A graphite-ceramic composite crystallizer and its manufacturing method

Abstract

This invention discloses a graphite-ceramic composite crystallizer and its manufacturing method. The inner and outer layers of the composite crystallizer are composed of artificial graphite, silicon carbide ceramic, and resin carbon composite, while the middle layer consists of oriented natural flake graphite, mesophase carbon microspheres, and resin carbon. The manufacturing process mainly includes the following steps: powder preparation, hot pressing of the crystallizer blank, carbonization treatment, vacuum pressure impregnation, high-temperature sintering, and chemical vapor deposition. The prepared graphite-ceramic composite crystallizer exhibits good thermal conductivity, wear resistance, and oxidation resistance, with low surface roughness, high dimensional accuracy, and high shape accuracy. The provided process is simple, efficient, and low-cost, ensuring product quality and production efficiency. The obtained graphite-ceramic composite crystallizer can be used in the continuous casting industry of copper alloys and aluminum alloys.

Description

Technical Field

[0001] This invention relates to an antioxidant and wear-resistant graphite-ceramic composite crystallizer and its manufacturing method, belonging to the field of continuous copper alloy manufacturing technology. Specifically, it relates to a rapid manufacturing method for graphite-ceramic composite parts with long life, high hardness, and high thermal conductivity. As a crystallizer, it is applied in the continuous casting industry of copper alloys and aluminum alloys to ensure product quality and production efficiency. Background Technology

[0002] Compared with traditional casting technology, continuous casting technology simplifies the production process, improves production efficiency, reduces production costs, improves casting quality, facilitates automation, and is environmentally friendly. It has experienced rapid development both domestically and internationally and is being used by an increasing number of enterprises. The crystallizer is a key component of continuous casting equipment. It continuously injects molten copper or aluminum into its cavity, which is then forced to cool by a water-cooled copper sleeve (wall). This removes the heat from the molten copper or aluminum, causing it to solidify into a billet with the required cross-sectional shape and a certain shell thickness. This billet, with its core still in the liquid phase, is continuously pulled out from the bottom of the crystallizer, creating conditions for complete solidification in the subsequent secondary cooling zone. Therefore, the material quality, performance, and service life of the crystallizer play a crucial role in the quality, output, production efficiency, material consumption, and strength of the cast billet.

[0003] Currently, based on different materials, commonly used crystallizer types include copper-based alloy crystallizers, aluminum crystallizers, ceramic crystallizers, and graphite crystallizers. Copper-based alloy crystallizers have good thermal conductivity, excellent wear resistance, and a low coefficient of friction, remaining stable even at high temperatures. However, copper is expensive and difficult to process, increasing the manufacturing cost. Aluminum crystallizers possess excellent thermal conductivity, are easy to process, and have high strength, fitting well with complex crystallizer structures and helping to reduce production costs. However, they lack toughness, have low hardness, poor wear resistance, and poor thermal stability. Ceramic crystallizers have excellent high-temperature resistance and corrosion resistance, remaining stable even under extreme temperature conditions. However, ceramic materials are expensive and brittle, easily breaking upon impact. Graphite crystallizers have good thermal conductivity, slow cooling, lubricity, high-temperature resistance, a low coefficient of linear expansion, and a low coefficient of friction. However, they are prone to oxidation and wear, resulting in a shorter service life.

[0004] To address the shortcomings of existing graphite crystallizers, researchers applied coating technology to the graphite crystallizer forming process, successfully improving its quality and service life by 9-15 times compared to ordinary graphite crystallizers, and increasing daily output by about 15%, resulting in significant economic benefits. However, the coating technology is complex, requires stringent preparation conditions, and struggles to guarantee coating uniformity. Furthermore, it is prone to peeling and separation under thermal stress, and the coating is easily oxidized in high-temperature, oxygen-rich environments, resulting in a high coefficient of friction and susceptibility to corrosion, which further affects its service life and performance.

[0005] In summary, in the field of continuous casting of copper / aluminum alloys, there is currently a lack of effective process methods that can ensure both the thermal conductivity of graphite crystallizers and their oxidation resistance, wear resistance, and lifespan. Summary of the Invention

[0006] To address the shortcomings of current graphite crystallizer forming technology, this invention provides a graphite-ceramic composite crystallizer and its manufacturing method. Based on a micro-hot pressing process, mixed powders A and B are stacked together in an orderly manner under multiple extrusion pressures, with the oriented arrangement of natural flake graphite ensuring thermal conductivity. Further carbonization and impregnation with medium-temperature pitch improve density and compressive strength. Following high-temperature sintering, phenolic resin undergoes pyrolysis to generate resin carbon, which reacts in situ with silicon to form silicon carbide particles, thereby improving the hardness and wear resistance of the graphite-ceramic crystallizer. Utilizing the excellent self-sintering properties of mesophase carbon microspheres, the interlayer contact of graphite is more thorough and compact. At temperatures above 1000℃, the surface of the silicon carbide particles oxidizes to form a SiO2 film, which hinders oxygen penetration into the sample, slowing down the oxidation rate and enhancing high-temperature oxidation resistance. Finally, pyrolytic carbon is deposited in the composite crystallizer via chemical vapor deposition, increasing density and strength.

