Method for producing sintered corundum

Abstract

The invention discloses a method for producing sintered corundum, and relates to the technical field of sintered corundum preparation methods, and the method comprises the following preparation methods: S1, raw material preparation; s2, raw material pretreatment; s3, mixing the raw materials; s4, forming and drying; s5, sintering process; s6, strengthening treatment; and S7, classified screening. The high-alumina bauxite and the iron additive are respectively subjected to deep purification treatment, so that impurities and oxide layers on the surfaces of the raw materials are effectively removed, the introduction amount of the impurities in the sintering process is remarkably reduced, and the purity and compactness of the sintered corundum are improved; reinforcing fibers and a surface modifier are introduced in the raw material mixing stage, so that the internal binding force of the mixture is enhanced, the cracking phenomenon of a green body in the forming and sintering processes is avoided, and meanwhile, the mechanical strength of the corundum material is improved; the green bodies are stacked in a staggered arrangement manner, so that more uniform heat distribution in the sintering process is ensured, sufficient reaction among raw materials is promoted, and the sintering efficiency is improved.

Description

Technical Field

[0001] This invention relates to the technical field of sintered corundum preparation methods, specifically a method for producing sintered corundum. Background Technology

[0002] With the continuous development of refractory material technology, sintered corundum, as an important high-temperature material, is increasingly widely used in industrial fields. However, existing sintered corundum production methods still have certain shortcomings in raw material processing, process optimization, and product performance improvement, which limit its further promotion and application.

[0003] In Chinese patent CN101260004B, titled "A Method for Producing Sintered Brown Fused Alumina," the sintered brown fused alumina produced using this method has a comparable aluminum content, good thermal shock stability, and a cost only 37% of that of existing fused brown fused alumina. The sintered brown fused alumina produced using this method has α-Al₂O₃ as its main crystalline phase, a bluish-black cross-section, a dense texture, and regularly developed grains, most of which are above 10 μm, making it a very high-quality refractory raw material. However, the above method does not adequately treat the sintering material, and the clay minerals in the bauxite byproducts are not effectively removed. These minerals do not adhere to carbon materials and iron filings, causing the iron filings to oxidize and form rust. Upon heating, the rust forms black impurities, affecting the quality of the sintered brown fused alumina. Brown fused alumina made from conventional materials contains more impurities, has lower adhesion, and is prone to breakage during use, which is detrimental to its service life. When block blanks are directly fired, the heating uniformity is low, the sintering is incomplete, the material reaction is insufficient, and the proportion of brown fused alumina produced is small, resulting in material waste. In addition, if the sintered brown fused alumina is not further processed, its hardness will not be significantly enhanced, affecting its wear resistance. Summary of the Invention

[0004] The purpose of this invention is to provide a method for producing sintered corundum to solve the technical problems mentioned in the background section.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a method for producing sintered corundum, comprising the following preparation methods:

[0006] S1. Raw material preparation: Weigh out 30-50 parts of high-alumina bauxite, 1-3 parts of reducing agent, 20-40 parts of iron additive, 8-15 parts of flux, 3-7 parts of reinforcing fiber, and 10-20 parts of surface modifier by weight. The alumina content of the high-alumina bauxite is 60-70%, and the diameter of the reinforcing fiber is 5-10 μm and the length is 2-4 mm.

[0007] S2. Raw material pretreatment: The high-alumina bauxite is surface-purified and ground to a particle size of 80-200μm. The iron additives are surface-oxidized and ground to a particle size of 80-200μm. The reducing agent and flux are crushed to a particle size of 100-300μm respectively.

[0008] S3. Raw material mixing: Pretreated high-alumina bauxite, reducing agent, iron additive, and flux are added to the mixing equipment in sequence. Water is added for wet mixing. The mixing time is 2-4 hours to form a uniform slurry. Reinforcing fibers and surface modifiers are added to the slurry and mixed for 1-2 hours to form a viscous mixture.

[0009] S4. Molding and Drying: The mixture is injected into a mold and pressed into shape. The molding pressure is 10-20 MPa and the holding time is 5-10 min to form a sheet-like blank. The sheet-like blank is placed in a drying oven for drying. The drying temperature is 80-150℃ and the drying time is 10-20 h until the moisture content of the blank drops to below 1%.

