Ultrafine alumina with low oil absorption value and preparation method thereof

Abstract

The invention provides superfine aluminum oxide with a low oil absorption value and a preparation method of the superfine aluminum oxide, and belongs to the field of inorganic non-metallic materials. The method comprises the following steps: mixing boehmite with an oil absorption regulator to obtain a mixture; carrying out primary calcination on the mixture to obtain intermediate alumina powder; carrying out secondary calcination on the intermediate aluminum oxide powder to obtain alpha-aluminum oxide powder; the method comprises the following steps: crushing alpha-aluminum oxide powder to obtain superfine aluminum oxide with a low oil absorption value; the oil absorption regulator comprises one or more of boric acid, calcium fluoride and ammonium chloride. According to the preparation method, boehmite is adopted as a raw material, the boehmite and the oil absorption regulator are pretreated and then the calcination process is carried out, the pretreatment mode can effectively avoid growth of original crystals in the calcination process, meanwhile, the product morphology is accurately adjusted, and therefore the high alpha-phase conversion rate and the low oil absorption value are achieved; and the use requirements of thermal interface materials, electronic packaging and other application scenes can be fully met.

Description

Technical Field

[0001] This application relates to the field of inorganic non-metallic materials technology, and in particular to a low oil absorption value ultrafine alumina and its preparation method. Background Technology

[0002] With the rapid development of technologies such as 5G communication, new energy vehicles, and the Internet of Things, electronic devices are evolving towards higher frequencies, higher power, miniaturization, and integration, leading to a sharp increase in the power density of devices. "Thermal management" has become a bottleneck issue determining device performance, reliability, and lifespan. Alumina, with its excellent insulation and good thermal conductivity, has become the most widely used and cost-effective thermally conductive filler. Typically, the thermal conductivity of a product is improved by increasing the amount of alumina filled in the polymer. The oil absorption value is an indicator that indirectly reflects the specific surface area and flowability of the powder, and it is also an important factor affecting the performance of alumina powder in polymer applications. For alumina powder of the same particle size, the lower the oil absorption value, the higher its filling amount in the polymer, and the higher the thermal conductivity of the product.

[0003] Currently, the main method to reduce the oil absorption value of alumina is surface modification. However, due to its small particle size and poor dispersibility, ultrafine alumina cannot be adequately coated with coupling agents, resulting in poor surface treatment effects. With the continuous development of electronic materials, the research and development of ultrafine alumina with low oil absorption value has become an urgent problem to be solved in order to more effectively improve the thermal conductivity of thermal interface materials. Summary of the Invention

[0004] This application provides a low oil absorption value ultrafine alumina and its preparation method to solve the following technical problem: how to reduce the oil absorption value of alumina.

[0005] In a first aspect, embodiments of this application provide a method for preparing low oil absorption value ultrafine alumina, the method comprising: Boehmite was mixed with an oil-absorbing modifier to obtain a mixture; The mixture was calcined once to obtain intermediate alumina powder; The intermediate alumina powder is calcined a second time to obtain α-alumina powder; The α-alumina powder is pulverized to obtain ultrafine alumina with low oil absorption value; The oil-absorbing modifier includes one or more of boric acid, calcium fluoride, and ammonium chloride.

[0006] Optionally, the mass of the oil-absorbing modifier is 0.1% to 1% of the mass of the boehmite.

[0007] Optionally, the mass of the oil-absorbing modifier is 0.5% to 1% of the mass of the boehmite.

[0008] Optionally, the primary calcination is performed using a tunnel kiln.

[0009] Optionally, the temperature of the first calcination is 1100℃~1200℃, and the time of the first calcination is 0.5h~3h.

[0010] Optionally, the secondary calcination is performed using a shuttle kiln.

[0011] Optionally, the secondary calcination temperature is 1300℃~1400℃, and the secondary calcination time is 3h~5h.

[0012] Optionally, the pulverization is performed using an air jet mill, and the α-alumina powder is pulverized by air jet milling to a D50 of 0.5 μm to 1.0 μm.

