JP4552161B2 - Ultra-compact magnet with excellent corrosion resistance - Google Patents
Ultra-compact magnet with excellent corrosion resistance Download PDFInfo
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- JP4552161B2 JP4552161B2 JP31806099A JP31806099A JP4552161B2 JP 4552161 B2 JP4552161 B2 JP 4552161B2 JP 31806099 A JP31806099 A JP 31806099A JP 31806099 A JP31806099 A JP 31806099A JP 4552161 B2 JP4552161 B2 JP 4552161B2
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- H01F41/00—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties
- H01F41/02—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties for manufacturing cores, coils, or magnets
- H01F41/0253—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties for manufacturing cores, coils, or magnets for manufacturing permanent magnets
- H01F41/026—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties for manufacturing cores, coils, or magnets for manufacturing permanent magnets protecting methods against environmental influences, e.g. oxygen, by surface treatment
Description
【０００１】
【発明の属する技術分野】
この発明は、体積に対する面積の割合の大きい、例えば単重1g以下の超小型形状を有するNd-Fe-B系焼結永久磁石の耐食性の改良に関し、素材表面からのダメージの影響が顕著となる該超小型形状品の表面コーティングに起因する磁気特性の劣化を効果的に防止した耐食性のすぐれた超小型磁石に関する。
【０００２】
【従来の技術】
Nd-Fe-B系焼結永久磁石は、溶製した特定組成のNd-Fe-B系合金を粉砕して微粉末にし、これを磁界中で配向しながら成形し、得られた成形体を焼結して製造される。また、Nd-Fe-B系焼結磁石には、一般に磁石表面の腐食防止の目的で種々材質のコーティングが施される。
【０００３】
従来のコーティング方法としては、樹脂塗装、蒸着法などの気相めっき、電気めっきなどが一般に用いられている。特に、電気めっきによるニッケルを主体としたコーティングは耐食性にすぐれ、また、磁石の組み込まれる製品のコンタミネーションを防止する効果にすぐれているため、広く用いられている。
【０００４】
Nd-Fe-B系焼結磁石は、MRI、VCM、モータ、アクチュエータなどに広く使われており、実用磁石材料の中で最も高い磁気特性を有するため、これらの応用製品の小型化に貢献している。中でも、モータ、アクチュエータなどに用いられるNd-Fe-B系焼結磁石の形状は小型化の一途をたどっており、最近では最大寸法が数mm、単重が1g以下のものも珍しくない。
【０００５】
このような単重が1g以下の超小型形状のNd-Fe-B系焼結磁石を歩留まりよく製造する技術として、例えば、造粒によって流動性を高めた原料粉末を金型に供給後圧縮成形し、これを焼結することで寸法精度の高い磁石素材を得る方法が特開平10-270278号などに開示されている。
【０００６】
【発明が解決しようとする課題】
発明者らは、超小型形状のNd-Fe-B系焼結磁石の表面にコーティングを施す検討の過程において、従来技術には以下の問題点があることを知見した。
【０００７】
すなわち、単重が1g以下の超小型形状のNd-Fe-B系焼結磁石の表面に例えば電気めっきによるニッケル被膜を形成した場合、めっき後の該磁石を着磁して磁気特性を評価すると減磁曲線の角形性が著しく低下することがわかった。
【０００８】
さらに検討を加えると、この角形性の低下は、単重が1g以下の磁石素材の表面積がSmm2、体積がVmm3であるとき、S/Vの値が1mm-1以上の場合に特に顕著になることがわかった。
【０００９】
この発明は、上記の知見で明らかになった超小型形状のR-Fe-B系焼結磁石の表面に施した金属又は合金のコーティングにより減磁曲線の角形性が著しく低下する問題を解消し、磁気特性の劣化が少なく、かつ耐食性にすぐれたコーティング被膜の形成されたR-Fe-B系焼結永久磁石の提供を目的としている。
【００１０】
【課題を解決するための手段】
発明者らは、上記の単重が1g以下の超小型形状のR-Fe-B系焼結永久磁石の表面コーティングに伴う磁気特性の劣化の問題を解消すべく鋭意検討を重ねた結果、上記の問題のあるコーティング後の磁石素材と被膜に含まれる水素量の分析値は100ppmを超えており、コーティング前の磁石素材に含まれる水素量はたかだか10ppmなので、水素量の増加は電気めっき処理に起因することを知見した。
【００１１】
すなわち、電気めっき処理によって増加した水素原子の大半は、めっき被膜ではなく被膜よりも内側のNd-Fe-B系焼結磁石中に存在している。磁石素材のうち表面付近の水素を吸蔵した部分は、結晶磁気異方性が低下するため保磁力を失い、磁石としての性質を失ってしまう。また、磁石素材に一旦吸蔵された水素は容易に取り除くことができない。
【００１２】
そこで、電気めっき後の磁石を800℃以上に加熱すれば水素量を低減することは可能だが、この場合はめっき被膜そのものが剥離するなどの不具合が生じる。
従って、被膜形成に起因する磁気特性の劣化を防ぐには、コーティング処理中に磁石素材が水素を吸蔵しないように工夫することが必要不可欠である。
【００１３】
発明者らは、被膜形成の手段として無電解めっき、または気相めっきを採用し、かつ、磁石素材と被膜に含まれる水素量を100ppm以下にコントロールすれば、減磁曲線の角形性の低下が防止できることを知見し、また、上記の手段で形成した第1層の被膜上に同様のめっき法、または他のめっき法によって第2、第3の被膜形成を行っても、角形性の低下が比較的少ないことを知見し、この発明を完成させた。
【００１４】