[0007] The specific process is as follows:

[0008] (1) Preparation of mixed powder: Mix artificial graphite powder, silicon powder and thermosetting phenolic resin powder evenly to obtain mixed powder A; mix natural flake graphite powder, mesophase carbon microspheres and thermosetting phenolic resin powder evenly to obtain mixed powder B;

[0009] (2) Hot pressing of the crystallizer blank: The mixed powder A and mixed powder B mentioned in step (1) are added in batches according to the ABA region. Each time powder is added, it is pre-pressed once to obtain the graphite ceramic crystallizer blank.

[0010] (3) Carbonization treatment: The graphite ceramic crystallizer blank is carbonized in a vacuum and inert gas to obtain the graphite ceramic crystallizer blank;

[0011] (4) Vacuum pressure impregnation of medium temperature asphalt: The graphite ceramic crystallizer blank is impregnated with asphalt under vacuum, dried and taken out to obtain the graphite ceramic crystallizer preform.

[0012] (5) High-temperature sintering: The graphite ceramic crystallizer preform is sintered at high temperature under vacuum atmosphere protection and then taken out after cooling;

[0013] (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.

[0014] The artificial graphite powder has a carbon content of over 99% and a particle size of 500-1000 mesh; the silicon powder has a purity of over 99% and a particle size of 200-500 mesh; the thermosetting phenolic resin powder has a particle size of 500-900 mesh; the natural flake graphite has a carbon content of over 99.5% and a particle size of 100-250 mesh; and the mesophase carbon microspheres have a carbon content of over 99.5% and a particle size of 500-900 mesh.

[0015] In mixed powder A, the mass fraction of artificial graphite is 50–65 wt%, the mass fraction of silicon powder is 10–35 wt%, and the mass fraction of thermosetting phenolic resin powder is 15–25 wt%.

[0016] In mixed powder B, the mass fraction of natural flake graphite is 50-65 wt%, the mass fraction of mesophase carbon microspheres is 10-35 wt%, and the mass fraction of thermosetting phenolic resin powder is 15-25 wt%.

[0017] Add the mixed powders A and B to the ball mill in batches and mechanically mix for 4-8 hours, with the speed controlled at 200-300 rpm.

[0018] In step (2), the thickness of the mixed powder filling should not exceed 3 mm each time, the molding pressure should not be less than 15 MPa each time, the holding time should not be less than 5 min each time, and the density of the graphite ceramic crystallizer green body should not be less than 1.70 g / cm³. 3 .

[0019] The "not exceeding 3mm" refers to a layer thickness of 1-3mm; the "forming pressure not less than 15MPa per cycle" refers to a pressure of 15-30MPa; the "holding time not less than 5min per cycle" refers to a holding time of 5-30min; and the "density of the graphite ceramic crystallizer green body" is not less than 1.70g / cm³. 3 This refers to 1.70-1.95 g / cm³. 3 .

[0020] During the carbonization process in step (3), the vacuum is evacuated to 0-50 Pa, and high-purity argon or high-purity nitrogen is introduced for protection. The temperature is raised to 700-800℃ and held for 40-90 minutes. The furnace is then cooled to room temperature and removed.

[0021] In some embodiments, a gradient temperature increase is achieved during the carbonization process to ensure the stability of the carbonization process. For example, the vacuum is evacuated to 0-50 Pa, and high-purity argon or nitrogen gas with a purity greater than 99.99% is introduced for protection. The temperature is increased at 40-80°C / h to 60-200°C; the temperature is then increased at 40-80°C / h to 200-600°C; and finally increased at 120-150°C / h to 600-800°C. The temperature is held for 40-90 minutes, and then cooled to room temperature in the furnace before being removed.

[0022] In step (4), when impregnating medium-temperature asphalt under vacuum pressure, the vacuum is drawn to 0-50 Pa, and high-purity argon or high-purity nitrogen is introduced for protection. Impregnation is carried out at a pressure of 0.1 MPa-0.3 MPa, and the drying temperature is 80-100℃.

