Alumina corundum bricks for the arch roof of ultra-high temperature tunnel kilns and their preparation method

Abstract

This invention relates to the field of alumina corundum brick production technology, specifically to alumina corundum bricks for ultra-high temperature tunnel kiln arches and their preparation method. The alumina corundum bricks for ultra-high temperature tunnel kiln arches comprise the following chemical composition by mass fraction: Al₂O₃: 97.5-98.2%; Nb₂O₅: 0.1-0.3%; K₂O: 0.2-0.42%; Li₂O: 0.3-0.7%; the remainder being unavoidable impurities. The alumina corundum bricks prepared by this invention have a bulk density increased by more than 8.5%, compressive strength increased by more than 20%, high-temperature flexural strength increased by more than 80%, creep reduced by 40%, and load softening initiation temperature increased by 100°C.

Description

Technical Field

[0001] This invention relates to the field of alumina corundum brick production technology, specifically to alumina corundum bricks for the arch roof of ultra-high temperature tunnel kilns and their preparation method. Background Technology

[0002] As a special high-temperature firing equipment, the ultra-high temperature tunnel kiln needs to maintain a stable firing temperature range of 1750-1950℃. The core working area of ​​this equipment is the high-temperature firing zone, and the arch of the firing zone, as a key load-bearing and heat-insulating component of the kiln, is in an extreme high-temperature environment for a long time. This places stringent requirements on the high-temperature resistance, structural stability and creep resistance of refractory materials. Only a few special refractory materials can initially meet the adaptability of the application scenarios.

[0003] Currently, the mainstream refractory materials used in high-temperature kilns in the industry mainly include magnesia-chrome bricks, magnesia bricks, conventional alumina corundum bricks, and alumina hollow sphere bricks. However, they all have significant technical shortcomings in their application in the arched section of ultra-high temperature tunnel kilns.

[0004] Although magnesia-chrome bricks possess good thermal shock resistance, their high-temperature strength is significantly insufficient, limiting their use to short periods at temperatures of 1700℃ and below. Furthermore, they are prone to chromium formation under high-temperature oxidation conditions. 6+ It poses serious health hazards and environmental risks, and does not meet modern industrial green and safety standards;

[0005] Magnesia bricks have a lower production cost, but their upper limit of high temperature resistance is close to that of magnesia-chrome bricks. They are only suitable for working conditions below 1700℃ and cannot meet the firing temperature requirements of 1750~1950℃ for ultra-high temperature tunnel kilns.

[0006] The Al2O3 content of conventional alumina corundum bricks is usually controlled at 95-96%. In high-temperature environments above 1600℃, the β-corundum phase inside the brick is prone to crystal transformation and gradually transforms into the α-corundum phase. Accompanied by volume shrinkage and structural stress changes, the brick cracks and peels off, making it impossible to achieve long-term stable service in ultra-high temperature environments above 1800℃.

[0007] Although alumina hollow spherical bricks are lightweight and have certain thermal insulation properties, their structural density and mechanical strength are relatively low. Under the combined effects of ultra-high temperature and the load-bearing capacity of the kiln arch, they are prone to structural deformation and damage, and thus cannot meet the long-term use requirements of the arch of the firing zone in ultra-high temperature tunnel kilns.

[0008] In response to the aforementioned technical deficiencies of high-temperature refractory materials, relevant patent literature in the industry has proposed some improvement solutions, but none of them are designed for the special working conditions of ultra-high temperature tunnel kiln arches, resulting in insufficient technical adaptability.

[0009] Chinese patent application CN111517765A, published on August 11, 2020, discloses a production process and equipment for high-purity corundum fused casting bricks. By optimizing the mixture preparation, melting process and casting parameters, it improves the product quality and production efficiency of corundum bricks. However, its technical solution only focuses on improving the production process and does not specify the key indicators such as the upper limit of high temperature resistance and creep resistance of the high-purity corundum fused casting bricks, nor does it mention whether the material is suitable for ultra-high temperature tunnel kiln environments.

