Refractory for aluminium electrolytic cell

Electrolytic cell is the core equipment for producing electrolytic aluminum. The electrolytic cells are usually rectangular steel shells lined with carbon bricks. A carbon anode is suspended in an electrolytic cell, the bottom of which is a cathode. Aluminum electrolysis using cryolite, aluminum fluoride, lithium fluoride molten electrolyte, at about 970 ℃ will melt Al2O3, under the action of electric field force, ionization, electrolytic reduction of aluminum melt deposited on the bottom of the channel cathode, anode release oxygen and carbon anode reaction CO ₂ or CO. The heat released by the electrochemical reaction keeps the electrolytic cell and aluminum molten, and the liquid aluminum released from the cell for a certain period of time is added to the cell with a certain amount of alumina and cryolite. The electrolysis temperature is 900~1000℃.

(1) Aluminum electrolytic cell cathode refractory

The main requirements of cathode materials for aluminum electrolytic cell are: good electrical conductivity and resistance to the erosion of cryolite, NaF and liquid aluminum under high temperature. The working layer at the bottom of electrolytic cell used to be built with carbon blocks. However, new compounds are formed due to the reaction of carbon and sodium, and the brick lining structure is relaxed, the strength decreases, and the carbon blocks appear cracks. Then the electrolyte and aluminum liquid permeate along the crack and react with aluminum and carbon to form Al4C3 at high temperature. Al4C3 is loosely bound to carbon, which makes the crack spread and ultimately leads to the deformation of the electrolytic cell shell and the serious erosion of the lining, shortening the service life. Therefore, the cathode material at the bottom of electrolytic cell is being changed from amorphous carbon brick to semi-graphitized or graphitized carbon brick.

(2) Aluminum electrolytic cell side wall materials

The main reasons for the damage of the inner lining of the side wall of aluminum electrolytic cell are as follows: the oxidation of the material caused by inhalation of air between the steel shell and the brick lining; Corrosion of cryolite, NaF and liquid aluminum at high temperature; Erosion caused by melt flow; Temperature fluctuation and thermal expansion cause thermal stress.

In the past, amorphous carbon blocks, graphite blocks, etc. have been used as the side walls of aluminum electrolytic cell. The most fatal disadvantages of these materials are poor oxidation resistance and low strength. In order not to oxidize the side wall, but also has excellent high temperature mechanical properties and good thermal conductivity, condensing slag is easy to form inside; High resistivity, reduce the side wall current loss; The material is not easily oxidized; Does not react with liquid aluminum, cryolite and other melts; High mechanical strength, but also greatly less lining brick thickness, increase the volume of electrolytic cell, stable operation. For example, the thickness of the side wall is about 200~400mm when the original carbon brick is used, and the thickness of the back wall of the silicon carbide brick combined with silicon nitride is only 75mm.

(3) The barrier layer under the trough

In the electrolytic aluminum production, the vapor and liquid of Na and NaF can penetrate into the thermal insulation layer below through the cathode material at the bottom of the tank. After the heat insulation layer penetrates into NaF, the thermal conductivity increases, the thermal efficiency of electrolytic cell decreases, and the working condition deteriorates until the tank is damaged. The cathode material under the "barrier layer" is sandwiching a layer of material between the cathode refractory and thermal insulation material to prevent electrolyte penetration, and has good thermal insulation performance. A new type of "barrier layer" material, dry impermeable material, has been well applied at present.