WO2007014562A1 - Ceramic material resistant to thermal shocks and corrosion, process for producing the same and its use - Google Patents

Abstract

Ceramic material based on a zirconium dioxide-free oxide resistant to thermal shocks and corrosion, process for producing the same and its use. Shaped or unshaped products for the metallurgical industry, automobile industry, glass and cement industry and chemical industry can be produced from this ceramic material. According to the invention, the ceramic material resistant to thermal shocks and corrosion comprises a sintered matrix with a proportion of at least 90 % by weight of a dissolved zirconium dioxide-free refractory oxide, the matrix containing fissures formed in situ enclosing oxide zones, a ZrO<SUB>2</SUB>-rich zone with a positive coefficient of thermal expansion being at least partially enveloped by a TiO<SUB>2</SUB>-rich zone having a negative coefficient of thermal expansion or by a ZrO<SUB>2</SUB>-TiO<SUB>2</SUB>-Al<SUB>2</SUB>O<SUB>3</SUB>-mixed zone having a low coefficient of thermal expansion lower than that of the ZrO<SUB>2</SUB>-rich zone. Aluminium oxide and/or magnesium aluminate Spinel and/or mullite are used as refractory, zirconium dioxide-free oxide. Having a coefficient of thermal expansion of more than 7 10<SUP>-6</SUP>/K and a very low modulus of elasticity lower than 30 Gpa, the claimed material is suitable for a wide range of applications, in particular for hot gas particle filters, thermostable and corrosion-resistant catalytic converter substrates, as well as for filters and bioceramics.

Description

Thermal shock and corrosion resistant ceramic material, process for its preparation and use

The invention relates to a thermal shock and corrosion resistant ceramic material based on a zirconia-free oxide, e.g. Alumina or spinel or mullite, a process for its preparation and its use. From the ceramic material molded or unshaped products for the metallurgy, the automotive industry, the glass and cement industry and the chemical industry can be produced. It can be used as an exchange nozzle or outlet nozzle in metallurgy, as a porous filter body in hot gas filtration, for sound and / or thermal insulation and as a heat and / or sound insulating layer and / or as a carrier layer for membranes and / or as an intermediate layer for reducing thermomechanical stresses be used between substrates and end layers.

The three-phase system alumina-titania-zirconia provides an option to control the thermal shock parameters of zirconia-containing materials. From the patent DE 19938752 a ceramic material based on partially or fully stabilized zirconia is known, in which is removed by the addition of alumina and titanium dioxide during sintering and / or the application of MgO stabilizer from the zirconia lattice with the alumina Spinel reacts and, through spinel formation and zirconia destabilization, leads to crack networks that significantly increase the thermal shock resistance of the zirconia matrix. In this case, a significant reduction of the thermal expansion coefficient is registered.

German Offenlegungsschrift DE 1915787 discloses a temperature change-resistant refractory molded body based on aluminum titanate which has a matrix of zirconium silicate. The European patent EP 0997445 describes a of 1575 ⁰ C to 165o melted ⁰ C glass composition, the predominantly crystalline precipitates of titanium and zinkoxidreichem spinel (Zn, Mg) / (Al, Ti) contains ₂ O _4.

From the German patent DE 69917490 a slightly reduced molten grain of Al ₂ O ₃ and ZrO _{2 is} known, which contains according to claim 12 one to three percent by weight of TiO ₂ and one to two percent by mass of MgO. Melt-coated grains which This chemical composition is state of the art for deliveries of glass melting furnaces. Also in metallurgy, components made from melt-cast powder exhibit better corrosion resistance to steel / slag attacks.

European Patent EP 278 456 B1 discloses a ceramic composition with low thermal expansion which consists of a predominant Al ₂ TiO ₅ phase together with ZrTiO ₄ . The aforementioned materials all have low thermal expansion coefficients and are therefore resistant to thermal shock.

In the published patent application DE 10 2004 023 765 A1 is a dense high-strength and wear-resistant material based on alumina, which is to be used as a cutting ceramic in the cutting machining. This material has an aluminum oxide matrix as a wear phase - predominantly α-corundum alumina in the nanometer range from the sol-gel process and a binder phase, for example, from alumina and zirconia or from alumina-zirconia-titania in the nanometer range. The binder phase should not react with the wear phase (matrix material) and the zirconium dioxide should not destabilize during firing or at the operating temperature (no crack formation during destabilization) in order to achieve high strength on the one hand and not to increase the wear resistance of the matrix material affect. However, this material is not thermally shock resistant, which is not required for the intended application.

