Spherical-like aluminum oxide and preparation method thereof

Abstract

The invention provides sphere-like aluminum oxide and a preparation method thereof, and the method comprises the following steps: preparation of boehmite powder: carrying out hydrothermal reaction on slurry in a high-pressure reaction kettle to convert aluminum hydroxide or gamma aluminum oxide into boehmite, and drying to obtain the boehmite powder; and preparing the spheroidic aluminum oxide: uniformly mixing the boehmite powder with an additive, calcining to convert the boehmite powder into aluminum oxide, and grinding to obtain the spheroidic aluminum oxide. The spheroidic alumina obtained by the method has good sphericity and good dispersibility, and the method is simple in production process, low in cost and easy to industrialize.

Description

Technical Field

[0001] The present application belongs to the technical field of inorganic non-metallic materials, and specifically relates to a quasi-spherical aluminum oxide and a preparation method thereof. Background Art

[0002] Alumina has many crystal forms, which give it unique physical and chemical properties. Therefore, it is widely used in many fields such as electronics, petrochemicals, refractories, ceramics, and aerospace. The application performance of alumina products in many fields is closely related to the morphology and size of the raw powder particles. Among powder particles of different shapes, spherical particles have regular morphology, smaller specific surface area, larger bulk density and better fluidity, which can greatly improve the application performance of the products.

[0003] In the field of new energy vehicles, new energy vehicle batteries, electronic controls, and motors all use thermal interface materials such as thermal conductive materials and thermal conductive adhesives, and spherical alumina is a common inorganic filler in thermal interface materials; in 5G communications, the functions of electronic products are becoming increasingly complex and miniaturized, and solving the problem of heat dissipation of core components of electronic products has become a top priority, driving the development of thermal interface materials that can meet their heat dissipation upgrade needs. With the increasing demand for spherical alumina in various fields and the continuous expansion of the market, thermal conductive materials have become the most important application of spherical alumina.

[0004] Therefore, it is necessary to provide a method for preparing spherical alumina with a simple process. Summary of the invention

[0005] In view of this, the present application provides a quasi-spherical alumina and a preparation method thereof. The preparation method has a simple process, and the obtained quasi-spherical alumina has good sphericity and is evenly dispersed.

[0006] In a first aspect, the present application provides a method for preparing spherical aluminum oxide, comprising the following steps:

[0007] Preparation of boehmite powder: using aluminum hydroxide or gamma alumina slurry to perform hydrothermal reaction in a high-pressure reactor to convert aluminum hydroxide or gamma alumina into boehmite, and drying to obtain boehmite powder;

[0008] Preparation of quasi-spherical alumina: The boehmite powder is mixed with an additive, calcined to convert the boehmite powder into alumina, and then ground to obtain quasi-spherical alumina.

[0009] According to the present application, by using aluminum hydroxide or γ-alumina slurry as a raw material and conducting a hydrothermal reaction in a high-pressure reactor, a boehmite powder with a small particle size and uniform dispersion can be obtained. The boehmite powder is used as a precursor and mixed with an additive and calcined, which can intensify the evaporation-condensation diffusion mechanism in the growth process of α-Al2O3, so that the growth of the particles tends to spheroidize. At the same time, boehmite as a precursor has the advantage of stable structure. Therefore, the obtained spherical alumina has good sphericity and good dispersibility.

[0010] In some embodiments, in the preparation of the boehmite powder, the concentration of the aluminum hydroxide or gamma alumina slurry is 10% to 15%.

[0011] In some embodiments, in the preparation of the boehmite powder, the hydrothermal reaction conditions are: keeping warm at a temperature of 160 to 230° C. and a pressure of 0.5 to 3.0 MPa for 1 to 5 hours.

[0012] In some embodiments, the additive includes at least one of ammonium chloride, boric acid, magnesium hydroxide, and magnesium oxide.

[0013] In some embodiments, the mass of the additive is 0.1% to 1.5% of the boehmite powder.

[0014] In some embodiments, in the preparation of the quasi-spherical alumina, the mixing specifically includes: homogenizing the boehmite powder and the additive in a high-speed pulverizer for 5 to 30 minutes.

[0015] In some embodiments, in the preparation of the quasi-spherical alumina, the calcination conditions are: calcination at 1150-1400° C. for 1-4 hours.

[0016] In some embodiments, in the preparation of the quasi-spherical aluminum oxide, the grinding specifically includes: grinding the aluminum oxide using a ball mill to make the particle size Dv50 of the aluminum oxide be 0.3 to 1.5 μm.

