Method for deoxidizing tantalum powder and tantalum powder prepared by same

Abstract

The invention relates to a method for deoxidizing tantalum powder and the tantalum powder prepared by the method. The method includes separating the tantalum powder to be deoxygenated from a deoxidizer such as Mg magnesium powder / chips (e.g., by using a perforated metal plate / mesh), and vaporizing the deoxidizer by heating and contacting the deoxidizer with the tantalum powder to be deoxygenated.

Description

Technical Field

[0001] The invention belongs to the field of rare metal smelting, and in particular relates to a method for preparing tantalum powder for capacitors by deoxidizing gaseous magnesium metal.

[0002] In the electronics industry, the main use of tantalum powder is to manufacture electrolytic capacitors (often referred to as "capacitors" in this field, and the two can be used interchangeably in this article). The development trend of tantalum electrolytic capacitors is to require high capacitance, low leakage current and low equivalent series resistance (low loss for the anode). Tantalum powder, which is the main material for making tantalum electrolytic capacitor anodes, requires low impurity content, especially low O, C, Ni, Mg, and Fe content, because the presence of O, C, Mg, Fe, and Ni in tantalum powder will cause the capacitor leakage current to increase and the breakdown voltage to decrease. Therefore, it is hoped in the art to reduce one or more of these elements.

[0003] There are two main methods for producing tantalum powder for capacitors: one is to reduce potassium fluorotantalate with metallic sodium, purify tantalum powder after separating by-products, and then obtain tantalum powder through heat treatment; the second method is to reduce tantalum oxide with metallic magnesium, purify tantalum powder after separating by-products, and then obtain tantalum powder through heat treatment. Although the second method is also commonly used, sometimes it is found that the content of impurities such as residual magnesium in the obtained tantalum powder is relatively high.

[0004] In addition, among common impurities, oxygen has certain special properties. Since tantalum has a great affinity for oxygen, the tantalum powder prepared by the above method usually contains a high oxygen content, which is very unfavorable for the subsequent preparation of capacitors, especially in terms of leakage current, brittleness, etc., which brings great risks, so partial deoxidation treatment must be carried out. Usually, the deoxidation of tantalum powder is carried out using metal magnesium as a reducing agent.

[0005] In order to solve the deoxidation problem of tantalum powder for capacitors, many solutions have been proposed.

[0006] The conventional operation of deoxidizing tantalum powder in industrial production is generally as described in Chinese patent CN102965525A, that is, the tantalum powder to be deoxidized is mixed with metal magnesium powder / chips and evenly loaded into a tantalum crucible, heated to a suitable reaction temperature for deoxidation, and then the excess metal magnesium is separated by inert gas argon or vacuum evaporation. This method has two disadvantages: first, impurities (C, Fe, Ni, etc.) in the magnesium powder / chips will be brought into the tantalum powder; second, there is local liquid metal magnesium at the usual deoxidation temperature, which will cause local liquid phase sintering of the tantalum powder. As a result, the pore structure distribution of the anode block obtained by sintering the tantalum powder is poor. Moreover, the tantalum powder also has the problem of high content of impurity magnesium.

[0007] CN101052488A discloses a method for deoxidizing valve metal powder, in particular niobium powder, tantalum powder or alloys thereof. The method uses a deoxidizer selected from the group consisting of calcium, barium, lanthanum, yttrium and cerium to treat the valve metal powder, and can produce a valve metal powder characterized by low content of sodium, potassium and magnesium. The valve metal powder is characterized by a ratio of the sum of the sodium, potassium and magnesium contents to the capacitance of less than 3ppm / 10000μFV / g.

[0008] CN1123206A discloses a method for preparing tantalum powder by adding magnesium powder to tantalum powder prepared by reducing potassium fluorotantalate with sodium metal, removing oxygen present in the tantalum powder without conventional granulation heat treatment, then pickling and drying, and the tantalum powder prepared by the method. CN101774018B discloses a method for preparing electron tube metal powder, especially niobium and tantalum powder, by reducing the corresponding electron tube metal oxide powder with gaseous reducing metal / metal hydride in the presence of an inert carrier gas. The method requires the use of an inert carrier gas to drive magnesium vapor, which increases system complexity and cost.

[0009] CN105033283A discloses a method for preparing Ta and / or Nb fine metal powder containing or not containing one or more metals selected from Ta, Nb, Ti, Mo, W, V, Zr and Hf by contacting the metal oxide with a gaseous reducing agent, preferably an alkaline earth metal, until the reduction reaction is almost completed, followed by leaching, further deoxidation and sintering. The method requires the use of an inert carrier gas to drive magnesium vapor, which increases system complexity and cost.

