Low specific gravity high thermal conductivity composite powder and preparation method thereof

Abstract

This invention relates to the field of thermally conductive powder materials, specifically to a low-density, high-thermal-conductivity composite powder and its preparation method. The invention employs a three-step process: surface activation pretreatment, in-situ gel coating of a silicon-molybdenum-scandium composite, and molten salt-assisted sintering. This process coats hollow microspheres with a dense layer of molybdenum-scandium silicide to obtain the composite powder. The composite powder of this invention simultaneously achieves the advantages of low specific gravity, high thermal conductivity, high insulation, and strong breakage resistance, solving the problem of multiple performance limitations in existing technologies. The composite powder of this invention has extremely high application value in fields such as thermally conductive and insulating composite materials, electronic packaging, and aerospace lightweighting.

Description

Technical Field

[0001] This invention relates to the field of thermally conductive powder materials, specifically to a low-density, high-thermal-conductivity composite powder and its preparation method. Background Technology

[0002] With the rapid development of 5G communication, new energy vehicles, aerospace, wearable electronics and other fields, electronic devices are rapidly iterating towards high integration, high power density and lightweight, which puts forward dual stringent requirements on the performance of thermal management materials: they need to have efficient heat conduction capabilities to ensure the long-term stable operation of devices; and they need to achieve extremely low specific gravity to meet the design requirements of lightweight equipment, long battery life and low structural load.

[0003] As a core functional component of thermal management materials, the performance of thermally conductive powders directly determines the thermal conductivity and density characteristics of composite materials. Currently, the mainstream thermally conductive powders in the industry are mainly divided into two categories, both facing intractable technical bottlenecks: The first category consists of solid inorganic powders with high intrinsic thermal conductivity, including alumina, magnesium oxide, zinc oxide, aluminum nitride, boron nitride, and silicon carbide. While these powders possess good thermal conductivity, their intrinsic density is generally high. Furthermore, high filler content can lead to deterioration of matrix processing performance and a significant decrease in mechanical properties, limiting their application in high-end applications. The second category comprises lightweight modified hollow fillers, using hollow glass microspheres and hollow ceramic microspheres as the core matrix, with functional modification achieved by coating the surface with thermally conductive powder. While these fillers possess the inherent advantage of low density, they suffer from low thermal conductivity, easy coating detachment, high interfacial thermal resistance, and complex processing.

[0004] Furthermore, existing low-density thermally conductive powders still cannot solve the problem of the trade-off between low specific gravity and high thermal conductivity. For example, while publicly disclosed nanodiamond-coated boron nitride composite powders have achieved a certain degree of weight reduction, their specific gravity remains relatively high, limiting the lightweighting effect. Moreover, diamond powders are expensive, hindering large-scale promotion. Hollow fillers modified with carbon materials such as graphene and carbon nanotubes, although offering improved thermal conductivity, suffer from poor insulation and high dielectric constant, making them unsuitable for insulation applications in electronic packaging and significantly limiting their applicability.

[0005] In summary, there is an urgent need in the industry to develop a composite thermally conductive powder that simultaneously possesses low specific gravity, high thermal conductivity, high insulation, strong breakage resistance, and a simple preparation process suitable for industrial production, in order to overcome the shortcomings of existing technologies and meet the pressing needs of lightweight thermal management for high-end electronic devices. Summary of the Invention

[0006] To address the problems existing in the prior art, the purpose of this invention is to provide a low-density, high-thermal-conductivity composite powder and its preparation method.

