JPH0798980B2 - Distillation purification method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for distilling and refining a metal having a relatively low melting point and a high vapor pressure, and particularly to Se, Cd, Zn, Te,
The present invention relates to a distillation and purification method in which a metal such as Sb or Pb is evaporated and condensed in a cylindrical horizontal container at a pressure of atmospheric pressure or higher while a carrier gas is circulated. The present invention is AnSe, ZnTe,
It is useful for producing a high-purity metal used as a raw material for synthesizing a compound semiconductor such as a II-VI group compound semiconductor represented by CdTe and a III-V group compound semiconductor.

2. Description of the Related Art In recent years, there have been increasing demands for the purity of metals used as raw materials for synthesizing compound semiconductors. Many of the elements that make up compound semiconductors have relatively low melting points and high vapor pressures, such as Se, Cd, Zn, and T.
e, Sb, Pb, etc. In order to satisfy the requirement for high purity of such metals, several purification methods have been conventionally carried out, but the distillation method is a very effective means.

Since the vapor pressure of metal is often not so high in the vicinity of the melting point, a vacuum distillation method of heating to a high temperature under a reduced pressure has been conventionally used in order to perform the distillation efficiently.

2 and 3 show examples of such conventional devices. FIG. 2 shows a vacuum (vacuum) distillation apparatus for cadmium, zinc and the like. Raw materials are charged into the evaporation section 23 at the bottom end of the quartz crucible 21. The quartz crucible 21 is housed in a quartz furnace core tube 25.
The quartz furnace core tube 25 and the crucible 21 are heated by the heating furnace 27 in the evaporation section.
Placed inside. The upper end of the quartz furnace core tube is connected to a vacuum pump as a vacuum exhaust port 29. Above the heating furnace 27,
A water cooling device (28) for condensing the vaporized components is provided around the quartz furnace core tube and constitutes a condensing part (22).

FIG. 3 shows a horizontal tellurium decompression (vacuum) rectification unit. The inside of the furnace wall 32 of the container 31 constitutes the evaporation section 33. Raw material tellurium is charged into the graphite boat 30. The outer end of the container 31 protruding outside the furnace wall is connected to a vacuum pump at a vacuum exhaust port 35. The outer end of the container 31 is water-cooled by the water cooling device 36. A condenser 34 is formed outside the furnace wall, and a condenser container 37 made of, for example, stainless is inserted therein, and condensed tellurium adheres to the inside thereof.

However, these vacuum (vacuum) distillation methods have some serious drawbacks:

(1) In metals used for high-purity applications such as semiconductors, it is necessary to avoid the inclusion of trace amounts of oxides. Therefore, when performing vacuum distillation, expensive equipment that can obtain a high vacuum is required, and the manufacturing cost becomes extremely high.

(2) Evaporative gas metal components generated from the high temperature evaporating part move quickly to the low temperature evacuation side. Therefore, in order to recover the evaporating metal component with high yield, the evaporating part and the evacuation port should be connected. A device such as a cooling trap or a baffle plate must be provided between them.

(3) Moreover, even if such a measure is taken, the recovery rate is very poor because the evaporated metal escapes to the vacuum exhaust port side.

(4) Since a part or most of the recovered metal is deposited in the condensing part in the form of particles or powder having a large surface area, oxidation is likely to occur during the distillation process or when it is opened to the atmosphere after the distillation.

(5) Only the condensate needs to be heated and melted again in order to form an ingot having a small surface area and a fixed shape.

Taking the tellurium distillation apparatus shown in FIG. 3 as an example, the exhaust port is connected to an expensive vacuum facility, and the high-purity tellurium gas evaporated from the high-temperature evaporation section is collected in the condensing container cooled from the outside. Then, it is condensed, but part of it escapes to the outside of the condensation container, so the recovery rate is poor. Condensed tellurium is granular and its surface is slightly oxidized. In addition, ingot-shaped high-purity tellurium cannot be obtained unless the condensed tellurium is melted by heating only the container in another apparatus after the completion of distillation.

As described above, in the conventional metal vacuum distillation method, in addition to requiring equipment capable of obtaining a high vacuum, it is difficult to efficiently recover the vaporized components, and oxidation easily occurs.
There were problems such as inability to directly generate ingots.

OBJECT OF THE INVENTION The present invention is intended to solve such a technical problem, and particularly metal such as Se, Cd, Zn, Te, Sb and Pb having a relatively low melting point and a high vapor pressure is inexpensive. Distill in equipment,
It aims to develop a method for recovering refined metals in the form of ingots that are difficult to oxidize at a high rate.

