A method and system for pulsed arc plasma production of single-walled carbon nanotubes

Abstract

The application discloses a method and system for preparing single-wall carbon nanotubes by using pulsed arc plasma, and relates to the technical field of carbon nanomaterial preparation. P The method comprises the following steps: S1, in an inert atmosphere, a pulsed arc is applied to an anode containing a catalyst, so that the anode is evaporated to form catalyst vapor under the action of periodic high-energy input; by adjusting the frequency f, duty cycle D, peak current I and base current Ib of the pulsed arc, the time distribution of the pulsed arc energy and the heat input intensity are controlled, the pulse period T is set by a power supply or obtained by measuring a current waveform, and the pulse period T is used as a unified time reference for synchronous control of a carbon source pulse; by coupling the carbon source pulse and the pulsed arc pulse in a reaction zone in high-precision time sequence, a high-concentration carbon source supply stage is synchronized with a catalyst evaporation peak, so that large-particle metal condensation is inhibited, impurity content is reduced, invalid decomposition of the carbon source is avoided, the graphitization degree is improved, and the particle size distribution of catalyst particles is narrowed.

Description

Technical Field

[0001] This invention relates to the field of carbon nanomaterial preparation technology, specifically to a method and system for preparing single-walled carbon nanotubes using pulsed arc plasma. Background Technology

[0002] Pulsed arc discharge (PAC) is a classic technique for preparing high-quality single-walled carbon nanotubes. This method typically uses an anode containing catalysts such as iron, cobalt, or nickel as the evaporation source, and graphite or gaseous hydrocarbon molecules as the carbon source. High-temperature plasma is generated in an inert atmosphere using a DC pulsed arc, causing the catalyst and carbon material in the anode to evaporate simultaneously. The resulting product, containing carbon nanotubes, is deposited at the cathode or the cold wall of the reaction chamber. Due to the high temperature of the pulsed arc plasma and the thorough decomposition of the carbon source, this method can yield single-walled carbon nanotubes with high crystallinity.

[0003] However, the traditional continuous DC pulsed arc discharge mode has inherent structural defects, making it difficult to improve product purity and stability. First, the catalyst evaporation process is uncontrollable. Under continuous heat input conditions, the catalyst metal at the anode undergoes violent evaporation, and its evaporation rate varies with the pulsed arc heat load, forming metal vapor with a wide particle size distribution. Some of the metal vapor agglomerates into large particles during cooling. These particles have low catalytic activity and ultimately remain in the product as metal impurities, resulting in a metal content typically as high as 20–70%. Second, there is a time mismatch between the carbon source supply and the catalyst evaporation cycle.

[0004] In existing technologies, carbon source gas is mostly supplied continuously, while the catalyst evaporation process exhibits dynamic fluctuations. During peak evaporation, the catalyst vapor concentration increases instantaneously, while the carbon source concentration is relatively insufficient, affecting effective nucleation. During trough evaporation, the continuous carbon source may decompose excessively, generating amorphous carbon or graphite fragments, leading to a decrease in the graphitization degree of carbon nanotubes and a reduction in the Raman G / D ratio. This results in a mismatch between the carbon source supply and catalyst evaporation.

[0005] Furthermore, the evaporation, mixing, and growth processes are highly coupled and inseparable. Under continuous pulsed arc discharge, catalyst evaporation, carbon source cracking, and carbon nanotube growth occur almost simultaneously, with each stage superimposed on the others. The lack of independent control methods makes it difficult to achieve precise optimization of individual process parameters.

[0006] To address the aforementioned issues, existing improvement schemes mainly focus on optimizing the anode ratio, adjusting process parameters, or improving the furnace structure. While these measures can improve the growth environment to some extent, they still fail to solve the timing matching problem between catalyst supply and carbon source supply from a time perspective. Some studies have introduced pulsed arcs to control the evaporation end, but the carbon source is still supplied continuously, and a unified time reference between the evaporation process and the chemical reaction process has not been established, making it difficult to achieve synergistic optimization of the entire process. Summary of the Invention

[0007] The purpose of this invention is to provide a method and system for preparing single-walled carbon nanotubes by pulsed arc plasma, so as to overcome the above-mentioned shortcomings in the prior art.

[0008] To achieve the above objectives, the present invention provides the following technical solution: a method for preparing single-walled carbon nanotubes by pulsed arc plasma, the method comprising the following steps: S1, applying a pulsed arc to an anode containing a catalyst in an inert atmosphere, causing it to evaporate into catalyst vapor under periodic high-energy input; adjusting the frequency f, duty cycle D, and peak current of the pulsed arc... The base current Ib controls the time distribution of pulsed arc energy and the intensity of heat input. The pulse period T is set by the power supply or obtained by measuring the current waveform, serving as a unified time reference for the synchronous control of the carbon source pulse. S2. Based on the obtained period T, a carbon source gas pulse control signal is generated to introduce the carbon source gas into the reaction zone in the form of a pulse and synchronize it with the pulse arc pulse. The carbon source activation is set with an adjustable carbon source delay Δt relative to the peak value of the pulse arc to compensate for the gas transport delay, so that the high concentration supply stage of the carbon source and the high generation stage of catalyst vapor precisely coincide in the reaction zone, achieving high-precision timing coupling. S3. The carrier gas and carbon source gas can be premixed or transported independently, and coordinated and controlled according to the carbon source pulse rhythm; the gas flow rate and total amount design ensure that the carbon source pulse precisely coincides with the peak value of the pulsed arc in the reaction zone, while timely transporting the reaction products out of the high-temperature zone, maintaining the temperature uniformity of the reaction zone and the stability of the catalyst, thereby enhancing the time coupling effect of the carbon source and catalyst vapor; S4. Based on the stability of the pulsed arc or the product collection status, dynamically adjust the carbon source delay Δt to form a closed-loop control with phase offset as the only adjustable variable, realize high-precision coupling between the carbon source pulse and the pulsed arc pulse, optimize the growth quality of single-walled carbon nanotubes and reduce the content of metal impurities.

