DE102008013471A1 - Ceramic substrates whose sintering shrinkage can be adjusted comprise particles with specified maximum primary particle size and specified percentage by volume of particles of significantly greater primary particle size - Google Patents

Abstract

Ceramic substrates whose sintering shrinkage can be adjusted comprise particles with a maximum primary particle size of 100 nm and at least 10 vol% of particles of significantly greater primary particle size. Independent claims are included for: (A) production of the substrates by molding a mixture of the two types of particle as described; and (B) use of the substrates to produce ceramic sintered composites.

Description

The This invention relates to the field of ceramics and relates to ceramic Green body with adjustable sintering shrinkage, for example, for ceramic components with partially electrically conductive, magnetic or transparent Properties can be used and a procedure for producing such green bodies and their Use.

Of the Trend of technical developments is increasingly becoming multifunctional of components. It should have the properties of different materials to be used at certain locations. Become conventional individual components made for these composite materials and joined in a subsequent step. there In particular ceramic components are complicated and elaborate methods, such as active soldering or Diffusion welding. These methods require, among other things high temperatures, certain furnace atmospheres or high vacuum, as well as defined joining zone geometries and surface qualities. Furthermore, by the joining method, the Operating conditions, such as temperature or corrosion resistance of the network are restricted.

Becomes the joining step already integrated in the molding process, arise both economic and production engineering Advantages, as the composite is already realized in the green part and process steps can be saved.

A big challenge stems from the fact that the materials used during the manufacture of the same process parameters are exposed. As especially critical is the common heat treatment to see. When co-sintering The shrinkage of the partners must be within close tolerances be adapted, otherwise in the joining zone thermal Tensions arise, causing cracks and failure of the component to lead.

The production of material composites already in the shaping step is state of the art in the field of high-performance ceramics and traditional ceramics. These include multi-layer presses or multi-component presses, garnishing in the field of casting technology, multi-layer film casting [ Lenk et al., GIT Laboratory Journal, 43 (1999) 936-939 ], multi-component freezing [ DE 103 24 828 A1 ] as well as multi-component powder injection molding [ US 2003/0062660 ; DE 196 52 223 A1 ] to call.

The Production of ceramic bodies usually takes place over the shaping of powdery starting materials, which in a subsequent heat treatment below the melting temperature be compacted. The pore spaces are closed and the component undergoes a sintering shrinkage that depends of the packing density in the green body.

As a result, must be targeted to influence the shrinkage, the green density be set. For an increase in shrinkage For example, in the case of thermoplastic molding, the binder content can be increased become. However, these are often technological problems, like the segregation of solid and binder during the Shaping or too low green strength during associated with the removal of the child.

A Another method is to use powders of different particle sizes to use for adjusting the shrinkage.

The influence of the sinter shrinkage by changing the particle size is in US 2006/0043648 described. Here, for the production of ceramic films, the powder used is treated by dry grinding in a ball mill and determines the sintering shrinkage by varying the grinding time. In the process, this powder preparation process essentially serves quality assurance and reproducibility. The sintering shrinkage is varied only within narrow limits, since no powder mixtures are produced.

By using at least two fractions of ceramic particles with different mean grain size, it is known that it is easier to fill the interspaces of the grain and in this way to set higher green densities in the molded body [ DE 101 15 820 A1 ].

The use of multimodal powder mixtures can also change the packing density. According to information from publications [ DE 103 51 517 A1 . Shi et al. J. Am. Ceram. Soc. 84 (2000) 737-742 ] they are often used when particularly high packing densities are to be achieved in order to minimize sintering shrinkage and thus reduce the risk of sintering distortion.

adversely is that when using two powders that are in their Particle size only a little (not more than one Magnitude) differ from each other, the influence the higher sintering activity of the powder with the smaller particle size not noticeable comes to fruition.

According to the WO 2006/010523 bimodal powder mixtures are prepared in aqueous suspensions whose fines have a BET surface area of 10-500 m ² / g and the coarse fraction has a BET surface area of 0.1-10 m ² / g. The ceramic shaped bodies are obtained by pouring the slurry into a mold and then drying, the aim of this invention being the production of a near-net shape shaped body.

