Method for preparing high-temperature microcrystalline aluminum oxide from activated aluminum oxide

Abstract

The invention relates to a method for preparing high-temperature microcrystalline aluminum oxide by using activated aluminum oxide, which comprises the following steps: mixing a proper activated aluminum oxide raw material with water according to a certain proportion, adding a proper alkaline reagent to adjust the pH value of the mixture, and stirring for a certain time to obtain slurry; pumping the slurry into a pressure kettle, raising the temperature, keeping the temperature for a period of time at a certain temperature, and carrying out sufficient hydrothermal reaction; cooling the slurry subjected to the hydrothermal reaction, filtering and washing to obtain a wet filter cake of an intermediate product; feeding the wet filter cake into drying equipment for drying to obtain a dried intermediate product; and calcining the dried intermediate product to obtain the high-temperature microcrystalline alumina product. According to the method, sodium oxide can be prepared; the grain size is 1t; and moreover, equipment is universal and easy to purchase, the process method is simple, the overall production cost is low, and industrial application is facilitated.

Description

Technical Field

[0001] The present invention belongs to the technical field of special alumina production, and particularly relates to a method for preparing high-temperature microcrystalline alumina from activated alumina. Background Art

[0002] With the gradual improvement of the requirements for the performance of alumina in the fields of chip packaging, ceramic substrates, functional ceramics, refractory materials, grinding and polishing, etc., the requirements for the indicators of the raw materials themselves are also getting higher and higher, especially for the purity and primary crystal grain size of alumina. The traditional mineralizer or acid-washing and sodium-reducing calcination method cannot simultaneously meet the requirements of the product for sodium oxide, primary crystal grain size and crystal phase content. Other relatively advanced methods such as alcohol-aluminum hydrolysis method, metal-aluminum hydrothermal synthesis method and sol-gel method are difficult to achieve low-cost industrial production.

[0003] Prior Art Related to the Present Invention

[0004] 1. Technical solution of the prior art one (CN116081663 A)

[0005] Provide alumina raw materials, mix the alumina raw materials with a hydration slurry to obtain a first slurry; add a first acid agent for dissolving sodium oxide to the first slurry to obtain a second slurry; filter and wash the second slurry to obtain a first filter cake; calcine the first filter cake at a predetermined temperature, and obtain an alumina intermediate after cooling; mix the alumina intermediate with a hydration slurry to obtain a second slurry; stir, wash, filter and wash the second slurry to obtain a second filter cake; dry the second filter cake to obtain the low-sodium microcrystalline α-alumina. The present invention not only obtains microcrystalline α-alumina with sodium oxide < 0.02% and crystal grain size < 1 μm, but also compared with the traditional acid-washing and calcination method, only adds the steps of re-slurrying and washing and drying, and has relatively low production cost and simple process.

[0006] 2. Technical solution of the prior art two (CN114455619 A) Pretreat quartz sand to obtain pretreated quartz sand; mix the pretreated quartz sand and aluminum hydroxide raw materials to obtain a mixture; calcine the mixture to obtain low-sodium small primary α-alumina; wherein, by mass, the silicon content of the quartz sand is 97% - 99%, and the particle size D50 of the pretreated quartz sand is 0.10 μm - 0.15 μm; by adding a treated sodium-removing auxiliary agent, the purpose of producing calcined α-alumina for wear-resistant ceramics with sodium oxide less than 0.3% and primary crystal grain size less than 1.2 μm using ordinary high-sodium aluminum hydroxide can be achieved. Summary of the Invention

[0007] (I) Technical problems to be solved by the present invention (invention purpose) The object of the present invention is to solve the problems of cumbersome sodium reduction steps and relatively large primary crystal grain size of current microcrystalline α-aluminum oxide through a relatively simple hydrothermal process.

[0008] A method for preparing microcrystalline high-temperature aluminum oxide using activated alumina as a raw material, comprising the following steps: 1. Mix a suitable activated alumina raw material with water in a certain proportion, and add a suitable alkaline reagent to adjust the pH value of the mixture, and stir for a certain time to obtain a slurry; 2. Pump the slurry from step 1 into an autoclave for temperature increase, keep it at a certain temperature for a period of time, and conduct a sufficient hydrothermal reaction; 3. Cool the slurry after the reaction in step 2 and then filter and wash it to obtain a wet filter cake of the intermediate product; 4. Send the product from step 3 into a drying device for drying to obtain a dried intermediate product; 5. Calcinate the intermediate product obtained in step 4 to obtain the final product: microcrystalline high-temperature aluminum oxide.

