JP2009013057A - Method for manufacturing ceramic body having functionalized pore surface - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a ceramic body not exhibiting defects found in a conventional technology and having a functionalized pore surface which has a material composition different from that of residual base material and/or functionalization. <P>SOLUTION: The method for manufacturing the ceramic body having the functionalized pore surface includes (a) a process for mixing one or more kinds of inorganic pore forming agents with a ceramic matrix material, (b) a process for forming the resulting mixture into a formed body, and (c) a process for heat treating the formed body formed in the process (b). At this time, the one or more kinds of inorganic pore forming agents form the functionalized surface after the conversion in the process (c). The ceramic body produced by this method and its applications are also provided. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a ceramic body having a functionalized pore surface and a ceramic body having a functionalized pore surface, in particular for an exhaust gas aftertreatment device for an internal combustion engine. The filter element and carrier structure.

Prior art From the prior art, the production of porous members and shaped bodies is known. Such porosity in mostly ceramic parts or shaped bodies is usually caused by the so-called combustion of pore formers (Ausbrennen). For this purpose, usually cheap organic substances such as cellulose, carbon fibers, starch or wax are mixed into the ceramic powder prior to this shaping and burned during the sintering process. Depending on the form and size of the pore former, the pores remain in the ceramic structure. Such a method is used, for example, in the adjustment of this porosity in the porous layer in diesel-particle filters and exhaust gas sensors. The disadvantage here is that sintering must be carried out in the temperature range of decomposition and / or combustion of this organic pore former with a very small temperature-time gradient, If not, vigorous gas generation occurs and the ceramic body may be damaged. In addition, during the pyrolysis of the organic pore former, environmentally harmful substances can be generated, which must then be removed from the exhaust by labor. In addition, the exothermic reaction during combustion of the organic pore former can cause overheating of the furnace, thereby causing damage to the combustion product. This limits the potential charge of this furnace.

  For various applications, it is desirable that the pore surface of the compact has a different material composition and / or functionalization than the rest of the substrate material.

In DE 42 34 779 A1, the preparation of a supported catalyst consisting of a support material with open pores is described, which produces a polymer with macropores on the outer and inner surfaces, which is subsequently sulfonated. Gives the ion exchanger properties. The resulting ion exchange resin is mechanically and / or chemically fixed. The carrier material can be, for example, sintered glass with open holes or a ceramic material with open holes, based on aluminum silicate. For example, C ₆ -C ₁₆ -alkanes are used as pore formers for this polymer layer. This polymer layer is provided on the porous carrier material of this shaped body in an impregnation polymerization (Traenkpolymerisation) method or in precipitation polymerization (Faellungspolymerisation). In the impregnation polymerization method, the porous molded body is impregnated with the reaction mixture, the impregnated solution which has not been taken in is removed, and the polymerization is subsequently carried out. In the precipitation polymerization process, the compact is in an excessive amount of reaction mixture during the polymerization.

  Special filter elements such as diesel-particle filters and magnesium-aluminum-silicate based catalyst support substrates may be subject to significant thermal loads and thermochemical attack. It has already been shown that a corresponding protective coating can improve the temperature and alkali resistance, and thereby the service life of such a particularly required ceramic substrate (for example the filter elements mentioned above). I was able to. A polymer coating according to DE 42 34 779 A1 is not suitable for such use and can only be realized in the case of shaped bodies with open holes. Functionalization of the closed hole is not possible.

The creation and / or functionalization of pore surfaces with other coatings (eg based on ceramics) can in principle be carried out by subsequent coatings in a known manner. Pore coating is a separate process step in previously known production methods. For example, pore-coating can be performed by a sol-gel process, by dipping a porous substrate in a nanodisperse suspension, or by vapor deposition. The disadvantage of this coating process is that it is expensive and often even nanoscale to provide a protective coating without obstructing or disabling the pores of the substrate during the coating process. Some raw materials are needed. Due to the formation of tubules and gussets during drying, the coating provided by this method is additionally not of uniform thickness or the pores are incompletely coated. In particular, the inner coating of the pores presents a special problem. Furthermore, the closure hole cannot be covered so far. In an additional subsequent process step, this coating must be fired or sintered by itself, optionally then further in an additional costly heat treatment.
DE 42 34 779 A1

DISCLOSURE OF THE INVENTION A method according to the invention for producing a ceramic body having a functionalized pore surface comprises the following step (a) mixing one or several inorganic pore formers with a ceramic matrix material,
(B) a step of forming into a formed body, and (c) a step of heat-treating the formed body in step b), wherein the one or several inorganic pore forming agents are A functionalized pore surface is formed after the conversion in step c).

