Study Preparation And Mechanism Of High Properties MnZn Ferrites

MnZn ferrite is the key materials of modern electronic industry and information industry. With the rapid development of telecommunication and computer technology, MnZn ferrite is required for better performance. According to application characteristic, MnZn ferrite can be divided into three kinds, power ferrite, high permeability ferrite and EMI ferrite. Now the power ferrite is developing to use in higher frequency with lower power loss. For high permeability ferrite, higher initial permeability with better stability is needed. For this reason, this dissertation presents a deeply study on the preparation technology and mechanism of high properties MnZn ferrite.The magnetic origin of MnZn ferrite can be interpreted by the crystal structure of MnZn ferrite. The relationship between magnetic parameters such as magnetic torque, Courier temperature, saturation magnetic inductin, et al, and magnetic properties of MnZn ferrite have been studied using theory of Neer molecular field. The mechanism of MnZn ferrite magnetic characteristics, such as loss and initial permeability is discussed from the concept of magnetic domain. The methods of lowering power loss and improving the initial permeability are indicated.The preparation technology of MnZn ferrite is discussed. Some aspects of preparation technology should be considered completely. The formation mechanism and solid reaction kinetics of MnZn ferrite is studied. The effect of sintering parameters such as sintering temperature, atmosphere, cooling speed, on the MnZn ferrite magnetic properties is also discussed.The key technology for preparation low power loss MnZn ferrite is added in proper content dopants and sintered under optimal sintering condition. The effect of dopants CaCO3,SiO2,TiO2,ZrO2,Ta2O5,Er2O3 on the magnetic properties of power MnZn ferrite is systematically studied. The results showed that the magnetic loss of MnZn ferrite is lowered with containing proper content dopants in MnZn ferrite. From studying the microstructure of MnZn ferrite contained these dopants, the conclusion is drawn that the dopants atoms are enriched in the grain boundaries and developed a high ρlayer to lower the eddy current loss. The effect of SnO2 on the magnetic properties of MnZn ferrite is also studied. At this moment, the calcinations temperature is decreased. High properties MnZn ferrite is obtained. SnO2 added to MnZn ferrite dissolves in the ferrite grain during sintering and induces an excess amount of Fe2+, which form stable Fe2+-Sn4+ pairs. These pairs do not participate in the hopping mechanism and improve the grainρ. Part Sn4+ ion with the other ion enriched in the grain boundaries and developed a high ρlayer to lower the eddy current loss. The effect of nano-SiO2 and CaCO3 addition on the power loss of MnZn ferrites is investigated ultimately. The MnZn ferrite with nano-dopants can produce uniform grain structure and decrease the hysteresis and eddy current losses. These losses are thought to originate from the additive effect of Si atoms, which are enriched in grain boundaries to form a high resistivity layer and prevent Ca and Nb atoms being incorporated with the spinel lattice. High properties MnZn ferrite can be gained by sintering at optimum sintering temperature and equilibrium atmosphere.The key technology for preparation high initial permeability MnZn ferrite is chosen proper component, added in proper content dopants and sintered under optimal sintering condition. The effect of dopants Bi2O3,Mo2O3,PbO,Co2O3 and B2O3 on the magnetic properties of high permeability MnZn ferrite is systematically studied. The results showed that the permeability and density of MnZn ferrite is increased with containing proper content dopants in high permeability MnZn ferrite, for these dopants can promote grain growth.