JP2003128465A - Sintered translucent scandium oxide and process for making the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sintered scandium oxide showing a good translucency within visible and infrared regions, using an industrially applicable method. SOLUTION: A molded product whose green density is >=58% of the theoretical density and Al content is 5-100 wt.ppm, is prepared using a raw material powder of highly pure scandium oxide with a Si content of <=30 wt.ppm and a purity of >=99.9%. The molded product is burned at 1,400-1,800 deg.C under a vacuum, from which binders have been removed through heating. The process yields translucent ceramics showing a linear transmittance of >=77% at a wavelength of 500 nm-5 μm.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transparent scandium oxide sintered body represented by Sc ₂ O ₃ and a method for producing the same. The sintered body of the present invention is, for example, an infrared transmission window material, a polarizing plate,
It is preferably used as a discharge lamp envelope, an optical component, and a laser oscillator.

[0002]

_2. Description of the Related Art Scandium oxide represented by Sc ₂ O ₃ is
Its crystal structure is cubic and has no birefringence. for that reason,
By completely removing the pores and the segregation due to the impurities, it is possible to obtain a sintered body having excellent translucency. Scandium oxide has a melting point of higher than 2485 ° C. (Chemical Handbook, edited by the Chemical Society of Japan) and is known to be a material having excellent heat resistance and alkali resistance. Since it has higher thermal conductivity,
It is expected as a host material for solid-state lasers.

However, since scandium oxide is expensive, little research has been conducted on the method for producing crystals. Also, because its melting point is extremely high,
It is difficult to synthesize a large crystal that is optically excellent by the existing single crystal synthesis technology.

On the other hand, ceramics (polycrystal) is
Since it can be synthesized at a relatively low temperature below the melting point,
Similar to scandium oxide, yttrium oxide (yttria) having a high melting point and oxides of rare earth elements have been actively studied for application to infrared high temperature window materials, discharge lamp envelopes, corrosion resistant members, and the like. Examples of reports on sintered scandium oxide (for example, Adv Powder Me
tall.vol5.pp347 ~ 356 (1991) and JA Ceram.Soc.60 (No3 ~
4) Since pp167 to 168 (1977)) are few, the conventional technique will be explained by a method of producing yttria ceramics having relatively similar properties. Not only scandium oxide, but also the production of translucent sintered compacts, it is most important to successfully discharge pores due to grain growth during firing, and sintering aids should be used to control grain growth rate. The method of adding is common. Many of the yttria production methods that have been reported in the past are also methods in which a sintering aid is added.

[0005] As a method for producing a sintering aid with translucent yttria sintered body in a hydrogen by adding (1) ThO ₂ 210
Method of firing above 0 ℃ (Ceramic Bulletin Vol.52, No5
(1973)), (2) a method of firing Y ₂ O ₃ powder added with AlF ₃ by vacuum hot press (JP-A-53-120707), (3) hot pressing with addition of LiF or KF Method (JP-A-4-59658
No.), (4) A method of adding La ₂ O ₃ or Al ₂ O ₃ and sintering in a low O ₂ atmosphere (JP-A-54-17911, JP-A-54-17910), (5) CaO
And a method of adding ZrO ₂ and sintering in an atmosphere in which the partial pressure of nitrogen gas is controlled (JP-A-10-273364) and the like are disclosed.

In the method (1), although a sintered body having a relatively high degree of transparency can be obtained, thoria, which is a radioactive element which is difficult to obtain and handle, is added as a sintering aid. Further, since firing is performed at a high temperature for a long time, the average particle size is very large, 100 μm or more, and the material strength is extremely low. Therefore, it is not suitable for practical use as a consumer product. The hot pressing method (2) allows firing at a relatively low temperature, but only a linear transmittance of about 60% in the visible portion can be obtained. In the method (3), a hot press treatment at 1500 ° C. or higher makes it possible to produce a sintered body having a linear transmittance of about 80% in the infrared region of a wavelength of 2 μm or more.
The transmittance in the visible part is unclear because it is not specified, but the fluoride added as a sintering aid is a low melting point substance (LiF: 842 ° C, KF: 860 ° C) and Evaporation causes a difference in grain growth rate between the outer peripheral portion and the inner portion of the sample, so that it is difficult to produce a uniform sintered body in the case of a thick sample. In addition, according to Mashima et al.
Vol. 10 (1993) 1221-1226), when hot pressing with LiF as an auxiliary agent, even if the addition amount was optimized, fluorine remained in the center of the sample and its permeation compared to the outer periphery of the sample. It is stated that the rate will be lower. Therefore, it is not easy to produce a large-sized, thick-walled sintered body by using fluoride as a sintering aid.

