CN1308566A - Metal powders produced by the reduction of the oxides with gaseous magnesium - Google Patents

Abstract

Metal powder from the group Ta, Nb, Ti, Mo, W, V, Zr, Hf preferrably Ta or Nb, is made in a fine powder form by reduction of metal oxide by contact with a gaseous reducing agent, preferrably an alkaline earth metal, to near complete reduction, leaching, further deoxidation and agglomeration, the powder so produced being sinterable to capacitor anode form and processable to other usages.

Description

Metal powder produced by reduction of oxides of interest with gaseous magnesium

Field and background of the invention

The present invention relates to the production of tantalum, niobium and other metal powders and their alloys by reducing the corresponding metal oxides with gaseous reactive metals such as Mg, Ca and other elements and compounds in gaseous form.

Tantalum and niobium are metals of the same group which are difficult to separate in the free state, because their compounds are very stable, in particular their oxides. Reviewing the process of preparing tantalum studied in the past will suffice to illustrate the history of typical preparation processes for these metals. In the beginning of the twentieth century, potassium heptafluorotantalate (K) was prepared by reducing a double salt with sodium₂TaF₇) Tantalum metal powder was first prepared on a commercial scale in germany. The small pieces of sodium and tantalum containing salt were mixed and encapsulated in a steel tube. The top of the steel tube was heated with a ring flame lamp and after ignition, the reduction reaction proceeded rapidly down the tube. Cooling the reaction mixture andremoving unreacted K from the tantalum metal powder with a chisel₂TaF₇And sodium and other reaction products. The mixture is crushed and then leached with dilute acid to separate the tantalum from the components. Although this process is difficult to control, dangerous, and produces coarse and contaminated powders, it is nevertheless a major process for the subsequent production of high purity tantalumAnd (4) direction.

The united states began the commercial production of tantalum metal in the thirties of the twentieth century. Electrolyzing a liquid containing tantalum oxide (Ta) in a steel retort at 700 deg.C₂O₅) K of₂TaF₇The mixture is melted. When the reduction reaction is complete, the system is cooled and the solids are removed from the cell and then crushed and leached to separate the crude tantalum powder from the other reaction products. The dendritic powder is not suitable for direct application in capacitors.

In the late fifties of the twentieth century, Hellier and Martin developed modern processes for the production of tantalum (Hellier, e.g. and Martin, g.l., us patent 2950185, 1960). According to the Hellier and Martin processes, and the hundreds to thousands of devices or variations described later, a K is reduced with molten sodium in a stirred reactor₂TaF₇And a dilute salt, typically NaCl. Important reaction variables such as reaction temperature, reaction rate and reaction composition can be controlled by using the system. After many years, the process has improved and can produce surface areas in excess of 20,000cm²High quality powder/g, the surface area of the material is generally in the range from 5000-²(ii) in terms of/g. The preparation method still requires taking the solid reaction product out of the retort,the tantalum powder is separated from the salt by leaching and treated like sinteringto improve the physical properties. Most capacitor grade tantalum powders are also deoxidized with magnesium to reduce the oxygen content (Albrecht, w.w., Hoppe, h., Papp, v. and Wolf, r., us patent 4537641, 1985). It is also known today to pre-sinter primary particles into secondary particle form and incorporate certain substances to increase the capacitance (e.g. P, N, Si and C).

Although according to Ullmann's Encyclopedia of Industrial chemistry, 5^thEdition, Volume A26, p.80, 1993, reduction of K with sodium₂TaF₇To industrially produce high-performance, high-quality tantalum powder, and the consumption of tantalum for capacitors has reached 50% of the annual worldwide tantalum production of about 1000 tons, even though the raw material basis for niobium is much larger than tantalum, andpublications on powder preparation and capacitor production methods mention niobium and tantalum at the same time, and niobium has also been largely unused in capacitors.

Some of the difficulties in applying the above method to niobium are as follows:

although the type of preparation listed in Hellier and Martin (U.S. Pat. No. 2,950,185), i.e. the reduction of potassium heptafluorotantalate with sodium in a salt melt, is in principle useful for preparing high purity niobium powders from potassium heptafluoroniobate, it is not feasible in practice. Partly because of the difficulty of precipitating the corresponding heptafluoroniobium salts and partly because of the aggressive reactivity and corrosive nature of these salts, the niobium obtained by the above process is very impure. In addition, niobium oxide is generally unstable. See, e.g., N.F. Jackson et al, Electrical component Science and Technology, Vol.1, pp.27-37 (1974).

Niobium is therefore used only very sparingly in the capacitor industry and mainly where the quality requirements are low.

But niobium oxide has a dielectric constant about 1.5 times that of a tantalum oxide-like layer, and the capacitance of a niobium capacitor should be larger in principle, considering stability and other factors.

In the case of tantalum itself, although K₂TaF₇the/Na reduction process is successful, but there are still a number of disadvantages to this process.

The above method is a batch method in which there is inherent variability of conditions in the system; therefore, it is difficult to maintain consistency from batch to batch. The post-reduction processing (mechanical and pyrometallurgical separation, filtration) is complex, requires considerable manpower and capital, and is time consuming. Disposal of large amounts of reaction products containing fluoride and chloride is also a problem. Most importantly, the process has been developed to a mature stage with limited prospects for significant improvements in the properties of the tantalum powders produced.

Over the years, numerous attempts have been made to investigate alternative methods of reducing tantalum and similar metal compounds, including niobium compounds, to the metallic state (Miller, G.L. "tantalum and niobium", London, 1959, pp.188-94; Marden, J.W. and Rich, M.H., U.S. Pat. Nos. 1728941, 1927; and Gardner 686D., U.S. Pat. Nos. 2513, 1946; Hurd, U.S. Pat. No. 4687632). The above method uses active metals such as calcium, magnesium and aluminum instead of sodium, and uses raw materials such as tantalum pentoxide and tantalum chloride. As can be seen from Table 1 below, the negative Gibbs free energy change indicates that reactions are feasible to reduce tantalum, niobium and other metal oxides to the metallic state with magnesium; the reaction rate and reaction method established that this method can be used to produce high quality powders on a commercial scale. To date, none of these methods has been commercialized to a large extent because they have not produced high quality powders. It is obvious that these methods have failed in the past because they are carried out by mixing a reducing agent with a metal oxide to perform a reduction reaction. The reaction is carried out in contact with the molten reducing agent and under conditions where the highly exothermic reaction temperature cannot be controlled. Therefore, the morphology of the product and the content of residual reduced metal cannot be controlled.

TABLE 1

Gibbs free energy change by magnesium reduction of metal oxides

Temperature, C	Gibbs free energy change (kilocalories/mole oxide)
								Ta2O5	Nb2O5	TiO2	V2O3	ZrO2	WO2
200	-219	-254	-58	-133	-22	-143
							400	-215	-249	-56	-130	-21	-141
600	-210	-244	-55	-126	-20	-139
							800	-202	-237	-52	-122	-18	-137
1000	-195	-229	-50	-116	-15	-134
							1200	-186	-221	-47	-111	-13	-131
1400	-178	-212	-45	-106	-11	-128

The use of magnesium to deoxidize or reduce the oxygen content of tantalum metal is well known. The method includes mixing metal powder with 2-3% magnesium and heating to complete the reduction process. The magnesium is molten during heating. The objective in this case is to remove 1000-. However, when a larger amount of tantalum oxide is reduced, a larger amount of magnesium oxide is generated. Under conditions of poor temperature control, the resulting mixture of magnesium, tantalum oxide and magnesium oxide can form tantalum-magnesium-oxygen complexes that are difficult to separate from tantalum metal.

It is a primary object of the present invention to provide a novel method for producing high performance, capacitor grade tantalum and niobium powders that eliminates one or more, and preferably all, of the problems of conventional double salt reduction and post processing.

It is a further object of the present invention to make a continuous preparation process possible.

It is a further object of the present invention to provide improved metal morphology.

It is another object of the present invention to provide niobium/tantalum alloy powders of capacitor grade quality and morphology.

Summary of The Invention

We have found that when a large amount of metal oxide, such as Ta₂O₅、Nb₂O₅And its suboxides, are substantially or preferably completely reduced by magnesium in gaseous form, the problems of the prior art are eliminated. The oxide source should be substantially or preferably completely solid. The oxide is provided in the form of a porous solid with numerous access passages for the gaseous reducing agent.

The single or multiple (co-produced) metals that can be effectively produced by the present invention are Ta, Nb and Ta/Nb alloys, either alone or further including added or co-produced Ti, Mo, V, W, Hf and/or Zr. These metals may also be mixed or fused during or after preparation, and/or form useful compounds of these metals. Various stable and unstable oxide forms of these metals can be used as sources. The metal alloy may be prepared by fusing oxide precursors, for example by co-precipitating suitable precursors of the oxides.

