Mcgean-rohco, Inc.

Marlinda J Thomay

Craig V Bishop

Gary W Loar

Billie J Page

A method is described for preparing a black chromium-containing conversion coating on a zinc-nickel alloy surface containing at least about 8% nickel in the alloy or on a zinc-iron alloy surface. The method of the invention comprises contacting said surfaces with an aqueous acidic solution comprising trivalent chromium and an amount of a phosphorus acid selected from phosphoric acid, phosphorous acid, hypophosphorous acid, and mixtures thereof effective to provide a solution having a pH of from about 1.0 to about 2.5. Metal articles having zinc-nickel alloy surfaces containing at least about 8 % nickel in the alloy or having zinc-iron alloy surfaces which have been treated in accordance with the method of the invention exhibit the desired blackened surfaces and are characterized by improved corrosion resistance.

Black chromium-containing conversion coatings on zinc-nickel and

This invention relates to a method of controlling orthophosphite ion concentration in a hypophosphite-based electroless metal plating bath, comprising the steps of contacting the plating bath with a yttrium or a lanthanide series metal salt, and removing orthophosphite ions from the bath. The methods of the present invention provide effective means for controlling phosphite ion concentration in electroless metal plating baths and especially electroless nickel plating baths. The methods of the present invention provide means for increasing pH and removing orthophosphite ions from the plating bath.

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Parma, OH, United States of America

Marlinda J Thomay