JPH0250927A - Method for refining metal galimu - Google Patents

Abstract

PURPOSE:To obtain Ga of high quality at the time of growing seed crystals put on the side of a cooling medium of metallic Ga by finding the solidifying speed from a solid-liquid interface detected by the scanning with infrared rays or supersonic waves and regulating the progressing condition in the solidifying. CONSTITUTION:Seed crystals are put on the side of a cooling medium 2 of molten Ga 6, are grown and are solidified in the direction of the other side into crystal solidified metal 7. At this time, scanning is executed with infrared rays or ultrasonic waves to detect the interface between the liquid area (molten Ga 6) and the solid area (crystal solidified metal 7). By the result in the detection of the interface, the solidifying speed in the metallic Ga 7 is regulated to obtain Ga of high quality.

Description

[Detailed Description of the Invention] "Object of the Invention" The present invention relates to a method for refining metallic gallium, and aims to uniformly solidify metallic gallium in one direction, enable effective control, and achieve economical refining. It is something to do.

(Industrial application field) One-way solidification and purification technology for gallium, which is used as a raw material for semiconductor devices and light-emitting devices.

(Prior art) Gallium has excellent properties as a raw material for semiconductor elements and light emitting elements as an electronic material, and its demand has increased rapidly in recent years, and a considerable amount of research has been conducted on its production and purification methods. . In other words, although gallium exists uniformly in nature, it is scattered, and there is no ore that contains gallium in a profitable proportion, so it can be obtained as a by-product in the production of zinc, germanium, and especially aluminum. This has no choice but to happen. However, the purity of by-products from any of the above processes is at most about 99.999% (five nines), and the purity of gallium metal as a raw material for semiconductor devices is at least 99.9999%. % (Sixoxnine) or more, it is necessary to further refine the product to increase its purity.

However, known methods for refining gallium metal include a refining electrolytic method, a fractional crystallization method, a zone melting refining method, and a single crystal pulling method.

In other words, the refining electrolytic method utilizes the property of using crude gallium metal as an anode, dissolving gallium and metals more base than gallium in an aqueous solution with a controlled impurity concentration, and electrodepositing only gallium and metals more base than gallium on the cathode. It's a method. In addition, in the fractional crystallization method, since solid gallium is lighter than liquid gallium, the surface of the liquid gallium is gently brought below the melting point so that the solid gallium floats on the liquid surface as small lumps, which are then sorted and extracted. There is a method of purification that utilizes the so-called segregation phenomenon.

The zone melting refining method is the so-called zone melting method, and is a method in which, for example, a gallium metal held horizontally is alternately heated and cooled to remove impurities to the melt side by utilizing the segregation phenomenon. Also, the single crystal pulling method is J, G, tla
rper (US Pat. No. 3,088,853) or P
, de, Ia-Beteque (Mem, S
ci, Rev.

Met, 67 (1) 57-69 (1970
)) is a method in which the tip of a cooled seed crystal is brought into contact with molten gallium metal, and the single crystal of gallium that grows in that area is slowly pulled up and purified using the segregation phenomenon.

Furthermore, the present inventors have repeatedly studied ways to improve the purity of conventional methods as described above, or to eliminate operational disadvantages, and have filed Japanese Patent Application No. 110594/1983 (Japanese Patent Application Laid-open No. 62-110594).
270494) and Japanese Patent Application No. 6276080. That is, the surface of the molten gallium is cooled with gas under conditions in which seed crystals are present on the surface of the molten gallium, and the crystal growth rate by the seed crystals is controlled to solidify most of the molten gallium, thereby increasing impurities. This method removes the remaining molten gallium. Apart from this, the present inventors have also proposed the method of Japanese Patent Application No. 76080/1983 as a method suitable for processing large amounts of gallium. That is, by improving the above-mentioned method of the prior application, a cooling chamber for circulating a coolant is provided at one end of a container containing molten gallium, and a liquid cooling medium is used to increase cooling efficiency and, as a result, to facilitate control of the growth rate, and to grow gallium crystals. The speed is maintained within a predetermined range.

(Problems to be Solved by the Invention) There are still many problems in the conventional purification methods as described in the previous section. In other words, the purity of purified gallium using the purification electrolytic method is still 99.9% due to contamination from the electrodes or the difficulty of obtaining a high-purity gallium aqueous solution.
It stays at the 999% level. Furthermore, even in the fractional crystallization method, it is difficult to obtain high purity gallium because contaminated liquid gallium adheres to the surface of the solid.

