CN114874656A

CN114874656A - Composite powder, preparation method thereof and application thereof in heat dissipation coating

Info

Publication number: CN114874656A
Application number: CN202210623622.4A
Authority: CN
Inventors: 曾宪喆; 丁古巧; 何朋
Original assignee: Shanghai Institute of Microsystem and Information Technology of CAS
Current assignee: Shanghai Institute of Microsystem and Information Technology of CAS
Priority date: 2022-06-02
Filing date: 2022-06-02
Publication date: 2022-08-09
Anticipated expiration: 2042-06-02
Also published as: CN114874656B

Abstract

The invention relates to composite powder, which comprises graphene and silicon dioxide microspheres, wherein the graphene and the silicon dioxide microspheres are bonded together through chemical bonds, the average transverse size of the graphene is 5-30 mu m, and the particle size of the silicon dioxide microspheres is 0.5-20 mu m. The invention also relates to a preparation method of the composite powder and application of the composite powder in a heat dissipation coating, wherein the application comprises the following steps: the composite powder provides a heat dissipation coating, and then the heat dissipation coating forms a heat dissipation coating. According to the composite powder, the silicon dioxide microspheres can improve the heat resistance of the coating, prevent the agglomeration of graphene, improve the dispersibility of the graphene in the coating, change the orientation distribution of the graphene in the coating and increase the orientation proportion in the direction vertical to the substrate, so that the coating has excellent transverse and longitudinal heat conduction properties.

Description

Composite powder, preparation method thereof and application thereof in heat dissipation coating

Technical Field

The invention relates to a composite material, in particular to a composite powder, a preparation method thereof and application thereof in a heat dissipation coating.

Background

With the continuous development of the technology level, the power density of household appliances and electronic devices in life is continuously increased. This is accompanied by a substantial increase in the amount of heat generated by the various devices. If waste heat generated by the electronic equipment cannot be timely dissipated to the surrounding environment to generate local hot spots inside the equipment, the service life of the equipment can be shortened, and the normal operation of the equipment can be influenced, even potential safety hazards are caused.

The common heat dissipation modes of the existing high-power electrical appliance include active heat dissipation modes such as air cooling and water cooling. However, the devices required by the heat dissipation modes have complex structures and occupy a large amount of space, and the heat dissipation devices do not conform to the trend of miniaturization and light weight of the conventional electronic devices. At present, more and more electronic devices begin to use passive heat dissipation modes such as heat dissipation coatings to remove waste heat generated during the use of the electronic devices.

Graphene is one of the materials with the best heat-conducting property at present, and the ideal heat-conducting coefficient can reach 5300W/K.m ² The heat conducting filler can be used as a heat conducting filler of a heat radiating coating, and the heat conducting capacity of the heat radiating coating is greatly improved. CN112175512A, CN113956697A, CN111269592A, CN109021633A, etc. all relate to the research of graphene-based heat dissipation coatings. However, graphene is typically a two-dimensional material, in-plane and inter-planeThere is a very large variability in the performance of (c). In particular, in applications in the field of thermal conduction, the in-plane thermal conductivity of graphene is much higher than the in-plane thermal conductivity. Heat is more easily conducted in the in-plane direction of the graphene. Therefore, the distribution form of graphene in the heat dissipation coating has a great influence on the heat conduction performance of the graphene-based heat dissipation coating in a specific direction. Generally, the in-plane direction of the graphene filler tends to coincide with the spreading direction of the coating layer, and is perpendicular to the thickness direction of the coating layer, which is more pronounced in the coating layer formed by blade coating. This phenomenon can cause the lateral thermal conductivity of the graphene-based heat dissipation coating to be much higher than the longitudinal thermal conductivity. Meanwhile, as the graphene is very thin, the graphene is very easy to agglomerate, so that the graphene is unevenly distributed in the heat dissipation coating, and the heat conduction performance of the heat dissipation coating is reduced.

Disclosure of Invention

In order to solve the problems that the transverse thermal conductivity of the graphene-based heat dissipation coating is far higher than the longitudinal thermal conductivity and the graphene-based heat dissipation coating is not easy to disperse in the coating in the prior art, the invention provides composite powder, a preparation method thereof and application thereof in the heat dissipation coating.

One aspect of the invention provides composite powder, which comprises graphene and silica microspheres, wherein the graphene and the silica microspheres are bonded together through chemical bonds, the average transverse size of the graphene is 5-30 μm, and the particle size of the silica microspheres is 0.5-20 μm.

