A high-purity single-crystal spherical alumina powder and its preparation method and application

Abstract

The present invention provides a high-purity single-crystal spherical alumina powder and its preparation method and application, relating to the technical field of powder materials. The preparation method of the high-purity single-crystal spherical alumina powder provided by the present invention comprises the following steps: (1) ball-milling low-sodium spherical single-crystal α-alumina with an acid solution, adding ammonia water for neutralization, and obtaining a mixed slurry; (2) spray-drying the mixed slurry to obtain high-purity spherical single-crystal α-alumina; (3) spheroidizing the high-purity spherical single-crystal α-alumina to obtain high-purity single-crystal spherical alumina powder. The high-purity single-crystal spherical alumina powder prepared by the present invention has high density and high thermal conductivity, and has broad application prospects.

Description

Technical Field

[0001] The present invention relates to the technical field of powder materials, and in particular to a high-purity single-crystal spherical alumina powder and a preparation method and application thereof. Background Art

[0002] Spherical alumina powder is a new type of electronic material, boasting advantages such as high purity, high filling capacity, high thermal conductivity, high insulation, high fluidity, low thermal expansion, low wear, and high sphericity. It is widely used as a thermally conductive interface material, thermally conductive engineering plastics, and as a thermally conductive filler in aluminum-based copper-clad laminates. In recent years, it has found application in key areas such as new energy vehicle batteries and 5G base stations, leading to increasing demand for high-purity spherical alumina powder both domestically and internationally.

[0003] At present, there are two main processes for the large-scale production of spherical alumina powder: melt spraying and radio frequency plasma. Among them, the melt spraying method has the characteristics of simple process, low cost, and the spherical alumina produced has the characteristics of high sphericity and high α-phase alumina content. However, the raw material currently used to prepare spherical alumina with large particle size (above 10μm) is agglomerated α-alumina calcined powder. Because the melting process often forms crystal defects such as pores and vacancies inside the crystal, it will lead to a decrease in the density of the particles, thereby reducing their thermal conductivity, which restricts the application of spherical alumina in high-wattage thermal interface materials. Summary of the Invention

[0004] The purpose of the present invention is to provide a high-purity single-crystal spherical alumina powder and its preparation method and application. The high-purity single-crystal spherical alumina powder prepared by the present invention has high true density and high thermal conductivity and has broad application prospects.

[0005] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0006] The present invention provides a method for preparing high-purity single-crystal spherical alumina powder, comprising the following steps:

[0007] (1) ball-milling a low-sodium spherical single crystal α-alumina and an acid solution, and adding ammonia water for neutralization to obtain a mixed slurry;

[0008] (2) spray drying the mixed slurry to obtain high-purity spherical single-crystal α-alumina;

[0009] (3) Spheroidizing the high-purity quasi-spherical single-crystal α-alumina to obtain high-purity single-crystal spherical alumina powder.

[0010] Preferably, the purity of the low-sodium spherical single-crystal α-alumina is 99.7-99.8wt%, and the sodium content is 0.03-0.05wt%; the original crystal size of the low-sodium spherical single-crystal α-alumina is 2-40μm, and the sphericity is 70-80%.

[0011] Preferably, the acid solution is a mixture of hydrochloric acid and citric acid; the total concentration of the acid solution is 1 to 5 wt%;

[0012] The mass ratio of the low-sodium spherical single crystal α-alumina to the acid solution is 50-75:25-50.

[0013] Preferably, the ball milling mixing speed is 100 to 300 rap / min, and the time is 30 to 120 min.

[0014] Preferably, the spray drying conditions include: an inlet temperature of 300-400°C, a feed rate of 100-400 mL / min, and an outlet temperature of 100-150°C.

[0015] Preferably, the purity of the high-purity quasi-spherical single-crystal α-alumina is ≥99.9wt%, and the sodium content is ≤0.03wt%.

[0016] Preferably, the conditions for the spheroidization treatment include: a flame temperature of 2100 to 2400° C., and a discharge rate of 50 to 100 kg / h.

