Preparation And Properties Of Low Temperature Sintering Of Y-type Hexagonal Ferrite

Y-type hexagonal ferrite with planar magnetic structure have much higher initial permeab-ility,higher factor of quality and higher cut-off frequence in very higher frequence (VHF) and ultrahigh frequence (UHF) regions (300～800MHz), which make these materials the ideal cho-ice for preparing MLCI. Currently, the main development direction of chip inductor is multi-la yer chip inductor, However, the low-fired ferrite with high magnetic properties has been a key problem of MLCI production.The Y-type hexagonal ferrite powder was synthesized by co-precipitation, and disussd the pivotal technological conditions included pH, temperature, Rotate speed, Flow velocity of salinesolution, the concentration of CO32- and the concentration of SDBS. The particle of precursor was studied by Laser particle size analyzer (LPS), The results showed that the particle sizes were around 3μm and the minimum to maximum between 2.28～4.47μm, the conditions was pH=10.50, T=50℃, R=300rpm, V=0.35ml/min, SDBS=0.3～1.0g/L; the precurosr was calcined at 900℃then the mangnetic rings was sintered at 1000℃, the phase of ferrite were characterized via X-ray diffraction (XRD) indicated 0.3g/L of SDBS was better than others. The vibrating sample magnetometer (VSM) and HP4291A impedance analyzer were used to investigate magnetic properties, It was observed that the optimized technological conditions: pH=10.50, T=50℃, R=300rpm, V=0.35ml/min, SBDS=0.3g/L, at 100MHz, the specific saturation magnetization, coercitive force, residual magnetization, initial permeability and factor of quality of the sample wereσs≈29.72A·m2·kg-1,Hc≈4.11kA·m-1,σr≈7.74A·m2·kg-1,μi≈9 and Q≈18 respectively.The homogenous precursor with fine particles and high activity was calcined at different temperature from 600 to 1050℃. The variation of the composition and microstructure in the sintering process were characterized via Thermogravimetric analysis and Differential thermal analysis (TGA-DTA), X-ray diffraction (XRD) and Scanning Electron Microscope (SEM). It was observed that well defined hexagonal was formed at lower temperature (900℃) accompanying for crystal structure transition. The ceramic samples presented excellent ultrahigh frequency magnetic properties, the saturation magnetization arises with the ascending temperature, while initial permeability decreases with increasing heat treatment temperature first but rises to apex in the end. After sintered at 900℃at 100MHz, the specific saturation magnetization, coercitive force, initial permeability and factor of quality of the sample were 17.262 A·m2·kg-1,Hc≈5.146 kA·m-1, andμi≈7, Q≈14 respectively.Additions of Bi2O3 were used to decrease the sintering temperature and enhance the densification of Co2Y ferrite, with a small amount of Bi2O3 (0.5～2.0wt%) as a sintering aid. The samples were sintered at different temperatures (800℃,850℃,900℃,950℃), relative density was tested by displacement method, it showed the ceramic doped with 1.0wt% Bi2O3 and sintered at 900℃for 4h has high relative density and permeability, the relative density was 95% andμi≈10, Q≈13 respectively.