Electrolyte and its use for the deposition of black ruthenium coatings and coatings obtained in this way

Abstract

The invention relates to a ruthenium electrolyte which is suitable for the deposition of decorative and industrial layers having a particular blackness. The invention further relates to the use of the electrolyte of the invention in a process for the deposition of decorative and industrial layers of ruthenium having a particular blackness (“black ruthenium) on jewelry, decorative goods, consumer goods and industrial articles. The invention therefore likewise relates to corresponding layers and the articles coated in this way. The electrolyte is characterized in that it operates in the weakly acidic to alkaline pH range.

1 . An electrolyte having a pH of from≧5 to 12 for the deposition of decorative and industrial layers of ruthenium having a particular blackness, wherein
 the electrolyte has the following constituents: 
 a) dissolved ruthenium in a concentration of from 0.2 to 20 gram per liter (g/l) of electrolyte, calculated as ruthenium metal; 
 b) one or more anions of a dicarboxylic, tricarboxylic or tetracarboxylic acid in a concentration of 0.05-2 mol per liter; 
 c) one or more sulfur heterocycles; 
 d) one or more cationic surfactants. 
 
     
     
         2 . The electrolyte as claimed in  claim 1 , wherein
 ruthenium is present as a binuclear, anionic ruthenium nitrido halo complex of the formula [Ru 2 N(H 2 O) 2 X 8 ] 3− , where X is a halide ion.   
     
     
         3 . The electrolyte as claimed in  claim 1 , wherein
 the concentration of ruthenium after complete dissolution of the compound is in the range from 2 to 8 gram per liter of electrolyte.   
     
     
         4 . The electrolyte as claimed in  claim 1 , wherein
 the electrolyte is free of further transition metal ions.   
     
     
         5 . The electrolyte as claimed in  claim 1 , wherein
 the carboxylic acid is selected from the group consisting of oxalic acid, citric acid, tartaric acid, succinic acid, maleic acid, glutaric acid, adipic acid, malonic acid, malic acid.   
     
     
         6 . The electrolyte as claimed in  claim 1 , wherein
 the sulfur heterocycle is selected from the group consisting of 3-(2-benzothia-zolyl-2-mercapto)propanesulfonic acid sodium salt, saccharin sodium salt, saccharin N-propylsulfonate sodium salt,   6-methyl-3,4-dihydro-1,2,3-oxathiazin-4-one 2,2-dioxide, benzothiazole, 2-mercaptobenzothiazole, thiazole, isothiazole and derivatives thereof.   
     
     
         7 . The electrolyte as claimed in  claim 1 , wherein
 the surfactant is selected from the group consisting of octyltrimethylammonium bromide, octyltrimethylammonium chloride, decyltrimethylammonium bromide, decyltrimethylammonium chloride, dodecyltrimethylammonium bromide, dodecyltrimethylammonium chloride, tetradecyltrimethylammonium bromide, tetradecyltrimethylammonium chloride, hexadecyltrimethylammonium bromide, hexadecyltrimethylammonium chloride, ethyldimethylhexadecylammonium bromide, ethyldimethylhexadecylammonium chloride, benzyldimethyldecyl-ammonium chloride, benzyldimethyldodecylammonium chloride, benzyldimethyltetradecylammonium chloride and benzyldimethylhexadecylammonium chloride and mixtures thereof.   
     
     
         8 . The electrolyte as claimed in  claim 1 , wherein the pH of the electrolyte is in the range 7-8. 
     
     
         9 . The electrolyte as claimed in  claim 1 , wherein
 the electrolyte comprises a buffer system selected from the group consisting of borate, phosphate and carbonate buffers.   
     
     
         10 . A process for the deposition of black ruthenium coatings on conductive, in particular metallic, articles, comprising immersion of the article to be coated as cathode in the electrolyte of  claim 1  and establishment of a flow of electric current between the anode and the cathode. 
     
     
         11 . The process as claimed in  claim 10 , wherein
 ruthenium is present as a binuclear, anionic ruthenium nitrido halo complex of the formula [Ru 2 N(H 2 O) 2 X 8 ] 3− , where X is a halide ion.   
     
     
         12 . The process as claimed in  claim 10 , wherein
 the concentration of ruthenium after complete dissolution of the compound is in the range from 2 to 8 gram per liter of electrolyte.   
     
     
         13 . The process as claimed in  claim 10 , wherein
 the electrolyte is free of further transition metal ions.   
     
     
         14 . The process as claimed in  claim 10 , wherein
 the carboxylic acid is selected from the group consisting of oxalic acid, citric acid, tartaric acid, succinic acid, maleic acid, glutaric acid, adipic acid, malonic acid, malic acid.   
     
     
         15 . The process as claimed in  claim 10 , wherein
 the sulfur heterocycle is selected from the group consisting of 3-(2-benzothia-zolyl-2-mercapto)propanesulfbnic acid sodium salt, saccharin sodium salt, saccharin N-propylsulfonate sodium salt,   6-methyl-3,4-dihydro-1,2,3-oxathiazin-4-one 2,2-dioxide, benzothiazole, 2-mercaptobenzothiazole, thiazole, isothiazole and derivatives thereof.   
     
     
         16 . The process as claimed in one or more of  claim 10 , wherein
 the surfactant is selected from the group consisting of octyltrimethylammonium bromide, octyltrimethylammonium chloride, decyltrimethylammonium bromide, decyltrimethylammonium chloride, dodecyltrimethylammonium bromide, dodecyltrimethylammonium chloride, tetradecyltrimethylammonium bromide, tetradecyltrimethylammonium chloride, hexadecyltrimethylammonium bromide, hexadecyltrimethylammonium chloride, ethyldimethylhexadecylammonium bromide, ethyldimethylhexadecylammonium chloride, benzyldimethyldecyl-ammonium chloride, benzyldimethyldodecylammonium chloride, benzyldimethyltetradecylammonium chloride and benzyldimethylhexadecylammonium chloride and mixtures thereof.   
     
     
         17 . The process as claimed in  claim 10 , characterized in that wherein
 a current density of 0.1-10 A/dm 2  is set.   
     
     
         18 . The process as claimed in  claim 10 , wherein
 a temperature of 10-80° C. is set.   
     
     
         19 . The process as claimed in  claim 10 , wherein
 insoluble anodes made of a material selected from the group consisting of platinized titanium, graphite, iridium-transition metal mixed oxide and special carbon material and combinations of these anodes are used.   
     
     
         20 . A black ruthenium layer obtained by immersion of an article to be coated as cathode in the electrolyte of  claim 1  and establishment of a flow of electrode current between the cathode and an anode. 
     
     
         21 . The ruthenium layer as claimed in  claim 20 , wherein the layer
 has a thickness of from 0.1 to 3 μm.   
     
     
         22 . The ruthenium layer as claimed in  claim 20 , wherein
 the layer has a sulfur content of from 3% by weight to 6% by weight in the outer region of 1 μm.   
     
     
         23 . The ruthenium layer as claimed in  claim 20 , wherein
 the layer has a carbon content of from 1% by weight to 2% by weight in the outer region of 1 μm.   
     
     
         24 . The ruthenium layer as claimed in  claim 21 , wherein
 the layer has an oxygen content of from 15% by weight to 20% by weight in the outer region of 1 μm.   
     
     
         25 . An article having a ruthenium layer obtained by immersion of an article to be coated as cathode in the electrolyte of  claim 1  and establishment of a flow of electrode current between the cathode and an anode.