Alumina-carbon brick for cement kiln mouth with high temperature softening resistance and its preparation method

Abstract

The application discloses an aluminum-carbon brick for a cement kiln mouth, which is resistant to high-temperature softening, and a preparation method thereof, and belongs to the technical field of refractory materials. Raw materials of the aluminum-carbon brick include tabular corundum, fused white corundum, flaky graphite, carbon black, silicon carbide, hexagonal boron nitride, silicon powder, alumina micropowder, boron carbide, zirconium diboride and nano-silicon dioxide modified phenolic resin. The preparation method comprises the following steps: raw material pretreatment, step-by-step mixing and granulation, compression molding, three-stage gradient heat treatment and cooling. The three-stage gradient heat treatment comprises a low-temperature pretreatment stage, a medium-temperature whisker growth stage and a high-temperature densification stage in sequence. In the medium-temperature stage, mullite whiskers are generated in situ from the silicon powder and the alumina micropowder under a reducing atmosphere, boron carbide is oxidized to generate a high-melting-point boric acid phase to weld the grain boundaries, and a dense oxide protective layer is formed on the surface of the zirconium diboride. Through the synergistic effect of high-purity main materials and multi-element functional additives, and in combination with a gradient sintering process, the aluminum-carbon brick has excellent structural stability at high temperatures.

Description

Technical Field

[0001] This invention relates to the field of refractory materials technology, and in particular to an alumina-carbon brick for cement kiln inlet that is resistant to high-temperature softening and its preparation method. Background Technology

[0002] The kiln inlet of a cement kiln is one of the most demanding operating areas in a rotary kiln, enduring high temperatures above 1400℃, severe erosion from cement clinker, alkaline atmosphere corrosion, and frequent periodic thermal shocks. Alumina-carbon bricks (Al2O3-SiC-C system) are widely used as lining materials for cement kiln inlets due to their excellent resistance to slag erosion and thermal shock stability.

[0003] However, existing alumina-carbon bricks generally suffer from significant high-temperature softening during high-temperature service, mainly manifested in the following ways: First, traditional formulations often use high-alumina bauxite as the main raw material, which contains alkali metal impurities such as K2O and Na2O (usually 1.5-3%) that easily generate low-melting-point glass phases at high temperatures, leading to a sharp decrease in grain boundary strength and causing plastic creep or even collapse of the material under load. Second, conventional phenolic resin binders decompose in the medium-temperature range of 300-800℃ to generate amorphous glassy carbon, which corresponds to the critical temperature range of the kiln heating process, easily forming a strength "vacuum zone". Third, the interfacial bonding strength between the main crystalline phases (corundum, silicon carbide) and carbon components is insufficient, grain boundary slip intensifies at high temperatures, and carbon components are easily lost in an oxidizing atmosphere, further weakening the material structure. While current improvements include increasing silicon carbide content or adding small amounts of boron nitride, these methods largely rely on high proportions of single components, lacking a systematic, synergistic design for high-temperature softening resistance. Furthermore, the firing processes are mostly single-temperature firings, making it difficult to accommodate the reaction requirements of different functional components. Therefore, developing an alumina-carbon brick with self-reinforcing anti-softening capabilities at high temperatures and a controllable preparation process is of great significance for extending the service life of cement kiln inlets. Summary of the Invention

[0004] The main objective of this invention is to provide an aluminum-carbon brick for cement kiln inlet that is resistant to high-temperature softening and its preparation method, which can effectively solve the problems mentioned in the background art.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] A type of alumina-carbon brick for cement kiln inlet that resists high-temperature softening, comprising the following raw materials by weight:

[0007] 50-65 parts of tabular corundum, 10-20 parts of fused white corundum, 5-10 parts of flake graphite, 1-3 parts of carbon black, 8-15 parts of silicon carbide, 2-6 parts of boron nitride, 1-4 parts of metallic silicon powder, 2-6 parts of alumina micro powder, 0.5-2 parts of boron carbide, 0.5-2 parts of zirconium diboride, and 4-7 parts of nano-SiO2 modified phenolic resin.

[0008] Preferably, the tabular corundum has an Al2O3 content ≥99% and a particle size distribution of 20-30% for 5-3mm, 25-35% for 3-1mm, and 20-30% for ≤1mm; the fused white corundum has an Al2O3 content ≥99.5% and a particle size ≤0.045mm.

