A surface treatment process for the bottom of an aluminium electrolytic cell

Abstract

The application relates to the field of refractory materials, in particular to a surface treatment process for the bottom of an aluminum electrolysis cell, which solves the problem that composite metal objects are difficult to form a dense structure with non-metallic inorganic matters such as Si3N4 and SiC, and that more micropore gaps lead to the penetration of aluminum liquid and electrolyte into the refractory material and the damage of the refractory material, and the surface treatment process comprises the following steps: preparing a boric acid refractory brick, roughening the surface of a refractory bearing material, coating a permeable material on the outside of the refractory bearing material, the thickness of the permeable material being 1-10 mm, heat treatment at 1300-1420 DEG C for 5-12 h, removal of the excess permeable material to obtain a refractory material precursor, placing a barrier material on the surface of the refractory material precursor, forming a barrier layer through cold isostatic pressing, heat treatment, formation of a high-density impedance layer on the surface of the refractory material precursor, and completion of the surface treatment. The application can realize the combination of dense inorganic non-metal and metal, and improve the corrosion resistance of the refractory material.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of refractory materials, in particular to a surface treatment process for the bottom of an aluminum electrolysis cell. BACKGROUND

[0002] When the aluminum electrolysis cell is smelted, a composite structure is generally formed by combining the refractory materials of the furnace side and the bottom, but the bottom part not only receives the electrolyte but also contacts the liquid aluminum formed after electrolysis. Most of the existing materials use Si3N4 and SiC as the materials for receiving the electrolyte and the aluminum liquid. The steel rod at the lower part of the tank bottom is thus required to have a very high requirement for the material quality of the refractory material. Otherwise, the damage of the refractory material will cause the liquid aluminum to contact the steel rod, resulting in unstable electric field current, which has a great influence on the quality of the aluminum liquid and the refining efficiency.

[0003] The liquid metal aluminum obtained by electrolysis has a very strong penetration ability. Once it penetrates into the refractory brick, it will react with SiO2 in the brick to reduce Si, destroy the organizational structure of the refractory material, and cause the furnace lining to produce a metamorphic layer, loose and peel off and be damaged. The reaction is: 3SiO2+4A1--2A12O3+3SiO2. The electrolytic cell is composed of a rectangular steel shell and a carbon brick lining. The carbon bottom of the cell is a cathode. The aluminum electrolyte is selected from a molten liquid of cryolite, aluminum fluoride, lithium fluoride and the like. Al2O3 is melted at about 970 DEG C. Under the action of electric field force, it is ionized. The metal aluminum melt recovered by electrolysis is deposited on the cathode of the bottom of the cell. The electrolysis temperature is 900-1000 DEG C. In the production of electrolytic aluminum, the vapor and liquid of Na and NaF can enter the lower heat insulation layer through the cathode material of the bottom of the cell. After the heat insulation layer enters NaF, the thermal conductivity is added, the thermal efficiency of the electrolytic cell is reduced, the working condition is deteriorated, and the cell is damaged. Therefore, it is necessary to improve the anti-penetration performance of the refractory material, reduce the existence of micropores and gaps, and form a more dense refractory material or insulation layer.

[0004] The refractory material is easy to form SiF4 with the oxygen generated by electrolysis in the environment with fluoride, which causes serious damage to the refractory material. The electrolyte penetration also dissolves the generated protective oxide, which causes the structure of the bottom of the electrolytic cell to be degraded and damaged, thereby causing a series of problems such as unstable current, loss of aluminum liquid, pollution and frequent replacement of the electrolytic cell. Therefore, the existing technology uses a composite refractory material combined with a metal material and Si3N4 and SiC. However, the material has a problem of difficult densification between the inorganic non-metal and the metal phase. Specifically, the material will cause the generation of ion vacancies during the electrolyte corrosion process, resulting in the appearance of pores, and then the electrolyte penetration will cause the damage of the aluminum electrolytic cell. SUMMARY

[0005] In order to solve the problems that Si3N4, SiC and HF react to generate SiF4 and are corroded, the composite metal material is difficult to form a dense structure with Si3N4, SiC and other non-metallic inorganic materials, more micropore gaps are generated, and the molten aluminum and electrolyte penetrate into the refractory material to cause damage, the application provides a surface treatment process for the bottom of an aluminum electrolysis cell, and the technical scheme adopted by the application is as follows:

[0006] The treatment process is a surface treatment process for the bottom of an aluminum electrolysis cell, comprising the following specific treatment steps:

[0007] S1, borate refractory bricks are prepared, 0.5-2 parts of borate powder are added in 100 parts of the borate refractory bricks by weight, and a refractory bearing material is obtained by sintering, and the surface of the refractory bearing material is roughened;

[0008] S2, a permeating material is coated on the outside of the refractory bearing material, the thickness of the permeating material is 1-10mm, the temperature is raised to 1300-1420 DEG C for heat treatment for 5-12h, and the excess permeating material is stripped to obtain a refractory material precursor;

[0009] The permeating material comprises 10 parts of iron powder, 5-7 parts of silicon monoxide and 1-2 parts of europium oxide by weight;

[0010] S3, a barrier material is arranged on the surface of the refractory material precursor, a barrier layer is formed by cold isostatic pressing, heat treatment is carried out, a high-density impedance layer is formed on the surface of the refractory material precursor, and the surface treatment is completed;

[0011] The barrier material comprises 30-55 parts of calcium hexaluminate, 10-15 parts of aluminum-magnesium alloy powder, 20-40 parts of boron trioxide and 25-30 parts of aluminum powder by weight.

