A low thermal conductivity multilayer composite magnesium-aluminum spinel brick and its preparation method

Abstract

This invention belongs to the field of refractory materials technology, and specifically relates to a low thermal conductivity multilayer composite magnesium-aluminum spinel brick and its preparation method, comprising a working layer, a heat-insulating layer, and a thermal insulation layer. By introducing magnesium-aluminum spinel hollow microspheres during the preparation of the heat-insulating layer, heat conduction in the material is reduced, thus lowering the product's thermal conductivity. Furthermore, the introduction of hydroxyl iron oxide-modified diatomaceous earth provides a large number of hydroxyl groups on the diatomaceous earth surface, forming chemical bonds with water glass in the raw materials, resulting in a good interfacial bond. During the preparation of the working layer, water glass acts as an alkali activator, working together with metakaolin mixed with styrene-acrylic emulsion and a silane coupling agent to form a metakaolin-based polymer with a stable three-dimensional network structure, further improving the product's mechanical properties.

Description

Technical Field

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

[0002] Magnesium aluminum spinel is a cubic crystal system, with each unit cell consisting of 32 cubic close-packed O atoms. 2- 16 Al atoms in octahedral voids 3+ And 8 Mg atoms in the tetrahedral voids 2+ Composition. Mg 2+ The positions of the atoms are almost identical to those of carbon atoms in the diamond structure, indicating that spinel possesses high hardness and high density. Furthermore, due to the saturation of the magnesium aluminum spinel structure, it exhibits excellent thermal stability, resistance to chemical corrosion, and wear resistance. It also demonstrates excellent stability in both reducing and oxidizing atmospheres. However, due to the intrinsic properties of spinel and the methods used in its preparation, spinel-based refractories have a relatively high thermal conductivity, increasing the loss of high-temperature heat during industrial kiln operation and thus raising the cost of energy conservation and emission reduction.

[0003] Patent application number CN202011452149.5 discloses a synergistic treatment method for magnesia-alumina spinel bricks used in cement kilns, its preparation method, and its application. The main raw materials are flotation magnesia, high-purity magnesia, and fused magnesia-alumina spinel, along with calcined alumina powder. The bricks are prepared through high-temperature treatment. By combining high-purity magnesia and fused magnesia-alumina spinel with flotation magnesia, the method avoids the drawbacks of poor high-temperature toughness caused by the presence of free calcium in flotation magnesia, as well as the impact of irregular intergranular pores on corrosion resistance, effectively extending the service life. This improves the thermal shock resistance and high-temperature toughness of the material. Patent application CN201510936752.3 discloses a method for preparing low thermal conductivity magnesia-alumina spinel bricks, which are made by firing a refractory layer and an insulating layer at high temperatures. The refractory layer is made of high-purity magnesia-alumina spinel, and the insulating layer is made of magnesia-iron composite olivine. The refractory layer retains the good high-temperature mechanical properties of magnesia-alumina spinel bricks, such as erosion resistance, scour resistance, thermal shock resistance, and mechanical stress resistance. The insulating layer has strong anti-stripping ability, effectively improving its service life. However, with increasingly stringent requirements for energy conservation and emission reduction in high-temperature industrial fields, the preparation of refractory materials with high mechanical strength and low thermal conductivity has become a focus of attention. Summary of the Invention

[0004] To address the aforementioned problems, this invention provides a low thermal conductivity multilayer composite magnesium-aluminum spinel brick and its preparation method. First, a slurry containing a working layer and an insulation layer is added to a mold. After pressing, drying, and firing, a product with notches is obtained. Then, the insulation layer is bonded to the notches of the product to obtain the low thermal conductivity multilayer composite magnesium-aluminum spinel brick.

[0005] The technical solution adopted by the present invention to solve the above-mentioned technical problems is as follows:

[0006] A low thermal conductivity multilayer composite magnesium-aluminum spinel brick includes a working layer, a thermal insulation layer, and a heat insulation layer; the working layer is connected to the thermal insulation layer, and there is a notch in the thermal insulation layer, with the heat insulation layer located within the notch;

[0007] The working layer is composed of the following raw materials in parts by weight: 45-55 parts magnesium aluminum spinel, 20-28 parts aluminum-rich spinel, 18-26 parts magnesium-rich spinel, 10-18 parts metakaolin, 10-18 parts modified water glass, 0.2-0.5 parts styrene-acrylic emulsion, and 0.02-0.05 parts silane coupling agent; preferably, 50 parts magnesium aluminum spinel, 25 parts aluminum-rich spinel, 22 parts magnesium-rich spinel, 16 parts metakaolin, 12 parts modified water glass, 0.3 parts styrene-acrylic emulsion, and 0.03 parts silane coupling agent.

