Apparatus and Method for Directional Solidification Purification of Rare Earth Metals

Abstract

This invention discloses a directional solidification purification apparatus and method for rare earth metals. The apparatus includes a furnace body, a purification crucible, a water-cooled cover plate, a heating element, and a heat insulation layer. Water-cooling pipes are installed on the inner wall of the furnace body to cool the furnace body. The purification crucible is placed in the furnace cavity and is configured to contain rare earth metals. The water-cooled cover plate covers the top opening of the purification crucible and is configured to cool the material inside the crucible. The heating element includes a side heating element and a bottom heating element, configured to heat the material inside the purification crucible. The side heating element surrounds the outer periphery of the side wall of the purification crucible, and the bottom heating element is located below the bottom wall of the purification crucible. The heat insulation layer surrounds at least a portion of the purification crucible and the heating element, and is configured to keep the material inside the purification crucible warm. This apparatus has a simple structure and exhibits excellent purification effects for rare earth metals.

Description

Technical Field

[0001] This invention relates to an apparatus and method for directional solidification purification of rare earth metals. Background Technology

[0002] Segregation is an important industrial process for refining metals. Directional solidification is a type of segregation method that can be used to purify rare earth metals. Directional solidification utilizes the difference in solubility of impurity elements in the solid and liquid phases of a metal to cause the impurities to migrate in a specific direction. After solidification, the impurity elements tend to concentrate at both ends of the metal ingot, with fewer impurities in the middle section, thus achieving metal purification.

[0003] CN116588902A discloses a zone melting apparatus, including a hot exhaust vent, an outer cavity, an inner cavity, a zone melting tube, a zone melting boat, heating plates, heating elements, an intelligent control system, and a servo drive system. The hot exhaust vent is located at the center of the top of the apparatus and connects to an external exhaust system. The outer cavity is located between the inner cavity and the outer casing, and heat from the outer cavity is discharged through the exhaust vent. The inner cavity encloses the heating elements, and the inner cavity wall has an insulation layer. The spacing between adjacent heating elements is adjustable. Each group of heating elements has upper and lower heating plates. The servo drive system consists of a servo motor and a ball screw, with the heating elements mounted on the ball screw. This apparatus has a limited processing capacity and cannot meet the needs of large-volume metal processing.

[0004] CN218779075U discloses a solidification furnace, including a frame. A crucible lifting device is installed inside the frame, with a crucible cooling chamber formed at the output end of the lifting device. A crucible support rod is also installed at the output end of the lifting device, located inside the cooling chamber. A furnace body is mounted on the upper side of the frame, and a graphite crucible is installed inside the furnace body. The bottom of the graphite crucible is attached to one end of the crucible support rod, and a cooling chamber cover is mounted on the support rod. A water-cooled electrode is mounted on the furnace body. This device uses a crucible cooling chamber for cooling.

[0005] CN116604001A discloses an apparatus for directional solidification of silicon-molybdenum alloy for sputtering targets, comprising a directional solidification furnace with a protective gas inlet at the bottom and a protective gas outlet at the top. A ceramic crucible is placed inside the directional solidification furnace, and a graphite crucible is placed inside the ceramic crucible. A heat insulation layer is placed between the ceramic and graphite crucibles. A thermocouple is placed at the bottom of the graphite crucible. An infrared thermometer is placed above the graphite crucible inside the directional solidification furnace. A water-cooling mechanism is provided at the bottom of the ceramic crucible. An induction coil is placed outside the ceramic crucible inside the directional solidification furnace, and the induction coil is connected to a moving mechanism that drives the induction coil to move up and down. This apparatus, by adjusting the moving mechanism, creates a top-to-bottom temperature gradient in the melt within the graphite crucible, promoting directional solidification of the melt inside the graphite crucible. Summary of the Invention

[0006] In view of this, one object of the present invention is to provide a directional solidification purification apparatus for rare earth metals, which is suitable for large-scale directional solidification purification of rare earth metals. The apparatus has a simple structure, does not contain a cooling crucible or a motor, and reduces the equipment failure rate. The apparatus of the present invention exhibits excellent purification effects on rare earth metals. Another object of the present invention is to provide a method that can improve the purification effect of rare earth metals.

[0007] On the one hand, the present invention provides a directional solidification purification apparatus for rare earth metals, including a furnace body, a purification crucible, a water-cooled cover plate, a heating element and a heat insulation layer;

[0008] The furnace body has a furnace cavity, and a water-cooling pipe is provided on the inner wall of the furnace body. The water-cooling pipe is configured to cool the furnace body.

