DE102011114465A1 - Honeycomb structure useful for filtering exhaust gases in internal combustion engine or in heat exchangers, comprises several channels, which opens at inlet- and outlet surfaces, made of ceramic material comprising sintered grains - Google Patents

Abstract

Honeycomb structure comprises several channels (18), which opens at inlet- (26e) and outlet surfaces (26s). The structure is made of a ceramic material comprising sintered grains. The honeycomb structure exhibits an open crack exhibiting a length of 3-30 mm and a maximum width, which is less than 3 times the maximum size of the sintered grains, and is formed as a microcrack. Independent claims are also included for: (1) a composite body comprising a composition of the above honeycomb structure; (2) a device, preferably a heat exchanger and a particle filter (1) exhibiting at least one above sintered honeycomb structure; and (3) producing the honeycomb structure, comprising extruding the ceramic material through a nozzle to form a honeycomb-preform, drying, debinding and sintering the preform, and clogging optionally the channels of the sintered honeycomb structure, before or after sintering, where at least one portion of the preform is exposed during the debinding to an environment suitable for generating the microcrack such that the sintered honeycomb structure is obtained after sintering.

Description

Technical area

The invention relates to a honeycomb structure, in particular a honeycomb structure, which is intended for the filtration of exhaust gases from an internal combustion engine or for a heat exchanger.

In particular, it consists of a monolithic body, a composite body consisting of a composite of a plurality of individual blocks joined together by means of joints inserted between these individual blocks, and a single block intended for the manufacture of such a composite body.

Finally, the invention relates to a method for producing a honeycomb structure according to the invention.

State of the art

Before the combustion gases of an automobile are released into the ambient air, they can by means of a filter body like those in the 1 . 3 and 4 be cleaned, as is known in the art.

FR 2 928 562 . FR 2 903 918 describe examples of such filter bodies. However, they do not describe the operation of debinding.

EP 1 698 388 describes an operation of debinding, but the goal of the EP 1 698 388 it is a filter body without errors and deformations to obtain, which are able to lead in particular to cracks.

WO 2008/063738 describes in detail an installation that can be used to debond a honeycomb preform. During this operation, the gas environment is renewed to limit the oxygen content.

Like the arrows in 4 indicate the flow F of the combustion gases enters the filter body 3 through inlet openings of inlet channels, penetrate the filter walls of the channels to reach the outlet channels again, and escapes out through the outlet openings.

After a certain period of use, the particulates, or "soot", that accumulate in the channels cause a pressure drop, thus degrading engine performance. For this reason, the filter body must be regenerated regularly, for. B. every 500 km.

The regeneration or "decolmation" is to oxidize the soot. To do this it is necessary to heat it up to a temperature that allows it to ignite. During the regeneration phases, the temperature differs depending on the zones of the filter body 3 and does not vary evenly. In fact, the exhaust gases downstream transport the heat energy released by the combustion of the soot. In addition, the soot is not uniform in the different channels, where they are z. B. preferably in the zone of the filter body, which is in the vicinity of its longitudinal axis. The combustion zones are therefore not uniform in the filter body 3 distributed. The soot combustion thus causes a temperature increase in the heart of the filter body which is higher than that in the peripheral zones. Finally, the peripheral zones of the filter body 3 through the ambient air through the metallic enclosure 5 cooled through.

The temperature inhomogeneity inside the filter body 3 generates local voltages with large amplitudes. These stresses can lead to local breaks or cracks that directly affect filtration performance and lead to abnormally elevated emission levels downstream of the filter body (post-filter).

The filter body 3 has to be changed.

Summary of the invention

There is a continuing need for a honeycomb structure that provides excellent thermo-mechanical resistance, particularly for use in the filtration of exhaust gases from an internal combustion engine, particularly a diesel engine.

An object of the present invention is to meet this need.

The invention proposes a honeycomb structure, which is preferably formed by a ceramic material which consists of sintered grains, said honeycomb structure having an open crack with a length L _f which is between 3 mm and 30 mm, and a maximum width I _max which is less than three times the maximum size D _99.5 grains.

Such a crack is called "microcrack" in the following. The presence of cracks is classically considered harmful. In fact, the cracks that occur during the regeneration usually lead to the destruction of the honeycomb structure.

In contrast to this harmfulness, the inventors have discovered that, surprisingly, the presence of one or more microcracks improves the thermo-mechanical resistance of the honeycomb structure. Without being bound by theory, they believe that the microcracks allow the thermomechanical stresses to be more effectively absorbed resulting in deformations resulting from dilatation phenomena during regeneration, and thus may contribute to increasing the life of the filter increase.

microcrack

• – Das Verhältnis zwischen der maximalen Breite des Mikrorisses und der Maximalgröße der Körner, I_max/D_99,5 ist kleiner als 2,5, kleiner als 2,0, kleiner als 1,5, kleiner als 1,2, und/oder größer als 0,1, größer als 0,5, ja sogar größer als 0,8; auf wenigstens 90% seiner Länge weist der Mikroriss eine maximale Breite I_max auf, die kleiner 90 micron, kleiner als 80 micron, kleiner als 60 micron, kleiner als 50 micron, kleiner als 40 micron, ja sogar kleiner als 30 micron ist und/oder eine minimale Breite I_min aufweist, die größer als 3 micron, ja sogar größer als 5 micron ist;
• – der Mikroriss weist eine maximale Tiefe p_max auf, die bevorzugterweise kleiner als 100 micron, kleiner als 80 micron, kleiner als 60 micron, kleiner als 40 micron, kleiner als 30 micron ist und/oder größer als 10 micron, größer als 20 micron ist;
• – der Mikroriss weist eine Länge L_f auf, die bevorzugterweise größer als 5 mm, bevorzugterweise größer als 7 mm und/oder bevorzugt kleiner als 40 mm, bevorzugt kleiner als 30 mm, bevorzugt kleiner als 25 mm ist;
• – der Mikroriss weist eine Länge auf, die kleiner als 25%, kleiner als 20%, kleiner als 15%, kleiner als 12%, kleiner als 10%, kleiner als 8%, kleiner als 6%, kleiner als 4% und/oder größer als 1% der Länge der Wabenstruktur ist.
• – der Mikroriss erstreckt sich im Wesentlichen entlang der longitudinalen Richtung der Wabenstruktur. Insbesondere ist der Winkel zwischen einer senkrechten Ebene zur Hauptrichtung des Mikrorisses und einer Transversalebene (senkrechte Ebene zur longidutinalen Richtung) bevorzugterweise kleiner als 45°, kleiner als 30°, ja sogar kleiner als 20°.
• – Bevorzugterweise mündet der Mikroriss auf einer Oberfläche der Wabenstruktur, die an der Aussenseite der Wabenstruktur liegt. Insbesondere ist der Mikroriss vorzugsweise auf einer Seitenfläche eines Einzelblocks angeordnet.

