Synthesis And Characterization Of Nano-fe₃o₄ Via Ultrsound Enhanced Wet Chemical Method

Nano-Fe₃O₄ is a very important functional material especially used in high-tech electro communication fields. However, it has some disadvantages which restrict its possible wider applications in a few fields. The previous studies show that the properties of nano-Fe₃O₄ mostly depend on preparation method. The improvement of the preparation process has a great theoretical value and could further explore its applications.In this paper we applied ultrasound as an extra enhanced tool to prepare nano-Fe₃O₄ ferrite. Furthermore we especially investigated the effects of different ultrasound parameters on the morphology of nano-Fe₃O₄ ferrite and magnetic properties. The experimental parameters are as follows. (1) Ultrasound frequency: 25kHz, 40kHz, and 59kHz; (2) temperature: 40℃, 50℃, and 60℃; (3) ion ratio: Fe2+: Fe3+ =1.1:2; (4) precipitating agents: NaOH, and ammonia; (5) surfactants: polyvinylpyrrolidone (PVP), polyethylene glycol (PEG), and sodium dodecyl benzene sulfonate (SDBS).The experimental results show that nano-Fe₃O₄ ferrites under ultrasound conditions possess good properties. For example, (1) nano-Fe₃O₄ ferrites have a spherical morphology and narrow particle size distribution (about 15 to 20nm); (2) under lower ultrasonic frequency (25kHz), nano-Fe₃O₄ ferrites possess the smallest average particle size and the narrowest size distribution; (3) the magnetization curve near superparamagnetic saturation magnetization is higher than that of nano-Fe₃O₄ ferrites without ultrasound treatment; (4) the saturation magnetization increased gradually with the increasing of ultrasonic frequency; (5) ultrasound helped to improve the crystallinity of nano-ferrite; (6) the surfactants were useful to reduce the size of Fe₃O₄ moderately, while the effect of surfactants on the magnetic performance of nano Fe₃O₄ ferrite was insignificant.The mechanism of the ultrasound effects was discussed. The main reasons were due to the acoustic cavitation effects of ultrasound (high temperature, high pressure micro-bubble point), and the resulting physical and chemical fields effects, such as vigorous stirring and vibrating.