A thermal expansion compensation magnesium calcium brick and a preparation process thereof

Abstract

The present application relates to the technical field of magnesium calcium brick preparation, and provides a thermal expansion compensation magnesium calcium brick and a preparation process thereof.The magnesium calcium brick adopts a three-layer gradient structure design, including a porous layer, a transition layer and a dense layer, and negative thermal expansion composite particles, neutral thermal expansion adjusting particles and thermal sensitive expansion particles are introduced into the formula of each layer to jointly form a thermal expansion compensation system.The mechanical interlocking structure of dovetail grooves and dovetail protrusions between layers enhances the bonding strength and effectively avoids interlayer peeling.The preparation process includes the following steps of raw material surface modification, layered batching, mold design and loading, segmented temperature control sintering and coordinated cooling, etc.The present application effectively solves the problems of thermal expansion mismatch and easy cracking of traditional magnesium calcium bricks, and significantly improves the thermal shock resistance, structural stability and service life of the brick body.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of magnesium calcium brick preparation, and particularly relates to a thermal expansion compensation magnesium calcium brick and a preparation process thereof. BACKGROUND

[0002] The magnesium calcium brick is an alkaline refractory material mainly composed of magnesium oxide and calcium oxide. Due to its excellent high-temperature resistance and alkali slag erosion resistance, the magnesium calcium brick is widely used as the inner lining of high-temperature equipment such as a steel ladle refining furnace, a cement rotary kiln transition zone, and a non-ferrous metal smelting furnace in the metallurgical industry. The magnesium calcium brick needs to withstand severe temperature fluctuations during high-temperature application, and the thermal expansion behavior of the material directly affects the structural stability and service life.

[0003] In actual application, due to the difference between the thermal expansion coefficients of magnesium oxide and calcium oxide and the significant internal temperature gradient of the material, thermal stress concentration frequently occurs. The traditional homogeneous magnesium calcium brick is prone to produce microcracks and gradually expand under thermal cycle conditions, which affects the service life. Specifically, the interfacial bonding force of the conventional multi-layer magnesium calcium brick is weak, and interfacial peeling is prone to occur under the repeated action of thermal stress; the composition lacks the function of adjusting thermal expansion in the whole temperature range, which easily causes interface microcracks and affects the service life; the surface of the composition for adjusting thermal expansion is easily corroded or oxidized at high temperature, which reduces the long-term stability; the sintering shrinkage difference between different component layers is not considered in the homogenization sintering process, which aggravates the interfacial stress accumulation, and the thermal stress is not fully released during the cooling process, which causes cracking risk.

[0004] These technical defects cause the thermal shock resistance of the traditional magnesium calcium brick to decay, the service life to be shortened, and other problems, and it is urgent to design a thermal expansion compensation magnesium calcium brick and a preparation process thereof to solve the above problems. SUMMARY

[0005] To solve the problems in the background art, the present application provides a thermal expansion compensation magnesium calcium brick, which comprises a porous layer, a transition layer and a dense layer, and each layer contains the following components by weight:

[0006] The components of the porous layer are: 55-70 parts of magnesium oxide, 18-28 parts of calcium oxide, 2-4 parts of neutral thermal expansion adjusting particles, 1-3 parts of thermal sensitive expansion particles, 2-5 parts of modified binder, 2-5 parts of porous pore-forming agent, and 1.5-3.5 parts of thermal compensation additive;

[0007] The components of the transition layer are: 65-75 parts of magnesium oxide, 8-15 parts of calcium oxide, 2-5 parts of negative thermal expansion composite particles, 1-3 parts of neutral thermal expansion adjusting particles, 0.5-2 parts of thermal sensitive expansion particles, 3-6 parts of modified binder, 1-3 parts of porous pore-forming agent, and 0.8-2.3 parts of thermal compensation additive;

[0008] The dense layer component is: magnesium oxide 75-85 parts, calcium oxide 5-12 parts, negative thermal expansion composite particles 3-6 parts, neutral thermal expansion adjusting particles 1-2 parts, modified binder 4-7 parts, porous pore-forming agent 0.5-2 parts;

[0009] 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 adjusting particles contain β-quartz and MgAl2O4, and the heat-sensitive expansion particles are calcium silicate-coated calcium sulfate.

[0010] In a preferred scheme, the heat compensation additive contains the following components by weight: lithium carbonate 0.3-0.8 parts, boron oxide 0.5-1.2 parts, and titanium dioxide 1-3 parts; and the porous pore-forming agent contains, by weight: silicon powder 15-25 parts; ammonium bicarbonate 20-30 parts; lignin fiber 5-10 parts; starch 5-10 parts; polyvinyl alcohol powder 1-3 parts; water 8-12 parts; zirconium oxide powder 3-6 parts; and mullite powder 5-10 parts.

[0011] In a preferred scheme, a dovetail groove structure is arranged on the lower surface of the porous layer, and a dovetail convex structure matching the dovetail groove is arranged on the upper surface of the transition layer; a dovetail groove structure is arranged on the lower surface of the transition layer, and a dovetail convex structure matching the dovetail groove is arranged on the upper surface of the dense layer.

[0012] In a preferred scheme, the preparation process of the negative thermal expansion composite particles is as follows: ZrW2O8 powder is mixed with silica sol and alumina sol to prepare a slurry; coated particles are prepared by a spray granulation device; and the coated particles are calcined at 800-1000℃ for 1-3 hours to obtain negative thermal expansion composite particles coated with an Al2O3-SiO2 layer.

[0013] In a preferred scheme, the preparation process of the neutral thermal expansion adjusting particles is as follows: β-quartz powder is mixed with a magnesium aluminate spinel precursor; composite particles are prepared by a mechanical coating method; and the composite particles are heat-treated at 1100-1250℃ for 2-4 hours to obtain neutral thermal expansion adjusting particles.

[0014] In a preferred scheme, the preparation process of the heat-sensitive expansion particles is as follows: calcium sulfate particles are used as cores; calcium silicate is used as a coating material; coated particles are prepared by a dry coating process at 300-450℃ to obtain heat-sensitive expansion particles.

[0015] In a preferred scheme, 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;

[0016] The preparation process of the porous pore-forming agent is as follows: uniformly mixing silicon powder, zirconium oxide powder and mullite powder according to proportions to obtain an inorganic mineral powder mixture; adding lignin fibers and starch, dry stirring for 2-4 minutes; adding ammonium bicarbonate and polyvinyl alcohol powder, and continuing to dry stir for 2-3 minutes; spraying 8-12 parts of water, wet stirring until uniform without agglomerates, and controlling the water content; placing in a mold for compression molding; drying the molded body at 100-200 DEG C for 4-8 hours to remove free water; uniformly heating at 3-5 DEG C per hour to 650-800 DEG C to decompose ammonium bicarbonate and organic matter and form a porous structure; continuing to heat to 1500-1600 DEG C for 2-4 hours, and cooling to obtain the porous pore-forming agent particles.

[0017] The application also designs a preparation process of the thermal expansion compensation magnesium-calcium brick, including the following steps:

[0018] S1: performing surface modification treatment on the magnesium oxide particles, depositing iron oxide on the surface of the magnesium oxide particles by a wet chemical method to form a surface modification layer;

[0019] S2: respectively preparing mixed materials of the porous layer, the transition layer and the dense layer;

[0020] S3: preparing a layered molding mold with dovetail grooves and dovetail protrusions;

[0021] S4: loading the mixed materials of the porous layer, the transition layer and the dense layer into the mold, and adopting layered loading static pressure molding to obtain a molded green body;

[0022] S5: adopting a segmented control sintering process to sinter the molded green body;

[0023] S6: after sintering, performing coordinated cooling by adopting a segmented cooling system to cool from the sintering temperature to room temperature.

[0024] Further, the specific process of step S1 is as follows:

[0025] S11: dispersing the magnesium oxide particles in deionized water according to a weight ratio of 1:10, and stirring for 15-30 minutes to fully wet the magnesium oxide particles;

[0026] S12: slowly adding 0.1-0.3 mol / L ferrous sulfate solution under stirring, and the adding amount is 3-8% of the weight of the magnesium oxide;

[0027] S13: subsequently, adding 0.2-0.5 mol / L sodium hydroxide solution dropwise to adjust the pH value to 9-11;

[0028] S14: continuously stirring at 70-90 DEG C for 0.5-2 hours to make the iron oxide uniformly deposit on the surface of the magnesium oxide;

[0029] S15: After standing and layering, pour the supernatant and wash with deionized water for 3-5 times until neutral;

[0030] S16: Dry at 100-120°C for 4-8 hours to obtain magnesium oxide particles with a surface-deposited iron oxide modified layer, the modified layer thickness being 5-20nm;

[0031] The specific process of mixing the layering ingredients in step S2 is as follows:

[0032] S21: Porous layer ingredients: weigh the magnesium oxide, calcium oxide, neutral thermal expansion adjusting particles, thermal expansion particles, porous pore-forming agent and thermal compensation additive according to the proportion; first dry mix for 5 minutes, add the modified binder and mix for 15-30 minutes;

[0033] S22: Transition layer ingredients: weigh the magnesium oxide, calcium oxide, negative thermal expansion composite particles, neutral thermal expansion adjusting particles, thermal expansion particles, porous pore-forming agent and thermal compensation additive according to the proportion; first dry mix for 5 minutes; add 3-6 parts of the modified binder and mix for 15-30 minutes;

[0034] S23: Dense layer ingredients: weigh the modified magnesium oxide, calcium oxide, negative thermal expansion composite particles and neutral thermal expansion adjusting particles according to the proportion; first dry mix for 5 minutes; add the modified binder and porous pore-forming agent and mix for 15-30 minutes;