[0023] In step (5), during the high-temperature treatment, the graphite ceramic crystallizer is placed in a vacuum atmosphere sintering furnace, the vacuum is evacuated to below 10 Pa, and the temperature is raised to 300-380°C. Then, high-purity argon or high-purity nitrogen is introduced for protection, and the temperature is raised to 750-850°C and held for 0.5-1 h. The temperature is then raised to 1450-1550°C and held for 0.5-1 h. After cooling to room temperature with the furnace, the crystallizer is taken out to obtain the graphite ceramic crystallizer.

[0024] In some embodiments, the high-temperature treatment process employs a slow-then-fast heating method to achieve stable high-temperature carbonization. For example, during high-temperature treatment, the graphite ceramic crystallizer is placed in a vacuum atmosphere sintering furnace, evacuated to below 10 Pa, and simultaneously heated to 300-380°C at a rate of 120-360°C / h. Subsequently, high-purity argon or high-purity nitrogen (greater than 99.99%) is introduced for protection, and the temperature is further increased to 750-850°C and held at 750-850°C for 0.5-1 hour. The temperature is then increased to 1450-1550°C at a rate of 240-600°C / h and held for 0.5-1 hour. After cooling to room temperature in the furnace, the crystallizer is removed, thus obtaining the graphite ceramic crystallizer.

[0025] In step (6), during chemical vapor deposition, the vacuum is drawn to 0.1-0.5 MPa, and high-purity argon or high-purity nitrogen is introduced for protection and gas washing. Then, hydrocarbon gas is introduced, and deposition is carried out at 950-1200℃ and 5kPa-10kPa for 20-60 hours.

[0026] In some embodiments, to ensure uniformity during the vapor deposition process, the hydrocarbon gas is introduced at a constant rate, such as a flow rate of 100-450 ml / min. Pressure deposition is then performed by increasing the temperature to 950-1200°C at a rate of 20-40°C / min.

[0027] The hydrocarbon gas includes C1-C5 alkanes, alkenes, or alkynes.

[0028] 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.

[0029] Another technical solution of the present invention is to provide a graphite ceramic composite crystallizer, characterized in that the graphite ceramic composite crystallizer is prepared by the method described above, wherein the inner and outer layers of the graphite ceramic composite crystallizer are composed of graphite, silicon carbide ceramic and resin carbon composite, and the middle layer is composed of oriented natural flake graphite, mesophase carbon microspheres and resin carbon composite, 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%.

[0030] The advantages of the graphite ceramic crystallizer forming method described in this invention are as follows:

[0031] (1) The graphite ceramic crystallizer provided by the present invention is obtained by directly hot pressing a mixture of artificial graphite powder, high-purity silicon powder, thermosetting phenolic resin powder, natural flake graphite powder, mesophase carbon microspheres and other powders, and then sintering it at high temperature. Compared with the traditional processing and molding methods, it greatly improves the material utilization rate, reduces the production cost and improves the production efficiency.

[0032] (2) This invention utilizes natural flake graphite powder, which, under pressure, stacks together in a self-orienting and directional arrangement, exhibiting excellent thermal conductivity. Simultaneously, the mesophase carbon microspheres undergo a self-shrinkage reaction during sintering, increasing the bonding strength between the natural flake graphite particles. Furthermore, the impregnation with medium-temperature pitch after carbonization enhances density and strength. Therefore, the prepared graphite ceramic crystallizer possesses high compressive strength.

[0033] (3) The inner and outer layers of the graphite ceramic crystallizer in this invention are composed of graphite and silicon carbide ceramic composites, 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 generate a layer of SiO2 film. This SiO2 film can hinder the rate of oxidation to spread into the sample and slow down the oxidation rate of the sample. Therefore, the prepared graphite ceramic crystallizer has high oxidation resistance.

[0034] (4) The present invention utilizes 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, filling micropores and improving density and strength. Attached Figure Description

[0035] Figure 1The diagram shows the microstructure of two graphite-ceramic composite crystallizer materials. a is a cylindrical graphite-ceramic composite crystallizer, and b is a flat graphite-ceramic composite crystallizer.

[0036] Figure 2 The manufacturing process of graphite-ceramic composite crystallizer.

