Preparation method of large-size metal chromium target

Abstract

The invention belongs to the technical field of chromium target preparation, and discloses a preparation method of a large-size chromium target, which comprises the following steps: taking a solid graphite electrode as an anode and a hollow graphite electrode as a cathode, and carrying out electrifying heating, melting and heat preservation on a ceramic raw material in a vacuum or inert gas protection environment, so that the ceramic raw material is heated to form a high-temperature ceramic molten pool; under the vacuum or inert gas protection condition, metal chromium particles are added into the high-temperature ceramic molten pool through the cathode hollow structure, after the metal chromium particles fall in the high-temperature ceramic molten pool and are molten to form metal chromium liquid or part of the metal chromium particles are molten to form semi-solid metal chromium particles, the metal chromium particles sink to the bottom of the high-temperature ceramic molten pool under the gravity, and a chromium molten pool is formed; and cooling and solidifying in the crystallizer and continuously leading out of the crystallizer by the traction mechanism to obtain the large-size chromium target. The preparation method is simple, and the obtained large-size chromium target is of a solidified structure, low in gas element content and high in density.

Description

Technical Field

[0001] The present invention relates to the technical field of chromium target preparation, and particularly relates to a method for preparing a large-sized chromium target. Background Art

[0002] Target materials are key materials used in coating technologies, which can reduce environmental pollution problems caused by electroplating and electroless plating, reduce energy consumption and global carbon emissions, and improve the human living environment. Therefore, a large number of existing traditional electroplating and electroless plating industries will gradually adopt new coating technologies to solve industrial pollution problems. Developing high-end target material production technologies and industries is an important task for the coating industry.

[0003] Chromium targets are an important basic material that has been continuously developed with the development of sputtering coating technology in the past two decades. They have a wide range of applications in fields such as reflective films for automotive and architectural glass, chromium masking films in integrated circuits, multi-layer metal films in LEDs and semiconductor power devices, beam splitting films in optical devices, chromium carbide hard films on cutting tools, and anode targets in X-ray tubes.

[0004] Currently, the main method for preparing large-sized chromium targets at home and abroad is the powder metallurgy method. Its process methods include: (1) crushing pure metal chromium blocks obtained by aluminothermic method or pure metal chromium sheets obtained by electrolysis into metal chromium powder; (2) cold pressing and vacuum sintering and degassing the pure metal chromium powder in a steel mold; (3) welding and sealing the metal mold; (4) loading the sealed steel mold and the chromium powder therein into the cavity of a hot isostatic press, and densifying the chromium powder sealed in the steel mold at a temperature and pressure environment of 1200°C and above 50 MPa to prepare a chromium target material. The advantages of this process method are that it can prepare target materials of relatively large sizes (the maximum size is determined by the size of the hot isostatic press), and the target material can reach a relatively high density. However, the above preparation method still has the following defects: (1) large investment and high production cost: the price of a large-sized hot isostatic press is tens of millions of yuan per unit, and procedures such as vacuum exhaust and welding need to be carried out in advance during the hot isostatic pressing production process, resulting in very high production costs and low process safety; (2) low production efficiency: the production processes of mold loading, vacuum sintering, and hot isostatic pressing are complex and inefficient, and it is difficult to expand the production scale; (3) the hot isostatic pressing process consumes a set of metal molds each time, and the metal target material can only be obtained after machining to remove the residual molds on the surface, resulting in low material utilization rate; (4) the further enlargement of the hot isostatic pressing furnace is restricted by equipment capacity and price, and it is difficult to meet the technical requirements for large-sized chromium targets with a length of more than 3 meters; (5) the purity of the target material produced by the powder metallurgy method is restricted by the purity of the raw materials, and it is difficult to meet the requirements for continuously increasing purity of the target material. Summary of the Invention

[0005] In order to solve the above deficiencies in the prior art, the present invention provides a method for preparing a large-sized chromium target.

