A magnesium-aluminum spinel self-repairing castable based on stress orientation and temperature-sensitive phase change and a preparation method thereof

Abstract

This invention discloses a self-healing castable of magnesium aluminate spinel based on stress-directed and temperature-sensitive phase change and its preparation method. The castable includes basic refractory aggregate and matrix, temperature-sensitive phase change repair units, stress-directed repair units, a bonding system and additives, and 4.0-5.5% water by weight of the total weight of the above solid raw materials. The basic refractory aggregate and matrix comprise the following materials in parts by weight: 50-65 parts of fused magnesium aluminate spinel particles; 8-12 parts of sintered magnesium aluminate spinel fine powder; and 4-8 parts of active α-Al₂O₃ micro powder. The temperature-sensitive phase change repair unit comprises 2-5 parts by weight. The temperature-sensitive phase change repair unit is a microcapsule with a core-shell structure, the shell being a double-layer structure: an inner layer of porous mullite and an outer layer of dense magnesium aluminate spinel. The stress-directed repair unit comprises 1-3 parts by weight and is a sheet-like silicon carbide coated with a nano-zirconia coating. This material, through its two built-in functional units, can achieve an intelligent process from "damage perception and localization" to "graded and precise repair."

Description

Technical Field

[0001] This invention belongs to the field of advanced refractory materials technology, specifically relating to a magnesium aluminum spinel self-healing castable based on stress guidance and temperature-sensitive phase transformation and its preparation method. Background Technology

[0002] Magnesium-aluminum spinel castables are lining materials for key components of modern high-temperature industrial kilns, and their service life directly determines the operating cycle and cost. In actual service, microcracks induced by thermal shock, mechanical stress, and slag erosion are the initiation points of material failure. Existing technologies mainly suppress crack propagation by optimizing particle size distribution or introducing toughening phases (such as ZrO2), which is a passive defense strategy.

[0003] In the field of self-healing refractory materials, existing research mostly focuses on single repair mechanisms. For example, low-melting-point glass microcapsules are used to achieve thermally triggered repair, but this results in the formation of a high-temperature weak phase after repair and cannot provide a precise response to micro-cracks. Other technologies rely on the oxidation reaction of non-oxides (such as SiC), but this process is limited by oxygen partial pressure and diffusion rate, resulting in a slow and uncontrollable response. The common drawback of these methods is that the repair behavior is isolated and homogeneous, lacking the ability to target and repair the "heart of damage"—the crack tip—and cannot intelligently regulate the repair process according to the severity of the crack and the local temperature field. This leads to low repair efficiency, poor reliability, and difficulty in meeting the long-life requirements under complex working conditions. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of existing self-healing technologies and provide a magnesium-aluminum spinel self-healing castable based on the synergistic effect of stress-directed and temperature-sensitive phase transformation, as well as its preparation method. This solution, by developing a self-healing castable capable of actively sensing damage location and intelligently matching repair resources and modes according to crack size and temperature, represents a key breakthrough in existing technological bottlenecks. Through its two built-in functional units, this material enables an intelligent process from "damage sensing and localization" to "graded and precise repair."

[0005] One of the objectives of this invention is to provide a magnesium-aluminum spinel self-healing castable based on stress-directed and thermo-sensitive phase change, comprising basic refractory aggregate and matrix, thermo-sensitive phase change repair unit, stress-directed repair unit, bonding system and additives, and water at a total weight of 4.5%-5% of the above solid raw materials. The basic refractory aggregate and matrix include the following materials in parts by weight: 50-65 parts of fused magnesium aluminate spinel particles, 8-12 parts of sintered magnesium aluminate spinel fine powder, and 4-8 parts of active α-Al2O3 micro powder. The thermosensitive phase change repair unit is 2-5 parts by weight. The thermosensitive phase change repair unit is a microcapsule with a core-shell structure. The core of the microcapsule is composed of borosilicate glass powder and metallic silicon powder in a mass ratio of (1.5-2.5):1. The shell of the microcapsule has a double-layer structure, with the inner layer being porous mullite and the outer layer being dense magnesium aluminum spinel. The stress-directed repair unit is 1-3 parts by weight, and the stress-directed repair unit is a sheet-like silicon carbide with a nano-zirconia coating on its surface; The bonding system and additives include the following materials in parts by weight: 5-10 parts of sintered magnesia micro powder containing rare earth oxides, 1-2 parts of silica micro powder, 0.15-0.25 parts of composite polycarboxylate superdispersant, and 4-7 parts of low-calcium high-alumina cement.

[0006] As a preferred embodiment, the fused magnesium aluminum spinel particles are composed of the following parts by weight according to different particle size distributions: 15-20 parts for particles with a particle size of 5-3 mm, 20-25 parts for particles with a particle size of 3-1 mm, and 15-20 parts for particles with a particle size of 1-0 mm.

[0007] As a preferred option, the particle size of the sintered magnesium aluminum spinel fine powder is ≤0.088mm, and the particle size d of the active α-Al2O3 micro powder is... 50 ≤2μm.

[0008] As a preferred embodiment, the aspect ratio of the sheet-like silicon carbide is >10, and the thickness of the nano-zirconia coating is 50-200 nm.

[0009] As a preferred embodiment, the particle size of the sintered magnesia micro powder containing rare earth oxides is ≤0.044mm, and the particle size of the silica micro powder is ≤1μm; the particle size of the thermosensitive phase change microcapsules is 100-400μm, and the particle size of the sheet-like silicon carbide is not higher than 0.088mm.

[0010] As a preferred embodiment, the fused magnesium aluminum spinel particles contain Al2O3 with a mass fraction of 64%-68%, MgO with a mass fraction of 32%-36%, Fe2O3 with a mass fraction of ≤0.35%, and SiO2 with a mass fraction of ≤0.4%. The sintered magnesium aluminum spinel fine powder contains Al2O3 with a mass fraction of ≥64%, and the active α-Al2O3 micro powder contains Al2O3 with a mass fraction of ≥99.0%.

[0011] As a preferred embodiment, in the rare earth oxide-containing sintered magnesia micro powder, the rare earth oxide is Y2O3 or La2O3, and the purity of Y2O3 or La2O3 is ≥95.0%; in the silica micro powder, the mass fraction of SiO2 is ≥94%; in the core of the thermosensitive phase change microcapsule, the softening point of borosilicate glass powder is 850-920℃, and the mass ratio of borosilicate glass powder to metallic silicon powder is (1.5-2.5):1; in the sheet-like silicon carbide coated with nano-zirconia, the mass fraction of silicon carbide is ≥98%, and the thickness of the nano-zirconia coating on its surface is 50-200nm; and in the low-calcium high-alumina cement, the mass fraction of Al2O3 is ≥80%.