Technical object of the invention is to develop a thermal shock and corrosion resistant ceramic material with improved properties.

According to the invention, the object is achieved by a thermal shock and corrosion resistant ceramic material of a sintered matrix of a zirconium dioxide-free refractory oxide in a proportion of at least 90 wt.%, Wherein the matrix contains intrinsic cracks, are included in the areas of oxide zones, wherein a ZrO _2- rich zone with a positive thermal expansion coefficient of a TiO ₂ -rich zone with a negative thermal expansion coefficient or of a ZrO ₂ -TiO ₂ -Al ₂ O ₃ mixing zone with a low thermal expansion tion coefficient smaller than that of the ZrO ₂ -rich zone is at least partially encased.

The refractory, zirconia-free oxide used is alumina and / or magnesium aluminum spinel and / or mullite.

Surprisingly, it was found that the enclosed oxide zones act with their different thermal expansion coefficients like a spring and stabilize the system. The material according to the invention has a thermal expansion coefficient comparable to the starting oxide and a linear thermal expansion.

With a thermal expansion coefficient greater than 7 10 ^"6 / K and a very low modulus of elasticity less than 30 GPa, the material according to the invention is suitable for a wide range of applications, in particular for hot gas particle filters, thermostable and corrosion-resistant catalyst carriers but also for filters and bioceramics.

According to an advantageous embodiment of the ceramic material according to the invention is of a TiO ₂ -rich zone coated with a negative coefficient of thermal expansion ZrO ₂ -rich zone with a positive coefficient of thermal expansion of a ZrO ₂ -TiO ₂ -AI ₂ O ₃ -Mhz zone with a small thermal expansion coefficient at least partially enclosed. The ZrO ₂ -TiO ₂ -Al ₂ O ₃ mixing zone acts as an adhesive between refractory oxide matrix and the two oxide zones with the different thermal expansion coefficients.

In a further embodiment of the ceramic material according to the invention, the matrix additionally has areas with an Al ₂ Ti0 ₅ -rich zone.

The ceramic material according to the invention is obtainable by using a homogeneous starting mixture of a zirconia-free refractory oxide powder with a proportion of at least 90 wt.% And a particle size between 0.1 and 150 .mu.m, a MgO partially or fully stabilized zirconia powder with a share up to 5 wt % and a particle size between 0.1 and 20 μm and a titanium dioxide powder with a proportion of up to 5% by weight and a particle size between 0.05 μm and 20 μm, by the addition of dispersants and / or further auxiliaries on an organic and / or inorganic basis, a slurry or a plastic mass or a granulate is prepared and a workpiece is formed by casting or extrusion or pressing,

that the so-formed workpiece is sintered at temperatures above 1450 ⁰ C ₁ preferably above 1550 ⁰ C, so that forming during sintering or during the application of the ceramic material of MgO-stabilizer of the zirconium dioxide spinel phases and / or magnesium titanate and zirconia is destabilized , and / or zirconium titanate and / or aluminum titanate are formed, which in total lead to subcritical cracking in the ceramic matrix and improve the thermal shock resistance.

According to a further embodiment of the invention, the ceramic material may contain further oxides such as magnesium oxide and / or yttrium oxide and / or cerium oxide.

According to the invention, the thermal shock and corrosion resistant ceramic material is produced as follows:

Made of a mixture of

a) a zirconia-free refractory oxide powder with a proportion of at least 90 wt.% Based on the ceramic material and a particle size between 0.1 and 150 .mu.m b) a partially or fully stabilized MgO zirconium dioxide powder with a share up to 5 wt.% Based on the ceramic material and a particle size between 0.1 and 20 microns and c) a titanium dioxide powder with a proportion of up to 5 wt.% Based on the ceramic material and a particle size between 0.05 .mu.m up to 20 microns

If appropriate, with the aid of dispersants and / or auxiliaries on an organic and / or inorganic basis, a slip or a viscous mass or a granulate is prepared and a workpiece is molded by casting or extrusion or pressing. The thus formed workpiece is sintered at temperatures above 1450 ⁰ C, preferably above 1550 ⁰ C, so that during sintering or during use of the ceramic material, the MgO stabilizer of the zirconia forms spinel phases and / or magnesium titanate and the zirconia is destabilized and / or zirconium titanate and / or aluminum titanate are formed, resulting in subcritical areas in the ceramic matrix and the ther - Improve resistance to moistening.

