Graphite ceramic composite crystallizer and manufacturing method thereof

Abstract

The invention discloses a graphite ceramic composite crystallizer and a manufacturing method thereof. The inner layer and the outer layer of the composite crystallizer are composed of artificial graphite, silicon carbide ceramic and resin carbon in a composite mode, and the middle layer of the composite crystallizer is composed of natural crystalline flake graphite, mesocarbon microbeads and resin carbon which are arranged in a directional mode. The manufacturing process of the graphite ceramic composite crystallizer mainly comprises the following process links of mixed powder preparation, crystallizer biscuit hot press molding, carbonization treatment, vacuum pressure impregnation, high-temperature sintering, chemical vapor deposition and the like. The graphite ceramic composite crystallizer has the advantages of low surface roughness and high size precision and shape precision, the provided process is simple and efficient, the cost is low, the product quality and the production efficiency can be guaranteed, and the obtained graphite ceramic composite crystallizer can be used in the continuous casting industry of copper alloy and aluminum alloy.

Description

Technical Field

[0001] The present invention relates to an anti-oxidation and anti-wear graphite ceramic composite crystallizer and a manufacturing method thereof, belonging to the technical field of continuous manufacturing of copper alloys, and specifically to a method for rapidly manufacturing a graphite ceramic composite part with long life, high hardness and high thermal conductivity. As a crystallizer, the crystallizer is applied to the continuous casting industry of copper alloys and aluminum alloys to ensure product quality and production efficiency. Background Art

[0002] Compared with traditional casting technology, continuous casting technology can simplify production process, improve production efficiency, reduce production cost, improve casting quality, facilitate automation and be beneficial to environmental protection. It has been rapidly developed at home and abroad and is used by more and more enterprises. The crystallizer is a key component of continuous casting equipment. It is to force the copper or aluminum molten liquid continuously injected into its inner cavity to cool it through the water-cooled copper sleeve (wall), and to extract the heat of the copper or aluminum molten liquid to solidify it into a casting with the required cross-sectional shape and a certain thickness of the shell. The casting with the core still in liquid phase is continuously pulled out from the lower mouth of the crystallizer to create conditions for its complete solidification in the subsequent secondary cooling area. Therefore, the material quality, performance and service life of the crystallizer play a vital role in the quality, output, production efficiency, material consumption and strength of the casting.

[0003] At present, according to different materials, the commonly used crystallizer types include copper-based alloy crystallizers, metal aluminum crystallizers, ceramic crystallizers, and graphite crystallizers. Among them, the copper-based alloy crystallizer has good thermal conductivity, good wear resistance, and low friction coefficient. It can remain stable even in high temperature environments, but the cost of copper materials is relatively high and the processing is difficult, which increases the manufacturing cost of the crystallizer. The metal aluminum crystallizer has excellent thermal conductivity, is easy to process, and has high strength. It fits the complex structural design of the crystallizer and helps to reduce the production cost of the crystallizer, but its toughness is poor, hardness is low, wear resistance is poor, and thermal stability is poor. The ceramic crystallizer has extremely excellent high temperature resistance and corrosion resistance, and can still remain stable under extreme temperature conditions. However, the ceramic material is expensive and brittle, and it is easy to break when impacted. The graphite crystallizer has good thermal conductivity, slow cooling, lubricity, high temperature resistance, small linear expansion coefficient, and low friction coefficient, but it is easy to oxidize and wear, and has a short service life.

[0004] In view of the shortcomings of existing graphite crystallizers, researchers applied coating technology to the graphite crystallizer forming process, successfully improving its quality and service life, which is 9-15 times the life of ordinary graphite crystallizers, and increasing the production by about 15%, with significant economic effects. However, the coating technology is complex and the preparation conditions are harsh. The uniformity of the coating is difficult to ensure, and it is easy to peel off and separate under thermal stress conditions. The coating is easily oxidized in a high-temperature oxygen environment, the friction coefficient is high, and it will be corroded, affecting its service life and performance.

[0005] In summary, in the field of copper alloy / aluminum alloy continuous casting, there is currently a lack of effective process methods to ensure both the thermal conductivity of the graphite crystallizer and its oxidation resistance, wear resistance and life. Summary of the invention

