JP2008063201A - epsi-IRON OXIDE POWDER HAVING IMPROVED MAGNETIC PROPERTY - Google Patents
epsi-IRON OXIDE POWDER HAVING IMPROVED MAGNETIC PROPERTY Download PDFInfo
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本発明はε−Ｆｅ2Ｏ3系の磁性粉末に関する。 The present invention relates to an ε-Fe 2 O 3 based magnetic powder.
磁気記録の分野では低ノイズ化を図りながら記録密度を高めることが要求されている。そのために、磁気記録媒体の側では、媒体の保磁力Ｈｃをできるだけ大きくすること、そして媒体を構成する磁性粒子の微細化を図りながら磁気的分離化を促進することが肝要となる。さらには、磁性粒子が微細化しても記録状態が安定に保持されることも重要視される。 In the field of magnetic recording, it is required to increase recording density while reducing noise. Therefore, on the magnetic recording medium side, it is important to increase the coercive force Hc of the medium as much as possible and promote magnetic separation while miniaturizing the magnetic particles constituting the medium. Furthermore, it is important to keep the recording state stable even when the magnetic particles are miniaturized.
例えば、記録ビットを構成する磁気的に結合した磁気集合体の最小単位の磁気的エネルギー（ＫU×Ｖ）が、記録を乱そうとする熱エネルギー（ｋB×Ｔ）を大きく上回ることが挙げられる。ここで、ＫUは磁気異方性エネルギー定数、Ｖは磁気クラスター体積、ｋBはボルツマン定数、Ｔは絶対温度である。記録状態が安定に保持される指標として（ＫU×Ｖ）／（ｋB×Ｔ）を用い、この比がほぼ６０以上（〜１０年耐用）になることが一般的な目標とされている。このことは、一層の高記録密度化を図るためには、磁気クラスター体積Ｖを下げ、磁気異方性定数ＫUを上げざるを得ない状況にあると言える。ＫUについては、ＫU∝Ｈｃ（Ｈｃは保磁力）の関係にあるため、言い換えると、高記録密度の磁気記録媒体を目指すほど、高いＨｃを有する磁性材料が必要になる。 For example, the magnetic energy (K U × V) of the minimum unit of the magnetically coupled magnetic aggregate constituting the recording bit greatly exceeds the thermal energy (k B × T) that tries to disturb the recording. It is done. Here, K U is the magnetic anisotropy energy constant, V is the magnetic cluster volume, k B is the Boltzmann constant, and T is the absolute temperature. Using (K U × V) / (k B × T) as an index for stably maintaining the recording state, it is a general goal that this ratio is approximately 60 or more (10-year service life). . This is in order to further increase the recording density lowers the magnetic cluster volume V, it can be said that the situation inevitably raise the magnetic anisotropy constant K U. Since K U has a relationship of K U ∝Hc (Hc is a coercive force), in other words, a magnetic material having a higher Hc is required as a magnetic recording medium with a higher recording density is aimed.
また、（ＫU×Ｖ）／（ｋB×Ｔ）の値が１００以下の場合でも記録磁化が時間の経過につれて減少する事例も報告されており、このことは、低ノイズ化のためには磁気クラスター体積Ｖを下げる要求が強くなるほど、高い磁気異方性定数ＫUを持たねばならないことを意味する。したがって、低ノイズ化の観点からも、高記録密度の磁気記録媒体を目指すほど、高いＨｃを有する磁性材料が必要になる。 In addition, even when the value of (K U × V) / (k B × T) is 100 or less, there has been reported an example in which the recording magnetization decreases with the passage of time. as the request to reduce the magnetic cluster volume V becomes stronger, which means that must have a high magnetic anisotropy constant K U. Therefore, from the viewpoint of reducing noise, a magnetic material having a high Hc is required as a magnetic recording medium having a higher recording density is aimed.
非特許文献１〜３に示されるように、最近、ナノオーダーの粒子サイズで室温において２０ｋＯｅという巨大なＨｃを示すε−Ｆｅ2Ｏ3の存在が確認されている。Ｆｅ2Ｏ3の組成を有しながら結晶構造が異なる多形には最も普遍的なものとしてα−Ｆｅ2Ｏ3およびγ−Ｆｅ2Ｏ3があるが、ε−Ｆｅ2Ｏ3もその一つである。しかし、ε−Ｆｅ2Ｏ3の結晶構造と磁気的性質が明らかにされたのは、非特許文献１〜３に見られるように、ε−Ｆｅ2Ｏ3結晶をほぼ単相の状態で合成できるようになったごく最近のことである。このε−Ｆｅ2Ｏ3は巨大なＨｃを示すことから、前記のような高記録密度の磁気記録媒体への適用が期待される。 As shown in Non-Patent Documents 1 to 3, recently, existence of ε-Fe 2 O 3 exhibiting a huge Hc of 20 kOe at room temperature with a nano-order particle size has been confirmed. Α-Fe 2 O 3 and γ-Fe 2 O 3 are the most universal polymorphs having a composition of Fe 2 O 3 but different crystal structures, and ε-Fe 2 O 3 is one of them. One. However, the crystal structure and magnetic properties of ε-Fe 2 O 3 were clarified because, as seen in Non-Patent Documents 1 to 3, ε-Fe 2 O 3 crystals were synthesized in a substantially single-phase state. This is only recently. Since this ε-Fe 2 O 3 shows huge Hc, it is expected to be applied to a magnetic recording medium having a high recording density as described above.
非常に高いＨｃをもった磁性材料を記録媒体として実用化するためには、その記録媒体に実際に情報を書き込める記録磁場を発生する磁気ヘッドが必要である。磁気ヘッドの発生磁場は、一般的には、そこに使用される軟磁性膜の飽和磁束密度に比例するともいわれる。現在、１.５〜４.５ｋＯｅ（１.１９×１０5〜３.５８×１０5Ａ／ｍ）程度のＨｃをもつハードディスクが報告されているが、このようなハードディスクに情報を記録するための磁気ヘッドには、２.４Ｔといった高い飽和磁束密度をもつ材料が使用されている。 In order to put a magnetic material having a very high Hc into practical use as a recording medium, a magnetic head that generates a recording magnetic field capable of actually writing information on the recording medium is required. The magnetic field generated by the magnetic head is generally said to be proportional to the saturation magnetic flux density of the soft magnetic film used there. Currently, hard disks having Hc of about 1.5 to 4.5 kOe (1.19 × 10 5 to 3.58 × 10 5 A / m) have been reported. In order to record information on such hard disks. In the magnetic head, a material having a high saturation magnetic flux density of 2.4 T is used.
非特許文献１〜３に見られるように、２０ｋＯｅ（１.５９×１０6Ａ／ｍ）レベルの巨大なＨｃを持つε−Ｆｅ2Ｏ3の場合は、これを磁気記録媒体の磁気記録材料に用いても、現状よりもさらに高い飽和磁束密度をもつ材料が存在しないと、情報を記録することができない。すなわち、現状レベルの磁気ヘッド材料では磁気記録ができない。 As seen in Non-Patent Documents 1 to 3 , in the case of ε-Fe 2 O 3 having a huge Hc of 20 kOe (1.59 × 10 6 A / m) level, this is used as a magnetic recording material of a magnetic recording medium. However, information cannot be recorded unless there is a material having a higher saturation magnetic flux density than the current state. That is, magnetic recording cannot be performed with the current level of magnetic head material.
発明者らは詳細な検討の結果、ε−Ｆｅ2Ｏ3結晶のＦｅサイトの一部を、３価の金属元素Ｍで置換したとき、その置換量に応じて保磁力Ｈｃを低下させることができる場合があることを見出した。金属元素Ｍは例えばＡｌ、Ｇａ、Ｉｎなどである。このような置換手法を用いて保磁力Ｈｃをコントロールすることにより、磁気ヘッド等で磁気記録が可能な範囲内で非常に高いＨｃを呈する磁性粉末が構築でき、種々の用途で実用化が期待される。 As a result of detailed studies, the inventors have found that when a part of the Fe site of the ε-Fe 2 O 3 crystal is substituted with the trivalent metal element M, the coercive force Hc can be reduced according to the amount of substitution. I found out that I could do it. The metal element M is, for example, Al, Ga, In or the like. By controlling the coercive force Hc using such a replacement method, a magnetic powder exhibiting extremely high Hc can be constructed within a range where magnetic recording can be performed with a magnetic head or the like, and it is expected to be put to practical use in various applications. The
しかしながら、磁性粉末を実際に磁気記録媒体や電波吸収体などの磁性材料として利用するためには、［１］角形比ＳＱが高く、かつＳＦＤ（ｓｗｉｔｃｈiｎｇ ｆｉｅｌｄ ｄｉｓｔｒｉｂｕｔｉｏｎ）が小さいなど、総合的に優れた磁気特性を有することが要求され、また［２］高分子基材中への充填性が良好であることが要求される。さらに［３］液中や高分子基材中への粉末粒子の分散性が良好であることも重要である。磁場配向等の操作によって磁気記録媒体や電波吸収体の性能向上を図る際には、分散性と充填性の両方が良好であることが必須要件となる。 However, in order to actually use the magnetic powder as a magnetic material such as a magnetic recording medium or a radio wave absorber, [1] the square ratio SQ is high and the SFD (switching field distribution) is small. It is required to have magnetic properties, and [2] a good filling property in the polymer base material is required. [3] It is also important that the dispersibility of the powder particles in the liquid or the polymer base material is good. In order to improve the performance of the magnetic recording medium and the radio wave absorber by operations such as magnetic field orientation, it is essential that both the dispersibility and the filling property are good.
非特許文献１〜３に示されるように、ε−Ｆｅ2Ｏ3結晶は、逆ミセル法とゾル−ゲル法を組み合わせたプロセスにより合成することができる。しかし、そのようにして合成されたε−Ｆｅ2Ｏ3結晶の粉末は、必ずしも安定して総合的に優れた磁気特性を有するとは限らず、また、高分子基材中への充填性や、液中あるいは高分子基材中への分散性についても更なる改善が望まれる。そこで本発明は、上記の合成プロセスを利用して製造できる粉末であって、総合的な磁気特性が改善され、あるいはさらに高分子基材中への充填性や、液中や高分子基材中への分散性が改善されたε−Ｆｅ2Ｏ3結晶の粉末を提供することを目的とする。 As shown in Non-Patent Documents 1 to 3, the ε-Fe 2 O 3 crystal can be synthesized by a process combining a reverse micelle method and a sol-gel method. However, the powder of ε-Fe 2 O 3 crystal synthesized in such a manner does not always have stable and excellent magnetic properties, and the filling property into the polymer base material is not limited. Further improvement in the dispersibility in the liquid or the polymer substrate is desired. Therefore, the present invention is a powder that can be produced by using the above-described synthesis process, and has improved overall magnetic properties, or further, can be filled into a polymer base material, in a liquid or in a polymer base material. An object of the present invention is to provide a powder of ε-Fe 2 O 3 crystals having improved dispersibility.
