Fusion casting method for improving performance of AZS octagonal cylinder checker brick

Abstract

The invention relates to the field of high-temperature refractory materials, and discloses a fusion casting method for improving the performance of an AZS octagonal cylinder checker brick, which comprises the following steps: mixing and smelting main raw materials and a composite additive (containing surface-modified nano YAG particles and a rare earth core-shell structure) to obtain a high-purity melt in an inert atmosphere; staged vibration pouring is conducted in the vacuum environment, low-frequency vibration and high-frequency vibration are combined, and the melt filling compactness is improved; an alternating magnetic field is coupled in the gradient cooling process, grain growth is directionally regulated and controlled, and thermal stress is released; and annealing treatment is combined with a surface densified coating, so that the defects are further eliminated, and the erosion resistance is enhanced. According to the invention, through linkage of technologies such as strengthening of a crystal boundary by the composite additive, collaborative optimization of a structure by vibration-magnetic field, inhibition of phase change by a gradient process and the like, the material has excellent thermal shock resistance, high-temperature strength and molten medium corrosion resistance, and is suitable for harsh working conditions such as glass kilns and metallurgical high-temperature equipment.

Description

Technical Field

[0001] The present invention relates to the technical field of high-temperature refractory materials, and specifically to a casting method for improving the performance of AZS octagonal tube lattice bricks. Background Art

[0002] In the field of high-temperature industries, AZS (aluminum zirconium silicon) refractory materials are widely used in extreme environments such as glass furnaces due to their high-temperature resistance and erosion resistance. However, in traditional casting processes, materials are prone to problems such as microcrack propagation and grain boundary phase transformation instability under long-term thermal cycling and molten medium erosion, resulting in structure spalling or even overall fracture. Existing technologies mostly rely on single-process optimization, such as adjusting the ZrO2 content or introducing simple additives, but it is difficult to simultaneously improve the thermal shock resistance and erosion resistance. For example, a high ZrO2 content can enhance erosion resistance but may exacerbate thermal stress concentration due to volume effects caused by phase transformation; while conventional additives can improve grain boundary bonding in the short term but cannot stably exist at high temperatures for a long time. In addition, insufficient microstructure control during the melt pouring and cooling processes is prone to defects such as pores and segregation, further reducing the service life of the material. How to achieve precise microstructure design through process coordination has become a key problem in breaking through the performance bottleneck of AZS materials. Summary of the Invention

[0003] Aiming at the deficiencies of the existing technology, the present invention provides a casting method for improving the performance of AZS octagonal tube lattice bricks, which solves the problem that it is difficult to simultaneously improve the thermal shock resistance, erosion resistance, and high-temperature strength of existing AZS refractory materials due to microstructural defects and process limitations.

[0004] To achieve the above objectives, the present invention is realized through the following technical solutions: A casting method for improving the performance of AZS octagonal tube lattice bricks, comprising the following steps:

[0005] (1) Mix the main raw materials Al2O3, ZrO2, SiO2 with a composite additive and melt them. The composite additive includes nano-YAG particles and rare earth oxides;

[0006] (2) Conduct vibration casting in a vacuum environment, and adjust the vibration frequency in stages during the casting process;

[0007] (3) Apply a gradient cooling and alternating magnetic field coupling treatment to the cast melt;

[0008] (4) Anneal and surface densify the cooled brick body.

[0009] Preferably, the composite additive includes carboxyl-modified nano-YAG particles, La2O3@CeO2 core-shell structure particles, and a mixture of YAG and La2O3@CeO2 coated on the surface of ZrO2 particles.

[0010] Preferably, the carboxyl-modified nano YAG particles are prepared by the following steps:

[0011] Synthesize YAG precursor by sol-gel method, where the molar ratio of yttrium nitrate to aluminum nitrate is 3:4-5, and the molar ratio of complexing agent citric acid to total metal ions is 1.0-1.5:1;

[0012] Calcine the precursor xerogel at 800-1000 °C for 2-3 hours to obtain YAG particles with a particle size of 50-100 nm;

[0013] Immerse the YAG particles in 0.1-0.5 mol / L acrylic acid solution, adjust the pH to 3-4, and perform ultrasonic treatment for 30-60 minutes.

[0014] Preferably, the La2O3@CeO2 core-shell structure is prepared by the following steps:

[0015] Dissolve lanthanum nitrate and cerium nitrate in deionized water according to the molar ratio of La:Ce = 1:2-3 to form a mixed solution;

[0016] Dropwise add ammonia water to the mixed solution, adjust the pH to 9-10, and stir and react at 60-80 °C for 2-4 hours to generate a coprecipitate;

[0017] Centrifuge and wash the precipitate until it is neutral, dry it, and then calcine it at 600-800 °C for 2-3 hours to obtain La2O3@CeO2 core-shell structure particles.

[0018] Preferably, the ratio of the main raw materials is 38-45% Al2O3, 35-42% ZrO2, 12-20% SiO2, and the addition amount of the composite additive is 0.5-1.0% of the total mass.

[0019] Preferably, the melting is carried out under Ar gas protection, and the melting temperature is 1750-1800 °C.

[0020] Preferably, the step of vibration casting in a vacuum environment includes:

[0021] Apply 50-60 Hz low-frequency vibration when the melt temperature > 1400 °C;

[0022] Switch to 200-220 Hz high-frequency vibration when the melt temperature < 1400 °C.

[0023] Preferably, the gradient cooling is divided into two stages:

[0024] The first stage is from 1600 °C to 1200 °C, the cooling rate is 5-8 °C / min, and a 50-60 kHz alternating magnetic field is applied synchronously;

[0025] In the second stage, the temperature ranges from 1200 °C to 800 °C, the cooling rate is 3 - 5 °C / min, the magnetic field frequency is adjusted to 10 - 15 kHz, and the magnetic field direction forms an angle of 45° with the melt flow direction.

[0026] Preferably, in the annealing step for the cooled brick body, the annealing temperature is 800 - 850 °C, the heat preservation time is 12 - 15 hours, and the cooling rate ≤ 2 °C / min.