This microcrack may have one or more of the following optional features:

• The ratio between the maximum width of the microcrack and the maximum size of the grains, I _max / D _99.5, is less than 2.5, less than 2.0, less than 1.5, less than 1.2, and / or greater than 0.1, greater than 0.5, even greater than 0.8; at least 90% of its length, the microcrack has a maximum width I _{max of} less than 90 microns, less than 80 microns, less than 60 microns, less than 50 microns, less than 40 microns, even less than 30 microns, and / or has a minimum width I _min greater than 3 microns, even greater than 5 microns;
• The microcrack has a maximum depth p _max which is preferably less than 100 microns, less than 80 microns, less than 60 microns, less than 40 microns, less than 30 microns and / or greater than 10 microns, greater than 20 microns is;
• The microcrack has a length L _f which is preferably greater than 5 mm, preferably greater than 7 mm and / or preferably less than 40 mm, preferably less than 30 mm, preferably less than 25 mm;
• The microcrack has a length which is less than 25%, less than 20%, less than 15%, less than 12%, less than 10%, less than 8%, less than 6%, less than 4% and / or greater than 1% of the length of the honeycomb structure.
• The microcrack extends substantially along the longitudinal direction of the honeycomb structure. In particular, the angle between a vertical plane to the main direction of the microcrack and a transverse plane (vertical plane to the longidutinal direction) is preferably less than 45 °, less than 30 °, even less than 20 °.
• - Preferably, the microcrack opens on a surface of the honeycomb structure, which lies on the outside of the honeycomb structure. In particular, the microcrack is preferably arranged on a side surface of a single block.

Microcracked area

Preferably, the honeycomb structure has a plurality of microcracks, with more than 50%, more than 70%, even more than 90%, 95% or even 100% of the microcracks according to the invention having one or more of the optional features mentioned above.

The microcracks may be homogeneously distributed in the honeycomb structure or grouped together. The area of the microcracked block is called the "microcrack area". The microcrack area is limited by the closed envelope with the smallest possible volume, which is the totality the microcracks of the honeycomb structure includes and bounded by the side surface of the honeycomb structure and by the two transverse planes.

Preferably, the concentration of microcracks opening on the side surface of the honeycomb structure is greater than 0.001, preferably greater than 0.01 and / or less than 0.1 microcracks per cm ^{2 of} the side surface which limits the microcrack area. The inventors have also discovered that the microcrack region preferably does not extend the entire length of the honeycomb structure. It preferably extends for less than 50%, less than 40%, even less than 30% of the length of the honeycomb structure.

The position of the microcrack also modifies the achievements. Preferably, this area extends entirely in the part of the honeycomb structure which extends from one of the entrance surfaces and exit surfaces to 40%, 30%, even 20% of the length L of the honeycomb structure.

A honeycomb structure according to the invention may have more than 2, more than 3, more than 5, more than 10, more than 15, more than 20 microcracks.

Preferably, more than 50%, more than 70%, even more than 90% of the microcracks open on the outside of the honeycomb structure. Preferably, more than 50%, more than 70%, even more than 90% of the microcracks, in particular the transverse microcracks, even all microcracks, in particular the transverse microcracks on the side surface (or "outer") of the honeycomb structure, with the side surface is the outside of the honeycomb structure that extends between the entrance surface and the exit surface.

honeycomb structure

In general, the length L of a honeycomb structure according to the invention is smaller than 50 cm, smaller than 40 cm, smaller than 30 cm, smaller than 25 cm, even smaller than 20 cm and smaller than 15 cm, respectively.

A honeycomb structure according to the invention may be made of a material having a thermal expansion coefficient above 1.0 × 10 ^-6 C ^-1 between 20 and 1000 ° C. The invention is used in particular for the honeycomb structures of a material whose thermal expansion coefficient is greater than 2.5 × 10 ^-6 C ^-1 between 20 and 1000 ° C. It may in particular contain or even consist of silicon carbide SiC.

This feature is particularly useful in a composite filter body. During regeneration, the peripheral and central discrete blocks indeed have a very different deformation that generates transversally extending stresses (in the transverse planes) and eventually leads to longitudinal cracks in the connections. The presence of microcracks in the individual blocks turns out to be particularly advantageous in this situation.

A honeycomb structure according to the invention may be a monolithic body, a composite body or a single block intended for the fabrication of a composite body. It can be a preform or a sintered structure. It may or may not be filtered (with the channels closed at one end).

Preferably, a honeycomb structure according to the invention is novel, i. h. that it has never been used for filtration. It is thus without any trace of soot.

Preferably, a honeycomb structure according to the invention is a composite body, which is formed of a composition of individual blocks with interconnections, whether continuous or not.

The invention relates to a composite body, it being noteworthy that it consists of at least one single block according to the invention. Preferably at least 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, preferably all individual blocks of the composite body are constructed according to the invention.

When the composite body is intended for filtration of particles, particularly particles of the exhaust gas of an internal combustion engine, each individual block consists of an ensemble of adjacent channels extending between the entrance surface and the exit surface and separated from each other by the filter walls are closed by plugs, which are arranged upstream and downstream alternately in the vicinity of the entrance surface and the exit surface.

Preferably, each individual block according to the invention is arranged so that its microcrack region is closer to the exit surface than to the entry surface, preferably so that the region extends up to the exit surface, preferably to a length less than 30% of the length of the Single block is.

The thermo-mechanical stresses, particularly at the joints, are particularly strong in asymmetric bodies composed of single blocks, i. h., in such asymmetric bodies where the cross-sections of the input channels are different from those of the output channels. The arrangement of the microcrack region in the vicinity of the exit surface is particularly advantageous in the type of single block. The inventors believe that this particular arrangement allows the thermomechanical stresses in the vicinity of that area to be reduced.

The invention also relates to a device which is selected from a heat exchanger and a particle filter, this device being remarkable insofar as it consists of at least one sintered honeycomb structure according to the invention. This structure is preferably new, d. H. without signs of wear and especially without traces of russia.

In one embodiment, the honeycomb structure is never mounted in an exhaust line.

The invention equally relates to an exhaust line of an automobile equipped with a sintered honeycomb structure according to the invention, in particular an exhaust line of a diesel engine of a motor vehicle.

• a) Extrusion eines keramischen Materials durch eine Düse, um eine Vorform der Wabenstruktur zu formen,
• b) Trocknung,
• c) Entbinderung und Sinterung der Vorform, um eine gesinterte Wabenstruktur zu erhalten,
• d) optional vor oder nach der Sinterung, Verstopfung der Kanäle der gesinterten Wabenstruktur,
• e) optional Zusammenstellung der gesinterten Wabenstruktur mit anderen gesinterten Wabenstrukturen, vorzugsweise gemäß der Erfindung, derart, dass ein zusammengesetzter Körper erhalten wird (insbesondere gemäß den Schritten A) bis E) oder A') bis E').

The invention likewise relates to a production method for a honeycomb structure, which comprises the following method steps:

• a) extrusion of a ceramic material through a die to form a preform of the honeycomb structure,
• b) drying,
• c) debindering and sintering the preform to obtain a sintered honeycomb structure,
• d) optionally before or after sintering, clogging of the channels of the sintered honeycomb structure,
• e) optionally assembling the sintered honeycomb structure with other sintered honeycomb structures, preferably according to the invention, such that a composite body is obtained (in particular according to steps A) to E) or A ') to E').

This method is noteworthy in that, at the time of debindering, at least one region is developed in an environment capable of generating a microcrack, called a "microcracking environment", in the sintered honeycomb preform.

• – Umgebungstemperatur
• – Konzentration des oxidierenden Gases in der Umgebung;
• – Dauer des in Kontakthaltens dieser Umgebung mit besagter Region.

