Stabilization of Metastable W2C Nanoparticles by Carbon and Formation of WC Core-W Shell Nanoparticles by Thermal Treatment of a W/C Monolith

Investigations of low-temperature-transformation pathways that exist during tungsten carbide formation revealed the novel formation of ‘inverted’ core-shell nanoparticles comprising a tungsten carbide (WC) core and a tungsten shell assisted by an ‘asymmetric heating’ of a compacted tungsten/carbon monolith. X-ray Diffraction (XRD) characterization of the product revealed that tungsten was present in both elemental and carbide forms. The core-shell morphology of the tungsten carbide particles was deciphered from High Resolution Transmission Electron Microscopy (HRTEM) measurements and results from the thermal decomposition of the initially formed metastable W2C nanoparticles. Simultaneously, a portion of the initially formed metastable W2C nanoparticles in the vicinity of excess carbon became stabilized producing carbonensheathed W2C nanoparticles. These findings open new avenues to access unique core-shell morphologies of refractory carbides and for the ambient stabilization of metastable nanoparticles by means of asymmetric heating of monoliths of selected binary or higher compositions. Furthermore, the obtained core-shell nanoparticles provide a platform to produce other experimentally challenging structures. Keywords: Asymmetric, benzene, carbon, core, core-shell, decomposition, disproportionation, heating, HRTEM, shell, solid-state, thermal, tungsten carbide, tungsten, W2C, WC, XRD.