上記目的を達成するために、本発明では、ε−Ｆｅ2Ｏ3結晶（Ｆｅサイトの一部が金属元素Ｍで置換されたものを含む）を主相とする鉄酸化物の粒子からなり、ＴＥＭ写真により測定される粒子径において、平均粒子径が１０〜２００ｎｍ、かつ、粒子径１０ｎｍ未満の粒子の個数割合が２５％以下好ましくは８％以下である磁性粉末が提供される。なかでも充填性の良好な粉末として、さらに［粒子径の標準偏差］／［平均粒子径］×１００で表される変動係数が５０％以下好ましくは４０％以下であるように粒度調整されているものが提供される。前記のＭは、例えばＡｌ、Ｇａ、Ｉｎの１種以上からなる。
ただし、上記鉄酸化物におけるＭとＦｅのモル比をＭ：Ｆｅ＝ｘ：（２−ｘ）と表すとき、０≦ｘ＜１である。
In order to achieve the above object, the present invention comprises iron oxide particles whose main phase is an ε-Fe 2 O 3 crystal (including one in which a part of Fe site is substituted with a metal element M), A magnetic powder having an average particle diameter of 10 to 200 nm and a number ratio of particles having a particle diameter of less than 10 nm in a particle diameter measured by a TEM photograph is 25% or less, preferably 8% or less. Among them, as a powder having good filling properties, the particle size is adjusted so that the coefficient of variation represented by [standard deviation of particle diameter] / [average particle diameter] × 100 is 50% or less, preferably 40% or less. Things are provided. Said M consists of 1 or more types, for example, Al, Ga, and In.
However, when the molar ratio of M to Fe in the iron oxide is expressed as M: Fe = x: (2-x), 0 ≦ x <1.
上記の「鉄酸化物」は、この磁性粉末の粒子において、(i)α−Ｆｅ2Ｏ3と空間群が同じである結晶、(ii)γ−Ｆｅ2Ｏ3と空間群が同じである結晶、(iii)ε−Ｆｅ2Ｏ3と空間群が同じである結晶、(iv)Ｆｅ3Ｏ4と空間群が同じである結晶、および(v)ＦｅＯと空間群が同じである結晶のうち、１種以上で構成される部分である。「主相」とは、上記(i)〜(v)の各結晶のうち、鉄酸化物全体に占めるモル比が５０モル％以上である結晶を意味する。これら各結晶のモル比は、Ｘ線回折に基づくリードベルト法による解析で見積もることができる。 In the above-mentioned “iron oxide”, in this magnetic powder particle, (i) a crystal having the same space group as α-Fe 2 O 3 and (ii) a space group being the same as γ-Fe 2 O 3 (Iii) a crystal having the same space group as ε-Fe 2 O 3 , (iv) a crystal having the same space group as Fe 3 O 4 , and (v) a crystal having the same space group as FeO. Among these, it is a part comprised by 1 or more types. The “main phase” means a crystal having a molar ratio of 50 mol% or more to the whole iron oxide among the crystals of the above (i) to (v). The molar ratio of each of these crystals can be estimated by analysis by a lead belt method based on X-ray diffraction.
本発明の磁性粉末では、この主相はε−Ｆｅ2Ｏ3結晶である。ただし、本明細書でいう「ε−Ｆｅ2Ｏ3結晶」には、特に断らない限り、Ｆｅサイトが他の元素で置換されていない純粋なε−Ｆｅ2Ｏ3結晶の他、Ｆｅサイトの一部が３価の金属元素Ｍで置換されており、前記純粋なε−Ｆｅ2Ｏ3結晶と空間群が同じである（すなわち空間群がＰｎａ２1である）結晶が含まれる。 In the magnetic powder of the present invention, this main phase is ε-Fe 2 O 3 crystal. However, “ε-Fe 2 O 3 crystal” as used in this specification includes, unless otherwise specified, a pure ε-Fe 2 O 3 crystal in which the Fe site is not substituted with other elements, A crystal partially including a trivalent metal element M and having the same space group as the pure ε-Fe 2 O 3 crystal (that is, the space group is Pna2 1 ) is included.
また本発明では特に、分散性の良好な粉末として、前記鉄酸化物の粒子の表面にＳｉ酸化物が存在している、鉄酸化物とＳｉ酸化物の複合粒子からなり、Ｓｉ／（Ｆｅ＋Ｍ）×１００で表されるＳｉ含有量が０.１〜３０モル％に調整されている粉末が提供される。このＳｉ酸化物は、ＳｉＯ2を主体とするシリカ成分であると考えられるが、その形態は必ずしも結晶質とは限らず、ブロードなＸ線回折ピークを呈するアモルファス状のものであって構わない。存在量が少ないときはブロードなＸ線回折ピークも検出されない場合もある。またこの磁性粉末として、単磁区構造の磁性粒子で構成されるものが提供される。 Further, in the present invention, as a powder having good dispersibility, it is composed of a composite particle of iron oxide and Si oxide, in which Si oxide is present on the surface of the iron oxide particle, and Si / (Fe + M) A powder in which the Si content represented by x100 is adjusted to 0.1 to 30 mol% is provided. This Si oxide is considered to be a silica component mainly composed of SiO 2 , but the form is not necessarily crystalline, and may be an amorphous one exhibiting a broad X-ray diffraction peak. When the abundance is small, a broad X-ray diffraction peak may not be detected. Further, as the magnetic powder, a powder composed of magnetic particles having a single magnetic domain structure is provided.
本発明の磁性粉末の磁気特性として、保磁力Ｈｃが１０００〜１５０００ Ｏｅ（７.９６×１０4〜１.１９×１０6Ａ／ｍ）であり、かつＳＦＤ（ｓｗｉｔｃｈiｎｇ ｆｉｅｌｄ ｄｉｓｔｒｉｂｕｔｉｏｎ）が０.８０以下好ましくは０.５５以下であるものが好適な対象となる。 As magnetic characteristics of the magnetic powder of the present invention, the coercive force Hc is 1000 to 15000 Oe (7.96 × 10 4 to 1.19 × 10 6 A / m), and SFD (switching field distribution) is 0.80. A preferable target is below 0.55 or less.
ＴＥＭ（透過型電子顕微鏡）写真からの平均粒子径の計測は、６０万倍に拡大したＴＥＭ写真画像から各粒子の最も大きな径（ロッド状のものでは長軸径）を測定することにより求めることができる。独立した粒子３００個について求めた粒子径の平均値を、その粉末の平均粒子径とする。以下、これを「ＴＥＭ平均粒子径」ということがある。粒子径の標準偏差は、測定した各粒子の粒子径をマイクロソフト社の表計算ソフト「エクセル」に組み込まれているＳＴＤＥＶ関数を使って算出することができる。 Measurement of the average particle diameter from a TEM (transmission electron microscope) photograph is obtained by measuring the largest diameter of each particle (major axis diameter in the case of a rod-shaped one) from a TEM photograph image magnified 600,000 times. Can do. Let the average value of the particle diameter calculated | required about 300 independent particle | grains be the average particle diameter of the powder. Hereinafter, this may be referred to as “TEM average particle diameter”. The standard deviation of the particle diameter can be calculated by using the STDEV function incorporated in the spreadsheet software “Excel” of Microsoft Corporation for the measured particle diameter of each particle.
（１）この磁性粉末は常温付近で非常に高い保磁力Ｈｃが得られるので、磁気記録媒体の信頼性向上に寄与できる。また、その保磁力は添加元素Ｍの含有量によってコントロールできるので、保磁力が高すぎるためにε−Ｆｅ2Ｏ3が使えなかった磁性用途においても、使用可能な範囲において、できるだけ高い保磁力を有する磁性材料の提供が可能となる。
（２）この磁性粉末は、鉄が３価まで酸化された鉄酸化物の粒子からなるので、従来のメタル系磁性粉末と比べ、大気環境での耐食性が極めて良好である。
（３）この磁性粉末は、粒子径が極めて小さい「超常磁性」の粒子の存在割合が少なくなるように粒度調整されているので、角形比ＳＱが改善された良好な磁気特性が得られる。また、特に粒子径が狭い範囲に揃ったシャープな粒度分布の磁性粉末が提供され、高分子基材中などへの充填性が向上することにより、ε−Ｆｅ2Ｏ3結晶に特有の高保磁力特性や電波吸収特性の顕著な発揮が期待される。
（４）粒子表面に適量のＳｉ酸化物を有するものでは、液中や高分子基材中における粉末粒子の分散性が改善され、特に高分子基材中での磁場配向による顕著な特性向上効果が期待される。
(1) Since this magnetic powder has a very high coercive force Hc near room temperature, it can contribute to the improvement of the reliability of the magnetic recording medium. In addition, since the coercive force can be controlled by the content of the additive element M, even in magnetic applications where ε-Fe 2 O 3 cannot be used because the coercive force is too high, the coercive force is as high as possible within the usable range. It is possible to provide a magnetic material having the same.
(2) Since this magnetic powder consists of iron oxide particles in which iron is oxidized to trivalent, the corrosion resistance in the air environment is extremely good as compared with the conventional metal-based magnetic powder.
(3) Since this magnetic powder is adjusted in particle size so that the existence ratio of “superparamagnetic” particles having a very small particle diameter is reduced, good magnetic characteristics with improved squareness ratio SQ can be obtained. In addition, a magnetic powder having a sharp particle size distribution with a particularly narrow particle size is provided, and the high coercivity unique to the ε-Fe 2 O 3 crystal is improved by improving the filling property in a polymer base material. It is expected that the characteristics and radio wave absorption characteristics will be remarkably exhibited.
(4) In the case of having an appropriate amount of Si oxide on the particle surface, the dispersibility of the powder particles in the liquid or in the polymer base material is improved. There is expected.
非特許文献１〜３に記載されるように、逆ミセル法とゾル−ゲル法を組み合わせた工程と、熱処理（焼成）工程により、ε−Ｆｅ2Ｏ3ナノ微粒子を合成することができ、本発明でもこの合成プロセスを利用することができる。逆ミセル法は、界面活性剤を含んだ２種類のミセル溶液、すなわちミセル溶液Ｉ（原料ミセル）とミセル溶液II（中和剤ミセル）を混合することによって、ミセル内で水酸化鉄の沈殿反応を進行させることを要旨とする。ゾル−ゲル法は、ミセル内で生成した水酸化鉄微粒子の表面にシリカコーティングを施すことを要旨とする。表面がシリカで覆われた水酸化鉄微粒子は、液から分離されたあと、所定の温度（７００〜１３００℃の範囲内）で大気雰囲気下での熱処理に供される。この熱処理によりε−Ｆｅ2Ｏ3結晶が合成される。この結晶を主相とする鉄酸化物の粉末に対して、例えば分級操作を施す手法を利用して粒度分布を調整することによって、本発明の磁性粉末を得ることができる。 As described in Non-Patent Documents 1 to 3, ε-Fe 2 O 3 nanoparticles can be synthesized by a process combining a reverse micelle method and a sol-gel method and a heat treatment (firing) step. This synthesis process can also be used in the invention. In the reverse micelle method, two types of micelle solution containing a surfactant, ie, micelle solution I (raw material micelle) and micelle solution II (neutralizer micelle) are mixed to precipitate iron hydroxide in the micelle. The gist of this is to proceed. The gist of the sol-gel method is to apply a silica coating to the surface of the iron hydroxide fine particles generated in the micelle. The iron hydroxide fine particles whose surface is covered with silica are separated from the liquid and then subjected to a heat treatment in an air atmosphere at a predetermined temperature (in the range of 700 to 1300 ° C.). By this heat treatment, ε-Fe 2 O 3 crystals are synthesized. The magnetic powder of the present invention can be obtained by adjusting the particle size distribution using, for example, a classification operation for the iron oxide powder containing the crystal as a main phase.
