WO2015081508A1

WO2015081508A1 - Method for agglomerating tantalum powder with ultra-high specific volume, and tantalum powder prepared by using method

Info

Publication number: WO2015081508A1
Application number: PCT/CN2013/088482
Authority: WO
Inventors: 杨国启; 郑爱国; 程越伟; 张静
Original assignee: 宁夏东方钽业股份有限公司; 国家钽铌特种金属材料工程技术研究中心
Priority date: 2013-12-04
Filing date: 2013-12-04
Publication date: 2015-06-11
Also published as: CN104884195A; CN104884195B

Abstract

A method for agglomerating tantalum powder comprises the following steps: 1) providing tantalum powder; 2) pre-agglomerating the tantalum powder by using the following mode: adding water into the tantalum powder to completely wet the tantalum powder, separating surplus water out, and pouring part or all of the surplus water out; and 3) agglomerating the tantalum powder by using the following mode for a second time: freezing the pre-agglomerated tantalum powder until tantalum powder particles are agglomerated into blocks, and then taking the blocks out and performing vacuum drying of the blocks, pulverizing and sieving the blocks to obtain agglomerated tantalum powder.

Description

Method for agglomerating ultra-high specific volume tantalum powder and powdered powder prepared by the method

The invention relates to ultra high specific capacitance capacitor grade tantalum powder, in particular 5000 (^FV/ _g ~

Manufacture of 20000 (^FV/g high specific volume tantalum powder, more particularly lOOOOO FV/g ~ 20000 (^FV/g high specific volume ^.)

Metal ruthenium is a valve metal that forms a dense oxide film on the surface and has a unidirectional conductive property. The prepared anodic film is chemically stable (especially stable in an acidic electrolyte), has a high electrical resistivity (7.5 χ 10 ^1β Ω·«η), has a large dielectric constant (27.6), and has a small leakage current. In addition, it has a wide operating temperature range (-80 ~ 200. C:), high reliability, shock resistance and long service life. Therefore, it is an ideal material for making small and reliable tantalum capacitors.

The process of sodium reduction potassium citrate method is the most widely used and the most mature technology in the world.

The sodium reduction potassium citrate process is a method in which a capacitor grade is prepared by using K ₂ TaF ₇ and Na as main raw materials, and a halogen salt or a halogen salt mixture such as NaCl or KC1 is used as a diluent, and the main reaction thereof is as follows:

K ₂ TaF ₇ +5Na = Ta+5NaF+2KF (1) K ₂ TaF ₇ reacts with liquid sodium under argon gas protection and at a certain temperature. The reduced tantalum powder is washed with water and pickled to obtain a tantalum powder, and then heat-treated, and then deoxidized by magnesium to obtain a finished tantalum powder having a higher purity. It is well known that the specific volume of tantalum powder is proportional to its specific surface area, that is, the smaller the average particle size of the tantalum powder, the larger the specific surface area and the higher the specific volume. For the sodium-reduced potassium fluoroantimonate method, the core of the current research is to control the nucleation of the nano-reduction process by controlling the reduction conditions including the composition of the potassium fluoroantimonate and the soluble salt, the reduction temperature, the rate of sodium injection, and the like. Forming, distributing and growing, the desired tantalum powder having a high specific surface area and a small particle diameter is prepared.

At the same time as §^ is higher than ^1, a prominent problem is also revealed. That is, the higher the specific volume, the smaller the loose size and the higher the proportion of ultrafine powder. t The ϋ3⁄4 fine powder is a tantalum powder having a particle size of 400 mesh (i.e., "secondary particle size") after being agglomerated by a grouping process or a heat treatment. The higher the proportion of ultrafine powder of the powder after agglomeration, the worse the fluidity, and the poorer the moldability when making the capacitor, thus affecting the electrical properties of the product. The ratio of the particle size of the tantalum powder (between 80 mesh and 400 mesh) is as high as possible within a certain range. If the ratio is too high, if it is higher than about 95%, it will bring some problems such as poor bonding and poor formability. Below about 65%, the fluidity of the product is deteriorated, the molding property is not good, and the compaction is uneven, so the suitable range is between 65-95%. And as the specific volume of tantalum powder increases, this ratio increases slightly. The traditional method of agglomeration is used to effectively solve the problem of reducing the proportion of ultrafine powder.

Different methods have been proposed in the prior art to try to solve these problems.