[0012] To achieve the above objectives and solve the problems existing in the prior art, a self-healing castable prepared using the raw materials and method of this invention is presented. Through the synergy of two core mechanisms—"stress-directed" and "temperature-sensitive phase transition"—the repair process achieves intelligence and precision. The specific mechanism and advantages are as follows: Thermosensitive Phase Change Repair Unit (Microcapsule): This unit is key to achieving intelligent graded repair. Its double-layered ceramic shell (mullite / spinel) is physicochemically compatible with the matrix, ensuring stability under normal conditions. When crack propagation leads to shell rupture, the borosilicate glass powder in the core melts first upon reaching its specific softening point (850-920℃), acting as a thermosensitive phase and utilizing its excellent fluidity to achieve rapid crack sealing (primary repair). Subsequently, the metallic silicon powder in the core is oxidized or reacts with the matrix at higher temperatures to generate stable ceramic phases such as mullite, providing durable ceramic bonding reinforcement (secondary repair), thus achieving graded repair from "emergency" to "long-term".

[0013] Stress-directed repair unit (ZrO2-coated lamellar SiC): This unit achieves precise positioning and enhancement of the repair. The two-dimensional morphology of the lamellar SiC effectively deflects cracks and disperses stress. The nano-zirconia (ZrO2) coating on its surface undergoes a martensitic phase transformation (t→m) under the stress at the crack tip. This process not only consumes crack energy and passivates the crack tip, but more importantly, the resulting lattice distortion greatly promotes the diffusion of oxygen ions in the crack area. This guides the oxidation reaction of the lamellar SiC (generating the SiO2 glass phase) to preferentially and concentratedly occur in the crack tip region, achieving "stress-directed" and targeted delivery of the repair material, significantly improving repair efficiency and accuracy.

[0014] Sintered magnesia micro powder containing rare earth oxides: Yttrium oxide (Y2O3) and lanthanum oxide (La2O3) serve as high-temperature stabilizers and grain boundary purifiers. Y2O3 can dissolve in the spinel lattice, enhancing the material's resistance to high-temperature creep; La2O3 is enriched at grain boundaries and can react with trace impurities in the raw materials to generate high-melting-point compounds, purifying and strengthening the grain boundaries, thereby comprehensively improving the structural stability and durability of the material under long-term high-temperature service.

[0015] Active α-Al2O3 micro powder and silica micro powder: as key matrix components, they react with MgO at high temperature to generate secondary spinel in situ. The micro-expansion accompanying this process can effectively compensate for sintering shrinkage and greatly improve the medium and high temperature bonding strength of the matrix, which is the basis for the high strength and high thermal shock resistance of the castable body.

[0016] Low-calcium, high-alumina cement: provides the main room-temperature bonding strength, ensures the integrity of the castable during construction, demolding, and early curing stages, and is a prerequisite for achieving on-site casting of complex structures.

[0017] Composite superdispersant: effectively reduces interparticle friction and slurry viscosity, significantly reduces mixing water consumption while ensuring fluidity, thereby reducing porosity after casting and obtaining a denser microstructure, directly improving various physical properties of the material.

[0018] The second objective of this invention is to provide a method for preparing a self-healing magnesium-aluminum spinel castable based on stress-directed and temperature-sensitive phase transition, comprising the following steps: Step 1: Functional Unit Prefabrication Steps Step 11: Preparation of temperature-sensitive phase change microcapsules: The core material is dispersed by sol-gel and spray granulation method, and then mullite sol and spinel sol are deposited in sequence to form a double shell. After heat treatment at 800-1000℃, microcapsules of 100-400μm are obtained by sieving. Step 12, Stress-directed sheet silicon carbide preparation steps: A nano-zirconia coating is uniformly coated on the surface of the sheet silicon carbide using liquid phase deposition, and then cured by heat treatment at 600-800℃. Step 2: Castable Refractory Mixing Step: According to the proportion, fused magnesium aluminate spinel particles, sintered magnesium aluminate spinel fine powder, and sintered magnesia micro powder containing rare earth oxides are put into a mixer for dry mixing; activated alumina micro powder, silica micro powder, and composite superdispersant are added and dry mixing continues; 70%-80% of the total water volume is added and stirred to form a uniform slurry; finally, the temperature-sensitive phase change microcapsules, stress-directed sheet silicon carbide, and low-calcium high-alumina cement pre-prepared in Steps 11 and 12 are added, stirred at low speed, and the remaining water is added to adjust the fluidity to obtain the mixture; Molding and heat treatment steps: Vibrate the mixture obtained in step two to form a mold, cure at room temperature and then demold; after demolding, dry the blank and then perform segmented heat treatment.

[0019] As a preferred embodiment, the preparation steps of the temperature-sensitive phase change microcapsules include: Step 111, Core preparation and granulation: Weigh borosilicate glass powder and metallic silicon powder with a particle size ≤10μm according to a mass ratio of (1.5-2.5):1, and ball mill them together to obtain a uniform slurry; then spray dry to obtain spherical core precursors with a particle size of 80-150μm; Step 112, Mullite inner shell construction steps: The core precursor obtained in step 111 is placed in a fluidized bed and sprayed with mullite sol at a concentration of 0.8-1.2 mol / L at 40-60℃. After each coating, it is cured at 90-110℃. This process is repeated multiple times to form a porous mullite inner shell with a thickness of 5-10 μm, and particles with a porous mullite inner shell are obtained. Step 113, Spinel Shell Construction: At 40-60℃, the particles obtained in Step 112 are spray-coated with a magnesium aluminum spinel sol with a concentration of 1.0-1.5 mol / L. After each coating, the particles are cured at 100-120℃. This process is repeated multiple times to form a dense spinel shell layer with a thickness of 8-12 μm. Step 114, Heat Treatment and Sieving: The wet capsules coated with the shell layer in Step 113 are dried and then placed in a high-temperature furnace. The temperature is raised to 800-1000℃ in an air atmosphere and held for a certain time to completely ceramicize the shell layer. After natural cooling, the microcapsule products with a particle size of 100-400 μm are sieved out. As a preferred embodiment, the specific steps for preparing the stress-directed sheet-like silicon carbide are as follows: Step 121, Substrate pretreatment step: Select sheet-shaped silicon carbide with an aspect ratio >10, soak and wash it with hydrochloric acid until neutral, and dry it at a certain temperature to activate the surface; Step 122, Coating Deposition Step: Using zirconium oxychloride and urea as precursors, prepare a transparent solution containing 0.1-0.3 mol / L ZrO2; add the pretreated sheet-like silicon carbide from Step 121 into the transparent solution, controlling the solid-liquid ratio at 1g:(10-20mL), and stir at a constant temperature of 75-85℃ for 2-4 hours to uniformly deposit zirconium hydroxide on the silicon carbide surface; Step 123, Post-processing and Crystal Phase Control Steps: After the reaction in Step 122 is completed, filter, wash, and dry; then place the obtained powder in a muffle furnace and heat it to 600-800℃ in an air atmosphere, hold it for a certain time, so that the amorphous coating is transformed into nanocrystalline zirconia, and a mixed crystal phase of tetragonal and monoclinic phase is obtained, with a final coating thickness of 50-200nm.

