JP3777793B2 - Method for producing rare earth metal-iron-nitrogen based magnetic material - Google Patents
Method for producing rare earth metal-iron-nitrogen based magnetic material Download PDFInfo
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- JP3777793B2 JP3777793B2 JP13016698A JP13016698A JP3777793B2 JP 3777793 B2 JP3777793 B2 JP 3777793B2 JP 13016698 A JP13016698 A JP 13016698A JP 13016698 A JP13016698 A JP 13016698A JP 3777793 B2 JP3777793 B2 JP 3777793B2
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- H01F1/00—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties
- H01F1/01—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials
- H01F1/03—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity
- H01F1/032—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials
- H01F1/04—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials metals or alloys
- H01F1/047—Alloys characterised by their composition
- H01F1/053—Alloys characterised by their composition containing rare earth metals
- H01F1/055—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5
- H01F1/059—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and Va elements, e.g. Sm2Fe17N2
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Description
【0001】
【発明の属する技術分野】
本発明は、希土類金属−鉄窒化物の粉末による磁性材料、特に安定的に高い保磁力を有する磁性材料の製造方法に関する。
【0002】
【従来の技術】
希土類金属R−鉄Fe−窒素N系の磁性材料は、希土類金属R−鉄Fe合金に窒素を吸収させた窒化物系の粉末状の磁性材料で、磁性体の粉末は、樹脂等により固形化されたり、焼結されたりして、永久磁石として利用される。希土類金属−鉄−窒素系磁性材料は、残留磁化とさらに保磁力とが共に大きく、その用途が注目されている。
【0003】
希土類金属−鉄−窒素系磁性材料の製造には、従来は、溶解法と、還元拡散法とが知られている。溶解法は、原料として希土類金属と鉄とを溶解してインゴットに鋳造し、このインゴットを粉砕して希土類金属−鉄合金の粉末にし、この粉末を窒素中で加熱して窒化処理して窒素を含有させる方法である。
【0004】
還元拡散法は、原料として希土類金属酸化物粉末と金属鉄ないし酸化鉄の粉末との混合粉にCa粒を混合して、不活性雰囲気中で加熱することにより、Caによるこれら酸化物粉末を還元して、希土類金属−鉄合金粉末にし、これを窒化することにより、希土類金属−鉄−窒素系材料を粉末状で得る方法である(例えば、特開平6−81010号公報)。
【0005】
これらの磁性体粉末は、例えば、合成樹脂等のバインダと混練され、成形されるが、成形硬化過程で磁化することにより、所望の形状の強磁石として利用される。
【0006】
【発明が解決しようとする課題】
これらの製造方法で形成された希土類金属−鉄−窒素系磁性体粉末は、一般的には、高い残留磁化と高い保磁力とを備えているが、製造方法に依存してその製造ロットによっては、期待される程にはその磁気特性が高くなく、特に、保磁力が低くそのバラツキが大きくなることがあった。さらに、保磁力の低下は、製造工程で、微粉化のための粉砕や混合の過程と関連していることが明らかになった。この問題は、磁性体粉末とこれを使用した磁石の品質の保持のために重要である。
【0007】
本発明は、以上の如く、永久磁石に使用可能な磁性体粉末に関して、保磁力が安定して高く、そのバラツキが小さい希土類金属−鉄−窒素系磁性体粉末を提供することを目的としている。
【0008】
【課題を解決するための手段】
本発明は、希土類金属−鉄−窒素系磁性体粉末の保磁力の低下が窒化物系磁性体中の遊離金属鉄の存在に起因することの知見に基づくものである。即ち、希土類金属−鉄−窒素系磁性材料は、窒化物磁性体粉末中の金属鉄含有量をX線回折強度比で、その磁性体粉末の最大回折強度に対して3%以下に低減させ、これにより遊離金属鉄に起因した保磁力の低下を防止するものである。
【0009】
希土類金属−鉄−窒素系磁性体粉末は、希土類金属−鉄窒化物から粉末に形成されているが、粉末中に存在する金属鉄は、希土類鉄窒化物から遊離されて、bcc構造の純鉄又はその固溶体の結晶(即ち、α−Fe)である。金属鉄(α−Fe)は、軟磁性を示すので、上記磁性体粉末中の金属鉄の存在は、上記希土類金属−鉄窒化物の磁気特性、特に、保磁力を低下させる。本発明は、磁性体粉末中のこの金属鉄含有量を3%以下に規制して、この材料の優れた磁気特性を発揮させるものである。
【0010】
ここに、金属鉄の含有量は、X線回折強度比によるが、これは、X線回折法による磁性体粉末の回折最大強度に対する上記磁性体粉末のα−Fe相結晶の回折強度の比の100分率で示される。このように定義された金属鉄の含有量は、遊離したα−Feの含有量に対応している。X線回折強度から測定された金属鉄の含有量は、図2に示す検量線のように、この含有量と磁性体粉末中に混合された金属鉄(α−Fe)の重量で表した含有量と線形の関係があり、この検量線から重量%が容易に求められる。
【0011】
希土類金属−鉄−窒素系磁性材料は、上記の希土類金属−鉄−窒素系磁性体粉末が、原子%で、3〜30%の希土類金属と、5〜15%のNと、残部Fe及び不可避的不純物とからなるものが好ましい。この組成の磁性材料は、一般式
RxFe100-x-yNy・・・・・・・(1)
で表される組成の窒化物であり、ここに、Rは希土類金属元素であるサマリウムを示し、xは、希土類金属元素Rの原子%で3<x<30の範囲で、yは、窒素Nの原子%で5<y<15の範囲にある。
【0012】
希土類金属−鉄−窒素系の磁性材料の粉末粒子は微細である程優れた磁気特性を示すので、磁性体の粒子径は、10μm以下とする必要があり、特に、5μm以下とするのが好ましい。
【0013】
本発明の希土類金属−鉄−窒素系磁性材料の製造方法は、還元拡散法において、希土類金属酸化物粉末と金属鉄粉末と酸化鉄と金属カルシウム粒とから成る混合物を不活性雰囲気中で加熱してカルシウム還元を行う還元過程と、その生成物を窒素含有雰囲気中で加熱して窒化する窒化過程とを含み、希土類金属−鉄−窒素系磁性体粉末とする方法が利用される。
