JPS6353133B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing a ferromagnetic iron compound having a fine particle shape. More specifically, the present invention relates to a method for producing ferromagnetic iron oxide Fe ₃ O ₄ , γ-Fe ₂ O ₃ and/or metal (α-Fe) fine particles for magnetic recording. Magnetic materials for magnetic recording have a high coercive force (Hc), high saturation magnetic susceptibility (σ _S ) and residual magnetic susceptibility (σ _r ), and a large squareness ratio (R = σ _r /σ _S ). Magnetic properties such as these are required. In the case of iron-based ferromagnetic compounds, it is advantageous to give them a fine acicular particle morphology, and many methods for producing acicular iron oxyhydroxide particles and acicular iron oxide particles have been reported. For example, in Patent No. 166146 (August 4, 1989), _FeSO4・
Using 7H ₂ O as the iron raw material, after neutralization reaction with NaOH,
A method for producing acicular iron oxyhydroxide particles applying air oxidation and seeded crystallization methods is described. The disadvantages of these conventional methods for producing acicular iron compounds include (a) when fine acicular iron oxyhydroxide particles are catalytically reacted with a reducing gas to form acicular Fe ₃ O ₄ particles; (b) When the acicular Fe ₃ O ₄ particles are treated with an oxidizing gas to form acicular γ-Fe ₂ O ₃ particles, (c) fine acicular iron oxyhydroxide particles and/or iron oxide particles Therefore, when α-Fe particles are formed by a catalytic reaction with a reducing gas, most of the iron oxyhydroxide particles and/or iron oxide particles used as raw materials have a fine acicular morphology. However, as a result of catalytic reactions caused by oxidizing and/or reducing gases, particle breakage, destruction, and even sintering inevitably occur. As a result, the magnetic properties of the fine particles are significantly deteriorated, that is, the coercive force, saturation magnetic susceptibility, residual magnetic susceptibility, and squareness ratio are reduced, and the properties required for ferromagnetic iron compounds for magnetic recording are greatly impaired. An object of the present invention is to provide a method for producing ferromagnetic iron compound fine particles that does not cause such particle destruction. The present inventors have discovered that fine acicular iron oxyhydroxide fine particles containing one or more elements selected from the elements belonging to Group 3 show extremely good suitability as raw materials and are suitable for reduction and/or oxidation reactions. Therefore, the present invention was achieved by discovering the fact that particle shape damage, destruction, and even sintering hardly occur. The configuration of the present invention is such that when iron oxyhydroxide particles, which are the starting material for producing ferromagnetic iron compound particles, are precipitated from an aqueous solution of iron () or iron () ions,
It is characterized by containing a specific amount of a group element compound of the periodic table by coprecipitation. In the present invention, the ferrous salts used are sulfates, chlorides, or various mineral acid salts, and can be used alone or in combination of two or more. Sulfates are the most commonly used. Furthermore, ferric salts include sulfates,
These are nitrates, carbonates, chlorides and various mineral acid salts. When a sulfate is used as the ferrous salt, the ferric salt used in combination is preferably a sulfate and/or a nitrate, but is not necessarily limited thereto. Furthermore, the alkali used in the present invention is
Alkali hydroxides such as KOH and NaOH, K ₂ CO ₃ and
Alkali carbonates such as Na ₂ CO ₃ , and aqueous solutions of NH ₃ ,
Furthermore, it refers to substances such as urea that undergo thermal decomposition when heated in an aqueous solution state and have substantially the same effect as NH ₃ . It is essentially possible to implement the present invention by selecting any of these. The elements of Group 1 of the periodic table used in the method of the present invention may be any element alone or in combination, and in particular, the use of one or more of Mg, Ca, Ba, and Zn in combination has an excellent effect. show. The total amount of these Group Group elements of the periodic table needs to be in an atomic weight ratio of 0.001/100 to 10/100 with Fe,
Preferably 0.01/100 to 5/100, more preferably
It is within the range of 0.05/100 to 1/100. If the amount added is smaller than this, the effect of adding the group element will not be noticeable, and if the amount added is larger than this, it will be difficult to form fine acicular particles during the production of iron oxyhydroxide. Become. The method of introducing a group element of the periodic table as a subcomponent of acicular iron oxyhydroxide particles is to use a compound such as an inorganic salt of a group element as a fine powder, or to add the fine powder to water or a solvent compatible with water. A compound such as an inorganic salt may be added to the aqueous solution of the ferrous salt and/or ferric salt as a suspension or as a solution in water or a solvent compatible with water. Operational factors such as addition rate, solution concentration, solution temperature, and stirring intensity may be selected depending on the type of group element compound.
