Method for removing impurity oxygen in metal cobalt

Abstract

The invention discloses a method for removing impurity oxygen in metal cobalt, belongs to the technical field of metal material processing, and solves the problems that oxygen in cobalt is difficult to deeply remove and ultra-high-purity cobalt cannot be obtained in the prior art. The method comprises the following steps: S1, pretreating a metal cobalt raw material to obtain clean to-be-treated metal cobalt; s2, the to-be-treated metal cobalt is subjected to vacuum electron beam melting, and a metal cobalt cast ingot is obtained; wherein hydrogen is introduced in the vacuum electron beam smelting process, so that the hydrogen and hydrogen atoms formed by electron beam ionization react with oxygen on the surfaces of metal cobalt molten drops formed by smelting, and a metal cobalt cast ingot with the low oxygen content is obtained through smelting. According to the method, the oxygen in the metal cobalt is removed by combining the electron beam drop melting technology with hydrogen reduction, the driving force for removing the oxygen in the molten drops is increased, and therefore deep removal of the impurity oxygen in the metal cobalt is achieved.

Description

Technical Field

[0001] The invention relates to the technical field of metal material processing, and in particular to a method for removing impure oxygen in metal cobalt. Background Art

[0002] Due to its low resistivity and excellent anti-electromigration performance, cobalt metal is gradually replacing copper in advanced process chips below 7nm, and is expected to become a new generation of interconnect material. Advanced process semiconductor chips have extremely high requirements for the purity of cobalt, and the currently produced cobalt metal cannot meet the preparation needs of advanced process semiconductor chips.

[0003] The metallurgical process of high-purity cobalt mainly includes hydrometallurgy such as extraction, ion exchange, and electrolytic refining, as well as pyrometallurgy such as vacuum electron beam melting. At present, the hydrometallurgical process of "solution purification + electrolytic refining" is usually used to remove metal impurities such as Ni, Cu, Fe, Pb, Ti, Sn, Mn, Zn, and As in metal cobalt in a targeted manner; then, the vacuum electron beam melting pyrometallurgical process is used to further improve the density of the product, reduce the content of gas impurities (C, N, H, S, Cl, etc.) and volatile impurities (Na, K, etc.) in metal cobalt, and prepare large-sized metal cobalt ingots.

[0004] Although the current metallurgical process can produce 5N5 grade cobalt metal, the oxygen impurities therein are always difficult to effectively control. Due to the extremely high theoretical solid solubility of oxygen in cobalt, the traditional electron beam melting method is not only difficult to remove oxygen, but may even increase oxygen. The existing process is difficult to stably control the oxygen content in cobalt metal to below 20ppm. The oxygen content in high-purity cobalt used in advanced semiconductor integrated circuits needs to be controlled within 20ppm, and in some higher-end applications, the oxygen content requirements are even more stringent. Therefore, it is urgent to solve the problem that oxygen cannot be deeply removed from cobalt metal. Summary of the invention

[0005] In view of the above analysis, the present invention aims to provide a method for removing impure oxygen in metallic cobalt, so as to solve the problem that it is difficult to remove impurity oxygen in cobalt and difficult to obtain ultra-high purity cobalt in the existing process.

[0006] An embodiment of the present invention provides a method for removing impurity oxygen in metal cobalt, comprising the following steps: step S1, pretreating a metal cobalt raw material to obtain clean metal cobalt to be treated; step S2, vacuum electron beam melting the metal cobalt to be treated to obtain a metal cobalt ingot; wherein, hydrogen is introduced during the vacuum electron beam melting process, so that the hydrogen and hydrogen atoms formed by electron beam ionization react with oxygen on the surface of the metal cobalt droplets formed by melting, so as to melt and obtain a metal cobalt ingot with a low oxygen content.

[0007] Furthermore, step S2 includes: placing the metal cobalt to be processed in an electron beam melting furnace, and evacuating the electron beam melting furnace; controlling the electron beam to irradiate and melt the bottom ingot; when a molten pool is formed on the surface of the bottom ingot, feeding the metal cobalt to be processed so that its end is located above the molten pool, and controlling the electron beam to irradiate and melt the end of the metal cobalt to be processed, so that it melts to produce molten droplets and drips into the molten pool; introducing hydrogen on the dripping path of the molten droplets to react with hydrogen and hydrogen atoms with oxygen on the surface of the molten droplets; the molten droplets continue to drip into the molten pool, and the ingot is cooled and solidified by pulling the ingot to obtain a metal cobalt ingot.

