ABSTRACT
The rapid formation of tungsten oxide nanorods through electron beam (EB) irradiation on the surface of micron-sized flame formed tungsten-oxide fragments is reported. The micro-sized fragments (precursor material) were formed in a counter-flow methane diffusion flame on the surface of a tungsten wire. Nanorods of various lengths and aspect ratios were rapidly formed in the surrounding area of a transmission electron microscope copper grid as the micro-sized fragments were exposed to a concentrated electron beam. The EB was produced using a 200 keV transmission electron microscope. The length of the formed nanorods is inversely proportional to the distance of the precursor material. We show that the most significant growth or conversion of nanorods from a flame formed fragment occurs within the first second of the EB irradiation; principally owing to the considerable amount of residual stresses attained in the material as they are formed in a high flame temperature environment. It was found that the produced nanorods are composed of a lower oxygen state of tungsten oxide than the precursor material. A growth mechanism is proposed and discussed.
ABSTRACT
A green, rapid microwave-assisted solvothermal process using tetraethylene glycol (TEG) as a reducing agent has been explored as a soft-chemistry route for the preparation of various lower-valent transition metal oxides. To demonstrate the feasibility of the approach, lower-valent binary oxides such as V4O9, Mn3O4 or MnO, CoO, and Cu2O have been obtained within a short reaction time of 30 min by reducing, respectively, V2O5, MnO2, Co3O4, and CuO with TEG at <300 °C. Moreover, the approach has been used to extract oxygen from ternary oxides such as LaFeO3, SrMnO3, LaCoO3, LaNiO3, and La4Ni3O10. The oxidation state of the transition metal ions and the oxygen content in these ternary oxides could be tuned by precisely controlling the reaction temperatures from 160 to 300 °C. The products have been characterized by X-ray powder diffraction and iodometric titration. The versatility of this novel technique is demonstrated by the facile synthesis of V4O9, which has only been produced recently in single-phase form.
