Alumina-carbon brick for refining ladle lining and its preparation process

Abstract

The application relates to the technical field of refractory materials, in particular to an aluminum-carbon brick for refining ladle walls and a preparation process thereof, which comprises tabular corundum aggregates, alpha-type alumina micropowder, flaky graphite, oxide composite powder, silicon carbide-based composite powder, lanthanum-hafnium composite oxide nanometer powder, aluminum powder, carbon black and thermosetting phenolic resin. The oxide composite powder accelerates the reduction reaction of ferrous oxide on the surface of the brick body, so that the ferrous oxide is rapidly consumed by carbon in a very shallow layer on the contact surface of the brick, and the penetration of the ferrous oxide into the interior of the brick body is prevented; the silicon carbide-based composite powder fixes the liquid iron obtained by surface reduction in situ, so that the liquid iron cannot freely flow and contact the refining slag again; the lanthanum-hafnium composite oxide nanometer powder strengthens the structural stability, and the obtained brick body can better meet the use requirements of long-term high-strength service of the refining ladle walls.

Description

Technical Field

[0001] This invention relates to the field of refractory materials technology, specifically to an alumina-carbon brick for the wall of a refined steel ladle and its preparation process. Background Technology

[0002] The working layer of the ladle wall in refining steel ladles (LF furnace, RH furnace, VOD furnace, etc.) is in direct contact with high-temperature molten steel (1550~1680℃) and highly alkaline refining slag for extended periods during use, making it one of the fastest-wearing parts of the ladle. Alumina-carbon bricks, due to their good thermal shock resistance and high-temperature strength, have been attempted for use in the ladle walls of refining steel ladles in recent years, but they fail relatively quickly in actual service. Refining slag typically contains a certain amount of oxidizing components such as ferrous oxide. At high temperatures, ferrous oxide continuously penetrates into the brick body, undergoing a carbothermic reduction reaction with carbon in the brick along the penetration path (FeO+C→Fe+CO↑). As the penetration depth increases, extensive decarburization occurs inside the brick, forming a loose, porous layer. The molten slag then further penetrates into the brick body along the pores, reacting with alumina to form a low-melting-point phase, triggering structural spalling. This is the main failure path of alumina-carbon bricks.

[0003] To suppress the erosion of carbon in bricks by ferrous oxide, the mainstream existing technology involves adding antioxidants such as aluminum powder and silicon powder to the bricks. These antioxidants preferentially react with the penetrating ferrous oxide, consuming the oxidizing components and thus delaying carbon consumption. However, once the antioxidants are depleted, the bricks lose their resistance to ferrous oxide erosion. More importantly, the fate of the products of the carbothermic reduction reaction—liquid metallic iron—is not considered. At refining service temperatures (1550~1680℃), the reduced metallic iron exists in a liquid form with high fluidity. Due to the slow penetration of ferrous oxide and the dispersed occurrence of the reduction reaction in deeper areas of the brick, liquid iron is generated deep within the brick and continuously contacts the surrounding oxidizing refining slag, being re-oxidized back to ferrous oxide. The newly generated ferrous oxide then penetrates even deeper and is reduced again, and the reduction products are oxidized again, thus creating a vicious cycle. This cycle causes the decarburized area of ​​the brick to continuously expand inward, the porosity to continuously increase, and the slag penetration depth to gradually intensify with each furnace run, ultimately causing the bricks to fail more rapidly with each furnace run. Summary of the Invention

[0004] (1) Technical problems to be solved

[0005] The purpose of this invention is to provide an alumina-carbon brick for the wall of a refining steel ladle and its preparation process, in order to solve the problem that after ferrous oxide in the refining slag penetrates the brick and undergoes a carbothermic reduction reaction with the carbon in the brick, the resulting liquid iron is re-oxidized into ferrous oxide and penetrates deeper, repeatedly increasing the erosion depth of the brick and causing it to fail.

[0006] (2) Technical solution

[0007] To achieve the above objectives, on the one hand, the present invention provides an alumina-carbon brick for the wall of a refined steel ladle, comprising the following components by mass parts: 50-80 parts of tabular corundum aggregate, 5-10 parts of α-alumina micro powder, 8-15 parts of flake graphite, 5-15 parts of oxide composite powder, 5-15 parts of silicon carbide-based composite powder, 0.5-2.0 parts of lanthanum-hafnium composite oxide nanoparticles, 1-3 parts of metallic aluminum powder, 1-2 parts of carbon black, and 3-6 parts of thermosetting phenolic resin.

[0008] Furthermore, the tabular corundum aggregate comprises 15-25 parts of tabular corundum with a particle size of 3-5 mm, 20-30 parts of tabular corundum with a particle size of 1-3 mm, and 15-25 parts of tabular corundum with a particle size of 0-1 mm.

[0009] Furthermore, in the oxide composite powder, based on the percentage of each oxide in the total mass of the powder, the terbium oxide content is 10-15%, the hafnium oxide content is 6-10%, the dysprosium oxide content is 1-3%, the samarium oxide content is 2-5%, the cobalt oxide content is 0.5-2.0%, and the balance is magnesium aluminum spinel.

[0010] Furthermore, the preparation method of the oxide composite powder includes the following steps:

[0011] S11. Add magnesium aluminum spinel powder to an ammonium oxalate aqueous solution with a concentration of 0.05~0.10mol / L, stir at 60~70℃ for 1~2 hours, filter, wash twice with deionized water, and dry at 80℃ to obtain a surface-pretreated spinel carrier.

