CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of priority under 35 U.S.C. §119 of U.S. Provisional Application Serial No. 62/956,925 filed on January 3, 2020, the content of which is relied upon and incorporated herein by reference in its entirety.

BACKGROUND

[0002] The disclosure relates to ceramic honeycomb articles, and more particularly to ceramic honeycomb articles having non-uniform skin thickness configured to provide improved isostatic strength, and methods for their fabrication.

[0003] Ceramic bodies produced by extrusion are used in a wide variety of applications, such as substrates for automotive exhaust catalytic converters, particulate traps within diesel and gasoline engines, chemical filtration processes, and the like. Ceramic bodies having honeycomb cross-sectional shapes are frequently employed to provide a large catalytic surface area within a relatively small overall volume.

[0004] Thin-walled substrates need the ability to withstand isostatic compression and provide appropriate load bearing capability, for example to permit a ceramic honeycomb article to survive “canning” by which the article is received within a tubular canister for insertion into an engine exhaust stream to be treated. Without addressing isostatic strength limitations, it may be difficult to increase porosity and/or decrease skin thickness of ceramic honeycomb articles without sacrificing their structural integrity.

SUMMARY

[0005] A ceramic honeycomb article as disclosed herein comprises a skin having a tubular configuration surrounding walls that define a honeycomb structure, with the skin having non- uniform thickness regions that are registered with a plurality of wall-skin intersections and registered with a plurality of increased article width regions, wherein edge cells of the honeycomb structure comprise inner surface portions defined by the skin that are free of inward curvature. A method for producing such an article comprises extruding a plurality of walls defining a honeycomb structure, and providing a skin having a generally tubular configuration laterally surrounding the honeycomb structure. Registration between the increased skin thickness regions, the increased article width regions, and the wall-skin intersections permits isostatic compression forces to be transferred to walls intersecting the skin without causing inward curvature of the skin between wall-skin intersection regions, and increases isostatic strength of the article. Such regions allow for localization of high pressure directly in line with wall-skin intersections, where stress is directly transferred to the walls without being transferred by application of bending stress to the skin.

[0006] In one aspect, the present disclosure relates to a ceramic honeycomb article comprising a plurality of walls defining a honeycomb structure comprising a plurality of matrix cells along an interior of the honeycomb structure and a plurality of edge cells along a periphery of the honeycomb structure, and comprising a skin having a generally tubular configuration laterally surrounding the honeycomb structure, with a plurality of wall-skin intersections arranged along an inner surface of the skin. Individual edge cells of the plurality of edge cells are at least partially defined by two walls of the plurality of walls and an inner surface portion of the skin extending between the two walls. The ceramic honeycomb article comprises a plurality of increased article width regions extending in a longitudinal direction and alternating with a plurality of reduced article width regions distributed around a perimeter of the ceramic honeycomb article. The skin comprises a non-uniform thickness comprising a plurality of increased skin thickness regions extending in the longitudinal direction and alternating with a plurality of minimum skin thickness regions distributed around the perimeter of the ceramic honeycomb article. The plurality of increased skin thickness regions is registered with the plurality of wall-skin intersections and registered with the plurality of increased article width regions. For each individual edge cell of the plurality of edge cells, the inner surface portion extending between the two walls is free of inward curvature.

[0007] In certain embodiments, at least some edge cells of the plurality of edge cells comprise a three-sided shape. [0008] In certain embodiments, each minimum skin thickness region of the plurality of minimum skin thickness regions and each increased skin thickness region of the plurality of increased skin thickness regions has a thickness in a range of 0.05 mm to 1.27 mm (2 to 50 mils). In certain embodiments, each increased skin thickness region of the plurality of increased skin thickness regions has a maximum thickness in a range of 0.025 mm to 1.27 mm (1 to 5 mils) greater than the thickness of each minimum skin thickness region. In certain embodiments, each increased skin thickness region of the plurality of increased skin thickness regions has a maximum thickness in a range of 15 to 50 percent greater than the thickness of each minimum skin thickness region.

[0009] In certain embodiments, each minimum skin thickness region of the plurality of minimum skin thickness regions has a thickness in a range of 0.10 mm to 0.5 mm (4 to 20 mils), and each increased skin thickness region of the plurality of increased skin thickness regions has a maximum thickness in a range of 15 to 50 percent greater than the thickness of each minimum skin thickness region.

[0010] In certain embodiments, a cross-section of the ceramic honeycomb article taken perpendicular to the longitudinal direction comprises an outer surface having a substantially sinusoidal shape around the perimeter of the ceramic honeycomb article.

[0011] In certain embodiments, each minimum skin thickness region comprises a thickness that is greater than a thickness of each wall of the plurality of walls.

[0012] In certain embodiments, the plurality of walls comprises first and second pluralities of walls extending in a longitudinal direction substantially parallel to a longitudinal axis of the ceramic honeycomb article, and wherein the second plurality of walls is substantially perpendicular to the first plurality of walls.

[0013] In certain embodiments, the plurality of walls and the skin comprise a unitary extruded structure.