[0017] In some embodiments, the ball milling specifically includes: ball milling the alumina for 10 to 100 minutes.

[0018] In a second aspect, the present application provides a quasi-spherical alumina, which is prepared according to the method described in any embodiment of the first aspect, wherein the particle size Dv50 of the quasi-spherical alumina is 0.3 to 1.5 μm, and the specific surface area BET is 3 to 11 m 2 / g. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a scanning electron microscope image of the spherical alumina prepared in Example 1 of the present application.

[0020] Figure 2 This is the XRD diffraction pattern of the spherical alumina prepared in Example 1 of the present application.

[0021] Figure 3 This is the particle size distribution graph of the spherical alumina prepared in Example 1 of the present application. DETAILED DESCRIPTION

[0022] In order to make the purpose, technical solution and advantages of the present application more clear, the present application is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described here are only used to explain the present application and are not used to limit the present application.

[0023] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "illustrative embodiments", "examples", "specific examples", or "some examples" means that the specific features, structures, materials, or characteristics described in conjunction with the implementation or examples are included in at least one implementation or example of the present application. In this specification, the schematic representation of the above terms does not necessarily refer to the same implementation or example. Moreover, the specific features, structures, materials, or characteristics described may be combined in any one or more implementations or examples in a suitable manner.

[0024] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In the description of this application, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0025] As described in the background technology above, with the application of alumina in thermal conductive materials, spherical alumina can greatly improve the application performance of products due to its regular morphology, small specific surface area, large bulk density and good fluidity. Therefore, it is necessary to provide a preparation method of spherical alumina.

[0026] The process for preparing spherical alumina in the related art is relatively complicated. For example, patent CN112456527A discloses a method for preparing spherical alumina using gibbsite as a precursor. The method is to prepare industrial aluminum, industrial sodium hydroxide and water into a sodium aluminate solution, and add calcium oxide to the sodium aluminate solution for desiliconization, and then add a plate-forming agent to the desiliconized sodium aluminate solution for carbonation decomposition, and then filter to obtain an aluminum hydroxide filter cake, and finally pickle the filter cake to remove impurities, dry it, and calcine and ball mill it to obtain spherical alumina. The calcination process of this method can obtain the target spherical alumina by adding an appropriate amount of additives and adjusting the calcination system, but the method involves the desiliconization, pickling and other processes of the precursor, the process is complicated, acidic substances are used in the process, there are uncertain safety hazards, and calcium-containing waste is generated, which will bring other problems in industrial production.

[0027] Based on this, the present application provides a method for preparing quasi-spherical alumina, which uses aluminum hydroxide or γ-alumina slurry as a raw material, prepares boehmite powder with a small particle size and good dispersion by a hydrothermal method, and uses the boehmite powder as a precursor to obtain quasi-spherical alumina with good sphericity and dispersion by calcination. The specific implementation methods of the present application are described in detail below.

[0028] In a first aspect, the present application provides a method for preparing spherical aluminum oxide, comprising the following steps:

[0029] Preparation of boehmite powder: using aluminum hydroxide or gamma alumina slurry to perform hydrothermal reaction in a high-pressure reactor to convert aluminum hydroxide or gamma alumina into boehmite, and drying to obtain boehmite powder;

[0030] Preparation of quasi-spherical alumina: boehmite powder is mixed with an additive, calcined to convert the boehmite powder into alumina, and then ground to obtain quasi-spherical alumina.

[0031] Specifically, the inventors found that the formation of spherical α-Al2O3 may be related to the diffusion mechanism of aluminum oxide at high temperature, and the diffusion mechanism of aluminum oxide at high temperature is diverse, including surface diffusion, grain boundary diffusion, crystal plane diffusion and evaporation-condensation diffusion, etc. The morphology of aluminum oxide is affected by a variety of diffusion mechanisms, among which the evaporation-condensation diffusion mechanism can make the morphology of aluminum oxide particles tend to spheroidize, but because the vapor pressure of large aluminum oxide particles is very low, the evaporation-condensation diffusion mechanism has a weak effect in the growth process of α-Al2O3. By reducing the particle size of the precursor, the effect of the evaporation-condensation diffusion mechanism in the growth process of α-Al2O3 can be increased, thereby obtaining α-Al2O3 with better sphericity. However, if industrial aluminum oxide or industrial aluminum hydroxide is used as a precursor for calcination, the precursor needs to be pre-treated by processes such as ball milling, and desiliconization, acid washing and other processes are also required. On the one hand, the process flow will increase and the cost will increase. On the other hand, the dispersion of the small-particle precursor obtained by ball milling is poor, and the uneven particle size will make it difficult to stably control the quality of spherical aluminum oxide.