From fumed or nanoscale powders are known to have a have very high specific surface area and from this Reason an extremely high sintering activity have.

adversely in the processing of such powders, however, is that in molded articles produced therefrom due to the strong interparticle Interactions and high internal powder friction only relatively low Greening, which in turn is complete Compaction during sintering in the way.

task The invention is now, these disadvantages of the prior art to eliminate and give off ceramic green bodies, in which the sintering shrinkage for a subsequent sintering process is targeted and improved surface properties of the sintered green body, as well as a simple and inexpensive process for its production and indicate their use.

According to the invention this object by the invention specified in the claims solved. Advantageous embodiments are the subject of Dependent claims.

The ceramic green body according to the invention with adjustable sinter shrinkage consist of ceramic particles with at least two distinctly different primary particle sizes, which are homogeneously distributed, wherein at least one primary particle size ≤ 100 nm and the other primary particle size is significantly larger, and where the volume fraction the particles with the significantly larger primary particle size at least 10%.

advantageously, The ceramic particles consist of different ceramic Materials.

Also Advantageously, nanostructured ceramic particles with a primary particle size of ≤ 100 nm available.

Farther Advantageously, the median value of the two different ones differs Primary particle sizes at least 1 Magnitude (= a 10-power), even more advantageous by 2 to 4 orders of magnitude from each other.

And also advantageously, the one primary particle size is ≤40 nm.

Advantageous it is also when the one primary particle size ≤ 25 nm is.

Farther It is advantageous if the volume fraction of the particles with the significantly larger primary particle size 10% by volume to 99% by volume.

It is likewise advantageous if the d ₅₀ value of the particles having the primary particle size of ≦ 100 nm is ≦ 80 nm.

And it is also advantageous if the d ₉₅ value of the particles having the primary particle size of ≦ 100 nm ≦ 250 nm.

In the method according to the invention for producing ceramic green bodies with adjustable sintering shrinkage, ceramic particles having at least two distinctly different primary particle sizes are processed into a homogeneous particle distribution, wherein nanostructured ceramic particles having at least one primary particle size ≦ 100 nm and further ceramic particles having a significantly larger primary particle size are used, wherein at least 10 vol .-% of other ceramic particles are used with the much larger primary particle size, and the homogeneous particle distribution by tro be processed, thermoplastic, plastic or wet molding process to a ceramic green body with adjustable sinter shrinkage.

advantageously, is the homogeneous particle distribution by injection molding processed into a green body.

Also Advantageously, the homogeneous particle distribution by means of Dry presses processed into a green body.

According to the invention the ceramic green body with adjustable Sinterschwindung together with at least one other ceramic Green body whose sintering shrinkage of the set sintering shrinkage of the ceramic green body, for the production used of ceramic sintered composites.

With the solution according to the invention can by the targeted adjustment of the sintering shrinkage of ceramic green bodies an improved sintering activity and sintering compaction the materials are achieved. On the one hand, the high sintering activity of ceramic particles with primary particle sizes ≤ 100 nm exploited, according to the invention with the use of at least another ceramic particles with a clear larger primary particle size combined.

By the use of bimodal primary particles, which are homogeneously intertwined distributed, is in the ceramic green body achieved an adjustable green density, which is adjustable to a Sinterschwindung leads. It is with increasing share on ceramic particles with primary particle sizes ≤ 100 nm whose better sintering activity and higher specific Surface exploited, so that despite partially decreasing green light values an improved compression in the sintered body can be achieved can and thus also the strength and the surface properties of the sintered body can be improved.

The particular advantage of the invention is that, with the control of the ratio between coarser and finer primary particle fractions, a desired value of the sintering shrinkage can be set (see 1 ).

As is known, can be adjusted by adjusting the densest sphere packing of a bimodal Particle distribution of ceramic particles the lowest sintering shrinkage be achieved at the same time high green density.

The present solution, however, does not aim for the densest spherical packing of the bimodal particle distribution of the ceramic particles, but rather an excess of particles having primary particle sizes ≦ 100 nm. These particles having primary particle sizes ≦ 100 nm take up the significantly coarser primary particles and create more or less large distances them. Thus, high green density values are still achieved, which, coupled with the significantly better sintering activity of these particles with primary particle sizes ≦ 100 nm, lead to the setting of specific absolute values of the sintering shrinkage of this ceramic green body. From the green density present and the sintering densities known for the respective ceramic particles used, the sintering shrinkage can be easily determined in accordance with the relationship according to equation 1.

