Method for preparing ultra-pure metal through hydrogen refining and directional solidification

Abstract

The invention discloses a method for preparing ultra-pure metal through hydrogen refining and directional solidification, and belongs to the technical field of nonferrous metallurgy and metal material processing. Metal raw materials are heated and smelted, then hydrogen is dissolved, then directional solidification is conducted, finally heating and smelting are conducted, and high-purity metal is obtained through directional solidification. Based on the characteristic that the solubility of hydrogen in a liquid phase is far higher than that of a solid phase, in the directional solidification process, the hydrogen can generate a supersaturation phenomenon, nucleation, growth and floating spontaneously form bubbles at a solidification interface, and due to the fact that the surface energy of the hydrogen bubbles is high, impurities and inclusions at the solid-liquid interface can be adsorbed to the surfaces of the bubbles; the problems of high energy consumption and low purification efficiency in the prior art are effectively solved, and more efficient and more economical metal purification can be realized.

Description

Technical Field

[0001] The invention relates to a method for preparing ultra-high purity metal by hydrogen refining and directional solidification, belonging to the technical field of nonferrous metallurgy and metal material processing. Background Art

[0002] High-purity metals are important basic materials for modern high-tech, and their purity directly determines the performance of the materials. For example, high-purity metals are widely used in the preparation of target materials, and chemical purity is one of the key factors affecting the performance of thin film materials. At present, the purity of high-purity metal targets commonly used in integrated circuits (such as copper, nickel, nickel-platinum alloys, etc.) usually needs to reach 4N5 (99.995%) or above, and there are strict control requirements for the content of alkali metals, alkaline earth metals, radioactive metal elements and gas impurities. With the further reduction of technology nodes, the purity requirements for integrated circuit targets even exceed 6N (99.9999%).

[0003] At present, the industry commonly uses vacuum smelting methods to prepare ultra-high purity metals, mainly including vacuum distillation, vacuum zone melting, vacuum directional solidification, etc. Among them, the principle of vacuum distillation is to use the vapor pressure difference between metal and impurities under vacuum conditions to separate impurities by evaporation. However, this method has high requirements for the vacuum degree of the equipment, and only has a good removal effect on impurities with low boiling points (such as Mg, Zn, etc.). Since the decomposition pressure of metal oxides is extremely low, it is difficult to remove non-metallic impurities in metals by vacuum distillation. Vacuum zone melting achieves segregation and separation of impurities by moving the melting zone multiple times, but this method requires repeated zone melting (usually 4 to 20 times), and the diameter of the zone melting sample is usually less than 20 mm, so the purification efficiency is extremely low and is not suitable for large-scale production. The vacuum directional solidification method uses the difference in impurity distribution coefficients between the liquid phase and the solid phase of the metal during the solidification process to enrich impurities in the liquid phase. However, in order to ensure that the impurities can be fully segregated during the smelting process, directional solidification requires an extremely slow pulling speed (less than 0.4 mm / min). In order to improve this problem, electromagnetic stirring is usually introduced to promote the segregation of solutes. However, the introduction of electromagnetic stirring not only significantly increases energy consumption, but also easily increases the number of grains, causing impurities to accumulate at the grain boundaries, which in turn reduces the purification effect of the metal. Summary of the invention

[0004] In order to overcome the problems in the background technology, the purpose of the present invention is to provide a method for preparing ultra-high purity metal by hydrogen refining and directional solidification. During the solidification process, fine bubbles spontaneously formed by supersaturated hydrogen can efficiently remove impurities and inclusions to achieve efficient purification of the metal.

[0005] In order to achieve the above object, the present invention is implemented by the following technical solutions:

[0006] A method for preparing ultra-high purity metal by hydrogen refining and directional solidification, comprising the following steps:

[0007] (1) placing the metal raw material in a melting crucible in a directional solidification device;

[0008] (2) Pump the furnace pressure down to 10 -1 ~10 -3 After the temperature reaches the range of Pa, the metal raw material is heated and smelted until it is completely melted and forms a uniform metal melt;

[0009] (3) After the metal raw material is completely melted, hydrogen-containing gas is introduced into the furnace and the temperature is kept constant;

[0010] (4) Directional solidification is carried out after the insulation is completed;

[0011] (5) After the directional solidification is completed, the pressure in the furnace is reduced to 0.1 MPa and then vacuumed to 10 -3 ~10 -5 Pa; then the metal raw material is heated and melted again until a uniform metal melt is formed; finally, directionally solidified again to obtain a high-purity metal ingot.

