DE10135088A1 - Preparation of a powder mixture useful in which ceramic and metallic powders are mixed with a solvent and deagglomerated useful for production of sintered ceramic products - Google Patents

Abstract

Preparation of a powder mixture for production of ceramic sintered products in which one or more ceramic and metallic powders are mixed with a solvent, e.g. alcohol and optionally a dispersing agent, deagglomerated, so that on addition of organic additives as binder and plasticizer, the mixture can be homogenized and degassed by solvent evaporation and granulated to give a granulate for ceramic sintered products is new. A process for preparation of a powder mixture for production of ceramic sintered products for reaction conditions in which one or more ceramic and metallic powders is mixed with a solvent, e.g. alcohol and optionally a dispersing agent, deagglomerated, so that on addition of organic additives as binder and plasticizer, the mixture can be homogenized and after removal from, e.g. a grinding mill, degassed by solvent evaporation and granulated to give a granulate for ceramic sintered products. A mixture of preferably an alcoholic solvent and dispersing agent is made and divided into two halves, one of which contains at least one ceramic powder and in the other, separated half, at least one metallic powder in nano-dispersed form, and in order to ensure complete oxidization combined with the maximum particle size distribution of less than 55-10 micron, and a passivated oxide layer at room temperature, the mixture is deaggomerated and homogenized, so that the two separately deagglomerated and homogenized halves of ceramic and metallic powders are combined and then, by addition of organic additives are worked to a homogeneous mixture for granulate production.

Description

The invention relates to a method for producing powder mixtures from which with so-called reaction bonding of ceramic and metallic starting powder Granules are made from which by shaping and thermal treatment ceramic sintered products, for example technical ceramics, are produced.

It is known to produce shrinkage-reduced aluminum oxide-containing ones Ceramics based on the so-called RBAO process (reaction binding of Aluminum oxide, DE 43 02 721 A1). This will be a ceramic powder (Aluminum oxide) and metallic additives, such as aluminum, mixed and ground together and homogenized. This very intensive and technologically complex grinding and Homogenization process with a high energy input is carried out in an attritor and delivers a powder mixture, which after drying and pressing into a so-called Green body is suitable in the following heat treatment with special Ultimately, to sinter the time / temperature regime to the most homogeneous possible structure. It will Metallic aluminum oxidized to aluminum oxide with an increase in volume of 28%. According to this volume expansion, the manufacturing-related shrinkage of the created ceramic body counteracted. Shrinkage reduction is for one Production close to the final contour and advantageous for minimizing residual stress in the ceramic. With regard to the desired production of the sintered body with homogeneous Material properties are both a green body as homogeneous as possible before Sintering process as well as a largely complete oxidation of the aluminum Sintering sought.

The grinding and homogenization process in the attritor itself and the quality the resulting powder mixture is of crucial importance with regard to the process-specific effect of said RBAO process. To at the preparation of the powder mixture in the attritor the risk of To reduce aluminum hydroxide formation, the grinding and homogenization process in one non-aqueous liquid (ethanol, acetone, isopropanol). The formation of Aluminum hydroxide would be used in the reaction binding of aluminum oxide in the sintering process counteract a complete oxidation of the aluminum.

In addition, there is a risk that the oxidizability of the metal powder undesirable reactions with organic additives such as binders, dispersants and Plasticizers, is restricted. Own investigations of commercially available Aluminum powders have shown very different reaction effects here.

However, incomplete oxidation of the metal powder in the reaction binding limits the homogeneity of the resulting sintered body and last but not least influences it Material properties, such as density, porosity and so on Strength properties. Particles or agglomerates, which after the oxidation and sintering treatment in are still present in an undesirable manner, also do not contribute Shrinkage reduction at.

