JP4100665B2 - Method for producing hexagonal ferrite sintered body - Google Patents

Description

【００７７】
表１において、サンプルNo.１０２〜No.１０５では、６００〜１０００℃の温度範囲における低速降温域の持続時間が３時間以上である。そのため、これらのサンプルでは、基準パターンで焼結した基準サンプルNo.１０９に比べ保磁力が向上し、また、比抵抗、特に磁化容易軸方向の比抵抗が向上している。また、これらのうちサンプルNo.１０２〜No.１０３では、８００〜９００℃の温度範囲における低速降温域の持続時間が３時間以上であるため、保磁力および比抵抗の向上率が高い。
【００７８】
一方、サンプルNo.１０１では、１０００℃を超える温度範囲における低速降温域の持続時間が３時間を超えたため、保磁力向上は認められない。
【００７９】
実施例２（図５：パターンＢ）
焼結工程における温度変化パターンを図５に示すパターンＢとし、図５におけるＴ１を表２に示す温度としたほかは実施例１と同様にして、焼結磁石サンプルを作製した。パターンＢにおいてＴ１は、降温速度が５℃/minから０．１℃/minに変化する温度である。このパターンでは、降温速度を０．１℃/minとした温度域が低速降温域である。なお、降温速度を０．５℃/minとした温度域も低速降温域であるが、この温度域は６００℃以下であるため、本発明には関係しない。
【００８０】
これらのサンプルについて、実施例１と同様な測定を行った。結果を表２に示す。
【００８１】
【表２】

【００８２】
表２のサンプルNo.２０１〜No.２０３では、６００〜１０００℃の温度範囲における低速降温域の持続時間が１０時間以上である。そのため、これらのサンプルでは表１の基準サンプルNo.１０９に比べ保磁力が向上し、また、比抵抗、特に磁化容易軸方向の比抵抗が向上している。また、これらのうちサンプルNo.２０１では、８００〜９００℃の温度範囲における低速降温域の持続時間が１０時間以上であるため、保磁力および比抵抗の向上率が高い。
【００８３】
実施例３（図６：パターンＣ）
焼結工程における温度変化パターンを図６に示すパターンＣとし、８００〜９００℃の温度範囲における降温速度を表３に示す値としたほかは実施例１と同様にして、焼結磁石サンプルを作製した。このパターンでは、６００〜８００℃において降温速度を０．５℃/minとし、その持続時間は約６．７時間である。そのため、８００〜９００℃における降温速度によらず、本発明で限定する条件を満足する。
【００８４】
これらのサンプルについて、実施例１と同様にしてＨcJおよび磁化容易軸方向の比抵抗を測定した。結果を表３に示す。
【００８５】
【表３】

【００８６】
表３から、８００〜９００℃における降温速度を遅くするほど、すなわちこの温度範囲を通過する時間が長くなるほど、保磁力および比抵抗が高くなることがわかる。この結果から、８００〜９００℃の温度範囲内における降温速度の制御が重要であることがわかる。
【００８７】
実施例４（図７：パターンＤ）
焼結工程における温度変化パターンを図７に示すパターンＤとし、図７におけるＴ１を表４に示す温度としたほかは実施例１と同様にして、焼結磁石サンプルを作製した。パターンＤにおいてＴ１は、降温速度が５℃/minから０．０５℃/minに変化する温度である。
【００８８】
これらのサンプルについて、実施例１と同様にしてＨcJの測定を行った。結果を表４に示す。
【００８９】
【表４】

【００９０】
表４から、８００〜９００℃の温度範囲を通過する時間が長くなるほど、保磁力が高くなることがわかる。この結果から、８００〜９００℃の温度範囲内における降温速度の制御が重要であることがわかる。
【００９１】
実施例５（図８：パターンＥ）
焼結工程における温度変化パターンを図８に示すパターンＥとし、図８におけるＴ１を表５に示す温度としたほかは実施例１と同様にして、焼結磁石サンプルを作製した。パターンＥでは、降温速度０．０５℃/minの低速降温域より高温側に、１１００℃から始まる降温速度１５℃/minの高速降温域を設けてあり、Ｔ１は、降温速度が１５℃/minから０．０５℃/minに変化する温度である。このパターンは、図７に示すパターンＤに、高速降温域を付加したものである。
【００９２】
これらのサンプルについて、実施例１と同様な測定を行った。結果を表５に示す。
【００９３】
【表５】

【００９４】
表４と表５との比較から、高速降温域を付加することにより保磁力の最大値が向上することがわかり、また、最大保磁力を得るために必要な温度Ｔ１が、高温側にシフトすることがわかる。また、９００℃未満の温度まで急冷すると保磁力および比抵抗がかなり低下することから、８００〜９００℃の温度範囲を通過する時間が保磁力向上および比抵抗向上に大きく寄与することがわかる。
【００９５】
実施例６（図９：温度変化パターンＦ）
焼結工程における安定温度Ｔ０を１２３０℃とし、かつ、焼結工程における温度変化パターンを図９に示すパターンＦとしたほかは実施例１と同様にして、焼結磁石サンプルを作製した。パターンＦでは、９００℃に一定時間保持する低速降温域を設け、そのほかの温度における降温速度は５℃/minとしてある。表６に、９００℃における保持時間を示す。なお、保持時間が０時間（サンプルNo.６０４）のときは、降温過程の全域において降温速度が５℃/minとなる基準パターン（図３）である。
【００９６】
これらのサンプルについて、実施例１と同様にしてＨcJの測定を行った。結果を表６に示す。なお、表６に示す△ＨcJは、サンプルNo.６０４に対する保磁力の向上量である。
【００９７】
【表６】

【００９８】
表６から、９００℃における保持時間を２時間以上としたサンプルNo.６０１、No.６０２において大きな保磁力向上が認められ、特に保持時間の長いサンプルNo.６０１では保磁力が顕著に向上している。
【００９９】
なお、上記実施例１〜実施例６において、降温速度制御によって保磁力が向上したサンプルと基準ンプルNo.１０９との残留磁束密度を比較したところ、保磁力向上に伴う残留磁束密度低下は実質的に認められなかった。
【０１００】
実施例７（図９〜図１１：温度変化パターンＦ〜パターンＨ）
ＣａＣＯ₃の添加量を１．４５質量％としたほかは実施例６（パターンＦ）と同様にして、焼結磁石サンプルを作製した。
【０１０１】
また、焼結工程における温度変化パターンを、図１０に示すパターンＧまたは図１１に示すパターンＨとしたほかは上記サンプルと同様にして、焼結磁石サンプルを作製した。
【０１０２】
また、焼結工程における温度変化パターンを、図３に示す基準パターンとしたほかは上記サンプルと同様にして、焼結磁石サンプルを作製した。
【０１０３】
パターンＦ、パターンＧおよびパターンＨにおいて、９００℃における保持時間はいずれも１０時間とした。上記４種のパターンにおける焼結温度Ｔ０は、１２３０℃である。パターンＧは、焼結温度から９００℃までの温度域が降温速度１１℃/minの高速降温域であることが、パターンＦとの相違点である。一方、パターンＨは、９００℃から室温までの温度域が降温速度０．５℃/minの低速降温域であることが、パターンＦとの相違点である。
【０１０４】
これらのサンプルについて、実施例１と同様にしてＨcJの測定を行い、また、室温における残留磁束密度（Ｂｒ）の測定を行った。結果を表７に示す。なお、表７に示す△ＨcJは、基準パターンで焼結したサンプルNo.７０４に対する保磁力の向上量である。
【０１０５】
【表７】

【０１０６】
表７において、焼結温度から９００℃までの温度域を高速で降温するパターンＧを利用したサンプルNo.７０２では、パターンＦを利用したサンプルNo.７０１に比べ、保磁力が著しく向上している。この結果から、９００℃を超える温度域に高速降温域を設けることによる効果が明らかである。
【０１０７】
また、９００℃で１０時間保持後に低速で降温するパターンＨを利用したサンプルNo.７０３では、９００℃で１０時間保持だけを行うパターンＦを利用したサンプルNo.７０１に比べ、保磁力が著しく向上している。
【０１０８】
実施例８（図５：パターンＢ）
出発原料混合時に、出発原料の０．７質量％のＡｌ₂Ｏ₃を添加し、また、焼結温度Ｔ０を１２３０℃としたほかは実施例２（パターンＢ）と同様にして、焼結磁石サンプルを作製した。このサンプルの組成をＣ１とする。
【０１０９】
また、後添加物として添加するＳｉＯ₂の添加量を、出発原料全体の０．４６質量％とし、また、水酸化ランタンおよび酸化コバルトの添加量を、最終組成におけるモル比が
（Ｓｒ_0.77Ｌａ_0.23）（Ｆｅ_11.8Ｃｏ_0.2）Ｏ₁₉
となるように決定し、また、焼結温度Ｔ０を１２３０℃としたほかは実施例２（パターンＢ）と同様にして、焼結磁石サンプルを作製した。このサンプルの組成をＣ２とする。
【０１１０】
各サンプルについて、パターンＢにおける温度Ｔ１を表８に示す。
【０１１１】
これらのサンプルについて、実施例１と同様な測定を行った。結果を表８に示す。なお、表８に示す△ＨcJは、組成Ｃ１のものではサンプルNo.８０４を基準とした向上量であり、組成Ｃ２のものではサンプルNo.８０７を基準とした向上量である。
【０１１２】
【表８】

【０１１３】
表８から、本発明はさまざまな組成の磁石に対して有効であることがわかる。
【０１１４】
実施例９（図８：パターンＥ）
後添加物として水酸化ランタンおよび酸化コバルトを添加せず、替わりに出発原料として酸化ランタンおよび酸化コバルトを用い、最終組成を
Ｓｒ_1-xＬａ_x（Ｆｅ_12-yＣｏ_y）_zＯ₁₉
で表したときにｘ、ｙおよびｚが表９に示す値となるように酸化ランタンおよび酸化コバルトの添加量を決定したほかは実施例５（パターンＥ）と同様にして、焼結磁石サンプルを作製した。ただし、パターンＥにおける焼結温度Ｔ０は１２３０℃、温度Ｔ１は９００℃とした。
【０１１５】
これらのサンプルについて、実施例１と同様にしてＨcJおよび比抵抗を測定した。結果を表９に示す。
【０１１６】
また、比較のために、上記各サンプルとそれぞれ組成を同じとし、かつ、焼結工程における温度変化パターンを図３に示す基準パターン（Ｔ０＝１２３０℃）として作製した焼結磁石についても、ＨcJを測定した。これらの焼結磁石のＨcJを、その組成における基準ＨcJとして表９に併記する。表９に示す△ＨcJは、各サンプルのＨcJからその組成における基準ＨcJを減じた値である。また、これらの焼結磁石の比抵抗を、その組成における基準比抵抗として表９に併記する。
【０１１７】
【表９】

