Electrolyte and method for producing chromium layers
Disclosed is an electrolyte for the electrolytic deposition of chromium as a metal, comprising (a) a chromium (III) salt and (b) metallic chromium, the use of the electrolyte for producing chromium layers on rotationally symmetrical components, in particular gravure printing cylinders, and methods, in which this electrolyte is used.
1 . An electrolysis cell for the electrolytic deposition of chromium as a metal, comprising:
an electrolyte filling the electrolysis cell;
an anode immersed in the electrolyte; and
a cathode immersed in the electrolyte, wherein the electrolyte comprises a chromium(III) salt and metallic chromium, wherein the metallic chromium is placed in an electric field of the anode and the cathode, wherein the metallic chromium is a metallic chromium nugget mounted on the anode such that the metallic chromium nugget is conductively connected to the anode;
wherein the anode is a form-stable anode;
wherein a surface area of the metallic chromium nugget is 1% to 50% of a surface area of the form-stable anode,
wherein the chromium(III) salt prevents formation of Cr(VI) when the metallic chromium dissolves during electrolysis,
wherein the electrolysis cell is devoid of a membrane separating the anode from the cathode.
2 . The electrolysis cell of claim 1 , wherein the electrolyte further comprises:
a compound of the formula (I)
wherein R stands for NH 2 , OH or SO 3 H and n is an integer ranging from 1 to 3, and/or its salts, in particular, salts with monovalent cations such as Na + and/or K + or bivalent cations, and/or formic acid and/or its salts, in particular, salts with monovalent cations such as Na + and/or K + or bivalent cations.
3 . The electrolysis cell of claim 1 , wherein the chromium(III) salt includes an inorganic and/or organic chromium(III) salt, wherein the inorganic chromium(III) salt is selected from the group consisting of potassium chrome alum, ammonium chrome alum, chromium sulfate, chromium sulfamate (amido sulfonate), chromium bromide, chromium iodide, chromium phosphate, chromium pyrophosphate (diphosphate), chromium phosphonate, chromium hydroxy sulfate (alkali chromium sulfate), chromium chloride and mixtures of two or more of them, or wherein the organic chromium(III) salt is selected from the group consisting of chromium citrate, chromium formate, chromium oxalate, chromium methanesulfonate, chromium dimethanesulfonate and mixtures of two or more of them.
4 . The electrolysis cell of claim 1 , wherein the electrolyte further comprises an additive.
5 . The electrolysis cell of claim 4 , wherein the additive comprises a complexing agent and/or a wetting agent.
6 . The electrolysis cell of claim 1 , wherein the anode is a precious metal containing iridium mixed oxide anode.
7 . The electrolysis cell of claim 1 , wherein the electrolyte further comprises a sulfate.
8 . The electrolysis cell of claim 7 , wherein the sulfate is Na sulfate and/or K sulfate.
9 . The electrolysis cell of claim 7 , wherein an amount of the sulfate is in a range of 5 mM to 30 mM.
10 . The electrolysis cell of claim 1 , wherein the surface area of the form-stable anode equals to a surface area of the cathode.