Alpha-beta corundum brick with high thermal shock resistance and preparation method thereof

Abstract

The invention belongs to the technical field of preparation of refractory materials, and particularly relates to a preparation method of an alpha-beta corundum brick with high thermal shock resistance. The method comprises the following steps: mixing and grinding commercial alumina, alpha corundum micro powder, composite borate, magnesium oxide and yttrium oxide to obtain uniform slurry, and performing spray drying on the slurry to obtain dry powder; adding the dried powder into a preheated casting furnace mold, introducing inert gas for protection, heating to a melting temperature, preserving heat, carrying out gradient cooling and step-by-step cooling annealing on the melt subjected to heat preservation, and demolding, cleaning, finishing and drying the annealed product to obtain the alpha-beta corundum brick with high thermal shock resistance. The method can significantly improve the thermal shock resistance of the corundum brick, gives consideration to both high strength and structural stability, and is suitable for high-temperature frequent temperature change working conditions.

Description

Technical Field

[0001] This invention belongs to the field of refractory material preparation technology, specifically relating to a method for preparing αβ corundum bricks with high thermal shock resistance. 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. In actual working conditions, these equipment often face frequent heating and cooling cycles, as well as complex conditions such as high-temperature medium erosion and uneven temperature field distribution. This places extremely high demands on the thermal shock resistance of corundum bricks. Thermal shock resistance is a core indicator for measuring the ability of refractory materials to resist structural damage under rapid temperature changes, directly determining the service life of corundum bricks and the operational stability of equipment. Currently, most commercially available corundum bricks are composed mainly of α-corundum or β-corundum. Although they can meet basic high-temperature resistance requirements, under frequent temperature fluctuations, they are prone to micro-cracks due to internal thermal stress concentration, leading to brick spalling and breakage. This not only requires frequent shutdowns for replacement, increasing production and maintenance costs, but may also affect production continuity due to material failure, and even cause safety hazards. To improve the thermal shock resistance of corundum bricks, existing technologies often employ methods such as adding admixtures like magnesium oxide and zirconium oxide, or optimizing particle size distribution and adjusting sintering processes. However, these methods have significant limitations: the introduction of some admixtures can reduce the high-temperature strength and chemical stability of corundum bricks, leading to aging and failure in highly corrosive high-temperature media; simply adjusting particle size distribution or sintering processes has limited effectiveness and struggles to balance thermal shock resistance with other core properties, failing to meet the stringent requirements of high-end high-temperature equipment for refractory materials.

[0003] As high-temperature industries develop towards high efficiency, energy conservation, and long-cycle operation, higher standards are being set for the comprehensive performance of corundum bricks. They must maintain excellent high-temperature resistance and high strength while also possessing outstanding thermal shock resistance to adapt to long-term stable operation under complex conditions. Therefore, developing a corundum brick preparation technology that can balance multiple performance aspects, significantly improve thermal shock resistance, and has a controllable process has become a pressing technical challenge in the refractory materials field. This technology is of significant practical importance for promoting the upgrading of high-temperature industrial equipment and reducing production costs. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art. In a first aspect, this invention provides a high thermal shock resistant αβ corundum brick, which is obtained by melting and casting industrial alumina, α-corundum micro powder, composite borate, magnesium oxide and yttrium oxide in a mass ratio of 70-80:15-24:0.35-0.46:0.04-0.06:0.04-0.06; the composite borate is composed of lithium tetraborate and sodium tetraborate, and the mass ratio of lithium tetraborate to sodium tetraborate is 0.3-0.4:0.05-0.06.

[0005] Furthermore, the purity of the industrial alumina is 99.0-99.5%, the sodium oxide and potassium oxide content is 0.20-0.4%, and the silicon dioxide content is 0.10-0.2%. The particle size D50 of the α-corundum micro powder is 5-20 μm, the sodium oxide and potassium oxide content is 0.15-0.3%, and the silicon dioxide content is 0.10-0.15%.

