HK1181184A - Valve metal and valve metal oxide agglomerate powders and method for the production thereof - Google Patents

Description

Valve metal and valve metal oxide agglomerate powders and process for making same

The application is a divisional application with application number 2009801372969, and the application date of application number 2009801372969 is 8/25/2009.

The present invention relates to valve metal and valve metal oxide agglomerate powders (the valve metal being Nb, Ta, Ti, Zr, Hf, V, Mo, W, Al) and mixtures and alloys thereof, in particular niobium and/or tantalum or niobium suboxide valve metal and valve metal oxide agglomerate powders for the production of capacitors and sintered anode bodies for capacitors (sinterdenk @ straps).

Solid electrolyte capacitors used which have a very large effective capacitor area and are therefore of small design suitable for mobile communication electronics are primarily those which have a niobium pentoxide or tantalum pentoxide (Niob-bzw. tantalentoxid) barrier layer applied to a suitable electrically conductive support, wherein the stability of the support layer ("valve metal"), a higher dielectric constant and a pentoxide insulating layer which can be prepared with a very uniform layer thickness by means of an electrochemical production process are utilized. The support used is the metal or lower oxidation state (Suboxide) conductive precursor of the corresponding pentoxide. The carrier, which at the same time constitutes the electrode (anode) of the capacitor, is composed of a highly porous sponge-like structure that has been produced by sintering an ultrafine (feinstreiig) primary structure or for a sponge-like secondary structure. The surface of the support structure is electrolytically oxidized ("formed") to the pentoxide, the thickness of the pentoxide layer being determined by the maximum voltage of the electrolytic oxidation (forming voltage). The counter electrode is obtained by impregnating the sponge-like structure with manganese nitrate (which is thermally converted to manganese dioxide) or with a liquid precursor of a polymer electrolyte or polymer dispersion of a conductive polymer and polymerizing (e.g. PEDT). The electrical contact of the electrode is made on one side with a tantalum or niobium wire introduced by sintering during the production of the carrier structure and on the other side with a metal capacitor shell insulated from the wire.

The capacitance C of the capacitor is calculated by:

C=(F·e)/(d·V_F)

wherein F represents the capacitor surface area, e is the dielectric constant, d is the thickness of the insulator layer/volt forming voltage, V_FIs to form a voltage.

The sintering of the ultrafine primary and/or secondary structures produces a very large effective capacitor surface area, and closed pores whose surfaces are not effective are also formed. The closed pores thus reduce the volume based (volumenbenzogen) capacitance of the capacitor made from the powder. In case of using secondary structures without closed pores, due to the higher volume based capacitance, higher sintering temperatures can be used in the preparation of the anode body without loss of capacitance, which in turn leads to a thickened sintering neck (Sinterh ä se) and better wire joints compared to using conventional powders. Better wire bonds and thicker sintering necks result in more stable anode bodies and better leakage current, ESR and surge current performance (Sto β strom) (also known as surge performance) of the capacitor.

It is therefore desirable to reduce the number and volume of closed cells in capacitors.

One measure of the level of open porosity of the capacitor anode and the secondary structure (agglomerate powder) used in the capacitor production is its skeletal density (skelttdicht), which is defined as the ratio of the mass of the sintered body to (the sum of the volume of the solid content and the volume of the closed pores). The skeletal density of the anode structure was determined by mercury porosimetry (Quecksilber-injections-Porosimetrie), also known as Mercury porosimetry. Conventional sintering processes for obtaining capacitor anodes result in a skeletal density of 80-88% of the theoretical solid material density.

Processes for influencing the pore structure of niobium or tantalum capacitor anodes to obtain a broad or bimodal pore size distribution have become known, wherein so-called pore formers (Porenbildner) are used during the sintering step. Among these are, on the one hand (EP 1291100 a1, WO 2006/057455) as pore formers, organic substances which decompose or evaporate during heating to the sintering temperature, or metals or metal oxides or metal hydrides which can be removed from the sintered structure by acid leaching after the sintering step, and, on the other hand (DE 19855998 a 1) gaseous pore formers, by means of which adhesively bonded highly porous agglomerates (aggloberates) are obtained, which substantially maintain their porosity during sintering.