[0008] Further, in step S2, the flow rate of the introduced hydrogen is less than 1 L / min.

[0009] Furthermore, in step S2, the ingot pulling rate and the feeding rate of the metal cobalt to be processed are adjusted according to the dripping speed of the molten droplet, so that the dripping path of the molten droplet passes through the action area of ​​the hydrogen gas, while keeping the height of the molten pool unchanged.

[0010] Further, in step S2, the dripping speed of the molten drop is 0.1-0.5 or 0.5-1.0 kg / min, the ingot pulling rate is 2-12 or 12-20 mm / min, and the feeding rate is 5-30 or 30-50 mm / min.

[0011] Furthermore, in step S2, the base ingot is uniformly melted by circular scanning with a large-radius beam spot to form a molten pool.

[0012] Furthermore, the depth of the molten pool is not greater than 40 mm.

[0013] Furthermore, when the metal cobalt to be processed is completely melted, the introduction of hydrogen and the ingot pulling are stopped, and the electron beam continues to heat the molten pool; when the surface state of the molten pool is qualified, the power of the electron beam heating the molten pool is gradually reduced to 0kW.

[0014] Furthermore, in step S1, the metal cobalt raw material is pre-processed, including: when the metal cobalt raw material is in a plate shape, the metal cobalt raw material is processed into a long strip shape.

[0015] Furthermore, in step S1, the metal cobalt raw material is pretreated, and the process also includes: when there are attachments on the surface of the metal cobalt raw material, grinding and ultrasonic cleaning are performed on the surface of the metal cobalt raw material in sequence; when there are no attachments on the surface of the metal cobalt raw material, ultrasonic cleaning is performed on the metal cobalt raw material.

[0016] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0017] 1. The method of the present invention removes oxygen from metallic cobalt by electron beam drip melting technology combined with hydrogen reduction. During the electron beam drip melting process of metallic cobalt, a trace amount of H2 introduced and activated H atoms formed by its ionization react with oxygen on the surface of the droplet to increase the driving force for oxygen removal from the droplet, thereby achieving deep removal of impurity oxygen in metallic cobalt.

[0018] 2. Based on hydrogen reduction, the present invention accelerates the dissociation and evaporation mass transfer of oxygen on the surface of the melt through the disturbance effect and activation of electron beam bombardment on the melt surface, thereby achieving the purpose of deep deoxygenation.

[0019] 3. The method of the present invention, based on hydrogen reduction, adopts a large beam spot circular scanning method to create a shallow molten pool, thereby effectively increasing the temperature gradient of the melt and shortening the transmission distance of impure oxygen in the melt, thereby strengthening the convective mass transfer of impure oxygen in the melt and further reducing the content of impure oxygen.

[0020] 4. By adopting the method of the present invention, the oxygen content in the cobalt ingot can be controlled within 20 ppm, the H content can be controlled within 5 ppm, the content of non-gaseous impurities can be controlled within 1 ppm, and the purity of the prepared metallic cobalt can reach 6N.

[0021] In the present invention, the above-mentioned technical solutions can also be combined with each other to achieve more preferred combination solutions. Other features and advantages of the present invention will be described in the subsequent description, and some advantages can become obvious from the description, or can be understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained through the contents particularly pointed out in the embodiments of the description and the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The drawings are only for the purpose of illustrating particular embodiments and are not to be considered limiting of the present invention. Like reference symbols denote like components throughout the drawings.

[0023] Figure 1 This is a graph showing the solid solubility of oxygen in metallic cobalt as a function of temperature.

[0024] Figure 2 The figure is a schematic diagram of the principle of removing impurity oxygen in metal cobalt according to an embodiment of the present invention.

[0025] Figure 3 This is a photograph of the molten pool surface according to Example 1 of the present invention. DETAILED DESCRIPTION

[0026] In order to make the purpose, technical solutions and advantages of the present invention clearer, exemplary embodiments of the present invention will be described below in conjunction with the accompanying drawings. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. For the sake of clarity and conciseness, not all features of the actual implementation are described in the specification.

