JPS58103106A - Treatment of acicular gamma-fe2o3 - Google Patents

Abstract

PURPOSE:To increase the coercive force of gamma-Fe2O3 even under magnetic characteristics and to obtain stable coercive force having a few variation when cobalt is coated on gamma-Fe2O3 by a method wherein heat treatment is applied to acicular gamma-Fe2O3 containing phosphorus under reduced pressure condition. CONSTITUTION:Acicular Goethite made ferrous sulfate as a raw material and having shaft ration (L/W) 8, long shaft length (0.6mum) is dehydrated at 500 deg.C to form gamma-iron oxide. Then the gamma-iron oxide is reduced with hydrogen gas including vapor at 350 deg.C to obtain acicular magnesite. The magnesite is oxidized at 160 deg.C to obtain acicular gamma-Fe2O3. The acicular gamma-Fe2O3 is treated for one hour at 350l under reduced pressure of 10<-2> Torrs to obtain objective acicular gamma-Fe2O3. As the acicular gamma-Fe2O3 containing phosphorus, phosphorus is normally existed in mother liquor at the time of manufacturing alpha-FeOOH which is the precursor of the acicular alpha-Fe2O3 to contain phosphorus in the crystal of the alpha-FeOOH or acicular alpha-FeOOH or acicular alpha-Fe2O3. Normal dehydration, reduction, and furthermore, oxidation are done to obtain the acicular gamma-Fe2O3 contained phosphorus. Normally, shaft ration (L/W) of 5-20 is acceptable.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a simple method for treating acicular 7-Fe2O3, which involves simply heat-treating acicular 7-Fe2O3 containing spring equinox under reduced pressure.

Conventionally, in order to obtain acicular γ-Fe20s with good magnetic properties, attempts have been made to incorporate phosphorus into a precursor of this material and heat-treat it to produce acicular γ-Fe20-. A product with even higher magnetic properties is required, and even if acicular 7-FetO containing phosphorus is manufactured under the same conditions, it will not be able to develop magnetic properties, especially coercive force, after coating with cobalt. There is a lot of variation, which poses problems in industrial manufacturing, and improvements are desired.

It is known that the coercive force decreases when cobalt-coated magnetic iron oxide is heat-treated under reduced pressure, for example, at 10-5 Torr and 400°C for 4 hours (Powder Metallurgy Association, 1920-1999). It is not known that 1956 lecture abstracts, 2-15, p. 124) heat-treats magnetic iron oxide under reduced pressure before coating with cobalt.

The inventors first generally considered 7-F'e 20
s is reduced to Fe, 0. or γ-Fe20. ．． It is known that among the beltlide compounds obtained by partial reduction of Fe"/Fe"=0.12, those with an abnormal increase in coercive force (
(Japanese Patent Publication No. 39-10307) Therefore, γ-Fe20. When we tried the same treatment using phosphorus, we found that the coercive force actually decreased, and we focused on the fact that this phosphorus shows a peculiar behavior. When γ-Fe, O, was subjected to dry heat treatment under reduced pressure, the magnetic properties, especially the coercive force, increased, and those coated with cobalt had a stable coercive force. This knowledge was obtained and the present invention was completed.

That is, the present invention provides acicular γ~Fe2O containing phosphorus.
Acicular γ-
γ-Fe, 0°, obtained by the treatment of the present invention, which is a treatment method for Fe203, has good magnetic properties, but the coercive force increases, and furthermore, when this material is coated with cobalt, , there is an advantage of ~1 if a stable coercive force with less fluctuation can be obtained. The reason for this is not fully clear, but
In normal partial reduction or partial oxidation, this phenomenon does not occur and the surface becomes mimagnetite, which actually reduces the coercive force. However, when heat treatment is performed under reduced pressure, the partially reduced Fe" does not become magnetite. It is presumed that P-(')-Fe'' bonding occurs on the surface of γ-Fe20= without intervening oxygen, and the coercive force increases due to the increase in surface anisotropy.

