JPS606307B2 - Method for producing polycrystalline zinc selenide - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a dense and highly pure transparent polycrystalline body by heating and compressing zinc selenide (hereinafter referred to as ZnSe) powder using a hot isostatic press. .

ZnSe is a type of so-called low W group compound semiconductor material, and due to its good infrared transparency, mechanical properties, and thermal properties, it has recently attracted attention as a component for optical components, especially window materials for carbon dioxide lasers. There is.

In this case, it is desired to develop a material with a low content of voids and impurities. This is because these defects cause scattering and absorption of laser light, which in turn leads to overheating and destruction of the window material. ZnSe for laser window materials must have good mechanical properties (strength), and polycrystalline materials without virility are used.

As one of the methods for manufacturing ZnSe polycrystals, the hot pressing method of Zsen e powder has been put into practical use, but because pressure is applied only in one direction, abnormal grain growth and residual pores may occur due to uneven pressure. It was said that there were problems such as. In order to solve these problems, the present invention has developed a hot isostatic press (Hotls).
Regarding the method using ostaticPress (hereinafter referred to as HIP), we aim to provide a ZnSe polycrystal with high density and high purity by improving the heating compression process.

The mP method is known as a method for high-density compression processing of various materials in a high-temperature, high-pressure gas atmosphere.

This method has excellent densification power because it can apply high temperature and isotropic pressure at the same time. It is effectively used for removing defects (vacancies). This m
In order to obtain a polycrystalline material with fewer vacancies and impurities by increasing the density of the Z-sen e powder using the P method, there were the following problems.

First, it must be sealed in a sealed container (capsule).

Even when ZnSe powder is molded and solidified using ordinary powder metallurgy techniques, densification hardly occurs, and it is difficult to form the ZnSe powder into a closed pore state that does not require encapsulation. This is Z
At temperatures above 950° C., which is about 70% of the melting point of nSe (1520° C.=1793 K), the vapor pressure is high and sublimation becomes intense, so it is thought that densification does not proceed. In order to HIP something in Kansai-hole state, pressure medium (Ar gas) is required.
To prevent this from penetrating into the interior of the sample, it is usually vacuum sealed in a sealed container (capsule). In the case of ZnSe, commonly used metal capsules (such as mild steel) cannot be used because they react with ZnSe and break the airtightness, so glass capsules with less reactivity are suitable.

FIG. 1 shows the steps from encapsulation in a glass capsule to MP.

A shows the state after the workpiece (ZnSe) 2 is charged into the glass capsule 1, the mouth shows the state after vacuum sealing, and C shows the state after the m-grossing process, with the glass capsule and ZnSe in close contact. . This glass capsule has a temperature of mP of ZnSe (90
Pyrex glass is the most desirable material in terms of softening point, ease of availability, and processability.

However, this Pyrex glass is usually &03Na20
Because it contains many components such as
There was a problem of contamination of e. Table 1 shows the composition of Pyrex glass. These impurities are removed from the capsule and Zn as shown in Figure 1 after Hm.
Due to direct contact with Se, it diffuses into ZnSe, causing impurity contamination and causing a decrease in light transmittance.

The present inventors have determined the degree of impurity contamination and densification described above (
In order to examine the relationship between the amount of pores) and photogenicity, impurity analysis, attained density, and transmittance were measured at different temperatures. Table 2 shows the content, density and 0.3 side t of typical impurity elements.
The transmittance of 10.6 μm infrared light of a mirror-polished sample is shown.

As is clear from Table 2, as for impurity contamination, HI
The lower the P temperature, the smaller the effect, and the effect is particularly large on B.

This is considered to be due to the fact that B203 is the most abundant component in the composition of the glass capsule, and the vapor pressure of B203 is high. Regarding the density after HIP, it seems that the lower the HIP temperature, the easier it is to increase the density.

This is because in the final stage of sintering, where the density is 99% or more, the diffusion function contributes to the increase in density, and at low temperature mP with fine crystal grains, vacancies disappear due to grain boundary diffusion. It is assumed that this is because it is easy. On the other hand, regarding translucency, on the contrary, Hm
The higher the temperature, the better the transmittance (10.64).