[0006] Secondly, the present invention provides a method for preparing αβ corundum bricks with high thermal shock resistance, comprising the following steps:

[0007] Step S1: Mix all raw materials and ball mill to obtain a uniform slurry, then spray dry the slurry to obtain a dry powder; Step S2: Add the dried powder into the preheated melting furnace mold, introduce inert gas for protection, heat to the melting temperature and hold at that temperature; Step S3: The melt after heat preservation is subjected to gradient cooling and step-by-step annealing. The annealed product is demolded, cleaned, trimmed and dried to obtain αβ corundum brick with high thermal shock resistance.

[0008] Furthermore, in step S1, the dispersion medium for ball milling is anhydrous ethanol, the solid content is controlled at 30%-50%, and the ball-to-material ratio is 3-5:1.

[0009] Further, in step S1, the ball milling speed is 250-400 rpm, the time is 6-12 hours, and the particle size D50 of the slurry is ≤10μm.

[0010] Further, in step S1, the inlet temperature of the spray dryer is 180-220℃, the outlet temperature is 80-100℃, the feed rate is 10-30mL / min, and the moisture content of the dried powder is <0.5%.

[0011] Further, in step S2, the inert gas is high-purity argon or nitrogen, and the gas flow rate is 10-30 L / min; the melting temperature is 1950-2100℃, and the holding time is 1-2 h.

[0012] Furthermore, in step S3, the gradient cooling rate is 5-10℃ / min, and after cooling to 1200℃, the temperature is kept stable for 10-15min.

[0013] Furthermore, in step S3, the stepwise cooling annealing rate is 1-3℃ / min, cooling down to 1000℃, and then cooling down to 600℃ at a rate of 3-5℃ / min, followed by natural cooling to room temperature with the furnace.

[0014] Furthermore, in step S3, the demolding temperature is 200℃, the drying temperature is 100-120℃, and the drying time is 1-2 hours.

[0015] Beneficial effects: Composite borates are low-melting-point composite sintering aids that completely melt at 1950-2100℃ during casting to form a homogeneous liquid phase. This liquid phase serves as a sintering medium, filling the gaps between corundum particles to achieve liquid-phase sintering and significantly improve the material's density. The continuous liquid phase formed by composite borates is Mg. 2+ and Y 3+ The diffusion and migration of Mg provides a fast pathway, accelerating the process. 2+ Diffusion into the Al2O3 lattice and formation of magnesium aluminum spinel also promotes Y 3+ Al replacement 3+By dissolving the MgO and Y2O3 into the corundum lattice, the problems of slow ion diffusion and uneven doping in solid-state sintering are solved, allowing the modification effects of MgO and Y2O3 to be fully utilized in the casting process. During the melting and cooling process, MgO and Al2O3 form magnesium aluminum spinel. The spinel phase is dispersed at the corundum grain boundaries in nanometer / micrometer scale, forming hard pinning points that further hinder grain boundary movement. At the same time, the precipitation of spinel will divide the corundum grains, achieving grain refinement. During the high-temperature melting and heat preservation process, the composite borate completely melts to form a uniform boroaluminate molten phase. This molten phase undergoes a directional in-situ chemical reaction with harmful impurities such as Na2O, K2O, and SiO2 introduced from the raw materials and slight erosion of the furnace body in the corundum melt, completely transforming into a high-melting-point boroaluminate solid phase. The generated boroaluminate solid phase is uniformly dispersed in the corundum melt in the form of nanoparticles, providing a large number of uniform heterogeneous nucleation sites for the nucleation of αβ corundum in the subsequent gradient cooling stage. This breaks the barrier of homogeneous nucleation in pure corundum melt, significantly increasing the nucleation density of αβ corundum, effectively inhibiting abnormal grain growth, and ultimately forming a fine and uniform equiaxed crystal structure. The fine-grained structure is the key to improving the thermal shock resistance and fracture toughness of corundum materials, which can significantly extend the crack propagation path under thermal shock and reduce crack initiation and rapid propagation. The composite borate is first completely melted to form a uniform boroaluminate molten phase, which then reacts fully with harmful impurities. The resulting nano-solid particles are non-agglomerated and uniformly dispersed in the melt, resulting in a highly uniform chemical composition and solid phase distribution throughout the corundum melt. This avoids problems such as uneven αβ-corundum nucleation, inconsistent thickness of the grain boundary glass phase film, and solid phase precipitation segregation caused by localized compositional inhomogeneity in the melt. The melting and reaction process of the composite borate exhibits quantitative reaction characteristics, consuming only a proportion of composite borate that matches the amount of harmful impurities. The remaining unreacted trace amounts of composite borate remain uniformly dispersed in the melt in a molten state. This provides a precise ratio of raw material for the in-situ formation of a boroaluminate glass phase film at the grain boundaries during the subsequent gradient cooling stage. This avoids excessively thick or thin glass phase films caused by an excess or deficiency of composite borate, achieving a quantitative match between the raw materials for impurity passivation and grain boundary film formation, and precisely controlling the subsequent grain boundary structure. 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 A method for preparing αβ corundum bricks with high thermal shock resistance includes the following steps: Raw materials were weighed according to the following mass ratio: industrial alumina (99.5% purity), α-corundum micro powder (D50 = 20μm), lithium tetraborate, sodium tetraborate, magnesium oxide, and yttrium oxide, at 70:15:0.3:0.05:0.04:0.04, and added to a planetary ball mill jar in one go. An appropriate amount of anhydrous ethanol was added as a dispersion medium (solid content controlled at 30%). Zirconia grinding balls were added at a ball-to-material ratio of 3:1. Grinding was carried out at 250 rpm for 6 hours. After grinding, a uniform slurry with a particle size D50 ≤ 10μm was obtained. The slurry was dried using a spray dryer with an inlet temperature of 180℃, an outlet temperature of 80℃, and a feed rate of 10mL / min to ensure complete ethanol evaporation and to obtain a dry powder with a moisture content <0.5% and good flowability. The industrial alumina contains 0.20% sodium oxide and 0.10% potassium oxide, and 0.15% silicon dioxide; the α-corundum micro powder contains 0.15% sodium oxide and 0.10% potassium oxide.

