RU2303662C1 - Electrolyte for depositing silver-lead alloy - Google Patents

Abstract

FIELD: electroplating, possibly in instrument making for applying coatings with high corrosion resistance.

SUBSTANCE: electrolyte contains, g/l: silver nitrate, 25 - 35; lead nitrate, 3 - 5; Trilon, 30 - 40; ammonium acetate, 20 - 30; lactic acid, 0.3 - 0.5; water - till working volume.

EFFECT: increased dissipating capability of electrolyte, enhanced corrosion resistance of deposited coatings.

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Description

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

Known electrolyte for the deposition of silver-lead alloy containing silver and lead salts, potassium iron-sulphide, potassium thiocyanate, potassium carbonate and polyethylene polyamine [SU 386032 A, publ. 06/14/1973]. The specified electrolyte is characterized by low scattering power (according to the Film 42-46%) and coatings with a low corrosion resistance of 0.1 N are deposited from it. sulfuric acid solution (0.3-0.5 g / m ² · h).

The objective of the invention and the technical result is to increase the scattering power of the electrolyte and increase the corrosion resistance of the deposited coatings.

The specified technical result is achieved in that the electrolyte for the deposition of the silver-lead alloy contains nitric acid salts of silver and lead and additionally contains trilon B (ethylenediaminetetraacetic acid disodium salt - Na ₂ H ₂ C ₁₀ H ₁₂ O ₈ N ₂ · 2H ₂ O), acetic acid ammonium and lactic acid (C ₃ H ₅ O ₃ ) in the following ratio of components, g / l: silver nitrate - 25-35, lead nitrate - 3-5, trilon B - 30-40, ammonium acetate - 20-30, lactic acid - 0.3-0.5, water - to the working volume.

Trilon B binds silver and lead ions into strong trilonate complexes (logβ _AgEDTA = 7.32 and logβ _{Pb EDTA} = 18.04), which prevents the hydrolysis of salts and improves the stability of the electrolyte.

An additional introduction of ammonium acetate promotes an increase in the electrical conductivity of the solution and its buffer properties, and also improves the uniform distribution of the alloy on the cathode.

The introduction of lactic acid helps to improve the buffer properties of the solution, modifying the structure and clarifying the cathode deposits.

The electrolyte is prepared by dissolving silver nitrate salt, lead nitrate salt and Trilon B in separate portions of water. Half of Trilon B solution is added with stirring to the silver nitrate salt solution, and the other half of Trilon B is added to the lead nitrate salt solution. The mixture of solutions is left for 10-15 minutes for complete complexation, and then slowly (with vigorous stirring) a solution of lead complexonate is added to the silver complexonate solution. Ammonium acetate, lactic acid are added to the resulting mixture and the electrolyte volume is adjusted to the working water. The acidity of the electrolyte was adjusted with aqueous ammonia.

The electrodeposition of the coatings is carried out at a cathodic current density of 0.5-1.5 A / dm ² , a temperature of 20-25 ° C, pH 8.5-9.5 with stirring.

The boundary values of the concentrations of silver and lead nitrate salts in the electrolyte are determined by the composition of the obtained alloy, which, depending on the electrolysis conditions, can contain from 2 to 4% lead.

The upper limit of the concentration of Trilon B is due to its solubility in this electrolyte, the lower - due to precipitation.

The lower concentration limit of ammonium acetate is due to precipitation from the solution. The increase in concentration above the specified value does not affect the properties of the electrolyte and is impractical.

A decrease in the concentration of lactic acid in the electrolyte below the indicated value does not lead to a significant change in the structure, and with an increase in the concentration above the proposed limit, matte coatings with a rough surface are formed.

Specific examples of the use of electrolyte and some properties of the coatings are shown in table 1.

The dissipating ability of the proposed electrolyte due to increased polarization of the cathode when Trilon B and lactic acid are introduced into its composition increases by 20-25% compared to the known one.

The corrosion rate of coatings obtained from the proposed electrolyte is 2-3 times 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 1 hour and subsequent sharp cooling.

Table 1 Electrolyte components, g / l and research results The composition of the examples one 2 3 Silver nitrate 25 thirty 35 Lead nitrate 3 four 5 Trilon B thirty 35 40 Ammonium Acetate twenty 25 thirty Lactic acid 0.3 0.4 0.5 Current density, A / dm ² 0.5 1,0 1,5 Temperature ° C twenty 22.5 25 pH 8.5 9.0 9.5 Current output,% 95 98 99 PC electrolyte (by Field),% 52 55 59 Lead content,% 2.1 2.9 3.6 The corrosion rate, g / m ² · h 0.12 0.1 0.09 Appearance of coatings light gray, dense light, semi-shiny light, smooth, semi-shiny

Claims (1)

An electrolyte for the deposition of a silver-lead alloy containing nitric acid salts of silver and lead, characterized in that it additionally contains trilon B, ammonium acetate and lactic acid in the following ratio of components, g / l: silver nitrate 25-35 lead nitrate 3-5 Trilon B 30-40 ammonium acetate 20-30 lactic acid 0,3-05 water to working volume