Preparation method and application of silica aerogel modified phenolic resin binder for magnesia carbon bricks

Abstract

The present application relates to a kind of refractory binders, especially a kind of preparation method and application of silica aerogel modified phenolic resin binder for magnesite-carbon brick.The preparation method of the silica aerogel modified phenolic resin binder for magnesite-carbon brick, by hydrophobic silica aerogel pretreatment, premix liquid preparation, in-situ modification composite, low-temperature pre-curing and other steps, nanometer hydrophobic silica aerogel is uniformly dispersed in thermosetting phenolic resin, interface compatibility is improved by silane coupling agent, and modified phenolic resin binder for magnesite-carbon brick is prepared.The present application solves the technical problems of poor high-temperature oxidation resistance, loose residual carbon structure and weak interfacial bonding force of traditional phenolic resin.The prepared binder is used for the preparation of magnesite-carbon brick for metallurgical electric furnace, converter, ladle and other furnace linings, which can improve the high-temperature strength, thermal shock resistance and oxidation resistance of the material;The preparation process is simple, the conditions are mild, can be adapted to existing production line, has broad market prospect and application value.

Description

Technical Field

[0001] This invention relates to a preparation technique for refractory material binders, and more particularly to a method for preparing a silica aerogel-modified phenolic resin binder for magnesia-carbon bricks. Background Technology

[0002] Magnesia-carbon bricks, with their excellent high-temperature resistance, slag erosion resistance, and thermal shock resistance, are widely used in the linings of high-temperature industrial furnaces such as metallurgical converters, steel ladles, and electric furnaces. Phenolic resin is the most commonly used binder for magnesia-carbon bricks, ensuring the brick's molding strength and the stability of its high-temperature carbonized structure. However, traditional phenolic resins have shortcomings such as easy oxidation at high temperatures, low residual carbon content, loose structure after carbonization, and weak interfacial bonding with magnesia and graphite. These shortcomings lead to problems such as decarburization, strength reduction, thermal shock cracking, and shortened service life of magnesia-carbon bricks during high-temperature use. In existing technologies, phenolic resins are often modified by adding metal powders, antioxidants, and silane coupling agents. Although this can improve the binder's performance to some extent, it still suffers from limited improvement in high-temperature oxidation resistance, poor improvement in thermal shock stability, and poor compatibility with refractory materials.

[0003] Silica aerogel is a lightweight solid nanomaterial with a three-dimensional interconnected nanoporous network structure built up around a nano-silica framework. Its framework chemical composition is fumed silica, and the internal porosity of the nanoporous structure can reach 80% to 95%, with pore sizes concentrated in the range of 2 to 50 nm. The material is mainly composed of a nano-silica solid framework and air trapped in the pores. It has low thermal conductivity, high specific surface area and excellent high-temperature stability, and provides thermal insulation and oxygen barrier. It can be uniformly composited and modified with phenolic resin organic phase, significantly improving the phenolic resin's carbon residue rate, high-temperature oxidation resistance, thermal shock stability and sealing performance.

[0004] Currently, research on the composite of silica aerogel and phenolic resin mainly focuses on thermal insulation, sound absorption, and aerospace thermal protection. Considering the inherent properties of the materials, silica aerogel possesses advantages such as low thermal conductivity, high temperature resistance, oxidation resistance, thermal insulation and oxygen barrier properties, and high surface nano-activity, making it particularly suitable for modifying binder systems in magnesia-carbon bricks. However, existing technologies lack mature preparation processes for aerogel-modified phenolic resin binders suitable for magnesia-carbon brick applications; conventional modification processes generally suffer from uneven aerogel dispersion, low interfacial bonding strength with the resin matrix, and poor adaptability to production processes, making it difficult to meet the requirements for long-term stable operation of magnesia-carbon bricks at high temperatures.

