Special casting powder suitable for MCCR process technology

Abstract

The invention relates to the technical field of casting powder, in particular to special casting powder suitable for an MCCR process technology, which comprises the following raw materials: silicon dioxide, calcium oxide, magnesium oxide, cured slow-release boron oxide particles, core-shell hollow glass microspheres, sodium oxide and carbon black. According to the solidified slow-release boron oxide particles, a slow-release layer mainly comprising calcium silicate is constructed on the surface of boron oxide, gradient release of boron elements at high temperature is achieved, viscosity mutation caused by premature melting of boron-containing components is effectively avoided, and therefore on the basis that the viscosity stability of molten slag is improved, the uniformity of a slag film is improved; meanwhile, a firm nano composite shell layer is formed on the surface of the core-shell hollow glass microsphere, and then the core-shell hollow glass microsphere is subjected to high-temperature strengthening through the polysilazane-polysiloxane copolymer, so that the compressive strength and the thermal stability of the microsphere are greatly improved, the microsphere is not prone to breakage and sintering under high-temperature shearing, the heat insulation performance of the casting powder is maintained for a long time, and heat loss is reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of protective slag, in particular to a special protective slag suitable for MCCR process technology. BACKGROUND

[0002] In the metallurgical industry, MCCR process as an advanced short process production technology, puts forward extremely harsh requirements for the performance of protective slag in continuous casting crystallizer; the ideal protective slag needs to have stable melting characteristics, suitable lubricating properties and excellent heat insulation effect under the conditions of high-speed casting, high speed of drawing blank and severe thermal cycle.

[0003] The traditional protective slag usually adjusts the basicity of SiO2-CaO-Al2O3 and other basic components, and adds fluorides, carbonates and conventional carbon black and other materials to control the melting speed and crystallization behavior to meet the basic metallurgical process requirements; however, the existing protective slag is difficult to realize the controllability of borate release and the high temperature structural stability of light particles, resulting in lagging viscosity adjustment of molten slag, insufficient stability of slag film and uneven interface lubricating properties, so as to fail to meet the comprehensive needs of MCCR process for rapid response and high stability of protective slag behavior, therefore, we propose a special protective slag suitable for MCCR process technology. SUMMARY

[0004] The purpose of the present application is to provide a special protective slag suitable for MCCR process technology to solve the problems caused by the lack of controllability of borate release and high temperature structural stability of light particles of the existing protective slag as mentioned in the background.

[0005] The present application provides a special protective slag suitable for MCCR process technology, which comprises the following raw materials: silicon dioxide, calcium oxide, magnesium oxide, solidified slow-release boron oxide particles, core-shell hollow glass microspheres, sodium oxide and carbon black. The solidified slow-release boron oxide particles are prepared by low eutectic mixing of boron oxide and calcium silicate, sol-gel dispersion, hydrothermal solidification and drying; The core-shell hollow glass microspheres are prepared by hollow glass microspheres activated by oxygen plasma, acetyl acetic acid ethyl ester diisopropyl aluminum anchoring, oxide sol directional deposition and polysilazane-polysiloxane copolymer aging treatment.

[0006] As a preferred, the silicon dioxide is 20-45 parts by weight, the calcium oxide is 10-25 parts by weight, the magnesium oxide is 5-12 parts by weight, the solidified slow-release boron oxide particles are 8-18 parts by weight, the core-shell hollow glass microspheres are 3-10 parts by weight, the sodium oxide is 1-5 parts by weight and the carbon black is 2-8 parts by weight.

[0007] As a preferred, the preparation process of the solidified slow-release boron oxide particles is as follows: Boron oxide and calcium silicate were mixed at a mass ratio of 1:2.0-3.0, a eutectic agent was added, and the mixture was dispersed under nitrogen protection at 175-185℃ for 20-30 minutes to obtain a dispersion. Cool the dispersion to 60-80℃, add 1.0-2.0% organic kaolin by mass of the dispersion, transfer to a ball mill, and ball mill at 500-800 rpm, ball-to-material ratio of 3-5:1, while simultaneously spraying in 0.5-1.0% γ-glycidyl etheroxypropyltrimethoxysilane by mass of the dispersion. Ball mill for 25-35 min to obtain a sheet-coated slurry. Add 12-15% deionized water by mass to the sheet coating slurry, adjust the solid content to 55-60%, and perform hydrothermal curing at 0.3-0.5MPa and 130-150℃ for 45-60 minutes to obtain the cured slurry. The cured slurry is dried first in a vacuum dryer at 80-90℃ and -0.08MPa for 20-30 minutes, and then sprayed into granules in a nitrogen-protected spray dryer with an inlet air temperature of 150-170℃ and an outlet air temperature of 70-80℃ to obtain cured slow-release boron oxide particles.

[0008] Preferably, the eutectic flux is a mixture of pentaerythritol and malic acid in a mass ratio of 6:1, and its addition amount accounts for 1.0-3.0% of the mass of boron oxide.