In these processes, the pore formers used are used at a later process stage, in which sintered agglomerates with closed pores are already present, so that the formation of closed pores is not effectively prevented.

Moreover, carbon contamination of the capacitor anode body is disadvantageous when organic pore formers are used. Furthermore, when metals or metal compounds are used, considerable effort is required to remove them from the sintered structure, in addition to possible contamination.

It is an object of the present invention to provide a capacitor agglomerate powder capable of producing an anode body at a high skeleton density.

It is also an object of the present invention to provide a polymer with a high skeletal density and therefore a high volumetric efficiency (capacitance/volume, CV/cm)³) An anode for a solid electrolyte capacitor of (1).

Furthermore, it is an object of the invention to provide an anode body with better wire tensile strength (drahtzugfastungkeit), leakage current, ESR and/or surge current properties after further processing into the capacitor.

The invention provides valve metal and/or valve metal suboxide anode bodies, preferably niobium, tantalum and niobium suboxide anode bodies, more preferably of the formula NbO_x0.7 of the niobium suboxide anode body<x<1.3, more preferably 0.8 thereof<x<1.1, having a skeletal density of greater than 88%, preferably greater than 90%, particularly preferably greater than 92%, of the theoretical density. Framework densities of up to 94% and higher of the theoretical density of the (dense) anode material can also be achieved according to the invention. In the anode body of the invention, the cumulative volume of the closed pores is less than 12%, preferably less than 10%, particularly preferably less than 8% of the volume of the (compact) anode material.

In the context of the present invention, valve metal is understood to mean a metal from the group of niobium, tantalum and titanium.

The agglomerate powder according to the invention preferably consists of sintered primary particles having an average cross-sectional dimension determined by electron micrographs of 0.1 to 2 μm, an agglomerate size according to ASTM B822 ("Mastersizer", Daxad 11 wetting agent) D10 of 3 to 50 μm, D50 of 20 to 200 μm, D90 of 30 to 400 μm. The agglomerate powder particles may have any suitable shape, such as spherical, distorted spherical, fiber, flake, irregular, etc., with spherical agglomerate powder particles being preferred, all of the forms described having low closed pore volumes. The agglomerate powder has a good flowability (according to Hall, ASTM B213) of less than 60sec/25 g. In the case of niobium suboxide and niobium metal powders, the bulk density (according to Scott, ASTM B329) may advantageously be between 0.7 and 1.3g/cm³In the case of tantalum metal powder, 1.0 to 2.5g/cm³. The specific surface area ("BET", ASTM D3663) may advantageously be between 0.5 and 20m²(ii) in terms of/g. The agglomerate powder according to the invention preferably has a porosity (open pores) determined by mercurous, of 50 to 70% by volume, over 90% of the pore volume being formed by pores with a diameter of 0.1 to 5 μm.

The content of other impurities than conventional dopants (e.g. nitrogen, phosphorus and/or vanadium) should be as low as possible. Particularly preferred powders have a Fe, Cr, Ni, Cu content of less than 20ppm, an alkali metal content and a fluoride (fluorind) and chloride (chloride) content of less than 50ppm, respectively. The carbon content is preferably less than 40 ppm. The nitrogen content is advantageously from 10 to 6000 ppm. The phosphorus content of the niobium suboxide powder of the invention is generally not detrimental. In niobium and tantalum metal powders, no more than 500ppm of phosphorus is used to reduce the sintering activity during the creation of the secondary and anode structures. Optionally, the powder is treated with phosphoric acid, ammonium hydrogen phosphate or ammonium phosphate prior to sintering of the anode structure. Other, but less critical, impurities Al, B, Ca, Mn and Ti are preferably less than 10ppm, and Si less than 20 ppm.

