Process for the production of capacitor-grade tantalum powder from alkali earth metal reduced tantalum oxide

Abstract

The invention relates to a method for producing tantalum powder for capacitors from alkaline earth metal reduced tantalum oxide. In particular, the invention relates to a method for producing tantalum powder from alkaline earth metal reduced tantalum oxide, characterized in that the method comprises a reduction and a holding process in a hydrogen-containing atmosphere, preferably pure hydrogen or a mixture of hydrogen and an inert gas; and / or the hydrogen-containing atmosphere is obtained by introducing a gaseous hydrogen-containing atmosphere or by adding a hydrogen-containing substance and allowing it to release hydrogen.

Description

TECHNICAL FIELD

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

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

[0003] Currently, the main methods for industrial production of capacitor-grade tantalum powder are sodium reduction of potassium fluorotantalate, magnesium reduction of tantalum oxide, and tantalum ingot hydrogenation. The sodium reduction of potassium fluorotantalate method can easily produce tantalum powder with high specific capacity, but the problem is that the tantalum powder generally has low voltage resistance. The tantalum ingot hydrogenation method produces tantalum powder with excellent voltage resistance, but the problem is that the specific capacity of the tantalum powder is generally low. In order to continuously improve the voltage resistance of tantalum powder and increase the specific capacity of tantalum powder, the magnesium reduction of tantalum oxide method has been successfully developed and continuously improved. The magnesium reduction of tantalum oxide method has obvious advantages in producing capacitor-grade tantalum powder with improved specific capacity and voltage resistance by changing the state of the reactants.

[0004] CN114192791B discloses a method for producing capacitor-grade tantalum powder by reducing tantalum oxide with alkaline earth metals. In this method, halides of alkali metals or alkaline earth metals are added during the reduction process, and the reduction is carried out at a high temperature of 700℃ or above in a heating furnace filled with inert gas using an excess amount of alkaline earth metals. After the reduction is completed, the excess alkaline earth metals are separated from the tantalum-containing material, and then the material is further sintered at a high temperature of 750℃ or above. However, this method has the problem of using a large amount of alkaline earth metals, which may cause a fire when the furnace is discharged after reduction, posing a safety hazard. Moreover, this process is relatively complex and requires a separate sintering step, resulting in high energy consumption.

[0005] CN1308566A (application number 99808374.7), CN105033283A (application number 201510310262.2), and CN1251325A also disclose methods for reducing tantalum oxide with alkaline earth metals (including magnesium vapor) or rare earth metals to produce tantalum powder. However, the tantalum powder produced by these methods has a large specific surface area, high activity, and poor resistance to burning. The capacitor-grade tantalum powder produced has poor specific capacity whether it is breakdown voltage or high-voltage energized, and does not significantly improve the voltage resistance of capacitor-grade tantalum powder.

[0006] Existing technologies include a self-propagating high-temperature synthesis (SHS) method for preparing tantalum powder. However, this method requires temperatures above 2000°C, and the reaction is too rapid, making it difficult to control and placing excessive demands on the process equipment. Furthermore, the resulting tantalum powder is not uniform and cannot meet the requirements for manufacturing high-reliability capacitors.

[0007] Unbound by conventional theories, the inventors, after extensive research, discovered that existing tantalum powder preparation processes, due to the use of large amounts of alkaline earth metals, pose a safety hazard of fire hazards caused by these metals. Furthermore, the processes are complex and energy-intensive. Moreover, the overall electrical performance is not ideal. Summary of the Invention

[0008] One object of the present invention is to provide a method for preparing tantalum powder by reducing tantalum oxide with an alkaline earth metal such as magnesium in a hydrogen-containing atmosphere. The method of producing tantalum powder can reduce the amount of alkaline earth metal added, and also reduces the safety risk of alkaline earth metal ignition when the powder is taken out of the furnace after reduction.

[0009] Another object of the present invention is to provide a method for producing tantalum powder for capacitors that is simple to process, easier to operate and control, and safer. Accordingly, the present invention provides a method for preparing tantalum powder by reducing tantalum oxide with an alkaline earth metal such as magnesium, comprising the following steps:

[0010] (1) Mix tantalum oxide with an excess of alkaline earth metal reducing agent, and simultaneously mix in at least one alkali metal and / or alkaline earth metal halide at 10-200% by weight of tantalum oxide, load into a sealed reaction container, remove the air from the container, and place the container in a heating furnace.

[0011] (2) Raise the temperature of the heating furnace to 700-1000℃ and keep it at that temperature for 1-3 hours to allow tantalum oxide to fully undergo a reduction reaction with the reducing agent;

[0012] (3) After the heat preservation is completed, the temperature of the heating furnace is kept at 600-750℃ (preferably 620-680℃, such as 640℃), the furnace is evacuated, for example, evacuated to below 10Pa, and heat preservation is carried out under negative pressure (for example, heat preservation for 1-10 hours).

