MXPA00005090A - Ceramic network, method for the production and utilization thereof - Google Patents

Abstract

The invention relates to the field of ceramics and to a ceramic network which can, for example, be applied as a deep-bed filter and a method for the production and utilization thereof. The aim of the invention is to provide a ceramic network in which the mechanical stability is improved and/or an application dependent structure can be specifically adjusted. To this end, a ceramic network is provided which is comprised of two or three dimensional ceramic webs that are connected to one another. The cavities in the ceramic webs have a cross-sectional area with a circular or approximately circular or extensively circular or a convex or multiple convex contour. In addition, a method is provided in which a fiber network is produced. The fiber network is comprised of polymer fibers and/or natural fibers and/or other fibers, whereby the fibers each have a cross-sectional area with a circular or approximately circular or extensively circular or a convex or multiple convex contour. According to the invention, a ceramic network is utilized while in contact with liquids and/or gases.

Description

CERAMIC NETWORK, METHOD FOR ITS PRODUCTION AND UTILIZATION The invention relates to the field of ceramics and refers to a ceramic network, as such can be used, for example, as a deep-bed filter, more particularly as a molten metal filter, as a support for filtration, permutator heat, regenerator, electrically heatable thermostat, catalyst support, burner element for radiant heaters and space heaters, reaction chamber filler element, sound absorber, panel clamping element, or as a ceramic reinforcing material for the metal matrix compounds (MMC), and a method for the production and use of this.

Previous technique Ceramic networks in the form of open cell ceramic foams are known.

Methods for the manufacture of such open cell ceramic foams using the so-called "Schwartzwalder method", which is used industrially and is the most common, are known. According to this method, the desired component is cut from an open cell polymer foam and then impregnated with a suspension of ceramic particles and water or solvent. Then, the impregnated polymer foam is mechanically pressed one or more times, and then dried. Then, the polymer foam is burned, followed by the sintering of the remaining ceramic layer (US 3,090,094).

The open-cell ceramic foam made using this method is a replica of the polymer-like cell structure of the starting material. As a result of burning the polymer foam, the remaining ceramic columns are hollow. The cross section of these columns has three corners, and the shape of the cavities also has three corners in the cross section. The ceramic coating is often cracked at the edges of the cavities. The cavities and cracks produce a very low mechanical force. Because the susceptibility to cracking is further increased by the shrinkage of the ceramic layer during sintering, relatively low shrinkage materials are used, but these exhibit a high interior porosity after sintering. This also results in a low mechanical force (J. Am. Ceram. Soc. 77 (6), 1467-72 (1994)).

Thus, ceramic foams made from polymer foams with the aforementioned method have cavities with a concave cross section, and with corner corners inside the ceramic columns (Cahn, RW, Haasen, P., Kramer, EJ (ed. .): Material Science and Technology, Vol. 11, VCH 1994, page 474). The shape of this cavity is very unfavorable for the mechanical strength of the columns in the ceramic foam, since the area that supports the load at the tips of the triangles is very small. Due to the susceptibility of brittle ceramics to the formation of cracks, the very sharply pointed shape of the cavities with three corners is also problematic, since cracks almost always form from there, further decreasing the strength of the columns of ceramic (J. Am. Ceram. Soc. 77 (6), 1467-72 (1994)). Accordingly, the foams produced with the Schwartzwalder method have a low mechanical strength which is disadvantageous for the mentioned applications as well as for the handling and transportation of such ceramic foams.

The foam materials used for molding are produced by foaming a mixture of various chemical components. During the reaction of the fluid components together, a gas is produced which causes gas bubbles to form and grow in the fluid. Moreover, the initial components are polymerized, increasing the viscosity of the fluid. At the end of the reaction, a solid polymer is formed which contains a large number of gas bubbles (polymer foam). The size of the bubbles in the polymer foam can be controlled within certain limits by means of the choice of the initial components and by regulating the reaction.