[0012] S12. Dissolve terbium nitrate, hafnium oxychloride, dysprosium nitrate, and samarium nitrate in deionized water according to the mass ratio of the target oxides to prepare a quaternary mixed salt solution; ultrasonically disperse the surface-pretreated spinel carrier in deionized water to prepare a carrier slurry, and then slowly add the quaternary mixed salt solution to the carrier slurry and stir evenly to obtain a mixture;

[0013] S13. Add 12.5-14.0% dilute ammonia solution to the above mixture under vigorous stirring, adjust the pH to 9.5-10.0, age for 2 hours, filter, wash the filter cake with deionized water at least 3 times, wash it once with anhydrous ethanol, and dry it to obtain precursor powder.

[0014] S14. Place the precursor powder in a high-temperature furnace, heat it to 850-950℃ at 4-6℃ / min, keep it at that temperature for 3-5 hours, and after natural cooling, disperse it by ball milling with zirconia balls as the grinding medium and anhydrous ethanol as the medium. After drying, pass it through a 200-mesh sieve to obtain the intermediate powder.

[0015] S15. The intermediate powder is placed in an aqueous solution of cobalt nitrate hexahydrate, and cobalt nitrate is uniformly impregnated on the surface of the intermediate powder using an equal volume impregnation method according to the target cobalt oxide loading. After standing and impregnating at room temperature for 2 hours, it is evaporated and dried at 80℃, and then placed in a muffle furnace and heated to 350~400℃ at 3~5℃ / min and held for 2 hours. After cooling, it is passed through a 200-mesh sieve to obtain oxide composite powder.

[0016] Furthermore, the specific surface area of ​​the oxide composite powder is not less than 30 m². 2 / g, with an average particle size D50 of 1.0~3.0μm.

[0017] Furthermore, the preparation method of the silicon carbide-based composite powder includes the following steps:

[0018] S21. Weigh each component according to the mass fraction of 65-75% silicon carbide powder, 8-12% aluminum powder, 6-10% silicon powder, and 10-14% molybdenum dicarbide powder. Use zirconia balls as the grinding medium and anhydrous ethanol as the medium to ball-mill and mix them evenly. After drying, pass the mixture through a 100-mesh sieve to obtain mixed raw material powder.

[0019] S22. Place the mixed raw material powder in a high-temperature atmosphere furnace, evacuate until the residual pressure is below 10Pa, then fill with high-purity nitrogen to atmospheric pressure, and circulate for deoxygenation at least 3 times; raise the temperature to 1400~1500℃ at 8℃ / min, and then continuously purge with high-purity nitrogen and maintain a slight positive pressure in the furnace for 2~4 hours. Cool the furnace to room temperature under nitrogen protection to obtain sintered blocks.

[0020] S23. The sintered block is crushed, ball-milled, and passed through a 200-mesh sieve. It is then vacuum-dried at 150°C for 2 hours, cooled, and immediately vacuum-sealed to obtain silicon carbide-based composite powder.

[0021] Furthermore, the silicon carbide-based composite powder contains less than 0.5 wt% aluminum tetracarbide, has an average particle size D50 of 5.0~15.0 μm, and a specific surface area of ​​2.0~5.0 m². 2 / g.

[0022] Furthermore, the lanthanum-hafnium composite oxide nanopowder is prepared by co-precipitation of lanthanum nitrate and hafnium oxychloride, followed by ball milling after calcination at 950-1000℃. The average particle size is not greater than 100nm, the purity is not less than 99.5%, and it is vacuum dried at 150℃ for 2 hours before use.

[0023] On the other hand, the present invention also provides a process for preparing alumina-carbon bricks for the wall of a refining steel ladle, comprising the following steps:

[0024] S1. Mixing: Using a high-speed mixer, add plate-shaped corundum aggregate and half of the thermosetting phenolic resin in sequence and premix for 2 minutes. Then add α-alumina micro powder, oxide composite powder, lanthanum-hafnium composite oxide nano powder, metallic aluminum powder and carbon black and mix for 3 minutes. Add the remaining thermosetting phenolic resin and mix for 2 minutes. Finally, add flake graphite and silicon carbide-based composite powder. Continue mixing at a mixing temperature of 40~50℃ for a total mixing time of 15~20 minutes. The final temperature should not exceed 60℃ until the material is uniform, can be kneaded into a ball by hand, and there is no dry powder or stratification.

[0025] S2. Curing: The mixed mud is placed in a sealed container and cured at room temperature for 24 hours;

[0026] S3. Molding: Use a friction press or hydraulic press to form the brick at a pressure of 150~200MPa, hold the pressure for 5~10 seconds, and the brick blank should be intact and without cracks after molding.

[0027] S4. Drying: Heat the bricks at a rate of 5℃ / h to 80℃ and hold for 12 hours, then heat at a rate of 5℃ / h to 120℃ and hold for 8 hours. The residual moisture content of the bricks after drying should not exceed 0.5%.

[0028] S5. Heat treatment: Under the protection of a reducing atmosphere, the temperature is raised to 1000℃ in a stepwise manner and held for 5 hours. Then, under the protection of a reducing atmosphere, the temperature is cooled to below 800℃ and then naturally cooled to room temperature to obtain an aluminum-carbon brick for the wall of a refined steel ladle.

