Method for preparing high-purity chromium metal

Abstract

The invention discloses a method for preparing high-purity metal chromium. The electrolytic chromium sheet A is prepared into powder A, the metal chromium B is subjected to vacuum carbon reduction to prepare powder B, and the metal chromium C is prepared into powder C through an aluminothermic method; uniformly mixing the powder A, the powder B and the powder C according to a certain proportion; adding a certain amount of high-purity carbon powder and high-purity tin powder, and uniformly mixing again; the evenly mixed powder is physically compressed into small cylindrical ingots through a pressing machine; heating the small cylindrical ingot in a vacuum furnace, preserving heat, degassing, and cooling under atmosphere protection; and performing vacuum packaging to obtain the high-purity chromium metal. According to the method for preparing the high-purity chromium metal, the currently manufactured chromium metal can be further purified, customized production can be carried out according to customer requirements, special requirements are met, and the method is simple in process, low in cost and worthy of popularization.

Description

Technical Field

[0001] This invention relates to a method for preparing high-purity metallic chromium, which uses different raw material ratios to purify metallic chromium to meet the requirements of special steels and aerospace applications. Background Technology

[0002] Metallic chromium can be produced using the aluminothermic process, electrolysis, and vacuum carbon reduction. However, neither the aluminothermic nor electrolytic methods can meet the requirements for special steels and aerospace applications. The aluminothermic process is simple, low-cost, and produces high-volume chromium, but the product typically contains high levels of residual aluminum (Al) (from raw aluminum particles) and impurities such as silicon (Si) and iron (Fe) from the raw chromium green material. The oxygen (O) content may also be high, making it unsuitable for use. Electrolytic chromium, on the other hand, has high oxygen and sulfur content, also failing to meet requirements. Vacuum carbon reduction, which uses carbon to reduce chromium oxide at high temperatures in a vacuum, effectively removes oxygen (O) and volatile impurities (such as low-melting-point metals), resulting in a relatively controllable and low carbon (C) content. However, it may introduce trace amounts of residual carbon, also failing to meet requirements. With industrial development, particularly in semiconductors such as sputtering targets, the purity requirements for metals are increasing, necessitating a new process for further purifying metallic chromium.

[0003] This invention provides a method for preparing high-purity metallic chromium, which can further purify existing metallic chromium and can be customized according to customer requirements to meet special needs. The process is simple, low-cost, and worthy of promotion. Summary of the Invention

[0004] One object of the present invention is to solve at least the above-mentioned problems and / or defects, and to provide at least the advantages described below.

[0005] To achieve these and other advantages of the present invention, a method for preparing high-purity metallic chromium is provided, comprising the following steps; Step 1: Electrolytic chromium sheet A is prepared into powder A, vacuum carbon reduction of metallic chromium B is prepared into powder B, and aluminothermic method of metallic chromium C is prepared into powder C. Step 2: Mix powder A, powder B, and powder C evenly in a certain proportion; add a certain amount of high-purity carbon powder and high-purity tin powder, and mix evenly again; Step 3: The powder that was mixed evenly in Step 2 is physically compressed into cylindrical ingots using a press. Step 4: Heat and degas the cylindrical ingots in a vacuum furnace, then cool them under a protective atmosphere; vacuum package them to obtain high-purity metallic chromium.

[0006] Preferably, the particle size of powder A is 30-60 mesh, the particle size of powder B is 60-80 mesh, and the particle size of powder C is 30-80 mesh.

[0007] Preferably, the mixing mass ratio of powder A, powder B and powder C is 1-2:1-2:1-2.

[0008] Preferably, in step two, the method for achieving uniform mixing again is as follows: the material and zirconia balls are added to a ball mill jar, the ball mill jar is sealed, and a vacuum of -0.05 to -0.08 MPa is applied. Then, liquid argon is injected into the ball mill jar so that the material and zirconia balls are immersed in the liquid argon. The ball mill is then milled for 1 to 3 hours at a speed of 500 r / min to 100 r / min to obtain a uniformly mixed material; the ball-to-material ratio is 5 to 10:1.

