CN111363202B

CN111363202B - Kaolin ceramic microsphere, preparation method thereof and application thereof in heat-conducting filler

Info

Publication number: CN111363202B
Application number: CN202010097325.1A
Authority: CN
Inventors: 郭益平; 周建国; 赵智承; 赵宇驰
Original assignee: Inner Mongolia Tianzhijiao Kaolin Co ltd; Shanghai Jiaotong University
Current assignee: Inner Mongolia Tianzhijiao Kaolin Co ltd; Shanghai Jiaotong University
Priority date: 2020-02-17
Filing date: 2020-02-17
Publication date: 2022-03-01
Anticipated expiration: 2040-02-17
Also published as: CN111363202A

Abstract

The invention relates to kaolin ceramic microspheres and a preparation method and application thereof in heat-conducting fillers, wherein the kaolin ceramic microspheres comprise the following steps: (1) uniformly mixing kaolin powder, PVA aqueous solution and water to prepare slurry; (2) forming kaolin microspheres by the slurry in the step (1) by a thermal spraying granulation method; (3) sintering the kaolin microspheres obtained in the step (2) at the temperature of 1000-; (4) uniformly mixing the ceramic microspheres prepared in the step (3), boron nitride, PVA aqueous solution and water to prepare slurry; (5) and (4) forming the slurry prepared in the step (4) into kaolin microspheres loaded with boron nitride by a thermal spraying granulation method. Compared with the prior art, the kaolin ceramic microsphere prepared by the invention has simple process and high nodularity up to 96 percent, and is suitable for industrial production. The porous structure is beneficial to loading other materials to form the functionalized microspheres. The thermal conductivity coefficient of the insulating thermal conductive filler prepared by filling the microspheres loaded with boron nitride into the epoxy resin is improved to 340 percent of that of pure E51 type epoxy resin.

Description

Kaolin ceramic microsphere, preparation method thereof and application thereof in heat-conducting filler

Technical Field

The invention belongs to the field of multifunctional ceramic powder, and relates to a preparation method of kaolin ceramic microspheres and application thereof in the field of heat-conducting fillers.

Background

With the continuous development of electronic products, the size and integration of components are becoming smaller and more compactPeople put higher and higher demands on the heat dissipation performance of equipment. In industrial production, a filler with high insulation and thermal conductivity is often added into a component so as to ensure that the component can fully dissipate heat and prevent overheating damage under the condition of no electric leakage or short circuit. The traditional alumina ball filler has better insulating property and good fluidity, can be densely filled in gaps, but has lower thermal conductivity coefficient (30 wm)^-1K^-1). Although the thermal conductivity of boron nitride (125 wm)^-1K^-1) Compared with alumina, boron nitride is fluffy, the viscosity of the system is obviously increased after a large amount of boron nitride is filled, more gaps are generated when the boron nitride is used as a filler, and the excellent heat-conducting property of the boron nitride cannot be fully exerted. Meanwhile, compared with alumina, the cost of the raw materials of boron nitride is much higher, and the cost of the prepared microspheres will continue to rise, so that the wide application of the microspheres is limited.

The consumption of boron nitride can be reduced by loading the boron nitride on the microspheres of other substances, and the cost is saved. The microspheres with good fluidity can more densely fill gaps, and boron nitride on the surface can still form a good heat conduction network under the condition of close contact, so that low cost, high insulation and high heat conduction can be realized. Compared with alumina, kaolin has lower sintering temperature, better sintering property and lower raw material cost, so that the kaolin microspheres with good mechanical strength and high spheroidization rate can be formed by preparing slurry, firstly preparing composite microspheres of high polymers and kaolin and then sintering. Then, the boron nitride with good thermal conductivity is loaded on the surface of the kaolin ball, so that not only can good fluidity and thermal conductivity be realized, but also the cost of the filler can be reduced. In addition, the kaolin microspheres are used as carriers for loading functional materials, and can also be loaded with magnetic substances to prepare wave-absorbing coatings, and loaded with metals or metal oxides to prepare catalysts and the like, so the kaolin microspheres have good application prospects.

