A method for producing tantalum powder by reducing potassium fluoranthalate with sodium, and tantalum powder obtained by the method.

Abstract

The present invention relates to a method for producing tantalum powder by reducing potassium fluorantharate with sodium, characterized in that preheated metallic sodium is used as the reducing agent for the reduction, and the temperature of the metallic sodium is preferably above 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 further relates to the tantalum powder obtained by the method and the use of tantalum powder 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 manufacturing high-voltage and high-reliability capacitors and a manufacturing method therefor.

Background Art

[0002] Tantalum electrolytic capacitors (hereinafter referred to as tantalum capacitors) have advantages such as large capacitance, small volume, strong self-recovery ability, and high reliability, and are widely applied in advanced technology fields such as communication, computers, automotive electronics, medical devices, radar, aerospace, and automatic control devices. Tantalum powder is the main material for manufacturing tantalum capacitors, and only by using tantalum powder for capacitors with a larger specific capacitance and higher breakdown voltage can tantalum capacitors with a smaller volume and higher reliability be manufactured. Therefore, only by continuously developing tantalum powder for capacitors with a larger specific capacitance and higher breakdown voltage can the requirements of electronic devices and electronic circuits for the miniaturization and high-reliability development of tantalum capacitors be continuously met by the manufactured tantalum capacitors.

[0003] Currently, the main industrial methods for preparing capacitor-grade tantalum powder include the sodium reduction method of potassium fluorantharate and the magnesium reduction method of tantalum oxide. While the magnesium reduction method of tantalum oxide is expected to produce tantalum powder for capacitors with improved specific capacitance and dielectric strength due to the change in the reactant's state, the method is underdeveloped. Magnesium-reduced tantalum powder suffers from low production efficiency and high costs, limiting its widespread adoption and application. Tantalum powder prepared by the sodium reduction method of potassium fluorantharate has problems such as low specific capacitance, high leakage current, and low breakdown voltage under relatively high voltage conditions. However, the sodium reduction method of potassium fluorantharate, due to its advanced development, enables large-scale production at relatively low manufacturing costs. Furthermore, using the sodium reduction method of potassium fluorantharate allows for the easy preparation of tantalum powder with high specific capacitance. Currently, tantalum powder produced by the sodium reduction method accounts for over 80% of the market for tantalum powder for capacitors. It is extremely important to chemically improve tantalum powder produced by the sodium reduction method, which has problems such as low specific capacitance, high leakage current, and low breakdown voltage under high voltage current conditions.

[0004] Many studies have been conducted in the industry to improve the quality of tantalum powder produced by the sodium reduction method.

[0005] US4684399A discloses a method for producing tantalum powder by sodium reduction of potassium fluorantharate. Tantalum powder is obtained by continuously or semi-continuously introducing potassium fluorantharate and metallic sodium into a molten diluent for reduction while stirring. US4149876A proposes a method for producing tantalum powder by adding liquid sodium to a molten salt bath of molten potassium fluorantharate and diluent, which includes using a large proportion of diluent, rapidly injecting sodium at a lower sodium injection temperature to raise the material temperature, forcibly cooling, carrying out the reduction reaction at a lower temperature, and maintaining a constant temperature during the grain growth period to produce tantalum powder with fine and uniform particle size. This patent also focuses on reduction temperature, heating rate, forced cooling, etc.

[0006] Patent CN1069564C discloses a reduction method in which phosphorus, boron, nitrogen, oxygen, and silicon are added as additives to refine tantalum powder during reduction. The use of these refining agents significantly increases the specific capacitance of tantalum powder produced by the sodium reduction method. Other patents suggest improving the performance of tantalum powder using iodide or sulfate during reduction.

[0007] JP4828016B2 discloses a method for producing tantalum powder by reducing potassium fluorantharate with metallic sodium, comprising the steps of adding a small amount of potassium fluorantharate to a molten diluent, then adding metallic sodium for reduction, then adding a small amount of potassium fluorantharate for reduction with sodium, and repeating the steps to achieve the reaction of potassium fluorantharate at a low concentration, wherein the amount of diluent is 40 to 1000 times that of potassium fluorantharate in order to achieve the objective of improving the specific capacitance of the tantalum powder, and the specific capacitance of the tantalum powder produced by the method is 80,000 to 250,000 μFV / g.

[0008] CN201693181U discloses a method for achieving the reaction of dispersed metallic sodium with molten potassium fluorantharate using a sodium partition located at the end of a sodium injection tube; CN116100040A discloses a method for reducing potassium fluorantharate after dispersing metallic sodium by spraying gas onto it, wherein the tantalum powder product prepared by the method has a uniform particle size distribution and a uniform particle shape distribution.