[0020] The present invention has at least the following beneficial effects: This invention achieves intelligent and precise repair processes through the synergy of two core mechanisms: "stress-directed" and "temperature-sensitive phase transition." The specific mechanisms and advantages are as follows: 1. A pioneering "stress-guided" targeted repair mechanism enables precise delivery of repair materials: Traditional self-healing relies on the uniform distribution of repair agents and random contact with cracks, resulting in low efficiency. This invention's innovative stress-guided repair unit (sheet-like SiC coated with nano-ZrO2) changes this model. When a crack propagates in a material, a huge stress field is generated at its tip. The two-dimensional morphology of sheet-like SiC allows it to effectively guide and disperse crack propagation stress within the matrix. More importantly, the nano-ZrO2 coating on its surface undergoes a martensitic phase transformation (t→m) under the stress at the crack tip. This process not only consumes crack energy and passivates the crack tip, but more importantly, the lattice distortion and micro-strain generated by the phase transformation significantly enhance the diffusion dynamics of oxygen ions in the local crack region. This is equivalent to opening a "high-speed ion diffusion channel" at the crack tip, allowing the oxidation reaction of sheet-like SiC (generating the SiO2 glass phase) to be preferentially and rapidly confined to the crack tip—the area most in need of repair—achieving "active targeted" delivery of the repair material, improving efficiency by more than 50%.

[0021] 2. Constructing a "temperature-sensitive phase change" gradient repair procedure to achieve intelligent matching of repair intensity and temperature: The temperature-sensitive phase change repair unit (double-layer microcapsule) provides on-demand repair resources. Its spinel shell ensures compatibility with the matrix. When a crack penetrates the microcapsule, the core is released. The borosilicate glass powder within, acting as the temperature-sensitive phase, melts upon reaching its specific softening point (e.g., 850℃), rapidly flowing to seal the crack and achieving primary emergency sealing. As the temperature rises or time increases, the metallic silicon powder in the core begins to oxidize or react with the matrix, generating thermodynamically more stable ceramic phases such as mullite, achieving secondary long-term strengthening. This temperature-triggered gradient repair process, from amorphous glass phase to crystalline ceramic phase, ensures a suitable repair mechanism from low to high temperatures, and the high-temperature performance of the repaired product increases with increasing temperature.

[0022] 3. A dual-mechanism synergy achieves an intelligent closed loop of "sensing-localization-graded repair": The "stress-directed" mechanism senses and locates the core area of ​​damage (crack tip) and guides the repair response to focus there. The "temperature-sensitive phase transition" mechanism provides a matching repair phase based on the local temperature of the damaged area. Together, they form a complete intelligent system: crack generation → stress field activates the guiding unit, locating the damage and enhancing local reactivity → microcapsule rupture, releasing the repair agent → based on the temperature at that location, triggering the corresponding phase transition repair behavior. This closed-loop system transforms the repair behavior from "random and homogeneous" to "precise and graded," significantly improving repair reliability and material lifespan. Detailed Implementation

[0023] The technical solution of the present invention will be clearly and completely described below with reference to specific embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0024] It should be noted that, unless otherwise specified, the amounts of each raw material component in the following embodiments are all expressed in parts by mass, which represents the relative proportions between the components. Those skilled in the art can adjust the actual amount of each material according to the actual production scale. Different raw material ratios and process parameters are used in the following embodiments to illustrate that, within the scope defined by the claims of this invention, the objectives of this invention can be achieved and excellent self-healing effects obtained by adjusting the relevant parameters. Those skilled in the art can select and adjust within the above range according to actual performance requirements. To better understand the technical content of this invention, the following embodiments are provided in detail.

[0025] The raw materials used in the following examples; The fused magnesium aluminum spinel particles contain 64%-68% Al2O3, 32%-36% MgO, and ≤0.35% Fe2O3 and ≤0.4% SiO2 by mass. The mass fraction of Al2O3 in the sintered magnesium aluminum spinel fine powder is ≥64%; The active α-Al2O3 micro powder contains ≥99.0% Al2O3 by mass. The rare earth oxides in the sintered magnesia powder containing rare earth oxides are either Y2O3 or La2O3, and the purity of the rare earth oxides is ≥95.0%. The mass fraction of SiO2 in the silica micro powder is ≥94%; In the core of the thermosensitive phase change microcapsule, the softening point of borosilicate glass powder is 850-920℃, and the mass ratio of borosilicate glass powder to metallic silicon powder is (1.5-2.5):1. The stress-guided sheet-like SiC contains ≥98% SiC by mass, and its surface has a nano-zirconia (ZrO2) coating with a thickness of 50-200 nm. The mass fraction of Al2O3 in the low-calcium, high-alumina cement is ≥80%.

[0026] This invention also provides a self-healing magnesium-aluminum spinel castable based on stress-directed and temperature-sensitive phase transition, comprising the following steps: Step 1: Functional Unit Prefabrication Steps Step 11: Preparation of temperature-sensitive phase change microcapsules: Using a sol-gel combined spray granulation method, borosilicate glass powder and metallic silicon powder are mixed at a mass ratio of (1.5-2.5):1 to disperse the core material. Mullite sol and spinel sol are deposited sequentially to form a double shell. After heat treatment at 800-1000℃, microcapsules of 100-400μm are obtained by sieving.

[0027] The temperature-sensitive phase change microcapsules are prepared using a process combining spray granulation and sol-gel encapsulation, with the specific steps including: Step 111: Core preparation and granulation: Weigh borosilicate glass powder and metallic silicon powder (particle size ≤10μm) at a mass ratio of (1.5-2.5):1, and ball mill them together with anhydrous ethanol for 2-4 hours to obtain a uniform slurry; then spray dry the mixture, controlling the inlet temperature at 180-220℃ and the outlet temperature at 80-110℃, to obtain spherical core precursors with a particle size of 80-150μm. Step 112, Mullite inner shell construction steps: Place the core precursor in a fluidized bed and spray it with a mullite sol at a concentration of 0.8-1.2 mol / L at 40-60℃. After each coating, cure at 90-110℃ for 10-15 minutes. Repeat this process 3-5 times to form a porous mullite inner shell with a thickness of 5-10 μm. Step 113, Spinel Shell Layer Construction Step: Under the same conditions, the above particles are spray-coated with magnesium aluminum spinel sol with a concentration of 1.0-1.5 mol / L (MgO to Al2O3 molar ratio of approximately 1:1). After each coating, the particles are cured at 100-120℃. This process is repeated 4-6 times to form a dense spinel shell layer with a thickness of 8-12 μm. Step 114, Heat treatment and sieving steps: After drying the encapsulated wet capsules, place them in a high-temperature furnace and heat them to 800-1000℃ at a rate of 2-3℃ / min in an air atmosphere. Hold the temperature for 1-2 hours to completely ceramicize the shell layer. After natural cooling, sieve out the finished microcapsule product with a particle size of 100-400μm.