The vapor pressures of some of the reducing agents are listed below:

temperature (. degree.C.)	Aluminum pressure (atmospheric pressure)
		2,000	53.×10-2
2,100	1.0×10-1
		2,200	1.9×10-1
2,300	3.3×10-1
		2,400	5.6×10-1
2,500	9.0×10-1
		2,600	1.4

Temperature (. degree.C.)	Magnesium pressure (atmospheric pressure)
		800	4.7×10-2
850	8.9×10-2
		900	1.6×10-1
950	2.7×10-1
		1000	4.8×10-1
1050	7.2×10-1
		1100	1.1

Temperature (. degree.C.)	Calcium pressure (atmospheric pressure)
		1,000	1.7×10-2
1,100	5.1×10-2
		1,200	1.3×10-1
1,300	2.9×10-1
		1,400	6.0×10-1
1,500	1.1

Temperature (. degree.C.)	Lithium pressure (atmospheric pressure)
		1,000	5.1×10-2
1,100	1.4×10-1
		1,200	3.8×10-1
1,300	7.2×10-1
		1,400	1.4

The reduction temperature varies greatly depending on the reducing agent used. The reduction temperature range of the (Ta, Nb) oxide is: mg (magnesium)_(gas)-800-1,100℃，Al_(gas)-1,100-1,500℃，Li_(gas)-1,000-1,400℃，Ba_(gas)-1,300-1,900℃。

Within the effective reduction range, metal powder with different physical properties and forms can be prepared by reduction through changing the temperature and other processing conditions.

One embodiment of the present invention comprises: the first step is to reduce an oxide source of the selected metal, releasing substantially 80-100% by weight of the metal as primary powder particles; followed by a further step of leaching or hydrometallurgical separation of the metal from residual reductant oxide and other by-products of the reduction reaction, and from residual concentrated reductant (optionally); followed by one or more deoxidation steps at a concentration of reactants lower than that of the first total reduction step (and of the reducing agent in the molten state with better tolerance); further separation can then be carried out as desired.

A first embodiment of the present invention provides a one-step reduction method for preparing the above metal powder, comprising the steps of:

(a) providing an oxide or mixed oxide of the metal, the oxide itself being in a form that is permeable to gases,

(b) producing a gaseous reducing agent outside the oxide, and passing the gas through the oxide at an elevated temperature,

(c) the reactants, the porosity of the oxide, and the temperature and time of the reduction reaction are selected to substantially complete the reduction reaction of the oxide to release the metal portion thereof, and the residual oxide of the reducing agent formed during the reaction can be readily removed.

Thus, a high surface area flowable metal powder is formed in a process for preparing metal or alloy powders that substantially avoids the use of molten reducing agents.

In the reduction method of the first embodiment, the reducing agent used is preferably Mg, Ca and/or a hydride thereof. Mg is particularly preferred.

Preferably, Nb and/or Ta metals are prepared, optionally alloyed with each other and/or with doping elements selected from Ti, Mo, W, Hf, V and Zr.

A second embodiment of the present invention provides a two-step reduction process comprising the steps of:

(a) providing an oxide or mixed oxide of the metal, the oxide being in a form that is permeable to gases,

(b) passing a hydrogen-containing gas through the oxide, alone or with a gaseous diluent, at an elevated temperature in a manner to partially reduce the oxide,

(c) the porosity of the oxide, the temperature and time of the reduction reaction are selected to remove at least 20% of the oxygen contained in the oxide to obtain a suboxide,

(d) the suboxide is reduced by the reducing metal and/or one or more hydrides of the reducing metal to substantially completely reduce the oxide, releasing the metal portion therefrom.

Preferably, the reducing metal and/or metal hydride is contacted with the suboxide in gaseous form.

In the second reduction step of the second embodiment, the preferred reducing metal is Mg and/or Ca and/or their hydrides. Mg is particularly preferred.

The preferred reduction temperature (for Mg) is 850 ℃ to the conventional boiling point (1150 ℃).

In particular, the methods of the present invention (two embodiments) have been developed to provide capacitor grade tantalum, niobium, tantalum-niobium alloy powders and Ta/Nb materials, or for applications requiring the same purity and/or morphology. The largest gap in the state of the art is partially filled by the capacitor grade niobium produced by the present invention, and a portion of the tantalum process is enhanced accordingly. In all cases, the tantalum and/or niobium may be strengthened by fusing or blending other materials during or after the reduction reaction to produce tantalum/niobium. One of the requirements for these powders is to approximate a sphereA high specific surface area pre-sintered agglomerate structure of shaped primary particles which, after pressing and sintering, form an inherently porous body with interconnected pore systems of gradually narrowing diameter, an electrolyte for anodization and a manganese nitrate solution [ Mn (NO) for manganization]being formed₃)₂]It is easy to enter.

The reduction of the oxide with a gaseous reducing agent, at least in the initial reduction phase, allows easy control of the reduction temperature and avoids excessive presintering. Furthermore, in contrast to prior art methods of reducing metals using liquids, controlled reduction reactions using gaseous reducing metals do not contaminate the reduced metal by incorporation of the reducing metal into the reduced metal lattice. It has been found that this contamination occurs predominantly (in the case of Nb) from Nb₂O₅To NbO₂During the initial reduction process. This seems unexpected at first, since niobium dioxide (NbO)₂) Containing oxygen only in proportion to niobium pentoxide (NbO)_2.5) Less than 20 percent. This effect was explored because the suboxides formed a much denser crystal lattice than the pentoxide. NbO_2.5Has a density of 4.47g/cm³And NbO₂Has a density of 7.28g/cm³I.e., removal of only 20% of the oxygen, the density can be increased by a factor of 1.6. Considering the different atomic weights of niobium and oxygen, NbO_2.5Reduction to NbO₂The volume can be reduced by 42%. The applicant therefore believes (without limiting the scope of the invention) that the effect of the invention may be explained by the fact that, during the reduction of the pentoxide, the magnesium in contact with the oxide may diffuse relatively easily into the lattice and has a high activity, but the mobility of the magnesium in the lower oxide lattice is significantly reduced. Thus, during the reduction of the suboxide, magnesium substantially remains on the surface and readily reacts with the scrubbing acid.

This is even suitable in the case of controlled reduction reactions with gaseous magnesium. It is evident that in this case, too, during the initial reduction to the suboxide, the reduction reaction takes place only at the oxide surface, and the magnesium oxide formed during the reduction does not enter the oxide or suboxide powder. The preferred temperature during the reduction with magnesium gas is 900-1100 deg.C, and particularly preferred is 900-1000 deg.C.

After removal of at least 20% of the oxygen, the temperature may be increased up to 1200 ℃ to improve the pre-sintering.

The reduction of the pentoxide with hydrogen produces a suboxide which has been sintered into a sintered mass with stable sintering bridges and which has an advantageous structure to be used as a capacitor material.

The lower the temperature, the longer the reduction time is required. In addition, by selecting the reduction temperature and the reduction time, the degree of sintering of the produced metal powder can be adjusted in a predetermined manner. Preferably the reactor is lined with molybdenum sheets or with a ceramic that is not reduced by hydrogen to prevent contamination.

In addition, the reduction time and the reduction temperature may be selected to remove at least 20% of the oxygen from the pentoxide. A higher degree of reduction is harmless. However, the reduced oxygen is generally unlikely to exceed 60% over the operable time range and at acceptable temperatures.

After the degree of reduction reaches 20% or more, suboxides are produced. According to this method embodiment, the reduced product is preferably maintained (annealed) at 1000 ℃ for a period of time, most preferably about 60-360 minutes. This appears to allow the formation and stabilization of new, dense crystal structures. Since the reduction rate decreases very much with the degree of reduction, it is necessary to heat the suboxide in the presence of hydrogen and at the reduction temperature, optionally with a slight decrease in temperature. Typically, sufficient reduction and annealing times are in the range of 1100-1500 deg.C for 2-6 hours. In addition, the reduction with hydrogen has the advantage that impurities which are critical for capacitor applications, such as F, Cl and C, are reduced to less than 10ppm, preferably less than 2 ppm.

The suboxide is then cooled to room temperature (<100 ℃) in a reduction apparatus, the suboxide is then mixed with the finely ground reduced metal or metal hydride powder, and the mixture is heated to the reduction temperature of the second step under an inert gas. Preferably, the amount of reducing metal or metal hydride is stoichiometric with the residual oxygen of the acid earth metal suboxide, most preferably slightly greater than stoichiometric.

