Methods of forming monolithic articles

Abstract

A method of forming a monolithic article includes extruding an extrudable composition to form an extrudate, the extrudable composition including a binder, inorganic particles, and graphite particles, the extrudate including an exterior skin and a core disposed within the exterior skin; drying the extrudate; debinding the extrudate in a debinding atmosphere at one or more debinding temperatures to remove the binder from the extrudate; and sintering the extrudate in a sintering atmosphere at one or more sintering temperatures to remove the graphite particles from the exterior skin of the extrudate and to sinter the inorganic particles of the extrudate, to thereby form the monolithic article. The one or more debinding temperatures are less than 650 °C. The one or more sintering temperatures are greater than or equal to 650 °C and the sintering atmosphere includes an oxygen concentration less than or equal to 2.5%.

Description

METHODS OF FORMING MONOLITHIC ARTICLESCROSS REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of priority under 35 U.S.C. § 119 of U.S.Provisional Application Serial No. 63 / 604,317, filed on November 30, 2023, the content of which is relied upon and incorporated herein by reference in its entirety.Field

[0002] The present specification generally relates to monolithic articles and, in particular, to methods of forming monolithic articles having improved mechanical strength.Technical Background

[0003] One method of removing CO2 either from a point source or from ambient air includes flowing a CO2 laden stream through a monolith containing a sorbent that adsorbs the CO2. The CO2 may later be desorbed for removal (e.g., via heating of the monolith). One convenient way to provide heating of the monolith is via resistive heating. However, conventional fabrication processes for forming monolithic articles may not be cost-effective and / or have limited scalability.

[0004] Accordingly, a continual need exists for cost-effective and scalable methods of forming monolithic articles having improved mechanical strength.SUMMARY

[0005] According to a first aspect Al, a method of forming a monolithic article may comprise: extruding an extrudable composition to form an extrudate, the extrudable composition comprising a binder, inorganic particles, and graphite particles, the extrudate comprising an exterior skin and a core disposed within the exterior skin; drying the extrudate; debinding the extrudate in a debinding atmosphere at one or more debinding temperatures to remove the binder from the extrudate, wherein the one or more debinding temperature is lessthan 650 °C; and sintering the extrudate in a sintering atmosphere at one or more sintering temperatures to remove the graphite particles from the exterior skin of the extrudate and to sinter the inorganic particles of the extrudate, to thereby form the monolithic article, wherein the one or more sintering temperatures are greater than or equal to 650 °C and the sintering atmosphere comprises an oxygen concentration less than or equal to 2.5%.

[0006] A second aspect A2 includes the method of the first aspect Al, the sintering atmosphere comprises an oxygen concentration greater than or equal to 0.0% and less than or equal to 2.5%.

[0007] A third aspect A3 includes the method of the first aspect Al or the second aspect A2, wherein the one or more debinding temperatures are greater than or equal to 200 °C and less than 650 °C.

[0008] A fourth aspect A4 includes the method of any of the first through third aspects Al- A3, wherein the debinding comprises holding the extrudate at a hold debinding temperatures and in the debinding atmosphere for greater than or equal to 2 hours and less than or equal to 40 hours.

[0009] A fifth aspect A5 includes the method of the fourth aspect A4, wherein the debinding comprises increasing to the one of the one or more debinding temperatures in the debinding atmosphere at a first ramp rate greater than or equal to 5 °C / hour and less than or equal to 20 °C / hour.

[0010] A sixth aspect A6 includes the method of any of the first through fifth aspects Al- A5, wherein the debinding atmosphere comprises an oxygen concentration greater than or equal to 3% and less than or equal to 18%.

[0011] A seventh aspect A7 includes the method of any ofthe first through sixth aspects Al- A6, wherein the one or more sintering temperatures are greater than or equal to 650 °C and less than or equal to 1000 °C.

[0012] An eighth aspect A8 includes the method of any of the first through seventh aspects A1-A7, wherein the sintering comprises holding the extrudate at a hold sintering temperature and in the sintering atmosphere for greater than or equal to 0.5 hour to less than or equal to 8 hours.

[0013] A ninth aspect A9 includes the method of the eighth aspect A8, wherein the sintering comprises increasing to the hold sintering temperature at a second ramp rate greater than or equal to 5 °C / hour and less than or equal to 100 °C / hour.

[0014] A tenth aspect A 10 includes the method of any of the first through ninth aspects Al- A9, wherein at least one of the debinding atmosphere and the sintering atmosphere comprises nitrogen, argon, or a combination thereof.

[0015] An eleventh aspect Al 1 includes the method of any of the first through tenth aspects Al -A 10, wherein the binder comprises an organic binder, the organic binder comprising cellulose, a cellulose derivative, a polymer, a thermosetting resin, or a combination thereof.

[0016] A twelfth aspect A 12 includes the method of any of the first through eleventh aspects Al-Al l, wherein the inorganic particles comprise a borate, a phosphate, a transition metal oxide, an oxide, a hydroxide, a carbonate, a silicate, an alumino-silicate, or combinations thereof.

[0017] A thirteenth aspect A13 includes the method of the twelfth aspect A 12, wherein the inorganic particles comprise talc, clay, MgO, alumina, or combinations thereof.

[0018] A fourteenth aspect A 14 includes the method of any of the first through thirteenth aspects Al -A 13, wherein the graphite particles comprise graphite plates, graphite flakes, natural graphite, synthetic graphite, or combinations thereof.

[0019] A fifteenth aspect A15 includes the method of any of the first through fourteenth aspects A1-A14, wherein the extrudable composition further comprises a pore-forming material, the pore-forming material comprising a starch, a nut-shell flour, carbon, a natural polymer, a synthetic polymer, a carbonaceous material, crystalline carbon, amorphous carbon, or combinations thereof.

[0020] A sixteenth aspect A16 includes the method of any of the first through fifteenth aspects Al -A 15, wherein the extrudable composition further comprises a porous material, the porous material comprising paper, polymer, glass, glass-ceramic, ceramic, diatomaceous earth, perlite, pumice, or combinations thereof.

[0021] A seventeenth aspect A17 includes the method of the sixteenth aspect A 16, wherein the porous material comprises hollow glass beads.

[0022] An eighteenth aspect A 18 includes the method of any of the first through seventeenth aspects A 1 -A 17, wherein the core has a shape of a honeycomb structure comprising a pluralityof cells therein, the plurality of cells defining parallel channels running longitudinally through the honeycomb structure.

[0023] According to a nineteenth aspect A19, a monolithic article may comprise: an exterior skin comprising inorganic material; and a core disposed within the exterior skin, the core comprising a continuous graphite phase and an inorganic phase comprising the inorganic material, wherein the graphite phase and the inorganic phase together form an interconnected pore structure, wherein: a modulus of rupture of the exterior skin is at least 150% greater than a modulus of rupture of the core, as measured according to ASTM-D6272; and the monolithic article is electrically conductive.

[0024] A twentieth aspect A20 includes the monolithic article of the nineteenth aspect A 19, wherein the exterior skin is free or substantially free of graphite.

[0025] A twenty-first aspect A21 includes the monolithic article of the nineteenth aspect A19 or the twentieth aspect A20, wherein the continuous graphite phase is homogenously distributed throughout the core.

[0026] A twenty-second aspect A22 includes the monolithic article of any of the nineteenth through twenty-first aspects A19-A21, wherein the core has a shape of a honeycomb structure comprising a plurality of cells therein, the plurality of cells defining parallel channels running longitudinally through the honeycomb structure.

[0027] A twenty-third aspect A23 includes the monolithic article of any of the nineteenth through twenty-second aspects A19-A22, wherein the continuous graphite phase comprises fired graphite plates, graphite flakes, natural graphite, synthetic graphite, or combinations thereof.

[0028] A twenty-fourth aspect A24 includes the monolithic article of any of the nineteenth through twenty-third aspects A19-A23, wherein the inorganic material comprises a borate, a phosphate, a transition metal oxide, an oxide, a hydroxide, a carbonate, a silicate, an aluminosilicate, or combinations thereof.

[0029] A twenty-fifth aspect A25 includes the monolithic article of the twenty-fourth aspect A24, wherein the inorganic material comprises talc, clay, MgO, alumina, or combinations thereof.

[0030] A twenty-sixth aspect A26 includes the monolithic article of any of the nineteenth through twenty-fifth aspects A19-A25, wherein a Young’s modulus of the exterior skin is at least 50% greater than a Young’s modulus of the core, as measured according to ASTM C623.

[0031] A twenty-seventh aspect A27 includes the monolithic article of any of the nineteenth through twenty-sixth aspects A19-A26, wherein the core of the monolithic article has an electrical resistance greater than or equal to 1 ohm to less than or equal to 100 ohms.

[0032] A twenty-eighth aspect A28 includes the monolithic article of any of the nineteenth through twenty-seventh aspects A19-A27, wherein the monolithic article comprises a coating on the core, the coating comprising a catalyst, a sorbent that adsorbs and desorbs CO2, or combinations thereof.

[0033] A twenty-ninth aspect A29 includes a method of using the article of the twenty-eighth aspect A28, the method comprising: exposing the article to a gas stream comprising CO2 to adsorb at least some of the CO2 in the gas stream from the gas stream into the sorbent in the coating.

[0034] A thirtieth aspect A30 includes the method of the twenty-ninth aspect A29, the method further comprising: desorbing the CO2 from the coating.

[0035] A thirty-first aspect A31 includes the method of the thirtieth aspect A30, wherein the desorbing comprises applying an electrical potential across the article to heat the article.

[0036] According to a thirty-second aspect A32, a method of forming a porous electrically conductive article may comprise: heating a precursor body in a first heating atmosphere in a first atmosphere temperature range, the precursor body comprising a precursor composition comprising inorganic particles, one or more organic components, and an electrically conductive filler material, wherein the first atmosphere temperature range is below a combustion temperature of the electrically conductive filler material, wherein the precursor body comprises a core surrounded by an outer periphery having the same precursor composition, wherein the precursor body is heated in the first heating atmosphere at one or more first atmosphere temperatures in the first atmosphere temperature range, and wherein the heating in the first heating atmosphere is carried out for a first heating duration and at the one or more first atmosphere temperatures sufficient to remove the organic components from the precursor body while the electrically conductive filler material remains intact in the precursor body; and heating the precursor body in a second heating atmosphere in a second atmosphere temperaturerange, which comprises one or more second atmosphere temperatures at or above the combustion temperature of the electrically conductive fdler material, wherein the second heating atmosphere has a gaseous makeup which hinders combustion of the electrically conductive filler material, wherein the heating in the second heating atmosphere is carried out for a second heating duration and at the one or more second atmosphere temperatures sufficient to remove at least some of the electrically conductive filler material from the outer periphery of the precursor body while the electrically conductive filler material remains intact in the core of the precursor body.

[0037] A thirty-third aspect A33 includes the method of the thirty-second aspect A32, wherein the heating the precursor body in the second heating atmosphere is sufficient to cause the inorganic materials in the outer periphery of the precursor body to sinter.

[0038] A thirty-fourth aspect A34 includes the method of the thirty-second aspect A32 or a thirty-third aspect A33, wherein a strength of the outer periphery is greater than a strength of the core.

[0039] A thirty-fifth aspect A35 includes the method of the thirty-second through thirtyfourth aspects A32-A34, wherein the heating the precursor body in the first heating atmosphere increases porosity in the precursor body.

[0040] A thirty-sixth aspect A36 includes the method of any of the thirty-second through thirty-fifth aspects A32-A35, wherein the outer periphery has an average thickness that is less than 10% of a transverse hydraulic diameter of the precursor body.

[0041] A thirty-seventh aspect A37 includes the method of any of the thirty-second through thirty-sixth aspects A32-A36, wherein the precursor body comprises a honeycomb structure comprised of intersecting walls extending in an axial direction which form a plurality of parallel cells in a transverse face.

[0042] A thirty-eighth aspect A38 includes the method of any of the thirty-second through thirty-seventh aspects A32-A37, wherein the gaseous makeup which hinders combustion of the electrically conductive filler material in the second heating atmosphere is provided by adjusting oxygen input and / or level in the second atmosphere, adjusting fuel mixture of one or more burners that provide heat to the second atmosphere, adjusting introduction and / or level of recirculated products of combustion gases in the second atmosphere, adjusting introduction and / or level of inert gas in the second atmosphere, or combinations thereof.