A new method for producing agglomerated tantalum powder is disclosed in US Pat. No. 6,576,038, Bl, US Pat. No. 6,790,012, and US Pat. In particular, these patents relate to a method of agglomerating a base metal powder comprising mixing a volatile liquid with particles to form a wet powder, and compacting the powder to form a cake to form agglomerated particles. This powder has a flow rate of at least 65 mg/sec, which improves the pore size distribution and increases Scott density. A similar content is also described in US Pat. No. 6,790,912 and US Pat. Patent CN 1197707 AL discloses a new method for the production of agglomerates, which compacts and forms a compact, thereby increasing the agglomeration effect and capable of agglomerating at a lower temperature, thereby enabling Agglomerated powder with low oxygen content, good fluidity and formability. A similar patent is CN1068809 C.

Patent CN 1238251 AL provides a method for producing a porous agglomerated tantalum powder, which comprises the following steps: (1) shaking the fine tantalum powder in the presence of no binder at 900 ~ 1550 ^The heat treatment under ^e C causes agglomeration between the agglomerated particles.

CN1073480 C also relates to a similar method.

Patent US 3,976,435 discloses a method of producing a porous anode for use in making an electrolytic capacitor. First, the largest particle ΙΟμπι powder is wetted with 2-20% water, and then the block is coagulated and sintered into a porous body. The final sintered density is less than 12 g/cc, and the specific volume is not less than 2000 FV/g.

Patent JP2002-134367 discloses a porous molded body tantalum electrolytic capacitor anode, a capacitor thereof and a method of preparing the same. The invention discloses a method in which a liquid mixture of a solvent and a binder is filled in a container of a given shape, and dried under vacuum to form a porous formed body. A tantalum anode was obtained after sintering. Since the resin is greatly reduced in the molded body, the residual carbon content is lowered, and the pore diameter and porosity of the molded body can be controlled by adjusting the amount of the magnetic solvent of the solvent or the like. This patent is mainly used in the manufacture of capacitors.

The design of this patent is aimed at the production of tantalum powder for capacitors, and requires more than 4 solvents, binders and the like. Summary of the invention

SUMMARY OF THE INVENTION The object of the present invention is to provide a method for agglomerating a metal powder, which has a good effect of agglomerating powder and can effectively improve the particle size distribution of the tantalum powder.

In the art, particle size can generally be characterized by analysis of different sieves, i.e., by different sieve sizes. The number of meshes (ie, the number of holes) of the sieve analysis is the number of holes per square inch. The larger the size, the smaller the aperture. In general, the number of mesh X holes (in microbeams) -15000. For example, a 400 mesh screen has a pore size of about 38 |t, and a -400 mesh represents particles smaller than 38 microns.

As can be seen from Table 1 below, an advantage of the method proposed by the present invention is that the proportion of ultrafine powder (i.e., -400 mesh tantalum powder) can be effectively reduced, thereby improving the fluidity of the tantalum powder and solving the loosening during the agglomeration process. The problem of low density and superfine powder. Therefore, it is also possible to improve the utilization rate of the tantalum powder, reduce the cost, and satisfy the requirements of the capacitor product for the electrical properties of the tantalum powder. The invention is mainly applicable to 5000(^FV/g - 20000 (^FV/g high specific volume tantalum powder, especially lOOOOO FV/g ~ 20000 (^FV/g high specific volume tantalum powder).

As mentioned above, although there are several methods of agglomeration in the prior art, these agglomeration methods have certain defects on the high ratio, for example, the prepared medium ultrafine powder rate is high, which affects the fluidity of the product. . This is a common problem with high specific volume.

The invention provides a method for agglomeration, which specifically comprises the following steps:

1. mention

2. Pre-stacking the tantalum powder by adding water to the tantalum powder to wet the tantalum powder and to precipitate excess water, and then pouring out part or 4^5 of excess water;

3. Secondary agglomeration of the tantalum powder by: freezing the pre-agglomerated tantalum powder straight The particles are agglomerated into agglomerates, and then the cake is taken out for vacuum drying, and crushed and sieved to obtain the end of the agglomeration.

It should be understood that the water described herein is not limited to liquid water, but may include solid water, i.e., ice. That is, an ice or ice water mixture may be added during the pre-agglomeration, and the ice is melted into water by stirring to wet the tantalum powder.

