Potassium fluotantalate powder, method for reducing same with sodium to produce tantalum powder, tantalum powder obtained thereby, and use thereof

Abstract

The present invention relates to a potassium fluotantalate powder, a method for reducing same with sodium to produce tantalum powder, a tantalum powder obtained thereby, and the use thereof. The potassium fluotantalate powder is used as a raw material during the process of producing the tantalum powder by reducing potassium fluotantalate with sodium. The potassium fluotantalate powder comprises 5-1000 ppm (preferably 50-800 ppm, more preferably 100-850 ppm, more preferably 100-500 ppm, and more preferably 50-150 ppm and / or 300-500 ppm) of a halide salt of an alkaline earth metal, with the balance being potassium fluotantalate. The halide salt of the alkaline earth metal is selected from a halide salt of magnesium and / or a halide salt of calcium, e.g. magnesium chloride. The present invention also relates to a method for reducing the potassium fluotantalate powder with sodium to produce tantalum powder, the tantalum powder obtained thereby, and the use of the tantalum powder in capacitors.

Description

A potassium fluotantalate powder, a method for producing tantalum powder by sodium reduction of the powder, tantalum powder thus obtained and use thereof TECHNICAL FIELD

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

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

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

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

[0005] US4684399A discloses a method for producing tantalum powder by sodium reduction of potassium fluotantalate. Potassium fluotantalate and metallic sodium are continuously or semi-continuously added to a molten diluent in multiple portions for stirring reduction to obtain tantalum powder. US4149876A proposes a method for producing tantalum powder by adding liquid sodium to a molten potassium fluotantalate and diluent molten salt bath. This method involves rapid injection of sodium at a lower temperature to raise the temperature of the material, using a large proportion of diluent, forced cooling, and reduction reaction at a lower temperature, and maintaining a constant temperature during the grain growth period, thereby producing tantalum powder with fine and uniform particle size.

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

[0007] JP4828016B2 discloses a method for manufacturing tantalum powder by reducing potassium fluorotantalate with metallic sodium, which is achieved by adding a small amount of potassium fluorotantalate to the molten diluent, then adding metallic sodium for reduction, and then adding a small amount of potassium fluorotantalate for sodium reduction, and so on. This method realizes the reaction of potassium fluorotantalate at low concentration by repeating the above process, and the dilution salt amount is 40-1000 times that of potassium fluorotantalate, achieving the purpose of improving the specific capacity of tantalum powder. The specific capacity of tantalum powder produced by this method is 80000-250000 μFV / g.

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

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

[0010] Without being bound by general theories, the inventors have found through extensive research that current research on the sodium reduction potassium fluorotantalate process involves the state, temperature, and concentration of potassium fluorotantalate (using potassium chloride, sodium chloride, potassium fluoride, etc. as dilution salt to disperse potassium fluorotantalate); involves alkali metal halides as dilution salt; involves the use of additives such as phosphorus, boron, nitrogen, oxygen, silicon, iodine, sulfur, etc. for refining tantalum powder in the reduction process; involves the temperature and flowability of the injected metallic sodium; involves stirring and mixing during the reduction process; and involves equipment for optimizing the reduction process. However, current research on the sodium reduction potassium fluorotantalate process does not involve the reduction of tantalate in the sodium reduction potassium fluorotantalate system, and even almost no existing technology has focused on the generation and impact of tantalate. In fact, oxygen inevitably exists in the sodium reduction molten salt system, and due to the strong oxygen affinity of tantalum, tantalate is easily formed in the sodium reduction system, and the tantalum in the tantalate is difficult to be reduced by metallic sodium. If the tantalate is allowed to enter the tantalum powder, it will increase the oxygen content of the tantalum powder and increase the leakage current. On the other hand, most of the tantalate formed in the sodium reduction system exists in the form of extremely fine particles, which is removed as a harmful component during the water acid washing process, resulting in a decrease in the yield of the tantalum powder production process.

[0011] SUMMARY

[0012] According to one aspect of the present application, there is provided a potassium fluotantalate powder used as a raw material in a process for producing tantalum powder by sodium reduction of potassium fluotantalate, the potassium fluotantalate powder comprising an alkaline earth metal halide in an amount of 5-1000 ppm and a remainder of potassium fluotantalate. The potassium fluotantalate powder is used as a raw material in a process for producing tantalum powder by sodium reduction.

[0013] Halogen acid salt is also known as halide. In the present application, "alkaline earth metal halide" and "alkaline earth metal halogen salt" can be used interchangeably, and both refer to a compound containing an alkaline earth metal (such as magnesium and / or calcium) and a halogen, for example, magnesium chloride. Hereinafter, "potassium fluotantalate powder" contains an alkaline earth metal halogen salt in an amount of 5-1000 ppm, preferably more than 50 ppm, more preferably 100-850 ppm, even more preferably 100-500 ppm, most preferably 50-150 ppm and / or 300-500 ppm, and a remainder of potassium fluotantalate, unless otherwise specified. Since the amount is relatively small and does not significantly affect the macroscopic substance of the potassium fluotantalate powder, the potassium fluotantalate powder containing the above-mentioned amount of alkaline earth metal halogen salt will still be referred to as "potassium fluotantalate powder" hereinafter and in the claims, unless otherwise specified. Therefore, "potassium fluotantalate powder" and "potassium fluotantalate" are not interchangeable in the present application, the latter refers to potassium fluotantalate (K2TaF7) without containing an alkaline earth metal halide, unless otherwise specified.

[0014] According to another aspect of the present application, there is provided a process for producing tantalum powder by sodium reduction of potassium fluotantalate, the process comprising using the above-mentioned potassium fluotantalate powder as a raw material.

