阅读说明：本技术 一种各向同性石墨材料的制备方法 (Preparation method of isotropic graphite material ) 是由 张海霞 闫桂林 闫萍 胡春燕 余萍 王方丽 谭程程 于 2019-09-18 设计创作，主要内容包括：本发明公开了一种各向同性石墨材料的制备方法,具体为：将不同粒径的中间相炭微球与短切碳纤维掺杂后,经过液相氧化处理,然后通过二次冷等静压法进行模压成型加工,然后进行炭化和石墨化。本发明有效克服了现有以中间相碳微球为原料的墨制备技术所存在的产品开裂所导致的成品率低的问题,还提高了石墨材料的弯曲强度,提高致密性,降低电阻率和开孔率,从而改善石墨材料的性能。(The invention discloses a preparation method of an isotropic graphite material, which comprises the following steps: after the mesocarbon microbeads with different grain sizes and the short carbon fibers are doped, the mesocarbon microbeads are processed by liquid-phase oxidation, then the compression molding processing is carried out by a secondary cold isostatic pressing method, and then carbonization and graphitization are carried out. The invention effectively solves the problem of low yield caused by product cracking in the existing ink preparation technology taking the mesocarbon microbeads as raw materials, improves the bending strength of the graphite material, improves the compactness, reduces the resistivity and the aperture ratio, and further improves the performance of the graphite material.)

1. A preparation method of an isotropic graphite material is characterized by comprising the following steps:

crushing and screening intermediate phase carbon microspheres to obtain intermediate phase carbon microsphere granulated powder with different particle sizes;

crushing the chopped carbon fibers, and sieving with a 400-600-mesh sieve to obtain chopped carbon fiber granulation powder;

carrying out doping mixing modification on the mesophase carbon microsphere granulation powder and the chopped carbon fiber granulation powder with different particle sizes by a liquid phase dispersion method and wet ball milling to obtain modified mesophase carbon microsphere powder;

fourthly, mixing the modified mesocarbon microbeads prepared in the third step with a liquid-phase oxidant and then carrying out oxidation treatment to obtain green body raw materials with different particle sizes;

mixing the raw materials of the green bodies with different particle sizes according to a certain proportion, and then carrying out compression molding processing by a secondary cold isostatic pressing method to obtain green bodies;

sixthly, the blank prepared by the fifth step is vacuumized or N₂Heating to 800-1200 ℃ in the atmosphere, and preserving the heat for 1.5-2 h to obtain a carbon product;

seventhly, heating the carbon product prepared in the step sixthly to 2200-.

2. The method for preparing an isotropic graphite material as claimed in claim 1, wherein the dispersant used in the liquid phase dispersion method in step (iii) is sodium dodecylbenzenesulfonate.

3. The method for preparing an isotropic graphite material according to claim 1, wherein the step (iii) is performed by wet ball milling: material preparation: and (2.5-3) the ratio of water to water is 1: 0.8.

4. The method for preparing an isotropic graphite material as claimed in claim 1, wherein the mass ratio of the mesophase carbon microsphere granulated powder to the chopped carbon fiber granulated powder in the step (iii) is (90:10) - (98: 2).

5. The method for preparing an isotropic graphite material as claimed in claim 1, wherein the liquid-phase oxidizing agent is potassium bromate with a mass concentration of 5-15%.

6. The preparation method of the isotropic graphite material as claimed in claim 1, wherein the mass ratio of the modified mesophase carbon microspheres to the liquid-phase oxidant is 1:10 to 1: 15.

7. The method for preparing an isotropic graphite material according to any one of claims 1 to 6, wherein the step (c) is to mix 20 wt% to 38 wt% of the mesophase carbon microsphere granulated powder having a particle size of 5 to 10 μm, 15 wt% to 35 wt% of the mesophase carbon microsphere granulated powder having a particle size of 20 to 30 μm, and 40 wt% to 50 wt% of the mesophase carbon microsphere granulated powder having a particle size of 40 to 50 μm with the chopped carbon fiber granulated powder.

8. The method for preparing an isotropic graphite material as claimed in claim 7, wherein the pressure of the first cold isostatic pressing in the second cold isostatic pressing is 20 to 30MPa, and the pressure of the second cold isostatic pressing is 180 to 220 MPa.

9. The method for preparing an isotropic graphite material according to claim 8, wherein the step of (c) is performed under vacuum or N₂Heating to 800-1200 ℃ at a heating rate of 90-150 ℃/h in the atmosphere.

10. The method as claimed in claim 9, wherein the step of heating the carbonaceous product to 2200 ℃ and 2400 ℃ at a heating rate of 300-500 ℃/h under normal pressure and non-oxidizing atmosphere.

Technical Field

The invention relates to the technical field of graphite materials, in particular to a preparation method of an isotropic graphite material.

Background

Graphite is an indispensable conductive material and structural material for developing national economy such as metallurgy, chemical industry, electronics, nuclear industry and the like, and has high heat conductivity, low thermal expansion coefficient, good rupture strength, compressive strength and chemical stability. The graphite crystal structure is a mixed crystal structure: atoms on the layer surface are arranged in a hexagonal grid, the atomic distance is small, and the binding force is strong; the distance between the layers is larger, and the binding force is weaker; the difference between the properties of the film in the planar direction and the properties of the film perpendicular to the planar direction is large, and the difference is called "anisotropy". Many special applications place the requirement of "isotropy" on graphite materials. The isotropic graphite material with high breaking strength, high compressive strength and low thermal expansion coefficient is mainly applied to the advanced fields of graphite for military industry, aerospace, ultrahigh power electrodes, nuclear industry and the like. Therefore, the preparation of isotropic graphite is an important research direction for high-performance graphite.

