Directional condensation crystallization purification device and method

Abstract

The invention discloses a directional condensation crystallization purification device and method. The device comprises a furnace body system, a driving control system, a pressure control system and the like. One end of the furnace body is an evaporation end, and the other end is a condensation crystallization end; an end plate of the condensation crystallization end is used as an initial position of material condensation crystallization; the periphery of the furnace body is sleeved with a heating device, and the heating device is sequentially divided into a heating section, a transition section and a condensation section in the axial direction, the heating section of the heating device acts on the evaporation end of the furnace body, and the condensation section of the heating device acts on the condensation crystallization end of the furnace body; the furnace body and the heating device can move relatively in the axial direction, and the drive control system is used for controlling the condensation crystal growth face of materials and the condensation section of the heating device to be relatively static. According to the invention, the purpose of purification can be realized by cutting off the head crystallization material and the crucible residue material, and meanwhile, the condensation crystallization temperature can be always kept constant, and the purified material is high in crystallinity, large in crystal grain and high in product appearance consistency.

Description

Technical Field

[0001] The present invention belongs to the technical field of metal and compound purification, and in particular relates to a directional condensation crystallization purification device and method. Background Art

[0002] With the rapid emergence and development of new technologies such as quantum information, renewable energy, and artificial intelligence, the demand for high-purity metals and compounds has been greatly stimulated. When high-purity metals and compounds are used in high-tech fields such as the semiconductor industry, photovoltaic industry, and military industry, not only are extremely high requirements placed on their purity, but also on the crystal morphology and uniformity of the products. At present, vacuum distillation / sublimation is one of the mainstream technologies for preparing high-purity metals and compounds, which can effectively remove high and low vapor pressure impurities in metals / compounds. In the existing multi-stage, graded, and directional condensation technologies, the temperature in the condensation zone is usually gradient-distributed, and the vapor of the metal / compound can only condense in non-uniform temperature zones, resulting in different crystal forms of the condensate, huge differences in glossiness, poor consistency in product appearance, and some high vapor pressure impurities may also exceed the standard. Summary of the Invention

[0003] In view of this, the present invention provides a directional condensation crystallization purification device and method, which can not only achieve the purpose of purification, but also keep the condensation temperature of metal / compound vapor stable, thereby improving the appearance quality of the product. In order to solve the above technical problems, the technical solution of the present invention is to adopt a directional condensation crystallization purification device, including a cylindrical furnace body, one end of the furnace body is an evaporation end, and the other end is a condensation crystallization end; the crucible of the evaporation end serves as an evaporation source, and the end plate of the condensation crystallization end serves as the starting position for condensation and crystallization of the material; a heating device is provided on the outer periphery of the furnace body, and the heating device is divided into a heating section, a transition section and a condensation section with a decreasing temperature gradient in the axial direction; the heating section of the heating device acts on the evaporation end of the furnace body, and the condensation section of the heating device acts on the condensation crystallization end of the furnace body; the furnace body and the heating device can move axially relative to each other, so that the condensation crystallization growth surface of the material and the condensation section of the heating device are relatively stationary.

[0004] As an improvement, the furnace body and / or the heating device can move axially; it also includes a drive system for driving the heating device and / or the furnace body to move axially; the drive system includes a transmission rod arranged parallel to the furnace body, and the transmission rod is provided with a slider that can move axially along the transmission rod; the heating device or the furnace body is connected to the slider by a bracket. As a further improvement, the thermal conductivity of the end plate at the condensation and crystallization end of the furnace body is higher than that of the side wall of the furnace body. As another further improvement, the furnace body is a quartz tube, and the end plate of the condensation crystallization end is a graphite plate.

[0005] As an improvement, the heating end of the furnace body is provided with a crucible for holding materials, and the material of the crucible is high-purity graphite or quartz.

[0006] As an improvement, a pressure control system is further included, which includes an inert gas container connected to the furnace body and a vacuum pump.

[0007] As an improvement, during the relative movement between the furnace body and the heating device, the heating section of the heating device always acts on the crucible at the evaporation end of the furnace body.

