A magnesium-based coating for tundish and a preparation method thereof

Abstract

The application relates to the technical field of basic coating, in particular to a magnesium coating for a tundish and a preparation method thereof, which is composed of the following components: high-purity fused magnesite, sintered magnesite fine powder, active alpha-alumina micro powder, modified calcium aluminate cement, calcium carbonate, calcium lignosulfonate, citric acid, sodium hexametaphosphate, metallic aluminum powder and nano zirconium oxide; the comprehensive performance of the basic coating liquid is improved through reasonable formula optimization and improvement; the core problem of the performance deficiency of a traditional binding agent is solved from the aspect of interface combination through modification treatment of the calcium aluminate cement. Due to the four-step modification process of pretreatment, composite modification solution coating, nano magnesium oxide enhancement and vacuum drying ball milling, the cement water content is controlled to be less than or equal to 0.5% through drying, so that the excessive generation of pores in the hydration process is avoided.

Description

Technical Field

[0001] This invention relates to the field of alkaline coatings technology, specifically to a magnesium-based coating for intermediate packaging and its preparation method. Background Technology

[0002] In continuous casting production in iron and steel metallurgy, the tundish is a key piece of equipment connecting the ladle and the crystallizer. Its main functions include stabilizing molten steel flow, homogenizing the composition and temperature of the molten steel, and filtering inclusions. Its inner lining directly contacts molten steel and slag at temperatures exceeding 1500℃, requiring excellent high-temperature resistance, slag erosion resistance, room-temperature mechanical strength, and good workability. Magnesia-based coatings, rich in magnesium oxide, exhibit good chemical stability against alkaline components (such as CaO) in steel slag, making them one of the mainstream materials for tundish inner linings. In particular, they must meet the performance requirements for alkaline coatings used in tundishes as stipulated in the "Standard for Ferrous Metallurgy Industry of the People's Republic of China" (YB / T4121-2018).

[0003] As the steel industry develops towards higher efficiency and higher quality, the continuous casting cycle is extended (the service time of tundishes in some steel plants has reached more than 8 hours) and the temperature fluctuation range of molten steel is expanded, which puts forward higher requirements for the performance of magnesium coatings: on the one hand, it is necessary to ensure that the total MgO content of the coating is high enough to resist the corrosion of acidic components in steel slag and avoid the formation of low-melting-point magnesium olivine which would cause the lining to peel off; on the other hand, it is necessary to improve the room temperature mechanical properties of the coating to cope with the application pressure during construction and the scouring of molten steel during service, while controlling the permanent linear changes at high temperature to prevent the lining from cracking and leaking steel.

[0004] These problems restrict the operational stability of the tundish and the efficiency of continuous casting, requiring a magnesium coating technology that can balance high MgO content, excellent mechanical properties, high-temperature stability and workability. Summary of the Invention

[0005] The purpose of this invention is to provide a magnesium coating for intermediate packaging.

[0006] To achieve the above objectives, the present invention provides the following technical solution: A magnesium-based coating for intermediate packaging comprises the following components in parts by weight: 60-75 parts of high-purity fused magnesia, 10-18 parts of sintered magnesia fine powder, 3-8 parts of active α-alumina micro powder, 4-9 parts of modified calcium aluminate cement, 1-3 parts of calcium carbonate, 0.2-0.8 parts of calcium lignosulfonate, 0.1-0.5 parts of citric acid, 0.1-0.5 parts of sodium hexametaphosphate, 0.05-0.2 parts of metallic aluminum powder, and 0.5-2 parts of nano-zirconia; The total MgO content of the coating is ≥86%.

[0007] As a further technical solution, the high-purity fused magnesia has an MgO content ≥96% and a particle size of 5-10 mm; the sintered magnesia fine powder has an MgO content ≥92% and a particle size of 0.074-1 mm; the active α-alumina micro powder has a particle size ≤1 μm; the calcium carbonate and aluminum powder both have a particle size ≤0.074 mm; and the nano-zirconia has a particle size of 10-30 nm.

[0008] As a further technical solution, the preparation method of the modified calcium aluminate cement includes the following steps: S1 Pretreatment: Take ordinary CA-50 calcium aluminate cement, place it in a forced-air drying oven, dry at 80-100℃ for 4-6 hours, and control the cement moisture content to ≤0.5%; Preparation of S2 composite modified solution: Mix silane coupling agent with anhydrous ethanol at a mass ratio of 1:30-50, and stir magnetically for 10-15 min to prepare a silane coupling agent ethanol solution with a concentration of 1-3 wt%; add polyethylene glycol to the solution, wherein the amount of polyethylene glycol added is 5-6% of the mass of silane coupling agent, and continue stirring for 5-8 min to obtain the composite modified solution; S3 Gradient Coating: Add the dried calcium aluminate cement powder from step S1 to a high-speed mixer and stir at 1000-1200 rpm. While stirring, add the composite modification solution dropwise at a rate of 6-8 mL / min. After the addition is complete, maintain the stirring speed for 20-30 min. Then add nano-magnesium oxide with a particle size of 20-50 nm, the amount of which is 2-5% of the mass of the calcium aluminate cement. Increase the speed to 1500-2000 rpm and stir for 30-40 min to obtain a mixture. S4 Post-processing: Place the mixture from step S3 in a vacuum drying oven at 120-150℃ and dry for 8-10 hours, then grind it with a planetary ball mill until the particle size is ≤0.074mm to obtain modified calcium aluminate cement.

