Method for preparing low-oxygen tantalum powder through magnesium reduction

Abstract

The invention discloses a method for preparing low-oxygen tantalum powder through magnesium reduction. Aiming at the defects of more impurities, non-uniform particles, complex process and the like in the existing tantalum powder preparation technology, the method comprises the following steps: firstly, pretreating tantalum oxide powder and anhydrous calcium chloride, so that tantalum oxide is uniformly coated with calcium chloride; and mixing the pretreated raw materials with magnesium chips, introducing high-purity argon into a closed container for multiple times of replacement, carrying out heating and heat preservation to generate a reaction, separating a product, and then carrying out water washing, acid pickling and drying treatment to obtain the tantalum powder. According to the method, magnesium and tantalum oxide are fully reacted by virtue of heat absorption and fluxing effects of calcium chloride, so that composite substances such as tantalate are prevented from being generated, and impurity introduction is reduced. The oxygen content of the prepared low-oxygen tantalum powder is smaller than 3000 ppm, the apparent density is 1.3-1.5 g / cm < 3 >, powder particles are in a coralline shape and are uniform in size, operation is easy and convenient, the requirement for equipment is low, and the low-oxygen tantalum powder has good application prospects in the field of electronic component manufacturing.

Description

Technical Field

[0001] The invention belongs to the field of metal functional material smelting, and particularly relates to a method for preparing low-oxygen tantalum powder by magnesium reduction. Background Art

[0002] In the modern electronics industry, tantalum powder is a crucial material for manufacturing key electronic components such as capacitors, and its quality plays a decisive role in product performance. As electronic devices continue to evolve towards miniaturization and higher performance, the quality requirements for tantalum powder are becoming increasingly stringent. Low impurity content and uniform powder particle size have become key indicators of tantalum powder quality.

[0003] Currently, there are a variety of methods for preparing tantalum powder, but each method has certain limitations. For example, the sodium reduction of potassium fluorotantalate is a commonly used preparation process. In this method, liquid sodium metal is injected into a stirred, molten potassium fluorotantalate and a diluent salt, whereupon the potassium fluorotantalate is reduced by the sodium to produce tantalum powder. However, this reaction is highly exothermic, resulting in a large accumulation of localized heat, causing rapid nucleation growth during the tantalum powder preparation process and resulting in coarse primary tantalum powder particles. Furthermore, liquid-liquid reduction creates a large potassium fluorotantalate concentration gradient in the reaction system. While fine particles can be produced in low-concentration regions, it is difficult to improve the uniformity of the primary particles of sodium-reduced tantalum powder, significantly limiting its application in high-voltage, high-reliability capacitors. Furthermore, the addition of large amounts of diluents (such as halide salts such as NaCl, KCl, KF, or mixtures thereof) or mechanical stirring to inhibit rapid grain growth inevitably introduces a large number of impurities into the tantalum powder, thereby reducing its purity.

[0004] Tantalum ingot hydrogenation is another common preparation method. This method exploits the hydrogen embrittlement of metallic tantalum. The ingot is first hydrogenated, then crushed and pulverized, and then processed to produce tantalum powder for capacitors. While the tantalum powder produced by this process performs well in terms of voltage resistance, its specific capacitance is relatively low, making it difficult to meet the requirements of applications requiring high specific capacitance.

[0005] The magnesium reduction of tantalum oxide method, due to the change in the state of the reactants, theoretically has the potential to produce tantalum powder for capacitors with improved specific capacitance and voltage resistance. However, existing related processes still have many problems that need to be solved.

[0006] CN117840420A discloses a method for preparing high-pressure, high-specific-volume tantalum powder by reducing tantalum oxide with magnesium. The method comprises mixing porous spherical tantalum oxide particles with magnesium powder and alkali metal halide salts, and subjecting the mixture to reduction reaction, vacuum magnesium removal, acid and water washing, spheroidization and granulation, multiple heat treatments, and oxygen reduction treatments to obtain tantalum powder. However, this method has the disadvantages of being relatively complex, requiring high equipment and consuming high energy, and using a large amount of heat absorbent, which may introduce impurities that affect the purity of the tantalum powder.

[0007] CN1308566A discloses a method for producing tantalum powder by reducing tantalum oxide with magnesium vapor. However, the method has stringent requirements on raw materials and the reducing agent is in gaseous state, resulting in high costs and difficulty in process control.

