High-temperature-resistant sintering perforated brick and sintering process thereof

Abstract

The invention relates to the technical field of building materials, in particular to a high-temperature-resistant sintered perforated brick and a sintering process thereof. The problem that the existing porous brick is poor in durability is solved. The synthetic raw materials comprise coal gangue, shale, ceramsite, clay, bentonite tailing powder, fly ash, a modified retarder, composite sulfate and composite fibers. The preparation method comprises the following steps: grinding coal gangue, shale, ceramsite, clay and bentonite tailing powder to obtain mixed material slag I, carrying out ball-milling mixing on fly ash, a modified retarder, composite sulfate and composite fibers to obtain mixed material slag II, then mixing the mixed material slag I and the mixed material slag II, and carrying out extrusion molding treatment, and after drying, carrying out segmented sintering treatment to obtain the porous brick. The finally obtained porous brick is low in heat conductivity coefficient, high in density, free of scumming, high in compressive strength and suitable for being applied to multiple scenes.

Description

Technical Field

[0001] The invention relates to the technical field of building materials, in particular to a high temperature resistant sintered porous brick and a sintering process thereof. Background Art

[0002] Ordinary bricks are small building blocks made of shale and industrial waste as the main raw materials. According to the production process, bricks are divided into two categories: sintered products and non-sintered products. According to the different raw materials used, bricks are divided into clay bricks, shale bricks, coal-fired stone bricks, fly ash bricks, slag bricks, lime sand bricks, etc.; according to the appearance, bricks can be divided into solid bricks, microporous bricks, porous bricks and hollow bricks.

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

[0004] The current mainstream sintered porous bricks use clay, shale or fly ash as the main raw materials, and form 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, which has led to the destruction of arable land; shale sintering has high energy consumption, high carbon emission intensity, and excessive resource consumption; in conventional processes, the porosity is negatively correlated with the compressive strength, and the compressive strength of fly ash porous bricks is usually less than 10MPa, which is difficult to meet the requirements of load-bearing structures.

[0005] Nowadays, the recycling of industrial resources has gradually attracted people's attention. In the prior art, porous bricks can be fired with coal gangue as raw material, but the calorific value of coal gangue raw material is high, which will not only reduce the production of porous bricks during the firing process, but also cause the porous bricks to have the problem of frosting. There is also a process in the prior art of mixing and crushing coal gangue and shale and then making bricks, but there is still the problem of poor high temperature resistance, and the fired porous bricks have low compressive strength, which seriously affects industrial production.

[0006] From this, we can see that today's porous bricks still have shortcomings such as poor high temperature resistance, poor compressive strength and severe frost, which leads to a significant reduction in their durability and has a serious impact on industrial production and development.

[0007] Therefore, a high temperature resistant sintered porous brick and its sintering process are proposed. Summary of the invention

[0008] The purpose of the present invention is to design a high temperature resistant sintered porous brick and its sintering process. The synthetic raw materials of the present invention 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, and then the mixed slag one and the mixed slag two are mixed and extruded, and then dried and sintered in stages to obtain porous bricks. The porous bricks finally obtained have low thermal conductivity, high density, no frost, high compressive strength, and are suitable for multi-scenario applications.

[0009] To achieve the above object, the present invention provides the following technical solutions:

[0010] On one hand, the present invention provides a sintering process for high temperature resistant sintered porous bricks. The sintering process for the porous bricks comprises the following steps by weight:

[0011] S1: 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 mixed, and then dried and ground to obtain a mixed slag 1;

[0012] S2: 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 are ball-milled to obtain mixed material slag 2; the modified retarder includes chitosan, sodium hydroxide and chloroacetic acid;

[0013] S3: Mixed slag 1 and mixed slag 2 are placed in a mixer and mixed for 20 minutes, water is added, and the mixture is stirred for another 15 minutes to obtain a mixed material;

[0014] S4: extruding the mixed material in a vacuum brick extruder to obtain a brick blank;

[0015] S5: placing the green brick in a constant temperature drying oven and drying it at 100°C for 8 hours to obtain a dried green brick;