The Green densities of ceramic green bodies can known by mercury volume or geometric Methods are determined.

By the invention targeted setting the sintering shrinkage ceramic green body covered by dry, thermoplastic, plastic or wet molding processes become the dependencies of the sintering activity from the specific surface of ceramic powders and the green density of the mixing ratio of several Powder with significantly different particle size distribution exploited.

The packing density of powders depends on their particle size and shape, with intraparticle interactions determining the possible approach of the particles. For coarse powders with small surface-to-volume ratios, the packing density is determined by the geometrically possible arrangements of the par and the resulting cavities. By definition, so-called nanopowders have a primary particle size <100 nm. As the particle size decreases, the influence of the surface in relation to the volume increases. Due to the growing surface, the importance of intraparticulate forces, such as repulsion due to electrostatic interactions, increases. At the same time, the cohesive attraction and the adsorption of moisture on the surface increase, which increases the agglomeration tendency of the powder. These difficult to break up, porous agglomerates limit the feasible packing density for very fine powders.

in the The invention relates to nanostructured ceramic powders used. These nanostructured ceramic powders formed from ceramic primary particles ≤ 100 nm, which may be agglomerated in whole or in part.

critical however, for the present invention is the respective Primary particle size.

With the solution according to the invention, the volume predominant proportion of primary particles determines the properties of the ceramic green and sintered body. When the coarse particles form a network, the finer particles fill the voids between the coarse particles, thereby increasing the packing density ( 1A ). If the proportion of the fine powder exceeds the volume of the cavities, the coarse particles are forced apart and thus the packing density is reduced ( 1B ). Starting with the packing of fine powders, the surface can be reduced and the green density can be increased by using coarse particles ( 1C ).

Especially through the use of ceramic primary particles ≤ 100 nm, the effective total surface area is already low Fines significantly changed and the sintering shrinkage can be changed adjustable. In the molding process, in which solvents or high binder contents are used, causes the high surface of the fine fraction that excess Binder adsorbed and prevented segregation become.

By the generation of a homogeneous particle distribution using ceramic primary particles ≤ 100 nm, the Shrinkage of ceramic sintered bodies passing over dry, thermoplastic or wet molding processes be targeted during sintering.

The relationship between sinter shrinkage, specific surface area, sintering activity and green density in the ratio of coarse and fine particles in the primary particle size is in 2 shown in principle.

According to the invention not only the absolute amount of sintering shrinkage of the ceramic Green body to be adjusted, but also the Temperature range in which the sintering shrinkage begins and / or occurs be influenced within wide limits. This allows in particular Composites are made from materials that are normally have significantly different Sinterschwindungstemperaturen.

One Another advantage of the invention is that several ceramic Particles with significantly different particle sizes can be used, both from the same or Also different ceramic materials in combination with non-ceramic Materials can be used.

Farther the solution according to the invention is particular successfully applicable if the differences between the primary particle sizes at least two orders of magnitude (= two orders of magnitude) be.

following The invention will be closer to several embodiments explained.

example 1

The powders were a coarse ZrO ₂ powder (PYT05.005H, Unitec Ceramics) with BET = 4.3 m ² / g, d ₅₀ = 1 μm and a nanopatterned ZrO ₂ powder prepared by flame pyrolysis (VP Zirconium Oxide-3YSZ Evonik Degussa GmbH) with BET = 43 m ² / g, d ₅₀ = 20 nm.

The press offsets were prepared with different fine and coarse fractions X _fine = 25, 50, 75, 90% by mass via mixed grinding with ZrO 2 grinding balls for 24 h and subsequent freeze-drying. As green bodies, tablets having a diameter of 12 mm and a height of 6 mm were produced by uniaxial pressing at 150 MPa.

at These green bodies is a targeted attitude the sintering shrinkage reached.