[0006] In view of the shortcomings of the current graphite crystallizer forming process technology, the present invention provides a graphite ceramic composite crystallizer and a manufacturing method thereof. Based on the micro-hot pressing molding process, the mixed powders A and B are stacked together in order under the action of multiple extrusion forces, wherein the natural flake graphite is oriented to ensure thermal conductivity; after carbonization and impregnation with medium-temperature asphalt, the density and compressive strength are improved; then after high-temperature sintering treatment, the phenolic resin is pyrolyzed to generate resin carbon, and reacts with silicon in situ to generate silicon carbide particles, thereby improving the hardness and wear resistance of the graphite ceramic crystallizer; utilizing the good self-sintering type of the mesophase carbon microspheres, the contact between the graphite layers is more sufficient and tight; the surface of the silicon carbide particles will oxidize to form a layer of SiO2 film at above 1000°C, which can hinder the expansion of oxygen into the interior of the sample and slow down the oxidation rate of the sample, thereby improving the high-temperature oxidation resistance; finally, the pyrolytic carbon is deposited in the composite crystallizer by chemical vapor deposition, thereby improving the density and strength; The specific process is as follows: (1) Preparation of mixed powder: artificial graphite powder, silicon powder and thermosetting phenolic resin powder are mixed evenly to obtain mixed powder A; natural flake graphite powder, mesophase carbon microspheres and thermosetting phenolic resin powder are mixed evenly to obtain mixed powder B; (2) Hot pressing of a crystallizer blank: adding the mixed powder A and the mixed powder B described in step (1) in batches in order according to the ABA region, and pre-pressing once each time the powder is spread to obtain a graphite ceramic crystallizer blank; (3) Carbonization treatment: carbonizing the graphite ceramic crystallizer blank under vacuum and inert gas to obtain a graphite ceramic crystallizer blank; (4) Vacuum pressure impregnation with medium temperature asphalt: The graphite ceramic crystallizer blank is impregnated with asphalt under vacuum, and then taken out after drying to obtain a graphite ceramic crystallizer preform; (5) High temperature sintering: The graphite ceramic crystallizer preform is sintered at high temperature under vacuum atmosphere protection and taken out after cooling; (6) Chemical vapor deposition: Under vacuum and inert gas conditions, hydrocarbons are pyrolyzed and deposited in the sintered graphite ceramic crystallizer preform to obtain a graphite ceramic composite crystallizer.

[0007] The artificial graphite powder has a carbon content of more than 99% and a particle size of 500-1000 meshes; the silicon powder has a purity of more than 99% and a particle size of 200-500 meshes; the thermosetting phenolic resin powder has a particle size of 500-900 meshes; the natural flake graphite has a carbon content of more than 99.5% and a particle size of 100-250 meshes; the mesophase carbon microspheres have a carbon content of more than 99.5% and a particle size of 500-900 meshes.

[0008] In the mixed powder A, the mass fraction of artificial graphite is 50-65wt%, the mass fraction of silicon powder is 10-35wt%, and the mass fraction of thermosetting phenolic resin powder is 15-25wt%; In the mixed powder B, the mass fraction of natural flake graphite is 50-65wt%, the mass fraction of mesophase carbon microbeads is 10-35wt%; and the mass fraction of thermosetting phenolic resin powder is 15-25wt%.

[0009] Add the mixed powders A and B into the ball mill in batches and mix them mechanically for 4-8 hours with the rotation speed controlled at 200-300 rpm.

[0010] In step (2), the filling thickness of each mixed powder is not more than 3 mm, the molding pressure is not less than 15 MPa, the holding time is not less than 5 min, and the density of the graphite ceramic crystallizer is not less than 1.70 g / cm 3 . The "no more than 3mm" means a layer thickness of 1-3mm; the "each molding pressure is not less than 15MPa" means a pressure of 15-30MPa; the "each holding time is not less than 5min" means a holding time of 5-30min; the "graphite ceramic crystallizer body density is not less than 1.70g / cm 3 Refers to 1.70-1.95 g / cm 3 .

[0011] During the carbonization treatment in step (3), the vacuum is evacuated to 0-50 Pa, high-purity argon or high-purity nitrogen is introduced for protection, the temperature is raised to 700-800°C, and the temperature is kept for 40-90 minutes. The furnace is cooled to room temperature and the sample is taken out. In some embodiments, a gradient temperature rise is achieved during the carbonization process, the purpose of which is to achieve stability in the carbonization process. For example, the temperature is increased by 0-50 Pa, and a high-purity argon gas or high-purity nitrogen gas with a protection rate greater than 99.99% is introduced, and the temperature is increased to 60-200°C at 40-80°C / h; the temperature is further increased to 200-600°C at 40-80°C / h; the temperature is increased to 600-800°C at 120-150°C / h, and the temperature is kept for 40-90 minutes, and the furnace is cooled to room temperature and taken out.

[0012] In step (4), when the medium-temperature asphalt is impregnated with vacuum pressure, the vacuum is evacuated to 0-50 Pa, and high-purity argon or high-purity nitrogen is introduced for protection. The impregnation is performed at a pressure of 0.1 MPa-0.3 MPa, and the drying temperature is 80-100°C.

[0013] During the high temperature treatment in step (5), the graphite ceramic crystallizer is placed in a vacuum atmosphere sintering furnace, evacuated to below 10 Pa, and heated to 300-380°C; then high-purity argon or high-purity nitrogen is introduced for protection, and the temperature is continued to be raised to 750-850°C and kept warm for 0.5-1h; then the temperature is raised to 1450-1550°C and kept warm for 0.5-1h, and then the graphite ceramic crystallizer is taken out after cooling to room temperature with the furnace, thereby obtaining the graphite ceramic crystallizer.