The micro-racial character of an environment is characterized by the following three points:

• - Ambient temperature
• - concentration of oxidizing gas in the environment;
• - Duration of keeping this environment in contact with said region.

Preferably, the temperature is below 700 ° C and / or above 300 ° C, preferably above 400 ° C.

Preferably, the environment is gaseous and the oxygen concentration of the environment is greater than 15 vol and preferably less than 25 vol, with a concentration of 21% being appropriate. Air can be used. Preferably, the spent oxygen is renewed to maintain such an environment in contact with said region, for example by permanent blowing or not by oxygen-laden gas.

For example, a gas flow rate, in particular of air, may average between 5 and 20 × 10 ^-2 m ³ / s per m ^{2 of} the surface of the preform of the honeycomb structure exposed to that air (surface directly exposed to this air flow, ie, through which the river comes into contact with the preform for the first time) may be appropriate. This throughput thus depends on the bulk content of organic compounds to decompose additives in the extrusion mixture of hub preforms, especially the binders, plasticizers and foaming agents of an organic nature. The average air flow rate as just mentioned is particularly adapted to a mass content of organic compounds above 10% and below 30%.

Preferably, the operation of debinding takes longer than 1 hour.

Simple experiments should allow one skilled in the art to easily determine acceptable triplets.

Preferably, the preform of the honeycomb is exposed to a non-uniform temperature during debinding. Preferably, the gas is indexed approximately along the axis of the preform. Preferably, at least two regions of the preform are exposed to environments representing various potential oxidants. Advantageously, it is also possible to provide only a part of the sintered honeycomb structure with microcracks, and in particular to provide only the areas of the honeycomb structure with microcracks which suffer the strongest thermo-mechanical stresses in the desired application.

Vorzugszweise, the extruded ceramic mass more than 5%, advantageously more than 7% yes even more than 10% organic material, such as methyl cellulose in mass percentages. An increased content of organic material which is eliminated during debindering advantageously favors microcracking.

The classically used prior art debindering environments do not allow microcracking to be generated. On the contrary, such as in the WO 2008/063538 generally, the environment is adapted to eliminate any cracking.

After the debinding operation, the temperature of the honeycomb structure may be reduced, possibly to the ambient temperature prior to the sintering operation.

Preferably, debindering is an operation separate from sintering. In particular, the temperature of debindering is classically lower than the sintering temperature.

Preferably, the debinding operation comprises a step of maintaining the temperature below 700 ° C, preferably below 500 ° C, preferably for a period of more than 30 minutes, preferably more than 1 hour.

The invention also relates to a microcracked preform obtained in particular according to a debinder as described above.

definitions

A crack is called "open" when it opens to the outside of the material (as opposed to a closed tear that runs exclusively inside the material).

A microcrack is called "transverse" when it pierces a wall.

The length of a microcrack is measured on the surface on which the microcrack opens, following the direction of the microcrack (classically on a photo of this surface). The width is measured on the surface on which the microcrack opens, perpendicular to the curve.

The main direction of a microcrack is the direction defined by the connecting line of its two ends.

The "longitudinal" direction or the direction of the length "of a honeycomb structure (CC or DD in the 1 to 3 ) is defined by the general flow direction of the fluid through this honeycomb structure. Classically, all channels of a honeycomb structure extend parallel to the longitudinal direction. In a composite honeycomb structure, the individual blocks are generally assembled such that the connection surfaces between which a connection extends should be at least locally approximately parallel to the longitudinal direction, and preferably parallel to each other.

A "longitudinal" surface is an area that is parallel to the longitudinal direction of the honeycomb structure.

A "transversal" plane is a plane that is perpendicular to the longidutinal direction. In a honeycomb structure whose channels are all parallel to each other, a transverse plane is a plane perpendicular to the direction of these channels.

In a particle powder, the "size" of a particle is called the mean between its largest and smallest dimension. The percentages or "cubes" 10 (D ₁₀ ), 50 (D ₅₀ ), 90 (D ₉₀ ) and 99.5 (D _99.5 ) of a particle amount in a powder are the sizes of these particles corresponding to the volume percentages of 10%, 50%, 90% and 99.5% on the cumulative distribution curve of the sizes of the particles, the sizes being classified according to their increasing size. For example, 10% by volume of particles have a size smaller than D ₁₀ and 90% of the particles in volume have a size greater than or equal to D ₁₀ .

In a sintered material, one speaks of the "size" of a grain in a material cut as the means between its largest and smallest dimension. The size is classically measured with an electron microscope.

For a total of grains in a sintered material, the cubes 10 (D ₁₀ ), 50 (D ₅₀ ), 90 (D ₉₀ ) and 99.5 (D _99.5 ) are the sizes of these grains in a section plane corresponding to the percentages of Grain counts of 10%, 50%, 90% and 99.5% over the cumulative size distribution curve of the grains, the sizes being classified in ascending order. For example, 10% of the number of grains has a size less than D ₁₀ and 90% of the number of grains has a size greater than or equal to D ₁₀ . The ccillions can be determined by suitable analysis of image analysis of a metallographic section of the material used with an electron microscope. For an approximately homogeneous sintered material, the cumulative size distribution curve of the grains does not necessarily depend on the considered section plane.

Classically, the centille "D ₅₀ " is called "the medium size" and the centille "D _99.5 " is the "maximum size".

The "debindering" is a thermal treatment that allows to eliminate the binders and the temporary foaming agents. Classically, these binders are organic binders. The foam-forming additives are, in particular, those of the cellulose type such as polyethylene, polystyrene, amidone and graphite. They are for example in the applications JP 08-281036 or EP 1 541 538 described. Classically, debindering is effected at a maximum temperature above 300 ° C, preferably above 400 ° C and / or below 700 ° C, even below 500 ° C, preferably at a duration greater than 1 hour and less than 15 hours , Unless otherwise indicated, it is understood that "consisting of one" or "representing one""comprising at least one" or "representing at least one".

Brief description of the figures

The following description, which refers to the attached drawings, makes it possible to better understand and to judge the advantages of the invention.

In these drawings:

show the 1 schematically in perspective a composite filter body;

the 2 schematically in perspective a single block of the composite filter body as in 1 is shown;

the 3 schematically in perspective a monolithic filter body;

the 4 schematically a longitudinal section through the center following the cutting plane P, wherein the composite filter body, as in 1 is shown after insertion into its sleeve;

the 5 to 8th Photos of microcracks;

the 9 a debindering system that allows to obtain microcracks in single blocks and

the 10 schematically a microcrack on a single block.

In these non-limiting figures, the various elements are not necessarily shown to the same scale.

In particular, for reasons of clarity, the microcrack is 120 in the 10 not shown to scale.

Identical reference numerals are used on the various figures to designate identical or similar elements.

To improve the clarity of the figures, the number of channels shown is much smaller than that of the individual blocks or the classic commercial filter body.

Detailed description

honeycomb structure

A particle filter 1 classically consists of at least one filter body 3 , which is generally cylindrical in shape with the longitudinal axis CC, with a length L, which is typically between 10 and 50 cm, and that in a metallic envelope or sleeve 5 is introduced, also called "doses" ( 4 ).

The filter body 3 can be a monolithic body, ie of a single piece, without connection, as in the 3 shown.