[0035] The specific process of mold preparation and interface structure processing in step S3 is as follows:

[0036] S31: Prepare a three-section forming mold, the inner cavity of the mold is divided into upper, middle and lower sections, corresponding to the forming space of the porous layer, transition layer and dense layer;

[0037] S32: Process a dovetail groove male mold structure on the lower surface of the upper section mold, and a corresponding dovetail protrusion female mold structure on the upper surface of the middle section mold;

[0038] S33: Process a dovetail groove male mold structure on the lower surface of the middle section mold; process a dovetail protrusion female mold structure matching the dovetail groove on the upper surface of the lower section mold, the protrusion height matching the groove depth;

[0039] Further, the specific process of gradient layering forming in step S4 is as follows:

[0040] S41: Preheat the mold to 80-120°C and apply release agent;

[0041] S42: Load the dense layer mixture into the lower section mold, control the loading density to be 1.8-2.2g / cm 3 , and vibrate for 30-60 seconds;

[0042] S43: Apply pre-pressure 5-15 MPa, keep pressure 30-60 seconds, make the dense layer reach the design thickness and form a flat upper surface;

[0043] S44: Brush interface bonding enhancer on the upper surface of the dense layer, which is a composite solution of silica sol and alumina sol with solid content of 15-25%, and the application amount is 0.2-0.8 kg / m 2 ;

[0044] S45: Install the middle section mold, load the transition layer mixture, and control the loading density to 1.5-1.9 g / cm 3 , at this time the dovetail male mold contacts the upper surface of the dense layer, forming a dovetail structure;

[0045] S46: Apply pre-pressure 8-20 MPa to the transition layer to make the transition layer material fill the dovetail and form a dovetail protrusion structure;

[0046] S47: Install the upper section mold and load the porous layer mixture, control the density to 1.2-1.6 g / cm 3 ;

[0047] S48: Perform overall isostatic pressing, forming pressure 80-150 MPa, holding time 3-5 minutes, to realize the tight bonding and forming of each layer;

[0048] S49: After forming, perform layered demolding, first reduce the forming pressure to 5-10 MPa, maintain a slight pressure to prevent the green body from deforming;

[0049] S410: Slowly lift the upper section mold, control the demolding speed at 2-5 mm / min to avoid damage to the porous layer, and protect the surface of the porous layer during demolding;

[0050] S411: Horizontally move out the dovetail male structure of the middle section mold, first tilt the male structure outward by 3-8°, then vertically lift and move out, control the demolding force within 0.5-2 MPa to ensure the integrity of the transition layer dovetail protrusion structure;

[0051] S412: Use bottom jacking to demold, control the jacking speed at 1-3 mm / min, and simultaneously laterally support the dense layer dovetail protrusion structure to prevent damage during demolding;

[0052] S413: After demolding, the green body is placed at room temperature for 12-24 hours, and the ambient humidity is maintained at 40-60% to prevent surface cracking of the green body;

[0053] The specific process of shrinkage matching sintering in step S5 is as follows:

[0054] S51: Put the shaped blank into a sintering furnace with a partition heating function, and the furnace body is provided with three independent temperature control zones, i.e., upper, middle and lower zones;

[0055] S52: First-stage temperature rising: the temperature is raised to 400-600 DEG C at a rate of 5-10 DEG C / hour, and the temperature is kept for 1-3 hours in an air atmosphere, so that the binder is fully reacted and the bound water is removed, and initial solidification is realized;

[0056] S53: Second-stage temperature rising: the temperature is raised to 800-1000 DEG C at a rate of 8-15 DEG C / hour, and the temperature is kept for 2-5 hours in a weak reducing atmosphere with a carbon monoxide volume fraction of 8-15%, so that the components are reacted in solid phase to form intermediate phase combination;

[0057] S54: Third-stage temperature rising: the temperature is raised to 1400-1550 DEG C at a rate of 10-20 DEG C / hour, and the temperature is kept for 3-6 hours, so that full sintering densification of the layers is realized;

[0058] S55: Partition temperature control: the temperature of the upper zone is 10-20 DEG C lower than that of the middle zone, and the temperature of the middle zone is 5-15 DEG C higher than that of the lower zone;

[0059] The specific process of the coordinated cooling in step S6 is as follows:

[0060] S61: Starting from the highest sintering temperature of 1400-1550 DEG C, the temperature is cooled to 1100 DEG C at a rate of 8-15 DEG C / hour;

[0061] S62: The temperature is slowly cooled to 600 DEG C at a rate of 3-8 DEG C / hour from 1100 DEG C, and this temperature section is a stress sensitive zone, and the thermal stress is released by slow cooling;

[0062] S63: The temperature is cooled to 200 DEG C at a rate of 10-20 DEG C / hour from 600 DEG C;

[0063] S64: The temperature is naturally cooled to room temperature from 200 DEG C, and the total cooling time is controlled to be 24-48 hours.

[0064] The beneficial effects achieved by the present application are as follows:

[0065] Firstly, the present application realizes comprehensive compensation of thermal expansion of the magnesium-calcium brick through the three-layer gradient structure design and the synergistic effect of multiple functional composite particles. The magnesium oxide content of the porous layer, the transition layer and the dense layer is distributed in a gradient increasing manner, and the calcium oxide content is distributed in a gradient decreasing manner, so that the outer layer has excellent thermal shock resistance, and the inner layer effectively controls the volume expansion stress. The mechanical interlocking structure of the dovetail groove and the dovetail protrusion between the layers realizes firm connection, avoids the interlayer peeling problem which is prone to occur in the traditional planar bonding mode, and significantly improves the overall structural stability and service life of the brick body.

[0066] Secondly, the negative thermal expansion composite particles, neutral thermal expansion adjusting particles and thermal sensitive expansion particles constitute a complete thermal expansion compensation system, and play a synergistic effect in different temperature ranges. The ZrW2O8 core of the negative thermal expansion composite particles shrinks when heated, effectively offsetting the positive thermal expansion of the matrix material, and the Al2O3-SiO2 provides chemical protection and mechanical strength. The combination of β-quartz and MgAl2O4 of the neutral thermal expansion adjusting particles realizes the precise adjustment of thermal expansion, balances the thermal expansion difference between the layers. The thermal sensitive expansion particles expand in a specific temperature range, timely fill the micro-cracks generated due to shrinkage, and ensure the thermal stability of the brick in the whole temperature range.

[0067] Thirdly, the modified binder adopts a composite system of aluminum phosphate and phenolic resin, realizing the synergistic effect of organic-inorganic hybrid materials. Aluminum phosphate provides excellent high-temperature bonding strength and chemical stability, and phenolic resin ensures the forming property and toughness at room temperature, and the two form a three-dimensional network structure through Al-O-P bond and hydrogen bond, so that the binder has high-temperature stability and good processing performance. The porous pore-forming agent of the composite formula forms a refractory skeleton through silicon powder, zirconia powder and mullite powder, ammonium bicarbonate is decomposed at high temperature to form pores, and the organic component provides adhesion and toughness, and the pore structure has uniformity and stability.

[0068] Fourthly, the surface modification treatment process deposits an iron oxide modified layer on the surface of magnesium oxide particles through a wet chemical method, which significantly improves the interfacial bonding strength and chemical compatibility of magnesium oxide and other components. The layered charging and static pressure forming process precisely controls the charging density and forming pressure of each layer, ensuring the integrity of the interfacial and the optimal matching of the performance of each layer. The use of interfacial bonding enhancer further strengthens the interfacial bonding, and the precise forming of the dovetail structure ensures the mechanical bonding force, thereby improving the interfacial bonding strength of the multilayer composite material.

[0069] Fifthly, the segmented control of the sintering process and the coordinated cooling system fully considers the sintering characteristics and thermal expansion behavior differences of different layers of materials. The zoned temperature control enables each layer to sinter under the best temperature conditions, avoiding stress concentration and structural defects caused by temperature mismatch. The slow and 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 additive optimizes the sintering process, reduces the sintering temperature while improving the high-temperature stability, and the precise control of the whole preparation process ensures that the final product has excellent thermal stability, structural integrity and use reliability. BRIEF DESCRIPTION OF DRAWINGS

[0070] Figure 1 is the overall structure perspective view of the thermal expansion compensation magnesia calcia brick of the present application;

[0071] Figure 2 is Figure 1A cross-sectional structure schematic diagram of the application;

[0072] Figure 3 is a preparation process flow chart of the thermal expansion compensation magnesium calcium brick of the application.

[0073] Reference numerals in the drawing:

[0074] 1, porous layer; 2, transition layer; 3, dense layer; 4, dovetail groove; 5, dovetail protrusion. DETAILED DESCRIPTION

[0075] The technical solutions in the application will be clearly and completely described below with reference to the drawings in the application, and in addition, the forms of each structure described in the following embodiments are only examples, and the application is not limited to each structure described in the following embodiments. All other embodiments obtained by those of ordinary skill in the art without making creative efforts fall within the scope of protection of the application.

[0076] Reference Figures 1-2 , the application designs a thermal expansion compensation magnesium calcium brick, which comprises a porous layer 1, a transition layer 2 and a dense layer 3, and each layer comprises the following components by weight:

[0077] The components of the porous layer 1 are: 55-70 parts of magnesium oxide, 18-28 parts of calcium oxide, 2-4 parts of neutral thermal expansion adjusting particles, 1-3 parts of heat-sensitive expansion particles, 2-5 parts of modified binding agent, 2-5 parts of porous pore-forming agent and 1.5-3.5 parts of thermal compensation additive;

[0078] The components of the transition layer 2 are: 65-75 parts of magnesium oxide, 8-15 parts of calcium oxide, 2-5 parts of negative thermal expansion composite particles, 1-3 parts of neutral thermal expansion adjusting particles, 0.5-2 parts of heat-sensitive expansion particles, 3-6 parts of modified binding agent, 1-3 parts of porous pore-forming agent and 0.8-2.3 parts of thermal compensation additive;

[0079] The components of the dense layer 3 are: 75-85 parts of magnesium oxide, 5-12 parts of calcium oxide, 3-6 parts of negative thermal expansion composite particles, 1-2 parts of neutral thermal expansion adjusting particles, 4-7 parts of modified binding agent and 0.5-2 parts of porous pore-forming agent.

