A method for preparing submicron spherical aluminum oxide

Abstract

The present invention belongs to the technical field of aluminum oxide preparation, and discloses a method for preparing submicron spherical aluminum oxide, which comprises the following steps: S1, pretreatment: taking an aluminum compound with a particle size of less than or equal to 1 μm, adding a modifier, heating and stirring, and obtaining a pretreated powder; S2, melting spheroidization: heating a carrier gas and mixing it with the pretreated powder and spraying it into the flame generated by the combustion of gas in a spheroidizing furnace, performing melting spheroidization, and obtaining a crude aluminum oxide product; S3, cleaning and drying: cleaning the crude aluminum oxide product by filter pressing or membrane washing, and then drying; S4, dispersion: after drying, performing dispersion treatment, and obtaining submicron spherical aluminum oxide. The method adopts the method of jet melting spheroidization for preparation, and the process flow is simple, and there is no need to control the particle size by grinding processing. The obtained aluminum oxide is a submicron product with high sphericity, smooth and round surface, low viscosity, and narrow particle size distribution.

Description

Technical Field

[0001] The invention belongs to the technical field of aluminum oxide preparation, and in particular relates to a method for preparing submicron spherical aluminum oxide. Background Art

[0002] Alumina has stable chemical properties, high hardness, high strength, good insulation, high temperature and pressure resistance, thermal shock resistance, good thermal conductivity, etc. It is widely used in electronic products, thermal conductive fillers, precision polishing, spraying, ceramics and other technical fields. Submicron and nano-scale alumina also has significant surface effects, small size effects and quantum effects, and exhibits excellent electrical, magnetic, optical, mechanical and other properties. It has broad application prospects in composite materials, microelectronics, aerospace industry, fine ceramics and other fields. However, submicron and nano-scale alumina has problems such as difficult particle size and morphology control and complex process in the preparation process.

[0003] Patent CN108715650B discloses a "method for preparing low specific surface area submicron alumina". This method produces submicron-sized alumina by first grinding and drying, and then low-temperature calcining and crushing. However, the alumina produced by this method has low sphericity, and although the specific surface area is reduced, the surface smoothness is still poor.

[0004] Patent CN104528787B discloses a "method for preparing fine-grained alumina powder". This method obtains fine-grained alumina by two batches of molding and two calcinations. Although the particle size and morphology are controllable and the powder uniformity is high; however, this method introduces more impurity ions, affecting the purity of the product. In addition, the two calcinations have complicated processes, high energy consumption, and difficult to control production costs.

[0005] Patent CN101704680B discloses "a submicron alumina ceramic material and its preparation method". This method is prepared through the process of "raw material-ball milling-drying-screening-molding-firing-surface processing", and can produce submicron and alumina ceramic materials with high strength, high toughness and wear resistance, and can control the particle size of submicron alumina ceramic materials between 0.05-5μm. However, the "firing" process in this method requires the control of heating, cooling and heat preservation, and the control process is complicated and difficult to operate, which is not conducive to large-scale production.

[0006] In summary, the existing methods for preparing submicron alumina all have certain defects, and it is difficult to prepare submicron alumina with high sphericity. Therefore, we urgently need to develop a method for preparing submicron spherical alumina to obtain alumina with submicron particle size and high sphericity, and the process is simple and easy to scale up. Summary of the invention

[0007] The purpose of the present invention is to overcome the deficiencies of the prior art and provide a method for preparing submicron spherical alumina which has a simple process and is suitable for large-scale production.

[0008] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0009] A method for preparing submicron spherical alumina, the method comprising the following steps:

[0010] S1. Pretreatment: Take an aluminum compound with a particle size of less than or equal to 1 μm, add a modifier, heat and stir to obtain a pretreated powder;

[0011] S2, melting spheroidization: heating the carrier gas and mixing it with the pretreated powder, spraying it into the flame generated by the combustion of gas in the spheroidizing furnace to perform melting spheroidization to obtain crude alumina;

[0012] S3, washing and drying: washing the alumina crude product by filter pressing or membrane washing, and then drying;

[0013] S4. Dispersion: After drying, the product is dispersed to obtain submicron spherical alumina.