より具体的には、例えば以下のようにする。
ｎ−オクタンを油相とするミセル溶液Ｉの水相には、鉄源としての硝酸鉄（III）、鉄の一部を金属元素Ｍで置換させる場合はＭ源としてのＭ硝酸塩（例えばＡｌの場合、硝酸アルミニウム（III）９水和物、Ｇａの場合、硝酸ガリウム（III）ｎ水和物、Ｉｎの場合、硝酸インジウム（III）３水和物）、および界面活性剤（例えば臭化セチルトリメチルアンモニウム）を溶かし、同じくｎ−オクタンを油相とするミセル溶液IIの水相にはアンモニア水溶液を用いる。その際、ミセル溶液Ｉの水相に適量のアルカリ土類金属（Ｂａ、Ｓｒ、Ｃａなど）の硝酸塩を溶解させておくことができる。これらアルカリ土類金属の硝酸塩は形状制御剤として機能する。すなわち、アルカリ土類金属が液中に存在すると最終的にロッド形状のε−Ｆｅ2Ｏ3結晶を得ることができる。形状制御剤がない場合は、粒状のε−Ｆｅ2Ｏ3結晶を得ることができる。
More specifically, for example, the following is performed.
In the aqueous phase of the micelle solution I having n-octane as the oil phase, iron nitrate (III) as an iron source is used. When a part of iron is replaced with the metal element M, M nitrate (for example, Al Aluminum nitrate (III) 9 hydrate, Ga, gallium nitrate (III) n hydrate, In, indium nitrate (III) trihydrate), and surfactants (eg cetyl bromide) An aqueous ammonia solution is used for the aqueous phase of micelle solution II in which trimethylammonium) is dissolved and n-octane is used as the oil phase. At that time, an appropriate amount of alkaline earth metal (Ba, Sr, Ca, etc.) nitrate can be dissolved in the aqueous phase of the micelle solution I. These alkaline earth metal nitrates function as shape control agents. That is, when alkaline earth metal is present in the liquid, a rod-shaped ε-Fe 2 O 3 crystal can be finally obtained. When there is no shape control agent, granular ε-Fe 2 O 3 crystals can be obtained.
両ミセル溶液ＩとIIを合体させたあと、ゾル−ゲル法を併用する。すなわち、シラン（例えばテトラエトキシシラン、テトラメトキシシラン）を合体液に滴下しながら攪拌を続け、ミセル内で水酸化鉄の生成反応を進行させる。これにより、ミセル内で生成する微細な水酸化鉄沈殿の粒子表面にはシランの加水分解によって生成したシリカがコーティングされる。次いで、シリカコーティングされた水酸化鉄粒子を液から分離・洗浄・乾燥して得た粒子粉体を炉内に装入し、空気中で７００〜１３００℃、好ましくは９００〜１２００℃、さらに好ましくは９５０〜１１５０℃の温度範囲で熱処理（焼成）する。この熱処理によりシリカコート内で酸化反応が進行して、微細な水酸化鉄粒子は微細なε−Ｆｅ2Ｏ3粒子に変化する。この酸化反応の際に、シリカコートの存在がα−Ｆｅ2Ｏ3やγ−Ｆｅ2Ｏ3の結晶ではなく、ε−Ｆｅ2Ｏ3結晶の生成に寄与すると共に、粒子同士の焼結を防止する作用を果たす。 After combining both micelle solutions I and II, the sol-gel method is used in combination. That is, stirring is continued while dripping silane (for example, tetraethoxysilane, tetramethoxysilane) into the combined liquid, and the reaction of producing iron hydroxide proceeds in the micelle. As a result, the surface of fine particles of iron hydroxide produced in the micelle is coated with silica produced by hydrolysis of silane. Next, the particle powder obtained by separating, washing, and drying the silica-coated iron hydroxide particles from the liquid is charged into a furnace, and 700 to 1300 ° C, preferably 900 to 1200 ° C, more preferably in air. Is heat-treated (fired) in a temperature range of 950 to 1150 ° C. By this heat treatment, an oxidation reaction proceeds in the silica coat, and the fine iron hydroxide particles are changed to fine ε-Fe 2 O 3 particles. During this oxidation reaction, the presence of the silica coat contributes to the formation of ε-Fe 2 O 3 crystals, not α-Fe 2 O 3 or γ-Fe 2 O 3 crystals, and the particles are sintered together. Acts to prevent.
熱処理（焼成）前の段階で、シリカコートの量は、原料中に含まれるＳｉ含有量がＳｉ／（Ｆｅ＋Ｍ）×１００で表されるモル比で５０〜１０００モル％の範囲とすることができる。平均粒子径を小さくする場合ほどシリカコートの量を多くすることが望ましい。シリカコートの量が上記のモル比で５０モル％未満の量だと、粒子の焼結による粗大化が顕著になり、またα−Ｆｅ2Ｏ3結晶が生成しやすくなるので好ましくない。例えば、磁気記録に適した粒子径が１００ｎｍ以下の焼結の少ない磁性粉末を得るためには上記Ｓｉ含有量が１００モル％以上のシリカコートを施すことが好ましい。一方、１０００モル％を超えて過剰にシリカコートを施しても、粒子径は顕著には変化しないため、経済的に好ましくない。 In the stage before the heat treatment (firing), the amount of the silica coat can be in the range of 50 to 1000 mol% in terms of the molar ratio expressed by Si / (Fe + M) × 100 in the Si content contained in the raw material. . It is desirable to increase the amount of silica coat as the average particle size is reduced. When the amount of the silica coat is less than 50 mol% in the above molar ratio, coarsening due to sintering of the particles becomes remarkable and α-Fe 2 O 3 crystals are easily formed, which is not preferable. For example, in order to obtain a magnetic powder having a particle size of 100 nm or less suitable for magnetic recording and having little sintering, it is preferable to apply a silica coat having a Si content of 100 mol% or more. On the other hand, an excessive silica coating exceeding 1000 mol% is not economically preferable because the particle diameter does not change significantly.
熱処理（焼成）によって合成されるε−Ｆｅ2Ｏ3結晶を主相とする鉄酸化物粒子の粒子径は、熱処理（焼成）前の段階におけるシリカコートの量、焼成温度、焼成時間を調整することによりコントロール可能である。一般にシリカコートの量を多くすると平均粒子径は小さくなる。また、焼成温度を低くすると比較的小径側に狭い粒度分布を持つ粉末が得られやすい。しかしこの場合、結晶化が不十分となったり、超常磁性を示す極微細粒子の存在割合が多くなったりして磁気特性の低下を招きやすい。一方、焼成温度を高くすると粒子径のバラツキが大きいブロードな粒度分布の粉末が得られやすい。この場合、粒子の充填度が高い磁気記録媒体や電波吸収体を構築することが難しくなる。また、効果的な磁場配向を行うことが難しくなる。 The particle diameter of the iron oxide particles mainly composed of ε-Fe 2 O 3 crystals synthesized by heat treatment (firing) adjusts the amount of silica coat, the firing temperature, and the firing time before the heat treatment (firing). Can be controlled. In general, when the amount of silica coat is increased, the average particle size is decreased. Further, when the firing temperature is lowered, a powder having a narrow particle size distribution on the relatively small diameter side is easily obtained. However, in this case, crystallization is insufficient, or the presence ratio of ultrafine particles exhibiting superparamagnetism is increased, which tends to cause a decrease in magnetic properties. On the other hand, when the firing temperature is increased, a powder having a broad particle size distribution with a large variation in particle diameter is easily obtained. In this case, it becomes difficult to construct a magnetic recording medium or a radio wave absorber having a high degree of particle filling. In addition, it is difficult to perform effective magnetic field orientation.
このように、焼成時の粒子径コントロールだけでは、所望の粒度分布にコントロールすることは極めて困難である。そこで、上記のプロセスを利用してε−Ｆｅ2Ｏ3結晶を合成する場合、粒度分布をコントロールするには「分級」の操作を行うことが有効となる。ただし、分級を効率的に行うためには、粉末粒子が液中に十分に分散していることが重要である。したがって、分級に先立って、分散性を改善する処理を行うことが望ましい。 Thus, it is extremely difficult to control to a desired particle size distribution only by controlling the particle size during firing. Therefore, when the ε-Fe 2 O 3 crystal is synthesized using the above process, it is effective to perform a “classification” operation in order to control the particle size distribution. However, in order to perform classification efficiently, it is important that the powder particles are sufficiently dispersed in the liquid. Therefore, it is desirable to perform a process for improving dispersibility prior to classification.
分散性を改善する処理としては、上記のようにゾル−ゲル工程でシリカコーティングを施す場合には、熱処理（焼成）後に、そのシリカコートの大部分を除去し、適量のＳｉ酸化物が鉄酸化物粒子の表面に存在するようにコントロールすることが有効である。シリカコートの除去は、ＮａＯＨやＫＯＨなどの強アルカリを溶解させた水溶液中に、熱処理後の磁性粉末を入れて、撹拌することにより実施できる。溶解速度を上げる場合は、アルカリ溶液を加温するとよい。代表的には、ＮａＯＨなどのアルカリをシリカ分に対して、３モル倍以上添加し、水溶液温度が６０〜７０℃の状態で、磁性粉末を入れ撹拌すると、シリカを良好に溶解することができる。ただし、粒子表面に存在するＳｉ酸化物の量をＳｉ／（Ｆｅ＋Ｍ）×１００で表されるＳｉ含有量が０.１〜３０モル％になるように調整するためには、後述実施例に示す〔手順６−２〕のようにして、再溶解処理を実施することが極めて有効である。アルカリとしては、ＮａＯＨに限らず、ＮＨ3や、場合によってはＮ（ＣＨ3）4ＯＨのような有機アルカリの水溶液を用いても構わない。 As a treatment for improving dispersibility, when silica coating is applied in the sol-gel process as described above, most of the silica coat is removed after heat treatment (firing), and an appropriate amount of Si oxide is oxidized by iron. It is effective to control it so that it exists on the surface of the object particle. The removal of the silica coat can be carried out by putting the magnetic powder after the heat treatment in an aqueous solution in which a strong alkali such as NaOH or KOH is dissolved and stirring. In order to increase the dissolution rate, the alkaline solution may be heated. Typically, when alkali such as NaOH is added 3 mol times or more with respect to the silica content, and the magnetic powder is added and stirred while the aqueous solution temperature is 60 to 70 ° C., the silica can be dissolved well. . However, in order to adjust the amount of Si oxide present on the particle surface so that the Si content represented by Si / (Fe + M) × 100 is 0.1 to 30 mol%, it will be described in the examples below. It is extremely effective to perform the re-dissolution treatment as in [Procedure 6-2]. The alkali is not limited to NaOH, and an aqueous solution of organic alkali such as NH 3 or, in some cases, N (CH 3 ) 4 OH may be used.
