EP0537502B1 - Metal- and metal alloy powder comprising microcrystalline, spherical and dense particles and process and installation for preparing same - Google Patents

Metal- and metal alloy powder comprising microcrystalline, spherical and dense particles and process and installation for preparing same Download PDF

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Publication number
EP0537502B1
EP0537502B1 EP92116067A EP92116067A EP0537502B1 EP 0537502 B1 EP0537502 B1 EP 0537502B1 EP 92116067 A EP92116067 A EP 92116067A EP 92116067 A EP92116067 A EP 92116067A EP 0537502 B1 EP0537502 B1 EP 0537502B1
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Prior art keywords
powder
powders
particles
spherical
metal
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EP92116067A
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German (de)
French (fr)
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EP0537502A1 (en
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Alain Dauger
Gerard Labregere
Guy Roche
Rene Guinebretiere
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Evonik Operations GmbH
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Degussa GmbH
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
    • B22F1/06—Metallic powder characterised by the shape of the particles
    • B22F1/065—Spherical particles

Definitions

  • the invention relates to powders of metals and binary and ternary metal alloys in the form of microcrystalline, spherical and dense particles.
  • microcrystalline metal and metal alloy powders that are approximately spherical, free of cracks and pores, that is to say dense with a surface that is as smooth as possible.
  • Metal powders can be produced using chemical and physical processes that have a decisive influence on the properties of the powders.
  • the known processes consist in the production of the powders by atomizing the metal or metal alloy melts in a liquid or gaseous medium (see, for example, DE-OS 33 24 188, DE-OS 33 45 983, GB 952 457, GB 1 123 825 and EP- A 0 120 506).
  • the metal powder particles atomized with water according to DE-OS 33 24 188 have very irregular surfaces, and their specific surface area is considerably larger than that calculated geometrically.
  • metal powder with spherical particles is obtained, the particle size of which is described in GB 952 457, e.g. is between 10 and 50 ⁇ m.
  • EP-A 0 120 506 describes a special process for producing even finer metal powder by atomizing a melt stream using a gas.
  • the powder particles obtained with this method are dense and non-porous; they are approximately spherical with an average diameter between 5 and 35 microns.
  • a completely different method for producing spherical metal particles according to DE-OS 33 45 985 consists in a certain amount of coarse metal particles, for. B. scrap, chips or castings in the melting zone of a fluidized bed furnace, melt the particles, atomize the melt product in a hot gas stream in droplets and solidify the droplets.
  • This method which is just as expensive as the one described above, is suitable for the production of abrasives, but not for the production of microcrystalline powders.
  • EP-A 0 282 945 teaches a hydrometallurgical process for producing finely divided spherical precious metal powders. Starting from an aqueous solution containing a noble metal compound, a solid reducible salt or oxide is formed, this is reduced and the product obtained is passed through an oven by means of a carrier gas, in which the particles melt at least 50%; then it is cooled. Particles with a diameter of less than 20 ⁇ m are obtained.
  • metal powder such as the powder of precious metals and their alloys, which are produced by simple chemical reduction of the metal salts, very fine with a particle diameter between 0.001 and 0.1 ⁇ m. They have a large specific surface area of 10 to 40 m 2 / g, depending on which reducing agent was used.
  • the primary particles of these powders can be agglomerated by thermomechanical treatment. However, these particles are structured so that they usually have a small grain size with a large specific surface area. Under these conditions the powders are very reactive; this is disadvantageous for the production of sintered metals as well as electronic components and microelectronic hybrid circuits.
  • the two metals form slightly continuous series of single-phase solutions.
  • the temperature of the solid state and that of the liquid is between the melting point of the palladium at 1552 ° C and the melting point of the silver at 961 ° C.
  • the ratio Pd / Ag is chosen so that the melting point is above the sintering temperature of the non-conductor in order to prevent the electrode from melting during the sintering process.
  • the two metals form oxides when sintered in air.
  • Ag 2 O is the most stable oxidation level of silver at room temperature and up to 300 ° C.
  • the formation of oxide is impeded by the air and the decrease in the specific surface area of the silver during the first sintering phase.
  • Palladium on the other hand, easily forms the oxide PdO in the initial phase of the sintering process. The extent depends on the specific surface of the metal, the heating rate and the partial pressure of atmospheric oxygen. PdO with a tetragonal crystalline structure is thermodynamic up to approx. 800 ° C. stable and returns to the metallic state at higher temperatures.
  • the oxidation of the palladium can be accompanied by a volume expansion of up to 40%. Above 800 ° C the reduction of PdO to Pd is noticeable in a volume reduction. Both reactions cause tension, which is a reason for the flaking.
  • the oxidation reduction of the palladium is accelerated by adding silver.
  • powders consisting of 70 wt% Ag and 30 wt% Pd reach the oxidation maximum at 520 ° C compared to 790 ° C without silver.
  • the reduction end of PdO is reduced in the same way from 900 ° C to 700 ° C.
  • the fine powder can react catalytically with the organic medium to form warm spots, which leads to rapid degassing, bubble formation and the condensers peeling.
  • the shrinkage properties of very fine metal powders are usually very pronounced and cannot compensate for the properties of the surrounding dielectric materials. As a result, tiny metal "islands" form from the discontinuous metal groups with weaker conductivity.
  • the object of the invention is to provide inactive noble metal powders which are fine enough for use in screen printing pastes, but whose specific surface area has to be small enough so that the catalytic effect is slowed down.
  • Another object of this invention is to develop a method and an apparatus for producing such powders, starting from microcrystalline powders from non-spherical particles, the specific surface area of which is larger than the theoretically calculated value.
  • the invention therefore relates to powders made of noble metals or of binary and ternary noble metal alloys in the form of microcrystalline, completely spherical and dense particles, which are characterized in that the mean particle diameter is between 0.1 ⁇ m and less than 5 ⁇ m and the grain spectrum within 0.1 ⁇ m and 10 ⁇ m.
  • a process for the production of powders from precious metals and precious metal alloys in the form was also found microcrystalline, completely spherical and dense particles with an average grain diameter between 0.1 and 5 ⁇ m and a grain spectrum within 0.1 and 10 ⁇ m from starting powders of the precious metals or their alloys in the form of microcrystalline, non-spherical particles with a larger specific surface than that of the powders to be prepared, comprising suspending the starting powder in an inert carrier gas, passing the suspension (powder cloud) through a tubular oven with external heating, wherein the powder particles are at a temperature within the heating zone of the oven of 100 to 250 ° C above the melting temperature of the Powder particles are heated to a temperature above the melting point, cooling the suspension to solidify the molten powder particles by means of one or more cooling devices which are located between the heating zone and the outlet of the tubular furnace outside it and / or outside e it is arranged at the exit of the tubular furnace, the diameter of which is larger than that of the tubular furnace, and
