Method for reducing tantalum oxide by alkaline earth metal to produce tantalum powder for capacitor

Abstract

A method for reducing tantalum oxide by an alkaline earth metal to produce tantalum powder for a capacitor, prepared tantalum powder, an anode block made of the tantalum powder, and a use of the tantalum powder in the manufacturing of a capacitor. The present invention specifically relates to a method for reducing tantalum oxide by an alkaline earth metal such as magnesium, preferably magnesium particles, to produce tantalum powder. The method comprises a reduction process and a heat maintaining process carried out in a hydrogen-containing atmosphere. Preferably, the hydrogen-containing atmosphere is pure hydrogen or a mixed gas of hydrogen and an inert gas; and / or the hydrogen-containing atmosphere is obtained by introducing a gaseous hydrogen-containing gas, or by adding a hydrogen-containing substance and causing same to release hydrogen.

Description

Method for producing tantalum powder for capacitors by reducing tantalum oxide with alkaline earth metals Technical Field

[0001] This invention belongs to the field of rare metal functional material smelting, specifically relating to the production of tantalum powder for high-voltage, high-reliability capacitors and its manufacturing method. Background Technology

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

[0003] Currently, the main industrial methods for preparing capacitor-grade tantalum powder include the sodium reduction of potassium fluorotantalate, the magnesium reduction of tantalum oxide, and the tantalum ingot hydrogenation method. The sodium reduction of potassium fluorotantalate method easily produces tantalum powder with high specific capacitance, but its voltage withstand capability is generally low. The tantalum ingot hydrogenation method produces tantalum powder with excellent voltage withstand capability, but its specific capacitance is generally low. To continuously improve both the voltage withstand capability and specific capacitance of tantalum powder, the magnesium reduction of tantalum oxide method has been successfully developed and continues to evolve. Because it alters the state of the reactants, the magnesium reduction of tantalum oxide method has a significant advantage in preparing capacitor-grade tantalum powder with improved specific capacitance and voltage withstand capability.

[0004] CN114192791B discloses a method for producing tantalum powder for capacitors using alkaline earth metal reduction of tantalum oxide. This method involves adding alkali metal or alkaline earth metal halides during the reduction process. In a furnace filled with inert gas, excess alkaline earth metal is used for reduction at temperatures above 700°C. After reduction, the excess alkaline earth metal is separated from the tantalum-containing material, and then the material is further sintered at temperatures above 750°C. However, this method has a problem: the use of a large amount of alkaline earth metal may cause a fire when the material is removed from the furnace after reduction, posing a safety hazard. Furthermore, the process is relatively complex, requiring a separate sintering step and consuming a significant amount of energy.

[0005] CN1308566A (application number 99808374.7), CN105033283A (application number 201510310262.2), and CN1251325A also disclose methods for producing tantalum powder by reducing tantalum oxide with alkaline earth metals (including magnesium vapor) or rare earth metals. However, the tantalum powder produced by these methods has a large specific surface area, high activity, and poor burn-off resistance. The tantalum powder used in capacitors has poor specific capacitance regardless of breakdown voltage or high voltage energization, and does not significantly improve the voltage withstand performance of tantalum powder used in capacitors.

[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.

[0008] Summary of the Invention

[0009] 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.

[0010] 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:

[0011] (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.

[0012] (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;

[0013] (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).

[0014] (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.

[0015] (5) Separate the tantalum powder from the obtained mixture, for example by washing with water, acid washing, filtration, and drying.

[0016] In step (1), after the air is evacuated, the container is filled with hydrogen-containing gas, for example by introducing hydrogen-containing gas, or by adding a liquid or solid (preferably solid) hydrogen-containing substance and causing it to release hydrogen gas. Preferably, in the latter case, the hydrogen-containing substance is separated from other raw materials such as tantalum oxide powder, alkali metal and / or alkaline earth metal halides, which can be achieved, for example, by placing the hydrogen-containing substance (preferably hydrogen-containing tantalum powder) separately in a crucible.

[0017] Preferably, the hydrogen-containing substance is, for example, tantalum powder adsorbed with hydrogen (also known as hydrogen-containing tantalum powder), hydrogen-containing niobium powder, hydrogen-containing titanium powder, and hydrogen-containing compounds, which can release hydrogen gas at high temperatures.