[0009] Preferably, the amount of high-purity carbon powder added is the theoretical amount required for the oxygen element in the mixture of powder A, powder B and powder C to be converted into carbon monoxide, and the amount of tin powder added is the theoretical amount required for the sulfur element in the mixture of powder A, powder B and powder C to be converted into tin sulfide.

[0010] Preferably, the cylindrical ingot has an external dimension of Φ3cm*1-5cm; the density of the cylindrical ingot is 5-6g / cm³. 3 Cylindrical ingots are formed by pressing them under a pressure of 2-8 MPa.

[0011] Preferably, the heating rate of the vacuum furnace is 1-5 degrees Celsius / min.

[0012] Preferably, the temperature for heating, holding and degassing in the vacuum furnace is 1450-1550 degrees Celsius, the vacuum degree is 0.3-2.5 Pa, and the holding and degassing time is 20-30 hours.

[0013] Preferably, high-purity chromium is cooled to below 80 degrees Celsius under a protective atmosphere; the atmosphere is argon gas with a purity of 99.9%, the gas pressure inside the furnace is 5 Pa, and the cooling rate is: 2-3 degrees Celsius / min for temperatures above 800 degrees Celsius, and 0.5-2 degrees Celsius / min for temperatures below 800 degrees Celsius.

[0014] Preferably, the vacuum packaging consists of a PE inner plastic bag vacuum-sealed and an outer metal drum.

[0015] The present invention has at least the following beneficial effects: (1) This invention provides a method for preparing high-purity metallic chromium, which can further purify existing metallic chromium and can be customized according to customer requirements to meet special requirements. The process is simple and low-cost, and is worth promoting.

[0016] (2) This invention uses three raw materials in combination, which reduces production costs. The optimized powder particle size and vacuum degassing process further reduce the gas content of the product and improve product quality, making it worthy of promotion.

[0017] (3) The present invention mixes chromium powder from different process sources and adds high-purity carbon powder and tin powder. The purpose is to remove each other’s residual impurities by utilizing the chemical reaction and physical action between different components during the subsequent vacuum degassing / sintering process. Each method has its own purification limit. The use of mixtures can bypass the bottleneck of a single method (such as the difficulty of removing H by electrolysis, the difficulty of removing Al by aluminothermic method, and the need for strict control of C by carbon reduction method), and achieve a higher level of comprehensive purification.

[0018] Other advantages, objectives and features of the present invention will become apparent in part from the following description, and in part from those skilled in the art through study and practice of the invention. Attached image description: Figure 1 This is a process diagram of the method for preparing high-purity metallic chromium according to the present invention. Detailed implementation method: The present invention will be further described in detail below with reference to embodiments, so that those skilled in the art can implement it based on the description.

[0019] It should be understood that terms such as “having,” “comprising,” and “including” as used herein do not imply the presence or addition of one or more other elements or combinations thereof.

[0020] The method of this invention enables the preparation of higher purity chromium. During the preparation process, impurities are removed through mutual reactions. For example, residual aluminum (Al) in aluminothermic chromium powder can react with added tin powder (Sn) at high temperatures to form a low-melting-point Al-Sn alloy. These alloys are easily volatilized or migrated to the surface and removed under vacuum and high temperature. Simultaneously, aluminum can also react with carbon to form Al4C3 (which may be removed subsequently). Hydrogen (H) in electrolytic chromium powder can react with added carbon powder (C) under high temperature and vacuum to generate methane (CH4) gas, which escapes. Residual carbon (C) in carbon-reduced chromium powder can react with oxygen (O) from powders of different sources to generate CO gas, which is then removed. Oxygen (O) from different sources can be removed through carbon deoxidation reactions. Mixing dilutes specific impurities in the overall powder (e.g., Al mainly comes from aluminothermic powder). During high-temperature vacuum degassing / sintering, impurities (such as interstitial atoms H, O, or certain metallic impurities) have more opportunities to diffuse to the surface or grain boundaries, and are then removed by vacuum extraction or by combining with reactants. Furthermore, when powders of different particle sizes and morphologies are mixed, the cylindrical ingots pressed into them will form a more complex pore structure with potentially better connectivity, which is conducive to the escape of reaction gases (CH4, CO, Sn / Al vapor, etc.) under high temperature and vacuum.