[0009] As a further technical solution, the polyethylene glycol in step S2 has a molecular weight of 400-600.

[0010] As a further technical solution, the silane coupling agent in step S2 is KH-550.

[0011] As a further technical solution, the vacuum degree inside the vacuum drying oven in step S4 is ≤-0.09MPa.

[0012] As a further technical solution, the ball-to-material ratio for grinding in the planetary ball mill described in step S4 is 3:1; The grinding speed of the planetary ball mill is 200-300 rpm.

[0013] As a further technical solution, the coating is applied to a thickness of 50-80mm when used for coating the inner wall of the intermediate tundish, and to a thickness of 40-60mm when used for spraying.

[0014] A method for preparing magnesium-based coatings for intermediate ladles includes the following steps: (1) Ingredients: Weigh each ingredient according to the weight parts; (2) Aggregate gradation mixing: Add high-purity fused magnesia and sintered magnesia fine powder to a twin-shaft mixer and stir at 500-800 rpm for 10-15 min at room temperature, controlling the bulk density of the mixed aggregate to be ≥1.8 g / cm³. 3 ; (3) Micro powder synergistic dispersion: Add active α-alumina micro powder, calcium carbonate, metallic aluminum powder and nano zirconium oxide to the mixture in step (2), adjust the speed to 800-1000 rpm, stir for 15-20 min, and control the micro powder agglomeration particle size ≤5μm; (4) Additive-binder fusion: Add modified calcium aluminate cement, calcium lignosulfonate, citric acid and sodium hexametaphosphate, and stir at 1200-1500 rpm for 25-35 min to form a dry powder mixture; (5) Slurry preparation and aging: Add 5-8wt% deionized water to the dry powder mixture and stir at 300-500rpm for 10-15min to prepare a workable slurry with a viscosity of 500-800mPa·s; then age to obtain magnesium coating for intermediate packaging.

[0015] As a further technical solution, the aging temperature is 20-25℃ and the aging time is 10-20min.

[0016] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention improves the overall performance of alkaline coating liquid through reasonable formula optimization and improvement. By modifying calcium aluminate cement, this invention solves the core problem of insufficient performance of traditional binders at the interfacial bonding level. The four-step modification process—pretreatment, composite modification solution coating, nano-magnesium oxide reinforcement, and vacuum drying and ball milling—firstly, by controlling the cement moisture content to ≤0.5% through drying, excessive porosity during hydration is avoided. Secondly, a compound solution of silane coupling agent KH-550 and polyethylene glycol is used to form an organic-inorganic transition layer on the surface of cement particles, improving the interfacial compatibility between cement and magnesium aggregate, and reducing particle agglomeration through the lubricating effect of polyethylene glycol. Thirdly, gradient coating with nano-magnesium oxide utilizes the high specific surface area of ​​nanoparticles to form a rigid support layer, enhancing the deformation resistance of the cement matrix. Finally, vacuum drying and ball milling ensure the uniform dispersion of the modified cement. The synergistic effect of this series of modification steps improves the interfacial bonding strength between modified cement and magnesium aggregate compared to ordinary cement, thereby increasing the bulk density of the coating after drying and improving its compressive strength at room temperature. At the same time, it inhibits the shrinkage of the cement phase at high temperatures, and controls the permanent linear change during heating to within -2.2%, effectively solving the problems of high-temperature cracking and insufficient mechanical strength caused by the loose structure of the binder in traditional coatings.

[0017] 2. This invention optimizes the gradation of magnesia aggregate and the micro-powder system to construct a highly dense and slag-resistant microstructure, fundamentally improving the coating's resistance to slag erosion. By selecting high-purity fused magnesia with MgO content ≥96% and sintered magnesia fine powder with MgO content ≥92% in a weight ratio, and controlling the bulk density of the mixed aggregate through stirring, the total MgO content of the coating is ensured to remain stable at ≥86%, while the close packing of coarse and fine aggregates reduces macroscopic voids. Simultaneously, the addition of active α-alumina micro-powder fills the micro-voids between the aggregates; the magnesia-alumina spinel formed by its reaction with the magnesia phase effectively hinders the penetration of silica from steel slag. Nano-zirconia further enhances structural stability by inhibiting the crystal transformation of magnesia at high temperatures, preventing the volume expansion caused by the transformation from cubic to monoclinic phase. The oxidation of metallic aluminum powder at high temperatures to form alumina compensates for the slight shrinkage of the coating. Detailed Implementation

[0018] 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.

