Nanoscale silicon carbide microspheres, and preparation method and application thereof

Abstract

The application discloses nanometer silicon carbide microspheres, a preparation method and application thereof, and belongs to the technical field of silicon carbide preparation. The application adopts a synergistic assembly strategy of an organic silicon precursor containing an aromatic group and silicate, and after preparing a silica gel through sol-gel, the aromatic group is first directionally cracked at a low temperature to generate a high-activity free carbon species, which is uniformly embedded in a silicon-oxygen network at a nanometer scale, so as to provide a sufficient contact interface for subsequent carbon thermal reduction, and to construct a composite siloxane network with rigid aromatic ring modification; two-stage crystallization treatment is carried out in an inert protective atmosphere, the interface carbon thermal reduction reaction is completed, and after the unreacted free carbon and silicon are removed through a free carbon removal and a silicon dioxide removal step, monodisperse nanometer silicon carbide microspheres with high crystallinity and high purity can be obtained without strict control of the silicon-carbon ratio and complex process equipment, the nanometer silicon carbide microspheres have improved thermal conductivity and mechanical strength, the thermal conductivity of epoxy resin can be effectively improved, and the application of the epoxy resin in the field of high-power-density electronic devices is realized.

Description

Technical Field

[0001] This application relates to the field of silicon carbide preparation technology, and in particular to a silicon carbide nanosphere, its preparation method and application. Background Technology

[0002] Epoxy resins are widely favored in electronics, aerospace, and other fields due to their excellent insulation properties and structural strength. However, epoxy resins themselves have poor thermal conductivity, which can easily lead to heat accumulation in high-power-density electronic devices, thus affecting the lifespan and reliability of the devices. To enhance the thermal conductivity of epoxy resins, fillers with excellent thermal conductivity are usually added.

[0003] Silicon carbide (Silicon carbide) has attracted much attention due to its excellent thermal conductivity, high temperature resistance, and chemical stability, and is widely used to enhance the thermal conductivity of polymer materials. The thermal conductivity of Silicon carbide mainly occurs through the propagation of non-resonant elastic waves of phonons through a continuum. However, ordinary nano-silicon carbide fillers are irregular, exhibiting severe agglomeration and poor dispersibility, making it difficult to fully utilize its excellent thermal conductivity. Therefore, preparing monodisperse nano-silicon carbide microspheres to improve their dispersibility in epoxy resin matrices, thereby effectively enhancing the thermal conductivity of epoxy resins, has significant theoretical and practical value.

[0004] The main methods for preparing silicon carbide nanopowders include sol-gel method, laser-induced gas phase reaction synthesis method, and thermochemical gas phase reaction method. These methods have problems such as complex processes, high costs, and severe product agglomeration, making it difficult to obtain monodisperse silicon carbide nanospheres and failing to meet the needs of practical applications.

[0005] Therefore, there is an urgent need to develop methods for preparing monodisperse silicon carbide nanospheres. Summary of the Invention

[0006] Based on this, the main objective of this application is to provide a method for preparing monodisperse silicon carbide nanospheres, which can produce highly crystalline and high-purity monodisperse silicon carbide nanospheres without the need for complex process equipment. These nanospheres exhibit good dispersibility in epoxy resin, effectively improving the thermal conductivity of epoxy resin and enabling the application of epoxy resin in high-power-density electronic devices.

[0007] The first aspect of this application provides a method for preparing silicon carbide microspheres, comprising the following steps:

[0008] An aromatic silicone precursor, a silicate ester, and a solvent are mixed to form a mixed solution.

[0009] The mixed solution was subjected to acid hydrolysis, alkaline hydrolysis and solidification reaction in sequence, and then dried to prepare precursor powder;

[0010] The precursor powder was heat-treated in a first inert atmosphere to prepare carbon-silicon-oxygen composite powder.

[0011] The carbon-silicon-oxygen composite powder is subjected to pre-crystallization and crystallization treatment under a second inert atmosphere to remove free carbon and silicon dioxide, thereby preparing the nano-silicon carbide microspheres; the heat treatment temperature is 600-900℃; the pre-crystallization temperature is 1000-1150℃; and the crystallization treatment temperature is 1300-1600℃.

[0012] In some embodiments, the organosilicon precursor containing aromatic groups includes at least one of phenylsilane, hydroxytriphenylsilane, phenyltrimethoxysilane, phenyltriethoxysilane, methylphenyldimethoxysilane, and methylphenyldiethoxysilane.

[0013] And / or, the silicate ester includes at least one of methyl orthosilicate, tetraethyl orthosilicate, tetraphenyl orthosilicate, and isopropyl orthosilicate.

