CN112477181A - Construction method of graphene-based thermal interface material with mutually perpendicular structure - Google Patents
Construction method of graphene-based thermal interface material with mutually perpendicular structure Download PDFInfo
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Abstract
The invention discloses a construction method of a graphene-based thermal interface material with mutually vertical structures, which is characterized in that in order to realize the mutually vertical arrangement of graphene sheet layers, a flat plate is utilized to perform unidirectional freezing to introduce a temperature gradient, under the driving action of the gradient, the graphene sheets can realize the highly directional arrangement in the vertical direction, pre-reduced graphene hydrogel forms a bottom parallel structure under the induction of gravity and a container bottom, the upper part of the pre-reduced graphene hydrogel is maintained to be vertically arranged, and the bottom parallel structure and the upper part of the pre-reduced graphene hydrogel are maintained to be vertically arranged under the subsequent reduction. The prepared graphene macroscopic body has a special oriented structure with the bottom parallel and the upper part vertical, can give full play to the excellent performance of graphene in the plane direction, solves the problems of local hot spots and heat conduction at an interface, and can be applied to the field of thermal management as a thermal interface material.
Description
Technical Field
The invention belongs to the field of thermal interface materials, relates to a construction method of a high-performance thermal interface material, and particularly relates to a construction method of a graphene-based thermal interface material with a mutually vertical structure.
Background
The electronic equipment generates heat in the operation process, the normal operation of the equipment is influenced by the temperature rise, the service life of the equipment is shortened, and potential safety hazards exist, so that the effective heat dissipation is very important to the normal operation of the electronic equipment. Because of the micron-scale grooves on any surface, when two solid surfaces (typically the device and heat sink surfaces for electronic products) are in contact with each other, the effective contact area is less than 1%, these tiny gaps are filled with air, which is a poor conductor of heat and has a thermal conductivity of only 0.22W m-1K-1Preventing effective heat transfer between the two interfaces. The Thermal Interface Material (TIM) fills the gap, and its high thermal conductivity improves the heat conversion rate to reach the thermal balance, and improves the effective heat conduction of the interface. Graphene as a two-dimensional material has natural advantages for building macroscopic bodies, and single-layer graphene is known to have the highest thermal conductivity, about 5000W m-1K-1Meanwhile, the material has the characteristics of low thermal expansion coefficient, low contact resistance with a base material, large specific surface area, excellent mechanical property and the like, and the characteristics make the material become an ideal material for manufacturing TIM.
Graphene has ultra-high in-plane thermal conductivity, and thus application of graphene in TIM typically arranges it in a vertical orientation, thereby taking advantage of its in-plane thermal conductivity to conduct heat from a heat source to a heat sink material. However, one of the inevitable problems in this case is that the thermal conductivity in the TIM parallel direction is very poor (graphene out-of-plane thermal conductivity is very low), which severely affects the temperature spread (temperature equalization) of the hot spot. Therefore, if the graphene in the thin layer area contacted with the hot spot is designed to be arranged in parallel, the purpose of quickly equalizing the temperature is achieved, and meanwhile, the graphene on the upper part is vertically arranged, so that the diffused heat is effectively conducted to the radiator. The TIM with the upper part vertically arranged and the lower part arranged in parallel can effectively avoid overheating of local hot spots and effectively transfer heat, and is a relatively ideal thermal interface material. However, the existing TIM preparation methods are unable to prepare such materials with special structures.
Disclosure of Invention
In order to realize parallel arrangement of the bottom parts and vertical arrangement of the upper parts of the graphene, the invention provides a construction method of a graphene-based thermal interface material with a mutually vertical structure. In order to realize the mutually vertical arrangement of graphene sheet layers, a temperature gradient is introduced by utilizing flat plate one-way freezing, under the driving action of the gradient, the graphene sheets can realize the highly directional arrangement in the vertical direction, the pre-reduced graphene hydrogel forms a bottom parallel structure under the induction of gravity and the bottom of a container, the upper part of the pre-reduced graphene hydrogel is maintained to be vertically arranged, and the bottom parallel structure and the upper part of the pre-reduced graphene hydrogel are maintained to be vertically arranged under the subsequent reduction.