[0021] Furthermore, this invention enables customized production: by adjusting the mixing ratio of powders A, B, and C, the content range of specific impurities in the final product can be actively controlled. For example, if a customer requires a product with extremely low aluminum (Al) content, the proportion of aluminothermic powder C can be reduced, while the proportions of electrolytic powder A and carbon reduction powder B can be increased. If an extremely low oxygen (O) content product is required, the proportion of vacuum carbon reduction powder B (which has good deoxidation properties) can be increased, and the further deoxidation effect of carbon in the mixed powder can be utilized. If it is necessary to control specific trace elements, the mixture can be formulated by selecting powders from different sources. This flexibility is unmatched by a single process.

[0022] Although this invention utilizes powders from three different processes, it fully leverages the advantages of each. The aluminothermic method has the lowest cost and can be used extensively to reduce overall costs. The electrolytic method has the highest cost and purity, requiring only a small amount to significantly improve key purity indicators. The vacuum carbon reduction method strikes a balance between deoxidation and cost. By optimizing the proportions, it is possible to achieve a lower overall cost than solutions using only high-cost electrolytic powders while meeting purity requirements. Subsequent mixing, pressing, and degassing processes are relatively simple and also facilitate cost control.

[0023] Example 1: Step 1: Electrolytic chromium sheet A (containing 5000ppm oxygen, 200ppm sulfur, 100ppm iron, 20ppm aluminum, and 100ppm nitrogen) is prepared into 60-mesh powder A; vacuum carbon-reduced metallic chromium B (containing 1000ppm oxygen, 200ppm sulfur, 500ppm iron, 100ppm aluminum, and 100ppm nitrogen) is prepared into 30-mesh powder B; aluminothermic metallic chromium C (containing 2000ppm oxygen, 50ppm sulfur, 1200ppm iron, 1000ppm aluminum, and 200ppm nitrogen) is prepared into 30-mesh powder C. Step 2: Mix powder A, powder B, and powder C in a mass ratio of 1:1:1; add carbon powder and tin powder. The amount of carbon powder added is the theoretical amount required for the oxygen element in the mixture of powder A, powder B, and powder C to be converted into carbon monoxide, and the amount of tin powder added is the theoretical amount required for the sulfur element in the mixture of powder A, powder B, and powder C to be converted into tin sulfide; mix the materials again. Step 3: The material is physically compressed into cylindrical ingots with a diameter of 3cm and a diameter of 2.5cm using a press. Step 4: Sinter and degas the cylindrical Φ3cm*2.5cm ingot in a vacuum furnace at 1450 degrees Celsius for 25 hours, and then cool it down to 80 degrees Celsius under argon atmosphere protection. This will yield high-purity metallic chromium with an oxygen content of 100ppm, a sulfur content of 20ppm, an iron content of 500ppm, an aluminum content of 400ppm, a nitrogen content of 50ppm, and a chromium content of 99.5%.

