Method for producing tantalum powder

Abstract

FIELD: powder metallurgy.SUBSTANCE: invention relates to the production of tantalum powder. Heating and reduction of tantalum pentoxide with magnesium is carried out, placed in a reactor on the surface of magnesium in an inert gas atmosphere at a temperature of 900-1000 °C and inert gas pressure in the reactor of 1.05-1.30 atm. Heating is carried out in two stages: up to a temperature of 640-650 °C at a rate of 50-80 °C / min, and up to a temperature of 900-1000 °C at a rate of 5-15 °C / min. The reduction products are then vacuumed to remove residual magnesium, and magnesium oxide is acid-leached from the reduction products to produce tantalum powder. The powder is washed to a neutral state and dried.EFFECT: reduces oxygen content in tantalum powder, resulting in improved powder quality and increased productivity.2 cl, 3 ex

Description

[0001] The invention relates to non-ferrous metallurgy and can be used in the metallothermic production of tantalum powder suitable for smelting tantalum ingots.

[0002] Tantalum is widely used in electronics for the production of electrolytic capacitors, in chemical engineering for the manufacture of corrosion-resistant equipment, as well as in space and nuclear engineering and medicine. Tantalum is a member of the group of refractory metals, which are obtained in pure form from their compounds, such as fluorides, chlorides, or oxides. When these compounds are reduced, tantalum is obtained as a powder due to its high melting point (3020°C).

[0003] A method for producing tantalum powder is known (see Russian Patent 2397843, IPC B22F 9 / 22, B22F 1 / 02, C22B 34 / 24 (2006.01), 2010) by reducing fine-grained, partially sintered tantalum pentoxide Ta2O5 powders with vapors of a reducing agent (magnesium). The reduction temperature is 680-940°C. Vapor formation and reduction are carried out in a single reactor, so that the reduction temperature determines the vapor pressure of the reducing agent. The reduction process is carried out by passing an inert carrier gas (argon) containing magnesium vapor through a layer of powdered tantalum pentoxide located on a mesh substrate above a crucible with magnesium, that is, the reducing agent and tantalum pentoxide are spatially separated from each other. The carrier gas is preheated to the reactor temperature before or during introduction into the reactor to prevent condensation of the reducing metal vapors.After the reduction reaction is complete, the resulting reducing metal oxide is removed with a sulfuric acid solution, and the tantalum powder is washed with distilled water until neutral and dried. The resulting tantalum powder has a specific surface area of ​​2.7-15 m. 2 / g. The oxygen content in it is 0.81-4.02 wt.%.

[0004] This method is characterized by low quality of the resulting tantalum powder due to the elevated oxygen content. Furthermore, since tantalum pentoxide and the reducing metal are located at a distance from each other in the reactor, the argon carrier gas can only transport a limited amount of magnesium vapor into the reaction zone per unit of time. This reduces the rate of tantalum pentoxide reduction and, therefore, reduces the productivity of the method.

[0005] A method for producing tantalum powder is also known, adopted as a prototype (see Russian Federation Patent 2842191, IPC B22F 9 / 20, B22F 9 / 18 (2006.01), 2025), by reducing tantalum pentoxide with magnesium in a reactor in an inert gas atmosphere. When loading the batch into the reactor, tantalum pentoxide is placed directly on the surface of magnesium. Argon and / or helium are used as an inert gas. The reduction is carried out at a temperature of 650-850°C with a decrease in the total pressure in the reactor from 1 atm to 0.001 atm during the reduction. After the reduction, the reduction products are subjected to heat treatment in an inert gas atmosphere at a temperature of 1250-1600°C for 1-5 hours, cooled to room temperature and removed from the reactor. Then, acid leaching of magnesium oxide from the resulting products is carried out to obtain tantalum powder, which is washed until the washing solution is neutral and dried.In this case, the specific surface area of ​​the powder decreases to 0.5-1.1 m. 2 / g. The oxygen content is 0.3-0.7 wt.%.