[0014] In some embodiments, the temperature is raised in a slow-first-fast-later manner during the high-temperature treatment process to achieve the stability of high-temperature carbonization. For example, during high-temperature treatment, the graphite ceramic crystallizer is placed in a vacuum atmosphere sintering furnace, evacuated to below 10Pa, and heated to 300-380°C at 120-360°C / h; then, high-purity argon or high-purity nitrogen with a protection rate greater than 99.99% is introduced, and the temperature is continued to rise to 750-850°C, and kept at 750-850°C for 0.5-1h; the temperature is raised to 1450-1550°C at 240-600°C / h and kept at 0.5-1h, and then taken out after cooling to room temperature with the furnace, to obtain the graphite ceramic crystallizer.

[0015] During chemical vapor deposition in step (6), the vacuum is evacuated to 0.1-0.5 MPa, high-purity argon or high-purity nitrogen is introduced for protection and washing, and then hydrocarbon gas is introduced. The deposition is carried out at 950-1200° C. and 5 kPa-10 kPa for 20-60 hours.

[0016] In some embodiments, to ensure uniformity during the vapor deposition process, hydrocarbon gas is introduced at a uniform rate, such as at a flow rate of 100-450 ml / min, and the temperature is raised to 950-1200° C. at a rate of 20-40° C. / min for pressure deposition.

[0017] The hydrocarbon gas includes C1-C5 alkane, alkene or alkyne compounds.

[0018] In some embodiments, the hydrocarbon gas is selected from any one of methane, ethane, propane, butane, pentane, ethylene, propylene, butene, pentene, acetylene, propyne, butyne, and pentyne.

[0019] Another technical solution of the present invention is to provide a graphite ceramic composite crystallizer, characterized in that it is prepared by the method described, the inner and outer layers of the graphite ceramic composite crystallizer are composed of a composite of graphite, silicon carbide ceramics and resin carbon, the middle layer is composed of a composite of directional natural flake graphite, mesophase carbon microspheres and resin carbon, and the oxidation weight loss rate of the graphite ceramic composite crystallizer is lower than 0.2%, more preferably lower than 0.15%, and further preferably lower than 0.1%.

[0020] The graphite ceramic crystallizer forming method described in the present invention has the following advantages: (1) The graphite ceramic crystallizer provided by the present invention is obtained by directly hot pressing a mixed powder of artificial graphite powder, high-purity silicon powder, thermosetting phenolic resin powder, natural flake graphite powder, mesophase carbon microspheres, etc., and then undergoing a high-temperature sintering treatment. Compared with the traditional processing and molding method, it greatly improves the material utilization rate, reduces the production cost, and improves the production efficiency.

[0021] (2) The present invention utilizes natural flake graphite powder to be stacked layer by layer under pressure to form an autonomous orientation and orientation, which has good thermal conductivity. At the same time, the mesophase carbon microspheres undergo a self-shrinkage reaction during sintering, which increases the connection strength between natural flake graphite. After carbonization, they are impregnated with medium-temperature asphalt to increase the density and strength. Therefore, the prepared graphite ceramic crystallizer has a high compressive strength.

[0022] (3) The inner and outer layers of the graphite ceramic crystallizer in the present invention are composed of a composite of graphite and silicon carbide ceramics, which improves the hardness and wear resistance of the crystallizer. Because a silicon carbide ceramic phase is generated in the composite material, and when silicon carbide is heated to above 1000°C in air, it is only oxidized on its surface to form a layer of SiO2 film. This SiO2 film can hinder the speed of oxidation extending into the interior of the sample and slow down the oxidation rate of the sample. Therefore, the prepared graphite ceramic crystallizer has a high antioxidant performance.

[0023] (4) The present invention utilizes a chemical vapor deposition process to deposit pyrolytic carbon generated by high-temperature cracking of hydrocarbon gases such as methane and ethylene into graphite ceramic crystals, thereby filling microscopic pores and improving density and strength. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 Schematic diagrams of the organizational structures of two types of graphite ceramic composite crystallizer materials, a is a cylindrical graphite ceramic composite crystallizer, and b is a flat graphite ceramic composite crystallizer.

[0025] Figure 2 The present invention is a process flow for manufacturing graphite ceramic composite crystallizer.

