Method for preparing high-purity indium based on ultrasonic vacuum distillation-electromagnetic pulse zone melting

Abstract

The invention belongs to the field of high-purity indium preparation, and provides a method for preparing high-purity indium based on ultrasonic vacuum distillation-electromagnetic pulse zone melting purification, the method combines vacuum distillation and zone melting purification technologies, ultrasonic waves are applied in the vacuum distillation process to assist in removing low-boiling-point impurities such as Cd, Zn and the like, and the purity of the high-purity indium is improved. In the zone melting process, pulse current is applied through an induction coil to assist in removing impurities mainly including Sn, Pb and Fe, and stable preparation of a high-purity indium product with the purity larger than or equal to 99.9995% and the oxygen content smaller than or equal to 2 ppm is achieved by screening and controlling technological conditions. According to the method, the requirement for the purity of the raw material indium is low, and the preparation cost of a high-purity indium product can be reduced.

Description

Technical Field

[0001] This invention belongs to the field of high-purity indium preparation, and relates to a method for preparing high-purity indium based on ultrasonic vacuum distillation-electromagnetic pulse zone melting. Background Technology

[0002] Indium possesses excellent electrical conductivity, ductility, low melting point, and optoelectronic properties, playing a crucial role in numerous high-tech fields, particularly in displays, semiconductors, and photovoltaics. It is an indispensable core material supporting the modern electronic information industry. With the upgrading of display technology, the miniaturization of semiconductors, and the development of new energy sources, the strategic value of high-purity indium will become even more prominent, placing higher demands on its purity and oxygen content.

[0003] Traditional methods for preparing high-purity indium mainly include vacuum distillation, zone melting, and electrolytic refining. Vacuum distillation struggles to remove impurities with boiling points close to indium, such as Sn (2602℃) and Pb (1749℃). Zone melting cannot remove low-boiling-point impurities like Cd and Zn. Electrolytic refining struggles to remove impurities with potentials close to indium, such as Cd and Tl, and introduces colloidal impurities into the electrolyte. Therefore, a single purification method cannot effectively remove impurity elements with different properties, limiting further improvements in the purity of high-purity indium products and failing to meet the demands of the high-end electronics industry. To address the limited impurity removal capabilities of single indium purification methods, current approaches combine vacuum distillation with electrolytic refining or vacuum distillation with zone melting. For example, while vacuum distillation-electrolytic refining can more effectively remove impurities of different properties compared to a single purification method, this method requires step-by-step processing in vacuum distillation and electrolytic refining equipment, resulting in multiple intermediate steps, difficulty in effectively controlling pollution sources, and a high risk of secondary pollution and indium oxidation. As another example, CN120290896A discloses an apparatus and method for vacuum distillation-zone melting to remove impurities from low-melting-point metals. This apparatus uses interconnected vacuum distillation and zone melting zones within a vacuum furnace. The vacuum distillation zone is heated by graphite elements or electromagnetic induction coils, while the zone melting zone is heated by resistance wires. This allows the low-melting-point metal to evaporate and condense in a shaped condenser for vacuum distillation to remove impurities before being directly introduced into the zone melting zone for further impurity removal. This solves the problems of air oxidation and external contamination introduced by segmented feeding. This method mainly controls the separation of impurities and the collection of condensed indium by adjusting the angles of the planar airflow splitter and the triangular airflow separator. Changes in the evaporation rate and airflow disturbances may affect the stability of this method. Examples 1-9 of this method purified indium. According to the data recorded, this method requires indium with a purity of 4N5 as raw material, which requires high purity of raw material. This will increase the preparation cost of high-purity indium. At the same time, the method has poor ability to remove impurity Sn, which limits the further improvement of the quality of high-purity indium products. Summary of the Invention

[0004] Existing methods for purifying indium by setting up interconnected vacuum distillation and zone melting zones within the same vacuum furnace can avoid secondary contamination during material transfer. However, product purity may be affected by changes in evaporation rate and airflow disturbances, and the purity requirements for raw indium are high, which is not conducive to reducing the cost of high-purity indium production. Furthermore, the removal effect on Sn is unsatisfactory. This invention provides a method for preparing high-purity indium based on ultrasonic vacuum distillation and electromagnetic pulse zone melting. This method achieves stable production of low-oxygen-content high-purity indium products with a purity ≥99.9995% while reducing the purity requirements for raw indium, thereby improving the quality of high-purity indium products and reducing their production costs.

