JPH0375489B2

JPH0375489B2 -

Info

Publication number: JPH0375489B2
Application number: JP60290989A
Authority: JP
Inventors: Takuya Arase; Yoshuki Shibuya; Shigeo Daimon
Original assignee: Daikin Industries Ltd
Current assignee: Daikin Industries Ltd
Priority date: 1985-12-24
Filing date: 1985-12-24
Publication date: 1991-12-02
Also published as: JPS62148313A

Description

【発明の詳細な説明】（産業上の利用分野）本発明は炭化鉄の含有量が高いにも拘らず保磁
力の比効的低い、炭化鉄を含有する針状粒子及び
その製造方法に関する。（従来の技術）一般に磁気記録用磁性材料を用いた記録媒体の
記録密度を高める上では保磁力は高い方が良い。
しかし再生装置のヘツドの能力に応じて、種々の
保磁力を有する磁性材料が求められている。炭化鉄を含有する針状粒子は高保磁力を有する
上に、導電性があり、硬度も高く、優れた磁気記
録媒体用の磁性粉末である。かかる炭化鉄を含有
する針状粒子は、例えば針状オキシ水酸化鉄粒子
または針状酸化鉄粒子を還元炭化剤に250〜400℃
で接触させることにより製造される。この炭化鉄
を含有する針状粒子は炭化鉄の主成分として
Fe₅C₂を含み、その他Fe₃O₄（マグネタイト）及び
遊離炭素を含むことが知られている。しかし、こ
の炭化鉄は余りに高保磁力を有するためにヘツド
の能力によつて使用が制限される場合がある。そ
こで比較的低保磁力を有する炭化鉄の開発が要望
されるようになつた。炭化鉄の保磁力をコントロールするには(1)炭化
反応を途中で停止する、(2)炭化反応の温度を高く
するの２つの方法がある。しかし(1)の場合は
Fe₃O₄が多量に存在し、そのために保磁力分布の
悪化、記録内容の経時変化、磁気転写等をもたら
し好適な磁気記録材料が得られない。また(2)の場
合は副反応として還示炭化剤の分解により多量の
炭素が析出するので、全体として低磁化量の針状
粒子しか得ることができないという問題点があ
る。（発明が解決しようとする問題点）本発明の目的は比較的低保磁力を有する炭化鉄
を高い含有率で含有する針状粒子を提供すること
にある。また本発明の目的は保磁力分布等に優れ、針状
形状の保持性に優れた炭化鉄を含有する針状粒子
を提供することにある。また本発明の目的は用いるヘツドの能力に適合
した保磁力を有する、炭化鉄を含有する針状粒子
を提供することにある。（問題点を解決するための手段）本発明は(a)遊離炭素の含有量が15重量％以下で
あり、 (b)下記式で示されるFe₅C₂の配分率（ｘ）が85
％以上であり、保磁力が〔3x＋300〜7x＋270〕
Oeである炭化鉄を含有する針状粒子に係り、こ
の針状粒子は例えば針状FeOOH粒子を900〜
1000℃で加熱して得られた針状α−Fe₂O₃粒子を
任意に炭化作用を有しない還元剤と200〜700℃で
接触させた後、還元炭化剤と250〜400℃で接触さ
せることにより得られる。一般に磁性粉の保磁力を決定する因子として、
形状異方性と結晶磁気異方性等が知られている。
そして粒子形状が一定ならば形状異方性による保
磁力は一定となり結晶磁気異方性による保磁力に
左右される。本発明は粒子形状が一定の炭化鉄（Fe₅C₂）と
マグネタイト（Fe₃O₄）の形状異方性による保磁
力は一定（270〜300Hc）であり、全体の保磁力
は主にFe₅C₂の結晶磁気異方性の寄与により増大
し、そして、Fe₅C₂の重量比に比例することに基
づき、保磁力をFe₅C₂の配分率の関数として規定
し、決定したものである。ｘ＝（Fe₅C₂のＸ線回折強度）×100／（Fe₅C
₂のＸ線回折強度）＋（Fe₃O₄のＸ線回折強度）従来知られている炭化鉄を含有する針状粒子
（例えば特開昭60−71509号）は、その遊離炭素の
含有率が20重量％以下のとき、保磁力（ｙ）は上
記Fe₅C₂の配分率（ｘ）が特に70以上の範囲で
は、ｙ＝7x＋270を超えてｙ＝7x＋470以下で示さ
れる。そして本発明の目的とされるｙ＝7x＋270
（Oe）またはそれより低い保磁力の炭化鉄を含有
する針状粒子は知られていなかつた。第１図は、Fe₅C₂の配分率（ｘ）と保磁力
（ｙ）との関係を示すもので、従来の炭化鉄を含
有する針状粒子は、ABDCで囲まれる部分内の
点で示され、本発明の粒子は、CDFEで囲まれる
部分内の点で示される。本発明で上記のように比較的低保磁力の炭化鉄
を含有する針状粒子が得られる理由は明確ではな
いが、従来のα−Fe₂O₃粒子はFeOOHを350℃程
度の比較的低温で脱水して得られたもので、その
結晶子が比較的小さいのに対して、本発明では
