JP3871149B2

JP3871149B2 - Manufacturing method of low-loss ferrite sintered body

Info

Publication number: JP3871149B2
Application number: JP14888695A
Authority: JP
Inventors: 等上田; 徳和小湯原; 弘行笹尾; 晃夫内川; 豊樋口
Original assignee: Hitachi Metals Ltd
Current assignee: Proterial Ltd
Priority date: 1995-06-15
Filing date: 1995-06-15
Publication date: 2007-01-24
Anticipated expiration: 2022-01-24
Also published as: JPH08337465A

Description

【０００１】
【産業上の利用分野】
本発明は、従来技術による製品と同等以上の特性を持つＭｎ―Ｚｎ系ソフトフェライトを、安価に製造するためのソフトフェライト原料粉に関し、特に低損失なＭｎ―Ｚｎ系ソフトフェライト原料粉、フェライト焼結体及びその製造方法に関するものである。
【０００２】
【従来の技術】
従来のＭｎ―Ｚｎ系ソフトフェライトは、Ｆｅ₂Ｏ₃、Ｍｎ₃Ｏ₄、ＺｎＯの各酸化物を所定量に秤量し、混合し、その混合体を８００〜１０００℃で仮焼し、仮焼された仮焼体を粉砕し、所望の添加物及びバインダーを添加し、造粒し、それを金型内に充填し、所定の形状に成形し、１３００〜１４００℃の高温で焼成して、研磨工程等の必要な加工を経て、Ｍｎ―Ｚｎ系ソフトフェライトコアが得られている。
このように、従来のＭｎ―Ｚｎ系ソフトフェライトを得る方法は、工程が長く、煩雑で、仮焼及び本焼成と２回の焼成工程を経る為、コストが嵩むという問題があった。
この仮焼を行う理由は、成分の均質化、フェライト化反応の促進等であり（平賀・奥谷・尾島著、フェライト、丸善、昭６１．１１．３０、ｐ４８〜５１）、もし仮焼をしていない生の原料粉を直接造粒、成形、焼成すると、５００〜９００℃でのフェライト化反応による体積膨張、及びそれに引き続く焼結反応による体積収縮により、変形やひび割れが起こるという問題が生じる。
【０００３】
一方で、仮焼工程省略及び品質向上を狙った改良技術として、Ｆｅ、Ｍｎ等を含む複合酸化鉄粉を得る方法もいくつか提案されている。
例えば、特公昭４７―１１５５０号、特公昭６３―１７７７６号のように、フェライト構成金属の塩化物を水溶液状態で混合した後、高温ガス中で噴霧・焙焼し、直接仮焼粉相当の粉体を得る方法がある。この方法は、仮焼工程省略によるコストダウンの他に、溶融状態での混合の為、従来より成分の均質化に優れ、品質が向上するというメリットも期待されている。
【０００４】
また、このＭｎ―Ｚｎ系ソフトフェライト原料粉の主要な用途の一つにスイッチング電源用等に用いられるトランスがある。これらスイッチング電源用などに用いられるトランスには、近年、ますます軽量化、薄型化および小型化が求められている。このため駆動周波数が１００ｋＨｚから５００ｋＨｚへ、さらにはＭＨｚ帯へと高周波領域に広がりつつあり、それぞれの周波数において電力損失の小さいフェライト材料が望まれている。この電力損失の内、低周波領域で問題となるのは、主にヒステリシス損失であり、高周波領域で問題となるのは、渦電流損失である。
このヒステリシス損失は、保磁力や残留磁束密度を小さくすることにより、損失は小さくなる。このためには、フェライト焼結体の結晶粒径を均一に、かつ大きくすることが要求される。また渦電流損失は、フェライト焼結体の結晶粒径を小さくすることが要求される。このようにヒステリシス損失、渦電流損失は、フェライト焼結体の結晶粒径に影響され、しかも逆方向の特性であるため、使用周波数により適切な結晶粒径は異なる。
例えば、２５〜１００ｋＨｚでは、８〜２０μｍ程度の結晶粒径であることが望ましく、また１００〜５００ｋＨｚでは、４〜１２μｍ程度の結晶粒径であることが望ましく、５００〜１０００ｋＨｚでは、１〜６μｍ程度の結晶粒径であることが望ましい。またいずれにおいても、焼結密度が理論密度の９０％以上であることが望ましい。
【０００５】
【発明が解決しようとする課題】
従来の複合酸化鉄粉を得る方法では、特公昭６３―１７７７６号にも記述されている様に、塩化物の蒸気圧が高いＺｎが先に揮散してしまい焙焼後の複合酸化鉄粉体に取り込まれ難い、という問題がある。
この問題を解決する為に、特公昭６３―１７７７６号では、ＺｎＯはフェライト化反応を起こし易いという特長を利用して、塩化物蒸気圧の低いＦｅとＭｎの塩化物水溶液のみを混合・噴霧焙焼し、得られた粉体に後からＺｎＯ粉末を混合して造粒・成形・焼成している。この改良技術により、仮焼工程の省略は一応可能となったが、成形体の変形やひび割れの問題は完全には解決されていなかった。その理由は、Ｚｎフェライトは一旦形成されると安定であるが、Ｍｎフェライトは高温で形成されても冷却時に酸化されて一部再分解する為、Ｚｎを全く含まないＭｎ―Ｆｅ複合酸化鉄ではフェライト化が不十分な場合がある為と考えられる。
