Method for the electrolytic deposition of chromium and chromium alloys

Abstract

The invention relates to a method for depositing chromium and/or chromium alloys on metals, and particularly on sheet steel, wherein an alloy layer is electrolytically deposited on the metal from a solution containing chromium ions and/or chromium ions and further metal ions such as Zn, Cd, In, Pb, Bi, Mo, Cu, Fe, Ni, Co, Mn, Al, Sb, Ag, Sn, Mg, wherein chromium hydroxide precipitated from a chromium (III) solution is used for regenerating the electrolyte solution using chromium (III) ions.

1 . A method for depositing chromium and/or chromium alloys on metals and particularly on steel sheets, comprising:
 electrolytically depositing an alloy layer on the metal from a solution containing chromium ions alone and/or chromium ions and other metal ions selected from the group consisting of Zn, Cd, In, Pb, Bi, Mo, Cu, Fe, Ni, Co, Mn, Al, Sb, Ag, Sn, and Mg, and using chromium hydroxide precipitated from a chromium (III) solution to replenish the electrolyte solution with chromium (III) ions.   
     
     
         2 . The method as recited in  claim 1 , wherein the time between the precipitation of the chromium hydroxide from the chromium (III) solution and the introduction of the precipitated chromium hydroxide into the electrolytic solution is calculated so that the chromium hydroxide does not transform into a poorly soluble product. 
     
     
         3 . The method as recited in  claim 1 , comprising using an aqueous chromium (III) compound selected from the group consisting of alkaline chromium sulfate, chromium potassium sulfate, ammonium chromium sulfate, chromium chloride, chromium fluoride, chromium acetate, and chromium nitrate to produce the chromium (III) solution. 
     
     
         4 . The method as recited in  claim 1 , comprising using alkaline chromium sulfate as the soluble chromium (III) compound having the following composition in terms of oxides:
 20%-45% Cr 2 O 3 ,   20%-45% SO 3 ,   15%-40% Na 2 SO 4      10%-60% H 2 O.   
     
     
         5 . The method as recited in  claim 1 , comprising mixing in a first reaction vessel, water and the soluble chromium (III) compound, comprising alkaline chromium sulfate, with each other and then through the addition of an alkaline substance, raising the pH value in the solution and precipitating out chromium (III) hydroxide. 
     
     
         6 . The method as recited in  claim 1 , comprising mixing in a first reaction vessel, water, zinc oxide, and the soluble chromium (III) compound, comprising alkaline chromium sulfate, with one another and then through the addition of zinc oxide or other alkaline substances, raising the pH value in the solution and precipitating out chromium (III) hydroxide. 
     
     
         7 . The method as recited in  claim 1 , comprising filtering out the chromium hydroxide, together with excess ZnO that acts as a filtration agent, from sludge and then washing the chromium hydroxide. 
     
     
         8 . The method as recited in  claim 7 , comprising reducing a remaining sulfate content through single or multiple washing of the sludge; filtering the sludge and adding a filter cake composed of zinc oxide and chromium hydroxide to the electrolyte solution for the deposition of zinc chromium on metallic surfaces. 
     
     
         9 . A use of chromium hydroxide, which is precipitated from alkaline chromium sulfate by raising the pH value, for the replenishment of electrolytic solutions with chromium (III) ions.