Thermal insulation energy-saving microporous and multiphase reinforced magnesia spinel brick and preparation method thereof

Abstract

This invention belongs to the technical field of refractory materials for RH refining furnaces, and discloses a heat-insulating and energy-saving microporous-multiphase reinforced magnesia spinel brick and its preparation method. The raw materials consist of 60-70 parts of large-crystalline magnesia sand, 8-15 parts of lightweight aggregate, 3-6 parts of micropore forming agent, and 5-10 parts of composite additives, with an added binder accounting for 2-4% of the total weight of the raw materials. Magnesia spinel bricks are prepared through steps such as batching, mixing, vibration-pressurization molding, drying, and microwave crystallization sintering. This process constructs a microporous-multiphase synergistic structure, significantly reducing the sintering temperature and shortening the holding time, inhibiting abnormal grain growth, and obtaining a finer and more uniform grain structure. While ensuring excellent slag erosion resistance and high-temperature strength, the bulk density and thermal conductivity of the material are significantly reduced. This magnesia spinel brick features low thermal conductivity, high strength, excellent thermal shock resistance and slag erosion resistance, effectively reducing heat loss, protecting the metal shell, and extending the furnace lining life.

Description

Technical Field

[0001] This invention belongs to the technical field of refractory materials for RH refining furnaces, specifically relating to a heat-insulating and energy-saving microporous-multiphase reinforced magnesia spinel brick and its preparation method. Background Technology

[0002] With the increasing demands for energy conservation and emission reduction in the steel industry, heat loss from high-temperature industrial furnaces has become a growing concern. In metallurgy, building materials, and chemical industries, large-scale high-temperature equipment such as RH vacuum refining furnaces, cement rotary kilns, and glass kilns operate under extreme heat loads for extended periods. Heat loss from these furnaces accounts for a significant proportion of overall energy consumption, directly impacting the production line's comprehensive energy efficiency and carbon emission levels. Therefore, effectively reducing the thermal conductivity of furnace lining materials and minimizing the wasteful heat loss through the furnace walls has become a crucial technological pathway for improving energy efficiency and promoting the green transformation of high-temperature industries.

[0003] Magnesia spinel bricks, as a high-performance refractory material, are widely used in critical high-temperature components of RH vacuum furnaces due to their excellent resistance to slag erosion, superior high-temperature structural stability, and strong thermal shock resistance. During use, these materials effectively resist molten slag penetration and thermal stress damage, significantly extending furnace lining life. However, while pursuing high-temperature mechanical properties, traditional magnesia spinel bricks generally have a high thermal conductivity, leading to increased furnace outer wall temperature. This not only increases fuel consumption and equipment heat loss but also worsens the operating environment, increasing personnel risks and cooling load. Under long-term continuous production conditions, the accumulated energy consumption and carbon emission pressure from this problem cannot be ignored.

[0004] Traditional magnesia spinel bricks often employ a highly compacted design to achieve good erosion resistance, resulting in high bulk density and high thermal conductivity (typically 3.5–5.0 W / (m·K) at 1000℃). This high thermal conductivity not only causes significant heat loss, increasing energy consumption per ton of steel and carbon emissions, but also leads to excessively high temperatures in the furnace's metal outer shell, accelerating shell deformation, shortening the overall equipment lifespan, and exacerbating heat radiation in the workshop, thus worsening the working environment for operators. Magnesia sand itself also has a relatively high coefficient of thermal expansion. When Al powder in the matrix is ​​oxidized, it reacts with MgO to form magnesium aluminum spinel, which causes a volume expansion of about 8%. This makes the material prone to spalling damage under temperature fluctuations, thus limiting its service life.

