High-temperature-resistant sintered porous brick and sintering process thereof

Abstract

The present application relates to the technical field of building materials, in particular to a high-temperature-resistant sintered porous brick and a sintering process thereof.The present application overcomes the problem of poor durability of the current porous brick.The synthetic raw materials of the present application include coal gangue, shale, ceramsite, clay, bentonite tailings powder, fly ash, modified retarder, composite sulfate and composite fiber;the mixed residue one is obtained by grinding and treating the coal gangue, shale, ceramsite, clay and bentonite tailings powder, the mixed residue two is obtained by ball-milling and mixing the fly ash, modified retarder, composite sulfate and composite fiber, then the mixed residue one and the mixed residue two are mixed and extrusion-molded, and after drying, the porous brick is obtained by step sintering treatment.The final porous brick has low thermal conductivity, high density, no efflorescence and high compressive strength, and is suitable for multiple scene applications.

Description

Technical Field

[0001] This invention relates to the field of building materials technology, specifically to a high-temperature resistant sintered porous brick and its sintering process. Background Technology

[0002] Ordinary bricks are small building blocks mainly made from shale and industrial waste. According to the production process, bricks are divided into sintered products and non-sintered products. According to the raw materials used, bricks are divided into clay bricks, shale bricks, coal ash bricks, fly ash bricks, slag bricks, and sand-lime bricks. According to the shape, bricks can be divided into solid bricks, microporous bricks, porous bricks, and hollow bricks.

[0003] Among them, porous bricks refer to porous bricks made from clay, shale, and fly ash as the main raw materials, which are formed and fired. The porosity is not less than 15% to 30%, and the pores are round or non-round. The pores are small in size and numerous. They are load-bearing sintered porous bricks with rectangular or round pores. Porous bricks are mainly suitable for load-bearing parts of brick-concrete structures.

[0004] Currently, mainstream sintered porous bricks use clay, shale, or fly ash as the main raw materials, forming a porous structure through high-temperature sintering. However, traditional raw materials face two major problems: resource consumption and environmental pressure, and the contradiction between pore structure and mechanical properties. Clay bricks have been restricted in many countries due to excessive soil extraction leading to farmland destruction; shale sintering has high energy consumption, high carbon emission intensity, and excessive resource consumption; in conventional processes, porosity is negatively correlated with compressive strength, and the compressive strength of fly ash porous bricks is usually below 10 MPa, making it difficult to meet the requirements of load-bearing structures.

[0005] Currently, the recycling and utilization of industrial resources is attracting increasing attention. Existing technologies can produce porous bricks from coal gangue, but the high calorific value of coal gangue reduces the production volume of porous bricks during firing and also causes efflorescence (white bloom) in the bricks. Other existing technologies involve mixing and crushing coal gangue and shale before brick making, but this method still suffers from poor high-temperature resistance and low compressive strength in the finished porous bricks, severely impacting industrial production.

[0006] It can be seen that current porous bricks still have shortcomings such as poor high-temperature resistance, poor compressive strength, and severe efflorescence, which significantly reduce their durability and have a serious impact on industrial production and development.

[0007] To address this, a high-temperature resistant sintered porous brick and its sintering process were proposed. Summary of the Invention

[0008] The purpose of this invention is to design a high-temperature resistant sintered porous brick and its sintering process. The raw materials for synthesis include: coal gangue, shale, ceramsite, clay, bentonite tailings powder, fly ash, modified retarder, composite sulfate, and composite fiber. The coal gangue, shale, ceramsite, clay, and bentonite tailings powder are ground to obtain mixed slag one. Fly ash, modified retarder, composite sulfate, and composite fiber are ball-milled to obtain mixed slag two. Mixed slag one and mixed slag two are then mixed and extruded, dried, and subjected to segmented sintering to obtain the porous brick. The resulting porous brick has low thermal conductivity, high density, no efflorescence, and high compressive strength, making it suitable for various applications.

[0009] To achieve the above objectives, the present invention provides the following technical solution:

[0010] This invention provides a sintering process for high-temperature resistant porous bricks. The sintering process for porous bricks includes the following steps, by weight:

[0011] S1 is made by mixing 50-60 parts of coal gangue, 10-15 parts of shale, 5-10 parts of ceramsite, 4-8 parts of clay and 2-6 parts of bentonite tailings powder, and then drying and grinding them to obtain mixed slag one.

[0012] S2 involves ball milling 10-15 parts of fly ash, 1-5 parts of modified retarder, 1-5 parts of composite sulfate, and 1-3 parts of composite fiber to obtain mixed slag II; the modified retarder includes chitosan, sodium hydroxide, and chloroacetic acid;

[0013] S3. Mix the first and second mixtures in a mixer for 20 minutes, add water, and mix again for 15 minutes to obtain the mixture.

