Ceramic precursor composite magnesia-carbon refractory brick and method for producing the same

Abstract

This invention provides a ceramic precursor composite magnesia-carbon refractory brick and its preparation method, belonging to the field of refractory materials technology. The raw materials for the refractory brick include magnesia aggregate, double-modified flake graphite, a medium-temperature ceramic precursor, modified phenolic resin, and SiO2-B4C-La2O3 composite powder. The double-modified flake graphite is prepared by using flake graphite as a matrix, activating it with hydrochloric acid, coating it with aluminum sol, and then sintering it to form an Al2O3@graphite core-shell structure. It is then precipitated with triisopropyl borate and aluminum isopropoxide under alkaline conditions and sintered. The medium-temperature ceramic precursor is prepared by using boric acid and basic magnesium carbonate as raw materials, crosslinking them with aluminum phosphate aqueous solution to form a sol, drying, and sintering. The modified phenolic resin is prepared by using a methyl phenolic resin as the main chain, synergistically modified with 1,6-hexanediol and polyglycerol-10 isostearate, and then hydrolyzing and condensing it with tetrabutyl titanate and γ-aminopropyltriethoxysilane.

Description

Technical Field

[0001] This invention belongs to the field of ceramic refractory materials technology, specifically relating to a ceramic precursor composite magnesia-carbon refractory brick and its preparation method. Background Technology

[0002] Magnesia-carbon refractory bricks are a type of refractory material made from magnesium oxide as aggregate, graphite as carbonaceous component, organic resin as binder, and with the addition of a small amount of metal or non-metal additives. Due to their excellent high-temperature strength, slag erosion resistance and thermal shock stability, they are widely used in key high-temperature parts of steel metallurgy such as converters, electric furnaces, ladle slag lines, and refining furnaces. They are an indispensable functional structural material in modern high-temperature industries.

[0003] The main raw material system of existing traditional magnesia-carbon refractory bricks includes: fused magnesia or sintered magnesia as the main aggregate and matrix powder, whose main component is magnesium oxide (MgO), which has a high melting point, high chemical stability, and good refractoriness; flake graphite as a carbon source, which has the characteristics of not being wetted by molten steel and slag, high thermal conductivity, and low coefficient of thermal expansion, which can significantly improve the material's thermal shock resistance and slag penetration resistance; phenolic resin as a binder, which solidifies at low temperatures to form a carbon-bonded structure, providing the brick with molding strength and mid-temperature strength; at the same time, aluminum powder, silicon powder, borides, etc. are often added as antioxidants to inhibit the oxidation and burn-off of carbon components at high temperatures. During service, magnesia-carbon refractory bricks rely on the high-temperature stability of the magnesium oxide skeleton and the synergistic effect of the non-wetting properties of graphite to resist molten slag, high-temperature gas flow, and thermal shock. However, under the combined conditions of long-term high temperature, oxidation, erosion, and chemical corrosion, traditional magnesia-carbon refractory bricks still have a number of insurmountable complex technical problems, which seriously restrict their service life and application range.

[0004] First, the poor interfacial bonding between aggregates and the carbon matrix is ​​the most prominent defect. Magnesia is a polar hydrophilic oxide, while graphite is a non-polar hydrophobic material. The significant difference in surface energy and poor wettability between the two makes it difficult to form a tight, continuous interfacial bond during mixing, molding, and curing, easily leading to primary interfacial pores and microcracks. Under high temperature and thermal cycling, these weak interfaces easily expand, causing the brick to experience decreased strength, loose structure, and even spalling failure. Second, phenolic resin undergoes pyrolysis and weight loss during heating, weakening the bonding structure and affecting subsequent service performance. It is prone to thermal stress cracking and reduced mechanical properties. Third, the carbon phase is easily oxidized and decarburized, causing rapid structural deterioration. In an oxidizing atmosphere, graphite and bound carbon undergo an oxidation reaction to generate CO or CO2, forming a loose, porous decarburized layer on the brick surface. This decarburized layer not only loses its slag resistance but also accelerates slag penetration and erosion, leading to layered spalling and significantly shortening service life.

[0005] A system relying solely on graphite, magnesia, and simple antioxidants cannot simultaneously resolve the complex contradictions of weak interfacial bonding, poor oxidation resistance, and limited thermal shock stability and slag erosion resistance, making it difficult to meet the stringent requirements of current high-efficiency, long-life, and clean smelting processes. Therefore, to address the key technical challenges of existing magnesia-carbon refractory bricks, such as poor interfacial bonding, easy oxidation and decarburization, and insufficient thermal shock resistance, it is urgent to develop a composite magnesia-carbon refractory brick with optimized structure, strengthened interface, and synergistic effects of multiple components, thereby improving the overall performance of the material. Summary of the Invention

[0006] To address the aforementioned technical problems of existing magnesia-carbon refractory bricks, this invention provides a ceramic precursor composite magnesia-carbon refractory brick and its preparation method. Through graphite dual modification, in-situ synthesis of ceramic precursors, hybrid modification of resin binders, and synergistic structural optimization and interface strengthening design using multi-component antioxidant powders, this invention fundamentally solves the core problems of traditional magnesia-carbon bricks, such as poor interfacial bonding, easy oxidation and decarburization, strength collapse due to resin pyrolysis weight loss, and insufficient thermal shock stability and slag erosion resistance, effectively improving the service performance of the brick. The specific technical solution is as follows:

[0007] A ceramic precursor composite magnesia-carbon refractory brick, characterized in that, by mass parts, it comprises the following raw materials: 68-72 parts of magnesia aggregate, 7-9 parts of double-modified flake graphite, 4-6 parts of medium-temperature ceramic precursor, 4.5-5.5 parts of modified phenolic resin, and 5-6 parts of SiO2-B4C-La2O3 composite powder.

[0008] The double-modified flake graphite is prepared by using flake graphite as a matrix, which is activated by hydrochloric acid, coated with aluminum sol, and then sintered at 300℃~400℃, 600℃~700℃, and 900℃~1000℃ to form an Al2O3@graphite core-shell structure. Then, after precipitation of triisopropyl borate and aluminum isopropoxide under alkaline conditions, it is sintered at 550℃~600℃ to achieve a second coating modification to obtain Al2O3-boron aluminum compound double-coated flake graphite, i.e., double-modified flake graphite.

[0009] The medium-temperature ceramic precursor is prepared by using boric acid and basic magnesium carbonate as raw materials, cross-linking with aluminum phosphate aqueous solution to form a sol, and then drying and sintering at 350℃~380℃ to obtain magnesium boron aluminum phosphorus multi-element inorganic amorphous-microcrystalline composite ceramic powder, namely medium-temperature ceramic precursor.

[0010] The modified phenolic resin is prepared by using a methyl phenolic resin as the main chain, which is synergistically modified with 1,6-hexanediol and polyglycerol-10 isostearate, and then hydrolyzed and condensed with tetrabutyl titanate and γ-aminopropyltriethoxysilane to obtain a titanium-silicon-organic-inorganic hybrid crosslinked modified phenolic resin, i.e., modified phenolic resin.

[0011] Furthermore, the magnesia aggregate comprises fused magnesia and lightly calcined magnesia in a mass ratio of (80-85):(15-20).

[0012] Furthermore, the gradation of the fused magnesia is as follows: 3 < particle size ≤ 5 mm accounts for 25wt% to 30wt%, 1 < particle size ≤ 3 mm accounts for 20wt% to 25wt%, 0.1 < particle size ≤ 1 mm accounts for 15wt% to 20wt%, and particle size < 0.074 mm accounts for 10wt% to 15wt%.

[0013] Furthermore, the particle size of the lightly calcined magnesia is <0.074 mm.

[0014] Furthermore, the preparation of the dual-modified flake graphite includes: adding activated graphite to aluminum sol, stirring and dispersing, and removing water by vacuum evaporation; sintering at 300℃~400℃ for 1h~1.5h, 600℃~700℃ for 2h~2.5h, and 900℃~1000℃ for 1h~1.5h under nitrogen protection, and cooling to obtain Al2O3@graphite; adding Al2O3@graphite to anhydrous ethanol, stirring and dispersing, adding dropwise anhydrous ethanol solution containing triisopropyl borate and aluminum isopropoxide, adjusting the pH to 9.0~9.4 with ammonia, adding urea and stirring to react, filtering, drying, sintering at 550℃~600℃ for 2h~2.5h under nitrogen protection, cooling, and sieving to obtain dual-modified flake graphite.

