High-efficiency PAN material pre-oxidation method based on assistance of anode layer Hall ion source and pre-oxidized fiber

Abstract

The invention provides a PAN material efficient pre-oxidation method based on assistance of an anode layer Hall ion source and a pre-oxidized fiber, and relates to the technical field of carbon fiber preparation, and the method mainly comprises the following steps: placing a PAN precursor or fabric in a vacuum chamber, heating to 180-270 DEG C, and carrying out heat preservation; then, working gas is introduced into the vacuum chamber, and the indoor pressure is maintained to be 0.5-5 Pa; and finally, starting an anode layer Hall ion source, and carrying out ion beam treatment on the PAN material for 5-60 minutes under the conditions that the voltage of the ion source is 100-1000V and the ion beam current is 0.5-3.0 A. According to the invention, accurate injection of PAN molecular chain energy is realized, and activation energy of cyclization reaction is significantly reduced. Through the synergistic effect of heat energy and ion beam activation, the pre-oxidation time is greatly shortened, the energy consumption is reduced, and fiber etching damage easily caused by conventional plasmas is effectively avoided through accurate energy level regulation and control.

Description

Technical Field

[0001] This invention relates to the field of carbon fiber preparation technology, and more specifically, to a highly efficient pre-oxidation method for PAN materials and pre-oxidized fibers based on an anode layer Hall ion source assisted by an anode layer. Background Technology

[0002] Polyacrylonitrile (PAN)-based carbon fiber has become an irreplaceable key material in aerospace, defense, sporting goods, and high-end civilian industries due to its excellent properties such as high specific strength, high specific modulus, corrosion resistance, and high temperature resistance. The preparation of PAN-based carbon fiber mainly includes processes such as precursor fiber preparation, pre-oxidation, carbonization, and graphitization. Among these, pre-oxidation is a crucial step that connects the preceding and following processes, and its process control is closely related to the final performance of the carbon fiber.

[0003] The essence of pre-oxidation is to transform linear PAN macromolecular chains into heat-resistant ladder-structured polymers through chemical reactions such as cyclization, dehydrogenation, and oxidation. This stable ladder structure ensures that the fibers do not melt or decompose during subsequent carbonization processes at temperatures exceeding 1,000 degrees Celsius, while maintaining excellent mechanical properties and morphological structure.

[0004] The most common pre-oxidation method used in industrial production is the hot air circulation heating method. This method places the PAN material in a hot air environment at 200~300℃ and completes the pre-oxidation process by precisely controlling the heating program and residence time. Although this method is technically mature and widely used, its inherent limitations are also quite prominent.

[0005] First, it has high energy consumption and low efficiency. The pre-oxidation process is the most time-consuming link in the entire carbon fiber production chain. The long-term heating requires a lot of energy, resulting in high production costs.

[0006] Secondly, the reaction is intense and difficult to control. Both the cyclization and oxidation reactions of PAN are strongly exothermic. The heat transfer from the fiber surface to the interior can easily lead to temperature differences between the inside and outside of the fiber and cause uneven reaction. If the heat cannot be dissipated in time, it will cause local overheating or even cause the fiber to burn out or melt.

[0007] Furthermore, the "core-skin structure" is difficult to avoid. Since the rate of oxygen diffusion from the fiber surface to the core is much lower than the rate of thermally induced cyclization reaction, a dense cyclization layer often forms on the fiber surface, which hinders the diffusion of oxygen inward. This results in insufficient cyclization in the core, forming a significant "core-skin structure," which becomes a stress concentration point for carbon fibers and severely degrades their mechanical properties.

[0008] Finally, the process window is narrow, and process parameters such as temperature, time, and tension are coupled and controlled with extreme precision. Even a slight deviation in any parameter can have a significant impact on the quality of pre-oxidized fiber and the subsequent carbon fiber performance.