La of (4)₂O₃The method of adding
The amount is large, about 6 to 14 mol%, and La cannot be solid-dissolved.₂O₃Is the segregation layer
Is easily generated (for example, Journal of Materials Science 24
(1989) 863-872, etc.) to produce an optically uniform sintered body.
Not easy to make. Also, Al₂O₃Hand to add
In the method, the addition amount is set to 0.01 wt% to 5 wt%, and Y_FourAl₂O₉And Y ₂
O₃Dense by liquid phase sintering above the eutectic temperature (1920 ℃) between and
Making the body. However, firing at high temperature
However, the transmittance of the obtained sintered body is theoretical
The maximum rate remains at 80%. Similarly, Ca of (5)
O or ZrO_TwoThe addition amount of each is 100ppm to 4%
Or as high as 200ppm to 10%, the transmittance of the resulting sintered body
Is still 80% at maximum of the theoretical transmittance
There is.

A method for producing yttria without adding a sintering aid is, for example, (6) Japanese Patent No. 2773193 or (7) Japanese Patent Laid-Open No. 6-21157.
No. 3 is disclosed. In the method (6), yttria powder having a BET value of 10 m ² / g or more is hot pressed to densify it to a theoretical density ratio of 95% or more, and then HIP treatment is performed. The transmittance of the sintered body obtained by this is as good as about 80% in the infrared region of the wavelength of 3 to 6 μm, but stays at about 75% on average in the wavelength region of 0.4 to 3 μm. Despite the HIP process, the reason why the transparency in the short wavelength range is insufficient is
It is presumed that this is because the starting material uses ultrafine powder that is difficult to handle, so even if the surface is densified by hot pressing, it is likely to contain large voids that cannot be removed by HIP treatment even inside the sample. It Further, in the method (7), the easily sinterable raw material powder having an average particle size of 0.01 to 1 μm is used as a CI.
After P molding, vacuum baking at 1800 ℃ or 1600 ℃
The transparent body is produced by performing the HIP process as described above. The sintered body obtained by this method has a high average linear transmittance of 80% or more in the visible region, and it is described that a laser-oscillated sintered body can be produced by adding a luminescent element. However, in order to prepare a sample with high transparency, it is necessary to perform firing at a high temperature of around 2000 ° C in both cases of vacuum firing and HIP treatment, and when performing industrial continuous production, deterioration of the firing furnace But it is hard to maintain. Further, the transmittance is remarkably reduced as the wavelength is shortened (10% or more is reduced in the wavelength range of 1000 nm to 400 nm), and it is unsuitable for application to an optical member that attaches importance to translucency in the visible region.

The rare earth oxide raw material powder used in the conventional method is generally oxalate as a mother salt, but the raw material powder obtained by calcination of this has a non-uniform particle size distribution. Yes, it is composed of secondary particles that are highly agglomerated. Therefore, the packing cannot be sufficiently obtained by molding, and it is not easy to produce a dense body. In recent years, in order to improve this point, a method for producing a transparent body by low-temperature firing using easily sinterable raw material powder has also been disclosed (for example, JP-A-9-31586).
No. 5, No. 10-273364, No. 11-189413, No. 11-278933
issue).

In the above method, a carbonate is used as a mother salt for low temperature firing, and a powder having a relatively uniform particle size distribution and less agglomeration obtained by calcination of this is used as a starting material. Making a union. However, the linear transmittance in the visible part of the sintered body obtained by these methods is about 70% at the maximum, and it is said that the transparent body is comparable to a single crystal in comparison with the theoretical transmittance (≈82%). hard.

The above-mentioned method of manufacturing the existing translucent yttria has been described above. Industrially, a sintered body having an excellent translucency equivalent to that of a single crystal in the visible region to the infrared region can be easily produced industrially. There is no manufacturing method.

[0012]

DISCLOSURE OF THE INVENTION The present invention provides a scandium oxide sintered body (Claims 1 and 2) which exhibits good translucency in the visible region to the infrared region, and a method for producing the same by an industrially practical method. It is intended to provide a method (claims 3, 4).