  • a metal or metal alloy powder is used as the starting product, which was produced by chemical synthesis, preferably by chemical reduction of metal salts with possibly subsequent thermomechanical treatment.
  • all powders that can be suspended in the carrier gas can be used as the starting product.
  • the flow rate of the suspension through the furnace and the temperature of the heating zone are controlled so that the molten particles are spherical as they enter the cooling zone.
  • the heating zone is preferably set to a temperature which is 100 to 250 ° C above the melting temperature.
  • the particles solidify in a cooling device, which can be attached to the outside of the furnace tube or in a part of the tube and / or outside the furnace.
  • powders of base metals such as. B. copper, lead, tin, zinc, aluminum and powder of precious metals, preferably silver, gold, palladium and platinum.
  • the method is also applicable to binary and ternary metal alloys.
  • a powder of an Ag-Pd alloy produced by chemical reduction of a silver-palladium mixed carbonate using a reducing agent of the aldehyde type in the aqueous phase has a specific surface area of 10 m 2 / g (measured by means of N 2 gas adsorption after the BET method) and a particle diameter of less than 0.1 ⁇ m.
  • a powder with a specific surface area of 1 to 2 m 2 / g is obtained by thermomechanical treatment of the powder produced. With the method according to the invention, the specific surface area of the latter powder can be reduced to approximately 0.3 to 0.5 m 2 / g.
  • the 3 contains a device for suspending the powder (1), a tubular furnace (8), one or more devices for cooling the suspension (11) and a device (13) in which the powder consists of spherical particles Carrier gas is separated and recovered;
  • the device (1) consists of an airtight housing (2), a filling system the starting powder (3), at least one carrier gas supply (4), a device (5, 6) for intensive mixing of the powder with the gas and an outlet (7) connected to the beginning (9a) of the tube (9) of the tubular furnace (8) is connected;
  • the area (9b) of the pipe (9) is surrounded by one or more heating devices (10), the cooling device or devices (11) are inside and / or outside of the pipe (9) between the heating zone (9b) and the pipe outlet ( 9c) and / or inside and / or outside on the chimney (12), which is located between the pipe end (9c) and the recovery chamber (13).
  • the device (1) and its parts (2) to (6) can be designed in various ways.
  • the powder feed (3) can take place, for example, by conventional metering systems which are used for fine powders, such as cellular wheel sluices, metering screws or vibration chutes.
  • Fig. 3 shows a particularly suitable mixing device (5, 6); (5) is a rotor (5) driven by a motor (6).
  • the principle of mixing devices without mobile parts, whereby powder and carrier gas are introduced on one side of the fixed mixer, has also proven itself. Instead of via the feed line (4), the carrier gas can also be fed into the mixing chamber (2) via other connections.
  • the tube (9) of the tubular furnace (8) has a heating zone (9c) which is heated by one or more heating registers (10).
  • the heating can be done electrically or with gas; however, an electric heater is preferred because it enables the regulation and setting of the temperature program for the entire heating zone in a simple manner.
  • the pipe (9) is connected at one end (9a) to the mixing chamber (2) and at the other end (9c) to the recovery chamber (13) or any chimney (12) between the recovery chamber and the pipe (9).
  • the cooling system (s) (11) can be of different types and can be arranged at the end of the pipe (9) and / or in the vicinity of the possible chimney (12).
  • the suspension can be cooled in one or more steps respectively.
  • the cooling device (11) is at the end of the tube (9); this cooling system consists of a heat exchanger that is placed around the pipe and works with a refrigerant; (11a) and (11b) represent the supply or discharge of the refrigerant.
  • the optional cooling system (14) with supply and discharge (14a and 14b) of the refrigerant serves to stably close the pipe (9) with the chamber (2) connect. If a pipe element (12), which has the shape of a chimney and is equipped with a cooling device, can be installed between the pipe (9) and the recovery system (13), it will, due to its significantly larger diameter than the pipe (9), cause that the flow rate of the suspension decreases.
  • the powder can be separated from the carrier gas by settling in the simply constructed chamber (13); the powder moves towards the outlet (13b); the carrier gas escapes via the outlet (13a), which is optionally provided with dust filters, or it is completely or partially returned to the mixing chamber.
  • the continuous separation of the powder from the cooled suspension can also take place by means of other known devices, for example by means of a dust separator and / or dust filter.
  • microcrystalline metal or metal alloy powders which are present as non-spherical particles can, according to the invention, be converted into powders with spherical particles and a smooth surface in a production device specially developed for this process.
  • This process is particularly advantageous because it is much simpler and can work more economically than the known processes, which also start from solids.
  • the amount of gas required is considerably less than in the named methods; the energy and raw material costs are lower.
  • the powders produced by the process according to the invention have proven to be particularly suitable for the production of electronic components, such as ceramic multilayer capacitors. Due to its simple construction, the device is particularly suitable for the production of small powder batches of very expensive metals, such as precious metals and their alloys.
  • a device for producing the powders according to the invention can also be used to improve the crystal structure of the metal and metal alloy powders, even if they are treated at temperatures which are 100 to 200 ° C. below the melting temperature.
  • the starting powder can be in the form of spherical or non-spherical particles.
  • the starting powder - see FIG. 1 - is a silver / palladium alloy with 30% by weight of Pd, which was produced chemically and by thermomechanical treatment.
  • the particles are completely spherical - see Fig. 2; the grain size is between 0.2 and 3 ⁇ m, the specific surface is 0.43 m 2 / g (electron microscope).
  • the particles of the powder are completely homogeneous; the chemical composition has not changed.
  • the starting powder and the powder obtained were used to produce the internal electrodes of ceramic multilayer capacitors; Manufacture of capacitors using known methods:
  • the chips based on the starting powder showed some tiny metal islands as well as partial exfoliation of the layers after sintering at 1150 ° C.
  • the chips based on the spherical powder according to Example 1 showed no exfoliation after sintering at 1150 ° C.
  • Example 2 Starting powder and test conditions are identical to Example 1, the only difference is that the oven temperature is set to 1320 ° C.
  • the particles are completely spherical, the grain size is between 0.4 and 4 ⁇ m, the specific surface area is 0.34 m 2 / g.
  • the particles of the powder are completely homogeneous; the chemical composition has not changed.
  • the degree of oxidation of the palladium contained is 30% at the maximum oxidation temperature of 575 ° C.
  • the shrinkage measured at 1100 ° C is 12% compared to 40% of the starting powder.
  • the linear coefficient of thermal expansion at 0 and 900 ° C is close to that of the layer connection, ie 1.68 x 10 -5 / ° C.
  • the chips used for the production of the inner electrodes of ceramic multilayer capacitors, the chips showed no peeling after sintering at 1150 ° C.
  • the starting powder is a silver / palladium alloy with 70% by weight Pd, which was produced chemically and by thermomechanical treatment.
  • the particles are perfectly spherical; the grain size is between 0.2 and 3 ⁇ m, the specific surface is 0.5 m 2 / g.
  • the particles of the powder are completely homogeneous; the chemical composition has not changed.
  • the particles are perfectly spherical; the grain size is between 2 and 5 ⁇ m.
  • the particles are perfectly spherical; the average grain size is 8 ⁇ m, the specific surface 0.2 m 2 / g.