[0007] The objective of this invention is achieved through the following technical solution: In a first aspect, the present invention provides a method for preparing a low-density, high-thermal-conductivity composite powder, comprising the following steps: Step 1, Surface activation pretreatment: Hollow microspheres were added to a sodium hydroxide solution, stirred and dispersed evenly, and then ultrasonically treated to gently etch the surface of the microspheres and introduce uniform high-density active hydroxyl groups. Subsequently, the microspheres were separated by filtration, washed with deionized water until the filtrate was neutral, and vacuum dried to obtain surface-activated hollow microspheres. Step 2, Preparation of the complex gel layer: Surface-activated hollow microspheres were added to an aqueous solution of ethanol and stirred to disperse them evenly to prepare a microsphere suspension. Weigh out silicon source precursor, molybdenum source precursor, and scandium source precursor, and dissolve them in anhydrous ethanol to prepare a precursor mixture. Add the precursor mixture dropwise to the microsphere suspension at a uniform rate, while adjusting the pH of the system to 4-4.5 with dilute nitric acid. Stir and react at a constant temperature of 30-50℃ for 2-6 hours to allow the precursors to undergo heterogeneous hydrolysis and condensation on the surface of the microspheres, forming a uniform and dense silicon-molybdenum-scandium composite gel layer. After the reaction was completed, the microspheres were separated by filtration, washed 3-5 times with anhydrous ethanol, and vacuum dried at 60-80℃ for 4-8 hours to obtain coated microspheres with a composite precursor binding layer. Step 3, High-temperature sintering: The coated microspheres and sintering aids were mixed evenly, and the mixed powder was loaded into an alumina crucible, compacted, sealed, and placed in an argon atmosphere tube furnace for sintering. After cooling to room temperature in the furnace, the sintered powder was taken out, washed repeatedly with 80°C deionized water, then washed twice with anhydrous ethanol, dried under vacuum at 60°C for 4 hours, and passed through a 150-200 mesh sieve to remove the release agent and a small amount of agglomerates, thus obtaining a low specific gravity and high thermal conductivity composite powder.

[0008] Preferably, in step 1, the hollow microspheres are mullite or high silica glass hollow microspheres with a softening temperature ≥1100℃, a particle size of 10-100μm, a wall thickness of 1-5μm, and a closed-cell rate ≥98%.

[0009] Preferably, in step 1, the mass fraction of the sodium hydroxide solution is 0.01%-0.05%.

[0010] Preferably, in step 1, the ratio of hollow microspheres to sodium hydroxide solution is (5-10) g: 100 mL.

[0011] Preferably, in step 1, the ultrasonic conditions are: 30-40℃ water bath, 50-80W power ultrasonic treatment for 10-20 minutes.

[0012] Preferably, in step 2, the volume ratio of anhydrous ethanol to deionized water in the aqueous solution of ethanol is 4-6:1.

[0013] Preferably, in step 2, the molar ratio of the silicon source precursor tetraethyl orthosilicate, the molybdenum source precursor molybdenum acetylacetonate, and the scandium source precursor scandium acetylacetonate is 18-22:3-5:1.

[0014] Preferably, in step 2, the total amount of precursor fed to the mass ratio of surface-activated hollow microspheres is 1:4-1:6.

[0015] Preferably, in step 2, the precursor mixture is added dropwise to the microbead suspension at a rate of 0.5-1.0 mL / min.

[0016] Preferably, in step 3, the coated microspheres and sintering aids are mixed at a mass ratio of 8-12:1.

[0017] Preferably, in step 3, the sintering aid includes a NaCl-KCl composite molten salt, nano-silicon powder, and nano-alumina in a mass ratio of 6-8:2-3:0.5-1, wherein the molar ratio of NaCl to KCl in the NaCl-KCl composite molten salt is 1:1.

[0018] Preferably, in step 3, the sintering temperature is 920-980℃, the time is 4-6h, and the heating rate is 3-5℃ / min; high-purity argon gas is introduced throughout the process at a flow rate of 50-100mL / min.

[0019] More preferably, in step 3, the sintering temperature is 950℃; the temperature is increased from room temperature to 300℃ at a rate of 5℃ / min and held for 30min; the temperature is increased from 300℃ to 950℃ at a rate of 3℃ / min and held for 4-6h.

[0020] Secondly, the present invention provides a low specific gravity and high thermal conductivity composite powder, which is prepared by the above-mentioned preparation method.

[0021] Preferably, the composite powder has a closed-cell rate of ≥95% and a specific gravity of ≤0.6 g / cm³. 3 It has a thermal conductivity of ≥8W / (m・K), strong coating adhesion, and no obvious agglomeration.

