High-strength spherical boron nitride as well as preparation method and application thereof

Abstract

The invention discloses high-strength spherical boron nitride as well as a preparation method and application thereof, and belongs to the technical field of boron nitride materials. The high-strength spherical boron nitride is formed by interweaving boron nitride and aluminum borate whiskers generated in situ between the boron nitride. The preparation method comprises the following steps: preparing boron nitride containing boron oxide and aluminum oxide into slurry according to a specific molar ratio, carrying out spray granulation and glue removal, sintering in an inert atmosphere at 1200-1900 DEG C, generating aluminum borate whiskers through an in-situ reaction, and interlacing the aluminum borate whiskers with the boron nitride. The structure effectively solves the problems that traditional spherical boron nitride is low in strength and easy to break, and the product is high in particle size retention rate after being stirred at a high speed, has excellent thermal conductivity, is suitable for high-filling heat-conducting gaskets, is simple in process and environment-friendly, and is beneficial to industrial production.

Description

Technical Field

[0001] This invention belongs to the field of boron nitride material technology, specifically relating to a high-strength spherical boron nitride, its preparation method, and its application. Background Technology

[0002] Boron nitride, a ceramic material with high thermal conductivity, low dielectric constant, and good insulation, shows broad application prospects in fields such as electronic packaging and thermally conductive fillers. In particular, spherical boron nitride, due to its isotropic thermal conductivity, is better suited to meet the uniform heat dissipation requirements of high-end composite materials compared to anisotropic plate-shaped boron nitride.

[0003] Currently, spherical boron nitride is typically prepared by granulating and sintering flake boron nitride. However, this process faces two technical challenges: first, boron nitride itself has no distinct melting point, making it difficult to achieve densification through conventional sintering; second, the organic binder introduced during granulation leaves pores after decomposition during sintering. These problems collectively result in low strength and poor density in the final product. During use, the low-strength spherical boron nitride particles are easily broken, which not only increases the viscosity of the composite system, leading to deterioration in processability, but also causes the exposed fresh surface after breakage to adsorb more resin matrix, further increasing the system viscosity and potentially damaging the integrity of the thermally conductive network, ultimately resulting in substandard thermal conductivity of the composite material.

[0004] To address these issues, existing technologies have proposed several solutions, but the results remain unsatisfactory. For example, Chinese patent CN113336203B discloses a method for sintering agglomerates composed of nano- to submicron boron nitride particles to obtain spherical boron nitride agglomerates. However, the agglomerates obtained by this method have loose internal connections and insufficient structural stability, easily decomposing into the original sheet-like structure during use, failing to achieve the desired reinforcing effect. Another Chinese patent, CN115806435A, uses precursors such as polyboronazine to prepare boron nitride powder through complex chemical synthesis and heat treatment processes. While this method improves product purity and yield, it uses various chemical solvents, posing environmental risks, and the process is complex and costly, making large-scale industrial production difficult.

[0005] Therefore, there is an urgent need in this field to develop a new high-strength spherical boron nitride and its preparation method to solve the technical problems of insufficient strength and density of spherical boron nitride.

[0006] It should be noted that this part of the present invention only provides background technology related to the present invention, and does not necessarily constitute prior art or known technology. Summary of the Invention

[0007] This invention provides a high-strength spherical boron nitride, its preparation method, and its application, which at least solves the problems of insufficient strength caused by the loose structure and low density of spherical boron nitride in the prior art, as well as the complex preparation process and difficulty in industrialization.

[0008] To achieve the above objectives, in a first aspect, the present invention provides a high-strength spherical boron nitride composed of interwoven boron nitride and aluminum borate whiskers generated in situ between the boron nitride.

[0009] Preferably, the structure formed by the interweaving of boron nitride and aluminum borate whiskers is an interlocking structure.

[0010] Preferably, the aspect ratio of the aluminum borate whiskers is (5:1) to (10:1).

[0011] Preferably, the D50 particle size of the high-strength spherical boron nitride is 20 μm to 150 μm.

[0012] Preferably, after stirring the high-strength spherical boron nitride in the solution at a speed of 2000 r / min for 10 to 30 minutes, the decrease in the D50 particle size is less than 10%.

[0013] In a second aspect, the present invention provides a method for preparing the high-strength spherical boron nitride of the first aspect, comprising the following steps: Step S102: Using water as a solvent, a slurry is prepared by mixing boron nitride containing boron oxide, aluminum oxide, surfactant, and binder; the molar ratio of aluminum oxide to the total molar ratio of boron oxide and aluminum oxide is in the range of 0.1~0.8. Step S104: Spray granulation of the slurry to obtain granulated powder; Step S106: Sinter the granulated powder in an air atmosphere to remove organic matter; Step S108: Under an inert atmosphere, the granulated powder obtained in step S106 is sintered at 1200℃~1900℃ to allow boron oxide and aluminum oxide to react in situ, generating aluminum borate liquid phase and aluminum borate whiskers. The aluminum borate liquid phase promotes the growth of aluminum borate whiskers, and the aluminum borate whiskers intertwine with boron nitride to obtain high-strength spherical boron nitride blocks. Step S110: Screen the high-strength spherical boron nitride blocks to obtain high-strength spherical boron nitride.

[0014] Preferably, in step S102, the boron nitride is plate-shaped boron nitride with a particle size of 1μm to 6μm and a purity of ≥90%.

[0015] Preferably, in step S102, the alumina is angular or spherical alumina with a particle size of 1μm to 6μm, and the particle size of the alumina is smaller than that of the boron nitride.

[0016] Preferably, in step S102, the amount of alumina added accounts for 11% to 30% of the mass of boron nitride.

[0017] Preferably, in step S102, the surfactant is an anionic dispersant.

[0018] Preferably, in step S102, the adhesive includes at least one of polyethylene glycol, polyvinyl alcohol, and hydroxymethyl cellulose.

[0019] Preferably, in step S102, the solid content of the slurry is 25% to 40%.

[0020] Preferably, step S102 further includes adjusting the pH of the slurry to 8-9 using ammonia water, and stirring the slurry at a speed of 300 r / min-1000 r / min for 20-60 minutes.

[0021] Preferably, in step S106, the sintering temperature is 600℃~700℃, and the sintering time is 2 hours~6 hours.

[0022] Thirdly, the present invention provides a thermally conductive pad comprising high-strength spherical boron nitride as in the first aspect or high-strength spherical boron nitride prepared by the preparation method of the second aspect. The amount of high-strength spherical boron nitride added is 30% to 50% of the mass of the thermal pad.

[0023] The beneficial effects of this invention are as follows: This invention, through controlling the raw material ratio and sintering process, generates aluminum borate whiskers in situ inside spherical boron nitride, forming an interwoven structure with boron nitride. This unique microstructure solves the technical problems of low strength and easy breakage caused by the loose structure of traditional spherical boron nitride, enabling the product to maintain excellent structural integrity even under harsh processing conditions such as high-speed stirring, with an extremely low D50 particle size reduction rate. Simultaneously, this preparation method cleverly utilizes the inherent boron oxide in the boron nitride raw material to react with the added aluminum oxide at high temperatures. The process does not require the introduction of complex precursors or toxic chemical reagents, making it simple, environmentally friendly, and cost-controllable, with great industrialization potential. When the resulting high-strength spherical boron nitride is applied to composite materials such as thermal pads, its high sphericity, isotropy, and high thermal conductivity endow the products with excellent and stable thermal conductivity, exhibiting a unified combination of high strength, high thermal conductivity, and good processability. Attached Figure Description

[0024] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 The XRD pattern of the high-strength spherical boron nitride prepared in Example 2 is shown.

