| Magnetic materials are the important mainstay and elements of the national economy and defense industry. They play an important role in the computer, storage, processing and transmission of information. As the typical magnetic metal, the synthesis of cobalt or nickel and their magnetic properties have attracted extensive attention. In this thesis, The hollow cobalt spheres and hexagonal cobalt sheet was prepared in the surfactant system, and spinous sphere nickel also was prepared by hydrothermal reaction. The chain-like structure of cobalt hollow spheres, tower-like structure of cobalt, and chain-like structure of nickel was prepared by introducing the magnetic field. As well as the product of magnetic properties have been studied, the relationship between the structure and their magnetic properties was discussed.1. Preparation of Cobslt Hollow Spheres in the Surfactant System and the Magnetic PropertiesThe hollow cobalt spheres were prepared in the surfactant Brij30 system, and the structure was converted to hexagonal cobalt sheet. Various reaction conditions were studied. It was found that with the surfactant Brij30 concentration increased and reached 4.12×10-4 mol/L, the structure of product changed to the hollow structure, and only in the non-ionic surfactant Brij30 conditions can get the of hollow spheres structure product. The higher temperature is conducive to cobalt nucleation and crystallization. High temperature is also lead to the pore formation. By adjusting the pH value, the product can be converted to the hexagonal sheet structure. The saturation magnetization of controlled structured products are significantly improved.The formation of hollow cobalt mechanism was discussed, the study found that the high temperature made Brij30 dehydration and diffusion, the solid sphere depressed, resulting in hollow structure formation. 2. Self-assembly of Cobalt with Different Structure by Magnet Deposition and the Magnetic PropertiesChainlike structure of cobalt hollow spheres and towerlike structure products were obtained successfully by the introduction of magnetic field. It was found that the magnetic field is the main reason for the formation of chain structure, the role of surfactants is mainly on the hollow structure, and the other reaction condition has little effect on the chain formation. The pH value has a great affect on the structure of the products. The high pH makes the product of structure changes to the towerlike structure. The magnetic field is also the main reason for the towerlike structure.The saturation magnetization of chainlike structure is higher than the products of separated spherical structure.3. Preparation of Spinous Spheres Nickel in the Surfactant System and the Magnetic PropertiesSpinous spheres nickel was synthesized by one step hydrothermal reaction in water system without surfactant. The reaction conditions were studied and the results showed that the spinous spherical nickel is assembly of nickel nanoparticles with the reaction time increased. The suitable reaction temperature for spinous is 160°C, when the reaction temperature is 120°C, the reaction could not proceed. It was found that the additive of anionic surfactant SDS and the high pH value were both inhibited the formation of spinous spherical structure. The additive of non-ionic surfactant Bri30 and cationic surfactant DTAB did not completely inhibit the formation of spinous spherical structure. The structure would converd to the rod structure by changing the solvent to ethanol.The chainlike structure of nickel was also obtained through the introduction of magnetic field, it shows that the magnet deposition method may have some commonality in orderly assembly of magnetic materials. Magnetic characterization showed that the aturation magnetic susceptibility of chainlike structure is higher than the products of barbed spherical structure, and the barbed spherical structure is higher than separated nanospheres structure. |
PDF Full Text Request