[0037] Figure 3 This is a schematic diagram of micro-hot pressing molding. Detailed Implementation

[0038] A method for manufacturing a graphite ceramic crystallizer includes the following steps:

[0039] (1) Mix artificial graphite powder, high-purity silicon powder, and thermosetting phenolic resin powder in a certain proportion to form mixed powder A; mix natural flake graphite powder, mesophase carbon microspheres, and thermosetting phenolic resin powder in a certain proportion to form mixed powder B. Wherein, the mass fraction of artificial graphite powder is 50-65 wt%, the mass fraction of thermosetting phenolic resin powder is 15-25 wt%, and the mass fraction of silicon powder is 10-35 wt%; the mass fraction of natural flake graphite powder is 50-65 wt%, the mass fraction of mesophase carbon microspheres is 10-30 wt%, and the mass fraction of thermosetting phenolic resin powder is 15-25 wt%; the artificial graphite powder has a carbon content of not less than 99% and a particle size of 500-1000 mesh; The silicon powder has a purity of not less than 99% and a particle size of 200-500 mesh; the thermosetting phenolic resin powder has a particle size of 500-900 mesh; the natural flake graphite powder has a carbon content of not less than 99.5% and a particle size of 100-250 mesh; the mesophase carbon microspheres have a carbon content of not less than 99.5% and a particle size of 500-900 mesh; the above powders are added in batches to a dry high-efficiency drum ball mill and mechanically mixed for 4-8 hours, with the speed controlled below 300 rpm.

[0040] (2) Add the above mixed powder in batches according to the ABA area shown in the figure, pre-pressing once for each filler, and repeating this process multiple times to obtain a graphite ceramic crystallizer green body. It is recommended that the thickness of each mixed powder filler should not exceed 3 mm to ensure the density of the graphite ceramic crystallizer green body, which should not be less than 1.70 g / cm³. 3 The molding pressure should be no less than 15 MPa for each molding cycle, and the holding time should be no less than 5 minutes for each cycle.

[0041] (3) Place the graphite ceramic crystallizer blank into the carbonization furnace, evacuate to 50 Pa or below, and introduce high-purity argon or high-purity nitrogen with a purity greater than 99.99% for protection. Increase the temperature at 40-80℃ / h to 60-200℃; continue to increase the temperature at 40-80℃ / h to 200-600℃; finally increase the temperature at 120-150℃ / h to 600-800℃, hold for 40-90 minutes, cool to room temperature with the furnace, and take it out to obtain the graphite ceramic crystallizer blank.

[0042] (4) Place the graphite ceramic crystallizer blank into a vacuum pressure impregnation machine, evacuate to 50 Pa or below, and introduce 99.99% high-purity argon or high-purity nitrogen for protection. Impregnate the graphite ceramic crystallizer blank with medium-temperature asphalt at a pressure of 0.1 MPa to 0.5 MPa. Then place it in a hot air drying oven at 80°C to 100°C to dry it and obtain the graphite ceramic crystallizer preform.

[0043] (5) High-temperature treatment of graphite ceramic crystallizer preform under vacuum atmosphere protection. The graphite ceramic crystallizer blank is placed in a vacuum atmosphere sintering furnace, embedded with graphite powder with a carbon content of not less than 99%, and vacuumed to below 10 Pa. At the same time, the temperature is raised to 360℃ at 120-360℃ / h. Then, 99.99% high-purity argon or high-purity nitrogen is introduced for protection, and the temperature is raised to 800℃ and held at 800℃ for 0.5-1h. The temperature is raised to 1450℃-1550℃ at 240-600℃ / h and held for 0.5-1h. After cooling to room temperature in the furnace, it is taken out.

[0044] (6) A graphite ceramic crystallizer preform is treated by chemical vapor deposition to obtain a graphite ceramic crystallizer composite crystallizer. The graphite ceramic crystallizer preform is placed in a chemical vapor deposition furnace, vacuumed, and protected with high-purity argon or high-purity nitrogen gas of greater than 99.99%. The above operation is repeated 2-4 times for gas washing. Then, a hydrocarbon gas, such as methane or ethylene, is introduced at a flow rate of 100-450 ml / min. The temperature is increased from room temperature to 950-1200℃ at a heating rate of 20-40℃ / min, and the pressure is controlled at 5kPa-10kPa. The deposition is carried out in the furnace for 20-60 hours. After cooling, the preform is removed to obtain the graphite ceramic composite crystallizer.

[0045] In this invention, the compressive strength of the graphite ceramic crystallizer is tested according to GB / T 13465.3-2014 "Test Methods for Impermeable Graphite Materials Part 3: Compressive Strength"; the density is tested according to GB / T24529-2009, using the Archimedes displacement method; the Vickers hardness is tested using a Vickers hardness tester (MICRO-586): a conventional diamond pyramid indenter is used to apply a 100N load three times to the same sample, and the average value is recorded as the sample hardness result; the thermal conductivity is tested using a DRE-III thermal conductivity meter; and the oxidation weight loss rate is tested using a Swiss Mettler TGA / DSC3+ to assess the sample's oxidation resistance.