[0026] Figure 2 The XRD pattern of the high-strength spherical boron nitride prepared in Example 4 is shown.

[0027] Figure 3 This is a SEM image of the high-strength spherical boron nitride prepared in Example 2 of the present invention.

[0028] Figure 4 for Figure 3 A magnified view of a portion of the image.

[0029] Figure 5 This is a cross-sectional SEM image of the high-strength spherical boron nitride prepared in Example 2 of the present invention.

[0030] Figure 6 This is a cross-sectional SEM image of the high-strength spherical boron nitride prepared in Example 3 of the present invention.

[0031] Figure 7 This is an EDS result diagram of the high-strength spherical boron nitride prepared in Example 2 of the present invention. Detailed Implementation

[0032] In this invention, unless otherwise stated, directional terms such as "up," "down," "left," and "right" are generally understood in conjunction with the accompanying drawings and the directions shown in actual applications.

[0033] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0034] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "over," and "on top" of the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0035] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein. The terms "optional" and "discretionary" mean that they may or may not be included (or may or may not be present).

[0036] In a first aspect, the present invention provides a high-strength spherical boron nitride composed of boron nitride and aluminum borate whiskers formed in situ between boron nitride.

[0037] Preferably, the structure formed by the interweaving of boron nitride and aluminum borate whiskers is an interlocking structure.

[0038] Understandably, the term "interlocking structure" has a specific and explicit microstructural meaning in the context of this invention: The interlocking structure consists of boron nitride particles as the matrix phase and aluminum borate whiskers as the reinforcing phase. In this structure, the aluminum borate whiskers nucleate and grow from one end, anchored to the boron nitride particles in their in-situ growth matrix. Their main body extends and grows three-dimensionally in the pores and gaps between multiple boron nitride particles, and their other end further bridges and intercalates to one or more adjacent boron nitride particles. This multi-point anchoring and spatial intercalation between the whiskers and boron nitride creates a mechanical interlocking and locking mechanism.

[0039] The interlocking structure is achieved through an in-situ generation mechanism, specifically: during high-temperature sintering (≥1200℃), boron oxide (B2O3) in the raw material first melts to form a liquid phase. This liquid phase wets and encapsulates boron nitride particles, filling their interstices. Subsequently, added alumina (Al2O3) particles gradually dissolve in this B2O3 liquid phase, resulting in localized supersaturation of aluminum and boron ions in the liquid phase. The dissolved aluminum and boron ions are transported in the liquid phase, using the undissolved alumina particle solid-phase interface as a preferred heterogeneous nucleation site, precipitating aluminum borate nuclei. Driven by the rapid ion transport channels and interfacial energy provided by the liquid phase, the nuclei preferentially grow along a one-dimensional direction, forming aluminum borate whiskers. As the whiskers extend outward from the nucleation site, their growth tips advance unrestricted within the pore channels filled with the liquid phase. When the tip of a growing whisker randomly encounters a neighboring boron nitride particle in space, its growth behavior may continue due to interfacial interactions, thus bridging the adjacent particle; alternatively, the whisker may directly penetrate the thin liquid film enveloping the boron nitride particle during growth, achieving interpenetration. The random growth and interweaving of multiple whiskers at different positions and in different directions ultimately form a three-dimensional interlocking reinforcement network within the boron nitride matrix.

[0040] The interlocking structure appears as a three-dimensional interlocking reinforced network at the microscopic level. This does not mean that all whiskers are connected end to end to form a completely connected whole skeleton, but rather that a large number of randomly distributed, independently grown whiskers bridge adjacent boron nitride particles and overlap and interweave with each other in the pores, thereby forming a functional continuous network that can effectively transfer and disperse stress and runs through the entire spherical particle.

[0041] Understandably, the term "high strength" in this invention has a clear quantitative standard, rather than a vague qualitative description. It specifically refers to the ability of spherical boron nitride particles to resist mechanical breakage, particularly their structural stability under high shear stress conditions simulating downstream applications (such as thermal pad compounding). This can be quantified by a specific test method: after stirring the high-strength spherical boron nitride in solution at 2000 rpm for 10 to 30 minutes, the decrease in its D50 particle size is less than 10%. This indicator is a key performance parameter distinguishing the product of this invention from loose agglomerates in the prior art.

[0042] Understandably, the unique microstructure proposed in this invention is designed to fundamentally solve the technical defects of low strength and fragility commonly found in spherical boron nitride products in the background art. As mentioned in the background art section, existing spherical boron nitride, such as agglomerates prepared by conventional granulation and sintering processes (as disclosed in CN113336203B), are essentially loose agglomerates of plate-like boron nitride particles (with relatively loose connections). These agglomerates are mainly connected by weak van der Waals forces or insufficient sintering necks, resulting in extremely poor structural stability. This structural defect can have serious negative impacts in practical applications.

[0043] Specifically, one of the core applications of spherical boron nitride as a thermally conductive filler is in the manufacture of thermally conductive pads. This process requires mixing a high-filling-weight boron nitride filler with a high-viscosity polymer matrix (such as silicone oil). This process necessitates high-shear stirring (e.g., high-speed mechanical stirring) to achieve uniform dispersion of the filler. Under such stringent processing conditions, the low-strength, loose aggregates of existing technologies immediately break down, reverting to their original sheet-like structure. This particle breakage leads to two serious problems: First, the drastic reduction in particle size results in a sharp increase in the specific surface area of ​​the system, leading to a dramatic increase in the viscosity of the composite system (a surge in viscosity), causing deterioration in processability and even rendering further processing impossible. Second, the fresh surfaces exposed after breakage adsorb more resin, further increasing viscosity and preventing the filler from reaching the expected high filling weight, ultimately resulting in thermally conductive pads with significantly substandard thermal conductivity.

[0044] The interlocking structure proposed in this invention is designed to solve this technical problem. Instead of relying on weak physical agglomeration, this invention uses chemical means to construct a robust reinforcing framework within the particles. Specifically, this invention cleverly utilizes the inherent boron oxide (B2O3) impurities in the boron nitride raw material and introduces a specific amount of aluminum oxide (Al2O3) as a reactant. In the subsequent high-temperature sintering step, B2O3 and Al2O3 react in situ within the gaps between the boron nitride particles, generating a high-temperature liquid phase and high-strength aluminum borate whiskers.

[0045] These in-situ generated aluminum borate whiskers interweave, grow, and intertwine among the boron nitride particles, ultimately forming a dense, interlocking three-dimensional network. This interlocking structure firmly locks the originally loose boron nitride sheets together, transforming the entire spherical particle from a loose aggregate into a microscopic composite material.

[0046] Preferably, the aspect ratio of the aluminum borate whiskers is (5:1) to (10:1), and can be 5:1, 5.5:1, 6:1, 6.5:1, 7:1, 7.5:1, 8:1, 8.5:1, 9:1, 9.5:1, 10:1 and any value between them.

[0047] Understandably, limiting the aspect ratio of in-situ generated aluminum borate whiskers to (5:1) to (10:1) is to achieve the best reinforcement effect. The aspect ratio is a key geometric parameter that determines the whisker reinforcement efficiency. The mechanical properties of whisker-reinforced composites largely depend on the geometry of the reinforcing phase (whiskers). The aspect ratio, i.e., the ratio of the whisker's length to its diameter, is an important factor in determining whether it can effectively improve the toughness and strength of the matrix. The (5:1) to (10:1) range defined in this invention provides a window that balances reinforcement efficiency and process feasibility.

