Modified porous graphite, and preparation method and application thereof

Abstract

The application discloses modified porous graphite and a preparation method and application thereof, and belongs to the technical field of porous graphite preparation. The preparation method of the modified porous graphite comprises the following steps: after raw coke is crushed, classified and mixed, the raw coke is mixed, spheroidized and granulated with a binder and a pore-forming agent, the spheroidization and granulation time is 0.5-2 h, and the granulation size is 0.5-0.8 mm; the mass ratio of the raw coke, the binder and the pore-forming agent is 65-70:20-30:5-20; then, the raw coke is pressed, baked and high-temperature graphitized, and the modified porous graphite is obtained. The preparation process of the modified porous graphite is simple, the obtained modified porous graphite is uniform in composition, has ordered pore diameter distribution, high transmittance, few impurities and high porosity, and the required raw materials are widely available and cheap and easy to obtain.

Description

Technical Field

[0001] The present invention relates to the technical field of porous graphite preparation, in particular to modified porous graphite and a preparation method and application thereof. Background Art

[0002] The information disclosed in the background of the invention is only intended to enhance understanding of the overall background of the invention and should not necessarily be regarded as an admission or any form of suggestion that the information constitutes the prior art already known to a person skilled in the art.

[0003] Due to their advantages such as wide bandgap, high breakdown voltage, and high conductivity, third-generation semiconductor materials will be widely used in key areas such as new energy vehicles, microwave communications, and national defense. Currently, silicon carbide single crystals grown by physical vapor transport (PVT), as the most mature and representative of the new generation of semiconductor products, have become the primary target of industrialization. During the PVT single crystal growth process, porous graphite is placed in the graphite crucible to filter and screen the raw materials, purifying the single crystal growth atmosphere. This effectively reduces crystal defects such as microtubules and inclusions, improving crystal quality and reducing industrial production costs.

[0004] The pore size distribution of porous graphite will affect the single crystal growth process of the PVT method, affecting not only the production efficiency of silicon carbide single crystals, but also the growth quality of single crystals. Patent CN 116120079B (authorization announcement date: 2020.10.13) discloses a method for manufacturing porous graphite separators for growing silicon carbide crystals by physical vapor transport. The patent found that the porous graphite prepared by soaking ammonium chloride solution with mercerized cotton staple fibers with a diameter of about 20-40μm and a length of 15-25mm as raw materials has a moderate average pore size and a narrow pore size distribution, high open porosity and strength, and is suitable for making PVT-grown silicon carbide single crystal separators, which is conducive to the controlled transmission of gaseous substances; while the porous graphite that does not use mercerized cotton staple fibers as templates has an uneven pore size distribution. Mercerized cotton is additionally introduced as a template in the raw materials of this patent, and the addition amount is relatively high. It is a high-quality knitted fabric, so the cost of this preparation process is relatively high.

[0005] Therefore, how to provide a porous modified graphite for growing silicon carbide crystals by physical vapor transport method with simple preparation process, low cost, low impurity content, high porosity and uniform pore size distribution is an urgent problem to be solved. Summary of the Invention

[0006] In view of this, the present invention provides a modified porous graphite, a preparation method and application thereof. The preparation process of the modified porous graphite is simple, and the obtained modified porous graphite has uniform composition, orderly pore size arrangement, high transmittance, good high temperature and corrosion resistance, low impurity content and high porosity.

[0007] In a first aspect, the present invention provides a method for preparing modified porous graphite, comprising the following steps:

[0008] The raw coke is crushed, classified and mixed, and then mixed with a binder and a pore-forming agent for spheroidization and granulation. The mixing and spheroidization granulation time is 0.5 to 2 hours, and the granulation size is 0.5 to 0.8 mm. The mass ratio of the raw coke, the binder and the pore-forming agent is 65 to 70:20 to 30:5 to 20. The raw coke is then pressed, calcined and graphitized at high temperature to obtain the product.

[0009] Preferably, the raw coke comprises one of green petroleum coke, pitch coke or metallurgical coke. The raw coke is selected from the above materials, which has a high carbon content and is conducive to the subsequent roasting and high-temperature graphitization process, and is the main material of the modified porous graphite.

[0010] Preferably, the binder comprises one of phenolic resin, epoxy resin, graphite glue, or petroleum asphalt. The binder has two functions: first, it melts at 200-500°C to bond the raw coke, thereby increasing the strength of the product; second, it decomposes at high temperatures to increase carbonization and improve the density of the product.

[0011] Preferably, the pore-forming agent includes one or more of polyvinyl pyrrolidone, potassium chloride, styrene-butadiene rubber, glucose, or polyvinyl chloride. These pore-forming agents can completely decompose during the high-temperature calcination stage, creating pores in the product, increasing the number of pores within the product and improving the porosity.

[0012] Preferably, the crushing and grading step comprises: crushing the raw coke, and then mixing the raw materials into two grades, 40-80 mesh and 80-300 mesh, at a mass ratio of 20-30:70-80. The crushing and grading step is performed to achieve coordinated control of the product through-hole diameter and product density by combining raw coke of different particle sizes.