[0013] (4) Then, inert gas is introduced into the reaction vessel to maintain positive pressure. The reaction vessel is then cooled to room temperature and passivated to obtain a mixture containing halides and tantalum powder.

[0014] (5) Separate the tantalum powder from the obtained mixture, for example by washing with water, acid washing, filtration, and drying.

[0015] In step (1), after the evacuation of air, the container is provided with a hydrogen-containing gas, for example by introducing a hydrogen-containing gas or by adding a liquid or solid (preferably solid) hydrogen-containing substance and allowing it to release hydrogen. Preferably, in the latter case, the hydrogen-containing substance is separated from other raw materials such as the powder of the tantalum oxide, the halide of the alkali metal and / or the alkaline earth metal, for example by placing the hydrogen-containing substance (preferably hydrogen-containing tantalum powder) in a separate crucible.

[0016] Preferably, the hydrogen-containing substance is, for example, a tantalum powder to which hydrogen is adsorbed (also referred to as hydrogen-containing tantalum powder), a hydrogen-containing niobium powder, a hydrogen-containing titanium powder, and a hydrogen-containing compound, and the like, which can release hydrogen at high temperatures.

[0017] The alkaline earth metal reducing agent in step (1) is preferably magnesium, more preferably magnesium particles, and even more preferably magnesium particles having a purity of 3N5 or more (purity of 99.95% or more). The particle size of the magnesium particles is not limited. However, the applicants have found through extensive research that magnesium particles having a particle size of 150 to 4000 μm are more suitable for the present technology, and the tantalum powder obtained by reduction has better pressure resistance. The magnesium particles having a particle size in this range are not only safe during storage and transportation of the metal magnesium, but also facilitate uniform mixing. If the magnesium particles are too fine, they are too active and can easily catch fire; if the magnesium particles are too coarse, they are not conducive to uniform mixing and do not optimize the properties of the tantalum powder. The amount of excess reducing agent refers to the amount that exceeds the theoretical amount required for complete reduction of the tantalum oxide. In general, the theoretical amount required for complete reduction of one kilogram of tantalum oxide is 0.273 kilograms. In the present application, it is preferred that the amount exceeds this theoretical amount by 5 to 50%, preferably by 10 to 48%, more preferably by 10 to 45%, even more preferably by 10 to 15% or by 5 to 10% or by 15 to 20%.

[0018] In step (2), due to the heat generated by reduction, the tantalum powder inevitably sintered to some extent. The presence of the hydrogen-containing gas in the container further intensifies the sintering of the tantalum powder, so that a separate subsequent sintering step can be omitted. Since the prior art often has a separate sintering step, the present application undoubtedly simplifies the process. Moreover, under the conditions described in the present application, sintering and reduction occur simultaneously and in cooperation, making it easier to obtain tantalum powder with improved microstructure.

[0019] The amount of the alkali metal and / or alkaline earth metal halide added in step (1) is preferably 10 to 180% by weight, preferably 25 to 120% by weight, more preferably 70 to 120% by weight or 100 to 180% by weight, and most preferably 15 to 80% by weight, for example 25 to 80% by weight, of the weight of the tantalum oxide. The alkali metal or alkaline earth halide is preferably of analytical purity, and preferably of even higher purity. The alkali metal or alkaline earth halide is preferably in the form of particles. The particle size is not limited, but the applicants have found that particles having a size of 70 μm to 4000 μm are more suitable for the present technology, and the tantalum powder obtained by reduction has better pressure resistance.

[0020] Preferably, the halide of an alkali metal or an alkaline earth metal in step (1) is one or more of NaCl, KCl, KF, KI, and / or MgCl2. The alkali metal halide can be sodium chloride and / or potassium chloride. Preferably, it is a mixture of sodium chloride and potassium chloride, more preferably the mass ratio of sodium chloride to potassium chloride in the mixture is 1:1 to 10, most preferably about 1:1.

[0021] Preferably, one or more compounds containing B, P, and / or N elements can be added in step (1) as additives to dope the tantalum powder. Preferably, the amount of B element added is 1 to 100 ppm, more preferably 20 to 60 ppm; the amount of P element added is 10 to 200 ppm, more preferably 30 to 90 ppm; and the amount of N element added is 300 to 2500 ppm, more preferably 500 to 1200 ppm, in terms of effective elements. It should be understood that although compounds are added, the effective elements are B, P, and / or N, so the amounts mentioned here are calculated in terms of the amounts of B, P, and / or N.