[0014] In certain embodiments, the ceramic honeycomb article comprises a generally cylindrical shape. In certain embodiments, the inner surface of the skin comprises a substantially constant radius of curvature. [0015] In certain embodiments, the ceramic honeycomb article comprises a cross-section having an oval or rounded rectangular shape.

[0016] In certain embodiments, the plurality of matrix cells and the plurality of edge cells are hollow.

[0017] In certain embodiments, at least a portion of an outer surface of the skin comprises a machined surface.

[0018] In certain embodiments, an engine exhaust treatment apparatus comprises a ceramic honeycomb article as disclosed herein.

[0019] In another aspect, a method for fabricating a ceramic honeycomb article comprises extruding a plurality of walls defining a honeycomb structure comprising a plurality of matrix cells along an interior of the honeycomb structure and a plurality of edge cells along a periphery of the honeycomb structure, and providing a skin having a generally tubular configuration laterally surrounding the honeycomb structure, with a plurality of wall-skin intersections arranged along an inner surface of the skin. Individual edge cells of the plurality of edge cells are at least partially defined by two walls of the plurality of walls and an inner surface portion of the skin extending between the two walls. The ceramic honeycomb article comprises a plurality of increased article width regions extending in a longitudinal direction and alternating with a plurality of reduced article width distributed around a perimeter of the ceramic honeycomb article. The skin comprises a non-uniform thickness comprising a plurality of increased skin thickness regions extending in the longitudinal direction and alternating with a plurality of minimum skin thickness regions distributed around the perimeter of the ceramic honeycomb article. The plurality of increased skin thickness regions is registered with the plurality of wall- skin intersections and registered with the plurality of increased article width regions. For each individual edge cell of the plurality of edge cells, the inner surface portion extending between the two walls is free of inward curvature.

[0020] In certain embodiments, the providing of the skin comprises forming the skin by extrusion simultaneously with extrusion of the plurality of walls, with the plurality of walls and the skin forming a unitary extruded structure. [0021] In certain embodiments, the providing of the skin comprises applying the skin to an exterior of the honeycomb structure after the extrusion of the plurality of walls.

[0022] In certain embodiments, the method further comprises shaping at least a portion of an outer surface of the skin by machining.

[0023] In certain embodiments, each minimum skin thickness region of the plurality of minimum skin thickness regions and each increased skin thickness region of the plurality of increased skin thickness regions has a thickness in a range of 0.05 mm to 1.27 mm (2 to 50 mils), and each increased skin thickness region of the plurality of increased skin thickness regions has a maximum thickness in a range of 15 to 50 percent greater than the thickness of each minimum skin thickness region.

[0024] In another aspect, any of the foregoing aspects and/or other features disclosed herein may be combined for additional advantage.

[0025] Additional features and advantages will be set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art from that description or recognized by practicing the embodiments as described herein, including the detailed description which follows, the claims, as well as the appended drawings.

[0026] It is to be understood that both the foregoing general description and the following detailed description are merely exemplary, and are intended to provide an overview or framework to understanding the nature and character of the claims. The accompanying drawings are included to provide a further understanding, and are incorporated in and constitute a part of this specification. The drawings illustrate one or more embodiment(s), and together with the description serve to explain principles and operation of the various embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

[0027] FIG. 1A is a schematic perspective view of a honeycomb article comprising a skin arranged on an outer periphery of a honeycomb structure defined by walls according to exemplary embodiments of the disclosure.

[0028] FIG. IB is a schematic lengthwise cross-sectional view of the honeycomb article of

FIG. 1A [0029] FIG. 1C is a schematic top plan view of the honeycomb article of FIGS. 1A and IB.

[0030] FIG. 2 is a schematic top plan view of a peripheral portion of a known honeycomb article comprising skin of substantially constant thickness arranged on an outer periphery of a honeycomb structure defined by walls.

[0031] FIG. 3 is a schematic top plan view of a peripheral portion of a known honeycomb article similar to that shown in FIG. 2, but with edge cells of the honeycomb structure comprising inner surface portions defined by the skin having inward curvature between each wall-skin intersection.

[0032] FIG. 4A is a schematic top plan view of a peripheral portion of a honeycomb article according to exemplary embodiments of the disclosure, comprising a skin having non-uniform thickness regions that are registered with a plurality of wall-skin intersections and registered with a plurality of increased article width regions, with edge cells of the honeycomb structure comprising inner surface portions defined by the skin that are free of inward curvature.

[0033] FIG. 4B is a magnified schematic top plan view of a portion of FIG. 4A, including annotations to identify a minimum skin thickness region and a corrugation amplitude corresponding to the incrementally added thickness of an increased thickness region.

[0034] FIG. 5 is a schematic perspective view illustration of a ceramic honeycomb article being subjected to isostatic compression.

[0035] FIG. 6 is a schematic illustration of a symmetric finite element analysis (FEA) model including a wedge-shaped portion of a ceramic honeycomb article surrounded by a compressible boot and being subjected to isostatic compression.