[0015] Furthermore, the preparation of the dual-modified flake graphite includes: adding activated graphite to aluminum sol at a solid-liquid mass ratio of 1:(5-6), stirring and dispersing, and removing water by vacuum evaporation; sintering at 300℃-400℃ for 1-1.5h, 600℃-700℃ for 2-2.5h, and 900℃-1000℃ for 1-1.5h under nitrogen protection, followed by cooling to obtain Al2O3@graphite; adding anhydrous ethanol to Al2O3@graphite at a solid-liquid mass ratio of 1:(8-10), stirring and dispersing, and then adding 1 part by mass of Al2O3@graphite dropwise. Anhydrous ethanol solution containing 0.42 mol / L to 0.48 mol / L triisopropyl borate and 0.20 mol / L to 0.25 mol / L aluminum isopropoxide was added at 5 to 2 times the amount of the graphite. The mixture was stirred at 45 to 50°C, and the pH was adjusted to 9.0 to 9.4 with 1 mol / L to 2 mol / L ammonia. Urea (6% to 8% by weight of Al2O3@graphite) was added and stirred. The mixture was filtered, dried, and sintered at 550 to 600°C for 2 to 2.5 hours under nitrogen protection. After cooling, the mixture was passed through a 200-250 mesh sieve to obtain double-modified flake graphite.

[0016] Furthermore, the preparation of the activated graphite includes: adding flake graphite to 10wt% to 12wt% hydrochloric acid at a solid-liquid mass ratio of 1:(5-6), stirring, filtering, washing with deionized water to pH 6.0 to 6.8, filtering, drying, breaking up, and passing through a 200-250 mesh sieve to obtain activated graphite.

[0017] Furthermore, the preparation of the aluminum sol includes: mixing aluminum isopropoxide and deionized water at a mass ratio of 1:(80-90), adjusting the pH to 3.5-4.0 with 1mol / L-1.5mol / L nitric acid, and stirring to hydrolyze to obtain aluminum sol.

[0018] Furthermore, the preparation of the intermediate-temperature ceramic precursor includes: adding boric acid and basic magnesium carbonate in a mass ratio of 1:(0.25-0.3) to deionized water, stirring and dispersing evenly, adding dropwise 15%-20% of the total mass of boric acid and basic magnesium carbonate in a 0.5mol / L-0.6mol / L aluminum phosphate aqueous solution, stirring to form a sol, drying under reduced pressure, sintering at 350℃-380℃ for 2h-2.5h under nitrogen protection, cooling, pulverizing, and passing through a 200-250 mesh sieve to obtain the intermediate-temperature ceramic precursor.

[0019] Furthermore, the preparation of the modified phenolic resin includes: phenol, 37wt% formaldehyde aqueous solution, ethylene glycol, triethanolamine, 1,6-hexanediol, polyglycerol-10 isostearate, tetrabutyl titanate, and γ-aminopropyltriethoxysilane in a mass ratio of (180-220):(250-300):(15-25):(5-10):(1.5-2):(0.8-1.2):(10-15):(5-8); first, phenol and 37wt% formaldehyde... An aqueous solution, ethylene glycol, and triethanolamine were mixed and reacted at 75℃~80℃ to obtain a methyl phenolic resin prepolymer. 1,6-hexanediol and polyglycerol-10 isostearate diluted with anhydrous ethanol were added at 60℃~65℃ and stirred to disperse. Tetrabutyl titanate and γ-aminopropyltriethoxysilane were added at 50℃~55℃. The pH was adjusted to 4.5~5.0 with glacial acetic acid, and the mixture was stirred to hydrolyze and condense. The mixture was then evaporated under reduced pressure to a solid content of 80wt%~85wt% and cooled to obtain the modified phenolic resin.

[0020] Furthermore, the preparation of the SiO2-B4C-La2O3 composite powder includes: mixing B4C and La2O3 at a mass ratio of 2:(0.7-1.3) to obtain a mixed powder; adding 10%-15% by weight of silica sol to the mixed powder, wet mixing, drying, crushing and dispersing, sintering at 800℃-900℃ for 1-1.5 hours under nitrogen protection, pulverizing, and passing through a 200-250 mesh sieve to obtain the SiO2-B4C-La2O3 composite powder.

[0021] The preparation method of the above-mentioned ceramic precursor composite magnesia-carbon refractory brick includes the following steps:

[0022] S1: Add the double-modified flake graphite, medium-temperature ceramic precursor, and SiO2-B4C-La2O3 composite powder to a mixer and premix them evenly to obtain a premixed matrix powder.

[0023] S2: Add magnesia aggregate to a wet mill, add 50wt% to 60wt% of modified phenolic resin and mix evenly; add premixed matrix powder and the remaining modified phenolic resin, and mix evenly; during the mixing process, add anhydrous ethanol to adjust the humidity to obtain mud.

[0024] S3: The clay is sealed and trapped for 12-15 hours, then pressed into brick blanks at a pressure of 160-180 MPa, and dried at 180-220℃ for 10-15 hours to obtain refractory bricks.

[0025] The present invention provides a ceramic precursor composite magnesia-carbon refractory brick and its preparation method, which have the following beneficial effects:

[0026] I. The composite magnesia-carbon refractory brick of this invention fundamentally solves the core problems of traditional magnesia-carbon bricks, such as poor interfacial bonding, easy oxidation and decarburization, strength collapse due to resin pyrolysis weight loss, and insufficient thermal shock stability and slag erosion resistance, through graphite double modification, in-situ synthesis of ceramic precursors, hybrid modification of resin binders, and synergistic structural optimization and interface strengthening design of multi-component antioxidant powder. It achieves a comprehensive improvement in brick density and mechanical strength, while significantly enhancing its resistance to oxidation, thermal shock, and slag erosion.

[0027] II. In the preparation of double-modified flake graphite, flake graphite is activated with hydrochloric acid to introduce surface active sites, and then sintered stepwise to form an Al2O3-boron aluminum compound double-coated core-shell structure. This transforms the nonpolar hydrophobic surface of graphite into a polar hydrophilic surface, significantly reducing the interfacial energy difference with magnesia, improving wettability and interfacial bonding strength, and reducing primary porosity and microcracks. The double coating layer preferentially oxidizes at high temperature to form a dense glassy phase, blocking oxygen diffusion and protecting the internal graphite. At the same time, it buffers the thermal expansion mismatch between graphite and magnesia, reducing the probability of thermal shock crack initiation. During the preparation process, parameters such as staged sintering temperature, solid-liquid ratio, and pH value ensure the uniformity, continuity, and strong bonding of the coating layer, avoiding cracking and failure of the coating layer.

[0028] III. In the preparation of medium-temperature ceramic precursors, the magnesium-boron-aluminum-phosphorus multi-element amorphous-microcrystalline composite ceramic powder, prepared by cross-linking with aluminum phosphate aqueous solution and low-temperature sintering using boric acid and basic magnesium carbonate as raw materials, can undergo in-situ reaction to generate a continuous ceramic network in the critical region of resin pyrolysis weight loss. This network forms an organic-inorganic composite bond structure with the carbon from resin pyrolysis, rapidly filling the pores and structurally weak areas generated by resin pyrolysis. This fundamentally solves the strength collapse problem of traditional non-fired magnesia-carbon bricks during heating, providing stable strength support for the brick body and improving structural stability under thermal cycling. The raw material ratio, sintering temperature, and sol concentration parameters during the preparation process ensure the reactivity and in-situ network-forming ability of the ceramic precursor.

