Rohco, Inc.

Dale M Burdt

Donald J Guhde

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&lt;1). Chromate coatings on zinc, zinc alloy and cadmium surfaces are produced by contacting said surfaces with an aqueous acidic solution of the invention.

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North Olmsted, OH, United States of America

Dale M Burdt