[0005] In existing technologies, reducing the thermal conductivity of refractory materials typically involves introducing lightweight aggregates or pore-forming agents. However, this often comes at the cost of sacrificing the material's high-temperature strength, slag erosion resistance, and thermal shock stability. A key technological breakthrough lies in achieving this: how to reduce thermal conductivity while ensuring or even improving the material's overall performance under the harsh conditions of an RH furnace. For example, patent document CN107573037A discloses a magnesia spinel brick for an RH refining furnace. Its raw materials include magnesia sintered material, fused magnesia, and fused spinel, and it is produced by machine pressing and low-temperature drying using phenolic resin as a binder. While this technology achieves chromium-free production, its thermal conductivity remains relatively high, and the synergistic optimization of low thermal conductivity and high corrosion resistance remains unresolved. Patent document CN106946550B discloses a magnesia spinel brick with excellent anti-stripping properties. It uses carbon black to modify the surface of magnesia aggregate and spinel-bonded magnesia aggregate, reducing the material's coefficient of thermal expansion. However, this technology mainly improves anti-stripping performance by reducing the coefficient of thermal expansion, with limited effect on reducing thermal conductivity, and its preparation process is relatively complex. Patent document CN119569424A discloses a magnesium spinel brick for refining silicon steel in new energy motors. The magnesium spinel brick refractory material prepared by using large-crystal magnesia material, zirconium material and composite additives can resist the scouring of high-speed flowing molten steel in RH furnace, has good high-temperature strength, excellent thermal shock resistance, good volume stability under vacuum, is non-carbonized and high-purity, avoiding carburization of the lining material into the molten steel and the generation of non-metallic inclusions during service, and has strong resistance to slag erosion. However, its bulk density is relatively high and its thermal conductivity is relatively high, which can easily lead to an increase in the temperature of the outer wall of the furnace, increasing fuel consumption and equipment heat loss, accelerating shell deformation, and shortening the overall life of the equipment.

[0006] Therefore, developing a new generation of magnesia spinel bricks that combines low thermal conductivity with high slag erosion resistance and excellent thermal shock stability has significant industrial application value and environmental significance, and has become an urgent need for technological innovation in the industry. Summary of the Invention

[0007] To address the aforementioned technical problems, this invention provides a heat-insulating and energy-saving microporous-multiphase reinforced magnesium spinel brick and its preparation method. Through component design and process optimization, this invention constructs a multi-level porous structure by in-situ pore creation to reduce the thermal conductivity, rapidly sintersulates using microwave crystallization sintering technology, and enhances erosion resistance through multiphase composite bonding. This achieves synergistic optimization of low thermal conductivity and high erosion resistance to meet the needs of green and efficient production in high-temperature industrial kilns.

[0008] The technical solution adopted in this invention is: a heat-insulating and energy-saving microporous-multiphase reinforced magnesia spinel brick, comprising the following raw material components by weight: 60-70 parts of macrocrystalline magnesia material, including 10-15 parts of magnesia with a particle size of 5-3mm, 20-25 parts of magnesia with a particle size of 3-1mm, 15-20 parts of magnesia with a particle size of 1-0.5mm, 8-12 parts of magnesia with a particle size of 0.5-0mm, and 3-5 parts of 320-mesh magnesia; 8-15 parts of lightweight aggregate; 3-6 parts of micropore forming agent; 5-10 parts of composite additive; and an external binder accounting for 2-4% of the total weight of the raw material.

[0009] The lightweight aggregate is one or a combination of two of the following: hollow alumina spheres and hollow magnesium aluminum spinel spheres.

[0010] The micropore forming agent is one or a combination of two of graphene nanosheets, activated carbon, and polystyrene microspheres; the graphene nanosheets have a particle size of 1–20 μm; and the polystyrene microspheres have a diameter of 10–100 μm.

[0011] The composite additives include aluminum powder, silicon nitride powder, and ultrafine graphite powder.

[0012] The magnesium oxide content in the macrocrystalline magnesia material is >97wt%.

[0013] The lightweight aggregate has a particle size range of 1–3 mm and a bulk density of ≤1.5 g / cm³.

[0014] The composite additives contain 150-mesh aluminum powder with an aluminum content greater than 98.5 wt%, 250-mesh silicon nitride powder with a silicon nitride content greater than 98 wt%, and ultrafine graphite powder with a particle size less than 3 μm and a carbon content greater than 95 wt%.

[0015] The binder is one or a combination of phenolic resin, lignin sulfonate, and aluminum dihydrogen phosphate.

