Investigations of the nickel promotional effect on the reduction and sintering of tungsten compounds

In this article, Ni-coated W powders were firstly prepared by a liquid-solid doping method combined with air calcination and hydrogen reduction. X-ray diffraction analysis, scanning electron microscope, transmission electron microscope, X-ray photoelectron spectroscopy and temperature programmed reduction analysis were carried out to investigate the nickel doping process in WO 3 and its influence on the reduction behaviors of tungsten oxides. It reveals that after calcinations most Ni ions would occupy the lattice sites of host W ions and decrease the interplanar spacing of WO 3 . The latter is due to the promotion of oxygen vacancy generation within WO 3 rather than the changes in ionic radius. After hydrogen reduction, the doped Ni atoms precipitate onto the surface of W particles as thin metallic coatings, whereby the size and morphology of reduced W particles are varied greatly with increasing Ni addition. The presence of Ni has also been found to lower the reduction barriers for WO 3 by using first-principles calculation. Finally, W-Ni compacts were sintered at 1500 °C in hydrogen atmosphere and the accelerated densification phenomenon of W alloy upon Ni doping is discussed.