Patent Publication Number: US-11642813-B2

Title: Ceramic honeycomb bodies, honeycomb extrusion dies, and methods of making ceramic honeycomb bodies

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a Divisional of U.S. patent application Ser. No. 15/755,910, filed on Feb. 27, 2018, which is a national stage application under 35 U.S.C. § 371 of International Application No. PCT/US2016/048345, filed on Aug. 24, 2016, which in turn claims the benefit of priority to U.S. Provisional Application No. 62/211,981, filed on Aug. 31, 2015, the contents of each are incorporated herein by reference in their entireties. 
    
    
     BACKGROUND 
     Field 
     Exemplary embodiments of the present disclosure relate to ceramic honeycomb bodies. 
     Discussion of the Background 
     Ceramic wall flow filters can be used for the removal of particulate pollutants from fluid streams such as diesel, gasoline, or other combustion engine exhaust streams. There are a number of different approaches for manufacturing such filters from channeled honeycomb structures formed of porous ceramics. For example, one approach is to position cured plugs of sealing material at the ends of alternate channels of such structures, which can block direct fluid flow through the channels and force the fluid stream through the porous channel walls of the honeycombs before exiting the filter. 
     The above information disclosed in this Background section is only for enhancement of understanding of the background of the claimed invention and therefore it may contain information that does not form any part of the prior art nor what the prior art may suggest to a person of ordinary skill in the art. 
     SUMMARY 
     Exemplary embodiments of the present disclosure provide a honeycomb body comprising laminar skin. 
     Exemplary embodiments of the present disclosure also provide a method of making a honeycomb body comprising laminar skin. 
     Exemplary embodiments of the present disclosure also provide an extrusion die configured to extrude a batch of ceramic precursor material into a green honeycomb body comprising laminar skin. 
     Additional features of the invention as claimed will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the claimed invention. 
     Exemplary embodiments disclose a green honeycomb body, including a matrix of intersecting walls that form channels extending axially from a first end face to a second end face and a laminar skin disposed on the matrix at the periphery extending from the first end face to the second end face. A majority of the cross sectional area of the laminar skin comprises axially aligned particles substantially the same as the intersecting walls. 
     Exemplary embodiments also disclose a porous ceramic honeycomb body, including a matrix of intersecting walls that form channels extending axially from a first end face to a second end face and a laminar skin disposed on the matrix at the periphery extending from the first end face to the second end face. A majority of the cross sectional area of the laminar skin crystal structure includes an axially aligned texture substantially the same as the intersecting walls. 
     Exemplary embodiments also disclose a method of making a porous ceramic honeycomb body comprising intersecting walls that form channels extending axially from a first end face to a second end face. The method includes extruding batch material through central slots of an extrusion die to form a honeycomb matrix and through a plurality of annular slots to form peripheral skin on the honeycomb matrix, the central slots terminate at a first annular slot of the plurality of annular slots. Elongated particles in the batch material are axially aligned during the extruding through the central and annular slots. 
     Exemplary embodiments also disclose a honeycomb extrusion die including a die body comprising a die face comprising a plurality of central slots and a skin former region disposed peripheral to the central slots, the skin former region comprising a plurality of annular slots wherein the central slots terminate at a first annular slot of the plurality of annular slots. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are included to provide a further understanding of the disclosure and are incorporated in and constitute a part of this specification, illustrate exemplary embodiments of the disclosure, and together with the description serve to explain the principles of the disclosure. 
         FIG.  1 A  shows a schematic perspective view of a honeycomb body comprising a skin on an outer periphery of a honeycomb core according to exemplary embodiments of the disclosure.  FIG.  1 B  is a schematic cross section through the honeycomb body of  FIG.  1 A  according to these exemplary embodiments of the disclosure.  FIG.  1 C  is a schematic top view of the honeycomb body of  FIG.  1 A  according to these exemplary embodiments of the disclosure. 
         FIG.  2    is a cutaway isometric view of an extrusion die showing intersecting central slots that extend to peripheral slots beyond a skin forming surface. 
         FIG.  3 A  is a schematic sectional isometric view of platy particle orientations of an extruded green honeycomb body with co-extruded skin such as extruded from the die of  FIG.  2    and resulting oriented particle microstructure of fired ceramic honeycomb body.  FIG.  3 B  is a schematic of tensile stresses in extruded skin created by higher coefficient of thermal expansion (CTE) in areas having particle alignment disruption more than adjacent areas. 
         FIG.  4    is a cutaway isometric view of an extrusion die having a skin former region at the die periphery showing peripheral pins and slots according to some exemplary embodiments of the present disclosure. 
         FIG.  5 A  is a detailed view of the die of  FIG.  4    showing skin former peripheral pins and slots according to some exemplary embodiments of the present disclosure.  FIG.  5 B  illustrates that the base of skin former peripheral pins can be tapered according to some exemplary embodiments of the present disclosure. 
         FIG.  6    is a schematic cross section isometric view of an extrusion die having a skin forming region at the die periphery showing peripheral pins and slots, a mask, and plasticized batch in slots, knit together in knitting region, and extruded as laminar skin according to some exemplary embodiments of the present disclosure. 
         FIG.  7 A  is a schematic top view at die exit face of matrix slot that crosses skin former slots at the die periphery that can extrude non-laminar skin therefrom having misalignment zone and higher CTE than adjoining skin areas that may result in stress concentration in the misalignment zone or adjacent skin areas.  FIG.  7 B  is a schematic top view at die exit face of matrix slot that stops at a first skin former slot at the die periphery and extruded laminar skin therefrom having reduced misalignment zone confined to inner lamellae and according to some exemplary embodiments of the present disclosure. 
         FIG.  8 A  is a top view of an extrusion die exit face having a radial cell geometry matrix and skin former region at the die periphery showing peripheral pins and slots according to some exemplary embodiments of the present disclosure.  FIG.  8 B  is a cutaway isometric view of the extrusion die of  FIG.  8 A .  FIG.  8 C  is a cutaway isometric view of the extrusion die of  FIG.  8 A  having a mask in the skin former region. 
         FIG.  9    is a cutaway isometric view of an extrusion die having a skin former region at the die periphery showing peripheral pins and slots according to some exemplary embodiments of the present disclosure. 
         FIG.  10    is a cutaway isometric view of an extrusion die having a skin former region at the die periphery showing peripheral pins and slots according to some exemplary embodiments of the present disclosure. 
         FIG.  11    is a cutaway isometric view of the extrusion die of  FIG.  10    having a mask in the skin forming region at the die periphery according to some of these exemplary embodiments. 
         FIG.  12    is a cutaway isometric view of an extrusion die having a retrofit skin former at the die periphery showing peripheral slots according to some exemplary embodiments of the present disclosure. 
         FIG.  13 A  is a top view at the exit face of the extrusion die of  FIG.  12    without the retrofit skin former at the die periphery according to some of these exemplary embodiments of the present disclosure.  FIG.  13 B  is a top view at the exit face of the retrofit skin former of  FIG.  12    according to some of these exemplary embodiments of the present disclosure.  FIG.  13 C  is a bottom view at the input face of the retrofit skin former of  FIG.  12    according to some of these exemplary embodiments of the present disclosure. 
         FIG.  14 A  is a schematic to describe an S-value as an order parameter used to quantify the particle alignment in green extruded ware according to some exemplary embodiments of the present disclosure.  FIG.  14 B  is a micrograph of a sample “A” where S=0.8958 on the left having greater particle alignment than a sample “B” on the right where S=0.7163. 
         FIG.  15    is a backscatter scanning electron micrograph (SEM) image of a honeycomb body green ware cross section having non-laminar skin co-extruded on matrix showing three areas selected for S-value analysis. A die such as shown in  FIG.  2    having matrix slots extending into the skin former region was used to make the honeycomb body green ware of  FIG.  15   . 
         FIG.  16    is a backscatter SEM image of another honeycomb body green ware cross section having laminar skin co-extruded on matrix according to some exemplary embodiments of the present disclosure. In  FIG.  16   , three areas selected for S-value analysis are shown. A die such as shown in  FIG.  9    having some radially extending slots  463  in the skin former region was used to make the honeycomb body green ware of  FIG.  16   . 
         FIG.  17    is a backscatter SEM image of another honeycomb body green ware cross section having laminar skin co-extruded on matrix according to some exemplary embodiments of the present disclosure. Three areas selected for S-value analysis are shown in  FIG.  17   . A die such as shown in  FIG.  4    having only annularly extending slots in the skin former region was used to make the honeycomb body green ware of  FIG.  17   . 
     
