Apparatus and method for electrolytic deposition of metal layers on workpieces

Abstract

The present invention is related to an apparatus and a method for the electrolytic deposition of a zinc or zinc alloy layer on a workpiece, the apparatus comprising a container to hold the metal plating bath divided into at least two compartments with an electrode assembly in the container, the assembly comprises in a first compartment a soluble anode to provide ions of the at least one metal to be deposited and a cathode corresponding to the workpiece to be metal plated and in an anolyte compartment separated from the first compartment by an ion exchange membrane comprises an insoluble anode and wherein the electrode assembly in the compartments are connected by an adjustable power supply.

1 . Apparatus for the electrolytic deposition of a zinc or zinc alloy layer on a workpiece, the apparatus comprising:
 a) a container to hold the zinc or zinc alloy plating bath which comprises zinc ions;   b) an electrode assembly in the zinc or zinc alloy plating bath, the assembly comprises at least one soluble zinc anode to provide zinc ions to be deposited and a cathode corresponding to the workpiece to be zinc or zinc alloy plated and an enclosure defining an anolyte compartment and bearing on at least a portion thereof an ion exchange membrane in contact with the plating bath which comprises an acid and the electrode assembly further comprises an insoluble anode, and   c) at least one power supply connecting the electrode assembly and to provide an electric current for zinc or zinc alloy deposition, wherein the zinc or zinc alloy plating bath and the anolyte compartment have about the same pH value of between 0.5-6.   
     
     
         2 . Apparatus according to  claim 1 , comprising at least one means for adjusting the power supply that allows adjustment of the current distribution between the soluble zinc anode and the insoluble anode in order to determine the zinc ion dissolution rate of the soluble zinc anode. 
     
     
         3 . Apparatus according to  claim 1 , wherein the electrode assembly comprises a second soluble anode selected from the group consisting of nickel, cobalt, iron, chromium, cadmium, tin, copper, silver, gold, platinum, palladium, manganese, ruthenium, rhodium, iridium, osmium, rhenium, tungsten, molybdenum, vanadium, indium, bismuth, antimony, selenium, germanium, gallium, tantalum and niobium. 
     
     
         4 . Apparatus according to any of the foregoing claims  claim 1 , wherein the first soluble zinc anode, the second soluble anode and the insoluble anode are equipped individually with separate power supplies. 
     
     
         5 . Apparatus according to  claim 1 , wherein the ion exchange membrane is a cationic ion exchange membrane. 
     
     
         6 . (canceled) 
     
     
         7 . Apparatus according to  claim 1 , wherein the acid in the anolyte compartment is selected from hydrochloric acid and sulfuric acid. 
     
     
         8 . (canceled) 
     
     
         9 . (canceled) 
     
     
         10 . Apparatus according to  claim 1 , wherein the workpiece is a steel based material. 
     
     
         11 . Apparatus according to  claim 1 , wherein the insoluble anode is selected from the group consisting of titanium anodes, platinized titanium anodes, ceramic coated anodes, graphite anodes and carbon based anodes. 
     
     
         12 . (canceled) 
     
     
         13 . Method for electrolytic deposition of zinc or zinc alloys in an apparatus according to  claim 1  comprising the following steps:
 a) providing in the container a zinc or zinc alloy plating bath containing additives and an acid 
 b) depositing a zinc or zinc alloy layer on the cathode corresponding to the workpiece to be metal plated by providing an electrical current through the adjustable power supply. 
 
     
     
         14 . Method according to  claim 13 , wherein the anode efficiency of the soluble zinc anode is adjusted to correspond to the cathode efficiency of the cathode and the remainder of the anodic current is directed to the insoluble anode and consumed in a secondary anode reaction. 
     
     
         15 . Method according to  claim 13 , wherein the zinc alloy plating bath is a zinc nickel alloy plating bath and comprises organic additives selected from surfactants and complexing agents, a soluble nickel salt and a soluble zinc anode. 
     
     
         16 . Method according to  claim 14 , wherein the zinc alloy plating bath is a zinc nickel alloy plating bath and comprises organic additives selected from surfactants and complexing agents, a soluble nickel salt and a soluble zinc anode. 
     
     
         17 . Apparatus according to  claim 2 , wherein the electrode assembly comprises a second soluble anode selected from the group consisting of nickel, cobalt, iron, chromium, cadmium, tin, copper, silver, gold, platinum, palladium, manganese, ruthenium, rhodium, iridium, osmium, rhenium, tungsten, molybdenum, vanadium, indium, bismuth, antimony, selenium, germanium, gallium, tantalum and niobium. 
     
     
         18 . Apparatus according to  claim 2 , wherein the first soluble zinc anode, the second soluble anode and the insoluble anode are equipped individually with separate power supplies. 
     
     
         19 . Apparatus according to  claim 2 , wherein the ion exchange membrane is a cationic ion exchange membrane. 
     
     
         20 . Apparatus according to  claim 2 , wherein the insoluble anode is selected from the group consisting of titanium anodes, platinized titanium anodes, ceramic coated anodes, graphite anodes and carbon based anodes. 
     
     
         21 . Apparatus according to  claim 3 , wherein the first soluble zinc anode, the second soluble anode and the insoluble anode are equipped individually with separate power supplies. 
     
     
         22 . Apparatus according to  claim 3 , wherein the insoluble anode is selected from the group consisting of titanium anodes, platinized titanium anodes, ceramic coated anodes, graphite anodes and carbon based anodes.