[0080] The negative thermal expansion composite particle comprises 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 adjusting particle comprises a beta-quartz core and an MgAl2O4 outer layer, and the heat-sensitive expansion particle is calcium silicate-coated calcium sulfate. The thermal compensation additive comprises the following components in parts by weight: lithium carbonate 0.3-0.8 parts, boron oxide 0.5-1.2 parts, and titanium dioxide 1-3 parts; and the porous pore-forming agent comprises the following components in parts by weight: silicon powder 15-25 parts; ammonium bicarbonate 20-30 parts; lignin fiber 5-10 parts; starch 5-10 parts; polyvinyl alcohol powder 1-3 parts; water 8-12 parts; zirconium oxide powder 3-6 parts; and mullite powder 5-10 parts.

[0081] The thermal expansion compensation magnesium-calcium brick has the following structural features: the lower surface of the porous layer 1 is provided with a dovetail groove 4 structure, the upper surface of the transition layer 2 is provided with a dovetail protrusion 5 structure matched with the dovetail groove 4; the lower surface of the transition layer 2 is provided with a dovetail groove 4 structure, and the upper surface of the dense layer 3 is provided with a dovetail protrusion 5 structure matched with the dovetail groove 4.

[0082] The preparation process of the negative thermal expansion composite particle is as follows: ZrW2O8 powder is mixed with silica sol and alumina sol to prepare a slurry; the coated particle is prepared by a spray granulation device; and the negative thermal expansion composite particle with an Al2O3-SiO2 layer on the surface is obtained by calcining at 800-1000 DEG C for 1-3 hours.

[0083] The preparation process of the neutral thermal expansion adjusting particle is as follows: beta-quartz powder is mixed with a magnesium-aluminum spinel precursor; the composite particle is prepared by a mechanical coating method; and the neutral thermal expansion adjusting particle is obtained by heat treatment at 1100-1250 DEG C for 2-4 hours.

[0084] The preparation process of the heat-sensitive expansion particle is as follows: calcium sulfate particles are used as the core; calcium silicate is used as the coating material; the coated particle is prepared by a dry coating process at 300-450 DEG C to obtain the heat-sensitive expansion particle.

[0085] 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 reaction is carried out at 60-90 DEG C for 1-3 hours; and the modified binder is obtained after cooling.

[0086] The preparation process of the porous pore-forming agent is as follows: uniformly mixing silicon powder, zirconium oxide powder and mullite powder according to the proportion to obtain an inorganic mineral powder mixture; adding lignin fiber and starch, dry stirring for 2-4 minutes; adding ammonium bicarbonate and polyvinyl alcohol powder, and continuing to dry stir for 2-3 minutes; spraying 8-12 parts of water, wet stirring until uniform without agglomerates, and controlling the water content; placing in a mold for compression molding; drying the molded body at 100-200 DEG C for 4-8 hours to remove free water; uniformly heating at 3-5 DEG C per hour to 650-800 DEG C to decompose ammonium bicarbonate and organic matter and form a porous structure; continuing to heat to 1500-1600 DEG C for 2-4 hours, and obtaining the porous structure pore-forming agent particles after cooling.

[0087] The thermal expansion compensation magnesium calcium brick of the present application 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 the preferred scheme, 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, and the thermal expansion compensation magnesium calcium brick can effectively disperse thermal stress. The mechanical interlocking structure of dovetail groove 4 and dovetail protrusion 5 is used to connect between the layers, the dovetail groove 4 structure is arranged on the lower surface of the porous layer 1, the matching dovetail protrusion 5 structure is arranged on the upper surface of the transition layer 2, and 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 are interlocked, so that the firmness of the interlayer combination is ensured.

[0088] The components and proportions selected for the thermal expansion compensation magnesium calcium brick of the present application are repeatedly designed, and it is determined that magnesium oxide as the main raw material presents a gradient distribution feature, the content in the porous layer 1 is 55-70 parts, the content in the transition layer 2 is increased to 65-75 parts, and the content in the dense layer 3 is further increased to 75-85 parts, so as to provide different levels of structural strength and refractory performance. The distribution of calcium oxide presents an opposite trend, the content in the porous layer 1 is the highest, which is 18-28 parts, the content in the transition layer 2 is reduced to 8-15 parts, and the content in the dense layer 3 is the lowest, which is 5-12 parts, the higher content of calcium oxide in the outer layer can enhance the thermal shock resistance, and the lower content in the inner layer can reduce the volume expansion stress and avoid structural damage caused by mismatched thermal expansion.

[0089] The thermal expansion compensation magnesium calcium brick of the application designs three functional composite particles, forming a complete thermal expansion compensation system. The negative thermal expansion composite particle is composed of a ZrW2O8 core and an Al2O3-SiO2 outer layer, ZrW2O8 has unique negative thermal expansion characteristics, and will shrink when heated, effectively compensating the positive thermal expansion of the matrix material, reducing the overall thermal expansion coefficient, the particles are only distributed in the transition layer 2 and the dense layer 3, and the content is 2-5 parts and 3-6 parts respectively. The neutral thermal expansion adjusting particle contains a beta-quartz core and a MgAl2O4 outer layer, and its thermal expansion coefficient is close to neutral, which plays a buffering and adjusting role, and is distributed in the three layers, and the content decreases from 2-4 parts in the porous layer 1 to 1-2 parts in the dense layer 3, which can balance the thermal expansion difference between the layers. The heat-sensitive expansion particle is calcium silicate-coated calcium sulfate, which expands in a specific temperature range, and is mainly distributed in the porous layer 1 and the transition layer 2, and the content is 1-3 parts and 0.5-2 parts respectively, which can expand in time during the heating process to fill the micro-cracks caused by shrinkage.

[0090] The modified binder system adopts a composite of aluminum phosphate and phenolic resin, with a mass ratio controlled at 2-4:1, the aluminum phosphate provides high-temperature bonding strength, and the phenolic resin provides normal-temperature forming property, and the synergistic effect of the two ensures the bonding effect under different temperature conditions. The porous pore-forming agent adopts a composite formula design, containing silicon powder 15-25 parts as a skeleton strength provider, ammonium bicarbonate 20-30 parts for pore forming at high temperature, lignin fiber 5-10 parts for enhancing toughness, starch 5-10 parts for providing organic bonding, polyvinyl alcohol powder 1-3 parts for improving forming property, zirconium oxide powder 3-6 parts for improving refractoriness, and mullite powder 5-10 parts for enhancing structural stability.

[0091] The thermal compensation additive is composed of lithium carbonate, boron oxide and titanium dioxide, lithium carbonate 0.3-0.8 parts as a low-temperature flux to promote sintering, boron oxide 0.5-1.2 parts to reduce sintering temperature and improve fluidity, and titanium dioxide 1-3 parts as a stabilizer to improve high-temperature stability, and the synergistic effect of the three components ensures the smooth progress of the sintering process and the stability of the final product.

[0092] The core material of the negative thermal expansion composite particle ZrW2O8 is a zirconium tungstate crystal with a cubic crystal structure. The material exhibits negative thermal expansion characteristics in the range of -273°C to 1050°C, which is based on the dominance of transverse vibration in the lattice vibration mode, resulting in lattice shrinkage as the temperature rises. The Al2O3-SiO2 composite oxide outer layer forms a dense protective shell layer with a thickness of 0.5-3 μm, which is combined with the core through chemical bonding and physical adsorption, providing chemical stability and mechanical protection to prevent direct contact between ZrW2O8 and the external environment. The typical particle size range of the entire particle is 5-50 μm, which offsets the positive thermal expansion of the base material in the magnesium-calcium brick through the negative thermal expansion characteristics, reduces thermal stress concentration, and improves the thermal stability of the brick body.

[0093] The modified binder is an organic-inorganic hybrid material composed of an aluminum phosphate inorganic phase and a phenolic resin organic phase. Aluminum phosphate has a tetrahedral network structure, and phenolic resin is a thermosetting polymer formed by the condensation polymerization of phenol and formaldehyde. The two are compounded in a mass ratio of 2-4:1 to form a three-dimensional network structure through Al-O-P bonding and hydrogen bonding interaction. The use temperature of the composite can reach 800-1200°C, and the aluminum phosphate phase provides high-temperature stability. The normal temperature bonding strength is 15-25 MPa, and the high-temperature bonding strength is 8-15 MPa. The composite has good chemical stability in both alkaline and acidic environments, and the thermal expansion coefficient is between that of pure aluminum phosphate and phenolic resin, with good compatibility with the base material. Through a reaction time of 1-3 hours at 60-90°C, the aluminum phosphate and phenolic resin are fully crosslinked to form a stable three-dimensional network structure, achieving the best bonding performance.

[0094] The core material of the neutral thermal expansion adjustment particle β-quartz is hexagonal, with a special thermal expansion behavior. The α-β phase transition occurs near 573°C, accompanied by a volume expansion of about 0.82%. The MgAl2O4 magnesium aluminate spinel outer layer is cubic, with a low thermal expansion coefficient, acting as a buffer. The core accounts for 60-80wt%, and the outer layer accounts for 20-40wt%. A diffusion bonding interface is formed through high temperature treatment. The synergistic effect of the core-shell structure realizes the precise adjustment of thermal expansion, compensating for the expansion mismatch of the base material in a specific temperature range. Through 1100-1250°C heat treatment for 2-4 hours, the MgAl2O4 outer layer is completely formed into a spinel phase, and a good interface bonding is formed with the β-quartz core.