【0014】
本発明は、上記の還元拡散法において、原料混合物の希土類金属酸化物粉末と酸化鉄粉末とを、平均粒径5μm以下に規制し、且つ混合されて均一に分布させることを特徴としている。還元拡散法は、上記の還元過程及び窒化過程は、いずれも結晶粒の成長が比較的少ない。そこで予め希土類金属酸化物粉末と酸化鉄粉とを平均粒径5μm以下に調製しておくと、窒化後に生成した希土類金属−鉄−窒素系磁性体粉末も、粒子径おおよそ5μm以下の微細な粒径が得られる。これにより、磁性体粉末は、微細粒であることによる磁気的特性の改善と、且つ、粉砕を要しないので遊離鉄が析出しないことによる磁気特性低下防止により、本発明の方法は、高い保磁力を有する微粉末磁性体を得ることができる。
【0015】
この系の磁性材料中の金属鉄含有による保磁力の低下は、金属鉄粒子が磁性粒子中ないし磁石中のボイドであると仮定したときのボイドによる保磁力の低下よりもかに顕著に起こる。この理由は、金属鉄が、軟磁性を示すので、上記磁石を構成する希土類金属−鉄窒化物粉末中の金属鉄は、反対強磁場中に曝されると、低い磁界でも金属鉄の磁区の移動・回転が容易に生じ、これを起点として周辺の窒化物粒子への磁区の移動・回転が誘導されて、磁化を低下させ、従って、含有金属鉄の分布が上記希土類金属−鉄窒化物の磁気特性、特に、保磁力が著しく低下させるからである。
【0016】
磁性材料中の金属鉄は、希土類金属−鉄−窒素系磁性材料、又は窒化前の希土類金属−鉄合金を製造工程で粉砕することによって生成し増加することが判ってきた。従来の還元拡散法において、原料粒子が粗粒である場合に、磁性体粉末も粗粒となり、これを微細粒に調製する必要があるが、このために、磁性体粉末を微粉砕すると、α−鉄が析出し易くなり、却って磁性体粉末の磁気特性を低下させていた。磁性体粉末を粉砕すると、磁性体粉末の希土類金属−鉄窒化物粒子が歪み変形を受けて、他の中間相に変態し、この過程で、α−Feが析出するので、磁性体粉末粒子中にα−Feが増加するからである。
【0017】
本発明の製造法は、還元拡散法を利用して、原料の金属鉄粉末を平均粒径5μm以下に予め調製するので、還元されて後に窒化されて成る磁性体粉末は、粉砕をすることなく所望の粒径の微粒子に調製できる。従って、窒化処理後の磁性材料は、金属鉄含有量を3%以下に規制し得て、これが磁性体粉末に高い保磁力を与える。
【0018】
【発明の実施の形態】
本発明の実施の形態では、希土類金属−鉄−窒素系磁性体粉末が、原子%で、3〜30%の希土類金属と、5〜15%のNと、残部Fe及び不可避的不純物とから成るものが使用される。磁性体粉末中の遊離金属鉄(α−Fe)は、X線回折強度比で、その磁性体粉末の最大回折強度に対して3%以下とする。
【0019】
上記の磁性体粉末の主たる成分は、上記の式(1)を再掲すると、一般式
RxFe100-x-yNy・・・・(1)
で表される希土類金属Rと鉄Feと窒素Nから成る窒化物であり、希土類金属Rのxは、原子%xは、3〜30の範囲に、Nの原子%yは、5〜15(原子%)の範囲に、残部が主としてFeとされる。
【0020】
ここに、希土類金属Rを3〜30原子%と規定するのは、3原子%未満では、α−Fe相が分離して窒化物の保磁力が低下し、実用的磁石ではなくなり、30原子%を越えると、希土類金属が析出し、合金粉末が大気中で不安定になり、残留磁化が低下するからである。他方、窒素Nを5〜15(原子%)の範囲と規定するのは、3原子%未満では、殆ど保磁力が発現せず、15原子%を超えると、希土類金属、鉄及びアルカリ金属それ自体の窒化物が生成するからである。
【0021】
磁性体粉末においては、希土類金属元素Rとしては、Ce、Pr、Nd、Smが利用できるが、特に、Smが、磁性体の飽和磁化、磁気異方性を大きくし、永久磁石とするために好ましいので、採用される。この場合、特に、上記式(1)の一般式SmxFe100-x-yNyにおいて、SmのxとNのyは原子%で表して、xは8.1〜10.0、yは13.5〜13.9の範囲が特に好ましい。
【0022】
磁性体粉末の平均粒子径は、1〜5μmの範囲が好ましい。これより粗粒であると、保磁力が5kOe以下となり、他方、これより細粒であると、酸化し易く式(1)の組成を保持するのが難しい。
【0023】
本発明において、遊離金属鉄を3%以下とするが、3%を超えると、著しく保磁力が低下するからである。ここに、X線回折強度比は、粉末X線回折法により、その磁性体粉末の最大回折強度(窒化物からの最大回折強度)IRTNを求め、その粉末のα−Fe相の最大回折強度IFeを計測し、100×IFe/IRTNをもって表す。α−Fe相の最大回折強度IFeは、CuKαのX線条件で、回折角2θ/θ=44〜46°について、回折強度の平滑化と加重平均を行い、バックグラウンドを除去し、ピークトップ強度をIFeとされる。
【0024】
X線回折強度比は、希土類金属−鉄−窒素系磁性体粉末中の金属鉄の重量%とで表した含有量と直線関係がある。X線回折強度比でα−Feが0%の磁性体粉末中に同じ粒子径程度の金属鉄粉末を一定の重量%で配合し、この混合粉を上記の要領で同じく粉末X線回折法により、α−FeのX線回折強度比を求めた。図2には、このようにして求めた金属鉄の重量%の含有量と、X線回折強度比の含有量との検量線を示している。図2は、SmxFe100-x-yNy磁性体の粉末における検量線である。この検量線から、X線回折強度比の測定値から、希土類金属−鉄−窒素系の遊離鉄含有量を求めることができる。
【0025】
磁性材料を製造するには、上記の組成式から選ばれた組成を得るために配合量が調製された希土類金属酸化物粉末と金属鉄粉末及び酸化鉄と、さらに、これら酸化物を還元するに充分な量の金属カルシウム粒とから成る混合物が準備される。
【0026】
還元拡散法による希土類金属−鉄−窒素系磁性材料の製造方法では、特開平6−081011号公報により開示したように、概して言えば、上記原料混合物は、不活性雰囲気中で加熱して酸化物をカルシウムが還元する還元過程と、還元された生成粉を窒素含有ガス中で加熱して窒化する窒化過程とを、経て希土類金属−鉄−窒素系磁性粉末が得られる。
【0027】
本発明の方法は、上記混合物中の希土類金属酸化物粉末と金属鉄粉末とが、平均粒径5μm以下に予め調製されている。さらに、混合粉中には、希土類金属酸化物粉末と金属鉄粉末とは、均一に分布されるように混合処理がなされる。
【0028】
金属鉄の粉末は、予め平均粒径5μm以下に調製されて原料として使用されるが、市販の金属鉄は、最小径のカーボニル鉄でさえ5μm程度の大きさがあり、これを鉄源として、カルシウム還元拡散法を利用しても、得られる磁性粉末は、粒径が5μm以上の粗粒となる。そこで磁気特性を高めるには、さらに、微粉砕が必要であるが、この場合には、従来法と同様に、最終的に生成された磁性粉末中には、金属鉄含有量が増加して、却って、保磁力が低下してしまう。
【0029】
本発明の製造方法は、好ましくは、金属鉄粉末を使用せずに、粒度調製された希土類金属酸化物粉末と酸化鉄粉末とを、金属カルシウム粒で完全に還元することが可能である。この場合には、その混合物中の酸化物とその還元に必要な多量の金属カルシウムとが爆発的に反応するおそれがあり、上記組成の反応生成物を得るのが難しい。
【0030】
