Hierarchical porous graphite material, graphite device and preparation method thereof

Abstract

The invention provides a hierarchical porous graphite material, a graphite device and a preparation method thereof, and relates to the technical field of silicon carbide crystal manufacturing. The hierarchical pore graphite material provided by the invention has a hierarchical porous structure, the hierarchical porous structure comprises closed pores, penetrating pores and / or structural pores, the closed pores are non-penetrating pores, the pore diameter of the closed pores is 0.001-0.05 mm, the penetrating pores and the structural pores penetrate through the porous graphite material, and the pore diameter of the porous graphite material is 0.1-0.5 mm. The penetrating holes comprise first-level penetrating holes and second-level penetrating holes, the hole diameter of the first-level penetrating holes is 0.03-0.2 mm, the hole diameter of the second-level penetrating holes is 0.1-2 mm, and the hole diameter of the structural holes is 1-20 mm. The prepared hierarchical porous graphite material has good heat preservation performance, efficient filtering and screening efficiency and stable and efficient substance transmission performance.

Description

Technical Field

[0001] The invention relates to the technical field of silicon carbide crystal manufacturing, and in particular to a multi-level porous graphite material, a graphite device and a preparation method thereof. Background Art

[0002] As the third generation wide bandgap semiconductor material, silicon carbide crystal is an ideal material for the new generation of power devices and radio frequency devices. At present, the physical vapor transport (PVT) method is mainly used to produce silicon carbide crystals. In the process of silicon carbide crystal growth by PVT method, porous graphite devices are usually used to filter and screen the raw materials and purify the crystal growth atmosphere, which can effectively reduce crystal defects such as crystal microtubes and inclusions, improve the quality and output of silicon carbide crystals, and reduce industrial production costs.

[0003] At present, in the developed porous graphite material preparation technology, asphalt coke, artificial graphite powder, carbon black, etc. are often used as the main raw materials, and after adding a binder and a pore-forming agent to mix evenly, porous graphite carbon is obtained by pressing and high-temperature calcination, and then purified and graphitized to obtain porous graphite materials, and finally mechanically processed into porous graphite devices. Chinese patent application CN118026684 A discloses a modified porous graphite and its preparation method and application in the growth of silicon carbide crystals by the PVT method. The patent uses crushed raw coke as a material, and obtains porous graphite through the steps of mixing with a binder and a pore-forming agent, pressing, calcining, and high-temperature graphitization. Among them, foreign substances such as polyvinyl pyrrolidone, potassium chloride, styrene-butadiene rubber, glucose or polyvinyl chloride are used as pore-forming agents. Chinese patent CN 114988402 A discloses porous breathable graphite and its preparation method and application. The patent kneads the soft carbon material, pore-forming agent and binder twice, and then presses, carbonizes and graphitizes them in sequence. Among them, polyvinyl alcohol, polyvinyl butyral ester, ammonium carbonate, ammonium bicarbonate and ammonium chloride are used as pore-forming agents. Chinese patent CN116120079B discloses a method for manufacturing a porous graphite partition for growing silicon carbide crystals by physical vapor transmission. The patent uses ammonium chloride solution to soak and treat short silk cotton fibers as a template to prepare porous graphite. Although using silk cotton as a template is beneficial to improving the pore size distribution of porous graphite, its cost is relatively high. In addition, the porous structure graphite used in the existing PVT method for growing silicon carbide crystals also has the problems of poor thermal insulation, low filtration and screening efficiency, and unstable material transmission. Summary of the invention

[0004] In view of the deficiencies in the prior art, the present invention provides a multi-level porous graphite material, a graphite device and a preparation method thereof, and a graphite device. The multi-level porous graphite material has good thermal insulation, high filtration and screening efficiency, and stable and efficient material transmission performance.

[0005] The specific technical solutions of the present invention are as follows: In a first aspect, the present invention provides a multi-level porous graphite material having a graded porous structure, wherein the graded porous structure includes closed pores, through pores and / or structural pores, wherein the closed pores are non-penetrating pores, and the pore diameter of the closed pores is 0.001-0.05 mm, and the through pores and the structural pores penetrate the porous graphite material, wherein the through pores include first-level through pores and second-level through pores, the pore diameter of the first-level through pores is 0.03-0.2 mm, the pore diameter of the second-level through pores is 0.1-2 mm, and the pore diameter of the structural pores is 1-20 mm.

