RU2400570C1 - Zinc electroplating method - Google Patents

Abstract

FIELD: chemistry. ^ SUBSTANCE: method involves depositing zinc from an electrolyte which contains zinc sulphate or oxide and water with cathode current density of 1.0-1.5 A/dm2, whereby deposition takes place from an electrolyte which contains zinc sulphate or oxide in amount of 0.075-0.185 mol/l, 80% lactic acid 10-20 ml/l, at electrolyte temperature of 20-25C, pH 2.0-4.0 using a graphite anode. ^ EFFECT: obtaining uniform semi-lustrous zinc coatings having strong adhesion to a base and high current output. ^ 5 tbl, 1 dwg

Description

The invention relates to a galvanic method for producing zinc coatings.

Known electrolyte of the following composition:

1. ZnSO ₄ · 7H ₂ O - 250-300 g / l, Al ₂ (SO ₄ ) ₃ · 18H ₂ O - 30-40 g / l, Na ₂ SO ₄ · 10H ₂ O - 80-100, dextrin - 1-2 g / l, brightener CBU - 1.0 g / l, brightener-fixer U-2 - 1.5-2.0 g / l, pH 3.0-4.0, temperature 15-25 ° C The cathodic current density is 2.0-4.5 A / dm ² [1].

This galvanizing electrolyte has a number of drawbacks, among which it is possible to distinguish low dissipation ability, as well as the content in the electrolyte, in addition to zinc cations, toxic anions and organic substances, which significantly increase the complexity of the disposal of spent electrolyte and wastewater treatment from the galvanizing site.

Of the currently used electrolytes, the closest in composition and technological characteristics is an electrolyte containing: ZnCl ₂ - 60-120 g / l, KCl - 150-230 g / l, H ₃ BO ₃ - 15-30 g / l, Limeda NTs-10 - 30-70 g / l, Limeda NTs-20 - 2.5-5.0 g / l, pH - 4.5-5.5. The temperature range is 18-30 ° C. The working current density of 0.5-3.0 A / DM ² [1].

The use of additives in this electrolyte allows to increase the buffer capacity of the solution, which allows the process to be carried out at higher current densities (up to 3 A / dm ² ). Organic additives of this electrolyte increase the cathodic polarization, which leads to the formation of crystalline zinc deposits and an increase in the uniformity of coatings. However, the presence of organic additives complicates the disposal of spent electrolyte and wastewater treatment.

The technical result of the proposed method is to obtain uniform, semi-shiny, well adhered to the base of the zinc coatings with high current efficiency. The electrolyte should be easy to prepare and adjust, and not contain toxic organic additives. The working temperature of the electrolyte should not be higher than 25-30 ° C.

This is achieved by the fact that in the method of applying zinc plating from an electrolyte containing zinc ions and water at a cathodic current density of 1.0-1.5 A / dm ² , according to the invention, zinc sulfate or zinc oxide is dissolved in the amount of 0.075-0.185 mol / l, lactic acid (80%) - 10-20 ml / l, pH - 2.0-4.0, after which the process of electrolytic deposition of zinc is carried out at a temperature of 20-25 ° C using a graphite anode.

As a complexing agent, lactic acid was selected. It is used as a food supplement [2], it is widely distributed in nature, it is an intermediate of metabolic processes in biological tissues, it is easily biodegradable and therefore environmentally friendly.

Not identified solutions that have signs of the proposed method.

The method of applying zinc plating is as follows.

In distilled water, sulfate or zinc oxide is dissolved according to the composition of the electrolyte. Then add lactic acid, bring to volume with distilled water and mix. The deposition is carried out at a cathodic current density of 1-1.5 A / DM ² at a temperature of 20-25 ° C using a graphite anode.

Based on the studies performed, for the deposition of brilliant zinc coatings, an electrolyte of the following composition can be recommended:

- sulfate or zinc oxide - 0.075-0.185 mol / l, lactic acid (80%) - 10-20 ml / l, pH - 2.0-4.0. At a cathodic current density of 1 to 1.5 A / dm ² and a temperature of 20-25 ° C, the cathodic current efficiency is 55-65%, which corresponds to a deposition rate of 4-13 microns / hour. Uniform, semi-shiny coatings are deposited from this electrolyte without the addition of brightening agents.

Microphotographs of the surface of the zinc coating obtained using atomic force (see drawing, a) and metallographic (× 100) microscopes (see drawing, b) indicate that the coatings have a fine crystalline structure with block crystal growth.

The advantages of industrial use of the claimed electrolyte

1. The complex of zinc with lactic acid can be easily destroyed at the stage of wastewater treatment, by shifting the pH value above 5.

2. The electrolyte is relatively simple in composition, does not contain toxic organic additives, and allows to obtain good quality coatings with a rather high cathodic current output.

3. Lactic acid, unlike organic additives used in galvanizing electrolytes, is easily oxidized and does not create additional difficulties when disposing of spent electrolyte and wash water.

Table 1 Dependence of the cathodic current efficiency of zinc on the cathodic current density. i _k , A / dm ² 0.1 0.25 0.5 1,0 2.0 3.0 4.0 BT,% twenty 40 68 65 51 35 25

table 2 The dependence of the cathodic current efficiency of zinc on the concentration of zinc ions at a current density of 1.0 A / DM ² [Zn ²⁺ ], mol / L 0,022 0,043 0.129 0.173 BT,% thirty 45 74 77

Table 3 The dependence of the cathodic current efficiency of zinc on the concentration of lactic acid [Hlact], ml / l 5 10 twenty 40 BT,% 65.7 64.6 68,4 65.0

Table 4 The dependence of the cathodic current efficiency of zinc on pH at a cathodic current density of 1.0 A / DM ² pH 1,0 2.0 3.0 4.0 BT,% 31.3 76.8 84.6 93.9

Table 5 The dependence of the cathode current efficiency of zinc on temperature t, ° C 10 twenty 40 60 BT,% 55 70 75 85

Literature

1. Electroplating coatings in mechanical engineering. Directory. In 2 volumes / Ed. M.A.Shluger. - M.: Mechanical Engineering, 1985. - T.1. 1985.240 s., S.

2. GOST 490-2006 Food dairy acid. Technical conditions - M., Standartinform, 2007.

Claims (1)

A method of applying zinc plating to zinc, including the deposition of zinc from an electrolyte containing sulfate or zinc oxide and water, at a cathodic current density of 1.0-1.5 A / DM ² , characterized in that the deposition is carried out from an electrolyte containing zinc sulfate or zinc oxide in an amount of 0.075-0.185 mol / l, lactic acid (80%) - 10-20 ml / l, at an electrolyte temperature of 20-25 ° C, pH 2.0-4.0 using a graphite anode.

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