【０１１８】
表９から、本発明はさまざまな組成の磁石に対して有効であることがわかり、また、本発明が特に有効な磁石組成が存在することがわかる。
【０１１９】
表９において本発明により製造されたサンプルは、比抵抗の値自体は小さいが、基準比抵抗と比較すれば著しい向上が認められるので、本発明の効果が明らかである。なお、表９に示すサンプルにおいて比抵抗の値が小さくなったのは、
Ｓｒ_1-xＬａ_x（Ｆｅ_12-yＣｏ_y）_zＯ₁₉
においてｘ≠ｙｚであり、また、ｚ≠１であるために、Ｆｅ²⁺の生成量が多くなった結果と考えられる。
【０１２０】
実施例１０（図８：パターンＥ）
後添加物として水酸化ランタンおよび酸化コバルトを添加せず、替わりに出発原料として酸化ランタンおよび酸化コバルトを用い、最終組成が
Ｓｒ_0.87Ｌａ_0.13（Ｆｅ_11.902Ｃｏ_0.098）_1.02Ｏ₁₉
となるようにこれらの添加量を決定し、かつ、焼結助剤であるＣａＣＯ₃およびＳｉＯ₂を、質量比（ＣａＣＯ₃／ＳｉＯ₂）および合計添加量（ＣａＣＯ₃＋ＳｉＯ₂）が表１０に示す値となるように添加したほかは実施例５（パターンＥ）と同様にして、焼結磁石サンプルを作製した。ただし、仮焼温度は１１７０℃とし、また、パターンＥにおける焼結温度Ｔ０は１２００℃、温度Ｔ１は９００℃とした。
【０１２１】
これらのサンプルについて、実施例１と同様にしてＨcJを測定した。結果を表１０に示す。
【０１２２】
また、比較のために、上記各サンプルとそれぞれ組成を同じとし、かつ、焼結工程における温度変化パターンを図３に示す基準パターン（Ｔ０＝１２００℃）として作製した焼結磁石についても、ＨcJを測定した。これらの焼結磁石のＨcJを、その組成における基準ＨcJとして表１０に併記する。表１０に示す△ＨcJは、各サンプルのＨcJからその組成における基準ＨcJを減じた値である。
【０１２３】
【表１０】

【０１２４】
表１０から、本発明は焼結助剤添加パターンをさまざまに変化させても有効であることがわかり、また、本発明が特に有効となる焼結助剤添加パターンが存在することがわかる。
【０１２５】
実施例１１（図９：パターンＦ）
以下の手順で、ＬａおよびＣｏのいずれも含有しないフェライト焼結磁石サンプルを作製した。
【０１２６】
モル比で
ＳｒＣＯ₃：Ｆｅ₂Ｏ₃＝１：６
となるようにＳｒＣＯ₃とＦｅ₂Ｏ₃とを秤量し、湿式アトライタで粉砕して混合した。得られた混合物をロータリーキルンにより空気中で仮焼して、仮焼体を得た。仮焼温度は１２５０℃、仮焼時間は３時間とした。
【０１２７】
この仮焼体を振動ミルで解砕した後、ＳｉＯ₂およびＣａＣＯ₃を添加し、水を媒体として湿式アトライタで粉砕して混合することにより、スラリーとした。なお、ＳｉＯ₂およびＣａＣＯ₃の添加量は、出発原料全体のそれぞれ０．６質量％および１．４質量％とした。
【０１２８】
これ以降は実施例１と同様にして成形体を得た。この成形体を空気中において焼結した後、室温まで降温し、焼結磁石サンプルを得た。降温の際の温度変化パターンは、実施例６と同様に、図９に示すパターンＦとした。表１１に、９００℃における保持時間を示す。なお、保持時間が０時間（サンプルNo.１１０４）のときは、降温過程の全域において降温速度が５℃/minとなる基準パターン（図３）である。
【０１２９】
これらのサンプルについて、実施例１と同様にしてＨcJの測定を行った。結果を表１１に示す。なお、表１１に示す△ＨcJは、サンプルNo.１１０４に対する保磁力の向上量である。
【０１３０】
【表１１】

【０１３１】
表１１から、９００℃における保持時間を２時間以上としたサンプルNo.１１０１、No.１１０２において、大きな保磁力向上が認められることがわかる。
【０１３２】
実施例１２（図７：パターンＤおよびパターンＥ）
最終組成が、
Ｓｒ_1-xＬａ_x（Ｆｅ_12-yＣｏ_y）_zＯ₁₉
において
ｘ＝０．３、
ｙｚ＝０．２
となり、かつ、ｚが表１２に示す値となるようにし、かつ、焼結助剤であるＳｉＯ₂の添加量を０．６質量％、ＣａＣＯ₃の添加量を表１２に示す値とし、焼結時の温度制御を図７に示すパターンＤまたは図８に示すパターンＥとし、パターンＤおよびパターンＥのいずれにおいても、焼結温度Ｔ０を１２２０℃、温度Ｔ１を９００℃として、フェライト焼結磁石サンプルを作製した。
【０１３３】
これらのサンプルについて、室温においてＨcJおよびＢｒの測定を行った。結果を表１２および表１３に示す。
【０１３４】
また、比較のために、上記各サンプルとそれぞれ組成を同じとし、かつ、焼結工程における温度変化パターンを図３に示す基準パターン（Ｔ０＝１２２０℃）として作製した焼結磁石についても、ＨcJおよびＢｒを測定した。これらの焼結磁石のＨcJおよびＢｒを、その組成における基準ＨcJおよび基準Ｂｒとしてそれぞれ表１２および表１３に併記する。なお、表１２に示す△ＨcJは、各サンプルのＨcJからその組成における基準ＨcJを減じた値であり、表１３に示す△Ｂｒは、各サンプルのＢｒからその組成における基準Ｂｒを減じた値である。
【０１３５】
【表１２】

【０１３６】
【表１３】

【０１３７】
表１２から、本発明はさまざまな組成の磁石に対して有効であることがわかる。また、表１３から、本発明を適用したことによるＢｒの低下（△Ｂｒ）はほとんど認められないことがわかる。すなわち、ほとんどのサンプルにおいて、△Ｂｒは測定誤差（約３mT）以下となっており、△Ｂｒが測定誤差を大きく超えるサンプルはない。
【０１３８】
実施例１３
最終組成が、
Ｓｒ_1-xＬａ_x（Ｆｅ_12-yＣｏ_y）_zＯ₁₉
においてｚ＝１となり、かつ、ｘ、ｙおよびｘ／ｙが表１４に示す値となるようにし、かつ、焼結助剤であるＳｉＯ₂およびＣａＣＯ₃の添加量をそれぞれ０．６質量％および１．４質量％となるようにし、焼結時の温度制御を図７に示すパターンＤまたは図８に示すパターンＥとし、パターンＤおよびパターンＥのいずれにおいても焼結温度Ｔ０を１２２０℃、温度Ｔ１を９００℃として、フェライト焼結磁石サンプルを作製した。
【０１３９】
これらのサンプルについて、室温においてＨcJの測定を行った。結果を表１４に示す。
【０１４０】
また、比較のために、上記各サンプルとそれぞれ組成を同じとし、かつ、焼結工程における温度変化パターンを図３に示す基準パターン（Ｔ０＝１２２０℃）として作製した焼結磁石についても、ＨcJを測定した。これらの焼結磁石のＨcJを、その組成における基準ＨcJとして表１４に併記する。なお、表１４に示す△ＨcJは、各サンプルのＨcJからその組成における基準ＨcJを減じた値である。
【０１４１】
【表１４】

【０１４２】
表１４から、
Ｓｒ_1-xＬａ_x（Ｆｅ_12-yＣｏ_y）_zＯ₁₉
で表される磁石組成においてｘをｙより大きくすることにより、より優れた保磁力向上効果が得られることがわかる。
【０１４３】
実施例１４
次に、上記実施例で作製したサンプルから下記表１５に示すものを選んだ。これらのサンプル製造時の低速降温域の設定を、徐冷条件として表１５に示す。徐冷条件に△５℃とあるのは、降温速度５℃/minということである。
【０１４４】
これら各サンプルの粒界三重点の結晶化の有無および組成を、透過型電子顕微鏡（ＴＥＭ）により調べた。結晶化の有無については、電子線回折像において格子点が認められれば結晶化しているとし、格子点が見られずハロー状になっていれば非晶質であると判断した。組成は、ＴＥＭに装着されたエネルギー分散型Ｘ線分光器（ＴＥＭ−ＥＤＳ）により調べた。分析対象の三重点は、各サンプルにつき１０箇所以上とした。結果を表１５に示す。
【０１４５】
なお、組成分析の結果、三重点の組成は、表１５に示す組成Ｉ〜組成VIに分類できることがわかった。表１５には、測定対象の三重点に対する組成Ｉ〜組成VIのそれぞれに該当する三重点の数の比と、測定対象の三重点のうち結晶化していたものの比率とをそれぞれ示してある。
【０１４６】
【表１５】

