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Effects of Particle Shapes on DC-Biased Properties of Powder Cores and Modeling

DC-biased magnetic properties of powder cores made of pure iron powder have been investigated using a nonmagnetic grain boundary (NMGB) model taking into account the distribution of gap width between particles. Three kinds of powder were prepared by water atomization (a), sphericalization (b), and gas atomization (c). Various amounts of additives were added to (a) to investigate the gap width effect between the particles on the powder core (aa). B-H loops were measured, and differential permeability (μdif) was calculated at each magnetic field. They were compared with the value calculated from the NMGB model taking into account the gap width distribution. The more spherical particles were, the lower the μdif was at low magnetic field, and the smaller the fall rate of μdif was at high magnetic field. That indicated the DC-biased magnetic properties improved. From the calculation using the NMGB model, the geometric average value (δgave) of the gap width increased, and the geometric standard deviation(σg) decreased. The effect of μdif on DC-biased magnetic properties was also investigated. The greater the amount of aluminum oxide added to (a), the larger δgave became, the smaller σg became, and the smaller decreasing ratio of μdif at 6 k A/m against 0 k A/m became. However, the decreasing ratio of μdif(C) was smaller than that of (b). Relative inaccuracies for all samples between measured and calculated μdif were under ±6.20% at a magnetic field 0.6-17 k A/m .