[0009] Preferably, the preparation steps of the organic kaolin are as follows: Kaolin is dispersed in an ethanol solution of hexadecyltrimethylammonium bromide with a mass concentration of 20-35% at a solid-liquid ratio of 1:10-15, and stirred at 300-500 rpm for 4-6 hours at 60-80℃; after the reaction is completed, vacuum filtration is performed, and the filter cake is washed 2-3 times each with anhydrous ethanol and deionized water; finally, the washed filter cake is vacuum dried at 80-100℃ for 6-8 hours, and after pulverization and sieving, organic kaolin is obtained.

[0010] Preferably, the preparation process of the core-shell hollow glass microspheres is as follows: Hollow glass microspheres were placed in oxygen plasma for 20-120 s, and an ethanol solution of ethyl acetoacetate diisopropyl aluminum was added. The mixture was stirred at 25-45℃ for 10-30 min, then heated to 50-60℃ and held for 5-10 min. After cooling to room temperature, the microspheres were washed 1-2 times with anhydrous ethanol to obtain the treated microspheres. The treated microspheres were dispersed in a sol at a mass ratio of 1:0.08-0.12. After ultrasonic dispersion at 30℃ for 5-10 min, 0.1 mol / L ammonium bicarbonate solution was added dropwise until the pH reached 10.0-10.5. The temperature was raised to 50℃ and aged at 200 rpm for 30-45 min. Subsequently, 0.3-0.5% of polysilazane-polysiloxane block copolymer and 0.05% of dibutyltin dilaurate were added to the sol. The aging was continued at 50℃ under nitrogen protection for 60 min. Finally, the microspheres were centrifuged at 4000-6000 rpm for 5-10 min and vacuum dried at 80℃ for 2 h to obtain core-shell hollow glass microspheres.

[0011] Preferably, the ethanol solution of ethyl acetoacetate diisopropylaluminum has a mass concentration of 0.4-0.6%.

[0012] Preferably, the sol is prepared by mixing an aluminum nitrate solution with a concentration of 0.2 mol / L and a zirconium oxychloride solution with a concentration of 0.02 mol / L.

[0013] As a preferred embodiment, the preparation process of the special protective slag suitable for MCCR process technology is as follows: S1.1 Weigh each raw material according to its weight parts; S1.2 Add silica, calcium oxide and magnesium oxide to a ball mill and ball mill at 300-600 rpm for 10-60 min; then add solidified slow-release boron oxide particles and stir at 100-300 rpm for 5-20 min; add core-shell hollow glass microspheres and mix at 80-150 rpm for 5-15 min; finally add sodium oxide and carbon black and stir at 100-250 rpm for 5-15 min to obtain a homogeneous mixture. S1.3. The mixture is granulated and shaped, and then dried at 105-150℃ for 1-3 hours to obtain a special protective slag suitable for MCCR process technology.

[0014] Preferably, in step S1.3, granulation and shaping are carried out using a disc granulator. At a rotation speed of 20-35 rpm, deionized water accounting for 6-12% of the solid mass is sprayed into the mixture to obtain granules.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: In this invention, a special protective slag suitable for MCCR process technology is constructed by solidifying slow-release boron oxide particles through a low-eutectic mixing-sol-gel dispersion and hydrothermal solidification process. This process constructs a slow-release layer mainly composed of calcium silicate on the surface of boron oxide, achieving gradient release of boron at high temperatures. This effectively avoids the viscosity abrupt change caused by premature melting of traditional boron-containing components, thereby improving the viscosity stability of the slag and enhancing the uniformity and lubrication consistency of the slag film. Simultaneously, core-shell hollow glass microspheres are activated by oxygen plasma and directionally deposited with oxide sol, forming a robust nanocomposite shell on their surface. This shell is then strengthened at high temperature by polysilazane-polysiloxane copolymer, greatly improving the compressive strength and thermal stability of the microspheres. This makes them less prone to cracking and sintering under high-temperature shear, maintaining the thermal insulation performance of the protective slag for a long time and reducing heat loss. Detailed Implementation

[0016] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. 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 of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0017] This invention provides a special protective slag suitable for MCCR process technology, comprising the following raw materials: silica, calcium oxide, magnesium oxide, solidified slow-release boron oxide particles, core-shell hollow glass microspheres, sodium oxide, and carbon black; The solidified slow-release boron oxide particles are prepared by mixing boron oxide and calcium silicate in a eutectic process, followed by sol-gel dispersion, hydrothermal curing, and drying. The core-shell hollow glass microspheres are prepared by activating hollow glass microspheres with oxygen plasma, anchoring with ethyl acetoacetate diisopropylaluminum, directional deposition of oxide sol, and aging treatment of polysilazane-polysiloxane copolymerization.

[0018] Silica (CAS No.: 14808-60-7, purity AR, 99.5%), magnesium oxide (CAS No.: 1309-48-4, purity SP, 98%), boron oxide (CAS No.: 1303-86-2, purity AR, ≥98%), calcium silicate (CAS No.: 1344-95-2, purity CP), γ-glycidoxypropyltrimethoxysilane (CAS No.: 2530-83-8, purity BR, 98%), malic acid (CAS No.: 6915-15-7, purity BR, 99%), kaolin (CAS No.: 1332-58-7, purity CP, item number: S30588-500g), hexadecyltrimethylammonium bromide (CAS No.: 57-09-0, purity AR, 99%), and carbon black (CAS No.: 1333-86-4) were all purchased from Shanghai Yuanye Biotechnology Co., Ltd.