[0043] A thirty-ninth aspect A39 includes the method of the thirty-eighth aspect A38, wherein the fuel mixture of one or more burners is a lean fuel mixture.

[0044] A fortieth aspect A40 includes the method of the thirty-eighth aspect A38 or the thirty-ninth aspect A39, wherein the inert gas is nitrogen, argon, or combination thereof.

[0045] A forty-first aspect A41 includes the method of any of the thirty-second through fortieth aspects A32-A40, further comprising extruding an extrudable composition to form an extrudate, and cutting a portion of the extrudate.

[0046] A forty-second aspect A42 includes the method of the forty-first aspect A41 , wherein the core and the outer periphery of the precursor body are simultaneously extruded.

[0047] A forty-third aspect A43 includes the method of any of the thirty-second through forty-second aspects A32-A42, wherein the first atmosphere temperature range is greater than or equal to 200 °C and less than or equal to 650 °C.

[0048] A forty-fourth aspect A44 includes the method of any of the thirty-second through forty-third aspects A32-A43, wherein the oxygen content of the second atmosphere is in a second oxygen range greater than or equal to 0.0% and less than or equal to 2.5%.

[0049] A forty-fifth aspect A45 includes the method of any of the thirty-second through forty-fourth aspects A32-A44, wherein the oxygen content of the first atmosphere is in a first oxygen range greater than or equal to 3% and less than or equal to 18%.

[0050] A forty-sixth aspect A46 includes the method of any of the thirty-second through forty-fifth aspects A32-A45, wherein the first heating duration is greater than or equal to 2 hours and less than or equal to 10 hours.

[0051] A forty-seventh aspect A47 includes the method of any of the thirty-second through forty-sixth aspects A32-A46, wherein the second heating duration is greater than or equal to 0.5 hours and less than or equal to 8 hours.

[0052] A forty-eighth aspect A48 includes the method of any of the thirty-second through forty-seventh aspects A32-A47, wherein the precursor body further comprises hollow glass beads.

[0053] A forty-ninth aspect A49 includes the method of the forty-eighth aspect A48, wherein the hollow glass beads are softened as the precursor body is heated in the second heating atmosphere.

[0054] A fiftieth aspect A50 includes the method of the forty-eighth aspect A48 or the fortyninth aspect A49, wherein the hollow glass beads are hollow glass microspheres.

[0055] A fifty-first aspect A51 includes the method of any of the thirty-second through fiftieth aspects A32-A50, wherein the precursor body further comprises one or more porous material comprised of paper, polymer, glass, glass-ceramic, ceramic, diatomaceous earth, perlite, pumice, or combinations thereof.

[0056] A fifty-second aspect A52 includes the method of any of the thirty-second through fifty -first aspects A32-A51, wherein the organic components comprise one or more starch, one or more binder, one or more oil, one or more volatile organic compound, or combinations thereof.

[0057] A fifty-third aspect A53 includes the method of the fifty-second aspect A52, wherein the one or more binder is a cellulosic binder.

[0058] A fifty-fourth aspect A54 includes the method of any of the thirty-second through fifty-third aspects A32-A53, wherein the precursor body is monolithic, wherein the core and the outer periphery are made of the same composition.

[0059] Additional features and advantages of the monolithic articles and methods of forming same described herein will be set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art from that description or recognized by practicing the embodiments described herein, including the detailed description which follows, the claims, as well as the appended drawings.

[0060] It is to be understood that both the foregoing general description and the following detailed description describe various embodiments 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 of the various embodiments, and are incorporated into and constitute a part of this specification. The drawings illustrate the various embodiments described herein, and together with the description serve to explain the principles and operations of the claimed subject matter.BRIEF DESCRIPTION OF THE DRAWINGS

[0061] FIG. 1 is a flow chart of a method of forming a monolithic article, according to one or more embodiments described herein;

[0062] FIG. 2 is a schematic illustration of an extrudate used to form the monolithic article, according to one or more embodiments described herein;

[0063] FIG. 3 is a plot of shrinkage (lefty-axis; in dL / Lo) and expansion (right y-axis) versus temperature (x-axis; in °C) of monolithic articles subjected to different atmospheric conditions, according to one or more embodiments described herein;

[0064] FIG. 4 is a plot of shrinkage (lefty-axis; in dL / Lo) and expansion (right y-axis) versus temperature (x-axis; in °C) of a monolithic article in different atmospheric conditions, according to one or more embodiments described herein;

[0065] FIG. 5 is a plot of relative mass change (left y-axis; in percentage (%)) and heat flow (right y-axis; in watts / gram (W / g)) versus temperature (x-axis; in °C) of monolithic articles subjected to different atmospheric conditions, according to one or more embodiments described herein;

[0066] FIG. 6 is a plot of temperature (left y-axis; in °C) and weight loss (left y-axis; in percentage (%)) and dilatometer shrinkage (right y-axis; in mm) and oxygen content (right y- axis; in percentage (%)) versus time (x-axis; in hrs) of monolithic articles subjected to different atmospheric conditions, according to one or more embodiments described herein;

[0067] FIG. 7 is a plot of temperature (left y-axis; in °C) and dilatometer shrinkage (right y- axis (in mm)) as a function of time (x-axis; in hrs) of monolithic articles subjected to different atmospheric conditions, according to one or more embodiments described herein;

[0068] FIG. 8 is a plot of temperature (left y-axis; in °C) and oxygen content (right y-axis; in percentage (%)) versus time (x-axis; in hrs) of a monolithic article subjected to a given atmospheric condition, according to one or more embodiments described herein;

[0069] FIG. 9 is a plot of temperature (left y-axis; in °C) and oxygen content (right y-axis; in percentage (%)) versus time (x-axis; in hrs) of a monolithic article subjected to a given atmospheric condition, according to one or more embodiments described herein;

[0070] FIG. 10 is a photograph of an exemplary monolithic article, according to one or more embodiments described herein;

[0071] FIG. 11 is a photograph of an exterior skin of an exemplary monolithic article, according to one or more embodiments described herein;

[0072] FIG. 12 is a scanning electron microscope (SEM) image of the exterior skin of the exemplary monolithic article of FIG. 11 ;

[0073] FIG. 13 is a further magnified SEM image of the exterior skin of the exemplary monolithic article of FIG. 11 ;

[0074] FIG. 14 is a photograph of a core of the exemplary monolithic article of FIG. 11,

[0075] FIG. 15 is an SEM image of the core of the exemplary monolithic article of FIG. 11; and

[0076] FIG. 16 is a further magnified SEM image of the core of the exemplary monolithic article of FIG. 11.DETAILED DESCRIPTION

[0077] Reference will now be made in detail to various embodiments of methods of forming monolithic articles having improved mechanical strength. According to embodiments, a method of forming a transparent ceramic article includes extruding an extrudable composition to form an extrudate, the extrudable composition including a binder, inorganic particles, and graphite particles, the extrudate including an exterior skin and a core disposed within the exterior skin; drying the extrudate; debinding the extrudate in a debinding atmosphere at one or more debinding temperatures to remove the binder from the extrudate; and sintering the extrudate in a sintering atmosphere at one or more sintering temperatures to remove the graphite particles from the exterior skin of the extrudate and to sinter the inorganic particles of the extrudate, to thereby form the monolithic article. As used herein the term monolithic is intended to mean a structure having one or more continuous phases, but as disclosed herein, multiple separate continuous phases do not necessarily need to be bonded together, but instead may be physically held or locked together by being intertwined with each other. The one or more debinding temperatures are less than 650 °C. The one or more sintering temperatures are greater than or equal to 650 °C and the sintering atmosphere includes an oxygen concentration less than or equal to 2.5%.

[0078] According to other embodiments, a monolithic article includes an exterior skin comprising inorganic material and a core disposed within the exterior skin. The core includes a continuous graphite phase and an inorganic phase including the inorganic material. Thegraphite phase and the inorganic phase together form an interconnected pore structure. A modulus of rupture of the exterior skin is at least 150% greater than a modulus of rupture of the core, as measured according to ASTM-D6272. The monolithic article is electrically conductive.

[0079] Various embodiments of monolithic articles and methods of forming same will be described herein with specific reference to the appended drawings.

[0080] Ranges may be expressed herein as from “about” one particular value, and / or to “about” another particular value. When such a range is expressed, another embodiment includes from the one particular value and / or to the other particular value. Similarly, when values are expressed as approximations, by use of the antecedent “about,” it will be understood that the particular value forms another embodiment. It will be further understood that the endpoints of each of the ranges are significant both in relation to the other endpoint, and independently of the other endpoint.

[0081] Directional terms as used herein - for example up, down, right, left, front, back, top, bottom - are made only with reference to the figures as drawn and are not intended to imply absolute orientation.

[0082] Unless otherwise expressly stated, it is in no way intended that any method set forth herein be construed as requiring that its steps be performed in a specific order, nor that with any apparatus specific orientations be required. Accordingly, where a method claim does not actually recite an order to be followed by its steps, or that any apparatus claim does not actually recite an order or orientation to individual components, or it is not otherwise specifically stated in the claims or description that the steps are to be limited to a specific order, or that a specific order or orientation to components of an apparatus is not recited, it is in no way intended that an order or orientation be inferred, in any respect. This holds for any possible non-express basis for interpretation, including: matters of logic with respect to arrangement of steps, operational flow, order of components, or orientation of components; plain meaning derived from grammatical organization or punctuation, and; the number or type of embodiments described in the specification.

[0083] As used herein, the singular forms “a,” “an” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a” component includes aspects having two or more such components, unless the context clearly indicates otherwise.

[0084] “Oxygen” and “O2” are used interchangeably herein.

[0085] “Nitrogen” and “N2” are used interchangeably herein.

[0086] “dso diameter,” as used herein, refers to the average particle size by mass, such that the dso diameter of a material is both smaller than 50% of the material by mass and that is also larger than 50% of the material by mass.

[0087] ‘ ‘Modulus of rupture” or “MOR,” as used herein, is measured in accordance with by a 4-point bend test of a rectangular bar cut out of the fired parts, as per ASTM-D6272.

[0088] “Young’s modulus,” as used herein, is provided in units of gigapascals (GPa) and is measured in accordance with ASTM C623.

[0089] ‘ ‘Electrical resistance,” as used herein, is measured with a multimeter on a 2 inch x 6 inch (5 cm x 15 cm) sample.

[0090] “Porosity” or “total pore volume,” as used herein, are measured using mercury porosity according to ASTM D6761-07 (2012).

[0091] “Weight loss,” as used herein, is measured by measuring the sample before and after treatment.

[0092] ‘ ‘Standard volume exchange,” as used herein, refers to the number of times per hour that an atmosphere in the kiln is turned over.

[0093] Monolithic articles, specifically those containing graphite, may be used in CO2 capture applications, such as direct air capture (DAC) or capture of CO2 at an effluent source. During use, a CO2 laden stream flows through the monolith containing a sorbent that adsorbs the CO2. The CO2 may be desorbed after use for removal via heating of the monolith (e.g., resistive heating).

[0094] Conventional processes for forming monolithic articles may be conducted in low- oxygen or oxygen-free atmospheres (e.g., in nitrogen and / or argon-containing atmospheres) to prevent oxidation of graphite and to preserve graphite throughout the entire article. For example, an article may be fired in a closed ceramic domed crucible with a green cookie on top of the article acting as a sacrificial oxidizer to provide low oxygen to preserve as much of the graphite in the article as possible during firing. However, such conventional processes may not be cost-effective due to the use of nitrogen or argon or may have limited scalability due to the need to maintain a low-oxygen or oxygen-free atmosphere.