[0029] IV. In the preparation of modified phenolic resin, the main chain is methyl phenolic resin, which is synergistically modified with polyols and esters. Then, a Ti-O-Si organic-inorganic hybrid crosslinking network is formed by hydrolysis and condensation of tetrabutyl titanate and silane coupling agent. This significantly improves the pyrolysis residual carbon rate and crosslinking density of the resin, and reduces pyrolysis defects and porosity. At the same time, the resin can form chemical bonds with magnesia, double-modified graphite and ceramic precursors, strengthen the continuity of multiphase interface bonding, and improve the mechanical strength and structural integrity of the brick at room temperature and high temperature.

[0030] The rational addition of 1,6-hexanediol and polyglycerol-10 isostearate forms a synergistic modification system for flexibility, toughening, dispersion, and wetting, achieving comprehensive optimization from molecular structure, interfacial bonding, pyrolysis performance to the overall performance of the brick. 1,6-hexanediol reduces resin brittleness, buffers thermal stress, prevents microcrack initiation, and increases brick density. Polyglycerol-10 isostearate reduces resin surface tension, enhances the resin's wetting and coating ability on various solid phases, and prevents the aggregation of titanium-silicon coupling agents, ensuring the uniform formation of the hybrid crosslinking network. 1,6-hexanediol achieves flexible bridging between the organic resin and the inorganic titanium-silicon phase, while polyglycerol-10 isostearate anchors the resin and solid phases at the interface through its hydrophilic and hydrophobic ends, strengthening the continuity of multiphase interfacial chemical bonding. The two work synergistically to increase resin crosslinking density and pyrolysis residual carbon rate, resulting in a dense and continuous residual carbon structure. This structure interweaves with the ceramic network generated in situ from the ceramic precursor to form a carbon-ceramic composite structure, mitigating strength collapse during heating.

[0031] V. In the SiO2-B4C-La2O3 composite powder, the glassy phase generated by the high-temperature reaction seals the pores and oxidation channels of the brick body, inhibiting the internal diffusion of oxygen and the oxidation of carbon. Rare earth La2O3 increases the viscosity and high-temperature stability of the glassy phase, preventing its loss at high temperatures. Simultaneously, it refines grains and purifies grain boundaries, enhancing the high-temperature strength and thermal shock stability of the brick body. These three elements synergistically achieve a dual effect of anti-oxidation and high-temperature reinforcement, significantly reducing carbon oxidation weight loss, inhibiting the formation of a decarburized layer, and improving resistance to slag erosion. The sintering temperature and the amount of silica sol added during the preparation process ensure the dispersibility and synergistic efficiency of the composite powder.

[0032] VI. In magnesia aggregate, highly stable fused magnesia and highly reactive light-burned magnesia are compounded in a specific mass ratio and gradation, and combined with graded particle size design to achieve dense packing of aggregates and improve the density of bricks; the micro powder properties of light-burned magnesia can fill the gaps of fused magnesia, and at the same time, it can react weakly with other components to further strengthen the interfacial bonding, reduce thermal expansion mismatch stress, and improve the dimensional stability and structural uniformity of bricks.

[0033] VII. In the mixed preparation method, modified phenolic resin is added in steps. First, magnesia aggregate is mixed with a portion of the modified phenolic resin to uniformly coat the aggregate surface with a resin layer. Then, premixed matrix powder and the remaining resin are added to achieve uniform bonding between the aggregate and matrix, avoiding uneven bonding caused by excessive or insufficient resin in certain areas. Anhydrous ethanol is added during the mixing process to adjust the humidity, control the plasticity of the clay, and ensure the molding effect. The clay is sealed and conditioned for 12-15 hours to allow the resin to fully penetrate and diffuse between the aggregate and matrix, further eliminating internal stress generated during mixing, improving the uniformity and moldability of the clay, and reducing internal micro-cracks in the molded brick blank. Medium-temperature drying at 180℃-220℃ for 10-15 hours allows the modified phenolic resin to slowly cure, avoiding resin cracking and brick deformation caused by rapid drying, and ensuring the structural integrity and density of the brick blank.

[0034] In summary, the polar surface of the double-modified graphite in the refractory brick of this invention achieves a tight bond with the magnesia aggregate. The modified phenolic resin acts as a bridge to achieve chemical bonding with graphite, magnesia, and ceramic precursors. The ceramic network fills the pyrolysis pores of the resin. Together, these three components construct a continuous, dense, and robust multiphase interface structure, fundamentally solving the problem of weak interfaces in traditional magnesia-carbon bricks and improving the overall structural stability of the brick. The modified phenolic resin provides molding strength at low temperatures, and the ceramic precursor provides strength by forming an in-situ network within the resin pyrolysis zone during service heating. The SiO2-B4C-La2O3 composite powder forms a glassy phase at high temperatures to achieve oxidation resistance and high-temperature reinforcement, while the magnesia aggregate provides high-temperature skeletal support throughout the process. The dual-modified graphite and SiO2-B4C-La2O3 composite powder work synergistically to resist oxidation. The graphite coating layer blocks oxygen diffusion, and the composite powder seals the oxidation channels, resulting in a double barrier that significantly reduces carbon oxidation. The gradation design of the magnesia aggregate and the synergistic effect of each modified component improve thermal shock stability, reduce thermal expansion mismatch stress, reduce crack initiation and propagation, and enhance slag erosion resistance. Detailed Implementation

[0035] The following are some examples for further illustration, but the present invention is not limited to these examples.

[0036] Example 1

[0037] A ceramic precursor composite magnesia-carbon refractory brick, by weight, comprises the following raw materials: 70 parts magnesia aggregate, 8 parts double-modified flake graphite, 5 parts medium-temperature ceramic precursor, 5 parts modified phenolic resin, and 5.5 parts SiO2-B4C-La2O3 composite powder.

[0038] The magnesia aggregate comprises fused magnesia and lightly calcined magnesia in a mass ratio of 82:18.

[0039] The gradation of the fused magnesia is as follows: 3 < particle size ≤ 5 mm accounts for 25 wt%, 1 < particle size ≤ 3 mm accounts for 40 wt%, 0.1 < particle size ≤ 1 mm accounts for 20 wt%, and particle size < 0.074 mm accounts for 15 wt%.

[0040] The particle size of the lightly calcined magnesia is <0.074 mm.

[0041] The preparation of the double-modified flake graphite includes: adding flake graphite to 11wt% hydrochloric acid at a solid-liquid mass ratio of 1:5.5, stirring at 60℃~65℃ for 1.5h, filtering, washing with deionized water until pH 6.5, filtering, drying at 110℃ for 5.5h, breaking up, and passing through a 200-mesh sieve to obtain activated graphite. Aluminum isopropoxide and deionized water were mixed at a mass ratio of 1:85, and the pH was adjusted to 3.8 with 1.2 mol / L nitric acid. The mixture was hydrolyzed at 320 r / min for 2 h in a temperature range of 85℃ to 90℃ to obtain aluminum sol. Activated graphite was added to the aluminum sol at a solid-liquid mass ratio of 1:5.5, and the mixture was dispersed by stirring at 550 r / min for 70 min. Water was removed by vacuum evaporation in a temperature range of 80℃ to 85℃ under sealed conditions. Under nitrogen protection, the mixture was sintered at 350℃ for 1 h, then at 650℃ for 2 h, and finally at 950℃ for 1 h. After cooling, Al2O3@graphite was obtained. Al2O3@graphite was added to anhydrous ethanol at a solid-liquid mass ratio of 1:9 and stirred at 320 r / min for 40 min. Anhydrous ethanol containing 0.45 mol / L triisopropyl borate and 0.22 mol / L aluminum isopropoxide was added dropwise at 1.5 times the mass of Al2O3@graphite. The mixture was stirred at 320 r / min within a temperature range of 45℃~50℃. The pH was adjusted to 9.2 with 1.5 mol / L ammonia. Urea at 7% mass of Al2O3@graphite was added and stirred for 2 h. The mixture was filtered, dried at 88℃ for 11 h, and sintered at 580℃ for 2 h under nitrogen protection. After cooling, the mixture was passed through a 200-mesh sieve to obtain Al2O3-boron-aluminum compound double-coated flake graphite, i.e., double-modified flake graphite.