すなわち、この発明は、表面に、１層以上の金属又は合金の被膜からなりその合計膜厚が３μｍ以上３０μｍ以下である耐食性被膜を有する、Ｒ−Ｆｅ−Ｂ系焼結永久磁石の製造方法であって、単重が０．９ｇ以下で、表面積がＳｍｍ２、体積がＶｍｍ３であるとき、Ｓ/Ｖの値が１ｍｍ-1以上の素材形状を有している磁石素材を、外部電源によるめっき液と磁石素材との間の通電を行うことをせず還元剤と金属イオンとを含む無電解めっき用めっき液に浸漬して少なくとも第1層目の被膜を無電解めっき被膜とし、前記無電解めっき用めっき液に浸漬する前の磁石素材に含まれる水素量に対する、前記耐食性被膜形成後の磁石と耐食性被膜に含まれる水素量の増加を５０ｐｐｍ以下とする、耐食性のすぐれた超小型磁石の製造方法である。
【００１５】
【発明の実施の形態】
この発明の対象となるR-Fe-B系焼結永久磁石は、所要組成の原料粉末を成形して焼結したものであれば、公知のいかなる組成、製造方法で製造されたものでもよい。
【００１６】
以下にこの発明のR‐Fe‐B系磁石合金粉末の好ましい組成範囲を説明する。本系磁石合金粉末に使用される希土類元素Rはイットリウム(Y)を包含し、軽希土類及び重希土類を包含する希土類元素である。Rとしては、軽希土類をもつて足り、特にNd、Prが好ましい。また通例Rのうち1種もって足りるが、実用上は2種以上の混合物(ミッシュメタル、シジムなど)を入手上の便宜などの理由により用いることができ、なお、このRは純希土類元素でなくてもよく、工業上入手可能な範囲で製造上不可避な不純物を含有するもので差し支えない。
【００１７】
Rは、R‐Fe‐B系永久磁石を製造する合金粉末の必須元素であって、10原子%未満では高磁気特性、特に高保磁力が得られず、30原子%を超えると残留磁束密度(Br)が低下して、優れた特性の永久磁石が得られないため、Rは10原子%〜30原子%の範囲が好ましい。
【００１８】
Bは、R‐Fe‐B系永久磁石を製造する合金粉末の必須元素であって、1原子%未満では高い保磁力(iHc)は得られず、28原子%を超えると残留磁束密度(Br)が低下するため、優れた永久磁石が得られないため、1原子%〜28原子%の範囲が好ましい。
【００１９】
必須元素であるFeは、42原子%未満では残留磁束密度(Br)が低下し、89原子%を超えると高い保磁力が得られないので、Feは42原子%〜89原子%に限定する。また、Feの一部をCoで置換する理由は、永久磁石の温度特性を向上させる効果及び耐食性を向上させる効果が得られるためであるが、CoはFeの50%を超えると高い保磁力が得られず、優れた永久磁石が得られない。よってCoはFeの50%を上限とする。
【００２０】
この発明のR‐Fe‐B合金粉末において、高い残留磁束密度と高い保磁力を共に有する優れた永久磁石を得るためには、R12原子%〜16原子%、B4原子%〜12原子%、Fe72原子%〜84原子%を基本とする組成が望ましい。また、この発明のR‐Fe‐B合金粉末は、R、B、Feの他、工業的生産上不可避的不純物の存在を許容できるが、Bの一部を4.0原子%以下のC、3.5原子%以下のP、2.5原子%以下のS、3.5原子%以下のCuのうちすくなくとも1種、合計量で4.0原子%以下で置換することにより、磁石合金の製造性改善、低価格が可能である。
【００２１】
さらに、前記R、B、Fe合金あるいはCoを含有するR‐Fe‐B合金に、9.5原子%以下のAl、4.5原子%以下のTi、9.5原子%以下のV、8.5原子%以下のCr、8.0原子%以下のMn、5原子%以下のBi、12.5原子%以下のNb、10.5原子%以下のTa、9.5原子%以下のMo、9.5原子%以下のW、2.5原子%以下のSb、7原子%以下のGe、3.5原子%以下のSn、5.5原子%以下のZr、5.5原子%以下のHfのうち少なくとも1種添加含有させることにより、永久磁石合金の高保磁力が可能になる。
【００２２】
この発明において、R-Fe-B系焼結永久磁石の被膜形成前の素材の形状は、単重が1g以下で、表面積がSmm2、体積がVmm3であるとき、S/Vの値が1mm-1以上の形状を有するものに限定する。単重が1gを超えたり、S/Vの値が1mm-1未満の形状である場合は、この発明で問題としている磁石素材表面付近の変化に起因する減磁曲線の角形性の低下は多少はあるものの、体積に対する表面積の割合が小さいために、磁石全体で磁気特性を評価した場合に影響が頭著に表れてこない。
【００２３】
従って、単重が1gを超える場合や、S/Vの値が1mm-1未満の形状である場合はこの発明の対象外とする。この発明の効果は、単重が1g以下で少なければ少ないほど、また、S/Vの値が1mm-1を超えて大きければ大きいほど頭著となる。具体例を示すと、例えば一辺の長さが5mmの立方体形状のNd-Fe-B系焼結磁石の単重は0.9g、S/Vの値は1.2mm-1となり、この発明の対象となる条件を満たす。
【００２４】
S/Vの値の上限値については、製造技術の限界や、通常のNd-Fe-B系焼結磁石の結晶粒径である10μm以下の大きさの磁石は保磁力を持ち得ないことから、約50mm-1以下に限定される。この発明に用いる磁石素材の形状は、S/Vの値が1mm-1以上、50mm-1以下、好ましくは1.5mm-1以上、30mm-1以下、より好ましくは2mm-1以上、20mm-1以下である。
【００２５】
また、この発明において、磁石素材の表面積(S)の計算は被膜形成を行う全ての面の面積の合計で行い、例えば、リングなどの穴のあいた形状の場合は、穴の内部の面積も含まれるものとする。なお、この発明において、磁石素材の表面積Sを定量する際に、磁石表面における高低差50μm未満の凹凸は無視するものとする。
【００２６】
上記の条件で限定された寸法を有するR-Fe-B系焼結磁石を作製する方法としては、大きい素材から機械加工によって形状付与する場合と、なるべく加工せずに金型成形と焼結だけで形状付与を行う場合とがある。後者の場合には、小さな開口部を有する金型への原料粉末の供給が困難となるので、成形の前に予め原料粉末を造粒して流動性を高め、金型への給粉を容易にしておくことが好ましい。
【００２７】
この発明において、無電解めっきは、外部電源によるめっき液と磁石素材との間の通電を行うことをせず、還元剤と金属イオンとを含む無電解めっき用に調整されためっき液の中に磁石索材を浸漬し、素材表面に被膜形成を行う処理をいう。無電解めっき液には、ニッケル、銅をはじめさまざまな金属、合金の被膜形成を行うものが開発されているので、これらの公知の無電解めっき液を用いることができる。
【００２８】
無電解めっきにおいて、単重が1g以下でS/Vの値が1mm-1以上であっても、被膜の厚さが現実的な値、例えば50μm以下であれば、被覆後の磁石素材と被膜に含まれる水素量の増加を50ppm以下に抑制することができる。
【００２９】
一般に用いられる電気めっきと無電解めっきとで、被膜形成時に磁石素材に吸蔵される水素量が異なる理由は以下の通りである。いずれのめっき液にも液中に水素イオン(H+)、あるいはオキソニウムイオン(H3O+)が存在している。これらのイオンは金属イオンに比べて移動度が高く、めっき液中に電位差があれば容易に動くことができる。