[0009] To improve the dielectric strength of tantalum powder produced by the sodium reduction method of potassium fluorantharate, other methods include increasing the sintering temperature and extending the sintering time in subsequent processing; however, increasing the sintering temperature and extending the sintering time inevitably reduces the specific capacitance of the tantalum powder.

[0010] While not bound by general theory, the inventors have found, through diligent study, that current research on the sodium reduction method of potassium fluorantharate relates to the state, temperature, and concentration of potassium fluorantharate (dispersed using diluents such as potassium chloride, sodium chloride, and potassium fluoride); the use of alkali metal halides as diluents; the use of additives for refining tantalum powder during reduction, such as compounds containing phosphorus, boron, nitrogen, oxygen, silicon, iodine, sulfur, etc.; the temperature and fluidity of the injected liquid metallic sodium; stirring during reduction; and apparatus for optimizing the reduction method. However, current research on the sodium reduction method of potassium fluorantharate does not relate to the effect of the temperature of the liquid metallic sodium before injection on the particle morphology of the metallic tantalum powder in the sodium reduction method of potassium fluorantharate.

[0011] The object of the present invention is to provide a method for producing tantalum powder by reducing potassium fluorantharate with high-temperature metallic sodium. The method relates to the reduction of potassium fluorantharate with metallic sodium preheated to a temperature above 180°C, such as 210°C, more preferably 200-350°C, more preferably 200-260°C, and more preferably 190-240°C. The above method, when combined with existing tantalum powder refining techniques, can produce tantalum powder having improved morphology (such as a thick sintered neck, controllable specific surface area, and porous structure). The tantalum powder produced by the method is more suitable for the manufacture of tantalum capacitors requiring higher reliability after subsequent processing including water washing, pickling, purification, sintering, and oxygen reduction. Compared with tantalum powder for capacitors of the same grade produced by other methods, the tantalum powder has a higher specific capacitance, a higher breakdown voltage under high-voltage current conditions, and the dielectric strength of the tantalum powder for capacitors is clearly improved. In other words, tantalum powder for capacitors with different specific capacitances manufactured by the method of the present invention can withstand relatively higher voltages, and tantalum capacitors manufactured using tantalum powder are more reliable.

[0012] Another object of the present invention is a method for producing tantalum powder by sodium reduction of potassium fluorantharate, comprising the following steps: (1) A step of preparing a diluted salt (preferably selected from alkali metal halides), potassium fluorantharate, and metallic sodium as raw materials, wherein the amount of metallic sodium is in excess of the amount of potassium fluorantharate, 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), (2) A process in which the diluted salt is placed in a reducing container, the container is evacuated, an inert gas such as argon is introduced, and the diluted salt in the reducing container is heated and melted while the inert gas is flowing (e.g., at a flow rate of 20-100 l / min), (3) A process in which a portion of potassium fluorantharate is added to a reducing vessel, the temperature is monitored to ensure that the mixture of potassium fluorantharate and diluted salt is dissolved, then preheated metallic sodium is added to reduce a portion of the potassium fluorantharate, and this process is repeated multiple times until all of the potassium fluorantharate and metallic sodium raw materials are used up. (4) After the reduction is complete, the tantalum powder is aged, (5) Next, the process of separating the tantalum powder The objective is to provide a method that includes [this].

[0013] Optionally, the method is to follow step (5): (6) A process to obtain a tantalum powder product by subjecting tantalum powder to salt bath heat treatment and / or coagulation heat treatment, followed by oxygen reduction treatment with magnesium metal chips, pickling, purification and drying. It also includes.

[0014] In step (1), the diluent is selected from alkali metal halides (also called alkali metal halide salts, and the terms "halide salt" and "halide" may be used interchangeably herein) that are commonly referred to in the art, such as one or more of NaCl, KCl, KF, and KI. The ratio of the diluent to potassium fluorantharate is not particularly limited, and ratios commonly used in the prior art can be applied. Preferably, the diluent may also be mixed with tantalum powder refining agent. The amount of metallic sodium is in excess of the theoretical amount for the complete reduction of potassium fluorantharate, for example, 1-3%, preferably 1.5-2.5% excess. The metallic sodium is preheated to a range of over 180°C to 500°C, more preferably 200-350°C, more preferably 200-260°C, and more preferably 190-240°C, such as 210°C. Preferably, both the diluent salt and potassium fluorantharate are in powder form.