[0006] The present invention produces a metal chromium target by adopting a continuous melting and directional solidification technique to overcome the deficiencies of the current powder metallurgy method, and it is expected to achieve the preparation of large-sized chromium targets with arbitrary lengths. However, during the actual R & D process of the present invention, it is found that since chromium is a metal with an extremely high melting point, it is extremely difficult to obtain a large volume of chromium melt at one time; moreover, chromium melt has extremely high reactivity with most ceramic refractory materials, and it is almost impossible to obtain a large volume of metal chromium melt through the smelting process in terms of technology. The method of producing large-sized chromium targets by using the traditional casting process does not have industrial technical feasibility, so it is extremely difficult to combine the continuous melting and solidification techniques of metal chromium. Therefore, after experimental exploration, the present invention proposes a preparation method capable of continuously preparing large-sized chromium targets. The present invention uses a solid graphite electrode as the anode and a hollow graphite electrode as the cathode. First, by means of electric heating between the anode and the cathode, the ceramic raw materials are melted to form a high-temperature ceramic molten pool. By selecting a ceramic molten pool system that does not react significantly with the chromium melt, metal chromium particles are continuously added to the high-temperature ceramic molten pool through the hollow structure of the cathode, so that the chromium particles melt while descending in the high-temperature ceramic molten pool to form a fully liquid metal chromium melt or partially melt to form semi-solid chromium droplets; the metal chromium liquid or semi-solid droplets naturally sink to the crystallizer at the bottom of the high-temperature ceramic molten pool to form a chromium molten pool; after the chromium molten pool is cooled and solidified at the bottom of the crystallizer, it is gradually pulled out of the crystallizer by a traction mechanism. Through this continuous melting and continuous solidification process of metal chromium particles, the present invention can prepare a large-volume metal chromium target that is dense and defect-free, which has important scientific significance and practical value for the technical development of vacuum coating.

[0007] The purpose of the present invention is to provide a method for continuously melting metal chromium blocks in a high-temperature ceramic molten pool in sequence to form a fully liquid metal chromium melt or partially melt to form semi-solid droplets, and then continuously directionally solidifying to prepare a large-volume chromium target, so as to realize the low-cost large-scale preparation of large-volume metal chromium targets.

[0008] A preparation method of a large-sized chromium target according to the present invention is realized through the following technical solutions:

[0009] The present invention provides a preparation method of a large-sized chromium target, including the following steps:

[0010] Step 1, put ceramic raw materials into a crystallizer with a circulating water cooling structure at the bottom; use a solid graphite electrode as the anode and a hollow graphite electrode as the cathode, and bury both the solid graphite electrode and the hollow graphite electrode in the ceramic raw materials; the crystallizer is a crystallizer made of refractory metal.

[0011] Step 2: Apply an electric current between the anode and the cathode to conductively heat the ceramic raw material, causing the temperature of the ceramic raw material to rise and gradually melt to form a high-temperature ceramic melt pool with a temperature > 1950°C.

[0012] Step 3: Under vacuum or an inert atmosphere, continuously add chromium metal grains into the high-temperature ceramic melt pool through the hollow structure of the cathode, causing the chromium metal grains to melt while descending in the high-temperature ceramic melt pool to form a fully liquid chromium metal melt or partially melt to form semi-solid chromium droplets; the chromium metal liquid or semi-solid droplets naturally sink to the crystallizer at the bottom of the high-temperature ceramic melt pool to form a chromium melt pool; after the chromium melt pool cools and solidifies at the bottom of the crystallizer, it is gradually pulled out of the crystallizer by a traction mechanism to obtain the large-sized chromium target.

[0013] It should be noted in Step 1 that in a preferred embodiment of the present invention, in order to improve the conductivity of the initial ceramic raw material, chromium metal grains with a height of 20 mm to 100 mm are first added to the bottom of the crystallizer, then the ceramic raw material is added, and at the same time, the solid graphite electrode and the hollow graphite electrode are buried in the ceramic raw material. It should also be emphasized that for the purpose of achieving rapid heating during the first use, pre-melted liquid ceramic raw material heated externally can be added.

[0014] Considering that the purity of the obtained chromium target needs to be ensured in the present invention, when selecting the raw material for preparing the high-temperature ceramic melt pool, it is necessary to ensure that chromium does not react significantly with the ceramic raw material during the preparation process. Therefore, the present invention preferably uses a chromium carbide-based ceramic material that does not react with the chromium metal liquid as the ceramic raw material. For example, in some preferred embodiments of the present invention, the ceramic raw material is composed of the following components by mass percentage: 40 wt% to 70 wt% chromium carbide (Cr3C2), 10 wt% to 30 wt% calcium fluoride (CaF2), 5 wt% to 20 wt% calcium oxide (CaO), and 5 wt% to 20 wt% chromium oxide (Cr2O3), totaling 100%.

[0015] In some more preferred embodiments of the present invention, the ceramic raw material is composed of the following components by mass percentage: 50 wt% chromium carbide, 20 wt% calcium fluoride, 15 wt% calcium oxide, and 15 wt% chromium oxide, totaling 100%.