[0017] Preferably, the spheroidization treatment further includes airflow classification.

[0018] The present invention provides high-purity single-crystal spherical alumina powder prepared by the preparation method described in the above technical solution, with a purity of 99.9-99.99wt%, an average particle size of 2-40μm, and a sphericity of 95-98%.

[0019] The present invention provides the use of the high-purity single-crystal spherical alumina powder described in the above technical solution in thermal conductive fillers.

[0020] The present invention provides a method for preparing high-purity single-crystal spherical alumina powder. The method uses low-sodium spherical single-crystal α-alumina as raw material and prepares the high-purity single-crystal spherical alumina powder through acid washing, spray drying, and spheroidization. The high-purity single-crystal spherical alumina powder prepared by the present invention has a purity of 99.9-99.99 wt%, an average particle size of 2-40 μm, a sphericity of 95-98%, and a true density of 3.95-3.98 g / cm 3 , high thermal conductivity, and has good application prospects in thermal conductive fillers. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1This is a scanning electron microscope photograph of the low-sodium spherical single crystal α-alumina described in Example 3;

[0022] Figure 2 This is a scanning electron microscope photograph of the high-purity single-crystalline spherical alumina powder prepared in Example 1;

[0023] Figure 3 This is a scanning electron microscope photograph of the agglomerated α-alumina calcined powder described in Comparative Example 1;

[0024] Figure 4 This is a scanning electron microscope photograph of the spherical alumina powder prepared in Comparative Example 1;

[0025] Figure 5 This is a scanning electron microscope photograph of a slice of the low-sodium spherical single crystal α-alumina described in Example 3;

[0026] Figure 6 This is a scanning electron microscope photograph of a slice of spherical alumina powder prepared in Comparative Example 1. DETAILED DESCRIPTION

[0027] The present invention provides a method for preparing high-purity single-crystal spherical alumina powder, comprising the following steps:

[0028] (1) ball-milling a low-sodium spherical single crystal α-alumina and an acid solution, and adding ammonia water for neutralization to obtain a mixed slurry;

[0029] (2) spray drying the mixed slurry to obtain high-purity spherical single-crystal α-alumina;

[0030] (3) Spheroidizing the high-purity quasi-spherical single-crystal α-alumina to obtain high-purity single-crystal spherical alumina powder.

[0031] The present invention ball-mills low-sodium spherical single-crystal α-alumina with an acid solution, and then neutralizes the mixture with aqueous ammonia to obtain a mixed slurry. In the present invention, the purity of the low-sodium spherical single-crystal α-alumina is preferably 99.7-99.8wt%, more preferably 99.8wt%, and the sodium content is preferably 0.03-0.05wt%, more preferably 0.03-0.04wt%. The original crystal size of the low-sodium spherical single-crystal α-alumina is preferably 2-40μm, more preferably 10-30μm, and the sphericity is preferably 70-80%. In the present invention, the preparation method of the low-sodium spherical single-crystal α-alumina preferably includes: calcining large original crystal low-sodium spherical α-alumina powder at a high temperature to obtain low-sodium spherical single-crystal α-alumina.

[0032] In the present invention, the acid solution is preferably a mixture of hydrochloric acid and citric acid, and the mass ratio of HCl to citric acid in the acid solution is preferably 1:1. The total concentration of the acid solution is preferably 1-5 wt %, more preferably 3-4 wt %. In the present invention, the mass ratio of the low-sodium spherical single crystal α-alumina to the acid solution is preferably 50-75:25-50, more preferably 55-65:35-45.

[0033] In the present invention, the ball milling speed is preferably 100 to 300 rap / min, more preferably 200 to 250 rap / min; the time is preferably 30 to 120 minutes, more preferably 90 to 100 minutes. The purpose of treating the low-sodium spherical single-crystal α-alumina with an acid solution in the present invention is to remove sodium impurities on the surface of the powder and improve the purity of the powder.