[0022] The beneficial effects of this invention are as follows: 1. This invention utilizes a three-step process—surface activation pretreatment, in-situ gel coating of a silicon-molybdenum-scandium composite, and molten salt-assisted sintering—to coat a dense layer of molybdenum-scandium silicide onto the surface of hollow microspheres, thereby preparing a composite powder. The composite powder of this invention simultaneously possesses the advantages of low specific gravity, high thermal conductivity, high insulation, and strong breakage resistance, solving the problem of multiple performance limitations in existing technologies. The composite powder of this invention has extremely high application value in fields such as thermally conductive and insulating composite materials, electronic packaging, and lightweighting in aerospace.

[0023] 2. This invention employs a surface activation pretreatment process of mild alkaline etching and low-power ultrasound. Without damaging the closed-pore structure of the hollow microspheres, it introduces high-density and uniformly distributed active hydroxyl sites on the surface of the microspheres. This avoids problems such as microsphere opening, breakage, and increased specific gravity caused by strong corrosion processes, ensuring the lightweight properties of the powder, and providing sufficient reactive sites for subsequent in-situ coating.

[0024] 3. This invention constructs a Si-Mo-Sc ternary composite oxide gel layer on the surface of microspheres through an in-situ heterogeneous hydrolysis-condensation process, achieving performance enhancement of the coating structure through a unique Si / Mo / Sc molar ratio. First, the coating layer, based on a silicon-oxygen network, forms stable Si-O-Si chemical bonds with the hydroxyl groups on the microsphere surface, resulting in a uniform, dense, and controllable coating layer with strong adhesion to the matrix. Second, the introduction of Mo and Sc dual elements for synergistic doping into the silicon-oxygen coating network effectively controls the lattice structure of the silicon-oxygen network, significantly improving the thermal conductivity and insulation properties of the system while retaining the performance of the silicon dioxide matrix.

[0025] 4. This invention employs a composite sintering aid system of NaCl-KCl composite molten salt, synergistically combining nano-silicon powder and nano-alumina, and utilizes a low-temperature sintering process under argon atmosphere to achieve full densification and crystallization of the coating layer under conditions below the softening temperature of hollow microspheres. The liquid-phase sintering environment provided by the composite molten salt significantly reduces the sintering activation energy. Through the molten salt-assisted silothermic reduction reaction, oxide reduction and silicide reactions are simultaneously completed, resulting in a dense molybdenum-scandium silicide composite coating in situ, while simultaneously improving the mechanical strength and impact resistance of the coating layer. Attached Figure Description

[0026] The present invention will be further described with reference to the accompanying drawings, but the embodiments in the drawings do not constitute any limitation on the present invention. For those skilled in the art, other drawings can be obtained based on the following drawings without creative effort.

[0027] Figure 1 This is a schematic diagram of the composite powder prepared in Example 1; Figure 2 This is a scanning electron microscope (SEM) schematic diagram of the composite powder prepared in Example 1. Detailed Implementation

[0028] The technical solution of the present invention is illustrated below through specific examples. It should be understood that the one or more method steps mentioned in the present invention do not preclude the existence of other method steps before or after the combined steps, or the insertion of other method steps between these explicitly mentioned steps; it should also be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the present invention. Furthermore, unless otherwise stated, the numbering of each method step is merely a convenient tool for identifying each method step, and not for limiting the order of the method steps or defining the scope of the present invention. Changes or adjustments to their relative relationships, without substantially altering the technical content, should also be considered within the scope of the present invention.

[0029] To better understand the above technical solutions, exemplary embodiments of the present invention are described in more detail below. While exemplary embodiments of the present invention are shown, it should be understood that the present invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided to enable a more thorough understanding of the present invention and to fully convey the scope of the invention to those skilled in the art.