[0095] The heat-sensitive expansion particle is composed of a calcium sulfate core and a calcium silicate coating layer. The calcium sulfate can be CaS04 or CaS04·2H20, and has a layered or fibrous crystal structure. The calcium silicate coating layer mainly includes a C-S-H gel phase and a crystalline calcium silicate phase, and has a thickness of 1-5 μm, forming a continuous and dense coating layer. The overall particle size is 10-100 μm. The heat-sensitive expansion mechanism is based on the dehydration reaction of calcium sulfate during heating. CaS04·2H20 is converted into CaS04·0.5H20 at 120-180 °C, and is further converted into CaS04 at 180-220 °C. Each step of the reaction is accompanied by volume expansion. The calcium sulfate can also undergo a crystal transformation at high temperatures, resulting in additional volume changes. The overall volume expansion can be up to 5-15%. The calcium silicate coating layer controls the dehydration rate, prevents cracking caused by rapid expansion, and adjusts the expansion rate to achieve controllable expansion. The particle starts to expand significantly at 120-180 °C. The particle is prepared by a dry coating process at 300-450 °C, which ensures that the calcium silicate coating layer is well combined with the calcium sulfate core, while avoiding unnecessary phase changes of the calcium sulfate during preparation.

[0096] The structures and compositions of the above four key components play a synergistic role in the heat expansion compensation magnesium calcium brick, and function in different temperature ranges to achieve heat expansion compensation in the full temperature range. By adjusting the content of each component in different layers, the performance of the gradient functional material is achieved. Each component has good chemical stability in a high-temperature alkaline environment, solving the cracking and peeling problems of traditional magnesium calcium bricks during thermal cycling, and significantly improving the thermal stability and service life of the material.

[0097] The preparation process of the negative thermal expansion composite particle is introduced as follows. First, ZrW20s powder is mixed with silica sol and alumina sol to prepare a uniform slurry. The solid content and viscosity are controlled to ensure uniformity of the coating. Then, the coated particles are prepared by a spray granulation device. Key parameters such as inlet air temperature, atomization pressure, and feed flow rate need to be accurately controlled. Finally, the particles are calcined at 800-1000 °C for 1-3 hours. This calcination process can form a dense Al203-Si02 protective layer to prevent ZrW20s from oxidizing and failing in use, while also improving the mechanical strength of the particles to ensure their stability during subsequent use.

[0098] The preparation process of the neutral thermal expansion adjustment particle includes mixing β-quartz powder with magnesium aluminate spinel precursor, using mechanical coating method to prepare composite particles, using high-speed stirring or fluidized bed coating technology, and then heat treating at 1100-1250 °C for 2-4 hours. High-temperature heat treatment ensures the formation of MgAl204 spinel phase, and mechanical coating method ensures uniform thickness of the coating layer. The resulting composite particles have excellent thermal stability and controllable thermal expansion characteristics.

[0099] The preparation of the heat-sensitive expansion particles adopts a dry coating process, taking calcium sulfate particles as the core, and using calcium sulfate with a clear phase transition temperature as the coating material, and performing coating treatment at 300-450 DEG C. Low-temperature coating avoids the phase transition of the core material, and the calcium sulfate coating layer has good chemical compatibility, enabling controllable heat-sensitive expansion characteristics and playing a compensation role at a key temperature point.

[0100] 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 DEG C for 1-3 hours. Moderate reaction temperature avoids excessive crosslinking of the phenolic resin, and sufficient reaction time ensures the formation of a composite structure. The modified binder obtained after cooling has both the high-temperature performance of aluminum phosphate and the moldability of phenolic resin, realizing a synergistic effect.

[0101] The preparation process of the porous pore-forming agent involves multiple steps. First, silicon powder, zirconia powder and mullite powder are mixed uniformly at a certain ratio to obtain an inorganic mineral powder mixture. These inorganic components will form a refractory skeletal structure. Then, lignin fibers and starch are added, and dry stirring is performed for 2-4 minutes. Next, ammonium bicarbonate and polyvinyl alcohol powder are added, and dry stirring is continued for another 2-3 minutes to ensure uniform distribution of the components. Then, 8-12 parts of water are sprayed, and wet stirring is performed until uniform distribution without agglomerates. The key to this step is to control the uniform distribution of the water content. The mixture is then pressed into a mold and dried at 100-200 DEG C for 4-8 hours to remove free water. Then, the temperature is uniformly increased to 650-800 DEG C at a rate of 3-5 DEG C per hour to decompose the ammonium bicarbonate and organic matter. Slow heating ensures uniform decomposition of the organic matter and the formation of a uniform pore structure. The temperature is then increased to 1500-1600 DEG C and held for 2-4 hours to form a stable inorganic skeletal structure. After cooling, the porous pore-forming agent particles with a porous structure are obtained.

[0102] In combination Figure 3 The preparation process of the heat expansion compensation magnesium-calcium brick of the present application will be described in detail as follows:

[0103] S1: Surface modification treatment is performed on the magnesium oxide particles 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:

[0104] S11: The magnesium oxide particles are dispersed in deionized water at a weight ratio of 1:10, and stirred for 15-30 minutes to fully wet them;

[0105] S12: Under stirring, 0.1-0.3 mol / L ferrous sulfate solution is slowly added, and the amount added is 3-8% of the weight of the magnesium oxide;

[0106] S13: Then, 0.2-0.5 mol / L sodium hydroxide solution is added dropwise to adjust the pH value to 9-11;

[0107] S14: The reaction is continuously stirred at 70-90°C for 0.5-2 hours to make the iron oxide uniformly deposit on the surface of the magnesium oxide;

[0108] S15: After standing and layering, the supernatant is poured out, and the supernatant is washed with deionized water for 3-5 times until neutral;

[0109] S16: Drying at 100-120°C for 4-8 hours to obtain magnesium oxide particles with a modified layer of iron oxide deposited on the surface, and the thickness of the modified layer is 5-20 nm;

[0110] S2: The mixed materials of the porous layer 1, the transition layer 2, and the dense layer 3 are prepared respectively; the specific process of the layering and mixing of the mixed materials in step S2 is as follows:

[0111] S21: Preparation of the mixed materials of the porous layer 1: magnesium oxide, calcium oxide, neutral thermal expansion adjusting particles, thermal sensitive expansion particles, porous pore-forming agent, and thermal compensation additive are weighed according to the proportion; dry mixing is performed for 5 minutes, the modified binder is added, and mixing is performed for 15-30 minutes;

[0112] S22: Preparation of the mixed materials of the transition layer 2: magnesium oxide, calcium oxide, negative thermal expansion composite particles, neutral thermal expansion adjusting particles, thermal sensitive expansion particles, porous pore-forming agent, and thermal compensation additive are weighed according to the proportion; dry mixing is performed for 5 minutes; 3-6 parts of the modified binder are added, and mixing is performed for 15-30 minutes;

[0113] S23: Preparation of the mixed materials of the dense layer 3: modified magnesium oxide, calcium oxide, negative thermal expansion composite particles, and neutral thermal expansion adjusting particles are weighed according to the proportion; dry mixing is performed for 5 minutes; the modified binder and the porous pore-forming agent are added, and mixing is performed for 15-30 minutes;

[0114] S3: Preparation of the mold and interface structure, and processing of the layered forming mold with the dovetail groove 4 and the dovetail protrusion 5; the specific process of the mold preparation and interface structure processing in step S3 is as follows:

[0115] S31: Preparation of a three-section forming mold, the inner cavity of the mold is divided into an upper section, a middle section, and a lower section, corresponding to the forming spaces of the porous layer 1, the transition layer 2, and the dense layer 3;

[0116] S32: The dovetail groove 4 male structure is processed on the lower surface of the upper section mold, and the dovetail protrusion 5 female structure is processed on the upper surface of the middle section mold;

[0117] S33: The dovetail groove 4 male structure is processed on the lower surface of the middle section mold, and the dovetail protrusion 5 female structure matching the dovetail groove 4 is processed on the upper surface of the lower section mold, and the height of the protrusion matches the depth of the groove;

[0118] S4: Put the mixed materials of the porous layer 1, the transition layer 2 and the dense layer 3 into the mold respectively, and use the layered loading static pressure forming to obtain the formed blank; the specific process of the gradient layered forming in step S4 is as follows:

[0119] The specific process of the gradient layered forming in step S4 is as follows:

[0120] S41: Preheat the mold to 80-120℃, and brush the release agent;

[0121] S42: Put the mixed material of the dense layer 3 into the lower mold, and control the loading density to be 1.8-2.2g / cm 3 , and use the vibration table to vibrate and compact for 30-60 seconds;

[0122] S43: Apply the pre-pressure of 5-15MPa, and keep the pressure for 30-60 seconds, so that the dense layer 3 reaches the designed thickness and forms the flat upper surface;

[0123] S44: Brush the interface bonding enhancer, which is the composite solution of silica sol and alumina sol with the solid content of 15-25%, on the upper surface of the dense layer 3, and the application amount is 0.2-0.8kg / m 2 ;

[0124] S45: Install the middle mold, put the mixed material of the transition layer 2 into the middle mold, and control the loading density to be 1.5-1.9g / cm 3 , at this time, the male mold of the dovetail groove 4 contacts with the upper surface of the dense layer 3, and the dovetail groove 4 structure is formed;