[0016] A method for preparing a heat-insulating and energy-saving microporous-multiphase reinforced magnesia spinel brick includes the following steps:

[0017] Step 1: Ingredients: Weigh all ingredients according to the formula ratio;

[0018] Step 2, Mixing: First, put the magnesia particles with a particle size of 5-3mm, 3-1mm, and 1-0.5mm and the lightweight aggregate into the mixer and premix for 1-3 minutes. After mixing evenly, add the binder and continue mixing for 5-10 minutes. After mixing evenly, add the micropore forming agent, composite additives and magnesia fine powder with a particle size of 0.5-0mm and 320 mesh, and continue mixing for 10-15 minutes until the raw materials are uniform.

[0019] Step 3, Molding: Weigh the mixed raw materials according to the quality requirements, add them to the mold, and use vibration and uniform material feeding from all sides to form the material on a 1000-ton friction brick press or hydraulic press with a molding pressure greater than 25 MPa.

[0020] Step 4: Drying: The shaped brick blanks are baked in a drying kiln for 12 to 24 hours to dehydrate.

[0021] Step 5, Microwave Crystallization Firing: After natural cooling, the dried brick blank is placed in a microwave sintering chamber under a nitrogen atmosphere. Under the microwave crystallization firing regime, a heat-insulating and energy-saving microporous-multiphase reinforced magnesium spinel brick based on microwave crystallization sintering is obtained.

[0022] The bulk density of magnesium spinel bricks is At 1000℃, its thermal conductivity is 2.5~3.0W / (m·K) and its apparent porosity is 10~15%.

[0023] The drying process in step four adopts a segmented heat preservation system: first, heat preservation at 100-130℃ for 2-4 hours, then raising the temperature to 180-250℃ and preheating for 10-20 hours. Segmented heat preservation is beneficial to promoting the in-situ reaction between the composite additives.

[0024] The microwave crystallization firing process in step five is as follows: the dried brick blank is placed in a microwave sintering chamber and heated to 600-800°C at a heating rate of 30-60°C / min to remove residual moisture and binder volatiles. Heating continues at a heating rate of 50-100°C / min to 1250-1450°C, and held for 20-60 minutes. During this stage, the aluminum powder is preferentially activated in the microwave field, significantly increasing the nitriding reaction rate, and MgAlON and... The efficiency of solid solution formation is greatly improved; natural cooling or controlled cooling to room temperature, utilizing the instantaneous cutoff characteristics of the microwave field, avoids excessive grain growth that may occur during the slow cooling process of traditional tunnel kilns.

[0025] This invention innovatively introduces lightweight aggregates such as hollow alumina spheres and hollow magnesium aluminum spinel spheres to replace part of the dense magnesia aggregate. The lightweight aggregates themselves have a hollow structure and low bulk density. This approach reduces the bulk density of the matrix and the solid-phase heat transfer pathway at the material framework level. Simultaneously, by adding micropore-forming agents (graphene nanosheets, polystyrene microspheres) and precisely controlling their decomposition and oxidation behavior during dehydration, a uniform, closed-pore micro / nano pore structure is generated in situ within the matrix. The millimeter-scale pores introduced by the lightweight aggregate and the micro / nano pores generated in situ within the matrix together constitute a hierarchical pore structure, effectively increasing the interfacial thermal resistance for heat transfer, effectively isolating heat, and significantly reducing the material's thermal conductivity.

[0026] The low thermal conductivity magnesia spinel brick prepared by this invention utilizes microwave heating to simultaneously and synchronously decompose micropore-forming agents (graphene nanosheets, activated carbon, and polystyrene microspheres) within the brick blank. This avoids the uneven pore size problem caused by the outer layer decomposing first and the inner layer decomposing later due to delayed heat conduction in traditional firing processes. Rapid microwave heating causes the decomposition gases to escape in a concentrated manner within a short time, forming more closed-pore structures with low connectivity, increasing the closed-pore porosity, and further reducing thermal conductivity. More precise atmosphere control can be achieved within the microwave sintering chamber. Based on the interaction between composite additives (aluminum powder, silicon nitride powder, and ultrafine graphite powder) and matrix components and the furnace atmosphere, a multiphase solid solution with high thermodynamic stability, MgAlON, is generated in situ. .ensure The stable formation of solid solutions avoids excessive oxidation of carbon materials. The rapid heating characteristics of microwave sintering effectively suppress abnormal grain growth, keeping the pores small and uniform, further improving the thermal insulation effect.