【０００６】
また、噴霧焙焼技術の改良により、塩化物蒸気圧の高いＺｎを揮散させずに複合酸化鉄粉体に取り込む方法も各種研究されており、燃焼後の還元性物質を含まない高温度の高速ガス流に原料液を噴霧し、熱ガス流と並流させて焙焼する方法（特開平１―１９２７０８号）や、それと類似の並流焙焼法（特開平３―４０９２１号）、或は噴霧焙焼時の噴霧液滴径や、焙焼中又は焙焼後の温度・時間・雰囲気等を規定したもの（特開平５―５１２１８号、特開平５―３３０８２８号、特開平６―２４４０１５号、特開平６―２９３５２１号）等、多数の改良技術が開示されている。
これらの改良技術により、確かにＺｎが複合酸化鉄中に取り込まれ、例えば特開平６―２９３５２１号に見られる様に、ミクロな組成偏差も殆ど無い均質なフェライト化した原料粉が得られ、それらを直接造粒・成形・焼成した場合、従来よりも特性の大幅に優れたコアが得られる事は判った。
しかし、これらの改良噴霧焙焼法の問題点は、Ｚｎを取り込む為にガス流れと液滴流れを並行とし、急速加熱・急速冷却を行なう為、従来の噴霧焙焼法に比べて熱原単位が大幅に悪化し、コストアップにつながる。折角、Ｆｅ、Ｍｎ、Ｚｎの複合酸化鉄を作り、仮焼工程を省略してもその原料粉が高価になってしまい、結局フェライト製品のコストダウンにはつながらないという問題点があった。
【０００７】
また、この金属塩の水溶液を噴霧焙焼して得られたフェライト原料粉は、細かい粒子径の原料粉となり易く、この粒子径の細かい原料粉を用いてフェライト焼結体を製造する場合、１１００℃以下の低い温度で反応性を抑えながら焼結させることにより、比較的結晶粒径の小さいフェライト焼結体を得ることは出来るが、結晶粒径を大きくしようとして、焼結温度を上げると、たちまち急激な粒成長を生じ、結晶が粗大化して、損失の大きなフェライト焼結体となってしまい、使用出来なくなる。
しかしながら、上記のように使用周波数によって要求される適切な結晶粒径が異なるフェライト焼結体を得るためには、結晶粒径のコントロールが必要である。この粒子径の細かい金属塩の水溶液を噴霧焙焼して得られたフェライト原料粉を用いて、結晶粒径をコントロールすることは、上述のように極めて困難であった。
本発明は、複合酸化鉄粉を使用して、仮焼工程の省略を行うことができる安価なソフトフェライト原料粉を提供し、粒子径が細かい金属塩の水溶液を噴霧焙焼して得られたフェライト原料粉を用いて、結晶粒径をコントロールすることを目的とする。
【０００８】
【課題を解決するための手段】
本発明は、Ｆｅ、Ｍｎ又はＦｅ、Ｍｎ、Ｚｎの各塩化物の水溶液を噴霧焙焼して、比表面積が４〜２５ｍ^２／ｇで、且つＦｅ、Ｍｎ、Ｚｎの含有量がＦｅ_２Ｏ_３、ＭｎＯ、ＺｎＯのモル比に換算して、各４０〜６５％、１０〜５０％、０〜３５％の比率で含む複合酸化鉄粉を用意し、
この複合酸化鉄粉を全体の２０〜８０重量％とし、これに酸化鉄、酸化亜鉛、及び焼成してＭｎＯになるＭｎ化合物の粉末をそれぞれ所定のモル比で８０〜２０重量％混合したソフトフェライト原料粉に、更に焼結後にＬｉ、Ｂ、Ｍｇ、Ｓｉ、Ｋ、Ｃａ、Ｔｉ、Ｖ、Ｃｒ、Ｃｏ、Ｙ、Ｚｒ、Ｎｂ、Ｍｏ、Ｉｎ、Ｓｎ、Ｔｅ、Ｂａ、Ｈｆ、Ｔａ、Ｗ、ＴｌおよびＢｉの酸化物となる成分を１種乃至２種以上副成分として加え混合の後、このソフトフェライト原料粉を未仮焼のまま所定形状に成形して成形体となし、前記成形体を１１００℃以上で焼結し、焼結密度が理論密度の９０％以上で、かつ平均結晶粒径が１〜９．９μｍであり、全体のＦｅ、Ｍｎ、Ｚｎ含有量をＦｅ_２Ｏ_３、ＭｎＯ、ＺｎＯのモル比に換算して、各５０〜５５％、３５〜４５％、５〜１５％のフェライト焼結体を得る低損失フェライト焼結体の製造方法である。
【０００９】
【作用】
本発明では、複合酸化鉄粉と各酸化物などの生原料粉とを混ぜて使用することにより、仮焼なしで割れや変形のないソフトフェライトを得ることができる。即ち、Ｆｅ_２Ｏ_３、Ｍｎ_３Ｏ_４、ＺｎＯが混合された生原料粉中に、フェライト化が始まる５００〜６００℃の温度で焼結反応が起こり始めるような、比表面積の大きい活性度の高い複合酸化鉄粉が、重量比で２０％程度以上混合されていれば、フェライト化による体積膨張と焼結による体積収縮が打ち消し合い、焼結体の変形や割れは抑えられることが判った。混合比率の上限は、仮焼工程省略の観点からは特に制約が無いが、コストダウンの目的からは高価な複合酸化鉄粉を多く使用することは得策でなく、８０％以下が良い。また、複合酸化鉄粉の比表面積は、４〜２５ｍ^２／ｇが適当となる。４ｍ^２／ｇより小さいと焼結助剤としての効果が不十分であり、２５ｍ^２／ｇより大きいとスラリー粘度が上がり過ぎ、使用し難い。好ましくは、６〜２０ｍ^２／ｇである。また、複合酸化鉄は、スピネル化率が高い方が望ましく、好ましくは、９０％以上である。