    
    
     DETAILED DESCRIPTION 
     The disclosure is described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments of the disclosure are shown. This disclosure may, however, be embodied in many different forms and should not be construed as limited to the exemplary embodiments set forth herein. Rather, these embodiments are provided so that this disclosure is thorough, and will fully convey the scope of the disclosure to those skilled in the art. In the drawings, the size and relative sizes of layers and regions may be exaggerated for clarity. 
     It will be understood that when an element or layer is referred to as being “on” or “connected to” another element or layer, it can be directly on or directly connected to the other element or layer, or intervening elements or layers may be present. In contrast, when an element or layer is referred to as being “directly on” or “directly connected to” another element or layer, there are no intervening elements or layers present. It will be understood that for the purposes of this disclosure, “at least one of X, Y, and Z” can be construed as X only, Y only, Z only, or any combination of two or more items X, Y, and Z (e.g., XYZ, XYY, XY, YZ, ZZ, etc.). 
     While terms such as, top, bottom, side, upper, lower, vertical, and horizontal are used, the disclosure is not so limited to these exemplary embodiments. Instead, spatially relative terms, such as “top”, “bottom”, “horizontal”, “vertical”, “side”, “beneath”, “below”, “lower”, “above”, “upper” and the like, may be used herein for ease of description to describe one element or feature&#39;s relationship to another element(s) or feature(s) as illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as “below” or “beneath” other elements or features would then be oriented “above” the other elements or features. Thus, the exemplary term “below” can encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly. 
     “Include,” “includes,” or like terms means encompassing but not limited to, that is, inclusive and not exclusive. 
     “About” modifying, for example, the quantity of an ingredient in a composition, concentrations, volumes, process temperature, process time, yields, flow rates, pressures, viscosities, dimensions, and like values, and ranges thereof, employed in describing the embodiments of the disclosure, refers to variation in the numerical quantity that can occur, for example: through typical measuring and handling procedures used for preparing materials, compositions, composites, concentrates, or use formulations; through inadvertent error in these procedures; through differences in the manufacture, source, or purity of starting materials or ingredients used to carry out the methods; and like considerations. The term “about” also encompasses amounts that differ due to aging of a composition or formulation with a particular initial concentration or mixture, and amounts that differ due to mixing or processing a composition or formulation with a particular initial concentration or mixture. 
     In these exemplary embodiments, the disclosed articles, and the disclosed method of making one or more of the articles provide one or more advantageous features or aspects, including for example as discussed below. Features or aspects recited in any of the claims are generally applicable to all facets of the disclosure. Any recited single or multiple feature or aspect in any one claim can be combined or permuted with any other recited feature or aspect in any other claim or claims. 
     The after-treatment of exhaust gas from internal combustion engines may use catalysts supported on high-surface area substrates and/or a catalyzed filters for the removal of carbon soot particles. Catalyst supports may be refractory, thermal shock resistant, stable under a range of pO 2  conditions, non-reactive with the catalyst system, and offer low resistance to exhaust gas flow. Generally, porous ceramic flow-through honeycomb substrates and wall-flow honeycomb filters (generically referred to herein as honeycomb bodies) may be used in these applications. 
     Ceramic cement may be used to form an exterior skin of a honeycomb body which has been machined or “contoured” to a desired dimension, or an exterior skin may be co-extruded with the honeycomb body. Co-extrusion generally refers to batch flow through a die at the time of forming a honeycomb monolith or body segment. For example, when batch flows through a die to form a matrix and a skin the skin can be referred to as a co-extruded skin. As used herein, co-extrusion generally refers to batch flow through matrix regions and skin regions of the die simultaneously. Generally a co-extruded skin can be considered to be integral with the matrix. As used herein, the term “honeycomb body” includes single honeycomb monoliths and honeycomb body segments. Bodies formed by multiple honeycomb body segments that are secured together, such as by using a ceramic cement to form a segmented monolith can be referred to as a segmented honeycomb body. 
     The manufacture of porous ceramic honeycomb bodies may be accomplished by the process of plasticizing ceramic powder batch mixtures, extruding the mixtures through honeycomb extrusion dies to form honeycomb extrudate, and cutting, drying, and firing the extrudate to produce ceramic honeycomb bodies and segmented honeycomb bodies of high strength and thermal durability having channels extending axially from a first end face to a second end face. 
     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 the ceramic honeycomb bodies. In some embodiments, channels of the honeycomb bodies defined by intersecting walls (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 at both ends a partial filter can be produced. The honeycomb body, whether monolithic or segmented, can be catalyzed to produce a substrate. A non-plugged honeycomb body is generally referred to herein as a substrate. A catalyzed substrate can have an after applied catalyst or comprise an extruded catalyst. Further, filters and partial filters can be catalyzed to provide multi-functionality. The ceramic honeycomb bodies thus produced may be widely used as catalyst supports, as membrane supports, as wall-flow filters, as partial filters, and as combinations thereof for cleaning fluids such as purifying engine exhausts or other fluid streams such as air or gas streams or liquid or water streams. 
     Ceramic honeycomb body compositions are not particularly limited and can comprise major and minor amounts of cordierite, aluminum-titanate, mullite, β-spodumene, silicon carbide, zeolite and the like, and combinations thereof. As a further example, the ceramic honeycomb body can comprise an extruded catalyst, such as an extruded zeolite or other extruded catalyst material or combinations of materials. Likewise, the honeycomb body batch compositions can comprise one or more inorganic components that form cordierite, aluminum-titanate, mullite, β-spodumene, silicon carbide, zeolite and the like, and combinations thereof upon firing. 