[0015] It is generally believed in the prior art that the introduction of an alkaline earth metal halogen salt should be avoided in the process of sodium reduction of potassium fluotantalate, because the alkaline earth metal halogen salt can be reduced by sodium to form an alkaline earth metal, which can corrode the metal reduction vessel commonly used at present. However, the inventors have surprisingly found that in the process of the present application, since the potassium fluotantalate powder used as a raw material contains a small amount of alkaline earth metal halogen salt, the alkaline earth metal halogen salt is reduced by sodium to form an alkaline earth metal, which further reduces the harmful tantalate. Since the reduction of the alkaline earth metal halogen salt by sodium in the sodium reduction of potassium fluotantalate system is a weak equilibrium, but the alkaline metal, for example, magnesium metal, has a strong affinity for oxygen, so the magnesium metal produced is timely converted into magnesium oxide, losing the ability to corrode the sodium reduction of potassium fluotantalate vessel, so the corrosion of the reaction vessel for reducing potassium fluotantalate is greatly reduced. Therefore, the addition of an alkaline earth metal halogen salt in the process of sodium reduction of potassium fluotantalate will not corrode the reaction vessel and will not affect its service life.

[0016] According to still another aspect of the present application, there is provided a process for producing tantalum powder for capacitors by sodium reduction of potassium fluotantalate, the process comprising the following steps:

[0017] (1) providing potassium fluotantalate powder, diluent salt (preferably selected from alkali halide), and liquid sodium metal as raw materials, wherein the potassium fluotantalate powder contains 5-1000 ppm of alkaline earth metal halide,

[0018] (2) charging the diluent salt into a reduction vessel, evacuating the vessel, then introducing an inert gas such as argon, and then heating the diluent salt in the reduction vessel to melting while the inert gas is kept flowing (at a flow rate of 20-100 L / min),

[0019] (3) adding part of the potassium fluotantalate powder into the reduction vessel, and monitoring the temperature to ensure that the mixture of the potassium fluotantalate powder and the diluent salt is melted, then adding liquid sodium metal to reduce the part of the potassium fluotantalate, and repeating this process several times until all of the potassium fluotantalate powder and the sodium metal raw materials are used up,

[0020] (4) after the reduction is completed, aging the tantalum powder,

[0021] (5) then, separating the tantalum powder.

[0022] Optionally, after step (5) further comprising the step of:

[0023] (6) after the salt bath heat treatment and / or the agglomeration heat treatment of the tantalum powder, the oxygen reduction treatment of the magnesium turnings, and further acid pickling and drying, the product tantalum powder is obtained.

[0024] In step (1), the diluent salt is selected from the alkali halide salts mentioned in the prior art. The ratio of potassium fluotantalate to diluent salt is not limited, and the ratio commonly used in the prior art can be used. Preferably, the diluent salt can also be mixed with a tantalum powder refiner selected from one or more compounds containing sulfur, phosphorus, boron, nitrogen, oxygen, silicon, iodine, etc. Alternatively, high-purity nitrogen gas can also be introduced to play the role of a refiner. The amount of sodium metal is in excess of the theoretical amount required for complete reduction of potassium fluotantalate, for example, 1-3% excess, preferably 1.5-2.5% excess. Preferably, the metal sodium is preheated to more than 150°C, for example, 180°C-500°C, more preferably 200-350°C, more preferably 200-260°C, more preferably 190°C-240°C, for example, 210°C.

[0025] The melting point of sodium is 97.78°C. Even if solid sodium is added, it will be melted into liquid in the furnace relatively quickly. Therefore, the prior art has paid little attention to the temperature of the metal sodium itself, but only to the sodium injection temperature (i.e., the temperature of the reduction vessel or furnace when sodium is added). Although someone might have studied the effect of increasing the sodium injection temperature, this means that the temperature in the furnace needs to be increased as a whole, which brings a greater thermal load to the materials making up the reduction vessel and furnace, and is not conducive to their service life. Moreover, increasing the temperature in the furnace also means greater energy consumption. The prior art might also have studied improving the fluidity of liquid metal sodium by increasing the temperature of the liquid metal sodium itself, but since the fluidity of liquid sodium is almost stable as the temperature is increased above 120°C, metal sodium with a temperature of about 120°C or less is generally added at present. The present inventors have unexpectedly found, through extensive research, that by further increasing the temperature of the liquid metal sodium, not only is the good fluidity of the liquid sodium maintained, but the temperature of the reduction reaction point is also precisely increased without increasing the power of the heating furnace, the morphology of the tantalum powder is improved, and ultimately the electrical properties of the tantalum powder, such as breakdown voltage and leakage current, are improved.

[0026] Preferably, in step (1), both the dilution salt and the potassium fluotantalate are in the form of a powder. As mentioned previously, the content of the alkaline earth metal halide salt (preferably calcium chloride and magnesium chloride, and especially preferably magnesium chloride) in the potassium fluotantalate powder is, for example, 5-1000 ppm by weight, preferably more than 50 ppm, more preferably 100-850 ppm, still more preferably 100-500 ppm, and most preferably 50-150 ppm or 300-500 ppm. If the content of the alkaline earth metal halide salt in the potassium fluotantalate powder is too high, the alkaline earth metal obtained by reduction cannot be completely converted into an oxide, and this excess alkaline earth metal will corrode the reduction vessel, shortening the service life of the reduction vessel. Therefore, from the perspective of extending the service life of the reduction vessel, the upper limit of the alkaline earth metal halide salt is preferably 1000 ppm.

