RU2393943C2 - METHOD OF PRODUCING SILVER POWDERS "ПСр1" AND "ПСр2" - Google Patents

Abstract

FIELD: process engineering.

SUBSTANCE: invention relates to powder metallurgy, in particular, to production of electrolytic powders. To produce silver powders, silver is settled down from electrolyte containing hydrogen nitrate silver nitrate at electrolyser plant comprising soluble anode made from silver and cathode. Flocculants "АК" or "Магнафлок" are added as polyacrylamide-based surfactants into electrolyte in amount of 30-200 mg per 1 kg of produced silver powder. Deposition is performed at revering current and periodic change of anode and cathode polarity.

EFFECT: high yield of powders.

1 tbl, 1 ex

Description

The method for producing silver powders PSr1 and PSr2 relates to powder metallurgy, in particular to the production of electrolytic powders.

Silver powders PSr1 and PSr2 are obtained by the electrolytic method and are used for the production of cermet contacts and other conductive products. According to the requirements of TU 48-1-702-87 [1], the content of impurities and particle size PSR1 and PSr2 powders have some differences. In particular, PSr1 powders have a fineness of (-56) μm, and PSr2 (larger) - (-160) μm. According to the admissible content of impurities, both brands have the same values. The mass fraction of impurities in the powders upon their receipt mainly depends on the purity of the used reagents and the anode metal. The size of the silver powder is directly dependent on the parameters of the electrolysis process.

A known method for producing silver powders PSr1 and PSr2 [2], including the deposition of silver from an electrolyte containing nitric acid and silver nitrate, in an electrolysis unit with soluble silver anodes at constant current. The method adopted for the prototype.

The disadvantage of this method is the low yield of powders PSr1 and PSr2.

The technical result, the achievement of which the invention is directed, is the elimination of these disadvantages.

The desired technical result is achieved by the fact that in the known method for producing silver powders, including the deposition of silver powder from an electrolyte containing nitric acid and silver nitrate, in an electrolysis installation containing a soluble silver anode and cathode, AK or Magnaflock flocculants are added to the electrolyte "As a surfactant based on polyacrylamide at the rate of 30-200 mg per 1 kg of the obtained silver powder, and the deposition of silver powder is carried out at a reverse current with periodic changes in the polarity of the anode and cathode.

The essence of the method is as follows. According to (1), silver electrolytic powders of the PSr1 and PSr2 grades must have a fine-crystalline structure with a particle size of not more than 56 μm and not more than 160 μm, respectively. When silver is electrolyzed, solutions of its nitrate produce coarse-grained precipitates (3). This is probably due to the fact that silver has a high exchange current and most of its cations reduced at the cathode to metal are involved in crystal growth and only a small fraction in nucleation. When surfactant additives based on polyacrylamide are introduced into the electrolyte (AK, Magnaflock flocculants, etc.) and subsequent electrolysis, surfactant is adsorbed on the cathode surface, thereby creating a layer of increased electrical resistance, which in turn prevents the growth of crystals on cathode and contributes to the process of nucleation. The particle size of the resulting silver powders varies with the amount of surfactant additives. With the consumption of flocculants at the rate of 30-100 mg per 1 kg of the obtained silver powder, the yield of the PSr2 fraction is 97-98%, and the PSr1 powder is less than 50%. With an increase in surfactant consumption to 100-200 mg per 1 kg, a silver powder is predominantly formed, consisting of fine particles of PSr1, the proportion of which reaches 85-90%, while the yield of the PSr2 fraction also increases by 1-2%. Reducing the consumption of surfactants less than 30 mg per 1 kg of silver powder leads to the production of coarse-grained precipitates with a particle size of more than 160 microns. And an increase in flocculant additives of more than 200 mg per 1 kg of silver powder practically does not increase the yield of the desired quality, but leads to unproductive consumption of the reagent.

The silver powder that is formed during electrolysis must be separated from the cathode in order to prevent the formation of dendritic deposits. To do this, change the polarity of the electrodes (reverse current). In this case, nucleation and growth of powder particles occur in the cathode period, and in the anode period, the resulting powder is separated from the electrode, updating its surface, which further contributes to the process of nucleation.

Examples

To obtain PSr1 and PSr2 silver powders, an electrolysis unit with soluble silver anodes and titanium cathodes was used. The change in the direction of the current was carried out in automatic mode with a periodicity: after 1 minute of the forward current flow, switching for 20 seconds occurs with the reverse current flowing. The electrolyte consisted of a solution of silver nitrate with a concentration of 40-60 g / l and nitric acid 10-30 g / l. Before electrolysis, a surfactant based on polyacrylamide was added to the electrolyte solution in the form of a 0.1% solution. Flocculants of the AK and Magnaflock types were used as surfactants. The obtained powders were separated from the solution, washed in water, dried and analyzed by a sieve method for the content of fractions (-56 μm) and (-160 μm), which corresponds to the particle size in PSr1 and PSr2. The results of the experiments are presented in the table.

Table Experience number Type of flocculant Flocculant consumption, mg per 1 kg of silver powder The content in the powder fraction with particle size,%: Less than 56 μm (PSr1) Less than 160 microns (PSr2) one AK 10 25.9 47.8 2 65 45.3 97.4 3 150 88.6 98.9 four 300 89.3 98.4 5 Magnaflock 10 27.1 46.8 6 65 43.9 98.1 7 150 88.5 99.2 8 300 88.9 99.0

As can be seen from the above examples, the use of the proposed method allows to obtain silver powders with a high content of the product of a given size.

Literature

1. Specifications "Silver Powder" TU 48-1-702-87; GOSSTANDART OF RUSSIA, VNIIstandard, registered 04.17.97.

2. Kiparisov S.S .; Libenson G.A. Powder Metallurgy: Textbook for Technical Schools / 3rd ed .; reslave. - M: Metallurgy, 1991, p. 423.

3. Baimakov Yu.V., Zhurin A.I. Electrolysis in hydrometallurgy. - M.: Metallurgy, 1977, p.20.

Claims (1)

A method of producing silver powders of the PSr1 and PSr2 brands, including the deposition of silver powder from an electrolyte containing nitric acid and silver nitrate, in an electrolysis unit containing a soluble silver anode and cathode, characterized in that AK or Magnaflock flocculants are added to the electrolyte as a surfactant based on polyacrylamide at the rate of 30-200 mg per 1 kg of the obtained silver powder, and the deposition of silver powder is carried out at a reverse current with a periodic change in the polarity of the anode and cathode.