A particularly preferred operating step comprises: the second step is carried out in the same reactor using a stirred bed in the first step and without intermediate cooling, with addition of the reducing metal or metal hydride. If magnesium is used as the reducing metal, it is preferably added in the form of magnesium gas, since in this way the reaction to form the metal powder can be easily controlled.

After reduction to metal, whether according to a one-step reduction process or according to a two-step reduction process, the metal is cooled and then inert gas is passed into the reactor under conditions of gradually increasing oxygen content to passivate the metal powder. The oxide of the reduced metal is removed by acid washing in a manner known in the art.

Preferably, the tantalum and niobium pentaoxides used are ground powders. The primary particle size of the pentoxide powder should be about 2-3 times the primary particle size of the metal powder desired to be produced. The pentoxide particles preferably consist of a free-flowing sintered composition having an average particle size of 20-1000 μm, particularly preferred smaller ranges being the most preferred particle sizes of 50-300 μm.

The reduction of the niobium oxide with the gaseous reducing agent can be carried out in a stirred or fixed bed, for example in a rotary kiln, fluidized bed, rack kiln (rack kiln) or in a slide kiln. If a fixed bed is used, the depth of the bed should not exceed 5-15cm so that the reducing gas can penetrate the bed. If the packed bed used is a gas fed from the lower end, the depth of the bed may be greater. Preferred device options for tantalum are described in the following paragraphs between example 2 and examples 2 and 3, with reference to fig. 1-4.

Particularly preferred niobium powder morphology of the present invention is sintered primary particles having a primary particle size of 100-1000nm, wherein the particle size distribution of the sintered compact, as measured by a Master sizer (ASTM-B822), is: d10-3-80 μm, particularly preferably 3-7 μm, D50-20-250 μm, particularly preferably 70-250 μm, most preferably 130-. The powders of the invention have remarkable flow properties and compaction strength, which determine their processability for making capacitors. The sintered mass is characterized by stable sintered bridges which ensure a suitable porosity after processing into capacitors.

Preferably, the niobium powder of the present invention has an oxygen content of 2500-4500ppm per square meter surface, or a lower oxygen content, a nitrogen content of up to 10,000ppm, a carbon content of up to 150ppm, and does not takeinto account the metal content of other alloys having a maximum content of 350ppm, wherein the metal content is mainly the content of the reducing metal or the hydrogenation catalyst metal. The total content of other metals does not exceed 100 ppm. F. The total content of Cl and S is less than 10 ppm.

Capacitors were produced with the preferred niobium powders of the invention immediately after passivation and sieving through a sieve having a particle size of 400 μm. At a pressed density of 3.5g/cm³And 1100 ℃ and after forming at 40V, the specific capacitance of these capacitors is 80,000-250,000 μ FV/g (measured in phosphoric acid) and the specific leakage current density is less than 2nA/μ FV. After sintering at 1150 ℃ and forming at 40V, the specific capacitance was 40,000-150,000 μ FV/g and the specific leakage current density was less than 1nA/μ FV. After sintering at 1250 ℃ and shaping at 40V, the specific capacitance of the resulting capacitor was 30,000-80,000. mu.FV/g (measured in phosphoric acid), and the specific leakage current density was less than 1 nA/. mu.FV.

The BET specific surface area of the niobium powder preferred in the present invention is 1.5 to 30m²A/g, preferably of 2 to 10m²/g。

Surprisingly, it has been found that the specific capacitance of capacitors made from Nb/Ta alloy powders is higher than expected for capacitors made from pure Nb and pure Ta or simply linearly intercalated alloys. The capacitance (μ FV) of capacitors with sintered Nb powder positive electrodes and sintered Ta powder positive electrodes of the same surface area are approximately equal. This is because the greater thickness of the oxide layer formed per volt (anodization voltage) during anodization compensates for the higher dielectric constant of the insulating niobium oxide layer (41 compared to 26 for tantalum oxide). The oxide layer thickness of Nb per volt is about twice that of the oxide layer formed on Ta (Ta is about 1.8)nm/V, Nb is approximately 3.75 nm/V). Surface related capacitance (mu FV/m) of the alloy powder capacitor of the invention²) About 1.5-1.7 times higher than expected from linear insertion of Nb and Ta powder capacitors. This seems to indicate that the oxide layer thickness per volt of anodization voltage for the alloy powders of the present invention is close to Ta, but the dielectric constant of the oxide layer is close to Nb. The unexpectedly high capacitance of the above alloys may be due to the oxide structure morphology of the alloy components being different from the oxide structure on the surface of the pure Nb powder. In fact, preliminary measurements have confirmed that the oxide layer growth of the 15 at% Ta-85 at% Nb alloy is approximately 2.75 nm/V.

The invention accordingly further comprises an alloy powder for the production of electrolytic capacitors, wherein the alloy powder consists essentially of niobium and contains tantalum in a content of up to 40 atomic%, based on the total content of Nb and Ta. The alloy powder of the present invention will mean that a minor amount of the Ta component will be present in excess of the usual impurities of niobium metal, for example in an amount greater than 0.2% by weight (2000ppm, corresponding to 2 atomic% Ta).

Preferably, the Ta content is at least 2 atom%, particularly preferably at least 5 atom%, most preferably at least 12 atom%, based on the total Nb and Ta content

Preferably, the tantalum content of the alloy powder of the present invention is less than 34 atomic%. The capacitance increasing effect gradually increases as the atomic ratio of Nb to Ta increases until the ratio is about 3. Above 25 atomic% of tantalum, based on the total content of Nb and Ta, the effect increases only slightly.

Preferably, the BETsurface times the alloy density of the alloy powder of the invention is from 8 to 250 (m)²/g)×(g/cm³) Particularly preferably 15 to 80 (m)²/g)×(g/cm³). The density of the alloy substance can be calculated by multiplying the atomic ratio of each of Nb and Ta by the density of each of Nb and Ta.

The capacitance increasing effect of adding the alloying element is not limited to the powder having the structure of aggregated spherical particles. Thus the morphology of the alloy powder of the invention may be such that the BET surface times the density is preferably from 8 to 45 (m)²/g)×(g/cm³) The aggregate sheet of (1).

Particularly preferred alloy powders are those having a BET surface area multiplied by density of 15 to 60 (m)²/g)×(g/cm³) Is an aggregate of substantially spherical primary particles. The average diameter of the primary alloy powder (particles) is 100-1500nm, preferably 100-300 nm. Preferably in two directionsThe deviation from the mean diameter is less than 2.

The sintered powder had the same average particle size as the niobium powder disclosed above, as measured by ASTM-B822 (Master sizer).

It is particularly preferable that the ratio of Scott density to alloy density of the alloy powder is 1.5 to 3 (g/inch)³)/(g/cm³)。

Any of the methods known in the art for preparing capacitor grade tantalum powders may be utilized so long as the precursor used is a precursor for the melt alloy and not a precursor containing only tantalum, and the atomic ratio of niobium to tantalum contained is close to the atomic ratio of Nb to Ta desired in the metal powder alloy.

Useful alloy precursors can be obtained by coprecipitation of the (Nb, Ta) -compounds from an aqueous solutioncontaining water-soluble Nb-and Ta-compounds, for example by coprecipitating the (Nb, Ta) -hydrated oxide from an aqueous solution of the hexafluoro-complex, for example by addition of aqueous ammonia, and then calcining the hydrated oxide to the oxide.

The preparation of the flaky powder comprises the following steps: melting a mixture of high purity tantalum oxide and niobium oxide with an electron beam, reducing the above molten ingot, hydrogenating the ingot at a higher temperature, pulverizing the brittle alloy, dehydrogenating the alloy powder and forming it into flakes. The flakes are then sintered in the presence of a reducing metal such as Mg, optionally doped with P and/or N, heated to 1100 ℃ and 1400 ℃. The preparation of such "from ingot" powders is generally known from US-a 4,740,238 for the preparation of tantalum flake powders and from WO 98/19811 for the preparation of niobium flake powders.

Particularly preferred Nb-Ta alloy powders having the morphology of sintered spherical particles are prepared by reducing mixed (Nb, Ta) -oxides with the gaseous reducing agents described herein.

The metal powders prepared are suitable for use in electronic capacitors and other applications including, for example, the preparation of composite electro-optical, superconducting, and other metal and ceramic compounds, such as PMN structures and high temperature type metals and oxides.

The invention includes the above-described powders, methods of making the powders, certain derivative products made from the powders, and methods of making the derivative products.