[0013] Secondly, embodiments of this application provide a low oil absorption value ultrafine alumina prepared by the method described in any one of the first aspects, wherein the crystal form of the low oil absorption value ultrafine alumina is α-type.

[0014] Optionally, the low oil absorption value ultrafine alumina meets the following properties: α phase conversion rate ≥95%, particle size distribution D50 of 0.5μm~1μm, and oil absorption value ≤28g / 100g.

[0015] The technical solutions provided in this application have the following advantages compared with the prior art: This application provides a method for preparing ultrafine alumina with low oil absorption value. The method reduces the oil absorption value of alumina through the synergistic effect of an oil-absorbing modifier and a calcination process. The specific implementation path is as follows: First, boehmite is mixed with an oil-absorbing modifier (one or more of boric acid, calcium fluoride, and ammonium chloride) to achieve a uniform dispersion of the modifier within the boehmite, laying the foundation for subsequent targeted improvement of the powder structure. Then, the mixture undergoes a first and second calcination. During these two calcination processes, the oil-absorbing modifier plays a regulatory role, optimizing the morphology of the alumina product, promoting grain growth towards densification, and reducing the pore structure inside and on the surface of the powder. Pores are the main carriers for oil adsorption, and reducing the number of pores directly weakens the oil absorption capacity of the alumina powder. Finally, ultrafine alumina with low oil absorption value is obtained through a pulverization process. Throughout the process, the uniform dispersion of the oil-absorbing modifier and the synergistic effect of the two calcinations constitute the core logic for reducing the oil absorption value of alumina, ensuring that the final product possesses low oil absorption characteristics. Attached Figure Description

[0016] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0017] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a schematic flowchart illustrating a method for preparing low oil absorption value ultrafine alumina according to an embodiment of this application. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0020] The range descriptions used herein, such as numerical ranges and proportional ranges, include all possible sub-ranges and single numerical values ​​within that range. For example, the range descriptions of "1 to 6" or "1 to 6" cover all sub-ranges (such as 1 to 3, 2 to 5, etc.) and single numbers (such as 1, 2, 3, 4, 5, 6) between 1 and 6. Unless otherwise specified, the terms "including" and "contains" as used herein mean "including but not limited to"; relational terms such as "first" and "second" are used only to distinguish different entities or operations and do not imply an actual order or relationship; "and / or" indicates that multiple situations can exist individually or simultaneously; expressions such as "at least one," "multiple," and "at least one" refer to any combination of the corresponding objects, including combinations of single or multiple objects. The proportional relationships mentioned herein, such as mass ratios and molar ratios, should be understood as the correspondence between the first and second terms of a proportional formula, according to the order of description. The raw materials, reagents, instruments, and equipment used herein can all be obtained through commercial purchase or prepared using existing methods.

[0021] Figure 1 This is a schematic flowchart illustrating a method for preparing low oil absorption value ultrafine alumina according to an embodiment of this application.

[0022] like Figure 1 As shown in the embodiment of this application, a method for preparing ultrafine alumina with low oil absorption value is provided, the method comprising: S1. Mix boehmite with oil-absorbing modifier to obtain a mixture; S2. The mixture is calcined once to obtain intermediate alumina powder; S3. The intermediate alumina powder is calcined a second time to obtain α-alumina powder; S4. Pulverize the α-alumina powder to obtain ultrafine alumina with low oil absorption value; The oil-absorbing modifiers include one or more of boric acid, calcium fluoride, and ammonium chloride.

[0023] It should be noted that the mixing step in S1 mixes the boehmite and the oil absorbent agent evenly. The core function is to make the oil absorbent agent form a uniform dispersion in the boehmite, which provides the prerequisite for accurately adjusting the product morphology and promoting grain densification during the subsequent calcination process. It also ensures that the oil absorbent agent can fully interact with the boehmite, laying the foundation for reducing the product's oil absorption value and improving the α-phase conversion rate.

[0024] The first calcination step of S2 uses a tunnel kiln to calcine the mixture. Its core function is to initiate the crystal transformation process of boehmite to α-alumina and initially increase the α-phase conversion ratio. At the same time, under this temperature environment, the oil-absorbing modifier begins to play its role, inhibiting the excessive growth of the original crystals and initially optimizing the product morphology, laying the groundwork for the deep transformation and densification in the second calcination.

