Manufacture of ceramic body preforms and ceramic body preforms manufactured thereby

Abstract

Non-additive manufacturing processes to form a ceramic body preform utilize injection molding technology or slurry casting technology or isostatic pressing technology to produce a green body part in the desired shape that is processed to produce a porous ceramic body preform having an average backfill flow rate equal to or greater than 0.25 Torr per second, alternatively in a range of 0.50 to 1.50 Torr per second. When formed by injection molding technology, viscosities of feedstock are controlled to less than 800 Pascal-second, alternatively 100-150 Pascal-second, at a shear rate of 1000 s -1 to facilitate part formation and the green body part is further chemically and thermally processed resulting in rigidization. Further processing of the porous ceramic body preform forms a ceramic body fuel element preform, which is a shell for subsequent integration with fissionable fuel, typically UN TRISO fuel, to form sections that are assembled into a fuel element.

Description

PATENT Atty. Dkt. No.: 102085-5048-WOMANUFACTURE OF CERAMIC BODY PREFORMS AND CERAMIC BODY PREFORMS MANUFACTURED THEREBYFIELD OF THE DISCLOSURE

[0001] The present disclosure relates to the manufacture of ceramic body preforms, in particular as it relates to components and structures for fission reactors, such as ceramic body fuel element preforms.BACKGROUND

[0002] In the discussion that follows, reference is made to certain structures and / or methods. However, the following references should not be construed as an admission that these structures and / or methods constitute prior art. Applicants expressly reserve the right to demonstrate that such structures and / or methods do not qualify as prior art against the present invention.

[0003] Ceramic body fuel element preforms are currently manufactured through binder jet additive manufacture (AM) followed by chemical vapor infiltration (CVI) rigidization. Such preforms are used as a shell for subsequent integration with fissionable fuel, typically uranium nitride TRi -structural ISOtropic particle (UN TRISO) fuel, to form sections that are assembled into a fuel element. Examples of such ceramic body fuel element preforms and such AM manufacturing methods for such preforms and related fuel elements are disclosed in U.S. 11,285,635, U.S. 11,919,815, and in Terrani et al., Architecture and properties of TCR fuel form, Journal of Nuclear Materials, Volume 547, 2021, 152781, the entire disclosure of each is incorporated herein by reference.

[0004] However, the equipment and processes associated with additive manufacturing, such as binder jet AM, is expensive and specialized. In addition, the throughput of additive manufacturing is limited.DB1 / 156716277.1 1PATENT Atty. Dkt. No.: 102085-5048-WOSUMMARY

[0005] There is a need for improved manufacturing process to form ceramic body preforms, and in particular for non-AM manufacturing processes for the manufacture of ceramic body fuel element preforms.

[0006] In some embodiments, the manufacturing process to form a ceramic body preform utilizes injection molding technology to produce a green body part in the desired shape and that is subsequently chemically and thermally processed resulting in rigidization and producing the porous ceramic body preform. While in other embodiments, the manufacturing process to form a ceramic body preform utilizes slurry casting technology to produce a green body part in the desired shape and that is pyrolyzed producing a porous ceramic body preform. While in still other embodiments, the manufacturing process to form a ceramic body preform utilizes isostatic pressing technology to produce a green body part in the desired shape and that is pyrolyzed producing a porous ceramic body preform. In each embodiment, the porous ceramic body preform can be further processed to form a ceramic body fuel element preform, which is a shell for subsequent integration with fissionable fuel, typically UN TRISO fuel, to form sections that are assembled into a fuel element.

[0007] In exemplary embodiments, a manufacturing process to form a ceramic body preform utilizing injection molding technology comprises preparing a formulation including a first polymer component, a second polymer component, a ceramic powder component, and a dispersant, compounding the formulation to form a feedstock, forming a green body part from the feedstock by injection molding, debinding the green body part to form a friable body, and thermally processing the friable body to form the ceramic body preform, wherein the first polymer component has a first molecular weight range, the second polymer component has a second molecular weight range, and the first molecular weight range is less than the second molecular weight range, wherein a ratio of the first polymer component to the second polymer component is in a range of 30:70 to 70:30, alternatively 50:50 to 70:30 or 55:45 to 70:30, wherein the ceramic powder component includes silicon carbide, carbon black, or a refractory material, and wherein the ceramic body preform has an average backfill flow rate equal to or greaterDBl / 156716277.1 2PATENT Atty. Dkt. No.: 102085-5048-WOthan 0.25 Torr per second, alternatively in a range of 0.50 to 2.00 Torr per second or 0.50 to 1.50 Torr per second.

[0008] In exemplary embodiments, a manufacturing process to form a ceramic body preform utilizing slurry casting technology comprises preparing a formulation including a first resin component and a ceramic powder component, forming a slurry from the formulation, providing the slurry to a mold, curing the slurry in the mold to form a green body part, and pyrolyzing the green body part to form the ceramic body preform, wherein the first resin component is a pre-ceramic polymer or a carbon-forming resin, wherein the ceramic powder component includes silicon carbide, carbon black, or a refractory material, and wherein the ceramic body preform has an average backfill flow rate equal to or greater than 0.25 Torr per second, alternatively in a range of 0.50 to 2.00 Torr per second or 0.50 to 1.50 Torr per second.

[0009] In exemplary embodiments, a manufacturing process to form a ceramic body preform utilizing isostatic pressing technology comprises preparing a formulation including a polymeric binder, a ceramic powder component and a carrier fluid, forming a slurry from the formulation, creating a granulated flowable powder from the slurry, providing the granulated flowable powder to a mold, isostatically pressing the mold to form a green body part from the granulated flowable powder, and pyrolyzing the green body part to form the ceramic body preform, wherein the ceramic powder component includes silicon carbide, carbon black, or a refractory material, and wherein the ceramic body preform has an average backfill flow rate equal to or greater than 0.25 Torr per second, alternatively in a range of 0.50 to 2.00 Torr per second or 0.50 to 1.50 Torr per second.

[0010] All values used in the discussion of embodiments herein are reported as nominal (whether or not that term is used in the text) and all values in examples and tests are reported as actual.DBl / 156716277.1 3PATENT Atty. Dkt. No.: 102085-5048-WOBRIEF DESCRIPTION OF THE DRAWINGS

[0011] The following detailed description of preferred embodiments can be read in connection with the accompanying drawings in which like numerals designate like elements and in which:

[0012] Figure 1 schematically illustrates process steps for an exemplary manufacturing process to form a ceramic body preform utilizing injection molding technology.

[0013] Figure 2 is a graph of viscosity (in Pascal-seconds) as a function of shear rate (in s'1) for various compositions of feedstock.

[0014] Figure 3 schematically depicts the microstructure at certain points during the exemplary manufacturing process of Figure 1.

[0015] Figure 4 schematically illustrates process steps for an exemplary manufacturing process to form a ceramic body preform utilizing slurry casting technology.

[0016] Figure 5 schematically depicts the microstructure at certain points during the exemplary manufacturing process of Figure 4.

[0017] Figures 6A to 6C contain graphs showing pressure (Torr) as a function of time (second) for multiple samples.

[0018] Figure 7 schematically illustrates process steps for an exemplary manufacturing process to form a ceramic body preform utilizing a slurry and isostatic pressing technology.

[0019] Figure 8 schematically depicts the microstructure at certain points during the exemplary manufacturing process of Figure 7.DETAILED DESCRIPTION

[0020] Figure 1 schematically illustrates process steps for an exemplary manufacturing process to form a ceramic body preform utilizing injection molding technology.Embodiments of the method S100 comprise the steps of: preparing a formulation S105, compounding the formulation to form a feedstock S110, providing the feedstock to the injection molder S125; forming a green body part from the feedstock by injectionDB1 / 156716277.1 4PATENT Atty. Dkt. No.: 102085-5048-WOmolding S130, debinding the green body part S135, and thermally processing the debinded green body part to form the ceramic body preform S140.

