Facile Synthesis of Single-Phase Alpha-Tungsten Nanopowders from Ammonium Paratungstate by RF Induction Thermal Plasma and Thermochemical Reduction

Facile, economic methods of preparing tungsten (W) nanopowder are critically needed to meet industrial demand. Herein, we report a method of preparing single-phase alpha-W (α-W) nanopowders using ammonium paratungstate (APT) as a starting material and the optimum synthesis conditions. The process involves two stages: i) the radio-frequency (RF) induction thermal plasma treatment of APT, followed by ii) thermochemical reduction at 600-900 ℃. The crystallographic phase and morphological evolution of all products were systematically investigated using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), and transmission electron microscopy (TEM), and the effects of the annealing temperature on the phase and particle size of the obtained powders were also evaluated. When the RF induction thermal plasma treatment was conducted with and without H2, the XRD and FESEM results showed the formation of mixed-phase α- and beta-W (β-W) nanopowder and WO3 nanopowder, respectively. Single-phase α-W nanopowder was achieved by annealing the WO3 nanopowder in an H2 reductive atmosphere at 700 ℃ for 10 min, resulting in homogenous nanoparticles with a small particle size (d50) of 21.16 nm without any aggregation. (Received July 14, 2020; Accepted September 9, 2020)