Surface treatment process for bottom of aluminum electrolysis cell

Abstract

The invention relates to the field of refractory materials, in particular to a surface treatment process for the bottom of an aluminum electrolysis cell, and solves the problems that a composite metal object is difficult to form a compact structure with non-metal inorganic substances such as Si3N4 and SiC, and more micropore gaps cause infiltration of molten aluminum and electrolyte and damage to the refractory materials. The method comprises the following steps: carrying out roughening treatment on the surface of a refractory bearing material, coating the exterior of the refractory bearing material with a permeable material with the thickness of 1-10mm, heating to 1300-1420 DEG C, carrying out heat treatment for 5-12h, peeling off the redundant 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, and carrying out heat treatment to obtain the refractory material. And a high-density impedance layer is formed on the surface of the refractory material precursor, and surface treatment is completed. According to the invention, the combination between compact inorganic nonmetal and metal can be realized, and the corrosion resistance of the refractory material is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of refractory materials, and particularly relates to a surface treatment process for the bottom of an aluminum electrolysis cell. Background Art

[0002] When an aluminum electrolysis cell is smelting, it generally uses a composite structure formed by combining a furnace lining and refractory materials at the bottom. However, in addition to receiving the electrolyte, the bottom part also has to come into contact with the molten aluminum formed after electrolysis. Most of the existing materials use Si3N4 and SiC as the materials for receiving the electrolyte and the aluminum liquid. Below this material is the steel bar at the bottom of the tank. Therefore, there are extremely high requirements for the material of the refractory. Otherwise, the breakage of the refractory will cause the aluminum liquid to come into contact with the steel bar, resulting in unstable electric field current, which has a greater impact on the quality and refining efficiency of the aluminum liquid.

[0003] The molten metallic aluminum obtained by electrolysis has a strong penetration ability. Once it penetrates into the refractory brick, it will react with SiO2 in the brick to reduce Si, destroying the organizational structure of the refractory material, causing a metamorphic layer to form on the furnace lining, becoming loose and peeling off, and being damaged. The reaction is: 3SiO2 + 4Al - 2Al2O3 + 3SiO2. The electrolysis cell consists of a rectangular steel shell and a carbon brick lining. Its carbonaceous bottom is the cathode. The aluminum electrolyte selects molten salts such as cryolite, aluminum fluoride, and lithium fluoride as the electrolyte. At about 970°C, Al2O3 is melted and ionized under the action of the electric field force. The molten metal aluminum recovered by electrolysis deposits on the cathode at the bottom of the cell. The electrolysis temperature is 900 - 1000°C. In aluminum electrolysis production, the vapors and liquids of Na and NaF can enter the lower heat insulation layer through the cathode material at the bottom of the cell. After the heat insulation layer absorbs NaF, etc., its thermal conductivity increases, the thermal efficiency of the electrolysis cell decreases, and the operating conditions deteriorate until the cell is damaged. Therefore, it is necessary to improve the anti-permeability performance of the refractory, reduce the existence of micropores and gaps, and form a more dense refractory material or isolation layer.

[0004] Moreover, refractory materials are prone to form SiF4 with the oxygen generated by electrolysis in an environment with fluorides, resulting in serious damage to the refractory. Electrolyte penetration will also dissolve the generated protective oxides, leading to the degradation and damage of the structure of the bottom electrolysis cell, thus causing a series of problems such as unstable current, aluminum liquid loss, pollution, and frequent replacement of the electrolysis cell. Therefore, the existing technology uses a composite refractory material combining a metal substance with Si3N4 and SiC. However, this material has the problem that it is difficult to densify between the inorganic non-metal and the metal phase. Specifically, during the electrolyte erosion process of this material, it will cause the generation of ion vacancies, resulting in the appearance of pores, and then electrolyte penetration causes the damage of the aluminum electrolysis cell. Summary of the Invention

[0005] To solve the problems that Si3N4 and SiC react with HF to generate SiF4 and are corroded, and it is difficult for the composite metal to form a dense structure with non-metallic inorganic substances such as Si3N4 and SiC, resulting in more micropores and gaps, and the molten aluminum and electrolyte penetrate into the refractory material, leading to damage, the present invention provides a surface treatment process for the bottom of an aluminum electrolytic cell. The technical solutions adopted by the present invention are as follows:

[0006] This treatment process is a surface treatment process for the bottom of an aluminum electrolytic cell, including the following specific treatment steps:

[0007] S1. Prepare boric acid refractory bricks. For every 100 parts of boric acid refractory bricks by weight, there are 0.5 - 2 parts of boric acid powder. Fire to obtain a refractory bearing material, and roughen the surface of the refractory bearing material;

[0008] S2. Coating a permeating material on the outside of the refractory bearing material. The thickness of the permeating material is 1 - 10 mm. Heat-treat at 1300 - 1420 °C for 5 - 12 h. After peeling off the excess permeating material, a refractory precursor is obtained;

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

[0010] 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 highly dense impedance layer on the surface of the refractory precursor, completing the surface treatment;

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

[0012] This application mainly forms a permeating material on the roughened refractory brick surface by using iron powder and silicon monoxide. This permeating material can effectively increase the intermolecular bond length between Fe and other materials, weaken the intermolecular binding degree, which is beneficial to the subsequent indirect formation of composite grains by other elements and atoms during the heat treatment process. And europium oxide is also used as an intergranular strengthening material in this permeating material. After sintering treatment, the europium element in europium oxide can be used as an effective component to promote mass transfer and diffusion, making the surface of the inner - layer refractory brick rich in a large amount of Fe - SiO components and trivalent europium elements, which can specifically improve the subsequent strengthening materials, specifically manifested as enhancing grain growth, increasing the density of non - metallic inorganic materials, forming new crystal phases, and thus improving the resistance to molten aluminum and electrolyte substances.

[0013] In this application, calcium hexaaluminate is used as the main material to resist the erosion of molten aluminum. Research shows that calcium hexaaluminate can significantly improve the resistance to molten aluminum. Molten aluminum has strong reducibility. Thermodynamically, calcium oxide will not be reduced by molten aluminum, but calcium is prone to oxidation in an oxygen-rich and complex electrolyte environment to form a microstructure with many micropores, which does not have the characteristic of high density. Therefore, aluminum-magnesium alloy, boron trioxide, and pure aluminum powder are added and sintered together. At high temperatures, a boron magnesium oxide phase with a relatively high melting point can be formed. Among them, boron trioxide can be uniformly melted in the aluminum-magnesium alloy phase in a reduced state, so as to uniformly carry out mass transfer and diffusion, and combine with the permeating material inside, enabling whiskers to form between the B element and the Fe element with an increased molecular bond length, and forming Fe-M-B grains in the microstructure of calcium hexaaluminate, where M is Eu, Mg, or Si, which can fill the molecular gaps inside the non-metallic inorganic phase, thereby enhancing the density and preventing the corrosion and penetration of molten aluminum and electrolyte components.

[0014] Preferably, the raw materials of the boric acid refractory brick in step S1 further 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 brick is 1350-1450 °C, the firing atmosphere is nitrogen, and the pressure of the firing atmosphere is 0.02-0.04 Mpa.

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

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

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

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

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

[0020] The particle size of the iron powder in this application has a certain influence on the corrosion of molten aluminum. An overly small iron particle size will penetrate inward, while an overly large iron powder particle size is difficult to combine, and the corrosion resistance will decrease.

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

[0022] Through a surface treatment process for the bottom of an aluminum electrolytic cell provided by this application, a highly dense impedance layer can be formed on the surface of the treated refractory brick.

[0023] A surface treatment process for the bottom of an aluminum electrolytic cell provided by this application can be applied to related products of aluminum electrolytic cells.

[0024] The beneficial effects of the present invention are as follows:

[0025] By adding boric acid substances to the refractory bricks in this application, more micropores and cracks can be generated in the refractory bricks, which is beneficial to the infiltration of subsequent infiltration materials, and a source of infiltration materials can be formed during the heat treatment process, which can continuously provide Fe-SiO components and trivalent europium elements. These components can form a relatively uniform and dense anti-corrosion layer with the outer calcium hexaaluminate and metal components, effectively resisting the erosion of molten aluminum and electrolyte components, and can significantly increase the service life of the aluminum electrolytic cell.

[0026] This 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 a second-phase Fe-M-B grain, which fills the gaps between inorganic non-metallic particles, strengthens the interaction between grains, and significantly enhances the corrosion resistance of the refractory material. Description of the Drawings

[0027] Figure 1 It is a broken line graph of the corrosion depth of the examples and comparative examples of the present invention. Detailed Embodiments

[0028] The following will refer to the reference appendices Figure 1 The embodiments of the present invention 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 invention and are not intended to limit the protection scope of the present invention.