[0006] The multi-level porous graphite material provided by the present invention has a pore structure with different sizes and provides a variety of pore sizes. The closed pores with a pore size of 0.001-0.05 mm are used to adjust the temperature field and improve the structural strength, which is beneficial to improving the temperature and temperature uniformity of the raw material area during the growth of silicon carbide crystals, increasing the temperature difference between the raw material area and the crystal growth area, and improving the efficiency and quality of crystal growth. At the same time, the closed pores can also provide a large specific surface area and abundant active sites, and weaken the recrystallization phenomenon of the surface layer of the silicon carbide raw material; the first penetration holes with a pore size of 0.03-0.2 mm and the second penetration holes with a pore size of 0.1-2 mm are beneficial to filtering and screening the raw materials and purifying the crystal growth atmosphere, and can filter and screen the raw materials efficiently; the structural holes with a pore size of 1-20 mm provide a fast channel for material transmission, which can improve the stability of material flow in the whole growth process and improve the silicon carbide crystal interface.

[0007] Furthermore, the second level through-holes and the structural holes are prepared by additive manufacturing technology. The use of additive manufacturing technology can adjust the pore size and distribution in the multi-level porous graphite material according to the needs of the actual application scenario, and the internal pore structure can be prepared simultaneously during the graphite device forming process by additive manufacturing technology, avoiding the damage of the graphite device caused by the prior art of first forming the graphite device and then making the holes. This is because in the process of preparing through-holes and structural holes, as the porosity of the device continues to increase, the strength of the graphite device becomes very low, and the graphite device is easily damaged during the hole opening process.

[0008] Furthermore, in the multi-level porous graphite material, the closed pores, the through pores and / or the structural pores are in at least one of a parallel combination, a series combination, a modular combination, a hierarchical combination and a network combination. By adopting the above combination, the needs for multi-level porous graphite materials in practical applications can be met.

[0009] Furthermore, the parallel combination, the series combination, the modular combination, the hierarchical combination and the network combination are achieved by adjusting the additive manufacturing process, and the process includes at least one of model slicing processing method, layer thickness, filler spacing, filler method, slurry extrusion speed, slurry extrusion pressure, extrusion head size, nozzle resolution, ink drop size, inkjet pressure, laser power, spot size, scanning speed, printing path, temperature, humidity and protective gas.

[0010] Furthermore, the multi-level porous graphite material comprises N graphite layers, N≥2, and each of the graphite layers contains at least one of the closed pores, the through pores and the structural pores. The multi-level porous graphite material with the multi-layer structure can meet the requirements for various properties of porous graphite by matching the graphite layers with multiple different types of pores.

[0011] Furthermore, the distribution density of the second level through holes or the structural holes increases gradually from the center to the edge of the multi-level porous graphite material. The multi-level porous graphite material with the gradient structure can promote the diffusion of silicon carbide raw material gas from the edge of the multi-level porous graphite material to the silicon carbide growth area, which is conducive to stabilizing the gas flow in the silicon carbide growth area.

[0012] Furthermore, the porous graphite material has a network combination formed by interconnecting a core skeleton and ribs, the core skeleton has the closed pores and the first-level through holes, and the ribs have the closed pores, the first-level through holes and the second-level through holes.

[0013] In a second aspect, the present invention provides a graphite device, wherein the composition of the graphite device includes the above-mentioned multi-level porous graphite material.

[0014] In a possible implementation manner, the graphite device includes a graphite shelf, a graphite cylinder, a graphite frame, a graphite cover or a graphite crucible.