[0125] S46: Apply the pre-pressure of 8-20MPa to the transition layer 2, so that the transition layer 2 material fills the dovetail groove 4 and forms the dovetail protrusion 5 structure;

[0126] S47: Install the upper mold and put the mixed material of the porous layer 1 into the upper mold, and control the density to be 1.2-1.6g / cm 3 ;

[0127] S48: Perform the overall isostatic pressure forming, the forming pressure is 80-150MPa, the pressure keeping time is 3-5 minutes, and the tight combination of the layers is realized;

[0128] S49: After the forming is completed, perform the layered demolding, first reduce the forming pressure to 5-10MPa, and keep the slight pressure to prevent the deformation of the blank;

[0129] S410: Slowly lift the upper mold, and control the demolding speed to be 2-5mm / min to avoid the damage to the porous layer 1, and perform the protective covering on the surface of the porous layer 1 during the demolding process;

[0130] S411: horizontally move out the dovetail groove 4 male mold structure of the middle section mold, first tilt the male mold structure outward by 3-8°, then vertically lift and move out, the demolding force is controlled within the range of 0.5-2 MPa, and the integrity of the dovetail protrusion 5 structure of the transition layer 2 is ensured;

[0131] S412: adopt bottom jacking demolding, the jacking speed is controlled within the range of 1-3 mm / min, and the dovetail protrusion 5 structure of the dense layer 3 is laterally supported to prevent the structure from being damaged in the demolding process;

[0132] S413: the green body after demolding is placed at room temperature for 12-24 hours, the ambient humidity is maintained within the range of 40-60% during the period, and the surface cracking of the green body is avoided;

[0133] S5: adopt a segmented control sintering process to sinter the formed green body; the specific process of the shrinkage matching sintering in step S5 is as follows:

[0134] S51: put the formed green body into a sintering furnace with a partition heating function, and set three independent temperature control zones, i.e., upper, middle and lower zones, in the furnace body;

[0135] S52: first stage temperature rising: rise the temperature to 400-600°C at a rate of 5-10°C / hour, maintain for 1-3 hours, adopt air atmosphere, make the binder fully react and remove the combined water, and realize preliminary solidification;

[0136] S53: second stage temperature rising: rise the temperature to 800-1000°C at a rate of 8-15°C / hour, maintain for 2-5 hours, adopt a weak reducing atmosphere with a carbon monoxide volume fraction of 8-15%, make the components occur solid phase reaction, and form intermediate phase combination;

[0137] S54: third stage temperature rising: rise the temperature to 1400-1550°C at a rate of 10-20°C / hour, maintain for 3-6 hours, realize full sintering and densification of each layer;

[0138] S55: partition temperature control: the temperature of the upper zone is 10-20°C lower than that of the middle zone, and the temperature of the middle zone is 5-15°C higher than that of the lower zone;

[0139] S6: after sintering, adopt a coordinated cooling system to cool from the sintering temperature to room temperature. The specific process of the coordinated cooling in step S6 is as follows:

[0140] S61: start from the highest sintering temperature 1400-1550°C, and cool to 1100°C at a rate of 8-15°C / hour;

[0141] S62: slowly cool from 1100°C to 600°C at a rate of 3-8°C / hour, this temperature section is a stress sensitive zone, and the thermal stress is released through slow cooling;

[0142] S63: cooling from 600℃ to 200℃ at a rate of 10-20℃ / hour;

[0143] S64: natural cooling from 200℃ to room temperature, the total cooling time is controlled in 24-48 hours.

[0144] In the whole preparation process of the magnesium-calcium brick, the surface modification treatment of the magnesium oxide particles is to deposit a modified layer of iron oxide on the surface of the magnesium oxide particles by wet chemical method, forming a protective layer with a thickness of 5-20nm, which improves the bonding strength of magnesium oxide with the matrix material and enhances the chemical stability in high temperature environment. In the specific process, the magnesium oxide particles are dispersed in deionized water at a weight ratio of 1:10, and by controlling the concentration of ferrous sulfate solution at 0.1-0.3mol / L and adjusting the pH value of sodium hydroxide solution to 9-11 in an alkaline environment, it is ensured that the iron oxide can be uniformly deposited on the surface of the magnesium oxide.

[0145] The design of layered batching and mixing is based on the characteristics of gradient functional materials, and by adjusting the content ratio of each component in different layers, the gradual change from the porous structure of the outer layer to the dense structure of the inner layer is realized. The magnesium oxide content in the porous layer 1 batching is 55-70 parts, and the calcium oxide content is 18-28 parts, the higher calcium oxide content in the outer layer can enhance the thermal shock resistance, and the magnesium oxide content ensures the basic refractory performance. The magnesium oxide content in the transition layer 2 batching is increased to 65-75 parts, and the calcium oxide is reduced to 8-15 parts, which realizes the smooth transition of the thermal expansion coefficient between the layers, and avoids the stress concentration caused by sudden change of material performance. The magnesium oxide content in the dense layer 3 batching is increased to 75-85 parts, and the calcium oxide is the lowest of 5-12 parts, so that the inner layer can provide the highest structural strength and refractory performance, and the lower calcium oxide content reduces the volume expansion stress.

[0146] In the mold preparation process, by preparing a three-section forming mold, a mechanical engagement structure of dovetail groove 4 and dovetail protrusion 5 is designed at the interface of each layer, which realizes firm connection between layers through geometric physical constraint, avoiding the problem of interface delamination that may occur by relying solely on chemical bonding. The dovetail groove 4 structure on the lower surface of the upper mold and the dovetail protrusion 5 structure on the upper surface of the middle mold are accurately matched, so that the porous layer 1 and the transition layer 2 form a reliable bond, and the bonding mode of the transition layer 2 and the dense layer 3 is the same as the above mode. In the specific processing process, the dense layer 3 is controlled at a density of 1.8-2.2g / cm 3 , the transition layer 2 is 1.5-1.9g / cm 3 , and the porous layer 1 is 1.2-1.6g / cm 3, the decreasing density distribution forms a gradient structure with gradually decreasing density from inside to outside, effectively dispersing thermal stress; the pre-pressure layered application method is adopted, 5-15 MPa pre-pressure is applied to the dense layer 3, 8-20 MPa pre-pressure is applied to the transition layer 2, and it is ensured that each layer can reach the predetermined density. The interface bonding enhancer adopts a composite solution of silica sol and alumina sol with a solid content of 15-25%, and the application amount is controlled in the range of 0.2-0.8 kg / m 2 On the basis of mechanical interlocking, chemical bonding is increased to form a double bonding mechanism, thereby improving the interlayer bonding strength. The overall isostatic pressing forming adopts a forming pressure of 80-150 MPa and a pressure holding time of 3-5 minutes, so as to ensure the tight combination of each layer and eliminate internal defects. Layered demolding is adopted to control the demolding speed and demolding force to avoid structure damage. The demolding speed of the porous layer 1 is controlled in the range of 2-5 mm / min, the dovetail groove 4 positive mold structure is first inclined at an angle of 3-8° and then vertically lifted during demolding, and the demolding force is controlled in the range of 0.5-2 MPa to protect the structural integrity of the brick blank.

[0147] The segmented control sintering process is based on the physical and chemical change law of the material at different temperatures, and the ordered reaction of each component is realized through a three-stage temperature rising system. The first stage is slowly raised to 400-600℃ at a rate of 5-10℃ / h. The slow heating rate is advantageous for the binder to fully react and remove the combined water, thereby avoiding cracking caused by rapid heating. The second stage is raised to 800-1000℃ at a rate of 8-15℃ / h. A weak reducing atmosphere is adopted, and the volume fraction of carbon monoxide is 8-15%, which promotes the solid phase reaction and forms a stable intermediate phase combination. The third stage is further increased to 1400-1550℃ at a rate of 10-20℃ / h, which ensures sufficient reaction while improving production efficiency.

[0148] The present application designs a partition temperature control process, 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, which compensates for the shrinkage difference of different layers of materials and reduces thermal stress during sintering. The holding time is 3-6 hours to ensure that each layer is fully sintered and densified to obtain the best mechanical properties and thermal stability.

[0149] The coordinated cooling process is based on the stress release mechanism, and the effective release of thermal stress is realized by controlling the cooling rate in sections. From the highest sintering temperature, it is cooled to 1100℃ at a rate of 8-15℃ / h, and then it is cooled to 600℃ at a rate of 3-8℃ / h. Slow cooling in the stress sensitive interval maximally releases the thermal stress and avoids cracking during the cooling process. From 600℃, it is cooled to 200℃ at a rate of 10-20℃ / h, and finally it is naturally cooled to room temperature. The total cooling time is controlled in the range of 24-48 hours, and the design of long-time slow cooling ensures that the internal stress of the product is fully released.

[0150] The whole preparation process provides guarantee for the full play of the synergistic effect of functional additives. The negative thermal expansion composite particles compensate the positive thermal expansion of the matrix material through the negative thermal expansion characteristics of the ZrW2O8 core, and the neutral thermal expansion adjusting particles play a buffering and adjusting role. The thermal sensitive expansion particles fill the micro-cracks by phase change and expansion in a specific temperature range, realizing the thermal expansion matching in the whole temperature range and significantly improving the thermal stability of the material.

[0151] In example 1, a three-layer gradient structure design is adopted, and the total thickness is 100 millimeters. The porous layer 1 has a thickness of 15 millimeters and contains, by weight, 62 parts of magnesium oxide, 23 parts of calcium oxide, 3 parts of neutral thermal expansion adjusting particles, 2 parts of thermal sensitive expansion particles, 3.5 parts of modified binder, 3.5 parts of porous pore-forming agent, and 2.5 parts of thermal compensation additive. The thermal compensation additive is composed of 0.5 parts of lithium carbonate, 0.8 parts of boron oxide, and 2 parts of titanium dioxide, forming a composite system of low-temperature flux to promote sintering.

