High-performance tundish cover castable based on high-aluminum ceramic chip recycled aggregate and preparation method of high-performance tundish cover castable

Abstract

The invention relates to the technical field of castable, in particular to high-performance tundish cover castable based on high-aluminum ceramic chip recycled aggregate and a preparation method of the high-performance tundish cover castable. The castable comprises high-aluminum ceramic chip recycled aggregate, modified hollow alumina microspheres, andalusite and other components, and through roasting stabilization treatment of the recycled aggregate and multi-layer coating modification of the microspheres, the problems of poor heat preservation property and concentrated thermal stress caused by high doping amount of the recycled aggregate are solved. The andalusite cooperates with the modified microbeads to optimize aggregate-andalusite-microbead three-phase interface combination by virtue of the low-expansion characteristic and the active surface, so that the thermal shock resistance and the structural compactness are enhanced. The product has excellent heat preservation and heat insulation performance, high strength and slag corrosion resistance, resource efficient utilization of waste high-aluminum ceramic chips is achieved, and the service life of the tundish cover is prolonged.

Description

Technical Field

[0001] This invention relates to the field of castable technology, and in particular to a high-performance intermediate ladle cap castable based on high-alumina ceramic chip recycled aggregate and its preparation method. Background Technology

[0002] As a key functional refractory material in continuous casting systems, the tundish cover must balance high-temperature strength, slag erosion resistance, and thermal insulation performance to ensure stable steel temperature and energy consumption control. With the green development of refractory materials, utilizing industrial solid waste such as waste high-alumina ceramic shards to prepare recycled aggregates has become an important direction. Their high alumina content (Al2O3≥65%) can replace natural raw materials, reducing resource consumption and costs. However, when the recycled aggregate content is increased to the 55%-60% range, problems easily arise in the material system: although recycled aggregates can achieve matrix densification, their thermal stability differences and impurity residues lead to a significant increase in the high-temperature thermal conductivity of the castable, exacerbating heat loss from the tundish and increasing the risk of uncontrolled temperature drop during continuous casting.

[0003] Furthermore, the high thermal conductivity leads to localized thermal stress concentration, especially during the alternating thermal cycles of baking preheating and molten steel scouring, making it easier for microcracks within the matrix to propagate into through-cracks. These cracks not only become channels for slag penetration but also accelerate structural spalling under the coupled effect of slag erosion, resulting in decreased slag resistance and shortened service life. Existing technologies have attempted to introduce lightweight aggregates such as hollow alumina microspheres to improve thermal insulation, but the interfacial bonding between ordinary microspheres and a matrix with high-dosage recycled aggregates is weak. During the mixing and vibration molding stages, the shell is prone to fracture due to shear failure, and the instability of the hollow structure introduces stress concentration points.

[0004] Furthermore, the complexity of recycled aggregate sources leads to significant fluctuations in its composition. Non-refractory impurities (such as Fe2O3 and alkali metal oxides) easily form low-melting-point phases at high temperatures, exacerbating porosity defects and sintering inhomogeneity. While existing processes treat recycled aggregates through simple calcination, they fail to systematically regulate the microsphere-matrix interface structure and coating stability, resulting in difficulties in synergistically achieving thermal insulation and crack resistance. Particularly in high-dosage systems, the dispersibility of microspheres as insulating fillers and the thermal shock resistance of the shell are insufficient, leading to premature peeling of the coating under thermal cycling and accelerated degradation of the material's thermal insulation performance during long-term service. These problems collectively restrict the large-scale application of high-dosage recycled aggregates in tundish cover castables, necessitating a breakthrough in the technological bottleneck of synergistic thermal insulation and crack resistance. Summary of the Invention

[0005] In view of this, the purpose of this invention is to propose a high-performance tundish cover castable based on high-alumina ceramic chip recycled aggregate and its preparation method, so as to solve the problem that high-content recycled aggregate tundish cover castable is prone to crack propagation and local spalling due to insufficient thermal insulation performance and thermal stress concentration under the coupled action of thermal cycling and slag erosion.

[0006] To achieve the above objectives, the present invention provides a high-performance intermediate ladle cap castable based on high-alumina ceramic chip recycled aggregate, comprising: a recycled aggregate matrix and modified hollow alumina microspheres dispersed in the recycled aggregate matrix.

[0007] Furthermore, by weight, the castable is prepared from the following raw materials: 550-600 parts of high-alumina ceramic chip recycled aggregate, 172-232 parts of bauxite fine powder, 95 parts of fused white corundum fine powder, 60 parts of activated alumina micro powder, 30 parts of calcium aluminate cement, 10 parts of aluminum dihydrogen phosphate powder, 3 parts of sodium hexametaphosphate, 100-120 parts of andalusite, 20-30 parts of modified hollow alumina microspheres, and 63-65 parts of water.

[0008] Furthermore, the modified hollow alumina microspheres include a hollow alumina microsphere core and a phosphate anchoring layer, a mullite precursor coating layer, and a structural reinforcement layer sequentially coating the outer surface of the hollow alumina microsphere core.

[0009] Furthermore, the phosphate anchoring layer is a coating layer formed of aluminum dihydrogen phosphate, and the aluminum dihydrogen phosphate coating layer is formed by heat treatment and curing at 280-320℃; the mullite precursor coating layer is formed by a first acidic silica sol and activated alumina micro powder, and the mullite precursor coating layer is formed by heat treatment at 330-370℃; the structural reinforcement layer is formed by boron carbide powder, a first acidic silica sol and a second acidic silica sol, wherein the particle size of the first acidic silica sol is smaller than the particle size of the second acidic silica sol.