SUMMARY OF THE INVENTION To achieve the above object, the present inventors abandoned the conventional concept of vacuum distillation and worked on the establishment of a new distillation technique, and as a result, a carrier gas was used under atmospheric pressure or higher. Succeeded in developing the distillation technology. In order to increase the evaporation rate, it is necessary to reduce the thickness of the diffusion layer which is present immediately above the surface of the raw material and which is thought to control the evaporation rate. Therefore, at the same time when the carrier gas is blown into the evaporation section, It was conceived to utilize this carrier gas as a means for forcibly transferring the vaporized components. By transporting the vaporized component to the downstream side of the gas flow by the carrier gas and condensing it in this portion, it is possible to prevent the vaporized component from diffusing to other portions and lowering the recovery rate. By performing the distillation at a pressure higher than atmospheric pressure, the temperature at which the vaporized components generated in the container are recondensed can be increased, and the vaporized components are condensed in a liquid form with a small surface area, and after reaching the desired distillation rate. By cooling as it is, it is possible to directly recover the ingot with almost no oxidation.

Based on these findings, the present invention comprises an evaporation section and a condensation section, and charged the metal raw material into the evaporation section. The tubular container is inserted into a heating furnace having a temperature distribution corresponding to the evaporating section and the condensing section, and under the pressure of atmospheric pressure or higher, the carrier gas is circulated in the direction from the evaporating section toward the condensing section. There is provided a distillation and purification method characterized in that the metal raw material in the section is heated, the vaporized metal component is transferred to the condensing section by a carrier gas, and the vaporized metal component is condensed in the condensing section. The container is a horizontal tubular container that is divided into upper and lower halves, and has at least one partition that defines an evaporation part and a condensation part on the inner surface of the lower part of the container, and A structure having an inlet for carrier gas at one end on the side of the evaporator and a carrier gas outlet at the other end is preferable. It is also effective to insert the container into a pipe material of the same material and insert the whole pipe material into a heating furnace.

DETAILED DESCRIPTION OF THE INVENTION The present invention will be described with reference to FIG. The metal targeted by the present invention is a metal having a relatively low melting point such as Se, Cd, Zn, Te, Sb, and Pb, and a high vapor pressure.
-6N is an ultra-high-purity distillation purification system.

The container for storing the raw materials may be of any type as long as it is a cylindrical container having an evaporating section and an aggregating section. A structure having a partition that separates the condensation part is preferable.
The evaporation unit may be configured by simply placing a tray for storing the raw materials. The condenser section may be divided into a plurality of compartments. By selecting a material that does not undergo a dissolution reaction with the target metal and has poor wettability as the material of the container, the refining effect is improved, and the condensed refined metal and the distillation residue are easily recovered. Generally, high-purity graphite, quartz, ceramics such as boron nitride, or the like can be used.

In FIG. 1, the cylindrical container 1 is divided into an evaporator 5 and a condenser 7 by a partition 3. Raw material R in the evaporator 5
Is charged. A port 11 for inserting a gas introduction pipe 9 for introducing a carrier gas such as hydrogen or an inert gas into the container is provided at the end of the container 1 on the evaporation section side. A carrier gas discharge port 13 is provided at the end of the container on the condensation section side.

The container 1 is inserted into a heating furnace, here a furnace core tube 15. The temperature distribution inside the furnace core tube 15 is set to an appropriate temperature distribution corresponding to the evaporation section and the condensation section. The temperature distribution is selected according to the metal to be refined. For example, the evaporation part has a melting point of +90 to 11
To 0 ℃ (eg 100 ℃) and the condensing part melting point +5 to 15 ℃
(For example, + 10 ℃) should be set.

By circulating the carrier gas at a pressure higher than atmospheric pressure from the carrier gas inlet, and at the same time setting the temperature distribution in the furnace core tube to a predetermined value, the evaporation components generated in the evaporation section are transferred from the evaporation section to the condensation section. . The carrier gas flowing through the evaporation section sweeps the diffusion layer directly above the raw material melting surface to increase the evaporation rate. In this way, the metal components generated one after another are transferred to the condensing part, where they are condensed and collected in a liquid state. Since the atmosphere is at atmospheric pressure or higher, the vaporized component is stored in a liquid state at the bottom of the condenser.

When the desired distillation rate (raw material insertion weight-residue weight) / raw material charging weight x 100 (%) is reached, the condenser is cooled as it is and directly recovered in the form of an ingot.

In FIG. 1, the container 1 is inserted into a pipe material 17 made of the same material as the container 1. By doing so, all the vaporized substances that leaked out to the outside of the container during the distillation were collected to the inner surface of this tube material, so the recovery rate of the purified product was further improved and the vaporized material to the inner surface of the furnace core tube was further improved. Can be eliminated.

Inert gas or hydrogen gas is used as the carrier gas, but the use of high-purity hydrogen gas is effective for reducing the oxygen content of purified metal water, especially when dealing with metals that do not form hydrides at operating temperatures. Is.