[0008] Other preparation methods exist, such as self-propagating high-temperature synthesis (SHS). This method requires reactions at temperatures exceeding 2000°C, resulting in extremely high reaction speeds. This makes precise control difficult and places high demands on process equipment. Furthermore, the resulting tantalum powder has poor uniformity, making it unsuitable for manufacturing high-reliability capacitors.

[0009] Existing tantalum powder preparation methods are unable to fully meet the urgent demand for low-oxygen, high-performance tantalum powder in the current electronics industry. Therefore, developing a new method for preparing low-oxygen tantalum powder using magnesium reduction to obtain high-quality tantalum powder with low oxygen content, appropriate bulk density, and uniform particle shape is of great practical significance for promoting the development of industries such as electronic components. Summary of the Invention

[0010] The purpose of the present invention is to provide an innovative method for preparing low-oxygen tantalum powder by magnesium reduction, so as to address the shortcomings of existing tantalum powder preparation technology and meet the demand for high-quality tantalum powder in the electronics field.

[0011] The present invention provides a method for preparing low-oxygen tantalum powder by magnesium reduction, comprising the following steps:

[0012] (1) Raw material pretreatment: Select tantalum oxide powder with a purity of not less than 99.9%, metal magnesium chips with a particle size of 0.5-3mm, and anhydrous calcium chloride with a purity of not less than 99%. Calcium chloride is weighed accurately according to the molar ratio of tantalum oxide to calcium chloride of 1:(0.5-1.5), dissolved in deionized water, and prepared into a calcium chloride solution with a mass concentration of 20%-40%. Subsequently, the tantalum oxide powder is poured into the solution and stirred thoroughly to ensure uniform mixing, and then dried at 100-200°C. This process allows the calcium chloride to be evenly coated on the surface of the tantalum oxide particles, playing the role of fluxing and absorbing reaction heat, which not only helps to enhance the activity of the magnesium reduction reaction, but also acts as a barrier, inhibiting the occurrence of side reactions to a certain extent, and preventing the MgO produced by magnesium reduction from reacting with the remaining Ta2O5 to produce Mg4Ta2O9.

[0013] The raw materials of the present invention include a diluent, namely anhydrous calcium chloride, which has a melting point of 772°C. Since the reaction between magnesium and tantalum oxide is an exothermic reaction, calcium chloride can absorb the heat generated during the reaction, thereby controlling the reaction rate. In addition, the calcium chloride is coated on the surface of the tantalum oxide particles. When the temperature exceeds the melting point, it becomes molten calcium chloride. In the molten state, it can ionize calcium ions and chloride ions. These ions can enter the tantalum oxide particles, causing the crystal lattice to be distorted, weakening the chemical bonds within the substance, thereby lowering the melting point of the tantalum oxide and facilitating the magnesium reduction reaction.

[0014] (2) Raw material mixing: The pretreated tantalum oxide powder is mixed with metal magnesium chips in a molar ratio of 1:(5-15); theoretically, 5 mol of magnesium is required to fully react with 1 mol of tantalum oxide. In actual reactions, magnesium will be lost due to evaporation, so it is necessary to add excess magnesium chips to ensure that the tantalum oxide and magnesium are in full contact in the subsequent reduction reaction, thereby improving the reaction efficiency and making the reaction more complete and thorough.

[0015] (3) Reduction reaction: Place the mixed material in a sealed reaction vessel, introduce high-purity argon gas with a purity of ≥99.99% into the vessel, and perform 3-5 replacement operations to completely remove the air in the vessel to prevent impurities in the air from interfering with the reaction. After the replacement is completed, slowly heat the reaction system to 800-1000℃ at a heating rate of 5-15℃ / min, while controlling the pressure at 0.08-0.12Mpa, and maintain argon gas at a stable flow rate of 80-150ml / min throughout the reaction process; keep the temperature under this condition for 4-8h to promote the full reduction reaction of tantalum oxide and magnesium. By controlling the reaction temperature, pressure and gas flow rate, suitable thermodynamic and kinetic conditions can be provided for the reaction, effectively promoting the reduction reaction and improving the quality of tantalum powder. At the same time, the temperature fluctuation range is strictly controlled within ±10℃ during the insulation stage to ensure the stability of the reaction environment and avoid affecting the quality of tantalum powder due to excessive temperature fluctuations.