[0016] Moreover, in order to enable the continuous addition of chromium metal grains into the high-temperature ceramic melt pool during the subsequent treatment process and melt to form a fully liquid chromium metal melt or partially melt to form semi-solid droplets, so as to continuously prepare and form a large-sized chromium target, in a preferred embodiment of the present invention, the amount of the ceramic raw material is based on the height of the formed high-temperature ceramic melt pool being 50 mm to 350 mm.

[0017] It should also be noted that the refractory metal used in the present invention is pure molybdenum or tungsten-2wt% thorium oxide.

[0018] It should be noted in step 2 that in order to ensure that the ceramic raw materials in the mold can form a high-temperature ceramic melt pool with a temperature > 1950 °C, the present invention uses a solid graphite electrode as the anode and a hollow graphite electrode as the cathode. By placing them in the ceramic raw materials, the cathode and anode are in full contact with the ceramic raw materials, and electricity is passed through to form a resistance path through the ceramic raw materials between the solid graphite electrode and the hollow graphite electrode. Thus, the ceramic raw materials are heated by electricity using the principle of resistance heating to raise the temperature of the ceramic raw materials, melt them, and raise the temperature to > 1950 °C. And in order to ensure that the liquid ceramic raw materials can be heated to > 1950 °C by electric heating, in a preferred embodiment of the present invention, the voltage during the electric heating and temperature rise is 2 kV to 10 kV, and the current is 500 A to 3000 A.

[0019] Moreover, considering that the high-temperature ceramic melt pool formed should be able to melt the metal chromium particles added in the subsequent steps, the temperature of the formed high-temperature ceramic melt pool needs to be higher than the melting point of metal chromium. Therefore, before adding metal chromium, the temperature of the high-temperature ceramic melt pool needs to be > 1950 °C.

[0020] It should be noted in step 3 that in order to ensure that the added metal chromium particles can melt to form a fully liquid metal chromium melt or partially melt to form semi-solid droplets during the addition process, so as to facilitate continuous preparation to form a large-sized chromium target, in a preferred embodiment of the present invention, the particle size of the added metal chromium particles is ≤ 5 mm. And in another preferred embodiment of the present invention, the particle size of the added metal chromium particles is 1 mm to 5 mm.

[0021] Moreover, the metal chromium particles used in the present invention are obtained by crushing the metal chromium blocks obtained by aluminothermic reduction or the electrolytic chromium sheets obtained by electrolysis.

[0022] It should also be noted that the density of the high-temperature ceramic melt pool formed by chromium carbide, calcium fluoride, calcium oxide, and chromium oxide ceramic raw materials is less than the density of the chromium melt. Therefore, the liquid chromium or semi-solid particulate liquid chromium or semi-solid metal chromium particles will naturally sink to the bottom of the high-temperature ceramic melt pool under the action of gravity. And during the sinking process, the high-temperature ceramic melt pool will further purify and adsorb the possible oxidation and nitride inclusions in the chromium in the melted chromium melt. After the chromium melt is deposited in the water-cooled mold with water-cooling around, a chromium melt pool with a certain thickness is formed on the surface of the water-cooled bottom plate.

[0023] In order to ensure that the metal chromium particles are added to the high-temperature ceramic melt pool through the hollow structure of the hollow graphite electrode, in a preferred embodiment of the present invention, the inner diameter of the hollow structure of the hollow graphite electrode is 100 mm to 200 mm.

[0024] Moreover, in order to continuously add chromium metal particles into the high-temperature ceramic melt pool through the hollow structure of the hollow graphite electrode, in a preferred embodiment of the present invention, the discharge end of the charging head of the vacuum furnace is communicated with the upper end of the hollow graphite electrode. The chromium metal particles are continuously put into the charging head of the vacuum furnace in batches, and the chromium metal particles are continuously added into the high-temperature ceramic melt pool by vibrating the charging head. The vibration frequency during the vibration of the charging head is 5 times / min to 30 times / min, and the feeding rate is controlled at 100 g / min to 800 g / min. For the protective environment of inert gas, inert gas is filled into the vacuum furnace after evacuation.