[0027] Preferably, the surface densification treatment is plasma spraying of an Al2O3 - YAG composite coating, the coating thickness is 50 - 100 μm, and after spraying, it is sintered at 1200 - 1300 °C for 1 - 2 hours.

[0028] The present invention provides a casting method for improving the performance of AZS octagonal cylinder lattice bricks. It has the following beneficial effects:

[0029] 1. Through the synergistic effect of the composite additive in the present invention, the grain boundary bonding force is enhanced, and the ability to disperse thermal stress is improved. The coupled process of gradient cooling and alternating magnetic field further optimizes the grain orientation and phase distribution, making the material not prone to cracking in the rapid heating and cooling environment, and significantly reducing the risk of high - temperature phase change.

[0030] 2. The surface densification treatment of plasma spraying an Al2O3 - YAG composite coating in the present invention forms a protective layer with high hardness and low porosity, effectively blocking the penetration of molten glass liquid or corrosive media. At the same time, the synergistic effect of the high ZrO2 content and the core - shell structure further strengthens the erosion - resistant framework of the matrix.

[0031] 3. The staged vibration casting technology in the present invention combined with the vacuum environment reduces the porosity and segregation defects, and significantly improves the melt fluidity. The alternating magnetic field directionally regulates the grain growth, improves the grain size uniformity, and synchronously enhances the mechanical properties and thermal stability of the material.

[0032] 4. The gradient annealing process in the present invention releases the thermal stress during the casting and cooling processes, repairs the grain boundary defects, and reduces the probability of crack initiation. The phase - transformation toughening effect of ZrO2 particles and the composite additive jointly inhibit the propagation of micro - cracks.

[0033] 5. From the argon - protected melting to the surface coating sintering in the present invention, the process parameters of the whole process are precisely matched. The integration of technologies such as composite additives, vibration casting, and magnetic field regulation forms a closed - loop enhancement effect, and the comprehensive performance of the material breaks through the bottleneck of traditional refractory materials. Description of the Drawings

[0034] Figure 1 It is a schematic flow chart of the method of the present invention. Detailed Embodiments

[0035] Next, in conjunction with the accompanying drawings of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0036] Please refer to the attached Figure 1 , the present invention provides a casting method for improving the performance of AZS octagonal cell bricks, including the following steps:

[0037] S1. Mix the main raw materials Al2O3, ZrO2, SiO2 with a composite additive and then melt them;

[0038] During the casting process, Al2O3, ZrO2, and SiO2 serve as the main raw materials, providing excellent high-temperature strength, chemical erosion resistance, and thermal stability respectively. Among them, the ratio of the main raw materials is Al2O3 38 - 45%, ZrO2 35 - 42%, SiO2 12 - 20%, and the addition amount of the composite additive is 0.5 - 1.0% of the total mass.

[0039] ZrO2 helps to improve the corrosion resistance of AZS bricks to glass melt and reduce the wear of ceramics; SiO2 can improve the structural stability of the material and the matching of thermal expansion coefficients.

[0040] Nanometer YAG particles (yttrium aluminum garnet) and rare earth oxides are used as composite additives, which play the following roles during the melting process:

[0041] Nanometer YAG particles: Due to their unique crystal structure and high melting point, nanometer YAG particles can effectively enhance the high-temperature oxidation resistance and thermal stability of the material. These particles can form fine and uniform dispersed phases during the casting process, significantly improving the thermal shock resistance of the material and enhancing its high-temperature mechanical properties.

[0042] Rare earth oxides (such as La2O3, CeO2, etc.): Rare earth oxides can promote the phase transformation and crystal growth of the ceramic matrix at high temperatures, improving the high-temperature strength and chemical erosion resistance of the material. In particular, the addition of rare earth elements helps to promote the stability of grain boundaries, thereby reducing the brittleness of the material and improving the corrosion resistance at high temperatures.

[0043] S2. Conduct vibration casting in a vacuum environment, and adjust the vibration frequency in stages during the casting process;

[0044] Conducting vibration casting in a vacuum environment can effectively reduce bubbles and defects during the casting process and improve the density of the material. Due to the existence of the vacuum environment, the gas during the casting process is not easily dissolved in the melt, reducing the formation of pores and other defective defects.

[0045] During the vibration casting process, by adjusting the vibration frequency in stages, more precise control can be achieved, thereby optimizing the microstructure of the material:

[0046] Initial low-frequency vibration: At the initial stage of casting, low-frequency vibration helps to improve the fluidity of the material, enabling the melt to uniformly fill each part of the mold and avoiding pores or uneven solidification caused by uneven casting.

[0047] Subsequent high-frequency vibration: When the material begins to solidify, high-frequency vibration can effectively help promote the close arrangement of particles, reduce pores and defects in the material, and further improve the density and overall performance of the brick body.

[0048] Through the dynamic regulation of the vibration frequency, while ensuring the densification and structural uniformity of the material, it is possible to avoid the excessive disturbance caused by high-frequency vibration, which may lead to the instability of the internal structure of the ceramic.

[0049] S3. Apply a coupled treatment of gradient cooling and alternating magnetic field to the cast melt;

[0050] The purpose of gradient cooling is to control the cooling rate by controlling the cooling speed, enabling the ceramic material to experience different cooling rates in different regions, thereby controlling the grain size and distribution. Rapid cooling helps to refine the grains and improve the mechanical properties of the material; while slow cooling helps the grains to grow uniformly and increases the structural stability of the material. Through gradient cooling, the microstructure of AZS bricks can be optimized, and their thermal shock resistance, erosion resistance, and mechanical strength can be improved.

[0051] The introduction of an alternating magnetic field can effectively improve the organizational structure of the material. The magnetic field has a certain effect on orienting the particles and grains in the melt, which can promote uniform grain growth and reduce the non-uniformity that occurs during the cooling process of the raw materials. At the same time, the alternating magnetic field can also affect the electrical conductivity and heat conduction performance of the material, contributing to the improvement of the overall performance of the ceramic. By combining the alternating magnetic field with gradient cooling, not only can the densification of the material be improved, but also the crystal structure can be optimized, increasing its corrosion resistance to glass melt and high-temperature strength.