[0013]

The translucent scandium oxide sintered body of the present invention has an Al content of 5 wtppm or more and 100 wtppm or less, and has a linear transmittance of 77% at a thickness of 1 mm over a wavelength range of 500 nm to 5 μm. That is all (claim 1).

Preferably, the translucent scandium oxide sintered body has a Si content of 30 wtppm or less and an average particle size of 1 μm or more and 30
It is not more than μm (claim 2). Al and Si indicate the content in terms of metal.

The method for producing a translucent scandium oxide sintered body of the present invention uses a high-purity scandium oxide raw material powder having a Si content of 30 wtppm or less and a purity of 99.9% or more, and a molding density of 58%. With the above, the Al content is 5 wtppm or more 100
It is characterized in that a molded body of wtppm or less is produced, debindered by heat treatment, and then fired in a non-oxidizing atmosphere at a temperature of 1400 ° C or higher and 1800 ° C or lower (claim 3).

Preferably, after the firing, hot isostatic pressing (HIP) treatment is performed at a temperature of 1000 ° C. to 1800 ° C. and a pressure of 49 MPa to 196 MPa (claim 4).

[0017]

As a result of various investigations for solving the above-mentioned problems, the present inventors have found that, at a specific Al content, the linear transmittance over a wavelength range of 500 nm to 5 μm is 1 mm. It has been found that 77% or more of scandium oxide sintered body can be produced by (Claim 1). Here, the Si content is 30 wt.
Setting the content to ppm or less is effective for suppressing the grain growth and improving the light transmittance (claim 2).

In the production of scandium oxide sintered bodies, the purity of raw materials, especially the Si content is controlled to prepare a molded body in which the Al content and the density are controlled, and the binder is heat-treated to remove the non-oxidizing property. 1400 ° C or higher in an atmosphere such as hydrogen, a rare gas or a mixed atmosphere of these or in a vacuum
It suffices to perform firing in a temperature range of 1800 ° C or lower (claim 3). The sintered body obtained by firing in this atmosphere was
When hot isostatic pressing is performed at a temperature of 00 ° C and a pressure of 49MPa to 196MPa, pores of submicron or less can be discharged,
It is possible to prevent a decrease in light transmittance below 500 nm (claim 4).

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below. When firing scandium oxide, a very small amount (5 wt
(ppm to 100 wtppm) Al has a great effect as a sintering aid. As described in the prior art, various methods of adding a sintering aid have been disclosed, but in almost all of these cases, the aid segregates to the grain boundaries to reduce the migration speed of the grain boundaries. In this way, the grain growth rate is controlled to achieve densification. Although the details of the densification mechanism by firing when a trace amount of Al is contained are unknown, it exhibits the effect as a densification accelerator only when the average particle size of the sintered body is in the range of about 1 μm to 30 μm. In the above, a segregation phase is generated.

That is, when the firing temperature is less than 1400 ° C.,
Regardless of the presence or absence of Al, densification due to grain growth does not proceed sufficiently, so only an opaque or translucent sintered body can be obtained. Usually the average particle size in this case is less than 1 μm. If the firing temperature is 1400 ° C or higher and 1800 ° C or lower, and the Si content and Al content and the compact density are appropriately controlled, the average grain size of the obtained sintered body is 1 depending on the sinterability of the raw material used. It is in the range of up to 30 μm, and a sintered body having excellent translucency can be obtained. Al content is 5w
When a sample of tppm or less is similarly fired, the average particle size is still about 1 to 30 μm, but the obtained sintered body is a translucent body or an opaque body.

In the case of the sample containing Al in excess of 100 wtppm, the grains grew and the average grain size was larger than in the case of less than that. However, the obtained sintered body is a translucent body or an opaque body as in the case where the Al content is 5 wtppm or less. The effect of Al as a sintering aid acts as a densification accelerator in the range of 5 to 100 wtppm, and only in that case, a good transparent body can be obtained. However, when it exceeds 100 wtppm, it acts mainly as a grain growth promoter, and pores cannot be discharged sufficiently, so that a satisfactory transparent body cannot be obtained.