[0015] Preferably, in step (2), vacuuming and introduction of an inert gas such as argon are repeated multiple times, for example 2 to 3 times, to exhaust as much air as possible from the reduction vessel, thereby reducing air corrosion in the metal reduction vessel and reducing the adverse effects of air on the tantalum powder. To reduce adverse effects on reduction, such as water vapor and acid gas discharged during the heating and melting process being carried by argon and discharged outside the reduction vessel in a timely manner, the flow rate of the inert gas is preferably maintained at 20 to 100 l / min to allow for better discharge of water vapor, acid gas, etc. To ensure complete melting of the dilution salt and improve its viscosity to facilitate stirring, the dilution salt is preferably heated to a temperature 80°C, preferably 150°C, more preferably 200°C higher than its melting point. Preferably, after sufficient melting, heat preservation is further performed for, for example, 30 minutes. To ensure thorough mixing and maintain a uniform temperature, it is preferable to stir the dilution salt after heating to the target temperature. There are no specific requirements for the stirring conditions. Preferably, after the dilution salt has melted, it is preferably stirred continuously until the end of aging.

[0016] In step (3), potassium fluorantharate is repeatedly added to carry out reduction in order to lower the concentration of potassium fluorantharate in the dilution salt. The amount and number of times potassium fluorantharate is added each time are not particularly limited. However, as a result of diligent research, the inventors have found that a specific amount of potassium fluorantharate added each time is related to the desired specific surface area of ​​the final tantalum powder. When preparing tantalum powder with a larger specific surface area under the condition that a fixed amount of dilution salt is added in step (2), the amount of potassium fluorantharate added each time may be reduced so that potassium fluorantharate is reduced to a lower concentration, and when preparing tantalum powder with a smaller specific surface area, the amount of potassium fluorantharate added each time may be appropriately increased. In other words, the present invention achieves good control over the specific surface area of ​​tantalum powder. Of course, no matter how many times potassium fluorantharate is added, when adding metallic sodium at the end, all remaining raw materials are added to ensure that potassium fluorantharate is completely reduced. Preferably, in this step, melting is ensured by controlling the temperature in the reducing vessel to be higher than the melting point of the mixture of the diluting salt and potassium fluorantharate, for example, 80 to 400°C, preferably 250 to 350°C higher. It will be readily apparent to those skilled in the art that the melting temperature of the mixture of the diluting salt and potassium fluorantharate may differ from the melting point of the diluting salt or from the melting point of potassium fluorantharate. If the ratio of the two is different, the “melting point” (also called the apparent melting point) of the mixture when it is completely melted will also be different, but the apparent melting point can be determined from the phase diagram data. Preferably, the temperature is increased after each addition of potassium fluorantharate. Preferably, in order to make the resulting tantalum powder more uniform, the amount of high-temperature metallic sodium added each time before the final addition of metallic sodium is such that 70 to 95%, more preferably 70 to 85%, of the potassium fluorantharate in the potassium fluorantharate added immediately before is reduced. This method of addition avoids the reaction between excess metallic sodium in the reducing container and potassium fluorantharate that will be added next time (i.e., when it is not yet molten).

[0017] In step (4), preferably, heating is continued after the reduction is complete to age the tantalum powder by retaining its heat. Preferably, heating is continued for 0.5 to 5 hours, preferably 2 to 3 hours. Preferably, the temperature inside the reaction vessel is controlled to be the same as the temperature before the addition of metallic sodium in step (3). In this step, excess metallic sodium is carried out of the reduction vessel by argon and separated from the tantalum powder.

[0018] Preferably, in steps (3) and / or (4), a flow of an inert gas such as argon is maintained at all times in the reducing vessel. Preferably, in step (5), the reducing vessel is maintained under positive pressure until the mixture is removed from the reducing vessel.

[0019] Preferably, the separation of tantalum powder in step (5) includes stopping stirring, cooling to room temperature under conditions where the reduction vessel is maintained at positive pressure by introducing argon, removing the mixture containing the halide and tantalum powder from the reduction reaction vessel, separating and removing a portion of the by-product that does not contain tantalum powder, further separating the by-product by washing with water and pickling with acid, and then washing, purifying and drying to obtain the final tantalum powder.

[0020] Preferably, the method of the present invention further includes, after step (5), step (6): separating the tantalum powder by water washing and / or pickling, high-temperature high-vacuum heat treatment (or high-temperature high-vacuum heat treatment after auxiliary sintering in molten salt according to the present invention in patent CN114210973B), oxygen reduction, pickling, and, for example, filtration and drying, to obtain tantalum powder suitable for the manufacture of high-reliability tantalum capacitors. All of these processes are known in the prior art. In other words, any method known in the prior art may be used in these processes. For example, high-temperature, high-vacuum heat treatment and passivation may be carried out according to methods provided in patents CN201110039272.9, CN201120077798.1, CN201120077680.9, CN201120077305.4, etc., oxygen reduction may be carried out according to methods provided in patents CN201420777210.7 and CN201420777210.7, and pickling may be carried out according to methods provided in patents CN201210548101.3, CN201280077499.5, CN201210548008.2, etc.