The refractory oxide used is alumina and / or magnesium aluminate spinel and / or mullite.

In an advantageous embodiment of the invention, a further oxide powder with a proportion of up to 5 wt.% And a particle size between 0.1 and 20 microns, z. For example, magnesium oxide and / or yttrium oxide and / or cerium oxide are added.

According to a further advantageous embodiment of the invention, alumina is used with a proportion of at least 94 wt.% As zirconium oxide matrix material, this is titanium dioxide in a proportion up to 3 wt.% And preferably with MgO partially stabilized or fully stabilized zirconia with a share up to 3 wt .% added, optionally added dispersants and / or auxiliaries on an organic and / or inorganic basis and formed a workpiece which is sintered above 1590 ⁰ C.

Surfactant and / or polyacrylate and / or flour based temporary adjuvants are added to control the open porosity. Surfactant and / or polyacrylate based and / or flour based temporary adjuvants and / or water are added to control the sculptural properties for the production of honeycomb bodies.

Be the refractory inorganic mixture metals such. For example, iron, nickel, palladium, platinum and / or rhodium or their compounds admixed, catalysts can be prepared.

Due to its special properties, molded or unshaped products for the metallurgy, the automotive industry, the glass and cement industry and the chemical industry can be produced from the ceramic material. It can be used as an exchange spout or outlet nozzle in metallurgy, as a porous filter body in hot gas filtration, for sound and / or thermal insulation and as heat and / or sound-insulating layer and / or used as a carrier layer for membranes and / or as an intermediate layer for the reduction of thermo-mechanical stresses between substrates and end layers.

As a molded or unshaped product, the newly developed ceramic material can be used in metallurgy, in the automotive industry, in the glass and cement industry and in the chemical industry. The use as an exchange spout or outlet nozzle in metallurgy is possible. Furthermore, the ceramic material can be used as a porous filter body in the temperature range 50 to 1300 ⁰ C.

In addition, the ceramic material can be used due to the existing crack pattern without the addition of temporary excipients to control the porosity in the sound and / or thermal insulation.

Finally, the ceramic material according to the invention can be used as a heat and / or sound insulating layer and / or as a support layer for membranes and / or as an intermediate layer for the reduction of thermo-mechanical stresses between substrates and end layers, which by means of flame spraying or plasma spraying or via a cold process. be applied by means of a spray gun.

Among the preferred uses of the invention are hot gas particulate filters, catalyst supports, filters and bioceramics.

In the development of catalyst carriers and filter materials for exhaust aftertreatment systems, the thermal, chemical and mechanical properties are the focus of material technology. Even at temperatures below 1000 ^° C., reactions with ash constituents incorporated in the filter can occur. These time- and temperature-dependent reactions are dependent not only on the maximum permissible material operating temperature, but also on the atmosphere and on the ash composition. In particular, filter materials for diesel particulate filtration are very susceptible to corrosion reactions due to their high open porosity and large filter surface area. The material according to the invention has Al ₂ O ₃ as matrix material and is thus distinguished by a high corrosion resistance.

Due to doping with ZrO ₂ and TiO ₂ , the newly developed material has a low modulus of elasticity and achieves this in combination with linear thermal expansion as well the microcrack structure improved TWB behavior (TWB = thermal shock resistance) compared to pure Al ₂ O ₃ .

Because of its good properties, the porous ceramic material according to the invention is suitable as a catalyst support in an exhaust pipe of a diesel or gasoline engine or as a particulate filter in the exhaust pipe of a diesel engine.

In plant engineering and in particular in the chemical industry, Al ₂ O _{3 is} frequently used because of the high corrosion resistance in highly stressed components such as valves, membranes or filters. The stabilized material according to the invention is similar, as in the hot gas filtration due to the improved thermal and mechanical properties of the high alumina components superior.