[0019] Calcium oxide (CAS No.: 1305-78-8, purity 99%) was purchased from Shenyang Ketuo Chemical Co., Ltd.

[0020] Hollow glass microspheres (density 0.32-0.60 g / cc) were purchased from Sinosteel Maanshan Mining Institute New Materials Technology Co., Ltd.

[0021] Ethyl acetoacetate diisopropylaluminum (CAS No.: 14782-75-3, purity 99%) was purchased from Hubei Wande Chemical Co., Ltd.

[0022] The preparation steps of polysilazane-polysiloxane block copolymer are as follows: hexamethylcyclotrisiloxane and 2,4,6-trivinyl-2,4,6-trimethylcyclotrisiloxane are mixed in a molar ratio of 1:0.1 and added to a reactor to obtain a mixture. Acidic clay accounting for 1.5% of the mass of the mixture is added as a catalyst, and ring-opening polymerization is carried out at 100°C for 4 hours. Then the temperature is raised to 150°C and vacuum is applied for 1 hour to remove low-boiling substances. After cooling, polysilazane-polysiloxane block copolymer is obtained.

[0023] Hexamethylcyclotrisiloxane (CAS No.: 541-05-9, purity 98%) was purchased from Hubei Jiahuixingcheng Biotechnology Co., Ltd.

[0024] 2,4,6-Trivinyl-2,4,6-trimethylcyclotrisiloxane (CAS No.: 3901-77-7, purity 99%) was purchased from Hubei Xinfu Biotechnology Co., Ltd.

[0025] Dibutyltin dilaurate (CAS No.: 77-58-7, purity AR), sodium oxide (CAS No.: 1313-59-3, purity AR), and acid clay (CAS No.: 1340-68-7, purity AR) were all purchased from Guangdong Wengjiang Chemical Reagent Co., Ltd.

[0026] The preparation steps of organic kaolin are as follows: Kaolin is dispersed in an ethanol solution of 25% hexadecyltrimethylammonium bromide at a solid-liquid ratio of 1:12, and stirred at 400 rpm for 5 h at 60 °C. After the reaction is completed, vacuum filtration is performed, and the filter cake is washed twice each with anhydrous ethanol and deionized water. Finally, the washed filter cake is vacuum dried at 80 °C for 6 h, and after crushing and sieving, organic kaolin is obtained.

[0027] Example 1: A special protective slag suitable for MCCR process technology is prepared through the following steps: S1.1 Weigh the following raw materials in the following weight parts: 20 parts by weight of silicon dioxide, 10 parts by weight of calcium oxide, 5 parts by weight of magnesium oxide, 8 parts by weight of cured slow-release boron oxide particles, 3 parts by weight of core-shell hollow glass microspheres, 1 part by weight of sodium oxide and 2 parts by weight of carbon black. S1.2 Add silica, calcium oxide and magnesium oxide to a ball mill and ball mill at 300 rpm for 10 min; then add solidified slow-release boron oxide particles and stir at 100 rpm for 5 min; add core-shell hollow glass microspheres and mix at 80 rpm for 5 min; finally add sodium oxide and carbon black and stir at 100 rpm for 5 min to obtain a homogeneous mixture. S1.3. The mixture is granulated and shaped using a disc granulator. At a speed of 20 rpm, 6% of deionized water by solid mass is sprayed into the mixture to obtain granules. The granules are then dried at 105℃ for 1 hour to obtain a special protective slag suitable for MCCR process technology.

[0028] The preparation process of solidified slow-release boron oxide particles is as follows: Boron oxide and calcium silicate were mixed at a mass ratio of 1:2.5, and a eutectic agent (composed of pentaerythritol and malic acid at a mass ratio of 6:1, with the amount added accounting for 2.0% of the mass of boron oxide) was added. The mixture was then dispersed at 175°C for 20 min under nitrogen protection to obtain a dispersion. The dispersion was cooled to 60°C, and 1.0% of the organic kaolin by mass of the dispersion was added. The mixture was then transferred to a ball mill and milled at 500 rpm with a ball-to-material ratio of 3:1. Simultaneously, 0.5% of the γ-glycidyl etheroxypropyltrimethoxysilane by mass of the dispersion was sprayed into the mill. The mixture was then ball-milled for 25 min to obtain a sheet-coated slurry. Add 12% deionized water by mass to the sheet coating slurry to adjust the solid content to 55%, and perform hydrothermal curing at 0.3 MPa and 130℃ for 45 min to obtain the cured slurry; The cured slurry was dried first in a vacuum dryer at 80℃ and -0.08MPa for 20 minutes, and then sprayed into granules in a nitrogen-protected spray dryer with an inlet air temperature of 150℃ and an outlet air temperature of 70℃ to obtain cured slow-release boron oxide particles.

