JPH01242456A - Production of rare earth oxysulfide sintered compact - Google Patents

Abstract

PURPOSE:To produce the title sintered compact having luminous output with small scattering in a good yield by filling a specified substance together with rare earth oxysulfide powder in a metal capsule, by sealing after making vacuous and by heating and pressing. CONSTITUTION:In the production of rare earth oxysulfide (hereinafter referred to as Gd2O2S) sintered compact by filling Gd2O2S powder in the metal capsule, by sealing after making the capsule vacuous and by heating and pressing, the substance having higher vapor pressure of sulfur at >=500 deg.C than that of Gd2O2S (e.g., FeS2, CuS, Ag2S, PbS) is made to coexist in the capsule. Thereby, the decomposition of Gd2O2S at a high temp. is suppressed and the scattering of the characteristics of Gd2O2S sintered compact is remarkably decreased to obtain the sintered compact suitable as scintillator for X-ray CT.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for producing a scintillator material for radiation detection, and in particular, a rare earth oxysulfide material suitable as a scintillator for an X-ray computed tomography device (hereinafter abbreviated as X-ray CT). thing(
The present invention relates to a method for manufacturing a sintered body (hereinafter abbreviated as Gd202s).

[Conventional technology]

In recent years, GdzOxS powder has been dispersed in resins such as epoxy,
Solidified composite materials are being actively developed as scintillators for X-ray CT. However, the luminous efficiency of this composite material is lower than the theoretical value, and the light transmittance is low.
It is necessary to reduce the thickness. For this reason, the X-rays incident on the composite material directly reach the detection element such as a photodiode, and to prevent this, lead glass for X-ray absorption must be attached, resulting in a very complicated element structure. there were.

In recent years, to solve the above problems.

A detection element using a GdzOxS sintered body has been proposed (Japanese Patent Application Laid-Open No. 58-204088, Japanese Patent Application Laid-open No. 61-1276).
70).

These conventional methods for manufacturing GdzOzS sintered bodies can be divided into the following two methods.

The first method is a so-called hot press (hereinafter abbreviated as HP) method in which GclzOzS powder is filled into a heat-resistant die and heated while being pressed with upper and lower punches. GdzOzS is very easily oxidized, and GdzOzS is usually decomposed and oxidized by heating in air at about 500° C., releasing S compounds. Therefore, it is necessary to sinter GdzOzS in an oxygen-free atmosphere.

On the other hand, looking at the stability of GdzOzS against pressure, G
The inventors have confirmed that during the polishing work of the d20zS block, even when a slight polishing pressure is applied, the characteristic odor of S compounds caused by the decomposition of G d x○2S is emitted. That is, it can be said that GdzO2S is extremely unstable against oxidation and pressure, and is a compound that easily releases S.

According to JP-A-58-204088, it only states that a GdzOzS sintered body is produced by the HP method;
I can't find any description of specific examples, so Gdx
It is nearly impossible to put this conventional method into practical use as it is, as there is no consideration given to the problems specific to OzS.

The second method is a method for producing a GdzC)zS sintered body by hot isostatic pressing (hereinafter abbreviated as HIP).

That is, after filling a thin metal container with G d In this method, a dense GdzOzS sintered body is produced by applying pressure to the container directionally and applying pressure and heating at the same time.

In the HIP method, GdzOzS powder is placed in a metal container, which is evacuated and then hermetically sealed, so that the problem of oxidation and decomposition of GdzOzS due to oxygen in the outside air can be significantly prevented. Similarly, if the raw material powder is tightly packed in the metal container, decomposition of GdzOzS during pressurization can be prevented. In this way, the HIP method covers the essential drawbacks of GdzOzS by using a metal container,
GdzO2S with excellent properties that cannot be achieved with the HP method
A sintered body can be made.

As described above, the HIP method is a very promising method for producing GdzOxS sintered bodies, but from the viewpoint of the inherent stability of Gdz○18, the advantages of the HIP method are limited by the use of the metal container mentioned above. In other words, the problem is how to reduce the amount of oxygen in a metal container.

