Spherical nano-sized iron oxide particles were synthesized by a spray pyrolysis method using the aerosol technique described herein. The effects of reaction temperatures of 500, 700, 900 and 1100 degrees C; the type of carrier gas, i.e., air or argon; and the collection location of the particles, such as the flask collector or the tube exit, on the morphology and crystal structure of the iron oxide particles were investigated. It was observed that the crystallinity of the particles was increased by increasing the reaction temperature from 500 degrees C to 1100 degrees C. Particles collected from both the tube exit and the flask collector had a pure alpha-Fe2O3 phase when air was used as the carrier gas. These nanoparticles had sizes between 70 nm and 675 nm with uniform morphologies. The average particle sizes changed depending on the reaction temperature and collection location. On the other hand, depending on the reaction temperature, the particles collected from both the tube exit and the flask collector were Fe3O4 and/or alpha-Fe2O3 phase when argon was used as the carrier gas. Nanoparticles synthesized using argon as the carrier gas had sizes between 100 nm and 390 nm. A computational fluid dynamics (CFD) model of the horizontally positioned tube reactor was developed. Simulation results provided information about the residence time and the temperature distribution along the tube, which were observed to be correlated to the particle morphology. (C) 2014 Elsevier Ltd and Techna Group S.r.l. All rights reserved.