[0029] Further, the reducing atmosphere in step S5 is a carbon-buried atmosphere or a nitrogen protective atmosphere; the step-by-step heating program is as follows: from room temperature to 200℃ at 10℃ / h, from 200℃ to 600℃ at 15℃ / h, from 600℃ to 1000℃ at 20℃ / h, and after holding at 1000℃ for 5 hours, the furnace is cooled to 800℃ under the protection of a reducing atmosphere, and then naturally cooled to room temperature.

[0030] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0031] 1. This invention accelerates the reduction reaction of ferrous oxide on the surface of bricks using oxide composite powder, causing it to be rapidly consumed by carbon within a very shallow layer in contact with the brick surface, preventing ferrous oxide from penetrating into the interior of the brick, and reducing the total amount and depth of liquid iron generated from the source; the silicon carbide-based composite powder fixes the liquid iron obtained from the surface reduction in situ, preventing it from flowing freely and coming into contact with the refining slag again, thereby cutting off the cycle path of liquid iron being re-oxidized into ferrous oxide and deeply eroding the brick.

[0032] 2. In this invention, the lanthanum-hafnium composite oxide nanopowder enhances the structural stability of the two functional phases during long-term high-temperature service, prevents the iron-fixing trapping phase from failing due to grain growth, and improves the overall high-temperature strength and slag erosion resistance of the matrix, ensuring that the first two mechanisms remain effective without decaying during multiple furnace cycles.

[0033] 3. The brick of this invention has excellent and long-lasting comprehensive high-temperature service performance. After multiple thermal cycles of erosion, the high-temperature flexural strength retention rate is not less than 73%, and the number of thermal shock cycles is not less than 17. The attenuation of the above performance indicators after multiple furnace cycles is significantly lower than that of the same basic formula without the introduction of the above three substances, which can better meet the long-term high-strength service requirements of the ladle wall of refined steel. Attached Figure Description

[0034] Figure 1 This is a flowchart illustrating the preparation process of an alumina-carbon brick for the wall of a refining steel ladle, as described in Embodiment 1 of the present invention.

[0035] Figure 2 This is a physical image of an aluminum-carbon brick for the wall of a refining steel ladle, as described in Embodiment 1 of the present invention. Detailed Implementation

[0036] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0037] Example 1: This example discloses an alumina-carbon brick for the wall of a refined steel ladle, comprising the following components by mass: 65 parts of tabular corundum aggregate, 8 parts of α-alumina micro powder, 12 parts of flake graphite, 10 parts of oxide composite powder, 8 parts of silicon carbide-based composite powder, 1.0 part of lanthanum-hafnium composite oxide nanoparticles, 2 parts of metallic aluminum powder, 1.5 parts of carbon black, and 4.5 parts of thermosetting phenolic resin.

[0038] The tabular corundum aggregate includes 20 parts of tabular corundum with a particle size of 3-5 mm, 25 parts of tabular corundum with a particle size of 1-3 mm, and 20 parts of tabular corundum with a particle size of 0-1 mm.

[0039] In the oxide composite powder, based on the percentage of each oxide in the total mass of the powder, the terbium oxide content is 12%, the hafnium oxide content is 8%, the dysprosium oxide content is 2%, the samarium oxide content is 3%, the cobalt oxide content is 1.0%, and the magnesium aluminum spinel content is 74%.

[0040] The preparation method of the oxide composite powder includes the following steps:

[0041] S11. 75.00 kg of magnesium aluminum spinel micro powder (D50 of 1.5 μm, purity of 99.2%) was added to an ammonium oxalate aqueous solution with a concentration of 0.08 mol / L and stirred at 65 °C for 1.5 hours to allow the ammonium oxalate to react with the Al-OH groups on the spinel surface to form surface complex anchoring points; after filtration, it was washed twice with deionized water and dried at 80 °C to obtain a surface-pretreated spinel carrier;

[0042] S12. Weigh 30.24 kg of terbium nitrate hexahydrate, 25.62 kg of hafnium oxychloride octahydrate, 7.46 kg of dysprosium nitrate hexahydrate, and 10.87 kg of samarium nitrate hexahydrate, dissolve them in 500 L of deionized water, and stir until completely dissolved to prepare a quaternary mixed salt solution; ultrasonically disperse the surface-pretreated spinel carrier in 300 L of deionized water to prepare a carrier slurry, and then slowly pour the above quaternary mixed salt solution into the carrier slurry, stirring continuously for 30 minutes to obtain a mixture;

[0043] S13. Under vigorous stirring, 13% dilute ammonia solution was added dropwise to the mixture at a rate of 6 L / min to adjust the pH to 9.8, so that terbium ions, hafnium ions, dysprosium ions, and samarium ions were completely precipitated as hydroxides and chemically bonded to the surface of spinel particles through surface complexation anchoring points. After aging for 2 hours, the mixture was filtered, and the filter cake was washed three times with deionized water (500 L each time), then washed once with 200 L of anhydrous ethanol. After drying at 110℃ for 24 hours, the mixture was ground through an 80-mesh sieve to obtain the precursor powder.