[0095] Disclosed herein are methods of forming monolithic articles which mitigate the aforementioned problems. Specifically, the methods of forming a monolithic article disclosed herein control temperature and / or atmosphere during debinding and sintering, resulting in an electrically conductive monolithic article having improved mechanical strength. Specifically, the methods of forming a monolithic article disclosed herein include debinding at a relatively low temperature (e.g., less than 650 °C), which preserves graphite in the extrudate. The methods disclosed herein further include sintering the extrudate at a relatively high temperature (e.g., greater than or equal to 650 °C) and in a relatively low oxygen atmosphere (e.g., an oxygen concentration less than or equal to 2.5%), which removes graphite from an exterior skin of the extrudate while preserving graphite in a core of the extrusion. Graphite in the core allows the resultant monolithic article to be electrically conductive. As such, the resulting monolithic article is also referred to herein as “a porous electrically conductive article.” Removal of graphite from the exterior skin enables increased binding and sintering of inorganic particles in the exterior skin, thereby strengthening the exterior skin and the article overall (e.g., a modulus of rupture of the exterior skin is at least 150% greater than a modulus of rupture of the core).

[0096] Referring now to FIG. 1, a method of forming a monolithic article is shown at 100. The method begins at block 102 with extruding an extrudable composition to form an extrudate, also referred to herein as “a precursor body”. The extrudable composition, also referred to herein as “a precursor composition,” comprises a binder, inorganic particles, and graphite particles.

[0097] The binder, also referred to herein as “one or more organic components,” provides mechanical adhesion to the extrudable composition during extruding and drying. In embodiments, the binder may comprise an organic binder. In embodiments, the organic binder may comprise cellulose, a cellulose derivative, a polymer, a thermosetting resin, or a combination thereof. In embodiments, the cellulose derivative may comprise Ci- C3)alkylhydroxy(Ci-C3)alkyl cellulose, (Ci-C3)alkylhydroxy cellulose, (Ci-C3)alkylcellulose, (Ci-C3)alkyl(Ci-C3)alkylcellulose, methylhydroxypropyl cellulose, methylhydroxyethyl cellulose, methylhydroxymethyl cellulose, methylcellulose, ethylcellulose, propylcellulose, hydroxypropylcellulose, methylethyl cellulose, sodium carboxymethylcellulose, or combinations thereof. In embodiments, the binder may comprise a cellulosic binder.

[0098] In embodiments, the amount of the binder in the extrudable composition may be, in terms of superadditions to 100 parts of the inorganic particles, greater than or equal to 1 part, greater than or equal to 3 parts, or even greater than or equal to 5 parts. In embodiments, the amount of the binder in the extrudable composition may be, in terms of superadditions to 100 parts of the inorganic particles, less than or equal 15 parts, less than or equal to 10 parts, or even less than or equal to 7 parts. In embodiments, the amount of the binder in the extrudable composition may be, in terms of superadditions to 100 parts of the inorganic particles, greater than or equal to 1 part and less than or equal to 15 parts, greater than or equal to 1 part and less than or equal to 10 parts, greater than or equal to 1 part and less than or equal to 7 parts, greater than or equal to 3 parts and less than or equal to 15 parts, greater than or equal to 3 parts and less than or equal to 10 parts, greater than or equal to 3 parts and less than or equal to 7 parts, greater than or equal to 5 parts and less than or equal to 15 parts, greater than or equal to 5 parts and less than or equal to 10 parts, or even greater than or equal to 5 parts and less than or equal to 7 parts, or any and all sub-ranges formed from any of these endpoints.

[0099] The inorganic particles provide mechanical strength to the resultant monolithic article when sintered. Some inorganic particles, such as silicate, may also enhance extrudability of the extrudable composition. In embodiments, the inorganic particles may comprise a borate, a phosphate, a transition metal oxide, an oxide, a hydroxide, a carbonate, a silicate, an aluminosilicate, or combinations thereof. For example, in embodiments, the inorganic particles may comprise talc, clay, MgO, alumina, or combinations thereof.

[0100] A minimum amount of inorganic particles may be included in the extrudable composition (e.g., greater than or equal to 20 wt%) to ensure thatthe resultant monolithic article has sufficient mechanical strength (e.g., a modulus of rupture of the exterior skin is at least 150% greater than a modulus of rupture of the core). The amount of inorganic particles may be limited (e.g., less than or equal to 85%) to ensure that a continuous graphite phase may be achieved in the resultant monolithic article. In embodiments, the amount of the inorganic particles in the extrudable composition may be, based on a total dry weight of the extrudable composition, greater than or equal to 20 wt%, greater than or equal to 30 wt%, greater than or equal to 40 wt%, or even greater than or equal to 50 wt%. In embodiments, the amount of inorganic particles in the extrudable composition may be, based on a total dry weight of the extrudable composition, less than or equal to 85 wt%, less than or equal to 75 wt%, less thanor equal to 65 wt%, less than or equal to 55 wt%, or even less than or equal to 45 wt%. In embodiments, the amount of the inorganic particles in the extrudable composition may be, based on a total dry weight of the extrudable composition, greater than or equal to 20 wt% and less than or equal to 85 wt%, greater than or equal to 20 wt% and less than or equal to 75 wt%, greater than or equal to 20 wt% and less than or equal to 65 wt%, greater than or equal to 20 wt% and less than or equal to 55 wt%, greater than or equal to 20 wt% and less than or equal to 45 wt%, greater than or equal to 30 wt% and less than or equal to 85 wt%, greater than or equal to 30 wt% and less than or equal to 75 wt%, greater than or equal to 30 wt% and less than or equal to 65 wt%, greater than or equal to 30 wt% and less than or equal to 55 wt%, greater than or equal to 30 wt% and less than or equal to 45 wt%, greater than or equal to 40 wt% and less than or equal to 85 wt%, greater than or equal to 40 wt% and less than or equal to 75 wt%, greater than or equal to 40 wt% and less than or equal to 65 wt%, greater than or equal to 40 wt% and less than or equal to 55 wt%, greater than or equal to 40 wt% and less than or equal to 45 wt%, greater than or equal to 50 wt% and less than or equal to 85 wt%, greater than or equal to 50 wt% and less than or equal to 75 wt%, greater than or equal to 50 wt% and less than or equal to 65 wt%, or even greater than or equal to 50 wt% and less than or equal to 55 wt%, or any and all sub-ranges formed from any of these endpoints.

[0101] The graphite particles, also referred to herein as “electrically conductive fdler material,” are included in the extrudable composition such that the resultant monolithic article is electrically conductive. In embodiments, the graphite particles may comprise graphite plates, graphite flakes, natural graphite, synthetic graphite, or combinations thereof.

[0102] In embodiments, the graphite particles may comprise an elongated morphology and / or a planar shape having a smaller height than a length and a width. In embodiments, the graphite particles may have a median longest dimension (e.g., diameter) greater than or equal to 1 micron and less than or equal to 100 microns, greater than or equal to 1 micron and less than or equal to 75 microns, greater than or equal to 1 micron and less than or equal to 50 microns, greater than or equal to 1 micron and less than or equal to 25 microns, greater than or equal to 1 micron and less than or equal to 10 microns, greater than or equal to 10 microns and less than or equal to 100 microns, greater than or equal to 10 microns and less than or equal to 75 microns, greater than or equal to 10 microns and less than or equal to 50 microns, greater than or equal to 10 microns and less than or equal to 25 microns, greater than or equal to 25microns and less than or equal to 100 microns, greater than or equal to 25 microns and less than or equal to 75 microns, greater than or equal to 25 microns and less than or equal to 50 microns, greater than or equal to 50 microns and less than or equal to 100 microns, greater than or equal to 50 microns and less than or equal to 75 microns, or even greater than or equal to 75 microns and less than or equal to 100 microns, or any and all sub-ranges formed from any of these endpoints. In embodiments, the graphite particles may comprise an aspect ratio (e.g., thickness to diameter) of 1 :2 to 1: 100, 1:2 to 1:75, 1:2 to 1:50, 1:2 to 1:25, 1 :2 to 1: 10, 1: 10 to 1: 100, l: 10 to 1:75, 1: 10 to 1:50, 1: 10 to 1:25, 1:25 to 1: 100, 1:25 to 1:75, 1:25 to 1 :50, 1:50 to 1: 100, 1:50 to 1:75, or even from 1:75 to 1: 100, or any and all sub-ranges formed from any of these endpoints.

[0103] A minimum amount of graphite particles may be included in the extrudable composition (e.g., greater than or equal to 5 wt%) to ensure that a continuous graphite phase may be achieved to produce an electrically conductive monolithic article. The amount of the graphite particles may be limited (e.g., less than or equal to 40 wt%) to ensure that sufficient binding and sintering of the inorganic particles may be achieved to produce improved mechanical strength (e.g., a modulus of rupture of the exterior skin is at least 150% greater than a modulus of rupture of the core). In embodiments, the amount of the graphite particles in the extrudable composition may be, based on a total dry weight of the extrudable composition, greater than or equal to 5 wt%, greater than or equal to 10 wt%, or even greater than or equal to 15 wt%. In embodiments, the amount of the graphite particles in the extrudable composition may be, based on a total dry weight of the extrudable composition, less than or equal to 40 wt%, less than or equal to less than or equal to 35 wt%, less than or equal to 30 wt%, or even less than or equal to 25 wt%. In embodiments, the amount of the graphite particles in the extrudable composition may be, based on a total dry weight of the extrudable composition, greater than or equal to 5 wt% and less than or equal to 40 wt%, greater than or equal to 5 wt% and less than or equal to 35 wt%, greater than or equal to 5 wt% and less than or equal to 30 wt%, greater than or equal to 5 wt% and less than or equal to 25 wt%, greater than or equal to 10 wt% and less than or equal to 40 wt%, greater than or equal to 10 wt% and less than or equal to 35 wt%, greater than or equal to 10 wt% and less than or equal to 30 wt%, greater than or equal to 10 wt% and less than or equal to 25 wt%, greater than or equal to 15 wt% and less than or equal to 40 wt%, greater than or equal to 15 wt% and less than or equal to 35 wt%,greater than or equal to 15 wt% and less than or equal to 30 wt%, or even greater than or equal to 15 wt% and less than or equal to 25 wt%, or any and all sub-ranges formed from any of these endpoints.

[0104] In embodiments, the extrudable composition may further comprise a pore-forming material. The pore-forming material may degrade and / or pyrolyze (e.g., bum out) during debinding to form pores in the monolithic article. In embodiments, the pore-forming material may comprise a starch (e.g., a cross-linked starch, such as cross-linked pea starch), a nut-shell flour, carbon, a natural polymer, a synthetic polymer, a carbonaceous material, crystalline carbon, amorphous carbon, or combinations thereof.

[0105] In embodiments, the amount of the pore-forming material in the extrudable composition may be, in terms of superadditions to 100 parts of the inorganic particles, greater than or equal to 5 parts, greater than or equal to 10 parts, or even greater than or equal to 15 parts. In embodiments, the amount of the pore-forming material in the extrudable composition may be, in terms of superadditions to 100 parts of the inorganic particles, less than or equal to 45 parts, less than or equal to 35 parts, or even less than or equal to 25 parts. In embodiments, the amount of the pore-forming material in the extrudable composition may be, in terms of superadditions to 100 parts of the inorganic particles, greater than or equal to 5 parts and less than or equal to 45 parts, greater than or equal to 5 parts and less than or equal to 35 parts, greater than or equal to 5 parts and less than or equal to 25 parts, greater than or equal to 10 parts and less than or equal to 45 parts, greater than or equal to 10 parts and less than or equal to 35 parts, greater than or equal to 10 parts and less than or equal to 25 parts, greater than or equal to 15 parts and less than or equal to 45 parts, greater than or equal to 15 parts and less than or equal to 35 parts, or even greater than or equal to 15 parts and less than or equal to 25 parts, or any and all sub-ranges formed from any of these endpoints.

[0106] In embodiments, the extrudable composition may further comprise a porous material. In embodiments, the porous material may comprise paper, polymer, glass, glass-ceramic, ceramic, diatomaceous earth, perlite, pumice, or combinations thereof. In embodiments, the porous material may comprise hollow glass beads. In embodiments, the hollow glass beads may have a dso diameter greater than or equal to 10 microns and less than or equal to 100 microns, greater than or equal to 10 microns and less than or equal to 75 microns, greater than or equal to 10 microns and less than or equal to 50 microns, greater than or equal to 10 micronsand less than or equal to 25 microns, greater than or equal to 25 microns and less than or equal to 100 microns, greater than or equal to 25 microns and less than or equal to 75 microns, greater than or equal to 25 microns and less than or equal to 50 microns, greater than or equal to 50 microns and less than or equal to 100 microns, greater than or equal to 50 microns and less than or equal to 75 microns, or even greater than or equal to 75 microns and less than or equal to 100 microns, or any and all sub-ranges formed from any of these endpoints. In embodiments, the hollow glass beads may comprise hollow glass microspheres.