The sintering was carried out at 1650 ° C for 2 h, with densities> 96% based on the theoretical density were achieved. To determine the shrinkage, the compacts were measured and calculated from the volume shrinkage, the linear shrinkage. X _fine BET [m ² / g] Press density [%] Lin. Shrinkage [%] 25 14 52.4 18.3 50 23 50.5 19.7 75 33 47.1 21.6 90 39 44.2 23.6

Example 2

The powder was a coarse ZrO ₂ powder (PYT05.005H, Unitec Ceramics) with BET = 4.3 m ² / g, d ₅₀ = 1 .mu.m and a nanostructured ZrO ₂ powder prepared by flame pyrolysis (VP zirconium oxides -3YSZ, Fa. Evonik Degussa GmbH) with BET = 43 m ² / g, d ₅₀ = 20 nm.

Injection molding compounds, so-called feedstocks, having a fine fraction of X _fine = 25% by mass and using the binder system Licomont EK583 (Clariant) were produced. For good homogenization and reliable breakup of the agglomerates, the masses were compounded on a shear roller extruder (Bellaform) in 3 passes. The optimal degree of powder filling was determined by torque measurement with a measuring mixer (W50EHT, from Brabender). Rods with the dimensions 7 × 3.5 × 70 mm ^{3 were} sprayed on an injection molding machine (320S, Arburg).

at These green bodies is a targeted attitude the sintering shrinkage reached.

Debinding was carried out in air atmosphere up to 400 ° C. Subsequently, they were sintered at 1600 ° C for 4 hours. X _fine [%] Filling degree [%] Shrinkage [%] 25% 53 17.4

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• - DE 10324828 A1 [0005]
• US 2003/0062660 [0005]
• - DE 19652223 A1 [0005]
• US 2006/0043648 [0009]
• - DE 10115820 A1 [0010]
• - DE 10351517 A1 [0011]
• WO 2006/010523 [0013]

Cited non-patent literature

• Lenk et al., GIT Laboratory Journal, 43 (1999) 936-939 [0005]
• - Shi et al. J. Am. Ceram. Soc. 84 (2000) 737-742 [0011]

Claims (14)

Ceramic green body with adjustable Sinter shrinkage, consisting of ceramic particles with at least two distinctly different primary particle sizes, which are homogeneously distributed, wherein at least one primary particle size ≤ 100 nm and the other primary particle size is significantly larger, and where the volume fraction the particle with the much larger primary particle size at least 10%. Green body according to claim 1, at the ceramic particles of different ceramic materials consist. Green body according to claim 1, at the nanostructured ceramic particle having a primary particle size of ≤ 100 nm are present. Green body according to claim 1, at the median value of the two different primary particle sizes by at least 1 order of magnitude (= a 10 power) different from each other. Green body according to claim 4, at the median value of the two different primary particle sizes differs by 2 to 4 orders of magnitude from each other. Green body according to claim 1, at the one primary particle size ≤ 40 nm is. Green body according to claim 1, at the one primary particle size ≤ 25 nm is. Green body according to claim 1, at the volume fraction of the particles with the much larger Primary particle size 10 vol% to 99 Vol .-% is. Green body according to claim 1, wherein the d ₅₀ value of the particles having the primary particle size of ≤ 100 nm ≤ 80 nm. Green body according to claim 1, wherein the d ₉₅ value of the particles having the primary particle size of ≤ 100 nm ≤ 250 nm. Process for the production of ceramic green bodies with adjustable sintering shrinkage according to at least one of claims 1 to 10, wherein the ceramic particles with at least two distinctly different primary particle sizes are processed to a homogeneous particle distribution, wherein Nanostructured ceramic particles with at least one primary particle size ≤ 100 nm and other ceramic particles with a much larger Primary particle size can be used, wherein at least 10 vol .-% of further ceramic particles with the significantly larger primary particle size be used, and the homogeneous particle distribution by dry, thermoplastic, plastic or wet molding processes to a ceramic green body with adjustable sintering shrinkage are processed. The method of claim 11, wherein the homogeneous Particle distribution by injection molding to a green body is processed. The method of claim 11, wherein the homogeneous Particle distribution by means of dry pressing to a green body is processed. Use of a ceramic green body with adjustable sintering shrinkage according to at least one of the claims 1 to 10 and produced according to at least one of the claims 11 to 13 together with at least one further ceramic green body, its sintering shrinkage of the set sintering shrinkage of ceramic green body corresponds to the production of ceramic sintered composites.