[0027] Preferably, in step (2), the evacuation and inert gas such as argon is repeated several times, for example 2-3 times, to remove as much air as possible from the reduction vessel, reduce the corrosion of the metal reduction vessel by air, and reduce the adverse effects of air on the tantalum powder. In order to carry the water vapor, acid gas and other gases released during the heating and melting process by argon, and to timely remove them from the reduction vessel, reduce the adverse effects of the reduction, preferably, the inert gas flow rate is kept at 20-100 liters per minute, which can better remove water vapor and acid gas and the like. In order to ensure its complete melting and improve the viscosity of the dilute salt, so that the stirring is more smooth, the dilute salt is preferably heated to a temperature of more than 80°C above its melting point, preferably more than 150°C, more preferably more than 200°C. Preferably, after sufficient melting, it is also heat preserved, for example, heat preserved for 30 minutes. The dilute salt is preferably stirred after being heated to the target temperature, in order to mix thoroughly and keep the temperature uniform. There is no special requirement for the stirring conditions. Preferably, the stirring of the melted dilute salt is continued, preferably until the end of the aging.

[0028] In step (3), the addition of the potassium fluorotantalate powder is repeated in several portions (e.g. 3 to 20 portions) in order to reduce the concentration of the potassium fluorotantalate in the dilution salt. The amount of potassium fluorotantalate powder added at each portion and the number of portions is not limited. However, the inventors have found that the amount of potassium fluorotantalate powder added at each portion is related to the target specific surface area of the tantalum powder to be produced. If a tantalum powder with a high specific surface area is to be produced, the amount of potassium fluorotantalate powder added at each portion can be reduced, so that the potassium fluorotantalate is reduced at a lower concentration. If a tantalum powder with a low specific surface area is to be produced, the amount of potassium fluorotantalate powder added at each portion can be increased. That is, the present application allows a good control of the specific surface area of the tantalum powder. Of course, regardless of the number of portions in which the potassium fluorotantalate powder is added, the remaining amount of sodium is added at the last portion of the addition of the metal sodium, in order to ensure that the potassium fluorotantalate is completely reduced. Preferably, in this step, the temperature in the reduction vessel is controlled to be above the melting point of the mixture of the dilution salt and the potassium fluorotantalate powder, e.g. 80°C to 400°C above the melting point, preferably 250°C to 350°C above the melting point. It is well understood by the skilled person that the temperature at which the potassium fluorotantalate powder and the dilution salt are simultaneously molten can be different from the melting point of the dilution salt and from the melting point of the potassium fluorotantalate. The "melting point" of the mixture (also called apparent melting point) is different when the proportions of the two components are different, but it can be found in the phase diagram data. Preferably, the temperature is increased after each portion of the potassium fluorotantalate powder is added. Preferably, in order to obtain a more homogeneous tantalum powder, the amount of the high temperature metal sodium added before the last portion of the metal sodium is added is such that 70% to 95% of the potassium fluorotantalate of the potassium fluorotantalate powder added at the last portion is reduced. More preferably, the amount of the high temperature metal sodium added before the last portion of the metal sodium is added is such that 70% to 85% of the potassium fluorotantalate of the potassium fluorotantalate powder added at the last portion is reduced. Using such an addition mode, it is possible to avoid that an excess of metal sodium reacts with the potassium fluorotantalate added at the last portion too early (i.e. before the mixture is molten).

[0029] In step (4), preferably, the aging of the tantalum powder is performed by continuing the heating of the tantalum powder after the reduction is finished. Preferably, the heating is continued for 0.5 to 5 hours, preferably 2 to 3 hours. Preferably, the temperature in the reaction vessel is controlled to be the same as before the addition of the metal sodium in step (3). In this step, the excess metal sodium is carried out of the reduction vessel by the argon gas and separated from the tantalum powder.

[0030] Preferably, in step (3) and / or (4), an inert gas, e.g. argon, is continuously flown through the reduction vessel. Preferably, in step (5), the reduction vessel is kept under positive pressure until the mixture is taken out of the reduction vessel.

[0031] Preferably, the separating the tantalum powder in step (5) comprises: stopping stirring, then cooling to room temperature while keeping the reducing reaction container at positive pressure by passing argon, obtaining a mixture containing halide and tantalum powder, taking the mixture out of the reducing container, separating and removing part of the by-products not wrapping the tantalum powder, further separating the by-products by water and acid washing, purifying by washing and drying, and obtaining the final tantalum powder.

[0032] After step (5), the inventors calculated the yield of the tantalum powder and found that the yield of the tantalum powder was improved compared to the prior art.

[0033] Preferably, the method of the present application further comprises step (6) after step (5): water washing and / or acid washing, heat treatment such as high-temperature high-vacuum heat treatment (or high-temperature high-vacuum heat treatment after the sintering assisted by molten salt according to the patent CN114210973B invention), oxygen reduction, acid washing, and then separating the tantalum powder by, for example, filtering, drying, to obtain a tantalum powder suitable for making high-reliability tantalum capacitors. These treatments are all processes known in the prior art. In other words, these treatments can use any process known in the prior art. For example, the high-temperature high-vacuum heat treatment and passivation here can use the methods provided in patents CN201110039272.9, CN201120077798.1, CN201120077680.9, CN201120077305.4, etc., the oxygen reduction can use the methods provided in patents CN201420777210.7, CN201420777210.7, the acid washing can use the methods provided in patents CN201210548101.3, CN201280077499.5, CN201210548008.2, etc.

[0034] In the present application, N, P and / or B elements can also be doped into the tantalum powder after step (5) and / or (6). Of course, raw materials containing these elements can also be used directly. These elements can also be added in the aforementioned high-temperature high-vacuum heat treatment step. It is particularly preferred to add P elements. Adding P elements can increase the specific capacity, as long as the total amount of P doping is controlled, the effect of increasing the specific capacity is the same regardless of when the addition is made. These can be carried out in a conventional manner in the prior art, and will not be described in detail.