[0009] The purification crucible is disposed in the furnace cavity, and the purification crucible is configured to contain rare earth metals and / or rare earth metal melts;

[0010] The water-cooled cover plate covers the top opening of the purification crucible, and the water-cooled cover plate is configured to cool the substance inside the purification crucible;

[0011] The heating element includes a side heating element and a bottom heating element, and the heating element is configured to heat the substance inside the purification crucible; the side heating element surrounds the outer periphery of the side wall of the purification crucible, and the bottom heating element is disposed below the bottom wall of the purification crucible;

[0012] The insulation layer surrounds at least a portion of the purification crucible and the heating element, and the insulation layer is configured to keep the material inside the purification crucible warm.

[0013] According to the directional solidification purification apparatus of the present invention, preferably, the directional solidification purification apparatus further includes a first cooling water conveying pipeline, a cover plate water-cooled pump, a second cooling water conveying pipeline, and a furnace body water-cooled pump;

[0014] One end of the first cooling water delivery pipe is connected to the water-cooled cover plate, and the other end of the first cooling water delivery pipe is connected to the cover plate water-cooling pump.

[0015] One end of the second cooling water delivery pipe is connected to the water cooling pipe, and the other end of the second cooling water delivery pipe is connected to the furnace body water cooling pump.

[0016] In the directional solidification purification apparatus according to the present invention, preferably, a graphite tray is provided between the bottom heating element and the bottom wall of the purification crucible.

[0017] According to the directional solidification purification apparatus of the present invention, preferably, the directional solidification purification apparatus further includes a vacuum device, the vacuum device being configured to extract the gas inside the furnace chamber;

[0018] The vacuum equipment includes a low-vacuum vacuum pumping line, a roughing valve, a Roots pump, a mechanical pump, a high-vacuum pumping line, a main valve, a vacuum pump, and a pre-valve.

[0019] One end of the low vacuum pumping pipeline is connected to the furnace cavity, and the other end of the low vacuum pumping pipeline is connected to the mechanical pump. The low vacuum pumping pipeline is equipped with a roughing valve and a Roots pump, and the Roots pump is located at the rear end of the roughing valve.

[0020] The high-vacuum pumping line and the section of the low-vacuum pumping line equipped with the coarse pumping valve are connected in parallel. The high-vacuum pumping line is equipped with a main valve, a vacuum pump and a pre-valve in sequence. The vacuum pump is a molecular pump.

[0021] According to the directional solidification purification apparatus of the present invention, preferably, the directional solidification purification apparatus further includes a temperature measuring thermocouple;

[0022] The temperature-measuring thermocouple is installed on one side of the furnace body, and the temperature-measuring thermocouple is configured to measure the temperature inside the furnace cavity.

[0023] According to the directional solidification purification apparatus of the present invention, preferably, the distance between the side heating element and the outer wall of the purification crucible is 50-100 mm, and the thickness of the insulation layer is 50-200 mm.

[0024] On the other hand, the present invention provides a method for directional solidification purification of rare earth metals using the above-mentioned directional solidification purification device, comprising the following steps:

[0025] (1) With an inert atmosphere and a pressure of 0.02 to 0.15 MPa in the furnace cavity, rare earth metals in the purification crucible and cooling water flowing through the water cooling pipe, turn on the side heating element and the bottom heating element to bring the temperature in the furnace cavity to T1 and keep it at that temperature for 10 to 150 minutes; T1 is 10 to 150°C higher than the melting point of the rare earth metals in the purification crucible, and the melting point of the rare earth metals is based on the melting point of the rare earth metal elements;

[0026] (2) After the heat preservation is completed, cool water is introduced into the water-cooled cover plate, the side heating element is closed, and the bottom heating element is kept open to maintain the temperature in the furnace cavity at T1±10℃ for 10~120min.

[0027] (3) Adjust the output power of the bottom heating element so that the temperature of the furnace cavity drops to T2, and then turn off the bottom heating element; after the temperature in the furnace cavity reaches the ambient temperature, stop supplying cooling water to the water cooling pipe and the water cooling cover plate; T2 is 10 to 90°C below the melting point of the rare earth metal in the purification crucible, and the melting point of the rare earth metal is based on the melting point of the rare earth metal element.

[0028] According to the method of the present invention, preferably, the rate of heating to room temperature T1 is 10-35°C / min, and the rate of cooling to temperature T2 is 1-15°C / h.

