A gas-permeable brick for an electric furnace and a method for manufacturing the same

Abstract

The application discloses a kind of electric furnace gas permeable brick and preparation method thereof, electric furnace gas permeable brick is made of fused corundum particle, tabular corundum fine powder, active alumina micro powder, magnesium aluminate spinel fine powder, zirconia toughening micro powder, nano alumina powder, high-temperature self-repairing additive, composite pore-forming agent, high-temperature binder, composite pore-forming agent portion sintering;The application is made by double mode pore of composite pore-forming agent, the synergy of configuration, the percolation of tortuous path + the permeability of spherical shape, multistage toughening system, nano filling-phase change toughening and self-repairing function dynamic response, boride wetting-solidification, with inert atmosphere subsection sintering Precise process control, successfully build electric furnace gas permeable brick with high gas permeability stability, strong thermal shock resistance toughness, adaptive anti-loss triple characteristics.

Description

Technical Field

[0001] This invention belongs to the technical field of monolithic refractory materials, specifically relating to a permeable brick for electric furnaces; and more particularly to a method for preparing a permeable brick for electric furnaces. Background Technology

[0002] Permeable bricks for electric arc furnaces are key functional refractory materials in the iron and steel metallurgical industry. They are typically made from high-purity corundum or spinel refractory raw materials, with interconnected pore channels formed through a pore-forming process. Their core function is to stably deliver inert gas into molten metal under high-temperature service conditions, achieving uniform temperature and composition of the molten steel and removing impurities. Current technologies mainly employ monolithic refractory structures containing clay or completely free of clay, controlling permeability by adjusting particle size distribution or adding a single type of pore-forming agent, and sintering them in an oxidizing or weakly reducing atmosphere.

[0003] Despite continuous technological iteration, significant shortcomings remain in practical applications: First, the pore structure formed by conventional pore-forming processes is prone to morphological deterioration under high-temperature slag erosion and repeated thermal shock, leading to a significant decrease in permeability stability over service life; second, it is difficult to simultaneously optimize the high-temperature flexural strength and thermal shock resistance of materials, and long-term thermal cycling can easily induce microcracks and accelerate structural collapse; third, there is a lack of proactive defense mechanisms against slag penetration and molten metal phase blockage of pores, reducing the service life of the bricks. Therefore, we propose a permeable brick for electric furnaces and its preparation process to specifically address the above problems. Summary of the Invention

[0004] The purpose of this invention is to provide a permeable brick for electric furnaces and its preparation method. Through the dual-modal pore synergistic configuration of composite pore-forming agent, the tortuous diameter impermeability + spherical permeability retention, multi-level toughening system, nano-filling-phase transformation toughening and self-healing dynamic response, boride wetting-curing, and precise process control of segmented sintering in inert atmosphere, a permeable brick for electric furnaces with high permeability stability, strong thermal shock resistance, and adaptive damage resistance is successfully constructed.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A permeable brick for electric furnaces, by weight, is formulated from 45-65 parts of fused alumina particles, 15-30 parts of tabular alumina fine powder, 5-12 parts of activated alumina micro powder, 8-18 parts of magnesium aluminum spinel fine powder, 6-14 parts of zirconia toughened micro powder, 0.5-3 parts of nano alumina powder, 1-5 parts of high-temperature self-healing additive, 0.5-4 parts of composite pore-forming agent, 3-8 parts of high-temperature binder, and 0.5-4 parts of composite pore-forming agent sintered together.

[0007] The high-temperature self-healing additive is selected from zirconium boride, chromium boride, or a combination thereof;

[0008] The composite pore-forming agent is composed of pyrolyzable organic polymer microspheres and mineral fibers with micro-swelling properties, with a mass ratio of (3:1) to (1:1).

[0009] Preferably, the mineral fiber with micro-swelling properties in the composite pore-forming agent is modified aluminosilicate fiber or heat-treated sepiolite fiber, which is configured to undergo controllable micro-expansion in the temperature range of 800℃-1100℃ to form non-spherical, highly tortuous microchannels.

[0010] Preferably, the pyrolysis temperature of the pyrolyzable organic polymer microspheres is set to 350℃-550℃, and it is set to completely decompose within this temperature range to avoid overlapping with the swelling temperature range of the micro-swelling mineral fibers, thereby ensuring the formation of mutually independent and complementary pore morphologies.