[0021] In exemplary embodiments, the formulation includes polymer(s) 105a, a ceramic powder component 105b, and a dispersant 105c. One or more pore formers 105d can optionally be included in the formulation.

[0022] The polymers 105a in the formulation are thermoplastic polymers and include a first polymer component and a second polymer component. The first polymer component has a first molecular weight range, the second polymer component has a second molecular weight range, and the first molecular weight range is less than the second molecular weight range. In the formulation, a ratio of the first polymer component to the second polymer component is in a range of 30:70 to 70:30, alternatively, 50:50 to 70:30 or 55:45 to 70:30, such as, 60:40, by vol%.

[0023] The low molecular weight of the first polymer component helps keep the viscosity low and the melting temperature low which allows for easier workability when compounding and when injecting into the mold. The first polymer component is also capable of being chemical debinded utilizing a solvent, which creates pore networks for gas passage, both in any subsequent thermally debinding process as well as contributing to final porosity (and gas permeability) of the ceramic body preform.

[0024] The high molecular weight of the second polymer component supplies the mechanical properties (e.g., strength) of the green body part. The first polymer component is not subject to chemical debinding utilizing a solvent, but rather is capable of thermal debinding. Thus, the high molecular weight of the second polymer component also supplies strength after chemical debinding. Further, the second polymer component is a copolymer and during thermal debinding undergoes a two- stage mass loss, which contributes to prevent defects (which are more prevalent from a single mass loss debinding).

[0025] An example of a suitable first polymer component is paraffin wax having a molecular weight of 300 to 550 g / mol. An example of a suitable second polymer component is poly(ethylene vinyl acetate) having a molecular weight of 15,000 to 40,000 g / mol. The second polymer component can be in the form of a block copolymer;DBl / 156716277.1 5PATENT Atty. Dkt. No.: 102085-5048-WGfor example, polyethylene vinyl acetate) with polyvinyl acetate. It is noted that other potential second polymer components are high-density polyethylene (HDPE) and polyethylene glycol (PEG), but the viscosity of HDPE was high (melt index 12g / 10min @190 °C) and resulted in limiting how much ceramic powder could be loaded in the formulation and PEG did not supply enough strength to the green body part.

[0026] The ceramic powder component 105b in the formulation can be silicon carbide, carbon black, or a refractory material. In exemplary embodiments, the ceramic powder component is 35 vol% to 60 vol%, alternatively 45 vol% to 55 vol%, relative to a total vol% of the formulation. For example, when the ceramic powder component 105b in the formulation includes silicon carbide, silicon carbide is present at from 20 vol% or from 30 vol% or from 35 vol% or from 45 vol% to 45 vol% or to 55 vol% or to 60 vol%, such as 45 vol% to 60 vol%, alternatively 45 vol% to 55 vol%, relative to a total vol% of the formulation. Also for example, when the ceramic powder component 105b in the formulation includes carbon black, carbon black is present at from 20 vol% or from 30 vol% or from 35 vol% or from 45 vol% to 45 vol% or to 55 vol% or to 60 vol%, such as 35 vol% to 45 vol%, alternatively 38 vol% to 42 vol%, relative to a total vol% of the formulation. Also for example, when the ceramic powder component 105b in the formulation includes a refractory material, the refractory material is selected from the group consisting of tungsten-alloys, titanium-alloys, molybdenum-alloys, and zirconium- alloys. The refractory material can also be zirconium carbide or zirconium metal. The refractory material is present at from 20 vol% or from 30 vol% or from 35 vol% or from 45 vol% to 45 vol% or to 55 vol% or to 60 vol%, relative to a total vol% of the formulation.

[0027] The dispersant 105c in the formulation is selected to achieve adequate dispersion of the components of the formulation during compounding. In exemplary embodiments, the dispersant 105c has one end group attracted to the ceramic powder component 105b and another end group attracted to the polymers 105a, which promotes miscibility of the various components in the formulation. In an example formulation, the dispersant 105c is steric acid and is present at 5 vol% relative to the vol% of the ceramic powder component.DBl / 156716277.1 6PATENT Atty. Dkt. No.: 102085-5048-WO

[0028] The formulation is compounded to form a feedstock S110. Compounding combines the components of the formulation to obtain a feedstock in which the ceramic powder component 105b is present in a matrix of polymers 105a. The components of the formulation are blended to achieve a feedstock having a viscosity (at a shear rate of 1000 s-1) of less than 800 Pascal-second, alternatively ranging from 25 Pascal-second or from 50 Pascal-second or from 100 Pascal-second to 150 Pascal-second or to 200 Pascal-second or to 500 Pascal-second, such as from 50-500 Pascal-second or 100- 150 Pascal-second, and a filler loading of 20 vol% to 60 vol%, alternatively 35 vol% to 60 vol%, relative to a total vol% of the formulation.

[0029] In an example embodiment, blending occurs in a shear mixer operating at 450 RPM for a mixing cycle time of 80 to 100 mins, alternatively 90 to 95 mins. An example shear mixer is a Flacktek DAC 14000-20000 VAC Twin, which can measure torque, vibration, pressure, RPM, and temperature.

[0030] Figure 2 is a graph of viscosity (in Pascal-seconds) as a function of shear rate (in s'1) for various compositions of feedstock. The compositions of the feedstock are shown below in Table 1. Note, Table 1 includes additional examples not shown in Figure 2.

[0031] In each example, the first polymer component was paraffin wax having a molecular weight of 300 to 550 g / mol and the second polymer component was a block copolymer of polyethylene vinyl acetate) having a molecular weight of 15,000 to 40,000 g / mol with 12 wt% polyvinyl acetate and the ratio of (first polymer component): (second polymer component) was 60:40. A suitable second polymer component is available from DOW as ELVAX 660, an ethylene-vinyl acetate copolymer resin with 12 wt% vinyl acetate comonomer content. Table 1 reports the material of the ceramic powder component (silicon carbide (SiC) or carbon black (C)), vol.% of the ceramic powder component (relative to a total vol% of the formulation). In each example A-L, the dispersant was steric acid (present at 5 vol% relative to the vol% of the ceramic powder component).DBl / 156716277.1 7PATENT Atty. Dkt. No.: 102085-5048-WO

[0032] Table 1Ex Ex Ex Ex Ex Ex Ex Ex Ex Ex Ex Ex Ex A B C D E F G H I J K L Zceramic powderSiC SiC SiC SiC SiC SiC SiC SiC SiC SiC C C SiC componentVol% ceramicpowder 45 50 55 60 45 50 55 45 50 55 45 50 55 componentViscosity(Pa-sec) at a~1 ~1 ~1 2 48 77 147 58 100 147 29 48 ~1 shear rate of1000 s'1

[0033] From the graph in Figure 2, two different zones of viscosity at a shear rate of 1000 s'1can be seen: a first zone 205 in which each formulation has a viscosity less than 5 Pascal-second and a second zone 210 in which each formulation has a viscosity in the range of 25 to 150 Pascal-second. Of the formulations in the second zone 210, Examples G, I and J each had viscosity at a shear rate of 1000 s'1in the range of equal to or greater than 100 and equal to or less than 150 Pascal-second.

