JPS6051245B2 - Manufacturing method of NiZn ferrite - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing NiZn ferrite which has an extremely high sintered density, a uniform crystal grain size, a small permeability loss term especially in a high frequency band, and excellent high frequency characteristics. It is something.

BACKGROUND ART In recent years, with the expansion and progress of the field of magnetic recording applications, magnetic recording media, mainly magnetic tapes, have also made remarkable progress, making it possible to perform high-density recording.

Along with the recording medium, the magnetic head, which is essential for magnetic recording, has various magnetic properties and characteristics that are suitable for high-density recording.
Various required characteristics such as high frequency characteristics and wear resistance are becoming increasingly strict. Under these circumstances, ferrite magnetic heads have excellent frequency characteristics and wear resistance, although they are brittle such as chipping and cracking.Recently, magnetic recording materials with excellent frequency characteristics, especially in the MH2 band, are required. It's on trend. In order to satisfy these required properties, in addition to strict compositional considerations, the crystal grain size must be uniform and small, and the sintered body must be extremely dense, with a sintered density almost equal to the theoretical density. No. NiZn ferrite is
Industrially, it is mainly manufactured by a normal dry method, but in this case, the sintered density is limited to about 99.2%. A high-density sintered body produced by this method has large crystal grains due to the high sintering temperature, and often has a marked decrease in magnetic permeability at high frequencies. When sintered at an even higher temperature, a second phase, which is a type of reduced phase, is precipitated.
It is well known that significant variations in mechanical strength occur, resulting in cracking, chipping, and shedding of crystal grains during processing, and the inventors have also improved these drawbacks. We have already filed a patent application for a metal oxide magnetic core material with high mechanical strength. By the way, as a conventional method for manufacturing high-density UiZn ferrite, a powder prepared by a wet method such as a coprecipitation method or an air oxidation method, or a calcined powder having a predetermined composition obtained by a dry method is heated in a hot press. There is a method of sintering and increasing the density. This method is superior to the normal dry method, with an average grain size of about 5 to 20μ and a relative sintering density of 9.
A sintered body of about 9.0 to 99.8% can be obtained.
However, the drawbacks of the hot press method are that it is not possible to obtain sintered bodies with complex shapes because the pressurization method is not hydrostatic, and that it is difficult to obtain large sintered bodies due to equipment limitations. This is difficult, and it is not industrially advisable to use continuous hot breath. A further disadvantage of this method is that the ferrite must be coated with powder such as alumina and hot pressurized, making it impossible to prevent the solid phase reaction that occurs between the ferrite and the coating material during sintering. This is a point. Therefore, there are variations in structure between the center of the sintered body and the parts near the surface, especially near the surface.
Since other compounds are produced, a considerable portion must be removed from the surface of the sintered body, resulting in a decrease in yield. As a method for eliminating the above-mentioned drawbacks, a manufacturing method using hot isostatic pressing is known from JP-A-49-128296.

However, the details still need to be considered.
When using the hot isostatic pressing (hereinafter abbreviated as HIP) method, a sintered body with almost theoretical density can be obtained without the need for a covering material such as alumina. HI occurs due to the formation of a reduced phase due to the reducing atmosphere during HIP, or because the ferrite matrix itself is reduced to a composition that is slightly oxygen deficient compared to the stoichiometric composition.
The magnetic properties after P are significantly deteriorated. The strain stress can be recovered by performing strain relief annealing under appropriate conditions to recover the magnetic properties. However, since NiZn ferrite contains Ni2+, which has a very strong tendency to occupy octahedral positions, and Zn2+, which has a strong tendency to occupy tetrahedral positions, when sintered in a reducing atmosphere, these ions are often separated from the spinel phase. and Ni2+, respectively.
In the case of excess Zn2+, a second phase is formed which is considered to be a NaCl type structure, and in the case of excess Zn2+, a second phase is formed which is considered to be a hexagonal Zincite type structure.

The formation of these second phases causes compositional fluctuations in the ferrite matrix and is often generated as independent crystal grains, making it difficult to obtain desired magnetic properties and causing variations in mechanical properties such as hardness of the sintered body. , which significantly deteriorates workability. Furthermore, because HIP is usually performed in a K atmosphere due to equipment soil limitations, even in cases where the formation of a second phase is not involved, the NiZn ferrite after HIP treatment is
The composition becomes a somewhat oxygen-deficient composition, that is, a reduced composition, rather than the stoichiometric composition. A similar thing occurs when preliminary sintering is carried out in a reducing atmosphere;
NiZn ferrite sintered at temperatures above .degree. C. forms a reduced composition, thereby decreasing its electrical resistivity, and at the same time causing a decrease in magnetic permeability and an increase in loss in the high frequency band.