[0025] It should also be noted that after the molten chromium formed by melting reaches the bottom of the melt pool, a melt pool with a thickness of 10 mm to 100 mm is formed. The periphery of the melt pool is cooled by a water-cooled crystallizer, and the bottom is a water-cooled bottom plate that can move downward. A temperature field with the highest temperature on the top and the lowest temperature on the bottom is naturally formed. The solid chromium is formed at the lowest temperature at the bottom of the chromium melt pool and is pulled by the water-cooled bottom plate, and leaves the water-cooled crystallizer at a pulling speed of 1 mm / min to 20 mm / min. In the above-mentioned process, the chromium metal particles are continuously added into the high-temperature ceramic melt pool through the hollow structure of the hollow graphite electrode. After the added chromium metal particles are added, they naturally drop under their own gravity. And during the dropping process, due to the gradually decreasing distance from the high-temperature ceramic melt pool, the temperature of the chromium metal particles gradually increases during the dropping process, so that the chromium metal particles gradually melt during the dropping process. And when the chromium metal particles contact the high-temperature ceramic melt pool, they melt to form a fully liquid metal chromium melt or partially melt to form semi-solid droplets. The density of the high-temperature ceramic melt pool formed by the chromium carbide-based ceramic is less than the density of the molten chromium. Therefore, the molten chromium or semi-solid granular molten chromium or semi-solid chromium metal particles will naturally sink to the bottom of the high-temperature ceramic melt pool under the action of gravity to form a chromium melt pool. After the chromium melt pool contacts the circulating water cooling structure of the crystallizer at the bottom of the high-temperature ceramic melt pool, it cools and solidifies in the circulating water cooling structure. Subsequently, it is gradually pulled down by the traction mechanism and continuously solidifies to form a casting with a certain length (long plate shape, long tube shape or cylindrical shape), which can be machined into a large-size chromium target.

[0026] In a preferred embodiment of the present invention, when adding chromium metal particles under vacuum, the vacuum degree of the vacuum condition is < 100 Pa.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] In the present invention, a solid graphite electrode is used as the anode, and a hollow graphite electrode is used as the cathode. First, by means of energizing and heating between the anode and the cathode, the ceramic raw materials are melted to form a high-temperature ceramic molten pool. By selecting a ceramic molten pool system that does not react significantly with the chromium melt, metal chromium grains are continuously added to the high-temperature ceramic molten pool through the hollow structure of the cathode, so that the chromium particles melt while descending in the high-temperature ceramic molten pool to form a fully liquid metal chromium melt or partially melt to form semi-solid chromium droplets; the liquid metal chromium or semi-solid droplets naturally sink to the crystallizer at the bottom of the high-temperature ceramic molten pool under the action of gravity to form a chromium molten pool; after the chromium molten pool cools and solidifies at the bottom of the crystallizer, it is gradually pulled out of the crystallizer by a traction mechanism. Through this continuous melting and continuous solidification process of metal chromium grains, the present invention can prepare a large-sized metal chromium target with high density and no defects, which has important scientific significance and practical value for the technical development of vacuum coating.

[0029] The preparation method of the present invention is simple and does not require the extremely expensive hot isostatic pressing equipment used in the current production of chromium targets, greatly reducing the preparation difficulty and cost. Moreover, the reduction of the preparation difficulty effectively improves the preparation efficiency, which is conducive to the expansion of the production scale.

[0030] The preparation method of the present invention can be carried out continuously without the need to obtain the metal target after processing and removing the residual mold on the surface, improving the material utilization rate. Moreover, it gets rid of the limitation of the hot isostatic pressing equipment on the length of the target, and a large-sized chromium target of more than 3 m can be formed in one step. The purity of the large-sized chromium target prepared by the present invention is above 99%.

[0031] The large-sized chromium target obtained by the preparation method of the present invention is in a solidified state structure, with low gas element content and high density, and its performance is higher than that of the target prepared by the hot isostatic pressing method. Description of the Drawings

[0032] Figure 1 It is a schematic structural diagram of the metal chromium grain adding device used in the preparation process of the present invention. Detailed Embodiments

[0033] As described in the background art, the existing preparation methods are difficult to meet the requirements of industrial preparation of large-sized metallic chromium targets. In this regard, the inventors propose that if continuous melting and solidification techniques can be used to produce metallic chromium targets, the deficiencies of the current powder metallurgy method can be overcome, and the preparation of large-sized chromium targets is expected to be achieved. However, considering that chromium is a metal with an extremely high melting point, it is extremely difficult to obtain a large volume of chromium melt at one time, and chromium melt has extremely high reactivity with most ceramic refractory materials, making it extremely difficult to obtain a large volume of metallic chromium melt through the smelting process. The method of producing large-sized chromium targets using traditional casting processes is not feasible in industrial technology. The present invention provides a method for preparing a large-sized chromium target, in which chromium particles are continuously melted step by step in a high-temperature ceramic melting pool to form a small-volume melting pool at the bottom of the high-temperature ceramic melting pool, and a chromium target with a large length is prepared by continuous directional solidification.

[0034] The technical solutions in the embodiments of the present invention will be clearly and completely described below.