By means of a subsequent treatment known as crosslinking, the membranes separating the gas bubbles are completely removed by chemical or thermal means and creating the open cell polymer foam required for the manufacture of the ceramic. This foam consists now only of polymer columns that have formed between three adjacent gas bubbles (Klemper D. and Frisch K.C. (Ed.): Manual of Polymeric Foams and Foam Technology, Hanser 1991, page 24).

As a result of the nature of gas bubble foaming, the surfaces of the polymer foam are always concave in shape. Thus, the cross sections of the polymer columns forming the foam have the shape of triangles with concave sides having very sharply angled tips (Klemper D. and Frisch KC (Ed.): Handbook of Polymeric Foams and Foam Technology, Hanser 1991, page 28/29). This is considered as a law of nature for all foamed materials.

Also, the gas bubbles that occur during the foaming of the polymers can not be created in unlimited size. When the gas bubbles are too large, the subsidence of the foam before polymerization causes the foam to solidify (Klemper D. and Frisch KC (Ed.): Handbook of Polymeric Foams and Foam Technology, Hanser 1991, p. 9). The upper limit for the most commonly used polymer foam of flexible polyurethane foam is approximately 5 pores per inch (approximately 5 mm maximum cell size). This also presents a limitation in the possibilities for using polymer foam for the manufacture of ceramic foam.

It is also known that the foam used is generally polyurethane foam (Am. Ceram, Soc. Bull, 71 (11) 1992). However, a disadvantage of the use of polyurethane as the initial structure for making the ceramic foam is that gases that are toxic or harmful to health, eg, isocyanates or hydrogen cyanide, can be released during the necessary thermal decomposition of the polyurethane. (J. Polym, Sci. C, 23 (1968), 117-125).

To alleviate the problems of mechanical strength a little, the German documents DE 35 40 449 and DE 35 39 522 propose to apply multiple coatings to the polyurethane foam used. This increases the thickness of the ceramic columns and thus the mechanical strength of the sintered ceramic foam as well.

The increased cost of the process due to multiple coating is problematic. In addition, the ceramic layer has low strength only before sintering, and therefore the mechanical loading of the coated polymer foam necessary to remove the excessive suspension during the multiple coating frequently leads to new defects in the coating. In principle, however, the multiple coating does not eliminate the aforementioned disadvantage of the unfavorably formed concave cavities of three equine columns.

It is also known to use ceramic fibers as monofilaments or multifilaments for the manufacture of porous ceramics, whose fibers can be laid, woven, sewn or pasted (Symposium IChemE Series No. 99 (1986) 421-443; MTZ Jornal de Motomecánica 56 ( 1995) 2, 88-94).

Here a disadvantage is that such ceramic fibers are difficult and expensive to produce, and thus they are very expensive, and are difficult to process since they are very brittle. For example, linking techniques can only be used to a limited degree here. Thus, only a limited selection of ceramic materials can be used for such fibers which makes it difficult or almost impossible to modify the properties of the porous ceramic produced therefrom. Moreover, such porous structures are flexible since the fibers do not bond with each other at the point of contact. This is disadvantageous in the case of filtration or mechanical loads, because these ceramics are not very rigid in general and, in addition, abrasion of the fiber occurs, especially with multifilaments.

Joining such fibers can also be compromised (US 5,075,160), although this is only of interest for typical applications if the ceramic bond is created. This, too, is difficult and expensive to achieve, generally using CVD or CVI techniques, but the choice of materials is again very limited.

Furthermore, it is known to manufacture open pore materials of polymer fibers, natural fibers, or carbon fibers, and then convert them directly to a ceramic material, for example, by pyrolysis or with the addition of other chemical elements during the fluid phase. or gaseous and reaction of the fibers with these elements. However, the conversion of these initial fibers to open pore ceramics is complicated and can only be controlled by expensive methods; this severely limits the choice of materials and geometric shapes.

