A method for preparing porous tantalum powder by agglomeration heat treatment

Abstract

The application discloses a method for preparing porous tantalum powder based on agglomeration heat treatment of magnesium reduction pretreated tantalum powder. In view of the problems that the bulk density and specific surface area are difficult to be considered, the pore structure controllability is poor, and the electrical performance is unstable in the existing tantalum powder agglomeration process, the method takes the tantalum powder prepared by magnesium reduction of tantalum oxide as raw material, firstly realizes the initial spheroidization and homogenization of particles by pre-agglomeration of atomized spraying of anhydrous ethanol and screening, then strengthens the metallurgical bonding between particles by high-temperature agglomeration heat treatment in vacuum to stabilize the porous structure, and finally obtains the porous tantalum powder with good fluidity, bulk density of 1.71 g / cm3-1.94 g / cm3 and specific surface area of 0.43 m2 / g-0.48 m2 / g through slight crushing and secondary screening. The method is simple in process and good in repeatability, is suitable for the manufacturing of the tantalum powder for medium and high voltage capacitors, and has good industrial application prospect.

Description

Technical Field

[0001] This invention belongs to the field of deep processing of functional metal materials, and specifically relates to a method for preparing capacitor-grade tantalum powder by agglomeration heat treatment using magnesium-reduced tantalum powder as raw material. Background Technology

[0002] Tantalum powder is a key material for preparing high-reliability, high-specific-capacitance tantalum capacitors. Its particle morphology, pore structure, and flowability directly affect the electrical performance and molding process performance of the capacitors. With the development of electronic devices towards high voltage, high capacitance, and miniaturization, higher requirements are placed on the comprehensive performance of tantalum powder, especially requiring tantalum powder to maintain a high surface area and good particle size distribution while having a suitable loose packing density.

[0003] Currently, the preparation of porous tantalum powder largely relies on a direct heat treatment process following magnesium reduction of tantalum powder. This process involves directly subjecting the purified tantalum powder to high-temperature sintering and agglomeration. However, this method has significant drawbacks. During direct heat treatment, the agglomeration behavior of tantalum powder particles is uncontrollable, easily leading to localized over-sintering. This results in a high loose powder density and a significant decrease in specific surface area.

[0004] Tantalum powder agglomeration heat treatment often employs dry shaping, wet agglomeration, or a combination of both, aiming to improve particle flowability and formability. However, traditional methods often have the following problems: First, the agglomeration process easily causes surface pore closure, reducing the specific surface area and affecting subsequent energy transfer and cathode formation; second, the agglomerated particles have poor uniformity and a high content of fine powder, affecting the uniformity of powder filling and the reliability of capacitors; third, the process is complex, requiring high-level equipment and control, which is not conducive to large-scale stable production.

[0005] Some improved processes attempt to control particle agglomeration by adding binders, but the introduction of binders increases impurity content and affects the electrical stability of tantalum powder. Other processes use mechanical ball milling for pre-agglomeration. This method easily causes tantalum powder particle deformation, destroying the original porous structure and failing to achieve a balance between sphericity and specific surface area.

[0006] The existing patent CN1238251A discloses a method for producing porous agglomerated tantalum powder, which uses vibration rocking sieve and high-temperature sintering agglomeration. However, this method has weak control over the pore structure and is prone to causing surface pores.

[0007] The existing patent CN104858436A discloses a method for preparing tantalum powder for high-reliability, high-specific-capacitance electrolytic capacitors, but it does not involve the synergistic control of pore structure by a combination of dry and wet shaping process.

[0008] Existing patent CN1068809C discloses a method for compacting fine tantalum powder into a billet before agglomeration heat treatment, aiming to increase the agglomeration effect and reduce the agglomeration temperature to obtain powder with low oxygen content. However, this pre-compaction step increases the complexity of the process, and the compaction process may introduce internal stress, resulting in an uneven pore structure in subsequent heat treatment.

[0009] Therefore, developing a simple, highly controllable agglomeration heat treatment method that can simultaneously improve the specific surface area, flowability, and bulk density of tantalum powder is of great significance for promoting the development of tantalum powder for medium and high voltage capacitors. Summary of the Invention

[0010] The purpose of this invention is to provide a method for preparing porous tantalum powder by agglomeration heat treatment, so as to solve the defects of existing processes that make it difficult to balance loose packing density and specific surface area and have poor controllability of porous structure, and meet the performance requirements of medium and high voltage capacitors for tantalum powder.