[0018] The alkaline earth metal reducing agent mentioned in step (1) is preferably magnesium, more preferably magnesium particles, and even more preferably magnesium particles of 3N5 or higher (purity 99.95% or higher), and the higher the purity of the magnesium particles, the better. There is no limitation on the particle size of the magnesium particles. However, the applicant has found through extensive research that magnesium particles with a particle size of 150-4000 μm are more suitable for this technology, and the tantalum powder obtained by reduction has better pressure resistance. Magnesium particles in this particle size range are not only beneficial to the safety of the storage and transportation of metallic magnesium, but also to the uniform mixing. If the magnesium particles are too fine, they are too active and prone to spontaneous combustion; if the magnesium particles are too coarse, they are not conducive to uniform mixing and are not conducive to the optimization of tantalum powder performance. The amount of excess reducing agent added refers to the amount exceeding the theoretical amount required to completely reduce tantalum oxide. Generally speaking, the theoretical amount required to completely reduce one kilogram of tantalum oxide is 0.273 kg. In this invention, it is preferred to exceed the theoretical amount by 5-50%, more preferably 10-48%, more preferably 10-45%, and even more preferably 10-15%, 5-10%, or 15-20%.

[0019] In step (2), tantalum powder inevitably undergoes a certain degree of sintering due to the heat of reduction. The presence of hydrogen gas in the container further enhances the sintering phenomenon of tantalum powder, thus eliminating the need for a separate subsequent sintering step. Since existing technologies often involve a separate sintering step, this invention undoubtedly simplifies the process. Moreover, under the conditions described in this invention, sintering and reduction occur simultaneously and work together, making it easier to obtain tantalum powder with an improved microstructure.

[0020] The weight of the alkali metal and / or alkaline earth metal halide added in step (1) is preferably 10-180% of the weight of tantalum oxide, more preferably 25-120%, more preferably 70-120% or 100-180%, and most preferably 15-80%, for example 25-80%. The alkali metal or alkaline earth halide is preferably of analytical grade, and preferably of higher purity. The alkali metal or alkaline earth halide is preferably in particulate form. There is no limitation on its particle size, but the applicant has found that particles of 70 μm-4000 μm are more suitable for this technology, and the tantalum powder obtained from the reduction has better pressure resistance.

[0021] Preferably, the alkali metal or alkaline earth metal halide mentioned 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 1:1-10; most preferably, it is about 1:1.

[0022] Preferably, in step (1), one or more compounds containing elements B, P, and / or N may be added as additives to dope the tantalum powder. Based on the amount of effective elements, the amount of B added is preferably 1-100 ppm, more preferably 20-60 ppm; the amount of P added is preferably 10-200 ppm, more preferably 30-90 ppm; and the amount of N added is preferably 300-2500 ppm, more preferably 500-1200 ppm. It should be understood that although compounds are added here, the effective elements are B, P, and / or N, so the amounts mentioned here are calculated based on the amounts of B, P, and / or N.

[0023] Preferably, in step (2), the furnace is heated to 750–1000°C. More preferably, the furnace is heated to 900–965°C.

[0024] Unlike the inert atmosphere commonly used in the prior art, the hydrogen-containing gas used in step (1) is pure hydrogen or a mixture of hydrogen and an inert gas. The hydrogen can be gaseous hydrogen or hydrogen released by heating other liquid or solid hydrogen-containing substances. Importantly, this invention uses a hydrogen-containing gas as the atmosphere.

[0025] Although hydrogen is a common reducing agent, it cannot reduce tantalum oxide. That is, hydrogen does not act as a reducing agent in this invention. However, the inventors unexpectedly discovered that because hydrogen enhances the sintering that occurs during the reduction process, the process can be significantly simplified by omitting the sintering step. Furthermore, introducing hydrogen-containing gas into an inert atmosphere can reduce the amount of alkaline earth metal added as a reducing agent and improve the overall electrical properties of the product.

[0026] Preferably, a positive pressure is maintained inside the reaction vessel in step (1). Inside the reaction vessel, the partial pressure of hydrogen exceeds 0.050 kPa, preferably 0.1-200 kPa, more preferably 0.3-50 kPa, even more preferably 10-20 kPa, and even more preferably 0.5-10 kPa or 10-15 kPa, and even more preferably 0.1-0.3 kPa. The inventors have found that excessively low hydrogen partial pressure cannot sufficiently promote the reduction effect, so from this perspective, the hydrogen partial pressure should preferably not be too low; conversely, excessively high hydrogen partial pressure weakens the improvement of the reduction effect, and from the perspective of ensuring the absolute safety of hydrogen use, excessively high hydrogen partial pressure is preferably avoided.

