Fuel additives and heat treatment effects on nanocrystalline zinc ferrite phase composition

Nanocrystalline ZnFe2O4 powder was prepared by the auto-combustion method using citric acid, acetic acid, carbamide and acrylic acid as fuel additives. Pure spinel zinc ferrite with the crystallite size of about 15 nm can be obtained by using acrylic acid as fuel additive. Samples prepared using other fuel additives contain ZnO impurities. In order to eliminate ZnO impurities, the sample prepared with citric acid as fuel additive was annealed at different temperatures up to 1000 degrees C in air and in argon. Annealed powders have pure ZnFe2O4 phase when annealing temperature is higher than 650 degrees C in air. Sample annealed at 650 degrees C in air is paramagnetic. However, annealed powders become a mixture of Fe3O4 and FeO after annealing at 1000 degrees C in argon atmosphere due to Zn volatility and the reduction reaction. (C) 2010 Elsevier B.V. All rights reserved.