Ceramic articles made from ceramic beads having open porosity

Abstract

Ceramic article and method of manufacture. The ceramic article comprises a porous ceramic material having a microstructure with an interconnected network of porous spherical ceramic beads. The microstructure has a total open porosity, defined as the sum of the intra-bead open porosity of the beads and the inter-bead porosity, defined by the gaps between the beads in the interconnected network. The microstructure has a bimodal pore size distribution with an intra-bead peak corresponding to the intra-bead open porosity and an inter-bead peak corresponding to the inter-bead porosity. The intra-bead porosity has an intra-bead median pore size smaller than the inter-bead median pore size.

Description

Related Applications

[0001] This application claims priority under 35 U.S.C. §119 to U.S. Provisional Patent Application No. 63 / 071,717, filed August 28, 2020, and U.S. Provisional Patent Application No. 63 / 059,631, filed July 31, 2020, the contents of which are relied upon and incorporated by reference herein in their entireties. [Technical Field]

[0002] The present disclosure relates to ceramic articles, and more particularly to ceramic articles including ceramic honeycomb bodies having an interconnected network of ceramic beads with high open porosity. [Background technology]

[0003] Honeycomb bodies are used in a variety of applications, such as particulate filters and catalytic converters to treat pollutants in the exhaust of internal combustion engines. The process for manufacturing ceramic honeycomb bodies can include extruding batch materials through a honeycomb extrusion die and firing the resulting green honeycomb body. Summary of the Invention

[0004] Disclosed herein is a ceramic article comprising a porous ceramic material having a microstructure with an interconnected network of porous spherical ceramic beads, the microstructure having a total open porosity defined as the sum of the intra-bead open porosity of the beads and the inter-bead porosity defined by the gaps between the beads in the interconnected network, the microstructure having a bimodal pore size distribution with an intra-bead peak corresponding to the intra-bead open porosity and an inter-bead peak corresponding to the inter-bead porosity, and the intra-bead porosity having an intra-bead median pore size that is smaller than the inter-bead median pore size of the inter-bead porosity.

[0005] In some embodiments, the intra-bead open porosity is at least 10% relative to the total volume defined by the interconnected network, and the inter-bead porosity is at least 40% relative to the total volume of the interconnected network.

[0006] In some embodiments, the open intra-bead porosity is at least 9% by volume of the bead and the total porosity is at least 50%.

[0007] In some embodiments, the ceramic beads have at least 80% by weight cordierite.

[0008] In some embodiments, the porous ceramic beads comprise at least 85% by weight cordierite.

[0009] In some embodiments, the crystalline phase of the porous ceramic material comprises at least 90% by weight cordierite.

[0010] In some embodiments, the crystalline phase of the porous ceramic material comprises at least 95% by weight cordierite.

[0011] In some embodiments, the porous ceramic beads have a closed bead porosity of less than 5%.

[0012] In some embodiments, the porous ceramic beads have a closed bead porosity of less than 2.5%.

[0013] In some embodiments, the open intra-bead porosity is at least 12% by total volume.

[0014] In some embodiments, the open intra-bead porosity is at least 15% by total volume.

[0015] In some embodiments, the inter-bead porosity is at least 45%.

[0016] In some embodiments, the inter-bead porosity is at least 50%.

[0017] In some embodiments, the total porosity is at least 50%.

[0018] In some embodiments, the total porosity is at least 55%.

[0019] In some embodiments, the total porosity is at least 60%.

[0020] In some embodiments, the bead-to-bead half-maximum pore size distribution peak width is at most 6 μm as determined by mercury intrusion porosimetry.

[0021] In some embodiments, the bead-to-bead half-maximum pore size distribution peak width is at most 5.5 μm as determined by mercury intrusion porosimetry.

[0022] In some embodiments, the intra-bead half-maximum pore size distribution peak width is at most 2 μm as determined by mercury intrusion porosimetry.

[0023] In some embodiments, the intra-bead half-maximum pore size distribution peak width is at most 1.5 μm as determined by mercury intrusion porosimetry.

[0024] In some embodiments, the bimodal pore size distribution has a local minimum differential intrusion value at a pore size that is between the intra-bead median pore size and the inter-bead median pore size, as determined by mercury intrusion porosimetry, and the local minimum differential intrusion value is less than 20% of the maximum differential intrusion value of the inter-bead peak.

[0025] In some embodiments, the bimodal pore size distribution has a local minimum differential intrusion value at a pore size that is between the intra-bead median pore size and the inter-bead median pore size, as determined by mercury intrusion porosimetry, and the local minimum differential intrusion value is less than 15% of the maximum differential intrusion value of the inter-bead peak.

[0026] In some embodiments, the bimodal pore size distribution, as determined by mercury intrusion porosimetry, has a local minimum differential intrusion value at a pore size that is between the intra-bead median pore size and the inter-bead median pore size, and the local minimum differential intrusion value is less than the value of the intra-bead half-maximum pore size distribution peak width.

[0027] In some embodiments, the bimodal pore size distribution of the ceramic article has a D10 value of at most 3 μm, as determined by mercury intrusion porosimetry.

[0028] In some embodiments, the bimodal pore size distribution of the ceramic article has a D10 value of at most 2.5 μm, as determined by mercury intrusion porosimetry.

[0029] In some embodiments, the bimodal pore size distribution of the ceramic article has a D10 value of at most 2 μm, as determined by mercury intrusion porosimetry.

[0030] In some embodiments, the bimodal pore size distribution of the ceramic article has a D75-D50 value, as determined by mercury intrusion porosimetry, of at most 2 μm.

[0031] In some embodiments, the bimodal pore size distribution of the ceramic article has a D75-D50 value of at most 1.5 μm, as determined by mercury intrusion porosimetry.

[0032] In some embodiments, the ceramic article has a bimodal pore size distribution D50 / D10 ratio of at least 3, as determined by mercury intrusion porosimetry.

[0033] In some embodiments, the bimodal pore size distribution of the ceramic article has a D50 / D10 ratio of at least 4, as determined by mercury intrusion porosimetry.

[0034] In some embodiments, the bimodal pore size distribution of the ceramic article has a D50 / D10 ratio of at least 5, as determined by mercury intrusion porosimetry.

[0035] In some embodiments, the total porosity is at least 55%, the inter-bead median pore size is between 6 μm and 20 μm, the intra-bead median pore size is between 1.5 μm and 4 μm, the bimodal pore size distribution has an inter-bead half-maximum pore size distribution peak width of at most 5.5 μm, the bimodal pore size distribution has an intra-bead half-maximum pore size distribution peak width of at most 2 μm, and the local minimum differential intrusion value of the pore size distribution located at a pore size between the intra-bead median pore size and the inter-bead median pore size is less than 15% of the local maximum differential intrusion value of the inter-bead peak, as determined by mercury intrusion porosimetry.

[0036] In some embodiments, the total porosity is at least 55% and the bimodal pore size distribution has a D10 value of at most 3 μm, a D50 value of 5 μm to 18 μm, and a D75-D50 value of at most 2 μm, as determined by mercury intrusion porosimetry.

[0037] In some embodiments, the porous ceramic beads have an average intra-bead open porosity of at least 20% by volume of the beads.

[0038] In some embodiments, the material of the beads has an average intra-bead open porosity of at least 25% by volume of the bead.

[0039] In some embodiments, the material of the beads has an average intra-bead open porosity of at least 30% by volume of the bead.

[0040] In some embodiments, the inter-bead porosity has a median pore size in the range of 6 μm to 20 μm.

[0041] In some embodiments, the inter-bead median pore size is in the range of 8 μm to 18 μm.

[0042] In some embodiments, the inter-bead median pore size is in the range of 9 μm to 17 μm.

[0043] In some embodiments, the median pore size within the beads is in the range of 1 μm to 5 μm.

[0044] In some embodiments, the median pore size within the beads is in the range of 1.5 μm to 4 μm.

[0045] In some embodiments, the median pore size within the beads is in the range of 1.5 μm to 3 μm.

[0046] In some embodiments, the median pore size within the beads is in the range of 1.5 μm to 2 μm.

[0047] In some embodiments, the median pore size within the beads is in the range of 1 μm to 2 μm.

[0048] In some embodiments, the beads have a median particle size in the range of 20 μm to 50 μm.

[0049] In some embodiments, the beads have a median particle size in the range of 25 μm to 40 μm.

[0050] Also disclosed herein is a ceramic honeycomb body having the ceramic article of any one of the preceding paragraphs, wherein the ceramic article has a plurality of intersecting walls having a porous ceramic material, the intersecting walls forming a plurality of passages extending longitudinally through the ceramic honeycomb body from the first end face to the second end face.

[0051] In some embodiments, the intersecting wall porous ceramic material comprises at least 90% by weight cordierite, the porous ceramic beads have an intra-bead closed porosity of less than 5%, a total porosity of at least 50%, an intra-bead open porosity of the beads of at least 20% by volume of the beads, and the beads have a median particle size in the range of 20 μm to 50 μm.

[0052] Also disclosed herein is a particulate filter having a ceramic honeycomb body according to any of the above paragraphs.

[0053] In some embodiments, the passages of the honeycomb body are plugged in alternating checkerboard patterns on the first end face and the second end face.

[0054] Disclosed herein is a method of making a ceramic article, the method comprising: mixing together a batch mixture having a plurality of porous ceramic beads each having a porous ceramic material, the porous ceramic material of the porous ceramic beads having intra-bead open porosity, the porous ceramic beads having a median bead size of 25 to 40 μm; forming the batch mixture into a green ceramic article; and firing the green ceramic article to form the ceramic article by sintering the porous ceramic beads together into an interconnected network of porous ceramic beads, wherein the interstices between the beads in the interconnected network define the inter-bead porosity of the ceramic article, and the total porosity of the ceramic article, defined as the sum of the intra-bead porosity and the inter-bead porosity, is at least 50% relative to the total volume of the ceramic article, and the ceramic article has a bimodal pore size distribution, wherein the intra-bead median pore size of the intra-bead porosity is smaller than the inter-bead median pore size of the inter-bead porosity.

[0055] In some embodiments, prior to forming the batch mixture, the method further comprises forming a slurry mixture having a mixture of ceramic precursor materials, spheronizing the slurry mixture into spherical green agglomerates, and firing the green agglomerates to convert the ceramic precursor materials into porous ceramic material, thereby forming porous ceramic beads.

[0056] In some embodiments, the ceramic beads have at least 80% by weight cordierite.

[0057] In some embodiments, the crystalline phase of the porous ceramic material is at least 90% by weight cordierite.

[0058] In some embodiments, the method further comprises sieving the green agglomerates or sieving the porous ceramic beads to affect the median particle size of the porous ceramic beads prior to the step of mixing the batch mixture together.

[0059] In some embodiments, the step of spheronizing the slurry mixture comprises a spray drying process.

[0060] In some embodiments, the step of spheronizing the slurry mixture comprises a rotary evaporation process.

[0061] In some embodiments, the ceramic precursor material comprises a silica source, an alumina source, and a magnesia source, and the porous ceramic material of the porous ceramic beads comprises cordierite.

[0062] In some embodiments, the batch mixture further comprises an organic binder and an inorganic binder.

[0063] In some embodiments, the batch mixture has porous ceramic beads in an amount ranging from 60% to 95% by weight, based on the total weight of the inorganic binder and porous ceramic beads.

[0064] In some embodiments, the inorganic binder comprises a plurality of shear binder agglomerates, the shear binder agglomerates comprising an unfired mixture of one or more inorganic ceramic precursor materials and the binder.

[0065] In some embodiments, the intra-bead open porosity is at least 10% based on the total volume of the ceramic article.

[0066] In some embodiments, the inter-bead porosity is at least 40% by total volume of the ceramic article.

[0067] In some embodiments, the intra-bead porosity is at least 9% by volume of the bead.

[0068] In some embodiments, the intra-bead porosity is at least 15% by volume of the bead.

[0069] In some embodiments, the intra-bead porosity is at least 20% by volume of the bead.

[0070] In some embodiments, the ceramic article is a ceramic honeycomb body, and shaping the batch mixture includes extruding the batch mixture through a honeycomb extrusion die, and the ceramic honeycomb body has a plurality of intersecting walls having porous ceramic material, the intersecting walls forming a plurality of passages extending longitudinally through the honeycomb body from a first end face to a second end face.

[0071] In some embodiments, fabricating a filter from the honeycomb body further comprises plugging the passages alternating between the first end face and the second end face in a checkerboard pattern.

[0072] It is to be understood that both the foregoing general description and the following detailed description are exemplary only and are intended to provide an overview or framework for understanding the nature and character of the claimed subject matter. 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 embodiments and, together with the description, serve to explain the principles and operation of the various embodiments. [Brief explanation of the drawings]

[0073] [Figure 1] 1 illustrates a schematic representation of a honeycomb body according to one embodiment disclosed herein. [Figure 2] 1 illustrates a plugged honeycomb body according to one embodiment disclosed herein. [Figure 3]10A and 10B are schematic illustrations of through-wall gas flow in a plugged honeycomb body according to one embodiment disclosed herein; [Figure 4] 1 illustrates a schematic of an extrusion system for forming a green honeycomb body according to one embodiment disclosed herein. [Figure 5A] 1A and 1B illustrate schematic views of a portion of a wall of a ceramic honeycomb body having a network of spherical ceramic beads according to one embodiment disclosed herein. [Figure 5B] 1 shows a cross-sectional scanning electron microscope (SEM) image of a portion of an intersecting wall of a ceramic honeycomb body according to one embodiment disclosed herein. [Figure 6] FIG. 1 shows a close-up view of a network of spherical ceramic beads according to one embodiment disclosed herein. [Figure 7] 1 shows a cross-sectional SEM image of a portion of a network of spherical ceramic beads according to one embodiment disclosed herein. [Figure 8] 1 shows a spherical ceramic bead according to one embodiment disclosed herein. [Figure 9A] 1 shows a schematic representation of a first ceramic bead having high open porosity formed by interconnected narrow pore channels. [Figure 9B] 10A schematically illustrates a second ceramic bead having high open porosity formed by thin pore passages connecting between relatively wide pore voids. [Figure 9C] 10 schematically illustrates a third ceramic bead having high open porosity formed by relatively wide interconnected pore passages and relatively wide pore voids. [Figure 10] 1 illustrates various steps for making spherical ceramic beads according to one embodiment disclosed herein. [Figure 11] 1 shows a flow chart of a method for making spherical ceramic beads and a method for manufacturing a ceramic honeycomb body from a batch mixture having spherical ceramic beads. [Figure 12A] 1A-1D show SEM images showing surface and cross-sectional views of green aggregates according to various embodiments disclosed herein. [Figure 12B] 1A-1D show SEM images showing surface and cross-sectional views of green aggregates according to various embodiments disclosed herein. [Figure 12C] 1A-1D show SEM images showing surface and cross-sectional views of green aggregates according to various embodiments disclosed herein. [Figure 12D] 1A-1D show SEM images showing surface and cross-sectional views of green aggregates according to various embodiments disclosed herein. [Figure 12E] 1A-1D show SEM images showing surface and cross-sectional views of green aggregates according to various embodiments disclosed herein. [Figure 12F] 1A-1D show SEM images showing surface and cross-sectional views of green aggregates according to various embodiments disclosed herein. [Figure 12G] 1A-1D show SEM images showing surface and cross-sectional views of green aggregates according to various embodiments disclosed herein. [Figure 12H] 1A-1D show SEM images showing surface and cross-sectional views of green aggregates according to various embodiments disclosed herein. [Figure 13A] 1A-1C show cross-sectional SEM images of green aggregates and the resulting ceramic beads formed by firing at various maximum temperatures according to various embodiments disclosed herein. [Figure 13B] 1A-1C show cross-sectional SEM images of green aggregates and the resulting ceramic beads formed by firing at various maximum temperatures according to various embodiments disclosed herein. [Figure 13C] 1A-1C show cross-sectional SEM images of green aggregates and the resulting ceramic beads formed by firing at various maximum temperatures according to various embodiments disclosed herein. [Figure 13D] 1A-1C show cross-sectional SEM images of green aggregates and the resulting ceramic beads formed by firing at various maximum temperatures according to various embodiments disclosed herein. [Figure 14]FIG. 1 shows SEM images of calcined agglomerated powders obtained by calcination of spray-dried green agglomerates, and of calcined agglomerated powders obtained by calcination of first and second type green agglomerates made by the agglomeration process in a rotary evaporator. [Figure 15A] 1A-1C show SEM images at various magnifications of a fracture surface of intersecting walls of a ceramic honeycomb body having a network of spherical ceramic beads sintered together according to one embodiment disclosed herein. [Figure 15B] 1A-1C show SEM images at various magnifications of a fracture surface of intersecting walls of a ceramic honeycomb body having a network of spherical ceramic beads sintered together according to one embodiment disclosed herein. [Figure 15C] 1 shows an SEM image of a cross-section of intersecting walls of a ceramic honeycomb body having a network of spherical ceramic beads sintered together according to one embodiment disclosed herein. [Figure 15D] 1 shows an SEM image of a surface view of intersecting walls of a ceramic honeycomb body having a network of spherical ceramic beads sintered together according to one embodiment disclosed herein. [Figure 16A] 15A shows the bimodal pore size distribution of the porous ceramic materials of various honeycomb body examples in Table 15A compared to the unimodal pore size distribution of honeycomb bodies made from reactive batches, as measured by MIP. [Figure 16B] 1 shows the bimodal pore size distribution of the porous ceramic material of a honeycomb body made from porous cordierite beads as measured by MIP. [Figure 17] FIG. 1 shows a graph illustrating filtration efficiency by mass as a function of cumulative soot loading for filters made from conventional reactive batches compared to filters made from pre-reacted cordierite beads as described herein. [Figure 18] 1 shows a graph illustrating clean pressure drop as a function of flow rate for a reference filter made from a conventional reactive batch compared to various filters made from examples of honeycomb bodies described herein. [Figure 19] 1 shows a graph illustrating the surface area to volume ratio for filters made from two types of pre-reacted cordierite beads described herein compared to a reference filter made from a conventional reactive batch. [Figure 20] 1 shows a graph illustrating BET specific surface area as a function of intra-bead porosity for ceramic honeycomb bodies having porous ceramic beads according to embodiments disclosed herein. [Figure 21A] 10A-10C show polished SEM cross-sectional images of respective portions of a wall of a honeycomb body having an interconnected network of cordierite beads after washcoating of the honeycomb body according to embodiments disclosed herein. [Figure 21B] 10A-10C show polished SEM cross-sectional images of respective portions of a wall of a honeycomb body having an interconnected network of cordierite beads after washcoating of the honeycomb body according to embodiments disclosed herein. [Figure 22A] 1A-1C show different magnified views of a fractured wall of a washcoated honeycomb body having an interconnected network of cordierite beads hosting washcoat particles according to one embodiment disclosed herein. [Figure 22B] 1A-1C show different magnified views of a fractured wall of a washcoated honeycomb body having an interconnected network of cordierite beads hosting washcoat particles according to one embodiment disclosed herein. [Figure 23A] 1 shows a polished SEM cross-sectional image of a portion of a wall of a washcoated honeycomb body having an interconnected network of cordierite beads hosting washcoat particles according to one embodiment disclosed herein. [Figure 23B] FIG. 23B shows an enlarged view of the circled area in FIG. 23A, showing porous ceramic beads with washcoat particles deposited externally within the intra-bead pore structure and on the outer surface of the beads. DETAILED DESCRIPTION OF THE INVENTION

[0074] Reference will now be made in detail to the exemplary embodiments, as illustrated in the accompanying drawings. Wherever possible, the same reference numbers are used throughout the drawings to refer to the same or like parts. The components in the drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the exemplary embodiments. Numerical values, including range endpoints, may be expressed herein as approximations, preceded by terms such as "about," "approximately," or the like. In such instances, other embodiments include the particular values.