[0107] In embodiments, the amount of the porous material may be, based on a total dry weight of the extrudable composition, greater than or equal to 25 wt%, greater than or equal to 30 wt%, or even greater than or equal to 35 wt%. In embodiments, the amount of the porous material may be, based on a total dry weight of the extrudable composition, less than or equal to 55 wt% or even less than or equal to 25 wt%. In embodiments, the amount of the porous material may be, based on a total dry weight of the extrudable composition, greater than or equal to 25 wt% and less than or equal to 55 wt%, greater than or equal to 25 wt% and less than or equal to 45 wt%, greater than or equal to 30 wt% and less than or equal to 55 wt%, greater than or equal to 30 wt% and less than or equal to 45 wt%, greater than or equal to 35 wt% and less than or equal to 55 wt%, or even greater than or equal to 35 wt% and less than or equal to 45 wt%, or any and all sub-ranges formed from any of these endpoints.

[0108] In embodiments, the extrudable composition may include other additives to enhance extrudability or provide strength during handling, processing, or in the final product, such as boric acid, potassium carbonate, or combinations thereof. In embodiments, the extrudable composition may include other additives, such as lubricants like mineral oil.

[0109] In embodiments, the extrudable composition may further include one or more solvents, such as an aqueous solvent or an organic solvent. In embodiments, the solvent may comprise water, mineral oil, or combinations thereof. In embodiments, the amount of the solvent in the extrudable composition may be, in terms of superadditions to 100 parts of the inorganic particles, greater than or equal to 25 parts, greater than or equal to 35 parts, or even greater than or equal to 45 parts. In embodiments, the amount of the solvent in the extrudable composition may be, in terms of superadditions to 100 parts of the inorganic particles, less than or equal to 75 parts, less than or equal to 65 parts, or even less than or equal to 55 parts. In embodiments, the amount of the solvent in the extrudable composition may be, in terms ofsuperadditions to 100 parts of the inorganic particles, greater than or equal to 25 parts and less than or equal to 75 parts, greater than or equal to 25 parts and less than or equal to 65 parts, greater than or equal to 25 parts and less than or equal to 55 parts, greater than or equal to 35 parts and less than or equal to 75 parts, greater than or equal to 35 parts and less than or equal to 65 parts, greater than or equal to 35 parts and less than or equal to 55 parts, greater than or equal to 45 parts and less than or equal to 75 parts, greater than or equal to 45 parts and less than or equal to 65 parts, or even greater than or equal to 45 parts and less than or equal to 55 parts, or any and all sub-ranges formed from any of these endpoints.

[0110] Referring now to FIG. 2, the extrudate 150 comprises an exterior skin 152, also referred to herein as “outer periphery” or “outer periphery region,” and a core 154 disposed within and surrounded by the exterior skin 152. In embodiments, the exterior skin 152 and the core 154 may have the same extrudable composition. In embodiments, the method 100 may comprise cutting a portion of the extrudate 150, which is then debinded and sintered. In embodiments, the exterior skin 152 and core 154 may be simultaneous extruded.

[0111] In embodiments, the exterior skin 152 may an average thickness that is less than 10%, less than 8%, less than 6%, less than 4%, or even less than 2% of a transverse hydraulic diameter of the extrudate 150.

[0112] The extrudate 150 may have any shape such that the resultant monolithic article is sufficient for its intended purpose. For example, in embodiments, the core 154 may have a honeycomb structure 156 comprising a plurality of cells 158 therein. The plurality of cells 158 may define parallel channels 160 running longitudinally through the honeycomb structure 156. Intersecting walls 162 may extend in an axial direction to form the cells 158 in a transverse face.

[0113] The honeycomb structure 156 may have any suitable circumferential profile or shape, such as that of a circle, oval, square, rectangle, hexagon, triangle, polygon, or irregular shape. When viewed from an end of the honeycomb structure 156, the cells 158 may have any suitable profile, such as a profile of a circle, oval, square, rectangle, hexagon, triangle, polygon, or irregular shape, such as a honeycomb shape. For example, as shown in FIG. 2, one possible combination is a cylindrical article (circular circumferential profile) that has square-shaped cells. The use of a honeycomb structure 156 may advantageously result in a lower pressure drop of a fluid stream flowing from one axial end of the honeycomb structure 156 to the otherend in comparison to other forms (such as packed pellet beds). The honeycomb structure 156 may include any suitable number of cells 158 per square inch (e.g., as measured when viewed from an end). For example, in embodiments, the honeycomb structure 156 may have greater than or equal to 20 and less than or equal to 1000 cells per square inch, greater than or equal to 20 and less than or equal to 750 cells per square inch, greater than or equal to 20 and less than or equal to 500 cells per square inch, greater than or equal to 20 and less than or equal to 250 cells per square inch, greater than or equal to 20 and less than or equal to 100 cells per square inch, greater than or equal to 20 and less than or equal to 50 cells per square inch, greater than or equal to 50 and less than or equal to 1000 cells per square inch, greater than or equal to 50 and less than or equal to 750 cells per square inch, greater than or equal to 50 and less than or equal to 500 cells per square inch, greater than or equal to 50 and less than or equal to 250 cells per square inch, greater than or equal to 50 and less than or equal to 100 cells per square inch, greater than or equal to 100 and less than or equal to 1000 cells per square inch, greater than or equal to 100 and less than or equal to 750 cells per square inch, greater than or equal to 100 and less than or equal to 500 cells per square inch, greater than or equal to 100 and less than or equal to 250 cells per square inch, greater than or equal to 250 and less than or equal to 1000 cells per square inch, greater than or equal to 250 and less than or equal to 750 cells per square inch, greater than or equal to 250 and less than or equal to 500 cells per square inch, greater than or equal to 500 and less than or equal to 1000 cells per square inch, greater than or equal to 500 and less than or equal to 750 cells per square inch, or even greater than or equal to 750 and less than or equal to 1000 cells per square inch, or any and all sub-ranges formed from any of these endpoints. The cells 158 in the honeycomb structure 156 may have any suitable wall thickness. For example, in embodiments, the cells 158 in the honeycomb structure 156 may have a wall thickness greater than or equal to 0.001 inches and less than or equal to 0.1 inches, greater than or equal to 0.001 inches and less than or equal to 0.05 inches, greater than or equal to 0.001 inches and less than or equal to 0.01 inches, greater than or equal to 0.005 inches and less than or equal to 0. 1 inches, greater than or equal to 0.005 inches and less than or equal to 0.05 inches, greater than or equal to 0.005 inches and less than or equal to 0.01 inches, greater than or equal to 0.01 inches and less than or equal to 0.1 inches, or even greater than or equal to 0.01 inches and less than or equal to 0.05 inches, or any and all sub-ranges formed from any of these endpoints. In embodiments, the cells 158 in the honeycomb structure 156 may includea geometry of 100 / 8 or 2008 / cells per square inch / 0.001 inches wall thickness. In embodiments, the honeycomb structure 156 may have a diameter greater than or equal to 3 inches and less than or equal to 15 inches, greater than or equal to 3 inches and less than or equal to 12 inches, greater than or equal to 3 inches and less than or equal to 9 inches, greater than or equal to 3 inches and less than or equal to 6 inches, greater than or equal to 6 inches and less than or equal to 15 inches, greater than or equal to 6 inches and less than or equal to 12 inches, greater than or equal to 6 inches and less than or equal to 9 inches, greater than or equal to 9 inches and less than or equal to 15 inches, greater than or equal to 9 inches and less than or equal to 12 inches, or even greater than or equal to 12 inches and less than or equal to 15 inches, or any and all sub-ranges formed from any of these endpoints. In embodiments, the honeycomb structure 156 may have a length greater than or equal to 3 inches and less than or equal to 15 inches, greater than or equal to 3 inches and less than or equal to 12 inches, greater than or equal to 3 inches and less than or equal to 9 inches, greater than or equal to 3 inches and less than or equal to 6 inches, greater than or equal to 6 inches and less than or equal to 15 inches, greater than or equal to 6 inches and less than or equal to 12 inches, greater than or equal to 6 inches and less than or equal to 9 inches, greater than or equal to 9 inches and less than or equal to 15 inches, greater than or equal to 9 inches and less than or equal to 12 inches, or even greater than or equal to 12 inches and less than or equal to 15 inches, or any and all sub-ranges formed from any of these endpoints.

[0114] Referring back to FIG. 1, the method continues at block 104 with drying the extrudate 150 (FIG. 2). The drying may be any suitable drying that substantially removes solvent from the extrudate 150. In embodiments, the drying may comprise heating, air flow, exposing to microwaves or other energy sources, or combinations thereof. In embodiments, the drying may include placing the extrusion 150 under a vacuum. In embodiments, the drying may include drying at a sufficient temperature (e.g., greater than or equal to 80 °C and less than or equal to 130 °C) and for a sufficient time period to substantially remove all solvent from the extruded composition (e.g., such that the dried extrudate has a solvent content less than 5 wt%, or less than 2 wt%, less than 1 wt%, less than 0.5 wt%, or less than 0. 1 wt%, based on a total weight of the dried extrudate). The drying temperature and time may be dependent on the size and / or the solvent content of the extrudate.

[0115] Referring back to FIG. 1, the method continues at block 106 with debinding the extrudate 150 (FIG. 2) in a debinding atmosphere at one or more debinding temperatures to remove the binder from the extrudate 150. “Debinding atmosphere” is also be referred to herein as “a first heating atmosphere.” “One or more debinding temperatures” is also be referred to herein as “one or more first atmosphere temperatures” within “a first atmosphere temperature range.” Incomplete burnout of the binder may result in char (e.g., carbonaceous material) being present in the resultant monolithic article. As such, the debinding removes binder from the extrudate 150 to prevent charring. The debinding may also remove pore-forming material present in the extrudate 150, thereby forming pores in the extrudate 150 and increasing the porosity therein.

[0116] The one or more debinding temperatures may be less than 650 °C to limit or prevent graphite oxidation. In embodiments, the first atmosphere temperature range may be below a combustion temperature of the electrically conductive filler material. In embodiments, the one or more debinding temperatures may be greater than or equal to 200 °C to ensure sufficient binder removal and, if present, removal of the pore-forming material. Accordingly, in embodiments, the one or more debinding temperatures may be greater than or equal to 200 °C and less than 650 °C. In embodiments, the one or more debinding temperatures may be greater than or equal to 200 °C, greater than or equal to 250 °C, greater than or equal to 300 °C, greater than or equal to 350 °C, or even , greater than or equal to 400 °C. In embodiments, the debinding temperature may be less than 650 °C, less than or equal to 600 °C, less than or equal to 550 °C, less than or equal to 500 °C, less than or equal to 450 °C, or even less than or equal to 400 °C. In embodiments, the debinding temperature may be greater than or equal to 200 °C and less than 650 °C, greater than or equal to 200 °C and less than or equal to 600 °C, greater than or equal to 200 °C and less than or equal to 550 °C, greater than or equal to 200 °C and less than or equal to 500 °C, greater than or equal to 200 °C and less than or equal to 450 °C, greater than or equal to 200 °C and less than or equal to 400 °C, greater than or equal to 250 °C and less than 650 °C, greater than or equal to 250 °C and less than or equal to 600 °C, greater than or equal to 250 °C and less than or equal to 550 °C, greater than or equal to 250 °C and less than or equal to 500 °C, greater than or equal to 250 °C and less than or equal to 450 °C, greater than or equal to 250 °C and less than or equal to 400 °C, greater than or equal to 300 °C and less than 650 °C, greater than or equal to 300 °C and less than or equal to 600°C, greater than or equal to 300 °C and less than or equal to 550 °C, greater than or equal to 300 °C and less than or equal to 500 °C, greater than or equal to 300 °C and less than or equal to 450 °C, greater than or equal to 300 °C and less than or equal to 400 °C, greater than or equal to 350 °C and less than 650 °C, greater than or equal to 350 °C and less than or equal to 600 °C, greater than or equal to 350 °C and less than or equal to 550 °C, greater than or equal to 350 °C and less than or equal to 500 °C, greater than or equal to 350 °C and less than or equal to 450 °C, greater than or equal to 350 °C and less than or equal to 400 °C, greater than or equal to 400 °C and less than 650 °C, greater than or equal to 400 °C and less than or equal to 600 °C, greater than or equal to 400 °C and less than or equal to 550 °C, greater than or equal to 400 °C and less than or equal to 500 °C, or even greater than or equal to 400 °C and less than or equal to 450 °C, or any and all sub-ranges formed from any of these endpoints.