[0010] Preferably, the high-alumina ceramic chip recycled aggregate comprises: 273-298 parts of recycled aggregate with a particle size of 1-3 mm, 193-210 parts of recycled aggregate with a particle size of 3-5 mm, and 84-92 parts of recycled aggregate with a particle size of 5-10 mm; the high-alumina ceramic chip recycled aggregate is obtained by sieving waste high-alumina ceramic chips after iron removal, water washing, drying at 110℃ to constant weight, calcining at 1200-1300℃ for 1.5-2.5 h by heating at 4-6℃ / min.

[0011] Preferably, the high-alumina ceramic chip recycled aggregate is made from waste high-alumina ceramic chips, wherein the waste high-alumina ceramic chips have an Al2O3 content of 85wt% and an Fe2O3 content of 0.7wt%.

[0012] Preferably, the particle size of the hollow alumina microbead core is 0.06-0.1 mm.

[0013] Preferably, the first acidic silica sol is acidic silica sol SW15-30 / 1, and the second acidic silica sol is acidic silica sol SW60-30 / 1; the acidic silica sol SW15-30 / 1 has a particle size of 13-16 nm, a solid content of 30±1%, and a pH of 2.0-3.5; the acidic silica sol SW60-30 / 1 has a particle size of 50-70 nm, a solid content of 30±1%, and a pH of 2.0-3.5; and the boron carbide powder has a particle size of less than 10 μm.

[0014] Preferably, based on 18-27 parts by weight of hollow alumina microbead core, the amount of aluminum dihydrogen phosphate used in the preparation of the phosphate anchoring layer is 0.6-0.9 parts by weight; the amounts of the first acidic silica sol and the activated alumina micro powder used in the preparation of the mullite precursor coating layer are 0.9-1.4 parts by weight and 0.7-1.2 parts by weight, respectively; and the amounts of boron carbide powder, the first acidic silica sol, and the second acidic silica sol used in the structural reinforcement layer are 0.1-0.2 parts by weight, 0.7-1.2 parts by weight, and 1.3-1.9 parts by weight, respectively.

[0015] Furthermore, the present invention also provides a method for preparing a high-performance intermediate ladle cap castable based on high-alumina ceramic chip recycled aggregate, comprising the following steps: (1) Preparation of high-alumina ceramic chip recycled aggregate; (2) Preparation of modified hollow alumina microspheres; (3) Mix high-alumina ceramic chip recycled aggregate, bauxite fine powder, molten white corundum fine powder, activated alumina micro powder, calcium aluminate cement, aluminum dihydrogen phosphate powder and sodium hexametaphosphate, and add water and stir to obtain a wet matrix material. (4) Add andalusite and modified hollow alumina microspheres to the wet matrix and stir to obtain intermediate ladle cap casting material.

[0016] Preferably, step (2) includes: (21) Preparation of phosphate anchoring layer coated microspheres; (22) Preparation of mullite precursor-coated microspheres; (23) The mullite precursor-coated microspheres were placed in a planetary mixer and stirred. The first acidic silica sol was atomized and sprayed within 3 minutes. Boron carbide powder and sodium hexametaphosphate were added to deionized water and ultrasonically dispersed to obtain a boron carbide dispersion. The boron carbide dispersion was atomized and sprayed within 5 minutes. The second acidic silica sol was then atomized and sprayed within 4 minutes. After drying at 110°C for 2 hours, the microspheres were sieved through a 0.3 mm vibrating sieve to obtain modified hollow alumina microspheres.

[0017] Preferably, in step (3), the mixing is carried out in a forced mixer. The low-speed mixing speed is 35-40 rpm and the time is 2-3 min, and the high-speed mixing speed is 80-90 rpm and the time is 3-4 min. The water is deionized water and is added in 3 batches. After each addition of water, the mixer is stirred for 2 min. After the water addition is completed, the mixer is stopped and the tank is scraped once, and then the mixer is stirred for another 2-3 min.

[0018] Preferably, in step (4), the modified hollow alumina microspheres are evenly sprinkled into the wet matrix material and stirred at a low speed of 35-40 rpm for 2-3 minutes.

[0019] The beneficial effects of this invention are: This invention significantly improves the overall performance of castables through high-temperature calcination stabilization of recycled aggregates and the introduction of multi-layered modified microspheres. After impurity removal, washing, and specific calcination, the recycled aggregates exhibit reduced impurity content and enhanced phase stability. This allows them to form a more uniform high-alumina skeleton network when mixed with matrix components such as bauxite powder and white corundum powder, effectively reducing porosity defects caused by volatiles or low-melting-point phases, thereby improving the material's density and high-temperature volume stability.

[0020] A phosphate anchoring layer constructed on the surface of hollow alumina microspheres, through atomized spraying of aluminum dihydrogen phosphate aqueous solution and heat treatment, forms a strong bonding interface on the microsphere shell, enhancing its chemical bonding ability with the matrix. This structure not only mitigates the risk of shell rupture caused by mechanical shearing during stirring, but also ensures that the microspheres maintain their intact hollow morphology in the castable, thereby significantly reducing the high-temperature thermal conductivity of the material, achieving efficient heat preservation while avoiding localized thermal stress concentration.

