Preparation method of large-size high-purity alumina granulated powder

Abstract

The application relates to the field of advanced ceramic material preparation technology, and discloses a preparation method of large-size high-purity alumina granulating powder, which comprises the following steps: mixing high-purity alpha-Al2O3 powder, magnesium oxide, composite sintering additives of yttrium oxide, polyacrylamide ammonium salt dispersant and deionized water, and ball milling to obtain a suspension slurry; after the suspension slurry is screened, iron is removed, and defoaming is performed, the suspension slurry is sent to an atomizing nozzle at the top of a pressure tower, and is atomized into tiny droplets under the pressure of 1-3 MPa; the tiny droplets are dried by being in contact with an upward hot air flow in the pressure tower, the air inlet temperature at the top of the tower is controlled to be 180-220 DEG C, and the air outlet temperature at the bottom of the tower is controlled to be 80-110 DEG C; the granulating powder after drying is collected, the particles with the medium particle size D50 of 150-200 microns are selected through a vibrating screen, and then iron is removed and homogenization treatment is performed, so that the product is obtained. The application does not need to add an organic binder, carbon residue pollution is avoided, the obtained granulating powder has high sphericity and good fluidity, the sintering temperature is low, the energy consumption is small, and the application is suitable for large-scale continuous production.

Description

Technical Field

[0001] This invention relates to the field of advanced ceramic material preparation technology, and in particular to a method for preparing large-size high-purity alumina granulated powder. Background Technology

[0002] High-purity alumina ceramics (Al2O3 content ≥ 99.99%) are widely used in semiconductors, precision machinery, chemicals, and aerospace due to their excellent high insulation, high hardness, corrosion resistance, and thermal stability. In these applications, alumina ceramic components are mostly manufactured using powder metallurgy processes such as dry pressing and isostatic pressing. These forming processes have extremely high requirements for the flowability, filling properties, and particle strength of the raw powder. Therefore, it is necessary to process the raw alumina micro powder into spherical granulated powder with good granulation characteristics.

[0003] Currently, the mainstream method for preparing alumina granulated powder is spray granulation. However, traditional spray granulation technology still has many shortcomings in producing high-purity alumina granulated powder: to ensure particle strength, organic binders such as polyvinyl alcohol and methylcellulose are usually added to the slurry. These binders will leave carbon residues during subsequent high-temperature sintering, contaminating the ceramic products and degrading their electrical and optical properties; at the same time, the traditional method lacks precision in controlling particle morphology and particle size distribution, resulting in poor sphericity and poor flowability (large angle of repose) of the produced granules, affecting the uniformity of filling during automated molding; in addition, when adopting a binder-free route to pursue high purity, the sintering temperature needs to be increased to 1600~1800℃, which consumes a lot of energy, and existing equipment still has problems such as poor material feeding and uneven slurry mixing in continuous production, affecting production efficiency and product consistency.

[0004] To address the shortcomings of the existing technologies, there is an urgent need to develop a new method for preparing alumina granulated powder that can produce high-purity alumina granulated powder with high sphericity, excellent flowability, and good sintering activity without the introduction of organic binders, while achieving low-energy consumption and continuous and stable large-scale production. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing large-size, high-purity alumina granulated powder, which solves the problems of ceramic product contamination, insufficient particle sphericity and flowability, and high energy consumption in the binder-free sintering route caused by the addition of organic binders in the prior art.

[0006] To achieve the above objectives, the present invention provides a method for preparing large-size, high-purity alumina granulated powder, comprising the following steps: S1: High-purity α-Al2O3 powder, sintering aid, dispersant and deionized water are mixed in proportion and ball-milled to obtain a suspension slurry; S2: The suspended slurry is sequentially subjected to sieving, iron removal and vacuum degassing, and then transported to the atomizing nozzle at the top of the pressure tower by a high-pressure pump. S3: The suspended slurry is atomized into tiny droplets under high pressure through the atomizing nozzle. The tiny droplets come into contact with the rising hot air flow and are dried in the pressure tower. The dried granulated powder is collected at the bottom of the tower. S4: The collected granulated powder is subjected to vibrating sieving, iron removal and homogenization treatment to obtain high-purity alumina granulated powder product.

