Thermal expansion compensation magnesia-calcium brick and preparation process thereof

Abstract

The invention relates to the technical field of preparation of magnesia-calcium bricks, and provides a thermal expansion compensation magnesia-calcium brick and a preparation process thereof. The magnesia-calcium brick adopts a three-layer gradient structure design and comprises a porous layer, a transition layer and a compact layer, and negative thermal expansion composite particles, neutral thermal expansion adjusting particles and thermosensitive expansion particles are introduced into the formula of each layer to jointly form a thermal expansion compensation system. The bonding strength between layers is enhanced through a mechanical meshing structure of the dovetail grooves and the dovetail protrusions, and interlayer stripping is effectively avoided. The preparation process comprises the steps of raw material surface modification, layered burdening, mold design and charging, segmented temperature control sintering, coordinated cooling and the like. The problems that a traditional magnesia-calcium brick is not matched in thermal expansion and prone to cracking are effectively solved, the thermal shock resistance and structural stability of a brick body are remarkably improved, and the service life of the brick body is remarkably prolonged.

Description

Technical Field

[0001] This invention relates to the field of magnesium-calcium brick preparation technology, specifically to a thermal expansion-compensating magnesium-calcium brick and its preparation process. Background Technology

[0002] Magnesia-calcium bricks are alkaline refractory materials with magnesium oxide and calcium oxide as the main components. Due to their excellent high-temperature resistance and resistance to alkaline slag erosion, they are widely used in the lining of high-temperature equipment such as steel ladle refining furnaces, cement rotary kiln transition zones, and non-ferrous metal smelting furnaces in the metallurgical industry. Magnesia-calcium bricks need to withstand drastic temperature fluctuations during high-temperature applications, and the thermal expansion behavior of the material directly affects its structural stability and service life.

[0003] In practical applications, the difference in thermal expansion coefficients between magnesium oxide and calcium oxide, coupled with a significant internal temperature gradient, leads to frequent thermal stress concentration. Traditional homogeneous magnesia-calcium bricks are prone to microcracks that gradually propagate under thermal cycling conditions, affecting their ultimate service life. Specifically, conventional multilayer magnesia-calcium bricks exhibit weak interlayer bonding, making them susceptible to delamination under repeated thermal stress; the lack of components capable of regulating thermal expansion across the entire temperature range easily triggers interfacial microcracks, impacting service life; the surfaces of some thermal expansion-regulating components are susceptible to high-temperature melting or oxidation failure, reducing long-term stability; and the homogenization firing process fails to consider the differences in sintering shrinkage between different component layers, exacerbating interlayer stress accumulation, and insufficient thermal stress release during cooling leads to cracking risks.

[0004] These technical defects lead to problems such as decreased thermal shock resistance and shortened service life of traditional magnesia-calcium bricks, necessitating the design of thermal expansion-compensating magnesia-calcium bricks and their preparation process to solve these issues. Summary of the Invention

[0005] To address the problems existing in the prior art, the present invention provides a thermal expansion compensating magnesia-calcium brick, which includes a porous layer, a transition layer, and a dense layer, each layer comprising the following components by weight: The porous layer consists of: 55-70 parts magnesium oxide, 18-28 parts calcium oxide, 2-4 parts neutral thermal expansion regulating particles, 1-3 parts thermal expansion particles, 2-5 parts modified binder, 2-5 parts porous pore-forming agent, and 1.5-3.5 parts thermal compensation additive. The transition layer consists of: 65-75 parts magnesium oxide, 8-15 parts calcium oxide, 2-5 parts negative thermal expansion composite particles, 1-3 parts neutral thermal expansion regulating particles, 0.5-2 parts thermally sensitive expansion particles, 3-6 parts modified binder, 1-3 parts porous pore-forming agent, and 0.8-2.3 parts thermal compensation additive. The dense layer consists of: 75-85 parts magnesium oxide, 5-12 parts calcium oxide, 3-6 parts negative thermal expansion composite particles, 1-2 parts neutral thermal expansion regulating particles, 4-7 parts modified binder, and 0.5-2 parts porous pore-forming agent. The negative thermal expansion composite particles contain ZrW2O8 and Al2O3-SiO2, the modified binder is a composite of aluminum phosphate and phenolic resin, the neutral thermal expansion regulating particles contain β-quartz and MgAl2O4, and the thermosensitive expansion particles are calcium sulfate coated with calcium silicate.

[0006] In a preferred embodiment, the heat compensation additive comprises the following components by weight: 0.3-0.8 parts lithium carbonate, 0.5-1.2 parts boron oxide, and 1-3 parts titanium dioxide; the porous pore-forming agent comprises, by weight: 15-25 parts silica powder; 20-30 parts ammonium bicarbonate; 5-10 parts lignin fiber; 5-10 parts starch; 1-3 parts polyvinyl alcohol powder; 8-12 parts water; 3-6 parts zirconium oxide powder; and 5-10 parts mullite powder.

[0007] In a preferred embodiment, a dovetail groove structure is formed on the lower surface of the porous layer, and a dovetail protrusion structure matching the dovetail groove is formed on the upper surface of the transition layer; a dovetail groove structure is formed on the lower surface of the transition layer, and a dovetail protrusion structure matching the dovetail groove is formed on the upper surface of the dense layer.

[0008] In a preferred embodiment, the preparation process of the negative thermal expansion composite particles is as follows: ZrW2O8 powder is mixed with silica sol and alumina sol to form a slurry; coated particles are prepared by spray granulation equipment; and calcined at 800-1000℃ for 1-3 hours to obtain negative thermal expansion composite particles with Al2O3-SiO2 coating on the surface.

[0009] In a preferred embodiment, the preparation process of the neutral thermal expansion regulating particles is as follows: mixing β-quartz powder with magnesium aluminum spinel precursor; preparing composite particles by mechanical coating method; and heat-treating at 1100-1250℃ for 2-4 hours to obtain neutral thermal expansion regulating particles.

[0010] In a preferred embodiment, the preparation process of the thermosensitive expansion particles is as follows: calcium sulfate particles are used as the core; calcium silicate is used as the coating material; and coated particles are prepared at 300-450℃ using a dry coating process to obtain the thermosensitive expansion particles.

[0011] In a preferred embodiment, the modified binder is prepared by mixing aluminum phosphate and phenolic resin at a mass ratio of 2-4:1; reacting at 60-90°C for 1-3 hours; and obtaining the modified binder after cooling. The preparation process of the porous pore-forming agent is as follows: Silica powder, zirconium oxide powder, and mullite powder are mixed evenly in a certain proportion to obtain an inorganic mineral powder mixture; lignin fiber and starch are added, and dry-stirred for 2-4 minutes; ammonium bicarbonate and polyvinyl alcohol powder are added, and dry-stirred for another 2-3 minutes; 8-12 parts of water are sprayed in, and wet-stirred until uniform and free of agglomerates, controlling the moisture content; the mixture is placed in a mold and pressed into shape; the molded body is dried at 100-200℃ for 4-8 hours to remove free water; the temperature is uniformly increased to 650-800℃ at 3-5℃ per hour to decompose ammonium bicarbonate and organic matter, forming a porous structure; the temperature is further increased to 1500-1600℃ and held for 2-4 hours; after cooling, porous pore-forming agent particles are obtained.

[0012] This invention also designs a preparation process for thermal expansion compensating magnesia-calcium bricks, including the following steps: S1: Magnesium oxide particles are surface modified by depositing iron oxide on the surface of magnesium oxide particles using a wet chemical method to form a surface modification layer. S2: Prepare mixtures of porous layer, transition layer and dense layer respectively; S3: Mold preparation and interface structure processing, to prepare a layered molding mold with dovetail grooves and dovetail protrusions; S4: The mixture of porous layer, transition layer and dense layer is loaded into the mold and the molded blank is obtained by layered loading and static pressing. S5: The shaped green body is fired using a segmented controlled firing process; S6: After firing, coordinated cooling is carried out, using a segmented cooling system to cool from the firing temperature to room temperature.

