|
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.
|
|
Evaluation of glutathione content in plants as a marker of heavy metals environmental contamination
Borková, Marie ; Stoupalová, Michaela (referee) ; Opatřilová,, Radka (advisor)
Dependence of glutathione concentration on the amount of thallium in the plant was studied. Observed plant was maize (Zea mays) which was divided to two parts – root and overground. Two culture procedures were elaborated where seeds and young seedlings were cultivated in a solution of thallium of concentration 0, 1, 3, 5, 8, a 10 µmol/l. Extraction agents used during extraction were phosphate buffer and solution of ascorbic acid. Determination of glutathione was realized by capillary electrophoresis (CE) and high performance liquid chromatography (HPLC). Diode array detector (DAD) was used in both methods. Quantification of the thallium amount in the plant was done by method of inductively coupled plasma-atomic emission spectrometry (ICP-AES).
|
|
Enhancement of detection limits in Laser-Induced Breakdown Spectroscopy (LIBS) using nanoparticles
Képeš, Erik ; Prochazka, David (referee) ; Sládková, Lucia (advisor)
This bachelor's thesis describes the options of ehnancing the detection limits of laser-induced breakdown spectroscopy (LIBS). It summarizes different modifications of the classical LIBS apparatus, which are used by methods double-pulsed LIBS (DPLIBS), Townsend effect plasma sectroscopy (TEPS), resonance enhanced LIBS (RELIBS), spark discharge LIBS (SDLIBS), flame-enhanced LIBS (FELIBS), and new ways of sample preparation, such as are used in the method nanoparticle enhanced LIBS (NELIBS). It briefly describes the mechanisms, which are used by each method to reduce the detection limit and it contains an overview of obtained enhancements against the classical method LIBS. It deals with the method nanoparticle enhanced LIBS in more detail and experimentally verifies and studies the effects of nanoparticles of different types and sizes on the emission spectrum of the method LIBS.
|
|
Generation of short-wavelength (<160 nm) radiation by conventional lasers
Chalupský, Jaromír ; Malý, Petr (advisor) ; Krása, Josef (referee)
The theoretical part of this diploma thesis seeks to explain the methods used for generation of coherent short-wavelength radiation. It describes the principles and the operation conditions of direct laser sources and indirect coherent radiation sources based on non-linear effects. Special attention is then paid to the short-wavelength free-electron lasers. This work summarizes properties of numerous sources of this kind. The introductory part of the thesis deals with the physical background of the generation and the manipulation of shortwavelength (VUV/XUV) radiation. The experimental part gives a summary of the results obtained at the FLASH facility (Free Electron LASer in Hamburg; earlier known as VUV FEL) operated at DESY. Methods and instrumentation used for investigating the materials damage due to laser ablation are described in this part of the thesis. UV-vis emission spectra of ablation plume were measured. Main goal is here to determine the ablation thresholds and the effective atenuation lengths in poly (methyl methacrylate) (PMMA), quartz (a-SiO2) and monocrystalline silicon irradiated with pulsed (~30fs) short-wavelength (32nm) intense laser radiation.
|
|
Study of influence of organic dye structure on their decomposition in the diaphragm discharge in liquids
Pajurková, Jana ; Fasurová, Naděžda (referee) ; Kozáková, Zdenka (advisor)
The main goal of presented thesis is to study the influence of organic dyes structure on its degradation in diaphragm discharge in liquids. Diaphragm discharge is a kind of non-thermal plasma that can be generated in liquids by the application of high voltage. In plasma channels (so-called streamers), many physical and chemical processes are formed. High electrical field, shock waves and last but not least emission of electromagnetic waves in the range of visible and ultra-violet radiation appear among physical processes. The most important chemical process is generation of active species. These species initiate chemical reactions and could attack molecules of organic compounds contained in water solution. The reason why organic dyes were chosen in this study is its visible destruction, because it is related to its decolouration. Further, UV-VIS spectroscopy for the determination of concentration during the experiment can be used. Organic dyes are good models of organic substance often contained in waste water and for which removal classical biological, chemical and physical methods aren’t sufficient. Selected dyes were mostly from the group of azo-dyes: Acid Red 14, Acid Red 18, Acid Yellow 23, Direct Blue 53, Direct Red 79, Direct Red 80, Direct Yellow 29, Food Yellow 3 and further, Acid Blue 74 (indigotic dye) and Direct Blue 106 (oxazine dye). Experiments were carried out in a special batch discharge reactor with the anode and the cathode spaces divided by a non-conductive barrier, where the diaphragm with a pin-hole was placed. Measurement showed different removal in the anode and cathode space. We have supposed it was caused by different streamers features and energetic conditions. Dyes were decomposed with higher efficiency in the anode space where the final concentration reached 40 % of the initial concentration while it remained about 90 % in the cathode space. In this thesis the influence of dyes structure on the dye decomposition by electrical discharge was investigated. Dyes consisted of small molecules and dyes with many substitutes bounded on aromatic ring were decomposed more easily than dyes consisted of big molecules. The shift of characteristic wavelength on both directions (to shorter as well as longer wavelength) was observed during the experiments especially when the Direct dyes were decomposed. This phenomenon was probably due to the formation of intermediate product, which have different characteristic wavelength than the primary compound. In general, colourfulness is given by long conjugated systems of double bonds with substitutes bounded on an aromatic ring. Each change in the molecule structure provides the colour change and this could be the possible reason of the shift of characteristic wavelength. The other task was the comparison of degradation process efficiency by the mean of electrolysis and diaphragm discharge. Results showed that electrolysis (30 W) was more convenient for degradation of dyes consisted of small molecules while diaphragm discharge (130170 W) suited for complex molecules. For degradation of small molecules, oxidation on the anode assumed to be the most effective process that is initiated by electrolysis. For degradation of big molecules, attack of active species produced by the discharge is necessary.
