Dust core with specific relationship between particle diameter and coating thickness, and method for producing same
The object of the present invention is to provide a powder core and method for making the same that is equipped with insulative coating having superior heat resistance, with the coating making it possible to adequately restrict the flow of eddy currents between particles. The powder core is equipped with a plurality of compound magnetic particles bonded to each other. Each of said plurality of composite magnetic particles includes: a metal magnetic particle 10 ; an insulative lower layer coating 20 surrounding a surface 10 a of said metal magnetic particle 10 ; an upper layer coating 30 surrounding said lower layer coating 20 and containing silicon; and dispersed particles 50 containing a metal oxide compound and disposed in said lower layer coating 20 and/or said upper layer coating 30 . A mean particle diameter R of the dispersed particles 50 meets the condition 10 nm<R≦2 T, where the average thickness of the coating combining the lower layer coating 20 and the upper layer coating 30 is T.
1. A powder core comprising: a plurality of composite magnetic particles bonded to each other;
wherein each of said plurality of composite magnetic particles includes:
a metal magnetic particle,
an insulative lower layer coating surrounding a surface of said metal magnetic particle,
an upper layer coating surrounding said lower layer coating and containing silicon, and
dispersed particles containing a metal oxide compound and disposed in said upper layer coating and/or said lower layer coating;
wherein said dispersed particles includes at least one oxide selected from the group consisting of silicon oxide and aluminum oxide; and
wherein a mean particle diameter R of said dispersed particles meets a condition 10 nm<R≦2 T where T is an average thickness of a coating formed from said lower layer coating and said upper layer coating.
2. A powder core according to claim 1 wherein said lower layer coating includes at least one compound selected from a group consisting of a phosphorous compound, a silicon compound, a zirconium compound, and an aluminum compound.
3. A powder core according to claim 1 wherein said lower layer coating has an average thickness of at least 10 nm and no more than 1 micron.
4. A powder core according to claim 1 wherein said upper layer coating has an average thickness of at least 10 nm and no more than 1 micron.
5. A method for making a powder core according to claim 1 comprising:
a step for forming a shaped body by shaping said plurality of metal magnetic particles; and
a step for heat treating said shaped body at a temperature of at least 500 deg C. and less than 800 deg C.