For many years in the bioceramics density high-strength components made of Al ₂ O ₃ and ZrO ₂ and mixtures of these oxides state of the art. In addition to pure aluminum and zirconium oxide, mixtures of the two oxides as material are already known.

Due to the high flexural strength, however, these densely sintered materials are very brittle. The doping according to the invention of a matrix of a zirconium dioxide-free refractory oxide shows, as a densely sintered material, a greater elongation at break compared with the pure oxides and thus an increased fracture toughness.

As the porosity of the material increases, the modulus of elasticity continues to decrease. Doped alumina with a porosity and pore distribution which is suitable as a hot gas filter has at a sintering temperature of 1600 ⁰ C, an E-modulus of only 8.5 GPa. This makes it elastic like bone material and can be used as bioceramics.

With reference to attached figures, an embodiment of the invention will be explained in more detail. Showing: Fig. 1 SEM image, resolution 100Ox

Fig. 2 SEM image comparison product, resolution 100Ox

Fig. 3 SEM image, resolution 30Ox

Fig. 4 SEM image, resolution 400Ox

The production of a microstructure suitable for particle filtration for membrane or wallflow diesel particle filters is achieved by sintering a framework grain, so that pores remain between the particles. By selecting the particle size of the powders, the porosity and plasticizer and the control of the extrusion and sintering process, the pore size and the pore volume can be specifically influenced. State of the art in particle filtration are honeycomb bodies. The end faces of the channels are mutually closed, whereby the exhaust gas flows through the porous channel walls and it forms on the channel surface of a filter cake. The classification of the permeable porosity of the honeycomb body is carried out according to an industry standard by specifying the cell size in cells per square inch (cpsi).

The following describes the production route of extruding honeycomb bodies of 250 cpsi from a plastic mass (hereinafter referred to as AZT). As a comparative product, a porous honeycomb body of Al ₂ O _{3 is} formed (hereinafter referred to as AI). The mixing of the raw materials shown in Table 1 takes place in an intensive mixer. Added organic porosifying and plasticizing agents not only produce the required plastic properties but also the throughflowable porosity after sintering of the green bodies.

Table 1 :

Mixture for producing a porous honeycomb body as a filter body

The excipients are identical in quality and quantity for the examples AZT and AL. Also, the procedural parameters of mixing, extrusion and firing in the experimental series were kept constant.

The invention doped (AZT) and the undoped honeycomb body (AL) were sintered after drying at 1600 ° C. Compared to the sintered doped honeycomb body (AZT), the undoped Al ₂ O ₃ material has a lower shrinkage. Also on the structure of the doped clay is based on the grain growth of the higher sintering progress derived (see Fig. 1 and 2).

Fig. 3 shows in addition to the dark Al ₂ O ₃ matrix a bright finely divided phase. At higher resolution, in addition to the corundum grains, three further phases can be identified.

The ZrO ₂ , which was originally tetragonal stabilized with 3% by weight, destabilized during sintering. Determined by EDX analysis, this brightest region, which is designated as ZrO ₂ rich zone 1 in FIG. 4, now has only 0.5% by weight ZrO ₂ . The TiO ₂ rich zone 2 has in contrast to the zone 1 a negative coefficient of thermal expansion. The ZrO ₂ -TiO ₂ -Al ₂ O ₃ -rich zone partly envelops the region appearing bright in FIG. 4 and has a lower coefficient of thermal expansion than zone 1. This acts like an adhesive between the refractory oxide matrix and the two oxide zones with the different thermal zones expansion coefficient. The enclosed oxide zones (zones 1 and 2) with their different thermal expansion coefficients act as a spring and stabilize the system. Thus, the material (AZT) has a thermal expansion coefficient comparable to the starting oxide (AL), a linear thermal expansion (see Table 2).

The doping according to the invention not only has effects on the microstructure but also on the thermal and mechanical properties summarized in Table 2.

