KR100484686B1 - Method of Making Tantalum Metal Powder With Controlled Size Distribution and Products Made Therefrom - Google Patents

Abstract

The present invention relates to a method for controlling the size (pulverization) of tantalum powder containing aggregates of smaller particles, and the specific surface area of the volume average diameter, MV (measured by light scattering methods such as Microtrac analysis (micron units)) by this method. A tantalum powder having agglomerated particle distribution in the pulverized state is obtained, wherein the product of BET (m ² / g) is less than about 25. These powders typically have a ratio of Scott bulk density to BET surface area of about 20 to about 35 after being sized. At all stages of manufacture, i.e., having a relatively limited, more preferably single peak aggregation size distribution after the size control (ie, deagglomeration by grinding), thermal coagulation (ie, heat treatment), and deoxygenation steps. Tantalum powder. The powder thus obtained has a large surface area and excellent fluidity and exhibits controlled shrinkage with high porosity upon sintering. In addition, a sized and heat treated basic lot tantalum metal powder having a volume average diameter MV (in microns) multiplied by a specific surface area BET (in m ² / g) is about 90 to about 250 and has a cohesive particle size. In addition, a volume average diameter MV (micron unit) multiplied by a specific surface area BET (m ² / g unit) is about 90 to about 250, providing a deoxygenated sized and aggregated tantalum powder.

Description

Method of controlling tantalum powder, method of preparing tantalum metal powder with controlled size distribution, and product produced therefrom {Method of Making Tantalum Metal Powder With Controlled Size Distribution and Products Made Therefrom}

The present invention relates to a method for controlling the size of tantalum metal powder, and to a powder produced thereby. More particularly, the present invention relates to tantalum powders useful as, for example, capacitor electrodes suitable for use in the process for controlling the tantalum powder and for the production of sintered porous bodies.

Among many applications, tantalum powder is generally used for the manufacture of capacitor electrodes.

Tantalum capacitor electrodes have contributed greatly to the miniaturization of electronic circuits in particular. Such capacitor electrodes typically compress the agglomerated tantalum powder to less than half the original density of the metal using an electrode lead wire to form pellets, which sinter the pellets in a furnace to form a porous body (ie, an electrode). And then the porous body is anodized in a suitable electrolyte to form a continuous dielectric oxide film on the sintered body. The anodized porous body is then impregnated with cathode material, connected to the cathode lead wire and encapsulated.

The first particle size and the size of the agglomerate (aggregates are clusters of smaller first particles), and the first particle size and the size distribution of the agglomerates of the powder, the efficiency and efficacy of the subsequent sintering process in which the porous body is produced, and It is an important factor in the electrical properties of functional products such as incorporating electrolyte capacitors.

In attempts to obtain tantalum metal powders with the desired properties for the production of capacitor electrodes and similar products, the powders of the prior art have been limited by the way these powders are made. Recently, tantalum powders, for example, are generally produced by either mechanical or chemical methods. The mechanical method includes electron beam melting of tantalum to form an ingot, hydrogenating the ingot, pulverizing the hydride, and then dehydrogenating, pulverizing, and heat treating. This method produces powders of high purity, which are generally used in capacitor applications where high voltage or high reliability is required. However, the mechanical method has a problem due to the expensive production cost. In addition, tantalum powder produced by the mechanical method has a small surface area.

Another method commonly used for the production of tantalum powder is the chemical method. Chemical methods for the preparation of tantalum powders suitable for use in capacitors are known in the art. US Pat. No. 4,067,736 to Vartanian, and US Pat. No. 4,149,876 to Rerat, disclose methods for chemical preparations involving sodium reduction of potassium fluorotantalate, K ₂ TaF ₇ . It is disclosed in detail. An overview of typical techniques is also described in US Pat. No. 4,684,399 to Bergman et al. And US Pat. No. 5,234,491 to Chang.

Since tantalum powders produced by chemical methods have a larger surface area than powders produced by mechanical methods, tantalum powders produced by chemical methods are very suitable for use in capacitors. Chemical methods generally include chemically reducing tantalum compounds with a reducing agent. Typical reducing agents include hydrogen and active metals such as sodium, potassium, magnesium, and calcium. Typical tantalum compounds include potassium fluorotantalate (K ₂ TaF ₇ ), sodium fluorotantalate (Na ₂ TaF ₇ ), tantalum pentachloride (TaCl ₅ ), tantalum pentafluoride (TaF ₅ ), and mixtures thereof There is, but is not limited to this. The most common chemical method is the reduction of K ₂ TaF ₇ with liquid sodium.

Chemically reduced powders are referred to herein as "basic lot powders" and typically comprise aggregates or clusters of smaller first tantalum particles. These clusters or aggregates are referred to herein as "basic lot aggregates". The first particle size of these basic lot aggregates generally ranges from about 0.1 to about 5 microns in size. The size distribution with respect to the basic lot aggregate of normal tantalum powder is shown in FIG. 1 as a comparative example. The base lot aggregate size distribution of the base lot powder is typically multidispersed and substantially bimodal. The term "multivariate" as defined herein means a wide dispersion having a wide range of values, and the term "double vertex" means dispersed in a form having two vertices (i.e. significantly Frequent two different values).

The base lot powder is typically heat treated, pulverized or ground, and deoxygenated by reaction with magnesium. The final product, sometimes referred to herein as "heat treated and deoxygenated powder" or "finished powder", includes some aggregates that may be termed "heat treated and deoxygenated aggregates".

Products of this type can be compressed and sintered such that porous bodies such as anodes for capacitors are produced. However, capacitor electrodes made from powders of heat treated and deoxygenated tantalum suffer from nonuniform sintering and variable pore distribution.

The above described method is generally illustrated by the schematic block diagram included in FIG. 15.

The final surface area of the finished tantalum powder is an important factor in the manufacture of the capacitor. The lower power (CV) of a tantalum (eg) capacitor (typically measured in microfarad-volts) is directly related to the total surface area after sintering and anode treatment. Capacitors with a large surface area are preferred because the larger the surface area, the greater the unloading power of the capacitor. Of course, larger net surface areas can be obtained by increasing the amount of powder (g) per pellet. One way to achieve this is to pressurize a larger amount of tantalum powder so that porous pellets are formed before sintering. However, this approach is limited because the amount of powder that can be extruded to a given pellet size is inherently limited. By pellets compressed to a ratio greater than the general compression ratio, an anode having a poor pore distribution comprising a closed and nonuniform void is obtained. Open uniform voids are important in the anode and impregnation treatment steps of pellets for cathode formation.

As another method to increase the amount of tantalum powder used for pellet production, development efforts have been focused on finding tantalum powders with larger specific surface areas. By increasing the specific surface area of these powders, larger surface area anodes with larger capacitances can be obtained, while using smaller amounts of tantalum powder. Such larger capacitance values are typically measured based on the volume of pellets produced (ie CV / cc). As a result, by using a large surface area tantalum powder, the capacitor size can be reduced while maintaining the same level of capacitance. Alternatively, larger capacitance can be obtained for certain capacitor sizes.

Various tantalum powder processing techniques have been performed which attempt to maximize the production of powders having a desired small first particle size and, as a result, increased surface area. For example, US Pat. No. 4,149,876 to Rerat relates to a technique for controlling the surface area of tantalum powder products in a reduction process in which liquid sodium is added to a melt bath and dilute salt of K ₂ TaF ₇ . .

However, the various other powder processing techniques described above that produce powders with increased surface area also result in finished tantalum powders with widely multidispersed size distributions.

Summary of the Invention

The present invention includes a method for controlling the tantalum powder. This method involves grinding a tantalum powder having an aggregate comprising smaller particles of a first size, for example a powder produced by chemical reduction prior to heat treatment (eg thermal coagulation).

