Device and method for preparing high-purity tellurium by directional solidification

Abstract

The application discloses a device and a method for preparing high-purity tellurium by directional solidification. The device comprises a furnace body, a gas supply device, a charging device and a tail gas treatment device. The furnace body is arranged outside the charging device. The gas supply device and the tail gas treatment device are connected to two ends of the charging device through gas valves and gas pipelines respectively. The furnace body comprises a plurality of heaters which are arranged in parallel along the length direction of the charging device. The width of each heater is 100-150 mm. The transverse parallel spacing of each heater is 5.0-10 mm. The 5N tellurium ingot is used as the raw material. The tellurium is purified by using a directional solidification technology. The impurities can be fully diffused in the molten liquid phase. The impurity migration efficiency is improved. The purification period is shortened. The 6N high-purity tellurium is prepared.

Description

Technical Field

[0001] This invention belongs to the field of tellurium purification, and particularly relates to an apparatus and method for preparing tellurium by directional solidification. Background Technology

[0002] Tellurium possesses a wide bandgap and excellent semiconductor properties, making it widely used in semiconductors, 5G electronic communications, and other fields. For example, CdTe is an important solar cell material, HgCdTe, ZnCdTe, and PbSnTe are important materials for infrared detection research, and BiTe and PbTe are excellent cooling materials. Trace impurities in tellurium directly affect material properties. For instance, in CdTe, impurities can induce point defects, thus affecting the heat treatment process of CdTe and reducing its bandgap, thereby lowering the photoelectric conversion efficiency of the absorption layer. Therefore, tellurium purification is of great significance.

[0003] The higher the purity of tellurium, the better its physicochemical properties, but the more difficult its preparation. Currently, the market demand for tellurium purity of 6N and above has reached this level. Existing tellurium purification technologies mainly include chemical and physical methods. Chemical purification primarily uses electrolysis, while physical purification mainly uses vacuum distillation and zone melting. Electrolysis is difficult to produce high-purity tellurium of 5N and above, and the impurity removal process before electrolysis is complex and the production process is lengthy. Vacuum distillation requires multiple distillations to produce high-purity tellurium of 5N-6N, resulting in low production efficiency and high energy consumption.

[0004] Zone melting can prepare tellurium with a purity of 7N and above, but the impurity migration process in existing methods is slow and inefficient. Furthermore, there are two types of difficult-to-remove impurities during the preparation of high-purity tellurium: one type consists of impurities with vapor pressures close to that of tellurium, such as S, As, Na, and Se, which are difficult to remove using vacuum distillation; the other type consists of impurities with a partition coefficient (k0 = C). s / C l k0 represents the equilibrium distribution coefficient, C s C represents the equilibrium concentration of impurities in the tellurium solid phase. l Impurities whose equilibrium concentration is close to 1 (representing the concentration of impurities in the tellurium solid phase) are such as impurities Se, S, Si, etc. These impurities are difficult to remove by zone melting technology.

[0005] Chinese patent CN101892496A discloses a method for preparing 5N high-purity tellurium using 3N crude tellurium as raw material. This method first prepares a crude tellurium anode using 3N crude tellurium, then prepares an electrolyte using tellurium dioxide, and finally electrolyzes and refines the tellurium in an alkaline electrolytic cell using a titanium plate as the cathode for 3-5 days to obtain 5N tellurium. The electrolytic preparation of high-purity tellurium requires wet pretreatment of the raw materials, which is a lengthy, cumbersome process with high reagent consumption, a high risk of contamination, and relatively low current efficiency.

[0006] Chinese invention patent CN107313063A discloses a method for smelting 5N high-purity tellurium. This method first prepares 4N tellurium using a low-current-density electrodeposition method, then performs low-temperature vacuum distillation on the 4N tellurium ingot to produce distilled tellurium. Finally, the distilled tellurium is crushed into small particles and heated under a hydrogen flow to cast ingots, yielding 5N high-purity tellurium. Chinese invention patent CN107585745A discloses a 5N tellurium production process. This method significantly reduces the content of some impurities in the raw materials through screening or pretreatment, significantly reducing the content of difficult-to-separate impurities. Vacuum distillation, hydrogenation to reduce selenium, and medium-frequency casting are then performed to obtain 5N high-purity tellurium. Using the above technical solutions results in a long production cycle, low production efficiency, cumbersome process flow, and difficulty in obtaining 6N grade tellurium.

[0007] Therefore, there is currently a lack of a device and scheme for preparing high-purity tellurium that can efficiently produce 6N and above high-purity tellurium. Summary of the Invention

[0008] The technical problem to be solved by the present invention is that the existing high-purity tellurium technology has a long production cycle, low production efficiency, and complicated process. To overcome the shortcomings and defects mentioned in the background technology, the present invention provides an apparatus and preparation method for preparing high-purity tellurium by directional solidification.

