BN-SiC multiphase ceramic powder as well as preparation method and application thereof

Abstract

The invention discloses BN-SiC composite ceramic powder as well as a preparation method and application thereof. The composite ceramic powder is prepared from the following components in percentage by mass: 9 to 70.8 weight percent of BN nanosheets, 26.9 to 91 weight percent of SiC particles and 0 to 2.3 weight percent of residual silicon, the BN-SiC composite ceramic powder has typical micro-nano hierarchical structure characteristics, and the surfaces of equiaxial micron-sized SiC particles are wrapped with BN nanosheets. The BN-SiC multiphase ceramic powder has high infrared emissivity # imgabs0 # close to a black body in the wave band of 2.5-25 microns, meanwhile, due to the existence of a micro-nano hierarchical structure, the BN-SiC multiphase ceramic powder also has ultrahigh hydrophobicity, the contact angle is larger than or equal to 150 degrees, and the BN-SiC multiphase ceramic powder can be used as a functional filler for preparing a hydrophobic heat dissipation coating and has wide application prospects.

Description

Technical Field

[0001] The present invention relates to the technical field of preparation of composite ceramic powders, and more specifically, to a BN-SiC composite ceramic powder and a preparation method and application thereof. Background Art

[0002] Heat dissipation is a key issue to improve the reliability and life of high-power electronic devices. Materials with high thermal conductivity are usually used in components that require effective heat dissipation. Due to the characteristics of high thermal conductivity, light weight and low cost, aluminum and its alloy materials are widely used as heat sink materials. Radiative heat dissipation has received widespread attention as a passive, efficient and renewable heat dissipation method. However, the emissivity of aluminum is extremely low, only 0.1-0.2, which inhibits its effective radiative heat dissipation in the infrared region. In addition, it should be considered that in practical applications, dust or other solid particle pollutants will inevitably accumulate on the surface of radiative cooling materials. If the pollutants are not removed from the material surface in time, the infrared emissivity of the material surface will be severely reduced, and the radiative heat dissipation performance will be significantly reduced. Superhydrophobic surface technology can improve this situation, which can provide further protection for superhydrophobic surfaces. Therefore, it is necessary to develop multifunctional materials with effective radiative heat dissipation capabilities, superhydrophobicity, self-cleaning and corrosion resistance.

[0003] SiC is a typical infrared ceramic material with low density, excellent chemical stability, thermal stability and other characteristics. It is a promising material for mid-infrared applications. However, SiC is a hydrophilic material, so humid environments, dusty environments and other environments are prone to affect its radiation performance. Currently, some researchers have introduced low surface energy modifiers, such as those with -CH 3 The introduction of substances with low surface energy into the preparation of SiC materials can obtain super-hydrophobic effects. However, this low surface energy modifier will increase operating costs and complexity, and will also bring environmental risks. The 2D-BN crystal structure has excellent thermal conductivity, thermal stability and chemical stability, so the BN nanostructured film with super-hydrophobic properties has attracted widespread attention from scholars at home and abroad. However, there are also some problems in combining high-emissivity SiC with super-hydrophobic BN nanostructures to prepare functional materials, such as the high cost of BN sheets, the easy agglomeration of BN sheets and SiC particles, and the difficulty in uniform mixing, which all lead to BN-SiC composite ceramic materials being difficult to obtain easily. Summary of the invention

[0004] In order to solve the above problems, the first object of the present invention is to provide a BN-SiC composite ceramic powder. The BN-SiC composite ceramic powder has a high infrared emissivity close to that of a black body in the 2.5-25 μm band. At the same time, due to the existence of its micro-nano hierarchical structure, it also has ultra-high hydrophobic properties, with a contact angle of ≥150°, which can meet the needs of practical applications.

[0005] The second object of the present invention is to provide a method for preparing the BN-SiC composite ceramic powder as described above. The present invention adopts a simple and efficient combustion synthesis method, using low-cost silicon powder, boron carbide and carbon black as raw materials, and synthesizes multifunctional BN-SiC composite ceramic powder in situ under a nitrogen atmosphere.

[0006] The third object of the present invention is to provide an application of the BN-SiC composite ceramic powder as described above in the preparation of a hydrophobic heat dissipation coating.

[0007] The residual silicon in the present invention refers to the silicon powder raw material that has not reacted completely when preparing the BN-SiC composite ceramic powder.

[0008] In order to achieve the above first object, the present invention adopts the following technical scheme:

[0009] The present invention discloses a BN-SiC composite ceramic powder, which comprises, by mass percentage, 9-70.8wt% of BN nanosheets, 26.9-91wt% of SiC particles and 0-2.3wt% of residual silicon;

[0010] The BN nanosheets are wrapped around the surface of micron-sized SiC particles to form a micro-nano hierarchical structure.

