SU1227717A1 - Method of protecting graphitized and carbon electrodes from oxidation - Google Patents

Description

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The invention relates to non-ferrous metallurgy, in particular to the electrolytic refining of aluminum, and can be applied in other areas of metallurgy, where comfort is used with electrodes made of carbon-containing materials.

The purpose of the invention is to increase the lifetime of the electrodes.

According to the proposed method i, the impregnation is carried out at a cathode current density of 0.5-1.0 A / cm in a two-layer bath with full immersion of the graphite part into the electrolyte, the layer height of which is 1.2-1.8 times the height of the graphitized part of the electrode .

The indicated mode of impregnation of graphitized electrodes, while reducing the duration of impregnation by 4–12 times, ensures that the entire surface of the electrodes is impregnated to the required depth. The main factor influencing the wetting of graphite with electrolyte and,; therefore, at the rate of impregnation, is the cathode current density.

The highest impregnation rate is achieved at a current density of 0.5-1.0 A / cm. With a cathode current density of less than 0.5 A / cm, the impregnation rate is significantly reduced, and therefore the impregnation time increases, the power consumption increases. Current density at the cathodes. more than 1 A / cm is practically unrealizable, because of the high current strength, the electrodes overheat with the melting of the aluminum lead rod, and the electrolyzer as a whole overheat, which leads to a violation of the technological mode on the electrolyzer.

A prerequisite for this: the speed and uniformity of impregnation over the entire surface of the electrodes is fully immersed in the electrolyte. It has been found that when the upper part of the electrode is immersed in the cathode metal layer, the impregnation rate decreases and the upper part of the electrode is not impregnated with electrolyte. Full immersion of the electrodes in the electrolyte layer in the presence of a cathode metal layer is impossible due to the dissolution of the steel nipple in aluminum. Thus, complete immersion of the electrodes can be achieved with the elimination of the cathode metal layer, i.e. in a two-layer bath.

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The height of the electrolyte layer should be at least 1.2 of the height. rafit part of the electrode. Otherwise, with the full immersion of the electrode in the electrolyte, due to the small distance between the bottom surface of the electrode and the anode alloy, there is a significant uneven distribution of density, current on the surface of the electrode, and as a result, the speed and uniformity of impregnation of the electrode decrease. The upper limit of the height of the electrolyte layer (1.8 from the height of the electrode) is due to the fact that with a larger height of the electrolyte layer the electrical resistance increases so much that the temperature of the electrolyte and anode alloy overheats above the allowable limits and thus disrupts the electrolyzer process mode.

The duration of the impregnation is determined by the size of the electrodes and the parameters of the impregnation mode. The duration of the impregnation of less than 6 hours does not provide the necessary depth of impregnation, which leads to an increase in the oxidation of the electrodes of the electrodes and a decrease in their service life. For 12 hours, a full impregnation of the entire volume of the electrodes takes place and the further removal of the electrodes in the electrolyte is impractical.

The method of protection of graphite electrodes was tested on a laboratory .-. Installation.

Example 1. Chloride-fluoride electrolyte composition, wt.%: BaClx 60, NaF 17, AlFj 23 at the temperature introduced an anode alloy comprising 35%. Cu and 65% Al, installed, a graded electrode with a current lead element. so that the graphite part of it was completely immersed in the electrolyte, and the distance from the bottom of the electrode to the anode one. , The alloy was 0.8 heights of the graphitized part of the electrode. When a direct current was included in the circuit, the graphitized electrode was a cathode, and the current density was 1, OA / cm. Under these conditions, the graphitized electrode was impregnated, and the impregnation rate was determined by systematic weighing of the electrode. The rate of electrolyte penetration into the electrode is 20 mm / h.

Example 2. The same procedure was used to impregnate electrodes in other modes.

The test results are summarized in table.

The table shows that the proposed impregnation modes of the electrodes provide an impregnation rate of 15 to 20 mm / hour. For electrodes used in industry, for impregnation to a depth of 900, 4 0.5

0.8 1.0 0.8, 0.8 0.8 0.8

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 The upper part of the electrodes is not impregnated.

Editor M. Dylyn

Order 2267/30 Circulation 615 Subscription

VNIIPI USSR State Committee

for inventions and discoveries 113035, Moscow, Zh-35, Raushsk nab., 4/5

Production and printing company, Uzhgorod, st. Project, 4

227717 4

250 mm duration of impregnation 6- I 2.

The proposed method allows reducing the consumption of graphitized blocks by 15%, reducing the power consumption by 250 kWh per ton of refined aluminum, and increasing the productivity of the refining body by 1.5%.

nom metal, 2/3 in electrolyte

1/2 in the cathode metal

1/2 in electrolyte

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Compiled by A. Arnold

Tehred L.Oleynik Proof-reader S. Cherni

Claims (1)

METHOD FOR PROTECTING GRAPHIC. AND COAL ELECTRODES FROM OXIDATION, including impregnation of electrodes with molten salts of alkali and alkaline earth metals while maintaining the electrode at the cathode potential and cathode current density of 0.5-1.0 A / cm ² , characterized in that, in order to increase the service life of the electrodes, impregnation carried out in a two-layer bath with a complete immersion of the carbon-graphite part in an electrolyte, the layer height of which is 1.2-1.8 the height of the carbon-graphite part of the electrode - - _with <o SU ,,, 1227717 1'227717