[0014] In some embodiments, the molar ratio of the aromatic silicone precursor to the silicate ester is 1:0.1-0.8.

[0015] In some embodiments, the pre-crystallization time, the crystallization treatment time, and the heat treatment time are each independently 1-5 hours.

[0016] In some embodiments, the concentration of silicon in the mixed solution is 0.3-1 mol / L;

[0017] And / or, the solvent includes at least one of methanol, ethanol and isopropanol;

[0018] And / or, the acid hydrolysis includes the following conditions: the amount of acid added is 0.1-1 mol / L;

[0019] And / or, the alkaline hydrolysis includes the following conditions: the amount of alkali added is 1-10 mol / L;

[0020] And / or, the first inert atmosphere is nitrogen and / or argon;

[0021] And / or, the second inert atmosphere is argon;

[0022] And / or, the removal of free carbon includes the following conditions: heat preservation at 600-800℃ for 3-6 hours in an air atmosphere;

[0023] And / or, the removal of silica includes the following conditions: using a 20-40 wt% HF aqueous solution as an etchant, and treating at 30-60°C for 10-120 min.

[0024] In some embodiments, the acid hydrolysis includes the following conditions: stirring at 30-50°C and a rotation speed of 400-800 r / min for 30-180 min;

[0025] And / or, the alkaline hydrolysis includes the following conditions: stirring at 30-50°C and a speed of 400-800 r / min for 20-60 min.

[0026] The second aspect of this application provides silicon carbide microspheres prepared by the preparation method described in the first aspect.

[0027] A third aspect of this application provides the application of the nano-silicon carbide microspheres described in the second aspect in epoxy resin-containing composite materials.

[0028] A fourth aspect of this application provides an epoxy resin composite material comprising an epoxy resin matrix and the silicon carbide microspheres described in the second aspect dispersed in the epoxy resin matrix.

[0029] A fifth aspect of this application provides an electronic device comprising the silicon carbide microspheres described in the second aspect or the epoxy resin composite material described in the fourth aspect.

[0030] The beneficial effects of this application are:

[0031] 1. This application adopts a co-assembly strategy of organosilicon precursors containing aromatic groups and silicates. After preparing silica gel via sol-gel, the aromatic groups are first cleaved at low temperature to generate highly active free carbon species, which are uniformly embedded in the silicon-oxygen network at the nanoscale to provide sufficient contact interface for subsequent carbothermic reduction. A composite siloxane network with rigid aromatic ring modification is constructed. A two-stage crystallization treatment is carried out in an inert protective atmosphere to complete the interfacial carbothermic reduction reaction. After removing unreacted free carbon and silicon through steps of removing free carbon and silicon dioxide, monodisperse nanospheres with high crystallinity and high purity can be obtained.

[0032] 2. The preparation method of this application does not require strict control of the silicon-carbon ratio and complex process equipment to prepare monodisperse silicon carbide nanospheres with high crystallinity and high purity. These nanospheres have improved thermal conductivity and mechanical strength, and exhibit good dispersibility in epoxy resin. They can effectively improve the thermal conductivity of epoxy resin and enable the application of epoxy resin in the field of high power density electronic devices. Attached Figure Description

[0033] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. The drawings are only for illustrating preferred embodiments and are not intended to limit this application. Throughout the drawings, the same reference numerals denote the same parts. In the drawings:

[0034] Figure 1 The image shows a scanning electron microscope (SEM) image of the silicon carbide microspheres from Example 1.

[0035] Figure 2 The image shows the X-ray diffraction pattern of the silicon carbide microspheres from Example 1.

[0036] Figure 3 The image shows a scanning electron microscope (SEM) image of the silicon carbide microspheres in Comparative Example 1.

[0037] Figure 4 The image shows a scanning electron microscope (SEM) image of the silicon carbide microspheres in Comparative Example 2.

[0038] Figure 5 The image shows a scanning electron microscope (SEM) image of the untreated silicon carbide nanospheres in Comparative Example 3.

[0039] Figure 6 The X-ray diffraction pattern of the untreated silicon carbide nanospheres in Comparative Example 3 is shown.

[0040] Figure 7 This is a scanning electron microscope image of the treated silicon carbide microspheres in Comparative Example 3. Detailed Implementation

[0041] To make the objectives, technical solutions, and advantages of this application clearer and to provide a more thorough and comprehensive understanding of the disclosure of this application, the technical solutions of this application will be clearly and completely described below in conjunction with specific embodiments and corresponding drawings. The described embodiments are only some embodiments of this application, and not all embodiments.

[0042] The implementation of this application will be described in detail below with reference to the accompanying drawings. This embodiment is implemented based on the technical solution of this application, and provides detailed implementation methods and specific operation processes, but the protection scope of this application is not limited to the following embodiments.