[0029] According to the method of the present invention, preferably, it further includes the following steps: starting the mechanical pump and opening the roughing valve to reduce the pressure in the furnace chamber to 500-1000 Pa; then starting the Roots pump to reduce the pressure in the furnace chamber to 0.5-20 Pa; closing the roughing valve, opening the main valve and the pre-valve, and starting the vacuum pump to reduce the pressure in the furnace chamber to 10 Pa. -4 Below Pa; inert gas is introduced into the furnace cavity to bring the pressure inside the furnace cavity to 0.02-0.15 MPa.

[0030] According to the method of the present invention, preferably, it further includes the following steps: taking out the solid metal in the purification crucible, dividing the solid metal, and taking the middle part as the purified rare earth metal.

[0031] The apparatus of this invention uses forced cooling to fix the direction of heat flow during solidification, achieving directional solidification. The apparatus of this invention has a simple structure, large single-pass capacity, and good purification effect. The method of this invention can improve the purification effect of rare earth metals. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of the structure of a directional coagulation purification device according to the present invention.

[0033] The attached figures are labeled as follows:

[0034] 1-Furnace lid; 2-Water-cooled cover plate; 3-Water-cooled pipe; 4-Side heating element; 5-Purification crucible; 6-Furnace body; 7-Insulation layer; 8-Graphite tray; 9-Bottom heating element; 10-Support body; 11-Vacuum pump; 12-Pre-valve; 13-Mechanical pump; 14-Roots pump; 15-Main valve; 16-Roughing pump; 17-Furnace body water-cooled pump; 18-Cover plate water-cooled pump; 19-First cooling water delivery pipe; 20-Second cooling water delivery pipe; 21-Low vacuum extraction pipe; 22-High vacuum extraction pipe; 23-Support column. Detailed Implementation

[0035] The present invention will be further described below with reference to specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0036] Directional solidification purification device

[0037] The directional solidification purification apparatus of the present invention includes a main furnace body, a water cooling device, a vacuum device, and a temperature measuring thermocouple.

[0038] Main furnace body

[0039] The main furnace body of the present invention includes a furnace body, a purification crucible, a water-cooled cover plate, a heating element, and a heat insulation layer. In some embodiments, it also includes one or more of a graphite tray and a support body.

[0040] The furnace body of the present invention has a furnace cavity. The furnace body includes a furnace body and a furnace cover. The top of the furnace body has an opening. The furnace cover covers the top opening of the furnace body. The furnace cover is detachably connected to the furnace body. The furnace body and the furnace cover form the furnace cavity.

[0041] Water-cooling pipes are installed on the inner wall of the furnace body. In some embodiments, the water-cooling pipes are installed on the side wall of the furnace body and the inner wall of the furnace cover. The water-cooling pipes are used to cool the furnace body.

[0042] The purification crucible is placed inside the furnace cavity. The purification crucible is configured to contain rare earth metals and / or molten rare earth metals.

[0043] A water-cooled cover plate covers the top opening of the purification crucible. The water-cooled cover plate is used to cool the purification crucible. The diameter of the water-cooled cover plate can be slightly larger than the diameter of the purification crucible. The water-cooled cover plate is used to cool the substance inside the purification crucible. The water-cooled cover plate can be made of stainless steel.

[0044] The heating element includes a side heating element and a bottom heating element. The heating element is used to heat the substance inside the purification crucible. The side heating element and the bottom heating element are independently installed and do not affect each other.

[0045] The bottom heating element is positioned below the bottom wall of the purification crucible. The bottom heating element can be a silicon-molybdenum heating plate. A graphite tray can be placed between the bottom heating element and the purification crucible. The graphite tray supports the purification crucible and does not contact the bottom heating element. The bottom heating element can be connected to a bottom heating element controller. The bottom heating element controller controls the power of the bottom heating element.

[0046] The support column is installed inside the furnace cavity and fixed to the bottom wall of the furnace body. A portion of the support column passes through the bottom heating element. The support column contacts the graphite tray. The support column is used to support the graphite tray.

[0047] The side heating element is wrapped around the outer circumference of the side wall of the purification crucible. The distance between the side heating element and the outer surface of the side wall of the purification crucible can be 50-100 mm. The side heating element can be connected to a side heating element controller. The side heating element controller is used to control the power of the side heating element. The side heating element can be a U-shaped silicon molybdenum rod.

[0048] The support structure is located inside the furnace cavity and fixed to the bottom wall of the furnace body. The bottom heating element is located above the support structure.

