Alumina for electrical fillers and method for its production

Abstract

The application relates to an alumina for electrical fillers and a preparation method thereof. The alumina for electrical fillers presents a 'core-shell' structure, the structure can play a synergistic effect of inner and outer layer materials, and can break through the technical bottleneck that a traditional single preparation process is difficult to consider high strength and ideal micro morphology of the powder; when the alumina is used as an electrical filler, an ultra-high filling amount can be realized, and the mechanical strength of the system can be ensured; the preparation method is characterized in that industrial alumina and additives are fused to form a nucleus, an alpha-Al2O3 inner core with high compactness and high strength is prepared; then the alpha-Al2O3 inner core, an aluminum precursor and a mineralizer are mixed and sintered; in the sintering process, the alpha-Al2O3 is used as a crystal nucleus, the phase is completely converted into alpha-Al2O3 by means of the precursor, and a dense, accurate and controllable alpha-Al2O3 shell is grown on the surface of the crystal nucleus, and finally the alumina powder suitable for the field of electrical fillers and having high filling performance and high particle strength is prepared.

Description

Technical Field

[0001] This application relates to the technical field of electrical and electronic packaging insulation, and in particular to an alumina for electrical fillers and its preparation method. Background Technology

[0002] Currently, alumina products for electrical fillers mainly fall into two categories: electrofused products and sintered products. While electrofused products possess high strength, their particle morphology is poor, often exhibiting irregular polygonal shapes and low sphericity, resulting in lower filling rates in applications. Sintered products, although achieving ideal morphologies such as near-spherical or flake-like shapes through process control, suffer from lower particle density and insufficient individual particle strength, making them prone to breakage during subsequent processing, thus affecting the product's insulation performance and strength.

[0003] In view of this, it is necessary to design an alumina for electrical fillers and its preparation method to solve the above problems. Summary of the Invention

[0004] This application provides an alumina for electrical fillers and a method for preparing the same, in order to solve the current problem that it is difficult to simultaneously meet the dual requirements of high strength and ideal morphology for electrical fillers.

[0005] In a first aspect, this application provides an alumina for electrical fillers, the alumina for electrical fillers comprising an α-Al2O3 core and an α-Al2O3 shell covering the surface of the core.

[0006] In some embodiments, the purity of the alumina used for electrical fillers is 99.0% to 99.9%; the density of the alumina used for electrical fillers is 95% to 98%.

[0007] Secondly, this application provides a method for preparing the above-mentioned alumina for electrical fillers, comprising the following steps: Industrial alumina is mixed with additives to obtain the first mixture; The first mixture was melted to obtain α-Al2O3 frit; The α-Al2O3 molten block was crushed to obtain α-Al2O3 particles; The α-Al₂O₃ particles, the precursor, and the mineralizer are mixed to obtain a second mixture; and, The second mixture is subjected to sintering treatment to obtain the alumina for electrical filler.

[0008] In some embodiments, the melting temperature of the melt treatment is 2000℃~2400℃; and / or, The melting time for the melting treatment is 8h~12h.

[0009] In some embodiments, the heating rate of the sintering treatment is 3°C / min to 10°C / min; and / or, The sintering temperature for the sintering treatment is 800℃~1400℃; and / or, The sintering time for the sintering treatment is 1h to 6h.

[0010] In some embodiments, the additive includes any one or more of boric acid, magnesium oxide, and quartz sand.

[0011] In some embodiments, the precursor comprises either transition phase alumina or aluminum hydroxide micropowder; and / or, The median particle size D of the precursor 50 ≤2μm.

[0012] In some embodiments, the mineralizing agent includes any one or more of magnesium oxide, magnesium chloride, ammonium chloride, ammonium fluoride, aluminum fluoride, and fumed silica.

[0013] In some embodiments, in the first mixture, the mass ratio of the industrial alumina to the additive is 100:(0.5~2); and / or, In the second mixture, the total mass ratio of the α-Al₂O₃ particles and the precursor to the mineralizer is 100:(0.3~2); and / or, The mass ratio of the α-Al2O3 particles to the precursor is 1:(0.2~0.5).

[0014] In some embodiments, the median particle size D of the α-Al2O3 particles 50 ≤30μm; and / or, The particle size distribution range (D) of the α-Al2O3 particles used in the same batch 90 -D 10 ) / D 50 ≤2.00.

[0015] In some embodiments, the purity of the industrial alumina is ≥99.5%; and / or, The median particle size D of the industrial alumina 50 ≤70μm; and / or, The industrial alumina contains ≤0.5% sodium oxide by mass.