また、組成の均一性に関しては、仮焼していない生原料粉が混合されていても、低温で焼結反応が始まる活性度の高い複合酸化鉄粉が６０％以上混合されていれば１１００〜１２００℃程度、２０〜６０％の混合比率でも１２００〜１３００℃程度の焼成温度で十分拡散が起こり、実用上問題がないことが判った。もちろん、それぞれ上記温度以上で焼成することは可能である。この、焼成温度によって、焼結体の結晶粒径が変わり、従って、複合酸化鉄の混合比率、焼成温度の選択により、結晶粒径、電磁気特性を変更可能である。また、本発明では、複合酸化鉄粉に各酸化物などの生原料粉を混ぜて使用するため、複合酸化鉄粉の組成ずれが多少大きくても、後で混ぜる生原料により調整できるので、複合酸化鉄の噴霧焙焼時の精密制御が不要となり、設備費等のコストを低減できる。即ち、Ｆｅ、Ｍｎ、Ｚｎの組成比をミクロに見ても均一であるように厳密に制御しようとすると、揮散し易いＺｎを逃がさぬよう、例えば特開平６―２９３５２１号にあるように、噴霧焙焼時の液滴径、温度、雰囲気、冷却条件を厳しく制御しなければならず、急速加熱・急速冷却による熱ロスも大きくなるが、本発明によれば、焙焼時の組成ずれやミクロな組成の不均一はあまり問題にならず、製造方法の自由度が増し、コストダウンが可能となる。例えば、焙焼後のガスを冷却せずに、バグフィルターで製品を捕集した後、ダストの無いガスから十分に熱回収することもできる。また、本発明では、複合酸化鉄粉に各酸化物などの生原料粉を混ぜて使用するため、一つの複合酸化鉄粉から、組成の異なる複数種のフェライト製品の製造が可能である。もちろん、複合酸化鉄の混合量を２０〜８０重量％とし、目標とする組成も決定されれば、自ずと複合酸化鉄の組成範囲も制限される。これに対し、特開平６―２９３５２１号の様に複合酸化鉄粉を１００％使用する場合や、特公昭６３―１７７７６号の様に後から添加する粉の大部分はＺｎＯでＦｅ_２Ｏ_３、Ｍｎ_３Ｏ_４は微調整にしか用いない場合は、本発明の様にはできず、それぞれの複合酸化鉄粉を作り分けなければならない為、ロット切り替え時のロスが生じる。以上のことから、複合酸化鉄粉のＦｅ、Ｍｎ、Ｚｎの含有量は、Ｆｅ_２Ｏ_３、ＭｎＯ、ＺｎＯのモル比に換算して、各４０〜６５％、１０〜５０％、０〜３５％が適当である。より望ましくは、各々４５〜６０％、３０〜４５％、５〜１５％が良い。また、全体のＦｅ、Ｍｎ、Ｚｎ含有量をＦｅ_２Ｏ_３、ＭｎＯ、ＺｎＯのモル比に換算して、各５０〜５５％、３５〜４５％、５〜１５％としたのは、この範囲以外では、低損失なフェライトを得ることが困難となるからである。複合酸化鉄粉と各酸化物などの生原料粉とを混ぜて使用することにより、焼結性のコントロールが可能となり、フェライト焼結体の焼結密度が理論密度の９０％以上で、かつ平均結晶粒径が１〜２０μｍの範囲で制御できる。なお、本発明による技術が適用されるフェライトとしては、副成分として焼結後にＬｉ、Ｂ、Ｍｇ、Ｓｉ、Ｋ、Ｃａ、Ｔｉ、Ｖ、Ｃｒ、Ｃｏ、Ｙ、Ｚｒ、Ｎｂ、Ｍｏ、Ｉｎ、Ｓｎ、Ｔｅ、Ｂａ、Ｈｆ、Ｔａ、Ｗ、ＴｌおよびＢｉの酸化物となる成分を１種乃至２種以上含んでも良い。
【００１０】
【実施例】
以下に、本発明に係るフェライト材料の実施例を詳細に説明する。
実施例１
Ｆｅの塩化物とＭｎの塩化物とＺｎの塩化物とを混合した水溶液を噴霧焙焼して、Ｆｅ₂Ｏ₃、ＭｎＯ、ＺｎＯのモル比に換算して、Ｆｅ₂Ｏ₃ ５３．２ｍｏｌ％、ＭｎＯ３６．８ｍｏｌ％、ＺｎＯ１０．０ｍｏｌ％の成分を有する複合酸化鉄粉を用意し、この複合酸化鉄粉に対して、Ｆｅ₂Ｏ₃、Ｍｎ₃Ｏ₄、ＺｎＯの酸化物原料粉末（生原料粉）のそれぞれの粉末を上記と同組成となるように添加含有して、フェライト原料粉を作成した。このとき、複合酸化鉄粉の含有量を表１に示す種々の割合で作製した。尚、最終組成は、上記の組成となる様に設定した。このとき、Ｆｅ₂Ｏ₃の平均一次粒子径は、０．７８μｍ、Ｍｎ₃Ｏ₄の平均一次粒子径は、０．５６μｍ、ＺｎＯの平均一次粒子径は、０．６５μｍ、噴霧焙焼して得た複合酸化鉄粉の平均一次粒子径は、０．０８μｍ（比表面積が約１７ｍ²／ｇ）であった。これに、Ｖ₂Ｏ₅ ３００ｐｐｍ，ＳｉＯ₂ ６０ｐｐｍ、ＣａＣＯ₃ ７００ｐｐｍ、Ｔａ₂Ｏ₅ ５０ｐｐｍおよびＮｂ₂Ｏ₅ １５０ｐｐｍ、さらに所定量のイオン交換水および分散剤を添加した後、アトライタにて１時間混合し、これに原料に対して２ｗｔ％のバインダー（ポリビニルアルコール）を加え、スプレードライヤにて造粒し、５０メッシュのふるいにて整粒した顆粒を乾式圧縮成形機と金型を用いて、外径１６．８ｍｍ、内径８．５ｍｍ、高さ５．４ｍｍのリング状コアに成形圧２．５ｔｏｎ／ｃｍ²で成形した。これをバッチ式焼成炉を用いて、焼成温度１２５０℃、酸素分圧１％で焼成し、得られた焼結体の焼結密度、初透磁率、電力損失、平均結晶粒径を測定した。なお、電力損失は、１００ｋＨｚ、２００ｍＴの条件で測定した。この結果を表１に示す。表１中の電力損失は、最小値の値であり、括弧内はそのときの温度である。又、表１の備考欄に本発明の範囲のものは、本発明品とし、本発明の範囲外のものは比較例とした。
【００１１】
【表１】

