JPS58174509A - Preparation of spicular ferromagnetic iron powder - Google Patents

Abstract

PURPOSE:To obtain the spicular ferromagnetic iron powder excellent in coercive force, by heating and dehydrating spicular crystal-contg. iron oxide coated with hydrous silicic gel to obtain ferric oxide coated with silicic acid, granulating said ferric oxide to specified particle size, and reducing the resulting particles. CONSTITUTION:Spicular crystal-contg. iron oxide is dispersed and suspended in water to which polyphosphate is added as a dispersant, and a water-soluble silicate is added to the suspension at a ratio of 1-10wt% in terms of SiO2 to the spicular-crystalline iron oxide. Spicular crystal-contg. iron oxide coated with hydrous silicic gel is obtained by neutralizing and acidifying the suspension. The obtd. iron oxide is heated and dehydrated into ferric oxide coated with silicic acid, and then granulated to 6-250 meshes. The particles of this ferric oxide coated with silicic acid are brought into contact with reducing gas to obtain the spicular ferromagnetic iron powder. This iron powder has coercive force of Hc>=1,400 oersted in saturated magnetism of sigmas>=150emu/g.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing acicular ferromagnetic iron powder.
Method for producing acicular ferromagnetic iron powder with coercive force: HC≧1,400 oersted (2 related methods).

The acicular ferromagnetic iron powder manufactured by Ideal C2 has a large saturation magnetization (σS) and a high coercive force (Hc), and is a magnetic recording material that can be expected to have high output and high recording density. Since it is an important substance that can be applied to magnetic materials, various manufacturing methods have been proposed to bring it closer to the ideal.The general manufacturing method for acicular magnetic iron powder is as follows: (a) Raw material iron salt A step of oxidizing in an alkaline aqueous solution to produce acicular hydrated iron oxide (FeOQH), -) A step of coating or adhering silicate etc. to the acicular hydrated iron oxide obtained in step U), ( C) A step of heating and dehydrating the coated or adhered acicular hydrated iron oxide obtained in the same process to obtain ferric oxide (α-Fe), (B) ← The ferric oxide obtained in step 9 It consists of the step of reducing the particles into acicular magnetic iron powder (Fe).

The magnetic properties such as saturation magnetization and coercive force of the acicular magnetic iron powder largely depend on its shape anisotropy (acicularity), and the acicularity of the acicular crystal hydrated iron oxide obtained in the step (a) above is highly dependent on its shape anisotropy (acicularity). The major challenge is how to maintain this through the long process up to step 4 (to obtain the final acicular magnetic iron oxide). B) There are various proposals for each process, including the process. For example, regarding the step (a), methods for obtaining α-FeOOH using ferrous salt as raw materials are disclosed in Japanese Patent Publication No. 39-5610 and Japanese Patent Application Laid-open No. 56-226.
No. 37, etc. (there are two methods described, Ni, Z
n, 810! A method for producing α-Feα with improved acicularity as a ferric salt raw material in the presence of additives such as
Publication No. 166312, Japanese Unexamined Patent Publication No. 56-69231,
JP-A No. 56-20105, Patent No. 1lIi855-7
No. 1002, etc. (proposed in 2). Also, a method using ferric salt as a raw material, a method for obtaining β-Fe00H,
The method of using γ-FeOOH was published in 1986-4.
This method has been proposed in Japanese Patent Application Laid-Open No. 695, Japanese Patent Application Laid-open No. 149329-1980, Japanese Patent Publication No. 339-1983, Japanese Patent Application Laid-Open No. 3323-1983, and the like. ←) Step (As for the second step, the method for treating the acicular crystalline hydrated iron oxide +:8i0. coating obtained in step (a) is disclosed in Japanese Patent Publication No. 56-9005 and Japanese Patent Application Laid-Open No. 1988-66-
1:: JP-A-13411, JP-A-56-20105, JP-A-56-77931, etc. (A method for treating -1Aj and 81 coatings is described in JP-A-56-156706,
A method of coating e is described in Japanese Patent Publication No. 55-20366 (
: The method of coating with phosphate is disclosed in JP-A-54-37297.
The method of coating with silicone oil etc. is disclosed in Japanese Unexamined Patent Application Publication No. 1983-
No. 33091, Japanese Unexamined Patent Application Publication No. 155-85605, etc. (2).