[0014] In one embodiment of the present application, the aluminum compound is one or more of aluminum hydroxide, boehmite, gibbsite or alumina trihydrate.

[0015] In one embodiment of the present application, the particle size of the aluminum compound is 0.1-1.0 μm.

[0016] In one embodiment of the present application, the modifier is polysiloxane.

[0017] In one embodiment of the present application, the added amount of the modifier is 0.5-2wt% of the aluminum compound.

[0018] In one embodiment of the present application, in the step S1, the aluminum compound and the modifier are controlled to react under stirring at a temperature of 50-100°C, and the stirring frequency is controlled to be 10-20 Hz, and the stirring time is within the range of 15-30 min.

[0019] In one embodiment of the present application, the carrier gas is air or oxygen, and the temperature of the heated carrier gas is controlled to be 100-200° C. and the pressure is 0.4-0.7 MPa, and then the carrier gas is mixed with the pretreated powder and sprayed into the spheroidizing furnace.

[0020] In one embodiment of the present application, the fuel gas is natural gas, and the mass ratio of the flow rate of the natural gas to the pretreated powder is controlled to be 3-4:1.

[0021] In one embodiment of the present application, in step S3, microwaves are used for drying; and in step S4, an air flow disperser is used for dispersion treatment.

[0022] In one embodiment of the present application, the obtained submicron spherical alumina has a particle size of 0.2-0.8 μm.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] 1. The preparation method of submicron spherical alumina of the present invention controls the particle size of the raw aluminum compound, adds a hydrophobic modifier, and performs heating and stirring treatment to remove impurities such as hydroxyl groups on the surface of the raw aluminum compound, and allows the material to exist in the form of a single particle to maintain good fluidity and dispersibility; then, the pretreated powder is carried by a heated high-pressure carrier gas and sprayed into a flame for melt spheroidization, the material is preheated by the carrier gas, and the material is dispersed into the flame for melt spheroidization, the temperature of the melt spheroidization is maintained at a high level with little fluctuation, the melt spheroidization process is stable, the particles are dispersed for melt spheroidization, the particle size is well maintained, and sintering agglomeration is not easy to occur; finally, the crude alumina is washed to remove soluble impurities, microwave drying is used to reduce powder agglomeration, and airflow dispersion is used to obtain submicron spherical alumina with good dispersibility, low viscosity, uniform particle size, and narrow particle size distribution range. The preparation method has a simple process flow. Submicron spherical alumina powder can be obtained by jet melting and spheroidizing. There is no need to control the particle size through grinding processing, and it is easy to mass produce. The obtained product has a sphericity of ≥95%, a small specific surface area, low viscosity, and a narrow particle size distribution range. The submicron spherical alumina can fill extremely fine gaps in the grading of thermal conductive fillers to form a dense filling and achieve a high thermal conductivity effect.

[0025] 2. In the method of the present invention, the particle size of the raw material is first controlled, and then the raw material is pretreated, and then melt-spheroidized by preheating and spraying with a carrier gas. The material has good dispersion in the whole process, which effectively ensures the particle size and sphericity of the product. There is no need for grinding processing, and the particle size and morphology of the product are easier to control. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0027] Figure 1 This is the appearance morphology of the raw material aluminum hydroxide in the present invention.

[0028] Figure 2This is the appearance morphology of aluminum oxide prepared by the method of Example 1 of the present invention (I).

[0029] Figure 3 This is the appearance morphology of aluminum oxide prepared by the method of Example 1 of the present invention (II).

[0030] Figure 4 This is a graph showing the particle size distribution of aluminum oxide prepared by the method of Example 1 of the present invention.

[0031] Figure 5 This is the appearance morphology of aluminum oxide prepared by the method of comparative example 1 of the present invention (I).

[0032] Figure 6 This is the appearance morphology of aluminum oxide prepared by the method of comparative example 1 of the present invention (II). DETAILED DESCRIPTION

[0033] In the following, only some exemplary embodiments are briefly described. As those skilled in the art will appreciate, the described embodiments may be modified in various ways without departing from the spirit or scope of the embodiments of the present invention. Therefore, the drawings and descriptions are considered to be exemplary and non-restrictive in nature.