The purpose of the invention is realized by the following technical scheme:
a construction method of a graphene-based thermal interface material with a mutually vertical structure comprises the following steps:
the method comprises the following steps: and (3) placing the graphene oxide solution in a freezing mould, fully mixing the graphene oxide solution with a reducing agent and an organic solvent for promoting orientation, and then carrying out pre-reduction treatment.
In this step, the reducing agent is ascorbic acid, and may also be other reducing agents that promote gelation, such as potassium hydroxide, hydroiodic acid, hydrazine hydrate, sodium borohydride, and the like.
In this step, the organic solvent for promoting orientation is methanol, ethanol or other organic solvent.
In the step, the mixed solution needs to be subjected to pre-reduction treatment before the ice template is positioned, the pre-reduction degree is that the liquid has viscosity but does not flow, and the formation of a directional structure in the freezing process is ensured.
In the step, the thermal conductivity of the bottom of the freezing mould is 5-400W m-1K-1The side wall thermal conductivity of the metal (2) is 0.01-2W m-1K-1Is used as a base polymer.
In the step, the time of the pre-reduction treatment is controlled within 1-3 h.
In the step, the mass ratio of the graphene oxide to the reducing agent to the organic solvent is 40-60: 100: 1.
Step two: after pre-reduction, the mixed solution is subjected to thermal equilibrium.
In the step, heat balance treatment is carried out for 1-10 h at the temperature of 5-15 ℃.
Step three: and (4) placing the mixed solution after heat balance into a freezing device for directional freezing.
In this step, refrigerating plant includes cold source, freezing container, cold liquid, freezing mould, wherein: a uniform cooling liquid is arranged between the freezing container and the freezing mould; the cold source can be liquid nitrogen, the solution such as ethanol and the like is used as soaking solution in a stainless steel container, the freezing speed is controlled by controlling the using amount of the liquid nitrogen, or the freezing speed is adjusted by changing the heat conductivity of the material at the bottom of the freezing mould, and the cold source can also be other refrigerating fluid or any refrigerating material or device such as a semiconductor refrigerating plate and the like; the cold source can be a refrigerating device such as liquid nitrogen, a semiconductor refrigerating plate and the like; the cold homogenizing liquid can be organic solvent with low freezing point (below-40 deg.C) such as methanol and ethanol; the bottom of the freezing mould can be made of silver, copper, aluminum, stainless steel and the like with the thermal conductivity of 10-400 Wm-1K-1The side wall of the material is made of a material with the thermal conductivity of 0.1-5 Wm-1K-1The low thermal conductivity polymer can be silica gel, epoxy resin, acrylic plate, etc.
In the step, liquid nitrogen is used for directional freezing at normal temperature.
Step four: and thawing the frozen sample, and heating the sample under the air condition after completely thawing the sample to convert the sample into hydrogel.
In the step, the unfrozen sample is heated for 2-4 hours at 50-70 ℃ in air, so that the oriented structure is ensured to be maintained, and the preforming degree is that the surface of the sample is pressed to deform but is not sticky.
Step five: and cooling the hydrogel to room temperature, carrying out thermal equilibrium, and then placing the hydrogel in a freezing device for secondary directional freezing to strengthen the structural orientation.
In this step, directional freezing is performed under the same freezing conditions as in the third step, to further strengthen the directional structure.
In this step, the heat balance is performed under the same heat balance conditions as in the second step.
Step six: after the twice-frozen sample is completely thawed, heating is carried out under the air condition, so that the hydrogel is completely formed.
In the step, the unfrozen sample is reacted for 3-4 hours at 50-60 ℃ in air to completely form hydrogel.
Step seven: and cooling the completely formed hydrogel to room temperature, and freezing the hydrogel in a refrigerator to improve the mechanical property of the hydrogel.
In the step, the hydrogel is frozen at the temperature of between 20 ℃ below zero and 30 ℃ below zero for about 4 hours generally so as to strengthen the strength of the skeleton structure.