[0005] To achieve the above-mentioned objectives, the technical solution adopted by the present invention is as follows:

[0006] A method for preparing high-purity indium based on vacuum distillation-electromagnetic pulse zone melting purification includes the following steps:

[0007] (1) Device setup: The condenser receiver of the secondary condensation zone of the ultrasonic vacuum distillation furnace is connected to the zone melting tube in the electromagnetic pulse zone melting furnace through a high-temperature resistant pipe fitting. The inlet end of the high-temperature resistant pipe fitting is connected to the condenser receiver, and the outlet end of the high-temperature resistant pipe fitting is connected to the zone melting tube. A control valve is installed on the high-temperature resistant pipe fitting. The heating zone of the ultrasonic vacuum distillation furnace is equipped with an ultrasonic system.

[0008] (2) Ultrasonic-assisted vacuum distillation purification: Close the control valve, add raw material indium to the crucible of the ultrasonic vacuum distillation furnace under the protection of high-purity inert gas, and evacuate the ultrasonic vacuum distillation furnace until the pressure inside the furnace is <10. -3 Pa, the crucible is heated to 1200~1300℃ and kept at that temperature. During the heat preservation distillation process, ultrasonic waves are applied to the molten indium in the crucible to disturb it. The steam generated during the heat preservation distillation process enters the first and second condensation zones of the ultrasonic vacuum distillation furnace in sequence. The molten indium purified by vacuum distillation is collected in the first condensation zone with a condensation temperature of 900~1000℃, and low-boiling-point impurities are removed in the second condensation zone with a condensation temperature of 500~600℃.

[0009] In this step, the purity of the raw material indium is at the 3N level, and the pressure inside the ultrasonic vacuum distillation furnace is controlled to be <10 during the heating and heat preservation distillation process. -3 Pa;

[0010] (3) Electromagnetic pulse assisted zone melting and purification: The electromagnetic pulse zone melting furnace is evacuated until the furnace pressure is <10. -4To control the pressure in the electromagnetic pulse zone melting furnace to be lower than the pressure in the ultrasonic vacuum distillation furnace, open the control valve and introduce the molten indium purified by vacuum distillation into the zone melting tube through a high-temperature resistant pipe; close the control valve to maintain the pressure in the electromagnetic pulse zone melting furnace <10 Pa. -4 Pa, after the molten indium in the zone melting tube cools and solidifies, an indium rod is obtained. The indium rod is then zone-melted by reciprocating induction coil and using pulse current. The temperature of the molten zone is controlled at 180~200℃, and impurities are concentrated at the end of the indium rod. After cooling and solidification, the end of the indium rod with impurities concentrated is cut off to obtain a high-purity indium product.

[0011] (4) Product collection: High-purity indium product is collected under the protection of high-purity inert gas. The purity of the high-purity indium product is ≥99.9995% and the oxygen content is ≤2 ppm.

[0012] In step (3) of the above technical solution, the use of pulsed current to perform zone melting of indium rod is mainly to enhance the segregation effect of impurity elements (mainly Sn and Pb). Preferably, when using pulsed current to perform zone melting of indium rod in step (3), the peak pulse current is controlled to be 1000 A and the pulse frequency is 1 Hz.

[0013] In step (3) of the above technical solution, it is preferable to control the moving speed of the induction coil to 3~4 mm / min to ensure the removal effect of impurity elements (mainly Sn and Pb) and improve the melting accuracy.

[0014] In step (3) of the above technical solution, in order to fully enrich the impurity elements (mainly Sn, Pb and Fe) at the end of the indium rod, it is preferable to control the number of reciprocating movements of the induction coil to be 10 to 20 times. A pulse current is applied during the movement of the induction coil from the beginning to the end of the indium rod, and no current is applied during the movement of the induction coil from the end to the beginning of the indium rod. One reciprocating movement is completed when the induction coil moves from the beginning to the end and then back to the beginning of the indium rod.

[0015] In step (2) of the above technical solution, the purpose of applying ultrasound is to disturb the molten indium in the raw material crucible under the action of ultrasound, so as to destroy the oxide film covering the surface of the molten indium and improve the removal efficiency of low boiling point impurities (mainly Cd and Zn). In this step, it is preferable to control the frequency of the applied ultrasound to be 20~30 KHz.