[0016] The technical solutions provided in this application have the following advantages compared with the prior art: 1. The alumina for electrical fillers provided in this application presents a "core-shell" composite coating structure. This core-shell structure can leverage the synergistic effect of the inner and outer layers, overcoming the technical bottleneck of traditional single-process manufacturing that makes it difficult to simultaneously achieve high powder strength and ideal microstructure. When used as an electrical filler, it can achieve ultra-high filling volume while ensuring the mechanical strength of the system, significantly improving the overall comprehensive performance of the composite insulation material.

[0017] 2. This application also provides a method for preparing the above-mentioned alumina for electrical fillers. First, industrial alumina is melted with additives to create nuclei, resulting in highly dense, high-mechanical-strength α-Al₂O₃ core particles (α-Al₂O₃ particles). Then, the α-Al₂O₃ core, aluminum precursor, and mineralizer are mixed and sintered. During sintering, the α-Al₂O₃ particles serve as crystal nuclei, and the precursor drives the complete transformation of the phase into α-Al₂O₃. A dense, precisely morphologically controllable α-Al₂O₃ shell is epitaxially grown on the surface of the crystal nuclei, ultimately yielding alumina powder suitable for the electrical filler field, possessing both high filling performance and high particle strength. Attached Figure Description

[0018] 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.

[0019] 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.

[0020] Figure 1 An electron microscope image of alumina for electrical fillers provided in Embodiment 1 of this application is shown; Figure 2 An electron microscope image of alumina for electrical fillers provided in Embodiment 2 of this application is shown; Figure 3 An electron microscope image of alumina for electrical fillers provided in Embodiment 3 of this application is shown; Figure 4 An electron microscope image of alumina for electrical filler provided in Comparative Example 1 of this application is shown; Figure 5 An electron microscope image of alumina for electrical filler provided in Comparative Example 2 of this application is shown; Figure 6 An electron microscope image of alumina for electrical filler provided in Comparative Example 4 of this application is shown. Detailed Implementation

[0021] 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.

[0022] Various embodiments of this application may exist in the form of a range. It should be understood that the description in the form of a range is merely for convenience and brevity and should not be construed as a rigid limitation on the scope of this application. Therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical values ​​within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single numbers within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. In addition, whenever a numerical range is indicated in this application, it means including any referenced number (fraction or integer) within the indicated range. Unless otherwise specified, all raw materials, reagents, instruments, and equipment used in this application can be purchased commercially or prepared by existing methods. In this application, unless otherwise stated, directional terms such as "upper" and "lower" specifically refer to the drawing directions in the accompanying drawings. In addition, in this application, the terms "comprising," "including," etc., mean "including but not limited to." In this application, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, without necessarily requiring or implying any actual relationship or order between these entities or operations. In this application, "and / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A alone, A and B simultaneously, or B alone. A and B can be singular or plural. In this application, "at least one" means one or more, and "more than one" means two or more. "At least one," "at least one of the following," or similar expressions refer to any combination of these items, including any combination of single or plural items. For example, "at least one of a, b, or c," or "at least one of a, b, and c," can both represent: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can each be single or multiple.

[0023] This application provides an alumina for electrical fillers, the alumina for electrical fillers comprising an α-Al2O3 core and an α-Al2O3 shell covering the surface of the core.

[0024] The alumina used as an electrical filler provided in this application has a "core-shell" composite coating structure. This core-shell structure can leverage the synergistic effect of the inner and outer layers, overcoming the technical bottleneck of traditional single-process manufacturing that makes it difficult to achieve both high powder strength and ideal microstructure. When used as an electrical filler, it can achieve ultra-high filling volume while ensuring the mechanical strength of the system, significantly improving the overall performance of the composite insulation material.

[0025] As an optional implementation, in this embodiment of the application, the purity of the alumina used for electrical fillers is 99.0%~99.9%; the density of the alumina used for electrical fillers is 95%~98%.

[0026] Therefore, the alumina used in this electrical filler has both excellent single-particle compressive strength and high packing density, which can simultaneously meet the dual performance requirements of high strength and regular morphology of powder in the field of electrical fillers.

[0027] Based on a general inventive concept, this application provides a method for preparing the above-mentioned alumina for electrical fillers, comprising the following steps: Step 1: Mix industrial alumina and additives evenly to obtain the first mixture; Step 2: Melt the first mixture to obtain α-Al2O3 frit; Step 3: The α-Al2O3 molten block is crushed to obtain α-Al2O3 particles; Step 4: Mix the α-Al2O3 particles, precursor, and mineralizer evenly to obtain a second mixture; Step 5: Sinter the second mixture to obtain the alumina for electrical filler.

