CN109942297A - A kind of silicon carbide nanowire reinforced high-oriented graphite composite material and preparation method - Google Patents

Abstract

The invention discloses a silicon carbide nanowire reinforced high-orientation graphite composite material and a preparation method. A uniform layer of silicon carbide nanowires is grown on the surface as a reinforcing phase, which is evenly distributed among the graphite sheets to form silicon carbide nanowires reinforced The anisotropic structure of the oriented graphite flakes; in the process, the silicon carbide nanowires coated flake graphite powder was prepared by the molten salt method using silicon powder and flake graphite as raw materials, and then pre-pressed and formed at 1600 Spark plasma sintering is performed at ~2000 ℃, and the axial pressure applied during the sintering process makes the graphite sheets coated with silicon carbide nanowires directionally arranged, and the uniform three-dimensional ceramic skeleton formed after sintering can significantly improve the strength of the graphite matrix. And constrain the thermal expansion of graphite to form anisotropic composites with dense, high strength, high thermal conductivity along the sheet direction, and low thermal expansion perpendicular to the sheet direction. Heat dissipation and other aspects have broad application prospects.

Description

A kind of silicon carbide nanowire reinforced high-oriented graphite composite material and preparation method

technical field

The invention belongs to the technical field of thermal management material preparation, and in particular relates to a silicon carbide nanowire reinforced high-orientation graphite composite material and a preparation method.

Background technique

With the rapid development of modern technology, efficient heat conduction and heat dissipation have gradually become key issues in the field of thermal management. In the communication electronics and semiconductor industries, the integration of microelectronics and optoelectronic chip devices in large computers, notebook computers and other equipment has been greatly improved, the power density has become larger and larger, and more heat is accumulated per unit volume. If thermal management is not sufficient , the temperature is too high, it will reduce the working efficiency of the element/component and aggravate the aging. At the same time, the increased thermal stress between the device and the substrate material will cause thermo-mechanical damage and cracking problems, resulting in the failure of the component to be scrapped and affecting its normal use. In the aerospace industry, the quality of the aircraft is reduced as much as possible, the thermal conductivity of the device is improved, the working stability and service life of each component are ensured, and the flight cost is reduced. Therefore, the fields of electronics, aerospace and other fields have put forward higher and higher requirements for thermal management materials as an important part of thermal control.

Graphite is an allotrope of carbon and belongs to the hexagonal crystal system. Each carbon atom in the lamella is connected with three other carbon atoms by covalent bonds, in a honeycomb-like arrangement of multiple hexagons. The van der Waals connection makes it exhibit a lot of property anisotropy. At the same time, graphite also has light weight (density ~ 2.26g·cm ^-3 ), good high temperature resistance, thermal shock resistance, and corrosion resistance. In particular, graphite's high thermal conductivity (~2000 W·m ^-1 ·K ^-1 ) along the sheet direction makes it one of the most promising thermal management materials recently. However, due to the weak bonding force between graphite sheets, its thermal expansion coefficient in the direction perpendicular to the sheet is very high (28×10 ^-6 K ^-1 ), which will inevitably cause the thermal expansion coefficient of the highly oriented graphite material to increase greatly in this direction, resulting in the device The low thermal expansion performance requirements of the plane on which it is located cannot be achieved. At the same time, the low strength of graphite also limits its development in the field of thermal management materials for electronic devices.

SUMMARY OF THE INVENTION

In order to overcome the shortcomings of the above-mentioned prior art, the purpose of the present invention is to provide a silicon carbide nanowire reinforced high-oriented graphite composite material and a preparation method, which is simple to operate, and can effectively improve the uniformity of the ceramic skeleton and improve the graphite Comprehensive properties of the base material.

In order to achieve the above object, the present invention adopts the following technical solutions to be realized:

The invention discloses a silicon carbide nanowire reinforced high-orientation graphite composite material. The composite material uses lamellar graphite as a raw material and silicon carbide nanowires formed by molten salt reaction as a reinforcing phase. The reinforcing phase is evenly distributed among the lamellar graphites to form a composite material with anisotropic structure; among which, the lamellar graphite accounts for 20% to 90% and the silicon carbide nanowire accounts for 10% to 80% in terms of mass percentage.

Preferably, the relative density of the silicon carbide nanowire reinforced high-oriented graphite composite material is 90.25%-98.59%; the apparent porosity is 1.68%-8.64%; the strength perpendicular to the direction of the graphite sheet is 32.58-89.26MPa; At 300K, the thermal conductivity along the sheet direction is 95～216W/(m·K), the thermal conductivity perpendicular to the sheet direction is 36～54W/(m·K), and the thermal expansion coefficient is (5～8)× ^10-6 /K.

