Low-thermal-conductivity multilayer composite magnesio-hercynite brick and preparation method thereof

Abstract

This invention belongs to the field of refractory materials technology, specifically relating to a low thermal conductivity multilayer composite magnesium-iron-aluminum spinel brick and its preparation method. This invention uses 4-ethoxyphenylboronic acid as a modifier to introduce borate ester groups onto the surface of phenolic resin hollow microspheres, obtaining borate ester-modified phenolic resin hollow microspheres. An epoxy-based silicone resin is prepared using organosilicon resin and epoxy silane. Then, the epoxy-based silicone resin is used to modify alkaline silica sol, introducing organic polymers onto the particle surface to obtain modified silica sol. The modified silica sol is then mixed with sodium hexametaphosphate to obtain a composite binder. This invention combines high-purity magnesia, fused magnesia, fused iron-aluminum spinel, α-Al₂O₃ micropowder, metallic iron powder, metallic aluminum powder, a composite binder, and borate ester-modified phenolic resin hollow microspheres to prepare a multilayer composite magnesium-iron-aluminum spinel brick with low thermal conductivity, excellent mechanical properties, high-temperature resistance, and corrosion resistance.

Description

Technical Field

[0001] This invention belongs to the field of refractory materials technology, specifically relating to a low thermal conductivity multilayer composite magnesium-iron-alumina spinel brick and its preparation method. Background Technology

[0002] With the continuous development of infrastructure, the demand for cement is increasing, and the scale of cement production lines is also expanding. Rotary kilns utilize industrial and domestic waste as fuel, saving coal powder while achieving waste reduction, harmlessness, and resource recovery. Cement kilns offer advantages that other incinerators cannot match in co-processing waste; however, the kiln environment becomes increasingly harsh during this process. Due to the complex composition and large fluctuations in calorific value of the waste, it contains high levels of impurities such as K, Na, S, and Cl, as well as heavy metals, which severely erode and damage the cement kiln bricks, especially in high-temperature zones. This results in a shorter service life for refractory materials in these areas. Magnesia-iron-alumina spinel bricks, due to their excellent high-temperature performance, have become a hot research topic for scientists.

[0003] Patent application number CN201510569183.3 provides a magnesium-aluminum-iron spinel brick, comprising the following raw materials: high-iron high-purity magnesia with a particle size of 5-3mm, high-iron high-purity magnesia with a particle size of 3-1mm, high-iron high-purity magnesia with a particle size of 1-0.088mm, sintered aluminum-magnesia spinel with a particle size of 4-1mm, fused iron-aluminum spinel with a particle size of 2-1mm, high-purity magnesia powder with a particle size of d95 < 0.088mm, iron scale powder with a particle size of d95 < 0.088mm, magnesium chloride solution, and alkaline pulp. This invention utilizes high-purity magnesia sand, high-purity magnesia sand, sintered aluminum-magnesia spinel, and fused iron-aluminum spinel as main raw materials. By changing the method of introducing spinel into the material, and after high-temperature sintering, this product exhibits high-temperature resistance, corrosion resistance, and thermal shock resistance. Its thermal conductivity at 1100℃ is 2.60-2.62 W / (m·K). This product can be used in the calcination zone and transition zone of cement kilns, improving the service life of materials in these areas and reducing the cylinder temperature, thus achieving energy conservation and emission reduction. However, the transition zone lacks stable kiln lining protection. Excessive temperature in the cylinder can easily cause deformation, posing a safety hazard. Therefore, the thermal conductivity of the materials used in the cylinder is subject to stringent requirements. Patent application number CN202110991680.8 provides a microporous magnesium-iron-aluminum spinel brick for the firing zone of a cement rotary kiln, comprising the following raw materials: microporous high-purity magnesia, fused magnesia, fused iron-aluminum spinel, polystyrene spheres, silica sol, and industrial manganese powder. This invention, by adding polystyrene spheres to the mixing mill, exhibits excellent refractory properties, high high-temperature strength, good thermal stability, and resistance to various corrosions. The sintering process results in minimal changes and a low thermal conductivity. After use, the thermal conductivity of the magnesium-iron-aluminum spinel bricks is significantly reduced. By adding microporous high-purity magnesia and fused magnesia to the mixing mill, the thermal conductivity of the product is further reduced, thereby lowering the temperature of the cement kiln shell, reducing heat dissipation from the cement rotary kiln, reducing energy consumption, and simultaneously reducing carbon dioxide emissions and air pollution. This solves the problem of high thermal conductivity and the consumption of large amounts of coal. However, the strength of the magnesium-iron-aluminum spinel bricks provided by this invention is difficult to meet the diversified market demands. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the present invention aims to provide a low thermal conductivity multilayer composite magnesium-iron-aluminum spinel brick and its preparation method. This multilayer composite magnesium-iron-aluminum spinel brick has the characteristics of high strength, low thermal conductivity, and corrosion resistance, and can meet diverse market demands.

