films are generally much stronger and more adherent than most types of paint and metal plating, but also more brittle. This makes them less likely to crack and peel from aging and wear, but more susceptible to cracking from thermal stress.
Sorry couldn't resist.