900〜1000℃という高温で脱水するために、得ら
れるα−Fe₂O₃結晶子が比較的大きいためと推定
される。本発明で使用される針状オキシ水酸化鉄
（FeOOH）は針状のα−，β−及びγ−FeOOH
のいずれでも良く、これを約900〜1000℃で加熱
することにより針状のα−Fe₂O₃を得る。本発明では次いでこの針状α−Fe₂O₃を還元炭
化剤と250〜400℃で接触させることにより目的と
する炭化鉄を含有する針状粒子が製造される。こ
れを炭化作用を有しない還元剤、例えば水素を
200〜700℃で接触させた後行なうこともできる。本発明において針状オキシ水酸化鉄は平均軸比
が３以上のものが通常であり、３〜20のものが好
適であり、平均粒径（長軸）は、通常2μm以下、
好適には0.1〜2μm、最適には0.1〜1.0μmである。
後にも述べるように、製造される針状粒子は、平
均軸比及び平均粒径が、これらの原料のそれらと
比較して若干小さくなるが殆ど変らず、本発明の
針状粒子一般について通常このようなものが好適
であるからである。また、本発明で使用する針状オキシ水酸化鉄
は、形状が針状であり、主成分がオキシ水酸化鉄
である限り、少量の銅、マグネシウム、マンガ
ン、ニツケルの酸化物、炭酸塩；硅素の酸化物；
カリウム塩、ナトリウム塩等を添加して成るもの
であつてもよい。本発明において還元炭化剤としては下記化合物
の少なくとも１種以上を使用することができる。 CO 脂肪族、鎖状もしくは環状の、飽和もしくは
不飽和炭化水素、例えばメタン、プロパン、ブ
タン、シクロヘキサン、メチルシクロヘキサ
ン、アセチレン、エチレン、プロピレン、ブタ
ジエン、イソプレン、タウンガスなど。芳香族炭化水素、例えばベンゼン、トルエ
ン、キシレン、沸点150℃以下のこれらのアル
キル、アルケニル誘導体。脂肪族アルコール、例えばメタノール、エタ
ノール、プロパノール、シクロヘキサノール。エステル、例えばギ酸メチル、酢酸エチル等
の沸点150℃以下のエステル。エーテル、例えば低級アルキルエーテル、ビ
ニルエーテル等の沸点150℃以下のエーテル。アルデヒド、例えばホルムアルデヒド、アセ
トアルデヒド等の沸点150℃以下のアルデヒド。ケトン、例えばアセトン、メチルエチルケト
ン、メチルイソブチルケトン等の沸点150℃以
下のケトン。特に好ましい還元炭化剤はCO、CH₃OH、
HCOOCH₃、炭素数１〜５の飽和または不飽和
の脂肪族炭化水素である。本発明において還元炭化剤は希釈してあるいは
希釈せずに使用することができ、希釈剤として
は、例えばN₂、アルゴン、ヘリウム等を挙げる
ことができる。また希釈率は任意に選択できる
が、１を超えて10倍まで（容量比）にとどめて希
釈するのが好ましい。接触温度、接触時間、流速
等の接触条件は、例えば針状酸化鉄の製造履歴、
平均軸比、平均粒径、比表面積等に応じ変動する
ため、適宜選択するのがよい。好ましい接触温度
は、約250〜400℃、より好ましくは約300〜400
℃、好ましい接触時間は約0.5〜６時間である。
好ましい流速は、原料の針状酸化鉄１ｇ当り希釈
剤を除いて約１〜1000mlS.T.P／分、好ましくは
約５〜500mlS.T.P.／分である。なお、接触圧力
は、希釈剤をも含めて、１〜２気圧が常用される
が、特に制限はない。本発明において得られる粒子は、電子顕微鏡で
観察すると、平均的に一様な針状粒子であり、原
料の針状粒子と同形状で、これらの形骸粒子であ
り、これが一次粒子となつて存在している。ま
た、得られる針状粒子は、元素分析により炭素を
含有し、更にＸ線回折パターンにより、炭化鉄を
含有することが明らかである。Ｘ線回折パターン
は、面間隔が2.28、2.20、2.08、2.05及び1.92Åを
示す。かかるパターンは、Fe₅C₂に相当し、本発
明の炭化鉄の主成分はFe₅C₂からなる。また、本発明で得られる針状粒子は酸化鉄、主
としてFe₃O₄をも含有することが多い。また本発明の針状粒子は遊離炭素を含有するこ
とが多いが、その含有量は15重量％以下であるこ
とが必要である。15重量％を越える場合は磁化量
の低下をもたらすので不適当である。本発明で得られる針状粒子は式Ｘ＝（Fe₅C₂のＸ線回折強度）×100／（Fe₅C
₂のＸ線回折強度）＋（Fe₃O₄のＸ線回折強度）で示されるFe₅C₂の配分率が85％以上であり、保
磁力が〔3x＋300〜7x＋270〕Oe、好ましくは
〔3x＋300〜6x＋300〕Oeの範囲である。また、得られる針状粒子の平均軸比及び平均粒
径は、原料の針状粒子のそれらと比較して若干小
さくなるが殆ど差はない。従つて、この製法で得
られる針状粒子の平均軸比は、通常３以上、好適
には３〜20であり、平均粒径（長軸）は、通常
2μm以下、好適には0.1〜2μm、最適には0.1〜
1.0μmである。本発明の炭化鉄を含有する針状粒子は、前述の
特徴等から明らかなとおり、磁気記録用磁性材料
として用いることができるが、これに限られるも