There are also methods in which the entire amount of the group element compound is added to the iron salt aqueous solution at once, a method in which a portion is added continuously or intermittently in the middle of the neutralization reaction between the iron salt aqueous solution and the alkali, and a portion is added in parts in the middle of the neutralization reaction between the iron salt aqueous solution and the alkali. It is possible to use a method in which the components are added separately after neutralization and then aged at a certain temperature for a certain period of time. Various nitrates, sulfates, carbonates, or mineral acid salt compounds may be used as the source of the group element, and there are no particular restrictions on the form of the compound. Generally, many of these are water soluble;
Surprisingly, in the production of fine acicular iron oxyhydroxide particles through wet neutralization and oxidation reactions, the outstanding effects of the present invention are observed even when using group compounds that are almost insoluble in water. . The fine acicular iron oxyhydroxide particles can be produced according to known methods except for the addition of the group compound. That is, a ferrous salt or a mixture of a ferrous salt and a ferric salt is made into an aqueous solution, and an aqueous solution or suspension of one or more compounds selected from Group elements of the periodic table is added to the aqueous solution. is added, then an alkaline aqueous solution is added to perform a neutralization reaction to form an insoluble substance, and then an oxidation reaction is continued with air to form fine acicular iron oxyhydroxide. In this wet neutralization and oxidation reaction, the type, amount, and aqueous solution concentration of the iron salt, the type and amount of the group element compound of the periodic table, the type, amount, and aqueous solution concentration of the alkaline substance, and furthermore, There are many operating factors, such as temperature and holding time, and the amount, rate, and time of temperature and air supply to proceed with the oxidation reaction, which have a subtle influence on the morphology of the final product iron oxyhydroxide particles. The effects caused by introducing a compound of a group element of the periodic table as a subcomponent are complex and wide-ranging, but generally speaking, when compared with known cases that do not use compounds of a group element of the periodic table, The oxidation reaction temperature is 5~
Set the temperature 10°C higher, and in some cases increase the air supply by 20°C.
By increasing the amount by ~40%, iron oxyhydroxide particles having almost the same particle morphology can be produced. Iron oxyhydroxide particles formed through wet neutralization and oxidation reactions are usually washed with water and subjected to over-operation.
Dry in an air bath at 100 to 150°C, and if necessary, micronize or granulate to obtain dry iron oxyhydroxide particles. Depending on the case, it may be further calcined at 250 to 300°C to produce calcined iron oxyhydroxide particles. To produce ferromagnetic iron oxide (Fe ₃ O ₄ , γ-Fe ₂ O ₃ ) and/or ferromagnetic metal iron (α-Fe) particles using dried or calcined iron oxyhydroxide particles as a raw material , can be carried out according to known methods. That is, for example, a steel pipe reactor equipped with a preheater for the raw material gas for reaction and whose temperature can be regulated from the outside is filled with dried or calcined iron oxyhydroxide fine particles, and a reducing gas is introduced at 300 to 500°C. In some cases, Fe ₃ O ₄ particle powder can be obtained by carrying out a contact reaction with an appropriate amount of water.