[0020] Slowly add the dried powder to the preheated melting furnace mold, controlling the amount of material to ensure that the raw material completely covers the bottom of the mold and leaves a certain space for melting expansion. Continuously introduce high-purity nitrogen into the furnace at a flow rate of 10 L / min. Start the heating system and raise the temperature at a rate of 20℃ / min to 1950℃. After reaching the target temperature, hold it at that temperature for 1 hour.

[0021] After the heat preservation period, the cooling system is activated, and the furnace temperature gradient is cooled to 1200℃ at a cooling rate of 8℃ / min. During cooling, the temperature control system is precisely controlled to ensure a stable cooling rate and prevent internal stress in the brick due to rate fluctuations. The temperature is maintained stable for 12 minutes to allow the glass phase film to fully spread and ensure uniform grain boundary filling. Then, the temperature is lowered to 1000℃ at 1℃ / min, and then to 600℃ at 3℃ / min, allowing the furnace to cool naturally to room temperature. During this period, an inert gas protection is maintained to eliminate the condensation stress of the boroaluminate glass phase film. After the furnace temperature drops to room temperature, the furnace door is opened, the mold is removed, and the brick is demolded after the mold cools to below 200℃. The demolded brick is then surface-cleaned to remove attached impurities and mold residue. The brick is then dimensionally trimmed using a grinding wheel and dried at 100℃ for 1 hour to remove residual moisture from the surface and interior, resulting in a high thermal shock resistant αβ corundum brick.

