DE1796314C3 - Non-aqueous bath and process for the production of parts made of aluminum or aluminum alloys and provided with anodically produced colored oxide layers - Google Patents

Description

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The invention relates to a non-aqueous bath and a method for producing with anodically eryeug'en colored Oxidschichlcii provided parts ims aluminum or aluminum alloys, whereby The bath consists of a solution of boric acid in formamide.

When this known procedure is used, however, it has been found that the Elcktioivtbad only has an inadequate lifespan and is thicker and more resistant to produce Oxide layers require relatively high terminal voltages.

From Austrian patent specification 128 103 is Cs known for the electrolytic production of strong insulation layers on aluminum and its alloys a dilute aqueous oxalic acid solution containing oxidizing compounds Use oiler strong inorganic acids or boric acids sal / en / u. Such aqueous acid solutions However, in terms of composition and features, they are different from those treated here, non-aqueous jieii Electrolytes profoundly different and for the Unsuitable for intended purpose.

The task of the invention is now, an electrolyte june and a method of the type mentioned in the introduction, in which a substantially prolonged Lifespan of the bath and at the same time a considerable reduction in the required final cleaning fr /. is held.

In order to achieve this object, the electrolyte bath of the type mentioned at the outset is characterized according to the invention characterized by the fact that it also contains oxalic acid contains.

According to a preferred embodiment contains the electrolyte bath 30 to 50 percent by weight boric acid and 2 to 10 percent by weight oxalate anhydride.

The subject matter of the invention is also a method of the type mentioned Eins-ansjs, in which the Share in a bath of the aforementioned type at a Final voltage of 100 to 160 V anodically oxidized.

An aluminum cathode is used to carry out the process. When the current is switched on, a colored oxidation layer is created on the surface of the aluminum objects, the "color of which changes from yellow to black with increasing layer thickness and the blacker the greater the layer thickness. The desired color can be easily applied regulate <_i aie treatment time. Since the electric resisting country increases with ⁼ layer thickness increases, the voltage to maintain a constant current despite gradually, where appropriate, automatically. the oxide layer obtained is hard, corrosion and wear resistant and has extraordinary light and weather resistance. the larger Thickness, the oxide layer is free of cracks and can be used in particular in place of the previous black electroplating for the production of the black parts of photographic apparatus or modules a layer thickness of 50 μ a Vickers hardness of 450 to SOO. Since the oxide layer is also dense at the same time, it has a high level of corrosion resistance in its natural state without any further treatment.

example

In a series of tests, oxide layers were created with an electrolyte made from 50 g formamide and 400 g Boric acid produced with alternating addition of oxalic acid anhydride, with an aluminum anode plate of Ϊ00 cm- 'against an aluminum calhodic plate with a surface of 15.7 cm- switched and at a current density of 2 A / dm- 45 minutes was worked. An electrolyte solution containing no oxalic anhydride was also used for comparison isolated. The content of oxalic anhydride used in these experiments that with the same Electrolyte solution crziclbarc treatment length and the final voltage are summarized in the following table:

Tabel

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Addition to Kchandhmgs-
fleeting Endspannuni; attempt Oxalic acid
anhydride Weight c ItV- V percent 900 140 to 160 I. 4th 1 100 120 to 140 2 5 1,300 120 to 160 3 (Ί 900 110 to 140 4th 1 800 100 to 150 5 8th Comparison 400 200 to 250 attempt 0

The above numbers show that an addition of 5 to 6 percent by weight of oxalic anhydride receives particularly favorable results, since on the one hand the final voltage around the

Half is lower and, on the other hand, two to three times the service life of the solution is achieved. One The black-brown oxide layer produced in the process with a thickness of 32 μ had a Vickers hardness of 473 and passed the sand fall test according to the Japanese industrial standard with regard to smudging resistance (JIS) for about 30 minutes.

The method according to the invention is used in a preferred manner in the production of black parts of photographic apparatus.

Claims (3)

Patent claims: 1. Non-aqueous bath for anodic generation Vt) Ii colored oxide layers on aluminum or aluminum alloys, consisting of a solution of boric acid in formamide, thereby characterized in that it additionally contains oxalic anhydride. 2. Bath according to claim 1, characterized in that it is 30 to 50 percent by weight boric acid and contains 2 to 10 weight percent oxalic anhydride. 3. Process for the production of colored oxide layers provided with anodically produced Parts made of aluminum or aluminum alloys using a bath according to claim 1 or 2, characterized in that a final voltage of 100 to 160 volts is used will.