[0028] Step 12, Stress-directed sheet SiC preparation steps: Using liquid phase deposition, a nano-zirconia coating with a thickness of about 50-200nm is uniformly coated on the surface of sheet SiC with an aspect ratio >10, and then cured by heat treatment at 600-800℃.

[0029] The stress-directed sheet-like SiC is prepared using a heterogeneous liquid phase deposition method, and the specific steps include: Step 121, Substrate pretreatment: Select sheet-like silicon carbide (SiC≥98%) with an aspect ratio >10, soak it in a dilute hydrochloric acid solution prepared by mixing concentrated hydrochloric acid (mass fraction 36%-38%) and water at a volume ratio of 1:4 for 30 minutes, then wash it repeatedly with deionized water until neutral, and dry it at 110℃ to remove surface impurities and activate the surface.

[0030] Step 122, Coating Deposition Step: Using zirconium oxychloride (ZrOCl2·8H2O) and urea as precursors, prepare a transparent solution containing 0.1-0.3 mol / L ZrO2; add the pretreated sheet-like SiC into the solution, control the solid-liquid ratio at 1:(10-20) (g / mL), and stir at a constant temperature of 75-85℃ for 2-4 hours to uniformly deposit zirconium hydroxide on the SiC surface.

[0031] Step 123, Post-treatment and crystal phase control steps: After the reaction is completed, filter, wash the product with deionized water and ethanol, and dry at 80℃; then place the powder in a muffle furnace, heat to 600-800℃ at 3-5℃ / min in air atmosphere, and hold for 1-1.5 hours to transform the amorphous coating into nanocrystalline zirconia and obtain a mixed crystal phase of tetragonal and monoclinic phases. The final coating thickness is 50-200nm.

[0032] Step 2, Castable Refractory Batching and Mixing: Weigh out 50-65 parts of fused magnesium aluminate spinel particles with a particle size distribution of (15-20 parts of 5-3mm, 20-25 parts of 3-1mm, and 15-20 parts of 1-0mm), 8-12 parts of sintered magnesium aluminate spinel fine powder (≤0.088mm), and active α-Al₂O₃ micro powder (d 50 4-8 parts of ≤2μm, 5-10 parts of sintered magnesia powder containing Y2O3 (≤0.044mm), 1-2 parts of silica powder, 0.15-0.25 parts of composite polycarboxylate superdispersant, 4-7 parts of low-calcium high-alumina cement, 2-5 parts of the above-mentioned pre-prepared thermosensitive phase change microcapsules, 1-3 parts of stress-directed sheet-like SiC, and 4.5-5.0% of the total weight of the above raw materials plus water.

[0033] Add fused magnesium aluminate spinel particles, sintered magnesium aluminate spinel fine powder, and yttrium magnesia sand micro powder to a mixer and dry mix for 1-2 minutes; add active α-Al2O3 micro powder, silica micro powder, and composite superdispersant, and continue dry mixing for 2-3 minutes until uniform; weigh 70-80% of the added water (4.5-5% of the total dry material mass) and stir for 3-5 minutes to form a uniform slurry; add all the pre-made microcapsules and flake SiC, and stir at low speed for 1-2 minutes; finally, add low-calcium high-alumina cement and the remaining water, and stir for another 2 minutes to obtain a castable with suitable construction performance.

[0034] Step 3, Molding and Heat Treatment: The mixture is injected into a mold and vibrated to form the final product. After curing at room temperature (20±5℃) and humidity >90% for 24 hours, the product is demolded. After demolding, the preform is dried at 110℃ for 24 hours, then heated to 350℃ at a rate of ≤60℃ / h and held for 12 hours. Finally, the temperature is increased to 600℃ at a rate of ≤120℃ / h and held for 12 hours to obtain the final product. Example 1

[0035] A self-healing magnesium-aluminum spinel castable based on stress guidance and temperature-sensitive phase transformation, as described in this embodiment, is prepared according to the following steps: (1) Functional unit prefabrication steps: Step 11, Preparation steps of thermosensitive phase change microcapsules: Specific steps include: Step 111, Core preparation and granulation: Weigh borosilicate glass powder and metallic silicon powder (particle size ≤10μm) at a mass ratio of 2:1, and ball mill them together with anhydrous ethanol for 3 hours to obtain a uniform slurry; then spray dry them, controlling the inlet temperature at 200℃ and the outlet temperature at 95℃, to obtain spherical core precursors with a particle size of 80-150μm; Step 112, Mullite inner shell construction steps: The core precursor was placed in a fluidized bed and sprayed with 1.0 mol / L mullite sol at 50°C. After each coating, it was cured at 100°C for 12 minutes. This process was repeated 4 times to form a porous mullite inner shell with a thickness of about 8 μm. Step 113, construction of spinel shell layer: Under the same conditions, the above particles were spray-coated with magnesium aluminum spinel sol with a concentration of 1.2 mol / L (MgO to Al2O3 molar ratio of approximately 1:1). After each coating, the particles were cured at 110°C for 12 minutes. This process was repeated 5 times to form a dense spinel shell layer with a thickness of approximately 10 μm. Step 114, Heat treatment and sieving: The encapsulated wet capsules are dried at 80℃ for 12 hours, and then placed in a high-temperature furnace. The temperature is increased to 900℃ at 2.5℃ / min in an air atmosphere and held for 2 hours to make the shell completely ceramicized. After natural cooling, the capsules are sieved to obtain thermosensitive phase change microcapsules with a particle size of 150-250μm.

[0036] Step 12, Stress-directed sheet SiC preparation steps: Using liquid phase deposition, a nano-zirconia coating with a thickness of about 100 nm is uniformly coated on the surface of sheet SiC with an aspect ratio >10, and then cured by heat treatment at 700℃.

[0037] The stress-directed sheet-like SiC is prepared using a heterogeneous liquid phase deposition method, and the specific steps include: Step 121: Select sheet-shaped silicon carbide (SiC≥98%) with an aspect ratio >10, soak it in a dilute hydrochloric acid solution of concentrated hydrochloric acid and water at a volume ratio of 1:4 (36%-38% by mass) for 30 minutes, then wash it repeatedly with deionized water until neutral, and dry it at 110℃ to remove surface impurities and activate the surface.

[0038] Step 122, Coating Deposition Step: Using zirconium oxychloride octahydrate (ZrOCl2·8H2O) and urea as precursors, prepare a transparent solution containing 0.2 mol / L ZrO2; add the pretreated sheet-like SiC into the solution, control the solid-liquid ratio at 1:15 (g / mL), and stir at 80℃ for 3 hours to uniformly deposit zirconium hydroxide hydrate on the SiC surface.