[0075] In various embodiments, porous ceramic spherical particles, ceramic articles having such porous ceramic particles, methods of making such porous ceramic particles, and methods of making such ceramic articles are disclosed. In some embodiments, the ceramic article comprises a porous ceramic honeycomb body. In some embodiments, selected passages of the honeycomb body are plugged to prepare the honeycomb body as a particulate filter or wall-flow filter. For ease of discussion, the porous ceramic spherical particles may be referred to herein as "porous ceramic beads," "ceramic beads," or simply "beads." Thus, the ceramic beads referred to herein are spherical ceramic particles having a porous ceramic material having one or more ceramic phases, such as cordierite, aluminum titanate, mullite, silicon carbide, or combinations thereof.

[0076] As described herein, ceramic articles, such as ceramic honeycomb bodies, are formed by molding and firing a batch mixture containing porous ceramic beads. As a result, the porous ceramic walls of the ceramic article material, such as the honeycomb body, are formed as an interconnected network of porous ceramic beads. As such, the microstructure of the ceramic material exhibits a unique bimodal porosity defined by a first porosity of the beads themselves ("intra-bead porosity") and a second porosity of the interstices within the interconnected network formed by the beads ("inter-bead porosity"). That is, the microstructure of the porous ceramic material as described herein has an "intra-bead" porosity defined by the open pore structure of the material of each individual bead, and an "inter-bead" porosity defined by the interstices between the beads within the interconnected network of beads. Correspondingly, intra-bead porosity formed within the material of the beads themselves necessarily has a smaller intra-bead median pore size than the median particle size of the beads, and inter-bead porosity formed within the interstices between the beads has a relatively large inter-bead median pore size (e.g., several times larger than the intra-bead median pore size) that can approach the median particle size of the beads. That is, inter-bead porosity depends at least in part on the packing of the beads within the interconnected network, which packing is in turn at least in part determined by the size of the beads.

[0077] Advantageously, by providing intra-bead porosity as open porosity combined with relatively large pore size of inter-bead porosity, the resulting bimodal porosity of the microstructures of the ceramic articles described herein exhibits unique performance characteristics, useful, for example, when prepared as a honeycomb body for a particulate filter or catalyst substrate, for the treatment, reduction, or abatement of one or more substances (e.g., pollutants) from a fluid stream (e.g., engine exhaust). For example, in some embodiments, the bimodal porosity enables the honeycomb body to be prepared as a particulate filter having a high filtration efficiency (FE) that maintains low pressure drop at all levels of ash / soot deposition, even when clean (pre-ash / soot deposition). That is, the intra-bead open porosity provides a high surface area that provides anchor sites for ash, soot, or other particulates; the relatively small pore size of the intra-bead pore size distribution promotes capillary action and assists in trapping the ash, soot, or other particulates at the anchor sites; and the relatively large pore size of the inter-bead pore size distribution provides a relatively large flow path that maintains low pressure drop even at high particulate loads.

[0078] In some embodiments, the aforementioned bimodal porosity allows for the use of high catalytic material loadings without a significant tradeoff in pressure drop, particularly for catalyst-loaded particulate filters. That is, the high open porosity provided by the combination of inter-bead and intra-bead porosity provides a high pore volume capable of loading catalytic material and / or a large pore surface area capable of binding catalyst, while maintaining a high degree of interconnectivity of inter-bead pore passages. Furthermore, the relatively small pore size of the intra-bead pore size distribution relative to the inter-bead pore size distribution promotes capillary action and aids in drawing catalytic material onto and / or into the beads, while the relatively large pore size of the inter-bead pore size distribution provides a relatively large flow path that maintains low pressure drop.

[0079] Referring now to FIG. 1 , a ceramic article is shown in the form of a honeycomb body 100 having intersecting walls 102 that form a plurality of passages 104. As described herein, the walls 102 comprise a porous ceramic material. The walls 102 and passages 104 thus form a honeycomb structure that is surrounded by a skin or outer periphery 105. The passages 104 extend axially through the honeycomb body 100, e.g., parallel to one another, from a first end face 106 to a second end face 108. As described herein, the honeycomb body 100 may be useful in a variety of applications, for example, in the form of a catalytic converter (e.g., the walls 102 serving as a substrate for catalytic material) and / or for use as a particulate filter (e.g., some of the passages 104 are plugged to trap particulates within the honeycomb walls 108). Such honeycomb bodies 100 can thus assist in treating or mitigating contaminants from a fluid stream, for example, removing undesirable components from the exhaust stream of a vehicle's internal combustion engine. For example, the porous material of the walls 102 can support a catalytic material, such as a three-way catalyst, that treats one or more compounds in a fluid stream (e.g., engine exhaust) passing through the passages 104 of the honeycomb body 100.

[0080] As shown in Figures 2-3, some of the passages 104 of the honeycomb body 100 can be plugged with plugs 109 to form a plugged honeycomb body 101. As a result of the plugging, the passages are divided into "entrance passages" that open at an inlet face (e.g., first end face 106) and "exit passages" that open at an opposite outlet face (e.g., second end face 108). For ease of discussion herein, the entrance passages will be designated by reference numeral 104a and the exit passages will be designated by reference numeral 104b, and general references to "passages 104" will include all passages, whether they are entrance or exit passages.

[0081] The plugged honeycomb body 101 can form part of, or can refer to, or be considered to be, a particulate filter or a wall-flow filter (these terms are generally interchangeable). Plugging with the plugs 109 can be performed using any suitable plugging process (e.g., putty plugging, slurry plugging, etc.) and plugging material (e.g., cold-setting plugging cement). In some embodiments, some of the passages 104 are plugged at the first end face 106, and some of the passages 104 that are not plugged at the first end face 106 are plugged at the second end face 108. Any suitable plugging pattern can be used. For example, alternating passages 104 can be plugged at opposite ends 106, 108.

[0082] 3, plugging the passages 104 at alternate opposite ends allows a fluid stream F (e.g., engine exhaust) to enter the plugged honeycomb body 101 into the inlet passage 104a, which opens at the inlet end (e.g., end face 106 in FIG. 3), and then pass through the porous material of the wall 102 to the adjacent outlet passage 104b, which opens at the outlet end (e.g., end face 108 in FIG. 3). At least some of the particulate matter in the fluid stream F is prevented from flowing through the porous material of the wall 102 (e.g., such particles become trapped within the pore structure of the wall 102), thereby treating the fluid stream F as it exits the plugged honeycomb body 101.

[0083] Honeycomb body 100 can be formed in any suitable manner. For example, an extrusion system (or extruder) 10 that can at least partially form honeycomb body 100 is shown in FIG. 4. Extruder 10 has a barrel 12 extending in a direction 14 (e.g., an extrusion direction). A material feed port 16, which can include, for example, a hopper or other material feed structure, can be provided upstream of barrel 12 for feeding a ceramic forming mixture 110 (also referred to as a batch mixture) into extruder 10.

[0084] An extrusion die 18 is coupled downstream from the barrel 12 to shape the batch mixture 110 into a desired shape before it leaves the extruder 10 as extrudate 112. For example, the extrusion die 18 may be a honeycomb extrusion die for producing the extrudate 112 as a green honeycomb extrudate. The extrusion die 18 may be coupled to the barrel 12 by any suitable means, such as bolting, clamping, or the like. The extrusion die 18 may be preceded by other extrusion structures, such as a particle screen, a screen substrate, a homogenizer, or the like, within the extrusion assembly 20 to facilitate suitable flow characteristics, such as the formation of a stable plug flow front when the batch mixture 110 reaches the extrusion die 18.

[0085] The extruder 10 can be of any type, such as a twin-screw extruder or a hydraulic ram extruder, among others. In FIG. 4, the extruder 10 is shown as a twin-screw extruder having a pair of extrusion screws 22 mounted within the barrel 12. For example, a drive mechanism 24 located outside the barrel 12 may be included to operate the extrusion elements, such as the ram or screws 22 of a ram extruder in the embodiment of FIG. 4. The extrusion elements of the extruder 10, such as the pair of extrusion screws 22, the ram, etc., can act to move the batch mixture 110 through the barrel 12 in a pumping and mixing action in a longitudinal direction 14 corresponding to the extrusion direction.

[0086] The extruder 10 further includes a cutting device 26. For example, the cutting device 26 is configured to cut a green honeycomb body 100G from the extrudate 112. The green honeycomb body 100G generally resembles the honeycomb body 100, i.e., has a honeycomb structure with intersecting walls and channels, because the final ceramic honeycomb body 100 is produced by further processing the green body 100G. That is, after extrusion and cutting, the green body 100G can be further cut or ground to a desired axial length, dried, and fired, among other manufacturing steps to produce the final ceramic honeycomb body. The green body 100G can be extruded with a skin (i.e., forming the skin 105), or the skin can be added in a subsequent manufacturing step.

[0087] The ceramic-forming mixture 110 can be introduced into the extruder 10 continuously or intermittently. The ceramic-forming mixture 110 comprises porous ceramic beads according to various embodiments disclosed herein. The ceramic-forming mixture can further comprise one or more additional inorganic materials (e.g., alumina, silica, talc, clay or other ceramic materials, ceramic precursor materials or green agglomerated ceramic precursor powders), binders (e.g., organic binders, such as methylcellulose), pore-forming agents (e.g., starch, graphite, resins), liquid excipients (e.g., water), sintering aids, lubricants, or any other additives that aid in the fabrication, shaping, processing, and / or properties of the extrudate 112, the green honeycomb body 100G, and / or the ceramic honeycomb body 100.

[0088] According to embodiments described herein, the ceramic-forming mixture 110 comprises a plurality of porous ceramic beads that ultimately form the porous ceramic material of the walls 102 of the honeycomb body 100. For example, as shown schematically in FIG. 5A and in the polished scanning electron microscope (SEM) cross-section in FIG. 5B, the walls 102 have a microstructure comprising an interconnected network 120 of porous ceramic beads 122. That is, the plurality of beads 122 are bonded together into a continuous network, e.g., by sintering and / or reaction of the ceramic and / or ceramic-forming materials during firing of the green body 100G. For example, the beads 122 can be directly sintered together and / or indirectly bonded together (e.g., via sintering and / or reaction of one or more other inorganic materials within the mixture 110). An extrusion die 18 or other shaping mechanism can be utilized to define the shape and / or dimensions of the honeycomb body 100, e.g., the wall thickness t of the walls 102 shown in FIGS. 5A-5B, to prepare the interconnected network 120 of beads 122. Thus, the total volume of the wall 102 and / or interconnected network 120 can be defined by the wall thickness t multiplied by other basic dimensions of the wall 102 and / or network 120, which are generally delineated by the outer boundary of the beads 122.

[0089] As described in further detail herein, the porous ceramic beads 122 may be said to or considered to be “pre-reacted” beads because they already have one or more selected ceramic phases when incorporated into the batch mixture 110 (i.e., and therefore, such ceramic phases are already present in the green body 100G prior to firing of the honeycomb body 100). The beads 122 can be fully reacted so that continued firing does not produce larger amounts of the ceramic phases, or they can be at least partially reacted so that one or more ceramic phases are present but continue to react when the beads 122 are subjected to further firing. In either case, the “pre-reacted” nature of the beads 122 can be used to maintain the spherical shape of the beads during various manufacturing steps (e.g., batch paste mixing, extrusion, cutting, drying, and firing). For example, partially or fully reacted ceramic has higher strength than unreacted agglomerates, preventing fracture of the beads 122 during processes such as extrusion. As another example, ceramic beads 122 that already contain one or more reaction phases are more readily susceptible to continued reaction or sintering within each individual bead, as opposed to reaction with unreacted ceramic precursor materials in other beads. For example, reaction of components from different beads may be limited because there is no material diffusion path between beads that are not in contact with each other, and only limited diffusion paths exist for the beads in the form of point-to-point contact. In contrast, if a significant degree of mass transfer is possible between the reaction components, for example, due to the presence of a large amount of glass or liquid at high temperature, the material will lose this confinement, and instead of maintaining a spherical bead shape, the growth of large, inconsistent aggregates or large, elongated crystals will be promoted. By maintaining the spherical shape of the beads 122, the aforementioned interconnected network 120 of beads 122 can be created for the ceramic honeycomb body 100.

[0090] 6 and 7 show, respectively, a photograph and a polished SEM cross-section of a portion of an interconnected network 120 of beads 122 according to some embodiments. Referring to FIGS. 5A-7, the porous ceramic beads 122 can be seen to have an interconnected open pore structure 124 extending across each of the beads 122. The open pore structure 124 can have relatively narrow pore structures, e.g., passages, and relatively wide pore structures, e.g., pore voids or pore bodies, where the passages act as pore necks or throats into the voids or bodies. The pore structure 124 is considered "open" because the pores within the beads 122 are in fluid communication with the exterior of the beads 122. For example, as shown in FIGS. 6 and 7, the pore structure 124 has openings 126 on the outer surface of the beads 122 that provide fluid communication between the interior and exterior of the beads 122. Pore ​​structure 124 may be considered "interconnected" because the pores throughout bead 122 form a network that is in fluid communication with one another (e.g., directly to the exterior of bead 122 and / or through mutual openings). Thus, open pore structure 124 described herein facilitates flow into, through, and out of bead 122. According to some embodiments, at least 80%, or even at least 90%, of the porosity of bead 122 (relative to the total volume of bead 122) is open pores (as opposed to closed pores that are not in fluid communication with the exterior of the bead).

[0091] 5A-7 , the formation of the interconnected network 120 of beads 122 results in interstices 128 (which may alternatively be referred to as spaces or gaps) being formed between adjacent ones of the beads 122. Thus, in three-dimensional space, the interstices 128 form an open and interconnected pore structure intertwined with and / or around the interconnected network 120 of the beads 122. Advantageously, and as discussed in further detail herein, the openness and interconnectivity of the open pore structure 124 of the beads 122 and the interstices 128 between the beads can be used to provide various characteristics and / or benefits to the honeycomb body 100, such as a microstructure for the wall 102 material having a unique bimodal open porosity.

[0092] The microstructure (formed by the interconnected network 120 of porous ceramic beads 122) of the wall 102 material has a total porosity (i.e., relative to the total volume of the microstructure / wall), which has an intra-bead porosity defined by the porosity of the pore structure 124 of the beads 122 and an inter-bead porosity defined by the interstices 128 in the interconnected network 120 between the beads 122. Correspondingly, the intra-bead porosity formed within the bead material has an intra-bead median pore size that is a fraction of the median bead particle size, and the inter-bead porosity formed within the spaces between the beads has a relatively large inter-bead median pore size (e.g., several times larger than the intra-bead median pore size) that may approach the median bead particle size. Thus, the aforementioned bimodal porosity has both an intra-bead pore size distribution and an inter-bead pore size distribution, which differ from each other in that the pore sizes of the intra-bead porosity are, on average, smaller than the pore sizes of the inter-bead pore sizes. In other words, the intra-bead median pore size of the intra-bead pore size distribution is smaller than the inter-bead median pore size of the inter-bead pore size distribution.

[0093] The beads 122 formed as spherical ceramic particles can have one or more shapes, such as spheres, ellipsoids, oblate spheroids, spheroids, or toroids. The beads can be formed as ceramic particles by firing green aggregates of ceramic-forming raw materials under conditions (e.g., time and temperature) appropriate to cause the ceramic-forming mixture to react into one or more ceramic phases and / or sinter the ceramic grains together. For example, cordierite may be formed at firing temperatures of about 1200°C to about 1420°C. In some embodiments, firing of the green aggregates can range from about 30 minutes to about 6-8 hours at a selected firing temperature, with a higher degree of reaction (and therefore a higher percentage of ceramic phases formed) at longer durations and higher temperatures.

[0094] In some embodiments, the median particle size or diameter of the beads (or median bead size or diameter) is at least 25 μm, e.g., at least 30 μm. In some embodiments, the median particle size of the beads is at most 55 μm, e.g., 50 μm or 45 μm. In some embodiments, the median particle size of the beads is in the range of about 25 μm to 55 μm, e.g., 30 μm to 55 μm, 30 μm to 50 μm, 30 μm to 45 μm, or 30 μm to 40 μm. In some embodiments, beads having a median particle size of 25 μm are used in combination with beads having a median particle size of 25 μm or greater, e.g., a first type of beads having a median particle size in the range of 15 μm to 20 μm are used in combination with a second type of beads having a median particle size in the range of 30 μm to 50 μm.

[0095] An SEM image of one representative example of bead 122 is shown in Figure 8. Various embodiments of bead 122 are shown schematically in Figures 9A-9C, identified as beads 122A-122C, respectively, in which bead 122 is shown partially cut away to reveal both the exterior and interior portions of each bead. In particular, bead 122A has an open pore structure with a plurality of interconnected, relatively narrow pore passages extending entirely through bead 122A. Bead 122B has an open pore structure with a plurality of interconnected, relatively narrow pore passages interspersed with relatively large diameter pore voids or bodies. Bead 122C has an open pore structure with a plurality of interconnected, relatively wide pore passages interspersed with or interspersed with relatively large diameter pore voids or bodies. For example, including relatively narrow pores (e.g., passages in beads 122A and / or 122B) can be useful for increasing pore surface area for any given porosity value, and relatively wide pores (e.g., voids in beads 122B and / or 122C) can be useful for achieving increasingly larger porosities for beads 122. As described herein, relatively wide (relatively large) pores can be particularly advantageous for hosting catalyst particles and / or storing ash, and the increased pore surface area can be advantageous for providing anchoring sites for ash or catalyst particles.

[0096] The beads 122 may be formed by preparing a batch mixture of ceramic-forming materials (e.g., ceramic materials and / or ceramic precursor materials), spheronizing the batch mixture into green aggregates, and then firing the green aggregates to sinter and / or react the ceramic forming materials into one or more selected ceramic phases, such as cordierite. For convenience of discussion herein (e.g., to avoid confusion with the batch mixture 110 utilized to form the honeycomb body 100), the batch mixture utilized to form the green aggregates that are fired into the beads 122 may be referred to as a precursor slurry mixture or simply a slurry mixture.

