Porous graphite and preparation method

Abstract

Porous graphite and a preparation method belong to the technical field of semiconductors. A mixed raw material comprising 30-60 parts of carbon fibers with the average length of 100-300 microns and the average diameter of 10-20 microns and 35-70 parts of a carbonizable graphitized organic precursor substance is subjected to cold press molding under the pressure of 2-80 MPa, carbonization and graphitization are sequentially carried out, and the obtained porous graphite has the heat conductivity coefficient of 6-20 w / (m.K) at the test temperature of 1000 DEG C, the bending strength of 6-50 Mpa and the tensile strength of 6-50 Mpa at the test temperature of 1000 DEG C; when applied to the growth of silicon carbide crystals, the silicon carbide powder is not easy to fall off, has small secondary pollution, is not easy to deform due to strong airflow impact, and is favorable for controlling the temperature gradient, relieving the thermal shock and improving the growth quality of the silicon carbide crystals.

Description

Technical Field

[0001] This application relates to the field of semiconductor technology, and more specifically, to a porous graphite and a method for its preparation. Background Technology

[0002] Silicon carbide possesses properties such as a wide bandgap, high thermal conductivity, high electron saturation mobility, and high breakdown electric field, making it an ideal semiconductor material for manufacturing optoelectronic devices, high-frequency high-power devices, and high-temperature electronic devices.

[0003] Currently, in the growth process of silicon carbide crystal materials, porous graphite is typically used to separate the silicon carbide source powder and the silicon carbide seed crystal. During crystal growth, the silicon carbide source powder is heated to a certain temperature and sublimates, forming a gaseous substance. This sublimated gaseous substance passes through the porous graphite and is transported to the surface of the seed crystal for deposition and crystal growth.

[0004] However, when using porous graphite to prepare silicon carbide crystals, the silicon carbide crystals are prone to cracking, resulting in poor growth quality. Summary of the Invention

[0005] Based on the above-mentioned shortcomings, this application provides a porous graphite and its preparation method to improve the problem of poor silicon carbide crystal growth quality in related technologies.

[0006] This application is implemented as follows:

[0007] In a first aspect, an example of this application provides a porous graphite with a thermal conductivity of 6-20 W / (mK) at a test temperature of 1000 °C and a flexural strength of 6-50 MPa.

[0008] In the above process, porous graphite has a thermal conductivity of 6-20 W / (mK) and a bending strength of 6-50 MPa at a test temperature of 1000℃. It has both high bending strength and low thermal conductivity. When applied to silicon carbide crystal growth, it has high bending strength, is not prone to powder shedding, has little secondary pollution, and is not easily deformed by strong airflow. The low thermal conductivity can meet the requirements of precise control of temperature gradient in silicon carbide crystal growth, maintain the temperature stability of the crystal growth area, and mitigate the thermal shock caused by temperature changes, thereby improving the growth quality of silicon carbide crystals.

[0009] In conjunction with the first aspect, in an optional embodiment of this application, the thermal conductivity of porous graphite at a test temperature of 1000°C is 12.9-14.6 W / (mK).

[0010] In conjunction with the first aspect, in an optional embodiment of this application, the thermal conductivity of porous graphite at a test temperature of 1000°C is 14.6-16.6 W / (mK).

[0011] In conjunction with the first aspect, in an optional embodiment of this application, the flexural strength of porous graphite is 14.5-24.1 MPa.

[0012] In conjunction with the first aspect, in an optional embodiment of this application, the flexural strength of porous graphite is 24.1-34.1 MPa.

[0013] In conjunction with the first aspect, in an optional embodiment of this application, the flexural strength of porous graphite is 34.1-46.1 MPa.

[0014] In conjunction with the first aspect, in an optional embodiment of this application, the porous graphite has a bulk density of 0.7-1.25 g / ml and a total pore area of ​​0.05-1.8 m². 2 / g.

[0015] In conjunction with the first aspect, in an optional embodiment of this application, the bulk density of porous graphite is 0.92-1.02 g / ml.

[0016] In conjunction with the first aspect, in an optional embodiment of this application, the bulk density of porous graphite is 1.02-1.12 g / ml.

[0017] In conjunction with the first aspect, in an optional embodiment of this application, the total pore area of ​​the porous graphite is 0.05-0.5 μm. 2 / g.

[0018] In conjunction with the first aspect, in an optional embodiment of this application, the total pore area of ​​the porous graphite is 0.5-1.0 μm. 2 / g.

[0019] In conjunction with the first aspect, in an optional embodiment of this application, the total pore area of ​​the porous graphite is 1.0-1.5 μm. 2 / g.

[0020] In conjunction with the first aspect, in an optional embodiment of this application, the total pore area of ​​the porous graphite is 1.5-1.8 μm. 2 / g.

[0021] In conjunction with the first aspect, in an optional embodiment of this application, the apparent density of porous graphite is 1.725-1.814 g / ml.

[0022] In the above implementation process, the porous graphite provided in this application has a bulk density of 0.7-1.2 g / ml and an apparent density of 1.725-1.814 g / ml. The apparent density remains basically stable as the bulk density increases. By adjusting the ratio of open and closed pores, the heat transfer path of porous graphite during heat transfer and the force transfer path when subjected to force can be affected, so that porous graphite has high bending strength and low thermal conductivity.