[0044] S14. The precursor powder is placed in a high-temperature furnace and heated to 900℃ at a rate of 5℃ / min, and held for 4 hours to decompose the hydroxide and form a terbium-hafnium-dysprosium-samarium quaternary composite oxide fluorite-type solid solution in situ. The surface complexing groups introduced by the ammonium oxalate pretreatment are simultaneously converted into Tb-O-Mg and Sm-O-Al interfacial chemical bonds, which firmly bond the fluorite-type solid solution to the spinel carrier. After natural cooling, the powder is ball-milled for 4 hours with zirconia balls as the grinding medium (ball-to-material mass ratio 3:1) and anhydrous ethanol as the medium. After drying, the powder is passed through a 200-mesh sieve to obtain the intermediate powder.

[0045] S15. The intermediate powder was placed in an aqueous solution of cobalt nitrate hexahydrate, and cobalt nitrate was uniformly impregnated onto the surface of the intermediate powder using an equal-volume impregnation method at a target cobalt oxide loading of 1.0%. After standing at room temperature for 2 hours, it was evaporated and dried at 80°C, and then placed in a muffle furnace and heated to 380°C at a rate of 4°C / min and held for 2 hours to decompose the cobalt nitrate and form uniformly dispersed CoO nanoparticles in situ. After cooling, it was passed through a 200-mesh sieve to obtain the oxide composite powder. The specific surface area of ​​the obtained product was 39.2 m². 2 / g, with an average particle size D50 of 1.7μm.

[0046] The preparation method of the silicon carbide-based composite powder includes the following steps:

[0047] S21. Weigh 70.00 kg of silicon carbide powder, 10.00 kg of aluminum powder, 8.00 kg of silicon powder, and 12.00 kg of molybdenum dicarbide powder, load them into a ball mill, add zirconia balls (ball-to-material mass ratio 5:1) and anhydrous ethanol (liquid-to-solid ratio 0.8:1), and ball mill for 4 hours until uniformly mixed; dry at 80℃ for 12 hours and then pass through a 100-mesh sieve to obtain mixed raw material powder;

[0048] S22. The mixed raw material powder is loaded into a high-purity graphite crucible and placed in a high-temperature atmosphere furnace. After evacuating to a residual pressure below 10 Pa, high-purity nitrogen is introduced to atmospheric pressure, and the furnace is circulated for deoxygenation three times. The temperature is increased to 1450℃ at 8℃ / min, and held for 3 hours under the condition of continuous introduction of high-purity nitrogen (flow rate 3L / min, maintaining a slight positive pressure inside the furnace). This allows the aluminum powder and silicon powder to be nitrided in situ to form aluminum nitride and silicon nitride. Molybdenum dicarbide is thermodynamically stable under nitrogen atmosphere and is retained in its original phase. The furnace is then cooled to room temperature under nitrogen protection to obtain a sintered block.

[0049] S23. After coarsely crushing the sintered block, ball mill it for 2 hours using zirconia balls as the grinding medium (ball-to-material mass ratio 3:1) and anhydrous ethanol. After drying, pass it through a 200-mesh sieve. The resulting powder is vacuum dried at 150℃ for 2 hours, cooled, and immediately vacuum-sealed to obtain silicon carbide-based composite powder. The obtained product contains 0.3 wt% aluminum carbide (Al3Carbide), has an average particle size D50 of 9.8 μm, and a specific surface area of ​​3.2 m2. 2 / g.

[0050] It should be noted that the molybdenum dicarbide powder is prepared in advance by the following method: 13.80 kg of molybdenum trioxide powder and 2.42 kg of carbon black are weighed according to the molar ratio of MoO3 to carbon black of 1:2. They are ball-milled and mixed for 4 hours with zirconia balls as the grinding medium and anhydrous ethanol as the medium. After drying, they are passed through a 100-mesh sieve. The mixture is placed in a tube furnace and an Ar / H2 (volume ratio 95:5) gas mixture is introduced. The temperature is increased to 1150℃ at 5℃ / min and held for 3.5 hours to complete the carbothermic reduction reaction (MoO3+2C→Mo2C+3CO↑). After the furnace temperature drops below 200℃, the powder is taken out, ball-milled and crushed, and passed through a 200-mesh sieve. The D50 is controlled to be 1.8μm. The powder is then vacuum-dried at 150℃ and sealed for later use.

[0051] The preparation method of the lanthanum-hafnium composite oxide nanopowder is as follows: 4.33 kg of lanthanum nitrate hexahydrate and 4.09 kg of hafnium chloride octahydrate are weighed according to a La:Hf molar ratio of 1:1 and dissolved in 50 L of deionized water to prepare a mixed salt solution; under vigorous stirring, 13% dilute ammonia solution is added dropwise to adjust the pH to 9.8; after aging for 2 hours, the solution is filtered and thoroughly washed four times with deionized water until no Cl is detected by silver nitrate test. -The mixture was washed once with anhydrous ethanol, dried at 80°C, and then heated to 980°C at 5°C / min and held for 4 hours to form a single-phase lanthanum-hafnium composite oxide. After natural cooling, it was ball-milled at high energy to a D50 of 68 nm, and then vacuum-dried at 150°C for 2 hours before being immediately vacuum-sealed and packaged to obtain lanthanum-hafnium composite oxide nanopowder (purity 99.6%).