[0016] (4) Separation treatment: After the insulation is completed, first stop the introduction of argon gas, then start the vacuum pump to effectively separate the excess magnesium vapor from the tantalum powder and calcium chloride molten salt, and then cut off the power and cool down the mixture, with the cooling rate controlled at 10-20°C / min. When the temperature drops to 600-800°C, introduce argon gas again for protective cooling to prevent the tantalum powder from being oxidized during the cooling process. After continuing to cool to room temperature, the product is taken out of the reaction vessel. This separation treatment method can effectively remove excess magnesium vapor, reduce impurity residues, and ensure the purity of the tantalum powder. At the same time, protective cooling is performed during the cooling process to further improve the quality stability of the tantalum powder.

[0017] (5) Water washing: The removed product is crushed into fine particles using a crusher, so that the particles are large enough to pass through a 100-mesh screen. Next, the screened product is washed with hot pure water until the conductivity of the washing liquid is ≤40μS / cm. The water washing step can initially remove residual soluble impurities such as calcium chloride in the product, providing a purer material for the subsequent acid washing, which helps to further improve the purity of the tantalum powder.

[0018] (6) Pickling: The product after water washing is pickled with 10-20% hydrochloric acid. The pickling process is carried out in two stages. In the first stage, pickling is carried out for 2 hours under stirring. The stirring process allows the hydrochloric acid to fully contact the material, effectively removing the magnesium oxide impurities on the surface of the tantalum powder and between the particles; in the second stage, static soaking is carried out for 4 hours, allowing the hydrochloric acid to penetrate into the fine pores of the tantalum powder, further removing impurities inside the tantalum powder and effectively removing the impurity iron remaining during the crushing process. After the pickling is completed, the residual acid liquid on the upper layer is carefully removed, and then washed with hot pure water until the conductivity is ≤10μS / cm. This two-stage pickling method combined with the subsequent water washing operation can more thoroughly remove impurities in the tantalum powder and improve the purity of the tantalum powder.

[0019] (7) Drying: The acid-washed product is dried in a vacuum oven at a temperature of 60-80°C for 2-10 hours. Tantalum powder is easily oxidized in air. By controlling the drying temperature and time, the moisture in the tantalum powder can be completely removed while preventing the tantalum powder from coming into contact with air at high temperatures, which could lead to an increase in oxygen content.

[0020] The beneficial effects of the present invention are as follows:

[0021] 1. The tantalum powder prepared by this method can make magnesium and tantalum oxide react thoroughly with the help of the endothermic and fluxing effects of calcium chloride, without producing complex substances such as tantalate. Since calcium chloride is highly soluble in water, it is easy to remove and does not introduce other impurities. High-purity tantalum powder with low oxygen content and low impurity content can be produced.

[0022] 2. The tantalum oxide used in this method is a porous nanoparticle, which can increase the contact area with magnesium, making the reaction more complete, and only one reduction is required to achieve a complete reaction.

[0023] 3. The low oxygen tantalum powder prepared by this method has an oxygen content of <3000ppm and a bulk density of 1.3-1.5g / cm 3 The powder particles are coral-shaped and uniform in size. Compared with the traditional preparation method, it effectively reduces the oxygen content of the once-reduced tantalum powder and improves the uniformity of the powder particles, making it more in line with the requirements of electronic component manufacturing.

[0024] 4. This method is relatively simple to operate, has relatively low equipment requirements, and has good industrial application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is the SEM image of the raw material Ta2O5.

[0026] Figure 2 This is the SEM image of the low-oxygen tantalum powder of Example 2.

[0027] Figure 3 This is the XRD pattern of the low-oxygen tantalum powder of Example 2.

[0028] Figure 4 This is the XRD pattern of tantalum powder in comparative example 1. DETAILED DESCRIPTION

[0029] In order to more clearly and comprehensively illustrate the technical solution of the present invention and its practical application effects, the present invention is described in detail below in conjunction with specific embodiments. These embodiments are for illustrative purposes only and do not constitute any limitation to the scope of protection of the present invention.

[0030] The technical details are further illustrated below with reference to embodiments.

[0031] Example 1

[0032] Figure 1 This is a scanning electron microscope image of the raw material porous Ta2O5 in the present invention. After phase identification and microscopic morphology observation, the tantalum oxide particles are porous and have a fine particle size of about 200-600nm. This morphology is conducive to contact with magnesium during the reaction process.