  In other words, one or several precursors of one or several substances or substance mixtures can be used in step a) as inorganic pore formers, which Form. Precursor here and hereinafter is a substance or material that can be transferred to the desired substance or substance mixture as a pore surface and / or pore coating in the ceramic substrate during the heat treatment in step c) Is understood. This heat treatment is also used for densification of the object by sintering.

  According to the invention, the basic material on which the shaped body is formed is called a matrix material. As matrix material which is advantageous according to the invention, ceramic materials such as powders or powder mixtures are used. Examples for such ceramic materials are magnesium-aluminum-silicates, in particular cordierite and cordierite mixtures, aluminum titanate, zirconium oxide, magnesium oxide, silicon oxide, aluminum oxide and mullite and / or precursors thereof. It is.

  According to the present invention, a pore surface having a composition different from the matrix material of the substrate is referred to as a functionalized pore surface. Such functionalized pore surfaces are also referred to as coatings or pore coatings according to the present invention.

As an inorganic pore-forming agent, in one advantageous embodiment of the invention, one or several metal oxides, preferably MgO, ZrO ₂ , HfO ₂ , SiO ₂ , GeO ₂ , Ta ₂ O ₅ , SnO, are used. _One and several precursors of ₂ and / or lanthanide oxides can be used.

  Advantageously, organic pore formers can be abandoned. With the method according to the invention, the amount of organic combustion products during the heat treatment in step c) can therefore be significantly reduced or even avoided altogether. Vigorous gas generation caused by this, which can damage the ceramic body, cannot occur. The generation of environmentally harmful substances due to the thermal decomposition of the organic pore former is likewise avoided or at least reduced. Furthermore, the reaction of the metal oxide-precursor to the metal oxide can proceed endothermically, which can result in overheating of the furnace and thereby burnt damage. Can not.

  A further advantage of the method according to the invention is that both open holes as well as closed holes can be functionalised.

  The method according to the invention further has the advantage that the production of the porous body, the formation of the pores and the functionalization of the pore surface can be carried out simultaneously. In addition, advantageously the heat treatment that is optionally necessary for fixing the pore coating can be carried out together with the heat treatment of the object, which results in the additional cost required for others. The method steps can be omitted.

  Furthermore, significant savings in coating materials can be achieved over previously known methods, and in addition, raw materials that are not nanoscale and therefore less expensive can be used. The use of further pore formers can be abandoned by the present invention.

  Furthermore, with the method according to the invention, the coating on the pores can be produced significantly more uniformly and more uniformly in terms of density. This resulting coating is therefore significantly improved qualitatively over coating in an object coated in a separate step according to known methods.

  In a particularly advantageous embodiment of the process according to the invention, one or several metal-hydroxide-hydrates, metal-carbonate-hydrates, metal-nitrates or metal-as inorganic pore formers. Bicarbonate can be used.

This pore former can be incorporated as a powder in step a) during the treatment of the ceramic matrix material. This is followed by molding. During the subsequent heat treatment in step c) of the method according to the invention, the ceramic matrix material is first degreased. In parallel to this, water, CO ₂ or other low molecular weight compounds can first be separated as decomposition products from the inorganic pore former. Thus, first, for example, this corresponding hydroxide can be formed, which has a smaller volume relative to the starting compound. At this time, pores can be formed in the ceramic green compact (Gruenkoerper). At higher temperatures, the body can continue to sinter and the formation of the respective stable oxide from the pore former can take place, again compared to the hydroxide. Less specific volume. First, the pores generated in the green compact can be involved in general sintering shrinkage of the ceramic substrate. The resulting pore diameter in the ceramic molded body D is determined from the sintering shrinkage Δl / l ₀ , the particle diameter D ₀ of the pore forming agent, and the effective oxide content ν (in volume parts) in the pore forming agent. Arising from Formula I.

