Graphite product purification method

Abstract

The invention relates to the technical field of high-purity material preparation, in particular to a graphite product high-temperature heat treatment method based on high-temperature purification equipment, which comprises the steps of charging, vacuumizing, heating, purification reaction, cooling and discharging, and further comprises systematic inspection before charging, dual inspection before operation and protective vacuumizing operation. The systematic inspection before charging comprises the steps of circularly fastening a heater connecting piece, measuring insulation resistance, cleaning dust and inspecting the state of each system, and the protective vacuumizing operation comprises the steps of charging protective gas into a mechanical pump in a dynamic seal manner while starting the mechanical pump; the high-efficiency and deep removal of various impurities is realized by combining ultimate vacuum and periodic circulating inflation at the highest temperature section, a graphite product with extremely high purity can be stably prepared, and the harsh requirements of the semiconductor industry are met.

Description

Technical Field

[0001] This invention relates to the field of high-purity material preparation technology, and more specifically, to a high-temperature heat treatment method for graphite products based on a high-temperature purification device. Background Technology

[0002] Graphite is widely used in semiconductors, photovoltaics, aerospace, and nuclear industries due to its excellent electrical and thermal conductivity and high-temperature resistance. These applications require extremely high purity of graphite materials; even trace amounts of metallic impurities (such as Fe, Al, Ca, etc.) and boron can severely degrade its electrical and thermal properties.

[0003] Currently, the main industrial method for high-temperature purification of graphite is the halogen gas high-temperature purification method. This method utilizes high temperatures above 2000℃ to introduce halogen-containing gases (such as Freon, chlorine, etc.), which react with impurities in the graphite to form halides with low boiling points. These halides volatilize and are removed under high temperature and high vacuum conditions, thus achieving the purification purpose. However, existing technologies and equipment have the following technical problems in practical use: poor thermal uniformity, resulting in uneven heating of graphite products, insufficient purification in some areas, excessive etching in some areas, poor product consistency, low utilization rate of process gases, uneven gas distribution, insufficient reaction with impurities, low purification efficiency, and high gas consumption.

[0004] Based on this, the present invention discloses a method for purifying graphite products. Summary of the Invention

[0005] To address the issues raised in the background section, the current industrial high-temperature purification of graphite primarily employs halogen gas purification. This method utilizes halogen-containing gases (such as Freon or chlorine) at temperatures above 2000°C, causing them to react with impurities in the graphite to form low-boiling-point halides. These halides volatilize and are removed under high temperature and high vacuum conditions, thus achieving purification. However, existing technologies and equipment suffer from the following technical problems in practical use: poor thermal uniformity, leading to uneven heating of the graphite product, insufficient purification in some areas, excessive etching in others, poor product consistency, low utilization rate of process gases, uneven gas distribution, incomplete reaction with impurities, low purification efficiency, and high gas consumption. This invention provides a graphite product purification method. The equipment includes a furnace body, a thermal field composed of multiple heaters connected by high-strength carbon-carbon connectors, an infrared thermometer, a vacuum system including mechanical pumps and Roots pumps, a gas path system containing argon and R22, a cooling system including a water-cooling circuit and a forced-cooling device, and a control system. The method includes the following steps: S1. Charging: Place the graphite product to be purified in the uniform temperature zone inside the furnace, and close and seal the furnace body; S2. Evacuate to a low vacuum: Start the mechanical pump to evacuate the pressure inside the furnace to below 10 Pa; S3. Evacuate to a high vacuum: Start the Roots pump to evacuate the furnace pressure to a high vacuum state below 1 Pa; S4. Initial purging: Pour high-purity argon gas into the furnace cavity to -50kPa~-20kPa (relative pressure); S5. Heating stage: Start the heating system and heat up to 1400℃ at a rate of 100-200℃ / h; S6. Secondary vacuuming: At 1400℃, restart the vacuum system to reduce the pressure inside the furnace to below 1Pa; S7. Introduce process gas: Continue heating. When the temperature reaches 1800℃, introduce R22 gas into the furnace at a flow rate of 0.5-2L / min, while maintaining the dynamic vacuum in the furnace at 100-1000Pa. S8. High-temperature purification: Continue to raise the temperature to the target temperature of 2300-2500℃ and hold for 10-20 hours; during this stage, continuously introduce R22 gas and maintain dynamic vacuum to allow the impurities to fully react with the halogen free radicals generated by the decomposition of R22 and volatilize. S9. Cooling stage: After the heat preservation is completed, stop heating and stop the supply of R22, continue to evacuate to a high vacuum, and start the strong cooling device to cool the furnace temperature to below 1000℃ at a rate of 50-100℃ / h. S10. Material Removal: Argon gas is introduced into the furnace to atmospheric pressure. After the furnace temperature cools down to below 80°C, the high-purity graphite product is removed from the furnace.