[0019] This invention provides a magnesium coating for tundishes and its preparation method. The coating achieves a total MgO content of ≥86% while maintaining excellent room temperature mechanical properties and high temperature volume stability through specific component ratios and modification processes. Its preparation process solves the problems of easy cracking and poor slag resistance of traditional magnesium coatings through stepwise processes of aggregate gradation, micro powder dispersion, and additive fusion. It is especially suitable for tundish inner wall coating (application thickness 50-80mm) and spraying (application thickness 40-60mm) scenarios.

[0020] The specific raw materials include: High-purity fused magnesia: industrial-grade product with MgO content ≥96%, particle size controlled at 5-10mm, commercially available; Sintered magnesia fine powder: MgO content ≥92%, particle size 0.074-1mm, commercially available; Activated α-alumina micro powder: particle size ≤1μm, specific surface area ≥30m² / g, commercially available; Ordinary CA-50 type calcium aluminate cement: industrial grade, Al2O3 content 50-55%, commercially available; Calcium carbonate: analytical grade, particle size ≤0.074mm, commercially available; Calcium lignosulfonate: Industrial grade, purity ≥90%, commercially available as a water-reducing agent; Citric acid and sodium hexametaphosphate: both are industrial grade, with a purity of ≥98%, and are commercially available as retarder and dispersant. Aluminum powder: Industrial grade, particle size ≤0.074mm, purity ≥99%, commercially available; Nano-zirconia: Particle size 10-30nm, purity ≥99.5%, commercially available; Silane coupling agent KH-550: Industrial grade, purity ≥98%, commercially available; Polyethylene glycol: molecular weight 400-600, industrial grade, commercially available; Nano magnesium oxide: Particle size 20-50nm, purity ≥99%, commercially available.

[0021] The preparation methods of modified calcium aluminate cement include: Step S1: Preprocessing: Take ordinary CA-50 type calcium aluminate cement, place it in a forced-air drying oven, and dry it at 80-100℃ for 4-6 hours. Control the cement moisture content to ≤0.5% by weighing after drying.

[0022] Step S2: Preparation of composite modified solution: Mix silane coupling agent KH-550 with anhydrous ethanol at a mass ratio of 1:30-50, and stir in a magnetic stirrer for 10-15 minutes to prepare a silane coupling agent ethanol solution with a concentration of 1-3 wt%. Add polyethylene glycol (5-6% of the mass of silane coupling agent) to the solution and continue stirring for 5-8 minutes until the solution is homogeneous and transparent to obtain a composite modified solution.

[0023] Step S3: Gradient wrapping: Add the dried calcium aluminate cement powder from step S1 to a high-speed mixer and stir at 1000-1200 rpm. While stirring, add the composite modification solution dropwise through a constant pressure dropping funnel at a rate of 6-8 mL / min. After the addition is complete, maintain the stirring speed and continue stirring for 20-30 min. Then add nano magnesium oxide (2-5% of the mass of calcium aluminate cement) to the mixer, increase the speed to 1500-2000 rpm, and stir at high speed for 30-40 min to obtain a uniformly coated mixture.

[0024] Step S4: Post-processing: Place the mixture from step S3 in a vacuum drying oven, control the vacuum degree to ≤-0.09MPa and the temperature to 120-150℃, and dry for 8-10 hours. After drying, transfer the material to a planetary ball mill, add agate grinding balls at a ball-to-material ratio of 3:1, and grind at a speed of 200-300rpm for 1-2 hours. Finally, control the particle size of the ground material to ≤0.074mm to obtain modified calcium aluminate cement.

[0025] The preparation method of magnesium-based coating for intermediate treasury includes: Step (1) Ingredients: Weigh out 60-75 parts by weight of high-purity fused magnesia, 10-18 parts of sintered magnesia fine powder, 3-8 parts of active α-alumina micro powder, 4-9 parts of modified calcium aluminate cement, 1-3 parts of calcium carbonate, 0.2-0.8 parts of calcium lignosulfonate, 0.1-0.5 parts of citric acid, 0.1-0.5 parts of sodium hexametaphosphate, 0.05-0.2 parts of metallic aluminum powder, and 0.5-2 parts of nano-zirconia. Detect the total MgO content using X-ray fluorescence spectrometry to ensure that the total MgO content is ≥86%.

[0026] Step (2) Aggregate gradation mixing: Weigh out the high-purity fused magnesia and sintered magnesia powder and add them to a twin-shaft mixer. Stir at 500-800 rpm for 10-15 minutes at room temperature. Measure the bulk density of the mixed aggregate using a bulk density tester, and control the bulk density to ≥1.8 g / cm³. 3 .

[0027] Step (3) Co-dispersion of micro powders: Add active α-alumina micro powder, calcium carbonate, metallic aluminum powder and nano-zirconia to the mixed aggregate obtained in step (2), adjust the speed of the mixer to 800-1000 rpm and stir for 15-20 min; measure the agglomeration particle size of the micro powder by laser particle size analyzer and control the agglomeration particle size ≤5μm.

