Method for preparing spherical heat-conducting alumina powder by using sapphire single crystal degraded material and product thereof

Abstract

The present application relates to the technical field of inorganic functional powder and heat management materials, and particularly relates to a method for preparing spherical heat-conducting alumina powder from sapphire single crystal degradation material and a product thereof.The method uses sapphire single crystal degradation material, waste material and the like as raw materials, and the product is prepared through pretreatment, crushing and powdering, particle size grading (D90 / D10≤20), two-stage magnetic separation plus ultrasonic acid cleaning for impurity removal, melting and spheroidization, and post-treatment / surface modification.The alumina ceramic lining plate is used for reducing pollution during crushing, and the melting and spheroidization is suitable for multiple types of devices and atmospheres.The product is spherical alpha-alumina, D501-200 mu m, sphericity≥0.80, alpha phase≥90%, Al2O3≥99.0%, and the content of impurities and magnetic foreign matters is low.The present application realizes high-value utilization of sapphire solid waste, greatly reduces the cost of raw materials, and the product has excellent purity, heat conductivity and consistency, and the process has strong adaptability and is easy to be industrialized, and can be applied to heat management scenes such as heat-conducting silicone grease, electronic packaging thermal interface materials and the like.

Description

Technical Field

[0001] This invention relates to the field of inorganic functional powders and thermal management materials, specifically to a method for preparing spherical thermally conductive alumina powder using sapphire single crystal downgrade material and the resulting product. Background Technology

[0002] With the rapid development of industries such as 5G communication, new energy vehicles, big data centers, and artificial intelligence, electronic devices are rapidly iterating towards higher integration, higher power density, and miniaturization. The heat generated during device operation is increasing dramatically, making thermal management performance a core factor restricting the reliability, lifespan, and performance limits of electronic devices. Thermal interface materials (TIMs), as core materials filling the space between electronic devices and heat dissipation components, function to eliminate air gaps between interfaces, reduce contact thermal resistance, and achieve efficient heat transfer. Thermally conductive fillers are the core components that determine the thermal conductivity, processing performance, and reliability of thermal interface materials.

[0003] Among numerous thermally conductive fillers, spherical alumina powder has become the most widely used and consumed thermally conductive filler in the thermal management field due to its advantages such as moderate cost, excellent electrical insulation, stable chemical inertness, high filling fluidity, and low system viscosity. It is widely used in thermally conductive silicone grease, thermally conductive potting compounds, thermally conductive plastics, thermally conductive coatings, and electronic packaging composite materials. The mainstream preparation technology for spherical alumina powder is the high-temperature melt spheroidization method, including flame melt spheroidization and plasma melt spheroidization. Its core principle is to send alumina powder into a high-temperature field, causing the particles to melt instantly. Under the action of surface tension, they shrink to form spherical droplets, which are then rapidly cooled and solidified to obtain spherical alumina powder.

[0004] However, existing melt spheroidization technology has a series of unresolved industry pain points, making it impossible to simultaneously meet the performance requirements and cost control of high-end applications: Firstly, it is difficult to balance the purity and cost of raw materials. Existing technologies generally use industrial alumina, aluminum hydroxide, or fused alumina as raw materials. Industrial alumina is mostly prepared by the Bayer process and contains a large amount of impurities such as Na2O, SiO2, and Fe2O3. In particular, the Na content is usually above 300 ppm, or even exceeds 1000 ppm. These impurities not only reduce the thermal conductivity and insulation of alumina itself, but also form a low-melting-point glass phase during high-temperature spheroidization, affecting the stability of the α phase. At the same time, they increase the interfacial thermal resistance between the powder and the polymer matrix, significantly reducing the thermal conductivity of the composite system. On the other hand, high-purity ultrafine alumina raw materials are expensive, costing 3-5 times more than industrial alumina. This results in the high cost of high-end spherical alumina products, preventing their large-scale application.

[0005] Secondly, the high content of magnetic foreign matter and impurities means that the cleanliness cannot meet high-end requirements. During the crushing and grinding process of industrial alumina, magnetic foreign matter such as Fe, Cr, and Ni is easily introduced. Current technology lacks supporting deep impurity removal processes, and the magnetic foreign matter content of the products is usually above 50 ppm, or even exceeds 200 ppm. However, in high-end electronic packaging, new energy vehicles, aerospace and other fields, the requirement for magnetic foreign matter is usually below 30 ppm. Existing products cannot consistently meet this requirement, and the batch-to-batch fluctuation of impurity content is extremely large, which seriously affects the reliability and consistency of the products.

[0006] Third, the spheroidization effect is poor, resulting in insufficient product performance. The particle size distribution control of existing raw materials is coarse, with D90 / D10 often exceeding 20, or even 30. This leads to over-melting of fine powder and insufficient melting of coarse powder during the spheroidization process. The final product sphericity is generally below 0.85, containing a large number of irregularly shaped particles, hollow spheres, and satellite powders. This significantly reduces the powder's flowability, bulk density, and filling performance. Furthermore, industrial alumina raw materials are mostly transition phases such as γ-Al2O3 and θ-Al2O3. After spheroidization, the α-phase content fluctuates greatly, typically between 85% and 95%. The thermal conductivity of transition phases is much lower than that of stable α-Al2O3, further limiting the product's thermal conductivity. Fourth, the utilization rate of solid waste resources is low, resulting in serious resource waste.

[0007] On the other hand, sapphire is a single-crystal α-Al₂O₃ with extremely high purity (Al₂O₃ content typically ≥99.99%), excellent chemical stability, mechanical properties, and optical properties. It is widely used in LED substrates, optical windows, semiconductor substrates, and consumer electronics cover plates. Throughout the entire sapphire crystal growth, cutting, polishing, and processing industry chain, a large amount of degraded materials, waste, and scrap are generated. This includes B-grade and C-grade crystal rods produced during crystal growth (unsuitable for substrate processing due to excessive dislocation density, bubbles, cracks, and dimensional deviations), head and tail materials and scrap generated during cutting, and scrap wafers generated during polishing. Currently, most of this sapphire single-crystal waste is sold at low prices or even disposed of as industrial solid waste in landfills, resulting in extremely low resource utilization and a significant waste of high-quality resources. The main component of this sapphire waste is high-purity single-crystal α-Al₂O₃, with impurities such as Na, Fe, and Si typically below 100 ppm, far superior to industrial alumina and fused alumina, making it an ideal raw material for preparing high-end spherical thermally conductive alumina.

