Ionization process and distinctive characteristic of atmospheric pressure cold plasma jet driven resonantly by microwave pulses

In the present study,a coaxial transmission line resonator is constructed,which is always capable of generating cold microwave plasma jet plumes in ambient air in spite of using argon,nitrogen,or even air,respectively.Although the different kinds of working gas induce the different discharge performance,their ionization processes all indicate that the ionization enhancement has taken place twice in each pulsed periods,and the electron densities measured by the method of microwave Rayleigh scattering are higher than the amplitude order of 10^(18)m^(-3).The tail region of plasma jets all contain a large number of active particles,like NO,O,emitted photons,etc,but without O_(3).The formation mechanism and the distinctive characteristics are attributed to the resonance excitation of the locally enhanced electric fields,the ionization wave propulsion,and the temporal and spatial distribution of different particles in the pulsed microwave plasma jets.The parameters of plasma jet could be modulated by adjusting microwave power,modulation pulse parameters(modulation frequency and duty ratio),gas type and its flow rate,according to the requirements of application scenarios.

Cold Plasma Jet Construction to Use in Medical, Biology and Polymer Applications

Cold atmospheric pressure plasma jets were capable of generating cold plasma plumes that were not confined by electrodes, which make them very enticing for biological, medical and polymer applications. During this work, experimental study of a low frequency, atmospheric plasma-jet discharge in nitrogen has been presented. The experimental operation of this device was conducted with commercially neon power supply. The discharge process operated by using nitrogen as input gas with different flow rates. The experimental results showed that the maximum plasma jet length of 7 mm was detected at 3 Kv input voltage corresponding to 14 l/min as a nitrogen flow rate. The effect of distance from nozzle, nitrogen flow rate and input voltage on the plasma temperature was examined. The gas temperature decreased continuously as the flow rate of nitrogen increasing from 2 l/min to 14 l/min at 3 Kv as a fixed input voltage.

Development of a new atmospheric pressure cold plasma jet generator and application in sterilization

This paper reports that a new plasma generator at atmospheric pressure, which is composed of two homocentric cylindrical all-metal tubes, successfully generates a cold plasma jet. The inside tube electrode is connected to ground, the outside tube electrode is connected to a high-voltage power supply, and a dielectric layer is covered on the outside tube electrode. When the reactor is operated by low-frequency （6 kHz-20 kHz） AC supply in atmospheric pressure and argon is steadily fed as a discharge gas through inside tube electrode, a cold plasma jet is blown out into air and the plasma gas temperature is only 25-30℃. The electric character of the discharge is studied by using digital real-time oscilloscope （TDS 200-Series）, and the discharge is capacitive. Preliminary results are presented on the decontamination of E.colis bacteria and Bacillus subtilis bacteria by this plasma jet, and an optical emission analysis of the plasma jet is presented in this paper. The ozone concentration generated by the plasma jet is 1.0× 10^16cm^-3 which is acquired by using the ultraviolet absorption spectroscopy.

The Interactions of Two Cold Atmospheric Plasma Jets

This paper presents the interactions between two cold atmospheric plasma jets. By changing the experimental conditions including the gas flow rate, the applied voltage, the power supply frequency and the inter-electrode distance d, three different interaction modes, attraction, repulsion and combination, were observed. It is shown that the interaction modes of the two jets are principally affected by the electrodes, the gas flow rate, the plasma jets and the power supply frequency.

Influences of the inner diameter of the solid shielding tube on the characteristics of the radio-frequency cold atmospheric plasma jet

Active control of the local environment of the cold atmospheric plasma(CAP) jet is of great importance in actual applications since the CAP operates in an open atmosphere with the inevitable entrainment of the surrounding cold air. In this paper, the solid shielding effects of the cylindrical quartz tubes with different inner diameters on the characteristics of the CAP jets driven by a radio-frequency(RF) power supply are studied experimentally. The experimental results show that the total length of the shielded plasma jet can be increased significantly by an appropriate combination of the quartz tube inner diameter and that of the plasma generator nozzle exit with other parameters being unchanged. This phenomenon may be qualitatively attributed to the loss of diffusion of the charged particles in the radial direction under different inner diameters of the quartz tubes. Compared with the plasma free jet, the plasma shielding jet is produced with optimized parameters including longer plasma jet length, higher concentrations of chemically reactive species, higher rotational, vibrational, and electron excitation temperatures when the inner diameters of the solid shielding tube and the generator nozzle exit are the same. A maximum plasma jet length of 52.0 cm is obtained in contrast to that of 5.0 cm of the plasma free jet in this study. The experimental results indicate that the solid shielding effect provides a new method for the active control of the local environment of the RF-CAP jet operating in an open atmosphere.