Description of the invention The object of the invention is to describe a ceramic network and a method for the production of this in which the mechanical force is improved and / or in which a specific application structure of the ceramic network can be specifically controlled.

The object is achieved by means of the invention described in the claims. Further refinements are described in the dependent claims.

Using the solution according to the invention, a two-dimensional or three-dimensional ceramic network is obtained whose ceramic columns have cavities with a transversal area having a circular or almost circular or mainly circular or convex or multiple convex contour. In this way a uniform coating thickness is achieved, for example, a uniform area of load bearing. In addition, crack formation can be greatly avoided, whereby the ceramics according to the invention and manufactured according to the invention demonstrate a greater mechanical force.

For some open-pore ceramic network applications, for example, for use as a filtering, regenerating, or sound absorbing material, it is important that the structure of the emptied foam be almost the same in each direction in space. This is achievable with the known open-pore foamed ceramics of the prior art, but can also be achieved with the ceramic network according to the invention.

For some applications, however, it is a great advantage if the ceramic network can be constructed with a specific structure in one or two or all three directions in space. The structure may be uniform and / or may be repeated in an advantageous manner here. This means that a uniform, directionally dependent structure - with as many repetitions as desired - of the fiber network, for example, a cotton fabric woven with an interwoven pattern, can produce a ceramic network with exactly the same structure.

In the case of gas or fluid flow, it may be advantageous to produce a predominant direction or, in the case of use as a metal reinforcement, achieve a predominant direction of mechanical force. The structuring of the ceramic network in such a manner is not known and can not be achieved with the prior art, but it can be easily produced with the method according to the invention.

For example, a woven or woven fabric can be produced such that the flow through it in one direction in space is almost unimpeded. Then a ceramic net of this woven or woven fabric can be produced without difficulty using the method according to the invention.

Another advantage of the solution according to the invention is that relatively large cell sizes can be produced with the ceramic network according to the invention.

In the methods of the prior art, the polymer foams used as the basis for the open cell ceramic foams can only foam at a certain level. When this point is exceeded, the open cell structure of the foams is increasingly destroyed and the foam eventually sinks. The maximum cell size obtainable is approximately 5 mm.

Using the method according to the invention, ceramic networks with much larger cell sizes can be easily produced.

Furthermore, it is advantageous if the initial structure is made of polymer fibers and / or natural fibers or polymer and / or bundles of natural fiber, because clean decomposition products are created which are not toxic or dangerous to health when the fibers or bundles of fiber are removed or burned.

The increase in temperature when the fiber network is being burned can be chosen such that it is carried out linearly or non-linearly or in phases. All possible atmospheres may be present during the process. The combustion takes place until the fiber network is completely exhausted or is almost completely free of residue.

When the temperature increase in phases is chosen for this purpose, it is advantageous if the combustion occurs in the first or one of the first temperature phases.

The method according to the invention produces a ceramic network according to the invention, in which there is a congruent material connection between the individual ceramic columns. Here congruent material means that the columns and the connection between the columns is made of the same material.

Moreover, in the ceramic network according to the invention, there is an interconnection between the cavities in the columns and, in particular, the interconnected cavities are also present at the points of contact between the columns. This is produced by the manufacturing process according to the invention in which a contact point between two fibers, for example, is wrapped together by the ceramic suspension and, after both fibers have been burned, the ceramic columns They are continuous and also have a continuous cavity at the contact points.

In the method according to the invention, fibers that are not coated or not coated with ceramic material are advantageously used.

It is also possible here for the fiber bundle, for example, to be surrounded by an enclosing enclosure.

It is also advantageous that a network is designed such that it corresponds completely or almost completely or partially, with respect to its shape and / or structure, to the shape and / or structure of the component to be manufactured.

To this end, a fiber network is manufactured which completely or almost completely or partially has the shape and / or the structure of the component to be manufactured. Then this fiber network is treated according to the invention and the desired ceramic network is created.