[0016] In step (2) of the above technical solution, the holding distillation time should ensure that low-boiling-point impurities (mainly Cd and Zn) can be fully removed during the holding process. During the holding period, the composition of volatile gases can be monitored by mass spectrometer or spectrometer until the low-boiling-point impurities are fully removed. In this step, the holding distillation time is preferably controlled to be 1~2 h.

[0017] In step (3) of the above technical solution, in order to successfully use the pressure difference to introduce the molten indium purified by vacuum distillation into the zone melting tube, it is preferable to control the pressure in the electromagnetic pulse zone melting furnace to be at least one order of magnitude lower than the pressure in the ultrasonic vacuum distillation furnace.

[0018] In the above technical solution, the control valve is located outside the ultrasonic vacuum distillation furnace and the electromagnetic pulse zone melting furnace for ease of operation. To prevent the molten indium purified by vacuum distillation from solidifying due to excessively low temperature during the introduction of it into the zone melting tube through the high-temperature resistant fitting, it is best to install a heat insulation layer outside the high-temperature resistant fitting.

[0019] In the above technical solution, in order to smoothly introduce the molten indium purified by vacuum distillation into the zone melting tube, in step (1), when setting up the device, it is best to control the position of the inlet end of the high-temperature resistant tube to be higher than the position of the outlet end. For example, this can be achieved by controlling the placement or installation position of the ultrasonic vacuum distillation furnace to be higher than the placement or installation position of the electromagnetic pulse zone melting furnace.

[0020] In the above technical solution, to avoid secondary contamination of the indium product caused by high-temperature resistant tubing during the entire process, the high-temperature resistant tubing is preferably made of high-purity quartz or high-purity graphite. Meanwhile, the raw material crucible, condenser receiver, and zone melting tube are made of high-purity quartz or high-purity graphite. The purity of both the high-purity quartz and high-purity graphite is ≥99.999%.

[0021] In the above technical solutions, the high-purity quartz high-temperature resistant pipes, crucibles, and zone melting tubes involved must be soaked in aqua regia, rinsed with high-purity deionized water, and dried before use; the high-purity graphite high-temperature resistant pipes, crucibles, and zone melting tubes involved must be soaked in aqua regia, rinsed with high-purity deionized water, and then calcined at 1000℃ under vacuum to remove impurities before use.

[0022] In the above technical solution, the purity of the high-purity inert gas is ≥99.999%, and the high-purity inert gas is high-purity argon.

[0023] Compared with the prior art, the technical solution provided by the present invention has the following beneficial technical effects:

[0024] 1. This invention provides a method for preparing high-purity indium based on vacuum distillation and electromagnetic pulse zone melting purification. This method combines vacuum distillation and zone melting purification technologies. During vacuum distillation, ultrasonic waves are applied to assist in the removal of low-boiling-point impurities (mainly Cd and Zn), while during zone melting, pulsed current is applied through an induction coil to assist in the removal of impurity elements, primarily Sn, Pb, and Fe. By combining the screening and control of process conditions, such as precise control of distillation and condensation temperatures and electromagnetic pulse zone melting parameters, raw indium with a purity of 3N can be prepared into a high-purity indium product with a purity ≥99.9995% and an oxygen content ≤2 ppm. Compared to existing technologies, the method of this invention reduces the purity requirements of the raw indium, which is beneficial for reducing the preparation cost of high-purity indium products.

[0025] 2. Experiments have demonstrated that the high-purity indium products prepared by the method of this invention, under the same process conditions, exhibit good quality stability in different batches. The method of this invention avoids the problem in existing technologies that combine vacuum distillation and zone melting to purify indium, where product purity is easily affected by changes in evaporation rate and airflow disturbances, thus stably producing high-purity indium products with low oxygen content. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the connection of the device built in the embodiment. The reference numerals are as follows: 1 is the secondary condensation zone of the ultrasonic vacuum distillation furnace, 2 is the electromagnetic pulse zone melting furnace, 3 is the high temperature resistant pipe, 4 is the control valve, 5 is the condensation receiver, and 6 is the zone melting tube. Detailed Implementation

[0027] The following embodiments, in conjunction with the accompanying drawings, further illustrate the method for preparing high-purity indium based on ultrasonic vacuum distillation-electromagnetic pulse zone melting according to the present invention. It should be noted that the following embodiments are only for further illustration of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-essential improvements and adjustments made to the present invention by those skilled in the art based on the above-described invention will still fall within the scope of protection of the present invention.

