MXPA99004261A - Niobium powders and niobium electrolytic capacitors - Google Patents

Abstract

A flaked niobium powder is disclosed as well as electrolytic capacitors formed from the flaked niobium powders. Niobium powders having a BET surface area of at least about 0.50 m2/g are also disclosed and capacitors made therefrom, as well as niobium powders doped with an oxygen content of at least 2,000 ppm. Methods to reduce DC leakage in a niobium anode are also disclosed.

Description

NIOBIO POWDERS AND NIOBIO ELECTROLYTIC CAPACITORS BACKGROUND OF THE INVENTION The present invention relates to niobium powders and electrolytic capacitors using niobium powders, as well as to the methods for producing powders and electrolytic capacitors. For many years, the objective of several researchers has been to develop niobium electrolytic capacitors due to the high dielectric constant of this oxide and the relatively low cost of niobium compared to a variety of other metals. Initially, researchers in this field considered the possibility of using niobium as a substitute for tantalum capacitors. Consequently, many studies were carried out to determine the suitability of replacing tantalum with niobium. In some of these studies it has been concluded, however, that the niobium has serious fundamental deficiencies that need to be solved, inferring in this way that niobium was not acceptable as a substitute for tantalum. (See J. Electrochem, Soc. P. 408 C, Dec. 1977). In another study, it was concluded that the use of niobium in solid electrolytic capacitors was very unlikely due to several physical and mechanical problems, for example P ín / Q9MY field crystallization (Electrocomponent Science and Technology, Vol. 1, pp. 27-37 (1974)). In addition, in another study, the researchers concluded that the passive films formed anodically on niobium were different in electrical properties than those obtained with tantalum and that the use of niobium condoles to complexities that did not occur with tantalum (refer to Elecrochimica Act. , Vol 40, No. 16, pp. 2623-26 (1995)). Therefore, while there was an initial hope that niobium could be an adequate replacement for tantalum, evidence showed that niobium was not able to replace tantalum in the electrolytic capacitor market. In addition to tantalum electrolytic capacitors, there is a market for aluminum electrolytic capacitors. However, aluminum electrolytic capacitors have dramatically different performance characteristics than tantalum electrolytic capacitors. A driving force in today's electronic circuitry is the increasing movement towards lower Equivalent Series Resistance (ESR) and lower Equivalent Series (ESL) Inductance. As the performance of the integrated circuits increases with the submicron geometry, there is a need for lower noise margin and lower power supply voltage. At the same time, increasing the speeds of the integrated circuits requires greater power needs. These conflicting requirements create a demand for better energy management. This is being achieved through distributed energy supplies that need larger currents to decouple noise. The higher speeds of the integrated circuits also mean shorter switching times and higher transient current. The electrical circuit must, therefore, also be designed to reduce the transient load response. This wide range of requirements can be met if the circuit has a sufficiently large capacitance but a low ESR and a low ESL. Aluminum capacitors typically provide the largest capacitance among all types of capacitors. ESR decreases with increasing capacitance. Therefore, a large bank of high capacitance aluminum capacitors is currently used to meet the above requirements. However, aluminum capacitors do not really meet the designer's requirements for low ESR and low ESL. Its mechanical construction with liquid electrolyte inherently produces ESR in the milliohm lOOs together with a high impedance.

SUMMARY OF THE INVENTION A feature of the present invention is Pl TI 7 / OQ V provide niobium powders formed into flakes. A further feature of the present invention is to provide niobium powders, preferably having high surface areas and physical characteristics that allow niobium powders to be formed within a capacitor having high capacitance. Another feature of the present invention is to provide niobium powders which, when formed within the capacitors, have a low direct current leakage. A further feature of the present invention is to provide a method for reducing direct current leakage in a capacitor formed from niobium powder. Other advantages and features of the present invention will be partially established in the continuing description, and will be partially apparent from the description itself or may be learned with the practice of this invention. The present invention relates to niobium powder formed into flakes. Another aspect of the present invention relates to any niobium powder having a BET surface area of at least about 0.15 m / g. The present invention also relates to niobium powder, which when formed within an anode pnn / QQMY electrolytic capacitor, the anode has a capacitance of 30,000 hp / g at approximately 61,000 hp / g. The present invention also relates to a niobium powder having an oxygen content of at least about 2,000 ppm. Also, the present invention relates to a method for reducing direct current leakage in a niobium anode made from niobium powder comprising the step of doping the niobium powder with a sufficient amount of oxygen in order to reduce the Direct current leak. It should be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are intended to provide a more detailed explanation of the present invention, as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a graph showing the BET surface areas of the niobium powders and their respective capacitances, when forming anodes and sintering at a temperature of 1750 ° C. Figure 2 is a graph illustrating the BET surface areas of the niobium powders and their respective capacitances when formed in anodes and sintered at a temperature of 1600 ° C.

Figure 3 is a graph illustrating the BET surface areas of niobium powders and their respective capacitances when formed in anodes and sintered at a temperature of 1450 ° C. Figure 4 is a graph illustrating the BET surface areas of niobium powders and their respective capacitances when formed in anodes and sintered at a temperature of 1300 ° C. Figure 5 is a graph showing various sintering temperatures of the niobium anodes and their respective maximum calculated capacitances. Figure 6 is a graph illustrating the doping content of oxygen in the niobium powders as well as their respective direct current leak when formed in anodes and sintered at different temperatures and using a 50 volt forming voltage. Figure 7 is a graph showing niobium powders having various levels of doping with oxygen as well as their respective direct current leaks when formed in anodes and sintered at different temperatures and using a 30 volt forming voltage. Figure 8 is a graph showing the effects of various phosphorus levels that dope niobium powders and their respective capacitances when they form anodes.