In order to improve its thermo-mechanical resistance, in particular during the regeneration phases, it is therefore advantageous that it consists of a combination of a plurality of individual blocks 11 by means of connections 12 consists.

The filter body is thus a "composite body" as in the 1 and 4 shown.

A single block 11 ( 2 ) is conventionally in the form of a rectangular parallelepiped, with the axis DD having a length "L", a width "I" and a height "h" as in FIG 2 shown. The width "I" and the height "h" of a page surface 14a -D of such a single block are typically between 30 mm and 100 mm. The totality of side surfaces 14a -D of the single block form its "side surface".

A monolithic body and a single block 11 are examples of honeycomb structures, wherein a configuration "honeycomb" with the presence of a total of channels 18 or "conduits" arranged adjacent to one another in such a way as to form a regular pattern in section, for example in the form of a chessboard.

"Outer wall" is the peripheral wall of a honeycomb structure that defines the side surface.

The honeycomb structure may be made of a porous material having more than 30%, even more than 40% and / or less than 65%, in particular less than 50% of open porosity.

In one embodiment, the honeycomb structure is made of a material which, at a temperature which is between 20 ° C and 600 ° C, a thermal conductivity below 60 W / m ° C, in particular below 40 W / m ° C, and / or above 1 W / m ° C, in particular above 10 W / m ° C.

The honeycomb structure may be made of a material having a coefficient of expansion above 2.5 · 10 ^-6 ° C ^-1 between 20 and 1000 ° C, for which the invention is particularly useful.

Preferably, the honeycomb structure is made of a sintered material and also preferred, it contains more than 50%, more than 80%, even more than 95% or even more than 98% or 100% of a SiC mass, which is preferably recrystallized.

The silicon carbide (SiC) may be sintered and / or bonded by silicon.

Likewise, the honeycomb structure may be made of a material comprising at least 50% of aluminum titanate and / or mullite and / or cordierite (Mg ₂ Al ₄ Si ₂ O ₁₈ ) and / or of silicon nitrate and / or sintered metals.

In a composite body, all individual blocks can be made of identical material.

channels

Especially in a filtration application are the channels 18 , each through a side wall 22 are generally rectilinear and parallel to one another along the length L. The thickness of the side walls (or "filtration walls") may in particular be between 180 and 500 microns.

The cross section of the channels, which is preferably constant along the length, may be in particular between 0.4 and 9 mm ² .

Each channel opens outward via an upstream opening 24e on an entrance area 26e and through a downstream opening 24s on an exit surface 26s ,

In a filtration application, the number of channels of the honeycomb structure is typically between 7.75 and 62 per cm ^{2 of} the entrance surface, preferably between 150 to 400 cpsi.

Classically, a ceramic mass is extruded through a suitable die to produce a honeycomb structure. The extrusion die is formed so that the preform has the shape of a cylinder having a circular or ellipsoidal cross-section to make a monolithic body, or a cylinder of polygonal cross-section, such as square, hexagonal or rectangular, to make a single block.

caps

The channels of a honeycomb structure intended to fabricate a filter body eventually become on the entrance surface 26e or on the exit surface 26s through upstream plugs 30s and downstream plugs 30e sealed, as it is already known, to form channels called "exit channels" 18s and "entrance channels" 18e (please refer 4 ). In this way one obtains a "filtering" honeycomb structure.

Further preferably, the upstream and downstream plugs each extend along the entrance surface and along the exit surface.

Thus, the inlet and outlet channels define inlet and outlet chambers 34e and 34s , each by a side wall 22 , a closure plug and an outwardly opening opening are limited. Two adjacent inlet and outlet channels are fluidly connected by their common side wall.

In one embodiment, the inlet channels 18e and the exit channels 18s adjacent to each other and arranged one in relation to the other so that the entirety of the filtered through an input channel gas enters the adjacent output channels of the inlet channel. Thus, there are no zones of one or more inlet channels that open into another inlet channel, that is, zones that are not suitable for filtration. The filter surface (ie the used surface of the walls of the entrance channels), which is available for a given volume of the honeycomb structure, is thereby optimized.

Preferably, the entirety of the inlet and outlet channels are interlaced so that a checkerboard pattern is formed in cross-section, where said inlet channels alternate with said outlet channels.

The inlet channels preferably have a cross-section larger than that of the outlet channels to increase the volume available for storing residues. Advantageously, the cleaning frequency of the filter and the pressure loss are reduced. For this purpose, the channel walls are "deformed" to increase the total volume of the inlet channels at the expense of that of the outlet channels. For example, the walls may be concave to the side of an entrance channel and convex to the side of an exit channel adjacent to each other.

In particular, the partitions separating two lines or two columns of channels may have a wavy cross-section ("wavy" in English) with the intermediate wall extending approximately half a wavelength across the width of a channel. "Wavelength" is the distance that separates two points on this wave, which are arranged at the same height with the same slope direction. In the case of a periodic wave, "length" of the wave is called "period". Preferably, the wave is periodic, but the amplitude of the waves may be constant or variable. Vorzugszweise this amplitude is constant. Further preferably, the wave represents a sinusoid whose half-period is equal to the step "p" of the channel network, or a series of arcs arranged in a row, each arc having a length equal to the step "p".

Finally, preferably all the intermediate walls, which extend between two lines and / or between two columns of channels, have in cross section a wave of identical shape.

The "degree of asymmetry" of a "wavy" structure denotes the ratio of the amplitude "h _w " and the half-length of said wave, ie, in the case of a periodic wave, the ratio between the amplitude "h _w " and the half-period. Preferably, the degree of asymmetry is less than 40%, preferably less than 30%, preferably less than 20% and in a particularly preferred form less than or equal to 10% and / or greater than 2%, preferably greater than 5%. Advantageously, the pressure loss induced by the accumulation of soot by the block is greatly reduced, and the regeneration frequency of the filter body is thus limited.

With this asymmetrical channel configuration, the total volume of the input channels is greater than that of the output channels and the total surface area of the openings of the input channels on the entrance surface, i. H. the sum of the areas of these openings is greater than that of the openings of the exit channels on the exit surface. For optimum effect, the ratio r of the total volume Ve of the input channels to the total volume Vs of the output channels or the ratio r 'of the total inner surface of the input channels to the total inner surface of the output channels is preferably greater than 1.03, greater than 1.10, greater than 1.15 and / or less than 3, less than 2.5, preferably less than 2.

After sealing, the honeycomb structures are sintered.

The sintering may be preceded by a debinding step. Usually, the honeycomb structures are placed in an oven and subjected to a thermal debinding treatment at a temperature generally between 300 and 700 ° C.

After debindering, the honeycomb structures may be brought to a temperature above 1600 ° C, even above 1800 ° C, preferably between 1900 ° C and 2400 ° C, preferably between 2000 ° C and 2300 ° C, and even above 2100 ° C , preferably for a typical duration of between 2 and 10 hours, preferably between 4 and 6 hours, to be sintered.

To make a composite body, put the individual blocks together as described in the example below.

Generally, the side surface becomes 38 the monolithic filter body or the composite filter body with a peripheral coating 36 covered, also called "outer coating" or "coating", with a coating cement, which is thermally insulating and impermeable to the exhaust gases, such as in de EP 1 142 619 or EP 1 632 657 described. This peripheral coating can be made by means of a cement identical to that used for the joints.