[0048] First, it's necessary to understand the strengthening mechanism of whiskers. Inside high-strength spherical boron nitride particles, when microcracks attempt to propagate, in-situ generated aluminum borate whiskers can prevent crack propagation through various mechanisms, thereby improving the fracture toughness and strength of the particles. These mechanisms mainly include whisker bridging and whisker pull-out. Whisker bridging refers to the whisker acting like a bridge across the crack, preventing it from opening; whisker pull-out refers to the slow extraction of whiskers from the matrix as the crack propagates. This process requires a significant amount of energy, thus contributing to the material's high toughness.

[0049] Based on the above mechanism, this invention sets a lower limit for the aspect ratio. If the aspect ratio is too low, the whiskers are too short and thick, and their morphology is closer to that of particles than fibers. Such short whiskers cannot effectively bridge microcracks, nor can they obtain sufficient holding force in the matrix to achieve effective energy absorption (pull-out). When a crack encounters such short and thick whiskers, it will easily bypass them or directly cause cracking at the interface between the whisker and the matrix, thus failing to provide reinforcement. Therefore, whiskers with too low an aspect ratio cannot form an effective interlocking structure, and the resulting spherical boron nitride particles are still brittle and cannot pass the high-strength test proposed in this invention.

[0050] Similarly, this invention also limits the upper limit of the aspect ratio. This is mainly due to considerations of process feasibility and the mechanical stability of the whiskers themselves. If the aspect ratio is too high, it will bring two serious technical problems: First, process problems (difficulty in dispersion). Whiskers (or fibers) with high aspect ratios have a very strong tendency to agglomerate and entangle in the slurry. In the preparation method of this invention, although the whiskers are generated in situ, during their growth, an excessively high aspect ratio will cause them to become severely entangled and agglomerated when they grow in the high-temperature liquid phase. This will prevent the whiskers from being evenly distributed and interspersed between boron nitride particles, but instead form local whisker bundles, while lacking reinforcement in other areas. This non-uniform structure will lead to a large number of stress concentration points and structural defects inside the particles, which may reduce the overall strength. Second, mechanical stability problems. Excessively long and thin whiskers are more fragile and more likely to break under external force. This breakage may occur in the subsequent processing of the preparation process, or more likely in the high-shear stirring of downstream applications. Once the whiskers break, their aspect ratio decreases, and the reinforcing effect also decreases sharply.

[0051] In summary, through in-depth research, this invention has determined the range of (5:1) to (10:1). This range ensures that the whiskers have a suitable length, enabling effective crack bridging and pull-out, thereby providing high strength; at the same time, it avoids agglomeration, entanglement, and breakage problems during in-situ growth and subsequent processing, ensuring the formation of a uniform and stable interlocking structure.

[0052] Preferably, the D50 particle size of the high-strength spherical boron nitride is 20μm to 150μm, and can be 20μm, 30μm, 40μm, 50μm, 60μm, 70μm, 80μm, 90μm, 100μm, 110μm, 120μm, 130μm, 140μm, 150μm and any value between them.

[0053] Understandably, limiting the D50 particle size of the high-strength spherical boron nitride of this invention to the range of 20 μm to 150 μm can effectively form an interlocking structure and exert a reinforcing effect. The interlocking structure relies on the uniform distribution and tight interweaving between the boron nitride particles and the in-situ generated aluminum borate whiskers. When the particle size of the spherical boron nitride is between 20 μm and 150 μm, it can achieve sufficient and uniform mixing of alumina and boron nitride during spray granulation, providing an ideal microenvironment for the in-situ growth of aluminum borate whiskers and the construction of the interlocking structure in the subsequent sintering step.

[0054] If the particle size is too small, the specific surface area of ​​the particles increases sharply, which may lead to difficulties in slurry dispersion and a decrease in the mixing uniformity of alumina and boron nitride. This, in turn, affects the uniform generation and interweaving of aluminum borate whiskers, making it difficult to form a stable interlocking structure. Conversely, if the particle size is too large, regional component segregation may occur within the particles due to uneven mixing, preventing the aluminum borate whiskers from growing uniformly throughout the particle. This results in an incomplete interlocking structure and weakens its reinforcing effect. Therefore, a particle size range of 20 μm to 150 μm is the preferred range to ensure the uniform formation of the interlocking structure and achieve high strength properties.

[0055] Furthermore, this particle size range is also closely related to the mechanical properties of the interlocking structure. At the 20μm–150μm scale, in-situ generated aluminum borate whiskers can effectively interpenetrate and bridge boron nitride particles with a suitable aspect ratio of (5:1)–(10:1), forming a three-dimensional network that constructs a robust framework within the particles to resist external forces. This scale enhances the interaction area and bonding strength between the whiskers and boron nitride, allowing the interlocking structure to maintain its integrity even under conditions such as high-speed stirring, ultimately resulting in an extremely low rate of decrease in the D50 particle size.

[0056] Preferably, after stirring the high-strength spherical boron nitride in the solution at a speed of 2000 r / min for 10 to 30 minutes, the decrease in the D50 particle size is less than 10%.

[0057] Understandably, "a decrease in D50 particle size of less than 10%" is the core performance indicator of this invention, providing a clear and operable functional definition of the "high strength" of spherical boron nitride. The purpose of this strength test is to simulate the high-shear processing environment that the spherical boron nitride of this invention must undergo in downstream practical applications (such as the preparation of thermal pads), and thereby quantify the superiority of the product of this invention compared with the prior art.

[0058] As analyzed above, existing spherical boron nitride particles are essentially loose aggregates. They are prone to severe breakage under the high-shear stirring required for the fabrication of thermal pads. The strength test designed in this invention is precisely to reproduce this high-shear environment. By rapidly stirring the particles in a solution of a specific viscosity and measuring the change in D50 particle size before and after stirring, the structural integrity of the particles can be visually assessed.

[0059] The indicator that "the decrease in D50 particle size is less than 10%" means that the spherical boron nitride particles of this invention can maintain their spherical shape and particle size essentially unchanged under high shear force impact simulating actual working conditions, i.e., they will not break. This non-breakage characteristic is the cornerstone of achieving all the technical effects of this invention. In the application of thermal pads, the non-breakage of particles means: First, the viscosity of the system is controllable, and the specific surface area will not increase sharply. Therefore, the viscosity of the composite system can be maintained at a low and controllable level, ensuring good processability. Second, high filling can be achieved. It is precisely because the viscosity is controllable that it is possible to add a high content of filler to the polymer matrix. Third, high thermal conductivity can be achieved. High filling amount is a physical prerequisite for constructing an efficient thermal conduction path, thereby ensuring that the final thermal pad has excellent thermal conductivity.

[0060] In a second aspect, the present invention provides a method for preparing the high-strength spherical boron nitride of the first aspect, comprising the following steps: Step S102: Using water as a solvent, a slurry is prepared by mixing boron nitride containing boron oxide, aluminum oxide, surfactant, and binder; the molar ratio of aluminum oxide to the total molar ratio of boron oxide and aluminum oxide is in the range of 0.1~0.8. Step S104: Spray granulation of the slurry to obtain granulated powder; Step S106: Sinter the granulated powder in an air atmosphere to remove organic matter; Step S108: Under an inert atmosphere, the granulated powder obtained in step S106 is sintered at 1200℃~1900℃ to allow boron oxide and aluminum oxide to react in situ, generating aluminum borate liquid phase and aluminum borate whiskers. The aluminum borate liquid phase promotes the growth of aluminum borate whiskers, and the aluminum borate whiskers intertwine with boron nitride to obtain high-strength spherical boron nitride blocks. Step S110: Screen the high-strength spherical boron nitride blocks to obtain high-strength spherical boron nitride.