[0009] Preferably, the flake graphite has a C content ≥98% and a particle size ≤0.1mm; the carbon black has a particle size of 20~40nm; and the silicon carbide has a SiC content ≥98% and a particle size ≤0.074mm.

[0010] Preferably, the boron nitride is hexagonal boron nitride with a purity ≥99% and a particle size ≤5μm; the silicon metal powder has a Si content ≥99% and a particle size ≤0.044mm; the alumina micro powder is α-Al2O3, d 50 =1~2μm.

[0011] Preferably, the boron carbide has a B4C content of ≥98% and a particle size of ≤0.044mm; the zirconium diboride has a ZrB2 content of ≥99% and a particle size of ≤5μm; and the char residue of the nano-SiO2 modified phenolic resin is ≥50%.

[0012] Preferably, the raw material further includes 0.5 to 2 parts by weight of multi-walled carbon nanotubes.

[0013] Preferably, in the raw material, 10-20% of the portion of the tabular corundum with a particle size of 5-3 mm and / or 3-1 mm is replaced by lightweight mullite hollow spheres.

[0014] A method for preparing alumina-carbon bricks for cement kiln inlets resistant to high-temperature softening includes the following steps:

[0015] S1. The tabular corundum is graded and cleaned according to particle size. The fine powder of fused white corundum, silicon carbide, boron nitride, boron carbide, zirconium diboride, metallic silicon powder and alumina micro powder are dried to a moisture content of ≤0.2%. The carbon black is ultrasonically pre-dispersed in anhydrous ethanol.

[0016] S2. First, add 5-3mm and 3-1mm plate-shaped corundum particles to a high-performance mixer, then add 60% of the total amount of nano-SiO2 modified phenolic resin, and mix for 5-8 minutes; then add ≤1mm plate-shaped corundum fine powder, fused white corundum fine powder, silicon carbide, metallic silicon powder, alumina micro powder, and pre-dispersed carbon black, and mix for 10-12 minutes; finally, add flake graphite, boron nitride, boron carbide, zirconium diboride, and the remaining 40% of nano-SiO2 modified phenolic resin, and mix for 5-8 minutes to obtain the mixture;

[0017] S3. Press the mixture into shape under a pressure of 180~250MPa, and hold the pressure for 10~15 seconds to obtain a brick blank;

[0018] S4. Perform three-stage gradient heat treatment on the brick blanks: the first stage is to raise the temperature from room temperature to 300-400℃ at a heating rate of 2-3℃ / min and hold for 2-3 hours; the second stage is to raise the temperature from 400℃ to 1250-1300℃ at a heating rate of 1.5-2℃ / min and hold for 3-4 hours; the third stage is to raise the temperature from 1300℃ to 1450-1520℃ at a heating rate of 1-1.5℃ / min and hold for 4-6 hours.

[0019] S5. Cool to room temperature at a rate of ≤3℃ / min.

[0020] Preferably, in step S4, the second firing process is carried out under a reducing atmosphere, so that the silicon metal powder and alumina micro powder react in situ to generate mullite whiskers.

[0021] Preferably, after cooling in step S5, the method further includes a step of spraying a composite anti-oxidation coating on the surface of the aluminum-carbon brick: mixing zirconium sol and zirconium boride powder at a mass ratio of 1:1~3, spraying the mixture onto the surface of the brick with a thickness of 0.1~0.3 mm, and then drying and curing it at 80~120℃.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] This invention uses a combination of high-purity tabular corundum and fused white corundum as raw materials, keeping the overall alkali metal impurity content at a low level. It also introduces silicon carbide, hexagonal boron nitride, boron carbide, and zirconium diboride. Boron carbide, after oxidation at high temperatures, reacts with alumina to form a high-melting-point borate phase. A zirconium-silicon composite oxide layer forms on the surface of zirconium diboride. Additionally, metallic silicon powder and alumina micropowder are added, which can generate mullite whiskers in situ under a reducing atmosphere. The binder is a nano-silica modified phenolic resin. The firing process is divided into three stages: low-temperature pretreatment, medium-temperature whisker growth, and high-temperature densification. This formula and process result in a final material with fewer alkali metal impurities, high-melting-point borate phases distributed at grain boundaries, and particles firmly bonded together by high-melting-point substances, with internal needle-like crystals providing reinforcement, making the brick less prone to softening at high temperatures. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the preparation method of aluminum-carbon bricks for cement kiln inlets that are resistant to high-temperature softening, according to the present invention. Detailed Implementation

[0025] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below in conjunction with specific embodiments.

