JP3719483B2 - Rare earth magnetic powder and surface treatment method thereof - Google Patents
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- H01F1/00—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties
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- 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
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Description
【０００１】
【産業上の利用分野】
本発明は希土類系磁性粉末の粒子表面に緻密で均一なシリカ被膜を形成することにより耐酸化性を改良する技術に関する。
【０００２】
【従来の技術】
現在、高磁気特性を有する希土類磁石は、磁石の小型化、小片化を可能にし、それを組み込んだ通信機器、情報処理機器といったエレクトロニクス製品の小型化に欠くことのできない材料となっている。特に、希土類ボンド磁石は優れた形状加工性を有し、薄肉微小への成形が可能であることからその使用量は益々増加の一途をたどっている。
【０００３】
代表的な希土類ボンド磁石には、Ｓｍ−Ｃｏ系、Ｎｄ−Ｆｅ−Ｂ系、Ｓｍ−Ｆｅ−Ｎ系の磁性材料を使用し、これらはそれぞれ高い磁気特性を有している。ところが、これら希土類磁石は希土類元素を構成成分に含み、希土類元素は酸化されやすい元素であることから、基本的にそれを組成に含んだ希土類磁石は酸化されやすい。従って、実用性のある希土類ボンド磁石を得るためには、基本的には耐酸化性を克服しなければならない。
【０００４】
このような希土類磁石に対して、特開平３−２８０４０４号公報には焼結磁石あるいはボンド磁石の表面に、テトラエトキシシランを用いたゾルゲル法によるシリカガラスを析出させる方法が開示されている。しかし、磁石成形品の表面にこのような特殊な被覆を行うことは、製造工程の複雑化及び製造コストの増大を招き得策ではない。これに対し特開昭６２−１５２１０７号公報には、希土類磁性粉末そのものの粒子表面に、ケイ酸ナトリウム等のケイ酸塩により被覆する方法が、また、特開平２−２６５２２２号公報には、希土類磁性粉末の粒子表面に亜鉛金属およびシリカ粉を機械的に付着する方法が開示されている。
【０００５】
しかし、これらの方法により優れた耐酸化性を得るには粒子表面の被膜を厚くしなければならず、磁性粉末の本来の磁気特性を大幅に低下させてしまう。つまり、これらの技術では、耐酸化性と磁気特性がトレード・オフの関係となり、その点で十分に満足のいくものではない。
【０００６】
Ｓｍ−Ｆｅ−Ｎ系磁性材料の中でも、特に、Ｓｍ2Ｆｅ17Ｎ3系磁性材料は保磁力発現機構がニュークリエイションであり、他の２つのボンド磁石に比べて小粒径でより高い磁気特性を発現する特徴をもつ。従って、Ｓｍ2Ｆｅ17Ｎ3系ボンド磁石は、Ｓｍ−Ｃｏ系、Ｎｄ−Ｆｅ−Ｂ系、あるいは他のＳｍ−Ｆｅ−Ｎ系より、優れた成形加工性、薄肉微小成形の可能性を有する高性能ボンド磁石に成りうると期待できる。しかし、小粒径のため、他の希土類磁性材料に比べて比表面積の増加が大きくなり酸化を招きやすくなるという問題をもつ。
【０００７】
さらに、Ｓｍ−Ｆｅ−Ｎ系磁性材料の場合、耐酸化性を重視して表面処理を行っても、その耐酸化性は十分に向上しない。それはこの材料は基本的に窒化物粒子であり、粒子表面はイオン結合性のあまり高くない窒素原子が多く存在し、その結果、被膜成分との親和性が高くなく、被膜にクラックやピンホールができやすい。そのため、そのクラックやピンホール部分を核として磁性粉末の酸化部分が急速に拡散し、磁気特性が低下してしまうという問題がある。
【０００８】
【発明が解決しようとする課題】
従って、本発明は上述した問題を解決することを目的として成され、希土類磁性粉末の耐酸化性を改良すると同時に、耐酸化性を改良しても磁気特性を低下しない高品質な希土類系磁性粉末を得ることを目的としている。
【０００９】
特に、粒径の小さなＳｍ−Ｆｅ−Ｎ系磁性材料に適用しても、クラック、ピンホール等の発生のない高品質の被膜を形成でき、その結果、得られるＳｍ−Ｆｅ−Ｎ系磁性材料を使用することにより高磁気特性で、しかも優れた成形加工性、薄肉微小成形を可能にする高性能ボンド磁石を得ることを目的とする。
【００１０】
【課題を解決するための手段】
本発明者等は、上述した課題を解決するためには、希土類磁性粉末の粒子表面に、耐酸化作用のある被覆物を従来の方法よりもさらに均一に被覆することで解決できると考え、種々の被覆材料について鋭意検討したところ、エチルシリケートに代表されるアルキルシリケート（ケイ酸エステル化合物）を加水分解したときに得られるシリカを不活性雰囲気中で反応させると希土類磁石の粒子表面に微粒子シリカによる被覆が行われることを見いだし、本発明を完成するに至った。
【００１１】
すなわち、本発明の希土類系磁性粉末は、希土類磁性粉末の粒子表面にアルキルシリケートが加水分解して得られる微粒子シリカが均一に付着していることを特徴とする。また、希土類磁石には、特にＳｍ−Ｆｅ−Ｎ系合金粉末が好ましく使用できる。
【００１２】
本発明の希土類磁性粉末は、組成中に希土類元素を含有する合金または金属間化合物からなる希土類系磁性粉末の表面にシリカ被膜を形成する方法において、該磁性粉末にアルキルシリケートを混合した後、不活性雰囲気中の加熱を行うことを特徴とする。
【００１３】
また、希土類磁性粉末にアルキルシリケートを混合した後、不活性雰囲気中の加熱を行う前に水を添加することことが好ましい。
【００１４】
本発明で使用するアルキルシリケートは、組成式が次式で表されるエチルシリケートであり、その混合量は、該希土類磁性粉末１００重量部に対し、１〜５重量部であることが好ましい。
ＳｉnＯ(n-1)（ＯＣ2Ｈ5）(2n+2)
但し、１≦ｎ≦１０
【００１５】
前記不活性雰囲気中の加熱は、６０℃〜２５０℃の温度範囲で減圧状態で行うことが好ましい。
【００１６】
本発明において、磁性粉末にアルキルシリケートを混合する前に、水を添加し減圧状態で加熱する工程を備えることが好ましい。
【００１７】
【発明の実施の形態】