[0029] Preparation Example 1

[0030] Firing of boric acid refractory bricks

[0031] Mix 85 parts of industrial silicon powder, 40 parts of carbon black, and 25 parts of Si3N4 by weight after crushing, and use a mixer to stir and mix them. Then add 1.5 parts of boric acid powder and water accounting for 30% of the total mass to it until it is stirred evenly to form a blank mud. Press the blank mud with a mold to form a fired rough blank, place it in a vacuum nitrogen sintering furnace, set the firing temperature of the vacuum nitrogen sintering furnace to 1400 °C, the firing atmosphere to nitrogen, and the pressure of the firing atmosphere to 0.03 Mpa to obtain a refractory bearing material, that is, boric acid refractory brick.

[0032] Preparation Example 2

[0033] Firing of Boric Acid Refractory Brick

[0034] Mix 70 parts of industrial silicon powder, 30 parts of carbon black, and 20 parts of Si3N4 by weight after crushing, and use a mixer to stir and mix them. Then add 1.2 parts of boric acid powder and water accounting for 20% of the total mass to it until it is stirred evenly to form a blank mud. Press the blank mud with a mold to form a fired rough blank, place it in a vacuum nitrogen sintering furnace, set the firing temperature of the vacuum nitrogen sintering furnace to 1350 °C, the firing atmosphere to nitrogen, and the pressure of the firing atmosphere to 0.02 Mpa to obtain a refractory bearing material, that is, boric acid refractory brick.

[0035] Preparation Example 3

[0036] Firing of Boric Acid Refractory Brick

[0037] Mix 100 parts of industrial silicon powder, 50 parts of carbon black, and 30 parts of Si3N4 by weight after crushing, and use a mixer to stir and mix them. Then add 1.8 parts of boric acid powder and water accounting for 35% of the total mass to it until it is stirred evenly to form a blank mud. Press the blank mud with a mold to form a fired rough blank, place it in a vacuum nitrogen sintering furnace, set the firing temperature of the vacuum nitrogen sintering furnace to 1450 °C, the firing atmosphere to nitrogen, and the pressure of the firing atmosphere to 0.04 Mpa to obtain a refractory bearing material, that is, boric acid refractory brick.

[0038] Preparation Example 4 - Firing Refractory Brick without Adding Boric Acid

[0039] Firing of Refractory Brick

[0040] Mix 80 parts of industrial silicon powder, 40 parts of carbon black, and 20 parts of Si3N4 by weight after crushing, and use a mixer to stir and mix them. Then add water accounting for 30% of the total mass to it until it is stirred evenly to form a blank mud. Press the blank mud with a mold to form a fired rough blank, place it in a vacuum nitrogen sintering furnace, set the firing temperature of the vacuum nitrogen sintering furnace to 1400 °C, the firing atmosphere to nitrogen, and the pressure of the firing atmosphere to 0.03 Mpa to obtain a refractory brick.

[0041] Preparation Example 5 - Adding Excessive Boric Acid

[0042] Firing of Boric Acid Refractory Brick

[0043] 85 parts by weight of industrial silicon powder, 40 parts of carbon black, and 25 parts of Si3N4 are pulverized and then stirred and mixed using a blender. Then, 6 parts of boric acid powder and water accounting for 30% of the total mass are added thereto until evenly stirred to form a blank mud. The blank mud is pressed using a mold to form a fired rough blank, which is placed in a vacuum nitrogen sintering furnace. The firing temperature of the vacuum nitrogen sintering furnace is set to 1400 °C, the firing atmosphere is nitrogen, and the pressure of the firing atmosphere is 0.03 Mpa, obtaining a refractory bearing material, namely, a boric acid refractory brick.

[0044] Example 1

[0045] Treatment of the highly dense impedance layer

[0046] The refractory bearing material 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 by weight of iron powder, 6 parts of silicon monoxide, and 1.5 parts of europium oxide are weighed to form a mixed powder, and 1.5 parts of sodium hexametaphosphate is dissolved in water to form a bonding liquid with a concentration of 25 wt%. The bonding liquid is added to the mixed powder to form an infiltration material, and then the infiltration material is coated on the surface of the roughened refractory bearing material, controlling the thickness of the infiltration material to be between 4 mm. The refractory bearing material coated with the infiltration material is placed in a sintering kiln, heated to 1350 °C and heat-treated for 8 h. After sintering, a relatively crispy shell layer is formed on the surface of the refractory bearing material. After peeling off the excess shell layer, a refractory material precursor is obtained;