のではなく、低級脂肪族炭化水素のCOとH₂とか
らの合成のための触媒等として用いることもでき
る。（発明の効果）本発明の炭化鉄を含有する針状粒子は保磁力分
布、針状形状の保持性に優れている。また本発明の炭化鉄を含有する針状粒子は用い
るヘツドの能力に適合した保磁力とすることがで
き、且つ優れた導電性及び硬度を有している。また、本発明の針状粒子の磁化量は、保磁力が
ほぼ同等であるコバルト変成磁性粒子と比べて10
〜30％程度大である。（実施例）以下に実施例を挙げて詳しく説明する。実施例において、各種特性等はそれぞれ次の方
法によつて求めた。 (1) 磁気特性特別に記載がない限り次の方法によつて求め
る。磁化特性は最大磁場が2500Oeである理研
電子株式会社製BHH−50直流磁化特性自動記
録装置により測定る。 (2) 全炭素量の分析Ｃの元素分析を(株)柳本製作所製の
MT2CHNCORDER Yanacoを使用し、900℃
で酸素（ヘリウムキヤリヤ）を通じることによ
り常法に従つて行う。 (3) 遊離炭素量の分析遊離炭素量はCHN元素分析より求めた全炭
素量、Fe₅C₂による理論炭素量および配分率か
ら計算する。この場合、配分率は重量による配
分率（ｚ）、すなわち、ｚ＝（Fe₅C₂の重量）×100／（Fe₅C₂の重量）＋（Fe₃O₄の重量）にＸ線回折強度による配分率（ｘ）がほぼ一致
することにより配分率（ｘ）で代用する。参考例１針状α−FeOOH粒子５ｇをマツフル炉に入れ
800℃で１時間加熱して平均粒径0.7μm（長軸）、
平均軸比10の針状α−Fe₂O₃粒子を得た。この針
状α−Fe₂O₃粒子２ｇを磁製ボートに入れて管状
炉に挿入し、340℃に昇温し、その温度でCOを
200ml／minの流速で３時間接触させた。得られ
た粉末の特性を第１表に示す。実施例１〜２ α−FeOOHの加熱温度、α−Fe₂O₃の接触条
件を第１表に記載の通りにし、他は実施例１と同
様にして粉末を得た。結果を同様第１表に示す。参考例２〜４ α−FeOOHの加熱温度、α−Fe₂O₃の接触条
件を第１表に記載の通りにし、他は実施例１と同
様にして粉末を得た。結果を同様第１表に示す。【表】DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to acicular particles containing iron carbide, which have a low specific coercive force despite a high content of iron carbide, and a method for producing the same. (Prior Art) Generally, in order to increase the recording density of a recording medium using a magnetic material for magnetic recording, it is better to have a higher coercive force.
However, magnetic materials having various coercive forces are required depending on the capabilities of the head of the playback device. Acicular particles containing iron carbide have high coercive force, electrical conductivity, and high hardness, and are excellent magnetic powders for magnetic recording media. Such acicular particles containing iron carbide can be produced by heating, for example, acicular iron oxyhydroxide particles or acicular iron oxide particles at 250 to 400°C using a reducing carbonizing agent.
produced by contacting with This acicular particle containing iron carbide is the main component of iron carbide.