In one embodiment, the method of the present invention produces a tantalum powder comprising aggregates of smaller particles, and by this method, the volume average diameter, MV (measured by light scattering methods such as Microtrac analysis (micron units)). A tantalum powder with agglomerate size distribution in the pulverized state is obtained with a multiplication of the specific surface area BET (m ² / g) of less than about 25.

In a preferred aspect of the present invention, tantalum particles are obtained having agglomerate size distribution in which the agglomerates are pulverized to a specific range.

Preferably, the product produced according to the invention is relatively limited at all stages of manufacture, ie after size control (ie, deagglomeration by grinding), thermal coagulation (ie, heat treatment), and deoxygenation steps. More preferably tantalum powder having a single peak agglomeration size distribution. The powder thus obtained has a large surface area, high purity, and good flowability, and exhibits controlled shrinkage with high porosity upon sintering.

The invention also includes a sized and heat treated basic lot tantalum metal powder having a volume average diameter MV (in microns) multiplied by a specific surface area BET (in m ² / g) of about 90 to about 250 and having a cohesive particle size. do. The volume average diameter MV (in microns) multiplied by the specific surface area BET (in m ² / g) is from about 90 to about 250, and also provides deoxygenated sized and aggregated tantalum powder.

The invention also includes sintered porous bodies made from powders treated according to the invention, capacitor electrodes made from these powders, and capacitors comprising these electrodes. These electrodes and capacitors are described in commonly assigned US Pat. No. 5,217,526, the essential disclosure of which is incorporated herein by reference (not including improvements of the present invention). In one aspect, these capacitors can be made from the basic lot powder treated according to the invention in essentially any stage thereof by the technique described in the fourth column, patents 28 to 50 and referenced herein.

It is to be understood that the foregoing general description and the following detailed description are exemplary of the invention and are not intended to be limiting.

The invention is well understood from the following detailed description set forth in connection with the accompanying drawings.

1 is a narrow, substantially single vertex of a base lot agglomerate achieved by grinding a base lot powder in accordance with the present invention, compared to a multidisperse and substantially double peak distribution of a base lot agglomerate in an unground base lot powder state. Shows the phosphorus size distribution.

Figure 2 shows the change in the basic lot size distribution according to the process of the present invention as a function of the Vortec grinding mill rotational speed, compared to the multiple dispersion distribution of the basic lot aggregates not treated according to the present invention. .

FIG. 3 shows the change in Scott Bulk density of the basic lot powder scaled according to the process of the present invention as a function of the rotational speed of the Bortech grinding mill.

Figure 4 is a base lot powder sized in accordance with the process of the present invention, compared to the heat treatment and deoxygenated aggregate size distribution of the finished powder resulting from thermal coagulation and deoxygenation of the base lot powder that is not scaled. Shows the change in heat treatment and deoxygenated aggregate size distribution of the finished powder achieved by thermal agglomeration and deoxygenation.

FIG. 5 shows the change in aggregate size distribution of finished powders prepared from basic lot powders sized according to the process of the present invention as a function of thermal coagulation temperature.

FIG. 6 shows the change in aggregate size distribution of the finished powder prepared by thermal coagulation and deoxygenation of the basic lot powder having a size adjusted according to the process of the present invention at 1250 ° C. for 30 minutes shown in FIG. Show it.

Figure 7 shows the comparison of the basic lot aggregate size distribution of the base lot powder size adjusted according to the present invention before and after thermal coagulation and deoxygenation according to the present invention.

8 shows a graph of the strength of an anode made using a base lot powder sized and thermally coagulated and deoxygenated according to the present invention.

9 shows the die fill rate of the base lot powder sized and thermally coagulated and deoxygenated according to the present invention.

Figure 10 shows Scott bulk density as a function of the BET surface area of the base lot powder sized and thermally coagulated and deoxygenated according to the present invention.

FIG. 11 shows the die fill rate as a function of the specific capacitance of the base lot powder sized and thermally coagulated and deoxygenated according to the present invention.

Figure 12 shows the volumetric efficiency as a function of anode sinter density for base lot powders sized and thermally coagulated and deoxygenated according to the present invention and for powders prepared by conventional methods.

FIG. 13 shows a scanning electron micrograph of an unscaled base lot tantalum powder corresponding to Sample ID # A2-B.

FIG. 14 shows a scanning electron micrograph of the basic lot tantalum powder after being scaled according to the present invention corresponding to Sample ID # A2-BD.

FIG. 15 is a schematic block diagram illustrating a typical process for making high surface area tantalum powders suitable for making capacitor electrodes and such other products from chemically reduced tantalum based lot powder products comprising aggregates of small tantalum particles.

16 is a schematic block diagram illustrating one embodiment of the process of the present invention.

The size distribution range described below is defined as the range of D10 to D90 values of the particular particles discussed, where the D10 and D90 values are defined as size values where 10% by volume and 90% by volume of the particle / aggregate diameter falls below, respectively. do.

The following test methods were used in the measurement and evaluation of the analytical and physical properties of scaled tantalum powders according to the process of the present invention. Surface area measurement of tantalum powder was carried out using nitrogen BET (Brunauer, Emmett, Teller) method using a surface analyzer (Quantachrome Monosorb Surface Analyzer Model MS12). The purity of the tantalum powder was measured using a spectrometer in a method known in the art with a detection limit of 5 ppm for iron, nickel, chromium and molybdenum.

All particle sizes in the present invention except Sample ID # A2-BDR were measured by microtrack analysis using an analyzer [Leeds & Northrup Microtrac II Model 7998] without using a dispersant. The procedure consists of adding deionized water to the sample reservoir and then taking the backside record. The tantalum powder to be measured was added to the sample reservoir until the load index window of the analyzer indicated a sample concentration of 0.88 +/- 0.02 (T), at which time the particle size record was taken and reported immediately. The particle size distribution of Sample ID # A2-BDU was determined by microtrack analysis using the above-described analyzer [Leeds & Northrup Microtrac II Model 7998] but using ultrasonic waves to disperse the particles. The particle size of Sample ID # A2-BDR was determined using the instrument [Malvern Instruments MasterSizer X Ver. 1.2b].

The present invention relates to the control of the size of tantalum powder comprising aggregates of smaller particles to produce tantalum powder having an aggregate size distribution having a volume average diameter x specific surface area (MV × BET) in the range of about 90 to about 250. . The scaled tantalum powder of the present invention is particularly suitable for use in capacitors. Preferably, the scaled powders produced according to the invention are tantalum powders with narrow aggregate size distribution and more preferably single peaks.

In one embodiment, the size control method of the present invention takes a basic lot powder consisting of tantalum having a basic lot aggregate and (at the instant or otherwise) narrow aggregates at any point in the process prior to performing the desired heat treatment or sintering operation. Achieving a size distribution. Preferably, this step is achieved by grinding the tantalum based lot powder to produce a ground powder having a milled aggregate size of about 0.01 to about 20 μm with a median size of about 3 to 5 μm. This basic lot aggregate size after grinding can be seen in FIG. 14, a scanning electron micrograph at 15,000 times magnification of the scaled tantalum based lot powder according to Sample ID # A2-BD. For comparison, FIG. 13 shows a scanning electron micrograph at 15,000 times magnification of the tantalum base lot powder corresponding to unsized Sample ID # A2-B. From these micrographs, it can be seen that the powder sized according to the process of the present invention has a much smaller and more uniform aggregate size comprising a smaller number of main particles.

