Method for producing a molded article and molded article

Abstract

In order to provide a method for producing a molded article by means of which a molded article with good temperature resistance is easily producible, it is proposed that the method includes providing a mixture including a powdered base material which includes a pre-fired and/or ground cordierite material and/or a pre-fired and/or ground mullite material; producing a molded article by molding the mixture; and firing the molded article so that particles of the base material are bonded to one another while preserving the particulate property.

Claims

1. A method for producing a molded article which is a filter body, the method comprising: providing a mixture comprising: a powdered base material which comprises a pre-fired and/or ground cordierite material and/or a pre-fired and/or ground mullite material; producing a molded article by molding the mixture; firing the molded article at a temperature of at most about 1400 C. and with a temperature gradient of at least 2000 K per hour so that particles of the base material are bonded to one another while preserving the particulate property.

2. The method according to claim 1, wherein the mixture comprises corundum, zircon mullite and/or zircon silicate.

3. The method according to claim 1, wherein the mixture also comprises an alkali metal-containing and/or alkaline earth metal-containing material and/or that additionally an alkali metal-containing and/or alkaline earth metal-containing material is mixed into the mixture for molding thereof.

4. The method according to claim 1, wherein at least one substance of the mixture is screened before mixing with further substances of the mixture and/or that the whole mixture is screened, in order to obtain a desired grain size distribution.

5. The method according to claim 1, wherein at least one substance of the mixture is screened before mixing with further substances of the mixture and/or that the whole mixture is screened such that the d10 value of the at least one substance and/or of the mixture is at least approximately 1 m, the d50 value of the at least one substance and/or of the mixture is at least approximately 38 m, and/or the d90 value of the at least one substance and/or of the mixture is at least approximately 60 m.

6. The method according to claim 1, wherein at least one substance of the mixture is screened before mixing with further substances of the mixture and/or that the whole mixture is screened such that the d10 of the at least one substance and/or of the mixture is at most approximately 2 m, the d50 value of the at least one substance and/or of the mixture is at most approximately 49 m, and/or the d90 value of the at least one substance and/or of the mixture is at most approximately 80 m.

7. The method according to claim 1, wherein at least one substance of the mixture is screened before mixing with further substances of the mixture and/or that the whole mixture is screened such that the d10 of the at least one substance and/or of the mixture is at least approximately 5 m, the d50 value of the at least one substance and/or of the mixture is at least approximately 35 m, and/or the d90 value of the at least one substance and/or of the mixture is at least approximately 70 m.

8. The method according to claim 1, wherein at least one substance of the mixture is screened before mixing with further substances of the mixture and/or that the whole mixture is screened such that the d10 of the at least one substance and/or of the mixture is at most approximately 10 m, the d50 value of the at least one substance and/or of the mixture is at most approximately 40 m, and/or the d90 value of the at least one substance and/or of the mixture is at most approximately 80 m.

9. The method according to claim 1, wherein the mixture before the firing and/or the molded article after the firing comprises at least approximately 50% by mass of cordierite, at least approximately 5% by mass of corundum and/or at least approximately 5% by mass of mullite.

10. The method according to claim 1, wherein the mixture before the firing and/or the molded article after the firing comprises at most approximately 90% by mass of cordierite, at most approximately 50% by mass of corundum and/or at most approximately 30% by mass of mullite.

11. The method according to claim 1, wherein the mixture before the firing and/or the molded article after the firing comprises at least approximately 50% by mass of mullite, at least approximately 10% by mass of corundum and/or at least approximately 10% by mass of zircon mullite.

12. The method according to claim 1, wherein the mixture before the firing and/or the molded article after the firing comprises at most approximately 80% by mass of mullite, at most approximately 50% by mass of corundum and/or at most approximately 30% by mass of zircon mullite.

13. The method according to claim 1, wherein the molded article is fired in a firing cycle with a duration of at least approximately 300 min and/or at most approximately 480 min and/or with a temperature gradient of >2200 C./h.

Description

(1) This object is achieved according to the invention in that the molded article comprises a cordierite material and/or a mullite material, wherein particles of the cordierite material and/or particles of the mullite material are bonded to one another while preserving the particulate property.

(2) Particles of the cordierite material and/or particles of the mullite material are preferably substance-to-substance bonded to one another while preserving the particulate property.

(3) The molded article according to the invention can preferably be produced with the method according to the invention.

(4) The molded article according to the invention preferably has individual or several of the features and/or advantages described in relation to the method according to the invention. Furthermore, the molded article preferably has individual or several features and/or advantages which result from the execution of individual or several of the aforementioned method steps.

(5) The molded article is preferably manufactured from a powdered material. Preferably, the surfaces and/or boundary faces of the particles of the cordierite material and/or of the mullite material in the molded article are substantially like the surfaces of particles of a ground cordierite material and/or mullite material. In particular, by means of a scanning electron micrograph, clear boundaries of the particles of the cordierite material and/or of the mullite material relative to the environment are recognizable. The particles of the cordierite material and/or of the mullite material are preferably not fused together, but particularly merely embedded and/or integrated with one another, for example, substance-to-substance bonded to one another in punctiform manner.

