CN105254302A - Preparing method for graphene heat conduction sheet - Google Patents

Abstract

The invention discloses a method for preparing graphene heat-conducting flakes, adding graphene nanosheet powder and coal tar pitch powder with a high softening point into anhydrous ethanol according to the proportion, ultrasonication, suction filtration, and drying; the resulting mixed powder is introduced into a mold for 15~ Cold press at 20MPa for 3~5min to form, then sandwich the cold-pressed sheet between high-temperature alloy molds, apply pressure, and treat at 500-800°C for 1-3h in nitrogen, argon or helium atmosphere, and then hot-pressed Thin slices; place the obtained hot-pressed thin slices in a high-temperature tube furnace, and treat them at 900-1200°C for 1-3 hours in an atmosphere of nitrogen, argon or helium to obtain carbonized thin slices; place the obtained carbonized thin slices in a high-temperature graphitization furnace , in nitrogen, argon or helium atmosphere, at 2300-2700 °C for 0.5-2h to obtain graphitized graphene flakes. The prepared graphitized graphene flake has high thermal conductivity anisotropy, its preparation method is simple, and it is easy for industrial production.

Description

A kind of preparation method of graphene heat conduction sheet

technical field

The invention belongs to the field of materials science, and relates to a carbon material, in particular to a method for preparing a graphene heat-conducting sheet.

Background technique

At present, graphene has received widespread attention due to its unique structure and excellent properties, such as high thermal conductivity (in-plane thermal conductivity as high as 4800-6000W/m K), high electrical conductivity, etc. It has good application prospects in technical fields such as heat sealing materials and heating elements. The two-dimensional heat-conducting sheet based on the oriented arrangement of graphene sheets can give full play to its structural advantages, and can provide heat insulation in the thickness direction while dissipating heat in the sheet layer, which is conducive to its application in the field of thermal management.

Since graphene was exfoliated by the University of Manchester in 2004 through the micro-tape exfoliation method, people have focused extensively on how to obtain high-quality and high-yield graphene or the optimization of graphene preparation methods. Nowadays, there are countless methods for preparing graphene, such as micro-tape stripping method, chemical vapor deposition method, epitaxial growth method, epitaxy method, solvent stripping method, and chemical redox method. The mass production of graphene has also been preliminarily realized, but how to realize the industrial application value of graphene is still an urgent problem to be solved. People have also made many attempts, such as graphene films prepared by vacuum filtration method, spray coating method, spin coating method, vacuum suction filtration method, gas/liquid self-assembly method, Langmuir–Blodgett self-assembly method, etc., but the prepared The thin film is difficult to maintain its integrity, easy to break, many voids, low mechanical strength and other shortcomings, and the production cost is high and the operation is complicated.

Contents of the invention

In view of the above-mentioned technical problems in the prior art, the invention provides a kind of preparation method of graphene heat conduction sheet, the preparation method of described this graphene heat conduction sheet solves the method for preparing graphene heat conduction sheet in the prior art The prepared film is difficult to maintain its integrity, easy to break, has many voids, low mechanical strength, high production cost and complicated operation.

The invention provides a kind of preparation method of graphene heat conduction sheet, comprises the steps:

1) take graphene nanosheet powder and high softening point coal tar pitch powder according to mass ratio, the mass ratio of described graphene nano sheet powder and high softening point coal tar pitch powder is 5:0～0.5, graphene nano sheet The powder is mixed with high softening point coal tar pitch powder, then added to absolute ethanol for 0.5~2h ultrasonic, suction filtered, and dried to obtain the mixed powder; the amount of absolute ethanol is based on graphene powder: absolute ethanol Calculated for the ratio of 1g:350~500mL;

2) Import the mixed powder obtained in step (1) into the mold, adjust the pressure of the hydraulic press to 15~20MPa, and the time is 3~5min, and directly cold press the mixed powder into thin slices;

3) The cold-pressed sheet obtained in step (2) is sandwiched between superalloy molds with smooth surfaces, placed in a tube furnace, and a pressure of 0-5 MPa is applied by a hydraulic press, and the pressure is applied in a nitrogen, argon or helium atmosphere. Under any atmosphere, raise the temperature to 420~450℃ at a heating rate of 3~5℃/min, keep the temperature constant for 0.5~1.5h, and then raise it to 500~800℃ at a heating rate of 1~5℃/min. Under the thermal expansion effect of the superalloy, the system is boosted to 21~34MPa, kept at a constant temperature for 1~3h, and then naturally cooled to room temperature to obtain a hot-pressed graphene sheet; the thickness of the hot-pressed graphene sheet is 179~211μm.