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

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

[0018] Preferably, the drying and grinding process in S1 is: 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 by a conveyor, the preheating temperature is 100°C, and then the temperature is raised to 350°C, and after drying for 2 hours, the dried raw material is cooled to obtain a dry raw material; the dry raw material is conveyed to a grinder for a primary grinding at a speed of 18rpm-22rpm for 1.5h, followed by a secondary grinding at a speed of 25rpm-30rpm for 1h, and then sieved through a drum screen with an aperture of 1.5mm to obtain a 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 put into a three-necked flask, and after stirring for 10 minutes, 20 parts of sodium hydroxide solution are added, the mass percentage concentration of the sodium hydroxide solution is 30%, and then the mixture is stirred and reacted at 40°C for 3 hours to obtain a mixed solution A; 3 parts of chloroacetic acid are dissolved in 10 parts of isopropanol to obtain a mixed solution B; the mixed solution B is slowly added dropwise to the mixed solution A at a dropping speed of 1 drop / second, and the reaction temperature is maintained at 60°C during the dropping process. After the dropping is completed, the reaction is continued to be stirred for 4h-8h to obtain a reaction solution; after the reaction is completed, the reaction solution is cooled to room temperature, and the pH value is adjusted to 8 to obtain a neutralization solution; 50 parts of deionized water are added to the neutralization solution, and then suction 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 12h to obtain a modified retarder.

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

[0021] Preferably, the ball milling mixing process in S2 is: pass 10-15 parts of fly ash through a 200-mesh sieve and dry at 105°C for 2 hours to obtain dry fly ash; add the dry fly ash, 1-5 parts of modified retarder, 1-5 parts of composite sulfate and 1-3 parts of composite fiber to the feed port of the ball mill in sequence, first ball mill at a low speed of 100rpm-150rpm for 30min, then increase the speed to 200rpm-300rpm and ball mill again for 2h to obtain the ball-milled material; pass the material through a 100-mesh sieve to obtain the mixed slag II.

[0022] Preferably, the extrusion molding process in S4 is as follows: placing the mixed material in a closed container for aging for 48 hours to obtain a pretreated material; preheating the mold to 45°C, starting the vacuum pump, adjusting the vacuum degree to -0.08MPa, adjusting the compression ratio of the screw to 2.5:1, and the initial extrusion rate to 0.4m / min; slowly pouring the pretreated material into the vacuum brick extruder, starting the screw machine for low-speed pre-extrusion, the speed is 10rpm-15rpm, and gradually increasing the speed 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 by a wire cutter, and then allowed to stand in a temperature and humidity control room for 12 hours, wherein the temperature is 25°C and the humidity is 60 parts, to obtain a brick blank.

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

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

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

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

[0027] The composite fibers include polyester fibers and carbon fibers.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] 1. The present invention uses coal gangue, shale, ceramsite, clay and bentonite tailings powder as raw materials, controls the weight of the raw materials, and dries and grinds the raw materials to improve the compressive strength of porous bricks. Mining and selecting coal gangue in Zhongshan Coal Mine and using coal gangue as the main raw material is a secondary utilization of waste slag, which reduces environmental pollution and saves resources. When coal gangue and shale are mixed in a suitable proportion, the mineral phases formed by the two during the sintering process can be intertwined to enhance the stability of the brick structure; the combination of ceramsite and clay can not only ensure the lightweight characteristics of the brick body, but also use the adhesion of clay to better fix the ceramsite in the brick body, and jointly improve the compressive strength; bentonite tailings powder and other raw materials synergistically can effectively improve the microstructure of the brick body, improve its density and internal bonding force. Drying and grinding the raw materials can ensure the uniformity and fineness of the particles, so that the internal structure of the brick body is more uniform, thereby improving the compressive strength and improving its durability.

[0030] 2. The present invention mixes fly ash, modified retarder, composite sulfate and composite fiber by ball milling. The rotation speed of the ball mill determines the impact and grinding force of the grinding body on the raw materials. For improving the high temperature resistance of porous bricks, the appropriate rotation speed can make the particles of fly ash and modified retarder be properly refined and dispersed, so that the particles maintain uniformity, thereby ensuring the uniformity of the internal structure of the porous bricks. Fly ash itself has a certain thermal stability and can withstand high temperature to a certain extent without obvious structural damage. The modified retarder obtained by carboxymethylating chitosan will undergo carbonization reaction at high temperature. The formed carbide has a certain thermal stability and mechanical strength, which works together with fly ash to enhance the overall thermal stability of the porous brick, so that it can maintain a good shape and mechanical properties under high temperature environment, thereby improving the durability of the porous brick.

