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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.
Study of chemical processes in Titan atmosphere
Klohnová, Karolína ; Grossmannová, Hana (referee) ; Krčma, František (advisor)
The bachelor’s thesis deals with study of chemical processes in Titan atmosphere simulated under laboratory conditions. The abnormal glow discharge as a for-step for gliding arc discharge was used for the plasma generation in nitrogen-methane gas mixture corresponding to the Titan atmosphere composition. The optical emission spectroscopy was chosen as the basic plasma diagnostic method. The theoretic part of thesis describes briefly history of Titan atmosphere studies including the last space craft obtained results. Later, the fundamental properties of plasmas including their diagnostics are given. The general components determined in Titan atmosphere include N2, CH4, H2 molecules as well as a suite of lower weight hydrocarbons including HCN, C2H2 and C2H4; some traces of higher hydrocarbons and amino acids were determined, too. The electrode configuration corresponding to gliding arc arrangement with interelectrode gap of 2 mm was used with high voltage power supply giving power up to 300 W. Plasma was generated in the nitrogen-methane mixtures (0.5 – 2.5 % of methane) at atmospheric pressure. Both gases had purity better than 99.999% and all system was evacuated before measurement to suppress oxygen traces. Optical emission spectra were taken in dependence of applied power and gas mixture composition. Nitrogen and CN radical spectra as well as atomic lines of hydrogen and carbon were identified in the spectra. The vibrational temperatures of 2300 - 8000 K were determined from the spectra of nitrogen second positive, CN violet and C2 spectral systems. Rotational temperature calculated from nitrogen second positive and CN violet 0-0 bands varied in the interval of 1200 - 4800 K depending on the experimental conditions. The obtained results were submitted as a part of paper into international journal. The obtained results maybe used as a fundament for the future study of Titan atmosphere using also other discharge.
Characterization of plasma during organosilicone thin film deposition using haxamethyldisiloxane monomer
Blahová, Lucie ; Mazánková, Věra (referee) ; Krčma, František (advisor)
The aim of this thesis is plasma diagnostic during deposition of thin films based on organosilicones. Hexamethyldisiloxane was used as a precursor for plasma deposition in the presence of oxygen, and the diagnosis was performed by using optical emission spectroscopy. The theoretical part summarizes the basic characteristics of plasma and processes occurred at plasma polymerization and deposition. It also deals with thin films and their use in coating materials. A relatively large part is devoted to the specification of the physical-chemical nature of the used analytical method – optical emission spectroscopy. Finally, the principles of rotational, vibrational and electron temperature calculations are described. The contemporary deposition process was carried out in continuous and pulsed mode of radiofrequently excited capacitively coupled discharge. The effects of monomer flow rate, plasma power and duty cycle on the deposition process were studied. In the individual spectra, atomic hydrogen lines of Balmer’s series as well as an atomic oxygen line were identified. Molecular bands of CO have been identified as Angstrom’s system and 3. positive system. In the case of the identified fragments, the intensity dependencies on the monomer concentration in mixture, plasma power and duty cycle were detected. Electron temperature of plasma was also calculated using the relative intensities of atomic hydrogen lines of Balmer’s series. Vibrational and rotational temperature could not have been determined because no suitable fragments for their determination were found in the spectrum. Based on findings mentioned above, partial composition of plasma and some of its properties were estimated. The subject of the further research will be determination of the exact content and structure of the thin films and investigation of other plasma characteristics. Plasma deposition is influenced by many factors, and the study of their optimal combination for the most efficient deposition process is a goal for the future research.
Corrosion layers removal in low-pressure plasma
Kujawa, Adam ; Grossmannová, Hana (referee) ; Krčma, František (advisor)
A plasmachemical reduction of corrosion layers on copper was studied. In this case two series of copper samples were prepared and putted in two corrosive environments for one week. The first corrosive environment contained a concentrated nitric acid and the second environment contained a concentrated sulfuric acid. Samples thus prepared were ready to be plasmachemicaly treated. The plasmachemical reductions took place in low-temperature, low-pressure, non-isothermal, high-frequency-inducted hydrogen plasma on the Faculty of Chemistry in University of Technology in Brno. The discharge was generated in continual or pulse mode with changeable pulse ratio. To monitor the reduction process an optical emission spectroscopy was used. The radiation from plasma discharge was measured by an optical spectrometer in the intervals of 1 to 10 minutes. An object of our concern in collected spectrum was the radiation of OH radicals with electromagnetical wavelenght in a range of 305 – 330 nm, and which were produced in a reaction between the hydrogen radicals and the oxygen atoms, contained in the corosion layers. A rotation temperature of plasma was calculated from the spectrums of OH radicals in a dependence of discharge conditions. Gathered findings will give us a better knowing of this conservation technique, that is used for treatment of the corroded surfaces of the archeological artifacts, and will also allow more provident appliance of this method on a copper historical objects.