The agglomerate powder of the invention is also characterized by an increase in the compaction coefficient α and an increase in the sliding coefficient η compared to the powders of the prior art, which results in a better compactibility of the powder. Preferably, in the case of the niobium suboxide powder of the invention, m is²The product of BET surface area and slip coefficient expressed in/g is from 0.33 to 0.75, preferably from 0.45 to 0.58, in the case of the tantalum powder of the invention from 0.62 to 0.95, preferably from 0.65 to 0.86, in the case of the niobium powder of the invention from 0.38 to 0.8, preferably from 0.42 to 0.6. The compaction factor of the agglomerate powder of the invention is preferably greater than 0.07 for niobium suboxide powders and greater than 0.08 for niobium and tantalum powders.

The invention also provides niobium suboxide agglomerate powders which are compacted to 2.8g/cm³And after sintering at a temperature of more than 1340 c, preferably more than 1400 c, for 20 minutes, anode bodies having a skeleton density of more than 88%, preferably more than 90%, particularly preferably more than 92% can be produced therefrom.

Further, the invention provides tantalum agglomerate powders, when pressed to greater than 5g/cm³And after sintering at a temperature of 1250 ℃ or more for 20 minutes, anode bodies having a skeleton density of more than 88%, preferably more than 90%, particularly preferably more than 92% can be produced therefrom.

The invention also provides niobium agglomerate powder, pressed to 3.14g/cm³Has a pressed density of 1165 deg.C or more, preferably 1165 deg.C or moreAfter sintering at 1180 ℃ for 20 minutes, anode bodies having a skeleton density of more than 88% can be produced therefrom.

The invention also provides a process for preparing valve metal and/or valve metal suboxide agglomerate powders, characterized in that precursor particles of the agglomerate powder are mixed with a finely divided pore former, pore-rich, adhesively bonded agglomerates of the precursor particles are obtained by compacting the polymer (Verdichten) and evaporating or decomposing the pore former, the adhesively bonded agglomerates are subjected to a heat treatment at a temperature and for a duration sufficient to form a sinter bridge (Sinterberg ü ck), and the at least partially sintered agglomerates are further processed in a manner known per se to valve metal and/or valve metal oxide agglomerate powders.

The mixture can be dry compacted (Verdichtung) by pressing the mixture under pressure (Kompaktierung) or wet compacted by slurrying the mixture, for example in water, thickening the slurry by means of ultrasound, decanting the supernatant and drying.

Preference is given to preparing tantalum, niobium and/or NbO_xOf niobium suboxide agglomerates, wherein 0.7<x<1.3, preferably 0.8<x<1.1。

The precursor particles used according to the invention are preferably primary particles of valve metal, in particular niobium and/or tantalum, and/or oxides thereof, in particular pentoxide of niobium and/or tantalum, or secondary particles formed from only a few (wenig) primary particles, the average primary particle size in the direction of the smallest dimension being less than 1 μm, more preferably less than 0.5 μm, particularly preferably less than 0.3 μm. The particles may have any suitable shape. The precursor particles preferably have a particle size of more than 80m²A specific preference for a molar mass of more than 100m²Specific surface area in g.

Particularly preferably, the precursor particles used are hydroxides or hydrated pentaoxides obtained in the precipitation with ammonia from aqueous solutions of niobium fluoride and/or tantalum fluoride, which still have a sufficient water content of 25 to 35% by weight and a water content of more than 180 (in the case of Nb) or 100m²Specific surface area in g (in the case of Ta).

Preferred pore formers are ammonium salts, such as halides, carbonates or oxalates. Particular preference is given to using ammonium chloride and/or ammonium oxalate.

The pore former is preferably used in an average particle size of 0.5 to 20 μm, preferably 1.0 to 10 μm, particularly preferably 1.5 to 5 μm, and in an amount of 10 to 90 vol.%, preferably 15 to 60 vol.%, more preferably 20 to 50 vol.%, particularly preferably 30 to 45 vol.%, based on the volume of the precursor particles.

In the case of wet compaction, the precursor particles are preferably slurried with water. Other readily evaporable organic liquids with good wetting properties, such as methanol, alcohols, ketones and/or esters and mixtures thereof with water, are likewise suitable.

By slurrying the precursor particles, the finely divided pore former is vigorously mixed. The mixture is then compacted by shaking, preferably by ultrasound. The supernatant is optionally removed to form a moist mass.