[0029] The preparation process of core-shell hollow glass microspheres is as follows: Hollow glass microspheres were treated in oxygen plasma for 20 seconds, and then a 0.4% (w / w) ethanol solution of ethyl acetoacetate diisopropyl aluminum was added. The mixture was stirred at 25°C for 10 minutes, then heated to 50°C and held for 5 minutes. After cooling to room temperature, the microspheres were washed once with anhydrous ethanol to obtain the treated microspheres. A sol was obtained by mixing a 0.2 mol / L aluminum nitrate solution with a 0.02 mol / L zirconium oxychloride solution. The treated microspheres were dispersed in a sol at a mass ratio of 1:0.08. After ultrasonic dispersion at 30℃ for 5 min, 0.1 mol / L ammonium bicarbonate solution was added dropwise until the pH reached 10.0. The temperature was raised to 50℃ and aged at 200 rpm for 30 min. Subsequently, 0.3% of polysilazane-polysiloxane block copolymer and 0.05% of dibutyltin dilaurate were added to the sol, and aging was continued at 50℃ under nitrogen protection for 60 min. Finally, the microspheres were centrifuged at 4000 rpm for 5 min and vacuum dried at 80℃ for 2 h to obtain core-shell hollow glass microspheres.

[0030] Example 2: The difference between this example and Example 1 is that the mass ratio of boron oxide to calcium silicate is 1:2.0.

[0031] Example 3: The difference between this example and Example 1 is that the mass ratio of boron oxide to calcium silicate is 1:3.0.

[0032] Example 4: The difference between this example and Example 1 is that the amount of eutectic flux added accounts for 1.0% of the mass of boron oxide.

[0033] Example 5: The difference between this example and Example 1 is that the amount of eutectic flux added accounts for 3.0% of the mass of boron oxide.

[0034] Determination of the high-temperature sustained-release characteristics of boron oxide: 20 mg of solidified sustained-release boron oxide particles were placed in an alumina crucible; the temperature was increased from room temperature to 1300 °C at a rate of 10 °C / min, similar to the temperature curve in the MCCR crystallizer; the endothermic peaks related to the melting / dissolution of boron oxide were observed on the DSC curve; compared with the sharp, single endothermic peak of pure boron oxide, the endothermic peaks of the sustained-release particles were evaluated to see if they became broadened, flattened, or showed multiple continuous endothermic stages; the broader the peak and the more staged the endothermic stage, the smoother and more controllable the release process; the weight change steps caused by the release of boron oxide and its reaction with surrounding components could be observed on the TG curve, and the rate of change could be analyzed, which could also assess the smoothness of the release.

[0035] Determination of particle shell structure and mechanical strength: The particles were inlaid with epoxy resin and polished to form a cross-section. The particle cross-section was observed, and the average shell thickness was taken after measuring at least 20 particles. The nanoindenter was used to perform indentation tests on the polished particle shell cross-section, which directly reflects the mechanical strength and anti-breakage ability of the shell. The higher these two values ​​are, the more robust the shell is and the more reliable the sustained-release performance is.

[0036] Table 1 Performance data of solidified slow-release boron oxide particles

[0037] Comparing Examples 1, 2, and 3, it can be seen that the mixing ratio of boron oxide and calcium silicate directly affects the thickness and integrity of the slow-release shell.

[0038] As in Example 2 (1:2.0), the calcium silicate was relatively insufficient, resulting in a thinner shell (8.2 μm) and lower hardness (1.9 GPa). Therefore, boron oxide was released prematurely (starting temperature 700°C) and the release range was narrow (250°C), with poor smoothness (5 points).

[0039] Conversely, Example 3 (1:3.0) had the thickest and hardest shell, significantly delayed release, widest range, and best smoothness (9 points).

[0040] Example 1 (1:2.5) achieved a balance, ensuring sufficient sustained release while avoiding release difficulties caused by an excessively thick shell.

[0041] Comparing Examples 1, 4, and 5, it can be seen that the eutectic agent affects the uniformity of the initial dispersion, thereby affecting the quality of the subsequent coating layer.

[0042] Example 4 (addition amount 1.0%) Due to insufficient dispersion, the resulting coating layer is uneven and not dense, with poor shell thickness and hardness, and the sustained release performance is also affected (smoothness 6 points).

[0043] Although Example 5 (3.0% addition) showed improvement, the excessive organic matter introduced structural defects, and its performance was still slightly inferior to Example 1.

[0044] Example 6: A special protective slag suitable for MCCR process technology is prepared through the following steps: S1.1 Weigh the raw materials as follows: 45 parts by weight of silicon dioxide, 25 parts by weight of calcium oxide, 12 parts by weight of magnesium oxide, 18 parts by weight of cured slow-release boron oxide particles, 10 parts by weight of core-shell hollow glass microspheres, 5 parts by weight of sodium oxide and 8 parts by weight of carbon black. S1.2 Add silica, calcium oxide and magnesium oxide to a ball mill and ball mill at 600 rpm for 60 min; then add solidified slow-release boron oxide particles and stir at 300 rpm for 20 min; add core-shell hollow glass microspheres and mix at 150 rpm for 15 min; finally add sodium oxide and carbon black and stir at 250 rpm for 15 min to obtain a homogeneous mixture. S1.3. The mixture is granulated and shaped using a disc granulator. At a speed of 35 rpm, 12% of deionized water by solid mass is sprayed into the mixture to obtain granules. The granules are then dried at 150°C for 3 hours to obtain a special protective slag suitable for MCCR process technology.