The invention discloses a preparation method of silicon carbide nanowire reinforced high-orientation graphite composite material, comprising the following steps:

1) According to the molar ratio of silicon powder: flake graphite=1:50～2:1, take silicon powder and flake graphite and mix to obtain raw material powder, according to sodium chloride:sodium fluoride=1:3～6:1 According to the mass ratio of raw material powder:reaction medium=1:(4～12), fully mix the raw material powder and reaction medium to obtain mixed powder ;

2) Under vacuum or protective atmosphere, the mixed powder is raised from room temperature to 600°C at a heating rate of 5-15°C/min, and kept for 30 minutes; and then raised to 1000-1500°C at a heating rate of 5-10°C/min , heat preservation for 0.5~9h, rinsed with hot water for many times, and dried to obtain powder;

3) Load the obtained powder into a graphite mold, and pre-press molding first;

4) Place the graphite mold with the pre-pressed sample in the spark plasma sintering device, apply an axial pressure of not less than 30 MPa to the pre-pressed sample, and use pulses under vacuum or with a protective atmosphere. The pre-pressed sample is excited and activated by electric current for at least 60 s, and then heated from room temperature to 1600-2000 ℃ by increasing the electric current for sintering, and then cooled after heat preservation, to obtain a graphite matrix composite material with uniform silicon carbide nanowires reinforced with high orientation.

Preferably, in step 1), the particle size of the silicon powder used is in the range of 2-10 μm, and the purity is greater than 99.0%.

Preferably, in step 1), the flake graphite used has a width of 200-1000 μm, a width-to-thickness ratio of (10-20):1, and a purity greater than 99.0%.

Preferably, in step 1), mechanical stirring is used for mixing, and the stirring time is 20-40 min.

Preferably, in step 2), the temperature of the hot water is 80-100° C., and the rinse is not less than 50 times.

Preferably, in step 3), the pressure of the pre-compression molding is 30-90 MPa, and the pressure is maintained for 1-10 minutes.

Preferably, the sintering in step 4) is divided into two stages, the first stage is heated from room temperature to 1200 °C at a heating rate of 300 °C/min, and the second stage is heated from 1200 °C at a heating rate of 150 °C/min to the final sintering temperature.

Preferably, the holding time in step 4) is at least 3min.

Compared with the prior art, the present invention has the following beneficial effects:

The preparation method of the silicon carbide nanowire reinforced high-orientation graphite composite material disclosed in the present invention uses flake graphite as a template, grows a uniform layer of silicon carbide nanowires on its surface as a reinforcing phase, and is evenly distributed among the graphite flake layers to form Silicon carbide nanowires enhance the anisotropic structure of oriented graphite flakes; in the process, silicon powder and flake graphite are used as raw materials to prepare silicon carbide nanowire-coated flake graphite powder by molten salt method. After compression molding, spark plasma sintering is performed at 1600-2000 °C. The axial pressure applied during the sintering process makes the graphite sheets coated with the silicon carbide nanowires directionally arranged, and a uniform three-dimensional ceramic skeleton is formed after sintering. In the present invention, the silicon carbide coated on the graphite surface by the molten salt method is uniform and continuous, the interface between the silicon carbide and the graphite is well combined, and a certain axial pressure is applied during the sintering process, so that the graphite particle sheets coated with the silicon carbide nanowires can be uniformly oriented Arrangement, and anisotropic graphite composites reinforced by silicon carbide nanowires are prepared by spark plasma sintering. The method is simple to operate and suitable for popularization, and the spark plasma sintering method has the advantages of fast heating rate, short sintering period and high densification rate.

Through the above method of the present invention, anisotropic composite materials with dense, high strength, high thermal conductivity along the lamellar direction, and low thermal expansion perpendicular to the lamellar direction can be obtained. It has a wide range of application prospects in terms of heat and heat dissipation.

Description of drawings

FIG. 1 is a schematic structural diagram of a spark plasma sintering furnace adopted in the present invention.

2 is a microscopic topography photo of the silicon carbide-coated flake graphite powder (Example 1) prepared by the present invention, wherein (a) a low-power microscopic topography photo; (b) a high-power microscopic topography photo;

FIG. 3 is a microscopic photograph of the silicon carbide nanowire reinforced highly oriented graphite (Example 1) prepared by the present invention.