The moist mass consisting of the mixture of precursor particles and pore former particles is then dried by slow heating in a transport gas stream to a temperature of at most 150 c, and the pore former is completely removed from the mass by further slow heating to 350-600 c.

Alternatively, after intensive dry mixing, the precursor particles comprising the finely divided pore former can be compacted at a pressure of 30-100 bar and the pore former can then be removed, suitably by heating.

After optional crushing and sieving, the dry mass, comprised of the adhesively bonded precursor particles, is heated to a temperature sufficient to form sinter bridges to form a sintered open pore precursor agglomerate powder having a high pore volume, which is substantially free of closed pores.

The sinter precursor agglomerate powder is further processed in a manner known per se as described below to obtain the valve metal and/or valve metal suboxide agglomerate powder.

The invention further provides a process for the preparation of valve metal and/or valve metal oxide agglomerate powder, characterized in that precursor particles of the agglomerate powder are slurried in hydrogen peroxide or water containing carbon dioxide, the water is removed by drying to release oxygen or carbon dioxide to obtain pore-rich, adhesively bonded agglomerates of the precursor particles, the adhesively bonded agglomerates are subjected to a heat treatment at a temperature and for a duration sufficient to form sinter bridges, and the at least partially sintered agglomerates are further processed in a manner known per se to valve metal and/or valve metal oxide agglomerate powder.

During the drying of the slurry, water is removed therefrom, while the hydrogen peroxide decomposes to release oxygen or exceed the solubility limit of the carbon dioxide in the remaining water. The finely divided precursor particles in the slurry act as gas-releasing bubble nuclei (Bl ä schenkeim). As long as sufficient moisture is still present, the bubbles cannot escape from the slurry or accumulate as large bubbles to form an open pore block with a large pore volume. The size of the pores formed by the bubbles and the pore volume of the block can be controlled by the amount of carbon dioxide or hydrogen peroxide initially dissolved.

In the case of using carbon dioxide as a pore former, the slurry can also be prepared as follows: dispersing the precursor particles in water under a carbon dioxide atmosphere or by stirring the preferably used hydroxide or hydrated pentoxide (as obtained in the precipitation with ammonia from aqueous solutions of niobium fluoride and/or tantalum fluoride) under carbon dioxide atmosphere, optionally under pressure, which still has a sufficient water content of 25-35% by weight and a water content of more than 100m²Specific surface area in g.

To completely remove the water, the resulting dry block was heated to a temperature of 100-500 ℃.

Optionally after crushing and sieving, the dry mass comprised of the adhesively bonded precursor particles is heated to a temperature sufficient to form sinter bridges to form a sintered open-cell precursor agglomerate powder that is substantially free of closed pores.

When the precursor powder used is niobium and/or tantalum metal powder, the sintered precursor agglomerate powder resulting therefrom is deoxidized by mixing with magnesium chips and heating in an oxygen-free atmosphere or under high vacuum and then ground to the desired agglomerate size.

Optionally, doping with nitrogen and/or phosphorus and/or vanadium can be achieved by impregnation with a solution of a nitrogen and/or phosphorus and/or vanadium containing compound prior to deoxygenation, in a manner known per se.

When the precursor powder used is a pentoxide, which is reduced in a manner known per se in accordance with WO 00/67936, in the case of niobium pentoxide it is preferably first reduced to a dioxide by heating in a hydrogen-containing atmosphere, reduced to the metal with gaseous magnesium and optionally doped.

For preparing NbO having x defined above_xPowders starting from the above-mentioned pentoxide precursor agglomerate powder. Optionally after hydrogen reduction to dioxide, the pentoxide precursor agglomerate powder is intimately mixed with a stoichiometric amount of the corresponding finely divided niobium metal powder and heated in a hydrogen-containing atmosphere so that there is an exchange of oxygen between the oxide and the metal. The finely divided niobium metal powder used is preferably a niobium metal precursor agglomerate powder obtained according to the present invention.

According to another preferred method, the pentoxide precursor agglomerate powder together with the niobium metal powder is again mixed with a pore former, compacted, optionally after hydrogen reduction, the pore former is removed, optionally sieved, and the adhesively bonded powder mixture agglomerates are heated in a hydrogen atmosphere so that the oxygen equilibrium is achieved.