Further, the hot-pressed graphene sheet obtained in step (3) is placed in a high-temperature tube furnace, and carbonized at 900-1200°C for 1-3 hours in any atmosphere of nitrogen, argon or helium , to obtain carbonized graphene flakes.

Further, the obtained carbonized graphene flakes are placed in a high-temperature graphitization furnace, and are subjected to graphitization treatment at 2300-2700°C for 0.5-2 hours in any atmosphere of nitrogen, argon or helium to obtain graphite Graphene flakes.

Further, described graphene nanosheet powder is prepared by the following method:

1) Measure a certain amount of concentrated sulfuric acid and place it in a reaction container, add sodium nitrate therein, stir to dissolve the sodium nitrate, then add flake graphite, after the flake graphite is evenly dispersed, slowly add potassium permanganate to react, the whole The process uses an ice bath to keep the system at 0~5°C for 1~2h, then raise the temperature to 30~45°C for 1~3 hours, then slowly add the first batch of deionized water to the reaction system, and react for 20~40min. Then slowly add the second batch of deionized water, and then add H ₂ O ₂ , and continue the reaction for 5-20 minutes. The obtained reaction solution is suction filtered while it is hot, and the obtained filter cake is washed with HCl aqueous solution with a mass percentage concentration of 3-10%. washing to remove metal ions;

2) Then add deionized water into the filter cake, stir evenly, and then carry out centrifugal washing until the pH of the colloid is neutral, and ultrasonically 5-15min to obtain the graphene oxide colloid;

3) Take the graphene oxide colloid in a polytetrafluoroethylene container, add ammonia water to adjust the pH to 11, slowly add a hydrazine hydrate solution with a mass percentage concentration of 30 to 60% under stirring, and the quality of the graphene oxide colloid and hydrazine hydrate solution The ratio is 1:8~12, and then carry out microwave treatment; 20s microwave heating, 20s take out and stir as 1 cycle, repeat the operation for 3~8 cycles, then suction filter, freeze-dry to obtain graphene nanosheet powder.

Further, the mass percent concentration of the concentrated sulfuric acid is 60-98%.

Further, the material ratio of the concentrated sulfuric acid, sodium nitrate, graphite flakes, potassium permanganate, the first batch of deionized water, the second batch of deionized water, H ₂ O ₂ , and HCl aqueous solution is 96mL:2g:2g: 12g: 80mL: 200mL: 10mL: 1000mL.

Furthermore, the high softening point coal tar pitch powder described in step (1) has a softening point of 270-300°C, a TI content of 50-70%, and a QI content of 10-30%, and passes through a 150-300 mesh sieve.

Specifically, in step 1), the ultrasonic condition is 100W, 40KHz.

The method for preparing a graphene heat-conducting sheet of the present invention has no environmental pollution, and the anhydrous ethanol after suction filtration can be recycled and reused. The preparation of the heat-conducting sheet has a simple operation process and low cost, and can be used in large-scale industrial production. The graphene heat-conducting sheet obtained by the preparation method of a graphene heat-conducting sheet of the present invention has high thermal conductivity anisotropy, and the prepared graphitized graphene sheet has high thermal conductivity anisotropy, and the plane thermal conductivity is 300 ~ 405W /m·K, the axial thermal conductivity is 0.89~1.20W/m·K; graphitized graphene flakes have high strength, the tensile strength is 7.76~10.94MPa, and the deformation is 1.13~1.25%. It has potential practical application value.

Compared with the prior art, the technical progress of the present invention is remarkable. The invention utilizes the graphene nanosheets prepared by microwave-assisted exfoliation and reduction as raw materials, introduces coal tar pitch with a high softening point as a binder, and adopts a hot-pressing process to prepare graphene sheets, which have high mechanical strength, are not easily damaged, and have excellent thermal conductivity. , low manufacturing cost, simple preparation process, great potential application value and industrial mass production basis. The high thermal conductivity graphene flakes obtained by the invention have the characteristics of smooth surface, high tensile strength, less voids, high in-plane orientation of graphene flakes, high thermal conductivity and the like.

Description of drawings

Fig. 1 is a schematic diagram of the principle of measuring the in-plane orientation degree of graphene flakes.

Fig. 2 is the xrd diagram (a) of the graphene nanosheet in the step (1) of Example 1 and the xrd diagram (b) of the graphitized graphene flake obtained in the step (5).