そこで、本発明の製造方法は、鉄源として、粒度調製された金属鉄粉末と酸化鉄粉末との混合物が好ましく使用される。本発明の製造方法には、好ましくは、カルシウムによる還元拡散処理に先立って、酸化鉄予備還元処理過程を設けられる。金属鉄粉末には、酸化鉄粉末の一部を還元ガスにより予め還元した還元鉄が、極めて微細で、しかも、未還元の酸化鉄粉末と分離せずに一体化しているので、好ましく利用される。酸化鉄粉末の粒度を5μm以下とすることは製造上容易であるから、これにより、部分的に還元された金属鉄粉末も5μm以下とすることができる。
【0031】
酸化鉄からの金属鉄への還元率は、酸化鉄の酸素除去率で、50%以上であるのが好ましい。好ましくは、還元率は、70%以上がよい。ここに、酸化鉄の酸素除去率は、原料酸化鉄中に含まれる酸素量に対して、還元により除去された酸素量の割合を言う。原料としての酸化鉄は、ヘマタイト型(Fe2O3を主成分)でもマグネタイト型(Fe3O4を主成分)でもよく、その他の酸化鉄でもよい。好ましくは、Fe2O3型が使用される。予備還元処理過程では、水素還元又は一酸化炭素還元が利用されるが、水素還元の場合には、酸化鉄を水素気流中に300〜900℃の温度で一定時間保持して、その一部を鉄に還元させて、酸化鉄−金属鉄混合粉が得られる。予備還元処理に先立って、酸化鉄と希土類金属酸化物は、予め混合しておいてもよい。
【0032】
還元拡散処理は、反応容器中で、上記の酸化鉄−金属鉄混合粉に、微粒子の希土類金属酸化物粉末とを所定の配合に混合される。酸化物の酸素除去に必要且つ充分な量の金属カルシウム粒を均一に混合して、不活性雰囲気中でその混合物を600〜1100℃の温度で加熱すると、カルシウムとこれら酸化物とが反応し、酸化物を還元しながら発熱により高温になり、酸化物を合金粉末に還元する。この反応生成物を、冷却する。
【0033】
さらに、この反応生成物は、典型的にはそのまま、窒化処理のために、反応容器内で、雰囲気を窒素ガス又は窒素元素を含むガスに置換し、250〜800℃の温度範囲で加熱して保持して窒化され、希土類金属−鉄窒化物の粉末が形成される。
【0034】
この窒化処理された生成物は、洗浄処理により、水と弱酸溶液中で洗浄され、未反応カルシウムやその生成酸化物が除去されて、乾燥されて、希土類金属−鉄窒化物磁性粉末が得られる。このようにして得られた希土類金属−鉄窒化物磁性粉末は、粒径が5μm以下で、金属鉄含有量がX線回折強度比で3%以下である磁性粉末が得られる。
【0035】
ところで、従来の磁性粉末中の金属鉄の起源は、以下のように幾つか列挙することができる。第1の起源は、特に、溶解法におけるインゴットからの粉砕過程での金属α−鉄の析出である。溶解法では、インゴットの破砕と、窒化処理後の微粉砕の過程が利用されるが、これらの粉砕過程では、粒子表面が酸化され易く、α−鉄が析出し易くなる。
【0036】
第2の起源は、これも粉砕過程と関連があるが、還元拡散法において、原料粒子径が粗粒である場合に、磁性粉末を微細粒に調製するために、微粉砕する場合がある。この時にも、α−Feが析出し易くなる。
【0037】
第3の起源は、磁性粉末中のFe成分の偏析によるα−Feの析出である。還元拡散法において、原料の希土類金属酸化物と金属鉄ないし酸化鉄の混合が不十分で、粉末中部分的にFe成分が濃化偏析していると、α−Feが遊離鉄として析出し易くなる。
【0038】
本発明は、その製造過程で、このような従来の粉砕過程を必要としないので、α−Feの遊離がなく、α−Feに起因した保磁力の低下を防止することが容易にできるのである。
【0039】
【実施例】
純度99.9%で平均粒径1.2μmの酸化サマリウムSm2O3と、純度99.9%で平均粒径1.3μmの酸化鉄Fe2O3とを、湿式ボールミルにより1h(時間)の混合を行った。
【0040】
酸化鉄の予備還元過程として、上記の混合原料を水素気流中で、600℃の温度に保持して、酸化鉄の一部を鉄に還元した。酸化鉄の酸素除去率は、71%であった。
【0041】
カルシウム還元過程は、予備還元後の混合原料にカルシウム粒を、混合原料中の酸化物の酸素量の2倍量を混合し、このような混合原料を、真空加熱可能な容器に装入し、予め真空排気した後、Arガス気流中に1100℃に昇温し3h加熱保持して、カルシウム還元処理をおこない、容器内で50℃まで冷却した。次いで、窒化過程は、カルシウム還元後の粉末を容器内で真空排気後に、窒素ガスを流通させて、450℃に加熱して20h保持して、窒化処理を行い、その後冷却した。
【0042】
得られた窒化生成物は、多孔質の塊状であるが、イオン交換水中で容易に崩壊し粉化する。洗浄過程においては、この崩壊を利用して、生成物中のカルシアや窒化カルシウム、未反応のカルシウム等の副生成物が、イオン交換水中で水酸化カルシウムの形で除去される。デカンテーションを数回繰り返し、目的の磁性体粉末が、沈澱物として回収した。さらに、副生成物を完全に除くために、pH4.5に調製した酢酸水溶液中でデカンテーションを行い、水洗した。スラリー状の沈澱物は、遠心分離され、アルコールで置換され、得られたケーキは、80℃で真空乾燥され、磁性体粉末が得られた。以上の過程では、粉砕は、一切行わなかった。
【0043】
得られた磁性体粉末の組成と、α−Feの含有量、及び、粉末の残留磁化Brと保磁力iHcとを表1に示した。
【0044】
磁性体粉末は、X線回折法により、金属鉄(α−Fe)の含有量を測定した。X線回折強度測定の条件は、X線Cu−Kα、印加電圧40kV、電流40mA、発散スリット1°、散乱スリット1°、受光スリット0.15mm、走査を連続とし、走査速度4°/min、走査ステップ0.02°、走査範囲15〜70°とした。
【0045】
X線回折強度のデータから、その磁性体粉末の最大回折強度(窒化物からの最大回折強度)IRTNを求めた。α−Fe相の最大回折強度IFeは、回折角2θ/θ=44〜46°について回折強度の平滑化と加重平均を行い、バックグラウンドを除去し、ピークトップ強度をIFeを求めて、100×IFe/IRTNをもって、遊離金属鉄(α−Fe)の含有量とした。
【0046】
検量線は、組成Sm9.10Fe77.24O13.64(金属鉄含有量0.06%;X線回折強度比)の粉末に、カルボニル鉄(粒径5μm)を、重量%で、1%、2%、3%及び5%をそれぞれ混合して、標準試料を作り、上記の方法でその試料混合粉の鉄含有量をX線回折強度で測定した。図2は、磁性粉末中に混合された金属鉄(α−Fe)の重量で表した含有量とこの試料のX線回折強度比から測定された金属鉄の含有量との間の直線関係を示しており、良好な直線性が得られている。この直線を検量線として、X線回折強度比からの金属鉄含有量から、金属鉄の重量パーセントが求められる。
【0047】
実施例と比較例の磁性体粉末の残留磁化Brと保磁力iHcは、粉末をカプセルに充填し溶解させたパラフィン中で、20kOeで磁場を印加した50kOeパルス磁場で着磁した後、VSM磁気特性測定装置で調べた。
【0048】
実施例1は、表1に示すように、SmとFeとの原子%10.72%と89.28%の配合で、得られた磁性体粉末は、金属鉄の含有量がX線回折強度比で0.29%(換算した重量パーセントで、0.2%)、残留磁化13.8kG、保磁力15.8kOeであった。他の実施例は、実施例1の試料と比較して、Smの配合組成を順次高めたものである。
【0049】
比較例1は、溶融法による製造した磁性体粉末に関するものであるが、純度99.9%で金属サマリウムSmと、純度99.9%の金属鉄とを、原子%で、10.72%と89.28%になるように、高周波炉で溶解した合金をインゴットに鋳造し、インゴットを3cmの小塊にまで破砕した。この合金小塊は、Ar気流中で1400℃で、5hの均質化を行った。得られた合金小塊を、ボールミルにより、5μmの微粉に粉砕した。この微粉末を、窒素気流中で450℃で20hの加熱と窒化をおこない、窒化粉末をさらに5μmにまで粉砕して、サマリウム鉄窒化物磁性体粉末を得た。