[0012] The application mainly forms a layer of permeating material on the roughened refractory brick surface by using iron powder and silicon monoxide, the permeating material can effectively increase the intermolecular bond length of Fe and other materials, the degree of intermolecular combination is weakened, which is beneficial to the indirect formation of composite grains of other elements and atoms in the subsequent heat treatment process, and europium oxide is also used as an intergranular strengthening material in the permeating material, after sintering treatment, the europium element in the europium oxide can be an effective component for promoting mass transfer and diffusion, the surface of the inner refractory brick is rich in a large amount of Fe-SiO components and trivalent europium elements, which can specifically improve the subsequent strengthening material, and the specific performance is to enhance the grain growth, increase the density of non-metallic inorganic materials, form new crystal phases, and thus improve the resistance to molten aluminum and electrolyte.

[0013] The application uses calcium hexaluminate as the main material to resist the corrosion of aluminum liquid. Studies have shown that calcium hexaluminate can greatly improve the resistance to aluminum liquid. Aluminum liquid has super strong reducing property. According to thermodynamics, calcium oxide cannot be reduced by aluminum liquid, but calcium is easy to oxidize in an oxygen-rich and complex electrolyte environment to form a microstructure with many micropores, which does not have the characteristics of high density. Therefore, aluminum-magnesium alloy, boron trioxide and pure aluminum powder are added and fired together. At high temperature, an oxide boron magnesium phase with a high melting point can be formed. The boron trioxide in the reduced state can uniformly melt in the aluminum-magnesium alloy phase, thereby uniformly mass transfer and diffusion, and combined with the internal permeation material, so that the B element and the Fe element with increased molecular bond length form a whisker and form a Fe-M-B grain in the microstructure of calcium hexaluminate, wherein M is Eu, Mg or Si, which can be filled in the intermolecular gap of the non-metallic inorganic phase, thereby enhancing the density and preventing corrosion and penetration of aluminum liquid and electrolyte components.

[0014] Preferably, the raw material of the borate refractory brick in step S1 further comprises 70-100 parts by weight of industrial silicon powder, 30-50 parts by weight of carbon black and 20-30 parts by weight of Si3N4, the firing temperature of the borate refractory brick is 1350-1450℃, the firing atmosphere is nitrogen, and the pressure of the firing atmosphere is 0.02-0.04Mpa.

[0015] Preferably, the solution for the roughening treatment in step S1 is a sulfuric acid solution, the concentration of the sulfuric acid solution is 100g / L-250g / L, the temperature of the roughening treatment is 50-75℃, and the treatment time is 1-6h.

[0016] Preferably, the pressure of the cold isostatic pressing in step S3 is 200-500Mpa, and the time of the cold isostatic pressing is 1-30min.

[0017] Preferably, the temperature of the heat treatment in step S3 is 800-1000℃, and the time of the heat treatment is 6-24h.

[0018] Preferably, the permeation material in step S2 further comprises an aqueous solution of sodium hexametaphosphate, the amount of sodium hexametaphosphate accounts for 6-18% of the total weight of the permeation material, and the concentration of sodium hexametaphosphate is 25wt%.

[0019] Preferably, the particle size of the iron powder in step S2 is 18-38μm, the particle size of the silicon monoxide is 40-80μm, and the particle size of the europium oxide is 2-15μm.

[0020] The size of the iron powder particle in the application has a certain influence on the corrosion of aluminum liquid. Too small iron particles will penetrate into the interior, and too large iron powder particles are difficult to combine, which reduces the corrosion resistance.

[0021] Preferably, the calcium hexaluminate is 200-300 mesh, the particle size of the aluminum-magnesium alloy powder is 5-10 mu m, the boron trioxide is 100-200 mesh, and the particle size of the aluminum powder is 10-100 mu m.

[0022] The surface treatment process of the bottom of the aluminum electrolysis cell can form a high-density impedance layer on the surface of the treated refractory brick.

[0023] The surface treatment process of the bottom of the aluminum electrolysis cell can be applied to aluminum electrolysis cell related products.

[0024] The beneficial effects of the present application are:

[0025] The present application can produce more micropore cracks in the refractory brick by adding boric acid substances, which is beneficial for the subsequent penetration of the permeation material, and can provide a source of permeation material during heat treatment, continuously providing Fe-SiO components and trivalent europium elements, which can form a more uniform and dense anti-corrosion layer with the outer calcium hexaluminate and metal components, effectively resisting the corrosion of aluminum liquid and electrolyte components, and can significantly increase the service life of the aluminum electrolysis cell.

[0026] The present application mainly strengthens the intergranular structure with europium oxide, so that the external boron trioxide and aluminum-magnesium alloy react with the internal iron and a small amount of silicon to form second-phase Fe-M-B grains, filling the gaps between inorganic non-metallic particles, strengthening the interaction between grains, and significantly enhancing the corrosion resistance of the refractory material. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 The corrosion depth line graph of the examples and comparative examples of the present application. DETAILED DESCRIPTION

[0028] The following will be described with reference to the accompanying drawings Figure 1 The embodiments of the present application will be described in detail. Those skilled in the art should understand that these embodiments are only used to explain the technical principles of the present application, and are not intended to limit the protection scope of the present application.