[0011] This invention provides a method for preparing porous tantalum powder by agglomeration heat treatment, comprising the following steps:

[0012] 1) Pre-agglomeration and sieving: Tantalum powder raw material prepared by magnesium reduction method, and which has undergone water washing, acid washing purification and drying treatment. Anhydrous ethanol is evenly sprayed onto the powder through an atomizing nozzle, with the amount of anhydrous ethanol controlled between 5% and 15% of the weight of tantalum powder. After spraying, the moistened powder is allowed to stand for 10 to 30 minutes to allow the anhydrous ethanol to fully penetrate and wet the surface and shallow layer of the tantalum powder particles. Subsequently, the pre-agglomerated powder is transferred to a 100-mesh standard sieve and sieved using a mechanical vibrating sieve to collect the fine powder that passes through the sieve. This step aims to remove insufficiently wetted coarse particles and any possible agglomerates, obtaining pre-agglomerated powder with preliminary spheroidization.

[0013] 2) Agglomeration Heat Treatment: The pre-agglomerated powder obtained in step 1) is evenly spread in a high-purity tantalum crucible, with a thickness not exceeding 15 mm. The loading container is placed in a vacuum sintering furnace. The furnace cavity is evacuated to an ultimate vacuum degree ≤3×10⁻³ Pa, and the furnace temperature is raised to a set temperature between 1400℃ and 1500℃ at a heating rate of 5-15℃ / min, and held at this temperature for 30-40 minutes. During this process, tantalum powder particles form strong sintering necks through surface diffusion and volume diffusion mechanisms, achieving metallurgical bonding of the particles and thus stabilizing the porous framework structure. After the holding period, the cooling rate is controlled to ≤10 ℃ / min, and the furnace is cooled to below room temperature. After cooling, air is introduced every 30 minutes until atmospheric pressure is reached before opening the furnace.

[0014] 3) Light Crushing and Finished Product Screening: The slightly agglomerated powder formed after heat treatment in step 2) is removed. It is then lightly crushed by repeated pressing with a pure tantalum plate. The goal of crushing is to break up the larger agglomerates formed by the sintering neck connections, while avoiding over-grinding of the original particles. The crushed powder is then mechanically screened again using a 100-mesh standard sieve. The undersize material is collected to obtain a porous tantalum powder product with good flowability, regular particle morphology, and optimized pore structure.

[0015] The beneficial effects of this invention are as follows:

[0016] By introducing an anhydrous ethanol pre-agglomeration step, the volatility and moderate wettability of anhydrous ethanol are used to form liquid bridges on the particle surface, inducing fine particles to initially agglomerate and tend to become spherical under mild conditions. This provides a uniform starting powder for subsequent heat treatment and effectively avoids the rapid closure of surface pores caused by direct high-temperature treatment.

[0017] By employing medium-high temperature heat treatment within a specific temperature range, sintering necks of sufficient strength can be formed between particles to stabilize the agglomerate structure, significantly improving powder flowability. At the same time, the particle rearrangement optimization brought about by pre-agglomeration allows the powder to maintain a high specific surface area after heat treatment.

[0018] Subsequent light crushing and precise sieving can effectively control the particle size distribution of the final product, reduce the content of ultrafine powder (-325 mesh), and further improve the filling uniformity and formability of the powder.

[0019] The entire process is simple, requiring no complex binders or special molding equipment. The conditions are mild and controllable, with good reproducibility, making it suitable for continuous industrial production. The prepared porous tantalum powder possesses suitable specific surface area, good sphericity, and appropriate bulk density, making it particularly suitable for preparing tantalum powder for medium- and high-voltage capacitors. Attached Figure Description

[0020] Figure 1 (a) and Figure 1 (b) are respectively 50 times and 1×10 times the porous tantalum powder obtained in Example 2 of the present invention. 4 SEM photos of multiple times the size;

[0021] Figure 2 (a) and Figure 2 (b) are respectively 50 times and 1×10 times the porous tantalum powder obtained in Comparative Example 1 of the present invention. 4 SEM photos of multiple times the size; Detailed Implementation

[0022] The present invention will be further described below with reference to the embodiments and accompanying drawings, but the scope of protection of the present invention is not limited to the following embodiments.