[0015] In a third aspect, the present invention provides a method for preparing the above-mentioned graphite device, comprising the following steps: S1. Modeling: According to the functional requirements of the graphite device, a combination of closed pores, through pores and / or structural pores in the corresponding hierarchical porous structure is designed, and a three-dimensional model of the graphite device having the hierarchical porous structure is constructed; S2, mixed raw material preparation: the carbon source, the binder, the auxiliary agent and the solvent are fully mixed to form a mixed slurry; the mass ratio of the carbon source, the binder, the auxiliary agent and the solvent is (60-90): (0-40): (0-10): (30-100); S3, blank manufacturing: importing the three-dimensional model described in step S1 into the control module of the additive manufacturing equipment, adding the mixed slurry described in step S2 into the hopper of the additive manufacturing equipment, and performing three-dimensional printing to obtain the blank of the graphite device; S4, sintering: The green body of the graphite device in step S3 is subjected to carbonization treatment and graphitization treatment in sequence to obtain a graphite device.

[0016] The preparation method of the graphite device provided by the present invention controls the ratio of the mixed raw materials so that the sintered graphite device contains the closed pores and the first-level penetration holes of the mixed raw materials, and designs the second-level penetration holes and the structural holes in the three-dimensional model of the graphite device by modeling, and then forms the second-level penetration holes and the structural holes in the internal structure of the graphite device while printing the graphite device by subsequent three-dimensional printing, so as to prepare a graphite device with a multi-level pore structure that meets the design requirements. The preparation method of the graphite device provided by the present invention can prepare a graphite device with rich pore size, controllable pore size and pore size distribution, which overcomes the drawbacks of the existing porous graphite device preparation method such as the single pore size, the difficult control of the pore size, the uneven pore distribution and the easy formation of closed pores, which leads to the single function and low material transfer efficiency of the graphite device; in addition, no pore-forming agent is used in the preparation process, which avoids the introduction of foreign impurities to affect the purity of the graphite device, and also overcomes the problem of high production cost due to the expensive price of the pore-forming agent; and the preparation method provided by the present invention is simple and controllable, which is conducive to large-scale industrial production.

[0017] In a possible implementation manner, the combination method in step S1 is a parallel combination of the closed hole and the through hole.

[0018] In a possible implementation manner, the combination in step S1 is a hierarchical combination of the closed holes, the through holes and the structural holes.

[0019] In a possible implementation, the preparation process of the mixed raw material in step S2 further includes granulation, that is, spheroidizing and granulating the mixed slurry to obtain a mixed material. Spheroidizing and granulating can provide the mixed raw material with more closed pores and first-level penetrating pores.

[0020] In a possible implementation, the carbon source in step S2 includes at least one of natural graphite powder, isostatically pressed graphite powder, graphite electrode powder, asphalt coke, petroleum coke, metallurgical coke and carbon black.

[0021] Furthermore, the carbon source consists of the isostatically pressed graphite powder and the carbon black in a mass ratio of 1:1, the natural graphite powder and the petroleum coke in a mass ratio of 3:1, or the asphalt coke, the graphite electrode powder and the carbon black in a mass ratio of 5:3:2.

[0022] In a possible implementation, the binder in step S2 includes at least one of epoxy resin, phenolic resin, furan resin, urea-formaldehyde resin, polyurethane, polyvinyl alcohol, polymethyl methacrylate and polyvinyl butyral.

[0023] In a possible implementation manner, the auxiliary agent in step S2 includes at least one of a curing agent, a sintering aid, a dispersant and a diluent.

[0024] Furthermore, the curing agent includes at least one of a water-soluble sol curing agent, an acid curing agent, an amine curing agent, an acid anhydride curing agent and an ester curing agent.

[0025] In a possible implementation, the solvent in step S2 includes at least one of water, methanol, ethanol, acetone, ethylene glycol, xylene, ethyl acetate and petroleum ether.

[0026] In a possible implementation, the three-dimensional printing in step S3 adopts any one of slurry extrusion technology, three-dimensional printing technology, powder laser solidification technology and selective laser sintering technology.

[0027] Based on the common knowledge in this field, the above-mentioned implementation modes can be combined arbitrarily.

[0028] The reagents and raw materials used in the present invention are commercially available.