Although the zone melting refining method can be said to be an excellent method in principle, in the case of gallium metal, it is difficult to operate due to large supercooling, and it is not easy to take out the solidified metal. The single crystal pulling method is also useful as a method for purifying high-purity gallium, but to obtain gallium metal of 99.9999% or higher, it must be carried out repeatedly, requiring the preparation of a large number of equipment, and requiring a large amount of man-hours. Therefore, it is economically disadvantageous.

The proposal proposed by the present inventors to overcome these disadvantages is effective in obtaining high purity gallium simply and economically. However, when this method is operated on an industrial scale, the solidification rate is 5 to 3.
Qim/hr, and it is necessary to accurately control the solidification rate, and in cases where the solidification rate is slow even within the above range on average, it is necessary to concentrate in the molten gallium. Impurities are incorporated into the solid gallium that solidifies, or the impurities are not concentrated in the molten gallium in an orderly manner, impeding the purity of the solid gallium product and making it particularly unstable in terms of quality. Therefore, careful control is required during its refining, but conventionally, such control has to be done solely through visual inspection by workers, which is a heavy economic burden and has a high possibility of misidentification. For these reasons, as described above, restrictions on the coagulation rate and the amount of purification processed at one time have to be severe, making it difficult to increase productivity.

"Structure of the Invention" (Means for Solving the Problems) Seed crystals are made to exist on the cooling medium side of molten gallium, and by the cooling effect of the cooling medium, the seed crystals are grown and solidified toward the other side. In this process, a detection operation is performed so that infrared or ultrasonic scanning intersects the interface between the molten liquid region and the solidified solid region, and the solidification rate of metallic gallium is controlled and purified based on the results of this interface detection. Characteristic method for refining metallic gallium.

(Function) Seed crystals kept on the cooling medium side of the molten gallium grow due to the cooling effect of the cooling medium, solidification progresses toward the other side, and impurities in the molten gallium are concentrated in the molten gallium and solidified. Increases the purity of gallium metal.

By scanning with infrared rays or ultrasonic waves so as to cross the interface between the liquid and solid regions, the relationship between the position and the amount of infrared fouling, or the relationship between the position and the transmission speed of the ultrasonic waves, can be determined in the melt and solid parts. The interface is determined by detecting the change, and the solidification rate can be obtained from the relationship between this interface and time. Further, by controlling either or both of the temperature and the amount of the cooling medium according to the solidification rate, the progress of solidification as described above can be appropriately controlled.

That is, uniform solidification is achieved, impurities are smoothly concentrated in the melt portion, and the quality of the solidified solid is made uniform.

(Example) To explain the specific embodiments of the present invention, one example of specific equipment for carrying out the method of the present invention is shown in Section 1.2.
As shown in the figure, a diaphragm 3 having a corner portion 3a is provided on the cooling medium side of a boat 1 that accommodates molten gallium, and such a diaphragm 3 portion is located inside a cooling chamber 2. A coolant inlet 4 and a coolant outlet 5 are provided to circulate the coolant and provide a cooling effect to the gallium melt 6 accommodated in the boat 1 through the diaphragm 3 portion. That is, seed crystals were added to the corner part 3a of the gallium melt 6 stored in the boat 1, and the melt 6 surface was coated with a protective coating 8 such as diluted hydrochloric acid, and the cooling was performed as described above. By giving seed crystals grow, crystal metal 7
is moving toward the other side of the boat 1.

The present inventors have conducted detailed practical studies regarding refining using such a unidirectional solidification method. It is thought that the coagulation and refining process can be performed automatically according to the cooling temperature curve of the refrigerant using calorific value calculations, but in actual processing operations, it is difficult to completely control the ambient temperature during the coagulation and refining process, which lasts for quite a long time. In addition, it has been confirmed that it is difficult to effectively control the crystal growth direction of solid gallium, and that it is difficult to predict and specify the temperature gradient in solid gallium because the thermal conductivity differs depending on the direction of the crystal axis. It is difficult to control the rate, eg, it is not possible to maintain the solidification rate within ±10% of the set value. That is, such fluctuations in the solidification rate affect the quality of the obtained metallic gallium, making it impossible to obtain a stable product.

