JPS6369706A - Production of acicular particle containing iron carbide - Google Patents

Abstract

PURPOSE:To produce acicular particles contg. iron carbide having a relatively small coercive force and great degree of magnetization, by heating aq. suspension of ferric hydroxide (III) under a specified condition to convert the ferric hydroxide to acicular alpha-ferric oxide (III), then allowing the ferric oxide to contact with a reducing agent contg. carbon. CONSTITUTION:Ferric oxide (III) is converted to aq. suspension contg. <=ca. 1.5mol/l Fe, which is heated at >=ca. 100 deg.C in a closed vessel under alkaline condition in the presence of a water-soluble compd. having coordinating capacity for Fe (such as sodium citrate, ca. 1X10<-5>-3mol based on the amt. of 1g atom Fe). The acicular ferric oxide (III) generated by this method is optionally brought into contact with a reducing agent (e.g. H) contg. no carbon at ca. 200-700 deg.C, and is brought into contact with a reducing agent contg. carbon (e.g. CO, CH3OH, HCOOCH3, etc.) or a mixture of a reducing agent consisting of such reducing agent and a reducing agent contg. no C without allowing it to contact with a reducing agent contg. no C at ca. 250-400 deg.C and ca. 1-2atm for 0.5-6hr. By this method, acicular particles contg. iron carbide having ca. 600-750Oe coercive force and ca. 85-95emu/g saturation magnetization are obtd.

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) Generally, in order to increase the recording density of a recording medium using a magnetic material for magnetic recording, it is better for the magnetic material to have a higher coercive force.

However, magnetic materials having various coercive forces are required depending on the capabilities of the head of the reproducing device.

Acicular particles containing iron carbide are magnetic powders for magnetic recording media that have high coercive force, electrical conductivity, and excellent hardness. Such iron carbide-containing acicular particles are produced, for example, by contacting acicular iron oxyhydroxide particles or acicular iron oxide particles with a reducing carbonizing agent at 250 to 400°C. It is known that this acicular particle containing iron carbide contains Fe5C2 as a main component of iron carbide, and also contains Fe304 (magnetite) and free carbon. However, since the acicular particles containing iron carbide have an extremely high coercive force, their use may be limited depending on the performance of the head. Therefore, there has been a demand for the development of acicular particles containing iron carbide having a relatively low coercive force.

Furthermore, magnetic powder for magnetic recording media is required to have a large amount of magnetization in order to increase output.

There are two methods for controlling the coercive force of acicular particles containing iron carbide: (1) stopping the carbonization reaction midway, and (2) increasing the temperature of the carbonization reaction. However, in the case of 1), Fe50. exists in a large amount, and therefore a suitable magnetic recording material with a small amount of magnetization cannot be obtained. 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 a method for producing acicular particles containing iron carbide having a relatively low coercive force and a large amount of magnetization.

(Means for Solving the Problems) The present invention involves heating an aqueous suspension of iron(III) hydroxide under alkaline conditions in the presence of a water-soluble compound having a coordinating ability to iron to form acicular α. - iron carbide as iron(III) oxide, characterized in that it is brought into contact with a carbon-containing reducing agent or a mixture thereof with a carbon-free reducing agent, with or without contacting with a carbon-free reducing agent; This relates to the manufacturing method of the acicular particles contained therein.

Iron hydroxide (11F) used in the present invention may be produced by any method, but generally iron (III)
) salts, such as iron chloride (I [l), iron (III) sulfate, iron (III) nitrate, etc.], add an alkali such as potassium hydroxide, ammonia, etc., and thereby iron hydroxide (I) is obtained as an amorphous precipitate. Such methods are already well known. The resulting precipitate is
Depending on the reaction conditions, the iron(III) salt may still contain the constituent anions as its constituent atoms, but such a precipitate can also be used as the iron(III) hydroxide in the present invention.

The concentration of iron (III) hydroxide in the aqueous suspension of iron (I[l) hydroxide used is such that the suspension is mixed with a water-soluble compound having a coordinating ability for iron, as will be explained later. Preferably, when stirring in the presence of seed crystals, it is sufficient that stirring is not difficult, and the amount is usually 1.5 mol/1 or less in terms of iron, preferably 0.1 to 1 mol/1. be. .

The water-soluble compound having the ability to coordinate iron used in the present invention acts as a crystallization control agent, and is produced when an aqueous suspension of iron (I) hydroxide is heated due to its coordination ability. It is selected from water-soluble organic compounds or inorganic compounds that control the growth direction and speed of α-iron(I) oxide crystals to produce needle-like crystals.

Such a compound has at least one coordinating group in its molecule containing an atom capable of coordinating iron, such as an oxygen, nitrogen and/or sulfur atom. Specific examples of such coordination groups include -OH and -COOH.