Preferably, the ratio of the average lateral dimension of the graphene to the diameter of the silica microspheres is 1 to 10.

Preferably, the mass ratio of the graphene to the silica microspheres is 10: 3.

preferably, the graphene has an average lateral dimension of 22 μm.

Preferably, the thickness of the graphene sheet is 1 to 3 atomic layers. In a preferred embodiment, the graphene has a sheet thickness of less than 3 nm.

Preferably, the particle size of the silica microspheres is 3-10 μm.

Preferably, the surface of the silica microsphere is modified with hydroxyl and carboxyl.

Another aspect of the present invention provides a method for preparing a composite powder, comprising the steps of: s1, modifying the surface of graphene to enable the surface of the graphene to have at least one or a combination of organic groups such as hydroxyl, carboxyl, epoxy, acyl, amino and the like, so as to obtain modified graphene; s2, selecting a silicon dioxide microsphere of which the surface is modified with at least one organic group of hydroxyl and carboxyl, then enabling the organic group on the surface of the modified graphene to react with the organic group on the surface of the silicon dioxide microsphere, and bonding the graphene and the silicon dioxide microsphere together through a chemical bond.

Preferably, the mass ratio of the graphene to the silica microspheres is 1-5.

Preferably, the step S1 includes: adding graphene into an organic solvent, and shearing and dispersing to obtain a graphene dispersion liquid A; and then adding a modifier into the graphene dispersion liquid A for reaction to obtain a modified graphene dispersion liquid B. In a preferred embodiment, the organic solvent is N-methyl pyrrolidone or a tannic acid solution. In a preferred embodiment, the shear rate is 10000 rpm. In a preferred embodiment, the modifying agent is an epoxy organosilane or silane coupling agent (e.g., KH560 silane coupling agent). In a preferred embodiment, the modification is carried out in a constant temperature environment of 80-90 ℃.

Preferably, the step S1 includes: adding potassium persulfate and phosphorus pentoxide into concentrated sulfuric acid to obtain an oxidant A; adding graphene into an oxidant A for reaction to obtain a mixed solution B; adding water to dilute the mixed solution B to obtain a modified graphene dispersion solution C; centrifuging, washing and drying to obtain modified graphene; and adding the modified graphene into water, and shearing and dispersing to obtain a modified graphene dispersion liquid D. In a preferred embodiment, the shear rate is 50000 rpm.

Preferably, the step S2 includes: and adding the silicon dioxide microspheres into the modified graphene dispersion liquid B for reaction to obtain the composite powder. In a preferred embodiment, the compounding is carried out in a constant temperature environment of 100 ℃.

Preferably, the step S2 includes: adding the silicon dioxide microspheres into the modified graphene dispersion liquid D, heating and stirring, and slowly adding hydrochloric acid in the stirring process to obtain a composite powder dispersion liquid E; and centrifuging to obtain the composite powder. In a preferred embodiment, the hydrochloric acid is 37% hydrochloric acid.

The invention also provides an application of the composite powder in a heat dissipation coating, which comprises the following steps: the composite powder provides a heat dissipation coating, and then the heat dissipation coating forms a heat dissipation coating.

Preferably, the step of providing a heat-dissipating coating comprises: adding the composite powder into a dispersion medium, and shearing and dispersing to obtain a composite powder dispersion liquid C; and adding the structural adhesive into the composite powder dispersion liquid C, and adding the auxiliary agent in the stirring process to obtain the heat-dissipating coating. In a preferred embodiment, the shear rate is 5000 rpm. In a preferred embodiment, the stirring rate is 800 rpm.

Preferably, the heat dissipation coating further comprises a structural binder, a dispersion medium and an auxiliary agent. More preferably, the structural adhesive is one or more of epoxy resin, silicone resin, polyimide resin and fluorine resin. More preferably, the dispersion medium is one or more of toluene, xylene, N-methylpyrrolidone, N-dimethylformamide, ethyl acetate and acetone. More preferably, the auxiliary agent comprises one or more of a dispersing agent, a wetting agent, a defoaming agent, an anti-settling agent, an anti-flash rust agent, a tackifier, a thickening rheological auxiliary agent, a leveling auxiliary agent, a film forming auxiliary agent and a curing agent.