[0021] Based on the phosphate anchoring layer, the mullite precursor coating layer is transformed into an aluminosilicate shell structure at high service temperatures through the reactive design of acidic silica sol and activated alumina micropowder. This transformation process improves the thermal shock resistance and exfoliation strength of the microsphere shell, enabling the insulation filler to maintain structural integrity under thermal cycling conditions. Furthermore, the microsphere-matrix interface is less prone to crack initiation during thermal shock, thereby extending the material's thermal fatigue life.

[0022] The outer layer is formed by a time-sequential coating of boron carbide powder and dual-particle-size acidic silica sol, creating a boron-silica bridging structure. Under high-temperature oxidation conditions, this layer can generate a borosilicate glass phase, which blocks and passivates the tips of microcracks induced by thermal cycling, inhibiting crack propagation paths while preventing slag wetting and penetration. This design allows the castable to exhibit lower erosion and penetration depths in slag-resistant environments, improving the long-term stability of its slag-resistant properties. Andalusite and modified microspheres are added in the later stages of mixing the wet matrix, and controlled by low-speed, short-duration stirring to reduce mechanical damage to the microsphere structure caused by strong shear. This process ensures the integrity of the microsphere coating layer and its uniform dispersion in the matrix, maintaining excellent flowability of the castable during construction. After molding, it exhibits the synergistic advantages of low thermal conductivity, high flexural strength, and thermal shock resistance, meeting the long-life requirements of the intermediate cap in high-dosage regenerated systems. Furthermore, andalusite, with its low expansion characteristics and active surface groups, works synergistically with the multi-layered modified microspheres to optimize the aggregate-andalusite-microsphere three-phase interface, effectively alleviating internal thermal stress in the castable while improving structural density. The product combines excellent thermal shock resistance, slag erosion resistance, and thermal insulation performance, achieving efficient resource utilization of waste high-alumina ceramic tiles. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments.

[0024] Example 1: The waste high-alumina ceramic shards used in this embodiment are high-alumina ceramic shards or high-alumina ceramic tile scraps obtained from the dismantling of old materials from the continuous casting tundish cover of steel enterprises (by mass percentage: Al2O3 87.5%, SiO2 7.8%, Fe2O3 0.9%, TiO2 2.1%, CaO 1.0%, MgO 0.6%, Na2O 0.25%, K2O 0.18%, with the balance being other impurities); the bauxite fine powder is GAL-85 bauxite fine powder from Yangquan Zhenhui Refractory Materials Co., Ltd., with a particle size of 200 mesh; the white fused alumina fine powder is white fused alumina abrasive F-sand F220 from Zhengzhou Yufa Abrasive Group Co., Ltd.; the reactive alumina micro powder is CL 370 reactive alumina from Almatis GmbH; and the calcium aluminate cement is Almatis... The product used was CA-14M calcium aluminate cement from GmbH; the aluminum dihydrogen phosphate powder used was RSA aluminum dihydrogen phosphate powder from Zhengzhou Rongsheng Refractory Materials Co., Ltd.; the andalusite used was andalusite powder from Lingshou County Qiaoyi New Materials Co., Ltd., with a particle size of 0.5-1mm; the hollow alumina microspheres used were hollow alumina balls from Zhengzhou Haixu Abrasives Co., Ltd., with a particle size of 0.06-0.1mm; the silica sol used for constructing the microsphere shells was acidic silica sol SW15-30 / 1 (particle size 13-16nm, solid content 30±1%, pH 2.0-3.5) and SW60-30 / 1 (particle size 50-70nm, solid content 30±1%, pH 2.0-3.5) from Zhejiang Delixin Micro-Nano Technology Co., Ltd.; the boron carbide powder used was Sigma-Aldrich product 378119, with boron carbide powder <10μm and purity of 98%.