[0049] An insulation layer surrounds at least a portion of the purification crucible and the heating element. The insulation layer is configured to keep the material inside the purification crucible warm. In some embodiments, the top of the insulation layer is fitted around the outer periphery of the purification crucible and fixed to the side wall of the crucible. The bottom of the insulation layer is fitted around the outer periphery of a support and fixed to the support. The thickness of the insulation layer can be 50–200 mm.

[0050] Water-cooled equipment and temperature measuring thermocouples

[0051] The water-cooling equipment of the present invention includes a first cooling water conveying pipeline, a cover plate water-cooling pump, a second cooling water conveying pipeline, and a furnace body water-cooling pump.

[0052] One end of the first cooling water delivery pipe is connected to the water-cooled cover plate. The other end of the first cooling water delivery pipe is connected to the cover plate water-cooling pump. In some embodiments, a portion of the first cooling water delivery pipe extends into the furnace cavity through an opening in the center of the furnace cover, thereby connecting to the water-cooled cover plate. A sealing ring may be provided at this opening.

[0053] One end of the second cooling water delivery pipeline is connected to the water-cooling pipe. The other end of the second cooling water delivery pipeline is connected to the furnace body water-cooling pump.

[0054] The temperature-sensing thermocouple can be installed on one side of the furnace body. The thermocouple is configured to measure the temperature inside the furnace cavity. The thermocouple can be a double platinum-rhodium thermocouple.

[0055] Vacuum equipment

[0056] The vacuum equipment is designed to extract gas from the furnace chamber. The vacuum equipment includes a low-vacuum evacuation line, a roughing valve, a Roots pump, a mechanical pump, a high-vacuum evacuation line, a main valve, a vacuum pump, and a pre-valve.

[0057] One end of the low-vacuum evacuation line is connected to the furnace cavity, and the other end is connected to a mechanical pump. A Roots pump and a roughing valve are installed on the low-vacuum evacuation line. The Roots pump is located at the rear end of the roughing valve. Gas extracted from the furnace cavity first passes through the roughing valve and then through the Roots pump.

[0058] The high-vacuum evacuation line and the low-vacuum evacuation line are connected in parallel at a section equipped with a roughing valve. The high-vacuum evacuation line is sequentially equipped with a main valve, a vacuum pump, and a pre-valve. The main valve is located upstream of the vacuum pump. Gas extracted from the furnace chamber first passes through the main valve and then through the vacuum pump. The vacuum pump can be a molecular pump.

[0059] <Directional solidification purification method for rare earth metals>

[0060] The method of the present invention includes the following steps: (1) a first heat preservation step; (2) a second heat preservation step; (3) a cooling step; and (4) a step of obtaining purified rare earth metal. Specifically, it may also include the steps of vacuuming and filling with inert gas.

[0061] One-time heat preservation steps

[0062] With an inert atmosphere and a pressure of 0.02–0.15 MPa inside the furnace cavity, and with rare earth metals in the purification crucible and cooling water flowing through the water-cooling pipes, turn on the side heating element and the bottom heating element to bring the temperature inside the furnace cavity to T1, and then hold it at that temperature for 10–150 minutes.

[0063] The inert gas used to provide the inert atmosphere is preferably argon. The argon gas can be argon gas that has undergone secondary deoxygenation.

[0064] The pressure inside the furnace cavity is 0.02 to 0.15 MPa; preferably 0.1 to 0.12 MPa.

[0065] T1 is 10–150°C higher than the melting point of the rare earth metal in the purification crucible; preferably, T1 is 20–50°C higher than the melting point of the rare earth metal in the purification crucible; in some embodiments, T1 is 25–30°C higher than the melting point of the rare earth metal in the purification crucible. The melting point of the rare earth metal is calculated based on the melting point of the elemental rare earth metal.

[0066] The rare earth metal can be a rare earth metal with a low vapor pressure. For example, yttrium, lanthanum, cerium, praseodymium, neodymium, gadolinium, and terbium. In some embodiments, the rare earth metal is yttrium or terbium.

[0067] Rare earth metals can contain impurities such as Ca, F, Fe, Al, and Si. Specifically, rare earth metals can be prepared by the calcothermal reduction method.

[0068] The heat preservation time is 10 to 150 minutes; preferably 70 to 100 minutes.

[0069] The heating rate from the initial temperature to T1 can be 10–35 °C / min; preferably 15–20 °C / min. This can improve the purification effect.

[0070] Secondary insulation steps

[0071] After the heat preservation is completed, cool water is introduced into the water-cooled cover plate, the side heating element is closed, and the bottom heating element is kept on to maintain the temperature in the furnace cavity at T1±10℃ for 10 to 120 minutes.