[0052] The preparation process of the alumina-carbon brick for the wall of a refined steel ladle includes the following steps:

[0053] S1. Mixing: Using a high-speed mixer, add plate-shaped corundum aggregate and half of the thermosetting phenolic resin in sequence and premix for 2 minutes. Then add α-alumina micro powder, oxide composite powder, lanthanum-hafnium composite oxide nano powder, metallic aluminum powder and carbon black and mix for 3 minutes. Add the remaining thermosetting phenolic resin and mix for 2 minutes. Finally, add flake graphite and silicon carbide-based composite powder and continue mixing at a mixing temperature of 45°C for a total mixing time of 18 minutes and a final temperature of 55°C until the material is uniform, can be kneaded into a ball by hand, and has no dry powder or stratification.

[0054] S2. Curing: The mixed mud is placed in a sealed container and cured at room temperature for 24 hours;

[0055] S3. Molding: A hydraulic press is used to form the bricks under a pressure of 180MPa for 8 seconds. The brick blanks are intact and free of cracks after molding.

[0056] S4. Drying: Heat the bricks at a rate of 5℃ / h to 80℃ and hold for 12 hours, then heat at a rate of 5℃ / h to 120℃ and hold for 8 hours. The residual moisture content of the bricks after drying is 0.3%.

[0057] S5. Heat Treatment: Under a carbon-buried atmosphere, heat treatment is carried out according to a stepped heating program: the temperature is increased from room temperature to 200℃ at a rate of 10℃ / h, from 200℃ to 600℃ at a rate of 15℃ / h, and from 600℃ to 1000℃ at a rate of 20℃ / h. The temperature is then held at 1000℃ for 5 hours to completely carbonize the thermosetting phenolic resin and form a carbon-bonded network. The furnace is then cooled to 800℃ under a carbon-buried atmosphere and then naturally cooled to room temperature to obtain an alumina-carbon brick for the wall of a refined steel ladle. The preparation process is as follows: Figure 1 As shown, the actual object is as follows Figure 2 As shown.

[0058] Example 2: This example differs from Example 1 in that it includes the following components: 50 parts of tabular corundum aggregate, 5 parts of α-type alumina micro powder, 8 parts of flake graphite, 5 parts of oxide composite powder, 5 parts of silicon carbide-based composite powder, 0.5 parts of lanthanum-hafnium composite oxide nanoparticles, 1 part of metallic aluminum powder, 1 part of carbon black, and 3 parts of thermosetting phenolic resin; the tabular corundum aggregate includes 15 parts of tabular corundum with a particle size of 3-5 mm, 20 parts of tabular corundum with a particle size of 1-3 mm, and 15 parts of tabular corundum with a particle size of 0-1 mm; other components and preparation methods are the same as in Example 1.

[0059] Example 3: This example differs from Example 1 in that it includes the following components: 80 parts of tabular corundum aggregate, 10 parts of α-type alumina micro powder, 15 parts of flake graphite, 15 parts of oxide composite powder, 15 parts of silicon carbide-based composite powder, 2.0 parts of lanthanum-hafnium composite oxide nanoparticles, 3 parts of metallic aluminum powder, 2 parts of carbon black, and 6 parts of thermosetting phenolic resin; the tabular corundum aggregate includes 25 parts of tabular corundum with a particle size of 3-5 mm, 30 parts of tabular corundum with a particle size of 1-3 mm, and 25 parts of tabular corundum with a particle size of 0-1 mm; other components and preparation methods are the same as in Example 1.

[0060] Comparative Example 1: This comparative example differs from Example 1 in that the samarium component is omitted in the preparation of the oxide composite powder. In this comparative example, samarium nitrate hexahydrate is not added in step S12; only terbium nitrate hexahydrate, hafnium chloride octahydrate, and dysprosium nitrate hexahydrate are retained. The amounts of each salt are adjusted to maintain the total loading of terbium, hafnium, and dysprosium oxides consistent with the total loading of terbium, hafnium, dysprosium, and samarium in Example 1 (i.e., the loading of terbium is increased to 15%, while the loadings of hafnium and dysprosium remain unchanged). The steps of ammonium oxalate pretreatment (S11), precipitation (S13), calcination (S14), and cobalt oxide impregnation (S15) are the same as in Example 1. The resulting powder is a terbium-hafnium-dysprosium ternary composite oxide fluorite-type solid solution / magnesium aluminum spinel system. After omitting the samarium component, the oxygen vacancy density in the fluorite solid solution decreases, and the oxygen ion conduction flux weakens. The remaining components, dosages, and preparation processes of the brick are exactly the same as in Example 1.

[0061] Comparative Example 2: This comparative example differs from Example 1 in that terbium and samarium components are omitted in the preparation of the oxide composite powder. In this comparative example, terbium nitrate hexahydrate and samarium nitrate hexahydrate are not added in step S12; only hafnium oxychloride octahydrate and dysprosium nitrate hexahydrate are retained. The amount of each salt is adjusted to maintain the total loading of hafnium and dysprosium oxides consistent with that in Example 1. The unfilled loading of terbium and samarium is made up with magnesium aluminum spinel. The steps of ammonium oxalate pretreatment (S11), precipitation (S13), calcination (S14), and cobalt oxide impregnation (S15) are the same as in Example 1. The remaining components, amounts, and preparation processes of the brick are exactly the same as in Example 1.

