JPS6043644B2 - Manufacturing method of NiZn ferrite with high magnetic permeability in high frequency band - Google Patents

Description

Detailed Description of the Invention The present invention is directed to the production of NiZn ferrite which has an extremely high sintered density, an extremely uniform crystal grain size, a small permeability loss term especially in a high frequency band, and an extremely excellent frequency characteristic. It is related to the method.

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. For magnetic heads, which are indispensable for magnetic recording as transducers along with recording media, various required characteristics such as various magnetic properties, high frequency properties, and abrasion resistance to meet the demands for high-density recording 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.
There is a trend in which magnetic recording materials having excellent frequency characteristics in the band are required. 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. industrial N
The method for producing iZn ferrite is mainly a normal dry method, but in this case, the sintered density is limited to about 99.2%. In order to have the above-mentioned sintered density and satisfy predetermined magnetic properties, it is necessary to perform firing under optimal sintering conditions, but the average crystal grain size of the sintered body obtained under such conditions is large; Often grains of 50μ or more are contained in the sintered body. By the way, for high-density recording, it is necessary to make the spread of the recording magnetic field as narrow as possible from the point of view of recording demagnetization.Recently, the track width of the magnetic head core is 50μ or less, and the core thickness itself is 50μ or less. There is a trend towards even practical use of these products. Therefore, "NiZ" having the above-mentioned crystal grain size
If such a magnetic core is made of n-ferrite, the core will be composed of about 1 to 3 crystal grains along the thickness direction or track width, and there will be variations in magnetic properties due to the crystal orientation of the crystal grains and during processing. The mechanical strength of the steel becomes a problem. It is true that the real part μ'' of magnetic permeability due to crystal orientation tends to converge to a constant value when the operating frequency is high, but it cannot be denied that μ'' decreases in the high frequency band as the crystal grain size increases. It is also necessary to reduce the crystal grain size of the material. By the way, conventional methods for producing high-density ferrite with the above-mentioned defects removed as much as possible include 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. There is a method in which powder is sintered and densified by hot pressing. This method is superior to the normal dry method and has an average crystal grain size of 5 to 5.
A sintered body having a relative sintered density of about 20 μm and a relative sintered density of about 99.0 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 pressing direction is not static pressure, and it is difficult to obtain large sintered bodies due to equipment limitations. Therefore, it is not industrially advisable to use continuous hot breath. A further disadvantage of this method is that it is necessary to coat the ferrite with a powder such as alumina and then apply hot pressure, making it impossible to prevent the solid phase reaction that occurs between the ferrite and alumina during sintering. This is a point. Therefore, there are variations in structure between the center of the sintered body and the areas near the surface, and other compounds are generated especially near the surface, so a considerable portion of the sintered body surface must be removed. In addition, the yield also decreases. As a method for eliminating the above-mentioned drawbacks, a manufacturing method using hot static pressure pressing (hereinafter abbreviated as HIP) is known from JP-A-49-128296, but the details still need to be investigated. . When the HIP method is used, it is possible to obtain a sintered body with almost theoretical density without the need for a covering material such as alumina, but after HIP, the magnetic properties are significantly deteriorated due to strain accumulated during pressurization. Therefore, in order to obtain the desired magnetic properties, strain relief annealing must be performed under appropriate conditions. stomach. The heat treatment conditions are closely related to the primary sintering conditions and the HIP conditions, and if these conditions are inappropriate, residual grain boundary stress will cause the magnetic permeability μ and coercive force Hc, which have strong structure dependence, to decrease.
This causes significant deterioration in mechanical properties, and as will be described later, crystal grains fall off during processing, resulting in a significant deterioration in mechanical properties. The inventors conducted a detailed study on a method for producing NiZn ferrite using the HIP method and arrived at the present invention. The outline of the manufacturing method according to the present invention is to proceed with preliminary sintering of the compact to such an extent that no pores (open bores) communicating from the inside of the sample to the surface are formed, and then subjected to hydrostatic hot processing by HIP. This method uses pressure to achieve densification.

What should be noted in the method of the present invention is that since pressure is applied statically, if open bores exist in the sample, densification will not proceed, so open bores should not be generated during primary sintering. . However, it is not so difficult to prevent the formation of open bores during preliminary sintering, and the relative density of the primary sintered body (hereinafter referred to as d/DX; d: density of the sintered body, Dx: theoretical density) is approximately 95
% or more, no open bore will be generated. By the way, in the conventional method of densifying an oxide containing ferrite by HIP, a method of hot pressing at a temperature effectively lower than the preliminary sintering temperature has been adopted.