Fig. 3 is an optical photograph (a) of a hot-pressed graphene flake obtained in step (3) of Example 1, and an SEM image of a plane (b) and a cross section (c).

Fig. 4 is the in-plane orientation degree of the hot-pressed graphene flake obtained in step (3) of Example 1, the carbonized graphene flake obtained in step (4) and the graphitized graphene flake obtained in step (5).

Fig. 5 is the tensile properties of graphitized graphene flakes obtained in step (5) of Example 1.

detailed description

The present invention will be further elaborated below by means of embodiments in conjunction with the accompanying drawings, but the present invention is not limited.

The scanning electron microscope used in the examples of the present invention is PhenomPro.

The X-ray diffractometer used, model D/max2200PC (CuKα, λ=0.15406nm), was produced by Japan Rigaku Corporation.

The pole figures of the samples were tested by the multifunctional texture test bench installed on the D/max2200PC X-ray diffractometer, and the (002) crystal planes of different samples were observed by the Schulz reflection method.

In the embodiment of the present invention, the determination of the in-plane orientation degree of hot-pressed graphene flakes, carbonized graphene flakes and graphitized graphene flakes requires the sample to rotate in three-dimensional space. The schematic diagram of the test principle is shown in Figure 1, where α is Sample deflection angle, β is the sample rotation angle, α=0~70°, β=0~360°, and the sample rotation speed is 10°/min. Firstly, the accurate Bragg angles of different crystal planes of different samples are measured by pre-scanning, and then three-dimensional rotation is performed on the samples. During the rotation process, the crystal planes satisfying the Bragg angles will diffract, and the intensity distribution of the diffraction peaks can characterize the orientation of the crystal planes of the sample.

In the embodiment of the present invention, the thermal diffusivity (α, mm ² /s) of the graphene flakes is tested by the LFA447 flash method thermal conductivity analyzer of the German Reach Company, and the bulk density (ρ, g/cm ³ ) is divided by the mass of the flakes by The volume was calculated, the specific heat capacity (C _p , J/gK) of the sample was measured by a TAQ2000 differential scanning calorimeter, and the thermal conductivity (λ, W/mK) was calculated by λ=α×ρ×C _p .

Example 1

A kind of preparation method of graphene thermally conductive sheet, specifically comprises the steps:

(1) Mix 0.5g of graphene nanosheet powder and 0.03g of high softening point coal tar pitch powder, add to absolute ethanol, ultrasonically treat at 100W, 40KHz for 1h, filter with suction, and dry at 70°C to obtain mixed powder;

Dehydrated alcohol consumption, by graphene powder: dehydrated alcohol is the ratio calculation of 1g:350mL; Described graphene powder is made by catalytic oxidation multiple intercalation exfoliation technology;

(2) Import the mixed powder obtained in step (1) into the mold, adjust the pressure of the hydraulic press to 20MPa, and the time is 3min, and directly cold press the mixed powder into thin slices;

(3) The cold-pressed sheet obtained in step (2) is sandwiched between superalloy molds with smooth surfaces and placed in a tube furnace. The piston of the hydraulic press is in a nitrogen atmosphere when it contacts the upper surface of the mold but does not apply pressure. , with a heating rate of 5 °C/min, the temperature is raised to 450 °C, and the temperature is kept constant for 1.5 hours. Then, the temperature is raised to 600 °C at a heating rate of 5 °C/min. After that, then naturally cool to room temperature to obtain a hot-pressed graphene sheet with a thickness of 202 μm;

(4) Place the hot-pressed graphene flakes obtained in step (3) in a high-temperature tube furnace, and perform carbonization treatment at 1000°C for 3 hours in a nitrogen atmosphere to obtain carbonized graphene flakes;

(5) Place the carbonized graphene flakes obtained in step (4) in a high-temperature graphitization furnace, and perform graphitization treatment at 2700°C for 1 hour under an argon atmosphere to obtain graphitized graphene flakes;

The surface of the hot-pressed graphene sheet is smooth, metallic gray, and has certain hardness and tensile strength.

The xrd of the above-mentioned graphene nanosheets is shown in Figure 2(a). From Figure 2(a), it can be seen that the graphene nanosheets have a wide diffraction peak at about 26°, indicating that graphene oxide is formed after microwave-assisted stripping and reduction. Graphene nanosheets. Figure 2(b) is the xrd diagram of graphitized graphene flakes. A sharp diffraction peak can be clearly observed at 26.5°, indicating that the interlayer spacing between graphenes in graphitized graphene flakes is extremely reduced.