[0028] This application provides a method for preparing alumina for electrical fillers. First, industrial alumina is melted with additives to create nuclei, yielding highly dense, high-mechanical-strength α-Al₂O₃ core particles (α-Al₂O₃ particles). Then, the α-Al₂O₃ cores, aluminum precursor, and mineralizer are mixed and sintered. During sintering, the α-Al₂O₃ particles serve as crystal nuclei, and the precursor drives the complete transformation of the phase into α-Al₂O₃. A dense, precisely morphologically controllable α-Al₂O₃ shell is epitaxially grown on the surface of the crystal nuclei, ultimately producing alumina powder suitable for the electrical filler field, possessing both high filling performance and high particle strength. This solution effectively overcomes the pain points of existing technologies: the electrofusion method produces powder particles with disordered morphology and poor controllability, while the sintering method produces powder with insufficient mechanical strength per particle. Simultaneously, it completely solves the inherent defects of traditional electrofusion processes that rely on crushing and shaping, resulting in an inability to precisely control particle morphology.

[0029] As an optional implementation, in this embodiment of the application, the melting process includes: placing the first mixture in an electric arc furnace and heating it to 2000℃~2400℃, and holding it at a constant temperature of 2000℃~2400℃ for 8h~12h; then cooling it with the furnace to 0℃~40℃.

[0030] For example, the melting temperature of the melting treatment can be selected as 2000℃, 2100℃, 2200℃, 2300℃, or 2400℃; and the melting time of the melting treatment can be selected as 8h, 9h, 10h, 11h, or 12h.

[0031] This process allows for the complete melting of industrial alumina and additives, followed by cooling and shaping to obtain a highly dense α-Al₂O₃ frit. This frit is used to prepare a core with high density and excellent mechanical strength, providing a reliable mechanical support substrate for subsequent core-shell structured electrical alumina fillers. However, if the melting temperature exceeds 2400℃, it will result in abnormally coarse grains, severely impairing the material's mechanical strength and toughness. If the melting temperature is below 2000℃, the industrial alumina and additives cannot be completely melted. Therefore, this application controls the melting temperature within the range of 2000℃ to 2400℃.

[0032] As an optional implementation, in this embodiment of the application, the sintering process includes: heating the second mixture to 800℃~1400℃ at a heating rate of 3℃ / min~10℃ / min, and holding it at a constant temperature of 800℃~1400℃ for 1h~6h; then cooling it to 0℃~40℃ in the furnace.

[0033] For example, the sintering temperature of the sintering treatment can be selected as 800℃, 900℃, 1000℃, 1100℃, 1200℃, 1300℃, or 1400℃; and the sintering time of the sintering treatment can be selected as 1h, 2h, 3h, 4h, 5h, or 6h.

[0034] Preferably, the melting temperature of the melt treatment is 2000℃~2400℃; the melting time of the melt treatment is 8h~12h.

[0035] Thus, through sintering, a precisely controllable morphology α-Al₂O₃ coating shell can be epitaxially grown on the surface of a dense core. However, if the sintering temperature exceeds 1400℃, it will lead to over-sintering of the coating shell, abnormal grain growth, and compromise the precise controllability of the shell's morphology. If the sintering temperature is below 800℃, effective epitaxial growth or sintering will be impossible, resulting in a loose, discontinuous shell, or even the inability to form a complete coating layer. Therefore, this application controls the sintering temperature of the melting-sintering process within the range of 800℃ to 1400℃.

[0036] As an optional implementation, in the embodiments of this application, the additive includes any one or more of boric acid, magnesium oxide, and quartz sand.

[0037] In this way, additives can remove impurities from raw materials, purify the raw materials, and effectively improve the purity of the core powder.

[0038] As an optional implementation, in this embodiment of the application, the precursor includes any one of the transition phase alumina and aluminum hydroxide micro powder.

[0039] In this way, the precursor can promote the full transformation of the system phase into α-Al2O3, providing a sufficient alumina source for the epitaxial growth of the shell, ensuring that the shell is dense, intact, and has a controllable morphology.

[0040] In this embodiment of the application, the median particle size D of the precursor is... 50 ≤2μm.

[0041] This ensures that, under given temperature and sintering conditions, the precursor can be converted into α-Al2O3 more fully and rapidly.

[0042] As an optional implementation, in the embodiments of this application, the mineralizing agent includes any one or more of magnesium oxide, magnesium chloride, ammonium chloride, ammonium fluoride, aluminum fluoride, and fumed silica.

[0043] In this way, the crystal growth orientation can be controlled, the morphology of the particle shell can be precisely modified, and the morphology can be controlled. In addition, the magnesium oxide mineralizer used can also purify impurities in the system and improve the purity of the powder.

[0044] As an optional implementation, in this embodiment of the application, the mass ratio of the industrial alumina to the additive in the first mixture is 100:(0.5~2).

[0045] For example, in the first mixture, the mass ratio of the industrial alumina to the additive can be selected as 100:0.5, 100:1, 100:1.5, or 100:2.

[0046] Preferably, in the first mixture, the mass ratio of the industrial alumina to the additive is 100:(0.5~1).