     In some embodiments, cell density may be between about 100 and 900 cells per square inch (cpsi). Cell wall thicknesses can range from about 0.025 mm to about 1.5 mm (about 1 to 20 mil). For example, cell wall thicknesses can range from about 0.025 mm to about 0.30 mm (about 1 to 12 mil). For example, honeycomb body  100  geometries may be 400 cpsi with a wall thickness of about 8 mil (400/8) or with a wall thickness of about 6 mil (400/6). Other geometries include, for example, 100/17, 200/12, 200/19, 270/19, 600/4, 400/4, 400/3, 600/3, 750/2, 600/2, and 900/2, as well as other geometries. As used herein, honeycomb body  100  is intended to include a generally honeycomb structure but is not strictly limited to a square structure. For example, hexagonal, octagonal, triangular, rectangular or any other suitable cell shape or combination of cell shapes may be used. Also, a cross section of the cellular honeycomb body  100  may be circular, but it is not so limited, for example, the cross section may be elliptical, square, rectangular, other shape, or a combination thereof. 
     Some of the exemplary embodiments of this disclosure relate to a honeycomb body having a laminar integral skin on a central cell structure (matrix) having substantially the same physical thermal expansion properties as the matrix, that is, for example, substantially the same bulk coefficient of thermal expansion (CTE). For example, the skin CTE can be within 6 to 8×10 −7  K −1  of the matrix CTE, the skin CTE can be within 3 to 5×10 −7  K −1  of the matrix CTE, or the skin CTE can be within 1 to 2×10 −7  K −1  of the matrix CTE. Some of the exemplary embodiments of this disclosure relate to a method to form a honeycomb body having a laminar co-extruded skin on a matrix having substantially the same physical thermal expansion properties as the matrix. Some of the exemplary embodiments of this disclosure relate to an extrusion die configured to form a honeycomb body having a laminar integral skin on a matrix having substantially the same physical thermal expansion properties as the matrix. 
       FIG.  1 A  shows a honeycomb body  100  including a plurality of intersecting walls  110  that form mutually adjoining channels  112  extending axially in direction “Ao” between opposing end faces  114 ,  116 , according to exemplary embodiments of the disclosure.  FIG.  1 B  shows a schematic cross section through the honeycomb body  100  of  FIG.  1 A .  FIG.  1 C  shows a schematic top view of the honeycomb body  100  of  FIG.  1 A . “Cell” is generally used herein when referring to intersecting walls in cross section of the honeycomb body and “channel” is generally used when referring to a cell extending between the end faces  114 ,  116 . Cell and channel may be used interchangeably. The top face  114  refers to the first end face and the bottom face  116  refers to the second end face of the honeycomb body  100  positioned in  FIG.  1 A , otherwise the end faces are not limited by the orientation of the honeycomb body  100 . The top face  114  may be an inlet face and the bottom face  116  may be an outlet face of the honeycomb body  100  or the top face  114  may be an outlet face and the bottom face  116  may be an inlet face of the honeycomb body  100 . 
     The central cell structure  118 , also referred to herein interchangeably as the “matrix” or “cell matrix” of the honeycomb body  100 , includes the intersecting walls  110  defining the channels  112  therebetween. The periphery  124  of the matrix  118  joins the co-extruded skin  126  and has the co-extruded skin  126  disposed thereon. As will be described in more detail below, the co-extruded skin  126  can be considered integral with the matrix. That is, as batch is extruded through a die the co-extruded skin knits with the matrix. Upon drying and/or firing of the extrudate, the skin  126  and the matrix  118  can be integral. According to exemplary embodiments, the integral skin  126  comprises a laminar structure having substantially the same thermal expansion properties as the matrix  118 . For example, the laminar skin CTE can be within about 3-5×10 −7  K −l  of the matrix CTE. 
     In some of these exemplary embodiments, the integral skin  126  can have a thickness greater than the thickness of the walls  110 . For example, the integral skin  126  can have a thickness of greater than or equal to 0.004 inch (0.102 mm), greater than or equal to 0.010 inch (0.25 mm), or greater than or equal to 0.020 inch (0.508 mm). In some of these exemplary embodiments, the integral skin  126  can have a coefficient of thermal expansion (CTE) greater than or equal to the CTE of the walls. In some of these exemplary embodiments, the integral skin  126  can have a coefficient of thermal expansion (CTE) of less than or equal to 15×10 −7 ×10 −7  K −1  and the walls  110  have a CTE of less than or equal to 15×10 −7  K −1 . For example, the integral skin  126  can have a coefficient of thermal expansion (CTE) of less than or equal to 10×10 −7  K −1  and the walls  110  have a CTE of less than or equal to 10×10 −7  K −1 , or even the integral skin  126  can have a coefficient of thermal expansion (CTE) of less than or equal to 5×10 −7  K −1  and the walls  110  have a CTE of less than or equal to 5×10 −7  K −1 . 
     In some of these exemplary embodiments, the honeycomb body  100  can have a an isostatic strength that is greater than 200 psi (1.38 MPa), for example, greater than 500 psi (3.45 MPa), greater than 1000 psi (6.9 MPa), or even greater than 2000 psi (13.8 MPa). The integral laminar skin  126  having a small web affected zone on the honeycomb body matrix  118  provides a greater isostatic strength of the honeycomb body  100  than a honeycomb body without the integral laminar skin. 
     Skin-forming methods have been devised for producing an integral skin on honeycomb substrates, for example, as disclosed in U.S. Pat. No. 7,914,724, the entire contents of which is hereby incorporated by reference as if fully set forth herein. However, skin-forming methods have generally relied on collapsing or crushing extruded cellular matrix material to form a layer of skin on top of the cellular matrix. This can be accomplished through use of a shim and mask positioned at the periphery of the matrix at the die exit. Additionally, the pins on the face of the die may be shaved down and angled away from the edge of the matrix to help achieve a skin that does not impinge on the periphery of the matrix which aids in avoiding collapsed cells at the periphery.  FIG.  2    is a cutaway isometric view of an extrusion die  203  having a die body  207  with feed holes at an input surface  209  and extrusion slots at an exit surface  211 . The central feed holes  213  are configured to feed batch material to intersecting central slots  215  and peripheral feed holes  217  are configured to feed batch to intersecting peripheral slots  219 . The central slots  215  extend to the peripheral slots  219  beyond a skin former surface  221 . The skin former surface  221  can form a cavity with a mask (not shown) spaced apart from the skin former surface  221  by the thickness of the co-extruded skin at the matrix of the honeycomb body. 