[0005] The technical solution adopted by the present invention to achieve the above objectives is as follows:

[0006] A low thermal conductivity multilayer composite magnesium-iron-aluminum spinel brick comprises the following raw materials in parts by weight: 20-35 parts of high-purity magnesia with a particle size of 3-5 mm, 10-20 parts of high-purity magnesia with a particle size of 1-3 mm, 10-20 parts of high-purity magnesia with a particle size of 0-1 mm, 2-5 parts of fused iron-aluminum spinel with a particle size of 1-3 mm, 4-8 parts of fused iron-aluminum spinel with a particle size of 0-1 mm, 25-35 parts of fused magnesia, 3-7 parts of α-Al2O3 micro powder, 1-3 parts of metallic iron powder, 0.5-1.5 parts of metallic aluminum powder, 4-8 parts of composite binder, and 8-12 parts of borate ester modified phenolic resin hollow microspheres; wherein the composite binder is prepared by mixing modified silica sol and sodium hexametaphosphate, and the mass ratio of modified silica sol to sodium hexametaphosphate is 25-35:1;

[0007] The modified silica sol is prepared by:

[0008] Organosilicon resin was dissolved in toluene to obtain a mixture. Under stirring, 3-[(2,3)-epoxypropoxy]propylmethyldimethoxysilane and salicylic acid were mixed evenly and heated to 80-100℃. The mixture was added dropwise over 30-50 minutes. The reaction was allowed to proceed for 3-5 hours. Bisphenol A was then added, and the reaction continued for 1-3 hours. Toluene was removed by evaporation to obtain epoxy-based organosilicon resin. Under stirring, alkaline silica sol was heated to 70-80℃, and epoxy-based organosilicon resin was added. The reaction was allowed to proceed for 3-6 hours. The mixture was then cooled to room temperature to obtain modified silica sol.

[0009] The method for preparing the borate ester modified phenolic resin hollow microspheres is as follows:

[0010] Phenolic resin hollow microspheres were dispersed in xylene, heated to 55-65℃, and 4-ethoxyphenylboronic acid was added. The mixture was stirred for 3-5 hours, cooled to room temperature, and the solid and liquid were separated. The solid was washed and dried to obtain borate ester modified phenolic resin hollow microspheres.

[0011] Phenolic resin hollow microspheres are a novel chemical material with a hollow core and an outer layer of phenolic resin, possessing a unique hollow structure. They exhibit characteristics such as low density, low thermal conductivity, excellent thermal stability, low thermal conductivity and thermal conductivity coefficient, and the ability to absorb electromagnetic waves. They are commonly used as fillers in composite materials, reducing product weight while improving the mechanical and thermal properties of the composite material. They can be used as additives in lightweight adhesives in building materials and chemical industries, or as an ablative layer on material surfaces after being bonded with resin, protecting the internal structure of the material. To further expand their application range, this invention modifies phenolic resin hollow microspheres using 4-ethoxyphenylboronic acid, introducing borate ester groups onto the surface of the hollow microspheres. This improves the adhesion of the hollow microspheres, and the boron atoms in the borate ester groups form a boron-containing ceramic structure during sintering, significantly improving the material's high-temperature resistance and corrosion resistance. Inorganic binders possess advantages such as high and low temperature resistance, low cost, resistance to aging, simple structure, and high adhesion. These characteristics make them excellent in various applications, especially in environments requiring extreme temperature variations. Alkaline silica sol, as a binder for refractory materials, exhibits high adsorption and surface activity, enabling it to adsorb large amounts of water molecules and other substances. It also possesses high chemical stability and heat resistance, allowing it to remain stable at high temperatures. When alkaline silica sol comes into contact with other materials, the active groups in the silica sol adsorb onto the material surface, forming a silica sol film. This film creates a "suction cup"-like force, causing the materials to adhere together and exhibiting excellent adhesion. However, conventional alkaline silica sols suffer from poor stability and low surface functionalization, failing to meet the specific requirements of certain industries. This invention first prepares an epoxy-based silicone resin using organosilicon resin and epoxy silane, then uses this epoxy-based silicone resin to surface-modify the alkaline silica sol, resulting in a modified silica sol. This modified silica sol improves both its stability and adhesion, while also enhancing its compatibility with borate-modified phenolic resin hollow microspheres. By introducing organic polymers onto the surface of the alkaline silica sol, this invention significantly improves its stability and gel concentration, revealing new application potential.

[0012] Furthermore, the mass ratio of the organosilicon resin, 3-[(2,3)-epoxypropoxy]propylmethyldimethoxysilane, salicylic acid, and bisphenol A is 5:8-12:0.3-0.5:0.4-0.6, the amount of organosilicon resin added to the toluene is 0.25-0.55 g / mL, the mass ratio of the alkaline silica sol to the epoxy organosilicon resin is 20:0.5-1.5, the particle size of the alkaline silica sol is 15-25 nm, the SiO2 content is 20-30%, and the pH is 9-11.

