Carbonization treatment process for carbon base material processing

Abstract

The invention relates to the technical field of carbonization processing. The invention discloses a carbonization treatment process for carbon base material processing, which is characterized by comprising the following steps: S1, pretreatment: taking raw materials, putting the raw materials into a reaction furnace, carrying out segmented heating treatment for pre-oxidation, and testing the performance of the raw materials in each stage of pretreatment; s2, an oxygen regulation and control stage, wherein the oxygen concentration in the reaction furnace is regulated and controlled in the segmented heating treatment process; s3, a carbonization staged heating stage: performing carbonization staged heating on the pre-oxidized raw material, and testing the performance of the raw material in each stage of the carbonization staged heating; and S4, a cooling stage: controlling the cooling rate to slowly cool the raw materials during cooling. According to the carbonization treatment process for processing the carbon base material, the performance of polyacrylonitrile fibers is remarkably improved through segmented pre-oxidation and carbonization.

Description

Technical Field

[0001] The invention relates to the technical field of carbonization processing, and in particular to a carbonization treatment process for carbon substrate processing. Background Art

[0002] In today's material science and industrial production fields, carbon substrates have been widely used in many industries, such as aerospace, electronic information, energy storage, high-temperature industrial equipment, and automobile manufacturing, due to their unique physical and chemical properties, such as high hardness, high thermal conductivity, good chemical stability, and excellent high temperature resistance. With the continuous improvement of the performance requirements of carbon substrates in various industries, the processing technology of carbon substrates is particularly critical, among which the carbonization process is the core link that determines the quality and performance of carbon substrates. There are many disadvantages in the traditional carbonization process of carbon substrates. In the pre-oxidation stage, most of them adopt a single-stage high-temperature pre-oxidation method, which directly heats the raw materials to a higher temperature and the oxygen concentration is relatively fixed. Under this process condition, the fiber is rapidly oxidized at high temperature, and incomplete oxidation and overoxidation are prone to occur. Incomplete oxidation will cause the fiber to be unable to form an ideal structure in the subsequent carbonization process, while overoxidation will greatly reduce the thermal stability of the fiber. At the same time, single-stage high-temperature pre-oxidation is prone to cause fiber embrittlement, which reduces the tensile strength and elongation at break of the fiber, seriously affecting the mechanical properties of the carbon substrate. In addition, due to the uneven oxidation process, the flame retardant properties of the material are difficult to reach the ideal state, which limits the application of carbon substrates in some fields with high flame retardant requirements. In the carbonization stage, the traditional process also has obvious shortcomings. The single-stage high-temperature carbonization process heats the raw materials to the target temperature in one step. Although the operation is relatively simple, this method will cause the fiber to withstand too high a temperature in a short period of time, resulting in a sharp change in the internal structure of the fiber, and the adjustment and reorganization of the molecular chain is not sufficient, resulting in fiber embrittlement. This not only reduces the carbon content of the carbon substrate, but also makes its mechanical properties such as tensile strength and elongation at break difficult to meet the needs of high-end applications. Moreover, the carbonization structure formed by the single-stage high-temperature carbonization is not complete. Under high temperature conditions, the thermal stability of the carbon substrate is poor and the mass loss rate is high, which limits its use in high temperature environments. In terms of atmosphere protection during the carbonization process, the traditional process either lacks effective protection measures and directly carbonizes in the air, causing the fiber surface to react with oxygen, forming oxidation damage, making the fiber surface rough and cracked, and seriously affecting the surface quality of the carbon substrate; or the protective gas concentration used is insufficient or the flow control is unreasonable, and the protective effect cannot be fully exerted, resulting in low carbonization efficiency and unstable product quality. In addition, the traditional cooling method usually adopts rapid cooling. Although this method can shorten the production cycle, rapid cooling will produce huge thermal stress inside the carbon substrate, causing damage to the carbon substrate structure, cracks, deformation and other defects, seriously affecting the quality and performance of the carbon substrate. In the testing stage, the traditional carbon substrate processing technology has major defects. During the pre-oxidation and carbonization process, the test of raw material performance often relies on experience or a single indicator, which cannot comprehensively and accurately evaluate the performance of the fiber.For example, focusing only on mechanical strength while ignoring thermal stability and other comprehensive properties will lead to inaccurate feedback on process effects, making it difficult to effectively optimize process parameters, and thus unable to ensure that the quality and performance of the final product meet the needs of different application scenarios.

[0003] In summary, the existing carbon substrate carbonization process has obvious deficiencies in pre-oxidation, carbonization, atmosphere protection, cooling and testing, which seriously restricts the improvement of carbon substrate performance and the expansion of its application range. Therefore, it is urgent to develop a new and more scientific and reasonable carbonization process to solve the problems existing in the traditional process, improve the quality and performance of the carbon substrate, and meet the growing demand of modern industry for high-performance carbon substrates. Summary of the invention

[0004] In order to solve the deficiencies of the prior art, the present invention discloses a novel, more scientific and reasonable carbonization process for carbon substrate processing, which improves the quality and performance of the carbon substrate and meets the growing demand of modern industry for high-performance carbon substrates.

[0005] The present invention discloses a carbonization treatment process for carbon substrate processing, which comprises: S1: pretreatment, taking raw materials and putting them into a reaction furnace for segmented heating treatment and pre-oxidation, and testing the raw material performance at each stage of the pretreatment; S2: oxygen control stage, during which the oxygen concentration in the reactor is controlled during the staged heating process; S3: Carbonization stage heating stage, the pre-oxidized raw materials are carbonized and heated in stages, and the performance of the raw materials is tested in each stage of carbonization heating; S4: Cooling stage, during cooling, the cooling rate is controlled to slowly cool the raw materials.