[0009] To address these issues, plasma-assisted pre-oxidation can be employed. For example, radio frequency or microwave plasma can be used to treat PAN fibers at room temperature. However, these conventional plasma sources (such as radio frequency plasma) have a wide ion energy distribution and poor directionality. When treating PAN, the bombardment effect of high-energy particles often outweighs the chemical activation effect, easily leading to damage such as fiber surface etching and excessive molecular chain breakage, which ultimately reduces the performance of the carbon fibers. This etching effect is particularly pronounced in aerobic environments, making it difficult to achieve a balance between efficiently initiating cyclization and maintaining fiber structural integrity.

[0010] In summary, existing thermal oxidation technologies are inefficient and prone to producing core-sheath structures, while conventional plasma-assisted technologies, due to the inherent characteristics of the plasma source, are prone to etching damage to the fibers, failing to achieve an ideal balance between efficiently promoting cyclization and perfectly maintaining the fiber structural integrity. Therefore, developing a novel plasma pre-oxidation technology that enables precise energy injection and combines efficient activation with gentle processing characteristics is of paramount importance for promoting cost reduction, efficiency improvement, and performance enhancement in the carbon fiber industry. Summary of the Invention

[0011] The present invention aims to solve at least one of the aforementioned technical problems existing in the prior art.

[0012] Therefore, the first aspect of the present invention provides a highly efficient pre-oxidation method for PAN materials based on an anode layer Hall ion source assisted by the present invention.

[0013] A second aspect of the present invention provides a pre-oxidized fiber.

[0014] This invention provides a highly efficient pre-oxidation method for PAN materials based on an anode layer Hall ion source assisted by: The PAN material is placed in a vacuum chamber, the vacuum chamber is evacuated, and then the PAN material is heated to the pre-oxidation temperature and held at that temperature. The pre-oxidation temperature is 180~270℃. A working gas is introduced into the vacuum chamber to maintain the pressure in the vacuum chamber at 0.5~5 Pa. The working gas is an inert gas or a mixture of an inert gas and a reactive gas. The Hall ion source of the anode layer is turned on, and the PAN material is treated under the conditions of ion source voltage of 100~1000V and ion beam current of 0.5~3.0A for 5~60 minutes.

[0015] The efficient pre-oxidation method for PAN materials based on an anode layer Hall ion source assisted by the above-described technical solution of the present invention may further have the following additional technical features: In the above technical solution, the inert gas is one of argon and helium, or a mixture of both.

[0016] In the above technical solution, the reactive gas is oxygen.

[0017] In the above technical solution, when the working gas contains oxygen, the anode layer Hall ion source operates in pulse mode with a duty cycle of 5% to 60%.

[0018] In the above technical solution, the process of activating the Hall ion source in the anode layer to process the PAN material adopts a time-sequential step-by-step method, including: The first step involves performing a first ion treatment in a pure inert gas atmosphere at a first voltage; the first voltage is 400~1000V. The second step involves performing a second ion treatment in an oxygen-containing atmosphere at a second voltage; the second voltage is 200~500V and is lower than the first voltage.

[0019] In the above technical solution, the process of activating the Hall ion source in the anode layer to process the PAN material adopts a time-sequential step-by-step method, including: The first step involves performing a first ion treatment in a pure inert gas atmosphere at a first voltage; the first voltage is 400~1000V. The second step is to perform thermal oxygenation treatment in an oxygen-containing atmosphere with the ion source turned off.

[0020] In the above technical solution, the first ion treatment time in the first step is 10-30 minutes; And / or, the processing time for the second step is 10 to 30 minutes.

[0021] In the above technical solution, after activating the Hall ion source in the anode layer to treat the PAN material, the method further includes: Turn off the ion source, maintain the temperature or adjust the temperature to 200~280℃, and carry out subsequent heat treatment in an oxygen-containing atmosphere under normal pressure or low vacuum for 10~120 minutes.