[0011] The present invention adopts nitriding combustion synthesis technology to produce silicon powder (Si), boron carbide (B 4 C), carbon black (C) as solid raw materials, nitrogen as gas raw materials, based on the chemical reaction equation (1), for the first time synthesized BN-SiC composite ceramic powder material with both high emissivity and super hydrophobicity. The powder has typical micro-nano hierarchical structure characteristics, and BN nanosheets are wrapped on the surface of equiaxed micron-sized SiC particles.

[0012] Si+B 4 C+C+N 2 →SiC+BN (1)

[0013] After further study, it was found that the reaction path can be seen in chemical reaction equations (2)-(6) and Figure 1 :First, silicon reacts with nitrogen to form silicon nitride (Si 3 N 4 ), under high temperature and nitrogen-poor conditions, the newly generated Si 3 N 4 Decompose to obtain molten silicon and nitrogen; then the molten silicon is successively mixed with micron-sized B 4 C reacts with nano-scale carbon black to generate micron-scale silicon carbide and nano-scale silicon carbide respectively; finally, Si and B 4The amorphous B obtained by the C reaction reacts with nitrogen to form BN nanosheets. Due to the van der Waals force interaction between the boron nitride nanosheets, upright boron nitride nanosheets are obtained, and finally a BN-SiC composite ceramic powder with a micro-nano hierarchical structure is obtained.

[0014] 3Si+2N 2 =Si 3 N 4 (2)

[0015] Si 3 N 4 =3Si+2N 2 (3)

[0016] Si+B 4 C=SiC+4B (4)

[0017] Si+C=SiC (5)

[0018] 2B+N 2 =2BN (6)

[0019] Furthermore, in terms of mass percentage, the composite ceramic powder includes 20-70.8 wt % of BN nanosheets, 26.9-80 wt % of SiC particles, and 0-2.3 wt % of residual silicon.

[0020] Furthermore, the average infrared emissivity of the composite ceramic powder in the 2.5-25 μm band is The contact angle is ≥150°; preferably, the average infrared emissivity of the composite ceramic powder in the 2.5-25 μm band is More preferably, it is 0.93-0.96.

[0021] In order to achieve the above second purpose, the present invention adopts the following technical solutions:

[0022] The present invention discloses a method for preparing the BN-SiC composite ceramic powder as described above, comprising the following steps:

[0023] Silicon powder, boron carbide powder and carbon black are weighed in proportion to obtain raw material powder, which is then ball-milled and mixed. The uniformly mixed slurry is placed in an oven for drying, sieved and placed in a combustion synthesis reactor. A combustion synthesis reaction is carried out under a certain nitrogen pressure to obtain BN-SiC composite ceramic powder.

[0024] Furthermore, ethanol was added as a grinding medium during the ball milling process, and the grinding balls used were made of zirconium oxide (ZrO 2 ).

[0025] Furthermore, the particle size of the silicon powder is 1.5-15 μm, the particle size of the boron carbide is W1.5-W20, and the particle size of the carbon black is <1 μm.

[0026] Furthermore, in terms of mass percentage, silicon powder accounts for 33.6-67.2wt% of the raw material powder, boron carbide powder accounts for 5.28-66.4wt%, and carbon black powder accounts for 0-27.6wt%.

[0027] When the carbon black in the added raw materials exceeds the upper limit, most of the Si reacts with the carbon black to form small-sized nano-scale BN-SiC composite materials; conversely, when the boron carbide in the added raw materials exceeds the upper limit, most of the Si reacts with the BN-SiC composite materials to form nano-scale BN-SiC composite materials. 4 C reaction produces a BN-SiC composite material with a micro-nano hierarchical structure.

[0028] Furthermore, in terms of mass percentage, silicon powder accounts for 33.6-63.1wt% of the raw material powder, boron carbide powder accounts for 12.6-66.4wt%, and carbon black powder accounts for 0-24.3wt%.

[0029] Furthermore, the molar ratio of the silicon powder to boron carbide is 1 to 25:1.

[0030] Furthermore, the mass ratio of grinding balls to raw material powder during the ball milling process is 1 to 4:1, and the ball milling time is 1 to 4 hours.

[0031] Furthermore, the nitrogen pressure is 1-5 MPa.

[0032] Furthermore, the volume of the combustion synthesis reactor is 20L.

[0033] Furthermore, the drying condition is drying at 60-110° C. for 12-24 hours.