Capacitor applications may incorporate other known capacitor fabrication techniques, such as incorporating agents to inhibit sintering densification, or to enhance the capacitance, leakage and breakdown voltage of the finished product.

The present invention makes several significant breakthroughs in various fields of application.

First, the cost, complexity and time of preparing the well-known high performance tantalum powders for making computer/telecommunications grade solid electrolytes, small size capacitors (high capacitance per unit volume and with stable performance characteristics) are now substantially reduced.

Second, other active metals-particularly Nb and alloys, such as Ta-Nb, Ta-Ti, and Nb-Ti, can be substituted for Ta in capacitors in certain applications to reduce cost, or to replace the large Al product market with its higher performance, particularly to enable the same capacitance with smaller dimensions and the use of solid electrolytes. Commercial aluminum electrolytic capacitors employ a wet electrolyte system.

Other objects, features and advantages of the present invention will become apparent from the following detailed description of the preferred embodiments, which proceeds with reference to the accompanying drawings.

Brief Description of Drawings

FIGS. 1-4 set forth a sketch outline of an operating system embodying the present invention;

FIGS. 5A-12C are Scanning Electron Micrographs (SEMs) of powders made according to the present invention, including some prior art SEMs or SEMs that are not comparative examples of metal powders made according to the present invention;

FIGS. 13 and 14 are flow diagrams illustrating different uses of the powders and derivatives; and

FIG. 15 is a diagram showing a finished product (one of a plurality of capacitor applications) for use as a capacitor;

FIG. 16 is a plot of capacitance and surface area of Ta-Nb alloy powders versus alloy composition.

Detailed description of the preferred embodiments Example 1(comparative example)

Mixing Ta₂O₅And magnesium were loaded into the tantalum pan and capped with tantalum foil. The stoichiometry of magnesium is 109% of the stoichiometry required to completely reduce tantalum oxide. The mixture was heated at 1000 ℃ for 6 hours under an argon atmosphere. The mixture was not stirred during the reduction. After cooling, the product is passivated by the continuous addition of oxygen. After reduction, a black spongy substance which is difficult to break is obtained. The product was leached with dilute mineral acid to remove magnesium oxide, dried and sieved. The yield of crude (+40 mesh) material was as high as 25%. The contents (in% or ppm) and surface areas (SA, cm2/g) of the various impurities in fractions +40 and-40 are given in Table 1.1 below. The contents of magnesium and oxygen are high. It is not suitable for use in capacitors because of the large percentage of crude material and the poor quality of the product.

TABLE 1.1

O ％

N ppm

C ppm

S ppm

Na ppm

K ppm

Mg ppm

SA cm2/g

+40mesh	7.6	840	21	＜5	＜1	＜10	＞7000	17,000
									-40mesh	4.7	413	57	＜5	＜5	＜10	＞7000	35,000

Example 2

Referring to fig. 1, 200g of tantalum pentoxide bed material (3) was placed on a porous tantalum plate 4 suspended above a magnesium metal sheet (5) in a tantalum boat. The container was covered with tantalum and placed in a sealed retort into which argon (Ar) gas was passed through a nozzle (6). The boat was heated in an argon/magnesium atmosphere with a bed of solid magnesium flakes (5) completely separated from the oxide bed and held at 1000 ℃ for 6 hours. Cooling to room temperature, and introducingWill contain 2,4, 8 and 15 inches (Hg, partial pressure) of O, respectively₂(g) The argon-oxygen mixture is passed into the furnace to passivate the product mixture. Each mixture was separately contacted with the powder for 30 minutes. The retention time for the final passivation with air was 60 minutes.

Leaching with dilute sulfuric acid to separate magnesium oxide from the tantalum powder, and rinsing with high purity water to remove acid residue. The product was a free flowing powder. Scanning Electron Micrographs (SEMs) at 15,700, 30,900 and 60,300, respectively, taken by operating at 15KV in an electron microscope, are listed for a sample of this product (designated Ta GR-2D) in FIGS. 5A, 5B and 5C. FIGS. 5D and 5E show comparative photographs of 70,000 times (x) SEMs of tantalum powder prepared by sodium reduction. The properties of the tantalum powders of FIGS. 5A, 5B and 5C are set forth in Table 2.1 below.

TABLE 2.1

Content of chemical elements contained (ppm)										Surface area (cm2/g)
											O 12,900	N 126	C 75	Cr ＜5	Fe 23	Ni ＜5	Na ＜1	K ＜10	Ca ＜2	Si ＜8	37,600

The ratio of oxygen concentration to surface area is consistent with surface oxygen only, indicating that the tantalum oxide is fully reduced.

An alternative to the reactor set forth in fig. 1 (and discussed in example 2) is set forth in fig. 2-4. FIG. 2 shows a flash reactor 20 having a vertical tube surrounded by a heater 24, a source of metal oxide 25, a source of reductant (e.g., Mg) vapor 26 (mixed in argon), and an argon outlet 26'And a collector 28 of metal and reductant oxides. Equipped with valves V1 and V2. The oxide particles fall down the tube and undergo flash reduction. Figure 3 illustrates a rotary kiln 30 having a helical coil 32, heater 34,an oxide feed hopper 35, a source of gas (reducing agent and diluent, e.g. argon) 36 and outlet 36', and a collector 38 of metal and reducing agent oxides. Figure 4 illustrates a multiple hearth furnace 40 having a retort 42 with a rotating disk 43 and multiple grooved vanes 43 ', a heater 44, an oxide source 45, a gas source 46 and outlet 46', and a collector 48. Other types of reactor may also be used, such as the conventional reactor which is itself a fluidized bed furnace or a reactor of the Contop, KIVCET type.Example 3

The surface area prepared according to the procedure of example 2 was 57,000cm by mixing the powder with 2W/W% Mg and heating at 850 ℃ for 2 hours in an argon atmosphere²Per gram of tantalum powder. There is no need to separate the reducing agent source and the oxide in the deoxidation step. The deoxidized powder is cooled, then passivated, leached and dried. One SEM (100,000X) of the deoxidized (finished) powder is shown in FIG. 7A, and one SEM (70,000X) of the finished powder obtained by reduction with sodium is shown in FIG. 7B. Their morphological differences are evident. By adding a suitable amount of NH₄H₂PO₄To 100ppm P, the powder was pressed into a sheet weighing 0.14g at a pressed density of 5.0 g/cc. An SEM of the powder after further deoxidation is shown in FIG. 6. The above sheets were sintered for 20 minutes under vacuum at 1200 ℃. H at 80 ℃ and 0.1% by volume (V/V%)₃PO₄In solution, the above flakes were anodized to 30V. The formation current density was 100mA/g and the retention time at the formation voltage was 2 hours. The average capacitance of the anodized sheet was 105,000. mu.F (V)/g, and after applying 21V for 5 minutes, the leakage current was measured to be 0.1 nA/. mu.F (V).Example 4

Surface area 133,000cm prepared according to the procedure of example 2 was treated as in the procedure of example 3²(ii) g, bulk density 27.3g/m³The powder of (4). An SEM (56,600x) of a finished powder is shown in FIG. 7C. Using the method of example 3Conditions, flakes made from the deoxidized powder were anodized to 16V. The anodized foil had an average capacitance of 160,000 μ F (V)/g.Example 5

Reduction of 900g Ta with gaseous magnesium at 900 deg.C₂O₅For 2 hours. The magnesium oxide in the reaction product is removed by leaching with dilute sulfuric acid. The surface area of the resulting powder was 70,000cm²(ii)/g and deoxygenating the powder with 8W/W% magnesium at 850 ℃ for 2 hours. 1(1.0) W/W% NH₄Cl is added to the charge to nitridize the tantalum. The deoxygenated powder was processed according to the procedure described in example 3. The P incorporation was 200 ppm. With the same time and temperature profile, in the absence of NH₄Under the condition of Cl, the reaction solution is prepared,the powder was again deoxygenated with 2.0W/W% Mg. The residual magnesium and magnesium oxide were removed by leaching with dilute mineral acid. The chemical properties of the powder are listed in table 5.1 below. The surface area of the powder was 9,000cm²Has excellent fluidity per gram. The pressed tablets were sintered at 1,350 ℃ for 20 minutes and at 80 ℃ at 0.1V/V% H₃PO₄To anodize it to 16V.

The capacity of the anodized sheet was 27,500. mu.F (V)/g, and the leakage current was 0.43 nA/. mu.F (V).

TABLE 5.1

Chemical element (ppm)
										O 2610	N 2640	C 95	Cr 8	Fe 18	Ni ＜5	Na 1	K ＜10	Ca ＜2	Si 41

Example 6

Reduction of 500g Ta with gaseous magnesium at 1,000 deg.C₂O₅For 2 hours. The properties of the primary powders prepared are listed in table 6.1 below.