[0010] Chinese patent application CN115368150A, published on November 22, 2022, discloses the composition and casting process of a low-stripping electrofused alumina brick. By adjusting the proportions of Al2O3, CaO, SiO2, and other components, the internal stress of the brick is reduced and the crack incidence is lowered. Its technical objective is to adapt to the high-temperature environment of the upper space of an all-oxygen combustion glass furnace. However, it differs significantly from the load-bearing and long-term creep resistance requirements of the arch of an ultra-high temperature tunnel kiln and has no direct technical reference value.

[0011] Chinese patent application CN117362015A, published on January 9, 2024, discloses a high-purity corundum brick and its preparation method. By introducing components such as P2O5, B2O3, and Cr2O3, the flexural strength, thermal shock resistance, and glass erosion resistance of the brick are optimized. Its application scenario is clearly defined as the cooling section and clarification section of glass kilns, which is not compatible with the high-temperature firing zone of ultra-high temperature tunnel kilns.

[0012] Chinese patent application CN104529488A, published on April 22, 2015, discloses a high-strength, thermally shock resistant, lightweight, heat-insulating refractory brick and its preparation method. It uses mullite aggregate, nano-SiO2 powder and other raw materials, and is adapted to the thermal shock environment of the cooling zone of ceramic roller kiln. Its firing temperature is only 1550℃, which is far lower than the operating temperature of 1750~1950℃ of ultra-high temperature tunnel kiln, and cannot meet the high-temperature performance requirements.

[0013] Chinese patent application CN119551994A, published on March 4, 2025, discloses a dense, crack-resistant fused zirconia-corundum brick. It improves crack resistance by adding ZrO2, Nb2O5, MnO2 and other components. However, it does not explain the mechanism of action of Nb2O5, MnO2 and other components. Furthermore, MnO2 and CuO have contradictory effects of oxidation decolorization and staining under the erosion of glass melt. At the same time, the material is not designed for the creep resistance and high load softening temperature requirements of ultra-high temperature tunnel kilns.

[0014] Chinese patent application CN119390431A, published on April 8, 2025, discloses a dispersion permeable refractory brick made of silicon / titanium coated corundum particles as raw material, suitable for argon blowing treatment of molten steel, with a calcination temperature of 1500℃, which is very different from the temperature range of ultra-high temperature tunnel kilns and has no technical reference value.

[0015] In summary, there are currently no patent applications for alumina corundum bricks specifically designed for the arch of ultra-high temperature tunnel kilns. Conventional high-temperature refractory materials cannot meet the long-term stable use requirements of the arch of the firing zone in ultra-high temperature tunnel kilns due to insufficient upper limit of high temperature resistance, poor creep resistance, and low structural stability. There is an urgent need to develop a special alumina corundum brick with high load softening temperature, low creep rate, and high temperature strength to fill the technological gap in the industry. Summary of the Invention

[0016] In view of the shortcomings of the prior art, the purpose of this invention is to provide an alumina corundum brick for the arch of an ultra-high temperature tunnel kiln, which can work stably for a long time and is suitable for the arch of the high-temperature firing zone of an ultra-high temperature tunnel kiln.

[0017] Another objective of this invention is to provide a method for preparing alumina corundum bricks for the arch of an ultra-high temperature tunnel kiln. The resulting alumina corundum bricks have a bulk density increased by more than 8.5%, a compressive strength increased by more than 20%, a high-temperature flexural strength increased by more than 80%, a creep reduction of 40%, and a load softening start temperature increased by 100°C.

