Growth of single-crystal W whiskers during humid H2/N2 reduction of Ni, Fe–Ni, and Co–Ni doped tungsten oxide

Numbers of W whiskers were obtained by reducing Ni, Ni–Fe, and Ni–Co doped tungsten oxide in a mixed atmosphere of humid H2 and N2. The phases and morphologies of the reduction products were characterized by XRD and SEM. Intensive TEM and EDS analyses showed that the obtained whiskers were W single crystals which typical have alloyed particles (Ni–W, Fe–Ni, or Co–Ni–W) at the growth tips. The formed W whiskers were presumed to be induced by the alloyed particles. Our experimental results revealed that, during the reduction process of tungsten oxide, the pre-reduced Ni, Fe–Ni, or Co–Ni particles not only served as nucleation aids for the initial growth of W phase from W oxide but also played the roles of catalysts during the reductive decomposition of gaseous WO2(OH)2.