Magnetite nanoparticles prepared by precipitation from partially reduced ferric chloride aqueous solutions

Spherical magnetite particles with mean diameter of about 10 nm or less wer e prepared by means of a reduction-precipitation method with ferric chlorid e as starting material, which was partially reduced to ferrous salts by Na2 SO3 before alkalinizing with ammonia. It was found that the nature of the p roduct depends strongly on the initial ratio R-0 = [Fe3+](0)/[SO32-](0). Th e most appropriate ratio was 3 as proved by X-ray diffraction analysis on t he samples although the initial concentration of ferric chloride can be dif ferent. Particle diameter increased from ca, 3 to ca, 11 nm with an increas e 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 intermedi ate during the reduction process, which enables us to prevent the reoxidati on of the ferrous ions by adding precipitation agents at the end of the red uction reaction without the protection of nitrogen or argon, (C) 1999 Acade mic Press.