Spherical nano-crystalline Co-Fe particles were produced by ultrasonic spray pyrolysis (USP) of aqueous solutions of cobalt-iron chloride followed by thermal decomposition of generated aerosols in hydrogen atmosphere. The effect of the precursor solution in the range of 0.05 M, 0.1 M, 0.2 M and 0.4 M on the morphology and crystallite size of the Co-Fe alloy particles are investigated under the conditions of 1.5 h running time, 800 degrees C reduction temperature, and 1.0 l/min H(2) volumetric flow rate. X-ray diffraction (XRD) studies and Scherer crystallite size calculations show that the crystallite size varies between 25 nm and 27 nm. Scanning electron microscopy (SEM) observations reveal that the the precursor solution strongly influences the particle size of the synthesized Co-Fe alloy particles. Energy dispersive spectroscopy (EDS) results indicate that particles consist of iron and cobalt. Spherical nano-crystalline Co-Fe alloy particles in the range of 100-920 nm were obtained at 800 degrees C. (C) 2009 Elsevier B.V. All rights reserved.