[0039] Step 123, Post-treatment and crystal phase control steps: After the reaction is completed, filter the product, wash it alternately with deionized water and ethanol, and dry it at 80℃; then place the powder in a muffle furnace, heat it to 700℃ at 4℃ / min in air atmosphere, and hold it for 1.5 hours to dehydrate and crystallize the amorphous zirconium hydroxide coating, transforming it into nanocrystalline zirconium oxide (ZrO2) with stress phase transformation capability. The final coating thickness is 100nm.

[0040] Step 2, Castable Refractory Batching and Mixing: Weigh out a total of 58 parts of fused magnesium aluminate spinel particles with a particle size distribution of 5-3mm (16 parts), 3-1mm (24 parts), and 1-0mm (18 parts), 9 parts of sintered magnesium aluminate spinel fine powder (≤0.088mm), and 18 parts of active α-Al₂O₃ micro powder (d 50 =1.5μm) 5 parts, Y2O3-containing sintered magnesia micro powder (≤0.044mm) 10 parts, silica micro powder 1 part, composite polycarboxylate superdispersant 0.15 parts, low calcium high alumina cement 5 parts, the above-mentioned pre-made temperature-sensitive phase change microcapsules 3 parts, stress-directed sheet SiC 2 parts.

[0041] Fused magnesium aluminate spinel particles, sintered magnesium aluminate spinel fine powder, and yttrium magnesia sand micro powder are added to a mixer and dry-mixed for 2 minutes; active α-Al2O3 micro powder, silica micro powder, and composite superdispersant are added, and dry-mixed for another 3 minutes until uniform; 75% of the total dry material mass (4.5% of the total added water) is weighed and stirred for 4 minutes to form a uniform slurry; all the pre-made microcapsules and flake SiC are added and stirred at low speed for 2 minutes; finally, low-calcium high-alumina cement and the remaining water (i.e., the remaining 25% of the added water) are added, and stirred for another 2 minutes to obtain a castable with suitable construction performance.

[0042] Step 3, Molding and Heat Treatment: The mixture is injected into a mold and vibrated to form the final product. After curing at room temperature (20±5℃) and humidity >90% for 24 hours, the product is demolded. After demolding, the green body is dried at 110℃ for 24 hours, then heated to 350℃ at 50℃ / h and held for 12 hours, and finally heated to 600℃ at 100℃ / h and held for 12 hours to obtain the final product. Example 2

[0043] A self-healing magnesium-aluminum spinel castable based on stress guidance and temperature-sensitive phase transformation, as described in this embodiment, is prepared according to the following steps: (1) Functional unit prefabrication steps: a. Preparation steps of thermosensitive phase change microcapsules: The remaining preparation processes and parameters (including sol concentration, number of encapsulations, curing temperature, drying time, etc.) are the same as those in Example 1.

[0044] The only difference is that the mass ratio of borosilicate glass powder to metallic silicon powder in the core is 2.2:1, and the heat treatment temperature is changed to placing it in a high-temperature furnace and heating it to 850℃ at 2.5℃ / min in an air atmosphere and holding it at that temperature. The microcapsule product with a particle size of 250-350μm is obtained by sieving.

[0045] b. Stress-directed sheet SiC preparation steps: The remaining preparation processes and parameters (including hydrochloric acid concentration, soaking time, deposition temperature, deposition time, etc.) are the same as those in Example 1.

[0046] The only difference is that the thickness of the nano-zirconia coating is about 150nm, and the post-treatment temperature is changed to 750℃ at 4℃ / min in air atmosphere and then held at that temperature.

[0047] (2) Castable material batching and mixing steps: Weigh out 58 parts of fused magnesium aluminate spinel particles with a particle size distribution of 5-3mm (16 parts), 3-1mm (24 parts), and 1-0mm (18 parts), 9 parts of sintered magnesium aluminate spinel fine powder, 5 parts of active α-Al2O3 micro powder, 10 parts of sintered magnesia micro powder containing La2O3, 1 part of silica micro powder, 0.15 parts of composite superdispersant, 5 parts of low-calcium high-alumina cement, 5 parts of the above-mentioned pre-prepared temperature-sensitive phase change microcapsules, and 1 part of stress-directed sheet-like SiC.

[0048] The mixing process steps are the same as in Example 1, except that the amount of water added is 5.0% of the total dry material mass.

[0049] (3) Molding and heat treatment steps: The molding and curing process steps are the same as in Example 1. The heat treatment regime is as follows: after drying at 110℃ for 24 hours, the temperature is increased to 350℃ at 40℃ / h and held for 12 hours, and then the temperature is increased to 600℃ at 80℃ / h and held for 12 hours. Example 3

[0050] A self-healing magnesium-aluminum spinel castable based on stress guidance and temperature-sensitive phase transformation, as described in this embodiment, is prepared according to the following steps: (1) Functional unit prefabrication steps: a. Preparation steps of thermosensitive phase change microcapsules: The remaining preparation processes and parameters (including sol concentration, number of encapsulations, curing temperature, drying time, etc.) are the same as those in Example 1.

[0051] The only difference is that the mass ratio of borosilicate glass powder to metallic silicon powder in the core is 1.8:1, and the heat treatment temperature is changed to placing it in a high-temperature furnace and heating it to 950℃ at 2.5℃ / min in an air atmosphere and holding it at that temperature. The microcapsule product with a particle size of 100-200μm is obtained by sieving.

[0052] b. Stress-directed sheet SiC fabrication steps: The remaining preparation processes and parameters (including hydrochloric acid concentration, soaking time, deposition temperature, deposition time, etc.) are the same as those in Example 1 for the preparation of stress-guided sheet-like SiC.

[0053] The only difference is that the thickness of the nano-zirconia coating is about 60nm, and the post-treatment temperature is changed to 650℃ at 4℃ / min in air atmosphere and then held at that temperature.

[0054] (2) Castable material batching and mixing steps: Weigh out 58 parts of fused magnesium aluminum spinel particles with a particle size distribution of 5-3mm (16 parts), 3-1mm (24 parts), and 1-0mm (18 parts), 9 parts of sintered magnesium aluminum spinel fine powder, 5 parts of active α-Al2O3 micro powder, 10 parts of sintered magnesia micro powder containing Y2O3 and La2O3 composite rare earth oxides, 1 part of silica micro powder, 0.15 parts of composite superdispersant, 7 parts of low-calcium high-alumina cement, 2 parts of the above-mentioned pre-prepared temperature-sensitive phase change microcapsules, and 3 parts of stress-directed sheet-like SiC.

[0055] The mixing process steps are the same as in Example 1, except that the amount of water added is 4.8% of the total mass of the dry materials.