[0036] FIG. 7 is a multi-dimensional plot of normalized maximum principal stress as a function of minimum skin thickness and of maximum skin corrugation (i.e., skin thickness variation), with one (i.e., a first) superimposed data point representing a baseline value for a ceramic honeycomb article including a skin thickness of 15 mils and zero corrugation.

[0037] FIG. 8 reproduces the multi-dimensional plot of FIG. 7, with two (i.e., second and third) superimposed data points representing a ceramic honeycomb article having an 8.6 mil skin with zero corrugation, and a ceramic honeycomb article having an 8.6 mil skin with a 3 mil corrugation. [0038] FIG. 9 is a bar chart showing maximum principal stress values for the two data points illustrated and described in connection with FIG. 8.

[0039] FIG. 10 is a plot of contact pressure applied at the external skin of a FEA modeled ceramic honeycomb article having an 8.6 mil skin with zero corrugation.

[0040] FIG. 11 is a plot of contact pressure applied at the external skin of a FEA modeled ceramic honeycomb article having an 8.6 mil skin with a 3 mil corrugation.

[0041] FIG. 12 reproduces the multi-dimensional plots of FIGS. 7 and 8, with the first superimposed data point representing a baseline value for a ceramic honeycomb article including a skin thickness of 15 mils and zero corrugation, and the second superimposed data point representing a ceramic honeycomb article having an 8.6 mil skin with a 3 mil corrugation.

[0042] FIG. 13 is a bar chart showing maximum principal stress values for the two data points illustrated and described in connection with FIG. 12.

[0043] FIG. 14 reproduces the multi-dimensional plot of FIG. 7, with a first superimposed data point representing a baseline value for a ceramic honeycomb article including a skin thickness of 15 mils and zero corrugation, and a second superimposed data point representing a ceramic honeycomb article having a 15 mil skin thickness with a 5 mil corrugation.

[0044] FIG. 15 is a schematic top plan view of a wedge-shaped portion of a FEA modeled known honeycomb article corresponding to that shown in FIG. 3, with edge cells of the honeycomb structure including inner surface portions defined by the skin having inward curvature between adjacent wall-skin intersections, together with a magnified peripheral portion of the honeycomb article.

[0045] FIG. 16 includes a lower frame providing a schematic top plan view of a magnified peripheral portion of a ceramic honeycomb article having a skin of 15 mil thickness without any skin corrugation, with addition of shading corresponding to distribution of in-plane principal stress within the article, and includes an upper frame providing a top plan view of a wedge- shaped portion of the ceramic honeycomb article incorporating the magnified peripheral portion. [0046] FIG. 17 includes a lower frame providing a schematic top plan view of a magnified peripheral portion of a ceramic honeycomb article having a 15 mil thickness skin with inner and outer skin corrugation, with addition of shading corresponding to distribution of in-plane principal stress within the article, and includes an upper frame providing a top plan view of a wedge-shaped portion of the ceramic honeycomb article incorporating the magnified peripheral portion.

[0047] FIG. 18 is a schematic cross-sectional view of an engine exhaust treatment apparatus that comprises a ceramic honeycomb article as disclosed herein.

DETAILED DESCRIPTION

[0048] The embodiments set forth below represent the necessary information to enable those skilled in the art to practice the embodiments and illustrate the best mode of practicing the embodiments. Upon reading the following description in light of the accompanying drawing figures, those skilled in the art will understand the concepts of the disclosure and will recognize applications of these concepts not particularly addressed herein. It should be understood that these concepts and applications fall within the scope of the disclosure and the accompanying claims.

[0049] It will be understood that, although the terms first, second, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element, without departing from the scope of the present disclosure. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items.

[0050] Relative terms such as “below” or “above” or “upper” or “lower” or “horizontal” or “vertical” may be used herein to describe a relationship of one element, layer, or region to another element, layer, or region as illustrated in the drawing figures. It will be understood that these terms and those discussed above are intended to encompass different orientations of the device in addition to the orientation depicted in the drawing figures.

[0051] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises,” “comprising,” “includes,” and/or “including” when used herein specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.

[0052] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. It will be further understood that terms used herein should be interpreted as having a meaning that is consistent with their meaning in the context of this specification and the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

[0053] Ceramic honeycomb articles and related fabrication methods as disclosed herein permit isostatic strength of such articles to be improved. A ceramic honeycomb article comprises a skin having a tubular configuration with surrounding walls that define a honeycomb structure. The skin has non-uniform thickness regions that are registered with a plurality of wall- skin intersections and registered with a plurality of increased article width regions, wherein edge cells of the honeycomb structure comprise inner surface portions defined by the skin that are free of inward curvature. These registered regions may be referred to herein as “outward skin corrugations.” Outward skin corrugations improve isostatic strength by localizing external contact pressure (which may be applied by an external canister) in desirable locations, allowing for efficient force transfer within the honeycomb structure. Specifically, outward skin corrugations allow for localization of high contact pressure in regions directly in line with wall- skin intersections, permitting stress to be directly transferred to the walls. Outward skin corrugations also naturally create regions of localized low contact pressure where the skin spans between adjacent wall-skin intersections in edge cells.