In a preferred embodiment of the invention, the ultrafine powder ratio can be further reduced by subsequent heat treatment because the tantalum powder particles can also be combined and lengthened during the heat treatment.

An advantage of the present invention is that the bulk density of the product is increased by the method, the ratio of ultrafine powder in the medium is reduced, the utilization rate of the product is improved, and the cost is lowered.

Without being bound by the general theory, it is considered that the cerium powder particles, particularly the ultrafine powder particles and other particles, agglomerate each other during freezing to form particles having a larger particle diameter, thereby reducing the proportion of the ultrafine powder.

Surprisingly, the method of the present invention does not increase the proportion of overly coarse particles (i.e., +80 mesh) while reducing the proportion of ultrafine powder.

The present invention also relates to a tantalum powder according to the above method, and an anode block made of the tantalum powder and a capacitor comprising the anode block.

Detailed description of the invention

In one embodiment of the invention, the tantalum powder described in step 1 is a obtained by reducing Na potassium fluoroantimonate described above.

In one embodiment of the invention, the vibration and/or agitation of the tantalum powder is carried out while water is added in step 2.

In one embodiment of the present invention, the coagulation time in step 3 is 5 to 10 hours. It is preferably 6-9 hours, more preferably 7-8 hours.

In one embodiment of the invention, the drying temperature in step 3 is 80. C ~ 180. C, preferably 100-150. C, more preferably 120 - 140. C.

In one embodiment of the invention, the amount of water added in step 2 is preferably from 25 to 50%, preferably from 30 to 45%, most preferably from 35 to 40% by weight of the tantalum powder.

In one embodiment of the invention, the freezing in step 3 is carried out by adjusting the temperature of the pre-agglomerated tantalum powder to 0 to -20. Between C, preferably 0 to -10. C, more preferably 0 to -5. C, held at this temperature.

In a preferred embodiment of the present invention, the post-treatment of the agglomeration obtained in the step 3 is further carried out, for example, purification and further agglomeration, oxygen reduction, and the like to obtain a better agglomerated tantalum powder. It should be understood that the oxygen reduction is to mix the magnesium metal shavings and then remove the oxygen from the surface of the tantalum powder to reduce the oxygen content.

In one embodiment of the invention, the removal of impurities from the tantalum powder, such as by pickling, is included in step 1.

Preferably, in steps 1, 2 and / or 3 of the process of the invention, no solvent and/or binder is employed, thereby reducing costs and avoiding possible contamination.

The physical quantity used to describe the thickness of the metal particles is also the specific surface area (m ² /g) of the BET measurement by low-temperature nitrogen adsorption, and the average particle diameter (FSSS^m) measured by the Fischer sub-screener. The Fischer's average particle size is obtained by measuring the powder filled in the metal tube by gas permeation method using a Fischer sub-sifter, which is related to the size of the particles and to the cohesive strength of the powder; The original powder, the smaller the average particle size of the Fischer, the larger the specific surface area; and for the agglomerated metal powder, the powders with different specific surface areas may have similar Fischer's flat Average particle size; For powders of the same grade (ie, specific volume), the aggregated powder has a larger average particle size.

In order to further understand the present invention, the embodiments of the present invention are described in the accompanying drawings and the accompanying drawings. Example 1:

The 100000 FV/g high specific volume tantalum powder obtained by sodium reduction of potassium fluoroantimonate is used as a raw material. First, the high specific volume tantalum powder is pickled, the impurities are washed away, and then pre-agglomeration is started. The specific process is to place the tantalum powder on the vibrating tray, and add 45% water to the tantalum powder while vibrating the tray. Due to the excessive amount of water added, after the thorough wetting of the tantalum powder, a part of the excess is shaken out, and the excess water is poured out; then the pre-agglomerated tantalum powder is placed in the giant to be reagglomerated and adjusted to the temperature. It is maintained at -2 V and maintained at this temperature for 8 hours, which is sufficient to sufficiently agglomerate between the powder particles, particularly the ultrafine particles and other particles, to form a massive body. Then, the block was taken out for vacuum drying, and the drying temperature was 150 ^e C, and then the block was crushed, and 80 mesh was sieved to obtain agglomerated tantalum powder.

Finally, in order to facilitate the test, the obtained agglomerated tantalum powder is subjected to post-heat treatment, oxygen reduction and the like.

