Method for producing tantalum powder by reducing potassium heptafluorotantalate with sodium and tantalum powder obtained thereby

Abstract

The present invention relates to a method for preparing tantalum powder by reducing potassium heptafluorotantalate with sodium, which is characterized in that pre-heated metallic sodium is used as a reducing agent for reduction. Preferably, the temperature of the metallic sodium exceeds 180 °C, more preferably 200 - 350 °C, more preferably 200 - 260 °C, more preferably 160 - 190 °C and / or 210 - 240 °C. The present invention also relates to the tantalum powder thus produced and its use in capacitors.

Description

Technical Field

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

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

[0003] At present, the main methods for industrial preparation of capacitor-grade tantalum powder are the sodium reduction of potassium hexafluorotantalate method, the magnesium reduction of tantalum pentoxide method, etc. The magnesium reduction of tantalum pentoxide method is expected to produce tantalum powder for capacitors with improved specific capacitance and withstand voltage at the same time due to the change of the state of the reactants. However, due to the immature process, magnesium-reduced tantalum powder has the problems of low production efficiency and high cost, which limits its popularization and application. Although the sodium reduction of potassium hexafluorotantalate method for preparing tantalum powder has problems such as low specific capacitance, large leakage current, and low breakdown voltage under relatively high-voltage energization conditions, the sodium reduction of potassium hexafluorotantalate method has been industrialized due to its mature process, relatively low production cost, and is easy to prepare high-specific-capacitance tantalum powder. Therefore, at present, sodium-reduced tantalum powder accounts for more than 80% of the tantalum powder market for capacitors. Scientifically improving the problems of low specific capacitance, large leakage current, and low breakdown voltage of sodium-reduced tantalum powder under high-voltage energization conditions is of great significance.

[0004] In order to improve the quality of sodium-reduced tantalum powder, many studies have been carried out in the industry.

[0005] US4684399A discloses a method for producing tantalum powder by sodium reduction of potassium hexafluorotantalate. Potassium hexafluorotantalate and metallic sodium are continuously or semi-continuously added in multiple times to a molten diluent for stirring reduction to obtain tantalum powder. US4149876A proposes a method for producing tantalum powder by adding liquid sodium to a molten salt bath of potassium hexafluorotantalate and diluent. This method is to quickly inject sodium at a lower sodium injection temperature to increase the material temperature, use a large proportion of diluent, and perform forced cooling. The reduction reaction is carried out at a lower temperature, and a constant temperature is maintained during the grain growth period, thereby producing tantalum powder with fine and uniform particle size. This patent also focuses on reduction temperature, heating rate, and forced cooling, etc.

[0006] CN1069564C discloses a reduction process in which phosphorus, boron, nitrogen, oxygen, and silicon are added as additives for refining tantalum powder during the reduction process. The use of the refiner realizes a substantial increase in the specific volume of sodium-reduced tantalum powder. There are also patents proposing to use iodides or sulfates during the reduction process to improve the properties of tantalum powder.

[0007] JP4828016B2 discloses a method for manufacturing tantalum powder by reducing potassium heptafluorotantalate with metallic sodium. In this method, a small amount of potassium heptafluorotantalate is added to a molten diluent, then metallic sodium is added for reduction, and then a small amount of potassium heptafluorotantalate is added again for sodium reduction. This process is repeated to enable the reaction of potassium heptafluorotantalate at a low concentration. The amount of the dilution salt is 40 - 1000 times that of potassium heptafluorotantalate, achieving the purpose of increasing the specific volume of tantalum powder. The specific capacitance of the tantalum powder manufactured by this method is 80000 - 250000 μFV / g.

[0008] CN201693181U discloses a method for enabling the reaction of dispersed metallic sodium with molten potassium heptafluorotantalate through a sodium distributor provided at the end of a sodium injection tube; CN116100040A discloses a method for reducing potassium heptafluorotantalate after dispersing metallic sodium by jetting air onto the metallic sodium. The tantalum powder product obtained by this method has a uniform particle size distribution and a uniform particle shape distribution.

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

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

[0011] An object of the present invention is to provide a method for preparing tantalum powder by reducing potassium heptafluorotantalate with high-temperature metallic sodium. This method involves reducing potassium heptafluorotantalate, where metallic sodium preheated to above 180°C, more preferably 200 - 350°C, more preferably 200 - 260°C, more preferably 190°C - 240°C, such as 210°C, is used. The tantalum powder prepared by this method, combined with existing tantalum powder refinement techniques, can produce tantalum powder with improved morphology (for example, large sintering diameter, controllable specific surface area, and porous structure). After subsequent treatments such as existing water pickling purification, sintering, and oxygen reduction of the tantalum powder prepared by this process, it is more suitable for manufacturing tantalum capacitors with higher reliability requirements. Compared with tantalum powder of the same grade produced by other methods, this tantalum powder has a higher specific capacitance and a higher breakdown voltage under high-voltage energization conditions, significantly improving the withstand voltage performance of tantalum powder for capacitors. In other words, tantalum powder for capacitors with different specific capacitances produced by the method of the present invention can withstand relatively higher voltages, and the tantalum capacitors made from it have higher reliability.