Preferably, the step of forming the heat dissipation coating includes: and coating the heat dissipation coating on a substrate, and heating and curing to form the heat dissipation coating. In a preferred embodiment, the coating is cured by heating at 80-180 ℃. More preferably, the substrate is a metal, inorganic non-metal or organic material. In a preferred embodiment, the substrate is a stainless steel plate, a glass plate, or a tinplate. More preferably, the heat-dissipating coating forms the heat-dissipating coating layer by spray coating, blade coating, spin coating, or dip coating.

According to the composite powder and the preparation method thereof and the application of the composite powder in the heat dissipation coating, the graphene is used as the heat conduction filler of the heat dissipation coating, so that the heat conduction coefficient of the heat dissipation coating can be improved, the silicon dioxide microspheres can be used as a support to regulate the distribution angle of the graphene in the heat dissipation coating, and the proportion of the graphene filler distributed in the in-plane direction along the coating thickness direction is increased, so that the heat dissipation coating can have high transverse heat conductivity and longitudinal heat conductivity at the same time. Moreover, compared with simple mixing of graphene and silicon dioxide, the silicon dioxide microspheres in the composite powder provided by the invention can improve the dispersibility of graphene in the heat dissipation coating and improve the heat resistance of the heat dissipation coating. In a word, according to the composite powder, the silica microspheres can not only improve the heat resistance of the coating, but also hinder the agglomeration of graphene and improve the dispersibility of the graphene in the coating, and can also change the orientation distribution of the graphene in the coating and increase the orientation proportion in the direction perpendicular to the substrate, so that the coating has excellent transverse and longitudinal heat conduction performances, namely, the distribution form of the graphene in the heat dissipation coating is regulated and controlled by the silica microspheres, the proportion of the graphene filler distributed in the in-plane direction along the coating thickness direction is increased, and the obtained heat dissipation coating not only has a high transverse heat conduction coefficient to enlarge the heat dissipation area, but also has a high longitudinal heat conduction coefficient to improve the heat flux for dissipating heat to the surrounding environment.

Drawings

Fig. 1 is a schematic view of the internal microstructure of a heat-dissipating coating according to example 1 of the present invention;

fig. 2 is a schematic view of the internal microstructure of a heat-dissipating coating according to example 2 of the present invention;

fig. 3 is a schematic view of the internal microstructure of the heat-dissipating coating layer of comparative example 1 according to the present invention;

fig. 4 is a schematic view of the internal microstructure of the heat-dissipating coating layer of comparative example 2 according to the present invention;

fig. 5 is a schematic view of the internal microstructure of the heat-dissipating coating layer of comparative example 3 according to the present invention;

fig. 6 is a schematic view of the internal microstructure of the heat-dissipating coating layer of comparative example 4 according to the present invention.

Detailed Description

The preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

Example 1

1.1 preparation of composite powder

(1) 10g of graphene (prepared by a liquid phase stripping method, the oxygen content is less than 3 at.%, the average transverse dimension is 22 μm, the lamella thickness is less than 3nm), 3g of silicon dioxide microspheres (the particle size is 3 μm, the surface of which is modified with hydroxyl and carboxyl, and the microspheres are purchased from Korea Raymond science and technology Co., Ltd.), 100g of N-methyl pyrrolidone (ACS, 98%), 0.5g of epoxy organosilane (SH-023-7, Zaoyang Sihai chemical Co., Ltd.), and 0.2g of 37% hydrochloric acid for later use. In this embodiment, the graphene is selected from a powder having no group and having few defects, which is different from graphene oxide or modified graphene.

(2) Adding 10g of graphene into 100g of N-methyl pyrrolidone, and shearing and dispersing at a shearing rate of 10000rpm for 2h to obtain a graphene dispersion liquid A.

(3) And (3) adding 0.5g of epoxy organosilane into the graphene dispersion liquid A obtained in the step (2), uniformly stirring, and reacting for 8 hours at a constant temperature of 80 ℃ to obtain a modified graphene dispersion liquid B. It should be understood that epoxy groups are specifically added to the organosilane, and in fact, the organosilane contains not only epoxy groups, but also various groups such as hydroxyl, phenyl, methyl, carbonyl and the like, and the purpose of modifying the epoxy organosilane is to introduce epoxy groups on the surface of graphene, but also to introduce various groups simultaneously, so as to facilitate chemical bonding with silicon dioxide, and particularly, the epoxy groups can improve the bonding condition of graphene and resin.

