A fused cast β-cordierite brick and a method for producing the same

Abstract

The application discloses a kind of fused cast beta-corundum brick and preparation method thereof, belong to refractory material technical field.The fused cast beta-corundum brick is prepared by Ni (NO3) 26H2O, Co (NO3) 26H2O, alpha-Al2O3, Na2CO3 as raw material, by fusion casting method;Preparation steps include: preparation Ni (NO3) 26H2O and Co (NO3) 26H2O composite salt solution and infiltrate alpha-Al2O3 with Na2CO3 powder, by spray drying, ball milling, screening and obtain mixed powder;Preheat high-purity graphite crucible after charging, high-purity argon is imported, stage heating is kept to 1950-2050 DEG C, pouring is kept to preheating mould, finally cooling annealing and with furnace cooling to room temperature and obtain fused cast beta-corundum brick.The fused cast beta-corundum brick prepared by optimizing raw material ratio, fusion casting and annealing process parameters is stable in performance, preparation method process controllable, good repeatability, with good application prospect.

Description

Technical Field

[0001] This invention belongs to the field of refractory material preparation technology, specifically relating to a cast β-corundum brick and its preparation method. Background Technology

[0002] Corundum bricks, as a high-performance refractory material, are widely used in high-temperature industries such as metallurgy, building materials, chemicals, and ceramics due to their excellent high-temperature resistance, high strength, good chemical stability, and wear resistance. They are a core material for the lining of high-temperature kilns and melting equipment. Among them, cast β-corundum bricks, with β-Al2O3 as the main crystalline phase and extremely low glass phase content, are inert to alkaline vapors and have excellent thermal shock resistance. They are particularly suitable for key parts such as the upper structure of glass melting furnaces, the working pool of high-end glass furnaces, and the lining of the feeding section. They also show good application potential in new scenarios such as the construction of the dome of oxygen-enriched combustion glass melting furnaces and special metallurgical electrolytic cells. Currently, the preparation of cast β-corundum bricks is mainly based on the electrofusion method. The core process involves mixing α-Al2O3 raw materials with flux, melting and casting at high temperature, and then annealing to obtain the finished product. The selection and dosage of flux, as well as the control of melting and annealing process parameters, directly determine the crystalline phase composition, density, and service performance of cast β-corundum bricks. In existing technologies, Na₂CO₃ is typically used as a flux to introduce Na₂O, thereby lowering the melting temperature of α-Al₂O₃ and promoting the formation of the β-Al₂O₃ crystal phase. However, Na₂CO₃ is prone to volatilization loss during high-temperature decomposition, resulting in insufficient Na₂O content actually participating in the reaction. This makes it difficult to accurately control the amount of β-Al₂O₃ generated, thus affecting the structural uniformity and erosion resistance of the brick. Simultaneously, existing fused cast β-corundum brick preparation processes commonly suffer from defects such as shrinkage porosity, shrinkage cavities, and cracks within the brick, ultimately affecting its density and mechanical properties and shortening its service life. Furthermore, some preparation processes introduce various modifying components to improve brick performance, but these often suffer from uneven dispersion and poor bonding with the β-Al₂O₃ matrix, failing to fully realize their modifying effects and even introducing impurities. This can lead to phase transformation during high-temperature service, causing the brick to fracture. With the downstream industries shifting towards high-end and energy-saving technologies, especially the rapid development of high-end fields such as photovoltaic glass and semiconductors, higher performance requirements are being placed on fused cast β-corundum bricks. These bricks not only need excellent resistance to molten glass erosion, high-temperature strength, and thermal shock stability, but also require a crack-free, inclusion-free, and dense structure to avoid contaminating the melt or failing due to structural defects. However, existing preparation methods suffer from drawbacks such as high melting temperature, high energy consumption, difficulty in controlling process parameters, high product defect rate, and poor performance stability, making it difficult to meet the needs of high-end applications. Furthermore, the preparation process itself is energy-intensive.

[0003] Therefore, developing a simple, energy-efficient, and parameter-controllable method for preparing fused cast β-corundum bricks that can effectively reduce brick defects, improve product performance stability, and meet the application needs of high-end fields, and solve the aforementioned technical pain points in the existing technology, has become a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art. This invention provides a cast β-corundum brick, which is mainly obtained by casting Ni(NO3)2·6H2O, Co(NO3)2·6H2O, α-Al2O3, and Na2CO3 in a mass ratio of 0.21-0.25:0.12:37.6-38.5:2.4-2.8.

[0005] Furthermore, the preparation method of cast β-corundum bricks includes the following steps:

[0006] Step S1: Weigh the raw materials, prepare a composite salt solution and impregnate α-Al2O3 and Na2CO3 powders, then spray dry, ball mill, and sieve to obtain a mixed powder; Step S2: After preheating the high-purity graphite crucible, fill it with the mixed powder obtained in step S1 and compact it. Place the crucible in the center of the electric arc furnace, introduce high-purity argon gas to maintain a slight positive pressure inside the furnace, and gradually increase the temperature. Step S3: Continue heating to 1950-2050℃ and hold at that temperature. Pour the molten liquid into the preheated molding mold, and then transfer it to a heat-insulating cellar for slow cooling. Step S4: When the temperature of the brick in the mold naturally drops to 1400-1500℃, it is cooled and annealed, and then cooled to room temperature with the furnace to obtain fused cast β-corundum brick.

