Zinc electrolyte devoid of boric acid and ammonium for the electrodeposition of zinc coatings

Abstract

The invention relates to an aqueous electrolyte devoid of boric acid and ammonium for the electrodeposition of zinc coatings and to a method for producing such an electrolyte. The electrolyte comprises (a) Zn 2+ in a concentration of 15 to 70 g/L; (b) Cl − in a concentration of 100 to 200 g/L; (c) K + and/or Na + in a total concentration of 0.75 to 6.0 mol/L; (d) acetate in a concentration of 5.0 to 45 g/L; (e) glycine and/or alanine in a total concentration of 0.5 to 30 g/L; and (f) water. The electrolyte has a pH of 4.5 to 6.5. In a preferred variant, the electrolyte contains (g) nicotinic acid and/or (h) ethoxylated thiodiglycol. The invention also relates to a method for producing a component having a zinc coating, which uses the electrolyte.

1 . An aqueous electrolyte devoid of boric acid and ammonium for the electrodeposition of zinc coatings, comprising:
 (a) Zn 2+  in a concentration of 15 to 70 g/L;   (b) Cl −  in a concentration of 100 to 200 g/L;   (c) K +  and/or Na +  in a total concentration of 0.75 to 6.0 mol/L;   (d) acetate in a concentration of 5.0 to 45 g/L;   (e) glycine and/or alanine in a total concentration of 0.5 to 30 g/L; and   (f) water;   wherein the electrolyte has a pH of 4.5 to 6.5.   
     
     
         2 . The electrolyte according to  claim 1 , wherein the concentration of Zn 2+  in the electrolyte is 20 to 60 g/L, preferably 25 to 50 g/L, more preferably 30 to 40 g/L and most preferably 35 g/L. 
     
     
         3 . The electrolyte according to  claim 1 , wherein the concentration of Cl −  in the electrolyte is 120 to 190 g/L, preferably 130 to 180 g/L and more preferably 160 g/L. 
     
     
         4 . The electrolyte according to  claim 1 , wherein the electrolyte contains K +  and the concentration of K +  is 0.75 to 6.0 mol/L, preferably 2.7 to 4.8 mol/L and more preferably 3.3 to 4.1 mol/L. 
     
     
         5 . The electrolyte according to  claim 1 , wherein the concentration of acetate in the electrolyte is 7.5 to 30 g/L, preferably 10 to 20 g/L, most preferably 12 g/L. 
     
     
         6 . The electrolyte according to  claim 1 , wherein the total concentration of glycine and/or alanine in the electrolyte is in the range of 0.5 to 20 g/L, preferably 1.0 to 10 g/L, more preferably 1.5 to 5 g/L and most preferably 2.5 g/L. 
     
     
         7 . The electrolyte according to  claim 1 , wherein the electrolyte contains
 (a) Zn 2+  in a concentration of 20 to 60 g/L;   (b) Cl −  in a concentration of 120 to 190 g/L;   (c) K +  in a concentration of 2.7 to 4.8 mol/L and 0 to 0.5 mol/L Nat;   (d) acetate in a concentration of 7.5 to 30 g/L; and   (e) glycine and/or alanine in a total concentration of 0.5 to 20 g/L.   
     
     
         8 . The electrolyte according to  claim 1 , wherein the electrolyte additionally contains (g) nicotinic acid in a concentration of 0.01 to 2.0 g/L, preferably 0.05 to 1.0 g/L, more preferably 0.08 to 0.5 g/L, most preferably 0.1 g/L. 
     
     
         9 . The electrolyte according to  claim 1 , wherein the electrolyte additionally contains (h) ethoxylated thiodiglycol, with an average of at least 20 structural units derived from ethylene oxide, in a concentration of 0.3 to 10 g/L, preferably 0.5 to 5 g/L, more preferably 1.0 to 3.5 g/L and most preferably 2.1 g/L. 
     
     
         10 . The electrolyte according to  claim 1 , wherein the electrolyte contains
 (g) nicotinic acid in a concentration of 0.05 to 1.0 g/L, and/or   (h) ethoxylated thiodiglycol, with an average of at least 20 structural units derived from ethylene oxide, in a concentration of 0.5 to 5 g/L.   
     
     
         11 . A method for producing an aqueous electrolyte according to  claim 1 , comprising the steps of:
 A) forming an aqueous solution of
 (a′) zinc chloride and/or zinc acetate; 
 (b′) potassium chloride and/or sodium chloride; 
 (c′) at least one of potassium acetate, sodium acetate and acetic acid; 
 (d′) at least one from the group consisting of glycine, a salt thereof, alanine and a salt thereof; and 
 (e′) optionally nicotinic acid or a salt thereof; and 
 (f′) optionally ethoxylated thiodiglycol, with an average of at least 20 structural units derived from ethylene oxide; and 
   B) optionally setting the pH to 4.5 to 6.5 by adding hydrochloric acid or by adding potassium hydroxide and/or sodium hydroxide, which can be added as solids or in the form of an aqueous solution.   
     
     
         12 . A method for producing a component having a zinc coating, comprising the electrodeposition of zinc on a metal component from an electrolyte according to  claim 1 . 
     
     
         13 . The method according to  claim 12 , wherein the metal component comprises or consists of iron or an iron alloy. 
     
     
         14 . The method according to  claim 12 , wherein deposition occurs at a temperature of 20 to 50° C., preferably 25 to 40° C., and
 a current density of 0.2 to 10 A/dm 2 , preferably 0.5 to 6 A/dm 2 , is used for the deposition. 
 
     
     
         15 . The method according to  claim 12 , wherein after the electrodeposition the component having a zinc coating is subjected to a passivation treatment. 
     
     
         16 . The method according to  claim 12 , wherein after the electrodeposition the component having a zinc coating is annealed, optionally before or after a passivation treatment.