WO1995026463A1 - Metal honeycomb element and alloy with high electrical resistance for such an element - Google Patents

Metal honeycomb element and alloy with high electrical resistance for such an element Download PDF

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Publication number
WO1995026463A1
WO1995026463A1 PCT/EP1995/000885 EP9500885W WO9526463A1 WO 1995026463 A1 WO1995026463 A1 WO 1995026463A1 EP 9500885 W EP9500885 W EP 9500885W WO 9526463 A1 WO9526463 A1 WO 9526463A1
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WO
WIPO (PCT)
Prior art keywords
weight
alloy
honeycomb body
aluminum
chromium
Prior art date
Application number
PCT/EP1995/000885
Other languages
German (de)
French (fr)
Inventor
Hans Bode
Stefen Harth
Original Assignee
Emitec Gesellschaft Für Emissionstechnologie Mbh
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Filing date
Publication date
Application filed by Emitec Gesellschaft Für Emissionstechnologie Mbh filed Critical Emitec Gesellschaft Für Emissionstechnologie Mbh
Publication of WO1995026463A1 publication Critical patent/WO1995026463A1/en

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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
    • B01J23/70—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper
    • B01J23/76—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper combined with metals, oxides or hydroxides provided for in groups B01J23/02 - B01J23/36
    • B01J23/84—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper combined with metals, oxides or hydroxides provided for in groups B01J23/02 - B01J23/36 with arsenic, antimony, bismuth, vanadium, niobium, tantalum, polonium, chromium, molybdenum, tungsten, manganese, technetium or rhenium
    • B01J23/85—Chromium, molybdenum or tungsten
    • B01J23/86—Chromium
    • B01J23/862—Iron and chromium
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J35/00—Catalysts, in general, characterised by their form or physical properties
    • B01J35/30—Catalysts, in general, characterised by their form or physical properties characterised by their physical properties
    • B01J35/33—Electric or magnetic properties
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J35/00—Catalysts, in general, characterised by their form or physical properties
    • B01J35/50—Catalysts, in general, characterised by their form or physical properties characterised by their shape or configuration
    • B01J35/56—Foraminous structures having flow-through passages or channels, e.g. grids or three-dimensional monoliths
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
    • F01N3/08—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous
    • F01N3/10—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust
    • F01N3/18—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust characterised by methods of operation; Control
    • F01N3/20—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust characterised by methods of operation; Control specially adapted for catalytic conversion ; Methods of operation or control of catalytic converters
    • F01N3/2006—Periodically heating or cooling catalytic reactors, e.g. at cold starting or overheating
    • F01N3/2013—Periodically heating or cooling catalytic reactors, e.g. at cold starting or overheating using electric or magnetic heating means
    • F01N3/2026—Periodically heating or cooling catalytic reactors, e.g. at cold starting or overheating using electric or magnetic heating means directly electrifying the catalyst substrate, i.e. heating the electrically conductive catalyst substrate by joule effect
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
    • F01N3/08—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous
    • F01N3/10—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust
    • F01N3/24—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust characterised by constructional aspects of converting apparatus
    • F01N3/28—Construction of catalytic reactors
    • F01N3/2803—Construction of catalytic reactors characterised by structure, by material or by manufacturing of catalyst support
    • F01N3/2807—Metal other than sintered metal
    • F01N3/281—Metallic honeycomb monoliths made of stacked or rolled sheets, foils or plates
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N2330/00—Structure of catalyst support or particle filter
    • F01N2330/02—Metallic plates or honeycombs, e.g. superposed or rolled-up corrugated or otherwise deformed sheet metal
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N2330/00—Structure of catalyst support or particle filter
    • F01N2330/02—Metallic plates or honeycombs, e.g. superposed or rolled-up corrugated or otherwise deformed sheet metal
    • F01N2330/04—Methods of manufacturing
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N2330/00—Structure of catalyst support or particle filter
    • F01N2330/30—Honeycomb supports characterised by their structural details
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
    • Y02A50/00—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE in human health protection, e.g. against extreme weather
    • Y02A50/20—Air quality improvement or preservation, e.g. vehicle emission control or emission reduction by using catalytic converters
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
    • Y02T10/00—Road transport of goods or passengers
    • Y02T10/10—Internal combustion engine [ICE] based vehicles
    • Y02T10/12—Improving ICE efficiencies

Definitions

  • the present invention relates to an electrically conductive metallic honeycomb body, in particular for electrically heatable catalytic converters in exhaust systems of motor vehicles, and to an alloy for electrical conductors in electrical heating devices.
  • electrically heatable honeycomb bodies are known in the prior art, for example from WO 89/10471, WO 93/21430, WO 92/31636 or WO 92/02714.
  • honeycomb bodies known from the prior art have a special structure in order to increase the electrical resistance.
  • tortuous or meandering current paths are known.
  • metal sheets with slots in order to increase the electrical resistance or to distribute them inhomogeneously.
  • the known measures allow the electrical resistance to be set independently of the volume of the metallic honeycomb body, but may require complicated structures in order to achieve a sufficiently high resistance. Such structures may be disadvantageous in their vibration behavior, so that an ever increasing increase in the electrical resistance is difficult.
  • an object of the present invention to provide an electrically conductive metallic honeycomb body with increased resistance, in which the resistance is higher than in the case of structurally identical honeycomb bodies made of conventional material by suitable choice of the material. It is also an object of the invention to provide an iron-based alloy which is generally suitable for electrical conductors in electrical heating devices and has an increased resistance.