1 shows a narrow, single peak base lot aggregate size distribution achieved according to the process of the present invention using a high speed experimental blender [Waring Model 31BL40], which is a high shear device for performing wet grinding. Figure 2 shows a narrow basic lot aggregate size distribution achieved according to the process of the present invention using a Bortech impact milling apparatus that performs dry milling. These distributions allow subsequent thermal coagulation (ie, heat treatment) of the powder and sintering of the compacts to be in controlled form. According to the present invention, the high shear grinding method is most preferred because it produces a powder having a narrow, single peak size distribution as shown in FIG. This high shear method is performed using a device having a high speed blade that rotates at a speed sufficient to produce mechanical and hydraulic shear stresses that break down the metallurgically bonded particles. Typically, the tip speed used is about 3000 to about 4000 ft / min. Although less preferred, the impact crushing method according to the invention is also effective, which is a powder having a size distribution as shown in FIG. 2 which, although not in the form of a complete single peak, is still narrow enough to realize the secondary advantages of the invention. Because it is manufactured.

Figure 4 shows the finished powder prepared from agglomerate size distribution ("Comparative" curve) of the finished powder prepared by conventional methods and the sized base lot powder according to the invention (using a high shear mixer). Show the aggregate size distribution. Conventional methods result in multiple dispersion distributions, but the methods of the present invention result in narrow distributions with sharp "ends" that contribute to a small volume fraction of the overall distribution. 7 shows a narrow base lot aggregate size distribution resulting from a base lot powder sized in accordance with the present invention and a narrow, single peak agglomerate size resulting from base lot powder sized and thermally coagulated and deoxygenated according to the present invention. Show the distribution.

As mentioned above, in order to achieve uniform sintering and maintain the maximum surface area, metal powders having a narrow aggregate size distribution are preferred, most preferably a narrow, single peak distribution. In addition, controlled shrinkage and porosity are important because capacitor manufacturers compress and sinter these powders into smaller pellet sizes. The powder treated according to the invention has a narrow, more preferably narrow and single peak size distribution which facilitates better sintering control compared to conventional powders having a size distribution of multiple dispersions. It was found to prepare. The size distribution of a single vertex is defined as a size distribution with a graph similar to that shown in FIGS. 4 and 5, for example for a finished powder according to the invention.

Since shrinkage is a function of particle diameter, powders with a wide particle size distribution typically result in changes in shrinkage at the anode, which can result in very high nonuniformity and hermetic pores. In theory, since powders have a narrow particle size distribution, anodes made from these powders will result in uniform shrinkage. Thus, capacitors made from powders prepared according to the present invention will exhibit controlled shrinkage with higher porosity and uniform pore size than capacitors made using conventional multidisperse tantalum powders.

The grinding process of the present invention is carried out by applying high shear or impact stress in a wet or dry state to tantalum powder comprising aggregates of smaller particles. The following examples show both wet and dry grinding processes according to the present invention. Preferred metal powders to be sized are tantalum based lot powders prepared by chemical reduction, but it will be appreciated that other metal powders produced by other methods may be sized by the method of the present invention. Thus, the present invention is not limited to the specific examples described below, and may be used with other metal powders as can be readily identified by those skilled in the art.

In the following examples tantalum based lot powders to be sized, i.e., agglomerates of smaller particles prepared immediately upon chemical reduction, are prepared using conventional sodium reduction methods as described in the background section above. These basic lot aggregates generally fall into two main particle size ranges, each with multiple dispersion and substantially double peak basic lot aggregate size distributions. Five basic lot powders (designated lot numbers A1, A2, A3, A4, A5) with high surface area and basic lot aggregate size distributions ranging from about 2 to about 132 microns were prepared. To determine the effect of the main particle size on the base lot powder, a sixth base lot powder (denoted as B1) was prepared, which had a base aggregate size distribution in the range of about 5 to about 95 microns. Size distribution and Scott density data for these basic lot powders are shown in Table 2.

Although the particle size distribution data and the numerical values are shown to have a lower limit of 1, it should be understood that the present invention is not limited thereto. This is due to the fact that the analyzer [Leeds & Northrup Microtrac II Model 7998] cannot measure particle sizes below 1 μm. Instrument [Malvern Instruments MasterSizer X Ver. Sample A2-BDR, measured using 1.2b] (measurable to 0.02 μm or less), is provided as an example illustrating the low size distribution that can be achieved by the present invention. This basic lot powder is separated and ground into a sample lot as described later.

I. Wet grinding

A) Wet grinding using a wear ring blender

100 grams of basic lot powder A3 and A4 samples were separately mixed with 500 ml of cold (ie, room temperature) deionized water separately and ground in a high speed experimental blender [Waring Model 31BL40]. The mixture of powder and water was set to the highest rpm (20,000 rpm) and ground for 10 minutes. This process was repeated until 50 lbs of scaled powder was produced. The resulting shear modified powder was filtered, leached with acid, rinsed, dried, separated into samples, and then heat treated at various thermal coagulation temperatures. The heat treatment cycles used for samples taken from lot A3 (Sample ID # A3-BD) were 1200 ° C. (Sample ID # A3-BDH1) for 60 minutes, 1250 ° C. (Sample ID # A3-BDH2) for 60 minutes, and 60 minutes. 1350 ° C. (Sample ID # A3-BDH3). Lot A4 (Sample ID # A4-BD) Samples were heat treated at 1230 ° C. for 60 minutes (Sample ID # A4-BDH1). The properties of the basic lot powder before and after the heat treatment are shown in Table 2 and the derived variables are tabulated in Table 3.

B) Wet Grinding Using a Mixer [Ross Laboratory High-Shear Model 100 LC Mixer]

2500 ml of cold deionized water were placed in a 1 liter stainless steel beaker. This stainless steel beer beaker was placed in an ice bath under the rotation of a Ross 100 LC mixer set at 500 rpm. 1000 grams of each basic lot powder A1 and B1 was slowly added to deionized water while mixing at 500 rpm. The mixing speed was increased to maximum (10,000 rpm) and blended for a total of about 60 minutes. Ice was added continuously to keep the bath cold. The powder was then filtered and leached with a mixture of acids (eg diluted aqua regia) to remove all contaminants and dried.

The resulting shear modified powder was separated into samples and then heat treated at various thermal coagulation temperatures. The heat treatment cycles used for the samples taken from lot B1 (sample ID # B1-BD) were 1400 ° C. (sample ID # B1-BDH3) for 30 minutes and 1500 ° C. (sample ID # B1-BDH4) for 30 minutes. Lot A1 (Sample ID # A1-BD) Samples were heat treated at 1200 ° C. for 30 minutes (Sample ID # A1-BDH1). The properties of the basic lot powder before and after the heat treatment are shown in Table 2 and the derived variables are tabulated in Table 3.

C) Wet grinding using a commercial high shear mixer [Ross Model 105ME High-Shear Mixer]

Ten gallons of deionized water were placed in the vessel under a Roth 105 ME mixer rotation set at 500 rpm. 50 pounds of basic lot powder A2 was slowly added to deionized water while mixing at full speed (approximately 3000 rpm, which corresponds to a tip speed of 3500 ft / min). Blending was continued for a total of about 90 minutes and the water was decanted and the powder filtered. The powder was then washed with a mixture of acids to remove all contaminants.

The resulting shear deformed powder was filtered, dried to separate into samples and then heat treated at various thermal coagulation temperatures. The heat treatment cycles used for the samples taken from lot A2 (Sample ID # A2-BD) were 1250 ° C. (Sample ID # A2-BDH1) for 30 minutes and 1350 ° C. (Sample ID # A2-BDH2) for 30 minutes. The properties of the basic lot powder before and after the heat treatment are shown in Table 2 and the derived variables are tabulated in Table 3. For basic lot powder A2, the particle size distribution of Sample ID # A2-BD was determined by standard microtrack analysis, which measures the scattering of laser light through a powder suspension in water.

D) Ball grinding of wet base lot powder

One gallon ball mill was half filled with 1/2 inch diameter stainless steel balls. Thereafter, 600 ml of water and 285 grams of basic lot powder were added. The ball mill was shaken for 16 hours and the resulting tantalum powder was washed and dried.