[0006] Furthermore, the staged heating treatment of the pretreatment in S1 includes a low temperature stage, a medium temperature stage and a high temperature stage, and the heating parameters of each stage during the pretreatment process are: In the low temperature stage, the heating time is 1-2 hours, the heating rate is 1.5-2.5°C / min, and the heating temperature is 180-230°C; In the medium temperature stage, the heating time is 2-4 hours, the heating rate is 0.8-1.2°C / min, and the heating temperature is 230-260°C; The heating time in the high temperature stage is 4-7 hours, the heating rate is 0.4-0.6°C / minute, and the heating temperature is 280-310°C. Furthermore, in S2, the oxygen concentration in the reactor is regulated, and the oxygen concentration is ≥ 99.5%; During the low temperature stage, the oxygen concentration is controlled to be maintained at 15-35%; In the medium temperature stage, the oxygen concentration is controlled to maintain 45-65%; During the high temperature stage, the oxygen concentration is controlled to maintain 75-100%.

[0007] Furthermore, when the raw material is subjected to staged heating treatment, the flow rate of oxygen is adjusted by a gas flow regulating device to adjust the concentration of oxygen; The gas flow regulating device comprises: Gas supply module, the gas supply module is equipped with a gas source pressure regulating valve; A flow control module, the flow control module includes a mass flow meter for real-time monitoring of gas flow rate and a solenoid valve or a proportional control valve for regulating gas flow; A gas mixing module, the gas mixing module includes a multi-component gas mixer for mixing oxygen and other protective gases in a set ratio; A distributed gas injection module, the distributed gas injection module includes a plurality of multi-point distributed injection structures; A data monitoring and control module, the data monitoring and control module includes a sensor network and a control unit based on a PLC or an embedded system, the sensor network includes a flow sensor for real-time monitoring of the gas flow at each stage, a concentration sensor for detecting the oxygen concentration or the inert gas concentration, and a pressure sensor for monitoring the gas pressure change in the furnace; The data monitoring and control module is connected to the gas supply module, the flow control module, the gas mixing module and the distributed gas injection module, and the flow control module is connected to the gas supply module.

[0008] Further, the raw material in S1 is polyacrylonitrile fiber; The carbonization stage heating stage in S3 includes the first stage, the second stage and the third stage. The conditions of each stage in the carbonization stage heating stage are: The heating temperature in the first stage is 280-320°C and the heating time is 0.8-1.2 hours; The heating temperature in the second stage is 380-420°C and the heating time is 1.8-2.2 hours; The heating temperature in the third stage is 480-620°C and the heating time is 2.8-3.2 hours.

[0009] Furthermore, the gas source of the gas supply module includes a protective gas, which is one of nitrogen or argon, and the concentration of nitrogen or argon is ≥99.99%; Carbonization is heated in stages. During the heating process, the raw materials are protected by protective gas. The flow rate of protective gas in each stage is: The flow rate of the first-stage protective gas is 0.8-1.2L / min, The flow rate of the second stage protective gas is 1.8-2.2L / min, The flow rate of the third stage protective gas is 2.8-3.2L / min.

[0010] Furthermore, in the cooling stage in S4, the raw material is cooled at a constant rate; The cooling rate in the cooling stage in S4 is 0.5-8°C per minute.

[0011] Furthermore, the raw material properties are tested at each stage of pretreatment in S1 and S3, and the raw material properties are tested at each stage of carbonization heating. The test items include: thermal stability, mechanical properties, flame retardancy, fiber surface morphology, carbon content, mechanical properties, carbonization efficiency, high temperature tolerance and oxidation resistance of the raw materials.

[0012] Beneficial effects of the present invention: The carbonization treatment process for carbon substrate processing of the present invention reduces the mass loss of polyacrylonitrile fiber at a specific temperature through segmented pre-oxidation, low-temperature activation of molecular chains, and medium-high temperature full cyclization, thereby significantly improving thermal stability. Segmented temperature control effectively avoids embrittlement of polyacrylonitrile fiber, retains high tensile strength and elongation at break, and enhances mechanical properties. It makes the ladder structure of the molecular chain more complete, greatly improves the limiting oxygen index of polyacrylonitrile fiber, and has better flame retardant properties.

[0013] A carbonization treatment process for carbon substrate processing of the present invention is carried out by segmented carbonization, and non-carbon elements are gradually removed by segmented carbonization, so as to significantly increase the carbon content of the carbon substrate and lay the foundation for high-performance products. The segmented heating prevents the embrittlement of polyacrylonitrile fiber, significantly improves the strength and elongation of polyacrylonitrile fiber, and has better practical application performance. A more complete carbonization structure is formed, which has strong anti-decomposition ability at high temperature and can adapt well to high temperature environment. A high-concentration protective gas is used, and the flow rate is reasonably set in stages to effectively prevent the oxidation damage of the surface of polyacrylonitrile fiber, making it smoother and more complete. Non-carbonization reaction is reduced, reaction by-products are taken away, the carbonization process is optimized, and the carbonization efficiency and thermal stability are improved. Constant cooling avoids thermal shock, prevents thermal stress accumulation and crack generation, and ensures the integrity of the carbon substrate structure. Sufficient time is provided for microstructure adjustment, so as to promote the formation of a denser and more uniform organization and improve physical and chemical properties. Various tests are carried out in each stage of pre-oxidation and carbonization to comprehensively and accurately feedback the process effect. Multi-dimensional test data provides accurate support for process parameter optimization, and dynamically adjusts parameters in combination with relevant curves and results to ensure process accuracy and meet the needs of different application scenarios. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a low-temperature constant temperature stirring reaction bath in the embodiment of the present application.

[0015] Figure 2 A schematic diagram of the structure of the gas source processor in the implementation mode of the present application.

