Plasmachemical preparation of lead-tungstate bronze

0109587 - UFP-V 20040140 RIV CZ eng C - Konferenční příspěvek (zahraniční konf.)
Brožek, Vlastimil - Janča, J. - Eliáš, M.
Plasmachemical preparation of lead-tungstate bronze.
[Plazmochemická příprava olovnato-wolframové bronzi.]
Proceedings of the 14th Joint Seminar "Development of Materials Science in Research and Education". Praha: MAXDORF,s.r.o, 2004, s. 13-14. ISBN 80-7345-032-1.
[Joint Seminar Development in Material Science Research and Education/14th./. Lednice (CZ), 31.08.2004-03.09.2004]
Výzkumný záměr: CEZ:AV0Z2043910
Klíčová slova: tungsten bronzes, plasmachemical preparation, RF-discharge
Kód oboru RIV: JH - Keramika, žáruvzdorné materiály a skla

Tungsten bronzes are materials based on tungsten oxide that exhibit different colours, excellent chemical resistivity, metallic appearance and good conductivity. The doped tungsten bronzes may by used as anodic catalyst in fuel cells. The tungsten bronzes are prepared by reduction of tungstates. The reduction process is known for very long time, but the correlation between their stoichiometry, conductivity and colour are not yet completely understood. The published results about colour of products are very often misleading. In this paper, we study chemical reactions between lead-tungstate and hydrogen plasma. The reduction was performed in an inductively coupled r.f. discharge. The r.f. generator operated at the frequency of 27 MHz with the power output of 1 kW. The PbWO4 was heated by the discharge to the temperature of 900°C. The resulting samples were analysed by SEM, XRD and three point L*a*b* method. The XRD spectra of our plasmachemical product show diffraction patterns of metal tungsten and lead-tungstate bronze with a cubic phase similar to Pb0,261WO3 (P4/mbm). The diffraction peaks of original lead-tungstate bronze are higher for the sample reduced only 60 min than for 120 min. To obtain data for process kinetics observation, further experiments were performed with ground lead-tungstate powder at two size fractions. Analytical balance, after determining the W and Pb content, showed the bronze composition to be most likely close to Pb 1-X = 0,225.

Redukcí PbWO4 v induktivně buzeném vodíkovém plazmatu při 900°C byla připravena olovnato-wolframová bronz Pb0,261WO3 a metodou DE* změřeny parametry její barevnosti. Dále byla ověřena struktura této látky a sledovány změny obsahu kyslíku v závislosti na době redukce.
Trvalý link: http://hdl.handle.net/11104/0016696