[0072] The temperature inside the furnace cavity is maintained at T1±10℃; preferably T1±5℃.

[0073] The heat preservation time is 10 to 120 minutes; preferably 15 to 100 minutes.

[0074] Cooling steps

[0075] Adjust the output power of the bottom heating element until the temperature of the furnace cavity drops to T2, then turn off the bottom heating element; once the temperature inside the furnace cavity reaches the ambient temperature, stop supplying cooling water to the water-cooled pipes and water-cooled cover plate.

[0076] T2 is 10–90°C below the melting point of the rare earth metal in the purification crucible; preferably, T2 is 50–75°C below the melting point of the rare earth metal in the purification crucible. The melting point of the rare earth metal is calculated based on the melting point of the elemental rare earth metal.

[0077] The cooling rate to T2 can be 1–15 °C / h; preferably 2–10 °C / h; more preferably 5–8 °C / h. This can improve the purification effect.

[0078] Steps to obtain purified rare earth metals

[0079] Remove the solid metal from the purification crucible, divide the solid metal, and take the middle part as the purified rare earth metal.

[0080] The steps of vacuuming and filling with inert gas

[0081] With rare earth metals in the purification crucible and cooling water flowing through the water-cooling pipes, start the mechanical pump and open the roughing valve to reduce the pressure inside the furnace chamber to 500–1000 Pa; then start the Roots pump to reduce the pressure inside the furnace chamber to 0.5–20 Pa, preferably 1–10 Pa; close the roughing valve, open the main valve and the pre-valve, and start the vacuum pump to reduce the pressure inside the furnace chamber to 10 Pa. -4 Below 0.02 MPa; inert gas is introduced into the furnace cavity to bring the pressure inside the furnace cavity to 0.02–0.15 MPa. The test method is described below:

[0082] According to the current GB / T 12690 Chemical Analysis Methods for Non-Rare Earth Impurities in Rare Earth Metals and Their Oxides, the contents of Ca, F, Fe, Al and Si elements in rare earth metals before and after purification were determined by GDMS (Glow Discharge Mass Spectrometry).

[0083] The specific determination method is as follows: Rare earth metal samples are processed into cuboids with a length and width of 25 mm and a height of 10 mm. Oil stains on the sample surface are cleaned with ethanol, followed by rinsing with ultrapure water, surface etching with 5% (volume fraction) nitric acid solution, repeated rinsing with water, and drying with high-purity nitrogen before being fixed in the sample holder of a DC glow discharge mass spectrometer. The graphite cone, graphite guide tube, graphite anode cap, and ceramic cap are then installed sequentially. The sample holder is pushed into the ion source chamber, and "GD on" is activated until the vacuum reaches 10...-7 Pa, adjust the instrument to the optimal conditions, set the pre-sputtering time to 15 minutes, and collect data. The instrument software will automatically calculate the content of the impurity element to be measured.

[0084] Example 1

[0085] like Figure 1 As shown, the directional solidification purification device of this embodiment includes a furnace body, a purification crucible 5, a water-cooled cover plate 2, a heating element, a heat insulation layer 7, a graphite tray 8, a support body 10, a support column 23, a first cooling water conveying pipe 19, a cover plate water-cooling pump 18, a second cooling water conveying pipe 20, a furnace body water-cooling pump 17, a vacuum device, and a temperature measuring thermocouple (not shown).

[0086] The furnace body includes a furnace body 6 and a furnace cover 1. The top of the furnace body 6 has an opening. The furnace cover 1 covers the top opening of the furnace body 6. The furnace cover 1 is detachably connected to the furnace body 6. The furnace body 6 and the furnace cover 1 form the furnace cavity.

[0087] Water-cooling pipes 3 are installed on the inner side wall of the furnace body 6 and the inner wall of the furnace cover 1. The water-cooling pipes 3 are used to cool the furnace body.

[0088] The heating element includes a side heating element 4 and a bottom heating element 9. The heating element is used to heat the substance inside the purification crucible 5.

[0089] The bottom heating element 9 is located below the bottom wall of the purification crucible 5. The bottom heating element 9 can be a silicon molybdenum heating plate. A bottom heating element controller (not shown) is connected to the bottom heating element 9. The bottom heating element controller is used to control the power of the bottom heating element 9.

[0090] The support column 23 is disposed in the furnace cavity and fixed to the bottom wall of the furnace body 6. A portion of the support column 23 protrudes from the bottom heating element 9. The support column 23 is used to support the graphite tray 8.