[0005] Conventional aerogel-phenolic resin composites often employ low-speed stirring and simple physical mixing methods, which easily lead to agglomeration and sedimentation of aerogel particles, making it impossible to achieve uniform nanoscale dispersion. At the same time, the poor interfacial compatibility between aerogel and phenolic resin results in obvious interfacial defects, leading to a small increase in the residual carbon rate of the modified resin, insufficient high-temperature oxidation resistance, and a loose microstructure after carbonization. Consequently, it is difficult to improve the overall performance when applied to magnesia-carbon brick products.

[0006] Patent application number 201310499425.7 discloses a high-temperature resistant thermal insulation coating and its preparation method. Step (1) involves mixing liquid phenolic resin with aerogel to form a coating mixture; then, the coating mixture formed in step (1) is applied to a surface roughened metal surface and cured; finally, the cured metal surface is carbonized in an inert atmosphere. The coating obtained by the method according to this invention is heat-resistant, firmly bonded to the metal substrate, has a low thermal conductivity, and provides good thermal insulation, making it widely applicable for thermal insulation of high-temperature equipment. This invention only describes a general-purpose high-temperature resistant composite material, without specifying the grade or addition ratio of hydrophobic silica aerogel, and does not include a specific process for the positioning and synthesis / curing of magnesium-carbon refractory materials.

[0007] Therefore, developing a silica aerogel-modified phenolic resin binder that exhibits uniform aerogel dispersion, strong interfacial bonding, and excellent high-temperature comprehensive performance, and is suitable for use in the production of magnesia-carbon bricks, is a technical challenge that urgently needs to be solved in this field. Summary of the Invention

[0008] This invention addresses the shortcomings of existing technologies by proposing a method for preparing an aerogel-modified phenolic resin binder for magnesia-carbon bricks. The aerogel is uniformly dispersed, has strong process adaptability, and improves the interfacial bonding force between the aerogel and the resin matrix.

[0009] The modified phenolic resin binder prepared for use in the production of magnesia-carbon bricks can significantly improve the resistance of magnesia-carbon bricks to slag penetration and molten metal erosion, effectively inhibit the erosion and penetration of steel slag and structural spalling at high temperatures, and greatly improve the service safety and durability of converters, electric furnaces and other high-temperature smelting conditions.

[0010] The technical solution adopted in the invention: A method for preparing a silica aerogel-modified phenolic resin binder for magnesia-carbon bricks includes the following steps: (1) Pretreatment of hydrophobic silica aerogel: Select hydrophobic silica aerogel powder with a particle size of 50-200 nm and a porosity of ≥90%, vacuum dry it at 80-100℃ for 2-4 h, and cool it for later use. (2) Preparation of premixed solution: 100 parts by weight of thermosetting phenolic resin are added to the reaction vessel, and then 6 to 12 parts of anhydrous ethanol are added. The temperature is raised to 60 to 80°C and stirred at a constant temperature until the phenolic resin is completely dissolved. The stirring speed is 300 to 500 r / min. The free phenol content of the thermosetting phenolic resin is ≤8%, the solid content is ≥75%, and the viscosity is 2800 to 3500 mPa·s. (3) In-situ modification and composite: Add 2 to 6 parts by weight of pretreated silica aerogel powder to the reactor, and add 0.5 to 1.5 parts by weight of silane coupling agent to improve interfacial compatibility. Disperse at high speed for 60 to 90 minutes at a speed of 800 to 1200 r / min and a temperature of 70 to 90°C to make the nano-hydrophobic silica aerogel uniformly dispersed in the thermosetting phenolic resin. (4) Low temperature pre-curing: Reduce the stirring speed to 200-300 r / min, add 0.5-1 parts by weight of curing agent, pre-cur at 90-110℃ for 30-45 min, and control the viscosity of the system to 1500-2500 mPa·s; (5) Cooling and discharging: Cool down to 30-40℃, stop stirring, discharge the material, and prepare silica aerogel modified phenolic resin binder for magnesium carbon bricks.

[0011] The silane coupling agent is KH550, or KH560 or KH570; the curing agent can be hexamethylenetetramine, paraformaldehyde or trimethylol melamine, etc.

[0012] The preparation method of silica aerogel modified phenolic resin binder for magnesium carbon bricks involves in-situ modification and compounding, with high-speed dispersion using ultrasonic synergistic stirring at an ultrasonic power of 200-300W, which further improves the uniformity of aerogel dispersion.

