Studies On Magnetic Properties Of High-performance Hexagonal Strontium Ferrites

Magnetic materials are essential for automation of equipments in modern society. As the world changes in the environment, people realize the importance of environment protection and energy. It is an urgent requirement of social development about full use of energy. Permanent magnetic materials are important component of magnetic materials, which provide the necessary magnetic field in the application. Hexagonal ferrite has high coercivity and large saturation magnetization, chemical stability, good wear and corrosion resistance. It is cost effective without Ni, Co or high price of rare earth metals. It occupies most of the permanent magnet market.Our country is the strontium ferrite magnet material major producing country. Our country became the third largest producer of strontium ferrite magnet in 1975. In 1995 our country became the first in the world in strontium ferrite magnets output. Our country has become one of the largest production base and sales of magnetic materials markets, but the technology is not powerful. The core technologies and process of ferrite magnet material production control in the hands of large foreign companies. We prepared high magnetic properties of hexagonal strontium ferrites in this dissertation. It is important for the development of magnetic materials in our country.In this dissertation, high magnetic properties M-type strontium ferrite were prepared by ceramic processing with iron oxide, strontium carbonate as raw materials.We control the ball, feed, water ratio and grinding time in wet ball milling. Contring parameters such as the particle size, water content of wet pressing and magnetic field size. The process of experiment as follows:raw materials--ingredients--milling--pre-sintering--smash--the second additiving--milling--pressing--sintering--performance testing. The samples were studied by X-ray diffraction (XRD). vibrating sample magnetometer (VSM) and permanent magnet material measuring instrument and other equipment. The crystal structure and phase transition process of samples at different temperatures calcined, the impact of external magnetic field on the sample by wet-pressing and the second additives, dispersant were studied. The results were as follows:1, Theγ-Fe2O3 phase diffraction peaks gradually weaken and M phase diffraction peaks gradually change to enhance with the pre-sintering temperature gradually increase. When the pre-sintering temperature rises to 900℃,γ-Fe2O3 phase disappeared, single M-phase strontium ferrites were obtained:2. The sample magnetic properties can be gradually increased with the external magnetic field increases by wet-pressing. When the external magnetic field intensity increases to 550kA/m, the sample magnetic properties can basically do not change with the external magnetic field increases;3. The effects of second additives on the performance of the sample were studied by the wet-pressing experiment. The experiment be performed using combination doping, a single change in a certain additive amount of research methods. We got the appropriate amount of additive by summing up the samples magnetic properties with the changes of CaCO3, Al2O3, SiO2. H3BO3 and dispersant calcium gluconate;4. The optimal additive formulation with 0.8wt%CaCO3,0.8wt%Al2O3.0.2wt% SiO2,0.3wt%H3BO3,0.8wt% calcium gluconate have been established through the orthogonal experiment. The sample has a high remanence and coercivity:Br> 390 mT, Hjc>310kA/m.