[0062] Comparative Example 3: This comparative example differs from Example 1 in that the ammonium oxalate surface complexation pretreatment step is omitted in the preparation of the oxide composite powder. In this comparative example, in step S11, deionized water is used instead of the ammonium oxalate aqueous solution to soak and stir the magnesium aluminum spinel powder at the same temperature and time. The remaining washing and drying operations remain unchanged, and the surface of the resulting spinel carrier does not contain complexation anchoring points. Steps S12 to S15 are exactly the same as in Example 1, that is, the co-precipitation process is still carried out normally, the high-temperature calcination still forms a fluorite-type solid solution, and the cobalt oxide is still loaded by the equal-volume impregnation method. The composition of the resulting powder is the same as in Example 1, but the fluorite-type solid solution and the spinel carrier are only physically attached. The remaining components, amounts, and preparation processes of the brick are exactly the same as in Example 1.

[0063] Comparative Example 4: This comparative example differs from Example 1 in that the cobalt oxide loading treatment in step S15 is omitted in the preparation of the oxide composite powder, and the solid solution surface does not contain CoO nanoparticles. In this comparative example, after obtaining the intermediate powder in step S14, it is not subjected to equal-volume impregnation with cobalt nitrate and subsequent calcination treatment; the intermediate powder is directly passed through a 200-mesh sieve and used as the oxide composite powder. The surface of the resulting powder solid solution does not contain CoO nanoparticles, and the surface pre-activated units of FeO lattice oxygen are missing. The remaining components, amounts, and preparation processes of the brick are exactly the same as in Example 1.

[0064] Comparative Example 5: This comparative example differs from Example 1 in that the molybdenum dicarbide component is omitted in the preparation of the silicon carbide-based composite powder. In this comparative example, molybdenum dicarbide powder is not added in step S21, and the proportion of silicon carbide powder is increased to 82% to compensate for the mass. The amounts of aluminum powder and silicon powder remain unchanged. The operations of steps S22 and S23 are the same as in Example 1. The resulting powder contains only silicon carbide, aluminum nitride, and silicon nitride, and does not contain molybdenum dicarbide, thus lacking the functional phase for in-situ trapping of liquid iron. The remaining components, amounts, and preparation process of the brick are exactly the same as in Example 1.

[0065] Comparative Example 6: This comparative example differs from Example 1 in that the silicon carbide-based composite powder does not undergo high-temperature nitriding heat treatment. In this comparative example, after ball milling and mixing in step S21, the high-temperature nitriding sintering treatment in step S22 is skipped. The dried mixed raw material powder is directly passed through a 200-mesh sieve, vacuum dried at 150°C for 2 hours, and then vacuum-sealed and packaged for use as silicon carbide-based composite powder. That is, the components in the powder used in this comparative example exist simply as a mixture of raw materials (silicon carbide, aluminum powder, silicon powder, and molybdenum dicarbide), without the in-situ formation of aluminum nitride and silicon nitride. The remaining components, amounts, and preparation processes of the brick are exactly the same as in Example 1.

[0066] Comparative Example 7: This comparative example differs from Example 1 in that no oxide composite powder is added.

[0067] Comparative Example 8: This comparative example differs from Example 1 in that it does not contain silicon carbide-based composite powder.

[0068] Comparative Example 9: This comparative example differs from Example 1 in that it does not contain lanthanum-hafnium composite oxide nanoparticles.

[0069] Comparative Example 10: This comparative example differs from Example 1 in that it does not contain oxide composite powder, silicon carbide-based composite powder, or lanthanum-hafnium composite oxide nanoparticles.

[0070] Experimental verification:

[0071] Experiment 1: Verify the corrosion resistance of aluminum-carbon bricks under single erosion conditions of high ferrous oxide refining slag. The results are shown in Table 1.

[0072] Test samples: Examples 1-3 and Comparative Examples 1-10, with 3 samples prepared in parallel for each group.

[0073] Experimental Method: A static crucible method was used. Cylindrical erosion pits with a diameter of 30 mm and a depth of 30 mm were machined on each group of brick blanks. These pits were filled with synthetic refining slag (mass fraction: 8% ferrous oxide, 45% calcium oxide, 20% silicon dioxide, 15% aluminum oxide, and 12% magnesium oxide). The pits were placed in a silicon-molybdenum rod high-temperature furnace and held at 1600℃ for 3 hours and 6 hours respectively. After cooling to room temperature with the furnace, the pits were removed. A cross-section was cut along the central axis of the erosion pit. After grinding and polishing, the vertical distance from the bottom of the erosion pit to the original brick surface was measured using vernier calipers. The average value of three cross-sections was taken as the erosion depth (mm). Brick powder from the area 3-5 mm from the bottom of the erosion pit was collected, and the residual carbon content was determined using a carbon-sulfur analyzer. The residual carbon content retention rate (the ratio of residual carbon content to the carbon content of an un-eroded reference brick sample from the same batch, %) was calculated. The increase in apparent porosity of the entire brick after erosion (the difference between apparent porosity after erosion and apparent porosity before erosion, denoted as Δp) was determined using the Archimedes method. Each indicator in each group was measured in parallel three times, and the results are expressed as the mean range.

[0074] Table 1. Corrosion resistance of each group of samples under single erosion conditions of high ferrous oxide refining slag (FeO 8%) at 1600℃:

[0075]

[0076] Experiment 2: Verify the comprehensive high-temperature service performance of aluminum-carbon bricks under multiple thermal cyclic erosion conditions. The results are shown in Table 2.

