PREPARATION AND CHARACTERISTICS OF Fe3O4-ENCAPSULATED BaTiO3 POWDER BY ULTRASOUND-ENHANCED FERRITE PLATING

초록

Fe3O4-encapsulation was performed on the BaTiO3 powders of 500 ㎚ in grain size with ultrasound enhanced ferrite plating to prepare a magnetic- dielectric composite. The effects of the plating condition on the formation of Fe3O4 and the microwave absorbing properties of the Fe3O4-encapsulated BaTiO3 composite were investigated. The encapsulated Fe3O4 grains were magnetite(spinel) and grew in a sperical shape with the diameter of 35 ㎚. With increasing reaction time from 30 to 90 min, the coated thickness was increased up to 45 ㎚. As the molar concentration of a buffer(CH3COONH4) solution was increased from 0.1 M to 0.3 M, the Fe3O4 grains were more densely deposited on the surface of the BaTiO3 powders. At the molar concentration of the reaction solution was 0.06 M, the encapsulation of Fe3O4 occurred to coat all of BaTiO3 powders homogeneously during the plating. For measuring the microwave absorbing properties, specimens mixed with rubber were prepared in a toroidal shape using the Fe3O4/BaTiO3 composite powders. It was observed that the absorbing properties of the specimens were varied by the synthesis conditions of the composite powders. In the specimens of the composite powders, two absorption bands appeared at 8 and 13 GHz, while the specimen of a pure BaTiO3 had only one band at 9 GHz. The two absorption bands of the specimen using the composite powder prepared in the 0.2 M buffer solution had the reflection losses of 24 and 8 dB, respectively. In particular, the presence of the absorbing band at 13 GHz indicates that the composite powders can be used for a broad band microwave absorber. The specimens of the composite powders prepared in the higher concentration of the buffer solution exhibited the thinner matching thickness with increasing the matching frequency. The matching thickness of the composite specimen was reduced to 1.70 ㎜ at the matching frequency of 9 GHz using the powder prepared with the buffer solution of 0.3 M.