In situ HT‐XRD Study on the Formation of Hexagonal Ammonium Tungsten Bronze by Partial Reduction of Ammonium Paratungstate Tetrahydrate

Abstract

Keywords: Tungsten / Reduction / In situ studies / X-ray diffraction / X-ray photoelectron spectroscopy / Solid-state 1 H NMR spectroscopy

Structure and thermal decomposition of ammonium metatungstate

“…Previously AMT [1,33,38,[47][48][49][50][51][52] or a structure close to AMT [38] was said to be a decomposition product of APT at 240 °C. Based on these, it was unknown whether the decomposition of AMT would be the same as the decomposition of APT above 240 °C, or it would differ significantly.…”

Synthesis of Fe8V10W16O85 by a solution method

“…On the other hand, X-ray phase analysis has revealed that diffraction pattern of WP sample after heating at 375°C comprises a set of diffraction reflections which can be attributed to hexagonal WO 3 (h-WO 3 , PDF 04-007-2322) and monoclinic WO 3 (m-WO 3 , PDF 00-043-1035) [10][11][12]. We can't exclude, however, content of hexagonal ammonium tungsten bronze (NH 4 ) 0.33-x WO 3-y (HATB, PDF 00-058-0151) in this sample because there is no sharp division of diffraction reflections between h-WO 3 and HATB [10,13,14]. Powder diffraction pattern of WP sample heated at 600°C comprised only diffraction reflections characteristic for monoclinic WO 3 [10][11][12]14].…”

Investigating the solid–gas phase reaction between WO 3 powder, NH 3 and H 2 O vapors to prepare ammonium paratungstate

“…W O 3 powders prepared from the reference APT and from hexagonal ammonium tungsten bronze (HATB, (NH4) 0.33-x WO 3-y ) were used as precursors in the solid-gas phase reactions. HATB was obtained by heating APT at 400 °C in H 2 for 6h [38]. The precursor tungsten oxides with different compositions (oxidized or partially reduced), structures (monoclinic (m-WO 3 ) or hexagonal (h-WO 3 )) and particle sizes (70-90 or 100-300 nm) were prepared by thermal decomposition from APT or HATB by controlling the annealing temperature and atmosphere [39].…”