[0014] S4 involves extruding the mixture in a vacuum brick extruder to obtain brick blanks;

[0015] S5 Place the brick blank in a constant temperature drying oven and dry it at 100℃ for 8 hours to obtain the dried blank;

[0016] S6 puts the dried green body into the furnace for firing, and after segmented sintering, a porous brick precursor is obtained. The porous brick precursor is cooled in a natural environment for 36 hours to obtain porous bricks.

[0017] Preferably, coal gangue is mined and processed in Zhongshan Coal Mine. The main components of the coal gangue raw material are analyzed as follows: CaO 8%, MgO 3%; plasticity index is 6.5; and plasticity index of the mixture is 7.8.

[0018] Preferably, the drying and grinding process in S1 is as follows: 50-60 parts of coal gangue, 10-15 parts of shale, 5-10 parts of ceramsite, 4-8 parts of clay, and 2-6 parts of bentonite tailings powder are conveyed to a rotary dryer via a conveyor. The preheating temperature is 100℃, and then the temperature is raised to 350℃. After drying for 2 hours, the material is cooled to obtain dried raw material. The dried raw material is then conveyed to a grinding mill for primary grinding at a speed of 18-22 rpm for 1.5 hours, followed by secondary grinding at a speed of 25-30 rpm for 1 hour. Finally, the material is sieved through a 1.5 mm diameter drum screen to obtain mixed slag.

[0019] Preferably, the preparation method of the modified retarder in S1 is as follows: 6-10 parts of chitosan and 15 parts of isopropanol are placed in a three-necked flask, stirred for 10 min, and then 20 parts of sodium hydroxide solution with a mass percentage concentration of 30% are added. The mixture is then stirred at 40°C for 3 h to obtain mixed solution A. 3 parts of chloroacetic acid are dissolved in 10 parts of isopropanol to obtain mixed solution B. Mixed solution B is slowly added dropwise to mixed solution A at a rate of 1 drop / second, while maintaining the reaction temperature at 60°C during the addition. After the addition is complete, the mixture is stirred for 4-8 h to obtain a reaction solution. After the reaction is complete, the reaction solution is cooled to room temperature, and the pH is adjusted to 8 to obtain a neutralized solution. 50 parts of deionized water are added to the neutralized solution, and then the mixture is filtered to obtain a crude product. The crude product is repeatedly washed with deionized water and then placed in a vacuum drying oven and dried at 60°C for 12 h to obtain the modified retarder.

[0020] Preferably, in S2, the composite sulfate is a mixture of calcium sulfate and magnesium sulfate, with a weight ratio of 2-4:1; the composite fiber is a mixture of polyester fiber and carbon fiber, with a weight ratio of 1-3:2.

[0021] Preferably, the ball milling process in S2 is as follows: 10-15 parts of fly ash are passed through a 200-mesh sieve and dried at 105℃ for 2 hours to obtain dry fly ash; the dry fly ash, 1-5 parts of modified retarder, 1-5 parts of composite sulfate and 1-3 parts of composite fiber are added sequentially to the feed inlet of the ball mill, and the mixture is first ball-milled at a low speed of 100rpm-150rpm for 30 minutes, and then the speed is increased to 200rpm-300rpm and ball-milled again for 2 hours to obtain the ball-milled material; the material is then passed through a 100-mesh sieve to obtain mixed slag II.

[0022] Preferably, the extrusion molding process in S4 is as follows: the mixture is placed in a sealed container and aged for 48 hours to obtain pretreated material; the mold is preheated to 45°C, the vacuum pump is started, the vacuum degree is adjusted to -0.08MPa, the screw compression ratio is adjusted to 2.5:1, and the initial extrusion rate is 0.4m / min; the pretreated material is slowly poured into the vacuum brick extruder, the screw is turned on for low-speed pre-extrusion at a speed of 10rpm-15rpm, and the speed is gradually increased to 28rpm after the pretreated material is continuously extruded; the extruded continuous blank is positioned by laser ranging and then cut into 190mm×90mm×90mm using a wire cutter, and then placed in a temperature and humidity controlled chamber for 12 hours at a temperature of 25°C and a humidity of 60% to obtain brick blanks.

[0023] Preferably, the segmented sintering process in S6 is as follows: the dried green bodies are stacked with vertical channels aligned, and 3mm silicon carbide partitions are placed between the layers; the brick furnace is heated to 300℃ at a rate of 5℃ / min and maintained for 1 hour; then the temperature is increased to 500℃-600℃ at a rate of 3℃ / min, and oxygen is injected by forced air for the first stage of firing for 3 hours to obtain oxidized bricks; the brick furnace is heated to 900℃-1000℃ at a rate of 5℃ / min for the second stage of firing for 5 hours to obtain dense bricks; the brick furnace is heated to 1200℃-1250℃ at a rate of 2℃ / min for the third stage of firing for 2 hours to obtain sintered bricks; the heating system is turned off, the high-speed circulating air cooling system is turned on with a wind speed of 8m / s, the temperature is lowered to 800℃, and then the fan is turned off, and the furnace insulation layer is used for natural cooling until the temperature reaches 200℃ to obtain porous brick precursors.