[0043] Unless otherwise defined, all technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used in this application and in its specification is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.

[0044] the term

[0045] Unless otherwise stated or in case of conflict, the terms or phrases used in this application shall have the following meanings:

[0046] In this application, the terms "multiple" or "various" are used unless otherwise specified, referring to a quantity greater than or equal to 2. For example, "one or more" or "at least one" means one or more of two.

[0047] In this application, terms such as "further" and "especially" are used to describe purposes and indicate differences in content, but should not be construed as limiting the scope of protection of this application.

[0048] In this application, the technical features described in an open-ended manner include both closed technical solutions consisting of the listed features and open technical solutions that include the listed features.

[0049] In this application, when numerical intervals (i.e., numerical ranges) are mentioned, unless otherwise specified, the distribution of selectable numerical values ​​within the numerical interval is considered continuous, and includes the two endpoints of the numerical interval (i.e., the minimum and maximum values), as well as every numerical value between these two endpoints. Unless otherwise specified, when a numerical interval refers only to integers within that numerical interval, it includes the two endpoint integers of the numerical range, as well as every integer between the two endpoints, which is equivalent to directly listing every integer. When multiple numerical ranges are provided to describe features or characteristics, these numerical ranges can be merged. In other words, unless otherwise specified, the numerical ranges disclosed in this application should be understood to include any and all subranges included therein. The "numerical value" in the numerical interval can be any quantitative value, such as a number, percentage, ratio, etc. The term "numerical interval" can be broadly included to include numerical interval types such as percentage intervals, ratio intervals, and proportion intervals.

[0050] In this application, unless otherwise specified, the temperature parameters are permitted to be either constant-temperature treatment or variations within a certain temperature range. It should be understood that the constant-temperature treatment allows temperature fluctuations within the precision range of the instrument control. Fluctuations are permitted within ranges such as ±5℃, ±4℃, ±3℃, ±2℃, and ±1℃.

[0051] The term “and / or” as used in this application includes any and all combinations of one or more of the associated listed items.

[0052] In this application, unless otherwise specified, the temperature parameter can be either constant temperature treatment or treatment within a certain temperature range. The constant temperature treatment allows temperature fluctuations within the precision range controlled by the instrument. The room temperature mentioned in this application refers to 0-40℃, preferably 10℃-35℃, and more preferably 20℃-30℃.

[0053] In this application, if the unit of a data range is only followed by the right endpoint, it means that the units of the left and right endpoints are the same. For example, 500-600rpm means that the units of the left endpoint "500" and the right endpoint "600" are both rpm (revolutions per minute).

[0054] The first aspect of this application provides a method for preparing silicon carbide microspheres, comprising the following steps:

[0055] An aromatic silicone precursor, a silicate ester, and a solvent are mixed to form a mixed solution.

[0056] The mixed solution was subjected to acid hydrolysis, alkaline hydrolysis and solidification reaction in sequence, and then dried to prepare precursor powder;

[0057] The precursor powder was heat-treated in a first inert atmosphere to prepare carbon-silicon-oxygen composite powder.

[0058] The carbon-silicon-oxygen composite powder is subjected to pre-crystallization and crystallization treatment under a second inert atmosphere to remove free carbon and silicon dioxide, thereby preparing the nano-silicon carbide microspheres; the heat treatment temperature is 600-900℃; the pre-crystallization temperature is 1000-1150℃; and the crystallization treatment temperature is 1300-1600℃.

[0059] This application employs a synergistic assembly strategy of an organosilicon precursor containing aromatic groups and silicate esters. After preparing a silica gel via sol-gel, the aromatic groups are first cleaved at low temperature to generate highly active free carbon species, which are then uniformly embedded in a silicon-oxygen network at the nanoscale to provide a sufficient contact interface for subsequent carbothermic reduction. A composite siloxane network with rigid aromatic ring modification is then constructed. A two-stage crystallization process is performed in an inert protective atmosphere to complete the interfacial carbothermic reduction reaction. After removing unreacted free carbon and silicon through steps of removing free carbon and silicon dioxide, monodisperse silicon carbide nanospheres with high crystallinity and high purity can be obtained.

[0060] The pre-crystallization process is the nucleation induction period, where the temperature is raised to 1000-1150℃ to trigger the SiO2 / C interface pre-reaction and form SiC crystal nuclei. The crystallization process is the crystal growth period: the temperature is kept constant in the high-temperature range of 1300-1600℃, and the complete transformation of SiO2+3C→SiC+2CO↑ is achieved through the solid-phase diffusion mechanism, while maintaining the spherical topological structure of the precursor.