[0023] In conjunction with the first aspect, in an optional embodiment of this application, the median pore size of the porous graphite is 8.05-47.16 μm, and the average pore size is 0.476-30.89 μm.

[0024] In the above implementation process, the porous graphite provided in this application example has a mean pore size of 8.05-47.16 μm and an average pore size of 0.476-30.89 μm. By controlling the pore distribution, the flexural strength of the porous graphite can be improved while the thermal conductivity of the porous graphite is reduced.

[0025] In conjunction with the first aspect, in an optional embodiment of this application, the median pore size of the porous graphite is 15.84-25.44 μm.

[0026] In conjunction with the first aspect, in an optional embodiment of this application, the median pore size of the porous graphite is 25.44-34.44 μm.

[0027] In conjunction with the first aspect, in an optional embodiment of this application, the average pore size of the porous graphite is 0.843-8.17 μm.

[0028] In conjunction with the first aspect, in an optional embodiment of this application, the average pore size of the porous graphite is 8.17-16.17 μm.

[0029] In conjunction with the first aspect, in an optional embodiment of this application, the average pore size of the porous graphite is 16.17-24.17 μm.

[0030] In conjunction with the first aspect, in an optional embodiment of this application, the porosity of the porous graphite is 33.05%-58.51%.

[0031] In conjunction with the first aspect, in an optional embodiment of this application, the porosity of the porous graphite is 37.85%-40.45%.

[0032] In conjunction with the first aspect, in an optional embodiment of this application, the porosity of the porous graphite is 40.45%-44.45%.

[0033] In conjunction with the first aspect, in an optional embodiment of this application, the porosity of the porous graphite is 44.45%-48.45%.

[0034] In conjunction with the first aspect, in an optional embodiment of this application, the air permeability of porous graphite is 2.8-6.5 L / m³. 2 ·s.

[0035] In the above implementation process, the porous graphite provided in this application example has a porosity of 33.05%-58.51% and an air permeability of 2.8-6.5 L / m³. 2 By adjusting the ratio of open pores to closed pores in porous graphite, it is possible to improve the flexural strength of porous graphite while reducing its thermal conductivity.

[0036] In conjunction with the first aspect, in an optional embodiment of this application, porous graphite includes graphite fibers and graphite body composited on the surface of the graphite fibers; by weight, porous graphite includes 30-60 parts of graphite fibers and 20-40 parts of graphite body.

[0037] In conjunction with the first aspect, in an optional embodiment of this application, the porous graphite comprises 40-50 parts by weight of graphite fibers and 29-35 parts by weight of graphite body.

[0038] In the above process, graphite fibers have good bending strength. By combining a specific number of graphite fibers and graphite bodies, the pore size distribution and pore structure of porous graphite can be adjusted, thereby improving the bending strength of porous graphite while reducing its thermal conductivity.

[0039] In conjunction with the first aspect, in an optional embodiment of this application, the graphite fiber has an average length of 150-200 μm and an average diameter of 10-15 μm.

[0040] In the above-mentioned process, the porous graphite contains 40-50 parts of graphite fibers with an average length of 150-200 μm and an average diameter of 10-15 μm, which can combine with the graphite body to adjust the pore structure and pore size distribution of the porous graphite, and adjust the heat transfer path and force transmission path. This makes the flexural strength of the porous graphite increase significantly with the increase of bulk density, while its thermal conductivity increases slowly with the increase of bulk density. As a result, the porous graphite has high flexural strength while having low thermal conductivity.

[0041] In conjunction with the first aspect, in optional embodiments of this application, the graphite fibers contain graphite and carbon; and / or, the graphite body contains graphite and carbon.

[0042] In a second aspect, an example of this application provides a method for preparing porous graphite, comprising:

[0043] Obtaining the mixed raw materials: by weight, the mixed raw materials include 30-60 parts of carbon fiber and 35-70 parts of graphitizable organic precursor material, with the average length of the carbon fiber being 100-300 μm and the average diameter being 10-20 μm.

[0044] The mixed raw materials are cold-pressed at a pressure of 2-80 MPa to obtain a green body; the green body is then carbonized and graphitized sequentially.

[0045] In the above process, 30-60 parts of carbon fibers with an average length of 100-300 μm and an average diameter of 10-20 μm and 35-70 parts of carbonizable graphitizable organic precursor material are mixed evenly and then cold-pressed. The pressure of cold pressing is 2-80 MPa. After subsequent carbonization and graphitization, porous graphite with high bending strength and low thermal conductivity can be obtained.

[0046] In conjunction with the second aspect, in optional embodiments of this application, the carbonizable and graphitizable organic precursor material is selected from phenolic resin; the method for sequentially carbonizing and graphitizing the preform includes:

[0047] The preform is heated to 150-200℃ and cured for 2-18 hours; under inert gas protection, it is heated to 1000-1400℃ at a heating rate of 0.2-0.5℃ / min for carbonization for 1-4 hours, and then heated to 2300-2500℃ for graphitization for 1-4 hours; purification is carried out at 2000-2500℃ using Freon or chlorine as the purification gas.

[0048] In the above process, phenolic resin powder is mixed with carbon fiber and then cold-pressed under a pressure of 10-60 MPa. The preform is then heated to 150-200℃ and cured for 2-18 hours. Under inert gas protection, the temperature is increased to 1000-1400℃ at a heating rate of 0.2-0.5℃ / min for carbonization for 1-4 hours. Then, the temperature is increased to 2300-2500℃ for graphitization for 1-4 hours. Purification is carried out at a temperature of 2000-2500℃ using Freon or chlorine as the purification gas. This process can yield porous graphite with high flexural strength and low thermal conductivity. Attached Figure Description

[0049] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below.

