METHOD FOR PRODUCING TANTALUM POWDER BY REDUCING POTASSIUM FLUOTANTHALATE WITH SODIUM, TANTALUM POWDER OBTAINED BY THE METHOD

Abstract

The invention relates to a method for producing tantalum powder by reducing potassium fluorotantalate with sodium, characterized in that preheated metallic sodium is used as the reducing agent to carry out the reduction, wherein the metallic sodium has a temperature above 180°C, more preferably from 200 to 350°C, more preferably from 200 to 260°C, more preferably from 160 to 190°C and / or from 210 to 240°C. The invention further relates to the tantalum powder obtained by the method and to the use of the tantalum powder in a condenser.

Description

Method for producing tantalum powder by sodium reduction of potassium fluotantalate and the tantalum powder produced thereby TECHNICAL FIELD

[0001] The present application belongs to the field of rare metal functional materials smelting, and particularly relates to a tantalum powder for high-voltage and high-reliability capacitors and a manufacturing method thereof. BACKGROUND

[0002] Tantalum electrolytic capacitors (hereinafter referred to as tantalum capacitors) have the advantages of high capacity, small size, strong self-healing ability, and high reliability, and are widely used in high-end technical fields such as communication, computers, automotive electronics, medical devices, radars, aerospace, and automatic control devices. Tantalum powder is a key material for making tantalum capacitors. Only by using tantalum powder with higher specific capacity and higher voltage resistance for capacitors can tantalum capacitors with smaller size and better reliability be produced. Therefore, only by continuously developing tantalum powder for capacitors with higher specific capacity and higher voltage resistance can the tantalum capacitors produced meet the requirements of electronic devices and electronic circuits for the miniaturization and high reliability of tantalum capacitors.

[0003] Currently, the main methods for industrial production of capacitor-grade tantalum powder are sodium reduction of potassium fluotantalate and magnesium reduction of tantalum oxide. The magnesium reduction of tantalum oxide method is expected to produce capacitor-grade tantalum powder with improved specific capacity and voltage resistance due to the change in the state of the reactants. However, due to the immaturity of the process, the magnesium reduction tantalum powder has the problems of low production efficiency and high cost, which limits its popularization and application. Although the sodium reduction of potassium fluotantalate method for producing tantalum powder has the problems of low specific capacity, large leakage current, and low breakdown voltage under relatively high voltage energizing conditions, the sodium reduction of potassium fluotantalate method has been scaled up due to its mature process, relatively low production cost, and the ease of producing high specific capacity tantalum powder. Therefore, the sodium reduction tantalum powder currently accounts for more than 80% of the capacitor-grade tantalum powder market. It is of great significance to improve the problems of low specific capacity, large leakage current, and low breakdown voltage of sodium reduction tantalum powder under high voltage energizing conditions.

[0004] In order to improve the quality of sodium reduction tantalum powder, many studies have been conducted in the industry.

[0005] US4684399A discloses a method for producing tantalum powder by sodium reduction of potassium fluotantalate. Potassium fluotantalate and metallic sodium are continuously or semi-continuously added to a molten diluent in multiple stages for stirring reduction to produce tantalum powder. US4149876A proposes a method for producing tantalum powder by adding liquid sodium to a molten potassium fluotantalate and diluent molten salt bath. This method involves rapidly injecting sodium at a lower injection temperature to raise the temperature of the material, using a large proportion of diluent, forced cooling, and reducing at a lower temperature while maintaining a constant temperature during grain growth, thereby producing tantalum powder with fine and uniform particle size. The patent also focuses on reduction temperature, heating rate, and forced cooling, etc.

[0006] CN1069564C discloses a reduction process adding phosphorus, boron, nitrogen, oxygen, silicon as additives for refining tantalum powder. The use of refining agent realizes a substantial increase in the specific capacity of sodium-reduced tantalum powder. There are also patents that use iodide or sulfate in the reduction process to improve the performance of tantalum powder.

[0007] JP4828016B2 discloses a method for manufacturing tantalum powder by reducing potassium fluorotantalate with metallic sodium, which realizes the reaction of potassium fluorotantalate at low concentration by adding a small amount of potassium fluorotantalate to the molten diluent, then adding metallic sodium for reduction, and then adding a small amount of potassium fluorotantalate for sodium reduction, and repeating this process, so as to achieve the purpose of improving the specific capacity of tantalum powder. The specific capacity of the tantalum powder manufactured by this method is 80000-250000 μFV / g.

[0008] CN201693181U discloses a method for dispersing metallic sodium and molten potassium fluorotantalate by using a sodium dispenser provided at the end of a sodium injection pipe; CN116100040A discloses a method for reducing potassium fluorotantalate by dispersing metallic sodium through air injection, which can produce tantalum powder products with uniform particle size distribution and uniform particle shape distribution.