Example 2:

The 100000 FV/g high specific volume tantalum powder obtained by sodium reduction of potassium niobate is still used as a raw material. First, the lOOOOOO FV/g high specific volume tantalum powder after sodium reduction of potassium fluoroantimonate is pickled, and the impurities are washed off, and then pre-agglomeration is started. The specific process is to place the tantalum powder on the vibrating tray. 45% water was added to the tantalum powder while vibrating the tray. Due to the excessive amount of water added, after the thorough wetting, there is still a part of the excess? It is shaken out and the excess water is poured out. Then, the pre-agglomerated powder is placed in the ice to be rejected for secondary agglomeration and adjusted to the temperature. -15. C is maintained at this temperature for 6 hours, which is sufficient to sufficiently agglomerate between the tantalum powder particles, particularly the ultrafine particles and other particles, to form a massive body. The block was then taken out for vacuum drying and the drying temperature was 150. C, then the block material is broken, and 80 mesh is sieved to obtain agglomerated tantalum powder.

Example 3:

The 20,000 (^FV/g high specific volume tantalum powder) obtained by sodium reduction of potassium fluoroantimonate is used as a raw material. First, the high specific volume tantalum powder is pickled, and the impurities are washed off and then agglomerated. Place the tantalum powder on the vibrating tray, add 45% water to the tantalum powder while vibrating the tray, and then vibrate the tray. Due to the excess water added, there is still some excess vibration after thoroughly wetting the tantalum powder. Come out, pour out excess water; then pre-grouped

The ice refused to undergo secondary agglomeration and was adjusted to a temperature of -io. And maintaining the temperature at this temperature for ⁶ hours, which is sufficient to sufficiently coagulate the tantalum powder particles, particularly the ultrafine particles and other particles, to form a massive body. Then, the block body was taken out for vacuum drying, and the drying temperature was 130, and then the block body was crushed, and 80 mesh was sieved to obtain agglomerated tantalum powder.

Example 4:

Take 20,000 (^FV/g high specific volume tantalum powder) after sodium reduction as an example. First, sodium After the reduction of potassium fluoroantimonate, 20,000 (^FV/g high specific volume tantalum powder is pickled, and the impurities are washed off and then agglomerated. The specific process is to place the tantalum powder on the vibrating tray, in the vibrating tray At the same time, 45% water is added to the tantalum powder, and then the tray is vibrated. Due to the excessive amount of water added, a part of the excess 7j L is shaken out after thorough wetting, and excess water is poured out; The bismuth powder is placed in the ice to be rejected for secondary agglomeration, adjusted to a temperature of -5 ° C and held at this temperature for 6 hours, which is sufficient to coagulate between the bismuth particles, especially the ultrafine particles and other particles! The block body is formed. Then, the bulk material is taken out for vacuum drying, and the drying temperature is 80 C. Then, the block material is crushed, and 80 mesh is sieved to obtain agglomeration.

Comparative Example 5:

The lOOOOO FV/g high specific volume tantalum powder after sodium reduction is taken as an example for description. First, the lOOOOOO FV/g high specific volume tantalum powder after sodium reduction of potassium fluoroantimonate is pickled, and the impurities are washed off and then subjected to agglomeration treatment according to a conventional process.

Finally, in order to carry out the test, the obtained agglomerated tantalum powder is subjected to post-heat treatment, oxygen reduction and the like.

Comparative Example 6:

The 20,000 (^FV/g high specific volume tantalum powder) after sodium reduction is taken as an example. First, the 20,000 (^FV/g high specific volume tantalum powder after sodium reduction of potassium fluoroantimonate is pickled and washed away. After the impurities, the agglomeration treatment is started according to a conventional process.

Finally, in order to carry out the test, the obtained agglomerated tantalum powder is subjected to post-heat treatment, Oxygen reduction and other processes. Since the embodiment of the patent involves two grades of tantalum powder, the analysis is slightly different, so the analysis is performed separately.

Analysis of Example 1, Example 2, and Comparative Example 5, the results are as follows:

Table 1: Physical properties of tantalum powder

In the table, Fsss (μπι) represents the particle size of Feis, SBD (g/cc) represents the bulk density, +80 (%) represents the proportion of tantalum powder greater than 80 mesh, and -400 (%) represents less than 400. The proportion of the target powder.

Table 2: Major impurities in the ^ ^ (unit: ppm)

As can be seen from Table 2, the method of the present invention improves the product agglomeration performance while the impurity content is substantially unaffected.

