Numerical study of the effect of water content on OH production in a pulsed-dc atmospheric pressure helium–air plasma jet

A numerical study of the effect of water content on OH production in a pulsed-dc atmospheric pressure helium–air plasma jet is presented. The generation and loss mechanisms of the OH radicals in a positive half-cycle of the applied voltage are studied and discussed. It is found that the peak OH density increases with water content in air(varying from0% to 1%) and reaches 6.3×1018m-3when the water content is 1%. Besides, as the water content increases from 0.01%to 1%, the space-averaged reaction rate of three-body recombination increases dramatically and is comparable to those of main OH generation reactions.     

The interaction of an atmospheric pressure plasma jet using argon or argon plus hydrogen peroxide vapour addition with bacillus subtilis

This paper reports that an atmospheric pressure dielectric barrier discharge plasma jet, which uses argon or argon + hydrogen peroxide vapour as the working gas, is designed to sterilize the bacillus subtilis. Compared with the pure argon plasma, the bacterial inactivation efficacy has a significant improvement when hydrogen peroxide vapour is added into the plasma jet. In order to determine which factors play the main role in inactivation, several methods are used, such as determination of optical emission spectra, high temperature dry air treatment, protein leakage quantification, and scanning electron microscope. These results indicate that the possible inactivation mechanisms are the synergistic actions of chemically active species and charged species.     

Surface modification of polypropylene non-woven fabric using atmospheric nitrogen dielectric barrier discharge plasma

In this paper, a dielectric barrier discharge operating in nitrogen at atmospheric pressure has been used to improve the surface hydrophilic property of polypropylene (PP) non-woven fabric. The changes in the hydrophilic property of the modified PP samples are investigated by the contact angle measurements and the variation of water contact angle is obtained as a function of the energy density; micrographs of the PP before and after plasma treatment are observed by scanning electron microscopy (SEM) and the chemical composition of the PP surface before and after plasma treatment is also analyzed by Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). The results show that the surface hydrophilic property of the PP samples is greatly improved with plasma treatment for a few seconds, as evidenced by the fact that the contact angle of the treated PP samples significantly decreases after plasma treatment. The analysis of SEM shows that the surface roughness of the treated PP samples increases due to bonding and etching in plasma processing. The analyses of FTIR and the C1s peak in the high-resolution XPS indicate that oxygen-containing and nitrogen-containing polar functional groups are introduced into PP surface in plasma processing. It can be concluded that the surface hydrophilic property of the modified PP samples has been obviously improved due to the introduction of oxygen-containing and nitrogen-containing polar groups and the increase of the surface roughness on the PP surface.     

Comparison of two cold atmospheric pressure plasma jet configurations in argon

The present study compares the operation of two cold atmospheric plasma jet (CAPJ) configurations: needle-to-cylinder electrode configuration (CAPJ I) and single high-voltage cylinder electrode around the quartz tube (CAPJ II). The CAPJs were operated in argon flowing through a quartz capillary with 0.5-mm inner diameter into the ambient air, and the plasma was generated by sinusoidal kHz frequency AC power supplies. The main emphasis of the study was on the mechanism of the initiation of ionization waves for these two configurations. For both CAPJs, there appeared several ionization waves during one half-period of the applied voltage waveform, and the number of ionization waves increased at higher voltage amplitudes. However, we discovered marked differences in the initiation of the ionization waves for two different CAPJ configuration. The applied voltage controlled the initiation of consecutive ionization waves, which propagated from the grounded electrode towards the tube orifice in CAPJ I. In the case of CAPJ II, certain time had to pass for the initiation of a new ionization wave, and subsequent ionization waves within the same half-period started at the tube orifice. In addition to the differences in the initiation of the ionization waves, we observed that the CAPJ I was ignited and sustained at lower voltages, while CAPJ II produced a longer plasma jet. The observed advantages and deficiencies of investigated CAPJ configurations point out their potential in different applications.     

Basic characteristics of an atmospheric pressure rf generated plasma jet

A plasma jet has been developed which operates using radio frequency (rf) power and produces a stable homogeneous discharge at atmospheric pressure. Its discharge characteristics, especially the dependence of stable discharge operating range on the feed gas, were studied, and the electric parameters such as RMS current, RMS voltage and reflected power were obtained with different gas flows. These studies indicate that there is an optimum range of operation of the plasma jet for a filling with a gas mixture of He and O_2. Two "failure" modes of the discharge are identified. One is a filamentary arc when the input power is raised above a critical level, another is that the discharge disappears gradually as the addition of O_2 approaches 3.2%. Possible explanations for the two failure modes have been given. The current and voltage waveform measurements show that there is a clear phase shift between normal and failure modes. In addition, I－V curves as a function of pure helium and for 1% addition of oxygen have been studied.     

