Method for preparing high-purity indium by adopting vacuum purification and directional crystallization

Abstract

The invention discloses a method for preparing high-purity indium by adopting vacuum purification and directional crystallization, which comprises the following steps of: purifying crude indium into 6N-grade indium by using a vacuum furnace with a built-in special-shaped distillation condensing device, and then preparing the 6N-grade indium into 7N-grade high-purity indium by using a directional crystallization furnace. The lower graphite cylinder (2) and the upper graphite cylinder (4) are internally provided with a graphite crucible (3), the special-shaped crucible support (5) and the quartz crucible (6) are arranged at the bottom of the upper graphite cylinder, the graphite gas guide cylinder (7) is arranged on the upper graphite cylinder and provided with a graphite top cover (8) and a funnel-shaped cylinder bottom, and the quartz plate (9) is contained in the graphite gas guide cylinder. According to the method, the ultra-pure indium with the purity larger than 99.99999% is efficiently prepared, the product quality is stable, the needed equipment investment is small, and the production process is stable and reliable.

Description

Technical Field

[0001] The present invention relates to the technical field of high-purity metal preparation, and particularly to a method for preparing 7N-grade high-purity indium. Background Art

[0002] High-purity indium with a purity above 6N is a key basic material for semiconductors, mainly used for preparing semiconductor compounds such as indium phosphide, indium antimonide, and indium arsenide. The existing methods for preparing high-purity indium are mainly divided into two categories: chemical methods and physical methods. To prepare high-purity indium with a purity above 6N, generally, chemical methods and physical methods are used in combination to achieve the purification purpose. Commonly used chemical methods include extraction method, ion exchange method, electrolysis method, etc. Chemical methods have main problems such as difficult waste liquid purification, long process flow, and high treatment cost. Physical methods mainly include vacuum distillation method, directional crystallization method, zone melting method, etc. Physical methods have the advantages of short process flow, low consumption, and no pollution to the environment. Among them, the vacuum distillation method is widely used. The principle of purifying indium by the vacuum distillation method is to utilize the difference in the saturated vapor pressures of various impurity metals in crude indium. Metals with a large saturated vapor pressure preferentially volatilize into the gas phase. By controlling the distillation temperature, pressure, and heat preservation time, various impurity metals volatilize selectively and are enriched in the volatilized gas phase or the remaining liquid phase to achieve the purification purpose. Vacuum distillation can effectively reduce the impurity content in indium. After two distillations, 6N-grade high-purity indium can be prepared from 4N-5N-grade crude indium. However, since the production process requires stopping the furnace to take materials and then performing secondary distillation, impurities are easily introduced. The saturated vapor pressures of In and Sn are similar, and it is difficult to control the two-distillation process. The separation effect of In and Sn is poor, and the product quality is unstable. It is difficult to obtain high-purity indium with stable quality by using it alone. The essence of the directional crystallization method is that there is a difference in the equilibrium concentrations of impurities in the solid phase and the liquid phase. During the melting and solidification processes, impurities segregate into the solid phase or the liquid phase, thereby purifying the main metal. This method has no pollution during the process, high product purity, and can obtain single crystals with uniform composition. The efficiency of separating impurities by the directional crystallization method depends on the distribution coefficient k. Impurities with k>1 are distributed at the top of the grown crystal, impurities with k<1 remain in the melt, and impurities with a k value close to 1 are not easily removed by the directional crystallization method and need to be combined with other methods to remove impurities. Summary of the Invention

[0003] The purpose of the present invention is to provide a method for preparing 7N-grade high-purity indium with stable product quality and green environmental protection by combining vacuum purification and directional crystallization to prepare high-purity indium.