[0050] Figure 1 This is a SEM image of porous graphite provided in Embodiment 4 of this application;

[0051] Figure 2 SEM image of porous graphite provided in Comparative Example 1 of this application. Detailed Implementation

[0052] The embodiments of this application will be described in detail below with reference to examples. However, those skilled in the art will understand that the following examples are for illustrative purposes only and should not be considered as limiting the scope of this application. Unless otherwise specified in the examples, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0053] Currently, porous graphite is commonly used in the growth process of silicon carbide crystal materials.

[0054] For example, in the preparation of silicon carbide crystals, silicon carbide seed crystals are typically placed on porous graphite, which separates the silicon carbide source powder from the seed crystal. During crystal growth, the silicon carbide source powder is heated to a certain temperature and sublimates, forming a gaseous substance. This sublimated gaseous substance passes through the porous graphite and is transported to the surface of the seed crystal for deposition and crystal growth.

[0055] In the growth of silicon carbide crystals, the flexural strength of porous graphite has a significant impact on the control and quality of crystal growth. However, current methods for preparing silicon carbide crystals using porous graphite are prone to cracking, resulting in poor crystal growth quality.

[0056] Through analysis, the inventors discovered that commonly used porous graphite on the market currently exhibits high thermal conductivity and low strength. For example, porous graphite produced by a certain company has a bulk density of 1.13 g / ml, a thermal conductivity of 18 W / (mK) at a test temperature of 1000℃, and a flexural strength of 6.1 MPa. The inventors believe that the low flexural strength of current porous graphite makes it prone to fracture during the growth of large-sized silicon carbide crystals. It is also susceptible to powder shedding, secondary contamination, and deformation from strong airflow, which can lead to deformation or breakage of the silicon carbide crystals, thus affecting their quality.

[0057] Furthermore, the inventors discovered that to improve the flexural strength of porous graphite, it is usually necessary to increase its bulk density. However, with the increase of bulk density, the thermal conductivity of existing porous graphite also increases significantly.

[0058] For example, when the bulk density of porous graphite produced by a certain company is increased from 1.13 g / ml to 1.15 g / ml, its flexural strength increases from 6.1 MPa to 7.6 MPa, but its thermal conductivity at a test temperature of 1000℃ increases significantly from 18 W / (mK) to 30.0 W / (mK).

[0059] The inventors believe that although porous graphite with high thermal conductivity is beneficial for heat conduction and improving growth efficiency, it is not conducive to temperature gradient control, maintaining temperature stability, and mitigating thermal shock during crystal growth, which in turn is not conducive to optimizing the quality of silicon carbide crystals.

[0060] For example, compared to porous graphite with high thermal conductivity, porous graphite with low thermal conductivity can create a steeper temperature gradient, which is necessary for certain silicon carbide crystal growth techniques, such as physical vapor transport. The temperature gradient is one of the key parameters in silicon carbide crystal growth, affecting the growth direction, rate, and quality of the crystal. By controlling the thermal conductivity of porous graphite, the temperature distribution of the silicon carbide crystal growth environment can be finely adjusted, thereby optimizing the silicon carbide crystal growth conditions.

[0061] Furthermore, in silicon carbide crystal growth furnaces, porous graphite with low thermal conductivity can serve as a thermal insulation layer compared to porous graphite with high thermal conductivity, reducing heat transfer to the furnace wall and maintaining temperature stability in the growth region. This is crucial for maintaining the precise temperature conditions required for crystal growth.

[0062] For example, during crystal growth, if the temperature of the growth chamber changes suddenly, compared with porous graphite with high thermal conductivity, porous graphite with low thermal conductivity can slow down the rate of temperature change, reduce the impact of thermal shock on silicon carbide crystal growth, and help maintain the integrity of the crystal structure.

[0063] In addition, the use of porous graphite with low thermal conductivity can provide greater flexibility to the silicon carbide crystal growth process, allowing for the exploration of optimal growth conditions under different growth parameters, thereby optimizing crystal quality and yield.

[0064] Therefore, in order to improve the quality of silicon carbide crystals, it is necessary to provide a porous graphite with high flexural strength and low thermal conductivity.

[0065] This application provides an example of porous graphite and a method for preparing the same. The method for preparing porous graphite includes:

[0066] S1. Obtain the mixed raw materials; by weight, the mixed raw materials include 30-60 parts of carbon fiber and 35-70 parts of graphitizable organic precursor material, the average length of the carbon fiber is 100-300μm and the average diameter is 10-20μm.

[0067] S2. The mixed raw materials are cold-pressed at a pressure of 2-80 MPa to obtain a green body; the green body is then carbonized and graphitized sequentially.

[0068] 30-60 parts of carbon fibers with an average length of 100-300 μm and an average diameter of 10-20 μm are mixed with 35-70 parts of carbonizable graphitizable organic precursor material to obtain a mixed raw material. The mixed raw material is then placed under a pressure of 2-80 MPa for cold pressing. This allows for the control of the bulk density, pore distribution, and pore structure of the porous graphite obtained after subsequent carbonization and graphitization, in order to obtain porous graphite with high flexural strength and low thermal conductivity.