【００３０】
電気めっきでは、磁石素材の表面に金属を電析させるために負の電位をかけるが、このために素材の表面に垂直な電場勾配が発生する。水素イオン等は、この電場勾配のために金属イオンよりも高速で磁石表面に引き寄せられ、磁石の内部の電場勾配を駆動力としてさらに磁石内部へと拡散していく。
【００３１】
一方、無電解めっきでは、めっき液中に含まれる還元剤の作用で素材表面に金属被膜が形成されるが、この過程での電子のやりとりは素材表面のあらゆる位置でランダムに行われるため、電解めっきの場合のようなマクロな電場勾配は発生しない。また、仮に電場勾配が発生したとしても、それは素材表面に平行なものとなるため、水素イオン等を磁石内部に拡散させる駆動力とはなり得ない。
【００３２】
以上に述べた理由から、無電解めっきを採用した場合、電気めっきに比べて被膜形成時に磁石素材に吸蔵される水素量を著しく低下させることができる。
【００３３】
この発明において、磁石素材の表面に形成する被膜の材質にはクロム、鉄、コバルト、ニッケル、銅、亜鉛、パラジウム、銀、スズ、金、鉛、ハンダのうちの少なくとも1種の金属又は合金を用いることが好ましい。
【００３４】
前述の方法により、磁石素材の表面に上記の材質からなる第1層目の被膜を無電解めっきによって形成した場合、第1層目の被膜の外側にクロム、鉄、コバルト、ニッケル、銅、亜鉛、パラジウム、銀、スズ、金、鉛、ハンダのうちの少なくとも1種の金属又は合金からなる第2、第3の被膜を形成してもよい。
【００３５】
このような多層被膜の場合、第2層以上の被膜形成時には第1層目の被膜が水素が外部から磁石素材内に拡散することを防止できる。従って、第2層以上の被膜の形成方法は、必ずしも無電解めっきに限定せずとも、例えば電気めっきによっても最終的な水素含有量を100ppm以下に制御することが可能となり、角形性の低下が防止できる。
【００３６】
この発明において、形成される被膜の厚さは、磁石素材の形状とのバランスと、磁石の使用環境から求められる耐食性の程度とによって適宜選択される。この発明の対象となる形状を有する磁石素材の表面に形成されたすべての被膜の厚さの合計が50μmを超えると、磁石素材の体積に対する被膜の体積の割合が大きくなり、磁石表面の磁束密度が低下してしまい、あるいは一定の大きさの磁束密度を得るために磁石全体の体積を大きくする必要が生ずるので好ましくない。また、被膜厚みが3μmよりも薄いと十分な耐食性が得られない。
【００３７】
この発明における被膜の厚みの合計は、3μm以上、50μm以下にすることが好ましい。より好ましい被膜厚みは5μm以上、30μm以下である。
【００３８】
この発明において、被膜の形成に真空蒸着、スパッタリングなどの公知の気相めっき法を用いることは、水素含有量を100ppm以下に制御するために好ましい。
前記の無電解めっき、あるいは電気めっきと組み合せて多層被膜を形成することも可能である。また、この発明において多層被膜を形成する場合、第1層目の被膜と第2、第3以上の被膜の材質は同一であっても異なっていてもいずれでもよい。
【００３９】
R-Fe-B系焼結永久磁石は、水素を吸蔵しやすい性質を持っている。この発明の対象となる形状を有する磁石素材を同じ条件で電気めっきすると、水素が拡散、吸蔵される素材表面からの深さは大きな素材の場合と同等であっても、水素吸蔵によって保磁力が低下する部分の体積の割合が磁石全体の体積に比べて大きいために、磁石全体の磁気特性を評価すると減磁曲線の角形性が著しく低下する。
【００４０】
上記の体積比率を知るためには、被膜成形後の水素含有量を分析する方法が最も簡便である。すなわち、コーティング前の磁石素材に含まれる水素量はたかだか10ppm程度であり、コーティング処理中に吸蔵される水素はほとんどが被膜ではなく磁石素材の表面付近に存在する。従って、被覆後の磁石素材と被膜に含まれる水素量を分析すれば、磁石素材の中で水素吸蔵の影響を受けて保磁力が低下した部分の体積比率の目安が得られる。
【００４１】
この発明において、水素の含有量は絶対値でなく、分析した試料の重量に対する相対値(単位:ppm)で表すものとする。単重が1g以下で、S/Vの値が1mm-1以上の本系焼結磁石においては、上記の水素量が100ppmを超えると減磁曲線の角形性が顕著に低下するため、磁石素材と被膜に含まれる水素量は100ppm以下が好ましい。水素量のより好ましい範囲は50ppm以下である。
【００４２】
被膜成形後の本系焼結磁石に含まれる水素量を分析する方法としては、試料全体を加熱したときに放出されるガスを測定する方法が最も簡便である。より好ましくは、被膜部分を除く磁石素材のみに含まれる水素量が測定できればよいが、これは事実上不可能である。しかし、試料中の水素のほとんどは磁石素材中に存在しているので、磁石素材と被膜からなる試料全体の分析を行っても何ら差し支えない。
【００４３】
この発明が対象とする特定形状の超小型磁石の磁気特性の評価には、試料振動型磁力計(VSM)を用いるのが好ましい。減磁曲線の角形性は以下のように定義する。すなわち、試料をパルス磁界等によリフル着磁した後、VSMを用いて減磁曲線(J-H曲線)の第1象限と第2象限を測定し、適当な方法により反磁界の補正を行う。得られたグラフ上において、減磁曲線とy軸との交点のy座標は残留磁束密度Brを示す。グラフ上にx軸と平行でy座標がBr×0.9であるような直線を引き、その直線と減磁曲線との交点のx座標(-Hk)の絶対値Hkをこの減磁曲線の角形性と定義する。
【００４４】
角形性がすぐれた磁石では、第2象限の磁化Jは保磁力点HcJに至るまでほば一定で保磁力点で急激に低下するので、減磁曲線は直角に角張った形となる。この場合、HkはHcJの値とほとんど同じになる。一方、何らかの理由で角形性が低下している磁石では第2象限の磁化JはBrから徐々に低下し、Hkの値はHcJの値に比べて低くなる。角形性の低下は、磁石の内部の保磁力が一定でなく、部分的に保磁力の低いところが存在することを意味する。角形性が低下すると、B-H曲線上の保磁力HcBや最大エネルギー積(BH)maxが低下し、磁石表面の磁束密度も低下するため、磁気特性上好ましくない。
【００４５】
【実施例】
実施例１
Ｎｄが３１．０重量％、Ｂが１．０重量％、残部Ｆｅ及び不可避的に含有される元素からなる組成を有し、平均粒径が３．０μｍのＮｄ−Ｆｅ−Ｂ系原料粉末を磁界中で成形し、得られた成形体を１０８０℃で２時間焼結して焼結磁石を得た。その後、これを切断加工して１辺３．０ｍｍ（Ｓ／Ｖ＝２ｍｍ−１）、単重０．２ｇの立方体形状の磁石試料を多数個作製した。
【００４６】
得られた試料の水素含有量は8ppmであった。また、着磁後の磁気特性は、残留磁束密度Brが1.30T、保磁力HcJが1050kA/m、減磁曲線の角形性は950kA/mであった。
【００４７】
次に、得られた試料に表1に示す材質の被膜を同じく表1に示す厚みで真空蒸着、スパッタリング、または無電解めっきにより形成した。被膜形成後の試料に含まれる水素量と、着磁後の減磁曲線の角形性をそれぞれ測定した結果を表1に示す。