[0004] The technical solution adopted by the present invention is as follows: A method for preparing high-purity indium by combining vacuum purification and directional crystallization. First, use a vacuum furnace to purify crude indium into 6N-grade indium, and then use a directional crystallization furnace to prepare 6N-grade indium into 7N-grade high-purity indium; The vacuum furnace includes a furnace body and a special-shaped distillation and condensation device disposed in the furnace cavity. The special-shaped distillation and condensation device includes a lower graphite cylinder, a graphite crucible disposed in the inner cavity of the lower graphite cylinder, an upper graphite cylinder disposed on the lower graphite cylinder, a special-shaped crucible support disposed at the bottom of the upper graphite cylinder, a quartz crucible placed on the special-shaped crucible support, a graphite gas guide cylinder disposed on the upper graphite cylinder and having a graphite top cover and a funnel-shaped bottom cylinder, and quartz wafers contained in the graphite gas guide cylinder; heat insulation layers are respectively provided at the joint surface between the lower graphite cylinder and the upper graphite cylinder and at the joint surface between the upper graphite cylinder and the graphite gas guide cylinder. The special-shaped crucible support is composed of a cylindrical section and a conical section. The top surface of the cylindrical section is a hemispherical concave surface, and the bottom surface of the conical section is a conical surface with the cone tip downward. Radially arranged support beams are provided on the outer periphery of the lower end of the cylindrical section; the support beams are placed on the top of the upper graphite cylinder. The method for preparing high-purity indium is as follows: Put the crude indium in the graphite crucible, turn on the vacuum pump of the controlled vacuum furnace, and control the pressure in the furnace at 1x10 -2 ~5x10 -1 Pa. Set the temperature control program in the furnace. The area where the lower graphite cylinder is located is the lower temperature zone, and the temperature is controlled at 1150~1250°C. The area where the upper graphite cylinder is located is the upper temperature zone, and the temperature is controlled at 900~950°C. Then heat up, control the heating rate of the lower temperature zone and the upper temperature zone at 10-15°C / min. After heating to the end point, keep the temperature. The crude indium in the graphite crucible is distilled and vaporized and rises through the special-shaped crucible support and the upper graphite cylinder, enters the graphite gas guide cylinder, condenses into indium droplets on the quartz wafers, and then drips into the quartz crucible through the funnel-shaped bottom cylinder to obtain 6N-grade indium; after the indium droplets have dripped, stop keeping the temperature. After the temperature in the furnace drops to room temperature, turn off the vacuum pump, take out the quartz crucible, transfer the 6N-grade indium obtained by distillation into the rotating crucible of the directional crystallization furnace and continue to carry out directional crystallization purification. Control the pressure in the furnace of the directional crystallization furnace at 1x10 -3 ~5x10 -2 Pa, heat and melt the indium, the heating temperature is 550-600°C, the heating rate is 10-15°C / min. After the indium is completely melted and the bubbles are removed, cool down. Skim the oxidized slag at 210~230°C, insert an indium seed crystal with a purity greater than 99.99999% into the surface of the melt at 160-180°C for melt-induced crystal growth. Control the pulling speed at 30~40mm / h, the crystal rotation at 5~10rmp, and the crucible rotation at 8~10rmp. Stop pulling when the crystal grows to the required length, lower the rotating crucible to complete the finishing. After the temperature in the furnace drops to room temperature, open the furnace and take out the material, remove the impurities with k>1 distributed at the top of the grown crystal and the impurities with k<1 remaining in the melt to obtain ultra-high purity indium with a purity greater than 99.99999%.

[0005] Furthermore, the top surface of the lower graphite cylinder and the bottom surface of the upper graphite cylinder are respectively provided with mutually fitting stepped surfaces, and the top surface of the upper graphite cylinder and the bottom surface of the graphite gas guide cylinder are also respectively provided with mutually fitting stepped surfaces.

[0006] Furthermore, the support beams of the special-shaped crucible support are arranged in a cross shape; the inner cavity of the lower graphite cylinder is a rectangular inner cavity, and a groove for placing the support beams is provided at the top of the rectangular inner cavity.