[0008] The insulation layer is composed of the following raw materials in parts by weight: 18-25 parts of fused magnesia fine powder, 6-10 parts of lightly calcined magnesia powder, 14-22 parts of α-Al2O3 micro powder, 12-18 parts of magnesium aluminum spinel hollow microspheres, 8-16 parts of hydroxyl oxide modified diatomaceous earth, and 8-12 parts of modified water glass; preferably, 20 parts of fused magnesia fine powder, 8 parts of lightly calcined magnesia powder, 16 parts of α-Al2O3 micro powder, 14 parts of magnesium aluminum spinel hollow microspheres, 12 parts of hydroxyl oxide modified diatomaceous earth, and 10 parts of modified water glass.

[0009] The heat insulation layer is a nano-aerogel board.

[0010] Further, the preparation method of the magnesium-aluminum spinel hollow microspheres is as follows: industrial alumina powder, fused magnesia fine powder and lightly calcined magnesia powder are mixed evenly and fed into an electric arc furnace. After the mixture in the electric arc furnace melts, it is heated and kept at 2000-2200℃ for 1-3 hours. Then, the mixture is blown under a gas pressure of 0.8-1.0MPa to obtain magnesium-aluminum spinel hollow microspheres. The mass ratio of industrial alumina powder, fused magnesia fine powder and lightly calcined magnesia powder is 5-8:1-1.5:1. The obtained hollow microspheres are sieved to obtain three series: 3-2mm, 2-1mm and 1-0.2mm. The three series of 3-2mm, 2-1mm and 1-0.2mm are mixed in a mass ratio of 1:1:1.

[0011] Further, the preparation process of the ferric chloride-modified diatomaceous earth is as follows: ferric chloride hexahydrate and ammonium bicarbonate are mixed in anhydrous ethanol, and raw diatomaceous earth is added to it. The mixture is sealed and stirred at room temperature for 6-8 hours, then filtered under vacuum at a stirring speed of 100-150 r / min. The filtered material is dried, ground, and sieved through an 80-mesh sieve to obtain ferric chloride-modified diatomaceous earth. The drying conditions are: drying in a vacuum drying oven at 50-60℃ for 6-8 hours; the molar ratio of ferric chloride hexahydrate to ammonium bicarbonate is 1:2-5; the amount of ferric chloride hexahydrate in anhydrous ethanol is 0.02-0.03 g / mL, and the amount of diatomaceous earth in anhydrous ethanol is 0.03-0.05 g / mL.

[0012] Further, the modified water glass is prepared by placing water glass in a container and adding sodium tetraborate therein, then stirring to obtain a stable solution, which is the modified water glass; wherein the stirring conditions are 400-500 r / min, and stirring is performed for 20-40 min; the mass ratio of sodium tetraborate to water glass is 0.1:15-25.

[0013] This invention also provides a method for preparing low thermal conductivity multilayer composite magnesium-aluminum spinel bricks, comprising the following steps:

[0014] S1. Weigh each raw material according to the above-mentioned weight proportions and set aside;

[0015] S2. Ingredients: Working layer: Mix metakaolin and modified water glass in a mixer, add styrene-acrylic emulsion and silane coupling agent, mix evenly, then add magnesium aluminum spinel, aluminum-rich spinel and magnesium-rich spinel and mix evenly for later use; Insulation layer: Place all raw materials of the insulation layer in a mixer and mix evenly for later use.

[0016] S3. After the ingredients are prepared, the mold is divided into two parts with a length ratio of 1-3:1-2 using a partition. The slurry after the working layer and the insulation layer are mixed is added to the two compartments respectively. After the partition is removed, the brick blanks are pressed into brick blanks using a press and then placed in a dryer to dry.

[0017] S4. The qualified brick blanks dried in step S3 are loaded into the kiln car and put into the high-temperature tunnel kiln. After high-temperature firing and heat preservation, they are cooled. The nano aerogel board is bonded to the notch of the cooled product to obtain the low thermal conductivity multilayer magnesium aluminum spinel brick.