本発明の希土類磁性粉末は、組成中に希土類元素を含有する合金または金属間化合物からなる希土類系磁性粉末の表面に、シリカ被膜を形成する方法において、該磁性粉末にアルキルシリケートを混合して、不活性雰囲気中で加熱することを特徴とする。本発明の方法に従うことで、希土類磁性粉末の粒子表面に微粒子シリカを緻密にしかも均一に被覆することができ、その結果、耐酸化性改善に効果を発揮する。
【００１８】
本発明に使用するアルキルシリケートは、次のような一般式で示されるケイ酸エステルである。ＳｉnＯ(n-1) （ＯＲ）(2n+2)、ここでＲはアルキル基であり、メチル基、エチル基、プロピル基、ブチル基等が使用できる。アルキル基は、特にコストが安価なこと、また、毒性がなく取り扱いが簡単なことからエチル基を使用したエチルシリケートが好ましく使用できる。また、ｎの値はアルキルシリケートの分子量に関係し、ｎ＝１〜１０の範囲のものが好ましく使用できる。ｎが１０よりも大きくなると、緻密なシリカは得られにくくなる。
【００１９】
ｎの値がそれぞれ１、２、５、１０、及び３０であるエチルシリケートを使用し、Ｓｍ2Ｆｅ17Ｎ3系磁性粉末に表面に本発明の方法に従いシリカを被覆したサンプルを加速的熱劣化を行い、その劣化前及び劣化後の磁気特性（磁化、保磁力）を測定する耐酸化試験を行い結果を表１にまとめた。
【００２０】
【表１】
この表に示すように、エチルシリケートはｎの値が小さなものが耐酸化性が向上している。すなわち、分子量の小さい方が耐酸化性が良い。実際、ｎの値は１〜１０が特に好ましい。この範囲のエチルシリケートを用いれば、粒子表面を均一に被覆することができ、緻密なシリカ被膜を形成させることができる。ここで、加速熱劣化は、測定試料の磁性粉末０．５ｇを耐熱性容器に入れ、大気中２００℃で１時間加熱することで行った。
【００２２】
ｎが１１以上の、分子量の大きなエチルシリケートを用いた場合、エチルシリケートはゾル状のコロイド粒子となり、図１（Ｂ）に示すようなエチルシリケート間での立体障害が起こり、磁性粉末粒子とエチルシリケートが接触していない部分、隙間ができる。この隙間が後の加熱処理後にも残り、外部から水分や酸素が侵入し、磁性粉末は酸化される。
【００２３】
ｎが１０以下の分子量の小さいエチルシリケートを被覆させてからシリカ膜を形成させれば、図１（Ａ）に示すようにこの隙間ができず、緻密なシリカ膜が形成され、しかも少ないエチルシリケート添加量で耐酸化性が向上する。そのため、磁化の低下が少なくなる。これら（Ａ）及び（Ｂ）は典型的な例を模式的に説明したものである。
【００２４】
磁性材料の粒子表面にエチルシリケートを緻密に被覆するには、上述したようなエチルシリケートの立体障害の問題以外に、磁性粉末の粒子表面が、エチルシリケートと親和性が高いことが必要である。すなわち、緻密で密着性の高いシリカ被覆を形成するためには、エチルシリケートが加水分解によってシリカを析出する以前に、エチルシリケートが磁性粉末粒子と良く濡れることが必要とされる。そのような濡れ性の改良について、鋭意検討した結果、磁性材料に少量の水を添加して乾燥することで、表面状態が改質されることを見いだした。
【００２５】
この水の添加は、少量の水が磁性粉末にできるだけ行き渡るように十分に混合し、そして十分に乾燥を行うことが必要がある。それは、基本的に希土類磁性粉末は、水により酸化されやすく、磁気特性を容易に低下してしまうからである。従って、少量の水を全体に均一に混合し、また、残留水分が残らないようにすることが重要である。表２にＳｍ2Ｆｅ17Ｎ3系磁性粉末３００ｇに対し、水の添加量に対する給油量、耐酸化試験（加速熱劣化前後）の磁化、保磁力の関係を関係を示した。
【００２６】
【表２】
表２より、水を添加しなかった実施例３９は給油量が最も多く、水の添加量の増加と共に給油量は減少している。給油量は、濡れ性に大きく依存し、一般に対象の溶媒に対する濡れ性は、その溶媒を用いた給油量が少ない方が、その溶媒に濡れやすいといえる。従って、この発明において給油量の測定は、煮あまに油の代わりにエチルシリケート（ｎ＝５）を使用する以外ＪＩＳＫ５１０１−1991に準拠した次のよう方法で測定した。
【００２８】
平滑なガラス板の上に希土類磁性粉末を５ｇ載せて、その上にビュレットからエチルシリケートを徐々に滴下し、その都度ヘラで十分に練り合わせ、全体が急激に軟らかくなる直前を終点とし、そのときのエチルシリケートの滴下量を給油量とした。
【００２９】
従来、水の存在はＳｍ−Ｆｅ−Ｎ系磁性粉末のように粒径の小さい磁性粉末は特に酸化されやすく、水を添加あるいは混合した後の乾燥は磁気特性を低下させるだけであると考えられその必要性は全くなかった。しかし、本発明においてエチルシリケートの効果を最大限に引き出すために、水を分散させて予備乾燥することで濡れ性を向上し、耐酸化性を飛躍的に向上させることができる。
【００３０】
そのメカニズムは次のように推定している。磁性材料と水を接触させ上記した予備乾燥を行うことで、磁性粉末粒子表面の水酸基が増加し、それに伴って吸着水も増加する。本来親油性の強いＳｍ−Ｆｅ−Ｎ系磁性粉末は、水酸基が増加することで親水性が増加する。その結果、エチルシリケートとの濡れ性が改善される。また、この予備乾燥を行った磁性粉末は、後工程で解砕粉砕を行っても、濡れ性の効果は持続するので、解砕粉砕した磁性粉末を用いてシリカ被膜を形成させることも可能である。
【００３１】
予備乾燥温度が４０℃、５０℃、１００℃、３０℃、及び１５０℃の場合について、給油量、耐酸化性の試験の結果を表３にまとめた。これらは平均粒径が１０μｍのＳｍ2Ｆｅ17Ｎ3系の磁性粉末３００ｇに対し、０．６ｇの純水を噴霧し、窒素ガス中３０秒間混合し減圧状態で、それぞれの温度で３０分間予備乾燥した場合である。
【００３２】
【表３】
表３より、３０℃〜１００℃の乾燥温度で予備乾燥させることにより、濡れ性は改善され、しかも磁気特性の低下はない。
【００３４】
表４に、磁性材料として平均粒径１０μｍのＳｍ2Ｆｅ17Ｎ3系を選び、アルキルシリケートとして、エチルシリケート（ｎ＝５）を選択した場合の、希土類磁性粉末１００重量部に対するエチルシリケートの添加量と、耐酸化性試験の前後の磁気特性の結果をまとめた。エチルシリケートの添加は、ミキサ中で噴霧して窒素ガス中１分間混合し、磁性粉末を減圧状態２３０℃で３０分間乾燥することで行った。
【００３５】
【表４】
表４よりエチルシリケートの添加量は、磁性材料に対し１〜５重量部の範囲が磁気特性の低下が少なく、優れた耐酸化性を示し好ましい。
【００３７】