The tightness of the coating cement makes it possible to induce transverse microcracks in the thickness of the outer wall of the filter body without adversely affecting filter efficiency (by applying this cement so as to cover the openings of these microcracks).

The filter body 3 , composed or monolithic, can also be used in a sleeve 5 can be used, wherein a peripheral connection 40 , which is impermeable to the exhaust gases, between the side surface 38 of the filter body and the sleeve 5 is arranged.

Examples of filter bodies are in particular in the patent applications EP 816,065 . EP 1 142 619 . EP 1 455 923 or WO 2004/065088 on which one can obtain more details regarding their structure or their production.

Composite body

• A) Herstellung einer Vielzahl von gesinterten Einzelblöcken 11;
• B) Präparation eines Montagezements für die Zusammensetzung;
• C) Zusammenkleben der Einzelblocks mittels des frischen Montagezements;
• D) Härtung des frischen Montagezements derart, das Verbindungen 12 zwischen den Verbindungsflächen gebildet werden;
• E) Optional eine thermische Behandlung.

A method for producing a composite body traditionally includes the following method steps:

• A) Production of a large number of sintered individual blocks 11 ;
• B) preparation of an assembly cement for the composition;
• C) gluing together the individual blocks by means of the fresh assembly cement;
• D) Hardening of the fresh assembly cement so, the compounds 12 be formed between the connecting surfaces;
• E) Optionally a thermal treatment.

In step A, the individual blocks can be manufactured as described above.

In step B, the fresh mounting cement is prepared in view of the desired properties for the joints.

The two surfaces of the connection between which a connection extends may generally be flat.

The assembly cement which forms the joints generally consists of silica and / or of silicon carbide or aluminum nitrate. Vorzugszweise the assembly cement is substantially impermeable to the exhaust gases to be filtered. The cement at a temperature between 20 ° C and 600 ° C may have a thermal conductivity of above 0.1 W / mK, and preferably less than 5 W / mK, even less than 1 W / mK, to increase the thermomechanical stresses limit. Typically, the average thickness of a compound 12 is between 0.3 and 4 mm.

The total porosity of the assembly cement of the compounds may be above 5% and below 90%, preferably above 30% and / or below 85%. The assembly cement may advantageously comprise more than 0.05% and less than 5% of a heat-resistant plastic in percentages relative to the mass of the dry mineral material.

The assembly cement may be obtained from a mineral powder having a mass percentage relative to the mineral mass of less than 5% of particles whose mean size is between 0.1 and 10 microns, preferably between 0.3 and 5 microns. Preferably, the silicon carbide (SiC), the aluminate (Al ₂ O ₃ ), the zirconium (ZrO ₂ ), the titanium oxide (TiO ₂ ), the magnesium oxide, the silicate (SiO ₂ ) and the mixtures of these oxides, such as the titanate of Aluminum, mullite or zirconium altogether represents more than 85% of the mass of the dry mineral material of the assembly cement. The assembly cement may have a content of lime (CaO) below 0.5% by mass in relation to the dry mineral material. The mounting cement may be a composite material having grains of an inorganic material joined by a geopolymeric matrix.

The assembly cement may contain greater than 30%, greater than 50%, greater than 60%, even greater than 75% silicon carbide, in weight percent based on the dry mineral material, particularly to provide increased thermal conductivity. Preferably, the silicon carbide is in the form of particles whose average size is below 200 microns.

The silicon carbide thus has an expansion coefficient which is relatively increased. The content of silicon carbide must therefore be limited to ensure a thermo-mechanical resistance adapted to the application to particulate filters. A content of silicon carbide between 30 and 90%, preferably between 55 and 75% is particularly suitable.

The assembly cement preferably has less than 10%, preferably less than 5%, preferably less than 1% mineral fibers, in particular ceramic by mass based on the dry mineral material.

Vorzugszweise, the mounting cement has no such fibers.

Preferably, the mounting cement to an inorganic and / or organic compound.

Classically, the assembly cement is impermeable to the filtered gas. The tightness of the mounting cement thus advantageously provides the ability to provide in the thickness of the outer wall of a single block the generation of transverse microcracks without significant effect on the filtration effect (by placing this cement so as to cover the openings of the microcracks).

In step C, two adjacent individual blocks are adhered to each other by facing each other, preferably parallel to each other, each with the side surfaces 14a - 14d according to which fresh assembly cement is applied between these mutually opposite side walls (called connecting surfaces).

In step D, after it has been placed between the bonding surfaces of the individual blocks, the fresh assembly cement is dried, preferably at a temperature between 100 ° C and 200 ° C, preferably in air or an atmosphere with controlled humidity, preferably such that the residual moisture between 0 and 20%. Preferably, the duration of drying is between a few seconds and 10 hours, especially as a function of the bonding format and the composite ceramic body.

The individual blocks are preferably held in position in order to avoid expansion of the fresh assembly cement during curing, for example by clamping by means of spacers, as for example in the EP 1 435 348 is described, and binding the so-clamped individual blocks.

In step E, a heat treatment may be effected at a temperature sufficient to eliminate any particulates and / or organic fibers to eliminate them and thus to provide the marrow porosity, which is advantageous for achieving thermal stability Reduce conductivity.

The heat treatment is advantageously carried out under an oxidizing atmosphere, preferably at atmospheric pressure, at a temperature between 300 ° C to 1200 ° C. The heat treatment leads to the polymerization of the possibly present thermosetting plastic to cure the possibly present inorganic compound, to eliminate the possibly present organic components, even to a more or less complete sintering of the assembly cement, when the temperature exceeds 700 ° C. This heat treatment is generally accompanied by an improvement in the mechanical resistance.

Its duration is preferably from about 1 to 20 hours from heating to cooling and is variable as a function of materials but also the size and shape of the compounds.

The heat treatment can equally be effected in situ. In particular, in the case where composite filter bodies are intended for filtering in automobiles, the filter bodies may be incorporated into the automobile prior to the elimination of organic components of the mounting cement, the regeneration temperature being sufficient to eliminate them. For example, the combustion temperature of the cellulosic fibers is about 200 ° C, while the regeneration temperature is typically about 500 ° C, even higher.

The composite body thus constructed may thereafter be used to obtain a shape that conforms to the sleeve 5 is adapted, for example, to produce a cylindrical body with a circular cross-section.

• A') Herstellung einer Vielzahl von Einzelblocks 11, die nicht gesintert sind;
• B') Zubereitung eines frischen Montagezements;
• C') Verkleben der Einzelblöcke mittels des frischen Montagezements;
• D') Aushärtung des frischen Montagezements, um Verbindungen 12 zwischen den Verbindungsflächen zu bilden;
• E') Wärmebehandlung durch Sintern, derart, dass die Einzelblocks und der Montagezement gesintert werden und die Einzelblocks mit Mikrorissen versehen werden.

As an alternative to the method just described, a method according to the invention may also comprise the following steps:

• A ') Production of a large number of individual blocks 11 that are not sintered;
• B ') preparation of a fresh assembly cement;
• C ') gluing the individual blocks by means of the fresh assembly cement;
• D ') Curing the fresh assembly cement to compounds 12 to form between the bonding surfaces;
• E ') Heat treatment by sintering, such that the individual blocks and the mounting cement are sintered and the individual blocks are provided with microcracks.