[0047] In this way, the additives can play a full role in fluxing and stabilizing during the melting process, promoting the uniform development of α-Al2O3 grains and obtaining a highly dense core; while avoiding the excessive introduction of impurity phases or grain boundary segregation by the additives.

[0048] As an optional implementation, in this embodiment of the application, in the second mixture, the total mass ratio of the α-Al2O3 particles and the precursor to the mass ratio of the mineralizer is 100:(0.3~2).

[0049] For example, in the second mixture, the mass ratio of the total mass of the α-Al2O3 particles and the precursor to the mass of the mineralizer can be selected as 100:0.3, 100:0.5, 100:1, 100:1.5, or 100:2.

[0050] Preferably, in the second mixture, the total mass ratio of the α-Al2O3 particles and the precursor to the mineralizer is 100:(0.3~0.8).

[0051] Thus, the mineralizer can play a catalytic role during sintering, effectively reducing the activation energy of the precursor's transformation to the α-Al2O3 crystal form, promoting the rapid completion of the phase transformation at a lower temperature and favorable lattice orientation, thereby obtaining a dense, complete, and precisely controllable coated shell. However, if the mineralizer mass is too low, it will lead to insufficient catalytic effect; if the mineralizer mass is too high, it will cause excessive mineralizer to agglomerate at the grain boundaries, forming a glassy phase or impurity phase, exacerbating the abnormal growth of shell grains and morphological loss of control. Therefore, taking all factors into consideration, in the second mixture, this application controls the mass ratio of the total mass of α-Al2O3 particles and precursor to the mass of mineralizer in the range of 100:(0.3~2).

[0052] As an optional implementation, in this embodiment of the application, the mass ratio of the α-Al2O3 particles to the precursor is 1:(0.2~0.5).

[0053] For example, the mass ratio of the α-Al2O3 particles to the precursor can be selected as 1:0.2, 1:0.3, 1:0.4, or 1:0.5.

[0054] Preferably, the mass ratio of the α-Al2O3 particles to the precursor is 1:(0.3~0.5).

[0055] Thus, during sintering, a sufficient and appropriate amount of precursor grows epitaxially on the surface of α-Al2O3 particles, forming a uniform, dense, and complete coating shell. However, if the mass of the precursor is too low (i.e., the mass ratio of α-Al2O3 particles to precursor is greater than 1:0.2), the shell will not be able to form a continuous and complete coating layer on the surface of the α-Al2O3 particles; if the mass of the precursor is too high (i.e., the mass ratio of α-Al2O3 particles to precursor is less than 1:0.5), it will reduce the overall mechanical reliability of the filler. Therefore, taking all factors into consideration, this application controls the mass ratio of α-Al2O3 particles to precursor within the range of 1:(0.2~0.5).

[0056] As an optional implementation, in the embodiments of this application, the median particle size D of the α-Al2O3 particles is... 50 ≤5μm.

[0057] Thus, the α-Al₂O₃ frit is broken into particles with a median particle size D. 50 α-Al₂O₃ particles ≤5μm can be used as nuclei for subsequent growth.

[0058] As an optional implementation, in the embodiments of this application, the particle size distribution range (D) of the α-Al2O3 particles used in the same batch is... 90 -D 10 ) / D 50 ≤2.

[0059] In this way, the particle size distribution range of α-Al2O3 particles in the same batch is controlled within (D 90 -D 10 ) / D 50 A value of ≤2 can significantly improve the uniformity of the core particle size, ensuring uniform and dense growth of the subsequent shell layer, and effectively improving the overall mechanical strength of the finished alumina filler.

[0060] As an optional implementation, in this embodiment of the application, the purity of the industrial alumina is ≥99.5%, and the mass percentage of sodium oxide in the industrial alumina is ≤0.5%.

[0061] As an optional implementation, in this embodiment of the application, the median particle size D of the industrial alumina is... 50 ≤70μm.

[0062] As an optional implementation, in this embodiment of the application, after the second mixture is placed in a sagger and then placed in a tunnel kiln for sintering, the process further includes: sequentially performing sieving and grading, washing, and drying to obtain the alumina for electrical fillers with a particle size of 5μm~32.5μm.

[0063] 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. If no corresponding national standard exists, then generally accepted international standards, conventional conditions, or conditions recommended by the manufacturer are followed.

[0064] Example 1 Example 1 provides a method for preparing alumina for electrical fillers, comprising the following steps: Step 1: Mix industrial alumina and additives in a mixer at a mass ratio of 100:1 for 7 minutes to obtain the first mixture. The purity of industrial alumina is ≥99.5%, and the mass percentage of sodium oxide in industrial alumina is ≤0.5%; the median particle size D of industrial alumina is... 50 ≤70μm; additives are boric acid and quartz sand; the mass ratio of boric acid and quartz sand is 1:1.

