GB2033430A - Electrolyte for Cathodic Deposition of Alloys of Nickel with Tungsten - Google Patents

Abstract

An aqueous electroplating solution comprises nickel sulphosalicylate in a 0.1 to 1.05 M concentration, and a tungsten salt in a 0.001 to 0.1 M concentration. The solution may include nickel bromide in 0.01 to 0.2 M concentration, and disodium lauric sulphate surfactant in 0.002 to 0.04 M concentration. The electrolyte results in low stress platings.

Description

SPECIFICATION Electrolyte for Cathodic Deposition of Alloys of Nickel with Tungsten The invention concerns an electrolyte for cathodic deposition of alloys of nickel with tungsten.

Alloys of nickel with tungsten deposited electrolytically have better properties than chemically pure electrolytic nickel, especially hardness and resistance to oxidation under high temperatures. For these reasons, a number of methods of electrodeposition have been described. The electrolytes generally use nickel sulphate as the fundamental component of the electrolyte and include sodium chloride or nickel chloride for improvement of the solubility of the anodes and of the boric acid used. Tungsten is added in the form of disodium tungstate. It is necessary, in order to keep the tungsten in solution, to add complexing agents, such as salts of citric acid or tartaric acid. A disadvantage of these methods consists in that the deposited layers have for the most part a high internal stress value that limits and decreases their applicability, especially in the application of thick layers.For these reasons the electrolytes are usually used at high temperatures of about 900C-which leads to practical and technological difficulties.

The present invention provides an aqueous electroplating solution which comprises nickel sulphosaiicylate in a 0.1 to 1.05 M concentration, and a tungsten salt in a 0.001 to 0.1 M concentration. Preferably, the tungsten salt is disodium tungstate.

The solution preferably also comprises a nickel halide in order to improve solubility, for example nickel bromide, in a concentration of 0.0) to 0.2 M.

The solution may also comprise an ionic or non-ionic surfactant, for example disodium lauric sulphate, in a concentration of 0.002 to 0.04 M.

The invention also extends to an electroplated article having a coating which comprises an electroplated article having a coating which comprises nickel and tungsten in the ratio 0.1 to 1.05:0.001 to 0.1.

With regard to the complex forming properties of the basic anion, it is not necessary, in the case of lower contents of tungsten, to add complexforming agents which is an advantage.

The electrolyte produces a very low level of internal stresses even with temperatures as low as 400 C, but it may also be used with temperatures of up to 900C. The current densities range in the limits of 1 to 1 5 A.dm-2, according to the conditions of the electrolysis. The cathodic current efficiency is better than 90% at pH values greater than 2.9.

Embodiments of the invention are by the way of illustration described in the following examples.

Example 1 An electrolyte for cathodic deposition of an alloy of nickel with tungsten contained nickel sulphosalicylate in a concentration of 0.8 M and disodium tungstate in a concentration of 0.01 M.

The deposited layer containing 2.65% by weight of tungsten had an internal stress of 66.7 MPa and a hardness of 518 HM (average of three measurements). The pH of the bath was 4, the cathodic current density was 5 A.dm-2 and the temperature of the bath was 500C.

Example 2 An electrolyte for cathodic deposition of an alloy of nickel with tungsten with the use of a halide, contained nickel sulphosalicylate in a concentration of 0.75, nickel dibromide in a concentration of 0.05 M and disodium tungstate in a concentration of 0.01 M.

The cathodic current density amounted to 1 A.dm-2. The temperature of the bath was 500C and its pH 4. The deposited layer contained 3 percent by weight tungsten. The internal stress was 78.1 MPa and the measured microhardness was 735 HM.

Example 3 An electrolyte for cathodic deposition of an alloy of nickel with tungsten and a wetting agent consisted of nickel sulphosalicylate in concentration of 0.75 M, nickel bromide in a concentration of 0.05 M, disodium tungstate in a concentration of 0.03 M and disodium lauric sulphate in a concentration of 0.004 M.

The deposited layer contained 4.65 percent by weight tungsten. The internal stress amounted to 178 MPa and the microhardness was 600 HM.

The cathodic current density was 10 A.dm-2, the pH of the bath was 3.2 and its temperature was 650C.

Claims

1. An aqueous electroplating solution which comprises nickel sulphosalicylate in a 0.1 to 1.05 M concentration, and a tungsten salt in a 0.001 to 0.1 M concentration.

2. A solution according to claim 1, wherein the tungsten salt is disodium tungstate.

3. A solution according to any preceding claim, which further comprises a nickel halide in a 0.01 to 0.2 M concentration.

4. A solution according to claim 3, wherein the nickel halide is nickel bromide.

5. A solution according to any preceding claim, which further comprises an ionic or non-ionic surfactant in a 0.002 to 0.04 M concentration.