Step eight: and unfreezing the frozen hydrogel, and heating under an air condition to further reduce the graphene oxide hydrogel.
In the step, the unfrozen hydrogel is subjected to reduction in air at the temperature of 50-90 ℃, and the reduction time is 8-12 hours.
Step nine: and washing the reduced hydrogel for several times by using deionized water, removing the internal solution, and heating and drying to finally obtain the graphene aerogel with the mutually vertical structures.
In the step, the hydrogel cleaned by the deionized water is dried for about 5-10 hours at 50-70 ℃ in the air, and finally the oriented structure with the parallel bottom and the vertical upper part is obtained.
Step ten: under vacuum or inert atmosphere, the graphene aerogel is subjected to high-temperature treatment at 1000-3000 ℃, the heat is preserved for about 2 hours, and the crystallinity of the aerogel is further improved, so that the heat conductivity is improved.
Step eleven: and completely pouring the high-thermal-conductivity polymer into the graphene aerogel by adopting a method combining the positive pressure applied to the upper part and the vacuum negative pressure applied to the lower part, and curing to obtain the graphene-based thermal interface material with the mutually vertical structure.
In the step, when the polymer is poured, the upper part of the special mould is pressurized, the lower part of the special mould is vacuumized, and the polymer is completely filled into the aerogel framework under the working effect of vacuum negative pressure and external positive pressure. Wherein, the vacuum degree is lower than-1 Pa, and the external pressure can be 0.01M-0.8 MPa; the high heat-conducting polymer can be polymer such as epoxy resin, phase-change material, silica gel material and the like.
On the basis of an ice template method, graphene sponge macroscopic bodies with parallel arrangement at the bottom and vertical arrangement at the upper part are prepared by utilizing chemical reduction and shaping and combining two times of directional freeze casting, and the graphene sponge macroscopic bodies are immersed in a heat-conducting base material to obtain the high-efficiency thermal interface material. The key point of the preparation method is that graphene oxide with different reduction degrees is utilized, the liquid crystallinity of the graphene oxide is changed, and the preparation of the graphene sponge with the mutual structure is realized by combining external drive with an ice template method.
Compared with the prior art, the invention has the following advantages:
1. the present invention can control the freezing rate by controlling the content of liquid nitrogen used for freezing.
2. The invention can dry the water condensation under the air condition, thereby avoiding the conventional freeze drying and simplifying the preparation.
3. The invention can prepare samples with different sizes by designing moulds with different sizes, and can realize the preparation of large-size samples.
4. According to the invention, an upward temperature gradient is provided for the sample through the cold source (directional arrangement in the Z-axis direction is realized), the liquid crystallinity of the pre-reduced graphene oxide is changed, the mobility is poor, and a vertical structure can be maintained. And the bottom is influenced by gravity, walls and the like to form a parallel structure. Therefore, a special orientation structure with a parallel bottom and a vertical upper part is creatively prepared. As shown in fig. 1, a structure with parallel bottoms (high in-plane thermal conductivity) can play a good role in heat equalization, so that the heat of a heat source is rapidly spread, and the damage of local overheating to a device is avoided; while a vertical structure (high thermal conductivity in the vertical direction) can quickly transfer the spread heat to a heat dissipation system. Therefore, the mutually perpendicular graphene-based thermal interface material has excellent interface thermal diffusion and conduction performance.
5. The method utilizes the change of the liquid crystallinity of the graphene oxide with different reduction degrees, combines an ice template method to realize the oriented arrangement of the graphene oxide sheets, and utilizes chemical reduction molding to maintain the oriented structure. The prepared graphene macroscopic body has a special oriented structure with the bottom parallel and the upper part vertical, can give full play to the excellent performance of graphene in the plane direction, solves the problems of local hot spots and heat conduction at an interface, and can be applied to the field of thermal management as a thermal interface material.