[0013] The silica aerogel-modified phenolic resin binder prepared by the method is applied to the production of magnesium-carbon bricks. The amount of silica aerogel-modified phenolic resin binder added is 4 to 5% of the total weight of the magnesium-carbon brick raw materials.

[0014] The silica aerogel-modified phenolic resin binder is mixed with fused magnesia, flake graphite, and antioxidant according to the existing magnesia-carbon brick production process. After being molded under pressure of 50-120 MPa and heat-treated at low temperature of 200-260℃, the phenolic resin is fully cross-linked and cured to form a dense carbon binder network. At the same time, trace amounts of residual volatile matter are removed, and magnesia-carbon bricks can be obtained. For the preparation of magnesia-carbon bricks, the raw material ratio of fused magnesia, flake graphite, and antioxidant is as follows: fused magnesia: 75-85 parts; flake graphite: 10-15 parts; antioxidant: 3-6 parts. The antioxidant can be one or more of metallic aluminum powder, metallic silicon powder, boron carbide, and high-temperature pitch powder. This is a common raw material ratio combination in this field.

[0015] Beneficial effects of the invention: 1. This invention relates to a method for preparing silica aerogel-modified phenolic resin binders. It specifically utilizes hydrophobic silica aerogel to modify phenolic resin binders for magnesia-carbon bricks. Through in-situ composite and synergistic action of coupling agents, the aerogel is uniformly dispersed at the nanoscale in the resin, overcoming the technical difficulties of uneven aerogel dispersion and poor interfacial bonding in traditional processes, forming an organic-inorganic hybrid phase. By using high-speed dispersion combined with synergistic modification using the silane coupling agent KH550, a uniformly dispersed system is constructed in situ, solving the industry pain points of aerogel agglomeration and poor interfacial bonding. This significantly improves the residual carbon rate, high-temperature oxidation resistance, and interfacial bonding strength of the modified resin. The residual carbon rate of the modified binder increases by 15-20%, and after carbonization, a continuous and dense carbon-ceramic composite network is formed, meeting the application requirements of binders for magnesia-carbon bricks. This significantly improves the high-temperature oxidation resistance of magnesia-carbon bricks, reducing oxidation weight loss at 1000℃ by 40-50% and increasing high-temperature compressive strength by 20-30%. Conventional mixing processes cannot break the agglomeration forces between aerogel particles, making it difficult to achieve uniform nanoscale dispersion. The interfacial bonding is weak, the modification effect is unstable, and it is difficult to meet the stringent requirements of high-temperature service of magnesia-carbon bricks.

[0016] 2. The preparation method of the silica aerogel modified phenolic resin binder of the present invention is simple in preparation process, mild in reaction conditions, easy to operate, does not require the addition of large-scale production equipment, is fully compatible with existing industrial production lines for phenolic resin and magnesium carbon bricks, has strong operability, is suitable for large-scale production, has significant economic and application value, can meet the technological development needs of modern steel industry for long service life and green furnace lining materials, and has a very broad prospect for industrial application.

[0017] 3. The preparation method of the silica aerogel modified phenolic resin binder of the present invention has excellent interfacial compatibility with magnesia and graphite, which can significantly improve the thermal shock resistance of magnesia-carbon bricks, increase the number of water cooling cycles at 1100℃ by 2 to 3 times, and extend the service life of magnesia-carbon bricks by more than 30%. It solves the common technical problems in the industry such as poor high-temperature oxidation resistance, loose residual carbon structure, weak interfacial bonding with magnesia-carbon brick aggregates, and insufficient high-temperature service stability of traditional phenolic resins. The modified binder prepared can significantly optimize the internal structure of magnesia-carbon bricks, greatly improve the high-temperature strength, thermal shock resistance, and oxidation erosion resistance of the product, and effectively extend the service life of the furnace lining.