[0025] Step 1: Weigh 700g of waste high-alumina ceramic shards and manually remove visible metal parts, rubber sealing strips, coating residues, and other non-refractory impurities. Add 50g of deionized water and tumble wash for 10 minutes. Pour out the turbid liquid and add 30g of deionized water for a second wash of 5 minutes. Spread the cleaned ceramic shards on a stainless steel tray and dry them in a 110℃ oven for 8 hours. Then, feed them into a jaw crusher for coarse crushing to ≤20mm and then into a double roll crusher for fine crushing. Place the finely crushed material in an electric resistance furnace or gas kiln and heat it to 1250℃ at 5℃ / min. Hold it at that temperature for 2 hours and then let it cool naturally to room temperature. Then, classify the material by vibrating screen and weigh out 290g of recycled high-alumina ceramic shards with a particle size of 1-3mm, 205g of recycled high-alumina ceramic shards with a particle size of 3-5mm, and 90g of recycled high-alumina ceramic shards with a particle size of 5-10mm, totaling 585g. The remaining <1mm powder and >10mm coarse material are recycled separately and are not used in this embodiment. Step 2: Weigh 24g of hollow alumina spheres and place them in a planetary mixer, stirring at 60rpm. Separately, add 0.8g of aluminum dihydrogen phosphate powder to 3.2g of deionized water and magnetically stir for 20min in a 60℃ water bath to obtain an aluminum dihydrogen phosphate aqueous solution. While maintaining the mixer speed at 60rpm, atomize 4g of the above aluminum dihydrogen phosphate aqueous solution into the hollow alumina microspheres within 10min, continue stirring for 5min, and then spread it into a thin layer. First, dry at 110℃ for 2h, then heat to 300℃ at 2℃ / min and hold for 1h before cooling to obtain phosphate anchoring layer coated microspheres. Step 3: Weigh 24.8g of phosphate anchoring layer coated microspheres obtained in Step 2 and place them in a planetary mixer. Stir at a low speed of 60rpm. Add 1.2g of acidic silica sol SW15-30 / 1, 0.9g of reactive alumina micro powder, and 0.6g of deionized water in sequence, and stir at 80rpm for 8min. Spread the wet material into a thin layer, dry it at 110℃ for 2h, then heat it to 350℃ at 2℃ / min and keep it at that temperature for 1h and then cool it to obtain mullite precursor coated microspheres. Step 4: Place the mullite precursor-coated microspheres obtained in Step 3 into a planetary mixer and stir at a low speed of 60 rpm; first, add 1 g of acidic silica sol SW15-30 / 1 and continue stirring for 3 min; then, take 0.15 g of boron carbide powder and 0.01 g of sodium hexametaphosphate and add them to 0.3 g of deionized water and ultrasonically disperse for 10 min to form a boron carbide dispersion. Then, spray 0.46 g of this dispersion into the mixer within 5 min and continue stirring for 3 min; subsequently, add 1.7 g of acidic silica sol SW60-30 / 1 and continue stirring for 4 min to form an outer bridging coating; spread the resulting wet material into a thin layer, dry it at 110℃ for 2 h, and after cooling, lightly sieve it (0.3 mm sieve) to remove agglomerates to obtain structurally reinforced modified hollow alumina microspheres; Step 5: Dry mixing of high-content recycled aggregate matrix Weigh out 290g of high-alumina ceramic chip recycled aggregate with a particle size of 1-3mm, 205g of high-alumina ceramic chip recycled aggregate with a particle size of 3-5mm, 90g of high-alumina ceramic chip recycled aggregate with a particle size of 5-10mm, 190g of bauxite fine powder, 95g of white corundum fine powder, 60g of reactive alumina micro powder, 30g of calcium aluminate cement, 10g of aluminum dihydrogen phosphate powder, and 3g of sodium hexametaphosphate. Add them to a forced mixer and stir at 40 rpm for 2 minutes, then at 80 rpm for 3 minutes. Then weigh out 65g of deionized... Water was added in three stages: first, 25g of deionized water was added and stirred for 2 minutes; second, 25g of deionized water was added and stirred for 2 minutes; third, 15g of deionized water was added and stirred for 2 minutes. Then, the machine was stopped, the material was scraped once, and stirred for another 2 minutes to obtain a wet matrix material with self-flowing casting capability. 110g of andalusite and 27g of modified microspheres were evenly sprinkled into the mixer, and the mixer was switched to 40rpm and stirred for 2 minutes before stopping to obtain a high-performance intermediate ladle cap castable based on high-alumina ceramic chip recycled aggregate. Step 6: Pour the high-performance tundish cover castable based on high-alumina ceramic chip recycled aggregate into the tundish cover preform mold, and use an immersion vibrator to vibrate and form it at a frequency of 50Hz. Vibrate at a single point for 25s and end with the material surface no longer sinking significantly and no large air bubbles escaping. After smoothing the surface, let it stand for curing at 25℃ and 93% relative humidity for 24 hours before demolding. After demolding, place it in a drying oven at 110℃ for 24 hours. Then, heat it up to 350℃ at 2℃ / min and hold for 2 hours, then heat it up to 600℃ at 2℃ / min and hold for 3 hours, then heat it up to 900℃ at 2℃ / min and hold for 3 hours. After cooling, the tundish cover castable preform is obtained.

[0026] Example 2: The difference from Example 1 is as follows: (1) The amount of recycled aggregate used in step 1 is 600g, of which 1-3mm is 298g, 3-5mm is 210g and 5-10mm is 92g.

[0027] (2) The raw material amounts for preparing modified microspheres in steps 2-4 are adjusted as follows: 27g hollow alumina spheres, 0.9g aluminum dihydrogen phosphate powder, and 3.6g deionized water in step 2; 1.3g acidic silica sol SW15-30 / 1, 1g activated alumina micro powder, and 0.7g deionized water in step 3; 1.1g acidic silica sol SW15-30 / 1, 0.2g boron carbide powder, 0.01g sodium hexametaphosphate, 0.3g deionized water, and 1.9g acidic silica sol SW60-30 / 1 in step 4; thus, modified microspheres are obtained.

[0028] (3) In step 5, the amount of fine bauxite powder is 172g, the amount of andalusite is 120g, and the amount of modified microspheres is 30g.

[0029] The remaining conditions are the same as in Example 1.

[0030] Example 3: The difference from Example 1 is as follows: (1) The amount of recycled aggregate used in step 1 is 550g, of which 1-3mm is 273g, 3-5mm is 193g and 5-10mm is 84g.

[0031] (2) The raw material amounts for preparing modified microspheres in steps 2-4 are adjusted as follows: 18g of hollow alumina spheres, 0.6g of aluminum dihydrogen phosphate powder, and 2.4g of deionized water in step 2; 0.9g of acidic silica sol SW15-30 / 1, 0.7g of activated alumina micro powder, and 0.4g of deionized water in step 3; 0.7g of acidic silica sol SW15-30 / 1, 0.1g of boron carbide powder, 0.007g of sodium hexametaphosphate, 0.2g of deionized water, and 1.3g of acidic silica sol SW60-30 / 1 in step 4; thus, modified microspheres are obtained.