[0013] Furthermore, the mass ratio of the phenolic resin hollow microspheres to 4-ethoxyphenylboronic acid is 10:2-4, and the mass-to-volume ratio of the phenolic resin hollow microspheres to xylene is 0.5-1.5 mg / mL.

[0014] This invention also provides a method for preparing low thermal conductivity multilayer composite magnesium-iron-aluminum spinel bricks, comprising the following steps:

[0015] (1) Weigh each raw material according to the weight proportions and set aside;

[0016] (2) Mix high-purity magnesia with a particle size of 3-5mm, fused iron-aluminum spinel with a particle size of 1-3mm, and one-third of the fused magnesia evenly. After grinding and drying, add half of the composite binder and stir evenly to obtain material 1.

[0017] (3) Mix high-purity magnesia with a particle size of 1-3mm, high-purity magnesia with a particle size of 0-1mm, fused iron-aluminum spinel with a particle size of 0-1mm, the remaining fused magnesia, α-Al2O3 micro powder, metallic iron powder, and metallic aluminum powder evenly. After grinding and drying, add borate ester modified phenolic resin hollow microspheres and the remaining composite binder, and stir evenly to obtain material 2.

[0018] (4) First, spread half of the material 2 in a layer at the bottom of the mold, then spread another layer of material 1, and finally spread the remaining material 2 in another layer. After vacuum pressing, bake at 100-120℃ for 8-12 hours, then sinter at 1200-1500℃ for 3-5 hours, and cool naturally to room temperature to obtain a multi-layer composite magnesium iron aluminum spinel brick.

[0019] In steps (2) and (3), the grinding is carried out using an impact ball mill. The specific grinding operation is as follows: add grinding aid of twice the weight of the material and grinding balls of half the weight of the material, and grind using an impact ball mill. The grinding aid is anhydrous ethanol. The grinding time is 1-2 hours. The grinding balls are 2mm 304 stainless steel beads. The grinding process can be carried out using conventional operation in the field. The drying is carried out at 60-80℃ to constant weight.

[0020] The present invention has the following beneficial effects:

[0021] This invention uses 4-ethoxyphenylboronic acid as a modifier. Through the dehydration condensation reaction of boron hydroxyl groups with the phenolic hydroxyl groups in the phenolic resin hollow microsphere structure, borate ester groups are introduced onto the surface of the phenolic resin hollow microspheres, improving the adhesion of the hollow microspheres. Furthermore, the boron atoms in the borate ester groups form a boron-containing ceramic structure during sintering, adhering to the magnesium-iron-aluminum spinel material. This not only provides additional thermal insulation but also protects the material from external environmental erosion and damage, thus significantly improving the material's high-temperature resistance and corrosion resistance. During sintering, the borate-modified phenolic resin hollow microspheres form circular micropores within the composite magnesium-iron-aluminum spinel brick structure, increasing the gas-solid interface in the brick structure and enhancing phonon scattering during solid-phase thermal conductivity, thereby effectively reducing the brick's thermal conductivity. The circular micropores also provide stress buffering within the composite magnesium-iron-aluminum spinel brick during rapid heating and cooling, improving its thermal shock resistance. By combining borate-modified phenolic resin hollow microspheres with metallic iron powder, a reducing atmosphere can be created through the carbon in the borate-modified phenolic resin hollow microspheres. The plasticity of the residual iron powder in the brick after high-temperature sintering can be used to improve the toughness of the brick, thereby further improving its thermal shock resistance.

[0022] This invention utilizes organosilicon resin and epoxy silane to prepare an epoxy-based organosilicon resin. Then, through a ring-opening addition reaction between the epoxy-based organosilicon resin and alkaline silica sol, an organic polymer is introduced onto the surface of the alkaline silica sol particles. This improves the stability and adhesion of the modified silica sol, and enhances the compatibility between the modified silica sol and borate-modified phenolic resin hollow microspheres. By using a compound of modified silica sol, sodium hexametaphosphate, and borate-modified phenolic resin hollow microspheres, the adhesive strength of the composite binder is significantly enhanced, effectively improving the bonding strength between the raw material components before sintering, thereby increasing the density of the sintered product. When modified silica sol is used in combination with metallic aluminum powder, the metallic aluminum powder will form alumina after being oxidized by air during the sintering process. This alumina will seal the pores on the surface of the composite magnesium-iron-aluminum spinel brick, effectively preventing the oxidation and degeneration of the internal materials. This will ensure that the internal stress of the brick remains stable and reduce the phenomenon of peeling and detachment during rapid cooling and heating. At the same time, the silica structure in the silica sol can also sinter with raw materials such as alumina to form a mullite structure, further improving the thermal stability of the material.

