| Summary: | 碩士 === 國立成功大學 === 材料科學及工程學系碩博士班 === 90 === The eddy current loss of the Mn-Zn ferrite increases dramatically as used at MHz frequency range, of which problem can be eased by high saturation magnetization and low hysteresis loss. In order to prepare the kind of the ferrite for the high frequency application, SiO2 was selected as an additive in this study. The tetraethylorthosilicate (TEOS) was used as the precursor of SiO2, and was mixed into Mn-Zn ferrite nano-powders via the sol-gel coating route. The effect of SiO2 on sinterability, bulk density, shrinkage, microstructure and magnetic property of Mn-Zn ferrite were investigated. There are two ways to add TEOS in the Mn-Zn ferrite powders by introducing TEOS via hydrolysis to be adsorbed onto the surface of Mn-Zn ferrite powders at either before or after hydrothermal synthesis reaction. As TEOS was added into the AS-X specimens before the hydrothermal reaction, the silanoxide adsorbed on the surface of the powders would transfer into SiO2 during hydrothermal reaction. In contrast, as the TEOS added into the BS-X specimens after hydrothermal reaction, the TEOS transferred into SiO2 during the heat treatment. Change of the grain size and densification behavior of AS-X sample, sintered at 1100 oC for 2 h in N2 atmosphere, was not substantial. On the contrary, with the amount of SiO2 additive, the bulk density of the BS-X sintered bodies decreased due to the increase of porosity; furthermore, the grain size also increased.
It was found that the permeability, Q factor, saturation magnetization, and coercivity of the AS-X and BS-X sintered bodies increased with the increasing of SiO2 contents. The results showed that SiO2 had a great effect on the magnetic properties of Mn-Zn ferrite. Thus the sintered ceramics with desired magnetic properties can be prepared by the method proposed in this study.
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