Preparation method of large-particle single crystal alpha-alumina

Abstract

The invention discloses a preparation method of a large-particle single crystal alpha-alumina material. The preparation method comprises the following specific operation steps: step 1, grinding and mixing boric acid or aluminum fluoride with industrial alumina according to a certain mass ratio to obtain M1; step 2, carrying out pressure molding on the M1 to obtain M2; 3, the M2 is calcined, the calcination temperature is 1200-1600 DEG C, and the calcination time is 4-10 h; and step 4, carrying out crushing treatment on the calcined sample, and carrying out ball milling to obtain the large-particle single crystal alpha-aluminum oxide. The average particle size of the alpha-aluminum oxide prepared by the method is 40-100 microns, and the alpha-aluminum oxide is short in preparation time, simple in process, convenient to operate, low in cost and suitable for large-scale production.

Description

Technical Field

[0001] The invention relates to the technical field of alumina powder material preparation, and in particular to a method for preparing a granular single crystal alpha-alumina material. Background Art

[0002] Alumina (Al 2 O 3 ) undergoes many metastable polymorphs to form the thermodynamically stable α-Al 2 O 3 .

[0003] As a metal oxide, α-alumina belongs to the trigonal system, has a large lattice energy, good physical and chemical properties, strong intermolecular cohesion, good crystallinity, and can withstand a variety of chemical reactions. Due to its unique chemical, mechanical and thermal properties, α-alumina (α-Al 2 O 3 ) is one of the most important raw materials and is widely used in refractory, ceramic and polishing industries. At the same time, α-phase high-temperature alumina is widely used as a thermal conductive material in electronic devices in the form of filler due to its relatively high thermal conductivity, high resistivity and low cost.

[0004] Alumina is the most widely used thermal conductive filling material on the market, but due to its low thermal conductivity (30~35W / m. K), how to make it as close to the performance of the filling material as possible is a hot topic in current research and development. Previous studies have shown that thermal conductivity on grain boundaries is caused by phonon transmission and is greatly suppressed on grain boundaries. Therefore, large-grained single-crystal alumina is superior to polycrystalline alumina in thermal conductivity. Therefore, large-grained alumina is currently a more popular alumina thermal conductive filling material. However, due to the difficulty of single crystal growth, the abnormal growth of isotropic grains is common, and as the size increases, the difficulty of preparation also increases. Therefore, the current domestic market situation is that large-sized single crystals of alumina are not only expensive, but also rely on imports for a long time.

[0005] A Chinese patent (application number 202210490783.0) discloses a two-step calcination method for preparing large original crystal low-sodium α-alumina. The method uses industrial alumina as a raw material, adds a composite mineralizer containing fluoride (ammonium bifluoride, ammonium fluoride or aluminum fluoride) and chloride (aluminum chloride, magnesium chloride, ammonium chloride or calcium chloride), mixes with water, stirs and dries, and calcines once at 1100~1400 ℃ for 5~8 hours. In the secondary calcination, it is mixed with low-sodium aluminum hydroxide, a mineralizer (fluoride and boron oxide or calcium oxide), and water, stirred and dried, and then kept at 1400~1700 ℃ for 10~20 hours. After that, dry ball milling is carried out for 10~15 hours to obtain α-alumina with an average particle size of 20~30 um and a sodium content of 0.01~0.02 wt%.

[0006] A Chinese patent (application number 202210461818.8) discloses a secondary calcination method for preparing large original crystal α-alumina. The method uses industrial aluminum hydroxide or industrial aluminum oxide as raw materials, adds the first type of mineralizer (ammonium chloride, ammonium fluoride or ammonium citrate), and the weight of the additive accounts for 0.1~0.5 wt% of the mass of the aluminum source. After mixing evenly, calcine at 900~1200℃ for 2~8h, and add the second type of mineralizer (boric acid, aluminum fluoride, calcium fluoride, ammonium chloride, ammonium fluoride, ammonium citrate) after ball milling. The weight of the added mineralizer is 0.5~1.0 wt%. After ball milling, calcine at 1350~1600℃ for 2~20 hours. After ball milling, large original crystal α-alumina with a controllable size of 2~15 microns is obtained.

[0007] At present, people use various mineralizers to calcine alumina, but it is still difficult to prepare large-grained α-alumina powder materials with a micron size greater than 20 μm. Summary of the invention

[0008] The purpose of the present invention is to provide a method for preparing large-particle single-crystal α-alumina with low cost, simple process and high efficiency. The raw material used in the present invention is industrial alumina, and the average particle size of the prepared large-particle single-crystal α-alumina is between 40 and 100 μm.

