| Metal powder cores have the properties of high saturation magnetic flux density, outstanding constant permeability. Additionally, manufacturing process for metal powder is relative easier. These characteristics are significant helpful for producing electronic products with excellent performance such as high sensitivity, high accuracy, miniaturization and large capacity, et al. The powder cores prepared by Fe-6.5wt%Si powder of this kind of alloy can achieve excellent magnetic properties such as good DC bias characteristics, high frequency stability and low loss at high frequency which is suitable for technical requirements at high frequency, low voltage and high current power density. Powder cores mentioned above can be partial substitution of Fe, Fe-Ni and Fe-Si-Al magnetic cores in specific application areas.This paper focused on the effects of single phosphate coating, single SiO2 coating and phosphate/SiO2 hybrid coating process on organization and magnetic properties of Fe-6.5wt%Si powder and powder cores by using Fe-6.5wt%Si aerosolized powder as raw materials and combining with scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and AC measuring devices, et al.Ddifferent phosphate Fe-6.5wt% Si powders were researched at different phosphate concentrations. The phosphate layer thickness was gradually increased while increase the phosphate concentration. When the phosphide concentration even higher, significant cracks can be observed between phosphate coating and matrix material or even peeled off. The ruled magnet ring could be only achieved at high concentrations. XRD spectra showed that there is only α-Fe(Si) phase can be observed in Fe-6.5wt%Si powder before and after phosphating, but in FTIR which determineed that the phosphate coating component was FePO4. By using the DSC analysis, phosphate powder occured FePO4 crystallization reaction and synthesis reaction of SiO2 at 550℃,1000℃ separately. When increaseed the phosphate concentration, the saturation magnetization of Fe-6.5wt%Si phosphate powder, the density and the effective permeability of powder cores decreased while the core loss increased. Magnetic core with excellent performance was obtained when the phosphate concentration is 0.04. And the performance can be further improved by increasing pressing force and adding lubricant or binder, but increase annealing temperature will deteriorate the magnetic properties. The addition of 0.8wt% DC-805, gave rise to the optimal properties with μα=34, Ps=2861mWcm-3 at 50 mT,100 kHz.By controlling the contents of TEOS and APTES, Fe-6.5wt%Si powder with SiO2 coating was successfully prepared. Other than SiO2 generated, part of Fe oxidized to Fe2O3 during sol-gel reaction. XRD spectra showed that there was only a-Fe(Si) phase can be find in Fe-6.5wt%Si powder with SiO2 insulating. It was also shows that SiO2 coating powder has stable structure, excellent heat resistance, the SiO2 layer remains there after 600℃ annealing. When added 2mL TEOS, 1mL APTES, the Fe-6.5wt%Si powder cores with SiO2 coating exhibit optimum magnetic properties (μα=31, Ps=2722mWcm-3). Fe-6.5wt%Si powder cores with phosphate/SiO2 hybrid coating can significantly reduced the magnetic core losses and increase the effective permeability due to phosphate coating as the inner layer can effectively adhere to the surface of Fe-6.5wt%Si powder, SiO2 as the outer layer can block the decomposition and crystallization of the phosphate, meanwhile, the density of phosphated powder can be improved by adding SiO2. Compared to single phosphate, SiO2 and organic binder-phosphate coating, the hybrid coating exhibits excellent heat resistance and magnetic properties. Powder cores with optimum performance could be obtained when the phosphate concentration was 0.004, and the content of SiO2 was 0.04 with the effective permeability and total loss is 36 and 627mWcm-3 respectively. |
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