[0022] Preferably, in step (2), the heating furnace is heated to 750 to 1000°C. More preferably, the heating furnace is heated to 900 to 965°C.

[0023] Unlike the inert atmosphere commonly used in the prior art, the hydrogen-containing gas used in step (1) is pure hydrogen gas or a mixture of hydrogen gas and inert gas. The hydrogen gas can be gaseous hydrogen gas or hydrogen gas released by heating other liquid or solid hydrogen-containing substances. Importantly, the hydrogen-containing gas is used as the atmosphere in the present application.

[0024] Although hydrogen gas is a common reducing agent, hydrogen gas cannot reduce tantalum oxide. That is, hydrogen gas cannot act as a reducing agent in the present application. However, the inventors have unexpectedly found that, due to the sintering that is intensified by hydrogen gas during the reduction process, the process can be significantly simplified by omitting the sintering step. Moreover, the introduction of hydrogen-containing gas in the inert atmosphere can reduce the amount of alkaline earth metal added as a reducing agent and can also improve the overall electrical performance of the product.

[0025] Preferably, in step (1), the reaction vessel is kept at a positive pressure. In the reaction vessel, the hydrogen gas partial pressure is more than 0.050 KPa, preferably 0.1 to 200 KPa, more preferably 0.3 to 50 KPa, more preferably 10 to 20 KPa, even more preferably 0.5 to 10 KPa or 10 to 15 KPa, and even more preferably 0.1 to 0.3 KPa. The inventors have found that too low a hydrogen gas partial pressure cannot sufficiently promote the reduction effect, so from this perspective, the hydrogen gas partial pressure is preferably not too low; on the other hand, too high a hydrogen gas partial pressure weakens the improvement in the reduction effect, and from the perspective of ensuring absolute safety with hydrogen, it is preferable to avoid too high a hydrogen gas partial pressure.

[0026] Inert gas generally refers to rare gas, such as helium, neon, and argon. Although nitrogen is sometimes considered as inert gas due to its stable nature, it is generally not considered as inert gas in the field because of its high reduction temperature at which it is very active. However, the inventors have found that a small amount of nitrogen in the above-mentioned inert gas does not harm the inert atmosphere and can also achieve nitrogen doping of the tantalum powder. From the perspective of achieving better nitrogen doping effect of the tantalum powder, when a hydrogen-containing gas (such as pure hydrogen) is mixed with the inert gas in step (1), the nitrogen content can be preferably 0.5-10% based on the total amount of the hydrogen-containing gas and the inert gas.

[0027] In step (3), since the melting point of magnesium is relatively high, the magnesium vapor is difficult to diffuse to the outside of the reactor, but is condensed into a solid in the low-temperature zone of the reactor, thereby achieving separation.

[0028] Preferably, the temperature of the heating furnace in step (3) is 600-750°C. More preferably, the temperature of the heating furnace is raised to 620-680°C, for example, 640°C. Preferably, the heating furnace is evacuated to below 5 Pa, preferably below 0.5 Pa.

[0029] The hydrogen-containing gas in step (1) can be a mixture of hydrogen and inert gas, in which case the inert gas in step (1) and step (4) can be the same or different. Preferably, a positive pressure is maintained in the furnace in step (1) and / or (4). Preferably, a positive pressure is avoided in the reactor in step (3), because if a positive pressure is not conducive to the separation of excess alkaline earth metal, such as magnesium.

[0030] Preferably, the method of the present application further comprises, after step (5), heat treatment such as high-temperature high-vacuum heat treatment (or high-temperature high-vacuum heat treatment after the molten salt assisted sintering according to the invention of patent CN114210973B), oxygen reduction, pickling, and then separating the tantalum powder, for example, by filtration, drying, to obtain a tantalum powder suitable for making high-reliability tantalum capacitors. These treatments are known processes in the prior art. In other words, these treatments can use any known process 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 method provided in patent CN201420777210.7, the pickling can use the method provided in patents CN201210548101.3, CN201280077499.5, CN201210548008.2, etc.

[0031] As an alternative to the incorporation of N, P and / or B elements in step (1), the incorporation of these elements can also be included separately in the present application, for example after step (5). Of course, it is also possible to use raw materials that already contain these elements. It is also possible to add these elements during the aforementioned high-temperature high-vacuum heat treatment step. It is especially preferred to add P elements. The addition of P elements can increase the specific volume, which is the same regardless of when the addition is made, as long as the total amount of P addition is controlled.

[0032] The tantalum powder is pressed and sintered, and the energized block is tested for electrical properties. It is found that the energized block has good overall electrical properties. Therefore, the tantalum powder produced by the present application is more suitable for making high-voltage and high-reliability tantalum capacitors.

