Method for producing capacitor tantalum powder by reducing tantalum oxide with alkaline earth metal

Abstract

The present application relates to a kind of methods for producing capacitor tantalum powder using alkaline earth metal reduction of tantalum oxide.The method comprises the following steps: 1) mix tantalum oxide with excess alkaline earth metal reducing agent, while mixing in 10-200% of the weight of the tantalum oxide of at least one alkali metal or alkaline earth metal halide, heat the resulting mixture to a temperature of 700-1200°C in a heated furnace filled with inert gas, then hold for 1-10 hours to allow the reduction reaction between the tantalum oxide and the reducing agent to proceed fully; 2) after the holding period, cool to 600-800°C, and evacuate the furnace to below 10 Pa and maintain the negative pressure for 1-10 hours to separate the excess magnesium from the tantalum powder mixture; 3) then, under inert gas, raise the temperature of the furnace to 750-1200°C, preferably to 900-1050°C, and then hold for 1-6 hours to allow the tantalum powder to further sinter in the molten salt; 4) subsequently cool to room temperature and perform passivation treatment to obtain a mixture containing halide and tantalum powder; and 5) separate the tantalum powder from the resulting mixture.

Description

[0001] This application is a divisional application of Chinese Patent Application No. 202111533332.2, filed on December 15, 2021, entitled “Method for Producing Capacitor-Grade Tantalum Powder by Reducing Tantalum Oxide with Alkaline Earth Metal”. TECHNICAL FIELD

[0002] The present application belongs to the field of rare metal functional materials smelting, and specifically relates to a method for producing tantalum powder for high-voltage and high-reliability capacitors. BACKGROUND

[0003] 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, computers, automotive electronics, medical devices, radars, 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.

[0004] 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 is to inject liquid sodium into the stirring molten potassium fluorotantalate and dilute salt (such as KCl, NaCl, KF, etc.) at the same time. Potassium fluorotantalate is reduced by sodium to produce tantalum powder, and then subsequent processing is carried out to produce capacitor-grade tantalum powder. However, the voltage resistance of tantalum powder produced by this process is relatively poor. Currently, in order to improve the voltage resistance of tantalum powder produced by sodium reduction of potassium fluorotantalate, the general approach is to increase the sintering temperature and extend the sintering time of subsequent processing. However, increasing the sintering temperature and extending the sintering time will inevitably reduce the specific capacitance. The tantalum ingot hydrogenation method takes advantage of the brittleness of metallic tantalum. The tantalum ingot is hydrogenated, then crushed to powder, and then subjected to subsequent processing to produce capacitor-grade tantalum powder. The voltage resistance of tantalum powder produced by this process is excellent, but the specific capacity is relatively low.

[0005] The magnesium reduction of tantalum oxide method is expected to produce capacitor-grade tantalum powder with improved specific capacity and voltage resistance due to the change in the state of the reactants.

[0006] CN1308566A (application number 99808374.7) discloses a method for producing tantalum powder by reducing tantalum oxide with magnesium vapor. CN105033283A (application number 201510310262.2) also discloses a method for producing tantalum powder by reducing tantalum oxide with magnesium vapor. Although these two methods can produce tantalum powder, they have high cost and difficult process control because of the strict requirement for raw materials (both require a form that can be passed through by gas) and the use of gaseous reducing agents. Moreover, the tantalum powder produced by these methods has a large specific surface and strong activity, poor resistance to sintering, and poor specific capacitance of the capacitor made from the tantalum powder, whether in terms of breakdown voltage or after high-voltage energization, and the pressure resistance of the capacitor tantalum powder has not been significantly improved.

[0007] CN1251325A discloses a method for producing tantalum powder by reducing tantalum oxide with an alkaline earth metal or a rare earth metal. The reduction is performed in two stages at a controlled temperature, the first stage is to reduce the tantalum oxide to a composition corresponding to TaO x , where X = 0.5-1.5, and then the oxide of the reducing agent in the first-stage reduction product is removed by acid washing, and then the second-stage reduction is performed to produce tantalum powder. This method requires removal of the oxide of the reducing agent before the second-stage reduction, which is complicated. Moreover, the tantalum powder produced by this method has not significantly improved the pressure resistance of the capacitor tantalum powder.