     In these types of skin-forming methods with dies such as shown in  FIG.  2   , where the central slots  215  extend beyond the skin former surface  221  to peripheral slots  219 , the honeycomb body skin is formed by a different process than the honeycomb body matrix when co-extruded, resulting in physical properties of the skin different than physical properties of the matrix. For example, the coefficient of thermal expansion (CTE) has been found to vary across the skin and found to typically be higher than that measured in the matrix in the dried and fired ceramic honeycomb body. 
     While not wishing to be bound by theory, the variability in the CTE results from a disruption in the orientation of particles comprising the extruded webs. Referring to  FIGS.  2 ,  3 A, and  3 B , platy talc and clay particles  331  are often used in the production of ceramic, for example, cordierite, honeycomb bodies  333 . These platy particles  331  become oriented as they pass through the slots  215 ,  219  of the die  203  during the extrusion process and remain oriented in the extruded green part. Upon firing, the high degree of orientation produces a cordierite body with cordierite crystals that are preferentially oriented (aligned) with their low expansion c-axes  335  in the planes of the walls  337 . This orientation is referred to herein as “axially aligned texture”. This results in a lower thermal expansion coefficient than would be expected if the crystals were randomly oriented relative to the plane of the web. Since these types of skin-forming methods rely on the collapse of extruded webs through intersecting peripheral slots  219  to produce the skin  339 , the action of the collapse of the webs produces a particle microstructure which is considerably less oriented or more randomly oriented (misaligned)  341  than the neighboring matrix walls  337 . 
     The contrast between oriented particle microstructure in the matrix walls  337  and misaligned particle microstructure in the skin  339  can be most pronounced at points in the skin where there are no matrix walls  337  that are parallel with the skin  339 . This occurs everywhere except at the 90°s. Additionally, at the 90° points on the periphery, the skin  339  has been produced by material extruded through slots  219  that are both parallel and perpendicular to the skin  339 . Therefore, the sections of web that form the skin that were once oriented perpendicular to the skin must be collapsed down to become part of the skin  339 . This results in misalignment of the particles even in the region of the skin  343  at the 90°s. The result of this skin forming is the generation of stresses  345  at the skin-matrix interface under heating and cooling during use due to thermal expansion mismatch at the interface. The region of the skin  339  of misaligned particle microstructure  343  is referred to herein as the “web affected zone” and can have a higher CTE than the matrix walls  337 , as well as a higher CTE than adjoining skin  339  resulting in a tensile stress and cracking zone  347 . This situation exists for most cell geometries including square, round, hexagonal, rectangular etc. 
     A radial cell ceramic honeycomb design is disclosed in U.S. Pat. No. 7,575,793, the entire contents of which is incorporated by reference as if fully set forth herein. A feature of the radial cell ceramic honeycomb design is that the cell structure is comprised of radial walls emanating from a central location and a series of concentric ring walls intersecting the radial walls. The skin-forming section of a die used to produce the radial cell ceramic honeycomb structure contains web walls which are always parallel to the skin. This can help minimize the mismatch between matrix and skin physical properties mentioned. However, use of conventional skin-forming hardware would still rely on the collapse of both the concentric rings and the perpendicular radial webs. The inventors have surprisingly found as disclosed herein, a way to produce a skin which is comprised mainly or entirely from material produced in the slots forming the concentric rings, having particles in the green ware and particulate microstructure in the fired ceramic ware substantially oriented in the same manner and in substantially the same direction as the interior webs by eliminating the radial slots in the skin-forming regions. This new discovery according to exemplary embodiments disclosed herein results in an integral skin having substantially the same physical thermal expansion properties as the matrix. 
     According to exemplary embodiments of the disclosure, a honeycomb body having a laminar integral skin on a central cell structure having substantially the same physical thermal expansion properties as the matrix, a method to form the honeycomb body having the laminar integral skin, and an extrusion die configured to form the honeycomb body having the laminar integral skin reduce the web affected zones, and overcome stresses and cracking from mismatch of skin and matrix physical thermal expansion properties. 
       FIG.  4    is a cutaway isometric view of an extrusion die having a skin former region at the die periphery showing peripheral pins and slots according to some exemplary embodiments of the present disclosure. The extrusion die  403  has a die body  407  with feed holes at an input surface  409  and extrusion slots at an exit surface (die face)  411 . The central feed holes  413  are configured to feed batch material axially in direction “Ao” from a batch cavity to intersecting central slots  415  and peripheral feed holes  417  are configured to feed batch from the batch cavity to slots in a skin former region  419  at the periphery of the matrix.  FIG.  5    is a detailed view of the die of  FIG.  4    showing skin former peripheral pins and slots according to these exemplary embodiments of the present disclosure. The skin former region  419  can form a cavity with a mask. 
     Referring to  FIGS.  4 ,  5 A and  5 B , the intersecting central slots  415  define central matrix pins  421  and do not extend beyond a first annular ring  423  in the skin forming region  419 . The matrix pins  421  at the periphery of the matrix are spaced apart from the first annular ring  423  by a first annular slot  425 . A second annular ring  427  can be spaced apart from the first annular ring  423  by a second annular slot  429 . Optionally, one or more additional annular rings may be likewise arranged outwardly of the first and second annular rings  423 ,  427  forming one or more additional slots. 
