JPH0555024A - Manufacture of hard ferrite - Google Patents

Abstract

PURPOSE:To provide hard ferrite with a high magnetic characteristic by a simpler process and to easily obtain a target magnetic characteristic by a method wherein only required quantites of SiO2 and Al2O3 out of additives which are added in a composite manner are left as iron oxide in the stage where iron ore is refined. CONSTITUTION:A hard ferrite is manufactured in such a way that its fundamental composition in terms of the molar ratio of Fe2O3/MO (where M represents Sr or Ba) is 5.3 to 6.3. In this case, an iron ore which contains 0.25 to 0.5wt.% of SiO2 or 0.2 to 0.5wt.% of Al2O3 or a refined iron ore obtained by refining the ore so as to obtain the content of SiO2 or Al2O3 is used as a raw material for ferric oxide. Then, 0.1 to 1.2wt.% of CaO is added, and, after that, this mixture is baked. For example, a refined iron ore which contains 0.3% of SiO2 and 0.26% of Al2O3 is used, SrCO3 is added so as to obtain the molar ratio of Fe2O3/SrO=6.00. This mixture is crushed, mixed and calcined. Then, 0.9wt.% of CaO is added. This mixture is crushed fine; after that, it is molded and baked.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing hard ferrite used in various motors used in audio equipment, automobiles, computer peripheral equipment and the like.

[0002]

2. Description of the Related Art The magnetic properties of hard ferrite are described, for example, in "Powder and Powder Metallurgy" Vol. 34 (1987), No. 16
Page 9, "Electrical Steelmaking," Vol. 53 (1982), page 89,
As shown in "Sumitomo Special Metals Technical Report", Vol. 3, 1977, p. 29, it is closely related to the size of crystal grains, the degree of orientation of crystal grains, and the density. It is difficult to determine these factors based on the basic composition alone. Therefore, additives are generally used.

It is desirable that the additive has a function of promoting the sintering reaction to increase the degree of orientation and density and a function of inhibiting the growth of crystal grains, and many studies have been conducted so far. As such an additive, for example, Al
₂ O ₃ , SiO ₂ , CaO, B ₂ O ₃ , Cr ₂ O _{3 and the} like are used (see US Pat. Nos. 2,980,617 and 3,897,355). ..

Generally, this type of hard ferrite has a residual magnetic flux density (Br) of 3700 to Sr, for example.
4300G, coercive force (iHc) is 2800-5300O
It has the magnetic characteristics of e, and in the case of Ba system, Br is 3700 to 4
300G, iHc has magnetic properties of 2000 to 3500 Oe. However, depending on the application, a material having a high residual magnetic flux density may be required, or a material having a high coercive force may be required, and a material having a magnetic property intermediate between the two may be required. It may be needed. Therefore, conventionally, the type of additive and the amount added have been determined according to the required magnetic characteristics.

[0005]

When a hard ferrite magnet is made of a material having a high residual magnetic flux density (Br) for each magnetic characteristic, a material having a high coercive force (iHc), and an intermediate material, In the method, it is necessary to change the type and amount of a plurality of additives with respect to the basic composition of iron oxide and an auxiliary material (one or two of SrO and BaO).
There is a problem that the control for obtaining the target magnetic characteristics is complicated.

An object of the present invention is to provide a method for producing hard ferrite which has a high magnetic property and can easily obtain a target magnetic property in a simpler process.

[0007]

Means for Solving the Problems As a result of intensive studies for solving the above problems, the present inventor found that SiO ₂ and Al ₂ O ₃ are required in the step of refining iron ore among the additives to be added in a complex manner. The inventors have found that the target magnetic characteristics can be easily obtained only by adding CaO by simply adding CaO to iron oxide so that the present invention can be achieved.

That is, according to the present invention, the molar ratio of Fe ₂ O ₃ /
MO (where M is Sr and / or Ba) = 5.3
In producing a hard ferrite having a basic composition of ˜6.0, an iron ore containing 0.25 to 0.5% by weight of SiO ₂ and / or 0.2 to 0.5% by weight of Al ₂ O ₃ and / Or refined iron ore obtained by refining the iron ore to the above-mentioned SiO ₂ , Al ₂ O ₃ content is used as a raw material of ferric oxide,
The present invention provides a method for producing a hard ferrite, which comprises adding 0.1 to 1.2% by weight of CaO and then firing.

[0009]

The present invention will be described in more detail below. The hard ferrite manufacturing method generally follows the following process as shown in FIG. A molar ratio of Fe ₂ O ₃ / MO (M is Sr and / or Ba) = 5.3 to 6.0 is compounded and pulverized and mixed. This is calcined at a predetermined temperature, and after calcination, coarse pulverization and fine pulverization are performed. During this pulverization, SiO ₂ , CaO,
Additives such as Al ₂ O ₃ are compounded. After that, the hard ferrite magnet is manufactured by putting it in a mold, molding it, and sintering it at a predetermined temperature. This method is complicated because it is necessary to add a predetermined amount of multiple additives so that the target magnetic characteristics may be obtained during fine pulverization. Even if the additive is contained in the raw material and added during fine pulverization, the effect on the magnetic property per unit content is different, and it is difficult to obtain the target magnetic property. Further, it is necessary to know the amounts of SiO ₂ and Al ₂ O _{3 in} the raw material to be used, and add the amount by subtracting the amount.