  By means of the method according to the invention, pore surfaces that are functionalized in the sense of the invention, which are different from the rest of the composition of this object, can be targeted. This coating can thus be connected to the object very uniformly and very firmly. A further heat treatment step for sintering and / or for fixing the coating to the object is advantageously not necessary.

  In a further embodiment, the matrix material can react with the pore-forming agent and / or the resulting metal oxide, and depending on the phase state, the substance gradient is between the matrix material and the coating. In the form of mixed crystals or new phases can be formed. Thereby, the pore surface is also coated with a material for which no suitable precursor is present. The material gradient has the advantage that a fluid transition in material properties can be formed between this coating and the matrix material. Thereby, stress can be reduced or even avoided between peeling of this layer and this coating.

  One particularly advantageous embodiment of the process according to the invention envisages that zirconium-hydroxide-hydrate and / or zirconium-carbonate-hydrate are used as pore former. In this way, a zirconium oxide coating of the pores can be formed by the method according to the invention. Such coatings based on zirconium oxide are used as thermal insulation layers and / or result in an increase in heat capacity in the bodies produced according to the invention. Objects coated with such a thermal barrier, such as diesel particle filters, can therefore be more thermally loaded than uncoated substrates. This increased heat capacity can increase the tolerance (Toleranz), especially for short-term temperature maxima.

  In another embodiment of the process according to the invention, in carrying out the aqueous process in steps a) and / or b), the pore-forming agent is not water-soluble or contains one or several fine particles. The addition of pore former can be chosen to take place immediately after this aqueous process step and before the heat treatment in step c). The latter relates to most nitrates or bicarbonates, for example as pore formers. Also preferably, the maximum temperature generated in steps a) and b) does not exceed the decomposition temperature of the pore former.

  The invention further relates to the use of inorganic metal-hydroxide-hydrates and metal-carbonate-hydrates as pore formers for the production of ceramic substrates. Through the use of such inorganic pore formers, the amount of organic combustibles (Ausbrand) is significantly reduced or completely avoided during this heat treatment during the production of the porous ceramic body. Can even do. Vigorous gas generation caused by this can damage the ceramic body, but cannot. The generation of environmentally harmful substances due to the thermal decomposition of the organic pore former is likewise avoided or at least reduced. Furthermore, the reaction of the metal oxide-precursor to the metal oxide can proceed endothermically, so that this does not result in furnace overheating and combustible damage caused thereby.

  Hereinafter, the present invention will be described in detail based on examples, without being limited thereto.

Example 1
Having manufacturing particle size 10μm of Al ₂ O ₃ formed body having a ZrO ₂ pore coating, 75 _{wt% (= 34Vol%) Al 2} O to _{Zr (OH) 4 · xH 2} O with ZrO ₂ in a dry state Mixed with ₃ . Thereafter, molding was performed by a dry press process. During the subsequent heat treatment, the pore former was decomposed at least partially. At this time, pores related to general sintering shrinkage of the matrix material were generated in the untreated molded body.

At 20% sintering shrinkage, 7 μm diameter pores were formed, which had a surface coating of 0.5 μm thickness made of ZrO ₂ .

Example 2
Production of DPF filter bodies with ZrO ₂ coating Cordierite fillers for extrusion of honeycomb bodies, eg kaolin, sintered mullite and talc, as described in the examples of DE 2450071 B2 or EP 549873 B1, and water And organic assistants such as those composed of a plasticizer and a binder were mixed and kneaded. This mixing ratio was selected so as to obtain this stoichiometric composition Mg ₂ Al ₄ Si ₅ O ₁₈ . During the mixing, Zr (OH) ₄ .xH ₂ O having a particle diameter of 25 μm and containing 90% by mass (= 60 Vol%) ZrO ₂ was added. This mixture was then extruded in a conventional manner and subjected to a sintering process at a temperature of 1400 ° C. The binder and further auxiliaries are thereby combusted. The zirconium-hydroxy-hydrate decomposed and formed pores based on this volume reduction. The resulting pore walls in the object had ZrO ₂ still attached and a densely sintered protective layer was formed.