【００１２】
この表１に示すとおり、噴霧焙焼して得た複合酸化鉄粉のみを使用した（Ｎｏ．６、１００％）場合、平均結晶粒径が１２２．２μｍと粗大化し、電力損失が大きくなるが、本発明のように、酸化物粉末を混合することにより、平均結晶粒径が８．７〜９．９μｍとなり、電力損失の少ないフェライト焼結体を得ることができた。また、本発明品の焼結密度は、理論密度（５１００ｋｇ／ｍ^３）の９０％（４６００ｋｇ／ｍ^３）以上の密度を得ている。
【００１３】
実施例２
実施例１と同一手順で作製したリング状コアを、バッチ式焼成炉を用いて、焼成温度１１５０℃、酸素分圧０．１％で焼成し、得られた焼結体の焼結密度、初透磁率、電力損失、平均結晶粒径を測定した。なお、電力損失は、５００ｋＨｚ、５０ｍＴの条件で測定した。この結果を表２に示す。表２中の電力損失は、最小値の値であり、括弧内はそのときの温度である。又、表２の備考欄に本発明の範囲のものは、本発明品とし、本発明の範囲外のものは比較例とした。
【００１４】
【表２】

【００１５】
この表２に示すとおり、本発明によれば、酸化物粉末を混合することにより、平均結晶粒径が３．６〜３．８μｍで、電力損失の少ないフェライト焼結体を得ることができた。また、本発明品の焼結密度は、理論密度（５１００ｋｇ／ｍ³）の９０％（４６００ｋｇ／ｍ³）以上の密度を得ている。また、噴霧焙焼して得た複合酸化鉄粉のみ使用した（Ｎｏ．６、１００％）場合、結晶粒径のバラツキを生じ、電力損失が悪くなった。
【００１６】
実施例３
Ｆｅの塩化物とＭｎの塩化物とＺｎの塩化物を混合し、噴霧焙焼して得た複合酸化鉄粉であって、Ｆｅ、Ｍｎ、Ｚｎの含有量がＦｅ₂Ｏ₃、ＭｎＯ、ＺｎＯのモル比に換算して、Ｆｅ₂Ｏ₃ ５３．２ｍｏｌ％、ＭｎＯ３６．８ｍｏｌ％、ＺｎＯ１０．０ｍｏｌ％の複合酸化鉄粉と、Ｆｅ₂Ｏ₃、Ｍｎ₃Ｏ₄、ＺｎＯの相当量のそれぞれの酸化物原料粉末とを表３に示す最終組成になるように、種々の割合で秤量した。このとき、複合酸化鉄粉の含有量が６０ｗｔ％となるように設定した。そして、Ｆｅ₂Ｏ₃の平均一次粒子径は、０．７８μｍ、Ｍｎ₃Ｏ₄の平均一次粒子径は、０．５６μｍ、ＺｎＯの平均一次粒子径は、０．６５μｍ、噴霧焙焼して得たフェライト原料粉の平均一次粒子径は、０．０８μｍであった。これに、表３に示す所定量の添加物を副成分として加え、さらに所定量のイオン交換水および分散剤を添加した後、アトライタにて１時間混合し、これに原料に対して２ｗｔ％のバインダー（ポリビニルアルコール）を加え、スプレードライヤにて造粒し、５０メッシュのふるいにて整粒した顆粒を乾式圧縮成形機と金型を用いて、外径１６．８ｍｍ、内径８．５ｍｍ、高さ５．４ｍｍのリング状コアに成形圧２．５ｔｏｎ／ｃｍ²で成形した。これをバッチ式焼成炉を用いて、表４の焼成条件で焼成し、得られた焼結体の焼結密度、初透磁率、電力損失、平均結晶粒径を測定した。なお、電力損失は、５００ｋＨｚ、５０ｍＴの条件で測定した。この結果を表４に示す。表４中の電力損失は、最小値の値であり、括弧内はそのときの温度である。
【００１７】
【表３】

【００１８】
【表４】

【００１９】
上記実施例に示すように、本発明の実施例は、噴霧焙焼して得た複合酸化鉄粉の含有量を６０ｗｔ％とし、これに生原料粉を添加して、種々の所望の組成のソフトフェライトを得ることができた。しかも、本発明の実施例は、いずれも低電力損失であり、焼結密度が理論密度の９０％以上であって、平均結晶粒径が１〜２０μｍの範囲で制御することが出来ている。
【００２０】
実施例４
Ｆｅの塩化物とＭｎの塩化物とＺｎの塩化物とを混合した水溶液を噴霧焙焼して、Ｆｅ₂Ｏ₃、ＭｎＯ、ＺｎＯのモル比に換算して、Ｆｅ₂Ｏ₃ ５３．２ｍｏｌ％、ＭｎＯ３６．８ｍｏｌ％、ＺｎＯ１０．０ｍｏｌ％の成分を有する複合酸化鉄粉を用意し、この複合酸化鉄粉に対して、Ｆｅ₂Ｏ₃、Ｍｎ₃Ｏ₄、ＺｎＯの酸化物原料粉末（生原料粉）のそれぞれの粉末を上記と同組成となるように添加含有して、フェライト原料粉を作成した。このとき、複合酸化鉄粉の含有量が６０ｗｔ％となるように作製した。尚、最終組成は、上記の組成となる様に設定した。このとき、Ｆｅ₂Ｏ₃の平均一次粒子径は、０．７８μｍ、Ｍｎ₃Ｏ₄の平均一次粒子径は、０．５６μｍ、ＺｎＯの平均一次粒子径は、０．６５μｍ、噴霧焙焼して得た複合酸化鉄粉の平均一次粒子径は、０．０８μｍ（比表面積が約１７ｍ²／ｇ）であった。これに、ＳｉＯ₂、ＣａＣＯ₃、Ｎｂ₂Ｏ₅を表５に示す各所定量添加含有させ、さらに所定量のイオン交換水および分散剤を添加した後、アトライタにて１時間混合し、これに原料に対して２ｗｔ％のバインダー（ポリビニルアルコール）を加え、スプレードライヤにて造粒し、５０メッシュのふるいにて整粒した顆粒を乾式圧縮成形機と金型を用いて、外径１６．８ｍｍ、内径８．５ｍｍ、高さ５．４ｍｍのリング状コアに成形圧２．５ｔｏｎ／ｃｍ²で成形した。これをバッチ式焼成炉を用いて、焼成温度１２５０℃、酸素分圧１％で焼成し、得られた焼結体の焼結密度、初透磁率、電力損失、平均結晶粒径を測定した。なお、電力損失は、１００ｋＨｚ、２００ｍＴの条件で測定した。この結果を表６に示す。表６中の電力損失は、最小値の値であり、括弧内はそのときの温度である。
【００２１】
【表５】