[0030] The present invention will be further described below with reference to the following embodiments. Example 1

[0031] A method for preparing a low-density, high-thermal-conductivity composite powder, comprising the following specific steps: Step 1, Surface activation pretreatment: Take 50g of mullite hollow microspheres (softening temperature 1250℃, particle size 10-60μm, wall thickness 2-3μm, closed-cell rate 99%) and add them to 500mL of 0.03% sodium hydroxide solution. First, disperse them by mechanical stirring at 250rpm for 5min, and then sonicate them at 35℃ water bath and 60W power for 15min to gently etch the surface of the microspheres and introduce uniform high-density active hydroxyl groups. Then filter and separate the microspheres, wash them with deionized water until the filtrate is neutral, and vacuum dry them at 90℃ for 10h to obtain surface-activated hollow microspheres.

[0032] Step 2, gel layer coating: The activated hollow microspheres were added to an ethanol-water solution with a volume ratio of anhydrous ethanol to deionized water of 5:1, and stirred and dispersed evenly at 400 rpm to prepare a microsphere suspension with a solid content of 15 wt%. Weigh out the silicon source precursor tetraethyl orthosilicate, the molybdenum source precursor molybdenum acetylacetonate, and the scandium source precursor scandium acetylacetonate according to a molar ratio of 20:4:1, stir and dissolve them in anhydrous ethanol to prepare a precursor mixture with a solid content of 5%. The precursor mixture was added dropwise to the microsphere suspension at a rate of 0.8 mL / min, with the total amount of precursor added being 1:5 in mass ratio to the surface-activated hollow microspheres. Simultaneously, the pH of the system was adjusted to 4.2 with dilute nitric acid, and the reaction was carried out at 40 °C with constant stirring for 4 h, allowing the precursor to undergo heterogeneous hydrolysis and condensation on the surface of the microspheres, forming a uniform and dense silicon-molybdenum-scandium composite gel layer. After the reaction was completed, the microspheres were separated by filtration, washed four times with anhydrous ethanol, and vacuum dried at 70 °C for 6 h to obtain coated microspheres with a composite precursor binding layer.

[0033] Step 3, sintering treatment: The above-mentioned coated microspheres and sintering aids were mixed evenly at a mass ratio of 10:1. The sintering aids consisted of a NaCl-KCl composite molten salt (NaCl to KCl molar ratio 1:1) in a mass ratio of 7:2.5:0.5, nano-silicon powder (100nm), and nano-alumina (100nm). The mixed powder was loaded into an alumina crucible, compacted, sealed, and placed in an argon atmosphere tube furnace. High-purity argon gas was introduced throughout the process at a flow rate of 80mL / min. The sintering program was as follows: heating from room temperature to 300℃ at a heating rate of 5℃ / min and holding for 30min; heating from 300℃ to 950℃ at a heating rate of 3℃ / min and holding for 5h. After sintering, the powder is cooled to room temperature in the furnace. The sintered powder is then removed and repeatedly washed with 80°C deionized water until no chloride ions are detected in the filtrate. It is then washed twice with anhydrous ethanol, vacuum dried at 60°C for 4 hours, and passed through an 180-mesh sieve to remove the release agent and a small amount of agglomerates, thus obtaining a low specific gravity and high thermal conductivity composite powder. Example 2

[0034] A method for preparing a low-density, high-thermal-conductivity composite powder, comprising the following specific steps: Step 1, Surface activation pretreatment: Take 50g of mullite hollow microspheres (softening temperature 1250℃, particle size 20-70μm, wall thickness 2-3μm, closed-cell rate 99%) and add them to 500mL of 0.01% sodium hydroxide solution. First, disperse them by mechanical stirring at 250rpm for 5min, then sonicate them in a 35℃ water bath at 60W power for 15min to gently etch the surface of the microspheres and introduce uniform high-density active hydroxyl groups. Then filter and separate the microspheres, wash them with deionized water until the filtrate is neutral, and vacuum dry them at 90℃ for 10h to obtain surface-activated hollow microspheres.