[0018] Further, in step S2, during the preparation of the working layer, the metakaolin and modified water glass are mixed and stirred in a mixer at a speed of 80-100 r / min for 4-8 min, then the speed is changed to 150-200 r / min and stirred for 3-5 min. After adding styrene-acrylic emulsion and silane coupling agent, the mixture is stirred at a speed of 150-200 r / min for 5-8 min. After adding magnesium aluminum spinel, aluminum-rich spinel and magnesium-rich spinel, the mixture is stirred at a speed of 150-200 r / min for 5-8 min. The silane coupling agent is silane coupling agent KH550. During the preparation of the insulation layer, the raw materials of the insulation layer are placed in a mixer and stirred at a speed of 100-150 r / min for 15-20 min.

[0019] In step S3, the process of placing the pressed brick blanks in a dryer for drying is as follows: the drying process is divided into a constant-rate drying stage and a deceleration drying stage. Specifically, the temperature is increased to 100°C at a rate of 5°C / h and then increased to 180°C at a rate of 3°C / h until the residual moisture content inside the brick blank is 1-5%.

[0020] In step S4, the conditions for high-temperature firing and heat preservation are: 1500-1550℃ for 6-8 hours.

[0021] The present invention has the following beneficial effects:

[0022] This invention introduces magnesium-aluminum spinel hollow microspheres during the preparation of the insulation layer. During high-temperature heat treatment, the microspheres are strengthened through sintering with the surrounding powder particles, providing strength to the material. Simultaneously, the microspheres react with the alumina and magnesium oxide in the raw materials to create numerous micropores, which helps reduce heat conduction within the material. Furthermore, the introduction of hydroxyl iron oxide-modified diatomaceous earth provides a large number of hydroxyl groups on the diatomaceous earth surface, forming chemical bonds with the water glass in the raw materials, resulting in good interfacial bonding. Additionally, the use of sodium tetraborate to modify the water glass forms numerous chain-like and cyclic Si-OT (Si, B) structures, contributing to a denser material matrix. The enhanced properties improve the compressive strength of the material. Modified water glass is also added during the preparation of the working layer, resulting in a tighter bond between the working layer and the insulation layer due to their shared composition during pressing. Simultaneously, during the preparation of the working layer, water glass acts as an alkali activator, working in conjunction with styrene-acrylic emulsion and silane coupling agent to form a stable three-dimensional network polymer with metakaolin, further improving the product's mechanical properties. Furthermore, in the preparation process of magnesium-aluminum spinel bricks, a combination of constant-rate drying and deceleration drying is used to dry the brick blanks, preventing capillary cracks from forming during the drying process. Detailed Implementation

[0023] The technical solutions in the embodiments of this application will be clearly and completely described below with reference to the embodiments of this application. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0024] The magnesium aluminum spinel (Henan Hecheng MA70; particle size 5-3mm; 3-1mm; 1-0mm; ≤0.088mm), aluminum-rich spinel (Qingdao Anmai AR90, particle size ≤0.088mm), magnesium-rich spinel (Henan Hecheng MR65; particle size ≤0.088mm) and metakaolin used in this invention were purchased from Gongyi Youxing Mineral Products Co., Ltd., water glass was purchased from Hubei Xinrunde Chemical Co., Ltd. (purity 99%), and styrene-acrylic emulsion was purchased from Shandong Yilai New Material Technology Development Co., Ltd. (purity: 46-4). The following reagents were purchased from Guangzhou Dewei Chemical Co., Ltd.: 8%), fused magnesia fine powder (≤0.074mm, MgO mass fraction >97.4%), lightly calcined magnesia powder (≤0.074mm, MgO mass fraction >94.2%), α-Al2O3 micro powder (d50=2μm), and diatomaceous earth (average particle size 5μm). The following reagents were purchased from Hebei Shuhao Energy Saving Technology Co., Ltd.: industrial alumina powder (≤0.044mm, Al2O3 mass fraction >98.5%), and nano-aerogel. All reagents used were commercially available.