[0047] 45 parts by weight of calcium hexaaluminate, 12 parts of aluminum-magnesium alloy powder, 30 parts of boron trioxide, and 28 parts of aluminum powder are stirred and mixed evenly using a stirrer to form a barrier material. The barrier material and the refractory material precursor are placed in a cold isostatic press, and the pressure of the cold isostatic pressing is set to 300 Mpa, and the cold isostatic pressing time is 10 min, obtaining a rough blank of the refractory material with a barrier layer. The rough blank of the refractory material 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, forming a highly dense impedance layer on the surface of the refractory material precursor.

[0048] In this example, 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 hexaaluminate 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.

[0049] Example 2

[0050] Treatment of the highly dense impedance layer

[0051] The refractory bearing material prepared in Preparation Example 2 was roughened in a sulfuric acid solution with a concentration of 100 g / L. The roughening temperature was set at 50 °C and the roughening time was 1 h. 10 parts by weight of iron powder, 5 parts of silicon monoxide, and 1 part of europium oxide were weighed to form a mixed powder. Then, 1 part of sodium hexametaphosphate was dissolved in water to form a bonding liquid with a concentration of 25 wt%. The bonding liquid was added to the mixed powder to form an infiltration material. Then, the infiltration material was coated on the surface of the roughened refractory bearing material, and the thickness of the infiltration material was controlled to be between 1 mm. The refractory bearing material coated with the infiltration material was placed in a sintering kiln and heated to 1300 °C for heat treatment for 5 h. After sintering, a relatively brittle shell layer was formed on the surface of the refractory bearing material. After peeling off the excess shell layer, a refractory material precursor was obtained;

[0052] 30 parts by weight of calcium hexaaluminate, 10 parts of aluminum-magnesium alloy powder, 20 parts of boron trioxide, and 25 parts of aluminum powder were stirred and mixed evenly by a stirrer to form a barrier material. The barrier material and the refractory material precursor were placed in a cold isostatic press, and the pressure of the cold isostatic pressing was set at 200 Mpa and the cold isostatic pressing time was 30 min to obtain a rough blank of the refractory material with a barrier layer. The rough blank of the refractory material was placed in a heat treatment furnace for heat treatment. The heat treatment temperature was 800 °C and the heat treatment time was 6 h to form a highly dense impedance layer on the surface of the refractory material precursor.

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

[0054] Example 3

[0055] Treatment of the highly dense impedance layer

[0056] The refractory bearing material prepared in Preparation Example 3 was roughened in a sulfuric acid solution with a concentration of 250 g / L. The roughening temperature was set at 75 °C and the roughening time was 6 h. 10 parts by weight of iron powder, 7 parts of silicon monoxide, and 2 parts of europium oxide were weighed to form a mixed powder. Then, 3 parts of sodium hexametaphosphate was dissolved in water to form a bonding liquid with a concentration of 25 wt%. The bonding liquid was added to the mixed powder to form an infiltration material. Then, the infiltration material was coated on the surface of the roughened refractory bearing material, and the thickness of the infiltration material was controlled to be between 10 mm. The refractory bearing material coated with the infiltration material was placed in a sintering kiln and heated to 1420 °C for heat treatment for 12 h. After sintering, a relatively brittle shell layer was formed on the surface of the refractory bearing material. After peeling off the excess shell layer, a refractory material precursor was obtained;

[0057] Mix 55 parts of calcium hexaaluminate, 15 parts of aluminum-magnesium alloy powder, 40 parts of boron trioxide, and 30 parts of aluminum powder by weight using a stirrer to form a barrier material. Place the barrier material and the refractory precursor in a cold isostatic press, set the pressure of the cold isostatic pressing to 500 Mpa, and the cold isostatic pressing time to 1 min to obtain a refractory blank with a barrier layer. Place the refractory blank in a heat treatment furnace for heat treatment, with the heat treatment temperature being 1000 °C and the heat treatment time being 24 h to form a highly dense impedance layer on the surface of the refractory precursor.