[0025] The secondary calcination step of S3 uses a shuttle kiln to calcine the intermediate alumina powder after the primary calcination. Its core function is to further promote crystal transformation and ensure that the α-phase conversion rate reaches ≥95%. At the same time, this step can significantly improve the density of alumina grains, reduce the internal porosity of the powder, reduce the oil absorption value from the structure, and finally form a stable α-alumina powder.

[0026] The S4 pulverization step uses an air jet mill to pulverize the α-alumina powder after secondary calcination. Its core function is to break up the agglomerated powder particles and process them to the target particle size range, so that the product particle size distribution meets the requirement of D50 of 0.5 to 1.0 μm. At the same time, the pulverization process can improve the dispersibility of the product and avoid particle agglomeration from affecting the subsequent application effect in thermal interface materials, electronic packaging and other scenarios.

[0027] Meanwhile, this application selects one or more of boric acid, calcium fluoride and ammonium chloride as oil absorption modifiers. The core reason is that the physicochemical properties of these substances are highly compatible with the process conditions and performance objectives of this invention. They can achieve the core objectives of adjusting product morphology, promoting grain densification, improving α-phase conversion rate and reducing oil absorption value through precise action mechanisms.

[0028] Boric acid can form a low-melting-point molten phase within the calcination temperature range of 1100–1400℃, uniformly coating the surface of boehmite particles. This effectively inhibits excessive growth of the original crystals during calcination, preventing increased porosity caused by particle agglomeration, and guides grain growth along the densification direction, reducing the microporous structure inside and on the surface of the particles. Calcium fluoride, as a mineralizing agent, can lower the activation energy of the conversion of boehmite to α-alumina, accelerating the α-phase conversion process. At the same time, its lattice structure characteristics can optimize the geometry of alumina particles, making the particles more regular in shape, reducing surface defects and porosity, and structurally reducing oil absorption capacity. Ammonium chloride decomposes during calcination to produce volatile gases. This decomposition process not only removes trace impurities from boehmite, preventing the formation of pores caused by impurity residues, but also breaks down the adhesion between particles through gas escape, improving particle dispersibility. Moreover, the decomposition products leave no residue and do not affect the purity of the alumina product. In addition, the acidic atmosphere produced by its decomposition can slightly adjust the surface state of the particles, further promoting grain densification.

[0029] Furthermore, these three substances can achieve their core functions when used individually, and produce synergistic effects when used in combination. For example, the grain growth inhibition effect of boric acid combined with the α-phase conversion acceleration effect of calcium fluoride can further optimize particle density while ensuring a high α-phase conversion rate. Moreover, when their dosage is in the range of 0.1% to 1%, they can fully exert their effects without causing product performance fluctuations due to their own characteristics. At the same time, they are fully compatible with the calcination conditions of tunnel kilns and shuttle kilns and the pulverization process of air jet mills. Ultimately, they ensure that the product achieves performance indicators such as α-phase conversion rate ≥95%, oil absorption value ≤28g / 100g, and D50 of 0.5 to 1.0μm, meeting the usage requirements of thermal interface materials, electronic packaging and other application scenarios.

[0030] In some embodiments, the oil-absorbing modifier is 0.1% to 1% of the mass of boehmite.

[0031] The oil-absorbing modifier is limited to 0.1% to 1% of the boehmite mass. This range ensures that the modifier has a sufficient dosage to effectively adjust the product morphology, inhibit primary crystal growth, and promote grain densification, while avoiding performance fluctuations caused by improper dosage. This ensures that while improving the α-phase conversion rate, the oil absorption value of the product is stably reduced. For example, the proportion of the oil-absorbing modifier to the boehmite mass can be 0.1%, 0.2%, 0.35%, 0.5%, 0.65%, 0.8%, 0.9%, 1.0%, etc.

[0032] In some embodiments, the oil-absorbing modifier is 0.5% to 1% of the mass of boehmite.