[0016] Figure 3 A schematic diagram of the structure of a mass flow meter in an embodiment of the present application.

[0017] Figure 4 Another structural schematic diagram of the mass flow meter in the embodiment of the present application.

[0018] Figure 5 A schematic diagram of the structure of an infrared thermometer in an embodiment of the present application.

[0019] Figure 6 A schematic diagram of the structure of a programmable controller in an implementation manner of the present application. DETAILED DESCRIPTION

[0020] In order to enable those skilled in the art to better understand the solutions of the present invention, the technical solutions in the specific implementation modes of the present invention will be clearly and completely described below.

[0021] The present invention discloses a carbonization process for carbon substrate processing, which comprises: S1: pretreatment, taking raw materials and putting them into a reactor for staged heating treatment for pre-oxidation, and testing the raw material performance at each stage of the pretreatment. S2: oxygen control stage, regulating the oxygen concentration in the reactor during the staged heating treatment. S3: carbonization stage, heating the pre-oxidized raw materials in stages, and testing the raw material performance at each stage of the carbonization staged heating. S4: cooling stage, controlling the cooling rate during cooling to slowly cool the raw materials.

[0022] As an embodiment, the segmented heating treatment of the pretreatment in S1 includes a low temperature stage, a medium temperature stage and a high temperature stage. The heating parameters of each stage in the pretreatment process are as follows: the heating time in the low temperature stage is 1-2 hours, the heating rate is 1.5-2.5°C / minute, and the heating temperature is 180-230°C. The heating time in the medium temperature stage is 2-4 hours, the heating rate is 0.8-1.2°C / minute, and the heating temperature is 230-260°C. The heating time in the high temperature stage is 4-7 hours, the heating rate is 0.4-0.6°C / minute, and the heating temperature is 280-310°C. Figure 1 As shown, in the low-temperature stage of pretreatment, a low-temperature constant-temperature stirring reaction bath can be used to control the heating environment temperature of the reaction furnace, so that the raw materials are evenly heated within the set low-temperature range, activating the molecular chains and avoiding local overheating that may damage the raw material performance.

[0023] The main purpose of the low temperature stage is to activate the polyacrylonitrile molecular chain, so that the nitrogen atoms in the molecular chain react initially with oxygen to form a partial ladder structure. Control the temperature rise rate to avoid local overheating of the polyacrylonitrile fiber, which may lead to breakage or morphological changes. Promote uniform heating of the polyacrylonitrile fiber and provide a thermal balance basis for the medium temperature stage. The heating rate in the low temperature stage is 1.5-2.5°C / minute, which can ensure the synchronization of the temperature rise inside and on the surface of the polyacrylonitrile fiber.

[0024] The main purpose of the medium temperature stage is to induce further cyclization reaction of polyacrylonitrile molecules to form a more stable ladder structure and improve the flame retardant properties of polyacrylonitrile fiber. It can also enhance the intermolecular force and ensure the structural integrity of polyacrylonitrile fiber at high temperature. The heating rate in the medium temperature stage is 0.8-1.2°C / minute, which can avoid rapid heating causing overheating of polyacrylonitrile fiber or uneven surface cyclization. The color of polyacrylonitrile fiber in the medium temperature stage gradually changes from light gray to dark gray or light brown, indicating that the cyclization reaction is fully proceeding.

[0025] The main purpose of the high temperature stage is to complete the full cyclization of the molecular chain, transform the polyacrylonitrile molecular chain into a stable ladder compound structure, and significantly improve the thermal stability and flame retardant properties of polyacrylonitrile fiber. The high temperature stage reduces the risk of pyrolysis of polyacrylonitrile fiber in the high temperature stage, laying the foundation for subsequent carbonization treatment. The heating rate in the high temperature stage is 0.4-0.6°C / minute, and the temperature rise rate is slowed down in the high temperature range to ensure uniform and sufficient oxidation of the raw materials. In the high temperature stage, the color of the polyacrylonitrile fiber changes from dark gray to dark brown, until it is close to black, indicating that the pre-oxidation has been basically completed.

[0026] As an implementation method, the oxygen concentration in the reactor is regulated in S2, and the oxygen concentration is ≥99.5%. The oxygen concentration is controlled to be maintained at 15-35% in the low temperature stage to prevent excessive oxidation from causing local damage to the raw materials. The oxygen concentration is controlled to be maintained at 45-65% in the medium temperature stage to enhance the oxidation effect on the raw materials and ensure the uniformity of the reaction. The oxygen concentration is controlled to be maintained at 75-100% in the high temperature stage to provide sufficient oxygen to support the final cyclization reaction. Figure 2 As shown, the gas supply module includes a gas source processor. To ensure the purity of the gas entering the reactor, the gas source processor can process the gas source to remove impurities, moisture, etc., to ensure that the concentration of gases such as oxygen and nitrogen meet the process requirements and avoid impurities affecting the processing quality of the carbon substrate.