[0097] FIG. 10 illustrates representative steps (A)-(E) that may occur during the fabrication of beads 122 from green agglomerates according to some embodiments. Green agglomerates, prepared, for example, as a powder of spherical particles of agglomerated slurry mixture components, can be fired to partial or complete reaction to preserve the spherical shape of the green agglomerates to the resulting ceramic beads 122 upon firing. Firing may cause the green agglomerates to undergo several reactions, beginning with the burnout of binders, dispersants, and other organic materials, moisture loss of inorganic materials, and decomposition of any carbonates with the release of CO. Finally, depending on the particular ceramic precursors present, the onset of solid-state reaction may begin at temperatures between about 1000°C and 1200°C.

[0098] 10, green agglomerates 130 are formed as spherical particles having ceramic-forming materials. The green agglomerates 130 may be formed from an agglomerate slurry mixture having inorganic ceramic-forming materials (e.g., ceramic materials and / or ceramic precursors) that form one or more ceramic phases of the ceramic beads 122 during firing, such as talc, clay, alumina, boehmite, silica, magnesia (e.g., Mg(OH)2 or MgO), spinel, etc.; one or more binders (e.g., styrene-acrylic polymers or other polymers) to temporarily hold the shape of the green agglomerates 130 prior to firing; a pore-forming agent (e.g., resin, starch, graphite) to impart additional porosity to the beads 122, if desired; a dispersant to maintain loose particle packing; and any other additives (e.g., surfactants or antifoaming agents) to facilitate agglomerate formation or ceramic firing and / or reaction; and a liquid excipient (e.g., water). As described in further detail herein, the inorganic raw materials used to make 15-50 μm sized green agglomerates that can be fired to form ceramic beads of the same size can have a raw material median particle size in the range of about 3-5 μm or less, with the d90 values ​​of this raw material component typically being less than 7 μm, which particle size assists in achieving high open porosity and other properties disclosed herein.

[0099] The green agglomerates 130 can be produced by spheronization processes such as spray drying or rotary evaporation. For example, wet droplets are dried in a spray dryer and / or during mixing, converting (e.g., shrinking and / or condensing) to green agglomerates 130 upon water loss. Thus, spray drying and rotary evaporation can be used to efficiently produce dried green agglomerates 130 powder. Drying can be rapid under high airflow at elevated temperatures. The spherical shape of the green agglomerates 130 (e.g., as they exit a spray drying nozzle and / or are formed by a rotary evaporator) can exhibit high solids loading and low density of raw material particle packing, particularly for plate-like raw material particles such as talc. In some embodiments, the solids loading is about 10% to 30% by volume. A binder in the agglomerate slurry mixture can help hold the green agglomerates 130 together, thereby maintaining loose particle packing.

[0100] The spheroidized green agglomerates 130 are then fired, i.e., exposed to temperature for a time sufficient to cause conversion of the ceramic-forming mixture into porous spherical ceramic beads 122. Thus, steps (B) through (E) in Figure 10 show the green agglomerates 130 after firing over increasing amounts of time. Step (B) represents an early firing stage in which the binder material has burned off and all residual water (including from the water-containing materials) has been removed, but chemical reaction between the ceramic-forming precursor materials has not yet occurred.

[0101] As described in more detail herein, removal of the liquid excipient can cause migration of fine (e.g., less than 2 μm) solid particles toward the outer surface of the agglomerate as the liquid excipient wicks toward the outer surface and evaporates. This can cause the formation of a green shell 132 of particles at the outer surface of the agglomerate. The thickness of the green shell 132 can vary based on the raw materials in the aggregate slurry. For example, silica soot, colloidal silica, and other fine oxide particles (e.g., median particle size less than 1 μm) can be particularly contributory to the formation of the green shell 132 and the increase in the thickness of the green shell 132.

[0102] In step (C) of Figure 10, several solid-state reactions take place between the different ceramic-forming precursor materials. At this stage, the formation of one or more ceramic phases may begin, and thus the green agglomerates 130 begin to transform into ceramic beads 122. At this stage, the ceramic precursors have not fully reacted to the corresponding ceramic phases because the reaction is limited to the contact points between adjacent precursor particles. Further reaction of the ceramic precursors to arrive at larger amounts of selected ceramic phases is desirable in some embodiments to more fully establish the corresponding physical properties (e.g., strength) of the ceramic beads 122. However, as discussed in more detail below, at this stage, the particles forming the green shell 132 begin to react into the ceramic shell 133, which helps stabilize and strengthen the beads 122.

[0103] In stage (D), the reaction of the ceramic precursor materials spreads from the initial contact points throughout the ceramic precursor particles. Thus, in stage (D), one or more ceramic phases are fully formed or nearly formed, and the physical properties of the beads 122 are well established, for example, providing strength and toughness that prevent the beads 122 from collapsing during the subsequent mixing and extrusion processes. In stage (D), the ceramic beads 122 also exhibit an open pore structure 124.

[0104] While not wishing to be bound by theory, it is believed that shrinkage of beads 122 due to reaction of the ceramic precursors is limited at this stage because ceramic shell 133 helps stabilize and maintain the spherical shape of green agglomerates 130 as they transition into ceramic beads 122 during firing. However, if green shell 132 is too thick, the resulting ceramic shell 133 may sinter together with few or no openings 126, thereby inhibiting the formation of open pore pathways to the outer surface and resulting in hollow ceramic spherical particles. Therefore, the components of the aggregate slurry mixture can be selected to provide fine particles in amounts sufficient to create green shell 132 and resulting ceramic shell 133, but at a thickness that allows the formation of openings 126 in shell 133 during firing. Additionally or alternatively, the binder package and green agglomerate 130 formation conditions (e.g., spray dryer settings) can be selected to support migration of fine raw material particles to the agglomerate surface to promote the formation of green shell 132 (so that spherical shape and size are maintained during firing), but with a thickness that still allows openings 126 to form in shell 133 during solid-state reaction of the fine ceramic precursor materials during the subsequent firing and reaction stage.

[0105] As shown in stage (E) of Figure 10, further firing, e.g., at higher temperatures, longer durations, and / or in the presence of sintering aids (and / or glass or liquid formers), causes sintering or shrinkage resulting in dense particles with low or no open porosity (e.g., simply closed pores as shown in the image of stage (E) of Figure 10). At these advanced firing stages (e.g., "over-firing"), the spherical shape can no longer be maintained and the beneficial properties of high surface area and high open porosity can be lost.

[0106] Tables 1-4 provide various examples of slurry mixtures that can form green aggregates 130. For example, as described herein, the slurry mixtures can be formed into green aggregates 130 by a spheronization process, such as spray drying or evaporative mixing. In particular, the slurry mixtures in Tables 1-4 are suitable for green aggregates that can be fired to form porous ceramic beads 122 as cordierite-containing beads. All values ​​in Tables 1-4 are given as mass percent or, as indicated, as superadditive mass percent (mass % SA). In Tables 1-3, the inorganic components are added together to 100 mass%, while in Table 4, the sum of the starch pore former and inorganics is normalized to 100 mass%. The values ​​in micrometers (μm) in parentheses in the headings for some of the listed components indicate the approximate median particle size of the corresponding component. The slurry mixture can be aqueous-based (water as the liquid vehicle) with ceramic powder dispersants and / or binders to aid stabilization, but oils, alcohols, or other liquid vehicles can also be used with additives suitable for forming spherical green agglomerates. For example, in some embodiments, 2-3% of a styrene-acrylic copolymer (e.g., Duramax B1002, a material commercially available from The Dow Chemical Company) and 0.2%-1% of an ammonium salt of an acrylic polymer (e.g., Duramax D-3005, a material commercially available from The Dow Chemical Company) are added as a superadditive weight percent (wt% SA) based on the total weight of the other ingredients, even though other binders and dispersants can be added in the same amounts. Sodium stearate or other materials (e.g., other sources of sodium) can also be added as sintering aids to aid in the formation of ceramic beads during firing of the green agglomerates.

[0107] [Table 1]

[0108] [Table 2]

[0109] [Table 3]

[0110] [Table 4]

[0111] As outlined in Tables 1-4, various combinations of inorganic precursor materials can be used as cordierite precursors within green aggregates that are useful for producing cordierite beads upon firing. Generally, cordierite-forming slurry mixtures have a silica source, an alumina source, and a magnesia source. For example, the silica source can be clay (e.g., kaolin clay, kyanite clay, and / or hydrous clay), silica, silica soot, talc, clay, or other silicon-containing compounds. The alumina source can be clay (e.g., kaolin clay, kyanite clay, or hydrous clay), alumina, hydrous alumina, spinel, or other aluminum-containing compounds. The magnesia source can be talc, spinel, magnesium hydroxide, or other magnesium-containing compounds. The ceramic precursors, e.g., silica source, alumina source, and magnesia source, are included in amounts to provide the desired ceramic phase, or phases stable with minor variations in stoichiometry, composition, and substitution, such as Mg2Al4SiO4. 18The alumina, silica, and magnesia sources can be combined in amounts according to stoichiometric ratios to produce a phase such as cordierite having the general formula: ##STR00002## For example, in some embodiments, sources of alumina, silica, and magnesia are provided in ratios to form a desired primary ceramic phase, e.g., cordierite in an amount of at least 80% by weight of the ceramic article (and / or cordierite in an amount of at least 90% by weight of the crystalline phase). In some embodiments, the silica source, alumina source, and magnesia source are selected as cordierite precursors to provide a cordierite composition consisting essentially of about 49 to about 53% by weight SiO, about 33 to about 38% by weight AlO, and about 12 to about 16% by weight MgO.

[0112] FIG. 11 shows a flowchart of a method 200 for forming porous spherical ceramic beads (e.g., beads 122) and a method 300 for manufacturing a honeycomb body (e.g., honeycomb body 100) having a sintered network of porous spherical ceramic beads (e.g., network 120). In step 202, a slurry mixture of ceramic-forming raw material components is formed (e.g., according to any of Examples S1-S20). In step 204, the slurry mixture is spheronized into green agglomerates (e.g., green agglomerates 130). In some embodiments, spheronization is performed by spray drying. In some embodiments, spheronization is performed by a rotary evaporation process. Other processes, such as dry-pulverization, freeze-drying, laser melting, melt spinning, or liquid injection, can be used. The green agglomerates can be at least partially dried as part of the spheronization process or subsequent to the spheronization process. In step 206, the green agglomerates are fired under conditions (time and temperature) sufficient to convert the green agglomerates into porous ceramic beads (eg, beads 122).

[0113] In step 302, for example, porous ceramic beads obtained from method 200 can be used as the primary inorganic material in a batch mixture (e.g., batch mixture 110). In addition to the porous spherical ceramic beads, the batch mixture can have other ingredients, such as an organic binder, an inorganic binder material (e.g., a reactive cordierite-forming material), a pore-forming agent (e.g., starch, graphite, etc.), an oil or other lubricant, and a liquid carrier, such as water. In step 304, the batch mixture is formed (e.g., extruded through honeycomb extrusion die 18) into a green honeycomb body (e.g., green honeycomb body 100G). The green honeycomb body is converted into a ceramic honeycomb body (e.g., honeycomb body 100) by firing under conditions (time and temperature) sufficient for the porous ceramic beads to sinter together and / or react and / or sinter with any additional reactive inorganic binder material in the batch mixture.

[0114] Additional steps, such as drying and cutting, may be performed prior to firing. Because the ceramic beads have already reacted to form cordierite and / or any other selected ceramic phases, the firing temperature and / or firing time in step 306 can be significantly reduced compared to honeycomb bodies formed from reactive precursor materials. As described herein, because the ceramic beads have already reacted, the beads have sufficient strength to withstand the honeycomb body manufacturing process, such as mixing in an extruder and extrusion through a honeycomb extrusion die, without losing their spherical shape. Similarly, because the beads have already reacted, the beads sufficiently maintain their size and shape during firing of the honeycomb body in step 306, thereby creating a microstructure for a honeycomb body having an interconnected network of porous ceramic beads sintered together (e.g., interconnected network 120).

[0115] Optionally, in step 308, the passages (e.g., passages 104) of the ceramic honeycomb body can be plugged to form a plugged honeycomb body (e.g., plugged honeycomb body 101). For example, the plugged honeycomb body can be used as a particulate filter or a wall-flow filter. Optionally, in step 310, a catalytic material can be deposited into and / or on the porous walls (e.g., walls 102) of the ceramic honeycomb body, for example, by washcoating or other process. In some embodiments, the honeycomb body is both plugged and supports the catalytic material. [Example]

[0116] Various examples are now described for making green aggregates 130 made from the slurry mixtures of Tables 1-4, porous ceramic beads 122 made from the green aggregates 130, batch mixtures 110 having porous ceramic beads 122, and honeycomb bodies 100 made from the batch mixtures 110. While the beads in the examples discussed herein were made primarily from cordierite, it is reiterated that other materials or ceramic phases can be used for the beads 122. For example, cordierite generally exhibits good strength, durability, and environmental resistance, making it a convenient material for use as honeycomb bodies in engine exhaust aftertreatment. However, aluminum titanate, mullite, silicon carbide, and other ceramic materials (and combinations thereof) have also been successfully used in exhaust aftertreatment or other fluid treatment systems. Thus, as described herein and evidenced by modeling performed by or on behalf of the inventors, the combination of bead size distributions and inter- and intra-bead features described herein provides unique properties and performance that are exhibited by honeycomb bodies formed from beads having the same bead size distributions and inter- and intra-bead features, even if the beads were made from materials other than cordierite (and / or other ceramic phases in combination with cordierite).

[0117] Unsintered agglomerates Aqueous-based aggregate slurry mixtures containing cordierite precursor materials stabilized with low levels of organic binders and dispersants were used as raw materials in the spray-drying process. In particular, Table 5 shows various examples of green aggregates produced at different solid loadings using the slurry mixtures in Tables 1-4. The raw materials were slowly added to the water while mixing using a high-powered turbomixer (rotostator). To avoid clustering of raw material particles within the slurry, the raw materials were directly sucked into a slurry tank below the water level. The binder and dispersant were then added.

[0118] [Table 5]

[0119] Examples A1-10, A1-15, and A1-21 were made from the same slurry mixture (S1) at different solids loadings (10 vol.%, 15 vol.%, and 21 vol.%, respectively). Examples A1-10, A1-15, and A1-21 may be collectively referred to herein as "Example A1." Similar to the different solids loadings for Example A1, the solids loadings for green aggregates formed from any other slurry mixture, e.g., slurry mixtures A2-A20, may differ from those given in Table 5. Furthermore, the solids loadings shown in Table 5 are intended as estimates that may vary, for example, by up to 0.5 vol.%, when the slurry mixtures are actually made. In some embodiments, the solids loading in the spray-dried slurry mixture is about 8 vol.% to about 35 vol.%, e.g., 10 vol.% to 30 vol.%.

[0120] A medium-scale industrial spray dryer equipped with a two-fluid injection nozzle or rotary atomizer was used to spray dry the different combinations of slurry mixtures and solids loadings in Table 5 to form green agglomerates. Rates ranging from 6 kg / h to 20 kg / h were used. Spray dryer settings for forming the green agglomerates included an inlet temperature of 200°C, a cyclone temperature of 98°C, an inlet air velocity corresponding to a velocity head loss of 330 to 360 in. H2O (8382 mmH2O to 9144 mmH2O), and a cyclone air velocity corresponding to a head loss of approximately 5 in. H2O (127 mmH2O).

[0121] Two-point collection was used in the chamber and cyclone of a medium-scale spray dryer to separate smaller particle sizes (captured in the cyclone) from larger particles (captured in the main chamber). Different sizes and shapes of spray dryers, as well as different nozzle configurations and spray drying parameters, provide different size distributions. For example, a taller spray drying tower may be able to provide more refinement and may not require two-point collection to achieve the same particle size distribution.

[0122] Table 6 summarizes the particle size distribution values ​​collected for the green agglomerates of Table 5, as recorded for particles collected in both the chamber and cyclone for the spray drying apparatus used. In particular, Table 6 lists the d10, d50, and d90 values ​​as (d90-10) / d50 (i.e., this is the "d" of the corresponding particle size distribution). breadth " or "width") and d50-d10 / d50 (i.e., this is referred to herein as "d f " or "d factor "). As used herein, d10 refers to the particle size in the distribution where 10% of the particles are relatively small (90% are relatively large), d50 refers to the median particle size (50% of the particles are relatively large and 50% are relatively small), and d90 refers to the particle size in the distribution where 90% of the particles are relatively small (10% are relatively large).

[0123] [Table 6]

[0124] Capturing particles in both the spray dryer chamber and the cyclone outlet facilitates the ability to select or manipulate the particle size distribution of the agglomerates and / or beads made from the agglomerates as desired. For example, the cyclone collection point captures a smaller size fraction of the particles, while the chamber captures a larger size fraction of the particles. Further manipulation of the particle size distribution can be achieved by sorting or sieving the particles (e.g., green agglomerates or calcined beads) by removing the coarse (large) and / or fine (small) tails of the particle size distribution. In this manner, a narrow particle size distribution can be obtained for the green agglomerates (and the resulting ceramic beads after calcination). In some embodiments, a powder of green agglomerates is formed (e.g., by sorting and / or sieving) such that the median particle size (d50) of the green agglomerates in the powder ranges from about 10 μm to 80 μm, about 15 μm to 60 μm, or even about 20 μm to 50 μm. In some embodiments, the width of the particle size distribution of the green agglomerates 130 (given by (d90-d10) / d50) is less than 1.5, less than 1.0, less than 0.9, or even less than 0.8. factor (given by (d50-d10) / d50) is less than 0.5, less than 0.4, or even less than 0.3. Additionally or alternatively, air classification, sieving, or other processes can be used to remove one or more particle size ranges from the resulting particle size distribution to adjust the particle size distribution.

[0125] Figures 12A-12H show representative examples of spray-dried green aggregates A1, A2, A8, A9, A10, A11, A12, and A13 from Table 6 as collected from the spray-drying chamber (not the cyclone). More specifically, Figures 12A-12H show surface SEM images and polished cross-section SEM images for each of these green aggregate examples. To observe the polished cross-sections, the powders were impregnated with epoxy resin, sliced, and polished.

[0126] 12A-12H, it can be seen that spherical particles were consistently obtained despite a variety of different raw material mixtures (per Tables 1-4). However, the different raw material combinations used affected particle packing density and the formation of green shells from the fine particles (e.g., as described above with respect to green shell 132). Notably, green agglomerate Example A2 demonstrated the relationship between the amount of very fine raw material components and the thickness of green shell structure 132, since green agglomerate Example A2 used comparable high amounts of very fine components (e.g., silica soot with a median particle size of approximately 0.5 μm and hydrous alumina with a median particle size of approximately 0.1 μm per Table 2) and produced the thickest and most pronounced green shell.