[0012] Another object of the present invention is to provide a method for preparing tantalum powder by a sodium reduction potassium heptafluorotantalate process, comprising the following steps:

[0013] (1) Provide a diluent salt (preferably selected from alkali metal halides), potassium heptafluorotantalate, and metallic sodium as raw materials, where the amount of metallic sodium is in excess relative to the amount of potassium heptafluorotantalate, and preheat the metallic sodium to 180 - 350°C (preferably 200 - 350°C, more preferably 200 - 260°C, more preferably 160 - 190°C and / or 210 - 240°C) for standby,

[0014] (2) Load the diluent salt into a reduction container, evacuate the container, then introduce an inert gas such as argon, and then heat the diluent salt in the reduction container to melting while the inert gas keeps flowing (for example, flowing at a rate of 20 - 100 liters per minute),

[0015] (3) Add a part of potassium heptafluorotantalate into the reduction container, monitor the temperature to ensure that the potassium heptafluorotantalate and the diluent salt melt, and then add the preheated metallic sodium to reduce the part of potassium heptafluorotantalate. Repeat this process multiple times until all the raw materials of potassium heptafluorotantalate and metallic sodium are used up,

[0016] (4) After the reduction is completed, age the tantalum powder, and

[0017] (5) Then, separate the tantalum powder.

[0018] Optionally, after step (5), the method further includes the steps of:

[0019] (6) Perform salt bath heat treatment and / or agglomeration heat treatment on the tantalum powder, perform oxygen reduction treatment with metallic magnesium chips, and further pickle, purify, and dry it to obtain the product tantalum powder.

[0020] In step (1), the dilution salt is selected from alkali metal halides (also known as alkali metal halogen salts, and "halogen salt" and "halide" can be used interchangeably in this article) commonly mentioned in the prior art, such as one or more of NaCl, KCl, KF, and KI. There is no limitation on the ratio of the dilution salt to potassium heptafluorotantalate, and the ratios commonly used in the prior art can be adopted. Preferably, the dilution salt can also be mixed with a tantalum powder refiner. The amount of metallic sodium is in excess of the theoretical amount required for completely reducing potassium heptafluorotantalate, for example, in excess by 1-3%, preferably in excess by 1.5-2.5%. The metallic sodium is preheated to a temperature exceeding 180°C - 500°C, more preferably 200 - 350°C, more preferably 200 - 260°C, more preferably 190°C - 240°C, such as 210°C. Preferably, both the dilution salt and potassium heptafluorotantalate are in the form of powders.

[0021] Preferably, in step (2), evacuating and introducing an inert gas such as argon are repeated multiple times, for example, 2 - 3 times, to expel the air in the reduction container as much as possible, reduce the corrosion of the air on the metal reduction container, and reduce the adverse effects of the air on the tantalum powder. To enable the water vapor and acidic gases released during the heating and melting process to be carried by argon and discharged from the reduction container in a timely manner, reducing the adverse effects on the reduction, preferably, the flow rate of the inert gas is maintained at 20 - 100 liters per minute, which can better discharge water vapor and acidic gases, etc. To ensure its complete melting and improve the viscosity of the dilution salt, making the stirring smoother, preferably, the dilution salt is heated to a temperature exceeding its melting point by 80°C, preferably exceeding 150°C, more preferably exceeding 200°C. Preferably, after sufficient melting, heat preservation is also carried out, for example, for 30 minutes. Preferably, the dilution salt is stirred after being heated to the target temperature to ensure thorough mixing and maintain a uniform temperature. There are no special requirements for the stirring conditions. Preferably, the dilution salt is continuously stirred after melting, and preferably, it is continuously stirred until the aging ends.