[0013] Furthermore, the specific process of step S1 is as follows: S11: Disperse magnesium oxide particles in deionized water at a weight ratio of 1:10 and stir for 15-30 minutes to fully wet them; S12: Slowly add 0.1-0.3 mol / L ferrous sulfate solution while stirring, the amount added is 3-8% of the weight of magnesium oxide; S13: Then add 0.2-0.5 mol / L sodium hydroxide solution to adjust the pH to 9-11; S14: Stir continuously at 70-90℃ for 0.5-2 hours to allow iron oxide to be uniformly deposited on the surface of magnesium oxide; S15: After standing and separating into layers, pour off the supernatant and wash with deionized water 3-5 times until neutral. S16: Dry at 100-120℃ for 4-8 hours to obtain magnesium oxide particles with a surface-deposited iron oxide modified layer, the thickness of which is 5-20nm; The specific process of layered ingredient mixing in step S2 is as follows: S21: Porous layer formulation: Weigh magnesium oxide, calcium oxide, neutral thermal expansion regulating particles, thermosensitive expansion particles, porous pore-forming agent and thermal compensation additive according to the formula; dry mix for 5 minutes first, add modified binder, and mix for 15-30 minutes. S22: Transition layer ingredients: Weigh magnesium oxide, calcium oxide, negative thermal expansion composite particles, neutral thermal expansion regulating particles, thermosensitive expansion particles, porous pore-forming agent and thermal compensation additive according to the proportion; dry mix for 5 minutes first; add 3-6 parts of modified binder and mix for 15-30 minutes. S23: Dense layer ingredients: Weigh the modified magnesium oxide, calcium oxide, negative thermal expansion composite particles, and neutral thermal expansion regulating particles according to the proportion, and dry mix for 5 minutes; add the modified binder and porous pore-forming agent, and mix for 15-30 minutes. The specific process of mold preparation and interface structure processing in step S3 is as follows: S31: Prepare a three-section molding die. The inner cavity of the die is divided into an upper section, a middle section, and a lower section, which correspond to the molding space of the porous layer, the transition layer, and the dense layer. S32: A dovetail groove male mold structure is machined on the lower surface of the upper mold, and a corresponding dovetail protrusion female mold structure is machined on the upper surface of the middle mold. S33: A dovetail groove male mold structure is machined on the lower surface of the middle section mold; a dovetail protrusion female mold structure matching the dovetail groove is machined on the upper surface of the lower section mold, with the protrusion height matching the groove depth. Furthermore, the specific process of gradient layering shaping in step S4 is as follows: S41: Preheat the mold to 80-120℃ and apply release agent; S42: Fill the lower mold with a dense layer of mixture, controlling the density of the mixture to be 1.8-2.2 g / cm³. 3 Vibrate on a vibration table for 30-60 seconds; S43: Apply a pre-pressure of 5-15MPa and hold for 30-60 seconds to make the dense layer reach the designed thickness and form a flat upper surface; S44: Apply an interface bonding enhancer to the upper surface of the dense layer. This is a composite solution of silica sol and alumina sol with a solid content of 15-25%, applied at a rate of 0.2-0.8 kg / m². 2 ; S45: Install the intermediate mold, fill in the transition layer mixture, and control the filling density to 1.5-1.9 g / cm³. 3 At this point, the dovetail groove male mold comes into contact with the upper surface of the dense layer, forming a dovetail groove structure; S46: Apply a pre-pressure of 8-20 MPa to the transition layer so that the transition layer material fills the dovetail groove and forms a dovetail protrusion structure; S47: Install the upper mold and fill it with porous layer mixture, with a density controlled at 1.2-1.6 g / cm³.3 ; S48: Perform overall isostatic pressing, with a molding pressure of 80-150MPa and a holding time of 3-5 minutes to achieve tight bonding of each layer. S49: After molding is completed, demold in layers. First, reduce the molding pressure to 5-10MPa and maintain slight pressure to prevent the blank from deforming. S410: Slowly lift the upper mold section, control the demolding speed at 2-5mm / min to avoid damage to the porous layer, and provide a protective cover to the surface of the porous layer during the demolding process; S411: The dovetail groove male mold structure of the horizontally removed middle section mold is first tilted outward by 3-8°, and then vertically lifted out. The demolding force is controlled within the range of 0.5-2MPa to ensure the integrity of the dovetail protrusion structure of the transition layer. S412: Demolding is performed by bottom lifting, with the lifting speed controlled at 1-3 mm / min. At the same time, the dense layer dovetail protrusion structure is laterally supported to prevent structural damage during demolding. S413: After demolding, the blank should be left to stand at room temperature for 12-24 hours, during which time the ambient humidity should be maintained at 40-60% to prevent cracking of the blank surface; The specific process of shrinkage matching firing in step S5 is as follows: S51: The formed blank is loaded into a firing furnace with zoned heating function. The furnace body is set with three independent temperature control zones: upper, middle and lower. S52: First stage of heating: Heat to 400-600℃ at a rate of 5-10℃ / hour, hold for 1-3 hours, use an air atmosphere to allow the binder to react fully and remove the bound water to achieve initial curing; S53: Second stage heating: Heat to 800-1000℃ at a rate of 8-15℃ / hour, hold for 2-5 hours, use a weak reducing atmosphere, carbon monoxide volume fraction of 8-15%, so that the components undergo solid-phase reaction and form intermediate bonds. S54: Third stage heating: Heat to 1400-1550℃ at a rate of 10-20℃ / hour, hold for 3-6 hours to achieve full sintering and densification of each layer; S55: Zoned temperature control: The temperature of the upper zone is 10-20℃ lower than that of the middle zone, and the temperature of the middle zone is 5-15℃ higher than that of the lower zone; The specific process of coordinated cooling in step S6 is as follows: S61: Starting from the highest firing temperature of 1400-1550℃, cool down to 1100℃ at a rate of 8-15℃ / hour; S62: Slowly cool from 1100℃ to 600℃ at a rate of 3-8℃ / hour. This temperature range is a stress-sensitive area. Slow cooling releases thermal stress. S63: Cool from 600°C to 200°C at a rate of 10-20°C / hour; S64: Naturally cool from 200℃ to room temperature, with a total cooling time controlled within 24-48 hours.

[0014] The beneficial effects achieved by this invention are as follows: First, this invention achieves comprehensive compensation for the thermal expansion of magnesia-calcium bricks through a three-layer gradient structure design and the synergistic effect of various functional composite particles. The magnesium oxide content in the porous layer, transition layer, and dense layer increases in a gradient, while the calcium oxide content decreases in a gradient, giving the outer layer excellent thermal shock resistance and effectively controlling volume expansion stress in the inner layer. The layers are firmly connected by a mechanical interlocking structure of dovetail grooves and dovetail protrusions, avoiding the interlayer delamination problem that easily occurs with traditional planar bonding methods, significantly improving the overall structural stability and service life of the brick.

[0015] Secondly, the negative thermal expansion composite particles, neutral thermal expansion regulating particles, and thermosensitive expansion particles constitute a complete thermal expansion compensation system, playing a synergistic role in different temperature ranges. The ZrW2O8 core of the negative thermal expansion composite particles contracts upon heating, effectively offsetting the positive thermal expansion of the matrix material, while Al2O3-SiO2 provides chemical protection and mechanical strength. The combination of β-quartz and MgAl2O4 in the neutral thermal expansion regulating particles achieves precise regulation of thermal expansion, balancing the differences in thermal expansion between layers. The thermosensitive expansion particles undergo phase change expansion within a specific temperature range, promptly filling microcracks caused by shrinkage, ensuring the thermal stability of the brick across the entire temperature range.

[0016] Third, the modified binder employs a composite system of aluminum phosphate and phenolic resin, achieving a synergistic effect of organic-inorganic hybrid materials. Aluminum phosphate provides excellent high-temperature bonding strength and chemical stability, while phenolic resin ensures room-temperature moldability and toughness. The two form a three-dimensional network structure through Al-OP bonds and hydrogen bonds, giving the binder both high-temperature stability and good processability. The porous pore-forming agent in the composite formulation forms a refractory skeleton through silica powder, zirconium oxide powder, and mullite powder. Ammonium bicarbonate decomposes at high temperatures to create pores, while the organic components provide adhesion and toughness. The pore structure exhibits uniformity and stability.

[0017] Fourth, the surface modification process deposits an iron oxide modified layer on the surface of magnesium oxide particles using a wet chemical method, significantly improving the interfacial bonding strength and chemical compatibility between magnesium oxide and other components. The layered loading and static pressing process precisely controls the loading density and molding pressure of each layer, ensuring the integrity of the interlayer interface and optimized matching of the properties of each layer. The use of interfacial bonding enhancers further strengthens the interlayer bonding, and the precise molding of the dovetail groove structure ensures mechanical bonding force, improving the interfacial bonding strength of the multilayer composite material.

[0018] Fifth, the segmented controlled sintering process and coordinated cooling regime fully consider the differences in sintering characteristics and thermal expansion behavior of different layers. Zoned temperature control ensures that each layer is sintered under optimal temperature conditions, avoiding stress concentration and structural defects caused by temperature mismatch. The slow, coordinated cooling process effectively releases thermal stress, preventing cracking and deformation caused by rapid temperature changes. The synergistic effect of lithium carbonate, boron oxide, and titanium dioxide in the thermal compensation additives optimizes the sintering process, lowering the sintering temperature while improving high-temperature stability. Precise control of the entire preparation process ensures that the final product possesses excellent thermal stability, structural integrity, and reliability. Attached Figure Description

[0019] Figure 1 This is a perspective view of the overall structure of the thermal expansion compensation magnesium-calcium brick of the present invention; Figure 2 yes Figure 1 A schematic diagram of the cross-sectional structure; Figure 3 This is a process flow diagram of the preparation of thermal expansion compensation magnesium-calcium bricks according to the present invention.

[0020] Numbering on the map: 1. Porous layer; 2. Transition layer; 3. Dense layer; 4. Dovetail groove; 5. Dovetail protrusion. Detailed Implementation

[0021] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings. In addition, the forms of the various structures described in the following embodiments are merely illustrative. The present invention is not limited to the structures described in the following embodiments. All other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] Reference Figures 1-2 This invention designs a thermal expansion-compensating magnesia-calcium brick, comprising a porous layer 1, a transition layer 2, and a dense layer 3, each layer containing the following components by weight: The porous layer 1 consists of: 55-70 parts magnesium oxide, 18-28 parts calcium oxide, 2-4 parts neutral thermal expansion regulating particles, 1-3 parts thermal expansion particles, 2-5 parts modified binder, 2-5 parts porous pore-forming agent, and 1.5-3.5 parts thermal compensation additive. The transition layer consists of two components: 65-75 parts magnesium oxide, 8-15 parts calcium oxide, 2-5 parts negative thermal expansion composite particles, 1-3 parts neutral thermal expansion regulating particles, 0.5-2 parts thermally sensitive expansion particles, 3-6 parts modified binder, 1-3 parts porous pore-forming agent, and 0.8-2.3 parts thermal compensation additive. The dense layer consists of three components: 75-85 parts magnesium oxide, 5-12 parts calcium oxide, 3-6 parts negative thermal expansion composite particles, 1-2 parts neutral thermal expansion regulating particles, 4-7 parts modified binder, and 0.5-2 parts porous pore-forming agent. The negative thermal expansion composite particles comprise a ZrW2O8 core and an Al2O3-SiO2 outer layer. The modified binder is a composite of aluminum phosphate and phenolic resin. The neutral thermal expansion regulating particles comprise a β-quartz core and a MgAl2O4 outer layer. The thermosensitive expansion particles are calcium sulfate coated with calcium silicate. The thermal compensation additive comprises the following components by weight: 0.3-0.8 parts lithium carbonate, 0.5-1.2 parts boron oxide, and 1-3 parts titanium dioxide. The porous pore-forming agent comprises, by weight: 15-25 parts silica powder; 20-30 parts ammonium bicarbonate; 5-10 parts lignin fiber; 5-10 parts starch; 1-3 parts polyvinyl alcohol powder; 8-12 parts water; 3-6 parts zirconium oxide powder; and 5-10 parts mullite powder.