The optical photographs of the above-mentioned hot-pressed graphene flakes and the SEM images of the plane and cross-section are shown in Figure 3. Among Figure 3, a is the optical photograph of the hot-pressed graphene flakes, b is the plane SEM image of the hot-pressed graphene flakes, and c is the cross-section of the hot-pressed graphene flakes From the SEM image, it can be concluded from Figure 3 that the planar and cross-sectional structures of the graphene flakes present significant differences.

The degree of orientation of the graphene sheets in the hot-pressed, carbonized and graphitized graphene heat-conducting sheets of the above-mentioned gained is shown in Figure 4. From Figure 4, it can be drawn that the deflection angle of the hot-pressed graphene sheets accounts for 41% within 5°. %, about 91% within 20°; about 39% of the deflection angle of carbonized graphene flakes is within 5°, and about 90% of those within 20°; while the deflection angle of graphitized graphene flakes is within 5° accounted for about 42%, and accounted for about 93% within 20 °. Compared with hot pressing and carbonized flakes, the degree of orientation of graphitized flakes is obviously slightly higher than the former two, thus showing that the graphene flakes of the present invention have graphite The olefin sheet has a high degree of orientation along the plane.

After testing, the graphitized graphene flake obtained above has a volume density of 1.382g/cm ³ , a plane thermal conductivity of 405W/m·K, and an axial thermal conductivity of 1.19W/m·K; the maximum tensile strength of the graphitized graphene flake is The tensile stress can reach 10.94MPa, and the deformation is 1.21%.

Example 2

A kind of preparation method of graphene thermally conductive sheet, specifically comprises the steps:

(1) Mix 0.5g of graphene nanosheet powder and 0.01g of high softening point coal tar pitch powder, add to absolute ethanol, ultrasonicate at 100W, 40KHz for 1h, filter with suction, and dry at 70°C to obtain mixed powder;

Dehydrated alcohol consumption, by graphene powder: dehydrated alcohol is the ratio calculation of 1g:400mL; Described graphene powder is made by catalytic oxidation multiple intercalation exfoliation technology;

(2) Import the mixed powder obtained in step (1) into the mold, adjust the pressure of the hydraulic press to 15 MPa, and the time is 5 minutes, and directly cold press the mixed powder into thin slices;

(3) Place the cold-pressed sheet obtained in step (2) between superalloy molds with smooth surfaces, place it in a tube furnace, and apply a pressure of 3 MPa with a hydraulic press. The heating rate is to raise the temperature to 450°C, keep the temperature constant for 1 hour, and then increase the temperature to 600°C at a heating rate of 1°C/min. Under the thermal expansion effect of the superalloy, the system will self-boost to 30MPa, keep the temperature for 2 hours, and then naturally cool to room temperature. That is to obtain hot-pressed graphene flakes with a thickness of 187 μm;

(4) Place the hot-pressed graphene flakes obtained in step (3) in a high-temperature tube furnace, and perform carbonization treatment at 900°C for 2 hours in a nitrogen atmosphere to obtain carbonized graphene flakes;

(5) Place the carbonized graphene flakes obtained in step (4) in a high-temperature graphitization furnace, and perform graphitization treatment at 2300°C for 2 hours under an argon atmosphere to obtain graphitized graphene flakes;

After testing, the graphitized graphene flake obtained above has a bulk density of 1.327g/cm ³ , a plane thermal conductivity of 325W/m·K, and an axial thermal conductivity of 1.16W/m·K; the maximum tensile strength of the graphitized graphene flake is The tensile stress can reach 8.96MPa, and the deformation is 1.25%.

Example 3

A kind of preparation method of graphene thermally conductive sheet, specifically comprises the steps:

(1) Mix 0.5g of graphene nanosheet powder and 0.02g of high softening point coal tar pitch powder, add to absolute ethanol, ultrasonically treat at 100W, 40KHz for 1h, filter with suction, and dry at 70°C to obtain mixed powder;

Dehydrated alcohol consumption, by graphene powder: dehydrated alcohol is the ratio calculation of 1g:500mL; Described graphene powder is made by catalytic oxidation multiple intercalation exfoliation technology;

(2) Import the mixed powder obtained in step (1) into the mold, adjust the pressure of the hydraulic press to 20 MPa, and the time is 5 minutes, and directly cold-press the mixed powder into thin slices;

