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The Effect of Various Binder Additions on the Magnetic Properties of Soft Magnetic P/M Cores

H.J. Kim, K.S. Kim, J.J. Song, S.C. Yoon, S.I. Kim
Inje University, KR

Keywords: magnetic core, amorphous, binder, diluents


Recently, there has been a growing demand for soft magnetic materials used in miniaturized electromagnetic devices with high performance, which can be used at a high frequency range. These applications include Switch Moded Power Supply, magnetic heads, transformers and electronic devices, etc. Therefore, numerous studies have been performed with the aim to develop the amorphous powder, offering the lowest core loss and high saturation magnetization. According to the previous studies carried out in our laboratory, the core loss of Fe-Si-B amorphous powder compact was approximately ~90 W/kg at 0.1 tesla and ~ 50 kHz [Fig. 1]. On the contrary, the nanocrystalline Finemet powder compact mixed with diluted binders showed a remarkably decreased core loss after heat treatment for stress relief and crystallization [Fig. 2]. The minimum core loss was obtained from the core mixed with 2wt% water glass diluted by DI water at the ratio of 1:2, whose value was less than ~10W/kg (almost ~1/10, compared to conventional powder cores) at 0.1T and 50 kHz. Based on the previous experimental results, the modified powder mixing process showed a good potential to develop the advanced amorphous powder core with excellent magnetic properties. In this study, the Fe-Si-B base amorphous ribbons were fabricated via melt spinning at the cooling rate of about 106 /sec, which were firstly jet-milled, and then ball-milled for 30 hrs to make homogeneous fine powders of ~53 in size. One group of the amorphous alloy powders were mixed with 2wt% of water glass, diluted by DI Water and ethyl alcohol at the ratio of 1:2 and 1:4, respectively. And, the other group of alloy powders were mixed with polyimide, diluted by NMP(N-Methyl-pyrrolidone) at the ratio of 1:4. Cold compaction was performed at 650MPa to form toroidal-shaped soft magnetic cores, which were heat treated at 420 ~ 460 for 1h under a nitrogen atmosphere. The magnetic property of powder core was investigated using a B-H analyzer and a flux meter at the high frequency range of ~ 50KHz. As a result, the amorphous powder composite became to possess the excellent magnetic properties such as permeability and core loss. The microstructure was also observed using high resolution SEM and TEM to analyze the magnetization mechanism.
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