Disclosure of Invention

The invention aims to overcome the defects in the prior art and provide kaolin ceramic microspheres and a preparation method and application thereof in heat-conducting fillers.

The purpose of the invention can be realized by the following technical scheme: the preparation method of the kaolin ceramic microspheres comprises the following process steps:

(1) mixing kaolin powder, 5-15 wt% of PVA aqueous solution and water in a mass ratio of 1: 0.2-0.25: 1.2-1.5, evenly mixing to prepare slurry;

(2) forming the slurry in the step (1) into kaolin microspheres at 200-300 ℃ by using a thermal spraying granulation method. The collection of the microspheres is divided into two parts: collecting microspheres with the particle size of about 10-50 microns in the cyclone part, and collecting microspheres with the particle size of about 40-80 microns at the bottom of the tower;

(3) and (3) sintering the kaolin microspheres in the step (2) at the temperature of 1000-1350 ℃ to form ceramic microspheres.

(4) Taking the sintered kaolin microspheres prepared in the step (3), boron nitride, 5-15 wt% of PVA aqueous solution and water in a mass ratio of 1: 0.24-0.26: 0.27-0.3: 1.5-1.8, and evenly mixing to prepare slurry;

(5) and (4) forming the slurry in the step (4) into kaolin microspheres loaded with boron nitride at the temperature of 200-300 ℃ by using a thermal spraying granulation method. The collection of the microspheres is divided into two parts: collecting microspheres with the particle size of about 10-50 microns in the cyclone part, and collecting microspheres with the particle size of about 40-80 microns at the bottom of the tower;

(6) diaminodiphenylmethane (DDM) was dissolved in an appropriate amount of acetone, and then epoxy resin type E51 was added thereto with sufficient stirring. And (3) after uniform mixing, adding the microspheres in the step (5) into the mixture, fully stirring, then placing the mixture into a 70-80 ℃ water bath kettle, stirring for 1-2 hours, curing at 120-130 ℃ for 2-3 hours, and testing the thermal conductivity of the cut sample by using a laser thermal conductivity instrument (model LFA-457), wherein the testing temperature range is 25-200 ℃. Before testing, the surface of the sample is sprayed with carbon, so that the temperature distribution is uniform. The mass ratio of the Diamino Diphenylmethane (DDM) and E51 epoxy resin to the kaolin microspheres prepared in the step (5) is 4: 12-16: 4-6.

According to the invention, the kaolin slurry is prepared into microspheres by a thermal spraying granulation method, and then the microspheres are sintered and formed at a high temperature, so that the kaolin ceramic microspheres with good mechanical strength are finally formed. The microspheres have a diameter of about 10 to 80 microns, have a porous structure and have good mechanical strength. And then loading boron nitride sheets on the surfaces of the sintered kaolin microspheres by using a spray granulation method to obtain the heat-conducting filler with excellent fluidity.

The basic idea of the invention is as follows: the slurry is adjusted to a certain viscosity by PVA solution, kaolin balls are prepared by utilizing the characteristic that the slurry can be evaporated to dryness into balls at higher temperature, and then the kaolin balls are calcined at high temperature to remove PVA in the microspheres and sinter the kaolin at the same time to form the porous microspheres with good mechanical strength.

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

1. the kaolin microspheres prepared by the invention have relatively concentrated size distribution, and are approximately between 10 microns and 80 microns;

2. the spheroidization rate of the kaolin microspheres prepared by the method is up to 96%, the kaolin microspheres have good fluidity, can densely fill gaps, and are suitable for being used as heat-conducting fillers;

3. the kaolin microspheres prepared by the invention are broken in the processing and grinding processes and are damaged in use, which shows that the prepared kaolin microspheres have good mechanical strength, and the preparation method is simple and is easy for mass preparation.

4. The kaolin microspheres prepared by the method can be seen from the appearance of a scanning electron microscope (figure 3) that the kaolin microspheres have a porous surface structure and can be used for preparing functional composite ceramic microspheres. The kaolin microspheres loaded with boron nitride have the effect of remarkably improving the thermal conductivity.