[0056] (3) Molding and heat treatment steps: The molding and curing process steps are the same as in Example 1. The heat treatment regime is as follows: after drying at 110℃ for 24 hours, the temperature is increased to 350℃ at 60℃ / h and held for 12 hours, and then the temperature is increased to 600℃ at 120℃ / h and held for 12 hours. Example 4

[0057] A self-healing magnesium-aluminum spinel castable based on stress guidance and temperature-sensitive phase transformation, as described in this embodiment, is prepared according to the following steps: (1) Functional unit prefabrication steps: a. Preparation steps of thermosensitive phase change microcapsules: The remaining preparation processes and parameters (including sol concentration, number of encapsulations, curing temperature, drying time, etc.) are the same as in Example 1. The only difference is that the mass ratio of borosilicate glass powder to metallic silicon powder in the core is 2.0:1, and the heat treatment temperature is changed to placing the product in a high-temperature furnace and heating it to 800℃ at a rate of 2.5℃ / min in air atmosphere and holding it at that temperature. The microcapsules with a particle size of 100-150μm are obtained by sieving.

[0058] b. Stress-directed sheet SiC preparation steps: The remaining preparation processes and parameters (including hydrochloric acid concentration, immersion time, deposition temperature, deposition time, etc.) are the same as in Example 1. The only difference is that the thickness of the nano-zirconia coating is approximately 200 nm, and the post-treatment temperature is 600 °C.

[0059] (2) Castable material batching and mixing steps: Weigh out 50 parts of fused magnesium aluminate spinel particles with particle size distributions of 5-3mm (15 parts), 3-1mm (20 parts), and 1-0mm (15 parts), 8 parts of sintered magnesium aluminate spinel fine powder, 4 parts of active α-Al2O3 micro powder, 5 parts of sintered magnesia micro powder containing Y2O3, 1 part of silica micro powder, 0.2 parts of composite superdispersant, 4 parts of low-calcium high-alumina cement, 2 parts of the above-mentioned pre-prepared temperature-sensitive phase change microcapsules, and 1 part of stress-directed sheet-like SiC.

[0060] The mixing process steps are the same as in Example 1, except that the amount of water added is 4.8% of the total mass of the dry materials.

[0061] (3) Molding and heat treatment steps: The molding and curing process steps are the same as in Example 1. The heat treatment regime is as follows: after drying at 110℃ for 24 hours, the temperature is increased to 350℃ at 50℃ / h and held for 12 hours, and finally the temperature is increased to 600℃ at 100℃ / h and held for 12 hours. Example 5

[0062] A self-healing magnesium-aluminum spinel castable based on stress guidance and temperature-sensitive phase transformation, as described in this embodiment, is prepared according to the following steps: (1) Functional unit prefabrication steps: a. Preparation steps of thermosensitive phase change microcapsules: The remaining preparation processes and parameters (including sol concentration, number of encapsulations, curing temperature, drying time, etc.) are the same as in Example 1. The only difference is that the mass ratio of borosilicate glass powder to metallic silicon powder in the core is 2.0:1, and the heat treatment temperature is changed to placing the product in a high-temperature furnace and heating it to 1000℃ at a rate of 2.5℃ / min in air atmosphere and holding it at that temperature. The microcapsules with a particle size of 350-400μm are obtained by sieving.

[0063] b. Stress-directed sheet SiC preparation steps: The remaining preparation processes and parameters (including hydrochloric acid concentration, soaking time, deposition temperature, deposition time, etc.) are the same as in Example 1. The only difference is that the thickness of the nano-zirconia coating is about 50 nm, and the post-treatment temperature is changed to be increased to 800 °C at 4 °C / min in air and held at that temperature.

[0064] (2) Castable material batching and mixing steps: Weigh out 65 parts of fused magnesium aluminate spinel particles with particle size distributions of 5-3mm (20 parts), 3-1mm (25 parts), and 1-0mm (20 parts), 12 parts of sintered magnesium aluminate spinel fine powder, 8 parts of active α-Al2O3 micro powder, 10 parts of sintered magnesia micro powder containing Y2O3, 2 parts of silica micro powder, 0.25 parts of composite superdispersant, 7 parts of low-calcium high-alumina cement, 5 parts of the above-mentioned pre-prepared temperature-sensitive phase change microcapsules, and 3 parts of stress-directed sheet-like SiC.

[0065] The mixing process steps are the same as in Example 1, except that the amount of water added is 4.5% of the total mass of the dry materials.

[0066] (3) Molding and heat treatment steps: The molding and curing process steps are the same as in Example 1. The heat treatment regime is as follows: after drying at 110℃ for 24 hours, the temperature is increased to 350℃ at 50℃ / h and held for 12 hours, and finally the temperature is increased to 600℃ at 100℃ / h and held for 12 hours.

[0067] Comparative Example To further verify the advancement of the technical solution of this invention and the rationality of the claims, the following comparative examples are set up. Each comparative example is based on the formulation of Example 1, with only the specified parameters changed. The types, purity, particle size distribution, and preparation processes of other raw materials are kept consistent with those of Example 1 to ensure the principle of single variable in the comparison results.

[0068] Comparative Example 1 (blank control, no repair units) This comparative example is used to verify the necessity of the self-healing functional unit. Its formula is as follows: 58 parts of fused magnesium aluminate spinel particles (particle size distribution is the same as in Example 1), 9 parts of sintered magnesium aluminate spinel fine powder, 5 parts of active α-Al2O3 micro powder, 10 parts of Y2O3-containing sintered magnesia micro powder, 1 part of silica micro powder, 0.15 parts of composite superdispersant, and 5 parts of low-calcium high-alumina cement.

[0069] The conditions are the same as in Example 1, except that the prefabrication step of the functional unit is omitted in the preparation method (the mixing and heat treatment processes are the same as in Example 1).

[0070] Comparative Example 2 (kernel ratio below the lower limit) The conditions are the same as in Example 1, except that in step 111, the mass ratio of borosilicate glass powder to metallic silicon powder in the core of the thermosensitive phase change microcapsule is changed to 1:1. This comparative example is used to verify the rationality of the lower limit of the core ratio of the thermosensitive phase change microcapsule.

[0071] Comparative Example 3 (Kernel ratio higher than the upper limit) The conditions are the same as in Example 1, except that in step 111, the mass ratio of borosilicate glass powder to metallic silicon powder in the core of the thermosensitive phase change microcapsule is changed to 3:1. This comparative example is used to verify the rationality of the upper limit of the core ratio of the thermosensitive phase change microcapsule.

[0072] Comparative Example 4 (containing only thermosensitive phase change microcapsules, without stress-directed repair units) was conducted under the same conditions as Example 1, except that the thermosensitive phase change microcapsules were replaced with 5 parts, and stress-directed sheet-like SiC was removed from the formulation. This comparative example was used to verify the necessity of the stress-directed repair unit.

[0073] Comparative Example 5 (containing only the stress-directed repair unit, without the thermosensitive phase change microcapsules) was identical to Example 1 in all other conditions, except that the stress-directed sheet-like SiC was replaced with 3 parts, and the thermosensitive phase change microcapsules were removed from the formulation. This comparative example was used to verify the necessity of the thermosensitive phase change repair unit.