[0011] Preferably, the combination ratio and morphological design of the composite pore-forming agent result in the final permeable brick having a pore structure containing 20%-40% interconnected pores, and these interconnected pores are configured as tubular pathways that combine spherical pore walls with locally tortuous structures.

[0012] Preferably, the crystal structure of the zirconia toughening micropowder is partially stabilized so that it can undergo a metastable tetragonal-to-monoclinic phase transformation under in-service thermal stress, thereby toughening the micropowder and synergizing with the filling effect of the nano-alumina powder on microcracks.

[0013] Preferably, the average particle size of the nano-alumina powder is 20-100 nm, and it is set to preferentially fill the gaps between corundum particles and the submicron-sized voids formed in the zirconium oxide micro-powder aggregates.

[0014] A method for preparing a permeable brick for an electric furnace includes the following steps:

[0015] S1. Place fused alumina particles, tabular alumina fine powder, activated alumina micro powder, magnesium aluminum spinel fine powder, zirconia toughening micro powder, nano alumina powder, high-temperature self-healing additive, composite pore-forming agent and high-temperature binder into a mixer, dry mix for 10-20 minutes under controlled humidity, then add an appropriate amount of water or organic liquid and wet mix for 25-40 minutes to form a uniform plastic mud.

[0016] S2. Place the plastic clay in the mold and use an isostatic press or hydraulic press to hold the pressure at 80-150MPa for 2-8 minutes to form a green body with a preset geometric shape.

[0017] S3. Place the green body in a drying kiln and dry it at 60℃-120℃ for 24-48 hours. Then, in an air atmosphere, raise the temperature to 500℃-800℃ at 1-3℃ / min and hold it for 1-3 hours to remove most of the volatile components in the binder and pore-forming agent.

[0018] S4. After pre-firing, the green body is transferred into a high-temperature sintering furnace, and inert gas is introduced to replace the air. Under the protection of an inert atmosphere with a flow rate of 0.5-2L / min, the temperature is raised to 1550℃-1650℃ at a rate of 2-5℃ / min and held for 3-6 hours. Then, it is slowly cooled to room temperature at a rate of ≤3℃ / min to obtain the final permeable brick product.

[0019] Preferably, the mixing sequence is designed as follows: first, dry mix coarse particles and inert components, then fused alumina particles, tabular alumina fine powder, and magnesium aluminum spinel fine powder.

[0020] Then, nano-alumina powder, zirconium oxide toughened micro powder and active alumina micro powder are added in batches and dry-mixed. Finally, high-temperature binder solution and composite pore-forming agent are added and wet-mixed.

[0021] This sequence ensures that nanopowders and micropowders preferentially adsorb onto the surface of coarse particles to reduce agglomeration, and that the composite pore-forming agent is uniformly wrapped by the binder gel network, thereby forming dispersed pore cores during molding and sintering.

[0022] Preferably, the heating curve of the high-temperature sintering furnace is configured such that the heating rate is ≤2℃ / min in the range of 300℃-550℃, and ≤3℃ / min in the range of 800℃-1100℃, wherein:

[0023] The previous slow zone is matched with the pyrolysis temperature window of the pyrolysis organic polymer microspheres, so that the decomposition gas is released slowly and avoids impacting the pore walls.

[0024] The subsequent slow zone matches the swelling temperature window of the micro-swelling mineral fibers, allowing them to expand in a controllable manner to generate highly tortuous microchannels without tearing the matrix skeleton.

[0025] The technical effects and advantages of this invention are as follows:

[0026] The synergistic pore-forming mechanism of the composite pore-forming agent involves the formation of tortuous tubular channels by micro-swollen mineral fibers and regular spherical pores by pyrolytic organic microspheres, constructing a dual-mode pore network. This network exhibits the following characteristics at high temperatures: tortuous pores physically block capillary penetration of molten slag, reducing the penetration depth; and spherical pores maintain the initial air permeability and reduce airflow resistance due to smooth pore walls.

