JPS61111922A - Production of acicular particle containing iron carbide - Google Patents

Abstract

PURPOSE:To produce an acicular particle having excellent magnetic properties and high iron carbide content, by contacting an alkali-treated or Co-coated gamma-Fe2O3 with CO or a mixture of CO and H2. CONSTITUTION:An alkali-treated or Co-coated gamma-Fe2O3 is used as the starting material. The alkali treatment is carried out by conventional method, e.g. by contacting the iron oxide with and aqueous solution of an alkali such as sodium hydroxide (preferably >=10pH), and filtering and drying the treated material. The Co-coating is also carried out by conventional method, e.g. by putting the gamma-Fe2O3 in an aqueous solution of a Co salt (e.g. a dilute solution of 0.1-10wt% concentration), alkalinizing the solution with an alkaline aqueous solution, and filtering and drying the material. The treated gamma-Fe2O3 is made to contact with CO or a mixture of CO and H2 (preferably at 250-400 deg.C) to obtain an acicular particle containing iron carbide.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to a method for producing acicular particles containing iron carbide.

(Prior Art) The applicant has prepared acicular iron oxyhydroxide or acicular iron oxide in a cocoon.
Or, by contacting it with a mixture of this and H2 at 250 to 400°C, acicular particles containing iron carbide are produced, which are chemically stable and have a high coercive force, and are useful as a magnetic material for magnetic recording media. I discovered something and applied for a patent (
For example, Japanese Patent Application No. 58-171765, No. 58-2175
No. 30, No. 58-236753, No. 59-10400
issue). However, among the raw iron compounds, γ-F e203 is easily available, but the particles containing iron carbide obtained from it have a low proportion of iron carbide and have inferior magnetic properties compared to other materials. be.

(Problems to be Solved by the Invention) An object of the present invention is to provide a method for producing particles from easily available γ-Fe20z that have a high content of iron carbide and therefore have excellent magnetic properties.

(Means for solving the problems) The present invention provides γ-Fe20=
The present invention relates to a method for producing acicular particles containing iron carbide, which is characterized by contacting CO or a mixture of CO and N2.

In the present invention, as γ-Fe2O3, for example, a-F
eO○H1 β-FeOOH or γ-FeOOH is heated to approximately 200 to 350°C and dehydrated, or α, β, or γ-FeOOH is heated to approximately 30°C.
Heated to 0-600℃ and α-F e20-stitched, then F
γ-Fe20, which is reduced to e, O, and further oxidized at about 300 to 400° C. to make the crystal dense, can be used. γ-Fe2O3 is the raw material α-1
A product produced by dehydrating β-9γ-FeOOH with a surface pH of 5 or more can also be used.

In the present invention, γ-Fe2O3 usually has an average axial ratio of 3 or more, preferably 3 to 20, and the average particle size (elongated) is usually 5 μm or less, preferably 0.1 to 20. 2μ
m, optimally 0.1 to 1.0 μm. As will be described later, the particles produced have an average axial ratio and an average particle diameter of
Although it is slightly smaller than those of the raw material, there is almost no difference.
This is because such particles are generally suitable for the particles of the present invention.

Moreover, γ-Fe20. used in the present invention. has the principal component γ
-Fe2e, a small amount of copper, magnesium, manganese, nickel oxide or carbonate; silicon oxide; potassium salt, sodium salt, etc. may be added.

In the present invention, γ-Fe20. is treated with alkali or Co
The one covered is used.

The alkali treatment can be carried out by a known method, for example, the object to be treated is treated with an aqueous alkali solution such as sodium hydroxide, potassium hydroxide, or ammonium hydroxide (for example, p
H8 or higher, preferably 10 or higher), stirred for 30 minutes to 1 hour if necessary, filtered, and dried.

Co deposition may also be done by following a known method, for example, γ
-Fe20. It is preferable to add and stir at room temperature or under heating, make alkaline with an aqueous alkaline solution, stir for 30 minutes to 1 hour if necessary, separate and dry.

The raw material is coated with an anti-sintering agent such as a silicon compound, a boron compound, an aluminum compound, an aliphatic carboxylic acid or its salt, a phosphorus compound or a titanium compound, as described in Japanese Patent Application No. 58-250163. It can also be used.

