WO2024118341A1

WO2024118341A1 - Pre-pressed ceramic bodies for fabrication of ceramic fluidic modules via isostatic pressing

Info

Publication number: WO2024118341A1
Application number: PCT/US2023/080009
Authority: WO
Inventors: Alexander Lee CUNO; Travis James RAWSON; James Scott Sutherland; Akenda ZELLET-LUKASO
Original assignee: Corning Incorporated
Priority date: 2022-11-29
Filing date: 2023-11-16
Publication date: 2024-06-06

Abstract

A process for forming a fluidic module includes forming pre-pressed bodies, such as an aligning pre-pressed body, from binder-coated ceramic powder. The process further includes contacting a passage mold of a fluid passage with the aligning pre-pressed body to set an alignment of the passage mold. The passage mold defines a path of the fluid passage with the path having a tortuous shape and lying substantially in a mold plane. The process further includes covering the passage mold and the aligning pre-pressed body with the ceramic powder within a flexible mold. The process further includes isostatically pressing the flexible mold with the passage mold, the aligning pre-pressed body, and the ceramic powder therein to form a pressed body. The process further includes heating the pressed body to remove the passage mold and sintering the pressed body to form the fluidic module having the fluid passage extending therethrough.

Description

PRE-PRESSED CERAMIC BODIES FOR FABRICATION OF CERAMIC FLUIDIC MODULES VIA ISOSTATIC PRESSING CROSS-REFERENCE TO RELATED APPLICATIONS [0001] This application claims the benefit of priority under 35 U.S.C. § 119 of U.S. Provisional Application No. 63/428,563 filed November 29, 2022, the content of which is incorporated herein by reference in its entirety. FIELD [0002] The present disclosure relates to ceramic fluidic modules for continuous flow reactors and, more particularly, to processes that incorporate pre-pressed ceramic bodies to form ceramic fluidic modules via isostatic pressing. BACKGROUND [0003] Ceramic material is a desirable material for fluidic modules for flow chemistry production and/or laboratory work and for structures for other technical uses. Silicon carbide ceramic (SiC) is particular well-suited for fluidic module applications. SiC has relatively high thermal conductivity, which is useful in performing and controlling endothermic or exothermic reactions. SiC has good physical durability and thermal shock resistance. SiC also possesses extremely good chemical resistance. But these properties, combined with high hardness and abrasiveness, make the practical production of SiC structures with internal features, such as SiC flow modules with tortuous internal passages, challenging. [0004] Flow reactors and other structures formed of SiC and other ceramics have been fabricated recently by this Applicant using a variation of the “lost-material” approach. In this approach, a positive passage mold is incorporated within a volume of binder-coated ceramic powder. The ceramic powder with the positive passage mold inside is then pressed to form a green ceramic body, which thereafter undergoes further processing, such a demolding, debinding, and sintering, to form a sintered ceramic body with one or more smooth-surfaced fluid passages extending therethrough. [0005] Different pressing techniques have been used to form the green ceramic body, including uniaxial pressing and isostatic pressing. In uniaxial pressing, the application of pressure to the binder-coated ceramic powder is uniaxial, meaning the pressure is from one direction only. A rigid, metal die is typically used for compaction of the powder in uniaxial pressing. In contrast, the compaction of the binder-coated ceramic powder takes place under hydrostatic conditions in isostatic pressing. That is, the pressure is transmitted to the powder equally (or very nearly equally) in all directions. A flexible mold (e.g., a rubber mold) is typically used for compaction of the powder in isostatic pressing. [0006] When using isostatic pressing, the positive passage molds are generally oriented vertically (e.g., along the elongate dimension of the flexible mold) instead of stacked horizontally and separated by SiC powder layers as when using uniaxial pressing. The position of the positive passage molds within the flexible mold prior to isostatic pressing determines the final position of fluid passages within the fired fluidic module. As such, care should be taken to properly place the positive passage molds within the flexible mold prior to filling the flexible mold with the ceramic powder. Care should also be taken to ensure that the positive passage molds remain in the proper position while filling the flexible mold with the ceramic powder. FIGS. 28-30 are schematic top, front cross-sectional, and side cross-sectional views, respectively, of a flexible isostatic pressing mold 500 filled with binder-coated ceramic powder 402 and with two positive passage molds 408 positioned therein. The flexible mold 500 has a base 504 and sidewalls 508 that extend perpendicularly from the base 504 in a longitudinal direction. The two positive passage molds 408 are centrally positioned within the flexible mold 500 with a predetermined spacing between and each other and the sidewalls 508. The positive passage molds 408 also have an (ideal) vertical orientation relative to the sidewalls 508. [0007] FIG.31 and FIG.32 schematically illustrate an issue that may result from isostatic mold filling techniques. The positive passage molds 408 are usually positioned offset from the bottom of the flexible mold 500. To achieve this spacing, ceramic powder 402 can be poured into the flexible mold 500 to form a first layer at the bottom, as shown in FIG. 31. However, since the ceramic powder 402 is not able to fully stabilize the positive passage molds until the flexible mold 500 is nearly full of the ceramic powder, there is a concern that the positive passage molds 408 can become displaced from their intended position during ceramic powder filling, as depicted in FIG. 32. The positioning of the positive passage molds in the flexible mold is further complicated by the requirement that the positive passage mold that defines the fluid passage has a long length with a tortuous shape (e.g., serpentine shape shown in FIGS.6, 6A, 9, and 29) and cannot contact other positive passage molds. For example, the positive passage mold cannot contact itself or other positive passage molds that define other fluid passages (e.g., heat exchange channels) within the flexible mold. [0008] It has also been discovered that external structure of the fired fluidic module can distort, warp, and/or twist if the positive passage molds are not properly positioned within the flexible mold during isostatic pressing. It is believed these distortion effects may result because, when the positive passage molds become misaligned, the material of the positive passage molds may not compress the same amount as surrounding ceramic powder under application of the same isostatic pressure. [0009] Consequently, it would be advantageous to develop strategies to position the positive passage molds vertically and/or symmetrically within flexible isostatic molds during assembly thereof and to maintain such alignment during the filling of the flexible molds with ceramic powder prior to isostatic pressing. SUMMARY [0010] According to aspect (1), a process for forming a ceramic fluidic module for a flow reactor is provided. The method comprises: forming pre-pressed bodies from binder-coated ceramic powder, the pre-pressed bodies comprising an aligning pre-pressed body; contacting a first side of a positive passage mold of a fluid passage with a first major surface of the aligning pre-pressed body to set an alignment of the positive passage mold, the positive passage mold defining a path of the fluid passage with the path having a tortuous shape and lying substantially in a mold plane; covering the positive passage mold and the aligning pre-pressed body with a volume of the binder-coated ceramic powder within a flexible mold, the flexible mold having a base and sidewalls that extend perpendicularly from the base in a longitudinal direction; isostatically pressing the flexible mold with the positive passage mold, the aligning pre-pressed body, and the volume of the binder-coated ceramic powder therein to form a pressed body; heating the pressed body to remove the positive passage mold; and sintering the pressed body to form the ceramic fluidic module having the fluid passage extending therethrough. [0011] According to aspect (2), the process of aspect (1) is provided, wherein the first major surface of the aligning pre-pressed body is oriented substantially parallel to the mold plane. [0012] According to aspect (3), the process of aspect (1) or aspect (2) is provided, wherein the aligning pre-pressed body has a plate-like shape. [0013] According to aspect (4), the process of any one of the preceding aspects is provided, wherein contacting the first side of the positive passage mold with the first major surface of the aligning pre-pressed body comprises connecting the first side of the positive passage mold to the first major surface of the aligning pre-pressed body. [0014] According to aspect (5), the process of aspect (4) is provided, wherein connecting the first side of the positive passage mold to the first major surface of the aligning pre-pressed body comprises adhering the first side of the positive passage mold to the first major surface of the aligning pre-pressed body using an adhesive. [0015] According to aspect (6), the process of any one of the preceding aspects is provided, wherein contacting the first side of the positive passage mold with the first major surface of the aligning pre-pressed body comprises positioning the positive passage mold on a boss protruding from the first major surface of the aligning pre-pressed body. [0016] According to aspect (7), the process of aspect (6) is provided, wherein the positive passage mold is positioned on a plurality of bosses protruding from the first major surface of the aligning pre-pressed body. [0017] According to aspect (8), the process of aspect (7) is provided, wherein the bosses are spaced in a lateral direction across the first major surface of the aligning pre-pressed body. [0018] According to aspect (9), the process of aspect (8) is provided, wherein the bosses are spaced in the longitudinal direction on the first major surface of the aligning pre-pressed body. [0019] According to aspect (10), the process of aspect (9) is provided, wherein the bosses comprise upper bosses spaced in the lateral direction along a first longitudinal position and lower bosses spaced in the lateral direction along a second longitudinal position lower than the first longitudinal position. [0020] According to aspect (11), the process of aspect (10) is provided, wherein the path of the positive passage mold has a serpentine shape with a repeating pattern. [0021] According to aspect (12), the process of aspect (11) is provided, wherein the repeating pattern comprises a first linear segment, followed by an upper curved segment, followed by a second linear segment, and followed by a lower curved segment, the repeating pattern repeating at least two times. [0022] According to aspect (13), the process of aspect (12) is provided, wherein at least one upper boss is configured to abut at least one upper curved segment of the path of the positive passage mold. [0023] According to aspect (14), the process of aspect (12) is provided, wherein the upper bosses are configured to abut each upper curved segment of the path of the positive passage mold. [0024] According to aspect (15), the process of aspect (13) or aspect (14) is provided, wherein at least one lower boss is configured to abut at least one lower curved segment of the path of the positive passage mold. [0025] According to aspect (16), the process of any one of aspects (13)-(15) is provided, wherein the lower bosses are configured to abut each lower curved segment of the path of the positive passage mold. [0026] According to aspect (17), the process of any one of aspects (13)-(16) is provided, wherein the upper curved segment and the lower curved segment of the path of the positive passage mold each subtend an angle of approximately 180 degrees such that the first linear segment and the second linear segment of the path of the positive passage mold are parallel to one another. [0027] According to aspect (18), the process of aspect (17) is provided, wherein the upper bosses are configured to abut each adjacent pair of the first linear segments and the second linear segments of the path of the positive passage mold. [0028] According to aspect (19), the process of aspect (17) or aspect (18) is provided, wherein the lower bosses are configured to abut each adjacent pair of the first linear segments and the second linear segments of the path of the positive passage mold. [0029] According to aspect (20), the process of any one of aspects (10)-(19) is provided, wherein at least one upper boss has an upward projection that defines an upper slot between the upward projection and the first major surface of the aligning pre-pressed body, the positive passage mold at least partially disposed in the upper slot. [0030] According to aspect (21), the process of any one of aspects (10)-(20) is provided, wherein at least one lower boss has a downward projection that defines a lower slot between the downward projection and the first major surface of the aligning pre-pressed body, the positive passage mold at least partially disposed in the lower slot. [0031] According to aspect (22), the process of any one of the preceding aspects is provided, wherein the aligning pre-pressed body has a transverse thru hole oriented normal to the mold plane at a position proximate to one end of the path of the positive passage mold, and wherein an interconnection stub formed from a material of the positive passage mold is configured abut the one end of the path and extend through the transverse thru hole. [0032] According to aspect (23), the process of any one of the preceding aspects is provided, wherein the aligning pre-pressed body has a longitudinal thru hole and is configured to be spaced from the base of the flexible mold such that, during the covering, the binder-coated ceramic powder flows through the longitudinal thru hole and fills the flexible mold. [0033] According to aspect (24), the process of any one of the preceding aspects is provided, wherein contacting the positive passage mold with the aligning pre-pressed body forms a stacking unit, the process further comprising arranging n stacking units in the flexible mold one by one in a stacking direction oriented normal to the mold plane, and where n is an integer of 1 or greater. [0034] According to aspect (25), the process of aspect (24) is provided, wherein the aligning pre-pressed body has a second major surface facing opposite the first major surface and oriented substantially parallel to the mold plane, and wherein the aligning pre-pressed body of a first stacking unit of the n stacking units is configured to abut a first sidewall of the flexible mold with the second major surface thereof. [0035] According to aspect (26), the process of aspect (25) is provided, wherein the aligning pre-pressed body of each stacking unit of the n stacking units after the first stacking unit is configured to abut a second side of the positive passage mold of the immediate prior stacking unit. [0036] According to aspect (27), the process of aspect (26) is provided, wherein the pre- pressed bodies comprise a second aligning pre-pressed body configured to abut (i) a second side of the positive passage mold of the nth stacking unit on a first side of the second aligning pre-pressed body and (ii) a second sidewall of the flexible mold, opposite the first sidewall, on a second side of the second aligning pre-pressed body. [0037] According to aspect (28), the process of any one of aspects (1)-(22) is provided, wherein the pre-pressed bodies comprise a supporting pre-pressed body, the process further comprising contacting the aligning pre-pressed body with the supporting pre-pressed body to set an alignment of the aligning pre-pressed body. [0038] According to aspect (29), the process of aspect (23) is provided, wherein the supporting pre-pressed body defines a slot within which the aligning pre-pressed body is inserted to set the alignment of the aligning pre-pressed body. [0039] According to aspect (30), the process of aspect (23) or aspect (24) is provided, wherein the supporting pre-pressed body comprises a bottom pre-pressed body positioned on the base of the flexible mold and configured to abut at least one sidewall of the flexible mold. [0040] According to aspect (31), the process of any one of aspects (23)-(25) is provided, wherein the supporting pre-pressed body comprises a top pre-pressed body positioned opposite the base at a top of the flexible mold and configured to abut at least one sidewall of the flexible mold. [0041] According to aspect (32), the process of any one of the preceding aspects is provided, wherein the positive passage mold is contacted with the aligning pre-pressed body within the flexible mold. [0042] According to aspect (33), the process of any one of the preceding aspects is provided, wherein the positive passage mold is contacted with the aligning pre-pressed body outside of the flexible mold. [0043] According to aspect (34), the process of aspect (33) is provided, wherein contacting the positive passage mold with the aligning pre-pressed body comprises forming the positive passage mold on the aligning pre-pressed body. [0044] According to aspect (35), the process of any one of the preceding aspects, wherein each pre-pressed body is formed by pressing the binder-coated ceramic powder with a first pressure prior to the step of covering with the volume of the binder coated powder. [0045] According to aspect (36), the process of aspect (35) is provided, wherein the pressing to form the pre-pressed bodies is uniaxial pressing. [0046] According to aspect (37), the process of aspect (35) is provided, wherein the pressing to form the pre-pressed bodies is isostatic pressing. [0047] According to aspect (38), the process of any one of aspects (35)-(37) is provided, wherein the pressed body is formed by isostatically pressing the volume of binder-coated ceramic powder with a second pressure, and wherein the first pressure is lower than the second pressure. [0048] According to aspect (39), the process of aspect (38) is provided, wherein the first pressure is in a range of from about 1 MPa to about 10 MPa. [0049] According to aspect (40), the process of aspect (38) or aspect (39) is provided, wherein the second pressure is in a range of from about 20 MPa to about 200 MPa. BRIEF DESCRIPTION OF THE DRAWINGS [0050] FIG. 1 is a diagrammatic plan view outline of a fluid passage of a type useful in fluidic modules showing certain features of the fluid passage; [0051] FIG. 2 is a perspective external view of an embodiment of a fluidic module according to embodiments; [0052] FIG.3 is a diagrammatic cross-sectional view of an embodiment of a fluidic module according to embodiments; [0053] FIGS. 4A-4G are a stepwise series of cross-sectional representations of aspects of a process for producing the fluidic module of the present disclosure; [0054] FIG.5 is a cross-sectional representation of an embodiment of an apparatus for use in performing the pre-pressing step, demolding step, and/or isostatic pressing step of the process of FIGS.4A-4G; [0055] FIG. 6 and FIG. 7 are perspective representations of embodiments of pre-pressed bodies used in connection with the process of FIGS.4A-4G; [0056] FIG. 6A is a front plan view of positive passage mold having a shape useful in fluidic modules of the present disclosure; [0057] FIG.8 is a perspective representation of a further embodiment of a pre-pressed body that includes trenches proximate to the positive passage mold to facilitate powder filling; [0058] FIG. 9 is a front plan view showing the trenches in the pre-pressed body of FIG. 8 with different lengths relative to the positive passage mold; [0059] FIGS.10-12 are perspective representations of further embodiments of pre-pressed bodies used in connection with the process of FIGS.4A-4G; [0060] FIGS. 13-15 are perspective representations of yet further embodiments of pre- pressed bodies used in connection with the process of FIGS.4A-4G; [0061] FIGS. 16-18 are perspective representations of still further embodiments of pre- pressed bodies used in connection with the process of FIGS.4A-4G; [0062] FIGS.19-21 are a stepwise series of cross-sectional representations of aspects of a process for producing the fluidic module of the present disclosure, showing still further embodiments of pre-pressed bodies used in connection with the process; [0063] FIGS.22-24 are a stepwise series of cross-sectional representations of aspects of a process for producing the fluidic module of the present disclosure, showing an alternative pre- pressed body used for producing the fluidic module of the present disclosure; [0064] FIGS.25-27 are a stepwise series of cross-sectional representations of aspects of an alternative process for producing the fluidic module of the present disclosure without use of pre-pressed bodies; [0065] FIGS.28-30 are schematic top, front cross-sectional, and side cross-sectional views, respectively, of a flexible isostatic pressing mold filled with binder-coated ceramic powder, illustrating a vertical orientation of two positive passage molds positioned centrally therein; and [0066] FIG. 31 and FIG. 32 are a stepwise series of cross-sectional representations of a ceramic powder filling process that may result in misaligned positive passage molds. DETAILED DESCRIPTION [0067] For the purposes of promoting an understanding of the principles of the disclosure, reference will now be made to the embodiments illustrated in the drawings and described in the following written specification. It is understood that no limitation to the scope of the disclosure is thereby intended. It is further understood that the present disclosure includes any alterations and modifications to the illustrated embodiments and includes further applications of the principles disclosed herein as would normally occur to one skilled in the art to which this disclosure pertains [0068] As used herein, the term “and/or,” when used in a list of two or more items, means that any one of the listed items can be employed by itself, or any combination of two or more of the listed items can be employed. For example, if a composition is described as containing components A, B, and/or C, the composition can contain A alone; B alone; C alone; A and B in combination; A and C in combination; B and C in combination; or A, B, and C in combination. [0069] In this document, relational terms, such as first and second, top and bottom, and the like, are used solely to distinguish one entity or action from another entity or action, without necessarily requiring or implying any actual such relationship or order between such entities or actions. [0070] As used herein, the term “about” means that amounts, sizes, formulations, parameters, and other quantities and characteristics are not and need not be exact, but may be approximate and/or larger or smaller, as desired, reflecting tolerances, conversion factors, rounding off, measurement error and the like, and other factors known to those of skill in the art. When the term “about” is used in describing a value or an end-point of a range, the disclosure should be understood to include the specific value or end-point referred to. Whether or not a numerical value or end-point of a range in the specification recites “about,” the numerical value or end-point of a range is