SU1629356A1 - Electrolyte for tin alloy plating - Google Patents

Description

one

(21) 4477062/02

(22) 06.28.88

(46) 02.23.91. Bul N 7

(71) Institute of General Inorganic Chemistry, Academy of Sciences of Ukraine

(72) L.V. Bogdanovich, N.M. Sarnavsky, N.H.Tumanova and V.F.Lapshin

(53) 621.3577.:669.6.73 (088.8) (56) USSR Author's Certificate No. 637466, cl. C 23 P 3/60, 1978.

USSR Author's Certificate number 531897, cl. C 25 P 3/60, 1976.

(54) ELECTROLYTE TO DEPRESS COATINGS BY TIN ALLOY

(57) The invention relates to the electrochemical coating of metals, namely tin-cadmium alloy. The aim of the invention is to increase the corrosion resistance, the absorption of the coatings, as well as the stability of the electrolyte. The composition contains, g / l: cadmium sulfate 50-60, tin sulfate 30-40J sulfuric acid 80-100) ammonium formate 5-10, atony 1-2. An increase in corrosion resistance, electrolyte stability, and improvement in consumption are achieved through the introduction of ammonium formate and etonium. 3 tab.

The invention relates to electroplating, in particular to the electrochemical deposition of tin-cadmium coatings from aqueous solutions, and can be used in mechanical engineering, shipbuilding, as well as in electronics and radio engineering.

The purpose of the invention is to increase the corrosion resistance and the consumption of coatings, as well as the stability of the electrolyte.

The process is carried out when applying cathodic polarization at room temperature (), current density 0.5-2.0 A / dm i, for 20 minutes using anodes made of tin-cadmium alloy (1: O and cathode of various types of steel.

The optimal electrolyte composition and electrolysis conditions, providing high-quality gloss coatings, are listed in Table 1.

Comparative results of the study of the properties of coatings are given in Table 2, specific examples of implementation are given in Table 3.

Sulfates of tin and cadmium are sources of ions of discharging metals. Their content in solution depends on the composition of the resulting coating. Maximum CdSO Concentration. it is 60 g / l, since with a further increase in the salt concentration in the electrolyte, the content of cadmium in the coating does not change. At a CdSO concentration of less than 50 g / l, traces of metallic cadmium are found in the coating.

Ammonium formate is a complexing agent with which it is possible to control the composition of the resulting alloy with a constant concentration of Cd and Sn in solution. Ant

with

CO O1

about

rez Sn

Acidic ammonium, forming a strong complex with tin ions, causes a certain inhibition of the discharge reaction, reducing the discharge current Sn 2 f, which leads to a relative increase in the discharge current ЈA and an increase in the cadmium content in the alloy. In addition, the binding of the 8n (KNe) complex into the complex eliminates the possibility of hydrolysis of tin salts, which leads to the stabilization of the solution.

Thus, the addition of ammonia formic acid allows to control the composition of the precipitate, helps stabilize the solution, and also, due to its complexing properties, promotes the release of metal as a crystalline precipitate, rather than dendrites, which precipitate from the same solution without ammonium formate. The maximum limiting concentration of ammonium formic acid as a complexing agent is determined by the concentration of tin salts. An excess of salts is undesirable, since a certain acidity of the solution must be maintained. The determination of the minimum concentration (5 g / l) of ammonium formate depends on both the cadmium content in the coating and the solution cloudiness over time due to the hydrolysis of tin salts.

When etonium is introduced into the electrolyte as a surfactant, the structure of the sediment becomes even smaller due to the manifestation of inhibiting surface-active properties. From a solution containing ammonium formic acid and this, it is possible to obtain fine crystalline, dense glossy precipitates of Sn – Cd alloy. Etonium, as a surfactant, also provides good adhesion and uniformity of coating thickness.

The concentration of etoni is determined by its use as a surfactant, i.e. in trace amounts in relation to the volume of the solution. With a lack of etonium, separate large crystals are visible on the surface of the coating. Excess surfactant leads to a dark sediment, the formula etoni C30H62.

The content of sulfuric acid is determined by the need to provide a pH of 3-5 in the solution, since as the pH increases, the hydrolysis of the tin salts increases, which destabilizes the solution, and as the pH decreases,

0 25 30

35

40

45

50

55

The thickness of the coatings is due to the partial dissolution of the sediment.

At a current density of 0.3 A / dm and an optimal composition of the electrolyte, a thin coating with a lumen is formed on the substrate. At values of current density above 2 A / dm, the deposition rate of the alloy increases, and dendrites appear on the surface. Therefore, the optimum current density can be considered as values in the range of 0.5-2.0 A / dm (Table 2) ..

To prepare the electrolyte, all salt components are dissolved in a small amount of water, etonium, sulfuric acid is added and poured into a bath, followed by the volume of electrolyte. adjusted to a predetermined dilution rate with water.

After electrolysis, the steel samples serving as the cathode are removed from the solution, washed and dried, and then subjected to microscopic and X-ray phase analysis. Microscopic examination was carried out using an MIM-7 microscope, X-ray phase - on a DRON-1 apparatus with Fe K-d radiation. The thickness of the coating is determined by a magnetic thickness gauge.

The proposed electrolyte provides for obtaining high-quality coatings of tin-cadmium alloy with a high content of cadmium in the alloy (12-14%), which allows to improve the corrosion properties, the coating capacity and the stability of the electrolyte.

Claims (1)

Invention Formula The electrolyte for the deposition of coatings with a tin alloy, mainly a tin-cadmium alloy containing sulphate of tin and a co-precipitated metal, sulfuric acid and a surfactant, characterized in that it additionally contains ammonium formate, and as the sulfate salt of the metal being co-precipitated and the surfactant is cadmium sulfate and etonium, respectively, in the following ratio of components s, g / l: Sulphate cadmium50-60 30-40 80-100 The influence of various factors on the process The number of components Note. 1.5 A / dm Known electrolyte 440 2UO The proposed electrolyte 40 1.0 5.0 80 FROM Formic acid ammonium Etonius table 2 6.0 3.0 Light gray, fine crystalline 11-12 After 25 Light gray, finely crystalline, non-turbid, glossy ieet