[0042] The preparation of the intermediate-temperature ceramic precursor includes: adding boric acid and basic magnesium carbonate at a mass ratio of 1:0.28 to 9 times the total mass of boric acid and basic magnesium carbonate in 68°C deionized water, stirring and dispersing evenly; adding dropwise a 0.55mol / L aluminum phosphate aqueous solution containing 18% of the total mass of boric acid and basic magnesium carbonate; stirring to form a sol; drying under reduced pressure at 80°C–90°C to a moisture content of 1.8wt%; sintering at 360°C for 2 hours under nitrogen protection; cooling; pulverizing; and passing through a 200-mesh sieve to obtain magnesium-boron-aluminum-phosphorus multi-element inorganic amorphous-microcrystalline composite ceramic powder, i.e., the intermediate-temperature ceramic precursor.

[0043] The preparation of the modified phenolic resin includes: phenol, 37wt% formaldehyde aqueous solution, ethylene glycol, triethanolamine, 1,6-hexanediol, polyglycerol-10 isostearate, tetrabutyl titanate, and γ-aminopropyltriethoxysilane in a mass ratio of 200:280:20:8:1.8:1:13:7; under nitrogen protection, phenol, 37wt% formaldehyde aqueous solution, ethylene glycol, and triethanolamine are mixed, heated to 75℃~80℃, and stirred at 320r / min for 1.5h to obtain a methyl phenolic resin prepolymer (hydroxymethyl content 11wt%); then cooled to 6... At 2℃, 1,6-hexanediol and polyglycerol-10 isostearate diluted with anhydrous ethanol (mass ratio of anhydrous ethanol to polyglycerol-10 isostearate 1:1.8) were added, and the mixture was stirred at 320 r / min for 40 min to ensure uniform dispersion of the components. The temperature was further reduced to 52℃, and tetrabutyl titanate and γ-aminopropyltriethoxysilane were added. The pH was adjusted to 4.8 with glacial acetic acid, and the mixture was stirred for 40 min to hydrolyze and condense. The mixture was then evaporated under reduced pressure in the temperature range of 70℃ to 75℃ until the solid content reached 82 wt%. After cooling, the titanium-silicon-organic-inorganic hybrid crosslinked modified phenolic resin, i.e., modified phenolic resin, was obtained.

[0044] The preparation of the SiO2-B4C-La2O3 composite powder includes: mixing B4C (D 50 =3.5μm) and La2O3 (D 50 =3.2μm) were mixed at a mass ratio of 2:1 to obtain a mixed powder; 12% of the mass of the mixed powder was added to silica sol (SiO2 content 30%), and the mixture was wet-mixed at 220r / min for 2h. After drying at 110℃, the mixture was crushed and dispersed, sintered at 850℃ for 1h under nitrogen protection, pulverized, and passed through a 250-mesh sieve to obtain SiO2-B4C-La2O3 composite powder.

[0045] The preparation method of the above-mentioned ceramic precursor composite magnesia-carbon refractory brick includes the following steps:

[0046] S1: Add the double-modified flake graphite, medium-temperature ceramic precursor, and SiO2-B4C-La2O3 composite powder to the mixer and premix evenly for 10 minutes to obtain the premixed matrix powder.

[0047] S2: Add magnesia aggregate to a wet mill, add 55wt% of modified phenolic resin and mix evenly for 4 minutes; add premixed matrix powder and the remaining modified phenolic resin, and continue to mix evenly for 25 minutes; during the mixing process, add 1.2% of anhydrous ethanol of the total mass of all solid raw materials (magnesia aggregate + double-modified flake graphite + medium-temperature ceramic precursor + SiO2-B4C-La2O3 composite powder) to adjust the humidity, and obtain mud.

[0048] S3: The clay is sealed and trapped for 13 hours, then pressed into brick blanks under a pressure of 170 MPa, and dried at 200℃ for 12 hours to obtain refractory bricks.

[0049] Example 2

[0050] A ceramic precursor composite magnesia-carbon refractory brick, by weight, comprises the following raw materials: 68 parts magnesia aggregate, 9 parts double-modified flake graphite, 4 parts medium-temperature ceramic precursor, 5.5 parts modified phenolic resin, and 5 parts SiO2-B4C-La2O3 composite powder.

[0051] The magnesia aggregate comprises fused magnesia and lightly calcined magnesia in a mass ratio of 80:20.

[0052] The gradation of the fused magnesia is as follows: 30 wt% for particles smaller than 3 mm and ≤ 5 mm, 35 wt% for particles smaller than 1 mm and ≤ 3 mm, 20 wt% for particles smaller than 0.1 mm and 15 wt% for particles smaller than 0.074 mm.

[0053] The particle size of the lightly calcined magnesia is <0.074 mm.

[0054] The preparation of the dual-modified flake graphite includes: adding flake graphite to 12wt% hydrochloric acid at a solid-liquid mass ratio of 1:5, stirring at 60℃~65℃ for 1.5h, filtering, washing with deionized water to pH 6.8, filtering, drying at 100℃ for 6h, dispersing, and passing through a 200-mesh sieve to obtain activated graphite. Aluminum isopropoxide and deionized water are mixed at a mass ratio of 1:90, the pH is adjusted to 4.0 with 1mol / L nitric acid, and hydrolyzed at 85℃~90℃ and 300r / min for 2.5h to obtain aluminum sol; the activated graphite is added to the aluminum sol at a solid-liquid mass ratio of 1:5, stirred and dispersed at 600r / min for 60min, and the water is removed by vacuum evaporation at 80℃~85℃ under sealed conditions; under nitrogen protection, the temperature is raised to 400℃ for 1h, raised to 700℃ for 2h, raised to 1000℃ for 1h, and cooled to obtain Al2O3@graphite. Al2O3@graphite was added to anhydrous ethanol at a solid-liquid mass ratio of 1:10 and stirred at 300 r / min for 50 min. Anhydrous ethanol containing 0.48 mol / L triisopropyl borate and 0.20 mol / L aluminum isopropoxide was added dropwise at 1.5 times the mass of Al2O3@graphite. The mixture was stirred at 350 r / min within a temperature range of 45℃~50℃. The pH was adjusted to 9.4 with 1 mol / L ammonia water. Urea at 6% mass of Al2O3@graphite was added and the mixture was stirred for 2.5 h. The mixture was filtered, dried at 85℃ for 12 h, and sintered at 550℃ for 2.5 h under nitrogen protection. After cooling, the mixture was passed through a 200-mesh sieve to obtain Al2O3-boron-aluminum compound double-coated flake graphite, i.e., double-modified flake graphite.

[0055] The preparation of the intermediate-temperature ceramic precursor includes: adding boric acid and basic magnesium carbonate at a mass ratio of 1:0.25 to 10 times the total mass of boric acid and basic magnesium carbonate in 65°C deionized water, stirring and dispersing evenly; adding dropwise a 0.5 mol / L aluminum phosphate aqueous solution at 20% of the total mass of boric acid and basic magnesium carbonate; stirring to form a sol; drying under reduced pressure at 80°C–90°C to a moisture content of 2 wt%; sintering at 350°C for 2.5 h under nitrogen protection; cooling; pulverizing; and passing through a 200-mesh sieve to obtain magnesium-boron-aluminum-phosphorus multi-element inorganic amorphous-microcrystalline composite ceramic powder, i.e., the intermediate-temperature ceramic precursor.

[0056] The preparation of the modified phenolic resin includes: phenol, 37wt% formaldehyde aqueous solution, ethylene glycol, triethanolamine, 1,6-hexanediol, polyglycerol-10 isostearate, tetrabutyl titanate, and γ-aminopropyltriethoxysilane in a mass ratio of 180:300:15:10:1.5:1.2:10:8; under nitrogen protection, phenol, 37wt% formaldehyde aqueous solution, ethylene glycol, and triethanolamine are mixed, heated to 75℃~80℃, and stirred at 300r / min for 2h to obtain a methyl phenolic resin prepolymer (hydroxymethyl content 10wt%); then cooled to... At 60℃, 1,6-hexanediol and polyglycerol-10 isostearate diluted with anhydrous ethanol (mass ratio of anhydrous ethanol to polyglycerol-10 isostearate 1:2) were added, and the mixture was stirred at 300 r / min for 50 min to ensure uniform dispersion of the components. The temperature was then lowered to 50℃, and tetrabutyl titanate and γ-aminopropyltriethoxysilane were added. The pH was adjusted to 5.0 with glacial acetic acid, and the mixture was stirred for another 30 min for hydrolysis and condensation. The mixture was then evaporated under reduced pressure in the temperature range of 70℃ to 75℃ until the solid content reached 85 wt%. After cooling, the titanium-silicon-organic-inorganic hybrid crosslinked modified phenolic resin, i.e., the modified phenolic resin, was obtained.