[0031] 3. The composite sulfate and composite fiber in the present 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 temperature, play a supporting role inside the porous brick, and prevent the microstructure from collapsing or deforming at high temperature. The carbon fiber therein is partially oxidized at high temperature to form a carbon layer. The two work synergistically, so that the porous brick can maintain a relatively stable microstructure, thereby maintaining its compressive strength. After the extrusion molding process, the parameters in the extrusion molding process are controlled, and the brick blank is subjected to a uniform and large extrusion force, so that the particles inside the brick blank are arranged more closely, the porosity is reduced, and the structure is more compact, which helps to disperse the load more evenly when under pressure, reduce stress concentration, thereby improving the compressive strength of the porous brick, enabling it to withstand greater weight and external force, and improving the durability of the porous brick.

[0032] 4. The segmented sintering process of the present invention is divided into three stages for firing the dried green body. In the first stage, the green body is fired at a relatively low temperature, which can gently remove the moisture that may remain in the green body. At the same time, some additives in the green body begin to react preliminarily at low temperature to stabilize the green body structure and provide a solid foundation for subsequent high-temperature sintering, thereby enhancing the stability of the porous brick at high temperature and improving the high temperature resistance. After the second stage of heating treatment, the high temperature intensifies the atomic diffusion between the green body particles, and the particles fuse with each other, wherein the fly ash glass phase is formed, the porosity of the green body is reduced, and the green body is gradually densified. In the third stage, the green body is fired at the highest temperature. The high temperature conditions promote complex physical and chemical reactions inside the green body, and the mineral components in the raw materials undergo crystal phase transformation to generate a more stable and high temperature resistant mineral phase, thereby improving the mechanical properties and high temperature resistance of the porous brick, thereby improving durability. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 The figure is a flow chart of the sintering process of the porous bricks of the present invention. DETAILED DESCRIPTION

[0034] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0035] Specific reference Figure 1 The present invention provides a high temperature resistant sintered porous brick and its sintering process, and the technical scheme is as follows:

[0036] Example 1

[0037] Preparation of modified retarder:

[0038] 6 parts of chitosan and 15 parts of isopropanol were put into a three-necked flask, and after stirring for 10 minutes, 20 parts of sodium hydroxide solution were added, and the mass percentage concentration of the sodium hydroxide solution was 30%, and then the mixture was stirred and reacted at 40°C for 3 hours to obtain a mixed solution A; 3 parts of chloroacetic acid were dissolved in 10 parts of isopropanol to obtain a mixed solution B; the mixed solution B was slowly added dropwise to the mixed solution A at a dropping speed of 1 drop / second, and the reaction temperature was maintained at 60°C during the dropping process. After the dropping was completed, the reaction was continued to stir for 4 hours to obtain a reaction solution; after the reaction was completed, the reaction solution was cooled to room temperature, and the pH value was adjusted to 8 to obtain a neutralization solution; 50 parts of deionized water were added to the neutralization solution, and then suction 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, and the weight ratio of calcium sulfate to magnesium sulfate is 2:1; the composite fiber is a mixture of polyester fiber and carbon fiber, and the weight ratio of polyester fiber to carbon fiber is 1:2.

[0040] Sintered porous brick:

[0041] S1: 50 parts of coal gangue, 10 parts of shale, 5 parts of ceramsite, 4 parts of clay and 2 parts of bentonite tailings powder are conveyed to a rotary dryer through a conveyor, the preheating temperature is 100°C, and then the temperature is raised to 350°C, and dried for 2 hours and then cooled to obtain a dry raw material; the dry raw material is conveyed to a grinder for primary grinding at a speed of 18 rpm for 1.5 hours, and then secondary grinding is performed at a speed of 25 rpm for 1 hour. The particle mixture after the secondary grinding is sieved through a drum screen with an aperture of 1.5 mm to obtain a mixed slag 1;