このようなシリカコートの除去手法を用いて、Ｓｉ／（Ｆｅ＋Ｍ）×１００で表されるＳｉ含有量が０.１〜３０モル％になるように磁性粒子表面のＳｉ酸化物の量をコントロールすることにより、分級に適した分散性の良い粉末が得られる。磁性粒子表面のＳｉ酸化物はＳｉＯ2として存在していると考えられるが、前述のようにＸ線回折ピークがブロードなアモルファス状の状態として存在していて構わない。ＳｉＯ2は、水中では等電点がｐＨ２前後にあり、そのため、ｐＨ３以上の広いｐＨ範囲において水中での高い分散性を示す。シリカコートの除去試験を進めるうちに、Ｓｉ／（Ｆｅ＋Ｍ）×１００によるＳｉ含有量が０.１モル％を下回ると、液中での分散性の低下が観測された。この場合、Ｓｉ酸化物は鉄酸化物粒子の表面に島状に存在しているものと考えられる。このため、シリカコートを完全に除去してしまうのではなく、上式によるＳｉ含有量が０.１モル％以上になるようにＳｉ酸化物を残す。 Using such a silica coat removal method, the amount of Si oxide on the surface of the magnetic particles is controlled so that the Si content represented by Si / (Fe + M) × 100 is 0.1 to 30 mol%. Thus, a powder with good dispersibility suitable for classification can be obtained. Although it is considered that the Si oxide on the surface of the magnetic particles exists as SiO 2, as described above, the X-ray diffraction peak may exist in a broad amorphous state. SiO 2 has an isoelectric point around pH 2 in water, and therefore exhibits high dispersibility in water in a wide pH range of pH 3 or higher. As the silica coating removal test proceeded, when the Si content by Si / (Fe + M) × 100 was less than 0.1 mol%, a decrease in dispersibility in the liquid was observed. In this case, it is considered that the Si oxide exists in an island shape on the surface of the iron oxide particles. For this reason, the silica coat is not completely removed, but the Si oxide is left so that the Si content according to the above formula becomes 0.1 mol% or more.
Ｓｉ／（Ｆｅ＋Ｍ）×１００によるＳｉ含有量が０.１モル％未満の場合、Ｓｉ酸化物は鉄酸化物粒子の表面に島状に存在しているものと考えられる。ところが、０.１モル％以上の範囲では、鉄酸化物の粒子表面がほぼ完全にＳｉ酸化物で覆われた状態になると推測され、液中での分散性が顕著に改善される。Ｓｉ／（Ｆｅ＋Ｍ）×１００によるＳｉ含有量が０.５モル％以上となるようにＳｉ酸化物を存在させることがより好ましく、１モル％以上とすることが一層好ましい。 When the Si content by Si / (Fe + M) × 100 is less than 0.1 mol%, the Si oxide is considered to be present in the form of islands on the surface of the iron oxide particles. However, in the range of 0.1 mol% or more, it is presumed that the iron oxide particle surface is almost completely covered with Si oxide, and the dispersibility in the liquid is remarkably improved. The Si oxide is more preferably present such that the Si content by Si / (Fe + M) × 100 is 0.5 mol% or more, and more preferably 1 mol% or more.
一方、鉄酸化物粒子の表面に存在するＳｉ酸化物の量が過剰に多いと、Ｓｉ酸化物同士が、磁性粒子同士を架橋するようになり、激しい場合は、Ｓｉ酸化物中に磁性粒子が、分散しているような構造体となる。こうなると、分級は極めて困難となる。種々検討の結果、Ｓｉ／（Ｆｅ＋Ｍ）×１００によるＳｉ含有量が３０モル％以下の範囲になるようにＳｉ酸化物の付着量をコントロールする必要がある。２０モル％以下の範囲とすることがより好ましく、１０モル％以下が一層好ましく、５モル％以下がさらに一層好ましい。 On the other hand, if the amount of the Si oxide present on the surface of the iron oxide particles is excessively large, the Si oxides crosslink the magnetic particles, and if severe, the magnetic particles are contained in the Si oxide. It becomes a structure that is dispersed. If this happens, classification becomes extremely difficult. As a result of various studies, it is necessary to control the amount of Si oxide deposited so that the Si content by Si / (Fe + M) × 100 is within a range of 30 mol% or less. More preferably, it is within the range of 20 mol% or less, more preferably 10 mol% or less, and even more preferably 5 mol% or less.
磁性粒子の表面コーティング物質は、シリカに限らず、化学的に安定で、融点の高い物質であり、かつ磁性粒子を溶解させずに除去可能な物質であれば、ゾル−ゲル工程を利用して種々のものが使用できると考えられる。例えば、低温で合成されるアルミナは、シリカと同様にアルカリにより容易に除去できるため、好ましい。また、カルシアやマグネシアも、弱酸で容易に溶解できるため、磁性粒子の溶解を最小限にとどめ溶解させることが可能であり、使用できると考えられる。 The surface coating material for magnetic particles is not limited to silica, but is a chemically stable, high melting point material that can be removed without dissolving the magnetic particles. It is thought that various things can be used. For example, alumina synthesized at a low temperature is preferable because it can be easily removed by alkali like silica. In addition, calcia and magnesia can be easily dissolved with a weak acid, so that the dissolution of magnetic particles can be minimized and used.
分級の操作は、粒子径による液中での沈降速度の違いを利用した一般的な手法を利用して実施できる。具体的には、例えば上記のように液中での分散性を改善する処理を施すなどして、分散性の良好な磁性粉末を用意する。ただし、液中のイオン強度が高い場合は粒子同士の静電的反発力が損なわれるため分散状態が作りにくい。この場合は、適切な方法で上記磁性粉末を洗浄し、それを純水に分散したときに、水溶液の導電率が１ｍＳ／ｍ（ミリジーメンス）以下になるようにすると、磁性粉末が水中に良好に分散した混濁液を得ることができる。磁性粉末が分散した混濁液を遠心分離器にかけ、所定の回転数で遠心分離を実施すると、その遠心力で沈降する大きさの粒子のみが沈降し、その他の粒子は、分散したまま液中にとどまる。これにより、粒子を分級することができる。 The classification operation can be carried out using a general method using the difference in the sedimentation speed in the liquid depending on the particle diameter. Specifically, a magnetic powder having good dispersibility is prepared, for example, by performing a treatment for improving dispersibility in a liquid as described above. However, when the ionic strength in the liquid is high, the electrostatic repulsion between the particles is impaired, so that it is difficult to create a dispersed state. In this case, when the magnetic powder is washed by an appropriate method and dispersed in pure water, the magnetic powder is good in water if the conductivity of the aqueous solution is 1 mS / m (milli Siemens) or less. A turbid liquid dispersed in can be obtained. When the turbid liquid in which the magnetic powder is dispersed is applied to a centrifuge and centrifuged at a predetermined rotational speed, only particles of a size that settles by the centrifugal force settles, and other particles remain dispersed in the liquid. Stay. Thereby, particles can be classified.
ただし、このように方法で分級を成功させるためには、磁性粉末が１粒子ずつ極めて良好に、液中に分散することが重要である。粒子が凝集している場合は、その凝集体の大きさで沈降してしまため、一次粒子のレベルでの分級は望めない。シリカコーティングの溶解除去に、Ｎ（ＣＨ3）4ＯＨ水溶液を用いた場合は、Ｎ（ＣＨ3）4ＯＨが分散剤としても作用するため、より良好な分散状態を保つことができる。 However, in order to succeed in classification by such a method, it is important that the magnetic powder is dispersed in the liquid very well one by one. If the particles are agglomerated, they will settle at the size of the agglomerates, so classification at the primary particle level cannot be expected. The dissolution removal of the silica coating, the case of using N (CH 3) 4 OH aqueous solution, since N (CH 3) 4 OH acts as a dispersing agent, it is possible to maintain a better dispersion state.
磁気特性を改善させる観点からは、超常磁性を示す極微細粒子をできるだけ除去するように分級を行うことが極めて効果的である。具体的には、粒子径が５ｎｍより小さい粒子は、超常磁性であり、硬磁性体的振る舞いは示さず、軟磁性体的に振る舞うため、５ｎｍより小さい粒子が多く含まれると、その超常磁性の影響により粉体の磁気特性が著しく低下する。また、５〜１０ｎｍの範囲の粒子径も、すでに単磁区構造をとる臨界半径より小さいことが予想され、磁気特性の低下が観察される。したがって、粒子径５ｎｍ未満の粒子、好ましくは１０ｎｍ未満の粒子はできるだけ除去されていることが好ましい。種々検討の結果、ＴＥＭ写真により測定される粒子径において、粒子径１０ｎｍ未満の粒子の個数割合が２５％以下、好ましくは１０％以下、さらに好ましくは８％以下であるように粒度調整することが、超常磁性の悪影響を回避する上で極めて有効である。 From the viewpoint of improving magnetic characteristics, it is extremely effective to perform classification so as to remove as much as possible ultrafine particles exhibiting superparamagnetism. Specifically, particles having a particle size of less than 5 nm are superparamagnetic and do not exhibit a hard magnetic behavior, and behave like a soft magnetic material. The magnetic properties of the powder are significantly reduced due to the influence. In addition, the particle diameter in the range of 5 to 10 nm is also expected to be smaller than the critical radius already having a single magnetic domain structure, and a decrease in magnetic properties is observed. Therefore, it is preferable that particles having a particle diameter of less than 5 nm, preferably particles of less than 10 nm, are removed as much as possible. As a result of various studies, the particle size can be adjusted so that the number ratio of particles having a particle diameter of less than 10 nm is 25% or less, preferably 10% or less, and more preferably 8% or less in the particle diameter measured by a TEM photograph. It is extremely effective in avoiding the adverse effects of superparamagnetism.
このような磁気特性を改善した磁性粉末のＴＥＭ平均粒子径は１０〜２００ｎｍの範囲であることが望ましく、１０〜１００ｎｍの範囲であることがより好ましい。現在市販されているデータバックアップ用磁気記録テープにおいては、その磁性粒子の平均粒子径が２００ｎｍ以下のものが殆どであり、これより微細な磁性粒子のものが求められている。 The TEM average particle size of the magnetic powder with improved magnetic properties is preferably in the range of 10 to 200 nm, and more preferably in the range of 10 to 100 nm. Most of magnetic recording tapes for data backup currently on the market have an average particle size of 200 nm or less, and finer magnetic particles are required.
