Chromite coatings, electrolytes, and electrolytic method of forming the coatings
US4137132A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | May 31, 1977 |
| Grant date | Jan 30, 1979 |
| Priority date | — |
| Expiry date | May 31, 1997 |
Classification
- Technology area (CPC C)Chemistry; Metallurgy
- CPC primaryC25D11/38
- WIPO fieldSurface technology, coating
- WIPO sectorChemistry
Abstract
A method of producing chromium conversion coatings is described. The coatings are novel in that they are chromite i.e. Cr.sub.2 O.sub.3 coatings rather than the conventional chromate i.e. CrO.sub.3 coatings. The invention includes a novel electrolyte for depositing chromite layers. The electrolyte is an aqueous solution containing Cr.sup.III ions, a weak complexing agent for Cr.sup.III ions and a poison for the electrodeposition of chromium metal. The electrolyte preferably also contains conductivity salts and may include other additives such as fluoride ion and boric acid. Examples of poisons are Cr.sup.VI ions, peroxide, nitrate, polyamines, phosphates and formaldehyde. The chromite conversion coatings can be improved by aging and can be subsequently painted or lacquered. The electrolytes of the present invention are much less corrosive than Cr.sup.VI electrolytes and thus the substrates which can be coated include materials which cannot readily be chromate coated because they are reactive towards Cr.sup.VI electrolytes.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.