[0009] As a further supplement to the above, in S1, the pulse arc frequency f is 200-500Hz, the duty cycle D is 10%-70%, and the peak current is... 500-1500A, base current The range is 0-200A to maximize the transient cooling effect of the pulsed arc and control the catalyst evaporation rate.

[0010] As a further supplement to the above, the carbon source delay Δt is adjusted by a digital controller or a high-speed response valve, and the delay time range is 0-20 milliseconds, which is used to compensate for gas transport time and maintain high-precision timing coupling.

[0011] As a further supplement to the above, the carbon source gas is selected from one of methane, acetylene, ethylene, or a mixture thereof.

[0012] As a further supplement to the above, the carrier gas is argon or nitrogen, and the carrier gas and carbon source gas can be transported through separate pipelines or premixed before introduction to optimize pulse gas flow and temperature distribution in the reaction zone.

[0013] As a further supplement to the above, the closed-loop control includes the following steps: S41, real-time acquisition of the pulse arc pulse current waveform and the product state or pressure / temperature signal in the reaction zone to characterize the pulse arc energy release cycle and the coupling state of the reaction zone; S42, extraction of the pulse arc peak time and pulse period based on the pulse arc current waveform, and calculation of the timing deviation of the carbon source pulse relative to the pulse arc peak value in combination with the reaction zone state parameters, generating a corrected carbon source delay Δt; S43, driving the high-speed response valve to open or close the carbon source gas according to the corrected carbon source delay Δt, and adjusting the valve opening or pulse width to achieve millisecond-level precision carbon source pulse supply, aligning the carbon source supply cycle with the pulse arc peak value; S44, after the carbon source pulse and the pulse arc peak value are realigned, detecting whether the coupling state of the reaction zone reaches the set threshold; if the pulse arc state or product generation state changes, returning to S41 for detection and correction, forming a single-parameter closed-loop control with Δt as the only adjustable variable.

[0014] As a further supplement to the above, the opening or closing response time of the high-speed response valve is no more than 5 milliseconds.

[0015] A system for preparing single-walled carbon nanotubes by pulsed arc plasma includes an arc power supply assembly for outputting pulsed direct current operating at a reference frequency f with a period of T, wherein a peak current is set within each period. and conduction time On-time The ratio of the duty cycle to the period T constitutes the duty cycle parameter D, and the period T constitutes the unified time base of the system; Gas supply components, including a mass flow controller, are used to precisely regulate the flow rates of the carbon source gas and the carrier gas; The pulse timing coupling generation component is electrically connected to the arc power supply component. A carbon source gas pulse control model is constructed with period T as the time reference. A phase offset parameter Δθ is set in the control model to control the relative phase of the carbon source gas pulse start time with respect to the peak value of the pulse arc current, thereby establishing an adjustable phase coupling relationship between the pulse arc energy release section and the carbon source gas supply section. The state parameter calculation component is electrically connected to the pulse timing coupling generation component. It calculates the phase correction amount Δθ′ based on the pulse arc stability parameter and superimposes the phase correction amount onto the phase offset parameter Δθ to update the carbon source gas pulse start time. This allows the phase coupling relationship to be dynamically adjusted according to the pulse arc operation state, thereby forming a closed-loop control with the phase offset parameter as the only adjustable variable.

[0016] As a further supplement to the above, it also includes: a reaction chamber for forming a closed reaction space and controlling the heat load of the chamber; an electrode assembly disposed in the reaction chamber, including a cathode and an anode; and a product collection assembly disposed downstream of the reaction chamber for collecting the products generated by the pulsed arc reaction.

[0017] As a further supplement to the above, the anode is a 99.9% pure iron electrode or an iron-carbon composite electrode to form catalyst vapor and promote the growth of single-walled carbon nanotubes.

[0018] Beneficial effects

[0019] In the above technical solution, the present invention provides a method and system for preparing single-walled carbon nanotubes by pulsed arc plasma. This method achieves high-precision temporal coupling between the carbon source pulse and the pulsed arc pulse in the reaction zone, synchronizing the high-concentration carbon source supply stage with the catalyst evaporation peak. This suppresses the condensation of large metal particles, reduces impurity content, avoids ineffective carbon source decomposition, improves graphitization, and narrows the catalyst particle size distribution, thus promoting high-quality growth of single-walled carbon nanotubes. Simultaneously, the closed-loop phase adjustment structure decouples the evaporation and growth processes, improving system stability, carbon source utilization, and consistency in industrial production.

[0020] It should be understood that the foregoing general description and the following detailed description are exemplary and illustrative only, and are not intended to limit this disclosure.

[0021] This application provides an overview of various implementations or examples of the technology described in this disclosure, and is not a full disclosure of the entire scope or all features of the disclosed technology. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this invention. For those skilled in the art, other drawings can be obtained based on these drawings.

[0023] Figure 1 This is a schematic flowchart of a method for preparing single-walled carbon nanotubes using pulsed arc plasma according to an embodiment of the present invention. Figure 2-3 Raman spectra comparison diagrams of the products of the embodiments and comparative examples are provided for the purposes of this invention; Figure 4-5 This invention provides a comparison image of transmission electron microscopy (TEM) images of the products of the embodiments and comparative examples. Figure 6 This is a schematic diagram of a traditional DC pulse arc mode.

[0024] Figure 7 This is a schematic diagram of the pulse timing coupling mode of the present invention.

[0025] Figure 8 This is a schematic diagram of the system structure according to an embodiment of the present invention. Figure Labels

[0026] 1. Reaction chamber; 1.1. Cathode; 1.2. Anode; 2. Arc power supply assembly; 3. Product collection assembly; 4. Carrier gas; 5. Pulsed arc; 6. Carbon source gas. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of the embodiments of this disclosure clearer, the technical solutions of the embodiments of this disclosure will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this disclosure. All other embodiments obtained by those skilled in the art based on the described embodiments of this disclosure without creative effort are within the scope of protection of this disclosure.

