Method for treatment of a chromium finish surface

Patent metadata

Field	Value
Publication number	US-11078585-B2
Application number	US-201716323603-A
Country	US
Kind code	B2
Filing date	Sep 26, 2017
Priority date	Sep 27, 2016
Publication date	Aug 3, 2021
Grant date	Aug 3, 2021

Abstract

A method for post-treatment of a chromium finish surface to improve corrosion resistance comprising a) providing a substrate having a chromium finish surface, and at least one intermediate layer between the chromium finish surface and the substrate, selected from the group consisting of nickel, nickel alloys, copper and copper alloys, wherein the chromium finish surface is a surface of a trivalent chromium plated layer, obtained by electroplating the substrate, having the at least one intermediate layer, in a plating bath, the plating bath comprising chromium (III) ions; b) contacting the chromium finish surface with an aqueous solution, comprising a permanganate, at least one compound which is selected from a phosphorus-oxygen compound, a hydroxide, a nitrate, a borate, boric acid, a silicate, or a mixture of two or more of these compounds; c) forming a transparent corrosion protection layer onto the chromium finish surface during step b.

First claim

The invention claimed is:

1. A method for post-treatment of a chromium finish surface to improve corrosion resistance, comprising
a) providing a substrate having a chromium finish surface, and at least one intermediate layer between the chromium finish surface and the substrate, wherein the at least one intermediate layer is selected from the group consisting of nickel, nickel alloys, copper and copper alloys, wherein the chromium finish surface is a surface of a trivalent chromium plated layer, obtained by electroplating the substrate having the at least one intermediate layer, in a plating bath, the plating bath comprising chromium (III) ions as a main chromium source;
b) contacting the chromium finish surface with an aqueous solution, comprising
a permanganate, and
at least one compound which is selected from a phosphorus-oxygen compound, a hydroxide, a nitrate, a borate, boric acid, a silicate, or a mixture of two or more of these compounds; and

c) forming a transparent corrosion protection layer onto the chromium finish surface during contacting the chromium surface with the aqueous solution in step b, wherein in step b) an electric potential is applied between the chromium finish surface and an inert counter electrode, wherein the chromium finish surface serves as a cathode and the inert counter electrode serves as an anode.

2. The method of claim 1 , wherein the at least one compound is selected from inorganic phosphorus-oxygen compound as a phosphate, a hydrogenphosphate, a dihydrogenphospate, a pyrophosphate, a phosphonate or mixtures thereof; hydroxide; a borate or a nitrate.

3. The method according to claim 1 , wherein the plating bath is substantially free of chromium (VI) ions and the trivalent chromium plated layer comprises chromium in an amount of 45-90 at % (atom percent), oxygen in an amount of 5-20 at % with the proviso that the total amount of all chemical elements together will not exceed 100 at % and the chromium amount has in every case the highest amount within the trivalent chromium plated layer.

4. The method according to claim 1 , wherein the plating bath is substantially free of chromium (VI) ions and the trivalent chromium plated layer comprises chromium in an amount of 45-90 at %, oxygen in an amount of 5-20 at %, iron in an amount of 0-30 at %, carbon in an amount of 0-15 at %, sulfur in an amount of 0-15 at %, and further metals or nonmetals in an amount of 0-1 at %; with the proviso that the total amount of all chemical elements together will not exceed 100 at % and the chromium amount has in every case the highest amount within the trivalent chromium plated layer.

5. The method according to claim 1 , wherein
one of the at least one intermediate layer, which is directly in contact with the trivalent chromium plated layer, the trivalent chromium plated layer having pores or pores and cracks,
is a bright or satin nickel layer, obtained by electroplating the substrate, and further comprises at least one further intermediate layer which is not a bright nickel layer; or
is a MPS nickel layer, obtained by electroplating the substrate, and further comprises at least one further intermediate layer which is not a MPS nickel layer.

6. The method of claim 1 , wherein a current density of 0.005-5 A/dm 2 , related to the area of the chromium surface, is generated.

7. The method of claim 1 , wherein the electric potential is applied for 5-900 seconds.

8. The method according to claim 1 , comprising, as a further step
d) treating the chromium surface, after treatment with the aqueous solution in step b), with a component able to reduce and/or dissolve MnO 2 .

9. The method according to claim 8 , wherein the component is hydrogen peroxide, hydrazine, potassium iodide, sodium sulfite, hydroxylammonium sulfate or a carbohydrate.

10. The method according to claim 8 , wherein the component is selected from sulfuric acid, nitric acid, ascorbic acid and acetic acid.

11. The method according to claim 8 , comprising, as a further step: rinsing the chromium surface after treatment with the aqueous solution in step b), and before treatment with the acid and/or reducing agent in step d).

12. The method according to claim 1 , wherein concentration of permanganate in the aqueous solution is 0.05-4.5 mol/L.

13. The method according to claim 1 , wherein concentration of the phosphorus-oxygen compound, hydroxide, nitrate, borate, boric acid, or silicate in the aqueous solution is 0.05-2 mol/L.

14. The method according to claim 1 , further comprising using the chromium finish surface as a decorative chromium finish surface on a substrate in the automotive, white goods and sanitary industry.

15. The method according to claim 1 , further comprising applying a NSS test (ISO 922 7), wherein the treated chromium finish surface having the transparent corrosion protection layer does not show any alteration of the surface (area of defects: 0%) after applying the NSS test (ISO 922 7) for at least 120 h.

Assignees

• Atotech Deutschland Gmbh

Inventors

• Pfirrmann Christina
• Özkaya Berkem
• Wachter Philipp
• Born Nancy

Classifications

• C25D9/06

  by anodic processes · CPC title

• C25D11/38

  Chromatising · CPC title

• C25D5/627

  Electroplating characterised by the visual appearance of the layers, e.g. colour, brightness or mat appearance · CPC title

• C25D5/48 Primary

  After-treatment of electroplated surfaces · CPC title

• C25D9/08

  by cathodic processes · CPC title