[0127] cordierite beads The green agglomerate powders were then converted to cordierite bead powders in a firing process. The green agglomerate powders were fired in a variety of ways, including on alumina trays or setters, in batch furnaces, and / or in rotary calciners. While the specific firing equipment is not known to have a significant effect on the resulting cordierite beads, rotary calcination helped prevent sticking (sintering) in some examples. For example, green agglomerate Examples A1, A2, A3, A4, A17, and A20 could all be converted by firing on trays and showed no significant sticking of the green agglomerates to each other or to the trays. Other green agglomerate example powders benefited from rotary calcination to avoid sticking to the furnace equipment.

[0128] For batch rotary calcination, an electrically heated tube furnace was used in batch mode with a rotation speed of 1-3 rpm. Alumina tubes approximately 5 inches (12.7 cm) in diameter and 1 meter long were used. Typical furnace loads were 1.5 kg-2 kg. The furnace was charged and heated with the charge to a temperature between approximately 600-700 °C at a rate of 100-150 °C / h without closing the furnace tube (which allows air circulation and removes organic binder burnout products). The tube ends were then closed and heated at the same rate to a maximum temperature of 1350-1410 °C, held (or "soaked") for the desired time, and then cooled to room temperature at a rate of 100-150 °C / h. Typical hold times at maximum temperature ranged from approximately 4 h to 16 h.

[0129] For continuous rotary calcination, the green agglomerates were fed into the heated zone of the furnace and the calcined powder was collected at the tube outlet.

[0130] The green aggregate powder was loaded into a dense alumina setter box measuring 11.5 inches by 19 inches by 5 inches (approximately 29.21 cm by approximately 48.26 cm by approximately 12.7 cm), although any size setter box or tray can be used. Typical setter box loads for the tested examples were 4 kg to 7 kg. To help prevent the spherical particles from sticking to each other or to the tray (sintering), the temperature and / or firing time can be reduced, thereby maintaining the resulting cordierite beads as individual spherical particles.

[0131] As mentioned above, the green aggregates can be converted to partially to fully reacted cordierite spherical particles (cordierite beads) during high-temperature firing through several decomposition, solid-state reaction, and sintering steps. Depending on the nature of the aggregate slurry mixture raw materials, complete conversion of the precursor spheres required different temperatures and calcination times.

[0132] Microstructural evolution was followed as a function of firing temperature for examples of green aggregate powders and the resulting cordierite beads, and the resulting pore size and porosity values ​​are shown in Tables 7A-7D. Porosity and pore size within the beads were systematically evaluated by mercury intrusion porosimetry (MIP) and, for selected powders, by SEM and tomography. For example, tomography was used to confirm that beads made from slurry mixtures S1 and S6 had less than 1% closed porosity. SEM was performed on images with multiple bead cross sections to infer statistical values ​​for porosity and pore size.

[0133] Porosity values ​​were generated by MIP measurements of calcined cordierite beads using an Autopore IV 9500 porosimeter. Specifically, calcined cordierite bead powder was packed into a test vessel, sealed, and then mercury pressure was increased and infiltration measured. According to the MIP technique, as the pressure is increased, the inter-bead voids first fill rapidly at relatively low pressures, and then the smaller intra-bead pores are infiltrated next. As the pressure increases, the smaller and smaller pore bottlenecks are overcome, allowing pores to infiltrate beyond the bottleneck. This resulted in a dependence of mercury pressure on pore bottleneck size (reported as "intra-bead pore size" in Tables 7A-7D). Therefore, because only open porosity can be infiltrated and measured by the MIP technique, all porosity values ​​in Tables 7A-7D relate to open porosity.

[0134] A bimodal pore size distribution was obtained for each measured powder, with a first peak at a relatively small median pore size and a second peak at a relatively large median pore size. The median pore size may be referred to herein as D50 (denoted by an uppercase "D" in contrast to the median particle size d50, denoted by a lowercase "d"). The second peak, corresponding to the larger "pore size," corresponds to voids or openings between beads in a powder bed packed into a closed container (e.g., this is similar to and corresponds to the interstices 128 that define interbead porosity when beads 122 are sintered together into network 120), while the first peak, at the smaller pore size, corresponds to intrabead porosity within the beads. An example of a similarly bimodal pore size distribution with interbead and intrabead porosity resulting from beads 122 sintering into network 120 is described in more detail below in connection with FIG. 17. Using a simple separation of the contributions of powder / bead bed packing (first, larger peak) and intra-bead porosity (second, smaller peak) to the overall porosity, it was possible to isolate the intra-bead porosity and intra-bead pore size within the beads, with the corresponding values ​​summarized in Tables 7A-7D. The unit of "time" may be abbreviated as "hr" or simply "h" in any of the tables herein.

[0135] [Table 7A]

[0136] [Table 7B]

[0137] [Table 7C]

[0138] [Table 7D]

[0139] Within the fired powder, each bead is expected to deviate to some extent, so the reported intra-bead material porosity herein can be considered an average value for the beads (e.g., some beads within a sample or honeycomb body made using ceramic beads may have an intra-bead porosity that is less or greater than the intra-bead material porosity indicated).

[0140] As noted above, because mercury intrusion was utilized, the porosity and pore size values ​​in Tables 7A-7D refer to open, accessible passageways within the pores. This data was generally consistent with microscopic observations (e.g., by analysis of SEM images). In some embodiments, the porosity of the bead material (the intra-bead porosity of each bead relative to the volume of each bead) when fully reacted is at least 15%, at least 20%, or even at least 25%, e.g., about 15%-60%, 15%-50%, 15%-40%, 20%-60%, 20%-50%, 20%-40%, 25%-60%, 25%-50%, or 25%-40%.

[0141] Instead of conducting detailed compositional analysis of the fired beads to assess whether the beads are fully reacted, the maximum firing temperature and hold time can be used as a proxy to indicate whether the precursors in the green agglomerates have sufficiently reacted into cordierite beads. In some embodiments, cordierite beads obtained from firing green agglomerates at a temperature of at least 1300°C for at least 8 hours are considered sufficiently fully reacted. Thus, in some embodiments, the cordierite beads have an intra-bead open porosity (based on the volume of each bead) of at least 15%, at least 20%, or even at least 25%, e.g., about 15% to 60%, 15% to 50%, 15% to 40%, 20% to 60%, 20% to 50%, 20% to 40%, 25% to 60%, 25% to 50%, or 25% to 40%, after firing at a temperature of at least 1300°C for at least 8 hours. Thus, green aggregate examples A1, A2, A3, A4, A6, A8, A9, A10, A11, A12, A13, A15, and A16 all exhibited high open porosity at sufficiently high reaction levels in these embodiments.

[0142] Cordierite beads can also be evaluated based on their resistance to densification. For example, in some embodiments, cordierite beads made from green agglomerates yielded ceramic beads having at least 20% open intrabead porosity when fired at a maximum temperature of 1350°C for 8 hours, such as Examples A1, A3, A4, A6, A8, A10, A11, A13, A15, and A16, all of which exhibited a relatively low tendency to densify at higher firing temperatures. In some embodiments, cordierite beads made from green agglomerates yielded ceramic beads having at least 20% open intrabead porosity when fired at a maximum temperature of at least 1400°C, such as Examples A1, A3, A6, A8, A11, A15, and A16, all of which exhibited particularly good resistance to densification, even at the highest range of available firing temperatures.

[0143] Porosity data for green aggregate powder examples using slurries similar to Example A1 (e.g., Examples A6, A15, and A16 made from slurry mixes with starch but otherwise similar to Slurry Mix A1) showed that they maintained consistently high porosity over the entire temperature range tested. That is, the porosity decreased more slowly (slightly densified) with increasing temperature than observed in the other examples (i.e., Examples A1, A6, A15, and A16 were less sensitive to higher firing temperatures). Thus, Examples A1, A6, A15, and A16 may be particularly well suited for embodiments in which complete reaction of the cordierite beads (e.g., higher maximum temperatures and / or longer hold times) is desired.

[0144] The rice starch in Examples A6 and A15 did not appear to significantly affect open pore channel size or open porosity (compared to Example A1, which was made from a similar slurry mixture without starch), as the median open pore size was approximately 2 μm to 3 μm for beads 122 made from Examples A1, A6, and A15. The addition of corn starch, which has a larger median particle size than rice starch, in Example A16 did not appear to affect open porosity overall, but did substantially widen the median open pore size, e.g., to above 5 micrometers. Thus, the addition of corn starch, or other starches with relatively large particle sizes, may be advantageous in embodiments where relatively large intra-bead pore sizes are desired. Beads 122 made from Example A16 exhibited a particularly broad pore size distribution, with pore channels covering a size range of approximately 2 μm to 10 μm. The addition of larger talc particles (e.g., in Example A7) compared to smaller talc bases (e.g., in Examples A2 and A4) also appeared to cause an early and rapid loss of open porosity within the fired ceramic beads 122, resulting in only a small amount of open porosity (e.g., the green shell transformed into a dense ceramic shell) near 1300°C. These examples demonstrate that magnesium hydroxide in the precursor slurry generally correlated with relatively high open porosity in the fired beads. Thus, magnesium hydroxide is included as a magnesia source in some embodiments, particularly where higher intra-bead porosity is desired. In contrast, pure oxide precursor mixtures such as MgO, SiO2, Al2O3, or complex oxides such as MgAl2O4 appear to interact primarily via solid-state diffusion and reaction at the contact points between beads, with little or no glass or liquid formation, and therefore react only at extremely high temperatures compared to other examples, resulting in these beads sintering readily under shrinkage with relatively little or no intra-bead porosity.

[0145] Figures 13A-13D show the microstructural evolution of representative examples of green agglomerates and resulting ceramic beads as a function of firing temperature. More specifically, Figures 13A-13D show polished SEM cross sections of green agglomerate particles ("GRN") and resulting beads fired for 4 hours at temperatures of 1200°C, 1250°C, 1300°C, 1350°C, 1380°C, and 1410°C. For green particles containing bound water in the form of hydroxides, hydrated oxides, etc., all of the water was released below the 1200°C temperature shown in Figures 13A-13D. For green agglomerate powders with starch additive, starch burnout also occurred below 1200°C, leaving discernible pores (e.g., with a relatively large median pore size) at the locations of starch burnout seen in the corresponding examples of Figures 13A-13D. In general, for all of the green agglomerate examples analyzed, there were no other significant microstructural changes compared to the green agglomerates up to temperatures of about 1200° C. or higher.

[0146] The reaction toward the formation of cordierite generally begins above 1200°C, under the formation of relatively large pores and interconnected pore channels. As discussed herein, the formation of a ceramic shell (e.g., due to migration of fine green particles toward the outer surface of the green aggregate during drying) helps prevent bead shrinkage during firing. As a result, instead of undergoing densification, the porosity within the beads generally coarsens (expands) as the temperature increases from about 1200°C to about 1300°C or 1400°C, resulting in relatively large interconnected pore channels initially developing over the temperature range shown in many of the examples in Figures 13A-13D. However, as discussed further herein, as the temperature increases, diffusive transport and viscous flow of glass or liquid can occur within the time frame used for firing (e.g., 8 hours or less) for some examples, causing the porous spheres to densify into dense spheres under shrinkage.

[0147] Calcined cordierite beads made from green agglomerates with starch (e.g., beads from Examples A6, A15, and A16) initially showed the presence of relatively large pores in the range of 1200°C to 1250°C. The proportion of these relatively large pores increased with the proportion of starch (see, e.g., beads made from Examples A6 and A15). The size of the pores may also be affected by the type of starch. For example, rice starch (Examples A6 and A15) has smaller particles than corn starch (Example A16), and therefore generally produces beads with smaller pores during starch burnout.

[0148] At temperatures of about 1300°C, porosity begins to decrease in some particle types, while in others, it is maintained up to about 1400°C. For example, cordierite beads made from green aggregate powder Example A1 maintained significant high open porosity up to 1410°C with only slight densification. In contrast, cordierite beads formed from green aggregate powder Example A2, which exhibits a thick outer layer of fine particles forming the green shell 132 described above, developed a hard ceramic shell 133 during firing, resulting in very low levels of open porosity. At 1300°C, beads formed from green aggregate Example A2 significantly shrunk, densified, and began to sinter together. Beads formed from green aggregate powder Example A6 (containing starch) had higher porosity than examples without starch (e.g., Example A1), but also showed the onset of premature sintering above 1350°C, which led to the formation of increasingly larger pores. The porosity and pore size of beads made from green agglomerate Example A15 appeared significantly consistent with those made from Examples A1 and A6 over the temperature ranges shown in Figures 13A-13B. Beads made from green agglomerate powder Example A16 exhibited high open porosity with large pores due to the presence of cornstarch, and this porosity and pore channels remained significantly stable up to 1410°C. Beads made from green agglomerate powder Example A7 initially had a microstructure comparable to those made from green agglomerate powder Example A2 (which had a similar slurry mix to Example A7), but starting at about 1300°C, the beads from Example A7 became increasingly dense. Thus, the beads from green agglomerate Example A7 provide an example of spherical, dense particles after firing at relatively high temperatures (e.g., about 1300°C).

[0149] The ceramic phases present in the calcined powders were identified by X-ray diffraction (XRD). A Bruker D4 diffraction system equipped with a multi-strip LynxEye high-speed detector was utilized. Regardless of the specific green aggregate used, the amorphous (glassy) content was generally found to rapidly decrease during firing between 950 and 1150°C, then stabilize at approximately 10% glass by mass upon firing above 1250°C and subsequent cooling. In situ XRD showed that the amorphous / glassy phase can reach up to 50% at intermediate calcination stages for some compositions. The measured amount of glass in the calcined powder often depends on the powder cooling rate. For rapidly cooled powders, a maximum of 30% amorphous / glass was observed after firing below 1350°C, while for slowly cooled powders, the glass content was less than 7%. The onset temperature for cordierite (including the polymorph indialite) formation was approximately 1200–1250°C. The secondary phases and their exact amounts may vary for beads 122 made from each green agglomerate powder and may be the result of raw material impurities and / or stoichiometry. Secondary phases include sapphire, mullite, spinel, pseudobrookite, etc.

[0150] Table 8 provides examples of ceramic phase compositions obtained for beads produced at the two highest firing temperatures (1380°C and 1410°C) in Tables 7A-7D. Blanks in Table 8 indicate incomplete or invalid data. Only cordierite (including its polymorph indialite), sapphirine, and spinel phases are shown in Table 8. Because indialite is a polymorph of cordierite, any general reference to the amount of "cordierite" herein includes the sum of both cordierite and indialite phases. Rietveld refinements were used to quantify the contributions of phases that typically only include crystalline phases (no glass). Estimates of the glass phase are provided based on an amorphous background fit; therefore, it is understood that estimates of glass levels may have higher error bars than crystalline phases.

[0151] [Table 8]

[0152] Examples A18 and A19 were extremely underreacted after the firing conditions shown in Tables 7A-7D and 8, failing to develop any significant porosity upon firing and resulting in high levels of cristobalite, quartz, alumina, spinel, and sapphire. As a result, some compositions (e.g., Examples A18 and A19) may require extremely high temperatures and / or significantly long holding times to form cordierite. For example, significantly long firing times, e.g., up to 15 or even 20 hours, may be required to complete the reaction of the reactive ceramic precursors in Examples A18 and A19. Most clay, talc, or clay-talc-derived mixtures are readily converted to cordierite, and thereby to porous cordierite beads, under the conditions in Tables 7A-7D and 8. Only a few examples, including Example A2, developed porous structures that were not open porosity (i.e., closed porosity not visible based on MIP data but identified from a combination of SEM and tomography data analysis).

[0153] The formed ceramic beads having a high percentage of cordierite phase consistently exhibited high open porosity at all test temperatures. In other words, beads with a high percentage of cordierite composition generally were less sensitive to firing temperature (i.e., generally exhibited high resistance to densification even at relatively high temperatures), while lower cordierite beads were more sensitive to densification at relatively high temperatures. Thus, green aggregate powders resulting in a relatively high percentage of cordierite phase are advantageous in some embodiments to ensure that the beads can be fully reacted. Fully reacted beads may be particularly advantageous to enable relatively high-temperature firing of the final ceramic honeycomb body 100 without densification of the beads during firing of the final honeycomb body. In some embodiments, the beads 122 have at least 75%, at least 80%, or even at least 85% by weight cordierite (again, including the weight percent of indialite).

[0154] Calcination was also performed at very slow heating rates (10°C / h to 20°C / h) for the green agglomerate powder examples, and the resulting differential scanning calorimetry (DSC) results were analyzed. At relatively low temperatures (e.g., about 250°C to 450°C), binder / dispersant burnout was observed. The primary mass release for most green agglomerate powders was observed at about 400°C. In the temperature range of about 400°C to about 1000°C, decomposition reactions of hydroxides and carbonates were observed, resulting in the release of water and / or CO2. Hydrous raw materials include hydrous alumina, magnesium hydroxide, clay, and talc. Because bound water is significantly or even completely preserved during slurry preparation and spray drying, the spray-dried green agglomerate powder contains hydrous compounds. The decomposition of these compounds is observed as an endothermic reaction. Decomposition of hydrous alumina is observed at approximately 300°C, decomposition of magnesium hydroxide at approximately 400°C, dehydration of clay at approximately 520°C, and dehydration of talc at approximately 920°C, although the water loss temperatures may vary due to batch interactions.

[0155] Various mechanisms were investigated for this effect of establishing and maintaining high open porosity during calcination. In the first study, DSC was used to identify water and CO2 release phenomena within spray-dried agglomerates. The effects of water, CO2, and / or CO2 release during decomposition of hydrous species and carbonates were then correlated with porosity data from several calcined agglomerates to identify gradual changes in intra-bead porosity evolution that correlate with water or CO2 loss, e.g., whether the formation of water vapor or other gas bubbles causes the formation of high intra-bead porosity. High water loss at relatively high, moderate, or low maximum calcination temperatures was found not to cause intra-bead porosity formation during calcination of green agglomerate examples. Similar results were found regardless of the carbonate level in the green agglomerate powder used. Finally, no correlation was found between the green agglomerate powder and the development of intra-bead porosity, particularly with water or other gas-releasing raw materials (e.g., carbonates).

[0156] In a second investigation, we evaluated whether an intermediate glass or liquid contributes to or inhibits the development of intra-bead porosity during firing. In situ X-ray diffraction (XRD) and DSC were used to identify the onset of glass formation in several green aggregate powder examples, as shown in the table. The slurry mixtures used to make these aggregate powders contained various raw material combinations and compositions, with and without sodium (Na) addition. DSC and in situ XRD indicated that partial melting within the 1265°C to 1300°C temperature range did not necessarily correlate with the final intra-bead porosity. The sodium addition and the earlier onset of glass formation in Examples A2 and A3 compared to the sodium-free A1 and A4 had limited or no effect. No significant correlation was found between glass / liquid formation and intra-bead porosity. Varying the firing cycle around the glass formation threshold for various green aggregate powders also had no effect on the development of intra-bead porosity.