The HIP temperature is usually about 50 to 80% of the melting point of the oxide. Although the detailed mechanism by which sintered bodies with extremely poor malleability such as oxides become densified under the above HIP conditions is not clear, it can be considered that equation (1) holds true as a rough approximation from a thermodynamic point of view. can. PextΣPpOre+
2γ/r●●●●◆●(1) Here, Pext is the external pressure, that is, the HIP pressure, PpOre is the pore pressure inside the sintered body, and r
is the hole radius, and γ is the interfacial tension of the hole.

By the way, theoretically, the energy to break a chemical bond corresponds to a static pressure of about 1Cf'Atm, and the static pressure required for phase transition of a solid is usually about 101 to 1CPatm, so the energy required to break a chemical bond is approximately -2103atm due to HIP. The static pressure is 100
It is considered that even at a temperature of about 0° C., ions do not have a significant effect on crystal grains arranged by chemical bonding force. Therefore, when pressurized, most of the densification progresses as the crystal grains slide along the grain boundaries, which are balanced by a binding force (that is, interfacial tension) that is much weaker than the chemical bonding force. It is estimated that In fact, as long as the preliminary sintered body does not involve the formation of open bores, the more grain boundaries there are, that is, the smaller the grain size, the easier densification will progress during HIP, and NlZn ferrite can also be densified by this method. A dense sintered body can be obtained. However, since NiZn ferrite contains Ni2, which has a very strong tendency to occupy octahedrons, and Zn2, which has a strong tendency to occupy tetrahedrons, when sintered in a reducing atmosphere, these ions separate from the spinel phase and form Ni2, respectively. In case of excess, NaCf type, in case of excess Zn2, hexagonal Zin
A second phase having a cite type structure is formed. Since these second phases deteriorate magnetic properties and significantly degrade workability as described above, NiZn ferrite must be sintered in air or oxygen. When NiZn ferrite is primarily sintered in the above atmosphere, it is estimated that the pores inside the sintered body contain approximately several atmospheres of air or oxygen. HIP at a temperature lower than the primary sintering temperature
is carried out, and if densification progresses by the above mechanism, (
In formula 1), PpOre after HIP increases to about several hundred atmospheres, and the volume of the pores decreases to about 1/1 (1). Of course, 02 has a high diffusion rate in oxides.
A part of N2 will diffuse away from the grain boundaries to the surface of the sintered body during HIP, but if the primary sintering is performed in air, the slow diffusion rate of N2 will be reduced as mentioned above. A part of it is trapped in the grain boundaries under high pressure. When such a sample is annealed for a long time in order to obtain predetermined magnetic properties as described below, the volume of the compressed pores expands again, causing the sintered density to decrease again. Empowerment often occurs. NiZ internally embrittles such high-pressure gas.
When manufacturing magnetic cores such as magnetic heads using n-ferrite, crystal grains on the surface of the material may be removed by high-pressure gas during processing such as grinding and lapping, or even after the magnetic head is formed, magnetic disks or The particles come off due to contact with the magnetic tape, causing problems of wear and damage, and the lifespan of the magnetic head is significantly shortened. Therefore, in order to advance the densification of NiZn ferrite by such a mechanism, it is important to perform the primary sintering in oxygen. HIP to remove the above drawbacks
The following methods are available. In other words, after primary sintering is performed at a relatively low temperature to the extent that open bores are not formed, the effective temperature obtained by converting all the temperature, pressure, and atmosphere during HIP into temperature effects is a condition that is higher than the primary sintering temperature. This is a method of manufacturing high-density NiZn ferrite by pressurizing the NiZn ferrite. In this case, similar to hot pressing, some grain growth occurs during HIP, but in this process, the gas remaining at the grain boundaries is sequentially desorbed to the surface of the sintered body, so the resulting sintered A high-density sintered body with relatively uniform mechanical strength and excellent workability can be obtained. 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 has a molar ratio of NiO: 10 to 25%, Z
The composition consists of nO: 15-40% and Fe2O3: 45-60%.

In addition, for the purpose of obtaining a predetermined electrical resistance value, especially Mn in terms of weight ratio.
O2O. Although OOl~3.0% is blended, MnO2
A high-density sintered body can be obtained in the same manner without blending. 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 to have the above composition, thoroughly mixed in a ball mill or vibration mill, calcined at least 3 powders at 800 to 1100°C in air or oxygen, and then ball milled again. Alternatively, sufficient pulverization was performed using a vibrating mill or the like.