Ⅱ. Dry grinding

Water-washed and leached with acid, prepared by conventional sodium reduction method, gave a dried basic lot powder A5. Powders with a brittle high concentration of hydrogen (powders with low concentrations may be used but are preferably at least 1500 ppm) are selected. Data for this starting base lot powder is shown in Table 1 below. This basic lot powder was pulverized by single pass vortech pulverization in an M1 pulverizer to collect the product in a cyclone recovery system. Five pound lots of A5 basic lot powder were each selected at the machine speed selected as follows: 5,000; 7,500; 10,000; 15,000; And 20,000 rpm.

Scott density, oxygen content, D10, D50, D90 and volume average diameter (MV) data of vortech ground samples are shown in Table 1 below.

ID RPM Scott g / in ³ D10 micron D50 micron D90 micron MV micron A5-B Departure default lot 15.2 3.03 20.95 81.29 32.31 A5-BD1 5000 18.8 2.13 6.56 37.21 13.21 A5-BD2 7500 22.7 2.02 4.96 21.48 9.34 A5-BD3 10000 21.1 1.81 3.68 15.68 7.11 A5-BD4 15000 24.0 1.71 3.54 15.91 6.64 A5-BD5 20000 27.5 1.44 2.87 9.92 4.26

The size distribution range of this vortech pulverized powder is shown in FIG. 2, and the coat density thereof is shown in FIG. 3.

Although the method of the present invention has been exemplified by the various grinding methods described above, it is contemplated that other grinding methods, such as ultrasonic grinding and jet grinding, may be used.

III. Reduction of pulverized and heated lots

Samples were taken from each of the ground and heat treated basic lot powders of A1, A2, A3, A4, and B1 lots and subjected to magnesium deoxygenation. In the treatment, a small amount of magnesium metal powder (ie 1 to 2% by weight) was mixed with the heat treated tantalum powder. The mixture was heated to about 800 to about 1000 ° C. to react the magnesium and oxygen contained in the finished tantalum powder to reduce the oxygen. The tantalum powder was then filtered off and dried. The data as-is corresponding to the powder for all steps of preparation (ie, for the base lot powder upon reduction after sizing, after heat treatment, and after deoxygenation) are shown in Table 2 below. The resulting parameters are shown in Table 3.

The sample identification number in the table consists of a prefix referring to the basic lot powder number and a suffix indicating the treatment performed on the tantalum powder. The confirmation number is omitted as follows.

B = basic lot powder;

BD = scaled base lot powder;

BDH # = Basic Lot Powder Scaled and Heat Treated (Heat Treatment # is a subsequent processing step on the sample);

BDH # M = base lot powder with resizing, heat treatment and deoxygenation;

BDH # MS = Basic lot powder selected for resizing, heat treatment, deoxygenation and up to about 500 mesh; And

BH # M = Basic Lot Powder heated and deoxygenated.

Thus, by way of example, sample ID # A4-BDH1M is a basic lot powder from an A4 lot sized, heat treated and deoxygenated at 1230 ° C. for 60 minutes.

Sample ID BET D10 D50 D90 MV Die fill Scott m ² / g Μm Μm Μm Μm mg / s g / in ³ Basic lot A1-B 1.13 2.61 13.86 69.26 25.43 17 Basic lot A2-B 1.17 3.31 26.28 93.64 37.68 16 Basic lot B1-B 0.95 5.14 33.56 95.31 42.20 19 Basic lot A3-B 1.14 3.27 21.55 79.09 32.15 13 Basic lot A4-B 1.32 3.20 33.26 131.88 53.05 14 DA Ross 100LC A1-BD 1.14 1.77 3.67 13.58 5.91 33 DA Ross 105ME A2-BD 1.18 2.14 5.33 18.41 8.75 32 DA Ross 105ME A2-BDU 1.18 1.39 2.94 10.28 4.52 32 DA Ross 100LC B1-BD 0.99 2.04 5.81 15.53 7.39 32 DA wear ring A3-BD 1.10 1.81 3.44 10.53 5.41 31 DA wear ring A4-BD 1.33 1.83 3.54 9.89 4.86 25 DA Ross 105ME A2-BDR 1.18 0.19 0.41 0.98 0.41 HT 1200 C 30 minutes A1-BDH1 0.92 10.32 201.56 347.14 193.13 38 HT 1250 C 30 minutes A2-BDH1 0.70 7.58 111.69 299.71 129.58 27 HT 1350 C 30 minutes A2-BDH2 0.51 13.62 135.56 300.05 142.32 33 HT 1400 C 30 minutes B1-BDH3 0.47 10.47 132.39 301.55 138.29 42 HT 1500 C 30 minutes B1-BDH4 0.33 17.83 158.38 326.34 162.97 49 HT 1200 C 60 minutes A3-BDH1 0.89 3.61 107.77 286.50 122.56 28 HT 1250 C 60 minutes A3-BDH2 43.54 204.71 345.33 200.67 34 HT 1350 C 60 minutes A3-BDH3 1.22 38 HT 1230 C 60 minutes A4-BDH1 4.68 101.39 289.86 121.50 26 Deoxygenation A1-BDH1M 1.07 11.71 203.74 346.79 198.24 142 48 Deoxygenation A2-BDH1M 0.71 8.26 156.63 329.59 156.89 25 35 Deoxygenation A2-BDH2M 0.60 12.04 159.41 314.09 157.19 80 41 Deoxygenation B1-BDH3M 0.55 10.77 137.89 327.98 149.97 142 45 Deoxygenation B1-BDH4M 0.42 21.74 190.31 356.62 190.17 302 52 Deoxygenation A3-BDH1M 0.96 46.46 207.90 339.10 202.48 63 38 Deoxygenation A3-BDH2M 0.92 44.9 192.64 331.1 190.73 160 40 Deoxygenation A3-BDH3M 0.68 73.43 202.92 335.94 203.65 632 47 Deoxygenation A4-BDH1M 1.07 5.89 142.92 316.67 146.99 31 Selection A3-BDH1MS 85.16 212.55 342.1 214.29 345 Selection A3-BDH2MS 84.92 199.96 333.94 204.14 634

Sample ID BET X MV Flow / BET Scott / BET Basic lot A1-B 29 15 Basic lot A2-B 44 14 Basic lot B1-B 40 20 Basic lot A3-B 37 11 Basic lot A4-B 70 11 DA Ross 100 LC A1-BD 7 29 DA Ross 105ME A2-BD 10 27 DA Ross 105ME A2-BDU 5 27 DA Ross 100LC B1-BD 7 32 DA wear ring A3-BD 6 28 DA wear ring A4-BD 6 19 DA Ross 105ME A2-BDR 0.48 HT 1200 C 30 minutes A1-BDH1 178 HT 1250 C 30 minutes A2-BDH1 91 HT 1350 C 30 minutes A2-BDH2 73 HT 1400 C 30 min B1-BDH3 65 HT 1500 C 30 minutes B1-BDH4 54 HT 1200 C 60 minutes A3-BDH1 109 HT 1250 C 60 min A3-BDH2 HT 1350 C 60 minutes A3-BDH3 HT 1230 C 60 minutes A4-BDH1 Deoxygenation A1-BDH1M 212 133 45 Deoxygenation A2-BDH1M 111 35 49 Deoxygenation A2-BDH2M 94 133 68 Deoxygenation B1-BDH3M 82 258 82 Deoxygenation B1-BDH4M 80 719 124 Deoxygenation A3-BDH1M 194 66 40 Deoxygenation A3-BDH2M 183 167 42 Deoxygenation A3-BDH3M 138 929 69 Deoxygenation A4-BDH1M 135 Selection A3-BDH1MS Selection A3-BDH2MS

Table 4 below is a table of the characteristics of the comparative sample of the base lot powder of tantalum not scaled. The samples were prepared by conventional sodium reduction method of potassium fluorotantalate (K ₂ TaF ₇ ) as described above. Table 5 below shows the derived parameters of the comparative samples prepared by conventional powder methods without grinding.