[0077] Test samples: Examples 1-3 and Comparative Examples 1-10, 5 samples were prepared in parallel for each group.

[0078] Experimental Method: A single thermal cycle was used to simulate the service conditions of a refining furnace. Each group of brick samples was contacted with synthetic refining slag containing 8% ferrous oxide (composition same as in Experiment 1) at 1600℃ for 1 hour. The samples were then removed from the furnace and air-cooled to room temperature. After removing residual slag, the next cycle was performed, for a total of 10 cycles. After the 1st and 10th cycles, the erosion depth increment for each cycle was measured using vernier calipers, and expressed as Δd. 10-1 This represents the difference (mm) between the depth of the 10th single erosion and the depth of the 1st single erosion. A positive value indicates that erosion accelerates with each furnace cycle (continuous accumulation during re-oxidation cycles), while a negative value or value close to zero indicates that the erosion rate is stable or decreasing (protective layer is formed and remains effective).

[0079] After all 10 cycles were completed, the following tests were conducted on each group of brick samples: The high-temperature flexural strength before and after the cycle was measured at 1400℃ using a trapezoidal high-temperature flexural strength tester, and the high-temperature flexural strength retention rate (ratio of the retention rate after the cycle to that before the cycle, %) was calculated; the cumulative erosion depth (mm) of 10 cycles was calculated by accumulating the erosion depth increment of each cycle using calipers; following the standard procedure of holding at 1100℃ for 30 minutes followed by water cooling, the number of thermal shock cycles was determined with the high-temperature flexural strength retention rate dropping below 60% of the initial value as the failure criterion; the brick samples after 10 cycles were visually inspected and their cross-sectional structural integrity was rated (Excellent: no cracks or spalling on the surface and cross-section; Good: slight spalling at the edges but the working layer is generally intact; Medium: local cracking or obvious spalling in the working layer; Poor: large-area cracking or structural damage in the working layer). Each numerical indicator for each group was measured in parallel three times, and the structural integrity rating was calculated by taking the mode of all five ratings.

[0080] Table 2. Comprehensive high-temperature service performance of each group of samples under multiple thermal cyclic erosion conditions (10 cycles, 1600℃×1h / cycle):

[0081]

[0082] Based on the data in Tables 1 and 2, Examples 1-3 outperformed all comparative examples in all indicators in both tests, confirming that the present invention accelerates the reduction reaction of ferrous oxide on the brick surface through oxide composite powder, causing it to be rapidly consumed by carbon within a very shallow layer in contact with the brick surface, thus preventing ferrous oxide from penetrating into the brick interior; silicon carbide-based composite powder fixes the liquid iron obtained from surface reduction in situ, preventing it from flowing freely and coming into contact with refining slag again; lanthanum-hafnium composite oxide nanoparticles enhance structural stability. The bricks of the present invention can better meet the long-term high-strength service requirements of refining ladle walls.

[0083] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, and improvements made by those skilled in the art within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. An alumina-carbon brick for the wall of a refined steel ladle, characterized in that, The composition, by mass fraction, includes the following components: 50-80 parts of tabular corundum aggregate, 5-10 parts of α-alumina micro powder, 8-15 parts of flake graphite, 5-15 parts of oxide composite powder, 5-15 parts of silicon carbide-based composite powder, 0.5-2.0 parts of lanthanum-hafnium composite oxide nanoparticles, 1-3 parts of metallic aluminum powder, 1-2 parts of carbon black, and 3-6 parts of thermosetting phenolic resin.

2. The alumina-carbon brick for refining steel ladle walls according to claim 1, characterized in that, The tabular corundum aggregate includes 15-25 parts of tabular corundum with a particle size of 3-5 mm, 20-30 parts of tabular corundum with a particle size of 1-3 mm, and 15-25 parts of tabular corundum with a particle size of 0-1 mm.

3. The alumina-carbon brick for refining steel ladle walls according to claim 1, characterized in that, In the oxide composite powder, based on the percentage of each oxide in the total mass of the powder, the terbium oxide content is 10-15%, the hafnium oxide content is 6-10%, the dysprosium oxide content is 1-3%, the samarium oxide content is 2-5%, the cobalt oxide content is 0.5-2.0%, and the balance is magnesium aluminum spinel.

4. The alumina-carbon brick for the wall of a refining steel ladle according to claim 1, characterized in that, The preparation method of the oxide composite powder includes the following steps: S11. Add magnesium aluminum spinel powder to an ammonium oxalate aqueous solution with a concentration of 0.05~0.10mol / L, stir at 60~70℃ for 1~2 hours, filter, wash twice with deionized water, and dry at 80℃ to obtain a surface-pretreated spinel carrier. S12. Dissolve terbium nitrate, hafnium oxychloride, dysprosium nitrate, and samarium nitrate in deionized water according to the mass ratio of the target oxides to prepare a quaternary mixed salt solution; ultrasonically disperse the surface-pretreated spinel carrier in deionized water to prepare a carrier slurry, and then slowly add the quaternary mixed salt solution to the carrier slurry and stir evenly to obtain a mixture; S13. Add 12.5-14.0% dilute ammonia solution to the above mixture under vigorous stirring, adjust the pH to 9.5-10.0, age for 2 hours, filter, wash the filter cake with deionized water at least 3 times, wash it once with anhydrous ethanol, and dry it to obtain precursor powder. S14. Place the precursor powder in a high-temperature furnace, heat it to 850-950℃ at 4-6℃ / min, keep it at that temperature for 3-5 hours, and after natural cooling, disperse it by ball milling with zirconia balls as the grinding medium and anhydrous ethanol as the medium. After drying, pass it through a 200-mesh sieve to obtain the intermediate powder. S15. The intermediate powder is placed in an aqueous solution of cobalt nitrate hexahydrate, and cobalt nitrate is uniformly impregnated on the surface of the intermediate powder using an equal volume impregnation method according to the target cobalt oxide loading. After standing and impregnating at room temperature for 2 hours, it is evaporated and dried at 80℃, and then placed in a muffle furnace and heated to 350~400℃ at 3~5℃ / min and held for 2 hours. After cooling, it is passed through a 200-mesh sieve to obtain oxide composite powder.