Therefore, in the present invention, when purifying gallium according to the one-way solidification method as described above, an infrared thermometer 11 is used as shown in FIG.
Alternatively, using an ultrasonic flaw detector 15 as shown in FIG.
Control the refrigerant from. That is, the infrared thermometer 11 in FIG.
When using the infrared rays from above the boat 1, the infrared rays are scanned and measured at regular intervals in a direction crossing the interface between the solid metal 7 and the melt 6, and the relationship between the amounts of infrared rays at each measurement position is discontinuous. The interface position can be determined from the point. On the other hand, as shown in Figure 4, when using an ultrasonic flaw detector 15, a receiving probe 15a and a transmitting probe 15b are installed on both sides of the boat 1, and the probe is inserted in the direction along the crystal growth direction at regular intervals, that is, in the solid state. The ultrasonic transmission speed is measured by scanning the interface between the metal 7 and the melt 6 in the intersecting direction, and the relationship between the interface position and the transmission speed is determined. In other words, the speed of sound in solid gallium 7 is about 30% of the speed of sound in liquid gallium 6, which is a melt.
Since it is large, the interface position can be detected by the operation described above, and the solidification rate can be determined from the interface position detected at regular intervals using this method.

Therefore, by sending data to the computer or other calculation control mechanism 12 so that the solidification rate obtained in this way takes a preferable value, and by sending instructions for temperature and flow rate to the circulating constant temperature bath 13, the solidification rate can be automatically and accurately determined. can be controlled.

As the seed crystal described above, a separately prepared high-purity small gallium crystal is used, or cold water is added to precipitate the crystal nucleus, and then a separately prepared supercooled high-purity gallium crystal is touched to cool it appropriately. A crystal nucleus is formed by contacting the resulting rod-shaped body with a gallium melt, and the like is used. The ambient temperature around the boat 1 is preferably maintained at around 30°C, which is approximately the same as the melting point of gallium, or by heating from the lower part to maintain the temperature of the gallium melt within 2°C of the melting point. Achieves stable crystal growth and favorable purification effects.

Based on the results of practical studies conducted by the present inventors, it can be said that the freezing point of the gallium melt 6 is lowered depending on the type and amount of impurities. In other words, although there is no published literature regarding this relationship, in this type of purification process where the impurity concentration is at the hundreds of ppm level, the freezing point effect is at most 0.
．． It is less than 1°C and can be virtually ignored.

It has been confirmed that the higher the purity of gallium, the more pronounced the supercooling becomes.The temperature of the melt during crystal growth is generally 29 to 31℃, and the temperature of the melt is 29℃.
If it is less than C, the crystal growth surface will not be smooth and will tend to have an uneven shape under conditions where 1 kg or more is to be purified. Furthermore, if the melt temperature is 31°C or higher, crystal control becomes difficult. When applying a cooling effect to the tip of solidified metal gallium with water or the like to keep the melt side warm, the melting point temperature will only decrease by about 1°C at most, and should be kept within the range described above. It is possible to maintain a favorable temperature condition at the solidification interface.

The temperature of the cooling medium 2 for setting the crystal growth rate to a predetermined set value varies depending on the shape of the boat 1, its material, the amount of gallium metal melt to be processed, etc., but it can be set appropriately according to the design operation. good.

Water is usually sufficient as the cooling medium, but thickening the diaphragm or
If a diaphragm made of a material with low thermal conductivity is used or a large amount of gallium metal melt is used, the temperature of the cooling medium may have to be kept below 0°C, and if water is used in such cases, there is a risk of freezing. Therefore, fresh water to which a nonaqueous solvent such as silicone oil, alcohol, or ethylene glycol has been added may be used.

The preferred infrared wavelength range when determining the interface using the method of measuring the amount of infrared rays in Figure 3 described above is 0.75 to 20 μm.
If it deviates from this range, the measurement accuracy will decrease, which is not preferable. Further, when using the ultrasonic wave shown in FIG. 4, the preferable ultrasonic frequency range is 0.5 to 20 MHz, and measurement accuracy deteriorates in any case outside this range.

A specific example of purification according to the present invention will be described below.

