Method for controlling the chromium feed in an electrolysis process for producing chromium layers, and an electrolysis cell for this purpose

Abstract

The invention relates to a method for controlling the chromium feed in an electrolysis process for producing a chromium layer by means of direct current and use of an anode ( 44, 144, 244 ) and a cathode ( 48, 148, 248 ), comprising, during the electrolytic deposition of chromium with formation of a chromium layer: (E) applying a cathode voltage to the first auxiliary electrode ( 54, 154, 254 ), whereby the passivation layer of the chromium metal dissolves and chromium metal in the form of chromium (III) ions starts to go into solution in the electrolyte ( 25, 125, 225 ); (F) following the dissolution of the passivation layer, ending the current supply to, or switching off, the voltage on the first auxiliary electrode ( 54, 154, 254 ); and (G) without current, leaving the chromium metal to go into solution from the first auxiliary electrode ( 54, 154, 254 ) in the form of chromium (III) ions by action of the electrolyte ( 25, 125, 225 ). By topping up the chromium metal in the first auxiliary electrode during step (G), steps (E), (F) and (G) can be repeated as often as desired.

1 - 12 . (canceled) 
     
     
         13 . A method for controlling chromium feed in an electrolysis process for producing a chromium layer, wherein the chromium layer is produced by an electrolytic deposition of chromium from an electrolyte by means of direct current and use of an anode and a cathode, the method comprising the following steps:
 (A) providing a first auxiliary electrode that includes or consists of chromium metal;   (B) providing a second auxiliary electrode in the form of an inert electrode;   (C) immersing both of the first auxiliary electrode and the second auxiliary electrode in the electrolyte that contains at least one chromium(III) salt;   (D) interconnecting the first auxiliary electrode and the second auxiliary electrode in an electric circuit separate from the cathode and the anode; and   during electrolytic deposition of chromium with formation of a chromium layer:   (E) applying a cathode voltage to the first auxiliary electrode, as a result of which a passivation layer of chromium metal dissolves and chromium metal in the form of chromium(III) ions begins to go into solution in the electrolyte;   (F) following dissolution of the passivation layer, terminating a current supply to the first auxiliary electrode; and   (G) solubilizing the chromium metal from the first auxiliary electrode in the form of chromium(III) ions without current by action of the electrolyte, wherein currentless dissolution of the chromium occurs over a period of time sufficient to bring the chromium content of the electrolyte to a desired level, which can last from a few minutes up to several hours,
 wherein a replenishing of the chromium metal in the first auxiliary electrode occurs during step (G), and, subsequently, steps (E), (F) and (G) are performed successively in that order, wherein the first auxiliary electrode is selected from a holder or framework, in which the chromium metal is held in the form of chromium molds. 
   
     
     
         14 . The method of  claim 13 , wherein in order to terminate the process during step (G),
 an anode voltage is applied to the first auxiliary electrode, or   the first auxiliary electrode is pulled out of the electrolyte, or   the electrolyte is pumped out of an electrolysis cell, or   no replenishing of the chromium metal of the first auxiliary electrode is made.   
     
     
         15 . The method of  claim 13 , wherein in the electrolyte, a pH value is set in a range from 2.0 to 3.5. 
     
     
         16 . The method of  claim 13 , wherein one, two or more of the following conditions are met:
 a cathode voltage in step (E) is set in a range from 1.0 to 10.0 volts;   an anode voltage for terminating the process during step (G) is set in a range from 1.0 to 10.0 volts;   a surface area of the first auxiliary electrode is selected to be a same size as a surface area of the second auxiliary electrode;   a current density lies in a range from 2.5 to 4 A/dm 2 ;   the passivation layer is degraded by applying the cathode voltage to the first auxiliary electrode in step (E) within 5 to 60 seconds;   the passivation layer is formed again by applying the anode voltage to the first auxiliary electrode within 5 to 60 seconds to terminate the process during step (G); and   the chromium metal of the first auxiliary electrode is given as chromium molds selected from nuggets, chunks, lumps, platelets, bars, wires and grids that are held in a material resistant to an acidic electrolyte.   
     
     
         17 . The method of  claim 13 , wherein a third auxiliary electrode in the form of an inert electrode is provided, wherein the first auxiliary electrode in the form of a chromium electrode, the second auxiliary electrode and the third auxiliary electrode are interconnected to form one or more units, and wherein one unit is selected from: an inert electrode, a chromium electrode, and an inert electrode. 
     