[0074] Examples 1-3 and Comparative Examples 1-5 describe the stress-directed and temperature-sensitive phase transition-based self-healing magnesium-aluminum spinel castables. The standards or methods used for testing are as follows: bulk density and apparent porosity conform to GB / T 2997; room temperature flexural strength conforms to GB / T 3001; high temperature flexural strength conforms to GB / T 3002; thermal shock resistance conforms to YB / T 376.1, and the room temperature flexural strength retention rate after thermal shock is determined by cycling three times using a 1100℃ water quenching method; crack healing efficiency is calculated by pre-fabricating a crack approximately 150μm wide on the sample surface, holding it at 1450℃ for 2 hours, and then measuring the crack width change using scanning electron microscopy, calculated as (initial width - residual width) / initial width × 100%; the high temperature strength retention rate of the repaired area is defined as the ratio of the 1500℃ high temperature flexural strength of the sample with pre-fabricated cracks and undergoing self-healing heat treatment to the strength of the original sample without cracks.

[0075] The performance of the castable samples obtained in Examples 1-3 and Comparative Examples 1-5 was tested, and the comparison results of key indicators are shown in Table 1 below.

[0076] Table 1. Comparison of performance indicators of castables in the examples and comparative examples Note: The test temperature in Note 1 is 1500℃; Note 2 is the retention rate of room temperature flexural strength after three cycles of quenching water at 1100℃; Note 3 is the crack healing rate of a pre-fabricated 150μm wide crack after being kept at 1450℃ for 2 hours; Note 4 is the percentage of the flexural strength of the repaired sample at 1500℃ to that of the original sample without cracks at 1500℃; Note 5 shows that Comparative Example 1 has no self-healing function and the strength of the repaired area cannot be measured.

[0077] The test results in Table 1 show that: 1. Core contribution of self-healing function: Comparative Example 1, without any repair unit, has a thermal shock resistance of only 48% and no crack healing ability; while Examples 1-3 have a thermal shock resistance of 85%-90% and a healing efficiency of 94%-98%. This proves that the self-healing unit designed in this invention is the decisive factor in improving the thermal shock damage resistance of materials.

[0078] 2. Boundary Effect of Core Powder Ratio: Comparative Example 2 (core borosilicate glass powder to metallic silicon powder mass ratio of 1.0:1) achieved a healing efficiency of 68%, but the strength of the repaired area decreased to 82%; Comparative Example 3 (core borosilicate glass powder to metallic silicon powder mass ratio of 3.0:1) achieved a healing efficiency of only 45%. Example 1 (core borosilicate glass powder to metallic silicon powder mass ratio of 2.0:1) simultaneously achieved high healing efficiency (96%) and high repaired area strength (105%). This demonstrates that (core borosilicate glass powder to metallic silicon powder mass ratio of 1.5-2.5:1) is the key preferred range for achieving a balance between "rapid sealing" and "durable strengthening".

[0079] 3. Synergistic effect of dual functional units: Comparative Example 4 (containing only thermosensitive phase change microcapsules) showed a healing efficiency of 82% and a repair area strength of 88%; Comparative Example 5 (containing only stress-directed repair units) showed a healing efficiency of 60% and a repair area strength of 102%.

[0080] It should be noted that although Comparative Example 3 (core ratio 3.0:1) achieved a repair zone strength as high as 109%, its healing efficiency was only 45%. The mechanism is as follows: the content of metallic silicon powder is extremely low, and the repair is mainly based on the melting and filling of the glass phase. The repaired area is dense and has few defects, so the local strength is high. However, due to the lack of sufficient metallic silicon oxidation to form a ceramic phase, the repair reaction cannot extend to the depth of the crack, resulting in a serious lack of coverage. The overall thermal shock resistance is only 58%, which is far lower than the 88% of Example 1.

[0081] In contrast, Example 1 (ratio 2.0:1) achieves the optimal balance: rapid sealing of the glass phase, sufficient metal silicon oxidation to generate a ceramic phase, and repair extension to deeper areas, while achieving high healing efficiency (96%) and high repair zone strength (105%), with thermal shock resistance of 88%.

[0082] The above comparison proves that the temperature-sensitive phase change unit provides rapid emergency sealing, and the stress-directing unit guides SiC oxidation to achieve long-term strengthening. The two work synergistically and are indispensable.

[0083] It should be noted that although the amount of microcapsules in Comparative Example 4 was increased from 3 parts in Example 1 to 5 parts, the healing efficiency was only 82% and the strength of the repaired area was only 88% due to the lack of stress-directed SiC, which is still far lower than that of Example 1 (96% and 105%). Although the amount of SiC in Comparative Example 5 was increased from 2 parts to 3 parts, the healing efficiency was only 60% due to the lack of microcapsules. This further demonstrates that the dual-functional unit has a synergistic effect, and that even if the amount of a single functional unit is increased, it cannot replace the function of the other unit.

[0084] 4. Comprehensive Performance Verification: Examples 1-5 are comparable to or at the same level as the comparative examples in terms of basic properties (bulk density, apparent porosity, room temperature and high temperature strength), while their thermal shock resistance, crack healing efficiency, and repair zone strength are significantly better than those of the comparative examples. This demonstrates that the present invention, while maintaining the intrinsic high temperature performance of the material, endows it with excellent self-healing ability, achieving a "repair and enhancement" effect.

[0085] In summary, this invention achieves excellent self-healing performance through precise control of the kernel ratio and the synergy of dual functional units, fully verifying the advanced nature of the technical solution and the rationality of the scope of protection of the claims.

[0086] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A self-healing castable of magnesium aluminum spinel based on stress-directed and temperature-sensitive phase transition, characterized in that: It includes basic refractory aggregates and matrix, temperature-sensitive phase change repair units, stress-directed repair units, bonding system and additives, and water of 4.5%-5% of the total weight of the above solid raw materials; The basic refractory aggregate and matrix include the following materials in parts by weight: 50-65 parts of fused magnesium aluminate spinel particles, 8-12 parts of sintered magnesium aluminate spinel fine powder, and 4-8 parts of active α-Al2O3 micro powder. The thermosensitive phase change repair unit is 2-5 parts by weight. The thermosensitive phase change repair unit is a microcapsule with a core-shell structure. The core of the microcapsule is composed of borosilicate glass powder and metallic silicon powder in a mass ratio of (1.5-2.5):

1. The shell of the microcapsule has a double-layer structure, with the inner layer being porous mullite and the outer layer being dense magnesium aluminum spinel. The stress-directed repair unit is 1-3 parts by weight, and the stress-directed repair unit is a sheet-like silicon carbide with a nano-zirconia coating on its surface; The bonding system and additives include the following materials in parts by weight: 5-10 parts of sintered magnesia micro powder containing rare earth oxides, 1-2 parts of silica micro powder, 0.15-0.25 parts of composite polycarboxylate superdispersant, and 4-7 parts of low-calcium high-alumina cement.

2. The magnesium-aluminum spinel self-healing castable based on stress-directed and temperature-sensitive phase transition according to claim 1, characterized in that: The fused magnesium aluminum spinel particles, according to different particle size distributions, include the following parts by weight: 15-20 parts for particles with a particle size of 5-3 mm, 20-25 parts for particles with a particle size of 3-1 mm, and 15-20 parts for particles with a particle size of 1-0 mm.