[0009] 6. In the embodiments of the present invention, the activated alumina raw material in step 1 refers to alumina with a specific surface area of 100 - 400 m2 / g.

[0010] 7. In the embodiments of the present invention, the activated alumina raw material in step 1 is mixed with water in a certain proportion, wherein the mass of the mixing water is 3 - 6 times that of the raw material.

[0011] 8. In the embodiments of the present invention, the addition of a suitable alkaline reagent in step 1 refers to an alkaline reagent that can dissolve in water, including sodium hydroxide, sodium carbonate but not limited to the above two.

[0012] 9. In the embodiments of the present invention, the pH value of the mixture in step 1 is adjusted to 8 - 13.

[0013] 10. In the embodiments of the present invention, the activated alumina raw material and water in step 1 are mixed and stirred for a certain time of 10 - 40 minutes.

[0014] 11. In the embodiments of the present invention, the certain temperature in step 2 is 90 - 190 °C.

[0015] 12. In the embodiments of the present invention, the period of time in step 2 is 1 - 3 hours.

[0016] 13. In the embodiments of the present invention, the washing water in step 3 is demineralized water, and the dosage does not exceed 20 times the mass of the intermediate product.

[0017] 14. In an embodiment of the present invention, the drying temperature in step 4 does not exceed 300 °C. 15. In an embodiment of the present invention, the calcination temperature in step 5 is 1200 - 1600 °C.

[0018] 16. In an embodiment of the present invention, the calcination holding time in step 5 is 2 - 5 hours.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. Using hydrothermal reaction to hydrate and restructure the raw materials can fully release the impurities contained in the raw materials, and at the same time, the primary crystal grain size of the product is fundamentally refined.

[0020] 2. The sodium oxide content in the obtained high-temperature microcrystalline alumina product is < 0.02%, and the primary crystal grain size is < 0.3 μm.

[0021] 3. The equipment is commonly available and easy to purchase, the process method is simple, the overall production cost is low, and it is convenient for industrial application.

[0022] The technical key points and points to be protected of the present invention: The main technical key points of the present invention are: the selection of activated alumina raw materials, the mixing ratio of raw materials and water, and the adjustment of pH value, the temperature and time parameters of hydrothermal reaction, the filtration and washing requirements of the intermediate product after hydrothermal reaction, the calcination temperature and time parameters of the intermediate product, and the performance indicators of the microcrystalline high-temperature alumina obtained after calcination.

[0023] The main points to be protected are: the entire production process, including the raw material selection, the pH adjustment parameters of the slurry, the control parameters of hydrothermal reaction, the filtration and washing requirements of the intermediate product, the calcination parameters of the intermediate product, and the performance parameters of the product. Specific Embodiments

[0024] Example 1: A method for preparing high-temperature microcrystalline alumina using activated alumina, comprising the following steps: 1. Mix a suitable activated alumina raw material with water in a certain ratio, and add a suitable alkaline reagent to adjust the pH value of the mixture, and stir for a certain time to obtain a slurry; 2. Pump the slurry in step 1 into an autoclave to increase the temperature, keep it at a certain temperature for a period of time, and carry out a sufficient hydrothermal reaction; 3. Cool the slurry after the reaction in step 2 and then filter and wash it to obtain a wet filter cake of the intermediate product; 4. Send the product in step 3 into a drying device for drying to obtain a dry intermediate product; 5. Calcinate the intermediate product obtained in step 4 to obtain the final product: microcrystalline high-temperature alumina.

[0025] In step 1, activated alumina with a specific surface area of 100 - 400 m² / g is mixed with water in a mass ratio of 1:3 - 6, and an alkaline reagent such as sodium hydroxide or sodium carbonate is added to adjust the pH value to 8 - 13. Then, thorough stirring and mixing are carried out for 10 - 40 minutes to obtain a qualified slurry.

[0026] In this way, in an alkaline environment, the active components in the raw materials initially combine with water, but at a relatively slow rate. During the process of structural reorganization, the impurities therein will be released and dissolved in water. The pH value in step 1 should be adjusted according to the content of the active components in the raw materials.

[0027] Furthermore, the purpose of step 2 is to accelerate the combination rate of the raw materials with water. According to the pH value parameter of the slurry in step 1, the hydrothermal reaction temperature in step 2 is controlled at 90 - 190 °C, and the reaction time is controlled at 1 - 3 hours. By measuring the pH value of the slurry after hydrothermal treatment, the degree of the hydrothermal reaction can be determined.