[0021] The method may also include doping the tantalum powder with elements N, P, and / or B after step (5) and / or step (6). Of course, raw materials containing these elements can also be used directly. These elements can also be added in the high-temperature, high-vacuum heat treatment step described above. Adding element P is particularly preferred. Adding element P can improve the specific capacitance, and the effect of improving the specific capacitance is the same regardless of when element P is added, as long as the total amount of doped P is well controlled. These can be done conventionally in the prior art and will not be explained in detail.

[0022] The obtained tantalum powder product was briquetteed, sintered, and energized under high voltage conditions. The energized block was then tested for its electrical properties and found to have a higher specific capacitance and a higher breakdown voltage in the breakdown voltage test.

[0023] After being energized under the same high voltage conditions, the tantalum powder produced by the method of the present invention has a larger specific capacitance and results in an energized block showing a higher breakdown voltage in the breakdown voltage test compared to the tantalum powder for capacitors of the same grade produced by other methods. Therefore, the tantalum powder produced according to the present invention is more suitable for the production of high voltage and high reliability tantalum capacitors.

[0024] Although not restricted by the general theory, the inventor believes that the reason why the present invention achieves excellent effects lies in that the sodium reduction method of potassium fluotantalate is an intense exothermic method that locally releases a large amount of heat. Generally, thermal runaway is avoided by the addition of diluting salts. In step (2) of the present invention, when metallic sodium and potassium fluotantalate come into contact and react, the use of preheated metallic sodium causes the instantaneous temperature at the reaction point to rise, and the formation and growth of tantalum powder at the moment of reduction are affected by the temperature at the reaction point, thereby promoting sintering between particles and making the internal sintering neck of the tantalum powder thicker. However, through the control of other method 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 it is easier to construct a spatial structure suitable for the production of capacitors between the particles of the tantalum powder.

[0025] The melting point of sodium is 97.78 °C. Even if solid sodium is added, it melts relatively quickly in the furnace and becomes liquid. Therefore, in the prior art, little attention has been paid to the temperature of the metallic sodium itself, and only the sodium injection temperature (i.e., the temperature of the reduction container or the furnace when adding sodium) has been focused on. Although the influence of increasing the sodium injection temperature may have been considered, this means that the temperature inside the furnace as a whole needs to be increased, which results in a greater thermal load on the materials constituting the reduction container and the furnace and is disadvantageous for their service life. Furthermore, increasing the temperature inside the furnace also means that the energy consumption increases. Although improving the fluidity of liquid metallic sodium by increasing its temperature may have been considered in the prior art, since the fluidity of liquid metallic sodium tends to be almost stable as the temperature rises above 120 °C, currently, liquid metallic sodium at a temperature below 120 °C is generally added. As a result of intensive studies, the inventor has surprisingly found that by further increasing the temperature of liquid metallic sodium, not only is the good fluidity of liquid sodium maintained, but also under the condition of not increasing the output of the heating furnace, the temperature of the reduction reaction point is accurately increased, the morphology of the tantalum powder is improved, and finally the specific capacitance and breakdown voltage of the tantalum powder are improved.

[0026] The tantalum powder produced according to the present invention is subjected to high-temperature high-vacuum heat treatment (or high-temperature high-vacuum heat treatment after auxiliary sintering in molten salt according to the invention of Patent CN114210973B), oxygen reduction, and pickling according to the prior art. The tantalum powder obtained thereby still has a high specific capacitance under a high applied voltage, and its comprehensive electrical properties are improved. This tantalum powder is suitable for the manufacture of high-voltage high-reliability capacitors.

[0027] The following figures are provided to better understand the present invention. The figures are illustrative and are not intended to limit the scope of the present invention.

Brief Description of the Drawings

[0028] [Figure 1] Figure 1 shows a scanning electron microscope image of tantalum powder obtained according to the present invention. Detailed description of the form

[0029] The figure shows that the resulting tantalum powder has a more uniform particle size, smoother particles, and a thicker sintered neck.

[0030] To further illustrate the present invention, preferred embodiments are described below using a combination of examples that clearly demonstrate the object, features, and advantages of the present invention. However, this description is solely for the purpose of further illustrating the features and advantages of the present invention and is not intended to limit it. Examples where specific conditions are not specified were carried out under conventional conditions. All reagents or equipment used where the manufacturer is not indicated are commercially available conventional products.