[0007] Further, in step S1, the composite salt solution includes Ni(NO3)2·6H2O and Co(NO3)2·6H2O, with a total concentration of 0.14-0.20 g / mL.

[0008] Further, in step S1, the inlet air temperature of the spray dryer is 170-180℃ and the outlet air temperature is 80-90℃, the rotation speed of the ball mill is 300-400 r / min, and the time is 20-30 min.

[0009] Furthermore, in step S2, the preheating temperature of the high-purity graphite crucible is 250-300℃, and the time is 20-30 minutes.

[0010] Further, in step S2, the rate of introduction of the high-purity argon gas is 0.8-1.0 L / min, and the micro-positive pressure is 0.02-0.04 MPa.

[0011] Furthermore, in step S2, the staged heating mainly includes: A1: Increase the temperature to 300-400℃ at a rate of 4℃ / min and hold for 30min; A2: Increase the temperature to 600-800℃ at a rate of 2℃ / min and hold for 60-90min; A3: Increase the temperature to 1200℃ at a rate of 4℃ / min and hold for 40-60 minutes.

[0012] Furthermore, in step S3, the heat preservation time is 90-120 min, and the heating rate is 4℃ / min.

[0013] Furthermore, in step S3, the preheating temperature of the molding die is 1200℃, and the pouring temperature is 1900-1950℃.

[0014] Further, in step S4, the cooling annealing is as follows: cooling to 1100℃ at 2℃ / min and holding for 2-4 hours; then cooling to 600-800℃ at 0.5℃ / min; and then cooling to 500℃ at 1℃ / min and holding for 2 hours.

[0015] Beneficial effects: This invention introduces Ni(NO3)2 into the fused casting β-corundum brick preparation system. 6H2O and Co(NO3)2 6H2O, utilizing Ni 2+ with Ni 3+ Interconversion, Co 2+ With Co 3+ The reversible valence-changing redox process, combined with the synergistic effect of high-temperature melting and annealing, endows cast β-corundum bricks with excellent comprehensive properties. When microcracks are generated in the brick, the oxygen potential gradient between the crack region and the matrix triggers Ni… 2+ To Ni 3+ Co 2+ To Co 3+The oxidation reaction releases a small amount of heat, which is precisely concentrated in the crack area. Without external energy input, this provides sufficient energy for the melting of trace amounts of the low-melting-point Na₂O-Al₂O₃ phase in the system, initiating the self-healing process. The molten low-melting-point phase, aided by capillary action within the crack, quickly and uniformly fills the entire crack gap. Simultaneously, catalytic new phase particles (NiAl₂O₄, CoAl₂O₄) are uniformly dispersed within the molten material, acting as a skeletal support to prevent shrinkage and collapse upon cooling, ensuring the density of the crack filling. With temperature fluctuations in the high-temperature service environment, the molten material filling the crack gradually cools and crystallizes, undergoing a solid solution reaction with the β-Al₂O₃ main crystalline phase and the NiAl₂O₄-CoAl₂O₄ catalytic new phase, resulting in a strong bond between the crack area and the brick matrix. The thermal expansion coefficients of the catalytic new phases (NiAl2O4, CoAl2O4) are highly compatible with those of the β-Al2O3 matrix. Combined with the dense structure formed after the low-melting-point phase fills and heals, it can effectively buffer thermal stress during high-temperature cooling, resulting in no significant crack propagation after thermal shock. Simultaneously, the dense composite structure and the excellent inertness of the spinel phase to molten glass and alkali vapors enhance the brick's resistance to melt erosion, preventing melt contamination caused by crack penetration and erosion during high-temperature service. Detailed Implementation

[0016] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0017] Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of this invention. Experimental methods in the following embodiments that do not specify specific conditions are generally performed under conventional conditions or as recommended by the manufacturer. Unless otherwise stated, all percentages, ratios, proportions, or parts are by weight.

[0018] Unless otherwise specified, the reagents and raw materials used in the embodiments and comparative examples of this invention are commercially available.

[0019] Example 1 The preparation method of cast β-corundum bricks includes the following steps: Step S1: Accurately weigh Ni(NO3)2·6H2O and Co(NO3)2·6H2O, place them in a beaker, add deionized water, and stir until completely dissolved to prepare a composite salt solution with a total concentration of 0.16 g / mL. Weigh α-Al2O3 powder and Na2CO3 powder and place them in a dry beaker. Slowly pour in the prepared composite salt solution while stirring to ensure that the solution evenly wets each portion of powder. Let it stand for 25 minutes to allow the salt solution to fully penetrate. Send the impregnated material into a spray dryer, set the inlet air temperature to 175℃ and the outlet air temperature to 85℃, and spray dry to obtain a uniformly dispersed composite powder. Load the dried composite powder into a planetary ball mill, add wear-resistant grinding balls, set the speed to 350 r / min, dry grind for 25 minutes, pass through an 80-mesh standard sieve, and collect the sieved mixed powder for later use. The mass ratio of Ni(NO3)2·6H2O:Co(NO3)2·6H2O:α-Al2O3:Na2CO3 is 0.23:0.12:38.0:2.6.