[0026] Figure 3 Schematic diagram of micro hot pressing molding. DETAILED DESCRIPTION

[0027] A method for manufacturing a graphite ceramic crystallizer comprises the following steps: (1) Artificial graphite powder, high-purity silicon powder, and thermosetting phenolic resin powder are mixed in a certain proportion to form mixed powder A; natural flake graphite powder, mesophase carbon microspheres, and thermosetting phenolic resin powder are mixed in a certain proportion to form mixed powder B. Among them, the mass fraction of artificial graphite powder is 50-65wt%, the mass fraction of thermosetting phenolic resin powder is 15-25wt%, and the mass fraction of silicon powder is 10-35wt%; the mass fraction of natural flake graphite powder is 50-65wt%, the mass fraction of mesophase carbon microspheres is 10-30wt%, and the mass fraction of thermosetting phenolic resin powder is 15-25wt%; the carbon content of the artificial graphite powder is not less than 99%, and the particle size is 500-1000 mesh; The purity of the silicon powder is not less than 99%, and the particle size is 200-500 meshes; the particle size of the thermosetting phenolic resin powder is 500-900 meshes; the carbon content of the natural flake graphite powder is not less than 99.5%, and the particle size is 100-250 meshes; the carbon content of the mesophase carbon microspheres is not less than 99.5%, and the particle size is 500-900 meshes; the above powders are added in batches to a dry high-efficiency drum ball mill, mechanically mixed for 4-8 hours, and the rotation speed is controlled below 300rpm.

[0028] (2) Add the mixed powders in batches according to the ABA area shown in the figure, fill once, pre-press once, press each time, repeat multiple times, and obtain the graphite ceramic crystallizer blank. It is recommended that the thickness of the mixed powder filling each time should not exceed 3mm to ensure the density of the graphite ceramic crystallizer blank. The density of the graphite ceramic crystallizer blank should not be less than 1.70g / cm 3 Preferably, the molding pressure is not less than 15MPa each time, and the holding time is not less than 5min each time.

[0029] (3) Place the graphite ceramic crystallizer blank into a carbonization furnace, evacuate to 50 Pa or less, introduce high-purity argon or high-purity nitrogen with a protection rate greater than 99.99%, and heat up to 60-200°C at 40-80°C / h; continue to heat up to 200-600°C at 40-80°C / h; finally, heat up to 600-800°C at 120-150°C / h, keep warm for 40-90 min, cool to room temperature with the furnace, take out, and obtain a graphite ceramic crystallizer blank.

[0030] (4) Place the graphite ceramic crystallizer blank in a vacuum pressure impregnation machine, evacuate to 50Pa or below, introduce 99.99% high-purity argon or high-purity nitrogen for protection, and impregnate medium-temperature asphalt into the graphite ceramic crystallizer blank at a pressure of 0.1MPa~0.5MPa. Then, place it in a hot air drying oven at 80℃~100℃ for drying to obtain a graphite ceramic crystallizer preform.

[0031] (5) High-temperature treatment of the graphite ceramic crystallizer preform under vacuum atmosphere protection. Place the graphite ceramic crystallizer blank in a vacuum atmosphere sintering furnace, embed it with graphite powder with a carbon content of not less than 99%, evacuate it to below 10Pa, and heat it to 360℃ at 120~360℃ / h; then introduce 99.99% high-purity argon or high-purity nitrogen for protection, continue to heat it to 800℃, and keep it at 800℃ for 0.5~1h; heat it to 1450℃~1550℃ at 240~600℃ / h and keep it at 0.5~1h, and take it out after cooling it to room temperature with the furnace.

[0032] (6) Treating the graphite ceramic crystallizer preform by chemical vapor deposition to obtain a graphite ceramic crystallizer composite crystallizer. Place the graphite ceramic crystallizer preform in a chemical vapor deposition furnace, evacuate it, and introduce high-purity argon or high-purity nitrogen with a concentration greater than 99.99% for protection. Repeat the above operation 2-4 times for gas washing, and then introduce a hydrocarbon gas such as methane, ethylene, etc. at a flow rate of 100-450 ml / min, and increase the temperature from room temperature to 950-1200°C at a heating rate of 20-40°C / min, and control the pressure to 5kPa-10kPa, and deposit it in the deposition furnace for 20-60 hours. After cooling, take it out to obtain the graphite ceramic composite crystallizer.

[0033] The compressive strength test of the graphite ceramic crystallizer in the present invention adopts the test standard GB / T 13465.3-2014 "Test methods for impermeable graphite materials Part 3: Compressive strength" to test the compressive strength of the sample; the density test adopts the Archimedes drainage method to test the density of the sample with reference to GB / T24529-2009; the Vickers hardness test adopts a Vickers hardness tester (MICRO-586): a traditional diamond pyramid indenter is used to apply a load of 100N on the same sample three times, and the average value is recorded as the sample hardness result; the thermal conductivity test adopts a DRE-III thermal conductivity measuring instrument to test the thermal conductivity of the sample; the oxidation weight loss test adopts a Swiss Mettler TGA / DSC3+ to test the antioxidant performance of the sample.

[0034] The present invention will be further described below in conjunction with specific implementation modes.