[0033] Furthermore, the process of the present application is simple and easy to control. For example, in all steps of the present application, microwaves are not used, nor are excessively high temperatures above 1000℃ used, and the proportion of alkaline earth metals used for reduction is lower. Therefore, the equipment used is relatively simple, and the safety of the tantalum powder preparation process is better.

[0034] Without being bound by general theory, in combination with the theoretical analysis principles of powder liquid phase sintering, the inventors believe that the reason for the excellent effect of the present application is as follows: In step (2), reduction is more likely to occur in the presence of hydrogen in the atmosphere, and sintering is strengthened, making it easier to build a spatial structure suitable for capacitors between tantalum powder particles. The tantalum powder particles are uniform in size, and the particles are smooth, the sintering neck is thick, and there are few ultra-fine particles. Thereafter, the obtained tantalum powder is subjected to high-temperature high-vacuum heat treatment (or high-temperature high-vacuum heat treatment after molten salt assisted sintering according to the patent CN114210973B invention), oxygen reduction, and acid washing treatment, and a tantalum powder suitable for preparing high-voltage and high-reliability capacitors is obtained.

[0035] The "easier to build a spatial structure suitable for capacitors" described herein refers to the absence of ultra-fine pores in the anode block obtained after the obtained tantalum powder is pressed and sintered to make an anode block. These ultra-fine pores are detrimental to electrical properties, especially leakage current and ESR (equivalent series resistance).

[0036] The present application also relates to the tantalum powder obtained by the above method, the anode block made from the tantalum powder, and the use of the tantalum powder and / or anode block in the manufacture of capacitors. BRIEF DESCRIPTION OF DRAWINGS

[0037] The following drawings are provided to better understand the present application. These drawings are exemplary and are not intended to limit the scope of the present application.

[0038] Figure 1 A scanning electron microscope photograph of the tantalum powder obtained according to the present application is given.

[0039] The figure shows that the obtained tantalum powder has more uniform particle size, and the particles are smooth, the sintering neck is thick, and the ultra-fine particles are few. DETAILED DESCRIPTION

[0040] In order to further illustrate the present application, the preferred embodiments of the present application are described below in conjunction with examples, and the purposes, features and advantages of the present application can be obviously seen. However, these descriptions are only for further illustrating the features and advantages of the present application, and are not intended to limit the present application. The specific conditions not mentioned in the examples are carried out according to the conventional conditions. The reagents or instruments not mentioned by the manufacturers are all conventional products that can be commercially available.

[0041] For the purpose of this specification, all numbers expressing quantities of ingredients, reaction conditions, and so forth in the specification and claims are to be understood as being modified in all instances by the term "about", unless otherwise indicated. Accordingly, the numerical parameters given in the following description and attached claims are approximations only, and thus can vary depending upon the desired properties sought to be obtained by the present application, unless otherwise indicated. 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.

[0042] The analysis of the impurity content in the tantalum powder is carried out according to Chinese standard GB / T15076.1-15076.15, and the physical properties are carried out according to the provisions of industry standard YS / T573-2015. The test of the electrical properties of the tantalum powder is carried out according to the provisions of Chinese standard GB / T3137.

[0043] Example 1

[0044] Take 10.0 kg of tantalum oxide, add 3.1 kg of metal magnesium particles, and add 3.0 kg of potassium chloride (KCl) at the same time, mix uniformly, and then load into a reaction container. The air in the reaction container is separated (i.e. extracted). A mixed gas of hydrogen and argon is introduced into the reaction container, the hydrogen partial pressure is controlled to be 50 KPa, the reaction container is kept under positive pressure, and the reaction container is put into a heating furnace for heating, the temperature is raised to 940℃, and the tantalum oxide is reduced for 2.0 hours. Then, the temperature is lowered to 640℃ for evacuation, the pressure in the reaction container is reduced to 5.7 Pa, and the temperature is kept for 3 hours, and the evacuation is stopped. Then, argon is introduced into the reaction container and the temperature is lowered to room temperature, and passivation treatment is carried out. After the passivation is completed, the furnace is taken out, and the metal magnesium is stable without ignition and smoke phenomenon; then, the obtained halide and tantalum powder mixture is washed with water, pickled, filtered, and dried, so as to separate the tantalum powder.

[0045] Then, the tantalum powder is added with 50 ppm of P, and the tantalum powder is heated at 1450℃ and lower than 5.0×10 -3The tantalum powder is subjected to high-temperature high-vacuum heat treatment under a pressure of 1.0 Pa for 1.0 hour, and then subjected to oxygen reduction and acid washing 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 according to the requirements of the aforementioned GB / T3137. The anode block is energized under a voltage of 250 V, and then the electrical performance is tested according to the requirements of the aforementioned GB / T3137. In the specific capacitance test, the tantalum powder is tested in 30% H2SO4 solution and then in 10% H3PO4 solution, and the test results are listed in Table 1.