[0069] In step S1, 30-60 parts of carbon fiber and 35-70 parts of carbonizable graphitizable organic precursor are mixed. The carbonizable graphitizable organic precursor can form a graphite body structure of a certain mass on the surface of graphite fibers after subsequent carbonization and graphitization. The combination of graphite fibers and graphite body structure with appropriate mass ratio can form a porous structure with suitable pore size, pore shape, suitable total pore area, and suitable ratio of open and closed pores. This can improve the force transmission path of porous graphite under stress to increase the bending strength of porous graphite, and hinder the heat transfer path of porous graphite during the heat transfer process to reduce the thermal conductivity of porous graphite.

[0070] For example, the number of carbon fibers can be one or a range of any two of 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49 or 50 parts.

[0071] For example, the weight parts of the graphitizable organic precursor material can be 35 parts, 36 parts, 37 parts, 38 parts, 39 parts, 40 parts, 41 parts, 42 parts, 43 parts, 44 parts, 45 parts, 46 parts, 47 parts, 48 ​​parts, 49 parts, 50 parts, 51 parts, 52 parts, 53 parts, 54 parts, 55 parts, 56 parts, 57 parts, 58 parts, 59 parts, 60 parts, 61 parts, 62 parts, 63 parts, 64 parts, 65 parts, 66 parts, 67 parts, 68 parts, 69 parts, or 70 parts, or any combination thereof.

[0072] In some possible embodiments, the graphitizable organic precursor material may be selected from phenolic resins.

[0073] Furthermore, the mixed raw materials include 40-50 parts of carbon fiber and 50-60 parts of graphitizable organic precursor material.

[0074] For example, the conversion rate of phenolic resin to carbon is approximately 58%. In the prepared porous graphite, the weight parts of graphite body can be 29-35 parts, and the weight parts of graphite fibers can be 40-50 parts.

[0075] Furthermore, in step S1, the average length of the carbon fiber is 150-200 μm and the average diameter is 10-15 μm, which can improve the flexural strength of porous graphite, adjust the pore structure of porous graphite, and thus reduce the thermal conductivity of porous graphite.

[0076] For example, the average length of the carbon fiber can be one of 150 μm, 160 μm, 170 μm, 180 μm, 190 μm or 200 μm or any range between any two.

[0077] For example, the average diameter of the carbon fiber can be one of 10 μm, 11 μm, 12 μm, 13 μm, 14 μm or 15 μm or any combination thereof.

[0078] For example, the average length of the carbon fiber can be 180 μm and the average diameter can be 12 μm.

[0079] In step S2, the mixed raw materials are cold-pressed under a pressure of 2-80 MPa to form a blank. By adjusting the pressure during cold pressing of the mixed raw materials, the bulk density, pore size distribution, pore morphology and other porous structures of porous graphite can be controlled, thereby reducing the thermal conductivity and improving the bending strength.

[0080] Furthermore, the mixed raw materials are cold-pressed under a pressure of 10-60 MPa.

[0081] For example, cold pressing the mixed raw materials under a pressure of 10 MPa can produce porous graphite with a bulk density of 0.92 g / ml, a thermal conductivity of 12.9 w / (mK) at a test temperature of 1000℃, and a flexural strength of 14.5 MPa.

[0082] For example, cold pressing the mixed raw materials under a pressure of 25 MPa can produce porous graphite with a bulk density of 0.99 g / ml, a thermal conductivity of 13.0 W / (mK) at a test temperature of 1000 °C, and a flexural strength of 20.1 MPa.

[0083] For example, cold pressing the mixed raw materials under a pressure of 32 MPa can produce a bulk density of 1.02 g / ml, a thermal conductivity of 13.6 W / (mK) at a test temperature of 1000°C, and a flexural strength of 23.9 MPa.

[0084] For example, cold pressing the mixed raw materials under a pressure of 60 MPa can produce a bulk density of 1.12 g / ml, a thermal conductivity of 16.6 W / (mK) at a test temperature of 1000°C, and a flexural strength of 46.1 MPa.

[0085] Furthermore, in step S2, the method for sequentially carbonizing and graphitizing the cold-pressed preform includes:

[0086] The preform is heated to 150-200℃ and cured for 2-18 hours; under inert gas protection, it is heated to 1000-1400℃ at a heating rate of 0.2-0.5℃ / min for carbonization for 1-4 hours, and then heated to 2300-2500℃ for graphitization for 1-4 hours; purification is carried out at 2000-2500℃ using Freon or chlorine as the purification gas.

[0087] For example, the preform can be heated to 150°C, 160°C, 170°C, 180°C, 190°C or 200°C and cured for 2h, 5h, 10h, 15h or 18h.

[0088] For example, the temperature can be increased to 1000℃, 1100℃, 1200℃, 1300℃ or 1400℃ at a heating rate of 0.2℃ / min, 0.3℃ / min, 0.4℃ / min or 0.5℃ / min, and carbonization can be carried out for 1h, 2h, 3h or 4h.

[0089] For example, the carbonized porous carbon can be heated to 2300℃, 2400℃ or 2500℃ for graphitization for 1h, 2h, 3h or 4h.

[0090] For example, the graphitized porous graphene Freon or chlorine gas can be purified by heating it to a temperature of 2000°C, 2100°C, 2200°C, 2300°C, 2400°C or 2500°C.