[0025] Example 1

[0026] A low thermal conductivity multilayer composite magnesium-aluminum spinel brick includes a working layer, a thermal insulation layer and a heat insulation layer; the working layer is connected to the thermal insulation layer, and there is a notch in the thermal insulation layer, with the heat insulation layer located inside the notch;

[0027] The working layer is composed of the following raw materials in parts by weight: 50 parts magnesium aluminum spinel, 25 parts aluminum-rich spinel, 22 parts magnesium-rich spinel, 16 parts metakaolin, 12 parts modified water glass, 0.3 parts styrene-acrylic emulsion, and 0.03 parts silane coupling agent; the insulation layer is composed of the following raw materials in parts by weight: 20 parts fused magnesia fine powder, 8 parts lightly calcined magnesia powder, 16 parts α-Al2O3 micro powder, 14 parts magnesium aluminum spinel hollow microspheres, 12 parts hydroxyl iron oxide modified diatomaceous earth, and 10 parts modified water glass; the heat insulation layer is a nano aerogel board.

[0028] The preparation method of magnesium-aluminum spinel hollow microspheres is as follows: industrial alumina powder, fused magnesia fine powder and lightly calcined magnesia powder are mixed evenly and fed into an electric arc furnace. After the mixture melts in the electric arc furnace, it is heated and kept at 2100℃ for 2 hours. Then, magnesium-aluminum spinel hollow microspheres are obtained by blowing under a gas pressure of 1.0MPa. The mass ratio of industrial alumina powder, fused magnesia fine powder and lightly calcined magnesia powder is 7:1.2:1. The obtained hollow microspheres are sieved to obtain three series: 3-2mm, 2-1mm and 1-0.2mm. The three series of 3-2mm, 2-1mm and 1-0.2mm are mixed in a mass ratio of 1:1:1.

[0029] The preparation process of ferric chloride hexahydrate modified diatomaceous earth is as follows: ferric chloride hexahydrate and ammonium bicarbonate are mixed in anhydrous ethanol, and raw diatomaceous earth is added to the mixture. The mixture is sealed and stirred at 120 r / min for 8 hours at room temperature. After filtration, the filter material is placed in a vacuum drying oven and dried at 55℃ for 8 hours. The material is then ground and sieved through an 80-mesh sieve to obtain ferric chloride hexahydrate modified diatomaceous earth. The molar ratio of ferric chloride hexahydrate to ammonium bicarbonate is 1:3. The amount of ferric chloride hexahydrate in anhydrous ethanol is 0.025 g / mL, and the amount of diatomaceous earth in anhydrous ethanol is 0.04 g / mL.

[0030] The modified water glass is prepared by placing water glass in a container and adding sodium tetraborate, stirring at 450 r / min for 40 min to obtain a stable solution, which is the modified water glass; wherein the mass ratio of sodium tetraborate to water glass is 0.1:20.

[0031] A method for preparing a low thermal conductivity multilayer composite magnesium-aluminum spinel brick, the preparation process is as follows:

[0032] S1. Weigh each raw material according to the above-mentioned weight proportions and set aside;

[0033] S2. Ingredients: Working layer: Mix metakaolin and modified water glass in a mixer, add styrene-acrylic emulsion and silane coupling agent, mix evenly, then add magnesium aluminum spinel, aluminum-rich spinel and magnesium-rich spinel and mix evenly for later use; Insulation layer: Place all raw materials of the insulation layer in a mixer and mix evenly for later use.

[0034] S3. After the ingredients are prepared, the mold is divided into two parts with a length ratio of 3:2 using a partition. The slurry after the working layer and the insulation layer are mixed is added to the two compartments respectively. After the partition is removed, the brick blanks are pressed into brick blanks using a press and then placed in a dryer to dry.

[0035] S4. The qualified brick blanks dried in step S3 are loaded into the kiln car and put into the high-temperature tunnel kiln. After high-temperature firing and heat preservation, they are cooled. The nano aerogel board is bonded to the gap of the cooled product to obtain low thermal conductivity multilayer magnesium aluminum spinel brick.

[0036] In step S2, during the preparation of the working layer, metakaolin and modified water glass are mixed and stirred in a mixer at 90 r / min for 6 min, then the speed is changed to 180 r / min and stirred for 5 min. Styrene-acrylic emulsion and silane coupling agent KH550 are added and stirred at 180 r / min for 6 min. Magnesium aluminum spinel, aluminum-rich spinel and magnesium-rich spinel are added and stirred at 180 r / min for 6 min. During the preparation of the insulation layer, the raw materials of the insulation layer are placed in a mixer and stirred at 120 r / min for 20 min.

[0037] In step S3, the process of placing the pressed brick blanks in a dryer for drying is as follows: the drying process is divided into a constant-rate drying stage and a deceleration drying stage. Specifically, the temperature is increased to 100°C at a rate of 5°C / h and then increased to 180°C at a rate of 3°C / h until the residual moisture content inside the brick blank is 1%.