(3) Place the cold-pressed sheet obtained in step (2) between superalloy molds with smooth surfaces, place it in a tube furnace, and apply a pressure of 5 MPa with a hydraulic press. Heating rate: raise the temperature to 420°C, keep the temperature constant for 0.5h, and then raise the temperature to 500°C at a rate of 1°C/min. Under the thermal expansion effect of the superalloy, the system will self-boost to 32MPa, keep the temperature for 3h, and then naturally cool to room temperature , to obtain a hot-pressed graphene flake with a thickness of 182 μm;

(4) Place the hot-pressed graphene flakes obtained in step (3) in a high-temperature tube furnace, and perform carbonization treatment at 1200°C for 1 hour in a nitrogen atmosphere to obtain carbonized graphene flakes;

(5) Place the carbonized graphene flakes obtained in step (4) in a high-temperature graphitization furnace, and carry out graphitization treatment at 2500°C for 1.5 hours under an argon atmosphere to obtain graphitized graphene flakes;

After testing, the graphitized graphene flake obtained above has a bulk density of 1.447g/cm ³ , a plane thermal conductivity of 377W/m·K, and an axial thermal conductivity of 1.20W/m·K; the maximum tensile strength of the graphitized graphene flake is The tensile stress can reach 8.27MPa, and the deformation is 1.13%.

Example 4

A kind of preparation method of graphene thermally conductive sheet, specifically comprises the steps:

(1) Without adding pitch powder, add 0.5g of graphene nanosheet powder into absolute ethanol, ultrasonically treat at 100W, 40KHz for 1h, filter with suction, and dry at 70°C;

Dehydrated alcohol consumption, by graphene powder: dehydrated alcohol is the ratio calculation of 1g:450mL; Described graphene powder is made by catalytic oxidation multiple intercalation exfoliation technology;

(2) Import the powder obtained in step (1) into the mold, adjust the pressure of the hydraulic press to 20 MPa, and the time is 5 minutes, and directly cold-press the powder into thin slices;

(3) The cold-pressed sheet obtained in step (2) is sandwiched between superalloy molds with smooth surfaces and placed in a tube furnace. The piston of the hydraulic press is in a nitrogen atmosphere when it contacts the upper surface of the mold but does not apply pressure. , with a heating rate of 5°C/min, the temperature is raised to 450°C, and the temperature is kept constant for 1.5 hours, and then the temperature is raised to 500°C at a heating rate of 1°C/min. After that, then naturally cool to room temperature to obtain a hot-pressed graphene sheet with a thickness of 198 μm;

(4) Place the hot-pressed graphene flakes obtained in step (3) in a high-temperature tube furnace, and perform carbonization treatment at 1000°C for 3 hours in a nitrogen atmosphere to obtain carbonized graphene flakes;

(5) Place the carbonized graphene flakes obtained in step (4) in a high-temperature graphitization furnace, and perform graphitization treatment at 2700°C for 1 hour under an argon atmosphere to obtain graphitized graphene flakes;

After testing, the graphitized graphene flake obtained above has a volume density of 1.329g/cm ³ , a plane thermal conductivity of 300W/m·K, and an axial thermal conductivity of 1.20W/m·K; the maximum tensile strength of the graphitized graphene flake is The tensile stress can reach 7.76MPa, and the deformation is 1.16%.

Example 5

A kind of preparation method of graphene thermally conductive sheet, specifically comprises the steps:

(1) Mix 0.5g of graphene nanosheet powder and 0.04g of high softening point coal tar pitch powder, add to absolute ethanol, ultrasonicate at 100W, 40KHz for 1h, filter with suction, and dry at 70°C to obtain mixed powder;

Dehydrated alcohol consumption, by graphene powder: dehydrated alcohol is the ratio calculation of 1g:350mL; Described graphene powder is made by catalytic oxidation multiple intercalation exfoliation technology;

(2) Import the mixed powder obtained in step (1) into the mold, adjust the pressure of the hydraulic press to 15 MPa, and the time is 3 minutes, and directly cold press the mixed powder into thin slices;

(3) The cold-pressed sheet obtained in step (2) is sandwiched between superalloy molds with smooth surfaces and placed in a tube furnace. The piston of the hydraulic press is in a nitrogen atmosphere when it contacts the upper surface of the mold but does not apply pressure. , with a heating rate of 3 °C/min, the temperature is raised to 450 °C, and the temperature is maintained for 1 hour, and then the temperature is raised to 800 °C with a heating rate of 5 °C/min. , and then naturally cooled to room temperature to obtain a hot-pressed graphene sheet with a thickness of 211 μm;