In the present invention, CO or a mixture of CO and N2 can be used diluted or undiluted, and examples of the diluent include N2, CO2, argon, helium, and the like. When using a mixture of CO and N2, the mixing ratio can be selected as appropriate, but it is usually preferable that the volume ratio of CO and N2 is Ilo, 05 to 175. Further, the dilution rate can be selected arbitrarily, for example, about 1
．． It is preferable to dilute 1 to 10 times (volume ratio). Contact conditions such as contact temperature, contact time, flow rate, etc. are, for example, γ-Fe
Since it varies depending on the manufacturing history of 20s, average axial ratio, average particle diameter, specific surface area, etc., it is best to select it appropriately. The preferred contact temperature is about 250-400°C, more preferably about 3
00-380°C, the preferred contact time is about 1-12 hours. The preferred flow rate is the raw material γ-Fe20=(1g)
approximately 1 to 10100 OS, T, P/min. In addition,
The contact pressure, including the diluent, is usually 1 to 2 atmospheres, but is not particularly limited.

The particles obtained in the present invention are particles that are uniform on average and have the same shape as the raw material particles, and are skeletal particles that exist as large particles when observed with an electron microscope. There is. Further, it is clear that the obtained particles contain carbon according to elemental analysis, and further contain iron carbide according to the X-ray diffraction pattern. The X-ray diffraction pattern has interplanar spacings of 2.28.2.20.2.08.2.05 and 1.
92A is shown. The overcast pattern corresponds to Fe5C2, whereas the iron carbide of the present invention usually consists mainly of Fe2C.

Fe2oc 9 (F e2.2c ), Fe, C, etc. may coexist. Therefore, the iron carbide contained in the particles of the present invention is appropriately expressed as FexC (2≦Niku3).

In case of incomplete carbonization, the particles obtained according to the invention also contain iron oxides, mainly F ez O4.

Generally, regarding iron oxide, FeO, Fe, 0. and γ
-Fe20* is structurally related r), the oxygen atoms in all three have a cubic close-packed structure, and the actually existing Fe50< varies within these widths, so the above The iron oxide of is suitably denoted by Fe0y (1<y≦1.5).

In addition, the obtained particles contain iron carbide or iron oxide in some cases, but referring to the elemental analysis values of C, H and N,
Usually, it contains more carbon than the amount of carbon calculated from the chemical formula of iron carbide, which is confirmed by the X-ray diffraction pattern. It is unclear whether such excess carbon exists in combination with iron or as free carbon. In this sense, elemental carbon may be present in the particles obtained. Therefore,
The particles obtained are - particles consisting essentially of iron carbide or particles consisting of iron carbide, iron oxide and/or elemental carbon, in the form of large particles with an average axial ratio of 3 or more.

Therefore, the content of iron carbide and iron oxide in the obtained particles is determined by defining the respective main components Fe5C2 and Fe,'O, detected by X-ray diffraction analysis as the chemical formulas of iron carbide and iron oxide, and further It can be determined by elemental analysis and scorching heat gain. The content of iron carbide is preferably 20% by weight or more, more preferably 50% by weight or more. Also, iron oxide is 7
It is preferably 0% by weight or less, and more preferably 40% by weight or less.

Further, the average axial ratio and average particle diameter of the obtained particles are slightly smaller than those of the raw material γ-Fe2O3, but there is almost no difference. Therefore, the average axial ratio of the particles obtained by this manufacturing method is usually 3 or more, preferably 3 to 20, and the average particle diameter (long axis) is usually 5 μm or less, preferably 0.1 to 2 μm. The optimal value is 0.1 to 1.0u111.

As is clear from the above-mentioned characteristics, the iron carbide-containing 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 the synthesis of

(Effects of the Invention) According to the method of the present invention, particles with a high content of iron carbide and therefore excellent magnetic properties can be obtained using easily available γ-Fe203 as a raw material.

(Example) A detailed explanation will be given below using examples.

In Examples, various characteristics etc. were determined by the following methods.

(1) Magnetic properties Unless otherwise specified, it is determined by the following method.

