Low-thermal-conductivity multi-layer composite magnesium hercynite brick and preparation method thereof

Abstract

The invention belongs to the technical field of refractory materials, and particularly relates to a low-thermal-conductivity multi-layer composite magnesium hercynite brick and a preparation method thereof. The preparation method comprises the following steps: by taking 4-ethoxyphenylboronic acid as a modifier, introducing boric acid ester groups on the surfaces of phenolic resin hollow microspheres to prepare boric acid ester modified phenolic resin hollow microspheres; the preparation method comprises the following steps: preparing epoxy-group organic silicon resin from organic silicon resin and epoxy silane, modifying alkaline silica sol by using the epoxy-group organic silicon resin, introducing an organic polymer to the particle surface of the alkaline silica sol to prepare modified silica sol, and mixing the modified silica sol with sodium hexametaphosphate to prepare the composite binder. The high-purity magnesia, the fused magnesia, the fused hercynite, the alpha-Al2O3 micro powder, the metal iron powder, the metal aluminum powder, the composite binder and the borate modified phenolic resin hollow microspheres are compounded, and the prepared multi-layer composite magnesium hercynite brick is low in heat conductivity coefficient and also has excellent mechanical property, high temperature resistance and corrosion resistance.

Description

Technical Field

[0001] The invention belongs to the technical field of refractory materials, and in particular relates to a low thermal conductivity multilayer composite magnesia-iron-aluminum spinel brick and a preparation method thereof. Background Art

[0002] With the continuous development of infrastructure, the demand for cement is increasing, and the scale of cement production lines is also increasing. The rotary kiln uses industrial and domestic waste as fuel, which saves coal powder while achieving waste reduction, harmlessness and resource utilization. The co-treatment of waste in cement kilns has advantages that other incinerators cannot have, but in the process of co-treatment of waste in cement kilns, the environment in the kiln is becoming more and more harsh. Due to the complex composition of waste and large fluctuations in calorific value, the high content of impurities such as K, Na, S, Cl and heavy metal elements, the cement kiln bricks, especially the high-temperature zone, are seriously corroded and damaged, resulting in a short service life of the refractory materials in these parts. Magnesium iron aluminum spinel bricks have become a hot topic for scientists due to their excellent high-temperature performance.

[0003] The patent with application number CN201510569183.3 provides a magnesium-aluminum-iron spinel brick, which includes the following raw materials: high-iron high-purity magnesia sand with a particle size of 5-3mm, high-iron high-purity magnesia sand with a particle size of 3-1mm, high-iron high-purity magnesia sand with a particle size of 1-0.088mm, sintered aluminum-magnesium spinel with a particle size of 4-1mm, fused iron-aluminum spinel with a particle size of 2-1mm, high-purity magnesia sand powder with a particle size of d95 <0.088mm, iron scale powder with a particle size of d95 <0.088mm, magnesium chloride solution, alkaline pulp Waste liquid, this invention uses high iron and high purity magnesia sand, high purity magnesia sand, sintered aluminum magnesium spinel and fused iron aluminum spinel as the main raw materials, changes the way of introducing the spinel material, and after high temperature sintering, this product has the performance of high temperature resistance, corrosion resistance and thermal shock resistance, and the thermal conductivity coefficient at 1100℃ is 2.60-2.62W / (m·K). This product can be used in the calcining zone and transition zone of cement kiln, which can improve the service life of the material in this part and reduce the temperature of the cylinder, so as to achieve the effect of energy saving and emission reduction, but the transition zone does not have stable kiln skin protection, When the temperature of the cylinder is too high, it is easy to deform, causing safety hazards. Therefore, the thermal conductivity of the material of the cylinder is relatively stringent; the patent with application number CN202110991680.8 provides a microporous magnesia-iron-aluminum spinel brick for the firing zone of a cement rotary kiln, including the following raw materials: microporous high-purity magnesia sand, fused magnesia sand, fused iron-aluminum spinel, polylight balls, silica sol and industrial manganese powder. The invention adds polylight balls to the mixer, which has good refractory properties, high high temperature strength, good thermal stability, resistance to various corrosion, and heavy The fiber burning changes little and the thermal conductivity is small. After use, the thermal conductivity of the magnesia-iron-aluminum spinel brick is greatly reduced. By adding microporous high-purity magnesia sand and fused magnesia sand into the mixer, the thermal conductivity of the product is further reduced, thereby reducing the temperature of the cement kiln cylinder, reducing the heat dissipation of the cement rotary kiln, reducing energy consumption, and at the same time reducing carbon dioxide emissions, reducing air pollution, and solving the problems of high thermal conductivity and large consumption of coal. However, the strength of the magnesia-iron-aluminum spinel brick provided by this invention is difficult to meet the diversified market needs. Summary of the invention