[0007] Furthermore, the quartz crucible is a high-purity quartz crucible, the graphite crucible is a high-purity isostatic graphite crucible, the graphite gas guide cylinder is a high-purity isostatic graphite gas guide cylinder, the lower graphite cylinder is a high-purity isostatic graphite cylinder, the upper graphite cylinder is a high-purity isostatic graphite cylinder, and the graphite top cover is a high-purity graphite top cover.

[0008] The present invention provides a method for jointly preparing ultra-high purity indium with high reliability. The crude indium is subjected to a first vacuum distillation. By utilizing the difference in saturated vapor pressures between indium and other impurity elements, the vaporized indium is condensed and collected in a low-temperature zone of 900 - 950°C. High-boiling-point impurities such as Fe, Ag, Ni, and Sn remain in the high-temperature zone of 1150 - 1250°C, and low-boiling-point impurities such as Pb and Tl do not condense in the low-temperature zone and are discharged with the vacuum system. The collected material meets the 6N requirement, effectively removing impurities such as Pb, Sn, and Tl with a separation coefficient k of approximately 1. After removing most of the impurities, the obtained 6N-grade material is then sent into a directional crystallization furnace for directional crystallization to remove impurities with k > 1 at the top of the grown crystal and impurities with k < 1 remaining in the melt, and the middle section of the crystal is retained, which is ultra-high purity indium with a purity greater than 99.99999%.

[0009] The present invention combines the advantages of the vacuum distillation method and the directional crystallization method, fully utilizes the characteristics of the vacuum distillation process, such as short process flow, easy automation, and environmental friendliness, and also utilizes the advantage of high product stability and high purity of the directional crystallization method to efficiently prepare ultra-high purity indium with a purity greater than 99.99999%, where Si ≤ 0.05 ppm, Ti ≤ 0.005 ppm, Bi ≤ 0.01 ppm, and the product quality is stable, effectively removing impurity elements and meeting the requirements of the semiconductor industry. The method of the present invention requires less equipment investment, has a short process flow and is easy to control, and the production process is stable and reliable. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 is a schematic diagram of the vacuum furnace used in the present invention; Figure 2 is a schematic diagram of the special-shaped distillation and condensation device; Figure 3 is a schematic diagram showing the splicing of the lower graphite cylinder, the upper graphite cylinder, and the graphite gas guide cylinder of the special-shaped distillation and condensation device; Figure 4It is a top view of the special-shaped crucible support. Specific implementation mode

[0011] The content of the present invention will be further elaborated below in conjunction with the accompanying drawings of the specification.

[0012] A method for preparing high-purity indium by vacuum purification and directional crystallization. First, the crude indium is purified to 6N-grade indium by a vacuum furnace, and then the 6N-grade indium is prepared into 7N-grade high-purity indium by a directional crystallization furnace.

[0013] The vacuum furnace is as Figure 1 shown, and includes a furnace body 1 and a special-shaped distillation and condensation device arranged in the furnace cavity. The special-shaped distillation and condensation device is as Figure 1 , Figure 2 shown, and includes a lower graphite cylinder 2, a graphite crucible 3 arranged in the inner cavity of the lower graphite cylinder, an upper graphite cylinder 4 arranged on the lower graphite cylinder, a special-shaped crucible support 5 arranged at the bottom of the upper graphite cylinder, a quartz crucible 6 placed on the special-shaped crucible support, a graphite air guide cylinder 7 arranged on the upper graphite cylinder and having a graphite top cover 8 and a funnel-shaped bottom, and a quartz sheet 9 contained in the graphite air guide cylinder 7. Heat insulation layers are respectively arranged at the connection surfaces of the lower graphite cylinder 2 and the upper graphite cylinder 4, and at the connection surface of the upper graphite cylinder 4 and the graphite air guide cylinder 7.

