Nano silicon carbide microspheres as well as preparation method and application thereof

Abstract

The invention discloses nano silicon carbide microspheres as well as a preparation method and application thereof, and belongs to the technical field of silicon carbide preparation. According to the preparation method, an aromatic group-containing organic silicon precursor and silicate ester synergistic assembly strategy is adopted, after silica gel is prepared through sol-gel, aromatic groups are directionally cracked at low temperature to generate high-activity free carbon species, the high-activity free carbon species are uniformly embedded into a silicon-oxygen network in a nanoscale, a sufficient contact interface is provided for subsequent carbon thermal reduction, and the high-activity free carbon species are obtained; and constructing a composite siloxane network modified by a rigid aromatic ring, carrying out two-stage crystallization treatment in an inert protective atmosphere to complete an interface carbon thermal reduction reaction, and removing unreacted free carbon and silicon through the steps of free carbon removal and silicon dioxide removal to obtain the composite siloxane. Monodisperse nano silicon carbide microspheres with high crystallinity and high purity can be obtained without strictly controlling the silicon-carbon ratio and complex process equipment, and the nano silicon carbide microspheres have improved heat-conducting property and mechanical strength, can effectively enhance the heat-conducting property of epoxy resin, and realize the application of epoxy resin in the field of high-power-density electronic devices.

Description

Technical Field

[0001] The present application relates to the technical field of silicon carbide preparation, and in particular to a nano silicon carbide microsphere and a preparation method and application thereof. Background Art

[0002] Epoxy resin is widely favored in the fields of electronics, electrical engineering, aerospace, etc. due to its excellent insulation performance and structural strength. However, epoxy resin itself has poor thermal conductivity, which can easily cause heat accumulation in high-power density electronic devices, thus affecting the service life and reliability of the devices. In order to enhance the thermal conductivity of epoxy resin, fillers with excellent thermal conductivity are usually added.

[0003] 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 is mainly transmitted through the non-resonant elastic wave of phonons through the continuum. Ordinary nano-silicon carbide fillers are irregular, with serious agglomeration and poor dispersion problems, making it difficult to give full play to its excellent thermal conductivity. Therefore, it is of great theoretical significance and application value to prepare monodispersed nano-silicon carbide microspheres and improve their dispersion in the epoxy resin matrix, thereby effectively enhancing the thermal conductivity of epoxy resin.

[0004] The preparation methods of silicon carbide nanopowders mainly include sol-gel method, laser-induced gas phase reaction synthesis method, thermochemical gas phase reaction method, etc., which have problems such as complex process, high cost, and serious product agglomeration. It is difficult to obtain monodisperse nano-silicon carbide microspheres and cannot meet the needs of actual applications.

[0005] Therefore, there is an urgent need to develop a method for preparing monodispersed nano-SiC microspheres. Summary of the invention

[0006] Based on this, the main purpose of this application is to provide a method for preparing monodisperse nano-silicon carbide microspheres, which can prepare monodisperse nano-silicon carbide microspheres with high crystallinity and high purity without complex process equipment. The nano-silicon carbide microspheres have good dispersibility in epoxy resin, can effectively improve the thermal conductivity of epoxy resin, and realize the application of epoxy resin in the field of high power density electronic devices.

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

[0008] Mixing an aromatic group-containing organosilicon precursor, a silicate and a solvent to form a mixed solution;

[0009] The mixed solution is subjected to acid hydrolysis, alkaline hydrolysis and curing reaction in sequence, and dried to prepare a precursor powder;

[0010] heat-treating the precursor powder in a first inert atmosphere to prepare a carbon-silicon-oxygen composite powder;

[0011] The carbon-silicon-oxygen composite powder is pre-crystallized and crystallized in a second inert atmosphere to remove free carbon and silicon dioxide to prepare the nano-silicon carbide microspheres; the temperature of the heat treatment is 600-900°C; the temperature of the pre-crystallization is 1000-1150°C; the temperature of the crystallization treatment is 1300-1600°C.

