JPH0672045B2 - Translucent spinel sintered body and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to a polycrystalline spinel sintered body excellent in translucency, particularly a transmissive window suitable for use as an infrared transmissive window having a thickness of 3 mm or more. The present invention relates to an optical spinel sintered body and a method for manufacturing the same.

[Conventional technology]

Spinel (MgAl ₂ O ₄ ) is composed of magnesia (MgO) and alumina (Al
₂ O ₃ ), which is known to have good transparency when sintered at high density because scattering at grain boundaries does not occur easily because the crystal type is cubic. .

Usually, the transparency of spinel sintered bodies is 0.4μm in the visible region.
The wavelength rapidly increases from around m, and the wavelength in the infrared region is 3 to 5 μm.
The highest in the vicinity. Therefore, the spinel sintered body is promising as a translucent material such as an optical window, and its manufacture has been attempted by various methods.

For example, as described in JP-A-47-6028, there is a method of adding lithium fluoride (LiF) as a sintering aid and hot pressing in vacuum. As a sintering aid,
Besides LiF, calcium oxide (CaO) is known to be effective. Further, JP-A-55-27837 discloses a method in which the composition ratio of MgO and Al ₂ O ₃ is equimolar to a slight excess of Al ₂ O _3, and LiF is added as a sintering aid to carry out atmospheric pressure sintering. , And JP-A-59-
121158 discloses a method in which LiF is added to spinel fine powder obtained by hydrolyzing an alkoxide, and sintering is performed under normal pressure in hydrogen.

[Problems to be Solved by the Invention]

In any of the above-mentioned conventional methods for producing a translucent spinel sintered body, since a sintering aid such as LiF is added for densification, the second phase is likely to appear, and the light is not emitted due to the structural nonuniformity. There was a defect that the light was scattered and the direct transmittance was low.

In addition, in the former hot press method in vacuum, 1300 to 16
Since a high temperature of 00 ° C and a high pressure of 1000 kg / cm ² or more are required, the strength of conventional mold materials such as graphite is insufficient and it is difficult to manufacture a large sintered body. or,
In the latter atmospheric pressure sintering method, it is difficult to control grain growth and voids tend to remain, so the level of translucency is low, and when the composition ratio of MgO and Al ₂ O ₃ is changed in addition to the addition of a sintering aid. Also second
The phase is likely to appear and the direct transmittance is further lowered.

In the case of the translucent spinel sintered body manufactured by the conventional method as described above, the linear transmittance is about 75 to 80% at a sample thickness of 1 mm, and the infrared transmission used at a sample thickness of 3 mm or more. It was necessary to further improve the linear transmittance for use as a window material.

In view of such conventional circumstances, the present invention has a high purity and high density and a high level of translucency, and in particular, a translucent spinel sintered body having a linear transmittance suitable as an infrared transmissive window material having a thickness of 3 mm or more. , And its manufacturing method.

[Means for Solving the Problems]

In order to achieve the above object, in the method for producing a translucent spinel sintered body of the present invention, a purity of 99.5% or more and a specific surface area (BET
Value) Spinel powder of 10 m ² / g or more is densified to a theoretical density ratio of 95% or more by hot pressing in a vacuum at a temperature of 1200 to 1700 ° C and a pressure of 100 to 500 kg / cm ² , and then a temperature of 1400 to
HIP at 1800 ℃ and pressure of 500kg / cm ² or more.

The translucent spinel sintered body of the present invention produced by the above method is made of a polycrystalline spinel sintered body having a purity of 99.5% or more, and the linear transmittance at a sample thickness of 3 mm has a wavelength of 0.4 to 3 μm. Average visible light and near infrared light 65% or more, and wavelength 3-5 μm
It has a maximum infrared light of 75% or more and has an extremely excellent linear transmittance which has never been obtained, and its translucency is suitable as an infrared transmitting window material.

[Action]

As described above, in the present invention, by hot pressing in vacuum and subsequent HIP (hot isostatic pressing), spinel firing with high density and high linear transmittance is performed without adding a sintering aid such as LiF. You can get a unity.

The raw material spinel powder has a purity of 99.5% or more in order to prevent a decrease in translucency due to absorption of impurities.
The inclusion of transition metal elements such as Fe is not preferable. The spinel powder has a primary particle size of about 0.2 μm or less, that is, the surface area is B
An ET value of 10 m ² / g or more is necessary to obtain a dense sintered body. As such high-purity and fine spinel powder, those obtained by hydrolysis of alkoxide are suitable.

Further, since it is not particularly necessary to add a sintering aid such as LiF or CaO, there is no decrease in transmittance due to the second phase as in the conventional case.

The hot press is performed in a vacuum and the temperature is 1200 to 1700 ° C. It is difficult to obtain a high-density sintered body with a theoretical density ratio of 95% or more at a temperature below 1200 ° C, and in a vacuum above 1700 ° C.
MgO evaporates, and when cooled, the Al ₂ O ₃ (corundum) phase is likely to precipitate as the second phase, resulting in a decrease in the light-transmitting property.
Also, if the pressure of the hot press is less than 100 kg / cm ^2, it is difficult to obtain a high density sintered body with a theoretical density ratio of 95% or more, and 500 kg / cm ²
If it exceeds, it becomes difficult to use a normal graphite type in terms of strength.