[0028] In this way, the addition amount of the alkaline reagent in step 1 can be adjusted according to the pH value of the slurry after hydrothermal treatment, avoiding excessive consumption.

[0029] Furthermore, in step 3, the intermediate product needs to be washed with demineralized water. The qualification of the intermediate product is determined according to the pH value of the washing water, and the washing water consumption is controlled within 20 times the mass of the intermediate product.

[0030] In this way, according to the sequence of multiple washings, the wash water at different stages can be collected and reused, which can reduce the total amount of wash water, while ensuring the impurity removal effect and efficiency, and ensuring that the sodium oxide mass content of the product is < 0.02%.

[0031] Furthermore, the intermediate product in step 4 is a hydrate of alumina. To avoid changes in its chemical composition, the drying temperature needs to be controlled within 300 °C according to the chemical composition.

[0032] In this way, not only can the quality of the intermediate product be ensured to be stable, but also an increase in drying cost can be avoided.

[0033] Furthermore, to control the crystal phase content and primary crystal grain size of the product, the calcination temperature in step 5 is controlled at 1200 - 1600 °C, and the high-temperature section calcination time is controlled at 2 - 5 hours.

[0034] In this way, according to different requirements for the α-phase content and primary crystal grain size of the product, the calcination temperature and time can be adjusted within the above range to ensure that the sodium oxide mass content of the high-temperature microcrystalline alumina obtained in step 5 is < 0.02% and the primary crystal grain size is < 0.3 μm. Description of the Drawings To more clearly illustrate the technical solutions in the embodiments of the present invention, the following will briefly introduce the accompanying drawings required in the embodiments. Obviously, for those of ordinary skill in the art, without creative efforts, other accompanying drawings can also be obtained based on these drawings. Figure 1 It is a schematic flow chart of a method for preparing high-temperature microcrystalline alumina using activated alumina provided by an embodiment of the present invention.

Claims

1. A method for preparing high-temperature microcrystalline alumina using activated alumina, characterized in that, The method includes: Mixing a suitable activated alumina raw material with water in a certain proportion, adding a suitable alkaline reagent to adjust the pH value of the mixture, and stirring for a certain time to obtain a slurry; Pumping the slurry into an autoclave for temperature increase, keeping it at a certain temperature for a period of time, and carrying out a sufficient hydrothermal reaction; Cooling the slurry after the hydrothermal reaction and then filtering and washing it to obtain a wet filter cake of the intermediate product; Feeding the wet filter cake into a drying device for drying to obtain a dried intermediate product; Calcining the dried intermediate product to obtain a high-temperature microcrystalline alumina product.

2. The method for preparing high-temperature microcrystalline alumina according to claim 1, wherein, The activated alumina raw material refers to alumina with a specific surface area > 100 m2 / g.

3. The method for preparing high-temperature microcrystalline alumina according to claim 1, wherein The activated alumina raw material is mixed with water in a certain proportion, where the mass of the mixing water is 3 - 6 times that of the raw material.

4. The method for preparing high-temperature microcrystalline alumina according to claim 1, characterized in that, The addition of a suitable alkaline reagent refers to an alkaline reagent that can dissolve in water, including sodium hydroxide, sodium carbonate but not limited to the above two.

5. The method for preparing high-temperature microcrystalline alumina according to claim 1, wherein, The pH value of the mixture is adjusted to 8 - 13.

6. The method for preparing high-temperature microcrystalline alumina according to claim 1, wherein, The mixing and stirring of the activated alumina raw material and water for a certain time is 10 - 40 minutes.

7. The method for preparing high-temperature microcrystalline alumina according to claim 1, characterized in that, When pumping the slurry into the autoclave for temperature increase, the certain temperature is 90 - 190 °C.

8. The method for preparing high-temperature microcrystalline alumina according to claim 1, wherein When pumping the slurry into the autoclave for temperature increase, keeping it at a certain temperature for a period of time is 1 - 3 hours.

9. The method for preparing high-temperature microcrystalline alumina according to claim 1, characterized in that, When cooling the slurry after the hydrothermal reaction and then filtering and washing it, the washing water is demineralized water, and the water consumption does not exceed 20 times the mass of the intermediate product.

10. The method for preparing high-temperature microcrystalline alumina according to claim 1, wherein, The drying temperature does not exceed 300 °C.

11. The method for preparing high-temperature microcrystalline alumina according to claim 1, wherein, The calcination temperature is 1200 - 1600 °C.

12. The method for preparing high-temperature microcrystalline alumina according to claim 1, wherein, The calcination holding time is 2 - 5 hours.

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