[0009] To solve the above-mentioned technical problems, the technical solution proposed by this invention is as follows:

[0010] An apparatus for preparing high-purity tellurium by directional solidification is characterized in that the apparatus comprises a furnace body, a gas supply device, a charging device, and a tail gas treatment device; the furnace body is disposed outside the charging device, and the gas supply device and the tail gas treatment device are respectively connected to both ends of the charging device via gas valves and gas pipelines; the gas supply device comprises an inert gas cylinder and a hydrogen cylinder; the tail gas treatment device comprises a dust removal system and a hydrogen ignition device.

[0011] The furnace body includes multiple heaters arranged side by side along the length of the charging device. Each heater is 100-150mm wide and the lateral spacing between each heater is 5.0-10mm.

[0012] The directional solidification process requires very strict temperature control. If the temperature is too high or too low, or if it is not controlled in time, the purity of the prepared material will decrease. Furthermore, the temperature control conditions required for directional solidification vary for different materials.

[0013] This application employs multiple heaters for independent temperature control, which enables more precise temperature control and achieves energy saving. Specifically, during the directional solidification process, when the end heater moves to the end of the graphite boat, it can be turned off to save energy.

[0014] Considering the temperature control effect, a wider heater is not conducive to controlling the temperature at both ends of the tellurium rod, while a narrower heater is conducive to segmented temperature control, thereby controlling a relatively flat solidification interface and improving the efficiency of impurity removal; however, a heater that is too narrow will complicate the equipment. On the other hand, if the parallel spacing is too short, the temperature zones of two adjacent heaters will overlap too much, and if the spacing is too wide, the temperature gradient at the gap will be too large, affecting the temperature control accuracy of the device.

[0015] Therefore, in order to meet the demand for directional solidification of high-purity tellurium, this application sets the width of the heater to 100-150 mm and the lateral spacing between each heater to 5.0-10 mm, which can significantly improve the temperature control effect of the device and thus prepare tellurium products with high purity.

[0016] The gas supply device is used to deliver inert gases, including nitrogen or argon, and reducing gases, including hydrogen, to assist in the removal of Se / S impurities during directional solidification.

[0017] The exhaust gas treatment section is mainly used to treat the volatilized metal dust and unreacted hydrogen. The dust removal system contains asbestos, glycerin, etc.

[0018] Preferably, a mobile trolley is provided below the furnace body to carry the furnace body and move it along the length of the loading device. The furnace body is also connected to a control power supply to control the switching on and off of multiple heaters, the heating and cooling programs, and the moving speed of the mobile trolley.

[0019] More preferably, the furnace body includes five heaters, namely heater 1#, heater 2#, heater 3#, heater 4# and heater 5#, and each heater can achieve individual temperature control.

[0020] Preferably, the loading device includes a quartz tube, a sealing valve, and a graphite boat. The two ends of the quartz tube are provided with sealing valve 1# and sealing valve 2#. The gas supply device and the exhaust gas treatment device are respectively connected to the quartz tube through sealing valve 1# and sealing valve 2#.

[0021] The quartz tube contains a graphite boat, which is loaded with materials. The graphite boat is 500-700 mm long and has a purity requirement of less than 5 ppm ash content.

[0022] Preferably, the gas pipeline is equipped with multiple gas valves, wherein gas valve 1# and gas valve 2# control the inert gas cylinder and the hydrogen cylinder respectively, are connected in parallel through the gas pipeline, and the other end is connected to gas valve 3#, and the other end of gas valve 3# is connected to sealing valve 1#.

[0023] Air valve #4 is located between the dust removal system and sealing valve #2.

[0024] Under the same technical concept, the present invention also provides a method for preparing high-purity tellurium by directional solidification using the aforementioned device, comprising the following steps:

[0025] (1) Crushed tellurium raw material: Take crushed powder and load it into a graphite boat. Adjust the position of the furnace body, introduce inert gas into the quartz tube to drive out the air in the system, and then introduce hydrogen gas to make the hydrogen gas fully diffuse into the entire system. Turn on the heating and keep it warm to melt the material.

[0026] (2) After the heat preservation is completed, hydrogen is continuously introduced to control the heating of the furnace body and carry out directional solidification; after the directional solidification is completed, the heater is turned off to stop heating, the hydrogen is stopped, and then inert gas is introduced to cool down to room temperature.

[0027] (3) Remove the product, cut off the end of the product, and keep the remaining part;

[0028] (4) Use the remaining part as tellurium raw material and repeat steps (1), (2), and (3) 3 to 5 times to obtain high-purity tellurium products.