[0091] The porous graphite prepared by the above method includes graphite fibers and graphite bodies composited on the surface of the graphite fibers.

[0092] Graphite fibers are formed by graphitizing carbon fibers, while graphite bodies are formed by curing, carbonizing, and graphitizing carbon-based organic precursors such as phenolic resin attached to the surface of carbon fibers. Due to varying degrees of graphitization, graphite fibers may contain both carbon and graphite. Similarly, graphite bodies may contain both carbon and graphite.

[0093] The porous graphite prepared by the above method has a thermal conductivity of 6-20 W / (mK) at a test temperature of 1000℃ and a flexural strength of 6-50 MPa.

[0094] For example, the thermal conductivity of porous graphite at a test temperature of 1000℃ can be 6.0 W / (mK), 6.2 W / (mK), 10.0 W / (mK), 10.5 W / (mK), 11.0 W / (mK), 11.5 W / (mK), 12.0 W / (mK), 12.5 W / (mK), 13.0 W / (mK), 13.5 W / (mK), and 14.0 W / (mK). The range is one or any two of the following: 14.5w / (mK), 15.0w / (mK), 15.5w / (mK), 16.0w / (mK), 16.5w / (mK), 17.0w / (mK), 17.5w / (mK), 18.0w / (mK), 18.5w / (mK), 19.0w / (mK), 19.5w / (mK), or 20.0w / (mK).

[0095] In some possible embodiments, the thermal conductivity of porous graphite at a test temperature of 1000°C can be 6.2-12.9 W / (mK).

[0096] In some possible embodiments, the thermal conductivity of porous graphite at a test temperature of 1000°C can be 12.9-14.6 W / (mK).

[0097] In some possible embodiments, the thermal conductivity of porous graphite at a test temperature of 1000°C can be 14.6-16.6 W / (mK).

[0098] In some possible embodiments, the thermal conductivity of porous graphite at a test temperature of 1000°C can be 16.6-18.5 W / (mK).

[0099] In some possible embodiments, the thermal conductivity of porous graphite at a test temperature of 1000°C can be 18.5-19.7 W / (mK).

[0100] For example, the flexural strength of porous graphite can be one or a range between any two of 6 MPa, 8 MPa, 10 MPa, 15 MPa, 20 MPa, 25 MPa, 30 MPa, 35 MPa, 40 MPa, 45 MPa or 50 MPa.

[0101] In some possible embodiments, the flexural strength of porous graphite can be 6.1-14.5 MPa.

[0102] In some possible embodiments, the flexural strength of porous graphite can be 14.5-24.1 MPa.

[0103] In some possible embodiments, the flexural strength of porous graphite can be 24.1-34.1 MPa.

[0104] In some possible embodiments, the flexural strength of porous graphite can be 34.1-46.1 MPa.

[0105] In some possible embodiments, the flexural strength of porous graphite can be 46.1-50 MPa.

[0106] Furthermore, the porous graphite provided in this application example has a bulk density of 0.7-1.25 g / ml and a total pore area of ​​0.05-1.8 m². 2 / g.

[0107] The porous graphite prepared by the above method has a bulk density of 0.7-1.25 g / ml and a total pore area of ​​0.05-1.8 m². 2 The thermal conductivity of porous graphite at a test temperature of 1000℃ is 6-20 W / (mK), and its flexural strength is 6-50 MPa, exhibiting both high flexural strength and low thermal conductivity. When applied to silicon carbide crystal growth, porous graphite demonstrates high flexural strength, minimal powder shedding, low secondary pollution, and resistance to deformation from strong airflow. Its low thermal conductivity also enables temperature gradient control during silicon carbide crystal growth, maintains temperature stability in the crystal growth region, mitigates thermal shock from temperature changes, and improves the growth quality of silicon carbide crystals.

[0108] For example, the bulk density of porous graphite can be one or a range of any two of the following: 0.7 g / ml, 0.75 g / ml, 0.8 g / ml, 0.85 g / ml, 0.9 g / ml, 0.95 g / ml, 1.0 g / ml, 1.05 g / ml, 1.1 g / ml, 1.15 g / ml, 1.20 g / ml, or 1.25 g / ml.

[0109] In some possible embodiments, the bulk density of porous graphite can be 0.92-1.02 g / ml.

[0110] In some possible embodiments, the bulk density of porous graphite can be 1.02-1.12 g / ml.

[0111] For example, the total pore area of ​​porous graphite is 0.050 m². 2 / g, 0.080m 2 / g, 0.088m 2 / g, 0.090m 2 / g, 0.100m 2 / g, 0.150m 2 / g, 0.200m 2 / g, 0.2070m 2 / g, 0.250m 2 / g, 0.300m 2 / g, 0.500m 2 / g, 1.000m 2 / g, 1.600m 2 / g or 1.608m 2 / g is a range of one or both of them.

[0112] In some possible embodiments, the total pore area of ​​porous graphite can be 0.05-0.5 μm. 2 / g.

[0113] In some possible embodiments, the total pore area of ​​porous graphite can be 0.5-1.0 μm. 2 / g.

[0114] In some possible embodiments, the total pore area of ​​porous graphite can be 1.0-1.5 μm. 2 / g.

[0115] In some possible embodiments, the total pore area of ​​porous graphite can be 1.5-1.8 μm. 2 / g.