[0061] Understandably, the core of the preparation method disclosed in this invention lies in: first, the molar ratio limitation (stoichiometric control) in step S102; and second, the sintering temperature limitation (thermodynamic control) in step S108.

[0062] In step S102, the ratio of the molar number of aluminum oxide to the total molar number of boron oxide and aluminum oxide is specified to be 0.1~0.8 (i.e., mole Al2O3 / (B2O3+Al2O3) = 0.1~0.8). The ratio of the molar number of aluminum oxide to the total molar number of boron oxide and aluminum oxide can be 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, and any value between them. This molar ratio range is the chemical basis for achieving the interlocked structure of this invention, and its purpose is to control the products of the high-temperature reaction (S108). During the high-temperature sintering process of step S108 (1200℃~1900℃), Al2O3 and B2O3 undergo an in-situ reaction. During the high-temperature sintering process of step S108, aluminum borate whiskers and aluminum borate liquid phase must be generated simultaneously to prepare a high-strength product.

[0063] Specifically, aluminum borate whiskers are used to construct interlocking structures. The liquid phase of aluminum borate (i.e., molten aluminum borate at high temperatures) acts as a crucial flux and binder at high temperatures. It not only binds lamellar boron nitride, fills internal pores, and improves particle density, but more importantly, it serves as a solvent and ion transport medium for whisker growth, promoting the growth of aluminum borate whiskers.

[0064] The molar ratio range of 0.1 to 0.8 specified in this invention is precisely to ensure that the two products mentioned above can be generated simultaneously. A molar ratio that is too low (i.e., insufficient Al2O3 relative to B2O3) or too high (i.e., excess Al2O3 relative to B2O3) will prevent the formation of the aluminum borate liquid phase and aluminum borate whiskers, thus preventing the formation of an interlocking structure. The resulting product will still be a low-strength, loose aggregate. The aluminum borate liquid phase is crucial for achieving dense sintering and promoting whisker growth. Without the formation of the aluminum borate liquid phase, the sintering process will be incomplete, whisker growth will be inhibited, and a high-strength product will also be unattainable. A molar ratio that is too high will also result in the presence of excess alumina. The thermal conductivity of Al2O3 itself is much lower than that of boron nitride. Any unreacted, excess Al2O3 will remain as a thermal contamination impurity in the final spherical boron nitride product. The presence of this impurity will severely hinder the formation of thermal conductivity pathways, leading to a significant reduction in the thermal conductivity of the final product. Therefore, a molar ratio range of 0.1 to 0.8 is a necessary condition for achieving a balance between high strength (generating aluminum borate whiskers and aluminum borate liquid phase) and high thermal conductivity (reducing excess Al2O3) in this invention.

[0065] Furthermore, the limitation of the molar ratio of alumina to boron oxide in this invention is fundamentally due to the synergistic and competitive processes involved in the in-situ reaction to generate aluminum borate liquid phase and aluminum borate whiskers, which ultimately determine the quality of the microstructure. First, low-melting-point boron oxide (B₂O₃, melting point approximately 450°C) melts first during heating, forming the initial boron oxide liquid phase. This liquid phase provides a crucial mass transport medium for subsequent reactions. Subsequently, at higher temperatures (1200°C~1900°C), alumina (Al₂O₃) dissolves in this liquid phase and reacts with B₂O₃ to generate the target products—aluminum borate liquid phase and aluminum borate whiskers. When alumina is relatively insufficient (molar ratio too low), the initial boron oxide liquid phase is sufficient, but the total amount of aluminum borate generated is limited, resulting in insufficient whisker quantity and an inability to construct a complete interlocking network. Nevertheless, the sufficient initial liquid phase can still achieve a certain degree of densification by bonding boron nitride particles, forming a matrix with a certain strength. Conversely, when alumina is in excess (molar ratio too high), the limited boron oxide is largely consumed, resulting in insufficient initial boron oxide liquid phase. This severely restricts the total amount and sustainability of subsequent aluminum borate liquid phase formation. This not only greatly weakens the densification sintering effect of the liquid phase but also causes aluminum borate whiskers to generate a large number of short, thick, low aspect ratio ineffective reinforcements due to the lack of growth medium. At the same time, excess unreacted alumina remains as an isolated defect phase, further damaging the structural integrity and thermal conductivity pathways.

[0066] Step S108 specifies that "the granulated powder obtained in step S106 is sintered at 1200℃~1900℃". Sintering the granulated powder obtained in step S106 at 1200℃~1900℃ can be any temperature between 1200℃, 1300℃, 1400℃, 1500℃, 1600℃, 1700℃, 1800℃, and 1900℃. More preferably, the granulated powder obtained in step S106 is sintered at 1500℃~1900℃.

[0067] This temperature range, representing the thermodynamic window that synergizes with the aforementioned molar ratio, is one of the key technological steps enabling the successful construction of high-strength interlocking structures using this method. The purpose of setting this temperature range (1200℃~1900℃) is: First, this temperature range ensures a sufficient and efficient in-situ chemical reaction between Al₂O₃ and B₂O₃. At high temperatures of 1200℃ to 1900℃, atomic diffusion is significantly enhanced, providing sufficient impetus for mass transfer between reactants. This allows alumina to fully contact and react rapidly with boron oxide on the surface and in the gaps between boron nitride particles, which is a prerequisite for the large-scale, uniform production of aluminum borate products.

[0068] Second, this temperature range covers and exceeds the formation temperature of specific aluminum borate compounds (such as 9Al₂O₃·2B₂O₃) and their eutectic points. Sintering within this window not only ensures the formation of the target aluminum borate crystalline phase, but more importantly, it promotes the formation of an appropriate amount of aluminum borate liquid phase in the reaction system. This high-temperature liquid phase, as a highly efficient transport medium, greatly promotes the directional growth of aluminum borate whiskers through dissolution-precipitation, which is key to forming whiskers with high aspect ratios. At the same time, the liquid phase can wet the surface of boron nitride particles, fill the interparticle pores, and achieve particle rearrangement through viscous flow, thereby significantly improving the densification of spherical particles and providing a dense matrix for the interlocking structure.

[0069] Third, limiting the upper limit of sintering temperature is based on the simultaneous consideration of reaction efficiency and production cost. When sintering at 1900℃, the generation efficiency of aluminum borate whiskers and aluminum borate liquid phase is already high enough. Further increasing the sintering temperature will not significantly improve the generation efficiency, but will greatly increase energy consumption and equipment wear, which is not conducive to the economy and stability of industrial production.

[0070] At the same time, an inert atmosphere (such as nitrogen) is also necessary. Boron nitride, when exposed to an oxygen-containing atmosphere (such as air) at high temperatures of 1200℃~1900℃, will undergo a severe oxidation reaction (BN + O2 → B2O3 + N2), leading to the decomposition and destruction of the material itself. Therefore, the purpose of an inert atmosphere is to protect boron nitride from oxidation during high-temperature sintering.

[0071] In summary, the molar ratio range (0.1~0.8) in step S102 and the temperature range (1200℃~1900℃) in step S108 together constitute the core of the preparation method of the present invention, and they work together to ensure the construction of a high-strength interlocking structure.

[0072] Preferably, the aspect ratio of the aluminum borate whiskers is (5:1) to (10:1). This invention achieves directional control of the whisker aspect ratio by coordinating the raw material ratio (especially the boron oxide content) in step S102 and the sintering temperature in step S108 to regulate the in-situ growth behavior of the aluminum borate whiskers.