[0046] Example 2

[0047] 10.0 kg of tantalum oxide is mixed with 3.85 kg of magnesium metal particles and 3.0 kg of potassium chloride (KCl), and then loaded into a reaction container. The air in the reaction container is separated. A mixed gas of hydrogen and argon is introduced into the reaction container, and the hydrogen partial pressure is controlled to be 0.5 KPa. The reaction container is placed in a heating furnace under a positive pressure condition, heated to 940°C, and kept at this temperature for 2.0 hours. Then, the temperature is lowered to 650°C for evacuation, and the pressure in the reaction container is reduced to 5.7 Pa. The temperature is kept at 650°C for 8 hours, and then the evacuation is stopped. Then, argon is introduced into the reaction container, and the temperature is lowered to room temperature. After the passivation is completed, the furnace is discharged. The magnesium metal is stable during the discharge, and there is no ignition and smoke phenomenon. The obtained halide and tantalum powder mixture is subjected to water washing, acid washing, filtration and drying to separate the tantalum powder.

[0048] Then, the tantalum powder is mixed with 50 ppm of P, and subjected to high-temperature high-vacuum heat treatment at 1450°C and a pressure of less than 5.0 x 10 -3 The tantalum powder is subjected to high-temperature high-vacuum heat treatment under a pressure of 1.0 Pa for 1.0 hour, and then subjected to oxygen reduction and acid washing 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 according to the requirements of the aforementioned GB / T3137. The anode block is energized under a voltage of 250 V, and then the electrical performance is tested according to the requirements of the aforementioned GB / T3137. In the specific capacitance test, the tantalum powder is tested in 30% H2SO4 solution and then in 10% H3PO4 solution, and the test results are listed in Table 1.

[0049] Example 3

[0050] Take 10.0 kg of tantalum oxide, mixed with 3.50 kg of magnesium metal particles, while mixed with 3.0 kg of potassium chloride (KCl), mixed evenly and loaded into the reaction vessel, separate the air in the reaction vessel. Into the reaction vessel, a mixture of hydrogen and argon gas is introduced, and the hydrogen partial pressure is controlled at 100 KPa. The reaction vessel is placed in a heating furnace under positive pressure conditions, heated to 940°C, and kept for 2.0 hours. Then reduce the temperature to 640°C for evacuation, reduce the pressure in the reaction vessel to 5.7 Pa, keep for 5 hours, stop evacuation. Then, the reaction vessel is filled with argon and cooled to room temperature, and passivated. After passivation, the furnace is taken out, and the magnesium metal is stable without fire and smoke. The obtained halide and tantalum powder mixture is washed with water, acid washed, filtered, and dried to separate the tantalum powder.

[0051] Then, the tantalum powder is mixed with 50 ppm of P, and high-temperature high-vacuum heat treatment is carried out 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 are carried out to obtain the final tantalum powder. 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 aforementioned GB / T3137 requirements, the obtained final tantalum powder is made into an anode block, energized at 250V, and then tested for electrical performance according to the aforementioned GB / T3137 requirements. In the specific capacitance test, after testing with 30% H2SO4 solution, 10% H3PO4 solution is used for testing, and the test results are listed in Table 1.

[0052] Example 4

[0053] Take 10.0 kg of tantalum oxide, mixed with 3.90 kg of magnesium metal particles, while mixed with 2.0 kg of potassium chloride (KCl), mixed evenly and loaded into the reaction vessel, separate the air in the reaction vessel. Into the reaction vessel, a mixture of hydrogen and argon gas is introduced, and the hydrogen partial pressure is controlled at 0.1 KPa. The reaction vessel is placed in a heating furnace under positive pressure conditions, heated to 940°C, and kept for 2.0 hours. Then reduce the temperature to 640°C for evacuation, reduce the pressure in the reaction vessel to 5.7 Pa, keep for 7 hours, stop evacuation. Then, the reaction vessel is filled with argon and cooled to room temperature, and passivated. After passivation, the furnace is taken out, and the magnesium metal is stable without fire and smoke. The obtained halide and tantalum powder mixture is washed with water, acid washed, filtered, and dried to separate the tantalum powder.

[0054] Then, the tantalum powder is mixed with 50 ppm of P, and high-temperature high-vacuum heat treatment is carried out at 1450°C and a pressure of less than 5.0 x 10 -3The tantalum powder is mixed with 50 ppm P, and then high-temperature high-vacuum heat treatment is performed at a pressure of 5.0 x 10 Pa for 1.0 hour, followed by oxygen reduction and acid washing 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 in accordance with the requirements of the aforementioned GB / T3137. The anode block is energized at 250 V, and then electrical performance is tested in accordance with the requirements of the aforementioned GB / T3137. In the specific capacitance test, the tantalum powder is tested with 30% H2SO4 solution, and then tested with 10% H3PO4 solution. The test results are listed in Table 1.