[0004] In view of the deficiencies in the prior art, the purpose of the present invention is to provide a low thermal conductivity multi-layer composite magnesia-iron-aluminum spinel brick and a preparation method thereof. The multi-layer composite magnesia-iron-aluminum spinel brick has the characteristics of high strength, low thermal conductivity and corrosion resistance, and can meet diversified market demands.

[0005] The technical solution adopted by the present invention to achieve the above-mentioned purpose is:

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

[0007] The preparation method of the modified silica sol is:

[0008] Dissolve the organic silicone resin in toluene to obtain a mixed solution, mix 3-[(2,3)-epoxypropyloxy]propylmethyldimethoxysilane and salicylic acid evenly under stirring conditions, heat the mixture to 80-100°C, add the mixed solution dropwise, complete the addition within 30-50 minutes, react for 3-5 hours, then add bisphenol A, continue to react for 1-3 hours, evaporate to remove toluene, and obtain epoxy organic silicone resin; heat the alkaline silica sol to 70-80°C under stirring conditions, add the epoxy organic silicone resin, react for 3-6 hours, and cool to room temperature to obtain modified silica sol;

[0009] The preparation method of the borate-modified phenolic resin hollow microspheres is as follows:

[0010] The phenolic resin hollow microspheres are dispersed in xylene, heated to 55-65° C., 4-ethoxyphenylboric acid is added, stirred for reaction for 3-5 hours, cooled to room temperature, solid-liquid separation is performed, the solid is washed and dried, and the borate-modified phenolic resin hollow microspheres are obtained.

[0011] Phenolic resin hollow microspheres are a new chemical material with a special hollow structure, wherein the core is hollow and the outer layer is phenolic resin. The material has the characteristics of low density, low thermal conductivity, excellent thermal stability, low thermal conductivity and low heat conduction coefficient, and can absorb electromagnetic waves. The material is often used as a filler for composite materials, and the mechanical and thermal properties of the composite materials are improved while reducing the quality of the products. The material can be used as an additive for lightweight adhesives in building materials and chemical industry, and the hollow microspheres of phenolic resin can also be coated on the surface of the material as an ablation layer after being bonded with resin to protect the internal structure of the material. In order to further expand its scope of application, the present invention utilizes 4-ethoxyphenylboronic acid to modify the hollow microspheres of phenolic resin, introduces borate groups on the surface of the hollow microspheres of phenolic resin, improves the bonding property of the hollow microspheres, and the boron atoms in the borate groups can also form boron-containing ceramic structures during the sintering process, which significantly improves the high temperature resistance and corrosion resistance of the material. Inorganic binders have the advantages of high and low temperature resistance, low cost, not easy to age, simple structure and high adhesion. These characteristics make inorganic binders perform well in a variety of application scenarios, especially in environments that need to withstand extreme temperature changes. As a binder for refractory materials, alkaline silica sol can absorb a large amount of water molecules and other substances due to its high adsorption and surface activity. At the same time, it also has high chemical stability and heat resistance, and can exist stably under high temperature conditions. When alkaline silica sol comes into contact with other materials, the active groups in the silica sol will be adsorbed on the surface of the material to form a layer of silica sol film, and form a "suction cup"-like force, which makes the materials adsorb to each other and show excellent adhesion. However, conventional alkaline silica sols have poor stability and low surface functionalization, and cannot meet the special requirements of certain industries. The present invention first uses silicone resin and epoxy silane to prepare epoxy silicone resin, and then uses epoxy silicone resin to modify the surface of alkaline silica sol to obtain modified silica sol, which improves the stability and adhesion of alkaline silica sol, and also improves the compatibility of modified silica sol with borate-modified phenolic resin hollow microspheres. The present invention significantly improves its stability and gel concentration by introducing organic polymers on the surface of alkaline silica sol, so that it shows new application potential.