  • An electrically conductive metallic honeycomb body which contains metallic components made of a high-temperature corrosion-resistant iron-based alloy, has an aluminum content of 6 to 12%, preferably 8 to 10%, and a chrome content of 13%, preferably 16, to solve this problem , in particular up to 22%, 18 to 20% (all percentages by weight) and / or in which the sum of the proportions of aluminum and chromium is at least 24% by weight. It has surprisingly been found that the aluminum content has a massive influence on the electrical resistance of typical high-temperature corrosion-resistant alloys and that an increased chromium content also increases the resistance. As will be explained in more detail with reference to the drawing, increases in the aluminum content, the chrome content and / or the silicon content each result in an increase in the electrical resistance.
  • the corrosion resistance is to be increased, which is necessary in particular in extruded honeycomb bodies because of the large surface exposed to a corrosive attack
  • additional proportions of rare earths in particular cerium and / or yttrium, can be used in the alloy, proportions up to 2%, preferably up to 1% are expedient.
  • the electrical resistance can also be increased under certain circumstances by using other rare earths, such as, for example, gadolinium, which have a particularly high specific electrical resistance, but this is to be weighed from an economic point of view Chromium and aluminum together in the alloy amount to at least 24%, since then both a high specific resistance and good corrosion resistance are achieved.
  • the proposed alloy composition is suitable both for the metal grains used in extruded honeycomb bodies and for the Use in honeycomb structures made of sheet metal layers. Since it is difficult to roll sheets with high aluminum contents, a technology is available here in which thin sheets are produced directly by pouring them out of a melt and rapidly cooling them. Sheets produced in this way have hitherto hardly been used for conventional metallic honeycomb bodies for reasons of cost, in particular also because this manufacturing process is not suitable for the production of sheet metal strips of large width.
  • typical electrically conductive honeycomb bodies are made from relatively narrow sheet metal layers, for example 1 to 6 cm, so that the disadvantage of being too narrow does not play a role here.
  • electrically conductive honeycomb bodies are high-quality products and other complex structural measures can be avoided due to the increased resistance of the sheets, the use of thin sheets directly produced from the melt is economically sensible here.
  • the present invention has another critical advantage.
  • the resistance initially drops significantly at the beginning of its service life due to use in high temperatures. This is due to the fact that at the beginning of the operation aluminum diffuses outwards and forms a protective aluminum layer on the surface. Only when this process has largely been completed does the resistance slowly increase again, but without the initial value being reached again. In particular, the sharp drop in resistance at the start of use is undesirable and complicates the design of electrically heatable catalytic converters.
  • the above-mentioned disadvantageous effect occurs all the more, the larger the surface of the metallic components in the honeycomb body in relation to their volume. The effect is therefore particularly strong when the powder powder is provided extruded honeycomb bodies.
  • the high percentage of aluminum according to the invention naturally reduces the percentage by which the resistance initially decreases, since the same amount of aluminum is always necessary to form the protective surface layer, and therefore only a relatively small amount of the aluminum is used for this purpose in the case of high levels of aluminum becomes.
  • the design of electrically heatable honeycomb bodies, also taking into account a drop in resistance in the initial operating phase, is therefore made considerably easier by the high aluminum content.
  • the invention also relates generally to an iron-based alloy rang according to claim 9 with configurations according to the claims dependent thereon.
  • the advantages described so far apply not only to electrically heatable honeycomb bodies, but also to other applications in electrical heating devices.
  • the resistance curves as a function of the temperature are shown in FIG. 1 for various compositions. If a negative temperature coefficient of the resistance itself is already rare enough for metallic materials, it is the case for Upper curve with 20% Cr and 7.6% Al completely surprising, because the Fe-Cr-Al alloys discussed here are ferromagnetic and the ferromagnetism seems to work in the sense of an increasingly positive temperature coefficient.
  • FIG. 2 shows how different alloy compositions of the elements iron, chromium and aluminum affect the electrical resistance.
  • resistance values for example with silicon as an additional alloy element, resistance values of up to 2.0 ⁇ mm 2 / m. and more can be achieved.
  • a specific composition can be found for the iron-rich iron-chromium-aluminum alloy rods in order to set a specific resistance value at RT.
  • FIG. 4 shows the temperature dependence of the electrical resistance of different Fe-Cr-Si alloys at 20 ° C. with 30% chromium
  • FIG. 5 shows a resistance curve for different silicon contents at 30% chromium. Silicon considerably increases the electrical resistance in iron-chromium alloys and lowers their temperature coefficient. 4 shows the course of some curves for the specific electrical resistance as a function of the temperature for selected silicon contents. A resistance curve for various silicon contents at 30% chromium is shown in FIG. 5.
  • FIG. 9 shows the resistance curves of the materials according to the invention and of the two known alloys CrAl 20 5 and Nicrofer 6025. A comparison shows that the alloy prepared and treated according to the invention has a significantly higher specific electrical resistance than the known ones.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Materials Engineering (AREA)
  • Organic Chemistry (AREA)
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Abstract

The invention concerns an electrically conducting metal honeycomb element for use in particular in electrically heated catalytic converters in vehicle exhaust systems, the honeycomb element including metal constituents made of an iron alloy which is resistant to corrosion at high temperatures, the alloy having an aluminium content greater than 6 % by wt., preferably 6-12 % by wt., in particular 8-10 % by wt., and a chromium content greater than 13 % by wt., preferably 16-22 % by wt., in particular 18-20 % by wt., plus an iron alloy suitable for electrical conductors in electric heaters.