[0008] There is also a method for preparing tantalum powder by self-propagating high-temperature synthesis (SHS) in the prior art. However, this method needs to be performed at a temperature of at least 2000°C, and the reaction is too fast, which is difficult to control and has too high a requirement for the process equipment. In addition, the tantalum powder obtained is not uniform and cannot meet the needs of manufacturing high-reliability capacitors.

[0009] Without being bound by general theory, the inventors have found through extensive research that the tantalum powder produced by the current processes has a low specific capacitance under high-voltage energization conditions and a low breakdown voltage, and therefore has not significantly improved the pressure resistance of the capacitor tantalum powder. SUMMARY

[0010] An object of the present application is to provide a method for preparing capacitor tantalum powder by reducing tantalum oxide with an alkaline earth metal such as magnesium, and capacitor tantalum powder produced by this method, which has high reliability relative to other methods for producing the same grade of capacitor tantalum powder, and has a high specific capacitance under high-voltage energization conditions and a high breakdown voltage, significantly improving the pressure resistance of the capacitor tantalum powder. In other words, the capacitor tantalum powder produced by the method of the present application can withstand higher voltages and has higher reliability.

[0011] Another object of the present application is to provide a process for producing tantalum powder for capacitors, which is simple in process, easy to operate and control. Accordingly, the present application provides a process for producing tantalum powder by reducing tantalum oxide with an alkaline earth metal such as magnesium, comprising the steps of:

[0012] (1) mixing tantalum oxide with an excess amount of an alkaline earth metal reducing agent, while mixing in 10-200% by weight of the tantalum oxide of at least one halide of an alkali metal and / or an alkaline earth metal, charging the mixture into a container and placing the container in a heating furnace, raising the temperature of the heating furnace to a temperature of 700-1200°C in an inert gas and maintaining the temperature for a period of time, for example, 1-10 hours, to allow the tantalum oxide to be reduced with the reducing agent;

[0013] (2) after the maintenance, raising the temperature of the heating furnace to a temperature of 600-800°C, evacuating the heating furnace to a pressure of 10 Pa or less and maintaining the negative pressure for a period of time, for example, 1-10 hours, for example, 1-10 hours, to separate the excess magnesium from the mixture of the tantalum powder;

[0014] (3) then, raising the temperature of the heating furnace to a temperature of 750-1200°C in an inert gas and maintaining the temperature for a period of time, for example, 1-10 hours, to further sinter the tantalum powder in the molten salt;

[0015] (4) subsequently cooling to room temperature and performing a passivation treatment to obtain a mixture containing the halide and the tantalum powder;

[0016] (5) separating the tantalum powder from the obtained mixture, for example, by performing water washing, acid washing, filtration and drying.

[0017] The alkaline earth metal reducing agent in step (1) is preferably magnesium, more preferably magnesium particles. The particle size of the magnesium particles is not limited. However, the applicant has found through extensive research that magnesium particles having a particle size of 150-4000 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 for 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 easy to mix uniformly and are not conducive to optimization of the properties of the tantalum powder. The excess amount of the reducing agent refers to an amount exceeding 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, the excess amount is preferably 50-300% of the theoretical amount, more preferably 50-200%, more preferably 100-200%, more preferably 50-100% or 70-150%, more preferably 90-120%, and most preferably 100-150%.

[0018] In step (1), due to the appearance of reduction heat, the tantalum powder inevitably sinter to a certain extent. The present inventors have found through extensive research that the addition of excess magnesium metal and halides of alkali metals or alkaline earth metals can absorb a certain amount of reduction heat, adjust the sintering of the reduction heat on the tantalum powder, and make the sintering of the reduction heat on the tantalum powder reach an appropriate degree, which is more conducive to improving the pressure resistance of the tantalum powder.

[0019] The alkali metal and / or alkaline earth metal halide added in step (1) preferably accounts for 10-180%, preferably 25-120%, more preferably 70-120% or 100-180%, and most preferably 15-80%, for example 25-80%, of the weight of the tantalum oxide. The alkali metal or alkaline earth halide is preferably in the form of particles. No limitation is imposed on the particle size, but the applicants have found that particles of 70 μm-4000 μm are more suitable for the present technology, and the tantalum powder obtained by reduction has better pressure resistance.