[0061] This application utilizes the rigid framework of organosilicon microspheres as a topological template. During pre-crystallization and crystallization, through the synergistic effect of silicon-oxygen bond recombination and carbon atom diffusion, the nano-silicon carbide microspheres inherit the monodisperse spherical characteristics of the precursor, overcoming the morphology control challenge in traditional silicon carbide synthesis. High-crystallinity and high-purity monodisperse nano-silicon carbide microspheres can be prepared without strict control of the silicon-carbon ratio or complex process equipment. These microspheres exhibit good dispersibility in epoxy resins, effectively improving the thermal conductivity of epoxy resins and enabling their application in high-power-density electronic devices.

[0062] In a specific example, the temperature of the heat treatment can be 600℃, 650℃, 700℃, 750℃, 800℃, 850℃, 900℃, etc.

[0063] In a specific example, the pre-crystallization temperature is 1000-1150℃, such as 1000℃, 1050℃, 1100℃, 1150℃, etc.

[0064] In a specific example, the crystallization treatment temperature is 1300-1600℃, such as 1300℃, 1400℃, 1500℃, 1600℃, etc.

[0065] In one specific example, the organosilicon precursor containing aromatic groups includes at least one of phenylsilane, hydroxytriphenylsilane, phenyltrimethoxysilane, phenyltriethoxysilane, methylphenyldimethoxysilane, and methylphenyldiethoxysilane.

[0066] In one specific example, the silicate ester includes at least one of methyl orthosilicate, tetraethyl orthosilicate, tetraphenyl orthosilicate, and isopropyl orthosilicate.

[0067] In a specific example, the molar ratio of the aromatic organosilicon precursor to the silicate ester is 1:0.1-0.8, such as 1:0.1, 1:0.2, 1:0.3, 1:0.4, 1:0.5, 1:0.6, 1:0.7, 1:0.8, etc.

[0068] In a specific example, the pre-crystallization time, the crystallization treatment time, and the heat treatment time are each independently 1-5h, such as 1h, 2h, 3h, 4h, 5h, etc.

[0069] In a specific example, the heating rates of the pre-crystallization, the crystallization treatment, and the heat treatment are each independently 1-12℃ / min, such as 1℃ / min, 2℃ / min, 3℃ / min, 4℃ / min, 5℃ / min, 6℃ / min, 7℃ / min, 8℃ / min, 9℃ / min, 10℃ / min, 11℃ / min, 12℃ / min, etc.

[0070] In one specific example, the heating rate of the heat treatment is 2-8 °C / min.

[0071] In one specific example, the heating rate of the pre-crystallization is 5-12 °C / min.

[0072] In one specific example, the heating rate of the crystallization process is 1-5 °C / min.

[0073] In one specific example, the process of evacuating the precursor powder is included before heat treatment.

[0074] In a specific example, the concentration of silicon in the mixed solution is 0.3-1 mol / L, such as 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1 mol / L, etc.

[0075] In one specific example, the solvent includes at least one of methanol, ethanol, and isopropanol.

[0076] In a specific example, the acid hydrolysis includes the following conditions: the amount of acid added is 0.1-1 mol / L, for example 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, or 1 mol / L.

[0077] In a specific example, the alkaline hydrolysis includes the following conditions: the amount of alkali added is 1-10 mol / L, such as 1 mol / L, 2 mol / L, 3 mol / L, 4 mol / L, 5 mol / L, 6 mol / L, 7 mol / L, 8 mol / L, 9 mol / L, 10 mol / L, etc.

[0078] In a specific example, the first inert atmosphere is nitrogen and / or argon.

[0079] In a specific example, the second inert atmosphere is argon.

[0080] In a specific example, the acid hydrolysis includes the following conditions: stirring at 30-50℃ and a speed of 400-800 r / min for 30-180 min, wherein the acid hydrolysis temperature can be 30℃, 35℃, 40℃, 45℃, 50℃, etc., the stirring speed can be 400 r / min, 500 r / min, 600 r / min, 700 r / min, 800 r / min, etc., and the stirring time can be 30 min, 60 min, 90 min, 120 min, 150 min, 180 min, etc.

[0081] In a specific example, the alkaline hydrolysis includes the following conditions: stirring at 30-50℃ and a speed of 400-800 r / min for 20-60 min, wherein the alkaline hydrolysis temperature can be 30℃, 35℃, 40℃, 45℃, 50℃, etc., the stirring speed can be 400 r / min, 500 r / min, 600 r / min, 700 r / min, 800 r / min, etc., and the stirring time can be 20 min, 30 min, 40 min, 50 min, 60 min.