[0091] The graphite tray 8 is positioned between the bottom heating element 9 and the bottom wall of the purification crucible 5, but does not contact the bottom heating element 9. The graphite tray 8 is in contact with the support column 23. The graphite tray 8 is used to support the purification crucible 5.

[0092] The purification crucible 5 is positioned above the graphite tray 8. The bottom wall of the purification crucible 5 is in contact with the graphite tray 8. The purification crucible 5 is used to contain rare earth metals and / or molten rare earth metals.

[0093] A side heating element 4 surrounds the outer periphery of the side wall of the purification crucible 5. The distance between the side heating element 4 and the side wall (outer surface) of the purification crucible 5 is 50–100 mm. A side heating element controller (not shown) is connected to the side heating element 4. The side heating element controller is used to control the power of the side heating element 4. The side heating element 4 can be a U-shaped silicon molybdenum rod.

[0094] A water-cooled cover plate 2 covers the top opening of the purification crucible 5. The diameter of the water-cooled cover plate 2 may be slightly larger than the diameter of the purification crucible 5. The water-cooled cover plate 2 is used to cool the substance inside the purification crucible. The water-cooled cover plate 2 may be made of stainless steel.

[0095] The support 10 is installed in the furnace cavity and fixed to the bottom wall of the furnace body 6.

[0096] The insulation layer 7 surrounds at least a portion of the purification crucible 5 and the heating element. The top of the insulation layer 7 is fitted around the outer periphery of the purification crucible 5 and fixed to the side wall of the purification crucible 5. The bottom of the insulation layer 7 is fitted around the outer periphery of the support body 10 and fixed to the support body 10. The thickness of the insulation layer 7 can be 50–200 mm.

[0097] A portion of the first cooling water supply pipe 19 extends into the furnace cavity through an opening in the middle of the furnace cover 1. A sealing ring can be installed at this opening to improve the sealing performance of the furnace body. One end of the first cooling water supply pipe 19 is connected to the water-cooled cover plate 2, and the other end of the first cooling water supply pipe 19 is connected to the cover plate water-cooling pump 18.

[0098] One end of the second cooling water delivery pipe 20 is connected to the water cooling pipe 3, and the other end of the second cooling water delivery pipe 20 is connected to the furnace body water cooling pump 17.

[0099] Vacuum equipment is used to extract gas from the furnace chamber. Vacuum equipment includes a low vacuum evacuation line 21, a roughing valve 16, a Roots pump 14, a mechanical pump 13, a high vacuum evacuation line 22, a main valve 15, a vacuum pump 11, and a pre-valve 12.

[0100] One end of the low-vacuum evacuation line 21 is connected to the furnace cavity, and the other end is connected to the mechanical pump 13. A roughing valve 16 and a Roots pump 14 are installed on the low-vacuum evacuation line 21. The Roots pump 14 is located at the rear end of the roughing valve 16, meaning that the gas extracted from the furnace cavity first passes through the roughing valve 16 and then through the Roots pump 14.

[0101] The high-vacuum evacuation line 22 and the low-vacuum evacuation line 21 are connected in parallel, with a section of the coarse pump 16 installed. The high-vacuum evacuation line 22 is sequentially equipped with a main valve 15, a vacuum pump 11, and a pre-valve 12. The main valve 15 is located upstream of the vacuum pump 11; that is, the gas extracted from the furnace chamber first passes through the main valve 15 and then through the vacuum pump 11. The vacuum pump 11 is a molecular pump.

[0102] A temperature-sensing thermocouple (not shown) is installed on one side of the furnace body. The thermocouple is used to measure the temperature inside the furnace cavity. The thermocouple can be a double platinum-rhodium thermocouple.

[0103] Example 2

[0104] 10 kg of rare earth metal yttrium (the melting point of elemental yttrium is 1522℃) is placed into the purification crucible 5. The purification crucible 5 and the water-cooled cover plate 2 are assembled together, and then the furnace cover 1 and the furnace body 6 are assembled together. The furnace body water-cooling pump 17 is turned on to supply cooling water to the water-cooling pipe 3. The mechanical pump 13 is started, and the roughing valve 16 is opened to reduce the pressure inside the furnace chamber to 600 Pa; then the Roots pump 14 is turned on to reduce the pressure inside the furnace chamber to 1-10 Pa. The roughing valve 16 is closed, the main valve 15 and the pre-valve 12 are opened, and the vacuum pump 11 is started to reduce the pressure inside the furnace chamber to 10 Pa. -4 Pa. High-purity argon gas, which has undergone secondary deoxygenation, is introduced into the furnace cavity to bring the pressure inside the furnace cavity to 0.12 MPa.