[0018] This invention is achieved using the following technical solution:

[0019] The aforementioned alumina corundum bricks for the arch of ultra-high temperature tunnel kilns comprise the following chemical composition by mass fraction:

[0020] Al2O3: 97.5-98.2%;

[0021] Nb2O5: 0.1-0.3%;

[0022] K2O: 0.2-0.42%;

[0023] Li2O: 0.3-0.7%;

[0024] The remainder consists of unavoidable impurities. These impurities include SiO2, CaO, Fe2O3, TiO2, and Na2O.

[0025] Preferably, the alumina corundum brick has an Al2O3 content of 97.75%, an Nb2O5 content of 0.2%, a K2O content of 0.3%, and a Li2O content of 0.5%.

[0026] The α-phase conversion rate of the Al2O3 raw material is ≥92%, and the Al2O3 content is ≥99.0%.

[0027] The Nb2O5 raw material has a purity of ≥99.9% and a particle size of 100nm.

[0028] The raw material for the Li2O is lithium carbonate with a purity of ≥99.0% and a particle size of 300 mesh.

[0029] Alumina corundum bricks have a high-temperature flexural strength ≥15MPa at 1400℃; creep rate ≤0.3% under the condition of 1550℃ and heat preservation for 50h; and load softening start temperature T0.6 ≥1800℃.

[0030] The preparation method of the alumina corundum brick for the arch of the ultra-high temperature tunnel kiln includes the following steps:

[0031] (1) Mixing raw materials: Mix alumina powder, potassium carbonate and lithium carbonate in a certain proportion;

[0032] (2) Melting: The mixture is fed into a three-phase electric arc furnace, and the electrode position and current are controlled in stages:

[0033] Within 0-50 minutes after the raw material is added, the electrode is positioned above the raw material and close to the surface, with a current of 4200-5200A, and the raw material is continuously piled up around the electrode.

[0034] Within 50-90 minutes, bury the electrode below the liquid surface, with a current of 4500-6000A, and the electrode burying depth is not less than 30mm;

[0035] Then, the electrodes are raised to the surface of the liquid and placed close to the surface of the liquid. The current is 2800-3500A, and the temperature between the three electrodes is controlled to be no lower than 2060℃.

[0036] (3) Casting: The molten material is cast into a Y-shaped mold structure. The mold material is plate-shaped corundum, white corundum or black lead. The mold shape is Y-shaped and has a riser. The casting temperature is not lower than 1990℃ and the casting speed is not lower than 50kg / s. During the casting process, niobium pentoxide powder is added to the molten material through the furnace nozzle structure. The furnace nozzle structure is the furnace nozzle structure of patent CN220867269U.

[0037] (4) Re-casting: After casting, wait 3-10 minutes, break the surface of the riser and re-cast. For bricks weighing more than 800kg, re-cast twice;

[0038] (5) Annealing: After casting, cover the upper surface with alumina powder, and anneal naturally until the surface temperature is below 50°C. Then remove the product and process it.

[0039] In step (4), during the recasting process, wait 3 minutes for weights below 300kg, 6 minutes for weights between 300-800kg, and 10 minutes for weights above 800kg.

[0040] In step (2), the electrode is buried 30-60 mm below the liquid surface.

[0041] In step (3), the casting speed is 50-60 kg / s.

[0042] The Y-shaped mold structure is cast from the top and includes an outer sand mold, an inner product section, and a material cutting section, with the product section located below the material cutting section.

[0043] The two-layer mold structure includes an outer sand mold, an inner product section and a material cutting section. The product section is located below the material cutting section, and a pouring gate is located above the material cutting section.

[0044] Compared with the prior art, the beneficial effects of the present invention are:

[0045] (1) The alumina corundum brick prepared by the present invention has high compressive strength at room temperature and high flexural strength at high temperature. The compressive strength at room temperature is ≥240MPa and the flexural strength at high temperature is ≥15MPa, which is more than 30% higher than that of ordinary materials.

[0046] (2) The alumina corundum brick prepared by the present invention has a low creep rate. At 1550℃, the creep rate is ≤0.3% under the condition of heat preservation for 50h. The load softening temperature is high, and the load softening start temperature is ≥1800℃.