[0008] Currently, a few technologies have attempted to prepare alumina powder from sapphire waste, but all have significant technical shortcomings: some technologies simply crush the sapphire waste for use in abrasives and refractory materials, completely failing to utilize its intrinsic advantages of high-purity single crystals, resulting in low-value utilization; a few technologies used to prepare spherical alumina lack control over particle size distribution during the crushing and powdering process, leading to extremely low spheroidization yields and poor product consistency; there is no supporting deep purification process to remove metal impurities and magnetic foreign matter introduced during processing, and the product cleanliness cannot meet the requirements of high-end applications; at the same time, the spheroidization process is mismatched with the characteristics of the raw materials, making it impossible to consistently obtain products with high sphericity and high α-phase content, and the thermal conductivity of the final product has no significant advantage compared to existing industrial alumina spheroidized products, thus hindering industrial application.

[0009] To address the aforementioned shortcomings of existing technologies, this invention proposes a complete process for preparing spherical thermally conductive alumina powder using downgraded sapphire single crystal materials. This fully leverages the high-purity single crystal advantage of sapphire waste, solving industry pain points in existing technologies such as the difficulty in balancing high purity and low cost, high impurity and magnetic foreign matter content, poor spheroidization effect, and insufficient thermal conductivity of the product. This enables high-value resource utilization of sapphire industrial solid waste, while simultaneously producing spherical thermally conductive alumina powder that meets the requirements of high-end thermal management applications. Summary of the Invention

[0010] To address the problems in the prior art, this invention provides a method for preparing spherical thermally conductive alumina powder using sapphire single-crystal downgrade material, and the resulting product.

[0011] The technical solution adopted by the present invention to solve its technical problem is: a method for preparing spherical thermally conductive alumina powder using sapphire single crystal downgrade material, including the following steps: (1) Raw material pretreatment: select sapphire single crystal downgrade material, waste or scrap as alumina raw material, use deionized water with surfactant to clean the raw material, remove the cutting and abrasive materials, oil stains and foreign impurities attached to the surface, dry after cleaning, and obtain clean sapphire single crystal raw material; (2) Crushing and powdering: the clean sapphire single crystal raw material is subjected to coarse crushing, fine crushing and grinding treatment in sequence to obtain primary alumina powder; (3) Particle size classification: the primary alumina powder is subjected to sieving and air classification combined treatment to obtain graded powder in the target particle size range, and control the graded powder. The particle size distribution of the body is D90 / D10≤20; (4) Purification: The graded powder is subjected to magnetic separation and acid washing to remove magnetic foreign matter and metal impurities in the powder. After acid washing, it is washed with deionized water until the filtrate is neutral, and then dried to obtain purified powder; (5) Melting and spheroidizing: The purified powder is sent to the melting and spheroidizing device, and the powder particles are melted at least on the surface or as a whole under high temperature conditions. The particles form spherical particles under the action of surface tension, and then are rapidly cooled and solidified to obtain spherical powder; (6) Post-treatment: The spherical powder is screened and graded to obtain spherical thermally conductive alumina powder with the target particle size, or the screened powder is further surface modified to improve the dispersion and compatibility of the powder in the polymer matrix.

[0012] Specifically, the sapphire single crystal raw material is selected from one or more of the following: sapphire single crystal rod B grade, sapphire single crystal rod C grade, crystal cutting scraps, polishing / cutting waste crystals, and single crystal waste generated during crystal growth or processing.

[0013] Specifically, the volume median particle size D50 of the graded powder in the target particle size range is 1-200 μm, and the particle size distribution D90 / D10 ≤ 15.

[0014] Specifically, the crushing and grinding process employs one or more combinations of jaw crushers, roller crushers, impact mills, ball mills, stirred mills, and air jet mills. During the grinding process, the parts of the equipment that come into contact with the powder are lined with alumina ceramic plates or high-purity alumina grinding media to reduce metal contamination introduced by mechanical wear.

[0015] Specifically, the magnetic separation for impurity removal consists of at least two stages of high-gradient magnetic separation; the acid washing for impurity removal uses one or more of hydrochloric acid, nitric acid, and sulfuric acid, and ultrasonic treatment is used during the acid washing process to enhance the impurity removal effect.

[0016] Specifically, the molten spheroidizing device is one of a flame molten spheroidizing device, a plasma molten spheroidizing device, an induction molten spheroidizing device, or an electric arc molten spheroidizing device; the atmosphere of the molten spheroidizing process is one or two of an inert atmosphere and an oxygen-containing atmosphere, and the inert gas used in the inert atmosphere is one or two of argon and nitrogen.

[0017] Specifically, the surface modification treatment employs one or more of silane coupling agents, titanate coupling agents, and aluminate coupling agents, and is completed through dry modification or wet modification processes.

[0018] The spherical thermally conductive alumina powder product is prepared by the above method. The powder is spherical α-alumina particles with a median particle size D50 of 1-200 μm, sphericity ≥0.80, α phase content ≥90%, and Al2O3 mass content ≥99.0%.

[0019] Specifically, the content of magnetic foreign matter in the powder is ≤200ppm, and the individual mass content of Na, Fe, and Si elements is ≤500ppm each.

[0020] Applications of spherical thermally conductive alumina powder in thermally conductive silicone grease, thermally conductive potting compound, thermally conductive plastic, thermally conductive coating or thermal interface material for electronic packaging.

[0021] The beneficial effects of this invention are: First, it significantly reduces raw material costs, achieving both economic and environmental benefits. This invention uses downgraded materials, waste, and scraps generated from the sapphire industry chain as raw materials. These raw materials are abundant and inexpensive, costing only 1 / 3 to 1 / 5 of the price of high-purity alumina raw materials, thus significantly reducing the raw material cost of high-end spherical alumina. At the same time, it realizes the high-value resource utilization of industrial solid waste, solves the industry problem of waste disposal in the sapphire industry, reduces the environmental pressure caused by solid waste landfill, and achieves significant economic and environmental benefits.