[0008] The present invention also provides a directional condensation crystallization purification method, which is applied to the above-mentioned directional condensation crystallization purification device, comprising: After loading, vacuum is drawn into the furnace body and inert gas is injected into the furnace body to keep the pressure within the preset pressure range; The heating device is started to increase the temperature so that the temperatures of the heating section, the transition section, and the condensing section are respectively within the first temperature range, the second temperature range, and the third temperature range; the first temperature range, the second temperature range, and the third temperature range decrease in a gradient; The furnace body is vacuumed, so that the material forms vapor at the evaporation end of the furnace body and then condenses and crystallizes at the condensation end starting from the end plate of the condensation end; the direction of condensation and crystallization is along the axis of the furnace body and from far away from the evaporation end to close to the evaporation end; The furnace body and the heating device are driven to perform axial relative motion, and the motion rate is consistent with the axial crystal growth rate of the material, so that the crystal growth surface of the material and the condensation section of the heating device are relatively stationary.

[0009] As an improvement, when the material is antimony, the first temperature range is 680-780°C, the second temperature range is 635-640°C, and the third temperature range is 560-600°C; When the material is a cadmium telluride compound, the first temperature range is 750-800°C, the second temperature range is 700-710°C, and the third temperature range is 600-650°C.

[0010] As an improvement, after the condensation crystallization is completed, 8% to 12% of the crystals at the head are removed, and 4% to 6% of the material remains in the crucible.

[0011] The present invention is beneficial in that: During the directional condensation crystallization purification process, the condensation temperature remains stable and does not change as the crystal grows. The supercooled zone created by the graphite plate or condensed metal / compound allows the material vapor to continuously condense and deposit along the axial direction of the quartz tube, rather than condensing on the radial quartz sidewalls. To ensure a constant condensation temperature, the axial relative movement between the heating device and the furnace body prevents the vapor condensation temperature from changing. This results in a purified metal or compound with high crystallinity, high gloss, large grains, and a consistent product appearance.

[0012] Furthermore, during vacuum distillation / sublimation, the difference in vapor pressure between the metal / compound and impurities is exploited for further purification, leaving low-vapor-pressure / high-boiling-point impurities in the crucible. Since high-vapor-pressure / low-boiling-point impurities evaporate first during vacuum distillation / sublimation, the initial condensed distillation / sublimation product contains the highest concentration of these impurities, primarily deposited at the head of the crystal rod. After removing 8%-12% of the crystals from the head, leaving 4%-6% of the residue in the crucible, the remaining crystals are of a higher purity, thus achieving the desired purification goal. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 Schematic diagram of the device structure of Example 1.

[0014] Figure 2 This is a state change diagram of crystal condensation growth in Example 2.

[0015] Figure 3 This is a schematic diagram of the device structure of Example 2.

[0016] Markings in the figure: 101a heating section, 101b transition section, 101c condensation section, 102a pressure gauge, 102b inert gas container, 102c valve, 102d vacuum pump, 103a servo motor, 103b transmission rod, 103c bracket, 104a crucible, 104b end plate of condensation and crystallization end, 104c furnace body, 104d end plate of heating end. DETAILED DESCRIPTION

[0017] In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention is further described in detail below in conjunction with specific implementation methods.

[0018] Example 1 Prior art CN116875821A discloses a method and apparatus for preparing antimony. The method comprises placing crude antimony in a vacuum environment at a pressure of 1 Pa to 5 Pa, and performing vacuum distillation and multi-stage condensation from bottom to top, with the high-temperature section temperature set at 540°C to 543°C, the first transition section temperature set at 475°C to 483°C, the second transition section temperature set at 452°C to 460°C, and the low-temperature section temperature set at 417°C to 425°C, to obtain high-purity antimony.

[0019] The above-mentioned prior art employs multiple temperature zones, including a high-temperature zone of 540°C to 543°C for evaporating the material, and a low-temperature zone of 417°C to 425°C for crystallization and purification. Despite these temperature zones, the temperature of the low-temperature zone is still affected by the temperature of the high-temperature zone. Therefore, the above-mentioned prior art also incorporates a transition zone to mitigate the impact of thermal radiation from the high-temperature zone on the low-temperature zone. However, even with this transition zone, the impact of thermal radiation is unavoidable, resulting in a temperature gradient even within the low-temperature zone, with higher temperatures near the high-temperature zone and lower temperatures farther away.