[0012] Furthermore, the mass ratio of the silicone resin, 3-[(2,3)-epoxypropyloxy]propylmethyldimethoxysilane, salicylic acid, and bisphenol A is 5:8-12:0.3-0.5:0.4-0.6, the amount of silicone resin added to toluene is 0.25-0.55 g / mL, the mass ratio of the alkaline silica sol to the epoxy silicone resin is 20:0.5-1.5, the colloidal 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-ethoxyphenylboric acid is 10:2-4, and the mass volume ratio of the phenolic resin hollow microspheres to xylene is 0.5-1.5 mg / mL.

[0014] The present invention also provides a method for preparing a low thermal conductivity multilayer composite magnesia-iron-aluminum spinel brick, comprising the following steps:

[0015] (1) Weigh each raw material by weight and set aside;

[0016] (2) high-purity magnesia with a particle size of 3-5 mm, fused iron-aluminum spinel with a particle size of 1-3 mm, and one-third of the fused magnesia are mixed evenly, ground and dried, and then one-half of the composite binder is added and stirred evenly to obtain material 1;

[0017] (3) high-purity magnesia with a particle size of 1-3 mm, high-purity magnesia with a particle size of 0-1 mm, fused iron-aluminum spinel with a particle size of 0-1 mm, the remaining fused magnesia, α-Al2O3 powder, metallic iron powder, and metallic aluminum powder are uniformly mixed, ground and dried, and then borate-modified phenolic resin hollow microspheres and the remaining composite binder are added and stirred to obtain material 2;

[0018] (4) First, lay one-half of the material 2 on the bottom of the mold, then lay a layer of material 1, and finally lay the remaining material 2 again. After vacuum pressing and molding, bake at 100-120°C for 8-12h, then sinter at 1200-1500°C for 3-5h, and naturally cool to room temperature to obtain a multi-layer composite magnesia-iron-aluminum spinel brick;

[0019] The grinding in step (2) and step (3) is performed by a jarring ball mill. The specific grinding operation is as follows: adding a grinding aid twice the weight of the material and grinding balls half the weight of the material, and grinding the material by a jarring ball mill. The grinding aid is anhydrous ethanol, the grinding time is 1-2 hours, the grinding balls are 2 mm 304 stainless steel beads, and the grinding process is performed by conventional operations in the art. The drying is performed at 60-80° C. to constant weight.

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

[0021] The present invention uses 4-ethoxyphenylboric acid as a modifier, introduces borate groups on the surface of the phenolic resin hollow microspheres through the dehydration condensation reaction of boron hydroxyl groups and phenolic hydroxyl groups in the phenolic resin hollow microsphere structure, improves the adhesion of the hollow microspheres, and the boron atoms in the borate groups can also form boron-containing ceramic structures during the sintering process, which are attached to the magnesium-iron-aluminum spinel material, not only providing additional heat insulation functions, but also protecting the material from erosion and damage by the external environment, thereby significantly improving the high temperature resistance and corrosion resistance of the material. During the sintering process, the borate-modified phenolic resin hollow microspheres can form circular pore-shaped micropores in the internal structure of the composite magnesium-iron-aluminum spinel brick, increase the gas-solid interface in the brick structure, increase the phonon scattering of solid-phase heat conduction, thereby effectively reducing the thermal conductivity of the brick, and the circular pore-shaped micropores can also provide stress buffering for the interior of the composite magnesium-iron-aluminum spinel brick during the rapid cooling and heating process, thereby improving its thermal shock resistance. By compounding 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, and 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] The present invention uses silicone resin and epoxy silane to prepare epoxy silicone resin, and then introduces organic polymers on the surface of alkaline silica sol particles through ring-opening addition reaction between epoxy silicone resin and alkaline silica sol, thereby improving the stability and adhesion of modified silica sol, and improving the compatibility of modified silica sol and borate-modified phenolic resin hollow microspheres. By compounding modified silica sol, sodium hexametaphosphate, and borate-modified phenolic resin hollow microspheres, the bonding force of the composite binder is significantly enhanced, and the connection strength between the raw material components before sintering is effectively improved, thereby increasing the density of the sintered product. Modified silica sol is compounded with metal aluminum powder. During the sintering process, the metal aluminum powder will form alumina after being oxidized by air, thereby sealing the holes on the surface of the composite magnesia-iron-aluminum spinel brick, effectively preventing the oxidation and degeneration of the internal material, so that the stress inside the brick can always remain stable, reducing the phenomenon of peeling off during rapid cooling and heating. At the same time, the silicon dioxide structure in the silica sol can also be sintered with raw materials such as alumina to form a mullite structure, further improving the thermal stability of the material.