[0029] Impurities Se and S are difficult to remove during conventional vacuum distillation and zone melting processes. In order to remove impurities from high-purity tellurium, the method of this invention is mainly divided into two steps: the first step is melting the material, and the second step is directional solidification.

[0030] In the first step of the melting stage, tellurium bulk raw material is placed in a graphite boat. There are large gaps between the bulk materials. Before melting, hydrogen gas is introduced to allow the hydrogen gas to fully diffuse throughout the entire system and fill the gaps between the tellurium raw material. During the melting process, hydrogen gas is kept flowing in the quartz tube so that impurities Se and S can fully react with H2 to generate H2Se and H2S gases, which are then discharged with the gas flow, thus achieving the initial removal of impurities Se and S.

[0031] The second step is directional solidification. The principle of impurity removal is that impurity elements segregate between the solid and liquid phases of tellurium. When the solubility of an impurity in the solid phase is greater than that in the liquid phase, the impurity migrates into the solid phase; conversely, it migrates into the liquid phase. Therefore, the degree of impurity segregation in the solid and liquid phases depends not only on the distribution coefficient of the impurity but also primarily on its concentration in the solid-liquid boundary layer. Thus, when using the segregation principle for purification, timely reduction of the impurity concentration at the solid-liquid interface is crucial to the migration rate of impurities in the solid and liquid phases. For metallic tellurium, the distribution coefficient of impurities is less than 1, meaning that impurities migrate into the liquid phase. During directional solidification, there is a sufficiently long liquid phase region, allowing impurities to diffuse better in the molten zone during purification. This dilutes impurities dissolved from the solid phase, reduces the impurity content in the diffusion layer, and improves the migration efficiency of impurities in the diffusion layer, thereby increasing purification efficiency.

[0032] After one purification, impurities accumulate at the end of the tellurium rod. At this point, the impurity-rich area at the end needs to be removed to obtain a front-end product with lower impurity content. However, the product after one purification generally does not meet the high-purity standard, so the front-end product needs to be used as raw material for directional coagulation purification again, repeated 3-5 times to ensure the purification effect.

[0033] Preferably, in step (1), the amount of powder loaded is 500-800g, and it is evenly loaded into the graphite boat to increase the contact area between the tellurium block and hydrogen; when the inert gas is introduced, the inert gas flow rate is adjusted to 0.5-1.0L / min, and the gas introduction time is 60-120min; the introduction of inert gas fully removes the air in the system to prevent residual air from oxidizing the tellurium during the melting process, thereby causing pollution.

[0034] Preferably, when hydrogen is introduced in step (1), the hydrogen flow rate is adjusted to 0.4-0.6 L / min and the gas introduction time is 60-120 min; the hydrogen fully diffuses to all parts of the quartz tube, especially the gaps between the tellurium blocks, so that the hydrogen and the tellurium blocks can fully contact each other, thereby playing a preliminary purification role in the melting process.

[0035] Preferably, the melting temperature in step (1) is 500-700°C and the holding time is 60-90 min.

[0036] After reaching the set temperature, heat preservation is carried out. This allows the tellurium material to melt completely and also helps to further remove volatile impurities from the tellurium.

[0037] Preferably, when hydrogen is continuously introduced in step (2), the hydrogen flow rate is adjusted to 0.1-0.3 L / min; when inert gas is introduced, the inert gas flow rate is adjusted to 0.1-0.3 L / min.

[0038] Preferably, the directional solidification in step (2) specifically involves controlling the furnace body to move along the direction from the front end to the back end of the quartz tube to perform directional solidification, with a moving speed of 5.0 × 10⁻⁶. -6 ~1.0×10 -5 m / s, directional solidification temperature is 600~700℃.

[0039] Preferably, stopping heating after directional solidification is completed specifically involves: when the furnace body moves along the direction from the front end to the end of the quartz tube, multiple heaters arranged horizontally in parallel in the furnace body move sequentially to the end of the graphite boat, and the heaters are turned off sequentially according to the order in which they reach the end of the graphite boat.

[0040] Turning off the heater in time can achieve energy saving. In addition, since the tellurium with a high content of volatile impurities volatilized during the melting and directional solidification process condenses and adheres to the back end of the quartz tube, if the heater is not turned off in time, this part of the tellurium material may remelt and volatilize, thus causing secondary pollution. Therefore, turning off the heater in time can also prevent pollution.

[0041] Preferably, the purity of the tellurium raw material is 5N or higher, and the length of the tellurium raw material when loaded into the graphite boat is 20-30 mm shorter than the length of the graphite boat; the length of the product end cut off in step (3) is 80-120 mm.

