Method for preparing high-purity sheet tantalum powder through dry ball milling

Abstract

The invention relates to a method for preparing high-purity sheet tantalum powder by dry ball milling, belongs to the technical field of metal powder processing, and solves the problems of low efficiency, high impurity content, high cost and serious environmental pollution of sheet tantalum powder produced by the existing process. The method comprises the following steps of 1, raw material preparation, wherein coralline tantalum powder and a solid process control agent are subjected to dry mixing, and a mixed material is obtained; step 2, loading and atmosphere replacement: loading the mixed material and grinding balls into a ball-milling tank; 3, sealing the ball milling tank, and vacuumizing the ball milling tank; then filling inert gas into the ball milling tank; step 4, ball milling; and 5, discharging and sieving: opening the ball-milling tank after ball-milling is finished, taking out the material, and separating oxygen milling balls to obtain the ultra-high-purity sheet tantalum powder.

Description

Technical Field

[0001] This invention relates to the field of metal powder processing technology, and in particular to a method for preparing high-purity flake tantalum powder by dry ball milling. Background Technology

[0002] Tantalum powder is an important valve metal material, characterized by its high melting point, high chemical stability, good conductivity, and corrosion resistance, making it widely used in aerospace, electronic communications, and industrial automation. Among these, flake-shaped tantalum powder, due to its inherent flake shape, exhibits higher breakdown voltage and greater porosity, and is typically used in the production of medium- and high-voltage solid and liquid tantalum capacitors. Flake-shaped tantalum powder, with its high specific surface area, good conductivity, and shielding properties, also plays a crucial role in high-end electronic components, conductive coatings, and electromagnetic shielding.

[0003] Currently, the most common method for preparing flake tantalum powder is wet ball milling. A typical process involves mixing raw tantalum powder with an organic solvent (such as alcohol or acetone) and a process control agent, and then placing the mixture in a ball mill. The powder undergoes plastic deformation due to the impact and shearing action of the grinding balls, eventually flattening it into flakes. After ball milling, the powder must undergo multiple post-processing steps, including centrifugation, filtration, and vacuum drying, to obtain the final product.

[0004] Wet ball milling processes involve solvent drying, often requiring large amounts of organic solvents and surfactants. This not only increases production costs but also generates significant amounts of filtrate in subsequent processing, which is difficult to recover. Furthermore, organic solvents pose safety risks, and surfactants cause severe environmental pollution. Simultaneously, the liquid medium's obstruction of the grinding media weakens the impact and friction forces on tantalum powder particles, limiting the flake-like formation of the tantalum powder. Moreover, existing technologies typically use stainless steel balls as the milling media to prepare flake-like tantalum powder. This method introduces large amounts of impurities such as Fe, Cr, and C, which cannot be completely removed during subsequent acid washing, affecting the leakage current and breakdown voltage of the finished powder. With increasingly demanding requirements for tantalum powder performance and production efficiency across industries, traditional wet ball milling methods suffer from low efficiency, high impurity content, and high costs. Especially in high-voltage applications, existing tantalum powders lack sufficient voltage resistance and reliability, failing to meet the demands of higher-performance capacitor-grade tantalum powders. Therefore, exploring a highly efficient, environmentally friendly preparation process that effectively controls the flake-like formation of tantalum powder is of great significance. Summary of the Invention

[0005] Based on the above analysis, the present invention aims to provide a method for preparing high-purity flake tantalum powder by dry ball milling, in order to solve the problems of low efficiency, high impurity content, high cost, and serious environmental pollution caused by existing processes in producing flake tantalum powder.

[0006] The objective of this invention is mainly achieved through the following technical solutions:

[0007] This invention provides a method for preparing high-purity flake tantalum powder by dry ball milling, comprising the following steps:

[0008] Step 1: Raw material preparation: Dry mix coral-like tantalum powder with solid process control agent to obtain a mixture;

[0009] Step 2: Loading and Atmosphere Replacement: Load the mixture and grinding balls into the mill jar;

[0010] Step 3: Seal the milling jar and evacuate it; then fill the milling jar with inert gas.

[0011] Step 4: Ball milling;

[0012] Step 5: Discharge and sieving: After ball milling, open the ball mill jar, take out the material, separate the oxygen milling balls, and obtain ultra-high purity flake tantalum powder.

[0013] Optionally, in step 2, the mass ratio of grinding balls to the mixture is 10:1 to 14:1.

