JP2008063199A - epsi-IRON OXIDE-BASED MAGNETIC MATERIAL - Google Patents
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本発明はε−Ｆｅ2Ｏ3結晶を磁性相にもつ粒子の充填構造からなる磁性材料に関する。 The present invention relates to a magnetic material having a packed structure of particles having an ε-Fe 2 O 3 crystal as a magnetic phase.
ε−Ｆｅ2Ｏ3は酸化鉄の中でも極めて稀な相であるが、最近、ナノオーダーの粒子サイズで室温において２０ｋＯｅ（１.５９×１０6Ａ／ｍ）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。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。 ε-Fe 2 O 3 is an extremely rare phase among iron oxides. Recently, ε-Fe has a nano-order particle size and exhibits a huge Hc of 20 kOe (1.59 × 10 6 A / m) at room temperature. The presence of 2 O 3 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. The crystal structure and magnetic properties of ε-Fe 2 O 3 have been clarified as shown in Non-Patent Documents 1 to 3, so that ε-Fe 2 O 3 crystals can be synthesized in a substantially single phase state. It is very recent that became.
このε−Ｆｅ2Ｏ3は巨大なＨｃを示すことから、高記録密度の磁気記録媒体その他の磁性用途、あるいは電波吸収用途への適用が期待されている。 Since this ε-Fe 2 O 3 exhibits enormous Hc, it is expected to be applied to a high recording density magnetic recording medium, other magnetic uses, or radio wave absorption uses.
磁性粒子の充填構造によって構築される磁気記録媒体をはじめとする磁性材料では、一般に特定方向の磁場に対する磁気特性を特に顕著に向上させる目的で、磁性粒子の磁化容易軸が一方向に揃うように、製造過程において配向処理が施されることが多い。代表的な配向処理として磁場配向が挙げられる。これは、磁性粉体の粒子を樹脂等のバインダーとともに混練して、所定形状の充填構造を形成させ、バインダーがまだ流動性を有しているあいだにその充填構造に対して一方向の磁場を印加し、粒子の磁化容易軸を印加磁場の方向に揃える処理である。この配向処理を終えた後、バインダーを硬化させると、充填構造を構成する粒子は磁化容易軸が一定方向に揃った状態で固着される。 In magnetic materials such as magnetic recording media constructed with a magnetic particle filling structure, the easy magnetization axes of magnetic particles are generally aligned in one direction for the purpose of particularly remarkably improving the magnetic properties with respect to a magnetic field in a specific direction. Alignment treatment is often performed during the manufacturing process. A typical alignment process is magnetic field alignment. This is because magnetic powder particles are kneaded with a binder such as a resin to form a filling structure of a predetermined shape, and a magnetic field in one direction is applied to the filling structure while the binder is still fluid. This is a process in which the magnetization easy axis of the particles is aligned with the direction of the applied magnetic field. When the binder is cured after this orientation treatment, the particles constituting the filling structure are fixed with the easy magnetization axes aligned in a certain direction.
ところが、ε−Ｆｅ2Ｏ3結晶については、まだ再現性のある合成方法が明らかにされた段階であり、ε−Ｆｅ2Ｏ3結晶を用いた磁性材料について、磁場配向を実現した例は報告されていない。現時点で開発されているε−Ｆｅ2Ｏ3粉体の製法は、逆ミセル法とゾル−ゲル法を組み合わせたプロセスをとるものであり（非特許文献１〜３）、この場合、ε−Ｆｅ2Ｏ3結晶のナノ粒子はゾル−ゲル法で形成されるシリカ等の非磁性物質中に取り囲まれた状態で合成される。このシリカはアルカリによって溶解できるが、個々の粒子を独立して分散させた状態に維持することは非常に難しく、一般的な磁性粉と同様の手法で容易に磁場配向を実現できるものではない。上記の２０ｋＯｅ（１.５９×１０6Ａ／ｍ）という巨大な保磁力Ｈｃが観測されたε−Ｆｅ2Ｏ3結晶の試料は、配向処理を行っていない粉体からなるものであり、磁気特性に関しては、更なる改善の余地が残されている。 However, for ε-Fe 2 O 3 crystals, a reproducible synthesis method has yet to be clarified, and an example of magnetic field orientation using ε-Fe 2 O 3 crystals has been reported. It has not been. Preparation of ε-Fe 2 O 3 powder being developed at present, the reverse micelle method and the sol - are those taking a process combining gel method (Non-Patent Documents 1 to 3), in this case, epsilon-Fe 2 O 3 crystal nanoparticles are synthesized in a state surrounded by a nonmagnetic material such as silica formed by a sol-gel method. This silica can be dissolved by alkali, but it is very difficult to maintain individual particles in an independently dispersed state, and magnetic field orientation cannot be easily realized by a method similar to that of general magnetic powder. The sample of ε-Fe 2 O 3 crystal in which a huge coercive force Hc of 20 kOe (1.59 × 10 6 A / m) is observed is made of powder that has not been subjected to orientation treatment, and is magnetic. There is room for further improvement in terms of characteristics.
本発明は、ε−Ｆｅ2Ｏ3結晶に特有な優れた磁気特性がより一層効果的に発揮される磁性材料を提供することを目的とする。 An object of the present invention is to provide a magnetic material in which the excellent magnetic properties unique to the ε-Fe 2 O 3 crystal are more effectively exhibited.
発明者らは詳細な検討の結果、分散性の良いε−Ｆｅ2Ｏ3粉体の合成に成功し、それを用いて磁場配向させることにより上記目的が達成できることを見出した。
すなわち本発明では、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）を磁性相にもつ鉄酸化物粒子の充填構造を有し、その充填構造を構成する粒子の磁化容易軸が一方向に沿って配向している磁性材料が提供される。
As a result of detailed studies, the inventors have succeeded in synthesizing ε-Fe 2 O 3 powder with good dispersibility, and found that the above object can be achieved by using the magnetic field orientation.
In other words, the present invention has a filling structure of iron oxide particles having ε-Fe 2 O 3 crystals (including those in which a part of Fe site is substituted with the metal element M) in the magnetic phase, Provided is a magnetic material in which the easy magnetization axes of the constituent particles are oriented along one direction.
