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Method of making an article having a layer of a nickel-phosphorus alloy and coated with a protective layer

  • US 4,545,871 A
  • Filed: 11/02/1984
  • Issued: 10/08/1985
  • Est. Priority Date: 05/06/1982
  • Status: Expired due to Fees
First Claim
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1. A method of producing a protective layer consisting of a nickel-free conversion layer of a hydrated basic chromium phosphate which comprises the components CrPO4 and Cr(OH3), wherein Cr2 (SO4)3 may be present and in which the weight ratio Cr:

  • P;

    S=1;

    (0.2-1.5);

    (0-0.5) on an article coated with a layer consisting of a nickel-phosphorus alloy, by treating the coated article in an aqueous solution containing chromate ions characterized in that the coated article is connected as an electrode in aqueous solution of chromic acid at ambient temperature, the electrode being subjected to a periodically reversed current with a frequency between 0.1 and 50 Hz with a current density between 0.2 and 1 A/dm2 and a ratio of cathodic to anodic pulse durations between 0.05 and 20.

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