[0020] The inert gas generally refers to rare gases, such as helium, neon, and argon. Although nitrogen is sometimes regarded as an inert gas due to its stable nature, it is not suitable as an inert protective gas in the present application because of the relatively high reduction temperature, at which nitrogen is very active and not suitable as an inert protective gas. However, the applicants have found through extensive research that the presence of a small amount of nitrogen in the above-mentioned inert gas does not harm the inert protective atmosphere, and can also conveniently achieve nitrogen doping of the tantalum powder. From the perspective of achieving better nitrogen doping effect of the tantalum powder, the inert gas in step (1) can preferably contain 0.5-10% nitrogen.

[0021] Preferably, the halide of the alkali metal or 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 ratio of sodium chloride to potassium chloride in the mixture is 1:1-10, and most preferably about 1:1.

[0022] Preferably, one or more compounds containing B, P, and / or N elements can also be added as additives in step (1) to dope the tantalum powder. Preferably, the amount of B element added is 1-100 ppm, more preferably 20-60 ppm; the amount of P element added is preferably 10-200 ppm, more preferably 30-90 ppm; and the amount of N element added is preferably 300-2500 ppm, more preferably 500-1200 ppm, in terms of the amount of effective elements. 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 in terms of the amounts of B, P, and / or N.

[0023] Preferably, in step (1), the heating furnace is heated to 750-1000°C. More preferably, the heating furnace is heated to 900-1000°C.

[0024] In step 2), since the melting point of magnesium is relatively high, magnesium vapor is difficult to diffuse outside the reactor, but is condensed into solid in the low temperature zone of the reactor, thereby achieving separation.

[0025] Preferably, in step (2), the heating furnace temperature is 650-800°C. More preferably, the heating furnace temperature is 650-720°C. Preferably, the heating furnace is evacuated to below 5 Pa, preferably below 0.5 Pa.

[0026] The inert gas in step (3) can be the same as or different from the inert gas in step (1). Preferably, in step (1) and / or (3), a positive pressure is maintained in the furnace.

[0027] Preferably, in step (3), the heating furnace is heated to 900-1050°C.

[0028] Preferably, the method of the present application further comprises, after step (5), heat treatment such as high-temperature high-vacuum heat treatment, oxygen reduction, pickling, and then separation of tantalum powder, for example by filtration, drying, to obtain tantalum powder suitable for making high-reliability tantalum capacitors. These treatments are processes known in the art. In other words, these treatments can employ any process known in the art. For example, the high-temperature high-vacuum heat treatment and passivation herein can employ the methods provided in patents CN201110039272.9, CN201120077798.1, CN201120077680.9, CN201120077305.4, etc., the oxygen reduction can employ the methods provided in patents CN201420777210.7, CN201420777210.7, the pickling can employ the methods provided in patents CN201210548101.3, CN201280077499.5, CN201210548008.2, etc.

[0029] As an alternative to the incorporation of N, P and / or B elements in step (1), the present application can also separately comprise a 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 in the aforementioned high-temperature high-vacuum heat treatment step. It is particularly preferred to add P elements. The addition of P elements can increase the specific capacity, and as long as the total amount of P addition is controlled, the effect of increasing the specific capacity is the same regardless of when the addition is made.

[0030] The above product tantalum powder is pressed into a block, sintered, and energized under high pressure conditions, and the electrical properties of the energized block are tested, and it is found that the energized block has higher specific capacity and shows higher breakdown voltage in the breakdown voltage test.

[0031] Under the same high voltage condition, the tantalum powder manufactured by the present application has higher specific capacity and higher breakdown voltage than the same grade of capacitor tantalum powder manufactured by other methods. Therefore, the tantalum powder manufactured by the present application is more suitable for manufacturing high voltage and high reliability tantalum capacitor.

[0032] Furthermore, the process of the present application is simple and easy to control. For example, in all the steps of the present application, no microwave is used and no excessively high temperature above 1300℃ is used. Therefore, the equipment used is relatively simple and the tantalum powder preparation process is safer.