[0023] The present invention combines high-purity magnesia and fused magnesia as two raw materials, and compound fused iron-aluminum spinel, which has excellent chemical corrosion resistance. The iron-aluminum spinel phase is evenly distributed in the magnesia, and micropores that are beneficial to the toughness of the material are generated, which effectively reduces the crack propagation rate, reduces the heat load, resists damage such as thermal shock and spalling, and ensures the thermal shock resistance of the composite magnesia-iron-aluminum spinel brick. By compounding α-Al2O3 micropowder and metal iron powder, sintering can be promoted, and iron ions and aluminum ions can form in-situ spinel and continuous or semi-continuous solid solution with magnesium oxide, which can significantly improve the high-temperature performance of the material.

[0024] The present invention avoids agglomeration of material particles through graded mixing and graded grinding. At the same time, wet fine grinding is adopted to improve grinding efficiency, increase the specific surface area of ​​material particles, generate more activation sites on the surface of material particles, and form structural defects inside the particles, which is conducive to the occurrence of a solid phase reaction of mullite, shortens the sintering time, and reduces the sintering temperature.

[0025] The present invention adopts a sandwich structure of small and medium particle layer-large particle layer-small and medium particle layer. Relying on the advantages of the multi-layer composite structure, the mechanical strength and corrosion resistance of the composite magnesia-iron-aluminum spinel brick are guaranteed, while making its thermal conductivity lower than that of similar products, effectively solving the problems of high energy consumption and short service life of the existing cement kilns using magnesia-iron-aluminum spinel bricks. DETAILED DESCRIPTION

[0026] The following will be combined with the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0027] High-purity magnesia, particle size is 5-3mm, 3-1mm, 0-1mm, its chemical composition (w) mainly includes: MgO 95.44%, CaO1.50%, SiO2 1.56%, Fe2O3 0.93%, Al2O3 0.31%, volume density is 3.27g / cm 3 ; Fused iron-aluminum spinel, particle size 3-1mm, 0-1mm, its chemical composition (w) mainly includes: Al2O3 50.59%, Fe2O3 44.91%, SiO21.22%, MgO 0.96%, CaO 0.38%, volume density 4.24g / cm 3 , fused magnesia, particle size ≤ 0.074mm, its chemical composition (w) mainly includes: MgO 98.12%, CaO 0.9%, SiO2 0.32%, Fe2O3 0.41%, Al2O3 0.05%, volume density 3.44g / cm 3; α-Al2O3 powder, particle size is 500 mesh, its chemical composition (w) mainly includes: A12O3>99.3%, SiO2≤0.10%, Fe2O3≤0.04%, Na2O≤0.5%; metal iron powder, iron content ≥99.9%, particle size is 10000 mesh; metal aluminum powder, particle size is 400 mesh, aluminum content ≥99%; organic silicon resin, brand Dow Corning, model Z-6018, purchased from Guangzhou Huitu New Materials Co., Ltd.; phenolic resin hollow microspheres, item number FR-F-007-1, average particle size 40-70μm, purchased from Henan Fanrui Composite Materials Research Institute Co., Ltd. The raw materials used in the following examples are all common commercial products.

[0028] Example 1

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

[0030] The preparation method of the modified silica sol is as follows: dissolving an organic silicone resin in toluene to obtain a mixed solution, mixing 3-[(2,3)-epoxypropoxy]propylmethyldimethoxysilane and salicylic acid evenly under stirring at 180 rpm, heating to 90°C, adding the mixed solution dropwise, and completing the addition within 40 minutes, reacting for 4 hours, then adding bisphenol A, and continuing the reaction for 2 hours. After the reaction is completed, heating to 118-120°C, distilling off toluene, and obtaining an epoxy organic silicone resin; heating the alkaline silica sol under stirring at 180 rpm, and heating the alkaline silica sol to 90°C. The mixture was heated to 75°C, epoxy silicone resin was added, the reaction was continued for 5 hours, and the mixture was cooled to room temperature to obtain a modified silica sol; wherein the mass ratio of silicone resin, 3-[(2,3)-epoxypropoxy]propylmethyldimethoxysilane, salicylic acid, and bisphenol A was 5:10:0.4:0.5, the amount of silicone resin added to toluene was 0.45 g / mL, the mass ratio of alkaline silica sol to epoxy silicone resin was 20:1, the colloidal particle size of the 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: disperse the phenolic resin hollow microspheres in xylene, heat to 60°C, add 4-ethoxyphenylboric acid, react for 4 hours under stirring conditions of 160rpm, cool to room temperature, separate the solid and the liquid, take the solid, wash it three times with acetone, and vacuum dry it at 80°C for 12 hours to obtain borate-modified phenolic resin hollow microspheres; wherein the mass ratio of the phenolic resin hollow microspheres to 4-ethoxyphenylboric acid is 10:3, and the mass volume ratio of the phenolic resin hollow microspheres to xylene is 1 mg / mL.