[0018] 4. The modified phenolic resin binder prepared by this invention is used in the production of magnesia-carbon bricks. When using it, it is added at 4-5% of the total weight of the magnesia-carbon brick raw materials. After mixing with fused magnesia, flake graphite and antioxidant, it is molded under pressure of 50-120 MPa and cured at low temperature of 200-260℃. This allows the phenolic resin to be fully cross-linked and cured to form a dense carbon binder network. At the same time, trace amounts of residual volatile matter are removed, thus obtaining magnesia-carbon bricks.

[0019] 5. This invention uses a precise compounding of silane coupling agents to significantly improve the interfacial wetting and chemical bonding ability between hydrophobic silica aerogel and phenolic resin, magnesia, and graphite. It fundamentally solves the technical bottleneck of poor compatibility, easy stratification, and easy sedimentation of inorganic aerogels and organic resins, greatly improving the stability of the binder system, extending the storage period, and significantly improving the consistency of batch performance.

[0020] 6. This invention innovatively employs a low-temperature pre-curing controlled-viscosity process, gradually establishing a moderately cross-linked network during preparation. This effectively inhibits the aggregation, sedimentation, and stratification of hydrophobic silica nanoparticles, ensuring the aerogel remains uniformly suspended in the resin for a long period. Simultaneously, the binder viscosity is precisely controlled to an appropriate range, balancing mixing flowability, high-pressure molding stability, and low-temperature curing controllability. This effectively reduces the scrap rate and improves product dimensional accuracy and structural uniformity. Through low-temperature pre-curing, the aerogel is uniformly dispersed, without sedimentation or aggregation, and has a suitable viscosity (1500–2500 mPa·s), making it suitable for mixing and pressing magnesia-carbon bricks. After the brick blanks are formed, low-temperature curing at 200–260℃ achieves optimal strength and high-temperature comprehensive performance, significantly improving the magnesia-carbon bricks' resistance to slag penetration and molten metal erosion. Attached Figure Description

[0021] Figure 1 The image shown is a SEM image of the magnesium-carbon brick prepared by the ordinary phenolic resin binder in Comparative Example 1. Figure 2 The image shown is a SEM image of the magnesium-carbon brick prepared by silica aerogel-modified phenolic resin binder in Example 1. Figure 3 The image shown is a SEM image of the magnesium-carbon brick prepared by silica aerogel-modified phenolic resin binder in Example 2. Figure 4 The bar charts shown are the percentage of erosion area and penetration area of ​​the magnesia-carbon brick samples in Application Examples 1-3. Detailed Implementation

[0022] To make the technical concept and advantages of the invention clearer, the technical solution of the present invention will be further described in detail below with reference to the accompanying drawings. It should be understood that the following embodiments are merely preferred embodiments for explaining and illustrating the present invention, and should not be considered as, nor constitute a limitation on, the scope of patent protection claimed by the present invention. Example