[0022] In step (3), adding potassium heptafluorotantalate in several portions and completing the reduction is to reduce the concentration of potassium heptafluorotantalate in the dilution salt. There is no limitation on the amount of potassium heptafluorotantalate added each time and the number of additions. However, through a large amount of research, the inventor found that the specific amount of potassium heptafluorotantalate added 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 tantalum powder with a larger specific surface area is to be prepared, the amount of potassium heptafluorotantalate added each time can be reduced so that potassium heptafluorotantalate is reduced at a lower concentration. If tantalum powder with a smaller specific surface area is to be prepared, the amount of potassium heptafluorotantalate added each time can be appropriately increased. That is to say, the present invention realizes good control of the specific surface area of tantalum powder. Of course, regardless of the number of times potassium heptafluorotantalate is added, when adding metallic sodium for the last time, all the remaining raw sodium is added to ensure complete reduction of potassium heptafluorotantalate. Preferably, in this step, by controlling the temperature in the reduction container to exceed the melting point of the mixture of the dilution salt and potassium heptafluorotantalate to ensure its melting, for example, exceeding its melting point by 80°C - 400°C, preferably exceeding 250°C - 350°C. It is easy for those skilled in the art to understand that the temperature at which the mixture of the dilution salt and potassium heptafluorotantalate melts may be different from the melting point of the dilution salt and also different from the melting point of potassium heptafluorotantalate. When the ratio of the two is different, the "melting point" (also known as the apparent melting point) when the mixture completely melts is also different, but its apparent melting point can be found based on the phase diagram data. Preferably, the temperature is increased after each addition of potassium heptafluorotantalate. Preferably, in order to make the obtained tantalum powder more uniform, before adding metallic sodium for the last time, the amount of high-temperature metallic sodium added each time is such that 70 - 95%, more preferably 70 - 85% of the just-added potassium heptafluorotantalate is reduced. Adopting such an addition method can avoid premature reaction (i.e., when not melted) between excessive metallic sodium in the reduction container and the potassium heptafluorotantalate added in the subsequent addition.

[0023] In step (4), preferably, after the reduction is completed, the tantalum powder is aged by continuing to heat and keep it warm. Preferably, the heating is continued for 0.5 - 5 hours, preferably 2 - 3 hours. Preferably, the temperature in the reaction container is controlled at the temperature before adding metallic sodium in step (3). In this step, the excessive metallic sodium is carried away from the reduction container by argon and separated from the tantalum powder.

[0024] Preferably, in step (3) and / or (4), the flow of an inert gas such as argon is continuously maintained in the reduction container. Preferably, in step (5), the reduction container is kept under positive pressure until the mixed material starts to be taken out from the reduction container.

[0025] Preferably, the separation of tantalum powder in step (5) includes: stopping stirring, cooling to room temperature while introducing argon to maintain a positive pressure in the reduction reaction vessel, taking out the mixture containing halide and tantalum powder from the reduction vessel, separating and removing some by-products that do not wrap the tantalum powder, and then further separating the by-products by hydrofluoric acid washing, washing, purifying and drying to obtain the final tantalum powder.

[0026] Preferably, the method of the present invention further includes step (6) after step (5): water washing and / or acid washing, heat treatment such as high-temperature and high-vacuum heat treatment (or high-temperature and high-vacuum heat treatment after molten salt-assisted sintering according to the invention of patent CN114210973B), oxygen reduction, acid washing, and then separating the tantalum powder by filtration, drying, etc., and suitable tantalum powder for making high-reliability tantalum capacitors can be obtained. These treatments are all processes known in the prior art. In other words, these treatments can adopt any processes known in the prior art. For example, the high-temperature and high-vacuum heat treatment and passivation here can adopt the methods provided by patents CN201110039272.9, CN201120077798.1, CN201120077680.9, CN201120077305.4, etc., oxygen reduction can adopt the methods provided by patents CN201420777210.7, CN201420777210.7, and acid washing can adopt the methods provided by patents CN201210548101.3, CN201280077499.5, CN201210548008.2, etc.

[0027] In the present invention, it may also include doping the tantalum powder with elements N, P, and / or B after step (5) and / or (6). Of course, raw materials containing these elements can also be directly used. These elements can also be added in the aforementioned high-temperature and high-vacuum heat treatment step. Particularly preferably, element P is added. Adding element P can increase the specific capacitance. As long as the total amount of P doping is well controlled, the effect of increasing the specific capacitance is the same regardless of when it is added. This can be carried out in a conventional manner in the prior art and will not be elaborated.

[0028] The obtained product tantalum powder is compacted and sintered, and energized under high-pressure conditions. The electrical properties of the energized block are tested, and it is found that the energized block has a higher specific capacitance and shows a higher breakdown voltage in the breakdown voltage test.

[0029] After energization under the same high-pressure conditions, the tantalum powder manufactured by the present invention has a higher specific capacitance in the energized block and shows a higher breakdown voltage in the breakdown voltage test compared with the tantalum powder for capacitors of the same grade produced by other methods. Therefore, the tantalum powder manufactured by the present invention is more suitable for making high-voltage and high-reliability tantalum capacitors.

