The investigation of OH radicals produced in a DC glow discharge by laser-induced fluorescence spectrometry

In this paper the OH radicals produced by a needle-plate negative DC discharge in water vapor,N_(2)+H_(2)O mixture gas and He+H_(2)O mixture gas are investigated by a laser-induced fluorescence(LIF)system.With a ballast resistor in the circuit,the discharge current is limited and the discharges remain in glow.The OH rotation temperature is obtained from fluorescence rotational branch fitting,and is about 350 K in pure water vapor.The effects of the discharge current and gas pressure on the production and quenching processes of OH radicals are investigated.The results show that in water vapor and He+H_(2)O mixture gas the fluorescence intensity of OH stays nearly constant with increasing discharge current,and in N_(2)+H_(2)O mixture gas the fluorescence intensity of OH increases with increasing discharge current.In water vapor and N_(2)+H_(2)O mixture gas the fluorescence intensity of OH decreases with increasing gas pressure in the studied pressure range,and in He+H_(2)O mixture gas the fluorescence intensity of OH shows a maximum value within the studied gas pressure range.The physicochemical reactions between electrons,radicals,ground and metastable molecules are discussed.The results in this work contribute to the optimization of plasma reactivity and the establishment of a molecule reaction dynamics model.

Discharge characteristics and reactive species production of unipolar and bipolar nanosecond pulsed gas–liquid discharge generated in atmospheric N2

In this paper,unipolar pulse(including positive pulse and negative pulse)and bipolar pulse voltage are employed to generate diffuse gas–liquid discharge in atmospheric N2with a rumpetshaped quartz tube.The current–voltage waveforms,optical emission spectra of excited state active species,FTIR spectra of exhaust gas components,plasma gas temperature,and aqueous H2O2,NO2-,andNO3-production are compared in three pulse modes,meanwhile,the effects of pulse peak voltage and gas flow rate on the production of reactive species are studied.The results show that two obvious discharges occur in each voltage pulse in unipolar pulse driven discharge,differently,in bipolar pulse driven discharge,only one main discharge appears in a single voltage pulse time.The intensities of active species(OH(A),and O(3p))in all three pulsed discharge increase with the rise of pulse peak voltage and have the highest value at 200 ml min-1of gas flow rate.The absorbance intensities of NO2and N2O increase with the increase of pulse peak voltage and decrease with the increase of gas flow rate.Under the same discharge conditions,the bipolar pulse driven discharge shows lower breakdown voltage,and higher intensities of excited species(N2(C),OH(A),and O(3p)),nitrogen oxides(NO2,NO,and N2O),and higher production of aqueous H2O2,NO2-,andNO3-compared with both unipolar positive and negative discharges.

Volume added surface barrier discharge plasma excited by bipolar nanosecond pulse power in atmospheric air: optical emission spectra influenced by gap distance

In this paper, volume barrier discharge with different gap distances is added on the discharge border of high-voltage electrode of annular surface barrier discharge for generating volume added surface barrier discharge （V-SBD） excited by bipolar nanosecond high-voltage pulse power in atmospheric air. The excited V-SBDs consist of surface barrier discharge （d = 0 mm） and volume added surface barrier discharges （d = 2 mm and 3 mm）. The optical emission spectra are recorded for calculating emission intensities of N2 （C3 ∏u → B3∏g） and N2＋ （B2 ∑u＋ → X2 ∑g＋）, and simulating rotational and vibrational temperatures. The influences of gap distance of V-SBD on emission intensity and plasma temperature are also investigated and analyzed. The results show that d = 0 mm structure can excite the largest emission intensity of N2 （C3 ∏u → B3 ∏g）, while the existence of volume barrier discharge can delay the occurrence of the peak value of the emission intensity ratio of N2 ＋ （B2 ∑u＋ → X2 ∑＋g）/N2 （C3 ∏u → B3 ∏g） during the rising period of the applied voltage pulse and weaken it during the end period. The increasing factor of emission intensity is effected by the pulse repetition rate. The d = 3 mm structure has the highest threshold voltage while it can maintain more emission intensity of N2 （C3 ∏u→ B3∏g） than that of d = 2 mm structure. The structure of d = 2 mm can maintain more increasing factor than that of the d = 3 mm structure with varying pulse repetition rate. Besides, the rotational temperatures of three V-SBD structures are slightly affected when the gap distance and pulse repetition rate vary. The vibrational temperatures have decaying tendencies of all three structures with the increasing pulse repetition rate.

Spectroscopic study of bipolar nanosecond pulse gas-liquid discharge in atmospheric argon

Atmospheric gas-liquid discharge with argon as a working gas is presented by employed nanosecond pulse power. The discharge is presented in a glow-like mode. The discharge powers are determined to be less than 1 W, and remains almost constant when the discharge duration time increases. Bountiful active species are determined by capturing optical emission spectra, and their main generation processes are also discussed. The plasma gas temperature is calculated as 350 K by comparing the experimental spectra and the simulated ones of N2（C3Ⅱg→B3Ⅱg, △v=-2）. The time resolved vibrational and rotational temperature is researched to present the stability of discharge when pulse voltage and discharge duration vary. The electron density is determined to be 1016 cm-3 according to the Stark broadening effect of the Ha line.