[0028] Reference Figure 1-8 As shown, a method for preparing single-walled carbon nanotubes using pulsed arc plasma (PAP) includes the following steps: S1, applying a pulsed arc (PAP) to an anode 1.2 containing a catalyst in an inert atmosphere, causing it to evaporate into catalyst vapor under periodic high-energy input; adjusting the frequency f, duty cycle D, and peak current of the PAP 5... The base current Ib controls the time distribution of the pulse arc energy and the heat input intensity. The pulse period T is set by the power supply or obtained by measuring the current waveform, so as to serve as a unified time reference for the synchronous control of the carbon source pulse. S2. Based on the acquired period T, a pulse control signal for carbon source gas 6 is generated, causing carbon source gas 6 to be introduced into the reaction zone in pulse form and synchronized with the pulse arc 5. An adjustable carbon source delay Δt is set relative to the peak value of the pulse arc 5 to compensate for the gas transport delay, so that the high concentration supply stage of carbon source and the high generation stage of catalyst vapor precisely coincide in the reaction zone, achieving high-precision timing coupling. Among them, the carbon source delay Δt is adjusted by a digital controller or a high-speed response valve, and the delay time range is 0-20 milliseconds, which is used to compensate for the gas transport time and maintain high-precision timing coupling. The opening or closing response time of the high-speed response valve is no more than 5 milliseconds.

[0029] S3, carrier gas 44, and carbon source gas 66 can be premixed or transported independently, and coordinated and controlled according to the carbon source pulse rhythm; the gas flow rate and total amount design ensure that the carbon source pulse and the peak value of the pulse arc 5 are precisely coincident in the reaction zone, while the reaction products are transported out of the high temperature zone in a timely manner, maintaining the temperature uniformity of the reaction zone and the stability of the catalyst, thereby enhancing the time coupling effect of the carbon source and catalyst vapor; among them, carrier gas 4 is argon or nitrogen, and carrier gas 4 and carbon source gas 6 can be transported through separate pipelines or premixed before introduction to optimize the pulse gas flow and the temperature distribution of the reaction zone; carbon source gas 6 is selected from one of methane, acetylene, ethylene, or a mixture thereof.

[0030] S4. Based on the stability of pulsed arc 5 or the product collection status, dynamically adjust the carbon source delay Δt to form a closed-loop control with phase offset as the only adjustment variable, realize high-precision coupling between the carbon source pulse and the pulsed arc 5 pulse, optimize the growth quality of single-walled carbon nanotubes and reduce the content of metal impurities.

[0031] The closed-loop control includes the following steps: S41, real-time acquisition of the pulse current waveform of the pulse arc 5, and the product status or pressure / temperature signal in the reaction zone, to characterize the energy release cycle of the pulse arc 5 and the coupling state of the reaction zone; S42, extraction of the peak time and pulse period of the pulse arc 5 based on the pulse current waveform, and calculation of the timing deviation of the carbon source pulse relative to the peak value of the pulse arc 5, combined with the reaction zone state parameters, to generate a corrected carbon source delay Δt; S43, driving the high-speed response valve to open or close the carbon source gas 6 according to the corrected carbon source delay Δt, and adjusting the valve opening or pulse width to achieve millisecond-level precision carbon source pulse supply, so that the carbon source supply cycle is aligned with the peak value of the pulse arc 5; S44, after the carbon source pulse and the peak value of the pulse arc 5 are realigned, detecting whether the coupling state of the reaction zone reaches the set threshold; if the state of the pulse arc 5 or the product generation state changes, returning to S41 to re-detect and correct, forming a single-parameter closed-loop control with Δt as the only adjustable variable.

[0032] Specifically, in this invention, step S1 achieves controlled evaporation of the catalyst by applying a pulsed electric arc 5 to the catalyst-containing anode 1.2 in an inert atmosphere. The inert atmosphere is preferably argon or nitrogen to prevent oxidation damage to the catalyst and carbon source caused by the high-temperature plasma. Simultaneously, precise control of the gas flow rate and total volume maintains temperature uniformity in the reaction zone. The frequency f, duty cycle D, and peak current of the pulsed electric arc 5 are specified. The base current Ib is within a preset range, where f is 200-500Hz and D is 10%-70%. The pulsed arc voltage (Ib) is 500-1500A, and the current voltage (Ib) is 0-200A, to maximize the transient cooling effect of the pulsed arc 5 and control the catalyst evaporation rate. Simultaneously, the pulse period (T) is obtained by measuring the power supply or current waveform and used as a time reference for carbon source pulse synchronization, achieving precise control of the thermal load in the reaction zone and reducing the formation of metal impurities. The pulsed arc 5, through the collaboration of a digital controller and power supply, achieves real-time adjustment of its period, amplitude, and duty cycle, and incorporates dynamic feedback based on reaction zone temperature, pressure, and product state to ensure a stable, uniform, and repeatable catalyst evaporation process. This lays the foundation for high-precision timing coupling between the subsequent carbon source pulse and the pulsed arc 5 pulse.

[0033] To ensure the uniformity and controllability of catalyst evaporation, the materials and structure of the anode 1.2 are carefully designed. The anode 1.2 is preferably made of pure iron or iron-carbon composite material with a purity of not less than 99.9%, ensuring uniform distribution of catalyst components within the anode 1.2 and effectively reducing the impact of impurity metals on product quality. To enhance the stability of the pulsed arc 5 discharge and improve catalyst evaporation efficiency, the surface of the anode 1.2 can be pre-processed to form microporous or grooved structures. This structure not only increases the effective surface area of ​​the anode 1.2 but also creates localized high-temperature zones on the anode 1.2 surface, allowing the pulsed arc 5 to burn stably in these zones, thereby achieving uniform catalyst evaporation. The anode 1.2 can also be designed as a hollow structure or have cooling channels embedded within it, allowing for temperature regulation through circulation or carrier gas 4 cooling. This cooling measure effectively controls the temperature gradient of the anode 1.2, reducing heat load fluctuations caused by the transient high temperature of the pulsed arc 5, thus ensuring the controllability and repeatability of the catalyst evaporation rate. In practice, the geometry, micropore density, and cooling channel arrangement of the anode 1.2 can be optimized according to the pulsed arc power, reaction chamber size, and required evaporation rate to achieve high-precision and stable catalyst evaporation, laying the foundation for high-precision timing coupling of subsequent carbon source pulse supply.