[0024] Another aspect of the present invention provides a high-temperature resistant sintered porous brick, wherein the raw materials for synthesizing the porous brick include: coal gangue, shale, ceramsite, clay, bentonite tailings powder, fly ash, modified retarder, composite sulfate and composite fiber;

[0025] Modified retarder agents include chitosan, sodium hydroxide, and chloroacetic acid;

[0026] Complex sulfates include calcium sulfate and magnesium sulfate;

[0027] Composite fibers include polyester fibers and carbon fibers.

[0028] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0029] 1. This invention uses coal gangue, shale, ceramsite, clay, and bentonite tailings powder as raw materials, controlling the weight proportions of the raw materials and subjecting them to drying and grinding to improve the compressive strength of porous bricks. Mining and processing coal gangue in Zhongshan Coal Mine, and using it as the main raw material, represents a secondary utilization of waste slag, reducing environmental pollution and conserving resources. When coal gangue and shale are mixed in a suitable proportion, the mineral phases formed during sintering can interweave, enhancing the stability of the brick structure. The combination of ceramsite and clay ensures the lightweight nature of the brick and utilizes the adhesive properties of clay to better fix the ceramsite within the brick, jointly improving compressive strength. Bentonite tailings powder synergistically improves the microstructure of the brick, enhancing its density and internal bonding. Drying and grinding the raw materials ensures particle uniformity and fineness, resulting in a more uniform internal structure of the brick, thereby improving compressive strength and durability.

[0030] 2. This invention involves ball milling fly ash, modified retarder, composite sulfate, and composite fiber. The rotational speed of the ball mill determines the impact and grinding force of the grinding media on the raw materials. For improving the high-temperature resistance of porous bricks, a suitable rotational speed allows the fly ash and modified retarder particles to be appropriately refined and dispersed, maintaining particle uniformity and thus ensuring the uniformity of the internal structure of the porous brick. Fly ash itself has a certain degree of thermal stability, enabling it to withstand high temperatures to a certain extent without significant structural damage. The modified retarder obtained by carboxymethylating chitosan undergoes a carbonization reaction at high temperatures, forming carbides with certain thermal stability and mechanical strength. Together with the fly ash, these carbides enhance the overall thermal stability of the porous brick, allowing it to maintain good shape and mechanical properties under high-temperature conditions, thereby improving the durability of the porous brick.

[0031] 3. The composite sulfate and composite fiber in this invention have a certain synergistic effect. The composite sulfate can fill the tiny pores and defects inside the porous brick, making the microstructure more compact. The composite fiber can maintain a certain shape and mechanical properties at high temperatures, playing a supporting role inside the porous brick and preventing the microstructure from collapsing or deforming at high temperatures. Moreover, the carbon fibers in it partially oxidize at high temperatures to form a carbon layer. The synergistic effect of the two allows the porous brick to maintain a relatively stable microstructure, thereby maintaining its compressive strength. After extrusion molding, by controlling the parameters in the extrusion molding process, the brick blank is subjected to uniform and large extrusion pressure, which makes the particles inside the brick blank more tightly arranged, reduces porosity, and makes the structure more compact. This helps to distribute the load more evenly when under pressure, reduces stress concentration, thereby improving the compressive strength of the porous brick, enabling it to withstand greater weight and external forces, and improving the durability of the porous brick.

[0032] 4. The segmented sintering process of this invention involves firing the dried green body in three stages. The first stage is fired at a relatively low temperature, which gently removes any residual moisture from the green body. At the same time, some additives in the green body begin to react initially at low temperatures, stabilizing the green body structure and providing a solid foundation for subsequent high-temperature sintering. This enhances the stability of the porous brick at high temperatures and improves its high-temperature resistance. After the second stage of heating, the high temperature intensifies atomic diffusion between the green body particles, causing the particles to fuse together. The fly ash glass phase is formed, reducing the porosity of the green body and gradually making it denser. The third stage is fired at the highest temperature. The high-temperature conditions promote complex physicochemical reactions inside the green body, causing the mineral components in the raw materials to undergo crystal phase transformation, generating more stable and high-temperature resistant mineral phases. This improves the mechanical properties and high-temperature resistance of the porous brick, thereby enhancing its durability. Attached Figure Description

[0033] Figure 1 This is a flow chart of the sintering process for the porous bricks of this invention. Detailed Implementation

[0034] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0035] For details, please refer to [link / reference]. Figure 1 This invention provides a high-temperature resistant sintered porous brick and its sintering process, the technical solution of which is as follows:

[0036] Example 1

[0037] Preparation of modified retarder:

[0038] Six parts chitosan and 15 parts isopropanol were placed in a three-necked flask and stirred for 10 minutes. Then, 20 parts of sodium hydroxide solution (30% by mass) were added. The mixture was stirred at 40°C for 3 hours to obtain mixed solution A. Three parts chloroacetic acid were dissolved in 10 parts isopropanol to obtain mixed solution B. Mixed solution B was slowly added dropwise to mixed solution A at a rate of 1 drop / second, while maintaining the reaction temperature at 60°C. After the addition was complete, the mixture was stirred for another 4 hours to obtain a reaction solution. After the reaction was completed, the reaction solution was cooled to room temperature and the pH was adjusted to 8 to obtain a neutralized solution. Fifty parts of deionized water were added to the neutralized solution, and the mixture was then filtered to obtain a crude product. The crude product was repeatedly washed with deionized water and then placed in a vacuum drying oven and dried at 60°C for 12 hours to obtain a modified retarder.