[0157] In a third study, a clear correlation was found between poor (low-density) particle packing of the platy raw material (e.g., talc) and the occurrence of intra-bead porosity during firing. However, simply having large platy raw material was found to be insufficient. The use of excessively large platy raw material in some cases resulted in fired beads that were no longer spherical and / or broke into fragments (e.g., beads made from Example A7, an agglomerate formed from a clay-silica-alumina-talc mixture containing 15% large talc, and beads made from Example A12, an agglomerate formed from a mixture of clay and Mg(OH)2 that also had large talc particles). In some embodiments, the maximum dimension of the platy raw material is within at most 40%, at most 35%, at most 30%, or even at most 25% of the median particle size of the fired beads. For example, it was found that platy raw materials having a median particle size of up to about 10 μm are suitable for beads having a median particle size in the range of about 30 μm to 40 μm, but not for beads with smaller median bead (particle) sizes. Furthermore, high levels of platy raw materials did not necessarily promote the formation of intra-bead porosity during firing, as some beads fired from green agglomerates containing high talc slurry mixtures (e.g., beads made from green agglomerates Examples A17 and A18) maintained their agglomerate shape and did not develop intra-bead porosity. As previously described herein, the use of magnesium hydroxide in general, and high levels of magnesium hydroxide in particular (e.g., as the sole magnesia source) promoted the formation of high intra-bead open porosity.

[0158] Shrinkage of spray-dried green particles during sintering and / or solid-state reaction firing was also avoided by adding a sufficient proportion of fine particles to the slurry making the green agglomerates. As described in connection with FIG. 10, outward migration of the fine particles as a result of drying during green agglomerate formation causes the formation of green shell 132, which is converted to ceramic shell 133 during firing. The shell of the fine particles can be made thick enough for the rigidity of the spherical particles, thereby protecting them from shrinkage during sintering and solid-state reaction and helping to maintain bead size and porosity during high-temperature firing. However, as shown for beads made from green agglomerate powder Example A2, an excessively thick shell of the fine particles can promote sintering, densification, and / or high closed porosity.

[0159] Table 9 shows some representative calcination conditions that have been useful for complete reaction of various green agglomerate powders, although other conditions are possible as described herein.

[0160] [Table 9]

[0161] As evidenced by Table 9, many of the green aggregate powders could be converted to cordierite beads using a firing cycle with a heating rate of about 150°C / h, a maximum temperature of about 1350°C to 1415°C, and / or a hold time of 6 to 8 hours. In some embodiments, the heating rate is in the range of 100°C / h to 200°C / h, although other suitable rates are possible. Green aggregates containing both spinel and silica were shown to generally benefit from higher temperatures and / or longer hold times to achieve complete reaction. Powders containing talc, clay, and hydrous alumina components were generally converted at lower maximum temperatures and / or shorter hold times, e.g., 1350°C to 1380°C for 4 to 6 hours. A continuous rotary calciner was also able to successfully react the green aggregates and produce a high percentage of cordierite at these temperatures with short soak times of 20 minutes to 1 hour.

[0162] In general, heating rates of less than 200°C / h to a maximum temperature (e.g., a temperature of at least 1250°C) have been found to allow for the formation of fully reacted ceramic beads while maintaining the pore structure of the beads. For example, relatively high heating rates of 300°C / h to a maximum temperature (e.g., a temperature of at least 1250°C) have been found to cause an increased loss of porosity within the beads. While not wishing to be bound by theory, it is believed that densification at relatively high heating rates may be due to significant glass formation and accelerated sintering and reaction. In some embodiments, maximum temperatures of at least 1100°C, at least 1200°C, at least 1250°C, or at least 1300°C are suitable. In some embodiments, hold times of about 4 to 12 hours are suitable.

[0163] Table 10 shows the d10, d50, d90, d90-d10, and (d90-d10) / d50 values ​​obtained for cordierite beads formed from the various green agglomerate powders of Table 5 fired according to the conditions of Table 9. Multiple runs were performed for some of the examples to illustrate some variability in the properties of cordierite beads made from the same or similar green agglomerate powders under the same or similar firing conditions.

[0164] [Table 10]

[0165] Green agglomerate powder examples A1, A2, A3, A4, A6, and A17 successfully produced porous cordierite beads with high open porosity, example cordierite beads B1, B2, B3, B4, B6, and B17, respectively. However, green agglomerate powder examples A18, A19, and A20 produced cordierite beads B18, B19, and B20, respectively, were all dense cordierite beads with low open porosity.

[0166] The evolution of cordierite beads made from some of the green agglomerate powder examples during firing was previously described in connection with Tables A7-A7D and Figures 13A-13D. Correlatedly, cordierite beads B1, B2, B6, and B17 had microstructures corresponding to those made from the same green agglomerate examples at corresponding temperatures in the evolution of Tables A7-A7D and Figures 13A-A13D. For example, bead B1 (formed by firing green agglomerate example A1 from Tables A7-A7D at a maximum temperature of 1380°C) had a microstructure corresponding to the same stage of evolution as green agglomerate example A1 fired at a maximum temperature of 1380°C in Figure 13B. 13A-13D, cordierite bead example B1 exhibited large open porosity and narrow interconnected open pore passages (e.g., similar to representative beads 122A and / or 122B of FIGS. 9A and / or 9B), and cordierite beads B6, B15, and B16 exhibited large interconnected open porosity and large interconnected open pore passages (e.g., similar to representative bead 122C of FIG. 9C). Cordierite bead example B2, which corresponds to an advanced stage of green aggregate powder example A2 at 1350°C-1380°C of FIG. 13B, exhibited high intra-bead porosity but a thick outer ceramic shell with low interconnectivity and low intra-bead pore access (e.g., few or no openings 126).

[0167] The calcined cordierite bead powders made from green agglomerate powder Examples A1-A20 were characterized for sphericity by SEM and image analysis. Bead sphericity for the spray-dried beads, obtained by SEM image analysis as the aspect ratio between the smallest and largest bead dimensions, on a scale ranging from 0 (an infinitely long rod or plate) to 1 (a perfect sphere), was determined to be greater than 0.9. Additionally, Table 11 shows the calculated circularity and average circularity values ​​for a representative sampling of cordierite beads made from green agglomerate Examples A1, A8, A10, A11, and A12, as indicated.

[0168] [Table 11]

[0169] Circularity in Table 11 was calculated as the circumference of a circle having the same area as the bead divided by the circumference of a cross-section of the packed bead, and circularity was calculated as the diameter of a circle having the same area as the bead divided by the longest cross-sectional dimension (diameter) of the bead. For circularity, the two variables were determined as an average of all beads in an analysis of SEM images of a representative powder sample. For circularity, this value was calculated by first measuring the largest dimension of each bead to calculate the circularity of each bead individually, and then averaging the individually recorded circularity values ​​to generate the average circularity value in Table 11.

[0170] In addition to high open porosity, the ceramic beads 122 disclosed herein can have a high internal surface area. High internal surface area provides particular advantages in some applications for the honeycomb body 100, for example, when the honeycomb body is prepared as a particulate filter or catalyst support. This high surface area can be particularly advantageous when beads 122 with high internal surface area and high intra-bead open porosity are combined with inter-bead porosity created by interstices 128 when the beads 122 are sintered into the network 120, as described herein.

[0171] Tomograms of the bead material were created and analyzed to further evaluate the properties of the beads 122, such as the intra-bead surface area (i.e., the surface area of ​​the pore structure 124 inside each bead 122). The intra-bead median pore size and intra-bead closed porosity were also estimated. The internal pore structure and outer surface of a representative sample of beads were analyzed to estimate the external or outer surface area of ​​the outer surface of the beads and the internal or intra-bead surface area within the beads. Tables 12A and 12B provide examples of the slurry mixtures and firing conditions used to create beads in the representative powder samples analyzed, as well as the median size of the green agglomerates corresponding to each analyzed powder sample. The surface areas in Table 12B were derived from the single-point method or the Brunauer-Emmett-Teller (BET) method, as indicated. The internal surface area was also evaluated in Table 12A for whether it was contributed by open or closed pore structure. Table 12A also lists the ratio of total internal bead surface area to external bead surface area and the ratio of open internal surface area to external bead surface area. The estimated extra surface areas calculated in Table 12B were determined by subtracting the estimated external surface area (thus corresponding to the approximate total surface area of ​​the dense beads) from the BET surface area of ​​the porous beads (which has both the external surface area and the internal surface area due to open porosity). For example, the external surface area of ​​the beads can be estimated by approximating the beads as spheres. Because smaller beads have less volume to create surface area, the estimated extra surface areas were also normalized to bead size in Table 12B by dividing the extra surface area by the median aggregate size for each bead.

[0172] [Table 12A]

[0173] [Table 12B]

[0174] The tomographic data are useful for identifying trends, but are not precise because the tomographic resolution used (0.3 μm / voxel) cannot account for pores and passages smaller than approximately 0.6 μm. Table 13B lists both BET multipoint and single-point surface area measurements for various ceramic beads. While the BET measurement has the advantage of including even the smallest pore passages and thereby having good accuracy, this measurement only provides the total surface area combined with the intra-bead surface area and the bead's external surface area. However, the trends for both measurements agree well (and are consistent with the simple model in Table 13, described below), showing, for example, that beads made from aggregates A1 and A8 have a significant contribution of intra-bead surface area compared to beads made from aggregates A2, A12, and A13. It was also demonstrated that relatively small beads (e.g., about 18 μm median particle size) made from agglomerate Example A1 have substantially less surface area than relatively large (e.g., 30-35 μm) median particle size beads made from the same agglomerate Example A1.

[0175] In some embodiments, the ratio of open intrabead surface area to external surface area of ​​the porous ceramic beads is at least 5:1, at least 6:1, at least 7:1, at least 8:1, at least 9:1, or even at least 9.5:1, including any range including these ratios as endpoints, such as 5:1 to 10:1, 5:1 to 9.5:1, 5:1 to 9:1, 6:1 to 10:1, 6:1 to 9.5:1, 6:1 to 9:1, 7:1 to 10:1, 7:1 to 9.5:1, 7:1 to 9:1, 8:1 to 10:1, 8:1 to 9.5:1, 8:1 to 9:1, 9:1 to 10:1, 9:1 to 9.5:1, or even 9.5:1 to 10:1. In some embodiments, the closed porosity of the porous ceramic beads is at most 5%, at most 4%, at most 3%, or even at most 2.5%, including ranges having these endpoints, such as 0% to 5%, 0% to 4%, 0% to 3%, or 0% to 2.5%.

[0176] It can be seen that the beads made from slurry mix examples S1 and S8 have extremely high relative internal surface area to external surface area due to their relatively small median pore size and high open porosity. Due to the small amount of closed porosity in the beads made from slurry mix examples S1 and S8, the calculated surface area ratio does not change significantly relative to the high open porosity beads made from green aggregate examples A1 and A8 when the surface area for the closed porosity is excluded. In comparison, the beads made from green aggregate example A2 (slurry mix S2) have a relatively high closed porosity (e.g., due to the formation of ceramic shell 133 as described herein) and a large median pore size. As a result, the analyzed sample made from slurry mix S2 exhibits only an internal surface six times the external bead surface area, which further drops to a four-fold ratio when the closed porosity is excluded. Generally, the internal surface area decreases as the number of pores decreases and the size of the pores increases, but the open internal surface area decreases in association with an increase in closed porosity.

[0177] As noted above, there are trade-offs when considering either tomography-derived or BET surface area values. Simple models were also developed to experimentally validate observations from other techniques to further identify and evaluate trends. As such, the simple model values ​​presented in Table 13 are not expected to produce accurate predictions for any given scenario, but instead are expected to provide insight when considering trends among various scenarios.

[0178] According to the simple model, a simple approximation is that the surface area of ​​the bead (SB=4πr 2 ), the volume of the bead (VB=4 / 3πr 3 ), the volume of the pores / passages in the beads (VP=%P*VB), the volume of the pores / passages in the beads (V ch =πL(D 50 / 2) 2 ), the average surface area of ​​each pore / passage in the bead (S ch =2πL(D 50 / 2)), the number of pores / passages in the bead (N ch =VP / V ch ), and the total surface area of ​​all pores / passages (SN ch =N ch *S ch ) to calculate the approximate total surface area of ​​the beads (S = SN ch +SB), where r is half the median particle size (d50) of the beads, %P is the porosity of the beads, L is the average length of the pores / passages through the beads, and D 50 is the median diameter of the pore / passage. Furthermore, BET is ch The r value can be estimated from the model by (ρ + SB) / (ρ*VB*(1-%P)), where ρ is the density of the ceramic material. Table 13 summarizes the model calculations and shows the effect of changing the input values ​​of r, %P, and median pore size (D50) on the internal / external surface area ratio and the estimated BET value. For Table 13, ρ is 2.52 g / cm 3 and L is assumed to be equal to r on average, assuming the pores / channels extend throughout the entire bead.

[0179] [Table 13]

[0180] Alternative methods (apart from spray drying) for forming spherical ceramic beads were also investigated. In one embodiment, the same slurry mixture used in spray drying (i.e., Examples S1-S20) was dried in an oven, on a hot plate, and / or in a microwave, and the resulting cake was crushed into powder by grinding / sieving. This powder was then calcined to produce cordierite particles. However, as a result of grinding and / or sieving, the cordierite particles contained a large proportion of large, irregularly shaped agglomerates and small fragmented pieces or particles. These particles were not spherical and did not exhibit the advantageous intra- and inter-bead porosity described herein.

[0181] In other experiments, slurry mixtures (e.g., Examples S1-S20) were rapidly dried by rotary evaporation. Spherical-shaped green aggregate particles generally similar to the spray-dried aggregate Examples A1-A20, albeit somewhat more irregular (e.g., oval, oblate, teardrop-shaped, etc.), were obtained by rotary evaporation of the solvent from the slurry mixture, sieving the dried powder to a target particle size, and calcining the sieved powder at a maximum temperature above 1300°C to react the precursor raw materials to cordierite. This alternative process also provided microstructures similar to the spray-dried powder examples, with advantageously high open porosity and pore size distribution as described herein.

[0182] Figure 14 shows the microstructures of three cordierite beads produced by calcination: (i) Example A8, which was produced from slurry mixture S8 using the spray drying process described above; (ii) Example RV1, which was produced from slurry mixture S8 using the rotary evaporation process; and (iii) Example RV2, which was produced from slurry mixture S8 using the rotary evaporation process but further contained a pore-forming agent additive of 20% by volume cornstarch. As shown, green agglomerates with similar pore structures can be produced by the rotary evaporation technique. Furthermore, RV2 demonstrated that the addition of a pore-forming agent such as cornstarch can create relatively large pores, e.g., in the range of 5 to 10 μm for cornstarch. In other embodiments, smaller and larger starch particles can be used to form smaller and larger pores, respectively.

[0183] The porosity and pore size of the cordierite beads in Figure 14 were determined by mercury intrusion porosimetry. As shown in Table 14, there was a significant similarity in the porosity and pore size values ​​for Example A8, the green agglomerate derived from spray drying, and Example RV1, derived from a different rotary evaporation process, thereby indicating that rotary evaporation is a suitable alternative process to spray drying.

[0184] [Table 14]

[0185] Honeycomb body After preparing a powder of cordierite beads (e.g., ceramic beads 122) from a powder of green agglomerates (e.g., green agglomerates 130), various cordierite beads were included as components in a batch mixture (e.g., batch mixture 110), which was extruded to form a green honeycomb body (e.g., green honeycomb body 100G). The green honeycomb body was cut to length, dried, and then fired to form a ceramic honeycomb body (e.g., honeycomb body 100). The honeycomb body can be fired at a temperature lower than or similar to the temperature used to fire the cordierite beads, for example, in the range of about 1350°C to 1410°C. In some embodiments, the batch mixture, prior to addition of the liquid carrier and based on the total weight of the inorganic components in the batch, has at least 50%, at least 55%, at least 60%, at least 70%, at least 75%, at least 80%, at least 85%, or even at least 90% by weight porous ceramic beads, including ranges inclusive of these values ​​as endpoints, such as 55% to 95%, 55% to 90%, 55% to 85%, 55% to 80%, 60% to 95%, 60% to 90%, 60% to 85%, 60% to 80%, 70% to 95%, 70% to 90%, 70% to 85%, 70% to 80%, 75% to 95%, 80% to 95%, or 80% to 90% by weight. The inorganic binder, such as one or more ceramic precursor materials or shear binder aggregates as described herein, can be added to the porous ceramic beads in an amount such that the sum of these components adds up to 100% by weight, e.g., at least 5%, at least 10%, at least 15%, at least 20%, or at least 25% by weight, e.g., 5% to 25%, 5% to 20%, 5% to 15%, 5% to 10%, 10% to 25%, 10% to 20%, 10% to 15%, 15% to 25%, or 20% to 25% by weight.The pore-forming agent can be added in any suitable amount as a superadditive additive, for example, at least 10%, at least 20%, at least 30%, or at least 40% by weight, including any range inclusive of these values ​​as endpoints. The extrusion aid, e.g., oil, can be added in any suitable amount as a superadditive additive, for example, at least 0.5%, at least 0.75%, or at least 1% by weight, including any range inclusive of these values ​​as endpoints. The organic binder, e.g., methylcellulose, can be added in any suitable amount as a superadditive additive, for example, at 6% to 10% by weight or more.

[0186] In contrast to conventional reactive cordierite batches, which may require long and slow heating cycles to avoid defects such as crack formation, the use of already reacted (“pre-reacted”) cordierite beads allows for relatively rapid firing of honeycomb bodies with rapid ramp-up to maximum temperatures. Firing tests of full-size honeycomb bodies at ramp-up rates of 50°C / h, 100°C / h, 150°C / h, 200°C / h, and 300°C / h showed no appreciable difference in the resulting quality of the fired articles. The fired articles consistently exhibited excellent quality without cracking in both electric and gas furnaces. In some embodiments, the heating ramp rate is at least 50°C / h, at least 100°C / h, at least 150°C / h, at least 200°C / h, or even at least 300°C / h. Compared to conventional reactive cordierite batches, the hold time at maximum temperature was also extremely short, e.g., 4 h at 1380°C using a heating rate of 300°C / h. Thus, a complete firing cycle could be completed in 20 h instead of 50 h, 60 h, 80 h, or even 100 h for conventional reactive batch products.

[0187] In the first investigation, honeycomb bodies were extruded as 1-inch (approximately 2.54 cm) or 2-inch (approximately 5.08 cm) diameter elements using a ram extruder or as 2-inch (approximately 5.08 cm) diameter elements using a twin-screw extruder, and dried in a microwave dryer, followed by drying in a hot air oven, if necessary. For ram extrusion, the paste was first thoroughly mixed, for example, by passing it through a twin screw equipped with a screen and a large-opening die and / or by passing it through a spaghetti die several times, before being pressed through the ram extruder. For twin-screw extrusion, the batch mixture paste was loaded directly into the feeder for the extruder barrel. A screen package was generally used to protect the extrusion die and provide uniform batch paste flow. Additionally, the calcined cordierite beads were sieved, if necessary, through a 270- or 325-size mesh using an automated sieve, for example, to remove any remaining large-size agglomerates and thereby avoid blockage of the extrusion die slot during extrusion.