[0117] The extrudate 150 (FIG. 2) may be held at a hold debinding temperature (i.e., one of the one or more debinding temperatures) for an amount of time (i.e., a first heating duration) sufficient to remove binder from the extrudate 150 while the graphite particles remain intact, which may depend on the extrudable composition, the shape of the extrudate 150, and / or the dimensions of the extrudate 150. A ramp rate to the hold debinding temperature may also effect the debinding hold time and vice versa, as the extrudate 150 simply needs to be subjected to debinding for an amount of time sufficient to remove the binder. For example, if the ramp rate is relatively slow (e.g., 5 °C / hour), then the time at which the extrudates is held at the hold debinding temperature may be relatively short (e.g., 2 hours). In embodiments, the debinding may comprise holding the extrudate 150 at the hold debinding temperature for greater than or equal to 2 hours to less than or equal to 40 hours. In embodiments, the debinding may comprising holding the extrudate 150 at the hold debinding temperature for greater than or equal to 2 hours, greater than or equal to 4 hours, greater than or equal to 6 hours, greater than or equal to 8 hours, or even greater than or equal to 10 hours. In embodiments, the debinding may comprise holding the extrudate 150 at the hold debinding temperature for less than or equal to 40 hours, less than or equal to 30 hours, less than or equal to 20 hours, or even less than or equal to 10 hours. In embodiments, the debinding may comprise holding the extrudate 150 at the hold debinding temperature for greater than or equal to 2 hours to less than or equal to 40 hours, greater than or equal to 2 hours to less than or equal to 30 hours, greater than or equal to 2 hours to less than or equal to 20 hours, greater than or equal to 2 hours to less thanor equal to 10 hours, greater than or equal to 4 hours to less than or equal to 40 hours, greater than or equal to 4 hours to less than or equal to 30 hours, greater than or equal to 4 hours to less than or equal to 20 hours, greater than or equal to 4 hours to less than or equal to 10 hours, greater than or equal to 6 hours to less than or equal to 40 hours, greater than or equal to 6 hours to less than or equal to 30 hours, greater than or equal to 6 hours to less than or equal to 20 hours, greater than or equal to 6 hours to less than or equal to 10 hours, greater than or equal to 8 hours to less than or equal to 40 hours, greater than or equal to 8 hours to less than or equal to 30 hours, greater than or equal to 8 hours to less than or equal to 20 hours, greater than or equal to 8 hours to less than or equal to 10 hours, greater than or equal to 10 hours to less than or equal to 40 hours, greater than or equal to 10 hours to less than or equal to 30 hours, or even greater than or equal to 10 hours to less than or equal to 20 hours, or any and all sub-ranges formed from any of these endpoints.

[0118] Regarding ramp rate to the hold debinding temperature, as mentioned herein, the debinding hold time may effect the ramp rate to the hold debinding temperature and vice versa, as the extrudate 150 (FIG. 2) simply needs to be subjected to debinding for an amount of time sufficient to remove the binder. Additionally, the ramp rate to the one or the one or more debinding temperatures may need to be controlled in view of the dimensions of the extrudate 150. For example, with relatively larger extrudates 150, the temperature / heat may build up within the core 154 (FIG. 2) of the extrudate 150. As such, the ramp rate to the hold debinding temperature may be controlled such that the temperature differential between the core 154 and the exterior skin 152 (FIG. 2) is below a threshold where cracking may occur. In embodiments, the debinding may comprise increasing to the hold debinding temperature at a first ramp rate greater than or equal to 5 °C / hour and less than or equal to 20 °C / hour. In embodiments, the first ramp rate may be greater than or equal to 5 °C / hour or even greater than or equal to 10 °C / hour. In embodiments, the first ramp rate may be less than or equal to 20 °C / hour or even less than or equal to 15 °C / hour. In embodiments, the first ramp rate may be greater than or equal to 5 °C / hour and less than or equal to 20 °C / hour, greater than or equal to 5 °C / hour and less than or equal to 15 °C / hour, greater than or equal to 10 °C / hour and less than or equal to 20 °C / hour, or even greater than or equal to 10 °C / hour and less than or equal to 15 °C / hour, or any and all sub-ranges formed from any of these endpoints.

[0119] In embodiments, the debinding and sintering steps described herein may be conducted in a furnace (e.g., a kiln). As such, the debinding temperatures and the sintering temperatures described herein refer to a furnace temperature. The atmosphere in the furnace (e.g., kiln) may be controlled through a combination of O2 setpoints and optimizing the burner lambda to run in a slightly lean fuel mixture and / or by controlling the recirculation of product combustion gases, or additional excess nitrogen. In embodiments, a gaseous makeup of the first and / or second heating atmospheres may be provided by adjusting oxygen input and / or level in the atmosphere, adjusting fuel mixture of one or more burners that provide heat to the atmosphere, adjusting introduction and / or level of recirculated products of combustion gases in the atmosphere, adjusting introduction and / or level of inert gas in the atmosphere, or combinations thereof. In embodiments, the one or more burners is a lean fuel mixture. In embodiments, at least one of the debinding atmosphere and the sintering atmosphere described herein may comprise nitrogen, argon, or a combination thereof as an inert gas.

[0120] The debinding atmosphere may have a minimum oxygen concentration (e.g., greater than or equal to 3%) to ensure that there is enough oxygen available to remove the binder and, if present, the pore-forming material. The amount of oxygen concentration may be limited (e.g., less than or equal to 18%) to prevent graphite oxidation during the debinding. Accordingly, in embodiments, the debinding atmosphere may comprise an oxygen concentration, also referred to as “a first oxygen range,” greater than or equal to 3% and less than or equal to 18%. In embodiments, the oxygen concentration of the debinding atmosphere may be greater than or equal to 3%, greater than or equal to 5%, or even greater than or equal to 7%. In embodiments, the oxygen concentration of the debinding atmosphere may be less than or equal to 18%, less than or equal to 15%, less than or equal to 12%, or even less than or equal to 9%. In embodiments, the oxygen concentration of the debinding atmosphere may be greater than or equal to 3% and less than or equal to 18%, greater than or equal to 3% and less than or equal to 15%, greater than or equal to 3% and less than or equal to 12%, greater than or equal to 3% and less than or equal to 9%, greater than or equal to 5% and less than or equal to 18%, greater than or equal to 5% and less than or equal to 15%, greater than or equal to 5% and less than or equal to 12%, greater than or equal to 5% and less than or equal to 9%, greater than or equal to 7% and less than or equal to 18%, greater than or equal to 7% and less than or equal to 15%, greater than or equal to 7% and less than or equal to 12%, or even greater thanor equal to 7% and less than or equal to 9%, or any and all sub-ranges formed from any of these endpoints.

[0121] Referring back to FIG. 1, the method 100 continues at block 108 with sintering the extrudate 150 (FIG. 2) in a sintering atmosphere at one or more sintering temperatures to remove the graphite particles from the exterior skin 152 (FIG. 2) of the extrudate 150 and sinter the inorganic particles of the extrudate 150, to thereby form the monolithic article. “Sintering atmosphere” is also referred to herein as “a second heating atmosphere.” “One or more sintering temperatures” is also be referred to herein as “one or more second atmosphere temperatures” within “a second atmosphere temperature range.” The sintering occurs at a relatively high temperature (e.g., greater than or equal to 650 °C) and in a relatively low oxygen atmosphere (e.g., an oxygen concentration less than or equal to 2.5%), which oxidizes and removes graphite from an exterior skin of the extrudate while preserving graphite in a core of the extrusion. In embodiments, the second heating atmosphere has a gaseous makeup which hinders combustion of the electrically conductive filler material. Graphite in the core allows the resultant monolithic article to be electrically conductive. Removal of graphite from the exterior skin enables increased binding and sintering of inorganic particles in the exterior skin, thereby strengthening the exterior skin and the article overall ( (e.g., a modulus of rupture of the exterior skin is at least 150% greater than a modulus of rupture of the core).

[0122] As described herein, the one or more sintering temperatures may be greater than or equal to 650 °C to ensure graphite oxidation and sintering of the inorganic particles. In embodiments, the second atmosphere temperature range may be at or above the combustion temperature of the electrically conductive fdler. The one or more sintering temperatures may be limited (e.g., less than or equal to 1000 °C) to prevent oxidation of graphite within the core 154 of the extrudate 150 (FIG. 2). Accordingly, in embodiments, the one or more sintering temperatures may be greater than or equal to 650 °C and less than or equal to 1000 °C. In embodiments, the one or more sintering temperatures may be greater than or equal to 650 °C and less than or equal to 1000 °C. In embodiments, the one or more sintering temperatures may be greater than or equal to 650 °C, greater than or equal to 700 °C, greater than or equal to 750 °C, or even greater than or equal to 800 °C. In embodiments, the one or more sintering temperatures may be less than or equal to 1000 °C, less than or equal to 950 °C, less than or equal to 900 °C, or even less than or equal to 950 °C. In embodiments, the one or more sinteringtemperatures may be greater than or equal to 650 °C and less than or equal to 1000 °C, greater than or equal to 650 °C and less than or equal to 950 °C, greater than or equal to 650 °C and less than or equal to 900 °C, greater than or equal to 650 °C and less than or equal to 850 °C, greater than or equal to 700 °C and less than or equal to 1000 °C, greater than or equal to 700 °C and less than or equal to 950 °C, greater than or equal to 700 °C and less than or equal to 900 °C, greater than or equal to 700 °C and less than or equal to 850 °C, greater than or equal to 750 °C and less than or equal to 1000 °C, greater than or equal to 750 °C and less than or equal to 950 °C, greater than or equal to 750 °C and less than or equal to 900 °C, greater than or equal to 750 °C and less than or equal to 850 °C, greater than or equal to 800 °C and less than or equal to 1000 °C, greater than or equal to 800 °C and less than or equal to 950 °C, greater than or equal to 800 °C and less than or equal to 900 °C, or even greater than or equal to 800 °C and less than or equal to 850 °C, or any and all sub-ranges formed from any of these endpoints.

[0123] As described herein, the oxygen concentration of the sintering atmosphere may be limited (e.g., less than or equal to 2.5%) to preserve graphite in the core 154 of the extrusion 150 (FIG. 2). Accordingly, in embodiments, the sintering atmosphere may comprise an oxygen concentration less than or equal to 2.5%. In embodiments, the sintering atmosphere may comprise an oxygen concentration greater than or equal to 0.0% and less than or equal to 2.5%. In embodiments, the sintering atmosphere may comprise an oxygen concentration, also referred to herein as “a second oxygen range,” greater than or equal to 0.0% or even greater than or equal to 0.5%. In embodiments, the sintering atmosphere may comprises an oxygen concentration less than or equal to 2.5%, less than or equal to 2.0%, less than or equal to 1.5%, or even less than or equal to 1.0%. In embodiments, the sintering atmosphere may comprise an oxygen concentration greater than or equal to 0.0% and less than or equal to 2.5%, greater than or equal to 0.0% and less than or equal to 2.0%, greater than or equal to 0.0% and less than or equal to 1.5%, greater than or equal to 0.0% and less than or equal to 1.0%, greater than or equal to 0.5% and less than or equal to 2.5%, greater than or equal to 0.5% and less than or equal to 2.0%, greater than or equal to 0.5% and less than or equal to 1.5%, or even greater than or equal to 0.5% and less than or equal to 1.0%, or any and all sub-ranges formed from any of these endpoints.