[0022] In the above technical solution, when the vacuum chamber is evacuated, the evacuation continues until the background vacuum level is lower than [a certain value]. Pa.

[0023] The present invention also provides a pre-oxidized fiber, which is prepared by any one of the methods described above.

[0024] In summary, due to the adoption of the above-mentioned technical features, the beneficial effects of the present invention are: This invention achieves precise energy injection and efficient cyclization. By employing an anolyte Hall ion source, this invention can generate an ion beam with good monochromaticity and strong directionality. This characteristic allows the energy to act on the PAN molecular chain like "precision surgery," efficiently breaking CH bonds and generating a large number of free radicals. This synergistic effect of physical activation and thermal energy generation significantly reduces the activation energy required for the cyclization reaction, thereby fundamentally improving the rate and uniformity of cyclization.

[0025] This invention offers significant inventive advantages in protecting the integrity of the fiber structure. Unlike conventional plasma sources, which are prone to excessive physical sputtering due to their wide ion energy distribution, this invention effectively avoids molecular chain breakage and surface etching damage caused by high-energy ions or irregular impacts by using an inert gas and combining it with precise control of ion energy. This gentle yet precise processing method ensures that the pre-oxidized filaments maintain excellent fiber structural integrity while reacting rapidly, laying a solid foundation for subsequent high-quality carbonization.

[0026] This invention offers a highly effective solution to the long-standing problem of "core-skin structure" in the industry. Utilizing the extremely strong penetrating and activating effect of ion beams, the chemical reaction is no longer confined to the fiber surface but can be uniformly initiated from the surface to the core. This significantly reduces the uneven internal and external reactions caused by the limited oxygen diffusion rate in traditional thermal oxidation methods. The pre-oxidized fibers prepared by the method of this invention have a high degree of cyclization and a highly uniform structure. After subsequent carbonization treatment, the tensile strength and Young's modulus of the resulting carbon fibers are significantly improved.

[0027] From the perspective of production efficiency and industrial cost, the value of this invention is equally outstanding. By introducing the assistance of a Hall ion source, this process successfully reduces the total pre-oxidation time by more than 30% to 50% and demonstrates the potential to lower the pre-oxidation temperature. This leap in efficiency not only means a significantly shorter production cycle, but also provides a practical and feasible technical path for cost reduction and efficiency improvement in carbon fiber production by reducing the huge energy consumption required for continuous heating.

[0028] Additional aspects and advantages of the invention will become apparent in the following description or may be learned by practice of the invention. Attached Figure Description

[0029] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which: Figure 1 This is a process flow diagram of an embodiment of the present invention for a highly efficient pre-oxidation method of PAN material based on an anode layer Hall ion source assisted by the present invention; Figure 2This is a comparison of the FTIR spectra of the pre-oxidized fibers prepared in Example 1 and Comparative Example 1. (In the figure, the C=N peak of Example 1 of the present invention is stronger, and the C≡N peak is weaker). Detailed Implementation

[0030] To better understand the above-mentioned objectives, features, and advantages of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be noted that, unless otherwise specified, the embodiments and features described in these embodiments can be combined with each other.

[0031] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and therefore the scope of protection of the invention is not limited to the specific embodiments disclosed below.

[0032] The following reference Figures 1 to 2 This invention describes a highly efficient pre-oxidation method for PAN materials based on an anode layer Hall ion source assisted by some embodiments of the present invention.

[0033] Some embodiments of this application provide an efficient pre-oxidation method for PAN materials based on an anode layer Hall ion source assisted by an anode layer.

[0034] like Figure 1 As shown, this invention proposes a highly efficient pre-oxidation method for PAN materials based on an anode layer Hall ion source assisted by the present invention. In this method, the polyacrylonitrile (PAN) material to be treated, such as 12K PAN precursor yarn or related fabric, is first fixed on a heated sample stage in a vacuum chamber. The vacuum chamber is then evacuated until the background vacuum level reaches a certain threshold. The pressure is kept below Pa to eliminate interference from impurity gases on the pre-oxidation reaction.