上述したように、磁性材料の前処理剤として、エチルシリケートを添加する前に水を添加して乾燥したのに対し、エチルシリケートを磁性材料に添加した後、水を添加すると、エチルシリケートの加水分解反応がより促進される。本来、エチルシリケートの加水分解は次式に従って加水分解し、得られたシリカを磁性材料の上に被覆している。
【００３８】
ＳｉnＯ(n-1)（ＯＣ2Ｈ5）(2n+2) ＋ (n+1)Ｈ2Ｏ → nＳｉＯ2 ＋ (2n+2)Ｃ2Ｈ5ＯＨ
【００３９】
この水は、空気中、あるいは磁性材料粉末が僅かに不純物として含水している程度の量でも反応を起こすことができる。しかし、さらにこの反応の平衡をさらに生成系に移動するためには、後から水を添加することが効果がある。水の添加量は、水の蒸発もあって、エチルシリケートがシリカを形成させるのに必要な理論値の０．１〜３倍である。水は希土類系磁性粉末に対し非常に活性であるが、この範囲の水を添加しても、エチルシリケートの反応に消費されるので、磁性粉末の酸化は起こらない。しかし、水の添加量が、理論量の５倍以上になると磁性粉末の酸化も起こってしまい、磁気特性は低下する。
【００４０】
意図的に水の添加をしない場合、添加したエチルシリケートから析出してそれが磁性粉末の粒子表面に被覆する割合は４０％程度であり、それ以外は乾燥時にエチルシリケートとして蒸発してロスする。これに対し、水を理論量添加した場合、シリカの被覆量は理論量の８０％程度となる。シリカの被覆の効率を考えると、水は多い方が良いが、あまり多くなると上述したように磁性粉末の酸化の問題が起こるため、理論量の５倍までにしておくことが必要となる。
【００４１】
磁性粉末にアルキルシリケートを一様に分散して添加するには、減圧下で磁性粉末をアルキルシリケートに浸漬する浸漬法、混合機中で磁性粉末を混合しながらに所定量のアルキルシリケートを噴霧する方法、アルキルシリケートを磁性粉末に滴下により添加した後ミキサで混合する方法等が適用できる。磁性粉末を十分流動させることができる能力があれば、ミキサの種類は特に問わない。また、混合は磁性粉末の酸化を防ぐためには不活性雰囲気中で行う。水の添加分散は、アルキルシリケートと同時に添加すると、アルキルシリケートが反応してゾルを形成したりゲル化する。そのため、エチルシリケートの磁性粉末への分散を妨げることになる。
【００４２】
シリカ被膜形成の時の加熱温度と加速熱劣化による耐酸化試験の結果を表５に示す。
【００４３】
【表５】
表５より、加速熱劣化の後の磁気特性は反応工程の加熱温度に依存し、６０〜２５０℃の範囲でかなりの効果を発揮している。特に、２３０℃が磁化、保磁力ともに良好である。また、反応時間は０．５〜３時間、常温から反応温度まで昇温する時の昇温速度は５０〜４００℃／時間であることが緻密な結晶を得るには良いことが実験により分かった。反応時間がこの範囲よりも短くなると、未反応のエチルシリケートが多く残留する問題が有り、逆に、この範囲より長くても得られるシリカの収率及び品質に及ぼす影響は少ないは少なく、むやみに製造に要する時間を長くするだけとなり無意味である。昇温速度は、シリカ被膜の緻密さに関係し、この範囲より小さいと、シリカ被膜は粗くなり品質が低下する。逆に、昇温速度がこの範囲より遅くなっても、エチルシリケートの飛散量が多くなりシリカ被膜形成の収率が低下する問題がある。
【００４５】
被覆反応の加熱処理するときの雰囲気は、窒素ガス、希ガスの不活性ガス中、あるいは減圧状態である。これは酸素により酸化するのを防ぐ為である。乾燥時に、減圧状態で行うのは、上述したように、エチルシリケートからのシリカの析出反応は、シリカと同時に副成物としてアルコールを生成する。従って、この反応の収率を上げるには、積極的にアルコールを除去することが効果があるからである。
【００４６】
【実施例】
［実施例１］
平均粒径１０μｍのＳｍ2Ｆｅ17Ｎ3系磁性粉末を１００％エチルシリケート（ｎ＝５）溶液に浸漬し、５分間保持した後磁性粉を取り出した。取り出した磁性粉末を減圧状態、２３０℃、３０分間、加熱処理を行い、Ｓｍ2Ｆｅ17Ｎ3磁性粉末の表面にシリカ膜を形成させた。
【００４７】
得られた磁性粉末を最大磁場２０ｋＯｅのＶＳＭ（振動試料型磁力計）で磁気特性を測定した。このとき、合金粉末微粉をパラフィンワックスと共にサンプルケースに詰め、ドライヤーでパラフィンワックスを溶融させてから２０ｋＯｅの配向磁場でその磁化容易軸を揃え、着磁磁場４０ｋＯｅでパルス着磁した。またＳｍ2Ｆｅ17Ｎ3金属間化合物の真密度は７．６６ｇ／ｍｌとし反磁場補正せずに評価した。試料測定の結果、残留磁化は１３．１ｋＧ、保磁力は１２．５ｋＯｅであった。
【００４８】
この得られた磁性粉末に対して、上述した耐酸化試験を行った結果、残留磁化は１３．１ｋＧ、保磁力は１１．０ｋＯｅであった。
【００４９】
［実施例２〜４］［実施例３３］
平均粒径１０μｍのＳｍ2Ｆｅ17Ｎ3系磁性粉末３００ｇをミキサに投入し、粉に対して純水を０．６ｇ（０．２重量部）噴霧し、窒素ガス中０．５分間混合した。この場合、ミキサは粉が十分流動するものであれば特に問わない。磁性粉末を取り出し、減圧下５０℃で３０分間加熱処理（予備乾燥）した。磁性粉末を次に、エチルシリケート（ｎ＝１）、エチルシリケート（ｎ＝５）、エチルシリケート（ｎ＝１０）、及びエチルシリケート（ｎ＝３０）をそれぞれを７．５ｇ噴霧し、窒素ガス中１分間混合した。次に水１．０８ｇ（エチルシリケートの加水分解に必要とされる理論量）を噴霧した後窒素ガス中混合した。その後、磁性粉末を取り出し磁性粉末を取り出し、減圧下、２３０℃、３０分間加熱処理して実施例２〜４、及び実施例３３の磁性粉末を得た。
【００５０】
［実施例５〜７］［実施例３４］
平均粒径１０μｍのＳｍ2Ｆｅ17Ｎ3系磁性粉末３００ｇをミキサに投入し、粉に対して純水を０．６ｇ（０．２重量部）噴霧し、窒素ガス中０．５分間混合した。磁性粉末を取り出し、減圧下５０℃で３０分間加熱処理（予備乾燥）した。エチルシリケート（ｎ＝５）を、それぞれ３ｇ（１．０重量部）、７．５ｇ（２．５重量部）、１５ｇ（５重量部）、２２．５ｇ（７．５重量部）噴霧し、窒素ガス中１分間混合した。次に水１．０８ｇ（エチルシリケートの加水分解に必要とされる理論量）を噴霧した後窒素ガス中混合した。その後、磁性粉末を取り出し、減圧下２３０℃、３０分間加熱処理して実施例５〜７、及び実施例３４の磁性粉末を得た。
【００５１】
［実施例８、９］［実施例３５、３６］