[0034] The embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0035] Example 1

[0036] An embodiment of the present invention provides a method for preparing submicron spherical aluminum oxide, the method comprising the following steps:

[0037] S1. Preprocessing

[0038] Take aluminum hydroxide with a particle size of 0.1-1.0 μm (its appearance is as follows Figure 1 As shown, the powder is irregular in shape, with a smooth surface and poor roundness), 1.0wt% of the modifier polysiloxane is added, and the material (aluminum hydroxide and polysiloxane) is heated and stirred in a heating and stirring device, and the temperature of the material (aluminum hydroxide and polysiloxane) is controlled to be 80-100°C, and the stirring is carried out at a uniform speed, the stirring frequency is 15-20Hz, and the stirring time is 20-30min. After the heating and stirring treatment, a pretreated powder with good fluidity is obtained.

[0039] S2. Melt spheroidization

[0040] Air is used as carrier gas, heated to 150-170℃, and pressurized to 0.4-0.5Mpa, mixed with pre-treated powder, so that the carrier gas (heated air) carries the pre-treated powder and sprays it into the flame generated by the combustion of gas (natural gas) in the spheroidizing furnace. Aluminum hydroxide powder is melted and spheroidized at 1800-2300℃, and cooled to obtain powdered alumina crude product. Using heated compressed air as carrier gas can preheat the material, disperse and melt the material, and provide flame retardancy for melt spheroidization, making the spheroidization process more stable. The obtained alumina crude product has good dispersibility and stable and uniform morphological characteristics.

[0041] S3. Cleaning and drying

[0042] The obtained alumina crude product is washed by filter pressing or membrane washing, and then dried by microwave to reduce powder agglomeration.

[0043] S4. Dispersion

[0044] The dried material is dispersed by air flow to break up the lumps in the material, and then it can be dried by microwave and sieved to obtain submicron spherical alumina products.

[0045] like Figure 2 and Figure 3 As shown, the obtained alumina powder is in the shape of a sphere with a smooth and round surface, high sphericity, good dispersibility, uniform particle size, and a narrow particle size distribution range of about 0.2-0.8 μm.

[0046] like Figure 4 As shown in the figure, it can be seen that the particle size distribution range of alumina powder is narrow, and the median particle size D50 is 0.51μm.

[0047] Example 2

[0048] A method for preparing submicron spherical alumina, the method comprising the following steps:

[0049] S1. Preprocessing

[0050] Take boehmite with a particle size of 0.3-0.6μm, add 0.5wt% of the modifier polysiloxane, and heat and stir in a heating and stirring device, control the temperature of the materials (aluminum hydroxide and polysiloxane) to 50-70°C, stir at a uniform speed, the stirring frequency is 15-20Hz, and the stirring time is 20min. After heating and stirring, a pretreated powder with good fluidity is obtained.

[0051] S2. Melt spheroidization

[0052] Air is used as a carrier gas, heated to 150-200°C, and pressurized to 0.5-0.7Mpa, and mixed with the pretreated powder. The carrier gas (heated air) carries the pretreated powder and is sprayed into the flame generated by the combustion of gas (natural gas) in the spheroidizing furnace. The aluminum hydroxide powder is melted and spheroidized at 1800-2000°C, and cooled to obtain a powdered alumina crude product.

[0053] S3. Cleaning and drying

[0054] The obtained alumina crude product is washed by filter pressing or membrane washing, and then dried by microwave to reduce powder agglomeration.

[0055] S4. Dispersion

[0056] The dried material is dispersed by air flow to break up the lumps in the material, and then microwave dried and sieved to obtain submicron spherical alumina products. The obtained alumina powder is observed to be in the shape of a sphere with a smooth and round surface, high sphericity, good dispersibility and uniform particle size.

[0057] Example 3

[0058] A method for preparing submicron spherical alumina, which is basically the same as Example 1, except that the addition amount of the modifier polysiloxane is 2.0wt%, the stirring temperature is 60-70°C, the stirring frequency is 10-15Hz, and the stirring time is 15min.