Although a Hall element was used, the sample filling rate was 0 according to the mass meter.
．． 2, the measurement magnetic field was 5 kOe, and the coercive force (He.

Oe), saturation magnetization! (σs, e, m, u) and residual magnetization (σr, e, w, u) are measured.

(2) Elemental analysis of C, H and N Elemental analysis is performed using MT2CHNeORD manufactured by Yanagimoto Seisakusho Co., Ltd.
It is carried out according to a conventional method by using ERYanaco and passing oxygen (helium carrier) at 900°C.

(3) How to determine the composition The chemical formulas of iron oxide and iron carbide were determined by XM diffraction analysis, and the elemental analysis value of C and the weight increase due to the heat treatment described below were determined.6 For example, Fe=0° is 1 of the weight. .0
Fe2O, which is equivalent to 35 times its weight, and Fe2O, which is equivalent to 1,317 times its weight.

Calculations are performed assuming that the value changes to . Weight increase due to heat treatment can be measured by placing the sample in a platinum crucible and heating it in a Matsufuru furnace for 6 hours.
After heat treatment at 00℃ for 1 hour, Q-F was determined by X-ray diffraction.
After confirming the presence of e203, the weight increase due to heat treatment is determined according to a conventional method.

More specifically, the composition ratios of Fe, C2, Fe=O- and elemental carbon are Xs Y and 2% by weight, respectively.
Assuming that the carbon analysis value and the weight increase due to heat treatment are A and 8% by weight, respectively, X1V and 2 can be determined from the following three-dimensional equation.

+y 10z = 100 1.317x+ 1.0357= 100+ Bz +
0.079x ” A Reference Example 1 3 g of α-FeOOH was dehydrated at 600°C for 1 hour to form α-F.
e 203, H2 reduction was carried out at 400℃ for 1 hour, and 350
It was oxidized in air at ℃ for 1 hour to obtain γ-Fe20-. This γ-F C20a was added to 10% of a 2% aqueous sodium hydroxide solution.
The mixture was stirred at room temperature for 1 hour, and then split and dried to obtain alkali-treated χ-Fe20*.

Reference example 2 3 g of Q-FeOOH was added to 2% sodium hydroxide aqueous solution 20
The mixture was poured into a 0ml solution, stirred at room temperature for 1 hour, and then cracked and dried.

This α-FeooH was placed in a Matsufuru furnace and heated to 300℃ for 1
After heating for a period of time, γ-Fe2O3 was obtained.

Next, this was poured into 100 ml of 2% copal sulfate, adjusted to pH 10 with aqueous NaOH solution with stirring, stirred at 80°C for 30 minutes, and dried to remove the Co-coated γ-F.
C20s was obtained.

Reference Example 3 3 g of CI-FeOOH was dehydrated at 600°C for 1 hour to obtain γ-Fe20. Hereinafter, Co-coated γ-
Obtained 20 Fe.

Examples 1 to 5 2 g of acicular γ-Fe201 particles having a predetermined average particle diameter (long axis) and average axial ratio that have been treated with alkali or coated with Co as shown in Table 1 are placed in a porcelain boat and inserted into a tube furnace. After replacing the air with nitrogen, the mixture was heated to a predetermined contact temperature, contacted with a contact gas at a predetermined flow rate for a predetermined time at that temperature, and then allowed to cool to room temperature to obtain a black powder.

The X-ray diffraction patterns of the products are both ^STM
Ray Powder Data File 20
-509 Fe5C2Iron Carbide. The magnetic properties and composition are shown in Table #52.

IjS1 table Table 2 (that's all)

Claims (4)

[Claims] (1) γ-Fe_2O_ treated with alkali or coated with Co
A method for producing acicular particles containing iron carbide, characterized in that 3 is brought into contact with CO or a mixture of CO and H_2. (2) The manufacturing method according to claim 1, wherein the contact temperature is 250 to 400°C. (3) The manufacturing method according to claim 1, wherein the alkali treatment comprises contacting the object to be treated with an aqueous alkali solution, filtering and drying. (4) The manufacturing method according to claim 1, wherein the Co deposition comprises placing the object to be treated in an aqueous solution of Co salt, making it alkaline with an alkaline aqueous solution, separating it, and drying it.