【００４８】
比較例1
実施例1で作製したものと同じ磁石の一辺が3.0mmの立方体試料に対して、表1に示す材質の被膜を同じく表1に示す厚みで通電による電気めっきで形成した。被膜形成後の試料の水素含有量と、着磁後の減磁曲線の角形性をそれぞれ測定した結果を表1に示す。
【００４９】
表1に示した結果から、この発明によれば、超小型形状品の表面コーティングにおいて、磁石素材と被膜に含まれる水素量を100ppm以下とすることができ、その結果として、電気めっき法によるものと比較して、減磁曲線の角形性の値がコーティング前に比べて著しく減少する不具合が防止できることがわかる。
【００５０】
【表１】
実施例2
Ndが31.0重量%、Bが1.0重量%、残部Fe、および不可避的に含有される元素からなる組成を有し、平均粒径が3.0μmのネオジム-鉄-ボロン系原料粉末1kgにバインダーとしてポリビニルアルコールの10%水溶液を30g加え、さらに水を加えて攪拌することで濃度70%のスラリーを作製した。このスラリーをスプレードライヤーに供給して噴霧乾燥することで、平均粒子径(二次粒子径)が80μmの造粒粉を得た。
【００５２】
続いて、この造粒粉を金型に供給し、磁界中成形した後、得られた成形体を水素中において500℃で2時間、脱バインダーした。引き続き1080℃で2時間焼結して外径2.0mm、内径1.0mm、高さ1.0mm(単重0.018g、S/V=6mm-1)の試料を得た。
【００５３】
試料の配向方向は高さ方向であった。得られた試料の水素含有量は9ppmであった。また、着磁後の磁気特性は、残留磁束密度Brが1.25T、保磁力HcJが1080kA/m、減磁曲線の角形性は960kA/mであった。
【００５４】
次に、得られた試料に表2に示す気相めっき、または無電解めっきによる第1層目の被膜を形成した後、さらに表2に示す第2層目の被膜を成形した。得られた2層コーティング後の試料に含まれる水素量と、着磁後の減磁曲線の角形性をそれぞれ測定したを表2に示す。
【００５５】
比較例2
実施例2で用いたものと同じロットの試料に、表2に示す実施例2の第2層と同じ仕様の被膜を第1層に形成した後、試料に含まれる水素量と、着磁後の減磁曲線の角形性をそれぞれ測定した結果を表2に示す。
【００５６】
表2に示した結果から、この発明によれば、超小型形状品の表面コーティングにおいて電気めっきの下地として気相めっき、または無電解めっき層を設けることにより、磁石素材と被膜に含まれる水素量を100ppm以下とすることができた。
その結果として、下地層がない場合にと比較して、減磁曲線の角形性の値がコーティング前に比べて著しく減少する不具合が防止できることがわかる。
【００５７】
【表２】
【発明の効果】
この発明によると、超小型形状のR-Fe-B系焼結磁石の表面に施した金属又は合金のコーティングにより減磁曲線の角形性が著しく低下する問題が解消され、コーティング被膜の形成後の磁気特性の劣化が少なく、かつ耐食性にすぐれたR-Fe-B系焼結永久磁石が得られる。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to the improvement of the corrosion resistance of an Nd-Fe-B sintered permanent magnet having a large area ratio relative to the volume, for example, an ultra-compact shape with a unit weight of 1 g or less, and the influence of damage from the material surface becomes significant. The present invention relates to an ultra-small magnet with excellent corrosion resistance that effectively prevents deterioration of magnetic properties due to the surface coating of the ultra-small shaped product.
[0002]
[Prior art]
Nd-Fe-B sintered permanent magnets are prepared by crushing a melted Nd-Fe-B alloy with a specific composition into a fine powder, and molding the resulting molded body while orienting it in a magnetic field. Manufactured by sintering. Nd—Fe—B sintered magnets are generally coated with various materials for the purpose of preventing corrosion of the magnet surface.
[0003]
As a conventional coating method, resin coating, vapor phase plating such as vapor deposition, electroplating, or the like is generally used. In particular, a nickel-based coating by electroplating is widely used because of its excellent corrosion resistance and the effect of preventing contamination of products incorporating magnets.
[0004]
Nd-Fe-B sintered magnets are widely used in MRI, VCM, motors, actuators, etc. and have the highest magnetic properties among practical magnet materials, contributing to the miniaturization of these applied products. ing. Above all, the shape of Nd-Fe-B sintered magnets used for motors, actuators, etc. is steadily decreasing, and recently, it is not uncommon to have a maximum dimension of several millimeters and a unit weight of 1 g or less.
