Synthesis of Na_xCoO₂ Fine Particles by Ultrasonic Spray Pyrolysis Method

Abstract

Na_xCoO₂ powders with sub-micron, narrow-size-distribution, and phase-pure particles were synthesized by ultrasonic spray pyrolysis method from an aqueous cobalt nitrate and sodium carbonate solution. A tubular furnace with six independently controlled heating zones was used in the synthesis. The effect of gas flow rate and axial temperature profile in the reactor on the composition of as-prepared powders was examined with X-ray diffraction (XRD), inductively coupled plasma spectroscopy (ICP) and energy dispersion X-ray (EDX) analysis. Nano-structured β-Na_xCoO₂ fine particles were successfully synthesized at both constant temperature distribution (1073K) and increasing one (473K-473K-673K-873K-1073K-1073K) in the reactor at various gas flow rates. The phase transfer from β-phase to γ-phase Na_xCoO₂ occurred after the as-prepared samples were heated at 1073K for 2h in air.