TABLE 6.1

O，ppm	N，ppm	C，ppm	Na，ppm	K，ppm	SA，cm2/g
						19,000	1693	49	＜1	＜10	60,600

The primary powder was deoxygenated at 850 ℃ for 2 hours. Adding 4W/W% Mg and 1W/W% NH₄And (4) Cl. Extracting MgO by using inorganic acid. Then, by adding an equal amount of NH₄H₂PO₄200ppm P were added to the powder. The powder was deoxygenated a second time at 850 ℃ for 2 hours and then nitrided at 325 ℃ by adding a gaseous mixture containing 80% argon and 20% nitrogen. Some properties of the finished powderListed in table 6.2 below.

TABLE 6.2

TABLE 6.2
						O，ppm	N，ppm	C，ppm	Na，ppm	K，ppm	SA，cm2/g
6050	3430	54	＜1	＜10	24,300

Flakes were prepared from the above powder under conditions of a pressed density of 5.0 g/cc. At 80 ℃ at 0.1W/W% H₃PO₄The sintered sheets were anodized to 16V in solution. The capacitance and leakage as a function of sintering temperature are listed in table 6.3 below.

TABLE 6.3

Sintering temperature

Capacitor with a capacitor element

Leakage amount

(℃)	μF(V)/g，	μA/μF(V)
			1,200	143,000	0.77
1,250	121,000	0.88
			1,300	96,000	1.01

Example 7 (comparative example)

Potassium heptafluoroniobate (K) was reduced with sodium using a stirred reactor molten salt process similar to that described by Hellier et al and Hildreth et al in U.S. Pat. No. 5,442,978₂NbF₇). The diluent salt was sodium chloride and the reactor was made of Inconel alloy. By using dilute nitric acid (HNO)₃) Leaching, separating the niobium metal powder from the salt matrix, and then rinsing with water. The selected physical and chemical properties are listed in table 7.1 below. The concentration of metallic elements, nickel, iron and chromium is so high that the powder is not suitable for use as a capacitor grade material. The fouling effect is caused by K₂NbF₇Is caused by the inherent corrosiveness of the steel. This property makes sodium reduction unsuitable for making capacitor grade niobium powders.

TABLE 7.1

Sample (I)	SA	SBD	FAPD	O(ppm)	Ni	Cr	Fe
								1	13820	8.7	1.76	6080	18000	2970	2660
2	11700	9.4	1.48	4930	11300	4790	2060

SBD-Scott bulk Density (g/in)³) FAPD-Fisher mean particle diameter (. mu.)Example 8

200g of niobium pentoxide were reduced according to the procedure described in example 2. The resulting product was a free-flowing black powder with a surface area of 200,800cm²(ii) in terms of/g. The passivated product is leached with dilute nitric acid solution to remove magnesium oxide and residual magnesium, and then the residual acid is removed with high purity water. 10(10.0) W/W% Mg was mixed with the material and deoxygenated at 850 ℃ for 2 hours. The physical and chemical properties of the powder are listed in table 8.1 below. 100ppm P were incorporated into the powder as described in example 3.

TABLE 8.1

Physical and chemical properties of niobium powder

Chemical element (ppm)										Surface area cm2/g
											O	N	C	Cr	Fe	Ni	Na	K	Ca	Si

13000

620

40

27

45

21

8

1

3

41

40,900

SEMs (70,000x) of niobium powders prepared by reduction of liquid sodium (example 7) and magnesium gas (example 8) are shown in fig. 8A and 8B, respectively. The clusters of small particles attached to large particles in FIG. 8B are significantly more numerous than in FIG. 8A. Fig. 8C and 8D are SEMs (2,000x) of niobium powders prepared by sodium reduction and magnesium reduction, respectively.

Niobium powders prepared by liquid sodium reduction have large (>700nm) bound (300nm +) particle protrusions and facets that make the product massive and have fine particles as the adherent particles (on the order of 10nm, but some particles are up to 75 nm). However, the niobium powder produced by magnesium reduction had a primary particle diameter of about 400nm and had a particle diameter of about 20nmSmaller particles, many of which agglomerate themselves into particles up to 100nm in size.Example 9

The niobium powder prepared in example 8 was used to prepare a sheet weighing 0.14 g. At 80 ℃ at 0.1V/V% H₃PO₄The wafer is anodized in solution. The current density was 100mA/g and the retention time at the formation voltage was 2 hours. The electrical results are shown in table 9.1 below as a function of the pressed density of the sheet, the forming voltage and the sintering temperature.

TABLE 9.1Niobium powder electrical properties (capacitance and leakage) schedule at 3.0 and 3.5(g/cc) pressed densities

Sintering temperature (℃)		Capacitor with a capacitor element (μF(V)/g)		Leakage amount (nA/μF(V))
						3.0	3.5	3.0	3.5
16V forming voltage
					1300	29,500	20,000	1.6	4.7
1350	21,000	16,000	0.7	1.5
					40V forming voltage
1250	53,200	44,500	2.1	4.0
					1300	31,000	22,300	1.2	4.7
1350	26,500	20,000	0.7	1.0

Example 10

Niobium oxide was reduced with gaseous magnesium following the procedure described in example 8. Subjecting the obtainedThe powder was deoxygenated twice. During the first deoxidation, 2.0W/W% NH₄Cl was added to the charge to nitride the powder. Deoxygenation conditions were 7.0W/W% Mg deoxygenation at 850 deg.C for 2 hours. After leaching and drying, 200ppm P were incorporated into the powder. The second deoxidation was carried out at 850 ℃ for 2 hours with 2.5W/W% Mg. The surface area of the finished powder was 22,000cm²Has a good fluidity. The chemical properties are listed in table 10.1 below. The flakes were dried at 80 ℃ at 0.1V/V% H₃PO₄The solution was anodized to 16V at a current density of 100mA/g and a retention time of 2 hours. The electrical properties are listed in table 10.2 below.

TABLE 10.1

Chemical element (ppm)
									O 7490	N 8600	C 166	S 9	Cr ＜20	Fe 114	Ni ＜20	Si 34	Ta ＜200

TABLE 10.2

Electrical properties
			Sintering temperature (℃)	Capacitor with a capacitor element (μF(V)/g)	Leakage amount (nA/μF(V))
1250	68,000	0.24
			1300	34,500	0.14
1350	11,300	0.32

Example 11

a) Nb employed, determined according to FSSS (Fisher Sub Sieve classifier)₂O₅Has a particle diameter of 1.7 μm and has the following impurity contents: total (Na, K, Ca and Mg) 11ppm total (Al, Co, Cr, Cu, Fe, Ga),

Mn、Mo、Ni、Pb、Sb、Sn、

Ti, V, W, Zn and Zr) 19ppm Ta 8ppm Si 7ppm C<1ppm

Cl ＜3ppm

F 5ppm

S ＜1ppm

Under a slow flowing hydrogen atmosphere, Nb is added₂O₅Passed through a slide kiln and held in the hot zone of the furnace for 3.5 hours.

The composition of the resulting suboxides corresponds to NbO₂。

b) The product was placed on a fine grid, under which a crucible was placed, in which the magnesium content was 1.1 times the stoichiometric amount with respect to the oxygen content of the suboxides.

The apparatus with the grid and crucible was treated for 6 hours at 1000 c under argon blanket. During this step, magnesium vaporizes and reacts with the upper suboxide. The furnace is then cooled (<100 ℃) and gradually aerated to passivate the surface of the metal powder.

The product was washed with sulfuric acid until no more magnesium was detected in the filtrate, then washed with deionized water to neutrality and dried.

The niobium powder was analyzed to obtain the following impurity contents:

O 20,000(3300ppm/m²)

Mg 200ppm

Fe 8ppm

Cr 13ppm

Ni 3ppm

Ta 110ppm

C 19ppm

N 4150ppm

the particle size distribution, determined with a Mater classifier, corresponds to:

D10 4.27μm

D50 160.90μm

D90 318.33μm

the primary particle size was determined to be about 500nm with the naked eye. Scott bulk density 15.5g/inch³. BET specific surface area of 6.08m²(ii) interms of/g. The Flow was measured in the form of a Hall Flow and was 38 seconds.

c) Sintering niobium powder on a niobium wire mesh to prepare a niobium wire mesh having a diameter of 3mm, a length of 5.66mm,The anode block weighed 0.14g and had a pressed density of 3.5g/cm³The sintering time and sintering temperature of the anode are shown in Table 11.1.