【０１４７】
表１５から、本発明におけるＨcJ向上効果を考察した。ＨcJが最大であるサンプルNo.３０１は、９００℃からの徐冷により生成したと考えられる結晶化した三重点の比率が高くなっている。また、１０００℃から徐冷したサンプルNo.１０２も、結晶化した三重点の比率が高くなっている。以上から、ＨcJ向上のためには結晶化した三重点が多いことが必要と考えられる。
【０１４８】
低速降温域を設けない従来の方法により製造した比較サンプルNo.１０９について、三重点付近の透過型電子顕微鏡写真と、その三重点の電子線回折像を図１２に示す。また、本発明法により製造したサンプルNo.３０１について、三重点付近の透過型電子顕微鏡写真と、その三重点の電子線回折像を図１３に示す。図１２の電子線回折像はハロー状であり、比較サンプルNo.１０９の三重点が非晶質であることがわかる。これに対し図１３の電子線回折像はスポット状であり、サンプルNo.３０１の三重点が結晶化していることがわかる。
【図面の簡単な説明】
【図１】焼結工程に低速降温域を設けた場合の温度変化パターンを説明するためのグラフである。
【図２】焼結工程に低速降温域および高速降温域を設けた場合の温度変化パターンを説明するためのグラフである。
【図３】従来の焼結工程の温度変化パターンを説明するためのグラフである。
【図４】実施例における焼結工程の温度変化パターンを説明するためのグラフである。
【図５】実施例における焼結工程の温度変化パターンを説明するためのグラフである。
【図６】実施例における焼結工程の温度変化パターンを説明するためのグラフである。
【図７】実施例における焼結工程の温度変化パターンを説明するためのグラフである。
【図８】実施例における焼結工程の温度変化パターンを説明するためのグラフである。
【図９】実施例における焼結工程の温度変化パターンを説明するためのグラフである。
【図１０】実施例における焼結工程の温度変化パターンを説明するためのグラフである。
【図１１】実施例における焼結工程の温度変化パターンを説明するためのグラフである。
【図１２】結晶構造を表す図面代用写真であって、ａ）は、従来の方法により製造された焼結体の三重点付近の透過型電子顕微鏡写真であり、ｂ）は、前記三重点の電子線回折像である。
【図１３】結晶構造を表す図面代用写真であって、ａ）は、本発明法により製造された焼結体の三重点付近の透過型電子顕微鏡写真であり、ｂ）は、前記三重点の電子線回折像である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a hexagonal ferrite sintered body such as a magnetoplumbite type hexagonal ferrite sintered magnet.
[0002]
[Prior art]
As the oxide permanent magnet material, hexagonal magnetoplumbite type (M type) Sr ferrite or Ba ferrite is mainly used, and these are used as sintered magnets and bonded magnets.
[0003]
The present inventors have proposed a ferrite sintered magnet having a high residual magnetic flux density and a high coercive force, which could not be achieved by a conventional M-type ferrite sintered magnet, for example, in JP-A-11-154604. Yes. This sintered ferrite magnet contains at least Sr, La and Co and has a main phase of hexagonal M-type ferrite.
[0004]
[Problems to be solved by the invention]
The sintered magnet is manufactured by forming and firing raw material powder. If the particle size of the raw material powder is reduced, the crystal particle size of the sintered body can be reduced, so that the coercive force is improved. However, if the particle size of the raw material powder is reduced, the degree of orientation of the particles during molding in a magnetic field is lowered, so that there is a problem that residual magnetic flux density is lowered and moldability is also deteriorated. Further, as shown in JP-A-11-154604, the inclusion of La and Co can remarkably improve the coercive force and residual magnetic flux density of the sintered ferrite magnet, but Co is expensive. Therefore, the cost increases.
[0005]
Under such circumstances, it has been difficult to produce a sintered ferrite magnet having high coercive force and residual magnetic flux density at low cost.
[0006]
In addition, when a ferrite sintered magnet is applied to a motor, if the specific resistance of the magnet is low, eddy current loss increases, and heat generation of the motor increases. However, no simple means for improving the specific resistance of the sintered ferrite magnet is known.
[0007]
An object of the present invention is to improve the coercivity of a sintered ferrite magnet without substantially reducing the residual magnetic flux density and without increasing the amount of Co added. Another object of the present invention is to realize a hexagonal ferrite sintered body having a high specific resistance by a simple means.
[0008]
  Such purposes are as follows (1) to (3This is achieved by the present invention.
(1) It has a sintering process, and in the cooling process of this sintering process,A low temperature drop area and a high temperature drop area are set on the higher temperature side than the low temperature drop area.When the temperature drop rate is 0 ° C / min or more and less than 1 ° C / minYesThe duration of the low temperature drop region is 2 hours or more in the temperature range of 600 to 1000 ° C. and 0 to 3 hours in the temperature range exceeding 1000 ° C.The high temperature drop region is a region where the temperature drop rate is 5 ° C./min or more over a temperature range of 50 ° C. or more within the temperature range of at least 900 ° C. or more and the sintering temperature or less in the temperature drop process.A method for producing hexagonal ferrite.
(2) The above (with the temperature decreasing rate in the high temperature decreasing region being 10 ° C./min or more)1) Hexagonal ferrite sintered body.
(3) The hexagonal ferrite sintered body is Fe, element A (A is at least one selected from Sr, Ba, Ca and Pb), element R (R is at least selected from rare earth elements and Bi) (1) and the element M (M is at least one selected from Co, Mn, Ni and Zn) and is a sintered magnet having a hexagonal magnetoplumbite type ferrite as a main phase (1)Or (2)A method for producing a hexagonal ferrite sintered body.
[0009]
[Action and effect]
In the present invention, when manufacturing a ferrite sintered magnet, a low temperature drop region having a low temperature drop rate is provided in a specific temperature range of the temperature drop process during sintering. Thereby, the coercive force can be improved without substantially reducing the residual magnetic flux density.
[0010]
When the temperature drop rate is controlled based on the present invention, the coercive force is improved and the specific resistance of the magnet is increased. In addition, if the low temperature drop region is provided in a relatively high temperature range, the specific resistance increase rate can be further increased. Therefore, when the magnet manufactured according to the present invention is applied to, for example, a motor, eddy current loss is reduced, so that heat generation can be reduced. In the present invention, the specific resistance in the easy magnetization axis (c-axis) direction of the sintered ferrite magnet is particularly high, but the specific resistance is also improved in the hard magnetization axis direction orthogonal to the easy magnetization axis.
[0011]
The present invention is effective in the production of various hexagonal ferrite sintered magnets such as M-type, W-type, X-type, Y-type and Z-type, but the hexagonal M-type ferrite containing the element M and the element R This is particularly effective in the production of sintered magnets. That is, when the present invention is applied to the production of a magnet having this composition, the coercivity improvement rate is particularly high and the specific resistance improvement rate is also particularly high.
[0012]
When the present invention is applied to the production of a sintered ferrite magnet containing the element R and the element M, the specific resistance in the easy axis direction can be increased. In addition, the specific resistance in this specification is a value in 25 degreeC. That is, according to the present invention, a sintered ferrite magnet with high coercive force and high resistance is realized. However, since the effect of improving the coercive force is reduced if the specific resistance is remarkably increased by controlling the temperature lowering process, it is preferable to control the temperature lowering process so that the specific resistance does not exceed 100 kΩm.
[0013]
By the way, conventionally, as a magnetic material used for a high frequency coil, spinel ferrite, in particular, Ni—Zn ferrite is generally used. However, with the increase in the speed of applied electric / electronic devices, the frequency used is increasing. Therefore, hexagonal ferrite has attracted attention as a magnetic material that can handle frequencies higher than those of spinel magnetic materials. Among them, planar type ferrite having an easy axis of magnetization in the in-plane direction of the c-plane has a high frequency range. Particularly suitable for use at high frequencies to maintain permeability. However, the planar type ferrite has a lower specific resistance than the spinel ferrite. Therefore, it is necessary to take insulation measures at the time of manufacturing the coil, there is a problem that the cost is increased, and there is a problem that eddy current loss is increased. On the other hand, if the present invention is applied to the production of a planar type ferrite sintered body, the specific resistance can be improved.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, Fe, element A (A is at least one selected from Sr, Ba, Ca and Pb), element R (R is at least one selected from rare earth elements and Bi), and element M (M Will be described by taking as an example the case where the present invention is applied to the production of a hexagonal magnetoplumbite-type ferrite sintered magnet containing at least one selected from Co, Mn, Ni and Zn.
[0015]
Production method
The production method of the present invention has a sintering step of obtaining a sintered magnet by sintering a compact of a raw material powder. In the present invention, the coercive force of the sintered magnet is improved by providing a low temperature drop region with a low temperature drop rate in the temperature drop process of the sintering step.
[0016]
In the present invention, the temperature decrease rate in the low temperature decrease region is 0 ° C./min or more and less than 1 ° C./min, preferably 0 to 0.5 ° C./min, more preferably 0 to 0.1 ° C./min. If the temperature drop rate is too fast, the effect of the present invention cannot be realized.
[0017]
A temperature change pattern in the sintering process is schematically shown in FIG. The sintering process shown in FIG. 1 includes a temperature raising process, a stable temperature range, and a temperature lowering process. In addition, this invention is applicable also to the sintering process which consists of a temperature rising process and a temperature falling process, without providing a stable temperature range. The temperature lowering process in FIG. 1 is composed of the above-described low-temperature temperature-decreasing region and a normal temperature-decreasing region in which the temperature-decreasing rate is faster than the low-temperature temperature-decreasing region. T1 and T2 are the start temperature and the end temperature of the low-speed temperature fall region, respectively. Since the temperature decrease rate in the low temperature decrease range may be 0 ° C./min, T1 = T2.
[0018]
Next, the conditions that should be satisfied by the low temperature drop range will be described. In the present invention, within a temperature range of 600 to 1000 ° C, preferably within a temperature range of 700 ° C to 1000 ° C, more preferably within a temperature range of 800 to 1000 ° C, and even more preferably within a temperature range of 800 to 900 ° C, The low temperature drop region is provided so as to last for 3 hours or more, preferably 5 hours or more, more preferably 10 hours or more. Thereby, improvement of coercive force and improvement of specific resistance are realized at the same time. If the duration of the low temperature drop region within the above temperature range is too short, the coercive force improving effect and the specific resistance improving effect are not realized or become insufficient. On the other hand, since the productivity decreases as the duration is increased, the duration is usually 100 hours or less, particularly preferably 50 hours or less.
[0019]
The specific values of T1 and T2 are not particularly limited as long as the low temperature drop region satisfies the above-described conditions. For example, T2 may be room temperature, or T1 may be a temperature exceeding 1000 ° C. However, since the low temperature drop region existing in the temperature range below 600 ° C. does not substantially contribute to the improvement of coercive force and specific resistance, the normal temperature drop rate is set in the temperature range below 600 ° C. in order to improve productivity. It is preferable. Further, if the low temperature drop region extends to a high temperature range exceeding 1000 ° C. and the duration of the low temperature drop region in this temperature range is long, the effect of improving the coercive force is impaired. For this reason, the duration of the low temperature drop region in the temperature range exceeding 1000 ° C. is 0 to 3 hours.
[0020]
In addition, when the duration of the low temperature decrease range reaches a sufficient length in the temperature range of 800 to 1000 ° C., particularly in the temperature range of 800 to 900 ° C., the normal temperature decrease rate may be returned in the temperature range below that. . Thereby, a magnet with high coercive force and high specific resistance can be obtained in a relatively short time.
[0021]
The temperature decreasing rate in the normal temperature decreasing range shown in FIG. 1 is not particularly limited as long as it is faster than the low temperature decreasing range. However, the coercive force can be further improved by relatively increasing the temperature lowering rate on the higher temperature side than the low temperature range. In FIG. 2, the modification of the temperature change pattern in a sintering process is shown typically. In the pattern shown in FIG. 2, a high temperature cooling region is provided on the higher temperature side than the low temperature cooling region in the temperature decreasing process. TH shown in FIG. 2 is the start temperature of the high-speed temperature drop region. In the present specification, the temperature lowering rate in the high-speed temperature decreasing region is 5 ° C./min or more, preferably 10 ° C./min or more, more preferably 15 ° C./min or more. In the temperature range of 900 ° C. or more and the sintering temperature or less in the temperature lowering process, if such a high temperature fall region is provided with a temperature range of 50 ° C. or more, preferably a temperature range of 100 ° C. or more, more preferably over the entire temperature range, The coercive force can be further improved.
[0022]
In addition, although there is no upper limit of the temperature-fall rate in a high-speed temperature fall region, it is usually preferable to set it as 100 degrees C / min or less. Even if the temperature lowering rate is further increased, the coercive force is not further improved, and in order to significantly increase the temperature lowering rate, the furnace needs to be modified, resulting in an increase in cost.
[0023]
Conditions in the sintering step are not particularly limited except for the temperature change pattern, and may be the same as the conventional conditions. For example, the sintering temperature (maximum temperature or stable temperature) is preferably 1150 to 1250 ° C., more preferably 1160 to 1230 ° C., and the time for holding in this temperature range or the time for holding at the stable temperature (stable time) is Preferably it is 0.5 to 3 hours. The sintering step is usually performed in air, but may be performed in an atmosphere in which the oxygen partial pressure is controlled.
[0024]
Next, various conditions other than the sintering step in the production method of the present invention will be described.
[0025]
The raw material powder to be molded is not particularly limited as long as it has a hexagonal magnetoplumbite type (M type) ferrite phase. The raw material powder may be produced, for example, by so-called calcination by a solid phase reaction, or by a coprecipitation method or a hydrothermal synthesis method. Hereinafter, a case where a calcination step is mainly provided will be described.
[0026]
First, the starting materials are mixed and then calcined to obtain a calcined body. The calcined body is pulverized or pulverized to obtain a powder. And after shaping | molding this raw material powder, it bakes.
[0027]
As a starting material, a compound containing one of ferrite constituent elements (Fe, element A, element R, element M, etc.) or a compound containing two or more of these may be used. As the starting material containing the element A, it is preferable to use a hydroxide or a carbonate since stability at the time of stocking is good. In addition, Si compounds and / or Ca compounds are used as sintering aids. As Si compound, SiO₂The Ca compound is preferably CaCO_ThreeIs preferred. Si compound SiO₂The addition amount in terms of conversion may be about 0.1 to 2% by mass of the entire starting material._ThreeThe addition amount in terms of conversion may be about 0.2 to 4% by mass of the entire starting material.
[0028]
As the starting material, oxide powder or a compound that becomes an oxide by firing, such as carbonate, hydroxide, nitrate, or the like is used. Although the average particle diameter of the starting material is not particularly limited, it is usually preferable to be about 0.1 to 2 μm. In particular, it is preferable to use fine powders of iron oxide. Specifically, those having an average primary particle diameter of preferably 1 μm or less, more preferably 0.5 μm or less are used.
[0029]
The calcination is usually performed in an oxidizing atmosphere such as air. Although the calcining conditions are not particularly limited, the stable temperature is usually 1000 to 1350 ° C., and the stable time is 1 second to 10 hours, more preferably 1 second to 3 hours. The calcined body has a substantially magnetoplumbite-type ferrite structure, and the average primary particle diameter is preferably 2 μm or less, more preferably 1 μm or less, still more preferably 0.1 to 1 μm, most preferably 0.1 to 0.5 μm. The average particle diameter can be measured with a scanning electron microscope.
[0030]
It is not necessary to mix all starting material compounds before calcination, and a part or all of each compound may be added after calcination. In particular, it is preferable to add part, preferably all, of the Si compound and Ca compound used as the sintering aid after calcination.
[0031]
A method of adding at least a part of a compound other than the sintering aid, that is, a compound containing Fe, element A, element R, or element M after calcination is referred to as a post-addition method in this specification. In the post-addition method, first, a calcined body having at least hexagonal ferrite containing the element A as a main phase is manufactured. Subsequently, after this calcined body is pulverized or at the time of pulverization, a post-added compound (post-additive) is added to the calcined body, and then molded and sintered. If a compound to be added later is selected so that one or more elements selected from the element R and the element M, preferably both the element R and the element M are contained in the post-additive, a plurality of curie A magnet having temperature can be obtained, and as a result, high magnetic properties can be obtained.
[0032]
The amount of the post-additive is preferably 1 to 100% by volume of the calcined body, more preferably 5 to 70% by volume, and still more preferably 10 to 50% by volume. An R oxide can be used as the compound containing the element R. However, since the R oxide has a relatively high solubility in water, there is a problem that it flows out during wet molding. Moreover, since it has a hygroscopic property, it tends to cause a weighing error. Therefore, the R compound is preferably a carbonate or a hydroxide. What is necessary is just to add the post-additive of another element as an oxide or the compound which becomes an oxide by baking, for example, carbonate and a hydroxide.
[0033]
The post-additive may be added after calcination and before sintering, but is preferably added during pulverization described below. However, the post-additive may be added to particles that are not a calcined body but are manufactured by a coprecipitation method, a hydrothermal synthesis method, or the like and have at least the hexagonal ferrite containing the element A as a main phase.
[0034]
About the element R or the element M, it is desirable that 30% or more, more preferably 50% or more of the total amount contained in the magnet is added as a post-additive. For other elements, the amount added as a post-additive is not particularly limited. In addition, it is preferable that the average particle diameter of a post-additive is about 0.1-2 micrometers.
[0035]
Here, the addition amount of the post-additive will be specifically described. For example,
Sr: La: Fe: Co = 0.8: 0.2: 11.8: 0.2
When the purpose is to produce sintered magnets,
Sr: Fe = 0.8: 9.6 (= 1: 12)
The mixture is calcined at a ratio of
La: Fe: Co = 0.2: 2.2: 0.2
The sintered magnet having the above-described target composition can be obtained by adding the post-additives and firing. For example,
Sr: Fe = 0.8: 11.8 (= 1: 1.75)
(The calcined body is M-type Sr ferrite and α-Fe₂O_ThreeTo the calcined body obtained.
La: Co = 0.2: 0.2
The sintered magnet having the above-described target composition can also be obtained by adding the post-additives and firing.
[0036]
The reason why the sintered magnet manufactured by the post-addition method has a plurality of Curie temperatures is not clear, but is considered as follows. During sintering, the calcined body particles having the M-type ferrite phase react with the post-additive, and in the process, the M-type ferrite portion having a high La concentration and Co concentration, and the M-type ferrite portion having a low concentration thereof. It is thought that That is, if La and Co in the post-addition diffuse toward the center of the calcined body particles during sintering, the concentration of La and Co in the crystal grains after sintering is higher than that in the center. It is thought that it tends to be high at the surface layer. Since the Curie temperature depends on the amount of substitution of La and Co, particularly the amount of substitution of La, the presence of a plurality of Curie temperatures is considered to reflect the existence of the concentration distribution of La and Co in the crystal grains.
[0037]
Next, molding and pulverization that is the preceding process will be described.
[0038]