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

[0059] Comparative Example 1 - Use a refractory bearing material without adding boric acid

[0060] Treatment of the highly dense impedance layer

[0061] Place the refractory bearing material prepared in Preparation Example 4 in a sulfuric acid solution with a concentration of 200 g / L for roughening, set the roughening temperature to 60 °C, and the roughening time to 3 h; weigh 10 parts of iron powder, 6 parts of silicon monoxide, and 1.5 parts of europium oxide by weight to form a mixed powder, and dissolve 1.5 parts of sodium hexametaphosphate in water to form a bonding solution with a concentration of 25 wt%. Add the bonding solution to the mixed powder to form an infiltration material, then coat the infiltration material on the surface of the roughened refractory bearing material, control the thickness of the infiltration material to be between 4 mm, and place the refractory bearing material coated with the infiltration material in a sintering kiln, heat it to 1350 °C for heat treatment for 8 h. After sintering, a relatively brittle shell layer is formed on the surface of the refractory bearing material. After peeling off the excess shell layer, a refractory precursor is obtained;

[0062] Mix 45 parts of calcium hexaaluminate, 12 parts of aluminum-magnesium alloy powder, 30 parts of boron trioxide, and 28 parts of aluminum powder by weight using a stirrer to form a barrier material. Place the barrier material and the refractory precursor in a cold isostatic press, set the pressure of the cold isostatic pressing to 300 Mpa, and the cold isostatic pressing time to 10 min to obtain a refractory blank with a barrier layer. Place the refractory blank in a heat treatment furnace for heat treatment, with the heat treatment temperature being 900 °C and the heat treatment time being 12 h to form a highly dense impedance layer on the surface of the refractory precursor.

[0063] In this example, the particle size of the iron powder is 30 μm, the particle size of silicon monoxide is 60 μm, the particle size of europium oxide is 10 μm, the calcium hexaaluminate 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.

[0064] Comparative Example 2 - Using a refractory bearing material added with excessive boric acid

[0065] Treatment of the highly dense impedance layer

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

[0067] 45 parts by weight of calcium hexaaluminate, 12 parts of aluminum-magnesium alloy powder, 30 parts of boron trioxide, and 28 parts of aluminum powder were stirred and mixed evenly using a stirrer to form a barrier material. The barrier material and the refractory precursor were placed in a cold isostatic press, and the pressure of the cold isostatic pressing was set at 300 Mpa, and the cold isostatic pressing time was 10 min to obtain a rough blank of the refractory material with a barrier layer. The rough blank of the refractory material 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 highly dense impedance layer on the surface of the refractory precursor.

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

[0069] Comparative Example 3 - Without using the infiltration material

[0070] Treatment of the highly dense impedance layer

[0071] The refractory bearing material prepared in Preparation Example 1 was roughened in a sulfuric acid solution with a concentration of 200 g / L, the roughening temperature was set at 60 °C, and the roughening time was 3 h; a roughened refractory material was obtained;

[0072] Mix 45 parts of calcium hexaaluminate, 12 parts of aluminum-magnesium alloy powder, 30 parts of boron trioxide, and 28 parts of aluminum powder by weight using a stirrer to form a barrier material. Place the barrier material and the roughened refractory material in a cold isostatic press, set the pressure of the cold isostatic pressing to 300 Mpa, and the cold isostatic pressing time to 10 min to obtain a refractory blank with a barrier layer. Place the refractory blank in a heat treatment furnace for heat treatment, with the heat treatment temperature being 900 °C and the heat treatment time being 12 h, to form a highly dense impedance layer on the surface of the roughened refractory material.

[0073] In this example, the particle size of the iron powder is 30 μm, the particle size of silicon monoxide is 60 μm, the particle size of europium oxide is 10 μm, the calcium hexaaluminate 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.

[0074] Comparative Example 4 - Iron powder and silicon monoxide were not used in the permeating material.

[0075] Treatment of the highly dense impedance layer

[0076] Place the refractory bearing material prepared in Preparation Example 1 in a sulfuric acid solution with a concentration of 200 g / L for roughening, set the roughening temperature to 60 °C, and the roughening time to 3 h; weigh 1.5 parts of europium oxide by weight, dissolve 1.5 parts of sodium hexametaphosphate in water to form a bonding solution with a concentration of 25 wt%, add the bonding solution to the europium oxide powder to form a permeating material, then coat the permeating material on the surface of the roughened refractory bearing material, control the thickness of the permeating material to be between 4 mm, and place the refractory bearing material coated with the permeating material in a sintering kiln, heat it to 1350 °C for heat treatment for 8 h. After sintering, a relatively crispy shell layer is formed on the surface of the refractory bearing material. After peeling off the excess shell layer, a refractory precursor is obtained;