     
         18 . The method of  claim 13 , wherein:
 (a) the electrolyte comprises one or more chromium(III) salts selected from inorganic and/or organic chromium(III) salts;   additional components of the electrolyte are selected from:   (b) a compound of the formula (I)   
       
         
           
           
               
               
           
         
         wherein R is selected from NH 2 , OH or SO 3 H, and n represents an integer from 1 to 3, 
         and/or their salts with monovalent cations or bivalent cations; and 
         (c) formic acid and/or its salts with monovalent cations or bivalent cations. 
       
     
     
         19 . The method of  claim 18 , wherein the additional components of the electrolyte are further selected from complexing agents, alkali or alkaline earth salts, wetting agents, catalysts or mixtures thereof. 
     
     
         20 . The method of  claim 13 , wherein the chromium(III) content in the electrolyte is kept constant by comparing the weight of the chromium metal used in the first auxiliary electrode with the weight of the chromium metal used up for the chromium layer and replenishing the chromium metal in the first auxiliary electrode before the chromium(III) content in the electrolyte decreases. 
     
     
         21 . An electrolysis cell, comprising:
 an anode;   a cathode;   an electrolyte that contains at least one chromium(III) salt, wherein the anode and the cathode are immersed in the electrolyte;   a first circuit which connects the anode and the cathode and is configured to cause a deposition of a chromium layer by an electrolytic deposition of chromium from the electrolyte by means of direct current on the cathode;   a first auxiliary electrode that includes or consists of chromium metal;   a second auxiliary electrode in the form of an inert electrode, wherein both the first auxiliary electrode and the second auxiliary electrode are immersed in the electrolyte;   a second circuit which connects the first auxiliary electrode and the second auxiliary electrode in an electric circuit separate from the cathode and the anode;   wherein:   a cathode voltage is applied to the first auxiliary electrode so that a passivation layer of chromium metal on the first auxiliary electrode dissolves; or   no voltage is applied to the first auxiliary electrode so that, following dissolution of the passivation layer, the chromium metal from the first auxiliary electrode in the form of chromium(III) ions goes into solution into the electrolyte without current; or   an anode voltage is applied to the first auxiliary electrode so that the passivation layer forms again on the first auxiliary electrode,   wherein the first auxiliary electrode is selected from a holder or framework in which the chromium metal is given in the form of chromium molds, which allows the chromium metal in the first auxiliary electrode to be replenished while no voltage is applied to the first auxiliary electrode.   
     
     
         22 . The electrolysis cell of  claim 21 , wherein the electrolysis cell is composed of a trough, two troughs arranged one above the other, or two troughs arranged next to one another. 
     
     
         23 . The electrolysis cell of  claim 21 , wherein one, two or more of the following characteristics are fulfilled:
 in the electrolyte, a pH value is given in a range from 2.0 to 3.5;   the cathode voltage on the first auxiliary electrode lies in a range from 1.0 to 10.0 volts, or the anode voltage on the first auxiliary electrode lies in a range from 1.0 to 10.0 volts;   the cathode voltage on the first auxiliary electrode is applied for 5 to 60 seconds, or the anode voltage on the first auxiliary electrode is applied for 5 to 60 seconds;   a surface area of the first auxiliary electrode is selected to be a same size as a surface area of the second auxiliary electrode;   the current density is set in a range from 2.5 to 4 A/dm 2 ;   the chromium metal of the first auxiliary electrode is given as chromium molds selected from nuggets, chunks, lumps, platelets, bars, wires and grids that are held in a material resistant to the acidic electrolyte; and/or   (a) the electrolyte comprises one or more chromium(III) salts selected from inorganic and/or organic chromium(III) salts, and additional components of the electrolyte ( 25 ,  125 ,  225 ) are selected from:   (b) a compound of the formula (I)   
       
         
           
           
               
               
           
         
          wherein R is selected from NH 2 , OH or SO 3 H, and n represents an integer from 1 to 3, and/or their salts with monovalent cations or bivalent cations; 
         (c) formic acid and/or its salts with monovalent cations or bivalent cations. 
       
     
     
         24 . The electrolysis cell of  claim 23 , wherein the additional components of the electrolyte are further selected from complexing agents, alkali or alkaline earth salts, wetting agents, catalysts or mixtures thereof. 
     
     
         25 . The electrolysis cell of  claim 21 , further comprising:
 a third auxiliary electrode in the form of an inert electrode,   wherein the first auxiliary electrode in the form of a chromium electrode, the second auxiliary electrode and the third auxiliary electrode are interconnected to form one or more units,   wherein one unit is selected from: an inert electrode, a chromium electrode, and an inert electrode.