[0020] Step S2: Place the high-purity graphite crucible in an oven and preheat at 270℃ for 25 minutes to remove adsorbed gases and moisture from the crucible surface. Slowly fill the preheated graphite crucible with the sieved mixed powder, gently vibrating it as you fill to ensure compaction and prevent voids. Gently compact the powder with a pressure bar, ensuring the filling height does not exceed 2 / 3 of the crucible's volume. Place the graphite crucible containing the powder into the electric arc furnace, adjusting its position to be centered within the furnace body. Close the furnace door and check the furnace's seal to ensure there are no leaks. Turn on the argon supply system, introducing high-purity argon at a rate of 0.9 L / min to purge air from the furnace and maintain a slight positive pressure (0.03 MPa) within the furnace. Maintain argon flow throughout the process, with staged temperature increases for decomposition. First stage: Increase the temperature to 350℃ at a rate of 4℃ / min and hold for 30min; Second stage: Heat to 700℃ at 2℃ / min and hold for 80min to allow Ni(NO3)2 and Co(NO3)2 to decompose fully and generate NiO, CoO and gases such as NO2 and O2. The gases are discharged with argon. The third stage involves heating to 1200℃ at a rate of 4℃ / min and holding for 50 minutes to ensure complete decomposition of nitrates, while simultaneously allowing Na2CO3 to fully decompose into Na2O and CO2, and for NiO and CoO to initially diffuse and mix with Al2O3.

[0021] Step S3: After decomposition, continue heating to 2000℃ at a rate of 4℃ / min and hold for 100min; place the molding mold in another oven in advance, preheat at 1200℃ and hold for 60min, then remove and quickly place it at the casting station to prevent the mold temperature from dropping; stop the electric arc furnace heating, keep argon gas flowing, and wait for the furnace temperature to drop naturally to 1920℃; slowly tilt the furnace body and pour the molten liquid in the graphite crucible into the preheated molding mold in a stable thin stream, controlling the pouring speed to be uniform and avoiding splashing and flow interruption; after pouring, immediately transfer the mold to the heat preservation cellar, completely cover it with heat preservation cotton, and allow it to cool slowly to reduce the temperature gradient, and record the pouring temperature and time.

[0022] Step S4: When the temperature of the brick inside the mold naturally drops to 1450℃, send the brick along with the mold into the annealing furnace for staged annealing. First stage: Cool down to 1100℃ at 2℃ / min, and keep at 1100℃ for 3 hours to make the temperature inside and outside the brick uniform and initially eliminate thermal stress. Second stage: Slowly cool down to 700℃ at a rate of 0.5℃ / min; The third stage: the temperature is reduced to 500℃ at a rate of 1℃ / min, and then held at that temperature for 2 hours to further eliminate residual thermal stress; Fourth step: Turn off the annealing furnace and allow it to cool naturally to room temperature. Remove the bricks and inspect their appearance to ensure there are no cracks, deformations, or inclusions, thus obtaining cast β-corundum bricks.

[0023] Example 2 The preparation method of cast β-corundum bricks includes the following steps: Step S1: Accurately weigh Ni(NO3)2·6H2O and Co(NO3)2·6H2O, place them in a beaker, add deionized water, and stir until completely dissolved to prepare a composite salt solution with a total concentration of 0.14 g / mL. Weigh α-Al2O3 powder and Na2CO3 powder and place them in a dry beaker. Slowly pour in the prepared composite salt solution while stirring to ensure that the solution evenly wets each portion of powder. Let it stand for 20 minutes to allow the salt solution to fully penetrate. Send the impregnated material into a spray dryer, set the inlet air temperature to 170℃ and the outlet air temperature to 80℃, and spray dry to obtain a uniformly dispersed composite powder. Load the dried composite powder into a planetary ball mill, add wear-resistant grinding balls, set the speed to 300 r / min, dry grind for 20 minutes, pass through an 80-mesh standard sieve, and collect the sieved mixed powder for later use. The mass ratio of Ni(NO3)2·6H2O:Co(NO3)2·6H2O:α-Al2O3:Na2CO3 is 0.21:0.12:37.6:2.4.

