Homogeneous precipitation of uniform alpha-Fe2O3 particles from iron saltssolutions in the presence of urea

Uniform alpha-Fe2O3 particles within the nanometer range (100-300 nm) have been obtained by precipitation of iron (III) perchlorate in the presence of urea. Different morphology, from spheres to ellipsoidal particles with axi al ratio up to similar to 10, was obtained by adding to the initial solutio n increasing amounts of phosphate anions up to 7 x 10(-3) M. The main targe ts of this work are the reduction in particle size and precipitation time a nd the increase of the particles axial ratio, keeping a narrow particle siz e distribution, in comparison to other methods previously developed to obta in homogenous alpha-Fe2O3 particles. A detailed analysis of the reaction pr oducts and a systematic study of the influence of the different precipitati on conditions on the characteristics of the resulting particles have been c arried out, Finally, some information on the formation mechanism of the ell ipsoidal hematite particles in the iron (III) salt-urea-phosphate system is also given. (C) 1999 Academic Press.