In HIP processing, temperature of 1400-1800 ℃ and 500kg / cm ²
Since the sintered body is isotropically pressed by the above-mentioned pressure, the plastic deformation and the diffusion mechanism promote the removal of the pores, the density is further increased, and the translucency is further improved. The high-pressure gas used in HIP is preferably an inert gas such as Ar, N ₂ gas or O ₂ gas, or a mixed gas thereof. Especially, if O ₂ gas is mixed, deoxidation from the sintered body at the time of HIP treatment will result. There is an advantage that the reduction of translucency can be prevented. These gases 500 kg / cm ² or more (2000 kg / cm ² or less) high and moreover to work isotropically, the removal of conventional Hotsutopuresu method (about 1000 kg / cm ² in the vertical two-way pressure) vacancies than Densification progresses uniformly,
A spinel sintered body excellent in translucency can be obtained.

The theoretical density ratio of the sintered body obtained by hot pressing is 95%.
When less than, many of the residual pores become so-called open pores, and the high-pressure gas used in HIP penetrates into the sintered body through these pores, resulting in insufficient progress of densification by HIP. Become.

〔Example〕

Example 1 A high-purity spinel powder having a purity of 99.9% and a specific surface area of 14 m ² / g (BET value) was used in a vacuum of 1 × 10 ^-1 torr using a graphite type having an inner diameter of 50 mm at a temperature of 1400 ° C. and 300 kg / g. It was hot pressed at a pressure of cm ² for 2 hours to obtain a white sintered body having a theoretical density ratio of 97%. Next, this sintered body was put into a HIP device, and using Ar gas at a temperature of 1600 ° C. and a pressure of 2000 kg / cm ² for 2 hours.
HIP processing was performed. The obtained spinel sintered body was colorless and transparent in appearance.

This spinel sintered body was mirror-polished to a thickness of 3 mm, and the linear transmittance was measured with a spectrophotometer. The wavelength was 3 to 5 μm.
In the infrared region, the maximum light transmittance was 85%, and the average light transmittance was 75% in the wavelength region of 0.4 to 3 μm.

Example 2 A high-purity spinel powder having a purity of 99.7% and a specific surface area of 11 m ² / g (BET value) was heated in a vacuum of 3 × 10 ⁻³ torr using a graphite mold with an inner diameter of 50 mm at a temperature of 1600 ° C. and 200 kg / It was hot pressed at a pressure of cm ² for 1 hour to obtain a white sintered body having a theoretical density ratio of 96%. Further, this sintered body was put into a HIP device, and N ₂ gas was used for 3 hours at a temperature of 1700 ° C. and a pressure of 1000 kg / cm ² .
HIP processing was performed. The obtained spinel sintered body was colorless and transparent in appearance.

This spinel sintered body was mirror-polished to a thickness of 3 mm, and the linear transmittance was measured with a spectrophotometer. The wavelength was 3 to 5 μm.
In the infrared region, the maximum light transmittance was 83%, and the average light transmittance was 73% in the wavelength region of 0.4 to 3 μm.

Example 3 High-purity spinel powder having a purity of 99.8% and a specific surface area of 20 m ² / g (BET value) was heated in a vacuum of 8 × 10 ^-2 torr using a Graphite type having an inner diameter of 50 mm at a temperature of 1300 ° C. and 400 kg / g. It was hot pressed at a pressure of cm ² for 3 hours to obtain a white sintered body having a theoretical density ratio of 98%. Further, this sintered body was put into a HIP device and Ar-5% O ₂
HIP treatment was performed for 2.5 hours at a temperature of 1500 ° C. and a pressure of 1500 kg / cm ² using the mixed gas. The obtained spinel sintered body was colorless and transparent in appearance.

This spinel sintered body was mirror-polished to a thickness of 3 mm, and the linear transmittance was measured with a spectrophotometer. The wavelength was 3 to 5 μm.
In the infrared region, the maximum light transmittance was 82%, and the average light transmittance was 75% in the wavelength region of 0.4 to 3 μm.

〔The invention's effect〕

According to the present invention, it is possible to obtain a translucent spinel sintered body that has a high density and a very excellent linear transmittance in the visible and infrared regions without using a sintering aid. This translucent spinel sintered body is particularly useful as a material for an infrared transmissive window used in a thickness of 3 mm or more.

Claims (3)

[Claims] 1. A purity of 99.5% or more and a specific surface area (BET value) of 10 m
Spinel powder of ² / g or more, temperature 1200 ~ 1700 ℃ and pressure 1
Densified to a theoretical density ratio of 95% or more by hot pressing in a vacuum of 00 to 500 kg / cm ² , then temperature 1400 to 1800 ℃
And a method for producing a translucent spinel sintered body, which comprises HIPing at a pressure of 500 kg / cm ² or more. 2. The method for producing a translucent spinel sintered body according to claim 1, wherein the HIP treatment uses an inert gas, a nitrogen gas, an oxygen gas, or a mixed gas thereof. 3. A polycrystalline spinel sintered body having a purity of 99.5% or more, and a linear transmittance at a sample thickness of 3 mm has a wavelength of 0.4 to 3 μm.
m or more in visible and near infrared light 65% or more on average, wavelength 3-5 μm
The infrared transmissive spinel sintered body for infrared transmission windows, which has a maximum of 75% or more in infrared light.