[0035] Example 1

[0036] This embodiment provides a method for preparing a large-sized chromium target, including the following steps:

[0037] Step 1, prepare a mold made of refractory metal and having a circulating water cooling structure at the bottom:

[0038] Using pure molybdenum as the refractory metal, according to the method of mechanical combination of molybdenum plates, prepare a mold with a circulating water cooling structure at the bottom, the inner hole size of which is a hollow square hole column with a length of 200 mm, a width of 20 mm, a wall thickness of 20 mm, and a height of 250 mm. The outside of the column is cooled by circulating water to obtain the mold 1 as shown in Figure 1 in.

[0039] Step 2, prepare a high-temperature ceramic melting pool:

[0040] 1) Weigh the corresponding masses of the preparation raw materials according to the following ratio and mix them evenly to obtain ceramic raw materials for standby:

[0041] 50 wt% chromium carbide, 20 wt% calcium fluoride, 15 wt% calcium oxide, and 15 wt% chromium oxide.

[0042] 2) After weighing the ceramic raw materials and metallic chromium particles according to a mass ratio of 9:1, first load the metallic chromium particles into the mold 1 and then add the ceramic raw materials, and make the ceramic raw materials surround the solid graphite electrode 2 and the hollow graphite electrode 3. The loading height is about 200 mm.

[0043] 3) Apply power to the cathode and anode, with a voltage of 3 kV and the current gradually rising from 0 A to 3000 A. This causes the ceramic raw materials and metallic chromium grains to heat up and gradually melt. Ceramic raw materials and metallic chromium grains can continue to be added through the channels of the cathode, causing the ceramic raw materials to melt and form a high-temperature ceramic melt pool 5 with a height of about 190 mm in the crystallizer.

[0044] 4) When continuing to apply power, perform power-on heat preservation on the high-temperature ceramic melt. The temperature control is within the range of 1950 °C to 2000 °C, forming a stable high-temperature ceramic melt pool at the bottom of the crystallizer.

[0045] Step 4, forming a large-sized chromium target:

[0046] 1) Crush the metallic chromium blocks obtained by aluminothermic reduction into metallic chromium grains with a particle size of 3 mm to 5 mm. Place the metallic chromium grains in batches in the feed head 4, set the vibration frequency of the hopper 4 to 20 times / min. In a vacuum environment with a vacuum degree < less than 100 Pa, add the metallic chromium grains in batches through the hollow structure of the cathode 3 continuously into the high-temperature ceramic melt pool 5, causing the metallic chromium grains to melt while descending after being added, and then reaching the high-temperature ceramic melt pool 5. The melted metallic chromium is further purified by the high-temperature ceramic melt to adsorb possible oxidation and nitriding inclusions in the chromium blocks. Then, the fully liquid metallic chromium melt formed after melting or partially melted to form semi-solid droplets sink to the bottom of the high-temperature ceramic melt pool 5 to form a chromium melt pool 6. The periphery of the chromium melt pool 6 is a circulating water-cooling structure, and the bottom is a water-cooled bottom plate that can move downward, naturally forming a temperature field with the highest temperature at the top and the lowest temperature at the bottom. The solid chromium is formed at the lowest temperature at the bottom of the chromium melt pool and, under the traction of the water-cooled bottom plate 7, leaves the water-cooled crystallizer 1 at a descending speed of 10 mm / min. The above steps are carried out continuously, and the size of the chromium target obtained after the traction mechanism gradually pulls out is about 4560 mm in length, about 197 mm in width, and about 19.2 mm in thickness.

[0047] Detect the composition of the chromium target prepared in this example, and the detection results are shown in Table 1. It can be seen that the purity of the obtained chromium target is above 99%, which can meet the composition requirements of the chromium target.

[0048] Table 1 Composition of the chromium target prepared in Example 1

[0049] Element Cr Fe Al Si C O N Content (wt%) 99.58 0.17 0.028 0.12 <0.005 0.0058 0.007

[0050] It should be noted that, in subsequent actual use, the obtained chromium target can be milled into a chromium target with high surface finish for use.

[0051] Example 2

[0052] This example provides a method for preparing a large-sized chromium target, including the following steps:

[0053] Step 1, prepare a mold made of refractory metal with a circulating water cooling structure at the bottom:

[0054] Use tungsten-2wt% thorium oxide to make the refractory metal mold. According to the method of mechanical combination of tungsten plates, prepare a mold with a circulating water cooling structure at the bottom. Its inner hole size is a hollow cylinder with a length of 250mm, a width of 18mm, a wall thickness of 15mm, and a height of 300mm. The outside of the cylinder is cooled by circulating water.