[0152] The transition layer 2 has a thickness of 45 millimeters and contains, by weight, 70 parts of magnesium oxide, 12 parts of calcium oxide, 3.5 parts of negative thermal expansion composite particles, 2 parts of neutral thermal expansion adjusting particles, 1 part of thermal sensitive expansion particles, 4.5 parts of modified binder, 2 parts of porous pore-forming agent, and 1.5 parts of thermal compensation additive. The thermal compensation additive is composed of 0.4 parts of lithium carbonate, 0.7 parts of boron oxide, and 1.8 parts of titanium dioxide, ensuring that the transition layer 2 has good thermal matching performance.

[0153] The dense layer 3 has a thickness of 40 millimeters and contains, by weight, 80 parts of magnesium oxide, 8 parts of calcium oxide, 4.5 parts of negative thermal expansion composite particles, 1.5 parts of neutral thermal expansion adjusting particles, 5.5 parts of modified binder, and 1 part of porous pore-forming agent. The content of negative thermal expansion composite particles is the highest in the dense layer 3, effectively compensating the positive thermal expansion effect of the matrix material.

[0154] The preparation process is as follows:

[0155] The preparation process first performs surface modification treatment on the magnesium oxide particles. The magnesium oxide particles are dispersed in deionized water at a weight ratio of 1:10, stirred for 15 to 30 minutes to fully wet them, then a 0.1 to 0.3 mol / L ferrous sulfate solution is slowly added under stirring, the amount of addition is 3% to 8% of the weight of the magnesium oxide, then 0.2 to 0.5 mol / L sodium hydroxide solution is added dropwise to adjust the pH value to 9 to 11, and the stirring reaction is continued at 70 to 90 degrees Celsius for 0.5 to 2 hours to make the iron oxide uniformly deposited on the surface of the magnesium oxide, forming a modified layer with a thickness of 5 to 20 nanometers.

[0156] In the layered batching process, each layer of the mixture is weighed according to the proportion and then dry mixed for 5 minutes, and then the modified binder is added and mixed for 15 to 30 minutes to ensure uniform distribution of the components. The mold is designed in three sections, with the upper, middle and lower sections corresponding to the forming space of the porous layer 1, the transition layer 2 and the dense layer 3, respectively, and the dovetail groove 4 and dovetail protrusion 5 structures are processed at the corresponding positions.

[0157] In the layered charging static pressure forming process, the mold is preheated to 80 to 120 degrees Celsius, the dense layer 3 charging density is controlled to 1.8 to 2.2 grams per cubic centimeter, the transition layer 2 density is controlled to 1.5 to 1.9 grams per cubic centimeter, and the porous layer 1 density is controlled to 1.2 to 1.6 grams per cubic centimeter. On the upper surface of the dense layer 3, an interface bonding enhancer is brushed, a composite solution of silica sol and alumina sol is used, the solid content is 15% to 25%, and the application amount is 0.2 to 0.8 kilograms per square meter. The overall isostatic pressing forming adopts a forming pressure of 80 to 150 megapascals, and the pressure holding time is 3 to 5 minutes.

[0158] The firing process adopts segmented control, the first segment is heated at a rate of 5 to 10 degrees Celsius per hour to 400 to 600 degrees Celsius for 1 to 3 hours, the second segment is heated at a rate of 8 to 15 degrees Celsius per hour to 800 to 1000 degrees Celsius for 2 to 5 hours, and the third segment is heated at a rate of 10 to 20 degrees Celsius per hour to 1400 to 1550 degrees Celsius 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.

[0159] Comparative Example 1 uses a traditional single homogeneous structure, with a total thickness of 100 millimeters. It contains magnesium oxide 70 parts, calcium oxide 15 parts, modified binder 4 parts, porous pore former 2 parts, and thermal compensation additive 1.5 parts by weight. The thermal compensation additive is composed of lithium carbonate 0.4 parts, boron oxide 0.7 parts, and titanium dioxide 1.8 parts. The entire brick body is a homogeneous structure without any functional composite particles, and the interlayer uses a planar bonding method without dovetail groove 4 structure design. The preparation process is as follows:

[0160] Comparative Example 1 uses a traditional preparation process, and the magnesium oxide particles are not surface modified and are directly mixed with other components. In the batching process, the components are weighed according to the proportion and then mixed uniformly without layered batching. The forming adopts a common single layer charging method, the charging density is kept uniform, and the mold structure is simple without dovetail groove 4 design. The firing process uses a conventional temperature rising system without zoned temperature control, and the cooling process is a natural cooling method.

[0161] The comparative experiment design and results are as follows:

[0162] The test was carried out according to GB / T 2997-2000 "Test Method for Bulk Density, Apparent Porosity and True Porosity of Dense Shaped Refractory", GB / T 3001-2017 "Test Method for Cold Crushing Strength of Refractory Materials", GB / T 3002-2017 "Test Method for Hot Modulus of Rupture of Refractory Materials" and other national standards.

[0163] Table 1 Performance comparison of Example 1 and Comparative Example 1

[0164]

[0165] Table 2 Thermal expansion coefficient test results of Example 1 and Comparative Example 1

[0166]

[0167] The experimental results show that the three-layer gradient structure design adopted in Example 1 effectively disperses the thermal stress through the reverse gradient distribution of the gradient increase of the magnesium oxide content and the gradient decrease of the calcium oxide content. The mechanical engagement structure of the dovetail groove 4 and the dovetail protrusion 5 significantly improves the interlayer bonding strength.

[0168] In the present embodiment, the porous layer 1 contains, by weight parts, 58 parts of magnesium oxide, 25 parts of calcium oxide, 4 parts of neutral thermal expansion adjusting particles, 3 parts of heat-sensitive expansion particles, 4 parts of modified binder, 4 parts of porous pore-forming agent, and 3 parts of thermal compensation additive. The thermal compensation additive is composed of 0.6 parts of lithium carbonate, 1.0 parts of boron oxide, and 2.5 parts of titanium dioxide, forming a stronger sintering promotion effect.

[0169] The transition layer 2 contains, by weight parts, 68 parts of magnesium oxide, 10 parts of calcium oxide, 5 parts of negative thermal expansion composite particles, 3 parts of neutral thermal expansion adjusting particles, 2 parts of heat-sensitive expansion particles, 5 parts of modified binder, 2.5 parts of porous pore-forming agent, and 2 parts of thermal compensation additive. The content of the negative thermal expansion composite particles reaches the upper limit range, maximizing the negative thermal expansion properties of the ZrW2O8 core. The thermal compensation additive is composed of 0.5 parts of lithium carbonate, 0.9 parts of boron oxide, and 2.2 parts of titanium dioxide.

[0170] The dense layer 3 contains, by weight parts, 78 parts of magnesium oxide, 10 parts of calcium oxide, 6 parts of negative thermal expansion composite particles, 2 parts of neutral thermal expansion adjusting particles, 6 parts of modified binder, and 1.5 parts of porous pore-forming agent. The content of the negative thermal expansion composite particles reaches the highest ratio in the dense layer 3, achieving the best compensation effect through the synergistic effect of the ZrW2O8 core and the Al2O3-SiO2 outer layer. The preparation process is as follows:

[0171] The negative thermal expansion composite particles are prepared by mixing ZrW2O8 powder with silica sol and alumina sol to form a uniform slurry, controlling the solid content to ensure uniform coating, accurately controlling the inlet air temperature, atomization pressure and liquid flow during the preparation of coated particles by spray granulation equipment, and calcining at 800 to 1000 degrees Celsius for 1 to 3 hours to form a dense protective layer.

[0172] The neutral thermal expansion adjusting particles are prepared by mixing β-quartz powder with magnesium aluminate spinel precursor, using high-speed stirring mechanical coating method to prepare composite particles, ensuring uniform thickness of the coating layer, and heat treating at 1100 to 1250 degrees Celsius for 2 to 4 hours to fully form MgAl2O4 spinel phase.

[0173] The heat-sensitive expansion particles use calcium sulfate particles as the core and calcium silicate as the coating material, prepared by dry coating process at 300 to 450 degrees Celsius, avoiding unnecessary phase change of the core material, and forming controllable heat-sensitive expansion properties.

[0174] Comparative Example 2 uses the same three-layer structure but does not add any functional composite particles. The porous layer 1 contains magnesium oxide 67 parts, calcium oxide 25 parts, modified binder 4 parts, and porous pore former 4 parts by weight, without negative thermal expansion composite particles, neutral thermal expansion adjusting particles and heat-sensitive expansion particles.

[0175] The transition layer 2 contains magnesium oxide 78 parts, calcium oxide 10 parts, modified binder 5 parts, porous pore former 2.5 parts, and thermal compensation additive 2 parts by weight, also lacking the thermal expansion compensation mechanism of functional composite particles.

[0176] The dense layer 3 contains magnesium oxide 86 parts, calcium oxide 10 parts, modified binder 6 parts, and porous pore former 1.5 parts by weight, and the content of magnesium oxide is increased to 86 parts to compensate for the lack of functional particles.

[0177] The preparation process of Comparative Example 2 is relatively simple, as it does not contain functional composite particles, and the preparation step of composite particles is omitted. During the batching process, the components of each layer are mixed in the conventional manner, without special particle pretreatment.

[0178] The comparative experiment design and results are as follows:

[0179] Table 3 Thermal expansion performance comparison of Example 2 and Comparative Example 2

[0180]

[0181] Table 4 Microstructure changes during thermal cycling

[0182]

[0183] The experimental results show that the three 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 adjusting particle achieves precise adjustment of thermal expansion. The heat-sensitive expansion particle expands in a specific temperature range to timely fill the micro-cracks caused by shrinkage.