intended to include two embodiments: one modified by “about,” and one not modified by “about.” It will be further understood that the end-points of each of the ranges are significant both in relation to the other end-point, and independently of the other end-point. [0071] The terms “substantial,” “substantially,” and variations thereof as used herein, unless defined elsewhere in association with specific terms or phrases, are intended to note that a described feature is equal or approximately equal to a value or description. For example, a “substantially planar” surface is intended to denote a surface that is planar or approximately planar. Moreover, “substantially” is intended to denote that two values are equal or approximately equal. In some embodiments, “substantially” may denote values within about 10% of each other, such as within about 5% of each other, or within about 2% of each other. [0072] Directional terms as used herein—for example up, down, right, left, front, back, top, bottom, above, below, and the like—are made only with reference to the figures as drawn and are not intended to imply absolute orientation. [0073] As used herein the terms "the," "a," or "an," mean "at least one," and should not be limited to "only one" unless explicitly indicated to the contrary. Thus, for example, reference to "a component" includes embodiments having two or more such components unless the context clearly indicates otherwise. [0074] As used herein, a “tortuous” passage refers to a passage having no line of sight directly through the passage and with a path of the passage having at least two differing radii of curvature. As used herein, the “path” of the passage is defined mathematically and geometrically as a curve formed by successive geometric centers, along the passage, of successive minimum-area planar cross sections of the passage (that is, the angle of a given planar cross section is the angle which produces a minimum area of the planar cross section at the particular location along the passage) taken at arbitrarily closely spaced successive positions along the passage. Typical machining-based forming techniques are generally inadequate to form such a tortuous passage. Such passages may include a division or divisions of a passage into subpassages (with corresponding subpaths) and a recombination or recombinations of subpassages (and corresponding subpaths). [0075] A monolithic SiC structure does not imply zero inhomogeneities in the ceramic structure at all scales. As used herein, a “monolithic” SiC structure or a “monolithic” SiC fluidic module refers to a SiC structure or SiC fluidic module, with one or more tortuous passages extending therethrough, in which no (other than the passage(s)) inhomogeneities, openings, or interconnected porosities are present in the ceramic structure having a length greater than the average perpendicular depth d of the one or more passages P from the external surface of the structure or module 300, as shown in FIG.3. [0076] For SiC structures or SiC fluidic modules with other geometries, such as non-planar or circular geometries, the term “monolithic” refers to a SiC structure or fluidic module, with one or more tortuous passages extending therethrough, in which no (other than the passage(s)) inhomogeneities, openings, or interconnected porosities are present in the ceramic structure having a length greater than (i) the minimum depth of the one or more passages P from the external surface of the structure or module and (ii) the minimum spacing between separate, spaced-apart portions of the one or more passages P from one another. Fluidic ports that are machined and/or molded in the structure or module so as to intentionally enable fluid communication from the outside of the structure or module to the passages and/or between separate, spaced-apart portions of the passages, such as inlet ports and/or outlet ports, are excluded from the determination of the average perpendicular depth, the minimum depth, and/or the minimum spacing. Providing such a monolithic SiC structure or monolithic SiC flow module helps ensure fluid tightness and good pressure resistance of a flow reactor fluidic module or similar product. [0077] As used herein, a “unified” ceramic body, structure, or fluidic module is a body in which the ceramic material of the body may have two or more distinct mean densities with the different mean densities encompassed within different regions of the body that may have been formed at different times (e.g., pre-pressing) and/or with different pressing parameters (e.g., lower pre-press pressure), where grains within each region have a continuous and uniform distribution through an entirety of the region in any direction, and where grains at a boundary between adjacent regions grow into one another such that there is no mechanical seam or joint between the adjacent regions. A unified ceramic body, structure, or module encompasses the attributes of a monolithic SiC structure or a monolithic SiC fluidic module as defined herein. [0078] As used herein a “closed-porosity” ceramic body is a ceramic body in which the ceramic material of the ceramic body exhibits a pore topology that is closed such that the pores or cells in the material are isolated or connected only with adjacent pores or cells and have no permeability to fluid. [0079] As used herein, the term “ceramic particles” or “ceramic powder” whether by itself or preceded by any one of the terms “coated,” “binder-coated,” “ready-to-press,” “RTP,” and/or similar variations thereof refers to ceramic particles that include binder and/or lubricants that facilitate pressing of the ceramic particles. The term “ceramic particles” or “ceramic powder” has the meaning immediately above unless the term is preceded by any one or more of the terms “non-binder-coated,” “non-coated,” “uncoated,” “raw,” or it is otherwise indicated that no binder and/or lubricants have been added to the ceramic particles. [0080] A fluidic module 300 for a flow reactor (not shown) is disclosed in FIGS.1-3. The fluidic module 300 comprises a unified closed-porosity ceramic body 200 and a tortuous fluid passage P extending along a path through the ceramic body 200. The ceramic body 200 is formed from a ceramic material that includes any pressable powder that is held together by a binder and thermally processed to fuse the powder particles together into a structure. The ceramic material in some embodiments includes oxide ceramics, non-oxide ceramics, glass- ceramics, glass powders, metal powders, and other ceramics that enable high density, closed- porosity unified structures. Oxide ceramics are inorganic compounds of metallic (e.g., Al, Zr, Ti, Mg) or metalloid (Si) elements with oxygen. Oxides can be combined with nitrogen or carbon to form more complex oxynitride or oxycarbide ceramics. Non-oxide ceramics are inorganic, non-metallic materials and include carbides, nitrides, borides, silicides and others. Some examples of non-oxide ceramics that can be used for the ceramic body 200 include boron carbide (B₄C), boron nitride (BN), tungsten carbide (WC), titanium diboride (TiB₂), zirconium diboride (ZrB₂), molybdenum disilicide (MoSi₂), silicon carbide (SiC), silicon nitride (Si₃N₄), and sialons (silicon aluminum oxynitrides). The ceramic body 200 in the exemplary embodiment is formed from SiC. [0081] The tortuous fluid passage P has an interior surface 210. The interior surface 210 has a surface roughness in the range of from 0.1 to 80 μm Ra, or 0.1 to 50, 0.1 to 40, 0.1 to 30, 0.1 to 20, 0.1 to 10, 0.1 to 5, or even 0.1 to 1 μm Ra, which is generally lower than SiC fluidic modules have previously achieved. The surface roughness of the interior surface 210 exists along any measured profile of the interior surface 210. For instance, when viewed in a planar cross section oriented normal to the path, the interior surface 210 defines an interior profile that completely encircles the path of the passage P. The surface roughness of the interior surface 210 exists along an entirety of the interior profile at every position along the path. [0082] According to further embodiments, the ceramic body 200 of the fluidic module 300 has a density of at least 95% of a theoretical maximum density of the ceramic material, or even of at least 96, 97, 98, or 99% of the theoretical maximum density. The theoretical maximum density (also known as maximum theoretical density, theoretical density, crystal density, or x- ray density) of a polycrystalline material, such as SiC, is the density of a perfect single crystal of the sintered material. Thus, the theoretical maximum density is the maximum attainable density for a given structural phase of the sintered material. [0083] In the exemplary embodiment, the ceramic material is Į-SiC with a hexagonal 6H structure. The theoretical maximum density of sintered SiC(6H) is 3.214 ± 0.001 g/cm³. Munro, Ronald G., “Material Properties of a Sintered Į-SiC,” Journal of Physical and Chemical Reference Data, 26, 1195 (1997). The ceramic material in other embodiments includes a different crystalline form of SiC or a different ceramic altogether. The theoretical maximum density of other crystalline forms of sintered SiC can differ from the theoretical maximum density of sintered SiC(6H), for example, within a range of 3.166 to 3.214 g/cm³. Similarly, the theoretical maximum density of other sintered ceramics also differs from that of sintered SiC(6H). As used herein, a “high density” ceramic body is a ceramic body in which the sintered ceramic material of the ceramic body has a density that of at least 95% of the theoretical maximum density of the ceramic material. [0084] According to embodiments, the ceramic body 200 of the fluidic module 300 has an open porosity of less than 1%, or even of less than 0.5%, 0.4%, 0.2% or 0.1%. The ceramic body 200 in embodiments has a closed porosity of less than 3%, or less than 1.5%, or even less than 0.5%. [0085] According to still further embodiments, the ceramic body 200 of the fluidic module 300 has an internal pressure resistance under pressurized water testing of at least 50 bar, or even at least 100 bar, or 150 bar. [0086] The tortuous fluid passage P, according to embodiments, comprises a floor 212 and a ceiling 214 separated by a height h and two opposing sidewalls 216 joining the floor 212 and the ceiling 214. The sidewalls are separated by a width w (FIG. 1) measured perpendicular to the height h and the direction along the passage (corresponding to the predominant flow direction when in use). Further, the width w is measured at a position corresponding to one- half of the height h. According to embodiments, the height h of the tortuous fluid passage P is in the range of from 0.1 to 40 mm, or from 0.2 to 20 mm, or 0.3 to 12 mm. The width w of the tortuous fluid passage P can vary depending on the processes and/or reactions configured to take place along each position or region along the path. [0087] According to embodiments, the interior surface 210 of the fluid passage P where the sidewalls 216 meet the floor 212 has a radius curvature (at reference 218) of greater than or equal to 0.1 mm, or greater than or equal to 0.3, or even greater than or equal to 0.6 mm, or 1 mm or 5 mm, 1 cm or 2 cm. The interior surface 210 of the fluid passage P, when viewed in a planar cross section oriented normal to the path, can have the same geometry and/or different geometries at different positions along the path. For instance, the interior surface 210 in some embodiments can have a cross-sectional shape in the form of a square, a rectangle, a circle, an oval, a stadium (i.e., a circle elongated at a mirror plane), and other shapes. The relative size of the same or different geometries can also vary along the path. The transition of sizes and/or geometries of the interior surface along the path are gradual to avoid introducing step-like structures within the fluid passage P. The interior surface 210 