[0028] In the following embodiments and comparative examples, the high-purity quartz tubes, high-purity quartz crucibles, high-purity quartz zone melting tubes, and high-purity quartz condenser receivers involved must be soaked in aqua regia, rinsed with high-purity deionized water, and dried before use; the high-purity graphite tubes, high-purity graphite crucibles, high-purity graphite zone melting tubes, and high-purity graphite condenser receivers involved must be soaked in aqua regia, rinsed with high-purity deionized water, and then calcined at 1000°C under vacuum to remove impurities before use.

[0029] In the following embodiments, the ultrasonic vacuum distillation furnace and electromagnetic pulse zone melting furnace used are existing devices in the prior art. The ultrasonic vacuum distillation furnace is equipped with an ultrasonic system that can apply ultrasonic waves to the furnace cavity, such as to the crucible. The condenser receiver of the secondary condensation zone of the ultrasonic vacuum distillation furnace is connected to the zone melting tube in the electromagnetic pulse zone melting furnace through a high-temperature resistant pipe fitting. Both the furnace bodies of the ultrasonic vacuum distillation furnace and the electromagnetic pulse zone melting furnace have through holes matching the outer diameter of the high-temperature resistant pipe fitting. After connection, a sealing element is used for sealing.

[0030] Example 1

[0031] In this embodiment, a method for preparing high-purity indium based on ultrasonic vacuum distillation-electromagnetic pulse zone melting is provided, and the steps are as follows:

[0032] (1) Device setup: such as Figure 1 As shown, the condenser receiver of the secondary condensation zone of the ultrasonic vacuum distillation furnace is connected to the zone melting tube in the electromagnetic pulse zone melting furnace via a high-temperature resistant pipe fitting. The inlet end of the high-temperature resistant pipe fitting is connected to the condenser receiver, and the outlet end is connected to the zone melting tube. A control valve is installed on the high-temperature resistant pipe fitting, and the control valve is located outside the ultrasonic vacuum distillation furnace and the electromagnetic pulse zone melting furnace. The raw material crucible, condenser receiver, high-temperature resistant pipe fitting, and zone melting tube are all made of high-purity graphite.

[0033] (2) Ultrasonic-assisted vacuum distillation purification: Close the control valve, and under the protection of high-purity argon gas, add 100 g of raw material indium with a purity of 99.9% to the crucible of the ultrasonic vacuum distillation furnace, and evacuate the ultrasonic vacuum distillation furnace until the pressure inside the furnace is <10. -3 Pa, the raw material crucible is heated to 1200℃ and distilled for 2 h. During the distillation process, ultrasonic waves are applied to the molten indium in the crucible to disturb it, so as to break the oxide film covering the surface of the molten indium and promote the volatilization of low-boiling point impurities in the molten indium. The steam generated during the distillation process continuously enters the first and second condensation zones of the ultrasonic vacuum distillation furnace. The molten indium purified by vacuum distillation is collected in the first condensation zone with a condensation temperature of 1000℃, and the low-boiling point impurities (mainly Cd and Zn) are removed in the second condensation zone with a condensation temperature of 500℃.

[0034] In this step, during the heating and heat preservation distillation process, the pressure inside the ultrasonic vacuum distillation furnace is controlled to be <10. -3 Pa, the applied ultrasonic frequency is controlled to be 20 kHz.

[0035] (3) Electromagnetic pulse assisted zone melting and purification: The electromagnetic pulse zone melting furnace is evacuated until the furnace pressure is <10. -4Pa, the pressure inside the electromagnetic pulse zone melting furnace is controlled to be one order of magnitude lower than the pressure inside the ultrasonic vacuum distillation furnace. The control valve is opened, and the molten indium purified by vacuum distillation is introduced into the zone melting tube using the pressure difference between the ultrasonic vacuum distillation furnace and the electromagnetic pulse zone melting furnace. The control valve is then closed, maintaining the pressure inside the electromagnetic pulse zone melting furnace cavity <10 Pa. -4 After the molten indium in the zone melting tube cools and solidifies, an indium rod is obtained. The indium rod is then zone-melted by reciprocating induction coils and using pulsed current. The temperature of the melting zone is controlled at 200℃, and impurities (mainly Sn, Pb, and Fe) are enriched at the end of the indium rod. After cooling and solidification, the end of the indium rod enriched with impurities is cut off, with a cut length of 1~2 cm, to obtain a high-purity indium product.