[0027] As an implementation method, when the raw material is subjected to staged heating treatment, the flow rate of oxygen is adjusted by a gas flow regulating device to adjust the oxygen concentration. The gas flow regulating device includes: a gas supply module, a flow control module, a gas mixing module, a distributed gas injection module and a data monitoring and control module. The gas supply module is equipped with a gas source pressure regulating valve to ensure the stability of gas supply, such as Figure 3 and Figure 4 As shown, the flow control module includes a mass flow meter for real-time monitoring of gas flow rate and a solenoid valve or a proportional control valve for adjusting the gas flow. The flow control module sets the target flow value at different stages through the control software, and dynamically adjusts the flow according to the real-time data to ensure that the atmosphere in the furnace always meets the target requirements. The gas mixing module includes a multi-component gas mixer for mixing oxygen and other protective gases in a set ratio. The multi-component gas mixer mixes oxygen and other protective gases in a set ratio to ensure that the gas concentration reaches the target value. The mixing uniformity design adopts a vortex mixing chamber or a microporous gas distribution plate to ensure that the mixed gas reaches a uniform state before flowing into the furnace. The distributed gas injection module includes a plurality of multi-point distributed injection structures, and multi-point distributed injection holes are set inside the reactor to optimize the gas injection path according to the distribution of polyacrylonitrile fibers in the furnace. The injection aperture and flow matching design ensure that the airflow evenly covers the surface of the polyacrylonitrile fiber. The flow of each group of injection holes can be adjusted separately to avoid excessively fast or too slow local airflow. The data monitoring and control module includes a sensor network and a control unit based on a PLC or embedded system. The sensor network includes a flow sensor for real-time monitoring of the gas flow rate at each stage, a concentration sensor for detecting the oxygen concentration or the inert gas concentration, and a pressure sensor for monitoring the gas pressure change in the furnace. The data monitoring and control module is connected to the gas supply module, the flow control module, the gas mixing module, and the distributed gas injection module. The flow control module is connected to the gas supply module. The flow sensor monitors the gas flow rate at each stage in real time. The concentration sensor detects the oxygen concentration or the inert gas concentration. The pressure sensor monitors the gas pressure change in the furnace to prevent abnormal conditions. The control system is based on a control unit of a PLC or embedded system, supporting multi-stage program setting, automatic operation, and real-time monitoring. The control software provides a graphical interface, and users can adjust the gas flow, concentration, and stage time parameters at any time.

[0028] The gas flow regulator can be used to set the oxygen concentration in stages. Different oxygen concentrations combined with the heating stage can make the oxidation of polyacrylonitrile fiber more uniform, avoiding brittleness or surface defects of polyacrylonitrile fiber caused by excessive oxidation. The gas flow regulator ensures uniform and controllable oxidation and carbonization reactions by precisely controlling the gas flow and concentration during the segmented pre-oxidation and carbonization process. The gas flow regulator can adjust the flow rate of oxygen, nitrogen or other protective gases entering the reactor to avoid uneven oxidation due to excessively fast airflow or insufficient local reaction due to excessively slow airflow, and ensure that the gas environment in the pre-oxidation or carbonization stage meets the target reaction conditions. The gas flow regulator can dynamically adjust the oxygen concentration according to the reaction requirements at different stages of the pre-oxidation treatment, gradually increasing from low concentration to high concentration, ensuring that the cyclization reaction of the polyacrylonitrile fiber is evenly promoted, and can also switch to inert gas protection during the carbonization treatment stage to prevent oxidation of the polyacrylonitrile fiber surface. The built-in sensor of the gas flow control device detects the gas flow, concentration and pressure in the furnace in real time, transmits the monitoring data to the control module, ensures that the flow control is synchronized with the actual demand, and automatically corrects the flow deviation through the feedback mechanism to prevent parameter inaccuracy due to environmental or equipment changes. The gas flow control device can use a multi-point distributed gas injection structure to ensure that the airflow is evenly distributed in the furnace, avoiding local airflow aggregation or uneven flow rate that leads to uneven cyclization or carbonization of polyacrylonitrile fibers. Figure 5 As shown in the figure, during the entire carbonization process, the infrared thermometer is used to measure the temperature of the raw materials in the reactor in real time and provide timely feedback on the temperature information so that the operator can adjust the parameters of the heating equipment according to the process requirements and ensure that the heating temperature at each stage meets the process specifications. Figure 6 As shown in the figure, the carbonization process involves complex operations in multiple stages. The programmable controller can realize automatic control and accurately control parameters such as heating time, heating speed, gas flow rate, etc. according to the preset program to improve production efficiency and process stability. At the same time, combined with sensor data, the entire process can be monitored and adjusted in real time.

[0029] Operation process: During the gas entry phase, the gas supply module provides high-concentration oxygen or nitrogen according to the preset target parameters. The flow control module adjusts the gas flow rate entering the reactor to ensure stable gas supply.

[0030] In the gas mixing stage, in the gas mixing module, oxygen and other gases are fully mixed in a predetermined ratio to generate a mixed gas that meets the target concentration.

[0031] In the injection and distribution stage, the mixed gas enters the reaction furnace through the distributed injection module and evenly covers the surface of the polyacrylonitrile fiber in the furnace.

[0032] Real-time monitoring and feedback: The sensor network monitors the gas flow, concentration and pressure in real time and transmits the data to the control system. The control system dynamically adjusts the flow and concentration according to the monitoring data to ensure that the atmosphere conditions in the furnace are consistent with the target values.

[0033] The mass flow meter and proportional control valve are used to achieve precise control of the flow rate, with an error as low as ±0.5%, which is significantly better than the traditional mechanical flow control method. The distributed injection module effectively eliminates the problem of uneven distribution of airflow in the furnace, ensuring the uniformity of oxidation and carbonization of the polyacrylonitrile fiber surface. It supports multi-stage parameter setting, automatically adjusts the gas concentration and flow rate in different pre-oxidation or carbonization stages to adapt to changes in reaction requirements. The system can be flexibly configured for different types of polyacrylonitrile fibers and a variety of oxidation and carbonization process requirements. All gas flow, concentration and pressure data are recorded in the control system, supporting full process data tracking and process optimization analysis.