[0006] As a further improvement to this technical solution, in the heating stage of step S5 and the cooling stage of step S9, the pressure difference between the cooling water inlet and outlet is adjusted to 0.25 MPa to ensure heat exchange efficiency and control the heating and cooling rates.

[0007] As a further improvement to this technical solution, in steps S7 and S8, the temperature is monitored in real time by the infrared thermometer and its replaceable quartz glass protective window, and the data is fed back to the control system to achieve precise temperature control of ±5℃.

[0008] As a further improvement to this technical solution, the vacuum system is equipped with a filter device for capturing volatile metal halides; after every 5 consecutive furnace runs, the filter element of the filter device is forcibly cleaned or replaced to maintain the pumping efficiency of the vacuum system.

[0009] As a further improvement to this technical solution, the oxygen concentration in the surrounding environment is monitored in real time through an oxygen content detection device throughout the entire process, ensuring that the concentration is never lower than 19.5% to guarantee the safety of operators.

[0010] As a further improvement to this technical solution, if a main power supply failure occurs during the high-temperature stage or the early stage of cooling, the backup diesel generator set will automatically start within 10 seconds, prioritizing the continuous operation of the cooling system for more than 15 hours to prevent equipment damage due to overheating.

[0011] As a further improvement to this technical solution, graphite paper is placed between the connecting surfaces of the heater, and a 1mm graphite paper sheet is placed between the graphite electrode of the heater and the nut to ensure good electrical contact, reduce contact resistance, and ensure the uniformity and stability of the thermal field during long-term operation.

[0012] As a further improvement to this technical solution, the furnace body is provided with a heat insulation cage, and the distance between the heat insulation cage and the furnace wall is greater than 30mm, forming a heat dissipation air duct, thereby ensuring the heat insulation effect while taking into account the cooling efficiency of the furnace wall.

[0013] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. In this method for purifying graphite products, by combining ultimate vacuum and periodic cyclic gas filling at the highest temperature stage, a variety of impurities are efficiently and deeply removed, and graphite products with extremely high purity can be stably prepared to meet the stringent requirements of the semiconductor industry.

[0014] 2. In this method for purifying graphite products, the systematic inspection and cyclic tightening technology before loading the furnace achieves extremely high mechanical stability and electrical reliability of the thermal field under extreme high temperature conditions, effectively preventing short circuits and thermal field damage caused by loose connections, and ensuring the uniformity of product purity. Attached Figure Description

[0015] Figure 1 This is one of the process flow diagrams of the present invention; Figure 2 This is one of the process flow diagrams for the decomposition of the present invention. Detailed Implementation

[0016] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0017] Therefore, this invention provides a method for purifying graphite products. See [link to relevant documentation]. Figure 1 As shown, it includes systematic checks before loading the furnace, loading the furnace, double checks before operation, protective vacuuming, step heating, purification reaction, cooling, safe unloading, and post-processing steps.

[0018] For details, see Figure 1 and Figure 2 As shown, the systematic inspection before loading the furnace includes: using special tools to tighten all high-strength carbon-carbon connectors 2 between heaters 1 in sequence, repeating this process four times to eliminate potential loosening caused by thermal stress; using a megohmmeter to measure the insulation resistance between heater 1 and inner insulation carbon felt 3 to ensure that its value is greater than 12 kΩ; thoroughly cleaning the heating element, graphite electrode 4 and graphite dust in the thermal field; and checking that the water circuit, gas circuit, vacuum system (checking the oil level of mechanical pump 5) are all in normal condition.

[0019] During operation, this step lays a safety foundation for the entire process, ensuring the absolute reliability of the thermal field during subsequent high-temperature operation.

[0020] Further, see Figure 2 As shown, the protective vacuuming operation includes: after confirming that all manual valves are closed, starting the mechanical pump 5, and then filling it with 0.15 MPa of nitrogen gas through its dynamic sealing air inlet 6 to form an air curtain protection.

[0021] During operation, this operation can effectively prevent volatile graphite impurities and reaction byproducts from entering the pump oil and sealing system of mechanical pump 5, greatly extending the pump's maintenance cycle and service life.

[0022] Among them, see Figure 2 As shown, the purification reaction step is carried out in the isothermal stage of heating to 2400℃. The diffusion pump is started to draw the pressure in the furnace to the ultimate vacuum below 50Pa. Then, the gas charging cycle is performed, and a large flow of argon gas (120L) is charged into the furnace as a carrier, and R22 (1.5L) is charged as the reaction gas. Argon gas is then charged from the bottom (low charge 10L) and the top (top charge 10L) to ensure uniform atmosphere. After reacting for 15 minutes, the gas in the furnace is evacuated to 50Pa. This cycle is repeated 40 times.