[0034] In the example embodiments above, a viscosity of the feedstock at a shear rate of 1000 s'1of equal to or greater than 100 and equal to or less than 150 Pascal-second provides a suitable range for injection molding of the formulation. If the viscosity at a shear rate of 1000 s-1is less than 100 Pascal-second, then the flow rate of the formulation may be too high, the injection molding may be uncontrolled, and the resulting parts may have defects. If the viscosity at a shear rate of 1000 s-1is greater than 150 Pascal-second, then the formulation may have insufficient flow and may not adequately join at seams in the mold, and the resulting parts may have defects, particularly seam defects.

[0035] Further, the viscosity of the feedstock at a shear rate of 1000 s-1can be utilized as a parameter to monitor the compounding process. For example, the viscosity of theDBl / 156716277.1 8PATENT Atty. Dkt. No.: 102085-5048-WOfeedstock at a shear rate of 1000 s-1can the measured S115. If the viscosity is at a target viscosity, for example, 25-150 Pascal-second, alternatively 50-150 Pascal- second or 100-150 Pascal-second, the method S100 proceeds S120c and the feedstock is provided to the injection molder S125. If the viscosity is not at a target viscosity, for example, 25 -150 Pascal-second, alternatively 50-150 Pascal-second or 100-150 Pascal-second, the method S100 proceeds to adjust the formulation S120a and / or continue the compounding S120b. at least one of the step of preparing the formulation S105 and the step of compounding S110 (or both the step of preparing the formulation S105 and the step of compounding S110), followed by the step of measuring S115 the viscosity of the feedstock at the shear rate of 1000 s-1are iteratively repeated until the viscosity of the feedstock at a shear rate of 1000 s-1is at the target viscosity, for example, 25 -150 Pascal-second, alternatively 50-150 Pascal- second or 100-150 Pascal-second. Measurement of the viscosity can occur by suitable means, such as by a constant shear test using a capillary rheometer (RH2000).Measurement can be conducted in a stepwise manner in which the viscosity is measured, the formulation and / or compounding adjusted, and the viscosity remeasured. In an alternative method, variables such as temperature and torque at an inputted time and RPM can be continuously monitored and correlated to a viscosity, and the constituents of the formulation added to attain measurements of parameters that correlate to a viscosity of the feedstock at a shear rate of 1000 s-1of a target viscosity, for example, 25 -150 Pascal-second, alternatively 50-150 Pascal-second or 100-150 Pascal-second.

[0036] After providing the feedstock to the injection molder S125, a green body part is formed by injection molding S130. Here, conventional structures such as negative molds, hot runners, etc... are utilized in conjunction with an injection molder to form a green body part from the feedstock. Example injection molding parameters are: inject feedstock pressure of 500-800 bar (50 MPa to 80 MPa); melt temperature of 150 °C; injection flow rate of approximately 40 cc / s; mold temperature of 50 °C; hold pressure of 700 bar (70 MPa); and colling time of 60 seconds.DBl / 156716277.1 9PATENT Atty. Dkt. No.: 102085-5048-WO

[0037] Once removed from the mold, the green body part is subject to debinding S135. Both chemical debinding S135a and thermal debinding S135b can be utilized.

[0038] In chemical debinding S135a, one or more debinding chemicals (or a mixture of debinding chemicals) are used to remove the low molecular weight component, i.e, the first polymer component. Chemical debinding removes a majority of the first polymer component resulting in open networks for gasses evolved in a subsequent thermal debinding to leave without cracking the part. The second polymer component is inert to the debinding chemical.

[0039] Example methods of chemical debinding including submerging the green body part in a bath of the debinding chemical(s) with or without flow for a period of time. In one specific example in which the first polymer is paraffin wax, the second polymer component is a block copolymer of polyethylene vinyl acetate) having a molecular weight of 15,000 to 40,000 g / mol with 12 wt% polyvinyl acetate, and the dispersant is steric acid, isopentane is the debinding chemical. The bath is isopentane in a 3:1 ratio with a solvent (by vol) and the green body part is submerged in the bath (without flow) for 72 hours. After removal from the bath, the chemically debinded part is allowed to rest for 3 hours to allow for evaporation of residual solvents.

[0040] In thermal debinding S135b, the chemically debinded part is thermally heated to remove the high molecular weight component, i.e., the second polymer component. Thermal debinding degrades and pyrolyzes the second polymer component, which leaves the part in the form of a gas. After chemical debinding and thermal binding, the part is just powder compacted together a friable body.

[0041] Example methods of thermal debinding including heating the chemically debinded part in a furnace utilizing a heating profile. In one specific example in which the second polymer is block copolymer of polyethylene vinyl acetate) having a molecular weight of 15,000 to 40,000 g / mol with 12 wt% polyvinyl acetate, the chemically debinded part is placed in a furnace and the heating profile includes heating at a heating rate of 2 °C per minute to 700 °C, holding at 700 °C for 60 minutes, and ambient cooling to room temperature.DBl / 156716277.1 10PATENT Atty. Dkt. No.: 102085-5048-WO

[0042] The friable body is thermally processed by a high temperature heat treatment (with or without application of pressure) to rigidize the friable body into the ceramic body preform. In the high temperature heat treatment, adjacent powder particles undergo a degree of fusing to become connected by interparticle necking (for example, as described in Mazlan et al., Necking mechanism under various sintering process parameters - A review, Journal of Materials Research and Technology, 2023: 2189- 2201, the entire contents of which are incorporated herein by reference), which imparts a rigidity to the part allowing it to be handled for incorporation into a final product. An example high temperature heat treatment includes placing the friable body in a furnace and heating at a heating rate of 3 °C per minute to 1000 °C, holding at 1000 °C for 60 minutes, and cooling at a cooling rate of 3 °C per minute to room temperature.

[0043] Figure 3 schematically depicts the microstructure at certain points during the exemplary manufacturing process of Figure 1. In the schematic image 310, the microstructure corresponding to the green body part formed by injection molding prior to debinding is shown. The microstructure of the green body part includes the first polymer component 312, the second polymer component 314, the ceramic powder component 316, and the dispersant 318 distributed homogenously throughout the microstructure. In the schematic image 320, the microstructure corresponding to the chemically debinded part, i.e. , after chemical debinding, is shown. In the schematic image 320, a majority (alternatively all) of the first polymer component has been chemically removed resulting, while the second polymer component 314, which is inert to the debinding chemical, remains. In addition, the dispersant has also been chemically removed. Removal of the first polymer component creates open networks in the chemically debinded part. In the schematic image 330, the microstructure corresponding to the friable body 332, i.e., after both chemical debinding and thermal debinding, is shown. In the schematic image 330, the second polymer component has been degraded and pyrolyzed and the evolved gasses have escaped from the part via the open networks formed by removal of the first polymer during chemical debinding. In the friable body 332, the particles of the ceramic powder component 316 are loosely connected to each other via surface energies of the powder materials being high due toDBl / 156716277.1 11PATENT Atty. Dkt. No.: 102085-5048-WOthe surface area of the powder, causing necking to begin and the friable body 332 is handleable (though the friable body 332 has a tendency to break into smaller pieces under stress or contact). In the schematic image 340, the microstructure corresponding to the ceramic body preform, i.e. , after rigidization of the friable body, is shown. In the ceramic body preform, adjacent particles of the ceramic powder component 316 have undergone a degree of fusing to become connected by interparticle necking and a network of pores 342 has formed throughout the ceramic body preform. A region of particles of the ceramic powder component 316 connected by interparticle necking is depicted at 344.

[0044] Figure 4 schematically illustrates process steps for an exemplary manufacturing process to form a ceramic body preform utilizing slurry casting technology.Embodiments of the method S400 comprise the steps of: preparing a formulation S405, combining constituents of the formulation to form a slurry S410, providing the slurry to a mold S415; curing the slurry to form a green body part S420; removing the green body part from the mold S425, and pyrolyzing the green body part to form the ceramic body preform S430.