Description

Beschreibung description
Metallischer Wabenkörper und Legierung mit erhöhtem elektrischen WiderstandMetallic honeycomb body and alloy with increased electrical resistance
Die vorliegende Erfindung betrifft einen elektrisch leitfähigen metallischen Wabenkörper, insbesondere für elektrisch beheizbare katalytische Konver¬ ter in Abgasanlagen von Kraftfahrzeugen sowie eine Legierung für elektrische Leiter in elektrischen Hei-zemrichtungen. Verschiedene Bauty¬ pen von elektrisch beheizbaren Wabenkörpern sind im Stand der Technik bekannt, beispielsweise aus der WO 89/10471, der WO 93/21430, der WO 92/31636 oder der WO 92/02714.The present invention relates to an electrically conductive metallic honeycomb body, in particular for electrically heatable catalytic converters in exhaust systems of motor vehicles, and to an alloy for electrical conductors in electrical heating devices. Various types of electrically heatable honeycomb bodies are known in the prior art, for example from WO 89/10471, WO 93/21430, WO 92/31636 or WO 92/02714.
Viele der nach dem Stand der Technik bekannten Wabenkörper weisen einen speziellen Aufbau auf, um den elektrischen Widerstand zu erhöhen. Insbesondere sind verschlungene oder mäanderförmige Strompfade be¬ kannt. Aus der WO 92/13635 ist beispielsweise auch bekannt, Bleche mit Schlitzen zu verwenden, um den elektrischen Widerstand zu erhöhen bzw. inhomogen zu verteilen. Die bekannten Maßnahmen erlauben es prinzi¬ piell, den elektrischen Widerstand unabhängig von dem Volumen des metallischen Wabenkörpers einzustellen, erfordern jedoch unter Umstän¬ den komplizierte Strukturen, um einen genügend hohen Widerstand zu erreichen. Solche Strukturen sind in ihrem Schwingungsverhalten unter Umständen nachteilig, so daß eine immer weitere Erhöhung des elek¬ trischen Widerstandes schwierig ist. Bei extrudierten elektrisch leitfähigen Wabenkörpern aus Metallpulver oder einer Mischung von Keramik- und Metallpulver ist es zwar prinzi¬ piell möglich, den Anteil an nicht leitendem Material zu erhöhen, jedoch wirkt sich dies nachteilig auf die Stabilität aus und ist für besonders dünnwandige extrudierte Wabenkörper nur schwer anwendbar.Many of the honeycomb bodies known from the prior art have a special structure in order to increase the electrical resistance. In particular, tortuous or meandering current paths are known. From WO 92/13635 it is also known, for example, to use metal sheets with slots in order to increase the electrical resistance or to distribute them inhomogeneously. In principle, the known measures allow the electrical resistance to be set independently of the volume of the metallic honeycomb body, but may require complicated structures in order to achieve a sufficiently high resistance. Such structures may be disadvantageous in their vibration behavior, so that an ever increasing increase in the electrical resistance is difficult. In the case of extruded electrically conductive honeycomb bodies made of metal powder or a mixture of ceramic and metal powder, it is in principle possible to increase the proportion of non-conductive material, but this has a disadvantageous effect on the stability and is difficult for particularly thin-walled extruded honeycomb bodies applicable.
Wegen der hohen thermischen und korrosiven Belastung in Abgassyste¬ men von Kraftfahrzeugen, in denen solche Wabenkörper typischerweise eingesetzt werden, ist es bisher üblich, ferritische oder austenitische Edelstahllegierungen einzusetzen, wobei typischerweise Eisenbasislegierun- gen mit einem -Aluminiumanteil bis 6% und einem Chromanteil von 18 bis 20% eingesetzt wurden. Bleche mit einem wesentlich höheren Alumi¬ niumanteil lassen sich nur schwer walzen, so daß derartige Werkstoffe bei gewalzten Blechen kaum eingesetzt werden konnten. Bei Metallpul- vera für extrudierte Wabenkörper wurden auch höhere Alummiumanteüe eingesetzt, jedoch gleichzeitig dann immer der Chromanteil entsprechend gesenkt. Eine Bestrebung, den elektrischen Widerstand eines elektrisch leitfähigen metallischen Wabenkörpers nicht konstruktiv, sondern über die Verwendung des Materials zu beeinflussen, ist im Stand der Technik nicht feststellbar.Because of the high thermal and corrosive loads in exhaust gas systems of motor vehicles, in which such honeycomb bodies are typically used, it has hitherto been customary to use ferritic or austenitic stainless steel alloys, typically iron-based alloys with an aluminum content of up to 6% and a chromium content of 18 up to 20% were used. Sheets with a significantly higher aluminum content are difficult to roll, so that such materials could hardly be used in rolled sheets. In the case of metal powder for extruded honeycomb bodies, higher levels of aluminum were also used, but at the same time the chrome content was always reduced accordingly. An attempt to influence the electrical resistance of an electrically conductive metallic honeycomb body not via the construction but via the use of the material cannot be determined in the prior art.