[0022] Example 2 A method for preparing αβ corundum bricks with high thermal shock resistance includes the following steps: Raw materials were weighed according to the following mass ratios: industrial alumina (99.2% purity), α-corundum micro powder (D50 = 10μm), lithium tetraborate, sodium tetraborate, magnesium oxide, and yttrium oxide, at 75:20:0.35:0.055:0.05:0.05, and added to a planetary ball mill jar in one go. An appropriate amount of anhydrous ethanol was added as a dispersion medium (solid content controlled at 40%). Zirconia grinding balls were added at a ball-to-material ratio of 4:1. Grinding was carried out at 300 rpm for 8 hours. After grinding, a uniform slurry with a particle size D50 ≤ 10μm was obtained. The slurry was dried using a spray dryer. The inlet temperature was 200℃, the outlet temperature was 90℃, and the feed rate was 20mL / min to ensure complete ethanol evaporation and to obtain a dry powder with a moisture content < 0.5% and good flowability. The industrial alumina contains 0.40% sodium oxide and 0.20% potassium oxide, and 0.30% silicon dioxide; the α-corundum micro powder contains 0.15% silicon dioxide.

[0023] The dried powder was slowly added into the preheated casting furnace mold, controlling the amount of material to ensure that the raw material completely covered the bottom of the mold and leaving a certain space for melting expansion. High-purity argon gas was continuously introduced into the furnace at a flow rate of 20 L / min. The heating system was started, and the temperature was increased at a rate of 25 °C / min to raise the furnace temperature to 2000 °C. After reaching the target temperature, it was held at that temperature for 1.5 hours.

[0024] After the heat preservation period, the cooling system was activated, and the furnace temperature gradient was cooled to 1200℃ at a cooling rate of 8℃ / min. During the cooling process, the temperature control system was precisely controlled to ensure a stable cooling rate and prevent internal stress in the brick due to rate fluctuations. The temperature was maintained stable for 12 minutes to allow the glass phase film to fully spread and ensure uniform grain boundary filling. Then, the temperature was lowered to 1000℃ at 2℃ / min and to 600℃ at 4℃ / min, allowing the furnace to cool naturally to room temperature. During this period, an inert gas protection was maintained to eliminate the condensation stress of the boroaluminate glass phase film. After the furnace temperature reached room temperature, the furnace door was opened, the mold was removed, and the brick was demolded after the mold cooled to below 200℃. The demolded brick was then surface-cleaned to remove attached impurities and mold residue. The brick was then dimensionally trimmed using a grinding wheel and dried at 110℃ for 1.5 hours to remove surface and internal moisture, resulting in a high thermal shock resistant αβ corundum brick.

[0025] Example 3 A method for preparing αβ corundum bricks with high thermal shock resistance includes the following steps: Industrial alumina (99.0% purity), α-corundum micro powder (D50 = 5μm), lithium tetraborate, sodium tetraborate, magnesium oxide, and yttrium oxide were added to a planetary ball mill jar in a mass ratio of 80:24:0.4:0.06:0.06:0.06. An appropriate amount of anhydrous ethanol was added as a dispersion medium (solid content controlled at 50%). Zirconia grinding balls were added at a ball-to-particle ratio of 5:1. Grinding was carried out at 400 rpm for 12 hours. After grinding, a uniform slurry with a particle size D50 ≤ 10μm was obtained. The slurry was dried using a spray dryer. The inlet temperature was 220℃, the outlet temperature was 100℃, and the feed rate was 30mL / min to ensure complete ethanol evaporation and to obtain a dry powder with a moisture content <0.5% and good flowability. The industrial alumina contains 0.30% sodium oxide and 0.15% potassium oxide, and 0.20% silicon dioxide, while the α-corundum micro powder contains 0.12% silicon dioxide.

[0026] Slowly add the dried powder to the preheated melting and casting furnace mold, controlling the amount of material to ensure that the raw material completely covers the bottom of the mold and leaves a certain space for melting expansion. Continuously introduce high-purity nitrogen into the furnace at a flow rate of 30 L / min. Start the heating system and raise the temperature in the furnace to 2100℃ at a rate of 30℃ / min. After reaching the target temperature, hold it at that temperature for 2 hours.