[0031] For illustrative purposes, all numerical values ​​in this specification and the claims, representing amounts of components, reaction conditions, etc., should be understood to be modified in all examples with the term "approximately" unless otherwise specified. Accordingly, the numerical parameters given in this specification and the appended claims below are approximations that may vary depending on the desired properties to be obtained by the present invention, unless otherwise specified. At the very least, and not with the intention of limiting the application of the doctrine of equivalents to the claims, each numerical parameter should be interpreted in accordance with at least the reported number of significant figures and the usual rounding method.

[0032] The impurity content in tantalum powder is analyzed according to Chinese standard GB / T15076.1-15076.15, and the physical properties are tested according to the specifications of industry standard YS / T573-2015. The electrical properties of tantalum powder are tested according to the specifications of Chinese standard GB / T3137.

[0033] [Examples] To further illustrate the present invention, preferred embodiments of the invention are described below using a combination of examples that clearly demonstrate the object, features, and advantages of the invention. However, this description is solely for the purpose of further illustrating the features and advantages of the invention and is not intended to limit the invention. Examples where specific conditions are not specified were carried out under conventional conditions or conditions recommended by the manufacturer. All reagents or equipment used where the manufacturer is not indicated are commercially available conventional products.

[0034] For illustrative purposes, all numerical values ​​in this specification and the claims, representing amounts of components, reaction conditions, etc., should be understood to be modified in all examples with the term "approximately" unless otherwise specified. Accordingly, the numerical parameters given in this specification and the appended claims below are approximations that may vary depending on the desired properties to be obtained by the present invention, unless otherwise specified. At the very least, and not with the intention of limiting the application of the doctrine of equivalents to the claims, each numerical parameter should be interpreted in accordance with at least the reported number of significant figures and the usual rounding method.

[0035] The impurity content in tantalum powder is analyzed according to Chinese standard GB / T15076.1-15076.15, and the physical properties are tested according to the specifications of industry standard YS / T573-2007. The leakage current and capacitance of tantalum powder are tested according to the specifications of Chinese standard GB / T3137.

[0036] Example 1 Potassium fluorantharate, NaCl as a diluent, and metallic sodium were prepared as raw materials. The metallic sodium was preheated to a high temperature of 180°C.

[0037] 100 kg of sodium chloride (NaCl) was placed in the reduction vessel, the vessel was evacuated, and then argon was introduced to 0.10 MPa. Next, the evacuation and argon introduction to 0.10 MPa were repeated twice. The reduction vessel was placed in a heating furnace, and argon was introduced at a flow rate of 40 l / min to raise the temperature to 920°C, then stirring was started, and the vessel was then heated for 30 minutes. Next, 15 kg of potassium fluorantharate was added, the temperature was raised to 920°C, and then 3.95 kg of metallic sodium at 180°C for reduction was added. Next, the addition of potassium fluorantharate, heating, and reduction were repeated seven times. After the eighth addition of potassium fluorantharate, 8.20 kg of metallic sodium for reduction was added. After the reduction was complete, the tantalum powder was aged at 920°C for 180 minutes under an argon flow, and then stirring was stopped. The reaction vessel was cooled to room temperature while maintaining the pressure at 0.10 MPa. The mixture was removed from the reducing vessel, and a portion of the by-products that did not contain tantalum powder was separated to remove them. The by-products were further separated by washing with water and pickling with acid, and then washed, purified, and dried to obtain high-purity tantalum powder.

[0038] Next, tantalum powder is doped with 50 ppm of phosphorus and subjected to high-temperature, high-vacuum heat treatment for 5.0 × 10⁻⁶ days. -3 The tantalum powder was obtained by sintering at 1450°C for 1.0 hour under a pressure of less than Pa, followed by oxygen reduction and pickling. The obtained tantalum powder was used to fabricate a negative electrode block according to the negative electrode block mass, compressed density, negative electrode block sintering temperature, sintering time, and other conditions in accordance with the requirements of GB / T3137 as specified in Table 1. The block was then energized at 150V and tested for electrical properties in accordance with the requirements of GB / T3137 as described above. In the specific capacitance test, a 30% H2SO4 solution and then a 10% H3PO4 solution were used. The test results are shown in Table 1.

[0039] Comparative Example 1 Potassium fluorantharate, NaCl as a diluent, and metallic sodium were prepared as raw materials. The metallic sodium was preheated to a high temperature of 130°C.