[0188] The extruded green honeycomb bodies were fired at temperatures between 1340°C and 1420°C for 4 to 6 hours. At these times and temperatures, the cordierite beads were generally fully reacted before being added to the batch mixture, and firing times for the honeycomb bodies were kept short because no further solid-state conversion within the beads was required (only reaction of any reactive inorganic binder material added to the batch mixture and / or sintering between the beads was required). Firing was conducted in air without special oxygen control. Heating rates were generally between 100°C / h and 300°C / h (although slower heating rates and / or holds were used between about 400°C and 1000°C during organic burnout).

[0189] The ease of extrusion was found to be related to the ratio of the slot width of the extrusion die to the particle size distribution of the beads used in the batch mixture. Extrusion was carried out using a variety of different dies, including 600 / 4, 200 / 8, 300 / 8, 300 / 13, 300 / 14, and 300 / 15 dies (according to their designations, the first number indicates the approximate cells per square inch (cpsi) of the die, and the second number indicates the approximate slot width of the die), although other die configurations can also be used. In some embodiments (e.g., for dies with relatively thin slots, such as the 300 / 8 configuration), the median particle size of the cordierite beads in the batch mixture (e.g., where the inorganics can comprise 80% or more by weight of the batch mixture) was greater than 15% of the die width, or even greater than 20%, and the d90 value for the cordierite beads was 20% to 40% of the slot width. For example, the width of the slot in a 300 / 8 die may be about 200 μm, with the median bead size (d50) value for the cordierite beads being above 50 μm and the d90 value of the cordierite beads being greater than 50 μm, 60 μm, or even 70 μm. In some embodiments, it has been particularly advantageous to keep the d90 or d95 size of the cordierite beads less than one-third (e.g., 20% to 33%) of the slot width to prevent blockage of the slot by relatively large beads.

[0190] Cornstarch, rice starch, pea starch, and graphite were used as pore-forming agents, although other pore-forming agents can also be used to create pores. Methylcellulose functioned well as an organic binder to enable extrudability and maintain the shape of the green honeycomb body. The use of superadditive amounts of oil up to 10% by weight (based on the total weight of inorganics) and superadditive amounts of sodium stearate up to 2% by weight (based on the total weight of inorganics) was investigated, and the extrudability of the batch mixtures was clearly improved with some oils and some ratios of oil to sodium stearate. The addition of tall oil, stearic acid, and lubricating oil with antioxidant additives ("MOX oil") was investigated. MOX oil consistently performed well both alone and with the addition of sodium stearate. However, as described herein, many batch mixtures required unexpectedly high water demands to successfully produce honeycomb bodies. Higher feed rates were also possible than with comparable conventional reactive component batch mixtures.

[0191] Tables 15A-15E list a first set of batch mixtures and extrusion conditions used to successfully form (extrude) honeycomb bodies. The extruded green honeycomb bodies were converted to ceramic honeycomb bodies by a subsequent firing step. The honeycomb bodies have cross-walls with a nominal wall thickness of about 13-15 mils (about 0.3302 mm to about 0.381 mm) ("300 / 13", "300 / 14", and / or "300 / 15" configurations) or 8 mils (about 0.2032 mm) ("300 / 8" configuration), as shown, although other wall thicknesses can be used. The honeycomb bodies have a density of about 300 cells per square inch (300 cpsi (about 46.5 cells / cm)). 2 )), but had a pressure of 200 to 1000 cpsi (approximately 31.0 to 155.0 cells / cm 2Other cpsi values, such as .0100 psi, can be used instead. The batch mixes of the examples in Tables 15A-15E had reacted cordierite beads, e.g., fully reacted cordierite beads, having an average bead (particle) size ranging from 18 μm to 50 μm. In some of the batch mixes of the examples in Tables 15A-15E, an inorganic reactive binder material (e.g., talc, alumina, silica, etc.) was added to the batch mix along with the spherical cordierite beads. In some of the batch mixes in Tables 15A-15E, shear binder agglomerates (described in more detail below) containing inorganic binder material were used in addition to and / or in place of a separate inorganic binder material.

[0192] [Table 15A]

[0193] [Table 15B]

[0194] [Table 15C]

[0195] [Table 15D]

[0196] [Table 15E]

[0197] As used herein, the term "shear binder agglomerate" or simply "shear binder" refers to green spherical particles formed from the slurry mixtures described herein (i.e., according to slurry mixture examples S1-S20) and in a manner apparently identical to the green agglomerates 130 described herein, although higher solids loadings may be used during the spray-drying or other spheronization process. That is, the shear binder agglomerates referred to herein are substantially the same as the disclosed green agglomerates (thus, for example, green agglomerates A1-A20, etc., may be used as shear binder agglomerates). In some embodiments, shear binders are made from the same slurry mixtures as the green agglomerate samples described herein, but optionally at higher solids loadings. For example, solids loadings of 15-50% by volume can be used to form shear binder agglomerates useful as inorganic binder components during the manufacture of honeycomb bodies (compared to the approximately 10-30% by volume solids loadings used for green agglomerates).

[0198] The shear binder agglomerates aid in sintering the beads by providing additional inorganic material concentrated at or spread between contact points with the beads due to shearing (or deformation) of the shear binder agglomerates during mixing with the beads. Pursuant to its function as an inorganic binder for the beads, and notwithstanding the fact that various organic components may be present in the shear binder agglomerates (e.g., binders or dispersants as shown in Tables 1-4), the total mass of the shear binder agglomerates is considered herein to be part of the total mass of the minerals in the batch mixture. Thus, in many of the examples in which shear binder agglomerates are used, the mass of the beads and the mass of the shear binder agglomerates add up to 100% of the total mass of the minerals in the batch mixture.

[0199] The corresponding slurry mixtures used for the shear binder aggregates are shown for the relevant examples in Tables 15A-15E. The same or different shear binder compositions can be used as the calcined cordierite beads for any given honeycomb extrusion. Successful combinations were made from calcined cordierite beads obtained without Na addition, but combined with shear binder green aggregates containing small amounts of Na (e.g., less than 2 wt. % based on the total weight of the minerals in the shear binder aggregate). Such combinations produce relatively low CTEs, allowing for the use of relatively low honeycomb firing temperatures and / or relatively short hold times, via glass formation at pore contact points.

[0200] The required water demand was much higher for batch mixtures containing cordierite beads with high open porosity (e.g., compared to conventional reactive raw material batches or batch mixtures with dense or closed porosity beads). For example, in some embodiments, the water demand was greater than 30%, 40%, or even 50% by weight, based on the total weight of the mineral, as a superadditive addition. Without wishing to be bound by theory, this high amount of water is believed to be necessary to fill the intra-bead porosity of the beads, which acts with high capillary forces to draw water into the intra-bead pore structure of the beads. Thus, the water level required for extrusion generally increased with increasing intra-bead open porosity of the cordierite beads and with the median particle size of the beads. In general, friction within the batch and wall drag of the extrusion paste along the die wall are extremely low, and large amounts of oil or other lubricant are of limited benefit, especially for dies with wide slots (e.g., the 300 / 13 and 300 / 14 dies tested).

[0201] Figures 15A-15D show the microstructure of a fired honeycomb body exhibiting the inter-bead and intra-bead porosity described herein. More specifically, Figures 15A and 15B show surface views of the wall (wall 102) surface at 500x and 2000x magnification, respectively, for honeycomb body embodiment H9. Figures 15C and 15D show wall cross-sectional and wall surface views, respectively, for a honeycomb body produced according to example H10. The inter-bead pore size (the size of the gaps 128 between beads 122) was in the range of 10-20 μm, and the intra-bead pore size (the size of the pores within the beads) was in the range of approximately 1-5 μm.

[0202] The honeycomb bodies were fired at maximum temperatures ranging from 1330°C to 1410°C, corresponding to the highest maximum temperatures used for the formation of cordierite beads, as described above. Generally, temperatures below 1350°C were too low to permit sufficient cordierite formation within the inorganic components of the shear binder in some embodiments, particularly in the shear binder aggregates produced from slurry mixture Example S2. The inclusion of sodium (e.g., in the form of sodium stearate) was found to be useful for allowing lower reaction temperatures (e.g., temperatures below 1350°C) than Na-free batch mixtures, but could also cause insufficient cordierite formation and correspondingly brittle articles if sodium was not present in sufficient amounts (e.g., at least 0.2%, at least 0.5%, or at least 1.0%).

[0203] Ceramic honeycomb bodies were formed by firing green bodies obtained by extruding the indicated batch mixtures in Tables 15A-15E at 1320°C-1415°C for 4-20 hours. Tables 16A-16D provide the phase compositions of honeycomb bodies made by firing green honeycomb bodies from some of the examples in Tables 15A-15E under the indicated firing conditions as determined by XRD analysis followed by Rietveld analysis for the materials. Glass levels were derived for some examples by semi-quantitative estimation. A blank entry for a ceramic phase in these tables indicates that the phase was not present, and a blank entry for glass instead indicates that the example was not analyzed for its glass content. Glass is expected to amount to up to 15% by weight in all fired honeycomb examples, and SEM analysis indicates that many examples have glass contents of less than 5% by weight. In some embodiments, the crystalline phase (thus excluding glass) comprises at least 90% by weight cordierite, or even at least 95% by weight cordierite.

[0204] [Table 16A]

[0205] [Table 16B]

[0206] [Table 16C]

[0207] [Table 16D]

[0208] As shown in Tables 16A-16D, firing of some honeycomb bodies utilized a "spike" in which the temperature was first temporarily raised to a "spike" temperature above the maximum soak temperature, and then, after a period of up to about 30 minutes, lowered to the maximum soak temperature and held at that temperature. For example, the firing condition "1380°C / 4h-1410°C spike" indicates that the temperature was first raised (spiked) to 1410°C, then lowered and held at 1380°C for 4 hours.

[0209] In some embodiments, the honeycomb body has at least 80%, at least 85%, or even at least 90% by weight of cordierite phase (including both cordierite and indialite), e.g., 80% to 95%, 85% to 95%, 90% to 95%, 80% to 90%, 85% to 90%, or 85% to 94% by weight. In some embodiments, the honeycomb body has less than 15% by weight, e.g., 4% to 11% by weight, glass. In some embodiments, the honeycomb body has less than 3%, less than 2.5%, less than 2%, or even less than 1% by weight of a secondary ceramic phase. The fully fired honeycombs did not exhibit any significant amounts of cristobalite (e.g., less than 0.1% by weight) and exhibited relatively lower levels of secondary phases, such as spinel and sapphirine, than the fired cordierite beads themselves (e.g., as shown in Table 8). Glass levels within the honeycombs were typically found to be about 8-11% by weight, although it should be noted that the glass levels were only semi-quantitatively determined from background adjustments in Rietveld analysis and are therefore subject to some degree of error. However, SEM examination experimentally confirmed the generally low levels of glass present in various honeycomb body examples, e.g., less than 15%, less than 10%, or even less than 5% by weight.

[0210] Tables 17A-17D and 18A-18D provide various porosity and thermomechanical properties obtained at the indicated firing conditions for various of the honeycomb body examples in Tables 15A-15E, respectively. Tables 18A-18D report both axial and tangential (tangential) CTE values ​​from room temperature (RT) to both 800°C and 1000°C, as well as both transverse and axial i-ratio values ​​for some of the honeycomb bodies analyzed.

[0211] [Table 17A]

[0212] [Table 17B]

[0213] [Table 17C]

[0214] [Table 17D]

[0215] [Table 18A]

[0216] [Table 18B]

[0217] [Table 18C]

[0218] [Table 18D]

[0219] The total porosity (the sum of both inter-bead and intra-bead porosity) of the wall material of the ceramic honeycomb body material was greater than 50% and in the range of 55% to 65%. The overall median pore size (including both inter-bead and intra-bead pore sizes) was in the range of about 6 μm to about 12 μm. As described herein, the porosity of the wall material of the ceramic honeycomb body was bimodal, with an inter-bead porosity in the range of about 45% to 60% and an inter-bead median pore size (interstitial size) in the range of about 7 μm to 13.5 μm. The intra-bead porosity (relative to the total volume of the honeycomb body wall) of the wall material of the ceramic honeycomb body was in the range of about 10% to 15%, with an intra-bead median pore size in the range of about 1.8 μm to 2.6 μm. The range of inter-bead porosity was extremely narrow with d90-d10 ranging from approximately 12 μm to 19 μm.

[0220] The inter-bead pore size was found to depend, at least in part, on the median bead size of the spherical cordierite beads used in the batch mixture (larger beads produce larger inter-bead median pore sizes). Similarly, the range of inter-bead porosity was found to depend, at least in part, on the width of the spherical bead size distribution (the narrower the width of the cordierite bead size distribution used in the batch mixture, the narrower the width of the inter-bead pore size distribution). For example, a wide range was intentionally introduced for the cordierite beads used in honeycomb body Example H6 by blending beads of two different median bead sizes, resulting in a wide range of inter-bead pores for the resulting ceramic honeycomb body.

[0221] The coefficient of thermal expansion (CTE) of ceramic honeycomb body materials has been found to depend at least in part on the size of the cordierite beads used, since the domains do not extend beyond the bead size. The microcrack parameter Nb is approximately 0.3, with a range of approximately 0.05 to 0.55. 3 are achieved, which allow for CTE values ​​for ceramic honeycomb bodies comparable to those achievable with conventional reactive batch honeycomb bodies.

[0222] The CTE and other thermomechanical properties of ceramic honeycomb bodies are highly isotropic, as indicated by direct measurements of the axial and tangential CTE or i-ratio of the material. Both the axial and tangential i-ratios were very similar for all honeycomb body materials fabricated from batch mixtures containing porous spherical cordierite beads. The ratio of the two values ​​is typically in the range of about 0.99 to 1.04. In comparison, the ratio of the two i-ratio values ​​for cordierite honeycomb bodies fabricated from conventional reactive batches can be on the order of 1.5 or greater. While not wishing to be bound by theory, this lack of anisotropy is believed to be due to the spherical shape of the beads, which do not undergo alignment during extrusion, compared to plate-like, rod-like, or other non-spherical particles with large aspect ratios that are forced to align with the flow direction through slots in a honeycomb extrusion die.

[0223] In some embodiments, the material of the ceramic article has an intra-bead median pore size (measured by MIP) of less than 5 μm, less than 4 μm, less than 3.5 μm, less than 3 μm, less than 2.5 μm, or even less than 2 μm, including ranges having these values ​​as endpoints, such as from 1.5 μm to 5 μm, preferably from 1.5 μm to 4 μm, from 1.5 μm to 3.5 μm, from 1.5 μm to 3 μm, from 1.5 μm to 2.5 μm, or even from 1.5 μm to 2 μm.

[0224] In some embodiments, the material of the ceramic article has a median inter-bead pore size (measured by MIP) of at least 6 μm, at least 7 μm, at least 8 μm, at most 20 μm, at most 19 μm, or at most 18 μm, including ranges having these endpoints, such as 6 μm to 20 μm, 6 μm to 19 μm, 6 μm to 18 μm, 7 μm to 20 μm, 7 μm to 19 μm, 7 μm to 18 μm, 8 μm to 20 μm, 8 μm to 19 μm, or 8 μm to 18 μm. As described herein, the median inter-bead pore size is proportional to the size of the beads used to make the ceramic article and, therefore, can be influenced by selecting (e.g., sieving) the particle size distribution of the beads used.

[0225] In some embodiments, the material of the ceramic article has a median pore size (measured by MIP) of at least 5 μm, at least 6 μm, at least 7 μm, at most 18 μm, at most 17 μm, or at most 16 μm, including ranges having these endpoints, such as 5 μm to 18 μm, 5 μm to 17 μm, 5 μm to 16 μm, 6 μm to 18 μm, 6 μm to 17 μm, 6 μm to 16 μm, 7 μm to 18 μm, 7 μm to 17 μm, or 7 μm to 16 μm.

[0226] In some embodiments, the intra-bead porosity (as measured by MIP) relative to the total volume of the interconnected bead network is at least 10%, at least 12%, at least 15%, at least 18%, at least 20%, or even at least 25%, including ranges having these endpoints, such as 10% to 30%, 10% to 25%, 10% to 20%, 10% to 15%, 12% to 30%, 12% to 25%, 12% to 20%, 15% to 30%, 15% to 25%, 15% to 20%, 18% to 30%, 18% to 25%, 20% to 30%, or even 25% to 35%.

[0227] Instead of the total contribution of intra-bead porosity to the overall porosity of a material formed by a network of interconnected beads, the intra-bead porosity can instead be considered with respect to the individual volume of the bead itself. In some embodiments, the intra-bead porosity (measured by MIP) with respect to the individual volume of the bead is at least 9%, at least 10%, at least 12%, preferably at least 15%, at least 18%, or even more preferably at least 20%, at least 25%, or even at least 30%, including ranges having these values ​​as endpoints, such as 9% to 42%, 9% to 35%, 9% to 30%, 9% to 90%, 9% to 95 ... ~25%, 9%-20%, 9%-15%, 10%-35%, 10%-30%, 10%-25%, 10%-20%, 10%-15%, 12%-35%, 12%-30%, 12%-25%, 12%-20%, more preferably 15%-35%, 15%-30%, 15%-25%, 15%-20%, 18%-35%, 18%-30%, 18%-25%, or even more preferably 20%-35% or 20%-30%.

[0228] FIG. 16A is a plot showing the bimodal porosity of the indicated honeycomb body example from Table 15A obtained from MIP. As shown, the bimodal porosity is defined by a first peak, or local maximum, for a small pore size, indicated by reference numeral 134, corresponding to the intra-bead median porosity and pore size, and a second peak, or local maximum, for a large pore size, indicated by reference numeral 136, corresponding to the inter-bead median porosity and pore size. In the illustrated embodiment, the intra-bead porosity 134 has a median pore size less than 5 μm (e.g., indicating about 1 μm to 3 μm), and the inter-bead porosity 136 has a median pore size greater than 5 μm (e.g., indicating about 8 μm to 14 μm). The local maxima of the plot can be determined by known mathematical techniques. In some embodiments, the first local maximum, corresponding to the intra-bead median pore size, is in the range of 0.5 μm to 5 μm. In some embodiments, the second local maximum, corresponding to the inter-bead median pore size, is in the range of 5 μm to 20 μm. The pore size distribution of a reference filter having a unimodal porosity is shown by the dashed line. As referred to herein, the reference filter was made by plugging a honeycomb body made by extrusion and firing of a conventional reactive material batch, i.e., a reactive material batch without pre-reacted beads.