Description

Die Erfindung betrifft Pulver aus Metallen und binären sowie ternären Metallegierungen in Form von mikrokristallinen, kugelförmigen und dichten Teilchen.The invention relates to powders of metals and binary and ternary metal alloys in the form of microcrystalline, spherical and dense particles.

Für die Herstellung von gesinterten Metallblöcken sowie Bauteilen für die Elektronikindustrie ist eine erhöhte Nachfrage nach mikrokristallinen Metall- und Metallegierungspulvern festzustellen, die annähernd kugelförmig, risse- und porenfrei, also dicht sind mit einer möglichst glatten Oberfläche.For the production of sintered metal blocks and components for the electronics industry, there is an increased demand for microcrystalline metal and metal alloy powders that are approximately spherical, free of cracks and pores, that is to say dense with a surface that is as smooth as possible.

Metallpulver lassen sich mittels chemischer und physikalischer Verfahren, die einen entscheidenden Einfluß auf die Eigenschaften der Pulver ausüben, herstellen. Die bekannten Verfahren bestehen in der Herstellung der Pulver durch Zerstäuben der Metall- oder Metallegierungsschmelzen in einem flüssigen oder gasförmigen Medium (siehe z.B. DE-OS 33 24 188, DE-OS 33 45 983, GB 952 457, GB 1 123 825 und EP-A 0 120 506). Die mit Wasser zerstäubten Metallpulverteilchen nach DE-OS 33 24 188 besitzen sehr unregelmäßige Oberflächen, und ihre spezifische Oberfläche ist wesentlich größer als die geometrisch berechnete. Bei Verwendung eines gasförmigen Mediums erhält man im übrigen Metallpulver mit kugelförmigen Teilchen, deren Kornspektrum nach GB 952 457 z.B. zwischen 10 und 50 µm liegt.Metal powders can be produced using chemical and physical processes that have a decisive influence on the properties of the powders. The known processes consist in the production of the powders by atomizing the metal or metal alloy melts in a liquid or gaseous medium (see, for example, DE-OS 33 24 188, DE-OS 33 45 983, GB 952 457, GB 1 123 825 and EP- A 0 120 506). The metal powder particles atomized with water according to DE-OS 33 24 188 have very irregular surfaces, and their specific surface area is considerably larger than that calculated geometrically. When using a gaseous medium, metal powder with spherical particles is obtained, the particle size of which is described in GB 952 457, e.g. is between 10 and 50 µm.

EP-A 0 120 506 beschreibt ein spezielles Verfahren zur Herstellung noch feinerer Metallpulver durch Atomisieren eines Schmelzestroms mittels eines Gases. Die mit dieser Methode erhaltenen Pulverteilchen sind dicht und porenfrei; sie sind annähernd kugelförmig mit einem mittleren Durchmesser zwischen 5 und 35 µm.EP-A 0 120 506 describes a special process for producing even finer metal powder by atomizing a melt stream using a gas. The powder particles obtained with this method are dense and non-porous; they are approximately spherical with an average diameter between 5 and 35 microns.

Der Nachteil dieses bekannten Verfahrens zur Herstellung von Pulvern mittels Zerstäuben eines Metallschmelzstroms ist der hohe maschinentechnische Investitionsaufwand, der besonders zum Tragen kommt, wenn nur kleine Mengen wertvoller Metallpulver, z. B. von Edelmetallen, hergestellt werden. Außerdem lassen sich mit diesem Verfahren keine Metallpulver herstellen, deren mittlerer Teilchendurchmesser unter 5 µm liegt.The disadvantage of this known method for producing powders by atomizing a molten metal stream is the high investment in machine technology, which is particularly important when only small amounts of valuable metal powder, e.g. B. of precious metals. In addition, this process cannot be used to produce metal powders with an average particle diameter of less than 5 µm.

Ein völlig anderes Verfahren zur Herstellung kugelförmiger Metallteilchen nach DE-OS 33 45 985 besteht darin, eine bestimmte Menge grober Metallteilchen, z. B. Schrott, Späne oder Gußteile, in die Schmelzzone eines Wirbelschichtofens zu geben, die Teilchen zu schmelzen, das Schmelzprodukt in einem Heißgasstrom in Tröpfen zu zerstäuben und die Tröpfchen erstarren zu lassen. Dieses Verfahren, das genauso teuer wie die vorbeschriebenen ist, eignet sich für die Herstellung von Strahlmitteln, jedoch nicht für die Herstellung von mikrokristallinen Pulvern.A completely different method for producing spherical metal particles according to DE-OS 33 45 985 consists in a certain amount of coarse metal particles, for. B. scrap, chips or castings in the melting zone of a fluidized bed furnace, melt the particles, atomize the melt product in a hot gas stream in droplets and solidify the droplets. This method, which is just as expensive as the one described above, is suitable for the production of abrasives, but not for the production of microcrystalline powders.

In der EP-A 0 282 945 wird ein hydrometallurgisches Verfahren zur Herstellung fein verteilter kugelförmiger Edelmetallpulver gelehrt. Ausgehend von einer eine Edelmetallverbindung enthaltenden wäßrigen Lösung, wird ein festes reduzierbares Salz oder Oxid gebildet, dieses reduziert und das dabei erhaltene Produkt mittels eines Trägergases durch einen Ofen geleitet, worin die Teilchen zu mindestens 50 % schmelzen; dann wird abgekühlt. Erhalten werden Teilchen mit einem Durchmesser von kleiner 20 µm.EP-A 0 282 945 teaches a hydrometallurgical process for producing finely divided spherical precious metal powders. Starting from an aqueous solution containing a noble metal compound, a solid reducible salt or oxide is formed, this is reduced and the product obtained is passed through an oven by means of a carrier gas, in which the particles melt at least 50%; then it is cooled. Particles with a diameter of less than 20 μm are obtained.

Sehr feine Metall- und Metallegierungspulver werden nach der klassischen Methode durch chemische Synthese hergestellt. So sind z. B. Metallpulver, wie die Pulver von Edelmetallen und deren Legierungen, die durch einfache chemische Reduktion der Metallsalze hergestellt werden, sehr fein mit Teilchendurchmesser zwischen 0,001 und 0,1 µm. Sie besitzen eine große spezifische Oberfläche von 10 bis 40 m2/g je nachdem, welches Reduktionsmittel verwandt wurde. Die Primärteilchen dieser Pulver können durch thermomechanische Behandlung agglomeriert werden. Diese Teilchen sind jedoch so strukturiert, daß sie in der Regel eine geringe Korngröße mit großer spezifischer Oberfläche aufweisen. Unter diesen Bedingungen sind die Pulver sehr reaktiv; dies ist für die Herstellung von gesinterten Metallen sowie elektronischen Bauteilen und mikroelektronischen Hybridschaltkreisen von Nachteil.Very fine metal and metal alloy powders are produced by chemical synthesis using the classic method. So z. B. metal powder, such as the powder of precious metals and their alloys, which are produced by simple chemical reduction of the metal salts, very fine with a particle diameter between 0.001 and 0.1 µm. They have a large specific surface area of 10 to 40 m 2 / g, depending on which reducing agent was used. The primary particles of these powders can be agglomerated by thermomechanical treatment. However, these particles are structured so that they usually have a small grain size with a large specific surface area. Under these conditions the powders are very reactive; this is disadvantageous for the production of sintered metals as well as electronic components and microelectronic hybrid circuits.

Welch großen Einfluß die Morphologie der Metall- oder Metallegierungspulver ausübt wird deutlich im Fall der keramischen Vielschichtkondensatoren mit Innenelektroden bestehend aus einer Legierung des Systems Silber-Palladium.The great influence exerted by the morphology of the metal or metal alloy powder becomes clear in the case of the ceramic multilayer capacitors with internal electrodes consisting of an alloy of the silver-palladium system.

Die beiden Metalle bilden leicht fortlaufende Reihen einphasiger Lösungen. Die Temperatur des festen Aggregatszustandes und die des flüssigen liegt zwischen dem Schmelzpunkt des Palladiums bei 1552°C und dem Schmelzpunkt des Silbers bei 961°C. Um die genannten Kondensatoren herzustellen, wird das Verhältnis Pd/Ag so gewählt, daß der Schmelzpunkt über der Sintertemperatur des Nichtleiters liegt, um zu verhindern, daß die Elektrode während des Sinterprozesses schmilzt.The two metals form slightly continuous series of single-phase solutions. The temperature of the solid state and that of the liquid is between the melting point of the palladium at 1552 ° C and the melting point of the silver at 961 ° C. In order to produce the capacitors mentioned, the ratio Pd / Ag is chosen so that the melting point is above the sintering temperature of the non-conductor in order to prevent the electrode from melting during the sintering process.