[0077] Mix 45 parts of calcium hexaaluminate, 12 parts of aluminum-magnesium alloy powder, 30 parts of boron trioxide, and 28 parts of aluminum powder by weight using a stirrer to form a barrier material. Place the barrier material and the refractory precursor in a cold isostatic press, set the pressure of the cold isostatic pressing to 300 Mpa, and the cold isostatic pressing time to 10 min to obtain a refractory blank with a barrier layer. Place the refractory blank in a heat treatment furnace for heat treatment, with the heat treatment temperature being 900 °C and the heat treatment time being 12 h, to form a highly dense impedance layer on the surface of the refractory precursor.

[0078] In this example, the particle size of the iron powder is 30 μm, the particle size of silicon monoxide is 60 μm, the particle size of europium oxide is 10 μm, the calcium hexaaluminate 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.

[0079] Comparative Example 5 - Europium oxide was not used in the permeating material.

[0080] Treatment of High-Density Impedance Layer

[0081] The refractory bearing material prepared in Preparation Example 1 was roughened in a sulfuric acid solution with a concentration of 200 g / L, the roughening temperature was set at 60 °C, and the roughening time was 3 h; 10 parts by weight of iron powder and 6 parts of silicon monoxide were weighed to form a mixed powder, and 1.5 parts of sodium hexametaphosphate was dissolved in water to form a bonding liquid with a concentration of 25 wt%. The bonding liquid was added to the mixed powder to form an infiltration material, and then the infiltration material was coated on the surface of the roughened refractory bearing material, controlling the thickness of the infiltration material to be between 4 mm. The refractory bearing material coated with the infiltration material was placed in a sintering kiln, heated to 1350 °C and heat-treated for 8 h. After sintering, a relatively crispy shell layer was formed on the surface of the refractory bearing material. After peeling off the excess shell layer, a refractory material precursor was obtained;

[0082] 45 parts by weight of calcium hexaaluminate, 12 parts by weight of aluminum-magnesium alloy powder, 30 parts by weight of boron trioxide, and 28 parts by weight of aluminum powder were stirred and mixed evenly with a stirrer to form a barrier material. The barrier material and the refractory material precursor were placed in a cold isostatic press, and the pressure of the cold isostatic pressing was set at 300 Mpa, and the cold isostatic pressing time was 10 min to obtain a rough blank of the refractory material with a barrier layer. The rough blank of the refractory material 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, and a high-density impedance layer was formed on the surface of the refractory material precursor.

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

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

[0085] Treatment of High-Density Impedance Layer

[0086] The refractory bearing material prepared in Preparation Example 1 was roughened in a sulfuric acid solution with a concentration of 200 g / L, the roughening temperature was set at 60 °C, and the roughening time was 3 h; 10 parts by weight of iron powder, 6 parts of silicon monoxide and 1.5 parts of europium oxide were weighed to form a mixed powder, and 1.5 parts of sodium hexametaphosphate was dissolved in water to form a bonding liquid with a concentration of 25 wt%. The bonding liquid was added to the mixed powder to form an infiltration material, and then the infiltration material was coated on the surface of the roughened refractory bearing material, controlling the thickness of the infiltration material to be between 4 mm. The refractory bearing material coated with the infiltration material was placed in a sintering kiln, heated to 1350 °C and heat-treated for 8 h. After sintering, a relatively crispy shell layer was formed on the surface of the refractory bearing material. After peeling off the excess shell layer, a refractory material precursor was obtained;

[0087] Mix 45 parts of calcium hexaaluminate, 30 parts of boron trioxide, and 28 parts of aluminum powder by weight using a stirrer to form a barrier material. Place the barrier material and the refractory precursor in a cold isostatic press, set the pressure of the cold isostatic pressing to 300 Mpa, and the cold isostatic pressing time to 10 min to obtain a rough refractory blank with a barrier layer. Place the rough refractory blank in a heat treatment furnace for heat treatment, with the heat treatment temperature at 900 °C and the heat treatment time at 12 h to form a highly dense impedance layer on the surface of the refractory precursor.

[0088] In this example, the particle size of the iron powder is 30 μm, the particle size of silicon monoxide is 60 μm, the particle size of europium oxide is 10 μm, the calcium hexaaluminate 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.