[0023] The thermal expansion compensation magnesium-calcium brick of the present invention has the following structural features: a dovetail groove 4 structure is provided on the lower surface of the porous layer 1, and a dovetail protrusion 5 structure matching the dovetail groove 4 is provided on the upper surface of the transition layer 2; a dovetail groove 4 structure is provided on the lower surface of the transition layer 2, and a dovetail protrusion 5 structure matching the dovetail groove 4 is provided on the upper surface of the dense layer 3.

[0024] The preparation process of negative thermal expansion composite particles is as follows: ZrW2O8 powder is mixed with silica sol and alumina sol to form a slurry; coated particles are prepared by spray granulation equipment; and calcined at 800-1000℃ for 1-3 hours to obtain negative thermal expansion composite particles with Al2O3-SiO2 coating on the surface.

[0025] The preparation process of neutral thermal expansion regulating particles is as follows: β-quartz powder is mixed with magnesium aluminum spinel precursor; composite particles are prepared by mechanical coating method; and the particles are heat-treated at 1100-1250℃ for 2-4 hours to obtain neutral thermal expansion regulating particles.

[0026] The preparation process of thermosensitive expansion particles is as follows: calcium sulfate particles are used as the core; calcium silicate is used as the coating material; coated particles are prepared at 300-450℃ through a dry coating process to obtain thermosensitive expansion particles.

[0027] The preparation process of the modified binder is as follows: aluminum phosphate and phenolic resin are mixed at a mass ratio of 2-4:1; the mixture is reacted at 60-90℃ for 1-3 hours; and the modified binder is obtained after cooling. The preparation process of the porous pore-forming agent is as follows: Silica powder, zirconium oxide powder, and mullite powder are mixed evenly in a certain proportion to obtain an inorganic mineral powder mixture; lignin fiber and starch are added, and dry-stirred for 2-4 minutes; ammonium bicarbonate and polyvinyl alcohol powder are added, and dry-stirred for another 2-3 minutes; 8-12 parts of water are sprayed in, and wet-stirred until uniform and free of agglomerates, controlling the moisture content; the mixture is placed in a mold and pressed into shape; the molded body is dried at 100-200℃ for 4-8 hours to remove free water; the temperature is uniformly increased to 650-800℃ at 3-5℃ per hour to decompose ammonium bicarbonate and organic matter, forming a porous structure; the temperature is further increased to 1500-1600℃ and held for 2-4 hours; after cooling, porous pore-forming agent particles are obtained.

[0028] The thermal expansion compensation magnesia-calcium brick of this invention adopts a three-layer gradient structure design, including an outer porous layer 1, an intermediate transition layer 2, and an inner dense layer 3. In a preferred embodiment, the thickness of the dense layer 3 accounts for 30-45% of the total thickness, the thickness of the transition layer 2 accounts for 35-50% of the total thickness, and the thickness of the porous layer 1 accounts for 15-30% of the total thickness. The thermal expansion compensation magnesia-calcium brick can effectively disperse thermal stress. The layers are connected by a mechanical interlocking structure of dovetail grooves 4 and dovetail protrusions 5. The lower surface of the porous layer 1 has a dovetail groove 4 structure, and the upper surface of the transition layer 2 has a matching dovetail protrusion 5 structure. Similarly, the dovetail groove 4 on the lower surface of the transition layer 2 and the dovetail protrusion 5 on the upper surface of the dense layer 3 interlock with each other, ensuring the firmness of the interlayer bonding.

[0029] The thermal expansion compensation magnesia-calcium brick of this invention uses carefully designed components and proportions to determine that magnesium oxide, as the main raw material, exhibits a gradient distribution. The content is 55-70 parts in the porous layer 1, increasing to 65-75 parts in the transition layer 2, and further increasing to 75-85 parts in the dense layer 3, providing different levels of structural strength and refractory performance. The distribution of calcium oxide shows the opposite trend: the highest content is 18-28 parts in the porous layer 1, decreasing to 8-15 parts in the transition layer 2, and the lowest is 5-12 parts in the dense layer 3. The higher calcium oxide content in the outer layer enhances thermal shock resistance, while the lower content in the inner layer reduces volumetric expansion stress, preventing structural damage caused by thermal expansion mismatch.

[0030] The thermal expansion compensation magnesia-calcium brick of this invention incorporates three types of functional composite particles, forming a complete thermal expansion compensation system. The negative thermal expansion composite particles consist of a ZrW2O8 core and an Al2O3-SiO2 outer layer. ZrW2O8 possesses unique negative thermal expansion characteristics, shrinking upon heating to effectively compensate for the positive thermal expansion of the matrix material, thus reducing the overall thermal expansion coefficient. These particles are distributed only in the transition layer 2 and the dense layer 3, with contents of 2-5 parts and 3-6 parts, respectively. The neutral thermal expansion regulating particles comprise a β-quartz core and a MgAl2O4 outer layer. Their thermal expansion coefficient is close to neutral, acting as a buffer and regulating agent. These particles are distributed in all three layers, with their content decreasing from 2-4 parts in the porous layer 1 to 1-2 parts in the dense layer 3, effectively balancing the differences in thermal expansion between the layers. The thermosensitive expansion particles are calcium sulfate coated with calcium silicate. They undergo phase change expansion within a specific temperature range and are mainly distributed in porous layer 1 and transition layer 2, with contents of 1-3 parts and 0.5-2 parts, respectively. They can expand in a timely manner during the heating process to fill the microcracks caused by shrinkage.

[0031] The modified binder system uses a composite of aluminum phosphate and phenolic resin at a mass ratio controlled at 2-4:1. Aluminum phosphate provides high-temperature bonding strength, while phenolic resin provides room-temperature moldability. The synergistic effect of the two ensures the bonding effect under different temperature conditions. The porous pore-forming agent adopts a composite formulation design, including 15-25 parts of silica powder as a skeletal strength provider, 20-30 parts of ammonium bicarbonate for high-temperature decomposition and pore formation, 5-10 parts of lignin fiber to enhance toughness, 5-10 parts of starch to provide organic bonding, 1-3 parts of polyvinyl alcohol powder to improve moldability, 3-6 parts of zirconium oxide powder to improve refractoriness, and 5-10 parts of mullite powder to enhance structural stability.

[0032] The heat compensation additive consists of lithium carbonate, boron oxide, and titanium dioxide. 0.3-0.8 parts of lithium carbonate act as a low-temperature flux to promote sintering, 0.5-1.2 parts of boron oxide reduce the sintering temperature and improve fluidity, and 1-3 parts of titanium dioxide act as a stabilizer to improve high-temperature stability. The synergistic effect of these three components ensures the smooth progress of the sintering process and the stability of the final product.

[0033] The core material of the negative thermal expansion composite particles, ZrW₂O₈, is a zirconate tungstate crystal with a cubic crystal structure. This material exhibits negative thermal expansion characteristics in the temperature range of -273℃ to 1050℃, based on the dominance of transverse vibrations in its lattice vibration modes, leading to lattice contraction with increasing temperature. An outer layer of Al₂O₃-SiO₂ composite oxide forms a dense protective shell, 0.5-3 μm thick, which is chemically bonded to the core through physical adsorption, providing chemical stability and mechanical protection, preventing direct contact between ZrW₂O₈ and the external environment. The typical particle size range is 5-50 μm. In magnesia-calcium bricks, the negative thermal expansion characteristics offset the positive thermal expansion of the matrix material, reducing thermal stress concentration and improving the thermal stability of the brick.

[0034] The modified binder is an organic-inorganic hybrid material, composed of an inorganic phase of aluminum phosphate and an organic phase of phenolic resin. Aluminum phosphate has a tetrahedral network structure, while phenolic resin is a thermosetting polymer formed by the condensation of phenols and formaldehyde. The two are combined at a mass ratio of 2-4:1, forming a three-dimensional network structure through Al-OP bonds and hydrogen bonds. This composite can be used at temperatures up to 800-1200℃. The aluminum phosphate phase provides high-temperature stability, with a room-temperature bonding strength of 15-25 MPa and a high-temperature bonding strength of 8-15 MPa. The composite exhibits good chemical stability in both alkaline and acidic environments, and its coefficient of thermal expansion is between that of pure aluminum phosphate and phenolic resin, showing good compatibility with the matrix material. A reaction time of 1-3 hours at 60-90℃ ensures full cross-linking of aluminum phosphate and phenolic resin, forming a stable three-dimensional network structure and achieving optimal bonding performance.

[0035] The core material of the neutral thermal expansion regulating particles, β-quartz, is hexagonal and exhibits unique thermal expansion behavior, undergoing an α-β phase transition around 573℃ accompanied by approximately 0.82% volume expansion. The outer layer of MgAl2O4, a magnesium aluminum spinel, is cubic and has a low coefficient of thermal expansion, acting as a buffer. The core comprises 60-80 wt%, and the outer layer comprises 20-40 wt%, forming a diffusion-bonded interface through high-temperature treatment. The synergistic effect of the core-shell structure achieves precise regulation of thermal expansion, compensating for the expansion mismatch of the matrix material within a specific temperature range. Heat treatment at 1100-1250℃ for 2-4 hours ensures that the MgAl2O4 outer layer completely forms the spinel phase and achieves good interfacial bonding with the β-quartz core.