[0033] Weigh 500g of tantalum oxide powder and dissolve 125g of anhydrous calcium chloride in deionized water at a 1:1 molar ratio of tantalum oxide to calcium chloride to prepare a 30% calcium chloride solution. Pour the tantalum oxide powder into the solution and stir with a stirrer for 30 minutes to ensure a uniform mixture. Then, transfer the mixture to an oven and dry it at 150°C for 8 hours to evenly coat the surface of the tantalum oxide particles with the calcium chloride.

[0034] Metal magnesium chips with a particle size of 2 mm were selected, and the pretreated tantalum oxide powder and the metal magnesium chips were mixed in a molar ratio of tantalum oxide to magnesium of 1:10, that is, about 270 g of magnesium chips were weighed and mixed thoroughly.

[0035] Place the mixture into a sealed reaction vessel. Pass 99.99% high-purity argon gas into the vessel and perform three displacement operations. Each time, slowly vent the air after the pressure reaches 0.15 MPa to ensure that the air in the vessel is fully replaced. After the displacement is complete, heat the reaction system to 900°C at a rate of 5°C / min while controlling the pressure at 0.1 MPa. During the reaction, maintain a continuous flow of argon at a rate of 120 ml / min. Once the reaction temperature is reached, maintain the temperature for 4 hours.

[0036] After the insulation is complete, stop the argon flow and immediately start the vacuum pump. Set the evacuation time to 60 minutes and the vacuum to less than 10 Pa to effectively separate the excess magnesium vapor from the tantalum powder and calcium chloride molten salt. After separation, turn off the power and cool down the reaction at a rate of 15°C / min. When the temperature drops to 700°C, reintroduce argon for protective cooling. After further cooling to room temperature, open the reaction vessel and remove the product.

[0037] Post-processing (water washing, acid washing, drying): The taken-out product is crushed with a crusher so that it can pass through a 100-mesh sieve. Then, water washing, acid washing and subsequent treatment are carried out, as follows: the sieved product is first placed in hot pure water at a temperature of 80°C for water washing, constantly stirring, and continuing water washing until the conductivity of the washing liquid is less than 40μS / cm, to preliminarily remove the residual soluble impurities such as calcium chloride in the product; then the washed product is pickled with hydrochloric acid with a mass fraction of 15%. The pickling is divided into two stages. The first stage is pickling under stirring, the stirring speed is 200r / min, and the pickling time is 2h. The second stage is static immersion, and the immersion time is 4h to fully remove the magnesium oxide impurities on the surface and inside of the tantalum powder and the impurity iron remaining in the crushing process. After the pickling is completed, the upper residual acid solution is carefully removed; the pickled product is then washed with hot pure water until the conductivity of the washing liquid is less than 10μS / cm; finally, the washed product is placed in a vacuum drying oven, the drying temperature is set to 70°C, and the drying time is 6h to obtain tantalum powder.

[0038] The oxygen, nitrogen and hydrogen contents of the prepared tantalum powder were tested using an American LECO ONH836 analyzer. The bulk density of the tantalum powder was tested according to the method specified in the national standard GB / T1479.2-2011. The measured results are listed in Table 1.

[0039] Example 2

[0040] Figure 2 This is a scanning electron microscope photograph of the low-oxygen tantalum powder obtained in Example 2. Figure 3 This is the XRD diagram of the tantalum powder. After analysis, Example 2 obtained high-purity tantalum powder with a porous coral-like morphology, relatively uniform particle size, rounded particles, thick sintering necks, and fewer ultrafine particles, which can be used to prepare high-specific capacitance tantalum capacitors.

[0041] Weigh 500g of tantalum oxide powder and approximately 188g of calcium chloride, at a molar ratio of 1:1.5, in deionized water to dissolve the calcium chloride to create a 30% calcium chloride solution. Pour the tantalum oxide powder into the solution and stir with a stirrer for 30 minutes to ensure a uniform mixture. Dry the mixture in an oven at 120°C for 10 hours.

[0042] Magnesium metal chips with a particle size of 1.5 mm were selected and pretreated tantalum oxide powder and magnesium metal chips were mixed at a molar ratio of tantalum oxide to magnesium of 1:15. The magnesium chips weighed approximately 407 g and were thoroughly mixed to obtain a mixed material.