For forming the raw material powder, either a dry molding method or a wet molding method may be used. In any case, the effect of the present invention is realized. However, it is preferable to use a wet molding method in that higher magnetic properties can be obtained. In the wet molding, it is preferable to use a molding slurry containing raw material powder, water as a dispersion medium, and a dispersant. In order to further increase the effect of the dispersant, it is preferable to provide a wet pulverization step before the wet molding step. In addition, when calcined powder is used as a raw material powder, the calcined body is generally composed of granules, so that a dry coarse pulverization step is provided before the wet pulverization step for coarse pulverization or pulverization of the calcined body. It is preferable. In addition, when raw material powder is produced by a coprecipitation method or a hydrothermal synthesis method, a dry coarse pulverization step is usually not provided, and a wet pulverization step is not essential, but a wet method is required to increase the degree of orientation. It is preferable to provide a grinding step. Below, the case where a calcined body powder is used as a raw material powder and a dry coarse pulverization process and a wet pulverization process are provided is demonstrated.
[0039]
In the dry coarse pulverization step, pulverization is usually performed until the BET specific surface area is about 2 to 10 times. After pulverization, the average particle size is preferably about 0.1 to 1 μm, and the BET specific surface area is preferably 4 to 10 m.²It is about / g. The pulverizing means is not particularly limited, and for example, a dry vibration mill, a dry attritor (medium stirring mill), a dry ball mill, and the like can be used, and it is particularly preferable to use a dry vibration mill. What is necessary is just to determine a grinding | pulverization time suitably according to a grinding | pulverization means. In addition, when adding some starting materials after calcination, it is preferable to add in this dry-type coarse pulverization process. SiO₂And CaCO which becomes CaO by firing_ThreeIt is preferable to add at least a part of each in the dry coarse pulverization step or the subsequent wet pulverization step.
[0040]
Dry coarse pulverization also has the effect of reducing the coercive force HcB by introducing crystal distortion into the calcined particles. The decrease in coercive force suppresses particle aggregation and improves dispersibility. Further, the degree of orientation is improved by softening. The soft magnetized particles return to the original hard magnetism in the subsequent sintering step.
[0041]
After the dry coarse pulverization, a pulverization slurry containing pulverized particles and water is prepared, and wet pulverization is performed using the slurry. The content of the raw material powder in the pulverizing slurry is preferably about 10 to 70% by mass. The pulverizing means used for wet pulverization is not particularly limited, but it is usually preferable to use a ball mill, an attritor, a vibration mill or the like. What is necessary is just to determine a grinding | pulverization time suitably according to a grinding | pulverization means.
[0042]
After the wet pulverization, the pulverization slurry is concentrated to prepare a molding slurry. Concentration may be performed by centrifugation or the like. The content of the raw material powder in the molding slurry is preferably about 60 to 90% by mass.
[0043]
In the wet molding process, molding in a magnetic field is performed using a molding slurry. The molding pressure may be about 10 to 50 MPa, and the applied magnetic field strength may be about 0.5 to 1.5 T.
[0044]
When a non-aqueous dispersion medium is used for the molding slurry, a high degree of orientation can be obtained. However, in order to reduce the burden on the environment, it is preferable to use an aqueous dispersion medium. And in order to compensate for the fall of the orientation degree by using an aqueous dispersion medium, it is preferable to make a dispersing agent exist in the slurry for shaping | molding. The dispersant used in this case is an organic compound having a hydroxyl group and a carboxyl group, a neutralized salt thereof, a lactone thereof, an organic compound having a hydroxymethylcarbonyl group, or an acid. It is preferably an organic compound having an enol-type hydroxyl group that can be dissociated or a neutralized salt thereof. Such a dispersant is described, for example, in JP-A-11-214208.
[0045]
When a non-aqueous dispersion medium is used, for example, a surfactant such as oleic acid is added to an organic solvent such as toluene or xylene as described in JP-A-6-53064. Thus, a dispersion medium is obtained. By using such a dispersion medium, it is possible to obtain a high degree of magnetic orientation of up to about 98% even when sub-micron size ferrite particles that are difficult to disperse are used.
[0046]
After the wet molding, the molded body is dried, and then the added dispersant is sufficiently decomposed and removed by performing a degreasing treatment of heating to a temperature of preferably 100 to 500 ° C. in air or nitrogen. The drying and the degreasing treatment may be performed continuously. However, if the molded body is heated rapidly without being sufficiently dried, cracks are generated in the molded body, so that the temperature is raised slowly from room temperature to about 100 ° C. However, it is preferable to dry sufficiently in this temperature range. After the degreasing treatment, sintering is performed under the above-described conditions to obtain a sintered ferrite magnet.
[0047]
The compact is crushed using a crusher or the like, and classified by a sieve or the like so that the average particle size is about 100 to 700 μm to obtain magnetically oriented granules, which are dry magnetically shaped and then sintered. A magnet may be obtained.
[0048]
Sintered magnet
The present invention is effective for the production of a sintered ferrite magnet having hexagonal magnetoplumbite type (M type) ferrite as a main phase. Among them, in particular, Fe, element A (A is Sr, Ba, Ca and At least one selected from Pb), element R (R is at least one selected from rare earth elements and Bi) and element M (M is at least one selected from Co, Mn, Ni and Zn) It exhibits a remarkable effect in the production of sintered ferrite magnets containing. In the present specification, the rare earth elements are Y, Sc and lanthanoid.
[0049]
In such a ferrite sintered magnet, the ratio of the total of A, R, Fe and M to the total amount of metal elements is preferably
A: 1 to 13 atomic%,
R: 0.05 to 10 atomic%,
Fe: 80 to 95 atomic%,
M: 0.1 to 5 atomic%
And more preferably
A: 3 to 11 atomic%,
R: 0.2-6 atomic%
Fe: 83 to 94 atomic%,
M: 0.3-4 atomic%
And more preferably
A: 3-9 atomic%,
R: 0.5-4 atomic%,
Fe: 86-93 atomic%,
M: 0.5-3 atomic%
It is. If the content of element A is too small, M-type ferrite will not be generated, or α-Fe₂O_Three The nonmagnetic phase such as is increased. If the content of element A is too large, M-type ferrite will not be generated, or SrFeO_3-x The nonmagnetic phase such as is increased. If the content of the element R is too small, the solid solution amount of the element M is decreased, and the effect of improving the magnetic properties becomes insufficient. When there is too much content of element R, nonmagnetic heterogeneous phases, such as orthoferrite, will increase. If the content of the element M is too small or too large, the effect of improving the magnetic properties becomes insufficient.
[0050]
In the magnet, the atomic ratio of A, R, Fe and M is
Formula I A_1-xR_x(Fe_12-yM_y)_zO₁₉
Can be expressed as In the above formula I, x, y and z are
0.04 ≦ x ≦ 0.9,
0.04 ≦ y ≦ 1.0, especially 0.04 ≦ y ≦ 0.5,
0.4 ≦ x / y ≦ 5,
0.7 ≦ z ≦ 1.2
It is preferable not to deviate.
[0051]
In the above formula I, if x is too small, that is, if the amount of element R is too small, it becomes impossible to increase the solid solution amount of element M in hexagonal ferrite, thereby improving saturation magnetization and / or improving anisotropic magnetic field. The effect becomes insufficient. If x is too large, the element R cannot be substituted and dissolved in the hexagonal ferrite. For example, orthoferrite containing the element R is generated and the saturation magnetization is lowered. If y is too small, the saturation magnetization improvement effect and / or the anisotropic magnetic field improvement effect becomes insufficient. If y is too large, the element M cannot be substituted and dissolved in the hexagonal ferrite. Even in the range where the element M can be substituted and dissolved, the anisotropy constant (K₁) Or anisotropic magnetic field (H_A) Will increase. If z is too small, the nonmagnetic phase containing Sr and the element R increases, and the saturation magnetization becomes low. If z is too large, α-Fe₂O_ThreeSince the nonmagnetic spinel ferrite phase containing the phase or the element M is increased, the saturation magnetization is lowered.
[0052]
In the above formula I, if x / y is too small or too large, the valences of the element R and the element M cannot be balanced, and different phases such as W-type ferrite are likely to be generated. When the element M is a divalent ion and the element R is a trivalent ion, it is common to set x / y = 1 in terms of valence equilibrium. However, as described above, R is excessive. It is preferable to do. The reason why the allowable range is large in the region where x / y exceeds 1 is that even if y is small, Fe³⁺→ Fe²⁺This is because the valence is balanced by the reduction of.
[0053]
In order to achieve a sufficiently high coercive force improving effect according to the present invention, preferably
1 ≦ x / y, more preferably
1 <x / y, more preferably
1.3 ≦ x / y
Is desirable. However, since the coercive force itself decreases as x / y increases,
x / y ≦ 3, more preferably
x / y ≦ 2
And
[0054]
In addition, although the high specific resistance is obtained with the magnet manufactured by this invention, the value of specific resistance is influenced greatly also by a magnet composition. That is, the specific resistance is improved by the present invention when a magnet having the same composition is manufactured by the conventional manufacturing method and the method of the present invention and the specific resistance is compared, the magnet manufactured by the method of the present invention has a higher ratio. It means to show resistance. In the above formula I
0.04 ≦ x ≦ 0.9,
0.04 ≦ y ≦ 0.5,
0.9 ≦ x / y ≦ 1.4,
0.9 ≦ z ≦ 1.1
When the coercive force is 295 kA / m or more and less than 380 kA / m by using the manufacturing method of the present invention, the specific resistance in the easy axis direction at 25 ° C. is 0. When the coercive force is 380 kA / m or more and 410 kA / m or less when the coercive force is 380 kA / m or more and 410 kA / m or less, the specific resistance in the easy axis direction at 25 ° C. can be 0.6 kΩm or more, and the coercive force is more than 410 kA / m and 500 kA / m or less. In this case, the specific resistance in the easy axis direction at 25 ° C. can be made 0.2 kΩm or more.
[0055]
In the above formula I representing the composition, the number of oxygen (O) atoms is 19, which is that M is all divalent, R is all trivalent, and x = y and z = 1. The stoichiometric composition ratio of oxygen is shown. The number of oxygen atoms varies depending on the types of M and R and the values of x, y, and z. For example, when the firing atmosphere is a reducing atmosphere, oxygen deficiency (vacancy) may occur. Further, Fe is usually trivalent in M-type ferrite, but this may change to divalent. In addition, the valence of the element M such as Co may also change, which changes the ratio of oxygen to the metal element. In this specification, the number of oxygen atoms is displayed as 19 regardless of the type of R and the values of x, y, and z. However, the actual number of oxygen atoms may be a slightly deviated value.
[0056]
The magnet composition can be measured by fluorescent X-ray quantitative analysis or the like. The presence of the main phase can be confirmed by X-ray diffraction, electron beam diffraction, or the like.
[0057]
In order to increase the saturation magnetization and coercive force of the magnet, it is preferable to use at least one of Sr and Ca as the element A, and it is particularly preferable to use Sr. The proportion of Sr + Ca in A, particularly the proportion of Sr, is preferably 51 atomic percent or more, more preferably 70 atomic percent or more, and even more preferably 100 atomic percent. If the ratio of Sr in the element A is too low, it becomes impossible to obtain both the saturation magnetization and the significant improvement in coercive force.
[0058]
As the element R, preferably at least one of lanthanoids, more preferably at least one of light rare earths, more preferably at least one of La, Nd, and Pr is used, and it is particularly preferable to use La. The proportion of La in R is preferably 40 atomic% or more, more preferably 70 atomic% or more, and it is most preferable to use only La as R in order to improve saturation magnetization. This is because La is the largest when the solid solution limit amount for hexagonal M-type ferrite is compared. Therefore, if the ratio of La in R is too low, the solid solution amount of R cannot be increased. As a result, the solid solution amount of element M cannot be increased, and the effect of improving magnetic properties is reduced. End up. If Bi is used in combination, the calcination temperature and the sintering temperature can be lowered, which is advantageous in production.
[0059]
As the element M, it is preferable to always use at least one of Co and Zn, particularly Co. The proportion of Co in M is preferably 10 atomic% or more, more preferably 20 atomic% or more. When the ratio of Co in M is too low, the coercive force is not sufficiently improved.
[0060]
The magnet has B₂O_ThreeMay be included. B₂O_ThreeBy including the calcination temperature and the sintering temperature can be lowered, it is advantageous in production. B₂O_ThreeThe content of is preferably 0.5% by mass or less of the entire magnet powder. B₂O_ThreeWhen there is too much content, saturation magnetization will become low.
[0061]
The magnet powder may contain at least one of Na, K and Rb. Each of these is Na₂O, K₂O and Rb₂When converted to O, the total of these contents is preferably 3% by mass or less of the entire magnet powder. If these contents are too large, the saturation magnetization will be low. These elements are M^IIn the ferrite, M^IFor example
Sr_1.3-2aR_aM^I _a-0.3Fe_11.7M_0.3O₁₉
It is contained in the form of In this case, it is preferable that 0.3 <a ≦ 0.5. If a is too large, the saturation magnetization becomes low, and the element M during firing^IThis causes a problem that a large amount of water evaporates.
[0062]
In addition to these, for example, Ga, In, Li, Mg, Cu, Ti, Zr, Ge, Sn, V, Nb, Ta, Sb, As, W, and Mo may be contained as oxides. These contents are converted to oxides of stoichiometric composition, respectively, gallium oxide 5 mass% or less, indium oxide 3 mass% or less, lithium oxide 1 mass% or less, magnesium oxide 3 mass% or less, copper oxide 3 Mass% or less, titanium oxide 3 mass% or less, zirconium oxide 3 mass% or less, germanium oxide 3 mass% or less, tin oxide 3 mass% or less, vanadium oxide 3 mass% or less, niobium oxide 3 mass% or less, tantalum oxide 3 mass % Or less, antimony oxide 3 mass% or less, arsenic oxide 3 mass% or less, tungsten oxide 3 mass% or less, and molybdenum oxide 3 mass% or less.
[0063]
The magnet produced according to the present invention may have at least two different Curie temperatures. In this case, it is preferable that these Curie temperatures exist in the range of 400 ° C. to 480 ° C., and the absolute value of these differences is 5 ° C. or more. In the case of containing Co, by having a structure having a plurality of Curie temperatures in this manner, the squareness Hk / HcJ can be remarkably improved and the contents of expensive Co and R can be reduced. Such a magnet can be manufactured by the post-addition method described above.
[0064]
The average crystal grain size of the magnet is preferably 2 μm or less, more preferably 1 μm or less, and even more preferably 0.5 to 1.0 μm. In the present invention, even if the average crystal grain size exceeds 1 μm, it is sufficient. High coercivity can be obtained. The crystal grain size can be measured with a scanning electron microscope.
[0065]
The ferrite sintered magnet manufactured according to the present invention achieves high coercive force and high saturation magnetization. Therefore, if it has the same shape as a conventional sintered ferrite magnet that does not contain these elements, the generated magnetic flux density can be increased. Therefore, when it is applied to a motor, high torque can be achieved, and speakers and headphones can be realized. When applied to, it can contribute to the improvement of the performance of applied products. Further, if the same function as that of a conventional sintered ferrite magnet is sufficient, the size (thickness) of the magnet can be reduced (thinned), which can contribute to reduction in size and weight (thinning). In addition, even in a motor in which a field magnet is conventionally a wound electromagnet, this can be replaced with a sintered ferrite magnet, which can contribute to weight reduction, production process shortening, and cost reduction. . Furthermore, because of its excellent coercive force (HcJ) temperature characteristics, it can be used in low-temperature environments where there has been a risk of low-temperature demagnetization (permanent demagnetization) of sintered ferrite magnets. The reliability of the product used in the can be significantly increased.
[0066]
The magnet manufactured according to the present invention is processed into a predetermined shape and used for a wide range of applications as described below.
[0067]
For example, automotive motors for fuel pump, power window, ABS, fan, wiper, power steering, active suspension, starter, door lock, electric mirror, etc .; for FDD spindle, VTR capstan , VTR rotary head, VTR reel, VTR loading, VTR camera capstan, VTR camera rotary head, VTR camera zoom, VTR camera focus, radio cassette cassette capstan, CD, LD, MD spindle , CD, LD, MD loading, OA for CD, LD optical pickup, AV equipment motor; air conditioner compressor, refrigerator compressor, electric tool drive, electric fan, microwave fan, microwave plate rotation Mixer drive Motors for household appliances such as Yerfan, Shaver drive, Electric toothbrush, etc .; Robot shaft, joint drive, Robot main drive, Machine tool table drive, Machine tool belt drive, etc. FA equipment motor; Others, Motorcycle Generator, speaker / headphone magnet, magnetron tube, MRI magnetic field generator, CD-ROM clamper, distributor sensor, ABS sensor, fuel / oil level sensor, magnet latch, etc.
[0068]
【Example】
Example 1 (FIG. 4: pattern A)
SrCO as starting material_ThreeAnd Fe₂O_ThreeAnd these in molar ratios
SrCO_Three: Fe₂O_Three= 0.8: 5.9
And weighed and mixed with a wet attritor. The obtained mixture was calcined in the air with a rotary kiln to obtain a calcined body. The calcining temperature was 1250 ° C. and the calcining time was 3 hours.
[0069]
After this calcined body was crushed with a vibration mill, SiO was added as a post-additive.₂, CaCO_ThreeLanthanum hydroxide [La (OH)_Three] And cobalt oxide (Co_ThreeO_FourAnd sorbitol as a dispersant, and pulverized and mixed with a wet attritor using water as a medium to obtain a slurry. The amount of sorbitol added is 0.6% by mass based on the total amount of the raw material powder (starting material + post-additive), and SiO 2₂And CaCO_ThreeThe addition amount of was 0.6% by mass and 1.4% by mass, respectively, of the entire starting material. The addition amount of lanthanum hydroxide and cobalt oxide is such that the molar ratio in the final composition is
(Sr_0.8La_0.2) (Fe_11.8Co_0.2) O₁₉
It was decided to become.
[0070]
Next, the slurry was dehydrated and concentrated so that the solid content concentration was about 76% to obtain a molding slurry.
[0071]
Subsequently, the molding slurry was compression-molded while dehydrating to obtain a molded body having a diameter of 30 mm and a height of 18 mm. During compression molding, a 1T magnetic field parallel to the pressing direction was applied.
[0072]
This molded body was heated to 100 to 500 ° C. in the air and sufficiently degreased, then sintered in the air and then cooled to room temperature to obtain a sintered magnet sample.
[0073]
The temperature change pattern during the sintering was the reference pattern shown in FIG. 3 or the pattern A shown in FIG. In these patterns, T0 is a sintering temperature (stable temperature). In this example, T0 was 1220 ° C. and the stabilization time was 1 hour. In pattern A, T1 is a temperature at which the temperature lowering rate changes from 5 ° C./min to 0.5 ° C./min. In the pattern A, the temperature range where the temperature decrease rate is 0.5 ° C./min is the low temperature decrease range. T1 in the pattern A was set to the temperature shown in Table 1. In addition, when T1 = 0 ° C. (sample No. 109), it is a reference pattern in which the temperature decreasing rate is 5 ° C./min throughout the temperature decreasing process.
[0074]
The coercivity (HcJ) of the obtained sample was measured with a BH tracer at room temperature. Table 1 shows the HcJ of each sample and the value (ΔHcJ) obtained by subtracting HcJ when sintered with the reference pattern from the HcJ of each sample.
[0075]
In addition, a 2 mm × 2 mm × 10 mm prism is cut out from the inside of each sample, and the ratio between the specific resistance in the magnetic field application direction (easy magnetization axis direction) and the direction perpendicular to this (magnetization difficult axis direction). Resistance was measured. These results are shown in Table 1.
[0076]
[Table 1]