6. A solution according to claim 5, wherein the surfactant is disodium lauric sulphate.

7. An aqueous electroplating solution substantially as disclosed in any Example.

8. A method of electroplating which uses the

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (9)

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Electrolyte for Cathodic Deposition of Alloys of Nickel with Tungsten The invention concerns an electrolyte for cathodic deposition of alloys of nickel with tungsten. Alloys of nickel with tungsten deposited electrolytically have better properties than chemically pure electrolytic nickel, especially hardness and resistance to oxidation under high temperatures. For these reasons, a number of methods of electrodeposition have been described. The electrolytes generally use nickel sulphate as the fundamental component of the electrolyte and include sodium chloride or nickel chloride for improvement of the solubility of the anodes and of the boric acid used. Tungsten is added in the form of disodium tungstate. It is necessary, in order to keep the tungsten in solution, to add complexing agents, such as salts of citric acid or tartaric acid. A disadvantage of these methods consists in that the deposited layers have for the most part a high internal stress value that limits and decreases their applicability, especially in the application of thick layers.For these reasons the electrolytes are usually used at high temperatures of about 900C-which leads to practical and technological difficulties. The present invention provides an aqueous electroplating solution which comprises nickel sulphosaiicylate in a 0.1 to 1.05 M concentration, and a tungsten salt in a 0.001 to 0.1 M concentration. Preferably, the tungsten salt is disodium tungstate. The solution preferably also comprises a nickel halide in order to improve solubility, for example nickel bromide, in a concentration of 0.0) to 0.2 M. The solution may also comprise an ionic or non-ionic surfactant, for example disodium lauric sulphate, in a concentration of 0.002 to 0.04 M. The invention also extends to an electroplated article having a coating which comprises an electroplated article having a coating which comprises nickel and tungsten in the ratio 0.1 to 1.05:0.001 to 0.1. With regard to the complex forming properties of the basic anion, it is not necessary, in the case of lower contents of tungsten, to add complexforming agents which is an advantage. The electrolyte produces a very low level of internal stresses even with temperatures as low as 400 C, but it may also be used with temperatures of up to 900C. The current densities range in the limits of 1 to 1 5 A.dm-2, according to the conditions of the electrolysis. The cathodic current efficiency is better than 90% at pH values greater than 2.9. Embodiments of the invention are by the way of illustration described in the following examples. Example 1 An electrolyte for cathodic deposition of an alloy of nickel with tungsten contained nickel sulphosalicylate in a concentration of 0.8 M and disodium tungstate in a concentration of 0.01 M. The deposited layer containing 2.65% by weight of tungsten had an internal stress of 66.7 MPa and a hardness of 518 HM (average of three measurements). The pH of the bath was 4, the cathodic current density was 5 A.dm-2 and the temperature of the bath was 500C. Example 2 An electrolyte for cathodic deposition of an alloy of nickel with tungsten with the use of a halide, contained nickel sulphosalicylate in a concentration of 0.75, nickel dibromide in a concentration of 0.05 M and disodium tungstate in a concentration of 0.01 M. The cathodic current density amounted to 1 A.dm-2. The temperature of the bath was 500C and its pH 4. The deposited layer contained 3 percent by weight tungsten. The internal stress was 78.1 MPa and the measured microhardness was 735 HM. Example 3 An electrolyte for cathodic deposition of an alloy of nickel with tungsten and a wetting agent consisted of nickel sulphosalicylate in concentration of 0.75 M, nickel bromide in a concentration of 0.05 M, disodium tungstate in a concentration of 0.03 M and disodium lauric sulphate in a concentration of 0.004 M. The deposited layer contained 4.65 percent by weight tungsten. The internal stress amounted to 178 MPa and the microhardness was 600 HM. The cathodic current density was 10 A.dm-2, the pH of the bath was 3.2 and its temperature was 650C. Claims

1. An aqueous electroplating solution which comprises nickel sulphosalicylate in a 0.1 to 1.05 M concentration, and a tungsten salt in a 0.001 to 0.1 M concentration.

2. A solution according to claim 1, wherein the tungsten salt is disodium tungstate.

3. A solution according to any preceding claim, which further comprises a nickel halide in a 0.01 to 0.2 M concentration.

4. A solution according to claim 3, wherein the nickel halide is nickel bromide.

5. A solution according to any preceding claim, which further comprises an ionic or non-ionic surfactant in a 0.002 to 0.04 M concentration.

6. A solution according to claim 5, wherein the surfactant is disodium lauric sulphate.

7. An aqueous electroplating solution substantially as disclosed in any Example.

8. A method of electroplating which uses the solution of any preceding claim.

9. An electroplated article having a coating which comprises nickel and tungsten in the ratio 0.1 to 1.05:0.001 to 0.1.