By introducing an oxidizing gas at ~400°C and performing a catalytic oxidation reaction, γ-Fe ₂ O ₃ particle powder can be obtained. In addition, by directly using the dried or calcined iron oxyhydroxide fine particles powder or the above-mentioned ferromagnetic iron oxide fine particle powder as a raw material and carrying out a catalytic reduction reaction with a reducing gas at 200 to 500°C in a similar reactor, α
-It is possible to produce Fe fine particle powder. These oxidation or reduction reaction reactors are fixed bed,
Any type of moving bed may be used, and the reaction need not be at normal pressure, but may be under pressure. In the present invention, there is no need to impose any major restrictions on the supply amount or supply rate of raw material gas for reaction in principle, but gas hourly space velocity (GHSV)
When expressed as: 0.1 to 100 Nl/gr-Fe/hr, preferably 2 to 50 Nl/gr ^-Fe /hr, it is appropriate. If the amount is less than this range, the reaction progresses slowly and is not practical, and if the amount is more than this range, the pressure drop in the reactor increases, so it is not necessarily suitable for reaction operation. Furthermore, if the reaction temperature range deviates from the above range, the reaction progresses at low temperatures and takes a long time to complete, making it unrealistic. At high temperatures, the reaction speed is too fast, resulting in unnecessary particle damage. , tends to easily lead to destruction and even sintering. By the method of the present invention, ferromagnetic iron oxide (Fe ₃ O ₄ , γ-Fe ₂ O ₃ ) and metallic iron (α-Fe)
According to high-magnification electron microscopy, the morphology of the fine particles almost completely retains the morphology of the acicular iron oxyhydroxide fine particles used as the raw material. Phenomena such as sintering are hardly observed. Furthermore, the magnetic properties of the ferromagnetic iron compound produced by the method of the present invention, for example in terms of coercive force (Hc), vary depending on the particle size and acicular ratio, but Fe ₃ O ₃ and γ-Fe ₂ For _O3 , Hc
=350~550Oe, and in case of α-Fe, Hc=1000~
It has an extremely high Hc of 1500 Oe, satisfies the properties required for ferromagnetic iron compounds for magnetic recording, and has high practical value. Hereinafter, the present invention will be explained in detail with reference to Examples and Comparative Examples. Example 1 A. Production of iron oxyhydroxide acicular particles A reactor with an internal volume of 50 mm and equipped with a stirrer is used.
FeSO ₄・7H ₂ O 1000gr was kept at 50℃
Pour into _H2O20 to make an aqueous solution, and separately add Ca
An aqueous solution in which 10 gr of (NO ₃ ) ₂ ·4H ₂ O was dissolved in 100 ml of H ₂ O was added to the above iron compound aqueous solution, and stirring and mixing were continued for 10 minutes. Next, NaOH300 prepared in advance
Gradually add a 50°C aqueous solution of gr dissolved in 1000ml of H ₂ O, continue stirring and mixing for 50 minutes, complete the neutralization reaction, and then heat the liquid in the vessel to 73°C. Blow air at a supply rate of 100Nl/min.
The oxidation reaction was started and continued for 5 hours. At this stage, yellowish iron oxyhydroxide is obtained as insoluble precipitated particles. Next, the reactor was allowed to cool to room temperature, and then washed with water and suctioned to obtain a paste of iron oxyhydroxide particles, which was dried overnight at 110°C to obtain a solid solid of dry iron oxyhydroxide particles. This material was crushed into granules of 6 to 12 meshes using a wooden hammer to obtain dry iron oxyhydroxide particle granules. When this granule was subjected to electron microscopy at a magnification of 50,000 times using a conventional method, only well-shaped acicular fine particles were present as the smallest unit without agglomeration, and the size was mainly 0.2 to 0.3 μ along the long axis. Short axis 0.02~0.04μ
It was hot. B Production of Fe ₃ O ₄ magnetic particles and evaluation of magnetic properties The above fine acicular iron oxyhydroxide fine particle granules
100gr. was charged into a steel pipe reactor with an inner diameter of 1.5 inches, which has a preheater for the reaction gas and can control uniform heating in the long axis direction using a fluidized bath made of SiC particles, etc., and 6.00Nl of H ₂ gas. /hr supply rate, reduction was carried out at 385℃, and magnetic Ca-containing
Fe ₃ O ₄ particle granules were produced. The particle morphology of Ca-containing Fe ₃ O ₄ particle granules observed by electron microscopy has fine needle-shaped particles as the smallest particle unit, the long axis is 0.2 to 0.3μ, and the short axis is 0.02 to 0.3μ.