[0028] Step (4) Additive-Binder Fusion: Add modified calcium aluminate cement, calcium lignosulfonate, citric acid and sodium hexametaphosphate to the mixture in step (3), increase the speed of the mixer to 1200-1500 rpm, and stir for 25-35 minutes to form a uniform dry powder mixture.

[0029] Step (5) Preparation and Aging: Add 5-8 wt% deionized water to the dry powder mixture, reduce the mixer speed to 300-500 rpm, and stir for 10-15 min; measure the viscosity of the slurry using a rotational viscometer and control the viscosity to 500-800 mPa·s; then transfer the slurry to a sealed container and age it at 20-25℃ for 10-20 min to obtain a workable magnesium coating for intermediate packaging.

[0030] The following are specific examples: Example 1: Preparation of modified calcium aluminate cement: Step S1: Preprocessing: Ordinary CA-50 type calcium aluminate cement was placed in a forced-air drying oven and dried at 90℃ for 5 hours. The moisture content of the cement was found to be 0.35% by weighing after drying.

[0031] Step S2: Preparation of composite modified solution: Mix silane coupling agent KH-550 with anhydrous ethanol at a mass ratio of 1:40, and stir in a magnetic stirrer for 12 minutes to prepare a 2wt% silane coupling agent ethanol solution. Add polyethylene glycol (5.5% of the mass of silane coupling agent KH-550, with a molecular weight of 500) to the solution and continue stirring for 6 minutes until the solution is homogeneous and transparent to obtain the composite modified solution.

[0032] Step S3: Gradient wrapping: Add the dried calcium aluminate cement powder from step S1 to a high-speed mixer and stir at 1100 rpm. While stirring, add the composite modification solution dropwise through a constant pressure dropping funnel at a dropping rate of 7 mL / min. After the addition is complete, continue stirring at 1100 rpm for 25 min. Then add nano magnesium oxide (3% of the mass of calcium aluminate cement, with a particle size of 30 nm) to the mixer, increase the speed to 1800 rpm, and stir at high speed for 35 min to obtain a uniformly coated mixture.

[0033] Step S4: Post-processing: The mixture from step S3 was placed in a vacuum drying oven, and the vacuum degree was controlled at -0.095MPa and the temperature at 130℃ for 9 hours. After drying, the material was transferred to a planetary ball mill, and agate grinding balls were added at a ball-to-material ratio of 3:1. The mixture was ground at a speed of 250rpm, and the particle size of the ground material was finally controlled to be 0.06mm to obtain modified calcium aluminate cement.

[0034] The preparation of magnesium coating for intermediate treasury includes: Step (1) Ingredients: Weigh the following components by weight: 65 parts high-purity fused magnesia (MgO content 97% ≥ 96%, particle size 5-8 mm), 15 parts sintered magnesia fine powder (MgO content 93% ≥ 92%, particle size 0.1-0.8 mm), 5 parts active α-alumina micro powder (particle size 0.8 μm), 6 parts modified calcium aluminate cement, 2 parts calcium carbonate (particle size 0.06 mm), 0.5 parts calcium lignosulfonate, 0.3 parts citric acid, 0.3 parts sodium hexametaphosphate, 0.1 parts metallic aluminum powder (particle size 0.05 mm), and 1 part nano-zirconia (particle size 20 nm).

[0035] Step (2) Aggregate gradation mixing: The weighed high-purity fused magnesia and sintered magnesia powder were added to a twin-shaft mixer and stirred at 700 rpm for 12 minutes at room temperature. The bulk density of the mixed aggregate was measured to be 1.9 g / cm³. 3 .

[0036] Step (3) Co-dispersion of micro powders: Add active α-alumina micro powder, calcium carbonate, metallic aluminum powder and nano-zirconia to the mixed aggregate obtained in step (2), adjust the speed of the mixer to 900 rpm and stir for 18 min; the particle size of the micro powder agglomerates is 4 μm as determined by laser particle size analyzer.

[0037] Step (4) Additive-Binder Fusion: Add modified calcium aluminate cement, calcium lignosulfonate, citric acid and sodium hexametaphosphate to the mixture in step (3), increase the speed of the mixer to 1300 rpm and stir for 30 minutes to form a uniform dry powder mixture.

[0038] Step (5) Preparation and Aging: Add 6 wt% deionized water to the dry powder mixture, reduce the mixer speed to 400 rpm, and stir for 12 min; the viscosity of the slurry is measured to be 650 mPa·s by rotational viscometer; then transfer the slurry to a sealed container and age it at 22°C for 15 min to obtain an application-ready magnesium coating for intermediate packaging.

[0039] Example 2: Preparation of modified calcium aluminate cement: Step S1: Preprocessing: Ordinary CA-50 type calcium aluminate cement was placed in a forced-air drying oven and dried at 85℃ for 4.5 hours. The moisture content of the cement was found to be 0.3% by weighing after drying.

[0040] Step S2: Preparation of composite modified solution: Mix silane coupling agent KH-550 with anhydrous ethanol at a mass ratio of 1:35, and stir in a magnetic stirrer for 10 minutes to prepare a silane coupling agent ethanol solution with a concentration of 1.8 wt%. Add polyethylene glycol (5% of the mass of silane coupling agent KH-550, with a molecular weight of 400) to the solution and continue stirring for 5 minutes until the solution is homogeneous and transparent to obtain the composite modified solution.