[0077]
In Table 1, Samples No. 102 to No. 105 have a duration of the low temperature drop region in the temperature range of 600 to 1000 ° C. of 3 hours or more. Therefore, in these samples, the coercive force is improved as compared with the reference sample No. 109 sintered with the reference pattern, and the specific resistance, particularly the specific resistance in the easy axis direction is improved. Of these, Samples No. 102 to No. 103 have a high rate of improvement in coercive force and specific resistance because the duration of the low temperature drop region in the temperature range of 800 to 900 ° C. is 3 hours or more.
[0078]
On the other hand, in sample No. 101, since the duration of the low temperature drop region in the temperature range exceeding 1000 ° C. exceeded 3 hours, no improvement in coercive force was observed.
[0079]
Example 2 (FIG. 5: Pattern B)
A sintered magnet sample was produced in the same manner as in Example 1 except that the temperature change pattern in the sintering step was pattern B shown in FIG. 5 and T1 in FIG. 5 was changed to the temperature shown in Table 2. In pattern B, T1 is a temperature at which the temperature lowering rate changes from 5 ° C./min to 0.1 ° C./min. In this pattern, the temperature range where the temperature decrease rate is 0.1 ° C./min is the low temperature decrease range. The temperature range where the temperature decrease rate is 0.5 ° C./min is also a low temperature decrease range, but since this temperature range is 600 ° C. or less, it is not related to the present invention.
[0080]
About these samples, the same measurement as Example 1 was performed. The results are shown in Table 2.
[0081]
[Table 2]