5. The kaolin ceramic microspheres prepared by the invention have simple process and are suitable for industrial production. The porous structure is beneficial to loading other materials to form the functionalized microspheres. The thermal conductivity coefficient of the insulating thermal conductive filler prepared by filling the microspheres loaded with boron nitride into the epoxy resin is improved to 340 percent of that of pure E51 type epoxy resin. In addition, the porous structure has good heat insulation performance, can be used for heat insulation materials or coatings, and can also be used for loading magnetic substances to prepare wave-absorbing materials, loading metals or oxides to prepare catalysts and the like.

Drawings

FIG. 1 is (a) cyclone partially collected kaolin spheres, and (b) optical microscopic morphology after sintering;

FIG. 2 is (a) kaolin spheres collected at the bottom of the column, and (b) optical microscopy topography after sintering;

fig. 3 is a scanning electron microscope topography of sintered kaolin spheres collected at the bottom of the tower.

Detailed Description

The present invention is further described in detail below by means of specific examples which will enable one skilled in the art to more fully understand the present invention without in any way limiting it, and that one skilled in the art may, in light of the above teachings, make numerous insubstantial modifications and adaptations of the invention.

Example 1

The preparation method of the kaolin ceramic microspheres comprises the following process steps:

the first step is as follows: uniformly mixing 500g of kaolin powder, 116g of 10 wt% PVA aqueous solution and 626g of water to prepare slurry;

the second step is that: sucking the mixed slurry obtained in the first step into a thermal spraying granulator, keeping the granulation temperature at 250 ℃, and waiting for the slurry to be fully converted into microspheres;

the third step: and blowing out and collecting the microspheres prepared in the second step by using a cyclone device, taking out the microspheres, and sintering the microspheres for 1 hour at 1350 ℃ by using a muffle furnace, wherein the spheroidization rate of the kaolin microspheres is up to more than 96%.

Example 2

The preparation method and sintering schedule of the slurry in this example were the same as in example 1, except that the collection device was changed to collect the microspheres at the bottom of the tower that were not blown off by the cyclone device.

Example 3

The first step is as follows: 60.7g of the sintered kaolin microspheres prepared in example 1, 15.2g of boron nitride, 17.4g of 10 wt% PVA aqueous solution and 102g of water are uniformly mixed to prepare slurry;

the second step is that: and (4) forming kaolin microspheres by using the slurry in the step one through a thermal spraying granulation method at 250 ℃. The collection of the microspheres is divided into two parts: the cyclone part collects microspheres with the particle size of about 10-50 microns, the bottom of the tower collects microspheres with the particle size of about 40-80 microns, and the spheroidization rate of the prepared microspheres is higher than 96%;

the third step: 4g of diaminodiphenylmethane (DDM) are dissolved in an appropriate amount of acetone, and 16g of epoxy resin are added thereto with thorough stirring. And after uniformly mixing, adding 5g of microspheres collected at the bottom of the tower in the second step into the mixture, fully stirring, then putting the mixture into a 80-DEG water bath kettle, stirring for 2 hours, and then curing for 2 hours at 130 ℃. And cut into a rectangular parallelepiped with a thickness of about 1cmx1cm and a thickness of about 1.3mm, and the rectangular parallelepiped is recorded as a heat conductive sample. And finally, spraying carbon on the two surfaces to perform heat conduction test.

FIG. 1 is an optical micrograph of the cyclone partially collected kaolin microspheres and after sintering from example 1. It can be seen that the microspheres in the cyclone part have smaller particle size and wider particle size distribution, the size of the microspheres is obviously reduced after sintering, but the microspheres are not cracked after sintering, and the original spherical shape is well maintained.

FIG. 2 is an optical micrograph of kaolin microspheres collected at the bottom of the tower and after sintering from example 2. It can be seen that since the small-sized microspheres are partially blown away by the cyclone and collected, the microspheres remaining at the bottom of the column have a larger size and a more concentrated particle size distribution. The microspheres also retain their spherical shape after sintering and their size is reduced.

