RU2308553C1 - Method for electrochemical deposition of cadmium - Google Patents

Abstract

FIELD: electroplating, namely electrochemical deposition of cadmium, possibly in different branches of industry for coating parts in order to protect them against corrosion.

SUBSTANCE: method comprises steps of electrical deposition from electrolyte containing, g/l: cadmium sulfate, 40 - 60; sulfurous acid, 20 - 40; sodium sulfate, 40 - 60; gloss-forming additive 3 -4 with structural formula

. Electrical deposition is performed at temperature of electrolyte 15 - 30°C, density of cathode electric current 9 - 12 A/dm² and at electric current yield 85 -98%.

EFFECT: possibility for applying coatings with smooth surface at high electric current density values.

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Description

The invention relates to electroplating, in particular to the electrochemical deposition of cadmium, and can be used in various industries for coating parts in order to protect them from corrosion.

For the electrodeposition of cadmium, a large number of electrolytes are known. To cover parts of a simple configuration, acid cadmium electrolytes are usually used.

Of acidic electrolytes, sulfate electrolytes containing various organic substances are quite widely used [1, 2]. Closest to the invention relates to a sulfate cadmium electrolyte of the following composition [2, p.178], g / l:

- Cadmium sulfate - 40-60

- Sulfuric acid - 40-60

- Sodium sulfate - 40-60

- The drug OP-10 - 2-5

Deposition mode:

- Temperature, ° С - 15-50

- Cathode current density, A / dm ² - 1-6

- Current output,% - 95-98

The disadvantages of this electrolyte are:

1. It turns matte finish.

2. Low working current density.

3. The electrolyte does not have a leveling ability.

The purpose of the invention is the development of cadmium electrolyte, which would make it possible to obtain shiny coatings with a level surface at high current densities.

The goal is achieved by the fact that in the cadmium electrolyte containing cadmium sulfate, sulfuric acid, sodium sulfate, a bright-forming additive (a product of the condensation of phenol with formaldehyde) is introduced with the structural formula

in the following ratio of components, g / l:

- Cadmium sulfate - 40-60

- Sulfuric acid - 20-40

- Sodium sulfate - 40-60

- Brightening additive - 3-4

Deposition mode:

- Temperature, ° С - 15-30

- Cathode current density, A / dm ² - 9-12

- Current output,% - 85-98

The concentration of cadmium sulfate must be maintained in the range of 40-60 g / l. Deviation from these limits leads to a decrease in the interval of working current densities for receiving glossy sediments.

The concentration of sulfuric acid should be in the range of 20-40 g / l. Deviation from these limits results in matte and semi-gloss coatings.

Sodium sulfate in the electrolyte increases electrical conductivity and does not affect the appearance of coatings.

The concentration of the brightening additive in the electrolyte should be in the range of 3-4 g / l. At a concentration of less than 3 g / l, semi-shiny coatings are obtained. At a concentration of more than 4 g / l - silver coating.

The current density in the proposed electrolyte should vary between 9-12 A / DM ² . For i _k <9 A / dm ^{2, the} coatings are semi-shiny, for i _k > 12 A / dm ² (up to 20 A / dm ² ) brilliant coatings are obtained, but the current efficiency of cadmium decreases quite strongly (at i _k = 20 A / dm ² current output equal to 50%).

The temperature of the electrolyte varies from 15 to 50 ° C. However, at temperatures above 30 ° C, the degree of gloss of coatings is somewhat reduced.

As anodes, cadmium grade KD0 or KD1 is used. To avoid contamination of the electrolyte with anode sludge, cadmium anodes should be enclosed in covers made of polypropylene fabric.

Correction of the electrolyte for CdSO ₄ , H ₂ SO ₄ , Na ₂ SO _{4 is} carried out according to chemical analysis. Correction of the electrolyte according to the bright-forming additive must be carried out after passing 200 A · h / l, adding 1 g / l of the additive to the bath.

The cadmium electrolyte is prepared as follows. Three quarters of the capacity for the preparation of the electrolyte is filled with distilled water and sulfuric acid is added to it with stirring in small portions. Then the required amount of cadmium sulfate and sodium sulfate is dissolved. The solution is filtered. With stirring, a brightening additive (previously dissolved in distilled water at a temperature of 25-30 ° C) is added to the filtrate, topped up with distilled water to a predetermined level, and the electrolyte is ready for use.

The table shows the proposed (1-3) and known (4-5) electrolyte compositions and conditions for the electrodeposition of cadmium coatings.

As can be seen from the table, the proposed electrolyte (1-3), in contrast to the known (4-5), allows to obtain shiny coatings with a level surface at high current densities with high current efficiency.

The obtained brilliant coatings from the proposed electrolyte have a beautiful decorative appearance, a fine crystalline structure, non-porous with a thickness of 6 μm, firmly adhered to the base metal.

Table Components g / l Electrodeposition conditions Compositions one 2 3 four 5 Cadmium sulfate 40 fifty 60 40 60 Sulphuric acid twenty thirty 40 40 60 Sodium sulfate twenty 40 60 40 60 Brightening Additive 3 3,5 four - - OP-10 - - - 2 5 Temperature ° C fifteen thirty thirty fifteen fifty Cathode current density, A / dm ² 9-12 9-12 9-12 1-6 1-6 Current output,% 85-93 92-95 93-98 95 96 Appearance of coatings brilliant matte Degree of Alignment * 0.2-0.3 0.2-0.3 0.2-0.3 0 0 * the degree of alignment was determined by direct profilographic method on a gentle sinusoidal microprofile according to the formula of S. S. Kruglikov [3, p.17].

Information sources

1. Ilyin V.A. Galvanizing, cadmium plating, tinning and lead. Ed. 5th, rev. and add. - L .: Engineering, Leningrad. Separation. - 1983 .-- 87 s. (B-galvanic engineering / Ed. By P.M. Vyacheslavov. Issue 2).

2. Kudryavtsev N.T. Electrochemical coatings with metals. M .: Chemistry. - 1979. - 352 p.

3. Workshop on applied electrochemistry. Textbook manual for Universities / N.G. Bakhchisaraitsyan, G.K. Burkat et al. / Ed. V.N. Varyapaev, V.N. Kudryavtseva. - 3rd ed., Revised. - L .: Chemistry. - 1990. - 304 p.

Claims (1)

The method of electrodeposition of cadmium from an electrolyte containing cadmium sulfate, sulfuric acid, sodium sulfate and water, characterized in that the electrodeposition is carried out at an electrolyte temperature of 15-30 ° C, a cathode current density of 9-12 A / dm ² with a current output of 85-98 %, while a brightening additive with the structural formula is introduced into the electrolyte

in the following ratio of components, g / l: cadmium sulfate 40-60 sulphuric acid 20-40 sodium sulfate 40-60 brightening additive 3-4