[0014] Optionally, in step 2, the diameter of the grinding ball is 1.5-2.5 mm.

[0015] Optionally, in step 4, the rotational speed of the ball mill during the ball milling process is 200-500 rpm.

[0016] Optionally, in step 1, the solid process control agent includes one or a combination of stearic acid, stearamide, palmitic acid, and zinc stearate.

[0017] Optionally, in step 3, a vacuum is drawn until the vacuum level inside the tank is no higher than 10 Pa.

[0018] Optionally, in step 3, the inert gas is high-purity argon.

[0019] Optionally, in step 2, the grinding ball is a zirconia grinding ball.

[0020] This invention also provides an ultra-high purity flake-shaped tantalum powder, prepared using the method described above. The total amount of impurity elements in the flake-shaped tantalum powder is less than 5 μg / g, and it exhibits a regular two-dimensional flake morphology, good dispersibility, an aspect ratio of 2-10, and a specific surface area >0.5 m². 2 / g.

[0021] The present invention also provides the application of the above-mentioned tantalum powder in the production of high voltage solid and liquid tantalum capacitors.

[0022] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0023] This invention employs intermittent ball milling, combined with the selection of specific solid process control agents (one or a combination of stearic acid, stearamide, palmitic acid, and zinc stearate), and precise control of the amount of solid process control agent added. This effectively isolates the newly formed surface, inhibits cold welding, and thus achieves effective flattening. It solves the problem of insufficient impact and friction of tantalum powder particles caused by the obstruction of the grinding media by the liquid medium in traditional wet ball milling, significantly improving the plate-forming efficiency of tantalum powder particles. Specifically, the specific surface area of ​​tantalum powder increases from approximately 0.25 m² / g. 2 / g increased to 0.55m 2 The yield of / g or more (an increase of more than 120%) proves that the present invention efficiently realizes the transformation from three-dimensional dendrites to two-dimensional lamellar structures with uniform morphology.

[0024] High product purity: This invention employs a full zirconium oxide grinding system, meaning that the lining of the grinding jar and the grinding media are both made of high-purity, highly wear-resistant zirconium oxide material, fundamentally eliminating the introduction of metallic impurities such as Fe, Cr, Ni, and Zr, thereby improving the purity of the flake tantalum powder. Specifically, the total content of metals such as Fe, Cr, Ni, and Zr in the flake tantalum powder is less than 5 μg / g.

[0025] By jointly optimizing the stirring shaft speed (200-500 rpm), ball-to-material ratio (10:1 to 14:1), and controlling the size of the grinding media (zirconia grinding balls with a diameter of 1.5-2.5 mm), a dense shearing force is provided with low energy consumption and low wear, achieving efficient deformation and high purity.

[0026] The method of the present invention does not require the use of solvents, simplifies the process, effectively reduces costs, and eliminates safety and environmental hazards.

[0027] This invention can efficiently and completely transform coral-like tantalum powder with low specific surface area into flaky tantalum powder with uniform morphology. At the same time, the invention performs dry ball milling under an inert gas protective atmosphere, which effectively prevents the tantalum powder from being oxidized during the ball milling process. The oxygen content of the product after ball milling is controllable, providing a good precursor basis for further reducing the oxygen content.

[0028] In this invention, the above-described technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of this invention will be set forth in the following description, and some advantages will become apparent from the description or may be learned by practicing the invention. Attached Figure Description

[0029] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts.

[0030] Figure 1SEM image of the original coral-like tantalum powder used in this invention;

[0031] Figure 2 This is a SEM image of the flake-shaped tantalum powder prepared in Example 1 of the present invention;

[0032] Figure 3 SEM image of tantalum powder obtained in Comparative Example 1 (high rotation speed) of the present invention;

[0033] Figure 4 This is a SEM image of the material obtained in Comparative Example 2 of the present invention (stearic acid addition of 0.2%).

[0034] Figure 5 This is a SEM image of the material obtained in Comparative Example 3 (low ball-to-material ratio 5:1) of the present invention;

[0035] Figure 6 This is a SEM image of the material obtained in Comparative Example 4 of the present invention (high ball-to-material ratio 15:1). Detailed Implementation

[0036] The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which constitute a part of the present invention and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not intended to limit the scope of the present invention.