It is known to contain Fe ₅ C ₂ and also Fe ₃ O ₄ (magnetite) and free carbon. However, since iron carbide has an extremely high coercive force, its use may be limited by the capacity of the head. Therefore, there has been a demand for the development of iron carbide having a relatively low coercive force. There are two ways to control the coercive force of iron carbide: (1) stopping the carbonization reaction midway through, and (2) increasing the temperature of the carbonization reaction. However, in the case of (1)
A large amount of Fe ₃ O ₄ is present, which causes deterioration in coercive force distribution, changes in recorded content over time, magnetic transfer, etc., making it impossible to obtain a suitable magnetic recording material. In the case of (2), a large amount of carbon is precipitated as a side reaction due to the decomposition of the reducing carbonizing agent, so there is a problem that only acicular particles with a low magnetization amount can be obtained as a whole. (Problems to be Solved by the Invention) An object of the present invention is to provide acicular particles containing a high content of iron carbide having a relatively low coercive force. Another object of the present invention is to provide iron carbide-containing acicular particles that have excellent coercive force distribution and excellent retention of acicular shape. Another object of the present invention is to provide iron carbide-containing acicular particles having a coercive force suited to the capacity of the head used. (Means for Solving the Problems) The present invention provides (a) a free carbon content of 15% by weight or less, and (b) a distribution ratio (x) of Fe ₅ C ₂ expressed by the following formula of 85
% or more, and the coercive force is [3x+300 to 7x+270]
Regarding acicular particles containing iron carbide, which is Oe, these acicular particles contain acicular FeOOH particles, for example,
The acicular α-Fe ₂ O ₃ particles obtained by heating at 1000°C are optionally brought into contact with a reducing agent that does not have a carbonizing effect at 200 to 700°C, and then brought into contact with a reducing carbonizing agent at 250 to 400°C. It can be obtained by In general, the factors that determine the coercive force of magnetic powder are:
Shape anisotropy, magnetocrystalline anisotropy, etc. are known.