     The peripheral feed holes  417  can extend into the annular rings  423 ,  427  to form a reservoir  434  to provide batch feed into the radial slots  425 ,  429  as illustrated in  FIGS.  4 ,  5 A and  5 B . Alternatively or in addition, the radial slots  425 ,  429  can comprise a tapered base  436  to provide batch feed into the radial slots  425 ,  429  as illustrated in  FIG.  5 B  according to some of these exemplary embodiments. 
     The first and second annular rings  423 ,  427  can have exit surfaces  431 ,  433 , respectively, angled away from the center of the die body  407 , and a mask (not shown) can be placed on top of the die  403  in the skin former region  419  to produce a channel for the extruded skin to meet and bond to the matrix extrudate. In these types of skin-forming methods with dies such as shown in  FIGS.  4  and  5   , where the central slots  415  do not extend peripherally beyond the first annular ring  423  in the skin former region  419 , the honeycomb body skin is formed by a similar process to that of the honeycomb body matrix when co-extruded resulting in physical thermal expansion properties of the skin substantially the same as physical thermal expansion properties of the matrix. 
     According to some of these exemplary embodiments, the central slots  415  can comprise a thickness of greater than or equal to 0.001 inch (0.0254 mm) and less than or equal to 0.014 inch (0.356 mm) and the annular slots  425 ,  429  can comprise thicknesses of greater than or equal to 0.001 inch (0.0254 mm) and less than or equal to 0.014 inch (0.356 mm). According to some of these exemplary embodiments, the exit surfaces  431 ,  433  of the first and second annular rings  423 ,  427 , respectively, can be angled away from the center of the die body  407  by an angle greater than or equal to 0 degrees from parallel to the die exit face and less than or equal to 60 degrees from parallel to the die exit face. According to some of these exemplary embodiments, the number of annular slots is not particularly limited and may include 2 to 7 slots. For example, the number of annular slots may include 2 annular slots, may include 3 annular slots, may include 4 annular slots, or may include 5 annular slots. Since the web affected zone is significantly confined to the first annular slot adjacent the matrix slots, increasing the annular slots confines the web affected zone to a narrower portion of the skin in the skin thickness direction. 
       FIG.  6    is a schematic cross section isometric view of an extrusion die having a skin forming region at the die periphery showing peripheral pins and slots, a mask, and plasticized batch in slots, knit together in knitting region, and extruded as laminar skin according to some exemplary embodiments of the present disclosure. In  FIG.  6   , the matrix pins  421  having slots  415  therebetween include outermost pins  435  spaced apart from the first annular ring  423  by the first annular slot  425 . The annular rings  423 ,  427  can be considered pins, but are not pins in the traditional sense, but rather rings. Rings as used herein refers to the shape that circumscribes the matrix and is not intended to be limited to any particular shape, but can include circular, oval, asymmetrical, a combination of straight and curved segments and other shapes of honeycomb body cross sections.  FIG.  6    shows a schematic of the batch flow pattern through the slots to feed the skin. The batch flow through the slots to feed the matrix depicted in dashed lines is also shown. The batch material is shown in different shadings (A, B, C, and D) to differentiate the batch flowing through different flow paths within the skin former region and the matrix. 
     The skin  451  depicted in  FIG.  6    is referred to herein as laminar because, as described above, the platy particles in the batch that become oriented as they pass through the slots  413  and  425  of the die  403  during the extrusion process become misaligned in a web affected zone. However, the platy particles in the batch that become oriented as they pass through the outer annular slots  429  and  439  of the die  403  during the extrusion process hardly become misaligned and remain oriented in the extruded green part  449 . The web affected zone hardly extends to the batch from the outer annular slots  429 ,  439  that forms outer layers of the skin  451 . The plurality of annular slots  425 ,  429 ,  439  that orient the batch particles provide the laminar skin  451 . Upon firing, the high degree of orientation produces a ceramic body with ceramic crystals that are preferentially oriented (aligned) in the outer skin with their low expansion axes in the plane of the skin as the web walls have the low expansion axes of the ceramic crystals oriented with their low expansion axes in the planes of the walls. Such a fired ceramic skin is also referred to herein as laminar. 
     According to the exemplary embodiments shown in  FIG.  6   , the skin forming rings  423 ,  427  are recessed below the exit surface of the matrix pins  421 ,  435  and have exit surfaces  431 ,  433  on an angle away from the surface and the center of the die  403 . A mask  441  is depicted in the skin former region on a shim  443  to adjust batch material flow in the skin former region. The mask  441  and skin forming slots  425 ,  429 ,  439  are arranged to allow the batch to form a layered structure in the skin forming gap  457  as shown in the central portion of the figure. The edge of the mask  445 ,  447  which neighbors the outermost pins  435  is tapered toward the pins  435  to allow for compression and knitting of the layers of batch A, B, C to form the skin  451  in the skin forming gap  457 . A portion of the mask edge  447  toward the exit surface can have a slight angle to provide knitting of the layered skin structure to the matrix  453  in a knitting region  437 . 
     The extruded green honeycomb body walls  453  of the matrix are shown in dashed lines and meet the extruded laminar skin at the slots  415  between outermost matrix pins  435  and between the outermost matrix pins  435  and the first annular ring  423 . Thus, any orientation disruption in the batch particles can be limited to a small region of the skin thickness. For example, the web affected zone can be limited to not more than about half the thickness of the skin thickness when two skin forming slots are used and not more than about a third the thickness of the skin thickness when three skin forming slots are used. For example, when four skin forming slots are used, the web affected zone can be limited to not more than about a quarter the thickness of the skin thickness, when five skin forming slots are used, the web affected zone can be limited to not more than about a fifth of the thickness of the skin thickness, and when six skin forming slots are used, the web affected zone can be limited to not more than about a sixth of the thickness of the skin thickness. 