[0020] Due to the existence of the above-mentioned temperature difference, the material actually still crystallizes from the low temperature zone to the high temperature zone during the crystallization process. However, due to different temperatures, the appearance, morphology and glossiness of the crystallized material are also quite different. At the same time, some high vapor pressure impurities will condense and crystallize after entering the suitable temperature range, resulting in a decrease in the purity of the crystal.

[0021] In order to solve the problem in the prior art that material vapor cannot be crystallized in a constant temperature environment, such as Figure 1 As shown, the present invention provides a directional condensation crystallization purification device, including a cylindrical furnace body 104c, one end of the furnace body 104c is an evaporation end, and the other end is a condensation crystallization end; the crucible at the evaporation end serves as an evaporation source, and the end plate 104b at the condensation crystallization end serves as the starting position for material condensation and crystallization; a heating device is provided on the outer periphery of the furnace body 104c, and the heating device is divided into a heating section 101a, a transition section 101b and a condensation section 101c with a decreasing temperature gradient in the axial direction; the heating section 101a of the heating device acts on the evaporation end of the furnace body 104c, and the condensation section 101c of the heating device acts on the condensation crystallization end of the furnace body 104c; the furnace body 104c and the heating device can move relative to each other along the axial direction, so that the condensation crystallization growth surface of the material and the condensation section 101c of the heating device are relatively stationary. Of course, to ensure that the axial relative movement between the furnace body 104c and the heating device does not affect the heating of the material to form vapor, the heating section 101a of the heating device always acts on the crucible at the evaporation end of the furnace body during the relative movement between the furnace body 104c and the heating device. Therefore, it is understood that the length of the heating section 101a must meet the aforementioned requirements.

[0022] In the present invention, the material starts at the end plate 104b of the condensation crystallization end and moves along the axial direction of the furnace body 104c from the end away from the heating end to the end close to the heating end (i.e., from the end of the condensation crystallization end to the end of the condensation crystallization end). Figure 1 The so-called condensation crystal growth surface refers to the Figure 1 The A surface in the figure is the end face of the crystal.

[0023] Due to the influence of thermal radiation, even within the condensing section 101c, the temperature decreases axially. That is, the temperature is higher near the heating section 101a and lower away from it. To further reduce the thermal radiation effect of the heating section 101a on the condensing section 101c, a transition section 101b is provided between the heating section 101a and the condensing section 101c to mitigate temperature unevenness within the condensing section 101c.

[0024] In order to ensure that the temperature of the material vapor crystallization is consistent in the present invention, the heating device and the furnace body 104c are subjected to axial relative movement, so that the condensation crystallization growth surface and the condensation section 101c remain relatively still. For example, in the initial state, the end plate 104b of the condensation crystallization end, that is, the crystallization starting position, is aligned with position B of the condensation section 101c. As the condensation crystallization begins, the crystals continue to grow, causing the condensation crystallization growth surface to continue to extend to the left. Figure 2 As shown, at this time, the furnace body 104c or the heating device is driven to move axially so that the position B on the condensation section 101c is always aligned with the condensation crystallization growth surface. In this way, the temperature of the crystallization growth surface is ensured to be the same during the entire condensation crystallization process, so that the appearance and morphology of the crystalline material are consistent, thereby avoiding the difference in crystallinity affecting the quality of the product.

[0025] In the present invention, the furnace body 104c and / or the heating device can move axially. In this embodiment, in order to simplify the equipment and facilitate control, only the heating device can move axially.

[0026] The device also includes a drive system for driving the heating device and / or the furnace body in axial motion. The drive system includes a transmission rod 103b arranged parallel to the furnace body 104c. The transmission rod 103b is provided with a slider (not shown) that can move axially along the transmission rod 103b. The heating device is connected to the slider via a bracket 103c. More specifically, the transmission rod 103b is a screw, and the slider engages with the transmission rod 103b in a threaded engagement. Driven by the servo motor 103a, the transmission rod 103b rotates, causing the slider to move axially along the transmission rod 103b, thereby driving the heating device. It is foreseeable that since the material crystals grow axially from right to left within the furnace body 104c, the heating device also moves from right to left to ensure that the crystal growth surface of the material crystals remains stationary relative to the condensation section 101c of the heating device.

