JPS6158428B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to non-magnetic structural materials constituting various magnetic heads, particularly floppy disk heads. Conventionally, alumina, forsterite, steatite porcelain, etc. have been used as non-magnetic structural materials for magnetic heads. However, these drawbacks are that the composition of the magnetic material ferrite differs slightly depending on the specifications of the magnetic head, so the thermal expansion coefficient changes accordingly, and the thermal expansion coefficients of ferrite and non-magnetic material do not match, making it difficult to process the glass bonding process. This resulted in cracks occurring in one of the parts, resulting in a decrease in yield. This non-magnetic material for the magnetic head always slides along the floppy disk surface at high speed simultaneously with the ferrite. Therefore, if its wear resistance is not comparable to that of ferrite, a gap will be created between the ferrite portion and the non-magnetic material, reducing the functionality of the magnetic head. Furthermore, if there are voids of 30 microns or more on the surface of the material, minute chips may occur from the voids, causing scratches on the surface of the magnetic storage medium.
Furthermore, since these components are processed into magnetic heads through precise processing steps, appropriate machinability is required during machining. Alumina, forsterite, steatite, etc. cannot satisfy these requirements, and recently, for heads using Ni--Zn ferrite, BaO--, which is a known microwave dielectric material, has been used. It has become common to use TiO ₂ -ZrO ₂ based porcelain. This is BaO
―TiO ₂ ―ZrO ₂ -based porcelain has appropriate workability and wear resistance, and by adjusting the composition ratio, it has a thermal expansion coefficient in the range of 90 to 100 × 10 ^-7 /℃ without impairing mechanical properties. This is because it was discovered that it can be changed freely. However, as the performance of floppy disk devices has improved in recent years, the requirements for magnetic head materials have become increasingly severe, and a requirement for voids on the polished surface of 5 microns or less is becoming the standard. To meet this demand, BaO-TiO ₂ -ZrO _2- based porcelain cannot be manufactured using normal manufacturing methods, and hot pressing and hot isostatic pressing (HIP) are now used. These high-density techniques have made it possible to reduce the voids on the polished surface to a certain extent to meet the required performance, but their high cost has prevented their widespread use. The purpose of the present invention is to reduce voids on the polished surface to 5μ or less and to have a coefficient of thermal expansion of 90 to 100×, even though it is a normal sintering method.
The present invention provides a BaO-TiO ₂ -ZrO ₂ -based non-magnetic ceramic composition for magnetic heads with a temperature of 10 ^-7 /°C. The present invention uses _TiO2 80~91.0mol%, BaO6~
16.0mol%, _ZrO2 0.5~3.0mol%, _{Al2O3 0.05} ~
1.0 mol%, Y ₂ O ₃ 0.05 to 1.0 mol%, and the total composition is 100 mol%, and the thermal expansion coefficient is 90.
This is a non-magnetic ceramic composition for a magnetic head, characterized in that the magnetic flux is in the range of ×10 ^-7 /°C to 100 × 10 ^-7 /°C. In the BaO-TiO ₂ system, the mol ratio of TiO ₂ is 80 mol%
In the above composition range, it can be predicted from the normal phase equilibrium diagram that the crystalline phase consists of two crystalline phases: BaT ₄ O ₉ and TiO ₂ , but detailed research on microwave dielectrics suggests that the third crystalline phase is formed as a third crystalline phase. It has been confirmed that Ba ₂ Ti ₉ O ₂₀ exists, and it is also known that the greater the amount of this crystalline phase contained, the higher the strength of the porcelain. This depends on the calcination and sintering conditions.
Although the amount of Ba ₂ Ti ₉ O ₂₀ crystal phase produced differs, it has been recognized that including ZrO ₂ and SnO ₂ as additives can promote the formation of Ba ₂ Ti ₉ O ₂₀ crystal phase, and this Due to its improved dielectric properties, BaO−
TiO ₂ -ZrO ₂ ceramics were used as microwave dielectrics. BaO-TiO ₂ as a structural material for magnetic heads
- When looking at ZrO ₂ porcelain, the increased mechanical strength due to the formation of Ba ₂ Ti ₉ O ₂₀ is advantageous for applications. Also, by changing the ratio of BaO and TiO ₂
It has the advantage that the ratio of the Ba ₂ Ti ₉ O ₂₀ crystal phase to the TiO ₂ crystal phase can be controlled, and the coefficient of thermal expansion can be controlled by the volume ratio of both. For these reasons, BaO--TiO ₂ -ZrO _2- based porcelain has come to be commonly used as a structural material for magnetic heads. The blending ratio of TiO ₂ and BaO in the present invention is essential in order to control the thermal expansion coefficient between 90×10 ^-7 /°C and 100×10 ^-7 /°C. ZrO ₂ is for promoting the formation of the Ba ₂ Ti ₉ O ₂₀ crystal phase as explained above. If the amount of ZrO ₂ is less than 0.5 mol%, this effect will not be observed, and if it exceeds 3 mol%, the inside of the sintered body will be easily reduced during the sintering process. The size and amount of voids on the polished surface of the sintered body are inversely proportional to the particle size of the calcined powder after pulverization. That is, as the grinding progresses, the sintered density increases and the voids on the polished surface become smaller and less numerous. In order to obtain a sintered body with small voids, the key is how efficiently the pulverization after calcination can be carried out. One countermeasure is to lower the calcination temperature as much as possible and pulverize it into a soft powder, but if calcination is performed at too low a temperature, the raw material barium carbonate (BaCO ₃ ) may not decompose sufficiently, and Due to the gas (CO ₂ ) generated inside the solid, huge voids are created and have the opposite effect. As a result of trying various additives to the BaO-TiO ₂ -ZrO ₂ system, the inventor found that the addition of Al ₂ O ₃ and Y ₂ O ₃ suppressed the reaction during calcination, and that BaCO ₃ was sufficiently decomposed during calcination. It has been found that soft calcined powder can be obtained even under these conditions. Furthermore, the voids in the polished surface of the porcelain obtained by wet re-grinding, molding and sintering the powder obtained are as follows:
It has been found that the porcelain is significantly smaller and the number of particles is reduced compared to the BaO-TiO ₂ -ZrO _2- based porcelain obtained by the same calcining, crushing, and sintering process. The amounts of Al ₂ O ₃ and Y ₂ O ₃ added are both from 0.05 to 1.0.
The reason for limiting the amount is that if the amount added is less than this, the effect will be lost, and if it is more than this, the inside of the porcelain will be prone to ring formation during the sintering process, and the material will become hard and workability will deteriorate. Because it was recognized. The present invention will be explained in detail below with reference to Examples.
TiO ₂ , BaCO ₃ , and ZrO ₂ use reagents with a purity of 99% or higher, and the additives Al ₂ O ₃ and Y ₂ O ₃ also have high purity.
More than 99% of reagents were used. The raw materials were blended to have the composition shown in the table and wet mixed in a ball mill. After drying, it was crushed and calcined at between 1100°C and 1200°C for 3 hours. The calcined powder was ground for over 20 hours using a resin ball mill. Next, after drying, a binder was mixed and molded at a pressure of 1.0 to 2.0 t/cm ² . Sintering is
It was carried out in air between 1280°C and 1360°C. The density and coefficient of thermal expansion of the obtained sample were measured, and voids on the polished surface were observed using a metallurgical microscope. The results are shown in the table.