[0024] Step S2: Place the high-purity graphite crucible in an oven and preheat at 250℃ for 20 minutes to remove adsorbed gases and moisture from the crucible surface. Slowly fill the preheated graphite crucible with the sieved mixed powder, gently vibrating it as you fill to ensure compaction and prevent voids. Gently compact the powder with a pressure bar, ensuring the filling height does not exceed 2 / 3 of the crucible's volume. Place the graphite crucible containing the powder into the electric arc furnace, adjusting its position to be centered within the furnace body. Close the furnace door and check the furnace's seal to ensure there are no leaks. Turn on the argon supply system, introducing high-purity argon at a rate of 0.8 L / min to purge air from the furnace and maintain a slight positive pressure (0.02 MPa) within the furnace. Maintain argon flow throughout the process, with staged temperature increases for decomposition. First stage: Increase the temperature to 300℃ at a rate of 4℃ / min and hold for 30min; Second stage: Heat to 600℃ at 2℃ / min and hold for 60min to allow Ni(NO3)2 and Co(NO3)2 to decompose fully and generate NiO, CoO and gases such as NO2 and O2. The gases are discharged with argon. The third stage involves heating to 1200℃ at a rate of 4℃ / min and holding for 40 minutes to ensure complete decomposition of nitrates, while simultaneously allowing Na2CO3 to fully decompose into Na2O and CO2, and for NiO and CoO to initially diffuse and mix with Al2O3.

[0025] Step S3: After decomposition, continue heating at a rate of 4℃ / min to 1950℃ and hold for 90min; place the molding mold in another oven in advance, preheat at 1200℃ and hold for 60min, then remove and quickly place it at the pouring station to prevent the mold temperature from dropping; stop the electric arc furnace heating, keep argon gas flowing, and wait for the furnace temperature to drop naturally to 1900℃; slowly tilt the furnace body and pour the molten liquid in the graphite crucible into the preheated molding mold in a stable thin stream, controlling the pouring speed to be uniform and avoiding splashing and flow interruption; after pouring, immediately transfer the mold to the heat preservation cellar, completely cover it with heat preservation cotton, and allow it to cool slowly to reduce the temperature gradient, and record the pouring temperature and time.

[0026] Step S4: When the temperature of the brick inside the mold naturally drops to 1400℃, send the brick along with the mold into the annealing furnace for staged annealing. First stage: Cool down to 1100℃ at 2℃ / min, and keep at 1100℃ for 2 hours to make the temperature inside and outside the brick uniform and initially eliminate thermal stress. Second stage: Slowly cool down to 600℃ at a rate of 0.5℃ / min; The third stage: the temperature is reduced to 500℃ at a rate of 1℃ / min, and then held at that temperature for 2 hours to further eliminate residual thermal stress; Fourth step: Turn off the annealing furnace and allow it to cool naturally to room temperature. Remove the bricks and inspect their appearance to ensure there are no cracks, deformations, or inclusions, thus obtaining cast β-corundum bricks.

[0027] Example 3 The preparation method of cast β-corundum bricks includes the following steps: Step S1: Accurately weigh Ni(NO3)2·6H2O and Co(NO3)2·6H2O, place them in a beaker, add deionized water, and stir until completely dissolved to prepare a composite salt solution with a total concentration of 0.20 g / mL. Weigh α-Al2O3 powder and Na2CO3 powder and place them in a dry beaker. Slowly pour in the prepared composite salt solution while stirring to ensure that the solution evenly wets each portion of powder. Let it stand for 30 minutes to allow the salt solution to fully penetrate. Send the impregnated material into a spray dryer, set the inlet air temperature to 180℃ and the outlet air temperature to 90℃, and spray dry to obtain a uniformly dispersed composite powder. Load the dried composite powder into a planetary ball mill, add wear-resistant grinding balls, set the speed to 400 r / min, dry grind for 30 minutes, pass through an 80-mesh standard sieve, and collect the sieved mixed powder for later use. The mass ratio of Ni(NO3)2·6H2O:Co(NO3)2·6H2O:α-Al2O3:Na2CO3 is 0.25:0.12:38.5:2.8.

[0028] Step S2: Place the high-purity graphite crucible in an oven and preheat at 300℃ for 30 minutes to remove adsorbed gases and moisture from the crucible surface. Slowly fill the preheated graphite crucible with the sieved mixed powder, gently vibrating it as you fill to ensure compaction and prevent voids. Gently compact the powder with a pressure bar, ensuring the filling height does not exceed 2 / 3 of the crucible's volume. Place the graphite crucible containing the powder into the electric arc furnace, adjusting its position to be centered within the furnace body. Close the furnace door and check the furnace's airtightness to ensure no leaks. Turn on the argon supply system, introducing high-purity argon at a rate of 1.0 L / min to purge air from the furnace and maintain a slight positive pressure (0.04 MPa) within the furnace. Maintain argon flow throughout the process, with staged temperature increases for decomposition. First stage: Increase the temperature to 400℃ at a rate of 4℃ / min and hold for 30min; Second stage: Heat to 800℃ at 2℃ / min and hold for 90min to allow Ni(NO3)2 and Co(NO3)2 to decompose fully and generate NiO, CoO and gases such as NO2 and O2. The gases are discharged with argon. The third stage involves heating to 1200℃ at a rate of 4℃ / min and holding for 60 minutes to ensure complete decomposition of nitrates, while simultaneously allowing Na2CO3 to fully decompose into Na2O and CO2, and for NiO and CoO to initially diffuse and mix with Al2O3.