[0033] Without being bound by general theory, according to the analysis principle of powder liquid phase sintering theory, the inventors believe that the reason for the excellent effect of the present application is as follows: in step (1), as the temperature rises, the metal magnesium and the alkali metal or alkaline earth metal halide melt into liquid phase. The liquid magnesium has high reducing property, which reduces the tantalum oxide and generates new tantalum powder particles with strong surface activity. Under the conditions of the present application, the reduction heat realizes a certain degree of sintering of the tantalum powder particles, and constructs a suitable spatial structure for capacitor manufacturing; then, under the further sintering in the molten salt (mainly alkali metal halide) liquid phase, the edges and corners of the large particles of the tantalum powder and the excessively ultra-fine tantalum powder particles are dissolved in the liquid phase. As the process continues, the concentration of tantalum in the liquid phase exceeds the saturation concentration, and then it will be deposited and combined as part of the large particles in some parts of the large particles of tantalum. In this way, the size of the tantalum powder particles is more uniform, and the particles are smooth, the sintering neck is thick, and the ultra-fine particles are less. After that, the obtained tantalum powder is subjected to high temperature and high vacuum sintering, oxygen reduction and acid washing treatment according to the prior art, and the tantalum powder suitable for manufacturing high voltage and high reliability capacitor will be obtained. BRIEF DESCRIPTION OF DRAWINGS

[0034] 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.

[0035] Figure 1 A scanning electron microscope photograph of the tantalum powder obtained according to the present application is given.

[0036] This drawing illustrates that the size of the obtained tantalum powder particles is more uniform, and the particles are smooth, the sintering neck is thick, and the ultra-fine particles are less. DETAILED DESCRIPTION

[0037] 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 are not specified in the examples, and the conventional conditions are used. The reagents or instruments used are not specified by the manufacturer, and are all conventional products that can be obtained by purchase.

[0038] For purposes of this specification, the recitation of amounts, ranges, and other specifications in the specification and claims that follow mean "about" unless otherwise specified. Accordingly, the numerical parameters given in the

[0039] The analysis of impurity content in tantalum powder is carried out according to Chinese standard GB / T15076.1-15076.15, and the physical properties are carried out according to the provisions of industry standard YS / T573-2015. The test of electrical properties of tantalum powder is carried out according to the provisions of Chinese standard GB / T3137.

[0040] Example 1

[0041] Take 10.0 kg of tantalum oxide, add 5.46 kg of metal magnesium particles, and add 5.0 kg of potassium chloride (KCl) at the same time. After mixing uniformly, load into a reaction container, and separate (i.e. extract) the air in the reaction container. Introduce argon into the reaction container, and place the reaction container into a heating furnace under the condition of maintaining positive pressure, heat to 940℃, and keep for 4.0 hours to make the tantalum oxide fully reduced. Then, reduce the temperature to 680℃ to perform vacuum extraction, reduce the pressure in the reaction container to 5.7 Pa, keep for 6 hours, and stop vacuum extraction. Then, introduce argon into the reaction container again under the condition of maintaining positive pressure, heat to 940℃, and keep for 5 hours to sinter the tantalum powder in the molten halide. After the end of keeping, reduce to room temperature to perform passivation treatment; then, perform water washing, acid washing, filtration, and drying on the obtained mixture of halide and tantalum powder, so as to separate the tantalum powder.

[0042] Then, add 50 ppm of P to the tantalum powder, and perform high-temperature high-vacuum heat treatment at 1400℃ and under a pressure of less than 5.0x10 -3 Pa for 0.5 hours, and then perform oxygen reduction and acid washing to obtain the final tantalum powder. According to the provisions of the anode block mass, the pressing density, the anode block sintering temperature, and the sintering time 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 under the condition of 200V, and then the electrical properties are tested according to the aforementioned GB / T3137 requirements, and the measured results are listed in Table 1.

[0043] Example 2

[0044] Take 10.0 kg of tantalum oxide, mixed with 5.46 kg of magnesium metal particles, while mixing 2.5 kg of potassium chloride (KCl) and 2.5 kg of sodium chloride (NaCl), mix evenly and then load into the reaction container, separate the air in the reaction container. Argon is introduced into the reaction container, and the reaction container is placed in the heating furnace under positive pressure conditions, heated to 940°C, and kept for 1.0 hour, then the temperature is lowered to 650°C for evacuation, the pressure in the reaction container is reduced to 5.7 Pa, and kept for 8 hours. Stop evacuation, and then introduce argon into the reaction container under positive pressure conditions to raise the temperature to 940°C, and keep for 3 hours. After the holding period is over, the temperature is lowered to room temperature, and passivation treatment is performed; the obtained halide and tantalum powder mixture is washed with water, pickled, filtered, and dried to separate the tantalum powder.