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

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

[0014] In some embodiments, the molar ratio of the aromatic group-containing organosilicon precursor to the silicate 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 comprises at least one of methanol, ethanol and isopropanol;

[0018] And / or, the acid hydrolysis comprises 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 base added is 1-10 mol / L;

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

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

[0022] And / or, the free carbon removal comprises the following conditions: keeping at 600-800°C for 3-6h in air atmosphere;

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

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

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

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

[0027] The third aspect of the present application provides the use of the nano-silicon carbide microspheres described in the second aspect in a composite material containing epoxy resin.

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

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

[0030] Beneficial effects of this application:

[0031] 1. The present application adopts a strategy of collaborative assembly of organosilicon precursors containing aromatic groups and silicates. After preparing silica gel by sol-gel, the aromatic groups are firstly directionally cracked 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 carbon thermal reduction, and a composite siloxane network modified with rigid aromatic rings is constructed. A two-stage crystallization treatment is carried out in an inert protective atmosphere to complete the interfacial carbon thermal reduction reaction. After removing the unreacted free carbon and silicon through the steps of removing free carbon and removing silicon dioxide, monodispersed nano-silicon carbide microspheres with high crystallinity and high purity can be obtained.

[0032] 2. The preparation method of the present application does not require strict control of the silicon-carbon ratio and complex process equipment to prepare monodisperse nano-silicon carbide microspheres with high crystallinity and high purity. The microspheres have improved thermal conductivity and mechanical strength, and have good dispersibility in epoxy resin. They can effectively improve the thermal conductivity of epoxy resin and realize the application of epoxy resin in the field of high power density electronic devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following briefly introduces the drawings required for use in the embodiments or the prior art description. The drawings are only used to illustrate the preferred implementation methods and are not considered to be limitations of the present application. The same reference symbols are used throughout the drawings to represent the same components. In the drawings:

[0034] Figure 1 is a scanning electron microscope image of the nano-silicon carbide microspheres of Example 1;

[0035] Figure 2 is the X-ray diffraction pattern of the nano silicon carbide microspheres of Example 1;

[0036] Figure 3 This is a scanning electron microscope image of the nano-silicon carbide microspheres of Comparative Example 1;

[0037] Figure 4 This is a scanning electron microscope image of the nano-silicon carbide microspheres of Comparative Example 2;

[0038] Figure 5 This is a scanning electron microscope image of the untreated nano-silicon carbide microspheres of Comparative Example 3;

[0039] Figure 6 The X-ray diffraction pattern of the untreated nano silicon carbide microspheres of Comparative Example 3;

[0040] Figure 7 This is a scanning electron microscope image of the treated nano-silicon carbide microspheres of Comparative Example 3. DETAILED DESCRIPTION

[0041] In order to make the purpose, technical solution and advantages of this application clearer and to provide a more thorough and comprehensive understanding of the disclosed content of this application, the technical solution of this application will be clearly and completely described below in conjunction with the specific embodiments of this application and the corresponding drawings. The described embodiments are only part of the embodiments of this application, not all of them.

[0042] The implementation of the present application is described in detail below in conjunction with the accompanying drawings. This embodiment is implemented based on the technical solution of the present application, and a detailed implementation method and specific operation process are given, but the protection scope of the present 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 those commonly understood by those skilled in the art to which this application belongs. The terms used in this application and in the specification of this application are only for the purpose of describing specific embodiments and are not intended to limit this application.

[0044] the term

[0045] Unless otherwise specified or there is a contradiction, the terms and phrases used in this application have the following meanings:

[0046] In the present application, "plurality", "multiple" and the like, unless otherwise specified, refer to a number greater than or equal to 2. For example, "one or more" or "at least one" means one or greater than or equal to two.

[0047] In the present application, the terms "further", "particularly" and the like are used for descriptive purposes to indicate differences in content, but should not be construed as limiting the scope of protection of the present application.

[0048] In the present application, the technical features described in an open manner include closed technical solutions composed of the listed features, and also include open technical solutions containing the listed features.