ID D10 D50 D90 MV BET Scott Flow Μm Μm Μm Μm m ² / g g / in ³ Mg / s E1-BHM 16.32 66.25 203.42 88.10 0.48 E2-BHM 16.19 60.83 186.35 82.86 0.48 E3-BHM 17.03 65.26 187.64 86.11 0.48 E4-BHM 15.97 60.67 173.11 79.82 0.48 D1-BHM 15.62 63.05 183.27 83.69 0.65 D2-BHM 17.78 74.88 218.59 96.22 0.65 D3-BHM 14.43 59.09 166.74 76.69 0.65 D4-BHM 15.44 70.75 258.86 105.93 0.65 D5-DHM 15.60 60.62 234.64 94.80 0.65 D6-DHM 18.14 73.83 206.59 92.87 0.65 C1-BHM 13.29 57.88 207.18 84.06 0.45 C2-BHM 11.59 46.63 140.04 61.77 0.45 C3-BHM 13.19 54.82 179.08 78.26 0.45 C4-BHM 13.02 53.82 178.02 77.19 0.45 B2-BHM 10.75 46.40 153.56 65.50 0.66 B3-BHM 10.77 48.21 164.18 69.77 0.66 B4-BHM 10.81 47.87 162.79 69.14 0.66 B5-BHM  9.98 42.36 161.64 65.81 0.66 B6-BHM 10.62 47.54 174.59 71.40 0.66 B7-BHM 10.71 49.00 190.63 75.12 0.66 A5-BH1M  9.44 44.31 202.52 75.82 0.82 24.58 61 A5-BH1M  8.98 44.39 204.32 76.19 0.87 26.71 66 A5-BH2M 10.04 44.02 174.78 71.31 0.65 27.19 80 A5-BH2M 10.21 62.41 259.05 101.93 0.82 27.83 96 A5-BH3M 11.81 64.22 240.37 97.74 0.68 34.83 137 A5-BH3M 16.08 95.97 283.58 123.93 0.61 40.42 251 A5-BH4M 15.24 107.35 290.80 130.06 0.52 41.26 186 A5-BH4M 13.96 76.85 243.71 104.75 0.56 43.81 244 A5-BH1M  9.44 50.64 204.68 79.76 0.74 30.91 107 A5-BH1M 10.87 62.58 247.03 99.24 0.85 29.01 95 A5-BH2M 11.13 49.67 199.15 77.61 0.67 32.31 137 A5-BH2M 10.92 57.39 233.37 92.66 0.71 32.84 132 A5-BH3M 16.67 108.95 281.18 128.57 0.61 39.69 209 A5-BH3M 12.27 54.99 216.16 84.70 0.54 44.78 263 A5-BH4M 20.67 108.85 301.13 134.72 0.46 49.39 338 A5-BH4M 27.04 145.72 322.44 159.47 0.52 44.92 386

ID MV ^* BET Scott / BET Flow / BET E1-BHM 42 E2-BHM 40 E3-BHM 41 E4-BHM 38 D1-BHM 54 D2-BHM 63 D3-BHM 50 D4-BHM 69 D5-DHM 62 D6-DHM 60 C1-BHM 38 C2-BHM 28 C3-BHM 35 C4-BHM 35 B2-BHM 43 B3-BHM 46 B4-BHM 46 B5-BHM 43 B6-BHM 47 B7-BHM 50 A5-BH1M 62 30 75 A5-BH1M 66 31 76 A5-BH2M 46 42 123 A5-BH2M 84 34 117 A5-BH3M 66 51 202 A5-BH3M 76 66 412 A5-BH4M 68 79 357 A5-BH4M 59 78 436 A5-BH1M 59 42 144 A5-BH1M 84 34 112 A5-BH2M 52 48 205 A5-BH2M 66 46 186 A5-BH3M 78 65 343 A5-BH3M 46 83 486 A5-BH4M 62 107 736 A5-BH4M 83 86 743

The data in Tables 1, 2, 3, 4, and 5 were used to create the graphs of FIGS. 1-7 illustrating the tantalum powder having a narrow distribution of aggregate sizes at all stages during manufacture.

Analysis of the samples for powders ground by vortech pulverization showed that the Scott density was increased by single pass vortech pulverization while the size of the base lot aggregate was reduced. A comparison before and after microtrack analysis is provided in FIG. 2 showing the shift to finer basic lot aggregate sizes as the rotational speed after grinding increases. As a specific example, when comparing the microtrack analysis of a sample of the non-sized base lot powder and the sample of the basic lot powder scaled at 20,000 rpm, after the vortech grinding, there was substantially no particles of 30 microns or more, While size distribution peaks appear in microns, in the case of non-scaled base lots, substantially agglomerates appear above 100 microns. The Scott density obtained after vortech grinding is shown in FIG. 3.

Bortech pulverization can grind large base lot aggregates of base lot powder of tantalum without adversely affecting the chemical properties of the powder. The advantages of the process of the invention and the resulting powders are also discussed below.

IV. Chemical purity of base lot

The base pot powder of tantalum, prepared by reducing K ₂ TaF ₇ with sodium in the presence of diluent salts, typically contains impurities such as Fe, Ni, Na ⁺ and K ⁺ . The impurities are detrimental to the electrical performance of tantalum capacitors. It is believed that the tantalum powder of high purity is produced by releasing the contained impurities because the sizing method of the present invention scales the larger basic lot aggregates.

V. Improved fluidity of finished powder

Powders made using the process of the present invention show a dramatic improvement in flowability due to their aggregate size distribution. Powders prepared using conventional methods in the finished step have multiple dispersed distributions as illustrated in FIG. 4. Finished powders produced using the process of the invention have a narrow distribution of substantially single peaks after sizing, heat treatment, and deoxygenation, as can be seen in FIG. 4. 5 shows the effect of varying the heat treatment temperature in the production of the finished powder according to the invention.

The fluidity of the finished (heated and deoxygenated) powder was measured by a die fill test. The test mimics the conditions of tantalum powder used by capacitor manufacturers very similarly. Hoppers filled with 40 g of tantalum powder were passed through 10 holes 0.3175 cm (0.125 inches) in diameter equally two seconds with a passage time of 2.54 cm (1 inch) apart in a row. . The mass of the powder filling 10 holes after each passage was measured. This method was continued until the hopper was empty. Mean rates in mg / s were calculated by regression analysis. For high capacitance powders the die filling rate is preferably between 130 and 150 mg / s, with greater die filling rates being more preferred. Table 7 below compares the die fill flow rates of powders prepared by the invention with conventional powders. Since the die fill rate is dependent on the non-charge charge of the powder (high specific charge powders have lower die fill rates), powders with similar charge charges were compared in Table 6 and graphically shown in FIG. 11. Also shown in Figure 9 is the die flow rate graphically at various BET values.

powder Non-Charge (CV / g) (1F-V / g) Die filling rate (mg / s) Die Fill Rate after 20% Screening * (mg / s) Comparative example 37900 50 86 A3-BDH1M 39671 160 - A3-BDH1MS 39671 - 634 A3-BDH2M 40455 63 - A3-BDH2MS 40455 - 345 Comparative example 34000 55 125 A3-BDH3M 31985 632 Insufficient Differential to Screen (*): -500 mesh removed by screening.

One method of improving fluidity in conventional powders has been to sort out the fines. However, as shown in Table 6, the degree of improvement is not very large. The effect of selecting the powders prepared according to the method of the invention was also evaluated. It has been found that the flow performance of the pulverized powder of the present invention can be improved by a small amount of screening. Table 6 above shows the flow improvement obtained by screening for the size distribution of the ground particles. The fine "tail" of the distribution can be removed by screening to become a truly single peak narrow particle size distribution with greatly enhanced flow as shown in FIG. 6.