[0047] (3) The alumina corundum brick prepared by the present invention has a very high resistivity, with a resistivity ≥1000Ω·cm at 1600℃, and has a wider range of applications. Attached Figure Description

[0048] Figure 1 This is a front view of the Y-shaped mold structure of the present invention;

[0049] Figure 2 This is a side view of the Y-shaped mold structure of the present invention;

[0050] Figure 3 This is a top view of the Y-shaped mold structure of the present invention;

[0051] Figure 4 This is a front view of the two-layer mold structure of the present invention;

[0052] Figure 5 This is a side view of the two-layer mold structure of the present invention;

[0053] Figure 6 This is a top view of the two-layer molding sand mold structure of the present invention;

[0054] In the diagram: 1. Sand mold; 2. Product part; 3. Material cut-off part; 4. Pouring port. Detailed Implementation

[0055] To make the objectives and technical solutions of this invention clearer, the invention will be further described in detail below.

[0056] Unless otherwise specified, all raw materials used in the examples were commercially available.

[0057] The alumina raw material is alumina from Sumitomo Chemical Co., Ltd. of Japan, with the grade A. 210 calcined alumina; potassium carbonate is Qinghai Salt Lake Co., Ltd.'s superior grade type I potassium carbonate; niobium pentoxide and lithium oxide raw materials are Beijing Deco Island Gold Technology Co., Ltd.'s nano niobium pentoxide and Xinjiang Haoxin Lithium Salt Development Co., Ltd.'s industrial-grade lithium carbonate, respectively. Tabular corundum is from Jiangsu Jingxin New Materials Co., Ltd.'s tabular corundum. White corundum is from Shandong Ruishi Abrasive Materials Co., Ltd.

[0058] The α-phase conversion rate of the alumina raw material is ≥92%, and the Al2O3 conversion rate is ≥99.0%.

[0059] The niobium pentoxide has a purity of ≥99.9% and a particle size of 100 nm.

[0060] The lithium carbonate has a purity of ≥99.0% and a particle size of 300 mesh.

[0061] Tabular corundum and white corundum have Al2O3 ≥ 99%.

[0062] The chemical composition (mass fraction) of the alumina corundum bricks prepared in Examples 1-4 and Comparative Examples 1-4 is shown in Table 1.

[0063] like Figure 1-3 As shown, the Y-shaped mold structure is cast from the top and includes an outer sand mold 1, an inner product part 2, and a material cutting part 3. The product part 2 is located below the material cutting part 3.

[0064] like Figure 4-6 As shown, the two-layer mold structure includes an outer sand mold 1, an inner product part 2 and a material cutting part 3. The product part 2 is located below the material cutting part 3, and a pouring port 4 is provided above the material cutting part 3.

[0065] The burner nozzle structure is based on patent CN220867269U: a novel combined burner nozzle, including a base, a supporting outer frame fixedly connected to the base, a burner nozzle fixedly connected to the supporting outer frame, a supporting plate mounted on the supporting outer frame, mounting holes on the supporting plate, a storage tank installed in the mounting holes, a feeding port on the storage tank, a screen fixedly connected to the bottom of the storage tank with sieve holes, and the feeding port communicating with the sieve holes. The storage tank is a frustum-shaped funnel, wider at the top and narrower at the bottom, with the feeding port facing upwards. The screen and the storage tank are integrally formed. The length of the supporting outer frame is greater than half the length of the burner nozzle, and the length of the burner nozzle is not less than the length of the supporting outer frame. Cooling pipes are staggered and connected to both sides of the supporting outer frame. An arc-shaped groove is provided in the middle of the upper end of the base, and both the supporting outer frame and the burner nozzle are arc-shaped plates. The outer side of the supporting outer frame fits into the arc-shaped groove, and the outer side of the burner nozzle fits into the inner side of the supporting outer frame. The base is plate-shaped, with the length of the burner nozzle perpendicular to the surface of the base plate. The length of the support plate is perpendicular to the length of the burner nozzle. An arc-shaped clamp is fixed to the lower side of the support frame, with both ends of the arc-shaped clamp connected to the support plate. An arc-shaped limiting plate is fixedly connected to the inner end of the burner nozzle. One axial side of the arc-shaped limiting plate is flush with the side of the base, and the other side is fitted against the support frame, with the arc-shaped side of the limiting plate fitting against the base.