The niobium suboxide, niobium metal and tantalum metal powder of the invention is suitable for the preparation of solid electrolyte capacitors by conventional methods with a specific capacitance of 20000-plus 300000 μ FV/g and a very low residual current (Reststr) of less than 1nA/μ FV, preferably less than 0.2nA/μ FV.

Wherein, for the preparation of the anode body, the powder is arranged around a press moldMedium niobium or tantalum wire and pressing in the presence of a binder and a lubricant up to 2.3-3.5 g/cm in the case of niobium or niobium suboxide powders³Or 4.5-7g/cm in the case of tantalum powder³To obtain a green body, wherein a green body with a very advantageous compressive strength is obtained. The compact containing the contact line is then preferably placed in a niobium or tantalum boat at 1000-1500 ℃ at 10^-8Sintering under high vacuum of bar for a sintering time of 10-25 minutes. The sintering temperature and sintering time are preferably chosen such that the capacitor surface area, which can subsequently be calculated from the capacitance of the capacitor, has 65-45% of the specific surface determined for the powder.

Further, the present invention provides a capacitor comprising a valve metal and/or valve metal suboxide sintered capacitor anode body. The capacitor of the present invention can be used in various electrical devices.

Example (b):

A) preparation of precursor particles

V1: 75 l/H of H with an Nb concentration of 81 g/l₂NbF₇Aqueous solution and 75 l/h of 9% NH₃The aqueous solution was continuously added to 100 l of deionized water previously charged for 15 hours so that the pH was 7.6. + -. 0.4. The temperature of the solution was maintained at 63 ℃. The resulting suspension was filtered through a pressure suction filter using 3% NH₃Washed with aqueous solution and then with deionized water. The resulting wet niobium (V) hydroxide was dried in a drying oven at 100 ℃ for 24 hours. The niobium (V) hydroxide obtained had a value of 201m²Specific surface area in g and spherical morphology.

V2: 40 parts by volume of deionized water was added to 100 parts by volume of the niobium (V) ethoxide solution with stirring. The precipitated niobium (V) hydroxide (niobic acid) was filtered off through a suction filter and washed with deionized water. Then, the niobium (V) hydroxide was dried at 100 ℃ for 17 hours. The powder has a particle size of 130g/m²Specific surface area and irregular morphology.

V3: will be ahead ofThe bulk particles V1 were calcined in air at 500 ℃ for 4 hours and then ground in a jet mill to D90<10 μm (Mastersizer without sonication). Obtaining a solution having a thickness of 89m²Nb/g specific surface area₂O₅。

V4: 75 l/H of H with a Ta concentration of 155.7 g/l₂TaF₇Aqueous solution and 75 l/h of 9% NH₃The aqueous solution was continuously transferred to 100 l of deionized water previously charged for 30 hours, so that the pH of the solution was maintained at 7.6. + -. 0.4 and the temperature was maintained at 69 ℃ during the course of the reaction. After removal by filtration with 3% NH₃After washing with aqueous solution and deionized water, drying at 100 ℃ for 24 hours, a solid having a particle size of 106m is obtained²Specific surface area in g and spherical morphology of tantalum (V) hydroxide.

V5: the precursor particles V4 were calcined in air at 500 ℃ for 2 hours and ground in a jet mill to D90<10 μm. Obtained to have a thickness of 83m²Ta of specific surface area/g₂O₅And (3) powder.

B) Preparation of sintered agglomerate pentoxide powder (P1-P14)

To prepare the sintered pentoxide powders P1-P14, the precursors given in column 1 of Table 1 were used.

The precursor was mixed with a pore former having an average particle size of 1.5 μm in aqueous suspension (wet in column 4) or dry (dry in column 4) in the amounts given in column 2 of column 3 of table 1 (wt% based on the pentoxide). In the case of wet mixing, the suspension of the precipitated solid mixture was thickened by ultrasound, the clear overhead water was decanted and dried at 110 ℃ for 15 hours. In the case of dry mixing, the dry powder mixture was compacted at 75 bar for more than 1 minute using a laboratory hydraulic press (die diameter 5cm, fill height 3 cm).