【００２２】
【表６】

【００２３】
この表６において、試料Ｎｏ．４，５は他の実施例よりも電力損失が大きく、副成分として、ＳｉＯ₂を含有させる時は、０〜５００ｐｐｍの範囲が適当であり、ＣａＣＯ₃を含有させる時は、２０〜２０００ｐｐｍの範囲が適当である。このＳｉＯ₂、ＣａＣＯ₃は粒界に高抵抗層を形成するものであり、上記記範囲内にあると、電力損失が小さくなる。Ｎｂ₂Ｏ₅を含有させる時は、５０〜２０００ｐｐｍの範囲が適当である。また、Ｎｂ₂Ｏ₅は結晶成長促進材として機能するものであり、実施例１で用いたＶ₂Ｏ₅、Ｔａ₂Ｏ₅も同様の機能を有し、このＮｂ₂Ｏ₅、Ｖ₂Ｏ₅、Ｔａ₂Ｏ₅の１種又は２種以上を添加含有させることが望ましい。この場合、それぞれの含有量は、５０〜２０００ｐｐｍの範囲が適当である。この５０ｐｐｍより少ないと、添加効果が少なく、２０００ｐｐｍより多いと異常粒成長が生じる。
【００２４】
以上、実施例に示すように、本発明の実施例は、噴霧焙焼して得た複合酸化鉄粉の含有量としては、２０〜８０ｗｔ％とし、これに生原料粉を所定量添加して、所望の組成のソフトフェライトを得ることができた。しかも、本発明の実施例は、低損失フェライトとして使用可能なものであり、焼結密度が理論密度の９０％以上であって、平均結晶粒径が１〜９．９μｍの範囲で制御することが出来ている。
【００２５】
【発明の効果】
本発明によれば、複合酸化鉄粉と生原料粉とを所定量混合して使用することにより、仮焼工程を無くして、ソフトフェライトの製造が可能となるものであり、低損失Ｍｎ―Ｚｎ系ソフトフェライトを安価に製造することが可能となる。また、本発明によれば、フェライト焼結体の結晶粒径のコントロールも可能となる。[0001]
[Industrial application fields]
The present invention relates to a soft ferrite raw material powder for inexpensively producing Mn—Zn soft ferrite having characteristics equivalent to or better than those of products according to the prior art, and in particular, a low loss Mn—Zn soft ferrite raw material powder, The present invention relates to a bonded body and a manufacturing method thereof.
[0002]
[Prior art]
Conventional Mn—Zn-based soft ferrites are prepared by weighing and mixing Fe ₂ O ₃ , Mn ₃ O ₄ , and ZnO oxides in predetermined amounts, and calcining the mixture at 800 to 1000 ° C. Pulverizing the calcined body, adding desired additives and binder, granulating it, filling it into a mold, forming it into a predetermined shape, firing at a high temperature of 1300-1400 ° C, An Mn—Zn-based soft ferrite core is obtained through necessary processing such as a polishing process.
As described above, the conventional method for obtaining Mn—Zn-based soft ferrite has a long process and is complicated, and there is a problem that the cost is increased because it undergoes calcination and main firing and two firing steps.
The reason for this calcining is to homogenize the components and promote the ferritization reaction (Hiraga, Okutani, Ojima, Ferrite, Maruzen, Sho 61.11.30, p48-51). When raw raw powder that is not directly granulated, shaped, and fired, there arises a problem that deformation and cracking occur due to volume expansion by a ferritization reaction at 500 to 900 ° C. and subsequent volume shrinkage by a sintering reaction.
[0003]
On the other hand, several methods for obtaining composite iron oxide powder containing Fe, Mn, and the like have been proposed as improved techniques aimed at omitting the calcination step and improving quality.
For example, as described in Japanese Examined Patent Publication Nos. 47-11550 and 63-177776, a ferrite-constituting metal chloride is mixed in an aqueous solution, then sprayed and roasted in a high-temperature gas, and directly equivalent to a calcined powder. There is a way to get a body. In addition to cost reduction due to omission of the calcination step, this method is expected to have a merit of superior homogenization of components and improved quality because of mixing in a molten state.
[0004]
One of the main uses of the Mn—Zn soft ferrite raw material powder is a transformer used for a switching power source. In recent years, transformers used for such switching power supplies and the like are increasingly required to be lighter, thinner and smaller. For this reason, the driving frequency is spreading from 100 kHz to 500 kHz and further to the high frequency region, and a ferrite material having a small power loss at each frequency is desired. Of this power loss, the problem mainly in the low frequency region is hysteresis loss, and the problem in the high frequency region is eddy current loss.
The hysteresis loss is reduced by reducing the coercive force and the residual magnetic flux density. For this purpose, the crystal grain size of the ferrite sintered body is required to be uniform and large. Further, the eddy current loss is required to reduce the crystal grain size of the ferrite sintered body. Thus, the hysteresis loss and eddy current loss are affected by the crystal grain size of the ferrite sintered body, and are characteristics in the reverse direction, so that the appropriate crystal grain size differs depending on the operating frequency.
For example, the crystal grain size is preferably about 8 to 20 μm at 25 to 100 kHz, the crystal grain size is preferably about 4 to 12 μm at 100 to 500 kHz, and about 1 to 6 μm at 500 to 1000 kHz. The crystal grain size is desirable. In any case, the sintered density is desirably 90% or more of the theoretical density.
[0005]
[Problems to be solved by the invention]
In the conventional method of obtaining composite iron oxide powder, as described in Japanese Patent Publication No. 63-17776, Zn having a high vapor pressure of chloride is volatilized first, and the composite iron oxide powder after roasting is obtained. There is a problem that it is difficult to be taken in.
In order to solve this problem, Japanese Patent Publication No. 63-17776 uses only the feature that ZnO easily causes a ferritization reaction, so that only an aqueous chloride solution of Fe and Mn having a low chloride vapor pressure is mixed and sprayed. After baking, the obtained powder is mixed with ZnO powder and granulated, molded and fired. With this improved technique, the calcination step can be omitted, but the problems of deformation and cracking of the molded body have not been completely solved. The reason is that once the Zn ferrite is formed, it is stable, but even if the Mn ferrite is formed at a high temperature, it is oxidized during cooling and partially re-decomposed. This is thought to be due to the fact that ferritization may be insufficient.
[0006]
In addition, various methods have been studied for improving the spray roasting technology to incorporate Zn with high chloride vapor pressure into the composite iron oxide powder without volatilization. A method of spraying a raw material liquid into a gas flow and co-firing with a hot gas flow (Japanese Patent Laid-Open No. 1-192708), a similar co-current roasting method (Japanese Patent Laid-Open No. 3-40921), or Specified spray droplet diameter at spray roasting, temperature, time, atmosphere, etc. during or after roasting (JP-A-5-51218, JP-A-5-330828, JP-A-6-244015) JP-A-6-293521) and many other improved techniques are disclosed.
With these improved techniques, Zn is certainly incorporated into the composite iron oxide, and as shown in, for example, JP-A-6-293521, homogeneous ferritized raw material powders having almost no micro compositional deviation can be obtained. It was found that a core with significantly improved characteristics can be obtained by directly granulating, molding, and firing.
However, the problem with these improved spray roasting methods is that the gas flow and droplet flow are parallel in order to incorporate Zn, and rapid heating and cooling are performed. Will greatly deteriorate, leading to increased costs. Even if a complex iron oxide of Fe, Mn, and Zn is made and the calcining step is omitted, the raw material powder becomes expensive, and there is a problem that it does not lead to cost reduction of the ferrite product.
[0007]
Further, the ferrite raw material powder obtained by spray roasting the aqueous solution of the metal salt is likely to be a raw material powder having a fine particle size. When a raw material powder having a fine particle size is used to produce a ferrite sintered body, 1100 By sintering while suppressing the reactivity at a low temperature of ℃ or less, it is possible to obtain a ferrite sintered body having a relatively small crystal grain size, but when trying to increase the crystal grain size, raising the sintering temperature, As a result, rapid grain growth occurs, the crystal becomes coarse, and a ferrite sintered body with a large loss is formed, which cannot be used.
However, it is necessary to control the crystal grain size in order to obtain a ferrite sintered body having an appropriate crystal grain size required depending on the operating frequency as described above. As described above, it has been extremely difficult to control the crystal grain size using ferrite raw material powder obtained by spray roasting an aqueous solution of a metal salt having a fine particle size.
The present invention provides an inexpensive soft ferrite raw material powder capable of omitting the calcination step using composite iron oxide powder, and obtained by spray roasting an aqueous solution of a metal salt having a small particle size The object is to control the crystal grain size by using ferrite raw material powder.
[0008]
[Means for Solving the Problems]