[0007] In step S3: The inlet air temperature at the top of the pressure tower is controlled at 180~220℃, and the outlet air temperature at the bottom of the tower is controlled at 80~110℃, so that the tiny droplets undergo a gradient drying process inside the pressure tower.

[0008] In step S1: The α-Al2O3 powder has a purity of ≥99.99%, a median particle size D50 of 0.1~1.0μm, and an α phase content of ≥95%.

[0009] In step S1: The sintering aid is a composite additive of magnesium oxide and yttrium oxide, wherein the amount of magnesium oxide added is 0.05~0.3% of the total mass of the α-Al2O3 powder, and the amount of yttrium oxide added is 0.1~1.0% of the total mass of the α-Al2O3 powder.

[0010] In step S1: The dispersant is ammonium polyacrylate, and the amount added is 0.2~1.0% of the total mass of the α-Al2O3 powder.

[0011] In step S1, the solid content of the suspension slurry is 40-70 wt%, and the viscosity at 25°C is 100-400 mPa·s.

[0012] In step S2: The sieving process uses a 325-mesh sieve.

[0013] In step S3: The pressure of the atomizing nozzle is 1~3MPa.

[0014] In step S4: The vibrating screen selects particles with a median particle size D50 of 150~200μm as the target product.

[0015] In step S1: The particle size of the magnesium oxide is less than or equal to the particle size of the α-Al2O3 powder.

[0016] This invention discloses a method for preparing large-size, high-purity alumina granulated powder. The method involves mixing high-purity α-Al₂O₃ powder, a composite sintering aid of magnesium oxide and yttrium oxide, an ammonium polyacrylate dispersant, and deionized water in a specific ratio. The mixture is then ball-milled to obtain a suspension slurry with a solid content of 40-70 wt% and a viscosity of 100-400 mPa·s. The suspension slurry is then subjected to sequential sieving, iron removal, and vacuum degassing treatments. Finally, it is pumped to an atomizing nozzle at the top of a pressure tower using a high-pressure pump. Atomizing nozzles atomize the alumina into tiny droplets under a pressure of 1-3 MPa. These droplets come into contact with and are dried by rising hot air within a pressure tower. The inlet air temperature at the top of the tower is controlled at 180-220°C, and the outlet air temperature at the bottom is controlled at 80-110°C, allowing the droplets to undergo a gradient drying process. The dried granulated powder is collected at the bottom of the tower. The collected granulated powder is then screened by a vibrating sieve to select particles with a median particle size (D50) of 150-200 μm. After iron removal and homogenization, high-purity alumina granulated powder is obtained. This invention, by employing an organic binder-free formulation combined with a pressure tower gradient drying process, avoids carbon residue contamination of ceramic products from the source, ensuring high purity (≥99.99%) and excellent electrical properties of the alumina ceramic products. Through high-pressure atomization and precise temperature field control, sphericity ≥0.85, angle of repose ≤30°, and bulk density 1.0-1.2 g / cm³ are produced. 3 Tap density: 1.3~1.6 g / cm³ 3 The granulated powder significantly improves powder flowability and filling uniformity; simultaneously, the addition of composite sintering aids enables the green body to achieve full densification at 1500~1650℃, with a density of 3.92~3.95 g / cm³ after sintering. 3 (≥98.5% of theoretical density), reducing sintering energy consumption by about 10~20% compared to traditional processes, and controlling shrinkage rate at 15~20% and water absorption rate at 0.5~1.0%; in addition, through purification steps such as sieving, iron removal, and degassing, combined with an intelligent control pressure tower system, the problems of nozzle blockage, poor material feeding and wall adhesion are effectively solved, achieving continuous and stable large-scale production. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below.

[0018] Figure 1 This is a flowchart of the steps in the preparation method of large-size high-purity alumina granulated powder according to the present invention. Detailed Implementation

[0019] The embodiments of the present invention are described in detail below. Examples of the embodiments are shown in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, but should not be construed as limiting the present invention.