[0014] The special-shaped crucible support 5 is composed of a cylindrical section and a conical section. The top surface of the cylindrical section is a hemispherical concave surface, the bottom surface of the conical section is a conical surface with the cone tip downward, and radial support beams 5a are arranged around the lower end of the cylindrical section; the support beams are placed on the top of the upper graphite cylinder.

[0015] In order to ensure the sealing performance of the special-shaped distillation and condensation device, as Figure 3 shown, mutually matching step surfaces M are respectively arranged on the top surface of the lower graphite cylinder 2 and the bottom surface of the upper graphite cylinder 4, and mutually matching step surfaces M are also respectively arranged on the top surface of the upper graphite cylinder 4 and the bottom surface of the graphite air guide cylinder 7, so that the upper graphite cylinder 4 can be stably placed on the lower graphite cylinder 2, and the graphite air guide cylinder 7 can also be stably placed on the upper graphite cylinder 4. Heat insulation materials are arranged on the matching surfaces of the upper graphite cylinder 4 and the lower graphite cylinder 2, and heat insulation materials are also arranged on the matching surfaces of the graphite air guide cylinder 7 and the upper graphite cylinder 4, which not only play a heat insulation role but also play a sealing role.

[0016] As a preferred embodiment, the support beams 5a of the special-shaped crucible support 5 are arranged in a cross shape, as Figure 4 shown. The inner cavity of the lower graphite cylinder 2 is a rectangular inner cavity, and a groove 2a for placing the support beams 5a is arranged at the top of the rectangular inner cavity, as shown in Figure 3 .

[0017] To ensure the purity and quality of the prepared high-purity indium, the quartz crucible 6 is a high-purity quartz crucible, the graphite crucible 3 is a high-purity isostatic graphite crucible, the graphite gas guide cylinder 7 is a high-purity isostatic graphite gas guide cylinder, the upper graphite cylinder 4 is a high-purity isostatic graphite cylinder, the lower graphite cylinder 2 is a high-purity isostatic graphite cylinder, and the graphite top cover 8 is a high-purity graphite top cover. The high-purity quartz crucible is made of high-purity quartz material, the high-purity isostatic graphite crucible, the high-purity isostatic graphite gas guide cylinder, and the high-purity isostatic graphite cylinder are all made of high-purity isostatic graphite, and the high-purity graphite top cover is made of high-purity graphite. The high-purity quartz crucible, the high-purity isostatic graphite crucible, the high-purity isostatic graphite gas guide cylinder, the high-purity isostatic graphite cylinder, and the high-purity graphite top cover are all purchased components. Requirements are put forward for the production materials. Only by using high-purity materials can the required high-purity indium be ensured. The standard of the high-purity quartz material used for the high-purity quartz crucible is DB43T 1167-2016). The high-purity isostatic graphite crucible, the high-purity isostatic graphite gas guide cylinder, the high-purity isostatic graphite cylinder, and the high-purity graphite top cover are all made of high-purity graphite material, and the material use standard is JB / T2750-2020.