ここでいう「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。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。
As used herein, “ε-Fe 2 O 3 crystal” includes a pure ε-Fe 2 O 3 crystal in which the Fe site is not substituted with another element, and a part of Fe site is 3 unless otherwise specified. A crystal that is substituted with a valent metal element M and has the same space group as the pure ε-Fe 2 O 3 crystal (that is, the space group is Pna2 1 ) is included. M is made of, for example, one or more of 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.
ここでいう「鉄酸化物」には、ε−Ｆｅ2Ｏ3結晶の他に、(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)Ｆｅ3Ｏ4と空間群が同じである結晶、(iv)ＦｅＯと空間群が同じである結晶のうち、１種以上が含まれていて構わない。ただし、磁性相（磁性を担う結晶）のうち、５０モル％以上がε−Ｆｅ2Ｏ3結晶で占められていることが望ましい。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。 As used herein, “iron oxide” includes, in addition to ε-Fe 2 O 3 crystal, (i) crystal having the same space group as α-Fe 2 O 3 , (ii) γ-Fe 2 O 3 and One or more of a crystal having the same space group, (iii) a crystal having the same space group as Fe 3 O 4, and (iv) a crystal having the same space group as FeO may be included. However, it is desirable that 50 mol% or more of the magnetic phase (crystals responsible for magnetism) is occupied by ε-Fe 2 O 3 crystals. The molar ratio of each crystal can be estimated by analysis by the lead belt method based on X-ray diffraction.
「粒子の磁化容易軸が一方向に沿って配向している」とは、その一方向に垂直な結晶面からの反射が検出されるようにＸ線源、試料、および検出器の位置関係が保たれるＸ線回折試験装置によって測定されたＸ線回折パターンにおいて、空間群がＰｎａ２1である斜方晶の（２００）面に対応する回折ピークの相対強度が、同（１２２）面、（２０１）面、（３１２）面、（３３０）面のいずれの面に対応する回折ピークの相対強度よりも強い場合をいう。 “The easy axis of particles is oriented along one direction” means that the positional relationship between the X-ray source, the sample, and the detector is such that reflection from a crystal plane perpendicular to the one direction is detected. In the X-ray diffraction pattern measured by the maintained X-ray diffraction test apparatus, the relative intensity of the diffraction peak corresponding to the orthorhombic (200) plane whose space group is Pna2 1 has the same (122) plane ( The case where the relative intensity of the diffraction peak corresponding to any of the 201) plane, the (312) plane, and the (330) plane is greater.
前記の「充填構造」は、粒子同士が接しているかまたは近接している状態で、各粒子が立体構造を構成しているものを意味し、最密充填を意味する用語ではない。磁性材料（例えば磁気記録媒体や電波吸収体）として実用に供するためには充填構造を維持させる必要がある。その手法として、非磁性物質をバインダーとして、個々の粒子を固着させることによって充填構造を形成させる手法が採用できる。 The above “packing structure” means that each particle forms a three-dimensional structure in a state where the particles are in contact with each other or close to each other, and is not a term meaning close-packing. In order to be put into practical use as a magnetic material (for example, a magnetic recording medium or a radio wave absorber), it is necessary to maintain the filling structure. As the method, a method of forming a filling structure by fixing individual particles using a nonmagnetic substance as a binder can be employed.
この充填構造を構成する粒子は、ＴＥＭ（透過型電子顕微鏡）写真により測定される平均粒子径が例えば５〜２００ｎｍの範囲にある。ＴＥＭ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。充填構造を構成する粒子は単磁区構造を有していることが望ましい。 The particles constituting this packed structure have an average particle diameter measured by a TEM (transmission electron microscope) photograph, for example, in the range of 5 to 200 nm. The measurement of the average particle diameter from the TEM photograph can be obtained by measuring the largest diameter of each particle (major axis diameter in the case of a rod-shaped one) from the TEM photograph image magnified 600,000 times. 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 particles constituting the filling structure desirably have a single magnetic domain structure.
特に、粒子が球状であるものは、配向処理に際して粒子が向きを変えやすい点で、ロッド状の粒子より有利となる場合がある。そのような形態として、例えば、充填構造を構成する粒子のうち、個数割合で９０％以上の粒子が、アスペクト比３以下の球状粒子であるものが好適な対象となる。粒子のアスペクト比は、ＴＥＭ写真において観測される被測定粒子の最も大きい径（長径）をＤL、それに直角方向の径をＤSとするとき、ＤL／ＤSで表される。 In particular, a spherical particle may be more advantageous than a rod-shaped particle in that the particle can easily change its orientation during the orientation treatment. As such a form, for example, among the particles constituting the packed structure, particles having a number ratio of 90% or more are spherical particles having an aspect ratio of 3 or less. The aspect ratio of the particles, when the largest diameter (major axis) D L of the measured particles observed in TEM photographs, it the diameter of the direction perpendicular to D S, is represented by D L / D S.
保磁力Ｈｃに関しては、後述のように置換元素Ｍの種類およびその配合量によって、広範囲にコントロール可能であるが、本発明では極めて高い保磁力を有する磁性材料として、上記と同様の磁気ヒステリシスループにおいて、２０ｋＯｅ（１.５９×１０6Ａ／ｍ）を超える保磁力Ｈｃが観測されるものが提供される。 As will be described later, the coercive force Hc can be controlled over a wide range depending on the type of the substitution element M and its blending amount. However, in the present invention, as a magnetic material having an extremely high coercive force, , A coercive force Hc of greater than 20 kOe (1.59 × 10 6 A / m) is observed.
（１）この磁性材料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）この磁性材料は、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）この磁性材料は、ε−Ｆｅ2Ｏ3結晶の磁化容易軸が一方向に沿って配向しているので、ＳＦＤの低減、角形比ＳＱの向上など、ε−Ｆｅ2Ｏ3結晶における総合的な磁気特性の改善が達成される。また、これまで引き出すことのできなかった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）特に、保磁力Ｈｃに関しては、２４ｋＯｅ（１.９１×１０6Ａ／ｍ）レベルという、これまでの金属酸化物では考えられない極めて高い保磁力を呈する磁性材料が実現できる。現在、このような高保磁力材料に対して磁気記録を可能にするような手段は開発されていないが、強い磁場を発生する装置近傍で使用される磁性用途、その他において、この高保磁力特性の利用が期待される。
(1) Since this magnetic material 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 material consists of iron oxide particles in which iron is oxidized to trivalent, the corrosion resistance in the atmospheric environment is extremely good as compared with conventional metal-based magnetic powders.