[0029] Preparation Example 1

[0030] Burning of boric acid refractory brick

[0031] By weight, 85 parts of industrial silicon powder, 40 parts of carbon black and 25 parts of Si3N4 are crushed and mixed by stirring machine, then 1.5 parts of boric acid powder and 30% of water of total mass are added until the mixture is stirred uniformly to form a green body, which is pressed by a mold to form a sintering blank, and then placed in a vacuum nitrogen sintering furnace, the sintering temperature of which is set to 1400℃, the sintering atmosphere is nitrogen, and the pressure of the sintering atmosphere is 0.03Mpa, to obtain a refractory bearing material, i.e. boric acid refractory brick.

[0032] Preparation Example 2

[0033] Sintering of boric acid refractory brick

[0034] By weight, 70 parts of industrial silicon powder, 30 parts of carbon black and 20 parts of Si3N4 are crushed and mixed by stirring machine, then 1.2 parts of boric acid powder and 20% of water of total mass are added until the mixture is stirred uniformly to form a green body, which is pressed by a mold to form a sintering blank, and then placed in a vacuum nitrogen sintering furnace, the sintering temperature of which is set to 1350℃, the sintering atmosphere is nitrogen, and the pressure of the sintering atmosphere is 0.02Mpa, to obtain a refractory bearing material, i.e. boric acid refractory brick.

[0035] Preparation Example 3

[0036] Sintering of boric acid refractory brick

[0037] By weight, 100 parts of industrial silicon powder, 50 parts of carbon black and 30 parts of Si3N4 are crushed and mixed by stirring machine, then 1.8 parts of boric acid powder and 35% of water of total mass are added until the mixture is stirred uniformly to form a green body, which is pressed by a mold to form a sintering blank, and then placed in a vacuum nitrogen sintering furnace, the sintering temperature of which is set to 1450℃, the sintering atmosphere is nitrogen, and the pressure of the sintering atmosphere is 0.04Mpa, to obtain a refractory bearing material, i.e. boric acid refractory brick.

[0038] Preparation Example 4--sintering of refractory brick without adding boric acid

[0039] Sintering of refractory brick

[0040] By weight, 80 parts of industrial silicon powder, 40 parts of carbon black and 20 parts of Si3N4 are crushed and mixed by stirring machine, then 30% of water of total mass is added until the mixture is stirred uniformly to form a green body, which is pressed by a mold to form a sintering blank, and then placed in a vacuum nitrogen sintering furnace, the sintering temperature of which is set to 1400℃, the sintering atmosphere is nitrogen, and the pressure of the sintering atmosphere is 0.03Mpa, to obtain a refractory bearing material, i.e. boric acid refractory brick.

[0041] Preparation Example 5--adding too much boric acid

[0042] Sintering of boric acid refractory brick

[0043] 85 parts of industrial silicon powder, 40 parts of carbon black and 25 parts of Si3N4 powder are crushed and mixed by stirring, 6 parts of boric acid powder and 30% of water by total mass are added thereto until the mixture is stirred uniformly to form a green body, the green body is pressed by using a mold to form a fired green body, the fired green body is placed in a vacuum nitrogen sintering furnace, the sintering temperature of the vacuum nitrogen sintering furnace is set to 1400℃, the sintering atmosphere is nitrogen, and the sintering atmosphere pressure is 0.03Mpa, to obtain a refractory carrier, i.e., a boric acid refractory brick.

[0044] Example 1

[0045] Treatment of high-density impedance layer

[0046] The refractory carrier prepared in Preparation Example 1 is roughened in a sulfuric acid solution with a concentration of 200g / L, the roughening temperature is set to 60℃, and the roughening time is 3h; 10 parts of iron powder, 6 parts of silicon monoxide and 1.5 parts of europium oxide are weighed and mixed to form a mixed powder, 1.5 parts of sodium hexametaphosphate is dissolved in water to form a binder solution with a concentration of 25wt%, the mixed powder is added with the binder solution to form a permeated material, then the permeated material is coated on the surface of the roughened refractory carrier, the thickness of the permeated material is controlled to be between 4mm, and the refractory carrier coated with the permeated material is placed in a sintering kiln and heated to 1350℃ for heat treatment for 8h, after sintering, a relatively brittle shell layer is formed on the surface of the refractory carrier by the permeated material, and the refractory material precursor is obtained after the excess shell layer is peeled off.

[0047] 45 parts of calcium hexaluminate, 12 parts of aluminum-magnesium alloy powder, 30 parts of boron trioxide and 28 parts of aluminum powder are stirred and mixed by using a stirrer to form a barrier material, the barrier material and the refractory material precursor are placed in a cold isostatic pressing machine, the pressure of the cold isostatic pressing is set to 300Mpa, and the cold isostatic pressing time is 10min, to obtain a refractory material green body with a barrier layer, the refractory material green body is placed in a heat treatment furnace for heat treatment, the heat treatment temperature is 900℃, and the heat treatment time is 12h, to form a high-density impedance layer on the surface of the refractory material precursor.

[0048] In this embodiment, the particle size of the iron powder is 30μm, the particle size of the silicon monoxide is 60μm, the particle size of the europium oxide is 10μm, the particle size of the calcium hexaluminate is 300 mesh, the particle size of the aluminum-magnesium alloy powder is 8μm, the particle size of the boron trioxide is 150 mesh, and the particle size of the aluminum powder is 50μm.