The energy required for the oxidation is strongly dependent on the particle size and increases with increasing particle size. However, with smaller ones Particle diameters the advantage of better oxidizability of the aluminum with less Given energy expenditure, but increases in reaction binding, such as studies show the potential of volume increase by oxidation with reduction of Particle size decreases because the pre-oxidation proportion increases. The Preoxidation fraction is the ratio of that among normal, oxygenated ones Ambient conditions independently forming oxide layer and the total volume of the particle. Although using smaller particle size powders with said reduced effort to prepare the powder mixture would be accompanied however, on the other hand, the production of the sintered body and in particular also by RBAO process intended to reduce shrinkage effect with less Particle size affected. Obviously, in the professional world, these were compromises most favorable conditions found by using aluminum powder with a Grain size distribution between 20 microns and 100 microns used and together with the Aluminum oxide and the organic additives in the attritor to a grain size of 1 µm is processed, although firstly a high level of technological and energy expenditure are necessary and due to increased friction the temperatures are at least 10 to 40% pre-oxidation of the aluminum, which, as mentioned, leads to the Potential of the powder mixture to reduce shrinkage reduced.

The invention has for its object in a comparatively cost and energy-saving process to produce powder mixtures from which using the known reaction bandage as homogeneous and low-shrinkage as possible Sintered ceramics can be created.

According to the invention in separate mixtures with solvent and Disperser the ceramic powder or powder as well as the metallic powder each separately deagglomerated and homogenized, with one mixture metallic powder, preferably aluminum, in nanodisperse form and for the purpose complete oxidizability with a maximum particle size of less than 5-10 µm, preferably 0.5-1 µm, and passivated oxide layer at room temperature is used. The two separately deagglomerated and homogenized Mixtures of the ceramic and metallic powders are combined and then by Add the organic additives to the homogeneous mixture for the formation of granules as Refurbished raw material for sintered ceramics.

It was found that using the metallic powder with said Material quality and no common, but initially separate Deagglomeration of ceramic and metallic powders after combining them separately prepared mix approaches without complex milling processes a special one Powder mixture is created which is homogeneous and without any undesirable side reactions organic additives, such as binders and plasticizers, can be mixed further a very homogeneous mixture of substances coordinated in type and composition for the production of granules, from which a homogeneous green body is formed can be pressed for the sintering process. Elaborate attritor processing for Preparation of the powder mixtures, which apart from the energy and cost aspects so far were also accompanied with problems of unwanted pre-oxidation of the metal not mandatory; homogenization in a ball mill is sufficient.

By avoiding pre-oxidation during powder preparation, the im Sintering process with the reaction binding not desired increase in volume impaired, which the production of lower shrinkage and thus more precise Sintered ceramics enables.

A complete oxidation of the metallic components takes place during sintering, see above that from the granule-pressed green body also a very homogeneous sintered body without other impairment of the material properties, such as density and porosity, arises.

The invention will be explained in more detail below using exemplary embodiments.

Embodiment 1

• - Herstellung einer Lösungsmittelmischung aus Ethanol unter Zusatz von Polycarbonsäurepolymer als Verflüssiger und Teilung dieser Lösungsmittelmischung in zwei Mischungsansätze.
• - Einem dieser Mischungsansätze wird nanodisperses Aluminiumpulver mit bei Raumtemperatur passivierter Oxidschicht (45 Vol.-% Al, bezogen auf das Gesamtfeststoffvolumen; Partikelgrößenverteilung 0,5-1 µm) zugegeben; danach erfolgen Deagglomerierung und Homogenisierung in einer Kugelmühle.
• - Parallel dazu wird dem anderen Mischungsansatz Aluminiumoxid (55 Vol.-% Al₂O₃, bezogen auf das Gesamtfeststoffvolumen; Partikelgrößenverteilung 0,1-5 µm) zugegeben; danach Deagglomerierung und Homogenisierung ebenfalls in Kugelmühle.
• - Die beiden separat deagglomerierten und homogenisierten Mischungsansätze werden vereinigt; Zugabe von Polyvinylbutyrol als Bindemittel (4 Masse-%) und Dibutylphthalat als Weichmacher (2 Masse-%); anschließend wiederum Homogenisierung in der Kugelmühle.
• - Abtrennen von Mischkörpern der Kugelmühle.
• - Entgasung durch Lösungsmittelverdampfung unter Rühren der Mischung.
• - Herstellung von Granulat durch Siebgranulierung.