(3) In this magnetic material, since the easy magnetization axis of the ε-Fe 2 O 3 crystal is oriented along one direction, the SFD is reduced, the squareness ratio SQ is improved, and the like in the ε-Fe 2 O 3 crystal. An overall improvement in magnetic properties is achieved. In addition, it is expected that the high coercive force characteristic and the radio wave absorption characteristic peculiar to the ε-Fe 2 O 3 crystal that could not be drawn out so far will be exhibited.
(4) In particular, with respect to the coercive force Hc, a magnetic material exhibiting an extremely high coercive force of 24 kOe (1.91 × 10 6 A / m) level, which cannot be considered with conventional metal oxides, can be realized. At present, no means has been developed to enable magnetic recording for such a high coercive force material, but the use of this high coercive force characteristic is used in magnetic applications used in the vicinity of devices that generate strong magnetic fields. 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、球状の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, spherical 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。 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.
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、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。 The amount of the silica coat can be in the range of 50 to 1000 mol% in terms of the molar ratio represented 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 with a particle size of 100 nm or less and less sintering, it is preferable to apply a silica coat having the 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.
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。 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.
このようにして合成されるε−Ｆｅ2Ｏ3結晶は、シリカの中にε−Ｆｅ2Ｏ3結晶の粒子が取り囲まれたような形態で存在する。このままでは磁性粉体としての利用が難しい。したがって、上記のプロセスを利用して本発明の磁性材料を得るためには、熱処理（焼成）によりε−Ｆｅ2Ｏ3が合成された後に、シリカコートを除去することが重要となる。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。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。 The ε-Fe 2 O 3 crystal synthesized in this way exists in a form in which particles of ε-Fe 2 O 3 crystal are surrounded in silica. As it is, it is difficult to use it as a magnetic powder. Therefore, in order to obtain the magnetic material of the present invention using the above process, it is important to remove the silica coat after ε-Fe 2 O 3 is synthesized by heat treatment (firing). 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. . 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.
このようにしてシリカコートの大部分が除去されたε−Ｆｅ2Ｏ3結晶の粉末は、まだ粒子の表面にＳｉ酸化物がかなり存在している。しかし、液中や、充填構造のバインダーとなる非磁性物質中での分散性は大幅に改善されており、強力な磁場（例えば磁束密度２Ｔ）を印加することにより磁場配向が可能な状況となる。 In the ε-Fe 2 O 3 crystal powder from which most of the silica coat has been removed in this way, a considerable amount of Si oxide is still present on the surface of the particles. However, the dispersibility in the liquid and in the non-magnetic substance serving as the binder of the filling structure has been greatly improved, and a magnetic field orientation is possible by applying a strong magnetic field (for example, magnetic flux density 2T). .
もし、一般的な磁場配向装置で実現できる磁場（例えば磁束密度０.５Ｔ前後）においても磁場配向が可能なε−Ｆｅ2Ｏ3結晶の磁性粉体を得たいのであれば、さらに粒子の分散性を向上させる工夫が望まれる。発明者らは詳細な検討の結果、ε−Ｆｅ2Ｏ3結晶を磁性相にもつ鉄酸化物粒子の表面にＳｉ酸化物が存在しており、その存在量が、Ｓｉ／（Ｆｅ＋Ｍ）×１００で表されるＳｉ量で０.１〜３０モル％になるように調整されているとき、その粉体は極めて良好な分散性を示すことを見出した。すなわち、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量が０.１〜３０モル％、好ましくは０.５〜１０モル％になるようにＳｉ酸化物を残す。このように粒子表面のＳｉ酸化物の量をコントロールするためには、例えば、後述比較例２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。 If it is desired to obtain a magnetic powder of ε-Fe 2 O 3 crystal that can be magnetically oriented even in a magnetic field (for example, a magnetic flux density of about 0.5 T) that can be realized with a general magnetic field orientation device, further dispersion of particles A device to improve the performance is desired. As a result of detailed studies, the inventors have found that Si oxide is present on the surface of iron oxide particles having an ε-Fe 2 O 3 crystal as a magnetic phase, and the abundance thereof is Si / (Fe + M) × 100. It has been found that the powder exhibits extremely good dispersibility when it is adjusted to 0.1 to 30 mol% in the amount of Si represented by: That is, the silica coat is not completely removed, but the Si oxide is left so that the amount of Si according to the above formula is 0.1 to 30 mol%, preferably 0.5 to 10 mol%. In order to control the amount of Si oxide on the particle surface in this way, it is extremely effective to carry out a re-dissolution treatment, for example, as in [Procedure 6-2] shown in Comparative Example 2 described later.
さらに、ε−Ｆｅ2Ｏ3結晶の磁性粉体に含まれる極微細粒子をできるだけ除去するような粒度調整処理を行うことが、磁気特性の改善に有効である。すなわち、ＴＥＭ写真による粒子径が１０ｎｍ未満の粒子の個数割合が１０％以下好ましくは８％以下にまで低減できると、超常磁性を示す極微細粒子による悪影響が顕著に低減され、よりＳＦＤが低く、より角形比ＳＱの大きい磁気ヒステリシスループが観測されるようになる。また、この粒度調整処理は充填性の向上および磁場配向性の改善にも効果的であると考えられる。粒度調整処理の具体的手法として、後述比較例２の〔手順７−１〕〜〔手順７−４〕のような分級操作が有効である。このような分級操作に供するためには、まず、〔手順６−２〕のようにして極めて優れた分散性を実現させておくことが必要となる Furthermore, it is effective to improve the magnetic properties to perform a particle size adjustment process so as to remove as much as possible ultrafine particles contained in the magnetic powder of ε-Fe 2 O 3 crystal. That is, when the number ratio of particles having a particle diameter of less than 10 nm according to a TEM photograph can be reduced to 10% or less, preferably 8% or less, adverse effects due to ultrafine particles exhibiting superparamagnetism are remarkably reduced, and the SFD is lower. A magnetic hysteresis loop having a larger squareness ratio SQ is observed. Further, this particle size adjustment treatment is considered to be effective for improving the filling property and the magnetic field orientation. As a specific method of the particle size adjustment processing, classification operations such as [Procedure 7-1] to [Procedure 7-4] in Comparative Example 2 described later are effective. In order to provide such a classification operation, it is first necessary to realize extremely excellent dispersibility as in [Procedure 6-2].