This is considered to be due to a decrease in the proportion of grain boundaries due to grain growth and a decrease in light scattering at the grain boundaries. As shown above, it has become clear that there is a problem in setting the mP temperature in order to obtain a ZnSe polycrystal with high density, high purity, and high transparency.

The present invention solves the above-mentioned problems by dividing the mP process into two stages.
By performing mP at ~900℃) to close the pores, and (1) removing the glass capsule and at a relatively high temperature (~1300℃) to further increase the density and improve translucency, the density, The present invention provides a method for producing a ZnSe polycrystal with excellent purity and translucency.

In other words, after the first HIP process produced a sintered body with few impurities and high density (closed pore state), but with slightly poor translucency, the glass capsules that caused impurity contamination were removed. Then, the second stage of H-grading is performed to improve translucency while maintaining high purity and high density.

As a result of a detailed study of the temperature and pressure conditions for the first and second heat compression (HIP) steps, we found that the temperature and pressure of the first stage using a glass capsule is 800 to 1000 qo, the pressure is 50 p atm or more, and the second stage is We found that the optimum range is a temperature of 1000℃ to 1400℃ and a pressure of 500atm or more.
I put it out.

The reason for this is that under the temperature condition of less than 800 qo in the first stage, the ZnSe powder is insufficiently softened and lacks plastic deformability, so high density to the point where it becomes a closed pore state cannot be achieved.

Furthermore, if the temperature exceeds 1000 pm in the first stage, contamination with impurities such as B, Si, Na, etc. from the glass capsule increases, making it impossible to obtain high-purity ZnSe, which is the object of the present invention. At a temperature of less than 1000° C. in the second stage, good infrared light transmittance cannot be obtained, probably because crystal grain growth is insufficient.

In addition, at high temperatures exceeding 1400°C, crystal grain growth becomes excessively large, resulting in coarse crystal grains with a crystal grain size of several ribs or more, resulting in a significant decrease in mechanical strength, resulting in window materials for carbon dioxide lasers, etc. It is judged to be unsuitable as a material for infrared optical components. Also, the pressure in both the first and second stages is 5
It has been found that ZnSe polycrystals with high density and high translucency cannot be obtained by heat compression (daily compression) when the aphobic pressure is less than 0.

In principle, it is considered that the higher the pressure, the more effective the pressure, but the current limit is about 200 p atm due to the capacity of general heating compression (mP) equipment, and the effects of the present invention are recognized even at this pressure. The contents of the present invention will be explained below using examples.

Example inner diameter 25 kite. 99.999% pure Z
A molded body of nSe powder (80% densification) was charged and heated to 700
After heating and vacuuming at ℃ for 1 hour, the tube was sealed in vacuum.

This was heated at 900°C and 2000°C using Ar gas as a pressure medium.
HIP processing was performed for 3 hours at atmospheric pressure (first stage mP).

Once the capsule was taken out from the mP, the glass capsule was broken and removed, and after confirming that it had closed pores by specific gravity measurement, it was placed in the same Nichika equipment as it was without vacuum sealing. I performed 5 hours of m-kō 0 work at atmospheric pressure. (Second stage HIP). As a result of measuring this sample, as shown in Table 3, better results were obtained than mP with only one stage (shown in Table 2). Table 3

[Brief explanation of drawings]

Figure 1 A, mouth, and C are mP from encapsulation in a glass capsule.
The capsule shapes up to the process are shown in order. 1: Capsule, 2: ZnSe powder molded body, 3: Vacuum enclosure part. square diagram

Claims (1)

[Claims] 1. In a method of heating and compressing zinc selenide powder by hot isostatic pressing to obtain polycrystals with high density, high purity, and translucency, the above heating and compression step is performed using a glass capsule as an enclosure, A step of closing the pores by carrying out the process at 800 to 1000°C and 500 atm or higher, and after this,
A method for producing a translucent polycrystalline zinc selenide, which comprises two steps: removing the enclosure and heating and compressing at 1000° C. to 1400° C. and 500 atmospheres or more.