Figure 9 is a graph showing the effects of various phosphor doping levels on the niobium powder and their respective direct current leaks when anodes are formed.

DETAILED DESCRIPTION OF THE PRESENT INVENTION One aspect of the present invention relates to a niobium powder formed into flakes. The niobium powder formed into flakes can be characterized as a flat plate shape and / or platelet. As well, the niobium powder formed into a leaflet has a dimensional ratio (ratio of diameter to thickness) of between about 3 to about 300 and, preferably, of between about 3 to about 30. The niobium powder in flakes allows a surface area improved due to its morphology. Preferably, the BET surface area of the flake niobium powder is at least 0.15 m / g and, more preferably, it is at least about 1.0 μg and more preferably at least about 2.0 m / g. g. The preferred ranges of the BET surface area for the niobium powder formed into flakes are from about 1.0 m 2 / g to about 5.0 m2 / g, 9 more preferably from about 2.0 m / g to 2 2 about 5.0 m / g or about 2.0 m / g approximately 4.0 m / g. The BET interval is based on niobium powders formed into flakes and pre-agglomerates. The niobium powder formed into flakes can agglomerate. The niobium powder formed into flakes can also be subjected to a hydride cleaning process or not. The niobium powder formed into flakes preferably has a Density Scott of less than about 35 g / inch and, more preferably less than about 12 and still more preferably, less than about 5 g / inch. Preferably, the niobium powder formed into flakes and agglomerate has a flow rate of more than 80 mg / s, more preferably from about 80 mg / s to about 500 mg / s. The niobium powder formed into flakes can be prepared by taking a niobium ingot and causing the ingot to become brittle by subjecting it to hydrogen gas to form hydrides. The ingot resulting from this process can then be crushed into an angular powder for example with the use of a jaw crusher. The hydrogen can then be removed by heating the powder in vacuo and then the degassed angular powder can be subjected to grinding, for example with the use of a stirred ball mill where the powder is dispersed in a fluid medium (aqueous or non-aqueous) for example. ethanol, to form powder in flakes, due to the impact of stainless steel balls that move by the action of rotating rods. Various sizes of flakes can be made by treatment with hydrogen to make them brittle, followed by an impact grinding of the flakes, for example with the use of a fluidized bed jet mill, Vortec mill or any other suitable grinding step. The niobium powder in flakes may optionally have a high oxygen content, for example by doping. The amount of the doping content with oxygen may be at least about 2,000 ppm. More preferably, the niobium flake powder has an oxygen content of between about 2,000 ppm to about 20,000 ppm, and more preferably between about 2,750 ppm and about 10,000 ppm, and still more preferably between 4,000 ppm and about 9,000 ppm . Doping of niobium powder with oxygen can be done in a variety of ways including, but not limited to, heating tissue to vacuum at 900 ° C and cooling in air. In addition, flake niobium powder can also be doped with phosphorus alone or with oxygen. Doping of niobium powder with phosphorus is also optional. In one embodiment of the present invention, the amount of phosphorus that is doped to the niobium powder is less than about 400 ppm and more preferably less than about 100 ppm, still less preferably about 25 ppm. Based on the example set forth herein, the amount of phosphorus used for doping may not be important in relation to the leakage of direct current and the capacitance of an anode formed from the niobium powder having various levels of phosphorus as dopant or poison. Consequently, in a modality, low amounts of phosphorus are present even if the amounts are negligible or phosphorus is totally absent since this provides few benefits or no benefit to direct current leakage and capacitance with respect to certain anodes formed from niobium powders. In another embodiment of the present invention, the invention relates to niobium powder (eg in flakes, angular, nodular and mixtures thereof) having a significant level of oxygen present in niobium powder. The oxygen level can be achieved in the same way as described above. Preferably, the amount of oxygen in the niobium powder is at least about 2,000 ppm, and more preferably from about 2,000 ppm to about 20,000 ppm. Other preferred ranges of oxygen content in the niobium powder are from about 2,750 ppm to about 10,000 ppm and levels from about 4,000 ppm to about 9,000 ppm. In relation to these niobium powders, as is the case of the modality that relates only to niobium powder in flakes, phosphorus levels in niobium powders can be considerably lower for certain modalities. Preferably, in these embodiments, the level of phosphorus (as a dopant) is less than about 400 ppm and more preferably less than about 100 ppm and still more preferably less than about 25 ppm. In another embodiment, the present invention relates to niobium powders (eg in flakes, angular, nodular and mixtures thereof) having a BET surface area of at least 0.5 m / g and, preferably, at least about 1.0 mg and more preferably from about 1.0 to about 5.0 m / g, and still more preferably from about 2.0 to about 5.0 m / g. The BET intervals are based on pre-agglomerated niobium powders. The niobium powder may or may not be subjected to the hydride process. Also, the niobium powder can agglomerate. The niobium powder in this mode can be doped with nitrogen. Also, for certain uses, the niobium powder may have an oxygen content below about 2,000 ppm.