[0027] After the heat preservation period, the cooling system is activated, and the furnace temperature is gradually cooled to 1200℃ at a cooling rate of 10℃ / min. During cooling, the temperature control system is precisely controlled to ensure a stable cooling rate and prevent fluctuations that could cause internal stress in the brick. The temperature is maintained stable for 15 minutes to allow the glass phase film to fully spread and ensure uniform grain boundary filling. Then, the temperature is lowered to 1000℃ at 3℃ / min and to 600℃ at 5℃ / min, allowing the furnace to cool naturally to room temperature. During this period, an inert gas protection system is maintained to eliminate the condensation stress of the boroaluminate glass phase film. Once the furnace temperature has dropped to room temperature, the furnace door is opened, the mold is removed, and the brick is demolded after the mold has cooled to below 200℃. The demolded brick is then surface-cleaned to remove attached impurities and mold residue. The brick is then dimensionally trimmed using a grinding wheel and dried at 120℃ for 2 hours to remove surface and internal moisture, resulting in a high thermal shock resistant αβ corundum brick.

[0028] Comparative Example 1 A method for preparing αβ corundum bricks with high thermal shock resistance includes the following steps: Raw materials were weighed according to the following mass ratio: industrial alumina (99.5% purity), α-corundum micro powder (D50 = 20μm), boric acid, calcium oxide, and lanthanum oxide 70:15:0.35:0.08:0.08, and added to a planetary ball mill jar in one go. An appropriate amount of anhydrous ethanol was added as a dispersion medium (solid content controlled at 30%). Zirconia grinding balls were added at a ball-to-material ratio of 3:1. Grinding was carried out at 250 rpm for 6 hours. After grinding, a uniform slurry with a particle size D50 ≤ 10μm was obtained. The slurry was dried using a spray dryer. The inlet temperature was 180℃, the outlet temperature was 80℃, and the feed rate was 10mL / min to ensure complete ethanol evaporation and to obtain a dry powder with a moisture content < 0.5% and good flowability. Specifically, the industrial alumina contained 0.20% sodium oxide and potassium oxide, and 0.10% silicon dioxide; the α-corundum micro powder contained 0.15% sodium oxide and potassium oxide, and 0.10% silicon dioxide.

[0029] Slowly add the dried powder to the preheated melting furnace mold, controlling the amount of material to ensure that the raw material completely covers the bottom of the mold and leaves a certain space for melting expansion. Continuously introduce high-purity nitrogen into the furnace at a flow rate of 10 L / min. Start the heating system and raise the temperature at a rate of 20℃ / min to 1950℃. After reaching the target temperature, hold it at that temperature for 1 hour.

[0030] After the heat preservation period, the cooling system is activated, and the furnace temperature gradient is cooled to 1200℃ at a cooling rate of 8℃ / min. During the cooling process, the temperature control system is precisely controlled to ensure a stable cooling rate and prevent fluctuations that could cause internal stress in the bricks. The temperature is maintained stable for 12 minutes, then reduced to 1000℃ at 1℃ / min, and then to 600℃ at 3℃ / min, allowing the furnace to cool naturally to room temperature while maintaining inert gas protection. Once the furnace temperature has dropped to room temperature, the furnace door is opened, the mold is removed, and the bricks are demolded after the mold has cooled to below 200℃. The demolded bricks are then surface-cleaned to remove attached impurities and mold residue. The bricks are then dimensionally trimmed using a grinding wheel, and finally dried at 100℃ for 1 hour to remove surface and internal moisture, yielding αβ corundum bricks.

[0031] Comparative Example 2 A method for preparing αβ corundum bricks with high thermal shock resistance includes the following steps: Raw materials were weighed according to the following mass ratio: industrial alumina (99.2% purity), α-corundum micro powder (D50 = 10μm), lithium borate, zinc borate, strontium oxide, and cerium oxide, at 70:15:0.2:0.2:0.03:0.03, and added to a planetary ball mill jar in one go. An appropriate amount of anhydrous ethanol was added as a dispersion medium (solid content controlled at 30%). Zirconia grinding balls were added at a ball-to-material ratio of 3:1. Grinding was carried out at 250 rpm for 6 hours. After grinding, a uniform slurry with a particle size D50 ≤ 10μm was obtained. The slurry was dried using a spray dryer. The inlet temperature was 180℃, the outlet temperature was 80℃, and the feed rate was 10mL / min to ensure complete ethanol evaporation and to obtain a dry powder with a moisture content <0.5% and good flowability. The industrial alumina contains 0.40% sodium oxide and 0.20% potassium oxide, and 0.30% silicon dioxide; the α-corundum micro powder contains 0.15% silicon dioxide.