[0035] Example 1 (1) Preparation of mixed powder A: artificial graphite powder, high-purity silicon powder and thermosetting phenolic resin powder are prepared according to the following requirements (wherein the mass fraction of artificial graphite is 60wt% (carbon content 99.6%, particle size 800 mesh), the mass fraction of high-purity silicon powder is 25wt% (purity 99.5%, particle size 200 mesh), and the mass fraction of thermosetting phenolic resin powder is 15wt% (particle size 500 mesh)). Preparation of mixed powder B: natural flake graphite powder, mesophase carbon microspheres and thermosetting phenolic resin powder are prepared according to the following requirements (wherein the mass fraction of natural flake graphite powder is 60wt% (carbon content 99.6%, particle size 100 mesh), the mass fraction of mesophase carbon microspheres is 20wt% (carbon content not less than 99.5%, particle size 800 mesh), and the mass fraction of thermosetting phenolic resin powder is 20wt% (particle size 500 mesh)). The above mixed powders were added into a dry high-efficiency drum ball mill in batches and mechanically mixed for 6 hours at a rotation speed of 150 rpm. (2) Add the prepared mixed powder to the ABA area in batches according to the diagram, fill once, pre-press once, repeat multiple times until forming, and obtain the graphite ceramic crystallizer blank. For a graphite ceramic crystallizer with an inner diameter of 27mm, a thickness of 2mm, and a height of 30mm, the mixed powder is filled with a thickness of 3mm each time, the pre-pressing pressure is 30MPa each time, and the holding time is 15min, ensuring that the density of the graphite ceramic crystallizer blank reaches 1.9g / cm 3 .

[0036] (3) Place the graphite ceramic crystallizer blank into a carbonization furnace, first evacuate to below 50 Pa, introduce high-purity argon or high-purity nitrogen with a concentration greater than 99.99% for protection, and heat to 150°C at a heating rate of 40°C / h; then heat to 400°C at a heating rate of 40°C / h; finally, heat to 700°C at a heating rate of 120°C / h, keep warm for 40 min, cool to room temperature with the furnace, take out, and obtain a graphite ceramic crystallizer blank.

[0037] (4) Place the graphite ceramic crystallizer blank in a vacuum pressure impregnation machine, evacuate to 50 Pa or below, introduce 99.99% high-purity argon or high-purity nitrogen for protection, impregnate medium-temperature asphalt into the graphite ceramic crystallizer blank at a pressure of 0.1 MPa, and then place it in a hot air drying oven for drying at 80°C to obtain a graphite ceramic crystallizer preform.

[0038] (5) Take out the graphite ceramic crystallizer preform, put it into a vacuum sintering furnace, and completely embed the graphite ceramic crystallizer body with graphite powder with a carbon content of 99.5%, and perform high-temperature sintering. First, evacuate to 5Pa, and heat to 360℃ at 360℃ / h; then introduce 99.99% high-purity argon gas, continue to heat to 800℃, and keep it at 800℃ for 30min; heat to 1450℃ at 300℃ / h and keep it at 30min, and take it out after cooling to room temperature with the furnace.

[0039] (6) Place the graphite ceramic crystallizer preform into a chemical vapor deposition furnace, evacuate to below 50 Pa, introduce high-purity argon or high-purity nitrogen with a purity greater than 99.99%, repeat the above operation twice for gas washing, then introduce methane at a flow rate of 150 ml / min, increase the temperature from room temperature to 1200°C at a heating rate of 20°C / min, and control the pressure to 6 kPa. Deposit in the deposition furnace for 20 hours, cool to and then take out to obtain a graphite ceramic composite crystallizer.

[0040] The measured compressive strength of the graphite ceramic crystallizer is 156Mpa and the density is 1.85g / cm 3 , Vickers hardness 18.5Gpa, thermal conductivity 76.56W / m·k, oxidation weight loss rate at 1000℃ is 0.09% (the mass before oxidation weight loss is 33.46g, and the mass after oxidation weight loss is 33.43g).