If the particle shape is constant, the coercive force due to shape anisotropy is constant and depends on the coercive force due to magnetocrystalline anisotropy. In the present invention, the coercive force due to the shape anisotropy of iron carbide (Fe ₅ C ₂ ) and magnetite (Fe ₃ O ₄ ), which have a constant particle shape, is constant (270 to 300 Hc), and the overall coercive force is mainly due to Fe The coercive force is defined and determined as a function of the distribution ratio of Fe ₅ C ₂ based on the fact that it increases due to the contribution of the magnetocrystalline anisotropy of ₅ C ₂ and is proportional to the weight ratio of Fe ₅ C ₂ It is. x = (X-ray diffraction intensity of Fe ₅ C ₂ ) × 100 / (Fe ₅ C
(X-ray diffraction intensity of ₂ ) + (X-ray diffraction intensity of Fe ₃ O ₄ ) Conventionally known acicular particles containing iron carbide (for example, JP-A-60-71509) have a free carbon content of is 20% by weight or less, the coercive force (y) exceeds y=7x+270 and is shown as y=7x+470 or less, especially in the range where the distribution ratio (x) of Fe ₅ C ₂ is 70 or more. And y=7x+270 which is the object of the present invention
Acicular particles containing iron carbide with a coercivity of (Oe) or lower were not known. Figure 1 shows the relationship between the distribution ratio (x) of Fe ₅ C ₂ and coercive force (y). The particles of the present invention are shown as points within the area surrounded by CDFE. Although it is not clear why the present invention produces acicular particles containing iron carbide with a relatively low coercive force as described above, conventional α-Fe ₂ O ₃ particles are capable of producing FeOOH at a relatively low temperature of about 350°C. The crystallites are relatively small, whereas in the present invention, the crystallites are relatively small.
This is presumed to be because the α-Fe ₂ O ₃ crystallites obtained are relatively large due to dehydration at a high temperature of 900 to 1000°C. The acicular iron oxyhydroxide (FeOOH) used in the present invention is acicular α-, β- and γ-FeOOH.
Any of these may be used, and acicular α-Fe ₂ O ₃ is obtained by heating this at about 900 to 1000°C. In the present invention, the desired acicular particles containing iron carbide are produced by bringing the acicular α-Fe ₂ O ₃ into contact with a reducing carbonizing agent at 250 to 400°C. This is then treated with a reducing agent that does not have a carbonizing effect, such as hydrogen.
It can also be carried out after contact at 200 to 700°C. In the present invention, the acicular iron oxyhydroxide usually has an average axis ratio of 3 or more, preferably 3 to 20, and the average particle diameter (long axis) is usually 2 μm or less,
It is preferably 0.1 to 2 μm, most preferably 0.1 to 1.0 μm.
As will be described later, the average axial ratio and average particle diameter of the acicular particles produced are slightly smaller than those of these raw materials, but there is almost no difference, and this is usually the case for the acicular particles of the present invention in general. This is because something like this is suitable. In addition, the acicular iron oxyhydroxide used in the present invention is acicular in shape, and as long as the main component is iron oxyhydroxide, small amounts of copper, magnesium, manganese, nickel oxides, carbonates; silicon oxide;
It may be formed by adding potassium salt, sodium salt, etc. In the present invention, at least one of the following compounds can be used as the reducing carbonizing agent. CO Aliphatic, linear or cyclic, saturated or unsaturated hydrocarbons, such as methane, propane, butane, cyclohexane, methylcyclohexane, acetylene, ethylene, propylene, butadiene, isoprene, town gas, etc. Aromatic hydrocarbons, such as benzene, toluene, xylene, and their alkyl and alkenyl derivatives with a boiling point of 150°C or less. Aliphatic alcohols such as methanol, ethanol, propanol, cyclohexanol. Esters, such as methyl formate, ethyl acetate, etc., with a boiling point of 150°C or less. Ethers, such as lower alkyl ethers and vinyl ethers, with a boiling point of 150°C or less. Aldehydes, such as formaldehyde, acetaldehyde, etc., with a boiling point of 150°C or less. Ketones, such as acetone, methyl ethyl ketone, methyl isobutyl ketone, etc., with a boiling point of 150°C or less. Particularly preferred reducing carbonizing agents are CO, CH ₃ OH,
HCOOCH ₃ is a saturated or unsaturated aliphatic hydrocarbon having 1 to 5 carbon atoms. In the present invention, the reducing carbonizing agent can be used diluted or undiluted, and examples of the diluent include N ₂ , argon, helium, and the like. Further, the dilution ratio can be selected arbitrarily, but it is preferable to dilute to more than 1 and up to 10 times (volume ratio). Contact conditions such as contact temperature, contact time, and flow rate are determined based on, for example, the manufacturing history of acicular iron oxide,
Since it varies depending on the average axial ratio, average particle diameter, specific surface area, etc., it is best to select it appropriately. Preferred contact temperature is about 250-400°C, more preferably about 300-400°C
℃, the preferred contact time is about 0.5 to 6 hours.