[0045] The preparation process of solidified slow-release boron oxide particles is as follows: Boron oxide and calcium silicate were mixed at a mass ratio of 1:2.5, and a eutectic agent (composed of pentaerythritol and malic acid at a mass ratio of 6:1, with the amount added accounting for 2.0% of the mass of boron oxide) was added. The mixture was then dispersed at 185°C for 30 min under nitrogen protection to obtain a dispersion. The dispersion was cooled to 80°C, and 2.0% of the dispersion mass of organic kaolin was added. The mixture was then transferred to a ball mill and milled at 800 rpm with a ball-to-material ratio of 5:1. 1.0% of the dispersion mass of γ-glycidyl oxypropyltrimethoxysilane was sprayed in at the same time. The mixture was then ball-milled for 35 min to obtain a sheet-coated slurry. Add 15% deionized water by mass to the sheet coating slurry to adjust the solid content to 60%, and perform hydrothermal curing at 0.5 MPa and 150℃ for 60 min to obtain the cured slurry; The cured slurry was dried first in a vacuum dryer at 90°C and -0.08MPa for 30 minutes, and then sprayed into granules in a nitrogen-protected spray dryer with an inlet air temperature of 170°C and an outlet air temperature of 80°C to obtain cured slow-release boron oxide particles.

[0046] The preparation process of core-shell hollow glass microspheres is as follows: Hollow glass microspheres were treated in oxygen plasma for 120 s, and then a 0.5% (w / w) ethanol solution of ethyl acetoacetate diisopropyl aluminum was added. The mixture was stirred at 45 °C for 30 min, then heated to 60 °C and held for 10 min. After cooling to room temperature, the microspheres were washed twice with anhydrous ethanol to obtain the treated microspheres. A sol was obtained by mixing a 0.2 mol / L aluminum nitrate solution with a 0.02 mol / L zirconium oxychloride solution. The treated microspheres were dispersed in a sol at a mass ratio of 1:0.12. After ultrasonic dispersion at 30℃ for 10 min, 0.1 mol / L ammonium bicarbonate solution was added dropwise until the pH reached 10.5. The temperature was then raised to 50℃ and aged at 200 rpm for 45 min. Subsequently, 0.4% of polysilazane-polysiloxane block copolymer and 0.05% of dibutyltin dilaurate were added to the sol, and the aging was continued at 50℃ under nitrogen protection for 60 min. Finally, the microspheres were centrifuged at 6000 rpm for 10 min and vacuum dried at 80℃ for 2 h to obtain core-shell hollow glass microspheres.

[0047] Example 7: The difference between this example and Example 6 is that the mass concentration of the ethanol solution of ethyl acetoacetate diisopropyl aluminum is 0.4%.

[0048] Example 8: The difference between this example and Example 6 is that the mass concentration of the ethanol solution of ethyl acetoacetate diisopropyl aluminum is 0.6%.

[0049] Example 9: The difference between this example and Example 6 is that 0.3% of polysilazane-polysiloxane block copolymer by weight of the sol is added.

[0050] Example 10: This example differs from Example 6 in that 0.5% of the sol mass of polysilazane-polysiloxane block copolymer is added.

[0051] Determination of thermal stability and thermal insulation performance: Take a small amount of sample and heat it from room temperature to 1000℃ in an air or nitrogen atmosphere at a certain heating rate of 10℃ / min; analyze the weight change by TG curve to determine the decomposition of organic components and the thermal stability of the material; DSC curve is used to observe thermal effects such as phase transition and crystallization; the treated microspheres can be prepared into a specific shape and combined with the matrix material, and the thermal conductivity can be measured by a thermal constant analyzer.

[0052] Table 2 Performance data of core-shell hollow glass microspheres

[0053] Comparing Examples 6, 7, and 8, it can be seen that the concentration of the ethanol solution of ethyl acetoacetate diisopropylaluminum affects the quality and quantity of the initial anchoring layer, and thus affects the uniformity and integrity of the subsequent oxide sol deposition.

[0054] In Example 7 (0.4%), the low concentration of coupling agent resulted in insufficient anchoring points, leading to the thinnest (82 nm) and lowest hardness (3.5 GPa) deposited shell, resulting in poor thermal stability (weight loss rate of 3.0%). In Example 8 (0.6%), the shell was the thickest, but the high concentration caused the coupling agent molecules to self-aggregate, resulting in a decrease in shell uniformity. The density and hardness were slightly lower than those in Example 6 (0.5%).

[0055] The concentration (0.5%) in Example 6 achieved a balance between shell thickness and structural compactness.

[0056] Comparing Examples 6, 9, and 10, it can be seen that the addition of polysilazane-polysiloxane copolymer forms an inorganic ceramic phase through high-temperature pyrolysis, achieving organic-inorganic hybridization, which is the key to improving the high-temperature stability and mechanical strength of the shell.

[0057] Example 9 (addition amount 0.3%) has insufficient hybridization, resulting in limited strengthening and sealing effects of the shell at high temperatures. Therefore, it has the highest thermal weight loss rate (3.5%) and low hardness. Example 10 (addition amount 0.5%) forms a more complete and denser hybrid structure, exhibiting the best comprehensive performance: the highest hardness (4.5 GPa), the best thermal stability (weight loss rate of only 1.8%), and the best thermal insulation performance (thermal conductivity 0.046 W / m·K).