[0065] Step 2: Place the first mixture in an electric arc furnace for melting treatment to obtain α-Al2O3 frit; The melting process includes: heating the first mixture to 2000°C and holding it at 2000°C for 10 hours; then cooling it to 30°C in the furnace.

[0066] Step 3: Crush the α-Al2O3 molten block to obtain α-Al2O3 particles; The crushing process includes: primary crushing using a jaw crusher, followed by fine crushing using an air jet mill, and then sieving and classifying to achieve a median particle size D of α-Al2O3 particles. 50 ≤5μm; the particle size distribution range (D) of α-Al2O3 particles used in the same batch 90 -D 10 ) / D 50 ≤2.

[0067] Step 4: Place the α-Al2O3 particles, precursor, and mineralizer in a V-type mixer and mix for 30 minutes to obtain the second mixture; The total mass ratio of α-Al₂O₃ particles and precursor to mineralizer is 100:1.01; the mass ratio of α-Al₂O₃ particles to precursor is 1:0.5; the precursor has a median particle size D. 50Aluminum hydroxide micro powder with a particle size of ≤2μm; mineralizing agents include magnesium oxide, ammonium fluoride, aluminum fluoride, and fumed silica; the mass ratio of magnesium oxide, ammonium fluoride, aluminum fluoride, and fumed silica is 1:1:1:1.

[0068] Step 5: Place the second mixture in a sagger and then put it into a tunnel kiln for sintering, sieve and classify, wash and dry to obtain alumina for electrical fillers with a particle size of 6.4μm; The sintering process includes: heating the second mixture to 1250°C at a heating rate of 5°C / min, and sintering at 1250°C for 2 hours; then cooling it to 30°C in the furnace.

[0069] The alumina for electrical fillers prepared by the above method comprises: an α-Al2O3 core and an α-Al2O3 shell covering the surface of the core.

[0070] The purity of the alumina used for electrical packing is 99.6%; the density of the alumina used for electrical packing is 98%. In addition, electron microscopy analysis was performed on the product, and the results were as follows: Figure 1 As shown (the scale bar in the figure represents 20μm), the product consists of nearly spherical particles with a smooth surface.

[0071] Example 2 Example 2 provides a method for preparing alumina for electrical fillers, comprising the following steps: Step 1: Mix industrial alumina and additives in a mixer at a mass ratio of 100:1 for 7 minutes to obtain the first mixture. The purity of industrial alumina is ≥99.5%, and the mass percentage of sodium oxide in industrial alumina is ≤0.5%; the median particle size D of industrial alumina is... 50 ≤70μm; additives include boric acid and quartz sand; the mass ratio of boric acid and quartz sand is 1:1.

[0072] Step 2: Place the first mixture in an electric arc furnace for melting treatment to obtain α-Al2O3 frit; The melting process includes: heating the first mixture to 2000°C and holding it at 2000°C for 12 hours; then cooling it to 30°C in the furnace.

[0073] Step 3: Crush the α-Al2O3 molten block to obtain α-Al2O3 particles; The crushing process includes: primary crushing using a jaw crusher, followed by fine crushing using an air jet mill, and then sieving and classifying to achieve a median particle size D of α-Al2O3 particles. 50 ≤10μm; the particle size distribution range (D) of α-Al2O3 particles used in the same batch 90 -D 10 ) / D 50≤2.

[0074] Step 4: Place the α-Al2O3 particles, precursor, and mineralizer in a V-type mixer and mix for 30 minutes to obtain the second mixture; The total mass ratio of α-Al₂O₃ particles and precursor to mineralizer is 100:1.01; the mass ratio of α-Al₂O₃ particles to precursor is 1:0.5; the precursor has a median particle size D. 50 Aluminum hydroxide micro powder with a particle size of ≤2μm; mineralizing agent includes any one or more of magnesium oxide, magnesium chloride, ammonium chloride, ammonium fluoride, aluminum fluoride, and fumed silica.

[0075] Step 5: Place the second mixture in a sagger and then put it into a tunnel kiln for sintering, sieve and classify, wash and dry to obtain alumina for electrical fillers with a particle size of 12.3μm; The sintering process includes: heating the second mixture to 1300°C at a heating rate of 5°C / min, and sintering at 1300°C for 2 hours; then cooling it to 30°C in the furnace.

[0076] The alumina for electrical fillers prepared by the above method comprises: an α-Al2O3 core and an α-Al2O3 shell covering the surface of the core.

[0077] The purity of alumina used for electrical fillers is 99.5%; the density of alumina used for electrical fillers is 97%.

[0078] In addition, electron microscopy analysis was performed on the product, and the results were as follows: Figure 2 As shown (the scale bar in the figure represents 100μm), the product consists of nearly spherical particles with a smooth surface.