[0027] The MgAlON phase reaction proceeds significantly in the range of 1200–1500 °C. MgAlON has a face-centered cubic structure similar to magnesium aluminum spinel, but its lattice contains nitrogen atoms, which endows the material with the following properties: (1) High resistance to erosion: MgAlON is highly resistant to slag (especially (1) The wetting angle of the MgAlON crystal is large, which can effectively inhibit the penetration of slag along the pores; (2) Thermal expansion matching: its linear expansion coefficient is similar to that of periclase, which reduces microcracks caused by thermal stress; (3) Reinforcing matrix: MgAlON crystals are often in the form of strips or equiaxed shapes, filling the gaps between particles and significantly improving the strength of the material.

[0028] Solid solutions combine the advantages of both nitrides and carbides: (1) High thermal conductivity: Its thermal conductivity is much higher than that of oxide matrices, which can form rapid heat dissipation channels inside the material and alleviate thermal shock stress. (2) Low coefficient of thermal expansion: Its coefficient of thermal expansion is lower than that of MgAlON, which helps to offset the decrease in thermal shock resistance caused by the introduction of pores. (3) Anti-slag wetting: With a contact angle greater than 120° with molten slag, the material's resistance to slag erosion is significantly improved.

[0029] MgAlON and The two phases are uniformly interwoven at the microscale, forming an "interpenetrating network structure." The high-melting-point multiphase reinforcing phase fills the interparticle gaps, creating a "pinning" effect that strengthens the bond between the matrix and aggregate. Simultaneously, these reinforcing phases possess a moderate coefficient of thermal expansion, effectively compensating for potential mechanical property degradation and thermal shock resistance deterioration caused by the introduction of pores. These phases synergistically construct a "microporous-multiphase" reinforcing structure, characterized by enhanced composite layer barrier effect, rapid homogenization of thermal stress, suppression of crack propagation, and significantly improved creep resistance, achieving a synergistic optimization of low thermal conductivity with high erosion resistance and high thermal shock resistance.

[0030] The core of the low thermal conductivity of magnesium spinel bricks in this invention lies in the introduction of a large number of closed micro-nano pores to increase the scattering interface and reduce solid-phase heat transfer. Precise control of pore size is achieved through a three-pronged approach of "lightweight aggregate + micropore forming agent + microwave firing process". (1) Activated carbon and graphene nanosheets undergo oxidation reactions in the range of 800–1200℃: or By controlling parameters such as particle size, amount added, and oxygen partial pressure, approximately spherical independent pores are formed, with pore sizes mainly distributed between 5 and 30 μm. The pore size can be linearly controlled by adjusting the particle size of the carbon material. (2) Polystyrene microspheres completely decompose and vaporize at 300–500 °C. By controlling the diameter of the microspheres, the original size of the microspheres can be accurately replicated to form highly uniform spherical macropores (20–100 μm) with intact pore walls, which have little impact on the strength of the material.

[0031] The preparation method of this invention optimizes particle size distribution and molding pressure to ensure that the mixture containing lightweight aggregate and micropore forming agent has good molding performance. The use of a microwave crystallization sintering process ensures uniform decomposition of the micropore forming agent and sufficient in-situ reaction, thereby stabilizing product quality and enabling it to meet the production requirements of existing green and intelligent production lines, achieving stable, efficient, and low-energy industrial production.

[0032] This invention constructs a millimeter-scale porous framework by introducing lightweight aggregates, utilizes a micropore-forming agent to generate uniform micron-scale closed pores under precisely controlled temperature and atmosphere sintering, and combines this with the in-situ reaction of composite additives to generate MgAlON and The multiphase solid solution achieves dual synergistic reinforcement through "pore structure-phase". These reinforcing phases not only fill the interparticle gaps, strengthening the bond between the matrix and aggregate and improving the material's resistance to slag erosion and high-temperature strength, but also, due to their low coefficient of thermal expansion and high thermal conductivity, effectively compensate for the potential decrease in mechanical properties and deterioration in thermal shock stability caused by the introduction of pores. This achieves synergistic optimization of low thermal conductivity with high erosion resistance and high thermal shock performance, meeting the demanding operating conditions of the RH refining furnace.

