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

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.

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.