[0034] To achieve high-precision carbon source pulse supply in S2, firstly, based on the pulse period T obtained in S1, the peak moment and pulse interval of the pulse arc 5 are monitored in real time by the pulse arc 5 current waveform acquisition module, and transmitted to the digital controller as the time reference for carbon source pulse control. The digital controller generates a pulse control signal and drives the supply of carbon source gas 6 through a high-speed response actuator. The high-speed response actuator is preferably a solenoid valve or a piezoelectric valve, with an opening or closing response time of no more than 5 milliseconds, to ensure that the carbon source gas 6 can complete the start-stop action within milliseconds, thereby accurately matching the high-energy phase of the pulse arc 5.

[0035] The carbon source activation time relative to the peak value of the pulsed arc 5 can be set with an adjustable delay Δt, ranging from 0 to 20 milliseconds. This delay value can be calculated and generated by a digital controller and dynamically adjusted to compensate for the gas pipeline transport time and the reaction zone diffusion time, achieving precise overlap between the high-concentration carbon source supply stage and the high-catalyst vapor generation stage in the reaction zone. To ensure the stability of the pulsed gas flow, a flow regulating unit or mass flow meter can be configured on the carbon source pipeline to achieve precise control of the carbon source flow rate. The carbon source gas 6 is selected from one of methane, acetylene, ethylene, or a mixture thereof. The carrier gas 4 is preferably argon or nitrogen, which can be premixed with the carrier gas 4 before the carbon source is introduced, or transported separately through independent pipelines. The mixing method can be adjusted according to the reaction zone temperature and gas flow characteristics to optimize the pulsed gas flow transport efficiency and temperature distribution.

[0036] To ensure high-precision coupling between the carbon source pulse and the peak value of the pulsed arc 5, this invention also incorporates a closed-loop adjustment module in the control system. This module collects real-time signals of pressure, temperature, and product status in the reaction zone, calculates the timing deviation between the carbon source pulse and the peak value of the pulsed arc 5, generates a corrected delay Δt, and drives a high-speed response valve for correction. This achieves continuous adaptive adjustment, ensuring that the carbon source supply cycle is always aligned with the peak value of the pulsed arc 5. This effectively enhances the synchronous reaction between the carbon source and catalyst vapor, guarantees the crystallization quality of single-walled carbon nanotubes and the uniform distribution of the catalyst, and reduces the content of metal impurities.

[0037] The core technology of S3 lies in the precise control of the transport method, flow rate, and cycle time of the carrier gas 4 and the carbon source gas 6. This ensures the synchronous overlap of the carbon source pulse and the pulsed arc 5 pulse in the high-energy section of the reaction zone, and maintains the temperature uniformity and catalyst stability of the reaction zone. Specifically, to achieve this goal, the carbon source gas 6 and the carrier gas 4 can be transported in two modes: first, the carbon source and carrier gas 4 are fully mixed through a premixing pipeline before introduction to improve the uniformity of the gas flow and ensure uniform carbon source distribution; second, the carbon source and carrier gas 4 are transported independently, each pulsed through a high-speed response valve, and then mixed at the inlet of the reaction zone or in the reaction chamber 1, achieving dynamic and independent gas flow management. The two modes can be flexibly selected according to the reaction zone structure, gas flow characteristics, and product generation efficiency to optimize the pulsed gas flow transport and the temperature distribution of the reaction zone.

[0038] In terms of flow control, the flow rates of both carrier gas 4 and carbon source gas 6 are precisely regulated by mass flow meters or flow control valves. The total flow rate of carrier gas 4 is designed to meet the requirements for rapid transport of reaction products, ensuring that the reaction products in the high-temperature zone can leave the energy concentration area of ​​pulsed arc 5 in a timely manner, thereby avoiding catalyst agglomeration or carbon nanotube amorphization caused by excessively high local temperatures. The carbon source pulse flow rate is synchronized with the pulse of pulsed arc 5. The amplitude and duration of the carbon source pulse can be calculated in real time by a digital controller and driven by a high-speed response valve. The response time is controlled at the millisecond level, thereby ensuring that each carbon source pulse precisely coincides with the peak value of pulsed arc 5 in the reaction zone, achieving high-precision timing coupling.

[0039] Carrier gas 4 is argon or nitrogen. Carrier gas 4 and carbon source gas 6 can be introduced into the reaction zone independently through separate pipelines or after pre-mixing. Carbon source gas 6 is selected from methane, acetylene, ethylene, or a mixture thereof. To further optimize the temperature distribution in the reaction zone, a flow field guiding structure or flow regulating device can be designed at the pipeline outlet or reaction chamber inlet to ensure that the pulsed carbon source gas 6 can uniformly cover the reaction zone and rapidly mix the catalyst vapor with the carbon source gas 6, thereby improving the efficiency of the catalytic reaction and the crystallinity of carbon nanotubes.

[0040] S3 not only ensures the precise alignment of the carbon source pulse and the pulsed arc pulse 5, but also maintains uniform temperature in the reaction zone and stable catalyst distribution, thereby enhancing the high-precision temporal coupling effect between the carbon source and catalyst vapor, providing reliable conditions for the growth of high-quality single-walled carbon nanotubes, while reducing the content of metal impurities and the generation of amorphous carbon, improving the structural integrity of the product and the Raman G / D ratio.