[0054] Applicant has observed that outward skin corrugations may substantially increase isostatic strength of ceramic honeycomb articles having thin skins. For ceramic honeycomb articles having relatively thick skins, however, the effect of outward skin corrugation on isostatic strength may be reduced or negligible due to the native ability of thick skins to effectively redistribute the applied stress to walls of an underlying honeycomb structure.

[0055] Ceramic honeycomb articles disclosed herein comprise skin features that are generally counter to known articles. For example, although thinning the skin generally yields lower isostatic strength, Applicant has found that when ceramic honeycomb articles comprise outward skin corrugations in combination with reduced skin thickness, the resulting articles exhibit improved isostatic strength performance in a manner that could be considered counterintuitive in view of traditional designs.

[0056] Ceramic honeycomb articles without skin corrugations will be generally introduced in connection with the following discussion of FIGS. 1A-1C, and thereafter will be followed by disclosure of ceramic honeycomb articles incorporating skin corrugations as disclosed herein. [0057] FIG. 1A is a schematic perspective view of a ceramic honeycomb article 100 comprising a honeycomb structure 104 defined by plurality of intersecting walls 110 that form mutually adjoining cells 112, which define channels therein, extending axially in direction "A" between opposing first and second faces 114, 116. Unless otherwise understood by its context as used herein, a “shape” is the shape viewed in cross-section perpendicular to the axial direction “A”. An outer peripheral wall or “skin” 124 is arranged on an outer periphery of the honeycomb structure 104, with peripheral portions of the walls 110 contacting the skin 124 to form wall-skin intersections 120. FIG. IB is a schematic lengthwise cross-sectional view, and FIG. 1C is a schematic top plan view, of the ceramic honeycomb article 100 of FIG. 1A. The term “cell” as used herein generally refers to a region bounded by intersecting walls in a cross-section of a ceramic honeycomb article, and the term “channel” as used herein generally refers to the space or void inside a cell that extends between the end faces 114, 116. As shown in FIGS. IB and 1C, the ceramic honeycomb article 100 comprises edge cells 126 that constitute cells bounded in part by the skin 124, and comprises matrix cells 118 that are not bounded in part by the skin 124. The first face 114 may be an inlet face and the second face 116 may be an outlet face of the ceramic honeycomb article 100, or the first face 114 may be an outlet face and the second face 116 may be an inlet face of the ceramic honeycomb article 100. [0058] Although the ceramic honeycomb article 100 is intended to include a generally honeycomb structure, it is not limited to a structure with square cells. For example, hexagonal, octagonal, triangular, rectangular, or any other suitable cell shapes may be used. Also, while the illustrated ceramic honeycomb article 100 is generally cylindrical with a round cross-sectional shape, honeycomb articles are not so limited. For example, a ceramic honeycomb article 100 may have a cross section that is elliptical, oval, square, rectangular, rounded rectangular, other polygonal shape, other desired shape, or combinations of the foregoing. A ceramic honeycomb article may have cell densities of in a range of about 100 to 900 cells per square inch (cpsi).

[0059] Compositions of ceramic honeycomb articles disclosed herein are not particularly limited, and can comprise major and minor amounts of cordierite, aluminum- titanate, mullite, b- spodumene, silicon carbide, zeolite and the like, and combinations thereof. As a further example, a ceramic honeycomb article may comprise an extruded zeolite or other extruded catalyst.

[0060] In certain embodiments, ceramic honeycomb articles may be produced by plasticizing ceramic powder batch mixtures, extruding the mixtures through honeycomb extrusion dies to form honeycomb extrudate, cutting the extrudate to form green bodies, then drying and firing the green bodies to produce fired ceramic honeycomb articles of high strength and thermal durability having cells and associated channels extending axially between first and second end faces thereof. As used herein, a ceramic honeycomb article may comprise ceramic honeycomb monoliths and segmented ceramic honeycomb bodies.

[0061] A co-extruded or an after-applied exterior skin may form an outer peripheral surface extending axially from a first end face to a second end face of a ceramic honeycomb article. Channels of honeycomb bodies defined by intersecting walls (also known as webs), whether monolithic or segmented, can be plugged at an inlet face or an outlet face to produce a filter. When some channels are left unplugged, a partial filter can be produced. A honeycomb article, whether monolithic or segmented, can be catalyzed to produce a substrate. A non-plugged honeycomb article may be generally referred to as a substrate. A catalyzed substrate may comprise an extruded catalyst or a catalyst applied after extrusion. Additionally, filters and partial filters can be catalyzed to provide both filtering and catalyzing functions. Ceramic honeycomb articles as disclosed herein may be used as catalyst supports, membrane supports, wall-flow filters, partial filters, and the like.

[0062] FIG. 2 is a schematic top plan view of a peripheral portion of a known ceramic honeycomb article 100A having a skin 124A of substantially constant thickness without any skin corrugations arranged on an outer periphery of a honeycomb structure 104A defined by intersecting walls 110A that form cells 112A extending in a longitudinal direction. The cells 112A comprise edge cells 126A (which are bounded in part by the skin 124 A) and matrix cells 118A. Peripheral portions of the walls 110A contact the skin 124A to form wall-skin intersections 120 A. The skin 124A comprises an outer surface 128 A and an inner surface 122A. As illustrated, the skin 124A does not exhibit inward curvature into the edge cells 126A along spans of the skin 124A between wall-skin intersections 120A.