[0010] Moreover, a common problem in the prior art is that deoxidizers such as magnesium often contain various impurities, especially Fe, which will inevitably enter the final tantalum powder product together with a small amount of Mg in the deoxidizer, affecting the purity of the obtained tantalum powder product. Summary of the invention

[0011] The object of the present invention is to provide a method for preparing tantalum powder by deoxidizing gaseous magnesium metal and the tantalum powder prepared by the method in view of the deficiencies of the prior art.

[0012] An object of the present invention is to provide a method for preparing tantalum powder having a low overall impurity content (especially Mg and / or Fe, etc.).

[0013] Another object of the present invention is to provide a method for preparing tantalum powder which avoids local liquid phase sintering and ensures that the obtained tantalum powder product has a good pore structure, a low impurity content (especially Mg and / or Fe, etc.), and good electrical properties (especially low leakage current).

[0014] Another object of the present invention is to provide a method for preparing tantalum powder which is easy to operate and requires very simple equipment.

[0015] According to a first aspect, the present invention relates to a method for deoxidizing tantalum powder, the method comprising: separating the tantalum powder to be deoxidized from a deoxidizing agent such as Mg powder / chips (for example, by using a perforated metal plate / net), and vaporizing the deoxidizing agent by heating and contacting it with the tantalum powder to be deoxidized.

[0016] In a preferred embodiment, the method comprises the following steps:

[0017] (a) placing a deoxidizer such as magnesium powder / chips into the bottom of the crucible and preferably scraping it evenly;

[0018] (b) placing a perforated metal sheet / mesh on top of the deoxidizer;

[0019] (c) placing the tantalum powder to be deoxidized on a perforated metal plate / net;

[0020] (d) placing the crucible in a reaction vessel, evacuating the reaction vessel, and then filling the reaction vessel with an inert gas such as argon to normal pressure;

[0021] (e) heating the reaction vessel to 750-1000° C. (preferably by placing the reaction vessel in a furnace and heating it), and then keeping the temperature, preferably keeping the temperature for 0.5-3 hours;

[0022] (f) starting the vacuum system, evacuating the reactor to a vacuum (e.g., to 1000-70 Pa) to carry out the reaction, e.g., for 2-6 hours;

[0023] (g) cooling the reacted tantalum powder to room temperature; and

[0024] (f) Optionally, the deoxidized tantalum powder is acid-washed to remove by-products, washed with water, dried and sieved to obtain finished tantalum powder.

[0025] The crucible material mentioned in the above step (a) can be carbon steel, iron or tantalum, preferably tantalum. The "magnesium powder / chips" mentioned can be magnesium powder or magnesium chips, or a mixture of magnesium powder and magnesium chips. There is no limitation on the particle size, aspect ratio, etc. of the magnesium powder / chips, and the common ones in the prior art can be used. Since there is almost no difference in form between magnesium powder and magnesium chips, "magnesium powder", "magnesium chips" and "magnesium powder / chips" can be used interchangeably in this article. However, the inventor unexpectedly discovered that if magnesium powder / chips with a mesh size of -30 to +100 is used, it is not only easier to save energy, but also more conducive to obtaining a lower oxygen content. In an alternative embodiment of the present invention, the reducing agent in step (a) can also be Na.

[0026] The perforated metal plate / net in the above step (b) refers to a metal plate with pores. It may also be referred to as a metal plate mesh, or a metal mesh in the art. In this article, metal plate / net, metal plate mesh and metal mesh may be used interchangeably. The material thereof may be carbon steel, iron or tantalum, preferably tantalum. Preferably, the pore size of the metal plate / net is determined according to the tantalum powder to be deoxidized, so that neither obvious powder leakage nor blocking of the pores occurs easily. In step (b), the deoxidizer may or may not contact the metal plate / net. Preferably, the two are not in contact.

[0027] There is no limitation on the source of the tantalum powder to be deoxidized in step (c), and the tantalum powder commonly used in the art can be used. From the perspective of reducing costs, tantalum powder obtained by sodium reduction method is preferred. Preferably, the tantalum powder to be deoxidized is first agglomerated and granulated and heat-treated, and then placed on a metal plate / net. Preferably, after being placed on the metal plate / net, the tantalum powder is preferably evenly scraped flat. In an alternative embodiment, the tantalum powder to be deoxidized that has been agglomerated and granulated and heat-treated can be pressed into a porous oblate cylinder and then placed on a perforated metal plate / net.