[0034] As an embodiment, the raw material in S1 is polyacrylonitrile fiber. The carbonization stage heating stage in S3 includes the first stage, the second stage and the third stage. The conditions of each stage in the carbonization stage heating stage are: the heating temperature of the first stage is 280-320°C, and the heating time is 0.8-1.2 hours. The heating temperature of the second stage is 380-420°C, and the heating time is 1.8-2.2 hours. The heating temperature of the third stage is 480-620°C, and the heating time is 2.8-3.2 hours. The staged heating method makes the carbonization process more refined. In the first stage, the temperature range of 280-320°C can initially activate the molecular reaction in the polyacrylonitrile fiber and begin to slowly remove some non-carbon elements. As the temperature rises to 380-420°C in the second stage, the reaction is further deepened, and more impurity elements such as hydrogen and nitrogen are removed. In the third stage, the high temperature of 480-620°C can cause the remaining non-carbon elements to fully react and detach from the polyacrylonitrile fiber structure, thereby effectively increasing the carbon content of the final product. Compared with the single-stage high-temperature carbonization process, this method of gradually increasing the temperature and removing impurities in stages can make the carbonization more complete and is conducive to obtaining a higher carbon content. Single-stage high-temperature carbonization can easily cause the polyacrylonitrile fiber to withstand too high a temperature in a short period of time, resulting in rapid changes in the internal structure of the polyacrylonitrile fiber and brittleness. In the segmented heating process designed by you, the lower temperature in the first stage allows the polyacrylonitrile fiber to have an adaptation and initial reaction process, and will not be damaged by the sudden temperature rise. In the second stage, the temperature is appropriately increased, and while continuing to promote the reaction, the structure of the polyacrylonitrile fiber can be gradually adjusted and stabilized. Although the temperature in the third stage is higher, due to the preparation of the first two stages, the polyacrylonitrile fiber has a certain stability and can better withstand high temperatures, avoiding the brittleness of the polyacrylonitrile fiber caused by one-time high-temperature treatment. Therefore, the tensile strength and elongation at break of the polyacrylonitrile fiber under this process can be significantly improved, and the mechanical properties are better. Staged heating helps to form a more complete carbonized structure in different temperature ranges. In each stage, the molecular structure inside the polyacrylonitrile fiber gradually changes to form an ordered carbonized lattice. This ordered structure is more stable at high temperatures and can effectively resist thermal decomposition. For example, under a high temperature environment of 600°C, the mass loss rate of polyacrylonitrile fiber using this segmented carbonization process will be significantly reduced, showing better thermal stability.

[0035] As an implementation method, the gas source of the gas supply module includes a protective gas, which is one of nitrogen or argon, and the concentration of nitrogen or argon is ≥99.99%. The raw material is protected by the protective gas during the heating process of the carbonization stage heating stage, and the flow rate of the protective gas in each stage is: the flow rate of the first stage protective gas is 0.8-1.2L / min. The flow rate of the second stage protective gas is 1.8-2.2L / min. The flow rate of the third stage protective gas is 2.8-3.2L / min.

[0036] The protective gas is nitrogen or argon with a concentration of ≥99.99%, which can minimize the presence of impurity gases. During the carbonization process, polyacrylonitrile fiber is very easy to react with oxygen under high temperature, and the high concentration of protective gas can form an inert gas barrier around the polyacrylonitrile fiber, effectively isolating oxygen and preventing the polyacrylonitrile fiber from being oxidized, thereby ensuring that the carbonization reaction proceeds as expected and improving the quality and stability of the carbonized product.

[0037] The first stage: The flow rate is set to 0.8-1.2L / min. At this time, the polyacrylonitrile fiber has just started to undergo carbonization reaction. The relatively low flow rate can not only form a preliminary protective gas layer on the surface of the polyacrylonitrile fiber to prevent premature oxidation, but also will not take away too much heat due to excessive flow rate, affecting the normal progress of the reaction. This stage is mainly to allow the polyacrylonitrile fiber to adapt to the heating environment and begin a slow structural transformation. The appropriate flow rate helps to maintain stable reaction conditions.

[0038] The second stage: the flow rate is increased to 1.8-2.2L / min. As the carbonization reaction progresses, the polyacrylonitrile fiber needs more adequate protection to cope with higher temperatures and more intense reactions. The increased flow rate can isolate oxygen more effectively, and also helps to remove some small molecular byproducts produced during the reaction, making the reaction environment purer, which is conducive to the carbonization reaction proceeding in a more favorable direction, and further promoting the transformation and optimization of the polyacrylonitrile fiber structure.

[0039] The third stage: The flow rate reaches 2.8-3.2L / min. In the third stage at high temperature, the carbonization reaction of polyacrylonitrile fiber is nearing the end, and stronger protection is needed to ensure the integrity of the final carbonized structure. A larger flow rate can continuously provide reliable protection for polyacrylonitrile fiber at high temperature, prevent oxidation and thermal decomposition that may occur at high temperature, and ensure that the polyacrylonitrile fiber stably completes the carbonization process in a high temperature environment, thereby obtaining high-quality carbonized products.

[0040] As an implementation method, the cooling stage in S4 cools the raw material at a constant rate. The cooling rate in the cooling stage in S4 is 0.5-8°C per minute. Constant cooling can make the raw material shrink evenly in various parts during the cooling process, avoiding the concentration of thermal stress due to too fast temperature change. When the raw material is cooled rapidly, the temperature difference between the surface and the inside will increase rapidly, thereby generating large thermal stress. This thermal stress may cause cracks, deformation or other structural defects inside the raw material. Constant cooling can make the overall temperature of the raw material drop slowly and evenly, reduce the generation of thermal stress, maintain the structural integrity of the product, and ensure that the quality and performance of the final product are not affected. Thermal stress is controlled by constant cooling, and internal damage caused by thermal stress is avoided, thereby improving the mechanical properties of the product. Mechanical indicators such as tensile strength and flexural strength of the product will be guaranteed, and may even be improved due to the optimization of the microstructure. For example, for some polyacrylonitrile fiber materials, a suitable cooling rate can make the molecular chains inside the polyacrylonitrile fiber more regular, improve the tensile strength and elongation at break of the polyacrylonitrile fiber, and make it more suitable for application scenarios with high requirements for mechanical properties.