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.
本発明の磁性材料を構成する粒子の粒子径は、例えば上記工程において熱処理（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。また、前述の分級操作を加えることでより厳密な粒度調整が可能である。磁性粉体のＴＥＭ平均粒子径は５〜２００ｎｍの範囲であることが望ましく、５〜１００ｎｍの範囲であることがより好ましく、１０〜１００ｎｍの範囲が一層好ましい。あまり粒径が大きいと高密度磁気記録には適さない。また、単磁区構造の粒子が得られにくくなる。多磁区構造をとる粒子が存在してしまうと、ε−Ｆｅ2Ｏ3結晶粒子のもつ本来のポテンシャルが十分に発揮されない恐れがある。 The particle diameter of the particles constituting the magnetic material of the present invention can be controlled, for example, by adjusting the amount of silica coat, the firing temperature, and the firing time in the stage before the heat treatment (firing) in the above process. Further, more precise particle size adjustment is possible by adding the above classification operation. The TEM average particle size of the magnetic powder is preferably in the range of 5 to 200 nm, more preferably in the range of 5 to 100 nm, and still more preferably in the range of 10 to 100 nm. If the particle size is too large, it is not suitable for high-density magnetic recording. Moreover, it becomes difficult to obtain particles having a single magnetic domain structure. If particles having a multi-domain structure exist, the original potential of the ε-Fe 2 O 3 crystal particles may not be sufficiently exhibited.
粒子径が５ｎｍより小さい粒子は、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。このような粒度調整は前述の分級操作などによって実施できる。 Particles with a particle size of less than 5 nm do not exhibit a hard magnetic behavior, and behave like a soft magnetic material. Therefore, if many particles smaller than 5 nm are contained, the magnetic properties of the powder are significantly reduced due to the effect of superparamagnetism. To do. 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 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. Such particle size adjustment can be performed by the classification operation described above.
発明者らの研究によれば、ε−Ｆｅ2Ｏ3結晶の室温における磁化容易軸は、空間群がＰｎａ２1である斜方晶のａ軸であると考えられる。磁場配向の処理により、各粒子の磁化容易軸が印加磁場の方向に沿って（すなわちほぼ平行になるように）配向する。このとき、各粒子は充填構造中で回転し、向きを変える。ε−Ｆｅ2Ｏ3結晶は、メタル粉のように針状の形状に起因した磁気異方性ではなく、結晶構造に起因した結晶磁気異方性を利用して配向が可能である。このため、効率的に磁場配向を行うためには、ロッド状の粒子より、回転が起きやすい球状の粒子の方が有利である場合がある。そのような球状粒子からなる粉体として、個数割合で９０％以上の粒子が、アスペクト比３以下の粒子である粉体が好適な対象となる。また、個数割合で９０％以上の粒子が、アスペクト比２.５以下の粒子である粉体、あるいは個数割合で９０％以上の粒子が、アスペクト比２以下の粒子である粉体が一層好適な対象となる。 According to the studies by the inventors, the easy axis of magnetization of the ε-Fe 2 O 3 crystal at room temperature is considered to be an orthorhombic a-axis whose space group is Pna2 1 . By the magnetic field orientation process, the easy magnetization axis of each particle is oriented along the direction of the applied magnetic field (that is, substantially parallel). At this time, each particle rotates in the packed structure and changes its direction. The ε-Fe 2 O 3 crystal can be oriented by utilizing the magnetocrystalline anisotropy caused by the crystal structure, not the magnetic anisotropy caused by the needle shape like the metal powder. For this reason, in order to perform magnetic field orientation efficiently, spherical particles that are likely to rotate may be more advantageous than rod-shaped particles. As such a powder composed of spherical particles, a powder in which 90% or more of the particles are particles having an aspect ratio of 3 or less is suitable. Further, a powder in which particles having a number ratio of 90% or more are particles having an aspect ratio of 2.5 or less, or a powder in which particles having a number ratio of 90% or more are particles having an aspect ratio of 2 or less is more preferable. It becomes a target.
ε−Ｆｅ2Ｏ3結晶を磁性相にもつ鉄酸化物の粉体（以下「ε−Ｆｅ2Ｏ3結晶粉体」ということがある）の磁場配向を行うためには、粉末粒子をバインダーとなる非磁性物質中に分散させ、粒子の回転が拘束されないような充填構造を形成する。その後、この充填構造に対して、ある一方向に磁場を印加する。磁束密度２Ｔ程度の強力な磁場を印加することによりε−Ｆｅ2Ｏ3結晶粉体の磁場配向が可能である。上述のように極めて分散性の良い状態に処理されたε−Ｆｅ2Ｏ3結晶粉体であれば磁束密度０.５Ｔ前後の磁場でも配向が可能である。磁場配向を終えた後、このバインダーが粒子の回転を拘束する程度に硬化すれば、ε−Ｆｅ2Ｏ3結晶の磁場配向体からなる磁性材料が構築される。バインダーとしては、樹脂等の高分子物質の他、シリカを主体とする物質を使用することができる。 In order to perform magnetic field orientation of an iron oxide powder having an ε-Fe 2 O 3 crystal as a magnetic phase (hereinafter sometimes referred to as “ε-Fe 2 O 3 crystal powder”), the powder particles are combined with a binder. The non-magnetic material is dispersed to form a packed structure that does not restrain the rotation of the particles. Thereafter, a magnetic field is applied to the filling structure in a certain direction. By applying a strong magnetic field having a magnetic flux density of about 2T, the magnetic field orientation of the ε-Fe 2 O 3 crystal powder is possible. As described above, the ε-Fe 2 O 3 crystal powder treated in a very dispersible state can be oriented even in a magnetic field having a magnetic flux density of about 0.5 T. After the magnetic field orientation is completed, if the binder is cured to such an extent that the rotation of the particles is restricted, a magnetic material composed of a magnetic field orientation body of ε-Fe 2 O 3 crystal is constructed. As the binder, in addition to a polymer substance such as a resin, a substance mainly composed of silica can be used.