[0040] 100 kg of sodium chloride (NaCl) was placed in the reduction vessel, the vessel was evacuated, and then argon was introduced to 0.10 MPa. Next, the evacuation and argon introduction to 0.10 MPa were repeated twice. The reduction vessel was placed in a heating furnace, and argon was introduced at a flow rate of 40 l / min to raise the temperature to 920°C, then stirring was started, and the vessel was then heated for 30 minutes. Next, 15 kg of potassium fluorantharate was added, the temperature was raised to 920°C, and then 3.95 kg of 130°C metallic sodium was added for reduction. Next, the addition of potassium fluorantharate, heating, and reduction were repeated seven times. After the eighth addition of potassium fluorantharate, 8.20 kg of 130°C metallic sodium was added for reduction. After the reduction was complete, the tantalum powder was aged at 920°C for 180 minutes under an argon flow, and then stirring was stopped. The reaction vessel was cooled to room temperature while maintaining the pressure at 0.10 MPa. The mixture was removed from the reducing vessel, and a portion of the by-products that did not contain tantalum powder was separated to remove them. The by-products were further separated by washing with water and pickling with acid, and then washed, purified, and dried to obtain high-purity tantalum powder.

[0041] Next, tantalum powder is doped with 50 ppm of phosphorus and subjected to high-temperature, high-vacuum heat treatment for 5.0 × 10⁻⁶ days. -3 The tantalum powder was obtained by sintering at 1450°C for 1.0 hour under a pressure of less than Pa, followed by oxygen reduction and pickling. The obtained tantalum powder was used to fabricate a negative electrode block according to the negative electrode block mass, compressed density, negative electrode block sintering temperature, sintering time, and other conditions in accordance with the requirements of GB / T3137 as specified in Table 1. The block was then energized at 150V and tested for electrical properties in accordance with the requirements of GB / T3137 as described above. In the specific capacitance test, a 30% H2SO4 solution and then a 10% H3PO4 solution were used. The test results are shown in Table 1.

[0042] Example 2 Potassium fluorantharate, KCl and KF as diluents, and metallic sodium were prepared as raw materials. The metallic sodium was preheated to a high temperature of 220°C.

[0043] 50 kg of potassium chloride (KCl) and 50 kg of potassium fluoride (KF) were placed in a reduction vessel, the vessel was evacuated, and then argon was introduced to 0.10 MPa. Next, the evacuation and argon introduction to 0.10 MPa were repeated twice. The reduction vessel was placed in a heating furnace, and argon was introduced at a flow rate of 60 l / min to raise the temperature to 900°C, then stirring was started, and the mixture was then held at room temperature for 30 minutes. Next, 15 kg of potassium fluorantharate was added, the temperature was raised to 900°C, and then 4.0 kg of metallic sodium at 220°C for reduction was added. Next, the addition of potassium fluorantharate, heating, and reduction were repeated nine times. After the tenth addition of potassium fluorantharate, 8.9 kg of metallic sodium at 220°C for reduction was added. After the reduction was complete, the tantalum powder was aged at 900°C for 120 minutes under an argon flow, and then stirring was stopped. The reaction vessel was cooled to room temperature while maintaining a pressure of 0.10 MPa. The mixture was removed from the reduction vessel, and a portion of the by-products that did not contain tantalum powder was separated to remove them. The by-products were further separated by washing with water and pickling with acid, and then washed, purified, and dried to obtain high-purity tantalum powder.

[0044] Next, tantalum powder is doped with 60 ppm of phosphorus and subjected to high-temperature, high-vacuum heat treatment for 5.0 × 10⁻⁶ days. -3 The tantalum powder was obtained by sintering at 1400°C for 1.0 hour under a pressure of less than Pa, followed by oxygen reduction and pickling. The obtained tantalum powder was used to fabricate a negative electrode block according to the negative electrode block mass, compressed density, negative electrode block sintering temperature, sintering time, and other conditions in accordance with the requirements of GB / T3137 as specified in Table 1. The block was then energized at 100V and tested for electrical properties in accordance with the requirements of GB / T3137. In the specific capacitance test, a 30% H2SO4 solution and then a 10% H3PO4 solution were used. The test results are shown in Table 1.

[0045] Comparative Example 2 Potassium fluorantharate, KCl and KF as diluents, and metallic sodium were prepared as raw materials. The metallic sodium was preheated to a high temperature of 120°C.