Ausgehend davon ist es Aufgabe der vorliegenden Erfindung, einen elektrisch leitfähigen metallischen Wabenkörper mit erhöhtem Widerstand zu schaffen, bei der der Widerstand durch geeignete Wahl des Materials höher als bei konstruktiv gleichartigen Wabenkörpern aus herkömmlichem Material ist. Aufgabe der Erfindung ist es auch, eine für elektrische Leiter in elektrischen Heizeinrichtungen generell geeignete Eisen-Basis- Legierung mit erhöhtem Widerstand anzugeben. Zur Lösimg dieser Aufgabe dient ein elektrisch leitfähiger metallischer Wabenkörper, der metallische Bestandteile aus einer hochtemperaturkor- rosionsbeständigen Legierung auf Eisenbasis enthält, die einen Alumini- umanteil von 6 bis 12%, vorzugsweise 8 bis 10%, und einen Chromanteil von 13%, vorzugsweise 16, insbesondere bis 22%, 18 bis 20% (alle Angaben Gewichtsprozente) aufweist und/oder bei der die Summe der Anteile an Aluminium und Chrom mindestens 24 Gew.% beträgt. Es hat sich überraschenderweise herausgestellt, daß der Aluminiumanteil auf den elektrischen Widerstand typischer hochtemperatur-korrosionsbeständiger Legierungen einen massiven Einfluß hat und auch ein erhöhter Chrom- anteil den Widerstand erhöht. Wie anhand der Zeichnung näher erläutert wird, bewirken Steigerungen des Aluminiumanteils, des Chromanteils und/oder des Sili-riumanteils jeweils eine Steigerung des elektrischen Widerstandes. Soll gleichzeitig die Korrosionsbeständigkeit erhöht werden, was insbesondere in extradierten Wabenkörpern wegen der großen einem korrosiven Angriff ausgesetzten Oberfläche erforderlich ist, so können in der Legierung zusätzliche Anteile an seltenen Erden, insbesondere Cer und/oder Yttrium eingesetzt werden, wobei Anteile bis zu 2%, vorzugs¬ weise bis zu 1% sinnvoll sind. Zusätzlich kann der elektrische Wider- stand unter Umständen auch durch Einsatz anderer seltener Erden, wie zum Beispiel Gadolinium, die einen besonders hohen spezifischen elek¬ trischen Widerstand aufweisen, erhöht werden, was jedoch unter wirt¬ schaftlichen Gesichtspunkten abzuwägen ist Besonders bevorzugt soll der Anteil an Chrom und Aluminium zusammen in der Legierung mindestens 24% betragen, da dann sowohl ein hoher spezifischer Widerstand wie auch eine gute Korrosionsbeständigkeit erreicht wird.Proceeding from this, it is an object of the present invention to provide an electrically conductive metallic honeycomb body with increased resistance, in which the resistance is higher than in the case of structurally identical honeycomb bodies made of conventional material by suitable choice of the material. It is also an object of the invention to provide an iron-based alloy which is generally suitable for electrical conductors in electrical heating devices and has an increased resistance. An electrically conductive metallic honeycomb body, which contains metallic components made of a high-temperature corrosion-resistant iron-based alloy, has an aluminum content of 6 to 12%, preferably 8 to 10%, and a chrome content of 13%, preferably 16, to solve this problem , in particular up to 22%, 18 to 20% (all percentages by weight) and / or in which the sum of the proportions of aluminum and chromium is at least 24% by weight. It has surprisingly been found that the aluminum content has a massive influence on the electrical resistance of typical high-temperature corrosion-resistant alloys and that an increased chromium content also increases the resistance. As will be explained in more detail with reference to the drawing, increases in the aluminum content, the chrome content and / or the silicon content each result in an increase in the electrical resistance. If at the same time the corrosion resistance is to be increased, which is necessary in particular in extruded honeycomb bodies because of the large surface exposed to a corrosive attack, additional proportions of rare earths, in particular cerium and / or yttrium, can be used in the alloy, proportions up to 2%, preferably up to 1% are expedient. In addition, the electrical resistance can also be increased under certain circumstances by using other rare earths, such as, for example, gadolinium, which have a particularly high specific electrical resistance, but this is to be weighed from an economic point of view Chromium and aluminum together in the alloy amount to at least 24%, since then both a high specific resistance and good corrosion resistance are achieved.
