JPS60155522A - Production of acicular particle containing iron carbide - Google Patents

Abstract

PURPOSE:To produce acicular particle containing iron carbide, by contacting acicular beta-FeOOH or its dehydrated product with CO or a mixture of CO and H2. CONSTITUTION:Acicular beta-FeOOH is treated with an alkaline aqueous solution, e.g. with 1-10N NaOH solution at 30-100 deg.C for >=0.5hr. The beta-FeOOH is if necessary heated and dehydrated at 200-700 deg.C to alpha-Fe2O3, and is made to contact with CO or a mixture of CO and H2 at 250-400 deg.C to obtain acicular particle containing iron carbide. When a mixture of CO and H2 is used as a reactant, the volume ratio of CO/H2 is preferably <=1/5.

Description

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

Acicular particles containing iron carbide have high coercive force and magnetic field orientation, and are excellent as magnetic materials, especially magnetic recording materials. A patent application has already been filed (Patent application 1986-17)
No. 1765).

The method for producing the acicular particles containing iron carbide is to contact acicular iron oxyhydroxide without or after dehydration with CO or a mixture of the same and H2, the preferred method being The contact temperature is about 250-400°C, and the preferred acicular iron oxyhydroxides are acicular α- and γ-F e 00
It was (Japanese Patent Application No. 1982-171765 and patent application filed on December 14, 1988).

It is an object of the present invention to provide a method for producing acicular particles containing iron carbide from other suitable acicular iron oxyhydroxides.

The objective is achieved by using acicular β-Fe00H. This expands the range of suitable acicular iron oxyhydroxides.

That is, the present invention relates to a method for producing sword-shaped particles containing iron carbide, which is characterized by contacting acicular β-F e 00 It as it is or after dehydration with CO or a mixture of CO and H2.

Acicular β-Fe00 is obtained, for example, by hydrolysis of iron chloride, and its particle shape is α- or γ-Fe0.
Compared to 0H, it is characterized by being uniform and finely acicular, and the iron carbide-containing acicular particles obtained from this are expected to be uniform and fine.

Acicular β-F e 00 II usually has an average axial ratio of 3 or more, preferably 3 to 20, and the average particle diameter (long axis) is usually 2 μm or less, preferably 0.1~2
μm, optimally 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 with the acicular particles of the present invention in general. This is because it is suitable.

In addition, the acicular β-FeOOH according to the present invention is acicular in shape, and as long as the main component is iron oxyhydroxide, small amounts of oxides, carbonates, etc. of copper, magnesium, manganese, nickel, cobalt, etc. and/or oxides of silicon, potassium salts, sodium salts, and the like.

The acicular β-FeOOH suitable for the present invention is one treated with an alkaline aqueous solution. Examples of the alkali include sodium hydroxide, sodium carbonate, potassium hydroxide, and ammonia. Also, a mixture of these may be used. When the alkali treatment uses sodium hydroxide, for example, the concentration of the aqueous solution is preferably 1 to ION. Processing temperature is approximately 30-100℃, processing time is 0.5
It is preferable to set it as more than one hour. It is preferred to remove as much chloride as possible.

Also, acicular β-Fe00H is acicular α- or γ-F
As in the production of iron carbide-containing acicular particles from e00H, they may also be coated beforehand with an anti-sintering agent. As the sintering inhibitor, any sintering inhibitor that can be applied to acicular iron oxyhydroxide, which is a starting material during the production of acicular γ-Fe20-, can be used. For example, water glass, silicon compounds such as silane ring agents, boron compounds such as polyoxyethylene IJ cerol borate and laurate, aluminum compounds such as potassium aluminate and sodium aluminate, oleic acid, coconut oil fatty acids, and sodium oleate. aliphatic carboxylic acids or salts thereof, alkyl phosphate esters, phosphorus compounds such as sodium hexametaphosphate, and titanium compounds such as diisopropoxy bis(acetylacetone) titanate. These anti-sintering agents can be used singly or in combination, and the amount of coating depends on the type, but in general, acicular β-Fe
Approximately 0.01 to 0.5% by weight based on the weight of 0011
The details of the coating with the 1° anti-sintering agent, which is preferably 1°, are described in "Acicular Particles Containing Iron 1 Carbide and Process for Producing the Same" filed on December 28, 1982.

In the present invention, acicular β-Fe 00 It is used as it is,
Alternatively, it is heated and dehydrated at about 200 to 700°C to form α-Fe203, and then brought into contact with CO or a mixture of this and N2.

CO or its mixture with N2 can be used diluted or undiluted; diluents include, for example, N2, CO2, argon, helium, and the like. When using a mixture of CO and N2, the mixing ratio can be selected as appropriate, but usually CO/H2
(capacity ratio) is preferably up to 115. *Although the dilution rate can be arbitrarily selected, it is preferable to dilute to 10 times (volume ratio), for example. contact temperature, contact time,
The contact conditions such as the flow rate of CO or a mixture of CO and 82 are as follows:
For example, the manufacturing history of acicular β-Fe00ft, average axial ratio,
Since it varies depending on the average particle diameter, specific surface area, dilution ratio of CO or a mixture of CO and N2, etc., it is best to select it appropriately.