|
|
Compact device for fluorescence measurement by optical fiber in microfluidic chip
Ježek, Jan ; Pilát, Zdeněk ; Zemánek, Pavel
In our paper we present a device that combines fluorescence spectroscopy with fiber optics. The device allows high speed detection (in the order of kHz) of the fluorescence signal, which is coming from the sample by an inserted optical fiber, e.g. from a micro-droplet flow in a microfluidic chip, from the liquid flowing in the transparent capillary, etc. The device uses a laser diode at a wavelength suitable for excitation of fluorescence, excitation and emission filters, optics for focusing the laser radiation into the optical fiber, and a highly sensitive fast photodiode for detection of fluorescence.
|
|
Contribution to Efficient Use of Narrowband Radio Channel
Bobula, Marek ; Masopust, Jiří (referee) ; Syrovátka, Břetislav (referee) ; Prokeš, Aleš (advisor)
Předkládaná práce se soustředí na problematiku využívání úzkopásmového rádiového kanálu rádiovými modemy, které jsou určené pro průmyslové aplikace pozemní pohyblivé rádiové služby, specifikované v dominantní míře Evropským standardem ETSI EN 300 113. Tato rádiová zařízení se používají v kmitočtových pásmech od 30 MHz do 1 GHz s nejčastěji přidělovanou šířkou pásma 25 kHz a ve většině svých instalací jsou využívána ve fixních nebo mobilních bezdrátových sítích. Mezi typické oblasti použití patří zejména datová telemetrie, aplikace typu SCADA, nebo monitorování transportu strategických surovin. Za hlavní znaky popisovaného systému lze označit komunikační pokrytí značných vzdáleností, dané především vysokou výkonovou účinnosti datového přenosu a využívaní efektivních přístupových technik na rádiový kanál se semiduplexním komunikačním režimem. Striktní požadavky na elektromagnetickou kompatibilitu umožňují těmto zařízením využívat spektrum i v oblastech kmitočtově blízkým jiným komunikačním systémům bez nutnosti vkládání dodatečných ochranných frekvenčních pásem. Úzkopásmové rádiové komunikační systémy, v současnosti používají převážně exponenciální digitální modulace s konstantní modulační obálkou zejména z důvodů velice striktních omezení pro velikost výkonu vyzářeného do sousedního kanálu. Dosahují tak pouze kompromisních hodnot komunikační účinnosti. Úpravy limitů příslušných rádiových parametrů a rychlý rozvoj prostředků číslicového zpracování signálu v nedávné době, dnes umožňují ekonomicky přijatelné využití spektrálně efektivnějších modulačních technik i v těch oblastech, kde je prioritní využívání úzkých rádiových kanálů. Cílem předkládané disertační práce je proto výzkum postupů směřující ke sjednocení výhodných vlastností lineárních a nelineárních modulací v moderní konstrukci úzkopásmového rádiového modemu. Účelem tohoto výzkumu je efektivní a „ekologické“ využívání přidělené části frekvenčního spektra. Mezi hlavní dílčí problémy, jimiž se předkládaná práce zabývá, lze zařadit zejména tyto: Nyquistova modulační filtrace, navrhovaná s ohledem na minimalizaci nežádoucích elektromagnetických interferencí, efektivní číslicové algoritmy frekvenční demodulace a rychlé rámcové a symbolové synchronizace. Součástí práce je dále analýza navrhovaného řešení z pohledu celkové konstrukce programově definovaného rádiového modemu v rovině simulací při vyšetřování robustnosti datového přenosu rádiovým kanálem s bílým Gaussovským šumem nebo kanálem s únikem v důsledku mnohacestného šíření signálu. Závěr práce je pak zaměřen na prezentování výsledků praktické části projektu, v níž byly testovány, měřeny a analyzovány dvě prototypové konstrukce rádiového zařízení. Tato finální část práce obsahuje i praktická doporučení, vedoucí k vyššímu stupni využitelnosti spektrálně efektivnějších komunikačních režimů v oblasti budoucí generace úzkopásmových zařízení pozemní pohyblivé rádiové služby.