[0012] More preferably, the metal raw material is magnesium, nickel, iron, copper, gold, platinum or nickel-platinum alloy.

[0013] More preferably, the heating and smelting temperature is 600-2000°C.

[0014] More preferably, the hydrogen-containing gas is high-purity hydrogen or a mixed gas of hydrogen and argon.

[0015] More preferably, in step (3), hydrogen-containing gas is introduced into the furnace so that the total pressure of the gas in the furnace reaches 0.1 to 2.0 MPa, which can ensure that the hydrogen is fully dissolved in the molten metal. If the total pressure is greater than 2.0 MPa, the H in the molten metal will be supersaturated in advance before the start of directional solidification, and will precipitate before directional solidification, which will reduce the purity of the high-purity metal and cause defects in the ingot.

[0016] More preferably, the insulation time is 10 to 20 minutes.

[0017] More preferably, in step (4), the speed of directional solidification is 0.4-5.0 mm / min. When the gas pressure in the furnace is constant, the faster the directional solidification speed is, the less time the precipitated hydrogen bubbles will have to merge. Therefore, the smaller the precipitated hydrogen bubbles are, the easier it is to achieve efficient adsorption and removal of impurities. However, when the speed of directional solidification is greater than 5.0 mm / min, the metal solidifies faster, resulting in hydrogen not having enough time to escape from the melt, making it easy to form pores in the ingot, and causing impurities to remain on the pore walls in the ingot.

[0018] More preferably, in step (5), the directional solidification speed is 0.4-1.0 mm / min. When the solidification speed is too fast, it may be difficult to completely remove H in the ingot.

[0019] Beneficial effects of the present invention: The present invention utilizes that the solubility of hydrogen in metal has a sudden change near the melting point, that is, the solubility of hydrogen in the liquid phase is much higher than that in the solid phase. Therefore, during the directional solidification process, hydrogen will be supersaturated, and bubbles will nucleate, grow and float spontaneously at the solidification interface. Since the surface energy of hydrogen bubbles is relatively high, impurities and inclusions at the solid-liquid interface will be adsorbed to the bubble surface, and in the process of the bubbles floating, the impurities and inclusions will be taken out of the melt. The present invention effectively solves the problems of high energy consumption and low purification efficiency in traditional technologies, and can achieve more efficient and economical metal purification. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 The solubility curve of H in molten magnesium, nickel, iron, copper and gold at 0.1MPa changes with temperature.

[0021] Figure 2 It is a directional solidification device, which includes: 1-vacuum / high-pressure melting chamber, 2-crucible for melting, 3-medium frequency induction coil, 4-water cooling table, 5-infrared temperature measuring device, 6-lifting mechanism, 7-vacuum pump, 8-high-purity argon, 9-high-purity hydrogen, 10-air release valve, and 11-water chiller.

[0022] The smelting crucible is located inside the vacuum / high-pressure smelting chamber, the water cooling table is located at the bottom of the smelting crucible, the lifting mechanism passes through the bottom of the vacuum / high-pressure smelting chamber and is connected to the bottom of the water cooling table, and the lifting mechanism drives the smelting crucible and the water cooling table to move up and down; the chiller is connected to the water cooling table through a pipeline.

[0023] The outside of the melting crucible is wrapped with a medium-frequency induction coil; the vacuum / high-pressure melting chamber is connected to a vacuum pump, which is located outside the vacuum / high-pressure melting chamber; the infrared temperature measuring device is located on the top of the vacuum / high-pressure melting chamber to test the internal temperature of the vacuum / high-pressure melting chamber; high-purity argon and high-purity hydrogen enter from the top of the vacuum / high-pressure melting chamber through pipelines; and the air release valve is located on the vacuum / high-pressure melting chamber. DETAILED DESCRIPTION

[0024] The present invention is further described in detail below in conjunction with specific embodiments, but the protection scope of the present invention is not limited thereto.