[0024] Example 2: Step 1: Electrolytic chromium sheet A (containing 5000 ppm oxygen, 200 ppm sulfur, 100 ppm iron, 20 ppm aluminum, and 100 ppm nitrogen) is prepared into 30-mesh powder A; vacuum carbon-reduced metallic chromium B (containing 1000 ppm oxygen, 200 ppm sulfur, 500 ppm iron, 100 ppm aluminum, and 100 ppm nitrogen) is prepared into 40-mesh powder B; aluminothermic metallic chromium C (containing 2000 ppm oxygen, 50 ppm sulfur, 1200 ppm iron, 1000 ppm aluminum, and 200 ppm nitrogen) is prepared into 30-mesh powder C. Step 2: Mix powder A, powder B, and powder C in a mass ratio of 3:1:1; add carbon powder and tin powder. The amount of carbon powder added is the theoretical amount required for the oxygen element in the mixture of powder A, powder B, and powder C to be converted into carbon monoxide, and the amount of tin powder added is the theoretical amount required for the sulfur element in the mixture of powder A, powder B, and powder C to be converted into tin sulfide; mix the materials again. Step 3: The material is physically compressed into cylindrical ingots with a diameter of 3cm and a diameter of 2.5cm using a press. Step 4: Sinter and degas the cylindrical Φ3cm*2.5cm ingot in a vacuum furnace at 1450 degrees Celsius for 25 hours, and then cool it down to 80 degrees Celsius under argon atmosphere protection. This will yield high-purity metallic chromium with an oxygen content of 95ppm, a sulfur content of 17ppm, an iron content of 300ppm, an aluminum content of 200ppm, a nitrogen content of 48ppm, and a chromium content of 99.9%.

[0025] Example 3: Step 1: Electrolytic chromium sheet A (containing 5000ppm oxygen, 200ppm sulfur, 100ppm iron, 20ppm aluminum, and 100ppm nitrogen) is prepared into 30-mesh powder A; vacuum carbon-reduced metallic chromium B (containing 1000ppm oxygen, 200ppm sulfur, 500ppm iron, 100ppm aluminum, and 100ppm nitrogen) is prepared into 40-mesh powder B; aluminothermic metallic chromium C (containing 2000ppm oxygen, 50ppm sulfur, 1200ppm iron, 1000ppm aluminum, and 200ppm nitrogen) is prepared into 30-mesh powder C. Step 2: Mix powder A, powder B, and powder C in a mass ratio of 1:1:3; add carbon powder and tin powder. The amount of carbon powder added is the theoretical amount required for the oxygen element in the mixture of powder A, powder B, and powder C to be converted into carbon monoxide, and the amount of tin powder added is the theoretical amount required for the sulfur element in the mixture of powder A, powder B, and powder C to be converted into tin sulfide; mix the materials again. Step 3: The material is physically compressed into cylindrical ingots with a diameter of 3cm and a diameter of 2.5cm using a press. Step 4: Sinter and degas the cylindrical Φ3cm*2.5cm ingot in a vacuum furnace at 1450 degrees Celsius for 25 hours, and then cool it down to 80 degrees Celsius under argon atmosphere protection. This will yield high-purity metallic chromium with an oxygen content of 300ppm, a sulfur content of 40ppm, an iron content of 800ppm, an aluminum content of 600ppm, a nitrogen content of 45ppm, and a chromium content higher than 99.7%.