[0027] Inert gases generally refer to rare gases, such as helium, neon, and argon. Although nitrogen is sometimes used as an inert gas due to its stable properties, it is generally considered unsuitable as an inert protective gas in this field because of its high reduction temperature and strong reactivity at this temperature. However, after extensive research, the inventors discovered that the presence of a small amount of nitrogen in the aforementioned inert gases does not compromise the inert protective atmosphere and can also incidentally achieve nitrogen doping of tantalum powder. From the perspective of achieving better nitrogen doping effect of tantalum powder, when using a mixture of hydrogen-containing gas (such as pure hydrogen) and inert gas in step (1), it is preferable to include 0.5-10% nitrogen, based on the total amount of hydrogen-containing gas and inert gas.

[0028] In step (3), since the melting point of magnesium is relatively high, magnesium vapor is difficult to diffuse to the outside of the reactor, but condenses into a solid in the low temperature zone of the reactor, thus achieving separation.

[0029] Preferably, in step (3), the furnace temperature is 600–750°C. More preferably, the furnace temperature is 620–680°C, for example, 640°C. Preferably, the furnace is evacuated to below 5 Pa, more preferably below 0.5 Pa.

[0030] The hydrogen-containing gas in step (1) can be a mixture of hydrogen and an inert gas. In this case, the inert gas in step (1) and step (4) can be the same or different. Preferably, in steps (1) and / or (4), a positive pressure is maintained in the furnace. Preferably, a positive pressure is avoided in the reactor in step (3), because a positive pressure is not conducive to the separation of excess alkaline earth metals such as magnesium.

[0031] Preferably, the method of the present invention further includes, after step (5), heat treatment such as high-temperature high-vacuum heat treatment (or, according to patent CN114210973B, high-temperature high-vacuum heat treatment after molten salt assisted sintering), oxygen reduction, acid washing, and then separating tantalum powder, for example by filtration and drying, to obtain tantalum powder suitable for manufacturing high-reliability tantalum capacitors. These processes are all known in the prior art. In other words, these processes can employ any process known in the prior art. For example, the high-temperature high-vacuum heat treatment and passivation here can be performed using the methods provided by patents CN201110039272.9, CN201120077798.1, CN201120077680.9, CN201120077305.4, etc.; the oxygen reduction can be performed using the method provided by patent CN201420777210.7; and the pickling can be performed using the methods provided by patents CN201210548101.3, CN201280077499.5, CN201210548008.2, etc.

[0032] As an alternative to incorporating N, P, and / or B elements in step (1), the present invention may also include a separate step of incorporating these elements, for example, after step (5). Of course, raw materials containing these elements can also be used directly. These elements can also be added during the aforementioned high-temperature, high-vacuum heat treatment step. Incorporating P is particularly preferred. Adding P can increase the specific volume; as long as the total amount of P is controlled, the effect of increasing the specific volume is the same regardless of when it is added.

[0033] The tantalum powder of the above product was pressed into blocks and sintered, and then energized under high voltage conditions. The electrical performance of the energized block was tested, and it was found that the energized block has good overall electrical performance. Therefore, the tantalum powder manufactured by this invention is more suitable for making high voltage and high reliability tantalum capacitors.

[0034] Moreover, the process of this invention is simple and easy to control. For example, microwaves are not used in any step of this invention, nor are excessively high temperatures above 1000°C used, and the proportion of alkaline earth metals used for reduction is lower. Therefore, the equipment used is also relatively simple, and the tantalum powder preparation process is safer.

[0035] Without being bound by general theories, and combining the analysis principles of powder liquid phase sintering theory, the inventors believe that the reason for the excellent effect of this invention is as follows: In step (2), in the presence of hydrogen in the atmosphere, reduction is more likely to occur, and sintering is strengthened, making it easier for tantalum powder particles to construct a spatial structure suitable for capacitors. The tantalum powder particles are uniform in size, smooth, with large sintering necks and few ultrafine particles. Subsequently, the obtained tantalum powder is subjected to high-temperature and high-vacuum heat treatment according to existing technology (or first molten salt assisted sintering according to patent CN114210973B followed by high-temperature and high-vacuum heat treatment), oxygen reduction, and acid washing treatment to obtain tantalum powder suitable for preparing high-voltage and high-reliability capacitors.