[0023] This invention discloses a method for preparing a silica aerogel-modified phenolic resin binder for magnesia-carbon bricks. The method involves uniformly dispersing nano-hydrophobic silica aerogel in thermosetting phenolic resin, and supplementing it with a silane coupling agent to improve interfacial compatibility, thereby preparing a modified binder for magnesia-carbon bricks. The specific steps are as follows: (1) Pretreatment of hydrophobic silica aerogel: Select hydrophobic silica aerogel powder with a particle size of 50-200 nm and a porosity of ≥90%, place it in a vacuum drying oven, dry it at 80-100℃ for 2-4 hours to remove adsorbed moisture, and cool it to room temperature for later use. (2) Preparation of premixed solution Take 100 parts by mass / weight of liquid thermosetting phenolic resin, which has a viscosity of 2800-3500 mPa·s at 25°C, a solid content of 75%-85%, and a free phenol mass fraction of ≤8%; add 6-12 parts by weight of anhydrous ethanol to the reaction vessel, start stirring at 300-500 r / min, raise the temperature to 60-80°C, and stir at a constant temperature for 30-60 min until the phenolic resin is completely dissolved to obtain a homogeneous premixed solution. The resin viscosity is limited to 2000-3000 mPa·s, which can effectively inhibit the sedimentation and agglomeration of nano-silica aerogel powder, ensure the uniformity of system dispersion, and take into account the resin's wetting and bonding performance on magnesia and graphite particles, making it suitable for subsequent low-temperature pre-curing and magnesia-carbon brick pressing molding process requirements. (3) In-situ modified composite Add 2-6 parts of pretreated hydrophobic silica aerogel powder to the premix, and simultaneously add 0.5-1.5 parts of silane coupling agent KH550 to improve the interfacial compatibility between the aerogel and the resin; increase the stirring speed to 800-1200 r / min, maintain the temperature at 70-90℃, and disperse at high speed for 60-90 min to ensure that the aerogel is uniformly dispersed at the nanoscale in the resin matrix, thus obtaining a stable and homogeneous resin-aerogel composite premix; the silane coupling agent can also be KH560 or KH570. During the in-situ modification and compounding process, high-speed dispersion is achieved by ultrasonic synergistic stirring with an ultrasonic power of 200-300W to further improve the uniformity of aerogel dispersion. (4) Low-temperature pre-curing Reduce the stirring speed to 200–300 r / min, slowly add 0.5–1 part by weight of hexamethylenetetramine curing agent to the reaction system, maintain the temperature at 90–110℃, and perform a pre-curing reaction for 30–45 min, controlling the viscosity of the system at 1500–2500 mPa·s to obtain the modified phenolic resin prepolymer; the curing agent can also be paraformaldehyde or trimethylol melamine, etc. The purpose of low-temperature pre-curing is to allow the resin to partially cure, to reach a semi-hard state—not completely hard, but not fully cured—to pre-crosslink and shape it before complete curing. Ordinary phenolic resin does not require pre-curing; phenolic resin + curing agent → heated to 180–250℃ to harden directly. Its disadvantages are: direct hardening makes it too brittle and prone to cracking; crucially, aerogel cannot be added, resulting in uneven dispersion and clumping. When making magnesia-carbon bricks, it is difficult to mix and press, and prone to delamination. Low-temperature pre-curing (90–110℃) allows the resin to become a viscous gel at very low viscosity and high strength, without hardening, brittleness, or cracking. (5) Cooling and discharging The reaction system was cooled to 30-40℃, stirring was stopped, and the material was discharged to obtain silica aerogel modified phenolic resin binder for magnesium carbon bricks.

[0024] This invention proposes a complete process system for modified phenolic resin binders used in magnesia-carbon bricks. Combined with a series of proprietary process features, including magnesia-carbon brick binder formulation, anhydrous ethanol pre-dissolution, high-speed stirring at 800–1200 r / min, silane coupling agent KH550, and low-temperature pre-curing at 90–110℃, this system achieves the high residual carbon, strong thermal shock resistance, and high interfacial bonding strength required for the high-temperature service of magnesia-carbon bricks. This invention also addresses key challenges such as the nano-dispersion, interfacial coupling, and system stability of hydrophobic silica aerogels in phenolic resins, proposing a novel process method. Example

[0025] (1) Select hydrophobic silica aerogel with a particle size of 100 nm and a porosity of 92%, dry it under vacuum at 90 °C for 3 h, and cool it for later use. (2) Add 100 parts of thermosetting phenolic resin and 6 parts of anhydrous ethanol to the reaction vessel, stir at 400 r / min, heat to 70℃, and stir for 45 min until completely dissolved; (3) Add 5 parts of pretreated aerogel and 1 part of KH550 coupling agent, adjust the speed to 1000r / min, ultrasonic power 250W, disperse at 80℃ for 70min; (4) Reduce the rotation speed to 250 r / min, add 0.5 parts of hexamethylenetetramine, pre-cur at 100℃ for 35 min, and control the viscosity to 2000 mPa·s; (5) Cool down to 35°C and discharge to obtain the modified binder. Example

[0026] (1) Select hydrophobic silica aerogel with a particle size of 80 nm and a porosity of 90%, vacuum dry at 85 °C for 3.5 h, and cool for later use; (2) Add 100 parts of thermosetting phenolic resin and 10 parts of anhydrous ethanol to the reaction vessel, stir at 350 r / min, heat to 75℃, and stir for 50 min until completely dissolved; (3) Add 6 parts of pretreated aerogel and 1.2 parts of KH550 coupling agent, adjust the speed to 1100 r / min, ultrasonic power 280 W, disperse at 85℃ for 65 min; (4) Reduce the rotation speed to 280 r / min, add 1 part hexamethylenetetramine, pre-cur at 105℃ for 40 min, and control the viscosity to 2200 mPa·s; (5) Cool down to 38°C and discharge to obtain the modified binder.

