Preparation And Surface Modification Of Fe₃O₄ Nano-particles And The Effect In Magnetic Field

Due to their special physical and chemical properties, nano-sized magnetic particles put up different physical and chemical characteristics compared with general materials. The studies on nano-sized magnetic particles have become one of the most interesting fields in this world. Recently, although there are many preparing methods reported, the excellent technology which can satisfy the industrial producing is seldom heard. Compared with many chemical methods, and according to the valuable experience accumulated in the laboratory for many years, the author continues to prepare the nano-sized magnetic particles by the method of oxidation-coprecipitation phase transformation. The conditions of preparing well proportioned, size-controlled nano-sized magnetic powder material are discussed. The uniformity and dispersion of the Fe₃O₄ nano-particles is developed by surfactant. Meanwhile, the effect and the transformation law of the Fe₃O₄ nano-particles in magnetic field are also studied for its application in practice.The main research aspects are as follows:(1) The preparation of nano-sized magnetite particles. Use two heating styles----dynamic boiling reflux method and static water bath method, change the pH value, temperature, time and the dosage of H2O₂ of the system, study the effect of the generation and the particle size of Fe₃O₄ nano-particles in all conditions, and discuss the magnetic properties of the samples. The results show that the pure Fe₃O₄ nano-particles can be prepared when the pH value is in the range of 8¹2 by the method of dynamic boiling reflux. Along with the increase of the pH value, the particle size of the Fe₃O₄ will reduce gradually. The optimal pH value of getting the small-sized Fe₃O₄ nano-particles is 11.5. The particle size of Fe₃O₄ is in the range of 20⁴0nm by the dynamic boiling reflux method, and the particles are well-proportioned. The Fe₃O₄ nano-particles can be prepared at the room temperature by the method of static water bath. Along with the increasing of the temperature, the crystallization of the products is getting better. The pure Fe₃O₄ nano-particles are prepared at the proper temperature 80 degree centigrade with good crystallization, and the particle size of the products is in the range of 10⁵0nm. The Fe₃O₄ nano-particles which are prepared by the two heating styles both display magnetic properties. The square of the closed magnetic hysteresis loop produced by water bath method is obviously larger than the square which is produced by dynamic boiling reflux method.(2) The surface modification of Fe₃O₄ nano-particlesThe surface modification effect of several surfactants to Fe₃O₄ nano-particles is compared. Sodium dodecyl sulfonate, sodium dodecyl sulfate, CTMAB, sodium diphenylamine sulfonate and SDBS are discussed respectively. Change the heating style and the order of the surfactants which are put into the solution, and change the material rate between the surfactants and Fe₃O₄ nano-particles in order to find out the perfect surfactant and the best condition available. The conclusions are as follows: the sodium dodecyl sulfate performs better effect towards Fe₃O₄ nano-particles. When the material rate between the surfactant and Fe₃O₄ nano-particles is 8:1, the sodium dodecyl sulfate performs the best effect. Compared with the two heating styles, we can find that the Fe₃O₄ nano-particles are prepared in large size by water bath method, the morphology is also different. The method of boiling reflux is propitious to getting nano-sized magnetite particles with small-size and good dispersion. In addition, alter the entrance time of the surfactant, and compare single-visit with double-visit, we can also find that Fe₃O₄ nano-particles are prepared with small-size and good modification by single-visit. Compared with single-visit, double-visit can prepare Fe₃O₄ nano-particles with good modification, but the particle size is a little larger.(3) The liquid-state transformation effect of Fe₃O₄ nano-particles in magnetic fieldDiscuss the variety of the morphology and the particle size of the Fe₃O₄ nano-particles in magnetic field. Simultaneously, change the intensity of magnetic field, time, temperature and the volume of O₂, discuss the liquid-state transformation effect of Fe₃O₄ nano-particles in all conditions. The results show that, the magnetic field can affect the arrangement, the dispersion and the particle size of the Fe₃O₄ nano-particles. The Fe₃O₄ nano-particles arrange along a certain direction like chains in weak magnetic field. Along with the increase of the intensity of magnetic field, the particle-size will reduce, but the dispersion and the uniformity start to get bad. The increase of the intensity of magnetic field, the volume of O₂ and the enhancement of the temperature are propitious to transforming Fe₃O₄. In high magnetic field(E=250mT), insufflate the air, control the temperature at 100℃, and 36 hours later, the Fe₃O₄ nano-particles will transform intoα-Fe2O3 bascially.