Hitachi Metals, Ltd.

Tomohito Maki

Takeshi Nishiuchi

Satoshi Hirosawa

Noriyuki Nozawa

Katsunori Bekki

An R&#x2014;Fe&#x2014;B based porous magnet according to the present invention has an aggregate structure of NdFeB type crystalline phases with an average grain size of 0.1 &#x3bc;m to 1 &#x3bc;m. At least a portion of the magnet is porous and has micropores with a major axis of 1 &#x3bc;m to 20 &#x3bc;m.

R&#x2014;Fe&#x2014;B porous magnet and method for producing the same

R-Fe-B porous magnet and method for producing the same

An R&#x2014;Fe&#x2014;B based rare-earth alloy powder with a mean particle size of less than about 20 &#x3bc;m is provided and compacted to make a powder compact. Next, the powder compact is subjected to a heat treatment at a temperature of about 550&#xb0; C. to less than about 1,000&#xb0; C. within hydrogen gas, thereby producing hydrogenation and disproportionation reactions (HD processes). Then, the powder compact is subjected to another heat treatment at a temperature of about 550&#xb0; C. to less than about 1,000&#xb0; C. within either a vacuum or an inert atmosphere, thereby producing desorption and recombination reactions and obtaining a porous material including fine crystal grains, of which the density is about 60% to about 90% of their true density and which have an average crystal grain size of about 0.01 &#x3bc;m to about 2 &#x3bc;m (DR processes). Thereafter, the porous material is subjected to yet another heat treatment at a temperature of about 750&#xb0; C. to less than about 1,000&#xb0; C. within either the vacuum or the inert atmosphere, thereby further increasing its density to about 93% or more of their true density and making an R&#x2014;Fe&#x2014;B based microcrystalline high-density magnet.

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Osaka, Japan

Tomohito Maki