[0049] In the present application, when it comes to a numerical interval (i.e., a numerical range), unless otherwise specified, the distribution of the optional numerical values ​​in the numerical interval is considered to be continuous, and includes the two numerical endpoints (i.e., the minimum value and the maximum value) of the numerical interval, and each numerical value between the two numerical endpoints. Unless otherwise specified, when the numerical interval only refers to the integers in the numerical interval, it includes the two endpoint integers of the numerical range, and each integer between the two endpoints, which is equivalent to directly listing each 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 range disclosed in the present application should be understood to include any and all sub-ranges included therein. The "numerical value" in the numerical interval can be any quantitative value, such as a number, a percentage, a ratio, etc. "Numerical interval" allows broadly including numerical interval types such as percentage intervals, ratio intervals, and ratio intervals.

[0050] In this application, unless otherwise specified, the temperature parameter is allowed to be either a constant temperature treatment or to vary within a certain temperature range. It should be understood that the constant temperature treatment allows the temperature to fluctuate within the accuracy range controlled by the instrument. Fluctuations within the range of ±5°C, ±4°C, ±3°C, ±2°C and ±1°C are allowed.

[0051] As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items.

[0052] In this application, temperature parameters, unless otherwise specified, allow both constant temperature treatment and treatment within a certain temperature range. The constant temperature treatment allows the temperature to fluctuate within the accuracy range of instrument control. The room temperature described in this application refers to 0-40°C, preferably 10°C-35°C, and more preferably 20°C-30°C.

[0053] In this application, when referring to the unit of a data range, if there is a unit only after the right endpoint, it means that the units of the left endpoint and the right endpoint 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 the present application provides a method for preparing nano silicon carbide microspheres, comprising the following steps:

[0055] Mixing an aromatic group-containing organosilicon precursor, a silicate and a solvent to form a mixed solution;

[0056] The mixed solution is subjected to acid hydrolysis, alkaline hydrolysis and curing reaction in sequence, and dried to prepare a precursor powder;

[0057] heat-treating the precursor powder in a first inert atmosphere to prepare a carbon-silicon-oxygen composite powder;

[0058] The carbon-silicon-oxygen composite powder is pre-crystallized and crystallized in a second inert atmosphere to remove free carbon and silicon dioxide to prepare the nano-silicon carbide microspheres; the temperature of the heat treatment is 600-900°C; the temperature of the pre-crystallization is 1000-1150°C; the temperature of the crystallization treatment is 1300-1600°C.

[0059] The present application adopts a strategy of collaborative assembly of organosilicon precursors containing aromatic groups and silicates. After preparing silica gel by sol-gel, the aromatic groups are firstly directionally cracked at low temperature to generate highly active free carbon species, which are uniformly embedded in the silicon-oxygen network at the nanometer scale to provide sufficient contact interface for subsequent carbon thermal reduction, and a composite siloxane network modified with rigid aromatic rings is constructed. A two-stage crystallization treatment is carried out in an inert protective atmosphere to complete the interfacial carbon thermal reduction reaction. After removing the unreacted free carbon and silicon through the steps of removing free carbon and removing silicon dioxide, monodispersed nano-silicon carbide microspheres with high crystallinity and high purity can be obtained.

[0060] The pre-crystallization process is the nucleation induction period, and the temperature is raised to 1000-1150℃ to trigger the SiO 2 / C interface pre-reaction to form SiC nuclei; the crystallization process is the crystal growth period: the temperature is kept constant at 1300-1600℃, and the SiO 2 +3C→SiC+2CO↑, while maintaining the spherical topology of the precursor.

[0061] This application uses the rigid skeleton of organic silicon microspheres as a topological template. During the pre-crystallization and crystallization treatment, through the synergistic effect of silicon-oxygen bond reorganization and carbon atom diffusion, the nano-silicon carbide microspheres inherit the monodisperse spherical characteristics of the precursor, breaking through the morphology control problem in traditional silicon carbide synthesis. Without strictly controlling the silicon-carbon ratio and without complex process equipment, monodisperse nano-silicon carbide microspheres with high crystallinity and high purity can be prepared. They have good dispersibility in epoxy resin, can effectively improve the thermal conductivity of epoxy resin, and realize the application of epoxy resin in the field of high power density electronic devices.