[0033] The beneficial effects of this invention are as follows: This invention innovatively uses lightweight aggregate to replace part of the dense magnesia aggregate, and constructs a multi-level porous structure in situ with a micropore forming agent to reduce the thermal conductivity. At the same time, it utilizes composite additives such as aluminum powder and silicon nitride powder to generate a high-melting-point multiphase reinforcing phase in situ during baking and microwave firing, thus constructing a micropore-multiphase synergistic reinforcing structure. While significantly reducing the thermal conductivity of the material, it ensures its excellent slag erosion resistance, high-temperature strength and thermal shock stability, achieving synergistic optimization of low thermal conductivity and high erosion resistance and high thermal shock performance, so as to meet the needs of green and efficient production in high-temperature industrial kilns.

[0034] 1. Significantly reduced thermal conductivity, lower energy consumption, and green production: The thermal conductivity (1000℃) of the magnesia spinel bricks prepared by this invention can be reduced to 2.5-3.0 W / (m·K), which is more than 30% lower than that of traditional magnesia spinel bricks. When applied to high-temperature industrial kilns, it can effectively reduce furnace heat loss, reduce energy consumption per ton of steel by 10-15%, and significantly reduce carbon emissions.

[0035] 2. Excellent overall performance: Through the microporous-multiphase synergistic structure design, this invention achieves low thermal conductivity while ensuring the material's high-temperature strength (room temperature compressive strength > 120MPa), thermal shock resistance (> 10 cycles), and excellent slag erosion resistance, thus meeting the stringent requirements of high-end steel refining.

[0036] 3. Protect the metal shell and extend equipment life: Due to the reduced thermal conductivity of the material, the service temperature of the furnace metal shell decreases accordingly, effectively slowing down the deformation and damage caused by high-temperature creep and oxidation, and greatly improving the service life and safety factor of the entire refining system.

[0037] 4. Improved working environment: The significantly reduced surface heat radiation of the furnace body effectively improves the working environment for workshop operators, meeting the requirements of modern industry for occupational health and safety.

[0038] 5. Simple process, environmentally friendly, and easy to industrialize: The raw materials used are readily available, the process is compatible with existing refractory material production lines, the product is chromium-free, and there is no risk of hexavalent chromium pollution during production and use. Microwave sintering only heats the sintering material itself, effectively alleviating heat loss and improving energy efficiency. Heat source pollution is almost zero, energy consumption is low, and carbon emissions are minimal. Through technological optimization and equipment improvement, stable large-scale production can be achieved, resulting in good economic and social benefits. Detailed Implementation

[0039] The present invention will be further described in detail below with reference to specific embodiments.

[0040] Example 1:

[0041] A heat-insulating and energy-saving microporous-multiphase reinforced magnesia spinel brick, by weight, comprises the following raw material components: 65 parts of macrocrystalline magnesia material, including 12 parts of magnesia with a particle size of 5-3 mm, 22 parts of magnesia with a particle size of 3-1 mm, 18 parts of magnesia with a particle size of 1-0.5 mm, 10 parts of magnesia with a particle size of 0.5-0 mm, and 3 parts of magnesia with a particle size of 320 mesh; 12 parts of lightweight aggregate alumina hollow spheres with a particle size of 1-2 mm and a bulk density of 1.2 g / cm³; 6 parts of micropore forming agent activated carbon with a particle size <5 μm; 5 parts of composite additives (2 parts of metallic aluminum powder, 1 part of silicon nitride powder, and 2 parts of ultrafine graphite powder); and 3.0% of the total weight of the raw material as an external binder phenolic resin.

[0042] The preparation method of this heat-insulating and energy-saving microporous-multiphase reinforced magnesium spinel brick is as follows:

[0043] Step 1: Ingredients: Accurately weigh each ingredient according to the above formula.