[0057] The preparation of the SiO2-B4C-La2O3 composite powder includes: mixing B4C (D 50 =2.8μm) and La2O3 (D 50 =3.7μm) were mixed at a mass ratio of 2:0.7 to obtain a mixed powder; 15% by mass of silica sol (SiO2 content 30%) was added to the mixed powder, and the mixture was wet-mixed at 200r / min for 2.5h. After drying at 100℃, the mixture was crushed and dispersed, sintered at 900℃ for 1h under nitrogen protection, pulverized, and passed through a 250-mesh sieve to obtain SiO2-B4C-La2O3 composite powder.

[0058] The preparation method of the above-mentioned ceramic precursor composite magnesia-carbon refractory brick includes the following steps:

[0059] S1: Add the double-modified flake graphite, medium-temperature ceramic precursor, and SiO2-B4C-La2O3 composite powder to the mixer and premix evenly for 10 minutes to obtain the premixed matrix powder.

[0060] S2: Add magnesia aggregate to a wet mill, add 60wt% of modified phenolic resin and mix evenly for 3 minutes; add premixed matrix powder and the remaining modified phenolic resin, and continue to mix evenly for 30 minutes; during the mixing process, add 0.8% of anhydrous ethanol of the total mass of all solid raw materials (magnesia aggregate + double-modified flake graphite + medium-temperature ceramic precursor + SiO2-B4C-La2O3 composite powder) to adjust the humidity, and obtain mud.

[0061] S3: The clay is sealed and trapped for 15 hours, then pressed into brick blanks under a pressure of 180 MPa, and dried at 220℃ for 10 hours to obtain refractory bricks.

[0062] Example 3

[0063] A ceramic precursor composite magnesia-carbon refractory brick, by weight, comprises the following raw materials: 72 parts magnesia aggregate, 7 parts double-modified flake graphite, 6 parts medium-temperature ceramic precursor, 4.5 parts modified phenolic resin, and 6 parts SiO2-B4C-La2O3 composite powder.

[0064] The magnesia aggregate comprises fused magnesia and lightly calcined magnesia in a mass ratio of 85:15.

[0065] The gradation of the fused magnesia is as follows: 30 wt% for particles smaller than 3 mm and ≤ 5 mm, 35 wt% for particles smaller than 1 mm and 25 wt% for particles smaller than 0.1 mm and 10 wt% for particles smaller than 0.074 mm.

[0066] The particle size of the lightly calcined magnesia is <0.074 mm.

[0067] The preparation of the double-modified flake graphite includes: adding flake graphite to 10wt% hydrochloric acid at a solid-liquid mass ratio of 1:6, stirring at 60℃~65℃ for 2h, filtering, washing with deionized water until pH 6.0, filtering, drying at 120℃ for 5h, breaking up, and passing through a 250-mesh sieve to obtain activated graphite. Aluminum isopropoxide and deionized water were mixed at a mass ratio of 1:80, and the pH was adjusted to 3.5 with 1.5 mol / L nitric acid. The mixture was hydrolyzed at 350 r / min for 2 h in a temperature range of 85℃ to 90℃ to obtain aluminum sol. Activated graphite was added to the aluminum sol at a solid-liquid mass ratio of 1:6, and the mixture was stirred and dispersed at 500 r / min for 80 min. Water was removed by vacuum evaporation at a temperature range of 80℃ to 85℃ under sealed conditions. Under nitrogen protection, the mixture was sintered at 300℃ for 1.5 h, at 600℃ for 2.5 h, and at 900℃ for 1.5 h. After cooling, Al2O3@graphite was obtained. Al2O3@graphite was added to anhydrous ethanol at a solid-liquid mass ratio of 1:8 and stirred at 350 r / min for 30 min. Anhydrous ethanol containing 0.42 mol / L triisopropyl borate and 0.25 mol / L aluminum isopropoxide was added dropwise at twice the mass of Al2O3@graphite. The mixture was stirred at 300 r / min within a temperature range of 45℃–50℃. The pH was adjusted to 9.0 with 2 mol / L ammonia. Urea (8% of the mass of Al2O3@graphite) was added, and the mixture was stirred for 2 h. The mixture was filtered, dried at 90℃ for 10 h, and sintered at 600℃ for 2 h under nitrogen protection. After cooling, the mixture was passed through a 250-mesh sieve to obtain Al2O3-boron-aluminum compound double-coated flake graphite, i.e., double-modified flake graphite.

[0068] The preparation of the intermediate-temperature ceramic precursor includes: adding boric acid and basic magnesium carbonate at a mass ratio of 1:0.3 to 8 times the total mass of boric acid and basic magnesium carbonate in 70°C deionized water, stirring and dispersing evenly; adding dropwise 15% of the total mass of boric acid and basic magnesium carbonate in a 0.6 mol / L aluminum phosphate aqueous solution, stirring to form a sol, drying under reduced pressure in a temperature range of 80°C to 90°C until the moisture content is 1.6 wt%; sintering at 380°C for 2 hours under nitrogen protection; cooling; pulverizing; and passing through a 250-mesh sieve to obtain magnesium-boron-aluminum-phosphorus multi-element inorganic amorphous-microcrystalline composite ceramic powder, i.e., the intermediate-temperature ceramic precursor.

[0069] The preparation of the modified phenolic resin includes: phenol, 37wt% formaldehyde aqueous solution, ethylene glycol, triethanolamine, 1,6-hexanediol, polyglycerol-10 isostearate, tetrabutyl titanate, and γ-aminopropyltriethoxysilane in a mass ratio of 220:250:25:5:2:0.8:15:5; under nitrogen protection, phenol, 37wt% formaldehyde aqueous solution, ethylene glycol, and triethanolamine are mixed, heated to 75℃~80℃, and stirred at 350r / min for 1.5h to obtain a methyl phenolic resin prepolymer (hydroxymethyl content 12wt%); then cooled to 6... At 5℃, 1,6-hexanediol and polyglycerol-10 isostearate diluted with anhydrous ethanol (mass ratio of anhydrous ethanol to polyglycerol-10 isostearate 1:1.5) were added, and the mixture was stirred at 350 r / min for 30 min to ensure uniform dispersion of the components. The temperature was further reduced to 55℃, and tetrabutyl titanate and γ-aminopropyltriethoxysilane were added. The pH was adjusted to 4.5 with glacial acetic acid, and the mixture was stirred for 45 min for hydrolysis and condensation. The mixture was then evaporated under reduced pressure in the temperature range of 70℃ to 75℃ until the solid content reached 80 wt%. After cooling, the titanium-silicon-organic-inorganic hybrid crosslinked modified phenolic resin, i.e., modified phenolic resin, was obtained.

[0070] The preparation of the SiO2-B4C-La2O3 composite powder includes: mixing B4C (D 50 =2.4μm) and La2O3 (D 50 =2.6μm) were mixed at a mass ratio of 2:1.3 to obtain a mixed powder; 10% of the mass of the mixed powder was added to silica sol (SiO2 content 30%), and the mixture was wet-mixed at 250r / min for 2h. After drying at 120℃, the mixture was crushed and dispersed, sintered at 800℃ for 1.5h under nitrogen protection, pulverized, and passed through a 200-mesh sieve to obtain SiO2-B4C-La2O3 composite powder.

[0071] The preparation method of the above-mentioned ceramic precursor composite magnesia-carbon refractory brick includes the following steps:

[0072] S1: Add the double-modified flake graphite, medium-temperature ceramic precursor, and SiO2-B4C-La2O3 composite powder to the mixer and premix evenly for 15 minutes to obtain the premixed matrix powder.

