Novel mechanochemical process for synthesis of magnetite nanoparticles using coprecipitation method

A novel coprecipitation method using a high mechanical energy field as the synthesis reaction system of magnetite (Fe₃O₄) has been developed for preparing the superparamagnetic Fe₃O₄ nanoparticles with high crystallinity in water system. In the synthesis process, the suspension containing the precipitates of ferrous hydroxide and goethite was treated in a tumbling ball mill under a cooling condition. The mechanical energy generated by collision of ball media promoted the Fe₃O₄ formation reaction and simultaneously crystallized the formed Fe₃O₄ nanoparticles without using any conventional heating techniques by means of the mechanochemical effect. The collision energy of ball media was numerically analyzed by discrete element simulation of their motion in the ball mill. Size, crystallinity and magnetization of the Fe₃O₄ nanoparticles obtained under different ball-milling conditions were almost the same regardless of the amount of the collision energy. However, the reaction rate of Fe₃O₄ formation increased with the collision energy, which was analogous to increase of the reaction rate caused by increase of the heat energy applied to the reaction system. The reaction rate depended strongly on the number of collisions with the energy larger than a threshold value corresponding to the activation energy in this reaction system.