[0035] The obtained product tantalum powder was pressed into a block, sintered, and energized under high pressure conditions, and the electrical properties of the energized block were tested, and it was found that the energized block had a lower leakage current.

[0036] According to any aspect of the present application, the obtained product tantalum powder has the advantages of low oxygen content, small leakage current, larger specific capacity and / or higher breakdown voltage. Moreover, the yield of the tantalum powder is higher than that of the prior art. In particular, the present application has the advantage of enabling the product tantalum powder to have a low oxygen content.

[0037] The tantalum powder is pressed into a block, sintered, and the electrical properties of the energized block are tested. The energized block has a lower leakage current. Under the same conditions, the tantalum powder produced by the present application has a greater specific capacitance, a higher breakdown voltage, and / or a lower leakage current than the same grade of tantalum powder produced by other methods after being energized. Thus, the tantalum powder produced by the present application results in an improvement in the leakage current of a tantalum capacitor.

[0038] Without being bound by theory, the inventors believe that the reason for the excellent results achieved by the present application is as follows: the use of potassium fluorotantalate powder containing a small amount of an alkaline earth metal halide salt for the reduction to produce the tantalum powder, the sodium metal reduces both the potassium fluorotantalate and the alkaline earth metal halide salt, and the resulting alkaline earth metal reduces the tantalate, reducing the oxygen content of the final tantalum powder. In this way, the leakage current of the tantalum powder is reduced, and the electrical properties are improved. Also, the reduction of the tantalate to metallic tantalum deposits on the surface of the tantalum powder, and the yield of the tantalum powder is increased. BRIEF DESCRIPTION OF DRAWINGS

[0039] The following drawings are included to provide a better understanding of the present application. These drawings are illustrative only and are not intended to limit the scope of the present application.

[0040] Figure 1 shows a scanning electron micrograph of tantalum powder produced according to one embodiment of the present application.

[0041] This figure illustrates that the resulting tantalum powder has a more uniform particle size, and the particles are smooth and have a larger sintering neck. DETAILED DESCRIPTION

[0042] In order to further illustrate the present application, the preferred embodiments of the present application are described in detail below with reference to the following examples. It is apparent to those skilled in the art that the objects, features and advantages of the present application can be clearly understood from the following detailed description of the preferred embodiments. However, the following description is merely intended to further illustrate the features and advantages of the present application, and is not intended to limit the present application. In the examples, the specific conditions are not specified, and the conventional conditions are used. The reagents or instruments used are not specified, and are conventional products that can be obtained commercially.

[0043] For the purposes of the present specification, all numbers expressing quantities of ingredients, reaction conditions, and so forth, are to be understood as being modified in all instances by the term "about", unless otherwise indicated. Accordingly, the numerical parameters given in the description and claims are approximations only, and thus can vary by a small amount depending upon the desired property sought to be obtained by the present application. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.

[0044] The analysis of the impurity content in the tantalum powder was performed according to Chinese Standard GB / T 15076.1-15076.15, and the physical properties were performed according to the provisions of the industry standard YS / T 573-2015. The test of the electrical properties of the tantalum powder was performed according to the provisions of Chinese Standard GB / T 3137 (30% sulfuric acid solution was used).

[0045] Example 1

[0046] A potassium fluotantalate powder containing 50 ppm of magnesium chloride, NaCl as a diluent, and metallic sodium were provided as raw materials. The metallic sodium was heated to a high temperature of 180°C in advance for standby use.

[0047] 100 kg of sodium chloride (NaCl) was loaded into a reduction vessel, the reduction vessel was vacuumed and then filled with argon to 0.10 MPa, and the vacuuming and argon filling were repeated twice. The reduction vessel was placed in a heating furnace and heated, argon was introduced to flow at a flow rate of 40 L / min, and the temperature was raised to 920°C to start stirring, and the temperature was maintained for 30 min. Then, 15 kg of potassium fluotantalate powder was added, and after the temperature was raised to 920°C, 4.0 kg of metallic sodium was added for reduction; the temperature was raised and reduction was repeated 7 times. After the addition of potassium fluotantalate for the eighth time, 8.20 kg of metallic sodium was added for reduction. After the reduction was completed, the tantalum powder was aged at 920°C for 180 min under the condition of argon flow, and then the stirring was stopped, the pressure in the reaction vessel was maintained at 0.10 MPa, and the temperature was cooled to room temperature. The mixture was taken out of the reduction vessel, and part of the by-products not wrapped in tantalum powder was separated and removed, and then the by-products were further separated by water pickling, washed and purified, and dried to obtain high-purity tantalum powder. The oxygen content of the high-purity tantalum powder was analyzed, the yield of the tantalum powder was calculated, and the measured results are listed in Table 1.

[0048] Then, the tantalum powder was doped with 50 ppm of P, and high-temperature high-vacuum heat treatment was performed at 1450°C and a pressure of less than 5.0 x 10 -3 Pa for 1.0 h, and then oxygen reduction and acid pickling were performed to obtain the final tantalum powder. The final tantalum powder was made into an anode block according to the anode block mass, pressing density, anode block sintering temperature, and sintering time specified in Table 1, and other conditions were according to the requirements of the aforementioned GB / T 3137, the anode block was energized at 150 V, and then the electrical properties were tested according to the requirements of the aforementioned GB / T 3137, and the measured results are listed in Table 2.

[0049] Example 2

[0050] A potassium fluotantalate powder containing 50 ppm of calcium chloride, NaCl as a diluent, and metallic sodium were provided as raw materials. The metallic sodium was heated to a high temperature of 180°C in advance for standby use.

