The metastable phases of tungsten oxides or oxide bronzes, such as the hexagonal and the pyrochlore-types AxWO3, have caught much attention because of their one- or three-dimensional opened-tunnelling structures. They have been used in the fields of electrochromic devices, humidity and gas sensors and secondary battery.

Ammonium paratungstate（APT）is white crystalline salt, with the chemical formula (NH4)10(H2W12O42)•4H2O. It is the most important raw material for most of tungsten products. Intermediates such as tungsten trioxide, tungsten blue oxide, tungstic acid, can be obtained from APT, either by thermal decomposition or chemical conversion.

Tungsten powders are produced from wolframite or scheelite ores through the intermediate product of ammonium paratungstate (APT) or ammonium metatungstate (AMT). The existence form of As is FeAsO4 in scheelite ores and its weight percentage is amounts to 0.03–0.3%. Arsenic is removed as an injurious impurity in the preparation process of AMT (or APT). However, this process is very complicated and there is still about 0.001 wt% of As remained in the AMT (or APT).

It is discovered that arsenic could refine tungsten powder grains, makes it possible to use As in the scheelite ores to produce nanocrystalline tungsten powder by hydrogen reduction. keep and utilize the arsenic in scheelite ores to produce nanocrystalline W powders by hydrogen reduction tungsten oxide method. The W–As composite nanopowders have been produced using ammonium paratungstate as raw material.

The synthesis method of W–As composite nanopowders is as below: Commercially available ammonium metatungstate (AMT, purity >99.9%, mean particle size: 7.8 μm), ammonium paratungstate (APT, purity >99.9%, mean particle size: 37.5 μm) and arsenic (As) were purposely used as the raw materials. As-doped AMT (or APT) precursors were synthesized by a solution chemical process through a nitric acid solution (HNO3). The details of the precursor synthesis were described as following: firstly, arsenic was dissolved into an aqueous solution of 65–68 wt% nitric acid; then AMT (or APT) was added into the mixture solution of nitric acid and arsenic; lastly, the solution was dried at 80 °C in oven for 12 h to remove moisture and homogeneous mixture precursors were prepared. Four composite precursors of AMT, AMT–0.01%As, AMT–0.1%As, AMT–1%As (weight ratio of AMT:As equal 100:0, 99.99:0.01, 99.9:0.1 and 99:1, respectively) were synthesized by the above steps, respectively.

Thermal processing (calcination and reduction) of the precursors was carried out in a tube furnace. The four AMT–As composite precursors were calcined at 600 °C in non-flowing air for 2 h to form As doped WO3 composite powders, respectively. Subsequently, the As doped WO3 composite powders (3.0–4.0 g) were filled in an alumina ceramic boat with a size of 60 × 30 × 14 mm. The reduction process was carried out in a tube furnace at 800 °C for 3 h and cooled to room temperature in a flowing hydrogen (dew point: −40 °C), resulting in four samples of As doped W powders were prepared by this process and noted as W, W–0.01%As, W–0.1%As and W–1%As, respectively. All heating rate was controlled at 5 °C/min.

In summary, the W–1%As composite nanopowders with WAs2/W core–shell structured were prepared by AMT–1%As as raw materials combined with hydrogen reduction at 800 °C for 3 h. The W–1%As composite powders were uniform with the diameters about 80 nm. The WAs2 intermediate phase existed in the interior of tungsten grains and played an important role as heterogeneous nucleation core in the process of W nucleation, as a result of increasing the number of the nucleation.

The development of high-performance plasma-facing materials (PFMs) is one of the key issues in realizing the safe application of nuclear fusion reactors. The extreme working environment of PFMs in fusion devices is primarily characterized by high thermal load, high-energy particle bombardment, and high flux hydrogen (H)/helium (He) plasma irradiation. Tungsten and its alloys are promising plasma-facing materials (PFM) that were used for the international thermonuclear experimental (ITER) divertor and have been regarded as the most promising plasma materials for future fusion reactors.

Titanium dioxide (Titania) has been utilized in photocatalysis since the discovery of the early 1970s. Since then, researchers have developed a variety of methods to tune the nanostructure and the composition to optimize the photocatalytic efficiency. Compared with nanoparticles or the bulk materials, nanotubular-structure titania possesses larger specific surface area and stronger adsorption capacity that results to a better photocatalytic effect. These unique chemical and physical properties allow titania nanotubes (TNT) to be widely used in sewage treatment, air purification, and sterilization areas.