[0045] In exemplary embodiments, the formulation includes resin(s) 405a and a ceramic powder component 405b. One or more cross linking catalysts 405c can optionally be included in the formulation. Example cross linking catalysts include peroxide-based catalysts and precious metal catalysts such as platinum based catalysts.

[0046] The resins 405a in the formulation are thermoset resins and include at least one resin component. The at least one resin component can be a pre-ceramic polymer or a carbon-forming resin. Example pre-ceramic polymers include silicon-containing polymers (such as carbosilanes, silazanes, and siloxanes) and carbides (such as hafnium carbide, silicon carbide, and zirconium carbide). Example carbon-forming resins include phenolic resin, anthracene, and naphtha. The pre-ceramic polymer forming resins and carbon forming resins have pyrolytic yields (% of solid amount obtained at end of pyrolysis in inert atmosphere) from 1 to 100 wt%. For silicon- containing polymers, pyrolytic yields are 45 wt% to 85 wt%; for carbides, pyrolytic yieldsDBl / 156716277.1 12PATENT Atty. Dkt. No.: 102085-5048-WOare 26 wt% to 55 wt%; and for carbon-forming resins, pyrolytic yields are 35 wt% to 50 wt% (solvent free).

[0047] The ceramic powder component 405b in the formulation can be silicon carbide, carbon black, or a refractory material. In exemplary embodiments, the ceramic powder component is from 20 vol% or from 30 vol% or from 35 vol% or from 45 vol% to 45 vol% or to 55 vol% or to 60 vol%, such as 35 vol% to 60 vol%, alternatively 45 vol% to 55 vol%, relative to a total vol% of the formulation. For example, when the ceramic powder component 405b in the formulation includes silicon carbide, silicon carbide is present at from 20 vol% or from 30 vol% or from 35 vol% or from 45 vol% to 45 vol% or to 55 vol% or to 60 vol%, such as 45 vol% to 60 vol%, alternatively 45 vol% to 55 vol%, relative to a total vol% of the formulation. Also for example, when the ceramic powder component 405b in the formulation includes carbon black, carbon black is present at from 20 vol% or from 30 vol% or from 35 vol% or from 45 vol% to 45 vol% or to 55 vol% or to 60 vol%, such as 35 vol% to 45 vol%, alternatively 38 vol% to 42 vol%, relative to a total vol% of the formulation. Also for example, when the ceramic powder component 405b in the formulation includes a refractory material, the refractory material is zirconium carbide and is present from 20 vol% or from 30 vol% or from 35 vol% or from 45 vol% to 45 vol% or to 55 vol% or to 60 vol%, relative to a total vol% of the formulation.

[0048] The ceramic powder component 405b in the formulation used in the method S400 utilizing slurry casting technology has a particle size that ranges from nanometer sized to mm sized, alternatively micron sized, such as 25 to 45 microns. The ceramic powder component 405b in the formulation used in the method S400 utilizing slurry casting technology can have a mono-modal particle size distribution or a multi-modal particle size distribution.

[0049] Prior to combining the constituents to form the slurry S410, the constituents of the formulation are selected to achieve the desired properties of the ceramic body preform after pyrolyzing (resin pyrolytic yield, filler loading, porosity, strength, etc.).

[0050] Example 1 - High Resin Mass and Low Filler Example

[0051] A suitable formulation of a high resin mass and low filler example is set forth in Table 2 (below). The formulation of Example 1 includes allyl-hydridopolycarbosilaneDBl / 156716277.1 13PATENT Atty. Dkt. No.: 102085-5048-WO(AHPCS) as resin, dicumyl-peroxide (DICUP) as catalyst, and SiC as filler. No solvent is included. The Example 1 formulation was selected to achieve a 35 vol% loading and a loading of 200 gram.

[0052] Table 2 - Example 1 FormulationMASS MASS VOL VOL TYPE DENSITY (G) (%) (CC) (%) RESIN AHPCS 0.990 145.4 72.7 146.9 88.1 SOLVENT (not used) — 0.0 0.0 0.0 0.0 CATALYST DICUP 0.900 2.9 1.5 3.2 1.9FILLER SIC 3.100 51.7 25.8 16.7 10.0SUM200.0 100.0 166.8 100.0

[0053] In Example 1 , the relatively high resin mass% and low filler vol% is expected to result in a 10 vol% SiC filled system in the cured state. In this example, this would yield a 10 vol% SiC filler and 88 vol% resin system.

[0054] If the Example 1 Formulation were to pyrolyzed at 1000 °C, characteristics of the pyrolyzed Example 1 Formulation would be include those set forth in Table 3.

[0055] Table 3 - Example 1 Formulation - PyrolyzedMASS MASS VOL VOL TYPE DENSITY (G) (%) (CC) (%) RESIN AHPCS 2.500 90.1 63.6 36.1 21.6 SOLVENT (not used) — 0.0 0.0 0.0 0.0 CATALYST DICUP 0.900 0.0 0.0 0.0 0.0 FILLER SIC 3.100 51.7 36.4 16.7 10.0 OPENPOROSITY (OP) 114.04 68.4 SUM141.8 100.0 166.8 100.0DBl / 156716277.1 14PATENT Atty. Dkt. No.: 102085-5048-WO

[0056] The resin has a known pyrolytic yield of 60-62 mass% and a known density through pyrolysis. In the pyrolyzed state, the pyrolyzed body is expected to be 10 vol% SiC filler, and to have 21 vol% resin char and 68.4 vol% open porosity.

[0057] Example 2 - Low Resin Mass and High Filler Example

[0058] The suitable formulation of a low resin mass and high filler example is set forth in Table 4 (below). The formulation of Example 3 includes allyl-hydridopolycarbosilane (AHPCS) as resin, dicumyl-peroxide (DICUP) as catalyst, and SiC as filler. No solvent was included. The Example 2 formulation was selected to achieve a 35 vol% loading and a loading of 200 gram.

[0059] Table 4 - Example 2 FormulationMASS MASS VOL VOL TYPE DENSITY (G) (%) (CC) (%) RESIN AHPCS 0.990 23.6 11.8 23.8 29.4 SOLVENT (not used) — 0.0 0.0 0.0 0.0 CATALYST DICUP 0.900 0.5 0.2 0.5 0.6FILLER SIC 3.100 176.0 88.0 56.8 70.0SUM200.0 100.0 81.1 100.0

[0060] In Example 2, the relatively low resin mass% and high filler vol% is expected to result in a 70 vol% SiC filled system in the cured state. In this example, this would yield a 70 vol% SiC filler and 29 vol% resin system.

[0061] If the Example 2 Formulation were to pyrolyzed at 1000 °C, characteristics of the pyrolyzed Example 2 Formulation would be include those set forth in Table 5.DBl / 156716277.1 15PATENT Atty. Dkt. No.: 102085-5048-WO

[0062] Table 5 - Example 2 Formulation - PyrolyzedMASS MASS VOL VOL TYPE DENSITY (G) (%) (CC) (%) RESIN AHPCS 2.500 14.6 7.7 5.8 7.2(not 0.0 0.0 0.0 0.0 SOLVENT used) —CATALYST DICUP 0.900 0.0 0.0 0.0 0.0 FILLER SIC 3.100 176.0 95.3 56.8 70.0OPENPOROSITY (OP) 18.48 22.8SUM190.6 100.0 81.1 100.0

[0063] The resin has a known pyrolytic yield of 60-62 mass% and a known density through pyrolysis. In the pyrolyzed state, the pyrolyzed body is expected to be 70 vol% SiC filler, and to have 7 vol% resin char and 22.8 vol% open porosity.