[0041] The core technology of S4 lies in dynamically adjusting the carbon source delay Δt based on the stability of the pulsed arc 5 and the product formation state, realizing closed-loop control with phase offset as the only adjustable variable, thereby accurately synchronizing the carbon source pulse and the pulsed arc 5 pulse, optimizing the growth quality of single-walled carbon nanotubes and effectively reducing the content of metal impurities.

[0042] Specifically, to achieve this objective, this step includes the following technical means: First, in the initial stage S41 of closed-loop control, the pulse current waveform of the pulsed arc 5, as well as the product formation status or local pressure and temperature signals in the reaction zone, are acquired in real time through a high-speed data acquisition module. This data characterizes the transient energy release cycle of the pulsed arc 5 and the coupling state of the reaction zone, providing a precise basis for subsequent carbon source pulse adjustment. The data acquisition unit can employ a high-speed analog-to-digital converter (ADC) and a real-time data processor, with a sampling frequency of no less than 10kHz to ensure millisecond or even sub-millisecond time resolution.

[0043] Next, in S42, based on the acquired pulsed arc 5 current waveform, the peak time and pulse period T of each pulse are extracted, and combined with the reaction zone temperature, pressure or product collection state parameters, the timing deviation of the carbon source pulse relative to the peak value of pulsed arc 5 is calculated. The corrected carbon source delay Δt is generated using a digital controller or embedded processor. High-precision deviation calculation and signal processing are achieved through the following methods: real-time filtering of the acquired pulsed arc current signal (e.g., using moving average filtering, finite impulse response (FIR) filtering, or extended Kalman filtering) to suppress pulsed arc fluctuations and noise interference; precise identification of the peak moment of each pulse using digital peak detection algorithms (e.g., zero-crossing detection and quadratic interpolation), achieving peak capture accuracy of 1 millisecond or even higher; weighted synthesis of data collected from temperature and pressure sensors in the reaction zone, as well as downstream product collection rate signals, input to the control unit to correct the peak identification deviation of the pulsed arc, ensuring a high degree of matching between the carbon source pulse timing and the transient state of the reaction zone; and then, based on the calculated timing deviation, the corrected carbon source delay Δt is generated and transmitted to the control module of the carbon source gas 6 via a digital interface (e.g., high-speed PWM or SPI bus) to achieve precise driving of the valve body or pulse injection device.

[0044] The control unit can dynamically adjust filter parameters and peak recognition thresholds to adapt to different pulse arc frequencies, load changes, or temperature fluctuations, ensuring that the closed-loop control system maintains millisecond-level response capability even under pulse arc fluctuation conditions. The carbon source pulse can achieve high-precision synchronization with the pulse arc peak, providing a reliable timing reference for subsequent S43 high-speed response valve control. This ensures precise coupling between catalyst vapor and carbon source gas, significantly improving the crystallinity of single-walled carbon nanotubes while reducing the formation of amorphous carbon and large-particle metal impurities. Subsequently, in S43, the calculated Δt is transmitted to the high-speed response valve body control module, driving the valve body to complete the carbon source pulse release. The valve body can be a solenoid valve or a piezoelectric valve, with the opening / closing response time controlled within 5 milliseconds to ensure that the carbon source pulse precisely coincides with the peak value of the pulsed arc 5 in the reaction zone. Simultaneously, the valve body opening degree and pulse width are adjustable to ensure that the carbon source flow rate of each pulse matches the instantaneous carbon concentration in the reaction zone, achieving high-precision coupling between catalyst vapor and carbon source gas 6. The valve body control signal is sent by the control unit via PWM or a high-speed digital interface, and the pulse duration and delay Δt can be adjusted through real-time feedback to ensure that each pulse reaches the preset threshold range for carbon nanotube generation rate, reaction zone temperature uniformity, and product collection rate. Δt can be set within the range of 0–50 milliseconds, dynamically adjusted according to the frequency of the pulsed arc 5 and the response characteristics of the reaction zone.

[0045] The closed-loop control system also combines feedforward compensation and feedback adjustment: it monitors the coupling state of the reaction zone in real time, such as the peak value of the pulsed arc 5, temperature uniformity, and product formation rate. When a deviation or change is detected, the system automatically returns to S42 to re-acquire data, corrects Δt, and cyclically adjusts the carbon source pulse, achieving a closed-loop structure with a single phase shift Δt as the adjustment variable. The feedforward loop uses historical pulse and product formation data to predict the required Δt for the next pulse, fine-tuning the valve action in advance, while the feedback loop eliminates deviations in real time. The two are dynamically allocated through weighting coefficients within the controller. This structure ensures that the carbon source pulse is always highly synchronized with the peak value of the pulsed arc 5, maintaining high-temperature stability and catalyst distribution uniformity in the reaction zone even under conditions of pulsed arc 5 fluctuations or load changes, thereby optimizing the crystallization quality of single-walled carbon nanotubes and reducing the content of metal impurities.

[0046] In step S44, the closed-loop control system dynamically realigns the carbon source pulse and the peak value of the pulsed arc 5, determining whether a preset threshold has been reached by real-time monitoring of the coupling state of the reaction zone. Specifically, the control system collects multi-source signals such as the carbon nanotube product generation rate, the temperature uniformity of the reaction zone, and the product collection rate, and compares them with set reference values. The carbon nanotube product generation rate can be set to 0.01–1 mg / s, the allowable deviation for the temperature uniformity of the reaction zone is ±5–10°C, and the allowable deviation for the product collection rate is ±5–15%. When the monitored signal exceeds the threshold, the system automatically returns to step S41 to re-collect data from the gasification and mixing zones, and cyclically corrects the carbon source pulse delay Δt, forming a closed-loop control structure with a single phase offset Δt as the adjustment variable. Technically, the control unit uses a high-speed digital signal processor or FPGA to compare the carbon source valve drive signal and the peak value signal of the pulsed arc 5 in real time, and uses PID or model predictive control (MPC) algorithms to generate a Δt adjustment sequence, ensuring that the carbon source pulse and the peak value of the pulsed arc 5 remain highly synchronized. Under this closed-loop control mechanism, even if pulsed arc fluctuations or load changes occur, the reaction zone can still maintain high-temperature stability and catalyst distribution uniformity, thereby optimizing the crystallization quality of single-walled carbon nanotubes, significantly reducing the content of metal impurities in the product, and achieving a controllable and stable carbon nanotube growth process.