Detailed ways

In order to make those skilled in the art better understand the solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only Embodiments are part of the present invention, but not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

It should be noted that the terms "comprising" and "having" and any modifications thereof in the description and claims of the present invention are intended to cover non-exclusive inclusion, for example, a process or method comprising a series of steps or units The processes, systems, products or devices are not necessarily limited to those steps or units expressly listed, but may include other steps or units not expressly listed or inherent to these processes, methods, products or devices.

Below in conjunction with accompanying drawing, the present invention is described in further detail:

The silicon carbide nanowire reinforced high-orientation graphite-based composite material and the preparation process of the present invention are completed in a spark plasma sintering furnace. Put the prepared tungsten carbide-coated flake graphite powder into a graphite mold, pad a layer of graphite paper with a thickness of 0.2 mm on the indenter at both ends and the inner wall of the mold in advance, and place the graphite mold on the upper and lower graphite pads At the center position of the device, the pressure loading system is activated to apply an axial pressure of 30-60 MPa to the graphite pads at both ends, which is transmitted to the die to extrude the sample. The furnace chamber is closed, and the entire furnace chamber is evacuated through the vacuum system to form a vacuum chamber with a pressure less than 5Pa. Sintering is carried out under vacuum or argon protection. During sintering, the power system first used pulse current to activate the sample for 60s, and after the current excitation was completed, the temperature was increased by increasing the current, and sintering was performed. Due to the zigzag pulse current generated in the activation stage, a micro-discharge plasma is formed on the powder particles, which causes the instantaneous high temperature between the particles to induce atomic diffusion and necking, and eliminates the micro pores at the triangular grain boundary to achieve rapid densification, and then electrify The powder is heated, and the sintering process is completed by thermal diffusion and electrical diffusion effect. After the holding process is over, the cooling system allows the temperature of the sintering furnace and specimen to quickly drop to room temperature. Rapid sintering of the material can be achieved using this process.

Example 1

Weigh silicon powder and flake graphite with a molar ratio of 1:1 as raw materials, and 4:1 of sodium chloride and sodium fluoride as a medium, wherein the mass ratio of raw materials and medium is 1:7, and the raw materials and medium are grinded in agate. Mechanical stirring was carried out in the bowl for 30 min to mix well. Put the mixed powder into an alumina crucible, put the alumina crucible into a vacuum furnace, evacuate to 1×10 ^-3 Pa, raise the temperature to 600°C at a heating rate of 10°C/min, and keep the temperature for 30min; close the vacuum system , filled with argon protective gas to a slight negative pressure, and then raised to 1100°C at a heating rate of 10°C/min, raised to 1300°C at a heating rate of 5°C/min, kept for 1 hour, and heated by 80-100°C hot water. Rinse 30 to 50 times, and obtain silicon carbide nanowire-coated flake graphite powder after drying. The powder is graphite powder whose surface is covered by silicon carbide nanowires, and silicon carbide nanowires are formed by the reaction of silicon powder and graphite. of. Take the obtained powder and put it into a graphite mold. The upper and lower indenters and the inner wall of the mold are pre-filled with a layer of graphite paper, which is pre-pressed to form a sample, and then the graphite mold is put into the spark plasma sintering shown in Figure 1. in the furnace. The inside of the furnace cavity is evacuated to form a vacuum chamber with the pressure in the cavity less than 5Pa. An axial pressure of 50 MPa was applied to the graphite mold by the loading system. At the beginning of the sintering process, the sample was excited with a pulse current for 60 s, then the current was increased to rapidly heat up to 1200 °C, and then the temperature was raised to 1800 °C at a heating rate of 150 °C/min, held for 5 min, and then cooled to room temperature with the furnace to obtain silicon carbide. Nanowire-reinforced highly oriented graphite matrix composites.

The silicon carbide nanowire-coated flake graphite powder prepared in this example was characterized by a field emission scanning electron microscope (FESEM), and its microstructure can be referred to in FIG. 2 . The surface of the flake graphite is covered with a layer of silicon carbide nanowires with high straightness and uniformity. The formation of SiC nanowires enhanced the sintering activity and facilitated sample densification. The density measured by the Archimedes drainage method reached 3.05 g/cm ³ , the relative density reached 96.5%, and the apparent porosity was 2.6%. Through spark plasma sintering, under the action of pressure, the flake graphite powder coated with silicon carbide nanowires is oriented and arranged, and the silicon carbide is evenly distributed among the flake graphite to form a three-dimensional network ceramic framework (Figure 3). The bending strength test results show that the strength of the composite material perpendicular to the direction of the graphite sheet reaches 89.26MPa. At the same time, the thermal conductivity results of the composite material show that at a temperature of 300K, the thermal conductivity along the sheet direction is 131W/(m·K), and the direction perpendicular to the sheet layer is 54W/(m·K). anisotropy.