[0034] In order to achieve the third object, the present invention adopts the following technical solutions:

[0035] The present invention discloses the use of the BN-SiC composite ceramic powder as described above in the preparation of a hydrophobic heat dissipation coating.

[0036] The beneficial effects of the present invention are as follows:

[0037] The present invention discloses a BN-SiC composite ceramic powder and a preparation method and application thereof. The present invention adopts nitridation combustion synthesis technology, uses silicon powder, boron carbide, and carbon black as solid raw materials, and nitrogen as gas raw material to synthesize a multifunctional BN-SiC composite ceramic powder material with high emissivity and super hydrophobicity. The BN-SiC composite ceramic powder has a typical micro-nano hierarchical structure feature, and BN nanosheets are wrapped on the surface of equiaxed micron-sized SiC particles.

[0038] The BN-SiC composite ceramic powder provided by the present invention has a high infrared emissivity close to that of a black body in the 2.5-25 μm band. At the same time, due to the existence of its micro-nano hierarchical structure, it also has ultra-high hydrophobic properties, with a contact angle of ≥150°. It can be used as a functional filler to prepare hydrophobic heat dissipation coatings to meet the needs of practical applications and has broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] The specific implementation modes of the present invention are further described in detail below in conjunction with the accompanying drawings.

[0040] Figure 1 A schematic diagram of the reaction path for preparing BN-SiC composite ceramic powder in the present invention is shown.

[0041] Figure 2 The XRD patterns of the BN-SiC composite ceramic powders prepared in Example 1 and the comparative example are shown; wherein, Figure 2 (a) is Example 1, and (b) is a comparative example.

[0042] Figure 3 The microscopic morphology of the BN-SiC composite ceramic powder prepared in Example 1 and the comparative example is shown; wherein, Figure 3 (a) is Example 1, and (b) is a comparative example.

[0043] Figure 4 The contact angle test diagram of the BN-SiC composite ceramic powder prepared in Example 1 and the comparative example is shown; wherein, Figure 4 (a) is Example 1, and (b) is a comparative example.

[0044] Figure 5 The infrared emissivity of the BN-SiC composite ceramic powder prepared in Example 1 and the comparative example in the 2.5-25 μm band is shown. DETAILED DESCRIPTION

[0045] In order to more clearly illustrate the present invention, the present invention is further described below in conjunction with preferred embodiments and accompanying drawings. Similar components in the accompanying drawings are represented by the same reference numerals. It should be understood by those skilled in the art that the content specifically described below is illustrative rather than restrictive, and should not be used to limit the scope of protection of the present invention.

[0046] Example 1

[0047] 48.7 g of silicon powder with a particle size of 2.5 μm, 38.7 g of W3.5 boron carbide with a particle size of 12.5 g of carbon black with a particle size of 220 nm were used as reaction raw materials to obtain raw material powder, and ethanol was used as a grinding medium to ball mill the raw material powder for 2 hours, and the mass ratio of grinding balls to raw material powder was 2:1; after mixing evenly, the obtained mixture slurry was dried in an oven at 60° C. for 24 hours and passed through a 200-mesh sieve;

[0048] The sieved powder mixture is loaded into a porous graphite mold, and the graphite mold is placed in a 20L combustion reactor with a nitrogen pressure of 3MPa. The powder mixture is buried under the titanium powder placed on the top of the graphite mold, and the titanium powder is ignited by a tungsten coil with an ignition current of 10A. After the reaction is completed, the sample is crushed and ground. The phase composition of the product is BN, SiC and a very small amount of residual Si, among which according to Figure 2 The XRD calculation shown shows that the BN mass ratio is about 50.0wt%, the SiC mass ratio is about 47.7wt%, and the residual Si mass ratio is about 2.3wt%; the product has Figure 3 The micro-nano hierarchical structure of BN nanosheets coated with SiC results in the super hydrophobicity of the BN-SiC powder itself, with a CA of about 153.4±0.3° ( Figure 4 ), its average infrared emissivity in the 2.5-25μm band ( Figure 5 ), and the experimental data are summarized in Table 1.