[0058] Example 11: A special protective slag suitable for MCCR process technology is prepared through the following steps: S1.1 Weigh the following raw materials in the following weight parts: 30 parts by weight of silicon dioxide, 15 parts by weight of calcium oxide, 8 parts by weight of magnesium oxide, 13 parts by weight of cured slow-release boron oxide particles, 6 parts by weight of core-shell hollow glass microspheres, 3 parts by weight of sodium oxide and 4 parts by weight of carbon black. S1.2 Add silica, calcium oxide and magnesium oxide to a ball mill and ball mill at 400 rpm for 40 min; then add solidified slow-release boron oxide particles and stir at 200 rpm for 15 min; add core-shell hollow glass microspheres and mix at 120 rpm for 10 min; finally add sodium oxide and carbon black and stir at 150 rpm for 10 min to obtain a homogeneous mixture. S1.3. The mixture is granulated and shaped using a disc granulator. At a speed of 30 rpm, 10% of the solid mass of deionized water is sprayed into the mixture to obtain granules. The granules are then dried at 120°C for 2 hours to obtain a special protective slag suitable for MCCR process technology.

[0059] The preparation process of solidified slow-release boron oxide particles is as follows: Boron oxide and calcium silicate were mixed at a mass ratio of 1:2.5, and a eutectic agent (composed of pentaerythritol and malic acid at a mass ratio of 6:1, with the amount added accounting for 2.0% of the mass of boron oxide) was added. The mixture was then dispersed at 180°C for 25 min under nitrogen protection to obtain a dispersion. The dispersion was cooled to 70°C, and 1.5% of the organic kaolin by mass of the dispersion was added. The mixture was then transferred to a ball mill and milled at 600 rpm with a ball-to-material ratio of 4:1. Simultaneously, 0.7% of the γ-glycidyl oxypropyltrimethoxysilane by mass of the dispersion was sprayed into the mill. The mixture was then ball-milled for 30 minutes to obtain a sheet-coated slurry. Add 14% deionized water by mass to the sheet coating slurry to adjust the solid content to 60%, and perform hydrothermal curing at 0.4 MPa and 140℃ for 50 min to obtain the cured slurry; The cured slurry was dried first in a vacuum dryer at 85°C and -0.08MPa for 25 minutes, and then sprayed into granules in a nitrogen-protected spray dryer with an inlet air temperature of 160°C and an outlet air temperature of 75°C to obtain cured slow-release boron oxide particles.

[0060] The preparation process of core-shell hollow glass microspheres is as follows: Hollow glass microspheres were treated in oxygen plasma for 80 s, and then a 0.5% (w / w) ethanol solution of ethyl acetoacetate diisopropyl aluminum was added. The mixture was stirred at 30 °C for 20 min, then heated to 55 °C and held for 10 min. After cooling to room temperature, the microspheres were washed twice with anhydrous ethanol to obtain the treated microspheres. A sol was obtained by mixing a 0.2 mol / L aluminum nitrate solution with a 0.02 mol / L zirconium oxychloride solution. The treated microspheres were dispersed in a sol at a mass ratio of 1:0.10. After ultrasonic dispersion at 30℃ for 10 min, 0.1 mol / L ammonium bicarbonate solution was added dropwise until the pH reached 10.0. The temperature was raised to 50℃ and aged at 200 rpm for 40 min. Subsequently, 0.4% of polysilazane-polysiloxane block copolymer and 0.05% of dibutyltin dilaurate were added to the sol, and the aging was continued at 50℃ under nitrogen protection for 60 min. Finally, the microspheres were centrifuged at 5000 rpm for 10 min and vacuum dried at 80℃ for 2 h to obtain core-shell hollow glass microspheres.

[0061] Example 12: The difference between this example and Example 11 is that 8 parts by weight of solidified slow-release boron oxide particles are used.

[0062] Example 13: The difference between this example and Example 11 is that 18 parts by weight of solidified slow-release boron oxide particles are used.

[0063] Example 14: The difference between this example and Example 11 is that the core-shell hollow glass microspheres are used in 3 parts by weight.

[0064] Example 15: The difference between this example and Example 11 is that 10 parts by weight of core-shell hollow glass microspheres are used.

[0065] Procedure for determining high-temperature viscosity (1350℃): Take 5g of protective slag sample and place it in a platinum crucible; under nitrogen protection, heat to 1350℃ at 10℃ / min and hold for 10min; use a rotor to measure the viscosity at a shear rate of 10s⁻¹, repeat 3 times and take the average value (unit: Pa·s).

[0066] The procedure for determining melting temperature (melting point) is as follows: Press the sample into a Φ3mm×3mm cylinder, dry it, and place it in a high-temperature microscope furnace; increase the temperature at 10℃ / min and record the changes in the sample shape: initial deformation temperature (T1), hemispherical temperature (T2, defined as melting temperature), and flow temperature (T3); use T2 as the melting temperature (unit: ℃).

[0067] Method and steps for determining thermal conductivity (room temperature): After granulation of the protective slag, press it into a disc with a diameter of 10 mm and a thickness of 2 mm; at room temperature, measure the thermal diffusivity using the laser scintillation method, and calculate the thermal conductivity (unit: W / m·K) by combining the specific heat capacity and density.