[0064] From the above, one can observe the amount of filler and amount open porosity of the structure resulting from each of the input formulation. For example, the structure resulting from Example 2 has lower porosity (vol%) as compared to Example 1 , that would result in a lower gas permeability structure for Example 2. Also for example, the structure resulting from Example 2 has lower resin content (vol%) as compared to Example 1 , that would result in a lower strength structure for Example 2. The predicted results from examples, such as Example 1 and Example 2, can be used to design the manufacturing process for forming a ceramic body preform utilizing slurry casting technology so as to obtain selected properties such as porosity and strength.

[0065] The constituents of the formulation are combined to form a slurry S410. Here, the components of the formulation are combined by blending the resins 405a and ceramic powder component 405b to obtain a slurry in which the ceramic powder component 405b is present in a matrix of resins 405a. Blending also achieves the desired slurry properties (viscosity, filler loading, etc.). However, parameters for blending should avoid initiating cross-linking in the resins 405a.DBl / 156716277.1 16PATENT Atty. Dkt. No.: 102085-5048-WO

[0066] In an example embodiment, the components of the formulation are first blended in a planetary ball mill operating at 350 RPM for a mixing cycle time of 3 to 15 mins, to obtain a blend of the powder components. Then the ball-milled powder components of the formulation are blended to achieve a slurry having a filler loading of 20 vol% to 60 vol% relative to a total vol% of the formulation.

[0067] In an example embodiment, blending occurs by mixing in a commercial mixer. In one example, a shear mixer operating at 450 RPM for a mixing cycle time of 80 to 100 mins, alternatively 90 to 95 mins, can be used. An example shear mixer is a Flacktek DAC 14000-20000 VAC Twin, which can measure torque, vibration, pressure, RPM, and temperature.

[0068] After forming the slurry, the slurry is provided to the mold S415 and cured to form a green body part S420. Here, various mold structures, such as negative molds, and various slurry casting techniques, such as decanting excess slurry, can be used. Also, rigid or flexible molds can be used. Suitable materials for the molds include ceramics, metals, silicone, and graphite.

[0069] Once in the mold, the slurry is cured to form the green body part S420. Curing includes crosslinking of the at least one resin component of the resins 405a. Curing can be assisted by an optional crosslinking catalyst and / or by curing conditions, such as elevated temperature.

[0070] For example, for crosslinking of poly-carbosilanes, crosslinking without a catalyst occurs by heating from room temperature to at or about 300 °C at a heating rate of 3 to 5 °C / min and crosslinking with a catalyst occurs by heating from room temperature to 200 °C at a heating rate of 3 to 5 °C / min. For crosslinking of phenolic resin, crosslinking without a catalyst occurs by heating from room temperature to 125- 300 °C at a heating rate of 3 to 5 °C / min. Preferably, crosslinking occurs in an inert environment and at ambient pressure.

[0071] After curing, the green body part is removed from the mold S425.

[0072] The green body part is then pyrolyzed to form the ceramic body preform S430. Pyrolyzing converts the at least one resin component of the resins 405a to char. The char contributes some mechanical strength to the ceramic body preform. In addition,DBl / 156716277.1 17PATENT Atty. Dkt. No.: 102085-5048-WObecause of evolved gases and volume reduction during pyrolyzing, pyrolyzing can also create open networks in the ceramic body preform that contribute to porosity of the ceramic body preform.

[0073] For the particular resin and filler in the formulation, the pyrolyzing parameters of temperature and time influence the pyrolytic yield and the porosity in the ceramic body preform. In general, the pyrolyzing parameters are selected to achieve a pyrolytic yield resulting in an amount of void space in the ceramic body preform for the end application of the ceramic body preform. Example void spaces for ceramic body fuel element preforms are above 30 % pore volume, alternatively above 40 % pore volume or above 50 % pore volume. Example pyrolyzing parameters are heating from room temperature to a range of 800 °C to 1600 °C, alternatively room temperature to 1000 °C to 1200 °C, at a heating rate of 1 to 5 °C / min. Heating occurs in an inert environment and at ambient pressure.

[0074] Figure 5 schematically depicts the microstructure at certain points during the exemplary manufacturing process of Figure 4. In the schematic image 510, the microstructure corresponding to the cured green body part formed by slurry casting prior to pyrolyzing is shown. The microstructure of the cured green body part includes the at least one resin component 512 and the ceramic powder component 514 distributed throughout the microstructure. The at least one resin component 512 is crosslinked. In the schematic image 520, the microstructure corresponding to the ceramic body preform after pyrolyzing is shown. In the schematic image 520, a majority (alternatively all) of the first resins have been pyrolyzed and converted to char 522. Pyrolyzing the resins to char 522 creates a matrix phase in which the particles of the ceramic powder component 514 are distributed as well as creates open networks in the ceramic body preform. In the schematic image 530, the microstructure corresponding to a further processed ceramic body preform is shown. In the schematic image 530, the further processing is sintering. In the (optionally) sintered ceramic body preform 532, adjacent particles of the ceramic powder component 316 have undergone a degree of fusing to become connected by interparticle necking. A region of particles of the sintered ceramic body preform 532 connected by interparticle necking is depicted at 534.DBl / 156716277.1 18PATENT Atty. Dkt. No.: 102085-5048-WGBetween the connected particles, a combination of residual char (if any) and a network of pores 536 has formed throughout the sintered ceramic body preform 532.

[0075] The pore distribution in the sintered ceramic body preform 532 is a function of particle size of the ceramic powder component 514, the particle size distribution (mono- modal or bi-modal), and the volume of powder components added, as discussed previously herein.

[0076] Figure 7 schematically illustrates process steps for an exemplary manufacturing process to form a ceramic body preform utilizing a slurry and isostatic pressing technology. Embodiments of the method S700 comprise the steps of: preparing a formulation S705, combining constituents of the formulation to form a slurry S710, creating a granulated flowable powder from the slurry by, for example, spray drying S715; providing the granulated flowable powder to a die or a mold S720; isostatically pressing the die or mold to form the granulated flowable powder into a green body part S725; removing the green body part from the die or mold S730, and pyrolyzing the green body part to form the ceramic body preform S735.

[0077] In exemplary embodiments, the formulation includes binder(s), plasticizer(s) and dispersants 705a, a ceramic powder component 705b, and a carrier fluid 705c. In some embodiments, the formulation includes binder(s) 705a, a ceramic powder component 705b, and a carrier fluid 705c, and each of plasticizer(s), and dispersants, are optional. One or more pore formers 705d can also optionally be included in the formulation.

[0078] The binder(s) and plasticizer(s) 705a in the formulation are organic based materials. For example, the binder can be a polymeric binder. Examples of suitable polymeric binders are selected from the group consisting of polyvinyl acetate, acrylic emulsion, methocellulose, hydroxypropyl methocellulose, and polyvinyl alcohol. An example of a suitable plasticizer is polyethylene glycol (PEG).

[0079] The dispersant 705a in the formulation is selected to achieve adequate dispersion of the powder components of the formulation during formation of the slurry and is soluble in the carrier fluid. In exemplary embodiments, the dispersant 705a has one end group attracted to the ceramic powder component 705b and another end groupDBl / 156716277.1 19PATENT Atty. Dkt. No.: 102085-5048-WOattracted to the binder(s) and / or plasticizer(s) 705a, which promotes homogeneity of the various components in the formulation. In an example formulation, the dispersant 705c is oleic acid (for water based systems) or steric acid (for organic solvent based systems) and is present at 5 vol% relative to the vol% of the ceramic powder component.