[0124] The extrudate 150 (FIG. 2) may be held at a hold sintering temperature (i.e., one of the one or more sintering temperatures) for an amount of time (i.e., a second heating duration) (e.g., greater than or equal to 0.5 hour) sufficient to remove graphite from the exterior skin 152 (FIG. 2) and sinter the inorganic particles. The amount of time the extrudate 150 is held at the hold sintering temperature may be limited (e.g., less than or equal to 8 hours) to ensure that graphite oxidation does not occur in the core 154 (FIG. 2) of the extrudate 150 and the graphite particles remain intact in the core. Accordingly, in embodiments, the sintering may comprise holding the extrudate 150 at the hold sintering temperature for greater than or equal to 0.5 hour to less than or equal to 8 hours. In embodiments, the sintering may comprising holding the extrudate 150 at the hold sintering temperature for greater than or equal to 0.5 hour, greater than or equal to 1 hour, greater than or equal to 2 hours, or even greater than or equal to 4 hours. In embodiments, the sintering may comprise holding the extrudate 150 at the hold sintering temperature for less than or equal to 8 hours, less than or equal to 6 hours, or even less than or equal to 4 hours. In embodiments, the sintering may comprise holding the extrudate 150 at the hold sintering temperature for greater than or equal to 0.5 hour to less than or equal to 8 hours, greater than or equal to 0.5 hour to less than or equal to 6 hours, greater than or equal to 0.5 hour to less than or equal to 4 hours, greater than or equal to 1 hour to less than or equal to 8 hours, greater than or equal to 1 hour to less than or equal to 6 hours, greater than or equal to 1 hour to less than or equal to 4 hours, greater than or equal to 2 hours to less than or equal to 8 hours, greater than or equal to 2 hours to less than or equal to 6 hours, greater than or equal to 2 hours to less than or equal to 4 hours, greater than or equal to 4 hours to less than or equal to 8 hours, or even greater than or equal to 4 hours to less than or equal to 6 hours, or any and all subranges formed from any of these endpoints.

[0125] In embodiments, the sintering may comprise increasing to the hold sintering temperature at a second ramp rate greater than or equal to 5 °C / hour and less than or equal to 100 °C / hour. In embodiments, the second ramp rate may be greater than or equal to 5 °C / hour, greater than or equal to 10 °C / hour, greater than or equal to 20 °C / hour, greater than or equal to 30 °C / hour, greater than or equal to 40 °C / hour, or even greater than or equal to 50 °C / hour. In embodiments, the second ramp rate may be less than or equal to 100 °C / hour, less than or equal to 80 °C / hour, less than or equal to 60 °C / hour, less than or equal to 40 °C / hour, or even less than or equal to 20 °C / hour. In embodiments, the second ramp rate may be greater than orequal to 5 °C / hour and less than or equal to 100 °C / hour, greater than or equal to 5 °C / hour and less than or equal to 80 °C / hour, greater than or equal to 5 °C / hour and less than or equal to 60 °C / hour, greater than or equal to 5 °C / hour and less than or equal to 40 °C / hour, greater than or equal to 5 °C / hour and less than or equal to 20 °C / hour, greater than or equal to 10 °C / hour and less than or equal to 100 °C / hour, greater than or equal to 10 °C / hour and less than or equal to 80 °C / hour, greater than or equal to 10 °C / hour and less than or equal to 60 °C / hour, greater than or equal to 10 °C / hour and less than or equal to 40 °C / hour, greater than or equal to 10 °C / hour and less than or equal to 20 °C / hour, greater than or equal to 20 °C / hour and less than or equal to 100 °C / hour, greater than or equal to 20 °C / hour and less than or equal to 80 °C / hour, greater than or equal to 20 °C / hour and less than or equal to 60 °C / hour, greater than or equal to 20 °C / hour and less than or equal to 40 °C / hour, greater than or equal to 30 °C / hour and less than or equal to 100 °C / hour, greater than or equal to 30 °C / hour and less than or equal to 80 °C / hour, greater than or equal to 30 °C / hour and less than or equal to 60 °C / hour, greater than or equal to 30 °C / hour and less than or equal to 40 °C / hour, greater than or equal to 40 °C / hour and less than or equal to 100 °C / hour, greater than or equal to 40 °C / hour and less than or equal to 80 °C / hour, greater than or equal to 40 °C / hour and less than or equal to 60 °C / hour, greater than or equal to 50 °C / hour and less than or equal to 100 °C / hour, greater than or equal to 50 °C / hour and less than or equal to 80 °C / hour, or even greater than or equal to 50 °C / hour and less than or equal to 60 °C / hour, or any and all sub-ranges formed from any of these endpoints. During the debinding, binder removal and temperature differential may be taken into consideration when determining ramp rate to the hold debinding temperature. During the sintering, these debinding reactions have already occurred, which may allow the ramp rate to the hold sintering temperature to be relatively faster than the ramp rate to the hold debinding temperature.

[0126] In embodiments, the debinding and sintering may be conducted in a single step such that the furnace temperature is ramped from the hold debinding temperature to the hold sintering temperature. In other embodiments, the debinding and sintering may be conducted in two steps such that the temperature is reduced from the hold debinding temperature (e.g., to ambient temperature) and then ramped to hold sintering temperature.

[0127] The resultant monolithic article, formed by the methods disclosed herein, comprises an exterior skin and a core disposed within the exterior skin, similar to or the same as those disclosed with respect to the extrudate 150 shown in FIG. 2.

[0128] The exterior skin of the monolithic article may comprise an inorganic material. The inorganic material may be formed from the binding and sintering of the inorganic particles of the extrudable composition. As such, in embodiments, the inorganic material may comprise similar or the same materials as described hereinabove with respect to the inorganic particles of the extrudable composition. Because the sintering temperature used in the methods described herein is relatively low (e.g., less than or equal to 1000 °C), the inorganic particles are softened during the sintering and may not form a single phase (e.g., cordierite).

[0129] The methods disclosed herein remove graphite from the exterior skin 152 of the extrudate 150 (FIG. 2) such that the exterior skin of the monolithic article is free or substantially free of graphite. For example, in embodiments, the amount of graphite in the exterior skin of the monolithic article may be less than or equal to 10%, less than or equal to 5%, less than or equal to 3%, or even less than or equal to 1% of the amount of graphite in the exterior skin of the extrudate from which the monolithic article is formed.

[0130] The core of the monolithic article may comprise a continuous graphite phase and an inorganic phase comprising the inorganic material. The graphite phase and the inorganic phase together form an interconnected pore structure. In embodiments, the continuous graphite phase may be homogenously distributed throughout the core. The methods disclosed herein preserve graphite in the core 154 of the extrudate 150 (FIG. 2). As such, in embodiments, the continuous graphite phase of the core of the monolithic article may comprise fired graphite plates, graphite flakes, natural graphite, synthetic graphite, or combinations thereof. The graphite plates, graphite flakes, natural graphite, and / or synthetic graphite that are fired to form the continuous graphite phase may be the same as or similar as described hereinabove with respect to the graphite particles of the extrudable composition. In embodiments, the core 154 of the monolithic article may comprise an inorganic matrix with the electrically conductive material dispersed throughout the inorganic matrix.

[0131] In embodiments, the porous material, when present in the extrudable composition, may be present in the monolithic article. For example, while materials such as paper and polymer may burnout through the debinding and / or sintering processes, glass, glass-ceramic,ceramic, diatomaceous earth, perlite, and / or pumice may remain in the monolithic article. In embodiments, hollow glass beads present in the extrudate may be softened in the second heating atmosphere. In embodiments, the monolithic article may comprise hollow glass beads that have burst and / or broken, for example, as a result of sintering. In embodiments, the monolithic article may be free or substantially free of hollow glass beads that have not burst and / or broken. For example, in embodiments, an amount of unbroken and unburst hollow glass beads may be, based on a total weight of the monolithic article, less than or equal to 5 wt%, less than or equal to 4 wt%, less than or equal to 3 wt%, less than or equal to 2 wt%, less than or equal to 1 wt%, less than or equal to 0.5 wt%, less than or equal to 0.1 wt%, or even equal to 0 wt%.

[0132] The monolithic article may have improved mechanical strength as a result of graphite being removed from the exterior skin. In embodiments, the strength of the exterior skin may be greater than a strength of the core. In embodiments, a modulus of rupture of the exterior skin may be at least 150% greater than a modulus of rupture of the core. In embodiments, a modulus of rupture of the exterior skin may be at least 150% greater, at least 160% greater, at least 170% greater, at least 180% greater, at least 190% greater, or at least 200% greater than a modulus of rupture of the core.

[0133] In embodiments, the exterior skin of the monolithic article may have a modulus of rupture greater than or equal to 0.5 MPa, greater than or equal to 0.6 MPa, greater than or equal to 0.7 MPa, or even greater than or equal to 0.8 MPa. In embodiments, the exterior skin of the monolithic article may have a modulus of rupture less than or equal to 1.2 MPa, less than or equal to 1.1 MPa, or even less than or equal to 1.0 MPa. In embodiments, the exterior skin of the monolithic article may have a modulus of rupture greater than or equal to 0.5 MPa and less than or equal to 1.2 MPa, greater than or equal to 0.5 MPa and less than or equal to 1.1 MPa, greater than or equal to 0.5 MPa and less than or equal to 1.0 MPa, greater than or equal to 0.6 MPa and less than or equal to 1.2 MPa, greater than or equal to 0.6 MPa and less than or equal to 1. 1 MPa, greater than or equal to 0.6 MPa and less than or equal to 1.0 MPa, greater than or equal to 0.7 MPa and less than or equal to 1.2 MPa, greater than or equal to 0.7 MPa and less than or equal to 1.1 MPa, greater than or equal to 0.7 MPa and less than or equal to 1.0 MPa, greater than or equal to 0.8 MPa and less than or equal to 1.2 MPa, greater than or equal to 0.8MPa and less than or equal to 1. 1 MPa, or even greater than or equal to 0.8 MPa and less than or equal to 1.0 MPa, or any and all sub-ranges formed from any of these endpoints.

[0134] In embodiments, the core of the monolithic article may have a modulus of rupture greater than or equal to 0.1 MPa, greater than or equal to 0.2 MPa, or even greater than or equal to 0.3 MPa. In embodiments, the core of the monolithic article may have a modulus of rupture less than or equal to 0.6 MPa, less than or equal to 0.5 MPa or even less than or equal to 0.4 MPa. In embodiments, the core of the monolithic article may have a modulus of rupture greater than or equal to 0.1 MPa and less than or equal to 0.6 MPa, greater than or equal to 0.1 MPa and less than or equal to 0.5 MPa, greater than or equal to 0.1 MPa and less than or equal to 0.4 MPa, greater than or equal to 0.2 MPa and less than or equal to 0.6 MPa, greater than or equal to 0.2 MPa and less than or equal to 0.5 MPa, greater than or equal to 0.2 MPa and less than or equal to 0.4 MPa, greater than or equal to 0.3 MPa and less than or equal to 0.6 MPa, greater than or equal to 0.3 MPa and less than or equal to 0.5 MPa, or even greater than or equal to 0.3 MPa and less than or equal to 0.4 MPa, or any and all sub-ranges formed from any of these endpoints.

[0135] In embodiments, the exterior skin of the monolithic article may be stiffer than the core. In embodiments, a Young’s modulus of the exterior skin may be at least 50% greater than a Young’s modulus of the core. In embodiments, a Young’s modulus of the exterior skin may be at least 50% greater, at least 55% greater, at least 60% greater, at least 65% greater, at least 70% greater, or even 75% greater than a young’s modulus of the core.

[0136] In embodiments, the exterior skin of the monolithic article may have a Young’s modulus greater than or equal to 0.4 GPa or even greater than or equal to 0.5 GPa. In embodiments, the exterior skin of the monolithic article may have a Young’s modulus less than or equal to 0.7 GPa or even less than or equal to 0.6 GPa. In embodiments, the exterior skin of the monolithic article may have a Young’s modulus greater than or equal to 0.4 GPa and less than or equal to 0.7 GPa, greater than or equal to 0.4 GPa and less than or equal to 0.6 GPa, greater than or equal to 0.5 GPa and less than or equal to 0.7 GPa, or even greater than or equal to 0.5 GPa and less than or equal to 0.6 GPa, or any and all sub-ranges formed from any of these endpoints.