[0029] The positive and progressive effects of the present invention are: The multi-level porous graphite material provided by the present invention has a pore structure of different sizes and provides a rich pore size. Through different combination strategies of closed pores, penetrating pores and / or structural pores, a multi-level porous graphite material that meets various functional requirements can be obtained. The preparation method of the graphite device provided by the present invention is simple and controllable, which is conducive to large-scale industrial production. DETAILED DESCRIPTION

[0030] In order to make the above-mentioned purposes, features and advantages of the present invention more obvious and easy to understand, the specific embodiments of the present invention are described in detail below. It should be noted that the following embodiments are only used to illustrate the implementation method and typical parameters of the present invention, and are not used to limit the parameter range described in the present invention. Reasonable changes derived therefrom are still within the scope of protection of the claims of the present invention.

[0031] It should be noted that the endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed in this article.

[0032] Unless otherwise defined, all terms, symbols and other scientific terms used herein are intended to have the same meaning as those commonly understood by those skilled in the art to which the present invention belongs. In some cases, terms with conventionally understood meanings are defined herein for the purpose of clarification or ease of reference, and such definitions herein should not be construed as indicating significant differences from conventional understandings in the art. The technical methods described or cited herein are generally well understood by those skilled in the art and are adopted by conventional methods. Unless otherwise stated, the use of commercially available kits, reagents and instruments is carried out in accordance with the protocols and parameters given by the manufacturer.

[0033] Example 1

[0034] This embodiment provides a graphite cylinder for growing silicon carbide crystals, which is divided into three layers from the inside to the outside of the cylinder. The inner and outer layers are small-pore porous graphite, and the structure has closed holes with an average pore size of 0.005 mm and through holes with an average pore size of 0.1 mm; the middle layer is large-pore porous graphite, and the structure has a structural hole with a designed pore size of 10 mm in addition to closed holes with a pore size of 0.005 mm and through holes with a pore size of 0.1 mm. The existence of closed holes with a pore size of 0.005 mm plays a role in isolating temperature zones, which can adjust the temperature field inside and outside the cylinder and increase the temperature difference between the raw material area and the growth area. The through holes with a pore size of 0.1 mm and the structural holes with a pore size of 10 mm are fast channels for material transmission. The multi-level porous graphite structure with small pores in the inner and outer layers and large pores in the middle layer is conducive to efficient filtration and screening of raw materials, and is also conducive to ensuring its strength. Its bending strength is greater than 10 MPa and its porosity is greater than 50%.

[0035] It is prepared by the following preparation method: S1. Modeling: Design and draw the graphite cylinder drawings, which have a three-layer structure equally divided from the inside to the outside of the cylinder. Design a structural hole with a diameter of 10 mm in the middle layer. The height of the hole is the same as the thickness of the middle layer, and the axis of the hole is perpendicular to the axial direction of the graphite cylinder. Then construct the designed drawings into a three-dimensional model; S2, mixed material preparation: carbon source: binder: auxiliary agent: solvent according to the mass ratio of 60:5:2:33, put into a blender and mix thoroughly to form a mixed slurry; wherein the carbon source is composed of isostatically pressed graphite powder and carbon black in a mass ratio of 1:1, the binder is polyvinyl alcohol, the auxiliary agent is a water-soluble sol, and the solvent is water; S3, blank manufacturing: the three-dimensional model in step S1 is introduced into the slurry extrusion equipment, the mixed slurry in step S2 is loaded into the hopper of the slurry extrusion equipment, and the process conditions are set as follows: the model is sliced ​​automatically, the layer thickness is 0.3 mm, the extrusion head diameter is 0.4 mm, the filler interval is 0.4 mm, and the working temperature is 45°C. The extruded wire is deposited and solidified along the set path, and a continuous pore with a diameter of 0.1 mm is formed between the angles of the wires, and then accumulated layer by layer to prepare a graphite tube blank; S4, firing: the graphite tube blank in step S3 is subjected to carbonization and high-temperature graphitization in sequence to obtain a graphite tube with a multi-level pore structure.

[0036] Example 2

[0037] This embodiment provides a graphite shelf for growing silicon carbide crystals, which has closed holes with an aperture of 0.01 mm, first-level penetration holes with an aperture of 0.05 mm, and second-level penetration holes with an aperture of 0.25 mm, and the distribution density of the second-level penetration holes with an aperture of 0.25 mm increases stepwise from the center of the graphite shelf to the edge of the graphite shelf. Such a design promotes the diffusion of raw gas from the edge of the graphite shelf to the growth area, which is conducive to stabilizing the airflow in the growth area, making the filtration gas path unobstructed, and the permeability reaches 100%.