[0041] Step S3: Gradient wrapping: Add the dried calcium aluminate cement powder from step S1 to a high-speed mixer and stir at 1000 rpm. While stirring, add the composite modification solution dropwise through a constant pressure dropping funnel at a dropping rate of 6.5 mL / min. After the addition is complete, continue stirring at 1000 rpm for 22 min. Then add nano magnesium oxide (2.5% of the mass of calcium aluminate cement, with a particle size of 25 nm) to the mixer, increase the speed to 1600 rpm, and stir at high speed for 32 min to obtain a uniformly coated mixture.

[0042] Step S4: Post-processing: The mixture from step S3 was placed in a vacuum drying oven, and the vacuum degree was controlled at -0.092 MPa and the temperature at 125°C for 8.5 hours. After drying, the material was transferred to a planetary ball mill, and agate grinding balls were added at a ball-to-material ratio of 3:1. The mixture was ground at a speed of 220 rpm, and the particle size of the ground material was finally controlled to be 0.07 mm to obtain modified calcium aluminate cement.

[0043] The preparation method of magnesium coating for intermediate treasury includes: Step (1) Ingredients: Weigh the following components by weight: 60 parts of high-purity fused magnesia (MgO content 96.5% ≥ 96%, particle size 5-9 mm), 18 parts of sintered magnesia fine powder (MgO content 92.5% ≥ 92%, particle size 0.074-0.9 mm), 8 parts of active α-alumina micro powder (particle size 0.9 μm), 9 parts of modified calcium aluminate cement, 3 parts of calcium carbonate (particle size 0.07 mm), 0.8 parts of calcium lignosulfonate, 0.5 parts of citric acid, 0.5 parts of sodium hexametaphosphate, 0.2 parts of metallic aluminum powder (particle size 0.07 mm), and 2 parts of nano-zirconia (particle size 30 nm).

[0044] Step (2) Aggregate gradation mixing: The weighed high-purity fused magnesia and sintered magnesia powder were added to a twin-shaft mixer and stirred at 500 rpm for 15 minutes at room temperature. The bulk density of the mixed aggregate was measured to be 1.85 g / cm³. 3 .

[0045] Step (3) Co-dispersion of micro powders: Add active α-alumina micro powder, calcium carbonate, metallic aluminum powder and nano-zirconia to the mixed aggregate obtained in step (2), adjust the speed of the mixer to 800 rpm and stir for 20 min; the particle size of the micro powder agglomeration is 4.5 μm as determined by laser particle size analyzer.

[0046] Step (4) Additive-Binder Fusion: Add modified calcium aluminate cement, calcium lignosulfonate, citric acid and sodium hexametaphosphate to the mixture in step (3), increase the speed of the mixer to 1200 rpm and stir for 35 minutes to form a uniform dry powder mixture.

[0047] Step (5) Preparation and Aging: Add 8 wt% deionized water to the dry powder mixture, reduce the mixer speed to 300 rpm, and stir for 15 min; the viscosity of the slurry is measured to be 750 mPa·s by rotational viscometer; then transfer the slurry to a sealed container and age it at 25°C for 20 min to obtain an application-ready magnesium coating for intermediate packaging.

[0048] Example 3: Preparation of modified calcium aluminate cement: Step S1: Preprocessing: Ordinary CA-50 type calcium aluminate cement was placed in a forced-air drying oven and dried at 95℃ for 5.5 hours. The moisture content of the cement was found to be 0.4% by weighing after drying.

[0049] Step S2: Preparation of composite modified solution: Mix silane coupling agent KH-550 with anhydrous ethanol at a mass ratio of 1:45, and stir in a magnetic stirrer for 15 minutes to prepare a 2.5 wt% silane coupling agent ethanol solution. Add polyethylene glycol (6% of the mass of silane coupling agent KH-550, with a molecular weight of 600) to the solution and continue stirring for 8 minutes until the solution is homogeneous and transparent to obtain the composite modified solution.

[0050] Step S3: Gradient wrapping: Add the dried calcium aluminate cement powder from step S1 to a high-speed mixer and stir at 1200 rpm. While stirring, add the composite modification solution dropwise through a constant pressure dropping funnel at a dropping rate of 7.5 mL / min. After the addition is complete, continue stirring at 1200 rpm for 28 min. Then add nano magnesium oxide (4% of the mass of calcium aluminate cement, with a particle size of 40 nm) to the mixer, increase the speed to 1900 rpm, and stir at high speed for 38 min to obtain a uniformly coated mixture.

[0051] Step S4: Post-processing: The mixture from step S3 was placed in a vacuum drying oven, and the vacuum degree was controlled at -0.098 MPa and the temperature at 140℃ for 9.5 h. After drying, the material was transferred to a planetary ball mill, and agate grinding balls were added at a ball-to-material ratio of 3:1. The mill was then ground at a speed of 280 rpm, and the particle size of the ground material was finally controlled to be 0.05 mm (≤0.074 mm) to obtain modified calcium aluminate cement.