[0049] Example 2

[0050] Treatment of high-density impedance layer

[0051] The refractory carrier prepared in Preparation Example 2 is roughened in a sulfuric acid solution with a concentration of 100 g / L, the roughening temperature is set to 50°C, and the roughening time is 1 h; 10 parts of iron powder, 5 parts of silicon monoxide, and 1 part of europium oxide are weighed by weight parts to form a mixed powder, and 1 part of sodium hexametaphosphate is dissolved in water to form a binding solution with a concentration of 25 wt%, the mixed powder is added with the binding solution to form a permeating material, then the permeating material is coated on the surface of the roughened refractory carrier, the thickness of the permeating material is controlled to be between 1 mm, and the refractory carrier coated with the permeating material is placed in a sintering kiln, heated to 1300°C and heat treated for 5 h, after sintering, the permeating material forms a relatively brittle shell layer on the surface of the refractory carrier, and after peeling off the excess shell layer, a refractory material precursor is obtained;

[0052] 30 parts of calcium hexaluminate, 10 parts of aluminum-magnesium alloy powder, 20 parts of boron trioxide, and 25 parts of aluminum powder are stirred and mixed uniformly by a stirrer to form a barrier material, the barrier material and the refractory material precursor are placed in a cold isostatic pressing machine, the pressure of cold isostatic pressing is set to 200 MPa, and the cold isostatic pressing time is 30 min, to obtain a refractory material roughcast with a barrier layer, the refractory material roughcast is placed in a heat treatment furnace for heat treatment, the heat treatment temperature is 800°C, and the heat treatment time is 6 h, to form a high-density impedance layer on the surface of the refractory material precursor.

[0053] In this embodiment, the particle size of the iron powder is 18 μm, the particle size of the silicon monoxide is 40 μm, the particle size of the europium oxide is 2 μm, the calcium hexaluminate is 200 mesh, the particle size of the aluminum-magnesium alloy powder is 5 μm, the boron trioxide is 100 mesh, and the particle size of the aluminum powder is 10 μm.

[0054] Example 3

[0055] Treatment of high-density impedance layer

[0056] The refractory carrier prepared in Preparation Example 3 is roughened in a sulfuric acid solution with a concentration of 250 g / L, the roughening temperature is set to 75°C, and the roughening time is 6 h; 10 parts of iron powder, 7 parts of silicon monoxide, and 2 parts of europium oxide are weighed by weight parts to form a mixed powder, and 3 parts of sodium hexametaphosphate is dissolved in water to form a binding solution with a concentration of 25 wt%, the mixed powder is added with the binding solution to form a permeating material, then the permeating material is coated on the surface of the roughened refractory carrier, the thickness of the permeating material is controlled to be between 10 mm, and the refractory carrier coated with the permeating material is placed in a sintering kiln, heated to 1420°C and heat treated for 12 h, after sintering, the permeating material forms a relatively brittle shell layer on the surface of the refractory carrier, and after peeling off the excess shell layer, a refractory material precursor is obtained;

[0057] By weight, 55 parts of calcium hexaaluminate, 15 parts of aluminum-magnesium alloy powder, 40 parts of boron trioxide, and 30 parts of aluminum powder are mixed evenly using a stirrer to form a barrier material. The barrier material and the refractory precursor are placed in a cold isostatic press, and the cold isostatic pressing pressure is set to 500 MPa and the cold isostatic pressing time is 1 min to obtain a refractory blank with a barrier layer. The refractory blank is placed in a heat treatment furnace for heat treatment at a temperature of 1000℃ for 24 h to form a high-density resistance layer on the surface of the refractory precursor.

[0058] In this embodiment, the iron powder has a particle size of 38 μm, the silicon monoxide has a particle size of 80 μm, the europium oxide has a particle size of 15 μm, the calcium hexaaluminate has a particle size of 300 mesh, the aluminum-magnesium alloy powder has a particle size of 10 μm, the boron trioxide has a particle size of 200 mesh, and the aluminum powder has a particle size of 100 μm.

[0059] Comparative Example 1 – Using refractory load-bearing material without added boric acid

[0060] Treatment of high-density impedance layers

[0061] The refractory carrier material prepared in Example 4 was roughened in a sulfuric acid solution with a concentration of 200 g / L at a roughening temperature of 60 °C for 3 h. 10 parts by weight of iron powder, 6 parts by weight of silicon monoxide and 1.5 parts by weight of europium oxide were weighed to form a mixed powder. 1.5 parts by weight of sodium hexametaphosphate were dissolved in water to form a binder solution with a concentration of 25 wt%. The binder solution was added to the mixed powder to form a penetrant. The penetrant solution was then coated onto the surface of the roughened refractory carrier material, with the thickness of the penetrant solution controlled to be between 4 mm. The refractory carrier material coated with the penetrant solution was placed in a sintering kiln and heat-treated at 1350 °C for 8 h. After sintering, the penetrant solution formed a relatively brittle shell layer on the surface of the refractory carrier material. After peeling off the excess shell layer, the refractory precursor was obtained.

[0062] By weight, 45 parts of calcium hexaaluminate, 12 parts of aluminum-magnesium alloy powder, 30 parts of boron trioxide, and 28 parts of aluminum powder are mixed evenly using a stirrer to form a barrier material. The barrier material and the refractory precursor are placed in a cold isostatic press, and the cold isostatic pressing pressure is set to 300 MPa for 10 min to obtain a refractory blank with a barrier layer. The refractory blank is then placed in a heat treatment furnace for heat treatment at a temperature of 900℃ for 12 h to form a high-density resistance layer on the surface of the refractory precursor.