[0037] At present, wet ball milling is mainly used to produce flake tantalum powder. The technology of dry ball milling to prepare tantalum powder has not been fully developed and applied, mainly because the following technical difficulties have not been overcome: (1) Dry ball milling lacks the lubrication and dispersion effect of solvents, and the powder is very easy to quickly cold weld and agglomerate due to the newly generated surface energy, making it impossible to achieve effective flattening; (2) Efficiently flattening the solid coral-like structure into flakes requires sufficient energy input, but high energy will aggravate wear and temperature rise.

[0038] In a first aspect, the present invention provides a method for preparing flake-shaped tantalum powder by high-energy ball milling under inert gas protection. This method uses coral-like tantalum powder (oxygen content less than 2000 ppm, specific surface area 0.2-0.3 m² / g) as raw material, employs a full zirconia dry ball milling system, and uses a set of optimized, non-high-energy specific ball milling parameters to directly and rapidly transform the three-dimensional dendritic structure into an ultra-high purity two-dimensional flake structure under inert atmosphere protection.

[0039] The overall technical route of this invention is as follows: coral-like tantalum powder + solid process control agent → dry mixing in a full zirconium oxide system → vacuuming and argon filling → intermittent ball milling with optimized parameters in a stirred ball mill → sieving of the discharged material → high-purity flake tantalum powder.

[0040] Key methods include: ① a full zirconia grinding system (fundamentally eliminating metal contamination); ② an optimized combination of gentle ball milling parameters (stirring shaft speed 200-500 rpm, ball-to-material ratio 10:1 to 14:1, grinding ball diameter 1.5-2.5 mm, and ball milling time 2-4 hours, achieving high efficiency and low consumption deformation); ③ dry addition of solid process control agents and intermittent ball milling (preventing cold welding agglomeration and ensuring smooth operation).

[0041] Specifically, the preparation method of the present invention includes the following steps:

[0042] Step 1: Raw material preparation: Dry mix coral-like tantalum powder with solid process control agent to obtain a mixture;

[0043] Step 2: Loading and Atmosphere Replacement: Load the mixture and zirconia grinding balls together into a stirred ball mill jar with a zirconia liner;

[0044] Step 3: Seal the grinding jar and evacuate it; then fill the grinding jar with inert gas; repeat the "evacuation-inert gas filling" process 2-3 times to ensure that the air inside the jar is completely replaced.

[0045] Step 4: Ball milling: Turn on the cooling system of the ball mill and start the ball mill for intermittent ball milling;

[0046] Step 5: Discharge and sieving: After ball milling, wait for the ball mill jar to cool to room temperature, open the ball mill jar under inert gas protection, and take out the material; use a standard sieve to sieve the product, separate the zirconium oxide grinding balls, and obtain ultra-high purity flake tantalum powder.

[0047] In step 1, the solid process control agent includes one or a combination of several of stearic acid, stearamide, palmitic acid, and zinc stearate. The amount of solid process control agent added is 1.0%-1.5% of the mass of tantalum powder, for example, 1.0%, 1.1%, 1.2%, 1.25%, 1.3%, 1.35%, 1.4%, 1.45%, or 1.5%. Preferably, it is 1.25%.

[0048] In step 2, the mass ratio (ball-to-material ratio) of the zirconia grinding balls to the mixture is 10:1 to 14:1, for example, 10:1, 11:1, 12:1, 13:1, or 14:1. 12:1 is preferred.

[0049] In step 2, the diameter of the zirconia grinding ball is 1.5-2.5 mm, for example, 1.5 mm, 1.6 mm, 1.7 mm, 1.8 mm, 1.9 mm, 2 mm, 2.1 mm, 2.2 mm, 2.3 mm, 2.4 mm, or 2.5 mm. Preferably, it is 1.8-2.0 mm.

[0050] In step 3, evacuate the tank until the vacuum level does not exceed 10 Pa. The inert gas is high-purity argon (purity ≥ 99.999%). Fill the tank with inert gas until the gauge pressure is 0.05–0.5 MPa, for example, 0.05 MPa, 0.1 MPa, 0.15 MPa, 0.2 MPa, 0.25 MPa, 0.3 MPa, 0.35 MPa, 0.4 MPa, 0.45 MPa, or 0.5 MPa.

[0051] In step 3, the vacuum system used for evacuation consists of a mechanical vacuum pump and a Roots pump connected in series. Alternatively, other vacuum units capable of achieving the same vacuum level (≤10 Pa) can be used.

[0052] In step 3, during the final operation, inert gas is introduced until the gauge pressure is 0.2 to 0.4 MPa, for example, 0.2 MPa, 0.3 MPa, or 0.4 MPa, as a protective gas for the ball mill.