Furthermore, when densification is attempted by HIP, the atmosphere during preliminary sintering containing N2 forming the reducing composition significantly inhibits densification. In other words, when HIP is performed at a temperature lower than the primary sintering temperature, the mechanism by which densification progresses is not clear, but from a thermodynamic point of view, it can be considered that equation (1) holds true as a rough approximation. can.

Here, Pext is external pressure, that is, HIP pressure, PpOre
is the pore pressure inside the sintered body, r is the pore diameter, and γ is the interfacial tension of the pores.

By the way, the hydrostatic pressure of 103 atm due to HIP is 10
Even at around 00°C, ions have a chemical bonding strength (1CP~1
It is considered that this does not have a large effect on the crystal grains arranged by the hydrostatic pressure of σAtm). Therefore, if the effective temperature of HIP is lower than the primary sintering temperature, the crystal grains will form grain boundaries that are balanced by a binding force (i.e., interfacial tension) that is much weaker than the chemical bond force during pressurization. It is estimated that most of the densification progresses by walking along the . In fact, as long as the preliminary sintered body does not involve the formation of open bores, the more grain boundaries there are, i.e., the smaller the grain size, the easier densification will progress during HIP, and NiZn ferrite can also be densified by this method. A dense sintered body can be obtained. When NiZn ferrite is primarily sintered in air, it is estimated that the pores inside the sintered body contain air at a pressure of about several atmospheres. In the case where HIP is performed at a lower temperature than the primary sintering temperature and densification progresses by the above mechanism, Pp after HIP in equation (1) is
Ore rises to several hundred atmospheres, and the volume of the pores is 11
The number will decrease to about 100. Of course, a portion of 02, which has a high diffusion rate in the oxide, will diffuse away from the grain boundaries to the surface of the sintered body during HIP, but most of the N2, which has a slow diffusion rate, will be released under high pressure. It is expected that this will become a reducing atmosphere at the grain boundaries inside the sintered body along with the Ar atmosphere during HIP, and this will be one of the reasons for the precipitation of the second reduced phase and the composition shift of the ferrite matrix toward the reducing side. be done. In addition, it is thought that almost the same thing can occur even when the HIP temperature is higher than the primary sintering temperature. In fact, as described later in Examples, when such a sample is annealed for a long time in order to obtain predetermined magnetic properties, the volume of the compressed pores expands again, reducing the sintered density. cases often occur. In addition, when manufacturing magnetic cores such as magnetic heads using NlZn ferrite containing such high-pressure gas,
During processing such as grinding and lapping, crystal grains on the material surface are removed by high-pressure gas, or even after the magnetic head is formed, they may come into contact with the magnetic disk or magnetic tape, causing wear and damage. Problems arise and the life of the magnetic head is significantly shortened. The method of the present invention has been made to eliminate the above-mentioned drawbacks.

That is, in the method of the present invention, by performing the primary sintering in oxygen, the formation of the second phase and the reduction composition are prevented, and the gas in the internal pores of the primary sintered body is diffused. By setting the speed to 02, which is high, densification is promoted during HIP, and at the same time, the generation of pores containing high pressure gas after HIP is prevented as much as possible. The thus obtained sintered body is a high-density sintered body that has predetermined magnetic properties, has no variation in mechanical strength, and has excellent workability.

Another important feature is that the loss of magnetic permeability in the high frequency region is small. Embodiments of the present invention will be illustrated below based on Examples. Example N for magnetic core material manufactured using the method of the present invention
iZn ferrite, molar ratio NjOlO ~ 25%, Zn
The composition consists of 5 to 40% Ol and 45 to 60% Fe2O.

In addition, for the purpose of obtaining a predetermined electrical resistance value, MnO2O. Although OOl ~ 3.0% is blended, M
Similarly, a high-density sintered body can be obtained without adding nO2. It is comprised of a process in which the mixture is pressure-molded into a desired shape, sintered in a two-step process, and then heat-treated. That is, after blending each raw material so that it has the above composition, it is thoroughly mixed using a ball mill or a vibration mill, and the
After calcining at 1300° C. for 3 or more minutes, the mixture was thoroughly pulverized again using a ball mill, vibration mill, or the like.