Process for producing microcracks

A honeycomb structure according to the invention may be made using all current methods, provided that this process is suitable for producing microcracks, in particular, by adjusting the debindering step.

More particularly, the invention relates to a manufacturing process for producing a honeycomb structure comprising steps a) to d) as described above.

Preferably, in step b) drying may be by heat treatment and / or using microwaves for a time and temperature sufficient to bring the non-chemically bound water content below 1% by mass. Of course, other equivalent and known means may be considered without departing from the gist of the present invention.

In step c), the elimination of binding (or debindering) is preferably effected under an oxidizing atmosphere, especially under air, at a temperature preferably below 700 ° C to ensure a sufficient mechanical content prior to sintering and to exclude an unconjugated oxidation , in particular of the possibly present silicon carbide. Debinding may be effected under a less oxidizing atmosphere than air to prevent substantial oxidation of any silicon carbide present, but the debinding step is longer.

Methods and devices for debinding are, for example, in EP 1 541 538 . EP 1 902 766 . US 2007 054229 and WO2008 / 063538 described.

The sintering is realized at a temperature above 1600 ° C, even above 1800 ° C, preferably above 2000 ° C, more preferably above 2100 ° C. Preferably, this temperature is below 2400 ° C. Preferably, the sintering is carried out under a non-oxidizing atmosphere, for example in an argon atmosphere.

According to this method, the conditions specified in step c) are adapted so that the sintered honeycomb structure is provided with microcracks. In particular, microcracks may occur in the course of a debindering step which is effected under air in the conditions given above.

In order to be able to control the environment in which microcracks are to occur, it is possible to provide an injecting device for oxidizing gas, in particular air, having calibrated orifices oriented such that the oxidizing gas is in contact with the region in which the microcracks should arise, be renewed.

It is also possible locally to subject a region of a honeycomb structure, in particular the entry surface or the exit surface, locally to a variable flow of oxidizing gas and / or an oxidizing gas which has an oxygen concentration which is more or less increased. Debindering provokes a reaction that is all the more exothermic as the concentration of oxygen in the oxidizing gas and the flow of oxidizing gas are increased. The greater the release of heat, the more microcracking is possible.

Preferably, the injection device is selected such that microcracks are generated locally in the honeycomb structure, in particular in order to exclusively generate microcracks on the outer wall of the honeycomb structure.

In particular, it may be advantageous to inject the oxidizing gas through the channels of the honeycomb structure.

To better confine the microcracked area, the preform is advantageously placed in a "gazette".

As in 9 represented is a "Gazette" 100 a plate, generally of metal. This plate has a bottom 102 on which the honeycomb structures are placed, for example sintered individual blocks 11 , which form filter blocks, with dimensions of 25.4 × 3.6 × 3.6 cm ³ , side walls 104 and 106 and through the side walls 104 and 106 connected a front wall 108 and a back wall 110 , The "gazettes" are stacked on top of each other, such that during debindering the individual blocks 11 between the ground 102 the "Gazette" 100 on which they are positioned, and the ground 103 the "Gazette" above 100 ' are included, shown in phantom and placed on the Gazette 100 , The length L ₁₀₀ and the width I ₁₀₀ may be, for example, between 20 and 40 cm, for example 30 cm and the height h _100, for example, about 5 cm.

In the preferred embodiment, the individual blocks are 11 approximately parallel to each other, approximately along the direction of length L ₁₀₀ , at a distance δ from each other, for example, of about 1 cm. Also advantageous is the front wall in the direction of flow 108 with injection ports 112 provided, for example, have a diameter between 1 and 5 mm, for example about 2 mm. Preferably, each individual block is 11 in front of an injection port 112 arranged, vorzugszweise so that an axis DD with the corresponding injection port 112 corresponds. Preferably, the upstream face in the flow direction 108 an injection port, not the inflow or outflow surface of a single block 11 opposite.

It is further preferred that a single block 11 with its entrance area 26e an injection port 112 is opposite. In the case where the structure is asymmetric, the total mass of the plugs is on the entrance surface 26e greater than the total mass of the plugs on the exit surface 26s ,

The rear wall in the direction of flow has an outlet opening 114 which extends approximately over the entire height and the entire width of the back wall 110 extends, for example, at right angles, for example, over an area of about 100 to 150 cm ² .

The gazette stack is run in an oven maintained at the debinding temperature, for example at 450 ° C.

An oxidizing gas G, for example air, preferably at debinding temperature, is then passed through the injection ports 112 for example, blown by means of a spraying or ventilation device. The oxidizing gas G is thus in the direction of the inflow surface 26e a single block 11 directed, the exterior of the single block passes approximately parallel to the side surfaces of the single block 11 following its axis DD and flows through the outlet opening 114 out. The individual blocks are kept in this microcracking environment for more than 1 hour, for example 2 hours.

The temperature, the circulation of the oxidizing gas and the orientation of the individual blocks lead to microcracking of the individual blocks, in particular if the individual blocks are asymmetric.

Typically, airflow will appear through the injection port 112 that of the entrance area 26e a single block is located at between 5 and 20 x 10 ^-2 m ³ / s per m ^{2 of} the surface of said entrance surface 26e (The surface directly through the injection port 112 exposed to incoming air), on the lateral surface of the single block 11 Microcracks, especially near its exit surface 26s , In general, the microcracks obtained with the device described above are not branched.

As in 10 can represent a micro crack 120 especially on the upper side surfaces 14c of the single block 11 extend which of the side surface 14b opposite, with which the single block 11 on the ground 102 the gazette 100 rests. The microcrack 120 may in particular from the exit surface 26s extending outgoing. The main direction D ₁₂₀ , which is the two ends 122 and 124 of the micro crack 120 is substantially longitudinal, wherein the angle α between a transverse plane P ₁₁ and a plane P ₁₂₀ , which is perpendicular to the main direction D _{120 is} preferably less than 45 ° smaller than 30 °, even less than 20 °.

The length of the morror 120 measured along its direction 126 is typically between 3 and 30 mm.

The maximum width I _{max of} the microcrack 120 is less than 3 times the maximum size of the grains that make up the single block 11 build up.

The microcracks generated during the debindering are obtained in the baking process without at all affecting the modulus of rupture or the elastic modulus of the sintered honeycomb structure.

In step C), the debinding and sintering processes may be performed separately or simultaneously. Preferably, the steps are separated from one another, wherein debinding is preferably carried out under air and sintering under a controlled argon atmosphere.

Debinding and sintering can take place in a single oven, with the oven temperature not being lowered to ambient temperature after debindering.

According to the invention show the 5 to 8th the type of microcracks obtained (intermediate grain). The thickness of the illustrated microcrack is in the order of the average size D _{50 of} the grains forming the unit block.

The microcracks obtained are finer than the cracks obtained by the hard regenerations, which typically have a width of 1 mm. In addition, these cracks occurring in the regeneration can surround a single block, which reduces its filtration capacity, but also threatens its integrity. The microcrack may be continuous, especially if it is present in the thickness of the outer wall of the honeycomb structure. But he also can not be consistent, d. H. only open with a single opening. In other words, it does not penetrate the wall of the honeycomb structure on which it flows. Advantageously, such a microcrack does not degrade the filtration effect, even if it is present on a wall extending inside the honeycomb structure, referred to as an "internal wall", or on the outside wall of a monolithic filter body having no peripheral cladding.