[0052] S4. Anneal and surface densify the cooled brick body;

[0053] The main purpose of the annealing process is to eliminate the internal stress generated during the melting and casting and cooling processes of the material, preventing cracks caused by uneven thermal expansion. Annealing can relieve and rearrange the lattice structure inside the material, thereby improving the overall mechanical properties of the material. In addition, annealing can also promote the growth and optimization of grains, contributing to the improvement of the thermal shock resistance of the ceramic.

[0054] Surface densification treatment makes the surface layer of the material denser by applying heat treatment or atmosphere control to the cooled brick body, reducing the formation of surface microcracks. The densified surface layer can significantly improve the wear resistance, erosion resistance and thermal stability of AZS bricks, enhancing their long-term service life in high-temperature and corrosive environments.

[0055] In a preferred embodiment of the present invention, the composite additive includes carboxyl-modified nano-YAG particles, and the carboxyl-modified nano-YAG particles are prepared by the following steps:

[0056] Step 1, synthesize a YAG (yttrium aluminum garnet) precursor by the sol-gel method.

[0057] In this step, yttrium nitrate and aluminum nitrate are used as raw metal salts, and the molar ratio between the two is between 3:4 and 5. The selection of this metal salt ratio has an important influence on the structure and properties of the final product. By adjusting the ratio of yttrium nitrate and aluminum nitrate, the composition and quality of YAG crystals can be precisely controlled to ensure their stability at high temperatures and chemical erosion resistance. In addition, citric acid is used as a complexing agent, and the total molar ratio of citric acid to metal ions is set between 1.0 and 1.5:1, aiming to provide a stable complex to help the metal ions be evenly distributed and promote the synthesis process of the precursor. Citric acid can not only control the synthesis reaction of the precursor, but also prevent the aggregation of metal ions in the solution and avoid the formation of precipitation.

[0058] Step 2, after synthesizing the precursor, dry-gel it and calcine it in the temperature range of 800 to 1000 °C for 2 to 3 hours to obtain YAG particles with a particle size of 50 to 100 nanometers.

[0059] The main purpose of this step is to remove the organic components in the precursor through high-temperature calcination and promote the crystallization of metal oxides into YAG crystals. The selection of the calcination temperature is crucial for the control of the particle size. A higher temperature helps the growth of grains and the stability of the structure, while proper control of the calcination time can ensure uniform grains and avoid the influence of too large particles on subsequent properties.

[0060] The particle size of the calcined YAG particles is between 50 and 100 nanometers. The regulation of the particle size helps to improve the dispersibility of the particles in the casting process and their strengthening effect on the ceramic matrix. A smaller particle size helps to form a more uniform microstructure, improve the strength and high-temperature resistance of the material, and at the same time increase the specific surface area of the particles, which is beneficial to the combination with the matrix.

[0061] Step 3, immerse the prepared YAG particles in an acrylic acid solution with a concentration of 0.1 to 0.5 mol / L and adjust the pH of the solution to between 3 and 4.

[0062] The purpose of this step is to modify the surface of YAG particles with acrylic acid to introduce carboxyl functional groups. Carboxyl modification can make the surface of YAG particles carry negative charges, thereby improving their compatibility with the matrix during the casting process. The introduction of carboxyl groups not only improves the adhesion between the particles and the matrix, but also increases the dispersion of YAG particles in the ceramic matrix, thus improving the mechanical properties and thermal stability of the composite material. In addition, the modified YAG particles can provide better antioxidant ability and thermal shock stability in high-temperature environments, enhancing the corrosion resistance of the ceramic tiles.

[0063] Finally, by means of ultrasonic treatment, the YAG particles are treated in the acrylic acid solution for 30 to 60 minutes to ensure that the carboxyl modification is evenly attached to the particle surface. The introduction of ultrasonic waves helps to break the bubbles in the solution, improve the fluidity of the solution, make the modification reaction more uniform and efficient, and ensure that each YAG particle can evenly adsorb acrylic acid molecules, thereby forming a stable surface modification layer.

[0064] The carboxyl-modified nano YAG particles prepared by the above steps can significantly improve the overall performance of AZS octagonal cylinder lattice bricks during the casting process, especially showing more excellent performance in high-temperature resistance and chemical erosion resistance. Due to the stronger surface compatibility and dispersion of the carboxyl-modified YAG particles, they can be evenly distributed in the matrix, effectively enhancing the mechanical strength, thermal shock stability and corrosion resistance of the material.

[0065] In a preferred embodiment of the present invention, the composite additive includes La2O3@CeO2 core-shell structure particles, and the preparation method of the core-shell structure particles is as follows:

[0066] Step 1, dissolve lanthanum nitrate (La(NO3)3) and cerium nitrate (Ce(NO3)3) in deionized water according to the molar ratio of La:Ce of 1:2 to 3 to form a uniform mixed solution.

[0067] The selection of the molar ratio of lanthanum nitrate to cerium nitrate has an important influence on the stability of the final core-shell structure and its strengthening effect on the matrix. Cerium (Ce) mainly exists in the form of Ce 4+ , which has excellent antioxidant performance in high-temperature environments, while lanthanum (La) can promote the stability of the matrix and improve the thermal expansion matching of the composite material in the oxidized state. By reasonably controlling the ratio of La to Ce, the durability and erosion resistance under high-temperature conditions can be optimized while forming the core-shell structure.

[0068] Step 2, in the mixed solution, gradually add ammonia water solution and adjust the pH of the solution to 9 to 10.