[0034] In the present invention, the mass concentration of the aqueous ammonia is preferably 20-35%, more preferably 25-28%. In the present invention, the pH value of the slurry obtained after ball milling the low-sodium spherical single crystal α-alumina and the acid solution is preferably 2-4, more preferably 2-3. The pH value of the mixed slurry obtained by adding aqueous ammonia for neutralization is preferably 7. In the present invention, excess acid is removed by neutralization.

[0035] After obtaining the mixed slurry, the present invention spray-dries the mixed slurry to obtain high-purity, quasi-spherical single-crystalline α-alumina. In the present invention, the spray-drying conditions preferably include: an inlet temperature of preferably 300-400°C, more preferably 300-350°C; a feed rate of preferably 100-400 mL / min, more preferably 200 mL / min; and an outlet temperature of preferably 100-150°C. The present invention utilizes the above-described spray-drying process to obtain highly dispersed, high-purity, quasi-spherical single-crystalline α-alumina.

[0036] In the present invention, the purity of the high-purity quasi-spherical single-crystal α-alumina is preferably ≥99.9wt%, more preferably 99.99wt%; the sodium content is preferably ≤0.03wt%, more preferably 0.01-0.02wt%.

[0037] After obtaining high-purity, quasi-spherical single-crystalline α-alumina, the present invention performs a spheroidization process on the high-purity, quasi-spherical single-crystalline α-alumina to obtain high-purity, single-crystalline, spherical alumina powder. In the present invention, the spheroidization process preferably includes: a flame temperature of preferably 2100-2400°C, more preferably 2300-2400°C; and a discharge rate of preferably 50-100 kg / h, more preferably 60-80 kg / h. In the present invention, the spheroidization process is preferably performed in a high-temperature spheroidization furnace. The present invention utilizes the above-described spheroidization process to obtain high-purity, single-crystalline, spherical alumina powder with high sphericity.

[0038] In the present invention, the spheroidization treatment preferably further includes airflow classification. The present invention utilizes airflow classification to obtain high-purity single-crystal spherical alumina powders with different particle size ranges.

[0039] The present invention provides a high-purity single-crystal spherical alumina powder prepared by the preparation method described in the above technical solution. In the present invention, the purity of the high-purity single-crystal spherical alumina powder is 99.9-99.99wt%, more preferably 99.92-99.98wt%; the average particle size is 2-40μm, preferably 5-30μm; the sphericity is 95-98%, more preferably 96-97%. In the present invention, the true density of the high-purity single-crystal spherical alumina powder is preferably 3.95-3.98g / cm 3 , more preferably 3.96 to 3.97 g / cm 3 In the present invention, the thermal conductive silicone grease and the high-purity single-crystal spherical alumina powder are mixed in a mass ratio of 1:9 and cured at room temperature for 24 hours to obtain a thermally conductive potting compound. The thermal conductivity of the obtained thermally conductive potting compound is preferably 3.5 to 5 W / (m·K), and more preferably 4 to 5 W / (m·K).

[0040] The present invention provides the use of the high-purity single-crystal spherical alumina powder described in the above technical solution in thermal conductive fillers.

[0041] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions of the present invention. Obviously, the embodiments described are only some of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0042] Example 1

[0043] The low-sodium spherical single-crystal α-alumina used in this embodiment has a primary crystal size of 2 μm, a sodium content of 0.03 wt%, a sphericity of 80%, and a purity of 99.8 wt%;

[0044] 75 kg of the low-sodium spherical single-crystal α-alumina and 25 kg of a 1 wt % mixed acid solution of hydrochloric acid and citric acid (the mass ratio of HCl to citric acid in the mixed acid solution is 1:1) were ball-milled at a ball-milling speed of 100 rap / min for 120 min, and then 25 wt % ammonia water was added for neutralization to obtain a mixed slurry with a pH value of 7;

[0045] The mixed slurry was spray-dried at an inlet temperature of 400° C., a feed rate of 200 mL / min, and an outlet temperature of 150° C. to obtain high-purity spherical single-crystalline α-alumina with a sodium content of 0.01 wt% and a purity of 99.99 wt%;

[0046] The high-purity quasi-spherical single-crystal α-alumina is placed in a high-temperature spheroidizing furnace for spheroidization treatment, the flame temperature is 2100°C, and the discharge rate is 50kg / h. The obtained single-crystal spherical alumina powder is subjected to air flow classification to obtain high-purity single-crystal spherical alumina powder.