[0030] Not bound by general theories, the inventors believe that the reasons for the excellent effects of the present invention are as follows. The process of reducing potassium heptafluorotantalate with sodium is a highly exothermic process, which releases a large amount of heat locally. Generally, heat runaway is avoided by adding diluting salts. In step (2) of the present invention, when metallic sodium contacts and reacts with potassium heptafluorotantalate, due to the use of pre-heated metallic sodium, the instantaneous temperature at the reaction point increases. The growth of tantalum powder during the reduction instant is affected by the temperature at the reaction point, promoting the sintering between particles, increasing the sintering diameter inside the tantalum powder. However, due to the control of other process conditions (for example, the reaction of potassium heptafluorotantalate at a low concentration), the specific surface area of the tantalum powder is still well controlled, and it is easier to construct a spatial structure suitable for capacitor production between the tantalum powder particles.

[0031] 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 rarely pays attention to the temperature of metallic sodium itself, but only focuses on the sodium injection temperature (that is, the temperature of the reduction container or furnace when sodium is added). Although someone may have studied the influence of increasing the sodium injection temperature, this means that the temperature inside the furnace needs to be increased as a whole, bringing a greater thermal load to the materials used to make the reduction container and the furnace, which is not conducive to their service life. Moreover, increasing the temperature inside the furnace also means greater energy consumption. The prior art may also have improved the fluidity of liquid metallic sodium by increasing its temperature. However, since the fluidity of liquid sodium almost stabilizes when the temperature is increased above 120 °C, currently, metallic sodium with a temperature of about 120 °C or below is generally added. The inventors of the present invention unexpectedly found through a large amount of research that by further increasing the temperature of liquid metallic sodium, not only the good fluidity of liquid sodium is maintained, but also the temperature of the reduction reaction point is accurately increased without increasing the power of the heating furnace, improving the morphology of the tantalum powder, and ultimately increasing the specific volume and breakdown voltage of the tantalum powder.

[0032] After subjecting the tantalum powder obtained according to the present invention to high-temperature and high-vacuum heat treatment according to the prior art (or first subjecting it to molten salt-assisted sintering according to the invention of Patent CN114210973B and then performing high-temperature and high-vacuum heat treatment), oxygen reduction, and pickling treatment, the tantalum powder still has a high specific volume at a high energizing voltage, and its comprehensive electrical properties are improved, making it suitable for preparing tantalum powder for high-voltage and high-reliability capacitors. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The following drawings are provided for a better understanding of the present invention. These drawings are exemplary and are not intended to limit the scope of the present invention.

[0034] Figure 1 A scanning electron microscope photograph of the tantalum powder obtained according to the present invention is given.

[0035] This drawing shows that the obtained tantalum powder particles are more uniform in size, the particles are smooth, and the sintering necks are thicker. DETAILED DESCRIPTION OF THE INVENTION

[0036] To further illustrate the present invention, the preferred embodiments of the present invention will be described below in conjunction with examples, and it can be clearly seen the objectives, features and advantages of the present invention. However, these descriptions are only for further illustrating the features and advantages of the present invention, rather than limiting the present invention. For those not specified in the examples, the conventional conditions are followed. For reagents or instruments without indicating the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0037] For the purposes of this specification, all numbers representing amounts of ingredients, reaction conditions, etc. in the specification and claims should be understood to be modified by the term "about" in all cases, unless otherwise specified. Accordingly, the numerical parameters given in the following specification and appended claims are approximate values, which may vary depending on the desired properties sought to be obtained by the present invention, unless there is a contrary indication. At the very least, and not intending to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should be construed in accordance with at least the number of significant digits reported and in accordance with ordinary rounding techniques.

[0038] The analysis of the impurity content in tantalum powder is carried out according to Chinese standards GB / T15076.1~15076.15, and the physical properties are carried out according to the regulations in industry standard YS / T573-2015. The test of the electrical properties in tantalum powder is carried out according to the regulations of Chinese standard GB / T3137.

[0039] Examples

[0040] To further illustrate the present invention, the preferred embodiments of the present invention will be described below in conjunction with examples, and it can be clearly seen the objectives, features and advantages of the present invention. However, these descriptions are only for further illustrating the features and advantages of the present invention, rather than limiting the present invention. For those not specified in the examples, the conventional conditions or the conditions recommended by the manufacturer are followed. For reagents or instruments without indicating the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0041] For the purposes of this specification, all numbers representing amounts of ingredients, reaction conditions, etc. in the specification and claims should be understood to be modified by the term "about" in all cases, unless otherwise specified. Accordingly, the numerical parameters given in the following specification and appended claims are approximate values, which may vary depending on the desired properties sought to be obtained by the present invention, unless there is a contrary indication. At the very least, and not intending to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should be construed in accordance with at least the number of significant digits reported and in accordance with ordinary rounding techniques.