[0042] S2: 10 parts of fly ash are passed through a 200-mesh sieve and dried at 105°C for 2 hours to obtain dry fly ash; dry fly ash, 1 part of modified retarder, 1 part of composite sulfate and 1 part of composite fiber are added to the feed port of the ball mill in sequence, firstly ball-milled at a low speed of 100 rpm for 30 minutes, then the speed is increased to 200 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 mixed slag II;

[0043] S3: Mixed slag 1 and mixed slag 2 are placed in a mixer and mixed for 20 minutes, water is added, and the mixture is stirred for another 15 minutes to obtain a mixed material;

[0044] S4: placing the mixed material in a sealed container for aging for 48 hours to obtain a pre-treated material; preheating the mold to 45°C, starting the vacuum pump, adjusting the vacuum degree to -0.08MPa, adjusting the compression ratio of the screw to 2.5:1, and the initial extrusion rate to 0.4m / min; slowly pouring the pre-treated material into the vacuum brick extruder, starting the screw machine for low-speed pre-extrusion, the speed is 10rpm, and gradually increasing the speed to 28rpm after the pre-treated material is continuously extruded; the extruded continuous green body is positioned by laser ranging, and then cut into 190mm×90mm×90mm by a wire cutter, and then standing in a temperature and humidity control room for 12 hours, wherein the temperature is 25°C and the humidity is 60 parts, to obtain a brick;

[0045] S5: placing the green brick in a constant temperature drying oven and drying it at 100°C for 8 hours to obtain a dried green brick;

[0046] S6 stacks the dried green bodies in a vertical channel and places 3mm silicon carbide partitions between the layers; heats the brick-firing furnace to 300℃ at a rate of 5℃ / min and maintains for 1h; then heats the furnace to 500℃ at a rate of 3℃ / min, and injects oxygen by blasting for the first stage firing for 3h to obtain an oxidized brick body; heats the furnace to 900℃ at a rate of 5℃ / min for the second stage firing for 5h to obtain a dense brick body; heats the furnace to 1200℃ at a rate of 2℃ / min for the third stage firing for 2h to obtain a sintered brick body; turns off the heating system, turns on the high-speed circulating air cooling system with a wind speed of 8m / s, turns off the fan after cooling to 800℃, and uses the furnace insulation layer to cool naturally until the temperature reaches 200℃ to obtain a porous brick precursor, and the porous brick precursor is cooled in a natural environment for 36h to obtain a porous brick.

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

[0048] Table 1 Parameter conditions of Examples 1-6

[0049]

[0050] Comparative Example 1 refers to the parameter conditions in Example 1, except that shale is not added.

[0051] Comparative Example 2 refers to the parameter conditions in Example 1, except that ceramsite is not added.

[0052] Comparative Example 3 refers to the parameter conditions in Example 1, except that no clay is added.

[0053] Comparative Example 4 refers to the parameter conditions in Example 1, except that no bentonite tailings powder is added.

[0054] Comparative Example 5 refers to the parameter conditions in Example 1, except that only the first grinding process is performed.

[0055] Comparative Example 6 refers to the parameter conditions in Example 1, except that only a secondary grinding process is performed.

[0056] Comparative Example 7 refers to the parameter conditions in Example 1, except that no drying and grinding treatment is performed.

[0057] Experimental Example 1: Compressive Strength and Blooming Degree Test

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

[0059] Table 2 Compressive strength and blooming degree test of Examples 1-6 and Comparative Examples 1-7

[0060]

[0061]