[0023] The basic tantalum powder used in all examples and comparative examples was prepared by magnesium reduction of tantalum oxide and underwent the following standard post-treatment process: after crushing, the product was acid-washed with 15% hydrochloric acid under stirring for 2 hours, followed by standing soaking for 4 hours to fully remove magnesium oxide and trace iron impurities; after acid washing, it was washed with warm pure water until the conductivity of the washing solution was <20μS / cm, and finally dried to constant weight under vacuum at 80℃. The loose density of this basic tantalum powder is approximately 1.7-1.9 g / cm³, with uneven particle size distribution, a high proportion of ultrafine powder, and irregular coral-like particles.

[0024] The performance index testing methods involved in this embodiment are as follows:

[0025] Loose packing density (SBD): Determined according to GB / T 1479.1-2011 "Determination of loose packing density of metal powders - Part 1: Funnel method", repeated three times and the average value is taken.

[0026] Specific surface area: Measured using a Micron ASAP2460 fully automated rapid specific surface area and porosity analyzer at 77 K liquid nitrogen temperature with nitrogen as the adsorbate. Calculated according to the Brunauer-Emmett-Teller equation. Repeated tests were performed, and the average value was taken.

[0027] Particle size distribution: According to GB / T 1480-2012 "Determination of particle size composition of metal powder by dry sieving", the mass percentage of -325 mesh (<45 μm) powder was determined.

[0028] Example 1

[0029] Weigh 500.0 g of the above-mentioned basic tantalum powder and place it in two high-purity tantalum crucibles, spreading it to a thickness of 15 mm. Use an atomizing spray gun to evenly spray anhydrous ethanol into the powder in a mist form. The amount of anhydrous ethanol added is 5% of the weight of the tantalum powder. After spraying, allow the powder to stand at room temperature for 10 minutes.

[0030] After the settling period, transfer the pre-agglomerated powder to a mechanical vibrating sieve equipped with a 100-mesh standard sieve and sieve for 5 minutes. Collect the fine powder that passes through the sieve.

[0031] The pre-agglomerated powder was evenly packed into two high-purity tantalum crucibles, spreading it to a thickness of approximately 15 mm. The crucibles were then pushed into a vacuum sintering furnace. The furnace door was closed, and the vacuum system was activated to evacuate the furnace to ≤3.0×10⁻³ Pa and maintain this pressure. The heat treatment program was set as follows: the temperature was increased to 1400 °C at a rate of 10 °C / min, and then held at this temperature for 30 minutes. During the holding phase, the vacuum level was maintained at 1.0×10⁻³ Pa. 3Below Pa. After the holding time is complete, the furnace body is cooled to below room temperature at a rate of 5 °C / min. The heating power is turned off, air is introduced into the furnace to atmospheric pressure, and after cooling to room temperature, the crucible is removed.

[0032] After heat treatment, the powder spread in a tantalum crucible is repeatedly and lightly pressed for 10 minutes using a pure tantalum plate to slightly deagglomerate the powder.

[0033] After deagglomeration, the powder is sieved again on a vibrating screener using a 100-mesh standard sieve for 5 minutes. The material passing through the sieve is collected to obtain the finished product.

[0034] Example 2

[0035] Figure 1 The image shows a scanning electron microscope (SEM) image of the porous tantalum powder obtained in Example 2. Analysis shows that the porous tantalum powder obtained in Example 2 exhibits a loose and porous coral-like network structure with relatively uniform particle size, rounded particle edges, and open and well-connected pores, demonstrating high porosity characteristics. It can be used to prepare medium and high voltage capacitors.

[0036] Weigh 500.0 g of the same base tantalum powder. Use the same container and spraying method as in Example 1, but adjust the amount of anhydrous ethanol added to 10% of the weight of the tantalum powder. After spraying and mixing with anhydrous ethanol, let the powder stand for 20 minutes to impregnate it.

[0037] After soaking, transfer the powder to a mechanical vibrating sieve equipped with a 100-mesh standard sieve and sieve for 5 minutes. Collect the fine powder that passes through the sieve.

[0038] The pre-agglomerated powder was evenly packed into two high-purity tantalum crucibles, spreading it to a thickness of approximately 15 mm. The crucibles were then pushed into a vacuum sintering furnace. The furnace door was closed, and the vacuum system was activated to evacuate the furnace to ≤3.0×10⁻³ Pa and maintain this pressure. The heat treatment program was set as follows: the temperature was increased to 1450 °C at a rate of 10 °C / min, and then held at this temperature for 30 minutes. During the holding phase, the vacuum level was maintained at 1.0×10⁻³ Pa. 3 Below Pa. After the holding time is complete, the furnace body is cooled to below room temperature at a rate of 5 °C / min. The heating power is turned off, air is introduced into the furnace to atmospheric pressure, and after cooling to room temperature, the crucible is removed.