[0028] The present invention does not limit the vacuum degree in step (d), and the vacuum degree commonly used in the art can be used. Although this step also uses an inert atmosphere, it is only used to provide a protective atmosphere.

[0029] The holding time in the above step (e) is suitable to ensure the melting of the magnesium powder / chips.

[0030] The inventors have found that the vacuum degree in the above step (f) can control the reaction speed, preferably 1000-70 Pa, more preferably 800-200 Pa, and more preferably 600-400 Pa. The operations of pickling and drying in step (f) can adopt the conventional treatment methods for tantalum powder for capacitors.

[0031] According to a second aspect, the present invention relates to a tantalum powder, the tantalum powder having low impurities. Preferably, the tantalum powder according to the second aspect is obtained by the above method according to the first aspect.

[0032] For example, the tantalum powder according to the second aspect has: a C content of ≤10 ppm, preferably ≤8 ppm; an O content of ≤2800 ppm, such as 1800-2800 ppm or 2100-2600 ppm; and a Mg content of ≤0.5 ppm, preferably ≤0.3 ppm, more preferably ≤0.15 ppm. In a preferred embodiment, the tantalum powder has:

[0033] 3.0-5.0 μm Fisher particle size, and / or

[0034] 1.5-1.8g / cm 3 of bulk density, and / or

[0035] 7-12s / 50g fluidity, and / or

[0036] -325 mesh ≤ 28% sieve particle size.

[0037] According to a third aspect, the present invention relates to use of the tantalum powder obtained by the method according to the first aspect or the tantalum powder according to the second aspect in a tantalum capacitor.

[0038] According to a fourth aspect, the present invention relates to an anode block made of the tantalum powder obtained by the method of the first aspect or the tantalum powder of the second aspect. Preferably, when the anode block is soaked in phosphoric acid and sulfuric acid respectively and the specific capacitance is measured according to GB / T 3137, the difference between the two is ≤600μFV / g, preferably ≤500μFV / g, more preferably ≤400μFV / g. Preferably, the leakage current of the anode block is ≤10μA / g.

[0039] According to a fifth aspect, the present invention also relates to a tantalum electrolytic capacitor comprising an anode block made according to the fourth aspect.

[0040] According to a sixth aspect, the present invention also relates to a method for characterizing ultrafine porosity of an anode block by soaking the anode block in phosphoric acid and sulfuric acid, respectively, and comparing the measured specific capacitances.

[0041] Without being bound by general theories, the inventors believe that, since a metal plate mesh is used in the present invention, the deoxidizer such as magnesium does not directly contact the tantalum powder to be deoxidized (i.e., to be deoxidized), but infiltrates into the tantalum powder to be deoxidized through the pores in the metal plate after the deoxidizer is vaporized. The gaseous deoxidizer is in uniform contact with the tantalum powder to be deoxidized, and the reaction is more complete. Moreover, since the physical properties of the deoxidizer such as metal magnesium, especially the melting point or boiling point, are significantly different from those of the impurities contained therein, such as Fe or Ca, this method of first vaporizing and then infiltrating upward through the pores of the metal plate mesh can not only make the tantalum powder have a better microstructure, but also make full use of the difference between the melting point and the boiling point to leave some high melting point and boiling point impurities below to avoid entering the tantalum powder, thereby better improving the purity of the final tantalum powder product, so that the obtained tantalum powder has high purity, which is beneficial to the electrical properties of the tantalum capacitor, and the method is simple, the equipment is simple to operate and is very easy to obtain.

[0042] The inventors believe that the anode block obtained from the tantalum powder of the present invention has an improved pore distribution. In particular, the anode block does not contain ultrafine pores (e.g., ultrafine pores with a pore size of ≤0.3 μm). The ultrafine pore size is extremely unfavorable for the electrical properties of the anode block (e.g., leakage current and / or specific capacity). In the prior art, although the size of the ultrafine porosity can be characterized by testing the porosity distribution with a mercury pressure meter, it is currently difficult to accurately quantify it because the pore size is too fine. After a lot of research work, the inventors found that when the anode block is soaked in phosphoric acid and sulfuric acid respectively according to GB / T 3137 and the specific capacitance is measured, the smaller the difference between the two, the fewer the ultrafine pores. The possible reason is that the surface tension of phosphoric acid and hydrochloric acid is different, so the ability to enter the ultrafine pores is different, which leads to different measured specific capacitances. This means that if the pores are fewer, the difference is smaller. That is, by soaking the anode block in phosphoric acid and sulfuric acid respectively and comparing the measured specific capacitances, it may be more convenient and accurate to characterize the amount of ultrafine pores. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] The following drawings are provided to better illustrate the present invention. These drawings are only for illustration purposes and are not intended to limit the scope of protection of the present invention.