In particular, the maximum depth p _{max of} the microcrack can be greater than 0.8, greater than 0.9 times the thickness of the external wall of the honeycomb structure, and even as large as this thickness (continuous microcracking).

The maximum depth p _{max of} the microcrack may in particular be less than 0.7, less than 0.6, even less than 0.5 times the thickness of the wall of the honeycomb structure on which it is arranged, in particular if this wall has an internal thickness Wall is. Advantageously, the filter effect thus remains very satisfactory.

Microcracks may be created especially near the entrance or exit face, preferably near the exit face, by local modification of the airflow. The more important the flow of oxidizing gas introduced locally during debindering, the more the exothermic reaction of debindering generates microcracks generating local stresses.

In order to produce a composite body according to the invention, at least one of the individual blocks is prepared in step A), following steps a) to d) (see above).

Examples

All individual blocks of the examples are prepared by the following method:
In a stirred vessel mixed silicon carbide powder, a foaming agent of the polyethylene type and an organic compound of the methylcellulose type.

More precisely, in a first period, 70% by weight of a SiC powder whose grains have a mean diameter D ₅₀ of 10 microns is mixed with a second SiC powder 30% by weight whose grains have an average diameter D ₅₀ of 0.5 microns , To this mixture is added a foaming agent of the polyethylene type in a proportion equal to 4.5% by weight of the total weight of the grains of SiC and an additive in the form of the cellulose type in a proportion equal to 10% by weight of the total weight of the SiC. grains.

Add water and stir until a homogeneous paste is obtained and its plasticity allows extrusion through a die. This paste is then extruded through a die adapted for the manufacture of a honeycomb preform having the dimensional characteristics of Table 1.

The preforms are then dried by microwave in air for a time sufficient to bring the non-chemically bound water content to at least one percent by mass.

Alternatively, one then clogs the channels on the entrance surface and on the exit surface of the preforms according to known techniques, for example as in the application WO2004 / 065088 described.

The preforms are then debinded at 500 ° C for one hour in air and then baked after a cycle having a temperature rise of 20 ° C / hr to a temperature on the order of 2200 ° C, after which this temperature is maintained for 2 hours becomes.

This gives a series of single blocks of silicon carbide which are substantially identical, whose characteristics are listed in Table 1: Cross section of the channels square Density of the channels (Channels per square inch) 180 cpsi wall thickness 350 microns length 25.4 cm width 3,6 cm Open porosity (measured by porometry on mercury) about 47% mean diameter of the pores (measured by porometry on Mercury) about 15 microns Table 1

The individual blocks according to the invention each had a continuous microcrack on one of their side surfaces. The length of this microcrack was about 1 cm and its maximum width I _max was about 1 times the maximum size D _{99.5 of} the grains.

According to the teaching of the patent application EP 816,065 then 16 individual blocks are assembled by gluing together. For the composite body 1 According to the invention, 14 of 16 individual blocks were compliant with the invention. The individual blocks were subjected to debindering in "gazettes", the gazettes having injection openings as described above, the amount of air in the direction of the entry surfaces of the individual blocks being of the order of 8 · 10 ^-2 m ³ / s per m ² Surface of said entry surfaces (each entry surface is placed directly opposite an injection port).

For the comparative composite body C1, none of the 16 individual blocks was compliant with the invention. Single blocks were debinded in "gazettes" having the injection ports as described above, with the amount of air toward the input face of the single blocks being on the order of 2 x 10 ^-2 m ³ / s per m ² of surface area Entry surface is.

• – 66-Gewichtsprozent eines Sic-Pulvers deren Korngröße zwischen 10 und 200 micron liegt,
• – 3-Gewichtsprozent eines reaktiven Aluminatpulvers, welches durch die Gesellschaft Almatis gehandelt wird mit einer mittleren Größe von ungefähr 3 micron,
• – 24% Hohlkugeln, welche durch Enviro-spheres unter dem Namen „e-spheres” gehandelt wird, die eine chemische Zusammensetzung darstellt, welche 60% SiO₂ und 40% Al₂O₃ enthält und eine mittlere Größe in der Größenordnung von 100 micron aufweist,
• – 6% Siliciumrauch vom Type Elkem 971,
• – 0,8-Gewichtsprozent einer temporären und plastifizierenden Verbindung vom Typ Zellulose,
• – 0,2-Gewichtsprozent eines Entflockungsmittels vom Typ TPPNa (Natriumtripolyphosphat).

For the bonding of the individual blocks prepares a mounting cement, in which one mixes the following proportions.

• - 66% by weight of a Sic powder whose particle size is between 10 and 200 microns,
• 3% by weight of a reactive aluminate powder sold by the company Almatis with a mean size of approximately 3 microns,
• - 24% hollow spheres, which is traded by Enviro spheres under the name "e-spheres", which represents a chemical composition containing 60% SiO ₂ and 40% Al ₂ O ₃ and an average size of the order of 100 micron having,
• - 6% silicon smoke of the type Elkem 971,
• 0.8% by weight of a cellulose-type temporary and plasticizing compound,
• 0.2% by weight of a deflocculant of the TPPNa (sodium tripolyphosphate) type.

An amount of water is added, which constitutes about 15% by weight of this mixture, to obtain a fresh assembly cement of adequate viscosity.

In all examples, the fresh assembly cement has been applied without pressure and evenly between the individual blocks, such that compounds having an average thickness of about 1 mm are obtained, filling the entire space between the bonding surfaces.

The compositions of the individual blocks are then dried under air at 100 ° C for 1 hour, then baked at 1000 ° C under air for 1 hour, so that filtering composite bodies are obtained. The filtering composite bodies are then used to To obtain composite bodies of circular cross section, with a volume of the order of 4.1 l (5.66 '' x 10 ''). The composite bodies are then subjected to the following tests:

Control of the thermo-mechanical resistance

The composite bodies thus obtained are installed in an exhaust line of a 2.0 liter direct injected diesel engine, with the engine running at full power (4000 rpm) for 30 minutes, after which they are disassembled and weighed to determine their initial mass.

The assembled bodies are then re-mounted on a motor bench, in a range of 3000 revolutions per minute and a torque of 50 N · m for an appropriate period to obtain a soot amount of 8 g / L (in volume of the assembled body). The composite bodies thus loaded are mounted again on the exhaust line to be subjected to strong regeneration: After stabilizing the engine running at 1700 rpm for a torque of 95 N · m for 2 minutes, a post-injection is realized with 70 ° phase for a Nachinjektionsmenge of 18 mm ³ / stroke. Once the combustion of the soot has begun, ie when the load loss is reduced for at least 4 seconds, the engine power is lowered to 1050 rpm for a torque of 40 N · m for 5 minutes to accelerate the soot combustion.

The composite bodies are then subjected to engine power of 4000 rpm for 30 minutes to eliminate residual soot.

The regenerated composite bodies are examined after disassembly to reveal the eventual presence of visible cracks. The thermo-mechanical resistance is estimated by the number of cracks, with a small number of cracks indicating a thermo-mechanical resistance that is acceptable for use as a filter body.