平均粒径１０μｍのＳｍ2Ｆｅ17Ｎ3系磁性粉末３００ｇをミキサに投入し、粉に対して純水を０．６ｇ（０．２重量部）噴霧し、窒素ガス中０．５分間混合した。磁性粉末を取り出し、減圧下５０℃で３０分間加熱処理（予備乾燥）した。エチルシリケート（ｎ＝５）を７．５ｇ（２．５重量部）噴霧し、窒素ガス中１分間混合した。次に水をそれぞれ１．０８ｇ（エチルシリケートの加水分解に必要とされる理論量）、１．６２ｇ（理論量の１．５倍）、０ｇ、及び３．２４ｇ（理論量の３倍）を噴霧した後、窒素ガス中混合した。その後、磁性粉末を取り出し、減圧下２３０℃で３０分間加熱処理して実施例８、９、実施例３５、及び３６の磁性粉末を得た。耐酸化試験の結果を表６に示す。
【００５２】
【表６】
［実施例１０〜１３］［実施例３７、３８］
平均粒径１０μｍのＳｍ2Ｆｅ17Ｎ3系磁性粉末３００ｇをミキサに投入し、粉に対して純水を０．６ｇ（０．２重量部）噴霧し、窒素ガス中０．５分間混合した。磁性粉末を取り出し、減圧下５０℃で３０分間加熱処理（予備乾燥）した。エチルシリケート（ｎ＝５）を７．５ｇ（２．５重量部）噴霧し、窒素ガス中１分間混合した。次に水１．０８ｇ（エチルシリケートの加水分解に必要とされる理論量）を噴霧した後窒素ガス中混合した。その後、磁性粉末を取り出し、減圧下それぞれ、６０℃、１００℃、２００℃、２５０℃、５０℃、及び３００℃で３０分間加熱処理して実施例１０〜１３、実施例３７及び実施例３８の磁性粉末を得た。
【００５４】
［実施例１４〜１８］［実施例３９］
平均粒径１０μｍのＳｍ2Ｆｅ17Ｎ3系磁性粉末３００ｇをミキサに投入し、粉末に対して純水を、それぞれ０．１ｇ、０．１５ｇ、０．６０ｇ、３．００、４．５０、及び０ｇ噴霧し、窒素ガス中０．５分間混合した。磁性粉末を取り出し、減圧下５０℃で３０分間加熱処理（予備乾燥）した。次に、エチルシリケート（ｎ＝５）を７．５ｇ（２．５重量部）噴霧し、窒素ガス中１分間混合した。次に水１．０８ｇ（エチルシリケートの加水分解に必要とされる理論量）を噴霧した後窒素ガス中混合した。その後、減圧下２３０℃で３０分間加熱処理して実施例１４〜１８、及び実施例３９の磁性粉末を得た。
【００５５】
［実施例１９〜２１］［実施例３１、３２］
平均粒径１０μｍのＳｍ2Ｆｅ17Ｎ3系磁性粉末３００ｇをミキサに投入し、粉末に対して０．２重量部の純水を０．６ｇ噴霧し、窒素ガス中０．５分間混合した。磁性粉末を取り出し、減圧状態、乾燥温度をそれぞれ、４０℃、５０℃、及び１００℃で３０分間予備乾燥した。次に、エチルシリケート（ｎ＝５）を７．５ｇ（２．５重量部）を噴霧し、窒素ガス中１分間混合した。次に水１．０８ｇ（エチルシリケートの加水分解に必要とされる理論量）を噴霧した後窒素ガス中混合した。その後、減圧下２３０℃で３０分間加熱処理して実施例１９〜２１、実施例３１及び３２の磁性材料を得た。
【００５６】
［比較例１］
通常の方法により得られた平均粒径１０μｍのＳｍ2Ｆｅ17Ｎ3系磁性粉末について、ＶＳＭによる磁気特性測定した結果、残留磁化は１３．８ｋＧ、保磁力は１２．７ｋＯｅであった。因みに本発明において、Ｓｍ2Ｆｅ17Ｎ3系磁性粉末については、基本的にこの磁性粉末を原料として使用した。この磁性粉末に対して上述した耐酸化試験を行った結果、残留磁化は５．０ｋＧ、保磁力は４．１ｋＯｅであった。
【００５７】
［比較例２］
平均粒径１０μｍのＳｍ2Ｆｅ17Ｎ3系磁性粉末３００ｇをミキサに投入し、シランカップリング剤としてγ―アミノプロピルトリエトキシシランを３ｇ噴霧し、窒素ガス中１分間混合した。その後、磁性粉末を取り出し、減圧状態２３０℃で６０分間加熱処理し比較例７の磁性粉末を得た。ＶＳＭによる磁気特性測定した結果、残留磁化は１３．０ｋＧ、保磁力は１２．４ｋＯｅであった。この磁性粉末に対して上述した耐酸化試験を行った結果、残留磁化は１２．５ｋＧ、保磁力は６．５ｋＯｅであった。
【００５８】
【発明の効果】
上述したように、本発明を適用した磁性粉末は、特に加速熱劣化後の磁気特性の劣化の程度は極めて小さくなり、そのことから、耐酸化性が大きく改善されていることは理解される。さらに、耐酸化性を客観的に評価する目的で、示差走査熱分析を適用した測定結果のチャートを図２に示す。
【００５９】
測定試料は、▲１▼は何の表面処理も施していない比較例１の磁性粉末、▲２▼は比較例２のシランカップリング剤によりシリカ被膜を被覆した場合、▲３▼は実施例６の磁性粉末である。図２は、各々の測定試料２０ｍｇをアルミナの微小な測定セルに充填し、大気中で常温から５００℃まで、１０℃／分の一定の速度で昇温し、この際の測定試料の燃焼等の化学変化から発生する反応熱を記録計に書かせたものである。
【００６０】
▲１▼は２００℃付近で先ず発熱反応が現れ、さらに、４００℃付近でも別の発熱過程が観察され、４５０℃を超える辺りからこの発熱反応は激しく起こっている。▲２▼は▲１▼の場合に比べ、２００℃付近、４００℃付近の発熱はかなり低下しているが、やはり４５０℃辺りからの発熱反応は急激に起こっている。これに対し、▲３▼の曲線は２００、４００℃における発熱は他の曲線に比べ極めて低く抑えられ、しかも、▲１▼及び▲２▼で起こった４５０℃付近の急激な発熱は完全に抑えられ、５１０℃を超える辺りまで発熱反応はシフトしている。
【００６１】
４５０℃辺りから起こる発熱は、Ｓｍ2Ｆｅ17Ｎ3磁性粉末の結晶の分解であり、これは酸素存在下で誘引される。本発明において、この発熱反応が高温度にシフトしているのは、本発明によるシリカ被膜が緻密に均一に磁性材料を被覆していることで、磁性粉末への酸素の侵入が起こりにくくなっているためといえる。
【００６２】
このようにして得られた本発明の磁性粉末を使用したボンド磁石は、磁気特性に優れ、しかも、ボンド磁石としても優れた耐食性を有する。さらに、減磁の少ない、特に熱による現時の少ない磁石を得ることができる。
【図面の簡単な説明】
【図１】本発明に磁性粉末（Ａ）と比較例の磁性粉末（Ｂ）の模式拡大図
【図２】磁性粉末の示差走査熱分析結果のチャート図[0001]
[Industrial application fields]
The present invention relates to a technique for improving oxidation resistance by forming a dense and uniform silica coating on the surface of rare earth-based magnetic powder particles.