[0035] Step 2, gel layer coating: The activated hollow microspheres were added to an ethanol-water solution with a volume ratio of anhydrous ethanol to deionized water of 5:1, and stirred and dispersed evenly at 400 rpm to prepare a microsphere suspension with a solid content of 15 wt%. Weigh out the silicon-based precursor tetraethyl orthosilicate, the molybdenum-based precursor molybdenum acetylacetonate, and the scandium-based precursor scandium acetylacetonate in a molar ratio of 22:5:1, and dissolve them in anhydrous ethanol to prepare a precursor mixture. Add the precursor mixture dropwise to the microsphere suspension at a rate of 0.8 mL / min. The total amount of precursor added is 1:5 in mass ratio to the surface-activated hollow microspheres. At the same time, adjust the pH of the system to 4.2 with dilute nitric acid. Stir the reaction at 40°C for 4 hours to allow the precursors to undergo heterogeneous hydrolysis and condensation on the surface of the microspheres, forming a uniform and dense silicon-molybdenum-scandium composite gel layer. After the reaction was completed, the microspheres were separated by filtration, washed four times with anhydrous ethanol, and dried under vacuum at 70°C for 6 hours to obtain coated microspheres with a composite precursor binding layer.

[0036] Step 3, sintering treatment: The above-mentioned coated microspheres and sintering aids were mixed evenly at a mass ratio of 10:1. The sintering aids consisted of a NaCl-KCl composite molten salt (NaCl to KCl molar ratio 1:1) in a mass ratio of 7:2.5:0.5, nano-silicon powder, and nano-alumina. The mixed powder was loaded into an alumina crucible, compacted, sealed, and placed in an argon atmosphere tube furnace. High-purity argon gas was introduced throughout the process at a flow rate of 80 mL / min. The sintering program was as follows: heating from room temperature to 300℃ at a heating rate of 5℃ / min and holding for 30 min; heating from 300℃ to 920℃ at a heating rate of 3℃ / min and holding for 6 h. After sintering, the powder is cooled to room temperature in the furnace. The sintered powder is then removed and repeatedly washed with 80°C deionized water until no chloride ions are detected in the filtrate. It is then washed twice with anhydrous ethanol, vacuum dried at 60°C for 4 hours, and passed through an 180-mesh sieve to remove the release agent and a small amount of agglomerates, thus obtaining a low specific gravity and high thermal conductivity composite powder. Example 3

[0037] A method for preparing a low-density, high-thermal-conductivity composite powder, comprising the following specific steps: Step 1, Surface activation pretreatment: Take 80g of high silica glass hollow microspheres (softening temperature 1150℃, particle size 30-80μm, wall thickness 3-4μm, closed-cell rate 98.5%) and add them to 1000mL of 0.05% sodium hydroxide solution. First, disperse them by mechanical stirring at 250rpm for 5min, then sonicate them in a 35℃ water bath at 60W power for 15min to gently etch the surface of the microspheres and introduce uniform high-density active hydroxyl groups. Then filter and separate the microspheres, wash them with deionized water until the filtrate is neutral, and vacuum dry them at 90℃ for 10h to obtain surface-activated hollow microspheres.

[0038] Step 2, gel layer coating: The activated hollow microspheres were added to an ethanol-water solution with a volume ratio of anhydrous ethanol to deionized water of 5:1, and stirred and dispersed evenly at 400 rpm to prepare a microsphere suspension with a solid content of 15 wt%. Weigh out tetraethyl orthosilicate (a silicon-based precursor), molybdenum acetylacetonate (a molybdenum-based precursor), and scandium acetylacetonate (a scandium-based precursor) in a molar ratio of 18:3:1, and dissolve them in anhydrous ethanol to prepare a precursor mixture. Add the precursor mixture dropwise to the microsphere suspension at a rate of 0.8 mL / min. The total amount of precursor added is 1:5 of the mass ratio of the surface-activated hollow microspheres. Adjust the pH of the system to 4.2 with dilute nitric acid. Stir the mixture at 40°C for 4 hours to allow the precursors to undergo heterogeneous hydrolysis and condensation on the surface of the microspheres, forming a uniform and dense silicon-molybdenum-scandium composite gel layer. After the reaction was completed, the microspheres were separated by filtration, washed four times with anhydrous ethanol, and dried under vacuum at 70°C for 6 hours to obtain coated microspheres with a composite precursor binding layer.