【table】

[Table] Experimental samples Nos. 1 to 27 are a group of samples in which the ratio of TiO ₂ to BaO is constant, but the amounts of ZnO ₂ , Al ₂ O ₃ , and Y ₂ O ₃ are different. The coefficient of thermal expansion is determined approximately by the ratio of TiO ₂ and BaO.
Non-magnetic porcelain for magnetic heads using Ni--Zn ferrite is required to have a coefficient of thermal expansion of 90 to 100 x 10 ^-7 /°C. Samples that can satisfy this are No. 1~
25, and the mixing ratios of these TiO ₂ and BaO are respectively
It can be seen that they are 80 to 91.0 mol% and 6 to 16.0 mol%. The effect of _ZrO2 improves the sinterability of porcelain, and the mechanical strength is improved. It also had the effect of preventing reduction, and this effect was observed at least up to 0.5 mol%. On the other hand, if the amount of _ZnO2 exceeds 3 mol%, reduction tends to occur and voids on the polished surface become larger. Samples No. 1, 11, 16, and 21 have excessive ZrO ₂ , so the mechanical strength of the porcelain is weak and the voids on the polished surface are large, which is preferable, and samples 5, 10, 15, 20, and 25 do not contain ZrO ₂ . and the inside of the sintered body is partially reduced,
The color turns gray, which is not practical. Al ₂ O ₃ is effective in inhibiting grain growth during sintering and obtaining a dense sintered body. The effect is
It was observed at 0.05 mol% or more. However, if it exceeds 1.0 mol%, the porcelain becomes hard and brittle, resulting in poor workability.
Also, depending on the ratio of BaO and TiO ₂ , reduction becomes easier. Y ₂ O ₃ has the effect of suppressing the reaction during calcination, facilitating the pulverization of the calcined powder, and narrowing the voids in the sintered body. The effect was observed at 0.05 mol% or more. On the other hand Y ₂ O ₃
When the content of Al ₂ O ₃ increases and exceeds 1.0 mol%,
Similarly, it hardens the material and deteriorates workability. 4,
Samples Nos. 9, 14, 19, and 24 are examples in which either Al ₂ O ₃ or Y ₂ O ₃ was present in excess, and the processability was poor. As is clear from the description of the above examples, the present invention provides a non-magnetic porcelain composition having a coefficient of thermal expansion in the range of 90 to 100×10 ^-7 /°C, having few voids, and having high mechanical strength. You can get this, which is
Suitable as a non-magnetic structural material for magnetic heads.

Claims (1)

[Claims] 1 _TiO2 80~91.0mo%, BaO6~16.0mo%,
_ZrO2 0.5~3.0mo%, _{A2O3 0.05} ~1.0mo
%, Y ₂ O ₃ 0.05 to 1.0 mo%, and the total amount is 100 mo%.