Low loss Sendust powder cores comprised of particles coated by sodium salt insulating layer

Abstract

Toroid-shaped Sendust powder cores were prepared from cold pressing mechanically pulverized Fe-Si-Al powder that had been coated using an inorganic insulating layer. The present work focuses on the effect of the sodium salt-coated Sendust particles upon the high frequency magnetic properties. Sendust powders, having a particle size range of ∼125 μm, exhibit a high saturation magnetization of 118.9 A·m2/kg and a low coercivity of 56 A/m. The experiments indicate that the sodium-based glass insulating layer synthesized from sodium metaphosphate and sodium metaborate can effectively reduce the change in permeability with frequency or DC bias field, yielding high effective permeability (μe) of ∼113 over a wide frequency range from 10 kHz–1 MHz. Furthermore, the effective permeability is measured at ∼27 at H = 7854 A/m, indicating stable and high effective permeability under a DC bias field. The measurements of permeability under DC bias field indicate a peak in the quality factor (Q) values corresponding to a DC-bias field of 1.5–6 (kA/m) at frequencies from 50 to 200 kHz: The effective permeability remains at ∼74. The sodium salt-coated granular cores demonstrate a core loss of 68 mW/cm3 at Bm = 50 mT and f = 50 kHz: These values compare favorably to those of silicone coated Sendust particles.