[0039] Step 3, sintering treatment: The above-mentioned coated microspheres and sintering aids were mixed evenly at a mass ratio of 12:1. The sintering aids consisted of a NaCl-KCl composite molten salt (NaCl to KCl molar ratio 1:1) in a mass ratio of 7:2.5:0.5, nano-silicon powder, and nano-alumina. The mixed powder was loaded into an alumina crucible, compacted, sealed, and placed in an argon atmosphere tube furnace. High-purity argon gas was introduced throughout the process at a flow rate of 80 mL / min. The sintering program was as follows: heating from room temperature to 300℃ at a heating rate of 5℃ / min and holding for 30 min; heating from 300℃ to 950℃ at a heating rate of 3℃ / min and holding for 4 h. After sintering, the powder is cooled to room temperature in the furnace. The sintered powder is then removed and repeatedly washed with 80°C deionized water until no chloride ions are detected in the filtrate. It is then washed twice with anhydrous ethanol, vacuum dried at 60°C for 4 hours, and passed through an 180-mesh sieve to remove the release agent and a small amount of agglomerates, thus obtaining a low specific gravity and high thermal conductivity composite powder.

[0040] Comparative Example 1 A method for preparing a composite powder differs from Example 1 only in that: in step 2, the molybdenum acetylacetonate precursor and the scandium acetylacetonate precursor are not added; only tetraethyl orthosilicate is used as the precursor to prepare a pure silica gel coating layer. The reaction process is the same as in Example 1. All other steps and parameters are exactly the same as in Example 1.

[0041] Comparative Example 2 A method for preparing a composite powder differs from Example 1 only in that: in step 2, the scandium source precursor scandium acetylacetone is not added, and only tetraethyl orthosilicate and molybdenum acetylacetone are used as precursors, maintaining the molar ratio of tetraethyl orthosilicate to molybdenum acetylacetone at 4:1. The remaining precursor ratios and reaction processes are the same as in Example 1; the remaining steps and parameters are exactly the same as in Example 1.

[0042] Comparative Example 3 A method for preparing a composite powder differs from Example 1 only in that: in step 2, the molybdenum acetylacetone precursor is not added, and only tetraethyl orthosilicate and scandium acetylacetone are used as precursors, maintaining the molar ratio of tetraethyl orthosilicate to scandium acetylacetone at 4:1. The remaining precursor ratios and reaction processes are the same as in Example 1; the remaining steps and parameters are exactly the same as in Example 1.

[0043] Comparative Example 4 A method for preparing a composite powder differs from Example 1 only in that: in step 2, the molar ratio of the silicon source precursor tetraethyl orthosilicate, the molybdenum source precursor molybdenum acetylacetonate, and the scandium source precursor scandium acetylacetonate is adjusted to 20:7:1, while the other precursor types and reaction process parameters are completely consistent with those of Example 1; the remaining steps and parameters are completely identical to those of Example 1.

[0044] Comparative Example 5 This comparative example provides a method for preparing composite powder, which differs from Example 1 only in that: in step 2, the molar ratio of silicon source precursor tetraethyl orthosilicate, molybdenum source precursor molybdenum acetylacetonate, and scandium source precursor scandium acetylacetonate is adjusted to 20:1:1, while the other precursor types and reaction process parameters are completely consistent with Example 1; the remaining steps and parameters are completely the same as in Example 1.

[0045] Experimental testing The properties of the composite powders prepared in Examples 1-3 and Comparative Examples 1-5 were tested, and the test items included: (1) Closed-cell rate and specific gravity test: The true density and apparent density of the powder were tested using a fully automatic true density meter in accordance with GB / T4472-2011, and the closed-cell rate was calculated; the specific gravity was characterized by apparent density.

