FLAKED TANTALUM POWDER AND PREPARATION METHOD THEREOF

Abstract

Provided are a flaked tantalum powder and method for preparation thereof; said flaked tantalum powder contains 300-1800 ppm of nitrogen, 10-100 ppm of phosphorus, and 1-40 ppm of boron. The flaked tantalum powder has high capacity and low leakage current, good puncture-resistance, and particularly outstanding high-frequency attributes. Doping with nitrogen during oxygen reduction is performed before three thermal treatments are carried out; the solution of performing three thermal treatments and a subsequent process improves the uniformity of distribution of elemental nitrogen and makes up for the deficiency of an oxide film, thereby increasing the pressure resistance of the product, and especially its high-frequency attributes.

Claims

1. A method for preparing flaked tantalum powder comprising: 1) subjecting flaked tantalum powder to a first heat treatment; 2) subjecting the first heat treated tantalum powder to a first deoxidation; 3) subjecting the first deoxidized tantalum powder to low temperature nitridation; 4) subjecting the low-temperature nitrided tantalum powder to a second heat treatment; and optionally 5) subjecting the second heat-treated tantalum powder to a second deoxidation, and then optionally subjecting the second deoxidized tantalum powder to one or more processes selected from the group consisting of pickling, water washing, drying, and sieving to obtain a finished flaked tantalum powder.

2. The method according to claim 1, wherein the flaked tantalum powder of 1) is first prepared by reducing potassium fluotantalate with sodium, and subjecting the tantalum powder produced thereby to ball milling, pickling and impurity removal.

3. The method according to claim 1, wherein the first deoxidation of 2) comprises keeping the temperature within the range of from about 800 to about 1000 C. for a period of time of from about 3 to about 6 hours.

4. The method according to claim 1, wherein the low temperature nitridation of 3) begins (a) when the temperature of the first deoxidation treatment of 2) is lowered, or (b) by reheating after the temperature in the deoxidation treatment of 2) is lowered to room temperature.

5. A flaked tantalum powder suitable for use in a high frequency capacitor, the flaked tantalum powder comprising nitrogen within the range of from about 300 to about 1800 ppm, and optionally phosphorus and/or boron.

6. An anode of an electrolytic capacitor comprising the flaked tantalum powder according to claim 5, wherein the anode has a capacity of about 3000 to 30000 FV/g under the condition of an energization voltage of 100-250 V and a test frequency of 5000-30000 Hz.

7. The flaked tantalum powder according to claim 5, wherein the tantalum powder contains boron within the range of from about 1 to about 80 ppm.

8. The flaked tantalum powder according to claim 5, wherein the tantalum powder has an oxygen content of from about 800 to about 3000 ppm.

9. The flaked tantalum powder of claim 5, wherein the tantalum powder has a phosphorus content of from about 10 to about 100 ppm.

10. The flaked tantalum powder according to claim 5, wherein the Scott bulk density of the power is within the range of from about 1.4 to about 2.0 g/cm.sup.3.

11. The method according to claim 2, wherein ball milling is selected from vibration ball milling or agitating ball milling.

12. The method according to claim 3, wherein the first deoxidation of 2) comprises keeping the temperature within the range of from about 850 to about 950 C. for a period of time of from about 4 to about 6 hours.

13. The method according to claim 3, wherein the first deoxidation of 2) comprises keeping the temperature within the range of from about 750 to about 980 C. for a period of time of from about 3 to about 5 hours.

14. The method according to claim 4, wherein the low temperature nitridation of 3) begins when the temperature of the first deoxidation treatment of 2) is lowered to a temperature within the range of from about 500 to about 240 C.

15. The flaked tantalum powder of claim 5, wherein the tantalum powder comprises nitrogen within the range of from about 500 to about 1,500 ppm.

16. The flaked tantalum powder of claim 15, wherein the tantalum powder comprises nitrogen within the range of from about 700 to about 1,300 ppm.

17. The flaked tantalum powder of claim 7, wherein the flaked tantalum powder comprises from about 10 to about 65 ppm of boron.

18. The flaked tantalum powder of claim 17, wherein the flaked tantalum powder comprises from about 20 to about 50 ppm of boron.