[0052] The preparation method of magnesium coating for intermediate treasury includes: Step (1) Ingredients: Weigh the following components by weight: 75 parts high-purity fused magnesia (MgO content 98% ≥ 96%, particle size 8-10 mm), 10 parts sintered magnesia fine powder (MgO content 93.5% ≥ 92%, particle size 0.5-1 mm), 3 parts active α-alumina micro powder (particle size 0.7 μm), 4 parts modified calcium aluminate cement, 1 part calcium carbonate (particle size 0.065 mm), 0.2 parts calcium lignosulfonate, 0.1 parts citric acid, 0.1 parts sodium hexametaphosphate, 0.05 parts metallic aluminum powder (particle size 0.06 mm), and 0.5 parts nano zirconium oxide (particle size 15 nm).

[0053] Step (2) Aggregate gradation mixing: The weighed high-purity fused magnesia and sintered magnesia powder were added to a twin-shaft mixer and stirred at 800 rpm for 10 minutes at room temperature. The bulk density of the mixed aggregate was measured to be 2.0 g / cm³. 3 .

[0054] Step (3) Co-dispersion of micro powders: Add active α-alumina micro powder, calcium carbonate, metallic aluminum powder and nano-zirconia to the mixed aggregate obtained in step (2), adjust the speed of the mixer to 1000 rpm and stir for 15 min; the particle size of the micro powder agglomerates is 3.5 μm as determined by laser particle size analyzer.

[0055] Step (4) Additive-Binder Fusion: Add modified calcium aluminate cement, calcium lignosulfonate, citric acid and sodium hexametaphosphate to the mixture in step (3), increase the speed of the mixer to 1500 rpm and stir for 25 minutes to form a uniform dry powder mixture.

[0056] Step (5) Preparation and Aging: Add 5 wt% deionized water to the dry powder mixture, reduce the mixer speed to 500 rpm, and stir for 10 min; the viscosity of the slurry is measured to be 550 mPa·s by a rotational viscometer; then transfer the slurry to a sealed container and age it at 20°C for 10 min to obtain an application-ready magnesium coating for intermediate packaging.

[0057] Example 4: Preparation of modified calcium aluminate cement: Step S1: Preprocessing: Ordinary CA-50 type calcium aluminate cement was placed in a forced-air drying oven and dried at 100℃ for 6 hours. The moisture content of the cement was found to be 0.38% by weighing after drying.

[0058] Step S2: Preparation of composite modified solution: Silane coupling agent KH-550 and anhydrous ethanol were mixed at a mass ratio of 1:30 and stirred in a magnetic stirrer for 13 minutes to prepare a 3 wt% silane coupling agent ethanol solution. Polyethylene glycol (5.2% of the mass of silane coupling agent KH-550 and a molecular weight of 450) was added to the solution and stirred for another 7 minutes until the solution was homogeneous and transparent to obtain the composite modified solution.

[0059] Step S3: Gradient wrapping: Add the dried calcium aluminate cement powder from step S1 to a high-speed mixer and stir at 1150 rpm. While stirring, add the composite modification solution dropwise through a constant pressure dropping funnel at a dropping rate of 6 mL / min. After the addition is complete, continue stirring at 1150 rpm for 24 min. Then add nano magnesium oxide (3.5% of the mass of calcium aluminate cement, with a particle size of 20 nm) to the mixer, increase the speed to 1700 rpm, and stir at high speed for 34 min to obtain a uniformly coated mixture.

[0060] Step S4: Post-processing: The mixture from step S3 was placed in a vacuum drying oven, and the vacuum degree was controlled at -0.096MPa and the temperature at 135℃ for 8 hours. After drying, the material was transferred to a planetary ball mill, and agate grinding balls were added at a ball-to-material ratio of 3:1. The mixture was ground at a speed of 240rpm, and the particle size of the ground material was finally controlled to be 0.065mm to obtain modified calcium aluminate cement.

[0061] The preparation method of magnesium coating for intermediate treasury includes: Step (1) Ingredients: Weigh the following components by weight: 70 parts high-purity fused magnesia (MgO content 97.5% ≥ 96%, particle size 6-9 mm), 12 parts sintered magnesia fine powder (MgO content 93% ≥ 92%, particle size 0.2-0.8 mm), 6 parts active α-alumina micro powder (particle size 0.6 μm), 7 parts modified calcium aluminate cement, 1.5 parts calcium carbonate (particle size 0.068 mm), 0.6 parts calcium lignosulfonate, 0.2 parts citric acid, 0.2 parts sodium hexametaphosphate, 0.08 parts metallic aluminum powder (particle size 0.065 mm), and 1.5 parts nano-zirconia (particle size 25 nm).