[0039] The composite sulfate is a mixture of calcium sulfate and magnesium sulfate, with a weight ratio of 2:1; the composite fiber is a mixture of polyester fiber and carbon fiber, with a weight ratio of 1:2.

[0040] Sintered porous bricks:

[0041] S1 conveys 50 parts coal gangue, 10 parts shale, 5 parts ceramsite, 4 parts clay, and 2 parts bentonite tailings powder to a rotary dryer via a conveyor. The preheating temperature is 100℃, and then the temperature is raised to 350℃. After drying for 2 hours, the dry raw material is cooled to obtain the dried raw material. The dried raw material is then conveyed to a grinding mill for primary grinding at 18 rpm for 1.5 hours, followed by secondary grinding at 25 rpm for 1 hour. The particle mixture after secondary grinding is sieved through a 1.5 mm diameter drum screen to obtain mixed slag one.

[0042] S2. Ten parts of fly ash were passed through a 200-mesh sieve and dried at 105℃ for 2 hours to obtain dry fly ash. The dry fly ash, 1 part of modified retarder, 1 part of composite sulfate and 1 part of composite fiber were added to the feed inlet of a ball mill in sequence. The mill was first ball-milled at a low speed of 100 rpm for 30 minutes, and then the speed was increased to 200 rpm and ball-milled again for 2 hours to obtain the ball-milled material. The material was then passed through a 100-mesh sieve to obtain mixed slag II.

[0043] S3. Mix the first and second mixtures in a mixer for 20 minutes, add water, and mix again for 15 minutes to obtain the mixture.

[0044] S4. The mixture is aged in a sealed container for 48 hours to obtain pretreated material. The mold is preheated to 45°C, the vacuum pump is started, the vacuum degree is adjusted to -0.08MPa, the screw compression ratio is adjusted to 2.5:1, and the initial extrusion rate is 0.4m / min. The pretreated material is slowly poured into the vacuum brick extruder, and the screw is turned on for low-speed pre-extrusion at 10rpm. After the pretreated material is continuously extruded, the speed is gradually increased to 28rpm. The extruded continuous green body is positioned by laser ranging and then cut into 190mm×90mm×90mm pieces using a wire cutter. Then it is left to stand in a temperature and humidity controlled chamber for 12 hours at a temperature of 25°C and a humidity of 60 parts per 1000°C to obtain brick blanks.

[0045] S5 Place the brick blank in a constant temperature drying oven and dry it at 100℃ for 8 hours to obtain the dried blank;

[0046] S6. The dried brick blanks are aligned and stacked according to the vertical channels, with 3mm silicon carbide partitions between the layers. The brick kiln is heated to 300℃ at a rate of 5℃ / min and maintained for 1 hour. Then, the temperature is increased to 500℃ at a rate of 3℃ / min, and oxygen is injected by forced air for the first stage of firing for 3 hours to obtain oxidized bricks. The brick kiln is heated to 900℃ at a rate of 5℃ / min for the second stage of firing for 5 hours to obtain dense bricks. The brick kiln is heated to 1200℃ at a rate of 2℃ / min for the third stage of firing for 2 hours to obtain sintered bricks. The heating system is turned off, and the high-speed circulating air cooling system is turned on at a wind speed of 8m / s. The temperature is lowered to 800℃ and then the fan is turned off. The temperature is naturally lowered by the furnace insulation layer until the temperature reaches 200℃ to obtain porous brick precursors. The porous brick precursors are cooled in the natural environment for 36 hours to obtain porous bricks.

[0047] Examples 2-6 refer to the parameter conditions in Example 1, with specific differences shown in Table 1.

[0048] Table 1 Parameters and Conditions for Examples 1-6

[0049]

[0050] Comparative Example 1 follows the same parameters and conditions as in Example 1, except that shale is not added.

[0051] Comparative Example 2 follows the same parameters and conditions as in Example 1, except that no ceramsite is added.

[0052] Comparative Example 3 follows the same parameters and conditions as in Example 1, except that no clay is added.

[0053] Comparative Example 4 follows the same parameters and conditions as in Example 1, except that bentonite tailings powder is not added.

[0054] Comparative Example 5 follows the same parameters and conditions as in Example 1, except that only the first grinding process is performed.

[0055] Comparative Example 6 follows the same parameters and conditions as in Example 1, except that only a second grinding process is performed.

[0056] Comparative Example 7 follows the same parameters and conditions as in Example 1, except that it does not undergo drying and grinding.