[0032] (3) In step 5, the amount of fine bauxite powder is 232g, the amount of andalusite is 100g, and the amount of modified microspheres is 20g.

[0033] The remaining conditions are the same as in Example 1.

[0034] Example 4: The difference from Example 1 is as follows: (1) In step 1, the dried material is placed in an electric resistance furnace or gas kiln and heated to 1200°C at 4°C / min and kept at that temperature for 1.5 hours. After cooling to room temperature with the furnace, it is taken out and graded to obtain recycled aggregate.

[0035] (2) After drying at 110℃ for 2 hours in step 2, the temperature is increased to 280℃ at 2℃ / min and kept at that temperature for 1 hour.

[0036] (3) In step 3, the mullite precursor slurry is prepared by mixing 1g of acidic silica sol SW15-30 / 1, 0.8g of active alumina micro powder and 0.5g of deionized water; after the atomized spraying is completed, continue stirring for 10min; after drying at 110℃ for 2h, the temperature is increased to 330℃ at 2℃ / min and kept at that temperature for 1h.

[0037] (4) In step 4, 0.8g of acidic silica sol SW15-30 / 1 was atomized and sprayed within 3 minutes; the boron carbide dispersion was prepared by ultrasonically dispersing 0.1g of boron carbide powder, 0.008g of sodium hexametaphosphate and 0.25g of deionized water for 8 minutes and atomized and sprayed within 5 minutes; 1.5g of acidic silica sol SW60-30 / 1 was atomized and sprayed within 4 minutes; modified microspheres were obtained.

[0038] The remaining conditions are the same as in Example 1.

[0039] Example 5: The difference from Example 1 is as follows: (1) In step 1, the dried material is placed in an electric resistance furnace or gas kiln and heated to 1300°C at 6°C / min and kept at that temperature for 2.5 hours. After cooling to room temperature with the furnace, it is taken out and then graded to obtain recycled aggregate.

[0040] (2) After drying at 110℃ for 2 hours in step 2, the temperature is increased to 320℃ at 2℃ / min and kept at that temperature for 1 hour.

[0041] (3) In step 3, the mullite precursor slurry is prepared by mixing 1.4g of acidic silica sol SW15-30 / 1, 1.1g of active alumina micro powder and 0.7g of deionized water; after the atomized spraying is completed, continue stirring for 6min; after drying at 110℃ for 2h, the temperature is increased to 370℃ at 2℃ / min and kept at that temperature for 1h.

[0042] (4) In step 4, 1.2 g of acidic silica sol SW15-30 / 1 was atomized and sprayed within 3 min; the boron carbide dispersion was prepared by ultrasonically dispersing 0.2 g of boron carbide powder, 0.012 g of sodium hexametaphosphate and 350 g of deionized water for 12 min, and then atomized and sprayed within 5 min; 1.9 g of acidic silica sol SW60-30 / 1 was atomized and sprayed within 4 min; modified microspheres were obtained. The remaining conditions were the same as in Example 1.

[0043] Example 6: The difference from Example 1 is as follows: In step 5, the low-speed dry mixing speed is 35 rpm and the dry mixing time is 3 min; the high-speed dry mixing speed is 90 rpm and the dry mixing time is 4 min; the amount of deionized water is 63g, which is added to the mixer in 3 parts: 24g of water is added in the first part, 24g of water is added in the second part, and 15g of water is added in the third part. After each addition of water, the mixer is stirred for 2 min; after the water is added, the mixer is stopped and the tank is scraped once, and then the mixer is stirred for 3 min; after the andalusite and modified microspheres are sprinkled in, the mixer is stirred at low speed of 35 rpm for 3 min.

[0044] The remaining conditions are the same as in Example 1.

[0045] Comparative Example 1: The difference from Example 1 is that in step 2, after the aluminum dihydrogen phosphate coated microspheres are dried at 110°C for 2 hours, they are not heated to 300°C at a rate of 2°C / min and held at that temperature for 1 hour. Instead, they are directly cooled to room temperature in the furnace before proceeding to steps 3 and 4 to prepare the modified microspheres. All other conditions are the same as in Example 1.

[0046] Comparative Example 2: The difference from Example 1 is that in step 3, after the mullite precursor-coated microspheres are dried at 110°C for 2 hours, they are not heated to 350°C at a rate of 2°C / min and held at that temperature for 1 hour. Instead, they are directly cooled to room temperature in the furnace before proceeding to step 4 to prepare the modified microspheres. All other conditions are the same as in Example 1.

[0047] Comparative Example 3: The difference from Example 1 is that the spraying sequence of the acidic silica sol in step 4 is changed. Specifically, the mullite precursor-coated microspheres are added to a planetary mixer and stirred at 60 rpm. Within 3 minutes, 1.7 g of acidic silica sol SW60-30 / 1 is atomized and sprayed onto the surface of the mullite precursor-coated microspheres. Separately, 0.15 g of boron carbide powder and 0.01 g of sodium hexametaphosphate are added to 0.3 g of deionized water and ultrasonically dispersed for 10 minutes to obtain a boron carbide dispersion. Within 5 minutes, the boron carbide dispersion is atomized and sprayed onto the surface of the mullite precursor-coated microspheres. After spraying, stirring is continued for 5 minutes. Within 4 minutes, 1 g of acidic silica sol SW15-30 / 1 is atomized and sprayed into the mixer. After spraying, stirring is continued for 4 minutes. The mixer is then stopped and the material is discharged. Subsequent drying and sieving to 0.3 mm are the same as in Example 1. All other conditions are the same as in Example 1.

