A method for deoxidizing tantalum powder and the tantalum powder obtained by the method

Abstract

This invention relates to a method for deoxidizing tantalum powder and the tantalum powder obtained by the method. The method includes: separating the tantalum powder to be deoxidized from a deoxidizing agent, such as magnesium Mg powder / shavings (e.g., by using a perforated metal plate / mesh), and vaporizing the deoxidizing agent by heating it to contact the tantalum powder to be deoxidized.

Description

Technical Field

[0001] This invention belongs to the field of rare metal smelting, and specifically relates to a method for producing tantalum powder for capacitors by deoxidizing gaseous magnesium metal.

[0002] In the electronics industry, tantalum powder is primarily used in the manufacture of electrolytic capacitors (often simply referred to as "capacitors" in this field; the two terms are used interchangeably in this document). The development trend for tantalum electrolytic capacitors demands high capacitance, low leakage current, and low equivalent series resistance (low loss for the anode). As the main material for manufacturing the anode of tantalum electrolytic capacitors, tantalum powder requires low impurity content, particularly low levels of O, C, Ni, Mg, and Fe, because the presence of O, C, Mg, Fe, and Ni in tantalum powder increases leakage current and lowers breakdown voltage. Therefore, it is desirable in the art to reduce the content of one or more of these elements.

[0003] There are currently two main methods for producing tantalum powder for capacitors: one method involves reducing potassium fluorotantalate with metallic sodium, separating the byproducts, purifying the tantalum powder, and then heat-treating it to obtain tantalum powder; the second method involves reducing tantalum oxide with metallic magnesium, separating the byproducts, purifying the tantalum powder, and then heat-treating it to obtain tantalum powder. Although the second method is also commonly used, it is sometimes found that the resulting tantalum powder has a higher content of residual magnesium and other impurities.

[0004] In addition, oxygen has certain unique characteristics among common impurities. Because tantalum has a strong affinity for oxygen, the tantalum powder prepared by the above method usually contains a high oxygen content, which is very detrimental to the subsequent fabrication of capacitors, especially posing a great risk in terms of leakage current and wire brittleness. Therefore, partial deoxidation treatment must be performed, and magnesium metal is usually used as a reducing agent for the deoxidation of tantalum powder.

[0005] To address the deoxidation problem of tantalum powder used in capacitors, many solutions have been proposed.

[0006] The conventional operation for deoxidizing tantalum powder in industrial production is generally as described in Chinese patent CN102965525A: the tantalum powder to be deoxidized is uniformly mixed with magnesium powder / shavings and placed in a tantalum crucible, heated to a suitable reaction temperature for deoxidation, and then excess magnesium is separated by inert gas argon or vacuum evaporation. This method has two drawbacks: first, impurities (C, Fe, Ni, etc.) in the magnesium powder / shavings are carried into the tantalum powder; second, at normal deoxidation temperatures, localized liquid magnesium exists, causing localized liquid-phase sintering of the tantalum powder. As a result, the pore structure distribution of the anode block obtained from the sintered tantalum powder is poor. Furthermore, the tantalum powder also suffers from a high magnesium impurity content.

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

[0008] CN1123206A discloses a method for obtaining 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, followed by acid washing and drying, and the tantalum powder obtained by this method. CN101774018B discloses a method for manufacturing electron tube metal powder, particularly niobium and tantalum powder, by reducing corresponding electron tube metal oxide powder with gaseous reduction of metal / metal hydride in the presence of an inert carrier gas. This method requires magnesium vapor to be driven by an inert carrier gas, increasing system complexity and cost.

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

[0010] Moreover, a common problem in existing technologies is that deoxidizers, such as magnesium, often contain various impurities, especially Fe. These impurities inevitably enter the final tantalum powder product along with a small amount of Mg from the deoxidizer, affecting the purity of the resulting tantalum powder product. Summary of the Invention

[0011] The purpose of this invention is to address the shortcomings of existing technologies by providing a method for producing tantalum powder using gaseous magnesium metal through deoxidation, and the tantalum powder obtained by this method.