[0036] In this step, when using pulsed current to perform zone melting on indium rods, the peak pulse current is controlled to be 1000 A, the pulse frequency is 1 Hz, the moving speed of the induction coil is controlled to be 3 mm / min, and the number of times the induction coil is moved back and forth is controlled to be 10 times.

[0037] (4) Product collection: High-purity indium products are collected under the protection of high-purity argon gas.

[0038] (5) Repeat steps (2) to (4) twice to prepare a total of 3 batches of ultrapure indium products.

[0039] The impurity content of three batches of high-purity indium products prepared in this example was determined by atomic glow discharge mass spectrometry (GDMS). The results showed that:

[0040] The first batch of products has a purity of 99.9997%, with impurity elements Pb content ≤0.12 ppm, Sn content ≤0.18 ppm, Cd content ≤0.06 ppm, Zn content ≤0.05 ppm, Fe content ≤0.18 ppm, and oxygen content ≤1.6 ppm.

[0041] The second batch of products has a purity of 99.9998%, with impurities of Pb ≤ 0.12 ppm, Sn ≤ 0.13 ppm, Cd ≤ 0.05 ppm, Zn ≤ 0.03 ppm, Fe ≤ 0.15 ppm, and oxygen ≤ 1.5 ppm.

[0042] The third batch of products has a purity of 99.9998%, with impurities of Pb ≤ 0.1 ppm, Sn ≤ 0.12 ppm, Cd ≤ 0.05 ppm, Zn ≤ 0.05 ppm, Fe ≤ 0.13 ppm, and oxygen ≤ 1.3 ppm.

[0043] The three batches of high-purity indium products prepared in this embodiment showed a high degree of consistency in quality, which indicates that the method described in this invention has excellent stability.

[0044] Comparative Example 1

[0045] The operation of this comparative example is basically the same as that of Example 1, except that the ultrasonic waves are not turned on, that is, the ultrasonic waves are not applied to disturb the molten indium in the raw material crucible in Example 1.

[0046] The high-purity indium product prepared in this comparative example was analyzed for all elemental impurities using atomic glow discharge mass spectrometry (GDMS). The results showed that the product purity was 99.998%, and the impurity elements were Pb ≤ 0.6 ppm, Sn ≤ 0.8 ppm, Cd ≤ 1.3 ppm, Zn ≤ 1.4 ppm, Fe ≤ 1.1 ppm, and oxygen ≤ 6 ppm.

[0047] Compared to Example 1, the high-purity indium product prepared in Comparative Example 1 had a lower purity than that of Example 1, while its oxygen content and the contents of impurity elements Cd and Zn were significantly higher. This indicates that, under the same indium purity, if ultrasonic waves are not applied to disturb the molten indium during the heat-holding distillation process, even if vacuum distillation is combined with electromagnetic pulse zone melting, it is difficult to effectively improve the removal of low-boiling-point impurities such as Cd and Zn from the indium raw material.

[0048] Example 2

[0049] In this embodiment, a method for preparing high-purity indium based on ultrasonic vacuum distillation-electromagnetic pulse zone melting purification is provided, and the steps are as follows:

[0050] (1) Device setup: Same as in Example 1.

[0051] (2) Ultrasonic-assisted vacuum distillation purification: Close the control valve, and under the protection of high-purity argon gas, add 100 g of raw material indium with a purity of 99.9% to the crucible of the ultrasonic vacuum distillation furnace, and evacuate the ultrasonic vacuum distillation furnace until the pressure inside the furnace is <10. -3 Pa, the raw material crucible is heated to 1300℃ and distilled at this temperature for 1.5 h. During the distillation process, ultrasonic waves are applied to the molten indium in the crucible to disturb it, thereby breaking the oxide film covering the surface of the molten indium and promoting the volatilization of low-boiling-point impurities in the molten indium. The steam generated during the distillation continuously enters the primary and secondary condensation zones of the ultrasonic vacuum distillation furnace. The molten indium purified by vacuum distillation is collected in the primary condensation zone at a condensation temperature of 950℃, and the low-boiling-point impurities (mainly Cd and Zn) are removed in the secondary condensation zone at a condensation temperature of 600℃.