[0184] Example 3, Example 3 uses a modified binder system of aluminum phosphate combined with phenolic resin and a carefully designed porous pore former formula. The porous layer 1 contains magnesium oxide 65 parts, calcium oxide 20 parts, neutral thermal expansion adjusting particles 3.5 parts, heat-sensitive expansion particles 2.5 parts, modified binder 5 parts, porous pore former 5 parts, thermal compensation additive 3.5 parts by weight.

[0185] The modified binder is prepared by mixing aluminum phosphate and phenolic resin at a mass ratio of 3:1, reacting at 75 degrees Celsius for 2 hours to ensure the formation of a stable three-dimensional network structure. The porous pore former contains silicon powder 20 parts, ammonium bicarbonate 25 parts, lignin fiber 7 parts, starch 7 parts, polyvinyl alcohol powder 2 parts, water 10 parts, zirconium oxide powder 4.5 parts, mullite powder 7.5 parts by weight, forming a composite functional pore forming system. The preparation process is as follows:

[0186] The reaction conditions of aluminum phosphate and phenolic resin in the preparation of modified binder are strictly controlled. The reaction temperature of 75 degrees Celsius avoids excessive crosslinking of phenolic resin, and the reaction time of 2 hours ensures the full formation of composite structure. After cooling, the modified binder has both the high temperature performance of aluminum phosphate and the molding property of phenolic resin.

[0187] The porous pore former is prepared by first mixing silicon powder, zirconium oxide powder, and mullite powder in proportion to form an inorganic mineral powder mixture, then adding lignin fiber and starch for dry stirring for 2 to 4 minutes, then adding ammonium bicarbonate and polyvinyl alcohol powder for dry mixing for 2 to 3 minutes, and finally adding 8 to 12 parts of water for wet stirring until uniform without agglomeration. After molding, dry at 100 to 200 degrees Celsius for 4 to 8 hours to remove free water, heat at a rate of 3 to 5 degrees Celsius per hour to 650 to 800 degrees Celsius to decompose the organic matter and form a porous structure, and continue to heat to 1500 to 1600 degrees Celsius for 2 to 4 hours to form a stable inorganic skeleton.

[0188] Comparative Example 3, Comparative Example 3 uses a traditional phosphoric acid binder and a simple pore-forming agent formula as a comparison. The porous layer 1 contains magnesium oxide 65 parts, calcium oxide 20 parts, neutral thermal expansion adjusting particles 3.5 parts, heat-sensitive expansion particles 2.5 parts, phosphoric acid binder 5 parts, traditional pore-forming agent 5 parts, and thermal compensation additive 3.5 parts by weight. The phosphoric acid binder uses an 85% phosphoric acid solution, which does not have the complex effect of a modified binder.

[0189] The traditional pore-forming agent contains sawdust 30 parts, starch 20 parts, water 15 parts, and other fillers 35 parts by weight. The formula is simple and lacks the synergistic effect of multifunctional components, and cannot form a stable and uniform pore structure.

[0190] The preparation process of Comparative Example 3 uses a traditional method, and the phosphoric acid binder is directly mixed with the raw materials without a complex reaction process. The traditional pore-forming agent is prepared by physically mixing the components.

[0191] The design and results of the comparative experiment are as follows:

[0192] Table 5 Performance comparison of binder system of Example 3 and Comparative Example 3

[0193]

[0194] Table 6 Comparison of porous pore-forming agent effect of Example 3 and Comparative Example 3

[0195]

[0196] Table 7 Comparison of high-temperature performance of Example 3 and Comparative Example 3

[0197]

[0198] The 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-O-P bonds and hydrogen bonds, realizing the synergistic effect of organic-inorganic hybrid materials. The porous pore-forming agent of the composite formula forms a refractory skeleton through silicon powder, zirconium oxide powder, and mullite powder, ensuring the uniformity and stability of the pore structure.

[0199] Example 4, Example 4 verifies the effect of surface modification treatment and staged sintering process. The porous layer 1 contains surface modified magnesium oxide 60 parts, calcium oxide 22 parts, neutral thermal expansion adjusting particles 3 parts, heat-sensitive expansion particles 2 parts, modified binder 4 parts, porous pore-forming agent 4 parts, and thermal compensation additive 2.5 parts by weight. The thermal compensation additive is composed of lithium carbonate 0.6 parts, boron oxide 0.9 parts, and titanium dioxide 2.3 parts, and the ratio is optimized and adjusted.

[0200] The surface modified magnesium oxide is prepared by wet chemical method, a 15 nm thick iron oxide modification layer is deposited on the surface of magnesium oxide particles, which significantly improves the interfacial bonding strength and chemical compatibility. The component ratio of the transition layer 2 and the dense layer 3 is basically consistent with that of the standard example, but the surface modified magnesium oxide raw material is used. The preparation process is as follows:

[0201] In the surface modification process of magnesium oxide, the magnesium oxide particles are dispersed in deionized water at a weight ratio of 1:10, 5% of the weight of magnesium oxide is added to a 0.2 mol / L ferrous sulfate solution, a 0.3 mol / L sodium hydroxide solution is used to adjust the pH to 10, and the reaction is carried out at 80 degrees Celsius for 1 hour. After washing and drying, the magnesium oxide particles with a 15 nm thick iron oxide modification layer deposited on the surface are obtained.

[0202] The staged control sintering process uses precise temperature control, the first stage is raised to 500 degrees Celsius at a rate of 8 degrees Celsius per hour and kept for 2 hours, the second stage is raised to 900 degrees Celsius at a rate of 12 degrees Celsius per hour and kept for 3 hours in a weak reducing atmosphere with a carbon monoxide volume fraction of 12%, and the third stage is raised to 1480 degrees Celsius at a rate of 15 degrees Celsius per hour and kept 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.

[0203] The coordinated cooling process is cooled 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 naturally cooled, with strict control of the total cooling time.

[0204] In Comparative Example 4, untreated ordinary magnesium oxide raw material is used, the porous layer 1 contains ordinary magnesium oxide 60 parts, calcium oxide 22 parts, neutral thermal expansion adjustment particles 3 parts, thermal expansion particles 2 parts, modified binder 4 parts, porous pore-forming agent 4 parts, and thermal compensation additive 2.5 parts by weight. The ordinary magnesium oxide lacks a surface modification layer, and the interfacial bonding strength with other components is relatively low.

[0205] Comparative Example 4 uses a traditional sintering process, which directly raises the temperature to 1450 degrees Celsius at a constant rate of 10 degrees Celsius per hour, keeps it for 3 hours, and then naturally cools to room temperature without a zoned temperature control system.

[0206] The comparative experiment design and results are as follows:

[0207] Table 8 Comparison of magnesium oxide surface modification effects of Example 4 and Comparative Example 4

[0208]

[0209] Table 9 Comparison of sintering process effects of Example 4 and Comparative Example 4

[0210]

[0211] Table 10 Comparison of thermal stress release effect of Example 4 and Comparative Example 4

[0212]

[0213] Table 11 Comparison of service life prediction of Example 4 and Comparative Example 4

[0214]

[0215] The experimental results show that Example 4 significantly improves the interfacial bonding strength and chemical compatibility with other components by surface modification treatment of magnesium oxide particles, the layering charging static pressure forming process precisely controls the charging density and forming pressure of each layer, and the segmented control of the sintering process and the coordinated cooling process is targeted at the sintering characteristics and thermal expansion differences of different layers of materials, effectively releases the thermal stress, and prevents cracking and deformation caused by rapid temperature change.

[0216] From the above comparative experiments, it can be seen that the three-layer gradient structure design significantly improves the structural stability and interlayer bonding strength through the reverse gradient distribution and dovetail slot 4 mechanical engagement structure. The functional composite particle thermal expansion compensation system realizes the thermal expansion matching in the whole temperature range, reduces the thermal expansion coefficient and thermal stress concentration. The surface modification treatment and the segmented sintering process realize the strengthening of the interfacial bonding and the effective release of the thermal stress.

[0217] The above only describes the preferred embodiments of the present application and is not used to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A thermal expansion compensating magnesia calcia brick, characterized by: It comprises a porous layer, a transition layer and a dense layer, each layer comprises the following components by weight: The porous layer components are: magnesium oxide 55-70 parts, calcium oxide 18-28 parts, neutral thermal expansion adjusting particles 2-4 parts, thermal sensitive expansion particles 1-3 parts, modified binder 2-5 parts, porous pore forming agent 2-5 parts, thermal compensation additive 1.5-3.5 parts; The transition layer components are: magnesium oxide 65-75 parts, calcium oxide 8-15 parts, negative thermal expansion composite particles 2-5 parts, neutral thermal expansion adjusting particles 1-3 parts, thermal sensitive expansion particles 0.5-2 parts, modified binder 3-6 parts, porous pore forming agent 1-3 parts, thermal compensation additive 0.8-2.3 parts; The dense layer components are: magnesium oxide 75-85 parts, calcium oxide 5-12 parts, negative thermal expansion composite particles 3-6 parts, neutral thermal expansion adjusting particles 1-2 parts, modified binder 4-7 parts, porous pore forming agent 0.5-2 parts; The negative thermal expansion composite particles comprise ZrW2O8 and Al2O3-SiO2, the modified binder is a composite of aluminum phosphate and phenolic resin, the neutral thermal expansion adjusting particles comprise β-quartz and MgAl2O4, the thermal sensitive expansion particles are calcium silicate coated calcium sulfate; the thermal compensation additive comprises the following components by weight: lithium carbonate 0.3-0.8 parts, boron oxide 0.5-1.2 parts, titanium dioxide 1-3 parts; The porous pore forming agent comprises, by weight: silicon powder 15-25 parts; ammonium bicarbonate 20-30 parts; lignin fiber 5-10 parts; starch 5-10 parts; polyvinyl alcohol powder 1-3 parts; water 8-12 parts; zirconium oxide powder 3-6 parts; mullite powder 5-10 parts.