[0009] In order to improve the pressure resistance of tantalum powder produced by the method of reducing potassium fluorotantalate with sodium, other methods include increasing the sintering temperature of subsequent processing and prolonging the sintering time, but increasing the sintering temperature and prolonging the sintering time will inevitably reduce the specific capacity of the tantalum powder.

[0010] Without being bound by general theory, the inventors have found through extensive research that current research on the process of reducing potassium fluorotantalate with sodium involves the state, temperature, and concentration of potassium fluorotantalate (using potassium chloride, sodium chloride, potassium fluoride, etc. as dilution salt to disperse potassium fluorotantalate); involves alkali metal halides as dilution salt; involves the use of additives such as sulfur, phosphorus, boron, nitrogen, oxygen, silicon, and iodine compounds for refining tantalum powder during the reduction process; involves the temperature and fluidity of liquid metallic sodium during injection; involves stirring and mixing during the reduction process; and involves equipment for optimizing the reduction process. However, current research on the process of reducing potassium fluorotantalate with sodium does not involve the effect of the temperature of liquid metallic sodium before injection on the particle morphology of metallic tantalum powder during the process of reducing potassium fluorotantalate with sodium.

[0011] SUMMARY

[0012] It is an object of the present invention to provide a method for producing tantalum powder from potassium fluotantalate by reduction with hot metallic sodium. The method involves reducing potassium fluotantalate, wherein preheated metallic sodium is used, which is heated to more than 180°C, more preferably 200-350°C, more preferably 200-260°C, more preferably 190°C-240°C, for example 210°C. The tantalum powder produced by this method, in combination with existing tantalum powder refining techniques, allows for the production of tantalum powder with improved morphology (e.g. sintering diameter is large, specific surface area is controllable, and has a porous structure). The tantalum powder produced by this process, after subsequent processing such as existing water pickling purification, sintering and oxygen reduction, is more suitable for making tantalum capacitors with higher reliability requirements. Compared to other methods for producing the same grade of capacitor tantalum powder, the specific capacity of the tantalum powder is high under high voltage energizing conditions, and the breakdown voltage is high, significantly improving the voltage resistance performance of the capacitor tantalum powder. In other words, the different specific capacity capacitor tantalum powder produced by the method of the present invention can withstand relatively higher voltage, and the tantalum capacitors made using it have higher reliability.

[0013] It is a further object of the present invention to provide a method for producing tantalum powder from a sodium reduction potassium fluotantalate process, comprising the following steps:

[0014] (1) providing dilution salt (preferably selected from alkali metal halides), potassium fluotantalate and metallic sodium as raw materials, wherein the amount of metallic sodium is in excess relative to the amount of potassium fluotantalate, and the metallic sodium is preheated to 180-350°C (preferably 200-350°C, more preferably 200-260°C, more preferably 160-190°C and / or 210-240°C) for use,

[0015] (2) loading the dilution salt into a reduction vessel, evacuating the vessel, then introducing an inert gas such as argon, then heating the dilution salt in the reduction vessel to melting while the inert gas is kept flowing (e.g. at a flow rate of 20-100 liters / minute),

[0016] (3) adding part of the potassium fluotantalate to the reduction vessel and monitoring the temperature to ensure that the potassium fluotantalate is melted with the dilution salt, then adding preheated metallic sodium to reduce the part of the potassium fluotantalate, repeating multiple times until all of the potassium fluotantalate and metallic sodium raw materials are used up,

[0017] (4) after the reduction is complete, aging the tantalum powder, and

[0018] (5) then, separating out the tantalum powder.

[0019] Optionally, after step (5) further comprising the step:

[0020] (6) after salt bath heat treatment and / or agglomeration heat treatment of the tantalum powder, oxygen reduction treatment of the metallic magnesium chips and further pickling purification and drying, the product tantalum powder is obtained.

[0021] In step (1), the diluent salt is selected from the alkali metal halides (also referred to as alkali metal halogen salts, herein "halogen salt" and "halide" are used interchangeably) commonly mentioned in the prior art, such as one or more of NaCl, KCl, KF, KI. The ratio of the diluent salt to the potassium fluorotantalate is not limited, and the ratio commonly used in the prior art can be used. Preferably, the diluent salt can also be mixed with a tantalum powder refiner. The amount of sodium metal is in excess of the theoretical amount required for the complete reduction of the potassium fluorotantalate, for example, 1-3% excess, preferably 1.5-2.5% excess. The sodium metal is preheated to more than 180°C-500°C, more preferably 200-350°C, more preferably 200-260°C, more preferably 190°C-240°C, for example 210°C. Preferably, both the diluent salt and the potassium fluorotantalate are in the form of a powder.