[0116] Furthermore, the bulk density of porous graphite is 0.92-1.12 g / ml, the thermal conductivity at a test temperature of 1000℃ is 12.9-16.6 w / (mK), and the flexural strength is 14.5-46.1 MPa.

[0117] Furthermore, in some possible embodiments, the apparent density of porous graphite is 1.725-1.814 g / ml.

[0118] For example, the apparent density of porous graphite can be one of 1.725 g / ml, 1.763 g / ml, 1.785 g / ml, 1.798 g / ml or 1.814 g / ml or any two of them.

[0119] Furthermore, the median pore size of porous graphite is 8.05-47.16 μm, and the average pore size is 0.476-30.89 μm.

[0120] For example, the median pore size of porous graphite can be one of or between any two of the following: 8.05 μm, 13.17 μm, 15.84 μm, 25.44 μm, 33.71 μm, 34.44 μm, 39.44 μm, 43.89 μm, or 47.16 μm.

[0121] In some possible embodiments, the median pore size of porous graphite can be 15.84-25.44 μm.

[0122] In some possible embodiments, the median pore size of porous graphite can be 25.44-34.44 μm.

[0123] For example, the average pore size of porous graphite can be one of 0.476 μm, 0.709 μm, 0.843 μm, 8.17 μm, 8.246 μm, 16.17 μm, 24.17 μm or 30.89 μm or any combination thereof.

[0124] In some possible embodiments, the average pore size of porous graphite can be 0.476-8.17 μm.

[0125] In some possible embodiments, the average pore size of porous graphite can be 0.843-8.17 μm.

[0126] In some possible embodiments, the average pore size of porous graphite can be 8.17-16.17 μm.

[0127] In some possible embodiments, the average pore size of porous graphite can be 16.17-24.17 μm.

[0128] Furthermore, the porosity of porous graphite ranges from 33.05% to 58.51%, and its air permeability is 2.8 to 5.6 L / m³. 2 ·s.

[0129] For example, the porosity of porous graphite can be one of 33.05%, 36.67%, 37.85%, 40.45%, 43.6%, 44.45%, 48.45%, or 58.51%, or any combination thereof.

[0130] In some possible embodiments, the porosity of porous graphite can be 37.85%-40.45%.

[0131] In some possible embodiments, the porosity of porous graphite can be 40.45%-44.45%.

[0132] In some possible embodiments, the porosity of porous graphite can be 44.45%-48.45%.

[0133] For example, the air permeability of porous graphite can be 2.8 L / m³. 2 ·s、3L / m 2 ·s、3.2L / m 2 ·s、3.9L / m 2 ·s, 4.0L / m 2·s、4.2L / m 2 ·s, 4.5L / m 2 ·s、5.2L / m 2 ·s or 6.5L / m 2 The range between one or any two of s.

[0134] For example, the porous graphite has a bulk density of 0.92 g / ml, a thermal conductivity of 12.9 W / (mK) at a test temperature of 1000℃, and a flexural strength of 14.5 MPa.

[0135] For example, the porous graphite has a bulk density of 0.99 g / ml, a thermal conductivity of 13.0 W / (mK) at a test temperature of 1000℃, and a flexural strength of 20.1 MPa.

[0136] For example, the porous graphite has a bulk density of 1.02 g / ml, a thermal conductivity of 13.6 W / (mK) at a test temperature of 1000℃, and a flexural strength of 23.9 MPa.

[0137] For example, the porous graphite has a bulk density of 1.12 g / ml, a thermal conductivity of 16.6 W / (mK) at a test temperature of 1000℃, and a flexural strength of 46.1 MPa.

[0138] The porous graphite provided in this application example can achieve a significant increase in flexural strength while slowly increasing thermal conductivity as the bulk density increases, thus exhibiting both high flexural strength and low thermal conductivity.

[0139] The porous graphite of this application will be further described in detail below with reference to the embodiments.

[0140] Example 1

[0141] Example 1 provides a porous graphite, prepared by the following method:

[0142] (1) Weigh 45 parts of carbon fiber (average fiber length 180μm, average diameter 12μm) and 55 parts of phenolic resin powder.

[0143] (2) Dry mix the raw materials in step (1) in a mixer until they are evenly mixed to obtain mixed raw materials.

[0144] (3) Place the mixed raw material obtained in step (2) into a cold press mold, press it into a blank of equal density, the molding pressure is 10MPa, and heat and solidify it at 175℃ for 5h.

[0145] (4) The blank formed in step (3) is carbonized in a carbonization furnace in the absence of oxygen. The carbonization temperature is 1200℃, the heating rate is 0.2℃ / min, and the holding time is 2h to obtain porous carbon material.

[0146] (5) The porous carbon material from step (4) is placed in a graphitization furnace and graphitized under argon protection at a temperature of 2400℃ for 2 hours to obtain porous graphite material.

[0147] (6) The porous graphite material from step (5) is placed in a purification furnace for purification. The purification gas is Freon or chlorine, and the purification temperature is 2200℃. After the purification process is completed, porous graphite is obtained.

[0148] Example 2

[0149] Example 2 provides a porous graphite, which differs from Example 1 in that the molding pressure in step (3) is 25 MPa.

[0150] Example 3

[0151] Example 3 provides a porous graphite, which differs from Example 1 in that the molding pressure in step (3) is 32 MPa.

[0152] Example 4

[0153] Example 4 provides a porous graphite, which differs from Example 1 in that the molding pressure in step (3) is 60 MPa.