[0047] The high-purity single-crystal spherical alumina powder prepared in this example has a purity of 99.99 wt%, an average particle size of 2 μm, a sphericity of 98%, and a true density of 3.95 g / cm 3 .

[0048] The thermal conductive silicone grease and the high-purity single crystal spherical alumina powder were mixed in a mass ratio of 1:9, and cured at room temperature for 24 hours to obtain a thermal conductive potting compound. The thermal conductivity of the obtained thermal conductive potting compound was 3.5 W / (m·K).

[0049] Example 2

[0050] The low-sodium spherical single-crystal α-alumina used in this embodiment has a primary crystal size of 40 μm, a sodium content of 0.05 wt%, a sphericity of 70%, and a purity of 99.7 wt%;

[0051] 75 kg of the low-sodium spherical single-crystal α-alumina and 25 kg of a 1 wt % mixed acid solution of hydrochloric acid and citric acid (the mass ratio of HCl to citric acid in the mixed acid solution is 1:1) were ball-milled at a ball-milling speed of 300 rap / min for 30 min, and then neutralized by adding 20 wt % ammonia water to obtain a mixed slurry with a pH value of 7;

[0052] The mixed slurry was spray-dried at an inlet temperature of 300° C., a feed rate of 200 mL / min, and an outlet temperature of 100° C. to obtain high-purity quasi-spherical single-crystalline α-alumina having a sodium content of 0.02 wt % and a purity of 99.9 wt %.

[0053] The high-purity quasi-spherical single-crystal α-alumina is placed in a high-temperature spheroidizing furnace for spheroidization treatment with a flame temperature of 2400°C and a discharge rate of 100 kg / h. The obtained single-crystal spherical alumina powder is subjected to air flow classification to obtain high-purity single-crystal spherical alumina powder.

[0054] The high-purity single-crystal spherical alumina powder prepared in this example has a purity of 99.9 wt %, an average particle size of 40 μm, a sphericity of 95%, and a true density of 3.98 g / cm 3 .

[0055] The high-purity single-crystal spherical alumina powder was made into a thermally conductive potting compound according to the method of Example 1, and the thermal conductivity was 5 W / (m·K).

[0056] Example 3

[0057] The low-sodium spherical single-crystal α-alumina used in this embodiment has a primary crystal size of 20 μm, a sodium content of 0.04 wt%, a sphericity of 75%, and a purity of 99.8 wt%;

[0058] 60 kg of the low-sodium spherical single-crystal α-alumina and 40 kg of a 3 wt % mixed acid solution of hydrochloric acid and citric acid (the mass ratio of HCl to citric acid in the mixed acid solution is 1:1) were ball-milled at a ball-milling speed of 200 rap / min for 90 min, and then neutralized by adding 35 wt % ammonia water to obtain a mixed slurry with a pH value of 7;

[0059] The mixed slurry was spray-dried at an inlet temperature of 350° C., a feed rate of 200 mL / min, and an outlet temperature of 150° C. to obtain high-purity quasi-spherical single-crystalline α-alumina having a sodium content of 0.01 wt % and a purity of 99.98 wt %.

[0060] The high-purity quasi-spherical single-crystal α-alumina is placed in a high-temperature spheroidizing furnace for spheroidization treatment, the flame temperature is 2200°C, and the discharge rate is 80kg / h. The obtained single-crystal spherical alumina powder is subjected to air flow classification to obtain high-purity single-crystal spherical alumina powder.

[0061] The high-purity single-crystal spherical alumina powder prepared in this example has a purity of 99.98 wt%, an average particle size of 20 μm, a sphericity of 96%, and a true density of 3.96 g / cm 3 .

