JPS59194405A - Manufacture of ferrite magnet - Google Patents

Abstract

PURPOSE:To utilize easily obtainable mill-scale as iron raw material by a method wherein the mill-scale which is included in Fe components composing elements is oxidized beforehand and a W-type ferrite magnet is composed. CONSTITUTION:Mill-scale and BaCO3 are subjected to wet pulverization and mixing using denatured alcohol. The mixture is dried at the room temperature. Then the mixture is subjected to thermal-oxidization in the air. The mixture is temporarily baked while the temperature and the oxygen partial pressure are varied within the range of 1,270-1,400 deg.C and 0.002-0.03atm respectively. After approximately 0.5wt% of SiO2 is added to the temporarily baked powder, the powder is pulverized in acetone. The pulverized powder is compressed and molded by the pressure of approximately 500kg/cm<2> in the static magnetic field of approximately 8,000Oe. Then the partial pressure of oxygen is varied within approximately 0.02X10<-2>-1.0X10<-2>atm and the temperature is increased approximately upto 1,170 deg.C. The molded body is sintered at the temperature 1,190-1,230 deg.C for approximately 60sec. The partial pressure of oxygen is varied when the temperature is rising and then the molded body is cooled.

Description

DETAILED DESCRIPTION OF THE INVENTION As described in Japanese Unexamined Patent Publication No. 57-18305 regarding a method for manufacturing a ferrite magnet consisting of a W-ferrite phase, W-type ferrite basically consists of the following 1 (1). Formula % Formula % (1) means a ferrite phase having a stoichiometric composition represented by one or more of Ni, Mn, and Mg.

M/ (A2+ +F e3+)"' 1/18
In the W-type ferrite, for example, Bickf
ordJr,, L kL,, J-Appl, P
hys 51259 S (1960)K As reported, CQ2, in which most of A2+ consists of COZ+
Except in the case of +-W type ferrite, the easy axis of magnetization is parallel to the C axis of the hexagonal system, and has the same magnetocrystalline anisotropy as normal M type ferrite. A2+ of W type 7 elite
For Fe2W ferrite where is Fez+, for example, Wizn, H, P, J, Nature 17070
7 (1952), the saturation magnetization (4πI S ) at 20°C is 5220 G,
Essentially higher residual magnetic flux density (Br) is expected compared to the theoretical values of normal M-type 7 elite, that is, 47750 for Ba-7 elite and 4652 G for Sr-ferrite.

In fact, in Japanese Patent Application Laid-Open No. 57-18505, Ba
Using C0, and Fe2O, as a starting mixture, BaFe,
Create a W-type 7 elite indicated by 8027, and set Br=4
770GHc = 17000e, (BH)m = 4
．． 2 77) Characteristic values are reported.

W-type ferrite contains divalent metal ions, as is clear from the above formula (1). Therefore, if the divalent ion is an iron ion, pe2+ = Ii' due to the oxygen partial pressure
Since the e3+10e- reaction occurs, the firing must be carried out under conditions where the oxygen partial pressure is controlled.

On the other hand, one of the main raw materials for W-type ferrite magnets is Fe, 0
．． can be mentioned. This Fe2O is mainly FeC1, -nH2O or Fe50 obtained through the pickling process of copper plates.
It is made by roasting ゜・7H,0, etc. However, the supply of Fe2O3 is expected to become tighter in the long term due to the steel industry's production cutbacks and the change in the pickling process itself to dry descaling methods such as shot blasting and isitalin. therefore,
In the future, the iron raw material for ferrite magnets will be made from the above Fe2O3.
It is expected that there will be a need to look for other things.

In view of this situation, an object of the present invention is to create a W-type ferrite magnet that has substantially the same magnetic properties as when Fe2O is used, even if an easily available iron raw material is used as at least a part of the main raw material. An object of the present invention is to provide a method for manufacturing the obtained ferrite magnet.

