What is black oxide?

What is black oxide?

  Black oxide is a conversion coating type that provides an improved matte black appearance for metal parts. Conversion coatings describe processes that occur by electrochemical or chemical treatment of the surface in question.

  As for the black oxide, the coating is formed by a chemical reaction after the part is dipped into an alkaline aqueous salt solution. Normally, this happens at about 285 degrees Fahrenheit.

  The reaction between the iron in the alloy and the oxide produces a compound called magnetite. Magnetite is deposited on the surface of the component to give it a finish.

  Oxidized black surface treatment not only improves the appearance of parts, but also improves the dimensional stability of parts. It also reduces light reflection from the surface, which is an important requirement for parts involving radiation.

  When the steel is treated with black oxidation, the thickness of the steel increases. While this may be a tiny increase, it helps improve materials like screwdrivers and drills.

Black oxidation process

  In general, there are five simple and important steps to a black oxide coating. These steps include cleaning, rinsing, blackening oxide, rinsing, and replenishing coating.

  Steps such as alkaline descaling and pickling may need to be included if the part has scales or rust. These steps will be important prior to the completion of the black oxide process. Parts with flash holes also require neutralization and/or secondary flushing. This will help eliminate bleeding or "flowering."

  Each coating on the component must be stripped before the black oxide coating can be applied. The supplementary coating, the back finish of the metal part, will determine the overall appearance of the part. It will also have a significant impact on the functionality of the component.

  If a painting or print is labeled "oxidized black" without post-treatment, it is interpreted as "oxidized black and oil." Black oxide coatings have poor corrosion resistance without post-treatment. However, the inclusion of oil, paint, or wax ensures good corrosion protection.

  Black oxidized steel with appropriate supplemental coating can provide better results. The corrosion protection of oxidized black stainless steel and brass is top of the line, mainly because of their inherent properties. It is important to note that the configuration and end use of the parts will determine the rear finish. The oil finish will give the surface a shine.