Regarding the (c) process, 4-←) A method of heating the acicular hydrated iron oxide coated or adhered in the step 4- to a temperature of 400 to 750°C to dehydrate it is disclosed in JP-A-55-115920. , a method of heating and dehydrating under reduced pressure was disclosed in JP-A-55-6.
Japanese Patent Application Laid-Open No. 56-20105 discloses a method of heating and dehydrating in the presence of a sufficient HIO partial pressure. Regarding the further (=, ni) step (-), the method of reducing the coated ferric oxide (α-Fe, 0.) obtained in the H step with hydrogen at a temperature of 275 to 420°C (=,
Japanese Unexamined Patent Publication No. 315-115902, etc. (2.
JP-A-54-62915 discloses a method in which the reaction is carried out in two stages in the temperature ranges of 0 to 350°C and 330 to 400°C.

However, many proposals such as those mentioned above (2 points: 1
1. :11 The magnetic properties of the acicular magnetic iron powder obtained are the saturation magnetization of the magnetic iron powder; σS≧150 emu/g, or the magnetic properties obtained by applying a magnetic paint prepared by kneading the magnetic iron powder with a suitable binder. When the saturation magnetic flux density of a magnetic recording medium is Bs≧3500 Gauss, it is extremely rare for the coercive force Hc to exceed 1400 Oersteds, and the manufacturing method thereof consists of extremely complicated steps (= despite the fact that the magnetic Since the characteristics vary widely and reproducibility is poor, this is not an industrially applicable manufacturing method.

The present invention provides an industrial method for producing acicular ferromagnetic iron powder capable of producing with good reproducibility a acicular ferromagnetic iron powder having saturation magnetization; σ3≧150 emu/jl and coercive force; The purpose is to provide

In order to achieve the above-mentioned purpose, the present inventors have conducted extensive research,
It was discovered that acicular magnetic iron powder with maintained acicularity can be obtained with good reproducibility by reducing particles of a certain particle size range of silicate-coated ferric oxide (α-Fs, O,), and the present invention has been made. completed.

The present invention relates to a method for producing magnetic iron powder in which acicular crystal hydrated iron oxide coated with a silicate is heated and dehydrated and then reduced. 250 meshier to 6 of silicic acid coated ferric oxide obtained by dehydration
Messier: A method for producing acicular ferromagnetic iron powder characterized by reducing granulated particles.

In the present invention (-), acicular crystal hydrated iron oxide coated with hydrated silicic acid gel is obtained by heating and dehydrating the acicular crystal hydrated iron oxide.
ferric oxide (α-Fe, 0. ) coated with
refers to something that can generate Acicular crystal hydrated iron oxide (Pe0Q
H) is substantially acicular, preferably with an axial ratio (major axis/minor axis) of 5 to 2, and a major axis length of 0.3 μm to 2.0 pm.
As long as it has less branching, its crystal form is α-form,
It may be either β-form or γ-form, or a mixture thereof. Furthermore, its manufacture (per 2, consisting essentially of C dihydric iron oxide (F"eOOH), even with the addition of other metal salts, oxides, or hydroxides than iron salts) Especially in alkaline aqueous solutions of ferrous salts,
Acicular crystalline hydrated iron oxide (α-Fe0) obtained by introducing oxygen-containing gas in the presence of nickel ions and zinc ions
0H) is preferable because it has less variation in axial ratio and major axis length and less branching. Hydrous silicic acid gel can also be obtained by neutralizing and acidifying an aqueous solution of water-soluble silicate, such as No. 1 to No. 3 water glass, sodium metasilicate pentahydrate, sodium sesquisilicate hexahydrate, etc. It is a hydrous silicic acid gel produced by There is no limit to the method of coating the acicular hydrated iron oxide using the hydrated silicic acid gel (2). In this, the INI of the soluble silicate is converted to 81, and acicular crystal hydrated iron oxide (add 1 to 10% by weight per pair, then neutralize and acidify) = acicular crystals. Crystalline hydrated iron oxide surface (
A preferred coating of dihydrate silicic acid gel is formed.

According to the present invention, 250 mesh to 6 mesh of silicate-coated ferric oxide (α-Fe, 01) obtained by heating and dehydrating the acicular hydrated iron oxide coated with the hydrated silicic acid gel. The silicic acid-coated ferric oxide particles are dried to about 10% hydrated silica, and then processed using conventional methods such as extrusion granulation, transfer granulation, etc. It is produced by pulverizing the sludge into 250 to 6 mesh granules, then heating and dehydrating it, or crushing the sludge as appropriate, heating and dehydrating it, and then pulverizing and classifying it into 250 meth to 6 mesh granules. The heat-dehydrated silicic acid-coated ferric oxide can be easily crushed by a conventional method, such as kneading it with a vehicle in a ball mill, without impairing the acicularity of the acicular crystal hydrated iron oxide. I can do it,
After crushing, it is classified and the particle size is between 250 mesh V and 6 mesh I! Sort the grains to I. The acicular hydrated iron oxide coated with hydrated silicic acid gel is thermally dehydrated at a temperature of 350°C to 800°C for 3 to 1 hour, preferably by B, E, T method of the produced silicic acid coated ferric oxide. The measured specific surface area is 30d
41 to 100 rd/II.

