JPH02129077A - Production of sintered oxide material having high density - Google Patents

Abstract

PURPOSE:To obtain the subject sintered material having uniform properties and nearly theoretical relative density by sintering an oxide to high relative density and subjecting the obtained sintered oxide to hot isostatic pressing treatment using dry air having low water content or a mixture of said dry air and N2 gas as a pressure medium. CONSTITUTION:A sintered oxide sintered to a relative density of >=92%, e.g., sintered oxide ceramics such as Mn-Zn-ferrite, is subjected to hot isostatic press(HIP) under the following conditions. The HIP treatment of the sintered oxide is carried out by using dried air having a water content of <=50ppm or a gaseous mixture of said dried air and N2 as a pressure medium. A high- density sintered oxide having a relative density of >=99% can be produced by this process. The present process can be carried out without using an expensive inert gas such as Ar and, accordingly, the production cost can be remarkably reduced compared with the conventional sintered oxide production process using HIP treatment.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to the production of oxide ceramics, which are typical ceramic materials, and in particular, the present invention relates to the production of oxide ceramics, which are typical ceramic materials. The present invention relates to a manufacturing method using a hot isostatic press (hereinafter abbreviated as old P) method in which pressure is applied.

(Prior art) As a method for producing a high-density ceramic sintered body without pores, the relative density is 92 to 9 by a normal sintering method.
A sintered body with 7% closed pores is prepared, and this is heated under high temperature using an inert gas such as argon as a pressure medium to form several 100 to 200 pores.
A method of pressurizing at a pressure of 0 kgf/csJ to form a high-density sintered body is used industrially.

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

However, recently, Mn-Zn-ferrite, Ni-Z
IIIP treatment is being applied to composite oxide ceramics such as n-fluorite and PZT, and oxide ceramics such as zirconia.In this case, if IIIP treatment is performed using an inert gas such as argon, In ferrite, the desired magnetic properties may not be obtained or the surface layer may turn into wustite, causing hair cracks. In addition, zirconia may turn black, or the tetragonal grains of partially stabilized zirconia may become monoclinic. It has been found that the desired strength characteristics may not be obtained due to changes in the strength of the material.In order to improve this problem, the use of a mixture of argon and oxygen as a pressure medium gas is being considered. In particular, in the recently discovered old P treatment of superconducting ceramics, it is essential to mix oxygen into the pressure medium gas to give an appropriate oxygen partial pressure in order to control the amount of oxygen in the ceramics. Therefore, attempts have been made to perform IIIP processing using the above-mentioned mixed gas of argon and oxygen.

(Problems to be Solved by the Invention) As mentioned above, in the IIP treatment of some oxide ceramics, if there is no partial pressure of oxygen in the pressure medium gas, oxygen vacancies may occur in the treated product during the HIP treatment. However, while this method is effective in suppressing the occurrence of oxygen vacancies, it has the following disadvantages in terms of industrial use. It has the following drawbacks.

First, in many cases, it is necessary to maintain the oxygen partial pressure, that is, the mixing ratio of argon gas and oxygen, within a predetermined range for each IIIP process, and it is essential to produce a mixed gas with a specific amount of oxygen. becomes.

Argon gas itself is quite expensive, and it also requires mixing the argon gas and oxygen and analysis to check the amount of mixture, making the resulting mixed gas very expensive.

In addition, when used pressure medium gas is recovered and used repeatedly, it is necessary to replenish the amount of oxygen absorbed by treated products and electric furnace parts, and for this purpose, the gas after use must be analyzed each time. It is necessary to calculate the amount of oxygen to be replenished, find the amount of oxygen to be replenished, mix it, stir it sufficiently, and then perform further analysis, which is a complicated process. To avoid this, the gas must be made disposable, but in this case, the cost of processing the old P would be extremely high, and industrial use cannot wait.

The present invention has been invented to address the above-mentioned actual situation and solve the problem.In particular, by specifying the pressure medium, the cost of HIP treatment of oxide ceramics can be significantly reduced. The purpose is also to reduce variations in the properties of treated materials.

(Means for Solving the Problems) That is, the feature of the present invention that meets the above object is that an oxide sintered body sintered to a relative density of 92% or more is heated in dry air with a moisture content of 50 ppm or less. or using the mixed gas of dry air and nitrogen as a pressure medium) 11P treatment,
The objective is to increase the relative density to 99% or more.

Here, the oxide sintered body to which the above treatment is applied is as follows:
Typical ceramic materials include oxide ceramic sintered bodies, such as the aforementioned MnZn-ferrite,
Composite oxide ceramics such as Ni-Zn-ferrite and PZT, oxide ceramics such as zirconia,
Furthermore, recent superconducting ceramics and the like 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, ordinary air contains a considerable amount of moisture, and if this air is used as is, dew condenses inside the high-pressure vessel, causing poor insulation and short circuits in the electrodes of the electric furnace built into the high-pressure vessel. Since dry air was a problem, it was decided to use dry air with a moisture content of 50 ppm or less.

Hereinafter, the features of the present invention described above will be further explained in detail.

First, the technical problems when using air as described above as a pressure medium in the old P treatment are the above-mentioned moisture problem and the possibility of generation of nitrogen oxides (NOx) under high temperature and high pressure conditions.

Regarding the former, the previous Ar or N2 III
Based on our experience in operating the P equipment, that is, the presence or absence of condensation due to concentration of water as an impurity that inevitably occurs during repeated use of these gases, we have learned that if the water content is less than 50 ppm by volume, there will be a problem of poor insulation in the electrode part. The conclusion was reached that it would not occur.