Die beiden Metalle bilden Oxide, wenn sie an der Luft gesintert werden. Ag2O stellt bei Raumtemperatur und bis zu 300°C die stabilste Oxydationsstufe des Silbers dar. Die Oxidbildung wird jedoch durch die Luft und die Abnahme der spezifischen Oberfläche des Silbers während der ersten Sinterphase behindert.The two metals form oxides when sintered in air. Ag 2 O is the most stable oxidation level of silver at room temperature and up to 300 ° C. However, the formation of oxide is impeded by the air and the decrease in the specific surface area of the silver during the first sintering phase.

Palladium dagegen bildet leicht das Oxid PdO in der Anfangsphase des Sintervorgangs. Der Umfang hängt ab von der spezifischen Oberfläche des Metalls, der Aufheizgeschwindigkeit und dem Partialdruck an Luftsauerstoff. PdO mit tetragonaler kristalliner Struktur ist thermodynamisch bis ca. 800°C. stabil und kehrt bei höheren Temperaturen in den metallischen Zustand zurück.Palladium, on the other hand, easily forms the oxide PdO in the initial phase of the sintering process. The extent depends on the specific surface of the metal, the heating rate and the partial pressure of atmospheric oxygen. PdO with a tetragonal crystalline structure is thermodynamic up to approx. 800 ° C. stable and returns to the metallic state at higher temperatures.

Beim Sintern der Kondensatoren kann die Oxydation des Palladiums von einer Volumenausdehnung bis zu 40% begleitet sein. Oberhalb 800°C macht sich die Reduktion von PdO zu Pd in einer Volumenverringerung bemerkbar. Beide Reaktionen verursachen Spannungen, die ein Grund für das Aufblättern sind.When the capacitors are sintered, the oxidation of the palladium can be accompanied by a volume expansion of up to 40%. Above 800 ° C the reduction of PdO to Pd is noticeable in a volume reduction. Both reactions cause tension, which is a reason for the flaking.

Die Oxydation-Reduktion des Palladiums wird durch Zugabe von Silber beschleunigt. Zum Beispiel erreichen Pulver, die aus 70 Gew.-% Ag und 30 Gew.-% Pd bestehen, das Oxydationsmaximum bei 520 °C gegenüber 790 °C ohne Silber. Das Reduktionsende von PdO wird auf die gleiche Weise von 900 °C auf 700 °C herabgesetzt.The oxidation reduction of the palladium is accelerated by adding silver. For example, powders consisting of 70 wt% Ag and 30 wt% Pd reach the oxidation maximum at 520 ° C compared to 790 ° C without silver. The reduction end of PdO is reduced in the same way from 900 ° C to 700 ° C.

Während der Brennphasen kann das feine Pulver katalytisch mit dem organischen Medium reagieren unter Bildung von warmen Punkten, wobei es zu einer raschen Entgasung, Blasenbildung und zum Aufblättern der Kondensatoren kommt. Die Schwindungseigenschaften sehr feiner Metallpulver sind in der Regel sehr ausgeprägt und können die Eigenschaften der umgebenden dielektrischen Materialien nicht ausgleichen. Folglich bilden sich aus den diskontinuierlichen Metallgruppen mit schwächerer Leitfähigkeit winzige Metall-"Inseln".During the firing phases, the fine powder can react catalytically with the organic medium to form warm spots, which leads to rapid degassing, bubble formation and the condensers peeling. The shrinkage properties of very fine metal powders are usually very pronounced and cannot compensate for the properties of the surrounding dielectric materials. As a result, tiny metal "islands" form from the discontinuous metal groups with weaker conductivity.

Der Erfindung liegt die Aufgabe zugrunde, inaktive Edelmetallpulver bereitzustellen, die fein genug sind für den Einsatz in Siebdruckpasten, deren spezifische Oberfläche aber klein genug sein muß, damit die katalytische Wirkung gebremst wird. Eine weitere Aufgabe dieser Erfindung besteht darin, ein Verfahren und eine Vorrichtung zur Herstellung solcher Pulver, ausgehend von mikrokristallinen Pulvern aus nicht-sphärischen Teilchen, deren spezifische Oberfläche größer ist als der theoretisch berechnete Wert, zu entwickeln.The object of the invention is to provide inactive noble metal powders which are fine enough for use in screen printing pastes, but whose specific surface area has to be small enough so that the catalytic effect is slowed down. Another object of this invention is to develop a method and an apparatus for producing such powders, starting from microcrystalline powders from non-spherical particles, the specific surface area of which is larger than the theoretically calculated value.

Die Erfindung betrifft deshalb Pulver aus Edelmetallen oder aus binären sowie ternären Edelmetallegierungen in Form von mikrokristallinen, vollkommen kugelförmigen und dichten Teilchen, die dadurch gekennzeichnet sind, daß der mittlere Teilchendurchmesser zwischen 0,1 µm und weniger als 5 µm und das Kornspektrum innerhalb 0,1 µm und 10 µm liegt.The invention therefore relates to powders made of noble metals or of binary and ternary noble metal alloys in the form of microcrystalline, completely spherical and dense particles, which are characterized in that the mean particle diameter is between 0.1 μm and less than 5 μm and the grain spectrum within 0.1 µm and 10 µm.

Gefunden wurde ferner ein Verfahren zur Herstellung von Pulvern aus Edelmetallen und Edelmetallegierungen in Form von mikrokristallinen, vollkommen kugelförmigen und dichten Teilchen mit einem mittleren Korndurchmesser zwischen 0,1 und 5 µm und einem Kornspektrum innerhalb 0,1 und 10 µm aus Ausgangspulvern der Edelmetalle oder deren Legierungen in Form von mikrokristallinen, nicht-sphärischen Teilchen mit einer größeren spezifischen Oberfläche als die der herzustellenden Pulver, umfassend Suspendieren des Ausgangspulves in einem reaktionsträgen Trägergas, Durchleiten der Suspension (Pulverwolke) durch einen rohrförmigen Ofen mit externer Beheizung, worin die Pulverteilchen bei einer Temperatur innerhalb der Heizzone des Ofens von 100 bis 250 °C oberhalb der Schmelztemperatur der Pulverteilchen auf eine Temperatur oberhalb des Schmelzpunktes erhitzt werden, Abkühlen der Suspension zwecks Erstarren der geschmolzenen Pulverteilchen mittels einer oder mehrerer Kühlvorrichtungen, welche zwischen der Heizzone und dem Ausgang des rohrförmigen Ofens außerhalb desselben und/oder außerhalb eines sich an den Ausgang des rohrförmigen Ofens anschließenden Kamins, dessen Durchmesser größer ist als derjenige des rohrförmigen Ofens, angeordnet sind und Abtrennung der kugelförmigen Pulverteilchen aus der Suspension mittels bekannter Methoden.A process for the production of powders from precious metals and precious metal alloys in the form was also found microcrystalline, completely spherical and dense particles with an average grain diameter between 0.1 and 5 µm and a grain spectrum within 0.1 and 10 µm from starting powders of the precious metals or their alloys in the form of microcrystalline, non-spherical particles with a larger specific surface than that of the powders to be prepared, comprising suspending the starting powder in an inert carrier gas, passing the suspension (powder cloud) through a tubular oven with external heating, wherein the powder particles are at a temperature within the heating zone of the oven of 100 to 250 ° C above the melting temperature of the Powder particles are heated to a temperature above the melting point, cooling the suspension to solidify the molten powder particles by means of one or more cooling devices which are located between the heating zone and the outlet of the tubular furnace outside it and / or outside e it is arranged at the exit of the tubular furnace, the diameter of which is larger than that of the tubular furnace, and separating the spherical powder particles from the suspension by means of known methods.