19. The flaked tantalum powder of claim 10, wherein the Scott bulk density of the power is within the range of from about 1.55 to about 1.9 g/cm.sup.3

Description

EXAMPLE 1

[0038] The flaked tantalum powder obtained by adopting the prior art was used as a raw material 1. The parameters of the flaked tantalum powder obtained by testing are shown in Table 1. 5 Kg of raw material 1 was taken, and boric acid of 40 ppm based on the amount of boron elements was added, after uniformly mixing and carrying out agglomeration treatment on the mixture, the mixture was put into a heat treatment furnace, the temperature was kept at 1450 C. for 60 minutes followed by cooling and passivating, after that, discharging out of the furnace, sieving by a 60-mesh screen and carrying out magnetic separation. Then, the magnesium powder of 1.5% based on the weight of the tantalum powder was doped, the temperature was raised to 900 C. and was kept for 4 hours under the protection of inert gas followed by lowering the temperature and cooling to 450 C., after that, evacuation replacement was carried out, and high-purity nitrogen was filled until the pressure reaching a positive pressure (+0.01 MPa), then the temperature was kept for 60 minutes, and cooling and passivating were carried out, after that, discharging out of the furnace, and after carrying out pickling and impurity removal with the prior art process, it was put into a heat treatment furnace again, then the temperature was kept at 1430 C. for 60 minutes, and then cooling and passivating, after that, discharging out of the furnace, sieving by a 60-mesh screen and carrying out magnetic separation.

[0039] Next, the magnesium powder of 1.5% based on the weight of the tantalum powder was doped, the temperature was raised to 900 C. and was kept for 4 hours under the protection of inert gas followed by cooling and passivating, after that, discharging out of the furnace, and carrying out pickling and impurity removal with the prior art process to obtain a finished product. The chemical impurities and the physical properties of the finished product are shown in Table 2.

[0040] The powder sample was pressed and formed into a compact that had a density of 5.0 g/cm.sup.3, and a weight of the core powder of 0.20 g. The compact was sintered at 1600 C. for 15 minutes to obtain a sintered compact. The sintered compact was energized by 150 v in a 0.01% phosphoric acid solution. The capacity and loss of the sintered compact were measured at a test frequency of 5000-30000 Hz. The measured electrical properties of the sample are listed in Table 3.

COMPARATIVE EXAMPLE 1

[0041] The raw material was the same as that used in Example 1. 5 Kg of raw material was taken, and boric acid of 40 ppm based on the amount of boron element was added, after uniformly mixing and carrying out agglomeration treatment on the mixture, the mixture was put into a heat treatment furnace, the temperature was kept at 1450 C. for 60 minutes followed by cooling and passivation, after that, discharging out of the furnace, sieving by a 60-mesh screen and carrying out magnetic separation. Then, the magnesium powder of 1.5% based on the weight of the tantalum powder was doped, the temperature was raised to 900 C. and was kept for 4 hours under the protection of inert gas followed by lowering the temperature, and cooling and passivating were carried out, after that, discharging out of the furnace, and after carrying out pickling and impurity removal with the prior art process, it was put into a heat treatment furnace again, then the temperature was kept at 1430 C. for 60 minutes, and cooling and passivating were carried out, after that, discharging out of the furnace, sieving by a 60-mesh screen and carrying out magnetic separation.

[0042] Next, the magnesium powder of 1.3% based on the weight of the tantalum powder was doped, the temperature was raised to 900 C. and was kept for 4 hours under the protection of inert gas followed by lowering the temperature and cooling to 450 C., after that, evacuation replacement was carried out, and high-purity nitrogen was filled until the pressure reaching a positive pressure (+0.01 MPa), then the temperature was kept for 60 minutes, and cooling and passivating were carried out, after that, discharging out of the furnace, and carrying out pickling and impurity removal with the prior art process to obtain a finished product. The chemical impurities and the physical properties of the finished product are shown in Table 2.

[0043] The above powder was subjected to electrical properties detection by using the same condition as Example 1. The measured electrical properties of the sample are listed in Table 3.

EXAMPLE 2

[0044] The same raw material as Example 1 was used. Its parameters obtained by testing are shown in Table 1. After agglomeration treatment, the raw material was put into a heat treatment furnace, the temperature was kept at 1400 C. for 60 minutes followed by cooling and passivating, after that, discharging out of the furnace, sieving by a 60-mesh screen and carrying out magnetic separation, and then ammonium hexafluorophosphate of 70 ppm based on the amount of phosphorus element was added, and magnesium powder of 2.0% based on the weight of the tantalum powder was doped with uniformly mixing, the temperature was raised to 880 C. and was kept for 4 hours under the protection of the inert gas followed by lowering the temperature and cooling to 350 C., then evacuation replacement was carried out, and high-purity nitrogen was filled until the pressure reaching a positive pressure (+0.01 MPa), then the temperature was kept for 60 minutes, and cooling and passivating were carried out, after that, discharging out of the furnace, and after carrying out pickling and impurity removal with the prior art process, it was put into a heat treatment furnace again, then the temperature was kept at 1400 C. for 60 minutes, and cooling and passivating were carried out, after that, discharging out of the furnace, sieving by a 60-mesh screen and carrying out magnetic separation.

