Coating solutions of trivalent chromium for coating zinc and cad

Details Coating solutions of trivalent chromium for coating zinc and cad Coating solutions of trivalent chromium for coating zinc and cad

1979-12-21

1981-04-21

Smith, Ronald H.

Metal treatment

Compositions

Heat treating

106302, 148 621, 423596, 4273837, 427405, C23F 726

Patent

active

042630592

ABSTRACT:
Aqueous acidic chromate coating solutions are described for treating zinc, zinc alloy, or cadmium surfaces comprising trivalent chromium as substantially the only chromium ion present, fluoride ion and an acid, the trivalent chromium ions comprising a mixture of green and blue trivalent chromium. One method of preparing the green trivalent chromium is by reducing an aqueous solution of hexavalent chromium with sufficient reducing agent to reduce all of the hexavalent chromium to trivalent chromium. The blue trivalent chromium can be prepared by reducing hexavalent chromium with reducing agent and adding an acid and fluoride ion (pH<1). Chromate coatings on zinc, zinc alloy and cadmium surfaces are produced by contacting said surfaces with an aqueous acidic solution of the invention.

REFERENCES:
patent: 3535168 (1970-10-01), Thompson
patent: 3932198 (1976-01-01), Schneider
patent: 4067747 (1978-01-01), Mansmann et al.
patent: 4141758 (1979-02-01), Glassman et al.
patent: 4171231 (1979-10-01), Bishop et al.

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