Acicular γ-Fe20 containing phosphorus used in the present invention
= is usually produced by making phosphorus present in the mother liquor during the production of its precursor Q-FeOOI (ff-Fe0OH).
or acicular a-FeOO
H or acicular ff-Fe2O3 is coated with phosphorus on the surface, and then subjected to normal dehydration (in air, 300 to 700
°C), reduction (in hydrogen or hydrogen containing water vapor, 300~
500℃), further oxidation (in air or oxygen, 120~
400℃), and usually the axial ratio (L/W
> may be 5 to 20. The phosphorus content relative to γ-F e20- is generally 0.1 to 1% by weight in terms of P.
If this amount is too small, sintering will be promoted during heat treatment such as reduction, and the shape will become distorted, making it impossible to maintain high acicularity and resulting in poor orientation. - Necessary and adversely affect subsequent cobalt deposition. Examples of the phosphorus used in the above treatment include orthophosphoric acid, polyphosphoric acid, pyrophosphoric acid, metaphosphoric acid, phosphorous acid, and salts thereof. From acicular Fe=04 to acicular γ-Fe
20>, in the oxidation step when inducing 120 to 22
Low-temperature oxidation at a temperature of 0° C., preferably 130 to 190° C., is preferred because it provides better magnetic properties.

In the treatment method of the present invention, acicular γ-
Fe20- is heat-treated under reduced pressure, and this reduced pressure is generally 100 Torr or less, preferably 10 Torr.
rr or less, and if this pressure is too high than the above range, the desired effect cannot be obtained, and the temperature of this heat treatment is generally 20
The temperature is 0°C or higher, preferably 300 to 450°C; if this temperature is too low than the range E, the desired effect will not be obtained;
On the other hand, if it is too high, 3F hemata will occur and non-magnetic material will be produced, resulting in a decrease in saturation magnetization, which is not desirable. The duration during this treatment is generally 0.5 to 5 hours.

The acicular γ-Fe treated according to the present invention is suitable for depositing a cobalt compound, and can be used as a magnetic recording material to further expand its use. When depositing a cobalt compound in this way, ordinary acicular γ-Fe
, 0. This method is carried out by neutralizing a cobalt salt with an alkali in a slurry of cobalt.
Examples include manganese, zinc, and nickel. Acicular γ-F coated with a cobalt compound obtained in this way
e 203 slurry or this slurry is filtered and washed with water to form a wet cake, which is then dispersed again in water to form a slurry.
Wet heat treat the above in an autoclave at 100-200'C or heat the wet cake at 60 = 2S 0C.
It is possible to obtain more preferable magnetic properties by heat-treating the wet cake in the presence of water vapor at 100 DEG C. or by subjecting the wet cake to dry heat treatment at 100 to 300 DEG C. after drying.

Example 1 Axial ratio (L/W) 8 made from vi1 iron sulfate,
After dehydrating the long axis length (), 6μ needle-like daisy) [P content (P equivalent) 0.40%] at 500°C to obtain a-iron oxide, it was heated to 350°C with hydrogen gas containing water vapor. Acicular magnetite was obtained by reduction at 160°C, and this magnetite was oxidized at 160°C to obtain acicular γ-Fe203 (a).

The acicular γ-Fe203 (a) obtained above was
Treated at a temperature of 350° C. for 1 hour under a reduced pressure of Torr,
The desired acicular γ-Fe2(')) (A) was obtained.
'The coercive magnetic force of these samples (Ki and (A)) was measured by the usual method, and the thermal properties were measured by the following method. The results are shown in Table 1 below.

(Thermal characteristics) This relates to the temperature dependence of coercive force and is calculated by the following formula.

Comparative Example 1 A needle-shaped needle with an axial ratio (L/W) of 6 and a major axis length of 0.6 μ made from ferrous sulfate as a raw material [P content (P exchange) 0]
% by weight] in the same manner as in Example 1 to obtain acicular γ-F.
e20. I got (b).

Acicular γ-Fe20 obtained above. (b) is obtained in the same manner as in the case of implementation V41, and the target acicular γ-Fe, 0=
(B) was obtained.

The coercive force and thermal characteristics of these samples (B) and (B) were measured in the same manner as in Example 1, and the results are shown in Table 1 below.

6- As is clear from the results in Table 1 above, γ that does not contain phosphorus
-Fe20. γ-Fe20.
It can be seen that the coercive force increases.