Purification Example 1 The equipment as shown in Fig. 3 was constructed, and a polyethylene boat 1 having a length of 20 cm as shown in Fig. 1.2 was used, and Cu: 4.9 ppm as impurities.
In: 22ppm, Sn: 9. Oppm
Inject 1 kg of molten gallium at 30°C containing
30°C warm water is fed and circulated from the constant temperature bath 13 at a rate of about 2β/min, and crystal nuclei prepared in advance in another container are added as seed crystals to the corner part 3a of the diaphragm 3 of the boat 1. However, since the crystal growth is unstable at first, the temperature is gradually lowered, and when the size of the crystal exceeds the size of the part of the corner protruding into the cooling chamber 2, the solidification rate decreases to 20%.
Adjust the temperature of the cooling medium to approximately 15°C to obtain m+e/hr.
From that point on, the solidification rate decreases to a wavelength of 8 to 13μ.
Purification was carried out for about 12 hours under the control of the detection results of an infrared thermometer (portable digital radiation thermometer IR-AHOT manufactured by Chino Co., Ltd.) 11. When the fluctuation of the solidification rate was determined from the relationship between the purification time and the solidification length, it was confirmed that it was within 4.5% of the set value, and the average value of impurities in the obtained purified gallium was cu: 0.28pp.
m, In: 0.38ppm XSn: 0.2
6 ppm, and very high quality purified gallium could be stably obtained.

As a comparative example, when refining was performed under the same conditions as above while visually determining and controlling the interface, the solidification rate fluctuation was 10.0 to 20.0% of the set value, and the impurities in purified gallium were Average value is Cu: 0.56pp
m, In: 0.63 ppm, Sn: 0.
It was 52 ppm, and the purification efficiency was about 30 to 50% worse than when it was controlled based on the detection results of an infrared thermometer.

Purification Example 2 As shown in Fig. 4, ultrasonic transmitter m (U.S. Sonic Corporation) measures the transmitting probe and the receiving probe by making them contact the outer sides of both long sides of the boat 1 and sliding them in the horizontal direction.
Instruments stationary MKII ultrasonic deep wound instrument) 1
5, measured at 2 MHz, using the same gallium as in Purification Example 1, and the same solidification rate as 20 mm/h.
The purification treatment was carried out by controlling the temperature to be r.

The fluctuation of the solidification rate was determined from the relationship between the purification time and the solidification length, and the result was 18.5 to 21.5ii/hr, which was within 7.5% of the set value, and the average value of impurities in purified gallium was 18.5 to 21.5ii/hr. , Cu: 0.30ppm, In:
0.42ppm, Sn: 0.30ppm,
It was confirmed that the product was of high quality as in Purification Example 1.

"Effects of the Invention" According to the present invention as explained above, high-quality gallium can be obtained by accurately controlling the solidification rate with a stable rate, and since it does not require full-time workers, it is possible to produce gallium at low cost and in large quantities. This invention has the advantage of being able to rationally process raw material metals, making it a highly effective invention industrially.

[Brief explanation of the drawing]

The drawings show the technical contents of the present invention, and FIG. 1 is a plan view of a refining port used in carrying out the present invention, and FIG. 2 is a sectional view showing the state in the middle of coagulation and refining. FIG. 3 is a schematic diagram showing one embodiment of the present invention using an infrared radiation thermometer, and FIG. 4 is a schematic explanatory diagram of another embodiment using an ultrasonic flaw detector. In these drawings, 1 is a bow I, 2 is a cooling chamber, 3 is a diaphragm, 3a is a part of the corner, 4 is an inlet, and 5 is a diaphragm.
is the discharge port, 6 is the molten gallium, 7 is the crystal solidified metal,
8 is a protective coating such as dilute hydrochloric acid, 11 is an infrared thermometer, 12
13 is a calculation control mechanism, 13 is a circulation type constant temperature bath, 15 is an ultrasonic flaw detector, 15a is its transmitting probe, and 15b is its receiving probe. Patent applicant Nippon Light Metal Co., Ltd. Mitsubishi Kasei Co., Ltd. Inventor Akiharu Ajimura Doshin Isei Hamabe Yoshihiko

Claims (1)

[Scope of Claims] 1. When seed crystals are present on the cooling medium side of the molten gallium, and the seed crystals are grown by the cooling effect of the cooling medium and solidified toward the other side, scanning with infrared rays or ultrasonic waves is performed. A method for refining metallic gallium, characterized in that a detection operation is performed so that gallium intersects the interface between a molten liquid region and a solidified solid region, and the solidification rate of metallic gallium is controlled and purified based on the detection result of this interface. . 2. The method for purifying metallic gallium according to claim 1, wherein the solidification rate of metallic gallium is controlled by adjusting one or both of the temperature and flow rate of the fluid cooling medium.