[0080] The ceramic powder component 705b in the formulation can be silicon carbide, carbon black, or a refractory material. In exemplary embodiments, the ceramic powder component is 35 vol% to 60 vol%, alternatively 45 vol% to 55 vol%, relative to a total vol% of the formulation. For example, when the ceramic powder component 705b in the formulation includes silicon carbide, silicon carbide is present at from 20 vol% or from 30 vol% or from 35 vol% or from 45 vol% to 45 vol% or to 55 vol% or to 60 vol%, such as 45 vol% to 60 vol%, alternatively 45 vol% to 55 vol%, relative to a total vol% of the formulation. Also for example, when the ceramic powder component 705b in the formulation includes carbon black, carbon black is present at from 20 vol% or from 30 vol% or from 35 vol% or from 45 vol% to 45 vol% or to 55 vol% or to 60 vol%, such as 35 vol% to 45 vol%, alternatively 38 vol% to 42 vol%, relative to a total vol% of the formulation. Also for example, when the ceramic powder component 705b in the formulation includes a refractory material, the refractory material is selected from the group consisting of tungsten-alloys, titanium-alloys, molybdenum-alloys, and zirconium- alloys. The refractory material can also be zirconium carbide or zirconium metal. The refractory material is present at from 20 vol% or from 30 vol% or from 35 vol% or from 45 vol% to 45 vol% or to 55 vol% or to 60 vol%, relative to a total vol% of the formulation.

[0081] The ceramic powder component 705b in the formulation used in the method S700 utilizing isostatic pressing technology has a particle size that ranges from nanometer sized to mm sized, alternatively micron sized, such as 25 to 45 microns. The ceramic powder component 705b in the formulation used in the method S700 utilizing isostatic pressing technology can have a mono-modal particle size distribution ora multi-modal particle size distribution.

[0082] The carrier fluid provides fluidity to the formulation. The carrier fluid can be water or can be an organic solvent, such as isopropyl alcohol or ethanol.DBl / 156716277.1 20PATENT Atty. Dkt. No.: 102085-5048-WG

[0083] Prior to combining the constituents to form the slurry S710, the constituents of the formulation are selected to achieve the desired properties of the ceramic body preform after pyrolyzing (resin pyrolytic yield, filler loading, porosity, strength, etc.).

[0084] Example 3

[0085] A suitable formulation of a slurry for granularization and isostatic pressing is set forth in Table 6 (below). The formulation of Example 3 includes Duramax 1022 (45 wt% binder solids content) as binder, polyethylene glycol (PEG) (400 molecular weight) as plasticizer, SiC as filler, and water as carrier fluid.

[0086] Table 6 - Example 3 FormulationMASS MASS TYPE (G) (%)Duramax 1022 (45 wt%BINDER binder solids content) 3.35 1.7 PLASTICIZER PEG (400 MW) 1.65 0.8CARRIER WATER 150 75.0 FILLER SIC 45 22.5SUM 200.0 100.0

[0087] After pyrolysis at a suitable temperature, the pyrolyzed body formed from the Example 3 Formulation is expected to be 100 wt% SiC filler with an open porosity.Example pyrolysis temperatures range from 1000 °C to 1600 °C.

[0088] The constituents of the formulation are combined to form a slurry S710. Here, the components of the formulation are combined by blending the binder(s), plasticizer(s) and dispersants 705a and ceramic powder component 405b to obtain a slurry in which the ceramic powder component 705b is present in a matrix of binder(s), plasticizer(s) and dispersants 705a. Blending also achieves the desired slurry properties (viscosity, filler loading, etc.). However, parameters for blending should avoid initiating cross-DBl / 156716277.1 21PATENT Atty. Dkt. No.: 102085-5048-WOlinking in any of the components of the binder(s), plasticizer(s) and dispersants 705a. Ball milling and shear mixing are suitable techniques for blending.

[0089] After forming the slurry, a granulated flowable powder is created from the slurry using suitable processes S715. One suitable process for creating granulated flowable powder is spray-drying. In example embodiments, the spray-drying parameters are selected to obtain an average granule size of 100-200 microns.

[0090] The granulated flowable powder is then provided to a die or mold S720 and isostatically pressed to form a green body part S725. Here, various die and mold structures, such as negative dies / molds can be used. Also, rigid or flexible dies / molds can be used. Suitable materials for the dies / molds include ceramics, metals, silicone, and graphite. Once in the die / mold, the granulated flowable powder is subject to isostatic pressing. In one embodiment, the isostatic pressing is cold isostatic pressing and the parameters of the cold isostatic pressing include pressing at 20-200 MPa.Lower pressures result in a lower solids loading of the SiC or refractory powder and result in the pyrolyzed preform having a higher backfill flow rate.

[0091] After isostatic pressing, the green body part is removed from the die / mold S730.

[0092] The green body part is then pyrolyzed to remove binders and pore formers and to form the ceramic body preform S735. Pyrolyzing removes the binder(s) and plasticizer(s) components and formed connections between ceramic particles provide some mechanical strength to the ceramic body preform. In addition, because of evolved gases and volume reduction during pyrolyzing, pyrolyzing can also create open networks in the ceramic body preform and remove any pore formers, both of which contribute to porosity of the ceramic body preform.

[0093] For the particular binder(s) and plasticizer(s) in the formulation, the pyrolyzing parameters of temperature and time influence the pyrolytic yield and the porosity in the ceramic body preform. In general, the pyrolyzing parameters are selected to achieve a pyrolytic yield resulting in an amount of void space in the ceramic body preform for the end application of the ceramic body preform. Example void spaces for ceramic body fuel element preforms are above 30 % pore volume, alternatively above 40 % poreDBl / 156716277.1 22PATENT Atty. Dkt. No.: 102085-5048-WOvolume or above 50 % pore volume. The pyrolyzing temperature is selected to provide adequate bridging of ceramic particles to provide adequate mechanical strength to the ceramic body preform. Example pyrolyzing parameters are heating from room temperature to a range of 700 °C to 1600 °C, alternatively room temperature to 800 °C to 1000 °C, at a heating rate of 1 to 5 °C / min. Heating occurs in an inert environment and at ambient pressure.

[0094] Figure 8 schematically depicts the microstructure at certain points during the exemplary manufacturing process of Figure 7. In the schematic image 810, the microstructure corresponding to the cured green body part formed by slurry casting prior to pyrolyzing is shown. The microstructure of the cured green body part includes the binder, plasticizer and dispersant components 812, 816 and the ceramic powder component 814 distributed throughout the microstructure. Optional pore formers 818 can be included and distributed thought the microstructure. The binder and / or plasticizer components 812, 816 can each be crosslinked. In the schematic image 820, the microstructure corresponding to the ceramic body preform after pyrolyzing is shown. In the schematic image 820, a majority (alternatively all) of the binder, plasticizer and dispersant components 812, 816 have been pyrolyzed and converted to char 822 Pyrolyzing the binder, plasticizer and dispersant components 812, 816 to char 822 creates a matrix phase in which the particles of the ceramic powder component 814 are distributed as well as creates open networks in the ceramic body preform. If present, pore formers 818 are also pyrolyzed leaving open pores 824 in the microstructure. In the schematic image 830, the microstructure corresponding to a further processed ceramic body preform is shown. In the (optionally) sintered ceramic body preform 832, adjacent particles of the ceramic powder component 816 have undergone a degree of fusing to become connected by interparticle necking. A region of particles of the sintered ceramic body preform 832 connected by interparticle necking is depicted at 834. Between the connected particles, a combination of residual char (if any) and a network of pores 836 (a) formed from the sintering of char and (b) remaining from the previously formed open pores 824 are present throughout the sintered ceramic body preform 832.DBl / 156716277.1 23PATENT Atty. Dkt. No.: 102085-5048-WO

[0095] The pore distribution in the sintered ceramic body preform 832 is a function of particle size of the ceramic powder component 814, the particle size distribution (mono- modal or bi-modal), and the volume of powder components added. As discussed previously herein.