[0089] Comparative Example 7 - Boron trioxide is not used in the barrier material

[0090] Treatment of the highly dense impedance layer

[0091] Roughen the refractory bearing material prepared in Preparation Example 1 in a sulfuric acid solution with a concentration of 200 g / L, set the roughening temperature to 60 °C, and the roughening time to 3 h; weigh 10 parts of iron powder, 6 parts of silicon monoxide, and 1.5 parts of europium oxide by weight to form a mixed powder, and dissolve 1.5 parts of sodium hexametaphosphate in water to form a bonding liquid with a concentration of 25 wt%. Add the bonding liquid to the mixed powder to form an infiltration material, then coat the infiltration material on the surface of the roughened refractory bearing material, control the thickness of the infiltration material to be between 4 mm, and place the refractory bearing material coated with the infiltration material in a sintering kiln, heat it to 1350 °C for heat treatment for 8 h. After sintering, a relatively brittle shell layer is formed on the surface of the refractory bearing material. After peeling off the excess shell layer, a refractory precursor is obtained;

[0092] Mix 45 parts of calcium hexaaluminate, 12 parts of aluminum-magnesium alloy powder, and 28 parts of aluminum powder by weight using a stirrer to form a barrier material. Place the barrier material and the refractory precursor in a cold isostatic press, set the pressure of the cold isostatic pressing to 300 Mpa, and the cold isostatic pressing time to 10 min to obtain a rough refractory blank with a barrier layer. Place the rough refractory blank in a heat treatment furnace for heat treatment, with the heat treatment temperature at 900 °C and the heat treatment time at 12 h to form a highly dense impedance layer on the surface of the refractory precursor.

[0093] In this example, the particle size of the iron powder is 30 μm, the particle size of silicon monoxide is 60 μm, the particle size of europium oxide is 10 μm, the calcium hexaaluminate 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.

[0094] Experiments and data

[0095] The refractory materials with a highly dense impedance layer obtained through surface treatment in the above-mentioned respective embodiments and respective comparative examples were subjected to porosity (%), bulk density (g / cm 3 ), compressive strength (Mpa) tests, and penetration depth (mm).

[0096] Among them, the most commonly used method for penetration depth is as follows: After eroding the surface of the refractory materials in the examples and comparative examples with a cryolite melt having a molecular ratio of 2.1 at 900°C for 3 hours, the thickness of the discolored layer was measured, with the unit of mm.

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

[0098] Table 1

[0099] Porosity % <![CDATA[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] A line graph was plotted for the above-mentioned porosity and penetration depth, as Figure 1 shown.

[0101] Analysis

[0102] According to the data in Table 1, it can be seen that in Examples 1, 2, and 3, through the treatment process of the present application, a highly dense impedance layer can be formed on the surface of the refractory precursor, having low porosity, qualified compressive strength, and extremely low penetration resistance, which can better protect the aluminum electrolytic cell from corrosion and increase the service life of the aluminum electrolytic cell.

[0103] According to the data in Table 1, it can be seen that the porosity of Comparative Example 1 is relatively large, and the penetration depth is also very large. Only the compressive strength is qualified. The refractory bearing material used in Comparative Example 1 did not add boric acid, so microporous gaps were formed, and thus less of the subsequent penetration material remained. Therefore, when the barrier material was treated subsequently, it was unable to effectively form sufficient strengthened grains with the molecules in the barrier material, so strengthening was not achieved between the calcium hexaaluminate molecules. Therefore, the porosity is relatively large and it is easily penetrated by molten aluminum or electrolyte. It can be known that adding an appropriate amount of boric acid can effectively reduce the number of pores and prevent corrosion effectively.

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

[0105] According to the data in Table 1, it can be seen that the porosity of Comparative Example 3 is relatively large, the bulk density has decreased to a certain extent, and the penetration depth is relatively deep. The difference between Comparative Example 3 and the examples is that no infiltration material was used to treat the refractory bearing material. Therefore, a strengthening layer connecting the two could not be formed between the barrier material and the refractory bearing material, the metal components in the barrier material could not be combined, the molecular gaps could not be opened, and it was difficult to densify the micropores of the inorganic non-metallic material and fill its molecular vacancies. Therefore, the porosity is relatively high. So, using the infiltration material can effectively improve the infiltration resistance of the refractory material to erosive substances.