[0022] Secondly, the purity and cleanliness of the product are significantly improved, meeting the stringent requirements of high-end applications. The sapphire raw material used in this invention is high-purity single-crystal α-Al2O3, with an Al2O3 content typically ≥99.9%, and impurity content far lower than that of industrial alumina and fused alumina raw materials. Simultaneously, through a combined deep purification process of two-stage magnetic separation and ultrasonic acid washing, metallic impurities and magnetic foreign matter introduced during the crushing and grinding process can be stably removed. The final product's magnetic foreign matter content can be stably controlled below 30 ppm, and the individual contents of impurities such as Na, Fe, and Si can be stably controlled below 150 ppm, far superior to existing industrial alumina spheroidized products. This fully meets the stringent requirements for powder cleanliness and reliability in high-end electronic packaging, new energy vehicles, aerospace, and other fields.

[0023] Third, the spheroidizing effect and production efficiency are significantly improved, and the product consistency is excellent. This invention obtains graded powder with a narrow particle size distribution through the combination of crushing processes and precise control of the grading window, ensuring that the powder particles are heated evenly during the melting and spheroidizing process. This effectively avoids the problems of over-melting of fine powder and insufficient melting of coarse powder. The yield of qualified products in the spheroidizing process is more than 20% higher than that of existing technologies. At the same time, the sphericity of the product can be stably controlled to ≥0.90, the powder particles have high density, no obvious hollow or cracked defects, and the proportion of satellite powder is extremely low. The flowability and bulk density of the powder are significantly better than existing products, and the performance fluctuation between batches is minimal, exhibiting excellent batch stability.

[0024] Fourth, the product exhibits outstanding thermal conductivity and significant application advantages. This invention fully utilizes the intrinsic advantages of high-purity single-crystal α-Al₂O₃ from sapphire raw materials. Combined with precise control of the melt spheroidization process, the final product's α-phase content can be stably maintained at ≥95%, avoiding the decrease in thermal conductivity caused by the presence of transition phases. The high sphericity, high density, and low impurity powder, when filled into a polymer matrix, effectively reduces interfacial thermal resistance, constructing a continuous and efficient thermally conductive network. Under the same matrix material, the same filling amount, and the same processing technology, the thermal conductivity of the composite system is more than 40% higher than existing industrial alumina spheroidized products and more than 35% higher than electrofused corundum spheroidized products, significantly reducing the thermal resistance of the thermal interface material and greatly improving the efficiency of the thermal management system.

[0025] Fifth, the process is highly adaptable and easy to scale up for industrial production. The process chain of this invention is complete and controllable. By adjusting the grading parameters, stable preparation of products with a full particle size range of 1-200μm can be achieved. Multiple product families of specifications can be produced using the same raw material system, covering different application scenarios such as thermally conductive silicone grease, thermally conductive potting compound, thermally conductive plastic, and thermally conductive coating. At the same time, the equipment used in this invention are all general-purpose industrial equipment, eliminating the need for customized special equipment. The process parameters are stable and controllable, making it easy to achieve large-scale and continuous production, and possessing extremely strong industrialization and promotion value. Attached Figure Description

[0026] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0027] Figure 1 The flowchart illustrates the method for preparing spherical thermally conductive alumina powder using sapphire single-crystal downgrade material provided by this invention. Detailed Implementation

[0028] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below in conjunction with specific embodiments.

[0029] like Figure 1As shown, the method for preparing spherical thermally conductive alumina powder using sapphire single-crystal downgrade material according to the present invention includes the following steps: (1) Raw material pretreatment: Sapphire single crystal downgrade material, waste or scrap material is selected as alumina raw material. The raw material can be selected from one or more of the following: sapphire single crystal rod B grade, sapphire single crystal rod C grade, crystal cutting scrap, polishing / cutting scrap crystal, single crystal waste generated during crystal growth or processing. First, the raw material is pre-sorted to remove obvious foreign inclusions, oil stains and severely oxidized parts. Then, the raw material is ultrasonically cleaned with deionized water and non-ionic surfactant. The cleaning temperature is controlled at 40-60℃ and the cleaning time is 20-60min to fully remove the cutting abrasive, metal debris, oil stains and other contaminants attached to the surface of the raw material. After cleaning, the raw material is rinsed with deionized water 2-3 times and then placed in a forced-air drying oven at 105-120℃ for 4-8h to obtain clean sapphire single crystal raw material.

[0030] (2) Crushing and grinding: The clean sapphire single crystal raw material is subjected to coarse crushing, fine crushing and grinding in sequence to obtain primary alumina powder. Among them, the coarse crushing adopts a jaw crusher to crush the raw material to particles with a particle size ≤5mm; the fine crushing adopts a roller crusher or double roller crusher to further crush the coarse crushed particles to fine particles with a particle size ≤1mm; the grinding process can adopt one or more combinations of impact mill, ball mill, stirred mill and air jet mill. In order to reduce the metal contamination such as Fe, Cr, Ni introduced by mechanical wear during the grinding process, the parts in the crushing and grinding equipment that come into direct contact with the powder are all lined with alumina ceramic plates or non-metallic plates such as polyurethane; in the ball mill or stirred mill process, high-purity alumina grinding balls are used as grinding media, and the particle size of the grinding media is adjusted according to the target particle size, and the ball-to-material ratio is controlled at (3-10):1.

[0031] (3) Particle size classification: The primary alumina powder is subjected to a combination of sieving and air classification to obtain graded powder within the target particle size range. First, the primary powder is pre-screened using a standard vibrating screen to remove excessively large coarse particles and excessively fine micro powder. Then, an air classifier is used to accurately classify the pre-screened powder to obtain graded powder within the target particle size range. The volume median particle size (D50) of the graded powder within the target particle size range is 1-200 μm, which can be adjusted to different ranges such as 5-20 μm, 20-60 μm, and 45-150 μm according to application requirements. At the same time, the particle size distribution of the graded powder is strictly controlled so that D90 / D10≤20, preferably controlled to D90 / D10≤15. Through narrow particle size control, the uniformity of heating of powder particles is ensured during the subsequent melting and spheroidizing process, avoiding the problem of over-melting of fine powder and insufficient melting of coarse powder due to excessive particle size difference, thereby improving the spheroidizing yield and reducing the proportion of satellite powder, hollow spheres, and irregularly shaped particles.

