JP3931960B2 - Fe (2) O (3) and production method thereof - Google Patents

Description

（（１）式中、［ＯＨ⁻］は前記アルカリ水溶液中の水酸基のｍｏｌ数、［Ｆｅ^２＋］は前記鉄塩を含む水溶液中のＦｅ^２＋のｍｏｌ数、［Ｆｅ^３＋］は前記鉄塩を含む水溶液中のＦｅ^３＋のｍｏｌ数を示す。）
（３）前記中和工程における前記鉄塩を含む溶液中のＦｅ ^３＋ 濃度が、Ｆｅ ^２＋ とＦｅ ^３＋ の合計濃度に対して２〜５０％であり、上記（１）に記載のＦｅ _２ Ｏ _３ が得られる、上記（２）に記載のＦｅ _２ Ｏ _３ の製造方法。
【０００８】
【発明の実施の形態】
以下に、本発明を詳細に説明する。
本発明のＦｅ₂ Ｏ₃ は、Ｃｌの含有量が３００ｐｐｍ以下であり、かつＳＯ₄ ^2- 換算でのＳの含有量が３００ｐｐｍ以下であることを特徴とする。Ｃｌ含有量および／またはＳＯ₄ ^2-換算でのＳ含有量が３００ｐｐｍを超える場合、製造されるフェライト中のＣｌおよび／またはＳＯ₄ ^2- の含有量が多くなり、Ａｇなどの電極とフェライトを積層した構造を取る場合に、フェライトに含まれるＣｌおよび／ＳＯ₄ ^2-がＡｇと反応することにより電極が断線するなどの問題が発生しやすくなる。また、Ｃｌおよび／またはＳＯ₄ ^2- を多く含有すると、低温で仮焼した際に、フェライトの焼結密度が充分に上がらないという問題を有する。本発明のＦｅ₂ Ｏ₃ は、ＣｌおよびＳＯ₄ ^2-換算でのＳ含有量がそれぞれ３００ｐｐｍ以下であるため、上記した電極の断線問題やフェライトの焼結密度の問題が解消されている。
ＣｌおよびＳＯ₄ ^2-換算でのＳの含有量はそれぞれ、より好ましくは２００ｐｐｍ以下であり、１００ｐｐｍ未満であることが特に好ましい。
【０００９】
本発明のＦｅ₂ Ｏ₃ は、主に湿式法での中和時に使用されるアルカリ溶液を起源とするＮａ，Ｋ，ＣａおよびＭｇの含有量が低く、具体的にはこれらの合計含有量が１００ｐｐｍ未満であることを特徴とする。Ｎａ，Ｋ，ＣａおよびＭｇの含有量が高い場合、具体的は合計含有量が１００ｐｐｍ以上である場合、仮焼工程でフェライト化するのに必要な温度が上昇するため、低温で仮焼できなくなる問題が生じる。また９００℃程度の低温で焼成する場合に焼結密度が充分に上がらない、あるいは高い磁気特性が得られないなどの問題を生じる。本発明のＦｅ₂ Ｏ₃ は、Ｎａ，Ｋ，ＣａおよびＭｇの合計含有量が１００ｐｐｍ未満であることにより、低温での仮焼が可能であり、また、フェライトの焼結工程でより低温から焼結が開始するため、９００℃程度の低温で焼成しても焼結密度が高く、高い初透磁率を示すフェライト焼結体を得ることができる。
Ｎａ，Ｋ，ＣａおよびＭｇの合計含有量は、好ましくは８０ｐｐｍ未満であり、５０ｐｐｍ未満であることがより好ましく、３０ｐｐｍ未満であることがもっとも好ましい。
【００１０】
本発明のＦｅ_２Ｏ_３ は比表面積が６〜６０ｍ^２／ｇである。比表面積が６ｍ^２／ｇ未満のＦｅ_２Ｏ_３では、仮焼時間を充分下げることができず、そのため仮焼工程で粒成長が進み、粉砕時間を長くする必要があり、粉砕機器からの不純物の混入（コンタミ）も増加するため、小型磁気素子用として相応しくない。逆に比表面積が６０ｍ^２／ｇを超えるＦｅ_２Ｏ_３では、仮焼温度は低下できるものの反応性が高くなるため、仮焼工程で粒成長が進みやすい。このため、やはり粉砕時間が長くなり、粉砕機器からのコンタミが増加するため、小型磁気素子用として適さないものとなる。Ｆｅ_２Ｏ_３の比表面積が６〜６０ｍ^２／ｇであれば、仮焼工程で粒成長が進みすぎることがなく、その結果短時間で所定の粒径まで粉砕することができ、粉砕機器からのコンタミが少なく、小型磁気素子用フェライト粉末として特に適したものとなる。より好ましいＦｅ_２Ｏ_３の比表面積は１０〜４０ｍ^２／ｇである。
【００１１】
本発明のＦｅ₂ Ｏ₃ は、上記以外に、Ｆｅ₂ Ｏ₃ の物性に悪影響を及ぼさない限り、Ｆｅ₂ Ｏ₃ の不可避的不純物として公知の元素または化合物を通常の含有量で含んでもよい。例えば不可避的不純物としては、Ｓｉ，Ｍｎ，Ａｌ，Ｃｒ，Ｎｉ，Ｃｏ，Ｐ，Ｂやこれらの酸化物などである。
【００１２】
次に本発明のＦｅ₂ Ｏ₃ の製造方法について説明する。
本発明では、いわゆる湿式法によりＦｅ₂ Ｏ₃ を製造する。すなわち、塩化鉄、硫酸鉄のような鉄塩を含む水溶液をアルカリ水溶液で中和して、水酸化鉄を得、これを酸化して、一旦Ｆｅ₃ Ｏ₄ を製造して、これをさらに加熱酸化することによりＦｅ₂ Ｏ₃ を製造する、
本発明のＦｅ₂ Ｏ₃ の製造方法では、まず鉄塩を含む水溶液に、アルカリ水溶液を混合して、溶液を中和させる。これにより、水溶液中で鉄塩が解離して生成したＦｅ²⁺（第一鉄イオン）、Ｆｅ³⁺（第二鉄イオン）からＦｅ（ＯＨ）₂ （水酸化第一鉄）、Ｆｅ（ＯＨ）₃ （水酸化第二鉄）が生成する。
原料の鉄塩は、塩化第一鉄、塩化第二鉄、硫酸第一鉄および硫酸第二鉄のいずれでもよく、またはこれらいずれか２以上の組み合わせであってもよい。
【００１３】
なかでも水溶液中にＦｅ²⁺とＦｅ³⁺が存在すると、生成するＦｅ₃ Ｏ₄ （マグネタイト）を小粒径化することができる。またＦｅ₃ Ｏ₄ 中にＮａ，Ｋ，ＣａおよびＭｇを取り込みやすくなる。このためＦｅ²⁺とＦｅ³⁺を含む水溶液を使用することが好ましい。
なお、Ｆｅ²⁺とＦｅ³⁺を含む水溶液を使用する場合、溶液中におけるＦｅ²⁺濃度が、Ｆｅ³⁺濃度よりも高いことが好ましい。より好ましくは、溶液中におけるＦｅ³⁺濃度は、Ｆｅ²⁺とＦｅ³⁺の合計濃度に対して２〜５０％である。溶液中におけるＦｅ²⁺とＦｅ³⁺の含有割合がこのような範囲であれば、途中工程で生成するＦｅ₃ Ｏ₄ の粒径を小さく制御することができ、粒度分布がシャープで、しかも分散性に優れたＦｅ₃ Ｏ₄ を得ることができる。このようなＦｅ₃ Ｏ₄ を加熱、酸化すれば、比表面積が６〜６０ｍ² ／ｇ、より好ましくは１０〜４０ｍ² ／ｇのＦｅ₂ Ｏ₃ を得ることができる。
【００１４】
アルカリ水溶液としては、水酸化ナトリウム、水酸化カリウム、水酸化カルシウム、水酸化マグネシウムなどのアルカリ金属若しくはアルカリ土類金属の水酸化物や、炭酸ナトリウムのようなアルカリ金属若しくは炭酸アルカリ土類金属の炭酸塩の水溶液、またはアンモニア水溶液等の一般的なアルカリ水溶液を使用することができる。ただし、本発明の製造方法では、後で詳述するように、生成したＦｅ₃ Ｏ₄ に、アルカリ金属やアルカリ土類金属を一度取り込ませる必要があるため、アンモニア水溶液よりは、アルカリ金属若しくはアルカリ土類金属の水酸化物若しくは炭酸塩等の水溶液のほうが好ましい。
【００１５】
本発明のＦｅ₂ Ｏ₃ の製造方法では、この中和工程の際に、アルカリ水溶液と、鉄塩を含む水溶液との間に下記（１）式および（２）式で示される関係が成り立つ。
【数３】