The anode had a compressive strength of 6.37kg as determined by Chatillon. At a temperature of 80 ℃ and a current density of 100/150mA and a voltage as listed in Table 11.1, in a solution containing 0.1V/V% H₃PO₄Forming an anode in the electrolyte and measuring the characteristics of the capacitor; see table 11.1.

TABLE 11.1

Sample (A) Article (A)	Sintering temperature/time ℃/min	Sintered density g/cm3	Force of drawing wire N	Form a voltage V	Capacitor with a capacitor element μFV/g	Leakage current nA/μFV
							a	1250/20	5.1		16	41,126	0.47
b		5		40	41,725	0.7
							c		5		70	23,721	2.13
d	1150/20	3.9	35.6	16	111,792	0.77
							e		4	35.6	40	147,292	0.43
f	1100/20	3.75	36.6	16	194,087	0.4
							g		3.7	36.1	40	194,469	0.36

Example 12

The temperature in the first reduction step was changed to 1300 c and example 11 was repeated.

The metal powder has the following properties:

master classifier D1069.67 μm

D50 183.57μm

D90 294.5μm

Primary particle size (determined visually) 300-400nm

BET specific surface area 5m²/g

Free flow

The pressing strength is extremely high:

at a pressed density of 3.5g/cm³Under the conditions of (1) 13kg, and

at a pressed density of 3g/cm³Under the condition (2), 8 kg.

Sintering at 1100 deg.C for 20 min (pressed density of 3 g/m)³) And after being formed at 40V, the capacitance was found to be 222,498 μ FV/g, and the leak current was found to be 0.19nA/μ FV.Example 13

This example demonstrates the effect of reduction temperature on niobium powder performance in the first step:

three batches of niobium pentoxide were treated for 4 hours at 1100 deg.C, 1300 deg.C or 1500 deg.C, respectively, under hydrogen conditions, with the other conditions being the same.

The niobium pentoxide was then reduced to niobium metal with Mg gas (6 hours, 1000 ℃). With sulfuric acidThe MgO formed during the reaction was washed away together with excess Mg. The properties of the powder obtained were as follows: the reduction temperature is 1100 ℃, 1300 ℃ and 1500 DEG CLower oxides:BETm²/g¹⁾1.030.490.16 Hall flow²⁾25g in 48 seconds of no flow 25g in 20 seconds 25gNiobium metal:BETm²/g 9.93 7.8 5.23FSSSμm³⁾0.60.76.8 Hall flow 25g SDg/inch 25g 19 seconds within 85 seconds⁴⁾16.8 16.5 16.8Mgppm 240 144 210Oppm 40,000 28,100 16,600¹⁾BET specific surface area²⁾Fluidity of the resin³⁾Particle size measured by Fisher Sub Sieve classifier⁴⁾Bulk densityExample 14

A (Nb) was prepared as follows_x，Ta_1-x)₂O₅Precursor: aqueous ammonia was added to a mixed aqueous solution of heptafluoro compounds of niobium and tantalum under stirring to coprecipitate (Nb, Ta) -hydroxide, which was then calcined to form an oxide.

A large amount of mixed oxide powder, nominally consisting of Nb: Ta 90: 10 (by weight), was placed in a molybdenum boat, passed through a slide kiln under a slow flowing hydrogen atmosphere and heated in a furnaceThe zones were maintained at 1300 ℃ for 4 hours. After cooling to room temperature, the composition was found to be approximately (Nb) as measured by weight loss_0.944Ta_0.054)O。

The suboxide was placed on a fine wire grid, under which a crucible was placed, in which the magnesium content was 1.2 times the stoichiometric amount with respect to the oxygen content of the suboxide. The apparatus with the grid and crucible was treated for 6 hours at 1000 c under argon blanket. The furnace is then cooled to below 100 ℃ and gradually aerated to passivate the surface of the metal powder.

The product was washed with sulfuric acid until no more magnesium was detected in the filtrate, then washed to neutrality with deionized water and dried.

The above alloy powder was analyzed to obtain a tantalum content of 9.73 wt% and impurity contents (ppm) as follows:

O：20500，Mg：24，C：39，Fe：11，Cr：19，Ni：2，Mo：100。

the primary particle size was determined to be about 450nm with the naked eye. BET specific surface area of 6.4m²(g), Scott bulk density 15.1g/inch³The particle size (FSSS) was 0.87. mu.m.

Niobium powder having a diameter of 2.94mm, a length of 3.2mm and a pressed density of 3.23g/cm was prepared by sintering the niobium powder on a niobium wire net at 1150 ℃ for 20 minutes³Of (2) an anode. The sintered density was 3.42g/cm³. In a composition containing 0.25% H₃PO₄Until the final voltage was 40V.

With a 10% H₃PO₄Aqueous solution, the characteristics of the capacitor were measured as follows: the capacitance was 209117 μ FV/g, and the leakage current was 0.55nA/μ FV.Example 15

Alloy powders were prepared according to the procedure of example 14 using an oxide powder having a nominal composition of Nb: Ta of 75: 25 (weight ratio).

The above metal alloy powder was analyzed to obtain a tantalum content of 26.74 wt% and impurity contents (ppm) as follows:

O：15000，Mg：25，C：43，Fe：9，Cr：20，Ni：2，Mo：7，N：247。

the primary particle size was determined to be about 400nm with the naked eye. BET specific surface area of 3.9m²(g), Scott density 17.86g/in³Particle size (FSSS) was 2.95 μm and Hall Flow was 27.0 s.

The niobium powder was prepared to have a diameter of 2.99mm, a length of 3.23mm and a pressed density of 3.05g/cm by sintering the above niobium powder on a niobium wire mesh at 1150 ℃ for 20 minutes³Of (2) an anode. Sintered compactThe degree is 3.43g/cm³. In a composition containing 0.25% H₃PO₄Until the final voltage was 40V.

With a 10% H₃PO₄Aqueous solution, the characteristics of the capacitor were measured as follows: the capacitance was 290173 μ FV/g, and the leakage current was 0.44nA/μ FV.Example 16

Tantalum hydroxide is precipitated by adding ammonia to an aqueous tantalum fluoride complex. The precipitated hydroxide was calcined at 1100 ℃ for 4 hours to obtain Ta having the following physical data₂O₅Precursor: the mean particle diameter, measured with a Fisher Sub Sieve classifier (FSSS), was 7.3 μm and the bulk density (Scott) was 27.8g/in³A specific surface area (BET) of0.36m²The particle size distribution, measured on a Master sizer S without ultrasound and by laser diffraction, is: d10 ═ 15.07 μm, D50 ═ 23.65 μm, and D90 ═ 34.03 μm.

The morphology of the sintered pellets is shown in FIGS. 9A-9C (SEM pictures).

300g of the pentoxide precursor was placed on a sieve and 124g of Mg (1.5 times the stoichiometric amount required to reduce the pentoxide to metal) was placed at the bottom of the retort shown in FIG. 1.

The retort was evacuated, purged with argon and heated to 950 ℃ for 12 hours. After cooling to below 100 ℃ and passivation, the product is leached with an aqueous solution containing 23% by weight of sulfuric acid and 5.5% by weight of hydrogen peroxide and washed to neutrality with water. The product was dried overnight at 50 ℃ and sieved to less than 400 μm.

The above tantalum powder had the following analytical data: average particle size (FSSS): 1.21 μm, bulk density (Scott): 25.5g/in³BET surface area: 2.20m²Good flowability, Master sizer D10 ═ 12.38 μm, D50 ═ 21.47 μm, D90 ═ 32.38 μm. The form is as follows: please see fig. 10A-10C (SEM pictures) for chemical analysis: o: 7150 ppmN: 488 ppmH: 195ppm C: 50ppm ofSi：30ppmF：2ppmMg：6ppmNa：1ppmFe：3ppmCr：＜2ppmNi：＜3ppm

With NH containing 1mg of P per ml₄H₂PO₄The solution was soaked with the above powder and gently stirred, dried overnight at 50 ℃ to incorporate 150ppm P, and then sieved to less than 400 μm.

At a pressed density of 5.0g/cm³Strip ofUnder the condition, 0.047g of Ta powder is respectively used for sintering to prepare the capacitor anode, the sintering temperature is 1260 ℃, and the retention time is 10 minutes.

At 85 ℃with 0.1% by weight of H₃PO₄The solution was used as the forming electrolyte until the final voltage was 16V and was held for 100 minutes, resulting in a current density of 150 mA/g.