Examples 2 to 4 and Comparative Example 2 Instead of treating at a reduced pressure of 10-2 Torr and a temperature of 350°C for 1 hour, the predetermined pressures and temperatures shown in Table 2-2 were used.
Acicular γ-t''e2oo (C)-(F) was obtained in the same manner as in Example 1 except that the treatment was carried out with time. The coercive force and thermal properties were measured in the same manner as in Example 1, and the results are shown in Table 2 below.

7- Table 2 Example 5 Acicular γ-Fe20s (A)1 obtained in Example 1
00g is dispersed in 1g of water to make a slurry, and N2 is added to the liquid.
1 mole of cobalt sulfate 10 by stirring while blowing gas.
solution 60-ρ and sodium hydroxide 5 ml/Q solution 24
- was added over 1 hour, and an additional 5 liters of sodium hydroxide
271 ml (l) of the 7 L/ρ solution was added over 0.5 hours.Then, the slurry was heated from room temperature (28°C) to 90°C and stirred for 5 hours. After climbing and drying, dry heat treatment was performed at 230°C for 1 hour in N and TF gas atmosphere to obtain cobalt-containing acicular γ-F C20-(G).
I got it. When we measured the magnetic properties of this material, we found that He=
6180e%Tp=81%.

For samples (A) to (C11) and (A) to (G) obtained in Examples 1 to 5 and Comparative Examples 1 to 2, blends were prepared according to the following blending ratio 8-, and kneaded in a ball mill. A magnetic paint was produced.

(1) Magnetic iron oxide ioo parts by weight (2) Soybean lecithin 1
#(3) Surfactant
4 (4) Vinyl chloride-vinyl acetate copolymer resin 1
5 parts by weight (5) Dioctyl 7 tallate
5 (6) Methyl ethyl ketone 1
11 〃(7)) Ruen 1
22 Next, each magnetic paint was applied to a polyester film using a normal method, oriented and dried to a thickness of approximately 9 μm.
A magnetic tape with a thick magnetic coating was prepared. The coercive force (Hc) of each tape was determined by the usual method.
, squareness (Br/Bad), orientation (OR), and saturation magnetic flux density (B+m), and the results shown in Table 1 below were obtained.

9-Table 3 As is clear from the above results, it can be seen that the tape properties, especially the coercive force, of γ-Fe2O3 treated according to the present invention are increased. Furthermore, the results of Example 5 show that the material coated with a cobalt compound exhibits excellent magnetic properties, particularly coercive force and good thermal properties.

Patent Applicant: Ishihara Sangyo Co., Ltd. 110 Completed - Procedural Amendment January 20, 1980 Director-General of the Patent Office Kazuo Wakasugi 1, Indication of Case: 1981 Patent HIIi 201959 No. 2,
Title of the invention: Method 3 for treating acicular γ-F e 20-
, Relationship with the case of the person making the amendment Patent applicant 5, Subject of the amendment Detailed explanation of the invention in the specification column 6,
Contents of the amendment (1) Lines 10 to 11 of the second specification: ``If it decreases, -1
They found that if the phosphorus content was lowered by 1L,

(2) On page 3, lines 2 to 5 of the specification, [Although it is not clear enough, partially reduced Fe2÷] is changed to "Although it is not clear enough, one reason is that, for example, When acicular γ-F e20. containing phosphorous is partially reduced to form a bertolide compound, the surface becomes mil magnetite Y.
However, if heat treatment is performed under reduced pressure, the remaining Fe2+ is corrected to be 1.

(3) Correct the second line from the bottom of page 3 of the specification to read "Shape 1 is distorted."

(4) On page 3, line 11 of the specification, [not available] is corrected to "difficult to obtain."

(5) "Slurry or" in the 4th line of page 5 of the specification is corrected as [slurry or J].

(6) Specification No. 6 [Line 7 from the bottom [Same as in Example 1]" Dehydration, reduction,
6 (7) In the second line from the bottom of page 6 of the specification, change 1 to 1 in the same way.
Similarly, heat under reduced pressure and correct to 1.

that's all , 2 complete-

Claims (1)

[Claims] A method for processing acicular γ/Fe2O3, which is characterized by heat-treating acicular γ/Fe20a containing phosphorus under reduced pressure.