[0055] Example 5

[0056] The 10.0 kg of tantalum oxide is mixed with 3.1 kg of magnesium metal particles and 3.0 kg of potassium chloride (KCl), and then loaded into a reaction container. The air in the reaction container is separated. A mixture of hydrogen and argon is introduced into the reaction container, and the hydrogen partial pressure is controlled at 0.3 KPa. The reaction container is placed in a heating furnace and heated to 940°C, and kept at this temperature for 2.0 hours. Then, the temperature is lowered to 640°C, and the pressure in the reaction container is reduced to 5.7 Pa by evacuation. The temperature is kept at 640°C for 3 hours, and then the evacuation is stopped. Then, argon is introduced into the reaction container, and the temperature is lowered to room temperature. Passivation treatment is performed, and then the reaction container is taken out of the furnace. No magnesium metal is ignited or smokes during the taking out. The obtained halide and tantalum powder mixture is washed with water, washed with acid, filtered, and dried to separate the tantalum powder.

[0057] Then, the tantalum powder is mixed with 50 ppm P, and then high-temperature high-vacuum heat treatment is performed at a pressure of 5.0 x 10 -3 The tantalum powder is mixed with 50 ppm P, and then high-temperature high-vacuum heat treatment is performed at a pressure of 5.0 x 10 Pa for 1.0 hour, followed by oxygen reduction and acid washing 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 in accordance with the requirements of the aforementioned GB / T3137. The anode block is energized at 250 V, and then electrical performance is tested in accordance with the requirements of the aforementioned GB / T3137. In the specific capacitance test, the tantalum powder is tested with 30% H2SO4 solution, and then tested with 10% H3PO4 solution. The test results are listed in Table 1.

[0058] Example 6

[0059] Take 10.0 kg of tantalum oxide, mixed with 3.1 kg of magnesium metal particles, while mixing 1.5 kg of potassium chloride (KCl) and 1.5 kg of sodium chloride (NaCl), mix evenly and then put into the reaction container, and put another crucible into the reaction container, put 1.5 kg of tantalum powder containing 3500 ppm of hydrogen into the crucible, separate the air in the reaction container. A mixture of hydrogen and argon gas is introduced into the reaction container, the hydrogen partial pressure is controlled at 1.0 KPa, the reaction container is kept at positive pressure, and the reaction container is put into the heating furnace for heating, the temperature is raised to 940℃, and the temperature is kept for 2.0 hours, then the temperature is lowered to 640℃ for evacuation, the pressure in the reaction container is reduced to 5.7 Pa, and the temperature is kept for 3 hours, then the evacuation is stopped, then argon gas is introduced into the reaction container and the temperature is lowered to room temperature, and passivation treatment is carried out, after the passivation is finished, the furnace is taken out, and the magnesium metal is stable without fire and smoke phenomenon when taken out; The obtained halide and tantalum powder mixture is washed with water, pickled, filtered and dried to separate the tantalum powder.

[0060] Then, the tantalum powder is mixed with 50 ppm of P, and high-temperature high-vacuum heat treatment is carried out at 1450℃ and a pressure lower than 5.0 x 10 -3 Pa for 1.0 hour, and then oxygen reduction and acid pickling are carried out to obtain the final tantalum powder. 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 obtained final tantalum powder is made into an anode block, which is energized under the condition of 250V, and then the electrical performance is tested according to the requirements of the aforementioned GB / T3137. In the specific capacitance test, after testing with 30% H2SO4 solution, 10% H3PO4 solution is used for testing, and the test results are listed in Table 1.

[0061] Example 7

[0062] Take 10.0 kg of tantalum oxide, mixed with 3.1 kg of magnesium metal particles, while mixing 1.5 kg of potassium chloride (KCl) and 1.5 kg of sodium chloride (NaCl), mix evenly and then put into the reaction container, and put another crucible into the reaction container, put 1.5 kg of tantalum powder containing 3500 ppm of hydrogen into the crucible, separate the air in the reaction container. A mixture of hydrogen and argon gas is introduced into the reaction container, the hydrogen partial pressure is controlled at 1.0 KPa, the reaction container is kept at positive pressure, and the reaction container is put into the heating furnace for heating, the temperature is raised to 940℃, and the temperature is kept for 2.0 hours, then the temperature is lowered to 640℃ for evacuation, the pressure in the reaction container is reduced to 5.7 Pa, and the temperature is kept for 3 hours, then the evacuation is stopped, then argon gas is introduced into the reaction container and the temperature is lowered to room temperature, and passivation treatment is carried out, after the passivation is finished, the furnace is taken out, and the magnesium metal is stable without fire and smoke phenomenon when taken out; The obtained halide and tantalum powder mixture is washed with water, pickled, filtered and dried to separate the tantalum powder.