[0002]
[Prior art]
Presently, rare earth magnets having high magnetic properties enable magnets to be reduced in size and size, and are indispensable for miniaturization of electronic products such as communication devices and information processing devices incorporating the magnets. In particular, rare earth bonded magnets have an excellent shape processability and can be formed into thin and minute shapes, so that the amount of use thereof continues to increase.
[0003]
Typical rare earth bonded magnets use Sm—Co, Nd—Fe—B, and Sm—Fe—N based magnetic materials, each of which has high magnetic properties. However, these rare earth magnets contain a rare earth element as a constituent component, and the rare earth element is an element that is easily oxidized. Therefore, a rare earth magnet that includes the rare earth element in the composition is basically easily oxidized. Therefore, in order to obtain a practical rare earth bonded magnet, basically, oxidation resistance must be overcome.
[0004]
In contrast to such rare earth magnets, JP-A-3-280404 discloses a method of depositing silica glass by a sol-gel method using tetraethoxysilane on the surface of a sintered magnet or a bonded magnet. However, such special coating on the surface of the magnet molded product is not a possible measure because it complicates the manufacturing process and increases the manufacturing cost. In contrast, Japanese Patent Laid-Open No. 62-152107 discloses a method of coating the surface of rare earth magnetic powder itself with a silicate such as sodium silicate, and Japanese Patent Laid-Open No. 2-265222 discloses a rare earth. A method of mechanically attaching zinc metal and silica powder to the particle surface of magnetic powder is disclosed.
[0005]
However, in order to obtain excellent oxidation resistance by these methods, it is necessary to increase the thickness of the coating on the surface of the particles, which significantly reduces the original magnetic properties of the magnetic powder. In other words, in these techniques, the oxidation resistance and the magnetic properties are in a trade-off relationship, which is not satisfactory in that respect.
[0006]
Among Sm-Fe-N magnetic materials, especially Sm 2 Fe 17 N 3 magnetic materials have a new coercive force generation mechanism, and have a smaller particle size and higher magnetic properties than the other two bonded magnets. It has the feature to express. Therefore, Sm 2 Fe 17 N 3 -based bonded magnets have better processability and thin-walled micro-molding than Sm—Co, Nd—Fe—B, or other Sm—Fe—N systems. It can be expected to become a high-performance bonded magnet. However, due to the small particle size, there is a problem that the increase in the specific surface area becomes larger than other rare earth magnetic materials, and oxidation is likely to occur.
[0007]
Furthermore, in the case of an Sm—Fe—N-based magnetic material, even if surface treatment is performed with emphasis on oxidation resistance, the oxidation resistance is not sufficiently improved. This material is basically nitride particles, and the surface of the particles has many nitrogen atoms that are not so high in ion binding properties. As a result, the affinity with the coating components is not high, and there are cracks and pinholes in the coating. Easy to do. For this reason, there is a problem that the oxidized portion of the magnetic powder diffuses rapidly with the crack and pinhole portion as a nucleus, and the magnetic properties are deteriorated.
[0008]
[Problems to be solved by the invention]
Therefore, the present invention was made for the purpose of solving the above-mentioned problems, and improved the oxidation resistance of the rare earth magnetic powder, and at the same time, the high quality rare earth magnetic powder that does not deteriorate the magnetic properties even if the oxidation resistance is improved. The purpose is to obtain.
[0009]
In particular, even when applied to an Sm—Fe—N magnetic material having a small particle size, a high-quality film free from cracks, pinholes, etc. can be formed. As a result, the resulting Sm—Fe—N magnetic material It is an object of the present invention to obtain a high-performance bonded magnet that has high magnetic properties, excellent moldability, and enables thin and fine molding.
[0010]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the present inventors consider that the surface of the rare earth magnetic powder particles can be solved by coating the surface of the rare earth magnetic powder more uniformly than the conventional method. As a result of intensive investigations on the coating material, it was found that when silica obtained by hydrolyzing an alkyl silicate (silicate compound) represented by ethyl silicate is reacted in an inert atmosphere, the surface of the rare earth magnet particles is made of fine silica. It was found that coating was performed, and the present invention was completed.
[0011]
That is, the rare earth-based magnetic powder of the present invention is characterized in that fine particle silica obtained by hydrolyzing alkyl silicate is uniformly attached to the particle surface of the rare earth magnetic powder. For rare earth magnets, Sm—Fe—N alloy powders can be particularly preferably used.
[0012]
In the method of forming a silica film on the surface of a rare earth-based magnetic powder composed of an alloy or an intermetallic compound containing a rare earth element in the composition, the rare earth magnetic powder of the present invention is mixed with an alkyl silicate after being mixed with the magnetic powder. Heating in an active atmosphere is performed.
[0013]
Further, it is preferable to add water after mixing the alkyl silicate with the rare earth magnetic powder and before heating in an inert atmosphere.
[0014]
The alkyl silicate used in the present invention is ethyl silicate whose composition formula is represented by the following formula, and the mixing amount is preferably 1 to 5 parts by weight with respect to 100 parts by weight of the rare earth magnetic powder.
Si n O (n-1) (OC 2 H 5 ) (2n + 2)
However, 1 ≦ n ≦ 10
[0015]
The heating in the inert atmosphere is preferably performed under a reduced pressure in a temperature range of 60 ° C to 250 ° C.
[0016]
In the present invention, it is preferable to include a step of adding water and heating in a reduced pressure state before mixing the alkyl silicate with the magnetic powder.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
The rare earth magnetic powder of the present invention is a method of forming a silica film on the surface of a rare earth magnetic powder composed of an alloy or an intermetallic compound containing a rare earth element in the composition. In the method of forming a silica film, the magnetic powder is mixed with an alkyl silicate, It is characterized by heating in an inert atmosphere. By following the method of the present invention, the particle surface of the rare earth magnetic powder can be finely and uniformly coated with the fine particle silica, and as a result, the effect of improving the oxidation resistance is exhibited.
[0018]
The alkyl silicate used in the present invention is a silicate ester represented by the following general formula. Si n O (n-1) (OR) (2n + 2) , where R is an alkyl group, and a methyl group, an ethyl group, a propyl group, a butyl group, or the like can be used. As the alkyl group, ethyl silicate using an ethyl group can be preferably used because it is particularly inexpensive and is not toxic and easy to handle. The value of n is related to the molecular weight of the alkyl silicate, and those in the range of n = 1 to 10 can be preferably used. When n is larger than 10, dense silica is hardly obtained.
[0019]
Using ethyl silicates with n values of 1, 2, 5, 10, and 30, respectively, Sm2Fe17N3 magnetic powder was subjected to accelerated thermal degradation on a surface coated with silica according to the method of the present invention. An oxidation resistance test for measuring the magnetic properties (magnetization, coercivity) before and after deterioration was performed, and the results are summarized in Table 1.
