Method for production of oxide and silicon layers on a metal surface

Abstract

The invention relates to a method of producing oxide and silicate layers on metal surfaces in a liquid electrolyte, particularly for aluminum metals, magnesium metals and their alloys, as well as for tantalum, titanium, niobium and zirconium. During the production of the oxide and silicate layers in the liquid electrolyte, a bipolar power source is used whose polarity can be changed.

1 . A method of producing oxide-silicate layers on a metal surface in a liquid electrolyte, said method comprising: 
 connecting a bipolar power source to the metal surface, applying power and    alternating the polarity of the power.    
     
     
         2 . The method of  claim 1 , wherein said metal surface comprises at least one metal selected from the group consisting of aluminum, alloys of aluminum, magnesium, alloys of magnesium, tantalum, titanium, niobium and zirconium.  
     
     
         3 . The method of  claim 1 , wherein the step of alternating the polarity of the power source takes place in the millisecond range.  
     
     
         4 . The method of  claim 3 , wherein the time period during which the part to be coated is connected as an anode is shorter than the time period during which the part to be coated is connected as a cathode or is without current.  
     
     
         5 . The method of  claim 1 , further comprising the step of controlling the layer sequences created.  
     
     
         6 . The method of  claim 5 , wherein the layer sequences created are controlled by selecting an electrolyte.  
     
     
         7 . The method of  claim 1 , wherein the metal surface is immersed in a first electrolyte during a time in which power is applied.  
     
     
         8 . The method of  claim 7 , wherein the first electrolyte comprises an aqueous solution of potassium hydroxide and sodium fluoride.  
     
     
         9 . The method of  claim 7 , further comprising the steps of immersing the metal surface in a second electrolyte during a time in which power is applied.  
     
     
         10 . The method of  claim 9 , wherein the second electrolyte comprises an aqueous solution of potassium hydroxide, sodium fluoride and sodium metasilicate.  
     
     
         11 . The method of  claim 1 , wherein power having one polarity is applied for a period of at least  30  milliseconds.  
     
     
         12 . A metal surface having oxide-silicate layers thereon, wherein said metal surface is produced by the process of  claim 1 .  
     
     
         13 . A method of producing oxide-silicate layers on a metal surface in a liquid electrolyte, said method comprising: 
 immersing the metal surface in a first electrolyte,    connecting a bipolar power source to the metal surface, applying power,    alternating the polarity of the power,    immersing the metal surface in a second electrolyte, then    repeating the steps of applying power and    alternating the polarity of the power.