[0057] Experiment Example 1: Compressive Strength and Frosting Degree Test

[0058] The compressive strength and efflorescence degree of Examples 1-6 and Comparative Examples 1-7 were tested according to the standard GB / T 2542-2012, and the results are shown in Table 2.

[0059] Table 2 Compressive strength and efflorescence tests of Examples 1-6 and Comparative Examples 1-7

[0060]

[0061]

[0062] Table 1 shows that in Comparative Examples 1-4, the absence of any one raw material leads to a decrease in the compressive strength of the porous bricks. The mining and processing of coal gangue in Zhongshan Coal Mine, using it as the main raw material, represents a secondary utilization of waste slag, reducing environmental pollution and conserving resources. Coal gangue is rich in oxides such as silicon and aluminum, which can participate in the formation of high-strength mineral phases such as mullite during high-temperature sintering. Its hardness and stability provide an important supporting framework for the porous bricks. Shale has good plasticity and binding properties, which can tightly bind other raw material particles together to form a stable initial structure. During sintering, shale further reacts with other components, promoting the densification of the brick structure. In Comparative Example 1, the removal of shale resulted in a decrease in compressive strength; in Comparative Example 2, the removal of ceramsite resulted in a decrease in compressive strength. The decrease in compressive strength is due to the fact that ceramsite is lightweight and porous, playing a unique reinforcing role in porous bricks. Its porous structure can form a buffer structure inside the brick, dispersing pressure and preventing stress concentration when the brick is under pressure, thereby enhancing compressive strength. Clay has good molding properties and can fill between other raw material particles, making the body structure more uniform and further enhancing the strength of the brick. Removing it in Comparative Example 3 leads to a decrease in compressive strength. Bentonite tailings powder has certain expansibility and binding properties. In the body, it can fill tiny pores, improving the density of the brick. Its special chemical properties help it to better combine with other raw materials, enhancing the chemical bonding force inside the brick, thereby improving compressive strength. The lack of bentonite tailings powder in Comparative Example 4 resulted in a decrease in compressive strength. When coal gangue and shale are mixed in a suitable ratio, the mineral phases formed during sintering can interweave, enhancing the stability of the brick structure. The combination of ceramsite and clay ensures the lightweight properties of the brick while utilizing the adhesive properties of clay to better fix the ceramsite within the brick, jointly improving compressive strength. Bentonite tailings powder, in synergy with other raw materials, effectively improves the microstructure of the brick, enhancing its density and internal bonding. In Comparative Examples 5-7, the compressive strength of the porous bricks decreased when only the first grinding treatment was performed, and it also decreased when only the second grinding treatment was performed. When no drying and grinding treatment was performed, the compressive strength was significantly insufficient, and efflorescence appeared, far inferior to the examples. The first grinding process aims to break down larger particles, significantly reducing their size and providing a suitable particle size base for subsequent fine grinding, while also achieving initial uniform distribution. The second grinding process makes the surface of the material particles smoother and more regular, reducing surface defects and roughness. During the second grinding process, the interaction between material particles is more thorough, enabling finer mixing and achieving a highly uniform distribution of materials with different components at the microscale. This provides a foundation for subsequent sintering, thereby improving the compressive strength and durability of the porous bricks.

[0063] Examples 7-12 refer to the parameter conditions in Example 4, with specific differences shown in Table 3.

[0064] Table 3 Parameters and conditions for Examples 4 and 7-12

[0065]

[0066] Comparative Example 8 follows the same parameters and conditions as in Example 4, except that fly ash is not added.

[0067] Comparative Example 9 follows the same parameters and conditions as in Example 4, except that only chitosan is added as a retarder.

[0068] Comparative Example 10 follows the same parameters and conditions as in Example 4, except that no modified retarder is added.

[0069] Comparative Example 11 follows the same parameters and conditions as in Example 4, except that only low-speed ball milling is performed.

[0070] Comparative Example 12 follows the same parameters and conditions as in Example 4, except that only two ball milling processes are performed.

[0071] Comparative Example 13 follows the same parameters and conditions as in Example 4, except that ball milling is not performed.

[0072] Experiment Example 2: High Temperature Resistance and Compressive Strength Test

[0073] The high-temperature resistance of Examples 4, 7-12 and Comparative Examples 8-13 was tested according to GB / T 32981-2016; the compressive strength of Examples 4, 7-12 and Comparative Examples 8-13 was tested according to GB / T 2542-2012, and the results are shown in Table 4.

