JPH0791116B2 - Method for manufacturing high-density oxide sintered body - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to the production of oxide ceramics, which is a typical ceramic material, and particularly to the production of a high-density sintered body containing no pores under a high pressure gas at a high temperature. The present invention relates to a manufacturing method using a hot isostatic pressing (hereinafter abbreviated as HIP) method in which a pressure is applied.

(Prior art) As a method for producing a high-density ceramics sintered body with no pores, once the relative density was 92 to 97% by the ordinary sintering method.
The method of making a sintered body in the closed pore state and pressurizing it with a pressure of several 100 to 2000 kgf / cm ² at high temperature using an inert gas such as argon as a pressure medium to obtain a high density sintered body is It is used industrially.

At this time, usually, argon gas is used as the pressure medium gas, but the reason for this is that the HIP method has been applied to treated products such as cemented carbide and Ti alloy cast members that easily react with oxygen and nitrogen. That is, molybdenum and graphite, which have poor oxidation resistance, are often used as electric furnace members for HIP equipment.

Recently, however, HIP treatment has been applied to complex oxide ceramics such as Mn-Zn-ferrite, Ni-Zn-ferrite, and PZT, and oxide-based ceramics such as zirconia. When HIP treatment is performed using active gas, oxygen in the treated product escapes, the desired magnetic properties cannot be obtained with ferrite, or the surface layer part becomes wustite and hair cracks occur, and zirconia turns black. In some cases, the tetragonal grains of partially stabilized zirconia may change into monoclinic crystals and the desired strength characteristics may not be obtained.To improve this, argon was used as a pressure medium gas. The use of a mixture of oxygen is being considered. In particular, in the HIP treatment of superconducting ceramics that has recently been discovered, it is essential to control the amount of oxygen in the ceramics by mixing oxygen in the pressure medium gas and applying an appropriate oxygen partial pressure. The HIP treatment with the mixed gas of argon and oxygen has been attempted.

(Problems to be solved by the invention) As described above, in the HIP treatment of some oxide-based ceramics, if there is no partial pressure of oxygen in the pressure medium bath, oxygen deficiency may occur in the treated product during the HIP treatment. The mixed gas of argon and oxygen is being used because the effect of the period is not obtained.
While this method is effective in suppressing the generation of oxygen deficiency, it has the following drawbacks in industrial use.

First, in many cases, it is necessary to keep the oxygen partial pressure, that is, the mixing ratio of argon gas and oxygen within a predetermined range for each HIP treatment, and it is essential to manufacture a mixed gas having this specific amount of oxygen. Becomes Argon gas itself
In addition to being quite expensive, the work of mixing argon gas and oxygen and the analysis work for checking the mixing amount check are required, so that the resulting mixed gas becomes very expensive.

In addition, when the pressure medium gas after use is collected and repeatedly used, it is necessary to supplement the oxygen content absorbed by the processed product and the electric furnace member.For this purpose, the gas after use must be analyzed each time. It is necessary to calculate the amount of replenishment to obtain the amount of oxygen to be replenished, mix this, sufficiently stir, and then carry out further analysis. To avoid this,
There is no choice but to dispose of the gas, but in this case, the HIP processing cost becomes very high, and industrial use cannot be expected.

The present invention deals with the actual situation as described above, and has been invented to solve the problem, in particular, by specifying the pressure medium, it is possible to significantly reduce the HIP treatment cost of oxide ceramics, Moreover, it is intended to reduce the variation in the characteristics of the treated material.

(Means for Solving the Problems) That is, the feature of the present invention that meets the above-mentioned object is that an oxide sintered body sintered at a relative density of 92% or more is dried air having a water content of 50 ppm or less. Alternatively, hot isostatic pressing is performed by using the mixed gas of dry air and nitrogen as a pressure medium to increase the relative density to 99% or more.

Here, as the oxide sintered body to which the above treatment is applied,
Oxide ceramics sintered bodies, which are typical ceramic materials, can be mentioned, for example, the above-mentioned Mn-Zn-ferrite and Ni.
-Zn-ferrite, composite oxide ceramics such as PZT, oxide ceramics such as zirconia, and more recent superconducting ceramics are included.

The basic point of the above-mentioned treatment is to use air which has a stable oxygen content of about 19% and is inexpensive. However, normal air contains a considerable amount of water, and if this is used as it is, dew will condense inside the high-pressure vessel, causing insulation failure and short-circuit accidents in the electrode part of the electric furnace built into the high-pressure vessel. Since it is easy to use, dry air with a water content of 50 ppm or less has been used.

Hereinafter, the features of the present invention will be described in more detail.

First, the technical problem in the case of using the above-described air as pressure medium in HIP processing is the possibility of occurrence of the problems described above of water, oxides of nitrogen at high pressure conditions (NO _X).

For the former, from the experience of operating the HIP device with Ar or N ₂ up to now, that is, the presence or absence of dew condensation due to the concentration of water as impurities that inevitably occurs in repeated use of these gases, 50 ppm by volume or less It was concluded that the amount of water does not cause the problem of insulation failure in the electrode part.

Of course, even if the water content exceeds 50 volume ppm, 50 volume p
Even if it exceeds a little pm, it does not immediately lead to a short circuit accident due to poor insulation, but it has a character that depends on the absolute amount of water, that is, the amount of pressure medium gas. However, if the amount of water, especially the absolute amount, becomes too large, when the pressure medium gas passes through the pressure reducing valve during gas recovery, which is the last step of the HIP process, the decrease in the temperature of the recovered gas due to adiabatic expansion causes condensation of water. The clogging phenomenon may occur inside the pipe, and the smaller the water content, the better.