[0069] In an alkaline environment, La 3+ and Ce 3+Ions gradually undergo coprecipitation reactions to form a uniform precursor precipitate. This process requires stirring and reacting at a temperature of 60 to 80 °C for 2 to 4 hours to ensure the full reaction of metal oxides and promote the formation of the core-shell structure. During this process, La(OH)3 and Ce(OH)4 precipitate respectively, and due to the stronger oxidizing property of Ce 4+ , the nucleation rate of CeO2 is faster, and it can preferentially coat the particles of La2O3, thus forming the core-shell structure of La2O3@CeO2. The formation of the core-shell structure is crucial for the application of the material in cast refractory bricks. As the shell layer, CeO2 can provide excellent oxidation stability, while the presence of La2O3 helps to improve the thermal shock resistance and structural stability of the material.

[0070] Step 3: Centrifuge the coprecipitation product and wash it with deionized water until neutral to remove residual soluble impurities and unreacted ions during the reaction process.

[0071] The washed precipitate is dried to remove moisture and further stabilize the precursor structure. Subsequently, the dried powder is calcined at a temperature in the range of 600 to 800 °C for 2 to 3 hours to complete the solidification of the core-shell structure and improve the crystallinity of the material. The choice of calcination temperature directly affects the microstructure and phase distribution of La2O3@CeO2 particles. A lower calcination temperature may result in more hydroxyl groups remaining on the particle surface, affecting its stability during the casting process, while a higher calcination temperature helps to form a more uniform and dense core-shell structure, improving the high-temperature resistance and chemical erosion resistance of the particles.

[0072] The La2O3@CeO2 core-shell structure particles prepared by this method can significantly improve the high-temperature resistance and corrosion resistance of cast refractory bricks. The CeO2 shell layer can not only effectively prevent the phase decomposition of oxides but also provide additional antioxidant protection at high temperatures, improving the thermal stability of the material. The presence of the La2O3 core can optimize the thermal expansion matching of the material and reduce cracking or structural deterioration caused by thermal stress in a high-temperature environment. This special design of the core-shell structure makes the enhancement effect of the composite additive in refractory materials more significant, and can effectively improve the erosion resistance, thermal shock stability, and overall mechanical strength of AZS octagonal cylinder lattice bricks, providing a more excellent solution for high-temperature applications.

[0073] In a preferred embodiment of the present invention, the composite additive further includes a mixture of YAG and La2O3@CeO2 coated on the surface of ZrO2 particles, and its preparation method is as follows:

[0074] The mixture of YAG and La2O3@CeO2 is coated on the surface of ZrO2 particles by the uniform deposition method to enhance the high-temperature stability and erosion resistance of ZrO2.

[0075] ZrO2 is an excellent refractory material and is widely used due to its high melting point, high strength, and excellent resistance to glass melt erosion. However, ZrO2 may undergo phase transformation at high temperatures (such as the transformation from monoclinic phase to tetragonal phase or cubic phase), resulting in volume change and crack generation, which affects the structural stability of the material. Therefore, coating with a mixture of YAG and La2O3@CeO2 can effectively stabilize the crystal phase of ZrO2 and improve the thermal stability and crack resistance of the material.

[0076] During the preparation process, first, ZrO2 particles are dispersed in deionized water or ethanol solution and ultrasonicated for 30 to 60 minutes to ensure uniform dispersion of the particles and avoid agglomeration. Subsequently, the pre-prepared YAG and La2O3@CeO2 mixture sol is added to the dispersion, and uniform deposition is carried out under stirring. In this process, the YAG and La2O3@CeO2 mixture is gradually coated on the surface of ZrO2 particles through electrostatic adsorption and physical deposition, and a uniform composite coating is formed.

[0077] To further enhance the bonding strength and density of the coating layer, a temperature-controlled calcination method is used for treatment. First, the deposited ZrO2@(YAG+La2O3@CeO2) particles are dried at low temperature to remove the surface solvent, and then calcined at 800 to 1000 °C for 2 to 3 hours to cure the coating layer and optimize the microstructure. During the calcination process, YAG can form a good interfacial bond with ZrO2 particles, improving the thermal shock resistance and mechanical strength of ZrO2. At the same time, the addition of the La2O3@CeO2 core-shell structure can effectively prevent the phase transformation of ZrO2 at high temperatures and enhance the oxidation resistance of the material.

[0078] The ZrO2@(YAG+La2O3@CeO2) composite particles prepared by this method have significant advantages in the application of fused-cast refractory bricks. First, the presence of the YAG layer can improve the dispersibility of ZrO2 particles, making them form a more uniform reinforcing phase in the matrix and improving the overall mechanical properties of the refractory material. Second, the synergistic effect of La2O3@CeO2 effectively enhances the thermal shock stability and resistance to glass melt erosion of the material, enabling the AZS octagonal cylinder lattice brick to exhibit better durability in the high-temperature glass melting furnace environment. Finally, this composite coating structure not only enhances the stability of ZrO2 particles but also improves the lifespan of the overall material, providing a new technical route for the preparation of high-performance refractory materials.

[0079] In a preferred embodiment of the present invention, the smelting process is carried out under the protection of argon (Ar), and the smelting temperature is set at 1750 to 1800 °C.

[0080] During the smelting process, argon protection is adopted mainly to prevent oxygen from reacting with the molten materials. Especially at high temperatures, many metal oxides or additives may react with oxygen to form undesirable oxides, which can affect the properties of the materials. Argon is an inert gas that does not react with other substances. Therefore, it can effectively isolate oxygen, reduce the oxidation effect, and thus maintain the chemical stability of each component during the melting process. This is crucial for the uniform distribution of composite additives and the quality control of the final cast product.

[0081] Secondly, the smelting temperature is set within the range of 1750 °C to 1800 °C. This temperature range is selected as the most suitable one for the raw materials and additives used in the smelting. At this temperature, the raw materials can be completely melted and reach the required fluidity, while avoiding excessive oxidation or volatilization of material components that may be caused by too high a temperature. The smelting temperature of 1750 °C to 1800 °C ensures the full mixing of the melt, which helps the particles of composite additives such as YAG, La2O3@CeO2, ZrO2, etc. to be uniformly dispersed in the matrix, improving the properties of the final material.