[0036] Thermosensitive expansion particles consist of a calcium sulfate core and a calcium silicate coating layer. The calcium sulfate can be CaSO4 or CaSO4·2H2O, exhibiting a layered or fibrous crystal structure. The calcium silicate coating layer mainly consists of a CSH gel phase and a crystalline calcium silicate phase, with a coating thickness of 1-5 μm, forming a continuous and dense coating layer. The overall particle size is 10-100 μm. The thermosensitive expansion mechanism is based on the dehydration reaction of calcium sulfate during heating. CaSO4·2H2O transforms into CaSO4·0.5H2O at 120-180℃, and further transforms into CaSO4 at 180-220℃, with each step of the reaction accompanied by volume expansion. Calcium sulfate may also undergo a crystal transformation at high temperatures, resulting in additional volume changes, with a total volume expansion of 5-15%. The calcium silicate coating layer controls the dehydration rate, preventing cracking caused by rapid expansion, and adjusting the expansion rate achieves controllable expansion. The particles begin to expand significantly at 120-180℃. They are prepared using a dry coating process at 300-450℃ to ensure a good bond between the calcium silicate coating layer and the calcium sulfate core, while avoiding unnecessary phase transitions of the calcium sulfate during the preparation process.

[0037] The structure and composition of the above four key components play a synergistic role in thermal expansion compensation magnesia-calcium bricks, functioning in different temperature ranges to achieve thermal expansion compensation across the entire temperature range. By adjusting the content of each component in different layers, the performance of gradient functional materials is achieved. Each component has good chemical stability in a high-temperature alkaline environment, solving the cracking and spalling problems of traditional magnesia-calcium bricks during thermal cycling, and significantly improving the thermal stability and service life of the material.

[0038] The preparation process of negative thermal expansion composite particles is as follows: First, ZrW2O8 powder is mixed with silica sol and alumina sol to form a uniform slurry. The solid content and viscosity are controlled to ensure the uniformity of coating. Then, coated particles are prepared by spray granulation equipment. It is necessary to accurately control key parameters such as inlet air temperature, atomization pressure and liquid flow rate. Finally, the particles are calcined at 800-1000℃ for 1-3 hours. This calcination process can form a dense Al2O3-SiO2 protective layer to prevent ZrW2O8 from oxidizing and failing during use, while improving the mechanical strength of the particles and ensuring their stability in subsequent use.

[0039] The preparation process of neutral thermal expansion regulating particles includes mixing β-quartz powder with magnesium aluminum spinel precursor, preparing composite particles by mechanical coating method, using high-speed stirring or fluidized bed coating technology, and then heat-treating at 1100-1250℃ for 2-4 hours. High-temperature heat treatment ensures the full formation of MgAl2O4 spinel phase, and mechanical coating method ensures uniform coating layer thickness. The resulting composite particles have excellent thermal stability and controllable thermal expansion characteristics.

[0040] The thermosensitive expansion particles are prepared using a dry coating process, with calcium sulfate particles as the core. Calcium sulfate has a defined phase transition temperature, and calcium silicate is used as the coating material. The coating process is carried out at 300-450℃. The low-temperature coating avoids the phase transition of the core material. The calcium silicate coating layer has good chemical compatibility and can achieve controllable thermosensitive expansion characteristics, playing a compensating role at key temperature points.

[0041] The preparation process of the modified binder is relatively simple but requires precision. Aluminum phosphate and phenolic resin are mixed at a mass ratio of 2-4:1 and reacted at 60-90℃ for 1-3 hours. The appropriate reaction temperature avoids excessive cross-linking of the phenolic resin, and the sufficient reaction time ensures the formation of the composite structure. The modified binder obtained after cooling has both the high-temperature performance of aluminum phosphate and the moldability of phenolic resin, thus achieving a synergistic effect.

[0042] The preparation process of the porous pore-forming agent involves several steps. First, silica powder, zirconium oxide powder, and mullite powder are mixed evenly in a specific ratio to obtain an inorganic mineral powder mixture. These inorganic components will form a refractory skeleton structure. Then, lignin fiber and starch are added and dry-mixed for 2-4 minutes. Next, ammonium bicarbonate and polyvinyl alcohol powder are added, and dry-mixing continues for another 2-3 minutes to ensure uniform distribution of the components. Next, 8-12 parts of water are sprayed in and wet-mixed until homogeneous and free of agglomerates. The key to this step is controlling the uniform distribution of moisture content. After pressing the mixture into shape in a mold, it is dried at 100-200℃ for 4-8 hours to remove free water. Then, the temperature is uniformly increased to 650-800℃ at a rate of 3-5℃ per hour to decompose the ammonium bicarbonate and organic matter. Slow heating ensures uniform decomposition of the organic matter, forming a uniform pore structure. The temperature is then further increased to 1500-1600℃ and held for 2-4 hours for high-temperature sintering to form a stable inorganic skeleton structure. After cooling, pore-forming agent particles with a porous structure are obtained.

[0043] Combination Figure 3 The preparation process of the thermal expansion compensation magnesium-calcium brick of the present invention will be described in detail below. The specific steps are as follows: S1: The magnesium oxide particles are surface modified by depositing iron oxide on the surface of the magnesium oxide particles using a wet chemical method to form a surface modification layer; the specific process of step S1 is as follows: S11: Disperse magnesium oxide particles in deionized water at a weight ratio of 1:10 and stir for 15-30 minutes to fully wet them; S12: Slowly add 0.1-0.3 mol / L ferrous sulfate solution while stirring, the amount added is 3-8% of the weight of magnesium oxide; S13: Then add 0.2-0.5 mol / L sodium hydroxide solution to adjust the pH to 9-11; S14: Stir continuously at 70-90℃ for 0.5-2 hours to allow iron oxide to be uniformly deposited on the surface of magnesium oxide; S15: After standing and separating into layers, pour off the supernatant and wash with deionized water 3-5 times until neutral. S16: Dry at 100-120℃ for 4-8 hours to obtain magnesium oxide particles with a surface-deposited iron oxide modified layer, the thickness of which is 5-20nm; S2: Prepare mixtures of porous layer 1, transition layer 2, and dense layer 3 separately; the specific process of layered mixing in step S2 is as follows: S21: Porous layer 1 ingredients: Weigh magnesium oxide, calcium oxide, neutral thermal expansion regulating particles, thermally sensitive expansion particles, porous pore-forming agent and thermal compensation additive according to the formula; dry mix for 5 minutes first, add modified binder, and mix for 15-30 minutes. S22: Transition layer 2 ingredients: Weigh magnesium oxide, calcium oxide, negative thermal expansion composite particles, neutral thermal expansion regulating particles, thermally sensitive expansion particles, porous pore-forming agent and thermal compensation additive according to the formula; dry mix for 5 minutes first; add 3-6 parts of modified binder and mix for 15-30 minutes. S23: Dense Layer 3 Ingredients: Weigh the modified magnesium oxide, calcium oxide, negative thermal expansion composite particles, and neutral thermal expansion regulating particles according to the proportion, and dry mix for 5 minutes; add the modified binder and porous pore-forming agent, and mix for 15-30 minutes; S3: Mold preparation and interface structure processing, fabricating a layered molding mold with dovetail grooves 4 and dovetail protrusions 5; the specific process of mold preparation and interface structure processing in step S3 is as follows: S31: Prepare a three-section molding die. The inner cavity of the die is divided into an upper section, a middle section, and a lower section, which correspond to the molding space of porous layer 1, transition layer 2, and dense layer 3. S32: A dovetail groove 4 male mold structure is machined on the lower surface of the upper mold, and a corresponding dovetail protrusion 5 female mold structure is machined on the upper surface of the middle mold. S33: A dovetail groove 4 male mold structure is machined on the lower surface of the middle section mold; a dovetail protrusion 5 female mold structure matching the dovetail groove 4 is machined on the upper surface of the lower section mold, with the protrusion height matching the groove depth. S4: The mixture of porous layer 1, transition layer 2, and dense layer 3 is loaded into the mold, and a preform is obtained by layered loading and static pressing; the specific process of gradient layering molding in step S4 is as follows: The specific process of gradient layer forming in step S4 is as follows: S41: Preheat the mold to 80-120℃ and apply release agent; S42: Fill the lower mold with the dense layer 3 mixture, controlling the filling density to be 1.8-2.2 g / cm³. 3 Vibrate on a vibration table for 30-60 seconds; S43: Apply a pre-pressure of 5-15MPa and hold the pressure for 30-60 seconds to make the dense layer 3 reach the designed thickness and form a flat upper surface; S44: Apply an interface bonding enhancer to the upper surface of the dense layer 3. This enhancer is a composite solution of silica sol and alumina sol with a solid content of 15-25%, applied at a rate of 0.2-0.8 kg / m². 2 ; S45: Install the intermediate mold, fill in the transition layer 2 mixture, and control the filling density to 1.5-1.9 g / cm³. 3 At this time, the dovetail groove 4 male mold contacts the upper surface of the dense layer 3, forming the dovetail groove 4 structure; S46: Apply a pre-pressure of 8-20 MPa to the transition layer 2 so that the material of the transition layer 2 fills the dovetail groove 4 and forms a dovetail protrusion 5 structure; S47: Install the upper mold and fill it with porous layer 1 mixture, controlling the density to 1.2-1.6 g / cm³. 3 ; S48: Perform overall isostatic pressing, with a molding pressure of 80-150MPa and a holding time of 3-5 minutes to achieve tight bonding of each layer. S49: After molding is completed, demold in layers. First, reduce the molding pressure to 5-10MPa and maintain slight pressure to prevent the blank from deforming. S410: Slowly lift the upper mold section, control the demolding speed at 2-5mm / min, avoid damage to the porous layer 1, and provide a protective cover to the surface of the porous layer 1 during the demolding process; S411: The dovetail groove 4 male mold structure of the horizontally removed middle section mold is first tilted outward by 3-8°, and then vertically lifted out. The demolding force is controlled within the range of 0.5-2MPa to ensure the integrity of the transition layer 2 dovetail protrusion 5 structure. S412: Demolding is performed by bottom lifting, with the lifting speed controlled at 1-3 mm / min. At the same time, the dense layer 3 dovetail protrusions 5 structure are laterally supported to prevent structural damage during demolding. S413: After demolding, the blank should be left to stand at room temperature for 12-24 hours, during which time the ambient humidity should be maintained at 40-60% to prevent cracking of the blank surface; S5: The shaped green body is fired using a segmented controlled firing process; the specific process of shrinkage matching firing in step S5 is as follows: S51: The formed blank is loaded into a firing furnace with zoned heating function. The furnace body is set with three independent temperature control zones: upper, middle and lower. S52: First stage of heating: Heat to 400-600℃ at a rate of 5-10℃ / hour, hold for 1-3 hours, use an air atmosphere to allow the binder to react fully and remove the bound water to achieve initial curing; S53: Second stage heating: Heat to 800-1000℃ at a rate of 8-15℃ / hour, hold for 2-5 hours, use a weak reducing atmosphere, carbon monoxide volume fraction of 8-15%, so that the components undergo solid-phase reaction and form intermediate bonds. S54: Third stage heating: Heat to 1400-1550℃ at a rate of 10-20℃ / hour, hold for 3-6 hours to achieve full sintering and densification of each layer; S55: Zoned temperature control: The temperature of the upper zone is 10-20℃ lower than that of the middle zone, and the temperature of the middle zone is 5-15℃ higher than that of the lower zone; S6: After firing, coordinated cooling is performed using a segmented cooling system, cooling from the firing temperature to room temperature. The specific process of coordinated cooling in step S6 is as follows: S61: Starting from the highest firing temperature of 1400-1550℃, cool down to 1100℃ at a rate of 8-15℃ / hour; S62: Slowly cool from 1100℃ to 600℃ at a rate of 3-8℃ / hour. This temperature range is a stress-sensitive area. Slow cooling releases thermal stress. S63: Cool from 600°C to 200°C at a rate of 10-20°C / hour; S64: Naturally cool from 200℃ to room temperature, with a total cooling time controlled within 24-48 hours.