[0044] Figure 1 Comparison of porosity tests of Example 1 and Comparative Example 1 measured by mercury intrusion porosimetry.

[0045] Figure 1 The screen display data is copied directly from the instrument. Figure 1 It can be seen that the tantalum powder of the present invention has a smaller percentage of ultrafine pores. DETAILED DESCRIPTION

[0046] In order to further illustrate the present invention, the preferred embodiments of the present invention are described below in conjunction with the examples, and it can be clearly seen that the objects, features and advantages of the present invention. However, these descriptions are only for further illustrating the features and advantages of the present invention, rather than for limiting the present invention. In the examples, if specific conditions are not specified, they are carried out according to normal conditions or the conditions recommended by the manufacturer. If the manufacturer is not specified for the reagents, raw materials or instruments used, they are all conventional products that can be obtained commercially.

[0047] The physical property testing methods of tantalum powder in the embodiments of the present invention are as follows: the bulk density of tantalum powder is tested by GB / T 1479, the Fisher mean particle size of tantalum powder is tested by GB / T 3249, the fluidity of tantalum powder is tested by GB / T 1482, and the sieve analysis particle size distribution of tantalum powder is determined by GB / T 1480.

[0048] The measurement methods and instruments used for some impurity elements in tantalum powder are as follows.

[0049]

[0050] The electrical property test method of the tantalum powder in the embodiment of the present invention is carried out in accordance with the provisions of GB / T 3137. Other tests are conventional tests in the art.

[0051] For the purpose of this specification, all numbers indicating the amount of ingredients, reaction conditions, etc. in the specification and claims should be understood as being modified by the term "about" in all cases, unless otherwise specified. Accordingly, the numerical parameters given in the following specification and the appended claims are approximate values, which may vary according to the desired properties that the present invention attempts to obtain, unless otherwise indicated. At least, and without intending to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should be interpreted at least in accordance with the number of reported significant figures and in accordance with conventional rounding techniques.

[0052] Example 1

[0053] 10 kg of tantalum powder to be deoxidized (raw material 1) that has been agglomerated, granulated and heat-treated is taken as raw material. Its oxygen (O) content, bulk density, Fisher average particle size, sieve analysis and other characteristic data are shown in Table 1.

[0054] 500 g of magnesium powder / chips (commercially available, 30 mesh) were placed on the bottom of the crucible and scraped flat; a tantalum metal mesh with a pore size of 38 μm was placed on top of the magnesium powder.

[0055] Place the raw tantalum powder on the metal mesh and scrape it flat.

[0056] The crucible filled with the raw material tantalum powder is placed in a reaction container, the reaction container is evacuated, and then filled with argon gas to normal pressure.

[0057] The reaction vessel was transferred to a pit-type heating furnace and heated to 820° C., then kept warm for 1 hour, after which the vacuum system was started to evacuate the reaction vessel to 500 Pa and maintained for 4 hours.

[0058] Cooling the reacted tantalum powder to room temperature;

[0059] The deoxidized tantalum powder is pickled according to the conventional treatment method of tantalum powder for capacitors to remove by-products, washed with water, dried and sieved to obtain the finished tantalum powder.

[0060] The characteristic data of the finished tantalum powder, such as fluidity, average particle size, bulk density, sieve analysis, etc., are listed in Table 1, the chemical composition data of oxygen, carbon, iron, etc. are listed in Table 2, and the electrical property data are listed in Table 3.

[0061] Comparative Example 1

[0062] 10 kg of tantalum powder to be deoxidized (raw material 1) that has been agglomerated, granulated and heat-treated is taken as raw material. Its oxygen (O) content, bulk density, Fisher average particle size, sieve analysis and other characteristic data are shown in Table 1.

[0063] Mix 500 g of magnesium powder / chips (commercially available, 30 mesh) and the tantalum powder to be deoxidized (raw material 1), put them into a tantalum crucible, and scrape them flat.

[0064] The crucible filled with the raw material tantalum powder is placed in a reaction container, the reaction container is evacuated, and then filled with argon gas to normal pressure.