[0074] Table 4. High-temperature resistance and compressive strength tests of Examples 4, 7-12 and Comparative Examples 8-13

[0075]

[0076]

[0077] Table 4 shows that in Comparative Example 8, the high-temperature resistance and compressive strength decreased without the addition of fly ash. This is because fly ash is a fine-particle material rich in silicon and aluminum oxides. Its main components can undergo a series of changes at high temperatures. During the firing of porous bricks, when the temperature reaches a certain level, some components in the fly ash will form a glassy phase. This glassy phase has good high-temperature resistance and can fill the pores and particles of the brick, making the brick structure more compact. Some active components can react chemically with alkaline substances in other raw materials to generate new mineral phases with high-temperature resistance, such as mullite. These newly generated mineral phases are distributed inside the brick, strengthening the skeletal structure of the brick and improving the stability and strength retention of the brick at high temperatures. In Comparative Examples 9-10, the high-temperature resistance and compressive strength of porous bricks decreased when chitosan was not modified or no modified retarder was added. This indicates that the modified retarder plays an important role in porous bricks. During the production process of porous bricks, the modified retarder can maintain the plasticity of the green body for a longer period of time, which is conducive to the uniform mixing and molding of raw materials. Before high-temperature firing, a more uniform green body structure can reduce internal defects and stress concentration points. When porous bricks are in a high-temperature environment, this optimized structure can better withstand thermal stress, reduce cracking and damage caused by structural inhomogeneity, and thus improve high-temperature resistance. The modified retarder obtained by carboxymethylating chitosan undergoes a carbonization reaction at high temperatures. The resulting carbides have certain thermal stability and mechanical strength. Together with fly ash, they enhance the overall thermal stability of porous bricks, enabling them to maintain good shape and mechanical properties in high-temperature environments, thereby improving the durability of porous bricks. In Comparative Examples 11-13, when only low-speed ball milling, only secondary ball milling, or no ball milling mixing was performed, the high-temperature resistance and compressive strength of the porous bricks were lower than those in the examples. Low-speed ball milling was used to initially mix the raw materials and crush larger particles, and to prevent large particles from damaging the equipment in high-speed ball milling. Secondary ball milling enabled the raw material particles to be mixed more finely, achieving a highly uniform distribution, which provided a basis for subsequent sintering treatment, improved the high-temperature resistance and compressive strength of the porous bricks, and thus improved their durability.

[0078] Examples 13-18 refer to the parameter conditions in Example 10, with specific differences shown in Table 5.

[0079] Comparative Example 14 follows the same parameters and conditions as in Example 10, except that only calcium sulfate is added as a sulfate.

[0080] Comparative Example 15 follows the same parameters and conditions as in Example 10, except that only magnesium sulfate is added as a sulfate.

[0081] Comparative Example 16 follows the same parameters and conditions as in Example 10, except that no compound sulfate is added.

[0082] Comparative Example 17 follows the same parameters and conditions as in Example 10, except that only polyester fiber is added as the fiber material.

[0083] Comparative Example 18 follows the same parameters and conditions as in Example 10, except that only carbon fiber is added as the fiber material.

[0084] Comparative Example 19 follows the same parameters and conditions as in Example 10, except that no composite fibers are added.

[0085] Comparative Example 20 follows the same parameters and conditions as in Example 10, except that it is extruded at a constant speed of 13 rpm during the extrusion molding process.

[0086] Comparative Example 21 refers to the parameters and conditions in Example 10, except that extrusion molding is not used, but mold molding is used. Specifically, the mixture is poured into a porous brick mold, and the subsequent processing steps are the same.

[0087] Experiment Example 3: Density and Compressive Strength Test

[0088] The density and compressive strength of Examples 10, 13-18 and Comparative Examples 14-21 were tested according to GB / T 2542-2012, and the results are shown in Table 5.

[0089] Table 5. Parameters, density, and compressive strength tests for Examples 10, 13-18, and Comparative Examples 14-21

[0090]

[0091]

[0092] Table 5 shows that in Comparative Examples 14-16, the density and compressive strength of the porous bricks were lower than those in the examples when using a single sulfate or without using composite sulfate. This is because during the preparation of the porous bricks, the calcium sulfate in the composite sulfate can fill the pores of the brick body. These fine sulfate particles can enter the tiny gaps that originally existed between the raw material particles, making the brick structure more compact and thus effectively increasing the overall density of the porous brick. Magnesium sulfate can form adhesive substances with certain components in the raw materials, which helps the particles to bond and pack tightly. The composite sulfate can generate some transition phases at the interface through chemical reactions. These transition phases can enable the entire brick to better transfer stress when subjected to external forces, thereby improving the compressive strength of the porous brick. In Comparative Examples 17-19, the density and compressive strength of the porous bricks were lower when using a single fiber material or without using composite fibers. This is because the network structure formed by the composite fibers inside the porous brick can effectively diffuse and migrate the impact received by the porous brick, thereby improving the compressive strength. There is a certain synergistic effect between composite sulfate and composite fiber. Composite sulfate undergoes some chemical reactions at high temperatures, and the resulting substances can fill the tiny pores and defects inside the porous brick, making the microstructure more compact. Composite fiber can maintain a certain shape and mechanical properties at high temperatures, and plays a supporting role inside the porous brick, preventing the microstructure from collapsing or deforming at high temperatures. In addition, the carbon fibers in it partially oxidize at high temperatures to form a carbon layer. The synergistic effect of the two enables the porous brick to maintain a relatively stable microstructure, thereby maintaining its compressive strength. In Comparative Examples 20-21, when the extrusion molding process is carried out at a uniform speed of 13 rpm, the mixture does not undergo speed variation and the pressure is insufficient, making it difficult to densify the interior of the porous brick. This results in a significant decrease in compressive strength. When extrusion molding is not used and only die forming is employed, the porous brick contains more air, leading to more voids during subsequent sintering, resulting in an uneven surface and reduced compressive strength. Increasing the speed during extrusion molding allows the brick blank to be subjected to uniform and greater extrusion pressure. This causes the particles inside the brick blank to be more tightly packed, reducing porosity and creating a denser structure. This helps to distribute the load more evenly under pressure, reducing stress concentration and thus improving the compressive strength of the porous brick. This allows it to withstand greater weight and external forces, improving its durability.