[0038] It is prepared by the following preparation method: S1, Modeling: Design and draw the graphite shelf drawings, and then build them into a three-dimensional model; S2, mixed material preparation: carbon source: binder: auxiliary agent: solvent according to the mass ratio of 80:15:5:60, put into a blender and fully mix to form a mixed slurry, and then spheroidize and granulate to obtain a mixed material; wherein the carbon source is composed of natural graphite powder and petroleum coke in a mass ratio of 3:1, the binder is phenolic resin, the auxiliary agent is an amine curing agent, and the solvent is ethanol; S3, blank manufacturing: the three-dimensional model described in step S1 is introduced into the powder laser curing equipment, and the mixed material of step S2 is loaded into the equipment hopper. The process conditions adopted are: the model is sliced ​​manually, the layer thickness is 0.15 mm, the spot size is 0.2 mm, the laser power is 20 W, the laser scanning speed is 600 mm / s, the working temperature is 75 ° C, and N2 is filled as a protective gas in the operating space; during the blank manufacturing process, from the center to the edge of the model, the laser filling interval is gradually increased from 0.1 mm to 0.3 mm, so as to achieve a step-by-step increase in the distribution density of the 0.25 mm second-level penetration holes; S4, firing: the graphite tube blank described in step S3 is subjected to carbonization and high-temperature graphitization in sequence to obtain a graded porous graphite shelf for growing silicon carbide crystals.

[0039] Example 3

[0040] This embodiment provides a graphite cover for growing silicon carbide crystals, which is composed of a core skeleton and a rib network combination, wherein the core skeleton has closed holes with an average pore size of 0.03 mm and first-level through holes with an average pore size of 0.08 mm, which play a self-supporting role; the ribs are wrapped or involved around the core skeleton, and in addition to the closed holes with an average pore size of 0.03 mm and the first-level through holes with an average pore size of 0.08 mm, the ribs also have second-level through holes with an average pore size of 0.5 mm. The size of the ribs is designed according to the space where the raw materials are located, which plays a role in homogenizing the atmosphere in the raw material area and adjusting the direction of the airflow.

[0041] It is prepared by the following preparation method: S1, Modeling: Design and draw the graphite cover drawings, and then build them into a three-dimensional model; S2, mixed material preparation: carbon source: curing agent: solvent according to the mass ratio of 90:10:30, put into a blender and mix thoroughly to form a mixed slurry, and then spheroidize and granulate to obtain a mixed material; wherein the carbon source is composed of pitch coke, graphite electrode powder and carbon black in a mass ratio of 5:3:2, the curing agent is p-toluenesulfonic acid, and the solvent is water; S3, blank manufacturing: import the 3D model in step S1 into the 3D printing equipment, load the mixed material in step S2 into the equipment hopper, set the process conditions of 3D printing as follows: the sprayed ink is furan resin, the core skeleton area is 1200PDI inkjet resolution, the rib area is 400PDI inkjet resolution, and the printing layer thickness is 0.05 mm; S4, firing: the graphite cover blank of step S3 is subjected to carbonization and high-temperature graphitization in sequence to obtain a graded porous graphite cover for growing silicon carbide crystals.

[0042] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein by equivalents. However, these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A multi-level porous graphite material, characterized in that: The invention has a hierarchical porous structure, wherein the hierarchical porous structure includes closed holes, through holes and / or structural holes, wherein the closed holes are non-penetrating holes, and the pore size of the closed holes is 0.001-0.05 mm, and the through holes and the structural holes penetrate the porous graphite material, wherein the through holes include first-level through holes and second-level through holes, wherein the pore size of the first-level through holes is 0.03-0.2 mm, the pore size of the second-level through holes is 0.1-2 mm, and the pore size of the structural holes is 1-20 mm.

2. The multi-level porous graphite material according to claim 1, characterized in that: The second level penetration holes and the structural holes are prepared by additive manufacturing technology.