[0082] In a preferred embodiment of the present invention, the vibration casting process is carried out in a vacuum environment to improve the density and uniformity of the materials during the casting process. The vibration casting technology optimizes the fluidity, gas exhaust property, and crystal structure of the melt through different vibration modes, thereby improving the properties of the final product. The specific steps are as follows:

[0083] When the melt temperature is higher than 1400 °C, a low-frequency vibration of 50 - 60 Hz is applied. In this temperature range, the melt is still in a highly fluid state. The low-frequency vibration can promote the uniform flow of the melt, reduce component segregation, and accelerate the floating and removal of bubbles. The action mechanism of the low-frequency vibration is mainly reflected in:

[0084] Promote the internal convection of the melt, improve the component uniformity, and prevent phase separation or concentration gradient from occurring in the high-temperature melt during the casting process;

[0085] Help larger bubbles to float up, making it easier for them to escape from the melt, thereby reducing the porosity defects inside the formed material;

[0086] Enhance the filling effect of the melt on the mold and improve the integrity of the overall casting.

[0087] When the melt temperature drops below 1400 °C, it is switched to a high-frequency vibration of 200 - 220 Hz. At this time, the fluidity of the melt decreases, and the high-frequency vibration is mainly used to further improve the density of the material and optimize the solidification structure. The functions of the high-frequency vibration include:

[0088] Promote grain refinement, make the microstructure of the material more uniform, and contribute to improving its mechanical strength and thermal shock resistance;

[0089] Destroy the forming coarse dendritic structure, prevent the formation of columnar crystals, thereby improving the isotropy of the material and enhancing the overall heat resistance and erosion resistance;

[0090] Further remove microbubbles and inclusions, improving the purity and density of the final material.

[0091] In addition, the design of vibration casting in a vacuum environment helps to reduce the contact between the melt and air, avoid defects caused by oxidation or gas inclusions, and improve the stability of the formed material. Combining the dynamic switching of low-frequency and high-frequency vibrations enables the casting process to adapt to changes in the melt state, achieving full-process control from fluidity control to microstructure optimization, thereby effectively enhancing the performance and service life of refractory materials.

[0092] In a preferred embodiment of the present invention, gradient cooling is divided into two stages to optimize the microstructure during solidification and regulate the phase distribution and grain orientation through an alternating magnetic field, thereby enhancing the heat resistance and mechanical properties of the final material. The specific implementation method is as follows:

[0093] In the first stage (1600°C → 1200°C), the cooling rate is controlled at 5 - 8°C / min, and a high-frequency alternating magnetic field of 50 - 60 kHz is applied synchronously. This stage is in the high-temperature solidification range of the material, and the melt still has high fluidity. Through the action of the high-frequency alternating magnetic field, the microstructure of the melt can be effectively regulated, and the uniform distribution of elements can be enhanced. The action mechanisms of the magnetic field mainly include:

[0094] Promote solute diffusion, improve the uniformity of the melt, and avoid compositional segregation;

[0095] Suppress the temperature gradient and compositional gradient in the melt through the magnetohydrodynamic effect (MHD effect), thereby reducing macrosegregation and dendritic growth;

[0096] Suppress the formation of coarse dendrites, improve the refinement degree of the solidification structure, make the overall compactness of the material higher, and reduce internal defects.

[0097] As the temperature further decreases and enters the second stage (1200°C → 800°C), the cooling rate is adjusted to 3 - 5°C / min, the magnetic field frequency is adjusted to 10 - 15 kHz, and the magnetic field direction forms a 45° angle with the melt flow direction. The main objective of this stage is to optimize the grain growth in the low-temperature range and improve the overall structural stability of the material. The action mechanisms of the low-frequency alternating magnetic field include:

[0098] Reduce the accumulation of thermal stress in the low-temperature stage and reduce the risk of cracking of the material caused by thermal expansion and contraction;

[0099] By adjusting the angle between the magnetic field direction and the melt flow direction, the grain orientation growth is guided to form a more uniform and dense microstructure, improving the mechanical strength of the material;

[0100] Restrict the local enrichment of the residual melt, reduce microsegregation, and improve the high-temperature stability and erosion resistance of the material.

[0101] Through this two-stage gradient cooling scheme, while ensuring the overall cooling uniformity, combined with the dynamic regulation of the alternating magnetic field, precise control of the melt solidification process can be achieved, thereby optimizing the microstructure of the material and enhancing its high-temperature stability, wear resistance, and erosion resistance.

[0102] In a preferred embodiment of the present invention, the cooled brick body needs to be annealed to further optimize its microstructure and improve the thermal stability and thermal shock resistance of the material. The specific parameters of the annealing process are as follows:

[0103] The annealing temperature is set at 800 - 850 °C, and a heat preservation treatment is carried out for 12 - 15 hours, and then slowly cooled to room temperature at a cooling rate of ≤2 °C / min. The main purpose of this process is to release the thermal stress inside the brick body, improve the phase distribution, and enhance the overall mechanical properties of the material.

[0104] During the casting process, since the material has experienced high-temperature melting, vibration casting, and gradient cooling, there may be certain thermal stress residues inside. Especially during the melt solidification process, due to the differences in the thermal expansion coefficients of different phases, microcracks or local stress concentration areas may be formed.

[0105] In the temperature range of 800 - 850 °C, the thermal stress inside the brick body can be effectively relieved while ensuring the mechanical integrity of the material. The higher annealing temperature can provide sufficient atomic diffusion activity, enabling the stress concentration areas to gradually relax, thus avoiding cracking or spalling caused by thermal shock during subsequent use.

[0106] The annealing temperature is in the optimal temperature range for adjusting the microstructure of the material, which helps to stabilize the phase structure. Especially for the ZrO2-reinforced composite brick body, it can further improve the phase distribution of ZrO2 and avoid volume changes caused by phase transformation under high-temperature conditions. At the same time, the uniform diffusion of La2O3@CeO2 and YAG phases can further optimize the overall structure of the material and improve its high-temperature resistance.