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

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

[0064] In a specific example, the temperature of the crystallization process is 1300-1600° C., such as 1300° C., 1400° C., 1500° C., 1600° C., etc.

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

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

[0067] In a specific example, the molar ratio of the aromatic group-containing organosilicon precursor to the silicate is 1:0.1-0.8, for example, 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 time for pre-crystallization, the time for crystallization treatment and the time for heat treatment are each independently 1-5 hours, for example, 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 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°C / min, for example, 1°C / min, 2°C / min, 3°C / min, 4°C / min, 5°C / min, 6°C / min, 7°C / min, 8°C / min, 9°C / min, 10°C / min, 11°C / min, 12°C / min, etc.

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

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

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

[0073] In a specific example, before the heat treatment, a step of evacuating the precursor powder is also included.

[0074] In a specific example, the concentration of silicon element in the mixed solution is 0.3-1 mol / L, for example, 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 a 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, 1 mol / L.

[0077] In a specific example, the alkaline hydrolysis includes the following conditions: the amount of base added is 1-10 mol / L, for example, 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 uses nitrogen and / or argon.

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

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

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

[0082] In a specific example, the free carbon removal includes the following conditions: keeping warm at 600-800°C for 3-6h in an air atmosphere, the free carbon removal temperature can be 600°C, 650°C, 700°C, 750°C, 800°C, etc., and the free carbon removal time can be 3h, 4h, 5h, 6h, etc. The role of the free carbon removal step is to remove unreacted free carbon and improve the purity of nano-silicon carbide microspheres.

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

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

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

[0086] The third aspect of the present application provides the use of the nano-silicon carbide microspheres described in the second aspect in a composite material containing epoxy resin.

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

[0088] The fifth aspect of the present application provides an electronic device comprising the nano 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 embodiments.

[0091] Example 1

[0092] Preparation of Nano-SiC Microspheres

[0093] 1) Phenylsilane and tetrapropyl orthosilicate were mixed in a molar ratio of 1:0.3, and ethanol was added to dilute the mixture to form a mixed solution, so that the concentration of silicon in the mixed solution was 0.3 mol / L.

[0094] 2) Add hydrochloric acid at an amount of 0.1 mol / L, and stir at 600 r / min for 30 min at 50°C; then, add ammonia water at an amount of 5 mol / L, and continue stirring for 30 min; stop stirring, and stand in a 30±2°C water bath for 24 h to perform a curing reaction; alternately use deionized water and ethanol solvents for centrifugal washing 3 times, and dry to obtain a precursor powder;

[0095] 3) Place the precursor powder in an alumina crucible and evacuate it in a tube furnace for 3 times; in an argon atmosphere, heat it to 600°C at a rate of 5°C / min and keep it for 3 hours to prepare a carbon-silicon-oxygen composite powder; then, heat it to 1100°C at a rate of 5°C / min and keep it for 2 hours to perform a pre-crystallization treatment; heat it to 1300°C at a rate of 3°C / min and keep it for 5 hours to perform a crystallization treatment; in an air atmosphere, keep it at 600°C for 5 hours to remove the unreacted free carbon in the above-mentioned matrix material; soak it in a 30wt% HF solution at 30°C for 120 minutes to etch the excess silicon dioxide to prepare the nano-silicon carbide microspheres. Its morphology is as follows Figure 1 As shown, the size of the microspheres counted by SEM is about 0.65 microns, and the phase composition is as follows Figure 2 As shown, they are all β phase with a purity of 99.6%.

[0096] Example 2

[0097] Preparation of Nano-SiC Microspheres

[0098] 1) Phenyltrimethyloxysilane and ethyl orthosilicate were mixed in a molar ratio of 1:0.1, and methanol was added to dilute the mixture to form a mixed solution, so that the concentration of silicon element in the mixed solution was 0.5 mol / L.

[0099] 2) Add nitric acid at a rate of 0.2 mol / L, and stir at 600 r / min at 50°C for 60 min; then, add sodium hydroxide at a rate of 10 mol / L, and continue stirring for 30 min; stop stirring, and place in a 30±2°C water bath for 24 h to allow the curing reaction to proceed; alternately wash the mixture by centrifugation for 3 times using deionized water and ethanol solvent, and dry the mixture to obtain a precursor powder.