[0027] It is also necessary to explain here that, in order to avoid obscuring the present invention due to unnecessary details, only the device structure and / or processing steps closely related to the solution according to the present invention are shown in the accompanying drawings, while other details that are not closely related to the present invention are omitted.

[0028] In the traditional vacuum electron beam melting process, in order to avoid the high melting temperature of cobalt and the resulting large amount of volatilization loss, the melting power is controlled within a certain range so that the melting temperature is not too high. However, the properties of cobalt are different from most other metals. The solid solubility of oxygen in cobalt increases with the decrease of temperature. Figure 1 As shown, this means that the lower the melting temperature of metallic cobalt, the higher the oxygen content in the metallic cobalt, which makes it difficult to achieve deep removal of oxygen in cobalt by traditional electron beam melting process.

[0029] In order to deeply remove the impurity oxygen in metal cobalt and prepare high-purity cobalt suitable for semiconductor integrated circuits, an embodiment of the present invention provides a method for removing the impurity oxygen in metal cobalt, the method comprising the following steps:

[0030] Step S1, pre-treating the metal cobalt raw material to obtain clean metal cobalt to be treated;

[0031] Step S2, performing vacuum electron beam melting on the metal cobalt to be processed to obtain a metal cobalt ingot;

[0032] In the process of vacuum electron beam melting, hydrogen is introduced to make the hydrogen and hydrogen atoms formed by electron beam ionization react with oxygen on the surface of metal cobalt droplets formed by melting, so as to obtain metal cobalt ingots with low oxygen content.

[0033] The embodiments of the present invention introduce a trace amount of hydrogen during the electron beam droplet melting process of the metal cobalt raw material, utilize the trace amount of H2 and the activated H atoms formed by its ionization to react with the oxygen on the surface of the metal cobalt droplet to increase the driving force for oxygen removal in the droplet, thereby achieving deep removal of impurity oxygen in the metal cobalt.

[0034] In some embodiments, in step S2, a vacuum electron beam melting furnace is used to perform vacuum electron beam drip melting on the metal cobalt to be processed. Specifically, step S2 includes:

[0035] Step S21, placing the metal cobalt to be processed in an electron beam melting furnace, and evacuating the electron beam melting furnace to a target vacuum state;

[0036] Step S22, controlling the electron beam to irradiate and melt the bottom ingot;

[0037] Step S23, when a molten pool is formed on the surface of the bottom ingot, the metal cobalt to be processed is fed so that its end is located above the molten pool, and the electron beam is controlled to irradiate and melt the end of the metal cobalt to be processed, so that it melts to generate molten droplets and drips into the molten pool;

[0038] Step S24, introducing hydrogen gas into the droplet's dripping path, so that the hydrogen gas and hydrogen atoms react with oxygen on the droplet surface;

[0039] Step S25, the molten droplets continue to drip into the molten pool, and the ingot is pulled to cool and solidify to obtain a metal cobalt ingot.

[0040] In an embodiment of the present invention, a trace amount of hydrogen is introduced below the molten droplet of metallic cobalt to be treated (i.e., on the dripping path of the molten droplet), so that the hydrogen produces activated hydrogen atoms under the ionization action of the electron beam, and the hydrogen molecules and the activated hydrogen atoms undergo a reduction reaction with the oxygen on the surface of the molten droplet, thereby deoxidizing the molten droplet and reducing the content of oxygen impurities in the metallic cobalt.

[0041] In step S21, the target vacuum state of the electron beam melting furnace includes: the vacuum degree is not less than 5×10 -2 Pa.

[0042] In step S22, the bottom ingot is uniformly melted by circular scanning with a large-radius beam spot to form a molten pool. Circular scanning with a large-radius beam spot can improve the uniformity of heating, make the melting process of the bottom ingot more stable, and facilitate more accurate control of the depth of the molten pool. The radius of the electron beam spot is 5 to 20 mm.

[0043] In some embodiments, the depth of the molten pool is no more than 40 mm. The embodiments of the present invention use a large beam spot radius circular scanning method to create a shallow molten pool, so that the molten depth does not exceed 40 mm, thereby effectively increasing the temperature gradient of the melt and shortening the transmission distance of oxygen impurities in the melt, thereby strengthening the convective mass transfer of impure oxygen in the melt.