[0055] Step 3, crush metallic chromium:

[0056] After subjecting the metallic chromium flakes obtained by electrolysis to reduction treatment, crush them into metallic chromium grains with a particle size of 1 - 3mm, and place the metallic chromium grains in batches in the charge head, making the bottom of the charge head insert into the upper end of the hollow structure arranged at the cathode. For the connection state, please refer to Figure 1 .

[0057] Step 3, prepare a high-temperature ceramic molten pool:

[0058] 1) Weigh the corresponding masses of the preparation raw materials according to the following ratio and mix them evenly to obtain ceramic raw materials for standby:

[0059] 50wt% chromium carbide, 15wt% calcium fluoride, 20wt% calcium oxide, 15wt% chromium oxide.

[0060] 2) After weighing the ceramic raw materials and metallic chromium grains according to a mass ratio of 8.5:1.5, first load the metallic chromium grains into the mold and then add the ceramic raw materials, and make the ceramic raw materials surround the solid graphite electrode and the hollow graphite electrode. The loading height is about 260mm.

[0061] 3) Apply electricity to the cathode and anode, apply a voltage of 2kV, and gradually increase the current from 0A to 3000A to heat up and gradually melt the ceramic raw materials and the metallic chromium grains therein. Ceramic raw materials and metallic chromium grains can be continuously added through the channels of the cathode to melt the ceramic raw materials and form a high-temperature ceramic molten pool with a height of 230mm in the mold.

[0062] 4) When continuing to apply electricity, keep the high-temperature ceramic melt under electricity for heat preservation, and control the temperature within the range of 1950°C - 2000°C to form a stable high-temperature ceramic molten pool at the bottom of the mold.

[0063] Step 4, form a large-sized chromium target:

[0064] 1) Set the vibration frequency of the hopper to 15 times / min. Under an argon protection atmosphere, add chromium metal granules batch by batch continuously through the hollow structure of the cathode into the high-temperature ceramic melting pool, so that the chromium metal granules melt while descending after being added, and then reach the high-temperature ceramic melting pool. The melted chromium metal is further purified by the high-temperature ceramic melt to adsorb possible oxidation and nitridation inclusions in the chromium block. Then, the fully liquid metal chromium melt formed after melting or partially melted to form semi-solid droplets sink to the bottom of the high-temperature ceramic melting pool to form a chromium melting pool. The periphery of the chromium melting pool is a circulating water cooling structure, and the bottom is a water-cooled bottom plate that can move downward, naturally forming a temperature field with the highest temperature on the top and the lowest temperature on the bottom; the solid chromium is formed at the lowest temperature at the bottom of the chromium melting pool and is pulled by the water-cooled bottom plate and leaves the water-cooled crystallizer at a descending speed of 15 mm / min. The above steps are carried out continuously. After the traction mechanism gradually pulls out, the large-size chromium target obtained has a size of about 3510 mm in length, about 247 mm in width, and about 17.5 mm in thickness.

[0065] Detect the composition of the chromium target prepared in this example, and the detection results are shown in Table 2. It can be seen that the purity of the obtained chromium target is above 99%, which can meet the quality requirements of the chromium target.

[0066] Table 2 Composition of the chromium target prepared in Example 2

[0067] Element Cr Fe Al Si Mo W O N Content (wt%) 99.97 0.0091 0.000097 0.0011 0.0063 0.0011 0.0058 0.007

[0068] It should be noted that in subsequent actual use, the obtained chromium target can be milled into a chromium target with high surface finish for use.

[0069] Example 3

[0070] This example provides a method for preparing a large-size chromium target, including the following steps:

[0071] Step 1, prepare a crystallizer made of refractory metal with a circulating water cooling structure at the bottom:

[0072] Use pure molybdenum as the refractory metal. According to the method of mechanical combination of molybdenum plates, prepare a crystallizer with a circulating water cooling structure at the bottom. Its inner hole size is a hollow square hole column with a length of 200 mm, a width of 20 mm, a wall thickness of 20 mm, and a height of 250 mm. The outside of the column is cooled by circulating water to obtain the crystallizer 1 as shown in Figure 1 shown in.

[0073] Step 2, prepare a high-temperature ceramic melting pool:

[0074] 1) Weigh the corresponding masses of the preparation raw materials according to the following ratio and mix them evenly to obtain ceramic raw materials for standby:

[0075] 40 wt% chromium carbide, 30 wt% calcium fluoride, 10 wt% calcium oxide and 20 wt% chromium oxide.

[0076] 2) After weighing the ceramic raw materials and metal chromium grains according to a mass ratio of 9:1, first load the metal chromium grains into the crystallizer 1 and then add the ceramic raw materials, and make the ceramic raw materials surround the solid graphite electrode 2 and the hollow graphite electrode 3. The loading height is about 60 mm.