[0062] It can be found from Table 1 that in Comparative Examples 1-4, the lack of any raw material will lead to a decrease in the compressive strength of the porous bricks. Mining and selecting coal gangue in Zhongshan Coal Mine and using coal gangue as the main raw material is a secondary utilization of waste slag, which reduces environmental pollution and saves resources. It is rich in oxides such as silicon and aluminum, and can participate in the formation of high-strength mineral phases such as mullite during high-temperature sintering. Its own hardness and stability provide an important supporting skeleton for porous bricks; shale has good plasticity and adhesion, and it can tightly bond other raw material particles together to form a stable initial structure. During the sintering process, shale further reacts with other components to promote the densification of the brick structure. In Comparative Example 1, shale is removed, and its compressive strength is reduced; in Comparative Example 2, ceramsite is removed, and the compressive strength decreases. This is because ceramsite is light and porous, and can play a unique reinforcing role in porous bricks. Its porous structure can form a buffer structure inside the brick body. When the brick body is under pressure, ceramsite can disperse the pressure and avoid stress concentration, thereby enhancing the compressive strength; clay has good molding properties, it can be filled between other raw material particles to make the green body structure more uniform, further enhancing the strength of the brick body. Removing it in Comparative Example 3 will lead to a decrease in compressive strength; bentonite tailings powder has certain expansibility and adhesion. In the green body, it can fill tiny pores and improve the density of the brick body. Its special chemical properties help to better combine with other raw materials and enhance the chemical bonding force inside the brick body, thereby improving the compressive strength. Comparative Example 4 lacks bentonite tailings powder, and its compressive strength decreases. When coal gangue and shale are mixed in a suitable proportion, the mineral phases formed by the two during the sintering process can be intertwined, enhancing the stability of the brick structure; the combination of ceramsite and clay can not only ensure the lightweight characteristics of the brick body, but also use the cohesiveness of clay to better fix the ceramsite in the brick body, and jointly improve the compressive strength; bentonite tailings powder and other raw materials work synergistically, which can effectively improve the microstructure of the brick body, improve its density and internal bonding force. In comparative examples 5-7, when only the first grinding treatment is performed, the compressive strength of the porous brick decreases, and when only the second grinding treatment is performed, the compressive strength of the porous brick also decreases. When no drying and grinding treatment is performed, the compressive strength is obviously insufficient, and frosting occurs, which is far inferior to the embodiment. The first grinding process is to crush and decompose larger particles, greatly reduce their particle size, provide a suitable material particle size basis for subsequent fine grinding, and achieve initial uniform distribution; through the second grinding, the surface of the material particles can be made smoother and more regular, reducing surface defects and roughness. During the second grinding process, the interaction between the material particles is more sufficient, and a finer mixing can be achieved, so that materials of different components can be highly evenly distributed on a microscopic scale, providing a basis for subsequent sintering, thereby enhancing the compressive strength of the porous bricks and improving their durability.

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

[0064] Table 3 Parameter conditions of Example 4 and Examples 7-12

[0065]

[0066] Comparative Example 8 refers to the parameter conditions in Example 4, except that fly ash is not added.

[0067] Comparative Example 9 refers to the parameter conditions in Example 4, except that only chitosan is added as a retarder.

[0068] Comparative Example 10 refers to the parameter conditions in Example 4, except that no modified retarder is added.

[0069] Comparative Example 11 refers to the parameter conditions in Example 4, except that only low-speed ball milling is performed.

[0070] Comparative Example 12 refers to the parameter conditions in Example 4, except that only secondary ball milling is performed.

[0071] Comparative Example 13 refers to the parameter conditions in Example 4, except that no ball milling mixing is performed.

[0072] Experimental Example 2 High temperature resistance and pressure resistance test

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

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

[0075]

[0076]

[0077] It can be found from Table 4 that in Comparative Example 8, fly ash was not added, and its high temperature resistance and compressive resistance were reduced. This is because fly ash is a fine particle material rich in silicon aluminum oxide, and its main components can undergo a series of changes at high temperatures. In the process of firing porous bricks, when the temperature reaches a certain level, some components in the fly ash will form a glass phase. This glass phase has good high temperature resistance. It can fill the pores and particles of the brick body to make the brick structure denser. Some active ingredients 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 body, which enhances the skeleton structure of the brick body and improves the stability and strength retention ability of the brick body at high temperatures. In comparative examples 9-10, when chitosan is not modified or modified retarder is not added, the high temperature resistance and compressive resistance of the porous bricks are both reduced, which shows that the modified retarder plays an important role in the porous bricks. In the production process of porous bricks, the modified retarder can make the green body maintain plasticity for a long time, which is beneficial to the uniform mixing and molding of raw materials. Before high-temperature firing, the more uniform green body structure can reduce internal defects and stress concentration points. When the porous bricks are in a high temperature environment, this optimized structure can better withstand thermal stress and reduce cracking and damage caused by structural unevenness, thereby improving high temperature resistance. The modified retarder obtained by carboxymethylating chitosan will undergo a carbonization reaction at high temperature, and the formed carbide has a certain thermal stability and mechanical strength, which works together with fly ash to enhance the overall thermal stability of the porous brick, so that it can maintain a good shape and mechanical properties in a high temperature environment, thereby improving the durability of the porous brick. In Comparative Examples 11-13, when only low-speed ball milling, only secondary ball milling, or no ball milling mixing is performed, the high temperature resistance and compressive resistance of the porous bricks are lower than those in the embodiments. The low-speed ball milling is to perform preliminary mixing of the raw materials and crush larger particles, and prevent large particles from damaging the equipment during high-speed ball milling; the secondary ball milling enables finer mixing of the raw material particles and achieves a highly uniform distribution, providing a basis for subsequent sintering treatment, improving the high temperature resistance and compressive resistance of the porous bricks, and thus improving durability.