[0047] A system for preparing single-walled carbon nanotubes using pulsed arc plasma includes an arc power supply assembly 2 for outputting pulsed direct current operating at a reference frequency f with a period of T, wherein a peak current is set within each period. and conduction time On-time The ratio of the duty cycle to the period T constitutes the duty cycle parameter D, and the period T constitutes a unified time base; The gas supply assembly includes a mass flow controller 4 for precisely regulating the flow rates of the carbon source gas 6 and the carrier gas 4. The pulse timing coupling generation component is electrically connected to the arc power supply component 2. It constructs a carbon source gas 6 pulse control model with period T as the time reference. The phase offset parameter Δθ is set in the control model to control the relative phase of the carbon source gas 6 pulse opening time with respect to the peak current of the pulse arc 5, thereby establishing an adjustable phase coupling relationship between the energy release section of the pulse arc 5 and the supply section of the carbon source gas 6. The state parameter calculation component is electrically connected to the pulse timing coupling generation component. It calculates the phase correction amount Δθ′ based on the stability parameter of the pulse arc 5 and adds the phase correction amount to the phase offset parameter Δθ to update the pulse start time of the carbon source gas 6. This allows the phase coupling relationship to be dynamically adjusted according to the operating state of the pulse arc 5, thereby forming a closed-loop control structure with the phase offset parameter as the only adjustment variable.

[0048] It also includes: reaction chamber 1, used to form a closed reaction space and control the heat load of the chamber; An electrode assembly, disposed within the reaction chamber 1, includes a cathode 1.1 and an anode 1.2; Product collection component 3 is located downstream of reaction chamber 1 and is used to collect products generated by pulsed electric arc 5.

[0049] Specifically, high-precision, high-purity single-walled carbon nanotubes are prepared by controlling the temporal coupling of pulsed electric arc 5 and carbon source gas 6. The various components work together to ensure a high-precision match between the energy of pulsed electric arc 5, carbon source supply, and the state of the reaction zone, thereby optimizing the catalyst evaporation, carbon source decomposition, and carbon nanotube growth processes.

[0050] It includes: Arc power supply component 2: for outputting pulsed DC current operating at a reference frequency f with a period of T, and setting the peak current in each period. and conduction time , On-time The ratio of the period to the current waveform constitutes the duty cycle parameter D. The period T is determined by power supply or current waveform measurement, forming a unified time base. This is achieved by setting appropriate frequency f and peak current. The duty cycle D controls the evaporation rate of the catalyst at the anode (1.2), and creates a high-temperature plasma zone during the peak phase of each pulsed arc (5), providing an optimal growth environment for the catalyst vapor and carbon source reaction. The power supply unit can employ a highly stable DC pulsed power supply and is equipped with a real-time current monitoring module to ensure stable output waveform of the pulsed arc (5).

[0051] Gas supply components include channels for carrier gas 4 and carbon source gas 6. Carrier gas 4 can be either argon or nitrogen, and carbon source gas 6 can be methane, acetylene, ethylene, or a mixture thereof. Gas flow rate is precisely controlled by a mass flow meter, with a constant amplitude as the control reference. Based on this, a high-speed response valve (response time no greater than 5 milliseconds) modulates the carbon source gas 6 in the time domain to achieve pulsed supply. The high-speed response valve can be a solenoid valve or a piezoelectric valve, equipped with a digital drive module to achieve millisecond-level pulse width adjustment, ensuring that the carbon source pulse precisely coincides with the peak value of the pulsed arc 5.

[0052] Pulse timing coupling generation component: Electrically connected to arc power supply component 2, used to construct a carbon source gas 6 pulse control model. In this control model, using the pulse period T of pulsed arc 5 as the time reference, an adjustable phase offset parameter Δθ is set to control the relative phase of the carbon source gas 6 pulse's onset time with respect to the peak current of pulsed arc 5, thereby establishing an adjustable phase coupling relationship between the energy release section of pulsed arc 5 and the carbon source supply section. By adjusting Δθ, gas transport delay and reaction zone hysteresis effects can be compensated, achieving synchronization between the peak carbon source concentration and the peak catalyst vapor concentration, providing conditions for the high crystallinity growth of single-walled carbon nanotubes.

[0053] State parameter calculation component: Electrically connected to the pulse timing coupling generation component, it is used to collect state information such as the stability parameters of pulsed arc 5, reaction zone temperature, pressure, and product collection rate, and calculate the phase correction Δθ′. The phase correction Δθ′ is superimposed on the original phase offset Δθ to update the start time of the carbon source gas 6 pulse, realizing dynamic closed-loop control of the carbon source pulse and the pulsed arc 5 pulse. Through this single-parameter closed-loop control structure, the reaction zone temperature can be kept uniform and the catalyst vapor distribution stable under the conditions of pulsed arc 5 fluctuations or load changes, thereby optimizing the carbon nanotube crystallization quality and reducing metal impurities.

[0054] Reaction Chamber 1: Used to form a closed reaction space and control the heat load of the chamber, maintaining a stable temperature in the reaction zone. The chamber can be equipped with a high-efficiency heat exchange structure to ensure a suitable temperature difference between the high-temperature zone of the pulsed arc 5 and the collection zone, while avoiding excessive catalyst accumulation or overheating of the reaction zone.