[0023] This invention combines high-purity magnesia and fused magnesia as raw materials, and incorporates fused iron-aluminum spinel, which has excellent resistance to chemical corrosion. The iron-aluminum spinel phase is uniformly distributed in the magnesia, generating micropores that are beneficial to the toughness of the material, effectively reducing the crack propagation rate, reducing the heat load, and resisting damage such as thermal shock and spalling, thus ensuring the thermal shock resistance of the composite magnesia-iron-aluminum spinel brick. By incorporating α-Al2O3 micro powder and metallic iron powder, sintering can be promoted, and iron ions and aluminum ions can form in-situ spinel and continuous or semi-continuous solid solutions with magnesium oxide, which can significantly improve the high-temperature performance of the material.

[0024] This invention avoids the agglomeration of material particles through graded mixing and graded grinding. At the same time, the use of wet fine grinding improves grinding efficiency, increases the specific surface area of ​​material particles, generates more activation sites on the surface of material particles, and forms structural defects inside the particles, which is conducive to the solid-phase reaction of mullitization, and can shorten sintering time and reduce sintering temperature.

[0025] This invention adopts a sandwich structure of small-to-medium particle layer-large particle layer-small-to-medium particle layer. Relying on the advantages of multi-layer composite structure, it ensures the mechanical strength and erosion resistance of composite magnesium-iron-aluminum spinel bricks, while making its thermal conductivity lower than that of similar products. This effectively solves the problems of high energy consumption and short service life of existing cement kilns using magnesium-iron-aluminum spinel bricks. Detailed Implementation

[0026] The technical solutions in the embodiments of this application will be clearly and completely described below with reference to the embodiments of this application. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0027] High-purity magnesia, with particle sizes of 5-3mm, 3-1mm, and 0-1mm, has a chemical composition (w) mainly including: MgO 95.44%, CaO 1.50%, SiO2 1.56%, Fe2O3 0.93%, Al2O3 0.31%, and a bulk density of 3.27 g / cm³. 3 Fused iron-aluminum spinel, with grain sizes of 3-1 mm and 0-1 mm, has the following main chemical composition (w): Al₂O₃ 50.59%, Fe₂O₃ 44.91%, SiO₂ 1.22%, MgO 0.96%, CaO 0.38%, and a bulk density of 4.24 g / cm³. 3 Fused magnesia, with a particle size ≤0.074mm, has the following main chemical composition (w): MgO 98.12%, CaO 0.9%, SiO2 0.32%, Fe2O3 0.41%, Al2O3 0.05%, and a bulk density of 3.44g / cm³. 3The following materials were used: α-Al₂O₃ micro powder with a particle size of 500 mesh, whose main chemical composition (w) included: Al₂O₃ > 99.3%, SiO₂ ≤ 0.10%, Fe₂O₃ ≤ 0.04%, Na₂O ≤ 0.5%; metallic iron powder with an iron content ≥ 99.9% and a particle size of 10,000 mesh; metallic aluminum powder with a particle size of 400 mesh and an aluminum content ≥ 99%; silicone resin, brand Dow Corning, model Z-6018, purchased from Guangzhou Huitu New Materials Co., Ltd.; and phenolic resin hollow microspheres, item number FR-F-007-1, with an average particle size of 40-70 μm, purchased from Henan Fanrui Composite Materials Research Institute Co., Ltd. All raw materials used in the following examples were commercially available products.

[0028] Example 1

[0029] A multi-layer composite magnesium-iron-aluminum spinel brick comprises the following raw materials in parts by weight: 28 parts of high-purity magnesia with a particle size of 3-5 mm, 15 parts of high-purity magnesia with a particle size of 1-3 mm, 15 parts of high-purity magnesia with a particle size of 0-1 mm, 3 parts of fused iron-aluminum spinel with a particle size of 1-3 mm, 6 parts of fused iron-aluminum spinel with a particle size of 0-1 mm, 30 parts of fused magnesia, 5 parts of α-Al2O3 micro powder, 2 parts of metallic iron powder, 1 part of metallic aluminum powder, 6 parts of composite binder, and 10 parts of borate ester modified phenolic resin hollow microspheres; wherein the composite binder is prepared by mixing modified silica sol and sodium hexametaphosphate, and the mass ratio of modified silica sol to sodium hexametaphosphate is 30:1.