[0107] After a long time of heat preservation (12 - 15 hours), the grain structure inside the material can be further optimized, reducing grain boundary defects and improving the creep resistance of the material. Appropriate long-time annealing can also reduce microvoids, enhancing the overall density of the material.

[0108] Adopt a cooling rate of ≤2℃ / min to ensure that no new thermal stress is introduced due to rapid cooling during the cooling process of the brick body, and at the same time avoid uneven shrinkage of grain boundaries caused by excessive cooling rate, which affects the overall durability of the material. Slow cooling can also effectively reduce the residual stress of the glass phase or a small amount of amorphous phase, and improve the overall stability of the material.

[0109] Through this annealing process, the overall thermal stability and mechanical properties of the brick body have been significantly improved, which can effectively reduce the cracking risk during use and improve the thermal shock resistance, enabling it to serve in high-temperature molten environments such as glass furnaces and metallurgical smelting furnaces for a long time.

[0110] In a preferred embodiment of the present invention, the surface densification treatment adopts the process of plasma spraying Al2O3-YAG composite coating to improve the erosion resistance, thermal shock resistance and overall durability of the brick body. The specific implementation scheme is as follows:

[0111] First, use the plasma spraying technology to deposit the Al2O3-YAG composite coating on the surface of the brick body, and control the coating thickness within 50-100μm. Plasma spraying is a high-energy thermal spraying technology that uses the high temperature generated by the plasma arc to quickly melt the spraying material and deposit it on the surface of the substrate under the action of high-temperature and high-speed gas flow to form a dense protective layer. The ceramic coating formed by the composite of Al2O3 and YAG (yttrium aluminum garnet) has extremely high wear resistance and thermal shock resistance, which can effectively improve the service performance of the material in high-temperature environments.

[0112] Al2O3 itself has extremely high hardness (Mohs hardness 9), which can effectively resist the erosion of glass melt, molten metal or high-temperature atmosphere, and reduce the physical and chemical wear of the brick body.

[0113] YAG has excellent high-temperature stability and thermal shock resistance, which can enhance the durability of the coating under thermal cycling conditions and prevent the generation of thermal cracks.

[0114] The thermal expansion coefficients of Al2O3 and YAG match, making the coating not easy to peel off or crack in high-temperature environments.

[0115] The presence of YAG can improve the fracture toughness of the coating and reduce the thermal stress concentration under thermal shock conditions, improving the overall durability.

[0116] Due to the mechanical bonding and partial metallurgical bonding between the coating formed by plasma spraying and the substrate, the coating has a strong adhesion to the surface of the brick body and is not easy to peel off.

[0117] After spraying, the coating needs to be sintered at a high temperature of 1200-1300℃ for 1-2 hours to enhance the density and stability of the coating:

[0118] During the sintering process, Al2O3 and YAG particles are combined through diffusion, improving the mechanical strength and spalling resistance of the coating;

[0119] The selection of the sintering temperature ensures the uniformity of the coating while avoiding performance degradation caused by excessive grain growth;

[0120] After high-temperature sintering, the porosity of the coating decreases, further improving the anti-permeation ability and enhancing the corrosion resistance of the coating in the glass melting furnace or metallurgical smelting environment.

[0121] By plasma spraying the Al2O3-YAG composite coating and subjecting it to high-temperature sintering, the wear resistance, erosion resistance, and chemical erosion resistance of the brick surface are significantly improved, while reducing the spalling risk under high-temperature service conditions.

[0122] To better understand the present invention, the above method will be described in detail below in conjunction with specific embodiments.

[0123] Example 1:

[0124] Formulation (mass percentage):

[0125] Al2O3: 40.0%;

[0126] ZrO2: 38.0%;

[0127] SiO2: 18.0%;

[0128] Composite additive (La2O3@CeO2 + YAG): 0.8%;

[0129] Other trace elements: 3.2%.

[0130] Preparation process:

[0131] Melting: Melting at 1780°C under Ar gas protection;

[0132] Vibrating casting:

[0133] Melt temperature > 1400°C: Applying 55 Hz low-frequency vibration;

[0134] Melt temperature < 1400°C: Applying 210 Hz high-frequency vibration;

[0135] Gradient cooling:

[0136] 1600°C → 1200°C, cooling rate 6°C / min, applying 55 kHz alternating magnetic field;

[0137] 1200°C → 800°C, cooling rate 4°C / min, applying 12 kHz alternating magnetic field (at a 45° angle to the melt flow direction);

[0138] Annealing: 800 °C, holding for 14 hours, cooling rate 1.8 °C / min.

[0139] Example 2:

[0140] Formulation (mass percentage):

[0141] Al2O3: 42.0%;

[0142] ZrO2: 36.0%;

[0143] SiO2: 19.0%;

[0144] Composite additive (La2O3@CeO2 + YAG): 0.6%;

[0145] Other trace elements: 2.4%.

[0146] Preparation process:

[0147] Melting: Melting at 1750 °C under Ar gas protection;

[0148] Vibrating casting:

[0149] Melt temperature > 1400 °C: Applying 58 Hz low-frequency vibration;

[0150] Melt temperature < 1400 °C: Applying 205 Hz high-frequency vibration;

[0151] Gradient cooling:

[0152] 1600 °C → 1200 °C, cooling rate 7 °C / min, applying 58 kHz alternating magnetic field;

[0153] 1200 °C → 800 °C, cooling rate 3.5 °C / min, applying 10 kHz alternating magnetic field (at a 45° angle to the melt flow direction);

[0154] Annealing: 850 °C, holding for 12 hours, cooling rate 2.0 °C / min.

[0155] Example 3:

[0156] Formulation (mass percentage):

[0157] Al2O3: 38.5%;

[0158] ZrO2: 41.0%;

[0159] SiO2: 14.5%;

[0160] Composite additive (La2O3@CeO2 + YAG): 1.0%;

[0161] Other trace elements: 5.0%.