In the present invention, an aqueous solution of each chloride of Fe, Mn or Fe, Mn, and Zn is spray roasted to have a specific surface area of 4 to 25 m ² / g and a content of Fe, Mn, and Zn of Fe ₂ O. ₃ , Prepared composite iron oxide powder containing 40 to 65%, 10 to 50%, and 0 to 35% ratio in terms of molar ratio of MnO and ZnO,
Soft ferrite in which this composite iron oxide powder is mixed in an amount of 20 to 80% by weight and mixed with iron oxide, zinc oxide, and powder of Mn compound that is fired to become MnO at a predetermined molar ratio of 80 to 20% by weight. After sintering further to Li, B, Mg, Si, K, Ca, Ti, V, Cr, Co, Y, Zr, Nb, Mo, In, Sn, Te, Ba, Hf, Ta, W, After adding and mixing one or more components that become oxides of Tl and Bi as subcomponents, this soft ferrite raw material powder is formed into a predetermined shape without being pre- calcined to form a molded body. Sintered at 1100 ° C. or higher, the sintered density is 90% or more of the theoretical density, the average crystal grain size is 1 to 9.9 μm, and the total Fe, Mn, Zn content is Fe ₂ O ₃ , MnO , Converted to a molar ratio of ZnO, 50-55%, 3% 45%, is a method of producing low-loss ferrite sintered body to obtain a 5-15% of the ferrite sintered body.
[0009]
[Action]
In the present invention, soft ferrite free from cracking and deformation can be obtained without calcining by mixing and using composite iron oxide powder and raw material powder such as each oxide. That is, in the raw material powder in which Fe ₂ O ₃ , Mn ₃ O ₄ and ZnO are mixed, an activity with a large specific surface area such that a sintering reaction starts to occur at a temperature of 500 to 600 ° C. where ferritization starts. It has been found that if high composite iron oxide powder is mixed in a weight ratio of about 20% or more, volume expansion due to ferritization and volume shrinkage due to sintering cancel each other, and deformation and cracking of the sintered body can be suppressed. The upper limit of the mixing ratio is not particularly limited from the viewpoint of omitting the calcining step, but for the purpose of cost reduction, it is not a good idea to use a large amount of expensive composite iron oxide powder, and 80% or less is good. The specific surface area of the composite iron oxide powder is suitably 4 to 25 m ² / g. If it is smaller than 4 m ² / g, the effect as a sintering aid is insufficient, and if it is larger than 25 m ² / g, the slurry viscosity is excessively increased and is difficult to use. Preferably, it is 6-20 m < ² > / g. The composite iron oxide preferably has a higher spinelization rate, and is preferably 90% or more. In addition, regarding the uniformity of composition, even if raw raw powder that has not been calcined is mixed, if composite iron oxide powder having a high activity at which the sintering reaction starts at a low temperature is mixed by 60% or more, 1100 It was found that even at a mixing ratio of about 1200 ° C. and 20 to 60%, sufficient diffusion occurred at a firing temperature of about 1200 to 1300 ° C. and there was no practical problem. Of course, it is possible to fire at each of the above temperatures. The crystal grain size of the sintered body varies depending on the firing temperature. Therefore, the crystal grain size and electromagnetic characteristics can be changed by selecting the mixing ratio of the composite iron oxide and the firing temperature. In the present invention, since raw material powder such as each oxide is mixed with the composite iron oxide powder, even if the composition deviation of the composite iron oxide powder is somewhat large, it can be adjusted by the raw material to be mixed later. Precise control at the time of iron oxide spray roasting is not necessary, and costs such as equipment costs can be reduced. That is, if the composition ratio of Fe, Mn, and Zn is strictly controlled so as to be uniform even when viewed microscopically, Zn that is easily volatilized is not escaped. For example, as disclosed in JP-A-6-293521, The droplet diameter, temperature, atmosphere, and cooling conditions during roasting must be strictly controlled, and heat loss due to rapid heating / cooling increases. Such a non-uniform composition is not a significant problem, increasing the degree of freedom of the manufacturing method and reducing the cost. For example, after collecting the product with a bag filter without cooling the gas after roasting, it is possible to sufficiently recover heat from the dust-free gas. Moreover, in this invention, since raw raw material powders, such as each oxide, are mixed and used for composite iron oxide powder, the manufacture of the multiple types of ferrite product from which a composition differs from one composite iron oxide powder is possible. Of course, if the mixing amount of the composite iron oxide is 20 to 80% by weight and the target composition is determined, the composition range of the composite iron oxide is naturally limited. On the other hand, when 100% of the composite iron oxide powder is used as in JP-A-6-293521, or most of powder added later as in JP-B 63-17776 is ZnO, Fe ₂ O ₃ , When Mn ₃ O ₄ is used only for fine adjustment, it cannot be performed as in the present invention, and each composite iron oxide powder must be prepared separately, resulting in loss during lot switching. From the above, the Fe, Mn, and Zn contents of the composite iron oxide powder are each 40 to 65%, 10 to 50%, and 0 to 35 in terms of the molar ratio of Fe ₂ O ₃ , MnO, and ZnO. % Is appropriate. More preferably, 45 to 60%, 30 to 45%, and 5 to 15% are preferable. In addition, it is this range that the total Fe, Mn, and Zn contents are converted to molar ratios of Fe ₂ O ₃ , MnO, and ZnO, and are 50 to 55%, 35 to 45%, and 5 to 15%, respectively. This is because it is difficult to obtain low-loss ferrite. By mixing and using composite iron oxide powder and raw material powder such as each oxide, it becomes possible to control the sinterability, and the sintered density of the ferrite sintered body is 90% or more of the theoretical density, and the average The crystal grain size can be controlled in the range of 1 to 20 μm. The ferrite to which the technology according to the present invention is applied includes Li, B, Mg, Si, K, Ca, Ti, V, Cr, Co, Y, Zr, Nb, Mo, In, and the like after sintering as subcomponents. One or two or more types of components that form oxides of Sn, Te, Ba, Hf, Ta, W, Tl, and Bi may be included.
[0010]
【Example】
Below, the example of the ferrite material concerning the present invention is described in detail.
Example 1
An aqueous solution in which Fe chloride, Mn chloride, and Zn chloride are mixed is spray-roasted and converted to a molar ratio of Fe ₂ O ₃ , MnO, and ZnO, and 53.2 mol% of Fe ₂ O ₃ . , MnO 36.8 mol%, ZnO 10.0 mol% of composite iron oxide powder is prepared, Fe ₂ O ₃ , Mn ₃ O ₄ , ZnO oxide raw material powder ( Each raw material powder) was added and contained so as to have the same composition as described above to prepare a ferrite raw material powder. At this time, the content of the composite iron oxide powder was prepared at various ratios shown in Table 1. The final composition was set to be the above composition. At this time, the average primary particle diameter of Fe ₂ O ₃ is 0.78 μm, the average primary particle diameter of Mn ₃ O ₄ is 0.56 μm, the average primary particle diameter of ZnO is 0.65 μm, and spray roasting is performed. The average primary particle diameter of the obtained composite iron oxide powder was 0.08 μm (specific surface area was about 17 m ² / g). To this, V ₂ O ₅ 300 ppm, SiO ₂ 60 ppm, CaCO ₃ 700 ppm, Ta ₂ O ₅ 50 ppm and Nb ₂ O ₅ 150 ppm, and a predetermined amount of ion-exchanged water and a dispersing agent were added, followed by mixing with an attritor for 1 hour. Then, 2% by weight binder (polyvinyl alcohol) is added to the raw material, granulated with a spray dryer, and granulated with a 50 mesh sieve. A ring-shaped core having a diameter of 16.8 mm, an inner diameter of 8.5 mm, and a height of 5.4 mm was molded at a molding pressure of 2.5 ton / cm ² . This was fired at a firing temperature of 1250 ° C. and an oxygen partial pressure of 1% using a batch-type firing furnace, and the sintered density, initial permeability, power loss, and average crystal grain size of the obtained sintered body were measured. The power loss was measured under the conditions of 100 kHz and 200 mT. The results are shown in Table 1. The power loss in Table 1 is the minimum value, and the value in parentheses is the temperature at that time. Also, in the remarks column of Table 1, those within the scope of the present invention are those of the present invention, and those outside the scope of the present invention are comparative examples.
[0011]
[Table 1]