With respect to the manufacture of niobium powder in flakes or niobium powder having any morphology with the BET surface area, the examples show the preferred steps of forming the niobium powder that subsequently can form a flake or any other type of morphology. In general, the process is as follows and the examples provide specific details regarding the preferred embodiments of making niobium powders of the present invention. In general, when preparing niobium powders having a BET surface area of at least 0.5 m / g, a niobium ingot is hydrided (treatment with hydrogen) by heating the vacuum to form a cracked ingot that is crushed to form a dust. The hydrogen in the powders can optionally be removed by heating the particle in vacuo. The various BET surface areas can be achieved by subjecting the powder to grinding, preferably a grinding process. The larger the BET surface area in the powder, in general, a longer grinding time will be required. For example, with a grinding time of approximately 60 minutes, a BET surface area of approximately 1.0 m / g can be obtained. To obtain even larger BET surface areas, longer milling times will be needed and to achieve a BET surface area of between about 4 and about 5 m / g or greater, milling times of the order of about 24 hours or more in a mill by rub are a way of making these niobium powders having large ranges of BET surface area. In making these large surface areas, it is preferred to use a Union Process 30-SL type mill using 1,000 pounds of 3/16"SS medium, and about 80 pounds of niobium powder, with the mill set at a rotation of approximately 130 rpm Also, the mill will contain a sufficient amount of a medium such as ethanol, in the order of 13 or more gallons.After grinding, the niobium powders are then subjected to heat treatment and preferably the niobium powders can have a phosphorus content to help minimize the reduction in surface area during the heat treatment The heat treatment can be at any temperature sufficient to cause, in general, agglomeration and preferably without reducing the surface area. The heat treatment that can be used is approximately 1100 ° C for 30 minutes, however, the temperature and time can be modified to Ensure that the high BET surface area is not reduced. The various niobium powders described above can also be characterized by the electrical properties resulting from the formation of a capacitor using niobium powders of the present invention. In general, the niobium powders of this invention can be tested in their electrical properties by compressing the niobium powder to form an anode and sintering the compressed niobium powder at suitable temperatures and then anodizing the anode to produce an electrolytic capacitor anode which then it can be proven in its electrical properties. Accordingly, another embodiment of this invention relates to capacitors formed from niobium powders of the present invention. The anodes made from some niobium powders of this invention can have a capacitance of from 30,000 CV / g to about 61,000 CV / g. By forming the capacitor anodes of the present invention, a sintering temperature is used which will allow the formation of a capacitor anode having the desired properties. Preferably, the sintering temperature is between about 1200 ° C to about 1750 ° C, and more preferably between about 1200 ° C to about 1400 ° C, and still more preferably between about 1250 ° C and about 1350 ° C. The anodes formed from the niobium powders of the present invention are preferably formed at a voltage of less than about 60 volts and, preferably between about 30 and about 50 volts, and more preferably about 40 volts. Preferably, the operating voltages of the anodes formed from the niobium powders of the present invention are between about 4 and about 16 volts and more preferably between about 4 and about 10 volts. Also, the anodes formed from the niobium powders of this invention preferably have a direct current leakage of less than about 5.0 na / CV. In one embodiment of the present invention, the anodes formed from some of the niobium powders of the present invention have a direct current leakage from about 5.0 na / CV to about 0.50 na / CV. The present invention also relates to a capacitor according to the present invention having a niobium oxide film on the surface thereof. Preferably, the niobium oxide film comprises a film of niobium pentoxide. The capacitors of the present invention can be used in a variety of end uses such as automotive electronic components, cell phones, computers, for example monitors, master cards and the like, consumer electronic components that include TV and CRT devices, printers / copiers, power sources; modems; laptops and disk drives. The present invention will be further elucidated with the following examples, which are intended to exemplify the invention.

TEST METHODS Anode Fabrication: Size - 0.197"inches in diameter 3.5 Dp powder weight = 341 mg Sintering the anode: 1300 ° C - 10 minutes 1450 ° C - 10 minutes 1600 ° C - 10 minutes 1750 ° C - 10 minutes Anodization 30 V Ef: 30 V Ef @ 60 Degrees C / 0.1% Electrolyte H3P04 20 mA / g constant current Direct Current / Capacitance Leakage ^ ESR Test Direct Current Leakage Test 70% Ef (21 Direct Current Voltage) m -? ? n / o Q V Test voltage Charging time 60 seconds 10% H3PO4 @ 21 Degrees C Capacitance - Test DF 18% H2S04 @ 21 Degrees C 120 Hz Reform Anodization 50 V Ef: 50 V Ef @ 60 Degrees C / 0.1% of H3P04 Electrolyte 20 mA / g constant current Direct Current Leakage / Capacitance ^ ESR Test Direct Current Leakage Test 70% Ef Test Voltage (35 VDC) Load Time 60 seconds 10% H3P04 @ 21 Degrees C Capacitance - Test DF 18% H2S04 @ 21 Degrees C 120 Hz Reform Anodization 75 V Ef: 75 V Ef @ 60 Degrees C / 0.1% Electrolyte H3P04 20 mA / g constant current Direct Current Leakage / Capacitance - ESR Test Direct Current Leak Test 70% Test Voltage Ef (52.5 VDC) Load Time 60 seconds 10% H3P04 @ 21 Degrees C Capacitance - Test DF 18% H2S04 @ 21 Degrees C 120 Hz Scott's Density, oxygen analysis , phosphorus analysis and BET analysis were determined according to the procedures set forth in U.S. Patent Nos. 5,011,742; 4,960,471; and 4,964,906, all incorporated herein in their entirety as a reference.

