JPH0323269A - Transparent aluminum oxynitride sintered body and production thereof - Google Patents

Abstract

PURPOSE:To obtain a sintered body having superior linear transmissivity and optical uniformity in spite of its large size by making specified aluminum oxynitride powder dense by hot pressing under prescribed conditions in an atmosphere of gaseous nitrogen, etc., and by subjecting the dense powder to hot isostatic pressing (HIP). CONSTITUTION:Aluminum oxynitride powder having >=99% purity and >=3m<2>/g BET specific surface area is prepd. and made dense by hot pressing at 1,400-1,800 deg.C under 100-500kg/cm<2> pressure in vacuum or in gaseous nitrogen. The dense powder having >=95% theoretical density is subjected to HIP with an inert gas, gaseous nitrogen, gaseous oxygen or a mixture of such gases at 1,500-2,000 deg.C under >=500kg/cm<2> pressure.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is a polycrystalline aluminum oxynitride sintered body with excellent translucency, especially for use in durable optical window materials used with a thickness of 5 ms or more. The present invention relates to a translucent aluminum oxynitride sintered body suitable for use in, and a method for producing the same.

(Prior art) Aluminum oxynitride is a composite compound of aluminum oxide and aluminum nitride, and forms a cubic single phase when the molar fraction of aluminum nitride is in the range of 30 to 37 mol%, so It is known to have low photothermia and exhibit very high light transmittance when sintered at high density.

Normally, the light transmittance of an aluminum oxynitride sintered body increases sharply from a wavelength of about 0.3 μm in the visible region, and reaches a maximum at a wavelength of about 3 to 4 μm in the infrared region. Therefore, aluminum oxynitride sintered bodies are seen as promising as light-transmitting materials such as optical windows, and attempts have been made to manufacture them using various methods. No sintered body was obtained.

For example, JP-A-58-74577 discloses that aluminum oxynitride powder is constantly heated at a temperature of 1.900 C' or higher in nitrogen gas while mixing boron, isotrium, or their compounds or doping them from the gas phase. A method of pressure sintering is described. However, when boron, IJium, etc. are added or doped into the sintered body, a second phase tends to appear locally, and light is scattered due to this structural non-uniformity. When it comes to large materials, it is difficult to obtain optically uniform materials. Furthermore, pressureless sintering has the disadvantage that grain lengthening is unavoidable when densification is achieved to the point where translucency is obtained, resulting in a decrease in the strength of the resulting sintered body.

Another known method is to hot press aluminum oxynitride powder in nitrogen gas to obtain an aluminum oxynitride sintered body. However, due to the strength constraints of graphite molds in hot pressing, 5 Q Q kyCr
It is important to apply a higher pressure than this, and if the pressure is lower than this, the sintered body will not be sufficiently densified and a satisfactory linear transmittance will not be obtained. There wasn't.

Therefore, in the light-transmitting aluminum oxynitride sintered bodies manufactured by these conventional methods, the in-line transmittance at a wavelength of 0.4 to 4.5 μm is about 85% at the maximum, even for a thin material with a sample thickness of 2 brocades. The average in-line transmittance is as low as about 80%, and it is necessary to further improve the in-line transmittance for a light-transmitting material used in a durable optical window material with a thickness of 5w or more.

[Problem to be solved by the invention]

In view of such conventional circumstances, the present invention has optically uniform and excellent light transmittance even in large-sized materials, and has excellent straight-line transmission as a durable optical window material in the visible and infrared regions, especially when the thickness is 5 m or more. The object of the present invention is to provide a translucent aluminum oxynitride sintered body with high efficiency and strength, and a method for manufacturing the same.

(Means for Solving the Problems) - In order to achieve the object L, the method for manufacturing a translucent aluminum oxynitride sintered body of the present invention has a purity of 99% or more and a specific surface area (BET value) of 3trVg or more. Aluminum oxynitride powder was heated at a temperature of 1400~isooc'' and a pressure of 100°C.
It is densified to a theoretical density ratio of 95% or more by hot pressing in vacuum or nitrogen gas at ~500 kV'cm'', then at a temperature of 1500-2000 C' and a pressure of 500
It is characterized by performing HIP treatment at a pressure of 100 kg/cm" or more.