[0042] The analysis of the impurity content in tantalum powder is carried out according to Chinese standard GB / T15076.1~15076.15, and the physical properties are carried out according to the provisions in industry standard YS / T573-2007. The tests of leakage current and capacitance in tantalum powder are carried out according to the provisions of Chinese standard GB / T3137.

[0043] Example 1

[0044] Potassium heptafluorotantalate, NaCl as a diluent, and metallic sodium are provided as raw materials. The metallic sodium is preheated to a high temperature of 180 °C for standby.

[0045] Take 100 kg of sodium chloride (NaCl) and load it into a reduction container. After evacuating the reduction container, argon is filled to 0.10 MPa, and then the evacuation and argon filling to 0.10 MPa are repeated twice. The reduction container is placed in a heating furnace, heated, argon is introduced, and it flows at a flow rate of 40 liters per minute. The temperature is raised to 920 °C to start stirring, and it is kept warm for 30 minutes. Then 15 kg of potassium heptafluorotantalate is added. After the temperature rises to 920 °C, 3.95 kg of metallic sodium at 180 °C is added for reduction; this process of adding potassium heptafluorotantalate and raising the temperature for reduction is repeated 7 times. After adding potassium heptafluorotantalate for the 8th time, 8.20 kg of metallic sodium is added for reduction. After the reduction is completed, under the condition of argon flow, it is kept warm at 920 °C for 180 minutes for tantalum powder aging. Then the stirring is stopped, the pressure of the reaction container is maintained at 0.10 MPa, and it is cooled to room temperature. The mixture is taken out from the reduction container, and part of the by-products that do not wrap the tantalum powder are separated and removed. Then, it is further separated from the by-products by hydrofluoric acid pickling, washed, purified, and dried to obtain high-purity tantalum powder.

[0046] Then, 50 ppm of P is incorporated into the tantalum powder, and it is subjected to high-temperature and high-vacuum heat treatment at 1450 °C and a pressure lower than 5.0×10 -3 Pa for 1.0 hour. Then, oxygen reduction and pickling are carried out to obtain the final tantalum powder. According to the anode block quality, pressing density, anode block sintering temperature, and sintering time specified in Table 1, and other conditions according to the requirements of the aforementioned GB / T3137, the obtained final tantalum powder is made into an anode block, and it is energized under the condition of 150 V. Then, the electrical properties are tested according to the requirements of the aforementioned GB / T3137. In the specific capacitance test, after testing with 30% H 2 SO 4 solution, it is then tested with 10% H 3 PO 4 solution, and the measured results are listed in Table 1.

[0047] Comparative Example 1

[0048] Potassium heptafluorotantalate, NaCl as a diluent, and metallic sodium are provided as raw materials. The metallic sodium is preheated to 130 °C for standby.

[0049] Take 100 kg of sodium chloride (NaCl) and load it into a reduction container. After evacuating the reduction container, fill it with argon to 0.10 MPa, and then repeat the evacuation and filling with argon to 0.10 MPa twice. Place the reduction container in a heating furnace, heat it, introduce argon, let it flow at a rate of 40 liters per minute, raise the temperature to 920 °C, start stirring, and keep it warm for 30 minutes. Then add 15 kg of potassium heptafluorotantalate. After the temperature rises to 920 °C, add 3.95 kg of metallic sodium at 130 °C for reduction; repeat the addition of potassium heptafluorotantalate and temperature rise for reduction 7 times. After the 8th addition of potassium heptafluorotantalate, add 8.20 kg of metallic sodium at 130 °C for reduction. After the reduction is completed, under the condition of argon flow, keep it warm at 920 °C for 180 minutes for tantalum powder aging, then stop stirring, maintain the pressure of the reaction container at 0.10 MPa, and cool it to room temperature. Take out the mixture from the reduction container, separate and remove some by-products that do not wrap the tantalum powder, and then further separate the by-products, wash, purify and dry through hydrofluoric acid pickling to obtain high-purity tantalum powder.

[0050] Then, incorporate 50 ppm of P into the tantalum powder, and perform high-temperature and high-vacuum heat treatment at 1450 °C and a pressure lower than 5.0×10 -3 Pa for 1.0 hour, and then perform oxygen reduction and pickling to obtain the final tantalum powder. According to the anode block quality, pressing density, anode block sintering temperature, and sintering time specified in Table 1, and other conditions according to the requirements of the aforementioned GB / T 3137, make the obtained final tantalum powder into anode blocks, energize them under the condition of 150 V, and then test the electrical properties according to the requirements of the aforementioned GB / T 3137. In the specific capacitance test, after testing with 30% H 2 SO 4 solution, then test with 10% H 3 PO 4 solution, and list the measured results in Table 1.