Table 2:

Comparison of the mechanical and thermal properties of the doped (AZT 1500 and AZT 1600) and undoped aluminas (AL1600) according to the invention

Wie bereits erwähnt, weist das Material AZT welches bei 1600⁰C gesintert wurde, trotz der größeren Schwindung aufgrund des Kornwachstums eine höhere offene Porosität auf. Der für die Anwendung als Partikelfilterwerkstoff entscheidende mittlere Porendurchmesser ist ebenfalls höher als bei der undotierten Tonerde (AL 1600). Kennzeichnend für die Verbesserung des TWB-Verhaltens von AZT 1600 ist das Sinken des E-Moduls um 70 % im Vergleich zu AL 1600. Weiterhin verringert sich das E- Modul der dotierten Tonerde durch die Mikrorissbildung bei der Erhöhung der Sintertemperatur von 1500⁰C auf 1600⁰C. Die höhere Elastizität des Werkstoffes ist auf die Mikrorissbildung in diesem Temperaturbereich zurückzuführen. Über die Einstellung einer stabilen Mikrorissstruktur wird in Kombination mit der linearen Wärmedehnung und dem niedrigen E-Modul von nur 8,5 GPa die für die Heißgasfiltration notwendige Temperaturwechselbeständigkeit erreicht.

As already mentioned, the material AZT, which was sintered at 1600 ^° C., has a higher open porosity despite the greater shrinkage due to grain growth. The decisive for the application as a particle filter material average pore diameter is also higher than in the undoped alumina (AL 1600). Characteristic of the improvement of the TWB behavior of AZT 1600 is the decrease of the modulus of elasticity by 70% compared to AL 1600. Furthermore, the modulus of elasticity of the doped clay is reduced by the microcracking with the increase of the sintering temperature of 1500 ^° C. 1600 ⁰ C. The higher elasticity of the material is due to the microcracking in this temperature range. By setting a stable microcrack structure in combination with the linear thermal expansion and the low modulus of only 8.5 GPa, the thermal shock resistance necessary for hot gas filtration is achieved.

