Additive for silver-palladium alloy electrolytes

Abstract

The present invention relates to an electrolyte containing suitable reducing agents for adjusting the composition of silver-palladium layers. Furthermore, these reducing agents contribute to improving the layer appearance and to increasing the luminance (L value, CIE Lab) of the deposited layers. The present invention also discloses a method for the electrolytic deposition of silver-rich silver-palladium alloys. The alloys can be deposited on conductive surfaces over a wide current density range.

1 . Cyanide-free, acidic and aqueous electrolyte for the electrolytic deposition of bright silver-palladium alloys with a predominantly silver content which in its dissolved form contains the following components:
 a) a silver compound in a concentration of 1-300 g/l silver;   b) a palladium compound in a concentration of 0.1-100 g/l palladium;   c) a tellurium and/or selenium compound in a concentration of 0.002-10 g/l tellurium and/or selenium, based on the total amount of tellurium and selenium in the electrolyte;   d) urea and/or urea derivatives in a concentration of 0.05-1.5 mol/l, based on the total amount of urea and urea derivatives in the electrolyte and/or one or more amino acids, selected from the group consisting of alanine, aspartic acid, cysteine, glutamine, glutamic acid, glycine, lysine, leucine, methionine, phenylalanine, phenylglycine, proline, serine, tyrosine and valine in a concentration of 0.005-0.5 mol/l, based on the total amount of amino acids in the electrolyte;   e) at least one sulfonic acid in a concentration of 0.25-4.75 mol/l, based on the total amount of sulfonic acids;   f) at least one reducing agent selected from the group of formic acid, oxalic acid, ascorbic acid, hydrazine, hexamethylenetetramine, salts and/or esters of sulfurous acid, gaseous sulfites, sulfinic acids and their salts and/or esters, formaldehyde, sodium formaldehyde sulfoxylate, benzaldehyde, benzaldehyde derivatives, hydroxybenzenes and their esters, polyphenols and their esters, phenolsulfonic acids and their salts and/or esters, and glutathione and also its salts and/or esters in a concentration of 1-100 mmol/l, based on the total amount of these reducing agents.   
     
     
         2 . Electrolyte according to  claim 1 , wherein the silver compound is selected from silver nitrate, silver carbonate, silver methanesulfonate, silver chloride and silver oxide, 
     
     
         3 . Electrolyte according to  claim 1 , wherein the palladium compound is selected from palladium hydroxide, palladium chloride, palladium glycinate, palladium methanesulfonate and palladium sulfate. 
     
     
         4 . Electrolyte according to  claim 1 , wherein the selenium and/or tellurium compounds are selected from tellurites, selenites, tellurous acid, selenious acid, telluric acid, selenate and also tellurate. 
     
     
         5 . Electrolyte according to  claim 1 , wherein the α-amino acid is selected from alanine, glycine and valine. 
     
     
         6 . Electrolyte according to  claim 1 , wherein component (d) is urea. 
     
     
         7 . Electrolyte according to  claim 1 , wherein the at least one sulfonic acid is selected from ethanesulfonic acid, propanesulfonic acid, benzenesulfonic acid, and methanesulfonic acid. 
     
     
         8 . Electrolyte according to  claim 1 , wherein the at least one reducing agent is selected from hydroxyphenols, ascorbic acid and salts and/or esters of sulfurous acid. 
     
     
         9 . Method for the electrolytic deposition of silver-palladium layers predominantly containing silver from an electrolyte according to  claim 1 , wherein an electrically conductive substrate is immersed in the electrolyte and a flow of current established between an anode in contact with the electrolyte and the substrate as cathode. 
     
     
         10 . Method according to  claim 9 , wherein the electrolyte temperature is 25 to 70° C. 
     
     
         11 . Method according to  claim 9 , wherein the current is between 0.5 and 20 A/dm 2  during electrolysis. 
     
     
         12 . Method according to  claim 9 , wherein the pH value is set to a constant value of <2 during electrolysis.