[0079] Example 3 Example 3 provides a method for preparing alumina for electrical fillers, comprising the following steps: Step 1: Mix industrial alumina and additives in a mixer at a mass ratio of 100:1 for 7 minutes to obtain the first mixture. The purity of industrial alumina is ≥99.5%, and the mass percentage of sodium oxide in industrial alumina is ≤0.5%; the median particle size D of industrial alumina is... 50 ≤70μm; additives include boric acid and quartz sand; the mass ratio of boric acid and quartz sand is 1:1.

[0080] Step 2: Place the first mixture in an electric arc furnace for melting treatment to obtain α-Al2O3 frit; The melting process includes: heating the first mixture to 2000°C and holding it at 2000°C for 12 hours; then cooling it to 30°C in the furnace.

[0081] Step 3: Crush the α-Al2O3 molten block to obtain α-Al2O3 particles; The crushing process includes: primary crushing using a jaw crusher, followed by fine crushing using an air jet mill, and then sieving and classifying to achieve a median particle size D of α-Al2O3 particles. 50 ≤30μm; the particle size distribution range (D) of α-Al2O3 particles used in the same batch 90 -D 10 ) / D 50 ≤2.

[0082] Step 4: Place the α-Al2O3 particles, precursor, and mineralizer in a V-type mixer and mix for 30 minutes to obtain the second mixture; The total mass ratio of α-Al₂O₃ particles and precursor to mineralizer is 100:1.01; the mass ratio of α-Al₂O₃ particles to precursor is 1:0.5; the precursor has a median particle size D. 50 Aluminum hydroxide micro powder with a particle size of ≤2μm; mineralizers include magnesium oxide and aluminum fluoride; the mass ratio of magnesium oxide to aluminum fluoride is 1:1.

[0083] Step 5: Place the second mixture in a sagger and then put it into a tunnel kiln for sintering, sieve and classify, wash and dry to obtain alumina for electrical fillers with a particle size of 32.5μm. The sintering process includes: heating the second mixture to 1350°C at a heating rate of 5°C / min, and sintering at 1350°C for 3 hours; then cooling it to 30°C in the furnace.

[0084] The alumina for electrical fillers prepared by the above method comprises: an α-Al2O3 core and an α-Al2O3 shell covering the surface of the core.

[0085] The purity of alumina used for electrical packing is 99.7%; the density of alumina used for electrical packing is 96.5%.

[0086] In addition, electron microscopy analysis was performed on the product, and the results were as follows: Figure 3 As shown (the scale bar in the figure represents 100μm), the product consists of nearly spherical particles with a smooth surface.

[0087] Example 4 Example 4 provides a method for preparing alumina for electrical fillers. The difference from Example 1 is that the sintering temperature of the sintering process is different. In this example, the sintering temperature of the sintering process is 800℃.

[0088] The remaining steps and parameters are the same as in Example 1, and will not be repeated here.

[0089] The alumina for electrical fillers prepared by the above method comprises: an α-Al2O3 core and an α-Al2O3 shell covering the surface of the core.

[0090] The purity of the alumina used for electrical fillers is 99.0%; the density of the alumina used for electrical fillers is 95.5%.

[0091] Comparative Example 1 Comparative Example 1 provides a method for preparing alumina for electrical fillers, comprising the following steps: Step 1: Mix industrial alumina and additives in a mixer at a mass ratio of 100:1 for 7 minutes to obtain the first mixture. The purity of industrial alumina is ≥99.5%, and the mass percentage of sodium oxide in industrial alumina is ≤0.5%; the median particle size D of industrial alumina is... 50 ≤70μm; the additive is boric acid.

[0092] Step 2: Place the first mixture in an electric arc furnace for melting treatment to obtain α-Al2O3 frit; The melting process includes: heating the first mixture to 2000°C and holding it at 2000°C for 10 hours; then cooling it to 30°C in the furnace.

[0093] Step 3: Crush the α-Al2O3 molten block to obtain α-Al2O3 particles; The crushing process includes: primary crushing using a jaw crusher, followed by fine crushing using an air jet mill, and then sieving and classifying to achieve a median particle size D of α-Al2O3 particles. 50 ≤5μm; the particle size distribution range (D) of α-Al2O3 particles used in the same batch 90 -D 10 ) / D 50 ≤2.

[0094] Step 4: Use α-Al2O3 particles as electrical fillers.

[0095] The alumina for electrical packing prepared by the above method has a purity of 98.4% and a density of 94.6%.

[0096] In addition, electron microscopy analysis was performed on the product, and the results were as follows: Figure 4 As shown (the scale in the figure represents 20μm), the product has an irregular shape and a rough surface.