[0073] S2: Add magnesia aggregate to a wet mill, add 50wt% of modified phenolic resin and mix evenly for 5 minutes; add premixed matrix powder and the remaining modified phenolic resin, and continue to mix evenly for 20 minutes; during the mixing process, add 1.5% of anhydrous ethanol of the total mass of all solid raw materials (magnesia aggregate + double-modified flake graphite + medium-temperature ceramic precursor + SiO2-B4C-La2O3 composite powder) to adjust the humidity, and obtain mud.

[0074] S3: The clay is sealed and trapped for 12 hours, then pressed into brick blanks under a pressure of 160 MPa, and dried at 180℃ for 15 hours to obtain refractory bricks.

[0075] The indicators and raw material sources involved in the above embodiments are as follows: The MgO purity of fused magnesia is above 98%, and the melting temperature of the electric arc furnace is 2800℃~3000℃. The MgO purity of lightly calcined magnesia is above 92%, and the calcination temperature is 800℃~900℃. The particle size of flake graphite is 325 mesh sieve, and the purity is 99%, sourced from Qingdao Dongkai Graphite Co., Ltd. The aluminum phosphate aqueous solution is prepared by mixing phosphoric acid and aluminum isopropoxide in a molar ratio of 1.5:1, heating and reacting, and then diluting with water after cooling. Polyglycerol-10 isostearate is sourced from Wuhan Xinxin Jiali Biotechnology Co., Ltd., with a purity of 99% and an acid value ≤12mg KOH / g. Silica sol (SiO2 content 30%) is sourced from Hangzhou Jiupeng New Materials Co., Ltd., with a particle size of 10nm, a pH of 9, and water as the solvent. Basic magnesium carbonate is sourced from Shenyang Ketuo Chemical Co., Ltd., with a purity of 99%. (B4C's D) 50 <5μm, purity above 98%. D2 of La2O3 50 <5μm, purity ≥98%. All other unlisted raw materials have a purity ≥98%.

[0076] Comparative Example 1

[0077] The difference from Example 1 is that the double-modified flake graphite is changed to 14 parts, the medium-temperature ceramic precursor is changed to 2 parts, and the SiO2-B4C-La2O3 composite powder is changed to 2.5 parts.

[0078] Comparative Example 2

[0079] The difference from Example 1 is that the double-modified flake graphite is directly replaced by flake graphite.

[0080] Comparative Example 3

[0081] The difference from Example 1 is that the double-modified flake graphite is directly replaced by Al2O3@graphite.

[0082] Comparative Example 4

[0083] The difference from Example 1 is that the double-modified flake graphite is directly replaced by a mixture of flake graphite, Al2O3, and B2O3 in a mass ratio of 100:4:3.

[0084] Comparative Example 5

[0085] The difference from Example 1 is that the medium-temperature ceramic precursor is directly replaced by a mixture of boric acid, basic magnesium carbonate, and aluminum phosphate in a mass ratio of 100:28:2.

[0086] Comparative Example 6

[0087] The difference from Example 1 is that 5.5 parts of commercially available thermosetting phenolic resin were directly used to replace the modified phenolic resin.

[0088] Comparative Example 7

[0089] The difference from Example 1 is that 1,6-hexanediol and polyglycerol-10 isostearate are not added in the preparation of the modified phenolic resin.

[0090] Comparative Example 8

[0091] The difference from Example 1 is that: the double-modified flake graphite is directly replaced by a mixture of flake graphite, Al2O3, and B2O3 in a mass ratio of 100:4:3; the medium-temperature ceramic precursor is directly replaced by a mixture of boric acid, basic magnesium carbonate, and aluminum phosphate in a mass ratio of 100:28:2; and the modified phenolic resin is directly replaced by 5.5 parts of commercially available thermosetting phenolic resin.

[0092] In Comparative Example 4 above, the particle size of Al2O3 and B2O3 passed through a 200-mesh sieve. In Comparative Example 5 above, the particle size of boric acid, basic magnesium carbonate, and aluminum phosphate passed through a 200-mesh sieve. In Comparative Example 7 above, the phenolic resin was a liquid thermosetting phenolic resin sourced from Wuhan Jiyesheng Chemical Co., Ltd., with a solid content of 75%, used as a refractory brick binder.

[0093] I. Bulk density and apparent porosity:

[0094] Three parallel samples of 50mm×50mm×50mm cubic specimens were prepared. Following GB / T 2997 "Test Methods for Bulk Density, Apparent Porosity and True Porosity of Dense Shaped Refractory Products", the specimens were dried in an oven at 110℃ for 24 hours until constant weight, then transferred to a desiccator to cool to room temperature, and the dry weight m0 was measured. A vacuum was applied for 10 minutes, followed by the injection of distilled water, and the vacuum was continued for another 10 minutes. The specimens were then allowed to stand at normal pressure for 30 minutes. The specimens were removed, surface droplets were wiped off, and the apparent dry weight m2 was measured. The saturated specimens were then suspended in distilled water, and the suspended weight m1 was measured. Bulk density ρ (g / cm³) 3 =m0 / (m2-m1)×ρ w , ρ w The density of water at the test temperature is given; apparent porosity P = [(m2-m0) / (m2-m1)] × 100%.

[0095] II. High-temperature antioxidant properties:

[0096] Three parallel cubic specimens (50mm × 50mm × 50mm) were prepared. The specimens were dried at 110℃ for 24 hours, cooled, and weighed (m0). The temperature was then increased to 1200℃ at a rate of 10℃ / min, maintained at this temperature for 5 hours with an air flow rate of 2L / min, and cooled in the furnace. The loose oxide layer on the surface was removed, and the specimens were weighed (m1). The weight loss rate W = [(m0 - m1) / m0] × 100%.

[0097] III. Thermal shock stability:

[0098] Three parallel samples were prepared using a 100mm×50mm×50mm cubic specimen. Following GB / T 30873 "Test Method for Thermal Shock Resistance of Refractory Materials", the specimen was heated to 1100℃ and held for 30 minutes, then one end was immersed in 20℃ flowing water for rapid cooling for 5 minutes, and dried at 110℃ for 2 hours, constituting one cycle. This process continued until fracture, and the number of cycles was recorded.

[0099] IV. Slag erosion resistance:

[0100] Three parallel samples were prepared using a Φ50mm×50mm blind-hole crucible. Following GB / T 8931 "Test Method for Slag Erosion Resistance of Refractory Materials", 50g of molten slag (mass ratio of CaO:SiO2:Fe2O3:Al2O3 = 45:35:15:5) was placed in a high-temperature furnace. Under nitrogen protection, the temperature was increased to 1600℃ at a rate of 5℃ / min and held for 6 hours. After cooling in the furnace, the samples were cut axially and the maximum erosion depth was measured.

[0101] V. Compressive strength at room temperature:

[0102] Five parallel cylindrical specimens (Φ50mm × 50mm) were prepared. Following GB / T 5072 "Test Method for Compressive Strength of Refractory Materials at Room Temperature", the dimensions of the pressure-bearing surface were measured and the area S was calculated. The specimen was placed in the center of the pressure plate of the pressure testing machine and loaded at a rate of 0.5mm / min until failure. The maximum failure load F was recorded. The compressive strength at room temperature was calculated as: σc (MPa) = F / S.

[0103] VI. High-temperature compressive strength:

[0104] Five parallel cylindrical specimens (Φ50mm × 50mm) were prepared. Following GB / T 34218 "Test Method for High-Temperature Compressive Strength of Refractory Materials", the pressure-bearing surface area S of the specimen was measured. The specimen was heated to 1400℃ at a rate of 5℃ / min and held at that temperature for 30 min. Loading was then applied at a rate of 0.5mm / min until failure, and the maximum failure load Fh was recorded. The high-temperature compressive strength was calculated as: σh (MPa) = Fh / S.