[0082] In a specific example, the removal of free carbon includes the following conditions: maintaining a temperature of 600-800℃ in air for 3-6 hours. The specific temperatures for removing free carbon can be 600℃, 650℃, 700℃, 750℃, 800℃, etc., and the specific time for removing free carbon can be 3 hours, 4 hours, 5 hours, 6 hours, etc. The purpose of the free carbon removal step is to remove unreacted free carbon and improve the purity of the silicon carbide nanospheres.

[0083] In a specific example, the curing reaction includes the following conditions: standing at 20-40℃ for 12-48 hours, and the reaction time can be 12h, 18h, 24h, 30h, 36h, 42h, 48h, etc.

[0084] In a specific example, the silica removal process includes the following conditions: using a 20-40 wt% HF aqueous solution as an etchant, and treating at 30-60°C for 10-120 min. The HF concentration can specifically be 20 wt%, 25 wt%, 30 wt%, 35 wt%, or 40 wt%, etc.; the treatment temperature can be 30°C, 40°C, 50°C, 600°C, etc.; and the treatment time can be 10 min, 20 min, 40 min, 60 min, 80 min, 100 min, 120 min, etc. The purpose of the silica removal step is to remove residual silica and improve the purity of the silicon carbide nanospheres.

[0085] The second aspect of this application provides silicon carbide microspheres prepared by the preparation method described in the first aspect.

[0086] A third aspect of this application provides the application of the nano-silicon carbide microspheres described in the second aspect in epoxy resin-containing composite materials.

[0087] A fourth aspect of this application provides an epoxy resin composite material comprising an epoxy resin matrix and the silicon carbide microspheres described in the second aspect dispersed in the epoxy resin matrix.

[0088] A fifth aspect of this application provides an electronic device comprising the silicon carbide microspheres described in the second aspect or the epoxy resin composite material described in the fourth aspect.

[0089] Unless otherwise specified, the raw materials used in the following experiments can be purchased from the market.

[0090] The following are specific examples.

[0091] Example 1

[0092] Preparation of silicon carbide nanospheres

[0093] 1) Mix phenylsilane and tetrapropyl orthosilicate in a molar ratio of 1:0.3, and dilute with ethanol to form a mixed solution with a silicon concentration of 0.3 mol / L.

[0094] 2) Add hydrochloric acid at a rate of 0.1 mol / L and stir at 600 r / min for 30 min at 50 °C; then add ammonia water at a rate of 5 mol / L and continue stirring for 30 min; stop stirring and let stand in a water bath at 30 ± 2 °C for 24 h to carry out the curing reaction; wash by centrifugation three times alternately with deionized water and ethanol solvent, and dry to obtain the precursor powder;

[0095] 3) The precursor powder was placed in an alumina crucible and subjected to vacuum treatment three times in a tube furnace; under an argon atmosphere, the temperature was increased to 600℃ at a rate of 5℃ / min and held for 3 hours for heat treatment to prepare carbon-silicon-oxygen composite powder; subsequently, the temperature was increased to 1100℃ at a rate of 5℃ / min and held for 2 hours for pre-crystallization treatment; the temperature was increased to 1300℃ at a rate of 3℃ / min and held for 5 hours for crystallization treatment; under an air atmosphere, the temperature was held at 600℃ for 5 hours to remove unreacted free carbon from the matrix material; the powder was then immersed in a 30wt% HF solution at 30℃ for 120 minutes to etch excess silicon dioxide, thus preparing the silicon carbide nanospheres. Their morphology is as follows: Figure 1 As shown, the microsphere size, as determined by SEM, is approximately 0.65 micrometers, and the phase composition is as follows. Figure 2 As shown, all are β phase with a purity of 99.6%.

[0096] Example 2

[0097] Preparation of silicon carbide nanospheres

[0098] 1) Mix phenyltrimethyloxysilane and tetraethyl orthosilicate in a molar ratio of 1:0.1, and dilute with methanol to form a mixed solution with a silicon concentration of 0.5 mol / L.

[0099] 2) Add nitric acid at a rate of 0.2 mol / L and stir at 600 r / min for 60 min at 50 °C; then add sodium hydroxide at a rate of 10 mol / L and continue stirring for 30 min; stop stirring and let stand in a water bath at 30 ± 2 °C for 24 h to carry out the curing reaction; wash by centrifugation three times alternately with deionized water and ethanol solvent, and dry to obtain the precursor powder.