[0048] Comparative Example 4: The difference from Example 1 is that the order of adding the modified microspheres in step 5 is changed. Specifically, the recycled aggregate, bauxite powder, fused white corundum powder, activated alumina powder, CA-70 cement, aluminum dihydrogen phosphate powder, sodium hexametaphosphate, andalusite obtained in step 1, and 27g of the modified microspheres obtained in step 4 are simultaneously added to a forced mixer. The mixture is then dry-mixed at low speed (40 rpm) for 2 minutes, high speed (80 rpm) for 3 minutes, and then 65g of deionized water is added in three portions as in Example 1, and mixing is completed. All other conditions are the same as in Example 1.

[0049] Sample preparation: The intermediate ladle cap castables obtained in Examples 1-6 and Comparative Examples 1-5 were used to prepare standard specimens and precast specimens, respectively. The standard strip specimens were 160mm×40mm×40mm in size, and the cubic specimens were 50mm×50mm×50mm in size. All specimens were formed under the same immersion vibrator conditions as in step 6 of Example 1 (vibration frequency 50Hz, single-point vibration 25s). After casting, the specimens were covered with a plastic film and cured in an environment of 25℃ and 93% relative humidity for 24 hours before demolding. After demolding, the specimens were dried at 110℃ for 24 hours. Subsequently, the specimens were pretreated according to the heat treatment regime in step 6 of Example 1 (heating at 2℃ / min to 350℃ and holding for 2 hours, then heating at 2℃ / min to 600℃ and holding for 3 hours, then heating at 2℃ / min to 900℃ and holding for 3 hours, and then cooling to room temperature in the furnace). Unless otherwise specified, all tests were conducted under the above-mentioned 900℃ pretreatment conditions; at least 3 parallel samples were taken for each test, and the results were taken as the arithmetic mean.

[0050] Refractory flowability: Performed according to GB / T 4513.4-2017. Weigh the dry-mixed refractory samples and mix them in a forced mixer according to the water addition amount and sequence specified in the corresponding embodiment or comparative example. Immediately after mixing, fill the slurry into an oiled truncated conical metal mold and place it in the center of a slab. The truncated conical mold has a bottom inner diameter of 100mm, a top inner diameter of 70mm, and a height of 50mm. After filling, smooth the top surface and vertically lift the conical mold within 30 seconds. After the slurry has flowed and stabilized, measure the expanded diameter using two perpendicular diameters and take the average as the flow value (mm). Bulk density and apparent porosity: Performed according to GB / T 2997-2015. After deburring 50mm×50mm×50mm samples, each sample was dried at 110℃ for 2 hours, cooled to room temperature, and weighed as dry mass m0. The samples were then evacuated to -0.095MPa in a vacuum saturation apparatus and maintained for 30 minutes. Subsequently, deionized water was injected under vacuum to completely submerge the samples and maintained for 30 minutes. After restoring to normal pressure, the samples were soaked for another 24 hours. The surface water film was wiped off, and the saturated mass m1 was measured. The suspended mass m2 was also weighed in water. Bulk density (g / cm³) was calculated using the Archimedes method. 3 ) and apparent porosity (%).

[0051] Flexural strength at room temperature: according to GB / T 3001-2017. Take a 160mm×40mm×40mm strip specimen for each sample, load it on a three-point bending device, set the span to 125mm, the loading rate to 0.5mm / min, record the failure load and convert it to flexural strength at room temperature (MPa).

[0052] Room temperature compressive strength: according to GB / T 5072-2023. Take a 50mm×50mm×50mm cube specimen for each sample, apply pressure at a loading rate of 0.5MPa / s on a pressure testing machine until the specimen fails, record the failure load and calculate the room temperature compressive strength (MPa).

[0053] High-temperature flexural strength (1100℃): Tested according to GB / T 3002-2017. Take 160mm×40mm×40mm strip specimens and place them in a high-temperature flexural testing furnace. Heat to 1100℃ at a rate of 5℃ / min and hold for 30 minutes. Then, perform three-point bending loading at a constant temperature of 1100℃, with a span of 125mm and a loading rate of 0.5mm / min. Calculate the high-temperature flexural strength (MPa).

[0054] Thermal shock resistance (water cooling method, 1100℃): conducted according to GB / T 30873-2014. Take 40mm×40mm×160mm specimens for each sample. Preheat the test furnace to 1100℃±10℃ and maintain this temperature for 15 minutes. Place the specimen lengthwise into the furnace and heat for 15 minutes, then quickly remove it and immediately place it in flowing water at 20℃ to cool for 3 minutes. After removal, dry it at 110℃ for 30 minutes as one thermal shock cycle. Cycle until the specimen shows a through crack or breaks. Record the number of thermal shock cycles, n. After completing 10 cycles, take another specimen to determine the residual room temperature flexural strength and calculate the flexural strength retention rate (%).

[0055] Slag resistance: Tested according to GB / T 8931-2007. Take a 50mm×50mm×50mm cubic sample for each specimen, drill a cylindrical hole with a diameter of 20mm and a depth of 25mm in the center as a slag cup, fill it with 20g of synthetic slag (by mass percentage: CaO 40%, SiO2 35%, Al2O3 15%, MgO 5%, Fe2O3 5%), place the slag cup sample in an electric resistance furnace, heat it to 1500℃ at 10℃ / min and hold it at that temperature for 2h, cool it to room temperature with the furnace, cut it along the center and polish the cross section, and measure the erosion depth and penetration depth (mm) using vernier calipers.