[0032] Slowly add the dried powder to the preheated melting furnace mold, controlling the amount of material to ensure that the raw material completely covers the bottom of the mold and leaves a certain space for melting expansion. Continuously introduce high-purity nitrogen into the furnace at a flow rate of 10 L / min. Start the heating system and raise the temperature at a rate of 20℃ / min to 1950℃. After reaching the target temperature, hold it at that temperature for 1 hour.

[0033] After the heat preservation period, the cooling system is activated, and the furnace temperature gradient is cooled to 1200℃ at a cooling rate of 8℃ / min. During the cooling process, the temperature control system is precisely controlled to ensure a stable cooling rate and prevent fluctuations that could cause internal stress in the bricks. The temperature is maintained stable for 12 minutes, then reduced to 1000℃ at 1℃ / min, and then to 600℃ at 3℃ / min, allowing the furnace to cool naturally to room temperature while maintaining inert gas protection. Once the furnace temperature has dropped to room temperature, the furnace door is opened, the mold is removed, and the bricks are demolded after the mold has cooled to below 200℃. The demolded bricks are then surface-cleaned to remove attached impurities and mold residue. The bricks are then dimensionally trimmed using a grinding wheel, and finally dried at 100℃ for 1 hour to remove surface and internal moisture, yielding αβ corundum bricks.

[0034] Comparative Example 3 A method for preparing αβ corundum bricks with high thermal shock resistance includes the following steps: Raw materials were weighed according to a mass ratio of industrial alumina (99.0% purity), α-corundum micro powder (D50 = 5μm), borax, and neodymium oxide of 70:15:0.4:0.06 and added to a planetary ball mill jar in one go. An appropriate amount of anhydrous ethanol was added as a dispersion medium (solid content controlled at 30%). Zirconia grinding balls were added at a ball-to-material ratio of 3:1. Grinding was carried out at 250 rpm for 6 hours. After grinding, a uniform slurry with a particle size D50 ≤ 10μm was obtained. The slurry was dried using a spray dryer with an inlet temperature of 180℃, an outlet temperature of 80℃, and a feed rate of 10mL / min to ensure complete ethanol evaporation and to obtain a dry powder with a moisture content < 0.5% and good flowability. Specifically, the industrial alumina contained 0.30% sodium oxide and potassium oxide, and 0.15% silica; the α-corundum micro powder contained 0.20% sodium oxide and potassium oxide, and 0.12% silica.

[0035] Slowly add the dried powder to the preheated melting furnace mold, controlling the amount of material to ensure that the raw material completely covers the bottom of the mold and leaves a certain space for melting expansion. Continuously introduce high-purity nitrogen into the furnace at a flow rate of 10 L / min. Start the heating system and raise the temperature at a rate of 20℃ / min to 1950℃. After reaching the target temperature, hold it at that temperature for 1 hour.

[0036] After the heat preservation period, the cooling system is activated, and the furnace temperature gradient is cooled to 1200℃ at a cooling rate of 8℃ / min. During the cooling process, the temperature control system is precisely controlled to ensure a stable cooling rate and prevent internal stress in the bricks caused by rate fluctuations. The temperature is maintained stable for 12 minutes, then cooled to 1000℃ at 1℃ / min, and then to 600℃ at 3℃ / min, allowing the furnace to cool naturally to room temperature. Inert gas protection is maintained throughout this process. Once the furnace temperature has dropped to room temperature, the furnace door is opened, the mold is removed, and the bricks are demolded after the mold has cooled to below 200℃. The demolded bricks are then surface-cleaned to remove attached impurities and mold residue. The bricks are then dimensionally trimmed using a grinding wheel and dried at 100℃ for 1 hour to remove surface and internal moisture, yielding αβ corundum bricks.