磁気記録媒体や電波吸収体における磁性粒子の充填性を改善する観点からは、個々の粒子の粒子径ができるだけ狭い粒径範囲に揃っていることが望ましい。ただし、平均粒子径の変動に応じて、許容される粒子径のバラツキ（標準偏差）も変動する。発明者らの検討によれば、ＴＥＭ写真により測定される粒子径において、［粒子径の標準偏差］／［平均粒子径］×１００で表される変動係数が５０％以下であるような粒度分布をとることが、充填性向上に効果的である。変動係数が４０％以下であることがより好ましい。粒子径１０ｎｍ未満の粒子の割合を上記のように低減したε−Ｆｅ2Ｏ3結晶の粉体において、変動係数を安定的に３０％以下にコントロールする手法は現時点で確立されていないが、将来的にはそのような粉体を得ることも可能になると考えられる。 From the viewpoint of improving the packing properties of the magnetic particles in the magnetic recording medium and the radio wave absorber, it is desirable that the particle diameters of the individual particles are as narrow as possible. However, the variation (standard deviation) in the allowable particle diameter varies depending on the variation in the average particle diameter. According to the study by the inventors, the particle size distribution such that the variation coefficient represented by [standard deviation of particle size] / [average particle size] × 100 in the particle size measured by the TEM photograph is 50% or less. It is effective to improve the filling property. More preferably, the coefficient of variation is 40% or less. In the ε-Fe 2 O 3 crystal powder in which the proportion of particles having a particle diameter of less than 10 nm is reduced as described above, a method for stably controlling the coefficient of variation to 30% or less has not been established at present. In particular, it is considered possible to obtain such a powder.
変動係数のコントロールは、［１］シリカコートの量、焼成温度および焼成時間、［２］シリカコートの除去（分散性の確保）、［３］分級操作、という３者の条件を組み合わせることによって可能となる。 The coefficient of variation can be controlled by combining three conditions: [1] amount of silica coat, firing temperature and firing time, [2] removal of silica coat (ensuring dispersibility), and [3] classification operation. It becomes.
ところで、上記のようなε−Ｆｅ2Ｏ3結晶の合成においては、ε−Ｆｅ2Ｏ3結晶と空間群を異にする鉄酸化物結晶（不純物結晶）が混在する場合がある。そのような不純物結晶として、α−Ｆｅ2Ｏ3、γ−Ｆｅ2Ｏ3、ＦｅＯ、Ｆｅ3Ｏ4が挙げられる。金属元素Ｍが添加されている場合は、これらの不純物結晶のＦｅの一部もＭで置換されている可能性がある。不純物結晶の混在は、ε−Ｆｅ2Ｏ3結晶の特性をできるだけ多く引き出す上で好ましいとは言えないが、本発明の効果を阻害しない範囲で許容される。 By the way, in the synthesis of the ε-Fe 2 O 3 crystal as described above, an ε-Fe 2 O 3 crystal may be mixed with an iron oxide crystal (impurity crystal) having a different space group. Examples of such impurity crystals include α-Fe 2 O 3 , γ-Fe 2 O 3 , FeO, and Fe 3 O 4 . When the metal element M is added, part of Fe in these impurity crystals may be substituted with M. Mixing of impurity crystals is not preferable for extracting as much of the characteristics of the ε-Fe 2 O 3 crystal as possible, but is allowed as long as the effects of the present invention are not impaired.
例えば、鉄酸化物中に占めるε−Ｆｅ2Ｏ3結晶の割合が７５モル％以上である場合は、従来の磁性材料では実現が難しかった優れた磁気特性を呈し、種々の磁性用途で有用である。鉄酸化物中に占めるε−Ｆｅ2Ｏ3結晶の割合が５０〜７５モル％未満であっても、飽和磁化σｓが２ｅｍｕ／ｇ（２Ａ・ｍ2／ｋｇ）以上を満たすような磁性材料であれば、高感度の読み取り磁気ヘッドであるＧＭＲ（巨大磁気抵抗効果）ヘッドやさらに高感度であるトンネル効果を利用したＴＭＲヘッドを利用すると、書き込んだ信号を高い強度で読み取ることが可能であり、用途をなす。 For example, when the ratio of ε-Fe 2 O 3 crystal in iron oxide is 75 mol% or more, it exhibits excellent magnetic properties that are difficult to realize with conventional magnetic materials, and is useful in various magnetic applications. is there. Even if the ratio of the ε-Fe 2 O 3 crystal in the iron oxide is less than 50 to 75 mol%, the magnetic material satisfies the saturation magnetization σs of 2 emu / g (2 A · m 2 / kg) or more. If there is a GMR (giant magnetoresistive effect) head that is a high-sensitivity read magnetic head or a TMR head that uses the tunnel effect that is more sensitive, it is possible to read the written signal with high intensity, Make use.
置換元素Ｍについては、発明者らの詳細な検討によれば、置換量に応じて、ε−Ｆｅ2Ｏ3結晶の保磁力Ｈｃをコントロールしやすい元素Ｍとして、ＡｌおよびＧａを挙げることができる。実例を挙げると、置換後の結晶をε−ＭxＦｅ2-xＯ3と表記するとき、ＭがＡｌの場合、ｘ＝０（Ａｌ無添加の粒状粒子粉体）のときＨｃ＝１７.６ｋＯｅ（１.４０×１０6Ａ／ｍ）、ｘ＝０.４のときＨｃ＝１１.８ｋＯｅ（０.９４×１０6Ａ／ｍ）、ｘ＝０.５のときＨｃ＝１１.１ｋＯｅ（０.８８×１０6Ａ／ｍ）、ｘ＝０.６のときＨｃ＝９.７ｋＯｅ（０.７７×１０6Ａ／ｍ）、ｘ＝０.７のときＨｃ＝７.６ｋＯｅ（０.６１×１０6Ａ／ｍ）といった保磁力Ｈｃの変化挙動が見られた。またＭがＧａの場合、ｘ＝０（Ｇａ無添加、形状制御剤Ｂａ添加有りのロッド状粒子粉体）のときＨｃ＝１９.０ｋＯｅ（１.５１２×１０6Ａ／ｍ）、ｘ＝０.２２のときＨｃ＝１５.３ｋＯｅ（１.２２×１０6Ａ／ｍ）、ｘ＝０.４３のときＨｃ＝１０.７ｋＯｅ（０.８５１×１０6Ａ／ｍ）、ｘ＝０.６２のときＨｃ＝６.５ｋＯｅ（０.５２×１０6Ａ／ｍ）、ｘ＝０.８０のときＨｃ＝１.３ｋＯｅ（０.１０×１０6Ａ／ｍ）といった挙動が見られた。 Regarding the substitution element M, according to detailed examinations by the inventors, Al and Ga can be mentioned as the element M that can easily control the coercive force Hc of the ε-Fe 2 O 3 crystal according to the substitution amount. . For example, when the crystal after substitution is expressed as ε-M x Fe 2−x O 3 , when M is Al, when x = 0 (aluminum-free granular particle powder), Hc = 17. 6 kOe (1.40 × 10 6 A / m), when x = 0.4, Hc = 11.8 kOe (0.94 × 10 6 A / m), when x = 0.5, Hc = 11.1 kOe ( 0.88 × 10 6 A / m), when x = 0.6, Hc = 9.7 kOe (0.77 × 10 6 A / m), and when x = 0.7, Hc = 7.6 kOe (0.6). A change behavior of the coercive force Hc such as 61 × 10 6 A / m) was observed. When M is Ga, Hc = 19.0 kOe (1.512 × 10 6 A / m) and x = 0 when x = 0 (rod-shaped particle powder with no addition of Ga and shape control agent Ba) Hc = 15.3 kOe (1.22 × 10 6 A / m) when .22, Hc = 10.7 kOe (0.851 × 10 6 A / m) when x = 0.43, x = 0.62 Hc = 6.5 kOe (0.52 × 10 6 A / m), and when x = 0.80, Hc = 1.3 kOe (0.10 × 10 6 A / m).
また、ロッド形状のε−Ｆｅ2Ｏ3結晶を得る場合に添加されるアルカリ土類金属（Ｂａ、Ｓｒ、Ｃａなど）は、通常、生成する結晶の表層部などに存在する。これらのアルカリ土類金属元素をＡと表示するとき、その存在量（含有量）は、多くてもＡ／（Ｆｅ＋Ｍ）×１００で表される配合比が２０質量％以下の範囲であり、２０質量％を超えるアルカリ土類金属の含有は、形状制御剤としての機能を果たす上では一般に不必要である。１０質量％以下であることがより好ましい。 In addition, alkaline earth metals (Ba, Sr, Ca, etc.) that are added to obtain rod-shaped ε-Fe 2 O 3 crystals are usually present in the surface layer of the crystals to be produced. When these alkaline earth metal elements are denoted as A, the abundance (content) is at most a blending ratio represented by A / (Fe + M) × 100 within a range of 20% by mass or less, 20 The inclusion of alkaline earth metal in excess of mass% is generally unnecessary in order to function as a shape control agent. More preferably, it is 10 mass% or less.
なお、前述のとおり本発明のε−Ｆｅ2Ｏ3結晶の合成については、その前駆体となる水酸化鉄と水酸化アルミニウムの超微粒子を逆ミセル法で作製する例を挙げたが、数百ｎｍ以下の同様の前駆体が作製できれば、その前駆体作製は特に逆ミセル法に限られるものではない。 As described above, for the synthesis of the ε-Fe 2 O 3 crystal of the present invention, an example in which ultrafine particles of iron hydroxide and aluminum hydroxide as precursors thereof are produced by the reverse micelle method has been given. If a similar precursor of nm or less can be produced, the production of the precursor is not particularly limited to the reverse micelle method.
ε−Ｆｅ2Ｏ3結晶を以下の手順に従って合成した。置換元素ＭとしてＧａを使用した。 ε-Fe 2 O 3 crystals were synthesized according to the following procedure. Ga was used as the substitution element M.
《ε−Ｆｅ2Ｏ3結晶の合成》
〔手順１〕
ミセル溶液Ｉとミセル溶液IIの２種類のミセル溶液を調整する。
・ミセル溶液Ｉの作製
テフロン（登録商標）製のフラスコに、純水６ｍＬ、ｎ−オクタン１８.３ｍＬおよび１−ブタノール３.７ｍＬを入れる。そこに、硝酸鉄（III）９水和物を０.００２４０モル、硝酸ガリウム（III）ｎ水和物（和光純薬工業株式会社製の純度９９.９％でｎ＝７〜９のものを使用し、使用に当たっては事前に定量分析を行ってｎを特定してから仕込み量を計算した）を０.０００６０モル添加し、室温で良く撹拌しながら溶解させる。さらに、界面活性剤としての臭化セチルトリメチルアンモニウムを、純水／界面活性剤のモル比が３０となるような量で添加し、撹拌により溶解させ、ミセル溶液Ｉを得る。
このときの仕込み組成は、ＧａとＦｅのモル比をＧａ：Ｆｅ＝ｘ：（２−ｘ）と表すときｘ＝０.４０である。
<< Synthesis of ε-Fe 2 O 3 crystal >>
[Procedure 1]
Two kinds of micelle solutions, micelle solution I and micelle solution II, are prepared.
