RU2255150C1 - Silver powder production method - Google Patents

Abstract

FIELD: powder metallurgy, namely production of silver powder from aqueous electrolyte solution.

SUBSTANCE: method comprises steps of electrolytic deposition of silver on cathode by action of negative and positive electric current pulses while varying relations of negative and positive pulses of electric current in range (4 -20) : (1 - 5). According to invention deposition of silver is realized on rotary cathode whose axis is arranged in parallel relative to upper surface of electrolyte at revolution number of cathode 7 - 12 rev per min.

EFFECT: enhanced fineness and uniformness of powder particles.

6 cl, 1 tbl, 1 ex

Description

The invention relates to powder metallurgy, in particular to the production of silver powder by electrolysis from an aqueous electrolyte solution.

A known method of producing silver powder (AS USSR No. 1177397 from 09/07/1985, bull. No. 33), which consists in the fact that the cylindrical cathode is located between the anodes and the electrolysis is carried out at constant current.

The disadvantage of this method is that it does not provide a powder with a high dispersion, since during the electrolysis of direct current from an aqueous solution of silver nitrate, the growth of silver crystals occurs unevenly.

The closest analogue is a method for producing silver powder on a flat cathode by electrolysis using pulsed current (RF Patent No. 2210631 from 2000.12.26, IPC ⁷ , C 25 C 1/20).

This method consists in the fact that high dispersion is achieved by alternating exposure to pulses of positive and negative polarity, and the ratio of the power of the cathode and anode components is set both by the duration and frequency of the pulses, and their amplitude. However, this method does not allow to obtain silver powder with high uniformity, since, for example, at the edges of a flat cathode, the local current density is always higher than in the middle of the cathode. As a result of this redistribution of current, larger silver particles are formed at the edges.

The invention is aimed at increasing the dispersion and uniformity of the formation of particles of powdered silver.

Obtaining silver powder with uniform dispersion is carried out by deposition of silver on a rotating cylindrical cathode when exposed to current pulses of negative and positive signs with varying ratios of current pulses of negative and positive signs as / 4-20 /: / 1-5 / at a cylindrical cathode speed of 7-12 rev / min, and the axis of the cylindrical cathode is parallel to the level of the electrolyte and a smaller part of the circumference of the cylindrical cathode is located in the electrolyte.

Precipitated silver is removed from the surface of the cylindrical cathode, which is located outside the electrolyte, and silver powder is obtained.

The particle size of the silver powder is regulated by the amplitudes of the current pulses of the negative and positive signs, their duration and repetition rate, as well as the time spent on the surface of the cylindrical cathode in the electrolyte.

During rotation and exit of the surface of the cylindrical cathode from the electrolyte, the growth of silver crystals stops simultaneously along the entire length of the outgoing surface of the cylindrical cathode, thereby increasing the dispersion and uniformity of the formation of particles of powdered silver.

The method is confirmed by the following example.

A cylindrical stainless steel cathode was fixed on a shaft connected through a seal in the wall of the electrolyzer to an electric motor and gearbox, which allowed changing the rotation speed from 1 to 12 rpm.

As the electrolyte used a solution of the composition, wt.%: AgNO ₃ - 15-20; HNO ₃ - 4-5. Alternating packets of pulses with a frequency of f = 100 Hz and an amplitude of 15 V were applied to the electrolyzer, and the ratio of the cathode and anode components was used as 10: 1. The cathodic current density is 5 A / dm ² , t = 50 ° C. Anodes made of silver (Ag 99.99).

After electrolysis, the dispersion of silver particles was determined by the proposed method by measuring their linear sizes on a SM LUX HL microscope. For each cylinder rotation speed, 10 particles were selected from different parts of the silver powder from different parts. The results of particle measurements are given in the table.

Table №№ Particle size x _i silver powder, microns No rotation Drum rotation at a speed of V, rpm 1 3 5 7 10 12 1 33.5 8.0 11.0 5,0 0.5 2,5 2,5 2 16.5 2,5 0.5 5.5 2.0 0.5 2.0 3 8.0 13.0 6.0 6.5 1,5 3.0 1,0 4 12.0 10.5 3,5 8.0 3,5 0.5 0.5 5 21.0 6.5 7.0 9.0 2,5 2.0 1,5 6 6.0 8.0 8.5 1,5 0.5 3,5 2,5 7 20.5 20.5 12.5 0.5 2,5 1,5 0.5 8 29th 12.0 9.5 2,5 0.5 2,5 0.5 nine 24.5 11.5 5.5 10.5 2,5 3.0 1,0 10 2,5 1,5 10.5 6.0 0.5 0.5 0.5

17.5 9.5 7.5 5.5 1.7 2.0 1.3

8.4 4.1 3.0 2,5 0.95 0.95 0.7 Note:

- average particle size

- average deviation from the average particle size of silver

From the table it follows that without rotation, the average deviation from the average particle size of silver is 8.4 microns. At a rotation speed of 1 to 5 rpm, the average deviation from the average particle size of silver is reduced to 2.5 μm. The maximum dispersion and the minimum average deviation from the average particle size of silver is achieved at a cathode rotation speed of 7-12 rpm and is ≤0.95 μm. With a further increase in the rotation speed, the particle size remains practically unchanged, however, the productivity of the process for producing silver powder decreases.

Silver can also be deposited on a cylindrical cathode, half of which is located in the electrolyte, or most of which is located in the electrolyte.

Claims (6)

1. A method of producing silver powder, including electrolytic deposition of silver on the cathode when exposed to current pulses of negative and positive signs by varying the ratio of current pulses of negative and positive signs, as (4-20) :( 1-5), characterized in that the deposition of silver carried out on a rotating cathode, the axis of which is parallel to the electrolyte level, at a cathode rotation speed of 7-12 rpm 2. The method according to claim 1, characterized in that the deposition of silver is carried out on a cylindrical cathode. 3. The method according to claim 1, characterized in that the deposition of silver is carried out on a cylindrical cathode, a smaller part of the circumference of which is located in the electrolyte. 4. The method according to claim 1, characterized in that the deposition of silver is carried out on a cylindrical cathode, half of the circumference of which is located in the electrolyte. 5. The method according to claim 1, characterized in that the deposition of silver is carried out on a cylindrical cathode, most of the circumference of which is located in the electrolyte. 6. The method according to claim 1, characterized in that the particle size of the silver powder is controlled by the residence time of the surface of the cylindrical cathode in the electrolyte.