[0009] In order to obtain the above-mentioned results, the present invention adopts the following technical solutions: The present invention provides a method for preparing large-particle single-crystal α-alumina, and the specific implementation steps are as follows: S1, mixing industrial alumina and a mineralizer and grinding them to obtain M1, wherein the mineralizer is boric acid or aluminum fluoride; S2, pressure shaping the ground M1 to obtain M2; S3, calcining M2; S4. The calcined M2 is crushed in a mortar and ball-milled to obtain large-particle single-crystalline α-alumina.

[0010] In the present invention, based on the total weight of the aluminum source, the content of the mineralizer in step (1) is 0-0.8 wt%, more preferably 0.6 wt%, and the grinding time is 10-30 min, more preferably 20 min.

[0011] In the present invention, the shaping pressure in step (2) is 0-12 MPa, more preferably 10 MPa.

[0012] In the present invention, the calcination temperature in step (3) is 1200-1600° C., more preferably 1500° C. The holding time is 4-10 h, more preferably 8 h.

[0013] In the present invention, the ball milling time in step (4) is 2 to 12 h, more preferably 4 to 6 h.

[0014] In the present invention, the ratio of zirconium balls to micropowder used in the ball milling in step (4) is 10:1-15:1, and the ratio of the grinding ball diameters is 5 mm:0.3 mm=4:1.

[0015] The above solution provided by the present invention is used to prepare large-particle single-crystal α-alumina materials, and the average particle size can reach 40-100 μm.

[0016] The reagents and raw materials used in the present invention are commercially available.

[0017] The present invention provides a method for preparing large-particle single-crystal α-alumina. The method uses industrial alumina as a raw material, boric acid or aluminum fluoride as an added mineralizer, mixes the materials, and performs pressure shaping treatment to allow the alumina particles to fully contact each other, and then grinds the alumina particles after calcination to obtain large-particle single-crystal α-alumina. The method has high efficiency in preparing large-particle single-crystal α-alumina, simple procedures, convenient operation, low cost, and can be produced on a large scale. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1~2 is a scanning electron microscope image of the α-alumina prepared in Example 1; Figure 3 is an industrial micrograph of α-alumina prepared in Example 1; Figure 4 This is the XRD scan of the α-alumina prepared in Example 1; Figures 5 and 6 This is a scanning electron microscope image of the α-alumina prepared in Example 2. DETAILED DESCRIPTION

[0019] The present invention is further described below by way of examples, but the present invention is not limited to the scope of the examples. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principle of the present invention should be equivalent replacement methods and are included in the protection scope of the present invention. The experimental methods in the following examples that do not specify specific conditions are selected according to conventional methods and conditions, or according to the product instructions. Example 1

[0020] Industrial alumina and aluminum fluoride were fully ground and mixed in a mortar at a mass ratio of 100:0.6 to obtain a mixture M1. The mixture M1 was pressure-molded at 10 MPa to obtain a tablet M2. The tablet M2 was placed in a tubular furnace, and the temperature of the high-temperature furnace was set to 1500 °C. The insulation time was 8 hours, and it was naturally cooled to room temperature to obtain a large-particle single-crystal α-alumina tablet. The tablet was placed in a mortar for crushing, and then placed in a ball mill for grinding. The ratio of zirconium balls to micropowder used in ball milling is 12.5:1, the ratio of grinding ball diameters is 5 mm: 0.3 mm = 4:1, and the ball milling time is 4 h. The particle size of the α-alumina prepared in this example is 40~100 μm. The scanning electron microscope image of the alumina obtained in this example is shown in FIG. Figure 1 . Example 2

[0021] Industrial alumina and boric acid were fully ground and mixed in a mortar at a mass ratio of 100:0.6 to obtain a mixture M1. The mixture M1 was pressure-molded at 10 MPa to obtain a tablet M2. The tablet M2 was placed in a tubular furnace, and the temperature of the high-temperature furnace was set to 1500°C. The insulation time was 8 hours, and it was naturally cooled to room temperature to obtain a large-particle single-crystal α-alumina tablet. The tablet was placed in a mortar for crushing, and then placed in a ball mill for grinding. The ratio of zirconium balls to micropowder used in ball milling is 12.5:1, the ratio of the grinding ball diameter is 5 mm: 0.3 mm = 4:1, and the ball milling time is 4 h. The particle size of the α-alumina prepared in this example is 40~80μm. The scanning electron microscope image of the alumina prepared in this example is shown in FIG. Figure 2 . Example 3