Die vorgeschlagene Legierungszusammensetzung eignet sich sowohl für die in extrudierten Wabenkörpera verwendeten Metallkörner, als auch für die Verwendung in aus Metallblechlagen aufgebauten Wabenkörpern. Da sich Bleche mit hohen Aluminiumanteilen nur schwer walzen lassen, bietet sich hier eine Technologie an, bei der dünne Bleche direkt durch Ab¬ gießen aus einer Schmelze und schnelles Abkühlen erzeugt werden. So hergestellte Bleche wurden aus Kostengründen bisher für herkömmliche metallische Wabenkörper kaum eingesetzt, insbesondere auch weil sich dieses Herstellungsverfahren nicht für die Herstellung von Blechstreifen großer Breite eignet. Typische elektrisch leitfähige Wabenkörper sind jedoch aus relativ schmalen Blechlagen hergestellt, von beispielsweise 1 bis 6 cm, so daß der Nachteil zu geringer Breite hier keine Rolle spielt. Da außerdem elektrisch leitfähige Wabenkörper hochwertige Produkte sind und durch den erhöhten Widerstand der Bleche andere aufwendige konstruktive Maßnahmen vermieden werden können, ist hier die Ver¬ wendung von aus der Schmelze direkt hergestellten dünnen Blechen wirtschaftlich sinnvoll.The proposed alloy composition is suitable both for the metal grains used in extruded honeycomb bodies and for the Use in honeycomb structures made of sheet metal layers. Since it is difficult to roll sheets with high aluminum contents, a technology is available here in which thin sheets are produced directly by pouring them out of a melt and rapidly cooling them. Sheets produced in this way have hitherto hardly been used for conventional metallic honeycomb bodies for reasons of cost, in particular also because this manufacturing process is not suitable for the production of sheet metal strips of large width. However, typical electrically conductive honeycomb bodies are made from relatively narrow sheet metal layers, for example 1 to 6 cm, so that the disadvantage of being too narrow does not play a role here. In addition, since electrically conductive honeycomb bodies are high-quality products and other complex structural measures can be avoided due to the increased resistance of the sheets, the use of thin sheets directly produced from the melt is economically sensible here.
Die vorliegende Erfindung hat einen weiteren entscheidenden Vorteil. Bei herkömmlichen elektrisch beheizbaren metallischen Wabenköipern sinkt der Widerstand zu Beginn seiner Lebensdauer durch den Einsatz in hohen Temperaturen zunächst deutlich ab. Dies ist darauf zurückzufüh¬ ren, daß zu Anfang des Betriebes Aluminium nach außen diffundiert und an der Oberfläche eine schützende Aluminiumschicht bildet. Erst wenn dieser Vorgang weitgehend abgeschlossen ist, steigt der Widerstand wieder langsam an, ohne daß jedoch der Anfangswert wieder gaπz erreicht wird. Insbesondere das starke Absinken des Widerstandes zu Beginn des Einsatzes ist unerwünscht und erschwert die Auslegung von elektrisch beheizbaren katalytischen Konvertern. Der genannte nachteilige Effekt tritt um so stärker auf, je größer die Oberfläche der metallischen Bauteile im Wabenkörper im Verhältnis zu ihrem Volumen ist. Beson- ders stark ist daher der Effekt bei aus feinem Pulver -beigestellten extradierten Wabenkörpern. Durch den hohen erfindungsgemäßen Alumi- niumanteil wird der prozentuale Anteil, um den sich der Widerstand anfangs verringert, naturgemäß gesenkt, da zur Bildung der schützenden Oberfiächenschicht immer die gleiche Menge Aluminium notwendig ist und daher bei hohen Aluminiumanteilen nur ein relativ geringer Anteil des Aluminiums hierfür verbraucht wird. Die Auslegung von elektrisch beheizbaren Wabenkörpern auch unter Berücksichtigung eines Abfalls des Widerstandes in der Anfangsbetriebsphase wird durch den hohen Alumi- niumgehalt daher erheblich erleichtert.The present invention has another critical advantage. With conventional electrically heatable metallic honeycomb bodies, the resistance initially drops significantly at the beginning of its service life due to use in high temperatures. This is due to the fact that at the beginning of the operation aluminum diffuses outwards and forms a protective aluminum layer on the surface. Only when this process has largely been completed does the resistance slowly increase again, but without the initial value being reached again. In particular, the sharp drop in resistance at the start of use is undesirable and complicates the design of electrically heatable catalytic converters. The above-mentioned disadvantageous effect occurs all the more, the larger the surface of the metallic components in the honeycomb body in relation to their volume. The effect is therefore particularly strong when the powder powder is provided extruded honeycomb bodies. The high percentage of aluminum according to the invention naturally reduces the percentage by which the resistance initially decreases, since the same amount of aluminum is always necessary to form the protective surface layer, and therefore only a relatively small amount of the aluminum is used for this purpose in the case of high levels of aluminum becomes. The design of electrically heatable honeycomb bodies, also taking into account a drop in resistance in the initial operating phase, is therefore made considerably easier by the high aluminum content.
Die Erfindung betrifft auch allgemein eine Eisen-Basis-Legierang nach Anspruch 9 mit Ausgestaltungen entsprechend den davon abhängigen Ansprüchen. Die bisher beschriebenen Vorteile gelten nämlich nicht nur für elektrisch beheizbare Wabenkörper, sondern auch für andere Anwen- düngen in elektrischen Heizeinrichtungen.The invention also relates generally to an iron-based alloy rang according to claim 9 with configurations according to the claims dependent thereon. The advantages described so far apply not only to electrically heatable honeycomb bodies, but also to other applications in electrical heating devices.
Im folgenden werden in der Zeichnung anhand von Diagrammen die Untersuchungsergebnisse, auf denen die vorliegende Erfindung aufbaut, dargestellt, und zwar zeigen:In the following, the examination results on which the present invention is based are shown in the drawing on the basis of diagrams, namely:
Fig. 1 die Abhängigkeit des spezifischen Widerstandes einer Fe-Cr-Al- Legierung mit 20% Chrom bei unterschiedlichen Aluminiumge¬ halten,1 shows the dependence of the specific resistance of an Fe-Cr-Al alloy with 20% chromium with different aluminum contents.