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

[0013] Another objective of this invention is to provide a method for preparing tantalum powder that avoids localized liquid-phase sintering, resulting in a tantalum powder product with good pore structure, low impurity (especially Mg and / or Fe) content, and good electrical properties (especially low leakage current).

[0014] Another object of the present invention is to provide a method for preparing tantalum powder that is easy to operate and uses 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 magnesium Mg powder / shavings (e.g., by using a perforated metal plate / mesh), and vaporizing the deoxidizing agent by heating it to contact the tantalum powder to be deoxidized.

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

[0017] (a) A deoxidizer, such as magnesium powder / shavings, is placed at the bottom of the crucible, preferably scraped evenly;

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

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

[0020] (d) Place the crucible in the reaction vessel, evacuate the reaction vessel, and then fill it with an inert gas such as argon to atmospheric pressure;

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

[0022] (f) Start the vacuum system and evacuate the reactor (e.g., to 1000-70 Pa) to carry out the reaction, for example, for 2-6 hours;

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

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

[0025] In step (a) above, the crucible material can be carbon steel, iron, or tantalum, with tantalum being preferred. The "magnesium powder / shavings" mentioned can be magnesium powder or magnesium shavings, or a mixture of both. There are no limitations on the particle size, aspect ratio, etc., of the magnesium powder / shavings; any material commonly used in the prior art can be used. Since magnesium powder and magnesium shavings are almost indistinguishable in form, the terms "magnesium powder," "magnesium shavings," and "magnesium powder / shavings" can be used interchangeably in this document. However, the inventors unexpectedly discovered that using magnesium powder / shavings of -30 mesh to +100 mesh not only makes energy saving easier but also facilitates obtaining a lower oxygen content. In an alternative embodiment of the invention, the reducing agent in step (a) can also be Na.

[0026] The perforated metal plate / mesh in step (b) above refers to a metal plate with pores. It may also be called a metal plate mesh or metal mesh in the art. In this document, the terms metal plate / mesh, metal plate mesh, and metal mesh are used interchangeably. Its material can be carbon steel, iron, or tantalum, preferably tantalum. Preferably, the aperture of the metal plate / mesh is determined according to the tantalum powder to be deoxidized, so that there is neither significant powder leakage nor easy clogging of the pores. In step (b), the deoxidizer may or may not be in contact with the metal plate / mesh. Preferably, the two are not in contact.

[0027] There are no restrictions on the source of the tantalum powder to be deoxidized in step (c); any tantalum powder commonly used in the art can be used. From a cost-reduction perspective, tantalum powder obtained by the sodium reduction method is preferred. Preferably, the tantalum powder to be deoxidized is first agglomerated and granulated and then heat-treated before being placed on a metal plate / mesh. Preferably, after being placed on the metal plate / mesh, the tantalum powder is evenly scraped flat. In an alternative embodiment, the agglomerated, granulated, and heat-treated tantalum powder to be deoxidized can be pressed into porous flat cylinders before being placed on a perforated metal plate / mesh.

[0028] This invention does not limit the vacuum level in step (d); a vacuum level commonly used in the art can be used. Although an inert atmosphere is also used in this step, it is only for providing a protective atmosphere.

[0029] The holding time in step (e) above should be sufficient to ensure that the magnesium powder / shavings melt.

[0030] The inventors discovered that the vacuum level in step (f) above can control the reaction rate, preferably 1000-70 Pa, more preferably 800-200 Pa, and even more preferably 600-400 Pa. The pickling, drying, and other operations in step (f) can employ conventional processing methods for tantalum powder used in capacitors.

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

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

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

[0034] 1.5-1.8g / cm 3 Loose packing density, and / or

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

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

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

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

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

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

[0041] Unbound by conventional theories, the inventors believe that the use of a metal mesh in this invention prevents the deoxidizer, such as magnesium, from directly contacting the tantalum powder to be deoxidized (i.e., deoxidized). Instead, the deoxidizer, after vaporization, permeates into the tantalum powder through the pores in the metal mesh. This ensures uniform contact between the gaseous deoxidizer and the tantalum powder, resulting in a more complete reaction. Furthermore, because the physical properties of the deoxidizer, such as metallic magnesium, especially its melting or boiling point, are significantly different from those of the impurities it contains, such as Fe or Ca, this method of first vaporizing and then permeating upwards through the pores of the metal mesh not only gives the tantalum powder a better microstructure but also fully utilizes the difference in melting and boiling points to retain some high-melting-point and high-boiling-point impurities at the bottom, preventing them from entering the tantalum powder. This improves the purity of the final tantalum powder product, resulting in high-purity tantalum powder that is beneficial to the electrical performance of tantalum capacitors. Moreover, the method is simple, and the equipment is easy to operate and readily available.

