Study On Preparation And Static Magnetization Property Of Ferromagnetic Hollow Particles

The template preparation technique is the best method of fabricating hollow particles with controllable diameter. In this paper we prepared sub-micron hematite and ferromagnet hollow particles by template preparation techniques. The shell contains a large of mesoporous with thickness easily controlled in the range of 30-70nm.The investigation inclosed three special studies: (1) Synthesis and characterization of P(St-AA)template particles; (2) Preparation and characterization of P(St-AA) / Fe2O3 core-shell particles; (3)Calcination and characterization of ferro -magnet hollow particles. The main results are summarized as followings:In the first part, carboxylfunctionalized P(St-AA) colloid particles with diameter in a narrow bound were prepared by seed emulsifier-free emulsion polymerization. The experiment results indicate that the particle size is proportionate to the concentration of styrene and the ratio of AA/St. TEM images and IR spectra show that the AA was polymerized on the surface of PS particles and core-shell structure formed. The study of room temperature stability of P(St-AA) colloid emulsion shows the carboxylfunctionalized colloid particles cannot stay in water for a long time, but can be preserved after vacuum desiccation.The second part reported a novel and simple liquid phase deposition method to produce core-shell structure particles. The prepared P(St-AA) / Iron compound core-shell particles with Fe2O3 crystals coats on the P(St-AA) colloid particle and forms a strawberry like shape. During the process course there are two phase transformations from Fe(OH)3 to FeOOH and from FeOOH to Fe2O3,and H+ ion redound to facilitate the transformations to form a perfect coating layer. The thickness of the coating layer can be easily controlled by adjusting the concentration of Fe3+ ion and repeating the coating process. This method should be extendible to prepare composite particles of other materials.The third part studied the heat treatment conditions and has for the first time mentioned that the structure like strawberry is propitious to fabricate hollow particles. But the over-thick coating layer, over-rapid and over-slow heating rate make against to it. The structure and configuration did not devastated while the hematite hollow particles were deoxidizing to iron hollow particles at 500℃ in hydrogen. The diameter of the hollow particles was determined by the size of the copolymer template, and the wall thickness relied on the thickness of the coated layer. The iron hollow particles show better anti-oxidization ability at room temperature. They have typical ferromagnetic behavior, with saturation magnetization achieving 95.26 emu/g and maxium energy loss of the hysteresis loop increasing to 1.464E+3 J/m3. These properties are propitious to using the iron holloe particles as wave absorbing materials while their main mechanism of wave absorbing is energy loss.