[0032] According to the present application, by using aluminum hydroxide or γ-alumina slurry as raw material and conducting a hydrothermal reaction in a high-pressure reactor, boehmite powder with a smaller particle size and uniform dispersion can be obtained. Using the boehmite powder as a precursor, it is easier to obtain spherical alumina with better dispersion.

[0033] It should be noted that, since boehmite powder has the advantage of structural stability as a precursor, the higher the dispersibility of boehmite, the easier it is to control the dispersion of spherical alumina prepared by calcination. If conventional boehmite powder is directly used as a precursor, in order to strengthen the evaporation-condensation diffusion mechanism, the boehmite powder needs to be ground, and the grain morphology of boehmite powder is generally rhombus, which will lead to poor dispersion of the ground product, and then make the dispersion of spherical alumina difficult to control. In this application, the boehmite powder prepared by the hydrothermal method is directly used without additional grinding operations, so that it is easier to obtain spherical alumina with better dispersion.

[0034] Subsequently, the boehmite powder with a smaller particle size and uniform dispersion is mixed with an additive and calcined. The inventors found that if the above-mentioned boehmite powder is directly calcined alone, spherical alumina with good dispersion cannot be obtained. After analysis, the reason may be that the grains are prone to abnormal growth during the calcination process, resulting in the weakening of the evaporation-condensation diffusion mechanism, and the sphericity and dispersibility of the obtained alumina are poor; therefore, further adding an additive to the boehmite powder for calcination can cooperate with the above-mentioned boehmite to effectively reduce the temperature of boehmite conversion to α-Al2O3, increase the vapor pressure of alumina, and intensify the effect of the evaporation-condensation diffusion mechanism in the growth process of α-Al2O3. In addition, it can also inhibit the growth of grains, so that the growth of particles tends to spheroidize. At the same time, only the crystal form changes before and after calcination, while the morphology of the product can remain unchanged, and alumina with the same morphology can be obtained. Therefore, the obtained spherical alumina has good sphericity and good dispersibility. The method provided in the present application is simple in process and can obtain quasi-spherical alumina with good sphericity and dispersibility.

[0035] In some embodiments, in the preparation of boehmite powder, the concentration of aluminum hydroxide or gamma alumina slurry is 10% to 15%.

[0036] In some of the above embodiments, by controlling the concentration of aluminum hydroxide or γ-alumina slurry within the above range, it is more conducive to obtaining boehmite powder with smaller particle size and uniform dispersion, so that the spherical alumina obtained has better sphericity and dispersibility.

[0037] In some embodiments, in the preparation of boehmite powder, the conditions of the hydrothermal reaction are: keeping warm at a temperature of 160 to 230° C. and a pressure of 0.5 to 3.0 MPa for 1 to 5 hours.

[0038] In some of the above embodiments, the conditions of the hydrothermal reaction are further limited. Under the above conditions, the boehmite powder prepared has a smaller particle size and better dispersion, and the spherical alumina obtained has better sphericity and dispersion.

[0039] In some embodiments, the additive includes at least one of ammonium chloride, boric acid, magnesium hydroxide, and magnesium oxide.

[0040] In some of the above embodiments, the types of admixtures are further limited. The use of the above admixtures can effectively reduce the temperature of boehmite conversion to α-Al2O3 by coordinating with boehmite powder with smaller particle size and uniform dispersion, increase the vapor pressure of alumina, inhibit the growth of grains, and intensify the evaporation-condensation diffusion mechanism in the growth process of α-Al2O3, thereby improving the sphericity and dispersibility of alumina.

[0041] In some embodiments, the mass of the additive is 0.1% to 1.5% of the boehmite powder.

[0042] In some of the above embodiments, the amount of additive added is further limited, and the spherical alumina obtained at this time has better sphericity and dispersibility and lower impurity content.

[0043] In some embodiments, in the preparation of quasi-spherical alumina, the mixing specifically comprises: homogenizing the boehmite powder and the additive in a high-speed pulverizer for 5 to 30 minutes.

[0044] In some of the above embodiments, by using a high-speed pulverizer to homogenize the boehmite powder and the additive, the entire reaction system can be converted more completely and synchronously during the calcination process, so that the sphericity and dispersibility of the obtained spherical alumina are better.