When firing at a temperature of 1800 ° C. or higher,
Since grain growth proceeds remarkably regardless of the presence or absence of Al, pores are not sufficiently discharged, and it is not easy to produce a sintered body having sufficient translucency. The average particle size in this case is 35μ
It is more than m. At a firing temperature of 1800 ° C. or higher, an Al segregation phase occurs at grain boundaries even if the Al content is 100 wtppm or less. The precipitation of Al depends on the average grain size of the sintered body,
When it is 30 μm or less, no precipitation is observed in any firing atmosphere. However, the average particle size of the sintered body is 30
When it exceeds μm, segregation of Al starts to occur in the grain boundary phase, and when the average grain size becomes 40 μm or more, the phenomenon becomes remarkable.

Therefore, the content of Al is 5 wtppm or more and 100 wtppm
Only in the following cases, the effect as a densification accelerator is exerted, and only when it is fired so that the average particle size is 1 μm or more and 30 μm or less in the temperature range of 1400 ° C. or more and 1800 ° C. or less where precipitation does not occur Thus, it becomes possible to produce a sintered body having excellent translucency.

However, in order to produce a sintered body excellent in translucency by sufficiently exerting the effect of promoting densification by an extremely small amount of Al,
It is necessary to strictly control the amount of Si contained in the raw material, and the amount should be 30 wtppm or less, and the compact density should be 58%.
It is necessary to be above.

Impurities contained in high-purity scandium oxide powder of 99.9% or more as commercially available scandium oxide are about several wtppm for each element, and are less than about 10 wtppm at most. However, Si is 30w
About tppm, and if it is large, it may be contained in an amount close to 100 wtppm. The reason for this is not clear, but after purifying the scandium raw material by the wet method as an organic acid salt or an inorganic acid salt, the casket used when calcining is made of quartz, and the adhered water is slightly different from the quartz container. It is thought to react. It is also considered that the reaction tank may be made of glass or glass lining, or the precipitant may contain Si.

Since Si forms a liquid phase at the grain boundaries and promotes grain growth, a large amount of Si cancels the densification promoting effect by a trace amount of Al. Therefore, Si contained in the scandium oxide raw material powder to be used is 30 wtppm or less, preferably 5 wtppm or less. Most of the Si contained in the high-purity scandium oxide raw material is mixed from the calcination sagger and the reaction vessel.For example, use an alumina crucible or apply polytetrafluoroethylene lining to the reaction vessel. Thus, it is possible to easily obtain a raw material having a low Si content.

The molded product must be homogeneous and have a high density without containing large bubbles or voids inside. General translucent ceramics are fired at a temperature about 100 ° C. to 300 ° C. lower than the melting point, and the average particle size is about 50 μm or more. That is, since the voids inside the compact are discharged by grain growth, when a compact having many voids (low compact density) is fired, the dense body is produced by significantly growing the grains. On the other hand, when firing at a relatively low temperature of 1800 ° C or less, precipitation of Al does not occur, and the average particle size of the sintered body is
It can be made relatively small, 30 μm or less. Therefore, in order to produce a sintered body having excellent translucency without excessively expecting the effect of discharging pores due to grain growth, it is necessary to produce a homogeneous and high-density molded body and fire it.

Inside the molded product having a molded density of less than 58%, a large number of large voids are present due to insufficient packing. It is impossible to sufficiently densify such a molded product at a temperature of 1800 ° C. or lower. Not easy. On the other hand, the molding density is 58%
The above-mentioned molded product has relatively few pores inside, and can be sufficiently densified even at a low temperature. Therefore, in order to produce a sintered body with excellent translucency, its molding density should be 58%.
It is necessary to be above, preferably 60% or more.

If proper manufacturing conditions are selected, a sintered body having a sufficient linear light transmittance can be obtained, but the light transmittance of 500 nm or less may be extremely lowered. This is because the pores were not sufficiently discharged due to the temperature distribution in the furnace and many small pores of submicron size or less remained in the sintered body. Such a sintered body is hot isostatically pressed (H
By the IP) treatment, a sintered body having a good light transmission spectrum can be obtained. Ar gas that is normally used is sufficient as the pressurized gas, and the treatment temperature is preferably 1000 ° C to 1800 ° C. If it is lower than 1000 ° C, there is no treatment effect, and if it is higher than 1800 ° C, grain growth proceeds and an Al segregation phase occurs. The processing pressure is preferably 49 MPa or more and 196 MPa or less. If the pressure is 49 MPa or less, there is no treatment effect, and if the pressure is 196 MPa or more, the device is unnecessarily large-scaled and the treatment effect is not improved.