Preparation of novel Ni-Ir/γ-Al_2O_3 catalyst via high-frequency cold plasma direct reduction process

The novel Ni-Ir/γ-Al2O3 catalyst, denoted as NIA-P, was prepared by high-frequency cold plasma direct reduction method under ambient conditions without thermal treatment, and the conventional sample, denoted as NIA-CR, was prepared by impregnation, thermal calcination, and then by H2 reduction method. The effects of reduction methods on the catalysts for ammonia decomposition were studied, and they were characterized by XRD, N2 adsorption, XPS, and H2-TPD. It was found that the plasma-reduced NIA-P sample showed a better catalytic performance, over which ammonia conversion was 68.9%, at T = 450℃, P = 1 atm, and GHSV = 30, 000 h^-1. It was 31.7% higher than that of the conventional NIA-CR sample. XRD results showed that the crystallite size decreased for the sample with plasma reduction, and the dispersion of active components was improved. There were more active components on the surface of the NIA-P sample from the XPS results. This effect resulted in the higher activity for decomposition of ammonia. Meanwhile, the plasma process significantly decreased the time of preparing catalyst.

Pulsed cold plasma-induced blood coagulation and its pilot application in stanching bleeding during rat hepatectomy

This paper presents plasma-induced blood coagulation and its pilot application in rat hepatectomy by using a home-made pulsed cold plasma jet. Experiments were conducted on blood coagulation in vitro, the influence of plasma on tissue in vivo, and the pilot application of rat hepatectomy. Experimental results show that the cold plasma can lead to rapid blood coagulation. Compared with the control sample, the plasma-induced agglomerated layer of blood is thicker and denser, and is mostly composed of broken platelets. When the surface of the liver was treated by plasma, the influence of the plasma can penetrate into the liver to a depth of about 500 μm. During the rat hepatectomy, cold plasma was proved to be effective for stanching bleeding on incision. No obvious bleeding was found in the abdominal cavities of all six rats 48 h after the hepatectomy. This implies that cold plasma can be an effective modality to control bleeding during surgical operation.

Pulsed microwave-driven argon plasma jet with distinctive plume patterns resonantly excited by surface plasmon polaritons

Atmospheric lower-power pulsed microwave argon cold plasma jets are obtained by using coaxial transmission line resonators in ambient air.The plasma jet plumes are generated at the end of a metal wire placed in the middle of the dielectric tubes.The electromagnetic model analyses and simulation results suggest that the discharges are excited resonantly by the enhanced electric field of surface plasmon polaritons.Moreover,for conquering the defect of atmospheric argon filamentation discharges excited by 2.45-GHz of continued microwave,the distinctive patterns of the plasma jet plumes can be maintained by applying different gas flow rates of argon gas,frequencies of pulsed modulator,duty cycles of pulsed microwave,peak values of input microwave power,and even by using different materials of dielectric tubes.In addition,the emission spectrum,the plume temperature,and other plasma parameters are measured,which shows that the proposed pulsed microwave plasma jets can be adjusted for plasma biomedical applications.

The effect of gas additives on reactive species and bacterial inactivation by a helium plasma jet

In this paper,the influences of gas doping(O2,N2,Air)on the concentrations of reactive species and bactericidal effects induced by a He plasma jet are studied.Firstly,results show that gas doping causes an increase in voltage and a decrease in current compared with the pure He discharge under the same discharge power,which might be attributed to the different chemical characteristics of O2 and N2 and verified by the changes in the gaseous reactive species shown in the optical emission spectroscopy(OES)and Fourier transform infrared(FTIR)spectroscopy.Secondly,the concentrations of aqueous reactive oxygen species(ROS)and reactive nitrogen species(RNS)are tightly related to the addition of O2 and N2 into the working gas.The concentrations of aqueous NO-2 and NO-3 significantly increase while the concentrations of aqueous ROS decrease with the admixture of N2.The addition of O2 has little effect on the concentrations of NO-2 and NO-3 and pH values;however,the addition of O2 increases the concentration of O-2 and deceases the concentrations of H2O2 and OH.Finally,the results of bactericidal experiments demonstrate that the inactivation efficiency of the four types of plasma jets is He+O2>He+Air>He>He+N2,which is in accordance with the changing trend of the concentration of aqueous O.-2 Simultaneously to the better understanding of the formation and removal mechanisms of reactive species in the plasma–liquid interaction,these results also prove the effectiveness of regulating the concentrations of aqueous reactive species and the bacteria inactivation effects by gas doping.