A granulate is produced as a starting material mixture for industrial ceramics in the following way:

• - Production of a solvent mixture from ethanol with the addition of polycarboxylic acid polymer as a liquefier and division of this solvent mixture into two mixture batches.
• - Nanodisperse aluminum powder with an oxide layer passivated at room temperature (45% by volume Al, based on the total solid volume; particle size distribution 0.5-1 μm) is added to one of these mixture mixtures; This is followed by deagglomeration and homogenization in a ball mill.
• - In parallel, aluminum oxide (55 vol.% Al ₂ O ₃ , based on the total solid volume; particle size distribution 0.1-5 μm) is added to the other mixture mixture; then deagglomeration and homogenization also in a ball mill.
• - The two separately deagglomerated and homogenized mixture batches are combined; Addition of polyvinyl butyrene as binder (4% by mass) and dibutyl phthalate as plasticizer (2% by mass); then again homogenization in the ball mill.
• - Separation of mixing bodies from the ball mill.
• - Degassing by solvent evaporation while stirring the mixture.
• - Production of granules by sieve granulation.

The result of the powder preparation is a homogeneous powder mixture of aluminum, aluminum oxide and organic additives, which, for. B. can be formed by pressing into a homogeneous green body for a sintering process. Due to the aluminum content, the granulate has a high compressibility (approx. 74% TD at 400 MPa) and the green bodies that can be produced from it have a high, so-called green strength. The particle size of the aluminum powder and its homogeneous distribution enable a complete reaction binding process (100% oxidation of the aluminum, sintering ability of the entire aluminum oxide). The complete oxidizability was verified on the powder mixture with thermal analysis (DTA / TG) as well as on pressed test specimens (∅ 10 mm, height 4-10 mm) with the present increase in mass and calculation of the aluminum conversion as well as confirmed with scanning electron microscopy, electron beam microanalysis and phase analysis with the X-ray diffractomer. The sintered products produced from this showed complete oxidation of the metallic powder components, homogeneous structure with grain sizes of 0.5-5 µm, final densities of 92-96% TD, hardness HV 1 14-15 GPa, fracture toughness 3-4.5 MPa.m ^{1 / 2} and elastic moduli from 260-300 GPa. The shrinkage reduction due to aluminum oxidation was approx. 18%.

Embodiment 2

There was a powder mixture according to embodiment 1, but with modified Solids ratio (aluminum: 60 vol .-%, aluminum oxide: 40 vol .-%) produced. in the The result of the powder preparation is also a homogeneous powder mixture Aluminum, alumina and organic additives. The made from it Sintered products showed complete oxidation of the metallic powder components and comparable properties as in embodiment 1. The shrinkage reduction due to aluminum oxidation was up to approx. 33%.

Claims (5)

1. A process for the preparation of powder mixtures which are suitable for the production of ceramic sintered products under reaction bindings, in each of which one or more ceramic and metallic powders with solvents, for. B. alcohol, and optionally a dispersant mixed, deagglomerated and prepared by adding organic additives as binders and plasticizers to a homogeneous mixture, from which, optionally after separation from a grinder, degassing by solvent evaporation and granulation, a granulate for the ceramic sintered products is formed , characterized in that firstly a mixture of a preferably alcoholic solvent is mixed with a dispersant and divided into two mixture batches, that in one mixture batch the at least one ceramic powder and separately in the other batch batch the at least one metallic powder in nanodisperse form and for the purpose of one complete oxidizability with a maximum particle size distribution of less than 5-10 µm and with an oxide layer passivated at room temperature in each case deagglomerated and homogenized, that the two separately deagglomerated The mixed and homogenized mixtures of the ceramic and metallic powders are combined and then worked up by adding the organic additives to form a homogeneous mixture for the formation of granules. 2. The method according to claim 1, characterized in that as a metallic powder Aluminum or zirconium powder or both can be used. 3. The method according to claim 1, characterized in that as a metallic powder Aluminum powder with a particle size distribution of approximately 0.2-2 μm, preferably 0.5-1 µm, and with an oxide layer passivated at room temperature with a thickness of 6-9 nm is used. 4. The method according to claim 1, characterized in that as a metallic powder Aluminum powder with an aluminum content between 45% by volume and 75% by volume, preferably about 60 vol .-%, based on the solids volume, is used. 5. The method according to claim 1, characterized in that as organic additives Polycarboxylic acid polymer, lactimone, polyvinyl butyral and / or dibutyl phthalate with one Organic content between 15% by volume and 34% by volume, preferably approx. 15-20% by volume on the total volume.