[0038] In step S4, the conditions for high-temperature firing and heat preservation are: 1525℃ for 8 hours.

[0039] Example 2

[0040] This embodiment differs from Embodiment 1 in the following ways:

[0041] The working layer is composed of the following raw materials in parts by weight: 45 parts magnesium aluminum spinel, 20 parts aluminum-rich spinel, 18 parts magnesium-rich spinel, 10 parts metakaolin, 10 parts modified water glass, 0.2 parts styrene-acrylic emulsion, and 0.02 parts silane coupling agent; the insulation layer is composed of the following raw materials in parts by weight: 18 parts fused magnesia fine powder, 6 parts lightly calcined magnesia powder, 14 parts α-Al2O3 micro powder, 12 parts magnesium aluminum spinel hollow microspheres, 8 parts hydroxyl iron oxide modified diatomaceous earth, and 8 parts modified water glass.

[0042] In the preparation process of magnesium-aluminum spinel hollow microspheres, after the mixture in the electric arc furnace is melted, it is heated and kept at 2000℃ for 1 hour, and then blown under a gas pressure of 0.8MPa to obtain magnesium-aluminum spinel hollow microspheres; wherein the mass ratio of industrial alumina powder, fused magnesia fine powder and lightly calcined magnesia powder is 5:1:1.

[0043] In the preparation of ferric hydroxide modified diatomaceous earth, raw diatomaceous earth is added, sealed, and stirred at 100 r / min for 6 h at room temperature. After filtration, the filtrate is dried in a vacuum drying oven at 50 °C for 6 h. The molar ratio of ferric chloride hexahydrate to ammonium bicarbonate is 1:2. The amount of ferric chloride hexahydrate in anhydrous ethanol is 0.02 g / mL, and the amount of diatomaceous earth in anhydrous ethanol is 0.03 g / mL.

[0044] During the preparation of modified water glass, the stirring conditions were 400 r / min for 20 min; the mass ratio of sodium tetraborate to water glass was 0.1:15.

[0045] In the preparation process of low thermal conductivity multilayer composite magnesium-aluminum spinel bricks, in step S2, during the batching process of the working layer, metakaolin and modified water glass are mixed and stirred in a mixer at 80 r / min for 4 min, then the speed is changed to 150 r / min and stirred for 3 min. Styrene-acrylic emulsion and silane coupling agent KH550 are added and stirred at 150 r / min for 5 min. Magnesium-aluminum spinel, aluminum-rich spinel and magnesium-rich spinel are added and stirred at 150 r / min for 5 min. During the batching process of the insulation layer, each raw material of the insulation layer is placed in a mixer and stirred at 100 r / min for 15 min. In step S3, after the batching is completed, the mold is divided into two parts with a length ratio of 1:1 by a partition, pressed into brick blanks, and then placed in a dryer to dry until the residual dry moisture inside the brick blank is 3%. In step S4, the high-temperature firing and heat preservation conditions are: 1500℃ for 6 h.

[0046] Example 3

[0047] This embodiment differs from Embodiment 1 in the following ways:

[0048] The working layer is composed of the following raw materials in parts by weight: 55 parts magnesium aluminum spinel, 28 parts aluminum-rich spinel, 26 parts magnesium-rich spinel, 18 parts metakaolin, 18 parts modified water glass, 0.5 parts styrene-acrylic emulsion, and 0.05 parts silane coupling agent; the insulation layer is composed of the following raw materials in parts by weight: 25 parts fused magnesia fine powder, 10 parts lightly calcined magnesia powder, 22 parts α-Al2O3 micro powder, 18 parts magnesium aluminum spinel hollow microspheres, 16 parts hydroxyl iron oxide modified diatomaceous earth, and 12 parts modified water glass.

[0049] In the preparation process of magnesium-aluminum spinel hollow microspheres, after the mixture in the electric arc furnace is melted, it is heated and kept at 2200℃ for 3 hours, and then blown under a gas pressure of 1.0MPa to obtain magnesium-aluminum spinel hollow microspheres; wherein the mass ratio of industrial alumina powder, fused magnesia fine powder and lightly calcined magnesia powder is 8:1.5:1.