The method for producing the sintered body will be described below. For the production of the sintered body, a high-purity easy-sintering raw material powder having a purity of 99.9% or more and having a Si content of 30 wtppm or less is used. Transition elements such as Fe are not preferable because they serve as a coloring source for the sintered body.
Therefore, it is necessary to select a sufficiently purified starting material. However, this is not the case when intentionally added, as in the case of a laser medium or colored glass such as a color filter.

The sinterability of the raw material powder is said to depend on the mother salt. For example, in the case of yttrium, generally, (1) carbonate (2) hydroxide (3) oxalate ( 4) Ammonium sulfate (5) Sulfate in that order (e.g. LRFurlong, LP
Domingues, Bull. Am. Ceram. Soc, 45, 1051 (1966)). However, the types of these mother salts are not particularly limited, and those that are easily available may be used.

The primary particle diameter of the raw material powder to be used is not particularly limited, and a material suitable for the molding and firing process may be selected. That is, although the ultrafine powder has high sintering activity and densifies well at a relatively low temperature, it is not easy to handle, and it is not easy to increase the compacting density because there are many agglomerated particles. In the case of coarse particles,
Although the packing is easy, the sintering activity is low and it cannot be densified at low temperature. Therefore, sinterability, in view of the packing property and handling property, the specific surface area of the raw materials used is preferably about 3~12m ² / g, more preferably about 4~10m ² / g. Furthermore, it is most preferable to use the one having less aggregation and a uniform particle size distribution.

Next, a molded body having a desired shape is prepared using the scandium oxide raw material powder. Examples of ceramics molding methods include extrusion molding, injection molding, press molding, and casting molding. The molding is not limited to any one of the methods, and the molding density may be 58% or more and the mixing of impurities is small. At this time, if necessary, Al as a sintering aid is added so as to be uniformly dispersed according to various molding methods. For example, in the case of press molding, an appropriate amount of Al may be added to the slurry for producing granules, sufficiently mixed by a ball mill or the like, and then dried by a spray dryer or the like to obtain granules for molding.

The timing of adding Al is not particularly limited as long as it can be uniformly dispersed in the molded body, and there is no problem even if it is added at the raw material synthesis stage or the calcination stage. To make full use of the effect with a trace amount of Al,
Most preferably, it is mixed in the raw material.

The form of addition is not particularly limited. For example, when mixing in the molding step, alumina sol, aluminum hydroxide powder, or an aluminum compound such as γ- or α-Al ₂ O ₃ powder is used. It may be added in an appropriate amount. In addition, when added during raw material synthesis,
It may be added with aluminum chloride or aluminum hydroxide. Regarding the purity of the additive, it is not particularly limited because the added amount is very small, like the raw material powder,
It is preferable to use a highly pure one. When added in the form of powder, it is preferable to use those having the same size as or smaller than the primary particle diameter of the raw material powder.

The obtained molded body is debindered by thermal decomposition. The treatment temperature, time, and atmosphere at this time differ depending on the type of the molding aid added, but if the surface of the sample becomes closed pores, it becomes difficult to remove the binder. For this reason, the surface is closed for a sufficient period of time below the temperature at which it does not become closed pores.
Although this temperature depends on the calcination temperature of the raw material powder used, the sinterability, and the packing of the molded body, it is usually about 900 ° C to 1400 ° C, and it is preferable to carry out at a temperature below that. The atmosphere is most commonly an oxygen atmosphere, but if necessary, humidified hydrogen, Ar, or reduced pressure may be used without any problem.

After debinding, the sample is fired at a temperature of 1400 ° C. or more and 1800 ° C. or less in hydrogen, a rare gas, a mixed atmosphere of these, or a vacuum. Depending on the firing atmosphere and the thickness of the sample, if the sample thickness is usually about 1 to 5 mm, it is 0.
Firing for about 5 to 10 hours is preferable.

In order to obtain a sintered body with a good yield and a good light-transmitting property, after this atmosphere sintering, a temperature of 1000 ° C. to 1800 ° C. and
HIP treatment is performed at a pressure of 49 MPa to 196 MPa. This time also
Depending on the sample thickness, if it is about 1 to 5 mm, it is generally 0.1 to 10 hours, preferably 0.1 to 2 hours, and most preferably 0.5 to 2 hours.