The translucent aluminum oxynitride sintered body of the present invention produced by the above method is made of a polycrystalline aluminum oxynitride sintered body with a purity of 99% or more, and has a straight transmittance of 0.05 mm at a sample thickness of 5 mm. Average of 8 in visible and infrared region from 4 to 4.5 μm
It is characterized by being 0% or more.

[Function] The aluminum oxynitride powder, which is the raw material for the method of the present invention, has a purity of 99% or more to prevent a decrease in translucency due to absorption of impurities, and in particular contains 7!1 transfer metal elements such as Fe. is not desirable. In addition, the aluminum oxynitride powder has primary particles of about 0.5 μm or less, that is, a specific surface area of 3 m'/g or more in BET value, preferably 10 to 201 rVg, and is fine with an average particle size of 30 μm or less. This is necessary to obtain a dense aluminum oxynitride sintered body.

Such highly pure and fine aluminum oxynitride powder can be obtained by mixing fine aluminum oxide powder with chilibon powder and reducing it in nitrogen gas, or fine aluminum oxide powder and aluminum nitride powder. Powder obtained by mixing and reacting in nitrogen gas is suitable.

In the method of the present invention, hot pressing is performed in vacuum or nitrogen gas, and the sintering temperature is 1400 to 1800C. At a temperature below 1400 C', it is difficult to obtain a high-density sintered body with a theoretical density ratio of 95% or more, and at a temperature exceeding 1800 C', the grain length progresses too much and the effect of subsequent HIP becomes small.
This is also because the bending strength does not reach 250 MPa. Furthermore, if the pressure of the hot press is less than 1001 $m'', it is difficult to obtain a high-density sintered body with a theoretical density ratio of 95% or more;
If it exceeds k9Am, it will be better to use normal graphite type in terms of strength.

In addition, in the method of the present invention, there is no need to add a sintering aid such as aluminum oxide or to dope with boron or the like.

Even when adding sintering aids to lower the sintering temperature,
Since the amount is as small as 0.5% by weight or less, there is almost no decrease in transmittance or variation in refractive index due to precipitation of the second phase.

The sintered body obtained by the above hot pressing is subjected to the following H I
In the P treatment a temperature of 1600-2000 C' and 5
Since it is isotropically pressurized at a pressure higher than 00J9't'',
The removal of pores is promoted by the desired deformation and diffusion mechanism, and higher density and optical uniformity are achieved, further improving the translucency of the sintered body.

The gas used in HIP is preferably an inert gas such as Ar, nitrogen gas, oxygen gas, or a mixture thereof.
In particular, the use of oxygen gas or a mixed gas of oxygen can compensate for the deoxidation of the sintered body during HIF treatment, which has the advantage of preventing deterioration in translucency due to misalignment of the composition ratio.

In addition, the theoretical density ratio of the sintered body obtained by hot pressing is 95.
%, most of the remaining pores become so-called open pores, and the high-pressure gas used in 1{IP penetrates into the inside of the sintered body through these pores, so that densification by HIP does not proceed sufficiently. The result is not.

The aluminum oxynitride sintered body obtained by the method of the present invention has high purity and is also very dense, so it has an extremely high in-line transmittance, and even with a sample thickness of 51 lIs, the wavelength is 0.4 to 4. Average of 80 in visible and infrared range of 5μm
% or more of linear transmittance can be obtained.

In addition, since there is no structural non-uniformity, there is no local scattering of light, and an optically uniform material can be obtained even in a large material with a diameter of 50lI11I or more.

Furthermore, according to the method of the present invention, the grain length during sintering is suppressed to the minimum limit, resulting in an extremely fine structure with an average grain size of 30 μm or less, resulting in an oxynitrided product with excellent translucency and high strength. An aluminum sintered body is obtained.

〔Example〕

Example 1 Purity 99%, specific surface f1l5rr? /g (BIcT value)
High purity aluminum oxynitride powder of 5 x 10 -
``In the vacuum history of torr, using a graphite mold with an inner diameter of IQQss, a lagoon of 1650σ and 3 Q Q ky
A white sintered body with a theoretical density ratio of 97.5% was obtained by hot pressing L for 3 hours at a pressure of 1,800 C'' using Ar gas. H for 2 hours at a temperature of
IP processing was performed. The obtained aluminum oxynitride sintered body was colorless and transparent in appearance.

