RU2459016C1 - Electrolyte for depositing zinc-gallium alloy - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: electrolyte contains the following, in g/l: zinc chloride 40-50; gallium dichloride 5-10; aluminium chloride 30-40; complexing agent trilon B - ethylenediaminetetraacetic acid disodium salt 50-60; surfactant sorbitol 2-4 and water - to operating volume.

EFFECT: increased hardness and corrosion resistance of coatings.

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Description

The invention relates to the field of electroplating, in particular to electrolytic deposition of a zinc-gallium alloy.

Known electrolyte for the deposition of zinc-gallium alloy containing zinc, gallium, potassium hydroxide and gelatin [Khamudkhanova Sh.E. et al. // Dokl. Uzbek Academy of Sciences, 1969. No. 7. p. 39-40].

However, dark powdery precipitates with a low hardness (60-80 MPa) and corrosion resistance (7.4-7.9 g / m ² · h) of 0.1 N are obtained from the indicated electrolyte. sulfuric acid solution.

The task to which the claimed technical solution is directed is to develop an electrolyte composition with improved properties.

When implementing the claimed technical solution, the problem is solved by achieving a technical result, which consists in improving the quality of the resulting coatings, namely increasing their hardness and corrosion resistance.

The specified technical result is achieved in that in the known electrolyte for the deposition of zinc-gallium alloy containing chloride salts of zinc, gallium, a complexing agent and a surfactant, a feature is that it additionally contains aluminum chloride, while as a complexing agent contains trilon B - ethylenediaminetetraacetic acid disodium salt, and as a surfactant-sorbitol, in the following ratio of components, g / l: zinc chloride - 40-50; gallium chloride - 5-10; aluminum chloride - 30-40; Trilon B - 50-60; sorbitol - 2-4, water - to the working volume.

Trilon B binds zinc and gallium ions into strong trilonate complexes (log β Zn - EDTA = 16.50 and log β Ga - EDTA = 20.27), which prevents the hydrolysis of salts and improves the stability of the electrolyte.

The addition of aluminum chloride to the electrolyte increases the conductivity of the solution and its buffering properties, and also improves the uniformity of the distribution of metal on the cathode.

Sorbitol, adsorbed on the surface of a growing precipitate, increases the polarization of the cathode, grinds the structure and improves the quality of the resulting coatings.

The electrolyte is prepared by sequentially dissolving zinc salts, gallium salts and trilon B in separate portions of distilled water. A portion of the trilon B solution is added with stirring to the zinc salt solution, and the other half of the complexon is added to the gallium salt solution. Mixtures of solutions are left for 10-15 minutes for complete complexation, and then slowly (with vigorous stirring) a solution of gallium complexonate is added to the zinc complexonate solution. Aluminum chloride and sorbitol are added to the resulting mixture, and the volume of electrolyte is adjusted to the working water.

The electrodeposition of the coatings is carried out at a cathodic current density of 1-5 A / dm ² , room temperature 20-25 ° C, pH 3.5-5.5 with stirring and the use of zinc anodes.

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

Concentrations of electrolyte components are determined experimentally. When the concentration of zinc salt goes beyond the lower boundary, a noticeable deterioration in the quality of coatings is observed. Electrolysis at high concentrations of zinc salt is impractical due to the high energy consumption and consumption of reagents. A decrease in the concentration of gallium salt leads to too little inclusion of an alloying element (gallium) in the precipitate and a slight change in properties. An increase in the salt content of the alloying component in the electrolyte does not increase it in the alloy and adversely affects the quality of the coatings (hardness begins to decrease, the coatings peel off and crumble). A decrease in the concentration of aluminum chloride leads to an accelerated alkalization of the solution and the appearance of insoluble hydroxide compounds of coprecipitated metals in it. At a high concentration of this component, the current efficiency of the alloy decreases. With a low sorbitol content, rough, coarse-grained precipitates form; with a high precipitation, they darken.

The corrosion rate of coatings obtained from the proposed electrolyte is 25-40% less than coatings deposited from a known electrolyte. In addition, the use of the developed electrolyte by 25-30% strengthens the resulting coatings compared with precipitation obtained from a known solution.

Using the proposed electrolyte allows you to precipitate bright shiny and non-porous coatings having good adhesion to the copper base.

Table Components and properties of electrolyte Electrolyte components (g / l) and research results The composition of the examples one 2 3 Zinc chloride 40 45 fifty Gallium chloride 5 7.5 10 Trilon B fifty 55 60 Aluminum chloride thirty 35 40 Sorbitol 2 3 four The current density, A / DM ² one 3 5 Temperature ° C twenty 22.5 25 pH 3,5 4,5 5.5 Stirring rpm 60 60 60 Current output,% 76 80 83 Dissipation ability,% 55 62 65 The gallium content in the alloy,% 0.3 1,2 2.1 The corrosion rate, g / m ² · h 5.7 6.3 6.5 Microhardness, MPa 92 97 103 Appearance of coatings gray gray, semi-shiny bright, shiny

Claims (1)

The electrolyte for the deposition of zinc-gallium alloy containing zinc and gallium salts and a surfactant additive is a surfactant, characterized in that it additionally contains aluminum chloride and the complexing agent Trilon B-ethylenediaminetetraacetic acid disodium salt, zinc chloride as zinc and gallium salts and gallium chloride, and as a surfactant - sorbitol, in the following ratio of components, g / l:
zinc chloride 40-50 gallium chloride 5-10 aluminum chloride 30-40 Trilon B 50-60 sorbitol 2-4 water to working volume