Qiu Yu-chang

Surface Treatment of Polyethylene Terephthalate Film Using Atmospheric Pressure Glow Discharge in Air

Non-thermal plasmas under atmospheric pressure are of great interest in polymer surface processing because of their convenience, effectiveness and low cost. In this paper, the treatment of Polyethylene terephthalate (PET) film surface for improving hydrophilicity using the non-thermal plasma generated by atmospheric pressure glow discharge (APGD) in air is conducted. The discharge characteristics of APGD are shown by measurement of their electrical discharge parameters and observation of light-emission phenomena, and the surface properties of PET before and after the APGD treatment are studied using contact angle measurement, x-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). It is found that the APGD is homogeneous and stable in the whole gas gap, which differs from the commonly filamentary dielectric barrier discharge (DBD). A short time (several seconds) APGD treatment can modify the surface characteristics of PET film markedly and uniformly. After 10 s APGD treatment, the surface oxygen content of PET surface increases to 39%, and the water contact angle decreases to 19°, respectively.

Experimental Research of Inactivation Effect of Low-Temperature Plasma on Bacteria

The killing logarithms index in killing a vegetative form in an explosure of about 90 s and a spore in an explosure of about 120 s, by using a low-temperature plasma produced by dielectric barrier discharge (DBD), reached 5. The speed in killing the strains tested, by using a low-temperature plasma, was the highest with E. Coli, then S. Aureus and B. Subtilis var niger spore. The results of the scanning electron microscope showed that the low-temperature plasma destroyed the outer structure of the bacteria and that the vegetative form was more susceptible to the inactivation effect of the low-temperature plasma than was the spore. This indicated that the effects of the high voltage and high velocity particle flow, in plasma, penetrating through the outer structure of the bacteria might play a dominant role during the inactivation of the bacteria.

Improving Hydrophobicity of Glass Surface Using Dielectric Barrier Discharge Treatment in Atmospheric Air

Non-thermal plasmas under atmospheric pressure are of great interest in industrial applications, especially in material surface treatment. In this paper, the treatment of a glass surface for improving hydrophobicity using the non-thermal plasma generated by dielectric barrier discharge (DBD) at atmospheric pressure in ambient air is conducted, and the surface properties of the glass before and after the DBD treatment are studied by using contact angle measurement, surface resistance measurement and wet flashover voltage tests. The effects of the applied voltage and time duration of DBD on the surface modification are studied, and the optimal conditions for the treatment are obtained. It is found that a layer of hydrophobic coating is formed on the glass surface after spraying a thin layer of silicone oil and undergoing the DBD treatment, and the improvement of hydrophobicity depends on DBD voltage and treating time. It seems that there exists an optimum treating time for a certain applied voltage of DBD during the surface treatment. The test results of thermal aging and chemical aging show that the hydrophobic layer has quite stable characteristics. The interaction mechanism between the DBD plasma and the glass surface is discussed. It is concluded that CH3 and large molecule radicals can react with the radicals in the glass surface to replace OH, and the hydrophobicity of the glass surface is improved accordingly.

Experimental Study of the Multi-Gap Multi-Channel Gas Spark Closing Switch

A coaxial multi-gap multi-channel spark switch with stainless-steel-spring ring gap electrodes is designed and investigated. The switch is triggered by a pulse applied to the cylindrical electrode outside the discharging channel through a parasitic capacitance coupling. The jitter of the switch is reduced by several short-distance gas gaps in series, and its inductance is reduced by a multi-channel discharge on account of the inductance isolation between the coils of the spring ring electrode. The experimental results indicate that the switch is of low inductance (15-30 nH), low jitter (~3 ns), and stable breakdown performance.

Insulator Surface Charge Measurement Using an Improved Capacitive Probe

A surface charge measuring system using the capacitive probe method is analysed. The present study shows that the measuring system cannot have a steady-state output and that the error resulting from the finite leakage resistance of the measuring system will be accumulated during the measuring process. Based on the theoretical analysis a new type probe with a low charge leakage and high resolution is designed. The surface charge accumulated on the Teflon insulator under a DC voltage is measured using this new probe and some phenomena of the surface charging are reported.