|
|
Investigation of Miniature Devices for Collection of Hydride Forming Elements in Atomic Spectrometry Methods
Krejčí, Pavel ; Čelechovská, Olga (referee) ; Janoš, Pavel (referee) ; Otruba, Vítězslav (referee) ; Dočekal, Bohumil (advisor)
Capability of a prototype of miniature collection device based on a strip of the molybdenum foil for collecting hydride forming elements (As, Se, Sb and Bi) was studied. The device was combined with a miniature hydrogen diffusion flame for detection by atomic absorption spectrometry. The conditions for trapping and subsequent vaporization of analytes of interest were optimized. A twin-channel hydride generation system was used for study of mutual interference effects of co-generated hydride forming elements. The influence of modification of the molybdenum surface with noble metals - Rh, Pt and Ir on trapping and vaporization processes was also studied and changes of microstructure of the foil surface after modification were investigated using scanning electron microscope equipped with energy dispersive x-ray analyzer and electron backscattered diffraction system. Complementary radiotracer and radiography experiments were performed in order to determine trapping efficiency and to assess the spatial distribution of collected analytes within the device. Practical application of the method was demonstrated on determination of antimony in water samples at trace level. Possibility of multi-element analysis was demonstrated by combining the collection device with atomization and excitation of the analyte in microwave induced plasma and with detection by atomic emission spectrometry method. The results of the experiments proved that tested miniature collection device is capable of trapping analytes that form volatile hydrides. This device can be coupled to various types of atomizers, typically used in spectrometry methods. Thus, very sensitive and specific detection of hydride forming elements can be performed.
|
|
Chemical Wet Synthesis and Characterization of Copper-Silver Nanoparticles
Zobač, O. ; Sopoušek, J. ; Vykoukal, V. ; Buršík, Jiří ; Roupcová, Pavla
AgCu nanoparticles (NPs) of near-eutectic composition were prepared by various route of wet synthesis. Nanoparticles suspended in nonpolar solvents were synthesized by solvothermal synthesis from metalloorganic precursors. AgCu colloids in aqueous solution were obtained by the hydride reduction of Ag and Cu nitrates under action of different stabilization agents. Chemical characterizations of as-synthesized AgCu NPs were done using inductively-coupled plasma-optical emission spectrometry (ICP-OES). The optical properties of nanoparticles were monitored using UV-Vis spectrophotometer. The size of colloid nanoparticles were measured by both dynamic light scattering (DLS) and small angle X-ray scattering (SAXS) method in some extra cases.
|
|
ICP-OES with electrothermal vaporisation (ETV) as a possible tool for direct analysis of biologic samples
Matějková, Stanislava
Solid sampling electrothermal vaporization (ETV) inductively coupled plasma optical emission spectroscopy (ICP-OES) enable simple and rapid multielemental analysis of major, minor and trace elements without the need for pre-treatment of solid or liquid samples. By comparison with more common ICP-OES combined with a solution nebulization, the risk of contamination of analysed samples is reduced. The detection limits and the sample quantity needed for analysis via ETV-ICP-OES decrease as a result of the high-efectivity transport of the sample aerosol into the ICP torch. The connection of ETV unit to simultaneous ICP-OES allows us the fast direct and fully automatised analysis of numerous samples. The technique enable usually the combined calibration with home-made or certified solid and aqueous standards. We developed the methodology for tracking the carboran-based candidate-drugs time dependent concentration and for their pharmacokinetic evaluation. The method is based on direct boron or together boron and cobalt contents direct estimation in little amounts of fresh frozen mice tissues (5 – 10 mg of serum, brain or liver).\n
|
guest ::