[0006] Since tantalum pentoxide is placed directly on the magnesium surface, after the magnesium melts, reducing the argon pressure in the reactor accelerates the flow of magnesium vapor into the pentoxide powder pores. This increases the rate of tantalum pentoxide reduction. However, the known method is characterized by insufficient quality of the resulting tantalum powder due to the high oxygen content. Furthermore, the need for heat treatment of the reduction products at 1250-1600°C before acid leaching of the magnesium oxide increases the powder production process time and increases energy consumption per unit of output. This reduces the productivity of the method.

[0007] The present invention is aimed at achieving a technical result consisting in improving the quality of the obtained tantalum powder by reducing the oxygen content therein and in increasing the productivity of the method by reducing the number of operations.

[0008] The technical result is achieved in that in the method for producing tantalum powder, including heating and reducing tantalum pentoxide with magnesium, placed in a reactor on the surface of magnesium, in an inert gas atmosphere at an elevated temperature and a given total pressure, acid leaching of magnesium oxide from the reduction products to obtain tantalum powder, washing the powder to a neutral state of the washing solution and drying the powder, according to the invention, the reduction of tantalum pentoxide is carried out at a temperature of 900-1000 °C and an inert gas pressure in the reactor of 1.05-1.30 atm, followed by evacuation of the reduction products to remove residual magnesium, wherein the heating is carried out in two stages: to a temperature of 640-650 °C at a rate of 50-80 °C / min, and to a temperature of 900-1000 °C at a rate of 5-15 °C / min.

[0009] The technical result is also achieved by the fact that the vacuuming of the reduction products is carried out in two stages, with the first stage reaching a pressure of 0.5-0.6 atm, and the second stage reaching a pressure of 0.1-0.01 atm.

[0010] The essential features of the claimed invention, which determine the scope of legal protection and are sufficient to obtain the above-mentioned technical result, perform the functions and relate to the result as follows.

[0011] Reducing tantalum pentoxide at 900-1000°C improves the quality of the resulting tantalum powder and increases the productivity of the process. A reduction temperature of 900-1000°C reduces the oxygen content of the tantalum pentoxide by decreasing the specific surface area of ​​the powder due to increased wettability of the products with liquid magnesium, thereby increasing the yield of its coarse fractions. At reduction temperatures below 900°C, the contact angle of the reduction products with liquid magnesium will be insufficient to ensure wettability of the entire reaction volume. Reduction temperatures above 1000°C are undesirable due to increased energy consumption and increased corrosion of the equipment.

[0012] Reducing tantalum pentoxide at an inert gas pressure of 1.05-1.30 atm reduces unwanted magnesium evaporation losses, increases the proportion of tantalum pentoxide directly reduced by liquid magnesium, and, consequently, reduces oxygen content. Reduction at pressures below 1.05 atm is undesirable due to accelerated magnesium evaporation and the potential introduction of air into the reactor. Reduction at pressures above 1.30 atm requires higher mechanical strength of the equipment.

[0013] Vacuuming the reduction products to remove residual magnesium increases the degree of reduction and makes the process more cost-effective, as it allows excess magnesium used to ensure complete reduction of tantalum pentoxide to be returned to production and reduces acid consumption during leaching of the reduction products.

[0014] Heating to the reduction temperature in two stages: to a temperature of 640-650°C at a rate of 50-80°C / min, and to a temperature of 900-1000°C at a rate of 5-15°C / min improves the quality of the resulting powder and the productivity of the method. Heating at a rate of less than 50°C / min in the first stage and less than 5°C / min in the second increases the duration of the powder production process. Heating at a rate of more than 80°C / min in the first stage and more than 15°C / min in the second stage leads to excessively intense reduction, with the release of excess heat in the contact zone of tantalum pentoxide and liquid magnesium. This results in the formation of denser reduction products, which hinder the flow of magnesium to the overlying tantalum pentoxide layers. In addition, denser reduction products make it difficult to leach magnesium oxide, leading to an increase in the oxygen content of the tantalum powder.