[0027] In this embodiment, the heating device may be a heating resistance wire. It is foreseeable that the temperature of different sections can be controlled by setting the density or power of the heating resistance wire.

[0028] In order to provide a better crystallization site for the material vapor, the thermal conductivity of the end plate 104b at the condensation and crystallization end in this embodiment is higher than that of the furnace body 104c. For example, the furnace body 104c is a high-purity quartz tube, and the end plate 104b at the condensation and crystallization end is a high-purity graphite plate. The condensation and crystallization process is an exothermic process, and the graphite end plate has better heat transfer performance than the quartz furnace body 104c. The heat generated during the condensation of the material vapor can be continuously dissipated through the end plate, so that the temperature of the end plate 104b at the condensation and crystallization end is lower than the temperature of the side wall of the furnace body. Therefore, the material vapor preferentially condenses and crystallizes at the end plate 104b at the condensation and crystallization end. Controlling the condensation temperature of the condensation section 101c can achieve condensation of the material vapor on the end plate 104b instead of condensing on the side wall of the quartz tube. As condensation progresses, the condensation crystallization surface changes from the end plate 104b to the condensed material. Similarly, the thermal conductivity of the condensed material is better than that of the side wall of the quartz tube, so that the temperature of the crystallization surface growing along the axial direction of the condensation is lower than that of the side wall of the quartz tube. It is easier to condense and deposit the material along the axial direction of the quartz tube. However, due to the relatively poor thermal conductivity of the side wall of the quartz tube, it is difficult for the material vapor to condense on the side wall of the quartz tube. In summary, controlling the condensation temperature of the condensation section 101c can achieve directional condensation of the material vapor along the axial direction of the quartz tube. The changes before and after the directional condensation of the material vapor can be seen. Figure 1 and Figure 2 .

[0029] The heating end of the furnace is equipped with a crucible 104a for holding material. Crucible 104a can be made of high-purity graphite or quartz, allowing the material to evaporate and form vapor within crucible 104a. The heating end plate 104d is made of any material and can be quartz or graphite. This prevents material vapor from condensing toward the rear of the quartz tube 104c.

[0030] In addition, to allow the material to volatilize and prevent it from reacting with oxygen, the furnace body is vacuumed. To prevent the material from volatilizing and condensing before reaching the appropriate temperature, an inert gas is injected into the furnace body to prevent volatilization. Therefore, this embodiment also includes a pressure control system, which includes an inert gas container 102b connected to the furnace body 104c and a vacuum pump 102d. It is foreseeable that valves 102c are installed in front of the inert gas container 102b and the vacuum pump 102d. To facilitate monitoring of the air pressure within the furnace body, a pressure gauge 102a may also be installed on the pipe connecting the furnace body 104c.

[0031] Example 2 Different from Example 1, the axial relative movement between the furnace body and the heating device is achieved through the axial movement of the furnace body, thereby achieving the purpose of relative stillness between the crystal growth surface of the material and the condensation section of the heating device.

[0032] like Figure 3 As shown, in this embodiment, the drive system includes a drive rod 203b arranged parallel to the furnace body 204c. The drive rod 203b is provided with a slider that can move axially along the drive rod 203b. The furnace body 204c is connected to the slider via a bracket 203c. As can be expected, since the crystal grows axially from right to left within the furnace body 204c, the movement of the furnace body 204c is from left to right to ensure that the crystal growth surface and the condensation section 201c of the heating device remain stationary.

[0033] Example 3 The present invention also provides a directional condensation crystallization purification method, which is applied to the directional condensation crystallization purification apparatus provided in Examples 1 and 2. This purification method can be applied to the purification of metals and compounds. In this embodiment, antimony is used as an example of a metal and cadmium telluride is used as an example of a compound. The specific steps of the purification include: S1 pre-processing: The quartz tube (furnace body) and quartz crucible are soaked in aqua regia and cleaned with ultrapure water. The end plate of the condensation crystallization end and the end plate of the heating end are wiped clean with alcohol cotton cloth, and then baked in the quartz tube for 3 to 6 hours to remove moisture and other impurities before use.