During the manufacture of the ceramic network, a reduction in size compared with the fiber network as a result of the shrinkage may take place, although the shape and / or structure may still correspond to that of the desired component.

Best Way to Carry Out the Invention The invention is explained in more detail below, with several exemplary representations.

Example 1 A normal commercial conveyor mat of 40 x 40 x 20 mm3 of extruded and bonded polyamide monofilaments, whose individual fibers have a circular cross section of approximately 350 mm is used as a starter network. This network is impregnated with a water-based ceramic suspension with a solids volume of 60%. The ceramic solid consists of 80% SiC powder with a bimodal grain size distribution with two grain sizes of maximum 6 and 20 μm and up to 20% clay. The excess suspension is separated in a centrifuge at a mass of 35 grams. Then the coated mat is dried and the polyamide filaments are burned. Next, the sintering is carried out at 1200 ° C in air in a retort oven. The sited ceramic network has the same three-dimensional network structure as the polyamide conveyor mat. The columns of the SiC ceramic ceramic network are hollow. The cavities have a circular cross section with a diameter of approximately 350 μm. The individual strength of the columns was determined (J. Am. Ceram, Soc. 72 (6) 885-889) and compared to a ceramic foam that was produced from the same ceramic material using a polyurethane foam with a cell size of 10 ppi as the home network. The strength of the individual columns of this known ceramic foam is 90 MPa obtained as the average of 20 measurements. In the ceramic network according to the invention, the strength of the individual columns was determined at 160 MPa.

Example 2 As a starter network, a normal commercial three dimensional structure with dimensions of 60 x 60 x 10 μm3 is used which was manufactured as a dtex277 polyester monofilament fabric spacer using weaving technology. This tissue spacer consists of two densely woven surfaces that are connected at a distance of approximately 10 μm by filaments of spacers placed almost parallel. The parallel filaments are spaced approximately 1 μm apart. This fabric spacer fabric is impregnated with a water-based ceramic suspension with a solids volume of 60%. The ceramic solid consists of an SiC powder with an average grain size of 1 μm. The excess suspension is separated in a centrifuge at a mass of 20 grams. Then the coated fabric spacer is dried and the polyester filaments are burned at 600 ° C in an argon atmosphere. Next, sintering is carried out at 2300 ° C in an argon atmosphere. The sintered ceramic network has the same three-dimensional network structure directionally dependent on the polyester fabric spacer. The columns of the SiC ceramic ceramic network are hollow. The cavities have a circular cross section with a diameter of approximately 150 μm.

The compression force of the ceramic net differs depending on the direction. The force measured perpendicular to the direction of the parallel columns of the spacer is twice as much as that measured parallel to it.

Example 3 As a starter net, a normal commercial linen fiber of 125 x 40 x 20 μm3 is used in which the individual fibers have a rounded cross section. The linen fibers are bonded together by means of a latex adhesive. This network is impregnated with a water-based ceramic suspension with a solids volume of 78% by weight. The ceramic solid consists of a commercial sintered mixture of Al203 with an average grain size of 5 μm. The excess suspension is separated in a centrifuge at a mass of 60 grams. Then the coated felt is dried and the flax fibers are burned in air. Next, the sintering is performed at 1650 ° C in air in a retort oven. The sintered ceramic net has the same three-dimensional network structure as the linen felt, with a reduction scale of 20% caused by shrinkage of the ceramic during sintering. The columns of the ceramic ceramic network Al203 are hollow. The cavities have a rounded hollow cross section.

Example 4 As a starter network, a normal commercial structure is used which was manufactured as a polyester monofilament fabric spacer using weaving technology. The polyester monofilaments have a circular cross section.

In the x-y direction, the fabric spacer consists of uniform squares with sides that are 8 mm in length. The surface x-y extends over an area of 100x100 mm. From this surface, the filaments extend diagonally from the corners of the squares in the z direction in such a way that triangular channels result in the xz direction while in the yz direction rectangular channels result with 2 bent lateral surfaces spaced apart to 8 mm . In the z direction, a repetition of the x-y surface occurs to a space of 8 mm.