Drawings
Fig. 1 is a schematic thermal conduction diagram of a graphene-based thermal interface material, left: current graphene-based thermal interface materials, right: the graphene-based thermal interface material has a mutually perpendicular structure;
fig. 2 is a flow chart of graphene aerogel preparation with mutually perpendicular structures;
fig. 3 is a schematic view of a graphene aerogel preparation apparatus having a mutually perpendicular structure;
fig. 4 is a physical diagram of the graphene aerogel prepared in example 1;
FIG. 5 is an overall SEM photograph of a sample of example 1, wherein (a) and (b) are SEM photographs in both the vertical direction and the horizontal direction;
FIG. 6 is a partial SEM photograph of a sample of example 2-3;
in the figure, 1: heat source, 2: heat flow, 3: cold source, 4: freezing container, 5: freezing mold, 6: cooling the liquid.
Detailed Description
The technical solutions of the present invention are further described below with reference to the following examples, but the present invention is not limited thereto, and any modifications or equivalent substitutions may be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention.
Example 1
The embodiment provides a preparation method of a mutually perpendicular graphene aerogel, as shown in fig. 1, the method comprises the following specific steps:
1) preparing a graphene oxide dispersion liquid: weighing 4g of flake graphite, placing the flake graphite in a beaker, pouring 450ml of concentrated sulfuric acid and 50ml of phosphoric acid into the beaker to prepare a mixed solution I, and stirring the mixed solution I at room temperature for 40 min. And (3) placing the beaker in a water bath for heating in the water bath, adding 18g of potassium permanganate into the mixed solution I respectively for 8 times to obtain a mixed solution II, heating the mixed solution II at a constant temperature of 70 ℃, taking out the mixed solution II after 16 hours, and cooling the mixed solution at room temperature. And after cooling to room temperature, slowly pouring the mixed solution II into 700ml of hydrogen peroxide mixed ice water, standing for 24h, filtering out the supernatant, taking the lower layer solution, and performing centrifugal washing to obtain the high-concentration graphene oxide solution. And finally, dispersing the washed high-concentration graphene oxide solution in deionized water to obtain a graphene oxide dispersion liquid with the concentration of 20mg/mL for later use. And (3) placing the prepared graphene oxide dispersion liquid in an environment of 11 ℃ for heat balance. The preparation method of 700ml of hydrogen peroxide mixed ice water comprises the steps of dissolving 6ml of hydrogen peroxide solution with the mass fraction of 30% in water to form 700ml of mixed solution III, and placing the mixed solution III in a refrigerator in a subzero environment to be frozen to obtain the hydrogen peroxide mixed ice water.
2) Pre-reducing a graphene oxide solution: putting 50g of graphene oxide dispersion liquid with the concentration of 20mg/ml in a beaker, adding 2g of ascorbic acid in the beaker, manually stirring for 10min, putting the mixed solution in a vacuum device, vacuumizing, maintaining the pressure for 15min under the vacuum degree of-0.1 MPa, repeating for 3 times, putting the mixed solution in a room-temperature environment, standing for 2h, and carrying out pre-reduction treatment on the graphene oxide solution until the liquid has no fluidity.
3) And (3) placing the pre-reduced graphene oxide solution in an environment at 9 ℃ for 1h for heat balance.
4) After the removal, the assembly was ordered in a freezer. The distance between the liquid level of the liquid nitrogen and the top of the container is 4cm, and the freezing time is controlled to be 20 min. The refrigerating device comprises a cold source, a refrigerating container and a refrigerating mold, wherein the cold source is a heat-insulating polyethylene container, and liquid nitrogen is filled in the refrigerating container; the freezing container is a stainless steel container, and organic solvents such as ethanol and the like are filled in the freezing container to be used as soaking solution; the bottom of the freezing mold is a 13 × 1cm aluminum plate, the side wall of the freezing mold is a square silica gel frame with the width of 1cm and the thickness of 1.5cm, and the external length of the frame is 9 cm.
5) Unfreezing the frozen graphene oxide ice crystal mixture at room temperature, completely unfreezing, performing preforming treatment for 1.5h in air at 60 ℃, and taking out the sample when the sample is in a jelly shape and no hand sticking phenomenon exists during pressing.
6) After cooling to room temperature, the sample is put into an environment at 9 ℃ for heat balance for 1 hour, and secondary directional freezing is carried out after balance.