EXAMPLE 1 This example illustrates an embodiment of this invention comprising angular niobium powder. A niobium ingot produced by electron beam was subjected to hydride by heating the ingot at a vacuum of 10"torr at 850 ° C for 120 minutes.The vacuum was replaced by hydrogen gas purge at 21 kPa for sufficient time to make the brittle The vacuum was then pumped to -28"of mercury and refilled with argon at -5" Hg. The pressure was maintained until the temperature, measured by a working thermocouple, stabilized. increasing the pressure so that the working temperature did not rise, the brittle ingot was crushed to obtain angular powder in a DT 11 / Q QMV jaw crusher and it was classified extracting the powder that passed through a No. 325 mesh (equivalent to a particle size of 44 micrometers). The hydrogen was removed from the small hydrogen-containing particles by heating them to 850 ° C in a vacuum, until the pressure was no longer affected by the hydrogen that was being emitted from the particles, to provide the metal's angular powder. niobium with a Size Less than the Fisher Mesh of 10.6 micrometers, a Scott density of 2.67 g / cc (43.8 g / inch), a pre-agglomerated BET surface area of 0.17 m / g and 1770 ppm of oxygen, the proportion of Oxygen to the BET surface area was 10,400 ppm 0 / m2 / g and the flow was 19 mg / seconds. Approximately 0.34 g of samples of the non-agglomerated angular niobium powder were compressed in an anode mold 5 mm in diameter around a niobium conductive wire with a diameter of 0.6 mm to a density of 3.5 g / cc. The samples of the compressed niobium powder were sintered in vacuum (so _3 minus 10 Pa) at four different temperatures, ie 1300, 1450, 1600 and 1750 ° C for 10 minutes, then anodized by applying a constant current of 20 mA / g at 50 V to the anode submerged in 0.1% by weight phosphoric acid to produce electrolytic capacitor anodes, which were then washed and dried. The performance characteristics of the capacitor were evaluated D1117 / O QMY for the measurements taken in the anodes submerged in 18% by weight sulfuric acid and are reported in Table 1. The capacitance, determined at a frequency of 120 Hertz, was reported in units of microfarads volts per gram (CV / g) and microfarads volts per cubic centimeter of anode volume (CV / cc); direct current leakage, measured after 1 minute of 35 volt load, was reported in nanoamperes units per microfarad-volt (nA / CV).

EXAMPLE 2 This example illustrates one embodiment of the powder of this invention comprising agglomerated mixture of angular powder and powder in flakes. 2.5 lbs. Of the degassed angular powder prepared essentially in the form of Example 1, were processed in a ball mill with stirring type lS Union Process (285 rpm for 90 minutes) wherein the powder dispersed in 2,400 ml of ethanol medium 40 lbs. of the medium 440 SS 3/16"was formed into flake-shaped powders by the impact of stainless steel balls moved by the action of rotating rods.After the desired deformation to form the flakes, the niobium powder was removed and was washed to remove the present alcohol.The niobium powder was subsequently washed with a mixture of deionized water, hydrofluoric acid and hydrochloric acid in an amount of 500 ml / pounds, 4 ml / pounds and 250 ml / pounds, of niobium, respectively (18.6% HCl containing 22 ml / kg of HF) to remove metal contamination (for example iron, nickel, chromium and the like, transferred by contact with stainless steel balls). The niobium was washed again with deionized water and then dried. The acid-washed flake powder was dried in air at 85 ° F (30 ° C) and had a dimensional ratio (determined by observation of microphotographs) in the range of 50 to 70. The flake powder was mixed with angular powder of starting (in a weight ratio of 30:70) and with a powder containing phosphorus, ie NH4PF5, in an amount to provide 60 ppm of phosphorus, which serves as a grain retarding agent to decrease the reduction in surface area during the subsequent thermal treatment for the agglomeration. The pre-agglomerated BET surface area was 0.31 m / g. The mixed powders were agglomerated by heating under vacuum at 1100 ° C for 30 minutes to form an agglomerated mass. The agglomeration process was developed so that the material was subjected to a high vacuum and heated, with a heating rate of 3 ° C / minute up to 700 ° C and was maintained to remove the gas until it was achieved the high pressure. Heating continued in an oven at a heating rate of 8 ° C / minute to 1100 ° C under high pressure and was maintained for 30 minutes. Subsequently, the material was allowed to cool in the oven and the material was manually passivated by exposing it to the air. Then, the material was reduced to small agglomerated particles by crushing with a jaw; the small sized particles were passed through a No. 50 mesh (equivalent to a maximum agglomerated particle size of 300 microns) and exhibited a Scott density of 1.3 g / cc (21.7 g / inch) a BET surface area of 0.26 m / g, an oxygen content of 3693 ppm and a phosphorus content of 25 ppm, the ratio of oxygen to the BET surface area was 14,000 ppm 0 / m / g and a flow of 22 mg / seconds. The agglomerated powder was used to make anodes and the electrical properties of these were tested in the manner mentioned in Example 1, with the data reported in Table 1.

