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Black Iron Oxide Magnetite Treatment (BOM)

Posted by Jose Rueda on Sep 16th 2015

Black Magnetite Oxide Firearm Finishes

What is Black Magnetite Oxide?

See our line of products that utilize this fantastic BOM Finish!

Black Oxide, blackening, oxidizing, oxiding, black passivating. . . these terms all refer to the process of forming a black iron oxide on the surface of ferrous metals.

The black oxide process is a chemical conversion coating. This means that the black oxide is not deposited on the surface of the substrate like nickel or zinc electroplating. Instead, the black oxide coating is produced by a chemical reaction between the iron on the surface of the ferrous metal and the oxidizing salts present in the black oxide solution. These oxidizing salts include penetrates, catalysts, activators and proprietary additives which all take part in the chemical reaction. The result of this chemical reaction is the formation of black iron oxide, magnetite (Fe3O4), on the surface of the metal being coated. Black oxide has a range of unique properties and benefits that can be applied to a variety of industries.

Some Important features of Black Magneitite Oxide:

  • Corrosion Protection – Depending on the post-treatment applied, black oxide coating can give corrosion resistance equivalent to 144 hrs of salt spray exposure. Other applications are designed to provide extended shelf life for stored parts prior to their use or to prepare them for further surface treatment (painting).
  • Dimensional Stability – Black oxide adds no more than 5 to 10 millionths of an inch to the dimension of a part (it also penetrates to an approximate depth of 5 to 10 millionths). For all intents and purposes, the as-formed dimensions do not change (as they do when painted or plated). This provides corrosion protection for critical-size parts.
  • Improved Lubricity – Oil post-treatment not only protects against corrosion, but the oil itself results in smoother running, mating parts.
  • Anti-galling – Where break-in of mating parts is necessary, the anti-galling surface lets the outer lubricating layer be sacrificed during initial contact and abrasion while work-hardened surfaces are formed. The black oxide itself has a hardness of 5.5 on the Mohs’ Scale.
  • Reduced Light Glare – Moving machine parts, hand tools, and surgical instruments coated with black oxide reflect less light and reduce eye fatigue when used under bright lights.
  • Durability - Finish does not chip, flake, or peel