Chromite coatings, electrolytes, and electrolytic method of form

Details Chromite coatings, electrolytes, and electrolytic method of form Chromite coatings, electrolytes, and electrolytic method of form

1977-05-31

1979-01-30

Andrews, R. L.

Chemistry: electrical and wave energy

Processes and products

204 38S, 204 56R, 148 62, 148 621, C25D 1138

Patent

active

041371321

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.

REFERENCES:
patent: 2733199 (1956-01-01), Wick
patent: 3032487 (1962-05-01), Yonezaki et al.
patent: 3337431 (1967-08-01), Kitamura et al.
Chromium Plating by Morisset et al., 1954, p. 81.

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