[0035] The heating device is then activated to raise the PAN material to the pre-oxidation temperature and hold it at that temperature, which is limited to 180~270℃, using thermal energy to initially induce the movement of molecular chains.

[0036] The temperature is maintained stable, and working gas is introduced into the vacuum chamber to stabilize the pressure within the chamber at 0.5~5 Pa. Specifically, the working gas can be a pure inert gas such as argon or helium, or a mixture of inert gas and oxygen, depending on the reaction stage.

[0037] After activating the Hall ion source in the anode layer, the PAN material is subjected to ion beam treatment for 5 to 60 minutes by setting the ion source voltage to 100~1000V and the ion beam current to 0.5~3.0A. In some embodiments, in a mixed gas atmosphere containing oxygen, to prevent fiber ablation caused by excessive oxygen ion energy, the ion source can be switched to pulse mode, with the duty cycle controlled between 5% and 60%.

[0038] A key innovation of this invention lies in its use of a time-sequential step-by-step processing logic, which is divided into two steps. The duration of each step is preferably 10-30 minutes.

[0039] In some embodiments, the first step of the time-sequential method involves a first ion treatment in a pure inert gas atmosphere using a relatively high voltage (first voltage) of 400-1000V, aimed at efficiently breaking CH bonds and generating free radicals to induce the formation of the main cyclic structure; the second step switches to an oxygen-containing atmosphere (e.g., an argon-oxygen mixture, wherein the oxygen volume fraction is...). The ion source voltage is reduced to a lower voltage of 200~500V (second voltage) for second ion treatment, thereby completing the oxidative crosslinking while ensuring that the fiber is not etched.

[0040] In other embodiments, the first step of the time-sequential stepwise method involves a first ion treatment in a pure inert gas atmosphere using a relatively high voltage (first voltage) of 400-1000V, aimed at efficiently breaking CH bonds and generating free radicals to induce the formation of the main cyclic structure; the second step switches to an oxygen-containing atmosphere (e.g., an argon-oxygen mixture, wherein the oxygen volume fraction is...). ), directly shut down the ion source for pure thermal oxygen treatment.

[0041] It should be noted that the difference between the first ion treatment and the second ion treatment (pure thermo-oxygen treatment) is not a minor adjustment of a single variable, but a deep and synergistic change in the ion type (working gas) and treatment conditions (physical parameters). This is the most creative technical logic of the entire scheme.

[0042] The first ion treatment is essentially a physical activation stage, with its core task being the efficient induction of host cyclization. In this stage, the system is introduced with inert gases such as pure argon or helium, producing purely kinetic ions that do not participate in the chemical reaction. At this point, the ion source voltage is set at a relatively high level between 400 and 1000 V. Utilizing the high monochromaticity and strong directionality of the ion beam generated by the Hall ion source in the anode layer, energy is injected into the PAN molecular chain like a "precision surgery," breaking the CH bonds and generating a large number of free radicals. This high-energy injection can significantly reduce the activation energy of the cyclization reaction in a very short time, prompting the molecular chain to rapidly transform into a heat-resistant ladder structure.

[0043] The second ion treatment (pure thermal oxidative treatment) shifts to the chemical modification stage, focusing on oxidative crosslinking. At this stage, the working gas is switched to a mixture containing oxygen, introducing chemically active oxygen ions into the reaction system. In contrast to the first stage, to avoid the risks of surface etching and excessive molecular chain breakage caused by high-energy oxygen ions mentioned in the background technology, this stage specifically reduces the voltage significantly to 200-500V or shuts it off entirely. This lower energy setting provides a mild reaction environment, allowing oxygen ions to stably participate in chemical crosslinking. This solves the problem of oxygen's difficulty in diffusing into the interior (i.e., the "core-sheath structure") in traditional methods while ensuring the structural integrity of the fiber surface.