According to the present invention, as shown in FIG. 2, since SiO ₂ and Al ₂ O ₃ are contained in iron ore in an amount more than necessary among the additives to be added at the time of fine pulverization, a step of purifying this If the required amount is left, only CaO or the like except SiO ₂ and Al ₂ O ₃ can be added at the time of fine pulverization, and the target magnetic characteristics can be easily obtained. Therefore, in the present invention, the number of weighings and mixings can be reduced.

To refine iron ore, fine pulverization / classification and magnetic separation
Any SiO in combination with₂And Al ₂O₃To the level of
It can be controlled, and its fluctuation is SiO₂And σ = 0.
01%, Al₂O₃Is as small as 0.02%.

Both strontium ferrite and barium ferrite are generally SrO.nFe ₂ O ₃ and BaO.
It has a basic composition of nFe ₂ O ₃ (n = 5.3 to 6.0). SrO or BaO when n is smaller than 5.3
Is excessive and the saturation magnetization (Is) is reduced. On the other hand, when n is larger than 6.0, Fe ₂ O ₃ is excessive and Is is also reduced. Therefore, n = 5.3 to 6.0 is appropriate. Is. In the present invention, S is added to this basic composition as a grain control agent.
When iO ₂ is contained in an amount of 0.25 wt% or more, it is effective in controlling the crystal grains, and by setting the upper limit to 0.5 wt%, the decrease in Br can be minimized. A
Similarly for l ₂ O ₃ , the upper limit is 0.5 wt%.
For the same reason, the lower limit of Al ₂ O ₃ is 0.2 wt.
%. The CaO is effective to raise the residual magnetic flux density by increasing the sintered density (Br), SiO _2, Al
Depending on the level of ₂ O ₃ , 0.1 to 1.2% may be added so as to obtain the target magnetic characteristics.

[0013]

EXAMPLES The present invention will be specifically described below based on examples. (Embodiment 1) FIG. 3 is a diagram showing a relationship between magnetic properties and SiO _{2 in} iron oxide of barium ferrite showing an embodiment of the present invention. Barium carbonate (BaCO ₃ ) and iron oxide (Fe ₂
O ₃ ) was mixed such that BaO and Fe ₂ O ₃ were in a molar ratio of 1: 5.65 and calcined at 1250 ° C. for 1 Hr. When finely pulverizing this, according to the conventional method, SiO ₂ and CaO (and Al ₂ O ₃ if necessary) are 0.3% and 0.34%, respectively.
In the present invention, 0.56% of CaO alone was added and finely pulverized by a fine pulverizer to an average particle size of 1.0 μm.
A barium ferrite magnet was obtained by applying a pressure of 500 kg / cm ² and molding in a magnetic field of 7 KOe and then sintering at 1250 ° C. for 1 hour. According to FIG. 3, conventionally, SiO ₂ and CaO were post-added (Al ₂ O ₃ was added in some cases) to high-purity iron oxide obtained by spray roasting pickling waste acid of steel, but it was refined from iron ore. Originally, iron oxide is SiO ₂ , Al ₂ O
_Since it contains ₃ , the target magnetic characteristics can be obtained only by post-addition of CaO if the level is controlled in the refining stage.

Example 2 A hard ferrite was produced using the raw material iron oxide having the composition shown in Table 1. According to the invention,
Since the contents of SiO ₂ and Al ₂ O _{3 in} the raw iron oxide are controlled at the refining stage, it is understood that only CaO needs to be added later.

[0015]

[Table 1]

[Table 2]

[0016]

According to the present invention, it is contained in the raw material iron oxide.
SiO₂, Al₂O₃Except CaO, etc.
The target magnetic characteristics can be easily obtained. Also,
SiO in manufactured iron oxide₂, Al₂O₃The fluctuation range of
Since it is extremely small, the target magnetic characteristics can be stably maintained.
It Furthermore, in the process of refining iron oxide from iron ore
Even if it is SiO₂, Al₂O ₃Lower than necessary
The iron oxide product yield can be improved without the need to
There is also an effect. Also, during calcination, SiO₂, Al₂O₃Is acid
Compared with post-addition, the required amount is contained in iron oxide
Slow temperature sensitivity (change in magnetic properties due to temperature change)
There is also the effect. That is, even if the calcination temperature fluctuates,
Stable quality because there is less variation in magnetic properties compared to addition
There is also an effect that it is easy to obtain.

[Brief description of drawings]

FIG. 1 is a diagram showing a manufacturing process of a conventional hard ferrite.

FIG. 2 is a diagram showing a manufacturing process of the hard ferrite of the present invention.

FIG. 1 is a diagram showing a relationship between SiO _{2 in} iron oxide and magnetic characteristics.

Claims (1)

[Claims] 1. A hard ferrite having a basic composition with a molar ratio of Fe ₂ O ₃ / MO (where M is Sr and / or Ba) = 5.3 to 6.0 is produced, and SiO ₂ is added to an amount of 0. 25 to 0.5% by weight and / or iron ore and / or iron ore Al ₂ O ₃ containing 0.2 to 0.5 wt% was obtained by purifying the SiO _2, Al ₂ O ₃ content Purified iron ore is used as a ferric oxide raw material, and CaO is added in an amount of 0.1 to 0.1%.
A method for producing a hard ferrite, which comprises adding 1.2% by weight and then firing.