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

[0079] Comparative Example 14 refers to the parameter conditions in Example 10, except that only calcium sulfate is added as sulfate.

[0080] Comparative Example 15 refers to the parameter conditions in Example 10, except that only magnesium sulfate is added as sulfate.

[0081] Comparative Example 16 refers to the parameter conditions in Example 10, except that no composite sulfate is added.

[0082] Comparative Example 17 refers to the parameter conditions in Example 10, except that only polyester fiber is added as the fiber material.

[0083] Comparative Example 18 refers to the parameter conditions in Example 10, except that only carbon fiber is added as the fiber material.

[0084] Comparative Example 19 refers to the parameter conditions in Example 10, except that no composite fiber is added.

[0085] Comparative Example 20 refers to the parameter conditions in Example 10, except that the extrusion process is carried out at a constant speed of 13 rpm.

[0086] Comparative Example 21 refers to the parameter conditions in Example 10, except that instead of using extrusion molding, a mold molding process is used, specifically: pouring the mixed material into a porous brick mold, and the subsequent processing steps are the same.

[0087] Experimental Example 3 Density and compressive strength test

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

[0089] Table 5 Parameters, density and compressive strength test of Example 10, Examples 13-18 and Comparative Examples 14-21

[0090]

[0091]

[0092] It can be found from Table 5 that in Comparative Examples 14-16, when a single sulfate is used or when no composite sulfate is used, the density and compressive strength of the porous brick are lower than those in the embodiment. This is because in the preparation process of the porous brick, the calcium sulfate in the composite sulfate can be filled into the pores of the brick body, and these fine sulfate particles can enter the tiny gaps originally existing between the raw material particles, making the brick body structure more compact, thereby effectively improving the overall density of the porous brick, and magnesium sulfate can generate a viscous substance with certain components in other raw materials, which helps the bonding and close stacking of particles; the composite sulfate can generate some transition phases at the interface through chemical reactions, and these transition phases can enable the entire brick body to better transfer stress when subjected to external forces, thereby improving the compressive strength of the porous brick. In Comparative Examples 17-19, when a single fiber material is used or when no composite fiber is used, the density and compressive strength of the porous brick are lower, because the network structure formed by the composite fiber inside the porous brick can effectively diffuse and migrate the impact on the porous brick, thereby improving the compressive strength. There is a certain synergistic effect between the composite sulfate and the composite fiber. The composite sulfate will undergo some chemical reactions at high temperatures, and the generated substances can fill the tiny pores and defects inside the porous bricks, making the microstructure more compact; the composite fiber can maintain a certain shape and mechanical properties at high temperatures, and play a supporting role inside the porous bricks to prevent the microstructure from collapsing or deforming at high temperatures, and the carbon fibers therein are partially oxidized at high temperatures to form a carbon layer. The synergistic effect of the two enables the porous bricks to maintain a relatively stable microstructure, thereby maintaining its compressive strength. In comparative examples 20-21, when the mixed material is extruded at a uniform speed of 13 rpm during the extrusion molding process, the speed of the mixed material does not change, and the pressure is insufficient, making it difficult to make the interior of the porous brick dense, and the compressive strength at this time will be significantly reduced; when no extrusion molding is used and only mold molding is used, there is more air inside the porous brick at this time, and more voids will be generated during the subsequent sintering process, causing the surface of the porous brick to be uneven and the compressive strength to deteriorate; during the extrusion molding process, increasing the speed can make the brick blank subject to a uniform and larger extrusion force. At this time, the particles inside the brick blank are more closely arranged, the porosity is reduced, and the structure is denser, which helps to disperse the load more evenly when under pressure and reduce stress concentration, thereby improving the compressive strength of the porous brick, enabling it to withstand greater weight and external force, and improving the durability of the porous brick.