[0062] The high-purity single-crystal spherical alumina powder was made into a thermally conductive potting compound according to the method of Example 1, and the thermal conductivity was 4.2 W / (m·K).

[0063] Example 4

[0064] The low-sodium spherical single-crystal α-alumina used in this embodiment has a primary crystal size of 30 μm, a sodium content of 0.03 wt %, a sphericity of 80%, and a purity of 99.8 wt %;

[0065] 65 kg of the low-sodium spherical single-crystal α-alumina and 35 kg of a 4 wt % mixed acid solution of hydrochloric acid and citric acid (the mass ratio of HCl to citric acid in the mixed acid solution is 1:1) were ball-milled at a ball-milling speed of 300 rap / min for 120 min, and then 25 wt % ammonia water was added for neutralization to obtain a mixed slurry with a pH value of 7;

[0066] The mixed slurry was spray-dried at an inlet temperature of 400° C., a feed rate of 200 mL / min, and an outlet temperature of 100° C. to obtain high-purity quasi-spherical single-crystalline α-alumina with a sodium content of 0.01 wt% and a purity of 99.99 wt%;

[0067] The high-purity quasi-spherical single-crystal α-alumina is placed in a high-temperature spheroidizing furnace for spheroidization treatment, the flame temperature is 2400°C, and the discharge rate is 60kg / h. The obtained single-crystal spherical alumina powder is subjected to air flow classification to obtain high-purity single-crystal spherical alumina powder.

[0068] The high-purity single-crystal spherical alumina powder prepared in this example has a purity of 99.99 wt%, an average particle size of 30 μm, a sphericity of 97%, and a true density of 3.97 g / cm 3 .

[0069] The high-purity single-crystal spherical alumina powder was made into a thermally conductive potting compound according to the method of Example 1, and the thermal conductivity was 4.8 W / (m·K).

[0070] Example 5

[0071] The low-sodium spherical single-crystal α-alumina used in this embodiment has a primary crystal size of 10 μm, a sodium content of 0.05 wt%, a sphericity of 76%, and a purity of 99.7 wt%;

[0072] 55 kg of the low-sodium spherical single-crystal α-alumina and 45 kg of a 5 wt % mixed acid solution of hydrochloric acid and citric acid (the mass ratio of HCl to citric acid in the mixed acid solution is 1:1) were ball-milled at a ball-milling speed of 250 rap / min for 100 min, and then 28 wt % ammonia water was added for neutralization to obtain a mixed slurry with a pH value of 7;

[0073] The mixed slurry was spray-dried at an inlet temperature of 300° C., a feed rate of 200 mL / min, and an outlet temperature of 100° C. to obtain high-purity spherical single-crystalline α-alumina with a sodium content of 0.03 wt% and a purity of 99.92 wt%.

[0074] The high-purity quasi-spherical single-crystal α-alumina is placed in a high-temperature spheroidizing furnace for spheroidization treatment, the flame temperature is 2300°C, and the discharge rate is 50kg / h. The obtained single-crystal spherical alumina powder is subjected to air flow classification to obtain high-purity single-crystal spherical alumina powder.

[0075] The high-purity single-crystal spherical alumina powder prepared in this example has a purity of 99.92 wt%, an average particle size of 10 μm, a sphericity of 98%, and a true density of 3.96 g / cm 3 .

[0076] The high-purity single-crystal spherical alumina powder was prepared into a thermally conductive potting compound according to the method of Example 1, and the thermal conductivity was 3.8 W / (m·K).

[0077] Comparative Example 1

[0078] Industrial alumina with an average particle size of 75 μm is calcined at 1400° C. for 10 hours to obtain agglomerated α-alumina calcined powder; the agglomerated α-alumina calcined powder has a primary crystal size of 2 μm, a sodium content of 0.05 wt%, a sphericity of 60%, and a purity of 99.8 wt%;

[0079] The agglomerated α-alumina calcined powder was used as a raw material to replace the low-sodium spherical single-crystal α-alumina, and spherical alumina powder was prepared according to the method for preparing high-purity single-crystal spherical alumina powder in Example 1.