[0053] In step 4, a horizontal stirred ball mill is used, and the temperature of the cooling medium is 10-25℃, for example, 10℃, 15℃, 20℃, 25℃.

[0054] In step 4, the stirring shaft speed of the ball mill is 200-500 rpm, for example, 200 rpm, 250 rpm, 300 rpm, 350 rpm, 400 rpm, 450 rpm, or 500 rpm. Preferably, it is 300-400 rpm. The ball milling time is 2-4 hours, for example, 2 hours, 2.5 hours, 3 hours, 3.5 hours, or 4 hours. Intermittent ball milling uses a cycle of 20-40 minutes of running (e.g., 20 minutes, 25 minutes, 30 minutes, 35 minutes, or 40 minutes) followed by a 5-15 minute pause (e.g., 5 minutes, 10 minutes, or 15 minutes).

[0055] In step 5, the total amount of impurity elements (Fe, Cr, Ni, Zr) in the obtained flake-like tantalum powder is less than 5 μg / g, and it has a regular two-dimensional flake morphology, good dispersibility, an aspect ratio of 2-10, and a specific surface area >0.5 m². 2 / g, for example, 0.55-0.61m 2 / g, specific surface area of ​​the original powder (0.2-0.3m²) 2 The oxygen content was significantly increased to 5200-5400 ppm.

[0056] Optionally, step 5 may include post-treatment of the flake tantalum powder, including acid washing purification and / or vacuum annealing to reduce oxygen.

[0057] Acid washing purification includes: soaking or stirring the obtained flake tantalum powder in dilute acid, then washing with water and / or alcohol until neutral, and drying.

[0058] The dilute acid can be hydrofluoric acid, nitric acid, or a mixture thereof. The mass fraction of the dilute acid is 5%-15%, for example, 5%, 10%, or 15%.

[0059] Vacuum annealing for oxygen reduction includes: annealing flake tantalum powder (after acid washing, or without acid washing and purification) under high vacuum (≤1×10⁻⁶). - 2 Heat treatment is carried out at Pa) and then kept at that temperature.

[0060] The heat treatment temperature is 1200℃~1600℃, for example, 1200℃, 1300℃, 1400℃, 1500℃, 1600℃. The holding time is 1-4h, for example, 1h, 2h, 3h, 4h.

[0061] In addition, the experiment found that the process window for dry ball milling is very narrow, and the synergistic effect between various process parameters is very strong. It requires a lot of creative work through experiments to find the process conditions that provide dense shear force with low energy consumption and low wear, so as to achieve efficient deformation of coral-shaped tantalum powder and high product purity. This is also the main reason why dry ball milling is not currently used for the production of flake tantalum powder.

[0062] The present invention will now be described in detail with reference to specific embodiments.

[0063] Example 1

[0064] (1) Raw material preparation: Coral-shaped tantalum powder (morphology see) Figure 1 The tantalum powder was dry-mixed with stearic acid, a solid process control agent, in a glove box under inert gas protection; the amount of stearic acid added was 1.25% of the mass of the tantalum powder.

[0065] (2) Loading and Atmosphere Replacement: The mixture and zirconia grinding balls are loaded together into a stirred ball mill jar with a zirconia liner; the mass ratio of the zirconia grinding balls to the material (ball-to-material ratio) is 12:1; the diameter of the zirconia grinding balls is Φ1.8-2.0mm; after loading, the ball mill jar is sealed and connected to a vacuum system consisting of a mechanical vacuum pump and a Roots pump connected in series to evacuate the ball mill jar until the vacuum level inside the jar does not exceed 10Pa; then, high-purity argon gas (purity ≥99.999%) is introduced into the ball mill jar until the gauge pressure is 0.25MPa. Then, the gas inside the jar is evacuated again until it does not exceed 10Pa. This "vacuuming-argon filling" process is repeated 3 times to ensure that the air inside the jar is fully replaced. In the last operation, high-purity argon gas is introduced until the gauge pressure is 0.3MPa as a protective atmosphere for the ball mill.

[0066] (3) Ball milling: Turn on the cooling system of the horizontal stirred ball mill and control the temperature of the cooling medium at 10-25℃; start the ball mill for intermittent ball milling; the total ball milling time is 2 hours; the stirring shaft speed of the stirred ball mill is 300 rpm, and the ball milling is carried out in a cycle mode of running for 30 minutes and pausing for 10 minutes, with a total intermittent ball milling time of 2 hours.