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

[0094] Comparative Example 22 refers to the parameter conditions in Example 16, except that only the first stage firing is performed.

[0095] Comparative Example 23 refers to the parameter conditions in Example 16, except that only the second stage firing is performed.

[0096] Comparative Example 24 refers to the parameter conditions in Example 16, except that only the third stage firing is performed.

[0097] Comparative Example 25 refers to the parameter conditions in Example 16, except that the entire firing process is carried out at 950°C.

[0098] Experimental Example 4 High temperature resistance and compressive strength test

[0099] The high temperature resistance and compressive strength of Example 16, Examples 19-24 and Comparative Examples 22-25 were tested with reference 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 test of Example 16, Examples 19-24 and Comparative Examples 22-25

[0101]

[0102] It can be found from Table 6 that in Comparative Example 22, only the temperature of the first stage is used to fire the porous bricks, and the porous bricks will be underfired, and the chemical reaction inside the brick body is incomplete, resulting in a decrease in its compressive strength. In Comparative Example 23, only the temperature of the second stage is used to fire the porous bricks, and some additives are directly decomposed before they can play a role in this process, resulting in a decrease in the high temperature resistance and compressive strength of the porous bricks. In Comparative Example 24, only the temperature of the third stage is used to fire the porous bricks, which may destroy the pore structure in the bricks. The originally designed uniform porous structure may partially or completely collapse and clog due to high temperature, changing the porosity and pore size distribution of the porous bricks, seriously affecting their high temperature resistance and compressive strength. In Comparative Example 25, only one temperature is used for continuous calcination of the porous bricks, but their high temperature resistance and compressive resistance are still not good. This is because in the staged sintering process, the first stage is fired at a relatively low temperature, which can gently remove the moisture that may remain in the green body. At the same time, some additives in the green body begin to react preliminarily at low temperature, stabilize the green body structure, and provide a solid foundation for subsequent high-temperature sintering, thereby enhancing the stability of the porous bricks at high temperatures and improving the high temperature resistance; after the second stage of heating treatment, the high temperature intensifies the atomic diffusion between the green body particles, and the particles fuse with each other, wherein a fly ash glass phase is formed, the porosity of the green body is reduced, and it gradually densifies; in the third stage, the temperature is raised to the highest temperature for firing, and the high temperature conditions promote complex physical and chemical reactions inside the green body, and the mineral components in the raw materials undergo crystal phase transformation to generate a more stable and high temperature resistant mineral phase, which improves the mechanical properties and high temperature resistance of the porous bricks, thereby improving durability.

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

Claims

1. A sintering process for high temperature resistant sintered porous bricks, characterized in that: The sintering process of the porous brick comprises the following steps by weight: S1: 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 mixed, and then dried and ground to obtain a mixed slag 1; S2: 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 are ball-milled to obtain mixed material slag 2; the modified retarder includes chitosan, sodium hydroxide and chloroacetic acid; S3: putting the mixed slag 1 and the mixed slag 2 into a mixer and mixing them for 20 minutes, adding water, and stirring again for 15 minutes to obtain a mixed material; S4: extruding the mixture in a vacuum brick extruder to obtain a brick; S5: placing the green brick in a constant temperature drying oven and drying it at 100° C. for 8 hours to obtain a dried green brick; S6: putting the dried green body into a furnace for firing, and obtaining a porous brick precursor through staged sintering treatment. The porous brick precursor is cooled in a natural environment for 36 hours to obtain the porous brick.

2. The sintering process of a high temperature resistant sintered porous brick according to claim 1, characterized in that: The drying and grinding process described in S1 is: 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 through a conveyor, the preheating temperature is 100°C, and then the temperature is raised to 350°C, and after drying for 2 hours, the dried raw material is cooled to obtain a dry raw material; the dry raw material is conveyed to a grinder for primary grinding at a speed of 18rpm-22rpm for 1.5 hours, followed by secondary grinding at a speed of 25rpm-30rpm for 1 hour, and then sieved through a drum screen with an aperture of 1.5mm to obtain the mixed slag one.

