Black Oxide Processes
– Standard black oxide is magnetite (Fe) and provides better corrosion protection than red oxide (rust) Fe.
– Modern industrial approaches to forming black oxide include hot and mid-temperature processes.
– Traditional methods are of historical interest and useful for hobbyists.
– Low-temperature oxide is not a conversion coating but deposits a copper selenium compound.
– Blackening has advantages such as batch processing, minimal dimensional impact, and cost-effectiveness.
Hot Black Oxide
– Hot baths of sodium hydroxide (NaOH), nitrates, and/or nitrites are used to convert the surface to magnetite.
– The process involves dipping the part into various tanks containing alkaline detergent, water, sodium hydroxide, and sealant.
– Black oxide forms on the surface instead of red oxide, and oil is applied as a post-treatment to prevent corrosion.
– Advantages of blackening include large batch processing, minimal dimensional impact, and cost-effectiveness.
– Specifications for hot black oxide include MIL-DTL-13924, AMS 2485, ASTM D769, and ISO 11408.
Mid-Temperature Black Oxide
– Mid-temperature black oxide converts the surface to magnetite at a temperature of 90-120°C.
– It meets military specification MIL-DTL-13924 and AMS 2485.
– Mid-temperature black oxide does not produce caustic fumes.
– The process is advantageous due to its lower temperature requirement.
– Additional citations are needed for further information.
Cold Black Oxide
– Cold black oxide is applied at a temperature of 20-30°C.
– It is not an oxide conversion coating but a deposited copper selenide compound.
– Cold black oxide is convenient for in-house blackening but offers less abrasion resistance.
– Corrosion resistance can be increased by applying oil, wax, or lacquer.
– Applications for cold black oxide include tooling and architectural finishing on steel.
Black Oxide for Specific Materials
– Black oxide for copper converts the surface to cupric oxide.
– The finished coating is chemically stable and adherent.
– To increase corrosion resistance, the surface may be oiled, lacquered, or waxed.
– Black oxide on copper is used in aerospace and optical applications to minimize light reflection.
– It provides better adhesion for fiberglass laminate layers in printed circuit boards.
– Hot black oxide for stainless steel blackens various stainless steel alloys and offers abrasion resistance.
– Room-temperature blackening for stainless steel offers the same corrosion protection but less abrasion resistance.
– Hot black oxide is used on surgical instruments to reduce eye fatigue in light-intensive environments.
– Further information is needed for black oxide on zinc.
Note: The “See Also” section and references have been omitted as they do not contain relevant information for grouping. Source: https://en.wikipedia.org/wiki/Black_oxide
Black oxide or blackening is a conversion coating for ferrous materials, stainless steel, copper and copper based alloys, zinc, powdered metals, and silver solder. It is used to add mild corrosion resistance, for appearance, and to minimize light reflection. To achieve maximal corrosion resistance the black oxide must be impregnated with oil or wax. One of its advantages over other coatings is its minimal buildup.