[0052] In this step, during the heating and heat preservation distillation process, the pressure inside the ultrasonic vacuum distillation furnace is controlled to be <10. -3 Pa, the applied ultrasonic frequency is controlled to be 30 kHz.

[0053] (3) Electromagnetic pulse assisted zone melting and purification: The furnace cavity of the electromagnetic pulse zone melting furnace is evacuated to a pressure <10 ℃. -4 To control the pressure in the electromagnetic pulse zone melting furnace to be one order of magnitude lower than the pressure in the ultrasonic vacuum distillation furnace, open the control valve and use the pressure difference between the ultrasonic vacuum distillation furnace and the electromagnetic pulse zone melting furnace to introduce the distilled and purified molten indium into the zone melting tube; close the control valve to maintain the pressure in the electromagnetic pulse zone melting furnace <10 Pa. -4 After the molten indium in the zone melting tube cools and solidifies, an indium rod is obtained. The indium rod is then zone-melted by reciprocating induction coils and using pulsed current. The temperature of the melting zone is controlled at 200℃, and impurities (mainly Sn, Pb, and Fe) are enriched at the end of the indium rod. After cooling and solidification, the end of the indium rod enriched with impurities is cut off, with a cut length of 1~2 cm, to obtain a high-purity indium product.

[0054] In this step, when using pulsed current to perform zone melting on indium rods, the peak pulse current is controlled to be 1000 A, the pulse frequency is 1 Hz, the moving speed of the induction coil is controlled to be 3.5 mm / min, and the number of times the induction coil is moved back and forth is controlled to be 15 times.

[0055] (4) Product collection: High-purity indium products are collected under the protection of high-purity argon gas.

[0056] The high-purity indium product prepared in this example was analyzed for all elemental impurities using atomic glow discharge mass spectrometry (GDMS). The results showed that the product purity was 99.9999%, with impurity elements Pb content ≤0.07 ppm, Sn content ≤0.05 ppm, Cd content ≤0.03 ppm, Zn content ≤0.02 ppm, Fe content ≤0.02 ppm, and oxygen content ≤0.8 ppm.

[0057] Comparative Example 2

[0058] The operation of this comparative example is basically the same as that of Example 2, except that in step (3), no pulse current is applied during the zone melting process, and the temperature of the melting zone is controlled at 200°C.

[0059] The high-purity indium product prepared in this comparative example was analyzed for all elemental impurities using atomic glow discharge mass spectrometry (GDMS). The results showed that the product purity was 99.9992%, and the impurity elements were Pb ≤ 1.1 ppm, Sn ≤ 1.2 ppm, Cd ≤ 0.03 ppm, Zn ≤ 0.03 ppm, Fe ≤ 0.9 ppm, and oxygen ≤ 4 ppm.

[0060] Compared to Example 2, the high-purity indium product prepared in Comparative Example 2 had lower purity than that of Example 2, while also exhibiting higher levels of impurity elements and oxygen, particularly Pb, Sn, and Fe. This indicates that applying pulsed current to enhance electromagnetic stirring of the molten zone during zone melting can further improve the removal of impurity elements Pb and Sn.

[0061] Comparative Example 3

[0062] The operation of this comparative example is basically the same as that of Example 2, except that the ultrasonic waves are not turned on in step (2), and no pulse current is applied in step (3) during the zone melting process, and the temperature of the melting zone is controlled at 200°C.

[0063] The high-purity indium product prepared in this comparative example was analyzed for all elemental impurities using atomic glow discharge mass spectrometry (GDMS). The results showed that the product purity was 99.998%, and the impurity elements were Pb ≤ 1.2 ppm, Sn ≤ 1.4 ppm, Cd ≤ 0.8 ppm, Zn ≤ 0.9 ppm, Fe ≤ 1.1 ppm, and oxygen ≤ 6 ppm.

[0064] Compared to Example 2, the purity of the high-purity indium product prepared in Comparative Example 3 was significantly lower than that in Example 2. Simultaneously, its oxygen content and the contents of impurity elements Cd, Zn, Pb, Sn, and Fe were all significantly higher than in Example 2. This indicates that, under the same indium purity, if ultrasonic waves are not applied to disturb the molten indium during the heat-holding distillation process, and if pulsed current is not applied to the induction coil during the zone melting process, even combining vacuum distillation with electromagnetic pulse zone melting will hardly effectively improve the removal of impurity elements from multi-source indium.