[0026] Example 4: Step 1: Electrolytic chromium sheet A (containing 5000ppm oxygen, 200ppm sulfur, 100ppm iron, 20ppm aluminum, and 100ppm nitrogen) is prepared into 60-mesh powder A; vacuum carbon-reduced metallic chromium B (containing 1000ppm oxygen, 200ppm sulfur, 500ppm iron, 100ppm aluminum, and 100ppm nitrogen) is prepared into 30-mesh powder B; aluminothermic metallic chromium C (containing 2000ppm oxygen, 50ppm sulfur, 1200ppm iron, 1000ppm aluminum, and 200ppm nitrogen) is prepared into 30-mesh powder C. Step 2: Mix powder A, powder B, and powder C in a mass ratio of 1:1:1; add carbon powder and tin powder. The amount of carbon powder added is the theoretical amount required for the oxygen element in the mixture of powder A, powder B, and powder C to be converted into carbon monoxide, and the amount of tin powder added is the theoretical amount required for the sulfur element in the mixture of powder A, powder B, and powder C to be converted into tin sulfide; add the material and zirconia balls into a ball mill jar, seal the ball mill jar, and evacuate it to -0.06 MPa. Then, inject liquid argon into the ball mill jar so that the material and zirconia balls are immersed in liquid argon. Ball mill at a speed of 500 r / min for 2 hours to obtain a uniformly mixed material; the ball-to-material ratio is 10:1. Step 3: The material after ball milling in Step 2 is physically compressed into cylindrical ingots with a diameter of Φ3cm*2.5cm using a press; Step 4: Sinter and degas the cylindrical Φ3cm*2.5cm ingot in a vacuum furnace at 1450 degrees Celsius for 25 hours, and then cool it down to 80 degrees Celsius under argon atmosphere protection. This will yield high-purity metallic chromium with an oxygen content of 80ppm, a sulfur content of 15ppm, an iron content of 280ppm, an aluminum content of 180ppm, a nitrogen content of 40ppm, and a chromium content of 99.8%.

[0027] Comparative Example 1: Step 1: Prepare 30-mesh powder C from metallic chromium C (containing 2000 ppm oxygen, 50 ppm sulfur, 1200 ppm iron, 1000 ppm aluminum, and 200 ppm nitrogen) using the aluminothermic method. Step 2: Add carbon powder and tin powder to powder C. The amount of carbon powder added is the theoretical amount required for the oxygen element in the mixture of powder C to be converted into carbon monoxide, and the amount of tin powder added is the theoretical amount required for the sulfur element in the mixture of powder C to be converted into tin sulfide; mix the materials again. Step 3: The material is physically compressed into cylindrical ingots with a diameter of 3cm and a diameter of 2.5cm using a press. Step 4: Sinter and degas the cylindrical Φ3cm*2.5cm ingot in a vacuum furnace at 1450 degrees Celsius for 25 hours. Then, under argon atmosphere protection, cool down to 80 degrees Celsius to obtain metallic chromium with an oxygen content of 1000ppm, a sulfur content of 45ppm, an iron content of 1200ppm, an aluminum content of 110ppm, a nitrogen content of 112ppm, and a chromium content of 99.1%.

