Abstract

Nano magnetite particles have been prepared by two step reaction consisting of urea hydrolysis and ammonia addition at certain ranges of pH. Three different concentrations of aqueous solution of ferric (Fe3+) and ferrous (Fe2+) chloride (0.3 M-0.6 M, and 0.9 M) were mixed with 4 M urea solution and heated to induce the urea hydrolysis. Upon reaching at a certain pre-determined pH (around 4.7), 1 M ammonia solution were poured into the heated reaction vessels. In order to understand the relationship between the concentration of the starting solution and the final size of magnetite, in-situ pH measurements and quenching experiments were simultaneous conducted. The changes in the concentration of starting solution resulted in the difference of the threshold time for pH uprise, from I hour to 3 hours, during which the akaganeite (beta-FeOOH) particles nucleated and grew. Through the quenching experiment, it was confirmed that controlling the size of beta-FeOOH and the attaining a proper driving force for the reaction of beta-FeOOH and Fe2+ ion to give Fe_3O_4 are important process variables for the synthesis of uniform magnetite nanoparticles.

• Keywords: Nano magnetite;Urea decomposition;Co-precipitation;Akaganeite;