（（１）式中、［ＯＨ^- ］は前記アルカリ水溶液中の水酸基のｍｏｌ数、［Ｆｅ²⁺］は前記鉄塩を含む水溶液中のＦｅ²⁺のｍｏｌ数、［Ｆｅ³⁺］は前記鉄塩を含む水溶液中のＦｅ³⁺のｍｏｌ数を示す。）
【００１６】
本発明のＦｅ₂ Ｏ₃ の製造方法では、アルカリ水溶液の水酸基濃度と鉄塩を含む水溶液の鉄イオン濃度の間に上式で示される関係が成り立つことにより、後の工程で生成されるＦｅ₃ Ｏ₄ に、前記中和工程で使用されるアルカリ水溶液を起源とするＮａ，Ｋ，ＣａおよびＭｇが取り込まれやすくなる。本発明のＦｅ₂ Ｏ₃ の製造方法において、生成されるＦｅ₃ Ｏ₄ に、Ｎａ，Ｋ，ＣａおよびＭｇを一度取り込ませるのは、それにより生成されるＦｅ₃ Ｏ₄ にＣｌやＳＯ₄ ^2- が取り込まれにくくなるからである。この結果、生成されるＦｅ₃ Ｏ₄ 中のＣｌおよびＳＯ₄ ^2- の含有量は、低く保たれる。生成されるＦｅ₃ Ｏ₄ にＮａ，Ｋ，ＣａおよびＭｇが一度取り込まれないと、Ｆｅ₃ Ｏ₄ 中のＣｌおよびＳＯ₄ ^2-の含有量が高くなり、従って、製造されるＦｅ₂ Ｏ₃ でのＣｌおよびＳＯ₄ ^2- の含有量が高くなり、上で述べた問題が生じる。
【００１７】
上記（１）式は、水酸基と鉄イオンの当量比を示すものである。（１）式の値が０．９５未満の場合、Ｆｅ₃ Ｏ₄ 中に、ＣｌやＳが取り込まれる量が多くなり過ぎ、最終的に得られるＦｅ₂ Ｏ₃ 中のＣｌ，Ｓの含有量が３００ｐｐｍを超えてしまう。（１）式の値が１．５超の場合、使用するアルカリ水溶液の量が多くなるため、後のｐＨ調整工程で多量の酸が必要となるので、コストが高くなる。また使用するアルカリ水溶液の種類によってはＦｅ₃ Ｏ₄ 以外の相も生じる。
上記（２）式は、中和に用いるアルカリ水溶液の体積と鉄塩を含む水溶液の体積の比を示すものである。（２）式の値が０．１未満の場合、例えば、（１）式を満たすためには、使用するアルカリ水溶液の濃度が高くなり、溶液中の溶質（アルカリ成分）の量が溶解度よりも高くなって、アルカリ金属塩、アルカリ土類金属塩のような溶液のアルカリ成分が析出しやすくなる。この傾向は、水酸化ナトリウム水溶液の場合顕著である。（２）式の値が３．５超の場合、Ｆｅ₃ Ｏ₄ 中に、ＣｌやＳの取り込まれる量が多くなり過ぎ、最終的に得られるＦｅ₂ Ｏ₃ 中のＣｌ，Ｓの含有量が３００ｐｐｍを超えてしまう。
【００１８】
本発明のＦｅ₂ Ｏ₃ の製造方法では、上記手順で鉄塩を含む水溶液をアルカリ水溶液で中和して、水酸化鉄を生成させた後、酸素含有ガスを通気することにより、溶液中の水酸化鉄を酸化してＦｅ₃ Ｏ₄ 粒子を生成させる。この場合、酸化に用いる酸素含有ガスとしては、通常空気が用いられる。酸化時の水溶液温度は５０〜１００℃が好ましい。５０℃よりも低温では針状の含水酸化物が生成するため好ましくない。また１００℃よりも高温での合成は可能であるが、設備が大掛かりになるなど工業的には適さない。この酸化工程は、溶液中の水酸化鉄がすべて消費された段階で終了する。
【００１９】
この酸化によりＦｅ₃ Ｏ₄ を生成させる工程の後、Ｆｅ₃ Ｏ₄ は通常スラリーの状態で溶液中に存在する。本発明のＦｅ₂ Ｏ₃ の製造方法では、このスラリーを含む溶液に酸を添加して、溶液のｐＨを２〜６．５に調整する。溶液のｐＨを２〜６．５に調整するのは、生成したＦｅ₃ Ｏ₄ に一度取り込まれたＮａ，Ｋ，ＣａおよびＭｇを再びＦｅ₃ Ｏ₄ から溶液へと溶出させるためである。本工程では、塩酸、硫酸、硝酸および酢酸といった通常の酸を用いることができる。また、加熱により容易に分解する有機酸類も用いることが可能である。ただし残留してフェライト特性に悪影響を及ぼすような酸は好ましくない。
【００２０】
本工程でＦｅ₃ Ｏ₄ 中からＮａ，Ｋ，ＣａおよびＭｇが除去されることにより、後工程で製造されるＦｅ₂ Ｏ₃ のＮａ，Ｋ，ＣａおよびＭｇの合計含有量が１００ｐｐｍ未満に保たれる。本工程は、特開平８−１３３７４２号公報に示されたオキシ水酸化鉄又はマグネタイトの沈殿物を脱水して得られるケーキを水に分散させ、ｐＨを６〜８に調整後、脱水、水洗を行い、次いで再度脱水ケーキを水に分散させ、酸によりｐＨを２〜５の範囲に調整する方法に比べて、工程が少なく操作が容易である。本工程において、酸添加後のｐＨが低いと、Ｆｅ₃ Ｏ₄ 中に残留するＮａ，Ｋ，ＣａおよびＭｇをより低減することができるが、ｐＨが２よりも低い場合にはＣｌやＳＯ₄ ^2- などの酸の残留成分が増えたり、製造設備などが腐食しやすくなるため好ましくない。ｐＨが６．５を超える場合には、Ｎａ，Ｋ，ＭｇおよびＣａを充分除去することができず、後工程で製造されるＦｅ₂ Ｏ₃ のＮａ，Ｋ，ＣａおよびＭｇの合計濃度が１００ｐｐｍを超える。
【００２１】
本工程で酸添加後の溶液のｐＨは、より好ましくは３〜６．５であり、さらに好ましくは４〜６である。また、酸を添加する際の溶液の温度は５０℃以上が好ましい。常温でｐＨを調整するのに比べ、５０℃以上で酸を添加し、ｐＨを調整することで一層Ｎａ，Ｋ，ＣａおよびＭｇの除去率が向上する。
【００２２】
本発明のＦｅ₂ Ｏ₃ の製造方法では、溶液のｐＨを上記範囲に調整した後、
溶液を脱水（ろ過）することによりＦｅ₃ Ｏ₄ を分離する。前工程でｐＨを２〜６．５に調整したことで、Ｎａ，Ｋ，ＣａおよびＭｇがＦｅ₃ Ｏ₄ から溶液へと溶出しているため、脱水（ろ過）にすることによりＦｅ₃ Ｏ₄ とＮａ，Ｋ，ＣａおよびＭｇとを完全に分離することができ、高純度のＦｅ₃ Ｏ₄ 粒子が得られる。
本発明において、溶液のｐＨが２〜６．５に調整されているのは、ろ過時まででよく、ろ過後はｐＨが６．５以上に上昇してもＦｅ₃ Ｏ₄ 中のＮａ，Ｋ，ＣａおよびＭｇの濃度は増加しない。
ろ過方法としては、フィルタープレスなど通常の方法を用いることができる。ろ過により得られたＦｅ₃ Ｏ₄ ケーキは、通常の方法で水洗（脱塩）、さらに乾燥、解砕することにより高純度のＦｅ₃ Ｏ₄ 粉末が得られる。
【００２３】
本発明のＦｅ₂ Ｏ₃ の製造方法では、このようにして得られたＦｅ₃ Ｏ₄ 粒子を加熱酸化することにより、Ｆｅ₂ Ｏ₃ を得る。この時、加熱酸化温度が２００〜３００℃程度の低温であればマグヘマイト（γ−Ｆｅ₂ Ｏ₃ ）が得られ、３００℃以上５００℃程度以下の温度であればヘマタイト（α−Ｆｅ₂ Ｏ₃ ）が得られる。いずれも、フェライトとした場合、小型磁気素子用として適したものであり、必要とされる条件、用途等に応じて、加熱酸化温度を調節することにより、マグヘマイトまたはヘマタイトを選択的に得ることができる。