[0041] Example 2 (1) Preparation of mixed powder A: artificial graphite powder, high-purity silicon powder and thermosetting phenolic resin powder are prepared according to the following requirements (wherein the mass fraction of artificial graphite is 60wt% (carbon content 99.6%, particle size 600 mesh), the mass fraction of high-purity silicon powder is 20wt% (purity 99.5%, particle size 300 mesh), and the mass fraction of thermosetting phenolic resin powder is 20wt% (particle size 800 mesh)). Preparation of mixed powder B: natural flake graphite powder, mesophase carbon microspheres and thermosetting phenolic resin powder are prepared according to the following requirements (wherein the mass fraction of natural flake graphite powder is 60wt% (carbon content 99.6%, particle size 200 mesh), the mass fraction of mesophase carbon microspheres is 25wt% (carbon content not less than 99.5%, particle size 600 mesh), and the mass fraction of thermosetting phenolic resin powder is 15wt% (particle size 800 mesh)). The mixed powders were added into a dry high-efficiency drum ball mill in batches and mechanically mixed for 5 h at a rotation speed of 240 rpm. (2) Add the prepared mixed powder in batches according to the ABA area shown in the figure, fill once, pre-press once, repeat multiple times until forming, and obtain the graphite ceramic crystallizer blank. For a graphite ceramic crystallizer with an inner diameter of 27mm, a thickness of 1.5mm, and a height of 30mm, the mixed powder is filled with a thickness of 2.5mm each time, the pre-pressing pressure is 25MPa each time, and the holding time is 10min, ensuring that the density of the graphite ceramic crystallizer blank reaches 1.85g / cm3. (3) Place the graphite ceramic crystallizer blank into a carbonization furnace, first evacuate to below 50 Pa, introduce high-purity argon or high-purity nitrogen with a protection rate greater than 99.99%, and heat to 160°C at a heating rate of 50°C / h; then heat to 500°C at a heating rate of 60°C / h; finally, heat to 700°C at a heating rate of 130°C / h, keep warm for 50 min, cool to room temperature with the furnace, take out, and obtain a graphite ceramic crystallizer blank.

[0042] (4) Place the graphite ceramic crystallizer blank in a vacuum pressure impregnation machine, evacuate to 50Pa or below, introduce 99.99% high-purity argon or high-purity nitrogen for protection, impregnate medium-temperature asphalt into the graphite ceramic crystallizer blank at a pressure of 0.2MPa, and then place it in a hot air drying oven for drying at 90°C to obtain a graphite ceramic crystallizer preform.

[0043] (5) Take out the graphite ceramic crystallizer preform, put it into a vacuum sintering furnace, and completely embed the graphite ceramic crystallizer body with graphite powder with a carbon content of 99.5%, and perform high-temperature sintering. First, evacuate to 1Pa, and heat to 360℃ at 240℃ / h; then introduce 99.99% high-purity argon gas, continue to heat to 800℃, and keep it at 800℃ for 45min; heat to 1500℃ at 240℃ / h and keep it at 45min, and take it out after cooling to room temperature with the furnace. (6) Place the graphite ceramic crystallizer preform into a chemical vapor deposition furnace, evacuate to below 50 Pa, introduce high-purity argon or high-purity nitrogen with a purity greater than 99.9% for protection, repeat the above operation three times for gas washing, then introduce methane at a flow rate of 250 ml / min, increase the temperature from room temperature to 1200°C at a heating rate of 30°C / min, and control the pressure to 8 kPa. Deposit in the deposition furnace for 40 hours, and take out after cooling to obtain a graphite ceramic composite crystallizer.

[0044] The measured compressive strength of the graphite ceramic crystallizer is 147Mpa and the density is 1.79g / cm 3 , Vickers hardness 17.9 Gpa, thermal conductivity 74.96 W / m·k, oxidation weight loss rate at 1000°C is 0.14% (the mass before oxidation weight loss is 23.9 g, and the mass after oxidation weight loss is 23.86 g).

[0045] Example 3 (1) Preparation of mixed powder A: artificial graphite powder, high-purity silicon powder and thermosetting phenolic resin powder are prepared according to the following requirements (wherein the mass fraction of artificial graphite is 55wt% (carbon content 99.6%, particle size 600 mesh), the mass fraction of high-purity silicon powder is 20wt% (purity 99.5%, particle size 500 mesh), and the mass fraction of thermosetting phenolic resin powder is 25wt% (particle size 800 mesh)); Preparation of mixed powder B: natural flake graphite powder, mesophase carbon microspheres and thermosetting phenolic resin powder are prepared according to the following requirements (wherein the mass fraction of natural flake graphite powder is 55wt% (carbon content 99.6%, particle size 170 mesh), the mass fraction of mesophase carbon microspheres is 20wt% (carbon content not less than 99.5%, particle size 600 mesh), and the mass fraction of thermosetting phenolic resin powder is 25wt% (particle size 800 mesh)). The above mixed powders were added into a dry high-efficiency drum ball mill in batches and mechanically mixed for 3 h at a rotation speed of 290 rpm. (2) Add the prepared mixed powder in batches according to the ABA area shown in the figure, fill once, pre-press once, repeat multiple times until forming, and obtain the graphite ceramic crystallizer blank. For a graphite ceramic crystallizer with an inner diameter of 27mm, a thickness of 1.5mm, and a height of 20mm, the mixed powder is filled with a thickness of 2.0mm each time, the pre-pressing pressure is 20MPa each time, and the holding time is 8min, ensuring that the density of the graphite ceramic crystallizer blank reaches 1.8g / cm 3 .