[0068] Table 3 Performance data of special protective slags applicable to MCCR process technology

[0069] Comparing Examples 11, 12, and 13, it can be seen that when the amount of solidified slow-release boron oxide particles added increases from 8 parts (Example 12) to 18 parts (Example 13), the high-temperature viscosity decreases from 0.07 Pa·s to 0.03 Pa·s, and the melting temperature decreases from 1080°C to 1020°C. This is because boron oxide, as a network forger, reduces the viscosity and melting point of the slag when its release increases. Example 13 (18 parts) has too low viscosity (0.03 Pa·s), which will lead to excessive lubrication and too thin slag film, increasing the risk of steel leakage; Example 12 (8 parts) has high viscosity and melting point, which can easily cause viscosity adjustment lag.

[0070] Comparing Examples 11, 14, and 15, it can be seen that when the amount of core-shell hollow glass microspheres added increases from 3 parts (Example 14) to 10 parts (Example 15), the thermal conductivity decreases from 0.08 W / m·K to 0.04 W / m·K, indicating a significant improvement in thermal insulation performance; this is because the microsphere shell structure enhances thermal resistance.

[0071] Example 15 (10 parts) has a low thermal conductivity (0.04 W / m·K) which solves the problem of thermal insulation attenuation, but if the amount added is too high, attention should be paid to the uniformity of dispersion; Example 14 (3 parts) has poor thermal insulation, which will lead to increased heat loss in the crystallizer.

[0072] Example 11 is within the optimized range in terms of viscosity (0.05 Pa·s), melting temperature (1050 °C), and thermal insulation (0.06 W / m·K), which meets the requirements of MCCR process for rapid response and stability.

[0073] Based on the above measurements, Example 11 is selected as the optimal example. Comparative Example 1: The difference between this example and Example 11 is that no cured slow-release boron oxide particles and core-shell hollow glass microspheres were added.

[0074] Comparative Example 2: The difference between this example and Example 11 is that ordinary boron oxide powder is used instead of solidified slow-release boron oxide particles.

[0075] The difference between this embodiment and embodiment 11 is that ordinary hollow glass microspheres are used instead of core-shell hollow glass microspheres.

[0076] Table 4 Performance data of special protective slag applicable to MCCR process technology

[0077] Compared with Example 11, the performance of Comparative Example 1 (non-functional particles) failed to meet the requirements in all aspects: high viscosity (0.12), high melting point (1150℃), and poor thermal insulation (0.13). This fully demonstrates that without solidified slow-release boron oxide particles and core-shell hollow glass microspheres, the traditional basic formulation cannot meet the basic requirements of MCCR process for rapid melting, good lubrication and efficient thermal insulation.

[0078] Compared to Example 11, Comparative Example 2 (using ordinary boron oxide) exhibited severe performance instability: ordinary boron oxide melted rapidly in the early stages of heating, which significantly reduced the melting temperature of the protective slag (980°C), but its premature and concentrated release led to inhomogeneity of the melt structure; under high-temperature (1350°C) test conditions, it triggered the precipitation of local high-melting-point phases (such as high-silicon regions) or melt phase separation, causing the high-temperature viscosity to rise abnormally to 0.09 Pa·s, accompanied by fluctuations during the measurement process, verifying the lag and instability of viscosity adjustment; in contrast, Example 11 used solidified slow-release boron oxide particles, which released boron elements through a gradient, avoiding drastic changes in structure, and thus obtained a stable and suitable high-temperature viscosity (0.05 Pa·s) while maintaining a lower melting temperature (1050°C).

[0079] The thermal conductivity of Comparative Example 3 (using ordinary hollow glass microspheres instead of modified core-shell hollow glass microspheres) (0.11 W / m·K) was significantly higher than that of Example 11 (0.06 W / m·K), indicating a severe deterioration in its thermal insulation performance. This was mainly due to the structural instability, cracking, and sintering of the ordinary hollow glass microspheres at high temperatures. In contrast, the stable thermal insulation of Example 11 indicates that the special shell modification process endowed the microspheres with excellent thermal stability, thereby providing a long-lasting and reliable thermal insulation guarantee.

[0080] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely preferred examples and are not intended to limit the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A special protective slag suitable for MCCR process technology, characterized in that, The raw materials include: silicon dioxide, calcium oxide, magnesium oxide, solidified slow-release boron oxide particles, core-shell hollow glass microspheres, sodium oxide and carbon black; The solidified slow-release boron oxide particles are prepared by mixing boron oxide and calcium silicate through eutectic mixing, then dispersing through sol-gel, hydrothermal solidification and drying; The core-shell hollow glass microspheres are prepared by activating hollow glass microspheres through oxygen plasma, anchoring with ethyl acetoacetate diisopropyl aluminum, directional deposition of oxide sol and aging treatment of polysilazane-polysiloxane copolymer.

2. A special protective flux suitable for MCCR process technology as claimed in claim 1, wherein, The silicon dioxide is 20-45 parts by weight, the calcium oxide is 10-25 parts by weight, the magnesium oxide is 5-12 parts by weight, the solidified slow-release boron oxide particles are 8-18 parts by weight, the core-shell hollow glass microspheres are 3-10 parts by weight, the sodium oxide is 1-5 parts by weight and the carbon black is 2-8 parts by weight.