[0044] In this embodiment, after the surface of the bottom ingot is melted to form a molten pool, the electron beam is controlled to continuously scan the molten pool until all the metal cobalt to be processed is processed. The scanning method is circular scanning to ensure uniform heating.

[0045] During the electron beam melting process, the electron beam continuously scans the molten pool, which not only continuously heats the molten pool to prevent it from solidifying, but also causes disturbance of the melt by bombarding the surface of the molten pool with the electron beam. The disturbance effect of the melt and the activation effect of the electron beam accelerate the mass transfer, dissociation and evaporation of oxygen in the melt, further removing the oxygen content in the metallic cobalt and achieving the purpose of deep deoxygenation.

[0046] In some embodiments, the power of the electron beam for heating the bottom ingot and the molten pool is determined according to the diameter of the bottom ingot, and the power of the electron beam increases with the increase of the bottom ingot diameter, thereby ensuring the efficiency of the bottom ingot melting and the molten pool smelting, and improving the consistency of the temperature and depth of the molten pools of different diameters. Specifically, when the diameter of the bottom ingot is 80 to 120 mm, the power of the electron beam is 10 to 30 kW.

[0047] In step S23, when heating and melting the end of the metal cobalt to be processed, another electron beam can be used to irradiate the end of the metal cobalt to be processed, that is, two electron guns are used to heat the molten pool and the end of the metal cobalt to be processed respectively; or, the electron beam that scans the base ingot and the molten pool in step S22 can be used to simultaneously scan the metal cobalt to be processed, that is, the electron beam emitted by the same electron gun is controlled to act on the molten pool and the end of the metal cobalt to be processed at the same time.

[0048] When another electron beam is used to heat the end of the metal cobalt to be processed, the power of the electron beam is determined according to the diameter of the metal cobalt to be processed. The power of the electron beam increases with the increase of the diameter of the metal cobalt to be processed, thereby ensuring the smelting efficiency of the metal cobalt to be processed. Specifically, when the diameter of the metal cobalt to be processed is 40 to 80 mm, the power of the electron beam is 10 to 30 kW.

[0049] In step S24, the flow rate of the introduced hydrogen is less than 1 L / min. This embodiment can not only reduce and remove oxygen in the metal cobalt droplets by introducing a trace amount of hydrogen, but also ensure the target vacuum state in the electron beam melting furnace, avoid excessive hydrogen flow causing a significant decrease in vacuum, thereby affecting the normal operation of the equipment, and avoid dangers such as hydrogen explosion.

[0050] In step S25, the ingot pulling rate and the feeding rate of the metal cobalt to be processed are adjusted according to the dripping speed of the molten droplet, so that the dripping path of the molten droplet passes through the action area of ​​hydrogen and the height of the molten pool remains unchanged.

[0051] Specifically, the height of the molten pool will decrease during the ingot pulling process, while the molten droplets dripping into the molten pool will increase the height of the molten pool. Based on this, when the diameter of the metal cobalt to be processed is constant, the greater the power of the electron beam that heats the metal cobalt to be processed, the faster the dripping speed of the metal cobalt droplets, and the ingot pulling rate needs to be increased to ensure that the liquid level of the molten pool remains basically unchanged. Furthermore, in order to maintain the balance of the smelting and ingot pulling processes and to enable the smelting and ingot pulling to continue, the feeding rate of the metal cobalt to be processed needs to be increased at the same time.

[0052] The embodiments of the present invention control the feeding rate, the dripping speed of the molten droplets and the ingot pulling rate so that the liquid level of the molten pool remains basically unchanged, thereby avoiding the escape of excessive melt and the excessive temperature of the molten pool due to insufficient melt, thereby maintaining the entire smelting process stable and continuous.

[0053] Specifically, the droplet dripping speed is controlled to be 0.1-1.0 kg / min, the ingot pulling speed is 2-20 mm / min, and the feeding speed is 5-50 mm / min. Furthermore, the droplet dripping speed is 0.1-0.5 or 0.5-1.0 kg / min, the ingot pulling speed is 2-12 or 12-20 mm / min, and the feeding speed is 5-30 or 30-50 mm / min.