また、このようにして得られたＦｅ₂ Ｏ₃ は、酸化ニッケル、酸化亜鉛、酸化銅、酸化マンガンなどと混合、仮焼してフェライト粉末とする。フェライト粉末は、例えば、バインダーを混合してペーストとした後、印刷法やドクターブレード法などで磁性材層を形成させ、焼成後、積層チップインダクタや平面インダクタとすることができる。また、フェライト粉末とポリビニルアルコール（ＰＶＡ）などの結合剤や微量の添加元素を添加して、造粒、成形した後、焼成してフェライトコアとすることもできる。
【００２４】
【実施例】
以下、実施例により本発明の方法をさらに説明する。なお、実施例において、Ｆｅ₂ Ｏ₃ およびフェライトの評価は、以下の方法により実施した。
酸化鉄の分析
比表面積：ＢＥＴ法にて分析
Ｃｌ、ＳＯ₄ ^2- ：蛍光Ｘ線で分析
Ｎａ、Ｋ、ＣａおよびＭｇ：ＩＣＰ（誘導結合プラズマ原子蛍光分析）で分析
フェライトの評価
仮焼可能温度：ＸＲＤによりスピネル化率が９０％以上となる最低温度
【００２５】
（実施例１〜４）
塩化第一鉄溶液と塩化第二鉄溶液を溶液中のＦｅ³⁺濃度がＦｅ³⁺／Ｔｏｔａｌ- Ｆｅ＝８％になるように混合し、水を加えて全Ｆｅ濃度０．５８ｍｏｌ／ｌ、溶液量２５．７５リットルに調製した。
内容積４０リットルの容器に、８ｍｏｌ／ｌのＮａＯＨ溶液４．２５リットルを入れ、そこに窒素ガスを通気し攪拌しながら上記の塩化鉄溶液を混合した。この溶液を窒素雰囲気のまま９０℃まで昇温し、ｐＨを１０．２±０．１に保持しながら、空気を１０ｌ／ｍｉｎ通気して酸化を行いＦｅ₃ Ｏ₄ 粒子を合成した。反応が終了した後、反応溶液が９０℃の状態で硫酸を添加して表１に示すｐＨに調整した。その後、脱塩、ろ過、乾燥、解砕してＦｅ₃ Ｏ₄ 粉末を得た。この粉末を４５０℃で２時間加熱酸化して酸化鉄（ヘマタイト：α−Ｆｅ₂ Ｏ₃ ）とした。
次にこの酸化鉄を用いてフェライト粉末を作製した。フェライト粉末の試作は得られた酸化鉄を用いてＦｅ₂ Ｏ₃ ：ＮｉＯ：ＺｎＯ：ＣｕＯ＝４９：１１：３０：１０になるように秤量し、これをボールミルで１時間混合した後、乾燥させた。この粉末を６００℃以上で仮焼してＮｉＣｕＺｎフェライト粉末とした。仮焼はＸＲＤでスピネル化率が９０％以上となる最低温度で２時間行った。さらにボールミルで粉砕を行い、比表面積が６ｍ² ／ｇ以上になるまで続けた。得られた粉砕紛は乾燥後、ＰＶＡ溶液を混合して造粒した後、トロイダル形状にプレス成形した。得られた成形体を９００℃で焼成して焼結体を得た。焼結密度は焼結体の重量と寸法から算出した。初透磁率はＬＣＲメータを用いて９００℃で焼成したコアについて測定した。結果を表１に示した。
【００２６】
（比較例１、２）
反応終了後の溶液に硫酸を添加してｐＨを表３に示す値に調整した点以外は、実施例１〜４と同じ条件で試料の作製および評価を実施した。結果を表３に示した。
【００２７】
（実施例５）
塩化第一鉄溶液と塩化第二鉄溶液を溶液中のＦｅ³⁺濃度がＦｅ³⁺／Ｔｏｔａｌ- Ｆｅ＝１．５％になるように混合し、水を加えて全Ｆｅ濃度０．７１ｍｏｌ／ｌ、溶液量２５．２５リットルに調整した。
内容積４０リットルの容器に、８ｍｏｌ／ｌのＮａＯＨ溶液４．７５リットルを入れ、そこに窒素ガスを通気し攪拌しながら上記の塩化鉄溶液を混合した。この溶液を窒素雰囲気のまま８０℃まで昇温し、ｐＨを８．５±０．２に保持しながら、空気を１０ｌ／ｍｉｎ通気して酸化を行いＦｅ₃ Ｏ₄ 粒子を合成した。反応を終了した後、反応溶液を５５℃まで冷却し、塩酸を添加してｐＨ４．０に調整した。その後、脱塩、ろ過、乾燥、解砕してＦｅ₃ Ｏ₄ 粉末を得た。この粉末を２３０℃で３時間加熱酸化して酸化鉄（マグヘマイト：γ−Ｆｅ₂ Ｏ₃ ）とした。
評価は実施例１〜４と同様に行った。表１に結果を示した。
【００２８】
（実施例６）
塩化第一鉄溶液と塩化第二鉄溶液を溶液中のＦｅ³⁺濃度がＦｅ³⁺／Ｔｏｔａｌ- Ｆｅ＝６．５％になるように混合し、水を加えて全Ｆｅ濃度０．７１ｍｏｌ／ｌ、溶液量２５．２５リットルに調整した。
内容積４０リットルの容器に、８ｍｏｌ／ｌのＮａＯＨ溶液４．７５リットルを入れ、そこに窒素ガスを通気し攪拌しながら上記の塩化鉄溶液を混合した。以降、実施例５と同条件で試料の作製、評価を行った。結果を表１に示した。
【００２９】
（実施例７）
塩化第一鉄溶液と塩化第二鉄溶液を溶液中のＦｅ³⁺濃度がＦｅ³⁺／Ｔｏｔａｌ- Ｆｅ³⁺＝１２％になるように混合し、水を加えて全Ｆｅ濃度０．７２ｍｏｌ／ｌ、溶液量２５リットルに調整した。
内容積４０リットルの容器に、８ｍｏｌ／ｌのＮａＯＨ溶液５リットルを入れ、そこに窒素ガスを通気し攪拌しながら上記の塩化鉄溶液を混合した。以降、実施例５と同条件で試料の作製、評価を行った。結果を表１に示した。
【００３０】
（実施例８）
塩化第一鉄溶液と塩化第二鉄溶液を溶液中のＦｅ³⁺濃度がＦｅ³⁺／Ｔｏｔａｌ- Ｆｅ＝２４％になるように混合し、水を加えて全Ｆｅ濃度０．７２ｍｏｌ／ｌ、溶液量２５リットルに調整した。
内容積４０リットルの容器に、８ｍｏｌ／ｌのＮａＯＨ溶液５リットルを入れ、そこに窒素ガスを通気し攪拌しながら上記の塩化鉄溶液を混合した。以降、実施例５と同条件で試料の作製、評価を行った。結果を表１に示した。
【００３１】
（実施例９）
塩化第一鉄溶液と塩化第二鉄溶液を溶液中のＦｅ³⁺濃度がＦｅ³⁺／Ｔｏｔａｌ- Ｆｅ＝３２％になるように混合し、水を加えて全Ｆｅ濃度０．７２ｍｏｌ／ｌ、溶液量２４．５リットルに調整した。
内容積４０リットルの容器に、８ｍｏｌ／ｌのＮａＯＨ溶液５．５リットルを入れ、そこに窒素ガスを通気し攪拌しながら上記の塩化鉄溶液を混合した。以降、実施例５と同条件で試料の作製、評価を行った。結果を表１に示した。
【００３２】
（実施例１０）
塩化第一鉄溶液と塩化第二鉄溶液を溶液中のＦｅ³⁺濃度がＦｅ³⁺／Ｔｏｔａｌ- Ｆｅ＝４６％になるように混合し、水を加えて全Ｆｅ濃度０．７３ｍｏｌ／ｌ、溶液量２４リットルに調整した。
内容積４０リットルの容器に、８ｍｏｌ／ｌのＮａＯＨ溶液５．５リットルを入れ、そこに窒素ガスを通気し攪拌しながら上記の塩化鉄溶液を混合した。以降、実施例５と同条件で試料の作製、評価を行った。結果を表１に示した。
【００３３】
（比較例３）