-O-, >C=O, -8O,H, -PO3H21-NH
2,=N-OH, -3H, -8-.

>C=S, -082H, -CO8H, -0CN, etc. can be mentioned. Preferably, in the present invention, the water-soluble compound capable of coordinating iron has two or more of the above-mentioned coordinating groups of the same type or different types in the molecule.

Specific examples of water-soluble compounds having the ability to coordinate with iron that are preferably used in the present invention include polycarboxylic acids such as succinic acid, maleic acid, and nitrilotriacetic acid, particularly di- and tricarboxylic acids, citric acid, tartaric acid, and glycolic acid. ,
Hydroxycarboxylic acids such as malic acid, a-methylmalic acid, a-hydroxyglutaric acid, hydroxyglutaric acid, and salicylic acid, ami7carboxylic acids such as lysine and glycine, polyamines such as ethylenediamine, hydroxylamine, ami7tri(methylene phosphonic acid), ethylene diamino tetra (methylene phosphonic acid), ethylene-1,
1゛-diphosphonic acid, 1-hydroxyethylene-1,1
Organic phosphonic acids such as '-diethylenephosphonic acid, thiocarboxylic acids such as cysteine and mercaptoacetic acid, polyhydric alcohols such as mannitol and pentaerythritol, β-nocarbonyl compounds such as acetylacetone and ethyl acetoacetate, sulfophenyliminodiacetic acid, etc. Examples include aromatic sulfonic acids. Further, these water-soluble salts and esters can also be used in the present invention as long as they have the ability to coordinate with iron. For example, sodium citrate, sodium tartrate, 1-hydroxypropyl-1,
These include sodium 1'-diphosphonate, triethyl citrate, dimethyl hydroxysuccinate, ethyl mercaptoacetate, and the like. Further, phosphates can also be used in the present invention. Specific examples include sodium phosphate, potassium phosphate, ammonium phosphate, and the like.

In the present invention, various compounds can be used as described above, but particularly preferred are the aliphatic human mixicarboxylic acids and the following organic phosphonic acids, as well as their salts and esters.

That is, an organic phosphonic acid represented by the general formula (where n represents an integer of 2 to 6, and m represents an integer of 0 or 1 to 5), a salt thereof or an ester thereof, -ff formula (however, X and Y represents hydrogen, a hydroxyl group, an amide group, an alkyl group, or a 7-aryl group, and q represents an integer of 1 to 6.)
Organic phosphonic acids, salts thereof, or esters thereof; and organic phosphonic acids, salts thereof, or esters thereof, represented by the general formula (wherein R represents hydrogen or an alkyl group).

Specific examples of the organic phosphonic acid represented by the above formula (1) include ami7tri(methylenephosphonic acid), ethylenediaminotetra(methylenephosphonic acid), diethylenetriami/penta(methylenephosphonic acid), and triethylenetetraami7(methylenephosphonic acid). Hexa (methylene phosphonic acid), Tetraethylenepentaami 7 hepta (methylene phosphonic acid), Pentaethylene hexaami/octa (methylene phosphonic acid)
etc. can be mentioned. In the organic phosphonic acid represented by the above formula (II), the alkyl group preferably has 1 to 6 carbon atoms, and the aryl group preferably has 6 to 14 carbon atoms. Specific examples include methylene diphosphonic acid, ethylene-1,
1'-diphosphonic acid, ethylene-1,2-diphosphonic acid, propylene-1,1'-diphosphonic acid, propylene-
1,3-;,'phosphonic acid, hexamethylene-1,6-
Diphosphonic acid, 2,6-dihydroxybentamethylene-2,4-diphosphonic acid, 2,5-dihydroxyhexamethylene-2,5-diphosphonic acid, 2,3-dihydroxybutylene-2,3-diphosphonic acid, 1- Examples include hydroxybenzyl-1,1''-diphosphonic acid and 1-7-ethylene-1,1''-diphosphonic acid.

In the above formula (I[l), the alkyl group preferably has 1 to 5 carbon atoms, and specific examples of such organic phosphonic acids include hydroxymethylene phosphonic acid, 1-hydroxyethylene-1,1゛-diphosphonic acid, 1 Examples include -hydroxypropylene-1,11-diphosphonic acid, 1-hydroxybutylene-1,1'-diphosphonic acid, and 1-hydroxyhexamethylene-1,1'-nophosphonic acid.

The amount of the water-soluble compound having the ability to coordinate iron is not particularly limited as long as the amount is sufficient to control the growth direction and speed of α-iron(III) oxide crystals in the hydrothermal reaction, but usually , IXI (+-5 to 3 mol, preferably 1XIO-
'~lXl0-' mole. In general, if the amount of the water-soluble compound that has the ability to coordinate with iron is too small, it is difficult to obtain a-iron oxide with excellent acicular properties, whereas if it is too large, the reaction will take a long time, which is preferable. do not have.