On the other hand, with regard to the latter generation of nitrogen oxides, the generated amount does not depend only on the amounts and pressures of nitrogen and oxygen, and the temperature, but the amount of coexisting water, the amount of impurity gas components such as CH ₄ and CO, and further It also depends on the type of constituent material of the electric furnace of the HIP device.

Under normal HIP treatment conditions of 2000 kg / cm ² , up to about 1500 ° C, the generated amount is not so large that it does not deteriorate the electric furnace material and high pressure equipment components. However, regarding the release of the gas after use, it is preferable to perform the nitrogen oxide removal treatment before the release depending on the amount thereof.

The characteristic feature of the present invention is set in consideration of these problems, not only dry air having a water content of 50 ppm or less, but also mixed with nitrogen to this and diluted with oxygen to be used. The present invention may be embodied regardless of the implementation of the invention.

Generally, air contains about 80% of nitrogen, about 19% of oxygen, about 1% of argon, as well as the above-mentioned water, carbon dioxide, carbon monoxide, etc. Other components have almost no problem as long as they are normal contents.
However, in the case of Y-Ba-Cu-O-based superconducting ceramics, carbon dioxide easily reacts to form barium carbonate, so it is preferable to remove it by some method.

Next, examples of the present invention will be described in comparison with comparative examples.

(Example) After mixing Al ₂ O ₃ powder mixed with 0.3% by weight of MgO with a ball mill, a molded body of 30 × 50 × 6 (mm) was prepared by die molding, and this was molded at 1450 ° C. in the atmosphere. Density 3.9g after firing for 1 hour
A sintered body of / cm ³ (relative density 98%) was obtained. This sintered body was placed in a HIP device equipped with a platinum heater element. After evacuating the inside of the HIP device, dry air (water content 50p
pm) air. Further, air was injected under pressure up to 120 kg / cm ² . Then, the platinum heater was energized to raise the temperature to 1400 ° C. At this time, the pressure inside the HIP device is approximately 350 kg / cm ²
Became. Hold at 1400 ℃ for 1 hour, then lower the temperature to remove the gas.
It was released outside the HIP device. As a result of analyzing the amount of oxygen in the released gas, it was about 18%. The density of the treated sintered body was 3,975 g / cm ³ , and when the microstructure was examined by a scanning electron microscope, almost no pores were observed. The color tone of the sintered body was almost the same as when it was sintered in the air, and it was white with a slight orange tinge.

The same treatment was repeated 5 times, but the above results were almost reproduced.

(Comparative Example 1) An Al ₂ O ₃ sintered body prepared by the same procedure as in Example 1 was prepared by using a mixed gas of argon and oxygen (20%) as a pressure medium gas.
Treatment was carried out at 00 ° C. and 350 kg / cm ² for 1 hour. When the gas after the treatment was collected and analyzed, the amount of oxygen decreased to about 18%. The density of the sintered body was 3,975 g / cm ³ , which was almost the same as in Example 1 and no pores were observed.

Since the mixed gas of argon and oxygen is expensive, the recovered gas was repeatedly used as it was for five treatments. The shortage was argon + oxygen (20%). As a result, the amount of oxygen was decreased by 1.5 to 2% by one treatment. No significant change was observed in the density of the sintered body after the treatment, but a slight difference was generated in the color tone, and the reproducibility as in Example 1 was not observed.

Comparative Example 2 The Al ₂ O ₃ sintered body prepared by the same procedure as in Example 1 was treated with pure argon at 1400 ° C. and 350 kg / cm ² for 1 hour. The density of the sintered body was 3,980 g / cm ³ , which was slightly higher than those of Example 1 and Comparative Example 1, but the color tone was white, which was different from the color tone when sintered in air. Was.

(Comparative Example 3) Similar to Comparative Example 2, an attempt was made to perform treatment using normal air (moisture of about 100 ppm), but insulation failure of the heater occurred and operation was impossible.

A large amount of water was accumulated in the bottom part inside the HIP treatment.

(Effect of the invention) As described above, according to the present invention, in the production of a high-density oxide sintered body using the HIP treatment, by using dry air having a water content of 50 ppm or a mixed gas of nitrogen and Ar as a pressure medium, It is no longer necessary to use expensive inert gas such as or a mixed gas of the inert gas and oxygen, and the cost is significantly higher than that of the conventional production of oxide sintered body using HIP treatment. In addition to reducing the amount of oxygen, the use of air with a relatively stable oxygen content also makes it easier to control and control the amount of oxygen, and as a result, it is possible to reduce the variation in the characteristics of the treated material. Has an industrial effect.

In addition to the Al ₂ O ₃ -based oxide ceramics shown in the examples, the present invention is applicable to lead material zirconate titanate (PZT) -based, soft ferrite, barium titanate-based electronic material ceramics, and partially stabilized zirconia. Can also be applied, and the ripple effect is expected to be great due to the cost reduction of HIP processing, which was said to be expensive in the past.

Claims (1)

[Claims] 1. A hot isostatic pressing process is performed on an oxide sintered body having a relative density of 92% or more using dry air having a water content of 50 ppm or less or a mixed gas of the dry air and nitrogen as a pressure medium. A method for producing a high-density oxide sintered body, which comprises performing a densification to a relative density of 99% or more.