The present invention relates to a method of anodizing iron or steel, in particular non-stainless steel, i.e. carbon steel that contains less than 1% chromium.
Bare steels rust when exposed to fresh water, salt water, or high condensing humidity. The corrosion products on such steel after atmospheric exposure are flaky and non-adherent rust. The prior art methods of providing a barrier layer between the steel and the environment have proven to be unsatisfactory for many different reasons. It is therefore an object of the present application to provide a method of anodizing steel to form an adherent oxide coating on the steel.
This object, and other objects and advantages of the present application, will appear more clearly from the following specification in conjunction with the accompanying drawings, in which:
The method of anodizing steel pursuant to the present application includes the steps of connecting a steel object to a positive terminal of a power supply, connecting a counter electrode to a negative terminal of the power supply, placing the steel object and counter electrode into a 50% by weight solution of NaOH, and applying a voltage across the terminals to anodize the steel object, wherein applying the voltage results in the formation of an adherent blue-black or a colored semi-adherent dichroic oxide coating on the steel object. “Dichroic” refers to a surface that reflects different colors when viewed at different angles.
Referring now to the drawings in detail,
Although the counter electrode/vessel 10 can also be made of steel, it could also be made of any other material that can conduct electricity and that does not corrode in NaOH, such as, by way of example only, platinum or nickel.
By way of example only, the electrodes formed by the steel object 12 and the counter electrode/vessel 10 can be spaced 7 cm apart for a two-electrode system using the voltages reported herein. It should furthermore be noted that a three-electrode system could also be used, and the required voltages would change accordingly.
The presently preferred concentrations for the electrolyte solutions are 50% by weight NaOH. The 50% NaOH solution can be prepared by adding 760 g of deionized water to 760 g of NaOH to make one L of solution. Tests resulting in the data of the graphs of
Although it was indicated above that the solution could be heated, the temperature of the solution during anodization can be anywhere from 30° C. to the boiling point of the solution.
For a uniform, thick, blue-black adherent anodic oxide, the preferred voltages to be applied across the terminals of the power supply range from 1.5 to 3.0V, and the temperatures range from 30-115° C., for a NaOH solution. In addition, the voltage can be applied for from a few seconds to many hours, depending upon the desired thickness of the oxide coating that is to be formed.
Potential applications for applicants' method of anodizing steel include corrosion protection, pre-weathering of weathering steels, conversion coating to improve the adherence of organic coatings, such as paints, internal protection of, for example, boiler tubes, and architectural colored highlights.
The specification incorporates by reference the disclosure of the corresponding U.S. application Ser. No. 11/624,137, which was filed on Jan. 17, 2007.
The present invention is, of course, in no way restricted to the specific disclosure of the specification and drawings, but also encompasses any modifications within the scope of the appended claims.
The present application is a CIP application of U.S. application Ser. No. 11/624,137. Therefore, the present application should be granted the priority date of Jan. 17, 2007, the filing date of the corresponding patent application Ser. No. 11/624,137.
Number | Date | Country | |
---|---|---|---|
Parent | 11624137 | Jan 2007 | US |
Child | 13196814 | US |