[0054] Preferably, the dripping speed of the molten droplet is controlled to be 0.1-0.5 kg / min, the ingot pulling rate is 2-12 mm / min, and the feeding rate is 5-30 mm / min; or, the dripping speed of the molten droplet is controlled to be 0.5-1.0 kg / min, the ingot pulling rate is 12-20 mm / min, and the feeding rate is 30-50 mm / min.

[0055] In some embodiments, after the metal cobalt to be processed is melted, the introduction of hydrogen and the ingot pulling are stopped, and the electron beam continues to heat the molten pool; when the surface state of the molten pool is qualified, the power of the electron beam heating the molten pool is gradually reduced to 0 kW. In the embodiments of the present invention, after the metal cobalt to be processed is melted, the electron beam is still controlled to heat the molten pool until the surface state of the molten pool is qualified, so as to ensure the quality of the metal cobalt ingot after solidification.

[0056] Among them, Figure 3 As shown, the qualified surface condition of the molten pool includes: the surface of the molten pool is round, the surface of the molten pool is uniform, and there is no obvious unmelted area, so as to ensure that the surface of the metal cobalt ingot is relatively smooth after the molten pool stops heating and solidifies, thereby reducing the occurrence of defects.

[0057] In some embodiments, the electron beam drip melting process can be repeated according to the requirements for the total content of trace impurities and the oxygen content in the metal cobalt. For example, after the metal cobalt is drip-melted to obtain a metal cobalt ingot, the cut bottom ingot is cleaned and dried and then reloaded into the ingot pulling mechanism, and then the high-purity metal cobalt ingot is drip-melted twice or multiple times, that is, step S2 is repeated to obtain a metal cobalt ingot with a lower total impurity content and oxygen content, thereby meeting different impurity content and oxygen content requirements.

[0058] In some embodiments of the present invention, the metal cobalt raw material is pre-processed in step S1, including: when the metal cobalt raw material is in plate form, the metal cobalt raw material is processed into a long strip to facilitate subsequent feeding and electron beam drip melting. When the raw material is in rod form, no processing is required.

[0059] In some embodiments, the pretreatment of the metal cobalt raw material in step S1 also includes: when there is attachment on the surface of the metal cobalt raw material, grinding and ultrasonic cleaning are performed on the surface of the metal cobalt raw material in sequence; when there is no attachment on the surface of the metal cobalt raw material, ultrasonic cleaning is performed on the metal cobalt raw material to ensure the cleanliness of the raw material and prevent the attachment from entering the metal cobalt during the subsequent smelting process. After ultrasonic cleaning, the metal cobalt raw material is dried and subsequent electron beam drip melting can be performed.

[0060] In addition, in order to ensure that ultra-pure metallic cobalt can be obtained after smelting, when selecting metallic cobalt raw materials, raw materials with higher purity should be selected as much as possible. For example, the purity of the selected metallic cobalt raw materials can be 4N to 5N level (excluding gas impurity content).

[0061] In some embodiments of the present invention, Figure 2 As shown, the vacuum electron beam melting furnace used in step S2 includes a furnace body 10, a water-cooled copper mold 20, an electron gun, a bottom ingot 40, a horizontal feeding mechanism 50, a cooling water inlet and outlet 60, a hydrogen conduit 70, a vacuum system, an ingot pulling mechanism and an ingot rotating mechanism (not shown in the figure). Among them, the water-cooled copper mold 20 is arranged in the furnace body 10, and is used to accommodate the bottom ingot 40 and the metal cobalt melt. The cooling water inlet and outlet 60 is connected to the cooling water channel in the water-cooled copper mold 20. The cooling water 60 is used to cool the furnace body. The water-cooled copper mold 20 is used to cool the surrounding of the metal cobalt melt in contact with the copper mold. The bottom ingot 40 is installed on the ingot pulling mechanism, and the initial position of the bottom ingot 40 is located in the water-cooled copper mold 20. The horizontal feeding mechanism 50 is used to transport the metal cobalt to be processed into the furnace body 10, and the hydrogen conduit 70 is arranged below the horizontal feeding mechanism 50, and is used to introduce hydrogen into the furnace body 10. The ingot rotating mechanism is used to rotate the metal cobalt ingot and the melt in the water-cooled copper mold so that the molten pool is evenly scanned by the electron beam, thereby making the melt distribution more uniform.