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.
以下の手順に従って、置換元素Ｍを添加していないε−Ｆｅ2Ｏ3結晶を合成し、それを用いた充填構造（無配向体および配向体）について磁気特性を調べた。ここで「無配向体」は磁場による配向を実施していないε−Ｆｅ2Ｏ3結晶粉体の充填構造を意味し、「配向体」は磁場により結晶の磁化容易軸を一方向に沿って配向させたε−Ｆｅ2Ｏ3結晶粉体の充填構造を意味する（実施例２においても同じ）。 According to the following procedure, an ε-Fe 2 O 3 crystal to which the substitution element M was not added was synthesized, and the magnetic properties of the filled structure (non-oriented body and oriented body) using the same were examined. Here, “non-oriented body” means a packed structure of ε-Fe 2 O 3 crystal powder that has not been oriented by a magnetic field, and “oriented body” means that the easy axis of the crystal is aligned along one direction by a magnetic field. This means a packed structure of oriented ε-Fe 2 O 3 crystal powder (the same applies to Example 2).
〔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９ｍＬ、ｎ−オクタン２７.４ｍＬおよび１−ブタノール５.４ｍＬを入れる。そこに、硝酸鉄（III）９水和物を０.００６０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３５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。
[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, 9 mL of pure water, 27.4 mL of n-octane, and 5.4 mL of 1-butanol are added. Thereto is added 0.0006 mol of iron (III) nitrate nonahydrate and dissolved at room temperature with good stirring. Further, cetyltrimethylammonium bromide as a surfactant is added in an amount such that the pure water / surfactant molar ratio is 35, and dissolved by stirring to obtain a micelle solution I.
・ミセル溶液IIの作製
２５％アンモニア水４ｍＬを純水２ｍＬ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３.６ｍＬ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 4 mL of 25% aqueous ammonia is mixed with 2 mL of pure water and stirred, and further 18.3 mL of n-octane and 3.6 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６.０ｍＬ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 the procedure 2, 6.0 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１１５０℃で４時間の熱処理を施す。
[Procedure 5]
After drying the precipitate obtained in the procedure 4, heat treatment is performed at 1150 ° C. for 4 hours in an air atmosphere furnace.
〔手順６〕
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、水酸化テトラメチルアンモニウム(Ｎ（ＣＨ3）4ＯＨ、以下「ＴＭＡＯＨ」という) 水溶液１モル／Ｌにより７２時間、７０℃で撹拌して粒子表面に存在するであろうシリカの除去処理を行う。その後溶液を、遠心分離器（日立工機製ＣＲ２１ＧII）を用いて８０００ｒｐｍで遠心分離して、ε−Ｆｅ2Ｏ3結晶粉体からなる沈殿物を得る。この段階で、上澄みは濁っていたが、上澄み中の粒子が粒子径が小さく、超常磁性粒子を多く含有しているため、廃棄する。
[Procedure 6]
The heat-treated powder obtained in step 5 was carefully pulverized with an agate mortar, and then 72% by 1 mol / L of tetramethylammonium hydroxide (N (CH 3 ) 4 OH, hereinafter referred to as “TMAOH”) aqueous solution. The silica which will exist in the particle | grain surface is stirred for 70 hours at the time, and the removal process is performed. Thereafter, the solution is centrifuged at 8000 rpm using a centrifuge (CR21GII manufactured by Hitachi Koki Co., Ltd.) to obtain a precipitate made of ε-Fe 2 O 3 crystal powder. At this stage, the supernatant was cloudy, but the particles in the supernatant are discarded because they have a small particle size and contain a lot of superparamagnetic particles.
上記手順６により得られたε−Ｆｅ2Ｏ3結晶粉体を「試料粉体」と呼ぶ。
試料粉体のＴＥＭ写真を図１に示す。アスペクト比３以下の球状粒子の個数割合が９０％以上を占める粉体であることがわかる。ＴＥＭ平均粒子径は２７.６ｎｍ、粒子径の標準偏差は１３.０ｎｍ、［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は４７.０％であった。また、粒子径が１０ｎｍ未満の粒子の個数割合は１％であった。また、試料粉体を蛍光Ｘ線分析（日本電子製ＪＳＸ―３２２０）に供したところ、Ｓｉ／Ｆｅ×１００で表されるＳｉ含有量は９.４モル％であった。
The ε-Fe 2 O 3 crystal powder obtained by the procedure 6 is referred to as “sample powder”.
A TEM photograph of the sample powder is shown in FIG. It can be seen that the number ratio of spherical particles having an aspect ratio of 3 or less accounts for 90% or more. The TEM average particle diameter was 27.6 nm, the standard deviation of the particle diameter was 13.0 nm, and the coefficient of variation calculated by [standard deviation of particle diameter] / [TEM average particle diameter] × 100 was 47.0%. The number ratio of particles having a particle diameter of less than 10 nm was 1%. When the sample powder was subjected to fluorescent X-ray analysis (JSX-3220 manufactured by JEOL Ltd.), the Si content represented by Si / Fe × 100 was 9.4 mol%.
