|
|
Reactor for the preparation of nanoparticles in plasma discharge
Brožek, Vlastimil ; Benešová, L. ; Mastný, L. ; Sýkora, V.
New variety of a plasmachemical reactor for the preparation of nanoparticles from liquid or aerosol precursors in which liquid precursors were brought into the current of plasma in the places where the temperature reached 4000K–5000K was reconstructed. As a generator of plasma was used the plasma torch WSP® which was developed and patented by IPP AS CR. We worked on liquid precursors which were H[AuCl4],AgNO3 and H2[PtCl6],that decomposed in the high temperature environment and so colloidal solutions of metallic nanoparticles of gold, silver and platinum were emerged in concentration of 5mg/l–50mg/l with the size of particles 25nm–100nm depending on the starting point of the precursor concentration. Further experiments for preparation so-called double oxides served us as a check of universality of this method but also its wide adaptability.That was the preparation of spinel MgAl2O4 and ferrite CoFe2O4 from the sulfate solutions.By the horizontal device arrangement it is possible to
|
|
|
Production of nanoparticles utilizing water stabilized plasma
Bertolissi, Gabriele ; Brožek, Vlastimil ; Chráska, Tomáš ; Mušálek, Radek ; Neufuss, Karel ; Mastný, L. ; Sofer, Z.
Water stabilized plasma torch (WSP®) generates plasma jet with max. plasma velocity in the nozzle exit 7000m/s and temperature of 25000-30000 K. Reactants injected into the plasma jet undergo complicated radical reactions. Interaction of plasma with injected reactants depends on energy settings of the WSP plasma torch and lasts from 5 to 10 ms. Droplets of inorganic compound solution are fed to the plasma jet by pressurized spray nozzle device. Compounds of AgI,AlIII,TiIV,PtIV,VV, and CrVI undergo decomposition in the extremely high plasma temperature and the decomposed products are collected in liquid separators. Size of the produced nanoparticles in unsettled fraction is from 10 to 200 nm and depends primarily on concentration of inputting aerosol particles. In the case of 15 seconds reaction time and use of saturated solutions at 20°C, one can obtain colloidal solutions with silver, platinum, alumina, titania, vanadia, and chromia nanoparticles in concentrations of 3 to 180mg
|
|
| |
|
|
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.
|
|
| |
|
| |
|
|
Treatment of tungsten carbide in low temperature plasma
Brožek, Vlastimil ; Matějíček, Jiří ; Neufuss, Karel
Tungsten carbide powder was thermally processed in a water stabilized plasma, using the WSP plasma torch developed in the Institute of Plasma Physics, where the plasma temperatures can reach 30 000 K at the nozzle exit. Oxidation of the molten carbide was suppressed by a nitrogen atmosphere during deposition on substrates positioned immediately above liquid nitrogen level. Analyses of both the deposits and spheroidized particles in the 5 – 63 μm size range determined the W:W2C:WC ratios and mechanical properties.
|
|
|
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.
|
|
|
Plasma deposition of tungsten coatings
Brožek, Vlastimil ; Matějíček, Jiří ; Neufuss, Karel
Tungsten coatings on steel or ceramic substrates were prepared by water stabilized plasma generator WSP®. It operates on the Gerdien arc principle and produces plasma reaching temperatures up to 28000 K and velocities several Mach at the nozzle exit. Tungsten particles are melted and accelerated to velocities 30-70 m/s in the turbulent plasma that transports them to the substrate, where the particles rapidly solidify, forming characteristic splats and porous coatings. Protection of the molten 20-63 μm tungsten particles against oxidation by argon and acetylene shrouding was found to be inadequate. Therefore, a new method was tested, using hydrogen as a carrier gas in a special, house-built powder feeder. Another modification of the spraying process consisted of admixture of stoichiometric amount of tungsten monocarbide. During melting, it decomposes to W2C and carbon, which oxidizes and forms a protective cloud of carbon monoxide around the particles.
|
guest ::