7) And unfreezing the secondarily frozen sample, and reacting for 4 hours at the temperature of 60 ℃ in air until the sample is molded.
8) And cooling the molded sample to room temperature, freezing the molded sample in a refrigerator at the temperature of-30 ℃, and performing skeleton reinforcement treatment for 3 hours.
9) And taking out and unfreezing the completely frozen sample, transferring the sample into other containers from the mold after completely unfreezing, adding 10ml of deionized water, and reacting for 5 hours at 60 ℃ in air and for 6 hours at 80 ℃ in air to obtain the reduced graphene oxide hydrogel.
10) And (3) washing and drying the hydrogel: and cooling the reduced graphene oxide hydrogel, adding 50ml of deionized water for soaking and washing, heating the solution during washing at the heating temperature of 65 ℃, soaking for 15min, washing for 4 times, taking out the hydrogel, and heating and drying in a 60 ℃ forced air drying oven to obtain the oriented graphene aerogel with the parallel bottom and the vertical upper part (figure 4).
11) The aerogel is treated at 3000 ℃ under the protection of nitrogen.
12) Placing the aerogel in a pouring mold, pouring AB type epoxy resin (the mass ratio of the epoxy resin to the curing agent is 3: 1) and applying pressure of 0.8MPa to the upper part, vacuumizing the lower part, and curing at 60 ℃ for 12 hours after complete filling to obtain the graphene reinforced resin-based thermal interface composite material.
Fig. 5 is an overall SEM image of the graphene aerogel having the mutually perpendicular structure prepared in this example. As can be seen from fig. 5, the present embodiment produces an oriented structure with parallel bottom and vertical top, and the oriented structure is long-range ordered.
The thermal conductivity of the thermal interface material prepared in the embodiment is tested, and the thermal conductivity in the vertical direction can reach 12W/m.K, which is 2-3 times that of the existing commercial thermal interface material. The thermal interface material obtained by the embodiment has a plane temperature difference 2-3 ℃ lower than that of a commercial thermal interface material and shows excellent soaking and heat conducting performances when placed at a heat source with the same power.
Example 2
The embodiment provides a preparation method of a mutually perpendicular graphene aerogel, as shown in fig. 1, the method comprises the following specific steps:
1) preparing a graphene oxide dispersion liquid: weighing 4g of flake graphite, placing the flake graphite in a beaker, pouring 450ml of concentrated sulfuric acid and 50ml of phosphoric acid into the beaker to prepare a mixed solution I, and stirring the mixed solution I at room temperature for 40 min. And (3) placing the beaker in a water bath for heating in the water bath, adding 18g of potassium permanganate into the mixed solution I respectively for 8 times to obtain a mixed solution II, heating the mixed solution II at a constant temperature of 70 ℃, taking out the mixed solution II after 16 hours, and cooling the mixed solution at room temperature. And after cooling to room temperature, slowly pouring the mixed solution II into 700ml of hydrogen peroxide mixed ice water, standing for 24h, filtering out the supernatant, taking the lower layer solution, and performing centrifugal washing to obtain the high-concentration graphene oxide solution. And finally, dispersing the washed high-concentration graphene oxide solution in deionized water to obtain a graphene oxide dispersion liquid with the concentration of 20mg/mL for later use. And (3) placing the prepared graphene oxide dispersion liquid in an environment of 11 ℃ for heat balance. The preparation method of 700ml of hydrogen peroxide mixed ice water comprises the steps of dissolving 6ml of hydrogen peroxide solution with the mass fraction of 30% in water to form 700ml of mixed solution III, and placing the mixed solution III in a refrigerator in a subzero environment to be frozen to obtain the hydrogen peroxide mixed ice water.
2) Pre-reducing a graphene oxide solution: putting 50g of graphene oxide dispersion liquid with the concentration of 20mg/ml in a beaker, adding 2g of ascorbic acid in the beaker, manually stirring for 10min, putting the mixed solution in a vacuum device, vacuumizing, maintaining the pressure for 15min under the vacuum degree of-0.1 MPa, repeating for 3 times, putting the mixed solution in a room-temperature environment, standing for 2h, and carrying out pre-reduction treatment on the graphene oxide solution until the liquid has no fluidity.