[0045] Next, the magnesium powder of 1.8% based on the weight of the tantalum powder was doped, the temperature was raised to 880 C. and was kept for 4 hours under the protection of inert gas followed by cooling and passivating, after that, discharging out of the furnace, and carrying out pickling and impurity removal with the prior art process to obtain a finished product. The chemical impurities and the physical properties of the finished product are shown in Table 2.

[0046] The above powder sample was pressed and formed into a compact that had a density of 5.0 g/cm and a weight of the core powder of 0.20 g. The compact was sintered in a vacuum furnace of 10.sup.3 Pa at 1700 C. for 15 minutes to obtain a sintered compact. The sintered compact was energized by 140 v in a 0.01% phosphoric acid solution. The capacity and loss of the sintered compact were measured at a test frequency of 5000-30000 Hz. The measured electrical properties of the sample are listed in Table 3.

COMPARATIVE EXAMPLE 2

[0047] The same raw material as Example 2 was used. After agglomeration treatment, the raw material was put into a heat treatment furnace, the temperature was kept at 1400 C. for 60 minutes followed by cooling and passivating, after that, discharging out of the furnace, sieving by a 60-mesh screen and carrying out magnetic separation, and then magnesium powder of 2.0% based on the weight of the tantalum powder was doped with uniformly mixing, and the temperature was raised to 880 C. and was kept for 4 hours under the protection of the inert gas followed by lowering the temperature, cooling and passivating, after that, discharging out of the furnace, and after carrying out pickling and impurity removal with the prior art process, it was put into a heat treatment furnace again, then the temperature was kept at 1400 C. for 60 minutes, and cooling and passivating were carried out, after that, discharging out of the furnace, sieving by a 60-mesh screen and carrying out magnetic separation.

[0048] Next, the magnesium powder of 1.8% based on the weight of the tantalum powder was doped, and ammonium hexafluorophosphate of 70 ppm based on the amount of phosphorus element was added, the temperature was raised to 880 C. and was kept for 4 hours under the protection of inert gas followed by lowering the temperature and cooling to 350 C., then evacuation replacement was carried out, and high-purity nitrogen was filled until the pressure reaching a positive pressure, such as +0.01 MPa, then the temperature was kept for 60 minutes, and cooling and passivating were carried out, after that, discharging out of the furnace, and carrying out pickling and impurity removal with the prior art process to obtain a finished product. The chemical impurities and the physical properties of the finished product are shown in Table 2.

[0049] The above powder was subjected to electrical properties detection by using the same condition as Example 2. The measured electrical properties of the sample are listed in Table 3.

EXAMPLE 3

[0050] The flaked tantalum powder obtained with the prior art process was used as a raw material 2. Its properties are shown in Table 1. 5 Kg of raw material 2 was taken, and ammonium dihydrogen phosphate of 80 ppm base on the amount of phosphorus element was added, after uniformly mixing and carrying out agglomeration treatment on the mixture, the mixture was put into a heat treatment furnace, the temperature is kept at 1380 C. for 60 minutes followed by cooling and passivating, after that, discharging out of the furnace, sieving by a 60-mesh screen and carrying out magnetic separation. Then, the magnesium powder of 2.5% based on the weight of the tantalum powder was doped, the temperature was raised to 800 C. and was kept for 4 hours under the protection of inert gas followed by lowering the temperature and cooling to 320 C., after that, evacuation replacement was carried out, and high-purity nitrogen was filled until the pressure reaching a positive pressure (+0.01 MPa), then the temperature was kept for 60 minutes, and cooling and passivating were carried out, after that, discharging out of the furnace, and after carrying out pickling and impurity removal with the prior art process, it was put into a heat treatment furnace again, then the temperature was kept at 1450 C. for 60 minutes, and cooling and passivating were carried out, after that, discharging out of the furnace, sieving by a 60-mesh screen and carrying out magnetic separation.