[0096] Subsequent to the thermal processing step S1 0, S430, S735 in each of the respective methods S100, S400, S700 the ceramic body preform can optionally be further processed S150, S435, S740 such as by machining, grinding, coating, or other mechanical or chemical processes. In one exemplary embodiment, further processing S150, S435, S740 includes chemical vapor infiltration (CVI) or polymer infiltration and pyrolysis (PIP).

[0097] The ceramic body preform resulting from the disclosed methods S100, S400, S700 is porous.

[0098] In manufacturing processes to form a ceramic body preform utilizing injection molding technology, porosity occurs as a result of debinding and thermal rig id ization, which removes polymers 105a and forms a microstructure of particles of ceramic powder component connected by interparticle necking resulting in porosity that contributes to gas permeability of the porous ceramic body preform. Pore formers 105d can optionally be added to the formulation. The pore formers 105d are present in the green body part and subsequently burned out in the thermal processing step S140, leaving behind voids which contribute to porosity and gas permeability porous ceramic body preform. Example pore formers are phenolic beads and nylon beads. When present in the formulation, pore formers are >0 to 40 vol%.

[0099] In manufacturing processes to form a ceramic body preform utilizing slurry casting technology, porosity occurs as a result of pyrolyzing the green body part, which converts resins 405a to char and results in porosity that contributes to gas permeability of the porous ceramic body preform.

[0100] In manufacturing processes to form a ceramic body preform utilizing isostatic pressing technology, porosity occurs as a result of pyrolyzing the green body part, which converts binders, plasticizers, and dispersant 705a to char and results in porosity that contributes to gas permeability of the porous ceramic body preform. Pore formersDBl / 156716277.1 24PATENT Atty. Dkt. No.: 102085-5048-WO705d can also be added to the formulation of the slurry used to form a ceramic body preform utilizing isostatic pressing technology. The pore formers 705d are present in the green body part and subsequently burned out in the thermal processing step S735 leaving behind voids which contribute to porosity and gas permeability porous ceramic body preform. Example pore formers are phenolic beads and nylon beads. When present in the formulation, pore formers are >0 to 40 vol%.

[0101] In one aspect, the porous ceramic body preform is gas permeable and has an average backfill flow rate equal to or greater than 0.25 Torr per second, alternatively the average backfill flow rate is in the range of 0.25 to 2.00 Torr per second or 0.50 to 1.50 Torr per second.

[0102] The average backfill flow rate is determined in a backfill test that similar to determining decay rate in accordance with ASTM E2930. In the backfill test used herein, the porous ceramic body preform is connected via a vacuum hose to a vacuum vessel. An isolation valve isolates the porous ceramic body preform from the vacuum vessel and the vacuum vessel is evacuated to 200-260 Torr. Subsequently, the isolation valve is opened, exposing the porous ceramic body preform to the vacuum of the vacuum vessel and allowing gas to flow through the porous ceramic body preform into the vacuum vessel, which backfills and eventually reaches ambient pressure. The pressure is plotted as a function of time and, from the data, an average backfill flow rate (in Torr per second) can be determined. It should be noted that the average backfill flow rate is determined for values after the pressure of the system was allowed to stabilize after the opening of the isolation valve.

[0103] Figures 6A to 6C each contain a graph showing pressure (Torr) as a function of time (second) for multiple samples tested according to the backfill test described herein. In the Figures 6A to 6C recorded data, the pressure of the system was allowed to stabilize after the opening of the isolation valve before recording was started and, in each of Figures 6A to 6C, recording starting (i.e. , time = 0 seconds) at about 500 Torr. The samples in Figures 6A to 6C are identified in the graph by numbers 1-18, which correspond to the sample number in the following Table 7. Each graph contains results for a different D50 grit size grit size of particles used to make the sample. Also reportedDBl / 156716277.1 25PATENT Atty. Dkt. No.: 102085-5048-WOin Table 7 are the average backfill flow rate (in Torr per second) for each sample averaged between time 0 seconds (in the graph) and the time for the respective sample to reach ambient pressure.

[0104] Table 7 - Samples in Backfill Flow Rate Test of Figure 6Sample # Identification Percent weight gain Average Backfill (%) (w.r.t. Sample 17) Flow Rate (Torr / sec) 1 F280-0313-R1 107 0.13638 2 F280-0314-R2 55 0.7499 3 F280-0315-R3 56 1.0394 4 F280-0316-R4 48 0.9919 5 F280-0317-R5 26 1.0975 6 F320-0287-R1 103 0.2755 7 F320-0288-R2 77 0.4822 8 F320-0289-R3 119 0.0387 9 F320-0290-R4 43 0.5206 10 F320-0291-R5 25 0.7782 11 F400-0275-R1 94 0.1985 12 F400-0278-R2 62 0.3406 13 F400-0280-R4 51 0.7535 14 F400-0276-R5 25 0.9269 15 F400-0317-R3 73 0.2088 16 0% porosity standard N / A -0.0006 17 High porosity standard N / A 0.9037 18 No sample N / A 2.2307(open porosity standard)

[0105] Samples 1-15 reported in Table 7 are made with allyl-hydridopolycarbosilane (AHPCS) as resin, dicumyl-peroxide (DICUP) as catalyst, and SiC as filler. The sequence in the identification is AAAA-####-B#, where AAAA is grit size of particlesDBl / 156716277.1 26PATENT Atty. Dkt. No.: 102085-5048-WO(wherein F280 is a D50 grit size of 36.5 microns; F320 is a D50 grit size of 29.2 microns; and F400 is a D50 grit size of 17.3 microns), #### is unique part identification number, and B# is the location in the furnace during pyrolyzing. Sample 2 broke during the pyrolyzing process and results were obtained on a sample representing about 55% of the nominal sample volume.

[0106] Samples 16-18 are different standards that were tested. The results from Samples 16-18 can be used for reference to compare to the results from Samples 1-15. See, for example, FIGS. 6A to 6C, which each include results for the three standards of Samples 16-18. Sample 16 is a body having 0% porosity. Results from Sample 16 can be used as a reference standard for a completely solid, 0% porosity sample. Sample 17 is a body made by binderjetting (an additive manufacturing method) using 400 grit SiC particles and the body has a porosity of 55% and 60%. Results from Sample 17 can be used as a reference standard for a high porosity sample. Sample 18 had no body attached to the test fixture and the end of the vacuum hose was open to atmosphere. Results from Sample 18 can be used as a reference standard for an open porosity sample.

[0107] In general, a minimum average backfill flow rate is 0.25 Torr per second.Average backfill flow rates equal to or greater than 0.25 Torr per second, alternatively greater than 0.50 Torr per second, are generally acceptable. Average backfill flow rates greater than 2.00 Torr per second represent substantially unrestricted gas flow indicative of large defects in the porous ceramic body preform. In exemplary embodiments, the average backfill flow rate is in the range of 0.25 to 2.00 or 0.50 to 1.50 (Torr per second).

