Online evolved gas analyses (EGA by TG-FTIR and TG/DTA-MS) and solid state (FTIR, XRD) studies on thermal decomposition and partial reduction of ammonium paratungstate tetrahydrate

Imre Miklós Szilágyi, János Madarász, Ferenc Hange, György Pokol

Research output: Contribution to journalArticle

19 Citations (Scopus)

Abstract

Ammonium paratungstate tetrahydrate (NH4)10[H 2W12O42]·4H2O (APT), a starting material in powder metallurgy of tungsten, has been subjected to a complex thermoanalytical study. The weight loss stages and the various heat effects have been followed by simultaneous thermogravimetry and differential thermal analysis (TG/DTA) in flowing 10% H2/Ar and 10% H 2/He atmospheres up to 600 °C. Meanwhile evolution of gaseous products has also been analyzed and monitored by both on-line coupled mass spectrometer (TG/DTA-MS) and infrared gas cell (TG-FTIR). In atmospheres containing 10% H2, the evolution courses of H2O and NH3 traced by these EGA-methods and the TG/DTA curves up to 380 °C have been found quite similar to those of measured in air or in pure He. Effect of the reductive medium occurred above 380 °C, where solid products of intermediate temperatures have been structurally evaluated by both FTIR spectroscopy and powder X-ray diffraction (XRD). Based on significant changes in XRD patterns, the only small exothermic heat effect observed at 420-440 °C is assigned to the crystallization heat of a mixture of partially reduced tungsten oxide bronzes.

Original languageEnglish
Pages (from-to)583-586
Number of pages4
JournalSolid State Ionics
Volume172
Issue number1-4 SPEC. ISS.
DOIs
Publication statusPublished - Aug 31 2004

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Keywords

  • Ammonia
  • Ammonium paratungstate tetrahydrate
  • Coupled TG-EGA-FTIR
  • Coupled TG/DTA-EGA-MS
  • Evolved gas analysis
  • FTIR
  • Hydrogen
  • Simultaneous TG/DTA
  • Thermal decomposition
  • Water
  • XRD

ASJC Scopus subject areas

  • Chemistry(all)
  • Materials Science(all)
  • Condensed Matter Physics

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