Next, the pulverized powder is molded into a mold or rubber press by pressure, and then primary sintering of 3 or more powders is performed at 1250°C or less in air or oxygen, and then sintered in an N atmosphere for 50 minutes.
HIP was performed under conditions of 00-20001 tm11000-1250°C. Furthermore, as a final step, annealing (heat treatment) is performed at a temperature lower than the higher of the temperatures of the primary sintering or hot isostatic pressing, so that the crystal grain size is 20p or less and the sintered It was possible to produce NiZn ferrite with a condensation density of approximately 100%. Oxides are generally used as the raw materials, but
In the present invention, compounds such as carbonates, nitrates, sulfates, and oxalates, which can be easily converted into oxides during sintering, may be used in place of other oxides, but are not necessarily limited to such oxides. You can also do that. Table 1 is
The composition is A (NiOl7.5, ZnO3
2.5, Fe2O35O. O) and (NiOl8.O
, ZnO32.5, Fe2O349.5), a mixed powder in which 0.18 wt% of MnO2 was added to each raw material was sintered at 900°C in air, and primary sintered:
These are various properties of a sintered body manufactured under the conditions of 1120° C. in oxygen and annealing: 1080° C. in oxygen.

In the table, under the conditions of HIP temperature 1100℃ and HIP pressure 100 [Tm, the effective temperature during HIP is considered to be slightly higher than the primary sintering temperature, and the crystal grain sizes are also A and B, respectively.
In both compositions, it becomes larger by about 1.2 to 1.3 μ. On the other hand 1
Under the P conditions of 050° C. and 1000 atm, the effective temperature is considered to be lower than the primary sintering temperature, and grain growth does not occur during HIP, and densification progresses due to the stretching of grain boundaries. As is clear from the table, the sintered density after HIP becomes higher when the effective temperature is higher than the primary sintering temperature. Among magnetic properties, magnetic flux density group. , the coercive force Hc and the Curie point Tc do not show any significant difference depending on the effective temperature of HIP, but the frequency characteristics of the initial permeability μ″ and its loss term μ″ are significantly different. FIG. 1 shows the μ'' and μ'' frequency characteristics of Sample A shown in Table 1. It is shown in the figure. In other words, the sintered body 1 obtained at the HIP temperature of 1100°C has a larger μ″ in the high frequency region than the sintered body 2 obtained at the HIP temperature of 1050°C, and is suitable as a high frequency material. After HIPing under the same conditions, μ'' and -
The frequency characteristic of μ2 is significantly lower than μ2 compared to 1. Figure 2 shows sample B in Table 1 (HIP condition 11
μ″, μ2 at 00℃, 10001tm1) 3M pressure
and the average grain size is plotted against the annealing temperature. As is clear from the figure, as the annealing temperature becomes higher than the HIP effective temperature in sample B as well, rapid crystal grain growth occurs, and μ'' at high frequency rapidly decreases.First
When a magnetic head used at around 3 MHz was manufactured using sintered bodies 1 and 3 shown in the figure, both materials had approximately 100 MHz.
Despite having a sintered density of Remarkably, stable and good characteristics could not be obtained. Furthermore, in a material with a significantly large crystal grain size, the material itself becomes brittle, causing cracks to occur during processing and large grain shedding, resulting in an extremely low yield. As stated above,
Using the method of the present invention, N
iZn ferrite can be easily produced using a conventional HIP device.

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 drawings]

Figure 1 shows the frequency change in magnetic permeability of composition Al, 2 obtained by the method of the present invention and composition 3 obtained by the conventional HIP method, and Figure 2 shows the change in frequency of magnetic permeability with respect to the annealing temperature of the composition. FIG. 3 is a diagram showing changes in average crystal grain size and μ″ and μ2 at 3 MHz.

Claims (1)

[Claims] 1 A process of sintering the ferrite material to the extent that no open pores (pores extending from the sample surface to the center) are formed, and a process of hot static pressure pressing the ferrite material after the primary sintering. and a step of annealing the ferrite material after hot isostatic pressing at a temperature lower than the higher of the temperatures of the primary sintering or hot isostatic pressing to prevent μ from deteriorating at high frequency. A method for producing NiZn ferrite having high magnetic permeability in a high frequency band.