[0043] Place the mixed material in a reaction vessel and introduce 99.99% high-purity argon gas to displace the air three times. After replacement, raise the temperature to 850°C at a rate of 5°C / min, maintaining the pressure at 0.1 MPa and the argon flow rate at 100 ml / min. Hold the temperature for 6 hours.

[0044] After the insulation is completed, stop the argon flow and start the vacuum pump to evacuate for 60 minutes until the vacuum degree reaches less than 10 Pa. Turn off the power and cool down at a cooling rate of 12°C / min. When the temperature drops to 650°C, introduce argon for protective cooling and remove the product after it cools to room temperature.

[0045] Post-processing (water washing, acid washing, drying): The product is crushed by a crusher and passed through a 100-mesh sieve, then washed in 75°C hot pure water until the conductivity reaches 30μS / cm; then pickled with 12% hydrochloric acid, stirred for 2 hours, and statically soaked for 4 hours. After removing the upper layer of acid solution, it is washed with hot pure water until the conductivity is less than 10μS / cm; finally, the product is placed in a vacuum environment and dried at 65°C for 7 hours to obtain tantalum powder.

[0046] The oxygen, nitrogen and hydrogen content of the prepared tantalum powder was tested using an American LECO ONH836 analyzer. The bulk density of the tantalum powder was tested according to the method specified in the national standard GB / T1479.2-2011. The measured results are listed in Table 1. The tantalum powder was analyzed using a BRUKER / D8ADVANCE X-ray diffractometer. The results are as follows: Figure 3 As shown, the resulting surface phase is pure tantalum.

[0047] Example 3

[0048] Weigh 500g of tantalum oxide powder and 63g of anhydrous calcium chloride at a molar ratio of 1:0.5, prepare a solution of calcium chloride with a mass concentration of 35%, add tantalum oxide powder, stir evenly, and dry at 180°C for 6h.

[0049] Take 2mm-sized magnesium metal chips and mix them with pretreated tantalum oxide powder in a molar ratio of tantalum oxide to magnesium of 1:6. The amount of magnesium chips is about 163g, and the mixture is thoroughly mixed.

[0050] The mixture was placed in a reaction vessel, and 99.99% pure argon was introduced for replacement three times. The temperature was raised to 950°C at 5°C / min, the pressure was controlled at 0.10 MPa, the argon flow rate was 130 ml / min, and the temperature was maintained for 8 hours.

[0051] After the heat preservation is completed, stop the argon flow and evacuate for 50 minutes until the vacuum degree reaches less than 10 Pa. Turn off the power and cool at a cooling rate of 10℃ / min. Cool with argon again at 750℃ and cool to room temperature to take out the product.

[0052] Post-treatment (water washing, acid washing, drying): The product was crushed through a 100-mesh sieve, first washed with 85°C hot pure water until the conductivity was less than 40μS / cm, then pickled with 18% hydrochloric acid, stirred for 2 hours, and statically soaked for 4 hours. After removing the upper layer of acid solution, it was washed with water until the conductivity was 10μS / cm, and finally dried at 75°C in a vacuum for 4 hours to obtain tantalum powder.

[0053] The oxygen, nitrogen and hydrogen contents of the prepared tantalum powder were tested using an American LECO ONH836 analyzer. The bulk density of the tantalum powder was tested according to the method specified in the national standard GB / T1479.2-2011. The measured results are listed in Table 1.

[0054] Comparative Example 1

[0055] Figure 4 This is the XRD pattern of the tantalum powder obtained in Comparative Example 1. Analysis shows that magnesium tantalate compound is present therein, and therefore the powder has a high oxygen content. This is because magnesium oxide and tantalum oxide directly contact to form a complex during the reaction.

[0056] Weigh 500 g of tantalum oxide powder without adding anhydrous calcium chloride.

[0057] Metal magnesium chips with a particle size of 2 mm were selected, and tantalum oxide powder and metal magnesium chips were mixed in a molar ratio of tantalum oxide to magnesium of 1:10. The mass of the magnesium chips was about 270 g, and the mixture was fully mixed to obtain a mixed material.