[0062] In some embodiments, before the metal cobalt to be processed is subjected to electron beam drip melting, a base ingot needs to be prepared. Specifically, the metal cobalt ingot is processed into a base ingot, which is then cleaned and dried before being installed in an ingot pulling mechanism. The metal cobalt ingot used has the same inner diameter as the water-cooled copper mold 20 and a length of 200 to 400 mm.

[0063] In some embodiments, Figure 2 As shown, the vacuum electron beam melting furnace includes a first electron gun 31 and a second electron gun 32, which are respectively arranged above the water-cooled copper mold 20. The first electron gun 31 is used to heat the bottom ingot and the molten pool, and the second electron gun 32 is used to heat and melt the end of the metal cobalt to be processed. The second electron gun 32 is arranged on one side where the horizontal feeding mechanism 50 and the hydrogen conduit 70 are located, and the first electron gun 31 is arranged on the other side opposite thereto, so that the two electron guns can heat different areas respectively.

[0064] In some embodiments, the vacuum electron beam melting furnace only includes the first electron gun 31 , and the electron beam of the first electron gun 31 can act on the molten pool and the end of the metal cobalt to be processed at the same time, thereby achieving simultaneous heating of the two.

[0065] In some embodiments, in order to prepare large-sized ingots, the vacuum electron beam melting furnace also includes a backup feeding mechanism (not shown in the figure). When the cobalt ingot in the horizontal feeding mechanism 50 is completely melted, the backup feeding mechanism can be started to feed another metal cobalt to be processed.

[0066] In some embodiments, Figure 2 As shown, the vacuum system 80 includes a molecular pump 81 and a mechanical pump 82, the molecular pump 81 and the mechanical pump 82 are connected, and the molecular pump 81 is connected to the electron gun to evacuate the gun body of the electron gun. Specifically, when the vacuum electron melting furnace includes two electron guns, such as Figure 2 As shown, the vacuum system 80 includes two groups of molecular pumps 81 and mechanical pumps 82, one group of molecular pumps 81 and mechanical pumps 82 is connected to the first electron gun 31, and the other group of molecular pumps 81 and mechanical pumps 82 is connected to the second electron gun 32, so as to evacuate the gun bodies of the two electron guns respectively.

[0067] like Figure 2As shown, the vacuum system 80 also includes a diffusion pump 83, a primary Roots pump 84, a secondary Roots pump 85 and another mechanical pump 82, which are used to evacuate the furnace body 10. The furnace body 10 is connected to the gas inlet ends of the primary Roots pump 84 and the diffusion pump 83 through gas pipelines, the gas outlet end of the primary Roots pump 84 is connected to the secondary Roots pump 85, the secondary Roots pump 85 is connected to the mechanical pump 82, and the gas outlet end of the diffusion pump 83 is connected to the gas inlet end of the primary Roots pump 84. The high vacuum state inside the furnace body 10 is ensured by the joint action of the diffusion pump 83, the primary Roots pump 84, the secondary Roots pump 85 and the mechanical pump 82.

[0068] According to the method of the present invention, during the electron beam drop melting process, the introduced trace amount of H2 and the activated H atoms formed by ionization react with the oxygen on the surface of the metal cobalt droplet to increase the driving force for oxygen removal in the droplet; on this basis, a large radius beam spot annular scanning method is used to create a shallow molten pool, thereby effectively increasing the temperature gradient of the melt and shortening the transmission distance of oxygen impurities in the melt, thereby strengthening the convective mass transfer of impurity oxygen in the melt; in addition, an electron gun is used to bombard the surface of the melt to produce a disturbance effect and an activation effect, thereby accelerating the dissociation and evaporation of oxygen impurities on the surface of the melt. Through the synergistic effect of the above several approaches, the purpose of deep deoxygenation is achieved.

[0069] Compared with the traditional metal cobalt preparation process, the metal cobalt ingot prepared by the method of the embodiment of the present invention can effectively control the oxygen content in the cobalt ingot within 20ppm, the H content within 5ppm, the content of non-gaseous impurities within 1ppm, and the purity of the metal cobalt reaches 6N, which effectively solves the problem of high oxygen content and unstable oxygen content in the metal cobalt ingot prepared by the traditional process.