The preferred flow rate is about 1 to 1000 ml S.TP/min, preferably about 5 to 500 ml S.TP/min, excluding diluent, per gram of raw acicular iron oxide. The contact pressure, including the diluent, is usually 1 to 2 atmospheres, but is not particularly limited. When observed with an electron microscope, the particles obtained in the present invention are averagely uniform acicular particles, and have the same shape as the acicular particles of the raw material. are doing. Further, it is clear that the obtained acicular particles contain carbon according to elemental analysis, and further contain iron carbide according to the X-ray diffraction pattern. The X-ray diffraction pattern shows interplanar spacings of 2.28, 2.20, 2.08, 2.05 and 1.92 Å. Such a pattern corresponds to Fe ₅ C ₂ , and the main component of the iron carbide of the present invention consists of Fe ₅ C ₂ . In addition, the acicular particles obtained in the present invention often also contain iron oxide, mainly Fe ₃ O ₄ . Further, the acicular particles of the present invention often contain free carbon, but the content must be 15% by weight or less. If it exceeds 15% by weight, the amount of magnetization decreases, which is inappropriate. The acicular particles obtained in the present invention have _the formula: X=(X-ray diffraction intensity of Fe ₅ C ₂ )
The distribution ratio of Fe ₅ C ₂ expressed as (X-ray diffraction intensity of ₂ ) + (X-ray diffraction intensity of Fe ₃ O ₄ ) is 85% or more, and the coercive force is [3x + 300 to 7x + 270] Oe, preferably [3x + 300 ~6x+300〕Oe range. Further, the average axial ratio and average particle diameter of the obtained acicular particles are slightly smaller than those of the raw material acicular particles, but there is almost no difference. Therefore, the average axis ratio of the acicular particles obtained by this manufacturing method is usually 3 or more, preferably 3 to 20, and the average particle diameter (long axis) is usually 3 or more, preferably 3 to 20.
2 μm or less, preferably 0.1 to 2 μm, optimally 0.1 to 2 μm
It is 1.0 μm. As is clear from the above characteristics, the iron carbide-containing acicular particles of the present invention can be used as a magnetic material for magnetic recording, but are not limited thereto. It can also be used as a catalyst for synthesis from _H2 . (Effects of the Invention) The iron carbide-containing acicular particles of the present invention have excellent coercive force distribution and acicular shape retention. Further, the iron carbide-containing acicular particles of the present invention can have a coercive force suitable for the capacity of the head used, and have excellent electrical conductivity and hardness. Furthermore, the amount of magnetization of the acicular particles of the present invention is 10
~30% larger. (Example) Examples will be described in detail below. In the Examples, various characteristics etc. were determined by the following methods. (1) Magnetic properties Determine by the following method unless otherwise specified. The magnetization characteristics are measured using a BHH-50 DC magnetization characteristics automatic recorder manufactured by Riken Electronics Co., Ltd. with a maximum magnetic field of 2500 Oe. (2) Analysis of total carbon content Elemental analysis of C was carried out using Yanagimoto Seisakusho Co., Ltd.
