The rapid and catalyst-free flame synthesis of α-Nb_2O_5 micro/nanorods is reported. The synthesis is performed using 1mm diameter Nb probes (～%99.9 purity) as a metal source inserted in the oxygen-rich zone of a counter-flow flame. The fuel stream (96%CH_4 + 4%C_2H_2) flows from the top nozzle and the oxidizer stream (50%O_2 + 50%N_2) to the bottom nozzle. Probes were introduced radially into the flame parallel to the nozzles' planes. The Nb probes were inserted at two different heights of Z=12 mm and Z=13 mm. Z represents the distance between the fuel (top) nozzle and the center of the probe. Niobium oxide structures grow nearly instantaneously forming a white semi-oval layer of material surrounding the surface of the Nb probe. The morphology of the oxide layer strongly depends on the position of the probe inside the flame (temperature and oxygen content). At Z=12 mm the Nb oxide layer is composed of coalesced microrods with a diameter of ～1 μm. At Z=13 mm the formed Nb oxide layer is composed of individual and coalesced micro/nanorods with diameters ranging from 50 nm to 1 μm. The HR-TEM and SAED images reveal that grown nano/microrods are highly crystallized, monoclinic crystals with growth direction of [110]. The growth mechanism is discussed.
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