Studies on the Preparation and Conditions for the Formation of Ferrites by Hydrothermal Oxidative Crystallizing Method

The conditions for the preparation of ferrites MFe₂O₄（M=Mn,Fe,Co,Ni） were studied by the air oxidation of the suspension which is obtained by mixing M²⁺ ,Fe²⁺ and NaOH solutions.The influence of ratio of reagents,pH values,oxidation temperature and time on the formation of ferrites were examined.The shape and structure of precipitates during the course of oxidation were investigated by XRD and SEM.The results show that the optimum conditions are described as fllow:M_x/3Fe_1-x/3（OH）₂ suspension is oxidized by the air （300mL/h） for 10～25h at 343～358K,R=2OH^-/（M²⁺+Fe²⁺）=1.0 and M²⁺/Fe²⁺ =0.5（molerate）,under these conditions pure ferrites of spinel structure can be obtained.