Regarding this, the following technique is found in Japanese Patent Application Laid-Open No. 61-127670. In this conventional method, GdzOzS-based raw material powder is hermetically sealed in a double capsule made of quartz and iron, and then subjected to hot isostatic press sintering (hereinafter referred to as HIP) at 1300°C for 4 hours under 1500 atm. omitted).

However, the quartz in contact with the GdzOzS powder
It reacts very easily with zOzS, and if HIP sintered at high temperature for a long time, the properties of the sintered body may deteriorate significantly, the degree of mutual reaction may cause variations in properties, and an interaction layer may be formed. In addition, there are several problems such as a very small amount of high-quality parts in the sintered body, resulting in lower yields and higher costs. In order to solve the above problems caused by the use of quartz capsules, raw material powder is directly filled into iron capsules, the inside of the capsules is evacuated, and the capsules are subjected to HIP treatment to produce GdzO.
A method of manufacturing a zS sintered body has been proposed. That is, GdxOzS powder, which is the raw material for the scintillator material, was about 50 m in diameter and about 60 m in height.

It is filled into a stainless steel capsule with a wall thickness of about 1.5ws, and while the whole capsule is heated to 100 to 200℃, a tube with a diameter of about 1011I1 connected to the top of the capsule is filled.
The inside of the capsule is evacuated through a thin exhaust pipe No. 1, and after evacuation for a predetermined period of time, the exhaust pipe is hermetically sealed by heat pressure welding. Here, the degree of vacuum during evacuation is maintained at 10-2 to 10-4 torr by a vacuum gauge installed on the exhaust pump side. Next, set the vacuum-sealed capsule in the I-(rPi device,
1300℃, 3 hours.

HIP processing is performed under conditions such as 1500 atm.

The reason for heating the metal container here is to release air adsorbed by the raw material powder. In order for the raw material powder to remain stable without being oxidized, the inside of the metal container must be completely evacuated, but because the exhaust pipe is narrow and the gum pipe is connected to it, the exhaust pipe is become longer. Regardless of the conventional method, when using a metal container, the exhaust pipe is inevitably long due to its structure, and it is almost impossible to create a high vacuum inside the metal container even if the exhaust is evacuated for a long time. .

The vacuum gauge during evacuation is generally set near the exhaust pump, so even if this vacuum gauge indicates 10'torr, the degree of vacuum inside the metal container is about two orders of magnitude lower.
It is about 10-2. Therefore, at this degree of vacuum, air (oxygen) remains in the metal container, which oxidizes the raw material and deteriorates the characteristics of the sintered body. Furthermore, as mentioned above, the conventional technology
No consideration was given to deoxidizing the metal container for IP, and H
During the I-filtration process, the GdzOzS in the metal container is locally oxidized, which deteriorates the properties of the GdzO2S sintered body and increases the variation in properties between manufacturing lots.

Since detection elements for X-ray CT generally use a large number of scintillator materials, variations in the characteristics of the scintillator materials are a particularly large problem.

An object of the present invention is to provide a method for manufacturing a GdzO2S sintered body with small variations in light emission output and high output.

The degree of oxidation of GdxOxS by the adsorbed gas at this time depends on many factors, such as the degree of filling of the raw material powder in the capsule, the conditions of heating and evacuation, the particle size distribution and degree of drying of the raw material powder, and the size of the dead space in the capsule. Dominated by process factors that are difficult to control. Therefore, in the conventional method, GdzC
) Since no special consideration has been taken to prevent zS from oxidation or to prevent residual gas or adsorbed gas within the capsule, the status of the residual gas within the capsule changes with each HIP-sintered capsule.
As a result, the characteristic variation of the HIP-treated Gd2O2S sintered body reached 10% or more from production lot to production lot. In particular, an X-ray CT scintillator manufactured using a sintered body with large variations in characteristics causes ring irregularities and artifacts in the reproduced image, which is a serious problem in practice.

[Purpose of the invention]

The object of the present invention is to produce G
The object of the present invention is to reduce variations in the light emitting output characteristics of a dzOzS sintered body, and further to manufacture this sintered body at a high yield.