[0005]
As a technology for producing such ultra-compact Nd-Fe-B sintered magnets with a unit weight of 1 g or less with good yield, for example, raw material powder with improved fluidity by granulation is supplied to a mold and then compression molded Japanese Patent Laid-Open No. 10-270278 discloses a method for obtaining a magnet material with high dimensional accuracy by sintering.
[0006]
[Problems to be solved by the invention]
The inventors have found that the conventional technique has the following problems in the process of studying the coating on the surface of the ultra-small Nd—Fe—B sintered magnet.
[0007]
That is, when a nickel coating is formed on the surface of an ultra-compact Nd-Fe-B sintered magnet with a unit weight of 1 g or less, for example, by magnetizing the plated magnet and evaluating the magnetic properties It was found that the squareness of the demagnetization curve is significantly reduced.
[0008]
Further examination shows that this decrease in squareness is particularly noticeable when the surface area of a magnet material with a unit weight of 1 g or less is Smm 2 and the volume is Vmm 3 and the S / V value is 1 mm -1 or more. I found out that
[0009]
This invention has solved the problem that the squareness of the demagnetization curve is remarkably lowered by the coating of metal or alloy applied to the surface of the ultra-compact R-Fe-B sintered magnet, which has been clarified by the above knowledge. An object of the present invention is to provide an R-Fe-B sintered permanent magnet having a coating film with little deterioration of magnetic properties and excellent corrosion resistance.
[0010]
[Means for Solving the Problems]
As a result of intensive investigations to solve the problem of deterioration of magnetic properties associated with the surface coating of the ultra-small R-Fe-B sintered permanent magnet having a unit weight of 1 g or less as described above, The analysis value of the amount of hydrogen contained in the magnet material after coating and the film with the problem of over 100 ppm exceeds 100 ppm, and the amount of hydrogen contained in the magnet material before coating is at most 10 ppm. I found out that it was caused.
[0011]
That is, most of the hydrogen atoms increased by the electroplating treatment are present in the Nd—Fe—B-based sintered magnet inside the coating, not the plating coating. The portion of the magnet material that occludes hydrogen near the surface loses its coercive force due to a decrease in magnetocrystalline anisotropy and loses its properties as a magnet. Moreover, hydrogen once occluded in the magnet material cannot be easily removed.
[0012]
Therefore, it is possible to reduce the amount of hydrogen if the magnet after electroplating is heated to 800 ° C. or higher, but in this case, problems such as peeling of the plating film itself occur.
Therefore, in order to prevent the deterioration of the magnetic characteristics due to the film formation, it is essential to devise so that the magnet material does not occlude hydrogen during the coating process.
[0013]
If the inventors adopt electroless plating or vapor phase plating as a means for forming a film and control the amount of hydrogen contained in the magnet material and the film to 100 ppm or less, the squareness of the demagnetization curve is reduced. It is found that even if the second and third films are formed by the same plating method or other plating methods on the first layer film formed by the above-mentioned means, the squareness is not lowered. It was found that there was relatively little, and the present invention was completed.
[0014]
That is, the present invention is a method for producing an R—Fe—B sintered permanent magnet having a corrosion-resistant coating composed of one or more metal or alloy coatings on the surface and having a total film thickness of 3 μm or more and 30 μm or less. When the unit weight is 0.9 g or less, the surface area is Smm 2 , and the volume is Vmm 3 , a magnet material having a material shape with an S / V value of 1 mm −1 or more is supplied from an external power source. The electroless plating film containing at least a reducing agent and metal ions without being energized between the plating solution and the magnet material is immersed in an electroless plating solution to form at least the first layer coating as an electroless plating coating. An increase in the amount of hydrogen contained in the magnet and the corrosion-resistant film after the formation of the corrosion-resistant film with respect to the amount of hydrogen contained in the magnet material before being immersed in the plating solution for electrolytic plating is 50 ppm or less. It is a manufacturing method.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
The R—Fe—B sintered permanent magnet that is the subject of the present invention may be manufactured by any known composition and manufacturing method as long as the raw material powder having the required composition is molded and sintered.
[0016]
The preferred composition range of the R-Fe-B magnet alloy powder of the present invention will be described below. The rare earth element R used in the present magnet alloy powder includes yttrium (Y) and is a rare earth element including light rare earth and heavy rare earth. As R, a light rare earth is sufficient, and Nd and Pr are particularly preferable. In addition, one type of R is usually sufficient, but in practical use, a mixture of two or more types (Misch metal, shidim, etc.) can be used for reasons of availability, and this R is not a pure rare earth element. However, it may contain impurities that are inevitable in the manufacturing process as long as they are industrially available.
[0017]
R is an essential element of alloy powder for producing R-Fe-B permanent magnets, and if it is less than 10 atomic%, high magnetic properties, particularly high coercive force cannot be obtained, and if it exceeds 30 atomic%, residual magnetic flux density ( R) is preferably in the range of 10 atomic% to 30 atomic%, because a permanent magnet having excellent characteristics cannot be obtained due to a decrease in Br).
[0018]
B is an essential element of alloy powder for producing R-Fe-B permanent magnets, and high coercive force (iHc) cannot be obtained if it is less than 1 atomic%, and residual magnetic flux density (Br) if it exceeds 28 atomic%. ) Is reduced, and an excellent permanent magnet cannot be obtained. Therefore, the range of 1 atomic% to 28 atomic% is preferable.
[0019]
When Fe, which is an essential element, is less than 42 atomic%, the residual magnetic flux density (Br) decreases. When it exceeds 89 atomic%, a high coercive force cannot be obtained, so Fe is limited to 42 atomic% to 89 atomic%. The reason for substituting part of Fe with Co is to obtain the effect of improving the temperature characteristics of the permanent magnet and the effect of improving the corrosion resistance. However, when Co exceeds 50% of Fe, it has a high coercive force. It cannot be obtained and an excellent permanent magnet cannot be obtained. Therefore, the upper limit of Co is 50% of Fe.