A further advantage is realized in terms of yield which appears when sorting the finished powder according to the invention. As can be seen in FIG. 4, which shows the size distribution of the unselected and finished powder, the finished powder according to the invention has a higher yield of usability since it has a fine “tail” which constitutes a small volume percentage of the total distribution. The powder will remain after screening. Conversely, when sorting to the same mesh size by a conventional method for sorting finished powders with multiple distributed size distributions, large amounts of powder are removed. In addition, the size distribution of the powder remaining after the selection of conventional powders with the same mesh size is still not as narrow as the size distribution of the selected powders according to the present invention.

VI. Capacitors comprising powders prepared according to the invention

The charge of the powder is important in terms of the powder used to make the capacitor. Although the non-charge is generally represented by the name "CV / cc" and expressed in units of "μF-V / cc", those skilled in the art are entitled "CV / g" commonly used by powder manufacturers. It will also be appreciated that this may also be used and this name is expressed in units of "μF-V / g".

In order to evaluate the performance of the powders of the present invention, rectangular capacitor anodes (3.21 mm X 3.21 mm X 1.36 mm and 70 mg) were used for the production of tantalum powders prepared according to the invention between 5 and 7 g / cc using wire electrodes. Compressed into green density pellets and prepared by sintering the pellets under vacuum at a temperature between 1300 and 1500 ° C. for 10 minutes to produce a porous sintered body having uniform open pores. The porous body was then anodized by submersion in 0.1% by volume phosphoric acid while applying a voltage of 50-100 volts. After anode treatment, rinsing, and drying, the anode was first tested for leakage. A 10 volume% phosphoric acid test solution was used. The anode was immersed in the test solution up to the top and a voltage of 70% of the final forming voltage (ie 35 volts if anodized at 50 volts) was applied for 2 minutes and the leakage of the anode was measured. After completion of the leakage measurement, the non-charge was measured on the anode using the 1611B General Radio Capacitance Test Bridge type. Capacitors made using a forming voltage of 50 volts from the powder according to the invention typically ranged from 20,000 μF-V to 50,000 μF-V.

Comparative capacitor anode samples were prepared in the same manner using the comparative samples in Tables 4 and 5. Physical and electrical properties of capacitors prepared using conventional powders and powders of the present invention were evaluated. 8 and 12 graphically represent the data and serve to further illustrate the present invention with respect to the effect of scaling tantalum powder. 8 shows that the green strength of the anode is at least 25 lbs when compressed at a compression density of 6.0 g / cc or greater. The green strength is suitable for manufacturing capacitors.

In Figure 12 the volumetric efficiency of the anodes made from the powders according to the invention is compared with conventional powders with similar specific charges (CV / g). The powder of the present invention was higher in volume efficiency than conventional powder. This is considered to be the result of a unique combination of high bulk density and high specific charge of the powder of the present invention. The porosity distribution of the powder of the present invention was the same as that obtained when compressing a conventional powder selected by using a 325 mesh screen to about 45% by volume of conventional powder when compressed to a compression density of 6.5 g / cc. Thus greater volumetric efficiency is achieved compared to conventional powders. It is believed that conventional powders will not be able to be compressed to such compact densities unless screened. Generally, conventional powders are only compressed to a compression density of 5 to 5.5 g / cc.

VII. Better volume efficiency

An important parameter for high capacitance powders is the charge per unit volume. Capacitor manufacturers can use smaller case sizes to meet the charge requirements if the powder manufacturer can provide large CV / cc of powder. Powders prepared according to the invention have a bulk density (1.25 to 3.44) greater than the bulk density (1.25 to 1.6 g / cc or 20 to 25.6 g / inch ³ ) of conventional powders of similar surface area prepared using conventional methods. g / cc or 20 to 55 g / inch ³ ). See FIGS. 10 and 11. As a result, for similar specific surface areas, powders made according to the invention can be compressed to higher densities using the same compression ratio. Compressing conventional powders with low bulk density and irregular size distribution to high green density results in pore closure and consequently reduced surface area and capacitance. The powders of the invention can be used at high compression densities, for example 6.5 and 7.0 g / cc, while conventional powders can be reasonably used at 5.0 to 5.5 g / cc.

The improvement in electrical performance is well illustrated in FIG. 12 which clearly shows that at similar specific charges, powders made according to the invention have larger CV / cc values than conventional powders.

VIII. Earth leakage data

The leakage data of the capacitor prepared from the powder according to the present invention is shown in Table 7 below. Table 8 shows 30 minutes at 1400 ° C. for A6-BHM samples; 30 minutes at 1425 ° C. for B8-BHM samples; And for the A8-BHM samples, comparative leakage data of capacitors prepared from conventional powders sintered at 1450 ° C. for 30 minutes. When comparing capacitors with similar capacitance values, those made from the powders of the present invention had similar short circuits even when using lower sintering temperatures. For example 230,587 CV / cc prepared by compressing powder sample ID # A3-BDH2M of the present invention at a compression density of 5.0 g / cc and sintering at 1250 ° C. for 60 minutes to form a dielectric using a 50 volt forming voltage. The DC leakage value of the capacitor having a capacitance of 8.81 (μA / g) was found. This results in a capacitance of 219,218 CV / cc, prepared by compressing the comparative powder sample ID # A6-BHM at a compression density of 5.0 g / cc, sintering at 1400 ° C. for 30 minutes, and then forming a dielectric using a formation voltage of 50 volts. Comparable to 8.4 (μA / g), the DC leakage value obtained by the capacitor having.

Electrical Properties of Powders of the Invention Sample ID Compression density Sintering temperature Forming voltage Capacitance (CV / g) Capacitance (CV / cc) DC leakage value (uA / g) DC leakage value (nA / CV) g / cc C μF-V / g μF-V / cc (uA / g) (nA / μF-V) A3-BDH3M 5.0 1335 50 V 37,781 193,336 8.51 0.23 A3-BDH3M 5.3 1335 50 V 37,315 204,339 6.92 0.19 A3-BDH3M 5.6 1335 50 V 36,630 206,231 6.45 0.18 A3-BDH3M 5.9 1335 50 V 35,972 218,161 6.79 0.19 A3-BDH3M 6.2 1335 50 V 35,496 228,546 6.77 0.19 A3-BDH3M 6.5 1335 50 V 36,649 235,006 6.47 0.19 A3-BDH3M 6.8 1335 50 V 33,907 240,481 5.86 0.17 A3-BDH3M 5.0 1405 50 V 31,985 178,636 3.05 0.10 A3-BDH3M 5.3 1405 50 V 32,188 197,826 3.92 0.12 A3-BDH3M 5.6 1405 50 V 30,838 193,516 3.21 0.10 A3-BDH3M 5.9 1405 50 V 30,631 208,434 3.21 0.10 A3-BDH3M 6.2 1405 50 V 30,323 215,536 3.12 0.10 A3-BDH3M 6.5 1405 50 V 29,461 223,563 3.01 0.10 A3-BDH3M 6.8 1405 50 V 28,653 224,043 2.93 0.10 A3-BDH2M 5.0 1335 50 V 44,379 230,587 8.81 0.20 A3-BDH2M 5.3 1335 50 V 43,745 240,597 9.73 0.22 A3-BDH2M 5.6 1335 50 V 42,909 251,414 10.00 0.23

