Crystallisation and Processing of Ammonium Paratungstate (APT)

Abstract

This paper starts with the chemistry of tungsten in aqueous solutions. Various aspects of the crystallisation of the hydrates of ammonium paratungstate (APT) will be discussed in addition. This is then followed by the chemistry of the first pyrometallurgical treatment in non-sag (NS) tungsten manufacturing, the processing of APT into tungsten blue oxide. The section is mainly devoted to the chemistry of the thermal decomposition of APT in various atmospheres. Finally, parameters controlling tungsten blue oxide quality will be discussed.

Evaporation-Driven Deposition of WO3 Thin Films from Organic-Additive-Free Aqueous Solutions by Low-Speed Dip Coating and Their Photoelectrochemical Properties

“…When x was larger at 7.57−11.4 mM, on the other hand, the deposition area depended on the solution pH. The deposition on the whole substrate surface was observed at pH below 4.4 (Table 1 and Figure 2a−d), while the coating solutions of pH over 4.7 resulted in the partial deposition (Table 1 and Figure 2e,f), which may be due to the lower and higher solubility of tungsten species in aqueous solutions, 22,23 respectively. The higher (NH 4 ) 10 W 12 O 41 ·5H 2 O concentration (7.57−11.4 mM) and lower pH value (<pH 4.4) could thus provide a large amount of depositions of tungsten species during low-speed dip coating, resulting in the film formation on the whole substrate surface.…”

Sustainable and efficient leaching of tungsten in ammoniacal ammonium carbonate solution from the sulfuric acid converted product of scheelite

“…According to Eq (1), the concentration of NH3• H2O obviously influences the WO3 leaching yield from the converted product, as presented in Fig. 4 Berg, 1988Berg, /1989).…”

Solid-State 183W NMR Spectroscopy as a High-Resolution Probe of Polyoxotungstate Structures and Dynamics

“…Structural analyses of polyoxometalates have mostly relied on X-ray or neutron diffraction to establish the solid-state structures of compounds that can be isolated and purified, complemented by spectroscopic tools such as multinuclear solution NMR, Raman, and X-ray spectroscopies. , An illustrative example is ammonium paratungstate (APT), [NH 4 ] 10 [H 2 W 12 O 42 ]­(H 2 O) x , which is the prototypical precursor to tungsten-derived materials, including W oxides, W alloys, and W-based catalysts . APT is poorly soluble in water and dissolves predominantly through conversion of the [H 2 W 12 O 42 ] 10– anion (paratungstate B) into the [W 7 O 24 ] 6– anion (paratungstate A), followed by aqueous phase speciation that depends on the pH, temperature, and nature of cations. , Solution 183 W NMR spectroscopy has long been recognized as a powerful tool for analyzing dissolved polyoxotungstates − due to the sensitivity of 183 W chemical shifts to local structures. For instance, for APT and related tungstates, it has been used to establish ion binding sites and the influence of pH and temperature on aqueous speciation .…”