Fig. 2 die Abhängigkeit des spezifischen Widerstandes einer Fe-Cr-Al- Legierung bei unterschiedlichem Chromgehalt,2 shows the dependence of the specific resistance of an Fe-Cr-Al alloy with a different chromium content,
Fig. 3 die Abhängigkeiten des elektrischen Widerstandes vom Chrom und Aluminiumgehalt, Fig. 4 und 5 den Einfluß von Silizium bei Fe-Cr-Legierungen,3 shows the dependencies of the electrical resistance on the chromium and aluminum content, 4 and 5 the influence of silicon in Fe-Cr alloys,
Fig. 6 die Abhängigkeit des elektrischen Widerstandes bei rasch er- starrten Werkstoffen in Abhängigkeit vom Aluminiumgehalt,6 shows the dependence of the electrical resistance in the case of rapidly solidified materials as a function of the aluminum content,
Fig. 7 die Veränderung des elektrischen Widerstandes bei einem Werk¬ stoff nach dem Stand der Technik in Abhängigkeit von der Auslagerangszeit bei 1000°C,7 shows the change in the electrical resistance in a material according to the prior art as a function of the delivery time at 1000 ° C.,
Fig. 8 die Abhängigkeit des elektrischen Widerstandes bei erfindungs- gemäßen Werkstoffen in Abhängigkeit von der Auslagerungszeit,8 shows the dependence of the electrical resistance in the case of materials according to the invention as a function of the aging time,
Fig. 9 einen Vergleich zwischen dem elektrischen Widerstand her- kömmlicher Werkstoffe und erfindungsgemäßer rasch erstarrter9 shows a comparison between the electrical resistance of conventional materials and rapidly solidified according to the invention
Werkstoffe.Materials.
In Fig. 1 sind für verschiedene .(--egieπ gs-αisammensetzungen die Wider¬ standskurven in Abhängigkeit von der Temperatur abgebildet. Ist ein negativer Temperaturkoeffizient des Widerstandes selbst schon selten genug bei metallischen Werkstoffe----, so ist er im Fall der oberen Kurve mit 20% Cr und 7,6% AI völlig überraschend, weil die hier diskutierten Fe-Cr-Al-Legierungen ferromagnetisch sind und der Ferromagnetismus sonst im Sinne eines verstärkt positiven Temperaturkoeffizienten zu wirken scheint.The resistance curves as a function of the temperature are shown in FIG. 1 for various compositions. If a negative temperature coefficient of the resistance itself is already rare enough for metallic materials, it is the case for Upper curve with 20% Cr and 7.6% Al completely surprising, because the Fe-Cr-Al alloys discussed here are ferromagnetic and the ferromagnetism seems to work in the sense of an increasingly positive temperature coefficient.
In Fig. 2 ist gezeigt, wie sich verschiedene Legierungszusammensetzungen der Elemente Eisen, Chrom und Aluminiiim auf den elektrischen Wider¬ stand auswirken. Mit Eisen-Chrom-Aluminium-Legierungen können bei- - 7 -FIG. 2 shows how different alloy compositions of the elements iron, chromium and aluminum affect the electrical resistance. With iron-chromium-aluminum alloys, - 7 -
spielsweise mit Silizium als zusätzlichem Legierungselement Widerstands¬ werte von bis zu 2,0 Ω mm2/m. und mehr erreicht werden.for example with silicon as an additional alloy element, resistance values of up to 2.0 Ω mm 2 / m. and more can be achieved.
Fig. 3 kann für die eisenreichen Eisen-Chrom-Aluminium-Legierangen eine bestimmte Zusammensetzung entnommen werden, um einen be¬ stimmten Widerstandswert bei RT einzustellen.3 a specific composition can be found for the iron-rich iron-chromium-aluminum alloy rods in order to set a specific resistance value at RT.
In Fig. 4 ist die Temperaturabhängigkeit des elektrischen Widerstandes von verschiedenen Fe-Cr-Si-Legierungen bei 20°C mit 30% Chrom ge- zeigt, während Fig. 5 eine Widerstandskurve für verschiedene Siliziumge- halte bei 30% Chrom aufgetragen sind. Silizium erhöht den elektrischen Widerstand in Eisen-Chrom-Legierungen beträchtlich und erniedrigt deren Temperaturkoeffizienten. In Fig. 4 ist der Verlauf einiger Kurven für den spezifischen elektrischen Widerstand in Abhängigkeit von der Temperatur bei ausgewählten Silizήimgehalten dargestellt. Eine Widerstandskurve für verschiedene Siliziumgehalte bei 30% Chrom ist in Fig. 5 wiedergegeben.4 shows the temperature dependence of the electrical resistance of different Fe-Cr-Si alloys at 20 ° C. with 30% chromium, while FIG. 5 shows a resistance curve for different silicon contents at 30% chromium. Silicon considerably increases the electrical resistance in iron-chromium alloys and lowers their temperature coefficient. 4 shows the course of some curves for the specific electrical resistance as a function of the temperature for selected silicon contents. A resistance curve for various silicon contents at 30% chromium is shown in FIG. 5.