[0022] Preferably, in step (2), the evacuation and inert gas such as argon are repeated multiple times, for example 2-3 times, to remove as much air as possible from the reduction vessel, reduce the corrosion of the metal reduction vessel by air, and reduce the adverse effects of air on the tantalum powder. In order to carry the water vapor and acidic gases released during the heating and melting process by the argon gas and timely remove them from the reduction vessel, reduce the adverse effects of the reduction, preferably, the inert gas flow rate is maintained at 20-100 liters / minute, which can better remove water vapor and acidic gases, etc. In order to ensure its complete melting and improve the viscosity of the diluent salt, so that the stirring is more smooth, the diluent salt is preferably heated to a temperature of more than 80°C above its melting point, preferably more than 150°C, more preferably more than 200°C. Preferably, after sufficient melting, it is also subjected to heat preservation, for example, heat preservation for 30 minutes. The diluent salt is preferably stirred after being heated to the target temperature, in order to mix well and keep the temperature uniform. There is no special requirement for the stirring conditions. Preferably, the stirring of the melted diluent salt is continued, preferably until the end of the aging.

[0023] In step (3), the potassium fluorotantalate is added in several portions and the reduction is completed in order to reduce the concentration of the potassium fluorotantalate in the dilution salt. The amount of potassium fluorotantalate added at each time and the number of times of addition are not limited. However, the inventors have found through extensive research that the amount of potassium fluorotantalate added at each time is related to the target specific surface area of the final tantalum powder. In the case where a fixed amount of dilution salt has been added in step (2), if a tantalum powder having a large specific surface area is to be produced, the amount of potassium fluorotantalate added at each time can be reduced so that the potassium fluorotantalate is reduced at a lower concentration, and if a tantalum powder having a small specific surface area is to be produced, the amount of potassium fluorotantalate added at each time can be increased appropriately. That is, the present application enables good control of the specific surface area of the tantalum powder. Of course, regardless of the number of times of addition of the potassium fluorotantalate, the remaining amount of the raw material sodium is added at the time of the final addition of the metallic sodium so as to ensure complete reduction of the potassium fluorotantalate. Preferably, in this step, the temperature in the reduction vessel is controlled to be higher than the melting point of the mixture of the dilution salt and the potassium fluorotantalate so as to ensure melting thereof, for example, 80°C to 400°C higher than the melting point thereof, preferably 250°C to 350°C higher. It is easily understood by those skilled in the art that the temperature at which the mixture of the dilution salt and the potassium fluorotantalate is melted can be different from the melting point of the dilution salt and also different from the melting point of the potassium fluorotantalate. The "melting point" (also referred to as apparent melting point) at which the mixture is completely melted is different depending on the ratio of the two, but it can be found from the phase diagram data. Preferably, the temperature is increased after each addition of the potassium fluorotantalate. Preferably, in order to make the obtained tantalum powder more uniform, the amount of the high-temperature metallic sodium added before the final addition of the metallic sodium is such that 70 to 95%, more preferably 70 to 85%, of the potassium fluorotantalate added at the immediately preceding time is reduced. By adding the metallic sodium in this manner, it is possible to avoid the occurrence of an excessive amount of the metallic sodium in the reduction vessel and the premature (i.e., before melting) reaction of the metallic sodium with the potassium fluorotantalate added at the later time.

[0024] In step (4), preferably, the aging of the tantalum powder is performed by continuing the heating of the tantalum powder after the completion of the reduction. Preferably, the heating is continued for 0.5 to 5 hours, preferably 2 to 3 hours. Preferably, the temperature in the reaction vessel is controlled to be the same as the temperature before the addition of the metallic sodium in step (3). In this step, the excess metallic sodium is carried out of the reduction vessel by the argon gas and separated from the tantalum powder.

[0025] Preferably, in steps (3) and / or (4), the flow of an inert gas such as argon gas is maintained in the reduction vessel. Preferably, in step (5), the reduction vessel is maintained at a positive pressure until the mixture is taken out of the reduction vessel.

[0026] Preferably, the separation of the tantalum powder in step (5) comprises: stopping stirring, cooling to room temperature under the condition of maintaining the positive pressure of the reduction reaction container by argon, taking out the mixture containing halide and tantalum powder from the reduction container, removing part of the by-products not wrapped tantalum powder, and further separating the by-products by water and acid washing, washing and purifying, and drying to obtain the final tantalum powder.

