Functional chromium layer with improved corrosion resistance

Abstract

The aqueous electroplating bath according to the present invention comprises chromium(VI) ions, sulfate ions and methane-trisulfonic acid or a salt thereof as the catalyst. The functional chromium layer deposited from the aqueous electroplating bath according to the present invention has an increased corrosion resistance.

1 . An aqueous electroplating bath for depositing a functional chromium layer, comprising
 (i) a source for chromium(VI) ions,   (ii) a source for sulfate ions and   (iii) methane-trisulfonic acid or a salt thereof.   
     
     
         2 . The aqueous electroplating bath for depositing a functional chromium layer according to  claim 1  wherein the concentration of chromium(VI) ions ranges from 80 to 600 g/l. 
     
     
         3 . The aqueous electroplating bath for depositing a functional chromium layer according to  claim 1  wherein the concentration of sulfate ions ranges from 1 to 15 g/l. 
     
     
         4 . The aqueous electroplating bath for depositing a functional chromium layer according to  claim 1  wherein the salt of methane-trisulfonic acid is selected from sodium, potassium and ammonium salts. 
     
     
         5 . The aqueous electroplating bath for depositing a functional chromium layer according to  claim 1  wherein the concentration of methane-trisulfonic acid or a salt thereof ranges from 2 to 80 mmol/l. 
     
     
         6 . The aqueous electroplating bath for depositing a functional chromium layer according to  claim 1  comprising the methane-trisulfonic acid and one or more other alkyl-sulfonic acids selected from the group comprising methane-sulfonic acid, methane-disulfonic acid, ethane-sulfonic acid, 1,2-ethane-disulfonic acid, propyl sulfonic acid, 1,2-propane-disulfonic acid, 1,3-propane-disulfonic acid and 1,2,3-propane-trisulfonic acid. 
     
     
         7 . The aqueous electroplating bath for depositing a functional chromium layer according to  claim 1  wherein the plating bath further comprises a surface active agent which is selected from the group consisting of perfluorinated sulfonate tensides, perfluorinated phosphate tensides, perfluorinated phosphonate tensides, partially fluorinated sulfonate tensides, partially fluorinated phosphate tensides, partially fluorinated phosphonate tensides and mixtures thereof. 
     
     
         8 . The aqueous electroplating bath for depositing a functional chromium layer according to  claim 7  wherein the concentration of the surface active agent ranges from 0.05 to 4 g/l. 
     
     
         9 . A process for depositing a functional chromium layer onto a metallic substrate comprising, in this order, the steps of
 (i) providing a metallic substrate,   (ii) contacting said substrate with the aqueous electroplating bath according to  claim 1  and   (iii) applying an external current to said substrate as the cathode and thereby depositing a functional chromium layer onto said substrate.   
     
     
         10 . The process for depositing a functional chromium layer onto a metallic substrate according to  claim 9  wherein the aqueous electroplating bath is held at a temperature in the range of 10 to 80° C. during use. 
     
     
         11 . The process for depositing a functional chromium layer onto a metallic substrate according to  claim 9  wherein a current density in the range of 10 to 250 A/dm 2  is applied to the metallic substrate during use. 
     
     
         12 . The process for depositing a functional chromium layer onto a metallic substrate according to  claim 9  wherein an inert anode is used in step (iii). 
     
     
         13 . The process for depositing a functional chromium layer onto a metallic substrate according to  claim 12  wherein the inert anode has a surface selected from the group consisting of platinum metal, iridium oxide and mixtures thereof. 
     
     
         14 . The process for depositing a functional chromium layer onto a metallic substrate according to  claim 12  wherein the aqueous electroplating bath further comprises cations of an additional metal selected from the group consisting of silver, lead and mixtures thereof. 
     
     
         15 . The process for depositing a functional chromium layer onto a metallic substrate according to  claim 14  wherein the concentration of the cations of an additional metal ranges from 0.005 to 5 g/l. 
     
     
         16 . The aqueous electroplating bath for depositing a functional chromium layer according to  claim 6  wherein the plating bath further comprises a surface active agent which is selected from the group consisting of perfluorinated sulfonate tensides, perfluorinated phosphate tensides, perfluorinated phosphonate tensides, partially fluorinated sulfonate tensides, partially fluorinated phosphate tensides, partially fluorinated phosphonate tensides and mixtures thereof.