Method of Anodizing Steel

Abstract

A method of anodizing steel, wherein a steel object is connected to a positive terminal of a power supply, a counter electrode is connected to a negative terminal of the power supply, the steel object and counter electrode are placed into a solution of KOH or NaOH, and a voltage is applied across the terminals to anodize the steel object by forming a adherent blue-black or semi-adherent dichroic colored oxide coating thereon.

1 . A method of anodizing steel, including the steps of:
 a) connecting a steel object to a positive terminal of a power supply;   b) connecting a counter electrode to a negative terminal of the power supply;   c) placing the steel object and counter electrode into a solution of KOH or NaOH; and   d) applying a voltage across the terminals to anodize the steel object by forming an adherent blue-black or colored semi-adherent dichroic oxide coating on the steel object.   
     
     
         2 . A method according to  claim 1 , wherein said solution is stirred and/or heated during said step of applying a voltage. 
     
     
         3 . A method according to  claim 2 , wherein said oxide coating is essentially a disordered or nanometer-size crystalline magnetite (Fe 3 O 4 ). 
     
     
         4 . A method according to  claim 1 , wherein said counter electrode is steel, platinum, nickel, or any other material that can conduct electricity and does not corrode in KOH or NaOH. 
     
     
         5 . A method according to  claim 2 , wherein said solution is at a temperature of from room temperature to the boiling point of the solution. 
     
     
         6 . A method according to  claim 1 , wherein said solution is KOH at a concentration of about 50%. 
     
     
         7 . A method according to  claim 1 , wherein said solution is NaOH at a concentration of about 25%. 
     
     
         8 . A method according to  claim 1 , wherein the voltage applied across the terminals is from 1.6 to 2.0 V for a KOH solution and 1.9 to 2.1V for a NaOH solution, in order to grow a black adherent oxide. 
     
     
         9 . A method according to  claim 8 , wherein said voltage is applied for from a few seconds to several hours, as a function a desired oxide coating thickness to be formed thereby. 
     
     
         10 . A method according to  claim 8 , wherein the temperature of said solution is from 75-140° C. for KOH and from 40-80° C. for NaOH. 
     
     
         11 . A method according to  claim 1 , wherein the voltage applied across the terminals is greater than 2.0 V for a KOH solution, and greater than 2.2V for a NaOH solution, and the temperature and the time of application are such as to obtain a specified color of dichroic oxide film.