Spatiotemporal characteristics of nanosecond pulsed discharge in an extremely asymmetric electric field at atmospheric pressure

In this paper,high resolution temporal-spatial diagnostics are employed to research the optical characteristics of nanosecond pulsed dielectric barrier discharge in needle-plate electrode configuration.Temporal-spatial distributions of discharge images,the emission intensities of optical emission spectra,and plasma vibrational and rotational temperatures are investigated.By analyzing the evolution of vibrational and rotational temperatures in space and time dimensions,the energy distribution and energy transfer process in plasma are also discussed.It is found that a diffuse structure with high density plasma concentrated in the region near the needle tip can be presented in nanosecond pulsed discharge,and an obvious energy transfer from electronic energy to vibration energy can be observed in each discharge pulse.

Electrical characters and optical emission spectra of VBD coupled SBD excited by sine AC voltage in atmospheric air

In this paper,volume coupled surface barrier discharge（V-SBD） with three structures possessing different volumes is excited by sine AC power in atmospheric air.Discharge images,waveforms of applied voltage and discharge current,and optical emission spectra simulating rotational and vibrational temperatures are recorded and analyzed.The effects of applied voltage on emission intensities of N2（C^3Πu→ B^3Πg） and N2^＋（B^2∑u^＋ → X^2Eg^＋）,and rotational and vibrational temperatures are investigated.The results show that as applied voltage rises,emission intensities and rotational temperatures increase while vibrational temperatures decrease.In addition it is found that,as applied voltage varies,the rotational temperature of surface discharge changes faster than that of volume discharge.

Generation of reactive atomic species of positive pulsed corona discharges in wetted atmospheric flows of nitrogen and oxygen

The emission spectra of excited radicals（OH（A^2E）,O（3p^3 P）,Hα（3P）） and emissive species（N2^＋（B^2∑u^＋）,N2（C3Πu）） produced by positive pulsed high-voltage needle-plane corona discharges in atmospheric N2 and O2 flows wetted with 10%H2O at 80 ℃ are used to investigate the relative concentrations of the produced radicals.The results indicate that the tendencies of the concentrations of radicals with discharge conditions are similar to each other due to their similar excitation processes by electron collision.The influence of oxygen flow mixed with the nitrogen flow on the emission intensities of O（3p^5P → 3s^5S2^0.）,Hα（3P → 2S）,N2＋（B^2∑u^＋ → X^2∑g＋0-0）,and N2（C^3Πu → B^3Πg 1-0） is presented.When the flow rate of oxygen addition is varied from 0-30 ml min^-1,the emission intensities of O（3p^5P → 3s^5S2^0.）,Hα（3P → 2s）,and N2^＋（B^2∑u^＋ →X^2∑g 0-0） increase and reach a maximum.Then,if the oxygen flow rate increases further,the emission intensities tend to decrease.However,the intensity of N2（C^3Πu → B^3Πg1-0） decreases monotonously with the increasing oxygen flow,which indicates that the electron density decreases with the increasing oxygen flow.By the tendencies of the relative intensities to N2（C^3Πu → B^3Πg 1-0）,the concentrations of the total produced O,H,and N2^＋ are shown to increase with the oxygen flow.Based on the reactions for the production of H and O without and with the addition of O2,the analytic solutions for H and O production are derived in accordance with the experimental results.

Comparative research of plasma-assisted milling and traditional milling in synthesizing AIN

In this paper,traditional milling and discharge plasma-assisted milling are employed to synthesize aluminum nitride（AlN） powder at nanometer scale by milling the mixture of aluminum and lithium hydroxide monohydrate.AlN powders can be generated in traditional milling and plasma-assisted milling in an hour milling time.Differential thermal analysis curves show that the reaction temperature of the powders treated by plasma-assisted milling is lower than that of traditional milling.These results indicate that plasma-assisted milling has higher efficiency in the synthesis of AlN,getting smaller crystallite size and activating powder.Moreover,an optical emission spectrum is employed to demonstrate the active species in plasma.The different formation process of AlN in the two-milling process,and the promotion effects of plasma in the milling process are discussed.

房地产扩张对中国制造业工资的影响研究——基于劳动力再配置的视角

"用工荒"和劳动力成本快速上升是当前中国制造业发展面临的重要问题。本文利用2000-2007年中国工业企业数据、城市数据和农村家庭调查数据,实证分析了房地产扩张对制造业工资的推动作用及其内在机制。研究结果表明,房地产投资规模越大的城市,当地制造业的工资上涨幅度越大。通过对农村外出劳动力择业流向的考察,我们发现房地产扩张吸引劳动力流向房地产及相关行业是推动制造业工资上涨的重要原因。本文研究为理解制造业工资快速上涨提供了一个新的视角,也为房地产快速扩张对制造业的挤出效应提供了新的微观证据。

Dynamics of ionisation wave propagation in an applied external electric field

This study presents spatio-temporal development of the ionisation waves(IWs)along one dielectric tube with an extra alternating electric field.A pulsed direct current power supply is used for generating the IWs,and another alternating current power supply is used for altering the distribution of electric fields along the dielectric tube.The measurements show that the propagation velocity and density of IWs are strongly affected by the external electric field.The direct relation between external electric field and the velocity of the IWs is demonstrated.Further analysis indicates that the external electric field can be utilised to control the propagation of the IWs,resulting in a change of their density and velocity.