Mil-F-495, Chemical Finish; Black, (Copper)
Chemical Finish Black Oxide for Copper
This finshing and specification covers a black chemical finish for copper alloys.
Black oxide for copper, sometimes known by the trade name Ebonol C, converts the copper surface to cupric oxide. For the process to work the surface has to have at least 65% copper; for copper surfaces that have less than 90% copper it must first be pretreated with an activating treatment. The finished coating is chemically stable and very adherent. It is stable up to 400 °F (204 °C); above this temperature the coating degrades due to oxidation of the base copper. To increase corrosion resistance the surface may be oiled, lacquered, or waxed. It is also used as a pre-treatment for painting or enamelling. The surface finish is usually satin, but it can be turned glossy by coating in a clear high gloss enamel.
On a microscopic scale dendrites form on the surface finish, which trap light and increase absorptivity. Because of this property the coating is used in aerospace, microscopy and other optical applications to minimise light reflection.
In printed circuit boards, the use of black oxide provides better adhesion for the fiberglass laminate layers. The PCB is dipped in a bath containing hydroxide, hypochlorite, and cuprate, which becomes depleted in all three components. This indicates that the black copper oxide comes partially from the cuprate and partially from the PCB copper circuitry. Under microscopic examination, there is no copper oxide layer.
A uniform black corrosion retarding coating for copper & copper alloys. Coating has no abrasion resistance. Used to impart black color to and for gloss reduction purposes on copper alloy surfaces other than food service and water supply items. Also as a base for subsequent coatings such as lacquer, varnish, oil, and wax.
No dimensional change are effected with Chemical Finish finishes.