[0044] Step 2, Mixing: First, premix the large crystalline magnesia particles and lightweight aggregates in a forced mixer for 3 minutes; add phenolic resin and continue mixing for 5 minutes; finally, add micropore forming agent, composite additives and magnesia fine powder with a particle size of 0.5-0 mm and 320 mesh, and mix for 15 minutes until the raw materials are uniform.

[0045] Step 3: Molding: Weigh the mixed raw materials and add them into the mold. Use vibration pressure molding process to form the material on a 1000-ton hydraulic press with a molding pressure of 28MPa.

[0046] Step 4, Drying: The drying process in the kiln after the brick blanks are formed adopts a segmented heat preservation system: first, heat preservation at 120℃ for 3 hours, and then heat preservation at 180℃ for 20 hours to dehydrate.

[0047] Step 5: After natural cooling, place the dried brick blank in a microwave sintering chamber under a nitrogen atmosphere and heat it to 600°C at a heating rate of 30°C / min to remove residual moisture and binder volatiles. Continue heating to 1250°C at a heating rate of 50°C / min and hold for 20 minutes to obtain a heat-insulating and energy-saving microporous-multiphase reinforced magnesia spinel brick.

[0048] Example 2:

[0049] A high-efficiency, heat-insulating, and energy-saving microporous-multiphase synergistic reinforced magnesia spinel brick comprises the following raw material components and their weight proportions: 70 parts of macrocrystalline magnesia material, including 15 parts of magnesia with a particle size of 5-3 mm, 25 parts of magnesia with a particle size of 3-1 mm, 15 parts of magnesia with a particle size of 1-0.5 mm, 12 parts of magnesia with a particle size of 0.5-0 mm, and 3 parts of magnesia with a particle size of 320 mesh; 8 parts of lightweight aggregate magnesia-alumina spinel hollow spheres, with a particle size of 1-3 mm and a bulk density of... ; 3 parts of graphene nanosheets as micropore forming agent; 6 parts of composite additives, including 2.5 parts of aluminum powder, 1.5 parts of silicon nitride powder, and 2 parts of ultrafine graphite powder; and 4% of the total weight of the raw material as an external binder, lignin sulfonate.

[0050] The preparation method of this heat-insulating and energy-saving microporous-multiphase reinforced magnesium spinel brick is as follows:

[0051] Step 1: Ingredients: Accurately weigh each ingredient according to the above formula.

[0052] Step 2, Mixing: First, premix the large crystalline magnesia particles and lightweight aggregates in a forced mixer for 1 minute; add phenolic resin and continue mixing for 8 minutes; finally, add microporous forming agent, composite additives and magnesia fine powder with a particle size of 0.5-0 mm and 320 mesh, and mix for 12 minutes until the raw materials are uniform.

[0053] Step 3: Molding: Weigh the mixed raw materials and add them into the mold. Use vibration pressure molding process to form the material on a 1000-ton hydraulic press with a molding pressure of 30MPa.

[0054] Step 4, Drying: The drying process of the shaped brick blanks in the drying kiln adopts a segmented heat preservation system: first, it is kept at 100℃ for 4 hours, and then the temperature is raised to 200℃ and kept at 200℃ for 15 hours to dehydrate.

[0055] Step 5: After natural cooling, place the dried brick blank in a microwave sintering chamber under a nitrogen atmosphere and heat it to 700°C at a heating rate of 40°C / min to remove residual moisture and binder volatiles. Continue heating to 1300°C at a heating rate of 70°C / min and hold for 60 minutes to obtain a heat-insulating and energy-saving microporous-multiphase reinforced magnesia spinel brick.

[0056] Example 3:

[0057] A high-efficiency, heat-insulating, and energy-saving microporous-multiphase synergistic reinforced magnesia spinel brick comprises the following raw material components and their weight proportions: 60 parts of macrocrystalline magnesia material, including 10 parts of magnesia with a particle size of 5-3 mm, 20 parts of magnesia with a particle size of 3-1 mm, 18 parts of magnesia with a particle size of 1-0.5 mm, 8 parts of magnesia with a particle size of 0.5-0 mm, and 4 parts of magnesia with a particle size of 320 mesh; and 15 parts of lightweight aggregate, which is a 1:1 mixture of alumina hollow spheres and magnesia-alumina spinel hollow spheres, with a particle size of 1-3 mm and an average bulk density of [missing information]. ; 5 parts of polystyrene microspheres as micropore forming agent; 10 parts of composite additives, including 4 parts of aluminum powder, 2 parts of silicon nitride powder, and 4 parts of ultrafine graphite powder; and 2% of aluminum dihydrogen phosphate as an external binder.