上記試料粉体の一部を無配向体に使うために採取した後、以下のようにして配向体を作成した。
〔手順７〕配向体の作成
上記試料粉体（沈殿物）に純水を添加し、超音波洗浄器に３時間かけ分散させることにより、ε−Ｆｅ2Ｏ3結晶粉体の粒子が分散したコロイド溶液を得る。このとき、コロイド溶液中のε−Ｆｅ2Ｏ3結晶粉体の濃度は、１５ｇ／Ｌとする。配向体は、上記コロイド溶液にテトラメトキシシラン（Ｓｉ（ＣＨ3Ｏ）4、以下「ＴＭＯＳ」という）を加え、２Ｔ（２０ｋＯｅ）の磁場中で、水との加水分解反応によりＳｉＯ2ゲルを生成させる手法により作成する。まず上記コロイド水溶液０.３ｍＬと純水０.６ｍＬをよく混ぜておく。この液にＴＭＯＳを０.０９ｍＬ加えて、すばやく撹拌して容器（ガラス製シャーレ）に流し込む。超伝導磁石を使った２Ｔの磁場中に容器をセットし、２４時間待つ。その間に、磁場を受けながらコロイドがゲル化し、配向体が得られる。
After collecting a part of the sample powder for use in the non-oriented body, an oriented body was prepared as follows.
[Procedure 7] Preparation of Oriented Body Pure water was added to the sample powder (precipitate) and dispersed in an ultrasonic cleaner for 3 hours to disperse particles of ε-Fe 2 O 3 crystal powder. A colloidal solution is obtained. At this time, the concentration of the ε-Fe 2 O 3 crystal powder in the colloidal solution is 15 g / L. For the alignment material, tetramethoxysilane (Si (CH 3 O) 4 , hereinafter referred to as “TMOS”) is added to the colloidal solution, and a SiO 2 gel is formed by hydrolysis with water in a magnetic field of 2T (20 kOe). It is created by the technique to make. First, 0.3 mL of the colloidal solution and 0.6 mL of pure water are mixed well. To this solution, 0.09 mL of TMOS is added, stirred rapidly, and poured into a container (glass petri dish). Set the container in a 2T magnetic field using a superconducting magnet and wait for 24 hours. In the meantime, the colloid gels while receiving a magnetic field, and an oriented body is obtained.
上記の試料粉体からなる「無配向体」と、手順７で得られた「配向体」を、それぞれ粉末Ｘ線回折（ＸＲＤ：リガク製ＲＩＮＴ２０００、線源ＣｕＫα線、電圧４０ｋＶ、電流３０ｍＡ）に供した。配向体の測定では、配向方向（磁場の印加方向に対応）に垂直な結晶格子面からの反射が検出されるように、Ｘ線源、配向体、検出器の位置関係が保たれるようにして測定した。図２にこれらのＸ線回折パターンを示す。図２中にはε−Ｆｅ2Ｏ3結晶の指数付けをした。 The “non-oriented body” made of the above sample powder and the “oriented body” obtained in the procedure 7 are each subjected to powder X-ray diffraction (XRD: RINT2000 manufactured by Rigaku, source CuKα ray, voltage 40 kV, current 30 mA). Provided. In the measurement of the oriented body, the positional relationship between the X-ray source, the oriented body, and the detector should be maintained so that reflection from the crystal lattice plane perpendicular to the orientation direction (corresponding to the direction in which the magnetic field is applied) is detected. Measured. FIG. 2 shows these X-ray diffraction patterns. In FIG. 2, ε-Fe 2 O 3 crystals are indexed.
無配向体の回折パターンより、この試料粉体はε−Ｆｅ2Ｏ3の結晶構造（斜方晶、空間群Ｐｎａ２1）に対応するピークを有していることが確認された。その他には、不純物結晶としてα−Ｆｅ2Ｏ3の結晶構造（六方晶、空間群Ｒ−３ｃ）に対応する比較的弱いピークも観察された。 From the diffraction pattern of the non-oriented material, it was confirmed that this sample powder had a peak corresponding to the crystal structure of ε-Fe 2 O 3 (orthorhombic crystal, space group Pna2 1 ). In addition, a relatively weak peak corresponding to the crystal structure of α-Fe 2 O 3 (hexagonal crystal, space group R-3c) was observed as an impurity crystal.
配向体の回折パターンを見ると、ε−Ｆｅ2Ｏ3結晶（２００）面のピーク強度が、無配向体に比べ顕著に強くなっており、配向体作成時に印加した磁場の方向に沿ってε−Ｆｅ2Ｏ3結晶のａ軸が配向したと言うことができる。ただし、（２００）面に対して１５°傾いている（２０１）面や３０°傾いている（３３０）面に対応する回折ピークも観察される。その原因として、粒子同士がシリカ分により架橋されている部分が残っていて、それらの粒子の磁化容易軸が磁場印加方向に沿うように回転できなかったこと、あるいは、ゲル化した試料が乾燥するときの収縮によるマトリックスの変形が配向状態を乱したことが考えられる。なお、配向体の回折パターンには、２θが３０°付近より底角側で相対強度の盛り上がりが観測されるが、これは、配向体を作成するために使用したＴＭＯＳに由来するアモルファス状のシリカ分に起因するものと考えられる。 Looking at the diffraction pattern of the oriented body, the peak intensity of the ε-Fe 2 O 3 crystal (200) plane is significantly stronger than that of the non-oriented body, and along the direction of the magnetic field applied during the creation of the oriented body, ε It can be said that the a-axis of the —Fe 2 O 3 crystal is oriented. However, diffraction peaks corresponding to the (201) plane inclined by 15 ° with respect to the (200) plane and the (330) plane inclined by 30 ° are also observed. The cause is that the part where the particles are cross-linked by silica remains, and the magnetization easy axis of those particles could not be rotated along the magnetic field application direction, or the gelled sample dries. It is considered that the deformation of the matrix due to the shrinkage disturbed the orientation state. In addition, in the diffraction pattern of the oriented body, a rise in relative intensity is observed at the base angle side of 2θ near 30 °. This is an amorphous silica derived from TMOS used for producing the oriented body. Probably due to minutes.