[0045] In some embodiments, in the preparation of quasi-spherical alumina, the calcination conditions are: calcination at 1150-1400° C. for 1-4 h.

[0046] In some of the above embodiments, the calcination conditions are further defined, under which the boehmite powder can be fully converted into α-Al2O3, while also reducing the further growth of the grains, thereby obtaining spherical alumina with better sphericity and dispersibility.

[0047] In some embodiments, in the preparation of quasi-spherical aluminum oxide, grinding specifically includes: grinding the aluminum oxide using a ball mill to make the particle size Dv50 of the aluminum oxide be 0.3 to 1.5 μm.

[0048] In some of the above embodiments, since alumina will agglomerate to a certain extent during the calcination process, the agglomerated alumina can be ground to the original grain size using a ball mill, so that the particle size Dv50 of the alumina is 0.3-1.5 μm. At this time, the spherical alumina obtained has better sphericity and dispersibility.

[0049] It should be noted that Dv50 has a well-known meaning in the art, and refers to the particle size corresponding to 50% in the particle size distribution. It can be detected according to methods and instruments known in the art. As an example, it can be detected with reference to GB / T 19077-2016 using Mastersizer 3000 produced by Malvern.

[0050] In some embodiments, the ball milling specifically includes: ball milling the alumina for 10 to 100 minutes.

[0051] In a second aspect, the present application provides a quasi-spherical alumina, which is prepared according to the method of any embodiment of the first aspect, wherein the particle size Dv50 of the quasi-spherical alumina is 0.3 to 1.5 μm, and the specific surface area BET is 3 to 11 m 2 / g.

[0052] According to the present application, the spherical alumina is prepared according to the method of any embodiment of the first aspect, and thus has the beneficial effects of any embodiment of the first aspect, and the particle size Dv50 of the spherical alumina is 0.3 to 1.5 μm, and the specific surface area BET is 3 to 11 m 2 / g, thus having good thermal conductivity.

[0053] It should be noted that the specific surface area BET has a well-known meaning in the art and can be detected according to methods and instruments known in the art. As an example, it can be detected with reference to GB / T 19587-2017.

[0054] The scheme of the present application is described below in conjunction with the following specific examples. Unless otherwise specified, the raw materials used in the following examples are all from common commercial products, and the devices or equipment used are all purchased from conventional market sales channels.

[0055] Example 1

[0056] Preparation of boehmite powder: Industrial aluminum hydroxide is prepared into aluminum hydroxide slurry with distilled water, and the concentration of the aluminum hydroxide slurry is 11%. The prepared slurry is poured into a high-pressure hydrothermal autoclave with a stirring function and heated to 170°C for a hydrothermal reaction. The agitator is always in a working state during the reaction. After keeping warm for 5 hours, the pressure is released to obtain the boehmite slurry. After the obtained slurry is cooled to room temperature, it is rinsed and dried to obtain a rhombus-shaped boehmite powder, which is a precursor for preparing spherical alumina.

[0057] Preparation of quasi-spherical alumina: The obtained boehmite powder is used as a precursor, and boric acid is added as an additive. The amount of the additive is 0.5wt% of the boehmite powder. The prepared raw materials are homogenized by a high-speed crusher for 10 minutes to obtain a uniform mixture. The mixture is placed in a corundum crucible and calcined in a high-temperature furnace. The maximum calcination temperature is 1250°C, and the temperature is maintained for 2 hours. The product after calcination and cooling is ground to the original grain size by a ball mill to obtain quasi-spherical alumina.

[0058] The spherical alumina was observed using a scanning electron microscope, and the scanning electron microscope image is as follows Figure 1 In addition, the spherical alumina was subjected to X-ray diffraction analysis, and its XRD diffraction pattern is as shown Figure 2 As shown; the particle size of this type of spherical alumina is analyzed using a laser particle size analyzer, and its particle size distribution graph is as shown Figure 3 shown.

[0059] according to Figure 1 to Figure 3The prepared quasi-spherical alumina is α-Al2O3, with no impurity peaks, regular morphology, high sphericity, and narrow particle size distribution. Dv10 and Dv90 are 0.474μm and 1.219μm respectively, and the median particle size Dv50 is 0.764μm, with good dispersibility.