反応終了後の溶液に塩酸を添加してｐＨ１．７に調整した以外は、すべて実施例５と同条件で試料の作製、評価を行った。結果を表３に示した。
（比較例４）
反応終了後の溶液に塩酸を添加してｐＨ７．２に調整した以外は、すべて実施例５と同条件で試料の作製、評価を行った。結果を表３に示した。
（比較例５）
実施例７の条件で、中和工程での溶液の混合条件を変更した。すなわち、塩化第一鉄溶液と塩化第二鉄溶液を溶液中のＦｅ³⁺濃度がＦｅ³⁺／Ｔｏｔａｌ- Ｆｅ＝１２％になるように混合し、水を加えて全Ｆｅ濃度３．０ｍｏｌ／ｌ、溶液量６リットルに調整した。
内容積４０リットルの容器に、１．６７ｍｏｌ／ｌのＮａＯＨ溶液２４リットルを入れ、そこに窒素ガスを通気し攪拌しながら上記の塩化鉄溶液を混合した。以降、実施例５と同条件で試料の作製、評価を行った。結果を表３に示した。
【００３４】
（実施例１１〜１４）
容器に８．１ｍｏｌ／ｌのＮａＯＨ溶液４リットルを入れ、そこに窒素ガスを通気し攪拌しながら０．６２ｍｏｌ／ｌの硫酸第一鉄溶液２６リットルを混合した。この溶液を窒素雰囲気のまま８５℃まで昇温し、ｐＨを８．５±０．２に調整しながら、空気を１０ｌ／ｍｉｎ通気して酸化を行いＦｅ₃ Ｏ₄ 粒子を合成した。反応が終了した後、反応溶液が８５℃の状態で硫酸を添加して所定のｐＨに調整した。その後、脱塩、ろ過、乾燥、解砕してＦｅ₃ Ｏ₄ 粉末を得た。得られたＦｅ₃ Ｏ₄ は４００℃で１時間加熱酸化して酸化鉄（ヘマタイト：α−Ｆｅ₂ Ｏ₃ ）とし、実施例１と同じ評価を行った。結果を表２に示した。
【００３５】
（比較例６）
比較例６では、Ｆｅ₃ Ｏ₄ の生成後、溶液のｐＨを２〜６．５に調整せずに、Ｆｅ₂ Ｏ₃ を生成させた。
２．８ｍｏｌ／ｌのＮａＯＨ溶液１４リットルとＦｅ²⁺濃度１．５ｍｏｌ／ｌの硫酸第一鉄溶液１４リットルを混合した。この溶液を窒素雰囲気のまま９０℃まで昇温し、ｐＨを６．８±０．１に制御しながら空気を１０ｌ／ｍｉｎ通気して酸化を行いＦｅ₃ Ｏ₄ 粒子を合成した。その後、脱塩、ろ過、乾燥、解砕してＦｅ₃ Ｏ₄ 粉末を得た。得られたＦｅ₃ Ｏ₄ は４００℃で１時間加熱して酸化鉄（ヘマタイト：α−Ｆｅ₂ Ｏ₃ ）とした。得られたＦｅ₂ Ｏ₃ を用いて、実施例と同条件で評価を行った。結果を表３に示した。
【００３６】
（比較例７）
塩化第一鉄溶液を用いて噴霧焙焼法で製造し、水洗処理していない酸化鉄を用いて実施例１〜４と同条件で評価を行った。結果を表３に示した。
（比較例８）
比較例３と同様に噴霧焙焼法で製造し、焙焼後に水洗処理を行った酸化鉄を用いて、実施例１〜４と同条件で評価を行った。結果を表３に示した。
【００３７】
（実施例１５〜１８）
硫酸第一鉄溶液と硫酸第二鉄溶液を、溶液中のＦｅ³⁺濃度がＦｅ³⁺／Ｔｏｔａｌ- Ｆｅ＝５％になるように混合し、水を加えて全Ｆｅ濃度０．８２ｍｏｌ／ｌ、溶液量２５．５リットルに調整した。
内容積３０リットルの容器に、１０ｍｏｌ／ｌのＮａＯＨ溶液を４．５リットル入れ、そこに窒素ガスを通気し攪拌しながら上記の硫酸鉄溶液を混合した。この溶液を窒素雰囲気のまま７５℃まで昇温し、ｐＨを１０．３±０．１に保持しながら、空気を１０ｌ／ｍｉｎ通気して酸化を行いＦｅ₃ Ｏ₄ 粒子を合成した。反応が終了した後、反応溶液を６０℃まで冷却し、塩酸を添加して所定のｐＨに調整した。その後、脱塩、ろ過、乾燥、解砕してＦｅ₃ Ｏ₄ 粉末を得た。この粉末を２５０℃で２時間加熱酸化して酸化鉄（マグヘマイト：γ−Ｆｅ₂ Ｏ₃ ）とした。
評価は実施例１〜４と同条件で行った。結果を表３に示した。
【００３８】
（実施例１９〜２２、比較例９）
表４に示すような条件の塩化第一鉄溶液と塩化第二鉄溶液の混合溶液、および炭酸ナトリウム溶液を調製した。内容積４０リットルの容器に、アルカリ溶液を投入し、そこに窒素ガスを通気し攪拌しながら塩化鉄溶液を混合した。この溶液を８５℃まで昇温し、ｐＨ調整を行わずに、空気を１０ｌ／ｍｉｎ通気して酸化を行い、Ｆｅ₃ Ｏ₄ 粒子を合成した。反応が終了した後、反応溶液を６０℃まで冷却し、塩酸を添加して所定のｐＨに調整した。その後、脱塩、ろ過、乾燥、 解砕してＦｅ₃ Ｏ₄ 粉末を得た。この粉末を４３０℃で２時間加熱して酸化鉄（ヘマタイト：α−Ｆｅ₂ Ｏ₃ ）とした。評価は実施例１〜４と同条件で行った。結果を表４に示した。
表４の結果から、アルカリ溶液と鉄塩を含む溶液の当量比は、０．９５〜１．５の範囲が好ましいことがわかる。
【００３９】
（実施例２３〜２６、比較例１０）
表５に示すような条件の塩化鉄第一鉄溶液と塩化第二鉄溶液の混合溶液、および水酸化カリウム溶液を調製した。内容積４０リットルの容器に、アルカリ溶液を投入し、そこに窒素ガスを通気し攪拌しながら塩化鉄溶液を混合した。この溶液を８０℃まで昇温し、ｐＨ調整を行わずに、空気を１０ｌ／ｍｉｎ通気して酸化を行い、Ｆｅ₃ Ｏ₄ 粒子を合成した。反応が終了した後、反応溶液を６０℃まで冷却し、塩酸を添加して所定のｐＨに調整した。その後、脱塩、ろ過、乾燥、解砕してＦｅ₃ Ｏ₄ 粉末を得た。この粉末を４３０℃で２時間加熱して酸化鉄（ヘマタイト：α−Ｆｅ₂ Ｏ₃ ）とした。評価は実施例１〜４と同条件で行った。結果を表５に示した。
実施例２３〜２６、比較例５、比較例１０などの結果から、アルカリ溶液と鉄塩を含む溶液の体積比は０．１〜３．５の範囲が好ましいことがわかる。
【００４０】
実施例および比較例から、Ｃｌの含有量が３００ｐｐｍ以下で、ＳＯ₄ ^2-換算のＳ含有量が３００ｐｐｍ以下で、Ｋ、Ｎａ、ＣａおよびＭｇの合計含有量が１００未満で、かつ比表面積が６〜６０ｍ² ／ｇのＦｅ₂ Ｏ₃ を用いてフェライトを作製する場合、７００℃程度の低温で仮焼が可能であり、９００℃以下の低温で焼成しても高い焼結密度と、初透磁率が得られることが確認できる。
【００４１】
【発明の効果】
本発明の製造方法を用いれば、塩化鉄および硫酸鉄のいずれを原料とした場合であっても、製造されるＦｅ₂ Ｏ₃ に含まれるＣｌとＳＯ₄ ^2-が同時に低減される。これは塩化鉄と硫酸鉄とが混在する原料を用いてＦｅ₂ Ｏ₃ を製造する場合に特に効果的である。
本発明のＦｅ₂ Ｏ₃ を用いてフェライトを製造する場合、低温の仮焼が可能で、９００℃の低温で焼成しても高い焼結密度、初透磁率を得ることができる。また、本発明の製法により、上記のＦｅ₂ Ｏ₃ を得ることができる。
【００４２】
【表１】