また、上記の試料粉体からなる「無配向体」と、手順７で得られた「配向体」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。配向体に関しては、磁化容易軸方向とそれに垂直な方向（以下「磁化困難軸方向」という）の２通りについて測定した。磁気ヒステリシスループの測定は、カンタムデザイン社製のＭＰＭＳ７の超伝導量子干渉計（ＳＱＵＩＤ）を用いて、印加磁界７０ｋＯｅ（５.５７×１０6Ａ／ｍ）の条件で行ったものである。測定された磁気モーメントの値は酸化鉄の質量で規格化してある。その際、試料中のＳｉ、Ｆｅ、各元素は全てＳｉＯ2、Ｆｅ2Ｏ3で存在しているものと仮定し、各元素の含有割合については蛍光Ｘ線分析で求めた。得られた磁気ヒステリシスループ結果を図３（ａ）および図３（ｂ）に示す。配向体の磁化容易軸方向についての磁気ヒステリシスループは図３（ａ）、図３（ｂ）の両方に記載し、図３（ａ）には無配向体の磁気ヒステリシスループを、また図３（ｂ）には配向体の磁化困難軸方向についての磁気ヒステリシスループを併記してある。 Moreover, the magnetic hysteresis loop at normal temperature (300 K) was measured for the “non-oriented body” made of the above sample powder and the “oriented body” obtained in the procedure 7. With respect to the oriented body, the measurement was performed in two directions: an easy magnetization axis direction and a direction perpendicular thereto (hereinafter referred to as “difficult axis direction”). The measurement of the magnetic hysteresis loop was performed under the condition of an applied magnetic field of 70 kOe (5.57 × 10 6 A / m) using an MPMS7 superconducting quantum interferometer (SQUID) manufactured by Quantum Design. The measured magnetic moment values are normalized by the mass of iron oxide. At that time, it was assumed that Si, Fe, and each element in the sample were all present in SiO 2 and Fe 2 O 3 , and the content ratio of each element was determined by fluorescent X-ray analysis. The obtained magnetic hysteresis loop results are shown in FIGS. 3 (a) and 3 (b). The magnetic hysteresis loop in the direction of the easy axis of the oriented body is described in both FIG. 3 (a) and FIG. 3 (b). FIG. 3 (a) shows the magnetic hysteresis loop of the non-oriented body and FIG. b) shows a magnetic hysteresis loop in the direction of the hard axis of the oriented body.
図３（ａ）から、磁場配向により、磁気ヒステリシスループが角形化し、特定方向についての磁気特性が顕著に改善されることが確認された。また図３（ｂ）からは、上記の磁気特性の改善が磁化容易軸の配向に起因するものであることが肯定される。 From FIG. 3A, it was confirmed that the magnetic hysteresis loop was squared by the magnetic field orientation, and the magnetic characteristics in a specific direction were remarkably improved. Further, from FIG. 3B, it is affirmed that the improvement in the magnetic characteristics is caused by the orientation of the easy magnetization axis.
なお、これらの磁気特性値は以下のとおりである。
〔無配向体〕
保磁力Ｈｃ：２０.１８ｋＯｅ（１.６０７×１０6Ａ／ｍ）、飽和磁化σｓ：１３.６ｅｍｕ／ｇ（Ａ・ｍ2／ｋｇ）、残留磁化：７.１Ａ・ｍ2／ｋｇ、角形比ＳＱ（＝σｒ／σｓ）：０.５２
〔配向体の磁化容易軸方向〕
保磁力Ｈｃ：２３.６７ｋＯｅ（１.８８４×１０6Ａ／ｍ）、飽和磁化σｓ：１４.３ｅｍｕ／ｇ（Ａ・ｍ2／ｋｇ）、残留磁化：１１.５Ａ・ｍ2／ｋｇ、角形比ＳＱ（＝σｒ／σｓ）：０.８０
〔配向体の磁化困難軸方向〕
保磁力Ｈｃ：１３.７１ｋＯｅ（１.０９１×１０6Ａ／ｍ）、飽和磁化σｓ：１２.８ｅｍｕ／ｇ（Ａ・ｍ2／ｋｇ）、残留磁化：３.２Ａ・ｍ2／ｋｇ、角形比ＳＱ（＝σｒ／σｓ）：０.２５
These magnetic characteristic values are as follows.
(Non-oriented material)
Coercive force Hc: 20.18 kOe (1.607 × 10 6 A / m), saturation magnetization σs: 13.6 emu / g (A · m 2 / kg), residual magnetization: 7.1 A · m 2 / kg, square Ratio SQ (= σr / σs): 0.52
[Easy axis direction of orientation body]
Coercive force Hc: 23.67 kOe (1.884 × 10 6 A / m), saturation magnetization σs: 14.3 emu / g (A · m 2 / kg), remanent magnetization: 11.5 A · m 2 / kg, square Ratio SQ (= σr / σs): 0.80
[Direction of hard axis of oriented body]
Coercive force Hc: 13.71 kOe (1.091 × 10 6 A / m), saturation magnetization σs: 12.8 emu / g (A · m 2 / kg), remanent magnetization: 3.2 A · m 2 / kg, square Ratio SQ (= σr / σs): 0.25
ε−Ｆｅ2Ｏ3結晶を以下の手順に従って合成し、それを用いた充填構造（無配向体および磁気テープとした配向体）について磁気特性を調べた。ここでは置換元素ＭとしてＧａを添加した。 ε-Fe 2 O 3 crystals were synthesized according to the following procedure, and the magnetic properties of the filled structure (non-oriented body and oriented body made of magnetic tape) using the crystals were examined. Here, Ga was added as the substitution element M.
〔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。
[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。
〔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.
[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。ｐＨ１１に合わせるのは、ε−Ｆｅ2Ｏ3のゼータ電位を測定したところｐＨ７付近に等電点が存在したためである（実際に、分散時のｐＨを変化すると、ｐＨ７付近は凝集系であった）。
[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 and adjusting the pH to 11. The reason why it is adjusted to pH 11 is that when the zeta potential of ε-Fe 2 O 3 was measured, there was an isoelectric point in the vicinity of pH 7 (in fact, when the pH during dispersion was changed, the vicinity of pH 7 was an agglomerated system. ).
〔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。この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. The powder composing the precipitate 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.
ここでは、上記の沈殿粉を「試料粉体」として採用する。
この試料粉体のＴＥＭ写真を図４に示す。アスペクト比３以下の球状粒子の個数割合が９０％以上を占める粉体であることがわかる。ＴＥＭ平均粒子径は２１.８ｎｍ、粒子径の標準偏差は７.９ｎｍであった。［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は３６.５％であった。また、粒子径１０ｎｍ未満の粒子の個数割合は４.０％であった。
Here, the above-described precipitated powder is adopted as “sample powder”.