[0063] FIG. 3 is a schematic top plan view of a peripheral portion of a known ceramic honeycomb article 100B having a skin 124B with outward and inward corrugations 130B, 132B. The skin 124B is arranged on an outer periphery of a honeycomb structure 104B defined by intersecting walls 110B that form cells 112B extending in a longitudinal direction. The cells 112B comprise edge cells 126B (which are bounded in part by the skin 124B) and matrix cells 118B. Peripheral portions of the walls 110B contact the skin 124B to form wall-skin intersections 120B. The skin 124B comprises an outer surface 128B and an inner surface 122B. As illustrated, the skin 124B exhibits inward curvature into the edge cells 126B (i.e., inward corrugations 132B) along spans of the skin 124B between wall-skin intersections 120B.

[0064] FIGS. 4A and 4B provide schematic top plan views of a peripheral portion a ceramic honeycomb article 200 having a skin 224 with outward skin corrugations 230 according to one embodiment of the present disclosure. The skin 224 is arranged on an outer periphery of a honeycomb structure 204 defined by intersecting walls 210 (e.g., a first plurality of walls 210-1 extending in a first direction, and a second plurality of walls 210-2 extending in a second direction that is perpendicular to the first direction) that form cells 212 extending in a longitudinal direction. The cells 212 comprise edge cells 226 (which are bounded in part by the skin 224) and matrix cells 218. Peripheral portions of the walls 210 contact the skin 224 to form wall-skin intersections 220. The skin 224 comprises an outer surface 228 and an inner surface 222. The outward skin corrugations 230 comprise increased thickness regions of the skin 224 that are registered with the wall-skin intersections 220 and that are registered with increased width regions of the ceramic honeycomb article 200. Minimum skin thickness regions 227 of the skin 224 are provided between the outward skin corrugations 230. The outward skin corrugations 230 and the minimum skin thickness regions 227 each extend in a longitudinal direction and are distributed about a perimeter of the ceramic honeycomb article 200, with the outward skin corrugations 230 alternating with the minimum skin thickness regions 227. As shown in FIG. 4A, the skin 224 is free of (i.e., does not exhibit) inward curvature into the edge cells 226 along spans of the skin 224 between wall-skin intersections 220. As shown in FIG. 4B, the minimum skin thickness regions 227 may have a thickness of Ti, while increased skin thickness regions 225 may have a corrugation amplitude corresponding to an incrementally increased thickness of Ti relative to the minimum skin thickness regions 227. A total thickness of the skin 224 at each increased skin thickness regions 225 is the sum of the minimum thickness (Ti) and the corrugation amplitude (T2), represented as (Ti + T2).

[0065] In the embodiments shown in FIGS. 4A and 4B, various edge cells 226 comprise a generally three-sided shape, each being bounded by two walls 210 and a portion of the inner surface 222 of the skin 224. In certain embodiments, a cross-section of the ceramic honeycomb article 200 taken perpendicular to a longitudinal direction provides the outer surface 228 having a substantially sinusoidal shape due to periodic increasing and decreasing of the thickness of the skin 224 corresponding to alternating presence of the increased skin thickness regions 225 (i.e., outward skin corrugations 230) and minimum skin thickness regions 227. In certain embodiments, each minimum skin thickness region 227 comprises a thickness that is greater than a thickness of each of the walls 210 of the honeycomb structure 204. In certain embodiments, each minimum skin thickness region 227 has a thickness Ti and each increased skin thickness region 225 (i.e., corresponding to outward skin corrugation 230) has a maximum thickness Ti + T2, wherein each of Ti and (Ti + T2) is in a range of 0.05 mm to 1.27 mm (2 mils to 50 mils). Restated, 0.05 mm < Ti < 1.27 mm, and 0.05 mm < T2 < 1.27 mm, while Ti < T2. In certain embodiments, each outward skin corrugation 230 has a maximum thickness (Ti + T2) in a range of 0.025 mm to 1.27 mm (1 mil to 5 mils) greater than the thickness Ti of each minimum skin thickness region 227, such that 0.025 mm < Ti < 1.27 mm. In certain embodiments, each outward skin corrugation 230 has a maximum thickness (Ti + T2) in a range of 15 to 50 percent greater (or 20 to 40 percent greater) than the thickness Ti of each minimum skin thickness region 227, such that 1.15 < ((Ti + T2) / Ti) < 1.50. In certain embodiments, each minimum skin thickness region 227 has a thickness Ti in a range of 0.10 mm to 0.5 mm (4 mils to 20 mils), such that 0.10 mm < Ti < 0.5 mm. In such an embodiment, each increased skin thickness region 225 may have a thickness T2 in a range of 0.115 mm to 0.75 mm.