The preferred contact temperature is about 250 to 400°C, and the preferred contact time is about 1 to 10 hours after the raw iron compound used is reduced to FepO-.
The flow rate of the mixture with the raw material acicular β-Fe00H etc.1
Approximately 1-1-1000 S, T, P per g, 7 minutes. In addition, when using diluted CO or a mixture of CO and H2, the contact pressure is usually 1 to 2 atmospheres including a diluent, but there is no particular restriction.

When observed with an electron microscope, the particles obtained by the present invention are averagely uniform acicular particles, and the acicular β-F of the raw material
These particles have the same shape as the acicular particles of e00H, and exist as secondary particles. 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. X-ray diffraction batai has a lattice spacing of 2.28.2.20.
2.08.2.0 and 1.92A are shown. Such a pattern corresponds to Fe5C2, and the iron carbide of the present invention usually consists mainly of Fe5C2, but Fe2C, Fe2oCs
(Fe2.2C), Fe*C, etc. may coexist.

Therefore, the iron carbide contained in the acicular particles of the present invention is Fex
It is appropriate to express it as C (2≦x<3).

In addition, when carbonization is incomplete, the acicular particles obtained according to the present invention also contain iron oxide, mainly FeJ-.

Generally, for iron oxides, Fe01FejO+ and γ
-Fe20s are structurally related, and the oxygen atoms in all three have a cubic i-close packing structure, and the actually existing Fe, 0. Since it varies within these ranges, it is appropriate to indicate the above iron oxide as Fe0y (1<'y≦1.5).

In addition, the acicular particles obtained in the present invention contain iron carbide or iron oxide in some cases, but when referring to the elemental analysis values of C, H, and N, iron carbide, which is usually confirmed by the X-ray diffraction pattern, is Contains more carbon than the amount calculated by the chemical formula. 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 acicular particles obtained. Therefore, the particles obtained in the present invention are acicular particles having an average axial ratio of 3 or more and consisting essentially of iron carbide, or acicular particles consisting of iron carbide, iron oxide, and/or elemental carbon. It is.

Therefore, the content of iron carbide and iron oxide in the acicular particles obtained in the present invention can be determined by determining the chemical formulas of iron carbide and iron oxide based on the respective main components Fe5C2 and Fe3O4 detected by X#1 diffraction analysis. , which can be further determined by elemental analysis and pyrolysis. - The content of iron carbide is preferably 20% by weight or more, more preferably 50% by weight or more.

The iron oxide content is preferably 70% by weight or less, more preferably 40% by weight or less.

Further, the average axial ratio and average particle diameter of the obtained acicular particles are slightly smaller than those of the acicular β-Fe0011 as a raw material, but there is almost no difference. Therefore, the average axial ratio of the acicular particles obtained in the present invention is usually 3 or more, preferably 3 to 20, and the average particle diameter (long axis) is usually 2μ or less, preferably 0.1 to 20. 2μm1 is optimally 0.1-1.0I111.

When iron oxide is present in the acicular particles obtained in the present invention,
Acicular β-F e 00 H with CO or with l-12
It is produced as a result of a solid-gas reaction in which the produced acicular particles are brought into uniform contact with a mixture of Iron carbide or iron carbide and elemental carbon are
It is presumed that all or most of the iron oxide exists on the surface, and all or most of the iron oxide exists inside.

Reference examples and examples will be described below.

Reference Example 1 Water was added to FeCl+ (60 g) to make 1 liter of solution, 120 g of urea was added thereto, and the mixture was refluxed in a water-cooled cooling tube and maintained at 90° C. for 8 hours while stirring. After that, it is passed through the mouth, washed with water, and dried to obtain acicular β-F e 00 If
was manufactured. The average particle size (long sleeve) was 0.3 μl, and the average axial ratio was 6:1.

The acicular β-FeOOtl (4 g) obtained above was
Acicular β-F was added to 300 ml of N-Na011 aqueous solution, refluxed in a water-cooled condenser, kept at 95°C for 5 hours with stirring, filtered, washed with water, and dried to remove chloride.
e 00 H was obtained.

Example 1 Acicular β-FeOOH (2
g) was placed in a porcelain boat, inserted into a tube furnace, and Co(10
0%) at a flow rate of 200ml/min at 340°C.
After treatment for 5 hours, a black powder was obtained. The coercive force (He) of this powder is 5350e, and the saturation magnetization (σs) is 8
4.3e+nu/s, and the Xm diffraction pattern is Fe5
It showed C2.

(that's all) Patent applicant: Daikin Industries, Ltd. Representative Patent Attorney 1) Iwao Mura

Claims (3)

[Claims] (1) Nail-shaped β-FeOOH as it is or dehydrated,
1. A method for producing acicular particles containing iron carbide, which comprises contacting with co or a mixture of iron carbide and H2. (2) The method according to claim 1, wherein the acicular β-FeOOH is treated with an alkaline aqueous solution. (3) The manufacturing method according to claim 1, wherein the temperature of the contact is 250 to 400°C.