Fig. 3 is a scanning electron microscope image of the sintered microspheres in example 2, and it can be found that the microspheres are circular and have many holes on the surface, so that the microspheres are very suitable for preparing composite functional microspheres by loading functional materials.

Table 1 shows the thermal conductivity of the epoxy resin and the thermally conductive sample of example 3 at different temperatures.

It can be seen that the thermal conductivity of the kaolin microspheres loaded with boron nitride is obviously improved after the epoxy resin is filled with the kaolin microspheres, and the kaolin microspheres have good stability within 100 ℃. The boron nitride-loaded kaolin microspheres have the effect of remarkably improving the thermal conductivity.

Example 4

(1) mixing kaolin powder, 5 wt% of PVA aqueous solution and water in a mass ratio of 1: 0.2: 1.2, uniformly mixing to prepare slurry;

(2) forming kaolin microspheres by the slurry in the step (1) at 200 ℃ by utilizing a thermal spraying granulation method. The collection of the microspheres is divided into two parts: wherein, the cyclone part collects microspheres with the grain size of 10-50 microns, and the bottom of the tower collects microspheres with the grain size of 40-80 microns;

(3) and (3) sintering the kaolin microspheres obtained in the step (2) at 1000 ℃ to form ceramic microspheres.

(4) Taking the sintered kaolin microspheres prepared in the step (3), boron nitride, 5 wt% of PVA aqueous solution and water in a mass ratio of 1: 0.24: 0.27: 1.5, evenly mixing to prepare slurry;

(5) and (4) forming the slurry in the step (4) into kaolin microspheres loaded with boron nitride at 200 ℃ by using a thermal spraying granulation method. The collection of the microspheres is divided into two parts: wherein, the cyclone part collects microspheres with the grain diameter of 10-50 microns, the bottom of the tower collects microspheres with the grain diameter of 40-80 microns, and the spheroidization rates of the two microspheres are both higher than 96 percent.

(6) Diaminodiphenylmethane (DDM) was dissolved in an appropriate amount of acetone, and then epoxy resin type E51 was added thereto with sufficient stirring. After uniformly mixing, adding the microspheres obtained in the step (5) into the mixture, fully stirring the mixture, then putting the mixture into a water bath kettle at 70 ℃ for stirring for 2 hours, and then curing the mixture at 120 ℃ for 3 hours, wherein the mass ratio of the diaminodiphenylmethane (DDM) and the E51 type epoxy resin to the kaolin microspheres obtained in the step (5) is as follows: 4: 16: 6. the cut samples were tested for thermal conductivity using a laser thermal conductivity instrument (model number LFA-457) at a test temperature range of 25-200 ℃. Before testing, the surface of the sample is sprayed with carbon, so that the temperature distribution is uniform. The thermal conductivity of the obtained product is improved by 340 percent compared with that of pure E51 type epoxy resin.

Example 5

(1) mixing kaolin powder, 15 wt% of PVA aqueous solution and water in a mass ratio of 1: 0.2-0.25: 1.2-1.5, evenly mixing to prepare slurry;

(2) forming kaolin microspheres by the slurry in the step (1) at 300 ℃ by utilizing a thermal spraying granulation method. The collection of the microspheres is divided into two parts: collecting microspheres with the particle size of 10-50 microns at the cyclone part, and collecting microspheres with the particle size of 40-80 microns at the bottom of the tower;

(3) and (3) sintering the kaolin microspheres obtained in the step (2) at 1350 ℃ to form ceramic microspheres.

(4) Taking the sintered kaolin microspheres prepared in the step (3), boron nitride, 15 wt% of PVA aqueous solution and water in a mass ratio of 1: 0.26: 0.3: 1.8 evenly mixing to prepare slurry;

(5) and (3) forming the slurry in the step (4) into BN-loaded kaolin microspheres at 300 ℃ by utilizing a thermal spraying granulation method. The collection of the microspheres is divided into two parts: collecting microspheres with smaller particle size at the cyclone part, and collecting microspheres with larger particle size at the tower bottom; wherein, the cyclone part collects microspheres with the grain diameter of 10-50 microns, the bottom of the tower collects microspheres with the grain diameter of 40-80 microns, and the spheroidization rates of the two microspheres are both higher than 96 percent.