(4) Adding 3g of silicon dioxide microspheres into the modified graphene dispersion liquid B obtained in the step (3), uniformly stirring, heating to 100 ℃, and reacting at constant temperature for 12 hours. And after the reaction is finished, separating the powder in the dispersion liquid by a centrifugal method to obtain the composite powder.

1.2 preparation of Heat-dissipating coatings

(1) 3g of the composite powder prepared in 1.1, 60g of xylene (ACS, 98.5%) and 60g of organic silicon resin (HG-43, Zhonghao Chenguang chemical industry) were weighed and prepared for later use.

(2) And adding 3g of the composite powder into 60g of dimethylbenzene, and shearing and dispersing at a shearing rate of 5000rpm for 0.5h to obtain a composite powder dispersion liquid C.

(3) And (3) adding 60g of organic silicon resin into the composite powder dispersion liquid C obtained in the step (2) for stirring uniformly, wherein the stirring speed is 800rpm, the stirring time is 0.5h, and a leveling agent and an anti-settling agent are added in the stirring process to obtain the heat dissipation coating.

1.3 preparation of Heat-dissipating coating

(1) And scraping the heat dissipation coating on the stainless steel plate.

(2) And (2) putting the stainless steel plate coated with the coating obtained in the step (1) into an oven at 180 ℃ for heating for 3h for coating and curing, and taking out the stainless steel plate coated with the coating after the coating is finished.

Example 2

2.1 preparation of composite powder

(1) Weighing 10g of graphene (prepared by a liquid phase stripping method, the oxygen content is less than 3 at.%, the average transverse dimension is 10 μm, the lamella thickness is less than 3nm), 3g of silicon dioxide microspheres (the particle size is 10 μm, the surface of the silicon dioxide microspheres is modified with hydroxyl and carboxyl, and the silicon dioxide microspheres are purchased from Korea Raymond science and technology Co., Ltd.), 1kg of deionized water, 1g of tannic Acid (ACS) and 10gKH560 of silane coupling agent for later use.

(2) 1g of tannic acid was added to 1kg of deionized water, and stirred at 800rpm for 0.5 hour to obtain tannic acid solution A.

(3) And (3) adding 10g of graphene into the tannic acid solution A obtained in the step (2), and shearing and dispersing at a shearing rate of 10000rpm for 1h to obtain a graphene dispersion liquid B.

(4) And (3) adding a 10gKH560 silane coupling agent into the graphene dispersion liquid B obtained in the step (3), uniformly stirring, heating to 90 ℃, and reacting at constant temperature for 12h to obtain a modified graphene dispersion liquid C.

(5) And (3) adding 3g of silicon dioxide microspheres into the modified graphene dispersion liquid C obtained in the step (4), uniformly stirring, and reacting at a constant temperature of 85 ℃ for 8 hours. And after the reaction is finished, separating the powder in the dispersion liquid by a centrifugal method to obtain the composite powder.

2.2 preparation of Heat-dissipating coatings

(1) 3g of the composite powder prepared in 2.1, 60g of N-methyl pyrrolidone (ACS, 98%) and 60g of polyimide resin (PAA-2, Furun Special Plastic New Material Co., Ltd.) were weighed for later use.

(2) And adding 3g of the composite powder into 60g of N-methyl pyrrolidone for shearing and dispersing, wherein the shearing rate is 5000rpm, and the shearing time is 0.5h to obtain the composite powder dispersion liquid.

(3) And (3) adding 60g of polyimide resin into the composite powder dispersion liquid obtained in the step (2) to stir uniformly, wherein the stirring speed is 800rpm, the stirring time is 0.5h, and a leveling agent and an anti-settling agent are added in the stirring process to obtain the heat dissipation coating.

2.3 preparation of Heat-dissipating coating

(1) And spraying the heat dissipation coating on the glass plate.

(2) And (2) putting the glass plate coated with the coating obtained in the step (1) into an oven at 120 ℃ for heating for 4h for coating and curing, and taking out the glass plate coated with the coating after the coating is finished.

Example 3

3.1 preparation of composite powder

(1) Weighing 10g of graphene (prepared by a liquid phase stripping method, the oxygen content is less than 3 at.%, the average transverse dimension is 22 μm, the lamella thickness is less than 3nm), 100ml of concentrated sulfuric acid (98%), 2g of potassium persulfate, 2g of phosphorus pentoxide, 3kg of deionized water, 3g of silicon dioxide microspheres (the particle size is 10 μm, the surface of the silicon dioxide microspheres is modified with hydroxyl and carboxyl, and the silicon dioxide microspheres are purchased from Korea Raymi technology Co., Ltd.), and 10ml of 37% hydrochloric acid for later use.

