Dowa Mining Co., Ltd.

Seiji Isoyama

Yuichi Sato

Seiichi Hisano

Toshio Ueda

Masayasu Senda

Yasuo Watanabe

Masahiko Bannou

A permanent magnet made of an R--Fe--B--C or R--Fe--Co--B--C based alloy, where R is at least one rare-earth element, comprising individual magnetic crystal grains that are covered with an oxidation-resistant protective film. The protective film surrounding the individual magnetic crystal grains having a thickness of 0.001-30 .mu.m and 0.05-16 wt. % of the protective film comprising C.

Permanent magnet alloy having improved resistance

A process for producing a permanent magnet alloy based on a R--Fe--B--C system wherein R is at least one of the rare earth elements including Y, comprising the steps of preparing a molten crude alloy, producing a powder directly therefrom or after casting it into an alloy ingot and then grinding it into the powder, compacting the thus obtained powder and sintering the compacted product, the ingot or powder of the alloy before being sent to the compacting step being subjected to a heat treatment which is carried out at a temperature of 500.degree.-1,100.degree. C. for a period of 0.5 hour or more so as to produce a permanent magnet alloy based on an a R--Fe--B--C system whose individual magnetic crystal grains are covered with an oxidation-resistant protective film which has a C content higher than that of the individual crystal grains.

Process for production of permanent magnet alloy having improved

A permanent magnet made of an R-Fe-B-C or R-Fe-Co-B-C based alloy (where R is at least one rare-earth element) consisting of its individual magnetic crystal grains that are covered with an oxidation-resistant protective film is promising as a practicable next-generation magnet because of its having not only excellent magnetic properties inclusive of magnetic force that surpasses Sm-Co based magnets but also such highly improved oxidation resistance that may withstand use in practical applications for a prolonged time period without being coated on its outermost exposed surface with an oxidation-resistant protective film. Said protective film surrounding the individual magnetic crystal grains contains at least one, preferably substantially all, of the alloying elements of which said magnetic crystal grains are made, with 0.05-16 wt. %, preferably 0.1-16 wt. % of said protective film being composed of C.

Permanent magnet alloy having improved resistance to oxidation and

There is disclosed a novel dry process for the production of hexagonal-system ferrite having the formula: MO.multidot.nFe.sub.2 O.sub.3, wherein n represents a real number of 5.1-5.8 and M represents at least one metallic element selected from the group consisting of Ba, Sr and Pb. The ferrite is baked in the presence of the mixed additive comprising X-agent selected from the group consisting of KCl, NaCl and LiCl; and Y-agent selected from the group consisting of KBO.sub.2, NaBO.sub.2 and LiBO.sub.2 and/or the group consisting of K.sub.2 CO.sub.3, Na.sub.2 CO.sub.3 and Li.sub.2 CO.sub.3. After baking, the mixed additive is completely removed from the resulting ferrite by washing or by a wet-process disintegrating treatment. By changing the mixing ratio of said X-agent to said Y-agent, ferrite crystals having various characteristic properties can be obtained.

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Tokyo, Japan

Seiji Isoyama