[0056] Table 1 Summary of Performance Test Results

[0057] As can be seen from the data in Table 1, the flow value of the intermediate ladle cap castable prepared by this invention remains within the range required for self-flowing casting under different recycled aggregate dosages, modified microsphere dosages, and water addition regimes, indicating stable construction fluidity. The bulk density and apparent porosity show a synergistic regulatory relationship with the introduction of modified microspheres, but the room temperature flexural strength, room temperature compressive strength, and high temperature flexural strength still maintain high levels, indicating that the matrix balances densification and a lightweight closed structure. Furthermore, the number of water-cooled thermal shock cycles and the retention rate of flexural strength after thermal shock are generally high, and the slag erosion depth and slag penetration depth are relatively small, demonstrating the synergistic effect of thermal shock resistance and slag resistance. The reason is speculated to be that: the recycled aggregate of waste high-alumina ceramic chips treated at high temperature serves as a high-alumina skeleton, which, together with bauxite fine powder, white corundum fine powder, reactive alumina micro powder, andalusite and calcium aluminate cement, forms a continuous matrix; the phosphate anchoring layer and mullite precursor coating layer on the outer surface of the modified microspheres enhance the interfacial bonding between the microspheres and the matrix and improve the stability of the shell layer; the outer layer is a structural reinforcement layer formed by boron carbide powder and acidic silica sol of different particle sizes to inhibit slag wetting and penetration, thereby achieving a simultaneous improvement in thermal insulation structure and mechanical-slag resistance properties.

[0058] As can be seen from the data in Table 1 for Example 1 and Comparative Examples 1 and 2, when the phosphate anchoring layer-coated microspheres or the mullite precursor-coated microspheres were not subjected to corresponding heat treatment after drying, the room temperature and high temperature strength, the number of thermal shock cycles, and the retention rate of flexural strength after thermal shock all decreased, while the slag erosion resistance depth and slag penetration resistance depth increased. The main reason is that insufficient heat treatment leads to an unstable coating structure, weakened interfacial bonding between the microspheres and the matrix, and a greater likelihood of shell peeling and microcracks during thermal cycling, allowing slag phase to penetrate more rapidly along open pores and interfacial defects. Therefore, the synergistic stabilizing effect of the phosphate anchoring layer and the mullite precursor coating layer is key to obtaining high strength, thermal shock resistance, and slag resistance.

[0059] As can be seen from the data in Example 1 and Comparative Example 3 in Table 1, simply changing the atomization spraying sequence of acidic silica sol SW15-30 / 1 and acidic silica sol SW60-30 / 1, even while maintaining consistent boron carbide dispersion and sieving conditions, resulted in an overall decrease in high-temperature flexural strength, thermal shock resistance, and slag resistance. The presumed reason is that the change in spraying sequence leads to uneven bridging and coating of acidic silica sol with different particle sizes on the surface of the microspheres. This makes it difficult for the boron carbide dispersion to form a continuous outer layer structure for reinforcement. With the reduced integrity of the coating layer, slag is more easily wetted and penetrates through pore channels, and crack propagation is faster under thermal cycling. This indicates a significant sequence effect between multi-particle-size acidic silica sol and boron carbide powder.

[0060] As can be seen from the data in Example 1 and Comparative Example 4 in Table 1, adding modified microspheres simultaneously with recycled aggregate, bauxite powder, white corundum powder, reactive alumina powder, andalusite, and calcium aluminate cement during the dry mixing stage leads to a decrease in flowability, a reduction in the number of water-cooled thermal shock cycles, and a decrease in the retention rate of flexural strength after thermal shock, even though the room temperature strength and slag erosion resistance do not deteriorate synchronously. This is because the strong shearing during the dry mixing and high-speed stirring stages easily causes mechanical damage to the modified microspheres, impairing the integrity of the hollow structure and multi-layer coating, and weakening the crack passivation and stress relief effects. Simultaneously, the crushed fine powder increases water demand and forms local defects, making it easier to induce through-cracks under thermal cycling and molten slag action.

[0061] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the invention is limited to these examples; within the framework of the invention, the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations of the different aspects of the invention as described above, which are not provided in detail for the sake of brevity.

Claims

1. A high-performance intermediate ladle cap castable based on high-alumina ceramic chip recycled aggregate, characterized in that, include: Recycled aggregate matrix and modified hollow alumina microspheres dispersed in the recycled aggregate matrix; The castable is prepared from the following raw materials by weight: 550-600 parts of high-alumina ceramic chip recycled aggregate, 172-232 parts of bauxite fine powder, 95 parts of fused white corundum fine powder, 60 parts of activated alumina micro powder, 30 parts of calcium aluminate cement, 10 parts of aluminum dihydrogen phosphate powder, 3 parts of sodium hexametaphosphate, 100-120 parts of andalusite, 20-30 parts of modified hollow alumina microspheres, and 63-65 parts of water. The modified hollow alumina microspheres include a hollow alumina microsphere core and a phosphate anchoring layer, a mullite precursor coating layer, and a structural reinforcement layer sequentially coating the outer surface of the hollow alumina microsphere core. The phosphate anchoring layer is a coating layer formed of aluminum dihydrogen phosphate, and the aluminum dihydrogen phosphate coating layer is formed by heat treatment and curing at 280-320℃; the mullite precursor coating layer is formed by a first acidic silica sol and activated alumina micro powder, and the mullite precursor coating layer is formed by heat treatment at 330-370℃; the structural reinforcement layer is formed by boron carbide powder, a first acidic silica sol and a second acidic silica sol, wherein the particle size of the first acidic silica sol is smaller than the particle size of the second acidic silica sol.