[0046] 50 kg of potassium chloride (KCl) and 50 kg of potassium fluoride (KF) were placed in a reduction vessel, the vessel was evacuated, and then argon was introduced to 0.10 MPa. Next, the vacuuming and argon introduction to 0.10 MPa were repeated twice. The reduction vessel was placed in a heating furnace, and argon was introduced at a flow rate of 60 l / min to raise the temperature to 900°C, then stirring was started, and the mixture was then held at room temperature for 30 minutes. Next, 15 kg of potassium fluorantharate was added, the temperature was raised to 900°C, and then 4.0 kg of 120°C metallic sodium was added for reduction. Next, the addition of potassium fluorantharate, heating, and reduction were repeated nine times. After the tenth addition of potassium fluorantharate, 8.9 kg of 120°C metallic sodium was added for reduction. After the reduction was complete, the tantalum powder was aged at 900°C for 120 minutes under an argon flow, and then stirring was stopped. The reaction vessel was cooled to room temperature while maintaining a pressure of 0.10 MPa. The mixture was removed from the reduction vessel, and a portion of the by-products that did not contain tantalum powder was separated to remove them. The by-products were further separated by washing with water and pickling with acid, and then washed, purified, and dried to obtain high-purity tantalum powder.

[0047] Next, tantalum powder is doped with 60 ppm of phosphorus and subjected to high-temperature, high-vacuum heat treatment for 5.0 × 10⁻⁶ days. -3 The tantalum powder was obtained by sintering at 1400°C for 1.0 hour under a pressure of less than Pa, followed by oxygen reduction and pickling. The obtained tantalum powder was used to fabricate a negative electrode block according to the negative electrode block mass, compressed density, negative electrode block sintering temperature, sintering time, and other conditions in accordance with the requirements of GB / T3137 as specified in Table 1. The block was then energized at 100V and tested for electrical properties in accordance with the requirements of GB / T3137. In the specific capacitance test, a 30% H2SO4 solution and then a 10% H3PO4 solution were used. The test results are shown in Table 1.

[0048] Example 3 Potassium fluorantharate, KCl and KF as diluents, and metallic sodium were prepared as raw materials. The metallic sodium was preheated to a high temperature of 180°C.

[0049] 100 kg of potassium chloride (KCl) and 100 kg of potassium fluoride (KF) were placed in a reduction vessel, the vessel was evacuated, and then argon was introduced to 0.10 MPa. Next, the evacuating and argon introduction to 0.10 MPa were repeated twice. The reduction vessel was placed in a heating furnace, and argon was introduced at a flow rate of 70 l / min to raise the temperature to 900°C, then stirring was started, and the mixture was then held at room temperature for 30 minutes. Next, 10 kg of potassium fluorantharate was added, the temperature was raised to 920°C, and then 2.50 kg of 180°C metallic sodium was added for reduction. Next, the addition of potassium fluorantharate, heating, and reduction were repeated five times. After the sixth addition of potassium fluorantharate, 6.0 kg of 180°C metallic sodium was added for reduction. After the reduction was complete, the tantalum powder was aged at 900°C for 120 minutes under an argon flow, and then stirring was stopped. The reaction vessel was cooled to room temperature while maintaining a pressure of 0.10 MPa. The mixture was removed from the reduction vessel, and a portion of the by-products that did not contain tantalum powder was separated to remove them. The by-products were further separated by washing with water and pickling with acid, and then washed, purified, and dried to obtain high-purity tantalum powder.

[0050] Next, tantalum powder is doped with 100 ppm of P and subjected to high-temperature, high-vacuum heat treatment for 5.0 × 10 -3 The process was carried out at 1230°C for 1.0 hour under a pressure of less than Pa, followed by oxygen reduction and pickling to obtain the final tantalum powder. The obtained final tantalum powder was used to fabricate a negative electrode block according to the negative electrode block mass, compressed density, negative electrode block sintering temperature, sintering time, and other conditions in accordance with the requirements of GB / T3137 as specified in Table 1. The block was then energized at 60V and tested for electrical properties in accordance with the requirements of GB / T3137 as described above. In the specific capacitance test, a 30% H2SO4 solution and then a 10% H3PO4 solution were used. The test results are shown in Table 1.

[0051] Comparative Example 3 Potassium fluorantharate, KCl and KF as diluents, and metallic sodium were prepared as raw materials. The metallic sodium was preheated to a high temperature of 120°C.

[0052] 100 kg of potassium chloride (KCl) and 100 kg of potassium fluoride (KF) were placed in a reduction vessel, the vessel was evacuated, and then argon was introduced to 0.10 MPa. Next, the evacuation and argon introduction to 0.10 MPa were repeated twice. The reduction vessel was placed in a heating furnace, and argon was introduced at a flow rate of 70 l / min to raise the temperature to 900°C, then stirring was started, and the mixture was then heated for 30 minutes. Next, 10 kg of potassium fluorantharate was added, the temperature was raised to 900°C, and then 2.5 kg of 120°C metallic sodium was added for reduction. Next, the addition of potassium fluorantharate, heating, and reduction were repeated five times. After the sixth addition of potassium fluorantharate, 6.0 kg of 120°C metallic sodium was added for reduction. After the reduction was complete, the tantalum powder was aged at 900°C for 120 minutes under an argon flow, and then stirring was stopped. The reaction vessel was cooled to room temperature while maintaining a pressure of 0.10 MPa. The mixture was removed from the reduction vessel, and a portion of the by-products that did not contain tantalum powder was separated to remove them. The by-products were further separated by washing with water and pickling with acid, and then washed, purified, and dried to obtain high-purity tantalum powder.