EXAMPLE 3 This example illustrates one embodiment of the powder of this invention comprising agglomerated flake powder. The acid-leached powder with a dimensional ratio of about 50 to 70 was prepared essentially in the manner described in Example 2 (cycle time 60 minutes) except that the niobium powder was subjected to hydride treatment for a second time exposing it to hydrogen at 20.7 kPa (3 psig) and 850 ° C to provide a brittle flake, which was cooled and reduced in size by autoimpact in a fluidized bed jet mill (obtained from Hosoka to Micron Powder Systems, Summit, NJ) for making flake powder having an average particle size of 6 microns (as determined by laser scanning particle size). The pre-agglomerated BET surface area was 0.62 m / g. Small flake powder was agglomerated by heating in a hydrogen atmosphere, heating the oven at a rate of 10 ° C / minute to 1050 ° C under an oven subjected to vacuum and maintaining this temperature until the oven pressure decreased below 100 microns. Thick tantalum splinters (10-20 mesh) were used as a rater in a weight ratio of 1 Nb to 1-1.5 Ta. The furnace was then refilled with hydrogen to obtain a pressure of 360 mmHg and the oven temperature then increased to 1200 ° C and maintained for 1 hour. Subsequently the hydrogen was evacuated until the furnace pressure decreased to less than 1 miera and was allowed to cool to room temperature. The niobium powder was then passive in air for 30 cycles where the operating pressure increased by 20 torr per cycle and was maintained for 2 minutes before starting the next air filling. The agglomerated niobium powder was reduced in size to agglomerated particles by a jaw crusher, the niobium powder in agglomerated flakes and of reduced size was sieved through the No. 50 mesh (equivalent to a maximum particle size, of agglomerated flakes of 300 micrometers) and exhibited a Scott density of 1.21 g / cc (20.4 g / inch), a BET surface area of 0.46 m / g, an oxygen content of 8760 ppm, the proportion of oxygen to the area of BET surface was 19,000 ppm 0 / M2 / g, and a flow of less than 1 mg / second. With the agglomerated powder, anodes were prepared and their electrical properties were tested in the manner indicated in Example 1 and reported in Table 1.

EXAMPLE 4 This example illustrates another embodiment of the powder of this invention comprising niobium powder in agglomerated flakes, low oxygen content and high surface area. The niobium powder was prepared in the same manner as indicated in Example 3, except that the niobium powder was subjected to grinding by rubbing for 90 minutes and vacuum heat treatment was carried out at 1150 ° C for 30 minutes. The pre-agglomerated BET surface area was 0.85 m / g. The oxygen content of the amounts of flake niobium powder prepared essentially in the manner set forth in Example 3 was reduced by heating niobium powder mixed with 4 to 5% by weight of magnesium powder under argon, to a temperature in the range of 750 to 850 ° C for 2 hours. The magnesium content was established in the range of 2 to 3 times the stoichiometric amount of oxygen in the niobium powder. After cooling, magnesium and residual niobium oxides were removed in agglomerated flakes by leaching with nitric acid. The deoxidized flake niobium was washed with water, dried and separated by passing it through a No. 50 mesh. The screened niobium flakes exhibited a Scott density of 1.47 g / cc (24.1 g / inch), an area of 9 BET surface area of 0.96 m / g, an oxygen content of 3130 ppm, the ratio of oxygen to BET surface area was 3260 ppm 0 / m / g and a flow of 76 mg / second. With the agglomerated powder, anodes were manufactured and the electrical properties were tested in the manner indicated in Example 1 and reported in Table 1.

TABLE 1 Sintering temperature 1300 ° C 1450 ° C 1600 ° C 1750 ° C Example 1: Capacitance (CV / g) 8400 7500 6400 5500 (CV / cc) 40900 37000 33400 30000 Direct Current Leakage (na / CV) 53 2.8 2.3 2.4 Sintering Density (g / cc) 4.9 5.0 5.2 5.5 Example 2: Capacitance (CV / g) 13600 11900 10000 8200 (CV / cc) 46000 41600 36900 33400 Direct Current Leakage (na / CV) 25 1.7 2.1 2.5 Sintering density (g / cc) 3.4 3.5 3.7 4.1 E p e 3: Capacitance (CV / g) 32500 21400 13400 7100 (CV / cc) 114100 94300 73600 45800 Direct Current Leakage (na / CV) 5.8 4.1 2.4 2.0 Sintering density (g / cc) 3.5 4.4 5.5 6.4 Example 4: Capacitance (CV / g) 31,589 21,059 12,956 7,254 (CV / cc) 110,562 88,448 64,780 42,799 Direct Current Leakage (na / CV) 5.8 5.3 2.6 1.4 Sintering Density (g / cc) 3.5 4.2 5.0 5.9 EXAMPLE 5 A niobium powder was prepared in the same manner as in Example 4 except that the heat treatment was presented under vacuum at 1250 ° C for 30 minutes. The agglomerated BET surface area was 0.78 m / g. An anode was formed with the powder as in Example 1 which had the following performance characteristics.

Cv / g @ 50 Vf 19,600 (1450 ° C) 31,040 (1300 ° C) Sintering Density, g / cc 4.8 (1450 ° C) Direct Current Leakage, na / Cv 2.33 (1450 ° C) BET, m2 / g 0.80 Oxygen, ppm 2,815 Density Scott, G / inch3 24.0 Flow, mg / second 97 EXAMPLE 6 A niobium powder was prepared in the same manner as in Example 4, except that the niobium powder was subjected to a grinding by rubbing for 150 minutes and the heat treatment was carried out in a vacuum oven, where the pressure was brought to 1 miera and then the temperature was increased by 50 ° C / minute until reaching 950 ° C and remained there until the high vacuum was achieved. The temperature was then increased in steps of 15 ° C until a temperature of 1250 ° C was reached and maintained for 30 minutes.