【0050】
比較例2は、還元拡散法に粉砕過程を設定した例であるが、純度99.9%で平均粒径1.2μmの酸化サマリウムSm2O3と、純度99.9%で平均粒径50μmの粗大な還元鉄とを、SmとFeとの比が、原子%で、10.72%と89.72%になるように混合調製し、混合粉末に、実施例1同様に、酸素原子当量の2倍の当量の金属カルシウム粒を混合して還元し、窒化過程を経て磁性体粉末を製造した。この粉末は、平均60μmの粒径であったので、ボールミル6Hで粉砕し、平均粒子径5.2μmに調製した。この粉末は、Sm8.12Fe77.96N13.84Ca0.08の組成式であった。α−Feの含有量は、X線回折強度比で、4.6%で、残留磁化12.1kG、保磁力6.8kOeを示した。
【0051】
比較例3は、還元拡散法により、鉄源に金属鉄を利用し粉砕過程を設けた方法であるが、純度99.9%で平均粒径1.2μmの酸化サマリウムSm2O3と、純度99.9%で平均粒径5.2μmのカルボニル鉄とを、SmとFeとの比が、原子%で、10.72%と89.28%になるように混合調製し、混合粉末に、実施例1同様に、酸素原子当量の2倍量の金属カルシウムCaを混合し、実施例1と同様に還元過程と窒化過程により、磁性体粉末を製造した。この粉末は、平均8.2μmの粒径であったので、ボールミル6Hで粉砕し、平均粒子径3.2μmに調製した。この粉末は、Sm8.22Fe78.04N13.69Ca0.05の組成式であった。α−Feの含有量は、X線回折強度比で、3.6%で、残留磁化13.1kG、保磁力9.8kOeを示した。
【0052】
比較例4は、混合不十分の原料粉から、還元拡散法により製造する方法であるが、純度99.9%で平均粒径1.2μmの酸化サマリウムSm2O3と、純度99.9%で平均粒径1.3μmの酸化鉄(Fe2O3)とを、SmとFeとの比が、原子%で、10.72%と89.72%になるように配合し、合成樹脂フィルムの袋内で2min程度の混合を行った。この混合粉末は、EPMA観察により、SmとFeの偏析部分が全体の75%以上あることが認められた。この混合粉末を、水素気流中で予備還元したあと、実施例1同様に、酸素原子当量の2倍量の金属カルシウムCaを混合し、実施例1と同様に還元過程と窒化過程により、磁性体粉末を製造した。この粉末は、Sm8.14Fe78.19N13.61Ca0.06の平均組成であった。α−Feの含有量は、X線回折強度比で、3.12%で、残留磁化13.1kG、保磁力9.8kOeを示した。
【0053】
比較例1と実施例1の粉末法によるX線回折チャートを、それぞれ図3と図4に示すが、比較例1(図3)は、主結晶からの回折強度に対して、比較的大きなα−Fe相の回折ピークが検出されている。上記のX線回折強度では、α−Feの含有量は4.6%にも達する。これに対して実施例1(図4)は、α−Fe相の回折強度が小さく、X線回折強度で見たα−Feの含有量は、0.3%程度で極めて少ないことがわかる。
【0054】
【表1】
【0055】
上記の実施例と比較例の以上の結果を、表1と図1に示す。これから、磁性体粉末中の金属鉄(α−Fe)の含有量と保磁力(iHc)とは顕著な関係を有し、特に、X線回折強度比で見た金属鉄の含有量が3%以下の範囲で、金属鉄含有量の増加とともに、保磁力が著しく低下していることが判る。この結果から、金属鉄(α−Fe)の含有量は、3%以下とすべきことがわかる。特に、実施例1〜5のように、金属鉄(α−Fe)の含有量は、1%程度ないしは、それ以下とすべきである。
【0056】
【発明の効果】
本発明は、希土類金属−鉄−窒素系磁性粉末中の金属鉄の含有量がX線回折強度比で3%以下とするので、磁気的に特に保磁力の高い安定な希土類金属−鉄−窒素系磁性材料を提供することができる。
【0057】
さらに、本発明の製造方法は、希土類金属酸化物粉末と金属鉄粉末と酸化鉄と金属カルシウム粒とから成る混合物をカルシウム還元過程と、窒化する過程とにより、希土類金属酸化物粉末と金属鉄粉末とが、平均粒径5μm以下で、且つ均一に分布させるので、粉砕を回避して、磁気的に特に保磁力の高い安定な希土類金属−鉄−窒素系磁性材料を提供することができる。
【0058】
さらに、本発明方法は、原料混合物中の当該金属鉄が、酸化鉄微粉末の一部を還元ガスにより還元した還元鉄とするので、酸化鉄からの金属鉄への還元率が、酸化鉄の酸素除去率で、50%以上としておくので、カルシウム還元が安定化され、粉砕をすることなく、平均粒径5μm以下で且つ金属鉄の含有量がX線回折強度比で3%以下とすることが容易にできる。
【図面の簡単な説明】
【図1】本発明の実施例にかかる希土類金属元素−鉄−窒素系の磁性体粉末中の遊離鉄含有量と保磁力の関係を示す図。
【図2】希土類金属元素−鉄−窒素系の磁性体粉末中の遊離鉄のX線回折強度比で表した含有量と、重量%との関係を示す図。
【図3】比較例の磁性体粉末のX線回折チャートを示す。
【図4】本発明の実施例の磁性体粉末のX線回折チャートを示す。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a magnetic material using a rare earth metal-iron nitride powder, in particular, a magnetic material having a stable and high coercive force.
[0002]
[Prior art]
The rare earth metal R-iron Fe-nitrogen N-based magnetic material is a nitride-based powdered magnetic material in which nitrogen is absorbed by a rare earth metal R-iron Fe alloy, and the magnetic powder is solidified by a resin or the like. Or sintered and used as a permanent magnet. Rare earth metal-iron-nitrogen based magnetic materials have both large remanent magnetization and coercive force, and their use is drawing attention.
[0003]
Conventionally, a dissolution method and a reduction diffusion method are known for the production of rare earth metal-iron-nitrogen based magnetic materials. In the melting method, rare earth metal and iron are melted as a raw material and cast into an ingot. The ingot is pulverized to form a rare earth metal-iron alloy powder. It is a method of containing.
