Thermal decomposition of ammonium paratungstate tetrahydrate under non-reducing conditions
| Autor: | H.-J. Lunk, T. A. Frisk, M. Schneider, Michael Feist, J.N. Dann, Martin Fait |
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| Rok vydání: | 2008 |
| Předmět: |
Ammonium paratungstate
Tetrahydrate Evolved gas analysis Chemistry Inorganic chemistry Thermal decomposition Analytical chemistry Condensed Matter Physics Tungsten trioxide chemistry.chemical_compound Ammonia Differential thermal analysis Physical and Theoretical Chemistry Thermal analysis Instrumentation |
| Zdroj: | Thermochimica Acta. 469:12-22 |
| ISSN: | 0040-6031 |
| DOI: | 10.1016/j.tca.2007.12.007 |
| Popis: | The thermal decomposition of ammonium paratungstate tetrahydrate (APT·4H 2 O), (NH 4 ) 10 [H 2 W 12 O 42 ]·4H 2 O, in air to tungsten trioxide, WO 3 , was investigated under non-isothermal conditions using thermal analysis coupled on-line by a Skimmer ® system to a quadrupole mass spectrometer (TA-MS) for evolved gas analysis (EGA), with X-ray powder diffraction (XRD), with Fourier transform infrared (FT-IR) and Raman spectroscopy. The decomposition is characterized by three endothermic and one exothermic step. The first endothermic step comprises the release of crystal water resulting in the formation of crystal-water-free ammonium paratungstate. During the second endothermic step ammonia is released leaving behind ammonium hydrogen paratungstate, (NH 4 ) 6 H 4 [H 2 W 12 O 42 ]. The presence of protons in the “roasted” APT was supported by ex situ and in situ FT-IR spectroscopy (vibration bands at 1100 and 2160 cm −1 ). Ammonium hydrogen paratungstate is the precursor for the metatungstate anion, [H 2 W 12 O 40 ] 6− , which is formed during the digestion of “roasted” APT with hot water. |
| Databáze: | OpenAIRE |
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