[0100] 3) The precursor powder is placed in an alumina crucible and vacuumed in a tube furnace for 3 times; in an argon atmosphere, the temperature is increased to 700°C at a rate of 5°C / min and kept for 3 hours for heat treatment to prepare a carbon-silicon-oxygen composite powder; then, the temperature is increased to 1100°C at a rate of 10°C / min and kept for 5 hours for pre-crystallization treatment; the temperature is increased to 1400°C at a rate of 3°C / min and kept for 4 hours for crystallization treatment; in an air atmosphere, the temperature is kept at 700°C for 5 hours to remove unreacted free carbon; the nano-silicon carbide microspheres are prepared by immersing in a 30wt% concentration HF solution at 40°C for 60 minutes to etch excess silicon dioxide, and the nano-silicon carbide microspheres have a size of about 0.53 microns and a purity of 99.5%.

[0101] Example 3

[0102] Preparation of Nano-SiC Microspheres

[0103] 1) Phenyltriethyloxysilane and isopropyl orthosilicate were mixed at a molar ratio of 1:0.8, and isopropyl alcohol was added to dilute the mixture to form a mixed solution, so that the concentration of silicon element in the mixed solution was 1 mol / L.

[0104] 2) Add sulfuric acid at a rate of 0.5 mol / L, and stir at 600 r / min at 50°C for 180 min; then, add potassium hydroxide at a rate of 1 mol / L, and continue stirring for 30 min; stop stirring, and place in a 30±2°C water bath for 24 h to allow the curing reaction to proceed; alternately wash the mixture by centrifugation for 3 times using deionized water and ethanol solvents, and dry the mixture to obtain a precursor powder.

[0105] 3) The precursor powder is placed in an alumina crucible and vacuumed in a tube furnace for 3 times; in an argon atmosphere, the temperature is increased to 800°C at a rate of 5°C / min and kept for 3 hours for heat treatment to prepare a carbon-silicon-oxygen composite powder; then, the temperature is increased to 1100°C at a rate of 12°C / min and kept for 3 hours for pre-crystallization treatment; the temperature is increased to 1500°C at a rate of 3°C / min and kept for 2 hours for crystallization treatment; in an air atmosphere, the temperature is kept at 800°C for 5 hours to remove unreacted free carbon; the nano-silicon carbide microspheres are prepared by immersing in a 30wt% concentration HF solution at 60°C for 10 minutes to etch excess silicon dioxide, and the nano-silicon carbide microspheres have a size of about 0.55 microns and a purity of 99.8%.

[0106] Example 4

[0107] 1) Methylphenyldimethoxysilane and tetraethyl silicate were mixed at a molar ratio of 1:0.5, and methanol was added to dilute the mixture to form a mixed solution, so that the concentration of silicon element in the mixed solution was 0.7 mol / L.

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

[0109] 3) The precursor powder is placed in an alumina crucible and vacuumed in a tube furnace for 3 times; in an argon atmosphere, the temperature is increased to 900°C at a rate of 5°C / min and kept for 3 hours for heat treatment to prepare a carbon-silicon-oxygen composite powder; then, the temperature is increased to 1100°C at a rate of 7°C / min and kept for 1 hour for pre-crystallization treatment; the temperature is increased to 1600°C at a rate of 3°C / min and kept for 3 hours for crystallization treatment; in an air atmosphere, the temperature is kept at 800°C for 5 hours to remove unreacted free carbon; the nano-silicon carbide microspheres are prepared by immersing in a 30wt% concentration HF solution at 50°C for 30 minutes, etching excess silicon dioxide, and obtaining the nano-silicon carbide microspheres having a size of about 0.85 microns and a purity of 99.6%.

[0110] Comparative Example 1

[0111] The same procedures as in Example 1 are the same as those in Example 1 except that the step of “heating to 600° C. at a rate of 5° C. / min and keeping the temperature for 3 hours to prepare carbon-silicon-oxygen composite powder” is not included and the pre-crystallization treatment is directly performed.