[0033] In some implementations, a tunnel kiln is used for a single calcination.

[0034] In some embodiments, the temperature of a single calcination is 1100℃~1200℃, and the calcination time is 0.5h~3h.

[0035] The primary calcination temperature is limited to 1100℃~1200℃, and the holding time is 0.5h~3h. This temperature and time range can precisely initiate the crystal transformation reaction of boehmite, achieving the initial transformation of the α phase while avoiding over- or under-reaction. Simultaneously, it provides a suitable reaction environment for the oil-absorbing modifier to exert its initial effect, ensuring the basic properties of the intermediate alumina powder. For example, the primary calcination temperature can be 1100℃, 1115℃, 1130℃, 1145℃, 1160℃, 1175℃, 1190℃, 1200℃, etc., and the primary calcination time can be 0.5h, 0.8h, 1.2h, 1.6h, 2.0h, 2.3h, 2.6h, 3.0h, etc.

[0036] In some implementations, a shuttle kiln is used for secondary calcination.

[0037] In some embodiments, the secondary calcination temperature is 1300℃~1400℃, and the secondary calcination time is 3h~5h.

[0038] The secondary calcination temperature is limited to 1300℃~1400℃, and the holding time is 3h~5h. This temperature and time range provides sufficient energy for crystal transformation, ensuring that the α-phase conversion rate stably reaches ≥95%. Simultaneously, sufficient temperature and time promote sufficient grain densification, reducing the internal porosity of the powder and providing structural assurance for the performance indicator of oil absorption value ≤28g / 100g. For example, the secondary calcination temperature can be 1300℃, 1315℃, 1330℃, 1345℃, 1360℃, 1375℃, 1390℃, 1400℃, etc., and the secondary calcination time can be 3.0h, 3.3h, 3.6h, 3.9h, 4.2h, 4.5h, 4.7h, 5.0h, etc.

[0039] In some embodiments, the pulverization is performed using an air jet mill, and the α-alumina powder is air-jet pulverized to a D50 of 0.5 μm to 1.0 μm.

[0040] The particle size distribution D50 of the pulverized product is limited to 0.5μm to 1.0μm. This range allows the low oil absorption value ultrafine alumina to have a particle size suitable for applications such as thermal interface materials and electronic packaging. This ensures both the filling performance and thermal conductivity of the product, while also improving dispersibility, ensuring that the product can fully leverage its advantages of low oil absorption value and high stability in practical applications. For example, the particle size distribution D50 of the low oil absorption value ultrafine alumina can be 0.5μm, 0.6μm, 0.65μm, 0.7μm, 0.8μm, 0.85μm, 0.95μm, 1.0μm, etc.

[0041] Based on a general inventive concept, embodiments of this application provide an example of an ultrafine alumina with low oil absorption value prepared by any of the above methods, wherein the crystal form of the ultrafine alumina with low oil absorption value is α-type.

[0042] In some embodiments, the low oil absorption value ultrafine alumina meets the following properties: α phase conversion rate ≥95%, particle size distribution D50 of 0.5μm~1μm, and oil absorption value ≤28g / 100g.

[0043] This application, through the synergistic combination of raw material selection, process step design, the role of oil-absorbing modifiers, and control of key parameters, ultimately prepares ultrafine alumina with low oil absorption value, meeting the requirements of α-phase conversion rate ≥95%, particle size distribution D50 of 0.5μm~1μm, and oil absorption value ≤28g / 100g. The specific implementation path is as follows: The performance of α-phase conversion rate ≥95% is achieved through the synergistic effect of a secondary calcination process and an oil-absorbing modifier. Using boehmite as raw material, which inherently possesses the basic structure for conversion to α-alumina, the primary calcination, conducted at 1100℃~1200℃ with a holding time of 0.5h~3h, initiates the crystal transformation process of boehmite to alumina, initially increasing the proportion of the α-phase. The secondary calcination, using a higher temperature of 1300℃~1400℃ and a sufficient holding time of 3h~5h, provides ample energy for the crystal transformation, promoting the depth of α-phase conversion. Simultaneously, calcium fluoride in the oil-absorbing modifier acts as a mineralizer, lowering the activation energy of the boehmite-to-α-alumina conversion and accelerating the conversion reaction. The combination of these three factors ensures that the final product's α-phase conversion rate consistently reaches ≥95%.