[0004]
In the reduction diffusion method, Ca particles are mixed with a mixed powder of rare earth metal oxide powder and metal iron or iron oxide powder as a raw material, and heated in an inert atmosphere to reduce these oxide powder with Ca. Then, a rare earth metal-iron-alloy powder is obtained, and this is nitrided to obtain a rare earth metal-iron-nitrogen-based material in powder form (for example, JP-A-6-81010).
[0005]
These magnetic powders are, for example, kneaded with a binder such as a synthetic resin and molded, and are magnetized in a molding and curing process to be used as a strong magnet having a desired shape.
[0006]
[Problems to be solved by the invention]
The rare earth metal-iron-nitrogen based magnetic powders formed by these production methods generally have high remanent magnetization and high coercive force, but depending on the production method, depending on the production lot However, the magnetic properties are not as high as expected, and in particular, the coercive force is low and the variation is large. Furthermore, it has been clarified that the decrease in coercive force is related to the process of pulverization and mixing for pulverization in the manufacturing process. This problem is important for maintaining the quality of the magnetic powder and the magnet using it.
[0007]
As described above, an object of the present invention is to provide a rare earth metal-iron-nitrogen based magnetic powder having a stable and high coercive force and a small variation in magnetic powder usable for a permanent magnet.
[0008]
[Means for Solving the Problems]
The present invention is based on the finding that the decrease in coercive force of rare earth metal-iron-nitrogen based magnetic powder is due to the presence of free metallic iron in the nitride based magnetic body. That is, the rare earth metal-iron-nitrogen based magnetic material reduces the content of metallic iron in the nitride magnetic powder to 3% or less with respect to the maximum diffraction intensity of the magnetic powder by the X-ray diffraction intensity ratio, This prevents a reduction in coercive force due to free metal iron.
[0009]
The rare earth metal-iron-nitrogen based magnetic powder is formed from a rare earth metal-iron nitride powder, but the metallic iron present in the powder is released from the rare earth iron nitride to produce pure iron having a bcc structure. Or the crystal | crystallization (namely, (alpha) -Fe) of the solid solution. Since metallic iron (α-Fe) exhibits soft magnetism, the presence of metallic iron in the magnetic powder reduces the magnetic properties, particularly the coercive force, of the rare earth metal-iron nitride. In the present invention, the metallic iron content in the magnetic powder is restricted to 3% or less, and the excellent magnetic properties of this material are exhibited.
[0010]
Here, the content of metallic iron depends on the X-ray diffraction intensity ratio, which is the ratio of the diffraction intensity of the α-Fe phase crystal of the magnetic powder to the maximum diffraction intensity of the magnetic powder by the X-ray diffraction method. Shown in 100 minutes. The content of metallic iron defined in this way corresponds to the content of free α-Fe. The content of metallic iron measured from the X-ray diffraction intensity is the content represented by the weight of metallic iron (α-Fe) mixed in the magnetic powder as shown in the calibration curve shown in FIG. There is a linear relationship with the quantity, and the weight% can be easily obtained from this calibration curve.
[0011]
In the rare earth metal-iron-nitrogen based magnetic material, the above rare earth metal-iron-nitrogen based magnetic powder is composed of 3-30% rare earth metal, 5-15% N, balance Fe and inevitable in atomic percent. Those consisting of general impurities are preferred. The magnetic material having this composition is represented by the general formula R x Fe 100-xy N y (1)
In a nitride composition represented, here, R represents indicates samarium is a rare earth metal element, x is in the range of 3 <x <30 at% of rare earth metal element R, y is nitrogen N In the range of 5 <y <15.
[0012]
The finer the powder particles of the rare earth metal-iron-nitrogen based magnetic material, the better the magnetic properties. Therefore, the particle size of the magnetic material must be 10 μm or less, and particularly preferably 5 μm or less. .
[0013]
The method for producing a rare earth metal-iron-nitrogen based magnetic material of the present invention comprises heating a mixture of rare earth metal oxide powder, metal iron powder, iron oxide and metal calcium particles in an inert atmosphere in the reduction diffusion method. Thus, a rare earth metal-iron-nitrogen based magnetic powder is used, which includes a reduction process in which calcium reduction is performed and a nitridation process in which the product is heated and nitrided in a nitrogen-containing atmosphere.
[0014]
The present invention is characterized in that, in the above reduction diffusion method, the rare earth metal oxide powder and the iron oxide powder of the raw material mixture are regulated to have an average particle size of 5 μm or less and mixed to be uniformly distributed. In the reduction diffusion method, the growth of crystal grains is relatively small in both the reduction process and the nitriding process. Therefore, if the rare earth metal oxide powder and the iron oxide powder are prepared in advance with an average particle size of 5 μm or less, the rare earth metal-iron-nitrogen based magnetic powder produced after nitriding is also fine particles having a particle size of approximately 5 μm or less. The diameter is obtained. As a result, the magnetic material powder is improved in magnetic properties due to being fine particles, and since it does not require pulverization, the magnetic properties are prevented from deteriorating due to the precipitation of free iron. It is possible to obtain a fine powder magnetic body having
[0015]
The decrease in coercive force due to the inclusion of metallic iron in the magnetic material of this system occurs more significantly than the decrease in coercive force due to voids when it is assumed that the metallic iron particles are voids in the magnetic particles or magnets. The reason for this is that since metallic iron exhibits soft magnetism, the metallic iron in the rare earth metal-iron nitride powder constituting the magnet is exposed to an opposite strong magnetic field, and even in a low magnetic field, the magnetic domain of metallic iron is reduced. The movement and rotation easily occur, and the movement and rotation of the magnetic domain to the surrounding nitride particles is induced from this as a starting point, and the magnetization is lowered. Therefore, the distribution of the contained metal iron is the same as that of the rare earth metal-iron nitride. This is because the magnetic properties, particularly the coercive force, are significantly reduced.
[0016]
It has been found that the metallic iron in the magnetic material is generated and increased by grinding a rare earth metal-iron-nitrogen based magnetic material or a rare earth metal-iron alloy before nitriding in the manufacturing process. In the conventional reductive diffusion method, when the raw material particles are coarse particles, the magnetic powder also becomes coarse particles, and it is necessary to prepare this into fine particles. -Iron is likely to precipitate, and on the contrary, the magnetic properties of the magnetic powder are deteriorated. When the magnetic powder is pulverized, the rare earth metal-iron nitride particles of the magnetic powder are subjected to strain deformation and transformed into another intermediate phase, and α-Fe precipitates in this process. This is because α-Fe increases.
[0017]
In the production method of the present invention, the raw metal iron powder is prepared in advance to have an average particle size of 5 μm or less by utilizing the reduction diffusion method. Therefore, the magnetic powder obtained by nitriding after reduction is not pulverized. Fine particles having a desired particle diameter can be prepared. Therefore, the magnetic material after the nitriding treatment can regulate the metal iron content to 3% or less, which gives a high coercive force to the magnetic powder.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
In an embodiment of the present invention, the rare earth metal-iron-nitrogen based magnetic powder is composed of 3 to 30% rare earth metal, 5 to 15% N, the balance Fe and inevitable impurities. Things are used. Free metal iron (α-Fe) in the magnetic powder is 3% or less with respect to the maximum diffraction intensity of the magnetic powder in the X-ray diffraction intensity ratio.