[0042] If the impurity-rich area is not removed and directional solidification purification is carried out directly, impurity back-melting will occur, which will greatly reduce the purification efficiency.

[0043] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0044] (1) This invention uses 5N tellurium ingots as raw materials and adopts a directional solidification technique to purify tellurium, so that impurities can be fully diffused in the molten liquid phase, improve the impurity migration efficiency, shorten the purification cycle, and prepare 6N high-purity tellurium.

[0045] (2) The present invention adopts a coupled directional solidification technology of impurity volatilization-hydrogen reduction-impurity segregation. During the directional solidification process, there is a sufficiently long liquid phase region. During the purification process, impurities can diffuse better in the molten zone, so that the impurities dissolved from the solid phase can be fully diluted, reducing the impurity content in the diffusion layer and improving the migration efficiency of impurities in the diffusion layer, thereby improving the purification efficiency.

[0046] (3) The device provided by the present invention adopts independent temperature control technology of multiple heaters during the directional solidification process. In the process of tellurium purification, it can achieve energy saving on the one hand, and avoid the remelting and volatilization of tellurium condensate with high volatile impurity content attached to the back end of the quartz tube, which would cause secondary pollution, thereby helping to improve the purification efficiency. Attached Figure Description

[0047] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0048] Figure 1 This is a schematic diagram of the apparatus for preparing high-purity tellurium by directional solidification in Embodiment 1 of the present invention;

[0049] The components include: 1. Furnace body; 1-1 to 1-5. Heaters 1# to 5#; 2. Tellurium raw material; 3. Graphite boat; 4. Quartz tube; 5-1. Gas valve 1#; 5-2. Gas valve 2#; 5-3. Gas valve 3#; 5-4. Gas valve 4#; 6. Gas pipeline; 7-1. Sealing valve 1#; 7-2. Sealing valve 2#; 8. Mobile trolley; 9. Inert gas cylinder; 10. Hydrogen cylinder; 11. Equipment support; 12. Control power supply; 13. Dust removal system; 14. Hydrogen ignition device. Detailed Implementation

[0050] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to the accompanying drawings and preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0051] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0052] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0053] Example 1:

[0054] An apparatus for the directional solidification preparation of high-purity tellurium, the structure of which is as follows: Figure 1 As shown;

[0055] The furnace body 1 is located outside the charging device. The gas supply device and the tail gas treatment device are connected to both ends of the charging device through gas valves and gas pipelines 6, respectively. The gas supply device includes an inert gas cylinder 9 and a hydrogen cylinder 10, which are connected in parallel to the charging device through gas valves and gas pipelines 6, respectively. The tail gas treatment device includes a dust removal system 13 and a hydrogen ignition device 14 connected in series. The dust removal system 13 contains asbestos and glycerin.

[0056] Inside the furnace body 1, heaters 1#-5# are arranged side by side along the length of the charging device. Each heater is 100-150mm wide and the lateral spacing between each heater is 5.0mm.

[0057] A mobile trolley 8 is provided below the furnace body 1, which carries the furnace body 1 and moves along the length of the charging device. The mobile trolley 8 is set on the equipment support 11. The control power supply 12 controls the switching on and off of multiple heaters, the heating and cooling programs, and the moving speed of the mobile trolley 8.

[0058] The loading device includes a quartz tube 4, sealing valves, and a graphite boat 3. The quartz tube 4 is mounted on the equipment support 11. Sealing valves 1#7-1 and 2#7-2 are installed at both ends of the quartz tube 4. The gas supply device and the exhaust gas treatment device are connected to the quartz tube 4 through sealing valves 1#7-1 and 2#7-2, respectively. The graphite boat 3 is loaded with tellurium raw material 2 and is located inside the quartz tube 4. The graphite boat 3 has a length of 500-700 mm and a purity of less than 5 ppm ash content.

[0059] The exhaust gas treatment section includes a dust removal system 13 and a hydrogen ignition device 14. The dust removal system 13 and the hydrogen ignition device 14 are connected to the sealing valve 2#7-2 in sequence through the gas pipeline 6 and the gas valve 4#5-4.

[0060] Gas valves 1#5-1 and 2#5-2 are connected in parallel via gas pipeline 6 to control the gas supply from inert gas cylinder 9 and hydrogen cylinder 10, respectively. One end of gas valve 3#5-3 is directly connected to sealing valve 1#7-1 via gas pipeline 6 to control the gas entering the loading device, and the other end is connected to gas valves 1#5-1 and 2#5-2 via gas pipeline 6.

[0061] An apparatus for preparing high-purity tellurium by directional solidification, comprising the following steps:

[0062] (1) Molten material:

[0063] a. First, break the 5N tellurium ingot into small pieces to increase the contact area between the tellurium pieces and hydrogen, and then load them evenly into a graphite boat, 600g at a time, and then load the graphite boat into the solidification furnace.