[0034] After S2 is loaded, the furnace body is vacuumed and inert gas is injected into the furnace body to make the pressure inside the furnace body within the preset pressure range: The quartz crucibles are respectively filled with 6N antimony and 4N cadmium telluride for purification, and then the mechanical pump is turned on. After the vacuum is evacuated to below 20Pa, the valve near the vacuum pump is closed, the valve near the gas cylinder is opened, and inert gas is filled into the quartz tube system to ensure that the pressure in the system is within the range of 0.02-0.05MPa to prevent the condensation and crystallization zone from reaching the appropriate condensation temperature during the heating process, and the antimony metal vapor and cadmium telluride vapor begin to condense and grow crystals.

[0035] S3 temperature rise: The heating device is started to increase the temperature so that the temperatures of the heating section, the transition section and the condensation section are respectively within the first temperature range, the second temperature range and the third temperature range; the first temperature range, the second temperature range and the third temperature range decrease gradually.

[0036] Specifically, when the material is antimony, the first temperature range is 680-780°C, the second temperature range is 635-640°C, and the third temperature range is 560-600°C; When the material is a cadmium telluride compound, the first temperature range is 750-800°C, the second temperature range is 700-710°C, and the third temperature range is 600-650°C.

[0037] S4 crystal growth: The furnace body is vacuumed so that the material forms vapor at the evaporation end of the furnace body and then condenses and crystallizes at the condensation end with the end plate of the condensation end as the starting position; the direction of condensation and crystallization is along the axial direction of the furnace body and from far away from the evaporation end to close to the evaporation end; the furnace body or the heating device is driven to perform axial relative motion, and the movement rate is consistent with the axial growth rate of the material crystallization, so that the condensation crystallization growth surface of the material and the condensation section of the heating device are relatively stationary.

[0038] More specifically, after the temperatures in each section of the heating device stabilize (generally 30 minutes after reaching the predetermined temperature), the device is evacuated again to below 20 Pa. Antimony metal vapor and cadmium telluride vapor will slowly condense and grow on the graphite plate. Due to the continuous heat release during vapor condensation and the superior thermal conductivity of graphite compared to quartz, the temperature of the graphite plate is typically slightly lower than that of the quartz wall. By optimally controlling the condensation temperature (560-600°C for antimony and 600-650°C for cadmium telluride), the vapor condenses and deposits horizontally, avoiding condensation on the quartz tube wall. Once all the dominant condensation zones have crystallized, the movement of the heating element or quartz tube is controlled to ensure that the material vapor continues to condense and grow into rod-shaped crystals at the same condensation temperature. Simultaneously, due to the higher temperature in the transition section, vapor condenses less easily there and instead continuously passes through it, condensing and growing in the dominant condensation zone of the condensation section. The primary function of the transition section is to mitigate the influence of the heating section on the condensation temperature of the condensation section. The transition section can also be subdivided into multiple subsections, similarly with a decreasing temperature gradient.

[0039] Depending on the speed of condensation growth, a servo motor slowly moves the heating device or quartz tube via a drive rod, ensuring that the condensation growth surface always condenses within the optimal condensation zone. The movement speed of the heating device or furnace is controlled within a range of 20-40 mm / h to match the crystal growth rate. The crystal growth time can be determined based on the desired crystal length. In the present invention, the preferred growth time is controlled within 10-20 hours, with a crystal length of approximately 40 cm.

[0040] S5 furnace shutdown and discharge: After crystal growth is complete, the system is filled with inert gas to maintain a pressure within the range of 0.02-0.05 MPa. The purified antimony or cadmium telluride crystal rod is removed, and the 8%-12% of the crystal at the head, which contains high vapor pressure (low boiling point) impurities, is removed. The remaining crystal rod is 7N antimony and 5N cadmium telluride. Low vapor pressure (high boiling point) impurities remain in the crucible, accounting for approximately 4%-6% of the raw material.

[0041] Example 4 This example is used to purify antimony metal. The set temperatures for the heating, transition, and condensation stages are 730°C, 635°C, and 580°C, respectively. The movement speed is 35 mm / h, the growth time is 11 hours, and the crystal length is 39.5 cm. After purification, 6N antimony can be refined to 7N.

[0042] The raw material is 6N antimony, and the impurity content is as follows: The purity of the purified antimony crystal rod is 7N, and the impurity content is as follows:

[0043] Example 5 This example is used to purify cadmium telluride. The set temperatures for the heating, transition, and condensation stages are 770°C, 705°C, and 630°C, respectively. The movement speed is 40 mm / h, the growth time is 11 hours, and the crystal length is 43 cm. After purification, 4N cadmium telluride can be refined to 5N.