[0032] (4) Purification and purification: The graded powder is subjected to magnetic separation and acid washing to remove magnetic foreign objects and metal impurities introduced during the crushing and grinding process. The magnetic separation process uses at least two stages of high-gradient magnetic separation with the magnetic separation intensity controlled at 8000-15000 Gs. The first stage of magnetic separation removes large magnetic foreign objects, and the second stage further removes fine magnetic foreign objects. The feed rate of the powder is controlled during the magnetic separation process to ensure that the powder passes through the magnetic separation area evenly and improve the purification efficiency. The pickling medium used for impurity removal is one or more of hydrochloric acid, nitric acid, and sulfuric acid. The mass concentration of the acid solution is controlled at 5-20%, the pickling temperature is controlled at 60-90℃, and the pickling time is 2-6 hours. During the pickling process, stirring and ultrasonic treatment are used to enhance the reaction between the acid solution and the metal impurities on the powder surface, and to fully remove impurities such as Fe, Cr, Ni, Na, and Si adsorbed on the powder surface. After pickling, the powder is centrifuged and washed or filtered and washed with deionized water until the pH value of the washing filtrate is neutral (pH=6.5-7.5). Then, the washed powder is placed in a drying oven at 110-130℃ and dried for 6-12 hours to obtain purified powder.

[0033] (5) Melting and spheroidizing: The purified powder is fed into the melting and spheroidizing device through a quantitative powder feeding device. The melting and spheroidizing device can be selected from one of the following: flame melting and spheroidizing device, plasma melting and spheroidizing device, induction melting and spheroidizing device, or electric arc melting and spheroidizing device. In the high-temperature field of the melting and spheroidizing device, the powder particles are instantly heated to above the melting point of alumina (2050℃), so that the powder particles are at least surface-melted or completely melted. Under the action of their own surface tension, the molten droplets rapidly shrink to form perfect spherical particles. Then, the spherical droplets enter the cooling zone for rapid cooling and solidification, retaining the complete spherical structure, and spheroidized powder is obtained. The atmosphere of the melting and spheroidizing process can be selected from one or both of inert atmosphere and oxygen-containing atmosphere according to the requirements. The inert atmosphere uses one or both of argon and nitrogen. The inert atmosphere can effectively avoid the reaction between the powder and the equipment components during the high-temperature process, introducing impurities. At the same time, it can control the cooling rate of the powder and avoid the generation of hollow spheres. For coarse-sized powder, an oxygen-containing atmosphere can be used to improve the temperature stability of the high-temperature field and ensure that the coarse particles are fully melted. The powder feeding rate is adjusted according to the power of the spheroidizing device and the target particle size to ensure that the powder particles are fully heated and melted in the high-temperature field, while avoiding powder agglomeration. For fine-sized powders (D50<20μm), a plasma melting spheroidizing device is preferred, and the powder feeding rate is controlled at 0.5-5kg / h. For coarse-sized powders (D50≥20μm), a flame melting spheroidizing device or a plasma melting spheroidizing device can be used, and the powder feeding rate is controlled at 2-20kg / h.

[0034] (6) Post-processing: The spheroidized powder is sieved and classified. Agglomerates, irregularly shaped particles, excessively fine satellite powder, and excessively coarse unmelted particles generated during the spheroidization process are removed using a vibrating screen or air classifier to obtain spherical thermally conductive alumina powder products within the target particle size range. For powders that require high filling in a polymer matrix, the sieved powder can be further surface modified. The surface modification treatment uses one or more of silane coupling agents, titanate coupling agents, and aluminate coupling agents as modifiers. The amount of modifier is 0.1-2.0% of the powder mass, and it can be completed by dry modification or wet modification processes. Dry modification can be achieved using a high-speed mixer. The modifier is atomized and sprayed onto the powder surface at 100-130℃, followed by high-speed stirring for 10-30 minutes to complete surface coating. Wet modification involves dispersing the powder in anhydrous ethanol or deionized water, adding the modifier, and stirring at 60-80℃ for 1-4 hours. The mixture is then filtered, dried, and dispersed to obtain the surface-modified powder. Surface modification introduces organic functional groups onto the powder surface, significantly improving the dispersion and compatibility of the powder in polymer matrices such as silicone, epoxy resin, and engineering plastics, reducing the processing viscosity of the composite system, and increasing the upper limit of filler content.

[0035] In the embodiments and comparative examples of this invention, the detection methods for relevant performance indicators are as follows: Particle size distribution: Malvern Mastersizer 3000 laser particle size analyzer was used for detection, and the particle size and distribution of the powder were characterized by the volume median particle size D50, D10, and D90. Sphericity: Microscopic images of the powder were captured using a Zeiss Sigma 300 scanning electron microscope. No fewer than 500 particles were randomly selected, and the sphericity of the particles was calculated using image analysis software (sphericity = circumference of a circle with the same projected area as the particle / actual circumference of the particle projection), and the average value was taken. Phase composition and α-phase content: The phase content of α-Al2O3 was calculated by using a Bruker D8 Advance X-ray diffractometer and the K-value method. Chemical composition and impurity content: The content of metallic impurities such as Na, Fe, and Si in the powder was detected using an Agilent 720ES inductively coupled plasma atomic emission spectrometer; the purity of Al2O3 was detected using a Panaco Axios X-ray fluorescence spectrometer. Magnetic foreign matter content: Using the industry-standard magnetic foreign matter detection method, a certain mass of powder is dispersed in deionized water, and magnetic foreign matter is adsorbed by a strong magnetic rod. Then, ICP-OES is used to quantitatively detect the mass of magnetic foreign matter and calculate its mass fraction (ppm) in the powder. Tap density: The test was conducted using a powder tap density meter in accordance with the GB / T 5162-2006 standard. Thermal conductivity of the system: The powder was filled into a two-component addition-type silicone matrix with a filling amount of 90 wt%. Thermally conductive silicone sheets with a thickness of 2 mm were prepared under the same mixing and curing process conditions. The thermal conductivity of the sample was tested at 25℃ using the transient planar heat source method (Hot DiskTPS 2500S). The unit is W / m·K.

[0036] Example 1: Preparation of spherical alumina powder with a median particle size of 20-60 μm This embodiment provides a method for preparing spherical thermally conductive alumina powder with a median particle size of 20-60 μm using downgraded sapphire single crystal material. The specific steps are as follows: (1) Raw material pretreatment: Sapphire single crystal rod B produced during LED substrate processing was selected as raw material. This raw material could not be used for substrate processing due to excessive dislocation density. It had no obvious foreign inclusions and was mainly composed of high-purity single crystal α-Al2O3. First, the raw material was manually sorted to remove obvious foreign impurities such as cutting wire debris and silicon carbide abrasive particles attached to the surface of the raw material. Then, the raw material was crushed into blocks with a particle size ≤50mm and placed in an ultrasonic cleaning tank. Deionized water was used with 0.5wt% nonionic surfactant fatty alcohol polyoxyethylene ether (AEO-9) for ultrasonic cleaning. The cleaning temperature was controlled at 50℃, the ultrasonic power was 300W, and the cleaning time was 40min to fully remove the cutting abrasives, oil stains, and metal debris attached to the surface of the raw material. After cleaning, the raw material was taken out and rinsed repeatedly with deionized water 3 times to ensure that there was no surfactant residue on the surface. Then, the raw material was placed in a 110℃ forced-air drying oven and dried for 6h until the moisture content of the raw material was ≤0.1%, thus obtaining clean sapphire single crystal raw material.