【００４３】
【表２】

【００４４】
【表３】

【００４５】
【表４】

【００４６】
【表５】

[0001]
BACKGROUND OF THE INVENTION
The present invention is a high purity Fe suitable for small magnetic elements such as chip inductors.₂O_ThreeAnd a manufacturing method thereof.
[0002]
[Prior art]
With the widespread use of mobile electronic devices such as mobile phones, chip components such as chip inductors are frequently used. Further downsizing of chip parts corresponding to further enhancement of functions and reduction in size and weight of electronic devices is also progressing.
Multilayer chip inductors are manufactured by laminating and sintering a ferrite layer molded using a printing method or doctor blade method and internal electrodes molded by a printing method. It is performed by the method of using and connecting. Such a multilayer chip inductor is disclosed in, for example, Japanese Patent Laid-Open No. 4-180610. Such a multilayer chip inductor is advantageous for downsizing and has an outer iron structure, so that the leakage flux is small and suitable for high-density mounting.
[0003]
Ferrite raw material constituting the chip inductor is Fe₂O_Three, NiO, ZnO, CuO and the like are mixed, calcined and pulverized. Fe₂O_ThreeIncludes iron chloride (FeCl₂) Iron chloride Fe₂O_ThreeAnd iron sulfate (FeSO_FourIron sulfate Fe₂O_ThreeExists. Of these, iron chloride-based Fe₂O_ThreeContains a large amount of Cl originating from iron chloride, and iron sulfate Fe₂O_ThreeIs SO based on iron sulfate_Four ^2-Contains a lot. For example, iron chloride-based Fe produced by spray roasting₂O_ThreeIn this case, the source-origin Cl usually remains at 1000 ppm or more. Fe which was washed with water after roasting₂O_ThreeHowever, about 500 ppm of Cl remains. On the other hand, iron sulfate-based Fe₂O_ThreeIn the source SO_Four ^2-About 2000 ppm remains.
Therefore, the conventional Fe₂O_ThreeIn the manufacturing method, the manufactured Fe₂O_ThreeCl and SO contained in_Four ^2-Could not be reduced at the same time.
[0004]
Manufactured Fe₂O_ThreeCl and SO_Four ^2-Is included in the above-mentioned amount, when calcination is performed at a high temperature (about 1000 ° C.) as in the production of Mn—Zn ferrite,₂O_ThreeCl and SO contained in_Four ^2-Almost volatilizes, so Cl and SO remaining after calcination_Four ^2-Will be very small and will have little effect in subsequent processes. However, in the production of Ni—Cu—Zn ferrites often used in small magnetic elements such as chip inductors, calcining is often performed at a lower temperature (about 700 ° C.) than Mn—Zn. For this reason, Cl and SO are contained in the ferrite calcined powder._Four ^2-Will remain and will adversely affect subsequent processes. For example, Cl or SO_Four ^2-In the case where a large amount of iron remains, when a structure in which an electrode such as Ag and a ferrite are laminated is formed, Cl and SO contained in the ferrite_Four ^2-Reacts with Ag and the electrode is likely to break. As miniaturization of the small magnetic element progresses, the thickness of the ferrite layer and the electrode layer is further reduced, so that problems such as disconnection of the electrode are more likely to occur. For this reason, Cl and SO_Four ^2-Fe content is low in both₂O_ThreeIs required.
[0005]
Fe for small magnetic elements such as chip inductors₂O_ThreeIn order to obtain a high sintering density and high magnetic properties even when firing at a temperature of about 900 ° C., grain growth is suppressed by calcining at a low temperature (about 700 ° C.) and small by simple grinding. There is a demand for particle size reduction. However, Fe₂O_ThreeNaOH and Ca (OH) used in the neutralization process of the wet method₂If it contains a large amount of Na, K, Ca and Mg originating from an alkaline solution such as the above, it cannot be calcined at a low temperature, does not increase the sintered density when fired at a temperature of about 900 ° C., or has high magnetic properties The problem that cannot be obtained occurs. Therefore, the content of Na, K, Ca and Mg is as low as possible.₂O_ThreeIs required.
[0006]
[Problems to be solved by the invention]
In order to solve the above problems, the present invention provides Cl, SO_Four ^2-Fe with low content of Na, K, Ca and Mg₂O_ThreeIt is another object of the present invention to provide a manufacturing method thereof.
[0007]
[Means for Solving the Problems]
  Said subject is achieved by this invention shown below.
(1)Specific surface area of 6-60m ² / G,Cl having a content of 300 ppm or less and SO₄ ^2-Fe containing S in terms of conversion in terms of 300 ppm or less and Na, K, Ca and Mg having a total content of less than 100 ppm₂O₃.
(2) An aqueous solution containing an iron salt and an aqueous alkaline solution are mixed and neutralized to produce a solution containing iron hydroxide, and the iron hydroxide in the solution is oxidized to form Fe.₃O₄Fe that produces particles₃O₄Manufacturing process and the Fe₃O₄An acid is added to the solution containing particles to adjust the pH of the solution to 2 to 6.5, and from the solution adjusted to pH 2 to 6.5 in the pH adjustment step, Fe₃O₄A separation step of separating particles, and the Fe separated in the separation step₃O₄The particles are heated to oxidize Fe₂O₃To produce Fe₂O₃Fe having a manufacturing process₂O₃A manufacturing method of
  In the neutralization step, a relationship represented by the following formulas (1) and (2) is established between the alkaline aqueous solution and the aqueous solution containing the iron salt: Fe₂O₃Manufacturing method.
[Expression 2]

((1) In the formula, [OH⁻] Is the mol number of hydroxyl groups in the alkaline aqueous solution, [Fe²⁺] In the aqueous solution containing the iron salt²⁺Mol number of [Fe³⁺] In the aqueous solution containing the iron salt³⁺The number of moles is shown. )
(3) Fe in the solution containing the iron salt in the neutralization step ³⁺ Concentration is Fe ²⁺ And Fe ³⁺ 2 to 50% with respect to the total concentration of Fe, and Fe described in (1) above ₂ O ₃ The Fe as described in (2) above is obtained. ₂ O ₃ Manufacturing method.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
The present invention is described in detail below.
Fe of the present invention₂O_ThreeHas a Cl content of 300 ppm or less and SO_Four ^2-The S content in terms of conversion is 300 ppm or less. Cl content and / or SO_Four ^2-When the S content in terms of conversion exceeds 300 ppm, Cl and / or SO in the produced ferrite_Four ^2-Cl and / SO contained in ferrite in the case where a structure in which an electrode such as Ag and a ferrite are laminated is increased_Four ^2-The reaction of Ag with Ag tends to cause problems such as electrode disconnection. Cl and / or SO_Four ^2-When a large amount is contained, there is a problem that the sintered density of the ferrite does not sufficiently increase when calcined at a low temperature. Fe of the present invention₂O_ThreeAre Cl and SO_Four ^2-Since each S content in terms of conversion is 300 ppm or less, the above-mentioned problem of disconnection of electrodes and the problem of sintered density of ferrite are solved.
Cl and SO_Four ^2-Each S content in terms of conversion is more preferably 200 ppm or less, and particularly preferably less than 100 ppm.
[0009]
Fe of the present invention₂O_ThreeIs characterized by a low content of Na, K, Ca and Mg originating from an alkaline solution mainly used for neutralization in a wet process, specifically, a total content of these is less than 100 ppm. And When the content of Na, K, Ca, and Mg is high, specifically, when the total content is 100 ppm or more, the temperature required for ferritization in the calcination step increases, and therefore it cannot be calcined at a low temperature. Problems arise. Further, when firing at a low temperature of about 900 ° C., there arises a problem that the sintered density does not sufficiently increase or high magnetic properties cannot be obtained. Fe of the present invention₂O_ThreeSince the total content of Na, K, Ca and Mg is less than 100 ppm, calcining at a low temperature is possible, and sintering starts at a lower temperature in the ferrite sintering process. A sintered ferrite body having a high sintered density and high initial magnetic permeability can be obtained even when fired at a low temperature of about 0C.
The total content of Na, K, Ca and Mg is preferably less than 80 ppm, more preferably less than 50 ppm, and most preferably less than 30 ppm.
[0010]
  Fe of the present invention₂O₃ Is the ratioSurface area is 6-60m²/ G. Specific surface area is 6m²Fe less than / g₂O₃In this case, the calcining time cannot be reduced sufficiently, so that the grain growth proceeds in the calcining process, and it is necessary to lengthen the crushing time, and the contamination (contamination) of impurities from the crushing equipment also increases. Not suitable for use. Conversely, the specific surface area is 60m²/ G over Fe₂O₃Then, although the calcination temperature can be lowered, the reactivity is increased, and therefore grain growth is likely to proceed in the calcination step. For this reason, the pulverization time is also increased and the contamination from the pulverization equipment is increased, so that it is not suitable for a small magnetic element. Fe₂O₃Specific surface area of 6-60m²/ G, the grain growth does not proceed excessively in the calcining step, and as a result, it can be pulverized to a predetermined particle size in a short time, and there is little contamination from the pulverizing device, and as a ferrite powder for a small magnetic element Especially suitable. More preferable Fe₂O₃Specific surface area of 10-40m²/ G.
[0011]
Fe of the present invention₂O_ThreeIn addition to the above,₂O_ThreeUnless it adversely affects the physical properties of Fe₂O_ThreeA known element or compound as an inevitable impurity may be contained in a normal content. For example, inevitable impurities include Si, Mn, Al, Cr, Ni, Co, P, B, and oxides thereof.
[0012]
Next, the Fe of the present invention₂O_ThreeThe manufacturing method will be described.
In the present invention, the so-called wet method is used to form Fe.₂O_ThreeManufacturing. That is, an aqueous solution containing iron salts such as iron chloride and iron sulfate is neutralized with an alkaline aqueous solution to obtain iron hydroxide, which is oxidized, and once Fe_ThreeO_FourAnd is further oxidized by heating to produce Fe₂O_ThreeManufacturing,
Fe of the present invention₂O_ThreeIn the production method, an aqueous alkaline solution is first mixed with an aqueous solution containing an iron salt to neutralize the solution. Thereby, Fe salt formed by dissociation of iron salt in aqueous solution²⁺(Ferrous ion), Fe³⁺(Ferric ion) to Fe (OH)₂(Ferrous hydroxide), Fe (OH)_Three(Ferric hydroxide) is produced.
The raw material iron salt may be any of ferrous chloride, ferric chloride, ferrous sulfate, and ferric sulfate, or any combination of two or more thereof.
[0013]
In particular, Fe in aqueous solution²⁺And Fe³⁺When Fe is present, Fe is generated_ThreeO_Four(Magnetite) can be reduced in particle size. Fe_ThreeO_FourNa, K, Ca and Mg are easily taken into the inside. For this reason, Fe²⁺And Fe³⁺It is preferable to use an aqueous solution containing.
Fe²⁺And Fe³⁺When using an aqueous solution that contains Fe,²⁺Concentration is Fe³⁺It is preferably higher than the concentration. More preferably, Fe in solution³⁺Concentration is Fe²⁺And Fe³⁺It is 2 to 50% with respect to the total concentration. Fe in solution²⁺And Fe³⁺If the content ratio of Fe is such a range, Fe generated in the intermediate process_ThreeO_FourFe particle has a sharp particle size distribution and excellent dispersibility._ThreeO_FourCan be obtained. Such Fe_ThreeO_FourIf heated and oxidized, the specific surface area will be 6-60m²/ G, more preferably 10 to 40 m²/ G Fe₂O_ThreeCan be obtained.
[0014]
Examples of alkaline aqueous solutions include alkali metal or alkaline earth metal hydroxides such as sodium hydroxide, potassium hydroxide, calcium hydroxide, and magnesium hydroxide, and alkali metal or alkaline earth metal carbonates such as sodium carbonate. A common alkaline aqueous solution such as an aqueous salt solution or an aqueous ammonia solution can be used. However, in the production method of the present invention, as will be described in detail later, the produced Fe_ThreeO_FourIn addition, since it is necessary to once incorporate an alkali metal or an alkaline earth metal, an aqueous solution of an alkali metal or alkaline earth metal hydroxide or carbonate is preferable to an aqueous ammonia solution.
[0015]
Fe of the present invention₂O_ThreeIn this production method, the relationship shown by the following formulas (1) and (2) is established between the alkaline aqueous solution and the aqueous solution containing the iron salt in the neutralization step.
[Equation 3]

