NEW ELECTROPLATED BLACK COATING -- BLACK CHROMIUM
Abstract
A description is given of the electroplating of black chromium coating for use on instrument components to eliminate glare and to prevent corrosion. Plating is conducted in a solution of chromic anhydride and sodium nitrate for a period of 20 minutes at a current density of 30-60 amp/sq dm and a temperature of 15-40C. A lead-tin alloy (7 percent tin) is used as the anode, and the chromium oxide content in the solution is regularly checked by the Hull cell test for replenishment. Coating thickness determined by metallographic method is 4.8 microns at a 20 min period and current density of 60 amp/sq dm. The coating, containing a mixture of 75 percent chromium and 25 percent chromium oxide can be directly plated on aluminum and stainless steel components, and on iron components with undercoats of low tin-containing bronze. Results from humid heat tests and salt fog tests showed that the black chromium coating exhibits a better quality than the black nickel coating or bluing. Defects likely to occur in plating and their remedies are also given.
Document Details
- Document Type
- Technical Report
- Publication Date
- Mar 04, 1969
- Accession Number
- AD0693836
Entities
People
- Hsu Hsiao-feng
Organizations
- National Air and Space Intelligence Center