JPS6358781B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a method for producing high-density ferrite.

[Prior art]

Ferrite is a magnetic head for audio, VTR
They are widely used in magnetic heads for computers and magnetic heads for computers, etc., but in recent years, with the progress of higher quality and higher density recording, they have improved magnetic properties as well as pores that can cause damage to heads and media. There has been a growing demand for dense ferrite that is easy to work with and has a small amount of ferrite.

Conventional methods for producing high-density ferrite include the rubber press method, hot press method, and hot isostatic press method (hereinafter referred to as the HIP method), but these methods have a large pore elimination effect and have low productivity. A good HIP method is better than other methods. A method for producing high-density ferrite by the HIP method is known, for example, from Japanese Patent Publication No. 54-27558, Japanese Patent Publication No. 58-14050, and the like.

The method for producing high-density Ni-Zn ferrite using the HIP method is to use Fe ₂ O ₃ ,
NiO and ZnO oxides are wet mixed in a ball mill, filtered and dried, and then molded in the subsequent process and
In order to proceed with the next sintering process stably, the temperature is 900℃~1100℃.
It is pre-fired at a temperature of , changing it to more than 70% spinel phase. Thereafter, the powder is wet-pulverized for a predetermined time using a ball mill or an attritor to obtain the optimum powder.
After adding a binder, it is molded into the desired shape.
Primary sintering to have a relative density of 96% or more,
This method produces dense Ni-Zn ferrite by subjecting a sintered material with closed pores to high-pressure and high-temperature treatment in an Ar gas atmosphere, but this method produces uneven grain size growth, intragranular pores, and ZnO precipitation. At present, issues of equality remain. Therefore, in order to produce ferrite that is dense, uniform, small particle size, and has excellent magnetic properties, sufficient consideration must be given not only to the primary sintering and HIP conditions, but also to the previous powder manufacturing process. I had to pay. In other words, the calcining state, particle size, particle size distribution, etc., must be controlled extremely accurately, and the results are not always completely satisfactory.

[Purpose of the invention]

In view of the above-mentioned problems, the object of the present invention is to produce Ni that has dense, uniform, small grain size and high magnetic properties.
- To provide a manufacturing method that reliably provides Zn ferrite.

[Structure of the invention]

In the method of the present invention, the relationship between the reactivity of the powder in the pre-firing step, the amount of so-called spinel phase, and the powder properties in the grinding step, so-called particle size and particle size distribution, is
Focusing on the fact that the HIP treatment process has a large effect on the crystal grain structure and magnetic properties of Ni-Zn ferrite, we compressed and passed the mixed powder of ferrite raw materials in a roll mill before calcining, making it dense and uniform. This is to obtain a grain structure having a small grain size.

That is, according to the present invention, powder raw materials mainly composed of iron, nickel, and zinc oxides are mixed,
A method for producing high-density ferrite by pre-firing, crushing, press-molding, sintering, and hot isostatic pressing, characterized in that a roll mill compression treatment is performed between the mixing treatment and the pre-baking treatment. A method for producing Ni-Zn ferrite material is obtained.

〔Example〕

First, an experimental example will be shown showing that the ferrite mixed powder subjected to the roll mill treatment according to the present invention can be prefired at a lower temperature than the conventional powder. The ingredients of the raw materials used were those explained as composition A in the Examples described later. This ferrite mixed powder was first processed in a ball mill for 40 hours, then compressed and passed through a roll mill at a pressure of 3000 kg/cm ² and then subjected to a pre-firing treatment. In the conventional case, the material is subjected to pre-firing treatment without performing this compression passage step using a roll mill.

Figure 1 is a diagram showing the relationship between the pre-firing temperature and the amount of spinel determined by X-ray diffraction when the above-mentioned pre-firing process is carried out for one hour, comparing the manufacturing method of the present invention and the conventional manufacturing method. be. As you can easily see from Figure 1, if the pre-firing treatment time is set to 1 hour, which is reasonable from a practical point of view, the spinel single phase cannot be obtained unless the temperature is 900℃ to 1100℃ with the conventional method. On the other hand, the product of the present invention can be obtained at a low temperature of 800°C, so it is extremely effective in practice. This is understood to be because the powder compressed through a roll mill has a large compression strain and easily becomes a spinel single phase at low temperatures.

In the above, the compression pressure of the roll mill is 3000 Kg/cm ² as an example, but it is of course not limited to this and has a considerable vertical width. However, according to experiments, the compression pressure of the roll mill is 1000
At around Kg/cm ² , the amount of spinel obtained is not much different from that obtained by the conventional method, and at over 5000 Kg/cm ² , the powder cannot be easily sized by passing through a sieve, which is not preferable. In addition, the amount of spinel obtained by the above X-ray diffraction is determined by the sum of the diffraction intensities of the spinel phase detected in the range of γ-ray diffraction angle (2θ) of 30° to 90°, and the sum of the diffraction intensities of the spinel phase and α-Fe ₂ O ₃ . It is determined as a percentage of the total diffraction intensity.