[0077] 3) Apply electricity to the cathode and anode through a power supply, apply a voltage of 5 kV, and gradually increase the current from 0 A to 500 A to heat up and gradually melt the ceramic raw materials and metal chromium grains. The ceramic raw materials and metal chromium grains can be continuously added through the channel of the cathode, so that the ceramic raw materials melt and form a high-temperature ceramic melt pool 5 with a height of about 50 mm in the crystallizer.

[0078] 4) When continuing to apply electricity, the high-temperature ceramic melt is kept warm by electricity, and the temperature control is within the range of 1950 °C to 2000 °C to form a stable high-temperature ceramic melt pool at the bottom of the crystallizer.

[0079] Step 4, forming a large-sized chromium target:

[0080] 1) Crush the metal chromium block obtained by the aluminothermic reduction method into metal chromium grains with a particle size of 3 mm to 5 mm, and place the metal chromium grains in batches in the hopper head 4. Set the vibration frequency of the hopper 4 to 5 times / min. In a vacuum environment with a vacuum degree < less than 100 Pa, the metal chromium grains are continuously added to the high-temperature ceramic melt pool 5 through the hollow structure of the cathode 3 in batches through the hopper head 4, so that the metal chromium grains melt while descending after being added, and then reach the high-temperature ceramic melt pool 5. The melted metal chromium is further purified by the high-temperature ceramic melt to adsorb possible oxidation and nitriding inclusions in the chromium block, and then the fully liquid metal chromium melt formed after melting or partially melted to form semi-solid droplets sink to the bottom of the high-temperature ceramic melt pool 5 to form a chromium melt pool 6. The periphery of the chromium melt pool 6 is a circulating water-cooled structure, and the bottom is a water-cooled bottom plate that can move downward, naturally forming a temperature field with the highest temperature on the top and the lowest temperature on the bottom; the solid chromium is formed at the lowest temperature at the bottom of the chromium melt pool and is pulled by the water-cooled bottom plate 7 and leaves the water-cooled crystallizer 1 at a descending speed of 1 mm / min. The above steps are carried out continuously. After the traction mechanism gradually pulls out, a chromium target is obtained.

[0081] Moreover, the composition of the chromium target prepared in this example was detected, and the detection results showed that the purity of the chromium target prepared in this example was greater than 99%.

[0082] Example 4

[0083] This example provides a method for preparing a large-sized chromium target, including the following steps:

[0084] Step 1: Prepare a mold made of refractory metal with a circulating water cooling structure at the bottom:

[0085] Using pure molybdenum as the refractory metal, prepare a mold with a circulating water cooling structure at the bottom by the method of mechanical combination of molybdenum plates. Its inner hole size is a hollow square hole column with a length of 200 mm, a width of 20 mm, a wall thickness of 20 mm, and a height of 250 mm. The outside of the column is cooled by circulating water to obtain the mold 1 as shown in Figure 1 Figure 1.

[0086] Step 2: Prepare a high-temperature ceramic molten pool:

[0087] 1) Weigh the corresponding masses of the preparation raw materials according to the following ratio and mix them evenly to obtain ceramic raw materials for standby:

[0088] 70 wt% chromium carbide, 10 wt% calcium fluoride, 15 wt% calcium oxide, and 5 wt% chromium oxide.

[0089] 2) After weighing the ceramic raw materials and metal chromium grains according to a mass ratio of 9:1, first load the metal chromium grains into the mold 1 and then add the ceramic raw materials, and make the ceramic raw materials surround the solid graphite electrode 2 and the hollow graphite electrode 3. The loading height is about 360 mm.

[0090] 3) Apply electricity to the cathode and anode through a power supply, apply a voltage of 3000 V, and gradually increase the current from 0 A to 3000 A to heat up and gradually melt the ceramic raw materials and metal chromium grains. The ceramic raw materials and metal chromium grains can be continuously added through the channel of the cathode to melt the ceramic raw materials and form a high-temperature ceramic molten pool 5 with a height of about 350 mm in the mold.

[0091] 4) When continuing to apply electricity, the high-temperature ceramic molten liquid is kept warm by applying electricity, and the temperature control is within the range of 1950 °C to 2000 °C to form a stable high-temperature ceramic molten pool at the bottom of the mold.