Sample ID Compression density Sintering temperature Forming voltage Capacitance (CV / g) Capacitance (CV / cc) DC leakage value (uA / g) DC leakage value (nA / CV) g / cc C μF-V / g μF-V / cc (uA / g) (nA / μF-V) A3-BDH2M 5.9 1335 50 V 41,823 259,480 11.18 0.27 A3-BDH2M 6.2 1335 50 V 40,903 267,635 9.27 0.23 A3-BDH2M 6.5 1335 50 V 39,957 273,538 9.37 0.23 A3-BDH2M 6.8 1335 50 V 38,834 277,314 7.78 0.20 A3-BDH2M 5.0 1405 50 V 39,671 225,480 5.43 0.14 A3-BDH2M 5.3 1405 50 V 38,457 238,294 5.26 0.14 A3-BDH2M 5.6 1405 50 V 38,341 245,951 4.46 0.12 A3-BDH2M 5.9 1405 50 V 36,599 253,667 5.99 0.16 A3-BDH2M 6.2 1405 50 V 35,384 255,670 4.58 0.13 A3-BDH2M 6.5 1405 50 V 34,213 259,599 4.70 0.14 A3-BDH2M 6.8 1405 50 V 33,440 264,503 4.43 0.13 A3-BDH1M 5.0 1335 50 V 48,522 254,164 9.11 0.19 A3-BDH1M 5.3 1335 50 V 44,993 249,621 15.29 0.34 A3-BDH1M 5.6 1335 50 V 44,031 259,173 7.63 0.17 A3-BDH1M 5.9 1335 50 V 42,840 269,655 8.55 0.20 A3-BDH1M 6.2 1335 50 V 42,138 275,377 9.53 0.23 A3-BDH1M 6.5 1335 50 V 40,528 283,633 7.35 0.18 A3-BDH1M 6.8 1335 50 V 39,560 288,373 11.58 0.30 A3-BDH1M 5.0 1405 50 V 40,455 236,047 4.58 0.11 A3-BDH1M 5.3 1405 50 V 39,628 243,384 5.09 0.13 A3-BDH1M 5.6 1405 50 V 38,564 254,105 4.21 0.11 A3-BDH1M 5.9 1405 50 V 37,257 260,455 5.15 0.14 A3-BDH1M 6.2 1405 50 V 36,691 260,742 4.48 0.12 A3-BDH1M 6.5 1405 50 V 34,601 268,759 3.98 0.12 A3-BDH1M 6.8 1405 50 V 33,623 270,767 4.24 0.13 A1-BDH1M 6.0 1360 50 V 43,601 277,392 9.03 0.21 A1-BDH1M 6.0 1440 50 V 35,949 263,272 5.43 0.15 A1-BDH1M 6.0 1360 70 V 37,497 239,325 13.35 0.36 A1-BDH1M 6.0 1440 70 V 30,868 223,802 8.29 0.27 B1-BDH3M 6.0 1360 50 V 28,220 175,130 4.62 0.16 B1-BDH3M 6.0 1360 70 V 25,668 158,614 8.48 0.33 B1-BDH3M 6.0 1440 50 V 25,593 167,204 3.62 0.14 B1-BDH3M 6.0 1440 70 V 23,700 152,069 4.97 0.21 B1-BDH4M 6.0 1440 50 V 20,786 129,444 3.01 0.15 B1-BDH4M 6.0 1440 70 V 19,495 121,123 3.18 0.17 B1-BDH4M 6.0 1360 70 V 20,332 122,442 5.26 0.26 B1-BDH4M 6.0 1360 50 V 21,880 131,275 4.14 0.19

Electrical Characteristics of the Prior Art and Comparative Powders Sample ID Compression density Sintering temperature Forming voltage Capacitance (CV / g) Capacitance (CV / cc) DC short circuit DC leakage value (nA / CV) g / cc C ㎌-V / g ㎌-V / cc (uA / g) (nA / V-V) A6-BHM 5.0 1335 50 V 40,268 203,417 5.97 0.15 A6-BHM 5.3 1335 50 V 39,725 211,395 5.46 0.14 A6-BHM 5.6 1335 50 V 39,110 220,081 6.23 0.16 A6-BHM 5.9 1335 50 V 38,366 227,477 6.36 0.17 A6-BHM 6.2 1335 50 V 37,704 234,021 6.72 0.18 A6-BHM 6.5 1335 50 V 36,885 241,628 5.55 0.15 A6-BHM 6.8 1335 50 V 35,903 247,273 5.15 0.14 A6-BHM 5.0 1405 50 V 37,900 203,744 3.92 0.10 A6-BHM 5.3 1405 50 V 37,419 209,682 3.6 0.10 A6-BHM 5.6 1405 50 V 36,780 217,772 3.7 0.10 A6-BHM 5.9 1405 50 V 36,976 225,013 4.0 0.11 A6-BHM 6.2 1405 50 V 35,266 231,142 4.0 0.11 A6-BHM 6.5 1405 50 V 34,207 235,846 4.1 0.12 A6-BHM 6.8 1405 50 V 33,375 241,100 4.9 0.15 A6-BHM 5.0 1360 50 V 43,797 219,218 8.34 0.19 A6-BHM 5.0 1440 50 V 39,964 221,680 4.96 0.12 A6-BHM 5.0 1360 70 V 39,305 198,020 12.75 0.32 A6-BHM 5.0 1440 70 V 36,389 200,869 7.64 0.21 B8-BHM 5.0 1440 50 V 34,053 184,366 5.93 0.18 B8-BHM 5.0 1440 70 V 31,438 169,355 12.81 0.41 B8-BHM 5.0 1360 50 V 36,563 184,671 10.74 0.29 B8-BHM 5.0 1360 70 V 33,585 169,258 24.58 0.74 A8-BHM 5.0 1360 70 V 32,281 161,223 9.12 0.28 A8-BHM 5.0 1360 50 V 35,009 175,274 6.27 0.18 A8-BHM 5.0 1440 70 V 30,720 160,195 7.80 0.26 A8-BHM 5.0 1440 50 V 33,170 173,240 4.62 0.14

As generally exemplified by the above examples and illustrated in FIG. 16, the present invention produces powders of finely divided form having properties including particle size and particle size distribution from chemically reduced basic lot powders of tantalum. The powder produced by the method is particularly well suited for producing porous sintered bodies, such as capacitor electrodes with improved properties. The method is also believed to be useful for obtaining similar improvements in the final particle size and particle size distribution of any metal powder in pretreated form including aggregates of smaller particles. For example, this includes finished powders identified as "products" and agglomeration byproducts identified as "waste" in the conventional method illustrated in FIG.

Another embodiment compared to the method illustrated in FIG. 16 includes a similar method where grinding, directly or indirectly, precedes essentially any heat treatment step.

The present invention is particularly useful for controlling the size of the improved tantalum powder as specifically described above. However, although illustrated and described with reference to specific specific embodiments herein, there is no intention to limit the present invention to the details shown. Rather, various modifications may be made to the details without departing from the spirit of the invention within the scope and scope of the appended claims.

