| 摘要 |
PURPOSE: To keep a ferrite core high in initial permeability in a wide range of low frequency to high frequency by a method wherein the electric resistivity of the surface of a ferrite core is set higher than that of the center. CONSTITUTION: Materials are so kneaded as to be 25 to 38mol% of MnO, 10 to 25mol% of ZnO, and residual mol% of Fe2 O3 in final basic component composition and sintered in the air into Mn-Zn ferrite sintered powder. Then, a very small amount of CaO and SiO2 is added to the sintered powder for intergranular insulation, which is wet-ground. Binder is added to the ground powder, which is molded like a ring. The molded body is burned at temperatures of 1100 to 800 deg.C in an atmosphere which is so controlled in oxygen content as to make the surface of a ferrite core higher than the center by 10 to 50% in electrical resistivity. |