[0046] The present invention will be further described below with reference to specific embodiments.

[0047] Example 1

[0048] (1) Preparation of mixed powder A: Prepare artificial graphite powder, high-purity silicon powder, and thermosetting phenolic resin powder according to the following requirements (wherein, the mass fraction of artificial graphite is 60wt% (containing 99.6% carbon and a particle size of 800 mesh), the mass fraction of high-purity silicon powder is 25wt% (containing 99.5% purity and a particle size of 200 mesh), and the mass fraction of thermosetting phenolic resin powder is 15wt% (containing 500 mesh)); Preparation of mixed powder B: Prepare natural flake graphite powder, mesophase carbon microspheres, and thermosetting phenolic resin powder according to the following requirements (wherein, the mass fraction of natural flake graphite powder is 60wt% (containing 99.6% carbon and a particle size of 100 mesh), the mass fraction of mesophase carbon microspheres is 20wt% (containing not less than 99.5% carbon and a particle size of 800 mesh), and the mass fraction of thermosetting phenolic resin powder is 20wt% (containing 500 mesh)). The above-mentioned mixed powder was added in batches to a dry high-efficiency drum ball mill and mechanically mixed for 6 hours at a speed of 150 rpm.

[0049] (2) The prepared mixed powder is added in batches according to the ABA region shown in the figure. Each time the powder is added, it is pre-pressed once. This process is repeated multiple times until the desired shape is formed, thus obtaining a graphite ceramic crystallizer green body. For a graphite ceramic crystallizer with an inner diameter of 27 mm, a thickness of 2 mm, and a height of 30 mm, the mixed powder is added to a thickness of 3 mm each time. The pre-pressing pressure is 30 MPa each time, and the holding time is 15 min, ensuring that the density of the graphite ceramic crystallizer green body reaches 1.9 g / cm³. 3 .

[0050] (3) Place the graphite ceramic crystallizer blank into the carbonization furnace, first evacuate to below 50 Pa, then introduce high-purity argon or high-purity nitrogen with a purity 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, hold for 40 min, cool to room temperature with the furnace, and take it out to obtain the graphite ceramic crystallizer blank.

[0051] (4) Place the graphite ceramic crystallizer blank into a vacuum pressure impregnation machine, evacuate to 50 Pa or below, and introduce 99.99% high-purity argon or high-purity nitrogen for protection. Impregnate the graphite ceramic crystallizer blank with medium-temperature asphalt at a pressure of 0.1 MPa, and then place it in a hot air drying oven at 80°C to dry it, thereby obtaining the graphite ceramic crystallizer preform.

[0052] (5) Take out the graphite ceramic crystallizer preform and place it in a vacuum sintering furnace. Then, completely embed the graphite ceramic crystallizer blank with graphite powder containing 99.5% carbon and perform high-temperature sintering. First, evacuate to 5 Pa and simultaneously raise the temperature to 360℃ at 360℃ / h. Then, introduce 99.99% high-purity argon gas and continue to raise the temperature to 800℃, and hold at 800℃ for 30 min. Raise the temperature to 1450℃ at 300℃ / h and hold for 30 min. After cooling to room temperature in the furnace, take it out.

[0053] (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% for protection, repeat the above operation twice for gas washing, then introduce methane at a flow rate of 150 ml / min, raise the temperature from room temperature to 1200℃ at a heating rate of 20℃ / min, and control the pressure to 6 kPa. Deposit in the deposition furnace for 20 h, cool and remove to obtain the graphite ceramic composite crystallizer.

[0054] The compressive strength of the graphite ceramic crystallizer was measured to be 156 MPa, and its density was 1.85 g / cm³. 3 It has a Vickers hardness of 18.5 GPa, a thermal conductivity of 76.56 W / m·K, and an oxidation weight loss rate of 0.09% at 1000℃ (the mass before oxidation weight loss is 33.46 g, and the mass after oxidation weight loss is 33.43 g).