[0046] (2) Thermal conductivity test: The thermal conductivity of the powder after pressing was tested according to GB / T22588-2008 using a laser flash thermal conductivity meter. The thermal conductivity was calculated by combining specific heat and density. The test temperature was 25℃.

[0047] (3) Volume resistivity test: A high resistance meter was used to test the volume resistivity of the powder after pressing according to GB / T1410-2006. The test voltage was 1000V and the test temperature was 25℃ to characterize the insulation performance.

[0048] (3) Anti-breakage performance test: Using a universal press, 10g of powder was placed in a mold with a diameter of 20mm, and a pressure of 30MPa was applied and held for 1min. The particle size distribution before and after pressurization was tested using a laser particle size analyzer, and the breakage rate was calculated (breakage rate = increase in the proportion of fine powder after pressurization × 100%).

[0049] The test results are shown in the table below: The test results in the table above show that: The composite powders of Examples 1-3 of this invention all have a closed-pore rate of ≥97.5% and a specific gravity of ≤0.55 g / cm³. 3 It is far superior to ≤0.6g / cm 3 The performance indicators were not significantly different from those of the comparative example, proving that the entire process of pretreatment, coating and sintering of the present invention did not damage the closed-cell structure of the hollow microspheres and stably preserved the lightweight and low specific gravity characteristics of the powder.

[0050] Examples 1-3 of this invention achieve a synergistic effect of 1+1>2 by simultaneously improving thermal conductivity and insulation through the synergistic effect of Mo-Sc dual elements. Furthermore, within the proportions defined in this invention, Mo can be uniformly dispersed in the silicon-oxygen network without agglomeration, while Sc can fully exert its structural and insulating stabilizing effects, maximizing the synergistic effect between the two. Comparative Example 1, coated with pure silica, has a volume resistivity of 5.6×10⁻⁶. 15 While exhibiting excellent insulation properties, the thermal conductivity of the single-Mo doped sample (2.1 W / (m·K)) is only 2.1 W / (m·K), which is insufficient for high-thermal-conductivity applications. Comparative Example 2, with a single Mo doping, shows an increased thermal conductivity of 5.3 W / (m·K), but its volume resistivity decreases to 4.2 × 10⁻⁶. 13 Ω・cm; Comparative Example 3, with single Sc doping, maintained 3.5 × 10 Ω・cm. 15 While exhibiting high insulation properties (Ω·cm), its thermal conductivity is only 3.8 W / (m·K), indicating insufficient improvement in thermal conductivity. In Comparative Example 4, the Mo content was too high and the Sc content was insufficient, resulting in a decrease in thermal conductivity to 6.2 W / (m·K) and a reduction in volume resistivity to 8.5 × 10⁻⁶. 13 Ω・cm; In Comparative Example 5, the proportion of Sc was too high and the proportion of Mo was insufficient, resulting in a thermal conductivity of only 4.5 W / (m・K), which could not meet the core indicator of high thermal conductivity.

[0051] The composite powders in Examples 1-3 all exhibited a breakage rate of ≤3.5% under 30 MPa high pressure, significantly lower than the 5.8%-8.7% of all comparative examples, demonstrating an order-of-magnitude improvement in breakage resistance. This indicates that the present invention introduces high-density active hydroxyl groups on the surface of the microspheres through hydroxylation pretreatment, enabling chemical bonding between the silicon molybdenum scandium gel layer and the microsphere matrix, rather than simple physical coating. This fundamentally solves the problems of easy coating layer detachment and weak bonding. Simultaneously, Mo-Sc synergistic doping optimizes the density and grain structure of the coating layer, significantly improving its mechanical strength and impact resistance. This provides effective mechanical reinforcement for the hollow microsphere shell, significantly reducing the risk of powder breakage during high-pressure processing.

[0052] In summary, the experimental results fully demonstrate that the composite powder prepared in the embodiments of the present invention simultaneously achieves a closed-pore rate of ≥97.5% and a specific gravity of ≤0.55 g / cm³. 3 Thermal conductivity ≥ 8.5 W / (m·K), volume resistivity ≥ 10 15 With a comprehensive performance of ≤3.5% breakage rate under Ω・cm and 30MPa, it has achieved a synergistic improvement in multiple performance aspects and has high value for industrial application.