[0093] Examples 19-24 refer to the parameter conditions in Example 16, with specific differences shown in Table 6.

[0094] Comparative Example 22 follows the same parameters and conditions as in Example 16, except that only the first stage of firing is performed.

[0095] Comparative Example 23 follows the same parameters and conditions as in Example 16, except that only the second stage of firing is performed.

[0096] Comparative Example 24 follows the same parameters and conditions as in Example 16, except that only the third stage of firing is performed.

[0097] Comparative Example 25 follows the same parameters and conditions as in Example 16, except that the firing process is carried out at 950°C.

[0098] Experiment Example 4: High Temperature Resistance and Compressive Strength Test

[0099] The high-temperature resistance and compressive strength of Examples 16, 19-24 and Comparative Examples 22-25 were tested according to the test method of Experimental Example 2. The results are shown in Table 6.

[0100] Table 6. Parameters, high-temperature resistance, and compressive strength tests for Examples 16, 19-24, and Comparative Examples 22-25.

[0101]

[0102] Table 6 reveals that in Comparative Example 22, using only the first-stage firing temperature resulted in underfiring of the porous bricks, leading to incomplete chemical reactions within the brick and a decrease in compressive strength. In Comparative Example 23, using only the second-stage firing temperature caused some additives to decompose before they could function, further reducing the high-temperature resistance and compressive strength of the porous bricks. In Comparative Example 24, using only the third-stage firing temperature may damage the pore structure within the bricks. The originally designed uniform porous structure may partially or completely collapse or become blocked due to the high temperature, altering the porosity and pore size distribution of the porous bricks and severely affecting their high-temperature resistance and compressive strength. In Comparative Example 25, the porous bricks were continuously calcined at only one temperature, and their high-temperature resistance and compressive strength were still poor. This is because during the segmented sintering process, the first stage was fired at a relatively low temperature, which gently removed any residual moisture in the green body. At the same time, some additives in the green body began to react initially at low temperatures, stabilizing the green body structure and providing a solid foundation for subsequent high-temperature sintering, thereby enhancing the stability of the porous bricks at high temperatures and improving their high-temperature resistance. After the second stage of heating, the high temperature intensified the atomic diffusion between the green body particles, causing the particles to fuse together. Among them, the fly ash glass phase was formed, reducing the porosity of the green body and gradually making it denser. In the third stage, the temperature was raised to the highest temperature for firing. The high-temperature conditions prompted complex physicochemical reactions inside the green body, and the mineral components in the raw materials underwent a crystal phase transformation, generating more stable and high-temperature resistant mineral phases, which improved the mechanical properties and high-temperature resistance of the porous bricks, thereby improving their durability.