(4) Place the hot-pressed graphene flakes obtained in step (3) in a high-temperature tube furnace, and perform carbonization treatment at 1200°C for 3 hours in a nitrogen atmosphere to obtain carbonized graphene flakes;

(5) Place the carbonized graphene flakes obtained in step (4) in a high-temperature graphitization furnace, and carry out graphitization treatment at 2300°C for 1.5 hours under an argon atmosphere to obtain graphitized graphene flakes;

After testing, the graphitized graphene flake obtained above has a volume density of 1.411g/cm ³ , a plane thermal conductivity of 369W/m·K, and an axial thermal conductivity of 0.98W/m·K; the maximum tensile strength of the graphitized graphene flake is The tensile stress can reach 9.56MPa, and the deformation is 1.19%.

Example 6

A kind of preparation method of graphene thermally conductive sheet, specifically comprises the steps:

(1) Mix 0.5g of graphene nanosheet powder and 0.01g of high softening point coal tar pitch powder, add to absolute ethanol, ultrasonicate at 100W, 40KHz for 1h, filter with suction, and dry at 70°C to obtain mixed powder;

Dehydrated alcohol consumption, by graphene powder: dehydrated alcohol is the ratio calculation of 1g:400mL; Described graphene powder is made by catalytic oxidation multiple intercalation exfoliation technology;

(2) Import the mixed powder obtained in step (1) into the mold, adjust the pressure of the hydraulic press to 18MPa, and the time is 3min, and directly cold press the mixed powder into thin slices;

(3) Place the cold-pressed sheet obtained in step (2) between superalloy molds with smooth surfaces, place it in a tube furnace, and apply a pressure of 5 MPa with a hydraulic press. Heating rate: raise the temperature to 450°C, keep the temperature constant for 1.5h, and then increase the temperature to 600°C at a rate of 4°C/min. Under the thermal expansion effect of the superalloy, the system will self-boost to 34MPa, keep the temperature for 2h, and then naturally cool to room temperature , to obtain a hot-pressed graphene flake with a thickness of 179 μm;

(4) Place the hot-pressed graphene flakes obtained in step (3) in a high-temperature tube furnace, and perform carbonization treatment at 1000°C for 1 hour in a nitrogen atmosphere to obtain carbonized graphene flakes;

(5) Place the carbonized graphene flakes obtained in step (4) in a high-temperature graphitization furnace, and perform graphitization treatment at 2500°C for 2 hours under an argon atmosphere to obtain graphitized graphene flakes;

After testing, the graphitized graphene flake obtained above has a volume density of 1.331g/cm ³ , a plane thermal conductivity of 330W/m·K, and an axial thermal conductivity of 0.98W/m·K; the maximum tensile strength of the graphitized graphene flake is The tensile stress can reach 8.31MPa, and the deformation is 1.18%.

Example 7

A kind of preparation method of graphene thermally conductive sheet, specifically comprises the steps:

(1) Mix 0.5g of graphene nanosheet powder and 0.03g of high softening point coal tar pitch powder, add to absolute ethanol, ultrasonically treat at 100W, 40KHz for 1h, filter with suction, and dry at 70°C to obtain mixed powder;

Dehydrated alcohol consumption, by graphene powder: dehydrated alcohol is the ratio calculation of 1g:500mL; Described graphene powder is made by catalytic oxidation multiple intercalation exfoliation technology;

(2) Import the mixed powder obtained in step (1) into the mold, adjust the pressure of the hydraulic press to 20 MPa, and the time is 5 minutes, and directly cold-press the mixed powder into thin slices;

(3) The cold-pressed sheet obtained in step (2) is sandwiched between superalloy molds with smooth surfaces and placed in a tube furnace. The piston of the hydraulic press is in a nitrogen atmosphere when it contacts the upper surface of the mold but does not apply pressure. , with a heating rate of 3°C/min, the temperature is raised to 420°C, and the temperature is kept constant for 0.5h, and then the temperature is raised to 500°C at a heating rate of 1°C/min. After that, then naturally cool to room temperature to obtain a hot-pressed graphene sheet with a thickness of 208 μm;

(4) Place the hot-pressed graphene flakes obtained in step (3) in a high-temperature tube furnace, and perform carbonization treatment at 900°C for 1 hour in a nitrogen atmosphere to obtain carbonized graphene flakes;

(5) Place the carbonized graphene flakes obtained in step (4) in a high-temperature graphitization furnace, and perform graphitization treatment at 2500°C for 2 hours under an argon atmosphere to obtain graphitized graphene flakes;

After testing, the graphitized graphene flake obtained above has a volume density of 1.374g/cm ³ , a plane thermal conductivity of 388W/m·K, and an axial thermal conductivity of 0.96W/m·K; the maximum tensile strength of the graphitized graphene flake is The tensile stress can reach 10.56MPa, and the deformation is 1.20%.