Example 3
Production of hydrolysis-stable MgO filter bodies MgO powder is mixed with ZrO (CO ₃ ) xH ₂ O powder having a particle size of 20-40 μm and an effective ZrO ₂ content of 10 Vol% in a ball mill at high temperature ( Heissgiessmasse). This hot casting material consisted of a wax mixture having a melting point of 60-80 ° C. and a dispersant (Dispergator). This molding was performed by low pressure injection molding into a silicone mold. After degreasing in the powder layer, sintering was performed at 1500 ° C. During the sintering, MgO diffused into ZrO ₂ and formed mixed crystals here. This resulting mass transfer with a gradient resulted in a stable attachment of the ZrO ₂ coating to the pore inner surface. Pore with a diameter of 16-32 μm was produced, which was coated with a ZrO ₂ layer with a thickness of 0.5-1 μm. The MgO body can be superficially attacked by water. This produced MgO compact with ZrO ₂ coating was stable against water attack. Other pore sizes can be targeted and adjusted by grinding the ZrO (CO ₃ ) · xH ₂ O powder.

  The invention is not limited in its implementation to the advantageous embodiments described above. In addition, several variants with regard to the coating, in particular the pore coating, further members with functional porosity can be considered.

  In summary, the present invention provides an improved process for producing ceramic compacts having functionalized pores. The produced ceramic body can be, for example, a filter element for an internal combustion engine, a carrier structure for a catalyst for an internal combustion engine or other temperature- or corrosion-loaded ceramic body or member.

Claims (11)

A method for producing a ceramic body having functionalized pores, the following step (a) mixing one or several inorganic pore formers with a ceramic matrix material,
(B) a step of forming into a molded body, and (c) a step of heat-treating the molded body molded in step b),
A process for producing a ceramic body with functionalized pores, wherein the one or several inorganic pore formers then form a functionalized pore surface after the transformation in step c). One or several metal oxides, preferably MgO, ZrO ₂ , HfO ₂ , SiO ₂ , GeO ₂ , Ta ₂ O ₅ , SnO ₂ and / or lanthanide oxides as pore formers 2. A method according to claim 1, characterized in that several precursors are used.   The metal-hydroxide-hydrate and / or metal-carbonate-hydrate and / or nitrate or bicarbonate is used as the pore-forming agent. the method of. _{4. The} method according to claim 1, wherein the pore-forming agent is selected from Zr (OH) ₄ .xH ₂ O, ZrO (CO ₃ ) .xH ₂ O, or a mixture thereof. The method described in the paragraph.   The matrix material is selected from magnesium-aluminum-silicate, cordierite, cordierite-mixture, aluminum titanate, zirconium oxide, silicon oxide, aluminum oxide, magnesium oxide and mullite and / or precursors thereof. The method according to claim 1, characterized in that:   6. Process according to any one of claims 1 to 5, characterized in that the pore-forming agent and / or the substance or substance mixture resulting after the conversion in step c) reacts with the matrix material.   7. A process according to any one of claims 1 to 6, characterized in that the maximum temperature occurring in steps a) and b) does not exceed the decomposition temperature of the pore former.   When the aqueous process is carried out in steps a) and / or b), the pore-forming agent is not water-soluble or the addition of the pore-forming agent is immediately after this aqueous process step c The method according to claim 1, wherein the method is performed before the heat treatment.   9. A ceramic body having functionalized pores produced by the method of any one of claims 1-8.   Use of a ceramic body according to claim 9 as filter element and / or carrier structure for an exhaust gas aftertreatment device for an internal combustion engine.   Use of metal-hydroxide-hydrate and / or metal-carbonate-hydrate as a pore former for the production of porous ceramic bodies.