[0063] In this embodiment, the iron powder has a particle size of 30 μm, the silicon monoxide has a particle size of 60 μm, the europium oxide has a particle size of 10 μm, the calcium hexaaluminate has a particle size of 300 mesh, the aluminum-magnesium alloy powder has a particle size of 8 μm, the boron trioxide has a particle size of 150 mesh, and the aluminum powder has a particle size of 50 μm.

[0064] Comparative Example 2 - Use of refractory carrier with excess boric acid added

[0065] Treatment of high density resistive layer

[0066] The refractory carrier prepared in Preparation Example 5 was roughened in a 200 g / L sulfuric acid solution, the roughening temperature was set to 60°C, and the roughening time was 3 h; 10 parts of iron powder, 6 parts of silicon monoxide, and 1.5 parts of europium oxide were weighed by weight parts to form a mixed powder, and 1.5 parts of sodium hexametaphosphate was dissolved in water to form a binder solution with a concentration of 25 wt%, the mixed powder was added to the binder solution to form a permeation material, then the permeation material was coated on the surface of the roughened refractory carrier, the thickness of the permeation material was controlled to be between 4 mm, and the refractory carrier coated with the permeation material was placed in a sintering kiln and heated to 1350°C for 8 h. After sintering, the permeation material formed a relatively brittle shell layer on the surface of the refractory carrier, and after peeling off the excess shell layer, a refractory material precursor was obtained.

[0067] 45 parts of calcium hexaluminate, 12 parts of aluminum-magnesium alloy powder, 30 parts of boron trioxide, and 28 parts of aluminum powder were stirred and mixed uniformly by a stirrer to form a barrier material, the barrier material and the refractory material precursor were placed in a cold isostatic pressing machine, the pressure of the cold isostatic pressing was set to 300 MPa, and the cold isostatic pressing time was 10 min, to obtain a refractory material roughcast with a barrier layer. The refractory material roughcast was placed in a heat treatment furnace for heat treatment, the heat treatment temperature was 900°C, and the heat treatment time was 12 h, to form a high density resistive layer on the surface of the refractory material precursor.

[0068] In this embodiment, the particle size of the iron powder is 30 μm, the particle size of the silicon monoxide is 60 μm, the particle size of the europium oxide is 10 μm, the calcium hexaluminate is 300 mesh, the particle size of the aluminum-magnesium alloy powder is 8 μm, the boron trioxide is 150 mesh, and the particle size of the aluminum powder is 50 μm.

[0069] Comparative Example 3 - No use of permeation material

[0070] Treatment of high density resistive layer

[0071] The refractory carrier prepared in Preparation Example 1 was roughened in a 200 g / L sulfuric acid solution, the roughening temperature was set to 60°C, and the roughening time was 3 h; to obtain a roughened refractory material;

[0072] 45 parts of calcium hexaluminate, 12 parts of aluminum-magnesium alloy powder, 30 parts of boron trioxide and 28 parts of aluminum powder are mixed uniformly by a stirrer to form barrier material. The barrier material and the roughened refractory material are placed in a cold isostatic pressing machine, the pressure of cold isostatic pressing is set to 300 MPa, and the cold isostatic pressing time is 10 min to obtain a refractory material roughcast with a barrier layer. The refractory material roughcast is placed in a heat treatment furnace for heat treatment, the heat treatment temperature is 900 °C, and the heat treatment time is 12 h to form a high-density impedance layer on the surface of the roughened refractory material.

[0073] In this embodiment, the particle size of the iron powder is 30 μm, the particle size of the silicon monoxide is 60 μm, the particle size of the europium oxide is 10 μm, the particle size of the calcium hexaluminate is 300 mesh, the particle size of the aluminum-magnesium alloy powder is 8 μm, the particle size of the boron trioxide is 150 mesh, and the particle size of the aluminum powder is 50 μm.

[0074] Comparative Example 4 - no iron powder and no silicon monoxide in the permeation material

[0075] Treatment of the high-density impedance layer

[0076] The refractory carrier material prepared in Preparation Example 1 is placed in a sulfuric acid solution with a concentration of 200 g / L for roughening, the roughening temperature is set to 60 °C, and the roughening time is 3 h. 1.5 parts of europium oxide is weighed by weight parts, and 1.5 parts of sodium hexametaphosphate is dissolved in water to form a bonding solution with a concentration of 25 wt%. The bonding solution is added to the europium oxide powder to form a permeation material, which is then coated on the surface of the roughened refractory carrier material, with the thickness of the permeation material controlled to be between 4 mm. The refractory carrier material coated with the permeation material is placed in a sintering kiln, heated to 1350 °C for heat treatment for 8 h. After sintering, a relatively brittle shell layer is formed on the surface of the refractory carrier material by the permeation material. After peeling off the excess shell layer, a refractory material precursor is obtained.

[0077] 45 parts of calcium hexaluminate, 12 parts of aluminum-magnesium alloy powder, 30 parts of boron trioxide and 28 parts of aluminum powder are mixed uniformly by a stirrer to form barrier material. The barrier material and the roughened refractory material are placed in a cold isostatic pressing machine, the pressure of cold isostatic pressing is set to 300 MPa, and the cold isostatic pressing time is 10 min to obtain a refractory material roughcast with a barrier layer. The refractory material roughcast is placed in a heat treatment furnace for heat treatment, the heat treatment temperature is 900 °C, and the heat treatment time is 12 h to form a high-density impedance layer on the surface of the refractory material.