[0058] Place the mixture into a sealed reaction vessel. Pass 99.99% high-purity argon gas into the vessel and perform three displacement operations. Each time, slowly vent the air after the pressure reaches 0.15 MPa to ensure that the air in the vessel is fully replaced. After the displacement is complete, heat the reaction system to 900°C at a rate of 5°C / min while controlling the pressure at 0.1 MPa. During the reaction, maintain a continuous flow of argon at a rate of 120 ml / min. Once the reaction temperature is reached, maintain the temperature for 4 hours.

[0059] After the insulation is complete, stop the argon flow and immediately start the vacuum pump. Set the evacuation time to 60 minutes and the vacuum to less than 10 Pa to effectively separate the excess magnesium vapor from the tantalum powder and calcium chloride molten salt. After separation, turn off the power and cool down the reaction at a rate of 15°C / min. When the temperature drops to 700°C, reintroduce argon for protective cooling. After further cooling to room temperature, open the reaction vessel and remove the product.

[0060] Post-processing (water washing, acid washing, drying): The taken-out product is crushed with a crusher so that it can pass through a 100-mesh sieve. Then, water washing, acid washing and subsequent treatment are carried out, as follows: the sieved product is first placed in hot pure water at a temperature of 80°C for water washing, constantly stirring, and continuing water washing until the conductivity of the washing liquid is less than 40μS / cm, to preliminarily remove the residual soluble impurities such as calcium chloride in the product; then the washed product is pickled with hydrochloric acid with a mass fraction of 15%. The pickling is divided into two stages. The first stage is pickling under stirring, the stirring speed is 200r / min, and the pickling time is 2h. The second stage is static immersion, and the immersion time is 4h to fully remove the magnesium oxide impurities on the surface and inside of the tantalum powder and the impurity iron remaining in the crushing process. After the pickling is completed, the upper residual acid solution is carefully removed; the pickled product is then washed with hot pure water until the conductivity of the washing liquid is less than 10μS / cm; finally, the washed product is placed in a vacuum drying oven, the drying temperature is set to 70°C, and the drying time is 6h to obtain tantalum powder.

[0061] The oxygen, nitrogen and hydrogen content of the prepared tantalum powder was tested using an American LECO ONH836 analyzer. The bulk density of the tantalum powder was tested according to the method specified in the national standard GB / T1479.2-2011. The measured results are listed in Table 1. The tantalum powder was analyzed using a BRUKER / D8ADVANCE X-ray diffractometer. The results are as follows: Figure 4 As shown, magnesium tantalate was found in the product.

[0062] Table 1: Oxygen, nitrogen and hydrogen content and bulk density of tantalum powder

[0063] sample O / ppm N / ppm H / ppm <![CDATA[Bulk density / g / cm 3 > Example 1 3090 676 208 1.3 Example 2 2850 560 151 1.3 Example 3 4560 658 314 1.4 Comparative Example 1 67800 1600 200 3.4

[0064] As can be seen from Table 1:

[0065] The oxygen content of the tantalum powder prepared by the present invention can be controlled to be less than 3000ppm, and the bulk density is 1.3g / cm 3 The amount of magnesium added will also affect the oxygen content of tantalum powder. A comparative analysis of Example 2 and Example 3 shows that when the amount of magnesium used is 3 times the theoretical amount, i.e., 15 mol, the oxygen content of the tantalum powder obtained is significantly lower than that when 6 mol of magnesium is used. It can also be concluded from the results of Examples 1, 2, 3 and Comparative Example 1 that when calcium chloride is not added, tantalum oxide cannot be completely reduced even if an excess of magnesium is used, because the magnesium oxide produced in the initial stage of the reaction directly reacts with tantalum oxide and produces magnesium tantalate, which hinders the subsequent reduction reaction, resulting in the presence of a large amount of oxygen and a large bulk density, which does not meet the requirements for making capacitor tantalum powder.

[0066] An embodiment of the present invention discloses a method for preparing low-oxygen tantalum powder by magnesium reduction. The method comprises mixing tantalum oxide and calcium chloride to prepare a preformed powder, which is then mixed with magnesium chips and subjected to a reduction reaction at high temperature. The addition of calcium chloride absorbs excess heat from the reaction, thereby preventing abnormal growth of tantalum powder grains and eliminating the possibility of magnesium oxide, a byproduct, reacting with tantalum oxide to produce magnesium tantalate. Therefore, low-oxygen tantalum powder can be obtained through a single reduction. Furthermore, the preparation temperature range of the reaction is wide, and the size of the tantalum powder particles can be controlled by adjusting the temperature and holding time. The low-oxygen tantalum powder prepared by this method can be used to prepare tantalum capacitors with excellent performance through subsequent steps such as agglomeration heat treatment.