[0051] A 100 kg of sodium chloride (NaCl) was charged into a reduction vessel, the reduction vessel was vacuumed and then filled with argon to 0.10 MPa, and the vacuuming and filling with argon 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, and the temperature was raised to 920°C, and the stirring was started, and the temperature was maintained for 30 minutes. Then, 15 kg of potassium fluotantalate powder was added, and after the temperature was raised to 920°C, 4.0 kg of metallic sodium was added for reduction; the temperature raising and reduction were repeated 7 times. After the potassium fluotantalate was added for the 8th time, 8.20 kg of metallic sodium was added for reduction. After the reduction was completed, the tantalum powder was aged at 920°C for 180 minutes under the condition that argon was introduced at a flow rate of 40 L / min, and then the stirring was stopped, and the pressure in the reaction vessel was maintained at 0.10 MPa, and the temperature was cooled to room temperature. The mixture was taken out of the reduction vessel, and the by-products which were not coated with tantalum powder were separated and removed, and then the by-products were separated, washed, purified, and dried by acid washing, and high-purity tantalum powder was obtained. The oxygen content of the high-purity tantalum powder was analyzed, the yield of the tantalum powder was calculated, and the measured results are shown in Table 1.

[0052] Then, the tantalum powder was mixed with 50 ppm of P, and high-temperature high-vacuum heat treatment was performed at 1450°C and a pressure of less than 5.0 x 10 -3 Pa for 1.0 hour, and then oxygen reduction and acid washing were performed, and the final tantalum powder was obtained. The final tantalum powder was used to produce an anode block according to the anode block mass, the pressing density, the anode block sintering temperature, and the sintering time shown in Table 1, and other conditions were in accordance with the requirements of the aforementioned GB / T3137, the anode block was energized at 150 V, and then the electrical properties were tested according to the requirements of the aforementioned GB / T3137, and the measured results are shown in Table 2.

[0053] Comparative Example 1

[0054] A powder composed only of potassium fluotantalate, NaCl as a diluent, and metallic sodium as a raw material were provided. The metallic sodium was heated to a high temperature of 180°C in advance.

[0055] A 100 kg of sodium chloride (NaCl) was charged into a reduction vessel, the reduction vessel was vacuumed and then filled with argon to 0.10 MPa, the process of vacuuming and then filling with argon to 0.10 MPa was repeated twice. The reduction vessel was placed into a heating furnace and heated, argon was introduced at a flow rate of 40 L / min, the temperature was raised to 920°C and stirring was started, and the temperature was maintained for 30 minutes. Then 15 kg of potassium fluotantalate was added, after the temperature was raised to 920°C, 4.0 kg of metallic sodium was added for reduction. The process of raising temperature and reduction was repeated 7 times. After the 8th addition of potassium fluotantalate, 8.20 kg of metallic sodium was added for reduction. After the reduction was completed, the tantalum powder was aged at 920°C for 180 minutes under the condition of argon flow, then the stirring was stopped, the pressure of the reaction vessel was maintained at 0.10 MPa, and the temperature was cooled to room temperature. The mixture was taken out of the reduction vessel, the by-products which were not wrapped with tantalum powder were separated and removed, then the by-products were further separated by water pickling, washed, purified and dried, and high purity tantalum powder was obtained. The oxygen content of the high purity tantalum powder was analyzed, the yield of the tantalum powder was calculated, and the results were listed in Table 1.

[0056] Then, the tantalum powder was mixed with 50 ppm of P, high temperature and high vacuum heat treatment was carried out at 1450°C and under a pressure of less than 5.0 x 10 -3 Pa for 1.0 hour, then oxygen reduction and acid pickling were carried out, and the final tantalum powder was obtained. The final tantalum powder was made into an anode block according to the anode block mass, pressing density, anode block sintering temperature and sintering time specified in Table 1, and other conditions according to the requirements of the aforementioned GB / T3137, the anode block was energized at 150 V, and then the electrical performance was tested according to the requirements of the aforementioned GB / T3137, and the results were listed in Table 2.

[0057] Example 3

[0058] A powder of potassium fluotantalate containing 100 ppm of magnesium chloride, KCl and KF as diluents, and metallic sodium as raw material were provided. The metallic sodium was heated to a high temperature of 220°C in advance.

[0059] A 50 kg of potassium chloride (KCl) and 50 kg of potassium fluoride (KF) were charged into a reduction vessel, the reduction vessel was vacuumed and then filled with argon to 0.10 MPa, and the vacuuming and filling with argon were repeated twice. The reduction vessel was placed in a heating furnace and heated, and argon was introduced at a flow rate of 60 L / min, and the stirring was started at 900°C, and the temperature was maintained for 30 minutes. Then, 10 kg of potassium fluorotantalate powder was added, and after the temperature was raised to 900°C, 2.6 kg of sodium metal was added for reduction; this was repeated 14 times. After the addition of the potassium fluorotantalate powder in the 15th time, 8.20 kg of sodium metal was added for reduction. After the reduction was completed, the tantalum powder was aged at 900°C for 120 minutes under the condition of argon flow, and then the stirring was stopped, and the pressure in the reaction vessel was maintained at 0.10 MPa, and the temperature was cooled to room temperature. The mixture was taken out of the reduction vessel, and the by-products not wrapped in the tantalum powder were separated and removed, and further the by-products were separated by washing with water and acid, and washed and purified, and dried to obtain high-purity tantalum powder. The oxygen content of the high-purity tantalum powder was analyzed, and the yield of the tantalum powder was calculated, and the results are shown in Table 1.

[0060] Then, the tantalum powder was mixed with 60 ppm of P, and high-temperature high-vacuum heat treatment was performed at 1400°C and a pressure of less than 5.0 x 10 -3 Pa for 1.0 hour, and then oxygen reduction and acid washing were performed to obtain the final tantalum powder. The final tantalum powder was made into an anode block according to the anode block mass, the pressing density, the anode block sintering temperature, and the sintering time specified in Table 1, and other conditions were in accordance with the requirements of the aforementioned GB / T3137, and the obtained anode block was energized at 100 V, and then the electrical properties were tested in accordance with the requirements of the aforementioned GB / T3137, and the results are shown in Table 2.