By the above operation, a scandium oxide sintered body having an excellent light-transmitting property, which has a linear transmittance of 77% or more at a thickness of 1 mm over a wavelength range of 500 nm to 5 μm, can be obtained. In addition,
When the scandium oxide sintered body is used as a color filter or a laser medium, an activator such as Nd or Yb is added to cause specific absorption. In this case, the linear light transmittance is
It is well known to those in the industry that it is measured at a wavelength other than the specific absorption wavelength.

[0040]

Example 1 Scandium oxide having a purity of 99.9% or more and Si 5 ppm was dissolved in hydrochloric acid to prepare an aqueous scandium chloride solution having a concentration of 0.25 M (mol · dm ⁻³ ). 500 ml of this solution was placed in a beaker made of polytetrafluoroethylene and stirred. A 0.5 M (mol dm ⁻³ ) concentration of ammonium hydrogen carbonate solution was added dropwise to the scandium chloride aqueous solution at a rate of 5 ml / min until the pH reached 8.0, and curing was continued at room temperature for 10 days while stirring.
After curing, filtration and washing with ultrapure water were repeated several times, and then the product was placed in a dryer at 150 ° C and dried for 2 days. The obtained precursor powder was put into an alumina crucible and calcined in an electric furnace (1250 ° C
X 3 hours) to prepare scandium oxide raw material powder having an average primary particle diameter of 0.35 μm.

2 g of this raw material powder was placed in an alumina mortar,
Alumina sol equivalent to 45 wtppm in terms of Al metal with respect to the raw material
(Manufactured by Nissan Kagaku Co., Ltd.) was added and mixed and crushed. This powder φ
After inserting into a 10 mm die and performing primary molding at 20 MPa, CIP molding was performed at a pressure of 250 MPa. As a result of measuring the amount of Al contained in the molded body by ICP emission spectrometry, 48w
It was tppm. Moreover, the result of measuring the molding density by the Archimedes method was 61.2%. This molded product was heated to 1625 ° C at 100 ° C / hr in a vacuum furnace and held for 2 hours before being heated to 20 ° C.
Cooled at 0 ° C / hr. The degree of vacuum during sintering was set to 10 ^-1 Pa or less. The obtained sintered body was mirror-polished using diamond slurry, and the linear transmittance was measured with a spectrophotometer. As a result, linear transmittance at wavelengths of 500 nm and 800 nm
(t = 1 mm) was 77.9% and 80.0%, respectively. The linear transmittance of the sintered body of Example 1 is shown in FIG.

This sample was subjected to thermal etching in the air at 1500 ° C. for 2 hours, and the microstructure was observed. As a result, the average particle size was 15.8 μm. Here, the average particle size is 1.56C / (MN), where C is the length of a line arbitrarily drawn on a high-resolution image such as SEM, N is the number of particles on this line, and M is the magnification.
Sought as. The theoretical density ratio was 99.97% as a result of obtaining the sintered body density by the Archimedes method. After dissolving this sintered body in an autoclave, the amounts of Al and Si were determined by ICP emission spectrometry, and the results were Al 48 wtppm and Si 5 wtppm.

[0043]

[Examples 2-4 and Comparative Examples 1-3] Using a raw material powder having a Si content of 10 wtppm prepared in the same manner as in Example 1 and performing CIP molding under various molding pressures, the molding density was changed. A molded body was produced. These molded bodies were fired in vacuum at 1550 ° C. for 5 hours in the same manner as in Example 1. Table 1 shows the linear transmittance (t = 1.0 mm) at a wavelength of 500 nm of the obtained sintered body. The amount of Al contained in the sintered body was in the range of 45 to 55 wtppm in all cases.

Comparative Example 1 has a structure in which a densely sintered portion and a portion in which sintering has hardly progressed and a large amount of pores are continuously connected, and the average Observation of tissue and light transmission was not possible. The structure gradually becomes more uniform as the molding density is improved, and the light transmittance is also improved accordingly. From the results in Table 1, in order to obtain a sintered body having a light transmittance of 77% or more, the molding density is
It turns out that more than 58% is required.

[0045]

[Table 1]

[0046]

[Examples 5-8 and Comparative Examples 4-8] Purity 99.9% or more Si2wt
50 g of scandium oxide raw material powder having an average primary particle diameter of 0.3 μm in ppm, and alumina powder equivalent to 35 wtppm in terms of Al metal with respect to the raw material powder (TM-DAR average primary particle diameter of 0.3 μm manufactured by Daimei Kagaku)
m, TM-DAR is a product name) put in a nylon pot. Further, nylon balls and 50 g of ethyl alcohol were added and ball mill mixing was carried out for 50 hours. This slurry was put under vacuum 55
After drying at ℃, lightly loosen the obtained powder in an alumina mortar and then CIP molding in the same manner as in Example 1 to obtain a molding density of 6
A 2.9% molded body was produced. This molded body was vacuum fired for 2 hours at various firing temperatures. Table 2 shows the firing temperature, the average particle size of the obtained sintered body, and the linear transmittance at a wavelength of 500 nm.

