RU2456384C1 - Electrolyte for ematal coating of aluminium and its alloys - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: electrolyte contains, g/L: chromic anhydride 30-35, boric acid 1-2, 11-trimethyl-4-oxyfluoranten-3-sulfonic acid 0.7-2.0, O,O-diethyl-S-benzyl thiophosphate 1.5-3.6.

EFFECT: increased anticorrosion properties of protective ematal coatings.

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Description

The invention relates to the enameling of aluminum and its alloys to protect against corrosion.

Known chrome-borate enamel electrolyte containing chromic anhydride 100 g / l, boric acid 4 g / l (Rosenboim GB The emergence of enamel effect in chrome-borate electrolytes. Sat. "New technology of galvanic coatings of products in shipbuilding and engineering", L., Shipbuilding, 1974, p. 58). Due to the high concentration of chromic anhydride, the electrolyte is environmentally hazardous. In addition, the enamel coatings obtained in it have insufficient protective ability.

Closest to this proposed invention in technical essence and the results obtained is a diluted chromium-borate electrolyte with the addition of organic matter (USSR copyright certificate No. 1133313, С25D 11/06, priority January 7, 1983). The named electrolyte is environmentally noticeably less dangerous due to the low concentration of chromic anhydride (up to 30 g / l), but the enamel coatings deposited from it do not have sufficient protective effect for aluminum.

The technical problem, which was supposed to be solved in the present invention, is to enhance the anti-corrosion effect of enamel films on aluminum and its alloys.

The solution of this problem was carried out by introducing into the chromium-boron electrolyte an enamelling of two organic substances 11-trimethyl-4-hydroxyfluoranten-3-sulfonic acids and O, O-diethyl-S-benzylthiophosphate (fungicide), having the following structure:

11-trimethyl-4-hydroxyfluoranthene-3-sulfonic acid (hereinafter sulfonic acid)

Information on this compound is contained in the collection "Issues of Chemistry and Chemical Technology", Kharkov, Kharkov University, 1975, No. 39, p.16.

For enameling, an electrolyte of the following composition is taken (g / l):

chromic anhydride 30-35 boric acid 1-2 11-trimethyl-4-hydroxyfluoranthene-3-sulfonic acid 0.7-2.0 O, O-diethyl-S-benzylthiophosphate 1,5-3,6

When preparing the solution, first of all, boric acid and chromic anhydride should be dissolved, and then thiophosphate, while spending half the amount of water. In the second half, with vigorous stirring, 3-sulfonic acid dissolves, after which both solutions merge together. The enameling process is carried out at 40-50 ° C and with a stepwise increase in voltage: from 0 to 40 V in 5 minutes, then the indicated voltage value is maintained for 30 minutes, and at the third stage the voltage is increased to 80 V in about 1-3 minutes and maintain the achieved value either 17 min (option A) or 25 min (option B).

Samples with enamel coatings were tested in a G-4 hydrostat (regime 8 hours a day at 40 ° C, the rest of the day heating was turned off, humidity was maintained by water poured onto a hydrostat pan). The test duration is 20 days. After testing on the surface of the sample by applying a plexiglass plate with a grid of 100 squares, the number of corrosion damages is recorded and the frequency corrosion indicator, expressed as a percentage, is found. In addition, a so-called drop test is carried out by applying a drop of a solution containing an aqueous solution of hydrochloric acid and potassium dichromate to the surface of an enamel-coated sample. Measure the time taken to change the color of the drop from orange to green.

The results presented in the table allow us to draw the following conclusions.

1. The enamel films obtained in the electrolyte with the proposed additive showed a noticeable superiority compared to coatings from the electrolyte with the known additive: with a minimum concentration of the proposed additive, the protective properties increase by 6-7 or more times, and at the maximum concentration, complete protection is provided for all tested metals.

2. The best protection in terms of frequency is observed for pure aluminum, for both alloys it is only slightly weaker (at a minimum concentration).

3. Qualitatively similar results are shown for the drip sample: in the electrolyte with the proposed additive, the rate of the drop sample (37 min) is exceeded by about 2 times compared to films from the known electrolyte.

4. Both substances that make up the proposed additives increase the anodic polarization, which can be considered confirmation of their passivating effect.

The electrolyte is recommended for obtaining enamel coatings on aluminum and AMG and D-16 alloys in engineering, shipbuilding, household appliances and construction (for example, metro construction).

Claims (1)

The enamel electrolyte of aluminum and its alloys containing chromic anhydride and boric acid, characterized in that it additionally contains 11-trimethyl-4-hydroxyfluoranthene-3-sulfonic acid and O, O-diethyl-S-benzylthiophosphate at the following concentrations of electrolyte components, g / l:
chromic anhydride 30-35 boric acid 1-2 11-trimethyl-4-hydroxyfluorantene-3-sulfonic acid 0.7-2.0 O, O-diethyl-S-benzylthiophosphate 1,5-3,6