[0030] The modified silica sol is prepared as follows: Organosilicon resin is dissolved in toluene to obtain a mixture. Under stirring at 180 rpm, 3-[(2,3)-epoxypropoxy]propylmethyldimethoxysilane and salicylic acid are mixed evenly and heated to 90°C. The mixture is then added dropwise over 40 minutes. The reaction is allowed to proceed for 4 hours, followed by the addition of bisphenol A and a further 2 hours. After the reaction is complete, the temperature is raised to 118-120°C to remove toluene, yielding an epoxy-based organosilicon resin. Under stirring at 180 rpm, alkaline silica sol is then heated... The mixture was heated to 75℃, and epoxy-based organosilicon resin was added. The reaction was carried out for 5 hours and then cooled to room temperature to obtain modified silica sol. The mass ratio of organosilicon resin, 3-[(2,3)-epoxypropoxy]propylmethyldimethoxysilane, salicylic acid, and bisphenol A was 5:10:0.4:0.5. The amount of organosilicon resin added to toluene was 0.45 g / mL. The mass ratio of alkaline silica sol to epoxy-based organosilicon resin was 20:1. The colloidal particle size of alkaline silica sol was 15-25 nm, the SiO2 content was 25%, and the pH was 9-11.

[0031] The preparation method of borate-modified phenolic resin hollow microspheres is as follows: phenolic resin hollow microspheres are dispersed in xylene, heated to 60℃, 4-ethoxyphenylboronic acid is added, and the mixture is reacted for 4 hours under stirring at 160 rpm. After cooling to room temperature, the solid and liquid are separated, the solid is taken, washed three times with acetone, and dried under vacuum at 80℃ for 12 hours to obtain borate-modified phenolic resin hollow microspheres; wherein, the mass ratio of phenolic resin hollow microspheres to 4-ethoxyphenylboronic acid is 10:3, and the mass-volume ratio of phenolic resin hollow microspheres to xylene is 1 mg / mL.

[0032] A method for preparing a multilayer composite magnesium-iron-aluminum spinel brick includes the following steps:

[0033] (1) Weigh each raw material according to the weight proportions and set aside;

[0034] (2) Mix high-purity magnesia with a particle size of 3-5mm, fused iron-aluminum spinel with a particle size of 1-3mm, and one-third of the fused magnesia evenly. After grinding and drying, add half of the composite binder and stir evenly to obtain material 1.

[0035] (3) Mix high-purity magnesia with a particle size of 1-3mm, high-purity magnesia with a particle size of 0-1mm, fused iron-aluminum spinel with a particle size of 0-1mm, the remaining fused magnesia, α-Al2O3 micro powder, metallic iron powder, and metallic aluminum powder evenly. After grinding and drying, add borate ester modified phenolic resin hollow microspheres and the remaining composite binder, and stir evenly to obtain material 2.

[0036] (4) First, spread half of the material 2 in a layer at the bottom of the mold, then spread another layer of material 1, and finally spread the remaining material 2 in another layer. After vacuum pressing, bake at 110℃ for 10 hours, then sinter at 1400℃ for 4 hours, and cool naturally to room temperature to obtain a multi-layer composite magnesium iron aluminum spinel brick.

[0037] In steps (2) and (3), the grinding is carried out using an impact ball mill. The specific grinding operation is as follows: add grinding aid of twice the weight of the material and grinding balls of half the weight of the material, and grind using an impact ball mill. The grinding aid is anhydrous ethanol. The grinding time is 1.5 hours. The grinding balls are 2mm 304 stainless steel beads. The grinding process can be carried out using conventional operation in the field. The drying is carried out at 70°C to constant weight. The vacuum pressing molding in step (3) can be carried out using conventional technology in the field.

[0038] Example 2

[0039] A multi-layer composite magnesium-iron-aluminum spinel brick comprises the following raw materials in parts by weight: 22 parts of high-purity magnesia with a particle size of 3-5 mm, 20 parts of high-purity magnesia with a particle size of 1-3 mm, 20 parts of high-purity magnesia with a particle size of 0-1 mm, 2 parts of fused iron-aluminum spinel with a particle size of 1-3 mm, 8 parts of fused iron-aluminum spinel with a particle size of 0-1 mm, 27 parts of fused magnesia, 7 parts of α-Al2O3 micro powder, 1 part of metallic iron powder, 0.5 parts of metallic aluminum powder, 4 parts of composite binder, and 12 parts of borate ester modified phenolic resin hollow microspheres; wherein the composite binder is prepared by mixing modified silica sol and sodium hexametaphosphate, and the mass ratio of modified silica sol to sodium hexametaphosphate is 25:1;

[0040] The modified silica sol is prepared as follows: Organosilicon resin is dissolved in toluene to obtain a mixture. Under stirring at 180 rpm, 3-[(2,3)-epoxypropoxy]propylmethyldimethoxysilane and salicylic acid are mixed evenly and heated to 90°C. The mixture is then added dropwise over 40 minutes. The reaction is allowed to proceed for 4 hours, followed by the addition of bisphenol A and a further 2 hours of reaction. After the reaction is complete, the temperature is raised to 118-120°C to remove toluene, yielding an epoxy-based organosilicon resin. The alkaline silica sol is then heated under stirring at 180 rpm. At 75℃, epoxy-based organosilicon resin was added, and the reaction was carried out for 5 hours. After cooling to room temperature, modified silica sol was obtained. The mass ratio of organosilicon resin, 3-[(2,3)-epoxypropoxy]propylmethyldimethoxysilane, salicylic acid, and bisphenol A was 5:12:0.5:0.6. The amount of organosilicon resin added to toluene was 0.45 g / mL. The mass ratio of alkaline silica sol to epoxy-based organosilicon resin was 20:0.5. The colloidal particle size of alkaline silica sol was 15-25 nm, the SiO2 content was 25%, and the pH was 9-11.