3) And (3) placing the pre-reduced graphene oxide solution in an environment at 11 ℃ for 1h for heat balance.
4) After the removal, the assembly was ordered in a freezer. The distance between the liquid level of the liquid nitrogen and the top of the container is 6cm, and the freezing time is controlled to be 50 min.
5) Unfreezing the frozen graphene oxide ice crystal mixture at room temperature, completely unfreezing, performing preforming treatment for 1.5h in air at 60 ℃, and taking out the sample when the sample is in a jelly shape and no hand sticking phenomenon exists during pressing.
6) After cooling to room temperature, the sample is put into an environment at 12 ℃ for heat balance for 1 hour, and secondary directional freezing is carried out after balance.
7) And unfreezing the secondarily frozen sample, and reacting for 4 hours at the temperature of 60 ℃ in air until the sample is molded.
8) And cooling the molded sample to room temperature, freezing in a refrigerator at-25 ℃, and performing skeleton reinforcement treatment for 3 h.
9) And taking out and unfreezing the completely frozen sample, transferring the sample into other containers in a mold after the sample is completely unfrozen, adding 10ml of deionized water, and reacting for 5 hours at 60 ℃ in air and for 6 hours at 80 ℃ in air to obtain the reduced graphene oxide hydrogel.
10) And (3) washing and drying the hydrogel: and cooling the reduced graphene oxide hydrogel, adding 50ml of deionized water for soaking and washing, heating the solution during washing at the heating temperature of 65 ℃, soaking for 15min, washing for 4 times, taking out the hydrogel, and heating and drying in a 60 ℃ forced air drying oven to obtain the oriented graphene aerogel with the parallel bottom and the vertical upper part.
11) The aerogel is treated at 2000 ℃ under the protection of nitrogen.
12) Placing the aerogel in a pouring mold, pouring AB type epoxy resin (the mass ratio of the epoxy resin to the curing agent is 3: 1) and applying pressure of 0.8MPa to the upper part, vacuumizing the lower part, and curing for 12 hours at 60 ℃ after complete filling to obtain the graphene reinforced resin-based thermal interface composite material.
Fig. 6(a) - (b) show SEM images of the obtained orientation structure prepared in this embodiment, and it can be seen from the SEM images that, under the combination of chemical reduction and ice template, the orientation structure prepared in this embodiment has a structure with a bottom parallel to and an upper vertical to the orientation structure, and the obtained graphene aerogel can be used as a thermal interface material interface to solve the problems of local hot spots at the interface and thermal conduction between interfaces.
The thermal conductivity of the thermal interface material prepared in the embodiment is tested, and the thermal conductivity in the vertical direction can reach 8W/m.K, which is 1.5-2 times that of the existing commercial thermal interface material. The thermal interface material obtained by the embodiment has a plane temperature difference 2-3 ℃ lower than that of a commercial thermal interface material and shows excellent soaking and heat conducting performances when placed at a heat source with the same power.
Example 3
The embodiment provides a preparation method of a mutually perpendicular graphene aerogel, as shown in fig. 1, the method comprises the following specific steps:
1) preparing a graphene oxide dispersion liquid: weighing 4g of flake graphite, placing the flake graphite in a beaker, pouring 450ml of concentrated sulfuric acid and 50ml of phosphoric acid into the beaker to prepare a mixed solution I, and stirring the mixed solution I at room temperature for 40 min. And (3) placing the beaker in a water bath for heating in the water bath, adding 18g of potassium permanganate into the mixed solution I respectively for 8 times to obtain a mixed solution II, heating the mixed solution II at a constant temperature of 70 ℃, taking out the mixed solution II after 16 hours, and cooling the mixed solution at room temperature. And after cooling to room temperature, slowly pouring the mixed solution II into 700ml of hydrogen peroxide mixed ice water, standing for 24h, filtering out the supernatant, taking the lower layer solution, and performing centrifugal washing to obtain the high-concentration graphene oxide solution. And finally, dispersing the washed high-concentration graphene oxide solution in deionized water to obtain a graphene oxide dispersion liquid with the concentration of 20mg/mL for later use. And (3) placing the prepared graphene oxide dispersion liquid in an environment of 11 ℃ for heat balance. The preparation method of 700ml of hydrogen peroxide mixed ice water comprises the steps of dissolving 6ml of hydrogen peroxide solution with the mass fraction of 30% in water to form 700ml of mixed solution III, and placing the mixed solution III in a refrigerator in a subzero environment to be frozen to obtain the hydrogen peroxide mixed ice water.