[0067] (4) Discharge and sieving: After the ball milling is completed, wait for the ball milling jar to cool to room temperature, open the ball milling jar under the protection of inert gas, and take out the material; use a standard sieve to sieve the product and separate the zirconium oxide grinding balls to obtain the ultra-high purity flake tantalum powder.

[0068] The flake-shaped tantalum powder prepared in this embodiment was tested and characterized, and the results are as follows:

[0069] Morphology (SEM): See Figure 2 The coral-like structure has been largely transformed into a regular, flat sheet-like structure.

[0070] Specific surface area (BET): 0.55 m² 2 / g. (relative to raw material (0.25m) 2 ( / g), with a 120% increase in specific surface area.

[0071] Purity (ICP-MS, μg / g): Fe:<2, Cr:<1, Ni:<1, Zr:<1.

[0072] Oxygen content: 5200ppm.

[0073] Example 2

[0074] (1) Raw material preparation: Coral-shaped tantalum powder (morphology see) Figure 1 The oleic acid amine was dry-mixed with the solid process control agent stearamide in an inert gas-protected glove box; the amount of oleic acid amine added was 1% of the mass of tantalum powder.

[0075] (2) Loading and Atmosphere Replacement: The mixture and zirconia grinding balls are loaded together into a stirred ball mill jar with a zirconia liner; the mass ratio of the zirconia grinding balls to the material (ball-to-material ratio) is 10:1; the diameter of the zirconia grinding balls is Φ1.8-2.0mm; after loading, the ball mill jar is sealed and connected to a vacuum system consisting of a mechanical vacuum pump and a Roots pump connected in series to evacuate the ball mill jar until the vacuum level inside the jar does not exceed 10Pa; then, high-purity argon gas (purity ≥99.999%) is introduced into the ball mill jar until the gauge pressure is 0.05MPa. Then, the gas inside the jar is evacuated again until it does not exceed 10Pa. This "vacuuming-argon filling" process is repeated 3 times to ensure that the air inside the jar is fully replaced. In the last operation, high-purity argon gas is introduced until the gauge pressure is 0.2MPa as a protective atmosphere for the ball mill.

[0076] (3) Ball milling: Turn on the cooling system of the horizontal stirred ball mill and control the temperature of the cooling medium at 10℃; start the ball mill for intermittent ball milling; the stirring shaft speed of the stirred ball mill is 200 rpm, and the ball milling is carried out in a cycle mode of 40 minutes of operation and 5 minutes of pause, with a total intermittent ball milling time of 3 hours.

[0077] (4) Discharge and sieving: After the ball milling is completed, wait for the ball milling jar to cool to room temperature, open the ball milling jar under the protection of inert gas, and take out the material; use a standard sieve to sieve the product and separate the zirconium oxide grinding balls to obtain the ultra-high purity flake tantalum powder.

[0078] The flake-shaped tantalum powder prepared in this embodiment was tested and characterized, and the results are as follows:

[0079] Specific surface area (BET): 0.59 m² 2 / g.

[0080] Purity (ICP-MS, μg / g): Fe:<1, Cr:<1, Ni:<1, Zr:<1.

[0081] Oxygen content: 5400ppm.

[0082] Example 3

[0083] (1) Raw material preparation: Coral-shaped tantalum powder (morphology see) Figure 1 The tantalum powder is dry-mixed with stearic acid, a solid process control agent, in a glove box under inert gas protection; the amount of stearic acid added is 1.5% of the mass of the tantalum powder.

[0084] (2) Loading and Atmosphere Replacement: The mixture and zirconia grinding balls are loaded together into a stirred ball mill jar with a zirconia liner; the mass ratio of the zirconia grinding balls to the material (ball-to-material ratio) is 14:1; the diameter of the zirconia grinding balls is Φ1.8-2.0mm; after loading, the ball mill jar is sealed and connected to a vacuum system consisting of a mechanical vacuum pump and a Roots pump connected in series to evacuate the ball mill jar until the vacuum level inside the jar does not exceed 10Pa; then, high-purity argon gas (purity ≥99.999%) is introduced into the ball mill jar until the gauge pressure is 0.5MPa. Then, the gas inside the jar is evacuated again until it does not exceed 10Pa. This "vacuuming-argon filling" process is repeated 3 times to ensure that the air inside the jar is fully replaced. In the last operation, high-purity argon gas is introduced until the gauge pressure is 0.4MPa as a protective atmosphere for the ball mill.