[0041] The preparation method of borate-modified phenolic resin hollow microspheres is as follows: phenolic resin hollow microspheres are dispersed in xylene, heated to 60℃, 4-ethoxyphenylboronic acid is added, and the mixture is reacted for 4 hours under stirring at 160 rpm. After cooling to room temperature, the solid and liquid are separated, the solid is taken, washed three times with acetone, and dried under vacuum at 80℃ for 12 hours to obtain borate-modified phenolic resin hollow microspheres; wherein, the mass ratio of phenolic resin hollow microspheres to 4-ethoxyphenylboronic acid is 10:2, and the mass-to-volume ratio of phenolic resin hollow microspheres to xylene is 1 mg / mL.

[0042] A method for preparing a multilayer composite magnesium-iron-aluminum spinel brick is prepared according to the method described in Example 1, except that: in step (4), after being vacuum pressed, it is baked at 100°C for 12 hours and then sintered at 1200°C for 5 hours.

[0043] Example 3

[0044] A multi-layer composite magnesium-iron-aluminum spinel brick comprises the following raw materials in parts by weight: 33 parts of high-purity magnesia with a particle size of 3-5 mm, 12 parts of high-purity magnesia with a particle size of 1-3 mm, 12 parts of high-purity magnesia with a particle size of 0-1 mm, 5 parts of fused iron-aluminum spinel with a particle size of 1-3 mm, 4 parts of fused iron-aluminum spinel with a particle size of 0-1 mm, 33 parts of fused magnesia, 3 parts of α-Al2O3 micro powder, 3 parts of metallic iron powder, 1.5 parts of metallic aluminum powder, 8 parts of composite binder, and 8 parts of borate ester modified phenolic resin hollow microspheres; wherein the composite binder is prepared by mixing modified silica sol and sodium hexametaphosphate, and the mass ratio of modified silica sol to sodium hexametaphosphate is 35:1;

[0045] The modified silica sol is prepared as follows: Organosilicon resin is dissolved in toluene to obtain a mixture. Under stirring at 180 rpm, 3-[(2,3)-epoxypropoxy]propylmethyldimethoxysilane and salicylic acid are mixed evenly and heated to 90°C. The mixture is then added dropwise over 40 minutes. The reaction is allowed to proceed for 4 hours, followed by the addition of bisphenol A and a further 2 hours. After the reaction is complete, the temperature is raised to 118-120°C to remove toluene, yielding an epoxy-based organosilicon resin. Under stirring at 180 rpm, alkaline silica sol is then heated... The mixture was heated to 75℃, and epoxy-based organosilicon resin was added. The reaction was carried out for 5 hours and then cooled to room temperature to obtain modified silica sol. The mass ratio of organosilicon resin, 3-[(2,3)-epoxypropoxy]propylmethyldimethoxysilane, salicylic acid, and bisphenol A was 5:8:0.3:0.4. The amount of organosilicon resin added to toluene was 0.45 g / mL. The mass ratio of alkaline silica sol to epoxy-based organosilicon resin was 20:1.5. The colloidal particle size of alkaline silica sol was 15-25 nm, the SiO2 content was 25%, and the pH was 9-11.

[0046] The preparation method of borate-modified phenolic resin hollow microspheres is as follows: phenolic resin hollow microspheres are dispersed in xylene, heated to 60℃, 4-ethoxyphenylboronic acid is added, and the mixture is reacted for 4 hours under stirring at 160 rpm. After cooling to room temperature, the solid and liquid are separated, the solid is taken, washed three times with acetone, and dried under vacuum at 80℃ for 12 hours to obtain borate-modified phenolic resin hollow microspheres; wherein, the mass ratio of phenolic resin hollow microspheres to 4-ethoxyphenylboronic acid is 10:4, and the mass-to-volume ratio of phenolic resin hollow microspheres to xylene is 1 mg / mL.

[0047] A method for preparing a multilayer composite magnesium-iron-aluminum spinel brick is prepared according to the method described in Example 1, except that: after vacuum pressing in step (4), it is baked at 120°C for 8 hours and then sintered at 1500°C for 3 hours.