Example 2

The process of this example is the same as that of Example 1, except that some process parameters are changed: the molar ratio of silicon powder and graphite powder is 1:1, and the spark plasma sintering temperature is 1600°C.

The same performance test as in Example 1 was performed on the sintered sample of this example, and the results were as follows: the density reached 2.76 g/cm ³ , the relative density reached 90.25%, and the apparent porosity was 8.64%. The microstructure is similar to Figure 2, and the three-dimensional network-like ceramic framework is similar to Figure 3; the strength perpendicular to the direction of the graphite sheet reaches 59.57 MPa. At a temperature of 300K, the thermal conductivity along the sheet direction is 95W/(m·K) and perpendicular to the sheet direction is 39W/(m·K).

Example 3

The process of this example is the same as that of Example 1, except that some process parameters are changed: the molar ratio of silicon powder and graphite powder is 1:3, and the spark plasma sintering temperature is 1850°C.

The same performance test as in Example 1 was performed on the sintered sample of this example, and the results were as follows: the density reached 2.44 g/cm ³ , the relative density reached 94.57%, and the apparent porosity was 2.69%. The microstructure is similar to Figure 2, and the three-dimensional network-like ceramic framework is similar to Figure 3; the strength perpendicular to the direction of the graphite sheet reaches 72.95 MPa. At a temperature of 300K, the thermal conductivity along the sheet direction is 169W/(m·K) and perpendicular to the sheet direction is 42W/(m·K).

Example 4

The process of this example is the same as that of Example 1, except that some process parameters are changed: the molar ratio of silicon powder and graphite powder is 1:2, and the spark plasma sintering temperature is 1900°C.

The same performance test as in Example 1 is carried out on the sintered sample of this example, and the results are as follows: the density reaches 2.81 g/cm3, the relative density reaches 98.59%, and the apparent porosity is 1.02%. The microstructure is similar to Fig. 2, and the three-dimensional network-like ceramic framework is similar to that of Fig. 3; the strength perpendicular to the direction of the graphite sheet reaches 86.26 MPa. At the temperature of 300K, the thermal conductivity along the sheet direction is 195W/(m·K), and the vertical direction is 52W/(m·K).

Example 5

The process of this example is the same as that of Example 1, except that some process parameters are changed: the molar ratio of silicon powder and graphite powder is 1:20, and the spark plasma sintering temperature is 1900°C.

The same performance test as in Example 1 was performed on the sintered sample of this example, and the results were as follows: the density reached 2.29 g/cm ³ , the relative density reached 97.39%, and the apparent porosity was 1.68%. The microstructure is similar to Figure 2, and the three-dimensional network-like ceramic framework is similar to Figure 3; the strength perpendicular to the direction of the graphite sheet reaches 32.58MPa. At a temperature of 300K, the thermal conductivity along the sheet direction is 216W/(m·K), and the direction perpendicular to the sheet layer is 36W/(m·K).

To sum up, because silicon carbide has excellent mechanical properties, good corrosion resistance, high temperature resistance, oxidation resistance and thermal conductivity, and low thermal expansion coefficient. Especially silicon carbide nanostructures (whiskers, nanorods, nanotubes, etc.) have some unique mechanical, electronic and optical properties, as well as excellent sintering activity. The invention chooses to uniformly compound silicon carbide nanowires and graphite phases, which can introduce the advantages of silicon carbide ceramics and nanowires into the graphite matrix, and make up for the shortcomings of low graphite strength, difficult sintering, and high thermal expansion coefficient perpendicular to the lamellar graphite. Graphite matrix composites have broad application prospects in the field of thermal management.

Therefore, in the present invention, flake graphite is used as a template, and a layer of uniform silicon carbide nanowires is grown on its surface as a reinforcing phase, which is evenly distributed among the graphite flakes to form each of the graphite flakes in which the silicon carbide nanowires are reinforced and aligned. Anisotropic structure. Specifically, silicon carbide nanowires are first generated to coat flake graphite powder, and then a uniform silicon carbide framework reinforced high-oriented graphite matrix composite material is prepared by spark plasma sintering. Among them, the preparation of silicon carbide nanowires by molten salt method is simple and easy to operate, and spark plasma sintering is a new method, which has the advantages of fast heating speed, short sintering cycle, and high densification rate. The silicon carbide nanowire reinforced graphite matrix composite material obtained by the invention can be widely used in thermal management materials in the fields of electronics, aerospace, national defense and the like, and has broad application prospects.