Study of plasmachemical reduction of corrosive layers on bronze
Miková, Petra ; Selucká, Alena (referee) ; Krčma, František (advisor)
One of the important stages of the human history is certainly Bronze Age, on our territory dated 1900 - 800 BC. At that times, it was produced many objects of bronze, such as swords, spears, daggers, ornaments, jewelry. These artifacts are now found by archaeologists in excavations around the whole world. During the years there was an exposure to various types of substances and the environment and result in extensive corrosion of the used materials. To better understand the culture and traditions of our ancestors, it is necessary to carefully eliminate the corrosion and thorough inspection of these subjects. In this work, we consider the model corrosion layers removal by reduction in low-temperature hydrogen plasma. Plasma chemical reduction method was developed during the eighties years of last century and currently is further rapidly improved. Unfortunately, the process mechanism is not yet precisely known. Preparation of model corrosion layers were as follows: bronze blocks (weight approximately 80 g) were sharpend by electrical grinding machine (used paper 280 and then 600). Thus treated samples were rinsed in ethanol, dryed by hot dryer and stored in plastic bags. A Petri dish was placed at the bottom of the desiccator and it was poured by 20 ml of concentrated hydrochloric acid. Above the bowl has punched ceramic grid, on which the samples were placed. Closed desiccator was placed in darkness at the ambient laboratory temperature. To accelerate the samples corrosion process in a desiccator, the samples were sprinkled with acid. Plasma chemical treatment was carried out in a cylindrical reactor of quartz glass with outer copper electrodes. The RF (13.54 MHz) capacitivelly coupled plasma was used for the samples treatment. For each sample have been selected specific conditions: power (50 - 300 W), pulse (duty cycle of 10 – 25 %) or continuous mode. The optical emission spectroscopy monitored dependence of OH- intensity during the reduction. The decrease to the 1/10 of the maximum value leads to end the experiment. Based on this criterion, the treatment time of samples was in the range of 30 - 80 minutes. Corrosion has been removed from 7 samples. All the samples were covered by corrosion deep green color with a clearly visible crystalline structure before their inserting into the reactor. After the treatment, the color was dark black, and after leaving the air began to surface green, in some samples was observed in white and yellow tint. Surface top layer was removed on samples 1 and 5, where spontaneous dropout was reached. The pulse mode with duty cycle of 10 % and the powers of 200 and 300 W were applied for these two samples. The surface layer of samples treated with pulsed mode of 25 % was easily removable by spatula. The work demonstrated the applicability of hydrogen RF plasma in pulsed mode for the corrosion removal from bronze samples. The further work will be focused on the optimal treatment conditions search.
Diagnostics of diaphragm discharge in liquids
Dřímalková, Lucie ; Krčma, František (referee) ; Kozáková, Zdenka (advisor)
The main goal of this thesis is the diagnostics of the diaphragm discharge generated in liquids. Although many applications of electric discharge in liquids have been developed during the last years, the exact mechanism of the discharge ignition is not sufficiently known up to now. Based on this reason, this work focused on the investigation of processes before the discharge ignition, breakdown parameters and the discharge itself both in the irregular and stable regime. Using two kinds of inorganic salt solutions the work studied the influence of conductivity and electrolyte kind on the diaphragm discharge and its static current-voltage characteristics. The last task of the work investigated the emission spectra produced by the discharge. The theoretical part of the work presents mechanisms of the discharge generation in gases including the description of particular kinds of known discharges. The base theories of the discharge ignition in liquids are mentioned as well. Experiments were carried out in the reactor divided by the dielectric barrier (diaphragm) with a central pin-hole into two electrode spaces. Diaphragm was made of PET and the pin-hole initial diameter was 0.4 mm. Stainless steel electrodes were installed in the same distance of 2 cm from the barrier and symmetrically with respect to the diaphragm. Time resolved characteristics of current and voltage were recorded using two-channel oscilloscope which detected their output values. Parameters were measured by the constantly increasing DC voltage with a step of 50 V. When the regular discharge was ignited voltage had been gradually decreased. Used solutions contained sodium sulphate or sodium phosphate electrolyte at six different conductivities. Radiation emitted by the discharge was recorded by the spectrometer Jobin Yvon TRIAX 550. Emission spectra were investigated for one electrolyte at two different conductivities. The part with results presents all dependencies that were achieved during the measurements and all obtained data are compared. Recorded time resolved characteristics determine breakdown moment and describe current and voltage in particular parts within the static current-voltage curve. The work compares the influence of conductivity change on current-voltage characteristics as well as the effect of inorganic salt kind. By the conductivity enhancement the measured curve moves towards lower voltage which means that the breakdown voltage is decreased. Changing the inorganic salt the change of voltage related to the creation of bubbles in the diaphragm surroundings is observed. However, the change of electrolyte does not induce any significant change of the breakdown voltage. The last part of the work was focused on the optical emission spectroscopy of the discharge. Typical line system of OH radicals was identified in measured spectra which intensity was not dependent on the salt concentration. The work show particular processes taking place in the diaphragm surroundings when DC voltage is applied on the electrodes in electrolyte up to the diaphragm discharge ignition. Further, results describing the influence of conductivity and electrolyte changes on the processes are presented. The breakdown moment of the discharge and its dependence on the solution conductivity was determined. Optical emission spectroscopy revealed the contents of radiation emitted by the discharge.