[0073] In step S102, the boron oxide content is a key factor in controlling the aspect ratio of the whiskers. From the perspective of whisker growth mechanism, solid alumina serves as the matrix for spiral dislocations, while liquid boron oxide supplies the nuclei for growth. The aspect ratio of the whiskers mainly depends on the boron oxide content. When the boron oxide content is high, the liquid phase is sufficient, and the whiskers easily grow rapidly along the one-dimensional direction, resulting in a high aspect ratio. Conversely, when the boron oxide content is low, the liquid phase is limited, whisker growth is restricted, and the aspect ratio tends towards the lower limit. Simultaneously, the uniform dispersion of the slurry ensures the uniform distribution of alumina particles in the boron nitride interstices, providing a structural basis for uniform nucleation and controllable growth of the whiskers, and avoiding localized overgrowth or agglomeration.

[0074] The sintering temperature in step S108, as an auxiliary process parameter, mainly affects the kinetic environment of whisker growth. Within this temperature range, Al2O3 reacts with B2O3 to form an aluminum borate liquid phase. Increasing the temperature reduces the viscosity of the liquid phase and increases the ion diffusion rate, thereby accelerating whisker growth. By selecting an appropriate sintering temperature, the growth rate can be optimized, and in synergy with the boron oxide content, the aspect ratio of the whiskers can be stabilized within the target range.

[0075] In summary, this invention achieves precise control of the aspect ratio of in-situ generated aluminum borate whiskers by accurately controlling the boron oxide content and ensuring the uniformity of the precursor slurry, combined with the optimization of the sintering temperature. This stabilizes the whiskers within the ideal range of (5:1) to (10:1), which effectively constructs an interlocking structure while avoiding the whiskers' tendency to break or agglomerate.

[0076] Preferably, in step S102, the boron nitride is plate-shaped boron nitride with a particle size of 1μm to 6μm and a purity of ≥90%.

[0077] Understandably, flake boron nitride is the basic raw material for forming spherical granulated powder, and spray granulation is adept at agglomerating this anisotropic flake raw material into isotropic spherical particles. The particle size range of 1μm to 6μm facilitates slurry preparation and spray granulation, ensuring sufficient specific surface area for participation in the reaction and sintering, while avoiding the problem of excessively high slurry viscosity caused by excessively fine particles.

[0078] Understandably, the requirement of "purity ≥ 90%" essentially controls the B2O3 content. As mentioned earlier, the core chemical reaction of this invention is the reaction between Al2O3 and B2O3. B2O3 originates from boron nitride (as an impurity, boron nitride is easily hydrolyzed and oxidized to B2O3 in humid air). "Purity ≥ 90%" means that a maximum of 10% impurities (mainly B2O3) are allowed. This utilizes the impurities in the raw materials as reactants, reducing costs; on the other hand, it also limits the upper limit of the B2O3 content. If the B2O3 content is too high, the required amount of Al2O3 to be added may be too high when calculating the molar ratio (0.1~0.8), resulting in an excessive total amount of aluminum borate generated, which in turn affects the final thermal conductivity. Therefore, this limitation ensures that the B2O3 content is within a controllable and reasonable range.

[0079] Understandably, although the "purity ≥ 90%" requirement can effectively utilize the inherent B2O3 in the raw material and control its upper limit, in actual industrial production and for specific application scenarios, in order to achieve more precise control of the interlocking structure or adapt to different grades of boron nitride raw materials, exogenous boron oxide can also be added in addition to the boron nitride raw material containing boron oxide during the pulping process in step S102.

[0080] Preferably, in step S102, the alumina is angular or spherical alumina with a particle size of 1μm to 6μm, and the particle size of the alumina is smaller than that of the boron nitride.

[0081] Understandably, the limitation on the relative size of "alumina particle size is smaller than boron nitride particle size" is intended to ensure the uniformity of the slurry in step S102. The objective of this invention is to achieve a uniform in-situ reaction between alumina and B2O3 (present on the surface of boron nitride) in step S108, thereby forming an interlocking structure in all regions of the entire spherical particle. Therefore, only when both alumina and boron nitride are uniformly dispersed, without any individual component present, can an interlocking structure be fully formed.

[0082] To achieve this uniform dispersion, the present invention specifies that "the particle size of alumina is smaller than the particle size of boron nitride" (e.g., the particle size of boron nitride is 6 μm, and the particle size of alumina is 1 μm). The mechanism is that smaller alumina particles can more effectively fill the gaps between larger boron nitride flake particles. This, after steps S102 and S104, enables the formation of a microstructure within the granulated powder where alumina particles are uniformly distributed and tightly wrapped around boron nitride particles. If the particle size of alumina is greater than or equal to the particle size of boron nitride, it will lead to uneven mixing. Large alumina particles cannot effectively fill the gaps, and enriched regions of alumina and boron nitride will form in the slurry. This uneven slurry, after granulation, will form granulated powder with an uneven internal structure.

[0083] When this unevenly structured granulated powder enters the high-temperature sintering furnace in step S108, the in-situ reaction between Al2O3 and B2O3 will only occur in the Al2O3-enriched region, forming localized, bulky aluminum borate phases. In the boron nitride-enriched region, due to the lack of Al2O3 reactants, an interlocking structure cannot be formed, and this region remains a loose aggregate. The final product will not be a uniformly reinforced microcomposite material, but a macroscopic mixture full of internal defects, pieced together from fragile boron nitride regions and overly hard aluminum borate regions. These particles, filled with internal stress and weak interfaces, will have very low overall mechanical strength and are highly susceptible to breakage starting from these weak regions during strength testing or practical applications.

[0084] Preferably, in step S102, the amount of alumina added accounts for 11% to 30% of the mass of boron nitride.

[0085] Understandably, the alumina mass percentage range is the result of a specific implementation and experimental optimization of the molar ratio range (0.1~0.8) in actual industrial production of step S102. The molar ratio is a theoretical stoichiometric ratio, while the mass ratio (11%~30%) is an actual, executable process parameter measured in production. Through extensive experimental data, this invention has determined that the 11%~30% mass range represents the process window for achieving a balance between the dual objectives of high strength and high thermal conductivity.

[0086] Preferably, in step S102, the surfactant is an anionic dispersant. The surfactant can be at least one of polyacrylate and polymethacrylate. More preferably, the surfactant is polyacrylate.

[0087] The purpose of using anionic surfactants is to solve the problem of agglomeration of micron-sized particles (boron nitride and aluminum oxide) in water-based solvents. Without a dispersant, fine particles will aggregate due to mutual attraction such as van der Waals forces, which will prevent boron nitride and aluminum oxide from being uniformly dispersed.

[0088] Understandably, this invention uses anionic dispersants, whose core function is to ensure the uniform and stable dispersion of flake boron nitride and alumina particles in the slurry through electrostatic repulsion. High molecular weight anionic dispersants such as polyacrylates and polymethacrylates are rich in carboxyl groups (-COO) on their molecular chains. -In the alkaline environment (pH=8~9) adjusted in step S102, the alumina and boron nitride are fully ionized and adsorbed onto the particle surface, causing all solid particles to carry a strong negative charge of the same kind. The resulting strong electrostatic repulsion effectively overcomes the van der Waals attraction between particles, preventing local component segregation caused by particle agglomeration. This ensures uniform mixing of alumina and boron nitride at the microscale, guaranteeing uniform nucleation and growth of aluminum borate whiskers during subsequent sintering, and ultimately constructing a complete and stable interlocking structure within the entire spherical particle.

[0089] Preferably, in step S102, the adhesive includes at least one of polyethylene glycol, polyvinyl alcohol, and hydroxymethyl cellulose. More preferably, the adhesive is polyethylene glycol.

