National Repository of Grey Literature 171 records found  previous11 - 20nextend  jump to record: Search took 0.00 seconds. 
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.
Plasmachemical deposition and characterization of hexamethyldiloxane thin layers
Blahová, Lucie ; doc. Mgr. Vít Kudrle. Ph.D. (referee) ; Krčma, František (advisor)
Thin films have been used to modify surface properties of various materials for many years. Plasma Enhanced Chemical Vapor Deposition (PECVD) is one of the possible methods for their preparation and this technique is applied in this work as well. An organosilicone – hexamethyldisiloxane – is used as precursor. Thin films are created on the surface of the substrate using mixture of precursor and oxygen in radiofrequently excited capacitively coupled plasma. The aim of the thesis is to find the optimal deposition conditions for production of transparent thin layers with good barrier capabilities, low oxygen transmission rate especially. Thin film depositions were realized for different compositions of the deposition mixture in continuous and pulsed mode of plasma with varying supplied power and duty cycle values. The deposition process itself was monitored in situ by optical emission spectroscopy. Thin film coatings were analyzed to determine their physical chemical properties (infrared spectroscopy, surface energy) and barrier properties. Using optical emission spectroscopy, important particles were identified in the deposition plasma. Vibrational, rotational and electron temperatures were determined from relative intensities of chosen fragments. Composition of thin films was studied by infrared spectroscopy. The best results of oxygen transmission rate were achieved with layers prepared from deposition mixture with high oxygen content. It was possible to improve barrier properties by performing deposition in pulsed plasma mode with 20–30% duty cycle. In this diploma thesis, optimal deposition conditions of thin films from hexamethyldisiloxane with low oxygen transmission rate were determined. It is possible to use these results in practical applications, such as corrosion inhibitors for archaeological objects. Optionally, they can be used in various industry branches where it is desirable and feasible to prevent oxygen access to the material by deposition of barrier coatings.
Analysis of aromatic compounds in plasma treated onion
Krejsová, Lenka ; Kozáková, Zdenka (referee) ; Krčma, František (advisor)
This bachelor thesis deals with the analysis of fragrances in onions, which were exposed to plasma before planting. The adjustment was made to see if onion growth and yields would improve. The theoretical part deals with the quantitative and qualitative methods for the determination of volatile substances. It contains the principle and instrumentation of mass spectrometry as well as the tandem connection of gas chromatography with mass spectrometry. In the experimental part, a liquid sample was obtained by pressing. After 60 minutes, saturated vapors were analyzed by reactive ionization mass spectrometry (PTR-MS). Thanks to this analysis, the concentration of volatile substances was determined. Some samples were analyzed by gas chromatography with mass spectrometer as detector to identify the compounds, because PTR-MS does not allow distinguishing of isomers. Subsequently, the data were processed and evaluated. From the gathered obtained it is clear that the plasma treatment has an effect on the fragrances concentrations. After six months of storage, the presence of some volatile substances increased due to increased biological activity.
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.
Physical-chemical property characterisation of thin reflective layers on polymer substrates
Stružínský, Ondřej ; Dzik, Petr (referee) ; Krčma, František (advisor)
This work deals generally with surface diagnostic and optical properties of thin layers which are created by plasma polymerization of hexamethyldisiloxane monomer. The influence of oxygen adittion on thin layers properties was studied, too. This polymer layers are commercially made to protect reflective layers in the headlights. Thin layers were made in deposition chamber AluMet 1800V at Zlin Precision Company. Teoretical part of this work deals with methods which are used for deposition of thin layers, mainly physical (PVD) and chemical (PECVD, CVD) depositions. The conditions which influenced plasma polymerization itself are discussed as well as, monomers which are used for plasma polymerization and stability of thin polymer layers. Also there are mentioned the most frequent plasma processes diagnostic methods applicable during the deposition (optical emission spectroscopy) and methods for thin layers diagnostic (wettability, UV-VIS and infrared spectroscopy). Spectrometer Jobin Yvon Triax 320 was used for emission spectra acquisition during the plasma deposition. There were analyzed only two spectra created at same conditions as power at 3 kW and monomer flow rate at 100 sccm; the first one was in pure monomer, the second was obtained with oxygen addition of 150 sccm into the monomer flow. There was not found any essential differences between these spectra in the range 300 nm to 800 nm. Besides the thin layers analyzes after their formation, the samples were exposed to common aging conditions with respect to their use. One third of the prepared samples was exposed by ultraviolet radiation for 48 hours (exposure power of 0.68 W.m-2 at 340 nm) and the other part of samples was inserted for four days into NaCl solution of 50 g.l-1. The surface properties of layers were studied by their contact angle with three liquids (water, diiodmethane, and glycerol) that allowed their surface energy calculation. Results of this measuring are as following: Oxygen addition decreased contact angle of water after exposure of UV radiation. If the highest flow rate of monomer was used and oxygen was added, NaCl degradation did not have any significant influence on contact angle to water. Optical properties of prepared thin films were characterized by UV-VIS spectroscopy. Optical properties were measured only for samples after deposition and samples that were exposed by ultraviolet radiation. Results showed that oxygen addition into the reacting mixture increased the light absorption in UV-VIS (300-800 nm). The absorption was significantly increased after exposure of ultraviolet radiation. With respect to the application of these thin layers is necessary to say that this influence is undesirable. On the other hand, absorption of thin layers deposited at 2 kW, without oxygen addition and flow rate of monomer at 125 sccm a 150 sccm was decreased. Results of this work can be useful for investigation and study of deposited thin layers. The most useful can be with another work which deals with plasma diagnostics during the deposition even more closely. Then it will be possible to adjust and predict properties of deposited layers.