[0015] The combination of the above-mentioned features is necessary and sufficient to achieve the technical result of the invention, which consists in improving the quality of tantalum powder, as well as increasing the productivity of the method.

[0016] In particular cases of implementing the invention, the following operating parameters are preferred.

[0017] Vacuuming the reduction products to remove residual magnesium in two stages: to a pressure of 0.5-0.6 atm and to a pressure of 0.1-0.01 atm, facilitates complete reduction. Vacuuming to a pressure of over 0.6 atm in the first stage and to a pressure of over 0.1 atm in the second does not ensure full reduction of tantalum pentoxide and does not allow for the complete return of excess magnesium to the process, thereby increasing acid consumption during leaching of the reduction products. Vacuuming to a pressure of less than 0.5 atm in the first stage and to a pressure of less than 0.01 atm in the second stage is undesirable due to a decrease in the degree of reduction due to the more rapid removal of magnesium.

[0018] The above-mentioned particular features make it possible to implement the method in an optimal mode in terms of improving the quality of tantalum powder and the productivity of the method.

[0019] In general, the method for producing tantalum powder according to the invention is carried out as follows. Metallic magnesium is loaded into a metal crucible. Tantalum pentoxide powder Ta2O5 is placed on the surface of the metallic magnesium. The crucible is placed in a reaction vessel with a lid, which is installed in a reactor in the form of a stainless steel retort. The reactor is evacuated, filled with an inert gas in the form of argon, helium or a mixture thereof, heated to a temperature of 900-1000 ° C, with heating carried out in two stages: to a temperature of 640-650 ° C at a rate of 50-80 ° C / min, and then to a temperature of 900-1000 ° C at a rate of 5-15 ° C / min and reduction is carried out at a temperature of 900-1000 ° C and an inert gas pressure of 1.05-1.30 atm. After the reduction is complete, the products are vacuumed to remove residual magnesium in two stages, with the first stage being at a pressure of 0.5-0.6 atm, and the second stage at a pressure of 0.1-0.01 atm.After evacuation, the reactor is filled with an inert gas, cooled to room temperature, and a controlled supply of air is introduced. The reduction products, a mixture of magnesium oxide and tantalum powder, are extracted and treated with a mineral acid solution (HCl, HNO3, or H2SO4) to remove magnesium oxide. The tantalum powder is washed with distilled water until the solution is neutral and dried.

[0020] The specific surface area of ​​the powder is measured using the BET adsorption static method using a FlowSorb II 2300 surface analyzer with an accuracy of 3%. The oxygen concentration in the powder is measured using gas adsorption chromatography on a K-671 analyzer.

[0021] The essence and advantages of the proposed invention can be explained by the following examples of specific implementation.

[0022] Example 1. Magnesium metal weighing 104 g is loaded into a crucible. A powder of tantalum pentoxide (Ta2O5) weighing 350 g is placed on the surface of the magnesium. The amount of magnesium is 10% greater than its stoichiometric amount, calculated based on the oxygen content of Ta2O5. The crucible is placed in a reaction vessel with a lid, which is installed in the reactor.

[0023] The reactor is evacuated, filled with an inert gas - argon, heated to a temperature of 640 ° C at a rate of 50 ° C / min, and then to a temperature of 900 ° C at a rate of 15 ° C / min and reduced at this temperature and an inert gas pressure of 1.05 atm for 5 hours. Upon completion of the reduction, the products are evacuated to remove residual magnesium in two stages, with the first stage being evacuated to a pressure of 0.5 atm, and the second to 0.01 atm. Upon completion of the evacuation, the reactor is refilled with argon and cooled to room temperature, the reduction products are removed and treated with a solution of 10% hydrochloric acid HCl to remove magnesium oxide. The resulting tantalum powder is washed with distilled water until the solution is neutral and dried. The powder has a specific surface area of ​​0.82 m 2 / g, oxygen content - 0.25 wt.%.