[0061] Example 4

[0062] A potassium fluorotantalate powder containing 850 ppm of magnesium chloride, KCl and KF as diluents, and sodium metal as a raw material were provided. The sodium metal was heated to a high temperature of 220°C in advance.

[0063] 50 kg of potassium chloride (KCl) and 50 kg of potassium fluoride (KF) were charged into a reduction vessel, the reduction vessel was vacuumed and then filled with argon to 0.10 MPa, and the vacuuming and filling with argon were repeated twice. The reduction vessel was placed in a heating furnace and heated, and argon was introduced at a flow rate of 60 L / min, and the stirring was started when the temperature was raised to 900°C, and the temperature was maintained for 30 minutes. Then, 10 kg of potassium fluorotantalate powder was added, and after the temperature was raised to 900°C, 2.6 kg of sodium metal was added for reduction; the temperature was raised and the reduction was repeated 14 times. After the addition of potassium fluorotantalate powder in the 15th time, 8.20 kg of sodium metal was added for reduction. After the reduction was completed, the tantalum powder was aged at 900°C for 120 minutes under the condition of argon flow, and then the stirring was stopped, and the pressure of the reaction vessel was maintained at 0.10 MPa, and the temperature was cooled to room temperature. The mixture was taken out of the reduction vessel, and the by-products not wrapped in tantalum powder were separated and removed, and then the by-products were further separated by water washing, and the tantalum powder was purified by washing and drying, and high-purity tantalum powder was obtained. The oxygen content of the high-purity tantalum powder was analyzed, the yield of the tantalum powder was calculated, and the measured results are shown in Table 1.

[0064] Then, the tantalum powder was doped with 60 ppm of P, and high-temperature high-vacuum heat treatment was performed at 1400°C and a pressure of less than 5.0 x 10 -3 Pa for 1.0 hour, and then oxygen reduction and acid washing were performed to obtain the final tantalum powder. The final tantalum powder was made into an anode block according to the anode block mass, the pressing density, the anode block sintering temperature, and the sintering time specified in Table 1, and other conditions were according to the requirements of the aforementioned GB / T3137, the anode block was energized at 100 V, and then the electrical performance was tested according to the requirements of the aforementioned GB / T3137, and the measured results are shown in Table 2.

[0065] Comparative Example 2

[0066] A powder composed of potassium fluorotantalate, KCl and KF as diluents, and sodium metal as raw material were provided. The sodium metal was heated to a high temperature of 220°C in advance.

[0067] A 50 kg of potassium chloride (KCl) and 50 kg of potassium fluoride (KF) were charged into a reduction vessel, the reduction vessel was vacuumed and then filled with argon to 0.10 MPa, and the vacuuming and filling with argon were repeated twice. The reduction vessel was placed in a heating furnace and heated, and argon was introduced at a flow rate of 60 L / min, and the stirring was started at a temperature of 900°C, and the temperature was maintained for 30 minutes. Then, 10 kg of potassium fluorotantalate was added, and after the temperature was increased to 900°C, 2.6 kg of sodium metal was added for reduction; the temperature was increased and the reduction was repeated 14 times. After the addition of potassium fluorotantalate in the 15th time, 8.20 kg of sodium metal was added for reduction. After the reduction was completed, the tantalum powder was aged at 900°C for 120 minutes under the condition of argon flow, and then the stirring was stopped, and the pressure of the reaction vessel was maintained at 0.10 MPa, and the temperature was cooled to room temperature. The mixture was taken out of the reduction vessel, and the by-products not wrapped in tantalum powder were separated and removed, and then the by-products were further separated by washing with water and acid, and washed and purified, and dried to obtain high-purity tantalum powder. The oxygen content of the high-purity tantalum powder was analyzed, and the yield of the high-purity tantalum powder from the reduction of the input tantalum was calculated, and the measured results are shown in Table 1.

[0068] Then, the tantalum powder was doped with 60 ppm of P, and high-temperature high-vacuum heat treatment was performed at 1400°C and a pressure of less than 5.0 x 10 -3 Pa for 1.0 hour, and then oxygen reduction and acid washing were performed to obtain the final tantalum powder. The final tantalum powder was made into an anode block according to the anode block mass, pressing density, anode block sintering temperature, and sintering time specified in Table 1, and other conditions were according to the requirements of the aforementioned GB / T3137, and the anode block was energized at 100 V, and then the electrical performance was tested according to the requirements of the aforementioned GB / T3137, and the measured results are shown in Table 2.

[0069] Example 5

[0070] A potassium fluorotantalate powder containing 200 ppm of magnesium chloride, KCl and KF as diluents, and sodium metal as a raw material were provided. The sodium metal was heated to a high temperature of 180°C in advance.

[0071] A 100 kg of potassium chloride (KCl) and 100 kg of potassium fluoride (KF) were charged into a reduction vessel, the reduction vessel was vacuumed and then filled with argon to 0.10 MPa, and the vacuuming and filling with argon were repeated twice. The reduction vessel was placed in a heating furnace and heated, and argon was introduced at a flow rate of 70 L / min, and the stirring was started at 900°C, and the temperature was maintained for 30 minutes. Then, 8 kg of potassium fluorotantalate powder was added, and after the temperature was increased to 920°C, 2.15 kg of sodium metal was added for reduction; the temperature was increased and the reduction was repeated 9 times. After the addition of the potassium fluorotantalate powder for the 10th time, 5.0 kg of sodium metal was added for reduction. After the reduction was completed, the tantalum powder was aged at 900°C for 60 minutes under the condition of argon flow, and then the stirring was stopped, and the pressure of the reaction vessel was maintained at 0.10 MPa, and the temperature was cooled to room temperature. The mixture was taken out of the reduction vessel, and the by-products not wrapped in the tantalum powder were separated and removed, and then the by-products were further separated by washing with water and acid, and washed and purified, and dried to obtain high-purity tantalum powder. The oxygen content of the high-purity tantalum powder was analyzed, the yield of the tantalum powder was calculated, and the measured results are shown in Table 1.

