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Wide temperature and magnetic MnZn power ferrite grain growth kinetics

Author: LiuZuo
Tutor: YuZhong
School: University of Electronic Science and Technology
Course: Materials Science and Engineering
Keywords: MnZn power ferrites dopants microstructure magnetic properties dynamics
CLC: TM277
Type: Master's thesis
Year: 2011
Downloads: 59
Quote: 2
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Abstract


The low melting point dopants can support melting process and improve the grain size in the sintering process of MnZn ferrites. But the study of the low melting point dopants on the way of grain growth isn’t perfect in the MnZn ferrites. MnZn ferrites were prepared by conventional oxide techniques. The influences of ZnO, many kinds of low melting dopants and sintering temperature on the phase structure, microstructure and magnetic properties of MnZn ferrites were investigated. The influences of ZnO and dopants on the way of grain growth and the activation energy of reaction were analyzed.It can be observed that SiO2-CaCO3 dopants mainly segregate in the grain boundary, forming a new phase Ca2ZnSi2O7 with high electrical resistivity. when the concentration of SiO2-CaCO3 dopants is suitable, the microstructure and magnetic properties are improved, but the excessive dopants lead to exaggeated grain growth. When SiO2 dopant is 3.9×10-3wt% and CaCO3 dopant is 6.5×10-3wt%, the loss is the lowest and the initial permeability is the highest. With the increase of SiO2 additive, the grain size is improved, an initial decrease followed by a subsequent increase of the core loss is observed. However, the initial permeability changes contrarily. When SiO2 dopant is 6×10-3wt%, the loss is the lowest and the initial permeability is the highest. The lattice constants increase with the increase of CuO concentrations. When the concentration of CuO dopants is suitable, the microstructure is improved, the initial permeability increases, the power losses decrease. The most suitable concentration of CuO is 1.2×10-2wt%. The lattice constants increase with the increase of V2O5 concentrations. When the concentration of V2O5 dopants is suitable, the microstructure is improved, the initial permeability increases, the power losses decrease. The most suitable concentration of V2O5 is 2.76×10-2wt%. The secondary maximum peak ofμi～T curve moves to lower temperature with the increase of V2O5 concentrations. When V2O5 dopant is 2.76×10-2wt% and CuO dopant is 1.2×10-2wt%, the properties are best. The lattice constants increase with the increase of V2O5 and CuO concentrations. The secondary maximum peak ofμi～T curve moves to lower temperature with the increase of V2O5 and CuO concentrations. With the increase of Bi2O3 concentrations, the grain size is improved, an initial decrease followed by a subsequent increase of the core loss is observed. However, the initial permeability changes contrarily. Excessive Bi2O3 dopants result in the exaggerated grain growth and worsening properties. The most suitable concentration of Bi2O3 is 0.04wt%. With the increase of ZnO concentrations, the secondary maximum peak ofμi～T curve moves to lower temperature and the curie temperatures decrease. The most suitable concentration of ZnO is 12mol%. While the sintering temperature increases, the grain size is improved, an initial decrease followed by a subsequent increase of the core loss is observed. However, the initial permeability changes contrarily. The most suitable sintering temperature is 1350℃.The experiments show that the grain growth dynamics equation is D = K0t exp（-163·53/RT）1/2. The influence of ZnO, low melting point dopants of CuO, V2O5, CuO-V2O5, Bi2O3 on the action energy of reaction and the grain growth of MnZn ferrites was investigated, it can decrease the activation energy of reaction of and promote the grain growth.

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CLC: > Industrial Technology > Electrotechnical > Electrical materials > Magnetic materials,ferrite > Ferrite,oxide magnetic materials
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