[0064] b. Close the sealing valve, and open the gas valves 5-4, 5-3, and 5-1 in sequence, controlling the gas flow rate to 0.5 L / min and the time to 60 min, to fully expel the air in the system and prevent residual air from oxidizing the tellurium material during the melting process, thereby causing pollution;

[0065] c. Close gas valve 5-1, open gas valve 5-2, control the gas flow rate to 0.4 L / min, and control the time to 60 min;

[0066] d. Turn on the heater and set the temperature to 550℃. After reaching the set temperature, maintain the temperature for 60 minutes.

[0067] (2) Directional solidification:

[0068] a. After the heat preservation period, adjust the hydrogen flow rate to 0.1 L / min and control the furnace body moving speed to 6.0 × 10⁻⁶. -6m / s, directional solidification temperature is 600~700℃; when the end heater (heater 5#) moves to the end of the graphite boat, turn off heater 5#; when heater 4# moves to the end of the graphite boat, turn off heater 4#; the operation of the remaining heaters is carried out in the same way.

[0069] b. After directional solidification, turn off the heater power and hydrogen valve, open the inert gas valve, adjust the flow rate to 0.2 L / min, and cool to room temperature. Remove the tellurium sample, cut off 90 mm from the end of the tellurium sample, and retain the remaining part;

[0070] (3) The remaining part is used as raw material, and the above melting and directional solidification operations are repeated 3 times to obtain the 6N high-purity tellurium product.

[0071] Example 2:

[0072] Example 2 uses the apparatus described in Example 1 and includes the following steps:

[0073] (1) Molten material:

[0074] a. First, break the 5N tellurium ingot into small pieces to increase the contact area between the tellurium pieces and hydrogen, and then load them evenly into a graphite boat, with a load of 580g at a time. Then, load the graphite boat into the solidification furnace.

[0075] b. Close the sealing valve, and open the gas valves 5-4, 5-3, and 5-1 in sequence, controlling the gas flow rate to 0.6 L / min and the time to 80 min, to fully expel the air in the system and prevent residual air from oxidizing the tellurium material during the melting process, thus causing pollution;

[0076] c. Close gas valve 5-1, open gas valve 5-2, control the gas flow rate to 0.4 L / min, and control the time to 80 min;

[0077] d. Turn on the heater and set the temperature to 600℃. After reaching the set temperature, maintain the temperature for 60 minutes.

[0078] (2) Directional solidification:

[0079] a. After the heat preservation period, adjust the hydrogen flow rate to 0.15 L / min and control the furnace body moving speed to 5.0 × 10⁻⁶. -6 m / s, directional solidification temperature is 600~700℃; when the end heater (heater 5) moves to the end of the graphite boat, turn off heater 5; when heater 4 moves to the end of the graphite boat, turn off heater 4, and so on.

[0080] b. After directional solidification, turn off the heater power and hydrogen valve, open the inert gas valve, adjust the flow rate to 0.2 L / min, and cool to room temperature. Remove the tellurium sample, cut off 100 mm from the end of the sample, and retain the remaining portion;

[0081] (3) The remaining part is used as raw material, and the above melting and directional solidification operations are repeated 3 times to obtain the 6N high-purity tellurium product.

[0082] Example 3

[0083] Example 3 uses the apparatus described in Example 1 and includes the following steps:

[0084] (1) Molten material:

[0085] a. First, break the 5N tellurium ingot into small pieces to increase the contact area between the tellurium pieces and hydrogen, and then load them evenly into a graphite boat, with a load of 710g at a time. Then, load the graphite boat into the solidification furnace.

[0086] b. Close the sealing valve, and open the gas valves 5-4, 5-3, and 5-1 in sequence, controlling the gas flow rate to 0.6 L / min and the time to 80 min, to fully expel the air in the system and prevent residual air from oxidizing the tellurium material during the melting process, thus causing pollution;

[0087] c. Close gas valve 5-1, open gas valve 5-2, control the gas flow rate to 0.6 L / min, and control the time to 60 min;

[0088] d. Turn on the heater and set the temperature to 650℃. After reaching the set temperature, maintain the temperature for 60 minutes.

[0089] (2) Directional solidification:

[0090] a. After the heat preservation period, adjust the hydrogen flow rate to 0.2 L / min and control the furnace body moving speed to 8.0 × 10⁻⁶. -6 m / s, directional solidification temperature is 600~700℃; when the end heater (heater 5) moves to the end of the graphite boat, turn off heater 5; when heater 4 moves to the end of the graphite boat, turn off heater 4, and so on.