[0072] Then, the tantalum powder was doped with 100 ppm of P, and high-temperature high-vacuum heat treatment was performed at 1230°C and a pressure of less than 5.0 x 10 -3 Pa for 1.0 hour, and then oxygen reduction and acid washing were performed to obtain the final tantalum powder. The final tantalum powder was made into an anode block according to the anode block mass, pressing density, anode block sintering temperature, and sintering time specified in Table 1, and other conditions were according to the requirements of the aforementioned GB / T3137, the anode block was energized at 60 V, and then the electrical performance was tested according to the requirements of the aforementioned GB / T3137, and the measured results are shown in Table 2.

[0073] Comparative Example 3

[0074] A powder composed of potassium fluorotantalate, KCl and KF as diluents, and sodium metal as a raw material were provided. The sodium metal was heated to a high temperature of 180°C in advance for use.

[0075] A 100 kg of potassium chloride (KCl) and 100 kg of potassium fluoride (KF) were charged into a reduction vessel, the vessel was vacuumed and then filled with argon to 0.10 MPa, and the process was repeated twice. The vessel was placed in a heating furnace and heated to 900°C under argon flow at 70 L / min, and stirring was started. After 30 minutes of temperature maintenance, 8 kg of potassium fluorotantalate powder was added, and after the temperature rose to 920°C, 2.15 kg of sodium metal was added for reduction. This process was repeated nine times. In the tenth time, 5.0 kg of sodium metal was added for reduction after the addition of potassium fluorotantalate powder. After the reduction was completed, the tantalum powder was aged at 900°C for 60 minutes under argon flow, and then the stirring was stopped, the pressure of the reaction vessel was maintained at 0.10 MPa, and the vessel was cooled to room temperature. The mixture was removed from the vessel, and the by-products that were not coated with tantalum powder were separated. The by-products were further separated by washing with acid, washed and purified, and dried to obtain high-purity tantalum powder. The oxygen content of the high-purity tantalum powder was analyzed, and the yield of high-purity tantalum powder from the reduction of tantalum was calculated. The results are shown in Table 1.

[0076] Then, the tantalum powder was mixed with 100 ppm of P, and high-temperature high-vacuum heat treatment was performed at 1230°C and a pressure of less than 5.0 x 10 -3 Pa for 1.0 hour, and then oxygen reduction and acid washing were performed to obtain the final tantalum powder. The final tantalum powder was used to make anodes according to the anode block mass, pressing density, anode block sintering temperature, and sintering time specified in Table 1, and other conditions were in accordance with the requirements of GB / T3137. The anodes were energized at 60 V, and then the electrical properties were tested according to the requirements of GB / T3137. The results are shown in Table 2.

[0077] Example 7

[0078] Potassium fluorotantalate powder containing 300 ppm of magnesium chloride, KCl and KF as diluents, and sodium metal as raw material were provided. The sodium metal was heated to a high temperature of 150°C in advance.

[0079] A 100 kg of potassium chloride (KCl) and 100 kg of potassium fluoride (KF) were charged into a reduction vessel, the reduction vessel was vacuumed and then filled with argon to 0.10 MPa, and the vacuuming and filling with argon were repeated twice. The reduction vessel was placed in a heating furnace and heated, and argon was introduced at a flow rate of 90 L / min, and the stirring was started at 900°C, and the temperature was maintained for 30 minutes. Then, 5 kg of potassium fluorotantalate powder was added, and after the temperature was increased to 890°C, 1.3 kg of sodium metal was added for reduction; the temperature was increased and the reduction was repeated 11 times. After the 12th addition of potassium fluorotantalate powder, 3.8 kg of sodium metal was added for reduction. After the reduction was completed, the tantalum powder was aged at 890°C for 60 minutes under the condition of argon flow, and then the stirring was stopped, and the pressure of the reaction vessel was maintained at 0.10 MPa, and the temperature was cooled to room temperature. The mixture was taken out of the reduction vessel, and the by-products not wrapped in tantalum powder were separated and removed, and then the by-products were further separated by water washing, and the tantalum powder was washed, purified, and dried to obtain high-purity tantalum powder. The oxygen content of the high-purity tantalum powder was analyzed, the yield of the tantalum powder was calculated, and the measured results are shown in Table 1.

[0080] Then, the tantalum powder was mixed with 150 ppm of P, and high-temperature high-vacuum heat treatment was performed at 1150°C and a pressure of less than 5.0 x 10 -3 Pa for 1.0 hour, and then oxygen reduction and acid washing were performed to obtain the final tantalum powder. The final tantalum powder was made into an anode block according to the anode block mass, the pressing density, the anode block sintering temperature, and the sintering time specified in Table 1, and other conditions were according to the requirements of the aforementioned GB / T3137, the anode block was energized at 28 V, and then the electrical performance was tested according to the requirements of the aforementioned GB / T3137, and the measured results are shown in Table 2.

[0081] Comparative Example 4

[0082] A powder composed of potassium fluorotantalate, KCl and KF as diluents, and sodium metal as a raw material were provided. The sodium metal was heated to a high temperature of 150°C in advance for use.