[0046] (3) Place the graphite ceramic crystallizer blank into a carbonization furnace, first evacuate to below 50 Pa, introduce high-purity argon or high-purity nitrogen with a concentration greater than 99.99% for protection, heat up to 180°C at a heating rate of 60°C / h, then heat up to 500°C at a heating rate of 70°C / h; finally, heat up to 800°C at a heating rate of 140°C / h, keep warm for 60 min, cool to room temperature with the furnace, take out, and obtain a graphite ceramic crystallizer blank.

[0047] (4) Place the graphite ceramic crystallizer blank in a vacuum pressure impregnation machine, evacuate to 50Pa or below, introduce 99.99% high-purity argon or high-purity nitrogen for protection, impregnate medium-temperature asphalt into the graphite ceramic crystallizer blank at a pressure of 0.3MPa, and then place it in a hot air drying oven for drying at 90°C to obtain a graphite ceramic crystallizer preform.

[0048] (5) Take out the graphite ceramic crystallizer preform, put it into a vacuum sintering furnace, and completely embed the graphite ceramic crystallizer body with graphite powder with a carbon content of 99.5% for high-temperature graphitization treatment. First, evacuate to 0.1Pa, and heat to 360℃ at 120℃ / h; then introduce 99.99% high-purity argon gas, continue to heat to 800℃, and keep it at 800℃ for 60min; heat to 1550℃ at 480℃ / h and keep it at 35min, and take it out after cooling to room temperature with the furnace.

[0049] (6) Place the graphite ceramic crystallizer preform into a chemical vapor deposition furnace, evacuate to below 50 Pa, introduce high-purity argon or high-purity nitrogen with a purity greater than 99.9% for protection, repeat the above operation 4 times for gas washing, then introduce methane at a flow rate of 300 ml / min, increase the temperature from room temperature to 1200°C at a heating rate of 35°C / min, and control the pressure to 8 kPa. Deposit in the deposition furnace for 55 hours, and take out after cooling to obtain a graphite ceramic composite crystallizer.

[0050] The measured compressive strength of the graphite ceramic crystallizer is 152Mpa and the density is 1.75g / cm 3 , Vickers hardness 17.7Gpa, thermal conductivity 75.45 W / m·k, oxidation weight loss rate at 1000℃ is 0.19% (the mass before oxidation weight loss is 15.58g, and the mass after oxidation weight loss is 15.55g).

[0051] Comparative Example 1 For Example 1, the remaining steps are the same, and the graphite ceramic crystallizer obtained by chemical vapor deposition in step (6) is not performed. The graphite ceramic crystallizer is measured to have a compressive strength of 150 MPa, a density of 1.82 g / cm3, a Vickers hardness of 18.2 Gpa, a thermal conductivity of 70.87 W / m·k, and an oxidation weight loss rate of 9.73% at 1000°C (the mass before oxidation weight loss is 32.92 g, and the mass after oxidation weight loss is 29.72 g).

[0052] Comparative Example 2 For Example 1, the remaining steps are the same. When the addition amount of mesophase carbon microspheres is 5%, the compressive strength of the graphite ceramic crystallizer is measured to be 72 MPa, the density is 1.8 g / cm3, the Vickers hardness is 17.2 Gpa, the thermal conductivity is 46.72 W / m·k, and the oxidation weight loss rate at 1000°C is 1.15% (the mass before oxidation weight loss is 23.56 g, and the mass after oxidation weight loss is 32.19 g).

[0053] Comparative Example 3 For Example 1, the remaining steps are the same. When the addition amount of mesophase carbon microspheres is 30%, the compressive strength of the graphite ceramic crystallizer is measured to be 79 MPa, the density is 1.72 g / cm3, the Vickers hardness is 16.6 Gpa, the thermal conductivity is 43.53 W / m·k, and the oxidation weight loss rate at 1000°C is 3.72% (the mass before oxidation weight loss is 31.12 g, and the mass after oxidation weight loss is 29.96 g).

[0054]

[0055] It can be seen from the above table that the antioxidant capacity of the graphite ceramic crystallizer has been significantly improved after using chemical vapor deposition surface sealing. When a small amount of mesophase carbon microspheres are added, the ability to locally shrink the internal pores during self-sintering is not obvious, resulting in low compressive strength, density and hardness, reduced thermal conductivity, and low mechanical properties of the graphite ceramic crystallizer; when too many mesophase carbon microspheres are added, the local shrinkage during self-sintering is too severe, forming more pores, resulting in low density compressive strength, density and hardness, reduced thermal conductivity, and low mechanical properties of the graphite ceramic crystallizer.