[0066] With continued reference to FIG. 4B, in certain embodiments, minimum skin thickness regions 227 distributed around the perimeter of the ceramic honeycomb article 200 each have substantially the same minimum thickness Ti. In certain embodiments, increased skin thickness regions 225 distributed about the perimeter of the ceramic honeycomb article 200 each having substantially the same maximum thickness (Ti + T2). In certain embodiments, some variation in skin thickness due to manufacturing tolerances may be present among different minimum skin thickness regions 227 distributed about the perimeter of the ceramic honeycomb article 200 and/or may be present among different increased skin thickness regions 225 distributed about the perimeter of the ceramic honeycomb article 200. In certain embodiments, it is contemplated that any given minimum skin thickness region 227 may have a minimum thickness Ti that is substantially constant in a direction parallel to a central axis of the ceramic honeycomb article 200 (potentially subject to minor variation due to extrusion forming and/or subsequent handling processes), and that any given increased skin thickness region 225 may have a maximum thickness (Ti + T2) that is substantially constant in a direction parallel to the central axis of the ceramic honeycomb article 200 (again, potentially subject to minor variation due to extrusion forming and/or subsequent handling processes). In certain embodiments, a minimum skin thickness region 227 may refer to a region of local minimum thickness disposed between two corrugations (i.e., increased skin thickness regions 225), without necessarily requiring the particular minimum skin thickness region 227 to embody an absolute minimum thickness of the skin of the ceramic honeycomb article 200.

[0067] FIG. 5 is a schematic perspective view illustration of a ceramic honeycomb article 300 (having an outer skin 324 extending between a first end 314 and a second end 316) being subjected to isostatic compression. As shown, external pressure P is applied to external surfaces of the ceramic honeycomb article 300 in all directions.

[0068] Isostatic strength testing of a ceramic honeycomb article (e.g., sintered cordierite honeycomb articles) may be performed by placing the ceramic honeycomb article inside a rubber boot conforming to the shape of the ceramic honeycomb article, and covering the skin of the ceramic honeycomb article. One open end of the boot may be closed by placing, in a direction normal to the channels in the ceramic honeycomb article, a first endpiece (e.g., a Plexiglas plate) having the same contour as the ceramic honeycomb article and thereby closing off one end of the boot. The other end of the boot may be closed with a second endpiece (e.g., an aluminum block), also contoured to the shape of the ceramic honeycomb article, through which extends a tube that is open both to the interior of the boot and to the outside atmosphere. The second endpiece with an associated O-ring is clamped to the boot. Because the tube in the one endpiece of the "boot" is open to the atmosphere, pressure is applied only to the skin region of the honeycomb article, not axially through the ends into the center of the honeycomb structure. During isostatic pressure testing, the honeycomb article may be deemed to fail when the first audible cracking noise is discerned, with such noise corresponding to the collapse of the peripheral layer of cells nearest to the skin.

[0069] FIG. 6 is a schematic illustration of a symmetric finite element analysis (FEA) model including a wedge-shaped, one-eighth symmetric portion of the ceramic honeycomb article 300 having a honeycomb structure 304 and a skin 324 that is surrounded by a compressible boot 301 and being subjected to isostatic compression by application of pressure P to the exterior of the boot 301. The FEA model assumes frictionless contact between the ceramic honeycomb article 300 and the boot 301, and the one-eighth symmetric boundary condition is applied on the entire FEA model.

[0070] FEA computational modeling was performed for various ceramic honeycomb articles, utilizing parameter values according to the following Table 1.

Table 1: Ceramic honeycomb parameters for FEA study

[0071] Design of experiment factors considered for the FEA study included corrugation amplitude values of 0, 2.8, and 5.6 mils, and minimum skin thickness values of 8.6, 12, and 15 mils. The specific cases modeled by FEA are summarized in the following table.

Table 2: Corrugation amplitude and min. skin thicknesses for FEA study

[0072] Following performance of the FEA study, a multi-dimensional plot of normalized maximum principal stress as a function of minimum skin thickness [mils] and of maximum skin corrugation (i.e., skin thickness variation) [mils] was developed, as shown in FIGS. 7 and 8. Each plot shows a lowest stress region corresponding to minimum skin thickness of 8.6 mils combined with presence of maximum corrugation amplitude of 3 mils (i.e., corresponding to a maximum skin thickness of 11.6 mils). Along the x-axis, decreasing skin thickness alone (i.e., without presence of skin corrugations) served to increase principal stress. Along the y-axis, for skin thickness of 8.6 mils, increasing corrugation amplitude initially served to reduce principal stress, but beyond corrugation amplitude values of about 3.25 mils, further increases were correlated to increases in principal stress. FIG. 7 shows the multi-dimensional plot with one superimposed data point 330 representing a baseline value for a ceramic honeycomb article including a skin thickness of 15 mils and zero corrugation. FIG. 8 shows the same multi dimensional plot with two superimposed data points - namely, a second data point 332 representing a ceramic honeycomb article having an 8.6 mil skin with zero corrugation, and a third data point 334 representing a ceramic honeycomb article having an 8.6 mil skin with a 3 mil corrugation amplitude. FIG. 9 is a bar chart showing normalized maximum principal stress values for the two data points 332, 334 illustrated and described in connection with FIG. 8. As shown in FIG. 9, modifying the skin of a ceramic honeycomb article having a minimum skin thickness of 8.6 mils by providing external skin corrugations with an amplitude of 2.8 mils (thereby providing localized skin thickness values of 11.4 mils) served to decrease normalized maximum principal stress by 35%.