[0059] Example 4

[0060] A method for preparing submicron spherical alumina, which is basically the same as Example 1, except that oxygen is used as a carrier gas, heated to 100-150°C, and pressurized to 0.4-0.5Mpa, and mixed with a pretreated powder, so that the carrier gas (oxygen) carries the pretreated powder and is sprayed into the flame generated by the combustion of gas (natural gas) in a spheroidizing furnace, and the aluminum hydroxide powder is melt-spheroidized at 2000-2300°C.

[0061] Comparative Example 1

[0062] A method for preparing submicron spherical alumina, the method comprising the following steps:

[0063] S1. Raw material selection

[0064] Aluminum hydroxide with a median particle size D50 of 0.3-0.6 μm was selected.

[0065] S2. Melt spheroidization

[0066] Air is used as a carrier gas, heated to 150-170°C, and pressurized to 0.4-0.5Mpa, and mixed with aluminum hydroxide powder. The carrier gas (heated air) carries the pre-treated powder and is sprayed into the flame generated by the combustion of gas (natural gas) in the spheroidizing furnace. The aluminum hydroxide powder is melted and spheroidized at 1800-2300°C, and cooled to obtain powdered alumina crude product.

[0067] S3. Cleaning and drying

[0068] The obtained alumina crude product is washed by filter pressing or membrane washing, and then dried by microwave to reduce powder agglomeration.

[0069] S4. Dispersion

[0070] The dried material is dispersed by air flow to break up the lumps in the material, and then microwave dried and sieved to obtain submicron spherical alumina products.

[0071] like Figure 5 and Figure 6 As shown, the obtained alumina powder is in the shape of a sphere with a rounded surface and a high sphericity of the powder, but has poor dispersibility, poor particle size uniformity, and a wide particle size distribution range.

[0072] Comparative Example 2

[0073] The submicron spherical alumina powder prepared in Example 1 and the commercially available submicron alumina powder product were used as thermal conductive fillers, respectively. The viscosity of the thermal conductive filler of the submicron spherical alumina powder prepared in Example 1 was measured to be 2003210 mPa.s at 1 inverse second and 408589 mPa.s at 10 inverse seconds; the viscosity of the thermal conductive filler of the commercially available submicron alumina powder product was 4631390 mPa.s at 1 inverse second and 454737 mPa.s at 10 inverse seconds.

Claims

1. A method for preparing submicron spherical alumina, characterized in that: The method comprises the following steps: S1. Pretreatment: Take an aluminum compound with a particle size of less than or equal to 1 μm, add a modifier, heat and stir to obtain a pretreated powder; Wherein, the aluminum compound is one or more of aluminum hydroxide, boehmite, gibbsite or alumina trihydrate; The modifier is polysiloxane; the amount of the modifier added is 0.5-2wt% of the aluminum compound; The heating and stirring treatment is to stir the reaction at a temperature of 50-100°C, and the stirring frequency is controlled to be 10-20Hz, and the stirring time is within the range of 15-30min; S2, melting spheroidization: heating the carrier gas and mixing it with the pretreated powder, spraying it into the flame generated by the combustion of gas in the spheroidizing furnace to perform melting spheroidization to obtain crude alumina; S3, washing and drying: washing the alumina crude product by filter pressing or membrane washing, and then drying; S4. Dispersion: After drying, the product is dispersed to obtain submicron spherical alumina.

2. The method for preparing submicron spherical alumina according to claim 1, characterized in that: The particle size of the aluminum compound is 0.1-1.0 μm.

3. The method for preparing submicron spherical alumina according to claim 1, characterized in that: The carrier gas is air or oxygen. The temperature of the carrier gas after heating is controlled to be 100-200° C. and the pressure is 0.4-0.7 MPa. Then, the carrier gas is mixed with the pretreated powder and sprayed into the spheroidizing furnace.

4. The method for preparing submicron spherical alumina according to claim 1, characterized in that: In the step S3, microwaves are used for drying; in the step S4, an air flow disperser is used for dispersion treatment.

5. The method for preparing submicron spherical alumina according to claim 1 or 4, characterized in that: The obtained submicron spherical aluminum oxide has a particle size of 0.2-0.8 μm.

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