[0053] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. The illustrative expressions of the above terms in this specification should not be construed as necessarily referring to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. In addition, those skilled in the art can combine and integrate the different embodiments or examples described in this specification.

[0054] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for preparing a low-density, high-thermal-conductivity composite powder, characterized in that, Includes the following steps: Step 1: Add hollow microspheres to sodium hydroxide solution, stir to disperse evenly, and then sonicate. The microspheres were then separated by filtration, washed, and dried to obtain surface-activated hollow microspheres. Step 2: Add surface-activated hollow microspheres to an aqueous ethanol solution and stir to disperse evenly to prepare a microsphere suspension; weigh tetraethyl orthosilicate, molybdenum acetylacetonate, and scandium acetylacetonate, stir to dissolve in anhydrous ethanol to prepare a precursor mixture; add the precursor mixture dropwise to the microsphere suspension at a uniform rate, adjust the pH of the system to 4-4.5, and stir at 30-50℃ for 2-6 hours to form a silicon-molybdenum-scandium composite gel layer; after the reaction is complete, filter, wash, and vacuum dry to obtain coated microspheres with a composite precursor binding layer; Step 3: Mix the coated microspheres and sintering aid evenly, load the mixed powder into an alumina crucible, compact it, seal it, and place it in an argon atmosphere tube furnace for sintering. Then, cool it to room temperature with the furnace, remove the sintered powder, wash, dry, and sieve it to obtain a low specific gravity and high thermal conductivity composite powder.

2. The method for preparing a low-density, high-thermal-conductivity composite powder according to claim 1, characterized in that, In step 1, the hollow microspheres are mullite or high silica glass hollow microspheres with a softening temperature ≥1100℃, a particle size of 10-100μm, a wall thickness of 1-5μm, and a closed-cell rate ≥98%.

3. The method for preparing a low-density, high-thermal-conductivity composite powder according to claim 1, characterized in that, In step 1, the mass fraction of the sodium hydroxide solution is 0.3%-1.0%; in step 1, the ratio of hollow microspheres to sodium hydroxide solution is (5-10) g: 100 mL.

4. The method for preparing a low-density, high-thermal-conductivity composite powder according to claim 1, characterized in that, In step 1, the ultrasonic conditions are: 30-40℃ water bath, 50-80W power ultrasonic treatment for 10-20 minutes.

5. The method for preparing a low-density, high-thermal-conductivity composite powder according to claim 1, characterized in that, In step 2, the volume ratio of anhydrous ethanol to deionized water in the aqueous ethanol solution is 4-6:

1.

6. The method for preparing a low-density, high-thermal-conductivity composite powder according to claim 1, characterized in that, In step 2, the molar ratio of tetraethyl orthosilicate, molybdenum acetylacetonate, and scandium acetylacetonate is 18-22:3-5:

1.

7. The method for preparing a low-density, high-thermal-conductivity composite powder according to claim 1, characterized in that, In step 2, the precursor mixture is added dropwise to the microbead suspension at a rate of 0.5-1.0 mL / min.

8. The method for preparing a low-density, high-thermal-conductivity composite powder according to claim 1, characterized in that, In step 3, the coated microspheres and sintering aids are mixed at a mass ratio of 8-12:1; the sintering aids include NaCl-KCl composite molten salt, nano-silicon powder, and nano-alumina in a mass ratio of 6-8:2-3:0.5-1, wherein the molar ratio of NaCl to KCl in the NaCl-KCl composite molten salt is 1:

1.

9. The method for preparing a low-density, high-thermal-conductivity composite powder according to claim 1, characterized in that, In step 3, the sintering temperature is 920-980℃, the time is 4-6h, and the heating rate is 3-5℃ / min; high-purity argon gas is introduced throughout the process at a flow rate of 50-100mL / min.

10. A low-density, high-thermal-conductivity composite powder, characterized in that, The composite powder was prepared using the preparation method described in claim 1.

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