[0012]
As shown in Table 1, when only the composite iron oxide powder obtained by spray roasting is used (No. 6, 100%), the average crystal grain size becomes as large as 122.2 μm, and the power loss increases. As in the present invention, by mixing the oxide powder, the average crystal grain size became 8.7 to 9.9 μm, and a ferrite sintered body with little power loss could be obtained. Further, the sintered density of the product of the present invention is 90% (4600 kg / m ³ ) or more of the theoretical density (5100 kg / m ³ ).
[0013]
Example 2
The ring-shaped core produced by the same procedure as in Example 1 was fired at a firing temperature of 1150 ° C. and an oxygen partial pressure of 0.1% using a batch-type firing furnace. The permeability, power loss, and average crystal grain size were measured. The power loss was measured under conditions of 500 kHz and 50 mT. The results are shown in Table 2. The power loss in Table 2 is the minimum value, and the temperature in parentheses is the temperature at that time. Further, in the remarks column of Table 2, those within the scope of the present invention are those of the present invention, and those outside the scope of the present invention are comparative examples.
[0014]
[Table 2]

[0015]
As shown in Table 2, according to the present invention, a ferrite sintered body having an average crystal grain size of 3.6 to 3.8 μm and low power loss could be obtained by mixing oxide powder. . Further, the sintered density of the product of the present invention is 90% (4600 kg / m ³ ) or more of the theoretical density (5100 kg / m ³ ). Moreover, when only the composite iron oxide powder obtained by spray roasting was used (No. 6, 100%), the crystal grain size varied and the power loss deteriorated.
[0016]
Example 3
A composite iron oxide powder obtained by mixing Fe chloride, Mn chloride, and Zn chloride and spray roasting, wherein the content of Fe, Mn, Zn is Fe ₂ O ₃ , MnO, ZnO In terms of the molar ratio of Fe ₂ O ₃ 53.2 mol%, MnO 36.8 mol%, ZnO 10.0 mol% complex iron oxide powder, and Fe ₂ O ₃ , Mn ₃ O ₄ , ZnO Each oxide raw material powder was weighed in various proportions so as to have the final composition shown in Table 3. At this time, it set so that content of complex iron oxide powder might be 60 wt%. The average primary particle diameter of Fe ₂ O ₃ is 0.78 μm, the average primary particle diameter of Mn ₃ O ₄ is 0.56 μm, the average primary particle diameter of ZnO is 0.65 μm, and obtained by spray roasting. The average primary particle diameter of the ferrite raw material powder was 0.08 μm. To this, a predetermined amount of additives shown in Table 3 were added as subcomponents, a predetermined amount of ion-exchanged water and a dispersant were added, and then mixed for 1 hour in an attritor. Add a binder (polyvinyl alcohol), granulate with a spray dryer, and adjust the size of the granules with a 50-mesh sieve using a dry compression molding machine and a mold, outer diameter 16.8 mm, inner diameter 8.5 mm, high A 5.4 mm ring-shaped core was molded at a molding pressure of 2.5 ton / cm ² . This was fired under the firing conditions shown in Table 4 using a batch firing furnace, and the sintered density, initial permeability, power loss, and average crystal grain size of the obtained sintered body were measured. The power loss was measured under conditions of 500 kHz and 50 mT. The results are shown in Table 4. The power loss in Table 4 is the minimum value, and the temperature in parentheses is the temperature at that time.
[0017]
[Table 3]