[0055] Electrode assembly: Located within reaction chamber 1, it includes an anode 1.2 and a cathode 1.1. The anode 1.2 is an electrode containing a catalyst material, such as pure iron or an iron-carbon composite electrode, while the cathode 1.1 can be made of highly conductive graphite or copper. The electrode assembly is precisely positioned and mechanically supported to ensure the stable generation of the pulsed arc 5 and to reduce the adverse effects of electrode gap fluctuations on the morphology of the pulsed arc 5 and catalyst evaporation.

[0056] Product collection component 3: Located downstream of reaction chamber 1, it is used to collect the carbon nanotube products generated in the reaction. The collector can employ a multi-stage condenser or filter device to collect the carbon nanotubes, amorphous carbon, and metal particles generated in the reaction zone in stages. At the same time, with airflow optimization, the products can be quickly removed from the high-temperature zone to avoid further decomposition or agglomeration.

[0057] Through the synergistic effect between the components, high-precision timing coupling between the pulsed electric arc 5 and the carbon source gas 6 can be achieved, forming a stable high-temperature reaction zone and a uniform catalyst vapor distribution. This enables the preparation of single-walled carbon nanotubes with high crystallinity and low metal impurity content, providing a reliable technical means for industrial production.

[0058] All the following experiments were conducted in reaction chamber 1 with a diameter of 600 mm. The anode 1.2 was pure iron (99.9% purity), the carbon source gas was methane, and the carrier gas was argon.

[0059] Example 1: Timing Coupling of Pulsed Arc and Carbon Source The pulsed arc parameters are: f = 200 Hz, D = 30%. =800A, Ib=0A, carbon source pulse and pulse arc frequency are synchronized (200Hz), phase delay Δt=2ms, pulse width is 80% of the peak width of the pulse arc, argon flow rate is 80m³ / h, and methane average flow rate is 8m³ / h.

[0060] Test results: Yield 98.5 g / h; metal content 9.8%; Raman G / D ratio 32.1; TEM showed catalyst particle size 3–8 nm and high crystallinity of carbon nanotubes.

[0061] Example 2: Optimizing Timing Matching The pulsed arc parameters are: f=500Hz, D=20%. =1000A, Ib=0A; carbon source pulse synchronization 500Hz, Δt=1ms; argon 100m³ / h, methane average flow rate 10m³ / h.

[0062] Test results: Yield 102 g / h; metal content 7.5%; Raman G / D ratio 35.4; catalyst particle size 2–6 nm.

[0063] The results show that by increasing the frequency and optimizing the phase matching, the metal residue was further reduced, the catalyst particle size was reduced, and the orderliness of the carbon nanotube structure was further improved.

[0064] Comparative Example 1: Continuous DC Pulse Arc Pulsed arc parameters: continuous current I = 800A; gas parameters: argon 80m³ / h, methane continuous 8m³ / h.

[0065] Test results: Yield 10 g / h; Metal content 65.4%; G / D ratio 5.2.

[0066] This indicates that under continuous pulsed arc conditions, there is a severe mismatch between catalyst evaporation and carbon source supply, resulting in a large amount of metal residue and structural disorder.

[0067] Comparative Example 2: Pulsed electric arc + continuous carbon source The pulsed arc parameters are the same as in Example 1 (f=200Hz, D=30%). =800A).

[0068] Gas parameters: continuous methane supply 8 m³ / h; yield 95 g / h; metal content 1.2%; G / D ratio 28.5.

[0069] Under identical pulsed arc conditions, canceling only the carbon source pulse matching resulted in an increase in metal content and a decrease in the G / D ratio, indicating that controlling catalyst evaporation alone without controlling the carbon source timing cannot achieve the optimal reaction coupling state.

[0070] Comparative Example 3: High Current + High Gas Flow Quenching Pulsed arc parameters: continuous current I = 1500A; gas parameters: argon 150m³ / h, continuous carbon source supply.

[0071] Test results: High yield but product agglomeration; metal content approximately 70%; G / D ratio less than 10.

[0072] This demonstrates that simply increasing energy input or enhancing airflow quenching cannot solve the reaction timing mismatch problem.

[0073] Comprehensive analysis shows that, under the same physical conditions of pulsed electric arc (Example 1 and Comparative Example 2), simply by introducing a carbon source pulse and establishing a temporal coupling with the pulsed electric arc pulse, the metal content can be significantly reduced (1.2% → 9.8%), and the structural order can be improved (G / D ratio 28.5 → 32.1).

[0074] After further optimization of the phase parameters, i.e. Example 2, the metal content was reduced to 7.5%, the G / D ratio was increased to 35.4, and the catalyst particle size was further refined.

[0075] The above results show that by establishing an adjustable phase coupling relationship between the carbon source supply section and the pulsed arc energy release section, the present invention has achieved a shift from single evaporation control to reaction process control, solving the problem of mismatch between energy release cycle and carbon source supply cycle in the prior art, thereby significantly improving purity and structural quality while ensuring yield.

[0076] The foregoing has only described certain exemplary embodiments of the present invention by way of illustration. Undoubtedly, those skilled in the art can modify the described embodiments in various ways without departing from the spirit and scope of the present invention. Therefore, the foregoing drawings and descriptions are illustrative in nature and should not be construed as limiting the scope of protection of the claims of the present invention.