[0032] A method for preparing a multi-layer composite magnesia-iron-aluminum spinel brick comprises the following steps:

[0033] (1) Weigh each raw material by weight and set aside;

[0034] (2) high-purity magnesia with a particle size of 3-5 mm, fused iron-aluminum spinel with a particle size of 1-3 mm, and one-third of the fused magnesia are mixed evenly, ground and dried, and then one-half of the composite binder is added and stirred evenly to obtain material 1;

[0035] (3) high-purity magnesia with a particle size of 1-3 mm, high-purity magnesia with a particle size of 0-1 mm, fused iron-aluminum spinel with a particle size of 0-1 mm, the remaining fused magnesia, α-Al2O3 powder, metallic iron powder, and metallic aluminum powder are uniformly mixed, ground and dried, and then borate-modified phenolic resin hollow microspheres and the remaining composite binder are added and stirred to obtain material 2;

[0036] (4) First, lay one-half of the material 2 on the bottom of the mold, then lay a layer of material 1, and finally lay the remaining material 2 again. After vacuum pressing and forming, bake at 110°C for 10 hours, then sinter at 1400°C for 4 hours, and naturally cool to room temperature to obtain a multi-layer composite magnesia-iron-aluminum spinel brick;

[0037] The grinding in step (2) and step (3) is performed by a jarring ball mill. The specific grinding operation is as follows: adding a grinding aid twice the weight of the material and grinding balls half the weight of the material, and grinding the material by a jarring ball mill. The grinding aid is anhydrous ethanol, the grinding time is 1.5 hours, and the grinding balls are 2 mm 304 stainless steel balls. The grinding process can be performed by conventional operations in the art. The drying is performed at 70° C. to constant weight. The vacuum pressing molding in step (3) can be performed by conventional techniques in the art.

[0038] Example 2

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

[0040] The preparation method of the modified silica sol is as follows: dissolving an organic silicone resin in toluene to obtain a mixed solution, mixing 3-[(2,3)-epoxypropoxy]propylmethyldimethoxysilane and salicylic acid evenly under stirring at 180 rpm, heating to 90°C, adding the mixed solution dropwise, and completing the addition within 40 minutes, reacting for 4 hours, then adding bisphenol A, and continuing the reaction for 2 hours. After the reaction is completed, heating to 118-120°C, distilling off toluene, and obtaining an epoxy organic silicone resin; heating the alkaline silica sol under stirring at 180 rpm, to 75° C., adding epoxy silicone resin, reacting for 5 hours, and cooling to room temperature to obtain modified silica sol; wherein the mass ratio of silicone resin, 3-[(2,3)-epoxypropoxy]propylmethyldimethoxysilane, salicylic acid, and bisphenol A is 5:12:0.5:0.6, the amount of silicone resin added to toluene is 0.45 g / mL, the mass ratio of alkaline silica sol to epoxy silicone resin is 20:0.5, the colloidal particle size of alkaline silica sol is 15-25 nm, the SiO2 content is 25%, and the pH is 9-11;

[0041] The preparation method of borate-modified phenolic resin hollow microspheres is as follows: disperse the phenolic resin hollow microspheres in xylene, heat to 60°C, add 4-ethoxyphenylboric acid, react for 4 hours under stirring conditions of 160rpm, cool to room temperature, separate the solid and the liquid, take the solid, wash it three times with acetone, and vacuum dry it at 80°C for 12 hours to obtain borate-modified phenolic resin hollow microspheres; wherein the mass ratio of the phenolic resin hollow microspheres to 4-ethoxyphenylboric acid is 10:2, and the mass volume ratio of the phenolic resin hollow microspheres to xylene is 1 mg / mL.