[0085] (3) Ball milling: Turn on the cooling system of the horizontal stirred ball mill and control the temperature of the cooling medium at 25°C; start the ball mill for intermittent ball milling; the total ball milling time is 2 hours; the stirring shaft speed of the stirred ball mill is 500 rpm, and the ball milling is carried out in a cycle mode of running for 20 (20-40 min) minutes and pausing for 15 minutes, with a total intermittent ball milling time of 4 hours.

[0086] (4) Discharge and sieving: After the ball milling is completed, wait for the ball milling jar to cool to room temperature, open the ball milling jar under the protection of inert gas, and take out the material; use a standard sieve to sieve the product and separate the zirconium oxide grinding balls to obtain the ultra-high purity flake tantalum powder.

[0087] The flake-shaped tantalum powder prepared in this embodiment was tested and characterized, and the results are as follows:

[0088] Specific surface area (BET): 0.61 m² 2 / g.

[0089] Purity (ICP-MS, μg / g): Fe:<1, Cr:<1, Ni:<1, Zr:<1.

[0090] Oxygen content: 5300ppm.

[0091] Comparative Example 1 (High Speed)

[0092] (1) Raw material preparation: The coral-like tantalum powder (morphology see) is prepared by adding the coral-like tantalum powder (morphology see see) Figure 1 The tantalum powder was dry-mixed with stearic acid, a solid process control agent, in a glove box under inert gas protection; the amount of stearic acid added was 1.25% of the mass of the tantalum powder.

[0093] (2) Loading and Atmosphere Replacement: The mixture and zirconia grinding balls are loaded together into a stirred ball mill jar with a zirconia liner; the mass ratio of the zirconia grinding balls to the material (ball-to-material ratio) is 12:1; the diameter of the zirconia grinding balls is Φ1.8-2.0mm. After loading, the ball mill jar is sealed and connected to a vacuum system consisting of a mechanical vacuum pump and a Roots pump connected in series. The ball mill jar is evacuated until the vacuum level inside the jar does not exceed 10Pa; then, high-purity argon gas (purity ≥99.999%) is introduced into the ball mill jar until the gauge pressure is 0.25MPa. Then, the gas inside the jar is evacuated again until it does not exceed 10Pa. This "vacuuming-argon filling" process is repeated 3 times to ensure that the air inside the jar is fully replaced. In the last operation, high-purity argon gas is introduced until the gauge pressure is 0.4MPa as a protective atmosphere for the ball mill.

[0094] (3) Ball milling: Turn on the cooling system of the horizontal stirred ball mill and control the temperature of the cooling medium at 10-25℃; start the ball mill for intermittent ball milling; the total ball milling time is 2 hours; the stirring shaft speed of the stirred ball mill is 800 rpm; adopt the cycle mode of running the ball mill for 30 minutes and pausing for 10 minutes, and the total intermittent ball milling time is 2 hours.

[0095] (4) Discharge and sieving: After the ball milling is completed, wait for the ball milling jar to cool to room temperature, open the ball milling jar under the protection of inert gas, and take out the material; use a standard sieve to sieve the product and separate the zirconium oxide grinding balls to obtain the ultra-high purity flake tantalum powder.

[0096] The flake-shaped tantalum powder prepared in this comparative example was tested and characterized, and the results are as follows:

[0097] Morphology (SEM): See Figure 3 The powder was severely broken and curled up.

[0098] Purity (ICP-MS, μg / g): Fe: 29, Cr: 12, Ni: <2, Zr: 650.

[0099] Oxygen content: 13300ppm.

[0100] This comparative example demonstrates that the extreme impact caused by excessively high rotational speeds not only damages the powder morphology but also drastically exacerbates the wear of the zirconia grinding system, leading to a surge in zirconium (Zr) impurity content. At the same time, the oxygen content increases significantly due to intense friction and the newly formed surface effect.

[0101] Comparative Example 2 (Insufficient PCA dosage)

[0102] (1) Raw material preparation: The coral-like tantalum powder (morphology see) is prepared by adding the coral-like tantalum powder (morphology see see) Figure 1 The tantalum powder was dry-mixed with stearic acid, a solid process control agent, in a glove box under inert gas protection; the amount of stearic acid added was 0.2% of the mass of the tantalum powder.