[0020]
In the R-Fe-B alloy powder of the present invention, in order to obtain an excellent permanent magnet having both a high residual magnetic flux density and a high coercive force, R12 atomic% to 16 atomic%, B4 atomic% to 12 atomic%, Fe72 Compositions based on atomic percent to 84 atomic percent are desirable. In addition, the R-Fe-B alloy powder of the present invention can tolerate the presence of impurities unavoidable for industrial production in addition to R, B, and Fe, but a part of B is 4.0 atomic% or less of C, 3.5 atoms. By substituting at least one of P of% or less, S of 2.5 atomic% or less, or Cu of 3.5 atomic% or less, with a total amount of 4.0 atomic% or less, it is possible to improve the manufacturability and lower the price of the magnet alloy. .
[0021]
Further, R-Fe-B alloy containing R, B, Fe alloy or Co, 9.5 atomic% or less Al, 4.5 atomic% or less Ti, 9.5 atomic% or less V, 8.5 atomic% or less Cr, 8.0 atomic percent or less Mn, 5 atomic percent or less Bi, 12.5 atomic percent or less Nb, 10.5 atomic percent or less Ta, 9.5 atomic percent or less Mo, 9.5 atomic percent or less W, 2.5 atomic percent or less Sb, 7 By adding at least one of Ge of atomic percent or less, Sn of 3.5 atomic percent or less, Zr of 5.5 atomic percent or less, and Hf of 5.5 atomic percent or less, a high coercive force of the permanent magnet alloy can be achieved.
[0022]
In this invention, when the R-Fe-B sintered permanent magnet has a material shape before the coating is formed, when the unit weight is 1 g or less, the surface area is Smm 2 and the volume is Vmm 3 , the value of S / V is Limited to those having a shape of 1 mm -1 or more. When the unit weight is over 1 g or the S / V value is less than 1 mm -1 , there is a slight decrease in the squareness of the demagnetization curve due to the change in the vicinity of the surface of the magnet material, which is a problem in this invention. However, since the ratio of the surface area to the volume is small, there is no significant effect when evaluating the magnetic properties of the entire magnet.
[0023]
Therefore, when the unit weight exceeds 1 g, or when the S / V value is less than 1 mm −1 , it is not covered by this invention. The effect of the present invention becomes more remarkable as the unit weight is 1 g or less, and as the S / V value is larger than 1 mm −1 , the effect is greater. As a specific example, for example, the unit weight of a cubic Nd-Fe-B sintered magnet having a side length of 5 mm is 0.9 g, and the value of S / V is 1.2 mm -1 . Satisfies the condition.
[0024]
As for the upper limit of the S / V value, the limit of manufacturing technology and the magnet size of 10 μm or less, which is the crystal grain size of ordinary Nd-Fe-B sintered magnets, cannot have a coercive force. , Limited to about 50 mm −1 or less. The shape of the magnet material used in the present invention has an S / V value of 1 mm -1 or more and 50 mm -1 or less, preferably 1.5 mm -1 or more and 30 mm -1 or less, more preferably 2 mm -1 or more, 20 mm -1 It is as follows.
[0025]
In the present invention, the calculation of the surface area (S) of the magnet material is performed by the sum of the areas of all surfaces on which the film is formed.For example, in the case of a shape with a hole such as a ring, the area inside the hole is also included. Shall be. In the present invention, when the surface area S of the magnet material is quantified, irregularities with an elevation difference of less than 50 μm on the magnet surface are ignored.
[0026]
R-Fe-B sintered magnets with dimensions limited under the above conditions can be produced by machining from large materials by machining, and only by molding and sintering without processing. In some cases, the shape may be added. In the latter case, it is difficult to supply the raw material powder to a mold having a small opening, so that the raw material powder is granulated in advance before molding to improve fluidity and facilitate the powder supply to the mold. It is preferable to keep it.
[0027]
In this invention, the electroless plating does not energize between the plating solution and the magnet material by an external power source, but in a plating solution adjusted for electroless plating containing a reducing agent and metal ions. It refers to the process of immersing the magnet cord material and forming a film on the surface of the material. As electroless plating solutions, those for forming coatings of various metals and alloys including nickel and copper have been developed, and these known electroless plating solutions can be used.
[0028]
In electroless plating, even if the unit weight is 1 g or less and the S / V value is 1 mm -1 or more, if the thickness of the coating is a practical value, for example, 50 μm or less, the magnet material and coating after coating The increase in the amount of hydrogen contained in can be suppressed to 50 ppm or less.
[0029]
The reason why the amount of hydrogen occluded in the magnet material at the time of coating formation differs between electroplating and electroless plating that are generally used is as follows. In any of the plating solutions, hydrogen ions (H + ) or oxonium ions (H 3 O + ) are present in the solution. These ions have higher mobility than metal ions, and can easily move if there is a potential difference in the plating solution.
[0030]
In electroplating, a negative electric potential is applied to deposit the metal on the surface of the magnet material, which causes an electric field gradient perpendicular to the surface of the material. Hydrogen ions and the like are attracted to the magnet surface at a higher speed than the metal ions due to this electric field gradient, and are further diffused into the magnet using the electric field gradient inside the magnet as a driving force.
[0031]
On the other hand, in electroless plating, a metal film is formed on the surface of the material due to the action of the reducing agent contained in the plating solution. In this process, electrons are exchanged randomly at any position on the surface of the material. There is no macro electric field gradient as in the case of plating. Even if an electric field gradient is generated, it becomes parallel to the surface of the material and cannot be a driving force for diffusing hydrogen ions or the like inside the magnet.
[0032]
For the reasons described above, when electroless plating is employed, the amount of hydrogen occluded in the magnet material during film formation can be significantly reduced compared to electroplating.
[0033]
In this invention, the material of the coating formed on the surface of the magnet material is at least one metal or alloy of chromium, iron, cobalt, nickel, copper, zinc, palladium, silver, tin, gold, lead, and solder. It is preferable to use it.
[0034]
When the first layer film made of the above-mentioned material is formed on the surface of the magnet material by electroless plating by the above-described method, chromium, iron, cobalt, nickel, copper, zinc is formed on the outer side of the first layer film. The second and third films made of at least one metal or alloy of palladium, silver, tin, gold, lead, and solder may be formed.
[0035]
In the case of such a multilayer coating, when the coating of the second layer or more is formed, the first coating can prevent hydrogen from diffusing from the outside into the magnet material. Therefore, the method for forming the coating of the second layer or more is not necessarily limited to electroless plating, but it is possible to control the final hydrogen content to 100 ppm or less even by electroplating, for example, and the squareness is reduced. Can be prevented.