[0090] The purpose of the binder is to provide the necessary mechanical strength for the granulated powder obtained after step S104. In step S104, the slurry is atomized into tiny droplets, while the moisture is rapidly evaporated by hot air. If the slurry contains only solid particles (boron nitride and aluminum oxide) and water, then after the moisture evaporates, the resulting product is merely a loose mixture of boron nitride and aluminum oxide powders, which cannot form or maintain spherical granulated powder.

[0091] This invention utilizes water-soluble polymers such as PEG or PVA as binders pre-dissolved in the slurry. When water evaporates in S104, these polymers precipitate out, forming polymer bridges between the contact points of boron nitride and alumina particles, thus binding these inorganic particles together. This allows the dried granulated powder to maintain a stable spherical structure and possess sufficient mechanical strength to withstand subsequent operations without breaking or crumbling.

[0092] It is important to emphasize that this adhesive is temporary, and its effect is limited to the transition phase between steps S104 and S108. It must be completely removed before step S108, which is the core task of the subsequent step S106.

[0093] Preferably, in step S102, the solid content of the slurry is 25% to 40%. This range is the process window determined in step S104 of the present invention to balance production efficiency and product quality. If the solid content is too low (i.e., the slurry is too thin), the slurry contains too much water, which means that a large amount of energy needs to be consumed in step S104 to evaporate this water, resulting in low production efficiency and high cost. When droplets with too low a solid content are sprayed into the drying tower, the solid particles in the droplets are sparse. During the drying process, a thin solid shell will first form on the surface of the droplets, and the vapor pressure generated after the internal water evaporates will cause this thin shell to expand, or cause the thin shell to collapse after the water escapes. Both of these effects will lead to the formation of defective particles with extremely low mechanical strength, which will be easily crushed in subsequent processing or applications. If the solid content is too high (i.e., the slurry is too thick), the viscosity of the slurry will increase sharply with the increase of solid content. This high-viscosity fluid will first cause delivery failure, and the peristaltic pump may not be able to pump it effectively to the spray tower. More seriously, it will cause atomization failure. The core of spray granulation is that the atomizing disc disperses the slurry into uniform tiny droplets. Excessively high viscosity will prevent the slurry from being effectively dispersed, causing the atomizing disc to become clogged, or large droplets or streaks to be sprayed out, thus causing step S104 to fail and making it impossible to obtain spherical particles of 20μm~150μm.

[0094] Preferably, step S102 further includes adjusting the pH of the slurry to 8-9 using ammonia water, and stirring the slurry at a speed of 300 r / min-1000 r / min for 20-60 minutes.

[0095] Understandably, the present invention adjusts the pH of the slurry to 8-9 to facilitate interaction with anionic dispersants. As mentioned above, the mechanism of anionic dispersants utilizes the electrostatic repulsion generated by the ionization of negative charges. This ionization reaction is inhibited under acidic or neutral conditions (low pH). The present invention regulates the pH of the slurry within an alkaline range of 8-9 using an alkaline regulator. The purpose of this is that this pH range is the optimal operating range for anionic dispersants, enabling them to ionize and generate negative charges on the particle surface, thereby providing electrostatic repulsion. This allows the slurry to maintain low viscosity and high fluidity even at subsequent high solids contents. If the pH is too low, the dispersant becomes ineffective, and the slurry will immediately agglomerate and thicken, leading to failure in subsequent stirring and granulation.

[0096] Furthermore, the slurry is stirred at a speed of 300 r / min to 1000 r / min for 20 to 60 minutes. The purpose is to achieve high homogenization of the slurry at the microscale through controllable mechanical shear force. The stirring has the following technical effects: First, it breaks up the initial agglomerates formed by boron nitride and alumina particles due to van der Waals forces, especially the layered agglomerates that are prone to form in plate-like boron nitride; Second, it ensures that the individual particles that have been deagglomerated by the dispersant can fully and randomly interpenetrate and distribute themselves, thereby maximizing the filling and uniform distribution of alumina particles in the gaps between boron nitride particles before granulation.

[0097] If the stirring speed is too low or the stirring time is too short, the provided shear force will be insufficient to effectively break up the firmly aggregated particles, resulting in a large number of mixing dead zones and undispersed agglomerates in the slurry. This microscopic inhomogeneity will solidify in the subsequent granulation powder and cause the reaction between Al2O3 and B2O3 to occur only locally during high-temperature sintering, failing to generate a uniform and continuous interlocking network of aluminum borate whiskers throughout the spherical particles, ultimately severely weakening the product's strength. Conversely, if the stirring speed is too high or the stirring time is too long, although the dispersion effect can be guaranteed, it will lead to uneconomical energy consumption and may cause the flake-like boron nitride particles to break due to excessive shear force, or cause desorption of the adsorbed dispersant particles, or even introduce too many air bubbles, which will negatively affect the stability of the slurry and the performance of the final product.

[0098] Preferably, in step S104, by adjusting the atomization frequency of the spray granulation tower, the D50 particle size of the obtained granulated powder can be controlled within the range of 20μm to 150μm.

[0099] Understandably, pre-controlling the particle size of the granulated powder can ultimately yield high-strength spherical boron nitride with a specific particle size. During spray granulation, the rotation frequency of the atomizing disc directly determines the size of the droplets dispersed from the slurry. A higher atomization frequency results in finer droplets and smaller particle size of the granulated powder after drying; conversely, a lower frequency results in larger particle size. This invention, by using atomization frequency as a controllable process parameter, enables the stable and precise preparation of spherical granulated powder with a D50 particle size between 20 μm and 150 μm.

[0100] Preferably, in step S106, the sintering temperature is 600℃~700℃, and the sintering time is 2 hours~6 hours.

[0101] Understandably, the purpose of step S106 is to remove the organic binder (e.g., PEG, PVA, etc.) that was intentionally added in step S102 for granulation. As mentioned above, the binder forms the granulated powder. If the granulated powder containing the binder is directly fed into step S108, the organic binder will undergo pyrolysis under high temperature and oxygen-deficient conditions, resulting in carbon residue. This carbon will remain in the pores and grain boundaries of the boron nitride particles in the form of amorphous carbon or graphite, forming serious defects.

[0102] Thirdly, the present invention provides a thermally conductive pad comprising high-strength spherical boron nitride as in the first aspect or high-strength spherical boron nitride prepared by the preparation method of the second aspect. The amount of high-strength spherical boron nitride added is 30% to 50% of the mass of the thermal pad.

[0103] Understandably, limiting the addition amount of the high-strength spherical boron nitride in the thermal pad to 30%~50% is a direct manifestation and a necessary requirement in practical applications of the high-strength characteristics brought about by the interlocking structure of the present invention. This filling range is key to achieving the high thermal conductivity of the thermal pad, and its feasibility depends entirely on the excellent structural stability exhibited by the spherical boron nitride of the present invention during high-speed shear mixing.

[0104] Existing technologies require filling the polymer matrix with a high content of thermally conductive fillers to form an effective thermally conductive network in order to achieve high thermal conductivity. However, traditional spherical boron nitride particles are prone to breakage during high-shear mixing in a high-viscosity polymer matrix before reaching the required high filler content (e.g., 30%–50%) due to insufficient strength. Particle breakage leads to a sharp increase in specific surface area, significantly increasing the viscosity of the composite system, causing a rapid deterioration in processing performance, ultimately making it difficult to achieve the high filler content, and thus the thermal conductivity cannot reach the expected target.