In the present invention, the silicate-coated ferric oxide (α-Fa
,0. ) Contacting the particles with a reducing gas 1: The desired acicular ferromagnetic iron powder (Fe 2 ) can be obtained.

The silicate-coated ferric oxide is brought into contact with the reducing gas using a fixed bed reduction furnace, a rotary retort furnace, or preferably a fluidized bed reduction furnace at a reducing temperature of 430°C to 550°C (conducted in two batches. The reduction rate becomes faster at higher temperatures, but at 550℃
At temperatures exceeding 430°C, deformation and sintering of the unit particles of acicular iron powder that make up the granules are likely to occur, and at temperatures below 430°C, even if a large amount of reducing gas, such as dry hydrogen gas, is used, reduction will not occur. The speed is slow and undesirable. Further 4: Residence time distribution of iron powder particles in the reduction furnace - To avoid widening of the distribution width of the two magnetic property values (- The reduction operation is a batch operation.

The present invention is based on the conventional manufacturing process of magnetic iron powder (Improved C: which adds a granulation process of hydrous silicate gel-coated iron powder or silicate-coated ferric oxide obtained by heating and dehydrating it). Each step is carried out in a preferred manner, for example, when the axial ratio is 5.
to 81 (converted to 1 to 10 % by weight of hydrated silicic acid gel, and the acicular crystal hydrated iron oxide coated with the hydrated silicic acid gel is granulated and then heated and dehydrated, or B%E that is granulated after heated and dehydrated.
1T, specific surface area measured by method is 30d/I to 100
d/II (D) 250 mesh blades to 6 mesh gourds of silicate-coated ferric oxide particles are brought into contact with hydrogen gas in a batchwise manner at a temperature of 480° C.9 to 550° C. using a fluidized fluidized reduction furnace. 62, the ferric oxide (α
-FelOa) is reduced without impairing the acicularity of the original acicular hydrated iron oxide, and the acicularity (=excellent saturation magnetization;
! SOemu/I, coercive force; He ≧140
The present invention provides a method capable of producing acicular ferromagnetic iron powder of 0 oersteds. In addition, since no special binder is used to obtain granulated silicic acid-coated ferric oxide particles, troubles caused by additives can be prevented. Since ferric particles are reduced, scattering loss due to carryover is small even if a fluidized bed reduction furnace is used.

The present invention provides a method for efficiently producing acicular ferromagnetic iron powder with saturation magnetization: σS≧150@mu77 and coercive force: HC≧1400 Oersteds, and has industrial significance. is extremely large.

Hereinafter, the present invention will be explained in further detail with reference to Examples.

However, the present invention is not limited to the following examples.

10- Example 1゜0) Manufacture of goethite Water 504 was heated to 60°C while blowing N gas into it, stirred for 0.5 hours, and the content of Fe'' ions in the liquid was reduced to It was confirmed that the concentration was 2.5% or less.This solution 1: Ni804.6H10; 328.6jl and Z
n804-7H,o;179.71I was added and dissolved, and then filtered to obtain a clear liquid.

Separately 501 water C: solid N hot OH (flake-like, purity 9
7%) 10.31 odor was dissolved and maintained at 60° C., and the solution containing Fe No. 80 and others was added with stirring to obtain a suspension of ferrous hydroxide. The circumferential speed of the stirring blade tip is 5. ILLS, 4
m: (= increase the stirring speed and then add air to 201
The oxidation reaction was continued at 60° C. with blowing at a rate of 15+.

Reaction solution chimple 5 ml'k 5% HCI 45m
After the reaction, the oxidation reaction was stopped when residual Fe"+ ions were detected using Fel test paper. This reaction solution was subjected to f-filtration using a filter press. and washed with 300 J of water to reduce N1 to 3.85
atomic% (vs. Fe atoms), Zn 1.20 atomic% (vs. Fe atoms)
A goethite wet flAP slag (cake) having an axial ratio of 10 to 20 and a length of 1.0 to 1.5 was obtained.

←) Water-containing silicic acid gel coating at 80°C (; While stirring preheated pure water 501 with a Homomixer [F] manufactured by Tokushu Kika Kogyo (2° 2kw) ~ add xametaphosphate sodium 2ON, and prepare the mixture obtained in step B) above. wet r
155 g of slag (reagent) was dissolved in 11 parts of pure water, and then high-speed stirring was continued for 6 hours.