[0020]
[Table 1]
As shown in this table, ethyl silicate having a small value of n has improved oxidation resistance. That is, the smaller the molecular weight, the better the oxidation resistance. In fact, the value of n is particularly preferably 1-10. If ethyl silicate in this range is used, the particle surface can be uniformly coated and a dense silica coating can be formed. Here, accelerated thermal degradation was performed by placing 0.5 g of the magnetic powder of the measurement sample in a heat-resistant container and heating in the atmosphere at 200 ° C. for 1 hour.
[0022]
When n is 11 or more and a large molecular weight ethyl silicate is used, the ethyl silicate becomes a sol-like colloidal particle, and steric hindrance occurs between the ethyl silicate as shown in FIG. There are gaps and gaps where the silicate is not in contact. This gap remains after the subsequent heat treatment, moisture and oxygen enter from the outside, and the magnetic powder is oxidized.
[0023]
If a silica film is formed after coating with a low molecular weight ethyl silicate having an n of 10 or less, this gap cannot be formed as shown in FIG. 1 (A), and a dense silica film is formed, and there is little ethyl silicate. Addition amount improves oxidation resistance. Therefore, the decrease in magnetization is reduced. These (A) and (B) schematically describe typical examples.
[0024]
In order to densely coat ethyl silicate on the particle surface of the magnetic material, in addition to the problem of steric hindrance of ethyl silicate as described above, it is necessary that the particle surface of the magnetic powder has high affinity with ethyl silicate. That is, in order to form a dense and highly adherent silica coating, it is necessary that the ethylsilicate be well wetted with the magnetic powder particles before the ethylsilicate is precipitated by hydrolysis. As a result of diligent investigations on such wettability improvement, the inventors have found that the surface condition is improved by adding a small amount of water to the magnetic material and drying it.
[0025]
This addition of water needs to be thoroughly mixed so that a small amount of water is distributed as much as possible to the magnetic powder and sufficiently dried. This is because the rare earth magnetic powder is basically easily oxidized by water and easily deteriorates the magnetic properties. Therefore, it is important that a small amount of water is mixed uniformly throughout and that no residual moisture remains. Table 2 shows the relationship between the amount of oil supplied with respect to the amount of water added, the magnetization in the oxidation resistance test (before and after accelerated thermal degradation), and the coercive force for 300 g of Sm2Fe17N3 magnetic powder.
[0026]
[Table 2]
From Table 2, Example 39 in which no water was added had the largest amount of oil supply, and the amount of oil supply decreased as the amount of water added increased. The amount of oil supply greatly depends on the wettability. Generally, the wettability with respect to a target solvent can be said to be more easily wet when the amount of oil supply using the solvent is smaller. Therefore, in this invention, the amount of oil supply was measured by the following method based on JIS K5101-1991 except that ethyl silicate (n = 5) was used instead of oil for boiled sesame.
[0028]
5g of rare earth magnetic powder is placed on a smooth glass plate, and ethyl silicate is gradually dropped from the burette, and kneaded thoroughly with a spatula each time. The amount of ethyl silicate added was defined as the amount of oil supply.
[0029]
Conventionally, the presence of water is considered to be particularly easy to oxidize magnetic powders with small particle diameters such as Sm-Fe-N magnetic powders, and drying after adding or mixing water is thought to only reduce the magnetic properties. There was no need for it. However, in order to maximize the effect of ethyl silicate in the present invention, water can be dispersed and pre-dried to improve wettability and dramatically improve oxidation resistance.
[0030]
The mechanism is presumed as follows. By bringing the magnetic material and water into contact with each other and performing the above-described preliminary drying, the hydroxyl groups on the surface of the magnetic powder particles are increased, and the adsorbed water is also increased accordingly. The Sm—Fe—N magnetic powder, which is inherently highly lipophilic, increases in hydrophilicity due to an increase in hydroxyl groups. As a result, wettability with ethyl silicate is improved. In addition, even if this pre-dried magnetic powder is pulverized and pulverized in a subsequent step, the wettability effect is maintained, so it is also possible to form a silica coating using the pulverized and pulverized magnetic powder. is there.
[0031]
Table 3 summarizes the results of the oil supply amount and oxidation resistance tests when the preliminary drying temperature was 40 ° C, 50 ° C, 100 ° C, 30 ° C, and 150 ° C. These are sprayed with 0.6 g of pure water to 300 g of Sm 2 Fe 17 N 3 based magnetic powder having an average particle size of 10 μm, mixed in nitrogen gas for 30 seconds, and preliminarily maintained at each temperature for 30 minutes. This is the case when it is dried.
[0032]
[Table 3]
From Table 3, the wettability is improved by pre-drying at a drying temperature of 30 ° C. to 100 ° C., and the magnetic properties are not deteriorated.
[0034]
Table 4 shows the addition of ethyl silicate to 100 parts by weight of rare earth magnetic powder when Sm 2 Fe 17 N 3 system having an average particle size of 10 μm is selected as the magnetic material and ethyl silicate (n = 5) is selected as the alkyl silicate. The amount and the result of the magnetic properties before and after the oxidation resistance test are summarized. The ethyl silicate was added by spraying in a mixer and mixing in nitrogen gas for 1 minute, and drying the magnetic powder at 230 ° C. for 30 minutes under reduced pressure.
[0035]
[Table 4]
From Table 4, the addition amount of ethyl silicate is preferably in the range of 1 to 5 parts by weight with respect to the magnetic material, since the decrease in magnetic properties is small and excellent oxidation resistance is exhibited.
[0037]
As described above, as a pretreatment agent for the magnetic material, water was added and dried before adding ethyl silicate, whereas when ethyl silicate was added to the magnetic material and then water was added, ethyl silicate was hydrolyzed. The decomposition reaction is further promoted. Originally, hydrolysis of ethyl silicate is performed according to the following formula, and the obtained silica is coated on a magnetic material.
[0038]
Si n O (n-1) (OC 2 H 5 ) (2n + 2) + (n + 1) H 2 O → nSiO 2 + (2n + 2) C 2 H 5 OH
[0039]
This water can cause a reaction even in the air or in such an amount that the magnetic material powder slightly contains water as an impurity. However, in order to further transfer the equilibrium of this reaction to the production system, it is effective to add water later. The amount of water added is 0.1 to 3 times the theoretical value required for ethyl silicate to form silica due to water evaporation. Although water is very active with respect to rare earth magnetic powder, even if water in this range is added, it is consumed for the reaction of ethyl silicate, so that oxidation of the magnetic powder does not occur. However, when the amount of water added exceeds 5 times the theoretical amount, the magnetic powder also oxidizes, and the magnetic properties deteriorate.
[0040]
When water is not intentionally added, the ratio of depositing from the added ethyl silicate and covering it on the particle surface of the magnetic powder is about 40%. Otherwise, it evaporates and loses as ethyl silicate during drying. On the other hand, when the theoretical amount of water is added, the coating amount of silica is about 80% of the theoretical amount. Considering the efficiency of silica coating, it is better to have more water, but if it is too much, the problem of oxidation of the magnetic powder occurs as described above, so it is necessary to keep it up to 5 times the theoretical amount.