[0080] The spherical alumina powder prepared in this comparative example has a purity of 99.8 wt %, an average particle size of 20 μm, a sphericity of 95%, and a true density of 3.85 g / cm 3 .

[0081] The spherical alumina powder was made into a thermally conductive potting compound according to the method of Example 1, and the thermal conductivity was 2.5 W / (m·K).

[0082] Test Case

[0083] Figure 1 This is a scanning electron microscope photograph of the low-sodium spherical single crystal α-alumina described in Example 3; Figure 3 This is a scanning electron microscope photograph of the agglomerated α-alumina calcined powder described in Comparative Example 1. By comparison, it can be seen that the low-sodium spherical single-crystal α-alumina used in the present invention is a single crystal powder, while the raw material used in the comparative example is an agglomerated polycrystalline powder. Figure 5 This is a scanning electron microscope photograph of a slice of the low-sodium spherical single-crystal α-alumina described in Example 3, confirming that the powder is a single grain with no pores.

[0084] Figure 2 This is a scanning electron microscope photograph of the high-purity single-crystalline spherical alumina powder prepared in Example 1; Figure 4 This is a scanning electron microscope photograph of the spherical alumina powder prepared in Comparative Example 1. By comparison, it can be seen that the spherical alumina powder obtained in the present invention is a single crystal powder, while the spherical alumina powder obtained in the comparative example is a polycrystalline powder. Figure 6 This is a scanning electron microscope photograph of a slice of the spherical alumina powder prepared in Comparative Example 1, which confirms that the powder is a polycrystalline powder and has a large number of pores.

[0085] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A method for preparing high-purity single-crystal spherical alumina powder, comprising the following steps: (1) ball-milling a low-sodium spherical single-crystal α-alumina and an acid solution, and adding ammonia water for neutralization to obtain a mixed slurry; the purity of the low-sodium spherical single-crystal α-alumina is 99.7-99.8 wt%, and the sodium content is 0.03-0.05 wt%; the original crystal size of the low-sodium spherical single-crystal α-alumina is 2-40 μm, and the sphericity is 70-80%; (2) spray drying the mixed slurry to obtain high-purity spherical single-crystal α-alumina; (3) spheroidizing the high-purity quasi-spherical single-crystal α-alumina to obtain high-purity single-crystal spherical alumina powder; The spheroidization treatment conditions include: a flame temperature of 2100-2400°C, a discharge rate of 50-100 kg / h; the purity of the high-purity single-crystal spherical alumina powder is 99.9-99.99 wt%, an average particle size of 2-40 μm, a sphericity of 95-98%, and a true density of 3.95-3.98 g / cm 3 .

2. The preparation method according to claim 1, characterized in that The acid solution is a mixture of hydrochloric acid and citric acid; the total concentration of the acid solution is 1 to 5 wt%; The mass ratio of the low-sodium spherical single crystal α-alumina to the acid solution is 50-75:25-50.

3. The preparation method according to claim 1, characterized in that The ball milling mixing speed is 100 to 300 rap / min, and the time is 30 to 120 minutes.

4. The preparation method according to claim 1, characterized in that The spray drying conditions include: an inlet temperature of 300-400°C, a feed rate of 100-400 mL / min, and an outlet temperature of 100-150°C.

5. The preparation method according to claim 1, characterized in that The purity of the high-purity quasi-spherical single crystal α-alumina is ≥99.9 wt % and the sodium content is ≤0.03 wt %.

6. The preparation method according to claim 1, characterized in that The spheroidization process also includes air flow classification.

7. The high-purity single-crystal spherical alumina powder prepared by the preparation method according to any one of claims 1 to 6 has a purity of 99.9-99.99 wt%, an average particle size of 2-40 μm, a sphericity of 95-98%, and a true density of 3.95-3.98 g / cm 3 .

8. Use of the high-purity single-crystal spherical alumina powder according to claim 7 in thermal conductive fillers.

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