[0049] Example 2

[0050] 63.1 g of silicon powder with a particle size of 2.5 μm, 12.5 g of boron carbide with a particle size of W3.5, and 24.3 g of carbon black with a particle size of 220 nm were used as reaction raw materials to obtain raw material powder, and ethanol was used as a grinding medium to ball mill the raw material powder for 2 hours, and the mass ratio of grinding balls to raw material powder was 2:1; after mixing evenly, the obtained mixture slurry was dried in an oven at 60° C. for 24 hours and passed through a 200-mesh sieve;

[0051] The sieved powder mixture is loaded into a porous graphite mold, and the graphite mold is placed in a 20L combustion reactor with a nitrogen pressure of 3MPa; the powder mixture is buried under the titanium powder placed on the top of the graphite mold, and the titanium powder is ignited by a tungsten coil with an ignition current of 10A; after the reaction, the sample is crushed and ground. The phase composition of the product is BN and SiC, where the mass ratio of BN is about 20wt% and the mass ratio of SiC is about 80wt% calculated according to the XRD spectrum; the product has a micro-nano hierarchical structure of BN nanosheets coated with SiC, which leads to the super hydrophobicity of the BN-SiC powder itself, with a CA of about 151.7±1.6°, and its average infrared emissivity in the 2.5-25μm band The experimental data are summarized in Table 1.

[0052] Example 3

[0053] 48.7 g of silicon powder with a particle size of 2.5 μm, 38.7 g of W10 boron carbide with a particle size of 220 nm, and 12.5 g of carbon black with a particle size of 220 nm were used as reaction raw materials to obtain raw material powder, and ethanol was used as a grinding medium to ball mill the raw material powder for 2 hours, and the mass ratio of grinding balls to raw material powder was 2:1; after mixing evenly, the obtained mixture slurry was dried in an oven at 60° C. for 24 hours and passed through a 200-mesh sieve;

[0054] The sieved powder mixture is loaded into a porous graphite mold, and the graphite mold is placed in a 20L combustion reactor with a nitrogen pressure of 3MPa; the powder mixture is buried under the titanium powder placed on the top of the graphite mold, and the titanium powder is ignited by a tungsten coil with an ignition current of 10A; after the reaction, the sample is crushed and ground. The phase composition of the product is BN, SiC and a very small amount of residual Si, wherein the BN mass ratio is about 50.2wt% calculated according to the XRD spectrum, the SiC mass ratio is 47.8wt%, and the residual Si mass ratio is 2.0wt%; the product has a micro-nano hierarchical structure of BN nanosheets coated with SiC, which leads to the super hydrophobicity of the BN-SiC powder itself, with a CA of about 153.1±1.1°, and its average infrared emissivity in the 2.5-25μm band The experimental data are summarized in Table 1.

[0055] Example 4

[0056] 48.7 g of silicon powder with a particle size of 15 μm, 38.7 g of W3.5 boron carbide with a particle size of 15 μm, and 12.5 g of carbon black with a particle size of 220 nm were used as reaction raw materials to obtain raw material powder, and ethanol was used as a grinding medium to ball mill the raw material powder for 2 hours, and the mass ratio of the grinding ball to the raw material powder was 2:1; after mixing evenly, the obtained mixture slurry was dried in an oven at 60° C. for 24 hours and passed through a 200-mesh sieve;

[0057] The sieved powder mixture is loaded into a porous graphite mold, and the graphite mold is placed in a 20L combustion reactor with a nitrogen pressure of 3MPa; the powder mixture is buried under the titanium powder placed on the top of the graphite mold, and the titanium powder is ignited by a tungsten coil with an ignition current of 10A; after the reaction, the sample is crushed and ground. The phase composition of the product is BN, SiC and a very small amount of residual Si, wherein the mass ratio of BN is about 50.6wt%, the mass ratio of SiC is 47.3wt%, and the mass ratio of residual Si is 2.1wt% according to the XRD spectrum; the product has a micro-nano hierarchical structure of BN nanosheets coated with SiC, which leads to the super hydrophobicity of the BN-SiC powder itself, with a CA of about 152.6±1.5°, and its average infrared emissivity in the 2.5-25μm band The experimental data are summarized in Table 1.

[0058] Example 5

[0059] 48.7 g of silicon powder with a particle size of 2.5 μm, 38.7 g of W3.5 boron carbide with a particle size of 12.5 g of carbon black with a particle size of 220 nm were used as reaction raw materials to obtain raw material powder, and ethanol was used as a grinding medium to ball mill the raw material powder for 2 hours, and the mass ratio of grinding balls to raw material powder was 2:1; after mixing evenly, the obtained mixture slurry was dried in an oven at 60° C. for 24 hours and passed through a 200-mesh sieve;

[0060] The sieved powder mixture is loaded into a porous graphite mold, and the graphite mold is placed in a 20L combustion reactor with a nitrogen pressure of 5MPa. The powder mixture is buried under the titanium powder placed on the top of the graphite mold, and the titanium powder is ignited by a tungsten coil with an ignition current of 10A. After the reaction, the sample is crushed and ground. The phase composition of the product is BN, SiC, and a very small amount of residual Si. According to the XRD spectrum, the mass ratio of BN is about 50.3wt%, the mass ratio of SiC is 47.9wt%, and the mass ratio of residual Si is 1.8wt%. The product has the following characteristics: Figure 3 The micro-nano hierarchical structure of BN nanosheets coated with SiC is shown, which leads to the super hydrophobicity of the BN-SiC powder itself, with a CA of about 153.4±0.3° and an average infrared emissivity of 2.5-25μm. The experimental data are summarized in Table 1.