大气压直流氩等离子体射流工作特性研究

介绍了一种新型大气压直流双阳极等离子喷枪,并对其电特性参数和发射光谱进行了测量.通过对氩等离子体射流的电信号进行时域和频域分析,研究了载气流量和弧电流的变化对射流脉动的影响,结果表明氩等离子体电弧的伏安特性呈上升趋势,射流脉动属于接管模式,电源特性中的交流分量引起的电压波动是影响氩等离子体射流脉动的主要因素. 通过光谱法测量了氩等离子体射流在弧室内和弧室出口的发射光谱,利用玻尔兹曼曲线斜率法计算了射流的激发温度,根据Ar I谱线的斯塔克展宽得到了射流的电子密度,并对等离子体射流满足局域热力学平衡(LTE) 关键词： 等离子喷枪 射流脉动 激发温度 局域热力学平衡     

Surface cleaning of metal wire by atmospheric pressure plasma

In this study, the possible application of atmospheric pressure dielectric barrier discharge plasma for the annealing of metallic wire is examined and presented. The main purpose of the current study is to examine the surface cleaning effect for a cylindrical object by atmospheric pressure plasma. The experimental setup consists of a gas tank, plasma reactor, and power supply with control panel. The gas assists in the generation of plasma. Copper wire was used as an experimental cylindrical object. This copper wire was irradiated with the plasma, and the cleaning effect was confirmed. The result showed that it is possible to remove the tarnish which exists on the copper wire surface. The experiment reveals that atmospheric pressure plasma is usable for the surface cleaning of metal wire. However, it is necessary to examine the method for preventing oxidization of the copper wire.     

Measurement of optical signals as a plasma propagation in the atmospheric pressure plasma jet columns

The propagation of plasma jets with argon gas is characterized in terms of two factors, the effect of electric field distribution along the tube and the effect of voltage polarity, from the observed results of optical signals along the entire column of plasma. The optical signal of plasma propagates from the high electric-field region of high-voltage electrode toward the low field region of the open air-space, regardless of the polarity of the voltage. The optical intensity and the propagation velocity are higher for the positive voltage than for the negative voltage. Moreover, the length of plasma plume exited from the end of the glass tube into the open air is shorter for the negative voltage. When the optical intensity is strong enough, a secondary peak signal follows the primary peak. In the plasma column on the inside of the glass tube, the optical intensity and the propagation velocity depend on the strength of the electric field; they are both high at the high-field region of voltage terminal and decay toward the end of the tube. The velocity is as fast as 10⁴ m/s at the high-field region and slows down to 10³ m/s at the low-field region of the glass-tube end. However, the plasma accelerates drastically to be (10⁴–10⁵) m/s after exiting the glass tube toward open air, even though the electric field is a quite low and thus the optical signal decays low before fading out. The experimental observations present in this report are explained with the propagation of the plasma diffusion waves.     

Surface chemistry of atmospheric plasma modified polycarbonate substrates

Surface of polycarbonate substrates were activated by atmospheric plasma torch using different gas pressure, distance from the substrates, velocity of the torch and number of treatments. The modifications were analyzed by contact angle measurements, X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and UV-vis spectrophotometry. Plasma treatment caused the surface characteristics to become more hydrophilic as measured by the water contact angle, which decreased from 88° to 18°. The decrease in contact angle was mainly due to oxidation of the surface groups, leading to formation of polar groups with hydrophilic property. XPS results showed an increase in the intensity of -(C-O)- groups and also introduction of new functional groups i.e. -(O-CO)- after the treatment process. AFM topographic images demonstrated an increase in the rms roughness of the surface from 2.0 nm to 4.0 nm caused by the treatment. Increase in rms roughness of the surface caused relevant decrease in transmission up to ∼2-5%.     