[0045] Then, the tantalum powder is mixed with 50 ppm of P, and high-temperature high-vacuum heat treatment is performed at 1400°C and a pressure of less than 5.0 x 10 -3 Pa for 0.5 hours, and then oxygen reduction and pickling are performed 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 obtained anode block is energized under the condition of 200V, and then the electrical performance is tested according to the requirements of the aforementioned GB / T3137. The test results are listed in Table 1.

[0046] Example 3

[0047] Take 10.0 kg of tantalum oxide, mixed with 5.46 kg of magnesium metal particles, while mixing 2.5 kg of potassium chloride (KCl) and 2.5 kg of sodium chloride (NaCl), mix evenly and then load into the reaction container, separate the air in the reaction container. Argon is introduced into the reaction container, and the reaction container is placed in the heating furnace under positive pressure conditions, heated to 940°C, and kept for 1.0 hour, then the temperature is lowered to 650°C for evacuation, the pressure in the reaction container is reduced to 5.7 Pa, and kept for 8 hours. Stop evacuation, and then introduce argon into the reaction container under positive pressure conditions to raise the temperature to 940°C, and keep for 3 hours. After the holding period is over, the temperature is lowered to room temperature, and passivation treatment is performed; the obtained halide and tantalum powder mixture is washed with water, pickled, filtered, and dried to separate the tantalum powder.

[0048] Then, the tantalum powder is mixed with 50 ppm of P, and high-temperature high-vacuum heat treatment is performed at 1400°C and a pressure of less than 5.0 x 10 -3The final tantalum powder is obtained by high temperature and high vacuum heat treatment of the tantalum powder under a pressure of 5.0 x 10 Pa for 0.5 hours, followed by oxygen reduction and acid washing. 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 according to the aforementioned GB / T3137, and the anode blocks are energized under a voltage of 200 V, and then the electrical properties are tested according to the aforementioned GB / T3137, and the test results are listed in Table 1.

[0049] Example 4

[0050] Take 10.0 kg of tantalum oxide containing 50 ppm boron, mix in 4.00 kg of magnesium metal particles, and simultaneously mix in 1.5 kg of potassium chloride (KCl) and 1.5 kg of sodium chloride (NaCl), mix uniformly, and then load into a reaction container, and separate the air in the reaction container. Argon gas is introduced into the reaction container, and the reaction container is placed into a heating furnace under a positive pressure condition, heated, and raised to a temperature of 950°C, and held for 4.0 hours, and then the temperature is lowered to 680°C for evacuation, and the pressure in the reaction container is reduced to 5.7 Pa, and held for 6 hours, and then the evacuation is stopped, and argon gas is introduced into the reaction container under a positive pressure condition, and the temperature is raised to 950°C, and held for 1 hour. After the holding is completed, the temperature is lowered to room temperature, and passivation treatment is performed; the obtained halide and tantalum powder mixture is washed with water, washed with acid, filtered, dried, and the tantalum powder is separated.

[0051] The tantalum powder is mixed with 50 ppm of P, and high temperature and high vacuum heat treatment is performed at 1400°C and a pressure of less than 5.0 x 10 -3 Pa for 0.5 hours, and then oxygen reduction and acid washing are performed to obtain the 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 according to the aforementioned GB / T3137, and the anode blocks are energized under a voltage of 200 V, and then the electrical properties are tested according to the aforementioned GB / T3137, and the test results are listed in Table 1.