Subsequently, the material was allowed to cool to ambient temperature under vacuum and passive for 30 cycles, where the pressure increased by 20 torr after each cycle and was maintained for 2 minutes before starting the next air filling. Subsequently, the powder was crushed in a jaw crusher to a -50 mesh and deoxidized by mixing the powder with 4% magnesium metal w / w and placing the material in a retort and applying a vacuum of 100 microns. The pre-agglomerated BET surface area was 1.05 m / g. Later, the furnace was filled with argon at a pressure of 800 torr and the pressure increased to 800 ° C and was maintained for 2 hours. Subsequently, the material was allowed to cool to room temperature and passively in air for 30 cycles in the same manner as mentioned above in Example 3. The material was then washed with a mixture of deionized water (500 ml / lb), acid hydrofluoric acid (4 ml / lb) and nitric acid (250 ml / lb). The powder was then washed with deionized water and dried. The niobium powder was used to form an anode as in Example 1 which had the following performance characteristics.

CV / g @ 50 Vf (Temp of 24,300 (1450 ° C) 41,700 Sintering) (1300 ° C) Sintering Density, g / cc 4.0 (1450 ° C) Direct Current Leakage, na / Cv 1.5 (1450 ° C) ) BET, m2 / g 1.11 Oxygen, ppm 3,783 Density Scott, g / inch 24.4 Flow, mg / second 112 EXAMPLE 7 Niobium powder was prepared in the same manner as in Example 6, except that the niobium powder was mixed with phosphorus before heat treatment to achieve a phosphorus charge of 56 ppm. The pre-agglomerated BET surface area was 1.05 m / g. The material was subjected to hydrogen treatment, as in Example 3 and ground, heat treated and deoxidized as in Example 6. Subsequently with the niobium powder an anode was formed as in Example 1 which had the following characteristics performance: Cv / g @ 50 Vf (Temp of 29,900 (1450 ° C) 45,400 Sintering) (1300 ° C) Sintering Density, g / cc 3.7 (1450 ° C) Direct Current Leakage, na / Cv 1.3 (1450 ° C) BET, m2 / g 1.07 Oxygen, ppm 3.690 Scott Density, g / inch 23.2 Flow, mg / second 76 EXAMPLE 8 Niobium powder was prepared in the same manner as in Example 4, except that the niobium powder was ground in a 30 S (130 rpm) grinding mill for 8 hours using 1,000 lbs. medium SS 3/16", 80 pounds of niobium powder and 13 gallons of ethanol The ground powder was leached with acid and washed in the same manner as described above and the material had the following characteristics.

BET m / g 1.39 Oxygen, ppm 8.124 Density Scott, g / inch ~ EXAMPLE 9 Figures 1, 2, 3 and 4 show the parameters CV / g versus BET for various Nb powders having a range of BETs. Each figure represents the measurement of CV / g for the powders determined at a specific sintering temperature. As shown in the Figures, the higher the sintering temperature the greater the loss of the surface area of the anode and there is also a general reduction in CV / g for any particular dust sample as the sample is tested at a temperature of higher sintering (CV / g is proportional to the residual specific surface area of the anode after sintering). As illustrated in Figures 1 to 4, for any specific sintering temperature, the achieved CV / g ratio will have a relationship with the starting BET for the sample. As noted, the low BET will produce a low net CV / g and as the BET increases the CV / g ratio will rise. For materials that have high BET, the degree of surface area loss during sintering is so great as to eliminate so much surface area that only a small fraction of the originally high BET is conserved, expressed as CV / g after sintering, so that the CV / g falls with the highest BETs. For this reason, the response of CV / g against BET shows a maximum at a BET value that retains most of the net specific surface area after sintering. In general, as shown in the Figures, a lower sintering temperature will obtain an optimal CV / g with higher BET material, while high sintering temperatures, which are very destructive for small BET particles above, will achieve an optimum CV / g with less BET powder. In general there is an optimum BET that is used at a specific sintering temperature and the set of all the optimal BETs forms a relative response surface for the sintering temperatures. As shown in the Figures, the CV / g in general is proportional to the BET and the CV / g shows a relationship with the sintering temperatures. Therefore, Figure 5 shows the CV / g for each sintering temperature of Figures 1 to 3 plotted against the sintering temperature. Figure 5 shows the CV / g that would be obtained at a sintering of 1300 ° C, so that it was of the order of approximately 61,000. The preparation of Figure 5 is done based on an objective and mathematically correct procedure to determine the maximum CV / g for each of Figures 1 to 3. Because the response of CV / g against BET in each of the Figures 1 to 3 show a maximum, the requirement was solved by finding the maximum of the best functional fit to the data for each Figure. The actual response of CV / g to BET is a complex function of the variables, however, the Taylor Series function expansion shows that all the functions can be approximately of the first three terms of the Taylor series with a limited domain of the independent variable (in the BET case). These quantities approximate the quadratic function (F (x) = ax + bx + c) valid within a limited neighborhood of any value selected for x. This calculation is valid as long as the values of x are within the neighborhood. The optimal BET in each case was used as the center of the neighborhood of the BET domain so that the approximation is much more valid for BET near this value and, in this way, take the maximum of the quadratic adjustment with respect to the data for which are the best estimate of the CV / g peak of the data in Figures 1 to 3. For this reason, a better fit of data is made in Figures 1 to 3 with respect to a quadratic function using the curve fitting tool in Microsoft Excel version 5.0, which generated the parabolic curves superimposed on the data measured in Figures 1 to 3. The maximum of the parabolas adjusted in Figures 1 to 3 was used as the input data to elaborate Figure 5. The game of maximum CV data / g versus sintering temperature in Figure 5 was first adjusted to an exponential decay function using the curve fitting tool in Microsoft Excel version 5.0. The reason for selecting the exponential decay as the best approximation to the response of maximum CV / g to sintering temperature is because, as shown in the figures, CV / g will decrease with increasing sintering temperature; however CV / g can, in principle, never be less than 0.0 since the specific surface area can not be made less than zero (it can not be negative). The exponential function decaying asymptotically to zero is the simplest form of function that can be used with the data in Figure 5 that do not predict the negative CV / g. The best fit of an exponential curve as determined by Microsoft Excel version 5.0 was added to the data in Figure 5 and this allowed the calculation of maximum CV / g that would have been achieved with a sintering temperature of 1300 ° C based on all the data of Figures 1 to 3, as already explained above. Figure 4 is the actual data for the sample Nb available tested at the sintering temperature of 1300 ° C; however, it is observed in Figure 4 that the data do not present a peak since none of the samples had an optimum BET for the sintering of 1300 ° C. The data was fitted to the quadratic function as used in Figures 1 to 3 and the result shown superimposed in Figure 4 shows the peak that should have been following the observations of the peaks in Figures 1 to 3; and the peak is shown to be CV / g > 55,000 and BET > 1.7. It is readily apparent in the case of Figure 4 that the CV / g peak predicted using the same analysis used for the elaboration of the data in Figure 5, describes a maximum CV / g very close to the maximum derived independently and estimated by the Figure 5. The agreement between two separate determinations of the maximum CV / g at sintering of 1300 ° C agrees and makes clear that materials made with BET > 1.7 (BETs of the order of 2 or more) will display CV / g > 55,000 (CV / g of the order of 60,000) when tested at sintering conditions of 1300 ° C.