[0036]
In the present invention, the thickness of the coating film to be formed is appropriately selected depending on the balance with the shape of the magnet material and the degree of corrosion resistance required from the environment where the magnet is used. When the total thickness of all the coatings formed on the surface of the magnet material having the shape that is the object of the present invention exceeds 50 μm, the ratio of the volume of the coating to the volume of the magnet material increases, and the magnetic flux density on the magnet surface Is reduced, or in order to obtain a certain magnetic flux density, it is necessary to increase the volume of the entire magnet. Further, if the coating thickness is thinner than 3 μm, sufficient corrosion resistance cannot be obtained.
[0037]
In this invention, the total thickness of the coating is preferably 3 μm or more and 50 μm or less. A more preferable film thickness is 5 μm or more and 30 μm or less.
[0038]
In the present invention, it is preferable to use a known vapor phase plating method such as vacuum deposition or sputtering for the formation of the film in order to control the hydrogen content to 100 ppm or less.
It is also possible to form a multilayer coating in combination with the electroless plating or electroplating. In the present invention, when the multilayer coating is formed, the material of the first coating and the second, third or more coatings may be the same or different.
[0039]
R-Fe-B sintered permanent magnets have the property of easily absorbing hydrogen. When electroplating a magnet material having the shape that is the object of the present invention under the same conditions, even if the depth from the surface of the material where hydrogen is diffused and occluded is the same as that of a large material, the coercive force is obtained by occlusion of hydrogen. Since the ratio of the volume of the reduced portion is larger than the volume of the entire magnet, the squareness of the demagnetization curve is significantly reduced when the magnetic characteristics of the entire magnet are evaluated.
[0040]
In order to know the volume ratio, the method of analyzing the hydrogen content after film formation is the simplest. That is, the amount of hydrogen contained in the magnet material before coating is at most about 10 ppm, and most of the hydrogen occluded during the coating process is not near the film but near the surface of the magnet material. Therefore, if the magnet material after coating and the amount of hydrogen contained in the coating are analyzed, an indication of the volume ratio of the portion of the magnet material where the coercive force has decreased due to the influence of hydrogen occlusion can be obtained.
[0041]
In the present invention, the hydrogen content is not an absolute value, but a relative value (unit: ppm) relative to the weight of the analyzed sample. In this system sintered magnet with a unit weight of 1 g or less and an S / V value of 1 mm -1 or more, the squareness of the demagnetization curve is significantly reduced when the hydrogen content exceeds 100 ppm. The amount of hydrogen contained in the coating is preferably 100 ppm or less. A more preferable range of the amount of hydrogen is 50 ppm or less.
[0042]
The simplest method for analyzing the amount of hydrogen contained in the sintered magnet after film formation is to measure the gas released when the entire sample is heated. More preferably, it is sufficient that the amount of hydrogen contained only in the magnet material excluding the coating portion can be measured, but this is practically impossible. However, since most of the hydrogen in the sample is present in the magnet material, there is no problem even if the entire sample consisting of the magnet material and the coating is analyzed.
[0043]
It is preferable to use a sample vibration type magnetometer (VSM) for evaluating the magnetic characteristics of the micro magnet of a specific shape targeted by the present invention. The squareness of the demagnetization curve is defined as follows. That is, after the sample is fully magnetized with a pulse magnetic field or the like, the first and second quadrants of the demagnetization curve (JH curve) are measured using a VSM, and the demagnetizing field is corrected by an appropriate method. On the obtained graph, the y coordinate of the intersection of the demagnetization curve and the y axis indicates the residual magnetic flux density Br. On the graph, draw a straight line that is parallel to the x axis and whose y coordinate is Br × 0.9, and the absolute value H k of the x coordinate (-H k ) of the intersection of the straight line and the demagnetization curve It is defined as squareness.
[0044]
In a magnet having excellent squareness, the magnetization J in the second quadrant is almost constant until it reaches the coercive force point H cJ , and rapidly decreases at the coercive force point. Therefore, the demagnetization curve becomes square at right angles. In this case, H k is almost the same as the value of H cJ . On the other hand, in a magnet whose squareness has decreased for some reason, the magnetization J in the second quadrant gradually decreases from Br, and the value of H k becomes lower than the value of H cJ . The decrease in squareness means that the coercive force inside the magnet is not constant, and there is a part where the coercive force is partially low. If the squareness is lowered, the coercive force HcB and the maximum energy product (BH) max on the BH curve are lowered, and the magnetic flux density on the magnet surface is also lowered.
[0045]
【Example】
Example 1
An Nd—Fe—B-based raw material powder having a composition comprising Nd of 31.0% by weight, B of 1.0% by weight, the balance Fe and elements inevitably contained, and an average particle size of 3.0 μm Molding was performed in a magnetic field, and the obtained compact was sintered at 1080 ° C. for 2 hours to obtain a sintered magnet. Thereafter, this was cut to produce a large number of cube-shaped magnet samples having a side of 3.0 mm (S / V = 2 mm −1 ) and a unit weight of 0.2 g .
[0046]
The obtained sample had a hydrogen content of 8 ppm. The magnetic characteristics after magnetization were a residual magnetic flux density Br of 1.30 T, a coercive force HcJ of 1050 kA / m, and a demagnetization curve having a squareness of 950 kA / m.
[0047]
Next, a film of the material shown in Table 1 was formed on the obtained sample with the thickness shown in Table 1 by vacuum deposition, sputtering, or electroless plating. Table 1 shows the results of measuring the amount of hydrogen contained in the sample after the film formation and the squareness of the demagnetization curve after magnetization.
[0048]
Comparative Example 1
A film of the material shown in Table 1 was formed by electroplating with the same thickness as shown in Table 1 on a cube sample having the same side of a magnet of 3.0 mm as the one produced in Example 1. Table 1 shows the results of measuring the hydrogen content of the sample after the film formation and the squareness of the demagnetization curve after magnetization.
[0049]
From the results shown in Table 1, according to the present invention, in the surface coating of ultra-small shaped products, the amount of hydrogen contained in the magnet material and the coating can be reduced to 100 ppm or less, and as a result, by electroplating method It can be seen that a problem that the squareness value of the demagnetization curve is remarkably reduced compared to before coating can be prevented.