[0073] FIG. 10 is a plot of contact pressure at the external skin of a FEA modeled ceramic honeycomb article 400 having an 8.6 mil skin thickness with zero corrugation, for an applied isostatic pressure of 1.4 MPa. Contact pressure along the perimeter of the skin 424 is represented by a shaded band along the skin 424. Such figure demonstrates negligible variation in contact pressure, since all shades correspond to contact pressure values of 1.40 MPa. The ceramic honeycomb article 400 comprises a skin 424 of substantially constant thickness without any skin corrugations arranged on an outer periphery of a honeycomb structure 404 defined by intersecting walls 410 that formed cells 412, with such cells 412 comprising edge cells 426 and matrix cells 418. Inner surfaces 422 of the skin 424 do not exhibit inward curvature in spans between adjacent wall-skin intersections 420.

[0074] FIG. 11 is a plot of contact pressure at the external skin of a FEA modeled ceramic honeycomb article 500 having an 8.6 mil minimum skin thickness with a 3 mil corrugation, for an applied isostatic pressure of 1.4 MPa. Contact pressure along the perimeter of the skin 524 is represented by a shaded band along the skin 524. The ceramic honeycomb article 500 comprises a skin 524 with minimum skin thickness regions 527 (i.e., valleys) corresponding to low contact pressure, and corrugation regions 530 (i.e., increased skin thickness regions registered with wall- skin intersections 520 and registered with increased article width regions) corresponding to high contact pressure. Contact pressure varied from 0.9 to 1.7 MPa around the perimeter of the ceramic honeycomb article 500. The skin 524 is arranged on an outer periphery of a honeycomb structure 504 defined by intersecting walls 510 that form cells 512, with such cells 512 comprising edge cells 526 and matrix cells 518. As illustrated, inner surfaces 522 of the skin 524 do not exhibit inward curvature in spans between adjacent wall-skin intersections 520.

[0075] FIG. 12 reproduces the multi-dimensional plot of FIGS. 7 and 8, with two superimposed data points - namely, the first data point 330 (of FIG. 7) representing a baseline value for a ceramic honeycomb article including a skin thickness of 15 mils and zero corrugation, and the third data point 334 (of FIG. 8) representing a ceramic honeycomb article having an 8.6 mil skin with a 3 mil corrugation. FIG. 13 is a bar chart showing normalized maximum principal stress values for the two data points illustrated and described in connection with FIG. 12. FIGS. 12 and 13 show that a thin skin (i.e., minimum skin thickness reduced 42% from 15 mils to 8.6 mils) in combination with outer skin corrugations (having an amplitude of 2.8 mils) yields a 27% reduction in normalized maximum principal stress applied to the article by isostatic loading.

[0076] FIG. 14 reproduces the multi-dimensional plot of FIG. 7, with the first superimposed data point 330 representing a baseline value for a ceramic honeycomb article including a skin thickness of 15 mils and zero corrugation, and a fourth superimposed data point 336 representing a ceramic honeycomb article having a 15 mil skin thickness with a 5 mil corrugation. The normalized maximum principal stress values for the two data points 330, 336 is substantially unchanged, demonstrating that external skin corrugation may have little to no effect if the minimum skin thickness and/or maximum corrugation amplitude values are increased beyond certain thresholds.

[0077] FIG. 15 is a schematic top plan view of a wedge-shaped portion of a FEA modeled known ceramic honeycomb article 100B corresponding to the ceramic honeycomb article 100B shown in FIG. 3, together with a magnified peripheral portion of the ceramic honeycomb article 100B. The skin 124B is arranged on an outer periphery of a honeycomb structure 104B defined by intersecting walls 11 OB that form cells 112B, comprising edge cells 126B and matrix cells 118B. FIG. 15 shows edge cells 126B comprising inner surface portions 122B of the skin 124B having inward curvature between adjacent wall-skin intersections 120B. In this regard, the skin 124B comprises outward and inward corrugations 130B, 132B.

[0078] FIG. 16 includes a lower frame providing a schematic top plan view of a magnified peripheral portion of a FEA modeled ceramic honeycomb article 100A (corresponding to the article shown in FIG. 2) having a skin 124A of 15 mil thickness without any skin corrugation, with addition of shading corresponding to distribution of in-plane principal stress within the ceramic honeycomb article 100A comprising the honeycomb structure 104A thereof. FIG. 16 further comprises an upper frame providing a top plan view of a FEA modeled wedge-shaped portion of the same ceramic honeycomb article 100A incorporating the magnified peripheral portion. A maximum normalized stress value of 5.57 was calculated.