[0037] 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 αβ corundum bricks was determined by X-ray fluorescence spectroscopy.

[0038] The test data is as follows: Table 1 shows the test indicators of the high thermal shock resistant αβ corundum bricks prepared in the examples and comparative examples.

[0039] As shown in Table 1, the αβ corundum bricks prepared in Examples 1-3 are significantly better than those in Comparative Examples 1-3 in terms of bulk density, apparent porosity, room temperature compressive strength, strength retention rate, and number of thermal shock cycles. The core reason is that the examples adopted a suitable composite borate system, a synergistic modification formula of MgO and Y2O3, and a gradient strengthening casting-cooling annealing process, which achieved a synergistic improvement in efficient impurity passivation, precise optimization of grain boundary structure, and material densification. Examples 1-3 use composite borates composed of lithium tetraborate and sodium tetraborate. Their melting characteristics are highly matched with those of corundum melt. They can melt rapidly and completely at a melting temperature of 1950-2100℃. On the one hand, they can undergo in-situ chemical reactions with low-melting-point harmful impurities such as Na2O, K2O, and SiO2 in corundum melt to generate a high-temperature stable boroaluminate solid phase, which completely passivates the impurities and prevents them from agglomerating at grain boundaries to form a low-melting-point glass phase. This prevents the grain boundaries from softening and cracking due to the low-melting-point phase during thermal shock. On the other hand, the trace amounts of composite borate that do not participate in the impurity reaction will form a uniform boroaluminate glass phase film in situ during cooling. This film precisely fills the micro-gaps and micropores of corundum grain boundaries, which not only improves the material's density but also alleviates the internal stress generated at grain boundaries during thermal shock. The comparative borate systems all exhibited significant defects. Comparative Example 1 used single boric acid instead of composite borate, which easily generated a gaseous phase upon melting and decomposition, failing to form stable boroaluminate and introducing additional pores. Comparative Example 2 used a combination of lithium borate and zinc borate, resulting in borate products with poor high-temperature stability, ineffective impurity passivation, weak glass phase formation ability, and poor grain boundary filling. Comparative Example 3 used single borax, which had a slow reaction rate with impurities, poor binding, incomplete impurity passivation, and no significant grain boundary strengthening effect. Examples 1-3 introduced a composite modifier of MgO and Y2O3, which formed a synergistic modification effect: MgO refined corundum grains, reducing grain boundary stress concentration caused by large grains, while promoting the directional growth of β-Al2O3 and improving the bonding force between grain phases; Y2O3, as a rare earth stabilizer, stabilized the corundum grain boundary structure, inhibited abnormal grain growth at high temperatures, and improved the high-temperature viscosity and stability of the boroaluminate glass phase, preventing grain boundary bonding failure due to softening and loss of the glass phase during thermal shock cycling. The two work together to improve the material's room temperature mechanical strength and structural stability under thermal shock.

[0040] Table 2 shows the chemical composition of the high thermal shock resistant αβ corundum bricks prepared in the examples and comparative examples.

[0041] As shown in Table 2, in Examples 1-3, both α-Al₂O₃ and β-Al₂O₃ exhibit a gradually increasing gradient characteristic, and the total proportion of α+β corundum crystal phases exceeds 98%, indicating high matrix purity and sufficient crystal phase development. The increase in β-Al₂O₃ is attributed to the gradient strengthening effect of the casting process. High-temperature, long-term heat treatment promotes the directional recrystallization of the alumina melt, and MgO, acting as a nucleating agent for β-Al₂O₃ crystal growth, accelerates the formation and growth of the β phase. A moderate increase in the β phase can alleviate the grain boundary stress concentration of the α phase during thermal shock, thus improving thermal shock stability. As the core boron source for boroaluminates, B2O3's gradient increases, leading to a more complete reaction with impurities (Na2O, K2O, SiO2), resulting in a larger amount of high-temperature stable boroaluminate solid phase and more thorough impurity passivation. Simultaneously, it provides sufficient components for the formation of boroaluminate glass phase films during cooling, resulting in better grain boundary filling. Li2O, as a characteristic component of lithium tetraborate, has an increased gradient that enhances the high-temperature fluidity of the borate melt, making the mixing of borate and corundum melts more uniform and the reaction more complete. Furthermore, Li2O can increase the high-temperature viscosity of the boroaluminate glass phase, preventing the glass phase from softening and leaching during thermal shock cycling, thus preventing grain boundary bonding failure.