[0229] FIG. 16B shows a plot of another example of a bimodal pore size distribution resulting from intra-bead and inter-bead porosity as described herein. The data in FIG. 16B was obtained by MIP. As shown in FIG. 16B, the bimodal pore size distribution is characterized by a first peak 240 corresponding to intra-bead porosity and a second peak 242 corresponding to inter-bead porosity. Accordingly, the first and second peaks may be referred to herein as the intra-bead and inter-bead pore size distribution peaks, respectively, or more simply, the intra-bead and inter-bead peaks. As described herein, for example, with reference to FIG. 16, the first and second peaks 240 and 242 can each be characterized by a median pore size, which can be determined as the local maximum of each of the peaks. Thus, in the example of FIG. 16B, the intra-bead median pore size corresponding to the first peak 240 is approximately 2 μm, occurring at a differential indentation of slightly more than 0.4 ml / g, and the inter-bead median pore size corresponding to the second peak 242 is approximately 13 μm, occurring at a differential indentation of approximately 16.5 ml / g.

[0230] Each of the peaks 240, 242 can also be characterized by a full width at half maximum (FWHM) value. In other words, it is the distance between opposite sides of the peak along the x-axis at a y-axis value equal to half the maximum value of the y-axis. The FWHM value provides a measure for characterizing the width (e.g., relative wideness or narrowness) of the pore size distribution peaks 240, 242. Accordingly, the FWHM values ​​of the peaks may be referred to herein as the intra-bead half-maximum pore size distribution peak width and the inter-bead half-maximum pore size distribution peak width, respectively. For example, the first peak 240 is labeled with an arrow 244 indicating the corresponding intra-bead half-maximum pore size distribution peak width for the first peak 240, and the second peak 242 is labeled with an arrow 246 indicating the corresponding inter-bead half-maximum pore size distribution peak width, as shown in FIG. 16B. In the example of Figure 16B, the maximum of the first peak 240 occurs at about 0.4 ml / g, so the intra-bead half-maximum pore size distribution peak width is measured at about 0.2 ml / g, corresponding to a value of about 2 µm. Similarly, in the example of Figure 16B, the maximum of the second peak 242 occurs at about 1.65 ml / g, so the inter-bead half-maximum pore size distribution peak width is measured at about 0.825 ml / g, corresponding to a value of about 5.5 µm.

[0231] In some embodiments, the intra-bead half-maximum pore size distribution peak width is at most 2.5 μm, at most 2 μm, or even at most 1.5 μm, including any range having these endpoints, such as 1.5 μm to 2.5 μm, 1.5 μm to 2 μm, 2 μm to 2.5 μm, or even 1 μm to 1.5 μm. In some embodiments, the inter-bead half-maximum pore size distribution peak width is at most 6 μm, at most 5.5 μm, or even at most 5 μm, including any range having these endpoints, such as 5 μm to 6 μm, 5 μm to 5.5 μm, 5.5 μm to 6.0 μm, or even 4.5 μm to 5 μm.

[0232] As also shown in FIG. 16B , a valley may exist between the two peaks 240, 242, which can be defined as a local minimum 248 in the pore size distribution between the intra-bead and inter-bead peak maxima. Generally, these peaks become more pronounced and narrower as the local minimum approaches zero. In some embodiments, the local minimum 248 has a value less than the intra-bead half-maximum pore size distribution peak width, as shown in FIG. 16B . In some embodiments, the local minimum 248 has a value less than 20%, less than 15%, or even less than 10% of the maximum of the inter-bead pore size distribution peak 242. For example, in the example of FIG. 16B , the local minimum 248 has a value of about 0.175 ml / g, which is less than 15% of the inter-bead peak maximum of about 1.65 ml / g.

[0233] Some of the honeycomb body examples in Tables 15A-15E were used to fabricate particulate filters. To fabricate the filters, 2-inch (approximately 5.08 cm) diameter honeycomb bodies extruded through a 300 / 8 die were cut to 6-inch (approximately 15.24 cm) lengths, and the opposite end faces (e.g., end faces 106 and 108 in Figures 1-2) were masked and plugged with cordierite plugging cement in a checkerboard pattern (e.g., as shown for plugged honeycomb body 101 in Figure 2). A reference filter was also fabricated from a batch mixture having reactive raw ingredients (without porous cordierite beads). All honeycomb bodies used to make the filters were extruded through the same die, but the reactive component filters and the porous cordierite bead filters had different cell shapes (primarily due to growth of the reactive component honeycomb bodies during firing), so the cell shapes were 285 cpsi (approximately 44.2 cells / cm) for the filters made from batch mixtures containing cordierite beads. 2 ) for filters made from reactive feedstock batch mixtures, and 315 cpsi (approximately 48.8 cells / cm 2) These filters were evaluated as is, i.e., without any additional membranes, coatings, or other materials applied after firing. The diameter and coating thickness also differed proportionally with the difference in cpsi. As a result, standardization to the same geometry was necessary to compare filter performance for the same properties.

[0234] FIG. 17 shows plots of mass-based filtration efficiency (FE) as a function of soot load for the reference filter and multiple filters made from the honeycomb body examples in Tables 15A-15E. As soot load increases, the filtration efficiency of all filters asymptotically approaches 100%. However, it can be seen that the reference filter has a substantially lower clean (no soot load) filtration efficiency (e.g., about 70% FE for the clean case, increasing to about 80% at 0.01 g / L soot). All filters made from the honeycomb body examples in Table 15A with porous cordierite beads had substantially higher clean filtration efficiencies. In all cases, the clean FE (no soot load) was greater than 80%, and in some cases, even greater than 90%. Furthermore, the filtration efficiency at 0.01 g / L soot exceeded 90% for all of the filters with porous beads, many of which exceeded 95%, 96%, 97%, or even 98% FE.

[0235] Figure 18 is a plot showing the pressure drop, in terms of backpressure at zero soot load, for the various filters of Figure 18 as a function of gas (exhaust) flow. After standardizing the geometry of the reference filter to that of the tested example filters (because filtration efficiency depends on dimensional values ​​such as length, diameter, cpsi, etc., the reference filter was modified to have the same geometry as the example filters), apparently similar pressure drop values ​​were achieved for all the tested filters. Similar observations were made regarding backpressure as the filters were increased in load from zero soot to 5 g / L soot load.

[0236] FIG. 19 is a plot showing pore surface area relative to pore volume as a function of material porosity. The characteristic of open (accessible) intra-bead pore surface area relative to intra-bead open porosity correlates with filtration efficiency. More specifically, it is understood that intra-bead pore paths become more numerous and tortuous as the ratio between pore surface area and volume increases. The pore surface area for filters made according to honeycomb body Examples H1-H5 (filled circles) is substantially greater than the pore surface area of ​​a reference filter made from a reactive component batch (triangles). Data corresponding to a filter with cordierite beads made from aggregate Example A2 (slurry mixture Example S2) is also provided (open circles); this filter did not have the high open pore surface area described above and therefore did not demonstrate favorable filtration efficiency when used in a neat clean particulate filter (although this filter may exhibit beneficial properties or characteristics for other applications).

[0237] One contributing factor to high filtration efficiency is the morphology of the intra-bead porosity (i.e., pore structure 124). That is, the pore structure 124 is organized in the form of interconnected serpentine channels, with serpentine pore channels extending to and connecting through the outer surface of the bead at openings 126. These pore channels that penetrate the outer bead surface have high capillarity (narrow opening geometry). High capillarity generates a correspondingly high capillary force that attracts small particles, such as soot or ash, in the gas (exhaust) stream. The high intra-bead surface area of ​​the intra-bead pore structure 124 provides abundant capture sites for particulate matter after it is attracted to the bead by capillary forces. As a result, filtration efficiency generally increases as the median pore size decreases and as the number of serpentine intra-bead pore channels intersecting the bead surface increases.

[0238] In another study, several ceramic honeycomb bodies made according to the examples in Tables 15A-15E and fired at the conditions shown in Table 19 were evaluated to measure their respective BET surface area values. Table 19 also includes intra-bead porosity values ​​for the ceramic honeycomb bodies analyzed so that a comparison can be made between surface area and intra-bead porosity.

[0239] [Table 19]

[0240] Figure 20 shows the BET-derived values ​​of specific surface area as a function of intra-bead porosity contribution. From Figure 20, it can be seen that there is a clear relationship between specific surface area and intra-bead porosity. That is, as the intra-bead porosity in bead 122 increases, the bead surface area increases proportionally. In general, beads with high intra-bead open porosity have high internal surface areas by BET, while beads with lower open porosity and / or higher closed porosity have relatively small surface areas. Expectedly, the internal open surface area within the bead also decreases with decreasing median bead size.

[0241] In a separate investigation, honeycomb bodies having so-called "full size" diameters were fabricated (e.g., diameters greater than 4 inches (approximately 10.16 cm), corresponding to sizes applicable to or used in current automotive exhaust aftertreatment systems). Table 20 shows the batch mixtures and extruder conditions for fabricating these additional honeycomb body examples. All cordierite bead powders used to form the examples in Table 20 were sieved to 325 mesh size (approximately 44 μm) and were all formed through a "200 / 8" shaped extrusion die attached to a ram extruder.

[0242] [Table 20]

[0243] The green honeycomb bodies extruded according to Examples H27-H31 were then fired to obtain ceramic honeycomb bodies. The porosity properties for the ceramic honeycomb bodies produced from Examples H27-H33, fired under the indicated firing conditions, were measured and are shown in Table 21.

[0244] [Table 21]

[0245] Honeycomb firing cycles with short hold times of only up to 4 hours at the maximum temperature have been used successfully. Such short firing cycles with high heat-up rates and short maximum soak times allow for extremely high throughput (e.g., through a tunnel kiln), but green goods can also be successfully fired using longer soak times (e.g., greater than 4 hours) and slow heat-up rates (e.g., less than 50°C / hour). However, the use of longer maximum temperature hold times (e.g., 9-10 hours, as shown in Table 21), especially at higher temperatures (e.g., 1400°C or higher), generally results in densification of the beads and, therefore, correspondingly lower porosity.

[0246] In particular, because the inorganic components of the cordierite beads have already reacted during firing of the beads, as described herein, the components of the batch mixture for the honeycomb body need not be subjected to a significant degree of further reaction. For example, reaction may be limited only to reactive inorganic components in the inorganic binder and / or shear binder aggregates added to the batch; these reactive inorganic components assist in sintering the cordierite beads together, and the beads themselves are not subjected to a significant degree of further reaction. Furthermore, even if the beads are subjected to some additional reaction, material diffusion paths are limited only within each individual bead and / or at contact points between the beads, as described herein.

[0247] As disclosed, the pre-reacted nature of the porous cordierite beads also enables the beads to remain stable in size, dimensions, and porosity during extrusion and firing of the honeycomb body. Such porosity and dimensional stability is particularly achievable when the maximum honeycomb firing temperature is selected to be at least slightly lower (e.g., at least 5°C to 10°C lower) than the maximum firing temperature used to form the beads. Thus, in the tested green articles, essentially only the pore former must be burned out; minor inorganic binder components, such as those contained in the green shear binder aggregates, must be exposed to reaction into cordierite, i.e., must assist in binding the cordierite beads together into network 120.

[0248] The ceramic materials of the produced ceramic honeycomb bodies exhibited the bimodal pore size distribution described herein, with interbead porosity and corresponding interbead pore size set by bead packing, and intrabead porosity of the bead material itself, with a corresponding intrabead median pore size. All honeycomb body examples exhibited a total porosity (interbead + intrabead) greater than 50%, with many examples having a total porosity greater than 60%. The median pore size was approximately 9-15 μm, based on the cordierite beads used. More specifically, the median bead size significantly determined the interbead packing and, therefore, the interbead pore size (distance between beads) of the resulting honeycomb body.

[0249] Table 22 shows the phase assemblages of the ceramic honeycomb bodies obtained by Examples H27 to H31 fired under the indicated firing conditions.

[0250] [Table 22]

[0251] The ceramic honeycomb body was then plugged to form a wall-flow filter. The honeycomb body yielded an extremely high percentage of cordierite (along with the indialite polymorph), e.g., greater than 90%, 95%, 96%, 97%, or even 98% by weight. Secondary ceramic phases, such as sapphirine, spinel, rutile, mullite, and / or pseudobrookite, were generally present in amounts less than 5%, 4%, 3%, or even 2% by weight.

[0252] Honeycomb bodies with bimodal porosity and high interbead surface area also exhibit advantageous properties for use as substrates or supports for supporting catalytic materials. In some embodiments, honeycomb bodies (e.g., manufactured according to any of the embodiments described herein) are both plugged (as described above) and support catalytic materials to function as particulate filters. In some embodiments, honeycomb bodies are plugged without supporting catalytic materials, while in other embodiments, honeycomb bodies support catalytic materials without being plugged. Support of catalytic materials within the porous walls of ceramic honeycomb bodies can be achieved, for example, by a washcoating process in which the catalytic material is carried onto and / or into the porous walls by a liquid carrier in a washcoat slurry, resulting in the deposition of the catalytic material.

[0253] Tests were conducted to evaluate the applicability of the porous, spherical cordierite bead honeycomb bodies described herein for loading catalytic material and to assess the interaction of these honeycomb bodies with the washcoat process. The honeycomb bodies were immersed in slurries containing ultrafine (approximately 0.5 μm median particle size) and fine (approximately 1.5 μm median particle size) alumina particles. The alumina slurries were selected to serve as a substitute for catalytic washcoats. Figures 21A and 21B show SEM cross sections of cordierite honeycombs made from Example H12 immersed in high-solids loading slurries containing ultrafine and fine alumina particles, respectively. The alumina particles of the washcoat could be seen to be drawn into the intra-bead pores (intra-bead pore structure 124) in the porous beads, leaving the inter-bead channels (interstices 128) around the beads open for gas (exhaust) flow (thereby maintaining a desirable pressure drop when used in a filter). Without wishing to be bound by theory, it is believed that, as previously described, capillary forces promote interaction between the catalytic material deposited within the intra-bead pore structure and the exhaust gases during use of such catalyst-supported honeycomb bodies.

[0254] In another study, various honeycomb bodies were formed, optionally plugged, and then washcoated with a washcoat slurry as described herein. After plugging, the honeycomb bodies prepared here as wall-flow filters were then washcoated to a washcoat concentration of approximately 75-80 g / L. The washcoat slurry contained a fine support of alumina particles with a median particle size of up to approximately 1 μm, with a bimodal distribution of fine particles in the submicron range and larger particles in the median size range of approximately 7-10 μm, along with larger alumina, zirconia, and ceria particles. The 7-10 μm washcoat particles did not fully penetrate the relatively small intra-bead pores. However, the smaller washcoat particles penetrated the porous ceramic walls and were uniformly distributed within the inter-bead pore spaces. Both the relatively small and larger washcoat particles were anchored in the bead network around the outside of the beads within the inter-bead pore spaces without significantly reducing the inter-bead pore size. The washcoat particles appeared to be well anchored on the cordierite bead surface within the bead surface pores, thus providing a high accessible surface area to promote catalytic activity.

[0255] Figures 22A and 22B show SEM images of a fracture surface of a washcoated porous ceramic wall of an exemplary washcoated honeycomb body made from aggregate A1 at approximately 500x magnification and a representative portion of the fracture surface of an exemplary washcoated honeycomb body at approximately 3000x magnification, and Figure 23A shows a polished surface of an exemplary washcoated honeycomb body at approximately 1000x magnification, with the circled area in Figure 23A being further enlarged in Figure 23B. In Figures 22A-23B, the cordierite material is shown in gray, the pores are shown in black, and the washcoat particles are shown in white. As described herein, due to the large surface area of ​​the open pores of the beads, it can be seen in Figures 22A-23B that the catalyst material is well distributed within the open pore structure of the beads as well as on the outer surface of the beads. Furthermore, due to the bimodal pore size distribution, many of the inter-bead pores (interstices between the beads) remain substantially unblocked and open even after washcoating, thereby allowing for low pressure drop when the honeycomb body is prepared as a filter and providing high catalytic activity with catalytic material supported within and / or on the internal and / or external surfaces of the beads.

[0256] The bimodal nature of the pore size distribution is also reflected in the percentile pore size values ​​of the pore size distribution (e.g., D10, D50, and D75 values). As used herein, percentile pore size values ​​indicate that D10 is the pore size value in the pore size distribution that is greater than 10% of the pores in the pore size distribution, D50 is the median pore size value (the pore size value in the pore size distribution that is greater than 50% of the pores in the pore size distribution), D75 is the pore size value that is greater than 75% of the pores in the pore size distribution, etc.

[0257] As described herein, pore size percentile values ​​(e.g., D10, D50, D75, D90) can be used to characterize the bimodal nature of the pore size distribution. For example, the presence of an intra-bead peak (e.g., peak 240 in FIG. 16B ) not found in the pore size distribution of ceramic articles made from conventional reactive batches results in a concentration of small pores and a corresponding D10 value that is significantly smaller than the D10 value occurring in ceramic articles made from reactive batches. Table 23 shows the D10, D50, and D75 values, as well as the D50 / D10 and D75-D50 values, for ceramic bodies made from the various honeycomb body examples described above.

[0258] [Table 23]

[0259] Ceramic bodies made from conventional reactive batches do not have a bimodal pore size distribution, for example, as discussed above with respect to Figures 16A and 16B. For ceramic articles with at least 50% porosity, D10 is expected to be >6 μm, D50 about 8-18 μm, D75 >16 μm, D50 / D10 <2, and D75-D50 >3 μm. In some embodiments described herein, for a porosity of at least 50% (e.g., 50% to 70%, e.g., 55% to 65%), D10 is less than 4 μm, or even more preferably less than 3 μm, less than 2.5 μm, or even less than 2 μm, including ranges having these values ​​as endpoints, such as 2 μm to 4 μm, 2 μm to 3 μm, 2 μm to 2.5 μm, 2.5 μm to 4 μm, 2.5 μm to 3 μm, or even 1.5 μm to 2 μm.

[0260] As a result of the concentration of smaller pores corresponding to the intra-bead peak, the D50 / D10 value is also significantly higher compared to ceramic articles made from reactive batches that do not have a bimodal pore size distribution. In some embodiments, the D50 / D10 value is greater than 2.5, or more preferably greater than 3, greater than 4, or even greater than 5, and in some cases up to 6, including ranges having these values ​​as endpoints, such as 2.5 to 6, 3 to 6, 4 to 6, or even 5 to 6.

[0261] Due to the bimodal pore size distribution and aided by the narrow pore size distribution peak widths of the intra- and inter-bead peaks (e.g., as described with respect to Figures 16A-16B), the difference between the D75 and D50 values ​​(i.e., D75-D50) is also narrow. In some embodiments, the D75-D50 value is less than 2.5 μm, or more preferably less than 2 μm, or even less than 1.5 μm, including ranges having these values ​​as endpoints, such as 1 μm to 2.5 μm, 1 μm to 2 μm, or even 1 μm to 1.5 μm.