[0027] Preferably, the method of the present application further comprises step (6) after step (5): water washing and / or acid washing, heat treatment such as high-temperature high-vacuum heat treatment (or high-temperature high-vacuum heat treatment after sintering assisted by molten salt according to the invention of patent CN114210973B), oxygen reduction, acid washing, and then separating the tantalum powder by, for example, filtration, drying, to obtain tantalum powder suitable for making high-reliability tantalum capacitors. These treatments are processes known in the prior art. In other words, these treatments can use any process known in the prior art. For example, the high-temperature high-vacuum heat treatment and passivation here can use the methods provided in patents CN201110039272.9, CN201120077798.1, CN201120077680.9, CN201120077305.4, etc., the oxygen reduction can use the methods provided in patents CN201420777210.7, CN201420777210.7, the acid washing can use the methods provided in patents CN201210548101.3, CN201280077499.5, CN201210548008.2, etc.

[0028] In the present application, N, P and / or B elements can also be doped into the tantalum powder after step (5) and / or (6). Of course, raw materials containing these elements can also be used directly. These elements can also be added in the aforementioned high-temperature high-vacuum heat treatment step. It is particularly preferred to add P element. Adding P element can increase the specific capacity, as long as the total amount of P doping is controlled, the effect of increasing the specific capacity is the same regardless of when the addition is made. This can be done in a conventional manner in the prior art, which is not described in detail.

[0029] The obtained product tantalum powder is pressed into a block, sintered, and energized under high pressure conditions, and the electrical properties of the energized block are tested, and it is found that the energized block has higher specific capacity and higher breakdown voltage in the breakdown voltage test.

[0030] After energization under the same high pressure conditions, the tantalum powder produced by the present application has higher specific capacity and higher breakdown voltage in the breakdown voltage test compared to the same grade of capacitor tantalum powder produced by other methods. Therefore, the tantalum powder produced by the present application is more suitable for making high-voltage high-reliability tantalum capacitors.

[0031] Without being bound by general theory, the inventors believe that the reason for the excellent effect of the present application is as follows. The sodium reduction of potassium fluotantalate is a violent exothermic process, which can release a large amount of heat locally. Generally, heat runaway is avoided by adding dilute salt. In step (2) of the present application, when the metallic sodium comes into contact with potassium fluotantalate, the temperature of the reaction point is instantaneously raised due to the use of preheated metallic sodium. The generation and growth of tantalum powder at the moment of reduction are affected by the temperature of the reaction point, which promotes the sintering between particles, making the internal sintering diameter of the tantalum powder thicker. However, due to the control of other process conditions (such as the reaction of potassium fluotantalate at a low concentration), the specific surface area of the tantalum powder is still well controlled, and the space structure between the tantalum powder particles is more easily constructed to be suitable for capacitor production.

[0032] The melting point of sodium is 97.78 degrees. Even if solid sodium is added, it will quickly melt into a liquid in the furnace. Therefore, the prior art pays little attention to the temperature of the metallic sodium itself, but only to the sodium injection temperature (i.e., the temperature of the reduction container or furnace when the sodium is added). Although someone may have studied the effect of increasing the sodium injection temperature, it means that the temperature in the furnace needs to be increased as a whole, which brings a greater thermal load to the materials used to make the reduction container and furnace, which is not conducive to their service life. Moreover, increasing the temperature in the furnace also means greater energy consumption. The prior art may also improve the flowability of liquid metallic sodium by increasing its temperature, but since the flowability of liquid sodium is almost stable when the temperature is increased above 120°C, metallic sodium with a temperature below about 120°C is generally added. The inventors have unexpectedly found through extensive research that by further increasing the temperature of liquid metallic sodium, not only does it maintain good flowability of the liquid sodium, but it also precisely increases the temperature of the reduction reaction point without increasing the power of the heating furnace, improves the morphology of the tantalum powder, and ultimately increases the specific capacity and breakdown voltage of the tantalum powder.

[0033] After the tantalum powder obtained according to the present application is subjected to high-temperature high-vacuum heat treatment (or first subjected to patent CN114210973B invention molten salt assisted sintering and then high-temperature high-vacuum heat treatment), oxygen reduction, and acid washing treatment, the tantalum powder still has a high specific capacity under high energized voltage, and the comprehensive electrical performance is improved, making it suitable for preparing high-voltage high-reliability capacitors. BRIEF DESCRIPTION OF DRAWINGS

[0034] The following drawings are provided to better understand the present application. These drawings are exemplary and are not intended to limit the scope of the present application.

[0035] Figure 1 shows a scanning electron microscope photograph of the tantalum powder obtained according to the present application.