[0026] like Figure 1 The preparation method shown is a schematic diagram. The following is a detailed embodiment to illustrate the process.

[0027] I. Raw Material Composition

[0028] According to the aforementioned raw material composition, take 50 to 65 parts by weight of tabular corundum, 10 to 20 parts by weight of fused white corundum, 5 to 10 parts by weight of flake graphite, 1 to 3 parts by weight of carbon black, 8 to 15 parts by weight of silicon carbide, 2 to 6 parts by weight of boron nitride, 1 to 4 parts by weight of metallic silicon powder, 2 to 6 parts by weight of alumina micro powder, 0.5 to 2 parts by weight of boron carbide, 0.5 to 2 parts by weight of zirconium diboride, and 4 to 7 parts by weight of nano-silica modified phenolic resin.

[0029] The alumina content of tabular corundum is not less than 99%, and it adopts three particle size distributions: 5 to 3 mm, 3 to 1 mm, and ≤1 mm, with the mass ratio between the three within a defined range. The purpose of this distribution is to allow large particles to form a skeleton, medium particles to fill the gaps between large particles, and fine particles to further fill the micropores, thereby achieving high bulk density and green strength after pressing. The alumina content of fused white corundum is not less than 99.5%, and it consists entirely of fine powder ≤0.045 mm. It is used to fill the micropores between the tabular corundum particles and reacts with other fine powders in the matrix during high-temperature sintering to improve the density and bonding strength of the matrix.

[0030] Flake graphite, with a carbon content of no less than 98% and a particle size of ≤0.1 mm, serves as one of the main sources of carbon components. Carbon black, with a particle size of 20 to 40 nanometers, is advantageous for uniform dispersion in the resin binder and for forming a continuous carbon network after firing. The combined use of both ensures both uniform distribution of carbon components in the brick and continuity of the carbon network. Silicon carbide, with a silicon carbide content of no less than 98% and a particle size of ≤0.074 mm, exhibits high strength and oxidation resistance at high temperatures. Its particle distribution within the brick helps to anchor grain boundaries and inhibit high-temperature slip.

[0031] The boron nitride used is hexagonal boron nitride with a purity of not less than 99% and a particle size of less than or equal to 5 micrometers. Hexagonal boron nitride has a graphite-like layered structure, exhibiting good lubricity and chemical stability at high temperatures, which helps reduce internal stress concentration in the brick during thermal shock. The silicon metal powder has a silicon content of not less than 99% and a particle size of less than or equal to 0.044 millimeters. The alumina micropowder is alpha alumina with a median particle size of 1 to 2 micrometers. Both will undergo an in-situ reaction during the subsequent firing process to form mullite whiskers.

[0032] The boron carbide content is not less than 98%, and the particle size is less than or equal to 0.044 mm. The zirconium diboride content is not less than 99%, and the particle size is less than or equal to 5 micrometers. These two substances are the key high-temperature softening functional additives in this invention. The residual carbon rate of the nano-silica-modified phenolic resin is not less than 50%. The nano-silica particles are uniformly dispersed in the phenolic resin and act as nucleating agents during the resin pyrolysis process, promoting the transformation of carbon into an ordered graphitized structure.

[0033] As an optional step, 0.5 to 2 parts by weight of multi-walled carbon nanotubes can be added to the formulation to further strengthen the matrix. Lightweight mullite hollow spheres can replace 10% to 20% of the 5 to 3 mm or 3 to 1 mm particle size portion of the tabular corundum in the formulation to reduce the overall weight of the brick.

[0034] II. Raw Material Pretreatment

[0035] The tabular corundum was cleaned according to three particle size levels: 5 to 3 mm, 3 to 1 mm, and less than or equal to 1 mm, to remove surface dust and impurities, and then dried for later use.

[0036] Fine powder of fused white corundum, silicon carbide, boron nitride, boron carbide, zirconium diboride, metallic silicon powder, and alumina micro powder were placed separately in a drying oven and dried at 110℃ for 24 hours to reduce their moisture content to below 0.2%. Excessive moisture content will reduce the curing effect of the resin binder during subsequent mixing and generate excessive porosity during firing.