(2) Adding 100ml of concentrated sulfuric acid into a reaction kettle, cooling to 0 ℃, then slowly adding 2g of potassium persulfate and 2g of phosphorus pentoxide, uniformly stirring, and heating to 80 ℃ to obtain the oxidant A.

(3) And (3) adding 10g of graphene into the oxidant A obtained in the step (2), stirring and reacting for 4 hours, and then cooling to room temperature to obtain a mixed solution B.

(4) And (4) diluting the mixed solution B obtained in the step (3) with 500ml of deionized water, and standing for 8 hours to obtain a modified graphene dispersion solution C.

(5) And (4) centrifuging the modified graphene dispersion liquid C obtained in the step (4), washing precipitates with a large amount of deionized water, and then drying in an oven at 80 ℃ to obtain the modified graphene.

(6) And (3) adding the modified graphene obtained in the step (5) into 500g of deionized water, and shearing and dispersing at the shearing rate of 50000rpm for 1h to obtain a modified graphene dispersion liquid D.

(7) And (3) adding 3g of silicon dioxide microspheres into the modified graphene dispersion liquid D obtained in the step (6), heating to 80 ℃, stirring at 800rpm for 6h, and slowly adding 10ml of 37% hydrochloric acid during stirring to obtain a composite powder dispersion liquid E.

(8) And (4) centrifuging the composite powder dispersion liquid E obtained in the step (7) to obtain composite powder.

3.2 preparation of Heat-dissipating coatings

(1) 3G of the composite powder prepared in 3.1, 60G of xylene (ACS, 98.5%), 60G of epoxy resin (YDF-170, national chemical industry) and 36G of polyamide curing agent (G-640, national chemical industry) are weighed for later use.

(2) And adding 3g of the composite powder into 60g of dimethylbenzene, and shearing and dispersing at a shearing rate of 5000rpm for 0.5h to obtain a composite powder dispersion liquid.

(3) And (3) adding 60g of epoxy resin into the composite powder dispersion liquid obtained in the step (2) to stir uniformly, wherein the stirring speed is 800rpm, the stirring time is 0.5h, and adding a polyamide curing agent, a flatting agent and an anti-settling agent in the stirring process to obtain the heat dissipation coating.

3.3 preparation of Heat-dissipating coating

(1) The heat dissipation coating is scraped and coated on a tin plate.

(2) And (2) putting the tinplate coated with the coating obtained in the step (1) into an oven at 80 ℃ for heating for 8h for coating and curing, and taking out the tinplate coated with the coating after the coating is finished.

Comparative example 1

Compared with the example 1, the comparative example does not use the composite powder in the preparation process of the heat-dissipation coating, but uses the graphene instead, and the composition of the comparative example is as follows: 3g of graphene (prepared by a liquid phase stripping method, the oxygen content is less than 3 at.%, the average transverse dimension is 22 μm, the lamella thickness is less than 3nm), 60g of xylene (ACS, 98.5%), and 60g of organic silicon resin (HG-43, Zhonghao morning light chemical industry). The heat-dissipating coating material was prepared as described in 1.2 of example 1. A heat-dissipating coating was prepared as described in 1.3 of example 1.

Comparative example 2

Compared with the embodiment 1, in the comparative example, the preparation process of the heat-dissipating coating does not use composite powder, but uses the non-composite graphene and silica microspheres, and the components of the comparative example are as follows: 2.3g of graphene (prepared by a liquid phase stripping method, with an oxygen content of less than 3 at.%, an average transverse dimension of 22 μm, and a lamella thickness of less than 3nm), 0.7g of silica microspheres (with a particle size of 3 μm, surface modified with hydroxyl and carboxyl groups, available from korea technologies ltd.), 60g of xylene (ACS, 98.5%), 60g of silicone resin (HG-43, zhonghao morning light chemistry). The heat-dissipating coating material was prepared as described in 1.2 of example 1. A heat-dissipating coating was prepared as described in 1.3 of example 1.