[0105] This invention endows spherical boron nitride with extremely high strength through its interlocking structure, enabling it to withstand the high-shear processing environment during the fabrication of thermal pads. After high-speed stirring tests, the high-strength spherical boron nitride of this invention exhibits an extremely low D50 particle size reduction rate (less than 10%), effectively maintaining its structural integrity. The absence of particle breakage ensures the controllability of the viscosity of the composite system during mixing, thus allowing for the successful achievement of a high filling content of 30% to 50%. At this filling content, the high-strength spherical boron nitride can form a dense and continuous thermally conductive pathway within the matrix, fully utilizing the high thermal conductivity of boron nitride itself, ultimately resulting in excellent and stable thermal conductivity for the thermal pad.

[0106] The present invention will be further described in detail below with reference to specific embodiments, but these are exemplary and do not limit the scope of protection of the present invention in any way.

[0107] Example 1 This embodiment provides a method for preparing high-strength spherical boron nitride, specifically including the following steps: Step S102: Pulping: Flake boron nitride (2% boron oxide content, 98% purity, 6μm particle size), angular alumina (1μm particle size, added at 11wt% of boron nitride mass), surfactant (polyacrylate), and binder (polyethylene glycol) are mixed. The pH of the slurry is adjusted to 8-9 using ammonia, and mechanically stirred at 1000 r / min for 30 minutes to obtain a homogeneous slurry with a solid content of 32%.

[0108] Based on the boron oxide content and alumina addition in the boron nitride raw material, the molar number of alumina accounts for approximately 0.79 of the total molar number of boron oxide and alumina.

[0109] Step S104: Granulation: Use a peristaltic pump to introduce the uniformly mixed slurry into the atomizing disc of the spray granulation tower for granulation. Adjust the atomization frequency to 200Hz to obtain spherical granulated powder.

[0110] Step S106: Debinding: Sinter the granulated powder at 650°C for 4 hours in air atmosphere to remove organic matter.

[0111] Step S108: Sintering: The powder after debinding is sintered at 1600℃ for 4 hours under an inert atmosphere (argon) to allow boron oxide and aluminum oxide to react in situ, generating aluminum borate liquid phase and aluminum borate whiskers, and finally forming an interlocked structure of aluminum borate whiskers and boron nitride, resulting in high-strength spherical boron nitride blocks.

[0112] Step S110: Screening: Screen the material blocks to obtain high-strength spherical boron nitride products.

[0113] Example 2 The preparation method of Example 2 is the same as that of Example 1, except that the boron oxide content in the boron nitride raw material is 5%, the amount of alumina added is 15wt% of the boron nitride mass, the atomization frequency of spray granulation is 250Hz, and the solid content of the slurry is 35%.

[0114] Based on the boron oxide content and alumina addition in the boron nitride raw material, the molar number of alumina accounts for approximately 0.67% of the total molar number of boron oxide and alumina.

[0115] Example 3 The preparation method of Example 3 is the same as that of Example 1, except that the boron oxide content in the boron nitride raw material is 5%, the amount of alumina added is 20wt% of the boron nitride mass, the atomization frequency of spray granulation is 280Hz, and the solid content of the slurry is 38%.

[0116] Based on the boron oxide content and alumina addition in the boron nitride raw material, the molar number of alumina accounts for approximately 0.73% of the total molar number of boron oxide and alumina.

[0117] Example 4 The preparation method of Example 4 is the same as that of Example 1, except that the boron oxide content in the boron nitride raw material is 5%, the amount of alumina added is 30wt% of the boron nitride mass, the atomization frequency of spray granulation is 280Hz, and the solid content of the slurry is 40%.

[0118] Based on the boron oxide content and alumina addition in the boron nitride raw material, the molar number of alumina accounts for approximately 0.8% of the total molar number of boron oxide and alumina.

[0119] Example 5 The preparation method of Example 5 is the same as that of Example 1, except that the sintering temperature of step S108 is 1200℃.

[0120] Example 6 The preparation method of Example 6 is the same as that of Example 1, except that the sintering temperature of step S108 is 1900℃.

[0121] Example 7 The preparation method of Example 7 is the same as that of Example 1, except that the alumina used is spherical alumina (particle size 1 μm).

[0122] Example 8 The preparation method of Example 8 is the same as that of Example 1, except that the particle size of the sheet-like boron nitride used is 4 μm and the particle size of the angular alumina is 2 μm.

[0123] Example 9 The preparation method of Example 9 is the same as that of Example 1, except that the atomization frequency of spray granulation is adjusted to 390Hz.

[0124] Example 10 The preparation method of Example 10 is the same as that of Example 1, except that the atomization frequency of spray granulation is adjusted to 100Hz.

[0125] Example 11 The preparation method of Example 11 is the same as that of Example 1, except that the boron oxide content in the boron nitride raw material is 10%, the amount of alumina added is 1.7 wt% of the boron nitride mass, and the solid content of the slurry is 32%.

[0126] Based on the boron oxide content and alumina addition in the boron nitride raw material, the molar number of alumina accounts for approximately 0.1% of the total molar number of boron oxide and alumina.

[0127] Comparative Example 1 The preparation method of Comparative Example 1 is the same as that of Example 1, except that no alumina powder is added, and only boron nitride, surfactant and binder are used for granulation and sintering.

[0128] Since no aluminum oxide was added, the molar number of aluminum oxide accounted for 0% of the total molar number of boron oxide and aluminum oxide.

[0129] Comparative Example 2 The preparation method of Comparative Example 2 is the same as that of Example 1, except that the boron oxide content in the boron nitride raw material used is 10%, and the amount of alumina added is 0.8 wt% of the boron nitride mass.

[0130] Based on the boron oxide content and alumina addition in the boron nitride raw material, the molar number of alumina accounts for approximately 0.05 of the total molar number of boron oxide and alumina.

[0131] Comparative Example 3 The preparation method of Comparative Example 3 is the same as that of Example 1, except that the boron oxide content in the boron nitride raw material used is 2%, and the amount of alumina added is 26.5 wt% of the boron nitride mass.

[0132] Based on the boron oxide content and alumina addition in the boron nitride raw material, the molar number of alumina accounts for approximately 0.9% of the total molar number of boron oxide and alumina.

[0133] Comparative Example 4 The preparation method of Comparative Example 4 is the same as that of Example 1, except that the sintering temperature of step S108 is 1100℃.

[0134] Test case Strength testing method: Add 50.6g of the spherical boron nitride powder to be tested to 200g of a solution with a viscosity of 200 mPa·s, and stir using a mechanical stirrer at a speed of 2000 r / min. Samples are taken from the upper, middle, and lower layers of the solution at 10, 20, and 30 minutes of stirring, respectively, to obtain sample T10min, T20min, and T30min. The D50 particle size of the original powder and each sample is tested, and the percentage decrease in D50 particle size is calculated to evaluate the strength. The lower the percentage decrease, the higher the particle strength and the more stable the structure.

[0135] Thermal conductivity testing method: Spherical boron nitride powder, vinyl silicone oil, hydrogen-containing silicone oil, inhibitor, and catalyst are mixed according to the formula to form a 2mm thick thermally conductive silicone pad, in which the spherical boron nitride filling amount is 41% (accounting for 41% of the mass of the thermally conductive pad). The thermal conductivity is tested using a DRL-Ⅲ thermal conductivity meter. Two thermally conductive silicone pads are tested for each sample, and the average value is taken.

[0136] Method for determining the aspect ratio of aluminum borate whiskers: A spherical boron nitride cross-section image was taken using a scanning electron microscope (SEM). At least 50 complete aluminum borate whiskers were randomly selected, and their length (L) and diameter (D) were measured. The aspect ratio (L / D) of each whisker was calculated, and the arithmetic mean of all measurements was taken as the aspect ratio of the sample.