And (3) test results: sintering density: 4.6g/cm³Capacitance: 100577 μ FV/g, leakage current: 0.73 nA/. mu.FV.Example 17

First, high purity optical grade Ta is applied at 1700 deg.C₂O₅Firing for 4 hours followed by 16 hours at 900 ℃ to produce a tighter, coarser precursor particle. The physical properties of the pentoxide powder were: average particle size (FSSS): 20 μm bulk density (Scott): 39g/inch³And (4) screening results: 400-

Morphology is shown in FIGS. 11A-11C (SEM pictures).

The above oxide powder was reduced to metal as described in example 16, but at 1000 ℃ for 6 hours.

The leaching and P doping steps were the same as in example 16.

The tantalum powder had the following analytical data: average particle size (FSSS): 2.8 μm, bulk density (Scott): 28.9g/inch³BET surface area: 2.11m²(iv)/g, flow through a non-vibrating funnel having a 60 ° angle and a 0.1 inch opening: 25g in 35 seconds, a Master classifier D10-103.29 μm, D50-294.63 μm and D90-508.5 μm. The form is as follows: please see fig. 12A-12C (SEM pictures) for chemical analysis: o: 7350 ppmN: 207 ppmH: 174ppm C: 62ppm Mg: 9 ppmFe: 5ppm Cr:<2 ppmNi:<3 ppmP: 150ppm of

Capacitor anodes were prepared and anodized as in example 16.

And (3) test results: sintering density: 4.8g/cm³Capacitance: 89201 μ FV/g leakage Current: 0.49 nA/. mu.FV

The sintering temperature was raised to 1310 c and a second seriesof capacitors were prepared in the same way.

And (3) test results: sintering density: 5.1g/cm³Capacitance: 84201 mu FV/gLeakage current: 0.68 nA/. mu.FVExample 18

Separately reducing WO with gaseous magnesium at 950 deg.C₃、ZrO₂And V₂O₃For 6 hours, each sample was approximately 25 g. The reduction product is leached with dilute sulfuric acid to remove residual magnesium oxide. The product was in each case a ferrous metal powder. The oxygen content in the tungsten powder and the zirconium powder was 5.9 and 9.6W/W%, respectively, indicating that the metal oxide was reduced to the metallic state.

The present method appears to represent only an exemplary method for preparing high quality chemically reduced niobium powders. The reduction of metal oxides with a gaseous reducing agent, such as magnesium as exemplified herein, is particularly suitable for the preparation of powders useful as the matrix of metal-metal oxide capacitors. Although the reduction process is carried out by contacting the metal oxide in the bed with a source of magnesium gas, the reduction reaction may also be carried out in a fluidized bed, rotary kiln, flash reactor, multiple hearth furnace or similar system, provided that the magnesium or other reducing agent is in the gaseous state. The process is equally applicable to other metal oxides or metal oxide mixtures having a negative gibbs free energy change, using reduction with gaseous magnesium or other reducing agents.

The gaseous reduction process described herein has a number of advantages. By reduction of K, for example, with sodium in a molten salt system₂TaF₇Compared with the post-reduction operation of the tantalum powder prepared by the liquid phase reaction, the treatment of the reduction product is simpler and more convenient, and the costis lower. No fluoride or chloride residues are produced in the process. This avoids potentially serious disposal problems or the need to build an expensive waste recovery system. The surface area of the powder prepared by reducing the metal oxide with the gaseous reducing agent is much greater than the powder prepared by the molten salt/sodium reduction method. Compared with the traditional method, the novel method is easy to prepare powder with extremely high surface area; the use of magnesium or other gaseous reducing agents makes it more likely to produce capacitors of very high performanceGrade powder.

The invention also illustrates for the first time the superiority of Ta-Nb powder for capacitor fabrication.

FIG. 16 lists the maximum capacitance (μ FV/g) and the maximum BET surface area (m) achievable with the powder in relation to the alloy composition²Ratio of/g). A and C represent pure Ta-and Nb-powders, respectively, as measured in inventive example 16. As disclosed in examples 2, 5 and 7 of WO 98/47249, B represents the highest value of the known pure Ta powder capacitors. Curve 1 represents the expected values for the alloy powder capacitors resulting from the linear insertion of the pure Ta and Nb powder capacitors. E represents an imaginary Nb powder capacitor in which the insulating oxide layer thickness per volt is the same as in the Ta powder capacitor, but the dielectric constant of niobium oxide is different. Curve 11 represents a linear interpolation between B and E. D represents the measured value of a 25 wt% Ta/75 wt% Nb alloy powder capacitor as provided in inventive example 15. Curve III represents the estimated dependence of the capacitance of the alloy powder capacitor of the invention on the alloy composition.

FIG. 13 is a block diagram showing the steps for realizing the use of the electrolytic capacitor of the present invention. The steps comprise: reducing the metal oxide with a gaseous reducing agent; separating the reductant oxide from the resulting metal mass; cracking the metal to powder form and/or primary particle size; classifying; optionally pre-sintering to form sintered secondary particles (controlled mechanical methods and control of the initial reduction and separation steps also have an effect on the formation of agglomerates); deoxidizing to reduce the oxygen concentration; compacting the primary or secondary particles into a porous coherent mass by cold isostatic pressing with or without a compacting binder or lubricant; sintered into a porous anode form (which may be an elongated cylinder, or a sheet, or a small section of a sheet); embedding an anode lead in the anode before sintering or welding into a sintered anode compact; forming exposed metal surfaces in the porous electrode by electrolytic oxidation to form a dielectric oxide layer; impregnating the solid electrode by dipping the precursor into a porous block and performing one or more steps of pyrolysis, or by other impregnation methods; preparing a cathode; and packaging. Various additional washing and testing steps are not listed. The partially cut Ta or Nb (or Ta-Nb alloy) capacitor 101 finished product (cylindrical) is illustrated in fig. 15: a porous Ta or Nb (or Ta-Nb alloy) anode 102 impregnated in a solid electrolyte, surrounded by a counter electrode (cathode) 104 and a packaging shell 105, and a dense lead of Ta or Nb (typically matching the powder composition) 106 connected to the anode by a weld joint 107. As mentioned above, the invention can take other known capacitor forms (different form factors, different metals and different electrolyte systems anode lead connections, etc.).

Fig. 14 is a block schematic diagram generally illustrating the preparation and use of some other derived products of the invention, including the use of the powder as a slip, and made into molded and loose filler form for further reaction, and/orconsolidation by sintering, hot isostatic pressing (h.i.p.) or in a sintering furnace/h.i.p. process. The powder itself and/or the consolidated powder can be used for the preparation of composites, combustion, chemical synthesis (as a reactant) or catalysis, alloying elements (e.g. ferrous metallurgy), and coatings. The consolidated powder can be used to prepare rolled products and fabricated components.

In some cases, the finished product made with the powder produced by gas reduction will be similar to the finished product made with the prior art (e.g., reduced) powder, but in other cases the product will be new and have unique physical, chemical, or electrical properties due to the unique morphology of the powder produced by gaseous reducing agent reduction as described herein. The process of preparation from the powder to a finished product or end use can also be adjusted to improve impurity distribution and morphology depending on the powder and its method of preparation.

The preparation of rolled products and fabricated components may include remelting, casting, annealing, dispersion strengthening and other well-known basic techniques. The finished product prepared by further reaction of the metal powder may include high purity oxides, nitrides, silicides and other derivatives such as composite ceramics used in ferroelectric electrical and optical applications, for example perovskite structure PMW compounds.

It will now be apparent to those skilled in the art that other embodiments, modifications, details, and uses can be made consistent with the above disclosure in the form and content of the patent, which is to be construed in accordance with the patent laws, including the doctrine of equivalents, limited only by the following claims.