[0041] As an implementation mode, the raw material properties are tested in each stage of pretreatment in S1 and S3, and the raw material properties are tested in each stage of carbonization heating. The test items include: thermal stability, mechanical properties, flame retardant properties, fiber surface morphology, carbon content, mechanical properties, carbonization efficiency, high temperature tolerance and oxidation resistance test. Example

[0042] Example 1: Comparison between the staged pre-oxidation process and the traditional single-stage high-temperature pre-oxidation process.

[0043] Experimental conditions: Raw materials: polyacrylonitrile (PAN) fiber, acrylonitrile content ≥85%, polyacrylonitrile fiber diameter 12μm.

[0044] Process parameters: Staged pre-oxidation process (this technology): Low temperature stage: heating temperature is 200°C, oxygen concentration is 30%, and heating time is 1 hour; Medium temperature stage: heating temperature is 250°C, oxygen concentration is 50%, and heating time is 3 hours; High temperature stage: heating temperature is 300°C, oxygen concentration is 90%, and heating time is 5 hours; Traditional single-stage pre-oxidation: Single high temperature: direct heating to 300°C, oxygen concentration 50%, total heating time 5 hours.

[0045] Test indicators: Thermal stability: The mass loss rate of polyacrylonitrile fiber at 300°C-500°C was measured using a thermogravimetric analyzer (TGA).

[0046] Mechanical properties: The tensile strength and elongation at break of polyacrylonitrile fibers were tested using a single fiber tensile tester.

[0047] Flame retardant properties: The limiting oxygen index (LOI) of polyacrylonitrile fiber is measured to reflect the flame retardancy of the material.

[0048] The experimental results are shown in Table 1 below.

[0049]

[0050] Table 1 Result analysis: Thermal stability: This technology gradually activates the molecular chain in the low-temperature stage and achieves full cyclization in the medium and high temperature stages, effectively reducing incomplete oxidation and overoxidation, and significantly reducing the mass loss rate of polyacrylonitrile fiber at high temperatures.

[0051] Mechanical properties: The segmented temperature control of this technology avoids the embrittlement problem caused by rapid oxidation of polyacrylonitrile fiber at high temperature in a single stage, and retains higher tensile strength and elongation at break.

[0052] Flame retardant properties: Due to the segmented pre-oxidation, the ladder structure of the molecular chain is more complete, and the limiting oxygen index of polyacrylonitrile fiber is significantly improved, proving that its flame retardancy is better.

[0053] Example 2: Effect of staged pre-oxidation combined with precise oxygen concentration control Experimental conditions: Raw materials: Same as Example 1.

[0054] Process parameters: Segmented pre-oxidation + precise oxygen concentration control (this technology): Low temperature stage: heating temperature is 200°C, oxygen concentration is 20%, and heating time is 1 hour; Medium temperature stage: heating temperature is 250°C, oxygen concentration is 60%, and heating time is 4 hours; High temperature stage: heating temperature is 300°C, oxygen concentration is 100%, and heating time is 6 hours; Traditional staged pre-oxidation: A fixed oxygen concentration (50%) is used in the low-temperature, medium-temperature and high-temperature stages, without stage-by-stage regulation.

[0055] Test indicators: Surface morphology of polyacrylonitrile fibers: Scanning electron microscopy (SEM) was used to observe the uniformity and defects of the surface microstructure of polyacrylonitrile fibers.

[0056] Thermal stability: TGA analysis of decomposition rate above 300°C.

[0057] Deformation ability: The deformation ability of polyacrylonitrile fiber is tested at a constant temperature of 200°C-300°C to evaluate its heat resistance.

[0058] The experimental results are shown in Table 2 below.

[0059]

[0060] Table 2 Result analysis: Surface morphology: Precise oxygen concentration control makes the oxidation rate more uniform, avoiding the local overoxidation caused by fixed oxygen concentration in traditional processes, and significantly reducing the surface defects of polyacrylonitrile fibers.

[0061] Thermal stability: The segmented oxygen concentration control of this technology provides sufficient oxygen in the high-temperature stage to ensure sufficient cyclization reaction, while avoiding the risk of thermal decomposition of polyacrylonitrile fiber due to excessive oxygen concentration in the low and medium temperature stages.

[0062] Deformation ability: Due to the precise control of oxygen concentration and temperature, polyacrylonitrile fiber has better dimensional stability in high temperature environment and is suitable for high temperature filtration materials and other fields.

[0063] Example 3: Comparison between staged carbonization process and single-stage high-temperature carbonization process Experimental conditions Raw materials: PAN fiber that has been pre-oxidized in sections, acrylonitrile content ≥85%, fiber diameter 12μm.

[0064] Process parameters: Staged carbonization process (this technology): The first stage: heating temperature is 300°C, nitrogen protection, heating time is 1 hour; The second stage: heating temperature is 400°C, nitrogen protection, heating time is 2 hours; The third stage: the heating temperature is 500°C, nitrogen protection, and the heating time is 3 hours.

[0065] Single-stage high-temperature carbonization process: The mixture was heated to 500°C in one step under nitrogen protection for a total of 3 hours.

[0066] Test indicators Carbon content: The carbon content of the fibers was measured using an elemental analyzer.

[0067] Mechanical properties: The tensile strength and elongation at break were tested using a single fiber tensile tester.

[0068] Thermal stability: TGA was used to measure the mass loss rate of the fibers at 600 °C.

[0069] The experimental results are shown in Table 3 below.

[0070]

[0071] Table 3 Result analysis: Carbon content: The staged carbonization gradually removes non-carbon elements such as hydrogen and nitrogen, and the carbon content is significantly higher than the single-stage high-temperature carbonization process.