Next, the powder obtained by the above-mentioned pre-calcination treatment is subjected to a subsequent ball mill treatment (second time), and the particle size distribution of the resulting pulverized powder will be explained by comparing the particle size distribution of the present invention and the conventional one. The raw materials used and the first ball milling were the same as in the case of FIG. 1 above. The raw material powder was pre-fired at 850°C in the case of the present invention and at 1000°C in the conventional case using the results obtained previously. This pre-fired powder was wet-milled for 12 hours in a ball mill (second stage).
times).

Figure 2 shows the particle size distribution of the pulverized powder obtained in this way, and shows that the particle size is approximately
0.6μm, whereas in the case of the present invention it is approximately 0.2μm
However, the distribution shape is becoming narrower. The reason why the powder according to the present invention is small is because the temperature of the pre-baking treatment, which is a pre-process, is low in the present invention and the grain growth of the powder is suppressed. A powder with good properties can be obtained. When this powder is subjected to the next press treatment, a powder with a relative density of 96% or more is obtained. Note that ZnO seems to play a major role, considering that roll milling of ferrites other than Ni-Zn-based ferrites does not show the same effect as Ni-Zn-based ferrites.

The two embodiments described above describe the process from roll milling to press processing, which is a feature of the present invention, but the embodiments to be described from now on will be performed on products that have undergone all steps. In this example, two types of compositions are used as raw materials. One raw material is Fe ₂ O ₃
49.5mol%, NiO 19.0mol%, ZnO 31.5mol%
It is an oxide powder with the composition of
Fe ₂ O ₃ is 49.5 mol%, NiO is 17.0 mol%, ZnO is
It is an oxide powder with a composition of 33.5 mol%. Hereinafter, the former will be named composition A, and the latter will be named composition B. Exactly the same treatment is then performed on these two raw material powders. That is, in any composition, the oxide raw material powder is first wet-mixed in a ball mill for 40 hours, dried, and then compressed in a roll mill at a pressure of 3000 kg/cm ² . After that, it was pre-fired at a temperature of 800℃ for 1 hour in the air, and then ground in a ball mill for 20 hours to obtain a powder with an average particle size of 0.2μm.A binder was added to this powder, and 2000Kg/
A compact of 60 x 30 x 10 mm was made at a pressure of cm ² , and 1150
Primary sintering was performed in the air at a temperature of 1,100° C. for 2 hours, followed by HIP treatment for 2 hours in an argon atmosphere at a treatment temperature of 1,100° C. and a pressure of 1,000 Kg/cm ² .

Figure 3 shows the high density obtained as described above.
FIG. 2 is a diagram showing some properties of Ni--Zn ferrite in comparison with properties obtained by a conventional method that does not involve compression passing through a roll mill.

Further, FIG. 4 is a diagram showing a similar comparison of effective magnetic permeability, which is one of the dynamic characteristics.

Particularly notable points in Figure 3 are:
The characteristics of the ferrite obtained by the method of the present invention are that it has a high specific resistance, a small average particle size and a small porosity, and a high resistive strength compared to conventional ferrite. Note that the high bending strength, together with the high magnetic properties, is extremely effective when this ferrite is used as a magnetic head.

Also, it can be seen from Figure 4 that the frequency used is 2M.
When the frequency exceeds about Hz, the effective magnetic permeability becomes large in the present invention, and excellent frequency characteristics are exhibited. That is, for example, at 3MHz, composition A
In the case of composition B, it is about 6.7×10 ² in the conventional case, while it is about 7.3×10 ² in the case of the present invention, and the case of composition B also shows an improvement at almost the same rate. This means that the specific resistance, average particle size, and porosity are improved in terms of the characteristics shown in Figure 3.If we go back to the origin of this, we can say that the second round of compression by the roll mill compression used in the present invention is improved. This is because the particle size of the powder obtained by ball milling is about 0.2 μm, which is about one-third smaller than the conventional size.

〔Effect of the invention〕

As explained above, according to the present invention, high-density Ni--Zn ferrite with excellent magnetic and mechanical properties can be easily produced, and is extremely useful as a ferrite material for magnetic heads.

[Brief explanation of drawings]

Figure 1 shows the relationship between the pre-firing temperature of Ni-Zn ferrite and the amount of spinel obtained by this pre-firing, comparing the present invention and the conventional one. Figure 3 compares the particle size distribution of the pulverized powder of the present invention and the conventional one. Figure 3 compares the characteristics of the Ni-Zn ferrite that has been subjected to HIP treatment, the one of the present invention and the conventional one. Figure 4 is a diagram comparing the effective magnetic permeability, which is one of the characteristics of Ni--Zn ferrite, between the one of the present invention and the conventional one.

Claims (1)

[Claims] 1. A method for producing high-density ferrite by mixing, pre-sintering, pulverizing, press-molding, sintering, and hot isostatic pressing powder raw materials containing iron, nickel, and zinc oxides as main components, A method for producing a Ni--Zn ferrite material, characterized in that a roll mill compression treatment is performed between the mixing treatment and the calcination treatment.