[0028] Comparative Example 2: Step 1: Electrolytic chromium sheet A (containing 5000ppm oxygen, 200ppm sulfur, 100ppm iron, 20ppm aluminum, and 100ppm nitrogen) is prepared into 60-mesh powder A, and aluminothermic metallic chromium C (containing 2000ppm oxygen, 50ppm sulfur, 1200ppm iron, 1000ppm aluminum, and 200ppm nitrogen) is prepared into 30-mesh powder C. Step 2: Mix powder A and powder C at a mass ratio of 1:1; add carbon powder and tin powder. The amount of carbon powder added is the theoretical amount required for the oxygen element in the mixture of powder A and powder C to be converted into carbon monoxide, and the amount of tin powder added is the theoretical amount required for the sulfur element in the mixture of powder A and powder C to be converted into tin sulfide; mix the materials again. Step 3: The material is physically compressed into cylindrical ingots with a diameter of 3cm and a diameter of 2.5cm using a press. Step 4: Sinter and degas the cylindrical Φ3cm*2.5cm ingot in a vacuum furnace at 1450 degrees Celsius for 25 hours, and then cool it down to 80 degrees Celsius under argon atmosphere protection; the resulting metal chromium has an oxygen content of 200ppm, a sulfur content of 40ppm, an iron content of 1200ppm, an aluminum content of 100ppm, a nitrogen content of 100ppm, and a chromium content of 99.3%. Comparative Example 3: Step 1: Vacuum carbon reduction of metallic chromium B (containing 1000 ppm oxygen, 200 ppm sulfur, 500 ppm iron, 100 ppm aluminum, and 100 ppm nitrogen) to prepare 30-mesh powder B; aluminothermic process of metallic chromium C (containing 2000 ppm oxygen, 50 ppm sulfur, 1200 ppm iron, 1000 ppm aluminum, and 200 ppm nitrogen) to prepare 30-mesh powder C. Step 2: Mix powder B and powder C at a mass ratio of 1:1; add carbon powder and tin powder. The amount of carbon powder added is the theoretical amount required for the oxygen element in the mixture of powder B and powder C to be converted into carbon monoxide, and the amount of tin powder added is the theoretical amount required for the sulfur element in the mixture of powder B and powder C to be converted into tin sulfide; mix again. Step 3: The material is physically compressed into cylindrical ingots with a diameter of 3cm and a diameter of 2.5cm using a press. Step 4: Sinter and degas the cylindrical Φ3cm*2.5cm ingot in a vacuum furnace at 1450 degrees Celsius for 25 hours, and then cool it down to 80 degrees Celsius under argon atmosphere protection. The resulting metal chromium has an oxygen content of 150ppm, a sulfur content of 30ppm, an iron content of 1200ppm, an aluminum content of 100ppm, a nitrogen content of 80ppm, and a chromium content of 99.2%. This invention utilizes a complementary mixture of chromium powders from three different processing sources and innovatively introduces tin powder as a highly efficient purification aid into the purification process of high-melting-point metallic chromium. Its unique physicochemical properties (low melting point, liquid phase formation, and volatility) enhance impurity removal, a significant technological highlight. Combined with an optimized powder metallurgy vacuum processing flow, this achieves efficient, flexible, and low-cost secondary purification of existing metallic chromium. The key innovation of this invention lies in the addition of high-purity tin powder, whose role in this process is: 1. Formation of a low-melting-point eutectic / liquid phase: Tin has a low melting point (232°C). During subsequent heating / holding processes, tin will melt or form a low-melting-point eutectic phase with chromium / impurities. The role of this liquid phase: (1) Dissolving and capturing impurities: especially those impurities that are low in solubility in solid chromium or difficult to volatilize (such as certain metallic impurities).

[0029] (2) Promotes impurity diffusion and volatilization: The liquid phase channel provides a fast path for impurity atoms to migrate to the surface, which is beneficial for removing impurities (especially gaseous impurities such as oxygen, nitrogen, and sulfur, as well as some metal impurities captured by tin) during the vacuum degassing stage.

[0030] (3) Promote densification: Liquid phase sintering helps the bonding between powder particles and the filling of pores, thereby increasing the density of the final ingot.

[0031] II. The volatility of tin itself: Under high temperature and vacuum conditions, tin has a high vapor pressure and is easily volatilized. During the volatilization process, it may carry away impurities that are bound to it or dissolved in its liquid phase.

[0032] The main advantages of this invention are: I. Effective secondary purification This method does not produce primary chromium, but rather further purifies existing commercial or industrial-grade metallic chromium produced by different processes. Through the complementary effects of mixing and tin powder additives, the content of various impurities can be effectively reduced, resulting in a product with higher purity than that obtained from a single raw material.

[0033] II. Customizable Production Customized production is achieved through proportional mixing. This is difficult to achieve with raw materials from a single source. It is adaptable to different raw materials and can process chromium raw materials of varying sources and purities.

[0034] Third, the process is relatively simple and the cost is low. By utilizing existing mature products, the raw materials are readily available electrolytic chromium sheets and metallic chromium, eliminating the need for complex smelting or electrolysis from scratch.

[0035] IV. Technical approach: Mixing, pressing, and vacuum sintering are relatively mature powder metallurgy processes with strong equipment versatility and relatively simple operation.

[0036] V. Efficiency of Tin Powder Additives: The addition of tin powder may reduce the high temperature and harsh vacuum conditions required to achieve high purity, or improve the efficiency of impurity removal, thereby shortening the process time or reducing energy consumption.