[0091] b. After directional solidification, turn off the heater power and hydrogen valve, open the inert gas valve, adjust the flow rate to 0.2 L / min, and cool to room temperature. Remove the tellurium sample, cut off 100 mm from the end of the sample, and retain the remaining portion;

[0092] (3) The remaining part is retained as raw material, and the above melting and directional solidification operations are repeated 4 times to obtain the 6N high-purity tellurium product.

[0093] Example 4

[0094] Example 4 uses the apparatus described in Example 1 and includes the following steps:

[0095] (1) Molten material;

[0096] a. First, break the 5N tellurium ingot into small pieces to increase the contact area between the tellurium pieces and hydrogen, and then load them evenly into a graphite boat, with a load of 650g at a time. Then, load the graphite boat into the solidification furnace.

[0097] b. Close the sealing valve, and open the gas valves 5-4, 5-3, and 5-1 in sequence, controlling the gas flow rate to 0.6 L / min and the time to 80 min, to fully expel the air in the system and prevent residual air from oxidizing the tellurium material during the melting process, thus causing pollution;

[0098] c. Close gas valve 5-1, open gas valve 5-2, control the gas flow rate to 0.6 L / min, and control the time to 80 min;

[0099] d. Turn on the heater and set the temperature to 600℃. After reaching the set temperature, maintain the temperature for 80 minutes.

[0100] (2) Directional solidification:

[0101] a. After the heat preservation period, adjust the hydrogen flow rate to 0.2 L / min and control the furnace body moving speed to 1.0 × 10⁻⁶. -5 m / s, directional solidification temperature is 600~700℃; when the end heater (heater #5) moves to the end of the graphite boat, turn off heater #5; when heater #4 moves to the end of the graphite boat, turn off heater #4, and so on. The spacing between the heaters is 5.0mm;

[0102] b. After directional solidification, turn off the heater power and hydrogen valve, open the inert gas valve, adjust the flow rate to 0.2 L / min, and cool to room temperature. Remove the tellurium sample, cut off 100 mm from the end of the sample, and retain the remaining portion;

[0103] (3) The remaining part is retained as raw material, and the above melting and directional solidification operations are repeated 4 times to obtain the 6N high-purity tellurium product.

[0104] Comparative Example 1

[0105] Comparative Example 1 uses the same apparatus as Example 1 in other aspects, employs a heater for purification, and follows the same experimental conditions as Example 4, including the following steps:

[0106] (1) Molten material;

[0107] a. First, break the 5N tellurium ingot into small pieces to increase the contact area between the tellurium pieces and hydrogen, and then load them evenly into a graphite boat, with a load of 650g at a time. Then, load the graphite boat into the solidification furnace.

[0108] b. Close the sealing valve, and open the gas valves 5-4, 5-3, and 5-1 in sequence, controlling the gas flow rate to 0.6 L / min and the time to 80 min, to fully expel the air in the system and prevent residual air from oxidizing the tellurium material during the melting process, thus causing pollution;

[0109] c. Close gas valve 5-1, open gas valve 5-2, control the gas flow rate to 0.6 L / min, and control the time to 80 min;

[0110] d. Turn on the heater and set the temperature to 600℃. After reaching the set temperature, maintain the temperature for 80 minutes.

[0111] (2) Directional solidification:

[0112] a. After the heat preservation period, adjust the hydrogen flow rate to 0.2 L / min and control the furnace body moving speed to 1.0 × 10⁻⁶. -5 m / s, directional solidification temperature is 600~700℃;

[0113] b. After directional solidification, turn off the heater power and hydrogen valve, open the inert gas valve, adjust the flow rate to 0.2 L / min, and cool to room temperature. Remove the tellurium sample, cut off 100 mm from the end of the sample, and retain the remaining portion;

[0114] (3) The remaining portion is used as raw material, and the above melting and directional solidification operations are repeated 4 times to obtain tellurium products. The directional solidification process is difficult to control the liquid-solid interface, which is not conducive to the migration of impurities. The product contains excessive levels of impurities such as Se, Cu, and Ag.

[0115] Comparative Example 2

[0116] The apparatus used in Comparative Example 2 is otherwise identical to that in Example 1. As a comparative example, the heater spacing is 20 mm, and the experimental conditions are consistent with those in Example 4, including the following steps:

[0117] (1) Molten material;

[0118] a. First, break the 5N tellurium ingot into small pieces to increase the contact area between the tellurium pieces and hydrogen, and then load them evenly into a graphite boat, with a load of 650g at a time. Then, load the graphite boat into the solidification furnace.