[0062] Step (2) Aggregate gradation mixing: The weighed high-purity fused magnesia and sintered magnesia powder were added to a twin-shaft mixer and stirred at 600 rpm for 14 minutes at room temperature. The bulk density of the mixed aggregate was measured to be 1.88 g / cm³. 3 .

[0063] Step (3) Co-dispersion of micro powders: Add active α-alumina micro powder, calcium carbonate, metallic aluminum powder and nano-zirconia to the mixed aggregate obtained in step (2), adjust the speed of the mixer to 950 rpm and stir for 17 min; the particle size of the micro powder agglomerates is 4.2 μm as determined by laser particle size analyzer.

[0064] Step (4) Additive-Binder Fusion: Add modified calcium aluminate cement, calcium lignosulfonate, citric acid and sodium hexametaphosphate to the mixture in step (3), increase the speed of the mixer to 1400 rpm and stir for 32 minutes to form a uniform dry powder mixture.

[0065] Step (5) Preparation and Aging: Add 7wt% deionized water to the dry powder mixture, reduce the mixer speed to 450rpm, and stir for 13min; the viscosity of the slurry is measured to be 680mPa·s by rotational viscometer; then transfer the slurry to a sealed container and age it at 23℃ for 18min to obtain an application-ready magnesium coating for intermediate packs.

[0066] Comparative Example 1: Same as Example 1, except that "6 parts of modified calcium aluminate cement" was replaced with "6 parts of ordinary CA-50 calcium aluminate cement", and no modification treatment was performed.

[0067] Comparative Example 2: Same as Example 1, except that “5 parts of active α-alumina micro powder” and “1 part of nano-zirconia” were removed.

[0068] Comparative Example 3: Same as Example 1, except that "adding nano-magnesium oxide" was removed from step S3 of the modified calcium aluminate cement preparation process, while the other steps remained unchanged.

[0069] test: Bulk density, room temperature compressive strength, and permanent linear change under heating test; Test method: Sample preparation: The coatings of the examples and comparative examples were molded according to GB / T4513.5 (vibration time 45s, curing at 20℃ for 24h) to make 40mm×40mm×40mm samples; Bulk density: determined according to GB / T4513.6 (after drying at 110℃ for 24h); Compressive strength at room temperature: determined according to GB / T4513.6 (after drying at 110℃ for 24 hours); Permanent linear change during heating: determined according to GB / T4513.6 (1500℃×3h, cooled with furnace); results are as follows: Table 1 Example 1 2.2 5.5 -2.0 Example 2 2.15 5.2 -2.2 Example 3 2.25 5.8 -1.8 Example 4 2.22 5.6 -1.9 Comparative Example 1 1.9 3.2 -3.2 Comparative Example 2 1.85 3.0 -3.5 Comparative Example 3 2.0 4.0 -2.8 As shown in Table 1, the performance of the examples is significantly better than that of the comparative examples: the bulk density of the examples is ≥2.15 g / cm³. 3 The compressive strength at room temperature is ≥5.2MPa, and the permanent linear change upon heating is ≥-2.2%. Due to the synergistic effect of modified cement, α-alumina, nano-zirconia and other components and the process, the structural density and high-temperature stability are improved. Comparative Example 1: Ordinary CA-50 cement without silane coupling agent interface modification and nano-magnesium oxide reinforcement has weak bonding force, resulting in low density and strength, and large high-temperature shrinkage. Comparative Example 2 lacks α-alumina (to fill micro-voids) and nano-zirconia (to inhibit high-temperature crystal transformation), resulting in a loose structure and intensified high-temperature shrinkage. Comparative Example 3 modified cement lacked nano-magnesium oxide, and the coating layer lacked rigid support, resulting in decreased interfacial bonding strength and weakened strength and volume stability.

[0070] Room temperature flexural strength and workability testing; Test method: Flexural strength at room temperature: determined according to GB / T4513.6 (after drying at 110℃ for 24h, three-point bending method, span 100mm, loading rate 5mm / min); Workability: Evaluation was conducted based on application smoothness (manual application, no noticeable jamming is considered acceptable) and 1-hour water retention (tested according to GB / T27907, water retention rate ≥85% is considered acceptable). The results are as follows: Table 2 Example 1 2.8 Pass 92 Example 2 2.6 Pass 90 Example 3 3.0 Pass 93 Example 4 2.9 Pass 91 Comparative Example 1 1.5 Pass 82 Comparative Example 2 1.4 Choking 80 Comparative Example 3 2.0 Pass 88 As can be seen from Table 2, the overall performance of the example is excellent: the flexural strength at room temperature is ≥2.6MPa, the workability is qualified, the smoothness and water retention are good, and the components work together to enhance the structural strength while ensuring the dispersibility and water retention of the slurry. Comparative Example 1: Ordinary cement has weak interfacial bonding, insufficient flexural strength, poor water retention, rapid cement hydration, and easy water loss. Comparative Example 2 showed no dispersion effect from α-alumina and nano-zirconia, resulting in severe slurry agglomeration and application difficulties; poor water retention was also due to the lack of micro-powder, preventing the formation of a continuous water-retaining network. Comparative Example 3: The modified cement without nano-magnesium oxide showed decreased interfacial bonding strength and weakened flexural properties.