[0042] The inventors believe that the anode block obtained from the tantalum powder of this invention has an improved porosity distribution. Specifically, the anode block does not contain ultrafine pores (e.g., pore sizes ≤ 0.3 μm). Such ultrafine pores are extremely detrimental to the electrical performance of the anode block (e.g., leakage current and / or specific capacitance). In the prior art, although the porosity distribution can be characterized by testing with a mercury piezometer, precise quantification is currently difficult due to the extremely fine pore size. Through extensive research, the inventors discovered that when the anode block is immersed 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. This is likely because phosphoric acid and hydrochloric acid have different surface tensions, thus different abilities to penetrate the ultrafine pores, leading to different measured specific capacitances. This means that the fewer the pores, the smaller the difference. Therefore, by immersing the anode block in phosphoric acid and sulfuric acid respectively and comparing the measured specific capacitance, the amount of ultrafine pores may be more convenient and accurate to characterize. Attached Figure Description

[0043] The following figures are provided to better illustrate the invention. These figures are merely illustrative and are not intended to limit the scope of protection of the invention.

[0044] Figure 1 A comparison of porosity tests in Example 1 and Comparative Example 1, measured using the mercury intrusion porosimetry method.

[0045] Figure 1 It was obtained by directly copying the data displayed on the instrument's screen. Figure 1 It can be seen that the tantalum powder of the present invention has a lower percentage of ultrafine pores. Detailed Implementation

[0046] 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 or conditions recommended by the manufacturer are followed. Reagents, raw materials, or instruments used without specified manufacturers are all commercially available conventional products.

[0047] The physical property testing methods for tantalum powder in this embodiment of the invention are as follows: the loose density of tantalum powder is tested by GB / T 1479, the average particle size of tantalum powder is tested by GB / T 3249, the flowability of tantalum powder is tested by GB / T 1482, and the particle size distribution of tantalum powder by sieve analysis is determined by GB / T 1480.

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

[0049]

[0050] The electrical performance testing method for tantalum powder in this embodiment of the invention is performed according to GB / T 3137. Other tests are conventional tests in the art.

[0051] 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.

[0052] Example 1

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

[0054] Place 500 grams of magnesium powder / shavings (commercially available, 30 mesh) at the bottom of the crucible and level it; place a tantalum metal mesh with a 38μm aperture on top of the magnesium powder.

[0055] Place the raw material tantalum powder on the metal mesh and smooth it out.

[0056] Place the crucible containing the raw material tantalum powder into the reaction vessel, evacuate the reaction vessel, and then fill it with argon gas to atmospheric pressure.

[0057] The reaction vessel was transferred to a pit furnace and heated to 820°C. It was then held at that temperature for 1 hour. After that, the vacuum system was activated to evacuate the reaction vessel to 500 Pa and maintain the vacuum for 4 hours.

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

[0059] After deoxidation, the tantalum powder is acid-washed to remove byproducts, washed with water, dried, and sieved according to the conventional processing method for tantalum powder used in capacitors to obtain the finished tantalum powder.

[0060] The flowability, average particle size, loose density, and sieve analysis characteristics of the finished tantalum powder are listed in Table 1, the chemical composition data such as oxygen, carbon, and iron are listed in Table 2, and the electrical properties are listed in Table 3.

[0061] Comparative Example 1

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

[0063] Mix 500 grams of magnesium powder / shavings (commercially available, 30 mesh) with the tantalum powder to be deoxidized (raw material 1), put it into a tantalum crucible, and level it.

[0064] Place the crucible containing the raw material tantalum powder into the reaction vessel, evacuate the reaction vessel, and then fill it with argon gas to atmospheric pressure.