Example 8

A kind of preparation method of graphene thermally conductive sheet, specifically comprises the steps:

(1) Mix 0.5g of graphene nanosheet powder and 0.04g of high softening point coal tar pitch powder, add to absolute ethanol, ultrasonicate at 100W, 40KHz for 1h, filter with suction, and dry at 70°C to obtain mixed powder;

Dehydrated alcohol consumption, by graphene powder: dehydrated alcohol is the ratio calculation of 1g:400mL; Described graphene powder is made by catalytic oxidation multiple intercalation exfoliation technology;

(2) Import the mixed powder obtained in step (1) into the mold, adjust the pressure of the hydraulic press to 20MPa, and the time is 3min, and directly cold press the mixed powder into thin slices;

(3) Place the cold-pressed sheet obtained in step (2) between high-temperature alloy molds with smooth surfaces, place it in a tube furnace, and apply a pressure of 3 MPa with a hydraulic press. Heating rate: raise the temperature to 420°C, keep the temperature constant for 1.5h, and then increase the temperature to 600°C at a rate of 5°C/min. Under the thermal expansion effect of the superalloy, the system will self-boost to 30MPa, keep the temperature for 1h, and then naturally cool to room temperature , to obtain a hot-pressed graphene sheet with a thickness of 209 μm;

(4) Place the hot-pressed graphene flakes obtained in step (3) in a high-temperature tube furnace, and perform carbonization treatment at 900°C for 1 hour in a nitrogen atmosphere to obtain carbonized graphene flakes;

(5) Place the carbonized graphene flakes obtained in step (4) in a high-temperature graphitization furnace, and perform graphitization treatment at 2500°C for 2 hours under an argon atmosphere to obtain graphitized graphene flakes;

After testing, the graphitized graphene flake obtained above has a volume density of 1.407g/cm ³ , a plane thermal conductivity of 358W/m·K, and an axial thermal conductivity of 0.89W/m·K; the maximum tensile strength of the graphitized graphene flake is The tensile stress can reach 9.03MPa, and the deformation is 1.23%.

Embodiment 9 A kind of preparation method of graphene nanosheet powder

Measure 96mL of concentrated sulfuric acid and place it in a dry round bottom flask, add 2g of sodium nitrate to it, stir to dissolve the sodium nitrate, then add 2g of flake graphite, after the flake graphite is evenly dispersed, slowly add 12g of potassium permanganate, the reaction is 1.45 h, use an ice bath to keep the system at 0~5°C throughout the process, then raise the temperature to 35°C for 2 hours, then slowly add 80 mL of deionized water to the reaction system, react for 30 minutes, and then slowly add 200 mL of deionized water, Then 10 mL of H ₂ O ₂ was added, and the reaction was continued for 10 min. The obtained reaction liquid was suction filtered while it was hot, and the obtained filter cake was washed with 1000 mL of 5% HCl aqueous solution to remove metal ions. Then add an appropriate amount of deionized water to the filter cake, stir evenly, and then perform centrifugal washing until the pH of the colloid is neutral, and ultrasonically for 10 minutes to obtain the graphene oxide colloid;

Take 40mL of 1.5mg/mL graphene oxide colloid in a polytetrafluoroethylene container, add ammonia water to adjust the pH to 11, slowly add 0.6g of 50% hydrazine hydrate solution under stirring, and then place the container in a microwave oven with a power of 800W for Microwave; 20s microwave heating, 20s take out and stir for 1 cycle, repeat the operation for 5 cycles, then filter with suction, and freeze-dry at -50°C and 1Pa vacuum to obtain graphene nanosheet powder.

