Method for depositing a nickel-metal layer

Abstract

A method for depositing nickel-metal layers for colouring surfaces, and a bath for depositing such a layer. This is made possible by depositing a nickel-metal layer from a bath for the electroless deposition of nickel which contains at least one further metal compound, a voltage being additionally applied enable the metal of the metal compound to be incorporated while forming a nickel-metal layer.

Claims

1. A method for depositing a nickel-metal layer on a workpiece, comprising the following steps: a) disposing the workpiece in a nickel bath containing ionic nickel and a second ionic metal; and b) depositing the nickel-metal layer on the workpiece by simultaneous b1) electroless deposition of nickel by reduction of the ionic nickel from the nickel bath onto the workpiece and b2) voltage-supported deposition, having a current density, of a second metal by reduction of the second ionic metal from the nickel bath onto the workpiece; b3) wherein the current density is increased in a plurality of successive steps from a first voltage to a second, higher voltage.

2. The method as claimed in claim 1, wherein the nickel bath further comprises a phosphorus compound or a boron compound; and wherein the method further comprises a simultaneous step of: b4) electroless deposition of phosphorus or boron by reduction of the phosphorus compound or the boron compound from the nickel bath onto the workpiece.

3. The method as claimed in claim 1, wherein the voltage-supported deposition is carried out at a temperature above 50 C.

4. The method as claimed in claim 1, wherein the second ionic metal comprises ionic zinc.

5. The method as claimed in claim 1, wherein the second ionic metal is present in the bath in a range between 0.05 mol/l and 0.5 mol/l relative to the ionic nickel.

6. The method as claimed in claim 1, wherein a graphite electrode is used for the voltage-supported deposition.

7. The method as claimed in claim 1, wherein the bath additionally contains at least one conducting salt.

8. The method as claimed in claim 1, wherein the current density is between 0.01 and 5 A/dm.sup.2, inclusive.

9. The method as claimed in claim 1, further comprising performing before step b) a step of electroless deposition of nickel by reduction of the ionic nickel from the nickel bath onto the workpiece.

10. The method as claimed in claim 1, wherein each step of the plurality of successive steps corresponds to a voltage increase of 0.1-5 V , and wherein a dwell time per step is between 30 seconds and 15 minutes.

11. The method as claimed in claim 10, wherein each step in the plurality of successive steps corresponds to a voltage increase of 0.5-1 V.

Description

(1) In the Drawing

(2) FIG. 1 shows a schematic representation of a method according to the invention.

(3) FIG. 1 shows a typical flow chart of a method according to the invention. In a first step, a bath is provided for electroless deposition of nickel (100). At least one compound of another metal, and optionally at least one conducting salt (110), are added to this bath. The compound of another metal is preferably a zinc compound, especially preferably a zinc salt, especially preferably zinc chloride. The conducting salt also optionally added is preferably a potassium salt, preferably potassium chloride. In this way a bath is obtained for deposition of a nickel-metal layer (120) in the sense of the invention.

(4) The substrate is inserted in the bath. Then the bath is adjusted to the conditions for electroless deposition of nickel, i.e. especially temperature and pH are adjusted. Then a voltage is applied between the substrate and an electrode, which is already present or has been introduced into the bath, in order to cause voltage-supported deposition of the metal in the nickel layer (130). This results in formation of a nickel-metal layer (140).

EXAMPLE

(5) 32 g/l zinc chloride and 40 g/l potassium chloride were added to the nickel bath described at the beginning. The pH was adjusted to 4.0 with H.sub.2SO.sub.4. The bath was heated to 88 C. Chemical-reduction nickel-phosphorus deposition began spontaneously, with zinc already being co-deposited. In this phase the layer was a light anthracite color. After a short time graphite electrodes were introduced into the bath, with the workpiece connected as the cathode and the electrodes as the anode. The ratio of the projected workpiece area to the anode area in the electrolyte was 1:1 (with a deviation of +/50%). An auxiliary field was applied on the electrodes, establishing a final current density of 0.1-0.33 A/dm.sup.2 (field strength relative to the workpiece surface area, voltage from 1 V to 3.5 V). The auxiliary electric field was adjusted in increasing steps up to the final field strength, the steps being selected between 0.5 V and 1 V, with a dwell time per step between 30 s and 5 minutes, e.g. 1 V/1 min; 2 V/1 min, 3 V/2 min; 3.5 V/4 min. A deep-black layer was obtained on the workpiece.

(6) The layer has electrical and thermal conductivity and is heat-resistant to above 250 C.

(7) Moreover, the layer obtained is acid-resistant, and is in particular resistant to hydrochloric acid.

(8) The black coloring can be attributed to the incorporation of zinc. This can be demonstrated by treatment with a post-dip solution (e.g. Slotopas ZN 301/2, Schtter company) based on Cr(III), which is suitable for the treatment of Ni/Zn coatings. For the layers according to the invention, it shows a definite reaction, which indicates incorporation of Zn.

(9) The layers according to the invention show no color change after 48 h in a salt-spray test.

LITERATURE CITED

(10) U.S. Pat. No. 2,844,530 US 2006/0228569 A1 GB 1 222 969 A