[0044] For a particle size distribution (D50) of 0.5 μm to 1 μm, this is achieved through a combination of "pre-treatment suppression of agglomeration + subsequent precise pulverization." During the mixing and calcination stages, boric acid in the oil-absorbing modifier forms a low-melting-point molten phase that coats boehmite particles, effectively suppressing excessive growth of the original crystals and particle agglomeration during calcination, preventing the formation of large-sized agglomerates, and laying the foundation for subsequent pulverization. After calcination, an air jet mill is used to pulverize the α-alumina powder. The air jet mill's pulverization method can precisely control the degree of particle breakage, processing the powder to the target particle size range of 0.5 μm to 1 μm with D50, while ensuring particle dispersibility, ultimately achieving the required particle size index.

[0045] For an oil absorption value ≤28g / 100g, the core focus is on "reducing porosity and optimizing particle structure." Oil absorption modifiers play a crucial role: the molten phase formed by boric acid guides grain growth along the densification direction, reducing micropores inside and on the surface of the particles; calcium fluoride optimizes the geometry of alumina particles, making them more regular and reducing surface defects and porosity; the volatile gases produced by the decomposition of ammonium chloride during calcination carry away trace impurities from the raw materials, preventing impurity residues from forming pores, and simultaneously breaking down particle adhesion, further reducing gaps caused by agglomeration. Furthermore, the high-temperature, long-duration secondary calcination significantly improves grain density, further reducing internal porosity and structurally lowering the oil absorption capacity of the powder; and precisely controlled particle size range and good dispersibility prevent the adsorption of oil by voids formed by particle agglomeration, ultimately controlling the product's oil absorption value to ≤28g / 100g.

[0046] In summary, this application achieves simultaneous satisfaction of three performance indicators through the regulation of crystal transformation, grain structure, and particle morphology by oil-absorbing modifiers, the improvement of conversion efficiency and density by secondary calcination, and the precise control of particle size by air jet milling. These steps work together to achieve the desired effect.

[0047] The low oil absorption value ultrafine alumina is achieved based on the preparation method of the above-mentioned low oil absorption value ultrafine alumina. The specific steps of the preparation method of the low oil absorption value ultrafine alumina can be referred to the above embodiments. Since the low oil absorption value ultrafine alumina adopts some or all of the technical solutions of the above embodiments, it has at least all the beneficial effects brought about by the technical solutions of the above embodiments, which will not be repeated here.

[0048] In summary, this application possesses significant advantages in terms of process simplicity and suitability for industrial production. Its "mixing-primary calcination-secondary calcination-pulverization" process design is concise and free of redundancy, eliminating the need for complex pre- or post-treatment steps, and ensuring a clear and easily controllable operational flow. Furthermore, the selected tunnel kiln, shuttle kiln, and air jet mill are all mature and commonly used equipment in industrial production, requiring no customized special devices. This not only reduces equipment investment costs but also allows for rapid adaptation to existing production lines, facilitating large-scale mass production and effectively improving production efficiency while reducing operational complexity.

[0049] The raw material selection in this application has the advantages of easy availability and cost control. Boehmite, the core raw material, is widely available and has a stable supply. It also has an excellent basic structure for conversion to α-alumina, and can meet production requirements without complex purification processes. The oil absorption modifier is selected from one or more of boric acid, calcium fluoride, and ammonium chloride. These substances are all common chemical raw materials with convenient procurement channels and affordable prices. They do not rely on scarce or expensive reagents, which reduces the cost of raw materials from the source. At the same time, the raw materials are highly compatible with the process conditions, avoiding process fluctuations caused by special raw materials.