Claims (58)

Pulverizing a base lot powder of tantalum having a base lot aggregate comprising individual powder particles, The pulverizing step is continued until the pulverized product has a size distribution such that the volume average diameter MV (micron units) times the specific surface area BET (m ² / g units) has a size distribution of less than 25. . The method of claim 1, wherein the milling continues until the milled product has a milled aggregate size of 0.01 to 20 micrometers. The method of claim 1, wherein the milling continues until the size distribution of the milled aggregate product has a D10 value of less than 2.5 micrometers. The method of claim 1, wherein the milling continues until the size distribution of the milled aggregate product has a D90 value of less than 50 micrometers. The method of claim 1, wherein the size distribution of the milled aggregate has a D10 value of less than 2.5 micrometers and a D90 value of less than 50 micrometers. The method of claim 1, wherein the milled aggregate size distribution is substantially uniform. The method of claim 1, wherein the size distribution has a median size of milled aggregates of 10 micrometers or less. The method of claim 1, wherein the grinding step is performed by mixing the tantalum powder with a liquid using a high shear mixing device and grinding the tantalum powder and the liquid mixture. The method of claim 8, wherein the liquid comprises water. The method of claim 1 wherein said milling step is performed using an impact mill apparatus. The method of claim 10, further comprising reacting the tantalum powder with hydrogen prior to the milling step. The method of claim 1 wherein said milling step is performed using a ball mill apparatus. The method of claim 12, further comprising reacting the tantalum powder with hydrogen prior to the milling step. The method of claim 1, wherein the milling step is performed using an ultrasonic milling apparatus. 15. The method of claim 14, further comprising reacting the tantalum powder with hydrogen prior to the grinding step. The method of claim 1, further comprising reducing the tantalum salt with a reducing agent to first prepare a basic lot powder of the tantalum, and further comprising heat treatment, deoxygenation, leaching, and drying of the milled powder after the milling step. The method of claim 16, wherein the tantalum salt comprises K ₂ TaF ₇ . The method of claim 16, wherein said reducing agent is selected from the group consisting of sodium, potassium, magnesium, calcium, and hydrogen. The method of claim 1, further comprising, after the milling step, heat treating the scaled tantalum powder to form a heat treated tantalum powder having heat treated aggregates. 20. The method of claim 19, wherein after the heat treatment step, the heat treated tantalum particles are deoxygenated to form heat treated and deoxygenated aggregated powders having heat treated and deoxygenated aggregates. 20. The method of claim 19, wherein the heat treatment step is performed at a temperature of 800 ° C to 1600 ° C. 21. The method of claim 20, further comprising selecting the heat treated and deoxygenated tantalum powder to obtain a tantalum powder having a substantially single peak of heat treated and deoxygenated aggregate size distribution. The method of claim 22, wherein the aggregate size distribution of the substantially single vertex is in the range of 30 to 500 micrometers. 21. The method of claim 20, wherein the heat treated and deoxygenated aggregated powder has a size distribution in which the median size of the aggregate is 150 to 250 micrometers. Tantalum powder prepared according to the method of claim 1. Tantalum powder prepared according to the method of claim 6. Tantalum powder prepared according to the method of claim 14. Tantalum powder prepared according to the method of claim 22. Crushed tantalum powder with crushed agglomerated particles having a volume average diameter MV in microns multiplied by a specific surface area BET in m ² / g. 30. The ground tantalum powder of claim 29 having a ground aggregate size distribution having a D10 value of less than 2.5 micrometers. The ground tantalum powder of claim 29 having a ground aggregate size distribution having a D90 value of less than 20 micrometers. The ground tantalum powder of claim 29 having a ground aggregate size distribution having a D10 value of less than 2.5 micrometers and a D90 value of less than 20 micrometers. The heat treated aggregated particles having a volume average diameter MV (micron unit) of the heat treated aggregates multiplied by a specific surface area BET (m ² / g unit) in the range of 90 to 250 and having a BET of more than 0.7 m ² / g. Having a heat treated tantalum powder. 34. The heat treated tantalum powder of claim 33 having a heat treated aggregate size distribution having a D10 value of less than 45. 34. The heat treated tantalum powder of claim 33 having a heat treated aggregate size distribution having a D90 value of less than 350 microns. 34. The heat treated tantalum powder of claim 33 having a heat treated aggregate size distribution having a D10 value of less than 45 and a D90 value of less than 350. Heat treatment and wherein the volume average diameter MV (micron units) of the heat treated and deoxygenated aggregates is multiplied by a specific surface area BET (in m ² / g) in the range of 90 to 250 and the BET is greater than 0.7 m ² / g Heat treated and deoxygenated tantalum powder with deoxygenated aggregated particles. 38. The heat treated and deoxygenated tantalum powder of claim 37 having a heat treated and deoxygenated aggregate size distribution having a D10 value of less than 45. 38. The heat treated tantalum powder of claim 37 having a heat treated aggregate size distribution having a D90 value of less than 350 microns. 38. The heat treated and deoxygenated tantalum powder of claim 37 having a heat treated and deoxygenated aggregate size distribution having a D10 value of less than 45 and a D90 value of less than 350. Scott bulk density (g / in ³ units): crushed base lot powder of tantalum with crushed agglomerated particles having a ratio of BET surface area (m ² / g) in the range of 20 to 35. 30. The method of claim 29, wherein the tantalum powder has a ratio of Scott bulk density (g / in ³ units) to BET surface area (m ² / g) in a range of 38 to 50 after heat treatment and deoxygenation, and a BET of 0.86 m ² / g. Crushed tantalum powder with heat treated and deoxygenated agglomerated particles in excess. 30. The die fill rate (mg / s) of claim 29, wherein the tantalum powder has a BET of greater than 0.86 m ² / g after heat treatment and deoxygenation. Unit): crushed tantalum powder with heat treated and deoxygenated aggregated particles having a ratio of BET surface area (m ² / g) in the range from 66 to 160. 30. The die filling rate of claim 29, wherein the tantalum powder is subjected to a die filling rate (mg / s) after screening with +500 mesh for powders having a BET greater than 0.86 m ² / g after heat treatment and deoxygenation Unit): ground tantalum powder with heat treated and deoxygenated aggregated particles having a ratio of BET surface area (m ² / g) of 350 to 700. Crushed tantalum powder comprising pulverized flocculated particles having a substantially single peak aggregate size distribution and suitable for heat treatment and deoxygenation with a final tantalum powder useful for the manufacture of capacitors. 45. The milled tantalum powder of claim 44, wherein the milled aggregate is suitable for heat treatment with the final tantalum powder having a narrow aggregate size distribution in the range of 0.01-20 micrometers. 46. The pulverized tantalum powder of claim 45 wherein the pulverized agglomerate has a pulverized agglomerate size distribution having a median of the pulverized agglomerate size of 3-5 micrometers. (a) a substantially single agglomerated particle distribution, (b) a narrow aggregate size distribution in the range of 30 to 500 micrometers, and (c) an aggregate size distribution with a median aggregate size of 150 to 250 micrometers. Tantalum powder useful for manufacturing. A capacitor having a central electrode body comprising a sintered metal anode with electrode leads, wherein the anode comprises a sintered body made from the powder of claim 29. A capacitor having a central electrode body comprising a sintered metal anode with electrode leads, wherein the anode comprises a sintered body made from the powder of claim 25. A capacitor having a central electrode body comprising a sintered metal anode with electrode leads, wherein the anode comprises a sintered body made from the powder of claim 37. A capacitor having a central electrode body comprising a sintered metal anode with electrode leads, wherein the anode comprises a sintered body made from the powder of claim 41. A capacitor having a central electrode body comprising a sintered metal anode with electrode leads, wherein the anode comprises a sintered body made from the powder of claim 42. A capacitor having a central electrode body comprising a sintered metal anode with electrode leads, wherein the anode comprises a sintered body made from the powder of claim 43. A capacitor having a central electrode body comprising a sintered metal anode with electrode leads, wherein the anode comprises a sintered body made from the powder of claim 44. The primary lot powder of tantalum having individual powder particles forming the primary lot agglomerates was subjected to high shear grinding, thereby the size distribution having a volume average diameter MV (micron units) multiplied by a specific surface area BET (m ² / g units) of 25 or less Method of controlling the size of tantalum powder comprising the step of obtaining a scaled tantalum powder comprising a pulverized aggregate having a. Mechanically milling the aggregates of smaller particles to form an intermediate product having a predetermined volume average diameter MV (in microns) multiplied by a specific surface area BET (in m ² / g), and then thermally sintering the intermediate product A method for producing tantalum powder having a limited particle size distribution from a form comprising agglomerates of smaller particles, the method comprising agglomerating with a solid, and crushing the thermally agglomerated intermediate product. A method for producing tantalum powder comprising reducing a tantalum salt with a reducing agent to produce a tantalum powder and heat treating the tantalum powder, wherein the tantalum is pulverized before the heat treatment.