[0047]

[Table 2]

When the firing temperature was 1300 ° C. (Comparative Example 4), a dense sintered body was not obtained, and it was impossible to measure the transmittance. The sintered body density in this case was 89.2% of the theoretical density ratio. When fired at 1350 ° C to 1380 ° C (Comparative Examples 5 and 6),
The density of the sintered body was 99% or more, and although a translucent feeling was observed, a sufficient transparent body could not be obtained. As a result of observing the inside with a scanning electron microscope, many pores (pores) of 1 μm or less were observed. When the firing temperature was 1400 ° C. or higher and 1800 ° C. or lower (Example 5-8), a sintered body having a linear transmittance of 77% or more and having excellent translucency was obtained. The linear transmittance of these samples is
It was good at 77% or more in the wavelength range of 500 nm to 5 μm. Further, in this temperature range, since the densification progresses due to grain growth, it can be seen that the average grain size and the linear transmittance are in a proportional relationship. When the firing temperature is higher than 1800 ° C. (Comparative Examples 7 and 8), since the grain growth rapidly progresses and Al is further precipitated, the linear transmittance decreases as the firing temperature increases.

[0049]

Examples 9-11 and Comparative Examples 9-14 Based on Example 1, Sc ₂ O ₃ raw material powder was produced. Quartz saggers were used for calcination of the raw material powders, and the raw material powders with different Si contents were obtained by changing the sampling position in the sagger. (However, in the calcination of the raw materials used in Comparative Examples 9, 10, and 14 and Example 9, a high-purity alumina sagger was used.) The obtained raw material powder was used in the same manner as in Example 1. , Scandium oxide sintered bodies with different Al contents were prepared. Contained in raw materials
Table 3 shows the amount of Si, the amount of Al contained in the sintered body, and the linear transmittance (sample thickness 1 mm) at a wavelength of 500 nm. The compact density was 58% or more in all cases.

[0050]

[Table 3] Examples 9-11, Comparative Examples 9 to 14 Sample Si amount / wtppm Al / wtppm Average particle size / μm Linear transmittance /% Comparative Example 9 5 1 13.6 45.7 Comparative Example 10 3 3 14.1 49.3 Example 9 3 7 14.5 77.2 Example 10 24 15 13.9 77.0 Comparative Example 11 32 15 25.0 52.4 Comparative Example 12 74 30 31.1 59.5 Comparative Example 13 35 75 23.8 62.2 Example 11 28 77 25.4 77.8 Comparative Example 14 3 115 53.3 39.8

As in Comparative Examples 9 and 10, included in the sintered body
When the amount of Al is small, the effect is not sufficiently exerted, and therefore the translucency is not high even though the amount of Si mixed is small. When the Al content of Comparative Example 14 exceeds 100 wtppm,
The average particle size was 53 μm, which was more than three times that of Example 1, and many intragranular pores were observed. As a result of observing this sample by SEM equipped with EDX (energy dispersive X-ray analysis),
An Al segregation phase was confirmed. Conversely, from Comparative Example 11-13,
It can be seen that when the amount of Si contained in the raw material exceeds 30 wtppm, sufficient translucency cannot be obtained.

[0052]

Examples 12-23 and Comparative Examples 15 and 16 Sintered bodies obtained in the same manner as in Example 5 (linear transmittance at 500 nm and 400 nm: 77.2%, 58.0%, average particle size: 1.3 μm) were coated with HIP. Treatment was applied to improve the transmittance. Table 4 shows the average particle diameters and the linear transmittances at wavelengths of 400 and 500 nm when they are performed at various temperatures, times and pressures. The HIP treatment was carried out by a simultaneous temperature rising method using Ar gas as a pressure medium, and the temperature was raised at 800 ° C./hr and kept for a predetermined time, and then cooled at 1000 ° C./hr.