[0100] 3) The precursor powder was placed in an alumina crucible and subjected to vacuum treatment three times in a tube furnace; under an argon atmosphere, the temperature was increased to 700℃ at a rate of 5℃ / min and held for 3h for heat treatment to prepare carbon-silicon-oxygen composite powder; subsequently, the temperature was increased to 1100℃ at a rate of 10℃ / min and held for 5h for pre-crystallization treatment; the temperature was increased to 1400℃ at a rate of 3℃ / min and held for 4h for crystallization treatment; under an air atmosphere, the temperature was held at 700℃ for 5h to remove unreacted free carbon; the powder was immersed in a 30wt% HF solution at 40℃ for 60min to etch excess silicon dioxide, thus preparing the silicon carbide nanospheres with a size of approximately 0.53 μm and a purity of 99.5%.

[0101] Example 3

[0102] Preparation of silicon carbide nanospheres

[0103] 1) Mix phenyltriethyloxysilane and isopropyl orthosilicate at a molar ratio of 1:0.8, and dilute with isopropanol to form a mixed solution with a silicon concentration of 1 mol / L.

[0104] 2) Add sulfuric acid at a rate of 0.5 mol / L and stir at 600 r / min for 180 min at 50 °C; then add potassium hydroxide at a rate of 1 mol / L and continue stirring for 30 min; stop stirring and let stand in a water bath at 30 ± 2 °C for 24 h to carry out the curing reaction; wash by centrifugation three times alternately with deionized water and ethanol solvent, and dry to obtain the precursor powder.

[0105] 3) The precursor powder was placed in an alumina crucible and subjected to vacuum treatment three times in a tube furnace; under an argon atmosphere, the temperature was increased to 800℃ at a rate of 5℃ / min and held for 3 hours for heat treatment to prepare carbon-silicon-oxygen composite powder; subsequently, the temperature was increased to 1100℃ at a rate of 12℃ / min and held for 3 hours for pre-crystallization treatment; the temperature was increased to 1500℃ at a rate of 3℃ / min and held for 2 hours for crystallization treatment; under an air atmosphere, the temperature was held at 800℃ for 5 hours to remove unreacted free carbon; the powder was immersed in a 30wt% HF solution at 60℃ for 10 minutes to etch excess silicon dioxide, thus preparing the silicon carbide nanospheres with a size of approximately 0.55 micrometers and a purity of 99.8%.

[0106] Example 4

[0107] 1) Mix methylphenyldimethoxysilane and tetraethyl silicate at a molar ratio of 1:0.5, and dilute with methanol to form a mixed solution with a silicon concentration of 0.7 mol / L.

[0108] 2) Add hydrochloric acid at a concentration of 1 mol / L and stir at 600 r / min for 120 min at 50 °C; then add triethylamine at a concentration of 3 mol / L and continue stirring for 30 min; stop stirring and let stand in a water bath at 30 ± 2 °C for 24 h to carry out the curing reaction; wash by centrifugation three times alternately with deionized water and ethanol solvent, and dry to obtain the precursor powder.

[0109] 3) The precursor powder was placed in an alumina crucible and subjected to vacuum treatment three times in a tube furnace; under an argon atmosphere, the temperature was increased to 900℃ at a rate of 5℃ / min and held for 3 hours for heat treatment to prepare carbon-silicon-oxygen composite powder; subsequently, the temperature was increased to 1100℃ at a rate of 7℃ / min and held for 1 hour for pre-crystallization treatment; the temperature was increased to 1600℃ at a rate of 3℃ / min and held for 3 hours for crystallization treatment; under an air atmosphere, the temperature was held at 800℃ for 5 hours to remove unreacted free carbon; the powder was immersed in a 30wt% HF solution at 50℃ for 30 minutes to etch excess silicon dioxide, thus preparing the silicon carbide nanospheres with a size of approximately 0.85 micrometers and a purity of 99.6%.

[0110] Comparative Example 1

[0111] Except for the step of “heating to 600°C at a rate of 5°C / min and holding for 3 hours to prepare carbon-silicon-oxygen composite powder”, the pre-crystallization treatment is performed directly, and the rest is the same as in Example 1.

[0112] The purity of the prepared silicon carbide microspheres was 99.7%. Their morphology was as follows: Figure 3 As shown, the obtained silicon carbide nanospheres are doped with obvious fragments.

[0113] Comparative Example 2

[0114] Except for the step of “subsequently heating to 1100°C at a rate of 7°C / min and holding for 1 hour for pre-crystallization treatment”, the crystallization treatment is carried out directly, and the rest is the same as in Example 4.