The above powder sample was compression-molded, the density of the compact was 5.0 g/cm 3 , the weight of the core powder was 0.1 g, ^ : 03 mm, and then the sintered block obtained by sintering in nSO Omin for 20 minutes in a vacuum furnace of 10-3 Pa was 0.1. 20V energization in % phosphoric acid solution, energization time 120min, the enabling temperature: 90*Ό, the current density is 110mA/g, and the rest is tested according to the national standard GB/T 3137-2007. Time Determination of the electrical properties of each sample is listed in Table 3.

Table 3: Comparison of electrical performance

In the table, Κχ10 ^_4 (μΑ/μΓν) represents leakage current, CV( FV/g ) represents capacity, tgS (%) represents loss, SHD (%) represents radial shrinkage, and SHV (%) represents volume shrinkage. .

Analysis of Example 3, Example 4, and Comparative Example 6 showed the following results:

Table 4: Physical properties of tantalum powder

Table 5: Major impurities in the ^ ^ (unit: ppm)

The upper and lower samples were press-formed, the density of the compact was 5.0 g/cm ³ , the weight of the core powder was 0.1 g, and the mold was D3 mm, which was tested according to the standard. The sintered block obtained by sintering at 1150 ° C for 20 minutes in a vacuum oven at 10 ³ Pa was energized at 10 V in a 0.1% phosphoric acid solution with an energization time of 120 min and an energization temperature of 80. C, current density 110mA/g. Time Determination of the electrical properties of each sample is listed in Table 6.

Table 6: Electrical comparison

In Example 1, the bulk density of Example 2 was increased as compared with Comparative Example 5, and the ultrafine powder ratio (-400 mesh) was reduced. Finally, both the capacity and the leakage performance were improved in comparison with the sample of Comparative Example 5. The same trend is reflected in the fact that in Example 3, Example 4 and Comparative Example 6, the bulk density increased, the ultrafine powder ratio (-400 mesh) decreased, and finally reflected in the capacity and leakage performance compared with Comparative Example 6 The sample has improved.

The description and the embodiments of the present invention are set forth in the description of the embodiments of the invention. .

Claims

Rights request

A method for agglomerating powder, comprising the steps of:

1) mention

2) Pre-stacking the tantalum powder by adding water to the tantalum powder to thoroughly moisturize and deposit excess water, and then pouring out some or all of the excess water;

3) Secondary agglomeration of the tantalum powder by: freezing the pre-agglomerated tantalum powder until the particles agglomerate into a mass, and then taking out the cake for vacuum drying, and then crushing and sieving to obtain a dough.

The method of agglomerated tantalum powder according to claim 1, wherein the niobium powder in the step 1) is a obtained by a Na reduction of potassium fluoroantimonate method.

The method of agglomeration according to claim 1, wherein the coagulation time in the step 3) is 5 to 10 hours, preferably 6 to 9 hours, more preferably 7 to 8 hours.

The method of agglomerated tantalum powder according to any one of claims 1 to 3, wherein the drying temperature in the step 3) is 80. C ~ 180. C, preferably 100-150 ° C, more preferably 120 - 140. C.

The method of agglomerated tantalum powder according to any one of claims 1 to 3, wherein the amount of water added in step 2) is 25-50% by weight, preferably 30-45% by weight, most preferably 35-40 %.

The method of agglomerated tantalum powder according to any one of claims 1 to 3, wherein in the step 1), the tantalum powder is removed to remove impurities, for example, by pickling to remove impurities.

The method of agglomerated tantalum powder according to any one of claims 1 to 3, further comprising post-treating the agglomerated tantalum powder obtained in the step 3), for example, purifying and further agglomerating, reducing oxygen And other processes.

The method of agglomerated tantalum powder according to any one of claims 1 to 3, wherein the freezing in the step 3) is performed by adjusting the temperature of the pre-agglomeration to 0 to -20 °c. Between 0 and -10 is preferred. C, more preferably 0 to -5. C, and kept at this temperature.

The method of agglomerated tantalum powder according to any one of claims 1 to 3, wherein the water is added in step 2) while vibrating and/or stirring.

The method of agglomerated tantalum powder according to any one of claims 1 to 3, wherein in the steps 1), 2) and/or 3), no solvent and/or binder is used.

11. The agglomeration a prepared by the method of any of 1-10, and the anode block produced by the agglomeration and a capacitor comprising the anode block.