[0036] This figure illustrates that the obtained tantalum powder particles are more uniform in size and smooth in shape, with thicker sintering necks. DETAILED DESCRIPTION

[0037] In order to further illustrate the present application, the preferred embodiments of the present application will be described in more detail with reference to the following examples. It is readily apparent to those skilled in the art that the present application can be practiced without resort to the details of the following description. The following description is merely meant to further illustrate the features and advantages of the present application and is not meant to limit the scope of the present application. Unless otherwise indicated, the conditions in the examples are conventional conditions. Unless otherwise indicated, the reagents or instruments used are conventional products available on the market.

[0038] For purposes of the present description, all numbers expressing quantities of ingredients, reaction conditions, and so forth used in the specification and claims are to be understood as being modified in all instances by the term "about," unless otherwise indicated. Accordingly, the numerical parameters given in the description and claims are approximations only, and thus can vary by a small amount depending upon the desired properties sought to be obtained by the present application. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.

[0039] The analysis of impurity content in tantalum powder was carried out according to Chinese standard GB / T15076.1-15076.15, and the physical properties were carried out according to industry standard YS / T573-2015. The test of electrical properties in tantalum powder was carried out according to Chinese standard GB / T3137.

[0040] Examples

[0041] In order to further illustrate the present application, the preferred embodiments of the present application will be described in more detail with reference to the following examples. It is readily apparent to those skilled in the art that the present application can be practiced without resort to the details of the following description. The following description is merely meant to further illustrate the features and advantages of the present application and is not meant to limit the scope of the present application. Unless otherwise indicated, the conditions in the examples are conventional conditions or the conditions recommended by the manufacturer. Unless otherwise indicated, the reagents or instruments used are conventional products available on the market.

[0042] For purposes of the present description, all numbers expressing quantities of ingredients, reaction conditions, and so forth used in the specification and claims are to be understood as being modified in all instances by the term "about," unless otherwise indicated. Accordingly, the numerical parameters given in the description and claims are approximations only, and thus can vary by a small amount depending upon the desired properties sought to be obtained by the present application. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.

[0043] The analysis of the impurity content in the tantalum powder was performed according to Chinese Standard GB / T 15076.1-15076.15, and the physical properties were performed according to the industry standard YS / T 573-2007. The leakage current and the capacitance of the tantalum powder were tested according to the Chinese Standard GB / T 3137.

[0044] Example 1

[0045] Potassium fluotantalate, NaCl as diluent, and metallic sodium were provided as raw materials. The metallic sodium was heated to a high temperature of 180°C in advance for standby use.

[0046] 100 kg of sodium chloride (NaCl) was loaded into a reduction vessel, the reduction vessel was vacuumed and then filled with argon to 0.10 MPa, and the vacuuming and argon filling were repeated twice. The reduction vessel was placed in a heating furnace, argon was introduced, the flow rate was 40 L / min, the temperature was raised to 920°C, and the stirring was started. After 30 minutes of temperature maintenance, 15 kg of potassium fluotantalate was added, and after the temperature was raised to 920°C, 3.95 kg of metallic sodium at 180°C was added for reduction. The above process was repeated 7 times. After the addition of potassium fluotantalate for the eighth time, 8.20 kg of metallic sodium was added for reduction. After the reduction was completed, the tantalum powder was aged at 920°C for 180 minutes under the condition of argon flow, and then the stirring was stopped, the pressure of the reaction vessel was maintained at 0.10 MPa, and the temperature was cooled to room temperature. The mixture was taken out of the reduction vessel, and part of the by-products not wrapped with tantalum powder was separated and removed. Further, the by-products were separated, washed, purified, and dried by acid washing to obtain high-purity tantalum powder.

[0047] Then, the tantalum powder was mixed with 50 ppm of P, and high-temperature high-vacuum heat treatment was performed at 1450°C and a pressure of less than 5.0 x 10 -3 Pa for 1.0 hour, and then oxygen reduction and acid washing were performed to obtain the final tantalum powder. The final tantalum powder was made into an anode block according to the anode block mass, the pressing density, the anode block sintering temperature, and the sintering time specified in Table 1, and other conditions were according to the requirements of the aforementioned GB / T 3137. The anode block was energized at 150 V, and then the electrical properties were tested according to the requirements of the aforementioned GB / T 3137. In the specific capacitance test, after the test was performed using 30% H2SO4 solution, the test was performed using 10% H3PO4 solution, and the test results are listed in Table 1.

[0048] Comparative Example 1

[0049] Potassium fluotantalate, NaCl as diluent, and metallic sodium were provided as raw materials. The metallic sodium was heated to 130°C in advance for standby use.