[0029] Step S3: After decomposition, continue heating at a rate of 4℃ / min to 2050℃ and hold for 120min; place the molding mold in another oven in advance, preheat at 1200℃ and hold for 60min, then remove and quickly place it at the pouring station to prevent the mold temperature from dropping; stop the electric arc furnace heating, keep argon gas flowing, and wait for the furnace temperature to drop naturally to 1950℃; slowly tilt the furnace body and pour the molten liquid in the graphite crucible into the preheated molding mold in a stable thin stream, controlling the pouring speed to be uniform and avoiding splashing and flow interruption; after pouring, immediately transfer the mold to the heat preservation cellar, completely cover it with heat preservation cotton, and allow it to cool slowly to reduce the temperature gradient, and record the pouring temperature and time.

[0030] Step S4: When the temperature of the brick inside the mold naturally drops to 1500℃, send the brick along with the mold into the annealing furnace for staged annealing. First stage: Cool down to 1100℃ at 2℃ / min, and keep at 1100℃ for 4 hours to make the temperature inside and outside the brick uniform and initially eliminate thermal stress. Second stage: Slowly cool down to 800℃ at a rate of 0.5℃ / min; The third stage: the temperature is reduced to 500℃ at a rate of 1℃ / min, and then held at that temperature for 2 hours to further eliminate residual thermal stress; Fourth step: Turn off the annealing furnace and allow it to cool naturally to room temperature. Remove the bricks and inspect their appearance to ensure there are no cracks, deformations, or inclusions, thus obtaining cast β-corundum bricks.

[0031] Comparative Example 1 The preparation method of cast β-corundum bricks includes the following steps: Step S1: Weigh α-Al₂O₃ powder and Na₂CO₃ powder and place them into a planetary ball mill. Add wear-resistant grinding balls, set the speed to 350 r / min, dry grind for 25 min, pass through an 80-mesh standard sieve, and collect the sieved mixed powder for later use. The mass ratio of α-Al₂O₃ to Na₂CO₃ is 38.0:2.6.

[0032] Step S2: Place the high-purity graphite crucible in an oven and preheat at 270℃ for 25 minutes to remove adsorbed gases and moisture from the crucible surface. Slowly fill the preheated graphite crucible with the sieved mixed powder, gently vibrating it as you fill to ensure compaction and prevent voids. Gently compact the powder with a pressure bar, ensuring the filling height does not exceed 2 / 3 of the crucible's volume. Place the graphite crucible containing the powder into the electric arc furnace, adjusting its position to be centered within the furnace body. Close the furnace door and check the furnace's seal to ensure there are no leaks. Turn on the argon supply system, introducing high-purity argon at a rate of 0.9 L / min to purge air from the furnace and maintain a slight positive pressure (0.03 MPa) within the furnace. Maintain argon flow throughout the process, with staged temperature increases for decomposition. First stage: Increase the temperature to 350℃ at a rate of 4℃ / min and hold for 30min; Second stage: Increase the temperature to 700℃ at a rate of 2℃ / min and hold for 80min; Third stage: Increase the temperature to 1200℃ at a rate of 4℃ / min and hold for 50 minutes.

[0033] Step S3: After decomposition, continue heating to 2000℃ at a rate of 4℃ / min and hold for 100min; place the molding mold in another oven in advance, preheat at 1200℃ and hold for 60min, then remove and quickly place it at the casting station to prevent the mold temperature from dropping; stop the electric arc furnace heating, keep argon gas flowing, and wait for the furnace temperature to drop naturally to 1920℃; slowly tilt the furnace body and pour the molten liquid in the graphite crucible into the preheated molding mold in a stable thin stream, controlling the pouring speed to be uniform and avoiding splashing and flow interruption; after pouring, immediately transfer the mold to the heat preservation cellar, completely cover it with heat preservation cotton, and allow it to cool slowly to reduce the temperature gradient, and record the pouring temperature and time.

[0034] Step S4: When the temperature of the brick inside the mold naturally drops to 1450℃, send the brick along with the mold into the annealing furnace for staged annealing. First stage: Cool down to 1100℃ at 2℃ / min, and keep at 1100℃ for 3 hours to make the temperature inside and outside the brick uniform and initially eliminate thermal stress. Second stage: Slowly cool down to 700℃ at a rate of 0.5℃ / min; The third stage: the temperature is reduced to 500℃ at a rate of 1℃ / min, and then held at that temperature for 2 hours to further eliminate residual thermal stress; Fourth step: Turn off the annealing furnace and allow it to cool naturally to room temperature to obtain fused cast β-corundum bricks.

[0035] Comparative Example 2 The preparation method of cast β-corundum bricks includes the following steps: Step S1: Accurately weigh Ni(NO3)2·6H2O and place it in a beaker. Add deionized water and stir until completely dissolved, achieving a concentration of 0.16 g / mL. Set aside. Weigh α-Al2O3 powder and Na2CO3 powder and place them in a dry beaker. Slowly pour in the prepared nickel nitrate solution while stirring to ensure the solution evenly wets each portion of powder. Let stand for 25 minutes to allow the solution to fully penetrate. Send the impregnated material into a spray dryer, setting the inlet air temperature to 175℃ and the outlet air temperature to 85℃ for spray drying to obtain a uniformly dispersed composite powder. Load the dried composite powder into a planetary ball mill, add wear-resistant grinding balls, set the speed to 350 r / min, and dry grind for 25 minutes. Pass the powder through an 80-mesh standard sieve and collect the sieved mixed powder for later use. The mass ratio of Ni(NO3)2·6H2O:α-Al2O3:Na2CO3 is 0.23:38.0:2.6.