[Means for solving problems]

The above purpose is to tightly pack GdzOzS powder into a capsule made of gold HL, seal the inside of this capsule with a vacuum exhaust machine, and hot press this sealed capsule to produce a GdzOzS sintered body. This is achieved by coexisting with a substance that easily binds to oxygen in the capsule or a substance that releases such a substance.

The first example of the above-mentioned substances is a substance in which the vapor pressure of S at 500° C. or higher is higher than that of GdzOzS (hereinafter referred to as a first group substance), such as Fe5z.

CuS, AgzS, PbS, FeS, CuzS.

There are groups such as WS and Mo5t.

The second substance mentioned above is 120, which has a greater affinity for oxygen than Gd20zS and which undergoes HIP.
Substances that form stable oxides even at high temperatures of 0 to 1400°C (hereinafter referred to as second group substances), for example, Tiv
There is a group consisting of metals with high oxide formation free energy, such as Z r HCa t Cr.

[Effect]

The effects of the first group of substances will be explained below.

When a metal capsule filled with GdzO2S powder is placed in a hot press and heated, G d x○2. A substance whose vapor pressure is higher than that of S emits a small amount of S vapor. On the other hand, the gas adsorbed on the inner wall of the capsule and the surface of the GclzOzS powder is desorbed with heating.

The oxygen in the desorbed gas and the released S vapor combine to form a sulfide gas such as Sow, which spreads inside the capsule. This formation of sulfide gas suppresses the release of S from GdzOzS.

If there was no substance in the capsule that releases S vapor, unstable GdxOzS would release S when heated, and the original GdzO2S composition would shift, resulting in a significant decline in its properties. become. Furthermore, if GdzOzS has a higher vapor pressure than the S vapor releasing substance, S vapor will be released from Gd20zS first during heating.

As mentioned above, G
Coexisting with dzOzS in the metal capsule has the effect of suppressing the decomposition of GdzOzS at high temperatures, thereby obtaining a high-quality GdzOzS sintered body. In particular, it is difficult to control the hermetically sealed position of the metal capsule, and the Gdz inside the metal capsule is difficult to control.
Due to the difficulty of controlling the volume of the space in which the OzS powder is not tightly packed, it is practically extremely difficult to keep the amount of residual gas in the metal capsule constant at all times. Gd20 per lot
The variation in properties of the zS sintered body was extremely large. However, due to the action of the S vapor releasing substance according to the present invention, the Gd
Characteristic variations in sintered zOzS can be significantly reduced.

In addition, GdzOzS has a concentration of about 5 in an atmosphere with a low oxygen partial pressure.
Since it is relatively stable up to around 00°C, it is desirable that the substance coexisting with GdzOzS in the metal capsule has a vapor pressure higher than that of GdzOzS at 500°C or higher.

The effects of the second group of substances in the present invention will be explained below.

When a metal capsule sealed with GdzOzS is placed in the HI filtration process, the air adsorbed to the inner wall of the capsule or exhaust pipe, and the air adsorbed to the GdzOzS powder, is desorbed from these adsorbed substances and is absorbed into the capsule. spread to In particular, the temperature at which the capsule is heated when evacuating (approximately 200℃)
In the HI filtration process, where the temperature is higher than that shown below), a large amount of gas is generated from the adsorbed object.

This generated gas becomes GdzOzS from the temperature near 500℃.
The powder begins to oxidize, and the oxidation progresses further as the temperature increases during HIP. If there is a substance in the metal container that easily combines with oxygen and easily forms oxides, that is, a metal with large oxide free energy, the oxygen in the air generated from the adsorbed object will easily combines with substances,
It can capture oxygen in generated gas and exhibits a so-called deoxidizing effect.

Metals such as Ti, Zr, and Cr are well known as deoxidizing agents when removing oxygen from argon gas and creating high-purity argon gas, and Ca is a metal well known as a deoxidizing agent for molten steel. , its performance, and there are no practical problems.