((1) In the formula, [OH^-] Is the mol number of hydroxyl groups in the alkaline aqueous solution, [Fe²⁺] In the aqueous solution containing the iron salt²⁺Mol number of [Fe³⁺] In the aqueous solution containing the iron salt³⁺The number of moles is shown. )
[0016]
Fe of the present invention₂O_ThreeIn this manufacturing method, the relationship shown by the above equation is established between the hydroxyl group concentration of the alkaline aqueous solution and the iron ion concentration of the aqueous solution containing the iron salt._ThreeO_FourIn addition, Na, K, Ca and Mg originating from the alkaline aqueous solution used in the neutralization step are easily taken in. Fe of the present invention₂O_ThreeProduced in the manufacturing method of_ThreeO_FourIncorporation of Na, K, Ca and Mg once causes Fe produced thereby_ThreeO_FourAnd Cl and SO_Four ^2-It is because it becomes difficult to be taken in. As a result, the generated Fe_ThreeO_FourCl and SO in_Four ^2-The content of is kept low. Generated Fe_ThreeO_FourIf Na, K, Ca and Mg are not once taken in_ThreeO_FourCl and SO in_Four ^2-The content of₂O_ThreeCl and SO at_Four ^2-As a result, the above-mentioned problems arise.
[0017]
The above formula (1) indicates the equivalent ratio of hydroxyl groups to iron ions. (1) When the value of the formula is less than 0.95, Fe_ThreeO_FourThe amount of Cl and S taken in becomes too large, and finally obtained Fe₂O_ThreeThe content of Cl and S inside exceeds 300 ppm. When the value of the formula (1) is more than 1.5, the amount of the alkaline aqueous solution to be used is increased, so that a large amount of acid is required in the subsequent pH adjustment step, resulting in an increase in cost. Depending on the type of alkaline aqueous solution used, Fe_ThreeO_FourOther phases also occur.
The above formula (2) indicates the ratio of the volume of the aqueous alkaline solution used for neutralization to the volume of the aqueous solution containing the iron salt. When the value of the formula (2) is less than 0.1, for example, in order to satisfy the formula (1), the concentration of the alkaline aqueous solution used is high, and the amount of the solute (alkali component) in the solution is higher than the solubility. It becomes high and it becomes easy to precipitate the alkaline component of solutions, such as an alkali metal salt and alkaline-earth metal salt. This tendency is remarkable in the case of an aqueous sodium hydroxide solution. (2) When the value of the formula exceeds 3.5, Fe_ThreeO_FourThe amount of Cl and S taken in becomes too large, and finally obtained Fe₂O_ThreeThe content of Cl and S inside exceeds 300 ppm.
[0018]
Fe of the present invention₂O_ThreeIn this production method, the aqueous solution containing the iron salt is neutralized with an alkaline aqueous solution in the above procedure to produce iron hydroxide, and then the oxygenated gas is vented to oxidize the iron hydroxide in the solution. Fe_ThreeO_FourGenerate particles. In this case, air is usually used as the oxygen-containing gas used for oxidation. The aqueous solution temperature during oxidation is preferably 50 to 100 ° C. A temperature lower than 50 ° C. is not preferable because acicular hydrated oxide is generated. Although synthesis at a temperature higher than 100 ° C. is possible, it is not industrially suitable because of the large equipment. This oxidation process ends when all of the iron hydroxide in the solution is consumed.
[0019]
This oxidation causes Fe_ThreeO_FourAfter the step of generating Fe_ThreeO_FourIs usually present in the solution in the form of a slurry. Fe of the present invention₂O_ThreeIn this production method, an acid is added to the solution containing the slurry to adjust the pH of the solution to 2 to 6.5. The pH of the solution is adjusted to 2 to 6.5 because the generated Fe_ThreeO_FourNa, K, Ca and Mg once taken in_ThreeO_FourThis is to elute from the solution to the solution. In this step, ordinary acids such as hydrochloric acid, sulfuric acid, nitric acid and acetic acid can be used. Also, organic acids that are easily decomposed by heating can be used. However, an acid that remains and adversely affects ferrite properties is not preferable.
[0020]
Fe in this process_ThreeO_FourFe produced in the subsequent process by removing Na, K, Ca and Mg from inside₂O_ThreeThe total content of Na, K, Ca and Mg is kept below 100 ppm. In this step, a cake obtained by dehydrating iron oxyhydroxide or magnetite precipitates disclosed in JP-A-8-133742 is dispersed in water, and the pH is adjusted to 6 to 8, followed by dehydration and washing with water. Then, compared with a method in which the dehydrated cake is dispersed again in water and the pH is adjusted in the range of 2 to 5 with an acid, the number of steps is small and the operation is easy. In this step, if the pH after acid addition is low, Fe_ThreeO_FourNa, K, Ca and Mg remaining therein can be further reduced, but when the pH is lower than 2, Cl and SO_Four ^2-It is not preferable because the residual components of the acid increase, and the production equipment is easily corroded. When the pH exceeds 6.5, Na, K, Mg and Ca cannot be sufficiently removed, and Fe produced in the subsequent process₂O_ThreeThe total concentration of Na, K, Ca and Mg exceeds 100 ppm.
[0021]
The pH of the solution after acid addition in this step is more preferably 3 to 6.5, and further preferably 4 to 6. Further, the temperature of the solution when adding the acid is preferably 50 ° C. or higher. Compared to adjusting the pH at room temperature, the removal rate of Na, K, Ca and Mg is further improved by adding an acid at 50 ° C. or higher and adjusting the pH.
[0022]
Fe of the present invention₂O_ThreeIn the production method, after adjusting the pH of the solution to the above range,
By dehydrating (filtering) the solution, Fe_ThreeO_FourIsolate. By adjusting the pH to 2 to 6.5 in the previous step, Na, K, Ca, and Mg are Fe._ThreeO_FourSince it elutes from the solution to the solution, it can be removed by dehydration (filtration)._ThreeO_FourAnd Na, K, Ca and Mg can be completely separated, and high purity Fe_ThreeO_FourParticles are obtained.
In the present invention, the pH of the solution is adjusted to 2 to 6.5 until the time of filtration. After filtration, even if the pH rises to 6.5 or more, Fe_ThreeO_FourThe concentration of Na, K, Ca and Mg in it does not increase.
As a filtration method, a normal method such as a filter press can be used. Fe obtained by filtration_ThreeO_FourThe cake is washed with water (desalted) in the usual way, then dried and crushed to obtain high purity Fe._ThreeO_FourA powder is obtained.
[0023]
Fe of the present invention₂O_ThreeIn the production method, Fe thus obtained_ThreeO_FourBy oxidizing the particles by heating, Fe₂O_ThreeGet. At this time, if the heating oxidation temperature is as low as about 200 to 300 ° C., maghemite (γ-Fe₂O_ThreeIf the temperature is not lower than 300 ° C. and not higher than about 500 ° C., hematite (α-Fe₂O_Three) Is obtained. When both are made of ferrite, they are suitable for small magnetic elements, and it is possible to selectively obtain maghemite or hematite by adjusting the heating oxidation temperature according to the required conditions, applications, etc. it can.
Also, the Fe thus obtained₂O_ThreeIs mixed with nickel oxide, zinc oxide, copper oxide, manganese oxide, etc. and calcined to obtain a ferrite powder. For example, the ferrite powder can be formed into a paste by mixing a binder, and then a magnetic material layer is formed by a printing method or a doctor blade method. Alternatively, a ferrite powder and a binder such as polyvinyl alcohol (PVA) and a small amount of additive elements may be added, granulated and molded, and then fired to obtain a ferrite core.
[0024]
【Example】
Hereinafter, the method of the present invention will be further described by way of examples. In the examples, Fe₂O_ThreeThe ferrite was evaluated by the following method.
Iron oxide analysis
Specific surface area: Analysis by BET method
Cl, SO_Four ^2-: Analysis by fluorescent X-ray
Na, K, Ca and Mg: analyzed by ICP (Inductively Coupled Plasma Atomic Fluorescence Analysis)
Ferrite evaluation
Calcination possible temperature: the lowest temperature at which the spinelization rate is 90% or more by XRD
[0025]
(Examples 1-4)
The ferrous chloride solution and the ferric chloride solution are mixed with Fe in the solution.³⁺Concentration is Fe³⁺/ Total-Fe = 8% and mixed, and water was added to prepare a total Fe concentration of 0.58 mol / l and a solution volume of 25.75 liters.
4.25 liters of 8 mol / l NaOH solution was put into a container with an internal volume of 40 liters, and the above iron chloride solution was mixed while agitating with nitrogen gas aerated. The solution was heated to 90 ° C. in a nitrogen atmosphere, and the air was oxidized by aeration of 10 l / min while maintaining the pH at 10.2 ± 0.1._ThreeO_FourParticles were synthesized. After the reaction was completed, sulfuric acid was added to the reaction solution at 90 ° C. to adjust the pH shown in Table 1. Then desalted, filtered, dried, crushed to Fe_ThreeO_FourA powder was obtained. This powder was heated and oxidized at 450 ° C. for 2 hours to obtain iron oxide (hematite: α-Fe₂O_Three).
Next, ferrite powder was produced using this iron oxide. Trial production of ferrite powder using the obtained iron oxide Fe₂O_Three: NiO: ZnO: CuO = 49: 11: 30: 10, and this was mixed with a ball mill for 1 hour and then dried. This powder was calcined at 600 ° C. or higher to obtain a NiCuZn ferrite powder. The calcination was performed for 2 hours at the lowest temperature at which the spinelization rate was 90% or more by XRD. Furthermore, grinding with a ball mill, the specific surface area is 6m²The process was continued until the weight became / g or more. The obtained pulverized powder was dried, mixed with a PVA solution and granulated, and then press-molded into a toroidal shape. The obtained molded body was fired at 900 ° C. to obtain a sintered body. The sintered density was calculated from the weight and dimensions of the sintered body. Initial permeability was measured on a core fired at 900 ° C. using an LCR meter. The results are shown in Table 1.
[0026]
(Comparative Examples 1 and 2)
Samples were prepared and evaluated under the same conditions as in Examples 1 to 4 except that sulfuric acid was added to the solution after completion of the reaction to adjust the pH to the values shown in Table 3. The results are shown in Table 3.
[0027]
(Example 5)
The ferrous chloride solution and the ferric chloride solution are mixed with Fe in the solution.³⁺Concentration is Fe³⁺/Total-Fe=1.5% and mixed to adjust the total Fe concentration to 0.71 mol / l and the solution volume to 25.25 liters by adding water.
Into a container having an internal volume of 40 liters, 4.75 liters of an 8 mol / l NaOH solution was put, and the above iron chloride solution was mixed while agitating with nitrogen gas. The solution was heated to 80 ° C. in a nitrogen atmosphere, and the air was oxidized by aeration of 10 l / min while maintaining the pH at 8.5 ± 0.2._ThreeO_FourParticles were synthesized. After completion of the reaction, the reaction solution was cooled to 55 ° C., and hydrochloric acid was added to adjust to pH 4.0. Then desalted, filtered, dried, crushed to Fe_ThreeO_FourA powder was obtained. This powder was heated and oxidized at 230 ° C. for 3 hours to obtain iron oxide (maghemite: γ-Fe₂O_Three).