Attach 5 100x100x8 mm mats, made of fabric spacer on top of each other using binding sheets of a normal commercial thermosetting plastic such that the corner tips of the squares lie on top of each other. Warm wire cutting is used to produce 40x40x24 mm blanks of this 5-ply mat in such a way that an area of 40x40 mm is found in each of the 3 different directions in space, x, y, z. These blanks are impregnated with a ceramic suspension of water base with a solids volume of 60%. The ceramic solid consists of a SiC powder with a bimodal grain size distribution with two grain sizes of maximum 6 and 20 mm. The suspension contains 6% of a water soluble resin. The excess suspension is separated in a centrifuge until the impregnated blanks have a mass of 49 grams. Then the coated blanks are dried and subjected to a two-phase temperature treatment in protection gas (argon) and / or vacuum. In the first phase, the polyester filaments are removed at 600 ° C in argon, then the blanks are placed in contact with a molten silicone liquid at a temperature of 1650 ° C under vacuum which causes the known bonding reaction to take place of SiC particles.

After cooling, 40x40x25 mm preforms are present with a 5-layer ceramic network and have ceramic columns consisting of silica carbide bonded by reaction and interconnected with connections of congruent material. The cross-sectional areas of the cavities in the ceramic columns are almost circular. The structure of the network is identical in shape and size to that of the tissue spacer described above.

Air measurements were made of the pressure drops in the ceramic preforms. The direction of flow was perpendicular to the surface 40x40 mm. At a flow volume of 20 1 / s, pressure losses of 500 Pa, 750 Pa and 1500 Pa were measured in the 3 samples oriented in different directions. In addition, indentation strength tests were performed with a cylindrical metal seal having a diameter of 25 mm, where this indentation was made on surfaces of 40x40 and the force at which the first columns of the samples broke was measured. . Loads of 80 N, 400 N, and 450 N were measured in the 3 samples oriented in different directions.

Example 5 As a starter network, a normal commercial mat is used which was manufactured as a polyamide monofilament fabric spacer using weaving technology. The polyamide monofilaments have a circular cross section. This tissue spacer consists of the x-y direction of parallelograms with sides of 2 mm in length. The surface x-y extends over an area of 100x100 mm. From this surface, the filaments extend vertically in the z-direction of the corner tips of the squares in such a way that rectangular channels result in the xz direction while in the yz direction square channels with 2 bent side surfaces spaced at 8 are formed. mm. In the z-direction, a repetition of the x-y surface occurs at a spacing of 4 mm.

Hot wire cutting is used to produce 40x40x24 mm blanks of this mat. These blanks are impregnated with a water-based ceramic suspension with a solids volume of 60%. The ceramic solid consists of 85% SiC powder with a grain size of 5 mm, and 15% clay. The suspension also contains 6% of a water-soluble resin. The excess suspension is removed in a centrifuge until the impregnated blanks have a mass of 35 grams. Then the coated blanks are dried and solidified by curing the resin 2 h at 160 ° C. The polymer is then removed by aging the samples 24 h in 10% hydrochloric acid. The samples are carefully washed, dried and then sintered in air at a temperature of 1150 ° C.

After cooling, the 40x40x25 mm preforms are present with a ceramic net and have columns consisting of silica carbide bonded by clay and interconnected with connections of congruent material. The transverse areas of the cavities in the ceramic column have an almost circular cross section. The structure of the network is identical in shape and size to that of the tissue spacer described above.

Claims (24)

1. Ceramic network of ceramic columns joined two-dimensionally or three-dimensionally together, in which the cavities in the ceramic columns have a connection of material congruent to each other and the ceramic columns also have an interconnected cavity above their contact points, and in that the cavities in the ceramic columns have a transverse area with a circular or almost circular or mainly circular or convex or multiple convex contour.