[0262] Because the D50 of the final ceramic article is significantly affected by the inter-bead median pore size, which in turn is significantly affected by the median particle size of the beads used to make the ceramic article, the D50 will depend at least in part on the median particle size of the beads used to make the ceramic article. Thus, the selected median particle size of the beads can be used to engineer the resulting D50 of the ceramic article.

[0263] For example, it has been found that a median bead size in the range of about 25 μm to 50 μm generally corresponds to a D50 of the ceramic article of up to about 20 μm (more specifically, in the range of about 8 μm to 18 μm). For example, selecting beads having a relatively large median bead size (e.g., a d50 of about 50 μm) can be used to shift the median pore size (D50) of the resulting ceramic article toward a larger value (e.g., toward a D50 of 18 to 20 μm, or even larger values ​​as larger beads are used). Similarly, selecting beads having a relatively small median bead size (e.g., a d50 of 25 μm) can be used to shift the median pore size (D50) of the resulting ceramic article toward a relatively small value (e.g., toward a D50 of 8 μm, or even smaller values ​​as smaller beads are used).

[0264] In accordance with the disclosure herein, the median particle size (d50) of the beads can be influenced, affected, or even set by removing one or more size fractions from the bead powder. In some embodiments, the removal of one or more bead fractions (e.g., the larger or smaller tails in the particle size distribution) is achieved by sieving. For example, removing larger size fractions can be performed to reduce the median bead size, and removing smaller size fractions can be performed to increase the median bead size.

[0265] 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 claimed subject matter. Accordingly, claimed subject matter is not to be restricted except in light of the attached claims and their equivalents.

[0266] Preferred embodiments of the present invention will be described below in detail.

[0267] Embodiment 1 1. A ceramic article comprising: a porous ceramic material having a microstructure comprising an interconnected network of porous spherical ceramic beads, said microstructure having a total open porosity defined as the sum of the intra-bead open porosity of said beads and the inter-bead porosity defined by the interstices between said beads within said interconnected network; the microstructure has a bimodal pore size distribution having an intra-bead peak corresponding to the intra-bead open porosity and an inter-bead peak corresponding to the inter-bead porosity, wherein the intra-bead porosity has an intra-bead median pore size that is smaller than the inter-bead median pore size of the inter-bead porosity; Ceramic articles.

[0268] Embodiment 2 2. The ceramic article of claim 1, wherein the intra-bead open porosity is at least 10% relative to the total volume defined by the interconnected network, and the inter-bead porosity is at least 40% relative to the total volume of the interconnected network.

[0269] Embodiment 3 3. The ceramic article of claim 1 or 2, wherein the intra-bead open porosity is at least 9% by volume of the bead and the total porosity is at least 50%.

[0270] Embodiment 4 4. The ceramic article of any one of claims 1 to 3, wherein the ceramic beads comprise at least 80% by weight cordierite.

[0271] Embodiment 5 5. The ceramic article of any one of claims 1 to 4, wherein the porous ceramic beads comprise at least 85% by weight cordierite.

[0272] Embodiment 6 6. The ceramic article of any one of claims 1 to 5, wherein the crystalline phase of the porous ceramic material comprises at least 90% by weight cordierite.

[0273] Embodiment 7 7. The ceramic article of any one of claims 1 to 6, wherein the crystalline phase of the porous ceramic material comprises at least 95% by weight cordierite.

[0274] Embodiment 8 8. The ceramic article of any one of claims 1 to 7, wherein the porous ceramic beads have a closed bead porosity of less than 5%.

[0275] EMBODIMENT 9 9. The ceramic article of any one of claims 1 to 8, wherein the porous ceramic beads have a closed bead porosity of less than 2.5%.

[0276] Embodiment 10 10. The ceramic article of any one of claims 1 to 9, wherein the intra-bead open porosity is at least 12% by total volume.

[0277] Embodiment 11 11. The ceramic article of any one of claims 1 to 10, wherein the intra-bead open porosity is at least 15% by total volume.

[0278] Embodiment 12 12. The ceramic article of any one of claims 1 to 11, wherein the inter-bead porosity is at least 45%.

[0279] Embodiment 13 13. The ceramic article of any one of claims 1 to 12, wherein the inter-bead porosity is at least 50%.

[0280] Embodiment 14 14. The ceramic article of any one of claims 1 to 13, wherein the total porosity is at least 50%.

[0281] Embodiment 15 15. The ceramic article of any one of claims 1 to 14, wherein the total porosity is at least 55%.

[0282] Embodiment 16 15. The ceramic article of any one of embodiments 1 to 14, wherein the total porosity is at least 60%.

[0283] Embodiment 17 17. The ceramic article of any one of embodiments 1 to 16, wherein the bead-to-bead half-maximum pore size distribution peak width is at most 6 μm, as determined by mercury intrusion porosimetry.

[0284] Embodiment 18 18. The ceramic article of any one of embodiments 1 to 17, wherein the bead-to-bead half-maximum pore size distribution peak width is at most 5.5 μm, as determined by mercury intrusion porosimetry.

[0285] Embodiment 19 19. The ceramic article of any one of embodiments 1 to 18, wherein the intra-bead half-maximum pore size distribution peak width is at most 2 μm, as determined by mercury intrusion porosimetry.

[0286] Embodiment 20 20. The ceramic article of any one of embodiments 1 to 19, wherein the intra-bead half-maximum pore size distribution peak width is at most 1.5 μm, as determined by mercury intrusion porosimetry.

[0287] Embodiment 21 21. The ceramic article of any one of claims 1 to 20, wherein the bimodal pore size distribution has a local minimum differential indentation value at a pore size between the intra-bead median pore size and the inter-bead median pore size, as determined by mercury intrusion porosimetry, that is less than 20% of the maximum differential indentation value of the inter-bead peak.

[0288] Embodiment 22 22. The ceramic article of any one of claims 1 to 21, wherein the bimodal pore size distribution has a local minimum differential indentation value at a pore size between the intra-bead median pore size and the inter-bead median pore size, as determined by mercury intrusion porosimetry, that is less than 15% of the maximum differential indentation value of the inter-bead peak.

[0289] Embodiment 23 23. The ceramic article of any one of claims 1 to 22, wherein the bimodal pore size distribution has a local minimum differential intrusion value at a pore size between the intra-bead median pore size and the inter-bead median pore size, as determined by mercury intrusion porosimetry, the local minimum differential intrusion value being less than a value of the intra-bead half-maximum pore size distribution peak width.

[0290] Embodiment 24 24. The ceramic article of any one of claims 1 to 23, wherein the bimodal pore size distribution of the ceramic article has a D10 value of at most 3 μm, as determined by mercury intrusion porosimetry.

[0291] Embodiment 25 25. The ceramic article of any one of claims 1 to 24, wherein the bimodal pore size distribution of the ceramic article has a D10 value of at most 2.5 μm, as determined by mercury intrusion porosimetry.

[0292] Embodiment 26 26. The ceramic article of any one of claims 1 to 25, wherein the bimodal pore size distribution of the ceramic article has a D10 value of at most 2 μm, as determined by mercury intrusion porosimetry.

[0293] Embodiment 27 27. The ceramic article of any one of claims 1 to 26, wherein the bimodal pore size distribution of the ceramic article has a D75-D50 value of at most 2 μm, as determined by mercury intrusion porosimetry.

[0294] Embodiment 28 28. The ceramic article of any one of claims 1 to 27, wherein the bimodal pore size distribution of the ceramic article has a D75-D50 value of at most 1.5 μm, as determined by mercury intrusion porosimetry.

[0295] Embodiment 29 29. The ceramic article of any one of claims 1 to 28, wherein the bimodal pore size distribution of the ceramic article has a D50 / D10 ratio of at least 3, as determined by mercury intrusion porosimetry.

[0296] Embodiment 30 30. The ceramic article of any one of claims 1 to 29, wherein the bimodal pore size distribution of the ceramic article has a D50 / D10 ratio of at least 4, as determined by mercury intrusion porosimetry.

[0297] Embodiment 31 31. The ceramic article of any one of claims 1 to 30, wherein the bimodal pore size distribution of the ceramic article has a D50 / D10 ratio of at least 5, as determined by mercury intrusion porosimetry.

[0298] Embodiment 32 32. The ceramic article of any one of claims 1 to 31, wherein the total porosity is at least 55%, the inter-bead median pore size is between 6 μm and 20 μm, and the intra-bead median pore size is between 1.5 μm and 4 μm, as determined by mercury intrusion porosimetry, the bimodal pore size distribution has an inter-bead half-maximum pore size distribution peak width of at most 5.5 μm, and the bimodal pore size distribution has an intra-bead half-maximum pore size distribution peak width of at most 2 μm, and a local minimum differential indentation value of the pore size distribution located at a pore size between the intra-bead median pore size and the inter-bead median pore size is less than 15% of the maximum differential indentation value of the inter-bead peak.

[0299] Embodiment 33 32. The ceramic article of any one of claims 1 to 31, wherein the total porosity is at least 55% and the bimodal pore size distribution has a D10 value of at most 3 μm, a D50 value of 5 μm to 18 μm, and a D75-D50 value of at most 2 μm, as determined by mercury intrusion porosimetry.

[0300] Embodiment 34 34. The ceramic article of any one of claims 1 to 33, wherein the porous ceramic beads have an average intra-bead open porosity of at least 20% by volume of the beads.

[0301] Embodiment 35 35. The ceramic article of any one of claims 1 to 34, wherein the bead material has an average intra-bead open porosity of at least 25% by volume of the bead.

[0302] Embodiment 36 36. The ceramic article of any one of claims 1 to 35, wherein the bead material has an average intra-bead open porosity of at least 30% by volume of the bead.

[0303] Embodiment 37 37. The ceramic article of any one of claims 1 to 36, wherein the inter-bead porosity has a median pore size in the range of 6 μm to 20 μm.

[0304] Embodiment 38 38. The ceramic article of any one of claims 1 to 37, wherein the inter-bead median pore size is in the range of 8 μm to 18 μm.

[0305] Embodiment 39 39. The ceramic article of any one of claims 1 to 38, wherein the inter-bead median pore size is in the range of 9 μm to 17 μm.

[0306] Embodiment 40 40. The ceramic article of any one of claims 1 to 39, wherein the median pore size within the beads is in the range of 1 μm to 5 μm.

[0307] Embodiment 41 41. The ceramic article of any one of claims 1 to 40, wherein the median pore size within the beads is in the range of 1.5 μm to 4 μm.

[0308] Embodiment 42 42. The ceramic article of any one of claims 1 to 41, wherein the median pore size within the beads is in the range of 1.5 μm to 3 μm.

[0309] Embodiment 43 43. The ceramic article of any one of claims 1 to 42, wherein the median pore size within the beads is in the range of 1.5 μm to 2 μm.

[0310] EMBODIMENT 44 44. The ceramic article of any one of claims 1 to 43, wherein the median pore size within the beads is in the range of 1 μm to 2 μm.

[0311] Embodiment 45 45. The ceramic article of any one of claims 1 to 44, wherein the beads have a median particle size in the range of 20 μm to 50 μm.

[0312] Embodiment 46 46. ​​The ceramic article of any one of claims 1 to 45, wherein the beads have a median particle size in the range of 25 μm to 40 μm.

[0313] Embodiment 47 A ceramic honeycomb body having the ceramic article of any one of embodiments 1 to 46, wherein the ceramic article has a plurality of intersecting walls having the porous ceramic material, the intersecting walls forming a plurality of passages extending longitudinally through the ceramic honeycomb body from a first end face to a second end face.

[0314] Embodiment 48 48. The ceramic honeycomb body of claim 47, wherein the porous ceramic material of the intersecting walls comprises at least 90% by weight cordierite, the porous ceramic beads have an intra-bead closed porosity of less than 5%, the total porosity is at least 50%, the intra-bead open porosity of the beads is at least 20% by volume of the beads, and the beads have a median grain size in the range of 20 μm to 50 μm.

[0315] Embodiment 49 A particulate filter comprising the ceramic honeycomb body according to embodiment 47 or 48.

[0316] Embodiment 50 50. A particulate filter according to embodiment 49, wherein the passages of the honeycomb body are alternately plugged in a checkerboard pattern at the first end face and the second end face.

[0317] Embodiment 51 1. A method of making a ceramic article, comprising: mixing a batch mixture with a plurality of porous ceramic beads, each having a porous ceramic material, wherein the porous ceramic material of the porous ceramic beads has an intra-bead open porosity, and the porous ceramic beads have a median bead size of 25 to 40 μm; forming the batch mixture into a green ceramic article; firing the green ceramic article to form the ceramic article by sintering the porous ceramic beads together into an interconnected network of the porous ceramic beads; and the interstices between the beads in the interconnected network define interbead porosity of the ceramic article; a total porosity of the ceramic article, defined as the sum of the intra-bead porosity and the inter-bead porosity, of at least 50% based on the total volume of the ceramic article; the ceramic article has a bimodal pore size distribution, wherein the intra-bead porosity has an intra-bead median pore size that is smaller than the inter-bead median pore size of the inter-bead porosity. method.

[0318] Embodiment 52 Prior to forming the batch mixture, the method comprises: forming a slurry mixture having a mixture of ceramic precursor materials; spheronizing the slurry mixture into spherical green agglomerates; firing the green agglomerates to convert the ceramic precursor material to the porous ceramic material, thereby forming the porous ceramic beads; 52. The method of embodiment 51, further comprising:

[0319] Embodiment 53 53. The method of embodiment 51 or 52, wherein the ceramic beads comprise at least 80% by weight cordierite.

[0320] EMBODIMENT 54 54. The method of any one of embodiments 51 to 53, wherein the crystalline phase of the porous ceramic material is at least 90% by weight cordierite.

[0321] Embodiment 55 55. The method of any one of embodiments 52 to 54, further comprising sieving the green agglomerates or sieving the porous ceramic beads to affect the median particle size of the porous ceramic beads before mixing the batch mixtures together.

[0322] Embodiment 56 56. The method of any one of embodiments 52 to 55, wherein the step of spheronizing the slurry mixture comprises a spray drying process.

[0323] Embodiment 57 57. The method of any one of embodiments 52 to 56, wherein the step of spheronizing the slurry mixture comprises a rotary evaporation process.

[0324] Embodiment 58 58. The method of any one of embodiments 52 to 57, wherein the ceramic precursor material comprises a silica source, an alumina source, and a magnesia source, and the porous ceramic material of the porous ceramic beads comprises cordierite.

[0325] Embodiment 59 59. The method of any one of embodiments 52 to 58, wherein the batch mixture further comprises an organic binder and an inorganic binder.

[0326] Embodiment 60 60. The method of any one of claims 52 to 59, wherein the batch mixture has the porous ceramic beads in an amount ranging from 60% by weight to 95% by weight, based on the total weight of the inorganic binder and the porous ceramic beads.

[0327] Embodiment 61 61. The method of embodiment 60, wherein the inorganic binder comprises a plurality of shear binder agglomerates, the shear binder agglomerates comprising an unfired mixture of one or more inorganic ceramic precursor materials and a binder.

[0328] Embodiment 62 62. The method of any one of claims 51 to 61, wherein the intra-bead open porosity is at least 10% relative to the total volume of the ceramic article.

[0329] Embodiment 63 63. The method of any one of embodiments 51 to 62, wherein the inter-bead porosity is at least 40% relative to the total volume of the ceramic article.

[0330] EMBODIMENT 64 64. The method of any one of embodiments 51 to 63, wherein the intra-bead porosity is at least 9% by volume of the bead.

[0331] Embodiment 65 65. The method of any one of embodiments 51 to 64, wherein the intra-bead porosity is at least 15% by volume of the bead.

[0332] Embodiment 66 65. The method of any one of embodiments 51 to 64, wherein the intra-bead porosity is at least 20% by volume of the bead.

[0333] Embodiment 67 The method of any one of embodiments 51 to 66, wherein the ceramic article is a ceramic honeycomb body, and the step of shaping the batch mixture includes extruding the batch mixture through a honeycomb extrusion die, and the ceramic honeycomb body has a plurality of intersecting walls having the porous ceramic material, the intersecting walls forming a plurality of passages extending longitudinally through the honeycomb body from a first end face to a second end face.

[0334] Embodiment 68 68. The method of embodiment 67, further comprising plugging the passages alternately in a checkerboard pattern on the first end face and the second end face to create a filter from the honeycomb body.

Claims

1. 1. A ceramic article comprising: a porous ceramic material having a microstructure comprising an interconnected network of porous ceramic beads having a spherical shape, said microstructure having a total open porosity defined as the sum of the intra-bead open porosity of said porous ceramic beads and the inter-bead porosity defined by the gaps between said porous ceramic beads within said interconnected network; the microstructure has a bimodal pore size distribution having an intra-bead peak corresponding to the intra-bead open porosity and an inter-bead peak corresponding to the inter-bead porosity, and the median diameter of the intra-bead pores of the intra-bead open porosity is smaller than the median diameter of the inter-bead pores of the inter-bead porosity; the intra-bead open porosity is at least 10% based on the total volume of the ceramic article, and the inter-bead porosity is at least 40% based on the total volume of the ceramic article; Ceramic articles.

2. The ceramic article of claim 1 , wherein the porous ceramic beads comprise at least 80% by weight cordierite.

3. 3. The ceramic article of claim 1 or 2, wherein the bead-to-bead half-maximum pore size distribution peak width is at most 6 μm as determined by mercury intrusion porosimetry.

4. 4. The ceramic article of claim 1, wherein the intra-bead half-maximum pore size distribution peak width is at most 2 μm, as determined by mercury intrusion porosimetry.

5. 5. The ceramic article of claim 1, wherein the bimodal pore size distribution has a D10 value of at most 3 μm, a D50 value of between 5 μm and 18 μm, and a D75-D50 value of at most 2 μm.

6. 6. The ceramic article of claim 1, wherein the open intra-bead porosity of the porous ceramic beads averages at least 20% by volume of the porous ceramic beads.

7. 7. The ceramic article of any one of claims 1 to 6, wherein one or more of the inter-bead porosities have a median pore size in the range of 6 μm to 20 μm, and the median intra-bead pore size is in the range of 1 μm to 5 μm.

8. 1. A method of making a ceramic article, comprising: mixing a batch mixture with porous ceramic beads made of a porous ceramic material, the porous ceramic material of the porous ceramic beads having an open intra-bead porosity, the porous ceramic beads having a median bead size of 25 to 40 μm; forming the batch mixture into a green ceramic article; firing the green ceramic article to form the ceramic article by sintering the porous ceramic beads together into an interconnected network of the porous ceramic beads; and the interstices between the porous ceramic beads in the interconnected network define inter-bead porosity of the ceramic article; the total open porosity of the ceramic article, defined as the sum of the intra-bead open porosity and the inter-bead porosity, is at least 50% based on the total volume of the ceramic article; the ceramic article has a bimodal pore size distribution in which the median diameter of intra-bead pores of the intra-bead open porosity is smaller than the median diameter of inter-bead pores of the inter-bead porosity. method.

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