[0018] The method for preparing high-purity indium is as follows: Open the furnace cover 1b of the vacuum furnace 1, place the crude indium in the graphite crucible 3, and after assembling the special-shaped distillation and condensation device, place it into the vacuum furnace. The vacuum furnace is equipped with two heating zones, which are independently controlled by PID. Turn on the vacuum pump 1a of the control vacuum furnace, and control the pressure in the furnace to be 1x10 -2 ~5x10 -1 Pa, set the temperature control program in the furnace. The area where the lower graphite cylinder 2 is located is the lower temperature zone, which is also the raw material zone, and the temperature is controlled at 1150~1250°C. The area where the upper graphite cylinder 4 is located is the upper temperature zone, which is also the distillation material collection zone, and the temperature is controlled at 900~950°C. Then heat up, control the heating rate of the lower temperature zone and the upper temperature zone at 10-15°C / min. After heating to the end point, keep it warm. The crude indium in the graphite crucible is distilled and vaporized and rises through the gaps between the support beams of the special-shaped crucible support 5, passes through the upper graphite cylinder 4 and enters the graphite gas guide cylinder 7. The area where the graphite gas guide cylinder is located is the condensation zone. The distilled vaporized matter condenses into indium liquid droplets on the quartz sheet 9 and then drips into the quartz crucible 6 through the funnel-shaped bottom of the cylinder, obtaining 6N-grade indium. The lower graphite cylinder 2, the special-shaped crucible support 5, and the upper graphite cylinder 4 are in different temperature zones, and the graphite gas guide cylinder 7 is not in the heating zone, so as to realize the separation of indium and other metal elements. After the indium liquid droplets have dripped, stop keeping warm. After the temperature in the furnace drops to room temperature, turn off the vacuum pump, take out the quartz crucible 6, transfer the 6N-grade indium obtained by distillation into the rotating crucible of the directional crystallization furnace and continue to carry out directional crystallization purification. Control the pressure in the furnace of the directional crystallization furnace to be 1x10 -3 ~5x10 -2Pa, heat and melt indium at a heating temperature of 550 - 600 °C and a heating rate of 10 - 15 °C / min. After indium is completely melted and bubbles are removed, cool it down. Skim off the oxidation slag at 210 - 230 °C. Insert an indium seed crystal with a purity greater than 99.99999% into the surface of the melt at 160 - 180 °C for melt-induced crystal growth. Control the pulling speed at 30 - 40 mm / h, the crystal rotation at 5 - 10 rmp, and the crucible rotation at 8 - 10 rmp. Stop pulling when the crystal grows to the required length, lower and rotate the crucible to complete the finishing. After the temperature in the furnace drops to room temperature, open the furnace to take out the material, remove the impurities with k > 1 distributed at the top of the grown crystal and the impurities with k < 1 remaining in the melt, and obtain ultra-high purity indium with a purity greater than 99.99999%.

[0019] Both the vacuum furnace and the directional crystallization furnace described in the present invention can adopt existing technical equipment. The operating methods of the vacuum furnace and the directional crystallization furnace are known to those skilled in the art.

[0020] Example 1 Put the crude indium into the graphite crucible 3 in the lower temperature zone of the vacuum furnace, and control the pressure in the furnace at 5×10 -1 Pa, the temperature in the lower temperature zone is 1200 °C, the temperature in the upper temperature zone is 900 °C, and the heating rates in the lower temperature zone and the upper temperature zone are 10 °C / min. After heating to the end point, keep it warm for 480 min. The crude indium in the graphite crucible is heated, distilled, and sublimated, rises into the graphite gas guide cylinder 7, and forms indium liquid droplets after condensation and drops into the quartz crucible 6 to obtain 6N grade high-purity indium. Transfer the high-purity indium obtained by distillation into the rotating crucible of the directional crystallization furnace, set the pressure in the furnace at 1×10 -3 Pa, heat and melt it at 600 °C with a heating rate of 10 °C / min. After complete melting and bubble removal, cool it down. Skim off the oxidation slag at about 210 °C, start crystal growth at 180 °C, set the pulling speed for crystal growth at 30 mm / h, the crystal rotation at 5 rmp, and the crucible rotation at 8 rmp. Stop pulling when the crystal grows to the required length, lower the crucible to complete the finishing. After cooling to room temperature, open the furnace to take out the material, remove the impurities with k > 1 distributed at the top of the grown crystal and the impurities with k < 1 remaining in the melt, and obtain ultra-high purity indium with a purity greater than 99.99999%, which contains 0.04 ppm of Si, 0.003 ppm of Ti, and 0.008 ppm of Bi.