[0037] (2) Crushing and grinding: Clean sapphire single crystal raw material is fed into a jaw crusher for coarse crushing. The jaw plate of the jaw crusher is made of alumina ceramic liner. The discharge gap is adjusted to 2mm to crush the raw material into coarse particles with a particle size ≤2mm. Then the coarse particles are fed into an impact mill for fine grinding. The chamber and hammer of the impact mill are made of alumina ceramic material to avoid introducing metal impurities during the grinding process. The speed of the classifying wheel of the impact mill is adjusted to 3000rpm to obtain primary alumina powder.

[0038] (3) Particle size classification: The obtained primary alumina powder is first pre-screened using a standard vibrating screen. Coarse particles larger than 100 μm and fine powder smaller than 20 μm are removed using standard screens of 150 mesh and 600 mesh, respectively. Then, the pre-screened powder is sent to an air classifier for precise classification. The classifying wheel speed of the air classifier is adjusted to 8000 rpm and the air volume is 120 m³ / h. 3 / h, graded powder within the target particle size range was obtained. Laser particle size analyzer measurements showed that the volumetric median particle size of the graded powder was D50 = 38.2 μm, D10 = 18.6 μm, and D90 = 59.7 μm, with a particle size distribution D90 / D10 = 3.21, far less than 15, meeting the narrow distribution control requirements.

[0039] (4) Purification and Removal: First, the graded powder is subjected to two-stage high-gradient magnetic separation for purification. The magnetic field strength of the first stage is 10000 Gs, and the feed rate is 50 kg / h to remove large magnetic foreign matter from the powder. The magnetic field strength of the second stage is 15000 Gs, and the feed rate is 30 kg / h to further remove fine magnetic foreign matter from the powder. After the magnetic separation is completed, the powder is placed in an acid washing reactor. A 10% hydrochloric acid solution is used as the acid washing medium, with a liquid-to-solid ratio of 5:1. The temperature is raised to 80℃, the stirring rate is 60 rpm, and ultrasonic treatment with 200 W is applied. The acid washing time is 4 h to fully remove Fe, Cr, Ni and other metallic impurities adsorbed on the powder surface. After acid washing, the mixture of powder and acid solution is sent to a centrifuge for solid-liquid separation. The powder is collected and then washed multiple times with deionized water. The pH value of the filtrate is measured after each wash until the pH value of the filtrate stabilizes between 6.8 and 7.2, completing the washing process. The washed powder is then placed in a 120℃ forced-air drying oven and dried for 8 hours. Subsequently, it is slightly dispersed using an air-jet agitator to obtain purified powder.

[0040] (5) Melting and spheroidizing: The purified powder is fed into the atmospheric plasma melting and spheroidizing device through a screw-type quantitative powder feeding device. The power of the plasma generator is 80kW, and the working gas is a mixture of argon and hydrogen, with an argon flow rate of 3m³ / h. 3 / h, hydrogen flow rate is 0.5m 3 / h, the carrier gas is argon, and the carrier gas flow rate is 0.8m³ / h. 3 The powder feeding rate is 3 kg / h. The powder is instantly heated to over 2200℃ in the plasma flame, and the particles are completely melted to form alumina droplets. Under the action of their own surface tension, the droplets rapidly shrink to form perfect spherical droplets, and then enter the cooling chamber, where they are rapidly cooled and solidified under an argon atmosphere, retaining the complete spherical structure to obtain spherical powder.

[0041] (6) Post-processing: The spheroidized powder is sieved and graded using a vibrating screen. Standard screens of 300 mesh and 800 mesh are used to remove agglomerates, unmelted coarse particles and excessively fine satellite powder generated during the spheroidization process, so as to obtain spherical thermally conductive alumina powder with a target particle size range of 20-60μm.

[0042] The spherical alumina powder prepared in this embodiment has the following performance indicators after testing: sphericity 0.94, α-phase content 98.2%, Al2O3 purity 99.85%, Na content 68 ppm, Fe content 52 ppm, Si content 76 ppm, magnetic foreign matter content 12 ppm, and tap density 2.18 g / cm³. 3 The powder was added to a two-component addition-type silicone matrix at a filling amount of 90 wt%, and the resulting thermally conductive silicone sheet had a thermal conductivity of 3.12 W / m·K, which is far superior to existing similar products. It can be widely used in high-end thermal management scenarios such as 5G base stations, servers, and new energy vehicle controllers.

[0043] Example 2: Preparation and Surface Modification of Fine-Particle-Density (5-20 μm) Spherical Alumina Powder This embodiment provides a method for preparing fine-grained spherical thermally conductive alumina powder with a particle size of 5-20μm using downgraded sapphire single crystal material, and performs surface modification treatment on the powder. The specific steps are as follows: (1) Raw material pretreatment: The head and tail materials and scraps generated during the sapphire crystal cutting process were selected as raw materials. Due to size deviations, these raw materials could not be used for subsequent processing. The main component was high-purity single crystal α-Al2O3. First, the raw materials were sorted to remove obvious oil stains, silicon carbide abrasive inclusions, and metal debris. Then, the raw materials were crushed into blocks with a particle size ≤30mm and placed in an ultrasonic cleaning tank. Ultrasonic cleaning was performed using deionized water with 0.3wt% of nonionic surfactant nonylphenol polyoxyethylene ether (TX-10). The cleaning temperature was controlled at 45℃, the ultrasonic power was 400W, and the cleaning time was 50min to fully remove cutting contaminants from the surface of the raw materials. After cleaning, the raw materials were rinsed three times with deionized water and then placed in a 105℃ forced-air drying oven for 8h to obtain clean sapphire single crystal raw materials.