[0044] In the entire preparation process of magnesia-calcium bricks, the surface modification treatment of magnesium oxide particles involves depositing an iron oxide modified layer on the surface of the magnesium oxide particles using a wet chemical method. This forms a protective layer with a thickness of 5-20 nm, improving the bonding strength between magnesium oxide and the matrix material, and enhancing chemical stability under high-temperature conditions. Specifically, magnesium oxide particles are dispersed in deionized water at a weight ratio of 1:10. The pH value is adjusted to an alkaline environment of 9-11 by controlling the concentration of ferrous sulfate solution (0.1-0.3 mol / L) and sodium hydroxide solution to ensure uniform deposition of iron oxide on the magnesium oxide surface.

[0045] The layered compounding design is based on the characteristics of graded functional materials. By adjusting the proportions of each component in different layers, a gradual transition from a porous outer layer to a dense inner layer is achieved. In the porous layer 1, the magnesium oxide content is 55-70 parts and the calcium oxide content is 18-28 parts. The higher calcium oxide content in the outer layer enhances thermal shock resistance, while the magnesium oxide content ensures basic fire resistance. In the transition layer 2, the magnesium oxide content is increased to 65-75 parts and the calcium oxide content is reduced to 8-15 parts, achieving a smooth transition in the coefficient of thermal expansion between layers and avoiding stress concentration caused by sudden changes in material properties. In the dense layer 3, the magnesium oxide content is increased to 75-85 parts and the calcium oxide content is at least 5-12 parts, enabling the inner layer to provide the highest structural strength and fire resistance, while the lower calcium oxide content reduces volume expansion stress.

[0046] During mold preparation, a three-section molding mold is fabricated. Dovetail grooves 4 and dovetail protrusions 5 are designed at the interfaces of each layer to create a mechanical interlocking structure. This geometric physical constraint achieves a strong connection between the layers, avoiding the interface delamination problem that may occur with chemical bonding alone. The dovetail groove 4 structure on the lower surface of the upper mold precisely matches the dovetail protrusion 5 structure on the upper surface of the middle mold, ensuring a reliable bond between the porous layer 1 and the transition layer 2. The bonding method between the transition layer 2 and the dense layer 3 is consistent with the above method. In specific processing, the packing density of the dense layer 3 is controlled at 1.8-2.2 g / cm³. 3 The transition layer 2 has a concentration of 1.5-1.9 g / cm³. 3 The porous layer 1 has a density of 1.2-1.6 g / cm³. 3 The decreasing density distribution forms a gradient structure with density gradually decreasing from the inside to the outside, effectively dispersing thermal stress. The pre-pressure layered application method applies a pre-pressure of 5-15 MPa to the dense layer 3 and 8-20 MPa to the transition layer 2, ensuring that each layer achieves the predetermined density. The interface bonding reinforcement uses a composite solution of silica sol and alumina sol with a solid content of 15-25%, and the application rate is controlled at 0.2-0.8 kg / m³. 2 Chemical bonding is added to the mechanical interlocking, forming a dual bonding mechanism and improving the interlayer bonding strength. The overall isostatic pressing uses a molding pressure of 80-150 MPa and a holding time of 3-5 minutes to ensure tight bonding between layers and eliminate internal defects. Layered demolding is employed, controlling the demolding speed and force to avoid structural damage. The demolding speed of the porous layer 1 is controlled at 2-5 mm / min. For the dovetail groove 4 male mold structure, it is first tilted 3-8° and then lifted vertically during demolding, with the demolding force controlled within the range of 0.5-2 MPa to protect the structural integrity of the brick blank.

[0047] The segmented controlled firing process is based on the physicochemical changes of materials at different temperatures, achieving orderly reactions of each component through a three-stage heating regime. The first stage involves a slow heating rate of 5-10℃ / hour to 400-600℃. This slow heating allows for sufficient reaction of the binder and removes bound water, preventing cracking caused by rapid heating. The second stage increases the heating rate to 8-15℃ / hour, reaching 800-1000℃, using a weakly reducing atmosphere with a carbon monoxide volume fraction of 8-15%, promoting solid-phase reactions and forming stable intermediate bonds. The third stage further increases the heating rate to 10-20℃ / hour, reaching 1400-1550℃, improving production efficiency while ensuring complete reaction.

[0048] This invention employs a zoned temperature control process, where the upper zone temperature is 10-20°C lower than the middle zone, and the middle zone temperature is 5-15°C higher than the lower zone. This compensates for the shrinkage differences between the different layers and reduces thermal stress during firing. A holding time of 3-6 hours ensures that each layer is fully sintered and densified to achieve optimal mechanical properties and thermal stability.

[0049] The coordinated cooling process is based on the stress release mechanism, effectively releasing thermal stress through segmented control of the cooling rate. Starting from the highest firing temperature, cooling is performed at a rate of 8-15°C / hour to 1100°C, followed by a slower rate of 3-8°C / hour to 600°C. This slow cooling within the stress-sensitive range maximizes the release of thermal stress and prevents cracking during cooling. From 600°C, cooling is performed at a rate of 10-20°C / hour to 200°C, and finally, natural cooling to room temperature is maintained. The total cooling time is controlled within 24-48 hours. This long, slow cooling design ensures that the product's internal stress is fully released.

[0050] The entire preparation process ensures the full synergistic effect of functional additives. The negative thermal expansion composite particles compensate for the positive thermal expansion of the matrix material through the negative thermal expansion characteristics of the ZrW2O8 core. The neutral thermal expansion regulating particles play a buffering and regulating role. The thermosensitive expansion particles undergo phase change expansion within a specific temperature range to fill microcracks, achieving thermal expansion matching across the entire temperature range and significantly improving the thermal stability of the material.

[0051] Example 1 employs a three-layer gradient structure design with a total thickness of 100 mm. The porous layer 1 is 15 mm thick and, by weight, comprises 62 parts magnesium oxide, 23 parts calcium oxide, 3 parts neutral thermal expansion regulating particles, 2 parts thermosensitive expansion particles, 3.5 parts modified binder, 3.5 parts porous pore-forming agent, and 2.5 parts thermal compensation additive. The thermal compensation additive consists of 0.5 parts lithium carbonate, 0.8 parts boron oxide, and 2 parts titanium dioxide, forming a composite system that promotes sintering using a low-temperature flux.

[0052] The transition layer 2 is 45 mm thick and, by weight, comprises 70 parts magnesium oxide, 12 parts calcium oxide, 3.5 parts negative thermal expansion composite particles, 2 parts neutral thermal expansion regulating particles, 1 part thermosensitive expansion particles, 4.5 parts modified binder, 2 parts porous pore-forming agent, and 1.5 parts thermal compensation additive. The thermal compensation additive consists of 0.4 parts lithium carbonate, 0.7 parts boron oxide, and 1.8 parts titanium dioxide, ensuring that the transition layer 2 has good thermal matching performance.

[0053] The dense layer 3 is 40 mm thick and contains, by weight, 80 parts magnesium oxide, 8 parts calcium oxide, 4.5 parts negative thermal expansion composite particles, 1.5 parts neutral thermal expansion regulating particles, 5.5 parts modified binder, and 1 part porous pore-forming agent. The content of negative thermal expansion composite particles is the highest in the dense layer 3, effectively compensating for the positive thermal expansion effect of the matrix material.