[0010] S5. Sintering process: The dried sheet blanks are stacked in a sintering furnace in a specific manner. The stacking height is 1.2-1.8m, the stacking width is 1.2-1.8m, and the stacking length is 1.2-1.8m. The adjacent layers of blanks are arranged in an alternating manner. The sintering furnace is started to carry out the sintering operation. The sintering temperature is 1800-2200℃, and the sintering time is 2-4h.

[0011] S6. Strengthening treatment: The sintered corundum material is quickly transferred to a cooling liquid for rapid cooling. The temperature of the cooling liquid is 10-30℃ and the cooling time is 5-15 minutes. The cooled corundum material is then placed in a heating furnace for secondary heat treatment. The heat treatment temperature is 200-300℃ and the heat treatment time is 2-5 hours.

[0012] S7. Grading and screening: The reinforced corundum material is crushed to a particle size range of 0.5-10mm. The particles are then divided into five groups using a wind-powered sorting device: 0.5-1mm, 2-3mm, 4-5mm, 6-7mm, and 8-10mm. Each group of particles is collected separately for later use.

[0013] Preferably, the surface purification treatment of the high-alumina bauxite includes the following steps:

[0014] S2101. Crush high-alumina bauxite into block materials with a particle size of 5-8mm, and soak them in deionized water for 1-2 hours.

[0015] S2102. Place the soaked high-alumina bauxite into a vibrating screen for washing. The vibration frequency is 1500-2500 times / min, and the washing time is 20-40min.

[0016] S2103. Take out the cleaned high-alumina bauxite and dry it at 80-120℃. After drying, use high-pressure airflow to blow away the residual micro-dust particles on the surface.

[0017] S2104. Place the high-alumina bauxite in a high-temperature furnace and calcine it at a temperature of 1200-1500℃ for 1-2 hours. Then let it cool naturally to room temperature for later use.

[0018] The surface oxide layer removal process for iron additives includes the following steps:

[0019] S2201. Place the iron additive in a high-speed centrifuge and rotate it for friction at a speed of 3000-5000 r / min for 10-20 min.

[0020] S2202. Immerse the iron additive in a 5-10% dilute nitric acid solution for 1-2 hours. During the immersion process, start the ultrasonic generator every 20 minutes to oscillate the solution at a frequency of 20-40 kHz.

[0021] S2203. Remove the iron additive from the dilute nitric acid solution, rinse it repeatedly with deionized water until neutral, and dry it at 100-150℃.

[0022] S2204. Place the dried iron additive into a stirring device, add graphite powder and mix for 10-20 minutes to ensure that the graphite powder is evenly attached to the surface of the iron additive, then remove and set aside.

[0023] Preferably, the surface oxide layer removal treatment of the iron additive in S2 includes placing it in a high-speed centrifuge and rotating and rubbing it at a speed of 3000-5000 r / min for 10-20 min, then immersing it in a 5-10% dilute nitric acid solution for 1-2 h, during which an ultrasonic generator is activated every 20 min to oscillate at an oscillation frequency of 20-40 kHz, after which it is taken out, rinsed with deionized water until neutral, and dried at 100-150°C, and finally mixed with graphite powder for 10-20 min.

[0024] Preferably, when mixing the raw materials in S3, the mixing time for high-alumina bauxite, reducing agent, iron additive, and flux is 2-4 hours, and the mixing time for reinforcing fiber and surface modifier is 1-2 hours.

[0025] Preferably, in S4, the sheet-like blank has a thickness of 8-12 mm, a length of 60-80 mm, a width of 20-30 mm, and a through hole with a diameter of 3-5 mm on its surface, with a hole spacing of 8-12 mm.

[0026] Preferably, the atmosphere inside the sintering furnace in S5 is an inert gas protective environment, with an inert gas flow rate of 5-10 L / min and an internal furnace pressure of 0.1-0.2 MPa;

[0027] When the sheet-like blanks in S5 are stacked, the staggered arrangement between adjacent layers of blanks makes the heat distribution more uniform.