[0103] (2) Loading and Atmosphere Replacement: The mixture and zirconia grinding balls are loaded together into a stirred ball mill jar with a zirconia liner; the mass ratio of the zirconia grinding balls to the material (ball-to-material ratio) is 12:1; the diameter of the zirconia grinding balls is Φ1.8-2.0mm. After loading, the ball mill jar is sealed and connected to a vacuum system consisting of a mechanical vacuum pump and a Roots pump connected in series. The ball mill jar is evacuated until the vacuum level inside the jar does not exceed 10Pa; then, high-purity argon gas (purity ≥99.999%) is introduced into the ball mill jar until the gauge pressure is 0.3MPa. Then, the gas inside the jar is evacuated again until it does not exceed 10Pa. This "vacuuming-argon filling" process is repeated 3 times to ensure that the air inside the jar is fully replaced. In the last operation, high-purity argon gas is introduced until the gauge pressure is 0.4MPa as a protective atmosphere for the ball mill.

[0104] (3) Ball milling: Turn on the cooling system of the horizontal stirred ball mill and control the temperature of the cooling medium at 10-25℃; start the ball mill for intermittent ball milling; the total ball milling time is 2 hours; the stirring shaft speed of the stirred ball mill is 300 rpm; adopt the cycle mode of running the ball mill for 30 minutes and pausing for 10 minutes, and the total intermittent ball milling time is 2 hours.

[0105] (4) Discharge and sieving: After the ball milling is completed, wait for the ball milling jar to cool to room temperature, open the ball milling jar under the protection of inert gas, and take out the material; use a standard sieve to sieve the product and separate the zirconium oxide grinding balls to obtain the ultra-high purity flake tantalum powder.

[0106] The flake-shaped tantalum powder prepared in this comparative example was tested and characterized, and the results are as follows:

[0107] Morphology (SEM): See Figure 4 The material is severely adhered and clumped, making it impossible to obtain dispersed powder.

[0108] This comparative example demonstrates that a sufficient amount of process control agent (preferably 1.25%) is indispensable for suppressing cold welding in dry ball milling, ensuring smooth process operation, and obtaining well-dispersed flake powder.

[0109] Comparative Example 3

[0110] The comparative example is basically the same as Example 1, except that the ball-to-material ratio is 5:1.

[0111] The flake-shaped tantalum powder prepared in this comparative example was tested and characterized, and the results are as follows:

[0112] Morphology (SEM): See Figure 5 The particles are relatively large, exhibiting an irregular blocky structure with a rough surface and irregular edges. Some particles are adhered together, indicating insufficient plastic deformation and inadequate grinding energy, resulting in insufficient particle extension.

[0113] Specific surface area: 0.15 m2 / g (insufficient morphological transformation, much lower than the 0.55 m2 / g of the example) Particle size D50: 28.5 μm (relatively coarse).

[0114] Oxygen content: 3590 ppm (low).

[0115] Purity (ICP-MS, μg / g): Fe: 16, Cr: <3, Ni: <3, Zr: 649 μg / g.

[0116] This comparative example demonstrates that an excessively low ball-to-powder ratio leads to insufficient grinding energy, preventing effective lamellar deformation. When the number of grinding balls is too small (5:1), each ball carries a relatively large amount of powder, resulting in extremely high local pressure during impact. Furthermore, the grinding balls themselves are more prone to violent collisions, leading to high wear on the zirconia grinding balls. Due to insufficient total energy, deformation is incomplete (specific surface area 0.15), resulting in fewer newly formed surfaces and a lower oxygen content (3590 ppm).

[0117] Comparative Example 4

[0118] The comparative example is basically the same as Example 1, except that the ball-to-material ratio is 15:1.

[0119] The flake-shaped tantalum powder prepared in this comparative example was tested and characterized, and the results are as follows:

[0120] Morphology (SEM): See Figure 6 The particles are fine, but exhibit significant breakage and adhesion, resulting in an incomplete flaky structure and broken edges. Due to excessively high collision energy, the particles underwent cold welding. Although the specific surface area increased (0.27 m²), the overall particle size remained relatively small. 2 / g), but the sheet-like structure is not ideal.

[0121] Specific surface area: 0.27 m² / g (still far lower than in the example).

[0122] Particle size D50: 68.0 μm (increased instead, indicating severe aggregation)

[0123] Oxygen content: 11200ppm (extremely high).

[0124] Purity (ICP-MS, μg / g): Fe: 54, Cr: 16, Ni: 4, Zr: 650.