[0027] Multi-level toughening mechanisms coupled with self-healing functions achieve dynamic performance improvement. Nano-alumina powder filling + zirconium oxide phase transformation toughening, tetragonal-monoclinic phase volume expansion effect, close submicron cracks, and improve matrix fracture toughness; high-temperature self-healing additives are oxidized at >1200℃ to generate B2O3-Al2O3 mobile phase, which fills microcracks along capillary force and then solidifies, improving residual strength retention rate after thermal shock cycling. Detailed Implementation

[0028] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0029] This invention proposes a permeable brick for electric furnaces and its preparation method. The permeable brick for electric furnaces is made by sintering fused alumina particles, tabular alumina fine powder, activated alumina micro powder, magnesium aluminum spinel fine powder, zirconia toughened micro powder, nano alumina powder, high-temperature self-healing additive, composite pore-forming agent, high-temperature binder, and composite pore-forming agent components.

[0030] The above formulation employs a multi-stage toughening and structural stability synergistic system:

[0031] Zirconia toughened micro powder introduces the zirconia phase transformation toughening mechanism, which significantly improves the material's ability to resist thermal stress and crack propagation, and improves thermal shock resistance;

[0032] Nano-alumina powder fills microcracks in the matrix, promotes low-temperature sintering densification, and improves the matrix strength and thermal conductivity. It works synergistically with zirconia toughening micropowder to form a two-tiered toughening structure at the micron and nano levels.

[0033] High-temperature self-healing additives, at service temperatures exceeding 1200℃, allow the molten B2O3 generated by the oxidation of boride surfaces or the liquid phase formed by the reaction with components in the slag to effectively flow and fill the microcracks and pore edges formed during sintering, achieving high-temperature in-situ self-healing, significantly slowing down the rate of structural deterioration and high-temperature erosion damage to the permeable pores, and extending service life.

[0034] Controllable and stable complex pore structure design:

[0035] The composite pore-forming agent combines two pore-forming agents with different mechanisms of action;

[0036] Organic polymer microspheres can be pyrolyzed, and after thermal decomposition, they form uniform spherical closed pores or interconnected pores.

[0037] Mineral fibers with micro-swelling properties undergo controllable micro-expansion or swelling (non-violent foaming) when heated in the early stage of sintering, forming uneven microchannels with high tortuosity.

[0038] The two are used in combination in a specific ratio (3:1)-(1:1) to construct a complex three-dimensional network structure in the material matrix, in which spherical channels and tortuous microchannels are interwoven, connected and evenly distributed, and have both high open porosity and sufficient tortuosity. This structure not only ensures high and stable air permeability, but also has better resistance to slag penetration and metal liquid flow impact and erosion. This combination avoids the disadvantages of single pore-forming agents (such as pure spherical ones) with straight channels that are easy to be corroded, or the unstable air permeability of pure fiber structures.

[0039] Optionally, the mineral fibers with micro-swelling properties in the composite pore-forming agent are modified aluminosilicate fibers or heat-treated sepiolite fibers, which are configured to undergo controllable micro-expansion in the temperature range of 800℃-1100℃ to form non-spherical, highly tortuous microchannels; the pyrolysis temperature of the pyrolytic organic polymer microspheres is set at 350℃-550℃, and they are set to completely decompose within this temperature range to avoid overlapping with the swelling temperature range of the micro-swelling mineral fibers, thus ensuring the formation of mutually independent and complementary pore morphologies.

[0040] The combination ratio and morphological design of the composite pore-forming agent result in a final permeable brick with 20%-40% interconnected pores in its pore structure. These interconnected pores are configured as tubular pathways with both spherical pore walls and local tortuous structures, thereby maintaining high permeability while improving resistance to slag penetration. The crystal structure of the zirconia toughening micropowder is partially stabilized so that it can undergo a metastable tetragonal to monoclinic phase transformation (phase transformation toughening) under the induction of thermal stress during service. This, combined with the filling effect of nano-alumina powder on microcracks, significantly improves the fracture toughness and thermal shock resistance of the matrix.

[0041] The average particle size of the nano-alumina powder is 20-100nm. It is designed to preferentially fill the gaps between corundum particles and the submicron-sized voids formed in the zirconia micro powder agglomerates, effectively improving the low-temperature sintering density and reducing the number of original microcracks in the matrix. The tabular corundum fine powder and the activated alumina micro powder form a synergistic sintering driving force. The lamellar structure of the tabular corundum inhibits the propagation of macroscopic cracks, while the activated alumina promotes solid-state sintering at temperatures below 1300℃, thereby constructing a high-strength skeleton at a lower sintering temperature.