[0025] All chemical reagents not specified in the examples and comparative examples of the present invention were commercially available analytically pure for experiments.

[0026] Example 1

[0027] Industrial pure copper (original metal raw material purity 99.99%) is used as raw material, and high-purity copper is refined by hydrogen refining and directional solidification. The specific steps are as follows:

[0028] (1) Cut industrial pure copper into blocks of uniform size, place them in a high-purity graphite crucible with a diameter of 50 mm and a height of 200 mm, and place them in a directional solidification device (such as Figure 2 )Inside.

[0029] (2) Pump the furnace pressure down to 10 -3 After 30 ℃, the industrial pure copper is heated to 1250℃ and kept warm for 20 minutes to form a uniform metal melt.

[0030] (3) High-purity hydrogen (purity ≥ 99.999%) is introduced to raise the total pressure of the gas in the furnace to 0.5 MPa and maintain it for 15 minutes to allow the hydrogen to fully dissolve in the copper melt.

[0031] (4) Directional solidification was carried out at a speed of 2 mm / min to obtain a high-purity copper ingot (diameter 50 mm and height 150 mm).

[0032] (5) Reduce the pressure in the furnace to 0.1 MPa and then evacuate to 10 -5 Pa. The high-purity copper refined by hydrogen was then heated to 1250°C again, kept at this temperature for 20 minutes, and then directionally solidified at a speed of 0.5 mm / min to completely remove the residual hydrogen in the metal.

[0033] Comparative Example 1

[0034] Industrial pure copper (original metal raw material purity 99.99%) is used as raw material, and high-purity copper is refined by hydrogen refining and directional solidification. The specific steps are as follows:

[0035] (1) Cut industrial pure copper into blocks of uniform size, place them in a high-purity graphite crucible with a diameter of 50 mm and a height of 200 mm, and place them in a directional solidification device (such as Figure 2 )Inside.

[0036] (2) Pump the furnace pressure down to 10 -3 After 30 ℃, the industrial pure copper is heated to 1250℃ and kept warm for 20 minutes to form a uniform metal melt.

[0037] (3) Directional solidification was carried out at a speed of 2 mm / min to obtain a high-purity copper ingot (diameter 50 mm and height 150 mm).

[0038] (4) Reduce the pressure in the furnace to 0.1 MPa and then evacuate to 10 -5Pa. The high-purity copper refined by hydrogen was then heated to 1250°C again, kept at this temperature for 20 minutes, and then directionally solidified at a speed of 0.5 mm / min to completely remove the residual hydrogen in the metal.

[0039] Example 2

[0040] Industrial pure nickel (original metal raw material purity 99.9945%) is used as raw material, and high-purity nickel is refined and prepared by hydrogen refining and directional solidification. The specific steps are as follows:

[0041] (1) Cut industrial pure nickel into blocks of uniform size, place them in a high zirconia crucible with a diameter of 30 mm and a height of 120 mm, and place them in a directional solidification device (such as Figure 2 )Inside.

[0042] (2) Pump the furnace pressure down to 10 -3 After 30 ℃, industrial pure nickel is heated to 1550℃ and kept warm for 20 minutes to form a uniform metal melt.

[0043] (3) High-purity hydrogen (purity ≥ 99.999%) is introduced to raise the total pressure of the gas in the furnace to 0.6 MPa and maintained for 15 minutes to allow the hydrogen to fully dissolve in the nickel melt.

[0044] (4) Directional solidification is carried out at a speed of 2 mm / min to obtain high-purity nickel (30 mm in diameter and 100 mm in height).

[0045] (5) Reduce the pressure in the furnace to 0.1 MPa and then evacuate to 10 -5 Pa. The high-purity nickel refined by hydrogen is then heated to 1550°C again, kept at this temperature for 20 minutes, and then directionally solidified at a speed of 0.5 mm / min to completely remove the residual hydrogen in the metal.

