Preparing AMT from APT

A process for preparing ammonium metatungstate (AMT) using ammonium paratungstate/APT as raw material comprising: leaching wet ammonium paratungstate/APT with nitrite acid to obtain a dilute solution of ammonium metatungstate; concentrating the dilute solution of ammonium metatungstate /AMT to be a concentrated solution of ammonium metatungstate/AMT; and spray-drying the concentrated solution of ammonium metatungstate/AMT to obtain powder of ammonium metatungstate/AMT.

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Tungsten Trioxide Photocatalysts:

Hexagonal (h-) and monoclinic (m-) tungsten trioxide (WO₃₎ nano particles with controlled composition  were prepared through annealing (NH₄)_xWO_3−y. The formation, structure, composition, morphology, and optical properties of the samples were analyzed by powder X-ray diffraction, scanning and transmission electron microscopy combined with electron diffraction, and Raman, X-ray photoelectron, H magic angle spinning nuclear magnetic resonance, diffuse reluctance ultraviolet–visual, and photoluminescence spectroscopy. Oxidized m-WO₃ (m-WO₃ ox) was the most active photocatalyst both in the aqueous and in the gas phase, followed by the oxidized h-WO₃ (h-WO₃ ox) sample. Reduced h-WO₃ (h-WO₃ red) and m-WO₃ (m-WO₃ red) exhibited much lower activity. Thus, in contrast to TiO₂, where crystalline structure (rutile or anatase) plays a key effect in photocatalysis, for WO₃, it is the composition that is of greatest importance: the more oxidized the WO₃ sample, the better a photocatalyst it is. The crystal structure of WO₃ has only an indirect effect, in that it influences the composition of WO₃ samples. Consequently, an oxidized monoclinic WO₃ material will always provide better photocatalytic activity than an oxidized hexagonal one.

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Nanostructure -- WO3

Nanostructured WO₃ has been developed as a promising water-splitting material due to its ability of capturing parts of the visible light and high stability in aqueous solutions under acidic conditions. In this review, the fabrication, photocatalytic performance and operating principles of photoelectrically cells (PECs) for water splitting based on WO₃ photoanodes, with an emphasis on the last decade, are discussed. The morphology, dimension, crystallinity, grain boundaries, defect and separation, transport of photo generated charges will also be mentioned as the impact factors on photocatalytic performance.

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XPS studies on tungsten oxide nano-wire film

WO₃ nano-wire film was bombarded by Ar ion beam in the analysis chamber of an X-ray photo electron spectroscopy (XPS) system to produce uniform tungsten cone arrays. The WO₃ nano-wire film itself served as an etching mask during the Ar⁺ bombardment. The changes of surface chemical states and electronic structures during bombardment were monitored by in situ XPS. The morphological evolution with different Ar⁺bombardment time was observed by ex situ scanning electron microscopy (SEM). At the start of Ar⁺bombardment partial W⁶⁺ in WO₃ was reduced to W⁵⁺ immediately, subsequently to W⁴⁺ and then to W^x+(intermediate chemical state between W⁴⁺ and W⁰), finally to W⁰. Multiple oxidation states of tungsten coexisted until finally only W⁰ left. SEM images showed that the nano-wires were broken and then fused together to be divided into clusters with a certain orientation after long-time high-energy ion beam bombardment. The mechanism of the ion-induced reduction during bombardment and the reason of the orientated cone arrays formation were discussed respectively.

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Crystal Structure of Zirconium Tungstate

The arrangement of the groups in the structure of cubic ZrW2O8 is analogous to the simple NaCl structure, with ZrO6 octahedral at the Na sites, and W2O8 groups at the Cl sites. The unit cell consists of 44 atoms aligned in a primitive cubic Bravais lattice, with unit cell length 9.15462 Angstroms.

The ZrO6 octahedral are only slightly distorted from a regular conformation, and all oxygen sites in a given octahedron are related by symmetry. The W2O8 unit is made up of two crystallographic ally distinct WO4 tetrahedral, which are not formally bonded to each other. These two types of tetrahedral differ with respect to the W-O bond lengths and angles. The WO4 tetrahedral are distorted from a regular shape since one oxygen is unconstrained (an atom that is bonded only to the central tungsten (W) atom), and the three other oxygen’s are each bonded to a zirconium atom (i.e. the corner-sharing of polyhedral).

The structure has P213 space group symmetry at low temperatures. At higher temperatures, a centre of inversion is introduced by the disordering of the orientation of tungstate groups, and the space group above the phase transition temperature (~180C) is Pa .

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Zirconium Tungstate Definition by Wiki

At high pressure, zirconium tungstate undergoes a series of phase transitions, first to an amorphous phase, and then to a U3O8-type phase, in which the zirconium and tungsten atoms are disordered.

Zirconium tungstate (Zr(WO4)2) is a metal oxide with unusual properties. The phase formed at ambient pressure by reaction of ZrO2and WO3 is a metastable cubic phase, which has negative thermal expansion characteristics, namely it shrinks over a wide range of temperatures when heated. In contrast to most other ceramics exhibiting negative CTE (coefficient of thermal expansion), the CTE of ZrW2O8 is isotropic and has a large negative magnitude (average CTE of -7.2x10−6K−1) over a wide range of temperature (-273 °C to 777 °C). A number of other phases are formed at high pressures.

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about ammonium paratungstate (APT)

Ammonium paratungstate, (APT) is a white crystalline salt of ammonium and tungsten.

APT is produced by separating tungsten from its ore. Once the ammonium paratungstate is prepared, it is heated to its decomposition temperature, 600 °C. Left over is WO₃, tungsten oxide. At that point, the oxide is heated in an atmosphere of hydrogen, reducing the tungsten to powder, leaving behind water vapor. From there, the tungsten metal powder can be fused into any number of things, from wire to bars to other shapes.

The WO3 content of APT manufactured and supplied by Chinatungsten Online is over 88.5%.

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