[0042] The zirconium boride or chromium boride in the high-temperature self-healing additive is designed to undergo selective surface oxidation in service environments exceeding 1200°C, forming a low-viscosity liquid phase rich in B2O3. This liquid phase then automatically migrates and fills adjacent microcracks via capillary action, achieving in-situ self-sealing. The liquid boron oxide formed by the high-temperature self-healing additive reacts locally with the magnesium aluminum spinel powder to generate magnesium aluminum borate compounds with higher melting points. This enhances the chemical stability of the repaired area while repairing cracks, preventing the area from becoming a new weak point for corrosion.

[0043] High-temperature sintering under inert atmosphere protection is carried out in a nitrogen- or argon-containing environment, with the maximum sintering temperature controlled at 1550℃-1650℃. This temperature is designed to fully activate the phase transformation potential of zirconia and complete the solid solution bonding between the corundum solid phases, while preventing premature damage to the pore-forming agent or excessive oxidation and burn-off of the self-healing components. In the initial stage of mixing, the activated alumina micro powder, nano alumina powder and high-temperature binder form a highly dispersed gel network, which encapsulates other solid particles and reduces the initial microcracks in the green body after molding. Furthermore, when this gel network decomposes in the early stage of sintering, it generates a temporary microenvironment that is conducive to the fine dispersion and distribution of nano alumina.

[0044] The aspect ratio of the tabular corundum fine powder is designed to be between 3:1 and 8:1, so that it can form a certain directional arrangement during mixing and molding to optimize the heat conduction path and serve as the main skeleton to enhance the material's ability to resist the macroscopic impact of molten metal flow, thereby compensating for the risk of strength reduction caused by high porosity. The magnesium aluminum spinel fine powder occupies the main intergranular position between the fused alumina particles. With its high melting point and good chemical compatibility with alumina, it forms a highly corrosion-resistant intergranular phase barrier, preventing slag from rapidly penetrating into the core permeable channel area along the grain boundaries.

[0045] In addition, a method for preparing permeable bricks for electric furnaces is proposed, including:

[0046] S1. Place fused alumina particles, tabular alumina fine powder, activated alumina micro powder, magnesium aluminum spinel fine powder, zirconia toughening micro powder, nano alumina powder, high-temperature self-healing additive, composite pore-forming agent and high-temperature binder into a mixer, dry mix for 10-20 minutes under controlled humidity, then add an appropriate amount of water or organic liquid and wet mix for 25-40 minutes to form a uniform plastic mud.

[0047] S2. Place the plastic clay in the mold and use an isostatic press or hydraulic press to hold the pressure at 80-150MPa for 2-8 minutes to form a green body with a preset geometric shape.

[0048] S3. Place the green body in a drying kiln and dry it at 60℃-120℃ for 24-48 hours. Then, in an air atmosphere, raise the temperature to 500℃-800℃ at 1-3℃ / min and hold it for 1-3 hours to remove most of the volatile components in the binder and pore-forming agent.

[0049] S4. The pre-fired green body is transferred into a high-temperature sintering furnace, and inert gas is introduced to replace the air. Under the protection of an inert atmosphere with a flow rate of 0.5-2L / min, the temperature is raised to 1550℃-1650℃ at a rate of 2-5℃ / min and held for 3-6 hours. Then, it is slowly cooled to room temperature at a rate of ≤3℃ / min to obtain the final permeable brick product.

[0050] In step S1, the mixing sequence is designed as follows: first, dry mix coarse particles and inert components (electrofused corundum particles, tabular corundum fine powder, and magnesium aluminum spinel fine powder); then, add nano alumina powder, zirconia toughened micro powder, and activated alumina micro powder in batches for dry mixing; and finally, add high-temperature binder solution and composite pore-forming agent for wet mixing. This sequence ensures that the nano powder and micro powder are preferentially adsorbed on the surface of coarse particles to reduce agglomeration, and that the composite pore-forming agent is uniformly wrapped by the binder gel network, thereby forming dispersed pore cores during molding and sintering.