Table 1:

then, to decompose the pore former, the dried (cohesive agglomerates) or compressed (green compact) powder mixture is heated to the temperature given in column 5 of table 1 for the time also given here. And then sintered in air at the temperature and duration given in column 6.

The sintered agglomerates were crushed with a jaw crusher, ground with a ball mill and sieved to <300 μm.

C) Preparation of Metal powder (M1-M14)

In the case of niobium pentoxide, after reduction to niobium dioxide by hydrogen at 1300 ℃, the pentoxide powder P1-P14 was converted to metal powder M1-M14 by reduction with magnesium vapour at 900 ℃ for 6 hours under argon as transport gas, cooling, passivation, sieving to less than 300 μ M, removal of magnesium oxide by 8% sulphuric acid and washing to neutrality with deionized water. Table 2 reports BET surface area, D50 values according to Mastersizer (without sonication), and iron, chromium and nickel; fluorine and chlorine; and a summary of the impurity levels of sodium and potassium.

Table 2:

powder of	M1	M2	M3	M4	M5	M6	M7	M8	M9	M10	M11	M12	M13	M14
															BET, m2/g	6.5	6.7	5.7	5.6	5.5	5.4	8.1	7.8	4.8	4.4	6.2	5.9	5.3	5.4
Fe+Cr+Ni, ppm	8	9	5	8	10	11	8	6	9	7	10	5	4	7
															F+Cl, ppm	<5	6	<5	6	5	<5	9	<5	<5	<5	9	<5	8	<5
Na+K, ppm	<3	<3	<3	4	<3	<3	<3	<3	<3	3	<3	<3	<3	<3
															D50, µm	41	39	162	159	169	172	123	110	37	32	68	73	143	154

D) Preparation of niobium suboxide powder (S1-S10)

To prepare the niobium suboxide powders, the niobium pentoxide given in column 1 of table 3 was in each case dry-mixed with three times the stoichiometric amount of the niobium metal given in column 2 of table 3 and the pore-forming agent given in column 3 (20% by weight based on metal and pentoxide), compacted at 75 bar and heat-treated at 600 ℃ for 3 hours to remove the pore-forming agent.

The dry block was then heated in a hydrogen atmosphere to the reaction temperature given in table 3 for 4 hours, cooled, passivated and sieved to <300 μm. Table 6 reports BET surface area, D50 values according to Mastersizer (without sonication), and iron, chromium and nickel; fluorine and chlorine; and a summary of the impurity levels of sodium and potassium. Additionally reported are the compaction coefficient α and the slip coefficient η, as defined further below, and the product of the slip coefficient η and the BET surface area.

Table 3:

fence (pen)	1	2	3	4
					Suboxide	Pentoxide compound	Metal	Pore-forming agent	Reaction temperature C
S1	P3	M3	NH4Cl	1050
					S2	P3	M3	NH4Cl	1250
S3	P3	M3	NH4Cl	1400
					S4	P3	M3	NH4Cl	1500
S5	P3	M3	-	1400
					S6	P4	M4	NH4Cl	1400
S7	P4	M4	-	1400
					S8	P3	M2	NH4Cl	1400
S9	P1	M1	NH4Cl	1400
					S10	P2	M2	-	1400

E) Preparation of deoxidized Metal agglomerate powder (D1-D14)

For deoxidation, powders M1-M8 and M10-M14 were each admixed with 8% by weight (niobium metal powder) or 5% by weight (tantalum metal powder) of magnesium chips and NH in an amount sufficient to dope them with 100ppm of phosphorus₄H₂PO₄The solutions were mixed and heated to 850 ℃ under argon for 2 hours, cooled and passivated, sieved to<300 mu m. Two samples of powder M9 were deoxygenated at 850 and 750 ℃ and hereinafter referred to as M9a and M9 b. Tables 4 and 5 report BET surface area, D50 values according to Mastersizer (without sonication), and iron, chromium and nickel; fluorine and chlorine; and sodium and potassium. Additionally reported are the compaction coefficient α and the slip coefficient η, as defined further below, and the product of the slip coefficient η and the BET surface area.