[0066] Example 1

[0067] The preparation method of the alumina corundum brick for the arch of the ultra-high temperature tunnel kiln includes the following steps:

[0068] (1) Mix 96.76wt% alumina powder, 1.1% limestone, 1.1% silica sand, 0.61% lithium carbonate and 0.3% potassium carbonate and then put them into a three-phase electric arc furnace;

[0069] (2) After the raw materials are added, the electrodes are placed above the raw materials and close to the surface of the raw materials. The current is 4200A. During this period, the raw materials need to be continuously piled up around the electrodes with a black lead shovel. Then continue melting for 90 minutes. During this period, the electrodes are buried below the surface of the liquid material. The current is 4500A and the depth of the electrodes buried below the surface of the liquid material is 30mm. Then the electrodes are raised above the surface of the liquid material and close to the surface of the liquid material. The current is 3500A. The temperature of the middle position of the three electrodes is measured to be 2060℃ using an infrared thermal imager. The melting operation is completed when the surface of the liquid material in the furnace is bright.

[0070] (3) After melting is complete, power is cut off for 3 minutes for clarification and cooling, and then casting begins;

[0071] (4) The molten material is poured into a Y-shaped mold structure. The mold material is plate-shaped corundum. The casting temperature is 1990℃ and the casting speed is 50kg / s. During the casting process, 0.1% of niobium pentoxide powder, which accounts for 0.1% of the total weight of the raw material, is added to the molten material through the furnace nozzle structure. After casting is completed, wait for 5 minutes, then break the surface of the riser and recast.

[0072] (5) After casting, cover the upper surface with alumina powder and perform natural annealing and heat preservation. When the surface temperature is below 50°C, take out the product and process it to obtain the final alumina corundum brick.

[0073] Example 2

[0074] The preparation method of the alumina corundum brick for the arch of the ultra-high temperature tunnel kiln includes the following steps:

[0075] (1) Mix 96.81wt% alumina powder, 0.83% limestone, 0.85% silica sand, 0.72% lithium carbonate and 0.33% potassium carbonate and put them into a three-phase electric arc furnace.

[0076] (2) After the raw materials are added, the electrodes are placed above the raw materials and close to the surface of the raw materials. The current is 4600A. During this period, the raw materials need to be continuously piled up around the electrodes with a black lead shovel. Then continue melting for 90 minutes. During this period, the electrodes are buried below the surface of the liquid material. The current is 5000A and the depth of the electrodes buried below the surface of the liquid material is 40mm. Then the electrodes are raised above the surface of the liquid material and close to the surface of the liquid material. The current is 3200A. The temperature of the middle position of the three electrodes is measured to be 2100℃ using an infrared thermal imager. The melting operation is completed when the surface of the liquid material in the furnace is bright.

[0077] (3) After melting is complete, power is cut off for 4 minutes for clarification and cooling, and then casting begins;

[0078] (4) The molten material is poured into the Y-shaped mold structure. The mold material is white corundum, the casting temperature is 2050℃, and the casting speed is 52kg / s. During the casting process, 0.15% of niobium pentoxide powder, which accounts for 0.15% of the total weight of the raw material, is added to the molten material through the furnace nozzle structure. After casting is completed, wait for 5 minutes, then break the surface of the riser and recast.

