Eddy-current-resistant SmCo5/CaF2 magnets produced via high-energy milling in polar and non-polar liquids

Abstract

Processes of high-energy ball milling of SmCo5 alloys were compared for three single-liquid environments without using additional surfactants. Both coarsely grained as-cast and nanocrystalline pre-milled SmCo5 precursors showed tendency toward formation of thin flakes if milled in polar liquids (acetone and ethanol) in a marked contrast to milling in non-polar heptane. CaF2 dielectric powder added prior to milling in the polar liquids tends to become attached on the flake surfaces. Milling in heptane in the presence of CaF2 produces flake-like SmCo5 particles which with increasing the milling time are found to incorporate an increasing amount of CaF2. The SmCo5—5wt% CaF2 mixtures milled for the optimum time in both the polar and non-polar liquids were successfully hot-pressed into laminated composite magnets having intrinsic coercivity of 25–30kOe, maximum energy product of approximately 6.5MGOe and electrical resistivity of 500–600μΩcm, which is more than 7 times the resistivity of conventional Sm–Co magnets.