[0137] The test results of each embodiment and comparative example are summarized in Table 1 below.

[0138] Table 1 Performance test results of the examples and comparative examples

[0139] Based on the experimental data in Table 1, the synergistic influence of various process parameters on the strength and thermal conductivity of spherical boron nitride can be obtained. Within the range of 0.1 to 0.8 moles of alumina relative to the total moles of boron oxide and alumina, the strength of the products from the examples is significantly better than that of the comparative examples. Specifically, after high-speed stirring for 30 minutes, the D50 particle size reduction rate of the spherical boron nitride prepared in all examples was less than 10%, far superior to that of comparative examples 1 to 3. This fully demonstrates the universality and decisive role of in-situ generation of aluminum borate whiskers to form an interlocking structure in improving particle strength. Examples 2 and 7 exhibited the best structural stability. The success of Examples 5 (sintered at 1200℃) and 6 (sintered at 1900℃) verified the feasibility of the sintering temperature window of 1200℃ to 1900℃. The good results of Examples 7 (using spherical alumina) and 8 (adjusting the raw material particle size) indicate that the present invention has a certain degree of inclusiveness towards raw materials of different morphologies.

[0140] The amount of alumina added and the sintering temperature are crucial for balancing the strength and thermal conductivity of spherical boron nitride. Too little or too much alumina will prevent the formation of an effective interlocking structure, resulting in insufficient strength; too much alumina will introduce excessive low-thermal-conductivity phases, affecting the thermal conductivity of the final application device. The high D50 particle size reduction rate in Comparative Example 4 (1100℃) demonstrates that when the temperature is below 1200℃, the system cannot form an aluminum borate liquid phase and aluminum borate whiskers.

[0141] Taking all factors into consideration, the appropriate alumina addition amounts and suitable sintering processes in Examples 2 and 7 represent the preferred approach for achieving a balance between high strength and high thermal conductivity. This approach ensures the formation of a robust interlocking structure, maintaining a very high particle size retention rate under harsh processing conditions, while minimizing the excessive presence of low thermal conductivity impurity phases, thereby endowing the thermal pad with excellent overall performance.

[0142] To further demonstrate the technical effectiveness of the present invention, the following analysis will be conducted in conjunction with specific experimental test results and images.

[0143] like Figure 1As shown, Figure 1 The XRD pattern of the high-intensity spherical boron nitride prepared in Example 2 is shown. It can be seen that the characteristic diffraction peaks corresponding to aluminum borate appear in the spectrum, while the characteristic peaks of boron nitride are still present. This directly proves the successful in-situ formation of aluminum borate whiskers, which together with boron nitride constitute a complex phase, providing crystallographic evidence for the existence of an interlocking structure.

[0144] like Figure 2 As shown, Figure 2 The XRD pattern of the high-strength spherical boron nitride prepared in Example 4 is shown. Characteristic peaks corresponding to unreacted Al₂O₃ can be observed, confirming the presence of excess alumina residue when too much alumina is added. This conclusion is consistent with the decreasing trend of thermal conductivity shown in Table 1.

[0145] like Figure 3 As shown, Figure 3 This is a SEM image of the high-strength spherical boron nitride prepared in Example 2 of the present invention. Figure 4 As shown, Figure 4 for Figure 3 A magnified view of a portion of the image. From Figure 3 and Figure 4 As can be seen, the prepared product exhibits a good spherical morphology, a relatively dense surface, and a uniform particle size distribution. This high sphericity and isotropic structure is beneficial for achieving high filling volume and isotropic thermal conduction pathways in the composite matrix when used as a thermally conductive filler.

[0146] like Figure 5 As shown, Figure 5 This is a cross-sectional SEM image of the high-strength spherical boron nitride prepared in Example 2 of the present invention. Figure 6 As shown, Figure 6 This is a cross-sectional SEM image of the high-strength spherical boron nitride prepared in Example 3 of the present invention. Figure 5 and Figure 6 The internal microstructure of the product of this invention is revealed. As can be observed from the figure, the interior of the entire spherical particle is not a loose accumulation of plate-like boron nitride, but rather a dense, mechanically interlocked three-dimensional network framework—an interlocking structure—formed by interwoven and interspersed plate-like boron nitride (the darker plate-like areas in the figure) and in-situ generated aluminum borate whiskers (the brighter needle-like or rod-like areas in the figure). It is this unique microstructure that allows the in-situ generated whiskers to firmly lock the loose boron nitride plates together, thereby endowing the spherical boron nitride with extremely high mechanical strength and density, enabling it to withstand the shear forces of high-speed stirring without breaking.

[0147] like Figure 7 As shown, Figure 7This is an EDS result image of the high-strength spherical boron nitride prepared in Example 2 of this invention. Through EDS elemental surface scanning analysis, the distribution of the four elements, B, N, Al, and O, can be observed. The results show that Al (aluminum) and O (oxygen) elements are not only enriched on the particle surface, but are uniformly distributed throughout the cross-section of the entire spherical particle. This result is consistent with... Figure 5 Corresponding to the cross-sectional SEM images, it was further confirmed that aluminum borate (composed of Al and O) was not externally coated, but rather generated in situ inside the particles and uniformly composited with the boron nitride matrix (composed of B and N), thus forming a high-strength interlocking structure.

[0148] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A high-strength spherical boron nitride, characterized by, The high-strength spherical boron nitride is composed of boron nitride and aluminum borate whiskers generated in-situ between the boron nitride and interwoven with each other.

2. The high-strength, spherical boron nitride of claim 1, wherein, The structure formed by the interwoven boron nitride and aluminum borate whiskers is an interlocking structure.

3. The high-strength, spherical boron nitride according to claim 1 or 2, characterized in that, The aspect ratio of the aluminum borate whiskers is (5:1)~(10:1).

4. The high-strength, spherical boron nitride of claim 1, wherein, The D50 particle size of the high-strength spherical boron nitride is 20μm~150μm. And / or, the D50 particle size of the high-strength spherical boron nitride decreases by less than 10% after stirring in a solution at a speed of 2000r / min for 10 minutes~30 minutes.

5. A method for producing the high-strength spherical boron nitride according to any one of claims 1 to 4, characterized by, The method comprises the following steps: In step S102, the boron nitride is flaky boron nitride with a particle size of 1μm~6μm, and the purity is ≥90%; And / or, in step S102, the alumina is angular or spherical alumina with a particle size of 1μm~6μm, and the particle size of the alumina is smaller than the particle size of the boron nitride. In step S102, the surfactant is an anionic dispersant. And / or, in step S102, the binder comprises at least one of polyethylene glycol, polyvinyl alcohol, and hydroxymethyl cellulose. In step S102, the added amount of the alumina accounts for 11%~30% of the mass of the boron nitride.

6. The production method according to claim 5, wherein And / or, in step S102, the solid content of the slurry is 25%~40%. And / or, step S102 further comprises adjusting the pH value of the slurry to 8~9 using ammonia water and stirring the slurry at a speed of 300r / min~1000r / min for 20 minutes~60 minutes.

7. The preparation method according to claim 5, characterized in that, In step S106, the sintering temperature is 600℃~700℃, and the sintering time is 2 hours~6 hours. 10.A thermal pad comprising the high-strength spherical boron nitride according to any one of claims 1 to 4 or prepared by the method according to any one of claims 5 to 9; 8. The preparation method according to claim 5, characterized in that, The added amount of the high-strength spherical boron nitride accounts for 30%~50% of the mass of the thermal pad. ​ ​ 9. The preparation method according to claim 5, characterized in that, ​ ​ ​

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