[0105] VII. Flexural strength at room temperature:

[0106] Five parallel cuboid specimens (150mm × 25mm × 25mm) were prepared. Following GB / T 3001 "Test Method for Flexural Strength of Refractory Materials at Room Temperature", the specimens were placed in a three-point bending fixture with a span of 100mm and loaded at a rate of 0.15mm / min until fracture. The maximum fracture load Ff was recorded. The flexural strength at room temperature was calculated as: σf (MPa) = (3 × Ff × L) / (2 × b × h) 2 ); test block width b, height h.

[0107] 8. High-temperature flexural strength:

[0108] Five parallel cuboid specimens (150mm × 25mm × 25mm) were prepared. Following GB / T 3002 "Test Method for High-Temperature Flexural Strength of Refractory Materials", the specimens were placed in a three-point bending fixture with a span of 100mm. The temperature was increased to 1400℃ at a rate of 5℃ / min and held for 30min. Loading was then applied at a rate of 0.15mm / min until fracture, and the maximum fracture load Ff was recorded. The high-temperature flexural strength was calculated as: σf (MPa) = (3 × Ff × L) / (2 × b × h) 2 ); test block width b, height h.

[0109] Table 1. Test Results (Average Values)

[0110]

[0111] In the refractory bricks of Examples 1 to 3, flake graphite is activated with hydrochloric acid to introduce surface active sites. Through stepwise sintering, a core-shell structure is formed with an Al2O3 inner layer and a boron-aluminum compound outer layer, transforming the graphite from a non-polar hydrophobic surface to a polar hydrophilic surface. This significantly reduces the interfacial energy difference with magnesia, improves wettability and interfacial bonding strength, significantly reduces primary porosity and microcracks, and increases the density of the brick. The double coating layer preferentially oxidizes at high temperatures to form a dense glassy phase, blocking oxygen diffusion and protecting the internal graphite from rapid oxidation. It also buffers the thermal expansion mismatch between graphite and magnesia, reducing the probability of thermal shock crack initiation. The magnesium-boron-aluminum-phosphorus multi-element amorphous-microcrystalline ceramic powder can react in situ in the resin pyrolysis weight loss range to generate a continuous ceramic network. It forms an organic-inorganic composite bond structure with the resin pyrolysis carbon, quickly filling the pores and structural weak areas generated by resin pyrolysis, providing stable strength support for the brick, and improving structural stability under thermal cycling. Modified phenolic resin forms a Ti-O-Si organic-inorganic hybrid crosslinking network through titanate and silane coupling agent, significantly improving the resin's pyrolysis residual carbon rate and crosslinking density, and reducing pyrolysis defects. The resin also forms chemical bonds with magnesia, modified graphite, and ceramic precursors, strengthening the continuity of multiphase interfacial bonding and improving mechanical strength and structural integrity at both room and high temperatures. SiO2-B4C-La2O3 composite powder achieves synergistic antioxidant and high-temperature reinforcement; the glassy phase generated at high temperatures seals pores and oxidation channels; rare earth La2O3 improves the viscosity and high-temperature stability of the glassy phase, preventing high-temperature loss of the glassy phase, while refining grains and purifying grain boundaries, thus enhancing high-temperature strength and thermal shock stability. The synergistic effect of the composite phases significantly reduces carbon oxidation weight loss, inhibits the formation of a decarburized layer, and improves resistance to slag erosion. The rational gradation of fused magnesia and lightly calcined magnesia, combined with step-by-step mixing, bridging, and high-pressure molding, ensures uniform matrix distribution and dense interfacial bonding, reduces thermal expansion mismatch stress, improves dimensional stability and structural uniformity, and further enhances thermal shock resistance and erosion resistance.

[0112] In Comparative Example 1, the component ratio was unbalanced: excessive addition of double-modified graphite diluted the magnesia oxide skeleton, reduced structural support, decreased density, and increased porosity; insufficient addition of medium-temperature ceramic precursor and composite antioxidant powder resulted in discontinuous medium-temperature ceramic network, incomplete antioxidant barrier, and decreased performance of various components.

[0113] In Comparative Example 2, the unmodified graphite had a non-polar hydrophobic surface with a large energy difference and poor wettability with magnesia. After mixing and molding, the interfacial bonding was weak, resulting in numerous primary pores and microcracks, leading to low brick density and high porosity. Without protective coating, the graphite was directly oxidized and burned at high temperatures, causing rapid formation of a decarburized layer and a sharp deterioration in mechanical strength, thermal shock stability, and slag erosion resistance.

[0114] In Comparative Example 3, only a single layer of Al2O3 coating was used: the single layer of Al2O3 coating only improved the interfacial wettability to a limited extent, but the density, high temperature stability and bonding strength of the coating layer were lower than those of the double-coated structure. It lacked the high temperature glass phase reinforcement and thermal expansion buffering effect of the boron aluminum compound outer layer. The coating layer was prone to cracking and failure at high temperature. Its oxidation resistance, interfacial bonding and thermal shock stability were all lower than those of the double-modified system.

[0115] In Comparative Example 4, the physical mixing of graphite and oxides (Al2O3, B2O3, and graphite) resulted in a uniform, robust, and continuous coating layer on the graphite surface. The particles only had mechanical contact, leading to minimal improvement in interfacial wettability and a tendency to agglomerate and form defect pores. Without a continuous antioxidant shell, oxygen and slag directly contacted the graphite, resulting in severe oxidation and erosion.

[0116] Comparative Example 5: Physical mixing of ceramic precursors: simple physical mixing of boric acid, basic magnesium carbonate, and aluminum phosphate resulted in low reactivity and poor dispersibility. It could not quickly form a uniform and continuous amorphous-microcrystalline ceramic network in the mid-temperature range. Local uneven reaction caused defects, the mid-temperature strength trough was still obvious, the interface bonding was discontinuous, and the density, oxidation resistance, and dimensional stability were all lower than those of the in-situ synthesized precursor system.

[0117] Comparative Example 6 uses ordinary commercially available phenolic resin: Ordinary phenolic resin has low pyrolysis carbon residue and low crosslinking density. Pyrolysis produces a large number of pores and defects. After medium-temperature pyrolysis, the structure weakens rapidly. At high temperatures, the carbon structure is loose and easily oxidized, resulting in deterioration of overall mechanical, antioxidant, thermal shock and slag resistance properties.

[0118] In Comparative Example 7, the modified phenolic resin lacked the addition of 1,6-hexanediol and polyglycerol-10 isostearate during preparation, missing the organic synergistic modification step. It relied solely on a titanium-silicon coupling agent for single-inorganic hybridization, ultimately leading to a systemic deterioration in the brick's performance. The resin itself was excessively brittle, resulting in poor thermal stress resistance. The introduction of long-chain flexible segments by 1,6-hexanediol resulted in excessively rigid resin with extremely poor toughness. Internal stress generated by thermal expansion and contraction during drying and heating could not be released, easily leading to microcracks within the resin and at the resin-solid particle interface. These microcracks became channels for oxygen and slag penetration, directly causing increased apparent porosity, increased oxidative weight loss, and decreased resistance to slag erosion in the brick. Polyglycerol-10 isostearate reduces the surface tension of resin systems. Its absence increases surface tension, significantly reducing the wetting and coating capabilities of solid particles such as magnesia, modified graphite, and ceramic precursors. This makes it difficult to form a continuous and uniform resin coating layer after mixing, resulting in numerous weak interfacial zones between particles and directly reducing the density and room-temperature mechanical strength of the brick. Without the dispersing effect of polyglycerol-10 isostearate, tetrabutyl titanate and silane coupling agents are prone to localized agglomeration, leading to uneven distribution of the Ti-O-Si hybrid crosslinking network and a decrease in the overall crosslinking density of the resin. 1,6-Hexanediol acts as a flexible bridge between the organic resin and the inorganic titanium-silicon phase, while polyglycerol-10 isostearate anchors the resin at the interface with the solid particles. The absence of both disrupts the continuity of chemical bonds at the multiphase interface, deteriorating various properties.

[0119] Comparative Example 8 shows the superimposed defects of the powder system: the simultaneous use of unmodified graphite, physically mixed additives, and ordinary resin resulted in multiple defects such as poor interfacial bonding, low mid-temperature strength, weak oxidation resistance, and fragile bonding system, leading to the worst performance.