Claims (56)

1. A method for the preparation of metal powders of Ta, Nb and Ta-Nb alloys, alone or with the addition or co-preparation of one or more metals selected from Ti, Mo, W, Hf, V and Zr, comprising the steps of:

   (a) providing an oxide or mixed oxide of the metal, the oxide itself being in a form that is permeable to gases,

   (b) a gaseous reducing agent is produced outside the oxide, and the gas is passed through the oxide at a higher temperature,

   (c) the reactants, the porosity of the oxide and the temperature and time of the reduction reaction are selected to substantially complete the reduction reaction of the oxide to release metal portions thereof, residual oxides of the reducing agent formed during the reaction are readily removed,

   thus, in the preparation of metal or alloy powders, a high surface area powder is formed by a process that substantially avoids the use of molten reducing agents.
2. A method for the preparation of metal powders of Ta, Nb and Ta-Nb alloys, alone or with one or more metals selected from Ti, Mo, W, Hf, V and Zr, comprising the steps of:

   (a) providing an oxide or mixed oxide of the metal, the oxide being in a form that is permeable to gases,

   (b) passing a hydrogen-containing gas through the oxide at an elevated temperature,

   (c) the porosity of the oxide, the temperature and time of the reduction reaction are selected to remove at least 20% of the oxygen contained in the oxide to obtain a suboxide,

   (d) the suboxide obtained in the second step is further reduced with a reducing agent selected from the group consisting of reducing metals and reducing metal hydrides, thereby substantially completely reducing the oxide, releasing the metal portion thereof.
3. 3. The process according to claim 1 or 2, wherein the reducing agent is selected from the group consisting of Mg, Ca, Al, Li, Ba and Sr, and hydrides thereof.
4. 4. A method according to any one of claims 1 to 3 wherein the metal or alloy powder is processed to an agglomerated secondary form.
5. 5. A method according to any one of claims 1 to 4 wherein the metal powder is further deoxidized by re-exposure to a gaseous reducing agent.
6. 6. A method according to claim 2, characterized in that the reduction in the first step is carried out at least until the volume of the solid is reduced by 35-50%.
7. 7. The method according to claim 2 or 6, characterized in that the reduction in the first step is carried outGo to MeO_xWhere Me represents Ta and/or Nb, x has a value of 1 to 2.
8. 8. A method according to any one of claims 2, 6 or 7, characterized in that the reduction product of the first step is kept at about the reduction temperature for a further 60-360 minutes.
9. 9. Process according to any one of claims 2 or 6 to 8, characterized in that Mg, Ca and/or hydrides thereof are used as reducing agents in the second step.
10. 10. The method of any of claims 1-9 wherein the metal consists essentially of tantalum and the oxide is tantalum pentoxide.
11. 11. The method of any of claims 1-10, wherein the metal comprises niobium and the oxide comprises niobium pentoxide or a niobium suboxide.
12. 12. The method of claim 11 wherein the tantalum content of the oxide is up to 50 atomic percent based on the total metal content.
13. 13. A process according to any one of claims 1 to 12 wherein the void volume in the form of an oxide through which gas can pass is at least 90%.
14. 14. The process as claimed in any of claims 1 to 13, wherein the oxide morphology provided is agglomerated primary oxide particles having a diameter of 100-1000nm and an average agglomerate size of 10-1000 μm (Master sizer D50).
15. 15. The process according to any one of claims 1 to 14, wherein the reducing agent is magnesium.
16. 16. A method according to any one of claims 1-15, wherein the elevated temperature during the passage of the gaseous reducing agent through the oxide is below 0.5TM, wherein TM refers to the melting point of the metal powder.
17. 17. The method of claim 16, wherein said temperature is less than 0.4 TM.
18. 18. A method according to any one of claims 1 to 17, wherein the primary metal powder is further deoxidised to produce a finished powder.
19. 19. A process according to claim 18, wherein one or more of the final deoxygenation steps is/are used as an extension of the reduction reaction.
20. 20. The method according to claim 19, wherein the final deoxygenation reaction is a separate treatment.
21. 21. A method according to any one of claims 1 to 20, wherein the metal powder is processed into an agglomerated secondary form.
22. 22. A method according to claim 21, wherein the deoxidation step is applied to the agglomerated secondary form of the powder.
23. 23. A method according to any one of claims 1 to 22, wherein the metal powder is further formed into an adherent porous mass.
24. 24. Niobium powder in the form of aggregated primary particles having a particle size of 100-1000nm, wherein the particle size of the aggregates, as determined by means of a Master classifier, corresponds to D10-3-80 μm, D50-20-250 μm and D90-30-400 μm.
25. 25. The niobium powder as claimed in claim 24, wherein the niobium powder contains only Ta up to 40 at%, or contains Ta up to 40 at% and one or more metals selected from Ti, Mo, W, Hf, V and Zr based on the total metal content.
26. 26. The niobium powder as claimed in claim 25, wherein the content of other metal is at least 2 atomic%.
27. 27. The niobium powder as claimed in claim 25, wherein the content of other metals is at least 3.5 atomic%.
28. 28. The niobium powder as claimed in claim 25, wherein the content of other metal is at least 5 atomic%.
29. 29. The niobium powder as claimed in claim 25, wherein the content of other metal is at least 10 atomic%.
30. 30. Niobium powder according to claims 25-29, wherein the content of other metals is up to 34 at%.
31. 31. Niobium powder according to any one of claims 25 to 30, containing tantalum as further metal.
32. 32. Powder according to any one of claims 24 to 31, which has a powder morphology of aggregated, essentially spherical primary particles with a diameter of 100 and 1500 nm.
33. 33. The powder according to any of claims 24 to 32, having a product of BET surface area and alloy density of 8 to 250 (m)²/g)×(g/cm³)。
34. 34. Powder according to any of claims 24 to 33, wherein the ratio of Scott density to alloy density is between 1.5 and 2.3 (g/inch)³)/(g/cm³)。
35. 35. A powder according to claim 32, wherein the agglomerated particle size D50 value, as determined according to the Master classifier, is between 20 and 300 μm.
36. 36. The niobium powder as claimed in any one of claims 24 to 35, wherein the oxygen content is 2500-4500ppm/m²BET surface, nitrogen content of up to 10,000ppm, carbon content of up to 150ppm, and total impurity metal content of less than 500 ppm.
37. 37. The niobium powder as claimed in any one of claims 24 to 35, wherein, after sintering at 1100 ℃ and shaping at 40V, the powder has a specific capacitor capacitance of 80,000-250,000 μ FV/g and a specific leakage current density of less than 2nA/μ FV.
38. 38. The niobium powder as claimed in any one of claims 24 to 35, wherein, after sintering at 1250 ℃ and shaping at 40V, the powder has a specific capacitor capacitance of 30,000-80,000 μ FV/g and a specific leakage current density of less than 1nA/μ FV.
39. 39. A capacitor anode prepared by sintering the powder of any one of claims 24 to 38 and anodizing.
40. 40. A capacitor comprising the anode of claim 39.
41. 41. The capacitor of claim 40 as a solid electrolyte capacitor.
42. 42. An alloy powder for use in the manufacture of an electrolytic capacitor, wherein the alloy powder consists essentially of niobium and contains up to 40 atomic percent tantalum, based on the total content of Nb and Ta.
43. 43. A powder according to claim 42, wherein the tantalum content is at least 2 atomic%.
44. 44. A powder according to claim 43, wherein the tantalum content is at least 3.5 atomic%.
45. 45. A powder according to claim 43, wherein the tantalum content is at least 5 atomic%.
46. 46. A powder according to claim 43, wherein the tantalum content is at least 10 atomic%.
47. 47. A powder according to claim 42, wherein the tantalum contentis from 12 to 34 atomic%.
48. 48. A powder according to any of claims 42 to 47, wherein the powder is such that the product of BET surface area and alloy density is from 8 to 45 (m)²/g)×(g/cm³) The aggregate sheet of (1).
49. 49. The powder according to any one of claims 42 to 47, wherein the powder is 1500nm with a diameter of 100 and the product of BET surface area and density is 15 to 60 (m)²/g)×(g/cm³) Aggregated, substantially spherical primary particles of (a).
50. 50. A powder according to claim 7 or 8, wherein the average particle size D50 value, determined according to the Master sizer, is between 20 and 250 μm.
51. 51. A powder according to any one of claims 42 to 50, wherein the Scott density is 1.5- (g/inch)³)/(g/cm³)。
52. 52. A capacitor anode prepared by sintering the powder of any one of claims 42 to 51 and anodizing.
53. 53. A capacitor comprising the anode of claim 52.
54. 54. A method of making the alloy powder of claim 48, comprising the steps of:

    (a) hydrogenating an electron beam melted alloy ingot comprising Nb and Ta, wherein the tantalum content is up to 40 atomic percent based on the total Nb and Ta, and

    (b) pulverizing the above hydrogenated alloy ingot, and

    (c) dehydrogenating the comminuted alloy obtained in step (b), and

    (d) making the above pulverized alloy into a sheet, and

    (e) aggregating said flakes at 800-1150 ℃ in the presence of an alkaline earth metal as reducing agent, and

    (f) the agglomerated alloy sheet is leached and washed to remove all residues and residual products of the reducing agent.
55. 55. A method as claimed in claim 54, wherein phosphorus and/or nitrogen is incorporated into the alloy powder during the agglomeration step.
56. 56. A niobium-tantalum alloy prepared by sintering and shaping, wherein the alloy powder is capable of achieving a ratio of specific capacitance to BET surface of the powder of greater than 65,000(μ FV/g)/(m)²/g), preferably greater than 70,000(μ FV/g)/(m)²/g)。

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