[0050]
[Table 1]
Example 2
Nd is 31.0% by weight, B is 1.0% by weight, the balance is Fe, and an inevitably contained element, and an average particle size of 3.0 μm neodymium-iron-boron-based raw material powder of 1 kg of polyvinyl as a binder 30 g of a 10% aqueous solution of alcohol was added, and water was further added and stirred to prepare a slurry having a concentration of 70%. This slurry was supplied to a spray dryer and spray-dried to obtain a granulated powder having an average particle size (secondary particle size) of 80 μm.
[0052]
Subsequently, the granulated powder was supplied to a mold and molded in a magnetic field, and then the obtained molded body was debindered in hydrogen at 500 ° C. for 2 hours. Subsequently, sintering was performed at 1080 ° C. for 2 hours to obtain a sample having an outer diameter of 2.0 mm, an inner diameter of 1.0 mm, and a height of 1.0 mm (unit weight: 0.018 g, S / V = 6 mm −1 ).
[0053]
The orientation direction of the sample was the height direction. The hydrogen content of the obtained sample was 9 ppm. The magnetic properties after magnetization were residual magnetic flux density Br of 1.25 T, coercive force HcJ of 1080 kA / m, and demagnetization curve squareness of 960 kA / m.
[0054]
Next, after forming a first layer coating by vapor phase plating or electroless plating shown in Table 2 on the obtained sample, a second layer coating shown in Table 2 was further formed. Table 2 shows the amount of hydrogen contained in the obtained sample after the two-layer coating and the squareness of the demagnetization curve after magnetization.
[0055]
Comparative Example 2
After forming a coating of the same specifications as the second layer of Example 2 shown in Table 2 on the sample of the same lot used in Example 2, the amount of hydrogen contained in the sample, and after magnetization Table 2 shows the results of measuring the squareness of each demagnetization curve.
[0056]
From the results shown in Table 2, according to the present invention, by providing a vapor phase plating or electroless plating layer as a base for electroplating in the surface coating of a microminiature product, the amount of hydrogen contained in the magnet material and coating Was 100 ppm or less.
As a result, it can be seen that it is possible to prevent a problem that the squareness value of the demagnetization curve is remarkably reduced as compared with the case before coating as compared with the case where there is no base layer.
[0057]
[Table 2]
【The invention's effect】
According to the present invention, the problem that the squareness of the demagnetization curve is remarkably lowered due to the coating of the metal or alloy applied to the surface of the ultra-compact R-Fe-B sintered magnet is solved. R-Fe-B sintered permanent magnets with little deterioration of magnetic properties and excellent corrosion resistance can be obtained.
Claims (2)
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| JP31806099A JP4552161B2 (en) | 1999-11-09 | 1999-11-09 | Ultra-compact magnet with excellent corrosion resistance |
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| JP31806099A JP4552161B2 (en) | 1999-11-09 | 1999-11-09 | Ultra-compact magnet with excellent corrosion resistance |
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| JP3897724B2 (en) * | 2003-03-31 | 2007-03-28 | 独立行政法人科学技術振興機構 | Manufacturing method of micro, high performance sintered rare earth magnets for micro products |
| WO2005001855A1 (en) * | 2003-06-27 | 2005-01-06 | Tdk Corporation | R-t-b based permanent magnet |
| WO2006085581A1 (en) * | 2005-02-10 | 2006-08-17 | Neomax Co., Ltd. | Ultra small rare earth magnet and method for manufacturing same |
| CN100464006C (en) * | 2006-07-14 | 2009-02-25 | 西南大学 | Process for preparing magnesium alloy surface function gradient film |
| CN100464007C (en) * | 2006-07-14 | 2009-02-25 | 西南大学 | Process for preparing neodymium-iron-boron permanent magnetic material surface gradient function coating layer |
| WO2014118971A1 (en) * | 2013-02-01 | 2014-08-07 | 株式会社日立製作所 | Rare earth magnet and method for producing same |
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| JPH0283905A (en) * | 1988-09-20 | 1990-03-26 | Sumitomo Special Metals Co Ltd | Corrosion-resistant permanent magnet and manufacture thereof |
| JPH02185004A (en) * | 1989-01-12 | 1990-07-19 | Tdk Corp | Permanent magnet |
| JPH0529119A (en) * | 1991-07-18 | 1993-02-05 | Kobe Steel Ltd | High corrosion-resistant rare earth magnet |
| JPH07130513A (en) * | 1993-10-29 | 1995-05-19 | Hitachi Metals Ltd | Highly corrosion resistant rare earth magnet |
| JPH07130520A (en) * | 1993-11-08 | 1995-05-19 | Sumitomo Metal Ind Ltd | High corrosion-proof permanent magnet and manufacture of the same |
| JPH083783A (en) * | 1994-06-22 | 1996-01-09 | Nippon New Chrome Kk | Method for treating surface of magnetic alloy |
| JPH10270278A (en) * | 1997-03-24 | 1998-10-09 | Sumitomo Special Metals Co Ltd | Manufacture of nd-fe-b sintered magnet for optical isolator |
| JP2001135538A (en) * | 1999-11-05 | 2001-05-18 | Citizen Watch Co Ltd | Producing method for permanent magnet material |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH0283905A (en) * | 1988-09-20 | 1990-03-26 | Sumitomo Special Metals Co Ltd | Corrosion-resistant permanent magnet and manufacture thereof |
| JPH02185004A (en) * | 1989-01-12 | 1990-07-19 | Tdk Corp | Permanent magnet |
| JPH0529119A (en) * | 1991-07-18 | 1993-02-05 | Kobe Steel Ltd | High corrosion-resistant rare earth magnet |
| JPH07130513A (en) * | 1993-10-29 | 1995-05-19 | Hitachi Metals Ltd | Highly corrosion resistant rare earth magnet |
| JPH07130520A (en) * | 1993-11-08 | 1995-05-19 | Sumitomo Metal Ind Ltd | High corrosion-proof permanent magnet and manufacture of the same |
| JPH083783A (en) * | 1994-06-22 | 1996-01-09 | Nippon New Chrome Kk | Method for treating surface of magnetic alloy |
| JPH10270278A (en) * | 1997-03-24 | 1998-10-09 | Sumitomo Special Metals Co Ltd | Manufacture of nd-fe-b sintered magnet for optical isolator |
| JP2001135538A (en) * | 1999-11-05 | 2001-05-18 | Citizen Watch Co Ltd | Producing method for permanent magnet material |
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