[0037] Compared to developing entirely new one-step processes for producing high-purity chromium (such as ultra-high temperature vacuum melting, zone melting, and special electrolysis), this method significantly reduces overall costs and is economically viable for industrialization.

[0038] The present invention has been illustrated with the above embodiments to explain the detailed method of the present invention. However, the present invention is not limited to the above detailed method, that is, it does not mean that the present invention must rely on the above detailed method to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions of the raw materials of the product of the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for preparing high-purity metallic chromium, characterized in that, Includes the following steps; Step 1: Electrolytic chromium sheet A is prepared into powder A, vacuum carbon reduction of metallic chromium B is prepared into powder B, and aluminothermic method of metallic chromium C is prepared into powder C. Step 2: Mix powder A, powder B, and powder C evenly in a certain proportion; add a certain amount of high-purity carbon powder and high-purity tin powder, and mix evenly again; Step 3: The powder that was mixed evenly in Step 2 is physically compressed into cylindrical ingots using a press. Step 4: Heat and degas the cylindrical ingots in a vacuum furnace, then cool them under a protective atmosphere; vacuum package them to obtain high-purity metallic chromium.

2. The method for preparing high-purity metallic chromium as described in claim 1, characterized in that, The particle size of powder A is 30-60 mesh, the particle size of powder B is 60-80 mesh, and the particle size of powder C is 30-80 mesh.

3. The method for preparing high-purity metallic chromium as described in claim 1, characterized in that, The mixing mass ratio of powder A, powder B and powder C is 1-2:1-2:1-2.

4. The method for preparing high-purity metallic chromium as described in claim 1, characterized in that, In step two, the method for re-mixing uniformly is as follows: add the material and zirconia balls into a ball mill jar, seal the ball mill jar, evacuate to -0.05~-0.08MPa, then inject liquid argon into the ball mill jar so that the material and zirconia grinding balls are immersed in liquid argon, and ball mill at a speed of 500r / min~1000r / min for 1~3 hours to obtain a uniformly mixed material; the ball-to-material ratio is 5~10:

1.

5. The method for preparing high-purity metallic chromium as described in claim 1, characterized in that, The amount of high-purity carbon powder added is the theoretical amount required for the oxygen element in the mixture of powder A, powder B and powder C to be converted into carbon monoxide, and the amount of tin powder added is the theoretical amount required for the sulfur element in the mixture of powder A, powder B and powder C to be converted into tin sulfide.

6. The method for preparing high-purity metallic chromium as described in claim 1, characterized in that, The cylindrical ingots have an outer diameter of Φ3cm*1-5cm; the density of the cylindrical ingots is 5-6g / cm³. 3 Cylindrical ingots are formed by pressing them under a pressure of 2-8 MPa.

7. The method for preparing high-purity metallic chromium as described in claim 1, characterized in that, The heating rate of the vacuum furnace is 1-5 degrees Celsius per minute.

8. The method for preparing high-purity metallic chromium as described in claim 1, characterized in that, The temperature for heating, holding, and degassing in the vacuum furnace is 1450-1550 degrees Celsius, and the vacuum degree is 0.3-2.5 Pa; the holding and degassing time is 20-30 hours.

9. The method for preparing high-purity metallic chromium as described in claim 1, characterized in that, High-purity chromium is cooled to below 80 degrees Celsius under a protective atmosphere. The atmosphere is argon gas with a purity of 99.9%, and the gas pressure inside the furnace is 5 Pa. The cooling rate is 2-3 degrees Celsius / min above 800 degrees Celsius and 0.5-2 degrees Celsius / min below 800 degrees Celsius.

10. The method for preparing high-purity metallic chromium as described in claim 1, characterized in that, Vacuum packaging consists of an inner PE plastic bag vacuum-sealed and an outer metal drum.

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