Apparatus and method for treatment of metal surfaces by inorganic electrophoretic passivation

Abstract

The present invention relates to an apparatus and a process for electrolytically treating a metal surface. The apparatus includes an electrochemical cell which includes an anodic chamber, a cathodic chamber, and a divider separating the anodic chamber from the cathodic chamber. The anodic chamber has an anode and contains a conductive anodic medium. The cathodic chamber has, as a cathode, the metal surface to be treated, and contains a conductive cathodic medium including a silica compound. In one embodiment, during operation of the apparatus, the anode remains substantially free of accumulation of foreign materials. In another embodiment, during operation of the apparatus, organic or inorganic compounds in the conductive cathodic medium remain substantially free of oxidation by the anode. In one embodiment, the treating comprises deposition of a silicon-containing mineral on the metal surface.

1 . An apparatus for electrolytically treating a metal surface, comprising 
 an electrochemical cell, wherein the electrochemical cell comprises 
 an anodic chamber having an anode disposed therein, and containing a conductive anodic medium;  
 a cathodic chamber containing the metal surface as a cathode, and containing a conductive cathodic medium comprising at least one silica-containing mineral composition; and  
 a divider separating the conductive anodic medium from the conductive cathodic medium.  
   
     
     
         2 . The apparatus of  claim 1 , wherein the treating comprises depositing a coating or film of a silicon-containing mineral by operation of the apparatus.  
     
     
         3 . The apparatus of  claim 1 , wherein the conductive anodic medium has a pH of about 9 or higher.  
     
     
         4 . The apparatus of  claim 1 , wherein the conductive anodic medium is free of oxidizable organic or inorganic additives.  
     
     
         5 . The apparatus of  claim 1 , wherein the conductive cathodic medium contains at least one organic or inorganic compound which would oxidize if in the anodic chamber.  
     
     
         6 . The apparatus of  claim 5 , wherein the at least one organic or inorganic compound remains substantially free of oxidation during operation of the apparatus.  
     
     
         7 . The apparatus of  claim 1 , wherein the divider comprises at least one of a salt bridge, an ion-selective membrane, a sol-gel, an ion-selective anode coating, an anode-conforming ion-selective membrane and a porous ceramic.  
     
     
         8 . The apparatus of  claim 1 , wherein the conductive cathodic medium further comprises a lubricant.  
     
     
         9 . The apparatus of  claim 8 , wherein the lubricant comprises one or more of a polyethylene wax, PTFE, a hydrocarbon oil, a vegetable oil, a chlorinated paraffin, a phosphate ester, a sulfurized oil, a sulfurized fat, a poly-α-olefin, a polyglycol, and a carboxylic ester.  
     
     
         10 . The apparatus of  claim 1 , wherein the anode comprises an active metal free of protection by a noble metal.  
     
     
         11 . The apparatus of  claim 1 , wherein the anode comprises an uncoated active metal.  
     
     
         12 . The apparatus of  claim 1 , wherein when the electrochemical cell is operated with an uncoated steel anode with applying an electric current at a constant potential across the electrochemical cell, substantially no loss of current flow is observed and substantially no anode residue is produced after 30 minutes.  
     
     
         13 . The apparatus of  claim 1 , wherein in operation of the apparatus the anode remains substantially free of accumulation of foreign materials.  
     
     
         14 . The apparatus of  claim 1 , wherein in operation of the apparatus organic or inorganic compounds in the conductive cathodic medium remain substantially free of oxidation by oxygen generated at the anode.  
     
     
         15 . The apparatus of  claim 1 , wherein the conductive cathodic medium comprises one or more of catechol, resorcinol and hydroxyquinone.  
     
     
         16 . A process of treating a metal surface, comprising 
 providing a metal surface;    providing an electrochemical cell, wherein the electrochemical cell comprises: 
 an anodic chamber having an anode disposed therein, and containing a conductive anodic medium;  
 a cathodic chamber containing the metal surface as a cathode, and containing a conductive cathodic medium comprising at least one silica-containing mineral composition; and  
 a divider separating the conductive anodic medium from the conductive cathodic medium  
   applying an electric current to the electrochemical cell at a rate and period of time sufficient for treating the metal surface.    
     
     
         17 . The process of  claim 16 , wherein the treating comprises depositing a coating or film of a silicon-containing mineral.  
     
     
         18 . The process of  claim 16 , wherein the conductive anodic medium has a basic pH.  
     
     
         19 . The process of  claim 16 , wherein the conductive anodic medium is free of oxidizable organic or inorganic additives.  
     
     
         20 . The process of  claim 16 , wherein the conductive cathodic medium contains at least one organic or inorganic compound which would oxidize if in the anodic chamber.  
     
     
         21 . The process of  claim 16 , wherein the divider comprises at least one of a salt bridge, an ion-selective membrane, a sol-gel, an ion-selective anode coating, an anode-conforming ion-selective membrane and a porous ceramic.  
     
     
         22 . The process of  claim 16 , wherein the conductive cathodic medium further comprises a lubricant.  
     
     
         23 . The process of  claim 22 , wherein the lubricant comprises one or more of a polyethylene wax, PTFE, a hydrocarbon oil, a vegetable oil, a chlorinated paraffin, a phosphate ester, a sulfurized oil, a sulfurized fat, a poly-α-olefin, a polyglycol, and a carboxylic ester.  
     
     
         24 . The process of  claim 16 , wherein the anode comprises an active metal free of protection by a noble metal.  
     
     
         25 . The process of  claim 16 , wherein the anode comprises an uncoated active metal.  
     
     
         26 . The process of  claim 16 , wherein when the electrochemical cell is operated with an uncoated steel anode with the applying an electric current at a constant potential across the electrochemical cell, substantially no loss of current flow is observed and substantially no anode residue is produced after 30 minutes.  
     
     
         27 . The process of  claim 16 , wherein during the applying an electric current, the anode remains substantially free of accumulation of foreign materials.  
     
     
         28 . The process of  claim 16 , wherein during the applying an electric current, organic or inorganic compounds in the conductive cathodic medium remain substantially free of oxidation by oxygen generated at the anode.  
     
     
         29 . The process of  claim 16 , wherein the conductive cathodic medium comprises one or more of catechol, resorcinol and hydroxyquinone.