(6) The molded article is preferably a honeycomb body, in particular a filter body.

(7) In particular, the molded article is suitable for use as a wall flow filter and/or as a flow-through filter, if appropriate, following further processing thereof.

(8) The molded article can be formed, for example, in an extrusion process.

(9) A molded article configured as a honeycomb body preferably has honeycombs arranged in a matrix form. In particular, it can be provided that the honeycomb body has a square cross-section and comprises honeycombs (cells) which are arranged in a matrix form and are configured cylindrical, wherein the honeycombs (cells) preferably also have a square cross-section.

(10) It can be favorable if the molded article comprises 100, 200 or 300 cells per square inch.

(11) Furthermore, the method according to the invention for producing a molded article and/or the molded article can have individual or several of the following features and/or advantages.

(12) The particles of the base material remain preferably chemically and/or physically essentially unaltered during the firing of the molded article.

(13) Preferably, the cordierite material and/or the mullite material of the molded article is not or is only to a non-appreciable extent produced during the firing of the molded article by conversion of a base material.

(14) Preferably, during the firing of the molded article, no or only a non-appreciable phase change of the base material into a desired mineral phase, particularly into cordierite and/or mullite takes place.

(15) The molded article can be produced, for example, from a mixture of cordierite chamotte, sintered corundum, sintered mullite, zircon mullite, zircon silicate and/or a sinter additive from the group of alkali metals and/or alkaline earth metals. In particular, by this means, there can be produced a molded article configured as a cordierite substrate which comprises, for example, a cordierite content of between approximately 20% by mass and approximately 90% by mass.

(16) The molded article preferably has no expansion anisotropy.

(17) A thermal shock parameter of the molded article is preferably greater than 300 K.

(18) The molded article is preferably heatable and/or firable with a temperature gradient of at least approximately 2000 K per hour.

(19) It can also be provided that a combination of sintered mullite, sintered corundum, zircon mullite, zircon silicate and/or a sinter additive from the group of alkali metals and/or alkaline earth metals is used for producing a molded article.

(20) The molded article can be used, in particular, as a soot filter, in particular as a diesel soot particle filter.

(21) The molded article is preferably dimensionally stable up to temperatures of more than approximately 1600 C., in particular with the use of a mullite material with a thermal shock parameter of more than 200 K, or up to temperatures above approximately 1500 C., for example, up to approximately 1550 C. with the use of cordierite material.

(22) The base material is preferably a pre-sintered material which can be fired, in particular, by means of a reactive sintering process with a sintering additive, to a dimensionally stable body.

(23) By means of selective screening of at least one substance, in particular the base material, and/or the mixture, a pore volume, particularly with a pore radius distribution of between approximately 0.004 mm and approximately 0.045 mm can be specifically set.

(24) In particular, if the molded article is a fine-walled honeycomb body, the use of pore-forming agents to adjust the pore volume and the median of the particle size distribution can be advantageous. This is advantageous particularly if the spacing of the centers of two adjacent honeycomb walls of the molded article (the pitch P) extending parallel to one another is relatively small, for example less than 0.27 mm.

(25) The molded body according to the invention is preferably more alkali-resistant and more corrosion-resistant than cordierite molded articles and/or mullite molded articles which are sintered at very high temperatures according to known production methods.

(26) The coefficient of expansion of the molded article comprising, for example, mainly cordierite in the range between approximately 20 C. and approximately 800 C. is essentially identical in all three spatial directions and lies, for example, between approximately 110.sup.6/K and approximately 610.sup.6/K, for example between approximately 1.710.sup.6/K and approximately 410.sup.6/K. Alternatively thereto, it can be provided that the coefficient of expansion of the molded article comprising, for example, mainly mullite is, for example, approximately 5.210.sup.6/K.

(27) It can be advantageous if the molded article is provided with a coating, in particular with a catalytically active coating.

(28) The molded article can be formed, for example, in an pressing process and/or in an extrusion process.

(29) It can be provided that the powdered base material, in particular the codierite material and/or the mullite material is pre-fired, for example at a temperature of up to approximately 1200 C. During firing of the molded article, the powdered base material is then preferably completely fired in order to preserve the final chemical property thereof The particulate property of the particles of the base material are herein preserved, however.

(30) Preferably, the mixture and/or the molded article comprises aluminum oxide (Al.sub.2O.sub.3), glass, particularly magnesium aluminum silicate, mullite and/or aluminosilicate following the firing.

(31) Preferably, aluminum oxide (Al.sub.2O.sub.3) is added to the mixture overstoichiometrically. By this means, in the event of undesirable overheating of the molded article during its use, for example as a particle filter, the molded article can resinter before any damage occurs.

(32) It can be advantageous if the mixture comprises an additive in order to increase the strength of the molded article.

(33) The thermal shock parameter is, in particular, a relative measure for an acceptable temperature difference based on the ratio between the bending strength of the material and the tension which is marked by a temperature gradient (in Kelvin per minute or Kelvin per hour). A molded article made of SiC has a thermal shock parameter of, for example, at most approximately 160 K. A molded article according to the invention preferably has a thermal shock parameter of at least approximately 180 K.