[0083] 100 kg of potassium chloride (KCl) and 100 kg of potassium fluoride (KF) are loaded into a reduction vessel, the reduction vessel is vacuumed and then filled with argon to 0.10 MPa, and the vacuuming and argon filling are repeated twice. The reduction vessel is placed in a heating furnace and heated, argon is introduced at a flow rate of 90 L / min, and the stirring is started when the temperature is raised to 900℃, and the temperature is kept for 30 minutes. Then 8 kg of potassium fluorotantalate powder is added, and after the temperature is raised to 890℃, 1.3 kg of sodium metal is added for reduction; the temperature is raised and reduction is repeated 11 times. In the 12th time, after the potassium fluorotantalate powder is added, 3.8 kg of sodium metal is added for reduction. After the reduction is completed, the tantalum powder is aged at 890℃ for 60 minutes under the condition of argon flow, and then the stirring is stopped, the pressure of the reaction vessel is maintained at 0.10 MPa, and the material is cooled to room temperature. The mixture is taken out of the reduction vessel, and part of the by-products not wrapped in tantalum powder is separated and removed, and then the by-products are further separated by water pickling, washed and purified, and dried to obtain high-purity tantalum powder. The oxygen content of the high-purity tantalum powder is analyzed, the yield of high-purity tantalum powder from the reduction of tantalum is calculated, and the measured results are shown in Table 1.

[0084] Then, the tantalum powder is mixed with 150 ppm of P, and high-temperature high-vacuum heat treatment is carried out at 1150℃ and a pressure of less than 5.0×10 -3 Pa for 1.0 hour, and then oxygen reduction and acid pickling are carried out to obtain the final tantalum powder. The final tantalum powder is made into an anode block according to the anode block mass, pressing density, anode block sintering temperature and sintering time specified in Table 1, and other conditions are according to the requirements of the aforementioned GB / T3137, the anode block is energized under the condition of 28V, and then the electrical performance is tested according to the requirements of the aforementioned GB / T3137, and the measured results are shown in Table 2.

[0085] Table 1 Analysis results of impurity yield of high-purity tantalum powder

[0086] Table 2 Analysis results of electrical performance of finished tantalum powder

[0087] As can be seen from Table 1, the yield of tantalum powder is increased, and the oxygen content of tantalum powder is reduced, which is beneficial to obtaining a low leakage current product after subsequent processing.

[0088] As can be seen from Table 2, the tantalum powder prepared by the present application has higher breakdown voltage and lower leakage current, and the electrical performance of the tantalum powder is improved.

Claims

1. Potassium fluotantalate powder for use as a raw material in the production of tantalum powder by the sodium reduction potassium fluotantalate method, which powder comprises 5-1000 ppm (preferably 50-1000 ppm, more preferably 100-850 ppm, more preferably 100-500 ppm, more preferably 50-150 ppm and / or 300-500 ppm) of an alkaline earth metal halogen salt selected from the group consisting of halogen salts of magnesium and / or halogen salts of calcium, such as magnesium chloride, and a remainder of potassium fluotantalate.

2. A method for producing tantalum powder by a sodium reduction potassium fluotantalate method, characterized by The tantalum powder according to claim 1 is used as a raw material.

3. A method for the production of tantalum powder for capacitors by the sodium reduction potassium fluotantalate process, comprising the steps of: (1) providing potassium fluotantalate powder, dilution salt (preferably selected from the group consisting of alkali metal halides), and liquid sodium metal as raw materials, wherein the potassium fluotantalate powder contains 5-1000 ppm of an alkaline earth metal halogen salt, (2) charging the dilution salt into a reduction vessel, evacuating the vessel, then introducing an inert gas such as argon, then heating the dilution salt in the reduction vessel to melting while the inert gas is kept flowing (at a flow rate of 20-100 liters / minute), (3) adding a portion of the potassium fluotantalate powder into the reduction vessel and monitoring the temperature to ensure that the mixture of potassium fluotantalate powder and dilution salt is melted, then adding liquid sodium metal to reduce the portion of potassium fluotantalate, repeating this several times (e.g. 3-10 times) until all of the potassium fluotantalate powder and sodium metal raw materials are used up, (4) after the reduction is complete, performing an aging of the tantalum powder, and (5) then, separating the tantalum powder.

4. The method according to claim 3, wherein after step (5) further comprising step (6): after the salt bath heat treatment and / or agglomeration heat treatment of the tantalum powder, the oxygen reduction treatment of the metallic magnesium chips and further acid pickling and drying, the product tantalum powder is obtained.

5. The method according to claim 3 or 4, wherein in step (1) the sodium metal is preheated to more than 150°C, such as 180°C-500°C, more preferably 200-350°C, more preferably 200-260°C, more preferably 190°C-240°C, such as 210°C.

6. The method according to any one of claims 3-5, wherein in step (1) the amount of sodium metal is made to be in excess of the theoretical amount required for the complete reduction of the potassium fluotantalate, such as 1-3% excess, preferably 1.5-2.5% excess.

7. The method according to any one of claims 3-6, wherein in step (2) the molten dilution salt is stirred, preferably the dilution salt is heated to a temperature more than 80°C above its melting point, preferably more than 150°C, more preferably more than 200°C.

8. The method according to any one of claims 3-7, wherein the melting of the mixture of dilution salt and potassium fluotantalate powder is ensured by controlling the temperature in the reduction vessel to be more than 80°C-400°C, preferably more than 250°C-350°C, above the melting point of the mixture.

9. The method according to any one of claims 3-8, wherein the amount of metallic sodium added each time is such that 70-95%, more preferably 70-85%, of the potassium fluotantalate in the just added potassium fluotantalate powder is reduced prior to the last addition of metallic sodium.

10. Use of a potassium fluotantalate powder as defined in claim 1 or a tantalum powder produced by the method according to any one of claims 2-9 and its use in capacitors.

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