[0037] Carbon black was added to anhydrous ethanol and pre-dispersed in an ultrasonic dispersion device. The ultrasonic power was 500 watts, and the time was 30 minutes. The purpose of this step was to break up the agglomerates between carbon black particles, so that they could be uniformly dispersed when mixed with resin in the subsequent process, avoiding structural inhomogeneity caused by local carbon enrichment.

[0038] III. Mixed Granulation

[0039] The mixing and granulation process is carried out in three steps using a high-powered mixer.

[0040] Step 1: Add 5-3 mm and 3-1 mm plate-shaped corundum particles to a high-performance mixer, then add 60% of the total amount of nano-silica modified phenolic resin. Mix for 5-8 minutes to ensure the resin evenly coats the surface of the coarse particles. The resin first contacts the coarse particles, forming a uniform adhesive film on their surface, which facilitates the subsequent adhesion of fine powder.

[0041] Step 2: Add plate-shaped corundum powder (1 mm or less), fused white corundum powder, silicon carbide, metallic silicon powder, alumina micro powder, and pre-dispersed carbon black to the mixer. Continue mixing for 10 to 12 minutes. During this stage, the fine powder and carbon black adhere to the surface of the coarse particles already coated with resin, forming a composite coating layer of resin and fine powder. This layered coating structure is beneficial for obtaining a uniform particle distribution after pressing and molding, and reduces the segregation of fine powder in the brick blank.

[0042] Step 3: Add flake graphite, boron nitride, boron carbide, zirconium diboride, and the remaining 40% nano-silica modified phenolic resin to the mixer. Continue mixing for 5 to 8 minutes. In this stage, the flake graphite and hexagonal boron nitride are in flake form, while the boron carbide and zirconium diboride are in fine powder form. They, along with the remaining resin, fill the spaces between the already coated particles to form the final mixture. Adding graphite and functional additives last reduces their excessive fragmentation or embedding, thus helping to maintain their flake morphology and dispersion.

[0043] IV. Compression Molding

[0044] The mixture is fed into a friction brick press for pressing and molding. The pressure specifications of the friction brick press range from 500 to 800 tons, with the actual molding pressure controlled between 180 and 250 MPa, and a holding time of 10 to 15 seconds. Under high pressure, the particles in the mixture rearrange, and the gaps between coarse particles are filled with fine powder and resin. Simultaneously, the resin further spreads under pressure, binding the components together to form a brick blank with a certain strength. A sufficiently long holding time ensures that the pressure is fully transmitted, reducing the risk of elastic recovery and delamination within the brick blank.

[0045] V. Three-stage gradient heat treatment

[0046] The formed brick blanks are placed in a high-temperature tunnel kiln and fired according to three different heating regimes and holding conditions. The entire firing process is carried out in a reducing atmosphere or a weakly oxidizing atmosphere, and the specific atmosphere is controlled by adjusting the excess air coefficient inside the kiln.

[0047] The first stage is the low-temperature pretreatment stage. The temperature is increased from room temperature to 300-400°C at a rate of 2-3°C per minute, and held at this temperature for 2-3 hours. The main function of this stage is to slowly cure the nano-silica-modified phenolic resin and release volatiles. The heating rate should not be too fast, otherwise the rapid escape of volatiles will cause cracking of the brick. Within this temperature range, low-molecular-weight substances in the resin gradually volatilize, and the resin begins to cross-link and cure, forming a preliminary carbon skeleton. Simultaneously, the nano-silica particles remain dispersed, providing nucleation sites for subsequent carbon structure transformation.

[0048] The second stage is the medium-temperature whisker growth stage. The temperature is increased from 400℃ to 1250-1300℃ at a rate of 1.5-2℃ per minute, and held at this temperature for 3-4 hours. This stage needs to be carried out in a reducing atmosphere, such as by introducing nitrogen or maintaining a slight positive pressure inside the kiln to reduce oxygen intake. In this temperature range, the metallic silicon powder and alumina powder begin to react, forming mullite whiskers. The reaction mechanism is as follows: the metallic silicon powder first reacts with trace amounts of oxygen or carbon oxides in the atmosphere at high temperature to generate silicon monoxide gas or silicon dioxide, and then reacts with the surrounding alumina to form mullite. Because this temperature range is below the upper limit of the stable growth temperature of mullite, the generated mullite is in the form of slender needle-like whiskers, rather than equiaxed particles. These whiskers grow in situ within the brick matrix, forming a three-dimensional interwoven network structure, which acts as a reinforcing agent for the brick, similar to steel reinforcement.