     When two or more annular skin forming slots are used, the integral laminar skin can be thicker than the matrix webs to provide improved strength to the honeycomb body. The thick laminar skin can still have substantially the same physical thermal expansion properties as the thin webs, thus avoiding spider cracks and fissures that can otherwise develop during processing, such as firing, and during use, such as in automotive exhaust treatment. 
       FIG.  7 A  is a schematic top view at die exit face of matrix slot  215  that crosses skin former slots  219  at the die periphery  223  that can extrude non-laminar skin  339  therefrom having misalignment zone  343  and higher CTE than adjoining skin areas that may result in stress concentration in the misalignment zone  343  or adjacent skin areas.  FIG.  7 B  is a schematic top view at die exit face  411  of matrix slot  415  that stops at a first skin former slot  425  at the die periphery  459  and extruded laminar skin  126  therefrom having reduced misalignment zone substantially confined to inner lamellae A apart from outer lamellae B and C according to some exemplary embodiments of the present disclosure. 
       FIG.  8 A  is a top view of an extrusion die  800  exit face  411  having a radial cell geometry matrix of slots  415  and pins  421 , and skin former region at the die periphery showing peripheral pins  423 ,  427  and slots  425 ,  429 ,  439  according to some exemplary embodiments of the present disclosure.  FIG.  8 B  is a cutaway isometric view of the extrusion die  800  of  FIG.  8 A .  FIG.  8 C  is a cutaway isometric view of the extrusion die  800  of  FIG.  8 A  having a mask  441  in the skin former region. The peripheral pins  423 ,  427  of extrusion die  800  have no radial slots. The extrusion die  800  has a die body  407  with open cavity feed at the input surface  409 . The central open cavities  442  are configured to feed batch material axially from the batch cavity to intersecting central slots  415  and peripheral open cavities  444  are configured to feed batch from the batch cavity to slots in the skin former region  419  at the periphery of the matrix. 
       FIG.  9    is a cutaway isometric view of an extrusion die  900  having a die body  125  with a skin former region at the die periphery showing peripheral pins  467 ,  469  and slots  425 ,  429  according to some exemplary embodiments of the present disclosure. The skin forming pins  467 ,  469  have radial slots  463  to enhance knitting between lamellae of skin. To maintain good orientation of particles in the laminar skin, the frequency of radial slots  463  is less than the frequency of the matrix slots at the first skin forming slot  425 . The skin forming pins  467 ,  469  are also referred to herein as rings and the radial slots  463  can have various depths  465  to enhance knitting between lamellae of skin. 
       FIG.  10    is a cutaway isometric view of an extrusion die  903  having a skin former region at the die periphery showing peripheral pins  467 ,  469  and slots  425 ,  429  according to some exemplary embodiments of the present disclosure. The extrusion die  903  is similar to the extrusion die  900 , but extrusion die  903  has hexagonal matrix pins  421 . Although not shown in  FIG.  10   , the outermost matrix pins  435  can also have a portion of the sides facing the first annular ring  425  angled away from the center of the die  903  similar to skin former surface  221  in  FIG.  2    and exit surfaces  431 ,  433  to allow knitting of the laminar skin to the matrix. 
       FIG.  11    is a cutaway isometric view of the extrusion die  903  of  FIG.  10    having a mask  441  in the skin forming region at the die periphery according to some of these exemplary embodiments. The mask  441  is shown transparent merely for illustration of the underlying die  903  structure in the skin former region  419 . 
       FIG.  12    is a cutaway isometric view of an extrusion die  905  having a retrofit skin former  911  at the die periphery showing peripheral slots  913 ,  915 ,  917 ,  919 ,  921  according to some exemplary embodiments of the present disclosure. The retrofit skin former  911  has annular rings  923 ,  925 ,  927 ,  929  to define the annular slots  913 ,  915 ,  917 ,  919 ,  921  for forming the laminar skin similar to the embodiments described previously with reference to  FIGS.  4  and  5   . In addition, the retrofit skin former  911  has feed holes  931 ,  933  configured to provide batch material to the annular slots  913 ,  915 ,  917 ,  919 ,  921 . 
     The retrofit skin former  911  can have a first surface  935  to contact a corresponding surface  937  on the die body  939 . The retrofit skin former  911  can have a second surface  941  to contact a corresponding surface  943  on the die body  939 . In this way the retrofit skin former  911  can fit snugly to the die body  939  with feed holes  417  in fluid communication with feed holes  931 ,  933 . Clamping, bolting, and the like (not shown) can be used to secure the retrofit skin former  911  to the die body  939  to avoid leakage of batch material. The die body  939  can have a chamber  945  in surface  937  to receive batch material from die feed holes  417  and provide batch material to retrofit skin former feed holes  931 ,  933 . 
       FIG.  13 A  is a top view at the exit face  411  of the extrusion die  905  of  FIG.  12    without the retrofit skin former  911  at the die periphery according to some of these exemplary embodiments of the present disclosure.  FIG.  13 B  is a top view at the exit face of the retrofit skin former  911  of  FIG.  12    according to some of these exemplary embodiments of the present disclosure. Opening  947  defined by second surface  941  is configured to fit around the matrix of die  905 .  FIG.  13 C  is a bottom view at the input face of the retrofit skin former  911  of  FIG.  12    according to some of these exemplary embodiments of the present disclosure. 
     EXAMPLES 
       FIG.  14 A  is a schematic to describe an S-value as an order parameter used to quantify the particle alignment in green extruded ware according to some exemplary embodiments of the present disclosure. To quantify how much order is present in a material (green extruded substrate material), an order parameter (S) is referred to herein as follows: 
     