[0050] This application offers advantages in precision and comprehensiveness in performance control. Through the synergistic effect of oil-absorbing modifiers and a secondary calcination process, the core performance of the product can be specifically optimized without the need for additional complex control methods. This allows for precise control of the three key indicators: α-phase conversion rate, oil absorption value, and particle size. This control method avoids imbalances in other indicators caused by optimizing a single performance, ensuring that the product simultaneously possesses characteristics of dense grains and good dispersibility, resulting in excellent overall performance that meets core usage requirements without the need for further processing.

[0051] This application boasts significant advantages in application adaptability and a wide range of applicability. The prepared low-oil-absorption ultrafine alumina exhibits core properties that highly align with the requirements of filler materials in various scenarios such as thermal interface materials and electronic packaging. It can be directly adapted to the needs of different fields without requiring significant process adjustments for specific applications. This broad application adaptability enhances the practical value of the technology, eliminating the need for repeated development of proprietary processes for different scenarios and further strengthening its competitiveness in practical applications.

[0052] The present application is further illustrated below with reference to specific embodiments. Experimental methods in the following embodiments that do not specify specific conditions are generally determined according to national standards / industry standards / the disclosure herein; if there are no corresponding national standards / industry standards / the disclosure herein, they are performed according to generally accepted international standards, conventional conditions, or conditions recommended by the manufacturer.

[0053] Example 1 This embodiment provides a method for preparing ultrafine alumina with low oil absorption value, which includes the following steps: S1. In a 1000L mixer, add 100kg of boehmite and 1% oil absorption modifier (0.5% ammonium chloride + 0.5% calcium fluoride), mix evenly to obtain a mixture; S2. The mixture is placed in a tunnel kiln for a first calcination at a temperature of 1100℃ for 3 hours to obtain intermediate alumina powder. S3. The intermediate alumina powder is calcined a second time at a temperature of 1300℃ for 5 hours to obtain α-alumina powder (with submicron grains). S4. Take 100 kg of α-alumina powder and pulverize it using an air jet mill to obtain ultrafine alumina with low oil absorption value.

[0054] The low oil absorption value ultrafine alumina of Example 1 was determined to be of the α-type crystal form, with an α-phase conversion rate of 95.0%, and a particle size and distribution of D50 of 0.831 μm and an oil absorption value of 27.8 g / 100 g.

[0055] Example 2 This embodiment provides a method for preparing ultrafine alumina with low oil absorption value, which includes the following steps: S1. In a 1000L mixer, add 100kg of boehmite and 0.8% oil absorption modifier (0.4% ammonium chloride + 0.4% boric acid), mix evenly to obtain a mixture; S2. The mixture is placed in a tunnel kiln for a first calcination at a temperature of 1130℃ for 2.5 hours to obtain intermediate alumina powder. S3. The intermediate alumina powder is calcined a second time at a temperature of 1340℃ for 4.5 hours to obtain α-alumina powder (with submicron grains). S4. Take 100 kg of α-alumina powder and pulverize it using an air jet mill to obtain ultrafine alumina with low oil absorption value.

[0056] The low oil absorption value ultrafine alumina of Example 2 was determined to be of the α-type crystal form, with an α-phase conversion rate of 95.2%, and a particle size and distribution of D50 of 0.850 μm and an oil absorption value of 26.4 g / 100 g.

[0057] Example 3 This embodiment provides a method for preparing ultrafine alumina with low oil absorption value, which includes the following steps: S1. In a 1000L mixer, add 100kg of boehmite and 0.7% oil absorption modifier (0.2% calcium fluoride + 0.4% boric acid + 0.1% ammonium chloride), mix evenly to obtain a mixture; S2. The mixture is placed in a tunnel kiln for a first calcination at a temperature of 1170℃ for 2 hours to obtain intermediate alumina powder. S3. The intermediate alumina powder is calcined a second time at a temperature of 1380℃ for 4 hours to obtain α-alumina powder (with submicron grains). S4. Take 100 kg of α-alumina powder and pulverize it using an air jet mill to obtain ultrafine alumina with low oil absorption value.

[0058] The low oil absorption value ultrafine alumina of Example 3 was determined to be of the α-type crystal form, with an α-phase conversion rate of 95.7%, and a particle size and distribution of D50 of 0.890 μm and an oil absorption value of 25.8 g / 100 g.