Plasma activated water prepared by electrical discharge in liquids
Možíšová, Aneta ; Krčma, František (referee) ; Kozáková, Zdenka (advisor)
The aim of the diploma thesis is generation of active particles in plasma activated water (PAW) using a low-temperature plasma discharge. In this work I focus on the determination of hydrogen peroxide, nitrites and nitrates as active particles. The practical part is focused on a specific case of use of a plasma discharge in selected electrolytes dissolved in an aqueous solution. Here, three phosphates, differing in the number of acidic hydrogens, were selected for each experiment, and sodium chloride and tap water were compared for comparison. Phosphates were selected for their stable pH during plasma discharge in solution to monitor the effect of pH. The experiments were focused on investigating the stability of active particles in PAW, under which conditions is the highest production rate of these particles and what effect the pH value has on the result. It was found that hydrogen peroxide is generated the most in an alkaline environment but shows better stability in neutral. The concentration of generated nitrites is not high, but it shows stability, regardless of the polarity of the main electrode used for PAW generation. Nitrites were generated the most in alkaline environment and nitrates in acidic environment. One of the conclusions is that nitrates are not a very stable particle in PAW. Thanks to the activation and oxidation properties of plasma activated water, this method can be used in medicine or agriculture
Study of plasma activated water influence on soil microorganisms
Poláková, Marianna ; Dvořáčková,, Helena (referee) ; Krčma, František (advisor)
Bachelor thesis is focused on the impact of plasma activated water on soil microorganisms. Reactive spieces of oxygen and nitrogen are present in plasma activated water, which are responsible for its biological and chemical properties. Thanks to its unique features, plasma activated water is used for therapeutic purpose or in agriculture. The theoretical part is concentrated on general information about soil, its properties and microorganisms found in it. Furthermore, it deals with basic information about plasma and sources used for its production. The last part presents the plasma activated water and its specific characteristics. Experimental part deals with the application of distilled water, plasma activated water and a mixture of distilled and plasma activated water on soil. In the first set of experiments, it was an application directly on the soil, the application to the soil extract was in the second set. Bacteria were inoculated on culture medium in concentrations 10-2, 10-4 and 10-6. The number of formed colonies was observed and then some microorganisms has been identified. Based on the results, it can be stated that plasma activated water had a positive effect on the microorganism colonies growth. However, the subject of further work will be to determine whether it is positive for pathogenic microorganisms or not.