[0050] In the preparation of ferric hydroxide modified diatomaceous earth, raw diatomaceous earth is added, sealed, and stirred at 150 r / min for 8 h at room temperature. After filtration, the filtrate is dried in a vacuum drying oven at 60℃ for 8 h. The molar ratio of ferric chloride hexahydrate to ammonium bicarbonate is 1:5. The amount of ferric chloride hexahydrate in anhydrous ethanol is 0.03 g / mL, and the amount of diatomaceous earth in anhydrous ethanol is 0.05 g / mL.

[0051] During the preparation of modified water glass, the stirring conditions were 500 r / min for 40 min; the mass ratio of sodium tetraborate to water glass was 0.1:25.

[0052] In the preparation process of low thermal conductivity multilayer composite magnesium-aluminum spinel bricks, in step S2, during the batching process of the working layer, metakaolin and modified water glass are mixed and stirred in a mixer at 100 r / min for 8 min, then the speed is changed to 200 r / min and stirred for 5 min. Styrene-acrylic emulsion and silane coupling agent KH550 are added and stirred at 200 r / min for 8 min. Magnesium-aluminum spinel, aluminum-rich spinel and magnesium-rich spinel are added and stirred at 200 r / min for 8 min. During the batching process of the insulation layer, the raw materials of the insulation layer are placed in a mixer and stirred at 150 r / min for 20 min. In step S3, after the batching is completed, the mold is divided into two parts with a length ratio of 1:2 by a partition, pressed into brick blanks, and then dried in a dryer until the residual dry moisture inside the brick blank is 5%. In step S4, the high-temperature firing and heat preservation conditions are: 1550℃ for 8 h.

[0053] Comparative Example 1

[0054] Compared with Example 1, this comparative example does not modify the diatomaceous earth in the raw material components; the original diatomaceous earth is added directly, and the rest is the same as in Example 1.

[0055] Comparative Example 2

[0056] Compared with Example 1, this comparative example does not modify the water glass in the raw material components; water glass is added directly, and the rest is the same as in Example 1.

[0057] Comparative Example 3

[0058] Compared with Example 1, this comparative example does not add magnesium aluminum spinel hollow microspheres to the raw material components, while the rest are the same as in Example 1.

[0059] Comparative Example 4

[0060] Compared with Example 1, this comparative example does not modify the diatomaceous earth and water glass in the raw material components, but directly adds the original diatomaceous earth and water glass, and the rest is the same as in Example 1.

[0061] Comparative Example 5

[0062] This embodiment differs from Embodiment 1 in the following ways:

[0063] The working layer is composed of the following raw materials in parts by weight: 45 parts magnesium aluminum spinel, 20 parts aluminum-rich spinel, 18 parts magnesium-rich spinel, 10 parts metakaolin, and 10 parts water glass; the insulation layer is composed of the following raw materials in parts by weight: 18 parts fused magnesia fine powder, 6 parts lightly calcined magnesia powder, 14 parts α-Al2O3 micro powder, 8 parts diatomaceous earth, and 8 parts water glass.

[0064] A method for preparing a low thermal conductivity multilayer composite magnesium-aluminum spinel brick, the preparation process is as follows:

[0065] S1, S3, and S4 are the same as steps S1, S3, and S4 in Example 1;

[0066] S2. Ingredients: Working layer: Place all the raw materials for the working layer into a mixer and stir at 90 r / min for 6 minutes, then change the speed to 180 r / min and stir for 11 minutes before use; Insulation layer: Place all the raw materials for the insulation layer into a mixer and stir at 120 r / min for 20 minutes before use.

[0067] Related tests

[0068] The composite magnesium-aluminate spinel bricks prepared in Examples 1-3 and Comparative Examples 1-5 were subjected to performance tests, and the test results are shown in Table 1. The apparent porosity of the prepared products was tested according to GB / T 2997-2000. The thermal shock resistance cycles were measured using the following method: a sample with dimensions of 20cm × 10cm × 10cm was heated to 1500℃ in a furnace and held for 15 minutes, then removed and cooled in air for 15 minutes. This cycle was repeated until cracks were observed to the naked eye; the number of cycles was counted as the thermal shock resistance cycles.

[0069] Table 1 Product Performance Test Results

[0070]

[0071] The composite magnesium-aluminate spinel bricks prepared in Examples 1-3 and Comparative Examples 1-5 were subjected to mechanical property tests. The room temperature flexural strength and room temperature compressive strength were tested according to GB / T3001-2017 and GB / T5072-2008, respectively. The room temperature flexural strength of the samples was tested by the three-point bending method.