[0042] 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 high thermal shock resistant αβ corundum brick, characterized in that, This corundum brick is obtained by melting and casting industrial alumina, α-corundum micro powder, composite borates, magnesium oxide and yttrium oxide in a mass ratio of 70-80:15-24:0.35-0.46:0.04-0.06:0.04-0.

06. The composite borate is composed of lithium tetraborate and sodium tetraborate, with a mass ratio of lithium tetraborate to sodium tetraborate of 0.3-0.4:0.05-0.

06.

2. The high thermal shock resistant αβ corundum brick according to claim 1, characterized in that, The industrial alumina has a purity of 99.0-99.5%, a sodium oxide and potassium oxide content of 0.20-0.4%, and a silicon dioxide content of 0.10-0.2%. The α-corundum micro powder has a particle size D50 of 5-20 μm, a sodium oxide and potassium oxide content of 0.15-0.3%, and a silicon dioxide content of 0.10-0.15%.

3. A method for preparing a high thermal shock resistant αβ corundum brick as described in claim 1 or 2, characterized in that, Includes the following steps: Step S1: Mix all raw materials and ball mill to obtain a uniform slurry, then spray dry the slurry to obtain a dry powder; Step S2: Add the dried powder into the preheated melting furnace mold, introduce inert gas for protection, heat to the melting temperature and hold at that temperature; Step S3: The melt after heat preservation is subjected to gradient cooling and step-by-step annealing. The annealed product is demolded, cleaned, trimmed and dried to obtain αβ corundum brick with high thermal shock resistance.

4. The method for preparing high thermal shock resistant αβ corundum bricks according to claim 3, characterized in that, In step S1, the dispersion medium for ball milling is anhydrous ethanol, the solid content is controlled at 30%-50%, and the ball-to-material ratio is 3-5:

1.

5. The method for preparing high thermal shock resistant αβ corundum bricks according to claim 3, characterized in that, In step S1, the ball milling speed is 250-400 rpm, the time is 6-12 hours, and the particle size D50 of the slurry is ≤10μm.

6. The method for preparing high thermal shock αβ corundum bricks according to claim 3, characterized in that, In step S1, the inlet temperature of the spray dryer is 180-220℃, the outlet temperature is 80-100℃, the feed rate is 10-30mL / min, and the moisture content of the dried powder is <0.5%.

7. The method for preparing high thermal shock resistant αβ corundum bricks according to claim 3, characterized in that, In step S2, the inert gas is high-purity argon or nitrogen, and the gas flow rate is 10-30 L / min; the melting temperature is 1950-2100℃, and the holding time is 1-2 h.

8. The method for preparing high thermal shock resistant αβ corundum bricks according to claim 3, characterized in that, In step S3, the gradient cooling rate is 5-10℃ / min, and after cooling to 1200℃, the temperature is kept stable for 10-15min.

9. The method for preparing high thermal shock resistant αβ corundum bricks according to claim 3, characterized in that, In step S3, the step-by-step cooling annealing rate is 1-3℃ / min, cooling down to 1000℃, and then cooling down to 600℃ at a rate of 3-5℃ / min, followed by natural cooling to room temperature with the furnace.

10. The method for preparing high thermal shock resistant αβ corundum bricks according to claim 3, characterized in that, In step S3, the demolding temperature is 200℃, the drying temperature is 100-120℃, and the drying time is 1-2 hours.

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