Expansion dynamics of atmospheric pressure helium plasma jet in ambient air

In this work, the expansion dynamics of a helium plasma jet in ambient air is examined. By using a fast imaging technique, the expansion of plasma jet from glass nozzle to air is captured which is in the form of plasma bullet propagating into the air. To understand the plasma bullet travel path from glass nozzle to plasma jet tip a drag force model is used. Moreover, the spatial variation of plasma density along the plasma jet length is estimated using drift velocity, plasma jet current and the cross-sectional area of the plasma jet. It is observed that the slight increase in plasma density is due to the combined effect of reduction of drift velocity, plasma jet current, and jet cross-sectional area. The obtained plasma density from glass nozzle to jet tip is in the range of (0.069-5.96) × 10¹² cm⁻³. The above parameters can be of the essence in biological and industrial applications.     

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研究了氮氧源大气压等离子体射流对表面大肠杆菌灭活作用,分析了氮氧源大气压等离子体射流的光谱性质.结果表明,在放电电压为6.8kV,气体流速为4L?min-1,处理3min时,氮氧比为1:4的大气压等离子体射流对大肠杆菌的灭活率达到98.4%,接近氧气源大气压等离子体射流灭菌效果.通过大气压等离子体射流发射光谱(OES)分析了氮氧源大气压等离子体射流中活性物质,进而解释大肠杆菌微生物灭活机理,认为NO-γ、OI、·OH等活性物质在表面大肠杆菌灭活过程中起到了重要作用.这将为大气压氮氧等离子体射流在环境卫生、微生物灭活等方面的应用研究提供实验基础和技术支持.     

纳秒脉冲放电等离子体射流特性

采用单针式电极,使用单极性重复频率脉冲电源,在常压氦气、氩气、氮气和空气中得到等离子体射流,并改变电压、流量和气体种类,分别观察不同的实验条件对等离子体射流的影响。实验结果表明：射流长度随施加电压的增加而增长;随着流量的连续变化,射流长度先逐渐变长,达到峰值后由于湍流影响,长度又逐渐缩短,达到一定流量后趋于饱和。此外,不同工作气体中的等离子体射流呈现截然不同的外观,氦气和氩气中射流呈针状模式,长度可达7 cm以上;而在氮气和空气中,射流呈现为长度不超过2 cm的刷状模式。     

纳秒脉冲放电等离子体射流特性

采用单针式电极,使用单极性重复频率脉冲电源,在常压氦气、氩气、氮气和空气中得到等离子体射流,并改变电压、流量和气体种类,分别观察不同的实验条件对等离子体射流的影响。实验结果表明:射流长度随施加电压的增加而增长;随着流量的连续变化,射流长度先逐渐变长,达到峰值后由于湍流影响,长度又逐渐缩短,达到一定流量后趋于饱和。此外,不同工作气体中的等离子体射流呈现截然不同的外观,氦气和氩气中射流呈针状模式,长度可达7 cm以上;而在氮气和空气中,射流呈现为长度不超过2 cm的刷状模式。     

大气压氮氧等离子体射流灭活表面大肠杆菌及其发射光谱分析研究

研究了氮氧源大气压等离子体射流对表面大肠杆菌灭活作用,分析了氮氧源大气压等离子体射流的光谱性质。结果表明,在放电电压为6.8kV,气体流速为4L?min?1,处理3min时,氮氧比为1:4的大气压等离子体射流对大肠杆菌的灭活率达到98.4%,接近氧气源大气压等离子体射流灭菌效果。通过大气压等离子体射流发射光谱(OES)分析了氮氧源大气压等离子体射流中活性物质,进而解释大肠杆菌微生物灭活机理,认为NO?γ、OI、?OH等活性物质在表面大肠杆菌灭活过程中起到了重要作用。这将为大气压氮氧等离子体射流在环境卫生、微生物灭活等方面的应用研究提供实验基础和技术支持。     

常压双频驱动Ar/CCl4等离子体射流制备碳薄膜的研究

在大气压下双频Ar/CCl4 等离子体射流的驱动下,固定低频功率,通过改变射频功率在硅基底上制备了非晶态碳薄膜,并且通过程序进行相应的数值模拟计算。结果给出了不同功率下电子与离子的密度、温度、电场、电势、角度分布等参数对碳材料样品形貌的影响;样品变化趋势的预测及其原因的分析,以及与实验结果的对比。结果表明,对于双频大气压等离子体,射频可以独立控制等离子体的能量和反应强度,可以相对地控制产物。这为制备薄膜材料的形貌提供重要的实验基础。     