2. The high-performance intermediate ladle cap castable based on high-alumina ceramic chip recycled aggregate according to claim 1, characterized in that, The high-alumina ceramic chip recycled aggregate comprises: 273-298 parts of recycled aggregate with a particle size of 1-3 mm, 193-210 parts of recycled aggregate with a particle size of 3-5 mm, and 84-92 parts of recycled aggregate with a particle size of 5-10 mm; the high-alumina ceramic chip recycled aggregate is obtained by sieving waste high-alumina ceramic chips after iron removal, water washing, drying at 110℃ to constant weight, calcining at 1200-1300℃ for 1.5-2.5 h by heating at 4-6℃ / min.

3. The high-performance intermediate ladle cap castable based on high-alumina ceramic chip recycled aggregate according to claim 1, characterized in that, The high-alumina ceramic chip recycled aggregate is made from waste high-alumina ceramic chips, which have an Al2O3 content of 85wt% and an Fe2O3 content of 0.7wt%.

4. The high-performance intermediate ladle cap castable based on high-alumina ceramic chip recycled aggregate according to claim 1, characterized in that, The hollow alumina microbeads have a particle size of 0.06-0.1 mm.

5. The high-performance intermediate ladle cap castable based on high-alumina ceramic chip recycled aggregate according to claim 1, characterized in that, The first acidic silica sol is acidic silica sol SW15-30 / 1, and the second acidic silica sol is acidic silica sol SW60-30 / 1; the acidic silica sol SW15-30 / 1 has a particle size of 13-16 nm, a solid content of 30±1%, and a pH of 2.0-3.5; the acidic silica sol SW60-30 / 1 has a particle size of 50-70 nm, a solid content of 30±1%, and a pH of 2.0-3.5; the boron carbide powder has a particle size of less than 10 μm.

6. The high-performance intermediate ladle cap castable based on high-alumina ceramic chip recycled aggregate according to claim 1, characterized in that, Based on 18-27 parts by weight of hollow alumina microbead core, the amount of aluminum dihydrogen phosphate used in the preparation of the phosphate anchoring layer is 0.6-0.9 parts by weight; the amounts of the first acidic silica sol and the activated alumina micro powder used in the preparation of the mullite precursor coating layer are 0.9-1.4 parts by weight and 0.7-1.2 parts by weight, respectively; and the amounts of boron carbide powder, the first acidic silica sol, and the second acidic silica sol used in the structural reinforcement layer are 0.1-0.2 parts by weight, 0.7-1.2 parts by weight, and 1.3-1.9 parts by weight, respectively.

7. A method for preparing a high-performance intermediate ladle cap castable based on high-alumina ceramic chip recycled aggregate as described in any one of claims 1-6, characterized in that, Includes the following steps: (1) Preparation of high-alumina ceramic chip recycled aggregate; (2) Preparation of modified hollow alumina microspheres; (3) Mix high-alumina ceramic chip recycled aggregate, bauxite fine powder, molten white corundum fine powder, activated alumina micro powder, calcium aluminate cement, aluminum dihydrogen phosphate powder and sodium hexametaphosphate, and add water and stir to obtain a wet matrix material. (4) Add andalusite and modified hollow alumina microspheres to the wet matrix and stir to obtain intermediate ladle cap casting material.

8. The method for preparing high-performance intermediate ladle cap castable based on high-alumina ceramic chip recycled aggregate according to claim 6, characterized in that, Step (2) includes: (21) Preparation of phosphate anchoring layer coated microspheres; (22) Preparation of mullite precursor-coated microspheres; (23) The mullite precursor-coated microspheres were placed in a planetary mixer and stirred. The first acidic silica sol was atomized and sprayed within 3 minutes. Boron carbide powder and sodium hexametaphosphate were added to deionized water and ultrasonically dispersed to obtain a boron carbide dispersion. The boron carbide dispersion was atomized and sprayed within 5 minutes. The second acidic silica sol was then atomized and sprayed within 4 minutes. After drying at 110°C for 2 hours, the microspheres were sieved through a 0.3 mm vibrating sieve to obtain modified hollow alumina microspheres.

9. The method for preparing high-performance intermediate ladle cap castable based on high-alumina ceramic chip recycled aggregate according to claim 6, characterized in that, In step (3), the mixing is carried out in a forced mixer. The low-speed mixing speed is 35-40 rpm and the time is 2-3 min. The high-speed mixing speed is 80-90 rpm and the time is 3-4 min. The water is deionized water and is added in 3 parts. After each addition of water, the mixer is stirred for 2 min. After the water addition is completed, the mixer is stopped and the tank is scraped once, and then the mixer is stirred for another 2-3 min.

10. The method for preparing high-performance intermediate ladle cap castable based on high-alumina ceramic chip recycled aggregate according to claim 6, characterized in that, In step (4), the modified hollow alumina microspheres are evenly sprinkled into the wet matrix material and stirred at a low speed of 35-40 rpm for 2-3 minutes.

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