When an aqueous suspension of iron (III) hydroxide is heated under alkaline conditions in the presence of a water-soluble compound capable of coordinating iron as described above, it produces substantially pore-free acicular α-Fe20.
However, by coexisting α-Fc203 seed crystals in addition to a water-soluble compound that has coordination ability for iron during this hydrothermal reaction, acicular α-Fe with a narrower particle size distribution is obtained.
20. can be obtained.

The shape of the particles of this seed crystal a-Fe203 is not particularly limited, and may be arbitrary, such as acicular, spherical, cubic, etc., but it is required that the average diameter of the shortest axis is 0.4 μm or less, Preferably it is 0.2 μm or less. When the average diameter of the shortest axis of the seed iron oxide exceeds 0.4 μm, the resulting acicular α-iron oxide has a small acicular ratio defined as the ratio of the opposite axis to the short axis, and/or Average particle size is too large. The lower limit of the shortest axis average diameter of the seed crystal α-iron oxide is not particularly limited, but is usually about 1008. α-Iron oxide having the shortest axis average diameter within such a range can be obtained as a commercial product or by a known production method.

Further, the amount of seed crystals used is 0.1 mol% to 25 mol%, preferably 0.1 mol% to 25 mol% in terms of iron, based on the raw material iron (III) hydroxide.
It is 5 to 15 mol%. When the amount used is less than 0.1 mol%, the obtained acicular α-iron oxide particles are too large, while when it is more than 25 mol%, the obtained acicular α-iron oxide particles are too large.
Iron oxide has a low acicular ratio and/or the particles are too small.

In the present invention, it is sufficient that the water-soluble compound (and seed crystal) having the ability to coordinate iron is present during the heat treatment of the iron(III) hydroxide aqueous suspension, and the order of addition thereof may be arbitrary. be. Therefore, for example, when precipitating iron hydroxide (CI) from an iron (III) salt aqueous solution, a water-soluble compound and/or seed crystals having a coordinating ability for iron may be added to the iron (III) salt aqueous solution in advance. In this case, the water-soluble compound that has the ability to coordinate with iron coordinates with the iron atom in iron (III) hydroxide and is included in the precipitate, so iron (III) hydroxide ! ! ! It is not necessary to newly add it during heat treatment of the suspension. However, it is usually preferred to add to the aqueous MA suspension of iron hydroxide (TIE) seed crystals and a water-soluble compound having coordinating ability for iron.

The heating reaction is carried out when l) H is 7 or more, preferably in the range of 8 to 12.5. The alkali used is not particularly limited, but is usually sodium hydroxide, potassium hydroxide, ammonia, etc., and iron (III) hydroxide before or after addition of a water-soluble compound having coordinating ability to iron or seed crystals. added to an aqueous suspension of.

In the present invention, the reaction temperature is generally preferably 100°C or higher. In reactions at temperatures lower than 100°C, cross-shaped or T-shaped branched particles with excellent acicular properties and α-Fe00
The formation of 8 particles was observed, and a Fe with excellent acicularity was observed.
It's hard to get 20z. By performing the reaction at a temperature higher than 100°C, the formation of branched particles and α-FeOOH is eliminated, but the upper limit of the reaction temperature is a temperature that does not cause thermal decomposition of the water-soluble compound that has the ability to coordinate with iron. It is.

Although pressure may be applied during the reaction, it is usually not necessary to apply pressure intentionally, and the reaction mixture may simply be heated and stirred in a closed container. In this case, the reaction temperature is usually 10
The temperature is about 0 to 250°C, preferably about 130 to 200°C.

The reaction time is not particularly limited, but is usually several tens of minutes to several hours.

Acicular α-iron oxide is obtained in this way, but its shape and dimensions depend on the heating temperature during the above reaction, as well as the type and amount of water-soluble compounds that have coordination ability for iron, and the seed crystals. It can also be controlled within a desired range by selecting the dimensions, amounts, etc.

In the present invention, this acicular α-Fe203 is then brought into contact with a carbon-containing reducing agent or a mixture of this and a carbon-free reducing agent without or without contacting with a carbon-free reducing agent. Acicular particles containing iron carbide are produced.

Examples of the reducing agent that does not contain carbon include hydrogen, and the contact with this is preferably carried out at a temperature of usually 200 to 700°C.

As the reducing agent containing carbon (hereinafter referred to as reducing carbonizing agent), at least one of the following compounds can be used.

■CO ■Aliphatic, linear or cyclic, saturated or unsaturated hydrocarbons, such as methane, propane, butane, cyclohexane, methylcyclohexane, acetylene, ethylene,
Propylene, butanoene, isoprene, and town gas.

(2) Aromatic hydrocarbons, such as benzene, toluene, xylene, and their alkyl and alkenyl derivatives having a boiling point of 150°C or less.