(34) The temperature gradient denotes a spatially or time-dependent temperature gradient and is measured in Kelvin per meter or Kelvin per minute or Kelvin per hour. In particular, to denote the heating speed, the time-dependent temperature gradient is given in Kelvin per minute in the range between approximately 120 C. and for example approximately 2000 C. A smaller temperature gradient can lead to an increase in the coefficient of expansion, a change in the pore structure and/or to a decrease in strength. A higher temperature gradient, for example, higher than approximately 2300 C./h can lead to a dimensionally stable molded article, in particular a honeycomb body with sufficient strength.

(35) For example, graphite, acrylate, acrylic glass, coconut flour and/or maize can be used as pore-forming agents for setting the degree of porosity and/or a pore size.

(36) Further preferred features and/or advantages of the invention are the subject matter of the following description of individual exemplary embodiments.

(37) In a first exemplary embodiment of a method for producing a molded article, in particular a honeycomb body, for example a diesel soot particle filter (DPF), it is provided that a mixture is used as the starting material. The mixture comprises a powdered base material which comprises pre-fired, calcinated substances, for example, cordierite, mullite, sintered mullite, corundum, sintered corundum and zircon mullite.

(38) The substances are ground and/or screened in order to obtain a desired grain size distribution (particle size distribution).

(39) In particular, the mixture, in particular the powdered base material, is ground and/or screened so that the d10 is between approximately 1 m and approximately 2 m, that the d50 value is between approximately 38 m and approximately 49 m and that the d90 value is between approximately 60 m and approximately 80 m. By this means, a pore volume of approximately 40% to approximately 58% can be obtained. A median of the pore size distribution preferably amounts to between approximately 10 m and approximately 20 m.

(40) With a median of the pore size distribution of approximately 10 m, the use of a pore-forming agent is preferably dispensable. However, the pore-forming agent can also be added in quantities of, for example, approximately 5% by mass to approximately 20% by mass in order, for example, to obtain an adjusted pore size distribution, in particular with a median of approximately 20 m.

(41) Alternatively, it can be provided that by means of an adjusted screening of the mixture, in particular the base material, a pore size distribution with a median of approximately 20 m is obtained. For this purpose, the mixture, in particular the powdered base material is screened so that the d10 is between approximately 5 m and approximately 10 m, that the d50 value is between approximately 35 m and approximately 40 m and that the d90 value is between approximately 70 m and approximately 80 m.

(42) The mineral composition of the base material amounts in the first embodiment to approximately 60% by mass of cordierite, approximately 15% by mass of corundum and approximately 25% by mass of mullite. Preferably a sinter-promoting material is added to the mixture. In particular, an aqueous solution which comprises approximately 0.1% by mass to approximately 2% by mass of alkali metal and/or alkaline earth metal ions is mixed in.

(43) The mixture is then brought into a desired shape in a pressing process or an extrusion process.

(44) The molded article thus obtained can then be, for example, freeze dried and further processed.

(45) In particular, the molded article is subsequently fired in order to obtain its final strength.

(46) The molded article is herein fired, for example, in a flow-through kiln at a feed rate of 10 cm/min to 30 cm/min, for example approximately 20 cm/min and a temperature gradient of more than 2200 K/h. The firing duration from the start of the firing process to the cooling down of the molded article is between approximately 300 minutes and approximately 480 minutes, for example approximately 360 minutes.

(47) The temperature of the molded article during the firing is preferably at most approximately 1400 C., for example, approximately 1330 C. By this means, it can be ensured that the particles of the powdered base material, in particular the cordierite material and/or the mullite material also have their particulate property unchanged following the firing step. In particular, given a suitably magnified view, including after passing through the firing step, clear borders or edges of the particles of the base material are recognizable in the molded article.

(48) Following production of the molded article, particularly following firing and cooling of the molded article, the molded article has, for example, a coefficient of expansion of between approximately 1.710.sup.6/K to 410.sup.6/K, in particular in the temperature range between approximately 20 C. and approximately 800 C.

(49) The molded article can be used, in particular, as a honeycomb article, for example, as a diesel soot particle filter. For this purpose, the molded article can be provided, for example, with a catalytic coating.

(50) A second embodiment of a method for producing a molded article and the molded articles obtained thereby differs from the method and the molded article according to the first embodiment essentially in that the powdered base material comprises approximately 70% by mass of sintered mullite, approximately 20% by mass of sintered corundum and approximately 10% by mass of zircon mullite. The molded article thereby obtained has a coefficient of expansion of approximately 5.210.sup.6/K in the temperature range between approximately 20 C. and approximately 800 C.

(51) Otherwise, the method for producing a molded article and the molded article according to the second embodiment coincide regarding the production steps, the design, the properties and the function with the method for producing a molded article or with the molded article according to the first embodiment, so that in this regard, reference is made to the above description thereof.

(52) Since in all the methods for producing a molded article, during firing of the molded article, particles of the base material are bonded to one another while preserving the particulate property, the molded article can be produced easily and can have a high temperature resistance.