[0027] Comparative Example 1 Unmodified ordinary thermosetting phenolic resin was mixed with silica aerogel, and a silica aerogel-phenolic resin binder was prepared by ordinary low-speed stirring and simple physical mixing.

[0028] Magnesia-carbon bricks produced using unmodified ordinary thermosetting phenolic resin and silica aerogel as binders in Comparative Example 1 were compared with magnesia-carbon bricks produced using modified phenolic resin binders from Examples 2 and 3, with the same raw materials and proportions. The process and test results are as follows: Magnesia-carbon bricks were prepared using the binders prepared in Examples 2 and 3 and Comparative Example 1, following the same process. The proportions and production process of the magnesia-carbon bricks are shown in Table 1. Table 1: Application ratio of magnesia-carbon bricks

[0029] Figures 1-3 The figures show the SEM microstructures of magnesium-carbon bricks with different phenolic resin systems. Figure 1 This is a comparative sample of MT-10C magnesia-carbon bricks prepared using ordinary phenolic resin and silica aerogel obtained through a simple physical mixing method. Figure 2 , Figure 3 The samples are MT-10C magnesium-carbon bricks prepared from silica aerogel-modified phenolic resin, as described in Examples 2 and 3, respectively.

[0030] from Figure 1 It can be seen that the carbon network structure formed by the carbonization of phenolic resin in the sample of Comparative Example 1 is sparse and has poor continuity, making it difficult to form a complete fibrous / network skeleton; the graphite is severely oxidized, the aggregate-matrix interface is loose, and there are many low-melting phases. At the same time, there are many interconnected pores inside the material, and the structure is loose. This will directly lead to the material having a low bulk density and high porosity, affecting its resistance to erosion and thermal shock.

[0031] In contrast, Example 2 ( Figure 2 ) and Example 3 ( Figure 3The microstructure of the resin was significantly improved, promoting in-situ carbon whisker growth, filling matrix pores, strengthening matrix bonding, resulting in tighter interfacial bonding and less low-melting-phase material. The carbon network structure formed after resin carbonization was denser and more continuous, with a more uniform distribution of fibrous carbon structures and a significantly higher residual carbon rate, effectively forming a complete carbon-bonded network. The number of pores inside the material was significantly reduced, with smaller and more uniform pore sizes, resulting in a significant increase in overall material density, corresponding to higher bulk density and lower porosity.

[0032] Among them, the carbon network structure of Example 3 is more developed and the matrix is ​​more compact, indicating that silica aerogel modified phenolic resin can significantly improve the carbonization behavior of the resin, promote the formation and retention of carbon network, thereby effectively optimizing the microstructure of magnesia-carbon bricks and improving the density and carbon bonding strength of the material.

[0033] Magnesia-carbon bricks were prepared using the binders prepared in Examples 2 and 3 and Comparative Example 1, respectively, according to the same process. The performance results of the magnesia-carbon bricks in various application scenarios are shown in Table 2. Table 2: Performance Test Results of Magnesia-Carbon Bricks in Application Scenarios

[0034] Test results show that this invention uses silica aerogel with a specific particle size and high porosity to modify phenolic resin. This silica aerogel is a pure inorganic material and does not contain any carbon components. Its nanoporous structure can adsorb small molecules produced by the high-temperature decomposition of phenolic resin, effectively inhibiting the volatilization and loss of carbon components. Simultaneously, silica can form a dense ceramic protective film at high temperatures, blocking oxygen penetration and reducing the oxidation and burning loss of residual carbon in the resin, thereby significantly improving the residual carbon rate of the phenolic resin.