[0036] Step S2: Place the high-purity graphite crucible in an oven and preheat at 270℃ for 25 minutes to remove adsorbed gases and moisture from the crucible surface. Slowly fill the preheated graphite crucible with the sieved mixed powder, gently vibrating it as you fill to ensure compaction and prevent voids. Gently compact the powder with a pressure bar, ensuring the filling height does not exceed 2 / 3 of the crucible's volume. Place the graphite crucible containing the powder into the electric arc furnace, adjusting its position to be centered within the furnace body. Close the furnace door and check the furnace's seal to ensure there are no leaks. Turn on the argon supply system, introducing high-purity argon at a rate of 0.9 L / min to purge air from the furnace and maintain a slight positive pressure (0.03 MPa) within the furnace. Maintain argon flow throughout the process, with staged temperature increases for decomposition. First stage: Increase the temperature to 350℃ at a rate of 4℃ / min and hold for 30min; Second stage: Increase the temperature to 700℃ at a rate of 2℃ / min and hold for 80min; Third stage: Increase the temperature to 1200℃ at a rate of 4℃ / min and hold for 50 minutes.

[0037] Step S3: After decomposition, continue heating to 2000℃ at a rate of 4℃ / min and hold for 100min; place the molding mold in another oven in advance, preheat at 1200℃ and hold for 60min, then remove and quickly place it at the casting station to prevent the mold temperature from dropping; stop the electric arc furnace heating, keep argon gas flowing, and wait for the furnace temperature to drop naturally to 1920℃; slowly tilt the furnace body and pour the molten liquid in the graphite crucible into the preheated molding mold in a stable thin stream, controlling the pouring speed to be uniform and avoiding splashing and flow interruption; after pouring, immediately transfer the mold to the heat preservation cellar, completely cover it with heat preservation cotton, and allow it to cool slowly to reduce the temperature gradient, and record the pouring temperature and time.

[0038] Step S4: When the temperature of the brick inside the mold naturally drops to 1450℃, send the brick along with the mold into the annealing furnace for staged annealing. First stage: Cool down to 1100℃ at 2℃ / min, and keep at 1100℃ for 3 hours to make the temperature inside and outside the brick uniform and initially eliminate thermal stress. Second stage: Slowly cool down to 700℃ at a rate of 0.5℃ / min; The third stage: the temperature is reduced to 500℃ at a rate of 1℃ / min, and then held at that temperature for 2 hours to further eliminate residual thermal stress; Fourth step: Turn off the annealing furnace and allow it to cool naturally to room temperature to obtain fused cast β-corundum bricks.

[0039] Comparative Example 3 The preparation method of cast β-corundum bricks includes the following steps: Step S1: Accurately weigh Co(NO3)2·6H2O and place it in a beaker. Add deionized water and stir until completely dissolved, achieving a concentration of 0.16 g / mL. Set aside. Weigh α-Al2O3 powder and Na2CO3 powder and place them in a dry beaker. Slowly pour in the prepared cobalt nitrate solution while stirring to ensure the solution evenly wets each portion of powder. Let stand for 25 minutes to allow the salt solution to fully penetrate. Send the impregnated material into a spray dryer, setting the inlet air temperature to 175℃ and the outlet air temperature to 85℃ for spray drying to obtain a uniformly dispersed composite powder. Load the dried composite powder into a planetary ball mill, add wear-resistant grinding balls, set the speed to 350 r / min, and dry grind for 25 minutes. Pass the powder through an 80-mesh standard sieve and collect the sieved mixed powder for later use. The mass ratio of Co(NO3)2·6H2O:α-Al2O3:Na2CO3 is 0.12:38.0:2.6.

[0040] Step S2: Place the high-purity graphite crucible in an oven and preheat at 270℃ for 25 minutes to remove adsorbed gases and moisture from the crucible surface. Slowly fill the preheated graphite crucible with the sieved mixed powder, gently vibrating it as you fill to ensure compaction and prevent voids. Gently compact the powder with a pressure bar, ensuring the filling height does not exceed 2 / 3 of the crucible's volume. Place the graphite crucible containing the powder into the electric arc furnace, adjusting its position to be centered within the furnace body. Close the furnace door and check the furnace's seal to ensure there are no leaks. Turn on the argon supply system, introducing high-purity argon at a rate of 0.9 L / min to purge air from the furnace and maintain a slight positive pressure (0.03 MPa) within the furnace. Maintain argon flow throughout the process, with staged temperature increases for decomposition. First stage: Increase the temperature to 350℃ at a rate of 4℃ / min and hold for 30min; Second stage: Increase the temperature to 700℃ at a rate of 2℃ / min and hold for 80min; Third stage: Increase the temperature to 1200℃ at a rate of 4℃ / min and hold for 50 minutes.