-Preparation of micelle solution I In a Teflon (registered trademark) flask, 6 mL of pure water, 18.3 mL of n-octane and 3.7 mL of 1-butanol are added. There, 0.0000 mol of iron (III) nitrate nonahydrate, gallium nitrate (III) n hydrate (99.9% purity by Wako Pure Chemical Industries, n = 7-9) Use and quantitatively analyze in advance and specify n, and then charge amount is calculated)) is added at 0.00060 mol and dissolved at room temperature with good stirring. Further, cetyltrimethylammonium bromide as a surfactant is added in such an amount that the molar ratio of pure water / surfactant becomes 30, and dissolved by stirring to obtain a micelle solution I.
The charged composition at this time is x = 0.40 when the molar ratio of Ga to Fe is expressed as Ga: Fe = x: (2-x).
・ミセル溶液IIの作製
２５％アンモニア水２ｍＬを純水４ｍＬに混ぜて撹拌し、その液に、さらにｎ―オクタン１８.３ｍＬと１−ブタノール３.７ｍＬを加えてよく撹拌する。その溶液に、界面活性剤として臭化セチルトリメチルアンモニウムを、（純水＋アンモニア中の水分）／界面活性剤のモル比が３０となるような量で添加し、溶解させ、ミセル溶液IIを得る。
-Preparation of micelle solution II 2 mL of 25% aqueous ammonia is mixed with 4 mL of pure water and stirred, and further 18.3 mL of n-octane and 3.7 mL of 1-butanol are added to the solution and stirred well. Cetyltrimethylammonium bromide as a surfactant is added to the solution in such an amount that the molar ratio of (pure water + water in ammonia) / surfactant is 30 and dissolved to obtain a micelle solution II. .
〔手順２〕
ミセル溶液Ｉをよく撹拌しながら、ミセルＩ溶液に対してミセル溶液IIを滴下する。滴下終了後、混合液を３０分間撹拌し続ける。
[Procedure 2]
While stirring the micelle solution I, the micelle solution II is added dropwise to the micelle I solution. After completion of the dropping, the mixture is continuously stirred for 30 minutes.
〔手順３〕
手順２で得られた混合液を撹拌しながら、当該混合液にテトラエトキシシラン６.１ｍＬを加える。約１日そのまま、撹拌し続ける。
[Procedure 3]
While stirring the mixed solution obtained in procedure 2, 6.1 mL of tetraethoxysilane is added to the mixed solution. Continue stirring for about 1 day.
〔手順４〕
手順３で得られた溶液を遠心分離機にセットして遠心分離処理する。この処理で得られた沈殿物を回収する。回収された沈殿物をクロロホルムとメタノールの混合溶液を用いて複数回洗浄する。
[Procedure 4]
The solution obtained in step 3 is set in a centrifuge and centrifuged. The precipitate obtained by this treatment is recovered. The collected precipitate is washed several times with a mixed solution of chloroform and methanol.
〔手順５〕
手順４で得られた沈殿物を乾燥した後、大気雰囲気の炉内で１１００℃で４時間の熱処理を施す。
[Procedure 5]
After drying the precipitate obtained in procedure 4, heat treatment is performed at 1100 ° C. for 4 hours in an air atmosphere furnace.
〔手順６−１〕
手順５で得られた熱処理粉を、メノウ製乳鉢により丁寧に解粒を実施したのち、１０モル／ＬのＮａＯＨ水溶液１Ｌ（リットル）中に入れ、液温７０℃で２４時間撹拌し、粒子表面に存在するであろうシリカの除去処理を行う。次いで、ろ過し、十分に水洗する。
[Procedure 6-1]
The heat-treated powder obtained in step 5 was carefully pulverized with an agate mortar, then placed in 1 L (liter) of 10 mol / L NaOH aqueous solution, stirred at a liquid temperature of 70 ° C. for 24 hours, and the particle surface The silica which will exist in this is removed. It is then filtered and washed thoroughly with water.
〔手順６−２〕
水洗された粉末を純水１Ｌ中に入れて分散させ、室温で撹拌しながらｐＨをモニターして希硝酸を少量ずつ添加していき、ｐＨ２.５〜３.０に調整する。撹拌を続けているとｐＨは変動するので、常にｐＨ２.５〜３.０に調整する。ｐＨ調整しながら、撹拌を１時間実施する。アルカリで熱処理粉を処理するとシリカ分は溶解するが、同時にＦｅもわずかながら溶解し、アルカリ溶液中で溶解し難い無定形なＦｅケイ酸塩が液中で合成することが確認されている。このＦｅケイ酸塩は、酸に対する溶解度が高いため、上記操作により除去を行う（再溶解処理）。
[Procedure 6-2]
The water-washed powder is dispersed in 1 L of pure water, pH is monitored while stirring at room temperature, and dilute nitric acid is added little by little to adjust to pH 2.5 to 3.0. Since the pH fluctuates when stirring is continued, the pH is always adjusted to 2.5 to 3.0. Stirring is carried out for 1 hour while adjusting the pH. When the heat-treated powder is treated with an alkali, the silica component is dissolved, but at the same time Fe is also slightly dissolved, and it has been confirmed that an amorphous Fe silicate which is difficult to dissolve in an alkaline solution is synthesized in the solution. Since this Fe silicate has high solubility in acid, it is removed by the above operation (re-dissolution treatment).
また、金属元素Ｍについても手順６−１で溶解が生じ、シリカ分と反応してＭ元素のケイ酸塩を合成する場合があることが確認されている。また、手順３や手順４のときにＳｉと金属元素Ｍが化合物を形成する場合があることも確認されている。特に、ＭがＡｌの場合、Ｓｉと化合物を形成しやすい傾向にある。このようにシリカがＭ元素とのケイ酸塩を形成するときは、手順６−１のアルカリ処理だけでは、目的とするＳｉ含有量までＳｉを除去できないことが起こりうる。このような場合にも、手順６−２は有効である。すなわち、後述の分級工程を実施するために必要となる分散性を備えた粉末を得るためには、目的とするＳｉ含有量になるまで、手順６−１と手順６−２を繰り返すことが、極めて効果的である。 Further, it has been confirmed that the metal element M is dissolved in the procedure 6-1 and may react with the silica component to synthesize the M element silicate. Further, it has been confirmed that Si and the metal element M may form a compound during the procedure 3 and the procedure 4. In particular, when M is Al, it tends to form a compound with Si. Thus, when silica forms a silicate with M element, it may happen that Si cannot be removed to the target Si content only by the alkali treatment in Procedure 6-1. Even in such a case, the procedure 6-2 is effective. That is, in order to obtain a powder having dispersibility necessary for carrying out the classification step described later, the procedure 6-1 and the procedure 6-2 are repeated until the target Si content is reached. It is extremely effective.
次に、手順６−２を終えて得られた粉末を以下の分級工程に供した。
《分級工程》
〔手順７−１〕
［１］超純水１Ｌ当たりに、乾燥重量５ｇに相当するウエット状態の粉末入れる。
［２］強撹拌を１時間実施し、粉末粒子を十分に分散させる。
［３］この分散液を遠心分離器（日立工機製ＣＲ２１ＧII）を用いて２００００ｒｐｍで遠心分離する。
［４］固液分離したのちに、上澄み液の導電率を測定する。測定後、上澄み液を廃棄する。
〔手順７−２〕
上記［４］で、上澄み液の導電率が１ｍＳ／ｍ（ミリジーメンス）より高い場合は、上記［１］〜［４］を繰り返す。
Next, the powder obtained after finishing the procedure 6-2 was subjected to the following classification step.
<< Classification process >>
[Procedure 7-1]
[1] A wet powder equivalent to a dry weight of 5 g is added per liter of ultrapure water.
[2] Strong stirring is performed for 1 hour to sufficiently disperse the powder particles.
[3] This dispersion is centrifuged at 20000 rpm using a centrifuge (CR21GII manufactured by Hitachi Koki Co., Ltd.).
[4] After the solid-liquid separation, the conductivity of the supernatant is measured. After measurement, discard the supernatant.
[Procedure 7-2]
In the above [4], when the conductivity of the supernatant liquid is higher than 1 mS / m (milli Siemens), the above [1] to [4] are repeated.
〔手順７−３〕
上澄み液の導電率が下がるにつれて、粒子が分散系になってくることが観察でき、上澄み液の導電率が１ｍＳ／ｍ以下になったものは、純水を入れ、強撹拌を行い、強力な超音波洗浄機にて１時間かける。さらに、少量のＮａＯＨを添加してｐＨ１１付近に調整することにより、極めて良好な分散状態を得ることができる。
[Procedure 7-3]
As the conductivity of the supernatant liquid decreases, it can be observed that the particles become dispersed. When the conductivity of the supernatant liquid is 1 mS / m or less, pure water is added and strong agitation is performed. Take 1 hour in an ultrasonic cleaner. Furthermore, a very good dispersion state can be obtained by adding a small amount of NaOH to adjust the pH to around 11.
Ｓｉ酸化物の等電点が、ｐＨ２前後であるから、基本的にはｐＨが高いほど静電的反発力が大きくなり、より良好な分散性を示すと考えられる。ただし、実際は、ｐＨを上昇させるためにＮａＯＨなどのアルカリを添加すると、イオン強度が高くなることにより、分散性を阻害する作用も生じる。したがって、Ｓｉ酸化物が表層に存在する粒子の場合は、静電的反発力による分散性向上作用と、イオン強度上昇に伴う凝集性増大作用とのバランスにより、最も分散性が良好となるｐＨが決定される。発明者らの詳細な検討によれば、ｐＨ１１±１.５、好ましくはｐＨ１１±０.５の範囲に調整することが望ましい。 Since the isoelectric point of the Si oxide is around pH 2, basically, the higher the pH, the greater the electrostatic repulsion, and it is considered that better dispersibility is exhibited. However, in practice, when an alkali such as NaOH is added to raise the pH, the ionic strength increases, and this also has the effect of inhibiting dispersibility. Therefore, in the case of particles in which Si oxide is present in the surface layer, the pH at which the dispersibility is the best is obtained by the balance between the dispersibility improving effect due to electrostatic repulsion and the agglomeration increasing effect accompanying the increase in ionic strength. It is determined. According to detailed investigations by the inventors, it is desirable to adjust the pH to within a range of pH 11 ± 1.5, preferably pH 11 ± 0.5.
