Metal article layered with a nickel-phosphorus alloy and a protective coating

• US 4,497,877 A
• Filed: 05/03/1983
• Issued: 02/05/1985
• Est. Priority Date: 05/06/1982
• Status: Expired due to Term

• Current Assignee: US Philips Corporation (Koninklijke Philips N.V.)
• Original Assignee: US Philips Corporation (Koninklijke Philips N.V.)
• Inventors: Van de Leest, Renaat E., Krijl, Gerrit
• Primary Examiner(s): O'Keefe, Veronica
• Application Number:
  US06/491,101
• Time in Patent Office: 644 Days
• Field of Search: 428/469, 428/472, 428/629, 428/633, 428/666, 428/679, 428/680, 428/935, 126/901, 148/31.5
• US Class Current: 428/628
• CPC Class Codes: C25D 11/36 Phosphatising
• CPC Class Codes: C25D 11/38 Chromatising
• CPC Class Codes: Y10S 126/908 Particular chemical
• CPC Class Codes: Y10S 428/926 Thickness of individual layer specified
• CPC Class Codes: Y10S 428/936 Chemical deposition, e.g. electroless plating
• CPC Class Codes: Y10T 428/12583 Component contains compound of adjacent metal
• CPC Class Codes: Y10T 428/1259 Oxide
• CPC Class Codes: Y10T 428/12847 Cr-base component
• CPC Class Codes: Y10T 428/12937 Co- or Ni-base component next to Fe-base component
• CPC Class Codes: Y10T 428/12944 Ni-base component
• CPC Class Codes: Y10T 428/261 In terms of molecular thickness or light wave length
• CPC Class Codes: Y10T 428/31678 Of metal

Abstract

A metal article which covered with a nickel-phosphorus alloy and which is covered on its outer surface with a protective layer which comprises CrPO₄, Cr(OH)₃ and may also comprise Cr₂ (SO₄)₃ and in which no nickel is present. The layer provides an excellent corrosion protection. In a particular embodiment the layer is black, scratch-resistant in normal use, cannot be wiped off and is not sensitive to finger prints and is extremely suitable for decorative applications. The layers can be obtained electrolytically in a bath which comprises chromic acid and optionally reversed current in a given frequency range, a given range of current densities and a given range of ratios of cathodic to anodic pulse durations. In order to obtain the black layers the cathodic time duration is only a fraction of black layers the anodic time duration.

Claims

1. A metal article which is coated with a layer consisting of a nickel-phosphorus alloy, which layer is coated on its outer surface by a protective layer, characterized in that the protective layer consists of a nickel-free conversion layer of a hydrated basic chromium phosphate which comprises the components CrPO₄ and Cr(OH₃), wherein Cr₂ (SO₄), may be present and in which the weight ratio Cr:

P;

S=1;

(0.2-1.5);

(0-0.5).

2. A metal article as claimed in claim 1, characterized in that the protective layer has black colour and consists of a hydrated chromium phosphate of the components CrPO₄ and Cr(OH)₃ wherein Cr₂ (SO₄)₃ may be present and in which the weight ratio Cr:

P;

S=1;

1;

(0-1.2).