[0041] Step S3: After decomposition, continue heating to 2000℃ at a rate of 4℃ / min and hold for 100min; place the molding mold in another oven in advance, preheat at 1200℃ and hold for 60min, then remove and quickly place it at the casting station to prevent the mold temperature from dropping; stop the electric arc furnace heating, keep argon gas flowing, and wait for the furnace temperature to drop naturally to 1920℃; slowly tilt the furnace body and pour the molten liquid in the graphite crucible into the preheated molding mold in a stable thin stream, controlling the pouring speed to be uniform and avoiding splashing and flow interruption; after pouring, immediately transfer the mold to the heat preservation cellar, completely cover it with heat preservation cotton, and allow it to cool slowly to reduce the temperature gradient, and record the pouring temperature and time.

[0042] Step S4: When the temperature of the brick inside the mold naturally drops to 1450℃, send the brick along with the mold into the annealing furnace for staged annealing. First stage: Cool down to 1100℃ at 2℃ / min, and keep at 1100℃ for 3 hours to make the temperature inside and outside the brick uniform and initially eliminate thermal stress. Second stage: Slowly cool down to 700℃ at a rate of 0.5℃ / min; The third stage: the temperature is reduced to 500℃ at a rate of 1℃ / min, and then held at that temperature for 2 hours to further eliminate residual thermal stress; Fourth step: Turn off the annealing furnace and allow it to cool naturally to room temperature to obtain fused cast β-corundum bricks.

[0043] Effect Example The following tests were performed on Examples 1-3 and Comparative Examples 1-3 described above: The test conditions were as follows: the bulk density and apparent porosity were tested according to GB / T2997-2015 "Test methods for apparent porosity, water absorption, bulk density and true density of dense shaped refractory products"; The room temperature compressive strength test shall be performed in accordance with GB / T5072-2008 "Test Method for Room Temperature Compressive Strength of Refractory Materials", by applying pressure to the standard specimen on a universal testing machine until it fails. Strength retention rate: The sample was heated from room temperature to 1000℃ on a heat plate and held at that temperature for 30 min. Then it was cooled in air. The flexural strength of the sample before and after thermal shock was tested, and the strength retention rate was calculated. Thermal shock cycle count: The sample was kept in a furnace at 1100℃ for 20 minutes and then quenched in room temperature water for 3 minutes as one cycle. The number of thermal cycles experienced when half of the heated end surface was damaged was recorded. The chemical composition of fused cast β-corundum bricks was determined by X-ray fluorescence spectroscopy.

[0044] The test data is as follows: Table 1 shows the test properties of the cast β-corundum bricks prepared in the examples and comparative examples.

[0045] As shown in Table 1, the bulk density, apparent porosity, room temperature compressive strength, strength retention rate, and number of thermal shock cycles of Examples 1-3 are all superior to those of Comparative Examples 1-3. Compared with Comparative Example 1, the bulk density of Example 1 increased by approximately 3.11%, the apparent porosity decreased by approximately 30.77%, the room temperature compressive strength increased by 30.26%, the strength retention rate increased by approximately 25.35%, and the number of thermal shock cycles increased by 100%. Compared with Comparative Example 2, the bulk density of Example 1 increased by approximately 1.84%, the apparent porosity decreased by approximately 21.74%, the room temperature compressive strength increased by approximately 17.86%, the strength retention rate increased by approximately 14.10%, and the number of thermal shock cycles increased by approximately 47.37%. Compared with Comparative Example 3, the bulk density of Example 1 increased by approximately 2.15%, the apparent porosity decreased by 25%, the room temperature compressive strength increased by 20%, the strength retention rate increased by approximately 17.11%, and the number of thermal shock cycles increased by approximately 55.56%. Compared with Comparative Examples 1-3, Examples 2 and 3 also show a trend of significantly increased bulk density, significantly reduced apparent porosity, and a substantial increase in room temperature compressive strength, strength retention, and number of thermal shock cycles. This is because Examples 1-3 used Ni(NO3)2. 6H2O and Co(NO3)2 6H2O composite doping and a composite dispersion process involving solution impregnation-spray drying-dry ball milling were used to achieve nanoscale uniform dispersion of Ni and Co precursors in the α-Al2O3 and Na2CO3 system. During high-temperature treatment, NiO and CoO generated from nitrate decomposition exist in solid solution or fine dispersion forms within the β-corundum grain boundaries and lattice. At high temperatures, NiO and CoO undergo in-situ solid-phase reactions with Al2O3 to generate nickel aluminate (NiAl2O4) spinel and cobalt aluminate (CoAl2O4) spinel phases. The spinel phase, a fine and dispersed second phase, pins the grain boundaries at high temperatures, inhibiting abnormal growth of β-corundum grains, resulting in finer and more uniform grains, thus significantly increasing bulk density and reducing apparent porosity. The spinel bonds strongly with the β-Al2O3 matrix, greatly enhancing grain boundary bonding strength and improving room-temperature compressive strength and high-temperature structural stability. Spinel phases exhibit excellent thermal shock stability and good thermal expansion matching with the β-corundum matrix. They can buffer thermal stress and passivate microcrack propagation, making the material less prone to cracking under rapid heating and cooling, and significantly improving strength retention and thermal shock cycle count. In Comparative Examples 2-3, the introduction of NiO or CoO alone only generates a single spinel, with limited strengthening effect; however, when NiAl2O4 and CoAl2O4 coexist, they can produce synergistic pinning, synergistic toughening, and synergistic strengthening effects, making the overall performance of the material far superior to single spinel-reinforced or spinel-free reinforcement systems.