[0065] The reaction vessel was transferred to a pit furnace and heated to 820°C, and held at that temperature for 1 hour. Then, the vacuum system was activated to evacuate the reaction vessel to 500 Pa and maintain the vacuum for 4 hours.

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

[0067] After deoxidation, the tantalum powder is acid-washed to remove byproducts, washed with water, dried, and sieved according to the conventional processing method for tantalum powder used in capacitors to obtain the finished tantalum powder.

[0068] The flowability, average particle size, loose density, and sieve analysis characteristics of the finished tantalum powder are listed in Table 1, the chemical composition data such as oxygen, carbon, and iron are listed in Table 2, and the electrical properties are listed in Table 3.

[0069] The tantalum powder products obtained in Example 1 and Comparative Example 1 were pressed into powders with a diameter of 3 mm and a density of 5.6 g / cm³. 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 pressure gauge, and the data are shown below. Figure 1 As can be seen from the data, 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] Take 10 kg of tantalum powder (raw material 1) that has been agglomerated, granulated and heat-treated as raw material. Its oxygen (O) content, loose density, average particle size of Fisher and sieve analysis and other characteristic data are shown in Table 1.

[0072] Place 500 grams of magnesium powder / shavings (commercially available, 30 mesh) at the bottom of the crucible and level it; place a carbon steel mesh with a 38μm aperture on top of the magnesium powder.

[0073] Place the raw material tantalum powder on the metal mesh and smooth it out.

[0074] Place the crucible containing the raw material tantalum powder into the reaction vessel, evacuate the reaction vessel, and then fill it with argon gas to atmospheric pressure.

[0075] The reaction vessel was transferred to a pit furnace and heated to 820°C and held for 1 hour. Then, the vacuum system was activated to evacuate the reaction vessel to 500 Pa and maintain the evacuation for 4 hours.

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

[0077] After deoxidation, the tantalum powder is acid-washed to remove byproducts, washed with water, dried, and sieved according to the conventional processing method for tantalum powder used in capacitors to obtain the finished tantalum powder.

[0078] The flowability, average particle size, loose density, and sieve analysis characteristics of the finished tantalum powder are listed in Table 1, the chemical composition data such as oxygen, carbon, and iron are listed in Table 2, and the electrical properties are listed in Table 3.

[0079] Example 3

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

[0081] Place 500 grams of magnesium powder / shavings (commercially available, 30 mesh) at the bottom of the crucible and level it; place a tantalum metal mesh with a 38μm aperture on top of the magnesium powder.

[0082] Place the raw material tantalum powder on the metal mesh and smooth it out.

[0083] Place the crucible containing the raw material tantalum powder into the reaction vessel, evacuate the reaction vessel, and then fill it with argon gas to atmospheric pressure.

[0084] The reaction vessel was transferred to a pit furnace and heated to 820°C and held for 1 hour. Then, the vacuum system was activated to evacuate the reaction vessel to 800 Pa and maintain the vacuum for 5.5 hours.

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

[0086] After deoxidation, the tantalum powder is acid-washed to remove byproducts, washed with water, dried, and sieved according to the conventional processing method for tantalum powder used in capacitors to obtain the finished tantalum powder.

[0087] The flowability, average particle size, loose density, and sieve analysis characteristics of the finished tantalum powder are listed in Table 1, the chemical composition data such as oxygen, carbon, and iron are listed in Table 2, and the electrical properties are listed in Table 3.

[0088] Example 4

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

[0090] Place 500 grams of magnesium powder / shavings (commercially available, 30 mesh) at the bottom of the crucible and level it; place a tantalum metal plate with a 75μm aperture on top of the magnesium powder.

[0091] The raw materials are compressed to a density of 3.5 cm³. 3 A porous flat cylinder with a thickness of 10 mm and a weight of 1 g is placed on a metal plate.

[0092] Place the crucible containing the raw material tantalum powder into the reaction vessel, evacuate the reaction vessel, and then fill it with argon gas to atmospheric pressure.

[0093] The reaction vessel was transferred to a pit furnace and heated to 820°C and held for 1 hour. Then, the vacuum system was activated to evacuate the reaction vessel to 500 Pa and maintain the evacuation for 4 hours.