TABLE 2 Example data used for Figures 1 to 4 1300 1300 1450 1450 1600 1600 1750 1750 BET CV / g BET CV / g BET CV / g BET CV / g 0. 8 30,302 0.8 22, 757 0.8 14, 433 0.8 7, 972 0. 8 30,423 0.8 22, 982 0.8 14,754 0.8 8,517 1. 16 45,440 1.16 29,916 1.16 16,495 1.16 7,785 0. 96 40,797 0.96 29,868 0.96 18, 480 0.96 9, 958 0. 96 35,350 0.96 27, 959 0.96 17, 742 0.96 9, 611 0. 96 40,235 0.96 30, 147 0.96 18, 707 0.96 9, 989 0. 96 35,481 0.96 27, 667 0.96 17, 977 0.96 9, 611 EXAMPLE 10 The effects of oxygen on niobium powders were studied. Five samples of niobium powder in flakes (prepared as in Example 5) each weighing 1 pound were tested. One of the samples was a control and the remaining four samples were processed in order to increase the oxygen content in the niobium powder. In particular, the four samples were thermally treated in a 900 ° C oven for 30 minutes. The powders were passivated in air in a manner similar to the air passivation discussed in the previous examples. Then, one of the four samples was removed and the remaining three samples were thermally treated and passivated again in the same manner as described above. As before, one of these three samples was removed and the procedure was repeated again with the remaining two samples. Subsequently, again one of the samples was removed and the final remaining sample was again thermally treated and passive as before. Therefore, five samples were prepared in which any of the heating cycles 0, 1, 2, 3 or 4 were carried out. Before the test for the oxygen content in each of these samples, the samples were individually passed to Through a 40 mesh screen, the powders were agglomerated and sintered at different temperatures and formed anodes based on three different formation voltages, as indicated in Table 3. The results of the direct current leak are set out in Table 3. As can be seen from the results in Table 3 and in Figures 6 and 7, the direct current leak decreases gradually as the oxygen content in the niobium increases. The decrease in direct current leakage was especially evident with lower formation voltages, for example 30 and 50 volts TABLE 3 Data showing the effect of 02 on na / CV at 30, 50 and 60 Volts Vf EXAMPLE 11 The effect of phosphorus on niobium powder was examined for this example. Six samples of niobium powder were prepared in a similar manner to Example 5 and tested. One of the samples was used as a control and to the remaining five samples sufficient phosphoric acid was added to achieve phosphorus levels of 5 ppm, 10 ppm, 30 ppm, 100 ppm and 500 ppm respectively. The phosphoric acid was added as a solution diluted with 150 ml of deionized water. The powder and the phosphoric acid solution were mixed and the sample was dried in a vacuum oven. After drying, the sample was mixed individually and the phosphorus levels were tested. The results are shown in Table 4. As can be seen in Table 4 and Figures 8 and 9, there was a small effect caused by doping with phosphorus and it was observed that the higher amounts of doping with phosphorus did not necessarily improve the leakage properties of direct current.

TABLE 4 Data from Niobium samples doped with P Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. It is intended that the specification and examples be considered only as exemplary, and that the true spirit and scope of the invention be indicated by the following claims.