[0049] Simultaneously, within this temperature range, the carbon generated from the pyrolysis of phenolic resin begins to transform into an ordered form. Nano-silica particles act as nucleating agents, promoting the transformation of carbon from an amorphous state to a graphite-like structure, increasing the graphitization degree of the residual carbon, and thus enhancing the strength of the carbon skeleton in the mid-temperature region. Additionally, boron carbide also begins to oxidize within this temperature range, generating boron trioxide. Boron trioxide is a low-melting-point oxide with a melting point of around 450℃, but at 1250 to 1300℃, it reacts with surrounding alumina to form aluminum borate, which has a melting point of approximately 1950℃. The aluminum borate phase is distributed in granular or thin-film form at the grain boundaries, essentially welding a layer of high-melting-point material between the particles.

[0050] The third stage is the high-temperature densification stage. The temperature is increased from 1300℃ to 1450-1520℃ at a rate of 1 to 1.5℃ per minute, and held at this temperature for 4 to 6 hours. The heating rate is further reduced in this stage to allow the brick to sinter fully without generating excessive thermal stress. Within this temperature range, the following changes occur in the brick: solid-phase diffusion between corundum particles and between corundum and silicon carbide intensifies, forming neck connections at the particle contact surfaces, significantly improving the overall strength and density of the brick; zirconium diboride exhibits good high-temperature stability in this temperature range, and its surface reacts with oxygen or water vapor in the atmosphere to form a dense zirconium dioxide and silicon dioxide composite oxide layer. This oxide layer covers the surface of the zirconium diboride particles, effectively preventing further diffusion of oxygen into the brick, thus protecting the carbon components in the brick from oxidation; the previously formed aluminum borate phase remains stable above 1450℃, does not remelt, but exists as a grain boundary strengthening phase for a long time; mullite whiskers continue to grow in this temperature range, but the growth rate slows down, mainly resulting in whisker coarsening and interweaving between whiskers. After the heat treatment is completed, the brick completes densification sintering.

[0051] VI. Cooling

[0052] The brick should be slowly cooled to room temperature at a rate not exceeding 3°C per minute. Slow cooling is crucial to prevent thermal shock cracking caused by excessive temperature differences within the brick. Because the brick contains a significant amount of carbon, its coefficient of thermal expansion differs from that of corundum, silicon carbide, and other ceramic phases; rapid cooling can easily lead to interface cracking. Using a cooling rate not exceeding 3°C per minute ensures a uniform temperature decrease throughout the brick, reducing thermal stress.

[0053] VII. Optional post-treatment: Spraying a composite anti-oxidation coating

[0054] For applications requiring higher oxidation resistance, a composite anti-oxidation coating can be sprayed onto the cooled alumina-carbon brick surface. The coating slurry is a mixture of zirconium sol and zirconium boride powder in a mass ratio of 1:1 to 3. It is evenly applied to the brick surface using a spraying method, with a coating thickness controlled between 0.1 and 0.3 mm. The coated brick is then dried and cured at 80 to 120°C, allowing the zirconium sol to gel and form a continuous film. This coating further sintersulates at high temperatures, forming a dense composite protective layer of zirconium dioxide and boron trioxide, which significantly slows the diffusion of oxygen from the brick surface to the interior, thereby extending the brick's service life. This step is optional and its implementation depends on the specific requirements of the application environment.

[0055] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. An alumina-carbon brick for cement kiln inlets resistant to high-temperature softening, characterized in that: It consists of the following raw materials in parts by weight: 50-65 parts of tabular corundum, 10-20 parts of fused white corundum, 5-10 parts of flake graphite, 1-3 parts of carbon black, 8-15 parts of silicon carbide, 2-6 parts of boron nitride, 1-4 parts of metallic silicon powder, 2-6 parts of alumina micro powder, 0.5-2 parts of boron carbide, 0.5-2 parts of zirconium diboride, and 4-7 parts of nano-SiO2 modified phenolic resin.