[0046] Table 2 shows the chemical composition of the cast β-corundum bricks prepared in the examples and comparative examples.

[0047] As shown in Table 2, the chemical compositions of Examples 1-3 all contain four components: Al2O3, Na2O, NiO, and CoO. NiO and CoO originate from the high-temperature decomposition of nickel nitrate and cobalt nitrate in the raw materials, and their content is basically consistent with the raw material ratio. In Comparative Example 1, only Al2O3 and Na2O were detected, while NiO and CoO were not detected; in Comparative Example 2, only Al2O3, Na2O, and NiO were detected, while CoO was not detected; in Comparative Example 3, only Al2O3, Na2O, and CoO were detected, while NiO was not detected. The above chemical composition results indicate that the embodiments of the present invention successfully achieved the composite introduction of NiO and CoO. Comparative Examples 1-3 represent systems without metal oxide doping, single NiO doping, and single CoO doping, respectively, providing a clear compositional comparison with Examples 1-3. Combined with the performance data in Table 1, it can be demonstrated that the co-existence of NiO and CoO and the in-situ formation of a composite spinel phase are the key reasons for the significant improvement in the density, strength, and thermal shock stability of the cast β-corundum bricks.

[0048] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A cast β-corundum brick, characterized in that, The cast β-corundum brick is mainly obtained by casting Ni(NO3)2·6H2O, Co(NO3)2·6H2O, α-Al2O3, and Na2CO3 in a mass ratio of 0.21-0.25:0.12:37.6-38.5:2.4-2.

8.

2. A method for preparing fused cast β-corundum bricks, characterized in that, Includes the following steps: Step S1: Weigh the raw materials, prepare a composite salt solution and impregnate α-Al2O3 and Na2CO3 powders, then spray dry, ball mill, and sieve to obtain a mixed powder; Step S2: After preheating the high-purity graphite crucible, fill it with the mixed powder obtained in step S1 and compact it. Place the crucible in the center of the electric arc furnace, introduce high-purity argon gas to maintain a slight positive pressure inside the furnace, and gradually increase the temperature. Step S3: Continue heating to 1950-2050℃ and hold at that temperature. Pour the molten liquid into the preheated molding mold and then transfer it to a heat-insulating cellar for slow cooling. Step S4: When the temperature of the brick in the mold naturally drops to 1400-1500℃, it is cooled and annealed, and then cooled to room temperature with the furnace to obtain fused cast β-corundum brick.

3. The method for preparing cast β-corundum bricks according to claim 2, characterized in that, In step S1, the composite salt solution includes Ni(NO3)2·6H2O and Co(NO3)2·6H2O, with a total concentration of 0.14-0.20 g / mL.

4. The method for preparing cast β-corundum bricks according to claim 2, characterized in that, In step S1, the inlet air temperature of the spray dryer is 170-180℃ and the outlet air temperature is 80-90℃, the rotation speed of the ball mill is 300-400 r / min, and the time is 20-30 min.

5. The method for preparing cast β-corundum bricks according to claim 2, characterized in that, In step S2, the preheating temperature of the high-purity graphite crucible is 250-300℃, and the time is 20-30 minutes.

6. The method for preparing cast β-corundum bricks according to claim 2, characterized in that, In step S2, the high-purity argon gas is introduced at a rate of 0.8-1.0 L / min, and the micro-positive pressure is 0.02-0.04 MPa.

7. The method for preparing cast β-corundum bricks according to claim 2, characterized in that, In step S2, the staged heating mainly includes: A1: Increase the temperature to 300-400℃ at a rate of 4℃ / min and hold for 30min; A2: Increase the temperature to 600-800℃ at a rate of 2℃ / min and hold for 60-90min; A3: Increase the temperature to 1200℃ at a rate of 4℃ / min and hold for 40-60 minutes.

8. The method for preparing cast β-corundum bricks according to claim 2, characterized in that, In step S3, the heat preservation time is 90-120 min, and the heating rate is 4℃ / min.

9. The method for preparing cast β-corundum bricks according to claim 2, characterized in that, In step S3, the preheating temperature of the molding die is 1200℃, and the pouring temperature is 1900-1950℃.

10. The method for preparing cast β-corundum bricks according to claim 2, characterized in that, In step S4, the cooling annealing is as follows: cooling to 1100℃ at 2℃ / min and holding for 2-4 hours; then cooling to 600-800℃ at 0.5℃ / min; and then cooling to 500℃ at 1℃ / min and holding for 2 hours.

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