Gemäß einer bevorzugten Ausführungsform des Verfahrens wird als Ausgangsprodukt ein Metall- oder Metallegierungspulver verwendet, welches durch chemische Synthese, vorzugsweise durch chemische Reduktion von Metallsalzen mit eventuell anschließender thermomechanischer Behandlung, hergestellt wurde.According to a preferred embodiment of the method, a metal or metal alloy powder is used as the starting product, which was produced by chemical synthesis, preferably by chemical reduction of metal salts with possibly subsequent thermomechanical treatment.

Als Ausgangsprodukt können im Prinzip alle Pulver verwendet werden, die sich im Trägergas suspendieren lassen. Die Durchlaufgeschwindigkeit der Suspension durch den Ofen und die Temperatur der Heizzone werden so geregelt, daß die geschmolzenen Teilchen beim Eintritt in die Kühlzone kugelförmig sind. Die Heizzone wird vorzugsweise auf eine Temperatur eingestellt, die 100 bis 250 °C über der Schmelztemperatur liegt. Die Teilchen erstarren in einer Kühlvorrichtung, die außen am Ofenrohr oder in einem Teil des Rohres und/oder außerhalb des Ofens angebracht sein kann.In principle, all powders that can be suspended in the carrier gas can be used as the starting product. The flow rate of the suspension through the furnace and the temperature of the heating zone are controlled so that the molten particles are spherical as they enter the cooling zone. The heating zone is preferably set to a temperature which is 100 to 250 ° C above the melting temperature. The particles solidify in a cooling device, which can be attached to the outside of the furnace tube or in a part of the tube and / or outside the furnace.

Nach dem erfindungsgemäßen Verfahren können Pulver von unedlen Metallen, wie z. B. Kupfer, Blei, Zinn, Zink, Aluminium sowie Pulver von Edelmetallen, vorzugsweise Silber, Gold, Palladium und Platin hergestellt werden. Darüber hinaus ist das Verfahren auf binäre und ternäre Metallegierungen anwendbar.According to the method of the invention, powders of base metals, such as. B. copper, lead, tin, zinc, aluminum and powder of precious metals, preferably silver, gold, palladium and platinum. The method is also applicable to binary and ternary metal alloys.

Beispielsweise weist ein Pulver einer Ag-Pd-Legierung, hergestellt durch chemische Reduktion eines Silber-Palladium-Mischcarbonates mit Hilfe eines Reduktionsmittels vom Typ eines Aldehyds in wäßriger Phase eine spezifische Oberfläche von 10 m2/g (gemessen mittels N2-Gasadsorption nach der BET-Methode) und einen Teilchendurchmesser von kleiner 0,1 µm aus. Durch thermomechanische Behandlung des hergestellten Pulvers erhält man ein Pulver mit einer spezifischen Oberfläche von 1 bis 2 m2/g. Mit dem erfindungsgemäßen Verfahren kann die spezifische Oberfläche des zuletztgenannten Pulvers auf ca. 0,3 bis 0,5 m2/g verringert werden.For example, a powder of an Ag-Pd alloy produced by chemical reduction of a silver-palladium mixed carbonate using a reducing agent of the aldehyde type in the aqueous phase has a specific surface area of 10 m 2 / g (measured by means of N 2 gas adsorption after the BET method) and a particle diameter of less than 0.1 µm. A powder with a specific surface area of 1 to 2 m 2 / g is obtained by thermomechanical treatment of the powder produced. With the method according to the invention, the specific surface area of the latter powder can be reduced to approximately 0.3 to 0.5 m 2 / g.

Eine Vorrichtung zur Durchführung des Verfahrens wird anhand der nachstehenden Beispiele und der anhängenden Figuren näher erläutert:

  • Fig. 1 zeigt die Morphologie eines Ausgangspulvers einer Ag-Pd-Legierung.
  • Fig. 2 zeigt die Morphologie eines Produktes, hergestellt nach dem erfindungsgemäßen Verfahren (Fig. 1 und 2 stellen Aufnahmen mit dem Rasterelektronenmikroskop dar).
  • Fig. 3 zeigt im Längsschnitt ein Schema einer Anlage zur Herstellung von Pulvern nach dem erfindungsgemäßen Verfahren.
A device for carrying out the method is explained in more detail with the aid of the examples below and the attached figures:
  • 1 shows the morphology of a starting powder of an Ag-Pd alloy.
  • FIG. 2 shows the morphology of a product produced by the method according to the invention (FIGS. 1 and 2 represent images with the scanning electron microscope).
  • Fig. 3 shows in longitudinal section a diagram of a plant for the production of powders according to the inventive method.

Die Anlage gemäß Fig. 3 enthält eine Vorrichtung zum Suspendieren des Pulvers (1), einen rohrförmigen Ofen (8), eine oder mehrere Vorrichtungen zum Abkühlen der Suspension (11) und eine Vorrichtung (13), in der das Pulver aus kugelförmigen Teilchen von Trägergas getrennt und zurückgewonnen wird; die Vorrichtung (1) besteht aus einem luftdichten Gehäuse (2), einem System zum Einfüllen des Ausgangspulvers (3), mindestens einer Trägergaszufuhr (4), einer Vorrichtung (5, 6)zum intensiven Mischen des Pulvers mit dem Gas und einem Ausgang (7), der mit dem Anfang (9a) des Rohres (9) des röhrenfömigen Ofens (8) verbunden ist; der Bereich (9b) des Rohres (9) ist mit einer oder mehreren Heizvorrichtungen (10) umgeben, die Kühlvorrichtung oder -vorrichtungen (11) sind innen und/oder außen am Rohr (9) zwischen der Heizzone (9b)und dem Rohrausgang (9c)und/oder innen und/oder außen am Kamin (12), der sich zwischen dem Rohrende(9c) und der Rückgewinnungskammer(13) befindet, angebracht.3 contains a device for suspending the powder (1), a tubular furnace (8), one or more devices for cooling the suspension (11) and a device (13) in which the powder consists of spherical particles Carrier gas is separated and recovered; the device (1) consists of an airtight housing (2), a filling system the starting powder (3), at least one carrier gas supply (4), a device (5, 6) for intensive mixing of the powder with the gas and an outlet (7) connected to the beginning (9a) of the tube (9) of the tubular furnace (8) is connected; the area (9b) of the pipe (9) is surrounded by one or more heating devices (10), the cooling device or devices (11) are inside and / or outside of the pipe (9) between the heating zone (9b) and the pipe outlet ( 9c) and / or inside and / or outside on the chimney (12), which is located between the pipe end (9c) and the recovery chamber (13).