The pressure inside the container is maintained at about atmospheric pressure to atmospheric pressure + several tens of mmH ₂ O by bubbling in the liquid after leaving the gas outlet.

In this way, in the condensation part, refined metal that has been distilled to a high purity in the form of an ingot rather than a grain is obtained.

Example 1 Using the apparatus shown in FIG. 1, 99.998% pure metal Cd was purified by distillation. The container was a high-purity graphite container that was divided into two upper and lower parts, and the dimensions were 70 mmφ × 900 mmL inside dimensions. Of the length of the vessel, 300 mm was partitioned as the distillation section and the remaining 600 mm as the condensation section.

After loading 2 kg of the raw material Cd ingot into the evaporation part, the upper lid was set, and the tube was inserted into the furnace core tube while being inserted into a high-purity graphite tube material (internal dimensions 85 mmφ x 1,100 mmL).

After the inside of the furnace core tube was once evacuated, high-purity hydrogen gas was allowed to flow at 2 l / min at atmospheric pressure while heating the evaporation part to 750 ° C and the condensation part to 350 ° C.

As a result, the distillation rate reached 80% in 3 hours, and cooling was performed there. After cooling, 98% (1560 g) of the raw material was recovered from the condensing part in the form of a metallic luster ingot, and the remaining amount (40 g) adhered to the inner surface of the pipe material, but was easily recovered. Table 1 shows the analytical values of the purified Cd together with those of the raw material Cd. The table also shows the residual resistance value ratio (electrical resistance value in 273K / electrical resistance value of 4.2K, which is used as an index of purity) and yield.

Comparative Example As a comparative example, using the vacuum distillation apparatus shown in FIG. 2, metal Cd having the same 99.998% purity as in Example 1 was vacuum distilled. The size of the quartz crucible was 60 mmφ × 90 mmL. 2 kg of raw material Cd was charged in the crucible bottom, the lower part of the crucible was heated to 400 ° C. while being evacuated, and the upper part of the crucible was water-cooled.

As a result, the distillation rate reached 80% in 2 hours, but 80% (1280 g) of the evaporated Cd accumulated in a granular form over the low temperature part 600 mm inside the crucible, and the remaining amount in the low temperature part of the furnace core tube outside the crucible. Adhering in powder form, these surfaces did not have a perfect metallic luster. Further, in order to collect these deposits, it was necessary to separately heat and melt the deposits with the crucible upside down and cast into a mold.

The results are shown in Table 1.

The method according to the present invention is excellent not only in the method for recovering purified Cd but also in the purification effect in terms of residual resistance.

Example 2 Zinc was distilled and purified using the same apparatus as in Example 1.
The same conditions were used except that the temperature of the evaporation section was set to 850 ° C and the temperature of the condensation section was set to 450 ° C. Zinc could be recovered with a yield of 98%. The raw material and the purity of purified zinc are shown.

EFFECTS OF THE INVENTION According to the present invention, it is possible to condense an evaporatively refined product in a shape that can be easily recovered at a high recovery rate with inexpensive equipment, as compared with a vacuum distillation method that is generally carried out for refining a metal material. In addition to the above, since a pure metal containing almost no oxide can be obtained, it is extremely effective as a refining means for a metal for electronic materials, and has a large economic contribution.

[Brief description of drawings]

FIG. 1 shows an example of an apparatus for carrying out the method of the present invention and its furnace temperature distribution, and FIGS. 2 and 3 show an example of a conventional apparatus. 1: Cylindrical container 3: Partition 5: Evaporator 7: Condenser 9: Carrier gas inlet pipe 11: Carrier gas inlet 13: Outlet port 15: Furnace core 17: Tubing

Claims (3)

[Claims] 1. A cylindrical container having an evaporation part and a condensation part, and a metal raw material charged in the evaporation part, is inserted into a heating furnace having a temperature distribution corresponding to the evaporation part and the condensation part, Under pressure equal to or higher than atmospheric pressure, the metal raw material in the evaporation part is heated while flowing the carrier gas in the direction from the evaporation part to the condensation part, and the evaporated metal component is transferred to the condensation part by the carrier gas and the condensation is performed. A distillation purification method, characterized in that vaporized metal components are condensed in the section. 2. The container is a model tubular container of upper and lower halves, the inner surface of the lower part of the container having at least one partition for dividing the evaporation part and the condensation part, and 2. The method according to claim 1, wherein the container has a structure in which a carrier gas inlet is provided at one end on the evaporator side and a carrier gas outlet is provided at the other end. 3. The method according to claim 1, wherein the container is put through a pipe material made of the same material, and the whole pipe material is inserted into a heating furnace.