[0028] Preferably, the coolant in S6 is an aqueous solution containing 0.5-1% nano-sized zirconia particles with a particle size of 20-50 nm.

[0029] Preferably, in the strengthening process of S6, the coolant is used to alter the microstructure of the corundum material by embedding nano-sized zirconia particles into the surface of the corundum material.

[0030] Preferably, the wind speed of the wind-powered sorting device in S7 is 10-20 m / s, and the sorting time is 1-3 min.

[0031] Compared with the prior art, the beneficial effects of the present invention are:

[0032] By performing deep purification treatment on high-alumina bauxite and iron additives respectively, impurities and oxide layers on the surface of raw materials are effectively removed, significantly reducing the amount of impurities introduced during sintering and improving the purity and density of sintered corundum.

[0033] Introducing reinforcing fibers and surface modifiers during the raw material mixing stage enhances the internal bonding force of the mixture, avoids cracking of the green body during molding and sintering, and improves the mechanical strength of corundum material.

[0034] By optimizing the sintering process parameters, especially by using an alternating arrangement for stacking the green bodies, a more uniform heat distribution during the sintering process was ensured, which promoted a full reaction between the raw materials and improved the sintering efficiency.

[0035] The strengthening process uses a coolant containing nano-sized zirconium oxide particles, which not only achieves rapid cooling but also further enhances the hardness and wear resistance of corundum material through the embedding effect of nanoparticles.

[0036] The grading and screening process utilizes wind-powered sorting equipment, which can efficiently separate particles of different sizes, meeting the needs of diverse application scenarios and improving product utilization. Attached Figure Description

[0037] Figure 1This is a schematic diagram of the steps of the present invention;

[0038] Figure 2 This is a schematic diagram of the surface purification process of high-alumina bauxite according to the present invention;

[0039] Figure 3 This is a schematic diagram of the process for removing the surface oxide layer of the iron additive of the present invention. Detailed Implementation

[0040] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0041] Example 1:

[0042] A method for producing sintered corundum, characterized by comprising the following preparation method:

[0043] S1. Raw material preparation: Weigh out 30-50 parts of high-alumina bauxite, 1-3 parts of reducing agent, 20-40 parts of iron additive, 8-15 parts of flux, 3-7 parts of reinforcing fiber, and 10-20 parts of surface modifier by weight. The alumina content of the high-alumina bauxite is 60-70%, and the diameter of the reinforcing fiber is 5-10 μm and the length is 2-4 mm.

[0044] The size range of the raw materials is strictly selected to ensure good integration with other materials during subsequent mixing and molding. The selection of reducing agents and fluxes needs to be determined according to actual process requirements. For example, reducing agents can be carbon powder or coke, and fluxes can be materials such as borax or calcium fluoride.

[0045] S2. Raw material pretreatment: The high-alumina bauxite is surface-purified and ground to a particle size of 80-200μm. The iron additives are surface-oxidized and ground to a particle size of 80-200μm. The reducing agent and flux are crushed to a particle size of 100-300μm respectively.

[0046] Specifically, the surface purification treatment of the high-alumina bauxite includes the following steps:

[0047] S2101. Crush high-alumina bauxite into block materials with a particle size of 5-8mm, and soak them in deionized water for 1-2 hours.

[0048] S2102. Place the soaked high-alumina bauxite into a vibrating screen for washing. The vibration frequency is 1500-2500 times / min, and the washing time is 20-40min.

[0049] S2103. Take out the cleaned high-alumina bauxite and dry it at 80-120℃. After drying, use high-pressure airflow to blow away the residual micro-dust particles on the surface.

[0050] S2104. Place the high-alumina bauxite in a high-temperature furnace and calcine it at a temperature of 1200-1500℃ for 1-2 hours. Then let it cool naturally to room temperature for later use.

[0051] The surface oxide layer removal process for iron additives includes the following steps:

[0052] S2201. Place the iron additive in a high-speed centrifuge and rotate it for friction at a speed of 3000-5000 r / min for 10-20 min.

[0053] S2202. Immerse the iron additive in a 5-10% dilute nitric acid solution for 1-2 hours. During the immersion process, start the ultrasonic generator every 20 minutes to oscillate the solution at a frequency of 20-40 kHz.