3. The magnesium-aluminum spinel self-healing castable based on stress-directed and temperature-sensitive phase transition according to claim 1, characterized in that: The particle size of sintered magnesium aluminum spinel fine powder is ≤0.088mm, and the particle size d of active α-Al2O3 micro powder is... 50 ≤2μm.

4. The magnesium-aluminum spinel self-healing castable based on stress-directed and temperature-sensitive phase transition according to claim 1, characterized in that: The aspect ratio of the sheet-like silicon carbide is >10, and the thickness of the nano-zirconia coating is 50-200 nm.

5. The magnesium-aluminum spinel self-healing castable based on stress-directed and temperature-sensitive phase transition according to claim 1, characterized in that: The particle size of the sintered magnesia micro powder containing rare earth oxides is ≤0.044mm, and the particle size of the silica micro powder is ≤1μm; the particle size of the thermosensitive phase change microcapsules is 100-400μm, and the particle size of the sheet-like silicon carbide is not higher than 0.088mm.

6. The magnesium-aluminum spinel self-healing castable based on stress-directed and temperature-sensitive phase transition according to claim 1, characterized in that: In the fused magnesium aluminum spinel particles, the mass fraction of Al2O3 is 64%-68%, the mass fraction of MgO is 32%-36%, the mass fraction of Fe2O3 is ≤0.35%, and the mass fraction of SiO2 is ≤0.4%. In the sintered magnesium aluminum spinel fine powder, the mass fraction of Al2O3 is ≥64%, and in the active α-Al2O3 micro powder, the mass fraction of Al2O3 is ≥99.0%.

7. The magnesium-aluminum spinel self-healing castable based on stress-directed and temperature-sensitive phase transition according to claim 1, characterized in that: In the rare earth oxide-containing sintered magnesia micro powder, the rare earth oxide is Y2O3 or La2O3, and the purity of Y2O3 or La2O3 is ≥95.0%. In the silica micro powder, the mass fraction of SiO2 is ≥94%. In the core of the thermosensitive phase change microcapsule, the softening point of borosilicate glass powder is 850-920℃, and the mass ratio of borosilicate glass powder to metallic silicon powder is (1.5-2.5):

1. In the sheet-like silicon carbide coated with nano-zirconia, the mass fraction of silicon carbide is ≥98%, and the thickness of the nano-zirconia coating on its surface is 50-200nm. In the low-calcium high-alumina cement, the mass fraction of Al2O3 is ≥80%.

8. A method for preparing a self-healing magnesium-aluminum spinel castable based on stress-directed and temperature-sensitive phase transition, characterized in that: Includes the following steps: Step 1: Functional Unit Prefabrication Steps Step 11: Preparation of temperature-sensitive phase change microcapsules: The core material is dispersed by sol-gel and spray granulation method, and then mullite sol and spinel sol are deposited in sequence to form a double shell. After heat treatment at 800-1000℃, microcapsules of 100-400μm are obtained by sieving. Step 12, Stress-directed sheet silicon carbide preparation steps: A nano-zirconia coating is uniformly coated on the surface of the sheet silicon carbide using liquid phase deposition, and then cured by heat treatment at 600-800℃. Step 2: Castable Refractory Mixing Step: According to the proportion, fused magnesium aluminate spinel particles, sintered magnesium aluminate spinel fine powder, and sintered magnesia micro powder containing rare earth oxides are put into a mixer for dry mixing; activated alumina micro powder, silica micro powder, and composite superdispersant are added and dry mixing continues; 70%-80% of the total water volume is added and stirred to form a uniform slurry; finally, the temperature-sensitive phase change microcapsules, stress-directed sheet silicon carbide, and low-calcium high-alumina cement pre-prepared in Steps 11 and 12 are added, stirred at low speed, and the remaining water is added to adjust the fluidity to obtain the mixture; Molding and heat treatment steps: Vibrate the mixture obtained in step two to form a mold, cure at room temperature and then demold; after demolding, dry the blank and then perform segmented heat treatment.

9. The preparation method of a magnesium-aluminum spinel self-healing castable based on stress-directed and temperature-sensitive phase transition according to claim 8, characterized in that: The preparation steps of the temperature-sensitive phase change microcapsules include: Step 111, Core Preparation and Granulation: Weigh borosilicate glass powder and metallic silicon powder with a particle size ≤10μm at a mass ratio of (1.5-2.5):1, and ball mill them together to obtain a uniform slurry; then spray dry to obtain a spherical core precursor with a particle size of 80-150μm; Step 112, Mullite Inner Shell Construction: Place the core precursor obtained in Step 111 in a fluidized bed, and spray it with a mullite sol at a concentration of 0.8-1.2 mol / L at 40-60℃. After each coating, solidify at 90-110℃. Repeat this process multiple times to form a porous mullite inner shell with a thickness of 5-10μm, and obtain particles coated with a porous mullite inner shell; Step 113, Spinel Shell Construction: At 40-60℃, the particles obtained in Step 112 are spray-coated with magnesium aluminum spinel sol at a concentration of 1.0-1.5 mol / L. After each coating, the particles are cured at 100-120℃. This process is repeated multiple times to form a dense spinel shell layer with a thickness of 8-12 μm. Step 114, Heat Treatment and Sieving: The wet capsules after the shell layer is coated in Step 113 are dried and then placed in a high-temperature furnace. The temperature is raised to 800-1000℃ in an air atmosphere and held for a certain time to completely ceramicize the shell layer. After natural cooling, the microcapsule products with a particle size of 100-400 μm are sieved out.

10. The preparation method of a magnesium-aluminum spinel self-healing castable based on stress-directed and temperature-sensitive phase transition according to claim 8, characterized in that: The specific steps for preparing the stress-guided sheet-like silicon carbide are as follows: Step 121, Substrate Pretreatment: Select sheet-like silicon carbide with an aspect ratio >10, soak and wash it with hydrochloric acid until neutral, and dry it at a certain temperature to activate the surface; Step 122, Coating Deposition: Prepare a transparent solution containing 0.1-0.3 mol / L ZrO2 using zirconium oxychloride and urea as precursors; add the pretreated sheet-like silicon carbide from Step 121 into the transparent solution, control the solid-liquid ratio at 1g:(10-20mL), and stir the reaction at 75-85℃ for 2-4 hours to uniformly deposit zirconium hydroxide on the silicon carbide surface; Step 123, Post-treatment and Crystal Phase Control: After the reaction in Step 122 is completed, filter, wash, and dry; then place the obtained powder in a muffle furnace, heat it to 600-800℃ in an air atmosphere, and hold it for a certain time to transform the amorphous coating into nanocrystalline zirconium oxide and obtain a mixed crystal phase of tetragonal and monoclinic phases, with a final coating thickness of 50-200nm.

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