Claims (56)

1. NOVELTY OF THE INVENTION Having described the present invention, it is considered as a novelty and, therefore, the content of the following CLAIMS is claimed as property: 1. A niobium powder in flakes.
2. 2. The niobium powder according to claim 1, wherein the powder is agglomerated.
3. 3. The powder according to claim 1, wherein the powder has a BET surface area of at least 0.15 m / g. .
4. The niobium powder according to claim 1, wherein the powder has a BET surface area of at least about 1.0 m / g.
5. 5. The niobium powder according to claim 1, wherein the powder has a BET surface area of at least about 2.0 m / g.
6. 6. The powder according to claim 1, wherein the powder has a BET surface area between about 1.0 to about 5.0 m / g.
7. The powder according to claim 1, wherein the powder has a BET surface area between about 2.0 to about 5.0 m / g.
8. 8. The niobium powder according to claim 1, wherein the powder is not subjected to hydride treatment.
9. The powder according to claim 1, wherein the powder has a Scott Density of less than about 35 g / inch.
10. The powder according to claim 1, wherein an electrolytic capacitor anode is formed with the powder, the anode has a capacitance of between about 30,000 CV / g at about 61,000 CV / g.
11. 11. A capacitor made from the niobium powder of claim 1.
12. 12. A niobium powder, where an electrolytic capacitor anode is formed with the powder, the anode has a capacitance of 30,000 hp / g approximately 61,000 hp / g .
13. The niobium powder according to claim 12, wherein the powder is subjected to hydride processing.
14. 14. A niobium powder having a BET surface area of at least 0.50 m / g.
15. 15. The niobium powder according to claim 14, having a BET surface area of at least about 1.0 m / g.
16. 16. The niobium powder according to claim 14, having a BET surface area of between about 1.0 to about 5.0 m / g.
17. 17. The niobium powder according to claim 14, having a BET surface area of at least about 2.0 m / g.
18. 18. The niobium powder according to claim 14, having a BET surface area of between about 2.0 m / g to about 4.0
19. 19. The niobium powder according to claim 14, having a BET surface area of between about 2.0 to about 5.0 m / g.
20. 20. The niobium powder according to claim 14, wherein the niobium powder is not subjected to the hydride process.
21. 21. The niobium powder according to claim 14, wherein the niobium powder is agglomerated.
22. 22. A capacitor prepared from a formulation comprising the niobium powder of claim 14.
23. 23. The capacitor according to claim 22, wherein the powder is sintered at a temperature between about 1200 ° C to about 1750 ° C. .
24. The capacitor according to claim 22, wherein the powder is sintered at a temperature between about 1200 ° C to about 1450 ° C.
25. 25. The capacitor according to claim 22, wherein the powder is sintered at a temperature between about 1250 ° C to about 1350 ° C.
26. 26. A capacitor prepared from a formulation comprising the niobium powder of claim 15.
27. 27. A capacitor prepared from a formulation comprising the niobium powder of claim 16.
28. 28. A capacitor prepared from a formulation comprising the niobium powder of claim 17.
29. 29. A capacitor prepared from a formulation comprising the niobium powder of claim 21.
30. 30. The niobium powder according to claim 14, which has a level of phosphorus of less than about 400 ppm.
31. 31. The niobium powder according to claim 14, which has a phosphorus level of less than about 100 ppm.
32. 32. The niobium powder according to claim 14, having a phosphorus level of less than about 25 ppm.
33. 33. The capacitor according to claim 22, wherein the capacitor is formed at a voltage between about 30 and about 50 volts.
34. 34. The capacitor according to claim 22, wherein the capacitor has a direct current leak less than about 5.0 na / CV.
35. 35. The capacitor according to claim 22, wherein the capacitor has a direct current leakage of less than about 5.0 na / CV to about 0.50 na / CV.
36. 36. The capacitor according to claim 26, wherein the capacitor is formed at a voltage between about 30 to about 50 volts.
37. 37. A method for reducing direct current leakage at a niobium anode made from niobium powder comprising the step of doping the niobium powder with a sufficient amount of oxygen to reduce the leakage of direct current.
38. 38. The method according to claim 37, wherein the niobium powder is doped with at least about 2,000 ppm of oxygen.
39. 39. The method according to claim 37, wherein the niobium powder is doped with oxygen in an amount of about 2,000 ppm to about 10,000 ppm.
40. 40. The method according to claim 37, wherein the niobium powder is doped with oxygen in an amount of about 3,000 ppm to about 7,000 ppm.
41. 41. The method according to claim 37, wherein the anode is formed at a voltage of between about 30 to about 50 volts.
42. 42. The method according to claim 37, wherein the anode is formed at a voltage of about 40 volts.
43. 43. The method according to claim 37, wherein the niobium powder has a phosphorus level of less than about 400 ppm.
44. 44. The method according to claim 37, wherein the niobium powder has a phosphorus level of less than about 100 ppm.
45. 45. The method according to claim 37, wherein the niobium powder has a phosphorus level of less than about 25 ppm.
46. 46. The method according to claim 37, wherein the anode is sintered at a temperature between about 1200 ° C to about 1750 ° C.
47. 47. The method according to claim 37, wherein the anode is sintered at a temperature between about 1200 ° C to about 1450 ° C.
48. 48. The method according to claim 37, wherein the anode is sintered at a temperature between about 1250 ° C to about 1350 ° C.
49. 49. A niobium powder having an oxygen doped content of at least about 2,000 ppm.
50. 50. The niobium powder according to claim 49, having an oxygen doped content of about 2,000 ppm to about 20,000 ppm.
51. 51. The niobium powder according to claim 49, having an oxygen doped content of about 2.750 ppm to about 10,000 ppm.
52. 52. The niobium powder according to claim 49, having an oxygen doped content of about 4,000 ppm to about 9,000 ppm.
53. 53. An electrolytic capacitor formed from the niobium powder according to claim 49.
54. The capacitor according to claim 25, further comprising a niobium oxide film on a surface thereof.
55. 55. The capacitor according to claim 54, wherein the film comprises niobium pentoxide film.
56. 56. The niobium powder according to claim 14, having an oxygen content of not less than about 2,000 ppm.