|
|
Krystalinita a slinovatelnost wolframu
Brožek, Vlastimil ; Maixner, J. ; Domlátil, J. ; Janča, J. ; Eliáš, M.
Sintering activity of tungsten powders of various origin was tested by modified technique according Agte. The size of crystallites calculated according to Scherrer formula corresponds with density values detected by Mercury porosimetry. Tungsten poder obtained by reduction of tungstates in hydrogen plasma can be recovered to 93 % of theoretical density at the temperature 1350°C. Next increase of the density needs simultaneous application of high pressure. By the BELT technique 95 % density was reached, by plasma spheroidization up to 98 %.
|
|
| |
|
| |
|
|
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.
|
|
| |
|
|
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.
|
|
|
Rozprašovací sušení vícesložkových suspenzí s rozdílnou hustotou
Brožek, Vlastimil ; Domlátil, J.
This article deals with the issues faced during the preparation of multi-component powders having largely different densities in spray dryers. On a model system, TiO2 – W with densities TiO2 ρ= 4,23 g/cm3 and W ρ= 19,3 g/cm3 , processed in an industrial facility with a 100kg/h capacity using a temporary binder carboxyl-methyl-cellulose, the dependence of composition on the size and distribution of primary particles. Compositional changes and inhomogeneous component distribution takes place due to sedimentation in the feed line between the suspension mixer and drying nozzle. The suspension density and the shape factor that influences the transport velocities of the starting powders, also play a role. The overall effect is assessed by analysis of the properties of the final product, plasma sprayed TiO2-W cermet.
|
guest ::