[0106] According to the data in Table 1, it can be seen that the porosity of Comparative Example 4 is relatively high and the penetration depth is also relatively large. The difference between Comparative Example 4 and Example 1 is that no iron powder and silicon monoxide were used. As a result, the mass transfer and diffusion of europium oxide were restricted, and a relatively firm crystal structure was not formed. Only part of the gaps in calcium hexaaluminate were filled, and the strengthening effect was not significant. From this, it can be seen that using iron and silicon monoxide can effectively increase the molecular gaps, and iron can also form a crystal with a certain strength with other substances, thereby densifying calcium hexaaluminate, reducing the porosity, and increasing the anti-corrosion performance.

[0107] According to the data in Table 1, it can be seen that the porosity of Comparative Example 5 is relatively high, the bulk density has decreased to a large extent, and the penetration depth is also relatively large. The difference between Comparative Example 5 and the examples is that europium oxide was not used in the infiltration material. Although iron also diffused to a certain extent, without the influence of the mass transfer and diffusion of trivalent europium ions, it could not effectively combine with calcium hexaaluminate, and it was even more difficult to generate Fe-M-B grains, and the porosity could not be effectively reduced. Therefore, the presence of europium oxide can effectively increase the densification effect.

[0108] According to the data in Table 1, it can be seen that the porosity of Comparative Example 6 has increased to a certain extent, the compressive strength has decreased to a certain extent, and the penetration strength has been improved to a certain extent. The difference between Comparative Example 6 and the examples is that aluminum-magnesium alloy was not used in the barrier material. Therefore, after boron trioxide is reduced, it is difficult to uniformly melt in the aluminum liquid, but forms agglomerated AlB2, which will not diffuse inward and combine with elements such as Eu, Fe, and internal Si, C, etc. Therefore, the anti-seepage performance has decreased, and it is difficult to achieve strong anti-seepage. Therefore, the presence of aluminum-magnesium alloy can enhance the participation of boron elements in the formation of new crystal phases of grains.

[0109] According to the data in Table 1, it can be seen that the porosity, bulk density, and compressive strength of Comparative Example 7 are all good, but there is a certain degree of penetration. The difference between Comparative Example 7 and the examples is that boron trioxide was not used in the barrier material, and grains with a higher melting point were not formed in the crystal phase. Therefore, after long-term use, it will still cause a certain degree of reduction penetration, resulting in a certain degree of erosion of the refractory material itself, proving that boron trioxide has a strong effect on improving the corrosion resistance of the refractory dense layer.

[0110] So far, the technical solution of the present invention has been described in conjunction with the preferred embodiments shown in the accompanying drawings. However, it is easily understood by those skilled in the art that the protection scope of the present invention is obviously not limited to these specific embodiments. Without departing from the principle of the present invention, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after these changes or substitutions will all fall within the protection scope of the present invention.

Claims

1. A surface treatment process for the bottom of an aluminum electrolytic cell, characterized in that: The specific processing steps include: S1, preparing boric acid refractory bricks, wherein 0.5-2 parts of boric acid powder are contained in every 100 parts of boric acid refractory bricks by weight, firing to obtain a refractory bearing material, and roughening the surface of the refractory bearing material; S2, coating the outside of the refractory support material with a penetrating material, wherein the thickness of the penetrating material is 1-10 mm, heating to 1300-1420° C. for heat treatment for 5-12 hours, and stripping off excess penetrating material to obtain a refractory precursor; The infiltration material comprises, by weight, 10 parts of iron powder, 5-7 parts of silicon monoxide and 1-2 parts of europium oxide; S3, placing a barrier material on the surface of the refractory precursor, forming a barrier layer by cold isostatic pressing, performing heat treatment, forming a high-density impedance layer on the surface of the refractory precursor, and completing the surface treatment; The barrier material comprises, by weight, 30-55 parts of calcium hexaaluminate, 10-15 parts of aluminum-magnesium alloy powder, 20-40 parts of boron trioxide and 25-30 parts of aluminum powder.

2. The surface treatment process for the bottom of an aluminum electrolytic cell according to claim 1, characterized in that: The raw materials of 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°C, the firing atmosphere is nitrogen, and the pressure of the firing atmosphere is 0.02-0.04Mpa.

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

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

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

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

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

8. 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 meshes, the aluminum-magnesium alloy powder has a particle size of 5-10 μm, the boron trioxide has a particle size of 100-200 meshes, and the aluminum powder has a particle size of 10-100 μm.

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

10. Application of the surface treatment process for the bottom of an aluminum electrolysis cell as described in claims 1-8 in an aluminum electrolysis cell.

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