[0044] (2) Crushing and grinding: The clean sapphire single crystal raw material is first coarsely crushed to particles with a diameter ≤1mm by a jaw crusher. The jaw plate is lined with alumina ceramic. Then the coarse particles are fed into a stirred mill for ultrafine grinding. The cylinder of the stirred mill is lined with polyurethane. The grinding media is high-purity alumina grinding balls with a diameter of 0.5-1mm. The ball-to-material ratio is 8:1. The filling rate of the grinding media is 70%. The grinding time is 3h to obtain ultrafine primary alumina powder.

[0045] (3) Particle size classification: The primary alumina powder is fed into an air classifier for precise classification. The classifier wheel speed is adjusted to 18,000 rpm and the air volume is 80 m³ / h. 3The process yields graded powder within the target particle size range at a rate of / h, while simultaneously removing ultrafine powder with a particle size less than 5μm and coarse particles with a particle size greater than 20μm. Laser particle size analyzer measurements show that the volumetric median particle size of the graded powder is D50 = 12.6μm, D10 = 6.2μm, and D90 = 19.4μm, with a particle size distribution D90 / D10 = 3.13, meeting the requirements for narrow particle size distribution control.

[0046] (4) Purification and Removal: First, the graded powder is subjected to two-stage high-gradient magnetic separation for purification. The magnetic field strength of the first stage is 12000 Gs, and the feed rate is 20 kg / h; the magnetic field strength of the second stage is 15000 Gs, and the feed rate is 15 kg / h, to fully remove magnetic foreign matter. After magnetic separation, the powder is placed in an acid washing reactor, using an 8% nitric acid solution as the acid washing medium, with a liquid-to-solid ratio of 6:1. The temperature is raised to 70℃, the stirring rate is 80 rpm, and ultrasonic treatment with 300W is applied. The acid washing time is 5 h to remove metallic impurities from the powder surface. After acid washing, the powder is repeatedly filtered and washed with deionized water until the pH of the filtrate is 6.5-7.5. Then, the powder is placed in a 115℃ forced-air drying oven for 10 h to dry, and then dispersed to obtain purified powder.

[0047] (5) Melting and spheroidizing: The purified powder is fed into the medium-frequency plasma melting and spheroidizing device through an atomizing powder feeding device. The plasma generator has a power of 50kW, the working gas is argon, and the flow rate is 2.5m³ / h. 3 / h, with argon as the carrier gas and a flow rate of 0.6m³ / h. 3 The powder feeding rate is 1.2 kg / h. The entire melting and spheroidizing process is protected by an argon inert atmosphere to prevent oxidation and agglomeration of fine powder and the introduction of impurities. The powder is completely melted in the high-temperature plasma flame to form spherical droplets, which are then rapidly cooled and solidified to obtain spherical powder.

[0048] (6) Post-treatment and surface modification: The spheroidized powder was subjected to secondary classification using an air classifier to remove ultrafine satellite powder and unmelted coarse particles, resulting in spherical alumina powder with a diameter of 5-20 μm. Subsequently, the powder was subjected to dry surface modification treatment using vinyltrimethoxysilane coupling agent (A-171) at a dosage of 0.8% of the powder mass. The specific modification process was as follows: the powder was placed in a high-speed mixer, heated to 110°C, and stirred at a high speed of 1200 rpm. At the same time, the silane coupling agent was evenly sprayed onto the powder surface through an atomizing nozzle. The mixture was stirred continuously for 20 min to complete the surface coating modification. After the modification was completed, the powder was naturally cooled to room temperature and sieved to obtain the surface-modified spherical thermally conductive alumina powder product.

[0049] The modified spherical alumina powder prepared in this embodiment has the following performance indicators after testing: sphericity 0.92, α-phase content 97.6%, Al2O3 purity 99.82%, Na content 72 ppm, Fe content 65 ppm, Si content 81 ppm, magnetic foreign matter content 18 ppm, and tap density 2.09 g / cm³. 3 The powder was added to a methyl vinyl siloxane matrix for thermal grease at a filling amount of 90 wt%. The viscosity of the composite system was 32,000 mPa·s (25℃, 5 rpm), which is much lower than the 128,000 mPa·s of the unmodified powder, exhibiting excellent processing fluidity. The thermal conductivity of the prepared thermal grease was 2.98 W / m·K, making it suitable as a thermal interface material for high-end CPUs, GPUs, and other consumer electronics chips, enabling efficient heat dissipation from the chip.

[0050] Example 3: Preparation of coarse-grained, highly packed spherical alumina with a particle size of 45-150 μm This embodiment provides a method for preparing coarse-grained, high-packing-size, spherical, thermally conductive alumina powder with a particle size of 45-150 μm using downgraded sapphire single crystal material. The specific steps are as follows: (1) Raw material pretreatment: C-grade crystal rods and scrap wafers generated during sapphire crystal processing were selected as raw materials. These raw materials cannot be used for optical and substrate processing due to appearance defects, cracks, bubbles and other problems. The main component is high-purity single crystal α-Al2O3. First, the raw materials were pre-sorted to remove severely contaminated parts and foreign inclusions. Then, the raw materials were crushed into blocks with a particle size ≤80mm and placed in a cleaning tank. Deionized water was used with 0.6wt% of anionic surfactant sodium dodecylbenzenesulfonate (SDBS) for heated cleaning at a temperature of 60℃ and a stirring cleaning time of 60min to remove oil, cutting abrasive and metal contaminants from the surface of the raw materials. After cleaning, the raw materials were rinsed with deionized water 4 times and then placed in a 120℃ forced-air drying oven for 5h to obtain clean sapphire single crystal raw materials.

[0051] (2) Crushing and Grinding: A three-stage crushing and grinding process is adopted. First, the clean sapphire single crystal raw material is fed into a jaw crusher for coarse crushing. The jaw plate is made of alumina ceramic liner, and the discharge gap is adjusted to 5mm to crush the raw material into coarse particles with a particle size ≤5mm. Then, the coarse particles are fed into a double roll crusher for medium crushing. The roller surface of the double roll crusher is made of alumina ceramic material, and the roller gap is adjusted to 0.5mm to crush the coarse particles into fine particles with a particle size ≤0.8mm. Finally, the fine particles are fed into an impact mill for fine grinding. The cavity, hammers, and classifying wheel of the impact mill are all made of alumina ceramic material, and the speed of the classifying wheel is adjusted to 1500rpm to obtain primary alumina powder. Throughout the crushing and grinding process, all parts in contact with the powder are made of non-metallic or alumina ceramic material to minimize iron contamination introduced by mechanical wear.