[0072] Table 2 Product Mechanical Performance Test Results

[0073] Group room temperature pressure resistance (MPa) Flexural strength at room temperature (MPa) Example 1 92 28 Example 2 88 26 Example 3 85 23 Comparative Example 1 75 16 Comparative Example 2 78 20 Comparative Example 3 62 10 Comparative Example 4 69 14 Comparative Example 5 54 8

[0074] As can be seen from the test results in Tables 1 and 2, the test results of Examples 1-3 are better than those of Comparative Examples 1-5. A comparison between Example 1 and Comparative Examples 1, 2, and 4 shows that the introduction of hydroxyl iron oxide-modified diatomaceous earth and sodium tetraborate-modified water glass effectively improves the product's performance, and the two have a synergistic effect. Furthermore, their addition further enhances the product's performance. A comparison between Example 1 and Comparative Example 3 shows that the introduction of hollow microspheres during the preparation process increases the apparent porosity. The addition of hollow microspheres also improves the room temperature compressive strength and room temperature flexural strength. This is because during high-temperature treatment, the contact between the hollow microspheres and other raw materials is strengthened due to sintering, enhancing the bond between the hollow microspheres and other raw materials, which is beneficial for improving the product's compressive strength and flexural strength.

[0075] This invention introduces magnesium-aluminum spinel hollow microspheres into the preparation process of the thermal insulation layer. During the mixing process, the powder mainly coats the surface of the hollow microspheres, filling the pores they form, and becomes a whole during molding and high-temperature firing. During high-temperature heat treatment, the contact between the hollow microspheres and the surrounding powder particles is enhanced by sintering, providing strength to the material. Simultaneously, the expansion effect of the magnesium-aluminum spinel generated by the reaction of alumina and magnesium oxide in the raw materials produces a large number of micropores, which is beneficial for reducing heat conduction in the material when combined with the hollow microspheres. Furthermore, the closed-pore structure of the hollow microspheres also helps to reduce the thermal conductivity of the product. Additionally, diatomaceous earth is a silicate material with good stability and high strength. With its characteristics of low thermal conductivity and good insulation effect, modified diatomaceous earth was introduced into the preparation of the insulation layer. The diatomaceous earth was modified by reacting ferric chloride hexahydrate with ammonium bicarbonate to generate ferric hydroxyl oxide, providing a large number of hydroxyl groups on the diatomaceous earth surface. This allows it to form chemical bonds with the water glass added to the raw materials, resulting in a good interfacial bond. Simultaneously, to further improve the product's strength, sodium tetraborate was used to modify the water glass. Boron enters the Si-O-Si network in the form of boron-oxygen tetrahedra, forming a Si-OB network structure. The presence of chain-like and cyclic Si-OT (Si, B) structures is beneficial to enhancing the density of the material matrix and improving the compressive strength. Modified water glass was also added during the preparation of the working layer. Therefore, during the pressing process, the working layer and the insulation layer, containing the same components, have a tighter bond compared to bonds between different materials. Simultaneously, during the preparation of the working layer, water glass acts as an alkali activator, working together with the metakaolin mixed with styrene-acrylic emulsion and silane coupling agent to form a metakaolin-based polymer with a stable three-dimensional network structure, further improving the mechanical properties of the product. Furthermore, in the preparation process of magnesium-aluminum spinel bricks, a combination of constant-rate drying and decelerated drying is used to dry the brick blanks. In the constant-rate drying stage, the physical water on the surface of the brick blanks is mainly removed; water evaporation occurs on the surface of the blanks. As the water is discharged… The brick shrinks accordingly, and the drying rate is reduced during this stage to prevent cracking caused by rapid shrinkage. After entering the deceleration drying stage, the evaporation of moisture gradually moves from the surface of the brick to the interior. The brick absorbs heat from the heat carrier, which increases the temperature of the brick and supplies moisture for evaporation. After evaporation in the pores, the moisture moves from the interior of the brick to the surface and then diffuses into the heat carrier. When the temperature of the brick rises and the amount of moisture evaporated is exactly the maximum amount of water vapor transferred outward from the pores, the safe drying rate of the brick is at its maximum. Therefore, this invention uses constant-rate drying and deceleration drying to dry the brick to ensure that the brick has the maximum safe drying rate and avoids the formation of capillary cracks in the brick during the drying process.