Using MT2CHNCORDER Yanaco, 900℃
This is carried out according to the conventional method by passing oxygen (helium carrier) through the tube. (3) Analysis of free carbon content The free carbon content is calculated from the total carbon content determined by CHN elemental analysis, the theoretical carbon content based on Fe ₅ C ₂ , and the distribution ratio. In this case, the distribution rate is the distribution rate by weight (z), that is, z = (weight of Fe ₅ C ₂ ) × 100 / (weight of Fe ₅ C ₂ ) + (Fe ₃ Since the distribution rate (x) based on the X-ray diffraction intensity almost matches the weight of O ₄ , the distribution rate (x) is used instead. Reference example 1 5g of acicular α-FeOOH particles are placed in a Matsufuru furnace.
Heated at 800℃ for 1 hour to obtain an average particle size of 0.7μm (long axis).
Acicular α-Fe ₂ O ₃ particles with an average axial ratio of 10 were obtained. 2g of these acicular α-Fe ₂ O ₃ particles were placed in a porcelain boat, inserted into a tube furnace, heated to 340℃, and CO was removed at that temperature.
Contact was carried out for 3 hours at a flow rate of 200 ml/min. The properties of the obtained powder are shown in Table 1. Examples 1 to 2 Powders were obtained in the same manner as in Example 1 except that the heating temperature of α-FeOOH and the contact conditions of α-Fe ₂ O ₃ were as shown in Table 1. The results are also shown in Table 1. Reference Examples 2 to 4 Powders were obtained in the same manner as in Example 1 except that the heating temperature of α-FeOOH and the contact conditions of α-Fe ₂ O ₃ were as shown in Table 1. The results are also shown in Table 1. 【table】

[Brief explanation of drawings]

第１図は、Fe₅C₂の配分率（ｘ）と保磁力
（Oe）を示すもので、従来のものは、ABDCに囲
まれた部分内にあり、CDFEで囲まれる部分が本
発明の針状粒子のものを示す。 Figure 1 shows the distribution ratio (x) and coercive force (Oe) of Fe ₅ C _2. In the conventional model, the area is surrounded by ABDC, and in the present invention, the area surrounded by CDFE is in the area surrounded by ABDC. Shows needle-like particles.

Claims

[Scope of Claims] 1 (a) The content of free carbon is 15% by weight or less, (b) The distribution ratio (x) of Fe ₅ C ₂ shown by the following formula is 85
% or more, and the coercive force is [3x+300 to 7x+270]
Acicular particles containing iron carbide, which is Oe. x = (X-ray diffraction intensity of Fe ₅ C ₂ ) × 100 / (Fe ₅ C
₂ ) + (X-ray diffraction intensity of Fe ₃ O ₄ ) 2 The acicular particles according to claim 1, having a coercive force in the range of [3x+300 to 6x+300] Oe. 3. The acicular α-Fe ₂ O ₃ particles are optionally brought into contact with a reducing agent that does not have a carbonizing effect at 200 to 700°C, and then brought into contact with a reducing carbonizing agent at 250 to 400°C to form acicular α-Fe 2 O 3 particles containing iron carbide. In the method of producing particles, acicular α-
Fe ₂ O ₃ particles are obtained by heating acicular FeOOH particles at 900 to 1000 °C, and the desired acicular particles (a) have a free carbon content of 15% by weight or less; (b) ) The distribution ratio (x) of Fe ₅ C ₂ shown by the following formula is 85
% or more, and the coercive force is [3x+300 to 7x+270]
A method for producing acicular particles containing iron carbide, characterized in that Oe. x = (X-ray diffraction intensity of Fe ₅ C ₂ ) × 100 / (Fe ₅ C
₂ ) + (X-ray diffraction intensity of Fe ₃ O ₄ ) 4 The manufacturing method according to claim 3, wherein the coercive force is in the range of [3x+300 to 6x+300] Oe.