[0105] Turn on the bottom heating element controller and the side heating element controller to heat the material in the purification crucible 5. After the temperature inside the furnace reaches 1550℃, hold it at that temperature for 90 minutes. The heating rate from the initial temperature to 1550℃ is 20℃ / min.

[0106] After the heat preservation is completed, turn off the side heating element 4, turn on the cover plate water cooling pump 18 to introduce cooling water into the water cooling cover plate 2, and control the bottom heating element 9 to maintain the temperature inside the furnace cavity at 1550℃ for 15 minutes.

[0107] Reduce the output power of the bottom heating element 9 to lower the temperature inside the furnace cavity to 1450℃ (T2) at a rate of 5℃ / h, then turn off the bottom heating element 9. After the temperature inside the furnace cavity drops to the ambient temperature, turn off the cover plate water cooling pump 18 and the furnace body water cooling pump 17.

[0108] After opening the furnace lid 1 and removing the purification crucible 5 from the furnace body 6, take out the solid metal inside the purification crucible 5. Divide the solid metal and take the middle part as the purified rare earth metal.

[0109] The contents of Ca, F, Fe, Al and Si in yttrium bulk rare earth metal and purified rare earth metal are shown in Table 1.

[0110] Table 1

[0111]

[0112] Example 3

[0113] A 10 kg block of rare earth metal terbium (the melting point of elemental terbium is 1356℃) is placed into the purification crucible 5. The purification crucible 5 and the water-cooled cover plate 2 are assembled together, and then the furnace cover 1 and the furnace body 6 are assembled together. The furnace body water-cooling pump 17 is turned on to supply cooling water to the water-cooling pipe 3. The mechanical pump 13 is started, and the roughing valve 16 is opened to reduce the pressure inside the furnace chamber to 600 Pa; then the Roots pump 14 is turned on to reduce the pressure inside the furnace chamber to 1-10 Pa. The roughing valve 16 is closed, the main valve 15 and the pre-valve 12 are opened, and the vacuum pump 11 is started to reduce the pressure inside the furnace chamber to 10 Pa. -4 Pa. High-purity argon gas, which has undergone secondary deoxygenation, is introduced into the furnace cavity to bring the pressure inside the furnace cavity to 0.12 MPa.

[0114] Turn on the bottom heating element controller and the side heating element controller to heat the material in the purification crucible 5. After the temperature inside the furnace reaches 1400℃, hold it at that temperature for 90 minutes. The heating rate from the initial temperature to 1400℃ is 20℃ / min.

[0115] After the insulation is completed, turn off the side heating element 4, turn on the cover plate water cooling pump 18 to introduce cooling water into the water cooling cover plate 2, and control the bottom heating element 9 to maintain the temperature inside the furnace cavity at 1400℃ for 15 minutes.

[0116] Reduce the output power of the bottom heating element 9 to lower the temperature inside the furnace cavity to 1300℃ (T2) at a rate of 5℃ / h, then turn off the bottom heating element 9. After the temperature inside the furnace cavity drops to the ambient temperature, turn off the cover plate water cooling pump 18 and the furnace body water cooling pump 17.

[0117] After opening the furnace lid 1 and removing the purification crucible 5 from the furnace body 6, take out the solid metal inside the purification crucible 5. Divide the solid metal and take the middle part as the purified rare earth metal.

[0118] The contents of Ca, F, Fe, Al and Si in terbium bulk rare earth metal and purified rare earth metal are shown in Table 2.

[0119] Table 2

[0120]

[0121] This invention is not limited to the above-described embodiments. Any modifications, improvements, or substitutions that can be conceived by those skilled in the art without departing from the essential content of this invention fall within the scope of this invention.