[0018]
[Table 4]

[0019]
As shown in the above examples, in the examples of the present invention, the content of the composite iron oxide powder obtained by spray roasting is set to 60 wt%, and raw material powder is added thereto to obtain various desired compositions. Soft ferrite could be obtained. Moreover, all the examples of the present invention have low power loss, the sintered density is 90% or more of the theoretical density, and the average crystal grain size can be controlled in the range of 1 to 20 μm.
[0020]
Example 4
An aqueous solution in which Fe chloride, Mn chloride, and Zn chloride are mixed is spray-roasted and converted to a molar ratio of Fe ₂ O ₃ , MnO, and ZnO, and 53.2 mol% of Fe ₂ O ₃ . , MnO 36.8 mol%, ZnO 10.0 mol% of composite iron oxide powder is prepared, Fe ₂ O ₃ , Mn ₃ O ₄ , ZnO oxide raw material powder ( Each raw material powder) was added and contained so as to have the same composition as described above to prepare a ferrite raw material powder. At this time, it produced so that content of composite iron oxide powder might be 60 wt%. The final composition was set to be the above composition. At this time, the average primary particle diameter of Fe ₂ O ₃ is 0.78 μm, the average primary particle diameter of Mn ₃ O ₄ is 0.56 μm, the average primary particle diameter of ZnO is 0.65 μm, and spray roasting is performed. The average primary particle diameter of the obtained composite iron oxide powder was 0.08 μm (specific surface area was about 17 m ² / g). SiO ₂ , CaCO ₃ , and Nb ₂ O ₅ were added to the respective predetermined amounts shown in Table 5 and further added with predetermined amounts of ion-exchanged water and a dispersing agent, and then mixed with an attritor for 1 hour. 2 wt% binder (polyvinyl alcohol) is added to the mixture, granulated with a spray dryer, and granulated with a 50-mesh sieve, the outer diameter is 16.8 mm using a dry compression molding machine and a mold. A ring-shaped core having an inner diameter of 8.5 mm and a height of 5.4 mm was molded at a molding pressure of 2.5 ton / cm ² . This was fired at a firing temperature of 1250 ° C. and an oxygen partial pressure of 1% using a batch-type firing furnace, and the sintered density, initial permeability, power loss, and average crystal grain size of the obtained sintered body were measured. The power loss was measured under the conditions of 100 kHz and 200 mT. The results are shown in Table 6. The power loss in Table 6 is a minimum value, and the temperature in parentheses is the temperature at that time.
[0021]
[Table 5]

[0022]
[Table 6]

[0023]
In Table 6, Sample No. 4 and 5 have a larger power loss than the other examples, and when SiO ₂ is contained as an accessory component, the range of 0 to 500 ppm is appropriate, and when CaCO ₃ is contained, the range is 20 to 2000 ppm. Is appropriate. These SiO ₂ and CaCO ₃ form a high resistance layer at the grain boundary, and if it is within the above range, power loss is reduced. When Nb ₂ O ₅ is contained, the range of 50 to 2000 ppm is appropriate. Nb ₂ O ₅ functions as a crystal growth promoting material, and V ₂ O ₅ and Ta ₂ O ₅ used in Example 1 also have the same function, and this Nb ₂ O ₅ , V ₂ O ₅ or 1 or 2 or more of Ta ₂ O ₅ is preferably added and contained. In this case, the range of 50 to 2000 ppm is appropriate for each content. If it is less than 50 ppm, the effect of addition is small, and if it exceeds 2000 ppm, abnormal grain growth occurs.
[0024]
As mentioned above, as shown in the Examples, the content of the composite iron oxide powder obtained by spray roasting is 20 to 80 wt%, and a predetermined amount of raw material powder is added thereto. Thus, soft ferrite having a desired composition could be obtained. Moreover, the examples of the present invention can be used as low-loss ferrite, and the sintered density is 90% or more of the theoretical density, and the average crystal grain size is controlled in the range of 1 to 9.9 μm. It is possible.
[0025]
【The invention's effect】
According to the present invention, by mixing a predetermined amount of composite iron oxide powder and raw material powder, it becomes possible to produce a soft ferrite without a calcining step, and a low loss Mn—Zn. -Based soft ferrite can be manufactured at low cost. Further, according to the present invention, the crystal grain size of the ferrite sintered body can be controlled.

Claims

An aqueous solution of Fe, Mn or Fe, Mn, and Zn chlorides is spray roasted to have a specific surface area of 4 to 25 m ² / g and Fe, Mn, and Zn contents of Fe ₂ O ₃ , MnO, In terms of the molar ratio of ZnO, a composite iron oxide powder containing 40 to 65%, 10 to 50%, and 0 to 35% ratio is prepared.
Soft ferrite in which this composite iron oxide powder is mixed in an amount of 20 to 80% by weight and mixed with iron oxide, zinc oxide, and powder of Mn compound that is fired to become MnO at a predetermined molar ratio of 80 to 20% by weight. After sintering further to Li, B, Mg, Si, K, Ca, Ti, V, Cr, Co, Y, Zr, Nb, Mo, In, Sn, Te, Ba, Hf, Ta, W, After adding and mixing one or more components that become oxides of Tl and Bi as subcomponents, this soft ferrite raw material powder is formed into a predetermined shape without being pre- calcined to form a molded body. Sintered at 1100 ° C. or higher, the sintered density is 90% or more of the theoretical density, the average crystal grain size is 1 to 9.9 μm, and the total Fe, Mn, Zn content is Fe ₂ O ₃ , MnO , Converted to a molar ratio of ZnO, 50-55%, 3% 45%, the production method of low-loss ferrite sintered body, characterized in that to obtain the 5-15% of the ferrite sintered body.