[0036] The phrase "easier to construct a suitable spatial structure for capacitors" refers to the absence of ultrafine pores in the anode block after the tantalum powder is pressed and sintered. These ultrafine pores are detrimental to electrical performance, particularly leakage current and ESR (equivalent series resistance).

[0037] The present invention also relates to tantalum powder obtained by the above method, an anode block made from the tantalum powder, and the use of the tantalum powder and / or the anode block in the manufacture of capacitors. Attached Figure Description

[0038] The following figures are provided to better understand the invention. These figures are exemplary and are not intended to limit the scope of the invention.

[0039] Figure 1 shows a scanning electron microscope image of the tantalum powder obtained according to the present invention.

[0040] The attached figure illustrates that the obtained tantalum powder particles are more uniform in size, with smooth particles, large sintering necks, and fewer ultrafine particles. Detailed Implementation

[0041] To further illustrate the present invention, preferred embodiments are described below with reference to examples, which clearly demonstrate the purpose, features, and advantages of the present invention. However, these descriptions are merely for further illustrating the features and advantages of the present invention and are not intended to limit the invention. Unless otherwise specified in the examples, conventional conditions were followed. Reagents or instruments used, unless otherwise specified, are all commercially available conventional products.

[0042] For the purposes of this specification, all figures indicating amounts of ingredients, reaction conditions, etc., in the specification and claims shall in all cases be understood to be modified by the term "about," unless otherwise specified. Accordingly, the numerical parameters given in the following specification and appended claims are approximate values, which may vary according to the desired properties sought to be obtained according to the invention, unless indicated to the contrary. At least, and without limitation, the application of the doctrine of equivalence to the scope of the claims is intended, each numerical parameter shall be interpreted at least according to the number of significant figures reported and in accordance with ordinary rounding techniques.

[0043] The analysis of impurity content in tantalum powder was conducted according to Chinese standards GB / T15076.1~15076.15, and the physical properties were performed according to industry standard YS / T573-2015. The testing of electrical properties in tantalum powder was conducted according to Chinese standard GB / T3137.

[0044] Example 1

[0045] Take 10.0 kg of tantalum oxide, add 3.1 kg of magnesium granules, and simultaneously add 3.0 kg of potassium chloride (KCl). After mixing thoroughly, place the mixture into a reaction vessel and remove (i.e., evacuate) the air from the reaction vessel. Introduce a mixture of hydrogen and argon into the reaction vessel, controlling the hydrogen partial pressure to 50 kPa. Maintain positive pressure inside the reaction vessel and place it in a furnace to heat to 940°C, holding for 2.0 hours to allow for complete reduction of the tantalum oxide. Then, lower the temperature to 640°C and evacuate, reducing the pressure in the reaction vessel to 5.7 Pa. Hold for 3 hours and then stop evacuation. Next, introduce argon into the reaction vessel and cool it to room temperature for passivation treatment. After passivation, remove the vessel from the furnace; the magnesium granules should be stable and show no signs of ignition or smoke upon removal. Then, wash the resulting mixture of halide and tantalum powder with water, acid, filter, and dry to separate the tantalum powder.

[0046] Then, tantalum powder was mixed with 50 ppm of P and subjected to treatment at 1450 °C and below 5.0 × 10⁻⁶. -3 The tantalum powder was subjected to high-temperature, high-vacuum heat treatment for 1.0 hour under a pressure of Pa, followed by deoxygenation and acid washing to obtain the final tantalum powder. The final tantalum powder was fabricated into anode blocks according to the anode block mass, pressing density, anode block sintering temperature, and sintering time specified in Table 1, with other conditions conforming to the aforementioned GB / T3137 requirements. The anode blocks were then energized at 250V, and their electrical properties were tested according to the aforementioned GB / T3137 requirements. In the specific capacitance test, the test was conducted using a 30% H2SO4 solution followed by a 10% H3PO4 solution. The results are listed in Table 1.