[0078] In this embodiment, the particle size of the iron powder is 30 μm, the particle size of the silicon monoxide is 60 μm, the particle size of the europium oxide is 10 μm, the particle size of the calcium hexaluminate is 300 mesh, the particle size of the aluminum-magnesium alloy powder is 8 μm, the particle size of the boron trioxide is 150 mesh, and the particle size of the aluminum powder is 50 μm.

[0079] Comparative Example 5 - no europium oxide in the permeation material

[0080] Treatment of high-density resistive layer

[0081] The refractory carrier prepared in Preparation Example 1 is roughened in a sulfuric acid solution with a concentration of 200 g / L, the roughening temperature is set to 60°C, and the roughening time is 3 h; 10 parts of iron powder, 6 parts of silicon monoxide, and 1.5 parts of europium oxide are weighed by weight parts to form a mixed powder, and 1.5 parts of sodium hexametaphosphate is dissolved in water to form a binding solution with a concentration of 25 wt%, the mixed powder is added with the binding solution to form a permeation material, then the permeation material is coated on the surface of the roughened refractory carrier, the thickness of the permeation material is controlled to be between 4 mm, and the refractory carrier coated with the permeation material is placed in a sintering kiln, heated to 1350°C for 8 h, after sintering, the permeation material forms a relatively brittle shell layer on the surface of the refractory carrier, and the refractory material precursor is obtained after peeling off the excess shell layer;

[0082] The 45 parts of calcium hexaluminate, 12 parts of aluminum-magnesium alloy powder, 30 parts of boron trioxide, and 28 parts of aluminum powder are stirred and mixed uniformly by a stirrer to form a barrier material, the barrier material and the refractory material precursor are placed in a cold isostatic pressing machine, the pressure of the cold isostatic pressing is set to 300 MPa, and the cold isostatic pressing time is 10 min, to obtain a refractory material roughcast with a barrier layer, the refractory material roughcast is placed in a heat treatment furnace for heat treatment, the heat treatment temperature is 900°C, and the heat treatment time is 12 h, to form a high-density resistive layer on the surface of the refractory material precursor.

[0083] In this embodiment, the particle size of the iron powder is 30 μm, the particle size of the silicon monoxide is 60 μm, the particle size of the europium oxide is 10 μm, the calcium hexaluminate is 300 mesh, the particle size of the aluminum-magnesium alloy powder is 8 μm, the boron trioxide is 150 mesh, and the particle size of the aluminum powder is 50 μm.

[0084] Comparative Example 6--Aluminum-magnesium alloy not used in barrier material

[0085] Treatment of high-density resistive layer

[0086] The refractory carrier prepared in Preparation Example 1 is roughened in a sulfuric acid solution with a concentration of 200 g / L, the roughening temperature is set to 60°C, and the roughening time is 3 h; 10 parts of iron powder, 6 parts of silicon monoxide, and 1.5 parts of europium oxide are weighed by weight parts to form a mixed powder, and 1.5 parts of sodium hexametaphosphate is dissolved in water to form a binding solution with a concentration of 25 wt%, the mixed powder is added with the binding solution to form a permeation material, then the permeation material is coated on the surface of the roughened refractory carrier, the thickness of the permeation material is controlled to be between 4 mm, and the refractory carrier coated with the permeation material is placed in a sintering kiln, heated to 1350°C for 8 h, after sintering, the permeation material forms a relatively brittle shell layer on the surface of the refractory carrier, and the refractory material precursor is obtained after peeling off the excess shell layer;

[0087] The barrier material is formed by mixing 45 parts of calcium hexaluminate, 30 parts of boron trioxide and 28 parts of aluminum powder by weight using a stirrer, and the barrier material and the refractory material precursor are placed in a cold isostatic pressing machine, the pressure of cold isostatic pressing is set to 300 MPa, and the cold isostatic pressing time is 10 min, to obtain a refractory material rough casting with a barrier layer, and the refractory material rough casting is placed in a heat treatment furnace for heat treatment, the heat treatment temperature is 900 °C, and the heat treatment time is 12 h, to form a high-density impedance layer on the surface of the refractory material precursor.

[0088] In this embodiment, the particle size of the iron powder is 30 μm, the particle size of the silicon monoxide is 60 μm, the particle size of the europium oxide is 10 μm, the particle size of the calcium hexaluminate is 300 mesh, the particle size of the aluminum-magnesium alloy powder is 8 μm, the particle size of the boron trioxide is 150 mesh, and the particle size of the aluminum powder is 50 μm.

[0089] Comparative Example 7 - No boron trioxide is used in the barrier material

[0090] Treatment of the high-density impedance layer

[0091] The refractory carrier material prepared in Preparation Example 1 is placed in a sulfuric acid solution with a concentration of 200 g / L for roughening, the roughening temperature is set to 60 °C, and the roughening time is 3 h; 10 parts of iron powder, 6 parts of silicon monoxide and 1.5 parts of europium oxide are weighed by weight parts to form a mixed powder, 1.5 parts of sodium hexametaphosphate is dissolved in water to form a binder solution with a concentration of 25 wt%, the mixed powder is added with the binder solution to form a permeation material, then the permeation material is coated on the surface of the roughened refractory carrier material, the thickness of the permeation material is controlled to be between 4 mm, and the refractory carrier material coated with the permeation material is placed in a sintering kiln, heated to 1350 °C and heat treated for 8 h, after sintering, the permeation material forms a relatively brittle shell layer on the surface of the refractory carrier material, and after peeling off the excess shell layer, a refractory material precursor is obtained.