[0013] Preferably, the equipment used for spheroidization and granulation of the mixture with the binder and pore-forming agent is a mixing granulator. The spheroidization and granulation modify the morphology of the mixture, making the spheroidized particles more uniform in spatial accumulation. After pressing and calcining, the sample pore morphology is complete and smooth, and the pore size and surface shape are evenly distributed.

[0014] Preferably, the pressing pressure is 15-30 MPa and the pressing time is 0.5-1 hour. The pressing equipment includes a hot extruder, a hot die press or a hot isostatic press.

[0015] Preferably, the calcination process is a gradient calcination, specifically: heating to 200-400°C at a heating rate of 2-5°C / min, and calcining for 24-36 hours; then heating to 500-700°C at a heating rate of 2-5°C / min, and calcining for 18-24 hours; finally heating to 900-1100°C at a heating rate of 2-5°C / min, and calcining for 24-150 hours.

[0016] Preferably, the temperature of the high-temperature graphitization is 2300° C., and the time of the high-temperature graphitization is 20 to 40 hours.

[0017] Furthermore, purified gas is introduced during the high-temperature graphitization process, and the purified gas includes chlorine and / or Freon.

[0018] In a second aspect, the present invention provides a modified porous graphite prepared by the above preparation method, wherein the volume density of the modified porous graphite is 1.3 g / cm 3 Below, the porosity is above 48%, the flexural strength is above 10MPa, and the impurity content is below 5ppm.

[0019] In a third aspect, the present invention provides the use of the modified porous graphite in the growth of silicon carbide single crystals using a physical vapor transport method.

[0020] Compared with the prior art, the present invention has achieved the following beneficial effects:

[0021] The preparation method provided by the present invention is simple, environmentally friendly and low-cost. The internal pores of the prepared product are smooth, the filtration air path is unobstructed, the permeability reaches 100%, the porosity is above 48%, and the volume density is 1.3g / cm 3 The modified porous graphite prepared is suitable for growing high-quality silicon carbide single crystals by physical vapor transport method. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The drawings, which constitute part of the present invention, are intended to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are intended to explain the present invention and do not constitute undue limitations thereon. It is obvious that one of ordinary skill in the art could derive other drawings based on these drawings without inventive effort.

[0023] Figure 1 This is a physical photo of the modified graphite material of Example 1 of the present invention;

[0024] Figure 2 This is a physical photo of the modified graphite material of Comparative Example 1 of the present invention. DETAILED DESCRIPTION

[0025] It should be noted that the following detailed descriptions are exemplary and intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the present invention belongs.

[0026] The technical solution of the present invention is further described below with reference to specific embodiments.

[0027] Example 1

[0028] This embodiment provides a method for preparing modified porous graphite, and the specific steps are as follows:

[0029] (1) Raw material selection: Raw petroleum coke was selected as the raw material coke, petroleum asphalt as the binder, and glucose as the pore-forming agent; all raw materials were purchased from the market.

[0030] (2) Batching: crush and grade the raw petroleum coke, and mix the raw materials of 40-80 mesh and 80-300 mesh in a mass ratio of 25:75 for standby use;

[0031] (3) Mixing: The raw petroleum coke mixed in step (2) and the binder and pore-forming agent are mixed in a mixing granulator for 1 hour to obtain a mixture, and the granulation particle size is 0.5 mm; the mass ratio of the raw materials, the binder and the pore-forming agent is 70:20:10;

[0032] (4) Molding: The mixture obtained in step (3) is pressed into a blank by a hot mold press; the pressing pressure is 20 MPa and the pressing time is 1 hour;

[0033] (5) Calcination: The blank obtained in step (4) was heated to 300°C at a heating rate of 3°C / min and calcined for 30 h, then heated to 600°C at a heating rate of 2°C / min and calcined for 20 h, and finally heated to 1000°C at a heating rate of 3°C / min and calcined for 150 h to obtain a porous material;

[0034] (6) Graphitization: The porous material prepared in step (5) is graphitized at 2300° C., with chlorine gas introduced to reduce impurities, for 30 h.

[0035] Example 2

[0036] This embodiment provides a method for preparing modified porous graphite, and the specific steps are as follows:

[0037] (1) Raw material selection: Raw petroleum coke was selected as the raw material coke, phenolic resin was selected as the binder, and polyvinyl pyrrolidone was selected as the pore-forming agent; all raw materials were purchased from the market.

[0038] (2) Batching: crush and grade the raw materials, and mix the raw materials of 40-80 mesh and 80-300 mesh in a mass ratio of 28:72 for later use;

[0039] (3) Mixing: The raw materials mixed in step (2) are mixed with a binder and a pore-forming agent to form granules, and the mixture is mixed for 1 hour to obtain a mixture with a granulation particle size of 0.75 mm; the mass fraction ratio of the raw materials, the binder and the pore-forming agent is 65:28:7;

[0040] (4) Molding: Pressing the mixture obtained in step (3) into a blank;

[0041] (5) Calcination: The blank obtained in step (4) was heated to 200°C at a heating rate of 3°C / min and calcined for 36 hours, then heated to 550°C at a heating rate of 2°C / min and calcined for 30 hours, and finally heated to 1000°C at a heating rate of 3°C / min and calcined for 80 hours to obtain a porous material;

[0042] (6) Graphitization: The porous material of step (5) was graphitized at 2300°C for 24 hours while passing chlorine and Freon to reduce impurities.