[0154] Example 5

[0155] Example 5 provides a porous graphite, which differs from Example 1 in that:

[0156] In step (1), the fiber has an average length of 150 μm and an average diameter of 11 μm.

[0157] In step (3), the molding pressure is 60 MPa.

[0158] Example 6

[0159] Example 6 provides a porous graphite, which differs from Example 1 in that:

[0160] In step (1), the fiber has an average length of 200 μm and an average diameter of 10 μm.

[0161] In step (3), the molding pressure is 80 MPa.

[0162] Example 7

[0163] Example 7 provides a porous graphite, which differs from Example 1 in that the molding pressure in step (3) is 5 MPa.

[0164] Example 8

[0165] Example 8 provides a porous graphite, which differs from Example 1 in that the molding pressure in step (3) is 2 MPa.

[0166] Test Example 1

[0167] Two types of porous graphite prepared by a certain company were used as Comparative Example 1 and Comparative Example 2. Microscopic analysis was performed on the porous graphite of Example 4 and Comparative Example 2.

[0168] The SEM image of the porous graphite provided in Example 4 is shown below. Figure 1 As shown.

[0169] SEM images of porous graphite provided in Comparative Example 2 are shown below. Figure 2 As shown.

[0170] Results analysis:

[0171] Depend on Figure 1 As can be seen, the porous graphite provided in Embodiment 4 of this application includes graphite fibers and graphite body composited on the surface of the graphite fibers. The graphite fibers are stably connected by the graphite body, giving the porous graphite high bending strength. The disordered mixed graphite fibers can form a large number of pore structures with significant differences in shape and size, which can reduce heat transfer efficiency to a certain extent, thereby reducing the thermal conductivity of the porous graphite.

[0172] Depend on Figure 2 It can be seen that existing porous graphite is generally in the form of granular aggregates with weak connections between particles. Furthermore, the pore structure in porous graphite is relatively uniform in shape and size, which is conducive to heat transfer. However, existing porous graphite has a high thermal conductivity and low bending strength.

[0173] Test Example 2

[0174] The porosity of porous graphite in Examples 1-8, Comparative Example 1, and Comparative Example 2 was tested using mercury porosimetry.

[0175] The thermal conductivity of porous graphite in Examples 1-8, Comparative Example 1, and Comparative Example 2 was tested using the laser flash method at a test temperature of 1000℃.

[0176] The flexural strength of the porous graphite in Examples 1-8, Comparative Example 1, and Comparative Example 2 was tested according to JBT8133.7. The test results are shown in Table 1.

[0177] Table 1

[0178]

[0179] Results analysis:

[0180] As can be seen from Table 1, compared with Comparative Example 1, the bulk density of Example 4 and Comparative Example 1 is basically the same. However, the flexural strength of the porous graphite provided in Example 4 is 46.1 MPa, which is much greater than the flexural strength of 6.1 MPa of Comparative Example 1 (the flexural strength of the porous graphite in Example 4 is about 7.5 times that of the porous graphite in Comparative Example 1). Furthermore, the thermal conductivity of the porous graphite prepared in Example 4 is 16.6 W / (mK), which is lower than the 18.0 W / (mK) of the porous graphite provided in Comparative Example 1. This indicates that the preparation method provided in the embodiments of this application can improve the flexural strength of porous graphite while reducing its thermal conductivity.

[0181] Generally, the flexural strength of porous graphite increases with increasing bulk density. However, comparing Example 1 and Comparative Example 2, the porous graphite prepared in Example 1, even with a lower bulk density than the porous graphite in Comparative Example 2 (0.92 g / ml for Example 1 and 1.15 g / ml for Comparative Example 2), still exhibits a higher flexural strength (14.5 MPa for Example 1 and 7.6 MPa for Comparative Example 2). This demonstrates that the preparation method provided in this application can effectively improve the flexural strength of porous graphite.

[0182] In addition, as can be seen from Examples 1-8, the porous graphite provided in this application exhibits a significant increase in flexural strength from 6.1 MPa to 50 MPa and a slow increase in thermal conductivity from 6.2 W / (mK) to 19.7 W / (mK) with increasing bulk density. In contrast, in Comparative Examples 1 and 2, the flexural strength slowly increases from 6.1 MPa to 7.6 MPa and the thermal conductivity significantly increases from 18 W / (mK) to 30 W / (mK) with increasing bulk density. This demonstrates that the porous graphite provided by the prior art, while increasing its flexural strength by increasing bulk density, also significantly increases its thermal conductivity. However, the porous graphite preparation method provided in this application, while increasing its flexural strength by increasing bulk density, essentially does not increase or only slowly increases its thermal conductivity, thus obtaining porous graphite with high flexural strength and low thermal conductivity.

[0183] Furthermore, comparing Examples 1, 3 to 8, it can be seen that the porous graphite prepared in this application has a basically unchanged apparent density (with slight fluctuations), a median pore size of 8.05 μm to 47.16 μm, an average pore size of 0.476 μm to 30.89 μm, and a porosity of 33.05% to 58.5%. This indicates that the preparation method provided in this application can control the ratio of open and closed pores, the pore size, and the pore distribution, thereby improving the flexural strength of porous graphite and reducing its thermal conductivity.