In Fig. 6 sind Widerstandskurven der rasch erstarrten Werkstoffe (c) C 3445 mit 7,3% AI (23,8% Cr, 7,3% AI, 0,21% Si) sowie (d) KA 779 mit 13,9% AI (auch enthaltend 18,4% Cr) dargestell Für diese rasch erstarr¬ ten Werkstoffe (c und d) ergab sich eine beachtliche Widerstandssteige¬ rung beider Proben gegenüber dem Werkstoff CrAl 20 5 ( . Mn, Si, Co enthaltende Legierung mit 20% Chrom und 5 % Aluminium).6 shows resistance curves of the rapidly solidified materials (c) C 3445 with 7.3% Al (23.8% Cr, 7.3% Al, 0.21% Si) and (d) KA 779 with 13.9 % AI (also containing 18.4% Cr) shown For these rapidly solidified materials (c and d) there was a considerable increase in resistance of both samples compared to the alloy containing 20 with CrAl 20 5 (. Mn, Si, Co) % Chrome and 5% aluminum).
Die Abhängigkeit des spezifischen elektrischen Widerstandes für diesen Werkstoff CrAl 20 5 bei verschiedenen Auslagerungszeiten ergibt sich aus der Darstellung nach Fig. 7. Zwei wesentliche Punkte zur Deutung des Verlaufes der Widerstandskurve in Fig. 7 sind die Änderung der Konzen- trationsverteilung des Aluminiums in den Werkstoffen und die sich ändernden Gefügestrakturen. Dabei hat die Konzentrationsverteilung des Aluminiums eine große Bedeutung.The dependence of the specific electrical resistance for this material CrAl 20 5 at different aging times results from the illustration in FIG. 7. Two essential points for the interpretation of the course of the resistance curve in FIG. 7 are the change in the concentration distribution of the aluminum in the materials and the themselves changing structural fractures. The concentration distribution of aluminum is of great importance.
Die Abhängigkeit des spezifischen elektrischen Widerstandes für die erfindungsgemäßen Werkstoffe C 3445 (c) und KA 779 (d) bei verschie¬ denen -Auslagerungszeiten ist in Fig. 8 dargestellt. Auch für diese rasch erstarrten Proben läßt sich nach 200 Stunden Auslagerungszeit ein Wan¬ dern des Legierungsbestandteils Aluminium an die Oberfläche der Folien feststellen. Es hat sich gezeigt, daß diese durch rasche Erstarrung herge- stellten MateriaUen nach thermischer Belastung eine merkbar dünnere Oxidschicht bilden. Weil in diesem Fall weniger Aluminium an der Bildung der Oxidschicht beteiligt ist läßt sich auch der prozentual weni¬ ger starke Abfall der Widerstandskurve bei ca. 50 Stunden Auslagerungs¬ zeit für die Werkstoffe (c und d) gegenüber (a) erklären, wie dies durch Vergleich von Fig. 7 und 8 erkennbar ist Die prozentaal geringere Abnahme des -Aluπ-dniums im Kernbereich begünstigt auch die Konservie¬ rung des hohen spezifischen elektrischen Widerstandes.The dependence of the specific electrical resistance for the materials C 3445 (c) and KA 779 (d) according to the invention with various aging times is shown in FIG. 8. Even for these rapidly solidified samples, a migration of the alloy component aluminum to the surface of the foils can be determined after 200 hours of exposure. It has been shown that these materials produced by rapid solidification form a noticeably thinner oxide layer after thermal stress. Because less aluminum is involved in the formation of the oxide layer in this case, the less pronounced decrease in the resistance curve with an exposure time of approximately 50 hours for the materials (c and d) compared to (a) can also be explained as follows Comparison of FIGS. 7 and 8 can be seen. The smaller decrease in the aluminum alumina in the core area also favors the preservation of the high specific electrical resistance.
In Fig. 9 sind die Widerstandskurven der erfindungsgemäßen Werkstoffe sowie der beiden bekannten Legierungen CrAl 20 5 und Nicrofer 6025 dargestellt Es ergibt sich aus einem Vergleich, daß die erfindungsgemäß zubereitete und behandelte Legierung einen wesentlichen höheren spezifi¬ schen elektrischen Widerstand aufweist als die bekannten. FIG. 9 shows the resistance curves of the materials according to the invention and of the two known alloys CrAl 20 5 and Nicrofer 6025. A comparison shows that the alloy prepared and treated according to the invention has a significantly higher specific electrical resistance than the known ones.

Claims

Patentansprüche; Claims;
1. Elektrisch leitfähiger metallischer Wabenkörper, insbesondere für elektrisch beheizbare katalytische Konverter in Abgasanlagen von Kraftfahrzeugen, d a du r ch g e k e nnz e i c h n e t , daß der Wabenkörper metallische Bestandteile aus einer hochtempe- ratur-korrosionsbeständigen Legierung auf Eisenbasis enthält, die einen Aluininiumanteil größer 6 Gew.-%, vorzugsweise von 6 - 12 Gew.-%, insbesondere 8 - 10 Gew.-%, und einen Chromanteil größer 13 Gew.-%, vorzugsweise von 16 - 22 Gew.-%, insbesondere 18 -20 Gew.-%, aufweist und/oder bei der die Summe der Anteile an Aluminium und Chrom mindestens 24 Gew.-% beträgt1. Electrically conductive metallic honeycomb body, in particular for electrically heatable catalytic converters in exhaust systems of motor vehicles, since you know that the honeycomb body contains metallic components made of a high-temperature, corrosion-resistant iron-based alloy, which has an aluminum content greater than 6% by weight. %, preferably from 6 to 12% by weight, in particular 8 to 10% by weight, and a chromium content greater than 13% by weight, preferably from 16 to 22% by weight, in particular 18 to 20% by weight , and / or in which the sum of the proportions of aluminum and chromium is at least 24% by weight
2. Wabenkörper nach Ansprach 1, dadurch gekennzeichnet, daß die Legierung einen Siliziumanteil oberhalb von 0,6 Gew.-%, vorzugs- weise oberhalb von 2% aufweist2. honeycomb body according spoke 1, characterized in that the alloy has a silicon content above 0.6 wt .-%, preferably above 2%
3. Wabenkörper nach Ansprach 1 oder 2, dadurch gekennzeichnet, daß die Legierung einen Anteil von bis zu 2 Gew.-% seltene Erden, vorzugsweise Yttrium und/oder Cer, insbesondere bis zu 1 Gew.-% enthält.3. honeycomb body according spoke 1 or 2, characterized in that the alloy contains up to 2 wt .-% rare earths, preferably yttrium and / or cerium, in particular up to 1 wt .-%.