[0125] This comparative example demonstrates that an excessive number of grinding balls, along with high collision frequency and energy, leads to excessive particle breakage, cold welding, and severe oxidation. While an excessively high ball-to-material ratio can promote deformation, an excessive number of grinding balls causes a sharp increase in collision frequency and energy, resulting in a dramatic increase in oxygen content and accelerating the wear of the zirconia grinding balls.

[0126] SEM images of the flake-shaped tantalum powder prepared in some of the embodiments and comparative examples are shown below. Figure 1-6 As shown. Figure 1 This is a SEM image of the original coral-like tantalum powder used in this invention. Figure 1 It can be seen that it has a coral-like structure and complex three-dimensional pores.

[0127] Figure 2 This is a SEM image of the flake-shaped tantalum powder prepared in Example 1 of the present invention. Figure 2 As can be seen, the coral-like structure has been completely transformed into regular flaky powder. The powder in the image exhibits a typical flaky structure that is regular, flat, large, and well-dispersed. The coral-like structure has completely disappeared, proving that the optimized parameters successfully achieved an efficient and thorough morphological transformation.

[0128] Figure 3 This is a SEM image of the tantalum powder obtained in Comparative Example 1 (high rotation speed) of the present invention. Figure 3 It can be seen that the powder was severely broken and refined due to the extreme impact force, and agglomerated into irregular particles, with the flaky morphology basically disappearing. With a ball-to-powder ratio of 12:1 being acceptable, the extremely high rotation speed of 800 rpm brought about a catastrophic impact, directly crushing the powder instead of flattening it.

[0129] Figure 4 This is a SEM image of the material obtained in Comparative Example 2 of this invention (stearic acid addition of 0.2%). Figure 4 As can be seen, the powder undergoes severe cold welding, agglomerating into large clumps, making it impossible to obtain dispersed flake powder. This figure visually illustrates the consequences of insufficient PCA; under the high energy of dry ball milling, the newly formed surfaces of the powder rapidly cold weld together, forming huge, dense agglomerates.

[0130] Figure 5 This is a SEM image of the material obtained in Comparative Example 3 of this invention (low ball-to-material ratio 5:1). (Source: [Insert SEM image here]) Figure 5 It can be seen that a low ball-to-material ratio will result in insufficient ball milling energy, making it impossible to achieve effective sheet-like deformation.

[0131] Figure 6 This is a SEM image of the material obtained in Comparative Example 4 of this invention (high-ball material ratio 15:1). Figure 6 It can be seen that an excessively high ball-to-material ratio can lead to excessive particle breakage and cold welding.

[0132] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing high purity flaky tantalum powder by dry ball milling, characterized by, The method comprises the following steps: Step 1: raw material preparation: dry mixing the coral-shaped tantalum powder with the solid process control agent to obtain a mixture; Step 2: loading and atmosphere replacement: loading the mixture and the grinding balls into a ball mill tank; Step 3: sealing the ball mill tank, vacuumizing the ball mill tank, and then filling the ball mill tank with inert gas; Step 4: ball milling; Step 5: discharging and sieving: opening the ball mill tank after the ball milling is completed, taking out the material, and separating out the oxygen grinding balls to obtain the ultra-high purity flaky tantalum powder.

2. The method of claim 1, wherein, In step 2, the mass ratio of the grinding balls to the mixture is 10:1 to 14:

1.

3. The method according to claim 1 or 2, characterized in that, In step 2, the diameter of the grinding balls is 1.5-2.5 mm.

4. The method of claim 1, wherein, In step 4, the rotating speed of the ball mill during the ball milling is 200-500 rpm.

5. The method of claim 1, wherein, In step 1, the solid process control agent comprises one or a combination of several of stearic acid, stearic amide, palmitic acid, and zinc stearate.

6. The method of claim 1, wherein, In step 3, the vacuumization is performed to a vacuum degree in the tank of no higher than 10 Pa.

7. The method according to any one of claims 4-6, characterized in that, In step 3, the inert gas is high-purity argon.

8. The method of claim 7, wherein, In step 2, the grinding balls are zirconia grinding balls.

9. An ultra-high purity flake tantalum powder, characterized by, The flaky tantalum powder prepared by the method of any one of claims 1-8 has a total amount of impurity elements less than 5 μg / g, a regular two-dimensional flaky morphology, a diameter-thickness ratio of 2-10, a specific surface area of >0.5 m 2 / g, and a purity of >99.99%.

10. The tantalum powder of claim 9 for use in the production of solid or liquid tantalum capacitors.

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