[0048] Comparative Example 1

[0049] A multilayer composite magnesium-iron-aluminum spinel brick, the raw material composition of which is the same as described in Example 1, except that the modified silica sol is replaced with alkaline silica sol.

[0050] A method for preparing a low thermal conductivity multilayer composite magnesium-iron-aluminum spinel brick is prepared according to the method described in Example 1.

[0051] Comparative Example 2

[0052] A multilayer composite magnesium-iron-aluminum spinel brick, the raw material composition of which is the same as described in Example 1, except that the borate ester modified phenolic resin hollow microspheres are replaced with phenolic resin hollow microspheres.

[0053] A method for preparing a low thermal conductivity multilayer composite magnesium-iron-aluminum spinel brick is prepared according to the method described in Example 1.

[0054] Comparative Example 3

[0055] A multilayer composite magnesium-iron-aluminum spinel brick, the raw material composition of which is the same as described in Example 1, except that: the modified silica sol is replaced with alkaline silica sol, and the borate ester modified phenolic resin hollow microspheres are replaced with phenolic resin hollow microspheres.

[0056] A method for preparing a low thermal conductivity multilayer composite magnesium-iron-aluminum spinel brick is prepared according to the method described in Example 1.

[0057] The multilayer composite magnesium-iron-alumina spinel bricks prepared in Examples 1-3 and Comparative Examples 1-3 were subjected to relevant performance tests. The room temperature compressive strength test was conducted according to GB / T 5072-2023 "Test Method for Room Temperature Compressive Strength of Refractory Materials"; the high temperature flexural strength test was conducted according to GB / T The test shall be conducted in accordance with GB / T 2002-2004 "Test Method for High Temperature Flexural Strength of Refractory Materials"; the thermal shock resistance test shall be conducted by drying the sample to constant weight at 120℃, then transferring it to a drying oven at 250-300℃ for 2 hours, then holding it at 1100℃ for 30 minutes, removing the sample, and blowing it with cold air for 5 minutes. This alternating hot and cold test shall be repeated 5 times. The thermal shock resistance is expressed by the retention rate of the sample's room temperature compressive strength, calculated as follows: Room temperature compressive strength retention rate (%) = Room temperature compressive strength of the sample after thermal shock / Room temperature compressive strength of the sample before thermal shock × 100%; the apparent porosity and bulk density tests shall be conducted in accordance with GB / T 2997-2000 "Test Method for Bulk Density, Apparent Porosity and True Porosity of Dense Shaped Refractory Products"; the thermal conductivity test shall be conducted in accordance with GB / T The tests were conducted according to GB / T 10295-2008 "Determination of Steady-State Thermal Resistance and Related Properties of Insulation Materials - Heat Flow Meter Method"; the softening temperature test was conducted according to GB / T 5989-2008 "Test Method for Softening Temperature under Load of Refractory Materials - Differential Heating Method"; the corrosion resistance test was conducted according to GB / T 14983-2008 "Test Method for Alkali Resistance of Refractory Materials"; all tests were repeated three times and the average value was taken. The test results are shown in Table 1. As can be seen from the data in Table 1, compared with Comparative Examples 1-3, the multilayer composite magnesium-iron-aluminum spinel bricks prepared in Examples 1-3 have superior room-temperature compressive strength, high-temperature flexural strength, thermal shock resistance, softening temperature under load, and corrosion resistance, while maintaining suitable apparent porosity, bulk density, and a lower coefficient. This shows that by modifying alkaline silica sol and phenolic resin hollow microspheres respectively, the modified silica sol and borate-modified phenolic resin hollow microspheres work synergistically with other raw material components to prepare multilayer composite magnesium-iron-aluminum spinel bricks that maintain low thermal conductivity while also possessing excellent mechanical properties, high-temperature resistance and corrosion resistance.

[0058] Table 1. Test results of relevant performance of multi-layer composite magnesium-iron-alumina spinel bricks

[0059] Test Project Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 room temperature pressure resistance / MPa 87 92 85 70 74 66 High temperature flexural strength / MPa 11.8 12.3 12.0 9.9 10.3 9.6 Room temperature compressive strength retention rate / % 88.6 89.4 89.0 79.4 82.2 77.9 Apparent porosity / % 24 22 25 27 29 30 <![CDATA[Apparent density (g / cm 3 )]]> 2.5 2.6 2.4 2.3 2.2 2.1 Thermal conductivity (W / (m·K)) 1.61 1.68 1.57 1.54 1.52 1.49 Softening temperature / ℃ 1786 1797 1775 1741 1712 1688 Corrosion resistance / % 3.5 3.7 3.9 4.3 4.6 4.7