■Aliphatic alcohols, such as methanol, ethanol,
Proper 7-R, go to Cyclo.

■ Ester, such as methyl formate, ethyl acetate, etc., α
Ester below 150℃.

(2) Ethers, such as lower alkyl ethers and vinyl ethers, having a boiling point of 150°C or less.

(2) Aldehydes, such as formaldehyde and acetaldehyde, which have a boiling point of 150°C or less.

(2) 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, CH30H1HCOO
CI-13 is a saturated or unsaturated aliphatic hydrocarbon having 1 to 5 carbon atoms.

In the present invention, the reducing carbonizing agent may be used diluted or not.
As a diluent, for example, N2,
Examples include argon and helium. 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 vary depending on, for example, the production history of the acicular iron oxide, average axial ratio, average particle diameter, specific surface area, etc., and are therefore preferably selected as appropriate. The preferred contact temperature is about 2
50-400°C1, preferably about 300-400°C
, the preferred contact time is about 0.5 to 6 hours. The preferred flow rate is about 1-1000+nl S, T, P/min, excluding diluent, per gram of acicular iron oxide raw material, preferably about 5
−500+nlS, T, P,/min. The contact pressure, including the diluent, is usually 1 to 2 atmospheres, but
There are no particular restrictions.

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. Existing. 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#i diffraction pattern has a lattice spacing of 2.28.2.20.2.0B, 2
．． 05 and 1.92A are shown. Such a pattern is Fe
5C2, and the main component of the iron carbide of the present invention is Fe5C2
Consisting of

In addition, the acicular particles obtained in the present invention are made of iron oxide, mainly F.
e50. It often also contains.

Furthermore, although the acicular particles of the present invention often contain free carbon, the content thereof must be 20% by weight or less. If it exceeds 20% by weight, the amount of magnetization decreases, which is inappropriate.

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 axial 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 sleeve) is usually 2 μm or less, preferably 0.1 to 2 μm.
The optimum value is 0.1 to 1.0 μI.

As is clear from the above-mentioned 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 82.

(Effects of the Invention) The iron carbide-containing acicular particles obtained by the present invention have a relatively low coercive force and a large amount of magnetization. That is, the acicular particles of the present invention generally have a coercivity f of about 60
Relatively low 0-7500e, saturation magnetization amount is approximately 85-9
5e+au/ [1 and large.

(Example) Examples and comparative examples will be given below to explain in detail. still,
The magnetic properties were determined by the following method.

magnetic properties Unless otherwise specified, it is determined by the following method.

The magnetization properties are measured using a BHH-50 direct current magnetization property automatic recorder manufactured by Riken Denshi Co., Ltd. with a maximum magnetic field of 25,000 e.

Example 1 Iron (III) chloride aqueous solution (concentration 0.2 mol/Z) lQ
Concentrated ammonia water was added dropwise to I) with vigorous stirring until H reached 8, and the precipitate was separated and washed with water to obtain iron (III) hydroxide particles. Disperse this in water and
A slurry of No. 1 was prepared. In this, sodium citrate 13B
was added, and sodium hydroxide was added until the volume became 12. The mixture thus obtained was heated at 150°C in a closed container for 3
Stir for hours. Thereafter, the precipitate was separated, washed with water, and dried to obtain a reddish-orange powder. The obtained powder was confirmed to be α-Fe203 by X#j1 diffraction, and by electron microscopy observation, the average particle diameter (long axis) was 0.3 μ chain, and the average axial ratio (
(long axis/short axis) was 4.

Next, 100 g of this α-Fe203 powder was dispersed in water 21, and 6 g of a silane coupling agent was added and adsorbed thereon, and then separated and dried.

2 g of the obtained powder was placed in a porcelain boat, which was then placed in a tube furnace at 340° C. and CO was passed through it at a flow rate of 200+nl/min for 5 hours. The obtained powder has a coercive force of 7250e.

The saturation magnetization amount was 92 emu/g.

Comparative Example 1 A powder obtained by contacting α-Fe203 obtained by heating and dehydrating a-iron oxyhydroxide powder with CO in the same manner as in Example 1 had a coercive force of 950 O.
e, the saturation magnetization amount was 75 emu/g.

(hereinafter “2)”

Claims (2)

[Claims] (1) An aqueous suspension of iron (III) hydroxide is heated under alkaline conditions in the presence of a water-soluble compound capable of coordinating iron to form acicular α-iron (III) oxide, and carbon A method for producing acicular particles containing iron carbide, which comprises bringing into contact a reducing agent containing carbon or a mixture of this and a reducing agent containing no carbon, with or without contacting with a reducing agent that does not contain iron carbide. (2) The method according to claim 1, wherein the acicular particles have a coercive force of about 600 to 750 Oe and a saturation magnetization of about 85 to 95 emu/g.