[0059] Example 4 This embodiment provides a method for preparing ultrafine alumina with low oil absorption value, which includes the following steps: S1. In a 1000L mixer, add 100kg of boehmite and 0.7% oil absorption modifier (0.2% boric acid + 0.5% ammonium chloride), mix evenly to obtain a mixture; S2. The mixture is placed in a tunnel kiln for a first calcination at a temperature of 1200℃ and held for 1 hour to obtain intermediate alumina powder. S3. The intermediate alumina powder is calcined a second time at a temperature of 1400℃ for 3.5 hours to obtain α-alumina powder (with submicron grains). S4. Take 100 kg of α-alumina powder and pulverize it using an air jet mill to obtain ultrafine alumina with low oil absorption value.

[0060] The low oil absorption value ultrafine alumina of Example 4 was determined to be of the α-type crystal form, with an α-phase conversion rate of 96.1%, and a particle size and distribution of D50 of 0.923 μm and an oil absorption value of 24.9 g / 100 g.

[0061] Comparative Example 1 This comparative example provides a method for preparing alumina, which includes the following steps: S1. Place 100 kg of boehmite in a tunnel kiln for a single calcination at a temperature of 1200℃ for 1.5 h to obtain intermediate alumina powder. S2. The intermediate alumina powder is calcined a second time at a temperature of 1400℃ for 2 hours to obtain α-alumina powder (with submicron grains). S3. Take 100 kg of α-alumina powder and pulverize it using an air jet mill to finally obtain alumina.

[0062] The alumina of Comparative Example 1 was determined to be of the α-type crystal form, with an α-phase conversion rate of 94.5%, a particle size and distribution of D50 of 1.054 μm, and an oil absorption value of 29.8 g / 100 g.

[0063] Comparative Example 2 This comparative example provides a method for preparing ultrafine alumina, which includes the following steps: S1. In a 1000L mixer, add 100kg of boehmite and 0.9% oil absorption modifier (0.3% boric acid + 0.6% ammonium chloride), mix evenly to obtain a mixture; S2. The mixture is placed in a tunnel kiln for a first calcination at a temperature of 1200℃ and held for 1 hour to obtain α-alumina powder. S3. Take 100 kg of α-alumina powder and pulverize it using an air jet mill to obtain ultrafine alumina.

[0064] The crystal form of the ultrafine alumina in Comparative Example 2 was determined to be α-type, with an α-phase conversion rate of 92.4%, and particle size and distribution: D50 of 0.998 μm and oil absorption value of 30.2 g / 100 g.

[0065] The properties of the alumina obtained from the examples and comparative examples are summarized in Table 1.

[0066] Table 1. Properties of alumina obtained in the examples and comparative examples.

[0067] As shown in Table 1, the crystal form of all samples prepared in the examples and comparative examples is α-type, indicating that different process conditions did not change the core crystal form properties of the products.

[0068] Regarding the α-phase conversion rate, the α-phase conversion rates of Examples 1 to 4 all reached 95.0% or higher, with Example 4 exhibiting the highest α-phase conversion rate at 96.1%. In contrast, the α-phase conversion rate of Comparative Example 1 was 94.5%, and that of Comparative Example 2 was only 92.4%, both lower than the α-phase conversion levels of the Examples. This difference stems from the fact that the Examples employed a synergistic process of oil-absorbing modifier and secondary calcination, while Comparative Example 1 did not add oil-absorbing modifier, and Comparative Example 2 did not undergo secondary calcination. This fully demonstrates the crucial role of oil-absorbing modifier and secondary calcination in improving the α-phase conversion rate.

[0069] Regarding particle size D50, the particle size D50 of Examples 1 to 4 are all between 0.831 μm and 0.923 μm, which meets the particle size requirements of ultrafine alumina with low oil absorption value. The particle size D50 of Comparative Example 1 is 1.054 μm, which exceeds the target particle size range. The particle size D50 of Comparative Example 2 is 0.998 μm, which is close to the upper limit of the target range, but is still greater than the particle size value of most examples. This indicates that the oil absorption modifier can effectively inhibit excessive particle growth during calcination, and can accurately control the particle size distribution when combined with air jet milling.