[0046] Comparative Example 2

[0047] Industrial pure nickel (original metal raw material purity 99.9945%) is used as raw material, and high-purity nickel is refined and prepared by hydrogen refining and directional solidification. The specific steps are as follows:

[0048] (1) Cut industrial pure nickel into blocks of uniform size, place them in a high zirconia crucible with a diameter of 30 mm and a height of 120 mm, and place them in a directional solidification device (such as Figure 2 )Inside.

[0049] (2) Pump the furnace pressure down to 10 -3 After 30 ℃, industrial pure nickel is heated to 1550℃ and kept warm for 20 minutes to form a uniform metal melt.

[0050] (3) Directional solidification is carried out at a speed of 2 mm / min to obtain high-purity nickel (diameter 30 mm and height 100 mm).

[0051] (4) Reduce the pressure in the furnace to 0.1 MPa and then evacuate to 10 -5 Pa. The high-purity nickel refined by hydrogen is then heated to 1550°C again, kept at this temperature for 20 minutes, and then directionally solidified at a speed of 0.5 mm / min to completely remove the residual hydrogen in the metal.

[0052] Example 3

[0053] Using nickel-platinum alloy (original metal raw material purity 99.9%) as raw material, high-purity nickel-platinum is refined by hydrogen refining and directional solidification. The specific steps are as follows:

[0054] (1) Cut the nickel-platinum alloy into blocks of uniform size, place them in a high zirconia crucible with a diameter of 30 mm and a height of 120 mm, and place them in a directional solidification device (such as Figure 2 )Inside.

[0055] (2) Pump the furnace pressure down to 10 -3 Pa, the nickel-platinum alloy is heated to 1750°C and kept warm for 20 minutes to form a uniform metal melt.

[0056] (3) High-purity hydrogen (purity ≥ 99.999%) is introduced to raise the total pressure of the gas in the furnace to 0.6 MPa and maintain it for 15 minutes to allow the hydrogen to fully dissolve in the nickel-platinum alloy melt.

[0057] (4) Directional solidification was performed at a speed of 2 mm / min to obtain a high-purity nickel-platinum alloy (30 mm in diameter and 100 mm in height).

[0058] (5) Reduce the pressure in the furnace to 0.1 MPa and then evacuate to 10 -5 Pa. The high-purity nickel-platinum alloy refined by hydrogen was then heated to 1550°C again, kept at this temperature for 20 minutes, and then directionally solidified at a speed of 0.5 mm / min to completely remove the residual hydrogen in the metal.

[0059] Comparative Example 3

[0060] Using nickel-platinum alloy (original metal raw material purity 99.9%) as raw material, high-purity nickel-platinum is refined by hydrogen refining and directional solidification. The specific steps are as follows:

[0061] (1) Cut the nickel-platinum alloy into blocks of uniform size, place them in a high zirconia crucible with a diameter of 30 mm and a height of 120 mm, and place them in a directional solidification device (such as Figure 2 )Inside.

[0062] (2) Pump the furnace pressure down to 10-3 Pa, the nickel-platinum alloy is heated to 1750°C and kept warm for 20 minutes to form a uniform metal melt.

[0063] (3) Directional solidification was performed at a speed of 2 mm / min to obtain a high-purity nickel-platinum alloy (30 mm in diameter and 100 mm in height).

[0064] (4) Reduce the pressure in the furnace to 0.1 MPa and then evacuate to 10 -5 Pa. The high-purity nickel-platinum alloy refined by hydrogen was then heated to 1550°C again, kept at this temperature for 20 minutes, and then directionally solidified at a speed of 0.5 mm / min to completely remove the residual hydrogen in the metal.

[0065] Effect example

[0066] The components of the high-purity metals prepared in Examples 1-3 and Comparative Examples 1-3 were detected using a glow discharge mass spectrometer (GDMS), an oxygen, nitrogen and hydrogen (ONH) analyzer and a carbon and sulfur (CS) analyzer. The results are shown in Tables 1-3.