[0041]
In order to uniformly disperse and add alkyl silicate to magnetic powder, a predetermined amount of alkyl silicate is sprayed while mixing magnetic powder in a mixer, soaking magnetic powder in alkyl silicate under reduced pressure. A method, a method in which an alkyl silicate is added dropwise to a magnetic powder, and then mixed with a mixer can be applied. The type of the mixer is not particularly limited as long as it has the ability to sufficiently flow the magnetic powder. The mixing is performed in an inert atmosphere in order to prevent oxidation of the magnetic powder. When water is added and dispersed simultaneously with the alkyl silicate, the alkyl silicate reacts to form a sol or gel. Therefore, dispersion of ethyl silicate into the magnetic powder is hindered.
[0042]
Table 5 shows the results of the oxidation resistance test based on the heating temperature and accelerated thermal degradation during the formation of the silica coating.
[0043]
[Table 5]
From Table 5, the magnetic properties after accelerated thermal degradation depend on the heating temperature of the reaction process, and exhibit a considerable effect in the range of 60 to 250 ° C. In particular, 230 ° C. is good in both magnetization and coercive force. Further, it was experimentally found that the reaction time is 0.5 to 3 hours, and the rate of temperature increase when raising the temperature from room temperature to the reaction temperature is 50 to 400 ° C./hour, which is good for obtaining dense crystals. . When the reaction time is shorter than this range, there is a problem that a large amount of unreacted ethyl silicate remains, and conversely, even if it is longer than this range, there is little influence on the yield and quality of the silica obtained, and it is insignificant. It only makes the time required for manufacturing longer, which is meaningless. The heating rate is related to the density of the silica coating, and if it is smaller than this range, the silica coating becomes rough and the quality is lowered. Conversely, even if the rate of temperature rise is slower than this range, there is a problem that the amount of ethyl silicate scattered increases and the yield of silica coating formation decreases.
[0045]
The atmosphere during the heat treatment of the coating reaction is in an inert gas such as nitrogen gas or a rare gas, or in a reduced pressure state. This is to prevent oxidation by oxygen. As described above, the silica is precipitated from ethyl silicate at the time of drying under reduced pressure to produce alcohol as a by-product simultaneously with silica. Therefore, in order to increase the yield of this reaction, it is effective to positively remove alcohol.
[0046]
【Example】
[Example 1]
Sm2Fe17N3 magnetic powder having an average particle size of 10 μm was immersed in a 100% ethylsilicate (n = 5) solution and held for 5 minutes, and then the magnetic powder was taken out. The magnetic powder taken out was subjected to heat treatment at 230 ° C. for 30 minutes under reduced pressure to form a silica film on the surface of the Sm2Fe17N3 magnetic powder.
[0047]
The magnetic properties of the obtained magnetic powder were measured with a VSM (vibrating sample magnetometer) having a maximum magnetic field of 20 kOe. At this time, the alloy powder fine powder was packed in a sample case together with paraffin wax, the paraffin wax was melted with a dryer, the easy magnetization axis was aligned with an orientation magnetic field of 20 kOe, and pulse magnetization was performed with a magnetization magnetic field of 40 kOe. Further, the true density of the Sm2Fe17N3 intermetallic compound was 7.66 g / ml, and the evaluation was performed without correcting the demagnetizing field. As a result of the sample measurement, the residual magnetization was 13.1 kG and the coercive force was 12.5 kOe.
[0048]
As a result of performing the above-described oxidation resistance test on the obtained magnetic powder, the residual magnetization was 13.1 kG and the coercive force was 11.0 kOe.
[0049]
[Examples 2 to 4] [Example 33]
300 g of Sm 2 Fe 17 N 3 magnetic powder having an average particle diameter of 10 μm was put into a mixer, 0.6 g (0.2 parts by weight) of pure water was sprayed on the powder, and mixed in nitrogen gas for 0.5 minutes. . In this case, the mixer is not particularly limited as long as the powder flows sufficiently. The magnetic powder was taken out and subjected to heat treatment (preliminary drying) at 50 ° C. for 30 minutes under reduced pressure. The magnetic powder is then sprayed with 7.5 g each of ethyl silicate (n = 1), ethyl silicate (n = 5), ethyl silicate (n = 10), and ethyl silicate (n = 30) in nitrogen gas. Mix for 1 minute. Next, 1.08 g of water (theoretical amount required for hydrolysis of ethyl silicate) was sprayed and mixed in nitrogen gas. Thereafter, the magnetic powder was taken out, and the magnetic powder was taken out and subjected to heat treatment at 230 ° C. for 30 minutes under reduced pressure to obtain magnetic powders of Examples 2 to 4 and Example 33.
[0050]
[Examples 5 to 7] [Example 34]
300 g of Sm 2 Fe 17 N 3 magnetic powder having an average particle diameter of 10 μm was put into a mixer, 0.6 g (0.2 parts by weight) of pure water was sprayed on the powder, and mixed in nitrogen gas for 0.5 minutes. . The magnetic powder was taken out and subjected to heat treatment (preliminary drying) at 50 ° C. for 30 minutes under reduced pressure. Ethyl silicate (n = 5) was sprayed at 3 g (1.0 part by weight), 7.5 g (2.5 parts by weight), 15 g (5 parts by weight), 22.5 g (7.5 parts by weight), respectively. Mix in nitrogen gas for 1 minute. Next, 1.08 g of water (theoretical amount required for hydrolysis of ethyl silicate) was sprayed and mixed in nitrogen gas. Thereafter, the magnetic powder was taken out and heat-treated at 230 ° C. under reduced pressure for 30 minutes to obtain magnetic powders of Examples 5 to 7 and Example 34.
[0051]
[Examples 8 and 9] [Examples 35 and 36]
300 g of Sm 2 Fe 17 N 3 magnetic powder having an average particle diameter of 10 μm was put into a mixer, 0.6 g (0.2 parts by weight) of pure water was sprayed on the powder, and mixed in nitrogen gas for 0.5 minutes. . The magnetic powder was taken out and subjected to heat treatment (preliminary drying) at 50 ° C. for 30 minutes under reduced pressure. 7.5 g (2.5 parts by weight) of ethyl silicate (n = 5) was sprayed and mixed in nitrogen gas for 1 minute. Next, 1.08 g of water (theoretical amount required for hydrolysis of ethyl silicate), 1.62 g (1.5 times the theoretical amount), 0 g, and 3.24 g (three times the theoretical amount), respectively. After spraying, it was mixed in nitrogen gas. Thereafter, the magnetic powder was taken out and heat-treated at 230 ° C. for 30 minutes under reduced pressure to obtain magnetic powders of Examples 8, 9, 35 and 36. Table 6 shows the results of the oxidation resistance test.