〔手順７−４〕
手順７−３で得られた分散液を構成する粉末（まだ分級されていない段階の粉末）を、ここでは「元粉」と呼ぶ。観察用および特性調査用の元粉試料を採取した後、元粉の分散液を遠心分離器にかけ、１８０００ｒｐｍで遠心分離を行う。これによって、沈殿物と、上澄み液が得られる。上澄みは濁っており、粒子が存在していることが目視で確認できる。すなわちこの遠心分離操作により、元粉が、粒度分布の異なる２種類の粉体に分級される。なお、この遠心分離を行う際には、分離の分解能を上げるために、途中に撹拌＋超音波による分散工程を入れて、複数回の遠心分離操作を行うことが望ましい。このようにして得られた沈殿物を構成する粉末を「沈殿粉」と呼び、上澄み中に存在する粉末を「上澄み粉」と呼ぶ。上澄み粉については、上澄み液に硝酸を少量ずつ添加し、等電点付近のｐＨ７に調整後、遠心分離器で１８０００ｒｐｍで遠心分離を行って固液分離することにより回収することができる。
[Procedure 7-4]
The powder constituting the dispersion obtained in the procedure 7-3 (powder that has not been classified yet) is referred to herein as “original powder”. After collecting the original powder sample for observation and characteristic investigation, the dispersion of the original powder is applied to a centrifuge and centrifuged at 18000 rpm. As a result, a precipitate and a supernatant are obtained. The supernatant is cloudy and it can be visually confirmed that particles are present. That is, by this centrifugation operation, the base powder is classified into two types of powders having different particle size distributions. When performing this centrifugation, it is desirable to perform a plurality of centrifugation operations with a stirring step and a dispersion process using ultrasonic waves in the middle in order to increase the resolution of the separation. The powder constituting the precipitate thus obtained is called “precipitate powder”, and the powder present in the supernatant is called “supernatant powder”. The supernatant powder can be recovered by adding nitric acid to the supernatant little by little and adjusting to pH 7 near the isoelectric point, followed by solid-liquid separation by centrifugation at 18000 rpm in a centrifuge.
元粉のＴＥＭ写真を図１（ａ）に、沈殿粉のＴＥＭ写真を図１（ｂ）に、上澄み粉のＴＥＭ写真を図１（ｃ）に示す。各粉末について、ＴＥＭにより個々の粒子の粒子径を測定することにより粒度分布を調べた。表１中に、ＴＥＭ平均粒子径、粒子径の標準偏差、［粒子径の標準偏差］／［ＴＥＭ平均粒子径］×１００により算出される変動係数、粒子径１０ｎｍ未満の粒子の個数％、Ｄｘ粒径を示してある。ここでＤｘ粒径は後述のＸ線回折により求められた粒子径（結晶子径）である。元粉から、粒径１０ｎｍ未満の粒子の多くを上澄み粉として除去して得られた沈殿粉が、本発明の対象粉末である。 A TEM photograph of the original powder is shown in FIG. 1 (a), a TEM photograph of the precipitated powder is shown in FIG. 1 (b), and a TEM photograph of the supernatant powder is shown in FIG. 1 (c). About each powder, the particle size distribution was investigated by measuring the particle diameter of each particle by TEM. In Table 1, TEM average particle diameter, standard deviation of particle diameter, [standard deviation of particle diameter] / [TEM average particle diameter] × 100 variation coefficient, number% of particles having a particle diameter of less than 10 nm, Dx The particle size is shown. Here, the Dx particle diameter is a particle diameter (crystallite diameter) obtained by X-ray diffraction described later. Precipitated powder obtained by removing many particles having a particle size of less than 10 nm as a supernatant powder from the original powder is the target powder of the present invention.
得られた各試料粉末（元粉、沈殿粉、上澄み粉）を粉末Ｘ線回折（ＸＲＤ：リガク製ＲＩＮＴ２０００、線源ＣｏＫα線、電圧４０ｋＶ、電流３０ｍＡ）に供したところ、図２に示した回折パターンが得られた。これら３種類の粉体の回折パターンは、いずれもε−Ｆｅ2Ｏ3の結晶構造（斜方晶、空間群Ｐｎａ２1）に対応する回折ピークを有している。したがって、その結晶がこれらの粉末における主相であることが明らかである。また、２θが３０°より低角側には、アモルファス状のＳｉＯ2に起因するブロードなピークが、わずかながら観察された。これは、手順６−１、６−２でシリカコートの大部分を除去したことに伴い、粒子表面に少量のＳｉ酸化物が存在していることを示すものである。（実施例２〜４においても同様であった）。 Each of the obtained sample powders (original powder, precipitated powder, and supernatant powder) was subjected to powder X-ray diffraction (XRD: RINT2000 manufactured by Rigaku, source CoKα line, voltage 40 kV, current 30 mA), and the diffraction shown in FIG. A pattern was obtained. The diffraction patterns of these three kinds of powders all have diffraction peaks corresponding to the crystal structure of ε-Fe 2 O 3 (orthorhombic crystal, space group Pna2 1 ). It is therefore clear that the crystals are the main phase in these powders. Moreover, a broad peak due to amorphous SiO 2 was slightly observed on the lower angle side of 2θ than 30 °. This indicates that a small amount of Si oxide is present on the particle surface as most of the silica coat is removed in procedures 6-1 and 6-2. (The same applies to Examples 2 to 4).
得られた各試料粉末を蛍光Ｘ線分析（日本電子製ＪＳＸ―３２２０）に供したところ、ＧａとＦｅのモル比をＧａ：Ｆｅ＝ｘ：（２−ｘ）と表すときのｘの値は、仕込み組成；ｘ＝０.４０であったのに対し、元粉；ｘ＝０.３８、沈殿粉；ｘ＝０.３９、上澄み粉；ｘ＝０.３８であった。元粉、沈殿粉、上澄み粉の違いによる組成の顕著なずれは観測されなかった（実施例２〜４でも同様）。また、各試料粉末の、Ｓｉ／（Ｆｅ＋Ｇａ）×１００によるＳｉ含有量（モル％）を表１に記載した。手順６−１、６−２で、粒子表面に存在するＳｉ酸化物の量を適正範囲にコントロールしたことにより液中分散性が向上し、上記のような分級操作が可能になったと言える。 When each obtained sample powder was subjected to fluorescent X-ray analysis (JSX-3220 manufactured by JEOL Ltd.), the value of x when the molar ratio of Ga to Fe is expressed as Ga: Fe = x: (2-x) is The raw composition; x = 0.38, the precipitated powder; x = 0.39, the supernatant powder; x = 0.38. No significant shift in composition due to the difference between the original powder, the precipitated powder, and the supernatant powder was observed (the same applies to Examples 2 to 4). In addition, Table 1 shows the Si content (mol%) of each sample powder according to Si / (Fe + Ga) × 100. It can be said that in steps 6-1 and 6-2, by controlling the amount of Si oxide present on the particle surface within an appropriate range, the dispersibility in the liquid was improved, and the classification operation as described above became possible.
また、得られた各試料粉末について、常温（３００Ｋ）における磁気ヒステリシスループを測定した。元粉の磁気ヒステリシスループを図３（ａ）に、沈殿粉のそれを図３（ｂ）に、上澄み粉のそれを図３（ｃ）に示す。また、図３（ａ）〜（ｃ）の磁気ヒステリシスループを重ねて表示したものが図３（ｄ）である。磁気ヒステリシスループの測定は、Ｄｉｇｔａｌ Ｍｅａｓｕｒｅｍｅｎｔ Ｓｙｓｔｅｍｓ社の振動試料型磁力計（ＶＳＭ）のＭＯＤＥＬ８８０を用いて、印加磁場１３ｋＯｅ（１.０３５×１０6Ａ／ｍ）の条件で行った。各粉体の保磁力Ｈｃ、飽和磁化σｓ、残留磁化σｒ、角形比ＳＱ（＝σｒ／σｓ）、ＳＦＤの値を表１に記載した。 Moreover, about each obtained sample powder, the magnetic hysteresis loop in normal temperature (300K) was measured. The magnetic hysteresis loop of the original powder is shown in FIG. 3 (a), that of the precipitated powder is shown in FIG. 3 (b), and that of the supernatant powder is shown in FIG. 3 (c). FIG. 3D shows the magnetic hysteresis loops of FIGS. 3A to 3C displayed in an overlapping manner. The measurement of the magnetic hysteresis loop was performed under the condition of an applied magnetic field of 13 kOe (1.035 × 10 6 A / m) using MODEL 880 of a vibrating sample magnetometer (VSM) manufactured by Digital Measurement Systems. Table 1 shows the coercive force Hc, saturation magnetization σs, residual magnetization σr, squareness ratio SQ (= σr / σs), and SFD of each powder.
図３（ａ）より、元粉では印加磁場＝０ Ｏｅ（以下「ゼロ磁場」という）付近で、曲線にわずかに歪みが生じていることがわかる。これは、磁性粉末中に超常磁性の粒子が含まれるときに観察される現象である。図３（ｂ）の沈殿粉では、この歪みがほとんど観察されずゼロ磁場付近でも滑らかな曲線を示す。一方、図３（ｃ）の上澄み粉では、ゼロ磁場付近での曲線の歪みが大きく、また、保磁力Ｈｃが大幅に低減している。これは超常磁性を呈する極微細粒子の存在割合が多いことに起因すると考えられる。図３（ｄ）からわかるように、元粉から、極微細粒子を多く含む上澄み粉を除去することによって分級された沈殿粉（本発明対象の粉末）では、元粉に対して、磁気特性の大幅な改善が認められる。（磁気特性に関し後述実施例２〜４でも概ね以上と同様ことが確認された）。また、表１に見られるように、沈殿粉は、元粉よりもＳＦＤが大幅に低下し、総合的な磁気特性の改善が認められた（後述実施例２〜４の表２〜４においても同じ）。 From FIG. 3A, it can be seen that the original powder has a slight distortion in the vicinity of the applied magnetic field = 0 Oe (hereinafter referred to as “zero magnetic field”). This is a phenomenon observed when superparamagnetic particles are contained in the magnetic powder. In the precipitated powder of FIG. 3B, this distortion is hardly observed and a smooth curve is shown even in the vicinity of zero magnetic field. On the other hand, in the supernatant powder of FIG. 3C, the distortion of the curve near the zero magnetic field is large, and the coercive force Hc is greatly reduced. This is thought to be due to the large proportion of ultrafine particles exhibiting superparamagnetism. As can be seen from FIG. 3 (d), in the precipitated powder (powder of the present invention) classified by removing the supernatant powder containing a lot of ultrafine particles from the original powder, the magnetic characteristics of the original powder are different from those of the original powder. Significant improvement is observed. (It was confirmed that the magnetic characteristics were substantially the same in Examples 2 to 4 described later). Moreover, as seen in Table 1, the SFD of the precipitated powder was significantly lower than that of the original powder, and an improvement in the overall magnetic properties was observed (also in Tables 2 to 4 of Examples 2 to 4 described later). the same).