The following grades can be awarded: +++ : Presence of very numerous cracks ++ : Presence of many cracks + : Presence of some cracks - : no or very few cracks

For regeneration under extreme conditions, the presence of some cracks ("+" mark) is acceptable. The notes "++" and "+++" speak for a poor thermo-mechanical resistance.

Indicator of filter efficiency

The index of filter efficiency is defined as the difference between the amount of soot particles at the entrance of the assembled body and the amount of soot particles at the outlet of this body relative to the amount of soot particles at the entrance of said composite body.

The index of filter efficiency is measured by means of smoke meters located at the entrance and exit of the assembled body, the latter being placed in the exhaust line of an engine with the engine running at full power at 4000 rpm for 30 minutes.

Measurements of the Young modules of the assembly cement and the filtering individual blocks:

The dynamic Young's modulus is determined according to Standard ASTM C1259-01 measured with a commercially available apparatus called Grindosonic MK5 by the company JW Lemmens.

At ambient temperature, the natural vibration frequency of a test specimen is measured in the "dynamic" mode. For this purpose, the specimen is positioned on two gum carriers, such that it does not interfere with the mode of vibration of the specimen. The supports are placed symmetrically to the center of the longitudinal axis of the test piece, the distance between the supports being 100 mm. Of the The specimen is then excited with a mechanical impact in the middle of its upper surface (opposite to the lower surface on the supports), for example by means of a rod, a pencil or a hammer supplied with the apparatus, the excitation energy being weak. This excitation causes a vibration inside the material of the specimen. A piezoelectric detector placed in contact with the specimen then registers that vibration and converts it into an electrical signal which determines the natural vibration frequency f (or "flexion resonance frequency").

Calculate the dynamic Young's modulus E (in Gpa) as a function of the mass m (in g) of the test specimen and the frequency (in Hz) according to the following formula: E = 9.1584 × 10 ^-9 × m × f ²

The dynamic Young's modulus is measured on the single-block filtering blocks of dimensions 36 × 36 × 254 mm ³ .

The dynamic Young's modulus is likewise measured on a test piece of 22 × 22 × 143 mm ³ in the mounting cement, which is prepared by casting and subjected to the same thermal treatment as that of the mounting cement when used in a composite body. The specimen is then dried at 110 ° C before being cooled down to ambient temperature. Results: C1 1 E (GPa) of the individual blocks 60 60 E (GPa) of the assembly cement 6 6 Number of microcracks per unit block according to the invention 0 1 Number of microcracks of the assembled body 0 14 Thermo-mechanical resistance of the composite body + - Number of cracks after regeneration on the composite body 22 2 filtration efficiency > 85% > 85% Table 2

• C1: Comparative Example
• Example 1: Example according to the invention

An increase in the number of microcracks clearly improves the thermomechanical behavior. However, this improvement does not result in a marked reduction in filtration efficiency.

Complementary measurements have confirmed that the presence of microcracks does not significantly modify the porosity and average pore diameter of the material composing the individual blocks.

The foregoing description allows to illustrate some possible implementations of the invention. It is to be understood, however, that this description is not limiting and that those skilled in the art can practice other variations of the invention without departing from the spirit thereof.

In particular, a honeycomb structure according to the invention could be used in applications other than filtration, and in particular as a catalyst.

In one embodiment, a part of the honeycomb structure is surrounded by a catalytic jacket, also called "wash coat", e.g. B. adapted for the treatment of polluting gases of the type CO, HC or NOx. For example, the catalytic jacket can only be used on the surfaces for optimum performance are arranged, which limit a portion of the channels, for example, only on the surfaces that define the inlet channels of the filter body.

In particular, for an application as a catalyst, the channels may not be clogged.

Otherwise, the examples represent single-block cylindrical blocks on a square basis, called "parallelepipedic". However, the invention is not limited to such blocks.

Finally, in other embodiments, the input channels and the adjacent output channels are not arranged to each other such that the entirety of the gas filtered by an arbitrary inlet channel flows into outlet channels adjacent to this inlet channel.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• FR 2928562 [0005]
• FR 2903918 [0005]
• EP 1698388 [0006, 0006]
• WO 2008/063738 [0007]
• WO 2008/063538 [0048, 0141]
• JP 08-281036 [0064]
• EP 1541538 [0064, 0141]
• EP 1142619 [0111, 0114]
• EP 1632657 [0111]
• EP 816065 [0114, 0177]
• EP 1455923 [0114]
• WO 2004/065088 [0114, 0173]
• EP 1435348 [0130]
• EP 1902766 [0141]
• US 2007054229 [0141]

Cited non-patent literature

• Standard ASTM C1259-01 [0191]

Claims (14)

A honeycomb structure having a plurality of channels opening on inlet and outlet surfaces, said structure being made of a ceramic material consisting of sintered grains, said honeycomb structure having an open crack having a length L _f between 3 mm and 30 mm and a maximum width I _max , which is below 3 times the maximum size D _{99.5 of} these grains, a so-called "micro-crack". A honeycomb structure according to the preceding claim, wherein the ratio between the maximum width of the microcrack and the maximum size of the grains, I _max / D _{99.5, is} less than 2.0. A honeycomb structure according to any preceding claim, wherein the microcrack has a length L _f greater than 5mm. A honeycomb structure according to any one of the preceding claims, wherein the microcrack opens on the outer surface of the honeycomb structure extending between said inlet and outlet surfaces. A honeycomb structure according to any one of the preceding claims, having a microcracked area bounded by the closed envelope representing the smallest possible volume and including all the microcracks and perpendicular through the outer surface of the honeycomb structure and two to the longitudinal direction of the honeycomb structure Plains is limited, wherein the microcracked region extends to less than 50% of the length of the honeycomb structure. A honeycomb structure according to any one of the preceding claims, which is made of a material having a thermal expansion coefficient of greater than 2.5 · 10 ^-6 C ^-1 between 20 and 1000 ° C. Honeycomb structure according to one of the preceding claims, characterized in that it has no traces of soot. Honeycomb structure according to one of the preceding claims, characterized in that it is new and unused. Composite body according to one of the preceding claims, which consists of a composition of honeycomb structures, wherein at least one of these honeycomb structures complies with one of the preceding claims. A composite body according to the preceding claim, in which the honeycomb structure is compliant with claim 5, wherein said microcracked area is closer to the outlet surface than the inlet surface of said honeycomb structure. Device selected from a heat exchanger and a particulate filter having at least one sintered honeycomb structure conforming to one of claims 1 to 8. Manufacturing method of a honeycomb structure, comprising the following steps: a) extrusion of a ceramic material through a nozzle such that a honeycomb preform is formed, b) drying, c) debinding and sintering of said preform, d) Optionally, before or after sintering, clogging the channels of the sintered honeycomb structure, wherein at least a portion of said preform is exposed during debindering to an environment suitable for generating microcracking, such that after sintering, a sintered honeycomb structure after one of claims 1 to 8 is obtained. Method according to the preceding claim, in which said environment: - Has a temperature below 700 ° C and / or Is gaseous and has an oxygen concentration above 15% by volume and below 25% by volume, and / or - is held for a period of more than 1 hour. Method according to one of the two preceding claims, wherein during the debindering the preform of an average amount of air flow between 5 and 20 · 10 ^-2 m ³ / s per m ^{2 of} the surface of said preform is exposed.

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