[0055] Example 2

[0056] (1) Preparation of mixed powder A: Prepare artificial graphite powder, high-purity silicon powder, and thermosetting phenolic resin powder according to the following requirements (wherein, the mass fraction of artificial graphite is 60wt% (containing 99.6% carbon and a particle size of 600 mesh), the mass fraction of high-purity silicon powder is 20wt% (containing 99.5% purity and a particle size of 300 mesh), and the mass fraction of thermosetting phenolic resin powder is 20wt% (containing 800 mesh)); Preparation of mixed powder B: Prepare natural flake graphite powder, mesophase carbon microspheres, and thermosetting phenolic resin powder according to the following requirements (wherein, the mass fraction of natural flake graphite powder is 60wt% (containing 99.6% carbon and a particle size of 200 mesh), the mass fraction of mesophase carbon microspheres is 25wt% (containing not less than 99.5% carbon and a particle size of 600 mesh), and the mass fraction of thermosetting phenolic resin powder is 15wt% (containing 800 mesh)). The above-mentioned mixed powder was added in batches to a dry high-efficiency drum ball mill and mechanically mixed for 5 hours at a speed of 240 rpm.

[0057] (2) The prepared mixed powder is added in batches according to the ABA region shown in the figure. Each time the powder is added, it is pre-pressed once. This process is repeated multiple times until the green body of the graphite ceramic crystallizer is formed, and a green body of graphite ceramic crystallizer is obtained. For a graphite ceramic crystallizer with an inner diameter of 27 mm, a thickness of 1.5 mm, and a height of 30 mm, the thickness of the mixed powder is 2.5 mm each time, the pre-pressing pressure is 25 MPa each time, and the holding time is 10 min to ensure that the density of the green body of graphite ceramic crystallizer reaches 1.85 g / cm3.

[0058] (3) Place the graphite ceramic crystallizer blank into the carbonization furnace, first evacuate to below 50 Pa, then introduce high-purity argon or high-purity nitrogen with a purity greater than 99.99% for protection, 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, hold for 50 min, cool to room temperature with the furnace, and take it out to obtain the graphite ceramic crystallizer blank.

[0059] (4) Place the graphite ceramic crystallizer blank into a vacuum pressure impregnation machine, evacuate to 50 Pa or below, and introduce 99.99% high-purity argon or high-purity nitrogen for protection. Impregnate the graphite ceramic crystallizer blank with medium-temperature asphalt at a pressure of 0.2 MPa, and then place it in a hot air drying oven at 90°C to dry it, thereby obtaining the graphite ceramic crystallizer preform.

[0060] (5) Take out the graphite ceramic crystallizer preform and place it in a vacuum sintering furnace. Then, completely embed the graphite ceramic crystallizer blank with graphite powder containing 99.5% carbon and perform high-temperature sintering treatment. First, evacuate to 1 Pa and simultaneously raise the temperature to 360°C at 240°C / h. Then, introduce 99.99% high-purity argon gas and continue to raise the temperature to 800°C and hold it at 800°C for 45 min. Raise the temperature to 1500°C at 240°C / h and hold it for 45 min. After cooling to room temperature in the furnace, take it out.

[0061] (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 3 times for gas washing, then introduce methane at a flow rate of 250 ml / min, raise the temperature from room temperature to 1200℃ at a heating rate of 30℃ / min, and control the pressure to 8 kPa. Deposit in the deposition furnace for 40 h, cool and take it out to obtain the graphite ceramic composite crystallizer.

[0062] The compressive strength of the graphite ceramic crystallizer was measured to be 147 MPa, and its density was 1.79 g / cm³. 3 It has a Vickers hardness of 17.9 GPa, a thermal conductivity of 74.96 W / m·K, and an oxidation weight loss rate of 0.14% at 1000℃ (the mass before oxidation weight loss is 23.9 g, and the mass after oxidation weight loss is 23.86 g).

[0063] Example 3

[0064] (1) Preparation of mixed powder A: Prepare artificial graphite powder, high-purity silicon powder, and thermosetting phenolic resin powder according to the following requirements (wherein, the mass fraction of artificial graphite is 55wt% (containing 99.6% carbon and a particle size of 600 mesh), the mass fraction of high-purity silicon powder is 20wt% (containing 99.5% purity and a particle size of 500 mesh), and the mass fraction of thermosetting phenolic resin powder is 25wt% (containing 800 mesh)); Preparation of mixed powder B: Prepare natural flake graphite powder, mesophase carbon microspheres, and thermosetting phenolic resin powder according to the following requirements (wherein, the mass fraction of natural flake graphite powder is 55wt% (containing 99.6% carbon and a particle size of 170 mesh), the mass fraction of mesophase carbon microspheres is 20wt% (containing not less than 99.5% carbon and a particle size of 600 mesh), and the mass fraction of thermosetting phenolic resin powder is 25wt% (containing 800 mesh)). The above-mentioned mixed powder was added in batches to a dry high-efficiency drum ball mill and mechanically mixed for 3 hours at a speed of 290 rpm.