[0053]

[Table 4] HIP conditions and average particle size, transmittance Linear transmittance /% Sample temperature / ° C x time / hr Pressure / MPa Average particle size / μm 500 nm 400 nm Example 12 950 × 1 196 1.3 77.2 58.0 Example 13 1025 × 1 196 1.3 77.5 62.3 Example 14 1200 × 0.5 49 1.3 77.6 65.4 Example 15 1200 × 2 45 1.3 77.3 58.0 Example 16 1500 × 0.5 98 12.1 77.7 68.8 Example 17 1500 × 0.5 196 12.3 77.9 70.5 Example 18 1500 × 1 45 12.5 77.3 58.0 Example 19 1625 × 0.5 98 17.9 78.3 71.3 Example 20 1800 × 1 49 24.2 78.5 74.8 Example 21 1800 × 0.5 196 25.0 78.7 75.1 Example 22 1800 × 2 196 27.1 79.0 77.0 Example 23 1800 × 2 45 24.6 77.2 55.0 Comparative example 15 1825 × 1 196 33.4 65.3 37.8 Comparative example 16 1850 × 1 196 52.2 38.1 17.2

The sintered body before HIP treatment had a transmittance of 77% or more at a wavelength of 500 nm, but had a transmittance of 58% at a wavelength of 400 nm.
It is significantly reduced to%. This is because many fine pores of submicron or smaller are contained inside the sintered body. From the results of the examples, it can be seen that the HIP treatment crushed the fine pores and significantly improved the transmittance particularly at 400 nm. Moreover, it is understood that the effect is not exhibited even if the HIP treatment is performed when the treatment pressure and temperature are low. Further, if the HIP temperature is too high, Al precipitation or abnormal grain growth occurs as in the case of the atmosphere firing, and conversely the transmittance decreases.

[0055]

Examples 24-30 and Comparative Examples 17 and 18 In the same manner as in Example 5, scandium oxide compacts having a compact density of 63.3% and Si and Al contents of 5,58 wtppm were produced. These molded bodies were fired at a predetermined temperature and holding time in a vacuum furnace (vacuum degree 10-1 Pa or less). At this time, the heating rate and the cooling rate were 400 and 600 ° C./hr, respectively. Average particle size of the obtained sintered body and linear transmittance at a thickness of 1 mm (measurement wavelength 500 nm)
Is shown in Table 5. As is clear from Table 5, the firing temperature is 140
The temperature is preferably 0 to 1800 ° C., and the firing time (holding time at the maximum temperature) is preferably 0.5 hours or more and 10 hours or less.

[0056]

[Table 5] Firing conditions and average particle size, linear transmittance Sample temperature / ° C x time / hr Average particle size / μm Linear transmittance /% (500 nm) Example 24 1400 x 1.0 1.2 77.0 Comparative Example 17 1450 x 0.1 2.7 57.3 Example 25 1450 × 0.5 3.1 77.3 Example 26 1450 × 1.5 4.0 77.6 Comparative Example 18 1600 × 0.1 5.3 62.7 Example 27 1600 × 0.5 17.5 77.9 Example 28 1780 × 0.5 24.2 78.4 Example 29 1780 × 2.0 26.5 78.6 Implementation Example 30 1780 × 8.0 28.9 78.8

[Brief description of drawings]

FIG. 1 is a characteristic diagram showing a spectrum of linear transmittance in an example.

Claims (4)

[Claims] 1. An Al content of 5 wtppm or more and 100 wtppm or less,
A scandium oxide translucent sintered body having a linear transmittance of 77% or more at a thickness of 1 mm over a wavelength range of 500 nm to 5 μm. 2. The Si content is 30 wtppm or less and the average particle size is 1.
The scandium oxide translucent sintered body according to claim 1, which has a size of not less than 30 μm and not more than 30 μm. 3. The Si content is 30 wtppm or less and the purity is 99.9%.
Using the above high-purity scandium oxide raw material powder, the molding density is 58% or more of the theoretical density, the Al content is 5 wtppm or more 100
Manufacture of a translucent scandium oxide sintered body, which is characterized by producing a molded body of wtppm or less, debinding by heat treatment, and then firing at a temperature of 1400 ° C to 1800 ° C in a non-oxidizing atmosphere. Method. 4. The translucent scandium oxide according to claim 3, wherein, after the firing, a hot isostatic pressing treatment is performed at a temperature of 1000 ° C. to 1800 ° C. and a pressure of 49 MPa to 196 MPa. Manufacturing method of sintered body.