[0051] Next, the magnesium powder of 2.0% based on the weight of the tantalum powder was doped, the temperature was raised to 860 C. and was kept for 4 hours under the protection of inert gas followed by cooling and passivating, after that, discharging out of the furnace, and carrying out pickling and impurity removal with the prior art process to obtain the finished product. The chemical impurities and the physical properties of the finished product are shown in Table 2.

[0052] The above powder sample was pressed and formed into a compact that had a density of 5.0 g/cm and a weight of the core powder of 0.15 g. The compact was sintered at 1500 C. for 20 minutes to obtain a sintered compact. The sintered compact was energized by 140 v in a 0.01% phosphoric acid solution. The capacity and loss of the sintered compact were measured at a test frequency of 5000-30000 Hz. The measured electrical properties of the sample are listed in Table 3.

COMPARATIVE EXAMPLE 3

[0053] The raw material was the same as that used in Example 3. 5 Kg of raw material was taken, and ammonium dihydrogen phosphate of 80 ppm based on the amount of phosphorus element was added, after uniformly mixing and carrying out agglomeration treatment on the mixture, the mixture was put into a heat treatment furnace, the temperature was kept at 1380 C. for 60 minutes followed by cooling and passivating, after that, discharging out of the furnace, sieving by a 60-mesh screen and carrying out magnetic separation. Then, the magnesium powder of 2.5% based on the weight of the tantalum powder was doped, the temperature was raised to 860 C. and the temperature was kept for 4 hours under the protection of inert gas followed by lowering the temperature, cooling and passivating, after that, discharging out of the furnace, and after carrying out pickling and impurity removal with the prior art process, it was put into a heat treatment furnace again, then the temperature was kept at 1450 C. for 60 minutes, and cooling and passivating were carried out, after that, discharging out of the furnace, sieving by a 60-mesh screen and carrying out magnetic separation.

[0054] Next, the magnesium powder of 2.0% based on the weight of the tantalum powder was doped, the temperature was raised to 860 C. and was kept for 4 hours under the protection of inert gas followed by lowering the temperature and cooling to 320 C., then evacuation replacement was carried out, and high-purity nitrogen was filled until the pressure reaching a positive pressure, such as +0.01 MPa, then the temperature was kept for 60 minutes, and cooling and passivating were carried out, after that, discharging out of the furnace, and carrying out pickling and impurity removal with the prior art process to obtain a finished product. The chemical impurities and the physical properties of the finished product are shown in Table 2.

[0055] The above powder was subjected to electrical properties detection by using the same condition as Example 3. The measured electrical properties of the sample are listed in Table 3.

EXAMPLE 4

[0056] The flaked tantalum powder obtained with the prior art process was used as a raw material 3. Its properties are shown in Table 1. 5 Kg of raw material 3 was taken, and boric acid of 40 ppm based on the amount of boron elements was added, after uniformly mixing and carrying out agglomeration treatment on the mixture, the mixture was put into a heat treatment furnace, the temperature was kept at 1520 C. for 60 minutes followed by cooling and passivating, after that, discharging out of the furnace, sieving by a 60-mesh screen and carrying out magnetic separation. Then, the magnesium powder of 1.5% based on the weight of the tantalum powder was doped, the temperature was raised to 920 C. and was kept for 4 hours under the protection of inert gas followed by lowering the temperature and cooling to 420 C., then evacuation replacement was carried out, and high-purity nitrogen was filled until the pressure reaching a positive pressure (+0.01 MPa), then the temperature was kept for 60 minutes followed by cooling and passivating, after that, discharging out of the furnace, and after carrying out pickling and impurity removal with the prior art process, it was put into a heat treatment furnace again, then the temperature was kept at 1520 C. for 60 minutes, and cooling and passivating were carried out, after that, discharging out of the furnace, sieving by a 60-mesh screen and carrying out magnetic separation to obtain a finished product. The chemical impurities and physical properties of the finished product are shown in Table 2.

[0057] The above powder sample was pressed and formed into a compact that had a density of 6.0 g/cm and a weight of the core powder of 3 g. The sintered compact that was obtained by sintering at 1700 C. for 30 minutes was energized by 150V in a 0.01% phosphoric acid solution. The capacity and loss of the sintered compact were measured at a test frequency of 5000-30000 Hz. The measured electrical properties of the sample are listed in Table 3.