[0051] The setting of the inert atmosphere (nitrogen / argon) protection in step S4 plays a crucial role in two aspects:

[0052] 1) Prevent the degradable organic polymer microspheres in the composite pore-forming agent from severely damaging the preset pore structure due to oxidation and combustion in the early stage of sintering (300℃-600℃);

[0053] 2) Inhibit the excessive oxidation and deactivation of high-temperature self-healing additives (zirconium boride / chromium) after exceeding 1000℃, ensuring that they still retain the ability to form a surface self-healing liquid phase at subsequent service temperatures (>1200℃).

[0054] The high-temperature binder used in step S1 preferentially forms a highly dispersed hydroxyl gel network in situ after contacting the activated alumina micro powder and nano alumina powder. This network gradually dehydrates during the drying and pre-firing stage to form a temporary nanoskeleton, effectively dispersing molding stress and reducing the initiation of microcracks inside the green body, thus providing a high-integrity matrix for subsequent high-temperature sintering.

[0055] The heating curve in step S4 is configured such that the heating rate is ≤2℃ / min in the range of 300℃-550℃ and ≤3℃ / min in the range of 800℃-1100℃. Specifically, the first slow zone is matched with the pyrolysis temperature window of the pyrolyzable organic polymer microspheres to allow the decomposition gas to be released slowly and avoid impacting the pore walls; the second slow zone is matched with the swelling temperature window of the micro-swellable mineral fibers to allow them to expand in a controlled manner to generate highly tortuous microchannels without tearing the matrix skeleton.

[0056] After the heat preservation in step S4, a slow cooling rate of ≤3℃ / min is adopted until the furnace temperature is below 800℃. This is set to preferentially promote the stress-induced phase transformation of the tetragonal phase to the monoclinic phase in the zirconia toughened micro powder (the toughening phase is retained) and the formation of a complete bonding bridge at the corundum grain boundary by the magnesium aluminum spinel fine powder. This process significantly improves the thermal stress resistance and grain boundary erosion resistance of the sintered body.

[0057] After step S4, the final sintered body needs to undergo a pore size homogenization treatment, which includes introducing water vapor (flow rate 0.1-0.5L / min) into an inert atmosphere at 1200℃-1300℃ and holding for 1-2 hours. The water vapor selectively etches the highly active amorphous phase at the thin wall of the pores, making the inner wall of the pores smooth, thereby reducing the resistance when the gas flows through and inhibiting the wetting and adhesion of slag at the pore opening.

[0058] Based on the above-mentioned permeable brick for electric furnaces and its preparation method, the following embodiments are provided:

[0059] Example 1

[0060] The formula for permeable bricks used in electric furnaces consists of the following components sintered together:

[0061] Fused corundum particles (3-1mm): 60 parts;

[0062] Plate-shaped corundum fine powder (≤0.045mm): 20 parts;

[0063] Activated alumina micro powder (d 50 =1μm): 8 portions;

[0064] Magnesium aluminum spinel fine powder: 7 parts;

[0065] Zirconia toughened micro powder (5 mol% Y2O3 stabilized): 3 parts;

[0066] Nano-alumina powder (30nm): 2 parts;

[0067] High-temperature self-healing additive (ZrB2 / CrB2=3:1): 1.5 parts;

[0068] Composite pore-forming agent (micro-swollen mineral fibers: carbonate-coated polymer microspheres = 2:1): 3 parts;

[0069] High-temperature binder (aluminum phosphate solution): 5 parts;

[0070] The preparation method is as described in steps S1-S4 above, with the following specific parameters:

[0071] Wet mixing time: first dry mix for 12 minutes, then add 4 parts water and wet mix for 30 minutes;

[0072] Molding pressure: 100MPa, holding pressure for 4 minutes;

[0073] Drying and pre-firing: Dry at 100℃ for 36 hours - keep warm at 650℃ for 2 hours (heating up 2℃ / min);

[0074] Sintering: N2 atmosphere 1L / min, 300-550℃ range ≤2℃ / min, to 800-1100℃ range ≤3℃ / min, to 1600℃ hold for 4 hours, to slow cool to room temperature (2℃ / min).

[0075] In this embodiment, the mineral fibers in the composite pore-forming agent swell at 800°C to form branched channels (accounting for 60%), and the polymer microspheres generate 0.2mm spherical pores (accounting for 40%) - the tortuosity of the dual-mode pore network reaches 1.85, thereby increasing the steel slag permeation resistance;

[0076] Nano-alumina and zirconia micropowder synergistically fill grain boundaries, reducing grain size to 15μm - flexural strength retention rate after thermal shock is 82% (1100℃ water cooling, 3 cycles).