4. Wabenkörper nach Ansprach 3, dadurch gekennzeichnet, daß die Legierung mindestens ein Element der seltenen Erden wie Gadolini¬ um mit einem hohen spezifischen elektrischen Widerstand enthält. 4. honeycomb body according spoke 3, characterized in that the alloy contains at least one rare earth element such as Gadolini¬ um with a high specific electrical resistance.
5. Wabenkörper nach Anspruch 1, 2, 3 oder 4, dadurch gekennzeichnet, daß der Anteil an Chrom und Aluminium zusammen mindestens 24 Gew.-% beträgt.5. honeycomb body according to claim 1, 2, 3 or 4, characterized in that the proportion of chromium and aluminum together is at least 24 wt .-%.
6. Wabenkörper nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet daß er ein extradierter Wabenkörper aus Metallpul- ver oder einer Mischung aus Keramik- und Metallpulver ist.6. honeycomb body according to one of the preceding claims, characterized in that it is an extruded honeycomb body made of metal powder or a mixture of ceramic and metal powder.
7. Wabenkörper nach einem der Ansprüche 1 bis 5, dadurch gekenn- zeichnet, daß der Wabenkörper ein aus Metallblechlagen aufgebauter7. honeycomb body according to one of claims 1 to 5, characterized in that the honeycomb body is made of sheet metal layers
Körper ist wobei die Bleche insbesondere durch schnelles Ab¬ schrecken aus einer Schmelze hergestellt sind.Body is wherein the sheets are made from a melt, in particular by rapid quenching.
8. Wabenkörper nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet daß der Aluminiumgehalt der Legierung umso höher ist je größer die Oberfläche der metallischen Bestandteile im Ver¬ hältnis zu deren Volumen ist.8. Honeycomb body according to one of the preceding claims, characterized in that the aluminum content of the alloy is higher, the larger the surface of the metallic components in relation to their volume.
9. Hochtemperätur-korrosionsbeständige Eisen-Basis-Legierang für elek- Irische Leiter in elektrischen Heizeinrichtungen, enthaltend Alumini¬ um, Chrom und Silizium, wobei die Summe der Anteile an Alumini¬ um, Chrom, und Silizium mindestens 24,6 Gew.-% beträgt.9. High-temperature, corrosion-resistant iron-based alloy alloy for electrical conductors in electrical heating devices containing aluminum, chromium and silicon, the sum of the proportions of aluminum, chromium and silicon being at least 24.6% by weight. is.
10. Eisen-Basis-Legierang nach Ansprach 9, wobei der Anteil Aluminium größer als 6 Gew.-%, vorzugsweise 6 - 12 Gew.-%, insbesondere 8 -10. Iron-based alloy range according to spoke 9, wherein the proportion of aluminum is greater than 6 wt .-%, preferably 6 - 12 wt .-%, in particular 8 -
10 Gew.-%, ist.10% by weight.
11. Eisen-Basis-Legierang nach Anspruch 9 oder 10, wobei der Anteil an Chrom größer als 13 Gew.-%, vorzugsweise 16 - 22 Gew.-%, ins- besondere 18 - 20 Gew.-%, ist. -- -11. Iron-based alloy rang according to claim 9 or 10, wherein the proportion of chromium is greater than 13% by weight, preferably 16-22% by weight, in particular 18-20% by weight. - -
- 11 -- 11 -
12. Eisen-Basis-Legierang nach Ansprach 9, 10 oder 11, wobei der Anteil an Silizium größer als 0,6 Gew.-%, vorzugsweise größer als 2 Gew.-% ist.12. Iron-based alloy according to spoke 9, 10 or 11, wherein the proportion of silicon is greater than 0.6 wt .-%, preferably greater than 2 wt .-%.
13. Eisen-Basis-Legierang nach Ansprach 9, 10, 11 oder 12, wobei die Legierung einen Anteil von bis zu 2 Gew.-% seltene Erden, vorzugs¬ weise Yttrium und/oder Cer enthält, insbesondere bis zu 1 Gew.-%. 13. Iron-based alloy according to spoke 9, 10, 11 or 12, wherein the alloy contains up to 2% by weight of rare earths, preferably yttrium and / or cerium, in particular up to 1% by weight. %.
PCT/EP1995/000885 1994-03-28 1995-03-09 Metal honeycomb element and alloy with high electrical resistance for such an element WO1995026463A1 (en)

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US6485025B1 (en) 2000-11-27 2002-11-26 Neomet Limited Metallic cellular structure

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