[0052] (3) Particle size classification: The primary alumina powder is first pre-screened using a standard vibrating screen. Coarse particles larger than 150 μm and fine powder smaller than 45 μm are removed using 100-mesh and 325-mesh standard screens, respectively. Then, the pre-screened powder is sent to an air classifier for precise classification. The classifier wheel speed is adjusted to 4000 rpm and the air volume is 150 m³ / h. 3 / h, graded powder within the target particle size range was obtained. Laser particle size analyzer measurements showed that the volumetric median particle size of the graded powder was D50 = 86.4 μm, D10 = 48.2 μm, and D90 = 147.6 μm, with a particle size distribution D90 / D10 = 3.06, far less than 18, meeting the requirements for narrow particle size distribution control.

[0053] (4) Purification and Removal: First, the graded powder is subjected to two-stage high-gradient magnetic separation for purification. The first-stage magnetic separation has a magnetic field strength of 8000 Gs and a feed rate of 80 kg / h to remove large magnetic foreign matter. The second-stage magnetic separation has a magnetic field strength of 12000 Gs and a feed rate of 50 kg / h to remove fine magnetic foreign matter. After magnetic separation, the powder is placed in an acid washing reactor. A 15% hydrochloric acid and sulfuric acid mixture (volume ratio of hydrochloric acid to sulfuric acid is 3:1) is used as the acid washing medium, with a liquid-to-solid ratio of 4:1. The temperature is raised to 85℃, the stirring rate is 50 rpm, and the acid washing time is 3 hours to fully remove metallic impurities from the powder surface. After acid washing, the powder is washed multiple times with deionized water until the pH of the filtrate is neutral. Then, the powder is placed in a 130℃ forced-air drying oven for 6 hours to dry. After dispersing, purified powder is obtained.

[0054] (5) Melting and spheroidizing: The purified powder is fed into the propane-oxygen flame melting and spheroidizing device through a gravity-type quantitative powder feeding device. The flame temperature is controlled above 2300℃ and the propane flow rate is 8m³ / h. 3 / h, oxygen flow rate 16m 3The powder feeding rate is 10 kg / h, and air is used as the carrier gas with a flow rate of 1.2 m³ / h. 3 / h. The powder melts instantly in a high-temperature flame, forming spherical droplets, which then rapidly cool and solidify during their fall, resulting in spherical powder.

[0055] (6) Post-processing: The spheroidized powder is sieved and classified using a vibrating screen. Standard screens of 120 mesh and 300 mesh are used to remove unmelted coarse particles, agglomerates and fine powder to obtain high-packing spherical thermally conductive alumina powder with a target particle size range of 45-150μm.

[0056] The spherical alumina powder prepared in this embodiment has the following performance indicators after testing: sphericity 0.90, α-phase content 96.8%, Al2O3 purity 99.78%, Na content 112 ppm, Fe content 126 ppm, Si content 135 ppm, magnetic foreign matter content 26 ppm, and tap density 2.32 g / cm³. 3 The powder exhibits excellent flowability (Hall flow rate) of 32 s / 50 g, with good flowability and bulk density. When this powder was added to a PA6 engineering plastic matrix at a filler content of 85 wt%, a thermally conductive plastic was prepared by granulation using a twin-screw extruder and injection molding. This plastic had a thermal conductivity of 2.76 W / m·K, a tensile strength of 58 MPa, and a notched impact strength of 4.2 kJ / m². 2 It combines excellent thermal conductivity and mechanical properties, making it suitable for applications such as heat dissipation housings for new energy vehicle battery packs, inverter housings, and heat dissipation structural components for electronic appliances.

[0057] Comparative Example 1: Direct Spheroidization without Impurity Removal The only difference between this comparative example and Example 1 is that the magnetic separation and acid washing purification steps in step (4) are omitted. The other raw materials, process parameters and equipment are exactly the same as in Example 1.

[0058] The spherical alumina powder prepared in this comparative example, after testing, exhibited the following performance indicators: sphericity 0.93, α-phase content 98.0%, Al₂O₃ purity 99.72%, Na content 216 ppm, Fe content 682 ppm, Si content 245 ppm, and magnetic impurity content 326 ppm. When this powder was added to an organosilicon matrix at a loading of 90 wt%, the resulting thermally conductive silicone sheet had a thermal conductivity of 2.24 W / m·K, significantly lower than the 3.12 W / m·K of Example 1. Furthermore, the content of magnetic impurities and metallic impurities in the powder far exceeded the requirements for high-end electronic packaging, with significant batch-to-batch fluctuations in impurity content, failing to meet the reliability requirements of high-end applications. This comparative example fully demonstrates the necessity of the impurity removal and purification steps in this invention. Through the combined impurity removal of magnetic separation and acid washing, the content of impurities and magnetic impurities in the powder can be significantly reduced, improving the thermal conductivity and cleanliness of the product.

[0059] Comparative Example 2: Spheroidization using industrial alumina as raw material The only difference between this comparative example and Example 1 is that the raw material used is commercially available industrial alumina powder (α phase content approximately 85%, Al2O3 purity 99.2%, Na content 860ppm, Fe content 320ppm), while the remaining particle size, process parameters, and equipment are exactly the same as in Example 1.

[0060] The spherical alumina powder prepared in this comparative example exhibited the following performance indicators after testing: sphericity 0.84, α-phase content 91.3%, Al₂O₃ purity 99.28%, Na content 782 ppm, Fe content 296 ppm, Si content 354 ppm, and magnetic impurity content 128 ppm. When this powder was added to an organosilicon matrix at a filling amount of 90 wt%, the thermal conductivity of the prepared thermally conductive silicone sheet was 1.96 W / m·K, only 62.8% of that in Example 1. This comparative example fully demonstrates the advantages of using sapphire single-crystal raw materials in this invention. Compared with industrial alumina raw materials, the product of this invention has a higher α-phase content, lower impurity content, and higher sphericity, ultimately exhibiting a significantly superior thermal conductivity in the composite system.

[0061] Comparative Example 3: Spheroidization using fused alumina as raw material The only difference between this comparative example and Example 3 is that the raw material used is commercially available white fused alumina powder (Al2O3 purity 99.3%, Na content 520ppm, Fe content 280ppm). The other particle size, process parameters, and equipment are exactly the same as in Example 3.