       
         
           
             
               
                 
                   S 
                   = 
                   
                     
                       ( 
                       
                         1 
                         / 
                         2 
                       
                       ) 
                     
                     &lt; 
                     
                       
                         3 
                         ⁢ 
                         
                           cos 
                           2 
                         
                         ⁢ 
                         θ 
                       
                       - 
                       1 
                     
                     &gt; 
                   
                 
               
               
                 
                   Equation 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   
                     ( 
                     1 
                     ) 
                   
                 
               
             
           
         
       
     
     Where theta (θ) is the angle between a determined direction and the long axis of each molecule. The brackets denote an average over all of the molecules in the sample. In an isotropic liquid, the average of the cosine terms is zero, and therefore the order parameter is equal to zero indicating completely random orientation of the molecules. For a perfect crystal (all molecules aligned in the same direction), the order parameter evaluates to one.  FIG.  14 B  is a micrograph of a sample “A1” where S=0.8958 on the left having greater particle alignment than a sample “A2” on the right where S=0.7163. 
       FIG.  15    is a backscatter scanning electron micrograph (SEM) image of a honeycomb body green ware cross section having non-laminar skin co-extruded on matrix showing three areas selected for S-value analysis. A die such as shown in  FIG.  2    having matrix slots extending into the skin former region was used to make the honeycomb body green ware of  FIG.  15   . 
       FIG.  16    is a backscatter SEM image of another honeycomb body green ware cross section having laminar skin co-extruded on matrix according to some exemplary embodiments of the present disclosure. In  FIG.  16   , three areas selected for S-value analysis are shown. A die such as shown in  FIG.  9    having some radially extending slots in the skin former region was used to make the honeycomb body green ware of  FIG.  16   . 
       FIG.  17    is a backscatter SEM image of another honeycomb body green ware cross section having laminar skin co-extruded on matrix according to some exemplary embodiments of the present disclosure. Three areas selected for S-value analysis are shown in  FIG.  17   . A die such as shown in  FIG.  4    having only annularly extending slots in the skin former region was used to make the honeycomb body green ware of  FIG.  17   . 
     Polished cross-sections were prepared from parts dried at 200° C. for 4 hours to help further dry them and to remove some of the oils to help with the epoxy impregnation process. The samples were cut and polished to generate separate specimens from each sample. The specimens were polished across the cross-section of the open face of the part. The polished cross-sections of comparative sample (CS) shown in  FIG.  15   , and exemplary samples (ES) shown in  FIG.  16    (ES1) and  FIG.  17    (ES2) were prepared with conductive carbon coating evaporated onto the samples to reduce charging. The samples were then analyzed with a Zeiss® 1550VP at 20 kV and 300× magnification. 
     The polished specimens were imaged at 300× magnification using the large area mapping automated image acquisition software package in Oxford Instruments Aztec EDS microanalysis® software to acquire large fields of view for observation of particle alignment in the skin. The stitched image montage for each specimen is shown. 
     Media Cybernetics Image Pro Premier® image analysis software was used to quantify the S-value parameter. The montage images were segmented to create an image mask that isolated the larger talc, silica and alumina particles from the smaller clay particles. The masked images were then used to quantify the angle in degrees of the long axis of each particle larger than 25 μm 2  from the reference 0° horizontal image axis. The angle in degrees of each particle was converted to radians and the S-value parameter as defined in Equation (1) was calculated. The average S-value parameter was calculated using the Descriptive Statistics program in Microsoft Excel®. 
     The S-value results are shown in Table 1 for comparative sample (CS), Table 2 for exemplary sample one (ES1), and Table 3 for exemplary sample two (ES2) below. The lower the S-value, the more random the particle alignment. 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 CS-Select Area S-Value 
               
            
           
           
               
               
               
               
               
            
               
                   
                   
                 Area 1 
                 Area 2 
                 Area 3 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
            
               
                   
                 Mean 
                 0.37 
                 0.45 
                 0.37 
               
               
                   
                 Standard Error 
                 0.02 
                 0.01 
                 0.01 
               
               
                   
                 Median 
                 0.48 
                 0.62 
                 0.47 
               
               
                   
                 Mode 
                 1.00 
                 0.25 
                 0.25 
               
               
                   