2. The thermal expansion compensating magnesia calcia brick according to claim 1, characterized in that: The lower surface of the porous layer is provided with a dovetail groove structure, and the upper surface of the transition layer is provided with a dovetail convex structure matched with the dovetail groove; the lower surface of the transition layer is provided with a dovetail groove structure, and the upper surface of the dense layer is provided with a dovetail convex structure matched with the dovetail groove.

3. The thermal expansion compensating magnesium calcium brick according to claim 1, characterized in that: The preparation process of the negative thermal expansion composite particles is: mixing ZrW2O8 powder with silica sol and alumina sol to prepare a slurry; preparing coated particles by spray granulation equipment; calcining at 800-1000℃ for 1-3 hours to obtain negative thermal expansion composite particles coated with an Al2O3-SiO2 layer on the surface.

4. The thermal expansion compensating magnesium calcium brick according to claim 1, characterized in that: The preparation process of the neutral thermal expansion adjusting particles is: mixing β-quartz powder with magnesium aluminate spinel precursor; Mechanical coating method is used to prepare composite particles; heat treatment at 1100-1250℃ for 2-4 hours to obtain neutral thermal expansion adjusting particles.

5. The thermal expansion compensating magnesium calcium brick according to claim 1, characterized in that: The preparation process of the thermal sensitive expansion particles is: taking calcium sulfate particles as the core; using calcium silicate as the coating material; preparing coated particles by dry coating process at 300-450℃ to obtain thermal sensitive expansion particles.

6. The thermal expansion compensating magnesium calcium brick according to claim 1, characterized in that: The preparation process of the modified binder is: mixing aluminum phosphate with phenolic resin at a mass ratio of 2-4:1; reacting at 60-90℃ for 1-3 hours; obtaining the modified binder after cooling; The preparation process of the porous pore-forming agent is as follows: uniformly mixing silicon powder, zirconia powder and mullite powder according to proportions to obtain an inorganic mineral powder mixture; adding lignin fiber and starch, dry stirring for 2-4 minutes; adding ammonium bicarbonate and polyvinyl alcohol powder, and continuing dry stirring for 2-3 minutes; spraying 8-12 parts of water, wet stirring until uniform without agglomerates, and controlling the water content; placing in a mold for compression molding; drying the molded body at 100-200 DEG C for 4-8 hours to remove free water; uniformly heating at 3-5 DEG C per hour to 650-800 DEG C to decompose ammonium bicarbonate and organic matter and form a porous structure; continuing to heat to 1500-1600 DEG C for 2-4 hours, and obtaining the porous pore-forming agent particle after cooling.

7. The process for producing a thermal expansion compensating magnesium calcium brick according to any one of claims 1 to 6, characterized in that: The method comprises the following steps: S1: performing surface modification treatment on the magnesium oxide particles, depositing iron oxide on the surface of the magnesium oxide particles by a wet chemical method to form a surface modified layer; S2: respectively preparing mixed materials of the porous layer, the transition layer and the dense layer; S3: preparing a layered molding mold with dovetail grooves and dovetail protrusions; S4: respectively loading the mixed materials of the porous layer, the transition layer and the dense layer into the mold, and adopting layered loading static pressure molding to obtain a molded body; S5: adopting a segmented control sintering process to sinter the molded body; S6: after sintering, adopting a segmented cooling system to cool from the sintering temperature to room temperature.

8. The manufacturing process of claim 7, wherein: The specific process of step S1 is as follows: S11: dispersing the magnesium oxide particles in deionized water according to a weight ratio of 1:10, and stirring for 15-30 minutes to fully wet the magnesium oxide particles; S12: slowly adding 0.1-0.3 mol / L ferrous sulfate solution under stirring, and the amount of the ferrous sulfate solution is 3%-8% of the weight of the magnesium oxide; S13: subsequently, adding 0.2-0.5 mol / L sodium hydroxide solution dropwise to adjust the pH value to 9-11; S14: continuously stirring at 70-90 DEG C for 0.5-2 hours to make the iron oxide uniformly deposited on the surface of the magnesium oxide; S15: after standing and stratifying, pouring the supernatant, and washing with deionized water for 3-5 times until neutral; S16: drying at 100-120 DEG C for 4-8 hours to obtain the magnesium oxide particles with a surface modified layer of iron oxide, and the thickness of the modified layer is 5-20 nm; The specific process of the layered mixing in step S2 is as follows: S21: porous layer mixing: weighing the magnesium oxide, calcium oxide, neutral thermal expansion adjusting particles, thermal sensitive expansion particles, porous pore-forming agent and thermal compensation additives according to the proportions, dry mixing for 5 minutes, and adding the modified binder and mixing for 15-30 minutes; S22: transition layer mixing: weighing the magnesium oxide, calcium oxide, negative thermal expansion composite particles, neutral thermal expansion adjusting particles, thermal sensitive expansion particles, porous pore-forming agent and thermal compensation additives according to the proportions, dry mixing for 5 minutes, adding 3-6 parts of the modified binder and mixing for 15-30 minutes; S23: dense layer mixing: weighing the modified magnesium oxide, calcium oxide, negative thermal expansion composite particles and neutral thermal expansion adjusting particles according to the proportions, dry mixing for 5 minutes, adding the modified binder and the porous pore-forming agent, and mixing 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 forming mold, and the inner cavity of the mold is divided into upper, middle and lower sections, corresponding to the forming space of the porous layer, the transition layer and the dense layer; S32: Process a dovetail groove male mold structure on the lower surface of the upper mold, and process a corresponding dovetail protrusion female mold structure on the upper surface of the middle mold; S33: Process a dovetail groove male mold structure on the lower surface of the middle mold; and process a dovetail protrusion female mold structure matching the dovetail groove on the upper surface of the lower mold, and the height of the protrusion matches the depth of the groove.

9. The manufacturing process of claim 8, wherein: The specific process of step S4 is as follows: S41: Preheat the mold to 80-120°C, and apply release agent; S42: The compacting layer mixture is charged into the lower die, and the charge density is controlled to be 1.8-2.2 g / cm 3 vibrating table for 30-60 seconds; S43: Apply a pre-pressure of 5-15 MPa, and keep the pressure for 30-60 seconds, so that the dense layer reaches the designed thickness and forms a flat upper surface; S44: On the surface of the dense layer, brush the interface bonding enhancer, which is a composite solution of silica sol and alumina sol with solid content of 15-25%, and the application amount is 0.2-0.8 kg / m 2 ; S45: install middle section mold, load transition layer mixture, control loading density to 1.5-1.9g / cm 3 At this time, the male dovetail groove contacts 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 upper section mold and charge the porous layer mixture, density control 1.2-1.6 g / cm 3 ; S48: Perform overall isostatic pressing, with a forming pressure of 80-150 MPa and a pressure holding time of 3-5 minutes, to realize the tight combination and forming of each layer; S49: After the forming is completed, perform layered demolding, first reduce the forming pressure to 5-10 MPa, and keep a slight pressure to prevent the billet from deforming; S410: Slowly lift the upper mold, and control the demolding speed at 2-5 mm / min to avoid damaging the porous layer, and perform protective covering on the surface of the porous layer during the demolding process; S411: Horizontally move out the dovetail groove male mold structure of the middle mold, first tilt the male mold structure outward by 3-8°, then vertically lift and move out, and control the demolding force in the range of 0.5-2 MPa to ensure the integrity of the dovetail protrusion structure of the transition layer; S412: Perform demolding by bottom jacking, control the jacking speed at 1-3 mm / min, and simultaneously perform lateral support on the dovetail protrusion structure of the dense layer to prevent the structure from being damaged during the demolding process; S413: After the demolding, the billet is placed at room temperature for 12-24 hours, and the environmental humidity is kept at 40-60% during the period to avoid the surface cracking of the billet; The specific process of step S5 is as follows: S51: Put the formed billet into a firing furnace with a partitioned heating function, and the furnace body is provided with upper, middle and lower three independent temperature control zones; S52: First stage temperature rising: rise the temperature to 400-600°C at a rate of 5-10°C / hour, keep the temperature for 1-3 hours, and use air atmosphere to make the binder fully react and remove the combined water, and realize preliminary solidification; S53: Second stage temperature rising: rise the temperature to 800-1000°C at a rate of 8-15°C / hour, keep the temperature for 2-5 hours, and use a weak reducing atmosphere with a carbon monoxide volume fraction of 8-15% to make the components undergo solid phase reaction and form intermediate phase combination; S54: Third stage temperature rising: rise the temperature to 1400-1550°C at a rate of 10-20°C / hour, keep the temperature for 3-6 hours, to realize full sintering and densification of each layer; S55: Partitioned temperature control: the temperature of the upper zone is 10-20°C lower than that of the middle zone, and the temperature of the middle zone is 5-15°C higher than that of the lower zone; The specific process of step S6 is as follows: S61: from the highest firing temperature 1400-1550℃, cooling to 1100℃ at a rate of 8-15℃ / hour; S62: slowly cooling from 1100℃ to 600℃ at a rate of 3-8℃ / hour, this temperature range is the stress sensitive zone, release thermal stress by slow cooling; S63: cooling from 600℃ to 200℃ at a rate of 10-20℃ / hour; S64: natural cooling from 200℃ to room temperature, the total cooling time is controlled in 24-48 hours.

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