[0094] Cool the reacted tantalum powder to room temperature and crush it through a 30-mesh sieve.

[0095] After deoxidation, the tantalum powder is acid-washed to remove byproducts, washed with water, dried, and sieved according to the conventional processing method for tantalum powder used in capacitors to obtain the finished tantalum powder.

[0096] The flowability, average particle size, loose density, and sieve analysis characteristics of the finished tantalum powder are listed in Table 1, the chemical composition data such as oxygen, carbon, and iron are listed in Table 2, and the electrical properties are listed in Table 3.

[0097] Example 5

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

[0099] Place 500 grams of magnesium powder / shavings (commercially available, 30 mesh) at the bottom of the crucible and level it; place a tantalum metal plate with a 75μm aperture on top of the magnesium powder.

[0100] The raw materials are compressed to a density of 3.5 cm³. 3 A porous flat cylinder with a thickness of 10 mm and a weight of 1 g is placed on a metal plate.

[0101] Place the crucible containing the raw material tantalum powder into the reaction vessel, evacuate the reaction vessel, and then fill it with argon gas to atmospheric pressure.

[0102] The reaction vessel was transferred to a pit furnace and heated to 820°C and held for 1 hour. Then the vacuum system was activated to evacuate the reaction vessel to 200 Pa and maintain the evacuation for 3 hours.

[0103] Cool the reacted tantalum powder to room temperature and crush it through a 30-mesh sieve.

[0104] After deoxidation, the tantalum powder is acid-washed to remove byproducts, washed with water, dried, and sieved according to the conventional processing method for tantalum powder used in capacitors to obtain the finished tantalum powder.

[0105] The flowability, average particle size, loose density, and sieve analysis characteristics of the finished tantalum powder are listed in Table 1, the chemical composition data such as oxygen, carbon, and iron are listed in Table 2, and the electrical properties are listed in Table 3.

[0106] Example 6

[0107] Take 10 kg of tantalum powder (raw material 2) that has been granulated and heat-treated for deoxidation as raw material. Its oxygen (O) content, loose density, average particle size of Fisher, sieve analysis and other characteristic data are shown in Table 1.

[0108] Place 500 grams of magnesium powder / shavings (commercially available, 30 mesh) at the bottom of the crucible and level it; place a tantalum metal mesh with a 38μm aperture on top of the magnesium powder.

[0109] Place the raw material tantalum powder on the metal mesh and smooth it out.

[0110] Place the crucible containing the raw material tantalum powder into the reaction vessel, evacuate the reaction vessel, and then fill it with argon gas to atmospheric pressure.

[0111] The reaction vessel was transferred to a pit furnace and heated to 860°C and held for 1 hour. Then, the vacuum system was activated to evacuate the reaction vessel to 500 Pa and maintain the evacuation for 4 hours.

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

[0113] After deoxidation, the tantalum powder is acid-washed to remove byproducts, washed with water, dried, and sieved according to the conventional processing method for tantalum powder used in capacitors to obtain the finished tantalum powder.

[0114] The flowability, average particle size, loose density, and sieve analysis characteristics of the finished tantalum powder are listed in Table 1, the chemical composition data such as oxygen, carbon, and iron are listed in Table 2, and the electrical properties are listed in Table 3.

[0115] Comparative Example 2

[0116] Take 10 kg of tantalum powder (raw material 2) that has been granulated and heat-treated for deoxidation as raw material. Its oxygen (O) content, loose density, average particle size of Fisher, sieve analysis and other characteristic data are shown in Table 1.

[0117] Mix 500 grams of magnesium powder / shavings (commercially available, 30 mesh) with the tantalum powder to be deoxidized (raw material 1), put it into a tantalum crucible, and level it.

[0118] Place the crucible containing the raw material tantalum powder into the reaction vessel, evacuate the reaction vessel, and then fill it with argon gas to atmospheric pressure.

[0119] The reaction vessel was transferred to a pit furnace and heated to 860°C and held for 1 hour. Then, the vacuum system was activated to evacuate the reaction vessel to 500 Pa and maintain the evacuation for 4 hours.