As a result of various studies to achieve this objective, the present inventors have found that Fe2O3 can be used even if scale generated during the hot rolling process (hereinafter referred to as mill scale) is used as the iron raw material for manufacturing W-type ferrite magnets. It has been found that a W-type ferrite magnet can be obtained which has magnetic properties substantially equivalent to those of the conventional method. Mill scale depends on the conditions when it occurs, but
Component-wise, it is formed from approximately FeO and Fe3O4, and the weight ratio is approximately FeO/Fe50. ' It is about 2/8 to 515 and contains a lot of Fe2+. As mentioned above, W-type ferrite needs to be sintered while controlling the oxygen partial pressure (PO2), and the range depends on the firing flow rate, but Po2 = 1
It is about 0-3 to 10" atm. This PO range is:
This is a range in which the Fe3O4 phase exists relatively stably, and it is difficult to directly generate a W-type ferrite magnet in a single-phase state from BaCO3 and mill scale under the above-mentioned PO2, for example. Therefore, the inventors of the present invention have conducted various studies. As a result, it is possible to use mill scale alone or mill scale B in advance.
The mixture with aC0, is heated to a temperature at which mill scale oxidation occurs, and the content ratio of Fe2+ to the total iron content Fe
It has been found that the material can be used as a raw material for W-phase ferrite by performing preliminary oxidation until 2"/(Fe" 0F e"") becomes approximately 20% or less, more preferably approximately 15% or less. Of course, it is also possible to use part of the mill scale in combination with ordinary Fe2O3.

The details of the present invention will be explained below with reference to Examples.

Example 1 FeO/Fe304 = 0.70710.295 (1 mole) ('FeO/Fe50. = 707H) w
t%) Narumi yv s'r-ru 669.63g<average particle size 1.5μm) t-3 and BaC0,100,OO
g (average particle size 2/jm)'Y weigh Ba/Fe =
1/1B atomic ratio), using denatured alcohol as the medium (・
Wet pulverization and mixing was carried out. After the mixing was completed, the mixture was dried at room temperature, and calothermal oxidation was performed in air at 800°C for 05 to 2 hours. Then, the pulverized product was heated to a temperature and oxygen partial pressure (PO2) of 1270 to 1400, respectively.
℃ and 2×10-” to 5×10-2 atm.The temperature range in which a single phase of Ba-W type ferrite is formed shifts to the high-boiling side as Po7 increases. , an example of the range is shown in Table 1.

Table 1 In this experiment, from a practical standpoint, no study was conducted in a high temperature range of 1400°C or higher. The produced phases shown in Table 1 were identified by powder X-ray diffraction using α-rays for Co-. Under each Po2 condition shown in Table 1, when the calcination temperature is lower than that in the table, α-Fe20. and M type 7 z 5ite BaO-6Fe, O, are generated as a mixed phase. Also, on the high temperature side, FeO.

A diffraction line of Fe3O4 was observed. The amount of FeZ+ remaining after the heating oxidation of the mill scale used in this example was carried out at 800°C for 50 to 2 hours was determined by Fe2+/
(pe2++p63+) = Atta at about 5-10%. It was confirmed that the residual amount of Kono applied to the case where mill scale and ordinary Fe, 03 were mixed and used.

Table 2 Saturation magnetization 4πIs of Ba-W type fullite phase after calcination.

Table 2 above shows a part of the total Fe amount and Fe2+ amount. The amount of Fe2+ in Ba-W type ferrite is 7.09 wt% in stoichiometric composition, but including the results in Table 2, the amount of FeZ+ in the range that shows Ba-W type ferrite single phase in X-ray diffraction is 7.09 wt%. It varies in the range of 1,29 to 8.56 wt%, and it is considered that a non-stoichiometric ratio of Fe2+/Fe3+ occurs. In fact, the lattice constant Co in the C-axis direction increases with Fe"t1711]. In Table 2, 4πIs
= Co of the samples showing 4850 and 4770G is C
o=32.93A.

Next, after adding 0.5 wt% of Sin to the calcined powder,
These powders were ground in acetone using a ball mill,
The pulverized powder was heated at 500 Yu/cr in a static magnetic field of a o 000e.
Compression molded at a pressure of 25 mm in outer diameter and 5 Tn in thickness.
A WL molded body was obtained.