Evaluation was performed similarly to Examples 1-4. Table 1 shows the results.
[0028]
(Example 6)
The ferrous chloride solution and the ferric chloride solution are mixed with Fe in the solution.³⁺Concentration is Fe³⁺/Total-Fe=6.5% and mixed to adjust the total Fe concentration to 0.71 mol / l and the solution volume to 25.25 liters by adding water.
Into a container having an internal volume of 40 liters, 4.75 liters of an 8 mol / l NaOH solution was put, and the above iron chloride solution was mixed while agitating with nitrogen gas. Thereafter, samples were prepared and evaluated under the same conditions as in Example 5. The results are shown in Table 1.
[0029]
(Example 7)
The ferrous chloride solution and the ferric chloride solution are mixed with Fe in the solution.³⁺Concentration is Fe³⁺/ Total-Fe³⁺= 12% and mixed to adjust the total Fe concentration to 0.72 mol / l and the solution volume to 25 liters by adding water.
In a container with an internal volume of 40 liters, 5 liters of an 8 mol / l NaOH solution was put, and the above iron chloride solution was mixed while agitating with nitrogen gas. Thereafter, samples were prepared and evaluated under the same conditions as in Example 5. The results are shown in Table 1.
[0030]
(Example 8)
The ferrous chloride solution and the ferric chloride solution are mixed with Fe in the solution.³⁺Concentration is Fe³⁺/ Total-Fe = 24% and mixed to adjust the total Fe concentration to 0.72 mol / l and the solution volume to 25 liters by adding water.
In a container with an internal volume of 40 liters, 5 liters of an 8 mol / l NaOH solution was put, and the above iron chloride solution was mixed while agitating with nitrogen gas. Thereafter, samples were prepared and evaluated under the same conditions as in Example 5. The results are shown in Table 1.
[0031]
Example 9
The ferrous chloride solution and the ferric chloride solution are mixed with Fe in the solution.³⁺Concentration is Fe³⁺/ Total-Fe = 32%, and mixed to adjust the total Fe concentration to 0.72 mol / l and the solution volume to 24.5 liters by adding water.
Into a container having an internal volume of 40 liters, 5.5 liters of an 8 mol / l NaOH solution was put, and the above iron chloride solution was mixed while agitating with nitrogen gas. Thereafter, samples were prepared and evaluated under the same conditions as in Example 5. The results are shown in Table 1.
[0032]
(Example 10)
The ferrous chloride solution and the ferric chloride solution are mixed with Fe in the solution.³⁺Concentration is Fe³⁺/ Total-Fe = 46% and mixed to adjust the total Fe concentration to 0.73 mol / l and the solution volume to 24 liters by adding water.
Into a container having an internal volume of 40 liters, 5.5 liters of an 8 mol / l NaOH solution was put, and the above iron chloride solution was mixed while agitating with nitrogen gas. Thereafter, samples were prepared and evaluated under the same conditions as in Example 5. The results are shown in Table 1.
[0033]
(Comparative Example 3)
Samples were prepared and evaluated under the same conditions as in Example 5 except that hydrochloric acid was added to the solution after completion of the reaction to adjust the pH to 1.7. The results are shown in Table 3.
(Comparative Example 4)
Samples were prepared and evaluated under the same conditions as in Example 5 except that hydrochloric acid was added to the solution after completion of the reaction to adjust the pH to 7.2. The results are shown in Table 3.
(Comparative Example 5)
The mixing conditions of the solution in the neutralization step were changed under the conditions of Example 7. That is, ferrous chloride solution and ferric chloride solution are mixed with Fe in the solution.³⁺Concentration is Fe³⁺/ Total-Fe = 12%, and mixed to adjust the total Fe concentration to 3.0 mol / l and the solution volume to 6 liters by adding water.
In a container with an internal volume of 40 liters, 24 liters of a 1.67 mol / l NaOH solution was placed, and the above iron chloride solution was mixed while agitating with nitrogen gas. Thereafter, samples were prepared and evaluated under the same conditions as in Example 5. The results are shown in Table 3.
[0034]
(Examples 11-14)
A container was charged with 4 liters of an 8.1 mol / l NaOH solution and mixed with 26 liters of a 0.62 mol / l ferrous sulfate solution while agitating with nitrogen gas and stirring. The solution was heated to 85 ° C. in a nitrogen atmosphere, and the air was oxidized by aeration of 10 l / min while adjusting the pH to 8.5 ± 0.2._ThreeO_FourParticles were synthesized. After the reaction was completed, sulfuric acid was added to the reaction solution at 85 ° C. to adjust to a predetermined pH. Then desalted, filtered, dried, crushed to Fe_ThreeO_FourA powder was obtained. Obtained Fe_ThreeO_FourIs oxidized by heating at 400 ° C. for 1 hour and iron oxide (hematite: α-Fe₂O_ThreeAnd the same evaluation as in Example 1 was performed. The results are shown in Table 2.
[0035]
(Comparative Example 6)
In Comparative Example 6, Fe_ThreeO_FourAfter the production of Fe, without adjusting the pH of the solution to 2 to 6.5, Fe₂O_ThreeWas generated.
14 liters of 2.8 mol / l NaOH solution and Fe²⁺14 liters of a ferrous sulfate solution having a concentration of 1.5 mol / l was mixed. The solution was heated to 90 ° C. in a nitrogen atmosphere, and was oxidized by aeration of air at 10 l / min while controlling the pH to 6.8 ± 0.1._ThreeO_FourParticles were synthesized. Then desalted, filtered, dried, crushed to Fe_ThreeO_FourA powder was obtained. Obtained Fe_ThreeO_FourIs heated at 400 ° C. for 1 hour and iron oxide (hematite: α-Fe₂O_Three). Obtained Fe₂O_ThreeWas evaluated under the same conditions as in the examples. The results are shown in Table 3.
[0036]
(Comparative Example 7)
It manufactured by the spray roasting method using the ferrous chloride solution, and evaluated on the same conditions as Examples 1-4 using the iron oxide which has not been washed with water. The results are shown in Table 3.
(Comparative Example 8)
It evaluated by the same conditions as Examples 1-4 using the iron oxide which manufactured by the spray roasting method similarly to the comparative example 3, and performed the washing process after roasting. The results are shown in Table 3.
[0037]
(Examples 15 to 18)
The ferrous sulfate solution and ferric sulfate solution are mixed with Fe in the solution.³⁺Concentration is Fe³⁺/ Total-Fe = 5% and mixed to adjust the total Fe concentration to 0.82 mol / l and the solution volume to 25.5 liters by adding water.
4.5 liters of a 10 mol / l NaOH solution was placed in a container with an internal volume of 30 liters, and the above-mentioned iron sulfate solution was mixed while agitating with nitrogen gas aerated. The solution was heated to 75 ° C. in a nitrogen atmosphere, and the air was oxidized by aeration of 10 l / min while maintaining the pH at 10.3 ± 0.1._ThreeO_FourParticles were synthesized. After the reaction was completed, the reaction solution was cooled to 60 ° C., and hydrochloric acid was added to adjust to a predetermined pH. Then desalted, filtered, dried, crushed to Fe_ThreeO_FourA powder was obtained. This powder was heated and oxidized at 250 ° C. for 2 hours to produce iron oxide (maghemite: γ-Fe₂O_Three).
Evaluation was performed under the same conditions as in Examples 1 to 4. The results are shown in Table 3.
[0038]
(Examples 19 to 22, Comparative Example 9)
A mixed solution of a ferrous chloride solution and a ferric chloride solution under the conditions shown in Table 4 and a sodium carbonate solution were prepared. An alkaline solution was put into a container having an internal volume of 40 liters, and an iron chloride solution was mixed while agitating with nitrogen gas and stirring. This solution was heated to 85 ° C., and without oxidizing the pH, air was passed through 10 l / min to oxidize, and Fe_ThreeO_FourParticles were synthesized. After the reaction was completed, the reaction solution was cooled to 60 ° C., and hydrochloric acid was added to adjust to a predetermined pH. Then desalted, filtered, dried, crushed to Fe_ThreeO_FourA powder was obtained. This powder was heated at 430 ° C. for 2 hours to obtain iron oxide (hematite: α-Fe₂O_Three). Evaluation was performed under the same conditions as in Examples 1 to 4. The results are shown in Table 4.
From the results in Table 4, it can be seen that the equivalent ratio of the alkali solution and the solution containing the iron salt is preferably in the range of 0.95 to 1.5.
[0039]
(Examples 23 to 26, Comparative Example 10)
A mixed solution of ferrous chloride solution and ferric chloride solution under the conditions shown in Table 5 and a potassium hydroxide solution were prepared. An alkaline solution was put into a container having an internal volume of 40 liters, and an iron chloride solution was mixed while agitating with nitrogen gas and stirring. This solution was heated to 80 ° C., and without oxidizing the pH, was oxidized by aeration of air at 10 l / min, and Fe_ThreeO_FourParticles were synthesized. After the reaction was completed, the reaction solution was cooled to 60 ° C., and hydrochloric acid was added to adjust to a predetermined pH. Then desalted, filtered, dried, crushed to Fe_ThreeO_FourA powder was obtained. This powder was heated at 430 ° C. for 2 hours to obtain iron oxide (hematite: α-Fe₂O_Three). Evaluation was performed under the same conditions as in Examples 1 to 4. The results are shown in Table 5.
From the results of Examples 23 to 26, Comparative Example 5 and Comparative Example 10, it can be seen that the volume ratio of the solution containing the alkaline solution and the iron salt is preferably in the range of 0.1 to 3.5.
[0040]
From the examples and comparative examples, the content of Cl is 300 ppm or less, SO_Four ^2-The converted S content is 300 ppm or less, the total content of K, Na, Ca and Mg is less than 100, and the specific surface area is 6 to 60 m.²/ G Fe₂O_ThreeIt can be confirmed that when ferrite is produced using, calcining is possible at a low temperature of about 700 ° C., and a high sintered density and initial permeability can be obtained even when firing at a low temperature of 900 ° C. or lower.
[0041]
【The invention's effect】
If the production method of the present invention is used, even if iron chloride or iron sulfate is used as a raw material, Fe is produced.₂O_ThreeCl and SO contained in_Four ^2-Are simultaneously reduced. This is done using a mixture of iron chloride and iron sulfate.₂O_ThreeIt is particularly effective when manufacturing.
Fe of the present invention₂O_ThreeIn the case of manufacturing ferrite using low temperature, calcining at a low temperature is possible, and high sintering density and initial magnetic permeability can be obtained even when firing at a low temperature of 900 ° C. In addition, by the production method of the present invention, the above Fe₂O_ThreeCan be obtained.
[0042]
[Table 1]