[0043] Comparative Example 1

[0044] The difference between this comparative example and Example 1 is that the mixing method is stirring mixing rather than mixing spheroidization granulation.

[0045] (1) Raw material selection: Raw petroleum coke was selected as the raw material coke, phenolic resin was selected as the binder, and polyvinyl pyrrolidone was selected as the pore-forming agent; all raw materials were purchased from the market.

[0046] (2) Batching: crush and grade the raw materials, and mix the raw materials of 40-80 mesh and 80-300 mesh in a mass ratio of 28:72 for later use;

[0047] (3) Mixing: The raw materials mixed in step (2) are stirred and mixed with a binder and a pore-forming agent for 1 hour to obtain a mixture with a particle size of about 0.37 mm (ungranulated). The mass fraction ratio of the raw materials, binder and pore-forming agent is 65:28:7;

[0048] (4) Molding: Pressing the mixture obtained in step (3) into a blank;

[0049] (5) Calcination: The blank obtained in step (4) was heated to 200°C at a heating rate of 3°C / min and calcined for 36 h, then heated to 550°C at a heating rate of 2°C / min and calcined for 30 h, and finally heated to 1000°C at a heating rate of 3°C / min and calcined for 150 h to obtain a porous material;

[0050] (6) Graphitization: The porous material of step (5) was graphitized at 2300°C for 30 hours while passing chlorine gas to reduce impurities.

[0051] The performance of the porous graphite of Examples 1-2 and Comparative Example 1 was tested, as shown in Table 1.

[0052] Table 1 Test results of porous graphite properties of Examples 1 to 2

[0053]

[0054]

[0055] From Table 1 and Figure 1 It can be seen that the modified porous graphite of Example 1 and Example 2 has a higher porosity and a lower bulk density, and the surface is uniform without cracking. Although the flexural strength is slightly lower than that of the comparative example, it can still be maintained above 10MPa. Comparative Example 1 has not undergone spheroidization and granulation, and obvious cracks appear on the surface of the actual picture. The cracks can extend to the interior of the block, indicating that there is a problem of uneven stress inside it and the pore size is uneven. The uneven distribution of pores in the cross section affects the gas phase transmission distribution in the PVT method, which will have an adverse effect on the face shape of the silicon carbide crystal.

[0056] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A method for preparing modified porous graphite, characterized in that: The steps include: The raw coke is crushed, classified and mixed, and then mixed with a binder and a pore-forming agent to form spheroidized granules. The mixing and spheroidizing granulation time is 0.5-2 hours, and the granule size is 0.5-0.8 mm. The mass ratio of the raw coke, binder and pore-forming agent is 65-70:20-30:5-20. The raw coke is then pressed, calcined and graphitized at high temperature to obtain the product. The raw coke includes one of green petroleum coke, pitch coke or metallurgical coke; The binder includes one of phenolic resin, epoxy resin, graphite glue or petroleum asphalt; The pore-forming agent includes one or more of polyvinyl pyrrolidone, potassium chloride, styrene-butadiene rubber, glucose or polyvinyl chloride; The crushing and classification step is specifically as follows: after the raw coke is crushed, two grades of raw materials, 40-80 mesh and 80-300 mesh, are mixed at a mass ratio of 20-30:70-80; The equipment used for mixing and spheroidizing granulation with the binder and pore-forming agent is a mixing granulator; The calcination process is a gradient calcination process, specifically: heating to 200-400°C at a heating rate of 2-5°C / min, and calcining for 24-36 hours; then heating to 500-700°C at a heating rate of 2-5°C / min, and calcining for 18-24 hours; finally heating to 900-1100°C at a heating rate of 2-5°C / min, and calcining for 24-150 hours; The temperature of the high-temperature graphitization is 2300° C., and the time of the high-temperature graphitization is 20 to 40 hours; Purified gas is introduced into the high-temperature graphitization process, wherein the purified gas is chlorine or chlorine and Freon; The volume density of the modified porous graphite is 1.3 g / cm 3 Below, porosity is above 48%, flexural strength is above 10 MPa, and impurity content is below 5ppm; The modified porous graphite is used for growing silicon carbide crystals by a physical vapor transport method.

2. The preparation method according to claim 1, wherein The pressing pressure is 15-30 MPa and the pressing time is 0.5-1 h; the pressing equipment includes a hot extruder, a hot mold press or a hot isostatic press.

3. Use of the modified porous graphite obtained by the preparation method according to any one of claims 1 to 2 in growing silicon carbide single crystals by physical vapor transport.

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