Note that metals such as Ti and Zr have a very high affinity for nitrogen gas, and therefore also have the effect of trapping nitrogen in the air within the metal container. During HIP, it is important that there is no gas in the metal container as much as possible.
From this point of view, Ti is desirable for making 2S sintered bodies.
, Zr denitrification effects can be expected.

〔Example〕

Hereinafter, an example of the present invention using the first group of substances will be described with reference to FIG.

[Example 1] FIG. 1 is a schematic cross-sectional view of the inside of a metal capsule for hot pressing according to the present invention. GdzO inside metal capsule 1
xS raw material powder 2 was tightly packed, 100°C, 30 minutes, 1
The conventional method is to partially seal the exhaust pipe 3 after exhausting at 0-8 torr to form an airtight sealing section 4. In contrast, in the present invention, the diameter is 60+m, the height is 50mm, and the wall thickness is 2III.
F of the size of 100 meshes is placed at the bottom of the metal capsule 1.
eS particles 6 are spread to a thickness of about 3I, a 150-mesh stainless steel spacer 5 is placed thereon, and the raw material powder 2 is tightly packed. Similarly to the lower part, spacers 5 and high vapor pressure substances 6 are placed on the upper part of the metal capsule, and then heated to 100°C and heated to 10-3 torr.
The air is evacuated for 30 minutes, and the exhaust pipe is heated and pressure welded to seal the airtight part 3.
make.

Next, this metal capsule was set in a hot isostatic press (abbreviated as HIP) device, and
c, 3 hours, 1000 atm (7) 7/L/gon (Ar)
Sintered in gas.

After the HIP was completed, the metal capsule was taken out from the HIP apparatus, the outer peripheral part of the metal capsule was removed by machining, and the G d z○2S sintered body block inside the capsule was taken out. This block was sliced using a diamond blade etc. to obtain 18 wafers with a thickness of 1.0 m.
Additionally, both sides of each wafer were polished.

Next, this polished wafer was heated to 1200°C.

After heat treatment in Ar for 3 hours, X#! The luminescence output due to irradiation was measured. Table 1 shows the results of comparing the variations in light emission output between four sintered blocks according to the present invention and between wafers within one sintered block with those of the conventional method. As will be seen, according to the present invention,
The variation in light emission output between sintered blocks is significantly larger than that of the conventional method, and the variation in characteristics among the 18 wafers within the same sintered block is also very small.

The reason why the variation in the luminescence output of the GdxOzS sintered body according to the present invention is reduced in this way is because Gd
This shows that almost no decomposition of zOzS has occurred, and this is due to the effect of having FeS, a high vapor pressure substance, present in the metal capsule.

On the other hand, the large variation in properties of GdzOzS sintered bodies in the conventional method is because the amount of residual gas in the metal capsule varies greatly from capsule to capsule, and this residual gas causes Gd
This is because zOzS is degraded and decomposed.

Table 1 [Example 2] The same raw materials and the same metal capsule as in Example 1 were used, and as shown in FIG.
About 5 to 1 m of CuS6 was spread to a thickness of about 4 m, and 40 meshes of stainless steel were set thereon as spacers 5, and then the Gd2O2S raw material was tightly packed. Furthermore, a 40-mesh stainless steel net is set as a spacer 5 on top of this densely packed raw material,
Furthermore, three Cu grains 6 were placed on top of the capsule, and after the inside of the capsule was evacuated in the same manner as in Example 1, the capsule was hermetically sealed.

Next, the three metal capsules were simultaneously HIP-sintered using the same HIP apparatus as in the example at 1320° C. for 3 hours with Ar gas at 1200 atm. The obtained sintered block was treated with X in the same manner as in Example 1.
The luminescence output during radiation irradiation was determined. As a result, the variation in luminous output among the three sintered blocks according to the present invention was 3.7
%, and was significantly superior to the conventional method shown in Table 1. Further, 18 wafers were obtained from one sintered block, and the variation in characteristics among the wafers was within 1.7%.

As mentioned above, the reason why the characteristic variation of the G d z○2S sintered body according to the present invention is small is due to the CuS present in the capsule.
This is because the evaporation of S from GdzOzS was suppressed.