[0021] Example 2 Put the crude indium into the graphite crucible 3 in the lower temperature zone of the vacuum furnace, and control the pressure in the furnace at 5×10 -1Pa, the temperature of the lower temperature zone is 1250 °C, the temperature of the upper temperature zone is 920 °C, the heating rate of the lower temperature zone and the upper temperature zone is 12 °C / min. After heating to the end point, keep warm for 480 min. The crude indium in the graphite crucible is heated to distill and sublimate, rises into the graphite gas guide cylinder 7, is condensed to form indium liquid droplets and drips into the quartz crucible 6 to obtain 6N grade high-purity indium. Transfer the high-purity indium obtained by distillation into the rotating crucible of the directional crystallization furnace, set the furnace pressure to 1x10 -2 Pa, heat and melt at 550 °C, the heating rate is 15 °C / min. After complete melting and removing bubbles, cool down. Skim off the oxidation slag at about 220 °C, initiate crystal growth at 170 °C, set the pulling speed of crystal initiation to 35 mm / h, crystal rotation speed to 7 rmp, crucible rotation speed to 8 rmp. Stop pulling when the crystal grows to the required length, lower the crucible to complete the finishing. After cooling to room temperature, open the furnace to take out the material, remove the impurities with k>1 distributed at the top of the growing crystal and the impurities with k<1 remaining in the melt to obtain ultra-high purity indium with a purity greater than 99.99999%, containing 0.05 ppm of Si, 0.005 ppm of Ti, and 0.01 ppm of Bi.

[0022] Example 3 Put the crude indium into the graphite crucible 3 in the lower temperature zone of the vacuum furnace, control the furnace pressure to 5x10 -2 Pa, the temperature of the lower temperature zone is 1150 °C, the temperature of the upper temperature zone is 950 °C, the heating rate of the lower temperature zone and the upper temperature zone is 15 °C / min. After heating to the end point, keep warm for 480 min. The crude indium in the graphite crucible is heated to distill and sublimate, rises into the graphite gas guide cylinder 7, is condensed to form indium liquid droplets and drips into the quartz crucible 6 to obtain 6N grade high-purity indium. Transfer the high-purity indium obtained by distillation into the rotating crucible of the directional crystallization furnace, set the furnace pressure to 1x10 -3 Pa, heat and melt at 580 °C, the heating rate is 12 °C / min. After complete melting and removing bubbles, cool down. Skim off the oxidation slag at about 230 °C, initiate crystal growth at 160 °C, set the pulling speed of crystal initiation to 40 mm / h, crystal rotation speed to 10 rmp, crucible rotation speed to 10 rmp. Stop pulling when the crystal grows to the required length, lower the crucible to complete the finishing. After cooling to room temperature, open the furnace to take out the material, remove the impurities with k>1 distributed at the top of the growing crystal and the impurities with k<1 remaining in the melt to obtain ultra-high purity indium with a purity greater than 99.99999%, containing 0.03 ppm of Si, 0.005 ppm of Ti, and 0.005 ppm of Bi.