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

[0121] After deoxidation, the tantalum powder is acid-washed to remove byproducts, washed with water, dried, and sieved according to the conventional processing method for tantalum powder used in capacitors to obtain the finished tantalum powder.

[0122] The flowability, average particle size, loose density, and sieve analysis characteristics of the finished tantalum powder are listed in Table 1, the chemical composition data such as oxygen, carbon, and iron are listed in Table 2, and the electrical properties are listed in Table 3.

[0123] Example 7

[0124] Take 10 kg of tantalum powder (raw material 2) that has been granulated and heat-treated for deoxidation as raw material. Its oxygen (O) content, loose density, average particle size of Fisher, sieve analysis and other characteristic data are shown in Table 1.

[0125] Place 500 grams of magnesium powder / shavings (commercially available, 30 mesh) at the bottom of the crucible and level it; place a carbon steel mesh with a 38μm aperture on top of the magnesium powder.

[0126] Place the raw material tantalum powder on the metal mesh and smooth it out.

[0127] Place the crucible containing the raw material tantalum powder into the reaction vessel, evacuate the reaction vessel, and then fill it with argon gas to atmospheric pressure.

[0128] The reaction vessel was transferred to a pit furnace and heated to 860°C and held for 1 hour. Then, the vacuum system was activated to evacuate the reaction vessel to 500 Pa and maintain the evacuation for 4 hours.

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

[0130] After deoxidation, the tantalum powder is acid-washed to remove byproducts, washed with water, dried, and sieved according to the conventional processing method for tantalum powder used in capacitors to obtain the finished tantalum powder.

[0131] The flowability, average particle size, loose density, and sieve analysis characteristics of the finished tantalum powder are listed in Table 1, the chemical composition data such as oxygen, carbon, and iron are listed in Table 2, and the electrical properties are listed in Table 3.

[0132] Example 8

[0133] Take 10 kg of tantalum powder (raw material 2) that has been granulated and heat-treated for deoxidation as raw material. Its oxygen (O) content, loose density, average particle size of Fisher, sieve analysis and other characteristic data are shown in Table 1.

[0134] Place 500 grams of magnesium powder / shavings (commercially available, 30 mesh) at the bottom of the crucible and level it; place a tantalum metal mesh with a 38μm aperture on top of the magnesium powder.

[0135] Place the raw material tantalum powder on the metal mesh and smooth it out.

[0136] Place the crucible containing the raw material tantalum powder into the reaction vessel, evacuate the reaction vessel, and then fill it with argon gas to atmospheric pressure.

[0137] The reaction vessel was transferred to a pit furnace and heated to 860°C and held for 1 hour. Then, the vacuum system was activated to evacuate the reaction vessel to 200 Pa and maintain the vacuum for 2 hours.

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

[0139] After deoxidation, the tantalum powder is acid-washed to remove byproducts, washed with water, dried, and sieved according to the conventional processing method for tantalum powder used in capacitors to obtain the finished tantalum powder.

[0140] The flowability, average particle size, loose density, and sieve analysis characteristics of the finished tantalum powder are listed in Table 1, the chemical composition data such as oxygen, carbon, and iron are listed in Table 2, and the electrical properties are listed in Table 3.

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

[0142]

[0143]

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

[0145]

[0146] As can be seen from Table 2, although the impurity content of raw materials 1 and 2 selected by the inventors was very low, the impurity content of C and Mg increased to varying degrees after deoxidation. This indicates that the reduction of O content often comes at the cost of an increase in other elements. However, the impurity content (especially Mg content) of the tantalum powder obtained in the examples was significantly lower than that of the tantalum powder obtained according to the prior art (i.e., the comparative example).

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

[0148]

[0149]

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

[0151]

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

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

[0154] Example 1 323 Comparative Example 1 677 Example 2 318 Example 3 334

Claims

1. A method for characterizing ultrafine pores in an anode block made of tantalum powder, characterized in that, According to GB / T 3137, the anode block is soaked in phosphoric acid and sulfuric acid respectively, and the specific capacitance is measured. Then the difference is calculated. The fewer the pores, the smaller the difference.

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