[0020] Please refer to Figure 1 This invention provides a method for preparing large-size, high-purity alumina granulated powder, comprising the following steps: S1: High-purity α-Al2O3 powder, sintering aid, dispersant and deionized water are mixed in proportion and ball-milled to obtain a suspension slurry; Specifically, the raw material preparation and slurry preparation are as follows: High-purity α-Al₂O₃ powder, sintering aid, dispersant, and deionized water are mixed in a certain proportion and ball-milled to obtain a uniform and stable suspension slurry. The purity of the α-Al₂O₃ powder is ≥99.99%, the median particle size D50 is 0.1-1.0 μm, and the α-phase content is ≥95%. The sintering aid is a composite additive of magnesium oxide (MgO) and yttrium oxide (Y₂O₃). The amount of MgO added is 0.05-0.3% of the total powder mass, and its particle size is smaller than or equal to that of the Al₂O₃ raw material, playing a "pinning" role in inhibiting abnormal grain growth during sintering. The amount of Y₂O₃ added is 0.1-1.0% of the total powder mass, which helps to promote sintering densification and improve the toughness of the material. The dispersant is ammonium polyacrylate, added at 0.2-1.0% of the total powder mass, used to improve slurry stability and prevent particle agglomeration.

[0021] The solid content of the slurry is controlled at 40-70 wt%, and the viscosity is adjusted to 100-400 mPa·s (measured at 25℃).

[0022] S2: The suspended slurry is sequentially subjected to sieving, iron removal and vacuum degassing, and then transported to the atomizing nozzle at the top of the pressure tower by a high-pressure pump. Specifically, the slurry purification and conveying process involves sequentially sieving (325 mesh), removing iron, and vacuum degassing the prepared slurry. It is then conveyed to the atomizing nozzle at the top of the pressure tower using a high-pressure pump. Once the slurry reaches the desired pressure within the pressure chamber, it proceeds to step S3.

[0023] S3: The suspended slurry is atomized into tiny droplets under high pressure through the atomizing nozzle. The tiny droplets come into contact with the rising hot air flow and are dried in the pressure tower. The dried granulated powder is collected at the bottom of the tower. Specifically, pressure tower spray granulation: the slurry is atomized into tiny droplets through a pressure atomizing nozzle under high pressure (1-3 MPa). The atomized droplets come into contact with the rising hot airflow within the pressure tower and are instantly dried. Crucially, this invention achieves a unique "gradient drying" process by precisely controlling the temperature and airflow fields within the pressure tower. The inlet air temperature at the top of the tower is set at 180-220℃ (the initial high temperature causes pressure instability and slurry flow rate instability in the initial spraying stage; the inlet air temperature is then gradually reduced), while the exhaust air temperature at the bottom is controlled at 80-110℃. This temperature gradient causes a dense, semi-dry shell to rapidly form on the droplet surface, and internal moisture then slowly evaporates through the micropores of the shell, naturally forming high-strength, hollow spherical particles. The dried granulated powder is collected at the bottom of the tower.

[0024] S4: The collected granulated powder is subjected to vibrating sieving, iron removal and homogenization treatment to obtain high-purity alumina granulated powder product.

[0025] Specifically, the post-processing involves: the collected coarse powder being screened by vibration to select particles within the target particle size range (e.g., D50 of 150-200μm), followed by an iron removal process, and finally homogenization to obtain the final high-purity alumina granulated powder product.

[0026] The pressure tower system includes a slurry supply unit, a pressure granulation tower body, a hot air system, a gas-solid separation and collection unit, and an intelligent control system. The slurry supply unit includes a batching tank, a ball mill, a storage tank, and a high-pressure pump equipped with a flow meter and pressure gauge. The pressure granulation tower body is a vertical cylindrical structure with an anti-stick lining on its inner wall. One or more high-pressure atomizing nozzles are installed at the center of the tower top. The hot air system includes an air filter, a heater, and a hot air distributor located at the top of the pressure granulation tower body, from which hot air is evenly distributed into the interior of the tower body. The gas-solid separation and collection unit includes a cyclone separator or bag filter located at the bottom of the pressure granulation tower body, and a vibrating collection hopper equipped with a cooling jacket. The intelligent control system integrates a PLC for real-time monitoring and control of inlet air temperature, exhaust air temperature, internal negative pressure, atomization pressure, and slurry flow rate.