[0070] In addition, the method of the embodiment of the present invention can also be applied to deeply remove impurity oxygen in other oxygen-philic metals, active metals or metals with high oxygen solid solubility.

[0071] The method for removing oxygen impurities from metallic cobalt of the present invention is further described below with reference to specific examples.

[0072] Example 1

[0073] Step S1, pre-treating the metal cobalt raw material: selecting a metal cobalt plate as a raw material, the purity of which is 5N, the total impurity content is 10ppm (excluding gas impurities), and the oxygen content is 80ppm; processing the metal cobalt plate into a long strip with a width of about 50mm; checking the surface state of the cobalt strip, and finding that there are attachments on the surface, grinding the surface, and then performing ultrasonic cleaning. After cleaning, the raw material is placed in a drying oven for drying to obtain a metal cobalt strip to be processed.

[0074] Step S2, using a vacuum electron beam melting furnace with dual electron guns to perform electron beam drip melting on the metal cobalt strip to be processed:

[0075] (1) Clean the contaminants on the furnace body and furnace wall of the vacuum electron beam melting furnace to avoid the introduction of foreign impurities during the drip melting process;

[0076] (2) Select a water-cooled copper mold with an inner diameter of 80 mm, polish and clean the water-cooled copper mold to ensure that the water-cooled copper mold is clean and pollution-free;

[0077] (3) Prepare a metal cobalt ingot with the same inner diameter as the water-cooled copper mold and a length of 300 mm, process it into a bottom ingot, and after cleaning and drying, load it into the ingot pulling mechanism to use it as the bottom ingot of the ingot pulling mechanism.

[0078] (4) Place the cobalt metal bar to be processed into the horizontal feeding mechanism, then close the silo door and the electron beam furnace door. Start the vacuum system, and after the diffusion pump is preheated, evacuate the furnace body and the gun body of the electron gun to the target vacuum state of 5×10 -2 Pa or more, then start the electron gun to preheat the equipment.

[0079] (5) After preheating, gradually increase the power of the first electron gun to 15 kW, and use a large-radius beam spot circular scanning method to evenly melt the bottom ingot, where the beam spot radius is 10 mm; after a molten pool is formed on the surface of the bottom ingot, start the ingot rotation mechanism and the horizontal feeding mechanism, and at the same time slowly increase the power of the second electron gun to 15 kW to melt the end of the metal cobalt bar to be processed, so that the molten droplets produced by it drip into the molten pool below.

[0080] (6) A small amount of high-purity hydrogen is introduced through a hydrogen conduit below the metal cobalt strip to be treated, with a hydrogen flow rate of 0.8 L / min, so that the hydrogen passes through the surface of the molten droplet and undergoes a deoxidation reaction with the molten droplet.

[0081] (7) Start the ingot pulling mechanism. At this time, the dripping speed of the molten droplet is about 0.35 kg / min. According to the dripping speed of the molten droplet, the ingot pulling rate is adjusted to about 8 mm / min and the feeding rate is about 20 mm / min, so that the dripping path of the molten droplet passes through the area where high-purity hydrogen acts, while keeping the height of the molten pool unchanged.

[0082] (8) When the horizontal feeding mechanism reaches the maximum stroke, the power of the second electron gun is reduced to 0 kW, the ingot pulling mechanism is stopped, and then the introduction of H2 is stopped; after the unmelted metal cobalt bar is returned, the standby feeding mechanism is started, and the power of the second electron gun is slowly increased to 15 kW to continue to melt the end of the metal cobalt bar to be processed, and a trace amount of H2 is continued to be introduced to allow the molten droplets to pass through the H2 action area and drip into the molten pool below.

[0083] (9) Start the ingot pulling mechanism. At this time, the dripping speed of the molten droplet is about 0.35 kg / min. According to the dripping speed of the molten droplet, the ingot pulling rate is adjusted to about 8 mm / min and the feeding rate is about 20 mm / min, so that the dripping path of the molten droplet passes through the area where the high-purity hydrogen acts, while keeping the height of the molten pool unchanged.