Comparative example 3

Compared with example 1, this comparative example uses silica microspheres with a particle size of 0.1 μm during the preparation of the composite powder. A composite powder was prepared as described in 1.1 of example 1. The heat-dissipating coating material was prepared as described in 1.2 of example 1. A heat-dissipating coating was prepared as described in 1.3 of example 1.

Comparative example 4

In comparison with example 1, this comparative example uses silica microspheres having a particle size of 30 μm in the preparation process of the composite powder. A composite powder was prepared as described in 1.1 of example 1. The heat-dissipating coating material was prepared as described in 1.2 of example 1. A heat-dissipating coating was prepared as described in 1.3 of example 1.

Comparative example 5

In comparison with example 1, this comparative example uses graphene having an average lateral dimension of 1 μm during the preparation of the composite powder. A composite powder was prepared as described in 1.1 of example 1. The heat-dissipating coating material was prepared as described in 1.2 of example 1. A heat-dissipating coating was prepared as described in 1.3 of example 1.

Comparative example 6

Compared with example 1, in the comparative example, 1g of silica microspheres (the mass ratio of graphene to silica microspheres is 10) were added in the preparation process of the composite powder. A composite powder was prepared as described in 1.1 of example 1. The heat-dissipating coating material was prepared as described in 1.2 of example 1. A heat-dissipating coating was prepared as described in 1.3 of example 1.

Comparative example 7

Compared with example 1, in the comparative example, 20g of silica microspheres (the mass ratio of graphene to silica microspheres is 0.5) were added in the preparation process of the composite powder. A composite powder was prepared as described in 1.1 of example 1. The heat-dissipating coating material was prepared as described in 1.2 of example 1. A heat-dissipating coating was prepared as described in 1.3 of example 1.

Test method

The method for testing the heat conductivity coefficient of the coating comprises the steps of putting the coating and the coated substrate into a heat conductivity tester for testing, and removing the influence of the substrate through calculation of a test result to obtain the heat conductivity coefficient of the coating, wherein the test direction of the longitudinal heat conductivity coefficient is the thickness direction of the coating, and the test direction of the transverse heat conductivity coefficient is the spreading direction of the coating.

The testing method of the heat-resisting temperature of the coating is in accordance with GB/T1735-2009.

The results of the performance test of the coatings obtained in examples 1 to 3 and comparative examples 1 to 2 are shown in Table 1 below.

TABLE 1 comparison of Performance parameters of examples 1-3 and comparative examples 1-7

As can be seen from Table 1, the heat-dissipating coating using the composite powder of the present invention has excellent properties, high thermal conductivity in both the transverse and longitudinal directions, and excellent heat resistance. In comparative example 1, the transverse and longitudinal thermal conductivities of the coating are not only lower than those of the coating in example 1, but also are greatly different from each other, and the longitudinal thermal conductivity is very low, so that the thermal conductivity requirement of the heat dissipation coating cannot be met. Fig. 3 is a schematic view of the internal microstructure of the heat-dissipating coating layer in comparative example 1. As can be seen from fig. 3, the alignment of the graphene fillers in the coating layer generally has an orientation in which the in-plane direction tends to coincide with the spreading direction of the coating layer and to be perpendicular to the thickness direction of the coating layer, which results in a transverse thermal conductivity of the coating layer that is much higher than a longitudinal thermal conductivity, and the graphene fillers are generally not easily dispersed, so that the transverse and longitudinal thermal conductivities of the coating layer are not ideal. Fig. 1 and 2 are schematic views of the internal microstructures of the heat-dissipating coatings in examples 1 and 2 (the differences in the internal microstructures of the coatings shown in fig. 1 and 2 are caused by the differences in the lateral dimensions of graphene and the particle size of silica microspheres in examples 1 and 2). As can be seen from fig. 1 and 2, the silica microspheres in the composite powder of the present invention can be used as a support to regulate the distribution angle of graphene in the coating, and increase the proportion of the graphene filler distributed in the in-plane direction along the thickness direction of the coating, so that the coating has high transverse thermal conductivity and high longitudinal thermal conductivity. And the silica microspheres can also hinder the agglomeration of graphene, improve the dispersibility of the graphene in the coating and improve the heat resistance of the coating. In comparative example 2, the graphene and silica microspheres were simply mixed together and were not complexed by chemical bonds. Therefore, although a small amount of graphene filler can change the distribution angle by virtue of the supporting effect of the silica microspheres, and slightly improve the longitudinal thermal conductivity of the coating, the dispersibility of graphene cannot be improved, and even segregation and agglomeration are generated due to the extrusion of the silica microspheres, so that the thermal conductivity is low. In comparative example 3, since the particle size of the silica microspheres is too small, the silica microspheres are only filled in the gaps of the graphene filler, and the effect of adjusting the distribution angle of the graphene filler is limited, the longitudinal thermal conductivity of the coating is not significantly improved. In comparative example 4, silica microspheres had a large interstitial space left when they were stacked due to their excessively large particle size (see fig. 6). These interstitial spaces are difficult to be filled with the graphene fillers distributed on the surface of the silica microspheres, so that the thermal conductivity is very low, and the overall thermal conductivity of the coating is affected. And the silica microspheres with too large particle size occupy a large volume space of the coating, so that the volume concentration of the graphene filler in the coating is too low, and the thermal conductivity of the coating is further reduced. In comparative example 5, the lateral size of the graphene powder is too small, which increases the contact area between the graphene fillers, thereby increasing the thermal contact resistance between the graphene fillers and further reducing the overall thermal conductivity of the coating. In comparative example 6, the mass ratio of the silica microspheres in the composite powder was too low, and although the transverse and longitudinal heat conductivity of the coating was improved to some extent, the effect was not significant enough. In comparative example 7, the mass fraction of graphene in the composite powder was too low, resulting in a coating lacking sufficient heat conductive filler to improve its heat conductive properties, and thus the coating had poor lateral and longitudinal thermal conductivities.