The above aluminum oxynitride sintered body was mirror-polished to a thickness of 5 m, and its straight cotton transmittance was measured using a spectrophotometer.
It exhibited excellent light transmittance of 85% on average in a 5 μm area. In addition, the four-point bending strength based on J Engineering SR 1601 is 310.
It showed an excellent value of MPa.

”A1ヱPurity 99%, specific surface area 10 rrl/g, (B E
T value) high purity aluminum oxynitride powder, I
Using a graphite mold with an inner diameter of 100 ms in a vacuum of 0-”torr, a temperature of 1600σ and 500 kvf
-Hot press at a pressure of m2 for 2 hours, theoretical density ratio 98
% white sintered body was obtained. Furthermore, this sintered body was placed in a HIP device and heated at a temperature of 1750 C' and 2
HIP treatment was performed for 2.5 hours at a pressure of 0001 vf-♂ to obtain an aluminum oxynitride sintered body that was colorless and transparent in appearance.

This aluminum oxynitride sintered body was mirror-polished to a thickness of 5 cm, and the linear transmittance measured with a spectrophotometer was 0.4 wavelength.
It was 81% on average in the region of ~2 μm and 85% on average in the region of wavelengths 2 to 4.5 μm. Moreover, the four-point bending strength of this sintered body was 340 MPa.

Example 3 Purity 99%, specific surface area 3 rrVg (BET value)
High-purity aluminum oxynitride powder is mixed with 0.5 wt% of yttrium oxide powder in ethanol using a ball mill,
．． The mixed powder was placed in nitrogen gas at 1 atm and had an inner diameter of 12 mm.
1550 C using a graphite mold of 01II11+
A white sintered body with a theoretical density ratio of 96% was obtained by hot pressing for 3 hours at a temperature of HIP treatment was carried out for 2.5 hours at a temperature of 1700σ and a pressure of 2000 kyAm.The obtained aluminum oxynitride sintered body was colorless and transparent in appearance.

This aluminum oxynitride sintered body was mirror-polished to a thickness of 5 mm, and the in-line transmittance determined by a spectrophotometer was 0.4 at wavelength.
It was 81% on average in the region of ~2 μm and 85% on average in the region of wavelengths 2 to 4.5 μm. Further, the four-point bending strength of this sintered body was 300 MPa.

〔Effect of the invention〕

According to the present invention, it has a high density and has an extremely excellent in-line transmittance of 80% or more on average at a sample thickness of 5 gIs in the visible and infrared regions, and even large materials with a diameter of 50 or more can be optically A uniform translucent aluminum oxynitride sintered body can be provided.

Moreover, this aluminum oxynitride sintered body has an average grain size of 3
Since it has a very fine structure of 0 μm or less and high strength, it is useful as a durable optical window material, especially as an infrared transmitting window material with a thickness of 5 mm or more that is used under adverse conditions.

Procedural amendment (voluntary) 1. Display of incidents Heihei 1st year patent l [No. 153889 l Person who makes corrections Relationship with the incident

Claims (4)

[Claims] (1) Purity 99% or more and specific surface area (BET value) 3m^
2/g or more of aluminum oxynitride powder at a temperature of 1400
It is densified to a theoretical density ratio of 95% or more by hot pressing in vacuum or nitrogen gas at ~1800°C and a pressure of 100~500 kg/cm^2, and then at a temperature of 1500~2
1. A method for producing a translucent aluminum oxynitride sintered body, characterized by performing HIP treatment at 000° C. and a pressure of 500 kg/cm^2 or more. (2) The method for producing a translucent aluminum oxynitride sintered body according to claim (1), wherein the HIP treatment uses an inert gas, nitrogen gas, oxygen gas, or a mixed gas thereof. (3) It is made of polycrystalline aluminum oxynitride sintered body with a purity of 99% or more, and the in-line transmittance at a sample thickness of 5 mm is 0.5 mm at a wavelength of 0.5 mm.
A translucent aluminum oxynitride sintered body, characterized in that it has an average strength of 80% or more in the visible and infrared regions of 4 to 4.5 μm. (4) The aluminum oxynitride sintered body according to claim (3), wherein the average grain size of the sintered body is 30 μm or less, and the four-point bending strength is 250 MPa or more.