Optical emission spectroscopy of the nitrogen post-discharge plasma with metal trace impurity
Bocková, Ivana ; Mazánková, Věra (referee) ; Krčma, František (advisor)
The bachelor´s thesis deals with the optical emission spectroscopy of the nitrogen post-discharge with metal trace impurity. The analysed sample introduced to the low-temperature plasma was zinc vapor and stannic chloride. As a diagnostic method was choosen optical emission spectroscopy as one of the simplest plasma diagnostic methods. The teoretical part is aimed to information about plasma and processes in the plasma. The special focus is deald for post-discharged plasma and the optical emission spectroscopy. Measurement itself is implemented in flowing regime of DC post-discharge under low pressure. The intensities of selected nitrogen bands and atomic lines are observed as a function of metal vapor presence. The simplified mechanism of the observed phenomen is presented. The possible excitation mechanisms are shown of metallic atoms during the post-discharge.
Study of plasmachemical reduction of corrosive layers on brass
Řádková, Lucie ; Selucká, Alena (referee) ; Krčma, František (advisor)
The main topic of this bachelor thesis is plasmachemical treatment of archeological artifacts, especially plasma chemical treatment of brass corrosion layers. Low-pressure, low-temperature hydrogen plasma is used for this process. Nowadays, the technology is used mainly for iron or silver based materials but even for them the optimal conditions for the corrosion removal are not fully known yet. The knowledge about other metallic materials is fully missing. Two sets of brass samples were prepared in different corrosion atmospheres. The first atmosphere was prepared using saturated vapors of HCl. The samples were in this atmosphere during one month, and corrosion layers were orange-brown. The second set was prepared using ammonium solution, the samples were in this atmosphere for one day, corrosion layers were blue. The generation of capacitively coupled plasma in continuous mode by different supplied power was done. The experiments were carried out at 100 Pa with hydrogen gas flow of 50 sccm. Discharge power was varied in the interval 50 – 200 W and the treatment duration was 70 – 140 min. The optical emission spectroscopy of OH radical was used to find out all changes those have been resulting from plasmachemical reactions. The OH radical integral intensities were observed, they were used to monitoring plasma chemical reduction process. Spectral intensity of spectroscope was in the range 290 – 330 nm. After the plasmachemical treatment, it was very difficult to remove corrosion layers of HCl, but removing of NH3 corrosion layers was easy. It was caused by type of corrosion process (corrosion layers were influenced by time of corrosion process). This bachelor thesis is the start to find out conduct corrosion layers of brass in plasma treatment. In future, plasma treatment could be used to treatment of real archaeological artifacts.
Study of processes during the organosilicone thin films deposition
Flamíková, Kristýna ; Rašková, Zuzana (referee) ; Krčma, František (advisor)
The aim of this work is plasma diagnostic during the deposition of thin films based on organosilicone compounds. Tetravinylsilane (TVS) was used in this study; the optical emission spectroscopy was applied for the diagnostics. The theoretical part of this work gives a basic fundaments of optical emission spectroscopy and brings the procedures for rotational, vibrational, and electron temperature calculations. The deposition process was carried out in pulsed regime with duty cycle 1:4 to 1:499. The pure TVS and TVS containing 10, 40 and 80 % with total gas mixture flow rate of 0.5 sccm were used during the deposition. The hydrogen atomic lines and many rotational lines of molecular hydrogen were identified in the spectra. Besides them, the molecular band of SiH, CH and C2 were observed. The atomic oxygen lines and continuum with a maximum at 550 nm were recorded in the case when oxygen was added. The rotational temperature calculated from 0-0 CH band was in the range 1700 - 2100 K depending on the discharge conditions. The electron temperature of about 1800 K was calculated from hydrogen atomic lines. The experimental results showed the partial plasma composition and some plasma basic characteristics were obtained.
Studium plazmatu během pulsní laserové depozice kompozitních vrstev nanokrystalického diamantu/amorfního uhlíku a jejich strukturní vlastnosti
Novotný, Michal ; Jelínek, Miroslav ; Bulíř, Jiří ; Vorlíček, Vladimír ; Mosnier, J.-P. ; Duclére, J.-R. ; Popov, C.
Nanocrystalline diamond/amorphous carbon composite thin films were prepared by hybrid technique combining pulsed laser deposition with a capacitively coupled radiofrequency discharge. Optical emission spectroscopy was performed for plasma monitoring during the deposition process.

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