[0092] The barrier material is formed by mixing 45 parts of calcium hexaluminate, 30 parts of boron trioxide and 28 parts of aluminum powder by weight using a stirrer, and the barrier material and the refractory material precursor are placed in a cold isostatic pressing machine, the pressure of cold isostatic pressing is set to 300 MPa, and the cold isostatic pressing time is 10 min, to obtain a refractory material rough casting with a barrier layer, and the refractory material rough casting is placed in a heat treatment furnace for heat treatment, the heat treatment temperature is 900 °C, and the heat treatment time is 12 h, to form a high-density impedance layer on the surface of the refractory material precursor.

[0093] In this embodiment, the particle size of the iron powder is 30 μm, the particle size of the silicon monoxide is 60 μm, the particle size of the europium oxide is 10 μm, the particle size of the calcium hexaluminate is 300 mesh, the particle size of the aluminum-magnesium alloy powder is 8 μm, the particle size of the boron trioxide is 150 mesh, and the particle size of the aluminum powder is 50 μm.

[0094] Experiments and data

[0095] The fired refractory materials with high density resistance layer obtained in each of the above examples and each of the comparative examples were tested for porosity (%), bulk density (g / cm 3 ), compressive strength (Mpa), and penetration depth (mm).

[0096] The penetration depth was measured by testing the thickness of the color change layer, in mm, after the refractory material surface in each of the examples and comparative examples was eroded by a molten cryolite with a molecular ratio of 2.1 at 900°C for 3h.

[0097] The experimental data are shown in Table 1 below:

[0098] Table 1

[0099] % open porosity Bulk density g / cm 3 ]] compressive strength Mpa penetration depth mm Example 1 3.63 2.98 74 0.6 Example 2 4.12 2.91 73 0.7 Example 3 3.88 2.96 74 0.6 Comparative Example 1 12.75 2.64 78 3.3 Comparative Example 2 3.518 2.95 37 0.6 Comparative Example 3 16.33 2.49 73 3.5 Comparative Example 4 9.10 2.73 72 3.3 Comparative Example 5 15.2 2.50 73 3.4 Comparative Example 6 8.74 2.65 66 1.7 Comparative Example 7 4.74 2.89 74 1.3

[0100] The porosity and penetration depth were plotted as a line graph, as shown in Figure 1 .

[0101] Analysis

[0102] According to the data in Table 1, the high density resistance layer formed on the surface of the refractory material precursor in Examples 1, 2, and 3 by the treatment process of the present application has low porosity, qualified compressive strength, and extremely low penetration resistance, which can better protect the aluminum electrolysis cell from corrosion and increase the service life of the aluminum electrolysis cell.

[0103] According to the data in Table 1, the porosity of Comparative Example 1 is large, the penetration depth is also large, and only the compressive strength is qualified. The refractory bearing material used in Comparative Example 1 does not contain boric acid, and therefore has fewer microporous gaps, so the subsequent penetration material is less likely to remain. Therefore, when the barrier material is treated subsequently, it cannot effectively form enough strengthened grains with the molecules in the barrier material, and therefore cannot form strengthening between calcium hexaluminate molecules. As a result, the porosity is large, and the aluminum liquid or electrolyte can easily penetrate. It can be seen that adding an appropriate amount of boric acid can effectively reduce the number of pores and effectively prevent corrosion.

[0104] According to the data in Table 1, the compressive strength of Comparative Example 2 is poor. The difference between Comparative Example 2 and the examples is that an excessive amount of boric acid is used. Excessive addition of boric acid can cause the matrix material itself to have a large number of microporous gaps, greatly reducing the strength of the refractory brick itself, making it difficult to have strong bearing capacity and mechanical strength, and easily breaking under external force.

[0105] According to the data in Table 1, the porosity of Comparative Example 3 is larger, the bulk density decreases to a certain extent, and the penetration depth is deeper. The difference between Comparative Example 3 and the examples is that no penetration material is used to treat the refractory carrier material, so that a reinforcing layer connecting the barrier material and the refractory carrier material cannot be formed, the metal components in the barrier material cannot be combined, the intermolecular gap cannot be opened, and the micropores of the dense inorganic non-metallic material and the molecular vacancies cannot be filled, so that the porosity is high. Therefore, the use of penetration material can effectively improve the penetration of the refractory material to the erosion.

[0106] According to the data in Table 1, the porosity of Comparative Example 4 is higher, and the penetration depth is also larger. The difference between Comparative Example 4 and Example 1 is that no iron powder and silicon monoxide are used, so that the mass transfer diffusion of europium oxide is limited, and a relatively firm crystal structure is not produced, only partially filling the gaps of calcium hexaluminate, and the reinforcing effect is not large. Therefore, the use of iron and silicon monoxide can effectively increase the intermolecular gap, and iron can also form a crystal with a certain strength with other substances, thereby densifying calcium hexaluminate, reducing the porosity, and increasing the corrosion resistance.