[0082]
In samples No. 201 to No. 203 in Table 2, the duration of the low-speed temperature drop region in the temperature range of 600 to 1000 ° C. is 10 hours or more. Therefore, in these samples, the coercive force is improved as compared with the reference sample No. 109 in Table 1, and the specific resistance, particularly the specific resistance in the easy axis direction is improved. Of these, Sample No. 201 has a high rate of improvement in coercive force and specific resistance because the duration of the low temperature drop region in the temperature range of 800 to 900 ° C. is 10 hours or longer.
[0083]
Example 3 (FIG. 6: Pattern C)
A temperature change pattern in the sintering process was changed to the pattern C shown in FIG. 6 and the temperature drop rate in the temperature range of 800 to 900 ° C. was changed to the values shown in Table 3, and a sintered magnet sample was prepared in the same manner as in Example 1. did. In this pattern, the cooling rate is set to 0.5 ° C./min at 600 to 800 ° C., and the duration is about 6.7 hours. Therefore, the conditions limited in the present invention are satisfied regardless of the temperature drop rate at 800 to 900 ° C.
[0084]
For these samples, HcJ and the specific resistance in the easy axis direction were measured in the same manner as in Example 1. The results are shown in Table 3.
[0085]
[Table 3]

[0086]
It can be seen from Table 3 that the coercive force and the specific resistance increase as the rate of temperature decrease at 800 to 900 ° C. decreases, that is, as the time for passing through this temperature range increases. From this result, it can be seen that it is important to control the cooling rate within the temperature range of 800 to 900 ° C.
[0087]
Example 4 (FIG. 7: Pattern D)
A sintered magnet sample was produced in the same manner as in Example 1 except that the temperature change pattern in the sintering process was pattern D shown in FIG. 7 and T1 in FIG. 7 was changed to the temperature shown in Table 4. In the pattern D, T1 is a temperature at which the temperature decrease rate changes from 5 ° C./min to 0.05 ° C./min.
[0088]
For these samples, HcJ was measured in the same manner as in Example 1. The results are shown in Table 4.
[0089]
[Table 4]