[0067] The present invention explores the change of hydrogen solubility in magnesium, nickel, iron, copper and gold with temperature under the condition of 0.1MPa, and finds that the solubility of hydrogen in metal has a sudden change near the melting point, that is, the solubility of hydrogen in the liquid phase is much higher than that in the solid phase. Therefore, during the solidification process, hydrogen will be supersaturated, nucleate, grow and float at the solidification interface. Since the surface energy of hydrogen bubbles is high, impurities and inclusions at the solid-liquid interface will be adsorbed on the bubble surface, and float up and overflow the melt with the hydrogen bubbles, thereby achieving efficient purification of the metal.

[0068] Table 1

[0069]

[0070]

[0071] According to Table 1, the purity of the high-purity copper prepared in Example 1 of the present invention reaches 6N1, and the purity of the high-purity copper prepared by the conventional vacuum directional solidification method is 4N8. In addition, the non-metallic impurities in the high-purity copper prepared in Example 1 are all lower than 2ppm, and the content of H is less than 1ppm.

[0072] Table 2

[0073]

[0074]

[0075] According to Table 2, the purity of the high-purity nickel prepared in Example 2 of the present invention reaches 6N, and the purity of the high-purity copper prepared by the conventional vacuum directional solidification method is 4N8. In addition, the non-metallic impurities in the high-purity nickel prepared in Example 2 are all less than 1ppm, and the content of H is less than 1ppm.

[0076] Table 3

[0077]

[0078]

[0079] According to Table 3, the purity of the high-purity nickel prepared in Example 3 of the present invention reaches 6N, and the purity of the high-purity copper prepared by the conventional vacuum directional solidification method is 4N5. In addition, the non-metallic impurities in the high-purity nickel prepared in Example 3 are all less than 1ppm, and the content of H is less than 1ppm.

[0080] Finally, it should be noted that the above preferred embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail through the above preferred embodiments, those skilled in the art should understand that various changes can be made in form and details without departing from the scope defined by the claims of the present invention.

Claims

1. A method for preparing ultra-high purity metal by hydrogen refining and directional solidification, characterized in that: The following steps are involved: (1) placing the metal raw material in a melting crucible in a directional solidification device; (2) Pump the furnace pressure down to 10 -1 ~10 -3 After the temperature reaches the range of Pa, the metal raw material is heated and smelted until it is completely melted and forms a uniform metal melt; (3) After the metal raw material is completely melted, hydrogen-containing gas is introduced into the furnace and the temperature is kept constant; (4) Directional solidification is carried out after the insulation is completed; (5) After the directional solidification is completed, the pressure in the furnace is reduced to 0.1 MPa and then vacuumed to 10 -3 ~10 -5 Pa; then the metal raw material is heated and melted again until a uniform metal melt is formed; finally, directionally solidified again to obtain a high-purity metal ingot.

2. The method for preparing ultra-high purity metal by hydrogen refining and directional solidification according to claim 1, characterized in that: The metal raw material is magnesium, nickel, iron, copper, gold, platinum or nickel-platinum alloy.

3. The method for preparing ultra-high purity metal by hydrogen refining and directional solidification according to claim 1, characterized in that: The heating and smelting temperature is 600-2000°C.

4. The method for preparing ultra-high purity metal by hydrogen refining and directional solidification according to claim 1, characterized in that: The hydrogen-containing gas is high-purity hydrogen or a mixed gas of hydrogen and argon.

5. The method for preparing ultra-high purity metal by hydrogen refining and directional solidification according to claim 1, characterized in that: In the step (3), hydrogen-containing gas is introduced into the furnace so that the total pressure of the gas in the furnace reaches 0.1 to 2.0 MPa.

6. The method for preparing ultra-high purity metal by hydrogen refining and directional solidification according to claim 1, characterized in that: The heat preservation time is 10 to 20 minutes.

7. The method for preparing ultra-high purity metal by hydrogen refining and directional solidification according to claim 1, characterized in that: In the step (4), the speed of directional solidification is 0.1 to 5.0 mm / min.

8. The method for preparing ultra-high purity metal by hydrogen refining and directional solidification according to claim 1, characterized in that: In the step (5), the speed of directional solidification is 0.4 to 1.0 mm / min.

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