RU2291917C1 - Electrolyte for deposition of bismuth-thallium alloy - Google Patents

Abstract

FIELD: electroplating, possibly in machine engineering.

SUBSTANCE: electrolyte contains, g/l: bismuth sulfate, 30 -40; thallium sulfate, 10 -20; Trilon, 40 - 50; aluminum sulfate, 20 -30; leveling agent A, 25 - 35.

EFFECT: improved corrosion resistance of coatings.

1 tbl

Description

The invention relates to the field of electroplating, in particular to electrolytic deposition of a bismuth-thallium alloy

Known electrolyte for the deposition of a bismuth-thallium alloy containing bismuth perchlorates, thallium, perchloric acid and sodium citrate [1]. However, rough matte coatings with a coarse-crystalline structure and low corrosion resistance (1.8-2.6 g / m ² · h) are deposited from this electrolyte.

The technical result of the invention is to increase the corrosion resistance of the resulting coatings.

The proposed electrolyte differs from the known one in that, in addition to bismuth and thallium salts, it contains trilon B (ethylenediaminetetraacetic acid disodium salt) and aluminum sulfate and a leveling agent A (benzene sulfate methyldiethylaminomethyl polyethylene glycol ether of alkyl phenol) are additionally added to its composition in the following ratio of components, g / l

 bismuth sulphate 30-40;  thallium sulfate 10-20;  Trilon B 40-50;  aluminum sulfate 20-30;  equalizer A 25-35.

Trilon B binds bismuth and thallium ions to very strong trilonate complexes (log β _Bi-EDTA = 27.9 and log β _T1-EDTA = 5.8), which prevents the hydrolysis of salts and improves the stability of the electrolyte.

The surfactant non-ionic substance - equalizer A - adsorbed on the cathode inhibits the recovery of metal ions, while improving the wettability of the precipitates. An additional introduction of aluminum sulfate contributes to an increase in the electrical conductivity of the solution and its buffer properties, and also improves the uniformity of the distribution of metal at the cathode.

The electrolyte is prepared by dissolving bismuth salts, thallium salts and trilon B in separate portions of water. A portion of the trilon B solution is added with stirring to the bismuth salt solution, and the second half of the complexone is added to the thallium salt solution. Mixtures of the solutions are left for 10-15 minutes for complete complexation, and then a thallium complexonate solution is added slowly (with vigorous stirring) to the bismuth complexonate solution. Aluminum sulfate and equalizer A are added to the resulting mixture and the electrolyte volume is adjusted to working water.

The electrodeposition of the coatings is carried out at a cathodic current density of 0.5-2.5 A / dm ² , at a temperature of 20-25 ° C, pH 1.5-2.5, with stirring using a bismuth anode.

Specific examples of the use of electrolyte and some properties of the coatings are given in the table.

The corrosion rate of alloys obtained from the proposed electrolyte is 30-60% less than coatings deposited from a known electrolyte.

Using the proposed electrolyte allows you to precipitate light, semi-shiny, tightly coupled to the base coating. Precipitation withstands bending at an angle of 90 ° without kink and does not exfoliate from the base after heating at 250 ° C for one hour and subsequent sudden cooling.

Table
Electrolyte Composition and Coating Properties Electrolyte components, g / l, and research results The composition of the examples one 2 3 Components: bismuth sulphate thirty 35 40 thallium sulfate 10 fifteen twenty Trilon B 40 45 fifty aluminum sulfate twenty 25 thirty equalizer A 2,5 3.0 3,5 Current density, A / dm ² 0.5 1,5 2,5 Temperature ° C twenty 22.5 25 pH 1,5 2.0 2,5 Stirring rpm 60 60 60 Current output,% 94 97 98 Thallium content,% 1.7 2,8 4,5 The corrosion rate, g / m ² · h 1,6 1.4 1,1 Appearance of coatings gray, matte light gray, dense light, smooth semi-shiny

Literature

1. Sadana Y.N., Kerr W. Metal Finishing., 1980. v. 78. No. 10. p. 43-47.

Claims (1)

An electrolyte for the deposition of a bismuth-thallium alloy containing bismuth and thallium compounds and complexon, characterized in that it additionally contains sulfuric acid aluminum and a leveling agent A - benzenesulfate methyldiethylaminomethyl polyglycol ether of alkyl phenol, and as complexon Trilon B - disodium salt of ethylenediaminetetraacetic acid the following ratio of components, g / l: Sulfuric Acid Bismuth 30-40 Sulfuric Acid Thallium 10-20 Trilon B 40-50 Sulfuric acid aluminum 20-30 Leveler A 25-35