[0054] The preparation process is as follows: The preparation process first involves surface modification of magnesium oxide particles. Magnesium oxide particles are dispersed in deionized water at a weight ratio of 1:10 and stirred for 15 to 30 minutes to fully wet them. Then, a ferrous sulfate solution with a concentration of 0.1 to 0.3 mol / L is slowly added while stirring, with the amount added being 3% to 8% of the weight of magnesium oxide. Subsequently, a sodium hydroxide solution with a concentration of 0.2 to 0.5 mol / L is added dropwise to adjust the pH value to 9 to 11. The reaction is carried out by stirring at 70 to 90 degrees Celsius for 0.5 to 2 hours, so that ferric oxide is uniformly deposited on the surface of magnesium oxide to form a modified layer with a thickness of 5 to 20 nanometers.

[0055] During the layered batching process, each layer of mixture is weighed according to the proportion and then dry-mixed for 5 minutes. Then, the modified binder is added and mixed for 15 to 30 minutes to ensure uniform component distribution. The mold adopts a three-section design, with the upper, middle, and lower sections corresponding to the forming spaces of porous layer 1, transition layer 2, and dense layer 3, respectively. Dovetail grooves 4 and dovetail protrusions 5 are machined at the corresponding positions.

[0056] During the layered isostatic pressing process, the mold is preheated to 80 to 120 degrees Celsius. The density of the dense layer 3 is controlled at 1.8 to 2.2 g / cm³, the density of the transition layer 2 at 1.5 to 1.9 g / cm³, and the density of the porous layer 1 at 1.2 to 1.6 g / cm³. An interface bonding reinforcing agent is brushed onto the upper surface of the dense layer 3 using a composite solution of silica sol and alumina sol, with a solid content of 15% to 25%, applied at a rate of 0.2 to 0.8 kg / m². The overall isostatic pressing is performed at a molding pressure of 80 to 150 MPa, with a holding time of 3 to 5 minutes.

[0057] The firing process employs segmented control. The first segment raises the temperature at a rate of 5 to 10 degrees Celsius per hour to 400 to 600 degrees Celsius and holds for 1 to 3 hours. The second segment raises the temperature at a rate of 8 to 15 degrees Celsius per hour to 800 to 1000 degrees Celsius and holds for 2 to 5 hours. The third segment raises the temperature at a rate of 10 to 20 degrees Celsius per hour to 1400 to 1550 degrees Celsius and holds for 3 to 6 hours. In the zoned temperature control, the upper zone temperature is 10 to 20 degrees Celsius lower than the middle zone, and the middle zone temperature is 5 to 15 degrees Celsius higher than the lower zone.

[0058] Comparative Example 1 uses a traditional single homogeneous structure with a total thickness of 100 mm. By weight, it contains 70 parts magnesium oxide, 15 parts calcium oxide, 4 parts modified binder, 2 parts porous agent, and 1.5 parts thermal compensation additive. The thermal compensation additive consists of 0.4 parts lithium carbonate, 0.7 parts boron oxide, and 1.8 parts titanium dioxide. The entire brick has a homogeneous structure, without any added functional composite particles, and uses a planar bonding method between layers, without a dovetail groove structure design. The preparation process is as follows: Comparative Example 1 uses a traditional preparation process where magnesium oxide particles are directly mixed with other components without surface modification. The batching process involves weighing each component according to the specified ratio and mixing them uniformly, without stratification. Molding employs a standard single-layer loading method, maintaining uniform loading density, and the mold structure is simple, eliminating the need for a dovetail groove design. The firing process uses a conventional heating regime without zoned temperature control, and the cooling process is a natural cooling method.

[0059] The experimental design and results are as follows: The tests were conducted in accordance with national standards such as GB / T2997-2000 "Test Methods for Bulk Density, Apparent Porosity and True Porosity of Dense Shaped Refractory Products", GB / T3001-2017 "Test Methods for Compressive Strength of Refractory Materials at Room Temperature", and GB / T3002-2017 "Test Methods for Flexural Strength of Refractory Materials at High Temperature".

[0060] Table 1 Performance comparison between Example 1 and Comparative Example 1

[0061] Table 2. Test results of thermal expansion coefficients of Example 1 and Comparative Example 1.

[0062] Experimental results show that the three-layer gradient structure design used in Example 1 effectively disperses thermal stress through an inverse gradient distribution of increasing magnesium oxide content and decreasing calcium oxide content. The mechanical interlocking structure of the dovetail groove 4 and the dovetail protrusion 5 significantly improves the interlayer bonding strength.

[0063] Example 2: In this example, the porous layer 1 comprises, by weight, 58 parts magnesium oxide, 25 parts calcium oxide, 4 parts neutral thermal expansion regulating particles, 3 parts thermosensitive expansion particles, 4 parts modified binder, 4 parts porous pore-forming agent, and 3 parts thermal compensation additive. The thermal compensation additive consists of 0.6 parts lithium carbonate, 1.0 part boron oxide, and 2.5 parts titanium dioxide, forming a stronger sintering promoting effect.

[0064] Transition layer 2, by weight, comprises 68 parts magnesium oxide, 10 parts calcium oxide, 5 parts negative thermal expansion composite particles, 3 parts neutral thermal expansion regulating particles, 2 parts thermosensitive expansion particles, 5 parts modified binder, 2.5 parts porous pore-forming agent, and 2 parts thermal compensation additive. The content of negative thermal expansion composite particles reaches the upper limit to maximize the negative thermal expansion characteristics of the ZrW2O8 core. The thermal compensation additive consists of 0.5 parts lithium carbonate, 0.9 parts boron oxide, and 2.2 parts titanium dioxide.

[0065] The dense layer 3, by weight, comprises 78 parts magnesium oxide, 10 parts calcium oxide, 6 parts negative thermal expansion composite particles, 2 parts neutral thermal expansion regulating particles, 6 parts modified binder, and 1.5 parts porous pore-forming agent. The negative thermal expansion composite particle content reaches the highest proportion in the dense layer 3, achieving optimal compensation through the synergistic effect of the ZrW2O8 core and the Al2O3-SiO2 outer layer. The preparation process is as follows: In the preparation of negative thermal expansion composite particles, ZrW2O8 powder is mixed with silica sol and alumina sol to form a uniform slurry. The solid content is controlled to ensure uniform coating. When preparing coated particles through spray granulation equipment, the inlet air temperature, atomization pressure and liquid flow rate are precisely controlled. The particles are calcined at 800 to 1000 degrees Celsius for 1 to 3 hours to form a dense protective layer.

[0066] In the preparation of neutral thermal expansion regulating particles, β-quartz powder is mixed with magnesium aluminum spinel precursor, and composite particles are prepared by high-speed stirring mechanical coating method to ensure uniform coating thickness. The particles are then heat-treated at 1100 to 1250 degrees Celsius for 2 to 4 hours to allow the MgAl2O4 spinel phase to fully form.

[0067] Thermosensitive expansion particles use calcium sulfate particles as the core and calcium silicate as the coating material. They are prepared by a dry coating process at 300 to 450 degrees Celsius to avoid unnecessary phase changes in the core material and form controllable thermosensitive expansion characteristics.

[0068] Comparative Example 2 uses the same three-layer structure but without adding any functional composite particles. The porous layer 1 contains 67 parts by weight of magnesium oxide, 25 parts of calcium oxide, 4 parts of modified binder, and 4 parts of porous pore-forming agent, and does not contain negative thermal expansion composite particles, neutral thermal expansion regulating particles, or thermally sensitive expansion particles.

[0069] The transition layer 2 contains 78 parts magnesium oxide, 10 parts calcium oxide, 5 parts modified binder, 2.5 parts porous pore-forming agent, and 2 parts thermal compensation additive by weight. It also lacks the thermal expansion compensation mechanism of functional composite particles.

[0070] The dense layer 3 contains 86 parts by weight of magnesium oxide, 10 parts of calcium oxide, 6 parts of modified binder, and 1.5 parts of porous pore-forming agent. To compensate for the lack of functional particles, the magnesium oxide content is increased to 86 parts accordingly.

[0071] The preparation process of Comparative Example 2 is relatively simplified. Since it does not contain functional composite particles, the preparation step of composite particles is omitted. During the batching process, the components of each layer are mixed in a conventional manner without any special particle pretreatment.

[0072] The experimental design and results are as follows: Table 3 Comparison of thermal expansion properties between Example 2 and Comparative Example 2

[0073] Table 4. Microstructural changes during thermal cycling.

[0074] Experimental results show that the three types of functional composite particles in Example 2 play a synergistic role in different temperature ranges. The ZrW2O8 core of the negative thermal expansion composite particle shrinks when heated, effectively offsetting the positive thermal expansion of the matrix material. The neutral thermal expansion regulating particle achieves precise regulation of thermal expansion. The thermosensitive expansion particle undergoes phase change expansion within a specific temperature range, timely filling the microcracks caused by shrinkage.

[0075] Example 3 uses a modified binder system composed of aluminum phosphate and phenolic resin, and a carefully designed porous pore-forming agent formulation. The porous layer 1, by weight, comprises 65 parts magnesium oxide, 20 parts calcium oxide, 3.5 parts neutral thermal expansion regulating particles, 2.5 parts thermosensitive expansion particles, 5 parts modified binder, 5 parts porous pore-forming agent, and 3.5 parts thermal compensation additive. The thermal compensation additive consists of 0.8 parts lithium carbonate, 1.2 parts boron oxide, and 3 parts titanium dioxide.