[0051] Example 2

[0052] Provide potassium heptafluorotantalate, KCl and KF as diluents, and metallic sodium as raw materials. Preheat the metallic sodium to a high temperature of 220 °C for standby.

[0053] Take 50 kg of potassium chloride (KCl) and 50 kg of potassium fluoride (KF) and load them into a reduction container. After evacuating the reduction container, fill it with argon to 0.10 MPa, and then repeat the evacuation and filling with argon to 0.10 MPa twice. Place the reduction container in a heating furnace, heat it, introduce argon, let it flow at a rate of 60 liters per minute, raise the temperature to 900 °C, start stirring, and keep it warm for 30 minutes. Then add 15 kg of potassium heptafluorotantalate. When the temperature rises to 900 °C, add 4.0 kg of metallic sodium at 220 °C for reduction; repeat the addition of potassium heptafluorotantalate and temperature increase for reduction 9 times. After the 10th addition of potassium heptafluorotantalate, add 8.9 kg of metallic sodium at 220 °C for reduction. After the reduction is completed, under the condition of argon flow, keep it warm at 900 °C for 120 minutes for tantalum powder aging, then stop stirring, maintain the pressure of the reaction container at 0.10 MPa, and cool it to room temperature. Take out the mixture from the reduction container, separate and remove some by-products that do not wrap the tantalum powder, and then further separate the by-products, wash, purify and dry through hydrofluoric acid pickling to obtain high-purity tantalum powder.

[0054] Then, incorporate 60 ppm of P into the tantalum powder and conduct high-temperature and high-vacuum heat treatment at 1400 °C and a pressure lower than 5.0×10 -3 Pa for 1.0 hour, and then conduct oxygen reduction and pickling to obtain the final tantalum powder. According to the anode block quality, pressing density, anode block sintering temperature, and sintering time specified in Table 1, and other conditions in accordance with the requirements of the aforementioned GB / T 3137, make the obtained final tantalum powder into anode blocks, energize them under the condition of 100 V, and then test the electrical properties according to the requirements of the aforementioned GB / T 3137. In the specific capacitance test, after testing with 30% H 2 SO 4 solution, then test with 10% H 3 PO 4 solution, and list the measured results in Table 1.

[0055] Comparative Example 2

[0056] Provide potassium heptafluorotantalate, KCl and KF as diluents, and metallic sodium as raw materials. Preheat the metallic sodium to 120 °C for standby.

[0057] Take 50 kg of potassium chloride (KCl) and 50 kg of potassium fluoride (KF) and load them into a reduction container. After evacuating the reduction container, fill it with argon to 0.10 MPa, and then repeat the evacuation and filling with argon to 0.10 MPa twice. Place the reduction container in a heating furnace, heat it, introduce argon, let it flow at a rate of 60 liters per minute, raise the temperature to 900 °C, start stirring, and keep it warm for 30 minutes. Then add 15 kg of potassium heptafluorotantalate. When the temperature rises to 900 °C, add 4.0 kg of metallic sodium at 120 °C for reduction; repeat the addition of potassium heptafluorotantalate and temperature increase for reduction 9 times. After the 10th addition of potassium heptafluorotantalate, add 8.90 kg of metallic sodium at 120 °C for reduction. After the reduction is completed, under the condition of argon flow, keep it warm at 900 °C for 120 minutes for tantalum powder aging, then stop stirring, maintain the pressure of the reaction container at 0.10 MPa, and cool it to room temperature. Take out the mixture from the reduction container, separate and remove some by-products that do not wrap the tantalum powder, and then further separate the by-products, wash, purify, and dry through hydrofluoric acid pickling to obtain high-purity tantalum powder.

[0058] Then, incorporate 60 ppm of P into the tantalum powder and conduct high-temperature and high-vacuum heat treatment at 1400 °C and a pressure lower than 5.0×10 -3 Pa for 1.0 hour, and then conduct oxygen reduction and pickling to obtain the final tantalum powder. According to the anode block quality, pressing density, anode block sintering temperature, and sintering time specified in Table 1, and other conditions in accordance with the requirements of the aforementioned GB / T 3137, make the obtained final tantalum powder into anode blocks, energize them under the condition of 100 V, and then test the electrical properties according to the requirements of the aforementioned GB / T 3137. In the specific capacitance test, after testing with 30% H 2 SO 4 solution, then test with 10% H 3 PO 4 solution, and list the measured results in Table 1.