[0162] Preparation process:

[0163] Smelting: Smelt at 1800 °C under Ar gas protection;

[0164] Vibrating pouring:

[0165] Melt temperature > 1400 °C: Apply 52 Hz low-frequency vibration;

[0166] Melt temperature < 1400 °C: Apply 200 Hz high-frequency vibration;

[0167] Gradient cooling:

[0168] 1600 °C → 1200 °C, cooling rate 5 °C / min, apply 52 kHz alternating magnetic field;

[0169] 1200 °C → 800 °C, cooling rate 3 °C / min, apply 15 kHz alternating magnetic field (at a 45° angle to the melt flow direction);

[0170] Annealing: 820 °C, hold for 15 hours, cooling rate 1.5 °C / min.

[0171] Comparative example 1:

[0172] Compared with the example, the difference is that the composite additive is removed, and the rest are the same.

[0173] Comparative example 2:

[0174] Compared with example 1, the difference is that vibrating pouring is cancelled, and the rest are the same.

[0175] Comparative example 3:

[0176] Compared with the example, the difference is that the alternating magnetic field is cancelled, and the rest are the same.

[0177] Comparative example 4:

[0178] Compared with example 2, the difference is that the ZrO2 content is reduced to 30.0%, and the rest are the same.

[0179] Comparative example 5:

[0180] Compared with example 2, the difference is that no annealing treatment is carried out, and the rest are the same.

[0181] Comparative example 6:

[0182] Compared with example 3, the difference is that no surface densification treatment is carried out, and the rest are the same.

[0183] Comparative example 7:

[0184] Compared with Example 3, the difference lies in that argon protection melting is cancelled, and the rest are the same.

[0185] Test Example 1:

[0186] Evaluate the thermal shock resistance of AZS octagonal cylinder lattice bricks of different examples and comparative examples during rapid heating and cooling cycles, and analyze their crack generation and propagation behaviors.

[0187] Experimental steps:

[0188] 1. Sample preparation:

[0189] Cut the bricks of Examples 1 - 3 and Comparative Examples 1 - 7 into a unified size (50 mm × 50 mm × 10 mm), and polish the surface until no visible defects.

[0190] Mark each group of samples with numbers (Example 1 is S1, Comparative Example 1 is C1, and so on).

[0191] 2. Heating and cooling cycles:

[0192] Put the samples into a high - temperature furnace, heat them to 1000 °C at a rate of 10 °C / min, and hold for 30 minutes.

[0193] Quickly transfer the samples to a flowing water tank at 25 °C, immerse them for 5 seconds and then take them out, and record the surface state after drying.

[0194] Repeat the above cycle until obvious cracks or fractures appear in the samples, and perform a maximum of 50 cycles.

[0195] 3. Data recording:

[0196] Observe and record after each cycle:

[0197] The number of cracks (pieces), the longest crack length (mm), and the proportion of the surface spalling area (%);

[0198] If the sample is completely fractured, terminate the experiment and record the number of cycles at termination.

[0199] The test results are shown in the following table:

[0200]

[0201] The thermal shock resistance test shows that the crack propagation in the examples is significantly inhibited. The YAG particles and La2O3@CeO2 core-shell structure in the composite additive lock the grain boundaries, and the thermal stress is dispersed at the grain boundaries. The gradient cooling process is combined with an alternating magnetic field, resulting in refined grains with regular orientations and reduced internal defects. In the comparative examples, due to the lack of these protections, the grain boundaries are fragile and the cracks penetrate rapidly. For example, in C1 without additives, the grain boundaries are preferentially eroded, and the concentration of thermal stress leads to fracture after 15 cycles; in C4 with insufficient ZrO2, the framework is loose and it disintegrates after 10 cycles.

[0202] Test Example 2:

[0203] Evaluate the erosion resistance of AZS octagonal cylinder lattice bricks of different examples and comparative examples in high-temperature molten glass, and analyze the surface damage degree and failure mode.

[0204] Experimental procedure:

[0205] 1. Sample preparation:

[0206] Process the bricks of Examples 1-3 and Comparative Examples 1-7 into a unified size (30 mm × 30 mm × 5 mm), and polish the surface to Ra ≤ 0.8 μm.

[0207] Mark each group of samples with numbers (Example 1 is S1, Comparative Example 1 is C1, and so on).

[0208] 2. Preparation of molten glass:

[0209] Prepare sodium-calcium silicate molten glass (composition: SiO2 72%, Na2O 14%, CaO 10%, Al2O3 4%), crush it and place it in a platinum crucible.

[0210] 3. Erosion experiment:

[0211] Vertically immerse the samples in the molten glass at 1500 °C for 24 hours (simulating the working conditions of a glass furnace).

[0212] After the experiment, cool it to room temperature at a rate of 5 °C / min.

[0213] 4. Post-erosion treatment:

[0214] Immerse the surface of the samples in a 10% hydrofluoric acid (HF) solution for 10 minutes to remove the attached glass layer.

[0215] After ultrasonic cleaning and drying, record the surface erosion morphology.

[0216] 5. Data measurement:

[0217] Use a laser scanning microscope to measure the erosion depth (take the average value of 3 different regions).

[0218] Calculate the erosion rate (erosion depth / time, unit: mm / h).

[0219] Observe and record the types of surface damage (cracks, holes, spalling, etc.).

[0220] The test results are shown in the following table:

[0221]

[0222]

[0223] The erosion resistance data show that the surface damage of the examples is slight. The plasma-sprayed Al2O3-YAG composite coating is as dense as a shield, and the molten glass is difficult to penetrate. The high ZrO2 content (≥38%) and La2O3@CeO2 act synergistically to form an erosion-resistant barrier. In the comparative examples, for C7, due to melting oxidation, the matrix is porous and the erosion rate soars; for C6, without surface treatment, the matrix is directly exposed and the penetration depth of the glass liquid doubles.

[0224] Test Example 3:

[0225] Evaluate the flexural strength of AZS octagonal cylinder lattice bricks of different examples and comparative examples in a high-temperature environment, and analyze the correlation between their mechanical properties and process parameters.

[0226] Experimental steps:

[0227] 1. Sample preparation:

[0228] Cut the bricks of Examples 1-3 and Comparative Examples 1-7 into a unified size (50 mm×10 mm×5 mm), and polish the surface until no visible defects are present.