in embodiments preferably has a circular cross-sectional shape, which enables higher pressure resistance. For geometries in which the cross-sectional shape is neither circular nor polygonal (e.g., oval cross-sectional shape), the hydraulic diameter of the cross-section can provide a parameter for describing the geometry of the interior profile and its relation to the flow through the tortuous fluid passage P. [0088] Embodiments of processes for forming ceramic fluidic modules, such as the fluidic module 300 of FIGS. 1-3, for flow reactors are shown and described with reference to FIGS. 4-27. The various embodiments of the processes and the fluidic modules that result therefrom have numerous advantages and desirable properties. Pre-pressed ceramic bodies formed from ready-to-press (RTP) binder-coated ceramic powder in advance of mold assembly and primary isostatic pressing can help support and align positive passage molds during filling/pouring and primary isostatic pressing, ensuring that the positive passage molds are properly positioned inside the flexible isostatic pressing mold. Bending, twist, and/or warpage of the isostatic pressed fluidic modules can be reduced, which helps the fluidic modules meet external geometry requirements and reduce/eliminate any secondary forming operations. Precision alignment of positive passage molds within the isostatically pressed fluidic module enables a potential increase of the internal fluid passage volume of the fluidic module by allowing more positive passage molds to be packed into the same flexible mold volume. [0089] Pre-pressed ceramic bodies can also reduce the complexity of processes for flexible mold filling with positive passage molds and ceramic powder by allowing the positive passage mold structures to be assembled outside of the flexible mold and then inserted into the flexible mold in a single operation. The process for assembling pre-pressed ceramic bodies and positive passage molds can be automated, simplifying the assembly process and reducing the potential for human error in assembling complex positive passage mold structures. [0090] The use of pre-pressed ceramic bodies incurs minimal cost increase because the ceramic powder would nonetheless still be used in filling the flexible isostatic pressing mold. There may be a minimal cost associated with pre-pressing the ceramic powder. The process for assembling pre-pressed ceramic bodies and positive passage molds can be automated, reducing assembly cost. The precise alignment of positive passage molds reduces the likelihood that a fluid passage will be positioned too close to another channel or the exterior wall of the isostatically pressed fluidic modules, reducing the probability that the fluidic module will not pass burst pressure testing because the fired ceramic material around a fluid passage is too thin. [0091] Aspects of a process for forming a ceramic fluidic module are described with reference to FIGS. 4A-4G. A schematic depiction of an isostatic press that can be used in connection with the process is described with reference to FIG. 5. FIGS. 6-21 schematically illustrate various features and strategies that can be used in connection with the process disclosed herein. FIGS. 22-24 illustrate an alternative process for forming a ceramic fluidic module. FIGS. 25-27 illustrate another alternative process for forming a ceramic fluidic module. [0092] With reference to FIG. 4A and FIG. 6, the process comprises forming pre-pressed bodies 400 from binder-coated ceramic powder. As used herein, the term “pre-pressed” means that the pre-pressed bodies 400 are formed prior to other steps in the process (e.g., the “contacting” steps and/or “covering” steps) that refer to the pre-pressed bodies 400 or specific configurations of the pre-pressed bodies in connection with those other steps. In embodiments, the binder-coated ceramic powder comprises ready-to-press (RTP) ceramic powder, such as RTP silicon carbide (SiC) powder. Such RTP SiC powder is commercially available from various suppliers, such as SiCS-18 from GNPGraystar of Buffalo, NY, United States; IKH 601 and 604 from Industriekeramik Hochrhein (IKH) GmbH of Wutöschingen, Germany; and StarCeram S alpha-SiC types SQ and RQ from KYOCERA Fineceramics Precision GmbH of Selb, Germany. The forming of the pre-pressed bodies 400 is described later in this disclosure. [0093] In embodiments, the pre-pressed bodies 400 include an aligning pre-pressed body 404, and the process further comprises contacting a first side of a positive passage mold 408 of a fluid passage P (FIG.3 and FIG.4G) with a first major surface 416 of the aligning pre-pressed body 404 to set an alignment of the positive passage mold 408. The positive passage mold 408 is configured to define a path 418 (FIG. 6A) of the fluid passage P. In embodiments, the path has a tortuous shape and lies substantially in a mold plane 420. [0094] As shown in FIGS. 4A-4C and FIG. 6, the aligning pre-pressed body 404 has a plate-like shape with a first major surface 416 and a second major surface 417 facing opposite the first major surface 416. The first major surface 416 and the second major surface 417 of the aligning pre-pressed body 404 are oriented substantially parallel to the mold plane 420 of the positive passage mold 408. In this configuration, the contact between the aligning pre- pressed body 404 and the positive passage mold 408 is configured to precisely position the positive passage mold 408 during its insertion into a flexible isostatic pressing mold, such as the flexible mold 500 previously discussed with reference to FIGS.28-30. [0095] In embodiments, as shown in FIG. 6A, the path 418 of the positive passage mold 408 can have a serpentine shape with a repeating pattern 428. The repeating pattern 428 can include a first linear segment 430, followed by an upper curved segment 432, followed by a second linear segment 434, and followed by a lower curved segment 436. In embodiments, the repeating pattern 428 repeats multiple times (e.g., repetition depicted using subscripts 1, 2, 3, and so on to indicate the individual instances of the repeating pattern 428). In embodiments, the repeating pattern 428 repeats 2 times, 3 times, 4 times, 5 times, or more. In embodiments, the serpentine shape may not repeat (e.g., 4281 only). In embodiments, the serpentine shape can begin or end with different segments such that it does not always begin with the first linear segment 430 or end with the lower curved segment 436. For example, as shown in FIG. 6A, the serpentine shape ends with a linear segment following the lower curved segment 436 of the third repeating pattern 428₃. [0096] The positive passage mold 408 can be obtained by molding, machining, three- dimensional (3D) printing, extrusion, pressing, and/or other suitable forming techniques or combinations thereof. In exemplary embodiments, the positive passage mold 408 is formed from a mold material that is preferably heat-meltable but also relatively incompressible, particularly in solid form. The mold material may include organic or inorganic particles suspended or otherwise distributed within the material as one way of decreasing expansion during heating/melting. Regarding incompressibility, the mold material preferably has low rebound after compression relative to the rebound of the pressed SiC powder after compression (e.g., .compression from primary pressing to form the green pressed body of the fluidic module). Mold materials loaded with particles can exhibit lower rebound after compression. Mold materials which are capable of some degree of non-elastic deformation under compression also naturally tend to have low rebound (e.g., materials with high loss modulus). Polymer substances with little or no cross-linking, for example, and/or materials with some local hardness or brittleness, which enables localized fracturing or micro-fracturing upon compression, can exhibit low rebound. Useful mold materials can include waxes with suspended particles, such as carbon and/or inorganic particles, rosin-containing waxes, high modulus brittle thermoplastics, and even organic solids suspended in organic fats, such as cocoa powder in cocoa butter—or combinations of these materials. Low melting point metal alloys also may be useful as mold materials, particularly alloys having low or no expansion on melting. The mold material can be a thermoplastic material in embodiments. [0097] The use of the pre-pressed bodies 400 enables flexibility with respect to where some aspects of the process take place relative to the flexible mold 500. In embodiments, the positive passage mold 408 is contacted with the aligning pre-pressed body 404 inside the flexible mold 500 (e.g., inside the mold volume defined by the flexible mold 500) within which the ceramic pre-pressed structures and loose ceramic powder are assembled prior to isostatic pressing. In embodiments, the positive passage mold 408 is contacted with the aligning pre-pressed body 404 outside of the flexible mold 500 and thereafter positioned inside the flexible mold 500. In embodiments in which the positive passage mold 408 is contacted with the alignment pre- pressed body 404 outside of the flexible mold 500, the process can comprise forming the positive passage mold 408 on the surface and/or into the surface (e.g., depressions) of the aligning pre-pressed body 404. Examples of forming positive passage molds on pre-pressed ceramic bodies for ceramic fluidic modules fabricated using uniaxial pressing techniques are described in International Application Publication WO2022/212338A1, filed on March 29, 2022, the disclosure of which is incorporated herein by reference in its entirety. [0098] In embodiments, as shown in FIG. 4A, the contacting of the positive passage mold 408 with the aligning pre-pressed body 404 is configured to form a stacking unit (e.g., first ^{stacking unit 440} _{1). In an exemplary embodiment, the positive passage mold 408 is offset or} spaced from the base 504 of the flexible mold 500. To form this offset, an offset layer of the ceramic powder 402 can be formed at the base 504 of the flexible mold 500 before positioning the positive passage mold(s) 408 therein. In embodiments, the process further comprises arranging n stacking units 440_n (e.g., 440₁, 440₂, 440₃, etc.) in the flexible mold 500 one by one in a stacking direction 442 oriented normal to the mold plane 420, where n is an integer of 1 or greater. FIG. 4B and FIG. 4C illustrate arranging three stacking units in the flexible mold 500. For example, FIG.4B illustrates arranging a second stacking unit 440₂ in the flexible mold 500 after the first stacking unit 440₁, and FIG. 4C illustrates arranging a third stacking unit 440₃ in the flexible mold 500 after the second stacking unit 440₂. [0099] In embodiments, as shown in FIG. 4A, the aligning pre-pressed body 404 of the first stacking unit 4401 of the n stacking units 440n is configured to abut a first sidewall 5081 of the flexible mold 500 with the second major surface 417 thereof. As shown in FIG. 4B and FIG. 4C, the aligning pre-pressed body 404 of each stacking unit of the n stacking units subsequent to the first stacking 440₁ (e.g., the second stacking unit 440₂ and the third stacking unit 440₃) is configured to abut a second side of the positive passage mold 408 of the immediate prior stacking unit. For example, as shown in FIG. 4B, the second major surface 417 of the aligning pre-pressed body 404 of the second stacking unit 440₂ abuts the second side of the positive passage mold 408 of the first stacking unit 440₁. Similarly, as shown in FIG. 4C, the second major surface 417 of the aligning pre-pressed body 404 of the third stacking unit 4403 abuts the second side of the positive passage mold 408 of the second stacking unit 4402. [0100] In embodiments, as shown in FIG. 4D, the pre-pressed bodies 400 comprise a second aligning pre-pressed body 446. The second aligning pre-pressed