[0062] The spherical alumina powder prepared in this comparative example exhibits the following performance indicators after testing: sphericity 0.85, α-phase content 94.2%, Al₂O₃ purity 99.35%, Na content 468 ppm, Fe content 254 ppm, Si content 312 ppm, and magnetic foreign matter content 106 ppm. When this powder was added to a PA6 engineering plastic matrix at a filler content of 85 wt%, the resulting thermally conductive plastic had a thermal conductivity of 1.88 W / m·K, only 68.1% of that in Example 3. Simultaneously, the powder's flowability and bulk density were significantly lower than in Example 3, and the system viscosity was high and the filler limit was low during processing. This comparative example fully demonstrates that the present invention, using sapphire single-crystal raw materials and precise process control, can obtain spherical alumina powder with performance far superior to fused corundum spheroidized products, exhibiting significant advantages in applications such as thermally conductive plastics.

[0063] Comparative Example 4: Direct spheroidization without controlled particle size distribution The only difference between this comparative example and Example 1 is that the airflow classification step (3) is omitted, and only simple pre-sieving is used. The resulting primary powder has a D50 of 42.6 μm, a D90 / D10 of 28.7, and a very wide particle size distribution. The remaining process parameters and equipment are exactly the same as those in Example 1.

[0064] The spherical alumina powder prepared in this comparative example had a sphericity of 0.78, with irregularly shaped particles accounting for over 30%, and a large number of hollow spheres and satellite particles present. The product yield for the target particle size range of 20-60 μm was only 42%, far lower than the 86% in Example 1. The α-phase content was 95.6%, and the magnetic foreign matter content was 86 ppm. When this powder was added to an organosilicon matrix at a filling amount of 90 wt%, the thermal conductivity of the prepared thermally conductive silicone sheet was 1.82 W / m·K. This comparative example fully demonstrates the importance of graded control of powder particle size distribution in this invention. Narrowly distributed powder can significantly improve the spheroidization yield and product sphericity, reduce the proportion of irregularly shaped particles and hollow spheres, thereby improving product performance and production efficiency.

[0065] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of protection claimed by the present invention. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing spherical thermally conductive alumina powder using sapphire single-crystal downgrade material, characterized in that, Includes the following steps: (1) Raw material pretreatment: Select sapphire single crystal downgrade material, waste or scrap as alumina raw material, use deionized water with surfactant to clean the raw material, remove the cutting and abrasive materials, oil and foreign impurities attached to the surface, and dry after cleaning to obtain clean sapphire single crystal raw material. (2) Crushing and grinding: The clean sapphire single crystal raw material is subjected to coarse crushing, fine crushing and grinding in sequence to obtain primary alumina powder; (3) Particle size classification: The primary alumina powder is subjected to a combination of sieving and air classification to obtain graded powder within the target particle size range, and the particle size distribution of the graded powder is controlled to be D90 / D10≤20. (4) Purification: The graded powder is subjected to magnetic separation and acid washing to remove magnetic foreign matter and metal impurities. After acid washing, it is washed with deionized water until the filtrate is neutral, and then dried to obtain purified powder. (5) Melting and spheroidizing: The purified powder is fed into the melting and spheroidizing device, and the powder particles are melted at least on the surface or entirely under high temperature conditions. The particles form spherical particles under the action of surface tension, and then are rapidly cooled and solidified to obtain spherical powder. (6) Post-processing: The spherical powder is sieved and classified to obtain spherical thermally conductive alumina powder with the target particle size, or the sieved powder is further surface modified to improve the dispersibility and compatibility of the powder in the polymer matrix.

2. The method for preparing spherical thermally conductive alumina powder using sapphire single-crystal downgrade material according to claim 1, characterized in that: The sapphire single crystal raw material is selected from one or more of the following: sapphire single crystal rod B grade, sapphire single crystal rod C grade, crystal cutting scraps, polishing / cutting waste crystals, and single crystal waste generated during crystal growth or processing.

3. The method for preparing spherical thermally conductive alumina powder using sapphire single-crystal downgrade material according to claim 1, characterized in that: The median volumetric particle size D50 of the graded powder within the target particle size range is 1-200 μm, and the particle size distribution D90 / D10 ≤ 15.

4. The method for preparing spherical thermally conductive alumina powder using sapphire single-crystal downgrade material according to claim 1, characterized in that: The crushing and grinding process employs one or more combinations of jaw crushers, roller crushers, impact mills, ball mills, stirred mills, and air jet mills. During the grinding process, the parts of the equipment that come into contact with the powder are lined with alumina ceramic plates or high-purity alumina grinding media to reduce metal contamination introduced by mechanical wear.

5. The method for preparing spherical thermally conductive alumina powder using sapphire single-crystal downgrade material according to claim 1, characterized in that: The magnetic separation for impurity removal consists of at least two stages of high-gradient magnetic separation; the acid washing for impurity removal uses one or more of hydrochloric acid, nitric acid, and sulfuric acid, and ultrasonic treatment is used during the acid washing process to enhance the impurity removal effect.

6. The method for preparing spherical thermally conductive alumina powder using sapphire single-crystal downgrade material according to claim 1, characterized in that: The molten spheroidizing device is one of a flame molten spheroidizing device, a plasma molten spheroidizing device, an induction molten spheroidizing device, or an electric arc molten spheroidizing device; the atmosphere of the molten spheroidizing process is one or two of an inert atmosphere and an oxygen-containing atmosphere, and the inert gas used in the inert atmosphere is one or two of argon and nitrogen.

7. The method for preparing spherical thermally conductive alumina powder using sapphire single-crystal downgrade material according to claim 1, characterized in that: The surface modification treatment employs one or more of silane coupling agents, titanate coupling agents, and aluminate coupling agents, and is completed through dry modification or wet modification processes.

8. A spherical thermally conductive alumina powder product, characterized in that, The powder is prepared by the method according to any one of claims 1-7, wherein the powder is spherical α-alumina particles with a median particle size D50 of 1-200 μm, sphericity ≥0.80, α phase content ≥90%, and Al2O3 mass content ≥99.0%.

9. The spherical thermally conductive alumina powder according to claim 8, characterized in that, The content of magnetic foreign matter in the powder is ≤200ppm, and the individual mass content of Na, Fe and Si elements is ≤500ppm each.

10. The use of the spherical thermally conductive alumina powder according to any one of claims 8 and 9 in thermally conductive silicone grease, thermally conductive potting compound, thermally conductive plastic, thermally conductive coating or thermal interface material for electronic packaging.

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