[0119] b. Close the sealing valve, and open the gas valves 5-4, 5-3, and 5-1 in sequence, controlling the gas flow rate to 0.6 L / min and the time to 80 min, to fully expel the air in the system and prevent residual air from oxidizing the tellurium material during the melting process, thus causing pollution;

[0120] c. Close gas valve 5-1, open gas valve 5-2, control the gas flow rate to 0.6 L / min, and control the time to 80 min;

[0121] d. Turn on the heater and set the temperature to 600℃. After reaching the set temperature, maintain the temperature for 80 minutes.

[0122] (2) Directional solidification:

[0123] a. After the heat preservation period, adjust the hydrogen flow rate to 0.2 L / min and control the furnace body moving speed to 1.0 × 10⁻⁶. -5 m / s, directional solidification temperature is 600~700℃; when the end heater (heater #5) moves to the end of the graphite boat, turn off heater #5; when heater #4 moves to the end of the graphite boat, turn off heater #4, and so on. The spacing between the heaters is 20mm;

[0124] b. After directional solidification, turn off the heater power and hydrogen valve, open the inert gas valve, adjust the flow rate to 0.2 L / min, and cool to room temperature. Remove the tellurium sample, cut off 100 mm from the end of the sample, and retain the remaining portion;

[0125] (3) The remaining portion is used as raw material, and the above melting and directional solidification operations are repeated 4 times to obtain tellurium products. The directional solidification process is difficult to control the liquid-solid interface, which is not conducive to the migration of impurities. The product contains excessive levels of impurities such as Se, Cu, and Ag.

[0126] Comparative Example 3

[0127] Comparative Example 3 uses the apparatus described in Example 1. As a comparative example, directional solidification is performed directly without melting the material. The directional solidification conditions are consistent with those in Example 4, including the following steps:

[0128] (1) Directional solidification:

[0129] a. First, break the 5N tellurium ingot into small pieces to increase the contact area between the tellurium pieces and hydrogen, and then load them evenly into a graphite boat, with a load of 650g at a time. Then, load the graphite boat into the solidification furnace.

[0130] b. Adjust the hydrogen flow rate to 0.2 L / min and control the furnace body moving speed to 1.0 × 10⁻⁶. -5m / s, directional solidification temperature is 600~700℃; when the end heater (heater #5) moves to the end of the graphite boat, turn off heater #5; when heater #4 moves to the end of the graphite boat, turn off heater #4, and so on. The spacing between the heaters is 5.0mm;

[0131] c. After directional solidification, turn off the heater power and hydrogen valve, open the inert gas valve, adjust the flow rate to 0.2 L / min, and cool to room temperature. Remove the tellurium sample, cut off 100 mm from the end of the sample, and retain the remaining portion;

[0132] (2) The remaining part is retained as raw material, and the above melting and directional solidification operations are repeated 4 times to obtain tellurium products.

[0133] The test results of raw materials and products are shown in Table 1. As can be seen from the structure of Table 1, the scheme in the embodiment of this application can prepare high-purity tellurium products, and the impurity status of the products meets the standards.

[0134] Based on the data from Comparative Examples 1 and 2, it can be seen that the arrangement of the heaters affects the accuracy of temperature control, which in turn affects the purification effect of tellurium products, and the prepared products have excessive levels of elements such as Se, Cu, and Ag.

[0135] Based on the data from Comparative Example 3, it can be seen that direct directional solidification without melting results in uneven distribution of raw material impurities in the system, residual oxidizing gas in the gaps, low removal rate of volatile impurities, poor removal effect of most impurities in the product, and excessive levels of impurities such as Se, Cu, and Ag.

[0136] Table 1. Statistical Table of Impurities in High-Purity Tellurium (ppbw)

[0137] element Mg Al Ca Fe Ni Cu Zn Se Ag Cd Pb As S Tellurium raw materials 68 72 65 42 40 91 40 243 31 12 25 66 48 standard <50 <50 <100 <50 <50 <10 <100 <100 <10 <50 <50 / / Example 1 12.4 7.8 10 5.5 5.2 <1 7.1 48 <1 <5 <5 9.3 7.4 Example 2 8.0 6.6 8.9 4.6 4.7 1.8 8.0 54 1.2 <5 <5 8.1 6.6 Example 3 6.1 <5 5.8 <1 2.8 <1 <5 36 <1 <5 <5 4.2 3.0 Example 4 6.0 <5 6.7 <1 3.0 <1 6.2 42 <1 <5 <5 4.8 3.7 Comparative Example 1 14.2 21 7.8 4.1 4.5 11 7.3 106 15 <5 <5 6.5 8.2 Comparative Example 2 16.5 18 7.2 5.6 4.6 14 8.2 113 12 <5 <5 9.3 10.6 Comparative Example 3 24.6 31 10.1 10.5 8.2 18 10.8 182 18 <5 <5 19.8 17.6