body 446 has a plate- like shape with a first major surface 447 and a second major surface 448 facing opposite the first major surface 447. The first major surface 447 and the second major surface 448 of the second aligning pre-pressed body 446 are oriented substantially parallel to the mold plane 420 of the positive passage mold 408. In embodiments, the first side 447 of the second aligning pre-pressed body 446 is configured to abut the second side of the positive passage mold 408 of the nth stacking unit 440n, and the second side 448 of the second aligning pre-pressed body 446 is configured to abut a second sidewall 5082 of the flexible mold 500, which is opposite the first sidewall 5081 of the flexible mold 500. [0101] In connection with the flexible mold filling process, the aligning pre-pressed bodies 404 can be inserted in the flexible mold 500 first, and then the positive passage molds 408 can be sandwiched between the aligning pre-pressed bodies 404 already positioned within the flexible mold 500. In embodiments, the positive passage mold 408 can be aligned and connected to the aligning pre-pressed body 404 using an adhesive or other fastening means. Additional stacking units 440n comprising additional aligning pre-pressed bodies 404 and additional positive passage molds 408, as described above with reference to FIGS.4A-4D, can be arranged in the flexible mold 500 to form thicker fluidic modules 300 with larger internal fluid passage. As schematically depicted in FIG. 7, an interconnection between the positive passage molds 408 can be drilled (e.g., along centerline 450) after isostatic pressing if a parallel fluid passage path is required through the fluidic module 300. [0102] As illustrated in FIG. 4D and FIG. 7, the aligning pre-pressed bodies 404 can be configured in embodiments so as to fit closely with the dimensions of the flexible mold 500. A footprint of the mold volume (e.g., mold volume footprint 512) of the flexible mold 500 is schematically depicted in FIG. 7 to illustrate the close fit between the lengthwise (e.g., along x-axis) and widthwise (e.g., along the y-axis) dimensions of the mold volume footprint 512 and the total lengthwise and widthwise dimensions of the stacking units 440₁, 440₂, 440₃ and the second aligning pre-pressed body 446. The aligning pre-pressed bodies 404 and the second aligning pre-pressed body 446 can also be sized to have approximately the same height (e.g., along the z-axis) as the flexible mold 500, as best shown in FIG.4D. Thus, when stacked with positive passage molds 408 for the fluid passages and/or positive passage molds for other passages (e.g., heat exchange fluid passages), the combined thickness of the stacking units 404n may match the internal thickness of the flexible mold 500. By sizing the aligning pre-pressed bodies 404 to the flexible mold 500, the aligning pre-pressed bodies 404 can be aligned with the internal surfaces (e.g., the sidewalls 508) of the flexible mold 500. This configuration enables the positive passage molds 408 that are sandwiched between the aligning pre-pressed bodies 404 to also be aligned to internal surfaces (e.g., the sidewalls 508) of the flexible mold 500. [0103] Once the aligning pre-pressed body 404 and the positive passage mold 408 (or the aligning pre-pressed bodies 404 and the positive passage molds 408 of two or more stacking units 440n) are aligned to each other within the flexible mold 500, the process comprises covering the positive passage mold 408 and the aligning pre-pressed body 404 (or the two or more stacking units 440n) with a volume of the binder-coated ceramic powder 402 within the flexible mold 500, as shown in FIG. 4D. The ceramic powder 402 is poured into the flexible mold 500 such that it is configured to flow and fill any unoccupied spaces within the flexible mold 500. Distribution of the ceramic powder 402 to all regions within the flexible mold 500 not occupied by the aligning pre-pressed bodies 404 and the positive passage molds 408 can be promoted by vibrating the flexible mold 500 during and/or after ceramic powder filling. As illustrated in FIG. 8 and FIG. 9, the ceramic powder filling process can be enhanced by providing one or more trenches or slots 452 in the aligning pre-pressed body 404 that extend vertically parallel to the first and second linear segments 430, 434 of the positive passage mold 408. The trenches or slots 452 can be arranged to vertically span at least a portion of the upper curved segments 432, so that as the ceramic powder 402 is poured into the flexible mold 500 and over the aligning pre-pressed bodies 404, a portion of the ceramic powder can fall through the trench or slot 452 to fill the cavity region directly below positive passage mold 408. In embodiments, the trenches or slots comprise short trenches or slots 452a that span proximate to the upper curved segments 432. In embodiments, the trenches or slots comprise long trenches or slots 452b that span vertically downward well past the upper curved segments 432. The ceramic powder 402 is added until the flexible mold is filled, at which point a top surface of the ceramic powder 402 is leveled and a separate flexible cap 516, formed from the same or a similar flexible material as the flexible mold 500, is inserted into the opening to the flexible mold 500. [0104] In embodiments, the process includes pulling a vacuum on the flexible mold 500 via a tube (not shown) that is configured to extend through the flexible cap 516. Pulling the vacuum causes the flexible mold 500 to draw in and press against the ceramic power 402, the aligning pre-pressed bodies 404, the positive passage mold 408, and the second aligning pre- pressed body 446, so as to stabilize these features with the surrounding ceramic powder 402. [0105] Referring now to FIG. 4E and FIG. 5, the process further comprises isostatically pressing the flexible mold 500 and the flexible cap 516 with the positive passage mold 408, the aligning pre-pressed body 404, the second aligning pre-pressed body 446, and the volume of the binder-coated ceramic powder 402 therein to form a pressed body 454 (FIG. 4E). In embodiments, as illustrated in FIG. 5, an isostatic press chamber 600 is configured to isostatically press the flexible mold 500, the flexible cap 516, and the contents therein. For example, the flexible mold 500, the flexible cap 516, and the contents therein are placed inside the isostatic press chamber 600, which contains fluid 604 (e.g., water) to which pressure is configured to be applied by the isostatic press chamber 600. In embodiments, the fluid 604 is configured to be pressurized so as to produce essentially isostatic pressure on all surfaces of the flexible mold 500, which causes the ceramic powder 402, the aligning pre-pressed body 404, and the second aligning pre-pressed body 446 therein to be compressed and densified. [0106] In embodiments, the fluid 604 is pressurized to a pressure (e.g., isostatic pressure, main pressure, and/or primary pressure) in a range of from about 20 MPa to about 200 MPa, or from about 25 MPa to about 195 MPa, or from about 30 MPa to about 190 MPa, or from about 35 MPa to about 185 MPa, or from about 40 MPa to about 180 MPa, or from about 45 MPa to about 175 MPa, or from about 50 MPa to about 170 MPa, and also comprising all sub- ranges and sub-values between these range endpoints. [0107] Without being bound by theory, it has been found that it is preferable that the ceramic powder 402 and the aligning pre-pressed bodies 404, 446 both compress by a similar amount under the applied isostatic pressure. If the compression is not by a similar amount, such differential compression may lead to issues. For example, differential compression may lead to undesirable cracks at the interface between the regions of the fired fluidic modules corresponding to the loose-filled ceramic powder 402 and the regions of the fired fluidic modules corresponding to the aligning pre-pressed bodies 404 (e.g., the dashed lines in FIG. 4E and FIG. 4F), which cracks can lead to low pressure resistance. Similarly, differential compression may lead to variations in the compressed density of the regions of the fired fluidic modules corresponding to the loose-filled ceramic powder 402 relative to the regions of the fired fluidic modules corresponding to the aligning pre-pressed bodies 404, which may lead to issues such as leaks. However, issues related to variations in the compressed density can be mitigated or eliminated by controlling/limiting the size of the density differential and/or controlling/limiting the size of the pre-pressed bodies. Finally, differential compression may lead to distortion of the isostatically pressed component, such as bending and twisting, which may cause the component to not meet geometrical requirements. [0108] As noted above, each pre-pressed body 400, including the aligning pre-pressed body 404, the second aligning pre-pressed body 446, and any other bodies or structures that correspond to the pre-pressed bodies 400, is formed by pressing the binder-coated ceramic powder 402 with a first pressure prior to the step of covering the contents of the flexible mold 500 with the volume of the binder coated powder, which covering step is depicted in FIG.4D. In embodiments, the first pressure (e.g., the pre-press pressure) is in a range of from about 0.1 MPa to about 30 MPa, or from about 0.2 MPa to about 25 MPa, or from about 0.5 MPa to about 20 MPa, or from about 1 MPa to about 15 MPa, or from about 2 MPa to about 10 MPa, or from about 3 MPa to about 5 MPa, and also comprising all sub-ranges and sub-values between these range endpoints. In embodiments, the pressing (e.g., the pre-pressing) to form the pre-pressed bodies 400 is uniaxial pressing. In embodiments, pre-pressing to form the pre-pressed bodies 400 is isostatic pressing. [0109] In embodiments, the pressed body 454 (FIG.4E) is formed by isostatically pressing the volume of the binder-coated ceramic powder 402 with a second pressure (e.g., isostatic pressure, main pressure, and/or primary pressure), such as the isostatic pressures indicated above, and the first pressure is lower than the second pressure. In embodiments, the first pressure (e.g., the pre-press pressure) is considerably lower than the second pressure. [0110] The relatively low pressing pressure (e.g., from about 1 MPa to about 10 MPa) used to pre-press the pre-pressed bodies 400 provides sufficient force to press the RTP SiC powder granules together so that they stick together after pressing, forming a green pressed body. It has been found that the pre-pressing pressure is low enough so that during pressing at the relatively high main pressure (e.g., from about 20 MPa to about 200 MPa) both the pre-pressed bodies 400 and the surrounding loose SiC powder 402 are compressed by a similar amount. Such similar compression may help prevent cracking at the interface between the SiC powder 402 and the pre-pressed bodies 400 and enables good knitting of the ceramic granules. As a result, the interface between the regions of the fired fluidic modules corresponding to the loose- filled ceramic powder 402 and the regions of the fired fluidic modules corresponding to the pre-pressed bodies 400 are essentially invisible upon inspection. Such similar compression may also help minimize distortion of the isostatically pressed fluidic modules after firing. [0111] After the isostatic pressing (FIG. 5), the pressed body 454 (FIG. 4E) is heated, preferably at a relatively high rate, such that the positive passage mold 408 is melted and removed from the pressed body 454 by flowing out of the pressed body 454 and/or by being blown and/or sucked out in addition so as to expose the fluid passages P. (FIG. 4F). In embodiments, this heating step can be divided into two parts, where first the pressed body is heated (optionally while applying pressure to the exterior of the body via, for example, heated isostatic pressing