Po2=0.02X10-2~1,QX
The temperature was increased to 1170°C while changing Po2 sequentially within the range of 100-2at. then 1190
After sintering at a temperature range of 60°C to 1260°C, cooling is performed while sequentially changing PO□ within the above Po2 range.

Table 5 shows the magnetic properties of the obtained magnet. The magnetic properties shown in Table 5 are the values obtained when powders calcined under conditions of black 5°6 and 8 in Table 2 are used.

The properties shown in Table 5 and Table 6 exceed the theoretical saturation magnetization value of normal M-type Ba ferrite, 4πl5=4775G, and can be applied industrially to high-performance magnets such as magnetrons. In addition, even if there is a shortage of iron oxide in the future, W-type ferrite can be produced by using a small amount of mill scale as part of the iron raw material. The oxidation is performed after mixing the mill scale with the mill scale, but after oxidizing the mill scale alone to reduce the p62+ content to approximately 20% or less of the total Fe content, it is mixed with B a CO, and calcined. It was also confirmed that almost the same conditions and characteristics as those shown in Tables 1 to 3 can be obtained even if the above steps are carried out.

Example 2 Fe07Fe, O, = 0.70710.293 (%
Lua mole) -Q mill scale 66.9.65g
C average particle size 15 to 20 μm) was weighed and placed in a gas furnace at 800 μm.
Fe”/(Fe
Pre-oxidation was carried out until the content of "-)-Fe") became 15% or less. Then, using a small Hensel mixer, S rc
After mixing with 74.81 g of O, the mixture was pulverized and mixed in a ball mill in the same manner as in Example 1, and then calcined under various conditions under PO□ control. The relationship between the 5r-W type ferrite single phase Po produced and the calcination temperature is shown in Table 4.

Table 4 Comparing Table 4 and Table 1, it is clear that the temperature range and PO range in which single phase is generated in Sr-W type ferrite are higher than those in Ba-W type 7 ferrite. I know it's narrow. In particular, control of Po2 is important in obtaining a single phase of 5r-W type ferrite. Single phase generation conditions and 4π engineering S
, and the amount of residual Fe2+ are shown in Table 5.

Table 5 In the stoichiometric composition of r-W type ferrite, the p62+ content is 7.50 W t%, but in this example, the p62+ content is 7.50 W t%.
As is clear from the table, it varies in the range of 3.73 to 9.18 wt%.

Next, the sintered powder shown in Table 5 was crushed under substantially the same conditions as in Example 1, compacted in a magnetic field, and sintered to obtain a 5r-W type ferrite magnet. The typical characteristics of this magnet were as shown in Table 6. As is clear from Table 6, the characteristics of the 5r-W type ferrite magnet are lower than those of the Ba-W type ferrite magnet.

Table 6 As far as the study in this example is concerned, in the case of a 5r-W type ferrite magnet, the optimum sintering conditions Po, compared to a Ba-W type ferrite magnet, range from 02 x 10'' to 0.
．． It is difficult to control PO within this range because it is extremely narrow at 5×10 −2 atn, and this is considered to be the reason why the magnetic properties remained as shown in Table 6.

As described in the examples above, by using iron raw material as the mill scale, it was possible to produce a Ba-W type ferrite magnet having magnetic properties equivalent to those of the conventional Fe203Y starting material. Since there are no known examples regarding the magnetic properties of Sr-W type ferrite magnets, it is currently not possible to compare them with conventional materials. Although we will have to wait for the future to evaluate it, it is quite possible to use mill scale as a raw material.

The use of mill scale as a raw material for ferrite magnets is known (Japanese Patent Publication No. 44-971).

Japanese Patent Publication No. 49-28077 (see Japanese Patent Publication No. 49-28077, etc.), but there is no example of using a W-type 7-elite magnet as in the present invention.

Claims (1)

[Claims] 1. A raw material mixture forming a W-ferrite phase containing mill scale as at least part of the Fe component is heated at a concentration that causes mill scale oxidation, and then calcined in an oxygen-containing atmosphere having a predetermined oxygen partial pressure. 1) A method for producing a ferrite magnet, comprising: pulverizing the calcined powder, compression molding it in a magnetic field, and sintering the obtained compact in an oxygen-containing atmosphere having a predetermined oxygen partial pressure.