[0112] The purity of the prepared nano-silicon carbide microspheres is 99.7%. Figure 3 As shown, the obtained nano-SiC microspheres are doped with obvious fragments.

[0113] Comparative Example 2

[0114] The same procedures as in Example 4 are as follows, except that the step of “subsequently, heating to 1100° C. at a rate of 7° C. / min and maintaining the temperature for 1 hour for pre-crystallization treatment” is not included, and the crystallization treatment is directly performed.

[0115] Comparative Example 3

[0116] Nano-SiC microspheres were prepared according to the method described in the journal ("Synthesis of Monodispersed Spherical Silicon Carbide Powder by Sol-Gel Process", F Hatakeyama et al., J.Am.Ceram.Soc.73 (7) 2017-10 (1990), denoted as Reference 1), and the heating temperature was 1500°C. The specific method is shown in the experimental method section in Section 2. The morphology of the obtained product (i.e., untreated nano-SiC microspheres) is as follows: Figure 5As shown, it is basically consistent with the description in the literature. The measured purity is 93.1%, which is close to the purity of 92.5% recorded in Literature 1. The main impurities in the preparation process of silicon carbide are unreacted free carbon and residual silicon dioxide. The purity is recorded as 92.5% in Literature 1, but no obvious impurities can be seen in its X-ray diffraction pattern, and the two are inconsistent.

[0117] Therefore, the applicant further conducted XRD analysis on the prepared nano-silicon carbide microspheres, and the results are shown in Figure 6 , it can be seen that there is an obvious mantou peak near 2θ=20°, which is the residual amorphous carbon and silicon. At the same time, the prepared nano-SiC microspheres were kept at 700℃ for 4h in air atmosphere to remove free carbon, and immersed in 30wt% HF solution at 40℃ for 60min to remove silicon dioxide. The purity of the obtained product (i.e. the treated nano-SiC microspheres) was 99.6%, and the morphology was as follows: Figure 7 As shown in the figure, it can be seen that the silicon carbide microspheres are more broken. This may be due to the lack of low-temperature cracking and pre-crystallization treatment, which leads to the collapse of the silicon-oxygen skeleton and the instantaneous decomposition of the benzene ring in the high temperature section (>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 of the embodiment and the comparative example were added to the epoxy resin EP-51, and ultrasonically stirred for 60 minutes at 60°C; then the curing agent methyltetrahydrophthalic anhydride MTHPA and the accelerator DMP-30 were added, and ultrasonic stirring was continued for 60 minutes; then the slurry was poured into a φ40mm mold (preheated at 80°C), and cured at 80°C for 1 hour and 120°C for 8 hours in a vacuum drying oven; after cooling, the sample was taken out and the edge burrs were polished to prepare the corresponding SiC / epoxy resin composite material. Among them, the mass ratio of silicon carbide, EP-51, MTHPA and DMP-30 is 1:2:1.65:0.02.

[0121] Application Example 2

[0122] Silicon carbide ceramic preparation

[0123] The nano silicon carbide microspheres and Y 2 O 3 and Sc 2 O 3The mixture was mixed in a mass ratio of 98.89:0.85:0.26, and a silicon carbide ceramic sample was 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 nano-silicon carbide microspheres of the examples and comparative examples was observed by SEM electron microscope, and the average particle size was calculated; at the same time, the phase composition and crystallinity were tested by X-ray diffractometer. The nano-silicon carbide microspheres prepared in Examples 1-4 were all monodisperse, and the morphology of Example 1 was shown in FIG. Figure 1 , X-ray diffraction pattern see Figure 2 ; The morphology of comparative examples 1-3 is shown in Figure 3-5 The average particle size of the nano-silicon carbide microspheres of the embodiments and comparative examples is shown in Table 1.

[0126] 2. Test the thermal conductivity of the SiC / epoxy resin composite material (referred to as the composite material) of Application Example 1: the sample size is φ40±1mm, the thickness is 10±1mm; the test equipment is 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 silicon carbide ceramics of 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, Examples 1-4 of the present application prepared monodisperse nano-silicon carbide microspheres with high crystallinity and high purity, and the prepared silicon carbide ceramics have excellent thermal conductivity and compressive strength, and the prepared SiC / epoxy resin composite material has good thermal conductivity.