in the isostatic press chamber 600), and then next, separately, the mold material can flow out of the body. It is also possible, in embodiments, to remove the positive passage mold 408 by heating the pressed body 454 to melt the mold, and only then drill holes or fluidic ports, while the pressed body is still hot, allowing the mold material to flow out and complete demolding in this manner. The heating may be under partial vacuum, if desired. [0112] Finally, the pressed body 454 is de-bound to remove ceramic powder binder, and then fired (sintered) to densify and further solidify the pressed body into a unified ceramic body 200 (FIG.4G). [0113] Various additional features and strategies that can be used in connection with the embodiments of the process for forming the fluidic modules are shown and described with reference to FIGS.10-21. [0114] Referring now to FIGS. 10-12, separate positive passage molds 408 can be joined in series to form long fluid passages useful for long residence time fluidic modules. In embodiments, positive passage molds 408 can be joined by bringing portions of the separate positive passage molds 408 into contact with one another before and/or during pressing. In such embodiments, the pressing can cause the positive passage molds 408 to fuse together to form a long continuous fluid passage through the body of the fluidic module. [0115] In embodiments, the positive passage molds 408 can be joined using one or more interconnection stubs 462 formed from the same mold material of the positive passage molds 408 or a similar heat-meltable material. The interconnection stubs 462 can be aligned to the positive passage mold 408 by mounting them in one or more transverse thru holes 466 disposed in the aligning pre-pressed bodies 404. FIG. 10 illustrates an example in which a transverse thru hole 466 is formed (e.g., drilled) to extend entirely through the aligning pre-pressed body 404, and the transverse thru hole 466 is sized to receive the interconnection stub 462. In embodiments, the interconnection stub 462 can be retained in the transverse thru hole 466 via friction, or a small amount of binder adhesive can be applied to sidewalls of the transverse thru hole 466 or sidewalls of the interconnection stub 462. [0116] In embodiments, a positive passage mold 408 can be sandwiched between two aligning pre-pressed bodies 404 such that one end of the positive passage mold 408 is aligned with the interconnection stub 462 positioned in a first of the two aligning pre-pressed bodies 404 whereas the other end of the positive passage mold 408 is aligned with the second of the two aligning pre-pressed bodies 404, as shown in FIG.12. The positive passage molds 408 may be aligned to the interconnection stubs 462 using additional alignment such as those described later in this disclosure. [0117] In embodiments, one or more of the interconnection stubs 462 can be bonded directly to one or more of the ends of the positive passage molds 408. Thereafter, the interconnection stubs 462 are inserted into the transverse thru holes 466 in the aligning pre- pressed bodies 404. The bonding process can be carried out by fusing the ends of the positive passage molds 408 and the interconnection stubs 462 together using the same mold material of the positive passage molds or a similar heat-meltable material. This approach automatically aligns the positive passage molds 408 to the aligning pre-pressed bodies 404, eliminating the need for additional alignment features such as those described later in this disclosure. [0118] If multiple positive passage molds 408 are positioned and aligned between multiple aligning pre-pressed bodies 404, as shown in FIG. 12, the interconnection stubs 462 can be made with an axial length or thickness (e.g., along the y-axis) that is half the thickness of a single aligning pre-pressed body 404. This configuration allows two interconnection stubs 462 from two positive passage molds 408 on opposite sides/faces of a single aligning pre-pressed body 404 to meet each other within the same transverse through hole 466 in the single aligning pre-pressed body 404. The interconnection stubs 462 can be made longer at the transverse thru holes 466 of the outermost aligning pre-pressed bodies 404 (e.g., the aligning pre-pressed body 404 of the first stacking unit 440₁ and the second aligning pre-pressed body 446) such that the interconnection stubs 462 project at least through the outermost aligning pre-pressed bodies 404 and possibly beyond them. [0119] Referring now to FIGS. 13-15, the aligning pre-pressed bodies 404 can be fabricated with raised features (e.g., bosses) or depressed features (e.g., a contour formed in the major surface of the aligning pre-pressed body) that help to align the positive passage molds 408 to the aligning pre-pressed bodies 404. In embodiments, for example, the process step of contacting the first side of the positive passage mold 408 with the first major surface 416 of the aligning pre-pressed body 404 can comprise positioning the positive passage mold 408 on a boss 470 protruding from the first major surface 416 of the aligning pre-pressed body 404. In embodiments, as shown in FIG. 13, the positive passage mold 408 is aligned to the aligning pre-pressed body 404 using an array of bosses 470 (e.g., a plurality of bosses). Here, the bosses provide 470 are configured to provide lateral alignment (e.g., along the x-direction) of the positive passage mold 408 on the aligning pre-pressed body 404. [0120] In embodiments, the bosses 470 are spaced in a lateral direction (e.g., along the x- direction) across the first major surface 416 of the aligning pre-pressed body 404. In embodiments, the bosses 470 can also be spaced in the longitudinal direction (e.g., along the z-direction) on the first major surface 416 of the aligning pre-pressed body 404. In embodiments, the bosses 470 comprise upper bosses spaced in the lateral direction along a first longitudinal position 472 and lower bosses spaced in the lateral direction along a second longitudinal position 474 lower than the first longitudinal position 472, as shown in FIG.13. [0121] In embodiments, different bosses 470 are configured to abut different portions of the positive passage mold 408. For example, in embodiments, at least one upper boss 470 (e.g., positioned along the first longitudinal position 472) is configured to abut at least one upper curved segment 432 of the path 418 of the positive passage mold 408 (see FIG.6A). Similarly, in embodiments, at least one lower boss 470 (e.g., positioned along the second longitudinal position 474) is configured to abut at least one lower curved segment 436 of the path 418 of the positive passage mold 408 (see FIG.6A). [0122] In embodiments, as shown in FIG.6A, the upper curved segment 432 and the lower curved segment 436 of the path 418 of the positive passage mold 408 each subtend an angle Į of approximately 180 degrees such that the first linear segment 430 and the second linear segment 434 of the path 418 of the positive passage mold 408 are parallel to one another. In such embodiments, as shown in FIG. 13, the upper bosses (e.g., positioned along the first longitudinal position 472) are configured to abut each adjacent pair of the first linear segments 430 and the second linear segments 434, and the lower bosses (e.g., positioned along the second longitudinal position 474) are configured to abut each adjacent pair of the first linear segments 430 and the second linear segments 434. [0123] In embodiments, the bosses 470 can be fabricated via ceramic powder molding, pressing (e.g., concurrently with the pre-pressing of the aligning pre-pressed body 404), casting, or machining operations. In embodiments, the bosses 470 can be fabricated separately via a pressing process and then applied to the aligning pre-pressed body 404 and held in place using a binder adhesive, a pressing operation, or friction fitting into cavities formed in the aligning pre-pressed body 404. [0124] In embodiments, the bosses 470 can be arranged to support and align the positive passage mold 408 when the aligning pre-pressed body 404 is oriented vertically (e.g., along the z-direction). When the vertically oriented aligning pre-pressed bodies 404 are inserted into the flexible mold 500 (e.g., when grouped together as shown FIG. 7 or FIG. 12), gap regions between the aligning pre-pressed bodies 404 that are not occupied by the positive passage molds 408 are easily filled via ceramic powder 402 during pouring (e.g., during the step of covering the contents of the flexible mold 500 prior to isostatic pressing). The bosses 470 are also configured to stabilize the positive passage molds 408 and prevent them from moving during the ceramic powder filling process. [0125] In embodiments, the bosses 470 that project from the first major surface 416 of the aligning pre-pressed body 404 can have the same thickness as the positive passage mold 408 that is supported by the bosses 470, or the bosses 470 can be thicker (e.g., extend farther from first major surface) than the positive passage mold 408. In embodiments, some of the bosses 470 on the first major surface 416 can have the same thickness as the positive passage mold 408 whereas other bosses 470 on the first major surface 416 can be thicker than the positive passage mold 408. When the aligning pre-pressed bodies 404 and the positive passage molds 408 are arranged in multiple stacking units 440n, as shown in FIG. 7 and FIG. 12, the thicker bosses 470 can function as precision spacers, forming controlled gaps or clearances that enable the ceramic powder to be poured to all locations between and around the aligning pre-pressed bodies 404. [0126] The gaps or clearances formed by the bosses 470 may be important for positive passage molds 404 with paths 418 that have a serpentine shape. For example, the lower curved segments 436 of the path 418 form upward-facing U-bends that are open in the direction in which ceramic powder is typically poured into the flexible mold 500 during the step of covering the contents of the flexible mold 500 with the ceramic powder. As such, the upward-facing U- bends easily fill with the ceramic powder 402 during the step of covering. However, the upper curved segments 432 of the path 418 form downward-facing U-bends that are generally closed in the direction in which ceramic powder is typically poured into the flexible mold 500 during the step of covering the contents of the flexible mold 500 with the ceramic powder. As such, the downward-facing U-bends may be more difficult to fill with the ceramic powder 402 during the step of covering. Providing thicker bosses 470 (vertically) relative to the downward-facing U-bends formed by the upper curved segments 432, as shown in FIG.13, can improve ceramic powder fill in these regions of the aligning pre-pressed body 404. The bosses 470 having the thickness of the positive passage mold 404 can be provided (vertically) relative to the upward- facing U-bends formed by the lower curved segments 436, as shown in FIG.13. [0127] If the bosses 470 are thicker than the positive passage mold 408, then it is possible for the positive passage mold 408 to slide across tops of the bosses 470, resulting in variation in the final position of the positive passage mold 408 after filing the flexible mold 500 with the ceramic powder 402. To address such possible sliding, the shape of the bosses 470 can be modified to retain the positive passage mold 408 in a predictable location during filing of the flexible mold 500 with the ceramic powder 402. For example, as shown in FIG. 14 and FIG. 15, at least one upper boss 470 (e.g., positioned along the first longitudinal position 472) has an upward projection 478 that defines an upper slot 482 between the upward projection 478 and the first major surface 416 of the aligning pre-pressed body 404. As shown in FIG.15, the positive passage mold 404 is at least partially