3. A special protective flux suitable for MCCR process technology as claimed in claim 2, wherein, The preparation process of the solidified slow-release boron oxide particles is as follows: The boron oxide and calcium silicate are mixed in a mass ratio of 1:2.0-3.0, a eutectic agent is added, and the mixture is dispersed at 175-185°C for 20-30 min under nitrogen protection to obtain a dispersion; The dispersion is cooled to 60-80°C, 1.0-2.0% of the mass of the dispersion of organically modified kaolin is added, and the mixture is transferred to a ball mill, which is treated by ball milling at 500-800 rpm, a ball-to-material ratio of 3-5:1, and 0.5-1.0% of γ-glycidyl ether propyltrimethoxysilane based on the mass of the dispersion is sprayed at the same time, and the mixture is treated by ball milling for 25-35 min to obtain a layer-coated slurry; Deionized water accounting for 12-15% of the mass of the layer-coated slurry is added to adjust the solid content to 55-60%, and the mixture is hydrothermally solidified at 0.3-0.5 MPa and 130-150°C for 45-60 min to obtain a solidified slurry; The solidified slurry is dried in a vacuum dryer at 80-90°C and -0.08 MPa for 20-30 min, and then granulated in a nitrogen-protected spray dryer, with an inlet air temperature of 150-170°C and an outlet air temperature of 70-80°C, to obtain the solidified slow-release boron oxide particles.

4. A special protective flux suitable for MCCR process technology as claimed in claim 3, wherein, The eutectic agent is prepared by mixing pentaerythritol and malic acid in a mass ratio of 6:1, and the addition amount is 1.0-3.0% of the mass of the boron oxide.

5. A special protective flux suitable for MCCR process technology as claimed in claim 3, wherein, The preparation steps of the organically modified kaolin are as follows: kaolin is dispersed in a 20-35% mass concentration of cetyltrimethylammonium bromide ethanol solution at a solid-to-liquid ratio of 1:10-15, and stirred at 300-500 rpm at 60-80°C for 4-6 h; after the reaction is completed, vacuum filtration is performed, and the filter cake is washed with absolute ethanol and deionized water for 2-3 times respectively; finally, the washed filter cake is vacuum dried at 80-100°C for 6-8 h, crushed and sieved to obtain the organically modified kaolin.

6. A special protective flux suitable for MCCR process technology as claimed in claim 2, wherein, The preparation process of the core-shell hollow glass microspheres is as follows: The hollow glass microspheres are placed in an oxygen plasma for 20-120s, an ethyl acetoacetate diisopropyl aluminum ethanol solution is added, stirring is carried out at 25-45℃ for 10-30min, then the temperature is increased to 50-60℃ for 5-10min, cooling to room temperature, and washing with anhydrous ethanol for 1-2 times, to obtain the treated microspheres; The treated microspheres are dispersed in a sol at a mass ratio of 1:0.08-0.12, ultrasonic dispersion is carried out at 30℃ for 5-10min, then 0.1mol / L ammonium bicarbonate solution is added dropwise until the pH is 10.0-10.5, the temperature is increased to 50℃, and aging is carried out at 200rpm for 30-45min; then 0.3-0.5% of a polysilazane-polysiloxane block copolymer and 0.05% of dibutyltin dilaurate are added, and the aging is continued at 50℃ under nitrogen protection for 60min; finally, centrifugation is carried out at a speed of 4000-6000rpm for 5-10min, and vacuum drying is carried out at 80℃ for 2h, to obtain the core-shell hollow glass microspheres.

7. A special protective flux suitable for MCCR process technology as claimed in claim 6, wherein, The mass concentration of the ethyl acetoacetate diisopropyl aluminum ethanol solution is 0.4-0.6%.

8. A special protective flux suitable for MCCR process technology as claimed in claim 6, wherein, The sol is prepared by mixing an aluminum nitrate solution with a concentration of 0.2mol / L and a zirconyl chloride solution with a concentration of 0.02mol / L.

9. A special protective flux suitable for MCCR process technology as claimed in claim 2, wherein, The preparation process of the special protective slag suitable for the MCCR process technology is as follows: S1.1, each raw material is weighed by parts by weight; S1.2, the silica, calcium oxide and magnesium oxide are added into a ball mill, and ball milling is carried out at a speed of 300-600rpm for 10-60min; then the solidified slow-release boron oxide particles are added, and stirring is carried out at 100-300rpm for 5-20min; the core-shell hollow glass microspheres are added, and mixing is carried out at a speed of 80-150rpm for 5-15min; finally, the sodium oxide and carbon black are added, and stirring is carried out at 100-250rpm for 5-15min, to obtain a uniform mixture; S1.3, the mixture is granulated and shaped, and then dried at 105-150℃ for 1-3h, to obtain the special protective slag suitable for the MCCR process technology.

10. A special protective flux suitable for MCCR process technology as claimed in claim 9, wherein, In S1.3, the granulation and shaping are carried out by a disc granulator, and 6-12% of deionized water based on the mass of the solid is sprayed into the mixture at a speed of 20-35rpm, to obtain granules.

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