We prepared Fe3O4 nanoparticles using chemical coprecipitation and studied the factors affecting the magnetic characteristics of nano-Fe3O4 particles.We identified four factors and three levels of an orthogonal experiment and investigated these four factors that affect the magnetic characteristics of the Fe3O4 particles.We obtained important information from this investigation.The Fe3+ to Fe2+ molar ratio,the iron precursor salt,the amount of surfactant and the amount of alkali were found to be important.We also studied the influence of the order of alkali and surfactant addition,the aging time and the stirring speed on the magnetic characteristics of the nano-Fe3O4 particles.The Fe3O4 preparation process was also analyzed.
LI JianLing LI DeCai ZHANG ShaoLan CUI HongChao WANG Cui
To improve the pressure capability of magnetic fluid seal with more than a 0.25 mm single edge gap,a magnetic fluid sealing structure with multiple magnetic sources which has five permanent magnets was designed.Magnetic field distributions under the pole pieces of the magnetic fluid seal with single and multiple magnetic sources were simulated by finite element method and its sealing pressure difference could be calculated according to the theoretical formula of the magnetic fluid seal.The effects of sealing gap height and magnetic source amount on the sealing capability were investigated experimentally.The theoretical and experimental results were compared,analyzed and discussed.The results demonstrated that the magnetic fluid seal with multiple magnetic sources was an effective method to improve the sealing capability for the rotary shaft with large gaps.The theoretical results agreed well with the experimental results when the height of the single edge gap was equal to 0.4 mm.However,it was found that when the height of the single edge gap was larger than 0.4 mm,the difference between the theoretical values and experimental values increased with the gap height because part of magnetic source had less or even no effect on magnetic fluid sealing capability.