(6) Diaminodiphenylmethane (DDM) was dissolved in an appropriate amount of acetone, and then epoxy resin type E51 was added thereto with sufficient stirring. After uniformly mixing, adding the microspheres obtained in the step (5) into the mixture, fully stirring the mixture, then putting the mixture into a water bath kettle at the temperature of 80 ℃, stirring the mixture for 1 hour, and curing the mixture at the temperature of 130 ℃ for 2 hours, wherein the mass ratio of the diaminodiphenylmethane (DDM) and the E51 type epoxy resin to the kaolin microspheres obtained in the step (5) is as follows: 4: 12: 4. the cut samples were tested for thermal conductivity using a laser thermal conductivity instrument (model number LFA-457) at a test temperature range of 25-200 ℃. Before testing, the surface of the sample is sprayed with carbon, so that the temperature distribution is uniform.

The thermal conductivity of the obtained product is improved by 340 percent compared with that of pure E51 type epoxy resin.

Although the preferred embodiments of the present invention have been described with reference to the accompanying drawings and tables, the present invention is not limited to the above-described embodiments, which are merely illustrative and not restrictive, and those skilled in the art can make various changes and modifications within the spirit and scope of the present invention without departing from the spirit and scope of the appended claims.

Claims

1. The preparation method of the kaolin ceramic microspheres is characterized by comprising the following steps:

(1) mixing kaolin powder, PVA aqueous solution and water in a mass ratio of 1: 0.2-0.25: 1.2-1.5, evenly mixing to prepare slurry; the concentration of the PVA aqueous solution is 5-15 wt%;

(2) forming kaolin microspheres by the slurry in the step (1) by a thermal spraying granulation method; the temperature of the thermal spraying granulation is 200-300 ℃; separating the microspheres obtained by thermal spray granulation by using a cyclone separation tower, wherein the cyclone part collects the microspheres with the particle size of 10-50 microns, and the tower bottom collects the microspheres with the particle size of 40-80 microns;

(3) sintering the kaolin microspheres obtained in the step (2) at the temperature of 1000-;

(4) taking the ceramic microspheres prepared in the step (3), boron nitride, PVA aqueous solution and water in a mass ratio of 1: 0.24-0.26: 0.27-0.3: 1.5-1.8, and evenly mixing to prepare slurry; the concentration of the PVA aqueous solution is 5-15 wt%;

(5) forming the slurry prepared in the step (4) into kaolin microspheres loaded with boron nitride by using a thermal spraying granulation method, wherein the temperature of the thermal spraying granulation is 200-300 ℃; the microspheres obtained by thermal spray granulation are separated by a cyclone separation tower, wherein the cyclone part collects the microspheres with the particle size of 10-50 microns, and the tower bottom collects the microspheres with the particle size of 40-80 microns.

2. Kaolin ceramic microspheres, obtainable by the process of claim 1, having a particle size of 10 to 80 μm.

3. The use of the kaolin ceramic microspheres of claim 2, wherein the use of the kaolin ceramic microspheres loaded with boron nitride as a thermally conductive filler, comprises the steps of: dissolving Diaminodiphenylmethane (DDM) in acetone, adding epoxy resin, and stirring; after being uniformly mixed, the kaolin ceramic microspheres are added into the mixture and fully stirred, then the mixture is put into a water bath kettle at the temperature of 70-80 ℃ and stirred for 1-2 hours, and then the mixture is solidified for 2-3 hours at the temperature of 120-130 ℃, thus obtaining the product.

4. The use of the kaolin ceramic microspheres of claim 3, wherein the mass ratio of diaminodiphenylmethane (DDM), epoxy resin to the kaolin ceramic microspheres is 4: 12-16: 4-6.