[Example 3] Using the same GdzC) and S powder as in Example 1 as raw materials, the second
As shown in the figure, it has a diameter of 50 m, a height of 40 rm, and a thickness of 2.
Using a capsule 1 made of mild steel with a diameter of 0 m, after tightly filling the original powder into this capsule, a spacer 5 is placed on the top surface of this tightly packed powder.
A 100-mesh mild steel wire mesh was laid down. Furthermore, in the exhaust pipe space 3 shown in FIG.
After packing the grains, an exhaust and airtight sealing section 4 was formed in the same manner as in Example 1.

These three hermetically sealed capsules were subjected to HI under the same conditions as in Example 2.
PI bonding was performed, and the variation in the light emission output of the obtained GdzOzS sintered block was determined.

As a result, the variation in luminous output of the sintered body according to the present invention was 4
．． 0%, and the characteristic variation among the 18 wafers in the same block was 1.8%.

In the present invention, the WS particles present in the capsule are
This is thought to be because S vapor was released during HIPI heating, which reacted with the residual atmosphere in the capsule to trap oxygen in the residual gas, which suppressed the decomposition of GdzOzS.

Examples of the present invention using substances of the second group will be described in detail below.

[Example 4] GdzO2S powder (activating material: P
LizGeFs is added as a sintering aid in an amount of 0.1 wt % to R, Ce, and F), and these are thoroughly and uniformly mixed and then dried to produce the raw material powder 2 shown in FIG. Next, this raw material powder 2 is
A metal container 1 made of mild steel with a diameter of 0 mn+, a height of 40 m, and a wall thickness of 1.0 inch is tightly packed. At this time, a sponge-like Ti6 with a diameter of about Im is placed on the bottom of the metal container in advance to a thickness of about 3 m.
Lay the rope evenly, and on top of it, attach a 20-mesh rope made of mild steel 5.
was placed and the raw material powder was filled on top of it.

Subsequently, the entire metal container is heated to about 150 to 200° C. while exhausting to 10-" 10-8 torr through the exhaust pipe 3 with a diameter of 10+ m+ located at the top of the metal container 1, and the air and adsorbed gas inside the metal container are heated. Next, while continuing this evacuation operation, an exhaust pipe sealing part 4 is attached to a part of the exhaust pipe 3.
and completed the hermetic sealing of the metal container. The four metal containers made in this way were heated using a graphite heating element.
Place it in an oven, pressurize with argon gas while heating, and HIP at 1300℃, 2h, 1000kg/d.
I did it.

After the HIPI was completed, the metal container was taken out from the HIPI equipment, the outer periphery of the metal container was removed by machining, and the GdzOzS sintered block inside the container was taken out. This block was sliced lengthwise using a diamond blade to obtain 20 wafers with a thickness of 1 inch, and both sides of each wafer were polished.

Next, this polished wafer was heated to 1200°C.

After performing heat treatment in argon gas for 3 hours, the luminescence output by X-ray irradiation was measured. Table 2 shows 4 according to the invention.
These are the results of comparing the variations in light output between two sintered blocks and the wafers within one sintered block with those of the conventional method. As is clear from this, according to the present invention, the variation in luminous output between sintered blocks is reduced to about 1/2 or less, and the variation in characteristics among 20 wafers within the same sintered block is also much greater than in the conventional method. becomes smaller.

Table 2 The reason why the variation in the luminous output of the GdzOzS sintered body according to the present invention is so small is that the GdzO
This shows that almost no oxidation of zS occurred, and this is due to the presence of Ti, which has a deoxidizing effect, in the metal container. On the other hand, the large variation in characteristics in the conventional method is due to the amount of air remaining in the metal container.
This refers to the large variation between metal containers.
This is due to unavoidable problems in the structure of the HIP metal container, such as the degree of filling of the raw material powder and the sealing position of the exhaust pipe.

[Example 5] The same raw materials and the same metal container as in Example 4 were used.