[0115] Comparative Example 3

[0116] Silicon carbide microspheres were prepared according to the method described in the journal article (“Synthesis of Monodispersed Spherical Silicon Carbide Powder by Sol-Gel Process”, F. Hatakeyama et al., J. Am. Ceram. Soc. 73(7) 2017-10(1990), referred to as Reference 1). The method involved heating to 1500℃. For details, please refer to Section 2, Experimental Methods. The morphology of the obtained product (i.e., untreated silicon carbide microspheres) is as follows: Figure 5As shown, the purity is basically consistent with the literature description, with a measured purity of 93.1%, which is close to the purity of 92.5% recorded in Literature 1. The main impurities in the silicon carbide preparation process are unreacted free carbon and residual silicon dioxide. Literature 1 records a purity of 92.5%, but no obvious impurities are visible in its X-ray diffraction pattern, which is inconsistent with the literature.

[0117] Therefore, the applicant further performed XRD analysis on the prepared silicon carbide nanospheres, and the results are shown in [Figure number missing]. Figure 6 As can be seen, there is a distinct peak near 2θ=20°, which represents residual amorphous carbon and silicon. Simultaneously, the prepared silicon carbide microspheres were incubated at 700℃ for 4 hours in air to remove free carbon, and then immersed in a 30wt% HF solution at 40℃ for 60 minutes to remove silica. The resulting product (i.e., the treated silicon carbide microspheres) had a purity of 99.6% and a morphology as shown... Figure 7 As shown, a significant number of silicon carbide microspheres are broken. This is likely due to the lack of low-temperature pyrolysis and pre-crystallization processes, leading to the collapse of the silicon-oxygen framework and the instantaneous decomposition of benzene rings at high temperatures (>1300℃), resulting in an imbalance in the carbon-silicon ratio.

[0118] Application Example 1

[0119] Preparation of SiC / epoxy resin composites

[0120] The nano-silicon carbide microspheres from the examples and comparative examples were added to epoxy resin EP-51 and stirred and sonicated at 60°C for 60 min. Then, methyltetrahydrophthalic anhydride (MTHPA) and accelerator (DMP-30) were added, and the mixture was stirred and sonicated for another 60 min. The slurry was then poured into a φ40 mm mold (preheated to 80°C) and cured in a vacuum drying oven at 80°C for 1 h, then at 120°C for 8 h. After cooling, the samples were removed, and the edges were polished to obtain the corresponding SiC / epoxy resin composite material. The mass ratio of silicon carbide, EP-51, MTHPA, and DMP-30 was 1:2:1.65:0.02.

[0121] Application Example 2

[0122] Preparation of silicon carbide ceramics

[0123] The nano-silicon carbide microspheres, Y2O3 and Sc2O3 of the examples and comparative examples were mixed in a mass ratio of 98.89:0.85:0.26, and silicon carbide ceramic samples were prepared according to the method described in the first paragraph of Section 2 of the literature (High thermal conductivity of spark plasma sintered siliconcarbide ceramics with yttria and scandia, Yu-Kwang Seo et al., Journal of the American Ceramic Society, 2017, 100(4):1290-1294).

[0124] Test case

[0125] 1. The surface morphology of the silicon carbide microspheres in the examples and comparative examples was observed using SEM electron microscopy, and the average particle size was calculated. Simultaneously, the phase composition and crystallinity were tested using X-ray diffraction. All microspheres prepared in Examples 1-4 were monodisperse silicon carbide microspheres. The morphology image of Example 1 is shown below. Figure 1 X-ray diffraction pattern can be found in [the image]. Figure 2 The morphological diagrams of Comparative Examples 1-3 are shown below. Figure 3-5 The average particle size of the nano-silicon carbide microspheres in the examples and comparative examples is shown in Table 1.

[0126] 2. Thermal conductivity of the SiC / epoxy resin composite material (hereinafter referred to as composite material) in Application Example 1 was tested: the sample size was φ40±1mm and the thickness was 10±1mm; the testing equipment was Xiangyi Instrument DER-V. The results are shown in Table 1.

[0127] 3. The thermal conductivity (sample size: φ12.7±0.2mm, thickness 10±0.3mm; equipment: Netzsch-LFA 427, Germany) and compressive strength (sample size: φ20±2mm, thickness 20±2mm; equipment: universal testing machine, SANS-UTM5305H, China) of the silicon carbide ceramics in Application Example 2 were tested. The results are shown in Table 1.

[0128] Table 1 Performance Summary

[0129]

[0130] As can be seen from Table 1, monodisperse silicon carbide nanospheres with high crystallinity and high purity were prepared in Examples 1-4 of this application. The silicon carbide ceramics prepared therefrom have excellent thermal conductivity and compressive strength, and the SiC / epoxy resin composite material prepared therefrom has good thermal conductivity.