Claims

1. A method for preparing single-walled carbon nanotubes using pulsed arc plasma, characterized in that, The method includes the following steps: S1, In an inert atmosphere, a pulsed electric arc (5) is applied to the anode (1.2) containing the catalyst, causing it to evaporate and form catalyst vapor under periodic high-energy input; by adjusting the frequency f, duty cycle D, and peak current of the pulsed electric arc (5) The base current Ib controls the time distribution of the pulse arc energy and the heat input intensity. The pulse period T is set by the power supply or obtained by measuring the current waveform. It serves as a unified time reference for the synchronous control of the carbon source pulse. S2. Based on the obtained period T, generate a carbon source gas (6) pulse control signal to introduce the carbon source gas (6) into the reaction zone in the form of a pulse and synchronize it with the pulse arc (5). The carbon source is turned on with an adjustable carbon source delay Δt relative to the peak value of the pulse arc (5) to compensate for the gas transport delay, so that the high concentration supply stage of the carbon source and the high generation stage of the catalyst vapor precisely coincide in the reaction zone, and achieve high precision time coupling. S3, the carrier gas (4) and the carbon source gas (6) can be premixed or transported independently, and coordinated and controlled according to the carbon source pulse rhythm; the gas flow rate and total amount design ensure that the peak value of the carbon source pulse and the pulse arc (5) are precisely coincident in the reaction zone, and at the same time, the reaction products are transported out of the high temperature zone in a timely manner, maintaining the temperature uniformity of the reaction zone and the stability of the catalyst, thereby enhancing the time coupling effect of the carbon source and the catalyst vapor; S4. Based on the stability of the pulsed arc (5) or the product collection status, dynamically adjust the carbon source delay Δt to form a closed-loop control with phase offset as the only adjustment variable, realize high-precision coupling between the carbon source pulse and the pulsed arc (5) pulse, optimize the growth quality of single-walled carbon nanotubes and reduce the content of metal impurities.

2. The method for preparing single-walled carbon nanotubes by pulsed arc plasma according to claim 1, characterized in that, In S1, the frequency f of the pulsed arc (5) is 200-500Hz, the duty cycle D is 10%-70%, and the peak current is... The current is 500-1500A, and the base current Ib is 0-200A, in order to maximize the transient cooling effect of the pulsed arc (5) and control the catalyst evaporation rate.

3. The method for preparing single-walled carbon nanotubes by pulsed arc plasma according to claim 1, characterized in that, The carbon source delay Δt is adjusted by a digital controller or a high-speed response valve, with a delay time range of 0-20 milliseconds, used to compensate for gas transport time and maintain high-precision timing coupling.

4. The method for preparing single-walled carbon nanotubes by pulsed arc plasma according to claim 1, characterized in that, The carbon source gas (6) is selected from one of methane, acetylene, ethylene, or a mixture thereof.

5. The method for preparing single-walled carbon nanotubes by pulsed arc plasma according to claim 1, characterized in that, The carrier gas (4) is argon or nitrogen. The carrier gas (4) and the carbon source gas (6) can be transported through separate pipelines or premixed before introduction to optimize the pulse gas flow and the temperature distribution in the reaction zone.

6. The method for preparing single-walled carbon nanotubes by pulsed arc plasma according to claim 1, characterized in that, The closed-loop control includes the following steps: S41, real-time acquisition of the pulse current waveform of the pulse arc (5), as well as the product status or pressure / temperature signal of the reaction zone, to characterize the energy release rhythm of the pulse arc (5) and the coupling state of the reaction zone; S42. Based on the pulse arc (5) current waveform, extract the peak time and pulse period of the pulse arc (5), and combine the reaction zone state parameters to calculate the timing deviation of the carbon source pulse relative to the peak of the pulse arc (5) and generate the corrected carbon source delay Δt. S43. According to the corrected carbon source delay Δt, drive the high-speed response valve to open or close the carbon source gas (6), and adjust the valve opening or pulse width to achieve millisecond-level precision carbon source pulse supply, so that the carbon source supply cycle is aligned with the peak of the pulse arc (5). S44. After the peak values ​​of the carbon source pulse and the pulsed arc (5) are realigned, check whether the coupling state of the reaction zone reaches the set threshold. If the state of the pulsed arc (5) or the state of product generation changes, return to S41 to re-detect and correct, forming a single-parameter closed-loop control with Δt as the only adjustment variable.

7. The method for preparing single-walled carbon nanotubes by pulsed arc plasma according to claim 6, characterized in that, The opening or closing response time of the high-speed response valve is no more than 5 milliseconds.

8. A system for preparing single-walled carbon nanotubes using pulsed arc (5) plasma, used in the method for preparing single-walled carbon nanotubes using pulsed arc (5) plasma according to any one of claims 1-7, characterized in that, Includes an arc power supply assembly (2) for outputting pulsed DC current operating at a reference frequency f with a period of T, wherein a peak current is set within each period. and conduction time On-time The ratio of the duty cycle to the period T constitutes the duty cycle parameter D, and the period T constitutes the unified time base of the system; The gas supply assembly includes a mass flow controller (4) for precisely regulating the flow rates of the carbon source gas (6) and the carrier gas (4); The pulse timing coupling generation component is electrically connected to the arc power supply component (2). The carbon source gas (6) pulse control model is constructed with the period T as the time reference. The phase offset parameter Δθ is set in the control model to control the relative phase of the carbon source gas (6) pulse opening time with respect to the peak current of the pulse arc (5), thereby establishing an adjustable phase coupling relationship between the energy release section of the pulse arc (5) and the supply section of the carbon source gas (6). The state parameter calculation component is electrically connected to the pulse timing coupling generation component. It calculates the phase correction amount Δθ′ based on the stability parameter of the pulse arc (5) and superimposes the phase correction amount onto the phase offset parameter Δθ to update the pulse start time of the carbon source gas (6). This allows the phase coupling relationship to be dynamically adjusted with the operating state of the pulse arc (5), thereby forming a closed-loop control with the phase offset parameter as the only adjustment variable.

9. The system for preparing single-walled carbon nanotubes by pulsed arc (5) plasma according to claim 8, characterized in that, Also includes: The reaction chamber (1) is used to form a closed reaction space and control the heat load of the chamber; An electrode assembly is disposed within the reaction chamber (1) and includes a cathode (1.1) and an anode (1.2). The product collection component (3) is located downstream of the reaction chamber (1) and is used to collect the products generated by the pulsed electric arc (5).

10. The system for preparing single-walled carbon nanotubes by pulsed arc (5) plasma according to claim 9, characterized in that, The anode (1.2) is a 99.9% pure iron electrode or an iron-carbon composite electrode to form catalyst vapor and promote the growth of single-walled carbon nanotubes.

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