[0070] Regarding the oil absorption value, the oil absorption values ​​of Examples 1 to 4 are ≤28g / 100g; while the oil absorption value of Comparative Example 1 is 29.8g / 100g and the oil absorption value of Comparative Example 2 is 30.2g / 100g, both of which are higher than the oil absorption value levels of the Examples. This is because the oil absorption modifier in the Examples can promote grain densification and reduce pore structure, and the secondary calcination further improves the powder density, thereby reducing the oil absorption capacity. In contrast, the Comparative Examples, due to the lack of oil absorption modifier or the secondary calcination process, have more pores in the powder, resulting in a higher oil absorption value.

[0071] In summary, the embodiments, through the addition of oil-absorbing modifiers, the setting of secondary calcination, and the coordinated control of various process parameters, ultimately produced low-oil-absorbing ultrafine alumina that outperformed the comparative example in three core properties: α-phase conversion rate, particle size distribution, and oil absorption value. This fully verifies the effectiveness of the preparation method of this application.

[0072] Furthermore, one or more technical solutions in the embodiments of this application have at least the following technical effects or advantages: In this embodiment, the provided low oil absorption value ultrafine alumina has excellent core performance. It has a suitable particle size distribution, low oil absorption value, and high α-phase conversion rate, which can fully meet the application requirements of thermal interface materials, electronic packaging and other application scenarios.

[0073] In this embodiment, boehmite is used as the raw material. It is pretreated with an oil-absorbing modifier before the calcination process. This pretreatment effectively prevents primary crystal growth during calcination and precisely adjusts the product morphology, thereby achieving a high α-phase conversion rate and a low oil absorption value. The subsequent pulverization process effectively improves the product's dispersibility, resulting in a final product with uniform grain size.

[0074] In the embodiments of this application, the preparation method is simple and efficient. Through the synergistic cooperation of each step, a low oil absorption value ultrafine alumina product with good dispersibility, low oil absorption value, and high α-phase conversion rate is finally obtained.

[0075] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A method for preparing ultrafine alumina with low oil absorption value, characterized in that, The method includes: Boehmite was mixed with an oil-absorbing modifier to obtain a mixture; The mixture was calcined once to obtain intermediate alumina powder; The intermediate alumina powder is calcined a second time to obtain α-alumina powder; The α-alumina powder is pulverized to obtain ultrafine alumina with low oil absorption value; The oil-absorbing modifier includes one or more of boric acid, calcium fluoride, and ammonium chloride.

2. The method according to claim 1, characterized in that, The mass of the oil-absorbing modifier is 0.1% to 1% of the mass of the boehmite.

3. The method according to claim 2, characterized in that, The mass of the oil-absorbing modifier is 0.5% to 1% of the mass of the boehmite.

4. The method according to claim 1, characterized in that, The primary calcination was carried out using a tunnel kiln.

5. The method according to claim 4, characterized in that, The temperature of the first calcination is 1100℃~1200℃, and the time of the first calcination is 0.5h~3h.

6. The method according to claim 1, characterized in that, The secondary calcination uses a shuttle kiln.

7. The method according to claim 6, characterized in that, The secondary calcination temperature is 1300℃~1400℃, and the secondary calcination time is 3h~5h.

8. The method according to claim 1, characterized in that, The pulverization is performed using an air jet mill, and the α-alumina powder is pulverized by air jet milling to a D50 of 0.5 μm to 1.0 μm.

9. A low-oil-absorption-value ultrafine alumina prepared by the method according to any one of claims 1 to 8, characterized in that, The crystal form of the low oil absorption value ultrafine alumina is α-type.

10. The low oil absorption value ultrafine alumina according to claim 9, characterized in that, The low oil absorption value ultrafine alumina meets the following properties: α phase conversion rate ≥95%, particle size distribution D50 of 0.5μm~1μm, and oil absorption value ≤28g / 100g.

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