[0131] Based on the SEM results, comparing Example 1 and Comparative Example 1, it can be seen that before pre-crystallization, heat treatment is performed first, and the low-temperature directional cracking of phenyl groups generates highly active free carbon species, which is beneficial to improving the integrity and thermal conductivity of the nano-silicon carbide microspheres, and further improving the thermal conductivity and compressive strength of the SiC / epoxy resin composite material and the silicon carbide ceramic.

[0132] Comparing Example 4 and Comparative Example 2, it can be seen that performing pre-crystallization treatment after heat treatment and before crystallization treatment is beneficial for refining grains and improving density, thereby improving the thermal conductivity of silicon carbide nanospheres and the related properties of SiC / epoxy resin composites and silicon carbide ceramics.

[0133] Comparing Examples 1-4 with Comparative Example 3, it can be seen that the silicon carbide microspheres of Examples 1-4 are complete spheres with monodispersity, high purity, and high crystallinity. Comparative Example 3, however, fails to balance purity and integrity. Before removing free carbon and silica, it is a complete sphere, but with low purity, leading to significantly degraded thermal conductivity. Simultaneously, due to the collapse of the silicon-oxygen framework, its mechanical strength is significantly degraded. After removing free carbon and silica, it cannot maintain a complete spherical shape, again resulting in significantly degraded thermal conductivity and mechanical strength. Therefore, compared to Comparative Example 3, this application, without requiring strict control of the silicon-carbon ratio, prepares silicon carbide microspheres with a more ideal silicon-oxygen framework, ideal morphology, and purity, exhibiting improved mechanical strength and thermal conductivity.

[0134] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0135] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A method for preparing nano-silicon carbide microspheres, characterized in that, Includes the following steps: An aromatic silicone precursor, a silicate ester, and a solvent are mixed to form a mixed solution. The mixed solution was subjected to acid hydrolysis, alkaline hydrolysis and solidification reaction in sequence, and then dried to prepare precursor powder; The precursor powder was heat-treated in a first inert atmosphere to prepare carbon-silicon-oxygen composite powder. The carbon-silicon-oxygen composite powder is pre-crystallized and crystallized under a second inert atmosphere to remove free carbon and silicon dioxide, thereby preparing the nano-silicon carbide microspheres; the heat treatment temperature is 600-900℃; the pre-crystallization temperature is 1000-1150℃; and the crystallization temperature is 1300-1600℃. The organosilicon precursor containing aromatic groups includes at least one of phenylsilane, hydroxytriphenylsilane, phenyltrimethoxysilane, phenyltriethoxysilane, methylphenyldimethoxysilane, and methylphenyldiethoxysilane.

2. The preparation method according to claim 1, characterized in that, The silicate ester includes at least one of methyl orthosilicate, tetraethyl orthosilicate, tetraphenyl orthosilicate, and isopropyl orthosilicate.

3. The preparation method according to claim 1 or 2, characterized in that, The molar ratio of the aromatic organosilicon precursor to the silicate ester is 1:0.1-0.

8.

4. The preparation method according to claim 1 or 2, characterized in that, The pre-crystallization time, crystallization time, and heat treatment time are each 1-5 hours independently.

5. The preparation method according to claim 1 or 2, characterized in that, The concentration of silicon in the mixed solution is 0.3-1 mol / L; And / or, the solvent includes at least one of methanol, ethanol and isopropanol; And / or, the acid hydrolysis includes the following conditions: the amount of acid added is 0.1-1 mol / L; And / or, the alkaline hydrolysis includes the following conditions: the amount of alkali added is 1-10 mol / L; And / or, the first inert atmosphere is nitrogen and / or argon; And / or, the second inert atmosphere is argon; And / or, the removal of free carbon includes the following conditions: heat preservation at 600-800℃ for 3-6 hours in an air atmosphere; And / or, the removal of silica includes the following conditions: using a 20-40 wt% HF aqueous solution as an etchant, and treating at 30-60°C for 10-120 min.

6. The preparation method according to claim 5, characterized in that, The acid hydrolysis includes the following conditions: stirring at 30-50℃ and a speed of 400-800 r / min for 30-180 min; And / or, the alkaline hydrolysis includes the following conditions: stirring at 30-50°C and a speed of 400-800 r / min for 20-60 min.

7. The silicon carbide microspheres prepared by the preparation method according to any one of claims 1-6.

8. The application of the nano-silicon carbide microspheres as described in claim 7 in epoxy resin-containing composite materials.

9. An epoxy resin composite material, characterized in that, It includes an epoxy resin matrix and the silicon carbide microspheres of claim 7 dispersed in the epoxy resin matrix.

10. An electronic device, characterized in that, It contains the nano-silicon carbide microspheres of claim 7 or the epoxy resin composite material of claim 9.

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