[0107] According to the data in Table 1, the porosity of Comparative Example 5 is higher, the bulk density decreases to a large extent, and the penetration depth is also larger. The difference between Comparative Example 5 and the examples is that no europium oxide is used in the penetration material. Although iron also diffuses to a certain extent, it is not affected by the mass transfer diffusion of trivalent europium ions, and cannot effectively combine with calcium hexaluminate, and it is more difficult to produce Fe-M-B grains, so it cannot effectively reduce the porosity. Therefore, the presence of europium oxide can effectively increase the densification effect.

[0108] According to the data in Table 1, the porosity of Comparative Example 6 increases to a certain extent, the compressive strength decreases to a certain extent, and the penetration strength is improved to a certain extent. The difference between Comparative Example 6 and the examples is that no aluminum-magnesium alloy is used in the barrier material. Therefore, after reduction, di boron oxide is difficult to uniformly melt in the aluminum liquid, but forms agglomerated AlB2, which does not diffuse inwardly and combine with Eu, Fe, and internal Si, C, and other elements. Therefore, the anti-infiltration performance decreases, it is difficult to achieve strong anti-infiltration, and therefore the presence of aluminum-magnesium alloy can enhance the participation of boron elements in the formation of new grain crystal phases.

[0109] According to the data in Table 1, the porosity, bulk density, and compressive strength of Comparative Example 7 are all good, but a certain degree of penetration occurs. The difference between Comparative Example 7 and the examples is that no di boron trioxide is used in the barrier material, and no high-melting-point grains are formed in the crystal phase. Therefore, after a long period of use, a certain degree of reduction penetration will occur, causing the refractory material itself to be eroded to a certain extent, proving that di boron trioxide has a strong corrosion-resistant enhancing effect on the refractory dense layer.

[0110] So far, the technical solutions of the present application have been described in combination with the preferred embodiments shown in the drawings, but it is easy for those skilled in the art to understand that the protection scope of the present application is obviously not limited to these specific embodiments. Those skilled in the art can make equivalent changes or replacements to the related technical features without departing from the principles of the present application, and the technical solutions after these changes or replacements will all fall within the protection scope of the present application.

Claims

1. A surface treatment process for the bottom of an aluminum electrolytic cell, characterized in that, The specific processing steps include the following: S1. Prepare boric acid refractory bricks, with 0.5-2 parts of boric acid powder per 100 parts by weight, and fire them to obtain refractory load-bearing material. Roughen the surface of the refractory load-bearing material. S2. Coat the outside of the refractory load-bearing material with a penetrating material thickness of 1-10 mm, heat-treat at 1300-1420℃ for 5-12 hours, and remove excess penetrating material to obtain the refractory precursor; the penetrating material includes 10 parts by weight of iron powder, 5-7 parts by weight of silicon monoxide and 1-2 parts by weight of europium oxide. S3. Place the barrier material on the surface of the refractory precursor, form a barrier layer by cold isostatic pressing, and perform heat treatment to form a high-density impedance layer on the surface of the refractory precursor, thus completing the surface treatment; the barrier material includes 30-55 parts by weight of calcium hexaaluminate, 10-15 parts of aluminum-magnesium alloy powder, 20-40 parts of boron trioxide and 25-30 parts of aluminum powder. The raw materials for the boric acid refractory bricks in step S1 also include 70-100 parts by weight of industrial silicon powder, 30-50 parts by weight of carbon black, and 20-30 parts by weight of Si3N4. The firing temperature of the boric acid refractory bricks is 1350-1450℃, the firing atmosphere is nitrogen, and the pressure of the firing atmosphere is 0.02-0.04 MPa.

2. The surface treatment process for the bottom of an aluminum electrolytic cell according to claim 1, characterized in that, The roughening treatment solution in step S1 is a sulfuric acid solution with a concentration of 100 g / L to 250 g / L. The roughening treatment temperature is 50-75°C, and the treatment time is 1-6 hours.

3. The surface treatment process for the bottom of an aluminum electrolytic cell according to claim 1, characterized in that, In step S3, the pressure of cold isostatic pressing is 200-500 MPa, and the time of cold isostatic pressing is 1-30 min.

4. The surface treatment process for the bottom of an aluminum electrolytic cell according to claim 1, characterized in that, The heat treatment temperature in step S3 is 800-1000℃, and the heat treatment time is 6-24h.

5. The surface treatment process for the bottom of an aluminum electrolytic cell according to claim 1, characterized in that, In step S2, the permeate also includes an aqueous solution of sodium hexametaphosphate, wherein the amount of sodium hexametaphosphate accounts for 6-18% of the total weight of the permeate, and the concentration of sodium hexametaphosphate is 25 wt%.

6. The surface treatment process for the bottom of an aluminum electrolytic cell according to claim 1, characterized in that, In step S2, the iron powder has a particle size of 18-38 μm, the silicon monoxide has a particle size of 40-80 μm, and the europium oxide has a particle size of 2-15 μm.

7. The surface treatment process for the bottom of an aluminum electrolytic cell according to claim 1, characterized in that, The calcium hexaaluminate has a particle size of 200-300 mesh, the aluminum-magnesium alloy powder has a particle size of 5-10 μm, the boron trioxide has a particle size of 100-200 mesh, and the aluminum powder has a particle size of 10-100 μm.

8. A refractory brick with a high-density impedance layer formed on the surface after surface treatment of the bottom of an aluminum electrolysis cell as described in any one of claims 1-7.

9. The application of the surface treatment process for the bottom of an aluminum electrolytic cell as described in any one of claims 1-7 in an aluminum electrolytic cell.

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