[0027] This invention employs a unique "gradient drying" granulation mechanism and a composite sintering aid system. Simultaneously, through secondary filtration and iron and foam removal steps, it strictly controls the safety hazards caused by large suspended particles in the slurry clogging the sintering nozzle, while ensuring the consistency of slurry flow. This guarantees the stability, high purity (≥99.99%), and excellent electrical properties of the final alumina ceramic product. This invention utilizes high-pressure atomization and precise temperature field control to prepare granulated powder with high sphericity (sphericity ≥ 0.85), narrow particle size distribution, and excellent flowability (angle of repose ≤ 30°). Its loose bulk density is 1-1.2 g / cm³. 3 The tap density is 1.3-1.6 g / cm³. 3 The density after sintering is 3.92-3.95 g / cm³. 3 The shrinkage rate is 15-20%, and the water absorption rate is 0.5-1.0%.

[0028] The trace composite sintering aids (MgO and Y2O3) added in this invention can effectively reduce the sintering temperature of alumina. The green body formed using the granulated powder of this invention can achieve sufficient densification (sintered body density ≥ 98.5% of theoretical density) at a relatively low temperature of 1500-1650℃, reducing energy consumption by about 10-20% compared with traditional processes.

[0029] The pressure tower system of this invention achieves precise parameter control, smooth material feeding, and good product consistency, making it suitable for continuous and large-scale production.

[0030] The above-disclosed embodiments are merely one or more preferred embodiments of this application and should not be construed as limiting the scope of this application. Those skilled in the art can understand that all or part of the processes for implementing the above embodiments and equivalent changes made in accordance with the claims of this application still fall within the scope of this application.

Claims

1. A method for preparing large-size, high-purity alumina granulated powder, characterized in that, Includes the following steps: S1: High-purity α-Al2O3 powder, sintering aid, dispersant and deionized water are mixed in proportion and ball-milled to obtain a suspension slurry; S2: The suspended slurry is sequentially subjected to sieving, iron removal and vacuum degassing, and then transported to the atomizing nozzle at the top of the pressure tower by a high-pressure pump. S3: The suspended slurry is atomized into tiny droplets under high pressure through the atomizing nozzle. The tiny droplets come into contact with the rising hot air flow and are dried in the pressure tower. The dried granulated powder is collected at the bottom of the tower. S4: The collected granulated powder is subjected to vibrating sieving, iron removal and homogenization treatment to obtain high-purity alumina granulated powder product.

2. The method for preparing large-size high-purity alumina granulated powder as described in claim 1, characterized in that, In step S3: The inlet air temperature at the top of the pressure tower is controlled at 180~220℃, and the outlet air temperature at the bottom of the tower is controlled at 80~110℃, so that the tiny droplets undergo a gradient drying process inside the pressure tower.

3. The method for preparing large-size high-purity alumina granulated powder as described in claim 1, characterized in that, In step S1: The α-Al2O3 powder has a purity of ≥99.99%, a median particle size D50 of 0.1~1.0μm, and an α phase content of ≥95%.

4. The method for preparing large-size high-purity alumina granulated powder as described in claim 1, characterized in that, In step S1: The sintering aid is a composite additive of magnesium oxide and yttrium oxide, wherein the amount of magnesium oxide added is 0.05~0.3% of the total mass of the α-Al2O3 powder, and the amount of yttrium oxide added is 0.1~1.0% of the total mass of the α-Al2O3 powder.

5. The method for preparing large-size high-purity alumina granulated powder as described in claim 1, characterized in that, In step S1: The dispersant is ammonium polyacrylate, and the amount added is 0.2~1.0% of the total mass of the α-Al2O3 powder.

6. The method for preparing large-size high-purity alumina granulated powder as described in claim 1, characterized in that, In step S1: the solid content of the suspension slurry is 40~70wt%, and the viscosity at 25℃ is 100~400mPa·s.

7. The method for preparing large-size high-purity alumina granulated powder as described in claim 1, characterized in that, In step S2: The sieving process uses a 325-mesh sieve.

8. The method for preparing large-size high-purity alumina granulated powder as described in claim 1, characterized in that, In step S3: The pressure of the atomizing nozzle is 1~3MPa.

9. The method for preparing large-size high-purity alumina granulated powder as described in claim 1, characterized in that, In step S4: The vibrating screen selects particles with a median particle size D50 of 150~200μm as the target product.

10. The method for preparing large-size high-purity alumina granulated powder as described in claim 1, characterized in that, In step S1: The particle size of the magnesium oxide is less than or equal to the particle size of the α-Al2O3 powder.

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