[0092] Step 4: Form a large-size chromium target:

[0093] 1) The metallic chromium blocks obtained by aluminothermic reduction are crushed into metallic chromium grains with a particle size of 3 mm to 5 mm, and the metallic chromium grains are placed in the charging head 4 in batches. The vibration frequency of the hopper 4 is set to 30 times / min. In a vacuum environment with a vacuum degree < less than 100 Pa, the metallic chromium grains are continuously added to the high-temperature ceramic molten pool 5 through the hollow structure of the cathode 3 in batches via the charging head 4, so that the metallic chromium grains melt while descending after being added, and then reach the high-temperature ceramic molten pool 5. The molten high-temperature ceramic liquid further purifies and adsorbs the possible oxidation and nitriding inclusions in the chromium blocks in the melted metallic chromium. Then, the fully liquid metallic chromium melt formed after melting or the semi-solid droplets formed by partial melting sink to the bottom of the high-temperature ceramic molten pool 5 to form a chromium molten pool 6. The periphery of the chromium molten pool 6 is a circulating water-cooling structure, and the bottom is a water-cooled bottom plate that can move downward, naturally forming a temperature field with the highest temperature at the top and the lowest temperature at the bottom; the solid chromium is formed by solidification at the lowest temperature at the bottom of the chromium molten pool and leaves the water-cooled crystallizer 1 at a descending speed of 20 mm / min under the traction of the water-cooled bottom plate 7. The above steps are carried out continuously. After the traction mechanism gradually pulls out, a chromium target is obtained.

[0094] Moreover, the composition of the chromium target prepared in this embodiment is detected, and the detection results show that the purity of the chromium target prepared in this embodiment is greater than 99%.

[0095] Obviously, the above embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts belong to the scope of protection of the present invention.

Claims

1. A method for preparing a large-sized chromium target, characterized in that, It includes the following steps: Using a solid graphite electrode as the anode and a hollow graphite electrode as the cathode, adding externally heated and melted ceramic raw materials into a crystallizer so that both the solid graphite electrode and the hollow graphite electrode are buried in the ceramic raw materials; the crystallizer is a crystallizer made of a refractory metal cooled by passing water; Applying an electric current between the anode and the cathode, and continuously adding solid ceramic raw materials to continuously heat the ceramic raw materials by passing an electric current, so that the ceramic raw materials are heated and melted to form a high-temperature ceramic molten pool with a temperature > 1950 °C; Under vacuum or an inert atmosphere, adding metal chromium grains continuously into the high-temperature ceramic molten pool through the hollow structure of the cathode, so that the metal chromium grains melt while descending in the high-temperature ceramic molten pool to form a fully liquid metal chromium melt or partially melt to form semi-solid chromium droplets; the metal chromium liquid or semi-solid droplets naturally sink to the crystallizer at the bottom of the high-temperature ceramic molten pool to form a chromium molten pool; after the chromium molten pool cools and solidifies at the bottom of the crystallizer, it is gradually pulled out of the crystallizer by a traction mechanism, and thus the large-size chromium target is obtained; Wherein, the density of the high-temperature ceramic molten pool is less than the density of the chromium molten pool.

2. The preparation method according to claim 1, characterized in that, During the process of adding metal chromium grains, continuously apply an electric current to maintain the temperature of the high-temperature ceramic molten pool > 1950 °C.

3. The preparation method according to claim 1, characterized in that, The ceramic raw materials are composed of the following components by mass percentage: 40wt% - 70wt% of chromium carbide, 10wt% - 30wt% of calcium fluoride, 5wt% - 20wt% of calcium oxide, and 5wt% - 20wt% of chromium oxide, totaling 100%.

4. The preparation method according to claim 1, characterized in that, The particle size of the metal chromium grains ≤ 5 mm.

5. The preparation method according to claim 1, characterized in that, When heating up by passing an electric current, the voltage is 2 kV - 10 kV, and the current is 500 A - 3000 A.

6. The preparation method according to claim 1, wherein The metal chromium grains are added into the hollow structure of the cathode by means of vibrating the feed head, and the vibration frequency during the vibration of the feed head is 5 times / min - 30 times / min, and the feeding speed is 100 g / min - 800 g / min.

7. The preparation method according to claim 1, characterized in that, The pulling-out rate of the traction mechanism is 1 mm / min - 20 mm / min.

8. The preparation method according to claim 1, characterized in that The height of the high-temperature ceramic molten pool is 50 mm - 350 mm.

9. The preparation method according to claim 1, characterized in that, The inner diameter of the hollow structure of the hollow graphite electrode is 100 mm - 200 mm.

10. The preparation method according to claim 1, characterized in that, The vacuum degree of the vacuum condition < 100 Pa; The inert gas environment is introducing argon or a hydrogen-argon mixture containing 5% hydrogen.

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