[0137] In embodiments, the core of the monolithic article may have a Young’s modulus greater than or equal to 0.2 GPa or even greater than or equal to 0.3 GPa. In embodiments, thecore of the monolithic article may have a Young’s modulus less than or equal to 0.4 GPa. In embodiments, the core of the monolithic article may have a Young’s modulus greater than or equal to 0.2 GPa and less than or equal to 0.4 GPa, or even greater than or equal to 0.3 GPa and less than or equal to 0.4 GPa, or any and all sub-ranges formed from any of these endpoints.

[0138] The monolithic article is electrically conductive as a result of graphite being preserved in the core. As such, the monolithic article may be considered a porous electrically conductive article. In embodiments, the core of the monolithic article may have an electrical resistance greater than or equal to 1 ohm to less than or equal to 100 ohms. In embodiments, the core of the monolithic article may have an electrical resistance greater than or equal to 1 ohm, greater than or equal to 5 ohms, greater than or equal to 10 ohms, greater than or equal to 25 ohms, or even greater than or equal to 50 ohms. In embodiments, the core of the monolithic article may have an electrical resistance less than or equal to 100 ohms, less than or equal to 75 ohms, less than or equal to 50 ohms, or even less than or equal to 25 ohms. In embodiments, the core of the monolithic article may have an electrical resistance greater than or equal to 1 ohm to less than or equal to 100 ohms, greater than or equal to 1 ohm to less than or equal to 75 ohms, greater than or equal to 1 ohm to less than or equal to 50 ohms, greater than or equal to 1 ohm to less than or equal to 25 ohms, greater than or equal to 5 ohms to less than or equal to 100 ohms, greater than or equal to 5 ohms to less than or equal to 75 ohms, greater than or equal to 5 ohms to less than or equal to 50 ohms, greater than or equal to 5 ohms to less than or equal to 25 ohms, greater than or equal to 10 ohms to less than or equal to 100 ohms, greater than or equal to 10 ohms to less than or equal to 75 ohms, greater than or equal to 10 ohms to less than or equal to 50 ohms, greater than or equal to 10 ohms to less than or equal to 25 ohms, greater than or equal to 25 ohms to less than or equal to 100 ohms, greater than or equal to 25 ohms to less than or equal to 75 ohms, greater than or equal to 25 ohms to less than or equal to 50 ohms, greater than or equal to 50 ohms to less than or equal to 100 ohms, or even greater than or equal to 50 ohms to less than or equal to 75 ohms, or any and all sub-ranges formed from any of these endpoints.

[0139] In embodiments, the monolithic article may have any suitable bulk density. “Bulk density,” as used herein, refers to the mass of the article divided by the total volume that the article occupies. The total volume that the article occupies includes particle volume, interparticle void volume, and internal pore volume (i.e., intraparticle void), but does not includelongitudinal channels (e.g., portions of the article when viewed from a longitudinal end of the article that are considered to be open frontal area). The total volume that an article with a honeycomb structure occupies may be defined as the portions of the article when viewed from a longitudinal end of the article that is considered to be closed frontal area (CFA) versus those of the open frontal area (OFA), with the CFA and OFA given as complementary percentages that sum to 100%. In particular, the OFA corresponds to the portions of the cross-sectional area occupied by the open channels of the honeycomb structure of the article, while the CFA corresponds to the remaining portions occupied by the matrix of intersecting walls. In embodiments, the monolithic article may have a bulk density greater than or equal to 0.5 g / cm3and less than or equal to 1.5 g / cm3, greater than or equal to 0.5 g / cm3and less than or equal to 1.25 g / cm3, greater than or equal to 0.5 g / cm3and less than or equal to 1.0 g / cm3, greater than or equal to 0.75 g / cm3and less than or equal to 1.5 g / cm3, greater than or equal to 0.75 g / cm3and less than or equal to 1.25 g / cm3, greater than or equal to 0.75 g / cm3and less than or equal to 1.0 g / cm3, greater than or equal to 1.0 g / cm3and less than or equal to 1.5 g / cm3, or even greater than or equal to 1.0 g / cm3and less than or equal to 1.25 g / cm3, or any and all sub-ranges formed from any of these endpoints.

[0140] In embodiments, the monolithic article may have an OFA greater than or equal to 60% and less than or equal to 90%, greater than or equal to 60% and less than or equal to 80%, greater than or equal to 70% and less than or equal to 90%, or even greater than or equal to 70% and less than or equal to 80%, or any and all sub-ranges formed from any of these endpoints.

[0141] In embodiments, the monolithic article may have any suitable total pore volume (i.e., porosity). In embodiments, the monolithic article may have a total pore volume greater than or equal to 40% and less than or equal to 95%, greater than or equal to 40% and less than or equal to 85%, greater than or equal to 40% and less than or equal to 75%, greater than or equal to 40% and less than or equal to 65%, greater than or equal to 50% and less than or equal to 95%, greater than or equal to 50% and less than or equal to 85%, greater than or equal to 50% and less than or equal to 75%, greater than or equal to 50% and less than or equal to 65%, greater than or equal to 60% and less than or equal to 95%, greater than or equal to 60% and less than or equal to 85%, greater than or equal to 60% and less than or equal to 75%, greater than or equal to 60% and less than or equal to 65%, greater than or equal to 70% and less thanor equal to 95%, greater than or equal to 70% and less than or equal to 85%, or even greater than or equal to 70% and less than or equal to 75%, or any and all sub-ranges formed from any of these endpoints.

[0142] In embodiments, the monolithic article may comprise a coating on the core. The coating may be continuous or discontinuous. The coating may comprise a catalyst (e.g., a catalyst for treating exhaust emissions in a catalytic converter, or another catalyst), a sorbent that adsorbs and desorbs CO2, or combinations thereof. The sorbent may comprise zeolite, sodium carbonate, activated carbon, carbon nanotubes, a metal-organic framework (MOF), an amine, or combinations thereof. In embodiments, the coating may be directly adhered to the monolithic article, wherein the monolithic article is free of any intervening bonding layer between the coating and the article. In other embodiments, the monolithic article may include a bonding layer, such as a washcoat material. The bonding layer may include a deposition of high surface area particles, such as gamma alumina, zeolite, activated carbon, or combinations thereof.

[0143] In embodiments, a method of using the monolithic article having a coating including a sorbent as described herein comprises exposing the article to a gas stream comprising CO2 to adsorb at least some of the CO2 in the gas stream from the gas stream into the coating; and desorbing the CO2 from the coating, the desorbing comprising applying an electrical potential across the article to heat the article. In embodiments, desorbing the CO2 from the coating on the monolithic article includes heating the monolithic article, such as via resistive heating, sending hot gas (e.g., steam) through the monolithic article, microwave heating, induction heating, via an external heat source at a periphery of the monolithic article, or combinations thereof. In embodiments, desorbing the CO2 from the coating may include sequestering the CO2, such as placing the CO2 in a storage tank.

[0144] In other embodiments, a method of using the monolithic articles having a coating including a catalyst as described herein may include exposing the monolithic article to a gas stream to catalyze a chemical reaction of one or more components of the gas stream using the catalyst.Examples

[0145] In order that various embodiments be more readily understood, reference is made to the following examples, which are intended to illustrate various embodiments of the monolithic articles described herein.

[0146] Table 1 below shows sources of ingredients used to form example extrudable compositions El and E2. Table 2 below shows example extrudable compositions El and E2, with methylcellulose, starch, mineral oil, and water given in terms of superadditions to 100 parts inorganics and all other components given in terms of weight percent (%), based on a total dry weight of the extrudable composition.

[0147] Table 1

[0148] Table 2superadditions

[0149] Referring now to FIGS. 3-5, the relationship between the shrinkage and expansion curves (FIGS. 3 and 4) and relative mass change and heat flow (FIG. 5) as a function of temperature is shown for honeycomb shaped extrudates formed from an example extrudable composition heated in the presence of N2 (i.e., relatively low oxygen content) and in air (i.e., relatively high oxygen content). Table 3 below shows the weight loss of the extrudate at various points for each of the atmospheric conditions. As shown in FIGS. 3-5 and Table 3, there was no substantial change in the extrudates until about 400 °C for both the N2 and air conditions. For temperatures between 400 °C and 600 °C, shrinkage for N2 and air conditions were roughly equivalent and may be attributed to clay shrinkage. Between 600 °C and 1000 °C, there was a difference in shrinkage between the N2 and air conditions, which may be attibuted to shrinkage associated with graphite removal. There was also shrinkage observed with the N2 condition, which may be attributed to talc endotherm reactions and softening of the hollow glass beads. Between 400 °C and 900 °C, there was a difference in weight percentage loss between the N2 and air conditions, which may be attributed mostly to the weight loss associated with organic char and graphite removal in the presence of O2.

[0150] Table 31ststep 2ndstep 3rdstep 4thstepTemp, range (°C) 160 - 210 210 - 320 340 - 440 600 - 800Weight loss - air 7.43 9.99 3.21 14.86(%)Weight loss - N2 (%) 7.35 8.99 ~1.5 -5.5

[0151] As exemplified by FIGS. 3-5 and Table 3, extended periods of time above 650 °C in the presence of O2 result in an increase in the amount of graphite oxidation. Accordingly, to limit graphite oxidation, the methods described herein include debinding at a debinding temperature less than 650 °C and sintering at a sintering temperature greater than or equal to 650 °C and in a sintering atmosphere comprising an oxygen concentration less than or equal to 2.5%.

[0152] Referring now to FIGS. 6-8, 5 cm x 15 cm honeycomb extrudates formed from example extrudable composition E 1 were subj ected to firing in a small scale chamber kiln using electoral heating and simulated atmosphere.

[0153] Referring now to FIG. 6, two honeycomb extrudates, Hl and H2, were subjected to debinding between 250 °C and 600 °C in an atmosphere of 8% O2 to remove binder from the extrudates. The honeycomb extrudates Hl and H2 were then sintered between 600 °C and 900 °C in an atmosphere that was either kept at 8% O2 (Hl) or reduced to 0.5% O2 (H2). As shown in FIG. 6, there was less weight loss and shrinkage of honeycomb extrudate H2 in the 0.5% O2 condition. As exemplified at FIG. 6, graphite may be retained in relatively low O2 conditions (e.g., oxygen concentration less than or equal to 2.5%).

[0154] Referring now to FIG. 7, two honeycomb extrudates, H3 and H4, were subjected to debinding at 250 °C for 4 hours in 8% O2. The honeycomb extrudates H3 and H4 were then subjected to sintering at 875 °C for either 2 hours (H3) or 4 hours (H4) in an atmosphere of about 0.5-1% O2. As shown in FIG. 7, there was a difference in shrinkage, in two directions, between the two conditions. As exemplified at FIG. 7, even in relatively low O2 conditions, weight loss and shrinkage may occur, due to sintering and graphite removal in the exterior skin and / or softening of the hollow glass beads. As such, controlling hold times may ensure desirable debinding and graphite removal.

[0155] Referring now to FIG. 8, a honeycomb extrudate, H5, was subjected to debinding at 250 °C for 4 hours in 8% O2. The honeycomb extrudate H5 was then sintered at 875 °C 4 hours in an atmosphere of about 0.5-1% O2. As shown in FIG. 8, there was an initial drop in the extrudate weight loss of 18% at 250 °C. The weight loss increased from 18% to 20% over the 4 hour hold. As exemplified by FIG. 8, controlling the O2 and debinding duration may ensure desirable debinding and graphite removal.

[0156] Referring now to FIG. 9, a honeycomb extrudate H6 formed from example extrudable composition E2 was subjected to debinding up to 600 °C in an atmosphere of 7.5% O2. The honeycomb extrudate H6 was then sintered between 600 °C and 900 °C at in an atmosphere of about 1.5% O2. As shown in Fig. 9, the exotherm requires about 5 hours for completion of the char burnout, as indicated by a “first bump” in the H6 temperature at about 7 hours and a “second bump” in the H6 temperature at about 12 hours. Referring now to Fig. 10, honeycomb article A6 formed from honeycomb extrudate H6 had graphite removed from the exterior skin (white).

[0157] Referring now to FIGS. 11-16, a honeycomb extrudate H7 formed from an example extrudable composition was subjected to debinding up to 600 °C in an atmosphere of 7.5% O2 and sintering at between 600 °C and 900 °C at in an atmosphere of about 1.5% O2. As shown in FIGS. 11-16, graphite was preserved in the core of the resulting honeycomb article A7, where graphite was removed from the exterior skin.