[0063] Then, the tantalum powder is mixed with 50 ppm of P, and high-temperature high-vacuum heat treatment is carried out at 1450℃ and a pressure lower than 5.0 x 10 -3The tantalum powder is subjected to high-temperature high-vacuum heat treatment at a pressure of 1.0 Pa for 1.0 hour, and then is subjected to oxygen reduction and acid washing to obtain final tantalum powder. The final tantalum powder is made into anode blocks according to the anode block mass, pressing density, anode block sintering temperature and sintering time specified in Table 1, and other conditions are in accordance with the requirements of the aforementioned GB / T3137. The anode blocks are energized at 250 V, and then the electrical properties are tested in accordance with the requirements of the aforementioned GB / T3137. In the specific capacitance test, the tantalum powder is tested in 30% H2SO4 solution and then in 10% H3PO4 solution, and the test results are listed in Table 1.

[0064] Comparative Example 1

[0065] 10.0 kg of tantalum oxide is mixed with 5.46 kg of metallic magnesium particles, 2.5 kg of potassium chloride (KCl) and 2.5 kg of sodium chloride (NaCl), and then is loaded into a reaction container. The air in the reaction container is separated. Argon is introduced into the reaction container, and the reaction container is heated in a heating furnace under positive pressure. The temperature is raised to 940°C, and the temperature is maintained for 1.0 hour. Then, the temperature is lowered to 650°C, and the pressure in the reaction container is reduced to 5.7 Pa. The temperature is maintained for 8 hours, and then the vacuum is stopped. Argon is introduced into the reaction container to maintain positive pressure, and the temperature is raised to 940°C. The temperature is maintained for 3 hours. After the temperature maintenance is completed, the temperature is lowered to room temperature, and passivation treatment is performed. After the passivation treatment is completed, the reaction container is taken out of the furnace. At this time, the metallic magnesium is on fire and smokes. The obtained halide and tantalum powder mixture is subjected to water washing, acid washing, filtration and drying to separate the tantalum powder.

[0066] Then, 50 ppm of P is added to the tantalum powder, and the tantalum powder is subjected to high-temperature high-vacuum heat treatment at a pressure of 1.0 Pa at 1450°C and below 5.0 x 10 -3 The tantalum powder is subjected to high-temperature high-vacuum heat treatment at a pressure of 1.0 Pa for 1.0 hour, and then is subjected to oxygen reduction and acid washing to obtain final tantalum powder. The final tantalum powder is made into anode blocks according to the anode block mass, pressing density, anode block sintering temperature and sintering time specified in Table 1, and other conditions are in accordance with the requirements of the aforementioned GB / T3137. The anode blocks are energized at 250 V, and then the electrical properties are tested in accordance with the requirements of the aforementioned GB / T3137. In the specific capacitance test, the tantalum powder is tested in 30% H2SO4 solution and then in 10% H3PO4 solution, and the test results are listed in Table 1.

[0067] Table 1 Electrical property data of finished tantalum powder

[0068]

[0069] As can be seen from Table 1, the tantalum powder prepared in Example 1 has better electrical properties than the tantalum powder prepared in Comparative Example 1.

[0070] The present application reduces the amount of magnesium used in the manufacture of tantalum powder, and the energizing of the powder can be carried out at a higher voltage (250V, as compared to 200V or less in the prior art), and the resulting energized block has a high specific capacity, and the difference between the results obtained in the specific capacity test using 30% H2SO4 solution and the results obtained using 10% H3PO4 solution is small, and the block shows a higher breakdown voltage in the breakdown voltage test.

[0071] As can also be seen from Table 1, the difference between the specific capacities obtained in the test using different acid solutions is smaller for the anode block made from the tantalum powder according to the present application. It is generally believed that the surface tension of phosphoric acid and sulfuric acid is different, and the ability to penetrate into the ultra-fine pores of the anode block is also different. Therefore, the difference in the specific capacities reflects the presence of ultra-fine pores in the anode block. Therefore, this proves that the use of the tantalum powder according to the present application can result in an anode block with fewer ultra-fine pores and a better microstructure.