Die Vorrichtung (1) und ihre Teile (2) bis (6) können in verschiedener Weise ausgeführt werden. Die Pulverzufuhr (3) kann z.B. durch herkömmliche Dosiersysteme erfolgen, die für feine Pulver verwendet werden, wie z.B. Zellradschleusen, Dosierschnecken oder Vibrationsrutschen. Fig. 3 zeigt eine besonders geeignete Mischvorrichtung (5, 6); (5)ist ein durch einen Motor (6)angetriebener Rotor (5). Das Prinzip von Mischvorrichtungen ohne mobile Teile, wobei an einer Seite feststehender Mischer Pulver und Trägergas eingeführt werden, hat sich ebenfalls bewährt. Anstatt über die Zuleitung (4)kann das Trägergas auch über andere Anschlüsse in die Mischkammer (2) geleitet werden. Das Rohr (9) des röhrenförmigen Ofens (8) besitzt eine Heizzone (9c),die durch ein oder mehrere Heizregister (10) beheizt wird. Die Beheizung kann elektrisch oder mit Gas erfolgen; eine elektrische Heizung wird jedoch bevorzugt, weil sie die Regelung und Einstellung des Temperaturprogramms für die gesamte Heizzone auf einfache Weise ermöglicht. Das Rohr (9)ist an einem Ende(9a) mit der Mischkammer (2)und am anderen Ende (9c) mit der Rückgewinnungskammer (13) oder einem eventuellen Kamin (12) zwischen der Rückgewinnungskammer und dem Rohr (9)verbunden. Das oder die Kühlsysteme (11) können unterschiedlich geartet und am Ende des Rohrs(9)und/oder in der Nähe des eventuellen Kamins (12) angeordnet sein. Das Abkühlen der Suspension kann in einem oder mehreren Schritten erfolgen. Nach dem bevorzugten Schema gemäß Fig.3 befindet sich die Kühlvorrichtung (11) am Ende des Rohres (9);
dieses Kühlsystem besteht aus einem Wärmetauscher, der um das Rohr gelegt ist und mit einem Kältemittel arbeitet; (11a) und (11b)stellen die Zufuhr bzw. Ableitung des Kältemittels dar. Das fakultative Kühlsystem (14) mit Zuleitung und Ableitung (14a und 14b) des Kältemittels dient dazu, das Rohr (9) stabil mit der Kammer (2)zu verbinden. Wird zwischen Rohr (9)und dem Rückgewinnungssystem (13)ein Rohrelement(12) eingebaut, das die Form eines Kamins hat und mit einer Kühlvorrichtung ausgerüstet, werden kann, so wird es aufgrund seines gegenüber Rohr (9) wesentlich größeren Durchmessers bewirken, daß sich die Durchströmgeschwindigkeit der Suspension verringert. Auf diese Weise kann in der einfach gebauten Kammer (13) das Pulver durch Absetzten vom Trägergas getrennt werden; das Pulver bewegt sich in Richtung Ablaß (13b); das Trägergas entweicht über des Ausgang (13a), der gegebenenfalls mit Staubfiltern versehen ist, oder es wird komplett oder teilweise in die Mischkammer zurückgeleitet. Anstelle in der Rückgewinnungskammer (13)der Fig. 3 kann die kontinuierliche Trennung des Pulvers von der abgekühlten Suspension auch mittels anderer bekannter Vorrichtungen erfolgen, etwa mittels eines Staubabscheiders und/oder Staubfilters.The device (1) and its parts (2) to (6) can be designed in various ways. The powder feed (3) can take place, for example, by conventional metering systems which are used for fine powders, such as cellular wheel sluices, metering screws or vibration chutes. Fig. 3 shows a particularly suitable mixing device (5, 6); (5) is a rotor (5) driven by a motor (6). The principle of mixing devices without mobile parts, whereby powder and carrier gas are introduced on one side of the fixed mixer, has also proven itself. Instead of via the feed line (4), the carrier gas can also be fed into the mixing chamber (2) via other connections. The tube (9) of the tubular furnace (8) has a heating zone (9c) which is heated by one or more heating registers (10). The heating can be done electrically or with gas; however, an electric heater is preferred because it enables the regulation and setting of the temperature program for the entire heating zone in a simple manner. The pipe (9) is connected at one end (9a) to the mixing chamber (2) and at the other end (9c) to the recovery chamber (13) or any chimney (12) between the recovery chamber and the pipe (9). The cooling system (s) (11) can be of different types and can be arranged at the end of the pipe (9) and / or in the vicinity of the possible chimney (12). The suspension can be cooled in one or more steps respectively. According to the preferred scheme according to Figure 3, the cooling device (11) is at the end of the tube (9);
this cooling system consists of a heat exchanger that is placed around the pipe and works with a refrigerant; (11a) and (11b) represent the supply or discharge of the refrigerant. The optional cooling system (14) with supply and discharge (14a and 14b) of the refrigerant serves to stably close the pipe (9) with the chamber (2) connect. If a pipe element (12), which has the shape of a chimney and is equipped with a cooling device, can be installed between the pipe (9) and the recovery system (13), it will, due to its significantly larger diameter than the pipe (9), cause that the flow rate of the suspension decreases. In this way, the powder can be separated from the carrier gas by settling in the simply constructed chamber (13); the powder moves towards the outlet (13b); the carrier gas escapes via the outlet (13a), which is optionally provided with dust filters, or it is completely or partially returned to the mixing chamber. Instead of in the recovery chamber (13) of FIG. 3, the continuous separation of the powder from the cooled suspension can also take place by means of other known devices, for example by means of a dust separator and / or dust filter.

Es wurde überraschenderweise gefunden, daß mikrokristalline Metall- oder Metallegierungspulver, die als nicht-sphärische Teilchen vorliegen, erfindungsgemäß in einer speziell für dieses Verfahren entwickelten Herstellvorrichtung in Pulver mit kugelförmigen Teilchen und glatter Oberfläche umgewandelt werden können. Dieses Verfahren ist besonders vorteilhaft, weil es wesentlich einfacher ist und wirtschaftlicher arbeiten kann als die bekannten Verfahren, die ebenfalls von Feststoffen ausgehen. Bei dem erfindungsgemäßen Verfahren ist die benötigte Gasmenge wesentlich geringer als bei den benannten Verfahren; die Energie- und Rohstoffkosten sind also niedriger. Durch gezielte Auswahl des Ausgangsproduktes und Variation seiner Verweildauer in der Heizzone unter Abänderung der Länge und Temperatur der Heizzone sowie der Durchströmgeschwindigkeit des Gases können Pulver der gewünschten Kornspektren in Bereichen hergestellt werden, die bisher noch nicht erreicht wurden. Die mit dem erfindungsgemäßen Verfahren hergestellten Pulver haben sich als besonders geeignet für die Herstellung von elektronischen Bauteilen, wie keramischen Vielschichtkondensatoren,erwiesen. Aufgrund ihrer einfachen Bauweise eignet sich die Vorrichtung besonders zur Herstellung kleiner Pulverchargen sehr teurer Metalle, wie z.B. von Edelmetallen und ihren Legierungen.It has surprisingly been found that microcrystalline metal or metal alloy powders which are present as non-spherical particles can, according to the invention, be converted into powders with spherical particles and a smooth surface in a production device specially developed for this process. This process is particularly advantageous because it is much simpler and can work more economically than the known processes, which also start from solids. In the method according to the invention, the amount of gas required is considerably less than in the named methods; the energy and raw material costs are lower. Through targeted selection of the starting product and variation of its residence time in the heating zone by changing the length and temperature of the heating zone and the flow rate of the gas, powders of the desired grain spectra can be produced in areas that have not yet been achieved. The powders produced by the process according to the invention have proven to be particularly suitable for the production of electronic components, such as ceramic multilayer capacitors. Due to its simple construction, the device is particularly suitable for the production of small powder batches of very expensive metals, such as precious metals and their alloys.

Im übrigen kann eine Vorrichtung zur Herstellung der erfindungsgemäßen Pulver auch zur Verbesserung der Kristallstruktur der Metall- und Metallegierungspulver verwendet werden, selbst wenn sie bei Temperaturen behandelt werden, die 100 bis 200°C unter der Schmelztemperatur liegen. In diesem Fall kann das Ausgangspulver die Form von kugelförmigen oder nicht-sphärischen Teilchen haben.Furthermore, a device for producing the powders according to the invention can also be used to improve the crystal structure of the metal and metal alloy powders, even if they are treated at temperatures which are 100 to 200 ° C. below the melting temperature. In this case, the starting powder can be in the form of spherical or non-spherical particles.