[0035] To verify the comprehensive performance of this invention in resisting slag erosion and penetration under practical application conditions, the static crucible test method in GB / T8931-2007 "Test Method for Slag Resistance of Refractory Materials" was used. Three groups of crucibles made from magnesia-carbon bricks prepared with different binders (Application Example 1, Application Example 2, and Application Example 3) were selected for slag erosion resistance tests. The crucible dimensions conformed to national standards. Alloy steel slag smelted in an industrial electric furnace was used as the erosion medium. The slag was crushed, ground, and sieved to a particle size of less than 0.1 mm. After drying, 70 g of slag was filled into each of the three crucibles and lightly compacted to ensure consistent filling amount and density. The samples were placed in a high-temperature air atmosphere furnace and held at 1550 °C for 3 hours for static slag erosion testing. After the test, the samples were slowly cooled to room temperature with the furnace. After cooling, the crucibles were cut along their central axis to accurately measure the slag penetration depth, penetration area, and erosion area, and the percentage of erosion area and penetration area were calculated.

[0036] Depend on Figure 4The bar charts showing the percentage of eroded and permeated areas of the magnesia-carbon brick samples reveal that the eroded area percentages of Application Example 1 and Application Example 2 are approximately 26.9% and 26.1%, respectively, and the permeated area percentages are approximately 15.6% and 14.5%, respectively, both significantly lower than those of Application Example 3 (approximately 33.5% eroded area percentage and approximately 20.5% permeated area percentage). This result demonstrates that the aerogel-modified phenolic resin binder described in this invention (Application Example 1 and Application Example 2) can significantly improve the high-temperature slag erosion and permeation resistance of magnesia-carbon bricks.

[0037] The reasons for this are twofold. On the one hand, the silica aerogel introduced into the modified binder reacts in situ with the slag components at high temperatures, generating a high-viscosity composite silicate phase, which effectively passivates the slag's corrosiveness and inhibits its dissolution and erosion of the brick matrix. On the other hand, the interfacial strengthening effect of the silane coupling agent and the low-temperature pre-curing process significantly improve the interfacial bonding state between the resin and aggregate, reduce the interconnected pores and microcracks inside the brick, and block the slag's penetration channels. In contrast, Application Example 3 uses a simple physical blending method of thermosetting phenolic resin binder and silica aerogel to prepare silica aerogel and phenolic resin binder. Because the silica aerogel cannot be uniformly dispersed, it cannot exert the interfacial strengthening effect, resulting in many interfacial defects. The slag easily penetrates along the pores and interfacial channels and undergoes an erosion reaction, thus significantly increasing both the erosion area and the penetration area.

[0038] In summary, Application Example 2 exhibits the best resistance to slag erosion and permeability, indicating that the binder formulation achieves optimal results in terms of the matching of aerogel addition amount, silane coupling agent dosage, and pre-curing process parameters, providing a reliable guarantee for the long-life application of magnesia-carbon bricks under high temperature and strong erosion conditions.

[0039] It is evident that the modified phenolic resin binder of this invention can optimize the internal matrix bonding structure of magnesia-carbon bricks. The nanoporous structure of the hydrophobic silica aerogel can efficiently adsorb small molecules from resin decomposition, inhibit the volatilization and loss of carbon components, and form a continuous and dense silica ceramic barrier layer at high temperatures to buffer thermal stress. This significantly improves the high-temperature strength, oxidation resistance, and thermal shock stability of magnesia-carbon bricks, enhances their resistance to slag penetration and molten metal erosion, and provides superior overall performance compared to traditional ordinary phenolic resins. It can meet the development needs of the metallurgical industry for long-term service and technological upgrading of magnesia-carbon bricks.