[0023] During operation, the extreme vacuum environment facilitates the evaporation of impurities. The circulating reaction gas (R22) can react with specific metallic impurities to generate volatile chlorides, which are effectively carried away by the inert gas (Ar), thereby achieving deep purification. The R22 mentioned above is difluorochloromethane, with the chemical formula CHClF2.

[0024] Among them, see Figure 2 As shown, the safe unloading procedure is as follows: After the process is completed, the furnace door can only be opened when the equipment is cooled to a temperature below 150°C. Before unloading, the temperature of the material 9 is confirmed to be below 100°C using an infrared thermometer, and the oxygen concentration in the furnace is confirmed to be ≥19.5% using an oxygen content detector before the operator can carry out the unloading operation.

[0025] During operation, dual safety standards ensure that operators are not at risk of burns from high temperatures, suffocation from lack of oxygen, or dust explosions.

[0026] Among them, see Figure 2 As shown, the post-processing steps are as follows: After the furnace is unloaded, if there is no production plan for more than 3 days, the furnace door needs to be closed again, and the vacuum system needs to be started to evacuate the furnace chamber 7 to a vacuum state and maintain it.

[0027] During operation, this measure keeps the furnace cavity dry and oxygen-free, preventing moisture and oxygen in the air from causing oxidation damage to the expensive carbon felt insulation material 3, and extending its service life by more than 100%.

[0028] In summary, this invention effectively solves the comprehensive technical problems of unstable thermal field, equipment damage, insufficient purity, poor safety, and high maintenance cost in the prior art through a set of interconnected and meticulous systematic methods.

[0029] The core principle of this invention is as follows: a stable and reliable thermal environment is constructed through the pre-protection of mechanical fastening and electrical insulation; the life of core components is extended through proactive protection before equipment operation; impurities are physically evaporated and chemically removed through the synergistic effect of high temperature, ultimate vacuum and circulating purging of reactive gas; ultimate operational safety is ensured through strict dual safety standards; and long-term maintenance of production equipment is achieved through vacuum protection after shutdown. The entire method systematically improves the quality, production safety and economy of high-purity graphite products.

[0030] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0031] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for high-temperature purification of graphite, comprising the steps of loading a furnace, vacuuming, heating, purification reaction, cooling, and unloading, characterized in that: It also includes systematic inspections before loading the furnace, double inspections before operation, protective vacuuming operations, and safe unloading and post-processing steps; The pre-loading systematic inspection includes cyclically tightening the heater connections, measuring insulation resistance, cleaning dust, and checking the status of each system. The protective vacuuming operation includes filling its dynamic seal with protective gas while starting the mechanical pump; The purification reaction steps include drawing an ultimate vacuum using a diffusion pump at the highest temperature range and repeatedly filling the tank with inert and reactive gases.

2. The method for high-temperature purification of graphite according to claim 1, characterized in that: During the pre-furnace systematic inspection, all high-strength carbon connectors of the heaters are cyclically tightened no less than four times.

3. The method for high-temperature purification of graphite according to claim 2, characterized in that: The insulation resistance measurement requires that the insulation resistance between the heater and the insulation layer / material be greater than 12 kΩ.

4. The method for high-temperature purification of graphite according to claim 3, characterized in that: During the protective vacuuming operation, compressed air or nitrogen at 0.1-0.2 MPa is introduced into the dynamic seal of the mechanical pump.

5. The method for high-temperature purification of graphite according to claim 4, characterized in that: The specific gas circulation process in the purification reaction step is as follows: 120L of argon gas and 1.5L of R22 gas are introduced, followed by 10L of argon gas for low-level purging and 10L of argon gas for top-level purging. The reaction is carried out for 15 minutes, and the gas is evacuated to 50Pa. This process is repeated 40 times.

6. The method for high-temperature purification of graphite according to claim 1, characterized in that: The heating process employs a stepped heating program: heating at a rate of 300℃ / h to 800℃, heating at a rate of 200℃ / h to 1500℃, heating at a rate of 150℃ / h to 1800℃, heating at a rate of 70℃ / h to 2250℃, and heating at a rate of 50℃ / h to 2400℃ and holding at that temperature for 2 hours.

7. The method for high-temperature purification of graphite according to claim 1, characterized in that: In the safe tapping and post-processing steps, the tapping conditions are that the material temperature is below 100℃ and the oxygen content in the furnace is ≥19.5%.

8. The method for high-temperature purification of graphite according to claim 1, characterized in that: If there are no work scheduled for 3 days or more, the equipment must be vacuum-sealed for storage.

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