COMPARATIVE EXAMPLE 4

[0058] The raw material was the same as that used in Example 4. 5 Kg of raw material was taken, and boric acid of 40 ppm based on the amount of boron elements was added, after uniformly mixing and carrying out agglomeration treatment on the mixture, the mixture was put into a heat treatment furnace, the temperature was kept at 1520 C. for 60 minutes followed by cooling and passivating, after that, discharging out of the furnace, sieving by a 60-mesh screen and carrying out magnetic separation. Then, the magnesium powder of 1.5% based on the weight of the tantalum powder was doped; the temperature was raised to 920 C. and was kept for 4 hours under the protection of inert gas, then the temperature is lowered.

[0059] Then, the temperature was raised to 450 C. under the protection of inert gas, after that, evacuation replacement was carried out, and high-purity nitrogen was filled until the pressure reaching a positive pressure (+0.01 MPa), then the temperature was kept for 60 minutes followed by cooling and passivating, after that, discharging out of the furnace to obtained a finished product. The chemical impurities and the physical properties of the finished product are shown in Table 2.

[0060] The above powder was subjected to electrical properties detection by using the same condition as Example 4. The measured electrical properties of the sample are listed in Table 3.

TABLE-US-00001 TABLE 1 Main impurity contents and physical properties of raw materials used in the present invention O N Fe Fsss SBD ppm ppm ppm (m) (g/cc) raw material 1 6020 120 20 0.65 1.00 raw material 2 8910 110 19 0.48 0.91 raw material 3 3520 80 18 0.90 1.08

TABLE-US-00002 TABLE 2 Main impurity contents and physical properties of samples of the Examples and Comparative Examples of the present invention O N Fe B P Fsss SBD ppm ppm ppm ppm ppm (m) (g/cc) Example 1 2020 1400 26 35 20 2.65 1.72 Comparative 1940 1580 25 32 22 2.70 1.69 Example 1 Example 2 1820 780 23 58 2.36 1.68 Comparative 1990 1040 25 62 2.47 1.76 Example 2 Example 3 2490 770 23 72 2.85 1.78 Comparative 2480 870 24 71 2.38 1.68 Example 3 Example 4 1530 570 29 28 10 4.59 1.87 Comparative 1770 520 27 24 10 4.53 1.90 Example 4

TABLE-US-00003 TABLE 3 Main electrical properties of samples of the Examples and Comparative Examples of the present invention under high frequency test Electrical Leakage properties current Capacity Breakdown Volume test K value (CV) Loss voltage shrinkage condition A/FV FV/g (tg ) % (VB) V (SHV) % 5000 Hz Example 1 2.2 10.sup.4 16407 98.8 175 7.1 Comparative 3.8 10.sup.4 13947 97.3 170 11.9 Example 1 20000 Hz Example 1 3.3 10.sup.4 11110 200.4 175 7.1 Comparative 5.9 10.sup.4 9060 191.2 170 11.9 Example 1 8000 Hz Example 2 1.5 10.sup.4 12236 90.5 210 14.8 Comparative 2 10.sup.4 10127 88 210 17.6 Example 2 25000 Hz Example 2 2.3 10.sup.4 7784 174.4 210 14.8 Comparative 3.2 10.sup.4 6337 157.2 214 17.6 Example 2 5000 Hz Example 3 4.0 10.sup.4 21483 85.2 205 16.9 Comparative 4.5 10.sup.4 17757 90.3 205 20.7 Example 3 15000 Hz Example 3 5.8 10.sup.4 14054 196.0 205 16.9 Comparative 6.0 10.sup.4 12972 200.9 205 20.7 Example 3 5000 Hz Example 4 1.5 10.sup.4 8158 71.0 269 14.1 Comparative 1.8 10.sup.4 6154 72.4 266 17.7 Example 4 30000 Hz Example 4 1.9 10.sup.4 4967 418 269 14.1 Comparative 2.0 10.sup.4 4419 430 266 17.7 Example 4

[0061] It is known from these values in the tables, the leakage current of the samples in the Examples is significantly reduced compared with those in the Comparative Examples. For example, the leakage current is reduced by at least 10%, and the capacity is significantly increased, for example, 5% or more. This has a great advantage for the tantalum powder with high-frequency characteristics, and is also unexpected.

[0062] It can be known from the data of Tables 2 and 3 that the tantalum powders obtained by the Examples have a small density ratio before and after sintering, the excess shrinkage caused by sintering is inhibited, so that the capacity is high under the high-frequency test condition, and the leakage current is relatively small; while for the tantalum powder obtained by the Comparative Examples, since they are not subjected to high-temperature treatment after nitrogen doping, the shrinkage caused by sintering is large, so that the capacity is relatively low under the high-frequency test condition, and the leakage current is relatively large.