[0053] Next, tantalum powder is doped with 100 ppm of P and subjected to high-temperature, high-vacuum heat treatment for 5.0 × 10 -3 The process was carried out at 1230°C for 1.0 hour under a pressure of less than Pa, followed by oxygen reduction and pickling to obtain the final tantalum powder. The obtained final tantalum powder was used to fabricate a negative electrode block according to the negative electrode block mass, compressed density, negative electrode block sintering temperature, sintering time, and other conditions in accordance with the requirements of GB / T3137 as specified in Table 1. The block was then energized at 60V and tested for electrical properties in accordance with the requirements of GB / T3137 as described above. In the specific capacitance test, a 30% H2SO4 solution and then a 10% H3PO4 solution were used. The test results are shown in Table 1.

[0054] [Table 1]

[0055] As can be seen from Table 1, the method of the present invention is suitable for the production of tantalum powder for high-voltage, high-reliability capacitors, which yields an energized block with high specific capacitance and low residual current after energizing under relatively high voltage conditions, shows relatively small differences between test results using 30% H2SO4 solution and 10% H3PO4 solution in specific capacitance testing, and has a high breakdown voltage in breakdown voltage testing and higher specific capacitance.

Claims

1. A method for producing tantalum powder by reducing potassium fluorantharate with sodium, characterized in that preheated metallic sodium is used as the reducing agent for the reduction, and the temperature of the metallic sodium is greater than 180°C, more preferably 200 to 350°C, more preferably 200 to 260°C, more preferably 160 to 190°C and / or 210 to 240°C.

2. A method for producing tantalum powder by reducing potassium fluoranthalate with sodium, comprising the following steps: (1) A step of preparing a diluted salt (selected from alkali metal halides), potassium fluorantharate, and metallic sodium as raw materials, wherein the amount of metallic sodium is in excess of the amount of potassium fluorantharate, and the metallic sodium is preheated to 180 to 350°C (preferably 200 to 350°C, more preferably 200 to 260°C, more preferably 160 to 190°C and / or 210 to 240°C), (2) A step of charging the diluted salt into a reduction container, evacuating the container, introducing an inert gas such as argon, and heating and melting the diluted salt in the reduction container while flowing the inert gas (e.g., at a flow rate of 20 to 100 l / min), (3) A step of adding a portion of the potassium fluorantharate to the reducing container, monitoring the temperature to ensure that the mixture of potassium fluorantharate and the diluted salt melts, then adding preheated metallic sodium to reduce a portion of the potassium fluorantharate, and repeating this process multiple times until all of the potassium fluorantharate and metallic sodium raw materials are used up. (4) After the reduction is completed, the tantalum powder is aged, (5) Next, the process of separating the tantalum powder Methods that include...

3. The method according to claim 2, wherein in step (2), the vacuuming and introduction of argon are repeated multiple times, for example, two to three times, and / or in step (2), the diluted salt is heated to a temperature 80°C, preferably 150°C, more preferably 200°C higher than its melting point, preferably further heat-storage for for example 30 minutes, and more preferably, the diluted salt is stirred after it has melted.

4. The method according to claim 2 or 3, wherein in step (3), the temperature in the reducing vessel is controlled to ensure that the temperature of the potassium fluorantharate and the potassium fluorantharate is, for example, 80 to 500°C, preferably 150 to 450°C higher than their apparent melting point, and preferably the temperature is increased after each addition of the potassium fluorantharate.

5. The method according to claim 2, 3, or 4, wherein in step (3) and / or (4), a flow of an inert gas such as argon is continuously maintained in the reducing vessel.

6. After step (5) above, (6) A process to obtain the tantalum powder product by subjecting the tantalum powder to salt bath heat treatment and / or coagulation heat treatment, oxygen reduction treatment with magnesium metal chips, pickling, purification and drying. The method according to claim 2, 3, or 4, further comprising:

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

8. The method according to any one of claims 2 to 7, wherein in step (5) above, the reducing container is maintained at positive pressure.

9. Tantalum powder produced by the method described in any one of claims 2 to 8.

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

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