[0059] Example 3

[0060] Provide potassium heptafluorotantalate, KCl and KF as diluents, and metallic sodium as raw materials. Preheat metallic sodium to a high temperature of 180 °C for standby.

[0061] Take 100 kg of potassium chloride (KCl) and 100 kg of potassium fluoride (KF) and load them into a reduction container. After evacuating the reduction container, fill it with argon to 0.10 MPa, and then repeat the evacuation and filling with argon to 0.10 MPa twice. Place the reduction container in a heating furnace, heat it, introduce argon, let it flow at a rate of 70 liters per minute, raise the temperature to 900 °C, start stirring, and keep it warm for 30 minutes. Then add 10 kg of potassium heptafluorotantalate. When the temperature rises to 920 °C, add 2.50 kg of metallic sodium at 180 °C for reduction; repeat the addition of potassium heptafluorotantalate and temperature increase for reduction 5 times. After the 6th addition of potassium heptafluorotantalate, add 6.0 kg of metallic sodium at 180 °C for reduction. After the reduction is completed, under the condition of argon flow, keep it warm at 900 °C for 120 minutes for tantalum powder aging, then stop stirring, keep the pressure of the reaction container at 0.10 MPa, and cool it to room temperature. Take out the mixture from the reduction container, separate and remove some by-products that do not wrap the tantalum powder, and then further separate the by-products, wash, purify and dry through hydrofluoric acid pickling to obtain high-purity tantalum powder.

[0062] Then, incorporate 100 ppm of P into the tantalum powder and conduct high-temperature and high-vacuum heat treatment at 1230 °C and a pressure below 5.0×10 -3 Pa for 1.0 hour, and then conduct deoxidation and pickling to obtain the final tantalum powder. According to the anode block quality, pressing density, anode block sintering temperature, and sintering time specified in Table 1, and other conditions according to the requirements of the aforementioned GB / T 3137, make the obtained final tantalum powder into anode blocks, energize them under the condition of 60 V, and then test the electrical properties according to the requirements of the aforementioned GB / T 3137. In the specific capacitance test, after testing with a 30% H 2 SO 4 solution, then test with a 10% H 3 PO 4 solution, and list the measured results in Table 1.

[0063] Comparative Example 3

[0064] Provide potassium heptafluorotantalate, KCl and KF as diluents, and metallic sodium as raw materials. Preheat the metallic sodium to a high temperature of 120 °C for standby.

[0065] Take 100 kg of potassium chloride (KCl) and 100 kg of potassium fluoride (KF) and load them into a reduction container. After evacuating the reduction container, fill it with argon to 0.10 MPa, and then repeat the evacuation and filling with argon to 0.10 MPa twice. Place the reduction container in a heating furnace, heat it, introduce argon, let it flow at a rate of 70 liters per minute, raise the temperature to 900 °C, start stirring, and keep it warm for 30 minutes. Then add 10 kg of potassium heptafluorotantalate. When the temperature rises to 900 °C, add 2.5 kg of metallic sodium preheated to 120 °C for reduction; repeat the addition of potassium heptafluorotantalate and temperature rise for reduction 5 times. After the 6th addition of potassium heptafluorotantalate, add 6.0 kg of metallic sodium at 120 °C for reduction. After the reduction is completed, under the condition of argon flow, keep it warm at 900 °C for 120 minutes for tantalum powder aging, then stop stirring, maintain the pressure of the reaction container at 0.10 MPa, and cool it to room temperature. Take out the mixture from the reduction container, separate and remove some by-products that do not wrap the tantalum powder, and then further separate the by-products, wash, purify and dry through hydrofluoric acid pickling to obtain high-purity tantalum powder.

[0066] Then, incorporate 100 ppm of P into the tantalum powder and conduct high-temperature and high-vacuum heat treatment at 1230 °C and a pressure below 5.0×10 -3 Pa for 1.0 hour, and then carry out oxygen reduction and pickling to obtain the final tantalum powder. According to the anode block quality, pressing density, anode block sintering temperature, and sintering time specified in Table 1, and other conditions in accordance with the requirements of the aforementioned GB / T 3137, make the obtained final tantalum powder into anode blocks, energize them under the condition of 60 V, and then test the electrical properties according to the requirements of the aforementioned GB / T 3137. In the specific capacitance test, after testing with 30% H 2 SO 4 solution, then test with 10% H 3 PO 4 solution, and list the measured results in Table 1.