[0229] Mark each group of samples with numbers (for example, Example 1 is S1, Comparative Example 1 is C1, and so on).

[0230] 2. Set up the high-temperature test environment:

[0231] Preheat the high-temperature furnace to 1000°C and keep the temperature fluctuation ≤±5°C.

[0232] Use a three-point bending fixture, set the span to 40 mm, and the radius of the loading head to 5 mm.

[0233] 3. Flexural strength test:

[0234] Place the sample in the high-temperature furnace and keep it warm for 30 minutes to ensure uniform temperature.

[0235] Apply pressure at a constant loading rate (0.5 mm / min) until the sample breaks.

[0236] Record the maximum load (N) and the fracture displacement (mm), and calculate the flexural strength (formula: where F is the load, L is the span, b is the width, and h is the thickness).

[0237] 4. Data recording:

[0238] Each group of tests was repeated 3 times and the average value was taken.

[0239] Observe the fracture surface morphology (intergranular fracture, transgranular fracture, etc.).

[0240] The test results are shown in the following table:

[0241]

[0242] The high-temperature flexural strength reveals that the mechanical advantages of the examples stem from process coupling. Vibration casting optimizes the melt flow and the porosity decreases; the alternating magnetic field guides the grain orientation growth and the strength increases. The ZrO2 of S3 reaches 41%, the transformation toughening effect is prominent, and the fracture displacement is the smallest while the strength is the highest. In Comparative Example C2, vibration casting is cancelled, the melt filling is uneven, and the local porosity reduces the strength; in C3, there is no magnetic field, the grains are coarsened, and the flexural performance drops suddenly by 30%. Each link of the process chain - from melting protection to coating sintering - is closely linked and indispensable.

[0243] Although the embodiments of the present invention have been shown and described, for those of ordinary skill in the art, it can be understood that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A melting and casting method for improving the performance of AZS octagonal tube checker bricks, characterized in that: The following steps are involved: (1) mixing main raw materials Al2O3, ZrO2, SiO2 and composite additives and then smelting, wherein the composite additives include nano YAG particles and rare earth oxides; (2) Vibration casting is performed under vacuum, and the vibration frequency is adjusted in stages during the casting process; (3) applying gradient cooling and alternating magnetic field coupling treatment to the cast melt; (4) Annealing and surface densification treatment are performed on the cooled brick body.

2. The melting and casting method for improving the performance of AZS octagonal tube checker bricks according to claim 1, characterized in that: The composite additive comprises carboxyl-modified nano YAG particles, La2O3@CeO2 core-shell structure particles, and a mixture of YAG and La2O3@CeO2 coated on the surface of ZrO2 particles.

3. The melting and casting method for improving the performance of AZS octagonal tube checker bricks according to claim 2, characterized in that: The carboxyl-modified nano YAG particles are prepared by the following steps: The YAG precursor is synthesized by a sol-gel method, wherein the molar ratio of yttrium nitrate to aluminum nitrate is 3:4-5, and the molar ratio of complexing agent citric acid to the total metal ion is 1.0-1.5:1; The precursor dry gel is calcined at 800-1000° C. for 2-3 hours to obtain YAG particles with a particle size of 50-100 nm; The YAG particles are immersed in a 0.1-0.5 mol / L acrylic acid solution, the pH is adjusted to 3-4, and ultrasonic treatment is performed for 30-60 minutes.

4. The melting and casting method for improving the performance of AZS octagonal tube checker bricks according to claim 2, characterized in that: The La2O3@CeO2 core-shell structure is prepared by the following steps: Dissolve lanthanum nitrate and cerium nitrate in deionized water at a molar ratio of La:Ce=1:2-3 to form a mixed solution; Add ammonia water dropwise to the mixed solution to adjust the pH to 9-10, and stir the mixture at 60-80° C. for 2-4 hours to generate a coprecipitate; The precipitate is washed by centrifugation until it becomes neutral, dried, and then calcined at 600-800°C for 2-3 hours to obtain La2O3@CeO2 core-shell structure particles.

5. The melting and casting method for improving the performance of AZS octagonal tube checker bricks according to claim 1, characterized in that: The main raw materials have a ratio of 38-45% Al2O3, 35-42% ZrO2 and 12-20% SiO2, and the added amount of the composite additive is 0.5-1.0% of the total mass.

6. The melting and casting method for improving the performance of AZS octagonal tube checker bricks according to claim 1, characterized in that: The smelting is carried out under Ar gas protection, and the smelting temperature is 1750-1800°C.

7. The melting and casting method for improving the performance of AZS octagonal tube checker bricks according to claim 1, characterized in that: The step of vibrating and casting under vacuum environment comprises: When the melt temperature is greater than 1400°C, apply 50-60Hz low-frequency vibration; When the melt temperature is less than 1400°C, it switches to a high frequency vibration of 200-220 Hz.

8. The melting and casting method for improving the performance of AZS octagonal tube checker bricks according to claim 1, characterized in that: The gradient cooling is divided into two stages: The first stage is from 1600℃ to 1200℃, with a cooling rate of 5-8℃ / min, and a 50-60kHz alternating magnetic field is applied simultaneously; In the second stage, the temperature is from 1200°C to 800°C, the cooling rate is 3-5°C / min, the magnetic field frequency is adjusted to 10-15kHz, and the direction of the magnetic field is at an angle of 45° to the melt flow direction.

9. The melting and casting method for improving the performance of AZS octagonal tube checker bricks according to claim 1, characterized in that: In the step of annealing the cooled brick body, the annealing temperature is 800-850° C., the heat preservation time is 12-15 hours, and the cooling rate is ≤2° C. / min.

10. The melting and casting method for improving the performance of AZS octagonal tube checker bricks according to claim 1, characterized in that: The surface densification treatment is plasma spraying of Al2O3-YAG composite coating with a coating thickness of 50-100 μm, and sintering at 1200-1300° C. for 1-2 hours after spraying.

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