[0067] The above embodiments are intended only to illustrate the technical concepts and features of the present invention. Their purpose is to enable those skilled in the art to understand the contents of the present invention and implement them accordingly. They are not intended to limit the scope of protection of the present invention. Any equivalent changes or modifications made in accordance with the spirit of the present invention are intended to be covered by the scope of protection of the present invention.

Claims

1. A method for preparing low-oxygen tantalum powder by magnesium reduction, characterized in that: The following steps are involved: 1) Raw material pretreatment: prepare tantalum oxide powder, magnesium metal chips, and anhydrous calcium chloride; weigh calcium chloride at a molar ratio of tantalum oxide to calcium chloride of 1:(0.5-1.5), dissolve it in deionized water to prepare a calcium chloride solution, then pour the tantalum oxide into the solution, stir evenly, and dry until the calcium chloride is evenly coated on the surface of the tantalum oxide particles; 2) Raw material mixing: the pretreated tantalum oxide powder and the magnesium metal chips are mixed evenly to obtain a mixed material; 3) Reduction reaction: Place the mixed material in a sealed reaction vessel, introduce inert gas and perform multiple displacement operations. After the air is replaced, heat it to 800-1000°C at a rate of 5-15°C / min, control the pressure at 0.08-0.12 MPa, and keep it warm for 4-8 hours. During the reaction, the inert gas is kept in circulation and the flow rate is controlled at 80-150 ml / min. 4) Separation treatment: After the insulation is completed, stop the inert gas flow and start the vacuum pump to separate the excess magnesium vapor from the tantalum powder and calcium chloride molten salt. Turn off the power to cool down and continue to flow the inert gas. Control the pressure at 0.12-0.18Mpa and remove from the furnace after it drops to room temperature. 5) Washing: After taking out the product, crush it into fine particles with a crusher, pass it through a 100-mesh sieve, and then wash it with hot pure water until the conductivity is ≤40μS / cm; 6) Pickling: The product after the treatment in step 5) is pickled with 10-20% hydrochloric acid, and then washed with hot pure water until the conductivity is ≤10μS / cm; 7) Drying: The product obtained in step 6) is dried in a vacuum oven at a temperature of 60-80° C. for 2-10 h.

2. The method for preparing low-oxygen tantalum powder by magnesium reduction according to claim 1, characterized in that: In step 1), the purity of the tantalum oxide powder is not less than 99.9%, the particle size of the metal magnesium chips is 0.5-3 mm, and the purity of the anhydrous calcium chloride is not less than 99%.

3. The method for preparing low-oxygen tantalum powder by magnesium reduction according to claim 1, characterized in that: The mass concentration of the calcium chloride solution in step 1) is 20%-40%, and the drying temperature is 100-200°C.

4. The method for preparing low-oxygen tantalum powder by magnesium reduction according to claim 1, characterized in that: The molar ratio of tantalum oxide to magnesium in step 2) is 1:(5-15).

5. The method for preparing low-oxygen tantalum powder by magnesium reduction according to claim 1, characterized in that: The inert gas in step 3) is high-purity argon (purity ≥ 99.99%), the replacement operation is performed 3-5 times, and the temperature fluctuation range during the insulation stage is controlled within ±10°C.

6. The method for preparing low-oxygen tantalum powder by magnesium reduction according to claim 1, characterized in that: In step 4), the evacuation time is 40-80 min, the vacuum degree is ≤10 Pa, the cooling rate is 10-20° C. / min, and argon is introduced for a second time for protective cooling when the temperature drops to 600-800° C.

7. The method for preparing low-oxygen tantalum powder by magnesium reduction according to claim 1, characterized in that: The hydrochloric acid pickling in step 6) is carried out in two stages: the first stage is pickling with 10-20% hydrochloric acid for 2 hours by stirring, and the second stage is static soaking with hydrochloric acid for 4 hours. After pickling, the upper residual acid solution is removed and then washed with water.

8. A low-oxygen tantalum powder prepared by the method according to any one of claims 1 to 7, characterized in that: Its oxygen content is less than 3000ppm and its bulk density is 1.3-1.5g / cm 3 , the powder particles are coral-shaped and uniform in size.

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