[0067] Table 1 Analysis Results of Electrical Properties of Finished Tantalum Powder

[0068]

[0069]

[0070] As can be seen from Table 1:

[0071] The present invention is suitable for manufacturing tantalum powder for high-voltage and high-reliability capacitors with higher specific capacitance. When energized under relatively high-voltage conditions, the obtained energized blocks have high specific capacitance and low residual current. And in the specific capacitance test, when testing with 30% H 2 SO 4 solution and 10% H 3 PO 4The difference in the solution test results is relatively small, and a high breakdown voltage is shown in the breakdown voltage test.

Claims

1. A method for improving the morphology of tantalum powder, which is accomplished by reducing potassium fluorotantalate with sodium, comprising the following steps: (1) providing diluted salt, potassium tantalate fluoroate and metallic sodium as raw materials, wherein the amount of metallic sodium is 1-3% in excess of the amount of potassium tantalate fluoroate, and the metallic sodium is preheated to 200-350° C. for standby use; (2) placing the diluted salt into a reduction container, evacuating the container, and then introducing an inert gas, and then heating the diluted salt in the reduction container until it melts while the inert gas is kept flowing at a flow rate of 20-100 liters / minute, (3) adding a portion of potassium fluorotantalate to a reduction vessel, monitoring the temperature to ensure that the potassium fluorotantalate and the dilute salt are melted, and then adding preheated metallic sodium to reduce the portion of the potassium fluorotantalate, repeating the process multiple times until all the potassium fluorotantalate and metallic sodium raw materials are used up. (4) After the reduction is completed, the tantalum powder is aged by continuing to heat and keep the tantalum powder warm, and (5) Then separate the tantalum powder, wherein in step (2), after the diluted salt is melted, it is continuously stirred, In step (3), before the last addition of metallic sodium, the amount of high-temperature metallic sodium added each time is such that 70-95% of the potassium fluorotantalate just added is reduced.

2. The method according to claim 1, wherein the diluting salt in step (1) is selected from alkali metal halides.

3. The method according to claim 1 or 2, wherein in step (1) the metallic sodium is preheated to 200-260°C.

4. The method according to claim 1 or 2, wherein in step (1) the metallic sodium is preheated to 210-240°C.

5. The method according to claim 1 or 2, wherein the inert gas in step (2) is argon, and in this step, evacuation and argon gas flow are repeated multiple times.

6. The method according to claim 5, wherein evacuating and passing argon gas are repeated 2-3 times.

7. The method according to claim 1 or 2, wherein in step (2) the diluted salt is heated to a temperature exceeding its melting point by 80°C.

8. The method according to claim 1 or 2, wherein in step (2) the diluted salt is heated to a temperature exceeding its melting point by 150°C.

9. The process according to claim 1 or 2, wherein in step (2) the diluted salt is heated to a temperature exceeding its melting point by more than 200°C.

10. The method according to claim 1 or 2, wherein step (2) further comprises heat preservation after melting.

11. The method according to claim 10, wherein the incubation is carried out for 30 minutes.

12. The method according to claim 1 or 2, wherein the incubation in step (4) lasts for 0.5-5 hours.

13. The method according to claim 1 or 2, wherein in step (3), the temperature of the diluent salt and potassium fluorotantalate is ensured to exceed the apparent melting point by controlling the furnace temperature.

14. The method according to claim 1 or 2, wherein in step (3), the temperature of the diluent salt and potassium fluorotantalate is ensured to exceed the apparent melting point by controlling the furnace temperature to 80°C to 500°C.

15. The method according to claim 1 or 2, wherein in step (3), the temperature of the diluent salt and potassium fluorotantalate is controlled to ensure that the temperature exceeds the apparent melting point by 150°C to 450°C.

16. The method according to claim 1 or 2, wherein in step (3), the temperature is increased after each addition of potassium fluorotantalate.

17. The method according to claim 1 or 2, wherein: In steps (3) and / or (4), the inert gas is always circulated in the reduction container.

18. The method according to claim 17, wherein the inert gas is argon.

19. The method according to claim 1 or 2, wherein: After step (5), the method further includes the following steps: (6) The tantalum powder is subjected to salt bath heat treatment and / or agglomeration heat treatment, the metal magnesium chips are subjected to oxygen reduction treatment, and further pickling, purification and drying are performed to obtain a tantalum powder product.

20. The method according to claim 1 or 2, further comprising doping the tantalum powder with N, P and / or B elements after step (5).

21. The method according to claim 19, further comprising doping the tantalum powder with N, P and / or B elements after step (6).

22. The process according to claim 1 or 2, wherein the amount of metallic sodium is in excess of 1.5-2.5% relative to the amount of potassium fluorotantalate.

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