Calculation of Electron Swarm Parameters of SF6/N2 in a Uniform Field Using an Improved Monte Carlo Collision Simulation Method

The electron swarm parameters of SF6/N2 are calculated in the present study using an improved Monte Carlo collision simulation method (MCS). And some improved sampling techniques are also adopted. The simulation results show that the improved simulation method can provide more accurate results.

Application of DBD and DBCD in SO2 Removal

The dielectric barrier corona discharge (DBCD) in a wire-cylinder configuration and the dielectric barrier discharge (DBD) in a coaxial cylinder configuration are studied. The discharge current in DBD has a higher pulse amplitude than in DBCD. The dissipated power and the gas-gap voltage are calculated by analyzing the measured Lissajous figure. With the increasing applied voltage, the energy utilization factor for SO2 removal increases in DBCD but decreases in DBD because of the difference in their electric field distribution. Experiments of SO2 removal show that in the absence of NH3 the energy utilization factor can reach 31 g/kWh in DBCD and 39 g/kWh in DBD.

Study on the Microsecond Pulse Homogeneous Dielectric Barrier Discharges in Atmospheric Air and Its Influencing Factors

The homogeneous dielectric barrier discharge (DBD) in atmospheric air between two symmetric-columnar copper electrodes with epoxy plates as the dielectric barriers is generated using a μs pulse high voltage power supply. The discharge characteristics are studied by measurement of its electrical discharge parameters and observation of its light emission phenomena, and the main discharge parameters of the homogenous DBD, such as discharge current and average discharge power, are calculated. Results show that the discharge generated is a homogeneous one with one larger single current pulse of about 2 μs duration appearing in each voltage pulse, and its light emission is radially homogeneous and covers the entire surface of the two electrodes. The influences of applied voltage amplitude, air gap distance and barrier thickness on the transition of discharge modes are studied. With the increase of air gap distance, the discharge will transit from homogeneous mode to filamentary mode. The higher the thickness of dielectric barriers, the larger the air gap distance for generating the homogeneous discharge mode. The average discharge power increases non-linearly with increasing applied voltage amplitude, and decreases non-linearly with the increase of air gap distance and barrier thickness. In order to generate stable and homogeneous DBD with high discharge power, thin barriers distance should be used, and higher applied voltage amplitude should be applied to small air gap.

Zinc Oxide Surface Flashover Triggering of Pseudospark Switch

Accurate and reliable triggering is one of the most important issues with high power pseudospark switch, because it not only has an impact on the design of discharge chamber of switch, but also has an influence on the dynamic range of operation voltage, repetition frequencies and lifetime of switch. The unique feature of pseudospark switch is its hollow cathode geometry. The hollow cathode effect produced by the hollow cathode provides the protection of the switch for the triggering unit from erosion by high discharge plasma. In this paper, a zinc oxide (ZnO) surface flashover triggering is presented. This trigger unit possesses an excellent time delay (80 ns-360 ns) and jitter (20 ns-50 ns) at the switch voltage of 30 kV-2 kV. The emitted plasma electron density is high enough to trigger switch reliably down to switch voltage of 440 V.

Determination of the Trigger-Electrode Position for the Field-Distortion Spark Gap

The optimal axial position of the trigger-electrode of the field-distortion spark gap is investigated through electric field calculation. The electric fields of the gap are calculated when locating trigger-electrode at different positions. It is shown that if the distance d between the trigger electride and the low electric potential electrode is greater than 1.3 mm, the maximum field intensity occurs at the edge of the trigger-electrode, which will facilitate the generation of multi-channel discharge. According to calculated results, the working characteristics of the gap is investigated and it shows that when d = 1.4 mm the field distortion gap can be triggered reliably.