[0090]
From Table 4, it can be seen that the longer the time for passing through the temperature range of 800 to 900 ° C., the higher the coercive force. From this result, it can be seen that it is important to control the cooling rate within the temperature range of 800 to 900 ° C.
[0091]
Example 5 (FIG. 8: pattern E)
A sintered magnet sample was produced in the same manner as in Example 1 except that the temperature change pattern in the sintering process was pattern E shown in FIG. 8 and T1 in FIG. 8 was changed to the temperature shown in Table 5. In pattern E, a high temperature drop region having a temperature drop rate of 15 ° C./min starting from 1100 ° C. is provided on the higher temperature side than the low temperature drop region having a temperature drop rate of 0.05 ° C./min, and T1 has a temperature drop rate of 15 ° C./min. To 0.05 ° C / min. This pattern is obtained by adding a high-speed cooling region to the pattern D shown in FIG.
[0092]
About these samples, the same measurement as Example 1 was performed. The results are shown in Table 5.
[0093]
[Table 5]

[0094]
From the comparison between Table 4 and Table 5, it can be seen that the maximum value of the coercive force is improved by adding the high-speed cooling region, and the temperature T1 necessary for obtaining the maximum coercive force shifts to the high temperature side. I understand that. Further, since the coercive force and the specific resistance are considerably lowered when rapidly cooled to a temperature of less than 900 ° C., it can be seen that the time passing through the temperature range of 800 to 900 ° C. greatly contributes to the improvement of the coercive force and the specific resistance.
[0095]
Example 6 (FIG. 9: Temperature change pattern F)
A sintered magnet sample was produced in the same manner as in Example 1 except that the stable temperature T0 in the sintering process was 1230 ° C. and the temperature change pattern in the sintering process was the pattern F shown in FIG. In the pattern F, a low-speed temperature decrease region that maintains a constant time at 900 ° C. is provided, and the temperature decrease rate at other temperatures is 5 ° C./min. Table 6 shows the holding time at 900 ° C. When the holding time is 0 hour (sample No. 604), it is a reference pattern (FIG. 3) in which the temperature decrease rate is 5 ° C./min throughout the temperature decrease process.
[0096]
For these samples, HcJ was measured in the same manner as in Example 1. The results are shown in Table 6. In addition, ΔHcJ shown in Table 6 is the amount of improvement in coercive force with respect to sample No. 604.
[0097]
[Table 6]

[0098]
From Table 6, a large improvement in coercive force was observed in samples No. 601 and No. 602 in which the holding time at 900 ° C. was 2 hours or more. Particularly, in sample No. 601 having a long holding time, the coercive force was remarkably improved. Yes.
[0099]
In Examples 1 to 6, when the residual magnetic flux density was compared between the sample with the coercive force improved by the temperature drop rate control and the reference sample No. 109, the decrease in the residual magnetic flux density accompanying the increase in the coercive force was substantially reduced. Was not accepted.
[0100]
Example 7 (FIGS. 9 to 11: temperature change pattern F to pattern H)
CaCO_ThreeA sintered magnet sample was prepared in the same manner as in Example 6 (Pattern F) except that the amount added was 1.45% by mass.
[0101]
Further, a sintered magnet sample was prepared in the same manner as the above sample except that the temperature change pattern in the sintering step was changed to the pattern G shown in FIG. 10 or the pattern H shown in FIG.
[0102]
Further, a sintered magnet sample was produced in the same manner as the above sample except that the temperature change pattern in the sintering process was the reference pattern shown in FIG.
[0103]
In Pattern F, Pattern G, and Pattern H, the holding time at 900 ° C. was 10 hours. The sintering temperature T0 in the above four patterns is 1230 ° C. The pattern G is different from the pattern F in that the temperature range from the sintering temperature to 900 ° C. is a high-speed temperature decrease region with a temperature decrease rate of 11 ° C./min. On the other hand, the pattern H is different from the pattern F in that the temperature range from 900 ° C. to room temperature is a low temperature decrease region with a temperature decrease rate of 0.5 ° C./min.
[0104]
For these samples, HcJ was measured in the same manner as in Example 1, and the residual magnetic flux density (Br) at room temperature was measured. The results are shown in Table 7. ΔHcJ shown in Table 7 is the amount of improvement in coercive force with respect to sample No. 704 sintered with the reference pattern.
[0105]
[Table 7]

[0106]
In Table 7, in sample No. 702 using pattern G that cools the temperature range from the sintering temperature to 900 ° C. at high speed, the coercive force is remarkably improved as compared with sample No. 701 using pattern F. . From this result, the effect by providing the high-speed temperature drop region in the temperature region exceeding 900 ° C. is clear.
[0107]
In addition, sample No. 703 using pattern H, which is cooled at a low speed after being held at 900 ° C. for 10 hours, has a significantly improved coercive force compared to sample No. 701 using pattern F which is held only at 900 ° C. for 10 hours. is doing.
[0108]
Example 8 (FIG. 5: Pattern B)
At the time of starting material mixing, 0.7% by mass of Al of the starting material₂O_ThreeIn addition, a sintered magnet sample was prepared in the same manner as in Example 2 (Pattern B) except that the sintering temperature T0 was set to 1230 ° C. The composition of this sample is C1.
[0109]
SiO added as a post-additive₂The amount of addition of lanthanum hydroxide and cobalt oxide is 0.46% by mass based on the total amount of the starting materials, and the molar ratio of the final composition is
(Sr_0.77La_0.23) (Fe_11.8Co_0.2) O₁₉
A sintered magnet sample was produced in the same manner as in Example 2 (Pattern B) except that the sintering temperature T0 was set to 1230 ° C. The composition of this sample is C2.
[0110]
Table 8 shows the temperature T1 in the pattern B for each sample.
[0111]
About these samples, the same measurement as Example 1 was performed. The results are shown in Table 8. ΔHcJ shown in Table 8 is an improvement amount based on sample No. 804 for the composition C1 and an improvement amount based on the sample No. 807 for the composition C2.
[0112]
[Table 8]

[0113]
From Table 8, it can be seen that the present invention is effective for magnets of various compositions.
[0114]
Example 9 (FIG. 8: Pattern E)
Do not add lanthanum hydroxide and cobalt oxide as post-additives, but instead use lanthanum oxide and cobalt oxide as starting materials,
Sr_1-xLa_x(Fe_12-yCo_y)_zO₁₉
A sintered magnet sample was prepared in the same manner as in Example 5 (Pattern E) except that the addition amounts of lanthanum oxide and cobalt oxide were determined so that x, y, and z had the values shown in Table 9. Produced. However, the sintering temperature T0 in the pattern E was 1230 ° C., and the temperature T1 was 900 ° C.
[0115]
For these samples, HcJ and specific resistance were measured in the same manner as in Example 1. The results are shown in Table 9.
[0116]
For comparison, HcJ is also applied to a sintered magnet having the same composition as each of the above samples and a temperature change pattern in the sintering process as a reference pattern (T0 = 1230 ° C.) shown in FIG. It was measured. HcJ of these sintered magnets is also shown in Table 9 as reference HcJ in the composition. ΔHcJ shown in Table 9 is a value obtained by subtracting the reference HcJ in the composition from the HcJ of each sample. The specific resistances of these sintered magnets are also shown in Table 9 as the reference specific resistance in the composition.
[0117]
[Table 9]

[0118]
From Table 9, it can be seen that the present invention is effective for magnets having various compositions, and that there are magnet compositions in which the present invention is particularly effective.
[0119]
In Table 9, the sample manufactured according to the present invention has a small specific resistance value, but a significant improvement is recognized as compared with the reference specific resistance, so the effect of the present invention is clear. In addition, in the sample shown in Table 9, the value of the specific resistance decreased.
Sr_1-xLa_x(Fe_12-yCo_y)_zO₁₉
Since x ≠ yz and z ≠ 1, Fe²⁺This is thought to be the result of an increase in the amount of produced.
[0120]
Example 10 (FIG. 8: Pattern E)
Without adding lanthanum hydroxide and cobalt oxide as post-additives, instead using lanthanum oxide and cobalt oxide as starting materials, the final composition is
Sr_0.87La_0.13(Fe_11.902Co_0.098)_1.02O₁₉
These addition amounts are determined so as to be CaCO which is a sintering aid._ThreeAnd SiO₂Of the mass ratio (CaCO_Three/ SiO₂) And total amount added (CaCO_Three+ SiO₂) Was added so as to have the values shown in Table 10, and a sintered magnet sample was produced in the same manner as in Example 5 (Pattern E). However, the calcination temperature was 1170 ° C., the sintering temperature T 0 in pattern E was 1200 ° C., and the temperature T 1 was 900 ° C.
[0121]
For these samples, HcJ was measured in the same manner as in Example 1. The results are shown in Table 10.
[0122]
For comparison, HcJ is also applied to a sintered magnet having the same composition as each of the above samples and a temperature change pattern in the sintering process as a reference pattern (T0 = 1200 ° C.) shown in FIG. It was measured. HcJ of these sintered magnets is also shown in Table 10 as the reference HcJ in the composition. ΔHcJ shown in Table 10 is a value obtained by subtracting the reference HcJ in the composition from the HcJ of each sample.
[0123]
[Table 10]