Claims

1. A ceramic precursor composite magnesia-carbon refractory brick, characterized in that, By weight, the following raw materials are included: 68 to 72 parts magnesia aggregate, 7 to 9 parts double-modified flake graphite, 4 to 6 parts medium-temperature ceramic precursor, 4.5 to 5.5 parts modified phenolic resin, and 5 to 6 parts SiO2-B4C-La2O3 composite powder. The double-modified flake graphite is prepared by using flake graphite as a matrix, activating it with hydrochloric acid, coating it with aluminum sol, and sintering it to form an Al2O3@graphite core-shell structure. Then, it is prepared by precipitating triisopropyl borate and aluminum isopropoxide under alkaline conditions and sintering it at 550℃~600℃ to achieve secondary coating modification. The medium-temperature ceramic precursor is prepared by cross-linking boric acid and basic magnesium carbonate with aluminum phosphate aqueous solution to form a sol, followed by drying and sintering at 350℃~380℃. The modified phenolic resin is prepared by using a first-order phenolic resin as the main chain, which is synergistically modified with 1,6-hexanediol and polyglycerol-10 isostearate, and then hydrolyzed and condensed with tetrabutyl titanate and γ-aminopropyltriethoxysilane.

2. The ceramic precursor composite magnesia-carbon refractory brick according to claim 1, characterized in that, The magnesia aggregate comprises fused magnesia and lightly calcined magnesia in a mass ratio of (80-85):(15-20); the gradation of the fused magnesia is as follows: 3 < particle size ≤ 5 mm accounts for 25wt%-30wt%, 1 < particle size ≤ 3 mm accounts for 20wt%-25wt%, 0.1 < particle size ≤ 1 mm accounts for 15wt%-20wt%, and particle size < 0.074 mm accounts for 10wt%-15wt%; the particle size of the lightly calcined magnesia is < 0.074 mm.

3. The ceramic precursor composite magnesia-carbon refractory brick according to claim 1, characterized in that, The preparation of the double-modified flake graphite includes: adding activated graphite to aluminum sol, stirring and dispersing, and removing water by vacuum evaporation; sintering at 300℃~400℃ for 1h~1.5h, 600℃~700℃ for 2h~2.5h, and 900℃~1000℃ for 1h~1.5h under nitrogen protection, and cooling to obtain Al2O3@graphite; adding Al2O3@graphite to anhydrous ethanol, stirring and dispersing, adding dropwise anhydrous ethanol solution containing triisopropyl borate and aluminum isopropoxide, adjusting the pH to 9.0~9.4 with ammonia water, adding urea and stirring to react, filtering, drying, sintering at 550℃~600℃ for 2h~2.5h under nitrogen protection, cooling, and sieving to obtain double-modified flake graphite.

4. The ceramic precursor composite magnesia-carbon refractory brick according to claim 3, characterized in that, The preparation of the dual-modified flake graphite includes: adding activated graphite to aluminum sol at a solid-liquid mass ratio of 1:(5-6), stirring and dispersing, and removing water by vacuum evaporation; sintering at 300℃-400℃ for 1-1.5h, 600℃-700℃ for 2-2.5h, and 900℃-1000℃ for 1-1.5h under nitrogen protection, followed by cooling to obtain Al2O3@graphite; adding anhydrous ethanol to Al2O3@graphite at a solid-liquid mass ratio of 1:(8-10), stirring and dispersing, and then adding 1.5 times the mass of Al2O3@graphite dropwise. Anhydrous ethanol solution containing 0.42 mol / L to 0.48 mol / L triisopropyl borate and 0.20 mol / L to 0.25 mol / L aluminum isopropoxide was added at approximately 2 times the volume. The mixture was stirred at 45°C to 50°C, and the pH was adjusted to 9.0 to 9.4 with 1 mol / L to 2 mol / L ammonia solution. Urea (6% to 8% by weight of Al2O3@graphite) was added and stirred. The mixture was filtered, dried, and sintered at 550°C to 600°C for 2 to 2.5 hours under nitrogen protection. After cooling, the mixture was passed through a 200-250 mesh sieve to obtain double-modified flake graphite.

5. A ceramic precursor composite magnesia-carbon refractory brick according to claim 3 or 4, characterized in that, The preparation of the activated graphite includes: adding flake graphite to 10wt% to 12wt% hydrochloric acid at a solid-liquid mass ratio of 1:(5 to 6), stirring, filtering, washing with deionized water to pH 6.0 to 6.8, filtering, drying, breaking up, and passing through a 200-250 mesh sieve to obtain activated graphite.

6. A ceramic precursor composite magnesia-carbon refractory brick according to claim 3 or 4, characterized in that, The preparation of the aluminum sol includes: mixing aluminum isopropoxide and deionized water at a mass ratio of 1:(80-90), adjusting the pH to 3.5-4.0 with 1mol / L-1.5mol / L nitric acid, stirring and hydrolyzing to obtain aluminum sol.

7. The ceramic precursor composite magnesia-carbon refractory brick according to claim 1, characterized in that, The preparation of the intermediate-temperature ceramic precursor includes: adding boric acid and basic magnesium carbonate in a mass ratio of 1:(0.25-0.3) to deionized water, stirring and dispersing evenly, adding dropwise 15%-20% of the total mass of boric acid and basic magnesium carbonate in a 0.5mol / L-0.6mol / L aluminum phosphate aqueous solution, stirring to form a sol, drying under reduced pressure, sintering at 350℃-380℃ for 2h-2.5h under nitrogen protection, cooling, pulverizing, and passing through a 200-250 mesh sieve to obtain the intermediate-temperature ceramic precursor.

8. The ceramic precursor composite magnesia-carbon refractory brick according to claim 1, characterized in that, The preparation of the modified phenolic resin includes: phenol, 37wt% formaldehyde aqueous solution, ethylene glycol, triethanolamine, 1,6-hexanediol, polyglycerol-10 isostearate, tetrabutyl titanate, and γ-aminopropyltriethoxysilane in a mass ratio of (180-220):(250-300):(15-25):(5-10):(1.5-2):(0.8-1.2):(10-15):(5-8); first, phenol and 37wt% formaldehyde aqueous solution are mixed... Ethylene glycol and triethanolamine were mixed and reacted at 75℃~80℃ to obtain a methyl phenolic resin prepolymer. 1,6-hexanediol and polyglycerol-10 isostearate diluted with anhydrous ethanol were added at 60℃~65℃ and stirred to disperse. Tetrabutyl titanate and γ-aminopropyltriethoxysilane were added at 50℃~55℃. The pH was adjusted to 4.5~5.0 with glacial acetic acid, and the mixture was stirred to hydrolyze and condense. The mixture was then evaporated under reduced pressure to a solid content of 80wt%~85wt% and cooled to obtain the modified phenolic resin.

9. The ceramic precursor composite magnesia-carbon refractory brick according to claim 1, characterized in that, The preparation of the SiO2-B4C-La2O3 composite powder includes: mixing B4C and La2O3 at a mass ratio of 2:(0.7-1.3) to obtain a mixed powder; adding 10%-15% by weight of silica sol to the mixed powder, wet mixing, drying, crushing and dispersing, sintering at 800℃-900℃ for 1-1.5 hours under nitrogen protection, pulverizing, and passing through a 200-250 mesh sieve to obtain the SiO2-B4C-La2O3 composite powder.

10. The method for preparing a ceramic precursor composite magnesia-carbon refractory brick according to claim 1, characterized in that, Includes the following steps: S1: Add the double-modified flake graphite, medium-temperature ceramic precursor, and SiO2-B4C-La2O3 composite powder to a mixer and premix them evenly to obtain a premixed matrix powder. S2: Add magnesia aggregate to a wet mill, add 50wt% to 60wt% of modified phenolic resin and mix evenly; add premixed matrix powder and the remaining modified phenolic resin, and mix evenly; during the mixing process, add anhydrous ethanol to adjust the humidity to obtain mud. S3: The clay is sealed and trapped for 12-15 hours, then pressed into brick blanks at a pressure of 160-180 MPa, and dried at 180-220℃ for 10-15 hours to obtain refractory bricks.

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