[0052] Example 5

[0053] Take 10.0 kg of tantalum oxide containing 50 ppm boron, mix in 4.00 kg of magnesium metal particles, and simultaneously mix in 1.5 kg of potassium chloride (KCl) and 1.5 kg of sodium chloride (NaCl), mix uniformly, and then load into a reaction container, and separate the air in the reaction container. Argon gas is introduced into the reaction container, and the reaction container is placed into a heating furnace under a positive pressure condition, heated, and raised to a temperature of 950°C, and held for 4.0 hours, and then the temperature is lowered to 680°C for evacuation, and the pressure in the reaction container is reduced to 5.7 Pa, and held for 6 hours, and then the evacuation is stopped, and argon gas is introduced into the reaction container under a positive pressure condition, and the temperature is raised to 950°C, and held for 1 hour. After the holding is completed, the temperature is lowered to room temperature, and passivation treatment is performed; the obtained halide and tantalum powder mixture is washed with water, washed with acid, filtered, dried, and the tantalum powder is separated.

[0054] The tantalum powder is then mixed with 50 ppm P and subjected to high-temperature high-vacuum heat treatment at 1400°C under a pressure of less than 5.0 x 10 -3 Pa for 0.5 hours, and then subjected to oxygen reduction and acid washing to obtain a 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 under a voltage of 200 V, and then the electrical performance is tested in accordance with the requirements of the aforementioned GB / T3137. The test results are listed in Table 1.

[0055] Example 6

[0056] 10.0 kg of tantalum oxide containing 1500 ppm of nitrogen is mixed with 4.00 kg of magnesium metal particles, and 1.5 kg of potassium chloride (KCl) and 1.5 kg of sodium chloride (NaCl) are added. The mixture is uniformly mixed and then loaded into a reaction container. The air in the reaction container is removed. Argon gas is introduced into the reaction container, and the reaction container is placed into a heating furnace under a positive pressure condition. The temperature is raised to 900°C, and the reaction container is maintained at this temperature for 4.0 hours. The temperature is then lowered to 680°C, and the pressure in the reaction container is reduced to 5.7 Pa by evacuation. The reaction container is maintained at this temperature for 6 hours. The evacuation is stopped, and the temperature is raised to 900°C by introducing argon gas into the reaction container under a positive pressure condition. The reaction container is maintained at this temperature for 6 hours. After the maintenance is completed, the temperature is lowered to room temperature, and passivation treatment is performed. The obtained halide and tantalum powder mixture is subjected to water washing, acid washing, filtration, and drying to separate the tantalum powder.

[0057] The tantalum powder is then mixed with 50 ppm P and subjected to high-temperature high-vacuum heat treatment at 1400°C under a pressure of less than 5.0 x 10 -3 Pa for 0.5 hours, and then subjected to oxygen reduction and acid washing to obtain a final tantalum powder.

[0058] 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 under a voltage of 200 V, and then the electrical performance is tested in accordance with the requirements of the aforementioned GB / T3137. The test results are listed in Table 1.

[0059] Example 7

[0060] Take 10.0 kg of tantalum oxide containing 80 ppm of phosphorus, add 4.00 kg of metallic magnesium particles, and 8.0 kg of potassium chloride (KCl) is added. Mix well and load into a reaction vessel. Remove air from the reaction vessel. Introduce argon gas into the reaction vessel. Keep the pressure positive and place the reaction vessel into a heating furnace. Heat to 900°C and maintain for 4.0 hours. Then reduce the temperature to 680°C and perform vacuum extraction to reduce the pressure in the reaction vessel to 5.7 Pa and maintain for 6 hours. Stop the vacuum extraction and introduce argon gas into the reaction vessel to maintain a positive pressure. Heat to 900°C and maintain for 6 hours. After the maintenance, reduce the temperature to room temperature and perform passivation treatment. Mix the obtained halide and tantalum powder, and perform water washing, acid washing, filtration, and drying to separate the tantalum powder.

[0061] Then, the tantalum powder is subjected to high-temperature high-vacuum heat treatment at 1400°C and a pressure lower than 5.0 x 10 -3 Pa for 0.5 hours. Then, oxygen reduction and acid washing are performed to obtain the final tantalum powder. The final tantalum powder is used to make 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 GB / T3137. The anode block is energized at 200 V, and then the electrical performance is tested according to the requirements of GB / T3137. The test results are listed in Table 1.