The particle diameter was 0.03μ, which closely followed the morphology of the smallest particle unit of the Ca-containing iron oxyhydroxide particle granules used as the raw material, and no broken, broken, or even sintered particles were observed. When the magnetic properties of this Ca-containing Fe ₃ O ₄ particle granule were evaluated, it was found that Hc = 512 Oe, σ _s = 76.5 emu/gr., and R = 0.52. Examples 2 to 8 Acicular iron oxyhydroxide particles containing various elements of Group Group of the Periodic Table were produced in the same manner as in Example 1.
The results are shown in Table 1. In addition, each of these acicular iron oxyhydroxide particle granules containing a group element of the periodic table was reduced with H ₂ in the same manner as in Example 1(B) to produce Fe ₃ O ₄ particle granules. . The results are shown in Table 2. Comparative Example 1 An attempt was made to produce acicular iron oxyhydroxide particles in the same manner as in Example 1(A) except that _150gr . of Ca( _NO3 ) _2.4H2O was dissolved in 1000ml of _H2O . However, even if air oxidation was continued for a long time, yellowish iron oxyhydroxide particles were not formed, and blackish water-containing particles were formed.
Fe ₃ O ₄ is obtained, and this hydrated Fe ₃ O ₄ is 0.4~
It only showed a spherical-like morphology with a diameter of about 0.7μ. Even when this was heated and dehydrated to form Fe ₃ O ₄ particles, the magnetic properties were unsatisfactory as Hc = 298 Oe. Comparative Example 2 In the method of Example 1, Ca(NO ₃ ) ₂・4H ₂ O
Neutralization temperature 45℃, oxidation temperature
At 68℃, main major axis 0.2~0.3μ, minor axis 0.02~
Iron oxyhydroxide particle granules having needle-like particles with a diameter of 0.03 μ as the smallest particle unit were produced. When Fe ₃ O ₄ particle granules were produced using this iron oxyhydroxide particle granule in exactly the same manner as in Example 1 (B), spheroid-like fine particles of about 0.2μ were observed in some parts. Furthermore, although the shape of the acicular fine particles, which is the smallest particle unit of the iron oxyhydroxide particle granules used as a raw material, is roughly maintained, the surface of the fine particles is
Roughness of approximately 0.05μ was observed. The magnetic property of the obtained Fe ₃ O ₄ particle granules is Hc
= 425 Oe, σ _S = 70.2 emu/gr and R = 0.46. Example 9 The Ca-containing Fe ₃ O ₄ particle granules described in Example 1 (B) were heated to 300°C using a hot air flow electric dryer.