[0047] Example 2

[0048] Take 10.0 kg of tantalum oxide, add 3.85 kg of magnesium granules, and simultaneously add 3.0 kg of potassium chloride (KCl). After mixing thoroughly, place the mixture into a reaction vessel and separate the air from the vessel. Introduce a mixture of hydrogen and argon into the reaction vessel, controlling the hydrogen partial pressure to 0.5 kPa. Under positive pressure, place the reaction vessel in a furnace and heat it to 940°C, holding for 2.0 hours. Then, lower the temperature to 650°C and evacuate the vessel, reducing the pressure to 5.7 Pa. Hold this temperature for 8 hours and then stop evacuation. Next, introduce argon into the reaction vessel and cool it to room temperature for passivation treatment. After passivation, remove the vessel from the furnace. The magnesium granules are stable upon removal, showing no signs of ignition or smoke. The resulting mixture of halide and tantalum powder is then washed with water, acid-washed, filtered, and dried to separate the tantalum powder.

[0049] Then, tantalum powder was mixed with 50 ppm of P and subjected to treatment at 1450 °C and below 5.0 × 10⁻⁶. -3 The tantalum powder was subjected to high-temperature, high-vacuum heat treatment for 1.0 hour under a pressure of Pa, followed by deoxygenation and acid washing to obtain the final tantalum powder. The final tantalum powder was fabricated into anode blocks according to the anode block mass, pressing density, anode block sintering temperature, and sintering time specified in Table 1, with other conditions conforming to the aforementioned GB / T3137 requirements. The anode blocks were then energized at 250V, and their electrical properties were tested according to the aforementioned GB / T3137 requirements. In the specific capacitance test, the test was conducted using a 30% H2SO4 solution followed by a 10% H3PO4 solution. The results are listed in Table 1.

[0050] Example 3

[0051] Take 10.0 kg of tantalum oxide, add 3.50 kg of magnesium granules, and simultaneously add 3.0 kg of potassium chloride (KCl). After mixing thoroughly, place the mixture into a reaction vessel and separate the air from the vessel. Introduce a mixture of hydrogen and argon into the reaction vessel, controlling the hydrogen partial pressure to 100 kPa. Under positive pressure, place the reaction vessel in a furnace and heat it to 940°C, holding for 2.0 hours. Then, lower the temperature to 640°C and evacuate the vessel, reducing the pressure to 5.7 Pa. Hold this temperature for 5 hours and then stop evacuation. Next, introduce argon into the reaction vessel and cool it to room temperature for passivation treatment. After passivation, remove the vessel from the furnace. The magnesium granules should be stable and show no signs of ignition or smoke upon removal. Wash the resulting mixture of halide and tantalum powder with water, acid, filter, and dry to separate the tantalum powder.

[0052] Then, tantalum powder was mixed with 50 ppm of P and subjected to treatment at 1450 °C and below 5.0 × 10⁻⁶. -3The tantalum powder was subjected to high-temperature, high-vacuum heat treatment for 1.0 hour under a pressure of Pa, followed by deoxygenation and acid washing to obtain the final tantalum powder. The final tantalum powder was fabricated into anode blocks according to the anode block mass, pressing density, anode block sintering temperature, and sintering time specified in Table 1, with other conditions conforming to the aforementioned GB / T3137 requirements. The anode blocks were then energized at 250V, and their electrical properties were tested according to the aforementioned GB / T3137 requirements. In the specific capacitance test, the test was conducted using a 30% H2SO4 solution followed by a 10% H3PO4 solution. The results are listed in Table 1.

[0053] Example 4

[0054] Take 10.0 kg of tantalum oxide, add 3.90 kg of magnesium granules, and simultaneously add 2.0 kg of potassium chloride (KCl). After mixing thoroughly, place the mixture into a reaction vessel and separate the air from the vessel. Introduce a mixture of hydrogen and argon into the reaction vessel, controlling the hydrogen partial pressure to 0.1 kPa. Under positive pressure, place the reaction vessel in a furnace and heat it to 940°C, holding for 2.0 hours. Then, lower the temperature to 640°C and evacuate the vessel, reducing the pressure to 5.7 Pa. Hold this temperature for 7 hours and then stop evacuation. Next, introduce argon into the reaction vessel and cool it to room temperature for passivation treatment. After passivation, remove the vessel from the furnace. The magnesium granules should be stable and show no signs of ignition or smoke upon removal. Wash the resulting mixture of halide and tantalum powder with water, acid, filter, and dry to separate the tantalum powder.

