Surface preparation process for recoating of used coated metallic electrodes

Abstract

A surface preparation process for use in recoating of used metallic electrodes coated with one or more platinum group metals, one or more iron group metals, or chemical compounds thereof, which comprises using said metallic electrode(s) as anode(s) and passing a current between said metallic electrode(s) and a steel cathode(s) in an aqueous solution of sulfuric acid, nitric acid, perchloric acid, salts thereof, chlorates or persulfates, or a mixture solution thereof, and then dipping said metallic electrode(s) into an aqueous solution of hydrofluoric acid or hydrochloric acid.

We claim: 
     
       1. A surface preparation process for recoating of a used coated metallic electrode coated with one or more platinum group .[.metals.]. .Iadd.metal oxides .Iaddend.or iron group metal oxides, comprising using said electrode as an anode and passing a current at about 1 to 100 A./dm. 2  of anode current density between said anode and steel cathodes, in an electrolytic bath containing an aqueous solution containing about 5 to 70 percent by weight of a salt selected from the group consisting of a sulfate, a nitrate, a perchlorate, a chlorate, a persulfate and a mixture thereof, at a temperature of about 0 to 50° C., for a period of time sufficient to effect removal of coating remaining on said used electrode. 
     
     
       2. A surface preparation process according to claim 1, wherein a current is passed at about 3 to 60 A./dm. 2  of anode current density. 
     
     
       3. A surface preparation process according to claim 1, wherein a current is passed at about 10 to 60 A./dm. 2  of anode current density in case the metallic electrode used as an anode is coated with a platinum group metal .Iadd.oxide. .Iaddend. 
     
     
       4. A surface preparation process according to claim 1, wherein a current is passed at about 3 to 20 A./dm. 2  of anode current density in case the metallic electrode used as an anode is coated with an iron group metal oxide. 
     
     
       5. A surface preparation process according to claim 1, wherein said bath also contains about 0.1 to 3 percent by weight of hydrogen peroxide as an oxidation accelerator. 
     
     
       6. A surface preparation process for recoating of a used coated metallic electrode coated with one or more platinum group .[.metals.].  .Iadd.metal oxides .Iaddend.or iron group metal oxides, comprising using said electrode as an anode and passing a current at about 1 to 100 A./dm. 2  of anode current density between said anode and steel cathodes, in an electrolytic bath containing an aqueous solution containing about 5 to 70 percent by weight of a salt selected from the group consisting of a sulfate, a nitrate, a perchlorate, a chlorate, a persulfate and a mixture thereof, at a temperature of about 0 to 50° C., for a period of time sufficient to effect removal of any remaining coating, thereafter lightly rubbing the surface of the thus treated electrode with a soft cloth and/or rinsing with water, and dipping the resulting electrode substrate into an about 5 percent by weight aqueous hydrofluoric acid solution or an about 8 to 17 percent by weight aqueous hydrochloric acid solution for a few minutes. 
     
     
       7. A surface preparation process for recoating of a used coated metallic electrode coated with one or more platinum group .[.metals.].  .Iadd.metal oxides.Iaddend., comprising using said electrode as an anode and passing a current at about 10 to 60 A./dm. 2  of anode current density between said anode and steel cathodes, in an electrolytic bath containing an aqueous solution containing about 5 to 70 percent by weight of a salt selected from the group consisting of a sulfate, a nitrate, a perchlorate, a chlorate, a persulfate and a mixture thereof, at a temperature of about 0 to 50° C., for a period of time sufficient to effect removal of any remaining coating, thereafter lightly rubbing the surface of a treated electrode with a soft cloth and/or rinsing with water, and dipping the resulting electrode substrate into about 5 percent by weight of an aqueous solution of hydrofluoric acid for a few minutes. 
     
     
       8. The process of claim 1, wherein said salt is sodium, potassium, lithium or ammonium sulfate. 
     
     
       9. The process of claim 1, wherein said salt is sodium, potassium, lithium, or ammonium nitrate. 
     
     
       10. The process of claim 1, wherein said salt is sodium, lithium or ammonium perchlorate. 
     
     
       11. The process of claim 1, wherein said salt is sodium, potassium or lithium chlorate. 
     
     
       12. The process of claim 1, wherein said salt is potassium or ammonium persulfate.