Claims

1. A method for preparing a silica aerogel-modified phenolic resin binder for magnesia-carbon bricks, characterized in that, Includes the following steps: (1) Pretreatment of hydrophobic silica aerogel: Select hydrophobic silica aerogel powder with a particle size of 50-200 nm and a porosity of ≥90%, vacuum dry it at 80-100℃ for 2-4 h, and cool it for later use. (2) Preparation of premixed solution: 100 parts by weight of thermosetting phenolic resin are added to the reaction vessel, and then anhydrous ethanol is added. The temperature is raised to 60-80℃ and stirred at a constant temperature until the phenolic resin is completely dissolved. The stirring speed is 300-500 r / min. The free phenol content of the thermosetting phenolic resin is ≤8%, the solid content is ≥75%, and the viscosity is 2800-3500 mPa·s. (3) In-situ modification and composite: Add 2 to 6 parts by weight of pretreated silica aerogel powder to the reactor, and add 0.5 to 1.5 parts by weight of silane coupling agent to improve interfacial compatibility. Disperse at high speed for 60 to 90 minutes at a speed of 800 to 1200 r / min and a temperature of 70 to 90°C to make the nano-hydrophobic silica aerogel uniformly dispersed in the thermosetting phenolic resin. (4) Low temperature pre-curing: Reduce the stirring speed to 200-300 r / min, add 0.5-1 parts by weight of curing agent, pre-cur at 90-110℃ for 30-45 min, and control the viscosity of the system to 1500-2500 mPa·s; (5) Cooling and discharging: Cool down to 30-40℃, stop stirring, discharge the material, and prepare silica aerogel modified phenolic resin binder for magnesium carbon bricks.

2. The preparation method of the silica aerogel-modified phenolic resin binder for magnesia-carbon bricks according to claim 1, characterized in that: During the preparation of the premix, the amount of anhydrous ethanol added is 6 to 12% of the weight of the thermosetting phenolic resin.

3. The preparation method of silica aerogel-modified phenolic resin binder for magnesia-carbon bricks according to claim 1, characterized in that: In the in-situ modification and compounding process of step (3), high-speed dispersion is achieved by ultrasonic synergistic stirring with an ultrasonic power of 200-300W.

4. The method for preparing the silica aerogel-modified phenolic resin binder for magnesia-carbon bricks according to any one of claims 1 to 3, characterized in that: The silane coupling agent used is KH550, or KH560 or KH570; the curing agent can be hexamethylenetetramine, paraformaldehyde or trimethylol melamine.

5. The preparation method of silica aerogel-modified phenolic resin binder for magnesia-carbon bricks according to claim 4, characterized in that: Add 5 parts by weight of pretreated silica aerogel powder and 1 part by weight of silane coupling agent, and ultrasonically disperse for 60-70 min at a stirring speed of 1000 r / min, ultrasonic power of 250 W, and temperature of 80℃. During the low-temperature pre-curing process, the stirring speed is controlled at 250 r / min, and 0.5 parts by weight of curing agent is added. Pre-curing is carried out at 100℃ for 35 min under stable conditions, and the viscosity is controlled at 2000 mPa·s.

6. The preparation method of silica aerogel-modified phenolic resin binder for magnesia-carbon bricks according to claim 4, characterized in that: Add 6 parts by weight of pretreated silica aerogel powder and 1.2 parts by weight of silane coupling agent, adjust the speed to 1100 r / min, ultrasonic power 280 W, disperse at 85℃ for 65 min; during the low temperature pre-curing process, control the stirring speed at 280 r / min, add 1 part by weight of curing agent, pre-cur under stable conditions at 105℃ for 40 min, and control the viscosity to 2200 mPa·s.

7. The silica aerogel-modified phenolic resin binder prepared by the method according to any one of claims 1 to 6, applied in the production of magnesia-carbon bricks, characterized in that: The amount of silica aerogel-modified phenolic resin binder added is 4-5% of the total weight of the magnesium-carbon brick raw materials.

8. The application according to claim 7, characterized in that: The silica aerogel-modified phenolic resin binder is mixed with fused magnesia, flake graphite, and antioxidant, and then molded under pressure of 50-120 MPa and heat-treated at low temperature of 200-260°C to fully crosslink and cure the phenolic resin, forming a dense carbon binder network. At the same time, trace amounts of residual volatiles are removed, thus obtaining the magnesia-carbon brick.

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