[0065] Example 3

[0066] In this embodiment, a method for preparing high-purity indium based on ultrasonic vacuum distillation-electromagnetic pulse zone melting purification is provided, and the steps are as follows:

[0067] (1) Device setup: Same as in Example 1.

[0068] (2) Ultrasonic-assisted vacuum distillation purification: Close the control valve, and under the protection of high-purity argon gas, add 100 g of raw material indium with a purity of 99.9% to the crucible of the ultrasonic vacuum distillation furnace, and evacuate the ultrasonic vacuum distillation furnace until the pressure inside the furnace is <10. -3 Pa, the raw material crucible is heated to 1250℃ and distilled at this temperature for 1.5 h. During the distillation process, ultrasonic waves are applied to the molten indium in the raw material crucible to disturb it, thereby breaking the oxide film covering the surface of the molten indium and promoting the volatilization of low-boiling-point impurities in the molten indium. The steam generated during the distillation continuously enters the primary and secondary condensation zones of the ultrasonic vacuum distillation furnace. The molten indium purified by vacuum distillation is collected in the primary condensation zone at a condensation temperature of 900℃, and the low-boiling-point impurities (mainly Cd and Zn) are removed in the secondary condensation zone at a condensation temperature of 550℃.

[0069] In this step, during the heating and heat preservation distillation process, the pressure inside the ultrasonic vacuum distillation furnace is controlled to be <10. -3 Pa, the applied ultrasonic frequency is controlled at 25 kHz.

[0070] (3) Electromagnetic pulse assisted zone melting and purification: The furnace cavity of the electromagnetic pulse zone melting furnace is evacuated to a pressure <10 ℃. -4 To control the pressure in the electromagnetic pulse zone melting furnace to be one order of magnitude lower than the pressure in the ultrasonic vacuum distillation furnace, open the control valve and use the pressure difference between the ultrasonic vacuum distillation furnace and the electromagnetic pulse zone melting furnace to introduce the distilled and purified molten indium into the zone melting tube; close the control valve to maintain the pressure in the electromagnetic pulse zone melting furnace <10 Pa. -4 After the molten indium in the zone melting tube cools and solidifies, an indium rod is obtained. The indium rod is then zone-melted by reciprocating induction coils and using pulsed current, with the melting temperature controlled at 180°C. Impurities (mainly Sn, Pb, and Fe) are concentrated at the end of the indium rod. After cooling and solidification, the end of the indium rod containing the impurities is cut off, with a cut length of 1-2 cm, to obtain a high-purity indium product.

[0071] In this step, when using pulsed current to perform zone melting on indium rods, the peak pulse current is controlled to be 1000 A, the pulse frequency is 1 Hz, the moving speed of the induction coil is controlled to be 4 mm / min, and the number of times the induction coil is moved back and forth is controlled to be 20 times.

[0072] (4) Product collection: High-purity indium products are collected under the protection of high-purity argon gas.

[0073] The high-purity indium product prepared in this example was analyzed for all elemental impurities using atomic glow discharge mass spectrometry (GDMS). The results showed that the product purity was 99.9998%, with impurity elements Pb≤0.15 ppm, Sn≤0.2 ppm, Cd≤0.04 ppm, Zn≤0.01 ppm, Fe≤0.08 ppm, and oxygen content≤1.2 ppm.

