Magnetite Nanoparticles Prepared by Precipitation from Partially Reduced Ferric Chloride Aqueous Solutions.

Spherical magnetite particles with mean diameter of about 10 nm or less were prepared by means of a reduction-precipitation method with ferric chloride as starting material, which was partially reduced to ferrous salts by Na2SO3 before alkalinizing with ammonia. It was found that the nature of the product depends strongly on the initial ratio R0 = [Fe3+]0/[SO2-3]0. The most appropriate ratio was 3 as proved by X-ray diffraction analysis on the samples although the initial concentration of ferric chloride can be different. Particle diameter increased from ca. 3 to ca. 11 nm with an increase of the concentration of aqueous ferric chloride from 0.075 to 0.45 mol dm-3. The advantage of this method lies in the formation of a red intermediate during the reduction process, which enables us to prevent the reoxidation of the ferrous ions by adding precipitation agents at the end of the reduction reaction without the protection of nitrogen or argon. Copyright 1999 Academic Press.