[0065] The reaction vessel was transferred to a pit-type heating furnace and heated to 820°C and kept at this temperature for 1 hour. After that, the vacuum system was started to evacuate the reaction vessel to 500 Pa and maintained for 4 hours.

[0066] Cooling the reacted tantalum powder to room temperature;

[0067] The deoxidized tantalum powder is pickled according to the conventional treatment method of tantalum powder for capacitors to remove by-products, washed with water, dried and sieved to obtain the finished tantalum powder.

[0068] The characteristic data of the finished tantalum powder, such as fluidity, average particle size, bulk density, sieve analysis, etc., are listed in Table 1, the chemical composition data of oxygen, carbon, iron, etc. are listed in Table 2, and the electrical property data are listed in Table 3.

[0069] The tantalum powders obtained in Example 1 and Comparative Example 1 were pressed into a 3 mm diameter and a density of 5.6 g / cm 3 , a single cylinder weighing 0.15g was sintered in a vacuum sintering furnace at 1360℃ for 30min; the porosity distribution of the sintered block was then tested using a mercury intrusion meter, and the data obtained are shown in Figure 1 It can be seen from the data that the number of micropores smaller than 0.3 μm in Example 1 is significantly lower than that in Comparative Example 1.

[0070] Example 2

[0071] 10 kg of tantalum powder to be deoxidized (raw material 1) that has been agglomerated, granulated and heat-treated is taken as raw material. Its oxygen (O) content, bulk density, Fisher average particle size, sieve analysis and other characteristic data are shown in Table 1.

[0072] 500 g of magnesium powder / chips (commercially available, 30 mesh) were placed on the bottom of the crucible and scraped flat; a carbon steel metal mesh with a pore size of 38 μm was placed on top of the magnesium powder.

[0073] Place the raw tantalum powder on the metal mesh and scrape it flat.

[0074] The crucible filled with the raw material tantalum powder is placed in a reaction container, the reaction container is evacuated, and then filled with argon gas to normal pressure.

[0075] The reaction vessel was transferred to a pit-type heating furnace and heated to 820°C and kept at this temperature for 1 hour. After that, the vacuum system was started to evacuate the reaction vessel to 500 Pa and maintained for 4 hours.

[0076] Cooling the reacted tantalum powder to room temperature;

[0077] The deoxidized tantalum powder is pickled according to the conventional treatment method of tantalum powder for capacitors to remove by-products, washed with water, dried and sieved to obtain the finished tantalum powder.

[0078] The characteristic data of the finished tantalum powder, such as fluidity, average particle size, bulk density, sieve analysis, etc., are listed in Table 1, the chemical composition data of oxygen, carbon, iron, etc. are listed in Table 2, and the electrical property data are listed in Table 3.

[0079] Example 3

[0080] 10 kg of tantalum powder to be deoxidized (raw material 1) that has been agglomerated, granulated and heat-treated is taken as raw material. Its oxygen (O) content, bulk density, Fisher average particle size, sieve analysis and other characteristic data are shown in Table 1.

[0081] 500 g of magnesium powder / chips (commercially available, 30 mesh) were placed on the bottom of the crucible and scraped flat; a tantalum metal mesh with a pore size of 38 μm was placed on top of the magnesium powder.

[0082] Place the raw tantalum powder on the metal mesh and scrape it flat.

[0083] The crucible filled with the raw material tantalum powder is placed in a reaction container, the reaction container is evacuated, and then filled with argon gas to normal pressure.

[0084] The reaction vessel was transferred to a pit-type heating furnace and heated to 820°C and kept at this temperature for 1 hour. After that, the vacuum system was started to evacuate the reaction vessel to 800 Pa and maintained for 5.5 hours.

[0085] Cooling the reacted tantalum powder to room temperature;

[0086] The deoxidized tantalum powder is pickled according to the conventional treatment method of tantalum powder for capacitors to remove by-products, washed with water, dried and sieved to obtain the finished tantalum powder.

[0087] The characteristic data of the finished tantalum powder, such as fluidity, average particle size, bulk density, sieve analysis, etc., are listed in Table 1, the chemical composition data of oxygen, carbon, iron, etc. are listed in Table 2, and the electrical property data are listed in Table 3.

[0088] Example 4

[0089] 10 kg of tantalum powder to be deoxidized (raw material 1) that has been agglomerated, granulated and heat-treated is taken as raw material. Its oxygen (O) content, bulk density, Fisher average particle size, sieve analysis and other characteristic data are shown in Table 1.