[0077] ZrB2 is oxidized at 1420℃ to form B2O3-Al2O3 phase, which fills surface microcracks with a length ≤0.1mm and has a self-healing efficiency of >90%.

[0078] Example 2

[0079] Based on Example 1, the difference between this example and the formulation of Example 1 is as follows:

[0080] The composite pore-forming agent was increased to 3.5 parts (micro-swelling fiber: polymer microspheres = 3:1), the fused alumina was reduced to 58 parts, the tabular alumina powder was increased to 22 parts, and the remaining formulas and mass fractions remained unchanged.

[0081] The difference between the preparation method in this embodiment and that in Example 1 is:

[0082] The pore-forming agent is added in two stages: first, it is dry-mixed with the coarse particles, and then added in the middle of the second wet mixing; the heating rate is ≤1.5℃ / min in the 300-550℃ range and ≤2.5℃ / min in the 800-1100℃ range; all other process parameters remain unchanged.

[0083] In this embodiment, the fiber content is increased to 70%, and after swelling, it forms a root-like ultra-torsional channel with a nitrogen permeability decay rate of 10% (after 8 hours of steel slag erosion at 1600℃). Slow heating ensures that the fiber swelling rate is above 95%, and an Al2O3-rich layer is formed on the pore wall, with a slag wetting angle of up to 112 degrees (SiO2-CaO slag system).

[0084] Example 3

[0085] Based on Example 1, the difference between this example and the formulation of Example 1 is as follows:

[0086] Zirconia toughened micro powder increased to 4 parts + nano alumina powder increased to 2.5 parts + self-healing agent increased to 2 parts; fused alumina particles reduced to 55 parts and magnesium aluminum spinel fine powder reduced to 6 parts, while the rest of the formula and mass parts remained unchanged.

[0087] The difference between the preparation method in this embodiment and that in Example 1 is:

[0088] Sintering regime strengthening: Hold at 1600℃ for 5 hours, and cool to the slow cooling zone (>1000℃) at a rate ≤1℃ / min;

[0089] Post-treatment enhancement: Treat with 0.3 L / min of steam at 1250℃ for 1.5 hours;

[0090] In this embodiment, nano-alumina forms a continuous network structure at the grain boundaries, exhibiting a room temperature flexural strength of 48 MPa; ultra-slow cooling ensures that the tetragonal zirconia phase retention reaches 75%, enhancing toughening potential and achieving a fracture energy of 360 J / m. 2 Water vapor etching removes the amorphous phase from the pore walls, resulting in a pore surface roughness Ra < 1 μm and a 18% reduction in airflow resistance.

[0091] The performance comparison of Examples 1-3 above is shown in the table below:

[0092] Performance Comparison Summary Table of Three Sets of Examples

[0093]

[0094] Table 1

[0095] The table above shows that Example 2 achieves a leap in porosity and impermeability by adjusting the ratio of pore-forming agent and process linkage, making it suitable for highly corrosive slag conditions.

[0096] Example 3 utilizes nano / micro powder thickening and slow cooling to enhance phase transition, making it the preferred choice for scenarios requiring resistance to thermo-mechanical stress.

[0097] Example 1 is characterized by the universality of its formulation and process, resulting in lower overall costs and meeting the needs of 80% of industrial scenarios.

[0098] In summary, the synergistic pore-forming mechanism of the composite pore-forming agent of this invention involves the formation of tortuous tubular channels by micro-swelled mineral fibers and regular spherical pores by pyrolytic organic microspheres, constructing a dual-mode pore network. This network exhibits the following characteristics at high temperatures: tortuous pores physically block capillary penetration of molten slag, reducing the penetration depth; spherical pores maintain the initial air permeability, and the smooth pore walls reduce airflow resistance.

[0099] Multi-level toughening mechanisms coupled with self-healing functions achieve dynamic performance improvement. Nano-alumina powder filling + zirconium oxide phase transformation toughening, tetragonal-monoclinic phase volume expansion effect, close submicron cracks, and improve matrix fracture toughness; high-temperature self-healing additives are oxidized at >1200℃ to generate B2O3-Al2O3 mobile phase, which fills microcracks along capillary force and then solidifies, improving residual strength retention rate after thermal shock cycling.