[0050] Take 100 kg of sodium chloride (NaCl) into the reduction vessel, vacuumize the reduction vessel and then fill it with argon to 0.10 MPa, repeat the vacuumization and then fill it with argon to 0.10 MPa twice. Put the reduction vessel into the heating furnace, and pass argon through it at a flow rate of 40 L / min, start stirring when the temperature reaches 920°C, and keep the temperature for 30 minutes. Then add 15 kg of potassium fluotantalate, and when the temperature reaches 920°C, add 3.95 kg of metallic sodium at 130°C to reduce it; repeat the addition of potassium fluotantalate and temperature increase and reduction 7 times. After the 8th addition of potassium fluotantalate, add 8.20 kg of metallic sodium at 130°C to reduce it, and after the reduction is completed, keep the temperature at 920°C for 180 minutes under the condition of argon flow to age the tantalum powder, then stop stirring, and maintain the pressure of the reaction vessel at 0.10 MPa to cool to room temperature. Take out the mixture from the reduction vessel, separate and remove part of the by-products that are not wrapped in tantalum powder, and further separate the by-products by water pickling, wash and purify, and dry to obtain high-purity tantalum powder.

[0051] Then, the tantalum powder is doped with 50 ppm of P, and high-temperature high-vacuum heat treatment is performed at 1450°C and a pressure of less than 5.0 x 10 -3 Pa for 1.0 hour, and then oxygen reduction, acid pickling are performed to obtain the final tantalum powder. The final tantalum powder is made into an anode block according to the anode block mass, pressing density, anode block sintering temperature, and sintering time specified in Table 1, and other conditions are according to the requirements of the aforementioned GB / T3137, the anode block is energized at 150V, and then the electrical performance is tested according to the requirements of the aforementioned GB / T3137, in the specific capacitance test, after testing with 30% H2SO4 solution, testing with 10% H3PO4 solution is performed, and the test results are listed in Table 1.

[0052] Example 2

[0053] Potassium fluotantalate, KCl and KF as diluents, and metallic sodium as raw materials are provided. The metallic sodium is heated to a high temperature of 220°C in advance for use.

[0054] A 50 kg of potassium chloride (KCl) and 50 kg of potassium fluoride (KF) were charged into a reduction vessel, the reduction vessel was vacuumed and then filled with argon to 0.10 MPa, and the vacuuming and filling with argon were repeated twice. The reduction vessel was placed in a heating furnace and heated, and argon was introduced at a flow rate of 60 L / min, and the stirring was started at 900°C, and the temperature was maintained for 30 minutes. Then, 15 kg of potassium fluorotantalate was added, and when the temperature reached 900°C, 4.0 kg of metallic sodium at 220°C was added for reduction; this was repeated 9 times by adding potassium fluorotantalate and increasing the temperature for reduction. After the addition of potassium fluorotantalate for the 10th time, 8.9 kg of metallic sodium at 220°C was added for reduction, and after the reduction was completed, the tantalum powder was aged at 900°C for 120 minutes under the condition of argon flow, and then the stirring was stopped, and the pressure in the reaction vessel was maintained at 0.10 MPa, and the temperature was cooled to room temperature. The mixture was taken out of the reduction vessel, and the by-products that were not wrapped in tantalum powder were separated and removed, and then the by-products were further separated by washing with acid, and washed and purified, and dried, to obtain high-purity tantalum powder.

[0055] Then, the tantalum powder was mixed with 60 ppm of P, and high-temperature high-vacuum heat treatment was performed at 1400°C and a pressure of less than 5.0 x 10 -3 Pa for 1.0 hour, and then oxygen reduction and acid washing were performed, to obtain the final tantalum powder. The final tantalum powder was made into an anode block according to the anode block mass, pressing density, anode block sintering temperature, and sintering time specified in Table 1, and other conditions were in accordance with the requirements of the aforementioned GB / T3137, and the anode block was energized at 100 V, and then the electrical properties were tested in accordance with the requirements of the aforementioned GB / T3137, and in the specific capacitance test, after testing with 30% H2SO4 solution, testing was performed with 10% H3PO4 solution, and the results of the test are shown in Table 1.

[0056] Comparative Example 2

[0057] Potassium fluorotantalate, KCl and KF as diluents, and metallic sodium were provided as raw materials. The metallic sodium was heated to 120°C in advance.

