What Does Oxide Layer Mean?
An oxide layer is a thin layer or coating of an oxide, such as iron oxide. Such a coating may be protective, decorative or functional. It is a passivating layer on the surface of the metal, preventing further corrosion. The corrosion-resistant properties of stainless steel are due to the formation of a passive chromium oxide layer.
The more dense and tightly bound the oxides are, the more corrosion resistant the material is. Any process that prevents the formation of these oxide layers or removes the oxide layers promotes more rapid corrosion wastage.
Corrosionpedia Explains Oxide Layer
An oxide layer is a chemical compound containing oxygen and one other element. The oxide layer is the main factor in determining the surface treatment for a metal surface.
A classic example for an oxide-layer-assisted corrosion-resistant alloy is stainless steel, in which the alloying element chromium (Cr) forms an impervious stable oxide layer (Cr2O3, also called chromia) along the grain boundaries and surface. Usually grain boundaries are prone to corrosion attack because of defects and high-energy sites unless they are protected via passivation.
The corrosion resistance of aluminum and its alloys can be attributed to the formation of a passive oxide layer on their surfaces. Untreated aluminum has very good corrosion resistance in most environments. This is primarily because aluminum spontaneously forms a thin but effective oxide layer that prevents further oxidation.
The buildup and thickness of the oxide layer depends on the humidity of the air or the composition of the water. The oxide layer does not offer protection against corrosion in all cases. Oxide layers and protective effects can be strengthened by the action of boiling water or steam. A surface layer of aluminum monohydrate (boehmite) of one- to two-thousandths of a millimeter thick forms on top of the barrier layer within a matter of minutes. Even more corrosion-resistant oxide layers are produced artificially by anodizing.