ＧａによるＦｅの置換量を変更した以外、実施例１と同様の実験を行った。すなわちここでは、ＧａとＦｅのモル比をＧａ：Ｆｅ＝ｘ：（２−ｘ）と表すとき、仕込み組成においてｘ＝０.３３とした。
元粉のＴＥＭ写真を図４（ａ）に、沈殿粉のＴＥＭ写真を図４（ｂ）に、上澄み粉のＴＥＭ写真を図４（ｃ）に示す。
元粉、沈殿粉、上澄み粉のＸ線回折パターンを図５に示す。測定条件は実施例１と同様である（実施例３、４において同じ）。
元粉、沈殿粉、上澄み粉についての磁気ヒステリシスループを図６に重ねて表示する。測定条件は実施例１と同様である（実施例３、４において同じ）。
前記表１と同様の項目について、実施例２の結果を表２に示す。
An experiment similar to that of Example 1 was performed except that the amount of substitution of Fe by Ga was changed. That is, here, when the molar ratio of Ga and Fe is expressed as Ga: Fe = x: (2-x), x = 0.33 in the charged composition.
FIG. 4A shows a TEM photograph of the original powder, FIG. 4B shows a TEM photograph of the precipitated powder, and FIG. 4C shows a TEM photograph of the supernatant powder.
FIG. 5 shows X-ray diffraction patterns of the original powder, the precipitated powder, and the supernatant powder. The measurement conditions are the same as in Example 1 (same in Examples 3 and 4).
Magnetic hysteresis loops for the original powder, the precipitated powder, and the supernatant powder are displayed superimposed on FIG. The measurement conditions are the same as in Example 1 (same in Examples 3 and 4).
Table 2 shows the results of Example 2 for the same items as in Table 1.
ＧａによるＦｅの置換量を変更した以外、実施例１と同様の実験を行った。すなわちここでは、ＧａとＦｅのモル比をＧａ：Ｆｅ＝ｘ：（２−ｘ）と表すとき、仕込み組成においてｘ＝０.４７とした。
元粉のＴＥＭ写真を図７（ａ）に、沈殿粉のＴＥＭ写真を図７（ｂ）に、上澄み粉のＴＥＭ写真を図７（ｃ）に示す。
元粉、沈殿粉、上澄み粉のＸ線回折パターンを図８に示す。
元粉、沈殿粉、上澄み粉についての磁気ヒステリシスループを図９に重ねて表示する。
前記表１と同様の項目について、実施例３の結果を表３に示す。
An experiment similar to that of Example 1 was performed except that the amount of substitution of Fe by Ga was changed. That is, here, when the molar ratio of Ga and Fe is expressed as Ga: Fe = x: (2-x), x = 0.47 in the charged composition.
FIG. 7 (a) shows a TEM photograph of the original powder, FIG. 7 (b) shows a TEM photograph of the precipitated powder, and FIG. 7 (c) shows a TEM photograph of the supernatant powder.
FIG. 8 shows X-ray diffraction patterns of the original powder, the precipitated powder, and the supernatant powder.
The magnetic hysteresis loops for the original powder, the precipitated powder, and the supernatant powder are displayed superimposed on FIG.
Table 3 shows the results of Example 3 for the same items as in Table 1.
ＧａによるＦｅの置換量を変更した以外、実施例１と同様の実験を行った。すなわちここでは、ＧａとＦｅのモル比をＧａ：Ｆｅ＝ｘ：（２−ｘ）と表すとき、仕込み組成においてｘ＝０.５２とした。
元粉のＴＥＭ写真を図１０（ａ）に、沈殿粉のＴＥＭ写真を図１０（ｂ）に、上澄み粉のＴＥＭ写真を図１０（ｃ）に示す。
元粉、沈殿粉、上澄み粉のＸ線回折パターンを図１１に示す。
元粉、沈殿粉、上澄み粉についての磁気ヒステリシスループを図１２に重ねて表示する。
前記表１と同様の項目について、実施例４の結果を表４に示す。
An experiment similar to that of Example 1 was performed except that the amount of substitution of Fe by Ga was changed. That is, here, when the molar ratio of Ga to Fe is expressed as Ga: Fe = x: (2-x), x = 0.52 in the charged composition.
FIG. 10A shows a TEM photograph of the original powder, FIG. 10B shows a TEM photograph of the precipitated powder, and FIG. 10C shows a TEM photograph of the supernatant powder.
FIG. 11 shows X-ray diffraction patterns of the original powder, the precipitated powder, and the supernatant powder.
Magnetic hysteresis loops for the original powder, the precipitated powder, and the supernatant powder are displayed superimposed on FIG.
Table 4 shows the results of Example 4 for the same items as in Table 1.
実施例１で得られた本発明の対象である「沈殿粉」を用いて、以下のように、磁性塗料を作り、これをテープに塗布し、磁場配向された磁気テープを作成した。 Using the “precipitated powder” that is the subject of the present invention obtained in Example 1, a magnetic paint was prepared as follows, and this was applied to the tape to produce a magnetically oriented magnetic tape.
〔磁性塗料の調製〕
磁性粉末（上記の沈殿粉）０.５００ｇを秤量し、これをポット（内径４５ｍｍ、深さ１３ｍｍ）に入れる。蓋を開けた状態で１０分間放置する。次にビヒクル〔塩ビ系樹脂ＭＲ−１１０（２２質量％）、シクロヘキサノン（３８.７質量％）、アセチルアセトン（０.３質量％）、ステアリン酸ｎブチル（０.３質量％）、メチルエチルケトン（ＭＥＫ；３８.７質量％）の混合液〕をマイクロピペットで０.７００ｍＬ採取し、これを前記のポットに添加する。その後直ちにスチールボール（２ｍｍ径）３０ｇ、ナイロンボール（８ｍｍ径）１０個をポットに加え、蓋を閉じ１０分間静置する。その後、このポットを遠心式ボールミル（ＦＲＩＴＳＣＨ Ｐ−６）にセットし、ゆっくりと回転数を上げ、６００ｒｐｍに合わせ、６０分間分散処理を行う。遠心式ボールミルが停止した後、ポットを取り出し、マイクロピペットを使用し、あらかじめ、ＭＥＫとトルエンを１：１で混合しておいた調整液を１.８００ｍＬ添加する。再度遠心式ボールミルにこのポットをセットし、６００ｒｐｍで５分間分散処理することにより、塗料を調製する。
[Preparation of magnetic paint]
Weigh 0.500 g of magnetic powder (precipitated powder) and put it in a pot (inner diameter 45 mm, depth 13 mm). Leave for 10 minutes with the lid open. Next, vehicle [vinyl chloride resin MR-110 (22 mass%), cyclohexanone (38.7 mass%), acetylacetone (0.3 mass%), n-butyl stearate (0.3 mass%), methyl ethyl ketone (MEK; (38.7% by mass) is collected with a micropipette and added to the pot. Immediately thereafter, 30 g of steel balls (2 mm diameter) and 10 nylon balls (8 mm diameter) are added to the pot, and the lid is closed and allowed to stand for 10 minutes. Thereafter, the pot is set on a centrifugal ball mill (FRITSCH P-6), and the number of rotations is slowly increased to 600 rpm, and dispersion treatment is performed for 60 minutes. After the centrifugal ball mill is stopped, the pot is taken out, and 1.800 mL of a preliminarily mixed solution of MEK and toluene at 1: 1 is added using a micropipette. The pot is set again in the centrifugal ball mill, and the paint is prepared by dispersing the mixture at 600 rpm for 5 minutes.
〔磁気テープの作成〕
前記の分散を終了した後に、ポットの蓋を開け、ナイロンボールを取り除き、調製された塗料をスチールボールごとアプリケーター（隙間５５μｍ）に入れ、支持フィルム（東レ株式会社製ポリエチレンフィルム：商品名１５Ｃ−Ｂ５００：膜厚１５μｍ）対して塗布を行う。塗布後素早く、５.５ｋＧの配向器のコイルの中心に置き、磁場配向させ、その後乾燥させる。
[Making magnetic tape]
After finishing the above dispersion, the pot lid is opened, the nylon balls are removed, the prepared paint is put together with the steel balls into an applicator (gap 55 μm), and a support film (polyethylene film manufactured by Toray Industries, Inc .: trade name 15C-B500) : Film thickness 15 μm). Immediately after application, it is placed in the center of a 5.5 kG orienter coil, magnetically oriented and then dried.
以上のようにして作成した磁気テープについて、実施例１の粉末の場合と同様に磁気ヒステリシスループを測定した。その結果を図４に示す。原料粉についての図３（ｂ）と比較すると、ループが大きくなり、磁化の配向が起きたことによる効果が確認できる。すなわち、磁場による配向が実現できた結果、テープの磁気特性は、原料粉（沈殿粉）の特性と比較すると、保磁力Ｈｃが７６４４Ｏｅ（６.０８×１０5Ａ／ｍ）から８６１３Ｏｅ（６.８５×１０5Ａ／ｍ）に、角形比ＳＱ（＝σｒ／σｓ）が０.６０から０.８２に、ＳＦＤが０.４０１から０.３８８にそれぞれ改善され、磁気特性の大幅な改善がもたらされた。
磁場をかけることにより粉末粒子の配向できたのは、沈殿粉が高分子基材に対して良好な分散性を有していることによる。
About the magnetic tape produced as mentioned above, the magnetic hysteresis loop was measured similarly to the case of the powder of Example 1. The result is shown in FIG. Compared with FIG. 3B for the raw material powder, the loop becomes larger, and the effect due to the occurrence of magnetization orientation can be confirmed. That is, as a result of realizing the orientation by the magnetic field, the magnetic properties of the tape are from coercive force Hc of 7644 Oe (6.08 × 10 5 A / m) to 8613 Oe (6. 6) compared with the properties of the raw material powder (precipitated powder). 85 × 10 5 A / m), the squareness ratio SQ (= σr / σs) has been improved from 0.60 to 0.82, and the SFD has been improved from 0.401 to 0.388. It was brought.
The reason why the powder particles can be oriented by applying a magnetic field is that the precipitated powder has good dispersibility with respect to the polymer substrate.
Claims (7)
ただし、上記鉄酸化物におけるＭとＦｅのモル比をＭ：Ｆｅ＝ｘ：（２−ｘ）と表すとき、０≦ｘ＜１である。 It consists of iron oxide particles whose main phase is ε-Fe 2 O 3 crystals (including those in which part of the Fe site is substituted with the metal element M). Magnetic powder having a diameter of 10 to 200 nm and a number ratio of particles having a particle diameter of less than 10 nm of 25% or less.
However, when the molar ratio of M to Fe in the iron oxide is expressed as M: Fe = x: (2-x), 0 ≦ x <1.
ただし、上記鉄酸化物におけるＭとＦｅのモル比をＭ：Ｆｅ＝ｘ：（２−ｘ）と表すとき、０≦ｘ＜１である。 It consists of iron oxide particles whose main phase is ε-Fe 2 O 3 crystals (including those in which part of the Fe site is substituted with the metal element M). Magnetic powder having a diameter of 10 to 200 nm and a number ratio of particles having a particle diameter of less than 10 nm is 8% or less.
However, when the molar ratio of M to Fe in the iron oxide is expressed as M: Fe = x: (2-x), 0 ≦ x <1.
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