Claims

1. An apparatus for preparing high purity tellurium by directional solidification, characterized in that, The device includes a furnace body (1), a gas supply device, a charging device, and a tail gas treatment device; the furnace body (1) is located outside the charging device, and the gas supply device and the tail gas treatment device are connected to both ends of the charging device via gas valves and gas pipelines (6), respectively; the gas supply device includes an inert gas cylinder (9) and a hydrogen cylinder (10); the tail gas treatment device includes a dust removal system (13) connected in series and a hydrogen ignition device (14). The furnace body (1) includes multiple heaters arranged side by side along the length of the charging device, each heater being 100-150mm wide and the lateral spacing between each heater being 5.0-10mm. A mobile trolley (8) is provided below the furnace body (1) to carry the furnace body (1) to move along the length of the loading device. The furnace body (1) is also connected to a control power supply (12), which controls the switching on and off of multiple heaters and the heating and cooling programs as well as the moving speed of the mobile trolley (8). The specific steps for stopping heating after directional solidification are as follows: When the furnace body moves along the direction from the front end to the end of the quartz tube, multiple horizontally arranged heaters in the furnace body move sequentially to the end of the graphite boat, and the heaters are turned off sequentially according to the order in which they reach the end of the graphite boat.

2. The apparatus for preparing high purity tellurium by directional solidification as claimed in claim 1, wherein The loading device includes a quartz tube (4), a sealing valve and a graphite boat (3). The two ends of the quartz tube (4) are provided with sealing valve 1# (7-1) and sealing valve 2# (7-2). The gas supply device and the exhaust gas treatment device are connected to the quartz tube (4) through sealing valve 1# (7-1) and sealing valve 2# (7-2) respectively. The quartz tube (4) is equipped with a graphite boat (3) inside, which is loaded with materials. The graphite boat (3) is 500-700mm long and the purity requirement is that the ash content is below 5ppm.

3. The apparatus for preparing high purity tellurium by directional solidification as claimed in claim 1, wherein The gas pipeline (6) is equipped with multiple gas valves, among which gas valve 1# (5-1) and gas valve 2# (5-2) control the inert gas cylinder (9) and hydrogen cylinder (10) respectively, and are connected in parallel through the gas pipeline (6). The other end is connected to gas valve 3# (5-3), and the other end of gas valve 3# (5-3) is connected to sealing valve 1# (7-1). Air valve 4# (5-4) is located between the dust removal system (13) and sealing valve 2# (7-2).

4. A method for producing high purity tellurium by directional solidification using the apparatus according to any one of claims 1 to 3, characterized by, Includes the following steps: (1) Crushed tellurium raw material: Take crushed powder and load it into a graphite boat. Adjust the position of the furnace body, introduce inert gas into the quartz tube to drive out the air in the system, and then introduce hydrogen gas to make the hydrogen gas fully diffuse into the entire system. Turn on the heating and keep it warm to melt the material. (2) After the heat preservation is completed, hydrogen is continuously introduced to control the heating of the furnace body and carry out directional solidification; after the directional solidification is completed, heating is stopped, hydrogen is stopped, inert gas is introduced again, and the temperature is reduced to room temperature. (3) Remove the product, cut off the end of the product, and keep the remaining part; (4) Use the remaining part as tellurium raw material and repeat steps (1), (2), and (3) 3 to 5 times to obtain high-purity tellurium products.

5. The method of claim 4, wherein, In step (1), the amount of powder loaded is 500~800g. When inert gas is introduced, the inert gas flow rate is adjusted to 0.5~1.0L / min and the gas introduction time is 60~120min. When hydrogen is introduced, the hydrogen flow rate is adjusted to 0.4~0.6L / min and the gas introduction time is 60~120min. The melting temperature is 500~700℃ and the holding time is 60~90min.

6. The method of claim 4, wherein, When hydrogen is continuously introduced in step (2), the hydrogen flow rate is adjusted to 0.1~0.3L / min; when inert gas is introduced, the inert gas flow rate is adjusted to 0.1~0.3L / min.

7. The method as described in claim 4, characterized in that, The directional solidification in step (2) is specifically: controlling the furnace body to move along the direction from the front end to the end of the quartz tube, and performing directional solidification, the moving speed is 5.0×10 -6 m / s, and the directional solidification temperature is 600-700℃. -5 m / s, and the directional solidification temperature is 600-700℃.

8. The method as described in claim 4, characterized in that, The purity of the tellurium raw material is 5N or higher, and the length of the tellurium raw material when loaded into the graphite boat is 20-30mm shorter than the length of the graphite boat; the length of the product end cut off in step (3) is 80-120mm.

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