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

[0043] Example 3

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

[0045] The preparation method of the modified silica sol is as follows: dissolving an organic silicone resin in toluene to obtain a mixed solution, mixing 3-[(2,3)-epoxypropoxy]propylmethyldimethoxysilane and salicylic acid evenly under stirring at 180 rpm, heating to 90°C, adding the mixed solution dropwise, and completing the addition within 40 minutes, reacting for 4 hours, then adding bisphenol A, and continuing the reaction for 2 hours. After the reaction is completed, heating to 118-120°C, distilling off toluene, and obtaining an epoxy organic silicone resin; heating the alkaline silica sol under stirring at 180 rpm, and heating the alkaline silica sol to 90°C. The mixture was heated to 75°C, epoxy silicone resin was added, the reaction was continued for 5 hours, and the mixture was cooled to room temperature to obtain a modified silica sol; wherein the mass ratio of silicone resin, 3-[(2,3)-epoxypropoxy]propylmethyldimethoxysilane, salicylic acid, and bisphenol A was 5:8:0.3:0.4, the amount of silicone resin added to toluene was 0.45 g / mL, the mass ratio of alkaline silica sol to epoxy silicone resin was 20:1.5, the colloidal particle size of the 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: disperse the phenolic resin hollow microspheres in xylene, heat to 60°C, add 4-ethoxyphenylboric acid, react for 4 hours under stirring conditions of 160rpm, cool to room temperature, separate the solid and the liquid, take the solid, wash it three times with acetone, and vacuum dry it at 80°C for 12 hours to obtain borate-modified phenolic resin hollow microspheres; wherein the mass ratio of the phenolic resin hollow microspheres to 4-ethoxyphenylboric acid is 10:4, and the mass volume ratio of the phenolic resin hollow microspheres to xylene is 1 mg / mL.

[0047] A method for preparing a multilayer composite magnesia-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 multi-layer composite magnesia-iron-aluminum spinel brick, the raw material composition of which is according to the method described in Example 1, except that the modified silica sol is replaced by alkaline silica sol.

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

[0051] Comparative Example 2

[0052] A multi-layer composite magnesia-iron-aluminum spinel brick, the raw material composition of which is according to the method described in Example 1, except that the borate-modified phenolic resin hollow microspheres are replaced by phenolic resin hollow microspheres.

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

[0054] Comparative Example 3

[0055] A multi-layer composite magnesia-iron-aluminum spinel brick, whose raw material composition is according to the method described in Example 1, except that the modified silica sol is replaced by alkaline silica sol, and the borate-modified phenolic resin hollow microspheres are replaced by phenolic resin hollow microspheres.

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

[0057] The multilayer composite magnesia-iron-aluminum 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 carried out in accordance with GB / T 5072-2023 "Test method for room temperature compressive strength of refractory materials"; the high temperature flexural strength test was carried out in accordance with GB / T 3002-2004 "Test Method for High-Temperature Flexural Strength of Refractory Materials"; For thermal shock resistance test, the sample was dried at 120°C to constant weight, transferred to a drying oven at 250-300°C and kept for 2h, then kept at 1100°C for 30min, the sample was taken out and blown with cold air for 5min, and the above hot and cold alternating test was repeated 5 times. The thermal shock resistance was expressed by the retention rate of the sample's room-temperature compressive strength, and the calculation formula was: 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 were carried out in accordance with GB / T2997-2000 "Test Method for Bulk Density, Apparent Porosity and True Porosity of Dense Shaped Refractory Products"; The thermal conductivity test was carried out in accordance with GB / T 10295-2008 "Determination of Steady-State Thermal Resistance and Related Properties of Insulating Materials by Heat Flow Meter Method"; the load softening temperature test is carried out in accordance with GB / T 5989-2008 "Refractories Load Softening Temperature Test Method Differential Temperature Rising Method"; the corrosion resistance test is carried out in accordance with GB / T 14983-2008 "Refractory Alkalinity Resistance Test Method"; the above tests are repeated three times and the average value is taken. The test results are shown in Table 1. It can be seen from the data in Table 1 that compared with Comparative Examples 1-3, the multi-layer composite magnesia-iron-aluminum spinel bricks prepared in Examples 1-3 have more excellent room temperature compressive strength, high temperature flexural strength, thermal shock resistance, load softening temperature and corrosion resistance, while maintaining suitable apparent porosity, volume density and lower coefficient. It can be seen that the alkaline silica sol and phenolic resin hollow microspheres are modified respectively, and the modified silica sol, borate-modified phenolic resin hollow microspheres work synergistically with other raw material components to prepare multilayer composite magnesia-iron-aluminum spinel bricks that maintain low thermal conductivity while also having excellent mechanical properties, high temperature resistance and corrosion resistance.