[0060] Example 2

[0061] Preparation of boehmite powder: Industrial aluminum hydroxide is prepared into aluminum hydroxide slurry with distilled water. The concentration of the aluminum hydroxide slurry is 12. The prepared slurry is poured into a high-pressure hydrothermal autoclave with a stirring function and heated to 180°C for a hydrothermal reaction. The agitator is always in a working state during the reaction. After keeping warm for 4 hours, the pressure is released to obtain boehmite slurry. After the obtained slurry is cooled to room temperature, it is washed and dried to obtain rhombus-shaped boehmite powder, which is the precursor for preparing spherical alumina.

[0062] Preparation of quasi-spherical alumina: The obtained boehmite powder is used as a precursor, and ammonium chloride is added as an additive. The amount of ammonium chloride added is 0.2wt% of the precursor. The prepared raw materials are homogenized by a high-speed crusher for 10 minutes to obtain a uniform mixture. The mixture is loaded into a corundum crucible and calcined in a high-temperature furnace. The maximum calcination temperature is 1300°C, and the temperature is kept for 3 hours. The product after calcination and cooling is ground to the original grain size by a ball mill to obtain quasi-spherical alumina.

[0063] Example 3

[0064] Preparation of boehmite powder: Industrial alumina is prepared into γ-alumina slurry with distilled water, and the concentration of the alumina slurry is 10%. The prepared slurry is poured into a high-pressure hydrothermal autoclave with a stirring function and heated to 230°C for a hydrothermal reaction. The agitator is always in a working state during the reaction. After keeping warm for 3 hours, the pressure is released to obtain the boehmite slurry. After the obtained slurry is cooled to room temperature, it is eluted and dried to obtain a rhombus-shaped boehmite powder, which is a precursor for preparing spherical alumina.

[0065] Preparation of quasi-spherical alumina: The obtained boehmite powder is used as a precursor, and an additive of magnesium hydroxide is added, and the amount of magnesium hydroxide added is 1%. The prepared raw materials are homogenized by a high-speed crusher for 20 minutes to obtain a uniform mixture. It is loaded into a corundum crucible and calcined in a high-temperature furnace. The highest calcination temperature is 1350°C, and the heat is maintained for 2 hours. The product after calcination and cooling is ground to the original grain size by a ball mill, and quasi-spherical alumina is obtained.

[0066] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent substitutions and improvements made within the principles of the present application should be included in the protection scope of the present application.

Claims

1. A method for preparing quasi-spherical aluminum oxide, characterized in that: The following steps are involved: Preparation of boehmite powder: using aluminum hydroxide or gamma alumina slurry to perform hydrothermal reaction in a high-pressure reactor to convert aluminum hydroxide or gamma alumina into boehmite, and drying to obtain boehmite powder; Preparation of quasi-spherical alumina: The boehmite powder is mixed with an additive, calcined to convert the boehmite powder into alumina, and then ground to obtain quasi-spherical alumina.

2. The method according to claim 1, characterized in that In the preparation of the boehmite powder, the concentration of the aluminum hydroxide or gamma alumina slurry is 10% to 15%.

3. The method according to claim 1, characterized in that In the preparation of the boehmite powder, the hydrothermal reaction conditions are: keeping warm for 1 to 5 hours at a temperature of 160 to 230° C. and a pressure of 0.5 to 3.0 MPa.

4. The method according to any one of claims 1 to 3, characterized in that: The additive includes at least one of ammonium chloride, boric acid, magnesium hydroxide and magnesium oxide.

5. The method according to claim 4, characterized in that The mass of the additive is 0.1% to 1.5% of the boehmite powder.

6. The method according to any one of claims 1 to 3, characterized in that: In the preparation of the quasi-spherical alumina, the mixing specifically includes: homogenizing the boehmite powder and the additive in a high-speed pulverizer for 5 to 30 minutes.

7. The method according to any one of claims 1 to 3, characterized in that: In the preparation of the quasi-spherical alumina, the calcination conditions are: calcination at 1150-1400° C. for 1-4 hours.

8. The method according to any one of claims 1 to 3, characterized in that: In the preparation of the quasi-spherical aluminum oxide, the grinding specifically includes: using a ball mill to ball-mill the aluminum oxide so that the particle size Dv50 value of the aluminum oxide is 0.3 to 1.5 μm.

9. The method according to claim 8, characterized in that The ball milling specifically includes: ball milling the alumina for 10 to 100 minutes.

10. A quasi-spherical aluminum oxide, characterized in that: The method according to any one of claims 1 to 9 is used to prepare the spherical alumina, wherein the particle size Dv50 of the spherical alumina is 0.3 to 1.5 μm, and the specific surface area BET is 3 to 11 m 2 / g.

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