[0062] Comparative Example 1

[0063] Take 10.0 kg of tantalum oxide and load into a rotary kiln type reaction vessel (refer to Figure Three of CN1308566A). Remove air from the reaction vessel and introduce argon gas into the reaction vessel. Keep the pressure positive and heat to 950°C. Rotate the rotary kiln to facilitate the reaction of magnesium vapor with the tantalum oxide. Introduce 3.62 kg of magnesium vapor and maintain for 4.0 hours. After the maintenance, reduce the temperature to room temperature and perform passivation treatment. Perform acid washing, filtration, and drying to obtain the tantalum powder. Due to the severe sintering of the tantalum powder when subjected to heat treatment at 1400°C and a pressure lower than 5.0 x 10 -3 Pa, the tantalum powder cannot be broken into powder. Therefore, a lower heat treatment temperature is used here. The tantalum powder is subjected to heat treatment at 1250°C and a pressure lower than 5.0 x 10 -3The tantalum powder obtained is subjected to high-temperature high-vacuum heat treatment at Pa for 0.5 hour, and then to oxygen reduction and acid pickling. The tantalum powder obtained is used to make anode blocks 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. Since the tantalum blank pressed from the tantalum powder has too large shrinkage and serious deformation after sintering at 1450°C and 1420°C, and the specific capacity is only 2370 μFV / g, a lower anode block sintering temperature is used here. Since the anode block has breakdown when the energizing voltage is 110V during the energizing process of the tantalum powder, the energizing cannot be carried out, and therefore the energizing is carried out at 100V. The electrical properties are then tested according to the requirements of the aforementioned GB / T3137, and the test results are listed in Table 1.

[0064] Comparative Example 2

[0065] 4.0 kg of magnesium metal is charged into a reactor with stirring paddle and external air cooling device (the reactor used in CN1251325A is referred to), the air in the reaction vessel is extracted, argon is introduced into the reaction vessel, and the temperature is raised to 780°C under the condition of maintaining positive pressure. The stirring paddle is rotated, and the tantalum oxide is added into the reactor in batches according to the requirements of patent CN1251325A. The temperature of the reactor is controlled at 780°C-800°C, and a total of 10.0 kg of tantalum oxide is added. The temperature is lowered to room temperature, and the obtained material is subjected to passivation treatment. The obtained material is subjected to acid pickling, filtration and drying to obtain a tantalum powder with an oxygen content of 4%. The tantalum powder with an oxygen content of 4% is reduced again with 4.0 kg of magnesium metal at a temperature of 800°C-815°C. The obtained material is subjected to acid pickling, filtration and drying to obtain a tantalum powder. Since the tantalum powder has too large shrinkage and serious deformation after sintering at 1400°C under a pressure of less than 5.0 x 10 -3 Pa, the sintering is serious, and the tantalum powder cannot be broken into powder. Therefore, a lower heat treatment temperature is used here. The tantalum powder is subjected to high-temperature high-vacuum heat treatment at 1250°C under a pressure of less than 5.0 x 10 -3 The tantalum powder obtained is subjected to high-temperature high-vacuum heat treatment at Pa for 0.5 hour, and then to oxygen reduction and acid pickling. The tantalum powder obtained is used to make anode blocks 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. Since the tantalum blank pressed from the tantalum powder has too large shrinkage and serious deformation after sintering at 1450°C and 1420°C, and the specific capacity is only 2370 μFV / g, a lower anode block sintering temperature is used here. Since the anode block has breakdown when the energizing voltage is 110V during the energizing process of the tantalum powder, the energizing cannot be carried out, and therefore the energizing is carried out at 100V. The electrical properties are then tested according to the requirements of the aforementioned GB / T3137, and the test results are listed in Table 1.

[0066] Table 1 Electrical property data of finished tantalum powder

[0067]

[0068] From Table 1, it can be seen that:

[0069] The tantalum powder produced by the present application can be energized under higher pressure conditions than other methods for producing the same grade of capacitor tantalum powder, and the energized block obtained has a higher specific capacity, and shows a higher breakdown voltage in the breakdown voltage test.