[0065] (2) The prepared mixed powder is added in batches according to the ABA region shown in the figure. Each time the powder is added, it is pre-pressed once. This process is repeated multiple times until the desired shape is formed, thus obtaining a graphite ceramic crystallizer green body. For a graphite ceramic crystallizer with an inner diameter of 27 mm, a thickness of 1.5 mm, and a height of 20 mm, the mixed powder is added to a thickness of 2.0 mm each time. The pre-pressing pressure is 20 MPa each time, and the holding time is 8 min, ensuring that the density of the graphite ceramic crystallizer green body reaches 1.8 g / cm³. 3 .

[0066] (3) Place the graphite ceramic crystallizer blank into the carbonization furnace, first evacuate to below 50 Pa, then introduce high-purity argon or high-purity nitrogen with a purity greater than 99.99% for protection, heat to 180°C at a heating rate of 60°C / h, then heat to 500°C at a heating rate of 70°C / h; finally heat to 800°C at a heating rate of 140°C / h, hold for 60 min, cool to room temperature with the furnace, and take out to obtain the graphite ceramic crystallizer blank.

[0067] (4) Place the graphite ceramic crystallizer blank into a vacuum pressure impregnation machine, evacuate to 50 Pa or below, and introduce 99.99% high-purity argon or high-purity nitrogen for protection. Impregnate the graphite ceramic crystallizer blank with medium-temperature asphalt at a pressure of 0.3 MPa, and then place it in a hot air drying oven at 90°C to dry it, thereby obtaining the graphite ceramic crystallizer preform.

[0068] (5) Take out the graphite ceramic crystallizer preform and put it into a vacuum sintering furnace. Then, completely embed the graphite ceramic crystallizer blank with graphite powder containing 99.5% carbon and carry out high-temperature graphitization treatment. First, evacuate to 0.1 Pa and simultaneously raise the temperature to 360°C at 120°C / h. Then, introduce 99.99% high-purity argon gas and continue to raise the temperature to 800°C and hold it at 800°C for 60 min. Raise the temperature to 1550°C at 480°C / h and hold it for 35 min. After cooling to room temperature in the furnace, take it out.

[0069] (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, raise the temperature from room temperature to 1200℃ at a heating rate of 35℃ / min, and control the pressure to 8 kPa. Deposit in the deposition furnace for 55 h, cool and take it out to obtain the graphite ceramic composite crystallizer.

[0070] The compressive strength of the graphite ceramic crystallizer was measured to be 152 MPa, and its density was 1.75 g / cm³. 3It has a Vickers hardness of 17.7 GPa, a thermal conductivity of 75.45 W / m·K, and an oxidation weight loss rate of 0.19% at 1000℃ (the mass before oxidation weight loss is 15.58 g, and the mass after oxidation weight loss is 15.55 g).

[0071] Comparative Example 1

[0072] For Example 1, the remaining steps are the same, except that the graphite ceramic crystallizer obtained by chemical vapor deposition in step (6) was not performed. The compressive strength of the graphite ceramic crystallizer was measured to be 150 MPa, the density was 1.82 g / cm3, the Vickers hardness was 18.2 Gpa, the thermal conductivity was 70.87 W / m·k, and the oxidation weight loss rate at 1000℃ was 9.73% (the mass before oxidation weight loss was 32.92 g, and the mass after oxidation weight loss was 29.72 g).

[0073] Comparative Example 2

[0074] For Example 1, the remaining steps were the same. When the amount of mesophase carbon microspheres added was 5%, the compressive strength of the graphite ceramic crystallizer was measured to be 72 MPa, the density was 1.8 g / cm3, the Vickers hardness was 17.2 GPa, the thermal conductivity was 46.72 W / m·K, and the oxidation weight loss rate at 1000℃ was 1.15% (the mass before oxidation weight loss was 23.56 g, and the mass after oxidation weight loss was 32.19 g).

[0075] Comparative Example 3

[0076] For Example 1, the remaining steps were the same. When the amount of mesophase carbon microspheres added was 30%, the compressive strength of the graphite ceramic crystallizer was measured to be 79 MPa, the density was 1.72 g / cm3, the Vickers hardness was 16.6 GPa, the thermal conductivity was 43.53 W / m·K, and the oxidation weight loss rate at 1000℃ was 3.72% (the mass before oxidation weight loss was 31.12 g, and the mass after oxidation weight loss was 29.96 g).