[0061] Comparative Example

[0062] 67.2 g of silicon powder with a particle size of 2.5 μm, 5.3 g of boron carbide with a particle size of W3.5, and 27.6 g of carbon black with a particle size of 220 nm were used as reaction raw materials to obtain raw material powder, and ethanol was used as a grinding medium to ball mill the raw material powder for 2 hours, and the mass ratio of grinding balls to raw material powder was 2:1; after mixing evenly, the obtained mixture slurry was dried in an oven at 60° C. for 24 hours and passed through a 200-mesh sieve;

[0063] The sieved powder mixture is loaded into a porous graphite mold, and the graphite mold is placed in a 20L combustion reactor with a nitrogen pressure of 3MPa. The powder mixture is buried under the titanium powder placed on the top of the graphite mold, and the titanium powder is ignited by a tungsten coil with an ignition current of 10A. After the reaction is completed, the sample is crushed and ground. The phase composition of the product is BN, SiC and a very small amount of residual Si, among which according to Figure 2 The XRD calculation shown shows that the BN mass ratio is about 5.4wt%, the SiC mass ratio is 92.5wt%, and the residual Si mass ratio is 2.1wt%; the product has a nanostructure of BN nanosheets coated with SiC, CA is about 142.0±1.7°, and its average infrared emissivity in the 2.5-25μm band The experimental data are summarized in Table 1.

[0064] Table 1

[0065]

[0066] Through the above experiments, it was found that a high emissivity and BN-SiC composite ceramic powders with super hydrophobic (CA≥150°) properties.

[0067] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not limitations on the implementation methods of the present invention. For ordinary technicians in the relevant field, other different forms of changes or modifications can be made based on the above description. It is impossible to list all the implementation methods here. All obvious changes or modifications derived from the technical solution of the present invention are still within the protection scope of the present invention.

Claims

1. A BN-SiC composite ceramic powder, It is characterized in that In terms of mass percentage, the composite ceramic powder comprises 9-70.8wt% BN nanosheets, 26.9-91wt% SiC particles and 0-2.3wt% residual silicon; the BN nanosheets are wrapped around the surface of the micron-sized SiC particles to form a micro-nano hierarchical structure.

2. The composite ceramic powder according to claim 1, It is characterized in that Calculated by mass percentage, the composite ceramic powder includes 20-70.8wt% of BN nanosheets, 26.9-80wt% of SiC particles and 0-2.3wt% of residual silicon.

3. The composite ceramic powder according to claim 1, It is characterized in that The average infrared emissivity of the composite ceramic powder in the 2.5-25 μm band Contact angle ≥150°.

4. A method for preparing a composite ceramic powder according to any one of claims 1 to 3, It is characterized in that The steps include: Silicon powder, boron carbide powder and carbon black are weighed in proportion to obtain raw material powder, which is then ball-milled and mixed. The uniformly mixed slurry is placed in an oven for drying, sieved and placed in a combustion synthesis reactor. A combustion synthesis reaction is carried out under a certain nitrogen pressure to obtain BN-SiC composite ceramic powder.

5. The preparation method according to claim 4, It is characterized in that The particle size of the silicon powder is 1.5-15 μm, the particle size of the boron carbide is W1.5-W20, and the particle size of the carbon black is <1 μm.

6. The preparation method according to claim 4, It is characterized in that In terms of mass percentage, the raw material powder contains 33.6-67.2wt% silicon powder, 5.28-66.4wt% boron carbide powder and 0-27.6wt% carbon black powder.

7. The preparation method according to claim 4, It is characterized in that The molar ratio of the silicon powder to boron carbide is 1 to 25:

1.

8. The preparation method according to claim 4, It is characterized in that During the ball milling process, the mass ratio of grinding balls to raw material powder is 1-4:1, and the ball milling time is 1-4 hours.

9. The preparation method according to claim 4, It is characterized in that The nitrogen pressure is 1-5 MPa.

10. Use of the BN-SiC composite ceramic powder according to any one of claims 1 to 3 in preparing a hydrophobic heat dissipation coating.

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