The conventional graphite material is prepared by two methods: firstly, the coke aggregate and the asphalt binder are kneaded, formed, carbonized and graphitized. The pitch binder is converted into carbon in the carbonization process, the carbon and the aggregate are carbon from two different sources, and a plurality of interfaces exist between the carbon and the aggregate, so that the performance of the graphite material is not very high, and the isotropy is poor. And the second is to directly mould-press the green coke or pitch intermediate phase pellet with self-sintering property, then to carbonize and graphitize. Because no binder is used, the prepared graphite material has few interfaces, and can be prepared into the graphite material with high strength, low expansion coefficient and good isotropy. However, the second method, although having many excellent properties, has significant drawbacks, such as:

1) in practice, the existing graphite preparation technology using mesocarbon microbeads as raw materials has the condition of large-area cracking of products in the forming and sintering processes, and the final yield is extremely low.

2) Poor mechanical properties, high brittleness and high porosity.

3) The mesophase petroleum asphalt fiber can become flexible and have certain mechanical strength only after being processed without melting, and the prior gas oxidation technology has the problems of long time consumption and large investment.

Therefore, how to provide a method for preparing an isotropic graphite material with high yield, excellent performance and low cost is a problem that needs to be solved by those skilled in the art.

Disclosure of Invention

In view of the above, the present invention provides a method for preparing an isotropic graphite material by doping mesophase carbon microspheres with different particle sizes and chopped carbon fibers, subjecting the mixture to liquid phase oxidation treatment, then performing compression molding processing by a secondary cold isostatic pressing method, and then performing carbonization and graphitization.

In order to achieve the purpose, the invention adopts the following technical scheme:

a preparation method of an isotropic graphite material comprises the following steps:

crushing and screening intermediate phase carbon microspheres to obtain intermediate phase carbon microsphere granulated powder with different particle sizes;

crushing the chopped carbon fibers, and sieving with a 400-600-mesh sieve to obtain chopped carbon fiber granulation powder;

carrying out doping mixing modification on the mesophase carbon microsphere granulation powder and the chopped carbon fiber granulation powder with different particle sizes by a liquid phase dispersion method and wet ball milling to obtain modified mesophase carbon microsphere powder;

fourthly, mixing the modified mesocarbon microbeads prepared in the third step with a liquid-phase oxidant and then carrying out oxidation treatment to obtain green body raw materials with different particle sizes;

mixing the raw materials of the green bodies with different particle sizes according to a certain proportion, and then carrying out compression molding processing by a secondary cold isostatic pressing method to obtain green bodies;

sixthly, the blank prepared by the fifth step is vacuumized or N₂Heating to 800-1200 ℃ in the atmosphere, and preserving the heat for 1.5-2 h to obtain a carbon product;

seventhly, heating the carbon product prepared in the step sixthly to 2200-.

Preferably, the dispersant used in the liquid phase dispersion method in the third step is sodium dodecyl benzene sulfonate.

Preferably, the ball is milled by a wet method in the third step: material preparation: and (2.5-3) the ratio of water to water is 1: 0.8.

Preferably, the mass ratio of the mesophase carbon microsphere granulated powder to the chopped carbon fiber granulated powder in the third step is (90:10) - (98: 2).

Preferably, the liquid-phase oxidizing agent is potassium bromate with the mass concentration of 5-15%.

Preferably, the mass ratio of the modified mesocarbon microbeads to the liquid-phase oxidant is 1: 10-1: 15.

Preferably, the third step is to mix 20 wt% -38 wt% of the mesophase carbon microsphere granulation powder with the particle size of 5-10 μm, 15 wt% -35 wt% of the mesophase carbon microsphere granulation powder with the particle size of 20-30 μm, and 40 wt% -50 wt% of the mesophase carbon microsphere granulation powder with the particle size of 40-50 μm with the chopped carbon fiber granulation powder.

Preferably, the pressure of the first cold isostatic pressing in the secondary cold isostatic pressing is 20-30 MPa, and the pressure of the second cold isostatic pressing is 180-220 MPa.

Preferably, the step is carried out under vacuum or N₂Heating to 800-1200 ℃ at a heating rate of 90-150 ℃/h in the atmosphere.

Preferably, the step (c) is to heat the carbonaceous product to 2200-.

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

1. the invention mixes the mesocarbon microbeads with different grain diameters, effectively improves the density of the material, reduces the most probable pore diameter of the material, improves the cracking resistance of the material and effectively solves the problem of low yield caused by cracking of products in the prior ink preparation technology taking the mesocarbon microbeads as raw materials.

2. The strength of the short carbon fibers is far greater than that of the graphite material, and the proper amount of the short carbon fibers can be doped to effectively improve the bending strength of the graphite material, improve the compactness and reduce the resistivity and the aperture ratio, so that the performance of the graphite material is improved.

3. The size of the short carbon fiber is nano-scale, the size of the mesocarbon microbeads is micron-scale, after the short carbon fiber and the mesocarbon microbeads are mixed, the barrier effect of the short carbon fiber on the mesocarbon microbeads is small, and the microbeads are easy to contact and bond together under low pressure.

4. According to the invention, the problem that the compactness of the blank is reduced because more gas is wrapped in the prepared blank and the gas forms high-pressure gas in the blank can be effectively avoided by secondary cold isostatic pressing during primary cold isostatic pressing.

5. The invention shortens the oxidation time by liquid phase oxidation, reduces the investment and lowers the cost.

6. The invention has simple preparation process, stable product quality and excellent performance because of no binder.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the provided drawings without creative efforts.

FIG. 1 is an SEM photograph of mesophase carbon microspheres employed in the present invention.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.