[0054] S2203. Remove the iron additive from the dilute nitric acid solution, rinse it repeatedly with deionized water until neutral, and dry it at 100-150℃.

[0055] S2204. Place the dried iron additive into a stirring device, add graphite powder and mix for 10-20 minutes to ensure that the graphite powder is evenly attached to the surface of the iron additive, then remove and set aside.

[0056] The purpose of this process is to completely remove the oxide layer from the surface of the iron additives while avoiding the introduction of new sources of contamination.

[0057] S3. Raw material mixing: Pretreated high-alumina bauxite, reducing agent, iron additive, and flux are added to the mixing equipment in sequence. Water is added for wet mixing. The mixing time is 2-4 hours to form a uniform slurry. Reinforcing fibers and surface modifiers are added to the slurry and mixed for 1-2 hours to form a viscous mixture.

[0058] Furthermore, when the raw materials are mixed, the mixing time for high-alumina bauxite, reducing agent, iron additive, and flux is 2-4 hours, and the mixing time for reinforcing fiber and surface modifier is 1-2 hours.

[0059] Specifically, during the mixing process, high-alumina bauxite serves as the main substrate, and the uniformity of its particle distribution directly affects the density of the final product. Reducing agents and fluxes respectively regulate the reaction environment and lower the melting point; both must be fully dispersed during mixing to maximize their contact area with the high-alumina bauxite. Subsequently, reinforcing fibers and surface modifiers are added to the slurry and mixed for 1–2 hours until a viscous mixture is formed. The addition of reinforcing fibers creates a network structure within the mixture, improving the crack resistance of the green body during molding and sintering, while the surface modifier enhances the bonding force between raw materials by altering interfacial properties.

[0060] S4. Molding and Drying: The mixture is injected into a mold and pressed into shape. The molding pressure is 10-20 MPa and the holding time is 5-10 min to form a sheet-like blank. The sheet-like blank is placed in a drying oven for drying. The drying temperature is 80-150℃ and the drying time is 10-20 h until the moisture content of the blank drops to below 1%.

[0061] Furthermore, the sheet-like blank has a thickness of 8–12 mm, a length of 60–80 mm, a width of 20–30 mm, and through holes with a diameter of 3–5 mm are provided on the surface of the blank, with a hole spacing of 8–12 mm.

[0062] Specifically, the heating rate needs to be controlled during the drying process to prevent the green body from cracking due to excessive moisture evaporation.

[0063] S5. Sintering process: The dried sheet blanks are stacked in a sintering furnace in a specific manner. The stacking height is 1.2-1.8m, the stacking width is 1.2-1.8m, and the stacking length is 1.2-1.8m. The adjacent layers of blanks are arranged in an alternating manner. The sintering furnace is started to carry out the sintering operation. The sintering temperature is 1800-2200℃, and the sintering time is 2-4h.

[0064] It should be further noted that the specific stacking method involves an alternating arrangement between adjacent layers of billets. This stacking method can optimize heat distribution and reduce local overheating or uneven cooling.

[0065] The atmosphere inside the sintering furnace is an inert gas protective environment, with an inert gas flow rate of 5–10 L / min and an internal pressure of 0.1–0.2 MPa. The use of inert gas can effectively isolate oxygen and prevent unnecessary oxidation reactions of the raw materials at high temperatures.

[0066] S6. Strengthening treatment: The sintered corundum material is quickly transferred to a cooling liquid for rapid cooling. The temperature of the cooling liquid is 10-30℃ and the cooling time is 5-15 minutes. The cooled corundum material is then placed in a heating furnace for secondary heat treatment. The heat treatment temperature is 200-300℃ and the heat treatment time is 2-5 hours.

[0067] The coolant is an aqueous solution containing 0.5-1% nano-sized zirconia particles with a particle size of 20-50 nm.

[0068] During the strengthening process, the coolant is embedded in the surface of the corundum material through nano-sized zirconia particles to alter its microstructure.