Next (add 10% H, 804 while stirring twice to pH 7.0
Further, pure water 11 (: Na, HPO4721
Dissolve and add IG (, Po, 34jl to pH 6,0.
And so. After 30 minutes): The stirring was reduced to low speed C″.The temperature was then kept at 80° C. for 2.5 hours, and low speed stirring was continued.

Heating and stirring were stopped, and the mixture was left overnight.

Filter the heavy liquid with a filter press and wash it with 3001 pure water, S10! A moist temperature f slag of coated goethite with 2.34 wt% of carbon content was obtained.

(c) Heating dehydration wet r slag is 15m x 15cm+ x 0.7C11
Since it is in the shape of a plate, it is dried at 130°C and heated at 350°C and 50°C.
The dehydration was carried out at temperatures of 0, 650 and 800°C to obtain massive hematite under four types of dehydration conditions.

2) Each of the four types of heftite in the form of crushed granulated lumps is crushed using a crusher similar to a stone mill (commonly called a coffee mill). Moisture 50
% and granulated using a Minimizer granulator (manufactured by Fuji Paudal), dried again at 130°C and sieved. In this way, a granulated product with a particle size of ω mesh of - to 32 mesh was obtained.

(e) Reduction For the above granulated products (4 types with different heating and dehydration temperatures), 10011 each were charged into two fluidized-bed reduction furnaces, and 10
It was passed through NI scrap and reduced at temperatures of 450°C, 480°C, and 500°C to obtain iron powder of 8N in total.

The magnetic properties of this iron powder are shown in Table 1. In Table 13, Td indicates dehydrated wet material, td indicates heating dehydration time, Tr indicates reduction temperature, and tr indicates reduction time.

Table 1 Example 2゜The goethite wet cake obtained in the same manner as the knee of Example 1 (a) was mixed with the amount of water glass in the step (0) by 2.
331 Na1HPO, tos, p +:, gift PO
a wo 8111 E except for the following changes (b) and (c))
Ten types of iron powder were obtained by carrying out the process in the same manner as in Example 1'. The magnetic properties of this powder are shown in Table 2. 8101 is 415 wt% per iron content.
Met.

Table 2 Example 3゜The same process as in Example 1 (a) was carried out.鵞HPO, 1441i 礪-亪PO, 1081 (: Other than the changes, the following is tc1) (
Perform the steps (c), (e)) in the same manner as in Example 1.
Ten types of iron powder with a 40 m coating of 6.35% iron content were obtained. The magnetic properties of this powder are shown in Table 3. Example 4: The goethite wet cake obtained in the same manner as in step (a) of Example 1 was mixed with the amount of water glass in step (b) of Example 1. 2209, N Town HPO, 102 #t:
K) (, P O, was 76.5.9' 4: Same as Ip of Example 1 except that the coating step was carried out and 81 was coated with 3.7 wt% of iron content. A #1 #l cake was obtained.

65 parts of this cake was dried at 130° C. and mixed with 35 parts of the remaining wet cake and kneaded in a niegu.

The moisture content of the line product on a dry basis was 1.61 r#/4 goethite. This was extruded and granulated using a Beretta double 0.7 m 11 ψ screen manufactured by Fuji Paudal Co., Ltd., and fluidized and dried at a hot air temperature of 130°C.
A granulated product of 3B was obtained. This was heated at 800°C for 1 hour and at 45°C.
When dehydrated and fired at 0°C for 4 hours, the fired product B
%E%T, legalized surface area is 39.1jl and 83.8 respectively.
There were 4 monks.

The magnetic properties of the iron powder obtained by reducing each of these ZOOI at a gas flow rate of 4 ONI for 1 minute at a temperature of 450° C. for 2.7 hours were as follows.

17- HC (Oersted) σs (aηu/11) σ
r/(fm(-)800℃Xi hour dehydration product 1680
154.0 0.57 4-hour dehydration product at 450°C 1480 156.0 0.53 Applicant: Nippon Soda Co., Ltd. Haruto Ito 2 Yokoyama
Yoshimi 18-

Claims (1)

[Claims] 1. Method for producing magnetic iron powder by heating and dehydrating and reducing acicular hydrated iron oxide coated with silicate (: In this step, acicular hydrated iron oxide coated with hydrated silicate gel is heated and dehydrated. 1. A method for producing acicular ferromagnetic iron powder, which comprises reducing granulated particles of 250 mesh to 6 mesh V of silicate-coated ferric oxide.