[0076] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0077] Although embodiments of this application have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of this application, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A low thermal conductivity multilayer composite magnesium-aluminate spinel brick, characterized in that, It includes a working layer, a thermal insulation layer, and a heat insulation layer; the working layer is connected to the thermal insulation layer, and there is a gap in the thermal insulation layer, with the heat insulation layer located inside the gap; The working layer is composed of the following raw materials in parts by weight: 45-55 parts magnesium aluminum spinel, 20-28 parts aluminum-rich spinel, 18-26 parts magnesium-rich spinel, 10-18 parts metakaolin, 10-18 parts modified water glass, 0.2-0.5 parts styrene-acrylic emulsion, and 0.02-0.05 parts silane coupling agent. The insulation layer is composed of the following raw materials in parts by weight: 18-25 parts of fused magnesia fine powder, 6-10 parts of lightly calcined magnesia powder, 14-22 parts of α-Al2O3 micro powder, 12-18 parts of magnesium aluminum spinel hollow microspheres, 8-16 parts of hydroxyl iron oxide modified diatomite, and 8-12 parts of modified water glass. The heat insulation layer is a nano-aerogel board; The mass ratio of industrial alumina powder, fused magnesia fine powder, and lightly calcined magnesia powder is 5-8:1-1.5:1; the industrial alumina powder is ≤0.044mm and has an Al2O3 mass fraction greater than 98.5%. Low thermal conductivity multilayer composite magnesium-aluminum spinel bricks are prepared through the following steps: S1. Weigh each raw material according to the above-mentioned weight proportions and set aside; S2. Ingredients: Working layer: Mix metakaolin and modified water glass in a mixer, add styrene-acrylic emulsion and silane coupling agent, mix evenly, then add magnesium aluminum spinel, aluminum-rich spinel and magnesium-rich spinel and mix evenly for later use; Insulation layer: Place all raw materials of the insulation layer in a mixer and mix evenly for later use. S3. After the ingredients are prepared, the mold is divided into two parts with a length ratio of 1-3:1-2 using a partition. The slurry after the working layer and the insulation layer are mixed is added to the two compartments respectively. After the partition is removed, the brick blanks are pressed into brick blanks using a press and then placed in a dryer to dry. S4. The qualified brick blanks dried in step S3 are loaded into the kiln car and put into the high-temperature tunnel kiln. After high-temperature firing and heat preservation, they are cooled. The nano aerogel board is bonded to the notch of the cooled product to obtain the low thermal conductivity multilayer composite magnesium aluminum spinel brick. The modified water glass is prepared by placing water glass in a container and adding sodium tetraborate, then stirring to obtain a stable solution, which is the modified water glass.

2. The low thermal conductivity multilayer composite magnesium-aluminate spinel brick according to claim 1, characterized in that, The method for preparing the magnesium-aluminum spinel hollow microspheres is as follows: industrial alumina powder, fused magnesia fine powder and lightly calcined magnesium powder are mixed evenly and fed into an electric arc furnace. After the mixture in the electric arc furnace melts, it is heated and kept at 2000-2200℃ for 1-3 hours. Then, the magnesium-aluminum spinel hollow microspheres are obtained by blowing under a gas pressure of 0.8-1.0MPa.

3. The low thermal conductivity multilayer composite magnesium-aluminate spinel brick according to claim 1, characterized in that, The preparation process of the ferric chloride modified diatomite is as follows: ferric chloride hexahydrate and ammonium bicarbonate are mixed in anhydrous ethanol, and raw diatomite is added to it. The mixture is sealed, stirred evenly at room temperature, and then filtered. The filtered material is dried, ground, and sieved to obtain ferric chloride modified diatomite.

4. The low thermal conductivity multilayer composite magnesium-aluminate spinel brick according to claim 1, characterized in that, In step S2, during the preparation of the working layer, metakaolin and modified water glass are mixed and stirred in a mixer at a speed of 80-100 r / min for 4-8 min, then the speed is changed to 150-200 r / min and stirred for 3-5 min. Styrene-acrylic emulsion and silane coupling agent are added and stirred at 150-200 r / min for 5-8 min. Magnesium aluminum spinel, aluminum-rich spinel and magnesium-rich spinel are added and stirred at 150-200 r / min for 5-8 min. During the preparation of the insulation layer, each raw material of the insulation layer is placed in a mixer and stirred at 100-150 r / min for 15-20 min.

Images