Next, the pulverized powder is molded into a mold or rubber press by pressure, and then primary sintered in oxygen at 1300°C or less for 30 minutes or more, and then sintered in an Ar atmosphere to form a 500-170°C
HIP was performed under conditions of 0[TmllOOOO~1250°C. Furthermore, as a final step, annealing is performed at a temperature below which significant crystal grain growth occurs and/or a temperature at which a second phase precipitates. is almost 100% N
iZn ferrite could be manufactured. Although oxides are generally used as the raw materials, the present invention is not necessarily limited to such oxides.
In place of other oxides, there are oxyhydroxides, hydroxides, carbonates, nitrates, etc. that can be easily converted into oxides during firing.
Compounds such as sulfates and oxalates can also be used.

Table 1 shows the composition of A(NlOl7.5
, ZnO32.5, Fe2O35O. O) and B(N
jOl8. O, ZnO32.5. Fe2O349.5)
A mixed powder in which 0.18 wt% of MnO2 was added to each raw material was calcined in air (1) according to the manufacturing process described above.
900℃ and (■) 1200℃, primary sintering: in oxygen,
(1) 1120℃ and (■) 1220'C1P: 1
1000C11000atm and 1200℃, 150
01tm1 annealing: in oxygen, (1) 1000°C and (■
) Characteristics of sintered bodies manufactured under various conditions of 1100°C.

As is clear from the table, the density of the sintered body obtained by the method of the present invention is 99.7 to 9 in relative value d/Dx (Dx: theoretical density).
It has an extremely high density of 9.9%.

Incidentally, the sintered bodies of composition A manufactured under optimal conditions using the conventional sintering method and hot pressing method had d/DX of 98.9% and 99.6%, respectively. However, even when sintering and primary sintering are performed in air,
By the HIP method, a sintered body with a d/DX of about 99.8% can be obtained. Among the magnetic properties, there is no major difference between the method of the present invention and the conventional HIP method and hot breath method in the magnetic flux density BlO coercive force HCl Curie point Tc, but the initial permeability P'' and its loss The frequency characteristics of term P'' are significantly different. FIG. 1 shows the μ″ and p″ frequency characteristics of Sample A shown in Table 1. As is clear from the figure, the sintered body A obtained by the method of the present invention (■) is different from the sample A obtained by the conventional HIP method in which calcination is performed in air, and the sample A obtained by the hot press method. Compared to,
In the high frequency band above 2MFIz, p″ is large and μ
2 has decreased significantly. That is, the NiZn ferrite produced by the method of the present invention is suitable as a magnetic recording material used in the M soil band, and when a magnetic core used in the vicinity of 3M1Iz was produced using the sintered body A and its output characteristics were measured, it was found that it was better than the conventional one. It was found that this material exhibits superior characteristics in that it is able to obtain a larger output voltage compared to the output characteristics of a magnetic core of the same shape and structure made from the same material. Figures 2 and 3
The figures show magnetic heads (magnetic core embedded in epoxy resin) manufactured using sintered bodies manufactured by the method of the present invention and the conventional HIP method in which calcination and primary sintering were performed in air. (This is an optical microscope structure photograph taken at a magnification of 500 times of the lapped surface obtained by polishing (final finishing buffing). With the magnetic core, a sharp lap surface can be obtained without crystal grains falling off, whereas with conventional methods, particles fall off during processing. In other words, the NiZn ferrite produced by the method of the present invention has extremely high density and has uniform mechanical properties.
It can be seen that the workability is extremely excellent and no second phase is formed. As described above, if the method according to the present invention is used, NiZn ferrite, which has extremely excellent magnetic properties in a high frequency band and is extremely easy to work with, can be easily produced using a normal HIP device. I can do it.

Furthermore, since materials having predetermined magnetic properties can be easily mass-produced using inexpensive industrial raw materials, they have great industrial value.

[Brief explanation of the drawing]

Figure 1 shows the frequency characteristics of magnetic permeability for each sintered body of composition A obtained by the method of the present invention, composition A obtained by the conventional HIP method, and composition C obtained by the hot pressing method. 2 and 3 are micrographs of the lap surfaces of NiZn ferrite magnetic head cores made from materials of composition A produced by the method of the present invention and the conventional HIP method, respectively.

Claims (1)

[Claims] 1. A step of calcining the raw material, a step of sintering the calcined powder to perform primary sintering to the extent that no open bores (holes extending from the surface of the sample to the center) are formed, and the primary sintering. Of the subsequent steps of hot isostatic pressing the ferrite material and annealing the ferrite material after the hot isostatic pressing,
A method for producing NiZn ferrite, characterized in that the primary sintering step is performed in an oxygen atmosphere.