[0076] The modified binder was prepared by mixing aluminum phosphate and phenolic resin at a mass ratio of 3:1 and reacting at 75 degrees Celsius for 2 hours to ensure the formation of a stable three-dimensional network structure. The porous pore-forming agent, by weight, comprises 20 parts silica powder, 25 parts ammonium bicarbonate, 7 parts lignin fiber, 7 parts starch, 2 parts polyvinyl alcohol powder, 10 parts water, 4.5 parts zirconium oxide powder, and 7.5 parts mullite powder, forming a composite functional pore-forming system. The preparation process is as follows: During the preparation of the modified binder, the reaction conditions between aluminum phosphate and phenolic resin are strictly controlled. The reaction temperature of 75 degrees Celsius is used to avoid excessive cross-linking of phenolic resin, and the reaction time of 2 hours is used to ensure that the composite structure is fully formed. After cooling, a modified binder that has both the high-temperature performance of aluminum phosphate and the moldability of phenolic resin is obtained.

[0077] The porous pore-forming agent is prepared by first mixing silica powder, zirconium oxide powder, and mullite powder in a specific ratio to form an inorganic mineral powder mixture. Then, lignin fiber and starch are added and dry-mixed for 2 to 4 minutes. Next, ammonium bicarbonate and polyvinyl alcohol powder are added and dry-mixed for another 2 to 3 minutes. Finally, 8 to 12 parts of water are sprayed in and wet-mixed until homogeneous and free of agglomerates. After molding, the mixture is dried at 100 to 200 degrees Celsius for 4 to 8 hours to remove free water. The temperature is then increased to 650 to 800 degrees Celsius at a rate of 3 to 5 degrees Celsius per hour to decompose the organic matter and form a porous structure. The temperature is then further increased to 1500 to 1600 degrees Celsius and held for 2 to 4 hours to form a stable inorganic framework.

[0078] Comparative Example 3 uses a traditional phosphate binder and a simple pore-forming agent formulation for comparison. Porous layer 1, by weight, contains 65 parts magnesium oxide, 20 parts calcium oxide, 3.5 parts neutral thermal expansion regulating particles, 2.5 parts thermosensitive expansion particles, 5 parts phosphate binder, 5 parts traditional pore-forming agent, and 3.5 parts thermal compensation additive. The phosphate binder uses an 85% phosphate solution and does not possess the composite effect of a modified binder.

[0079] Traditional pore-forming agents contain 30 parts wood chips, 20 parts starch, 15 parts water, and 35 parts other fillers by weight. The formula is simple and lacks the synergistic effect of multifunctional components, making it impossible to form a stable and uniform pore structure.

[0080] The preparation process of Comparative Example 3 adopted a traditional method, in which the phosphate binder was directly mixed with the raw materials without a complex reaction process. The preparation of traditional pore-forming agents is simple, involving the physical mixing of each component.

[0081] The experimental design and results are as follows: Table 5. Performance comparison of the binder systems in Example 3 and Comparative Example 3.

[0082] Table 6 Comparison of the effects of porous pore-forming agents in Example 3 and Comparative Example 3.

[0083] Table 7 Comparison of high-temperature performance between Example 3 and Comparative Example 3

[0084] Experimental results show that the aluminum phosphate and phenolic resin composite modified binder used in Example 3 forms a three-dimensional network structure through Al-OP bonds and hydrogen bonds, achieving a synergistic effect of organic-inorganic hybrid materials. The porous pore-forming agent in the composite formulation forms a refractory skeleton through silica powder, zirconium oxide powder, and mullite powder, ensuring the uniformity and stability of the pore structure.

[0085] Example 4 verifies the effectiveness of surface modification treatment and segmented firing process. The porous layer 1, by weight, comprises 60 parts of surface-modified magnesium oxide, 22 parts of calcium oxide, 3 parts of neutral thermal expansion regulating particles, 2 parts of thermosensitive expansion particles, 4 parts of modified binder, 4 parts of porous pore-forming agent, and 2.5 parts of thermal compensation additive. The thermal compensation additive consists of 0.6 parts of lithium carbonate, 0.9 parts of boron oxide, and 2.3 parts of titanium dioxide, with optimized proportions.

[0086] Surface-modified magnesium oxide was prepared via a wet chemical method, depositing a 15-nanometer-thick iron oxide modification layer on the surface of magnesium oxide particles, significantly improving interfacial bonding strength and chemical compatibility. The composition ratios of transition layer 2 and dense layer 3 were basically the same as in the standard embodiment, but surface-modified magnesium oxide raw material was used. The preparation process is as follows: In the magnesium oxide surface modification process, magnesium oxide particles are dispersed in deionized water at a weight ratio of 1:10, 5% of the magnesium oxide weight of 0.2 mol / L ferrous sulfate solution is added, the pH is adjusted to 10 with 0.3 mol / L sodium hydroxide solution, and the reaction is carried out at 80 degrees Celsius for 1 hour. After washing and drying, magnesium oxide particles with a 15-nanometer thick iron oxide modified layer are obtained.

[0087] The segmented firing process employs precise temperature control. The first stage raises the temperature to 500 degrees Celsius at a rate of 8 degrees Celsius per hour and holds for 2 hours. The second stage raises the temperature to 900 degrees Celsius at a rate of 12 degrees Celsius per hour and holds for 3 hours, using a weakly reducing atmosphere with a carbon monoxide volume fraction of 12%. The third stage raises the temperature to 1480 degrees Celsius at a rate of 15 degrees Celsius per hour and holds for 4 hours. In the zoned temperature control, the upper zone is 15 degrees Celsius lower than the middle zone, and the middle zone is 10 degrees Celsius higher than the lower zone.

[0088] The coordinated cooling process cools the temperature from 1480 degrees Celsius to 1100 degrees Celsius at a rate of 12 degrees Celsius per hour, then to 600 degrees Celsius at a rate of 5 degrees Celsius per hour, then to 200 degrees Celsius at a rate of 15 degrees Celsius per hour, and finally allows for natural cooling. The total cooling time is strictly controlled.

[0089] Comparative Example 4 used untreated ordinary magnesium oxide as raw material. The porous layer 1 contained, by weight, 60 parts of ordinary magnesium oxide, 22 parts of calcium oxide, 3 parts of neutral thermal expansion regulating particles, 2 parts of thermosensitive expansion particles, 4 parts of modified binder, 4 parts of porous pore-forming agent, and 2.5 parts of thermal compensation additive. Ordinary magnesium oxide lacks a surface modification layer, resulting in relatively low interfacial bonding strength with other components.

[0090] Comparative Example 4 uses a traditional firing process, directly heating to 1450 degrees Celsius at a constant rate of 10 degrees Celsius / hour, holding at that temperature for 3 hours, and then naturally cooling to room temperature without a zoned temperature control system.

[0091] The experimental design and results are as follows: Table 8 Comparison of magnesium oxide surface modification effects between Example 4 and Comparative Example 4

[0092] Table 9 Comparison of firing process effects between Example 4 and Comparative Example 4

[0093] Table 10 Comparison of thermal stress release effects between Example 4 and Comparative Example 4

[0094] Table 11 Comparison of lifespan predictions between Example 4 and Comparative Example 4

[0095] Experimental results show that, in Example 4, the surface modification treatment of magnesium oxide particles significantly improved the interfacial bonding strength and chemical compatibility with other components. The layered loading static pressing process precisely controlled the loading density and molding pressure of each layer. The segmented controlled firing process and coordinated cooling process effectively released thermal stress and prevented cracking and deformation caused by rapid temperature changes, taking into account the sintering characteristics and thermal expansion differences of different layers.

[0096] The comparative experiments above demonstrate that the three-layer gradient structure design, through its reverse gradient distribution and dovetail groove mechanical interlocking structure, significantly improves structural stability and interlayer bonding strength. The functional composite particle thermal expansion compensation system achieves thermal expansion matching across the entire temperature range, reducing the coefficient of thermal expansion and thermal stress concentration. Surface modification treatment and segmented firing processes enhance interfacial bonding and effectively release thermal stress.

[0097] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A thermal expansion compensating magnesium-calcium brick, characterized in that: It comprises a porous layer, a transition layer, and a dense layer, each layer containing the following components by weight: The porous layer consists of: 55-70 parts magnesium oxide, 18-28 parts calcium oxide, 2-4 parts neutral thermal expansion regulating particles, 1-3 parts thermal expansion particles, 2-5 parts modified binder, 2-5 parts porous pore-forming agent, and 1.5-3.5 parts thermal compensation additive. The transition layer consists of: 65-75 parts magnesium oxide, 8-15 parts calcium oxide, 2-5 parts negative thermal expansion composite particles, 1-3 parts neutral thermal expansion regulating particles, 0.5-2 parts thermally sensitive expansion particles, 3-6 parts modified binder, 1-3 parts porous pore-forming agent, and 0.8-2.3 parts thermal compensation additive. The dense layer consists of: 75-85 parts magnesium oxide, 5-12 parts calcium oxide, 3-6 parts negative thermal expansion composite particles, 1-2 parts neutral thermal expansion regulating particles, 4-7 parts modified binder, and 0.5-2 parts porous pore-forming agent. The negative thermal expansion composite particles contain ZrW2O8 and Al2O3-SiO2, the modified binder is a composite of aluminum phosphate and phenolic resin, the neutral thermal expansion regulating particles contain β-quartz and MgAl2O4, and the thermosensitive expansion particles are calcium sulfate coated with calcium silicate.

2. The thermal expansion compensating magnesia-calcium brick according to claim 1, characterized in that: The heat compensation additive comprises the following components by weight: 0.3-0.8 parts lithium carbonate, 0.5-1.2 parts boron oxide, and 1-3 parts titanium dioxide; The porous pore-forming agent, by weight, comprises: 15-25 parts of silica powder; 20-30 parts of ammonium bicarbonate; 5-10 parts of lignin fiber; 5-10 parts of starch; 1-3 parts of polyvinyl alcohol powder; 8-12 parts of water; 3-6 parts of zirconium oxide powder; and 5-10 parts of mullite powder.