[0084] (10) After the cobalt metal bar to be processed is melted, the power of the second electron gun is reduced to 0 kW, the introduction of H2 is stopped, and the ingot pulling mechanism is stopped. When the surface of the molten pool is in good condition, that is, the molten pool is circular, the surface of the molten pool is uniform, and there is no obvious unmelted area, the power of the first electron gun is slowly reduced to 0 kW, and the ingot rotating mechanism is stopped.

[0085] (11) Turn off the two electron guns to allow the metal cobalt ingot to be fully cooled under vacuum conditions. After cooling, take out the metal cobalt ingot and remove the bottom ingot to obtain the purified metal cobalt ingot.

[0086] The obtained metal cobalt ingot was tested and found to have an oxygen content of 18 ppm.

[0087] Comparative Example 1

[0088] The only difference between this comparative example and Example 1 is that hydrogen is not introduced during the electron beam drip melting of metal cobalt in step S2.

[0089] The obtained metal cobalt ingot was tested and found to have an oxygen content of 78 ppm.

[0090] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by any technician familiar with the technical field within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims

1. A method for removing impurity oxygen from metallic cobalt, characterized in that: The following steps are involved: Step S1, pre-treating the metal cobalt raw material to obtain clean metal cobalt to be treated; Step S2, performing vacuum electron beam melting on the metal cobalt to be processed to obtain a metal cobalt ingot; In the vacuum electron beam melting process, hydrogen is introduced to make the hydrogen and hydrogen atoms formed by electron beam ionization react with oxygen on the surface of the metal cobalt droplets formed by melting, so as to obtain a metal cobalt ingot with a low oxygen content.

2. The method according to claim 1, characterized in that The step S2 comprises: Placing the metal cobalt to be processed in an electron beam melting furnace, and evacuating the electron beam melting furnace; Controlling the electron beam to irradiate and melt the bottom ingot; After a molten pool is formed on the surface of the bottom ingot, the metal cobalt to be processed is fed so that its end is located above the molten pool, and the electron beam is controlled to irradiate and melt the end of the metal cobalt to be processed, so that it melts to generate molten droplets that drip into the molten pool; Introducing hydrogen gas into the dripping path of the molten droplet, so that the hydrogen gas and the hydrogen atoms react with oxygen on the surface of the molten droplet; The molten droplets continue to drip into the molten pool, and the metal cobalt ingot is obtained by cooling and solidifying the ingot through ingot pulling.

3. The method according to claim 2, characterized in that In step S2, the flow rate of the introduced hydrogen is less than 1 L / min.

4. The method according to claim 2, characterized in that: In step S2, the ingot pulling rate and the feeding rate of the metal cobalt to be processed are adjusted according to the dripping speed of the molten droplet, so that the dripping path of the molten droplet passes through the action area of ​​the hydrogen gas, while keeping the height of the molten pool unchanged.

5. The method according to claim 4, characterized in that In step S2, the dripping speed of the molten drop is 0.1-0.5 or 0.5-1.0 kg / min, the ingot pulling rate is 2-12 or 12-20 mm / min, and the feeding rate is 5-30 or 30-50 mm / min.

6. The method according to claim 2, characterized in that In step S2, the base ingot is uniformly melted by circular scanning with a large-radius beam spot to form the molten pool.

7. The method according to claim 6, characterized in that The depth of the molten pool is no more than 40 mm.

8. The method according to claim 2, characterized in that: When the metal cobalt to be processed is completely melted, the introduction of hydrogen and the ingot pulling are stopped, and the electron beam continues to heat the molten pool; When the surface condition of the molten pool is qualified, the power of the electron beam heating the molten pool is gradually reduced to 0 kW.

9. The method according to claim 1, characterized in that: In the step S1, the metallic cobalt raw material is pretreated, including: When the metal cobalt raw material is in a plate shape, the metal cobalt raw material is processed into a long strip shape.

10. The method according to claim 1, characterized in that In the step S1, the metal cobalt raw material is pretreated, and the step further includes: When there are attachments on the surface of the metal cobalt raw material, the surface of the metal cobalt raw material is polished and ultrasonically cleaned in sequence; When there is no attachment on the surface of the metal cobalt raw material, the metal cobalt raw material is ultrasonically cleaned.

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