Claims

1. A method for preparing tantalum powder by reducing tantalum oxide with magnesium particles, comprising the following steps: (1) Mix tantalum oxide with an excess of magnesium particle reducing agent, and simultaneously mix in 10-200% by weight of at least one alkali metal halide and / or alkaline earth metal halide of tantalum oxide. Place the mixture in a sealed reaction vessel, remove the air from the vessel, and place the vessel in a heating furnace. (2) Raise the temperature of the heating furnace to 700~1000℃ and then keep it at that temperature for 1h~3h to allow tantalum oxide and the reducing agent to undergo a full reduction reaction; (3) After the heat preservation is completed, the temperature is lowered to 600~750℃, and the furnace is evacuated to below 10Pa. The furnace is then kept warm under negative pressure to separate the excess magnesium metal and tantalum powder mixture. (4) Then, inert gas is introduced into the reaction vessel to maintain positive pressure. The reaction vessel is then cooled to room temperature and passivated to obtain a mixture containing halides and tantalum powder. (5) Separate tantalum powder from the obtained mixture. In step (1), after the air is evacuated, the container is filled with a hydrogen-containing gas containing 0.5-10% nitrogen. The presence of the hydrogen-containing gas further enhances the sintering of the tantalum powder, thereby eliminating the need for a separate subsequent sintering step. Furthermore, the amount of reducing agent added in step (1) exceeds 5-45% of the theoretical amount required for the complete reduction of tantalum oxide.

2. The method according to claim 1, characterized in that: In step (2), the temperature is raised to 750~970℃.

3. The method according to claim 2, characterized in that: In step (2), the temperature is raised to 900~950℃.

4. The method according to claim 1 or 2, characterized in that: In step (3), the temperature is reduced to 640~680℃.

5. The method according to claim 1 or 2, characterized in that: In step (1), the container is made to contain hydrogen gas by introducing hydrogen gas.

6. The method according to claim 5, wherein the hydrogen-containing gas introduced is pure hydrogen or a mixture of hydrogen and an inert gas.

7. The method according to claim 1 or 2, characterized in that: In step (1), the container is made to contain hydrogen gas by adding a hydrogen-containing substance and causing it to release hydrogen gas.

8. The method according to claim 7, characterized in that: The hydrogen-containing substance is tantalum metal that has adsorbed hydrogen.

9. The method according to claim 1 or 2, characterized in that: The amount of reducing agent added in step (1) is 10-45% more than the theoretical amount required for the complete reduction of tantalum oxide.

10. The method according to claim 1 or 2, characterized in that: The amount of reducing agent added in step (1) is 10-15% or 5-10% or 15-20% more than the theoretical amount required for the complete reduction of tantalum oxide.

11. The method according to claim 1 or 2, characterized in that: The alkali metal halide added in step (1) is 25-80% of the weight of tantalum oxide.

12. The method according to claim 1 or 2, characterized in that: The alkali metal halide or alkaline earth metal halide mentioned in step (1) is one or a mixture of NaCl, KCl, KI, and MgCl2.

13. The method according to claim 1 or 2, characterized in that: The alkali metal halide mentioned in step (1) is a mixture of NaCl and KCl, wherein the mass ratio of sodium chloride to potassium chloride in the mixture is 1:1-10.

14. The method according to claim 1 or 2, characterized in that: In step (1), one or more compounds containing elements B, P, and / or N are added as additives to dope tantalum powder. The amount of element B added is 1-100 ppm based on the amount of effective elements. And / or the added P element is 10-200 ppm; And / or the added nitrogen element is 300-2500 ppm.

15. The method according to claim 1 or 2, characterized in that: In step (1), one or more compounds containing elements B, P, and / or N are added as additives to dope tantalum powder. The amount of element B added is 20-60 ppm based on the amount of effective elements. And / or the added P element is 30-90 ppm; And / or the added nitrogen element is 500-1200 ppm.

16. The method according to claim 1 or 2, characterized in that: The hydrogen partial pressure of the hydrogen-containing gas in step (1) exceeds 0.050 kPa.

17. The method according to claim 1 or 2, characterized in that: The hydrogen partial pressure of the hydrogen-containing gas in step (1) is 0.1-200 kPa.

18. The method according to claim 1 or 2, characterized in that: The hydrogen partial pressure of the hydrogen-containing gas in step (1) is 0.3-20 kPa.

19. The method according to claim 1 or 2, characterized in that: The partial pressure of hydrogen in the hydrogen-containing gas in step (1) is 0.1-0.3 kPa.

20. The method according to claim 1 or 2, further comprising, after step (5): High-temperature, high-vacuum heat treatment; Oxygen reduction is achieved by incorporating a small amount of magnesium particles; and Separation is achieved through acid washing, filtration, and drying.

21. The method according to claim 1 or 2, characterized in that: In step (5), separation is carried out by water washing, acid washing, filtration and drying.

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