[0090] 500 g of magnesium powder / chips (commercially available, 30 mesh) were placed on the bottom of the crucible and scraped flat; a tantalum metal plate with a pore size of 75 μm was placed on top of the magnesium powder.

[0091] The raw material is pressed into a density of 3.5cm 3 / g, and a porous oblate cylinder with a thickness of 10 mm is placed on a metal plate.

[0092] The crucible filled with the raw material tantalum powder is placed in a reaction container, the reaction container is evacuated, and then filled with argon gas to normal pressure.

[0093] The reaction vessel was transferred to a pit-type heating furnace and heated to 820°C and kept at this temperature for 1 hour. After that, the vacuum system was started to evacuate the reaction vessel to 500 Pa and maintained for 4 hours.

[0094] The tantalum powder after the reaction was cooled to room temperature and crushed through a 30-mesh sieve;

[0095] The deoxidized tantalum powder is pickled according to the conventional treatment method of tantalum powder for capacitors to remove by-products, washed with water, dried and sieved to obtain the finished tantalum powder.

[0096] The characteristic data of the finished tantalum powder, such as fluidity, average particle size, bulk density, sieve analysis, etc., are listed in Table 1, the chemical composition data of oxygen, carbon, iron, etc. are listed in Table 2, and the electrical property data are listed in Table 3.

[0097] Example 5

[0098] 10 kg of tantalum powder to be deoxidized (raw material 1) that has been agglomerated, granulated and heat-treated is taken as raw material. Its oxygen (O) content, bulk density, Fisher average particle size, sieve analysis and other characteristic data are shown in Table 1.

[0099] 500 g of magnesium powder / chips (commercially available, 30 mesh) were placed on the bottom of the crucible and scraped flat; a tantalum metal plate with a pore size of 75 μm was placed on top of the magnesium powder.

[0100] The raw material is pressed into a density of 3.5cm 3 / g, and a porous oblate cylinder with a thickness of 10 mm is placed on a metal plate.

[0101] The crucible filled with the raw material tantalum powder is placed in a reaction container, the reaction container is evacuated, and then filled with argon gas to normal pressure.

[0102] The reaction vessel was transferred to a pit-type heating furnace and heated to 820°C and kept at this temperature for 1 hour. After that, the vacuum system was started to evacuate the reaction vessel to 200 Pa and maintained for 3 hours.

[0103] The tantalum powder after the reaction was cooled to room temperature and crushed through a 30-mesh sieve;

[0104] The deoxidized tantalum powder is pickled according to the conventional treatment method of tantalum powder for capacitors to remove by-products, washed with water, dried and sieved to obtain the finished tantalum powder.

[0105] The characteristic data of the finished tantalum powder, such as fluidity, average particle size, bulk density, sieve analysis, etc., are listed in Table 1, the chemical composition data of oxygen, carbon, iron, etc. are listed in Table 2, and the electrical property data are listed in Table 3.

[0106] Example 6

[0107] 10 kg of tantalum powder to be deoxidized (raw material 2) that has been agglomerated, granulated and heat-treated is taken as raw material. Its oxygen (O) content, bulk density, Fisher average particle size, sieve analysis and other characteristic data are shown in Table 1.

[0108] 500 g of magnesium powder / chips (commercially available, 30 mesh) were placed on the bottom of the crucible and scraped flat; a tantalum metal mesh with a pore size of 38 μm was placed on top of the magnesium powder.

[0109] Place the raw tantalum powder on the metal mesh and scrape it flat.

[0110] The crucible filled with the raw material tantalum powder is placed in a reaction container, the reaction container is evacuated, and then filled with argon gas to normal pressure.

[0111] The reaction vessel was transferred to a pit-type heating furnace and heated to 860°C and kept at this temperature for 1 hour. After that, the vacuum system was started to evacuate the reaction vessel to 500 Pa and maintained for 4 hours.

[0112] Cooling the reacted tantalum powder to room temperature;

[0113] The deoxidized tantalum powder is pickled according to the conventional treatment method of tantalum powder for capacitors to remove by-products, washed with water, dried and sieved to obtain the finished tantalum powder.

[0114] The characteristic data of the finished tantalum powder, such as fluidity, average particle size, bulk density, sieve analysis, etc., are listed in Table 1, the chemical composition data of oxygen, carbon, iron, etc. are listed in Table 2, and the electrical property data are listed in Table 3.

[0115] Comparative Example 2

[0116] 10 kg of tantalum powder to be deoxidized (raw material 2) that has been agglomerated, granulated and heat-treated is taken as raw material. Its oxygen (O) content, bulk density, Fisher average particle size, sieve analysis and other characteristic data are shown in Table 1.