F) Preparation of the Anode body

The deoxidized metal powders D1 to D14 and the niobium suboxide powders S1 to S8 were pressed around a tantalum wire of thickness 0.3mm placed in a press mold to the values given in tables 4, 5 and 6 in g/cm³The density was measured and the anode body was pressed to a diameter of 3.6mm and a length of 3.6mm, and then sintered under high vacuum at the temperature in deg.c given in the table for 20 minutes.

Table 4:

table 5:

table 6:

the compaction coefficient α (density α) and the slip coefficient η were determined in Powder test center model PTC-03DT from KZK Powder Tech corp.

The compaction factor is determined by: the powder (without binder or lubricant) is introduced into a die with a diameter D = 12.7 mm, pressed with a punch to a height H =12.694 mm, in which pressing the pressure p on the punch is determined_c. A typical graph showing the relationship between density and pressing pressure for niobium suboxide samples is given in fig. 1.

The compaction factor α is determined by the following equation:

｜log｜log ρ_ra｜｜ =α log ((p_r+p₀)/p₀) + ｜log｜log ρ_rp｜｜，

where ρ is_rpIs the tap density, p, of the powder_raIs at a pressure p_rAverage density of the compact after downward compression, p₀Is the gravitational pressure on the powder (weight of powder divided by the cross-sectional area of the die).

In order to determine the slip coefficient, it was additionally determined that the slip coefficient reached 4.8g/cm in the case of tantalum³In the case of niobium, 3.14g/cm³And up to 2.8g/cm in the case of niobium suboxide³Pressure p of the bottom of the mold at the time of pressing density of_d. The slip coefficient η is determined by the following equation:

p_d/p_c = η^SH/4F，

wherein S is the cross-sectional perimeter π D, and F is the cross-sectional area π D²/4。

Claims (11)

1. Niobium suboxide agglomerate powder in m²The product of BET surface area expressed in/g and slip coefficient eta is 0.33 to 0.75, preferably 0.45 to 0.58.

2. Niobium suboxide agglomerate powder having a compaction factor greater than 0.07.

3. Process for the preparation of valve metal and/or valve metal oxide agglomerate powders suitable for the preparation of sintered capacitor anode bodies, characterized in that precursor particles of the agglomerate powder are mixed with a finely divided pore former, pore-rich, adhesively bonded agglomerates of the precursor particles are obtained by compaction, the pore former is removed thermally, the adhesively bonded agglomerates are subjected to a heat treatment at a temperature and for a duration sufficient to form a sinter bridge, and the at least partially sintered agglomerates are further processed in a manner known per se to valve metal and/or valve metal suboxide agglomerate powders.

4. A method according to claim 3, characterized in that the pore former used is an ammonium salt having an evaporation, sublimation or decomposition temperature of less than 600 ℃.

5. A process according to claim 4, characterized in that the pore former used is finely divided ammonium chloride and/or ammonium oxalate.

6. The method according to any one of claims 3 to 5, characterized in that the pore former is used in an amount of 10 to 90% by volume, based on the volume of the precursor compound.

7. Process for the preparation of valve metal and/or valve metal suboxide agglomerate powder suitable for the preparation of sintered capacitor anode bodies, characterized in that precursor particles of the agglomerate powder are slurried in hydrogen peroxide or water containing carbon dioxide, the water is removed by drying to release oxygen or carbon dioxide to obtain pore-rich, adhesively bonded agglomerates of the precursor particles, the adhesively bonded agglomerates are subjected to a heat treatment at a temperature and for a duration sufficient to form a sinter bridge, and the at least partially sintered agglomerates are further processed in a manner known per se to valve metal and/or valve metal oxide agglomerate powder.

8. A method according to any of claims 3-7, characterized in that the precursor particles have a size of more than 80m²A/g, preferably greater than 100m²Specific surface area in g.

9. Capacitor anode made by pressing and sintering the agglomerate powder according to any of claims 1-2.

10. A capacitor comprising the capacitor anode of claim 9.

11. Use of the capacitor of claim 10 in an electrical device.