[0184] In summary, the porous graphite provided in this application has high flexural strength and low thermal conductivity. When applied to silicon carbide crystal growth, it is less prone to powder shedding, causes less secondary pollution, is less susceptible to deformation by strong airflow, meets the temperature gradient control requirements for silicon carbide crystal growth, maintains the temperature stability of the crystal growth region, mitigates the thermal shock caused by temperature changes, and improves the growth quality of silicon carbide crystals.

[0185] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A porous graphite, characterized in that, The porous graphite has a thermal conductivity of 6-20 W / (mK) and a flexural strength of 6-50 MPa at a test temperature of 1000℃.

2. The porous graphite according to claim 1, characterized in that, The thermal conductivity of the porous graphite at a test temperature of 1000℃ is 12.9-14.6 W / (mK).

3. The porous graphite according to claim 1, characterized in that, The porous graphite has a thermal conductivity of 14.6-16.6 W / (mK) at a test temperature of 1000℃.

4. The porous graphite according to claim 1, characterized in that, The flexural strength of the porous graphite is 14.5-24.1 MPa.

5. The porous graphite according to claim 1, characterized in that, The flexural strength of the porous graphite is 24.1-34.1 MPa.

6. The porous graphite according to claim 1, characterized in that, The flexural strength of the porous graphite is 34.1-46.1 MPa.

7. The porous graphite according to claim 1, characterized in that, The porous graphite has a bulk density of 0.7-1.25 g / ml and a total pore area of ​​0.05-1.8 m². 2 / g.

8. The porous graphite according to claim 7, characterized in that, The porous graphite has a bulk density of 0.92-1.02 g / ml.

9. The porous graphite according to claim 7, characterized in that, The porous graphite has a bulk density of 1.02-1.12 g / ml.

10. The porous graphite according to claim 7, characterized in that, The total pore area of ​​the porous graphite is 0.05-0.5m². 2 / g.

11. The porous graphite according to claim 7, characterized in that, The total pore area of ​​the porous graphite is 0.5-1.0 m². 2 / g.

12. The porous graphite according to claim 7, characterized in that, The total pore area of ​​the porous graphite is 1.0-1.5m². 2 / g.

13. The porous graphite according to claim 7, characterized in that, The total pore area of ​​the porous graphite is 1.5-1.8m². 2 / g.

14. The porous graphite according to claim 1, characterized in that, The apparent density of the porous graphite is 1.725-1.814 g / ml.

15. The porous graphite according to claim 1, characterized in that, The porous graphite has a median pore size of 8.05-47.16 μm and an average pore size of 0.476-30.89 μm.

16. The porous graphite according to claim 15, characterized in that, The median pore size of the porous graphite is 15.84-25.44 μm.

17. The porous graphite according to claim 15, characterized in that, The median pore size of the porous graphite is 25.44-34.44 μm.

18. The porous graphite according to claim 15, characterized in that, The average pore size of the porous graphite is 0.843-8.17 μm.

19. The porous graphite according to claim 15, characterized in that, The average pore size of the porous graphite is 8.17-16.17 μm.

20. The porous graphite according to claim 15, characterized in that, The average pore size of the porous graphite is 16.17-24.17 μm.

21. The porous graphite according to claim 1, characterized in that, The porosity of the porous graphite is 33.05%-58.51%.

22. The porous graphite according to claim 21, characterized in that, The porosity of the porous graphite is 37.85%-40.45%.

23. The porous graphite according to claim 21, characterized in that, The porosity of the porous graphite is 40.45%-44.45%.

24. The porous graphite according to claim 21, characterized in that, The porosity of the porous graphite is 44.45%-48.45%.

25. The porous graphite according to claim 1, characterized in that, Breathability is 2.8-6.5L / m 2 ·s.

26. A porous graphite according to claim 1, characterized in that, The porous graphite includes graphite fibers and graphite body composited on the surface of the graphite fibers; by weight, the porous graphite includes 30-60 parts of the graphite fibers and 20-40 parts of the graphite body.

27. The porous graphite according to claim 26, characterized in that, The porous graphite comprises 40-50 parts by weight of the graphite fibers and 29-35 parts by weight of the graphite body.

28. The porous graphite according to claim 26, characterized in that, The graphite fibers have an average length of 150-200 μm and an average diameter of 10-15 μm.

29. The porous graphite according to any one of claims 1-28, characterized in that, The graphite fibers contain graphite and carbon; and / or the graphite body contains graphite and carbon.

30. A method for preparing porous graphite according to any one of claims 1-29, characterized in that, include: Obtain the mixed raw materials; The mixed raw material comprises 30-60 parts by weight of carbon fiber and 35-70 parts by weight of carbonizable graphitizable organic precursor material, wherein the average length of the carbon fiber is 100-300 μm and the average diameter is 10-20 μm; the mixed raw material is cold-pressed at a pressure of 2-80 MPa to obtain a green body; the green body is then carbonized and graphitized sequentially.

31. The preparation method according to claim 30, characterized in that, The carbonizable and graphitizable organic precursor material is selected from phenolic resin; the method for sequentially carbonizing and graphitizing the preform includes: The preform is heated to 150-200℃ and cured for 2-18 hours; under inert gas protection, it is heated to 1000-1400℃ at a heating rate of 0.2-0.5℃ / min for carbonization for 1-4 hours, and then heated to 2300-2500℃ for graphitization for 1-4 hours; purification is carried out at 2000-2500℃ using Freon or chlorine as the purification gas.

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