disposed in the upper slot 482. In embodiments, at least one lower boss (e.g., positioned along the second longitudinal position 474) can have a downward projection that defines a lower slot between the downward projection and the first major surface 416 of the aligning pre-pressed body 404. The positive passage mold 404 can be at least partially disposed in the lower slot. In embodiments include the upper slot and/or the lower slot, the corresponding boss 470 engages the positive passage mold 408 to prevent the positive passage mold from moving out of contact with the aligning pre-pressed body 404. [0128] By registering the positive passage mold 408 to the aligning pre-pressed body 404 via the bosses 470 and registering the aligning pre-pressed body 404 to the flexible mold 500, vibration can be used to improve ceramic powder filling without concern for displacing positive passage mold 408. This configuration can greatly reduce the number and/or size of features (e.g., access ports and/or other openings) in the aligning pre-pressed body 404 that may normally be used for ceramic powder filling, such as the longitudinal thru hole(s) described later in this disclosure. [0129] FIGS. 16-18 schematically depict additional pre-pressed bodies 400 that can be used to align one or more stacking units 440_n in parallel within the flexible mold 500. In embodiments, the pre-pressed bodies 400 can comprise one or more supporting pre-pressed bodies, such as a bottom pre-pressed body 492 and/or a top pre-pressed body 494, and the process can further comprise contacting the aligning pre-pressed body 404 with the supporting pre-pressed body 492, 494 to set an alignment of the aligning pre-pressed body 404. In such embodiments, the supporting pre-pressed body 492, 494 defines a slot 496 within which the aligning pre-pressed body 404 is inserted to set the alignment of the aligning pre-pressed body 404. The slots 496 can be formed via sawing, pressing, extrusion, grinding, or machining. The slots 496 can also be fabricated by bonding pre-pressed ceramic strips onto a pre-pressed body 400. [0130] In embodiments, the bottom pre-pressed body 492 is positioned on the base 504 (FIG.29 and FIG.30) of the flexible mold 500 and configured to abut at least one sidewall 508 of the flexible mold 500. As shown in FIGS. 16-18, the stacking units 440n are lowered into slots 496 to align the aligning pre-pressed bodies 404 to the slots 496. The bottom pre-pressed body 492 can be sized so that it fits snuggly into the base 504 of the flexible mold 500. This snug-fit configuration helps to align each positive passage mold 408 to the sidewalls 508 of the flexible mold 500. The bottom pre-pressed body 492 can be inserted into the flexible mold 500 prior to the insertion of the aligning pre-pressed bodies 404 into the slots 496 of the bottom pre-pressed body 492. In embodiments, the aligning pre-pressed bodies 404 can be inserted into the slots 496 of the bottom pre-pressed body 492 prior to insertion into the flexible mold 500. [0131] In embodiments, the top pre-pressed body 494 is positioned opposite the base 504 at a top of the flexible mold 500 and configured to abut at least one sidewall 508 of the flexible mold 500. As shown in FIG. 17 and FIG. 18, top portions of each aligning pre-pressed body 404 can be aligned to one another using the top pre-pressed body 494. In embodiments, the top pre-pressed body 494 can be configured to be smaller than the bottom pre-pressed body 492. The smaller size of the top pre-pressed body allows the ceramic powder 402 to be more easily poured into the gaps or clearances between the aligning pre-pressed bodies 404. In embodiments, the top pre-pressed body 494 can be larger (e.g., but still fit within the flexible mold), but configured to have thru holes at various locations to allow the ceramic powder to be poured into the gaps or clearance between the aligning pre-pressed bodies 404. [0132] Referring now to FIGS. 19-21, the aligning pre-pressed bodies 404 can be fabricated with additional and/or alternative features that may improve the filling of the flexible mold 500 with the ceramic powder 402. In embodiments, the aligning pre-pressed body 404 has one or more longitudinal thru holes 498 and is configured to be spaced from the base 504 of the flexible mold 500 such that, during the covering, the binder-coated ceramic powder 402 flows through the longitudinal thru hole 498 and fills the flexible mold 500. The longitudinal thru holes 498 are configured to extend substantially parallel to the surface 416, 417 of the aligning pre-pressed body 404. In embodiments, the longitudinal thru holes 498 can be formed by drilling the aligning pre-pressed body 404 after pre-pressing, or by molding during the pressing process (e.g., using a compressible silicone mold form). [0133] FIGS. 19-21 show cross-sectional views of three aligning pre-pressed bodies 404 that are used to align two positive passage molds 408 within a flexible mold 500. As show in FIGS. 19-21, each aligning pre-pressed body 404 has at least one longitudinal thru hole 498 extending vertically therethrough. The positive passage molds 408 are aligned vertically by placing them on a layer of ceramic powder 402 disposed at the base 504 of the flexible mold 500. As shown in FIG. 20, the ceramic powder 402 has been poured into flexible mold 500 through the longitudinal thru holes 498 in the aligning pre-pressed body 404. Moreover, in FIG. 20, the longitudinal thru holes 498 are shown partially filled. The ceramic powder is configured to flow through the longitudinal hole 498 and fills any open cavities beneath the aligning pre-pressed bodies 404 within the flexible mold 500. After the flexible mold 500 is filled with the ceramic powder, it appears as shown in FIG.21. The aligning pre-pressed bodies 404 and the ceramic powder 402 are joined together after the isostatic pressing. [0134] FIGS.22-24 are a stepwise series of cross-sectional representations of aspects of a process for producing the fluidic module of the present disclosure, showing an alternative pre- pressed body used for producing the fluidic module of the present disclosure. In contrast to the relatively large aligning pre-pressed bodies 404 described above, the positive passage molds 408 can also be aligned by smaller pre-pressed bodies. In embodiments, the pre-pressed bodies 400 include lateral pre-pressed bodies 704. As shown in FIGS. 22-24, the lateral pre-pressed bodies 704 are configured to be inserted into the flexible mold 500 such that they rest on top of a layer of ceramic powder 402. The lateral pre-pressed bodies 704 are sized so that they align and sandwich respective positive passage molds 408. [0135] FIG.22 shows a cross-sectional view of a flexible isostatic pressing mold 500 after a layer of ceramic powder 402 has been poured into the base 504 of the flexible mold 500. Then, two positive passage molds 408 are oriented vertically and pressed downward into the ceramic powder layer 402. In embodiments, a pre-pressed body (not shown) could be used to limit the downward travel of the positive passage mold 408 into the ceramic powder and provide vertical alignment. Next, as shown in FIG. 22, a first set of lateral pre-pressed bodies 704 are positioned on both sides of the positive passage molds 408 so that they are properly aligned horizontally within the flexible mold 500. [0136] Next, as shown in FIG. 23, more ceramic powder 402 is poured into the flexible mold 500, and then a second set of lateral pre-pressed bodies 704 are placed on top of the ceramic powder 402. Next, as shown in FIG. 24, the lateral pre-pressed bodies 704 and the positive passage molds 408 are covered by additional ceramic powder 402. The flexible cap 516 (FIG.4D) is then inserted into the opening at the top of the flexible mold 500, and the flexible mold 500 is prepared for isostatic pressing. In embodiments, if horizontal fluidic interconnections are needed between positive passage molds 408, horizontal thru holes can be drilled in the lateral pre-pressed bodies 704 and interconnection stubs (e.g., 462 in FIGS. 10- 12) can then be inserted into the horizontal thru holes prior to placing the lateral pre-pressed bodies 704 in the flexible mold 500. [0137] In the exemplary embodiment described in connection with FIGS.22-24, six lateral pre-pressed bodies 704 are positioned inside the flexible mold 500 adjacent to the positive passage molds. In embodiments, each group of three lateral pre-pressed bodies 704 can be configured instead as a single lateral pre-pressed body that has been machined to provide clearance holes or slots configured to receive and align the positive passage molds 408. These unitary lateral pre-pressed bodies can be referred to as spacer sheets or spacer plates, and they can be fabricated via pressing, machining, or extrusion. The lateral pre-pressed bodies 704 (described above) and/or the spacer plates can include holes or slots that enable ceramic powder to be poured through the holes or slots to fill any open spaces in the flexible mold 500. [0138] FIGS.25-27 illustrate another technique for aligning positive passage molds within a flexible isostatic pressing mold 500. The technique includes use of a reusable alignment fixture 800 that is temporarily placed inside the flexible mold 500 during ceramic powder filling. In embodiments, as shown in FIGS.25-27, the alignment fixture 800 is in the shape of a comb that can engage and align two positive passage molds 408 that have been inserted into the flexible mold 500. FIG. 25 shows the alignment fixture 800 after it has been inserted into the flexible mold 500 along with two positive passage molds 408. A thin layer of ceramic powder 402 has been previously poured in the base of the flexible mold 500. The alignment fixture 800 can be configured with an active or passive gripping function that holds the positive passage molds 408 firmly in place until a later time when the grip is released. [0139] Next, as shown in FIG.26, additional ceramic powder 402 is poured through holes 804 in the alignment fixture 800 so that the flexible mold 500 fills up with ceramic powder. In embodiments, the holes 804 may be long drilled holes, as shown in the figures, or slots or open regions where ceramic powder 402 can be poured. As the ceramic powder 402 fills the flexible mold 500, it surrounds the positive passage molds 408 and prevents them from moving horizontally. Once the positive passage molds 408 are stabilized by the ceramic powder 402, the alignment fixture 800 can be removed from the flexible mold 500, as shown in FIG. 27. This removal process can be carried out gradually as the ceramic powder 402 is continuously poured into the flexible mold 500. In other embodiments, the alignment fixture 800 can be removed once the flexible mold 500 is filled up by a pre-defined amount of the ceramic powder 402. [0140] In embodiments, the alignment fixture 800 can be an appropriately sized rod or tube that is inserted vertically down into the flexible mold so that it acts like a spacer and holds the positive passage molds 408 in alignment. After the flexible mold 500 is filled with the ceramic powder 402, the rod or tube can be pulled out, allowing the ceramic powder to flow in the void formed by rod or tube removal. While some of the ceramic powder 402 is moved during this process, the bulk of the ceramic powder remains unmoved, providing stabilization for the positive passage molds 408 and helping them to remain properly aligned after removal of the rod or tube. [0141] While the disclosure has been illustrated and described in detail in the drawings and foregoing description, the same should be considered as illustrative and not restrictive in character. It is understood that only the preferred embodiments have been presented and that all changes, modifications and further applications that come within the spirit of the disclosure are desired to be protected.