[0079] (5) After casting, cover the upper surface with alumina powder and perform natural annealing and heat preservation. When the surface temperature is below 50°C, take out the product and process it to obtain the final alumina corundum brick.

[0080] Example 3

[0081] The preparation method of the alumina corundum brick for the arch of the ultra-high temperature tunnel kiln includes the following steps:

[0082] (1) Mix 96.74wt% alumina powder, 0.8% limestone, 0.8% silica sand, 1.01% lithium carbonate and 0.45% potassium carbonate and put them into a three-phase electric arc furnace.

[0083] (2) After the raw materials are put in, the electrodes are placed above the raw materials and close to the surface of the raw materials. The current is 4800A. During this period, the raw materials need to be continuously piled up around the electrodes with a black lead shovel. Continue melting for 90 minutes. During this period, the electrodes are buried below the surface of the liquid material. The current is 5500A and the depth of the electrodes buried below the surface of the liquid material is 50mm. Then the electrodes are raised above the surface of the liquid material and close to the surface of the liquid material. The current is 3000A. The temperature of the middle position of the three electrodes is measured to be 2150℃ using an infrared thermal imager. The melting operation is completed when the surface of the liquid material in the furnace is bright.

[0084] (3) After melting is complete, power is turned off for 5 minutes to clarify and cool, and then casting begins;

[0085] (4) The molten material is poured into the Y-shaped mold structure. The mold material is black lead, the casting temperature is 2030℃, and the casting speed is 60kg / s. During the casting process, 0.2% of niobium pentoxide powder, which accounts for 0.2% of the total weight of the raw material, is added to the molten material through the furnace nozzle structure. After casting is completed, wait for 10 minutes, then break the surface of the riser and recast.

[0086] (5) After casting, cover the upper surface with alumina powder and perform natural annealing and heat preservation. When the surface temperature is below 50°C, take out the product and process it to obtain the final alumina corundum brick.

[0087] Example 4

[0088] The preparation method of the alumina corundum brick for the arch of the ultra-high temperature tunnel kiln includes the following steps:

[0089] (1) Mix 96.91wt% alumina powder, 0.35% limestone, 0.39% silica sand, 1.42% lithium carbonate and 0.6% potassium carbonate and put them into a three-phase electric arc furnace.

[0090] (2) After the raw materials are added, the electrodes are placed above the raw materials and close to the surface of the raw materials. The current is 5200A. During this period, the raw materials need to be continuously piled up around the electrodes with a black lead shovel. Continue melting for 90 minutes. During this period, the electrodes are buried below the surface of the liquid material. The current is 6000A and the depth of the electrodes buried below the surface of the liquid material is 60mm. Then the electrodes are raised above the surface of the liquid material and close to the surface of the liquid material. The current is 2800A. The temperature of the middle position of the three electrodes is measured to be 2200℃ using an infrared thermal imager. The melting operation is completed when the surface of the liquid material in the furnace is bright.

[0091] (3) After melting is complete, power is turned off for 5 minutes to clarify and cool, and then casting begins;

[0092] (4) The molten material is poured into a Y-shaped mold structure. The mold material is black lead, the casting temperature is 2080℃, and the casting speed is 56kg / s. During the casting process, 0.3% of niobium pentoxide powder, which accounts for 0.3% of the total weight of the raw material, is added to the molten material through the furnace nozzle structure. After casting is completed, wait for 8 minutes, then break the surface of the riser and recast. After the surface cools, break the surface of the riser again and recast for the third time.

[0093] (5) After casting, cover the upper surface with alumina powder and perform natural annealing and heat preservation. When the surface temperature is below 50°C, take out the product and process it to obtain the final alumina corundum brick.

[0094] The typical composition uses alumina and alkali powder, with a weight ratio of 92.76% and 3.89%, respectively. The alkali powder used is heavy alkali powder from Shandong Jinjing. It is an α-β fused cast corundum brick produced by Zibo Aijiexu Corundum Materials Co., Ltd., with the grade ZM-G.