Das Verfahren wird durch nachstehende Beispiele näher erläutert:The process is explained in more detail by the following examples:

Beispiel 1example 1

Das Ausgangspulver - siehe Fig. 1 - ist eine Silber-/Palladium-Legierung mit 30 Gew.-% Pd, die auf chemischem Weg und durch thermomechanische Behandlung hergestellt wurde.The starting powder - see FIG. 1 - is a silver / palladium alloy with 30% by weight of Pd, which was produced chemically and by thermomechanical treatment.

Es besitzt folgende chemisch-physikalischen Eigenschaften:

  • Morphologie: Agglomerate von 3 bis 4 µm, in Einzelfällen bis zu 17 µm.
  • Spezifische Oberfläche: 1,8 m2/g (Gasadsorption noch der BET-Methode))
  • Oxydationsgrad: 60 - 80% des enthaltenen Palladiums oxidiert sich bei der maximalen Oxidationstemperatur.
It has the following chemical-physical properties:
  • Morphology: agglomerates of 3 to 4 µm, in individual cases up to 17 µm.
  • Specific surface area: 1.8 m 2 / g (gas adsorption still using the BET method))
  • Degree of oxidation: 60 - 80% of the palladium contained is oxidized at the maximum oxidation temperature.

Versuchsbedingungen:Test conditions:

  • Das Verfahren wurde in einer Vorrichtung gemäß Fig. 3 durchgeführtThe method was carried out in a device according to FIG. 3
  • Trägergas; Argon, Durchsatz: 1 l/min.Carrier gas; Argon, flow: 1 l / min.
  • Drehgeschwindigkeit des Rotors: 3000 U/min.Rotation speed of the rotor: 3000 rpm.
  • Ofentemperatur: 1460°COven temperature: 1460 ° C
Ergebnisse:Results:

Die Teilchen sind vollkommen kugelförmig - siehe Fig. 2; die Korngröße liegt zwischen 0,2 und 3 µm, die spezifische Oberfläche beträgt 0,43 m2/g (Elektronenmikroskop). Die Teilchen des Pulvers sind vollkommen homogen; die chemische Zusammensetzung hat sich nicht geändert.The particles are completely spherical - see Fig. 2; the grain size is between 0.2 and 3 µm, the specific surface is 0.43 m 2 / g (electron microscope). The particles of the powder are completely homogeneous; the chemical composition has not changed.

Einsatz:Commitment:

Das Ausgangspulver und das erhaltenen Pulver wurden zur Herstellung der Innenelektroden von keramischen Vielschichtkondensatoren eingesetzt; Herstellung der Kondensatoren nach bekannten Verfahren:The starting powder and the powder obtained were used to produce the internal electrodes of ceramic multilayer capacitors; Manufacture of capacitors using known methods:

Die Chips auf Basis der Ausgangspulver zeigten einige winzige Metall-Inseln sowie teilweises Aufblättern der Schichten nach dem Sintern bei 1150°C.The chips based on the starting powder showed some tiny metal islands as well as partial exfoliation of the layers after sintering at 1150 ° C.

Die Chips auf Basis des kugelförmigen Pulvers nach Beispiel 1 zeigten kein Aufblättern nach dem Sintern bei 1150°C.The chips based on the spherical powder according to Example 1 showed no exfoliation after sintering at 1150 ° C.

Beispiel 2:Example 2:

Ausgangspulver und Versuchsbedingungen sind identisch mit Beispiel 1, der einzige Unterschied besteht darin, daß die Ofentemperatur auf 1320°C eingestellt wird.Starting powder and test conditions are identical to Example 1, the only difference is that the oven temperature is set to 1320 ° C.

Ergebnisse:Results:

Die Teilchen sind vollkommen kugelförmig, die Korngröße liegt zwischen 0,4 und 4 µm, die spezifische Oberfläche beträgt 0,34 m2/g. Die Teilchen des Pulvers sind vollkommen homogen; die chemische Zusammensetzung hat sich nicht geändert.The particles are completely spherical, the grain size is between 0.4 and 4 µm, the specific surface area is 0.34 m 2 / g. The particles of the powder are completely homogeneous; the chemical composition has not changed.

Der Oxydationsgrad des enthaltenen Palladiums liegt bei 30% bei der maximalen Oxydationstemperatur von 575°C. Die bei 1100°C gemessene Schwindung beträgt 12% gegenüber 40% des Ausgangspulvers. Der lineare Wärmeausdehnungskoeffizient bei 0 und 900°C liegt nahe an dem der Schichtverbindung, d.h. 1,68 x 10-5/°C.The degree of oxidation of the palladium contained is 30% at the maximum oxidation temperature of 575 ° C. The shrinkage measured at 1100 ° C is 12% compared to 40% of the starting powder. The linear coefficient of thermal expansion at 0 and 900 ° C is close to that of the layer connection, ie 1.68 x 10 -5 / ° C.

Eingesetzt für die Herstellung der Innenelektroden von keramischen Vielschichtkondensatoren zeigten die Chips nach dem Sintern bei 1150°C kein Aufblättern.Used for the production of the inner electrodes of ceramic multilayer capacitors, the chips showed no peeling after sintering at 1150 ° C.

Beispiel 3Example 3

Das Ausgangspulver ist eine Silber-/Palladium-Legierung mit 70 Gew.-% Pd, die auf chemischem Weg und durch thermomechanische Behandlung hergestellt wurde.The starting powder is a silver / palladium alloy with 70% by weight Pd, which was produced chemically and by thermomechanical treatment.

Es besitzt folgende chemisch-physikalischen Eigenschaften:

  • Morphologie: Agglomerate von 3 bis 5 µm, in Einzelfällen bis zu 12 µm.
  • Spezifische Oberfläche: 1,5 m2/g
It has the following chemical-physical properties:
  • Morphology: agglomerates of 3 to 5 µm, in individual cases up to 12 µm.
  • Specific surface area: 1.5 m 2 / g

Versuchsbedingungen:Test conditions:

  • Vorrichtung gemäß Fig. 3 ,3,
  • Trägergas: Argon, Durchsatz: 5 l/min.Carrier gas: argon, flow rate: 5 l / min.
  • Drehgeschwindigkeit des Rotors: 3000 U/min.Rotation speed of the rotor: 3000 rpm.
  • Ofentemperatur: 1500°COven temperature: 1500 ° C
Ergebnisse:Results:

Die Teilchen sind vollkommen kugelförmig; die Korngröße liegt zwischen 0,2 und 3 µm, die spezifische Oberfläche beträgt 0,5 m2/g. Die Teilchen des Pulvers sind vollkommen homogen; die chemische Zusammensetzung hat sich nicht geändert.The particles are perfectly spherical; the grain size is between 0.2 and 3 µm, the specific surface is 0.5 m 2 / g. The particles of the powder are completely homogeneous; the chemical composition has not changed.