Claims

1. A method for preparing high-purity indium based on ultrasonic vacuum distillation-electromagnetic pulse zone melting, characterized in that, Includes the following steps: (1) Device setup: The condenser receiver of the secondary condensation zone of the ultrasonic vacuum distillation furnace is connected to the zone melting tube in the electromagnetic pulse zone melting furnace through a high-temperature resistant pipe fitting. The inlet end of the high-temperature resistant pipe fitting is connected to the condenser receiver, and the outlet end of the high-temperature resistant pipe fitting is connected to the zone melting tube. A control valve is installed on the high-temperature resistant pipe fitting. The heating zone of the ultrasonic vacuum distillation furnace is equipped with an ultrasonic system. (2) Ultrasonic-assisted vacuum distillation purification: Close the control valve, add raw material indium to the crucible of the ultrasonic vacuum distillation furnace under the protection of high-purity inert gas, and evacuate the ultrasonic vacuum distillation furnace until the pressure inside the furnace is <10. -3 Pa, the raw material crucible is heated to 1200~1300℃ and kept at that temperature. During the heat preservation distillation process, ultrasonic waves are applied to disturb the molten indium in the raw material crucible. The steam generated during the heat preservation distillation process continuously enters the first and second condensation zones of the ultrasonic vacuum distillation furnace. The molten indium purified by vacuum distillation is collected in the first condensation zone with a condensation temperature of 900~1000℃, and low-boiling-point impurities are removed in the second condensation zone with a condensation temperature of 500~600℃. In this step, the purity of the raw material indium is at the 3N level, and the pressure inside the ultrasonic vacuum distillation furnace is controlled to be <10 during the heating and heat preservation distillation process. -3 Pa; (3) Electromagnetic pulse assisted zone melting and purification: The electromagnetic pulse zone melting furnace is evacuated until the furnace pressure is <10. -4 To control the pressure in the electromagnetic pulse zone melting furnace to be lower than the pressure in the ultrasonic vacuum distillation furnace, open the control valve and introduce the molten indium purified by vacuum distillation into the zone melting tube through a high-temperature resistant pipe; close the control valve to maintain the pressure in the electromagnetic pulse zone melting furnace <10 Pa. -4 Pa, after the molten indium in the zone melting tube cools and solidifies, an indium rod is obtained. The indium rod is then zone-melted by reciprocating induction coil and using pulse current. The temperature of the molten zone is controlled at 180~200℃, and impurities are concentrated at the end of the indium rod. After cooling and solidification, the end of the indium rod with impurities concentrated is cut off to obtain a high-purity indium product. (4) Product collection: High-purity indium product is collected under the protection of high-purity inert gas. The purity of the high-purity indium product is ≥99.9995% and the oxygen content is ≤2 ppm.

2. The method for preparing high-purity indium based on ultrasonic vacuum distillation-electromagnetic pulse zone melting according to claim 1, characterized in that, In step (3), when using pulsed current to perform zone melting on indium rods, the peak pulse current is controlled to be 1000 A and the pulse frequency is 1 Hz.

3. The method for preparing high-purity indium based on ultrasonic vacuum distillation-electromagnetic pulse zone melting according to claim 1, characterized in that, In step (3), the moving speed of the induction coil is controlled to be 3~4 mm / min.

4. The method for preparing high-purity indium based on ultrasonic vacuum distillation-electromagnetic pulse zone melting according to claim 1, characterized in that, In step (3), the number of times the induction coil is moved back and forth is controlled is 10 to 20 times.

5. The method for preparing high-purity indium based on ultrasonic vacuum distillation-electromagnetic pulse zone melting according to any one of claims 1 to 4, characterized in that, The frequency of the ultrasonic waves applied in step (2) is 20~30 KHz.

6. The method for preparing high-purity indium based on ultrasonic vacuum distillation-electromagnetic pulse zone melting according to any one of claims 1 to 4, characterized in that, In step (2), the time for heat preservation and distillation is controlled to be 1~2 h.

7. The method for preparing high-purity indium based on ultrasonic vacuum distillation-electromagnetic pulse zone melting according to any one of claims 1 to 4, characterized in that, In step (3), the pressure in the electromagnetic pulse zone melting furnace is controlled to be at least one order of magnitude lower than the pressure in the ultrasonic vacuum distillation furnace.

8. The method for preparing high-purity indium based on ultrasonic vacuum distillation-electromagnetic pulse zone melting according to any one of claims 1 to 4, characterized in that, The raw material crucible, condenser receiver, and zone melting tube are made of high-purity quartz or high-purity graphite.

9. The method for preparing high-purity indium based on ultrasonic vacuum distillation-electromagnetic pulse zone melting according to any one of claims 1 to 4, characterized in that, The control valve is located outside the ultrasonic vacuum distillation furnace and the electromagnetic pulse zone melting furnace.

10. The method for preparing high-purity indium based on ultrasonic vacuum distillation-electromagnetic pulse zone melting according to any one of claims 1 to 4, characterized in that, High-purity inert gases include high-purity argon.

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