Evaluation of influence of cold atmospheric pressure argon plasma operating parameters on degradation of aqueous solution of Reactive Blue 198(RB-198)

The intention of this work is to remove Reactive Blue 198(RB-198)dye components from simulated water solution using cold atmospheric pressure argon plasma jet.Aqueous solutions of RB-198 dye were treated as a function of various operating parameters such as applied potential,reaction time and distance between the plasma jet and surface of the liquid.The efficiency of the degradation of RB-198 molecules was explored by means of UV-Vis spectroscopy.The reactive species involved during the treatment process were examined by optical emission spectra(OES).The present hydroxyl radicals(OH·radical)and hydrogen peroxide(H2O2)in the plasma-treated aqueous dye solutions were investigated using various spectroscopic techniques.The other parameters such as total organic carbon(TOC),conductivity and p H were also reviewed.The toxicity of plasma-treated RB-198 solution was finally studied by diffusion bacterial analysis and by tracking seed germination processes.The results show that a higher degradation percentage of99.27%was acquired for the RB-198 treated at higher reaction time and applied potential,and shorter distance between the plasma jet and water surface.This may be due to the formation of various reactive oxygen(OH·radical,atomic oxygen(O)and H2O2)and nitrogen species(nitric oxide(NO)radicals and N2 second positive system(N2 SPS))during the processes as confirmed by OES analysis and other spectroscopy analysis.TOC(17.7%-81.8%)and pH(7.5-3.4)values of the plasma-treated RB-198 decreased significantly with respect to various operation parameters,which indicates the decomposition of RB-198 molecules in the aqueous solution.Moreover,the conductivity of plasma-treated RB-198 aqueous solutions was found to have increased linearly during the plasma treatment due to the formation of various ionic species in aqueous solution.The toxicity analysis clearly exhibits the non-toxic behavior of plasma-treated RB-198 aqueous solution towards the bacterial growth and germination of seeds.

介质管介电常数对大气压Ar冷等离子体射流特性的影响

通过二维流体模型,研究介质管的介电常数对大气压氩气冷等离子体射流放电性质的影响.结果表明,射流在介质管内外具有不同的放电性质.当射流在介质管内时,电离波沿着介质管内表面向管口传播,因而呈现环状结构,其传播速度先增加后减小.介电常数越大,环形结构的半径越小,电子密度越低,射流传播的速度也越小.当射流喷出管口后,射流的传播速度迅速提升,然后减小,介电常数越大,提升越快.随着射流的传播,环状结构不断收缩,最终消失.研究结果对大气压冷等离子体源的设计和优化具有一定的理论指导意义.

氩气辅助激发大气压微波冷等离子体射流的研究

微波同轴谐振器已被广泛用作大气压等离子体射流的发生装置,其产生的等离子体射流已用于生物医学、材料表面处理等众多领域,大气压条件下微波放电等离子体源的功率阈值是影响其能否广泛应用的关键问题。文中设计的微波等离子体射流源工作频率2.6 GHz,回波损耗13.99 dB,工作气体为Ar气,大气压条件下产生紫色的丝状射流,击穿功率41.1 dBm(12.9 W),维持功率仅20 dBm(0.1 W)。结合实验观察和ANSYS Fluent流体力学仿真方法探究了等离子体射流长度与气体体积流量、输入功率的关系,发现层流状态下射流长度随气体体积流量增大而伸长,湍流状态下则反之,但不同气体体积流量下射流长度均随着输入功率单调增大。同时,实验发现关断Ar气后等离子体并未熄灭,而是诱发了同轴尖端附近位置的空气等离子体维持状态。在此基础上提出以Ar气或He气为先导气体,将其电离击穿后辅助激发难电离气体产生冷等离子体射流,在不需要提供高微波功率条件下实现了CO_(2)、N_(2)、O_(2)等冷等离子体射流。

低温等离子体射流病毒消杀实验平台设计及教学应用

针对冷链食品外包装新冠病毒消杀的问题,基于低温等离子体处理、微生物检测和活性评价等技术,结合环境工程专业实验教学核心知识点,设计出一套快速、高效、无害的低温等离子体射流消杀实验平台。平台由高压电源、低温等离子体射流模块、供气系统和控制系统构成,可实现低温条件下平整包装箱表面细菌或病毒的秒级、高效、无死角消杀。围绕社会热点,开发前沿技术与解决实际问题相结合的交叉实验,不仅有助于加深学生对低温等离子原理和微生物学知识的理解,也激发了学生的实验热情,培养学生学以致用、解决实际社会热点及工程问题的能力。

用常压高频冷等离子体射流还原Ni/γ-Al_2O_3催化剂的新方法

采用大气压高频冷等离子体炬,对用于甲烷和CO2重整反应的Ni/γ-Al2O3催化剂进行还原.考察了还原后催化剂的反应活性和选择性,并与常规方法还原的催化剂进行了对比.结果表明,采用这种新方法还原催化剂只需10 min,操作快速简便,并且还原后的催化剂的活性和选择性都明显优于常规催化剂.在850℃,原料气CH4和CO2的摩尔比为4/6的条件下反应时,可获得95.77%的甲烷转化率、75.65%的CO2转化率、100%的H2选择性和94.79%的CO选择性.此外,该新型催化剂具有较好的稳定性,连续反应36 h后,活性基本不下降.XRD表征结果发现,采用该方法还原的催化剂只有金属镍和γ-Al2O3相,没有检测到Ni Al2O4以及其它镍氧化物.与常规催化剂相比,采用等离子体还原的新型催化剂具有较小的镍晶粒尺寸,金属活性组分的分散度大大提高.