[0097] Comparative Example 2 Comparative Example 2 provides a method for preparing alumina for electrical fillers, comprising the following steps: Step 1: Place industrial alumina, precursor, and mineralizer in a V-type mixer and mix for 30 minutes to obtain a mixture; The mass ratio of industrial alumina and precursor to mineralizer is 100:1.01; the mass ratio of industrial alumina to precursor is 1:0.5; the purity of industrial alumina is ≥99.5%, and the mass percentage of sodium oxide in industrial alumina is ≤0.5%; the median particle size D of industrial alumina is... 50 ≤70μm; the precursor has a median particle size D 50 Aluminum hydroxide micro powder with a particle size of ≤2μm; mineralizing agents include magnesium chloride and aluminum fluoride; the mass ratio of magnesium chloride to aluminum fluoride is 1:1.

[0098] Step 2: Place the mixture in a sagger and then put it into a tunnel kiln for sintering treatment. Ball mill, sieve and classify, wash and dry to obtain alumina for electrical fillers with a particle size of 0.8μm. The sintering process includes: heating the second mixture to 1300°C at a heating rate of 5°C / min, and sintering at 1300°C for 2 hours; then cooling it to 30°C in the furnace.

[0099] The alumina for electrical packing prepared by the above method has a purity of 99.2% and a density of 94.2%.

[0100] In addition, electron microscopy analysis was performed on the product, and the results were as follows: Figure 5 As shown (the scale in the figure represents 2μm), the product has an irregular shape and a relatively rough surface.

[0101] Comparative Example 3 Comparative Example 3 provides a method for preparing alumina for electrical fillers. The difference between Comparative Example 3 and Example 1 is that the sintering temperature of the sintering treatment is different. The sintering temperature of the sintering treatment in this comparative example is 700°C.

[0102] The remaining steps and parameters are the same as in Example 1, and will not be repeated here.

[0103] The alumina for electrical fillers prepared by the above method comprises: an α-Al2O3 core and an α-Al2O3 shell covering the surface of the core.

[0104] The purity of the alumina used for electrical packing is 97.9%; the density of the alumina used for electrical packing is 96.5%.

[0105] Comparative Example 4 Comparative Example 4 provides a method for preparing alumina for electrical fillers. The difference between Comparative Example 4 and Example 1 is that the sintering temperature of the sintering treatment is different. The sintering temperature of the sintering treatment in this comparative example is 1600℃.

[0106] The remaining steps and parameters are the same as in Example 1, and will not be repeated here.

[0107] The alumina for electrical fillers prepared by the above method comprises: an α-Al2O3 core and an α-Al2O3 shell covering the surface of the core.

[0108] The purity of the alumina used for electrical packing is 99.4%; the density of the alumina used for electrical packing is 97.0%.

[0109] In addition, electron microscopy analysis was performed on the product, and the results were as follows: Figure 6 As shown (the scale bar in the figure represents 50μm), the product consists of nearly spherical particles with a smooth surface.

[0110] However, the sintering temperature in this process is too high, resulting in high energy consumption in industrial production, severe crucible adhesion, and difficulty in unloading.

[0111] Comparative Example 5 Comparative Example 5 provides a method for preparing alumina for electrical fillers. The difference between Comparative Example 5 and Example 1 is that the melting temperature of the melt treatment is different. The sintering temperature of the melt treatment in this comparative example is 1800°C.

[0112] The remaining steps and parameters are the same as in Example 1, and will not be repeated here.

[0113] The alumina for electrical fillers prepared by the above method comprises: an α-Al2O3 core and an α-Al2O3 shell covering the surface of the core.

[0114] The purity of the alumina used for electrical packing is 99.0%; the density of the alumina used for electrical packing is 93.0%.

[0115] Comparative Example 6 Comparative Example 6 provides a method for preparing alumina for electrical fillers, which differs from Example 1 in that no precursor is added.

[0116] The remaining steps and parameters are the same as in Example 1, and will not be repeated here.

[0117] The alumina for electrical fillers prepared by the above method comprises: an α-Al2O3 core and an α-Al2O3 shell covering the surface of the core.

[0118] The purity of the alumina used for electrical fillers is 98.5%; the density of the alumina used for electrical fillers is 95.4%.

[0119] Comparative Example 7 Comparative Example 7 provides a method for preparing alumina for electrical fillers, which differs from Example 1 in that no mineralizer is added.

[0120] The remaining steps and parameters are the same as in Example 1, and will not be repeated here.

[0121] The alumina for electrical fillers prepared by the above method comprises: an α-Al2O3 core and an α-Al2O3 shell covering the surface of the core.

[0122] The purity of the alumina used for electrical packing is 97.4%; the density of the alumina used for electrical packing is 96.2%.