[0055] Then, tantalum powder was mixed with 50 ppm of P and subjected to treatment at 1450 °C and below 5.0 × 10⁻⁶. -3 The tantalum powder was subjected to high-temperature, high-vacuum heat treatment for 1.0 hour under a pressure of Pa, followed by deoxygenation and acid washing to obtain the final tantalum powder. The final tantalum powder was fabricated into anode blocks according to the anode block mass, pressing density, anode block sintering temperature, and sintering time specified in Table 1, with other conditions conforming to the aforementioned GB / T3137 requirements. The anode blocks were then energized at 250V, and their electrical properties were tested according to the aforementioned GB / T3137 requirements. In the specific capacitance test, the test was conducted using a 30% H2SO4 solution followed by a 10% H3PO4 solution. The results are listed in Table 1.

[0056] Example 5

[0057] Take 10.0 kg of tantalum oxide, add 3.1 kg of magnesium granules, and simultaneously add 3.0 kg of potassium chloride (KCl). After mixing thoroughly, place the mixture into a reaction vessel and separate the air from the vessel. Introduce a mixture of hydrogen and argon into the reaction vessel, controlling the hydrogen partial pressure to 0.3 kPa. Under positive pressure, place the reaction vessel in a furnace and heat it to 940°C, holding for 2.0 hours. Then, lower the temperature to 640°C and evacuate the vessel, reducing the pressure to 5.7 Pa. Hold this temperature for 3 hours and then stop evacuation. Next, introduce argon into the reaction vessel and cool it to room temperature for passivation treatment. After passivation, remove the vessel from the furnace. The magnesium granules should be stable and show no signs of ignition or smoke upon removal. Wash the resulting mixture of halide and tantalum powder with water, acid, filter, and dry to separate the tantalum powder.

[0058] Then, tantalum powder was mixed with 50 ppm of P and subjected to treatment at 1450 °C and below 5.0 × 10⁻⁶. -3 The tantalum powder was subjected to high-temperature, high-vacuum heat treatment for 1.0 hour under a pressure of Pa, followed by deoxygenation and acid washing to obtain the final tantalum powder. The final tantalum powder was fabricated into anode blocks according to the anode block mass, pressing density, anode block sintering temperature, and sintering time specified in Table 1, with other conditions conforming to the aforementioned GB / T3137 requirements. The anode blocks were then energized at 250V, and their electrical properties were tested according to the aforementioned GB / T3137 requirements. In the specific capacitance test, the test was conducted using a 30% H2SO4 solution followed by a 10% H3PO4 solution. The results are listed in Table 1.

[0059] Example 6

[0060] Take 10.0 kg of tantalum oxide, add 3.1 kg of magnesium granules, 1.5 kg of potassium chloride (KCl), and 1.5 kg of sodium chloride (NaCl), mix thoroughly, and then load into a reaction vessel. Separate the air from the reaction vessel. Introduce a mixture of hydrogen and argon into the reaction vessel, controlling the hydrogen partial pressure to 1.0 kPa. Under positive pressure, place the reaction vessel in a furnace and heat it to 940°C, holding it at that temperature for 2.0 hours. Then, lower the temperature to 640°C and evacuate the vessel, reducing the pressure to 5.7 Pa. Hold this temperature for 3 hours, then stop evacuating. Next, introduce argon into the reaction vessel and cool it to room temperature for passivation treatment. After passivation, remove the vessel from the furnace. The magnesium granules should be stable and show no signs of ignition or smoke upon removal. The resulting mixture of halide and tantalum powder is then washed with water, acid-washed, filtered, and dried to separate the tantalum powder.

[0061] Then, tantalum powder was mixed with 50 ppm of P and subjected to treatment at 1450 °C and below 5.0 × 10⁻⁶. -3The tantalum powder was subjected to high-temperature, high-vacuum heat treatment for 1.0 hour under a pressure of Pa, followed by deoxygenation and acid washing to obtain the final tantalum powder. The final tantalum powder was fabricated into anode blocks according to the anode block mass, pressing density, anode block sintering temperature, and sintering time specified in Table 1, with other conditions conforming to the aforementioned GB / T3137 requirements. The anode blocks were then energized at 250V, and their electrical properties were tested according to the aforementioned GB / T3137 requirements. In the specific capacitance test, the test was conducted using a 30% H2SO4 solution followed by a 10% H3PO4 solution. The results are listed in Table 1.