3. The sintering process of a high temperature resistant sintered porous brick according to claim 1, characterized in that: The preparation method of the modified retarder described in S1 is as follows: 6-10 parts of chitosan and 15 parts of isopropanol are put into a three-necked flask, and after stirring for 10 minutes, 20 parts of sodium hydroxide solution are added, wherein the mass percentage concentration of the sodium hydroxide solution is 30%, and then the mixture is stirred and reacted at 40°C for 3 hours to obtain a mixed solution A; 3 parts of chloroacetic acid are dissolved in 10 parts of isopropanol to obtain a mixed solution B; the mixed solution B is slowly added dropwise to the mixed solution A at a dropping speed of 1 drop / second, and the reaction temperature is maintained at 60°C during the dropping process. After the dropping is completed, the reaction is continued to be stirred for 4h-8h to obtain a reaction solution; after the reaction is completed, the reaction solution is cooled to room temperature, and the pH value is adjusted to 8 to obtain a neutralization solution; 50 parts of deionized water are added to the neutralization solution, and then suction 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 12h to obtain the modified retarder.

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

2.

5. The sintering process of a high temperature resistant sintered porous brick according to claim 1, characterized in that: The ball milling and mixing process in S2 is: pass 10-15 parts of the fly ash through a 200-mesh sieve and dry at 105°C for 2 hours to obtain dry fly ash; add 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 to the feed port of the ball mill in sequence, first ball mill at a low speed of 100rpm-150rpm for 30min, then increase the speed to 200rpm-300rpm and ball mill again for 2h to obtain the ball-milled material; pass the material through a 100-mesh sieve to obtain the mixed slag II.

6. The sintering process of a high temperature resistant sintered porous brick according to claim 1, characterized in that: The extrusion molding process described in S4 is as follows: placing the mixed material in a closed container for aging for 48 hours to obtain a pretreated material; preheating the mold to 45°C, starting the vacuum pump, adjusting the vacuum degree to -0.08MPa, adjusting the compression ratio of the screw to 2.5:1, and the initial extrusion rate to 0.4m / min; slowly pouring the pretreated material into the vacuum brick extruder, turning on the screw machine for low-speed pre-extrusion, the speed is 10rpm-15rpm, and gradually increasing the speed 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 by a wire cutter, and then allowed to stand in a temperature and humidity control room for 12 hours, wherein the temperature is 25°C and the humidity is 60 parts, to obtain the brick blank.

7. The sintering process of a high temperature resistant sintered porous brick according to claim 1, characterized in that: The process of the segmented sintering treatment described in S6 is as follows: the dried green bodies are aligned and stacked according to the vertical channels, and 3mm silicon carbide partitions are placed between the layers; the brick-firing furnace is heated to 300°C at a rate of 5°C / min and maintained for 1 hour; then the temperature is raised to 500°C-600°C at a rate of 3°C / min, and oxygen is injected by blasting for the first stage firing for 3 hours to obtain an oxidized brick body; the brick-firing furnace is heated to 900°C-1000°C at a rate of 5°C / min for the second stage firing for 5 hours to obtain a dense brick body; the brick-firing furnace is heated to 1200°C-1250°C at a rate of 2°C / min for the third stage firing for 2 hours to obtain a sintered brick body; the heating system is turned off, and the high-speed circulating air cooling system is turned on with a wind speed of 8m / s. After the temperature drops to 800°C, the fan is turned off, and the furnace insulation layer is used to cool naturally until the temperature reaches 200°C to obtain the porous brick precursor.

8. A high temperature resistant sintered porous brick, characterized in that: The porous brick is obtained by sintering by the sintering process according to any one of claims 1 to 7; The synthetic raw materials of the porous bricks include: coal gangue, shale, ceramsite, clay, bentonite tailing powder, fly ash, modified retarder, composite sulfate and composite fiber; The modified retarder comprises chitosan, sodium hydroxide and chloroacetic acid; The composite sulfate includes calcium sulfate and magnesium sulfate; The composite fiber includes polyester fiber and carbon fiber.

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