[0071] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0072] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A magnesium-based coating for intermediate packaging, characterized in that, It is composed of the following components in parts by weight: 60-75 parts of high-purity fused magnesia, 10-18 parts of sintered magnesia fine powder, 3-8 parts of active α-alumina micro powder, 4-9 parts of modified calcium aluminate cement, 1-3 parts of calcium carbonate, 0.2-0.8 parts of calcium lignosulfonate, 0.1-0.5 parts of citric acid, 0.1-0.5 parts of sodium hexametaphosphate, 0.05-0.2 parts of metallic aluminum powder, and 0.5-2 parts of nano-zirconia; The total MgO content of the coating is ≥86%.

2. The magnesium-based coating for intermediate ladles according to claim 1, characterized in that, The high-purity fused magnesia has an MgO content ≥96% and a particle size of 5-10 mm; the sintered magnesia fine powder has an MgO content ≥92% and a particle size of 0.074-1 mm; the active α-alumina micro powder has a particle size ≤1 μm; the calcium carbonate and aluminum powder both have a particle size ≤0.074 mm; and the nano-zirconia has a particle size of 10-30 nm.

3. The magnesium coating for intermediate ladles according to claim 1, characterized in that, The preparation method of the modified calcium aluminate cement includes the following steps: S1 Pretreatment: Take ordinary CA-50 calcium aluminate cement, place it in a forced-air drying oven, dry at 80-100℃ for 4-6 hours, and control the cement moisture content to ≤0.5%; Preparation of S2 composite modified solution: Mix silane coupling agent with anhydrous ethanol at a mass ratio of 1:30-50, and stir magnetically for 10-15 min to prepare a silane coupling agent ethanol solution with a concentration of 1-3 wt%; add polyethylene glycol to the solution, wherein the amount of polyethylene glycol added is 5-6% of the mass of silane coupling agent, and continue stirring for 5-8 min to obtain the composite modified solution; S3 Gradient Coating: Add the dried calcium aluminate cement powder from step S1 to a high-speed mixer and stir at 1000-1200 rpm. While stirring, add the composite modification solution dropwise at a rate of 6-8 mL / min. After the addition is complete, maintain the stirring speed for 20-30 min. Then add nano-magnesium oxide with a particle size of 20-50 nm, the amount of which is 2-5% of the mass of the calcium aluminate cement. Increase the speed to 1500-2000 rpm and stir for 30-40 min to obtain a mixture. S4 Post-processing: Place the mixture from step S3 in a vacuum drying oven at 120-150℃ and dry for 8-10 hours, then grind it with a planetary ball mill until the particle size is ≤0.074mm to obtain modified calcium aluminate cement.

4. The magnesium-based coating for intermediate ladles according to claim 1, characterized in that, The polyethylene glycol mentioned in step S2 has a molecular weight of 400-600.

5. The magnesium coating for intermediate ladles according to claim 1, characterized in that, The silane coupling agent in step S2 is KH-550.

6. The magnesium coating for intermediate ladles according to claim 1, characterized in that, The vacuum degree inside the vacuum drying oven in step S4 is ≤-0.09MPa.

7. The magnesium coating for intermediate ladles according to claim 1, characterized in that, In step S4, the ball-to-material ratio in the planetary ball mill is 3:

1. The grinding speed of the planetary ball mill is 200-300 rpm.

8. The magnesium coating for intermediate ladles according to claim 1, characterized in that, When the coating is used for trowel inner wall application, the thickness is 50-80mm; when used for spraying, the thickness is 40-60mm.

9. A method for preparing a magnesium-based coating for intermediate packaging as described in any one of claims 1-8, characterized in that, Includes the following steps: (1) Ingredients: Weigh each ingredient according to the weight parts; (2) Aggregate gradation mixing: Add high-purity fused magnesia and sintered magnesia fine powder to a twin-shaft mixer and stir at 500-800 rpm for 10-15 min at room temperature, controlling the bulk density of the mixed aggregate to be ≥1.8 g / cm³. 3 ; (3) Micro powder synergistic dispersion: Add active α-alumina micro powder, calcium carbonate, metallic aluminum powder and nano zirconium oxide to the mixture in step (2), adjust the speed to 800-1000 rpm, stir for 15-20 min, and control the micro powder agglomeration particle size ≤5μm; (4) Additive-binder fusion: Add modified calcium aluminate cement, calcium lignosulfonate, citric acid and sodium hexametaphosphate, and stir at 1200-1500 rpm for 25-35 min to form a dry powder mixture; (5) Slurry preparation and aging: Add 5-8wt% deionized water to the dry powder mixture and stir at 300-500rpm for 10-15min to prepare a workable slurry with a viscosity of 500-800mPa·s; then age to obtain magnesium coating for intermediate packaging.

10. The method for preparing magnesium-based coating for intermediate ladles according to claim 9, characterized in that, The aging temperature is 20-25℃, and the aging time is 10-20 minutes.