[0019]
The main component of the magnetic powder is the general formula R x Fe 100-xy N y ... (1)
The rare earth metal R is a nitride composed of iron Fe and nitrogen N, and the rare earth metal R has an x in the range of 3 to 30 and an atomic% y of N in the range of 5 to 15 ( The balance is mainly Fe in the range of (atomic%).
[0020]
Here, the rare earth metal R is defined as 3 to 30 atomic%. If it is less than 3 atomic%, the α-Fe phase is separated and the coercive force of the nitride is reduced, and the practical magnet is not used. This is because rare earth metals are precipitated when the temperature exceeds the range, the alloy powder becomes unstable in the atmosphere, and the remanent magnetization decreases. On the other hand, nitrogen N is defined to be in the range of 5 to 15 (atomic%). When it is less than 3 atomic%, almost no coercive force is exhibited, and when it exceeds 15 atomic%, rare earth metal, iron and alkali metal itself. This is because the nitrides are formed.
[0021]
In the magnetic powder, Ce, Pr, Nd, and Sm can be used as the rare earth metal element R. In particular, since Sm increases the saturation magnetization and magnetic anisotropy of the magnetic material, it becomes a permanent magnet. Adopted because it is preferable. In this case, in particular, in the general formula Sm x Fe 100-xy N y of the above formula (1), x of Sm and y of N are expressed in atomic%, x is 8.1 to 10.0, and y is 13 A range of .5 to 13.9 is particularly preferred.
[0022]
The average particle size of the magnetic powder is preferably in the range of 1 to 5 μm. If it is coarser than this, the coercive force becomes 5 kOe or less. On the other hand, if it is finer than this, it is easy to oxidize and it is difficult to maintain the composition of formula (1).
[0023]
In this invention, it is because free metal iron shall be 3% or less, but if it exceeds 3%, a coercive force will fall remarkably. Here, the X-ray diffraction intensity ratio is determined by the powder X-ray diffraction method to obtain the maximum diffraction intensity (maximum diffraction intensity from nitride) I RTN of the magnetic powder, and the maximum diffraction intensity of the α-Fe phase of the powder. I Fe is measured and expressed as 100 × I Fe / I RTN . The maximum diffraction intensity I Fe of the α-Fe phase is obtained by smoothing the diffraction intensity and performing a weighted average for the diffraction angle 2θ / θ = 44 to 46 ° under the X-ray condition of CuKα, removing the background, The strength is I Fe .
[0024]
The X-ray diffraction intensity ratio has a linear relationship with the content represented by the weight percent of metallic iron in the rare earth metal-iron-nitrogen based magnetic powder. An iron powder of the same particle size is blended at a constant weight% in a magnetic powder having an X-ray diffraction intensity ratio of α-Fe of 0%, and this mixed powder is similarly obtained by the powder X-ray diffraction method as described above. , Α-Fe X-ray diffraction intensity ratio was determined. FIG. 2 shows a calibration curve of the content of metallic iron in weight% thus obtained and the content of the X-ray diffraction intensity ratio. FIG. 2 is a calibration curve for powder of Sm x Fe 100-xy N y magnetic material. From this calibration curve, the free iron content of the rare earth metal-iron-nitrogen system can be determined from the measured value of the X-ray diffraction intensity ratio.
[0025]
In order to produce a magnetic material, a rare earth metal oxide powder, a metal iron powder and an iron oxide whose blending amounts are prepared to obtain a composition selected from the above composition formula, and further to reduce these oxides. A mixture comprising a sufficient amount of metallic calcium particles is prepared.
[0026]
Generally speaking, in the method for producing a rare earth metal-iron-nitrogen based magnetic material by the reduction diffusion method, as disclosed in JP-A-6-0810111, generally speaking, the raw material mixture is heated in an inert atmosphere to produce an oxide. A rare earth metal-iron-nitrogen based magnetic powder is obtained through a reduction process in which calcium is reduced and a nitriding process in which the reduced product powder is heated in a nitrogen-containing gas for nitriding.
[0027]
In the method of the present invention, the rare earth metal oxide powder and the metal iron powder in the above mixture are prepared in advance with an average particle size of 5 μm or less. Further, the mixed powder is mixed so that the rare earth metal oxide powder and the metal iron powder are uniformly distributed.
[0028]
Metallic iron powder is prepared in advance with an average particle size of 5 μm or less and used as a raw material. However, commercially available metallic iron has a size of about 5 μm even with the smallest diameter carbonyl iron, and this is used as an iron source. Even when the calcium reduction diffusion method is used, the obtained magnetic powder becomes coarse particles having a particle size of 5 μm or more. Therefore, further pulverization is necessary to enhance the magnetic properties. In this case, as in the conventional method, in the finally produced magnetic powder, the content of metallic iron increases, On the other hand, the coercive force decreases.
[0029]
In the production method of the present invention, preferably, the rare earth metal oxide powder and the iron oxide powder whose particle sizes are adjusted can be completely reduced with metal calcium particles without using metal iron powder. In this case, the oxide in the mixture and a large amount of metallic calcium necessary for the reduction may react explosively, and it is difficult to obtain a reaction product having the above composition.
[0030]
Therefore, in the production method of the present invention, a mixture of metal iron powder and iron oxide powder whose particle size is adjusted is preferably used as the iron source. The production method of the present invention is preferably provided with an iron oxide preliminary reduction treatment process prior to the reduction diffusion treatment with calcium. The metal iron powder is preferably used because reduced iron obtained by reducing a part of the iron oxide powder in advance with a reducing gas is very fine and integrated with the unreduced iron oxide powder without being separated. . Since it is easy in production to make the particle size of the iron oxide powder 5 μm or less, the partially reduced metal iron powder can also be 5 μm or less.
[0031]
The reduction rate of iron oxide to metallic iron is preferably an oxygen removal rate of iron oxide of 50% or more. Preferably, the reduction rate is 70% or more. Here, the oxygen removal rate of iron oxide refers to the ratio of the amount of oxygen removed by reduction to the amount of oxygen contained in the raw iron oxide. The iron oxide as a raw material may be a hematite type (main component of Fe 2 O 3 ) or a magnetite type (main component of Fe 3 O 4 ), or other iron oxides. Preferably, Fe 2 O 3 type is used. In the preliminary reduction process, hydrogen reduction or carbon monoxide reduction is used. In the case of hydrogen reduction, iron oxide is kept in a hydrogen stream at a temperature of 300 to 900 ° C. for a certain period of time, and a part thereof is retained. Reduction to iron gives an iron oxide-metal iron mixed powder. Prior to the preliminary reduction treatment, the iron oxide and the rare earth metal oxide may be mixed in advance.
[0032]
In the reduction-diffusion treatment, fine particles of rare earth metal oxide powder are mixed with the above-mentioned iron oxide-metal iron mixed powder in a reaction vessel in a predetermined composition. When the calcium oxide particles necessary and sufficient for oxygen removal from the oxide are uniformly mixed and the mixture is heated at a temperature of 600 to 1100 ° C. in an inert atmosphere, the calcium and these oxides react, While reducing the oxide, the temperature rises due to heat generation, and the oxide is reduced to alloy powder. The reaction product is cooled.
