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Ceramic coatings prepared by liquid precursor plasma spraying
Brožek, Vlastimil ; Kutílek, Zdeněk ; Bertolissi, Gabriele ; Mastný, L.
LPPS method (Liquid precursor plasma spraying) was performed using aqueous solutions of ammonium vanadate and chromate in order to přepade nano-crystalline ceramic coatings on steel and ceramic substrates. Their structure was studied and verified by injecting at different conditions the liquid precursors into the stream of water stabilized plasma. The surface coverage of nano-coatings is inversely proportional to the concentration of precursor and largely depends on the geometric arrangement of the depositing device in which there is a complex process multistage precursor processing within milliseconds.
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Processes of Nanoparticle Formation in Low Temperature Plasma
Brožek, V. ; Mastný, L. ; Moravec, Pavel ; Neufuss, Karel ; Ondráček, Jakub ; Ždímal, Vladimír
This work describes the synthesis of nanoparticles during interaction of several different metals (Ag) or their respective oxides (TiO2, Cr2O3) with oxygen-hydrogen plasma having temperatures above 25000 K. Resulting nanoparticles and/or their aggregates in the size range of 25-300 nm were deposited on metallic targets and/or trapped in the water filters and separated using ultra-centrifugal apparatus. The aerosol spectrometer SMPS 3936 (scanning mobility particle sizer) was used to study the particle size distribution of generated nanoparticles in the size range 14 – 700 nm. In order to extend the measured particle size range towards larger sizes, the APS 3321 spectrometer (aerodynamic particle sizer) with the size range 500-20000 nm was used simultaneously. Both spectrometers were set-up to sample with three minute time resolution. Process conditions and production of inorganic nanoparticles of defined composition are discussed in this work.
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Photoactivity of water suspensions of titanium and tungsten oxides
Mastný, L. ; Šaněk, F. ; Brožek, Vlastimil
Generator of water-stabilised plasma WSP® may be used for the thermal disposal of organic substances for which the dwell time of 5 ms maximum at 30,000 K is sufficient to ensure their destruction. Apart from high temperature, the device generates also highly intensive UV radiation and radiation with wavelengths of around 660 nm (Hα) and 490 nm (Hβ). Radiation in this part of spectra allows for the activation of not only photocatalysts based on TiO2 but also of other semi conductive oxides with narrower forbidden band, such as tungsten oxides. Their photoactivity was observed using a model decomposition of organic substances in water suspensions. A series of experiments were initiated on the disposal of industrial toxic and explosive waste debris, such as sodium picraminate.
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Interaction of the water stabilized plasma radiation with photocatalytic suspensions
Mastný, L. ; Šaněk, F. ; Brožek, Vlastimil
The design of WSP® plasma torch with liquid used as stabilization agent, enables three different process zones for the decomposition of toxic chemicals. The first zone is inside the plasma stabilization chamber, where the liquid is in direkt contact with electric arc in the cathode zone. Second zone is at the exit notule in the outer space of the torch body. Here the nontransfered stream of the thermal plasma can act as heat source for thermal decomposition of chemical substances. The third zone was arranged in this work as a spiral from silica glass which acts as a tube flowed by the toxic liquid through and exposed to ultraviolet rays produced by the plasma. Inside such a tube the interaction of the water stabilized plasma radiation with photocatalytic suspensions was studied. As a model substances Orange II, nicotine and 2-nitroso-1-naphtol were used. The flow rate in frames 12 - 30 l/min was evaluated from the viewpoint of the effectivness of chemical decomposition.
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Photoactive catalyzers on WO3 basis
Domlátil, J. ; Mastný, L. ; Šrank, Z. ; Brožek, Vlastimil
Properties of tungsten trioxide photocatalysts with various oxygen stoichiometry have been studied. Samples have been prepared under low-temperature non-isothermal plasma conditions. Due to colourfulness of tungsten oxides the spectrophotometric determination of photoactivity to measuring colour changes has been preferred. The latter method is suitable for analysis of colourless TiO2 photocatalysts.
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Fotokatalytické vlastnosti plazmově zpracovaného oxidu wolframového
Brožek, Vlastimil ; Domlátil, J. ; Mastný, L. ; Šrank, Z. ; Janča, J. ; Eliáš, M.
Tungsten trioxide with the band gap about 2.58 eV is known as a material, which a photocatalytic effect after UV-radiation exposure can be observed. However, in some cases more detailed material specification and the consideration of its complex structural and stoichiometric uniqueness are lacked in its photoactivity data. The presented work is focused on the study of tungsten trioxide samples photoactivity using the unified method that determines the reference substances colour changes after 360 nm UV-radiation exposure. The samples were prepared by from ammonium paratungstate treated in oxygen or argon plasma, which was generated by capacitive coupled RF generator operated at low partial pressures. The differences in oxygen stoichiometry which depends on total temperature plasma, because especially the presence of hydrogen coming from the ammonium cation disintegration causes a partial reduction partly to the WO2.7 oxide.
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Photocatalytic activity of titanium precursors treated in low temperature plasma
Brožek, Vlastimil ; Matějíček, Jiří ; Šrank, Z. ; Mastný, L. ; Janča, J.
In order to obtain compact photocatalytically active materials, the possibility of preparation of new titania forms by oxidation of titanium compounds, having different crystal structures and oxidation degree, was verified. Four model substances were chosen: titanium carbide, nitride, diboride and Ti2O3. These compounds were prepared in the form of high-specific-surface powder, as well as large-area compact free-standing parts by CVD, PVD and especially plasma spraying. After high temperature treatment in a water stabilized plasma, generated by the WSP torch, a measurable photoactivity was observed; this could be further improved by controlled oxidation below 450°C. Oxidation in an RF-generated oxygen plasma appeared more efficient, especially in shorter reaction times. However, the experiments have shown that even keeping the reactor walls at 450°C did not prevent the uncontrolled temperature rise inside, during the reaction of the oxygen plasma with titanium compounds.
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Photocatalytic aktivity of plasma treated titanium precursors
Brožek, Vlastimil ; Matějíček, Jiří ; Šrank, Z. ; Mastný, L. ; Janča, J.
Photoactive solid parts of chemical reactors could be produced via plasma deposition of boron carbide and titanium diboride using water-stabilized plasma torch WSP. Photocatalytic effectivity of TiC and TiB2 was measured, as well as those of their oxidation products gained at 450 and 1000°C on air as well as at 450°C in oxygen plasma. Photocatalytic effectivity of all studied substances was compared with those of plasma- treated TiO2 and Ti2O3, whose photocatalytic activity is known from plenty of practical applications.
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