[0044] The raw material is 4N cadmium telluride, and the impurity content is as follows:

[0045] The purity of the purified cadmium telluride crystal rod is 5N, and the impurity content is as follows:

[0046] The above are merely preferred embodiments of the present invention. It should be noted that the above preferred embodiments should not be construed as limiting the present invention, and the scope of protection of the present invention should be determined by the scope defined in the claims. Persons skilled in the art will appreciate that improvements and modifications may be made without departing from the spirit and scope of the present invention, and such improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A directional condensation crystallization purification device, characterized in that: It comprises a cylindrical furnace body, one end of which is an evaporation end and the other end is a condensation and crystallization end; the crucible at the evaporation end serves as an evaporation source, and the end plate at the condensation and crystallization end serves as the starting position for condensation and crystallization of materials; a heating device is provided on the outer periphery of the furnace body, and the heating device is divided into a heating section, a transition section and a condensation section in axial direction with decreasing temperature gradient; the heating section of the heating device acts on the evaporation end of the furnace body, and the condensation section of the heating device acts on the condensation and crystallization end of the furnace body; the furnace body and the heating device can move relative to each other along the axial direction, so that the condensation and crystallization growth surface of the material and the condensation section of the heating device are relatively stationary.

2. A directional condensation crystallization purification device according to claim 1, characterized in that: The furnace body and / or the heating device can move axially; it also includes a driving system for driving the heating device and / or the furnace body to move axially; the driving system includes a transmission rod arranged parallel to the furnace body, and the transmission rod is provided with a slider that can move axially along the transmission rod; the heating device or the furnace body is connected to the slider by a bracket.

3. A directional condensation crystallization purification device according to claim 1, characterized in that: The thermal conductivity of the end plate at the condensation and crystallization end of the furnace body is higher than that of the side wall of the furnace body.

4. A directional condensation crystallization purification device according to claim 3, characterized in that: The furnace body is a quartz tube, and the end plate of the condensation crystallization end is a graphite plate.

5. A directional condensation crystallization purification device according to claim 1, characterized in that: The heating end of the furnace body is provided with a crucible for containing materials, and the material of the crucible is high-purity graphite or quartz.

6. A directional condensation crystallization purification device according to claim 1, characterized in that: The invention also comprises a pressure control system, wherein the pressure control system comprises an inert gas container connected to the furnace body and a vacuum pump.

7. A directional condensation crystallization purification device according to claim 1, characterized in that: During the relative movement between the furnace body and the heating device, the heating section of the heating device always acts on the crucible at the evaporation end of the furnace body.

8. A directional condensation crystallization purification method, applied to the directional condensation crystallization purification device according to any one of claims 1 to 7, characterized in that include: After loading, the furnace body is vacuumed and inert gas is injected into the furnace body so that the pressure inside the furnace body is within the preset pressure range; The heating device is started to increase the temperature so that the temperatures of the heating section, the transition section and the condensing section are respectively within the first temperature range, the second temperature range and the third temperature range; the first temperature range, the second temperature range and the third temperature range decrease in gradient; The furnace body is vacuumed so that the material forms steam at the evaporation end of the furnace body and then condenses and crystallizes at the condensation end with the end plate at the condensation end as the starting position; the direction of condensation and crystallization is along the axial direction of the furnace body and from far away from the evaporation end to close to the evaporation end; The furnace body and the heating device are driven to perform axial relative movement, and the movement rate is consistent with the axial crystal growth rate of the material, so that the condensation crystal growth surface of the material and the condensation section of the heating device are relatively stationary.

9. A directional condensation crystallization purification method according to claim 8, characterized in that: When the material is antimony, the first temperature range is 680-780°C, the second temperature range is 635-640°C, and the third temperature range is 560-600°C; When the material is a cadmium telluride compound, the first temperature range is 750-800°C, the second temperature range is 700-710°C, and the third temperature range is 600-650°C.

10. A directional condensation crystallization purification method according to claim 8, characterized in that: After condensation and crystallization, 8% to 12% of the crystals at the head are removed, and 4% to 6% of the material remains in the crucible.

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