SU1135811A1 - Method for reinforcing bottom of aluminium electrolytic cell - Google Patents

Abstract

A METHOD FOR STRENGTHENING ON; ALUMINUM ELECTROLYZER CINS, including the introduction of titanium or zirconium into the electrolyte with an oxidation at the bottom of refractory titanium and zirconium compounds, so that, in order to reduce the degree of contamination of electrolytic aluminum, titanium Zirconium is injected to an aluminum content of 0.5–4.0 wt.%, after which the boron compound is introduced in an amount that ensures the atomic ratio of boron to titanium and of zirconium within

Description

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x 1 The invention relates to non-ferrous metallurgy, in particular to the lining of electrolysis cells for the production of aluminum. There is a known method of lining electrodes, according to which cathodes consisting of graphite blocks are coated on top and side with a layer of borides, nitrides, carbides or silicides of metals of the first subgroups of the 4,5- or 6th group of the periodic system of elements. The coatings from the above materials are applied to the blocks by hot pressing. The disadvantage of this method is its complexity, i.e. Special equipment is required to provide hot pressing, which, with an increase in the dimensions of the cathode blocks, must also increase in size. In addition, when performing installation work from such blocks, seams remain between the blocks, which themselves dramatically reduce the reliability of operation of the hearth. There is also a known method of treating the bottom of the electrolyzer, according to which the carbon bottom is coated with a layer of titanium borides, titanium carbides or silicon carbides with a thickness O, 1 mm or more by means of plasma 2j. The disadvantages of the method are the complexity of the equipment, the large labor costs of applying the coating by the plasma method. W The closest to the technical essence of the invention and the achieved effect is a method of hardening electrodes, according to which a refractory metal (titanium or zirconium) or its compounds is introduced into the electrolyte to obtain a protective layer on the carbon cathode. A protective layer of carbides forms directly during the operation of the electrolyzer Z. A disadvantage of this method is that with the introduction of any electrolyte bath into the electrolyte, any compounds, especially high-melting metals (zirconium, titanium, silicon), increase the protective properties of the hearth. sodium, electrolytic aluminum is heavily polluted. The high content of pr 12 months of heavy metals in aluminum (more than 0.1%) impairs the electrical and casting properties of aluminum, which makes it almost impossible to use aluminum as a commercial product. The purpose of the invention is to reduce the degree of contamination of electrolytic aluminum. This goal is achieved by the fact that according to the method of hardening the bottom of the aluminum electrolysis cell, including the introduction of titanium or zirconium into the electrolyte with deposition of refractory compounds of titanium and zirconium on the bottom, the latter are introduced to an aluminum content of 0.5-. 4.0 May %, after which the boron compound is introduced in an amount that provides the atomic ratio of boron to titanium or zirconium within (2-3): 1. The initial introduction of titanium and zirconium prevents the formation of aluminum carbide on the surface of the bottom and makes it possible to realize the reaction of the interaction of carbon with titanium and zirconium with the formation of a dense layer of carbides. The subsequent introduction of boron leads to the interaction of boron with titanium and 1chrconium in the volume of liquid aluminum and the precipitation of titanium and zirconium borides from this volume onto the carbidized surface of the carbon graphite bottom. Titanium and zirconium borides crystals, having a specific weight significantly exceeding the specific weight of aluminum, are deposited under the influence of gravitational forces and temperatures, fill all unevenness on the bottom, sintered with a carbide layer, and thus a mixed protective carbide-boride layer of the coating is formed on the carbon graphite. . After reducing the content of titanium and zirconium in the alloy to 0.01%, commercial aluminum is obtained due to the increase in borides. When the content of titanium or zirconium in aluminum is below 0.5%, the formation of titanium and zirconium carbides on the surface is difficult due to the reduced activity of titanium and zirconium, a. When the content is higher than 4% intensively, AlaTi fAl.Zr compounds precipitate, which causes contamination of the electrolytic aluminum.

3,

When the atomic ratio of boron to titanium or zirconium is less than 2: 1, titanium and zirconium partially remain in aluminum, while titanium and zirconium borides are practically not precipitated. When the ratio is more than 3: I, free boron remains in aluminum, which also adversely affects the properties of electrolytic aluminum.

Example I. On a laboratory electrolyzer with a current of 40 A, a carbon-graphite sample is held under the cathode metal (aluminum containing 0.5% Ti) for 2 hours at 1050. A slot of I mm width and 2 mm depth is made in the sample. Mass of metal

"It is 180 g. Cathode current density is 86 A / cm. After that, 73 g of alyuts were added to the alloy, containing 0.83% boron (the B: Ti atomic ratio was 3: 1 in the resulting alloy).

After a five hour hold, the sample is removed from the bath. The surface layer and the product from the slot are subjected to X-ray phase analysis, which showed the presence of A1, TiB, AljTi in them, both on the sample surface and in the slot. In the cathode metal, the titanium content decreased to 0.008%.

Example 2. In the same electrolyzer, the sample is held under the cathode with aluminum containing 4.0% Zr, 48 hours at 950 °. The mass of the metal is 180 g. The cathode has a current density of 0.87 A / cm. After that, 205 g of aluminum containing 0.83% boron was introduced into the alloy (atomic ratio B: Zr in the resulting alloy

2.0: 1). After 1 hour watch 58II 4

The zirconium content in the alloy decreased to 0.007%. X-ray analysis of the surface layer of the sample and the material from the slot showed the presence of A1, 2 gVl, in them.

An example of an RZ. In an industrial bath of apemenia, 30 kg of titanium sponge is introduced. 12 hours after the introduction, titanium dissolves in aluminum and its concentration in the alloy is 0.93% by weight. Bath works at 965-9 70s 2 days. Then boron is introduced into the bath in the form that is added to the electrolyte in a mixture of cryolite 5-10 kg per day. A total of 61 kg was introduced, which provides a boron to titanium atomic ratio of 2.8: 1. 8 days after the start of the introduction of B, the co-concentration of titanium in aluminum

0 decreases to 0.008 wt.%. A bath with a hearth strengthened in this way will last 6.2 years.

The results of the experiments are given in the table.

5 Thus, it is clear from the examples j that the proposed method allows to simplify the coating and fill the seams with it. The industrial electrolyzer with the hearth processed by the proposed method worked for a long time - 1.2 years longer than the baths with the raw hearth.

The use of the proposed method of hardening the surface layer of a carbon bottom aluminum electrolyzers, compared with the known, provides a reduction in material, energy and labor costs, the possibility of improving the quality of ashomini and the service life of aluminum electrolyzers. I

The ratio of boron to titanium (or zirconium) in the mixed melt, at. May

Laboratory Laboratory Industrial {C; omyshphen (known. electrolysis}

Table continuation

Term

Service content of titanium (or zirconium)

electrolyzer, after aging,% h

0.008 0.007 0.008

6.2 5.0

Claims (1)

METHOD FOR STRENGTHENING THE BOTTOM OF AN ALUMINUM ELECTROLYZER, comprising introducing titanium or zirconium into the electrolyte with deposition of v on the bottom of the refractory compounds of titanium and zirconium, and it is necessary to introduce titanium or zirconium into the electrolyte to reduce the degree of contamination until their content in aluminum is 0.5-4.0 wt.%, after which a boron compound is introduced in an amount providing an atomic ratio of boron to titanium or zirconium in the range (2-3): I. II3581 I