[0033]
Further, this reaction product is typically left as it is for nitriding treatment by replacing the atmosphere with nitrogen gas or a gas containing nitrogen element in a reaction vessel and heating in a temperature range of 250 to 800 ° C. Holding and nitriding, rare earth metal-iron nitride powder is formed.
[0034]
This nitrided product is washed in water and a weak acid solution by a washing treatment to remove unreacted calcium and its generated oxide and dried to obtain a rare earth metal-iron nitride magnetic powder. . The rare earth metal-iron nitride magnetic powder thus obtained is a magnetic powder having a particle size of 5 μm or less and a metal iron content of 3% or less in terms of X-ray diffraction intensity ratio.
[0035]
By the way, the origin of the metallic iron in the conventional magnetic powder can be enumerated as follows. The first origin is, in particular, the deposition of metal α-iron during the grinding process from the ingot in the melting method. In the melting method, a process of ingot crushing and fine pulverization after nitriding is used. In these pulverization processes, the particle surface is easily oxidized, and α-iron is likely to precipitate.
[0036]
The second origin is also related to the pulverization process, but in the reduction diffusion method, when the raw material particle diameter is coarse, the magnetic powder may be finely pulverized to prepare fine particles. Also at this time, α-Fe is likely to precipitate.
[0037]
The third origin is the precipitation of α-Fe due to segregation of the Fe component in the magnetic powder. In the reduction diffusion method, α-Fe is likely to be precipitated as free iron if the raw material rare earth metal oxide and metal iron or iron oxide are not sufficiently mixed and the Fe component is partially concentrated and segregated in the powder. Become.
[0038]
Since the present invention does not require such a conventional pulverization process in the production process, there is no liberation of α-Fe and it is possible to easily prevent a decrease in coercive force due to α-Fe. .
[0039]
【Example】
A samarium oxide Sm 2 O 3 having a purity of 99.9% and an average particle diameter of 1.2 μm and iron oxide Fe 2 O 3 having a purity of 99.9% and an average particle diameter of 1.3 μm are mixed with a wet ball mill for 1 hour (hours). Was mixed.
[0040]
As a pre-reduction process of iron oxide, the mixed raw material was held at a temperature of 600 ° C. in a hydrogen stream, and a part of the iron oxide was reduced to iron. The oxygen removal rate of iron oxide was 71%.
[0041]
In the calcium reduction process, calcium particles are mixed with the mixed raw material after the preliminary reduction, twice the amount of oxygen in the mixed raw material, and the mixed raw material is charged into a vacuum heatable container. After evacuating in advance, the temperature was raised to 1100 ° C. in an Ar gas stream, heated and held for 3 hours, subjected to calcium reduction treatment, and cooled to 50 ° C. in the container. Next, in the nitriding process, the powder after calcium reduction was evacuated in a container, then nitrogen gas was circulated, heated to 450 ° C. and held for 20 hours, subjected to nitriding treatment, and then cooled.
[0042]
The obtained nitridation product is a porous lump, but easily disintegrates and powders in ion-exchanged water. In the washing process, by utilizing this disintegration, by-products such as calcia, calcium nitride, and unreacted calcium in the product are removed in the form of calcium hydroxide in ion-exchanged water. Decantation was repeated several times, and the target magnetic powder was recovered as a precipitate. Further, in order to completely remove the by-product, decantation was performed in an acetic acid aqueous solution adjusted to pH 4.5 and washed with water. The slurry-like precipitate was centrifuged and replaced with alcohol, and the resulting cake was vacuum-dried at 80 ° C. to obtain a magnetic powder. In the above process, no pulverization was performed.
[0043]
Table 1 shows the composition of the obtained magnetic powder, the content of α-Fe, the residual magnetization Br and the coercive force iHc of the powder.
[0044]
The magnetic powder was measured for the content of metallic iron (α-Fe) by X-ray diffraction. The X-ray diffraction intensity measurement conditions were: X-ray Cu-Kα, applied
[0045]
From the X-ray diffraction intensity data, the maximum diffraction intensity (maximum diffraction intensity from nitride) I RTN of the magnetic powder was determined. The maximum diffraction intensity I Fe of the α-Fe phase is obtained by smoothing and weighting the diffraction intensity for a diffraction angle 2θ / θ = 44 to 46 °, removing the background, and determining the peak top intensity I Fe . The content of free metal iron (α-Fe) was defined as 100 × I Fe / I RTN .
[0046]
The calibration curve is a powder of composition Sm 9.10 Fe 77.24 O 13.64 (metallic iron content 0.06%; X-ray diffraction intensity ratio), carbonyl iron (particle size 5 μm), 1%, 2% by weight, 3% and 5% were mixed to prepare a standard sample, and the iron content of the sample mixed powder was measured by X-ray diffraction intensity by the above method. FIG. 2 shows the linear relationship between the content expressed by the weight of metallic iron (α-Fe) mixed in the magnetic powder and the content of metallic iron measured from the X-ray diffraction intensity ratio of this sample. It shows that good linearity is obtained. Using this straight line as a calibration curve, the weight percentage of metallic iron is determined from the metallic iron content from the X-ray diffraction intensity ratio.
[0047]
The residual magnetization Br and the coercive force iHc of the magnetic powders of the examples and comparative examples were measured in the paraffin in which the powder was filled in a capsule and dissolved, and magnetized with a 50 kOe pulse magnetic field applied with a magnetic field of 20 kOe, and then VSM magnetic properties It investigated with the measuring apparatus.
[0048]
As shown in Table 1, Example 1 is composed of Sm and Fe in an atomic percentage of 10.72% and 89.28%, and the obtained magnetic powder has a metal iron content of X-ray diffraction intensity. The ratio was 0.29% (converted weight percent, 0.2%), remanent magnetization 13.8 kG, and coercive force 15.8 kOe. Other examples are obtained by sequentially increasing the composition of Sm as compared with the sample of Example 1.
[0049]
Comparative Example 1 relates to a magnetic powder produced by a melting method, and a metal samarium Sm having a purity of 99.9% and a metal iron having a purity of 99.9% are converted to 10.72% in atomic percent. The alloy melted in the high frequency furnace was cast into an ingot so as to be 89.28%, and the ingot was crushed into 3 cm small lumps. The alloy blob was homogenized at 1400 ° C. for 5 h in an Ar stream. The obtained alloy blob was pulverized into a fine powder of 5 μm by a ball mill. This fine powder was heated and nitrided at 450 ° C. for 20 hours in a nitrogen stream, and the nitrided powder was further pulverized to 5 μm to obtain a samarium iron nitride magnetic powder.
[0050]
Comparative Example 2 is an example in which the pulverization process is set in the reduction diffusion method, and samarium oxide Sm 2 O 3 having a purity of 99.9% and an average particle diameter of 1.2 μm, and an average particle diameter of 50 μm with a purity of 99.9%. Coarse reduced iron with a ratio of Sm and Fe in atomic% of 10.72% and 89.72% was prepared by mixing, and the mixed powder was subjected to oxygen atom equivalent as in Example 1. 2 times the equivalent amount of metal calcium particles was mixed and reduced, and a magnetic powder was produced through a nitriding process. Since this powder had an average particle size of 60 μm, it was pulverized with a ball mill 6H to prepare an average particle size of 5.2 μm. This powder had a composition formula of Sm 8.12 Fe 77.96 N 13.84 Ca 0.08 . The content of α-Fe was 4.6% in terms of X-ray diffraction intensity ratio, showing a remanent magnetization of 12.1 kG and a coercive force of 6.8 kOe.