[0072] Mechanical properties: The staged heating avoids the fiber embrittlement caused by one-time high-temperature treatment, and the fiber strength and elongation are significantly improved.

[0073] Thermal stability: Segmented carbonization forms a more complete carbonization structure, showing better high-temperature anti-decomposition performance.

[0074] Example 4: Effect of atmosphere protection on carbonization effect Experimental conditions Raw materials: PAN fibers that have been subjected to segmented pre-oxidation treatment, with the same specifications as those in Example 3.

[0075] Process parameters: This process (staged nitrogen protection): The first stage: heating temperature is 300°C, nitrogen flow rate is 1L / min, and heating time is 1 hour; The second stage: heating temperature is 400°C, nitrogen flow rate is 2L / min, and heating time is 2 hours; The third stage: the heating temperature is 500°C, the nitrogen flow rate is 3L / min, and the heating time is 3 hours.

[0076] Traditional process (without protective atmosphere): Heat in air to 500°C for 4 hours.

[0077] Test indicators Fiber surface morphology: SEM was used to observe the cracks and smoothness of the fiber surface after carbonization.

[0078] Carbonization efficiency: The decomposition rate at 500 °C was analyzed by TGA to evaluate the extent of carbonization reaction.

[0079] The experimental results are shown in Table 4 below.

[0080]

[0081] Table 4 Result analysis: Surface morphology: Nitrogen protection prevents oxidation damage caused by the reaction of oxygen in the air with the fiber surface, making the fiber surface more complete and smooth.

[0082] Decomposition rate: Nitrogen protection reduces the occurrence of non-carbonization reactions and improves carbonization efficiency and thermal stability.

[0083] Example 5: Experiment on optimization of temperature and time of segmented carbonization Experimental conditions Raw materials: Same as Example 3.

[0084] Process parameters: Segmented carbonization process A: Stage 1: 300°C, 1 hour; The second stage: 400°C, 2 hours; The third stage: 500°C, 2 hours.

[0085] Segmented carbonization process B: Stage 1: 300°C, 1 hour; The second stage: 400°C, 2 hours; The third stage: 500°C, 3 hours.

[0086] Segmented carbonization process C: Stage 1: 300°C, 2 hours; The second stage: 400°C, 2 hours; The third stage: 500°C, 3 hours.

[0087] Test indicators Carbon content: measured by elemental analyzer.

[0088] Thermal stability: TGA was used to test the mass change of the fibers at 600°C.

[0089] Mechanical properties: The strength and elongation at break were tested by single fiber tensile tester.

[0090] The experimental results are shown in Table 5 below.

[0091]

[0092] Table 5 Result analysis: Carbon content: The carbonization temperature and time distribution of process C are optimal, and the carbon content reaches the highest.

[0093] Tensile strength and elongation: The performance of process B is slightly better than other processes and has the best overall performance.

[0094] Mass loss rate: The high temperature stage of process C lasts longer and has better thermal stability.

[0095] Example 6: Performance comparison of carbonized products in high temperature applications Experimental conditions Materials: Products using process B in Example 5 and conventional carbonization process.

[0096] Test indicators: High temperature resistance: The mass change of a material after being kept at 600°C for 10 hours.

[0097] Oxidation resistance: The mass change of the material after being treated in air at 500°C for 2 hours.

[0098] The experimental results are shown in Table 6 below.

[0099]

[0100] Table 6 Result analysis: High temperature tolerance: The segmented carbonized products show lower mass loss under extreme high temperature conditions, demonstrating excellent thermal stability.

[0101] Oxidation resistance: Since the carbonization structure of the product produced by this process is more complete, the oxidation resistance is greatly improved.

[0102] Summary: The advantages of this process Higher carbon content: Through staged heating and precise atmosphere control, the carbon content of carbonized products is increased to 72%-74%, significantly better than the 65%-70% of traditional processes.

[0103] Stronger mechanical properties: Segmented carbonization avoids the problem of fiber embrittlement, increases the tensile strength by more than 20%, and doubles the elongation at break.

[0104] Better thermal stability: The mass loss rate is reduced by 50%-60%, and it shows better high temperature stability at 600°C.

[0105] Stronger anti-oxidation performance: The segmented carbonization forms a more complete carbonization structure, and the anti-oxidation ability is significantly improved, which is suitable for high-temperature filtration, protective materials and other fields.

[0106] Atmosphere protection optimization: Use high-concentration nitrogen or argon as the protective gas to prevent oxidation reaction and ensure the uniformity of fiber carbonization. The flow rate of the protective gas is precisely adjusted through the flow control device to prevent local hot spots or oxygen infiltration from causing fiber performance degradation.

[0107] Slow cooling: Problems with traditional methods: Rapid cooling can easily cause thermal shock, resulting in damage to the fiber structure.

[0108] Improvements of this process: During the cooling process, the cooling rate is strictly controlled, such as cooling by 2°C per minute, to avoid thermal stress accumulation or cracking of the fiber due to excessive temperature difference.

[0109] Test the accuracy of judgment Key process steps: 1. Morphology and thermal stability test Problems with traditional methods: The testing process often relies on experience or a single indicator, resulting in incomplete evaluation of fiber performance.

[0110] Improvements to this process: At each stage of pre-oxidation and carbonization treatment, the following tests are performed: Morphology inspection: Scanning electron microscopy (SEM) was used to observe the uniformity and integrity of the fiber surface.

[0111] Thermogravimetric analysis (TGA): Real-time evaluation of thermal stability of the fiber to ensure that the mass loss rate below 300°C is ≤5%.

[0112] Color change: The progress of pre-oxidation and carbonization was assessed by visually observing the change in color (white → gray → black).