[0158] A honeycomb extrudate H8 formed from example extrudable composition E2 was subjected to debinding and sintering. Referring now to Table 4, the porosity, MOR, Young’s modulus, and MOR and Young’s modulus differences (i.e., ((exterior skin value - core value ) / core value) x 100) for the exterior skin and core of the resulting honeycomb article A8 is shown. As shown in Table 4, the modulus of rupture of the exterior skin is 163% greater than the modulus of rupture of the core. As exemplified in Table 4, controlling temperature and / or atmosphere during debinding and sintering results in an electrically conductive monolithic article having improved mechanical strength.

[0159] Table 4A8 - Core A8 - Exterior skinPorosity (%) 63.19 69.44MOR (MPa) 0.32 0.84MOR difference (%) 163Young ’s modulus (GPa) 0.35 0.58Young ’s modulus difference (%) 66

[0160] Referring now to Table 5, honeycomb extrudates H9 to H12 formed from example compositions E3 and E2 were subjected to debinding and sintering conditions as shown in Table 5. The electrical resistance of the core resulting honeycomb articles A9 to A12 is shown in Table 5. As exemplified in Table 5, controlling temperature and / or atmosphere during debinding and sintering results in an electrically conductive monolithic article.

[0161] Table 5A9 A10 All A12 honeycomb extrudate H9 H10 Hl l H12 extrudable composition E3 E3 E2 E2 sintering temperature (°C) 875 875 875 875 sintering hold (hr) 6 2 4 4 sintering atmosphere - O21.6 1.5 2 2.4 concentration (%) electrical resistance (ohm) 4 4 160k 15M

[0162] It will be apparent to those skilled in the art that various modifications and variations may be made to the embodiments described herein without departing from the spirit and scope of the claimed subj ect matter. Thus, it is intended that the specification cover the modifications and variations of the various embodiments described herein provided such modification and variations come within the scope of the appended claims and their equivalents.

Claims

CLAIMS1. A method of forming a monolithic article, the method comprising: extruding an extrudable composition to form an extrudate, the extrudable composition comprising a binder, inorganic particles, and graphite particles, the extrudate comprising an exterior skin and a core disposed within the exterior skin; drying the extrudate; debinding the extrudate in a debinding atmosphere at one or more debinding temperatures to remove the binder from the extrudate, wherein the one or more debinding temperature is less than 650 °C; and sintering the extrudate in a sintering atmosphere at one or more sintering temperatures to remove the graphite particles from the exterior skin of the extrudate and to sinter the inorganic particles of the extrudate, to thereby form the monolithic article, wherein the one or more sintering temperatures are greater than or equal to 650 °C and the sintering atmosphere comprises an oxygen concentration less than or equal to 2.5%.

2. The method of claim 1, wherein the sintering atmosphere comprises an oxygen concentration greater than or equal to 0.0% and less than or equal to 2.5%.

3. The method of claim 1 or claim 2, wherein the one or more debinding temperatures are greater than or equal to 200 °C and less than 650 °C.

4. The method of any one of claims 1-3, wherein the debinding comprises holding the extrudate at a hold debinding temperatures and in the debinding atmosphere for greater than or equal to 2 hours and less than or equal to 40 hours.

5. The method of claim 4, wherein the debinding comprises increasing to the one of the one or more debinding temperatures in the debinding atmosphere at a first ramp rate greater than or equal to 5 °C / hour and less than or equal to 20 °C / hour.

6. The method of any one of claims 1-5, wherein the debinding atmosphere comprises an oxygen concentration greater than or equal to 3% and less than or equal to 18%.

7. The method of any one of claims 1-6, wherein the one or more sintering temperatures are greater than or equal to 650 °C and less than or equal to 1000 °C.

8. The method of any one of claims 1-7, wherein the sintering comprises holding the extrudate at a hold sintering temperature and in the sintering atmosphere for greater than or equal to 0.5 hour to less than or equal to 8 hours.

9. The method of claim 8, wherein the sintering comprises increasing to the hold sintering temperature at a second ramp rate greater than or equal to 5 °C / hour and less than or equal to 100 °C / hour.

10. The method of any one of claims 1-9, wherein at least one of the debinding atmosphere and the sintering atmosphere comprises nitrogen, argon, or a combination thereof.

11. The method of any one of claims 1-10, wherein the binder comprises an organic binder, the organic binder comprising cellulose, a cellulose derivative, a polymer, a thermosetting resin, or a combination thereof.

12. The method of any one of claims 1-11, wherein the inorganic particles comprise a borate, a phosphate, a transition metal oxide, an oxide, a hydroxide, a carbonate, a silicate, an alumino-silicate, or combinations thereof.

13. The method of claim 12, wherein the inorganic particles comprise talc, clay, MgO, alumina, or combinations thereof.

14. The method of any one of claims 1-13, wherein the graphite particles comprise graphite plates, graphite flakes, natural graphite, synthetic graphite, or combinations thereof.

15. The method of any one of claims 1-14, wherein the extrudable composition further comprises a pore-forming material, the pore-forming material comprising a starch, a nut-shellflour, carbon, a natural polymer, a synthetic polymer, a carbonaceous material, crystalline carbon, amorphous carbon, or combinations thereof.

16. The method of any one of claims 1-15, wherein the extrudable composition further comprises a porous material, the porous material comprising paper, polymer, glass, glassceramic, ceramic, diatomaceous earth, perlite, pumice, or combinations thereof.

17. The method of claim 16, wherein the porous material comprises hollow glass beads.

18. The method of any one of claims 1-17, wherein the core has a shape of a honeycomb structure comprising a plurality of cells therein, the plurality of cells defining parallel channels running longitudinally through the honeycomb structure.

19. A monolithic article comprising: an exterior skin comprising inorganic material; and a core disposed within the exterior skin, the core comprising a continuous graphite phase and an inorganic phase comprising the inorganic material, wherein the graphite phase and the inorganic phase together form an interconnected pore structure, wherein: a modulus of rupture of the exterior skin is at least 150% greater than a modulus of rupture of the core, as measured according to ASTM-D6272; and the monolithic article is electrically conductive.

20. The monolithic article of claim 19, wherein the exterior skin is free or substantially free of graphite.

21. The monolithic article of claim 19 or claim 20, wherein the continuous graphite phase is homogenously distributed throughout the core.

22. The monolithic article of any one of claims 19-21, wherein the core has a shape of a honeycomb structure comprising a plurality of cells therein, the plurality of cells defining parallel channels running longitudinally through the honeycomb structure.

23. The monolithic article of any one of claims 19-22, wherein the continuous graphite phase comprises fired graphite plates, graphite flakes, natural graphite, synthetic graphite, or combinations thereof.

24. The monolithic article of any one of claims 19-23, wherein the inorganic material comprises a borate, a phosphate, a transition metal oxide, an oxide, a hydroxide, a carbonate, a silicate, an alumino-silicate, or combinations thereof.

25. The monolithic article of claim 24, wherein the inorganic material comprises talc, clay, MgO, alumina, or combinations thereof.

26. The monolithic article of any one of claims 19-25, wherein a Young’s modulus of the exterior skin is at least 50% greater than a Young’s modulus of the core, as measured according to ASTM C623.

27. The monolithic article of any one of claims 19-26, wherein the core of the monolithic article has an electrical resistance greater than or equal to 1 ohm to less than or equal to 100 ohms.

28. The monolithic article of any one of claims 19-27, wherein the monolithic article comprises a coating on the core, the coating comprising a catalyst, a sorbent that adsorbs and desorbs CO2, or combinations thereof.

29. A method of using the article of claim 28, the method comprising: exposing the article to a gas stream comprising CO2 to adsorb at least some of the CO2 in the gas stream from the gas stream into the sorbent in the coating.

30. The method of claim 29, the method further comprising: desorbing the CO2 from the coating.

31. The method of claim 30, wherein the desorbing comprises applying an electrical potential across the article to heat the article.

32. A method of forming a porous electrically conductive article, the method comprising: heating a precursor body in a first heating atmosphere in a first atmosphere temperature range, the precursor body comprising a precursor composition comprising inorganic particles, one or more organic components, and an electrically conductive filler material, wherein the first atmosphere temperature range is below a combustion temperature of the electrically conductive filler material, wherein the precursor body comprises a core surrounded by an outer periphery having the same precursor composition, wherein the precursor body is heated in the first heating atmosphere at one or more first atmosphere temperatures in the first atmosphere temperature range, and wherein the heating in the first heating atmosphere is carried out for a first heating duration and at the one or more first atmosphere temperatures sufficient to remove the organic components from the precursor body while the electrically conductive filler material remains intact in the precursor body; and heating the precursor body in a second heating atmosphere in a second atmosphere temperature range, which comprises one or more second atmosphere temperatures at or above the combustion temperature of the electrically conductive filler material, wherein the second heating atmosphere has a gaseous makeup which hinders combustion of the electrically conductive filler material, wherein the heating in the second heating atmosphere is carried out for a second heating duration and at the one or more second atmosphere temperatures sufficient to remove at least some of the electrically conductive filler material from the outer periphery of the precursor body while the electrically conductive filler material remains intact in the core of the precursor body.

33. The method of claim 32, wherein the heating the precursor body in the second heating atmosphere is sufficient to cause the inorganic materials in the outer periphery of the precursor body to sinter.

34. The method of claim 32 or claim 33, wherein a strength of the outer periphery is greater than a strength of the core.

35. The method of any one of claims 32-34, wherein the heating the precursor body in the first heating atmosphere increases porosity in the precursor body.

36. The method of any one of claims 32-35, wherein the outer periphery has an average thickness that is less than 10% of a transverse hydraulic diameter of the precursor body.

37. The method of any one of claims 32-36, wherein the precursor body comprises a honeycomb structure comprised of intersecting walls extending in an axial direction which form a plurality of parallel cells in a transverse face.

38. The method of any one of claims 32-37, wherein the gaseous makeup which hinders combustion of the electrically conductive filler material in the second heating atmosphere is provided by adjusting oxygen input and / or level in the second atmosphere, adjusting fuel mixture of one or more burners that provide heat to the second atmosphere, adjusting introduction and / or level of recirculated products of combustion gases in the second atmosphere, adjusting introduction and / or level of inert gas in the second atmosphere, or combinations thereof.

39. The method of claim 38, wherein the fuel mixture of one or more burners is a lean fuel mixture.

40. The method of claim 38 or claim 39, wherein the inert gas is nitrogen, argon, or combination thereof.

41. The method of any one of claims 32-40, further comprising extruding an extrudable composition to form an extrudate, and cutting a portion of the extrudate.

42. The method of claim 41 , wherein the core and the outer periphery of the precursor body are simultaneously extruded.

43. The method of any one of claims 32-42, wherein the first atmosphere temperature range is greater than or equal to 200 °C and less than or equal to 650 °C.

44. The method of any one of claims 32-43, wherein the oxygen content of the second atmosphere is in a second oxygen range greater than or equal to 0.0% and less than or equal to 2.5%.

45. The method of any one of claims 32-44, wherein the oxygen content of the first atmosphere is in a first oxygen range greater than or equal to 3% and less than or equal to 18%.

46. The method of any one of claims 32-45, wherein the first heating duration is greater than or equal to 2 hours and less than or equal to 10 hours.

47. The method of any one of claims 32-46, wherein the second heating duration is greater than or equal to 0.5 hours and less than or equal to 8 hours.

48. The method of any one of claims 32-47, wherein the precursor body further comprises hollow glass beads.

49. The method of claim 48, wherein the hollow glass beads are softened as the precursor body is heated in the second heating atmosphere.

50. The method of claim 48 or claim 49, wherein the hollow glass beads are hollow glass microspheres.

51. The method of any one of claims 32-50, wherein the precursor body further comprises one or more porous material comprised of paper, polymer, glass, glass-ceramic, ceramic, diatomaceous earth, perlite, pumice, or combinations thereof.

52. The method of any one of claims 32-51, wherein the organic components comprise one or more starch, one or more binder, one or more oil, one or more volatile organic compound, or combinations thereof.

53. The method of claim 52, wherein the one or more binder is a cellulosic binder.

54. The method of any one of claims 32-53, wherein the precursor body is monolithic, wherein the core and the outer periphery are made of the same composition.

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