[0069] During the cooling process, nanoparticles form an embedding effect on the surface of the corundum material, thereby improving its hardness and wear resistance. After cooling, the corundum material is placed in a heating furnace for secondary heat treatment. This stage mainly eliminates internal stresses that may have been generated during cooling and further stabilizes the microstructure of the material.

[0070] S7. Grading and screening: The reinforced corundum material is crushed to a particle size range of 0.5-10mm. The particles are then divided into five groups using a wind-powered sorting device: 0.5-1mm, 2-3mm, 4-5mm, 6-7mm, and 8-10mm. Each group of particles is collected separately for later use.

[0071] The wind speed of the wind-powered sorting equipment is 10-20 m / s, and the sorting time is 1-3 min.

[0072] During the sorting process, particles of different sizes are separated due to differences in force, thus achieving efficient classification. The results of grading and screening can meet the needs of diverse application scenarios while improving product utilization.

[0073] Example 2

[0074] S1. Raw material preparation: Weigh out 30 parts of high-alumina bauxite, 1 part of reducing agent, 20 parts of iron additive, 8 parts of flux, 3 parts of reinforcing fiber, and 10 parts of surface modifier by weight. The alumina content of the high-alumina bauxite is 60-70%, and the diameter of the reinforcing fiber is 5-10 μm and the length is 2-4 mm.

[0075] The remaining steps are the same as those in Example 1.

[0076] Example 3:

[0077] S1. Raw material preparation: Weigh out 45 parts by weight of high-alumina bauxite, 2 parts by weight of reducing agent, 30 parts by weight of iron additive, 11 parts by weight of flux, 5 parts by weight of reinforcing fiber, and 15 parts by weight of surface modifier. The alumina content of the high-alumina bauxite is 60-70%, and the diameter of the reinforcing fiber is 5-10 μm and the length is 2-4 mm.

[0078] The remaining steps are the same as those in Example 1.

[0079] Example 4:

[0080] S1. Raw material preparation: Weigh out 50 parts of high-alumina bauxite, 3 parts of reducing agent, 40 parts of iron additive, 15 parts of flux, 7 parts of reinforcing fiber, and 20 parts of surface modifier by weight. The alumina content of the high-alumina bauxite is 60-70%, and the diameter of the reinforcing fiber is 5-10 μm and the length is 2-4 mm.

[0081] The remaining steps are the same as those in Example 1.

[0082] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for producing sintered corundum, characterized in that, The preparation methods include the following: S1. Raw material preparation: Weigh out 30-50 parts of high-alumina bauxite, 1-3 parts of reducing agent, 20-40 parts of iron additive, 8-15 parts of flux, 3-7 parts of reinforcing fiber, and 10-20 parts of surface modifier by weight. The alumina content of the high-alumina bauxite is 60-70%, and the diameter of the reinforcing fiber is 5-10 μm and the length is 2-4 mm. S2. Raw material pretreatment: The high-alumina bauxite is surface-purified and ground to a particle size of 80-200μm. The iron additives are surface-oxidized and ground to a particle size of 80-200μm. The reducing agent and flux are crushed to a particle size of 100-300μm respectively. S3. Raw material mixing: Pretreated high-alumina bauxite, reducing agent, iron additive, and flux are added to the mixing equipment in sequence. Water is added for wet mixing. The mixing time is 2-4 hours to form a uniform slurry. Reinforcing fibers and surface modifiers are added to the slurry and mixed for 1-2 hours to form a viscous mixture. S4. Molding and Drying: The mixture is injected into a mold and pressed into shape. The molding pressure is 10-20 MPa and the holding time is 5-10 min to form a sheet-like blank. The sheet-like blank is placed in a drying oven for drying. The drying temperature is 80-150℃ and the drying time is 10-20 h until the moisture content of the blank drops to below 1%. S5. Sintering process: The dried sheet blanks are stacked in a sintering furnace in a specific manner. The stacking height is 1.2-1.8m, the stacking width is 1.2-1.8m, and the stacking length is 1.2-1.8m. The adjacent layers of blanks are arranged in an alternating manner. The sintering furnace is started to carry out the sintering operation. The sintering temperature is 1800-2200℃, and the sintering time is 2-4h. S6. Strengthening treatment: The sintered corundum material is quickly transferred to a cooling liquid for rapid cooling. The temperature of the cooling liquid is 10-30℃ and the cooling time is 5-15 minutes. The cooled corundum material is then placed in a heating furnace for secondary heat treatment. The heat treatment temperature is 200-300℃ and the heat treatment time is 2-5 hours. S7. Grading and screening: The reinforced corundum material is crushed to a particle size range of 0.5-10mm. The particles are then divided into five groups using a wind-powered sorting device: 0.5-1mm, 2-3mm, 4-5mm, 6-7mm, and 8-10mm. Each group of particles is collected separately for later use.