[0077]

[0078] As can be seen from the table above, the oxidation resistance of graphite ceramic crystallizers was significantly improved after surface sealing with chemical vapor deposition. When a small amount of mesophase carbon microspheres were added, the ability to locally shrink internal pores during self-sintering was not significant, resulting in low compressive strength, density, hardness, thermal conductivity, and mechanical properties of the graphite ceramic crystallizer. When too many mesophase carbon microspheres were added, the local shrinkage during self-sintering was too severe, forming more pores, leading to low density, compressive strength, density, hardness, thermal conductivity, and mechanical properties of the graphite ceramic crystallizer.

Claims

1. A method for manufacturing a graphite-ceramic composite crystallizer, characterized in that, Includes the following steps: (1) Preparation of mixed powder: Mix artificial graphite powder, silicon powder and thermosetting phenolic resin powder evenly to obtain mixed powder A; mix natural flake graphite powder, mesophase carbon microspheres and thermosetting phenolic resin powder evenly to obtain mixed powder B; (2) Hot pressing of the crystallizer blank: The mixed powder A and mixed powder B mentioned in step (1) are added in batches and pre-pressed once each time powder is added to obtain the graphite ceramic crystallizer blank, so that the inner and outer layers are composed of graphite, silicon carbide ceramic and resin carbon composite, and the middle layer is composed of oriented natural flake graphite, mesophase carbon microspheres and resin carbon composite. (3) Carbonization treatment: The graphite ceramic crystallizer blank is carbonized in a vacuum and inert gas to obtain the graphite ceramic crystallizer blank; (4) Vacuum pressure impregnation of medium temperature asphalt: The graphite ceramic crystallizer blank is impregnated with asphalt under vacuum, dried and taken out to obtain the graphite ceramic crystallizer preform. (5) High-temperature sintering: The graphite ceramic crystallizer preform is sintered at high temperature under vacuum atmosphere protection and then 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 the graphite-ceramic composite crystallizer according to claim 1, characterized in that: The artificial graphite powder has a carbon content of over 99% and a particle size of 500-1000 mesh; the silicon powder has a purity of over 99% and a particle size of 200-500 mesh; the thermosetting phenolic resin powder has a particle size of 500-900 mesh; the natural flake graphite has a carbon content of over 99.5% and a particle size of 100-250 mesh; and the mesophase carbon microspheres have a carbon content of over 99.5% and a particle size of 500-900 mesh.

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

4. The method for manufacturing the graphite-ceramic composite crystallizer according to claim 1, characterized in that: In step (2), the thickness of the mixed powder filling should not exceed 3 mm each time, the molding pressure should not be less than 15 MPa each time, the holding time should not be less than 5 min each time, and the density of the graphite ceramic crystallizer green body should not be less than 1.70 g / cm³. 3 .

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

6. The method for manufacturing the graphite-ceramic composite crystallizer according to claim 1, characterized in that: In step (4), when impregnating medium-temperature asphalt under vacuum pressure, the vacuum is drawn to 0-50 Pa, and high-purity argon or high-purity nitrogen is introduced for protection. Impregnation is carried out at a pressure of 0.1 MPa-0.3 MPa, and the drying temperature is 80-100℃.

7. The method for manufacturing a graphite-ceramic composite crystallizer according to claim 1, characterized in that: In step (5), during the high-temperature treatment, the graphite ceramic crystallizer is placed in a vacuum atmosphere sintering furnace, the vacuum is evacuated to below 10 Pa, and the temperature is raised to 300-380°C. Then, high-purity argon or high-purity nitrogen is introduced for protection, and the temperature is raised to 750-850°C and held for 0.5-1 h. The temperature is then raised to 1450-1550°C and held for 0.5-1 h. After cooling to room temperature with the furnace, the crystallizer is taken out to obtain the graphite ceramic crystallizer.

8. The method for manufacturing a graphite-ceramic composite crystallizer according to claim 1, characterized in that: In step (6), during chemical vapor deposition, a vacuum is drawn, and high-purity argon or high-purity nitrogen is introduced for protection and gas washing. Then, hydrocarbon gas is introduced, and deposition is carried out at 950-1200℃ and 5kPa-10kPa 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 alkanes, alkenes, or alkynes.

10. A graphite-ceramic composite crystallizer, characterized in that, The graphite ceramic composite crystallizer prepared by the method according to any one of claims 1-9 has inner and outer layers composed of graphite, silicon carbide ceramic and resin carbon composite, and middle layer composed of oriented natural flake graphite, mesophase carbon microspheres and resin carbon composite, and the graphite ceramic composite crystallizer has an oxidation weight loss rate of less than 0.2%.

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