is oxidized in the air to form magnetic Ca-containing γ-Fe ₂ O ₃
A particle granule was produced. When the smallest particle unit of the Ca-containing γ-Fe ₂ O ₃ particle granules was observed with an electron microscope, the main long axis was 0.2 to
0.3μ, short axis 0.02-0.03μ, and showed an acicular particle morphology, with almost no particles showing breakage, destruction, or sintering, which was the smallest of the Ca-containing acicular Fe ₃ O ₄ particle granules used as raw materials. It faithfully inherited the form of each particle. The magnetic properties of this Ca-containing γ-Fe ₂ O ₃ particle granule are: Hc = 396 Oe, σ _S = 72.6 emu/gr., R = 0.52
It was hot. Examples 10 to 12 Conducted using acicular Fe ₃ O ₄ particle granules produced by H ₂ -reduction from the acicular iron oxyhydroxide particle granules containing Group Group elements of the periodic table of Examples 1 to 8. Example 9
γ-Fe ₃ O ₄ particle granules were produced by air oxidation in the same manner as above. The results are shown in Table 3. Comparative Example 3 The Fe ₃ O ₄ particle granules described in Comparative Example 2 were air oxidized in exactly the same manner as in Example 9 to produce γ-Fe ₂ O ₃ particle granules. Although the Fe ₃ O ₄ particle granules used as raw materials contained some spheroid-like particles of about 0.2μ, the produced γ-Fe ₂ O ₃
The particle granules also contain a somewhat increased number of spheroid-like particles of about 0.2 to 0.3μ, and further have long axes of 0.2 to 0.3μ,
Although the main component was acicular particles with a minor axis of 0.02 to 0.03μ, the particle surface contained many particles with conspicuous irregularities of about 0.05 to 0.08μ. The magnetic properties of this γ-Fe ₂ O ₃ particle granule are Hc
= 322 Oe, σ _S = 63.9 emu/gr., and R = 0.45. Examples 13 to 19 The acicular iron oxyhydroxide particle granules produced in Example 1(A) were used (Examples 13 and 14), and Example 2(A)
Acicular iron oxyhydroxide particle granules (Example 15),
Or the acicular Fe ₃ O ₄ particle granules produced in Example 1 (B) (Example 16), or the acicular Fe ₃ O ₄ of Example 4 (B)
The particle granule (Example 17), or the acicular γ-Fe ₂ O ₃ particle granule produced in Example 9 (Example 18), or the acicular γ-Fe ₂ O ₃ particle granule produced in Example 12 ( Example
19) was used to produce acicular α-Fe particle granules by H ₂ -reduction. 100g of raw material particle granules were charged into the reactor described in Example 9, and _H2 gas was added to GHSV=35Nl.
A reduction reaction was carried out at a predetermined temperature and for a predetermined time by flowing H ₂ /gr-Fe/hr. After the reaction was completed, the temperature was lowered to room temperature, the reduced particle granules were collected under an N ₂ gas atmosphere, and the X-ray diffraction images were measured. According to the calibration curve prepared in advance, all of the reduced particle granules were 98% or higher. showed a highly crystalline α-Fe crystal. The particle morphology and magnetic properties of these α-Fe particle granules were measured, and the results shown in Table 4 were obtained. Comparative Examples 4 to 6 Acicular iron oxyhydroxide particle granules described in Comparative Example 2, mainly acicular Fe ₃ O ₄ particle granules in which some changes in particle shape were observed in the comparative example, and further comparison Using the mainly acicular γ-Fe ₂ O ₃ particle granules with some changes in particle shape described in Example 3, H ₂ was added using the reactor described in Example 1 (B).
-I made a return. H ₂ gas supply rate: GHSV = 34.9Nl-H ₂ /gr-Fe/hr. Reduction temperature: T = 342°C Holding time: t = 18.0hrs. The crystal morphology and magnetism of the reduced particle granules were determined by the method described above. When the properties were measured, all of them were found to be 99% or more α-Fe crystals, and the results shown in Table 5 were obtained.

[Table] Used as raw material.
*2) An amount corresponding to the weight composition ratio was dissolved in 100 ml of H ₂ O and used. However, in Example 8, it was used in suspension.
*3) 300gr was dissolved in _H2O1 and used.

【table】

[Table] The major axis diameter and short axis diameter of the barrel are shown.

【table】

【table】

Claims (1)

[Claims] 1 The main component is ferrous salt or a mixture of ferrous salt and ferric salt, and one or two elements belonging to group of the periodic table are selected from the group consisting of Mg, Ca and Ba. Using a compound of the above elements as a subcomponent, iron oxyhydroxide fine particles are produced by a wet neutralization reaction with an alkali and an oxidation reaction,
Next, this product is washed with water, filtered and dried to produce iron oxyhydroxide fine particles or granules, and this product is reduced and/or oxidized under heating to produce ferromagnetic iron compound particles or granules for magnetic recording. A method for producing ferromagnetic iron compound particles for magnetic recording, characterized in that an element belonging to Group 3 of the periodic table is contained in an atomic weight ratio of 0.001/100 to 10/100 with respect to iron.