[0044] In some embodiments, after the above-mentioned ion treatment is completed, a subsequent heat treatment of 10 to 120 minutes in air or oxygen at 200 to 280°C may be selectively performed as needed to further improve the trapezoidal structure.

[0045] The following provides specific examples of pre-oxidation using the above method and comparative examples using the traditional pure thermal oxidation method.

[0046] Example 1: 1. Sample: 12K PAN precursor fiber.

[0047] 2. Steps: 1) Fix the PAN precursor fiber onto the heating stage of the vacuum chamber and evacuate to a vacuum level. Pa.

[0048] 2) with The rate of heating up to Keep it warm for 30 minutes.

[0049] 3) Introduce pure argon gas to the pressure... Pa.

[0050] 4) Start the Hall ion source and set the voltage. V, beam A, Continuous mode, processing minute.

[0051] 5) Introduce a mixture of pure argon and pure oxygen to the pressure... Pa, of which oxygen accounts for 80%.

[0052] 6) Turn on the Hall ion source and set the voltage. V, beam A, Continuous mode, processing minute.

[0053] 7) After processing, cool to room temperature under an argon atmosphere and then remove.

[0054] 3. Results: The obtained pre-oxidized fibers were golden yellow and soft in texture. FTIR calculations showed a cyclization conversion rate of [missing value]. .

[0055] Example 2: 1. Sample: Same as Example 1.

[0056] 2. Steps: 1) Same as Example 1.

[0057] 2) Same as Example 1.

[0058] 3) Same as Example 1.

[0059] 4) Same as Example 1.

[0060] 5) Same as Example 1.

[0061] 6) Turn on the Hall ion source and set the voltage. V, beam A, continuous mode, processing time 10 minutes.

[0062] 7) Heat to Keep it warm for 60 minutes.

[0063] 8) After processing, cool to room temperature under an argon atmosphere and then remove.

[0064] 3. Results: The obtained pre-oxidized fibers were reddish-brown and soft in texture. FTIR calculations showed that the cyclization conversion rate reached [percentage missing]. The presence of a moderate CO absorption peak indicates that good oxidative crosslinking has occurred; in other words, the FTIR spectrum shows obvious oxidative crosslinking characteristics, demonstrating the good synergy between ion beam activation and subsequent heat treatment in deep conversion.

[0065] Example 3: 1. Sample: Same as Example 1.

[0066] 2. Steps: 1) Same as Example 1.

[0067] 2) Same as Example 1.

[0068] 3) Same as Example 1.

[0069] 4) Same as Example 1.

[0070] 5) Same as Example 1.

[0071] 6) Turn off the Hall ion source and proceed with pure thermal oxygen treatment. minute.

[0072] 7) After processing, cool to room temperature under an argon atmosphere and then remove.

[0073] 3. Results: The obtained pre-oxidized fibers were reddish-brown and soft in texture. FTIR calculations showed that the cyclization conversion rate reached [percentage missing]. The presence of a moderate CO absorption peak indicates that good oxidative crosslinking has occurred.

[0074] Comparative Example 1 (pure thermal oxidation): 1. Sample: Same as Example 1.

[0075] 2. Steps: 1) Fix the PAN precursor fiber onto the heating stage of the vacuum chamber and evacuate to a vacuum level. Pa.

[0076] 2) with The rate of heating up to Keep it warm for 60 minutes.

[0077] 3. Results: The obtained pre-oxidized fibers were pale yellow, and their cyclization conversion rate was calculated by FTIR. .

[0078] Figure 2 The FTIR spectra of the pre-oxidized fibers prepared in Example 1 and Comparative Example 1 are shown in comparison, clearly demonstrating the superior performance of the method disclosed in this invention for the pre-oxidation of PAN materials. A comparison of the data from Examples 1-3 and Comparative Example 1 shows that the method described in this invention, utilizing the assistance of a Hall ion source in the anolyte layer, significantly improves cyclization efficiency while substantially shortening the processing time, effectively avoiding etching damage to the fiber surface, and producing pre-oxidized fibers of excellent quality.