[0022] Industrial alumina and aluminum fluoride were fully ground and mixed in a mortar at a mass ratio of 100:0.4 to obtain a mixture M1. The mixture M1 was pressure-molded at 10 MPa to obtain a tablet M2, which was placed in a tubular furnace, and the high-temperature furnace temperature was set to 1500°C. The insulation time was 8 hours, and the tablet was naturally cooled to room temperature to obtain a large-particle single-crystal α-alumina tablet. The tablet was placed in a mortar for crushing, and then placed in a ball mill for grinding. The ratio of zirconium balls to micropowder used in ball milling is 12.5:1, the grinding ball diameter ratio is 5 mm: 0.3 mm = 4:1, and the ball milling time is 4 h. The maximum particle size of the α-alumina prepared in this embodiment can reach 40 μm. Example 4

[0023] Industrial alumina and aluminum fluoride were fully ground and mixed in a mortar at a mass ratio of 100:0.6 to obtain a mixture M1. The mixture M1 was pressure-shaped at 10 MPa to obtain a tablet M2, which was placed in a tubular furnace, and the high-temperature furnace temperature was set to 1450°C. The insulation time was 8 hours, and the tablet was naturally cooled to room temperature to obtain a large-particle single-crystal α-alumina tablet. The tablet was placed in a mortar for crushing, and then placed in a ball mill for grinding. The ratio of zirconium balls to micropowder used in ball milling is 12.5:1, the grinding ball diameter ratio is 5 mm: 0.3 mm = 4:1, and the ball milling time is 4 h. The maximum particle size of the α-alumina prepared in this embodiment can reach 40 μm. Example 5

[0024] Industrial alumina and boric acid were fully ground and mixed in a mortar at a mass ratio of 100:0.6 to obtain a mixture M1. The mixture M1 was shaped at a pressure of 8 MPa to obtain a tablet M2. The tablet M2 was placed in a tube furnace, the high-temperature furnace temperature was set to 1500 ℃, the insulation time was 6 hours, and it was naturally cooled to room temperature to obtain a large-particle single-crystal α-alumina tablet. The tablet was placed in a mortar for crushing and then placed in a ball mill for grinding. The ratio of zirconium balls to micropowder used in ball milling was 12.5:1, the grinding ball diameter ratio was 5 mm:0.3 mm=4:1, and the ball milling time was 4 h.

Claims

1. A method for preparing large-particle single-crystal α-alumina powder, characterized in that The method uses industrial alumina as raw material and boric acid or aluminum fluoride as main mineralizer. Firstly, industrial alumina, boric acid or aluminum fluoride are fully mixed, then pressure shaping is performed, and finally high-temperature calcination is performed to prepare large-particle single crystal α-alumina.

2. The method for preparing large-particle single crystal calcined α-alumina micropowder according to claim 1, characterized in that The steps are as follows: S1. Grind and mix industrial alumina with different amounts of boric acid or aluminum fluoride; S2, pressure shaping the mixture; S3. The pressed samples are placed in a tube furnace for high-temperature calcination, crushed in a mortar, and ball-milled to obtain large-particle single-crystalline α-alumina.

3. The method for preparing calcined large-particle single-crystal α-alumina micropowder according to claim 1 or 2, characterized in that: The mass ratio of the industrial alumina to boric acid or aluminum fluoride is 100:0-0.

8.

4. The method for preparing calcined large-particle single-crystal α-alumina micropowder according to claim 1 or 2, characterized in that: The shaping pressure is 0~12 MPa.

5. The method for preparing calcined large-particle single-crystal α-alumina micropowder according to claim 1 or 2, characterized in that: The high temperature calcination temperature is 1200-1600°C, and the heat preservation time is 4-10 hours.

6. The method for preparing calcined large-particle single-crystal α-alumina micropowder according to claim 1 or 2, characterized in that: The ratio of zirconium balls to micropowder is 10:1~15:1, and the grinding ball diameter ratio is 5 mm:0.3 mm=4:

1.

7. The method for preparing calcined large-particle single-crystal α-alumina micropowder according to claim 1 or 2, characterized in that: The ball milling time is 2 to 12 h.

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