Claims

1. A method for preparing high-purity indium by vacuum purification and directional crystallization, characterized in that, First, crude indium is purified to 6N-grade indium using a vacuum furnace, and then the 6N-grade indium is prepared into 7N-grade high-purity indium using a directional crystallization furnace; The vacuum furnace includes a furnace body (1) and a special-shaped distillation and condensation device arranged in the furnace cavity. The special-shaped distillation and condensation device includes a lower graphite cylinder (2), a graphite crucible (3) arranged in the inner cavity of the lower graphite cylinder, an upper graphite cylinder (4) arranged on the lower graphite cylinder, a special-shaped crucible support (5) arranged at the bottom of the upper graphite cylinder, a quartz crucible (6) placed on the special-shaped crucible support, a graphite air guide cylinder (7) arranged on the upper graphite cylinder and having a graphite top cover (8) and a funnel-shaped bottom, and a quartz sheet (9) contained in the graphite air guide cylinder (7); heat insulation layers are respectively arranged at the connection surfaces of the lower graphite cylinder (2) and the upper graphite cylinder (4), and the upper graphite cylinder (4) and the graphite air guide cylinder (7). The special-shaped crucible support (5) is composed of a cylindrical section and a conical section. The top surface of the cylindrical section is a hemispherical concave surface, and the bottom surface of the conical section is a conical surface with the cone tip downward. Radially arranged support beams (5a) are provided at the outer periphery of the lower end of the cylindrical section; the support beams are placed on the top of the upper graphite cylinder. The method for preparing high-purity indium is as follows: Put the crude indium in the graphite crucible (3), turn on the vacuum pump of the controlled vacuum furnace, and control the pressure in the furnace at 1x10 -2 ~5x10 - 1 Pa. Set the temperature control program in the furnace. The area where the lower graphite cylinder is located is the lower temperature zone, and the temperature is controlled at 1150~1250°C. The area where the upper graphite cylinder is located is the upper temperature zone, and the temperature is controlled at 900~950°C. Then heat up, control the heating rate of the lower temperature zone and the upper temperature zone at 10-15°C / min. After heating to the end point, keep the temperature. The crude indium in the graphite crucible is distilled and vaporized, rises and passes through the special-shaped crucible support (5) and the upper graphite cylinder (4), enters the graphite gas guide cylinder (7), condenses into indium droplets on the quartz sheet (9), and then drops into the quartz crucible (6) through the funnel-shaped bottom of the cylinder to obtain 6N-grade indium; after the indium droplets have dropped, stop keeping the temperature. After the temperature in the furnace drops to room temperature, turn off the vacuum pump, take out the quartz crucible, transfer the 6N-grade indium obtained by distillation into the rotating crucible of the directional crystallization furnace and continue to carry out directional crystallization purification. Control the pressure in the furnace of the directional crystallization furnace at 1x10 -3 ~5x10 -2 Pa, heat and melt the indium, the heating temperature is 550-600°C, the heating rate is 10-15°C / min. After the indium is completely melted and the bubbles are removed, cool down. Remove the oxidation slag at 210~230°C, insert an indium seed crystal with a purity greater than 99.99999% into the surface of the melt at 160-180°C for melt-joining and crystal pulling. Control the pulling speed at 30~40mm / h, the crystal rotation at 5~10rmp, and the crucible rotation at 8~10rmp. Stop pulling when the crystal grows to the required length, lower the rotating crucible to complete the finishing. After the temperature in the furnace drops to room temperature, open the furnace and take out the material, remove the impurities with k>1 distributed at the top of the growing crystal and the impurities with k<1 remaining in the melt to obtain ultra-high purity indium with a purity greater than 99.99999%.

2. The method for preparing high-purity indium by vacuum purification and directional crystallization according to claim 1, wherein Mutually fitting stepped surfaces are respectively arranged on the top surface of the lower graphite cylinder (2) and the bottom surface of the upper graphite cylinder (4), and mutually fitting stepped surfaces are also respectively arranged on the top surface of the upper graphite cylinder (4) and the bottom surface of the graphite air guide cylinder (7).

3. The method for preparing high-purity indium by vacuum purification and directional crystallization according to claim 1 or 2, characterized in that, The support beams (5a) of the special-shaped crucible support (5) are arranged in a cross shape; the inner cavity of the lower graphite cylinder (2) is a rectangular inner cavity, and a groove (2a) for placing the support beams (5a) is arranged at the top of the rectangular inner cavity.

4. The method for preparing high-purity indium by vacuum purification and directional crystallization according to claim 1 or 2, characterized in that, The quartz crucible (6) is a high-purity quartz crucible, the graphite crucible (3) is a high-purity isostatic graphite crucible, the graphite air guide cylinder (7) is a high-purity isostatic graphite air guide cylinder, the lower graphite cylinder (2) is a high-purity isostatic graphite cylinder, the upper graphite cylinder (4) is a high-purity isostatic graphite cylinder, and the graphite top cover (8) is a high-purity graphite top cover.

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