[0100] 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 porous plug for an electric furnace, characterized by comprising: The formula of the air brick for electric furnace by mass fraction is sintered corundum particles 45-65 parts, tabular corundum powder 15-30 parts, active alumina powder 5-12 parts, magnesium aluminate spinel powder 8-18 parts, zirconia toughening powder 6-14 parts, nano-alumina powder 0.5-3 parts, high-temperature self-repairing additive 1-5 parts, composite pore-forming agent 0.5-4 parts, and high-temperature binder 3-8 parts; The high-temperature self-repairing additive is selected from zirconium boride, chromium boride, or a combination thereof; The composite pore-forming agent is composed of cleavable organic polymer microspheres and mineral fibers with micro-swelling properties, and the mass ratio is (3:1)-(1:1); The mineral fibers with micro-swelling properties in the composite pore-forming agent are modified aluminum silicate fibers or heat-treated sepiolite fibers, which are configured to undergo controlled micro-expansion to form non-spherical and high-curved micro-channels in the temperature range of 800-1100℃; The cleavage temperature of the organic polymer microspheres is set to 350-550℃, which is set to completely decompose in this temperature range to avoid overlapping with the swelling temperature range of the micro-swelling mineral fibers, ensuring the formation of mutually independent and complementary pore structures; The combination ratio and morphology design of the composite pore-forming agent make the final air brick have 20%-40% connected pores, and these connected pores are configured to have both spherical pore walls and locally curved tubular passages; During the preparation of the air brick for electric furnace, inert gas is introduced to replace air, and the temperature is raised to 1550-1650℃ at a rate of 2-5℃ / min under the protection of inert gas with a flow rate of 0.5-2L / min.

2. The porous plug of claim 1 wherein, The zirconia toughening powder is partially stabilized to make it undergo metastable tetragonal phase to monoclinic phase transition under the service thermal stress, which is a phase transition toughening, and cooperates with the nano-alumina powder to fill micro-cracks.

3. The porous plug of claim 1 wherein, The nano-alumina powder has an average particle size of 20-100nm, which is set to preferentially fill the gaps between corundum particles and the sub-micron gaps formed in the zirconia powder agglomerates.

4. A method for producing a porous plug for an electric furnace, which is used for producing the porous plug for an electric furnace according to any one of claims 1 to 3, characterized by, The method comprises the following steps: S1, placing sintered corundum particles, tabular corundum powder, active alumina powder, magnesium aluminate spinel powder, zirconia toughening powder, nano-alumina powder, high-temperature self-repairing additive, composite pore-forming agent, and high-temperature binder in a mixer, dry mixing for 10-20 minutes in a humidity controllable environment, then adding appropriate amount of water or organic liquid for wet mixing for 25-40 minutes to form a uniform plastic paste; S2, placing the plastic paste in a mold, and using isostatic pressing or a hydraulic press to form a green body with a predetermined geometric shape under a pressure of 80-150MPa for 2-8 minutes; S3, placing the green body in a drying kiln, drying at 60-120℃ for 24-48 hours, then heating to 500-800℃ at a rate of 1-3℃ / min in an air atmosphere, and keeping the temperature for 1-3 hours to remove most of the volatile components in the binder and pore-forming agent; S4, moving the pre-sintered blank into a high-temperature sintering furnace, replacing air with inert gas, under the protection of inert atmosphere with a flow rate of 0.5-2 L / min, heating to 1550-1650°C at a rate of 2-5°C / min, maintaining for 3-6 hours, and then slowly cooling to room temperature at a rate of ≤3°C / min to obtain the final gas-permeable brick product.

5. The method of producing a porous brick for an electric furnace according to claim 4, characterized by, The high-temperature sintering furnace heating curve is configured to have a heating rate of ≤2°C / min in the 300-550°C interval, and a heating rate of ≤3°C / min in the 800-1100°C interval, wherein: The former slow rate interval matches the cleavage temperature window of the cleavable organic polymer microspheres, allowing the decomposition gas to be released gently to avoid impacting the hole wall; The latter slow rate interval matches the swelling temperature window of the slightly swelling mineral fibers, allowing them to swell controllably to generate high tortuosity microchannels without tearing the matrix skeleton.

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