[0058] Table 1 Test results of relevant properties of multilayer composite MgFeAl spinel bricks

[0059] Test items Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Normal temperature compressive strength / 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[Bulk 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 the embodiments of the present application have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present application, and that the scope of the present application is defined by the appended claims and their equivalents.

Claims

1. A low thermal conductivity multi-layer composite magnesia-iron-aluminum spinel brick, characterized in that: The invention comprises the following raw materials in parts by weight: 20-35 parts of high-purity magnesia sand with a particle size of 3-5mm, 10-20 parts of high-purity magnesia sand with a particle size of 1-3mm, 10-20 parts of high-purity magnesia sand with a particle size of 0-1mm, 2-5 parts of fused iron-aluminum spinel with a particle size of 1-3mm, 4-8 parts of fused iron-aluminum spinel with a particle size of 0-1mm, 25-35 parts of fused magnesia sand, 3-7 parts of α-Al2O3 micropowder, 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-modified phenolic resin hollow microspheres; the composite binder is prepared by mixing modified silica sol with sodium hexametaphosphate; The preparation method of the modified silica sol is: Dissolve the organic silicone resin in toluene to obtain a mixed solution, mix 3-[(2,3)-epoxypropyloxy]propylmethyldimethoxysilane and salicylic acid evenly under stirring conditions, heat the mixture to 80-100°C, add the mixed solution dropwise, complete the addition within 30-50 minutes, react for 3-5 hours, then add bisphenol A, continue to react for 1-3 hours, evaporate to remove toluene, and obtain epoxy organic silicone resin; heat the alkaline silica sol to 70-80°C under stirring conditions, add the epoxy organic silicone resin, react for 3-6 hours, and cool to room temperature to obtain modified silica sol; The preparation method of the borate-modified phenolic resin hollow microspheres is as follows: The phenolic resin hollow microspheres are dispersed in xylene, heated to 55-65° C., 4-ethoxyphenylboric acid is added, stirred for reaction for 3-5 hours, cooled to room temperature, solid-liquid separation is performed, the solid is washed and dried, and the borate-modified phenolic resin hollow microspheres are obtained.

2. The low thermal conductivity multi-layer composite magnesia-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 multi-layer composite magnesia-iron-aluminum spinel brick according to claim 1, characterized in that: The mass ratio of the silicone 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 multi-layer composite magnesia-iron-aluminum spinel brick according to claim 1, characterized in that: The amount of the organic silicon resin added to the toluene is 0.25-0.55 g / mL.

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

5.

6. The low thermal conductivity multi-layer composite magnesia-iron-aluminum spinel brick according to claim 1, characterized in that: The alkaline silica sol colloidal particle size is 15-25nm, the SiO2 content is 20-30%, and the pH is 9-11.

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

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

9. The method for preparing the low thermal conductivity multi-layer composite Mg-Fe-Al spinel brick according to any one of claims 1 to 8, characterized in that: The following steps are involved: (1) Weigh each raw material by weight and set aside; (2) high-purity magnesia with a particle size of 3-5 mm, fused iron-aluminum spinel with a particle size of 1-3 mm, and one-third of the fused magnesia are mixed evenly, ground and dried, and then one-half of the composite binder is added and stirred evenly to obtain material 1; (3) high-purity magnesia with a particle size of 1-3 mm, high-purity magnesia with a particle size of 0-1 mm, fused iron-aluminum spinel with a particle size of 0-1 mm, the remaining fused magnesia, α-Al2O3 powder, metallic iron powder, and metallic aluminum powder are uniformly mixed, ground and dried, and then borate-modified phenolic resin hollow microspheres and the remaining composite binder are added and stirred to obtain material 2; (4) First, spread one-half of the material 2 on the bottom of the mold, then spread a layer of material 1, and finally spread the remaining material 2. After vacuum pressing and forming, bake at 100-120°C for 8-12h, and then sinter at high temperature at 1200-1500°C for 3-5h, and naturally cool to room temperature to obtain a multi-layer composite magnesia-iron-aluminum spinel brick.