3. The multi-level porous graphite material according to claim 2, characterized in that: In the multi-level porous graphite material, the closed pores, the through pores and / or the structural pores are in at least one of a parallel combination, a series combination, a modular combination, a hierarchical combination and a network combination.

4. The multi-level porous graphite material according to claim 3, characterized in that: The parallel combination, the series combination, the modular combination, the hierarchical combination and the network combination are realized by adjusting the process of the additive manufacturing technology, and the process includes at least one of model slicing processing method, layer thickness, filler spacing, filler method, slurry extrusion speed, slurry extrusion pressure, extrusion head size, nozzle resolution, ink drop size, inkjet pressure, laser power, spot size, scanning speed, printing path, temperature, humidity and protective gas.

5. The multi-level porous graphite material according to claim 1, characterized in that: The multi-level porous graphite material comprises N graphite layers, N≥2, and each of the graphite layers contains at least one of the closed pores, the through pores and the structural pores; And / or, in the multi-level porous graphite material, the distribution density of the second-level through holes or the structural holes increases gradually from the center to the edge of the material; And / or, the porous graphite material has a network combination formed by a core skeleton and ribs connected to each other, the core skeleton has closed pores and first-level through holes, and the ribs have the closed pores, the first-level through holes and the second-level through holes.

6. A graphite device, characterized in that: The composition of the graphite device includes the multi-level porous graphite material according to any one of claims 1 to 4.

7. The graphite device according to claim 6, characterized in that: The graphite device is a graphite shelf, a graphite cylinder, a graphite frame, a graphite cover or a graphite crucible.

8. A method for preparing the graphite device according to claim 6 or 7, characterized in that: The following steps are involved: S1. Modeling: According to the functional requirements of the graphite device, a combination of closed pores, through pores and / or structural pores in the corresponding hierarchical porous structure is designed, and a three-dimensional model of the graphite device having the hierarchical porous structure is constructed; S2, mixed raw material preparation: fully mix the carbon source, the binder, the auxiliary agent, and the solvent to form a mixed slurry; the mass ratio of the carbon source, the binder, the auxiliary agent, and the solvent is (60-90):(0-40):(0-10):(30-100); S3, blank manufacturing: importing the three-dimensional model described in step S1 into the control module of the additive manufacturing equipment, adding the mixed slurry described in step S2 into the hopper of the additive manufacturing equipment, and performing three-dimensional printing to obtain the blank of the graphite device; S4, sintering: The green body of the graphite device in step S3 is subjected to carbonization treatment and graphitization treatment in sequence to obtain a graphite device.

9. The method for preparing a graphite device according to claim 8, characterized in that: The preparation process of the mixed raw material in step S2 further includes granulation, that is, spheroidizing and granulating the mixed slurry to obtain a mixed material; And / or, the carbon source in step S2 includes at least one of natural graphite powder, isostatic graphite powder, graphite electrode powder, asphalt coke, petroleum coke, metallurgical coke and carbon black; And / or, the binder in step S2 includes at least one of epoxy resin, phenolic resin, furan resin, urea-formaldehyde resin, polyurethane, polyvinyl alcohol, polymethyl methacrylate and polyvinyl butyral; And / or, the auxiliary agent in step S2 includes at least one of a curing agent, a sintering aid, a dispersant and a diluent; And / or, the solvent in step S2 includes at least one of water, methanol, ethanol, acetone, ethylene glycol, xylene, ethyl acetate and petroleum ether; And / or, the three-dimensional printing in step S3 adopts any one of slurry extrusion technology, three-dimensional printing technology, powder laser solidification technology and selective laser sintering technology.

10. The method for preparing a graphite device according to claim 9, characterized in that: The carbon source is composed of the isostatically pressed graphite powder and the carbon black in a mass ratio of 1:1, the natural graphite powder and the petroleum coke in a mass ratio of 3:1, or the pitch coke, the graphite electrode powder and the carbon black in a mass ratio of 5:3:2; And / or, the curing agent includes at least one of a water-soluble sol curing agent, an acid curing agent, an amine curing agent, an acid anhydride curing agent and an ester curing agent.