2) Pre-reducing a graphene oxide solution: putting 50g of graphene oxide dispersion liquid with the concentration of 20mg/ml in a beaker, adding 2g of ascorbic acid in the beaker, manually stirring for 10min, putting the mixed solution in a vacuum device, vacuumizing, maintaining the pressure for 15min under the vacuum degree of-0.1 MPa, repeating for 3 times, putting the mixed solution in a room-temperature environment, standing for 2h, and carrying out pre-reduction treatment on the graphene oxide solution until the liquid has no fluidity.
3) And (3) placing the pre-reduced graphene oxide solution in an environment at 15 ℃ for 1h for heat balance.
4) After the removal, the assembly was ordered in a freezer. The distance between the liquid level of the liquid nitrogen and the top of the container is 2cm, and the freezing time is controlled to be 10 min.
5) Unfreezing the frozen graphene oxide ice crystal mixture at room temperature, completely unfreezing, performing preforming treatment for 1.5h in air at 60 ℃, and taking out the sample when the sample is in a jelly shape and no hand sticking phenomenon exists during pressing.
6) After cooling to room temperature, the sample is put into an environment at 15 ℃ for heat balance for 1 hour, and secondary directional freezing is carried out after balance.
7) And unfreezing the secondarily frozen sample, and reacting for 4 hours at the temperature of 60 ℃ in air until the sample is molded.
8) And cooling the molded sample to room temperature, freezing in a refrigerator at-25 ℃, and performing skeleton reinforcement treatment for 3 h.
9) And taking out and unfreezing the completely frozen sample, transferring the sample into other containers in a mold after the sample is completely unfrozen, adding 10ml of deionized water, and reacting for 5 hours at 60 ℃ in air and for 6 hours at 80 ℃ in air to obtain the reduced graphene oxide hydrogel.
10) And (3) washing and drying the hydrogel: and cooling the reduced graphene oxide hydrogel, adding 50ml of deionized water for soaking and washing, heating the solution during washing at the heating temperature of 65 ℃, soaking for 15min, washing for 4 times, taking out the hydrogel, and heating and drying in a 60 ℃ forced air drying oven to obtain the oriented graphene aerogel with the parallel bottom and the vertical upper part.
11) The aerogel is treated at 1000 ℃ under the protection of nitrogen.
12) Placing the aerogel in a pouring mold, pouring AB type epoxy resin (the mass ratio of the epoxy resin to the curing agent is 3: 1) and applying pressure of 0.8MPa to the upper part, vacuumizing the lower part, and curing at 60 ℃ for 12 hours after complete filling to obtain the graphene reinforced resin-based thermal interface composite material.
Fig. 6(c) - (d) show SEM images of the obtained orientation structure prepared in this embodiment, and it can be seen from the SEM images that, under the combination of chemical reduction and ice template, the orientation structure prepared in this embodiment has a structure with a bottom parallel to and an upper vertical to the orientation structure, and the obtained graphene aerogel can be used as a thermal interface material interface to solve the problems of local hot spots at the interface and thermal conduction between interfaces.
The thermal conductivity of the thermal interface material prepared in the embodiment is tested, and the thermal conductivity in the vertical direction can reach 5W/m.K, which is 1-1.5 times of that of the existing commercial thermal interface material. The thermal interface material obtained by the embodiment has a plane temperature difference 2-3 ℃ lower than that of a commercial thermal interface material and shows excellent soaking and heat conducting performances when placed at a heat source with the same power.