[0117] Mix 500 g of magnesium powder / chips (commercially available, 30 mesh) and the tantalum powder to be deoxidized (raw material 1), put them into a tantalum crucible, and scrape them flat.

[0118] The crucible filled with the raw material tantalum powder is placed in a reaction container, the reaction container is evacuated, and then filled with argon gas to normal pressure.

[0119] The reaction vessel was transferred to a pit-type heating furnace and heated to 860°C and kept at this temperature for 1 hour. After that, the vacuum system was started to evacuate the reaction vessel to 500 Pa and maintained for 4 hours.

[0120] Cooling the reacted tantalum powder to room temperature;

[0121] The deoxidized tantalum powder is pickled according to the conventional treatment method of tantalum powder for capacitors to remove by-products, washed with water, dried and sieved to obtain the finished tantalum powder.

[0122] The characteristic data of the finished tantalum powder, such as fluidity, average particle size, bulk density, sieve analysis, etc., are listed in Table 1, the chemical composition data of oxygen, carbon, iron, etc. are listed in Table 2, and the electrical property data are listed in Table 3.

[0123] Example 7

[0124] 10 kg of tantalum powder to be deoxidized (raw material 2) that has been agglomerated, granulated and heat-treated is taken as raw material. Its oxygen (O) content, bulk density, Fisher average particle size, sieve analysis and other characteristic data are shown in Table 1.

[0125] 500 g of magnesium powder / chips (commercially available, 30 mesh) were placed on the bottom of the crucible and scraped flat; a carbon steel metal mesh with a pore size of 38 μm was placed on top of the magnesium powder.

[0126] Place the raw tantalum powder on the metal mesh and scrape it flat.

[0127] The crucible filled with the raw material tantalum powder is placed in a reaction container, the reaction container is evacuated, and then filled with argon gas to normal pressure.

[0128] The reaction vessel was transferred to a pit-type heating furnace and heated to 860°C and kept at this temperature for 1 hour. After that, the vacuum system was started to evacuate the reaction vessel to 500 Pa and maintained for 4 hours.

[0129] Cooling the reacted tantalum powder to room temperature;

[0130] The deoxidized tantalum powder is pickled according to the conventional treatment method of tantalum powder for capacitors to remove by-products, washed with water, dried and sieved to obtain the finished tantalum powder.

[0131] The characteristic data of the finished tantalum powder, such as fluidity, average particle size, bulk density, sieve analysis, etc., are listed in Table 1, the chemical composition data of oxygen, carbon, iron, etc. are listed in Table 2, and the electrical property data are listed in Table 3.

[0132] Example 8

[0133] 10 kg of tantalum powder to be deoxidized (raw material 2) that has been agglomerated, granulated and heat-treated is taken as raw material. Its oxygen (O) content, bulk density, Fisher average particle size, sieve analysis and other characteristic data are shown in Table 1.

[0134] 500 g of magnesium powder / chips (commercially available, 30 mesh) were placed on the bottom of the crucible and scraped flat; a tantalum metal mesh with a pore size of 38 μm was placed on top of the magnesium powder.

[0135] Place the raw tantalum powder on the metal mesh and scrape it flat.

[0136] The crucible filled with the raw material tantalum powder is placed in a reaction container, the reaction container is evacuated, and then filled with argon gas to normal pressure.

[0137] The reaction vessel was transferred to a pit-type heating furnace and heated to 860°C and kept at this temperature for 1 hour. After that, the vacuum system was started to evacuate the reaction vessel to 200 Pa and maintained for 2 hours.

[0138] Cooling the reacted tantalum powder to room temperature;

[0139] The deoxidized tantalum powder is pickled according to the conventional treatment method of tantalum powder for capacitors to remove by-products, washed with water, dried and sieved to obtain the finished tantalum powder.

[0140] The characteristic data of the finished tantalum powder, such as fluidity, average particle size, bulk density, sieve analysis, etc., are listed in Table 1, the chemical composition data of oxygen, carbon, iron, etc. are listed in Table 2, and the electrical property data are listed in Table 3.

[0141] Table 1 Powder property data of the embodiments of the present invention and the comparative examples - physical properties

[0142]

[0143]

[0144] Table 2 Powder property data of the present invention and comparative examples - chemical composition

[0145]

[0146] It can be seen from Table 2 that although the impurity content of raw materials 1 and 2 selected by the inventor is very low, after deoxidation, the impurity content of C and Mg increases to varying degrees. This shows that the reduction of O content is often at the expense of the increase of other elements. However, the impurity content (especially Mg content) of the tantalum powder obtained in the embodiment is significantly lower than the impurity content of the tantalum powder obtained according to the prior art (i.e., the comparative example).

