RU2341592C1 - Method of plating by tin - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: method includes electrolyte preparation and tin settling, at that electrolyte is prepared by dissolution in distilled water 13-17 g/l of five-aquatic tin chloride (IV) in terms of metal and 140-160 g/l of lactic acid (80%) with electrolyte isolation during 24 hours at temperature 17-25°C for forming of lactate tin complex, and settling is implemented at cathode current density 0.5-1.0 A/dm², electrolyte temperature 20-28°C with usage of graphitic anode.

EFFECT: receiving of semiglittering, well-hitched to basis platings, increasing of outlet as current.

4 tbl, 1 ex

Description

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

Electrochemical tinning is carried out both in acidic and alkaline solutions. Solutions of tin salts based on sulfuric, hydrochloric, hydrofluoric, phenolsulfonic acids are used as acidic electrolytes, and stannate and pyrophosphate are used as alkaline.

In acidic electrolytes currently used in industry, tin is in a divalent state.

As an example, electrolytes of the following compositions (g / l) can be given [3]:

1. Tin (II) sulfate - 51; sulfuric acid - 100; joiner's glue - 2; technical phenol - 30. The process is carried out at a temperature of 20-30 ° C and a cathode current density of 1-3 A / dm ² [3].

2. Tin (II) sulfate - 25-50; sulfuric acid - 80-100; technical o-cresol - 8-10; joiner's glue - 1-2; 1,4-butynediol (35% solution) - 25-50 ml / l. The process is carried out at a temperature of 18-25 ° C and a cathodic current density of 2-7 A / dm ² with vigorous stirring [3].

In the absence of a surfactant, tin is released from these electrolytes without noticeable polarization. In this regard, precipitates obtained from acidic electrolytes without special organic additives are coarse-grained and become friable even with a small thickness. Dense, fine-grained tin coatings can be obtained from acidic electrolytes only by introducing special organic substances into them that increase the cathodic polarization. Moreover, precipitates of the best quality are obtained when several organic additives are added to the electrolyte at the same time [1, 2, 3]. So, for example, in electrolyte 1, a prerequisite is the use of technical phenol, which contains various organic substances as impurities, which contribute to the production of tin coatings of good quality. The content in the tinning solutions of a large number of various organic substances not only complicates the process of disposal of spent electrolyte and wash water, but also does not allow maintaining the concentration of most organic additives at a constant level, since for most of these additives there are only qualitative analysis methods.

Another significant drawback of acidic electrolytes containing tin salts with an oxidation state of +2 is their instability in operation, since tin (II) is oxidized, which significantly impairs the quality of the coating. In this regard, in these electrolytes, often during the coating process, it is necessary to add hydrogen peroxide or perhydrol and monitor the condition of the tin anodes (they must have a golden yellow color).

Of the known electrolytes, the closest in composition and technological characteristics is an electrolyte containing: 20-51 g / l of tin (II) sulfate, 100 g / l of sulfuric acid, 2 g / l of wood glue, 30 g / l of phenol. The range of operating temperatures is 20-30 ° C. The working current density of 1.0-3.0 A / DM ² [3].

In addition to tin ions, this electrolyte contains toxic organic substances, which makes it difficult to dispose of this electrolyte and purify the washings.

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

This is achieved by the fact that the electrolyte is prepared by dissolving 13-17 g / l of tin (IV) pentachloride in distilled water in terms of metal and 140-160 g / l of lactic acid (80%) with an electrolyte exposure of 24 hours at a temperature of 17 -25 ° C for the formation of the tin lactate complex, and deposition is carried out at a cathodic current density of 0.5-1.0 A / dm ² , an electrolyte temperature of 20-28 ° C using a graphite anode.

In an acidic electrolyte, tin (II) is replaced by tin (IV), which prevents its oxidation at the anode and in the electrolyte volume and the replacement of toxic complexing agents with a less toxic one - lactic acid. Lactic acid is widespread in nature, it is an intermediate in the metabolic process in biological tissues, it is easily biodegradable and therefore environmentally friendly.

The preparation of the electrolyte is as follows. According to the electrolyte composition, pentachine chloride of tin (IV) is dissolved in distilled water. Then add lactic acid, bring to the working volume with distilled water and mix. The electrolyte must be kept for 24 hours at a temperature of 17-25 ° C for the formation of the tin lactate complex.

An example of a specific implementation of the method.

For the electrochemical deposition of high-quality semi-brilliant, well-bonded tin coatings, an electrolyte of the following composition was prepared: tin (IV) pentachloride (in terms of metal) - 15 g / l, lactic acid (80%) - 150 g / l.

The deposition was carried out at a cathodic current density of 1.0 A / DM ² and a temperature of 20 ° C without stirring, because mixing this solution dramatically affects the quality of the precipitate and reduces the cathode current output. Graphite was used as anode material. The cathodic current efficiency was 95-98%, and the dissipating ability of the proposed electrolyte for metal was 43%, and for current it was 90%.

Tables 1-4 show the experimental data of the dependences of the cathode current output on the parameters of the deposition method.

The advantage of industrial use of the inventive electrolyte:

1. Tin is highly oxidized and therefore not oxidized. Thus, a stable electrolyte is obtained.

2. Complexes of tin with lactic acid can be easily destroyed at the stage of wastewater treatment by shifting the pH value above 6.

3. The electrolyte is relatively simple in composition, does not contain toxic organic additives, has good dispersing ability, and allows to obtain coatings of good quality.

Table 1. Dependence of the cathodic current output of tin on the cathodic current density. i _k , A / Dm ² 0.3 0.5 0.7 one 1,2 1,5 2 3 BT,% 95 96 90 87 82 78 73 57 Table 2. The dependence of the cathodic current output of tin on the concentration of tin ions at a cathodic current density of 0.5 A / DM ² . [Sn ⁺⁴ ], g / l 5 10 fifteen twenty BT,% 79 95 91 86 Table 3. The dependence of the cathodic current output of tin on the concentration of tin ions at a cathodic current density of 1 A / DM ² . [Sn ⁺⁴ ], g / l 5 10 fifteen twenty BT,% 68.5 87 97 93 Table 4 Dependence of the cathode current output of tin on the concentration of lactic acid. [Hiact], ml / l fifty one hundred 150 200 250 BT,% 93.7 95.5 98.6 97.3 84

Information sources

1. Yampolsky A.M., Ilyin V.A. Quick reference electroplating. - 3rd ed., Revised. and add. - L .: Engineering, Leningrad. Department, 1981. p. 124.

2. Larin I.O., Maksimenko S.A., Tyutina K.M., Kudryavtsev V.N. The influence of some organic substances on the oxidation of tin in acidic electrolytes for the deposition of tin and its alloys. Progressive technology and environmental issues in electroplating and PCB manufacturing: Conference proceedings. Penza, 1996.S. 6.

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

Claims (1)

A method of applying tin plating, including the preparation of an electrolyte and the deposition of tin, characterized in that the electrolyte is prepared by dissolving 13-17 g / l of pentachloride tin (IV) in distilled water in terms of metal and 140-160 g / l of lactic acid (80 %) with an electrolyte exposure of 24 hours at a temperature of 17-25 ° C to form a tin lactate complex, and deposition is carried out at a cathode current density of 0.5-1.0 A / dm ² , an electrolyte temperature of 20-28 ° C using graphite anode.