Claims

1. A method for directional solidification purification of rare earth metals using a directional solidification purification device, characterized in that, The directional solidification and purification device includes a furnace body, a purification crucible, a water-cooled cover plate, a heating element, and a heat insulation layer; The furnace body has a furnace cavity, and a water-cooling pipe is provided on the inner wall of the furnace body. The water-cooling pipe is configured to cool the furnace body. The purification crucible is disposed in the furnace cavity, and the purification crucible is configured to contain rare earth metals; The water-cooled cover plate covers the top opening of the purification crucible, and the water-cooled cover plate is configured to cool the substance inside the purification crucible; The heating element includes a side heating element and a bottom heating element, and the heating element is configured to heat the substance inside the purification crucible; the side heating element surrounds the outer periphery of the side wall of the purification crucible, and the bottom heating element is disposed below the bottom wall of the purification crucible; The insulation layer surrounds at least a portion of the purification crucible and the heating element, and the insulation layer is configured to keep the material inside the purification crucible warm. The method includes the following steps: (1) With an inert atmosphere and a pressure of 0.1 to 0.15 MPa in the furnace cavity, rare earth metals in the purification crucible and cooling water flowing through the water cooling pipe, turn on the side heating element and the bottom heating element to bring the temperature in the furnace cavity to T1 and keep it at that temperature for 70 to 100 minutes; T1 is 20 to 50°C higher than the melting point of the rare earth metals in the purification crucible, and the melting point of the rare earth metals is based on the melting point of the rare earth metal elements; the rare earth metals are selected from yttrium, lanthanum, cerium, praseodymium, neodymium, gadolinium, and terbium, and the impurities contained in the rare earth metals include Ca, F, Fe, Al, and Si; (2) After the heat preservation is completed, cool water is introduced into the water-cooled cover plate, the side heating element is closed, and the bottom heating element is kept open to maintain the temperature in the furnace cavity at T1±10℃ for 10 to 15 minutes. (3) Adjust the output power of the bottom heating element so that the temperature of the furnace cavity drops to T2 at a rate of 2 to 10℃ / h, and then turn off the bottom heating element; after the temperature in the furnace cavity reaches the ambient temperature, stop supplying cooling water to the water cooling pipe and water cooling cover plate; T2 is 50 to 75℃ below the melting point of rare earth metals in the purification crucible, and the melting point of rare earth metals is based on the melting point of rare earth metal elements; Remove the solid metal from the purification crucible, divide the solid metal, and take the middle part as the purified rare earth metal.

2. The method according to claim 1, characterized in that, The directional solidification and purification device also includes a first cooling water delivery pipeline, a cover plate water-cooled pump, a second cooling water delivery pipeline, and a furnace body water-cooled pump; One end of the first cooling water delivery pipe is connected to the water-cooled cover plate, and the other end of the first cooling water delivery pipe is connected to the cover plate water-cooling pump. One end of the second cooling water delivery pipe is connected to the water cooling pipe, and the other end of the second cooling water delivery pipe is connected to the furnace body water cooling pump.

3. The method according to claim 1, characterized in that, A graphite tray is provided between the bottom heating element and the bottom wall of the purification crucible.

4. The method according to claim 1, characterized in that, The directional solidification and purification device also includes a vacuum device, which is configured to extract the gas from the furnace chamber. The vacuum equipment includes a low-vacuum pumping line, a roughing valve, a Roots pump, a mechanical pump, a high-vacuum pumping line, a main valve, a vacuum pump, and a pre-valve. One end of the low vacuum pumping pipeline is connected to the furnace cavity, and the other end of the low vacuum pumping pipeline is connected to the mechanical pump. The low vacuum pumping pipeline is equipped with a roughing valve and a Roots pump, and the Roots pump is located at the rear end of the roughing valve. The high-vacuum pumping line and the section of the low-vacuum pumping line equipped with the coarse pumping valve are connected in parallel. The high-vacuum pumping line is equipped with a main valve, a vacuum pump and a pre-valve in sequence. The vacuum pump is a molecular pump.

5. The method according to claim 1, characterized in that, The directional coagulation and purification device also includes a temperature measuring thermocouple; The temperature-measuring thermocouple is installed on one side of the furnace body, and the temperature-measuring thermocouple is configured to measure the temperature inside the furnace cavity.

6. The method according to claim 1, characterized in that, The distance between the side heating element and the outer wall of the purification crucible is 50-100mm, and the thickness of the insulation layer is 50-200mm.

7. The method according to claim 1, characterized in that, The heating rate to T1 is 10–35 °C / min.

8. The method according to claim 1, characterized in that, It also includes the following steps: Start the mechanical pump and open the roughing valve to reduce the pressure inside the furnace chamber to 500–1000 Pa; then start the Roots pump to reduce the pressure inside the furnace chamber to 0.5–20 Pa; close the roughing valve, open the main valve and the pre-valve, and start the vacuum pump to reduce the pressure inside the furnace chamber to 10 Pa. -4 Below Pa; inert gas is introduced into the furnace cavity to bring the pressure inside the furnace cavity to 0.1-0.15 MPa.

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