Claims (7)

1. a preparation method of graphene thermally conductive sheet, is characterized in that comprising the steps: 1) Weigh the graphene nanosheet powder and the high softening point coal tar pitch powder according to the mass ratio, the mass ratio of the graphene nano sheet powder and the high softening point coal tar pitch powder is 5:0~0.5, and the graphene nanosheet powder The powder is mixed with high softening point coal tar pitch powder, then added to absolute ethanol for 0.5~2h ultrasonic, suction filtered, and dried to obtain the mixed powder; the amount of absolute ethanol is based on graphene powder: absolute ethanol Calculated for the ratio of 1g:350~500mL; 2) Import the mixed powder obtained in step (1) into the mold, adjust the pressure of the hydraulic press to 15~20MPa, and the time is 3~5min, and directly cold press the mixed powder into thin slices; 3) The cold-pressed sheet obtained in step (2) is sandwiched between superalloy molds with smooth surfaces, placed in a tube furnace, and a pressure of 0 to 5 MPa is applied by a hydraulic press in an atmosphere of nitrogen, argon or helium. Under any atmosphere, raise the temperature to 420~450℃ at a heating rate of 3~5℃/min, keep the temperature constant for 0.5~1.5h, and then raise it to 500~800℃ at a heating rate of 1~5℃/min. Under the thermal expansion effect of the superalloy, the system is boosted to 21~34MPa, kept at a constant temperature for 1~3h, and then naturally cooled to room temperature to obtain a hot-pressed graphene sheet; the thickness of the hot-pressed graphene sheet is 179~211μm. 2. The preparation method of graphene thermally conductive flakes as claimed in claim 1, characterized in that: the hot-pressed graphene flakes obtained in step (3) are placed in a high-temperature tube furnace, and heated in nitrogen, argon or helium Under any atmosphere in the atmosphere, carry out carbonization treatment at 900~1200℃ for 1~3h to obtain carbonized graphene flakes. 3. the preparation method of graphene thermally conductive sheet as claimed in claim 2 is characterized in that: the carbonized graphene sheet of gained is placed in high-temperature graphitization furnace, adopts any one in nitrogen, argon or helium atmosphere Under the atmosphere, graphitize at 2300~2700°C for 0.5~2h to obtain graphitized graphene flakes. 4. the preparation method of graphene thermally conductive sheet as claimed in claim 1, is characterized in that: described graphene nano sheet powder is prepared by following method: 1) Measure a certain amount of concentrated sulfuric acid and place it in a reaction container, add sodium nitrate to it, stir to dissolve the sodium nitrate, then add flake graphite, after the flake graphite is evenly dispersed, slowly add potassium permanganate to react, the whole The process uses an ice bath to keep the system at 0~5°C for 1~2h, then raise the temperature to 30~45°C for 1~3 hours, then slowly add the first batch of deionized water to the reaction system, and react for 20~40min. Then slowly add the second batch of deionized water, and then add H ₂ O ₂ , and continue the reaction for 5-20 minutes. The obtained reaction solution is suction filtered while it is hot, and the obtained filter cake is washed with HCl aqueous solution with a mass percentage concentration of 3-10%. washing to remove metal ions; 2) Then add deionized water to the filter cake, stir evenly, and then carry out centrifugal washing until the pH of the colloid is neutral, and ultrasonically for 5-15 minutes to obtain graphene oxide colloid; 3) Take the graphene oxide colloid in a polytetrafluoroethylene container, add ammonia water to adjust the pH to 11, slowly add a hydrazine hydrate solution with a mass percentage concentration of 30-60% under stirring, and the mass of the graphene oxide colloid and hydrazine hydrate solution The ratio is 1:8~12, and then carry out microwave treatment; 20s microwave heating, 20s take out and stir as 1 cycle, repeat the operation for 3~8 cycles, then suction filter, freeze-dry to obtain graphene nanosheet powder. 5. The preparation method of graphene heat-conducting sheet as claimed in claim 4, characterized in that: the mass percent concentration of the concentrated sulfuric acid is 60-98%. 6. the preparation method of graphene thermally conductive sheet as claimed in claim 4 is characterized in that: the vitriol oil, sodium nitrate, flake graphite, potassium permanganate, the first batch of deionized water, the second batch of deionized water, H The material ratio of ₂ O ₂ and HCl aqueous solution is 96mL: 2g: 2g: 12g: 80mL: 200mL: 10mL: 1000mL. 7. The preparation method of graphene thermally conductive flakes as claimed in claim 1, characterized in that: the high softening point coal tar pitch powder described in step (1) has a softening point of 270~300°C, and a TI content of 50~300°C. 70%, QI content is 10~30%, pass through 150~300 mesh sieve.