[0058] Take 50 kg of potassium chloride (KCl), 50 kg of potassium fluoride (KF) into the reduction vessel, vacuumize the reduction vessel and then fill it with argon to 0.10 MPa, repeat the vacuumization and then fill it with argon to 0.10 MPa twice. Put the reduction vessel into the heating furnace, and pass argon through it at a flow rate of 60 L / min, start stirring when the temperature reaches 900°C, and keep the temperature for 30 minutes. Then add 15 kg of potassium fluorotantalate, and when the temperature reaches 900°C, add 4.0 kg of metallic sodium at 120°C to reduce it; repeat the addition of fluorotantalate and temperature increase and reduction 9 times. After the 10th addition of fluorotantalate, add 8.90 kg of metallic sodium at 120°C to reduce it, and after the reduction is completed, keep the temperature at 900°C for 120 minutes under the condition of argon flow to age the tantalum powder, then stop stirring and maintain the pressure of the reaction vessel at 0.10 MPa to cool to room temperature. Take out the mixture from the reduction vessel, separate and remove part of the by-products that do not wrap the tantalum powder, and further separate the by-products by water pickling, wash and purify, and dry to obtain high-purity tantalum powder.

[0059] Then, the tantalum powder is doped with 60 ppm of P, and high-temperature high-vacuum heat treatment is carried out at 1400°C and a pressure of less than 5.0 x 10 -3 Pa for 1.0 hour, and then oxygen reduction, acid pickling are carried out to obtain the final tantalum powder. The final tantalum powder is made into anode blocks according to the anode block mass, pressing density, anode block sintering temperature, sintering time specified in Table 1, and other conditions according to the requirements of the aforementioned GB / T3137, the anode blocks are energized at 100 V, and then the electrical properties are tested according to the requirements of the aforementioned GB / T3137, in the specific capacitance test, after testing with 30% H2SO4 solution, testing with 10% H3PO4 solution is carried out, and the test results are listed in Table 1.

[0060] Example 3

[0061] Potassium fluorotantalate, KCl and KF as diluents, and metallic sodium as raw material are provided. The metallic sodium is heated to a high temperature of 180°C in advance for use.

[0062] Take 100 kg of potassium chloride (KCl), 100 kg of potassium fluoride (KF) into the reduction vessel, vacuumize the reduction vessel and then fill it with argon to 0.10 MPa, repeat the vacuumization and then fill it with argon to 0.10 MPa twice. Put the reduction vessel into the heating furnace, and pass argon through it at a flow rate of 70 L / min, and start stirring when the temperature is raised to 900°C, and keep the temperature for 30 minutes. Then add 10 kg of potassium fluorotantalate, and when the temperature is raised to 920°C, add 2.50 kg of metallic sodium at 180°C to reduce it; repeat the addition of fluorotantalate and temperature increase and reduction for 5 times. After the 6th addition of fluorotantalate, add 6.0 kg of metallic sodium at 180°C to reduce it, and after the reduction is completed, keep the temperature at 900°C for 120 minutes under the condition of argon flow to age the tantalum powder, and then stop stirring, and maintain the pressure of the reaction vessel at 0.10 MPa, and cool it to room temperature. Take out the mixture from the reduction vessel, separate and remove part of the by-products that are not wrapped with tantalum powder, and further separate the by-products by washing with acid, wash and purify, and dry to obtain high-purity tantalum powder.

[0063] Then, the tantalum powder is doped with 100 ppm of P, and high-temperature high-vacuum heat treatment is carried out at 1230°C and a pressure of less than 5.0 x 10 -3 Pa for 1.0 hour, and then oxygen reduction, acid washing are carried out to obtain the final tantalum powder. The final tantalum powder is made into an anode block according to the anode block mass, pressing density, anode block sintering temperature, sintering time specified in Table 1, and other conditions according to the requirements of the aforementioned GB / T3137, and the anode block is energized at 60 V, and then the electrical performance is tested according to the requirements of the aforementioned GB / T3137, and in the specific capacitance test, after testing with 30% H2SO4 solution, testing with 10% H3PO4 solution is carried out, and the test results are listed in Table 1.

[0064] Comparative Example 3

[0065] Potassium fluorotantalate, KCl and KF as diluents, and metallic sodium as raw material are provided. The metallic sodium is heated to a high temperature of 120°C in advance for use.

[0066] 100 kg of potassium chloride (KCl) and 100 kg of potassium fluoride (KF) are charged into a reduction vessel, the reduction vessel is vacuumed and then filled with argon to 0.10 MPa, and the vacuuming and argon filling are repeated twice. The reduction vessel is placed in a heating furnace and heated, argon is introduced at a flow rate of 70 L / min, and the temperature is raised to 900°C, the stirring is started, and the temperature is maintained for 30 minutes. Then, 10 kg of potassium fluorotantalate is added, and when the temperature rises to 900°C, 2.5 kg of sodium metal preheated to 120°C is added for reduction; the fluorotantalate is added for temperature rise and reduction for 5 times. After the addition of fluorotantalate for the sixth time, 6.0 kg of sodium metal at 120°C is added for reduction, and after the reduction is completed, the tantalum powder is aged at 900°C for 120 minutes under the condition of argon flow, and then the stirring is stopped, the pressure of the reaction vessel is maintained at 0.10 MPa, and the temperature is cooled to room temperature. The mixture is taken out of the reduction vessel, and part of the by-products not wrapped in tantalum powder is separated and removed, and then the by-products are further separated by water pickling, washed and purified, and dried to obtain high-purity tantalum powder.