3. The thermal expansion compensating magnesia-calcium brick according to claim 1, characterized in that: The lower surface of the porous layer has a dovetail groove structure, and the upper surface of the transition layer has a dovetail protrusion structure that matches the dovetail groove; the lower surface of the transition layer has a dovetail groove structure, and the upper surface of the dense layer has a dovetail protrusion structure that matches the dovetail groove.

4. The thermal expansion compensating magnesia-calcium brick according to claim 1, characterized in that: The preparation process of the negative thermal expansion composite particles is as follows: ZrW2O8 powder is mixed with silica sol and alumina sol to form a slurry; coated particles are prepared by spray granulation equipment; and calcined at 800-1000℃ for 1-3 hours to obtain negative thermal expansion composite particles with Al2O3-SiO2 coating on the surface.

5. The thermal expansion compensating magnesia-calcium brick according to claim 1, characterized in that: The preparation process of the neutral thermal expansion regulating particles is as follows: mixing β-quartz powder with magnesium aluminum spinel precursor; Composite particles were prepared by mechanical coating; after heat treatment at 1100-1250℃ for 2-4 hours, neutral thermal expansion regulating particles were obtained.

6. The thermal expansion compensating magnesia-calcium brick according to claim 1, characterized in that: The preparation process of the thermosensitive expansion particles is as follows: calcium sulfate particles are used as the core; calcium silicate is used as the coating material; coated particles are prepared at 300-450℃ through a dry coating process to obtain thermosensitive expansion particles.

7. The thermal expansion compensating magnesia-calcium brick according to claim 1, characterized in that: The modified binder is prepared by mixing aluminum phosphate and phenolic resin at a mass ratio of 2-4:1; reacting at 60-90℃ for 1-3 hours; and obtaining the modified binder after cooling. The preparation process of the porous pore-forming agent is as follows: Silica powder, zirconium oxide powder, and mullite powder are mixed evenly in a certain proportion to obtain an inorganic mineral powder mixture; lignin fiber and starch are added, and dry-stirred for 2-4 minutes; ammonium bicarbonate and polyvinyl alcohol powder are added, and dry-stirred for another 2-3 minutes; 8-12 parts of water are sprayed in, and wet-stirred until uniform and free of agglomerates, controlling the moisture content; the mixture is placed in a mold and pressed into shape; the molded body is dried at 100-200℃ for 4-8 hours to remove free water; the temperature is uniformly increased to 650-800℃ at 3-5℃ per hour to decompose ammonium bicarbonate and organic matter, forming a porous structure; the temperature is further increased to 1500-1600℃ and held for 2-4 hours; after cooling, porous pore-forming agent particles are obtained.

8. The preparation process of thermal expansion compensating magnesia-calcium bricks as described in any one of claims 1-7, characterized in that: Includes the following steps: S1: Magnesium oxide particles are surface modified by depositing iron oxide on the surface of magnesium oxide particles using a wet chemical method to form a surface modification layer. S2: Prepare mixtures of porous layer, transition layer and dense layer respectively; S3: Mold preparation and interface structure processing, to prepare a layered molding mold with dovetail grooves and dovetail protrusions; S4: The mixture of porous layer, transition layer and dense layer is loaded into the mold and the molded blank is obtained by layered loading and static pressing. S5: The shaped green body is fired using a segmented controlled firing process; S6: After firing, coordinated cooling is carried out, using a segmented cooling system to cool from the firing temperature to room temperature.

9. The preparation process according to claim 8, characterized in that: The specific process of step S1 is as follows: S11: Disperse magnesium oxide particles in deionized water at a weight ratio of 1:10 and stir for 15-30 minutes to fully wet them; S12: Slowly add 0.1-0.3 mol / L ferrous sulfate solution while stirring, the amount added is 3%-8% of the weight of magnesium oxide; S13: Then add 0.2-0.5 mol / L sodium hydroxide solution to adjust the pH to 9-11; S14: Stir continuously at 70-90℃ for 0.5-2 hours to allow iron oxide to be uniformly deposited on the surface of magnesium oxide; S15: After standing and separating into layers, pour off the supernatant and wash with deionized water 3-5 times until neutral. S16: Dry at 100-120℃ for 4-8 hours to obtain magnesium oxide particles with a surface-deposited iron oxide modified layer, the thickness of which is 5-20nm; The specific process of layered ingredient mixing in step S2 is as follows: S21: Porous layer formulation: Weigh magnesium oxide, calcium oxide, neutral thermal expansion regulating particles, thermosensitive expansion particles, porous pore-forming agent and thermal compensation additive according to the formula; dry mix for 5 minutes first, add modified binder, and mix for 15-30 minutes. S22: Transition layer ingredients: Weigh magnesium oxide, calcium oxide, negative thermal expansion composite particles, neutral thermal expansion regulating particles, thermosensitive expansion particles, porous pore-forming agent and thermal compensation additive according to the proportion; dry mix for 5 minutes first; add 3-6 parts of modified binder and mix for 15-30 minutes. S23: Dense layer ingredients: Weigh the modified magnesium oxide, calcium oxide, negative thermal expansion composite particles, and neutral thermal expansion regulating particles according to the proportion, and dry mix for 5 minutes; add the modified binder and porous pore-forming agent, and mix for 15-30 minutes. The specific process of mold preparation and interface structure processing in step S3 is as follows: S31: Prepare a three-section molding die. The inner cavity of the die is divided into an upper section, a middle section, and a lower section, which correspond to the molding space of the porous layer, the transition layer, and the dense layer. S32: A dovetail groove male mold structure is machined on the lower surface of the upper mold, and a corresponding dovetail protrusion female mold structure is machined on the upper surface of the middle mold. S33: A dovetail groove male mold structure is machined on the lower surface of the middle section mold; a dovetail protrusion female mold structure matching the dovetail groove is machined on the upper surface of the lower section mold, with the protrusion height matching the groove depth.

10. The preparation process according to claim 8, characterized in that: The specific process of gradient layer forming in step S4 is as follows: S41: Preheat the mold to 80-120℃ and apply release agent; S42: Fill the lower mold with a dense layer of mixture, controlling the density of the mixture to be 1.8-2.2 g / cm³. 3 Vibrate on a vibration table for 30-60 seconds; S43: Apply a pre-pressure of 5-15MPa and hold for 30-60 seconds to make the dense layer reach the designed thickness and form a flat upper surface; S44: Apply an interface bonding enhancer to the upper surface of the dense layer. This is a composite solution of silica sol and alumina sol with a solid content of 15-25%, applied at a rate of 0.2-0.8 kg / m². 2 ; S45: Install the intermediate mold, fill in the transition layer mixture, and control the filling density to 1.5-1.9 g / cm³. 3 At this point, the dovetail groove male mold comes into contact with the upper surface of the dense layer, forming a dovetail groove structure; S46: Apply a pre-pressure of 8-20 MPa to the transition layer so that the transition layer material fills the dovetail groove and forms a dovetail protrusion structure; S47: Install the upper mold and fill it with porous layer mixture, with a density controlled at 1.2-1.6 g / cm³. 3 ; S48: Perform overall isostatic pressing, with a molding pressure of 80-150MPa and a holding time of 3-5 minutes to achieve tight bonding of each layer. S49: After molding is completed, demold in layers. First, reduce the molding pressure to 5-10MPa and maintain slight pressure to prevent the blank from deforming. S410: Slowly lift the upper mold section, control the demolding speed at 2-5mm / min to avoid damage to the porous layer, and provide a protective cover to the surface of the porous layer during the demolding process; S411: The dovetail groove male mold structure of the horizontally removed middle section mold is first tilted outward by 3-8°, and then vertically lifted out. The demolding force is controlled within the range of 0.5-2MPa to ensure the integrity of the dovetail protrusion structure of the transition layer. S412: Demolding is performed by bottom lifting, with the lifting speed controlled at 1-3 mm / min. At the same time, the dense layer dovetail protrusion structure is laterally supported to prevent structural damage during demolding. S413: After demolding, the blank should be left to stand at room temperature for 12-24 hours, during which time the ambient humidity should be maintained at 40-60% to prevent cracking of the blank surface; The specific process of shrinkage matching firing in step S5 is as follows: S51: The formed blank is loaded into a firing furnace with zoned heating function. The furnace body is set with three independent temperature control zones: upper, middle and lower. S52: First stage of heating: Heat to 400-600℃ at a rate of 5-10℃ / hour, hold for 1-3 hours, use an air atmosphere to allow the binder to react fully and remove the bound water to achieve initial curing; S53: Second stage heating: Heat to 800-1000℃ at a rate of 8-15℃ / hour, hold for 2-5 hours, use a weak reducing atmosphere, carbon monoxide volume fraction of 8-15%, so that the components undergo solid-phase reaction and form intermediate bonds. S54: Third stage heating: Heat to 1400-1550℃ at a rate of 10-20℃ / hour, hold for 3-6 hours to achieve full sintering and densification of each layer; S55: Zoned temperature control: The temperature of the upper zone is 10-20℃ lower than that of the middle zone, and the temperature of the middle zone is 5-15℃ higher than that of the lower zone; The specific process of coordinated cooling in step S6 is as follows: S61: Starting from the highest firing temperature of 1400-1550℃, cool down to 1100℃ at a rate of 8-15℃ / hour; S62: Slowly cool from 1100℃ to 600℃ at a rate of 3-8℃ / hour. This temperature range is a stress-sensitive area. Slow cooling releases thermal stress. S63: Cool from 600°C to 200°C at a rate of 10-20°C / hour; S64: Naturally cool from 200℃ to room temperature, with a total cooling time controlled within 24-48 hours.

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