Claims

CLAIMS What is claimed is: 1. A process for forming a ceramic fluidic module for a flow reactor, comprising: forming pre-pressed bodies from binder-coated ceramic powder, the pre-pressed bodies comprising an aligning pre-pressed body; contacting a first side of a positive passage mold of a fluid passage with a first major surface of the aligning pre-pressed body to set an alignment of the positive passage mold, the positive passage mold defining a path of the fluid passage with the path having a tortuous shape and lying substantially in a mold plane; covering the positive passage mold and the aligning pre-pressed body with a volume of the binder-coated ceramic powder within a flexible mold, the flexible mold having a base and sidewalls that extend perpendicularly from the base in a longitudinal direction; isostatically pressing the flexible mold with the positive passage mold, the aligning pre-pressed body, and the volume of the binder-coated ceramic powder therein to form a pressed body; heating the pressed body to remove the positive passage mold; and sintering the pressed body to form the ceramic fluidic module having the fluid passage extending therethrough. 2. The process of claim 1, wherein the first major surface of the aligning pre-pressed body is oriented substantially parallel to the mold plane. 3. The process of claim 1 or claim 2, wherein the aligning pre-pressed body has a plate- like shape. 4. The process of any one of the preceding claims, wherein contacting the first side of the positive passage mold with the first major surface of the aligning pre-pressed body comprises connecting the first side of the positive passage mold to the first major surface of the aligning pre-pressed body.

5. The process of claim 4, wherein connecting the first side of the positive passage mold to the first major surface of the aligning pre-pressed body comprises adhering the first side of the positive passage mold to the first major surface of the aligning pre-pressed body using an adhesive. 6. The process of any one of the preceding claims, wherein contacting the first side of the positive passage mold with the first major surface of the aligning pre-pressed body comprises positioning the positive passage mold on a boss protruding from the first major surface of the aligning pre-pressed body. 7. The process of claim 6, wherein the positive passage mold is positioned on a plurality of bosses protruding from the first major surface of the aligning pre-pressed body. 8. The process of claim 7, wherein the bosses are spaced in a lateral direction across the first major surface of the aligning pre-pressed body. 9. The process of claim 8, wherein the bosses are spaced in the longitudinal direction on the first major surface of the aligning pre-pressed body. 10. The process of claim 9, wherein the bosses comprise upper bosses spaced in the lateral direction along a first longitudinal position and lower bosses spaced in the lateral direction along a second longitudinal position lower than the first longitudinal position. 11. The process of claim 10, wherein the path of the positive passage mold has a serpentine shape with a repeating pattern. 12. The process of claim 11, wherein the repeating pattern comprises a first linear segment, followed by an upper curved segment, followed by a second linear segment, and followed by a lower curved segment, the repeating pattern repeating at least two times. 13. The process of claim 12, wherein at least one upper boss is configured to abut at least one upper curved segment of the path of the positive passage mold.

14. The process of claim 12, wherein the upper bosses are configured to abut each upper curved segment of the path of the positive passage mold. 15. The process of claim 13 or claim 14, wherein at least one lower boss is configured to abut at least one lower curved segment of the path of the positive passage mold. 16. The process of any one of claims 13-15, wherein the lower bosses are configured to abut each lower curved segment of the path of the positive passage mold. 17. The process of any one of claims 13-16, wherein the upper curved segment and the lower curved segment of the path of the positive passage mold each subtend an angle of approximately 180 degrees such that the first linear segment and the second linear segment of the path of the positive passage mold are parallel to one another. 18. The process of claim 17, wherein the upper bosses are configured to abut each adjacent pair of the first linear segments and the second linear segments of the path of the positive passage mold. 19. The process of claim 17 or claim 18, wherein the lower bosses are configured to abut each adjacent pair of the first linear segments and the second linear segments of the path of the positive passage mold. 20. The process of any one of claims 10-19, wherein at least one upper boss has an upward projection that defines an upper slot between the upward projection and the first major surface of the aligning pre-pressed body, the positive passage mold at least partially disposed in the upper slot. 21. The process of any one of claims 10-20, wherein at least one lower boss has a downward projection that defines a lower slot between the downward projection and the first major surface of the aligning pre-pressed body, the positive passage mold at least partially disposed in the lower slot. The process of any one of the preceding claims, wherein the aligning pre-pressed body has a transverse thru hole oriented normal to the mold plane at a position proximate to one end of the path of the positive passage mold, and wherein an interconnection stub formed from a material of the positive passage mold is configured abut the one end of the path and extend through the transverse thru hole. 23. The process of any one of the preceding claims, wherein the aligning pre-pressed body has a longitudinal thru hole and is configured to be spaced from the base of the flexible mold such that, during the covering, the binder-coated ceramic powder flows through the longitudinal thru hole and fills the flexible mold. 24. The process of any one of the preceding claims, wherein contacting the positive passage mold with the aligning pre-pressed body forms a stacking unit, the process further comprising arranging n stacking units in the flexible mold one by one in a stacking direction oriented normal to the mold plane, and where n is an integer of 1 or greater. 25. The process of claim 24, wherein the aligning pre-pressed body has a second major surface facing opposite the first major surface and oriented substantially parallel to the mold plane, and wherein the aligning pre-pressed body of a first stacking unit of the n stacking units is configured to abut a first sidewall of the flexible mold with the second major surface thereof. 26. The process of claim 25, wherein the aligning pre-pressed body of each stacking unit of the n stacking units after the first stacking unit is configured to abut a second side of the positive passage mold of the immediate prior stacking unit. 27. The process of claim 26, wherein the pre-pressed bodies comprise a second aligning pre-pressed body configured to abut (i) a second side of the positive passage mold of the nth stacking unit on a first side of the second aligning pre-pressed body and (ii) a second sidewall of the flexible mold, opposite the first sidewall, on a second side of the second aligning pre- pressed body.

28. The process of any one of claims 1-22, wherein the pre-pressed bodies comprise a supporting pre-pressed body, the process further comprising contacting the aligning pre- pressed body with the supporting pre-pressed body to set an alignment of the aligning pre- pressed body. 29. The process of claim 23, wherein the supporting pre-pressed body defines a slot within which the aligning pre-pressed body is inserted to set the alignment of the aligning pre-pressed body. 30. The process of claim 23 or claim 24, wherein the supporting pre-pressed body comprises a bottom pre-pressed body positioned on the base of the flexible mold and configured to abut at least one sidewall of the flexible mold. 31. The process of any one of claims 23-25, wherein the supporting pre-pressed body comprises a top pre-pressed body positioned opposite the base at a top of the flexible mold and configured to abut at least one sidewall of the flexible mold. 32. The process of any one of the preceding claims, wherein the positive passage mold is contacted with the aligning pre-pressed body within the flexible mold. 33. The process of any one of the preceding claims, wherein the positive passage mold is contacted with the aligning pre-pressed body outside of the flexible mold. 34. The process of claim 33, wherein contacting the positive passage mold with the aligning pre-pressed body comprises forming the positive passage mold on the aligning pre- pressed body. 35. The process of any one of the preceding claims, wherein each pre-pressed body is formed by pressing the binder-coated ceramic powder with a first pressure prior to the step of covering with the volume of the binder coated powder. 36. The process of claim 35, wherein the pressing to form the pre-pressed bodies is uniaxial pressing.

37. The process of claim 35, wherein the pressing to form the pre-pressed bodies is isostatic pressing. 38. The process of any one of claims 35-37, wherein the pressed body is formed by isostatically pressing the volume of binder-coated ceramic powder with a second pressure, and wherein the first pressure is lower than the second pressure. 39. The process of claim 38, wherein the first pressure is in a range of from about 1 MPa to about 10 MPa. 40. The process of claim 38 or claim 39, wherein the second pressure is in a range of from about 20 MPa to about 200 MPa.