Study On Volume Uniform Nanosecond Pulsed Discharge Plasma And Preparation Of Carbon Nanoparticles

The atmospheric nanosecond pulsed plasma has the common advantages of the atmospheric non-thermal plasma, such as containing lots of and kinds of active particles, which can reduce the threshold of chemical reactions, simpleness for operation and convenience for applications, etc. Besides, it involves higher-energy electrons and is farther away from the equilibrium, has higher discharge efficiency and more active chemical properties, and so on. Due to the merits mentioned above, it is conceivable that the cold atmospheric nanosecond pulsed plasma jets have a great potential of application in the area of the preparation of new materials and ozone, the treatment of waste water and waste gas, etc.It is difficult to generate volume and uniform plasma at atmospheric pressure in air, because of the fact that the discharge is unstable. The contract of the discharge channel can lead the discharge transform to spark or arc mode easily. More ominously, the energy density of the contracted discharge channel is concentrated relatively, which can lead to a decline in plasma efficiency and to a damage to the material treated. The pulsed discharge could solve this problem. However, the theoretical and experimental research about it has not been perfect due to its instability and the complexity.In this paper, the work we had done which is mainly about the atmospheric positive nanosecond pulsed discharge plasma consists of these parts:1. The experiment platform about the high-voltage nanosecond pulsed discharge is built. During the connection and the debugging of the electric circuit, insulation, preventing surface discharge, anti-interference and anti-electromagnetic radiation must be mentioned because of the high voltage and the short pulses. It is introduced in three steps. First, the presentation of the power source parameters, the selection of the electric cables, the design and making of the water resistance and the discharge chamber are finished in the preparation phase. Second, in the connection stage, we adopt two patters based on the principle that the charge should be released as soon as possible. Third, the anti-interference and anti-electromagnetic radiation are the main work in our debugging stage.2. The characteristics of the nanosecond pulsed discharge plasma in a cone-to-plane air gap are studied. The effect of the distance between the electrodes and the taper of the cone on the appearance of the discharge is investigated in succession. Later, a quartz tube in the direction parallel to the electric field is inserted between the electrodes, in order to affect the discharge and gain stable volume uniform nanosecond pulsed plasma. As the spectrum simulation and calculation results shown, the change tendencies of the vibration temperature and the mean electron energy of the plasma with the distance between the tube and the plane electrodes are the same in two conditions. Besides, three kinds of devices, multi-needle configuration, multi-needle with quartz tube configuration and needle-to-porous dielectric slab configuration is proposed, also with the purpose to generate stable volume uniform nanosecond pulsed plasma.3. The characteristic of atmospheric nanosecond pulsed plasma jets are diagnosed by optical and electrical methods, and the mechanism is studied based on three different configurations. The first consists of an injection needle placed inside a hollow dielectric tube, while the second employs a ring electrode wrapped around a dielectric tube and the third is a hybrid of the first two configurations. The results demonstrate that plasma jet generated by nanosecond pulsed discharge is of the state of nonequilibrium, has higher reactive species, and, furthermore, has wider application field.4. A nanosecond pulse atmospheric argon cold plasma jet is used to prepare carbon nanoparticles. The experiment result of the pulsed power supply is contrasted with and, moreover, is better than that of the AC power supply. The average diameter of the produced carbon nanoparticles is 3-5 nm for a moderate pulsed discharge and the sizes of the nanoparticles are almost the same. The mechanism of the nanoparticles formation is disscussed.