A TEM photograph of this sample powder is shown in FIG. It can be seen that the number ratio of spherical particles having an aspect ratio of 3 or less accounts for 90% or more. The TEM average particle size was 21.8 nm, and the standard deviation of the particle size was 7.9 nm. The coefficient of variation calculated by [standard deviation of particle diameter] / [TEM average particle diameter] × 100 was 36.5%. The number ratio of particles having a particle diameter of less than 10 nm was 4.0%.
試料粉体の充填構造からなる無配向体を粉末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５に示す回折パターンが得られた。「沈殿粉」と記載したものが当該無配向体のパターンである。ε−Ｆｅ2Ｏ3の結晶構造（斜方晶、空間群Ｐｎａ２1）に対応するパターンが得られた。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。 When the non-oriented body consisting of the packed structure of the sample powder was subjected to powder X-ray diffraction (XRD: RINT2000 manufactured by Rigaku, radiation source CoKα ray, voltage 40 kV, current 30 mA), the diffraction pattern shown in FIG. 5 was obtained. What is described as “precipitated powder” is the pattern of the non-oriented material. A pattern corresponding to the crystal structure of ε-Fe 2 O 3 (orthorhombic crystal, space group Pna2 1 ) was obtained. 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.
試料粉体を蛍光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、分級後の沈殿粉（当該試料粉体）；ｘ＝０.３９であり、組成の顕著なずれは観測されなかった。また、試料粉体の、Ｓｉ／（Ｆｅ＋Ｇａ）×１００によるＳｉ含有量は２.２モル％であった。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 the sample powder was subjected to X-ray fluorescence analysis (JSX-3220 manufactured by JEOL Ltd.), the value of x when the molar ratio of Ga to Fe was expressed as Ga: Fe = x: (2-x) X = 0.40, but the classified powder (classified sample powder) after classification; x = 0.39, and no significant compositional deviation was observed. Moreover, Si content by Si / (Fe + Ga) * 100 of sample powder was 2.2 mol%. 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.
この試料粉体約２０ｍｇをアクリル製の円筒セル（内径６ｍｍ×深さ３ｍｍ）に詰め、バインダーとして東亞合成株式会社製の接着剤アロンアルファをアセトンで稀釈した液を１滴垂らすことによりε−Ｆｅ2Ｏ3結晶粉体の充填構造を形成した。バインダー中の接着剤成分が硬化するため、充填構造中において粒子は動かないように拘束されている。この充填構造からなる無配向体について、常温（３００Ｋ）における磁気ヒステリシスループを測定した。その結果を図６に示す。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。保磁力Ｈｃは７６４４Ｏｅ（６.０８×１０5Ａ／ｍ）、飽和磁化σｓは１６.９ｅｍｕ／ｇ（Ａ・ｍ2／ｋｇ）、残留磁化σｒは１０.１ｅｍｕ／ｇ（Ａ・ｍ2／ｋｇ）、角形比ＳＱ（＝σｒ／σｓ）は０.６０、ＳＦＤは０.４０１であった。 About 20 mg of this sample powder was packed in an acrylic cylindrical cell (inner diameter 6 mm × depth 3 mm), and ε-Fe 2 was dropped by dropping one drop of a solution obtained by diluting adhesive Aron Alpha manufactured by Toagosei Co., Ltd. with acetone as a binder. A filling structure of O 3 crystal powder was formed. As the adhesive component in the binder cures, the particles are constrained from moving in the filled structure. The magnetic hysteresis loop at normal temperature (300 K) was measured for the non-oriented body having this filled structure. The result is shown in FIG. 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. Coercive force Hc 7644Oe (6.08 × 10 5 A / m), saturation magnetization σs is 16.9emu / g (A · m 2 / kg), residual magnetization σr is 10.1emu / g (A · m 2 / kg), the squareness ratio SQ (= σr / σs) was 0.60, and the SFD was 0.401.
次に、上記の試料粉体（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。 Next, using the above sample powder (precipitated powder), a magnetic paint was prepared as follows, and this was applied to the tape to prepare a magnetic tape oriented in a magnetic field.
〔磁性塗料の調製〕
試料粉末（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 the sample 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、磁束密度０.５５Ｔ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 of magnetic tape]
After finishing the dispersion, the pot lid is opened, the nylon balls are removed, the prepared paint is put together with the steel balls in 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 the application, the film is placed in the center of a coil of an orienter having a magnetic flux density of 0.55 T, oriented in a magnetic field, and then dried.
以上のようにして作成した磁気テープは、塗膜が配向体を形成している。この磁気テープについて、磁場配向時に印加した磁場の方向に対して平行方向の磁気ヒステリシスループを、上記の試料粉体からなる無配向体の場合と同様条件で測定した。その結果を図７に示す。図６の無配向体と比べると、図７の配向体ではループが大きくなり、磁化容易軸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、テープの上に形成した配向体の磁気特性は、無配向体と比べ、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。 As for the magnetic tape produced as mentioned above, the coating film forms the oriented body. With respect to this magnetic tape, a magnetic hysteresis loop parallel to the direction of the magnetic field applied during magnetic field orientation was measured under the same conditions as in the case of the non-oriented body made of the sample powder. The result is shown in FIG. Compared with the non-oriented body of FIG. 6, the loop of the oriented body of FIG. 7 becomes larger, and the effect due to the orientation of the easy axis can be confirmed. That is, as a result of realizing the orientation by the magnetic field, the magnetic properties of the oriented body formed on the tape have a coercive force Hc of 7644 Oe (6.08 × 10 5 A / m) to 8613 Oe (6) compared with the non-oriented body. .85 × 10 5 A / m), squareness ratio SQ (= σr / σs) has been improved from 0.60 to 0.82, and SFD has been improved from 0.401 to 0.388. Was brought.
Claims (6)
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。 Magnetization of particles that have a packed structure of iron oxide particles having ε-Fe 2 O 3 crystals (including those in which a part of Fe site is substituted with the metal element M) in the magnetic phase, and the packed structure Magnetic material with easy axis oriented along one direction.
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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