[0124]
From Table 10, it can be seen that the present invention is effective even when the sintering aid addition pattern is variously changed, and that there is a sintering aid addition pattern in which the present invention is particularly effective.
[0125]
Example 11 (FIG. 9: Pattern F)
A ferrite sintered magnet sample containing neither La nor Co was prepared by the following procedure.
[0126]
In molar ratio
SrCO_Three: Fe₂O_Three= 1: 6
SrCO to be_ThreeAnd Fe₂O_ThreeWere weighed, pulverized with a wet attritor and mixed. The obtained mixture was calcined in the air with a rotary kiln to obtain a calcined body. The calcining temperature was 1250 ° C. and the calcining time was 3 hours.
[0127]
After this calcined body is crushed by a vibration mill, SiO₂And CaCO_ThreeWas added, and pulverized and mixed with a wet attritor using water as a medium to obtain a slurry. In addition, SiO₂And CaCO_ThreeThe addition amount of was 0.6% by mass and 1.4% by mass, respectively, of the entire starting material.
[0128]
Thereafter, a molded body was obtained in the same manner as in Example 1. The molded body was sintered in the air and then cooled to room temperature to obtain a sintered magnet sample. The temperature change pattern at the time of temperature drop was the pattern F shown in FIG. Table 11 shows the holding time at 900 ° C. When the holding time is 0 hour (sample No. 1104), it is a reference pattern (FIG. 3) in which the temperature decrease rate is 5 ° C./min throughout the temperature decrease process.
[0129]
For these samples, HcJ was measured in the same manner as in Example 1. The results are shown in Table 11. Note that ΔHcJ shown in Table 11 is the amount of improvement in coercive force with respect to Sample No. 1104.
[0130]
[Table 11]

[0131]
From Table 11, it can be seen that in samples No. 1101 and No. 1102 in which the holding time at 900 ° C. was 2 hours or more, a large coercive force improvement was observed.
[0132]
Example 12 (FIG. 7: Pattern D and Pattern E)
The final composition is
Sr_1-xLa_x(Fe_12-yCo_y)_zO₁₉
In
x = 0.3,
yz = 0.2
And z is a value shown in Table 12, and SiO is a sintering aid.₂The amount of addition is 0.6 mass%, CaCO_ThreeAnd the temperature control during sintering is the pattern D shown in FIG. 7 or the pattern E shown in FIG. 8, and the sintering temperature T0 is 1220 ° C. in both the pattern D and the pattern E. A ferrite sintered magnet sample was produced at a temperature T1 of 900 ° C.
[0133]
These samples were measured for HcJ and Br at room temperature. The results are shown in Table 12 and Table 13.
[0134]
Further, for comparison, a sintered magnet having the same composition as each of the above samples and a temperature change pattern in the sintering process as a reference pattern (T0 = 1220 ° C.) shown in FIG. Br was measured. HcJ and Br of these sintered magnets are also shown in Tables 12 and 13 as reference HcJ and reference Br in their compositions, respectively. ΔHcJ shown in Table 12 is a value obtained by subtracting the reference HcJ in the composition from HcJ of each sample, and ΔBr shown in Table 13 is a value obtained by subtracting the reference Br in the composition from Br of each sample. is there.
[0135]
[Table 12]

[0136]
[Table 13]

[0137]
From Table 12, it can be seen that the present invention is effective for magnets of various compositions. Moreover, it can be seen from Table 13 that almost no decrease in Br (ΔBr) is observed due to the application of the present invention. That is, in most samples, ΔBr is equal to or less than a measurement error (about 3 mT), and there is no sample in which ΔBr greatly exceeds the measurement error.
[0138]
Example 13
The final composition is
Sr_1-xLa_x(Fe_12-yCo_y)_zO₁₉
In this case, z = 1, x, y and x / y are values shown in Table 14, and SiO is a sintering aid.₂And CaCO_ThreeIs added to 0.6% by mass and 1.4% by mass, respectively, and temperature control during sintering is set to pattern D shown in FIG. 7 or pattern E shown in FIG. Also, a sintered ferrite magnet sample was prepared at a sintering temperature T0 of 1220 ° C. and a temperature T1 of 900 ° C.
[0139]
About these samples, HcJ was measured at room temperature. The results are shown in Table 14.
[0140]
For comparison, HcJ is also applied to a sintered magnet having the same composition as each of the above samples and a temperature change pattern in the sintering process as a reference pattern (T0 = 1220 ° C.) shown in FIG. It was measured. HcJ of these sintered magnets is also shown in Table 14 as reference HcJ in the composition. ΔHcJ shown in Table 14 is a value obtained by subtracting the reference HcJ in the composition from the HcJ of each sample.
[0141]
[Table 14]

[0142]
From Table 14,
Sr_1-xLa_x(Fe_12-yCo_y)_zO₁₉
It can be seen that by making x greater than y in the magnet composition represented by
[0143]
Example 14
Next, those shown in Table 15 below were selected from the samples prepared in the above examples. Table 15 shows the setting of the low temperature drop region during the production of these samples as slow cooling conditions. The slow cooling condition of Δ5 ° C. means that the temperature lowering rate is 5 ° C./min.
[0144]
The presence or absence of crystallization of the grain boundary triple points and the composition of each sample were examined by a transmission electron microscope (TEM). As for the presence or absence of crystallization, it was judged that crystallization was observed if a lattice point was observed in the electron diffraction image, and it was judged to be amorphous if the lattice point was not found and the shape was halo. The composition was examined by an energy dispersive X-ray spectrometer (TEM-EDS) attached to the TEM. The number of triple points to be analyzed was 10 or more for each sample. The results are shown in Table 15.
[0145]
As a result of the composition analysis, it was found that the triple point composition can be classified into Composition I to Composition VI shown in Table 15. Table 15 shows the ratio of the number of triple points corresponding to each of composition I to composition VI with respect to the triple point to be measured, and the ratio of the crystallized triple points to be measured.
[0146]
[Table 15]

[0147]
From Table 15, the HcJ improvement effect in the present invention was considered. Sample No. 301 having the maximum HcJ has a high ratio of crystallized triple points that are considered to be produced by slow cooling from 900 ° C. Sample No. 102 that was gradually cooled from 1000 ° C. also has a high ratio of crystallized triple points. From the above, it is considered necessary to increase the number of crystallized triple points in order to improve HcJ.
[0148]
FIG. 12 shows a transmission electron micrograph in the vicinity of the triple point and an electron beam diffraction image of the triple point for comparative sample No. 109 manufactured by a conventional method without providing a low temperature drop region. Further, with respect to Sample No. 301 produced by the method of the present invention, a transmission electron micrograph near the triple point and an electron diffraction image of the triple point are shown in FIG. The electron diffraction image of FIG. 12 is halo-shaped, and it can be seen that the triple point of Comparative Sample No. 109 is amorphous. In contrast, the electron diffraction image of FIG. 13 is spot-like, and it can be seen that the triple point of sample No. 301 is crystallized.
[Brief description of the drawings]
FIG. 1 is a graph for explaining a temperature change pattern in a case where a low temperature drop region is provided in a sintering process.
FIG. 2 is a graph for explaining a temperature change pattern in a case where a low temperature drop region and a high temperature drop region are provided in the sintering process.
FIG. 3 is a graph for explaining a temperature change pattern in a conventional sintering process.
FIG. 4 is a graph for explaining a temperature change pattern in a sintering process in an example.
FIG. 5 is a graph for explaining a temperature change pattern in a sintering process in an example.
FIG. 6 is a graph for explaining a temperature change pattern in a sintering process in an example.
FIG. 7 is a graph for explaining a temperature change pattern in a sintering process in an example.
FIG. 8 is a graph for explaining a temperature change pattern in a sintering process in an example.
FIG. 9 is a graph for explaining a temperature change pattern in a sintering process in an example.
FIG. 10 is a graph for explaining a temperature change pattern in a sintering process in an example.
FIG. 11 is a graph for explaining a temperature change pattern in a sintering process in an example.
FIG. 12 is a drawing-substituting photograph showing a crystal structure, wherein a) is a transmission electron micrograph near the triple point of a sintered body produced by a conventional method, and b) is a photograph of the triple point. It is an electron beam diffraction image.
FIG. 13 is a drawing-substituting photograph showing a crystal structure, wherein a) is a transmission electron micrograph near the triple point of a sintered body produced by the method of the present invention, and b) is a photograph of the triple point. It is an electron beam diffraction image.

Claims (3)

A sintering step, and in the temperature lowering process of the sintering step, a low-speed cooling region and a high-speed cooling region on the higher temperature side than the low-speed cooling region are provided,
The low temperature drop region has a temperature drop rate of 0 ° C./min or more and less than 1 ° C./min. The low temperature drop region has a duration of 2 hours or more within a temperature range of 600 to 1000 ° C. and 1000 ° C. 0 to 3 hours in the temperature range exceeding ,
In the hexagonal ferrite, the high-temperature temperature-decreasing region is a region in which a temperature-decreasing rate is 5 ° C / min or more over a temperature range of 50 ° C or more in the temperature range of at least 900 ° C or less and the sintering temperature or less in the temperature-decreasing process . Production method. The method for producing a hexagonal ferrite sintered body according to claim 1 , wherein the temperature lowering rate in the high-speed temperature falling region is 10 ° C./min or more. The hexagonal ferrite sintered body is Fe, element A (A is at least one selected from Sr, Ba, Ca and Pb), element R (R is at least one selected from rare earth elements and Bi). species) and elemental M (M is, Co, Mn, and containing at least one) selected from Ni and Zn, claim 1 or 2 is a sintered magnet having a hexagonal magnetoplumbite ferrite as a main phase A method for producing a hexagonal ferrite sintered body according to any of the above.

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