[0058] The preparation method of this heat-insulating and energy-saving microporous-multiphase reinforced magnesium spinel brick is as follows:

[0059] Step 1: Ingredients: Accurately weigh each ingredient according to the above formula.

[0060] Step 2, Mixing: First, premix the large crystalline magnesia particles and lightweight aggregates in a forced mixer for 2 minutes; add phenolic resin and continue mixing for 10 minutes; finally, add microporous forming agent, composite additives and magnesia fine powder with a particle size of 0.5-0 mm and 320 mesh, and mix for 10 minutes until the raw materials are uniform.

[0061] Step 3: Molding: Weigh the mixed raw materials and add them into the mold. Use vibration and pressure molding process to form the bricks on a 1000-ton friction brick press with a molding pressure of 30MPa.

[0062] Step 4, Drying: The drying process in the kiln after the brick blanks are formed adopts a segmented heat preservation system: first, heat preservation at 130℃ for 2 hours, and then heat preservation at 250℃ for 10 hours to dehydrate.

[0063] Step 5: After natural cooling, place the dried brick blank in a microwave sintering chamber under a nitrogen atmosphere and heat it to 800°C at a heating rate of 60°C / min to remove residual moisture and binder volatiles. Continue heating to 1450°C at a heating rate of 100°C / min and hold for 35 minutes to obtain a heat-insulating and energy-saving microporous-multiphase reinforced magnesia spinel brick.

[0064] The main performance indicators of the high-efficiency thermal insulation and energy-saving microporous-multiphase reinforced magnesia spinel bricks prepared in Examples 1-3 are shown in the table below:

[0065]

[0066] As shown in the table above, the bulk density of the magnesium spinel brick prepared in this embodiment of the invention is... It has a thermal conductivity (1000℃) of 2.5~3.0W / (m·K) and an apparent porosity of 10~15%; it has low bulk density and thermal conductivity, while maintaining high room temperature pressure resistance and excellent thermal shock stability, and has excellent comprehensive performance.

[0067] The parts of this invention not described in detail are prior art. The above embodiments will help those skilled in the art to further understand this invention, but do not limit this invention in any way. Various changes in form, detail, or equivalents made using this invention without departing from the scope of the appended claims are all within the protection scope of this invention.

Claims

1. A heat-insulating energy-saving microporous multiphase reinforced magnesia spinel brick, characterized in that, By weight, the raw material comprises the following components: 60-70 parts of macrocrystalline magnesia, including 10-15 parts of magnesia with a particle size of 5-3 mm, 20-25 parts of magnesia with a particle size of 3-1 mm, 15-20 parts of magnesia with a particle size of 1-0.5 mm, 8-12 parts of magnesia with a particle size of 0.5-0 mm, and 3-5 parts of 320-mesh magnesia; 8-15 parts of lightweight aggregate; 3-6 parts of microporous forming agent; 5-10 parts of composite additives; and 2-4% of the total weight of the raw material as external binder. The micropore-forming agent is polystyrene microspheres; The composite additives include aluminum powder, silicon nitride powder, and ultrafine graphite powder; The lightweight aggregate is one or a combination of two of the following: hollow alumina spheres and hollow magnesium aluminum spinel spheres; The preparation method of thermally insulating and energy-saving microporous-multiphase reinforced magnesia spinel bricks includes the following steps: Step 1: Ingredients: Weigh all ingredients according to the formula ratio; Step 2, Mixing: First, put the magnesia particles with a particle size of 5-3mm, 3-1mm, and 1-0.5mm and the lightweight aggregate into the mixer and premix for 1-3 minutes. After mixing evenly, add the binder and continue mixing for 5-10 minutes. After mixing evenly, add the micropore forming agent, composite additives and magnesia fine powder with a particle size of 0.5-0mm and 320 mesh, and continue mixing for 10-15 minutes until the raw materials are uniform. Step 3, Molding: Weigh the mixed raw materials according to the quality requirements, add them to the mold, and use vibration and even feeding method to shape them on a 1000-ton friction brick press or hydraulic press with a molding pressure greater than 25MPa. Step 4: Drying: The shaped brick blanks are baked in a drying kiln for 12 to 24 hours to dehydrate them; Step 5, Microwave Crystallization Firing: After natural cooling, the dried brick blank is placed in a microwave sintering chamber under a nitrogen atmosphere and heated to 600-800℃ at a heating rate of 30-60℃ / min to remove residual moisture and binder volatiles. The temperature is then increased to 1250-1450℃ at a heating rate of 50-100℃ / min and held for 20-60 minutes. Under the microwave crystallization firing regime, a heat-insulating and energy-saving microporous-multiphase reinforced magnesia spinel brick based on microwave crystallization sintering is obtained.