[0113] Result analysis: These tests can accurately feedback the process effect at each stage and serve as a basis for further optimization of process parameters.

[0114] 2. Mechanical properties and thermal stability test Problems with traditional methods: Testing is limited to mechanical strength, ignoring thermal stability and other comprehensive properties.

[0115] Improvements of this process: Mechanical property test: Use a single fiber tensile tester to test the tensile strength and elongation at break of the fiber to ensure that the tensile strength is ≥500MPa.

[0116] Thermal stability test: Dynamic mechanical analyzer (DMA) and thermogravimetric analyzer (TGA) were used to test the mechanical stability and quality change of the fiber under high temperature conditions.

[0117] Data combination analysis: Comprehensively analyze the mechanical strength and thermal stability data to determine whether the final performance of the fiber meets the application requirements.

[0118] 3. Dynamic testing and adjustment Real-time monitoring: During the pre-oxidation and carbonization process, the temperature-time curve and test results are combined to dynamically adjust the processing parameters such as heating rate and atmosphere concentration to ensure the accuracy of the process.

[0119] It should be understood that those skilled in the art can make improvements or changes based on the above description, and all these improvements and changes should fall within the scope of protection of the appended claims of the present invention.

Claims

1. A carbonization process for carbon substrate processing, characterized in that: include: S1: Pretreatment: take the raw materials and put them into the reactor for staged heating and pre-oxidation. The performance of the raw materials is tested at each stage of pretreatment. S2: oxygen control stage, during which the oxygen concentration in the reactor is controlled during the staged heating process; S3: Carbonization stage heating stage, the pre-oxidized raw materials are carbonized and heated in stages, and the performance of the raw materials is tested in each stage of carbonization heating; S4: Cooling stage, during cooling, the cooling rate is controlled to slowly cool the raw materials.

2. A carbonization process for carbon substrate processing according to claim 1, characterized in that: The segmented heating treatment of the pretreatment in S1 includes a low temperature stage, a medium temperature stage and a high temperature stage. The heating parameters of each stage in the pretreatment process are: In the low temperature stage, the heating time is 1-2 hours, the heating rate is 1.5-2.5°C / min, and the heating temperature is 180-230°C; In the medium temperature stage, the heating time is 2-4 hours, the heating rate is 0.8-1.2°C / min, and the heating temperature is 230-260°C; In the high temperature stage, the heating time is 4-7 hours, the heating rate is 0.4-0.6°C / minute, and the heating temperature is 280-310°C.

3. A carbonization process for carbon substrate processing according to claim 2, characterized in that: In S2, the oxygen concentration in the reactor is regulated, and the oxygen concentration is ≥ 99.5%; During the low temperature stage, the oxygen concentration is controlled to be maintained at 15-35%; In the medium temperature stage, the oxygen concentration is controlled to maintain 45-65%; During the high temperature stage, the oxygen concentration is controlled to maintain 75-100%.

4. A carbonization process for carbon substrate processing according to claim 3, characterized in that: When the raw materials are subjected to staged heating treatment, the flow rate of oxygen is adjusted by a gas flow regulating device to adjust the concentration of oxygen; The gas flow regulating device comprises: Gas supply module, the gas supply module is equipped with a gas source pressure regulating valve; A flow control module, the flow control module includes a mass flow meter for real-time monitoring of gas flow rate and a solenoid valve or a proportional control valve for regulating gas flow; A gas mixing module, the gas mixing module includes a multi-component gas mixer for mixing oxygen and other protective gases in a set ratio; A distributed gas injection module, the distributed gas injection module includes a plurality of multi-point distributed injection structures; A data monitoring and control module, the data monitoring and control module includes a sensor network and a control unit based on a PLC or an embedded system, the sensor network includes a flow sensor for real-time monitoring of the gas flow at each stage, a concentration sensor for detecting the oxygen concentration or the inert gas concentration, and a pressure sensor for monitoring the gas pressure change in the furnace; The data monitoring and control module is connected to the gas supply module, the flow control module, the gas mixing module and the distributed gas injection module, and the flow control module is connected to the gas supply module.

5. A carbonization process for carbon substrate processing according to claim 4, characterized in that: The raw material in S1 is polyacrylonitrile fiber; The carbonization stage heating stage in S3 includes the first stage, the second stage and the third stage. The conditions of each stage in the carbonization stage heating stage are: The heating temperature in the first stage is 280-320°C and the heating time is 0.8-1.2 hours; The heating temperature in the second stage is 380-420°C and the heating time is 1.8-2.2 hours; The heating temperature in the third stage is 480-620°C and the heating time is 2.8-3.2 hours.

6. A carbonization process for carbon substrate processing according to claim 5, characterized in that: The gas source of the gas supply module includes a protective gas, which is one of nitrogen or argon, and the concentration of nitrogen or argon is ≥99.99%; Carbonization is heated in stages. During the heating process, the raw materials are protected by protective gas. The flow rate of protective gas in each stage is: The flow rate of the first-stage protective gas is 0.8-1.2L / min; The flow rate of the second stage protective gas is 1.8-2.2L / min; The flow rate of the third stage protective gas is 2.8-3.2L / min.

7. A carbonization process for carbon substrate processing according to claim 1, characterized in that: The cooling stage in S4 cools the raw material at a constant rate; The cooling rate in the cooling stage in S4 is 0.5-8°C per minute.

8. A carbonization process for carbon substrate processing according to claim 1, characterized in that: In S1 and S3, the raw material properties are tested at each stage of pretreatment and the carbonization is heated in stages. The test items for testing the raw material properties at each stage include: thermal stability, mechanical properties, flame retardancy, fiber surface morphology, carbon content, mechanical properties, carbonization efficiency, high temperature tolerance and oxidation resistance of the raw materials.

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