Metal treatment – Compositions – Heat treating
Patent
1984-05-01
1987-03-10
Silverberg, Sam
Metal treatment
Compositions
Heat treating
204 376, C25D 1124
Patent
active
046489118
DESCRIPTION:
BRIEF SUMMARY
In the conventional anodic oxidation of metal surfaces, particularly surfaces of light metals, such as, for example, aluminum, by conversion of the top metal layers, protective layers of the corresponding metal oxide are formed. This results in fine-pore coatings which can be reacted with various reagents and/or colorants, which today make it possible to color, in particular, aluminum surfaces in a large number of shades. Dependng on the use of these products, known as anodized aluminum articles, for indoor or outdoor purposes, more or less weather-resistant surfaces are required. The large variety of colorants which are suitable for this purpose and their use are well known to one skilled in the art and do not require any further explanation here.
All anodic oxidation processes have in common that the resulting surfaces, regardless of whether they are colorless or have been colored in one of more stages, are sensitive to touch and to corrosive substances. In order to overcome this great disadvantage, various sealing processes have been developed, by which a touch-resistant and corrosion-resistant surface is obtained. The best known of these sealing processes comprises a treatment with boiling water of steam, and is known as hot water sealing or steam sealing process. These processes have a very high energy consumption. Another disadvantage of the hot water treatment is the formation of an undesirable deposit of lime and other salts and impurities dissolved in the bath water, it being necessary subsequently to remove this deposit mechanically in an additional operation. To prevent such deposits from forming, sealing additives have been proposed which are generally based on high molecular weight compounds but make the process more expensive because they have to be replenished.
Furthermore, metal salts, such as nickel salts, for example nickel acetate, have been proposed as additives for the hot water baths, in order to increase the sealing. These salt baths have a sealing effect at as low a temperature as 70.degree. C. and therefore do not have to be used at the boiling point; in this case too, however, a very thick coating is formed which cannot be left on the surface.
Another disadvantage of the seal processes proposed hitherto is that the relatively high content of silicates, phosphates, chlorides and the like in the water is sufficient to act as a "seal poison", i.e. the resulting layers are of unsatisfactory quality and are very rapidly decomposed and completely corroded in the salt test.
Another difficulty in connection with the seal baths known hitherto is that they usually have a working life of about 3 to 6 weeks. After this time, they are useless and have to be discarded.
A novel seal process has now been developed which permits a treatment at temperatures below 30.degree. C. and in particular at room temperature, does not result in contamination of the bath, does not require renewal of the bath but only replacement of the bath components removed by the material treated, and gives an outstanding sealing of the coatings.
Surprisingly, it has been found that these results can be achieved by treatment of the anodically oxidized, and if desired colored, metal surfaces, in particular aluminum surfaces, with an aqueous solution which contains a nickel salt and a fluoride.
The present invention therefore relates to a process for the sealing of anodically oxidized, uncolored or colored metal surfaces, in particular aluminium surfaces, which is characterized in that the still wet surface is treated at a temperature below 30.degree. C. with an aqueous solution which contains at least one nickel salt and at least one fluoride.
Suitable nickel salts are inorganic nickel salts, such as nickel chloride, sulfate, carbonate, nitrate, etc., as well as organic nickel salts, such as nickel acetate and others. The fluoride is preferably a fluoride of an alkali metal salt, such as sodium fluoride, potassium fluoride, etc., or an ammonium fluoride, for example (NH.sub.4)HF.sub.2, or an organic fluoride.
The salts are p
REFERENCES:
patent: 2927872 (1960-03-01), Cohn
patent: 3494839 (1970-02-01), Chambers
patent: 4045599 (1977-08-01), Remaley
Metal Finishing 12/1968.
FFA Flug-und Fahrzeugwerke AG
Silverberg Sam
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