2. The heat-insulating energy-saving micropore-multiphase reinforced magnesia spinel brick according to claim 1, characterized in that: The particle size range of lightweight aggregate is 1-3 mm, and the bulk density is ≤1.5 g / cm³.

3. The micro-porous and multiphase reinforced magnesia spinel brick of heat insulation and energy saving according to claim 1, characterized in that: The diameter of the polystyrene microspheres is 10–100 μm.

4. The micro-porous and multiphase reinforced magnesia spinel brick of heat insulation and energy saving according to claim 1, characterized in that: The binder is aluminum dihydrogen phosphate.

5. The heat-insulating and energy-saving microporous-multiphase reinforced magnesia spinel brick according to claim 1, characterized in that: The magnesium oxide content in the large crystalline magnesia material is >97wt%.

6. The heat-insulating and energy-saving microporous-multiphase reinforced magnesia spinel brick according to claim 1, characterized in that: In the composite additives, the aluminum powder has a particle size of 150 mesh and an aluminum content of >98.5 wt%; the silicon nitride powder has a particle size of 250 mesh and a silicon nitride content of >98 wt%; and the ultrafine graphite powder has a particle size of <3 μm and a carbon content of >95 wt%.

7. A process for the preparation of the micro-porous, multiphase, reinforced magnesia spinel brick as claimed in claim 1, characterized in that, Includes the following steps: Step 1: Ingredients: Weigh all ingredients according to the formula ratio; Step 2, Mixing: First, put the magnesia particles with a particle size of 5-3mm, 3-1mm, and 1-0.5mm and the lightweight aggregate into the mixer and premix for 1-3 minutes. After mixing evenly, add the binder and continue mixing for 5-10 minutes. After mixing evenly, add the micropore forming agent, composite additives and magnesia fine powder with a particle size of 0.5-0mm and 320 mesh, and continue mixing for 10-15 minutes until the raw materials are uniform. Step 3, Molding: Weigh the mixed raw materials according to the quality requirements, add them to the mold, and use vibration and even feeding method to shape them on a 1000-ton friction brick press or hydraulic press with a molding pressure greater than 25MPa. Step 4: Drying: The shaped brick blanks are baked in a drying kiln for 12 to 24 hours to dehydrate them; Step 5, Microwave Crystallization Firing: After natural cooling, the dried brick blank is placed in a microwave sintering chamber under a nitrogen atmosphere. Under the microwave crystallization firing regime, a heat-insulating and energy-saving microporous-multiphase reinforced magnesium spinel brick based on microwave crystallization sintering is obtained. The bulk density of magnesium spinel bricks is 2.9 g·cm³. -3 The thermal conductivity at 1000℃ is 2.8 W / (m·K), and the apparent porosity is 12%.

8. The preparation method of a heat-insulating and energy-saving microporous-multiphase reinforced magnesia spinel brick according to claim 7, characterized in that: The drying process in step four adopts a segmented heat preservation system, first keeping the temperature at 100-130℃ for 2-4 hours, and then raising the temperature to 180-250℃ and keeping it for 10-20 hours.

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