[0024] Example 2. Magnesium metal weighing 144 g is loaded into a crucible. A powder of tantalum pentoxide (Ta2O5) weighing 350 g is placed on the surface of the magnesium. The amount of magnesium is 50% greater than its stoichiometric amount, calculated based on the oxygen content of Ta2O5. The crucible is placed in a reaction vessel with a lid, which is installed in the reactor.

[0025] The reactor is evacuated, filled with an inert gas - argon, heated to a temperature of 650 ° C at a rate of 80 ° C / min, and then to a temperature of 1000 ° C at a rate of 5 ° C / min and reduced at this temperature and an inert gas pressure of 1.30 atm for 4 hours. Upon completion of the reduction, the products are evacuated to remove residual magnesium in two stages, with the first stage being reduced to a pressure of 0.6 atm, and the second to 0.1 atm. Upon completion of the evacuation, the reactor is refilled with argon, cooled to room temperature, the reduction products are removed and treated with a solution of 10% nitric acid HNO3 to remove magnesium oxide. The resulting tantalum powder is washed with distilled water until the solution is neutral and dried. The powder has a specific surface area of ​​0.36 m 2 / g, oxygen content - 0.18 wt.%.

[0026] Example 3. Magnesium metal weighing 125 g is loaded into a crucible. A powder of tantalum pentoxide (Ta2O5) weighing 350 g is placed on the surface of the magnesium. The amount of magnesium is 30% greater than its stoichiometric amount, calculated based on the oxygen content of Ta2O5. The crucible is placed in a reaction vessel with a lid, which is installed in the reactor.

[0027] The reactor is evacuated, filled with an inert gas - argon, heated to a temperature of 645 ° C at a rate of 70 ° C / min, and then to a temperature of 950 ° C at a rate of 10 ° C / min and reduced at this temperature and an inert gas pressure of 1.2 atm for 4.5 hours. Upon completion of the reduction, the products are evacuated to remove residual magnesium in two stages, with the first stage being evacuated to a pressure of 0.55 atm, and the second to 0.05 atm. Upon completion of the evacuation, the reactor is refilled with argon and cooled to room temperature, the reduction products are removed and treated with a solution of 15% sulfuric acid H2SO4 to remove magnesium oxide. The resulting tantalum powder is washed with distilled water until the solution is neutral and dried. The powder has a specific surface area of ​​0.34 m 2 / g, oxygen content - 0.20 wt.%.

[0028] The examples provided demonstrate that the claimed method reduces the oxygen content in tantalum powder to 0.18-0.25% by weight, improving the quality of the resulting powder. Furthermore, the method is more productive, as it eliminates the need for an additional step—heat treatment of the reduction products at elevated temperatures—before acid leaching of magnesium oxide, as in the prior art. The proposed method can be implemented in industrial settings.

Claims

1. A method for producing tantalum powder, which includes heating and reducing tantalum pentoxide with magnesium, placed in a reactor on the surface of magnesium in an inert gas atmosphere at an elevated temperature and a given total pressure, acid leaching of magnesium oxide from the reduction products to obtain tantalum powder, washing the powder to a neutral state of the washing solution and drying the powder, characterized in that the reduction of tantalum pentoxide is carried out at a temperature of 900-1000 °C and an inert gas pressure in the reactor of 1.05-1.30 atm, followed by vacuuming the reduction products to remove residual magnesium, wherein the heating is carried out in two stages: to a temperature of 640-650 °C at a rate of 50-80 °C / min, and to a temperature of 900-1000 °C at a rate of 5-15 °C / min.

2. The method according to paragraph 1, characterized in that the vacuuming of the reduction products is carried out in two stages, with the first stage reaching a pressure of 0.5-0.6 atm, and the second stage reaching a pressure of 0.1-0.01 atm.