5. The alumina-carbon brick for the wall of a refining steel ladle according to claim 4, characterized in that, The specific surface area of ​​the oxide composite powder is not less than 30m². 2 / g, with an average particle size D50 of 1.0~3.0μm.

6. The alumina-carbon brick for the wall of a refined steel ladle according to claim 1, characterized in that, The preparation method of the silicon carbide-based composite powder includes the following steps: S21. Weigh each component according to the mass fraction of 65-75% silicon carbide powder, 8-12% aluminum powder, 6-10% silicon powder, and 10-14% molybdenum dicarbide powder. Use zirconia balls as the grinding medium and anhydrous ethanol as the medium to ball-mill and mix them evenly. After drying, pass the mixture through a 100-mesh sieve to obtain mixed raw material powder. S22. Place the mixed raw material powder in a high-temperature atmosphere furnace, evacuate until the residual pressure is below 10Pa, then fill with high-purity nitrogen to atmospheric pressure, and circulate for deoxygenation at least 3 times; raise the temperature to 1400~1500℃ at 8℃ / min, and then continuously purge with high-purity nitrogen and maintain a slight positive pressure in the furnace for 2~4 hours. Cool the furnace to room temperature under nitrogen protection to obtain sintered blocks. S23. The sintered block is crushed, ball-milled, and passed through a 200-mesh sieve. It is then vacuum-dried at 150°C for 2 hours, cooled, and immediately vacuum-sealed to obtain silicon carbide-based composite powder.

7. The alumina-carbon brick for refining steel ladle walls according to claim 6, characterized in that, The silicon carbide-based composite powder contains less than 0.5 wt% aluminum tetracarbide, has an average particle size D50 of 5.0–15.0 μm, and a specific surface area of ​​2.0–5.0 m². 2 / g.

8. The alumina-carbon brick for the wall of a refining steel ladle according to claim 1, characterized in that, The lanthanum-hafnium composite oxide nanoparticles are prepared by co-precipitation of lanthanum nitrate and hafnium oxychloride, followed by ball milling after calcination at 950-1000℃. The average particle size is not greater than 100nm, and the purity is not less than 99.5%. Before use, they are vacuum dried at 150℃ for 2 hours.

9. The preparation process of an alumina-carbon brick for the wall of a refined steel ladle according to any one of claims 1 to 8, characterized in that, Includes the following steps: S1. Mixing: Using a high-speed mixer, add plate-shaped corundum aggregate and half of the thermosetting phenolic resin in sequence and premix for 2 minutes. Then add α-alumina micro powder, oxide composite powder, lanthanum-hafnium composite oxide nano powder, metallic aluminum powder and carbon black and mix for 3 minutes. Add the remaining thermosetting phenolic resin and mix for 2 minutes. Finally, add flake graphite and silicon carbide-based composite powder. Continue mixing at a mixing temperature of 40~50℃ for a total mixing time of 15~20 minutes. The final temperature should not exceed 60℃ until the material is uniform, can be kneaded into a ball by hand, and there is no dry powder or stratification. S2. Curing: The mixed mud is placed in a sealed container and cured at room temperature for 24 hours; S3. Molding: Use a friction press or hydraulic press to form the brick at a pressure of 150~200MPa, hold the pressure for 5~10 seconds, and the brick blank should be intact and without cracks after molding. S4. Drying: Heat the bricks at a rate of 5℃ / h to 80℃ and hold for 12 hours, then heat at a rate of 5℃ / h to 120℃ and hold for 8 hours. The residual moisture content of the bricks after drying should not exceed 0.5%. S5. Heat treatment: Under the protection of a reducing atmosphere, the temperature is raised to 1000℃ in a stepwise manner and held for 5 hours. Then, under the protection of a reducing atmosphere, the temperature is cooled to below 800℃ and then naturally cooled to room temperature to obtain an aluminum-carbon brick for the wall of a refined steel ladle.

10. The preparation process of an alumina-carbon brick for the wall of a refined steel ladle according to claim 9, characterized in that, The reducing atmosphere mentioned in step S5 is a carbon-buried atmosphere or a nitrogen protective atmosphere; the step-by-step heating program is as follows: the temperature is increased from room temperature to 200℃ at a rate of 10℃ / h, from 200℃ to 600℃ at a rate of 15℃ / h, from 600℃ to 1000℃ at a rate of 20℃ / h, and after holding at 1000℃ for 5 hours, the temperature is cooled to 800℃ in the furnace under the protection of the reducing atmosphere, and then naturally cooled to room temperature.

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