[0079] Other embodiments of the present invention propose a pre-oxidized filament prepared by the efficient pre-oxidation method of PAN material based on the anolyte layer Hall ion source assisted by any of the above embodiments.

[0080] The illustrative expressions used do not necessarily refer to the same embodiments or examples. Moreover, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0081] Any modifications, equivalent substitutions, or improvements made within the spirit and principles of this invention shall be included within the scope of protection of this invention.

Claims

1. A highly efficient pre-oxidation method for PAN materials based on an anode layer Hall ion source assisted by, characterized in that, include: The PAN material is placed in a vacuum chamber, the vacuum chamber is evacuated, and then the PAN material is heated to the pre-oxidation temperature and held at that temperature. The pre-oxidation temperature is 180~270℃. A working gas is introduced into the vacuum chamber to maintain the pressure in the vacuum chamber at 0.5~5 Pa. The working gas is an inert gas or a mixture of an inert gas and a reactive gas. The Hall ion source of the anode layer is turned on, and the PAN material is treated under the conditions of ion source voltage of 100~1000V and ion beam current of 0.5~3.0A for 5~60 minutes.

2. The efficient pre-oxidation method for PAN materials based on a Hall ion source assisted by an anode layer according to claim 1, characterized in that, The inert gas is one of argon and helium, or a mixture of both.

3. The efficient pre-oxidation method for PAN materials based on a Hall ion source assisted by an anode layer according to claim 1, characterized in that, The reactive gas is oxygen.

4. The efficient pre-oxidation method for PAN materials based on a Hall ion source assisted by an anode layer according to claim 3, characterized in that, When the working gas contains oxygen, the anode layer Hall ion source operates in pulse mode with a duty cycle of 5% to 60%.

5. The efficient pre-oxidation method for PAN materials based on a Hall ion source assisted by an anode layer according to claim 1, characterized in that, The process of activating the Hall ion source in the anode layer to process the PAN material adopts a time-sequential step-by-step method, including: The first step involves performing a first ion treatment in a pure inert gas atmosphere at a first voltage; the first voltage is 400~1000V. The second step involves performing a second ion treatment in an oxygen-containing atmosphere at a second voltage; the second voltage is 200~500V and is lower than the first voltage.

6. The efficient pre-oxidation method for PAN materials based on a Hall ion source assisted by an anode layer according to claim 1, characterized in that, The process of activating the Hall ion source in the anode layer to process the PAN material adopts a time-sequential step-by-step method, including: The first step involves performing a first ion treatment in a pure inert gas atmosphere at a first voltage; the first voltage is 400~1000V. The second step is to perform thermal oxygenation treatment in an oxygen-containing atmosphere with the ion source turned off.

7. The efficient pre-oxidation method for PAN materials based on an anode layer Hall ion source assisted according to claim 5 or 6, characterized in that, The first ion treatment in the first step takes 10-30 minutes; And / or, the processing time for the second step is 10 to 30 minutes.

8. The efficient pre-oxidation method for PAN materials based on a Hall ion source assisted by an anode layer according to claim 1, characterized in that, After activating the Hall ion source in the anode layer to process the PAN material, the process further includes: Turn off the ion source, maintain the temperature or adjust the temperature to 200~280℃, and carry out subsequent heat treatment in an oxygen-containing atmosphere under normal pressure or low vacuum for 10~120 minutes.

9. The efficient pre-oxidation method for PAN materials based on an anode layer Hall ion source assisted according to claim 1, characterized in that, When the vacuum chamber is evacuated, the evacuation continues until the background vacuum level is lower than [a certain value]. Pa.

10. A pre-oxidized fiber, characterized in that, The pre-oxidized fiber is prepared by the method described in any one of claims 1 to 9.

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