[0095] Comparative Example 1

[0096] The preparation method of alumina corundum bricks differs from that in Example 1 in that the sand mold adopts a two-layer mold structure. The proportions of each raw material are as follows: 96.89 wt% alumina powder, 0.9% limestone, 1.17% silica sand, 0.59% lithium carbonate, 0.31% potassium carbonate, and 0.12% niobium pentoxide.

[0097] Comparative Example 2

[0098] The preparation method of the alumina corundum brick differs from that in Example 2 in that, during the melting process from 50 to 90 minutes, the electrodes are placed close to the surface of the liquid material, and the current is 6000A. After 90 minutes, the current is controlled at 3200A, and the temperature at the middle position of the three electrodes is measured to be 2060℃ using an infrared thermal imager. The proportions of the raw materials are as follows: 96.85wt% alumina powder, 0.8% limestone, 0.77% silica sand, 0.72% lithium carbonate, 0.64% potassium carbonate, and 0.18% niobium pentoxide.

[0099] Comparative Example 3

[0100] The preparation method of alumina corundum bricks differs from that in Example 3 in that the casting speed is 40 kg / s. The proportions of each raw material are as follows: 96.87 wt% alumina powder, 0.7% limestone, 0.71% silica sand, 1% lithium carbonate, 0.48% potassium carbonate, and 0.23% niobium pentoxide.

[0101] Comparative Example 4

[0102] The preparation method of alumina corundum bricks differs from that in Example 4 in that no recasting is performed after the initial casting. The proportions of each raw material are as follows: 97.08 wt% alumina powder, 0.38% limestone, 0.34% silica sand, 1.38% lithium carbonate, 0.57% potassium carbonate, and 0.25% niobium pentoxide.

[0103] The dimensions of the cast sample bricks used in the examples and comparisons conform to JC / T494. The dimensions specified in the 2013 standard are as follows: the sample brick size is 300mm (length) × 200mm (width) × 300mm (height), and the analytical sample size is 150mm (length) × 100mm (width) × 120mm (height).

[0104] Table 1: Chemical composition (mass fraction) of alumina corundum bricks prepared in Examples 1-4 and Comparative Examples 1-4

[0105]

[0106] Example 1 above 4 and Comparative Example 1 4. The prepared alumina corundum bricks were tested according to GB / T2997 for bulk density, GB / T5072 for compressive strength, GB / T3002 for high-temperature flexural strength, GB / T5073 for creep, and GB / T5989 for load softening temperature. Resistivity was measured by drilling a Φ30mm circular sample from the specimen and using a three-terminal method based on the Wheatstone bridge principle at a frequency of 120Hz and a temperature of 1600℃. The performance test results of the alumina corundum bricks prepared in Examples 1-4 and Comparative Examples 1-4 are shown in Table 2.

[0107] Table 2 Performance test results of alumina corundum bricks prepared in Examples 1-4 and Comparative Examples 1-4

[0108]

[0109] As shown in Table 2, the Y-shaped alumina corundum brick exhibits higher bulk density, compressive strength, and high-temperature flexural strength compared to the two-layer design. Similarly, alumina corundum bricks using a casting speed of ≥50 kg / s, submerged arc melting, and recasting after casting also show significantly better performance in all aspects compared to those using a speed lower than 50 kg / s, non-submerged arc melting, and no recasting. Compared to conventional alumina cast bricks, the alumina corundum bricks prepared in this embodiment of the invention show an increase in bulk density of over 8.5%, a increase in compressive strength of over 20%, an increase in high-temperature flexural strength of over 80%, a decrease in creep of 40%, a 100-fold increase in the load softening initiation temperature, and a 100-fold increase in resistivity at 1600℃. Because molten alumina undergoes a 25% volume shrinkage during solidification and solidifies very quickly, it needs to be re-injected as soon as possible to replenish the required amount of molten alumina. The weight of the replenished molten alumina must also meet the requirements (Y-type sand mold design better meets these requirements), and rapid casting is used to address the fast solidification speed. Lithium carbonate, like Na₂O, K₂O, and Al₂O₃, forms a β-corundum phase such as R₂O·11Al₂O₃. However, due to the different shapes and particle sizes of the two β-corundum phases, a denser cross-shaped structure can be formed, promoting microstructure densification. Niobium pentoxide has two functions: first, it acts as a nucleating agent to refine the product's crystal grain size; second, after melting, it enters the glass, forming two coordination states, [NbO₄] and [NbO₆], within the glass structure, creating Nb-O-Si and Nb=O double bonds. These structures all possess high-temperature stability, thereby improving the product's high-temperature performance.