Claims

1. A method for manufacturing a graphite ceramic composite crystallizer, characterized in that: The following steps are involved: (1) Preparation of mixed powder: artificial graphite powder, silicon powder and thermosetting phenolic resin powder are mixed evenly to obtain mixed powder A; natural flake graphite powder, mesophase carbon microspheres and thermosetting phenolic resin powder are mixed evenly to obtain mixed powder B; (2) Hot pressing of a crystallizer blank: adding the mixed powder A and the mixed powder B described in step (1) in batches in order according to the ABA region, and pre-pressing once each time the powder is spread to obtain a graphite ceramic crystallizer blank; (3) Carbonization treatment: carbonizing the graphite ceramic crystallizer blank under vacuum and inert gas to obtain a graphite ceramic crystallizer blank; (4) Vacuum pressure impregnation with medium temperature asphalt: The graphite ceramic crystallizer blank is impregnated with asphalt under vacuum, and then taken out after drying to obtain a graphite ceramic crystallizer preform; (5) High temperature sintering: The graphite ceramic crystallizer preform is sintered at high temperature under vacuum atmosphere protection and taken out after cooling; (6) Chemical vapor deposition: Under vacuum and inert gas conditions, hydrocarbons are pyrolyzed and deposited in the sintered graphite ceramic crystallizer preform to obtain a graphite ceramic composite crystallizer.

2. The method for manufacturing a graphite ceramic composite crystallizer according to claim 1, characterized in that: The artificial graphite powder has a carbon content of more than 99% and a particle size of 500-1000 meshes; the silicon powder has a purity of more than 99% and a particle size of 200-500 meshes; the thermosetting phenolic resin powder has a particle size of 500-900 meshes; the natural flake graphite has a carbon content of more than 99.5% and a particle size of 100-250 meshes; the mesophase carbon microspheres have a carbon content of more than 99.5% and a particle size of 500-900 meshes.

3. The method for manufacturing a graphite ceramic composite crystallizer according to claim 1, characterized in that: In the mixed powder A, the mass fraction of artificial graphite is 50-65wt%, the mass fraction of silicon powder is 10-35wt%, and the mass fraction of thermosetting phenolic resin powder is 15-25wt%; In the mixed powder B, the mass fraction of natural flake graphite is 50-65wt%, the mass fraction of mesophase carbon microbeads is 10-35wt%; and the mass fraction of thermosetting phenolic resin powder is 15-25wt%.

4. The method for manufacturing a graphite ceramic composite crystallizer according to claim 1, characterized in that: In step (2), the filling thickness of each mixed powder is not more than 3 mm, the molding pressure is not less than 15 MPa, the holding time is not less than 5 min, and the density of the graphite ceramic crystallizer is not less than 1.70 g / cm 3 .

5. The method for manufacturing a graphite ceramic composite crystallizer according to claim 1, characterized in that: During the carbonization treatment in step (3), the vacuum is evacuated to 0-50 Pa, high-purity argon or high-purity nitrogen is introduced for protection, the temperature is raised to 700-800°C, and the temperature is kept for 40-90 minutes. The furnace is cooled to room temperature and the sample is taken out.

6. The method for manufacturing a graphite ceramic composite crystallizer according to claim 1, characterized in that: In step (4), when the medium-temperature asphalt is impregnated with vacuum pressure, the vacuum is evacuated to 0-50 Pa, and high-purity argon or high-purity nitrogen is introduced for protection. The impregnation is performed at a pressure of 0.1 MPa-0.3 MPa, and the drying temperature is 80-100°C.

7. The method for manufacturing a graphite ceramic composite crystallizer according to claim 1, characterized in that: During the high temperature treatment in step (5), the graphite ceramic crystallizer is placed in a vacuum atmosphere sintering furnace, evacuated to below 10 Pa, and heated to 300-380°C; then high-purity argon or high-purity nitrogen is introduced for protection, and the temperature is continued to be raised to 750-850°C and kept warm for 0.5-1h; then the temperature is raised to 1450-1550°C and kept warm for 0.5-1h, and then the graphite ceramic crystallizer is taken out after cooling to room temperature with the furnace, thereby obtaining the graphite ceramic crystallizer.

8. The method for manufacturing a graphite ceramic composite crystallizer according to claim 1, characterized in that: During chemical vapor deposition in step (6), the vacuum is evacuated to 0.1-0.5 MPa, high-purity argon or high-purity nitrogen is introduced for protection and washing, and then hydrocarbon gas is introduced. The deposition is carried out at 950-1200° C. and 5 kPa-10 kPa for 20-60 hours.

9. The method for manufacturing a graphite ceramic composite crystallizer according to claim 1, characterized in that: The hydrocarbon gas includes C1-C5 alkane, alkene or alkyne compounds.

10. A graphite ceramic composite crystallizer, characterized in that: The graphite ceramic composite crystallizer is prepared by the method described in any one of claims 1 to 9, wherein the inner and outer layers are composed of a composite of graphite, silicon carbide ceramics and resin carbon, and the middle layer is composed of a composite of directional natural flake graphite, mesophase carbon microspheres and resin carbon, and the oxidation weight loss rate of the graphite ceramic composite crystallizer is less than 0.2%, more preferably less than 0.15%, and more preferably less than 0.1%.

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