2. Ceramic network according to claim 1, wherein the two-dimensional or three-dimensional structure of the network is formed differently depending on the direction.

3. Ceramic network according to claim 1, wherein the two-dimensional or three-dimensional structure of the network is uniform and / or repeated.

4. Ceramic network according to claim 1, wherein the two-dimensional or three-dimensional structure of the network is directionally dependent and uniform and / or repeated.

5. Ceramic network according to claim 1, wherein the shape and / or structure of the network corresponds completely or essentially completely or in part with the shape and / or structure of the component to be manufactured.

6. Method for producing a ceramic network according to one of claims 1 to 5, wherein a fiber network is made from polymer fibers and / or natural fibers and / or other fibers, in which the fibers each have a cross-sectional area that has a circular or almost circular or mainly circular or convex or multiple convex contour, and the fiber network is impregnated one or more times with a ceramic suspension, then the excess suspension re removes, the impregnated fiber network dries and then the fiber network is completely or essentially completely or partially removed or burned, and then the remaining network is sintered.

7. The method according to claim 6, wherein polymer fibers and / or natural fibers and / or other fibers are used which have a structured or unstructured fiber network.

8. The method according to claim 6, wherein polymer fibers and / or natural fibers and / or other fibers are used which have a structured fiber network with a uniform and / or repeated structure.

9. The method according to claim 8, wherein polymer fibers and / or natural fibers and / or other fibers are used which have a structured fiber network with a uniform and / or repeated structure and in which this structure is directionally dependent.

10. The method according to claim 7, wherein the structured or non-structured fiber network is a two-dimensional and / or three-dimensional connection of the polymer fibers and / or natural fibers and / or other fibers that are manufactured from individual fibers and / or bundles of fiber joined by gluing, folding, felting, weaving, weaving, embroidery, sewing, embossing.

11. The method according to claim 6, wherein fibers of polyester, polyethylene, polyamide, cotton, cellulose, coconut, jute, hemp, linen, horse hair are used.

12. The method according to claim 6, wherein fibers are used that are not coated with ceramic material.

13. The method according to claim 12, wherein uncoated fibers are used.

14. The method according to claim 6, wherein the elimination of the fiber network is achieved by corrosion, dissolution or bacteriologically.

15. The method according to claim 6, wherein the combustion of the fiber network takes place by a temperature increase in linear or non-linear or in phases.

16. The method according to claim 15, wherein the combustion of the fiber network is carried out in an atmosphere of air or by reduction or oxidation or inert.

17. The method according to claim 6, wherein the combustion of the fiber network is completely achieved or is almost completely free of waste.

18. The method according to claim 15, wherein the combustion of the fiber network is achieved by an increase in temperature in phases and during which the complete or almost completely free combustion of waste occurs in the first or one of the first phases of temperature .

19. The method according to claim 6, wherein a fiber network is manufactured which has completely or essentially completely or partially the shape and / or structure of the component to be manufactured.

20. Use of a ceramic network according to one of claims 1 to 5 in contact with fluids and / or gases.

21. Use according to claim 20, wherein the fluids and / or flow of gases flow through the ceramic network or the ceramic network is filled with fluids and / or gases or frozen fluids (molten material).

22. Use according to claim 20, in the form of a filter, more particularly as a molten metal filter, deep-bed filter, or as a support for filtration, as a heat exchanger or regenerator, as a catalyst support or as a chamber filling element. reaction, as a burner element for radiant heaters and space heaters, as a heating element or control element for thermostats.

23. Use according to claim 20, in which the ceramic networks are subjected to a mechanical load.

24. Use according to claim 20, as a sound damping element, as an anchoring element for lightweight construction elements, such as mirror or as thermal protection tiles, as a ceramic reinforcement material for metal matrix compounds (MMC) or MMC light metal alloy, as a brake material, as an abrasive or as a vehicle for abrasives.