Claims

1. An alumina corundum brick for the arch roof of an ultra-high temperature tunnel kiln, characterized in that, Chemical composition including the following mass fractions: Al2O3: 97.5-98.2%; Nb2O5: 0.1-0.3%; K2O: 0.2-0.42%; Li2O: 0.3-0.7%; The remainder are unavoidable impurities; Alumina corundum bricks have a high-temperature flexural strength ≥15MPa at 1400℃; creep rate ≤0.3% under the condition of 1550℃ and heat preservation for 50h; and load softening start temperature T0.6 ≥1800℃. The preparation method of the alumina corundum brick for the arch of the ultra-high temperature tunnel kiln includes the following steps: (1) Mixing raw materials: Mix alumina powder, potassium carbonate and lithium carbonate in a certain proportion; (2) Melting: The mixture is fed into a three-phase electric arc furnace, and the electrode position and current are controlled in stages: Within 0-50 minutes after the raw material is added, the electrode is positioned above the raw material and close to the surface, with a current of 4200-5200A, and the raw material is continuously piled up around the electrode. Within 50-90 minutes, bury the electrode below the liquid surface, with a current of 4500-6000A, and the electrode burying depth is not less than 30mm; Then, the electrodes are raised to the surface of the liquid and placed close to the surface of the liquid. The current is 2800-3500A, and the temperature between the three electrodes is controlled to be no lower than 2060℃. (3) Casting: The molten material is cast into the Y-shaped mold structure. The mold material is plate-shaped corundum, white corundum or black lead. The mold shape is a riser shape. The casting temperature is not lower than 1990℃ and the casting speed is not lower than 50kg / s. During the casting process, Nb2O5 powder is added to the molten material through the furnace nozzle structure. (4) Re-casting: After casting, wait 3-10 minutes, break the surface of the riser and re-cast. For bricks weighing more than 800kg, re-cast twice; (5) Annealing: After casting, cover the upper surface with alumina powder, and anneal naturally until the surface temperature is below 50°C. Then remove the product and process it.

2. The alumina corundum brick for the arch of an ultra-high temperature tunnel kiln according to claim 1, characterized in that, The α-phase conversion rate of the Al2O3 raw material is ≥92%, and the Al2O3 content is ≥99.0%.

3. The alumina corundum brick for the arch of an ultra-high temperature tunnel kiln according to claim 1, characterized in that, The Nb2O5 raw material has a purity of ≥99.9% and a particle size of 100nm.

4. The alumina corundum brick for the arch of an ultra-high temperature tunnel kiln according to claim 1, characterized in that, The raw material for the Li2O is lithium carbonate with a purity of ≥99.0% and a particle size of 300 mesh.

5. The method for preparing alumina corundum bricks for the arch of an ultra-high temperature tunnel kiln according to claim 1, characterized in that, In step (2), the electrode is buried 30-60 mm below the liquid surface.

6. The method for preparing alumina corundum bricks for the arch of an ultra-high temperature tunnel kiln according to claim 1, characterized in that, In step (3), the casting speed is 50-60 kg / s.

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