常压高频冷等离子体炬制备的CH_4/CO_2重整用Ni/γ-Al_2O_3催化剂的表征

分别采用常规焙烧还原(C)、常规焙烧与常压高频冷等离子体炬还原相结合(PR),以及常压高频冷等离子体炬直接焙烧还原(PC&R)制备了Ni/γ-Al2O3催化剂.通过X射线衍射、H2-程序升温脱附、CO2-程序升温脱附、N2吸附-脱附实验、透射电镜和热重分析等方法对催化剂进行了表征.并考察了其CH4/CO2重整反应活性.结果表明,催化剂经等离子体处理后低温活性明显增加.在得到相同CH4和CO2转化率情况下,PC&R法制备的催化剂与常规催化剂相比,反应所需温度可以降低50oC.PC&R催化剂上Ni分散度提高了100%,Ni粒子粒径降低了70%,达到5nm,催化剂的抗积炭性能显著增强.所得催化剂较高的低温活性和抗积炭性能得益于常压高频冷等离子体炬对催化剂前驱体还原速率快,处理时间大为缩短,避免了由于长时间高温焙烧和还原所引起的对载体的烧结和金属Ni的团聚.

冷等离子体喷射流对甲烷二氧化碳重整用Ni/Al_2O_3催化剂的还原机制

采用理论计算与实验相结合的方法研究了常压冷等离子体喷射流还原Ni/Al2O3催化剂的机理.首先,在假设还原过程是H原子起主导作用的基础上,依据对冷等离子体喷射流的放电特性分析,计算得到H2的理论解离度和催化剂理论还原时间.其次,采用X射线衍射表征及活性评价的手段,考察了等离子体制得催化剂还原过程及实际还原时间.结果表明,理论结果与实验结果基本一致.

大气压氩气冷等离子体射流处理对芥菜种子发芽率及根长的影响

研究大气压条件下空气环境中氩气放电冷等离子体射流处理对芥菜种子发芽率及幼苗根长的影响。比较了不同的放电电压和不同的处理时间下芥菜种子的发芽率及根长。结果表明,与对照组比较,在放电电压1.6kV、处理时间120s 和30s 的条件下,等离子体射流处理对种子的生长起到了促进作用;在放电电压2.2kV、处理时间120s 及放电电压2.8kV 的条件下,等离子体射流处理对种子的生长发育起到了抑制作用。

射流低温等离子体改性增强聚甲基丙烯酸甲酯薄膜表面亲水性研究

用空气中射流低温等离子体对聚甲基丙烯酸甲酯(PMMA)薄膜进行表面改性,比较了改性前后PMMA表面水接触角和表面能的变化。研究了等离子体改性时间及改性距离对改性效果的影响,测量了改性后PMMA在空气中放置时的老化效应,并对改性机理进行了分析。结果表明,PMMA薄膜经射流低温等离子体改性后,水接触角下降,表面能上升,两者均在一定改性时间时达到饱和状态。当改性时间固定时,减小改性距离,可以得到更好的改性效果。改性后的材料存在老化效应,放置9天后,老化效应趋于稳定,但其表面水接触角仍远低于改性前的值。

复合镍基催化剂表面纳米团簇结构的调控及其催化应用

利用新型等离子体技术,将常压放电冷等离子体炬应用于催化剂制备,研究了制备方法、载体、活性组分和助剂对复合镍基催化剂表面纳米团簇结构的调控效果;并分析了催化剂表面纳米团簇结构的形成机理和催化剂性能的构效关系。结果表明:采用冷等离子体炬直接焙烧还原可调控表面纳米团簇;以-γAl2O3为载体的Ni催化剂(PC&R)具有较高的活性和稳定性;活性组分Ni对表面纳米团簇结构的调控效果较好,添加量为12%(质量分数)时,表面纳米团簇高度分散,其尺寸约5 nm;助剂Mg添加可有效提高催化剂活性,合适的添加量为1%,且催化剂仍保持良好的表面纳米团簇结构,尺寸约5 nm;表面纳米团簇结构优化后的催化剂抗积炭能力明显提高。

水切割技术在钛材切割加工中的应用

介绍了水切割技术的工作原理、特点和钛材水切割的参数和切割效能,比较了水切割和等离子切割技术应用于钛材切割的差异性,并分析了两种不同切割方式对钛材化学成分、力学性能和可加工性能的影响,进而为水切割技术的推广应用提供参考依据。