[0062] Example 7

[0063] Take 10.0 kg of tantalum oxide, add 3.1 kg of magnesium granules, 1.5 kg of potassium chloride (KCl), and 1.5 kg of sodium chloride (NaCl), mix thoroughly, and place the mixture into a reaction vessel. Place another crucible containing 1.5 kg of tantalum powder with 3500 ppm hydrogen in it, and separate the air from the reaction vessel. Introduce argon gas into the reaction vessel, maintaining positive pressure. Place the reaction vessel in a furnace and heat it to 940°C, holding for 2.0 hours. Then, lower the temperature to 640°C and evacuate the vessel, reducing the pressure to 5.7 Pa. Hold for 3 hours, then stop evacuation. Introduce argon gas again and cool the vessel to room temperature for passivation. After passivation, remove the vessel from the furnace. The magnesium granules should be stable and show no signs of ignition or smoke upon removal. Wash the resulting mixture of halide and tantalum powder with water, acid, filter, and dry to separate the tantalum powder.

[0064] Then, tantalum powder was mixed with 50 ppm of P and subjected to treatment at 1450 °C and below 5.0 × 10⁻⁶. -3 The tantalum powder was subjected to high-temperature, high-vacuum heat treatment for 1.0 hour under a pressure of Pa, followed by deoxygenation and acid washing to obtain the final tantalum powder. The final tantalum powder was fabricated into anode blocks according to the anode block mass, pressing density, anode block sintering temperature, and sintering time specified in Table 1, with other conditions conforming to the aforementioned GB / T3137 requirements. The anode blocks were then energized at 250V, and their electrical properties were tested according to the aforementioned GB / T3137 requirements. In the specific capacitance test, the test was conducted using a 30% H2SO4 solution followed by a 10% H3PO4 solution. The results are listed in Table 1.

[0065] Comparative Example 1

[0066] Take 10.0 kg of tantalum oxide, add 5.46 kg of magnesium granules, and simultaneously add 2.5 kg of potassium chloride (KCl) and 2.5 kg of sodium chloride (NaCl). After mixing thoroughly, place the mixture into a reaction vessel, and separate the air from the reaction vessel. Only argon gas is introduced into the reaction vessel. Under positive pressure, the reaction vessel is placed in a furnace and heated to 940°C, held for 1 hour, then the temperature is lowered to 650°C and evacuated to reduce the pressure in the reaction vessel to 5.7 Pa. The pressure is held for 8 hours, then evacuation is stopped. Argon gas is then introduced into the reaction vessel again, and the temperature is raised to 940°C under positive pressure, held for 3 hours. After holding at this temperature, the mixture is cooled to room temperature for passivation treatment. After passivation, the mixture is removed from the furnace. During removal, the magnesium granules ignite and emit smoke. The resulting mixture of halide and tantalum powder is washed with water, acid-washed, filtered, and dried to separate the tantalum powder.

[0067] Then, tantalum powder was mixed with 50 ppm of P and subjected to treatment at 1450 °C and below 5.0 × 10⁻⁶. -3 The tantalum powder was subjected to high-temperature, high-vacuum heat treatment for 1.0 hour under a pressure of Pa, followed by deoxygenation and acid washing to obtain the final tantalum powder. The final tantalum powder was fabricated into anode blocks according to the anode block mass, pressing density, anode block sintering temperature, and sintering time specified in Table 1, with other conditions conforming to the aforementioned GB / T3137 requirements. The anode blocks were then energized at 250V, and their electrical properties were tested according to the aforementioned GB / T3137 requirements. In the specific capacitance test, the test was conducted using a 30% H2SO4 solution followed by a 10% H3PO4 solution. The results are listed in Table 1.

[0068] Table 1 Electrical Performance Data of Finished Tantalum Powder

[0069] As can be seen from Table 1:

[0070] After reducing the amount of magnesium used, the present invention enables the tantalum powder to be energized under a high voltage of 250V (the prior art generally uses a voltage below 200V). The resulting energized block has a high specific capacitance, and in the specific capacitance test, the difference between the test results using 30% H2SO4 solution and the test results using 10% H3PO4 solution is relatively small. In the breakdown voltage test, it shows a higher breakdown voltage.