Helium/oxygen atmospheric pressure plasma jet treatment for hydrophilicity improvement of grey cotton knitted fabric

The influence of atmospheric pressure plasma jet (APPJ) treatment on the hydrophilicity of grey cotton knitted fabric (GCKF) was investigated. For comparison, specimens which had undergone different treatments were tested by contact angle measurement, scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), fourier-transform infrared attenuated total reflectance spectroscopy (FTIR-ATR) and X-ray diffraction (XRD). The results imply that helium/oxygen APPJ could improve the hydrophilicity of GCKF by modifying the surface properties. In addition, combining dewaxing processes with He/O₂ APPJ treatment was found to tremendously improve the hydrophilicity of GCKF. The mechanism of this was also confirmed by Ruthenium Red staining which showed most of pectic substances inside the cotton fiber existed beneath the waxy layer and on top of the cellulose microfibril.     

Wettability and sizing property improvement of raw cotton yarns treated with He/O2 atmospheric pressure plasma jet

Raw cotton fiber is water repellent due to the existence of the water repellent cuticle layer. This study is designed to systematically investigate how He/O₂ atmospheric pressure plasma jet (APPJ) treatments influence the wettability and the sizing property of cotton yarns. Water absorption time and adhesion of the sizing agent to the cotton roving are used to evaluate the improvement of wettability and sizing property of the yarn respectively. The water absorption time decreases with the increase of the treatment time and the oxygen flow rate, and the decrease of the jet to substrate distance (JTSD). An optimal water absorption time of 0.8 s is obtained with a treatment time of 20 s, JTSD of 1 mm and O₂ flow rate of 0.2 L/min. Scanning electron microscopy (SEM) shows that the etching effect increases with the decrease of the JTSD and X-ray photoelectron spectroscopy (XPS) presents increased oxygen contents after the plasma treatments. An increase of O-CO bonds while a decrease of C-OH/C-O-C bonds are observed when the JTSD is set at 2 mm. However, a remarkable increase of both C-OH/C-O-C and O-CO bonds are achieved when the JTSD is 1 mm. The roving impregnation test results show a nearly doubled adhesion of sizing and a slightly improved breaking elongation, indicating that the plasma treatment does effectively enhance the bonding strength between the fiber and the sizing.     

常压微波等离子体炬装置的模拟与设计

介绍了一台低成本的常压微波等离子体炬设备,给出了该设备构造及喷嘴的设计思路,分析了各种气体的非磁化微波等离子体的击穿电场强度,数值求解了设备中矩形TE103谐振腔中的电磁场分布,应用高频电磁场模拟分析软件HFSS优化了喷嘴在波导中的具体位置,并对优化后喷嘴周围的电场分布进行了模拟。模拟结果表明：微波输入有效功率为500 W,喷嘴伸出矩形波导1 mm时,喷嘴尖端处的电场强度在1.2×106 V·m-1以上,远大于氩气的击穿电场强度,更易于等离子体炬的激发。实验结果证明了模拟结果的正确性和装置的有效性。     

Influence of oxygen addition on the discharge characteristics of an argon plasma jet at atmospheric pressure

Plasma jet is an important low-temperature plasma source in extensive application fields. To promote the production of active oxygen species, oxygen is often introduced into the inert working gas. However, the influence of oxygen content on the discharge characteristics of an argon plasma jet is not clear. Aim to this status, an argon plasma jet in a single-electrode geometry is employed to investigate the influence of oxygen concentration (C_O) on discharge aspects. Results indicate that with increasing C_O (≤ 0.6%), the plume transits from a diffuse morphology to a hollow structure. Electrical and optical measurements reveal that both discharge number per voltage cycle and pulse intensity alter with varying C_O. Moreover, discharge morphologies of negative and positive discharges obtained by fast photograph also shift with varying C_O. Besides, optical emission spectra are collected to investigate atomic C_O, electron density, and electron temperature. The results mentioned above are explained qualitatively, which are believed to be of great significance for the applications of atmospheric pressure plasma jet.     

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通过测量大气压介质阻挡放电等离子体辐射信号,建立偶极子辐射模型,利用快速傅立叶变换,计算了大气压介质阻挡放电等离子体中离子速度分布。计算结果表明,速度分布偏离麦克斯韦分布,并且随着放电过程的进行,离子速度及相对离子数进行有规律的变化。