Metal treatment – Process of modifying or maintaining internal physical... – Processes of coating utilizing a reactive composition which...
Patent
1998-11-30
2000-05-09
Wyszomierski, George
Metal treatment
Process of modifying or maintaining internal physical...
Processes of coating utilizing a reactive composition which...
148274, 148275, 148276, C23C 2282
Patent
active
060598972
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to the production of corrosion-inhibiting and/or decorative coatings on metals by anodic oxidation. It relates to an improved process for postsealing porous, electrochemically-produced anodized coatings in order further to improve the properties thereof.
TECHNICAL BACKGROUND AND RELATED ART
Electrochemical anodic oxidation of metals in suitable electrolytes is a widely used process for the formation of corrosion-inhibiting and/or decorative finishes on metals suitable for this purpose. These processes are briefly described in Ullmann's Encyclopedia of Industrial Chemistry, 5th edition, volume 9 (1987), pp. 175-176. According to this reference, titanium, magnesium and aluminum and alloys thereof are anodizable, the anodization of aluminum and alloys thereof being of the greatest industrial significance. The electrolytically produced anodized coatings protect the aluminum surfaces from the action of weathering and other corrosive media. Anodized coatings are also applied in order to create a harder surface, thus increasing the wear resistance of aluminum. Particular decorative effects may be achieved by means of the intrinsic color of the anodized coatings or by absorptive or electrolytic coloring. Aluminum is anodized in an acidic electrolyte, sulfuric acid being most commonly used. Other suitable electrolytes are phosphoric acid, oxalic acid and chromic acid. The properties of the anodized coatings may be varied widely by selection of the electrolyte, the temperature thereof and by the current density and duration of anodization. Anodization is conventionally performed using direct current or using direct current having a superimposed alternating current.
Freshly anodized coatings may subsequently be colored by immersion in solutions of a suitable dye or by an alternating current treatment in an electrolyte containing a metal salt, preferably containing tin. As an alternative to subsequent coloring, colored anodized coatings may be obtained by so-called color anodization processes, in which anodization is performed in solutions of organic acids, such as in particular sulfophthalic acid or sulfanilic acid, each optionally mixed with sulphuric acid.
These anodically-produced protective coatings, the structure of which has been scientifically investigated (R. Kniep, P. Lamparter and S. Steeb: "Structure of Anodic Oxide Coatings on Aluminium", Angew. Chem. Adv. Mater. 101 (7), pp. 975-977 (1989)), are frequently described as "oxide coatings". The above investigation has, however, demonstrated that these coatings are vitreous and contain tetrahedrally-coordinated aluminum. Octahedrally-coordinated aluminum, as in aluminum oxides, was not found. Herein, the more general term "anodized coatings" is used instead of the misleading term "oxide coatings".
However, these coatings do not yet fulfill all requirements with regard to corrosion protection, as they still have a porous structure. It is consequently necessary to post-seal the anodized coatings. This post-sealing is frequently performed using hot or boiling water, alternatively using steam, and is described as "sealing". This treatment seals the pores, thus considerably increasing corrosion protection. There are numerous literature references relating to this post-sealing process. The following may be mentioned by way of example: S. Wernick, R. Pinner and P. G. Sheasby: "The Surface Treatment and Finishing of Aluminum and its Alloys" (volume 2, 5th edition, Chapter 11: "Sealing Anodic Oxide Coatings"), ASM International (Metals Park, Ohio, U.S.A.) and Finishing Publications Ltd. (Teddington, Middlesex, England) 1987.
However, not only are the pores sealed during post-sealing of the anodized coating, but a velvety deposit of a greater or lesser thickness, the so-called "sealing deposit", is formed over the entire surface. This deposit, which consists of hydrated aluminum oxide, is visually unattractive, reduces adhesion when bonding such aluminum components and promotes subsequent soiling and corrosion. Since th
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Ullmann's "Encyclopedia of Industrial Chemistry", 5th Ed., vol. 9, (1987), pp. 174-176.
R. Kniep, P. Lamparter and S. Steeb: "Structure of Anodic Oxide Coatings on Aluminum" Angew. Chem. Adv. Mater 101 (1989), pp. 975-977.
S. Wernick, R. Pinner and P.G. Sheasby: "The Surface Treatment and Finishing of Aluminum and it's Alloys", vol. 2, 5th Ed., Chapter 11: "Sealing Anodic Oxide Coatings".
DIN 50949.
DIN 50946.
Koerner Torsten
Kresse Josef
Harper Stephen D.
Henkel Kommanditgesellschaft auf Aktien
Jaeschke Wayne C.
Oltmans Andrew L.
Szoke Ernest G.
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