|
|
Optical emission spectoscopy of the nitrogen-argon post-discharge
Žáková, Marie ; Kudrle, Vít (referee) ; Krčma, František (advisor)
The study of plasmas generated in pure nitrogen and their afterglows are a subject of many hundreds works bringing a lot of information about the kinetic processes and energy transfer reactions. The effect of nitrogen pink afterglow has a specific position among the other kinds of discharges and post-discharges. The post-discharge, and especially the pink afterglow, is extremely sensitive to the presence of various impurities and experimental conditions (total gas pressure in a discharge tube, temperature, etc.) because of their significant influence on all kinetic processes. That is the reason, why it is so important to study this processes. The DC flowing afterglow (generated using the hollow molybdenum electrodes in the distance of 12 cm, power ± 290 W) was used for the experimental part of this work. The discharge was created in Pyrex discharge tube at different concentration ratio of nitrogen and argon. The total gas presure was in range from 500 Pa to 5000 Pa. The emission spectra of post-discharge were recorded by TRIAX 550 spectrometer with CCD detector in the range of 320-780 nm. The vibrational populations at individual vibrational levels were calculated using the emission bands of the first (N2 (B 3g) N2 (A 3u+)) and the second (N2 (C 3u) N2 (B 3g)) positive and the first negative (N2+ (B 2u+) N2+ (X 2g+) nitrogen spectral systems. The dependencies of intensity on decay time and relative vibrational populations on argon concentration and pressure were obtained. The pink afterglow was very sharp in pure nitrogen at low pressure. With the increasing total pressure it was shifted to the later decay times and it was visible for longer time, too. The same effect was observed with the increase of argon concentration in the gas mixture. At the highest argon concentrations, especially at lower pressure, the effect of pink afterglow dissapeared. The knowledge of these processes can give the solution of all kinetic reactions in plasma and this can be used in plasma chemistry and for development of new technologies. This will be a subject of further intensive studies.
|
|
|
Study of post-discharge kinetic processes by titration methods
Josiek, Stanislav ; Kozáková, Zdenka (referee) ; Mazánková, Věra (advisor)
Many experimental and theoretical works on plasma post-discharges have been published during the last more than fifty years. A part of these works was focused in details on nitrogen discharges and post-discharges and kinetic processes in it. The aim of the presented bachelor`s thesis was to study kinetic processes in post-discharge in pure nitrogen and nitrogen contained methane traces. Atomic nitrogen concentration at different methane concentrations was measured by the nitrogen monoxide titration into the post-discharge. All experimental results were obtained by the optical emission spectroscopy. Optical emission spectra were taken in the range of 300-600 nm. DC discharge was created in a quartz tube in a flowing regime. The flowing regime was chosen for this experiment because of better time resolution of the post-discharge. Nitrogen flow was 400 mln/min. Nitrogen oxide flow was in the range of 0-10 mln/min and it was added at the selected post-discharge time. Experiments were carried out for pure nitrogen and for four different methane concentrations – 0.006, 0.013, 0.019 and 0.025 %. Total gas pressure of 1000 Pa, discharge current of 150 mA and voltage of 1110 V were constant during all these experiments. Nitrogen first positive, second positive and first negative spectral systems, NO spectral system and NO2* spectral system were recognized in all measured spectra. The atomic nitrogen concentration was determined using NO and NO2* intensities, and it was increased by the increase of methane concentration. On the other hand, the nitrogen molecular ion emission was strongly quenched even at very low concentration of methane. From this point of view, this thesis is innovative and brings new results into the worldwide research.
|
guest ::