A sponge-like Z with a diameter of 0.5 to 2 m is attached to the bottom of this metal container.
R metal 6 was spread to a thickness of about 4 m, 40 meshes of stainless steel rope was set thereon as a spacer 5, and raw material powder 2 was then tightly packed. Furthermore, as shown in Fig. 1, a 40 mesh steel made by Stensess was set as a spacer 5 on the upper surface of this densely packed raw material, and a sponge-like Zr6 was placed on top of it as shown in Fig. 1. The inside of the metal container was evacuated and hermetically sealed in the same manner as in Example 4.

Next, using the same apparatus as in Example 4, the temperature was 1280°C.

3 hours with argon gas at 1400 kg/ci
HIP treatment was performed on two metal containers. For the three obtained sintered blocks, variations in light emission output were determined in the same manner as in Example 4. As a result, the variation in light emission output among the three blocks according to the present invention was very small, 3.6% or less, and was significantly superior to the conventional method shown in Table 2.

[Example 6] The same raw materials and metal container as in Example 4 are used. As shown in Fig. 3, Cr powder 6 with a size of 20 meshes or less is spread on the bottom to a thickness of about 3 mm, and spacers 5 are placed on top of it.
A mild steel fiber with a thickness of approximately 0.2Iff11 was installed to a thickness of approximately 2 m, and the raw material powder 2 was then tightly packed on top of the fiber, and the metal container was then hermetically sealed in the same manner as in Example 4. It stopped.

Subsequently, using the apparatus of Example 4, the temperature was 1300°C.

Five metal containers produced by the above method were subjected to HIP treatment using argon gas at 1200 kg/aJ for 5 hours.

The variation in luminous output among the five HIPed GdxOxS sintered blocks was 3.9% or less.

Compared to the GdzOzS sintered body produced by the conventional method, the variation in properties was extremely small. The reason that the variation in properties between blocks of the sintered body according to the present invention is small is that the Cr metal present in the metal container sufficiently exerts its deoxidizing function.

〔Effect of the invention〕

As described above, according to the present invention, G d 202S in the metal capsule is decomposed during HIP sintering.

Since deterioration can be suppressed, it has the effect of significantly reducing variations in the characteristics of the G d z○2S sintered body. In particular, the present invention has an extremely large effect on the practical application of X-ray CT detection elements by reducing variations in characteristics, and also has the effect of improving the yield of sintered bodies with good characteristics, thereby reducing the cost of detection elements. I can figure it out.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view of a metal capsule for explaining the present invention in detail, FIG. 2 is a schematic cross-sectional view of a metal capsule for explaining a third embodiment of the present invention, and FIG. FIG. 6 is a schematic cross-sectional view of a metal capsule for explaining a sixth embodiment of the present invention. 1...metal capsule, 2...raw material powder, 3...exhaust pipe,
4': 4) Ward 6 Hesago made by burning and crushing η page

Claims (4)

[Claims] 1. In the method of manufacturing a rare earth oxysulfide sintered body by filling a metal capsule with rare earth oxysulfide powder, evacuating the inside of the capsule, and then airtightly sealing the capsule, heating and pressurizing the capsule, A method for producing a rare earth oxysulfide sintered body, characterized in that a substance whose sulfur vapor pressure at 500° C. or higher is higher than that of the rare earth oxysulfide is coexisting. 2. FeS as a substance coexisting with rare earth oxysulfide
_2, CuS, Ag_2S, PbS, FeS, Cu_2
The method for producing a rare earth oxysulfide sintered body according to claim 1, characterized in that at least one of S, WS_2, and MoS_2 is used. 3. In the method of manufacturing a rare earth oxysulfide sintered body by filling a metal capsule with rare earth oxysulfide powder, evacuating the inside of the capsule, and then airtightly sealing the capsule, heating and pressurizing the capsule, A method for producing a rare earth oxysulfide sintered body characterized by coexisting a metal with a large oxide formation free energy. 4. As metals coexisting with rare earth oxysulfides, Z,
A method for producing a rare earth oxysulfide sintered body according to claim 3, using at least one of Ti, Zr, Cu, and Cr.