The above embodiments are merely preferred embodiments of the present invention, which are not intended to limit the scope of the present invention, and various changes may be made in the above embodiments of the present invention. All simple and equivalent changes and modifications made according to the claims and the content of the specification of the present application fall within the scope of the claims of the present patent application. The invention has not been described in detail in order to avoid obscuring the invention.

Claims

1. The composite powder is characterized by comprising graphene and silicon dioxide microspheres, wherein the graphene and the silicon dioxide microspheres are bonded together through chemical bonds, the average transverse size of the graphene is 5-30 mu m, and the particle size of the silicon dioxide microspheres is 0.5-20 mu m.

2. The composite powder according to claim 1, wherein the ratio of the average transverse dimension of the graphene to the diameter of the silica microspheres is 1 to 10.

3. The composite powder according to claim 1, wherein the graphene has a sheet thickness of 1 to 3 atomic layers.

4. A method for preparing the composite powder according to any one of claims 1 to 3, comprising the steps of:

s1, modifying the surface of graphene to enable the surface of the graphene to have at least one or a combination of organic groups such as hydroxyl, carboxyl, epoxy, acyl, amino and the like, so as to obtain modified graphene;

s2, selecting a silicon dioxide microsphere of which the surface is modified with at least one organic group of hydroxyl and carboxyl, then enabling the organic group on the surface of the modified graphene to react with the organic group on the surface of the silicon dioxide microsphere, and bonding the graphene and the silicon dioxide microsphere together through a chemical bond.

5. The preparation method according to claim 4, wherein the mass ratio of the graphene to the silica microspheres is 1 to 5.

6. The method for preparing a composite material according to claim 4, wherein the step S1 includes:

adding graphene into an organic solvent, and shearing and dispersing to obtain a graphene dispersion liquid A;

and then adding a modifier into the graphene dispersion liquid A for reaction to obtain a modified graphene dispersion liquid B.

7. The method for preparing a composite material according to claim 4, wherein the step S1 includes:

adding potassium persulfate and phosphorus pentoxide into concentrated sulfuric acid to obtain an oxidant A;

adding graphene into an oxidant A for reaction to obtain a mixed solution B;

adding water to dilute the mixed solution B to obtain a modified graphene dispersion solution C;

centrifuging, washing and drying to obtain modified graphene;

and adding the modified graphene into water, and shearing and dispersing to obtain a modified graphene dispersion liquid D.

8. Use of the composite powder according to any one of claims 1 to 3 in a heat-dissipating coating, comprising: the composite powder provides a heat dissipation coating, and then the heat dissipation coating forms a heat dissipation coating.

9. The use according to claim 8, wherein the heat-dissipating coating further comprises a structural binder, a dispersing medium and an auxiliary.

10. The use of claim 8, wherein the step of forming a heat-dissipating coating comprises: and coating the heat dissipation coating on a substrate, and heating and curing to form the heat dissipation coating.