[0051]
Comparative Example 3 is a method in which metallic iron is used as an iron source by a reduction diffusion method and a pulverization process is provided. Samarium oxide Sm 2 O 3 having a purity of 99.9% and an average particle size of 1.2 μm, 99.9% of carbonyl iron having an average particle size of 5.2 μm was mixed and prepared so that the ratio of Sm to Fe was 10.72% and 89.28% in atomic%. In the same manner as in Example 1, metallic calcium Ca having twice the oxygen atom equivalent amount was mixed, and the magnetic powder was produced by the reduction process and the nitriding process in the same manner as in Example 1. Since this powder had an average particle size of 8.2 μm, it was pulverized with a ball mill 6H to prepare an average particle size of 3.2 μm. This powder had a composition formula of Sm 8.22 Fe 78.04 N 13.69 Ca 0.05 . The content of α-Fe was 3.6% in terms of X-ray diffraction intensity ratio, showing a residual magnetization of 13.1 kG and a coercive force of 9.8 kOe.
[0052]
Comparative Example 4 is a method of producing from a raw material powder with insufficient mixing by a reduction diffusion method. Samarium oxide Sm 2 O 3 having a purity of 99.9% and an average particle diameter of 1.2 μm and a purity of 99.9% And an iron oxide (Fe 2 O 3 ) having an average particle size of 1.3 μm is blended so that the ratio of Sm to Fe is 10.72% and 89.72% in terms of atomic%. Was mixed for about 2 min. This mixed powder was confirmed by EPMA observation to have 75% or more of the segregated portion of Sm and Fe. After this mixed powder was pre-reduced in a hydrogen stream, metallic calcium Ca having an amount equivalent to twice the oxygen atom equivalent was mixed as in Example 1, and the magnetic substance was obtained by the reduction process and nitridation process as in Example 1. A powder was produced. This powder had an average composition of Sm 8.14 Fe 78.19 N 13.61 Ca 0.06 . The content of α-Fe was 3.12% in terms of X-ray diffraction intensity ratio, showing a residual magnetization of 13.1 kG and a coercive force of 9.8 kOe.
[0053]
X-ray diffraction charts of the powder method of Comparative Example 1 and Example 1 are shown in FIGS. 3 and 4, respectively. Comparative Example 1 (FIG. 3) has a relatively large α with respect to the diffraction intensity from the main crystal. A diffraction peak of -Fe phase is detected. With the above X-ray diffraction intensity, the α-Fe content reaches 4.6%. On the other hand, Example 1 (FIG. 4) shows that the diffraction intensity of the α-Fe phase is small, and the content of α-Fe in terms of X-ray diffraction intensity is about 0.3%, which is very small.
[0054]
[Table 1]
[0055]
The above results of the above examples and comparative examples are shown in Table 1 and FIG. From this, the content of metallic iron (α-Fe) in the magnetic powder and the coercive force (iHc) have a significant relationship, and in particular, the content of metallic iron in terms of X-ray diffraction intensity ratio is 3%. In the following range, it can be seen that the coercive force is remarkably lowered with the increase in the content of metallic iron. From this result, it is understood that the content of metallic iron (α-Fe) should be 3% or less. In particular, as in Examples 1 to 5, the content of metallic iron (α-Fe) should be about 1% or less.
[0056]
【The invention's effect】
In the present invention, since the content of metallic iron in the rare earth metal-iron-nitrogen based magnetic powder is 3% or less in terms of the X-ray diffraction intensity ratio, it is a stable rare earth metal-iron-nitrogen having a particularly high coercive force. A magnetic system material can be provided.
[0057]
Furthermore, the production method of the present invention includes a rare earth metal oxide powder, a metal iron powder, a metal iron powder, an iron oxide, and a metal iron powder by a calcium reduction process and a nitriding process. However, since it has an average particle size of 5 μm or less and is uniformly distributed, a stable rare earth metal-iron-nitrogen based magnetic material having a particularly high coercive force can be provided by avoiding pulverization.
[0058]
Furthermore, in the method of the present invention, since the metallic iron in the raw material mixture is reduced iron obtained by reducing a part of the iron oxide fine powder with a reducing gas, the reduction rate of iron oxide to metallic iron is Since the oxygen removal rate is set to 50% or more, the calcium reduction is stabilized, the average particle size is 5 μm or less, and the iron content is 3% or less in terms of the X-ray diffraction intensity ratio without pulverization. Can be easily done.
[Brief description of the drawings]
FIG. 1 is a graph showing the relationship between free iron content and coercivity in a rare earth metal element-iron-nitrogen based magnetic powder according to an example of the present invention.
FIG. 2 is a graph showing the relationship between the content expressed by the X-ray diffraction intensity ratio of free iron in a rare earth metal element-iron-nitrogen based magnetic powder and weight percent.
FIG. 3 shows an X-ray diffraction chart of a magnetic powder of a comparative example.
FIG. 4 shows an X-ray diffraction chart of a magnetic powder of an example of the present invention.
Claims (4)
前記酸化鉄粉と、前記過程により該酸化鉄粉の一部を還元した還元鉄を含む粉末と、希土類金属酸化物粉末と、金属カルシウム粒とから成る混合物を加熱してカルシウム還元する過程と、
還元後の生成物を窒素含有雰囲気で窒化する過程と
を含んで希土類金属−鉄−窒素系磁性体粉末にする希土類金属−鉄−窒素系磁性材料の製造方法において、
希土類金属酸化物粉末と酸化鉄粉とが、平均粒径5μm以下であって、且つ均一に混合されていることを特徴とする希土類金属−鉄−窒素系磁性材料の製造方法。 A pre-reduction treatment process in which a part of iron oxide is reduced to iron by hydrogen or carbon monoxide in a mixture of samarium oxide and iron oxide powder,
A process of reducing the calcium by heating a mixture of the iron oxide powder , a powder containing reduced iron obtained by reducing a part of the iron oxide powder by the process, a rare earth metal oxide powder, and metal calcium particles;
In the method for producing a rare earth metal-iron-nitrogen based magnetic material, including a step of nitriding the reduced product in a nitrogen-containing atmosphere to make a rare earth metal-iron-nitrogen based magnetic powder,
A method for producing a rare earth metal-iron-nitrogen based magnetic material, wherein the rare earth metal oxide powder and the iron oxide powder have an average particle size of 5 μm or less and are uniformly mixed.
一般式RxFe100-x-yNy・・・・・(1)
(Rは希土類金属元素であるサマリウムを示し、xは、希土類金属元素の原子%で3<x<30の範囲で、yは、窒素Nの原子%で5<y<15の範囲にある)。The above rare earth metal - iron - nitrogen based magnetic powder The method of manufacturing according to claim 1 or 2 which is a nitride composition represented by the following general formula,
General formula R x Fe 100-xy N y (1)
(R represents samarium which is a rare earth metal element, x is in the range of 3 <x <30 in terms of atomic% of the rare earth metal element, and y is in the range of 5 <y <15 in terms of atomic% of nitrogen N) .
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