                 Standard Deviation 
                 0.52 
                 0.49 
                 0.52 
               
               
                   
                 Sample Variance 
                 0.27 
                 0.24 
                 0.27 
               
               
                   
                 Kurtosis 
                 −1.35 
                 −0.99 
                 −1.34 
               
               
                   
                 Skewness 
                 −0.35 
                 −0.63 
                 −0.33 
               
               
                   
                 Range 
                 1.50 
                 1.50 
                 1.50 
               
               
                   
                 Minimum 
                 −0.50 
                 −0.50 
                 −0.50 
               
               
                   
                 Maximum 
                 1.00 
                 1.00 
                 1.00 
               
               
                   
                 Sum 
                 1093.56 
                 1417.13 
                 826.85 
               
               
                   
                 Count 
                 2963 
                 3061 
                 2255 
               
               
                   
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                 ES1-Select Area S-Value 
               
            
           
           
               
               
               
               
               
            
               
                   
                   
                 Area 1 
                 Area 2 
                 Area 3 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
            
               
                   
                 Mean 
                 0.39 
                 0.46 
                 0.51 
               
               
                   
                 Standard Error 
                 0.01 
                 0.01 
                 0.01 
               
               
                   
                 Median 
                 0.52 
                 0.62 
                 0.69 
               
               
                   
                 Mode 
                 1.00 
                 1.00 
                 1.00 
               
               
                   
                 Standard Deviation 
                 0.52 
                 0.51 
                 0.48 
               
               
                   
                 Sample Variance 
                 0.27 
                 0.26 
                 0.23 
               
               
                   
                 Kurtosis 
                 −1.32 
                 −1.11 
                 −0.76 
               
               
                   
                 Skewness 
                 −0.40 
                 −0.59 
                 −0.78 
               
               
                   
                 Range 
                 1.50 
                 1.50 
                 1.50 
               
               
                   
                 Minimum 
                 −0.50 
                 −0.50 
                 −0.50 
               
               
                   
                 Maximum 
                 1.00 
                 1.00 
                 1.00 
               
               
                   
                 Sum 
                 760.85 
                 1049.93 
                 1201.90 
               
               
                   
                 Count 
                 1952 
                 2293 
                 2354 
               
               
                   
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 3 
               
             
            
               
                   
               
               
                 ES2-Select Area S-Value 
               
            
           
           
               
               
               
               
               
            
               
                   
                   
                 Area 1 
                 Area 2 
                 Area 3 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
            
               
                   
                 Mean 
                 0.44 
                 0.43 
                 0.57 
               
               
                   
                 Standard Error 
                 0.01 
                 0.01 
                 0.01 
               
               
                   
                 Median 
                 0.56 
                 0.61 
                 0.77 
               
               
                   
                 Mode 
                 1.00 
                 1.00 
                 1.00 
               
               
                   
                 Standard Deviation 
                 0.49 
                 0.53 
                 0.47 
               
               
                   
                 Sample Variance 
                 0.24 
                 0.28 
                 0.22 
               
               
                   
                 kurtosis 
                 −1.11 
                 −1.24 
                 −0.31 
               
               
                   
                 Skewness 
                 −0.53 
                 −0.53 
                 −1.00 
               
               
                   
                 Range 
                 1.50 
                 1.50 
                 1.50 
               
               
                   
                 Minimum 
                 −0.50 
                 −0.50 
                 −0.50 
               
               
                   
                 Maximurn 
                 1.00 
                 1.00 
                 1.00 
               
               
                   
                 Sum 
                 988.39 
                 815.74 
                 1197.17 
               
               
                   
                 Count 
                 2263 
                 1900 
                 2110 
               
               
                   
                   
               
            
           
         
       
     
     It was found that there were some differences in the degree of particle alignment between samples. The laminar skin provides improved orientation in regions away from the skin to web interface. It was also found that there was greater alignment of the particles in the long axis, or extrusion direction, of the part and less of an alignment in the cross-section of the part. The large dark cracks in the micrographs were the result of low pressure experimental dies used in making the examples. However, the shape of these cracks in  FIG.  15    for CS Areas 1 and 2 indicate a large web affected zone. In contrast,  FIGS.  16  and  17    for ES1 and ES2, respectively, show less cracks, and the cracks are parallel to the skin surface indicating a much smaller web affected zone in accordance with the descriptions of exemplary embodiments of the disclosure set forth herein. 
     According to some of these exemplary embodiments, the order parameter S for greater than 50% of the skin wall thickness can be greater than or equal to 0.4, for example, greater than or equal to 0.45, or even greater than or equal to 0.5. Further, the order parameter S for greater than 60% of the skin wall thickness can be greater than or equal to 0.4, for example, greater than or equal to 0.45, or even greater than or equal to 0.5. Even further, the order parameter S for greater than 70% of the skin wall thickness can be greater than or equal to 0.4, for example, greater than or equal to 0.45, or even greater than or equal to 0.5. 
     According to exemplary embodiments of the disclosure a skin produced by the dies having annular rings to define annular slots to form the skin enables the reduction or elimination of stresses previously resulting from physical thermal expansion property mismatch between the matrix and skin during heating and cooling during use of the ceramic honeycomb bodies. Failures of ceramic honeycomb bodies in oven thermal shock testing generally occur in the skin, and so the integral laminar skin disposed on the matrix as disclosed herein having particles oriented as in the matrix can increase the failure temperature in oven thermal shock testing. The improved match in thermal expansion coefficient between skin and matrix can lead to improved thermal shock resistance of the honeycomb body. Furthermore, the methods disclosed herein to provide integral laminar skin disposed on the matrix having particles oriented as in the matrix can lead to improved skin thickness uniformity and improved honeycomb body isostatic strength. 
     It will be apparent to those skilled in the art that various modifications and variations can be made in the disclosed exemplary embodiments without departing from the spirit or scope of the disclosure. Thus, it is intended that the appended claims cover the modifications and variations of this disclosure provided they come within the scope of the appended claims and their equivalents.