In-Situ Formation of WO₃ Nanowires as Well as Tungsten Nanoparticles by Oxidation-Reduction Mechanism

It is suggested in current paper that WO₃ nanowires can be formed due to partial oxidation of tungsten particles and evaporation of resulted WO₃ at high temperature during sintering. It led to formation of needle like WO₃ nanowires with uniform distribution throughout compacts. These nanowires may be created based on nucleation and growth mechanism. By adequate controlling the thermal condition during sintering, linear growth of WO₃ nucleus will be predominated and then, linear growth of nanowires occurred. Subsequently, by interaction between WO₃ nanowires and hydrogen atmosphere, tungsten nanoparticles are formed on the micro-particles. Consequently, simple micro-particle powder mixture is replaced by a mixture containing uniformly distributed nanoparticles [1]. This in-situ formation of WO₃ nanowires following by in-situ formation of tungsten nanoparticles is illustrated in Figure 1. In summary, current proposed mechanism can be separated into some subsequently stages.

Figure 1:Different stages during in-situ formation of tungsten nanoparticles during sintering (a) formation of WO₃ nanowires due to nucleation of WO₃ vapors and subsequently linear growth, (b) hydrogenreduction of needle like WO₃ nanowires and continues formation of nanoparticles, (c) micro-particles are completely covered by nanoparticles that activate sintering of compact remarkably. .

On the other hand, when the sintering temperature continues to raise, reduction of WO₃ nanowires take place. Due to nanostructure of WO₃, reduction of nanowires resulted into formation of tungsten nanoparticles around the former particles (Figure 1b & 1c) It is well known that the hydrogen reduction process has a great effect on the morphology of the reduced tungsten particles, especially on the diameter [2]. It resulted into homogenous distribution of nanoparticles in the whole of system. Tungsten nanoparticles formation on the micro particles exhibits activating sintering at low temperature owing to the size effects. Accordingly, the sintering stress between nanoparticles and nanoparticle and micro-particle makes mass transport enhanced in the case of nanoparticle addition [3,4]. It led to enhanced densification in presence of nanoparticles.

1. Ahangarkani M (2018) Int J Refract Metal Hard Mater 70: 93-100.
2. Qin M (2017) Int J Refract Metal Hard Mater 68: 145-150.
3. Hyesook J (2011) Rev Adv Mater Sci 28: 200-206.
4. Tolochko OV (2009) Rev Adv Mater Sci 28: 192-197.