The above content is only to illustrate the technical idea of the present invention, and cannot limit the protection scope of the present invention. Any changes made on the basis of the technical solution according to the technical idea proposed by the present invention all fall within the scope of the claims of the present invention. within the scope of protection.

Claims (10)

1. a silicon carbide nanowire reinforced high-orientation graphite composite material, is characterized in that, this composite material takes lamellar graphite as raw material, takes the silicon carbide nanowire that molten salt reaction takes place to generate as reinforcement phase, adopts hot pressing sintering method to make. The reinforcing phase is uniformly distributed among the lamellar graphites to form a composite material with an anisotropic structure; wherein: In terms of mass percentage, lamellar graphite accounts for 20% to 90%, and silicon carbide nanowires account for 10% to 80%. 2. The silicon carbide nanowire-reinforced high-oriented graphite composite material according to claim 1, wherein the relative density of the silicon carbide nanowire-reinforced high-oriented graphite composite material is 90.25% to 98.59%; the apparent porosity is 1.68 %～8.64%; the strength perpendicular to the direction of the graphite sheet reaches 32.58～89.26MPa; at a temperature of 300K, the thermal conductivity along the direction of the sheet reaches 95～216W/(m·K), and the thermal conductivity perpendicular to the sheet direction The rate is 36 to 54 W/(m·K), and the thermal expansion coefficient is (5 to 8)×10 ^-6 /K. 3. a preparation method of silicon carbide nanowire reinforced high-oriented graphite composite material, is characterized in that, comprises the following steps: 1) According to the molar ratio of silicon powder: flake graphite=1:50～2:1, take silicon powder and flake graphite and mix to obtain raw material powder, according to sodium chloride:sodium fluoride=1:3～6:1 According to the mass ratio of raw material powder:reaction medium=1:(4～12), fully mix the raw material powder and reaction medium to obtain mixed powder ; 2) Under vacuum or protective atmosphere, the mixed powder is raised from room temperature to 600°C at a heating rate of 5-15°C/min, and kept for 30 minutes; and then raised to 1000-1500°C at a heating rate of 5-10°C/min , heat preservation for 0.5~9h, rinsed with hot water for many times, and dried to obtain powder; 3) Load the obtained powder into a graphite mold, and pre-press molding first; 4) Place the graphite mold with the pre-pressed sample in the spark plasma sintering device, apply an axial pressure of not less than 30 MPa to the pre-pressed sample, and use pulses under vacuum or with a protective atmosphere. The pre-pressed sample is excited and activated by electric current for at least 60 s, and then heated from room temperature to 1600-2000 ℃ by increasing the electric current for sintering, and then cooled after heat preservation, to obtain a graphite matrix composite material with uniform silicon carbide nanowires reinforced with high orientation. 4 . The preparation method of silicon carbide nanowire reinforced high-oriented graphite composite material according to claim 3 , wherein, in step 1), the silicon powder used has a particle size range of 2-10 μm and a purity greater than 99.0%. 5 . 5. The preparation method of silicon carbide nanowire reinforced high-oriented graphite composite material according to claim 3, wherein in step 1), the width of the flake graphite used is 200-1000 μm, and the aspect ratio is (10-20 μm) ): 1, the purity is greater than 99.0%. 6 . The method for preparing a silicon carbide nanowire reinforced high-oriented graphite composite material according to claim 3 , wherein, in step 1), mechanical stirring is used for mixing, and the stirring time is 20-40 min. 7 . 7 . The method for preparing a silicon carbide nanowire reinforced high-oriented graphite composite material according to claim 3 , wherein, in step 2), the temperature of the hot water is 80-100° C., and the rinse is not less than 50 times. 8 . 8 . The method for preparing a silicon carbide nanowire reinforced high-oriented graphite composite material according to claim 3 , wherein the pressure of the pre-compression molding in step 3) is 30-90 MPa, and the pressure is maintained for 1-10 minutes. 9 . 9 . The preparation method of silicon carbide nanowire reinforced high-oriented graphite composite material according to claim 3 , wherein the sintering in step 4) is divided into two stages, and the first stage is heated at a temperature of 300° C./min from room temperature in the first stage. 10 . The temperature was ramped up to 1200 °C at a rate of 1200 °C, and the second stage was heated from 1200 °C to the final sintering temperature at a heating rate of 150 °C/min. 10 . The method for preparing a silicon carbide nanowire reinforced high-oriented graphite composite material according to claim 3 , wherein the holding time in step 4) is at least 3 min. 11 .