Study of Plasma - Liquid Interactions
Němcová, Lucie ; Brablec, Antonín (referee) ; Obradovic, Bratislav (referee) ; Krčma, František (advisor)
Disertační práce se zabývá detailním studiem vlastností různých elektrických výbojů generovaných ve vodných roztocích. Tyto výboje se staly v posledním desetiletí velmi populárním tématem, a to zejména díky mnoha praktickým využitím jako například v biomedicíně, čištění odpadních vod, ekologii nebo nanoinženýrství. Studium je zaměřeno na generaci peroxidu vodíku, jakožto jednu z nejvýznamnějších částic generovaných právě elektrickými výboji v kapalinách. Pro první část této práce byla využita speciální výbojová komora zkonstruovaná na Fakultě chemické Vysokého Učení Technického v Brně. Komora byla rozdělena tenkou diafragmovou přepážkou na dvě poloviny, přičemž uvnitř přepážky se nacházela malá dírka. V každé části komory se nacházela jedna elektroda, a obě dvě části komory byly vyplněny kapalinou. Ze zdroje bylo do kapaliny aplikováno vysokofrekvenční napětí (1 a 2 kHz), které tak vlastně upravovalo roztok chloridu sodného (1.5 l). Bylo zjištěno, že tento druh napětí, v porovnání s DC, nezpůsobuje nežádoucí přehřívání roztoku (počáteční vodivost 100 - 800 S/cm) během jeho úpravy při zachování účinnosti produkce peroxidu. Experimentální aparatura pro druhou část práce byla sestavena na Gentské Univerzitě v Belgii. Stejnosměrný výboj byl generován v bublinách plynů (He, Ar, N2, vzduch) v prostředí vodných roztoků. Byla studována generace peroxidu vodíku a odbourávání organických barviv přítomných ve zkoumaném roztoku. Ke generaci peroxidu vodíku byl použit roztok NaH2PO4 . 2H2O (5 microS/cm, V= 750 ml), ke zkoumání rozkladu barviv byly použity roztoky organických barviv Direct Red 79 (20 mg/l) a Direct Blue 106 (20 mg/l, V= 750 ml). Minimální koncentrace peroxidu vodíku byla naměřena při aplikaci proudu 10 mA, zatímco maximální koncentrace peroxidu vodíku byla zaznamenána při použití proudu 30 mA. Rozklad organických barviv vykazoval stejné vlastnosti. Čím vyšší byla dodávaná energie, tím více barviva se odbouralo. Třetí část práce probíhala ve spolupráci s Queen's University of Belfast, Centrum for Plasma Physics, UK. K realizaci experimentů bylo využito vysokofrekvenčního plazmového skalpelu (Arthrocar). Bylo zjištěno, že hodnota koncentrace peroxidu vodíku dosahovala maxima v roztocích s nepatrným přídavkem alkoholu (0.25 %). Celkem byly studovány čtyři 0.15 M roztoky BaCl2, Na2CO3, KCl a NaCl (V= 20 ml), jejichž počáteční vodivost se pohybovala kolem 13 mS/cm. Z výsledků bylo patrné, že největší rozdíl hodnot pH byl zaznamenán u roztoků s přídavkem ethanolu. V optických emisních spektrech byly identifikovány především radikály OH, které jsou prekurzory peroxidu vodíku. Výsledky ukázaly, že plazma v takovémto roztoku je stále tvořeno, což může být považováno za první krok generace plazmatu v organických sloučeninách. Poslední část práce byla zaměřena na tzv. mikroplazmatický jet v přímém kontaktu s kapalnou fází. Tato experimentální práce byla realizována na pracovišti Nanotechnology & Integrated Bio-Engineering Centre (NIBEC), University of Ulster, UK během studijní stáže. Jako vodivé médium byl použit roztok trihydrátu kyseliny chlorozlatité s různou počáteční vodivostí. Zajímavým zjištěním je fakt, že při tomto druhu měření bylo generováno stabilní plazma i při velmi malém výbojovém proudu (0.05 a 0.2 mA), a tedy i peroxid vodíku vznikal při velmi malé vstupní energii, což může být považováno za velmi dobrý výsledek.
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.
Low pressure plasma application for the surface cleaning of archaeological objects
Bubnová, Kateřina ; Grossmannová, Hana (referee) ; Krčma, František (advisor)
This diploma thesis builds on my bachelor thesis, which was focused on the application of low-pressure hydrogen plasma and argon-hydrogen plasma on layers of corrosion products. According to results of the experiments, an appropriate temperature for plasma chemical treatment of lead samples was detected. However, the process of corrosion removal through plasma chemical treatment needs to be further optimized to prevent potential damage to the original historical artefacts. Optimization of the treatment process is therefore the main subject of this work’s research. The model samples with artificial corrosion layers with dual composition were prepared. These samples were put to desiccator with sand and organic acid. The samples corroded in environment of acetic acid or formic acid with the aim of creating the corrosion, which would be at least partially simulated with corrosion on the original artefacts. The process of corrosion lasted for eleven months. After that, the samples were dried out under reduced pressure, put to the protecting foil with humid and oxygen absorbers. In contrast with my bachelor thesis where the continuous regime was chosen for the treatment, the pulse regime with three different condition settings is used. Process of experiment was monitored by OES, surface of samples was analyzed by SEM, EDX, XRD methods. Results from experiments with model samples were used for treatment of original artefacts with missing documentation, so their eventual damaging was acceptable.

National Repository of Grey Literature : 171 records found   previous11 - 20nextend  jump to record:
See also: similar author names
1 Krčma, F.
Interested in being notified about new results for this query?
Subscribe to the RSS feed.