Claims

claims A thermal shock and corrosion resistant ceramic material of a sintered matrix of a zirconia-free refractory oxide in a proportion of at least 90 wt.%, Wherein the matrix contains insitu-formed cracks are included in the areas of oxide zones, wherein a ZrO ₂ -rich zone with a positive thermal expansion coefficient of a TiO ₂ -rich zone with a negative coefficient of thermal expansion or of a ZrO ₂ -TiO ₂ -AI ₂ O ₃ -MiSChZOHe with a low coefficient of thermal expansion is less than the ZrO ₂ -rich zone at least partially sheathed. 2. Ceramic material according to claim 1, characterized in that the coated of a Tiθ ₂ -rich zone with a negative coefficient of thermal expansion ZrO ₂ -rich zone with a positive coefficient of thermal expansion of a ZrO ₂ -TiO ₂ -AI ₂ θ3 mixing zone with a low thermal expansion coefficient is at least partially enclosed. 3. Ceramic material according to claim 1 or 2, characterized in that the matrix additionally has areas with an Al ₂ Ti0 ₅ -rich zone. 4. Ceramic material according to one of claims 1 to 3, characterized in that the refractory oxide is alumina and / or magnesium aluminate spinel and / or mullite. 5. Ceramic material according to one of claims 1 to 4, characterized in that it has a linear thermal expansion. 6. Ceramic material according to one of claims 1 to 5, characterized in that it has a thermal expansion coefficient greater than 7 10 ^"6 / K and an E-modulus less than 30 GPa. 7. Ceramic material according to one of claims 1 to 6, obtainable from that of a homogeneous starting mixture of a zirconia-free Feuerfestoxidpulver with a proportion of at least 90 wt.% And a particle size between 0.1 and 150 .mu.m, a MgO partially or fully stabilized zirconia powder with a proportion of up to 5% by weight and a particle size of between 0.1 and 20 μm and a titanium dioxide powder with a proportion of up to 5% by weight and a particle size of between 0.05 μm and 20 μm, via the addition of dispersant and / or other excipients on an organic and / or inorganic basis, a slip or a viscous mass or granules and processed by casting or extrusion or pressing a workpiece is formed so that the thus formed workpiece is sintered at temperatures above 1450 ⁰ C, so that during sintering or during application of the ceramic material, the MgO stabilizer of the zirconium dioxide spinel phases and / or Magnesium titanate forms and the zirconia is destabilized, and / or zirconium titanate and / or aluminum titanate are formed, which in total lead to subcritical cracking in the ceramic matrix and improve the thermal shock resistance. 8. Ceramic material according to one of claims 1 to 6, characterized in that it contains as further oxides magnesium oxide and / or yttrium oxide and / or cerium oxide. 9. A method for producing a thermal shock and corrosion resistant ceramic material, wherein from a mixture of a) a zirconia-free refractory oxide powder with a proportion of at least 90 wt.% Based on the ceramic material and a particle size between 0.1 and 150 .mu.m b) a partially or fully stabilized MgO zirconium dioxide powder with a share up to 5 wt.% Based on the ceramic material and a particle size of between 0.1 and 20 μm and c) a titanium dioxide powder with a proportion of up to 5% by weight, based on the ceramic material, and a particle size of between 0.05 and 20 μm optionally with the aid of dispersants and / or excipients on an organic and / or inorganic basis, a slurry or a viscous mass or granules and processed by casting or extrusion or pressing a workpiece is formed, which is sintered at temperatures above 1450 ⁰ C, so during sintering or during application of the ceramic material, the zirconium dioxide MgO stabilizer forms spinel phases and / or magnesium titanate and the zirconia is destabilized and / or zirconium titanate and / or aluminum titanate are formed, resulting in subcritical areas in the ceramic matrix improve the thermal shock resistance. 10. The method according to claim 9, characterized in that is used as the refractory oxide alumina and / or magnesium aluminate spinel and / or mullite. 11. The method according to claim 9 or 10, characterized in that a further oxide powder is added in a proportion of up to 5 wt.% Based on the ceramic material and a particle size between 1 and 20 microns. 12. The method according to claim 11, characterized in that as further oxide powder magnesium oxide and / or yttrium oxide and / or cerium oxide is added. 13. The method according to claim 10, characterized in that the zirconia-free refractory oxide alumina with a proportion of at least 94 wt.% MgO partially stabilized or fully stabilized zirconia with a share up to 3 wt.% And titanium dioxide with a share up to 3 wt. % are added and the molded workpiece is sintered above 1590 ⁰ C. 14. The method according to any one of claims 9 to 13, characterized in that the mixture temporary additives are added to surfactant and / or Polyakrylat- and / or flour-based for controlling the open porosity. 15. The method according to any one of claims 9 to 13, characterized in that the mixture of temporary adjuvants are added to surfactant and / or Polyakrylat- and / or flour-based and / or water for controlling the Bildsamkeit for the production of honeycomb bodies. 16. The method according to any one of claims 9 to 15, characterized in that the refractory inorganic mixture of metallic catalysts selected from iron, platinum, nickel, palladium and / or rhodium, are admixed. 17. The method according to any one of claims 9 to 16, characterized in that the refractory inorganic mixture nitrate-forming solid is added. 18. Porous workpiece made of a ceramic material according to one of claims 1 to 8, characterized in that the workpiece has a honeycomb structure. 19, hot gas particulate filter for the exhaust pipe of a diesel engine, comprising at least one porous ceramic material according to one of claims 1 to 8. 20. Catalyst support consisting of at least one ceramic material according to one of claims 1 to 8. 21. Catalyst support according to claim 20, characterized in that it has catalytically active coatings. 22. A filter comprising at least one porous ceramic material according to one of claims 1 to 8. 23. Bioceramics, comprising at least one porous ceramic material according to one of claims 1 to 8. 24. Ceramic material according to one of claims 9 to 17, characterized in that the mixture of a) a zirconium dioxide-free refractory oxide powder with a content of at least 90 wt.% Based on the ceramic material and a particle size between 0.1 and 150 microns b) a MgO partially or fully stabilized zirconium dioxide powder with a proportion of up to 5% by weight, based on the ceramic material and a particle size between 0.1 and 20 μm and c) a titanium dioxide powder with a proportion of up to 5% by weight, based on the ceramic material and a particle size between 0.05 up to 20 microns and optionally dispersants, and / or auxiliaries is applied by means of flame spraying onto a substrate. 25. Application of a porous ceramic material according to one of claims 1 to 8 as a catalyst support in an exhaust pipe of a diesel or gasoline engine or as a particle filter in the exhaust pipe of a diesel engine.