NEW TRIVALENT CHROMIUM CONVERSION COATING FOR ZINC, ZINC-NICKEL PLATING
With the current restrictions on the use of hexavalent chromium right around the corner, all chemical companies supplying the plating industry are scurrying to find suitable replacements. All, that is, except for the Aldoa Company (Detroit, MI) which has pioneered environmentally friendly processes such as non-cyanide zinc and cadmium processes and Novalyte ZNA, a zinc-nickel plating that is one of the most widely used substitutes for cadmium plating. Now, a new trivalent chromium salts conversion coating for electroplated acid zinc deposits has been introduced. Called Aldokote ZN-3, the formulation is a two component solution that produces a bright and highly corrosion-resistant clear to slightly iridescent conversion coating, ideal for fasteners, supports and brackets. The coating formulation provides an easy to prepare, use and maintain bath that requires no additional steps or secondary top coats. Under mild agitation (either mechanical or solution circulation) and an immersion time of between 30 and 60 seconds, Aldokote ZN-3 can provide a protection of more than 120 hours of neutral salt spray testing against the appearance of white corrosion, easily surpassing typical automotive and other industry specifications.
A working solution of Aldokote ZN-3 is prepared from 2-3% of Aldokote ZN-3A and 8 pounds per 100 gallons of Aldokote ZN-3S. Operating parameters to achieve optimum results include a temperature of 70 to 85oF and a pH of 1.6-2.0.
Through regularly scheduled and standard analytical monitoring procedures, consistent results for both appearance and corrosion protection are readily obtained. The pH is easily adjusted through the addition of a nitric acid or ammonium hydroxide solution, while the trivalent chromium level can be increased by adding the ZN-3 concentrate.
Aldokote ZN-3 is suitable for use in both rack and barrel applications and it works at room temperature.
Aldoa is a manufacturer of electroplating chemicals for the metal finishing industry. They have been supporting the plating industry since 1957 by developing alternative materials and processes. Aldoa markets its products through a network of distributors.