Of course, even if there is water exceeding 50 volume ppn+,
Even if it slightly exceeds 50 ppm by volume, it does not immediately lead to a short circuit accident due to poor insulation, but it depends on the absolute amount of moisture, that is, the amount of pressurized gas. However, if the water content, especially the absolute amount, becomes too large, I
During gas recovery, which is the last step in IIP processing, when the pressurized gas passes through the pressure reducing valve, the temperature of the recovered gas decreases due to adiabatic expansion, causing moisture to condense and causing a blockage phenomenon inside the piping. The smaller the amount, the more preferable.

On the other hand, regarding the latter generation of nitrogen oxides, the amount generated does not simply depend on the amount of nitrogen and oxygen, pressure, and temperature, but also depends on the amount of coexisting impurity gas components such as moisture, CH, GO, etc.
Furthermore, it also depends on the type of constituent material of the electric furnace of the IIIP apparatus.

Normal IIIP processing conditions 2000 kg/cyi,
The amount generated is not so large up to about 1500°C, and is at a level that does not alter the quality of electric furnace materials or high-pressure equipment components. However, depending on the amount, it is preferable to carry out nitrogen oxide removal treatment before releasing the gas after use.

The requirements characteristic of the present invention were set after taking these problems into consideration, and include not only dry air with a moisture content of 50 ppm or less, but also the use of diluted oxygen by mixing nitrogen with it. The invention may be carried out without any problems and is included within the scope of the invention.

Generally, air contains about 80% nitrogen, 19% oxygen, and about 1% argon, as well as the aforementioned moisture, carbon dioxide, and carbon oxide, but l! From the point of view of the operation of the IP device, there is almost no problem if the components other than wood removal are contained in the usual amount. However, in the case of Y-Ba-Cu-0 type superconducting ceramics, carbon dioxide easily reacts to produce barium carbonate, so it is preferable to remove it by some method.

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

(Example) A 6203 powder mixed with 0.3% by weight of MgO was mixed in a ball mill, and then molded into 30 x 50 pieces.
A molded body of X6 (fl) was prepared and exposed to air for 14 hours.
It was fired at 50° C. for 1 hour to obtain a sintered body with a density of 3.9 g/cal (relative density 98%). This sintered body was charged into a IIIP device equipped with a platinum-shaped heater element.

After vacuuming the inside of the old P device, dry air (moisture 50p
pm) of air. Further, air was injected under pressure to 120 kg/(J+. Then, the platinum heater was energized and the temperature was raised to 1400°C. At this time, the pressure inside the old P device was about 350 kg/cal. At 1400°C, After holding for a certain period of time, the temperature was lowered and the gas was discharged to the outside of the IIIP apparatus.

Analysis of the amount of oxygen in this released gas revealed that it was approximately 18%. The density of the sintered body after treatment is 3°975g.
/cj, and when the microstructure was examined using a scanning electron microscope, almost no pores were observed. The color tone of the sintered body was almost the same as when sintered in the air, and was slightly orange-tinged white.

The same process was repeated five times, and the above results were almost reproduced.

(Comparative Example 1) A ^1203 sintered body prepared in the same procedure as Example 1 was
Using a mixed gas of argon and oxygen (20%) as the pressure medium, treatment was performed at 1400°C and 350 kg/ci for 1 hour. When the gas after treatment was collected and analyzed, the oxygen content had decreased to about 18%. The density of the sintered body is
3, 975 g/cal, almost the same as in Example 1, and no pores were observed.

Since mixed gas of argon and oxygen is expensive, the treatment was performed five times by repeatedly using the recovered gas as it was. Argon + oxygen (20%) was used to make up for the shortage. As a result, the amount of oxygen decreased by 1.5-2% per treatment. Although no major change was observed in the density of the sintered body after treatment, some differences occurred in color tone, and reproducibility as good as in Example 1 was not observed.

(Comparative Example 2) A 1 zox sintered body based on the same procedure as Example 1 was heated at 1400° C. and 350 kg using pure argon.
/cla for 1 hour. The density of the sintered body is
Although the value was 3,980 g/cd, which was slightly higher than that of Example 1 and Comparative Example 1, the color tone was white, which was different from the color tone when sintered in the air.

(Comparative Example 3) In the same manner as Comparative Example 2, normal air (moisture content 1100p
p+) was attempted, but insulation failure of the heater occurred and operation was not possible.

A large amount of water had accumulated at the bottom of the HIP process.

(Effects of the Invention) As described above, the present invention uses dry air with a moisture content of 50 ppm or a mixed gas of nitrogen and dry air as a pressure medium in the production of a high-density oxide sintered body using the old P treatment. There is no need to use expensive inert gases such as In addition to making it possible to reduce costs, since air with a relatively stable oxygen content is used, the amount of oxygen can be easily managed and controlled, and as a result, variations in the properties of treated materials can be reduced. It has a remarkable industrial effect.

In addition, the present invention is applicable to A I shown in Examples, 0. In addition to oxide-based ceramics, lead zirconate titanate (PZT)
It can be applied to electronic material ceramics such as ferrite, soft ferrite, barium titanate, and partially stabilized zirconia, and H! The reduction in cost of P processing is expected to have a significant ripple effect.

Claims (1)

[Claims] 1. An oxide sintered body sintered to a relative density of 92% or more,
A high-density oxide sintered material characterized in that it is densified to a relative density of 99% or more by hot isostatic pressing using dry air with a water content of 50 ppm or less or a mixed gas of the dry air and nitrogen as a pressure medium. Method for producing solids.