[0147] Table 3 Characteristic data of the powders of the present invention and the comparative examples - electrical properties

[0148]

[0149]

[0150] Table 4 Characteristic data of the powders of the present invention and the comparative examples - electrical properties

[0151]

[0152] The specific capacity differences between the powder of the embodiment of the present invention and the comparative example obtained by the two measurement methods (i.e., immersion in sulfuric acid and phosphoric acid) were also calculated according to Table 4. This is shown in Table 5. Table 5 clearly shows that the specific content difference of the anode block made of the tantalum powder obtained according to the present invention is smaller.

[0153] Table 5 Differences in specific capacity between the powders of some embodiments of the present invention and the comparative examples obtained by two measurement methods

[0154] Tantalum powder number The difference between the specific capacitance measured after immersion in sulfuric acid and the specific capacitance measured after immersion in phosphoric acid (μFV / g) Example 1 323 Comparative Example 1 677 Example 2 318 Example 3 334

Claims

1. A method for deoxidizing tantalum powder, the method comprising: The tantalum powder to be deoxidized is separated from the deoxidizer such as Mg powder / chips (for example, by using a perforated metal plate / net), and the deoxidizer is vaporized by heating and brought into contact with the tantalum powder to be deoxidized.

2. A method for deoxidizing tantalum powder, the method comprising the following steps: (a) placing a deoxidizer such as magnesium powder / chips (the particle size of the magnesium powder / chips is preferably -30 mesh to +100 mesh) into the bottom of the crucible, and preferably scraping it evenly; (b) placing a perforated metal sheet / mesh on top of the deoxidizer; (c) placing the tantalum powder to be deoxidized on a perforated metal plate / net; (d) placing the crucible in a reaction vessel, evacuating the reaction vessel, and then filling the reaction vessel with an inert gas such as argon to normal pressure; (e) heating the reaction vessel to 750-1000° C. (preferably by placing the reaction vessel in a furnace and heating it), and then keeping the temperature, preferably keeping the temperature for 0.5-3 hours; (f) starting the vacuum system, evacuating the reactor to a vacuum (e.g., to 1000-70 Pa, more preferably to 800-200 Pa, more preferably to 600-400 Pa) to carry out the reaction, e.g., for 2-6 hours; (g) cooling the reacted tantalum powder to room temperature; and (f) Optionally, the deoxidized tantalum powder is acid-washed to remove by-products, washed with water, dried and sieved to obtain finished tantalum powder.

3. The method according to claim 2, wherein in step (c) the tantalum powder to be deoxidized is first agglomerated, granulated and heat-treated, and then placed on a metal plate / net, and optionally, the agglomerated, granulated and heat-treated tantalum powder to be deoxidized is pressed into a porous oblate cylinder and then placed on a perforated metal plate / net.

4. A tantalum powder having: C content ≤ 10ppm, preferably ≤ 8ppm; O content ≤ 2800 ppm, for example 1800-2800 ppm or 2100-2600 ppm; The Mg content is ≤0.5 ppm, preferably ≤0.3 ppm, more preferably ≤0.15 ppm.

5. The tantalum powder according to claim 4, wherein: 3.0-5.0 μm Fisher particle size, and / or 1.5-1.8g / cm 3 of bulk density, and / or 7-12s / 50g fluidity, and / or -325 mesh ≤ 28% sieve particle size.

6. Use of the tantalum powder according to claim 5 or the tantalum powder obtained according to the method of any one of claims 1 to 3 for preparing tantalum capacitors.

7. An anode block made of tantalum powder, wherein: When the anode block is immersed in phosphoric acid and sulfuric acid respectively and the specific capacitance is measured according to GB / T 3137, the difference between the two is ≤600 μFV / g, preferably ≤500 μFV / g, and more preferably ≤400 μFV / g. 8 . The anode block according to claim 7 , wherein a leakage current of the anode block is ≤10 μA / g.

9. A tantalum electrolytic capacitor comprising the anode block according to claim 7 or 8.

10. A method for characterizing ultrafine pores in an anode block, characterized in that: The anode block is soaked in phosphoric acid and sulfuric acid respectively and the specific capacitance is measured (preferably according to GB / T 3137), and then the difference is calculated.

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