[0052]
[Table 6]
[Examples 10 to 13] [Examples 37 and 38]
300 g of Sm 2 Fe 17 N 3 magnetic powder having an average particle diameter of 10 μm was put into a mixer, 0.6 g (0.2 parts by weight) of pure water was sprayed on the powder, and mixed in nitrogen gas for 0.5 minutes. . The magnetic powder was taken out and subjected to heat treatment (preliminary drying) at 50 ° C. for 30 minutes under reduced pressure. 7.5 g (2.5 parts by weight) of ethyl silicate (n = 5) was sprayed and mixed in nitrogen gas for 1 minute. Next, 1.08 g of water (theoretical amount required for hydrolysis of ethyl silicate) was sprayed and mixed in nitrogen gas. Thereafter, the magnetic powder was taken out and subjected to heat treatment at 60 ° C., 100 ° C., 200 ° C., 250 ° C., 50 ° C., and 300 ° C. for 30 minutes under reduced pressure, respectively, in Examples 10 to 13, Example 37, and Example 38. A magnetic powder was obtained.
[0054]
[Examples 14 to 18] [Example 39]
300 g of Sm 2 Fe 17 N 3 magnetic powder having an average particle size of 10 μm was put into a mixer, and pure water was added to the powder in 0.1 g, 0.15 g, 0.60 g, 3.00, 4.50, And 0 g was sprayed and mixed in nitrogen gas for 0.5 minutes. The magnetic powder was taken out and subjected to heat treatment (preliminary drying) at 50 ° C. for 30 minutes under reduced pressure. Next, 7.5 g (2.5 parts by weight) of ethyl silicate (n = 5) was sprayed and mixed in nitrogen gas for 1 minute. Next, 1.08 g of water (theoretical amount required for hydrolysis of ethyl silicate) was sprayed and mixed in nitrogen gas. Then, it heat-processed for 30 minutes at 230 degreeC under pressure reduction, and obtained the magnetic powder of Examples 14-18 and Example 39. FIG.
[0055]
[Examples 19 to 21] [Examples 31 and 32]
300 g of Sm 2 Fe 17 N 3 magnetic powder having an average particle size of 10 μm was put into a mixer, and 0.6 g of 0.2 parts by weight of pure water was sprayed on the powder and mixed in nitrogen gas for 0.5 minutes. The magnetic powder was taken out and preliminarily dried at a reduced pressure and a drying temperature of 40 ° C., 50 ° C., and 100 ° C. for 30 minutes, respectively. Next, 7.5 g (2.5 parts by weight) of ethyl silicate (n = 5) was sprayed and mixed in nitrogen gas for 1 minute. Next, 1.08 g of water (theoretical amount required for hydrolysis of ethyl silicate) was sprayed and mixed in nitrogen gas. Then, it heat-processed for 30 minutes at 230 degreeC under pressure reduction, and obtained the magnetic material of Examples 19-21, Examples 31 and 32. FIG.
[0056]
[Comparative Example 1]
The Sm 2 Fe 17 N 3 magnetic powder having an average particle diameter of 10 μm obtained by a usual method was measured for magnetic properties by VSM. As a result, the remanent magnetization was 13.8 kG and the coercive force was 12.7 kOe. Incidentally, in the present invention, the Sm2Fe17N3 magnetic powder is basically used as a raw material. As a result of performing the above-mentioned oxidation resistance test on this magnetic powder, the residual magnetization was 5.0 kG and the coercive force was 4.1 kOe.
[0057]
[Comparative Example 2]
300 g of Sm 2 Fe 17 N 3 magnetic powder having an average particle size of 10 μm was put into a mixer, 3 g of γ-aminopropyltriethoxysilane was sprayed as a silane coupling agent, and mixed in nitrogen gas for 1 minute. Thereafter, the magnetic powder was taken out and heat-treated at a reduced pressure of 230 ° C. for 60 minutes to obtain a magnetic powder of Comparative Example 7. As a result of measuring the magnetic characteristics by VSM, the remanent magnetization was 13.0 kG and the coercive force was 12.4 kOe. As a result of performing the above-described oxidation resistance test on this magnetic powder, the remanent magnetization was 12.5 kG and the coercive force was 6.5 kOe.
[0058]
【The invention's effect】
As described above, in the magnetic powder to which the present invention is applied, it is understood that the degree of deterioration of the magnetic properties especially after accelerated thermal deterioration is extremely small, and thus the oxidation resistance is greatly improved. Further, FIG. 2 shows a chart of measurement results obtained by applying differential scanning calorimetry for the purpose of objectively evaluating oxidation resistance.
[0059]
As for the measurement sample, (1) is the magnetic powder of Comparative Example 1 that has not been subjected to any surface treatment, (2) is the silica coating with the silane coupling agent of Comparative Example 2, and (3) is Example 6 Magnetic powder. FIG. 2 shows that 20 mg of each measurement sample is packed in a fine measurement cell of alumina, heated from ambient temperature to 500 ° C. at a constant rate of 10 ° C./min, and the measurement sample is combusted at this time. The heat of reaction generated from the chemical change of the is written on the recorder.
[0060]
In (1), an exothermic reaction first appears around 200 ° C., and another exothermic process is observed around 400 ° C., and this exothermic reaction takes place vigorously from around 450 ° C. Compared with the case of (1), the exothermic reaction near 200 ° C. and 400 ° C. is considerably reduced in (2), but the exothermic reaction from around 450 ° C. is still abrupt. On the other hand, the heat generation at 200 and 400 ° C in the curve (3) is extremely low compared to the other curves, and the sudden heat generation near 450 ° C that occurred in (1) and (2) is completely suppressed. The exothermic reaction has shifted to around 510 ° C.
[0061]
The exotherm that occurs from around 450 ° C. is the decomposition of the crystals of the Sm 2 Fe 17 N 3 magnetic powder, which is induced in the presence of oxygen. In the present invention, this exothermic reaction is shifted to a high temperature because the silica coating according to the present invention coats the magnetic material densely and uniformly, so that oxygen does not easily enter the magnetic powder. It can be said that.
[0062]
The bonded magnet using the magnetic powder of the present invention thus obtained has excellent magnetic properties and also has excellent corrosion resistance as a bonded magnet. Furthermore, it is possible to obtain a magnet with less demagnetization, particularly less heat due to heat.
[Brief description of the drawings]
FIG. 1 is a schematic enlarged view of a magnetic powder (A) according to the present invention and a magnetic powder (B) of a comparative example. FIG. 2 is a chart of differential scanning calorimetry results of the magnetic powder.
Claims (5)
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| US7335392B2 (en) | 2002-11-29 | 2008-02-26 | Neomax Co., Ltd. | Method for producing corrosion-resistant rare earth metal-based permanent magnet |
| US7419527B2 (en) * | 2003-05-08 | 2008-09-02 | Particle Sciences, Inc. | Increased density particle molding |
| JP4501546B2 (en) * | 2004-06-21 | 2010-07-14 | 住友金属鉱山株式会社 | Rare earth bonded magnet composition and rare earth bonded magnet obtained using the same |
| JP5499738B2 (en) | 2009-02-03 | 2014-05-21 | 戸田工業株式会社 | Surface-treated rare earth magnetic powder, resin composition for bonded magnet containing the rare earth magnetic powder, and bonded magnet |
| JP7400241B2 (en) * | 2019-07-25 | 2023-12-19 | Tdk株式会社 | Composite magnetic powder and powder magnetic core using the same |
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