[0067] Then, the tantalum powder is doped with 100 ppm of P, and high-temperature high-vacuum heat treatment is carried out at 1230°C and a pressure of less than 5.0 x 10 -3 Pa for 1.0 hour, and then oxygen reduction and acid pickling are carried out to obtain the final tantalum powder. The final tantalum powder is made into an anode block according to the anode block mass, pressing density, anode block sintering temperature, and sintering time specified in Table 1, and other conditions are according to the requirements of the aforementioned GB / T3137, the anode block is energized at 60V, and then the electrical performance is tested according to the requirements of the aforementioned GB / T3137, in the specific capacitance test, after testing with 30% H2SO4 solution, testing with 10% H3PO4 solution is carried out, and the test results are listed in Table 1.

[0068] Table 1 Analysis results of the electrical performance of the finished tantalum powder

[0069] As can be seen from Table 1:

[0070] The present application is suitable for manufacturing tantalum powder for high-voltage and high-reliability capacitors with higher specific capacity, and the energized block obtained under relatively high pressure conditions has high specific capacity, low residual current, and the difference between the test results in the specific capacitance test using 30% H2SO4 solution and the test results using 10% H3PO4 solution is small, and the breakdown voltage test shows high breakdown voltage.

Claims

1. A method for preparing tantalum powder by sodium reduction of potassium fluorotantalate, characterized in that: The reduction is carried out using preheated metallic sodium as a reducing agent. Preferably, the temperature of the metallic sodium exceeds 180°C, more preferably 200-350°C, even more preferably 200-260°C, and even more preferably 160-190°C and / or 210-240°C.

2. A method for preparing tantalum powder by sodium reduction of potassium fluorotantalate, comprising the following steps: (1) A diluent salt (selected from alkali metal halides), potassium fluorotantalate, and sodium metal are provided as raw materials, wherein the amount of sodium metal is in excess relative to the amount of potassium fluorotantalate, and the sodium metal is preheated to 180-350°C (preferably 200-350°C, more preferably 200-260°C, even more preferably 160-190°C and / or 210-240°C) for later use. (2) The diluted salt is placed into a reduction container, the container is evacuated, and then an inert gas such as argon is introduced. The diluted salt in the reduction container is then heated until it melts while the inert gas is kept flowing (e.g., at a flow rate of 20-100 liters / minute). (3) Add a portion of potassium fluorotantalate to the reduction container and monitor the temperature to ensure that the potassium fluorotantalate melts with the diluted salt. Then add preheated metallic sodium to reduce the portion of potassium fluorotantalate. Repeat this process several times until all the potassium fluorotantalate and metallic sodium raw materials are used up. (4) After reduction, tantalum powder aging is performed, and (5) Then the tantalum powder is separated.

3. The method according to claim 2, wherein in step (2), the evacuation and argon gas are repeated multiple times, for example 2-3 times, and / or, in step (2), the diluted salt is heated to a temperature exceeding its melting point of 80°C, preferably exceeding 150°C, more preferably exceeding 200°C, and preferably held at that temperature, for example for 30 minutes, and also preferably stirred after melting.

4. The method according to claim 2 or 3, wherein in step (3), the temperature of potassium fluorotantalate and potassium fluorotantalate is ensured to exceed the apparent melting point by controlling the furnace temperature, for example, exceeding the melting point by 80°C-500°C, preferably exceeding by 150°C-450°C, and preferably, the temperature is raised after each addition of potassium fluorotantalate.

5. The method according to claim 2, 3, or 4, wherein, In steps (3) and / or (4), an inert gas, such as argon, is continuously circulated within the reduction container.

6. The method according to claim 2, 3, or 4, wherein, The step following step (5) is as follows: (6) Tantalum powder is subjected to salt bath heat treatment and / or agglomeration heat treatment, magnesium metal chips are subjected to deoxygenation treatment, and further acid washing, purification and drying are performed to obtain tantalum powder product.

7. The method according to any one of claims 2-6, further comprising doping the tantalum powder with N, P and / or B elements after step (5) and / or (6).

8. The method according to any one of claims 2-7, wherein, In step (5), the reduction container is kept under positive pressure.

9. Tantalum powder manufactured by the manufacturing method according to any one of claims 2-8.

10. Use of the tantalum powder according to claim 1 or the tantalum powder according to claim 9 in a capacitor.