Method of anodizing steel

Abstract

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

1 . An apparatus, comprising:
 an anodized non-stainless steel object, wherein said object is provided with an adherent blue-black or colored semi-adherent dichroic anodic oxide film directly on a steel surface of said object, and wherein the oxide film has a thickness of from 0.04 to 15 microns.   
     
     
         2 . An apparatus according to  claim 1 , wherein the oxide film is essentially a nano-crystalline magnetite (Fe 3 O 4 ). 
     
     
         3 . A method of anodizing non-stainless steel, including the steps of:
 a) connecting a non-stainless steel object to a positive terminal of a power supply;   b) connecting a counter electrode to a negative terminal of the power supply or to a vessel;   c) placing the non-stainless steel object and counter electrode into a solution of NaOH in the vessel; and   d) applying a voltage across the terminals to anodize the non-stainless steel object by growing an adherent blue-black or colored semi-adherent dichroic oxide film directly on a steel surface of the object.   
     
     
         4 . A method according to  claim 3 , wherein said solution is stirred and/or heated during said step of applying a voltage. 
     
     
         5 . A method according to  claim 3 , wherein said oxide film is essentially a nano-crystalline magnetite (Fe 3 O 4 ). 
     
     
         6 . A method according to  claim 3 , wherein said counter electrode is steel, platinum, nickel, or any other material that can conduct electricity and does not corrode in NaOH. 
     
     
         7 . A method according to  claim 3 , wherein said solution is at a temperature in the range of from room temperature to the boiling point of the solution. 
     
     
         8 . A method according to  claim 3 , wherein said solution is NaOH at a concentration of about 50% by weight. 
     
     
         9 . A method according to  claim 3 , wherein the voltage applied across the terminals is from 1.7 to 2.2V in order to grow a black adherent oxide. 
     
     
         10 . A method according to  claim 9 , wherein said voltage is applied for from a few seconds to several hours, as a function of a desired oxide film thickness to be formed thereby. 
     
     
         11 . A method according to  claim 9 , wherein the temperature of said solution is from 40-80° C. 
     
     
         12 . A method according to  claim 3 , wherein the voltage applied across the terminals is greater than 1.5V and the temperature and the time of application are such as to obtain a specified color of dichroic oxide film. 
     
     
         13 . A method according to  claim 3 , wherein said film has a thickness of from 0.04 to 15 microns.