[0043]
[Table 2]

[0044]
[Table 3]

[0045]
[Table 4]

[0046]
[Table 5]

Claims (3)

A specific surface area of 6 to 60 m ² / g, a Cl content of 300 ppm or less, a S content of 300 ppm or less in terms of SO ₄ ²⁻ , a total content of Na, K, Ca and less than 100 ppm Fe ₂ O ₃ containing Mg. An aqueous solution containing an iron salt and an aqueous alkali solution are mixed and neutralized to produce a solution containing iron hydroxide, and iron hydroxide in the solution is oxidized to produce Fe ₃ O ₄ particles. The pH of the Fe ₃ O ₄ production step, the pH adjustment step of adjusting the pH of the solution to 2 to 6.5 by adding an acid to the solution containing the Fe ₃ O ₄ particles, and the pH adjustment step. A separation step of separating Fe ₃ O ₄ particles from the solution adjusted to 2 to 6.5, and heating and oxidizing the Fe ₃ O ₄ particles separated in the separation step to produce Fe ₂ O ₃ a method of manufacturing a _Fe 2 _{O 3} having a Fe ₂ O ₃ production process,
In the neutralization step, between the aqueous solution containing the iron salt and the alkali aqueous solution, a method of manufacturing Fe ₂ O _3, wherein the relation holds as represented by the following formula (1) and (2) .

(In formula (1), [OH ⁻ ] is the number of moles of hydroxyl group in the alkaline aqueous solution, [Fe ²⁺ ] is the number of moles of Fe ^{2+ in} the aqueous solution containing the iron salt, and [Fe ³⁺ ] is the iron salt. (The number of ^moles of Fe ^{3+ in} the aqueous solution is shown.)   Fe in the solution containing the iron salt in the neutralization step ³⁺ Concentration is Fe ²⁺ And Fe ³⁺ 2 to 50% based on the total concentration of Fe, ₂ O ₃ The Fe of claim 2, wherein ₂ O ₃ Manufacturing method.