Claims

1. A method for producing tantalum powder from tantalum oxide by using magnesium particles, comprising the steps of: (1) mixing tantalum oxide with an excess of magnesium particles, while mixing in 10 to 200% by weight of the tantalum oxide of at least one halide of an alkali metal or a halide of an alkaline earth metal, heating the resulting mixture in a furnace filled with an inert gas to a temperature of 700 to 1200°C, and then holding the temperature, so that the tantalum oxide and the magnesium particles undergo a reduction reaction; (2) after the holding is completed, cooling to 600 to 800°C, and evacuating the furnace to 10 Pa or less, and holding the temperature under negative pressure; (3) then, under an inert gas, raising the temperature of the furnace to 750 to 1200°C, and then holding the temperature, so that the tantalum powder is further sintered in a molten salt; (4) then, cooling to room temperature and performing a passivation treatment, to obtain a mixture containing a halide and tantalum powder; and (5) separating the tantalum powder from the resulting mixture, characterized in that, in step (1), one or more compounds containing B, P, and / or N elements are added as an additive to dope the tantalum powder, the amount of B element added is 1 to 100 ppm in terms of the effective element amount, and / or the amount of P element added is 10 to 200 ppm, and / or the amount of N element added is 300 to 2500 ppm, and wherein the magnesium particles have a particle size of 150 to 4000 μm. The amount of B element added is 20 to 60 ppm in terms of the effective element amount, and / or the amount of P element added is 30 to 90 ppm, and / or the amount of N element added is 500 to 1200 ppm. The amount of magnesium particles added in step (1) is 50 to 300% more than the theoretical amount required for complete reduction of the tantalum oxide. The inert gas in step (1) is an inert gas containing 0.5 to 10% of nitrogen. In step (1), the resulting mixture is heated to 900 to 1000°C. The holding in step (1) is continued for 1 to 10 hours. In step (2), after the holding is completed, the temperature is cooled to 650 to 800°C. In step (1), the halide of an alkali metal is added in an amount of 10 to 180% by weight of the tantalum oxide. In step (2), the furnace is evacuated to 0.5 Pa or less. The holding in step (2) is continued for 1 to 10 hours. In step (3), the temperature is raised to 900 to 1050°C. The separation is performed by water washing, acid washing, filtration, and drying. The amount of magnesium particles added in step (1) is 100 to 200% more than the theoretical amount required for complete reduction of the tantalum oxide. The amount of magnesium particles added in step (1) is 90 to 120% more than the theoretical amount required for complete reduction of the tantalum oxide. The amount of the halide of an alkali metal added in step (1) is 25 to 120% by weight of the tantalum oxide. The amount of the halide of an alkali metal added in step (1) is 25 to 80% by weight of the tantalum oxide. The halide of an alkali metal or an alkaline earth metal in step (1) is a mixture of one or more of NaCl, KCl, KF, KI, and MgCl2. The halide of an alkali metal or an alkaline earth metal in step (1) is a mixture of NaCl and KCl. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2. The method of claim 1, wherein: ​ ​ ​ 3. The method according to claim 1 or 2, characterized in that: ​ 4. The method according to any one of claims 1-3, characterized by: ​ 5. The method according to any one of claims 1-3, characterized by: ​ 6. The method of any one of claims 1-3, wherein: ​ 7. The method of any one of claims 1-3, wherein: ​ 8. The method of claim 1, wherein: ​ 9. The method of any one of claims 1-3, wherein: ​ 10. The method of any one of claims 1-3, wherein: ​ 11. The method of any one of claims 1-3, wherein: ​ 12. The method of any one of claims 1-3, wherein: ​ 13. The method of any one of claims 1-3, wherein: ​ 14. The method of any one of claims 1-3, wherein: ​ 15. The method of claim 8, wherein: ​ 16. The method of claim 15, wherein: ​ 17. The method of any one of claims 1-3, wherein: ​ 18. The method of claim 17, wherein: ​ 19. The method of claim 18, wherein: The ratio of NaCl to KCl in the mixture of NaCl and KCl is 1:

1.

20. The method of any one of claims 1-3, wherein: The inert gas in step (3) is the same as or different from the inert gas in step (1).

21. The method according to any one of claims 1-3, wherein the excess metallic magnesium is separated from the tantalum powder mixture in step (2).

22. The method according to any one of claims 1-3, further comprising after step (5): high temperature high vacuum heat treatment; oxygen reduction; and separation.

23. The method according to claim 22, wherein the oxygen reduction is performed by incorporating a small amount of magnesium particles.

24. The method according to claim 22, wherein the separation is performed by pickling, filtering, and drying.

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