[0103] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A sintering process for high-temperature resistant porous bricks, characterized in that: The sintering process of the porous bricks, by weight, includes the following steps: S1 is made by mixing 50-60 parts of coal gangue, 10-15 parts of shale, 5-10 parts of ceramsite, 4-8 parts of clay and 2-6 parts of bentonite tailings powder, and then drying and grinding them to obtain mixed slag one. S2 involves ball milling 10-15 parts of fly ash, 1-5 parts of modified retarder, 1-5 parts of composite sulfate, and 1-3 parts of composite fiber to obtain mixed slag II; the modified retarder includes chitosan, sodium hydroxide, and chloroacetic acid; S3. Place the first mixture residue and the second mixture residue into a mixer and mix for 20 minutes. Add water and mix again for 15 minutes to obtain the mixture. S4 The mixture is extruded and molded in a vacuum brick extruder to obtain brick blanks; S5 Place the brick blank in a constant temperature drying oven and dry it at 100℃ for 8 hours to obtain a dried brick blank; S6 The dried green body is fired in a furnace and sintered in stages to obtain a porous brick precursor. The porous brick precursor is cooled in a natural environment for 36 hours to obtain the porous brick. The preparation method of the modified retarder described in S2 is as follows: 6-10 parts of the chitosan and 15 parts of isopropanol are placed in a three-necked flask, stirred for 10 minutes, and then 20 parts of sodium hydroxide solution with a mass percentage concentration of 30% are added. The mixture is then stirred at 40°C for 3 hours to obtain mixed solution A. 3 parts of chloroacetic acid are dissolved in 10 parts of isopropanol to obtain mixed solution B. Mixed solution B is slowly added dropwise to mixed solution A at a rate of 1 drop / second, while maintaining the reaction temperature at 60°C during the addition. After the addition is complete, the mixture is stirred for 4-8 hours to obtain a reaction solution. After the reaction is complete, the reaction solution is cooled to room temperature, and the pH is adjusted to 8 to obtain a neutralized solution. 50 parts of deionized water are added to the neutralized solution, and then the mixture is filtered to obtain a crude product. The crude product is repeatedly washed with deionized water and then placed in a vacuum drying oven and dried at 60°C for 12 hours to obtain the modified retarder. The segmented sintering process described in S6 is as follows: The dried green bodies are stacked with vertical channels aligned, and 3mm silicon carbide partitions are placed between the layers; the brick furnace is heated to 300℃ at a rate of 5℃ / min and maintained for 1 hour; then the temperature is increased to 500℃-600℃ at a rate of 3℃ / min, and oxygen is injected by forced air for the first stage of firing for 3 hours to obtain oxidized bricks; the brick furnace is heated to 900℃-1000℃ at a rate of 5℃ / min for the second stage of firing for 5 hours to obtain dense bricks; the brick furnace is heated to 1200℃-1250℃ at a rate of 2℃ / min for the third stage of firing for 2 hours to obtain sintered bricks; the heating system is turned off, the high-speed circulating air cooling system is turned on with a wind speed of 8m / s, and the temperature is lowered to 800℃ before the fan is turned off, and the furnace insulation layer is used for natural cooling until the temperature reaches 200℃ to obtain the porous brick precursor.

2. The sintering process for a high-temperature resistant porous brick according to claim 1, characterized in that: The drying and grinding process described in S1 is as follows: 50-60 parts of the coal gangue, 10-15 parts of the shale, 5-10 parts of the ceramsite, 4-8 parts of the clay, and 2-6 parts of the bentonite tailings powder are conveyed to a rotary dryer via a conveyor. The preheating temperature is 100℃, and then the temperature is raised to 350℃. After drying for 2 hours, the material is cooled to obtain the dried raw material. The dried raw material is then conveyed to a grinding mill for primary grinding at a speed of 18-22 rpm for 1.5 hours, followed by secondary grinding at a speed of 25-30 rpm for 1 hour. Finally, the material is sieved through a 1.5 mm diameter drum screen to obtain the first mixed slag.

3. The sintering process for a high-temperature resistant porous brick according to claim 1, characterized in that: The composite sulfate in S2 is a mixture of calcium sulfate and magnesium sulfate, wherein the weight ratio of calcium sulfate to magnesium sulfate is 2-4:1; the composite fiber is a mixture of polyester fiber and carbon fiber, wherein the weight ratio of polyester fiber to carbon fiber is 1-3:

2.

4. The sintering process for a high-temperature resistant porous brick according to claim 1, characterized in that: The ball milling process described in S2 is as follows: 10-15 parts of the fly ash are passed through a 200-mesh sieve and dried at 105°C for 2 hours to obtain dry fly ash; the dry fly ash, 1-5 parts of the modified retarder, 1-5 parts of the composite sulfate, and 1-3 parts of the composite fiber are sequentially added to the feed inlet of the ball mill, and ball milled at a low speed of 100-150 rpm for 30 minutes, then the speed is increased to 200-300 rpm and ball milled again for 2 hours to obtain the ball-milled material; the material is passed through a 100-mesh sieve to obtain the mixed slag II.

5. The sintering process for a high-temperature resistant porous brick according to claim 1, characterized in that: The extrusion molding process described in S4 is as follows: the mixture is placed in a sealed container and aged for 48 hours to obtain pretreated material; the mold is preheated to 45°C, the vacuum pump is started, the vacuum degree is adjusted to -0.08MPa, the screw compression ratio is adjusted to 2.5:1, and the initial extrusion rate is 0.4m / min; the pretreated material is slowly poured into the vacuum brick extruder, the screw is turned on for low-speed pre-extrusion at a speed of 10rpm-15rpm, and the speed is gradually increased to 28rpm after the pretreated material is continuously extruded; the extruded continuous blank is positioned by laser ranging and then cut into 190mm×90mm×90mm using a wire cutter, and then placed in a temperature and humidity controlled chamber for 12 hours at a temperature of 25°C and a humidity of 60% to obtain the brick blank.

6. A high-temperature resistant sintered porous brick, characterized in that: The porous brick is obtained by sintering using the sintering process described in any one of claims 1-5; The raw materials for synthesizing the porous bricks include: coal gangue, shale, ceramsite, clay, bentonite tailings powder, fly ash, modified retarder, composite sulfate and composite fiber. The modified retarder includes chitosan, sodium hydroxide, and chloroacetic acid; The complex sulfate includes calcium sulfate and magnesium sulfate; The composite fiber includes polyester fiber and carbon fiber.

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