2. The alumina-carbon brick for cement kiln inlet resistant to high-temperature softening according to claim 1, characterized in that: The tabular corundum has an Al2O3 content ≥99% and a particle size distribution of 20-30% for 5-3mm, 25-35% for 3-1mm, and 20-30% for ≤1mm; the fused white corundum has an Al2O3 content ≥99.5% and a particle size ≤0.045mm.

3. The alumina-carbon brick for cement kiln inlet resistant to high-temperature softening according to claim 1, characterized in that: The flake graphite has a C content ≥98% and a particle size ≤0.1mm; the carbon black has a particle size of 20~40nm; and the silicon carbide has a SiC content ≥98% and a particle size ≤0.074mm.

4. The alumina-carbon brick for cement kiln inlet resistant to high-temperature softening according to claim 1, characterized in that: The boron nitride is hexagonal boron nitride with a purity ≥99% and a particle size ≤5μm; the silicon metal powder has a Si content ≥99% and a particle size ≤0.044mm; the alumina micro powder is α-Al2O3, d 50 =1~2μm.

5. The alumina-carbon brick for cement kiln inlet resistant to high-temperature softening according to claim 1, characterized in that: The boron carbide has a B4C content of ≥98% and a particle size of ≤0.044mm; the zirconium diboride has a ZrB2 content of ≥99% and a particle size of ≤5μm; and the char residue of the nano-SiO2 modified phenolic resin is ≥50%.

6. The alumina-carbon brick for cement kiln inlet resistant to high-temperature softening according to claim 1, characterized in that: The raw materials also include 0.5 to 2 parts by weight of multi-walled carbon nanotubes.

7. The alumina-carbon brick for cement kiln inlet resistant to high-temperature softening according to claim 1, characterized in that: In the raw material, 10-20% of the 5-3mm and / or 3-1mm particles in the tabular corundum are replaced by lightweight mullite hollow spheres.

8. A method for preparing alumina-carbon bricks for cement kiln inlets resistant to high-temperature softening as described in any one of claims 1 to 7, characterized in that: Includes the following steps: S1. The tabular corundum is graded and cleaned according to particle size. The fine powder of fused white corundum, silicon carbide, boron nitride, boron carbide, zirconium diboride, metallic silicon powder and alumina micro powder are dried to a moisture content of ≤0.2%. The carbon black is ultrasonically pre-dispersed in anhydrous ethanol. S2. First, add 5-3mm and 3-1mm plate-shaped corundum particles to a high-performance mixer, then add 60% of the total amount of nano-SiO2 modified phenolic resin, and mix for 5-8 minutes; then add ≤1mm plate-shaped corundum fine powder, fused white corundum fine powder, silicon carbide, metallic silicon powder, alumina micro powder, and pre-dispersed carbon black, and mix for 10-12 minutes; finally, add flake graphite, boron nitride, boron carbide, zirconium diboride, and the remaining 40% of nano-SiO2 modified phenolic resin, and mix for 5-8 minutes to obtain the mixture; S3. Press the mixture into shape under a pressure of 180~250MPa, and hold the pressure for 10~15 seconds to obtain a brick blank; S4. Perform three-stage gradient heat treatment on the brick blanks: the first stage is to raise the temperature from room temperature to 300-400℃ at a heating rate of 2-3℃ / min and hold for 2-3 hours; the second stage is to raise the temperature from 400℃ to 1250-1300℃ at a heating rate of 1.5-2℃ / min and hold for 3-4 hours; the third stage is to raise the temperature from 1300℃ to 1450-1520℃ at a heating rate of 1-1.5℃ / min and hold for 4-6 hours. S5. Cool to room temperature at a rate of ≤3℃ / min.

9. The preparation method according to claim 8, characterized in that: In step S4, the second firing process is carried out under a reducing atmosphere, which allows the silicon metal powder and alumina micro powder to react in situ to generate mullite whiskers.

10. The preparation method according to claim 8, characterized in that: After cooling in step S5, the process also includes spraying a composite anti-oxidation coating onto the surface of the aluminum-carbon brick: mixing zirconium sol and zirconium boride powder at a mass ratio of 1:1~3, spraying the mixture onto the brick surface with a thickness of 0.1~0.3mm, and then drying and curing it at 80~120℃.

Images