Beispiel 4Example 4

Das Ausgangspulver besteht aus Silberteilchen, die durch chemische Reduktion gewonnen wurden. Es besitzt folgende chemisch-physikalischen Eigenschaften:

  • Morphologie: Agglomerate von 5 bis 7 µm, in Einzelfällen bis zu 25 µm.
  • Spezifische Oberfläche: 1 m2/g
The starting powder consists of silver particles that have been obtained by chemical reduction. It has the following chemical-physical properties:
  • Morphology: agglomerates of 5 to 7 µm, in individual cases up to 25 µm.
  • Specific surface area: 1 m 2 / g

Versuchsbedingungen:Test conditions:

  • Vorrichtung gemäß Fig. 3 ,3,
  • Trägergas: Argon, Durchsatz: 5 l/min.Carrier gas: argon, flow rate: 5 l / min.
  • Drehgeschwindigkeit des Rotors: 3000 U/min.Rotation speed of the rotor: 3000 rpm.
  • Ofentemperatur: 1200°COven temperature: 1200 ° C
Ergebnisse:Results:

Die Teilchen sind vollkommen kugelförmig; die Korngröße liegt zwischen 2 und 5 µm.The particles are perfectly spherical; the grain size is between 2 and 5 µm.

Beispiel 5Example 5

Das Ausgangspulver besteht aus Kupferteilchen, die durch thermische Dissoziation unter Stickstoff bei 300°C aus einem pulverisierten Kupfer-Formiat gewonnen wurden.

  • Morphologie: Agglomerate bis zu 50 µm.
  • Spezifische Oberfläche: 0,8 m2/g
The starting powder consists of copper particles obtained from a powdered copper formate by thermal dissociation under nitrogen at 300 ° C.
  • Morphology: agglomerates up to 50 µm.
  • Specific surface area: 0.8 m 2 / g

Versuchsbedingungen:Test conditions:

  • Vorrichtung gemäß Fig. 3 ,3,
  • Trägergas: Argon.Carrier gas: argon.
  • Drehgeschwindigkeit des Rotors: 3000 U/min.Rotation speed of the rotor: 3000 rpm.
  • Ofentemperatur: 1300°COven temperature: 1300 ° C
Ergebnisse:Results:

Die Teilchen sind vollkommen kugelförmig; die mittlere Korngröße beträgt 8 µm, die spezifische Oberfläche 0,2 m2/g.The particles are perfectly spherical; the average grain size is 8 µm, the specific surface 0.2 m 2 / g.

Claims (4)

  1. Powders of precious metals or of binary and ternary precious metal alloys in the form of microcrystalline, completely spherical and dense particles,
    characterised in that
    the average particle diameter is between 0.1 µm and less than 5 µm and the spectrum of particle sizes is within 0.1 µm and 10 µm.
  2. Powders according to claim 1,
    characterised in that
    they consist of silver, gold, palladium or platinum or alloys thereof.
  3. Process for the preparation of powders of precious metals and precious metal alloys in the form of microcrystalline, completely spherical and dense particles with an average particle diameter of between 0.1 and 5 µm and a spectrum of particle sizes within 0.1 and 10 µm from starting powders of the precious metals or their alloys in the form of microcrystalline, non-spherical particles with a larger specific surface than the powders to be prepared, comprising suspending the starting powder in an inert carrier gas, passing the suspension (powder cloud) through a tubular furnace with external heating, in which the powder particles are heated to a temperature above the melting point at a temperature within the heating zone of the furnace from 100 to 250°C above the melting temperature of the powder particles, cooling of the suspension for the purpose of hardening the molten powder particles by means of one or more cooling devices which are arranged between the heating zone and the outlet of the tubular furnace outside the same and/or outside a chimney connected to the outlet of the tubular furnace, the diameter of which is greater than that of the tubular furnace, and separation of the spherical powder particles from the suspension by means of known methods.
  4. Process according to claim 3,
    characterised in that
    a precious metal or precious metal alloy powder which has been produced by chemical synthesis, preferably by chemical reduction of metal salts with possible subsequent thermomechanical treatment, is used as the starting product.
EP92116067A 1991-10-18 1992-09-19 Metal- and metal alloy powder comprising microcrystalline, spherical and dense particles and process and installation for preparing same Expired - Lifetime EP0537502B1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
FR9112890A FR2682625B1 (en) 1991-10-18 1991-10-18 POWDERS OF METALS AND METAL ALLOYS IN THE FORM OF SPHERICAL AND COMPACT MICROCRYSTALLINE GRAINS, AND PROCESS AND DEVICE FOR MANUFACTURING POWDERS.
FR9112890 1991-10-18

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EP0537502A1 EP0537502A1 (en) 1993-04-21
EP0537502B1 true EP0537502B1 (en) 1997-07-23

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EP (1) EP0537502B1 (en)
JP (1) JPH05214410A (en)
DE (1) DE59208720D1 (en)
FR (1) FR2682625B1 (en)

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US7128852B2 (en) 1997-02-24 2006-10-31 Cabot Corporation Aerosol method and apparatus, particulate products, and electronic devices made therefrom
US7749299B2 (en) 2005-01-14 2010-07-06 Cabot Corporation Production of metal nanoparticles
US8167393B2 (en) 2005-01-14 2012-05-01 Cabot Corporation Printable electronic features on non-uniform substrate and processes for making same
US8334464B2 (en) 2005-01-14 2012-12-18 Cabot Corporation Optimized multi-layer printing of electronics and displays
US8383014B2 (en) 2010-06-15 2013-02-26 Cabot Corporation Metal nanoparticle compositions
US8597397B2 (en) 2005-01-14 2013-12-03 Cabot Corporation Production of metal nanoparticles

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US7625420B1 (en) 1997-02-24 2009-12-01 Cabot Corporation Copper powders methods for producing powders and devices fabricated from same
US6159267A (en) * 1997-02-24 2000-12-12 Superior Micropowders Llc Palladium-containing particles, method and apparatus of manufacture, palladium-containing devices made therefrom
US6699304B1 (en) 1997-02-24 2004-03-02 Superior Micropowders, Llc Palladium-containing particles, method and apparatus of manufacture, palladium-containing devices made therefrom
DE10120484A1 (en) * 2001-04-25 2002-10-31 Degussa Method and device for the thermal treatment of powdery substances
EP3216545B2 (en) * 2016-03-07 2022-09-28 Heraeus Deutschland GmbH & Co. KG Precious metal based powder and its use in the preparation of components

Family Cites Families (3)

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Publication number Priority date Publication date Assignee Title
US2038251A (en) * 1933-01-03 1936-04-21 Vogt Hans Process for the thermic treatment of small particles
FR823216A (en) * 1936-06-18 1938-01-17 Lignes Telegraph Telephon Heat treatment of powders
US4731110A (en) * 1987-03-16 1988-03-15 Gte Products Corp. Hydrometallurigcal process for producing finely divided spherical precious metal based powders

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US7128852B2 (en) 1997-02-24 2006-10-31 Cabot Corporation Aerosol method and apparatus, particulate products, and electronic devices made therefrom
US8333820B2 (en) 1997-02-24 2012-12-18 Cabot Corporation Forming conductive features of electronic devices
US7749299B2 (en) 2005-01-14 2010-07-06 Cabot Corporation Production of metal nanoparticles
US8167393B2 (en) 2005-01-14 2012-05-01 Cabot Corporation Printable electronic features on non-uniform substrate and processes for making same
US8334464B2 (en) 2005-01-14 2012-12-18 Cabot Corporation Optimized multi-layer printing of electronics and displays
US8597397B2 (en) 2005-01-14 2013-12-03 Cabot Corporation Production of metal nanoparticles
US8668848B2 (en) 2005-01-14 2014-03-11 Cabot Corporation Metal nanoparticle compositions for reflective features
US8383014B2 (en) 2010-06-15 2013-02-26 Cabot Corporation Metal nanoparticle compositions

Also Published As

Publication number Publication date
FR2682625B1 (en) 1997-04-11
FR2682625A1 (en) 1993-04-23
DE59208720D1 (en) 1997-08-28
EP0537502A1 (en) 1993-04-21
JPH05214410A (en) 1993-08-24

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