[0123] Analysis of experimental results: Comparing Example 1 with Comparative Examples 1 and 6-7, it can be seen that the absence of any one or more of the precursor and mineralizer affects both purity and morphology. Specifically, the absence of the precursor results in uneven morphology, while the absence of the mineralizer leads to low purity.

[0124] Comparative Examples 1, 4, and 3-4 show that the sintering temperature affects the purity.

[0125] Comparative Examples 1 and 5 show that the melting temperature affects the density.

[0126] Comparing Example 2 and Comparative Example 2, it can be seen that additives and melt treatment have an impact on density.

[0127] In summary, this invention provides an alumina for electrical fillers and its preparation method, which exhibits a "core-shell" composite coating structure. This core-shell structure allows for the synergistic effect of the inner and outer layers, overcoming the technical bottleneck of traditional single-process manufacturing that struggles to simultaneously achieve high powder strength and ideal microstructure. When used as an electrical filler, it enables ultra-high filling capacity while ensuring the mechanical strength of the system, significantly improving the overall performance of composite insulation materials. The preparation method involves first melting industrial alumina with additives to create nuclei, yielding highly dense, high-mechanical-strength α-Al₂O₃ core particles (α-Al₂O₃ particles). Subsequently, the α-Al₂O₃ core, aluminum precursor, and mineralizer are mixed and sintered. During sintering, the α-Al₂O₃ particles serve as crystal nuclei, with the precursor driving the complete phase transformation into α-Al₂O₃. A dense, precisely morphologically controllable α-Al₂O₃ shell is epitaxially grown on the surface of the crystal nuclei, ultimately producing alumina powder suitable for the electrical filler field, possessing both high filling performance and high particle strength. This preparation process allows for customized particle morphology, producing powders in various forms such as spherical and flake shapes. The resulting alumina exhibits excellent single-particle compressive strength and packing density.

[0128] 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 in this application.

Claims

1. An alumina filler for electrical applications, characterized in that, The alumina used for electrical fillers includes an α-Al2O3 core and an α-Al2O3 shell covering the surface of the core.

2. The method for preparing alumina for electrical fillers according to claim 1, characterized in that, The purity of the alumina used for electrical fillers is 99.0%~99.9%; the density of the alumina used for electrical fillers is 95%~98%.

3. A method for preparing alumina for electrical fillers as described in claim 1 or 2, characterized in that, Includes the following steps: Industrial alumina is mixed with additives to obtain the first mixture; The first mixture was melted to obtain α-Al2O3 frit; The α-Al2O3 molten block was crushed to obtain α-Al2O3 particles; The α-Al₂O₃ particles, the precursor, and the mineralizer are mixed to obtain a second mixture; and, The second mixture is subjected to sintering treatment to obtain the alumina for electrical filler.

4. The method for preparing alumina for electrical fillers according to claim 3, characterized in that, The melting temperature of the melt treatment is 2000℃~2400℃; and / or, The melting time for the melting treatment is 8h~12h.

5. The method for preparing alumina for electrical fillers according to claim 3, characterized in that, The heating rate of the sintering process is 3℃ / min to 10℃ / min; and / or, The sintering temperature for the sintering treatment is 800℃~1400℃; and / or, The sintering time for the sintering treatment is 1h to 6h.

6. The method for preparing alumina for electrical fillers according to claim 3, characterized in that, The additives include any one or more of boric acid, magnesium oxide, and quartz sand.

7. The method for preparing alumina for electrical fillers according to claim 3, characterized in that, The precursor includes any one of transition phase alumina and aluminum hydroxide micro powder; and / or, The median particle size D of the precursor 50 ≤2μm.

8. The method for preparing alumina for electrical fillers according to claim 3, characterized in that, The mineralizing agent includes any one or more of magnesium oxide, magnesium chloride, ammonium chloride, ammonium fluoride, aluminum fluoride, and fumed silica.

9. The method for preparing alumina for electrical fillers according to claim 3, characterized in that, In the first mixture, the mass ratio of the industrial alumina to the additive is 100:(0.5~2); and / or, In the second mixture, the total mass ratio of the α-Al₂O₃ particles and the precursor to the mineralizer is 100:(0.3~2); and / or, The mass ratio of the α-Al2O3 particles to the precursor is 1:(0.2~0.5).

10. The method for preparing alumina for electrical fillers according to claim 8, characterized in that, The median particle size D of the α-Al2O3 particles 50 ≤30μm; and / or, The particle size distribution range (D) of the α-Al2O3 particles used in the same batch 90 -D 10 ) / D 50 ≤2.

00.

11. The method for preparing alumina for electrical fillers according to any one of claims 3 to 10, characterized in that, The purity of the industrial alumina is ≥99.5%; and / or, The median particle size D of the industrial alumina 50 ≤70μm; and / or, The industrial alumina contains ≤0.5% sodium oxide by mass.

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