Claims (10)
1. A construction method of a graphene-based thermal interface material with a mutually perpendicular structure is characterized by comprising the following steps:
the method comprises the following steps: placing the graphene oxide solution in a freezing mould, fully mixing the graphene oxide solution with a reducing agent and an organic solvent for promoting orientation, and then carrying out pre-reduction treatment, wherein the mass ratio of the graphene oxide to the reducing agent to the organic solvent is controlled to be 40-60: 100: 1;
step two: carrying out thermal equilibrium on the mixed solution after pre-reduction;
step three: placing the mixed solution after heat balance in a freezing device for directional freezing;
step four: unfreezing the frozen sample, and heating the sample under the air condition after completely unfreezing to convert the sample into hydrogel;
step five: cooling the hydrogel to room temperature, carrying out thermal equilibrium, then placing the hydrogel in a freezing device for secondary directional freezing, and enhancing the structural orientation;
step six: completely unfreezing the secondarily frozen sample, and heating under the air condition to thoroughly form the hydrogel;
step seven: cooling the completely formed hydrogel to room temperature, and freezing the hydrogel in a refrigerator to improve the mechanical property of the hydrogel;
step eight: unfreezing the frozen hydrogel, heating the frozen hydrogel under an air condition, and further reducing the graphene oxide hydrogel;
step nine: washing the reduced hydrogel with deionized water for several times, removing the internal solution, and heating and drying to obtain the graphene aerogel with mutually perpendicular structures;
step ten: carrying out high-temperature treatment on the graphene aerogel at 1000-3000 ℃ in vacuum or inert atmosphere;
step eleven: and completely pouring the high-thermal-conductivity polymer into the graphene aerogel by adopting a method combining the positive pressure applied to the upper part and the vacuum negative pressure applied to the lower part, and curing to obtain the graphene-based thermal interface material with the mutually vertical structure.
2. The method for constructing a graphene-based thermal interface material having a mutually perpendicular structure according to claim 1, wherein in the first step, the reducing agent is one of ascorbic acid, potassium hydroxide, hydroiodic acid, hydrazine hydrate, and sodium borohydride; the organic solvent is methanol, ethanol or other organic solvents; the thermal conductivity of the bottom of the freezing mould is 5-400W m-1K-1The side wall thermal conductivity of the metal (2) is 0.01-2W m-1K-1Is used as a base polymer.
3. The method for constructing a graphene-based thermal interface material having a perpendicular structure according to claim 1, wherein in the first step, the time for the pre-reduction treatment is controlled within 1 to 3 hours.
4. The method for constructing a graphene-based thermal interface material having a perpendicular structure according to claim 1, wherein in the second and fifth steps, the thermal equilibrium treatment is performed at 5 to 15 ℃ for 1 to 10 hours.
5. The method for constructing a graphene-based thermal interface material having a perpendicular structure according to claim 1, wherein in the fourth step, the thawed sample is heated at 50 to 70 ℃ for 2 to 4 hours in air.
6. The method for constructing a graphene-based thermal interface material having a mutually perpendicular structure according to claim 1, wherein in the sixth step, the thawed sample is reacted in air at 50 to 60 ℃ for 3 to 4 hours to completely form a hydrogel.
7. The method for constructing a graphene-based thermal interface material having a perpendicular structure according to claim 1, wherein in the seventh step, the hydrogel is frozen at-20 to-30 ℃.
8. The method for constructing a graphene-based thermal interface material having a perpendicular structure according to claim 1, wherein in the eighth step, the thawed hydrogel is subjected to reduction in air at 50 to 90 ℃ for 8 to 12 hours.
9. The method for constructing a graphene-based thermal interface material having a perpendicular structure according to claim 1, wherein in the ninth step, the hydrogel washed with deionized water is dried at 50 to 70 ℃ for 5 to 10 hours in air.
10. The method for constructing a graphene-based thermal interface material having a mutually perpendicular structure according to claim 1, wherein in the eleventh step, the degree of vacuum is lower than-1 Pa, the applied pressure is 0.01M to 0.8MPa, and the high thermal conductive polymer is an epoxy resin, a phase change material, or a silica gel material.
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