2. The method for producing sintered corundum according to claim 1, characterized in that: The surface purification treatment of the high-alumina bauxite includes the following steps: S2101. Crush high-alumina bauxite into block materials with a particle size of 5-8mm, and soak them in deionized water for 1-2 hours. S2102. Place the soaked high-alumina bauxite into a vibrating screen for washing. The vibration frequency is 1500-2500 times / min, and the washing time is 20-40min. S2103. Take out the cleaned high-alumina bauxite and dry it at 80-120℃. After drying, use high-pressure airflow to blow away the residual micro-dust particles on the surface. S2104. Place the high-alumina bauxite in a high-temperature furnace and calcine it at a temperature of 1200-1500℃ for 1-2 hours. Then let it cool naturally to room temperature for later use. The surface oxide layer removal process for iron additives includes the following steps: S2201. Place the iron additive in a high-speed centrifuge and rotate it for friction at a speed of 3000-5000 r / min for 10-20 min. S2202. Immerse the iron additive in a 5-10% dilute nitric acid solution for 1-2 hours. During the immersion process, start the ultrasonic generator every 20 minutes to oscillate the solution at a frequency of 20-40 kHz. S2203. Remove the iron additive from the dilute nitric acid solution, rinse it repeatedly with deionized water until neutral, and dry it at 100-150℃. S2204. Place the dried iron additive into a stirring device, add graphite powder and mix for 10-20 minutes to ensure that the graphite powder is evenly attached to the surface of the iron additive, then remove and set aside.

3. The method for producing sintered corundum according to claim 1, characterized in that: The surface oxide layer removal treatment of the iron additive in S2 includes placing it in a high-speed centrifuge and rotating and rubbing it at a speed of 3000-5000 r / min for 10-20 min, then immersing it in a 5-10% dilute nitric acid solution for 1-2 h. During the immersion process, an ultrasonic generator is activated every 20 min to oscillate at a frequency of 20-40 kHz. After removal, it is rinsed with deionized water until neutral and dried at 100-150℃. Finally, it is mixed with graphite powder for 10-20 min.

4. The method for producing sintered corundum according to claim 1, characterized in that: When mixing the raw materials in S3, the mixing time for high-alumina bauxite, reducing agent, iron additive, and flux is 2-4 hours, and the mixing time for reinforcing fiber and surface modifier is 1-2 hours.

5. A method for producing sintered corundum according to claim 1, characterized in that: The sheet-like blank in S4 has a thickness of 8-12 mm, a length of 60-80 mm, and a width of 20-30 mm. The surface of the blank is provided with through holes with a diameter of 3-5 mm and a hole spacing of 8-12 mm.

6. The method for producing sintered corundum according to claim 1, characterized in that: The atmosphere inside the sintering furnace in S5 is an inert gas protective environment, with an inert gas flow rate of 5-10 L / min and an internal pressure of 0.1-0.2 MPa. When the sheet-like blanks in S5 are stacked, the staggered arrangement between adjacent layers of blanks makes the heat distribution more uniform.

7. A method for producing sintered corundum according to claim 1, characterized in that: The coolant in S6 is an aqueous solution containing 0.5-1% nano-sized zirconia particles with a particle size of 20-50 nm.

8. A method for producing sintered corundum according to claim 1, characterized in that: In the strengthening process of S6, the coolant is used to alter the microstructure of the corundum material by embedding nano-sized zirconia particles into its surface.

9. A method for producing sintered corundum according to claim 1, characterized in that: The wind speed of the wind-powered sorting device in S7 is 10-20 m / s, and the sorting time is 1-3 min.

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