[0071] Table 1 also shows that the anode blocks made with the tantalum powder described in this invention exhibit smaller differences in specific capacity after being energized, as tested with different acid solutions. It is generally believed that phosphoric acid and sulfuric acid have different surface tensions, resulting in different abilities to penetrate the ultrafine pores in the anode block. Therefore, the difference in specific capacity reflects the presence of ultrafine pores in the anode block. This further confirms that using the tantalum powder according to this invention can yield anode blocks with fewer ultrafine pores and a better microstructure.

Claims

1. A method for preparing tantalum powder by reducing tantalum oxide with an alkaline earth metal, such as magnesium (preferably magnesium particles), characterized in that: The method includes a reduction and heat preservation process carried out in a hydrogen-containing atmosphere, preferably, the hydrogen-containing atmosphere being pure hydrogen or a mixture of hydrogen and an inert gas; and / or The hydrogen-containing gas is obtained by introducing gaseous hydrogen-containing gas, or by adding a hydrogen-containing substance and causing it to release hydrogen gas.

2. A method for preparing tantalum powder by reducing tantalum oxide with an alkaline earth metal such as magnesium (preferably magnesium particles), comprising the following steps: (1) Mix tantalum oxide with an excess of alkaline earth metal reducing agent, and simultaneously mix in at least 10-200% by weight of at least one alkali metal 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°C (more preferably to 750-970°C, and even more preferably to 900-950°C), and then keep it at that temperature for, for example, for 1-3 hours, so that tantalum oxide and the reducing agent can fully undergo a reduction reaction. (3) After the heat preservation is completed, the temperature is lowered to 600-750℃ (preferably the heating furnace is lowered to 640-680℃), and the heating furnace is evacuated, for example, to below 10Pa, such as 5Pa, preferably to below 0.5Pa, and heat preservation is carried out under negative pressure to achieve the separation of excess metallic magnesium 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 the tantalum powder from the obtained mixture, for example by washing with water, acid washing, filtration, and drying. In step (1), after the air is extracted, the container is made to contain hydrogen gas, for example by introducing hydrogen gas (e.g., pure hydrogen, or a mixture of hydrogen and an inert gas), or by adding a hydrogen-containing substance (e.g., tantalum metal with adsorbed hydrogen) and causing it to release hydrogen gas. Preferably, the hydrogen-containing gas contains 0.5-10% nitrogen gas.

3. The manufacturing method according to claim 2, characterized in that: The amount of reducing agent added in step (1) is 5-50% more than the theoretical amount required for the complete reduction of tantalum oxide, preferably 10-48%, more preferably 10-45%, even more preferably 10-15% or 5-10%, or 15-20%.

4. The manufacturing method according to claim 2 or 3, characterized in that: The alkali metal chloride added in step (1) is 10-180% by weight of tantalum oxide, preferably 25-120%, more preferably 70-120% or 100-180%, and most preferably 15-80%, for example 25-80%.

5. The manufacturing method according to any one of claims 2-4, characterized in that: The alkali metal or alkaline earth metal halide mentioned in step (1) is one or more of NaCl, KCl, KF, KI, and MgCl2, preferably a mixture of NaCl and KCl, more preferably a mixture in which the mass ratio of sodium chloride to potassium chloride is 1:1-10, and most preferably about 1:

1.

6. The manufacturing method according to any one of claims 2-5, 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. Preferably, the amount of element B added is 1-100 ppm, more preferably 20-60 ppm, based on the amount of effective elements. And / or the added P element is 10-200 ppm, more preferably 30-90 ppm; And / or the added nitrogen element is 300-2500 ppm, more preferably 500-1200 ppm.

7. The manufacturing method according to claim 2, characterized in that: The hydrogen partial pressure of the hydrogen-containing gas in step (1) exceeds 0.050 kPa, preferably 0.1-200 kPa, more preferably 0.3-50 kPa, more preferably 0.3-20 kPa, even more preferably 0.5-2 kPa or 2-8 kPa, and even more preferably 0.1-0.3 kPa.

8. The manufacturing method according to any one of claims 1-7, further comprising, after step 5): High-temperature, high-vacuum heat treatment; To reduce oxygen levels, for example, by adding a small amount of magnesium particles; and Separation can be achieved, for example, through acid washing, filtration, and drying.

9. Tantalum powder manufactured by the manufacturing method according to any one of claims 1-8, and an anode block made from the tantalum powder.

10. Use of the tantalum powder according to claim 9 in the manufacture of capacitors.

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