[0079] FIG. 17 includes a lower frame providing a schematic top plan view of a magnified peripheral portion of a FEA modeled ceramic honeycomb article 100B (as shown in FIG. 3) having a skin 124B of 15 mil thickness with inner and outer skin corrugations 122B, 130B, with addition of shading corresponding to distribution of in-plane principal stress within the ceramic honeycomb article 100B comprising the honeycomb structure 104B thereof. FIG. 17 further includes an upper frame providing a top plan view of a FEA modeled wedge-shaped portion of the same ceramic honeycomb article 100B incorporating the magnified peripheral portion. A maximum normalized stress value of 6.63 MPa was calculated. For thin skinned ceramic honeycomb articles, hoop compression causes high bending stresses and reduced performance. Comparing the maximum normalized stress values of FIGS. 16 and 17, it is clear that presence of inner and outer corrugations in FIG. 17 led to higher maximum normalized stress than the absence of any corrugations in FIG. 16. It is therefore concluded that inner and outer corrugations in combination are detrimental relative to absence of any corrugations at all. This makes the beneficial effect of outer corrugations alone in embodiments of the present disclosure surprising relative to known ceramic honeycomb article configurations. [0080] Aspects of the present disclosure further provide methods for fabricating ceramic honeycomb articles as described herein. In certain embodiments, such a method comprises extruding a plurality of walls defining a honeycomb structure comprising a plurality of matrix cells along an interior of the honeycomb structure and a plurality of edge cells along a periphery of the honeycomb structure, and providing a skin having a generally tubular configuration laterally surrounding the honeycomb structure, with a plurality of wall-skin intersections arranged along an inner surface of the skin. Individual edge cells are at least partially defined by two walls and an inner surface portion of the skin extending between the two walls. The ceramic honeycomb article comprises a plurality of increased article width regions extending in a longitudinal direction and alternating with a plurality of reduced article width regions distributed around a perimeter of the ceramic honeycomb article. The skin comprises a non-uniform thickness comprising a plurality of increased skin thickness regions extending in the longitudinal direction and alternating with a plurality of minimum skin thickness regions distributed around the perimeter of the ceramic honeycomb article. The plurality of increased skin thickness regions is registered with the plurality of wall-skin intersections and registered with the plurality of increased article width regions. For each individual edge cell of the plurality of edge cells, the inner surface portion extending between the two walls is free of inward curvature.

[0081] In certain embodiments, the providing of the skin comprises forming the skin by extrusion simultaneously with extrusion of the plurality of walls, with the plurality of walls and the skin forming a unitary extruded structure. In certain embodiments, the providing of the skin comprises applying the skin to an exterior of the honeycomb structure after the extrusion of the plurality of walls.

[0082] In certain embodiments, outward skin corrugations (including increased article width regions extending in a longitudinal direction and alternating with a plurality of reduced article width regions distributed around a perimeter of a ceramic honeycomb article) may be formed by post-treatment of fired ware, such as by laser scoring or selective contouring, which may be performed by machining or other methods. In certain embodiments, outward skin corrugations may be provided using an axial skinning approach, by which ridges are formed at web-skin intersections as a skin is applied in a longitudinal direction over a preformed honeycomb (core) structure. In certain embodiments, outward skin corrugations may be formed during an extrusion process, and may be solidified by one or more drying and/or firing steps.

[0083] In certain embodiments, shaping at least a portion of an outer surface of the skin is performed by machining.

[0084] It is to be appreciated that the present disclosure encompasses engine exhaust treatment apparatuses incorporating ceramic honeycomb articles as disclosed herein. For example, FIG. 18 is a schematic cross-sectional view of an engine exhaust treatment apparatus 600. An exhaust conduit 604 is configured to receive exhaust gases 606 from an internal combustion engine 602. A canister 610 containing a ceramic honeycomb article 200 is positioned to receive exhaust gases 606 from the exhaust conduit 604. The canister an expander section 608 upstream of a first end 214 of the ceramic honeycomb article 200 and a reducer section 612 downstream of a second end 216 of the ceramic honeycomb article 200. A skin 224 of the ceramic honeycomb article 200 is arranged in direct contact with the canister 610, with the skin 224 surrounding a honeycomb structure 204. An exhaust pipe 614 positioned downstream of the reducer section 612 is configured to expel treated exhaust gases 606A following passage through the ceramic honeycomb article 200.

[0085] Technical benefits that may be provided by embodiments of the present disclosure include one or more of the following: improving isostatic strength of ceramic honeycomb articles; enabling increased porosity and/or decreased skin thickness of ceramic honeycomb articles without sacrificing their structural integrity; and enabling increased geometric surface area, faster light-off, and reduced back pressure compared to known articles.

[0086] It will be apparent to those skilled in the art that various modifications and variations can be made without departing from the spirit or scope of the invention.

[0087] Many modifications and other embodiments of the embodiments set forth herein will come to mind to one skilled in the art to which the embodiments pertain having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the description and claims are not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. It is intended that the embodiments cover the modifications and variations of the embodiments provided they come within the scope of the appended claims and their equivalents. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.