[0131] By comparing Example 1 and Comparative Example 1 in combination with the SEM results, it can be seen that before the pre-crystallization treatment, a heat treatment is first performed to directional crack the phenyl groups at low temperature to generate 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 of the SiC / epoxy resin composite material and the thermal conductivity and compressive strength of the silicon carbide ceramics.

[0132] By comparing Example 4 and Comparative Example 2, it can be seen that pre-crystallization treatment is performed after heat treatment and before crystallization treatment, which is beneficial to grain refinement and increased density, thereby improving the thermal conductivity of nano-silicon carbide microspheres and improving the related properties of SiC / epoxy resin composites and silicon carbide ceramics.

[0133] Comparing Examples 1-4 and Comparative Example 3, it can be seen that the nano-silicon carbide microspheres of Examples 1-4 are complete spheres with monodispersity, high purity and high crystallinity. However, Comparative Example 3 cannot take into account both purity and integrity. Before removing free carbon and silicon dioxide, it is a complete sphere, but the purity is low, resulting in significantly degraded thermal conductivity. At the same time, due to the collapse of the silicon-oxygen skeleton, the mechanical strength is significantly degraded; and after removing free carbon and silicon dioxide, it is impossible to maintain a complete sphere, which also leads to significantly degraded thermal conductivity and mechanical strength. It can be seen that compared with Comparative Example 3, the present application has prepared nano-silicon carbide microspheres with a more ideal silicon-oxygen skeleton, an ideal morphology and purity, and improved mechanical strength and thermal conductivity without strictly controlling the silicon-carbon ratio.

[0134] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described 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 above-mentioned embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent of the present application shall be subject to the attached claims.

Claims

1. A method for preparing nano silicon carbide microspheres, characterized in that: The steps include: Mixing an aromatic group-containing organosilicon precursor, a silicate and a solvent to form a mixed solution; The mixed solution is subjected to acid hydrolysis, alkaline hydrolysis and curing reaction in sequence, and dried to prepare a precursor powder; heat-treating the precursor powder in a first inert atmosphere to prepare a carbon-silicon-oxygen composite powder; The carbon-silicon-oxygen composite powder is pre-crystallized and crystallized in a second inert atmosphere to remove free carbon and silicon dioxide to prepare the nano-silicon carbide microspheres; the temperature of the heat treatment is 600-900°C; the temperature of the pre-crystallization is 1000-1150°C; the temperature of the crystallization treatment is 1300-1600°C.

2. The preparation method according to claim 1, characterized in that The aromatic group-containing organosilicon precursor comprises at least one of phenylsilane, hydroxytriphenylsilane, phenyltrimethoxysilane, phenyltriethoxysilane, methylphenyldimethoxysilane and methylphenyldiethoxysilane; And / or, the silicate includes at least one of methyl orthosilicate, tetraethyl silicate, tetraphenyl silicate, tetrapropyl orthosilicate and isopropyl orthosilicate.

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

8.

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

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 comprises at least one of methanol, ethanol and isopropanol; And / or, the acid hydrolysis comprises 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 base added is 1-10 mol / L; And / or, the first inert atmosphere uses nitrogen and / or argon; And / or, the second inert atmosphere uses argon; And / or, the free carbon removal comprises the following conditions: keeping at 600-800°C for 3-6h in air atmosphere; And / or, the silicon dioxide removal includes the following conditions: using 20-40wt% HF aqueous solution as an etchant, treating at 30-60°C for 10-120min.

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

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

8. Use of the nano-silicon carbide microspheres as claimed in claim 7 in a composite material containing epoxy resin.

9. An epoxy resin composite material, characterized in that: The invention comprises an epoxy resin matrix and the nano-silicon carbide microspheres according to claim 7 dispersed in the epoxy resin matrix.

10. An electronic device, characterized in that: Contains the nano silicon carbide microspheres as claimed in claim 7 or the epoxy resin composite material as claimed in claim 9.

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