[0060] Although embodiments of this application have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of this application, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A low thermal conductivity multilayer composite magnesium-iron-aluminum spinel brick, characterized in that, The raw materials comprise the following parts by weight: 20-35 parts of high-purity magnesia with a particle size of 3-5 mm, 10-20 parts of high-purity magnesia with a particle size of 1-3 mm, 10-20 parts of high-purity magnesia with a particle size of 0-1 mm, 2-5 parts of fused iron-aluminum spinel with a particle size of 1-3 mm, 4-8 parts of fused iron-aluminum spinel with a particle size of 0-1 mm, 25-35 parts of fused magnesia, 3-7 parts of α-Al₂O₃ micro powder, 1-3 parts of metallic iron powder, 0.5-1.5 parts of metallic aluminum powder, 4-8 parts of composite binder, and 8-12 parts of borate ester modified phenolic resin hollow microspheres; wherein the composite binder is prepared by mixing modified silica sol and sodium hexametaphosphate. The modified silica sol is prepared by: Organosilicon resin was dissolved in toluene to obtain a mixture. Under stirring, 3-[(2,3)-epoxypropoxy]propylmethyldimethoxysilane and salicylic acid were mixed evenly and heated to 80-100℃. The mixture was added dropwise over 30-50 minutes. The reaction was allowed to proceed for 3-5 hours. Bisphenol A was then added, and the reaction continued for 1-3 hours. Toluene was removed by evaporation to obtain epoxy-based organosilicon resin. Under stirring, alkaline silica sol was heated to 70-80℃, and epoxy-based organosilicon resin was added. The reaction was allowed to proceed for 3-6 hours. The mixture was then cooled to room temperature to obtain modified silica sol. The method for preparing the borate ester modified phenolic resin hollow microspheres is as follows: Phenolic resin hollow microspheres were dispersed in xylene, heated to 55-65℃, and 4-ethoxyphenylboronic acid was added. The mixture was stirred for 3-5 hours, cooled to room temperature, and the solid and liquid were separated. The solid was washed and dried to obtain borate ester modified phenolic resin hollow microspheres.

2. The low thermal conductivity multilayer composite magnesium-iron-aluminum spinel brick according to claim 1, characterized in that, The mass ratio of the modified silica sol to sodium hexametaphosphate is 25-35:

1.

3. The low thermal conductivity multilayer composite magnesium-iron-aluminum spinel brick according to claim 1, characterized in that, The mass ratio of the organosilicon resin, 3-[(2,3)-epoxypropoxy]propylmethyldimethoxysilane, salicylic acid, and bisphenol A is 5:8-12:0.3-0.5:0.4-0.

6.

4. The low thermal conductivity multilayer composite magnesium-iron-aluminum spinel brick according to claim 1, characterized in that, The amount of organosilicon resin added to the toluene is 0.25-0.55 g / mL.

5. The low thermal conductivity multilayer composite magnesium-iron-aluminum spinel brick according to claim 1, characterized in that, The mass ratio of the alkaline silica sol to the epoxy-based silicone resin is 20:0.5-1.

5.

6. The low thermal conductivity multilayer composite magnesium-iron-aluminum spinel brick according to claim 1, characterized in that, The alkaline silica sol has a particle size of 15-25 nm, a SiO2 content of 20-30%, and a pH of 9-11.

7. The low thermal conductivity multilayer composite magnesium-iron-aluminum spinel brick according to claim 1, characterized in that, The mass ratio of the phenolic resin hollow microspheres to 4-ethoxyphenylboronic acid is 10:2-4.

8. The low thermal conductivity multilayer composite magnesium-iron-aluminum spinel brick according to claim 1, characterized in that, The mass-to-volume ratio of the phenolic resin hollow microspheres to xylene is 0.5-1.5 mg / mL.

9. The method for preparing low thermal conductivity multilayer composite magnesium-iron-aluminum spinel bricks according to any one of claims 1-8, characterized in that, Includes the following steps: (1) Weigh each raw material according to the weight proportions and set aside; (2) Mix high-purity magnesia with a particle size of 3-5mm, fused iron-aluminum spinel with a particle size of 1-3mm, and one-third of the fused magnesia evenly. After grinding and drying, add half of the composite binder and stir evenly to obtain material 1. (3) Mix high-purity magnesia with a particle size of 1-3mm, high-purity magnesia with a particle size of 0-1mm, fused iron-aluminum spinel with a particle size of 0-1mm, the remaining fused magnesia, α-Al2O3 micro powder, metallic iron powder, and metallic aluminum powder evenly. After grinding and drying, add borate ester modified phenolic resin hollow microspheres and the remaining composite binder, and stir evenly to obtain material 2. (4) First, spread half of the material 2 in a layer at the bottom of the mold, then spread another layer of material 1, and finally spread the remaining material 2 in another layer. After vacuum pressing, bake at 100-120℃ for 8-12 hours, then sinter at 1200-1500℃ for 3-5 hours, and cool naturally to room temperature to obtain a multi-layer composite magnesium iron aluminum spinel brick.