[0039] After heat treatment, the powder spread in a tantalum crucible is repeatedly and lightly pressed with a pure tantalum plate for 15 minutes to slightly deagglomerate the powder.

[0040] After deagglomeration as in Example 1, the powder is sieved again on a vibrating sieve for 5 minutes using a 100-mesh standard sieve. The material passing through the sieve is collected to obtain the finished product.

[0041] Example 3

[0042] Weigh 500.0 g of the same base tantalum powder. Use the same container and spraying method as in Example 1, but adjust the amount of anhydrous ethanol added to 15% of the weight of the tantalum powder. After spraying and mixing with anhydrous ethanol, allow the powder to stand and soak for 30 minutes.

[0043] After soaking, transfer the powder to a mechanical vibrating sieve equipped with a 100-mesh standard sieve and sieve for 5 minutes. Collect the fine powder that passes through the sieve.

[0044] The pre-agglomerated powder was evenly packed into two high-purity tantalum crucibles, spreading it to a thickness of approximately 15 mm. The crucibles were then pushed into a vacuum sintering furnace. The furnace door was closed, and the vacuum system was activated to evacuate the furnace to ≤3.0×10⁻³ Pa and maintain this pressure. The heat treatment program was set as follows: the temperature was increased to 1500 °C at a rate of 10 °C / min, and then held at this temperature for 30 minutes. During the holding phase, the vacuum level was maintained at 1.0×10⁻³ Pa. 3 Below Pa. After the holding time is complete, the furnace body is cooled to below room temperature at a rate of 5 °C / min. The heating power is turned off, air is introduced into the furnace to atmospheric pressure, and after cooling to room temperature, the crucible is removed.

[0045] After heat treatment, the powder spread in a tantalum crucible is repeatedly and lightly pressed with a pure tantalum plate for 20 minutes to slightly deagglomerate the powder.

[0046] After crushing, the powder is sieved again on a vibrating screener using a 100-mesh standard sieve for 5 minutes. The material passing through the sieve is collected to obtain the finished product.

[0047] Comparative Example 1

[0048] Figure 2 The image shows a scanning electron microscope (SEM) image of the porous tantalum powder obtained in Comparative Example 1. Analysis revealed that the tantalum powder particles obtained in Comparative Example 1 were too densely packed and excessively fused, resulting in a significant reduction in the proportion of open pores and narrow, blocked channels. This makes it difficult to meet the requirements of high-capacitance tantalum capacitors for pore structure, and its applicability is poor.

[0049] Weigh 500.0 g of the same base tantalum powder as in the examples, without anhydrous ethanol spraying or static soaking treatment. Directly feed the raw tantalum powder into a vibrating sieve, pass it through a 100-mesh sieve, collect the undersize material, and obtain the un-pre-agglomerated control powder.

[0050] The comparative powder was placed in the same vacuum sintering furnace as in Example 1, using the same high-purity tantalum crucible, and the heat treatment procedure was performed: vacuuming to ≤3.0×10⁻³ Pa, heating to 1500 ℃ at 10 ℃ / min, holding for 30 minutes, and the holding conditions and vacuum breaking operation were the same as in Example 1.

[0051] After heat treatment, the powder was deagglomerated using the same process as in Example 1.

[0052] After deagglomeration, the powder is sieved again on a vibrating screener using a 100-mesh standard sieve for 5 minutes. The material passing through the sieve is collected to obtain the finished product.

[0053] The tantalum powders prepared in Examples 1-3 and Comparative Example 1 were tested for loose density, specific surface area and particle size distribution. The test data are summarized in Table 1.

[0054] Table 1: Comparison of Physical Properties of Porous Tantalum Powder

[0055] Example 1 1.71 0.48 8.5 Example 2 1.83 0.46 7.2 Example 3 1.94 0.43 6.8 Example 4 2.24 0.37 5.5

[0056] Based on the data in Table 1 and the testing process, the following conclusions can be drawn:

[0057] The porous tantalum powder prepared by this invention has a loose density that can be controlled between 1.71 g / cm³ and 1.94 g / cm³, a specific surface area of ​​0.43 m² / g and 0.48 m² / g, and a -325 mesh ultrafine powder content of 6.8% to 8.5%. The amount of anhydrous ethanol sprayed is a key process parameter for controlling the performance of the tantalum powder. As shown in Examples 1, 2, and 3, at agglomeration heat treatment temperature of 1400~1500℃, as the amount of anhydrous ethanol sprayed increases from 5% to 15% of the tantalum powder weight, the loose density of the tantalum powder gradually increases, while the specific surface area and the proportion of -325 mesh ultrafine powder slightly decrease. By controlling the loose density, specific surface area, and particle size distribution of the tantalum powder within an excellent range, the properties of the obtained tantalum powder meet the requirements for the preparation of tantalum powder for medium and high voltage tantalum capacitors. Without anhydrous ethanol pre-agglomeration treatment, even with the same vacuum high-temperature agglomeration heat treatment and subsequent crushing and sieving process, the loose density of the resulting tantalum powder increased to 2.24 g / cm³, and the specific surface area decreased to 0.37 m² / g. The particles underwent excessive sintering and fusion, and the proportion of open pores was significantly reduced. The pore structure and physical properties were difficult to adapt to the preparation requirements of tantalum powder for medium- and high-voltage, high-specific-capacitance tantalum capacitors. This verifies the feasibility and effectiveness of the anhydrous ethanol pre-agglomeration process of this invention in optimizing the comprehensive performance of porous tantalum powder.

[0058] This invention provides a method for preparing porous tantalum powder through agglomeration heat treatment. The process steps are simple, the conditions are mild and controllable, and the reproducibility is high. This method is particularly suitable for the deep processing of primary tantalum powder with high specific surface area and irregular morphology prepared by magnesium reduction, and can effectively synergistically optimize its key physical properties such as specific surface area, particle morphology, particle size distribution, and bulk density. The prepared porous tantalum powder has excellent comprehensive properties and is an ideal raw material for preparing tantalum powder for medium and high voltage tantalum capacitors, with broad prospects for industrial application.

[0059] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the present invention. Any adaptive adjustments, equivalent substitutions, or improvements made by those skilled in the art to the process parameters within the principles and scope disclosed in the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing porous tantalum powder by agglomeration heat treatment, characterized in that, It includes the following steps: 1) Take tantalum powder that has been reduced and dried by magnesium, spray anhydrous ethanol evenly onto it, let it stand for pre-agglomeration, pass it through a 100-mesh sieve, and collect the powder that passes through the sieve. 2) The sieved powder obtained in step 1 is placed in a vacuum environment for agglomeration heat treatment; 3) The powder after vacuum breaking in step 2 is lightly crushed and then sieved twice through a 100-mesh sieve to obtain a porous tantalum powder product.

2. The method for preparing porous tantalum powder by agglomeration heat treatment according to claim 1, characterized in that, The amount of anhydrous ethanol sprayed in step 1 is 5%-15% of the weight of tantalum powder.

3. The method for preparing porous tantalum powder by agglomeration heat treatment according to claim 1, characterized in that, After spraying anhydrous ethanol as described in step 1, the tantalum powder is allowed to stand for 10-30 minutes to allow the anhydrous ethanol to fully wet the tantalum powder particles.

4. The method for preparing porous tantalum powder by agglomeration heat treatment according to claim 1, characterized in that, The sieving time mentioned in step 1 is 5-7 minutes.

5. The method for preparing porous tantalum powder by agglomeration heat treatment according to claim 1, characterized in that, The temperature for the agglomeration heat treatment in step 2 is 1400-1500 ℃, and the holding time is 30-40 minutes.

6. The method for preparing porous tantalum powder by agglomeration heat treatment according to claim 1, characterized in that, The vacuum level of the vacuum environment described in step 2 is ≤ 3×10⁻³ Pa.

7. The method for preparing porous tantalum powder by agglomeration heat treatment according to claim 1, characterized in that, After the agglomeration heat treatment described in step 3 is completed, the furnace temperature is first reduced to below 25°C (room temperature), and then air is introduced into the furnace to gradually restore the furnace pressure to atmospheric pressure.

8. The method for preparing porous tantalum powder by agglomeration heat treatment according to claim 1, characterized in that, The mild crushing method described in step 3 is to lightly crush a pure tantalum plate.

9. The method for preparing porous tantalum powder by agglomeration heat treatment according to claim 1, characterized in that, The sieving time in step 3 is 5-7 minutes. After sieving, the particle size of the collected undersize powder is ≤ 150 μm.

10. A porous tantalum powder prepared by the method according to any one of claims 1-9, characterized in that, The porous tantalum powder has a loose packing density of 1.7 g / cm³-1.9 g / cm³ and a specific surface area of ​​0.43 m². 2 / g -0.48 m 2 / g.

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