[0108] Although discussed herein with regard to a general “preform” or “part” or “body” or “structure”, the compositions, structures and methods disclosed herein are particularly suitable for making structural parts for nuclear power applications, in particular for nuclear thermal propulsion (NTP) reactors and direct flow reactors. In one particular application, the compositions, structures and methods disclosed herein can be used to make a shell for subsequent integration with fissionable fuel, typically UN TRISO fuel, to form sections that are assembled into a fuel element.DBl / 156716277.1 27PATENT Atty. Dkt. No.: 102085-5048-WO

[0109] Although the present invention has been described in connection with embodiments thereof, it will be appreciated by those skilled in the art that additions, deletions, modifications, and substitutions not specifically described may be made without departure from the spirit and scope of the invention as defined in the appended claims. For example, although described in relation to fissionable fuel materials, nuclear reactors, and associated components, the principles, compositions and processes described herein can also apply to other materials, other compositions, and other structures as well as to their manufacture.

[0110] While reference has been made to specific embodiments, it is apparent that other embodiments and variations can be devised by others skilled in the art without departing from their spirit and scope. The appended claims are intended to be construed to include all such embodiments and equivalent variations.DBl / 156716277.1 28

Claims

PATENT Atty. Dkt. No.: 102085-5048-WOCLAIMSWhat is claimed is:

1. A method to manufacture a ceramic body preform, the method comprising the steps of:preparing a formulation including a first polymer component, a second polymer component, a ceramic powder component, and a dispersant;compounding the formulation to form a feedstock;forming a green body part from the feedstock by injection molding; debinding the green body part to form a friable body; andthermally processing the friable body to form the ceramic body preform, wherein the first polymer component has a first molecular weight range, the second polymer component has a second molecular weight range, and the first molecular weight range is less than the second molecular weight range,wherein a ratio of the first polymer component to the second polymer component is in a range of 30:70 to 70:30,wherein the ceramic powder component includes silicon carbide, carbon black, or a refractory material, andwherein the ceramic body preform has an average backfill flow rate equal to or greater than 0.25 Torr per second, alternatively in a range of 0.25 to 2.00 or 0.50 to 1.50 Torr per second.DB1 / 156716277.1 29PATENT Atty. Dkt. No.: 102085-5048-WO2. The method according to claim 1 , wherein the step of debinding the green body part to form the friable body includes a chemical debinding process followed by a thermal debinding process.

3. The method according to claim 2, wherein the chemical debinding process removes the first polymer component from the green body part and the thermal debinding process removes the second polymer component from the green body part.

4. The method as in any one of claims 1 -3, wherein a viscosity of the feedstock at a shear rate of 1000 s-1is less than 800 Pascal-second, alternatively 50-500 Pascal- second or 100-150 Pascal-second.

5. The method as in any one of claims 1-3, wherein the ratio of the first polymer component to the second polymer component is in the range of 50:50 to 70:30, wherein the ceramic body preform has an average backfill flow rate of 0.50 to 2.00 Torr per second,wherein the ceramic powder component is 35 vol% to 60 vol% relative to a total vol% of the formulation, andwherein a viscosity of the feedstock at a shear rate of 1000 s-1is less 50-500 Pascal-second.DB1 / 156716277.1 30PATENT Atty. Dkt. No.: 102085-5048-WO6. The method as in any one of claims 1-3, further comprising, prior to the step of forming the green body by injection molding, a step of measuring a viscosity of the feedstock at a shear rate of 1000 s-1, andwherein:if the viscosity is 50-150 Pascal-second, proceeding with the step of forming the green body part from the feedstock by injection molding, andif the viscosity is not 50-150 Pascal-second, repeating at least one of the step of preparing and the step of compounding, followed by the step of measuring the viscosity of the feedstock at the shear rate of 1000 s-1until the viscosity is 50-150 Pascal-second.

7. The method as in any one of claims 4-6, wherein the first polymer component is paraffin wax, the second polymer component is a block copolymer of polyethylene vinyl acetate), and the dispersant is steric acid.

8. The method according to claim 7, wherein the first molecular weight range is for the paraffin wax and is 300 to 550 g / mol and wherein the second molecular weight range is for the poly(ethylene vinyl acetate) and is 15,000 to 40,000 g / mol.

9. The method according to claim 7 or 8, wherein the chemical debinding process uses isopentane to remove the first polymer component from the green body part and theDB1 / 156716277.1 31PATENT Atty. Dkt. No.: 102085-5048-WOthermal debinding process heats the green body part to 700 °C to remove the second polymer component from the green body part.

10. The method as in any one of claims 4-9, wherein the ceramic powder component includes silicon carbide.

11. The method as in any one of claims 4-9, wherein the ceramic powder component includes carbon black.

12. The method as in any one of claims 4-9, wherein the ceramic powder component includes a refractory material and the refractory material is selected from the group consisting of tungsten-alloys, titanium-alloys, molybdenum-alloys, and zirconium-alloys.

13. The method as in any one of claims 4-9, wherein the ceramic powder component includes a refractory material and the refractory material is zirconium carbide or zirconium metal.

14. The method as in any one of claims 10-13, wherein the ceramic powder component is 20 vol% to 60 vol%, alternatively 35 vol% to 45 vol% or 38 vol% to 42 vol%, relative to a total vol% of the formulation.

15. The method according to claim 14, wherein the dispersant is 5 vol% relative to the vol% of the ceramic powder component.DB1 / 156716277.1 32PATENT Atty. Dkt. No.: 102085-5048-WO16. The method as in any preceding claim, wherein the step of thermally processing the friable body to form the ceramic body preform heats the friable body to 1000 °C.

17. The method as in any preceding claim, wherein the formulation further includes a pore former.

18. The method as in any preceding claim, wherein the first molecular weight range is for the paraffin wax and is 300 to 550 g / mol and wherein the second molecular weight range is for the polyethylene vinyl acetate) and is 15,000 to 40,000 g / mol.

19. A ceramic body preform manufactured by the method as in any preceding claim.

20. The ceramic body preform according to claim 19, wherein the ceramic body preform is for a fuel element.

21. A method to manufacture a ceramic body preform, the method comprising the steps of:preparing a formulation including a first polymer component, a second polymer component, a ceramic powder component, and a dispersant;compounding the formulation to form a feedstock;forming a green body part from the feedstock by injection molding; debinding the green body part to form a friable body; andDB1 / 156716277.1 33PATENT Atty. Dkt. No.: 102085-5048-WOthermally processing the friable body to form the ceramic body preform, wherein prior to forming the green body by injection molding, the method comprises:measuring a viscosity of the feedstock at a shear rate of 1000 s-1, and: if the viscosity is 50-500 Pascal-second, proceeding with the step of forming the green body part from the feedstock by injection molding, andif the viscosity is not 50-500 Pascal-second, repeating at least one of the step of preparing and the step of compounding, followed by the step of measuring the viscosity of the feedstock at the shear rate of 1000 s-1until the viscosity is 50-500 Pascal-second,wherein the first polymer component has a first molecular weight range, the second polymer component has a second molecular weight range, and the first molecular weight range is less than the second molecular weight range,wherein a ratio of the first polymer component to the second polymer component is in a range of 55:45 to 70:30,wherein the ceramic powder component is silicon carbide, carbon black, or a refractory material,wherein the ceramic body preform has an average backfill flow rate in a range of 0.50 to 1.50 Torr per second,wherein the step of debinding the green body part to form the friable body includes a chemical debinding process followed by a thermal debinding process, and DB1 / 156716277.1 34PATENT Atty. Dkt. No.: 102085-5048-WOwherein the chemical debinding process removes the first polymer component from the green body part and the thermal debinding process removes the second polymer component from the green body part.

22. The method according to claim 21 , wherein the first polymer component is paraffin wax, the second polymer component is a block copolymer of poly(ethylene vinyl acetate), and the dispersant is steric acid,wherein the first molecular weight range is for the paraffin wax and is 300 to 550 g / mol and wherein the second molecular weight range is for the poly(ethylene vinyl acetate) and is 15,000 to 40,000 g / mol,wherein the chemical debinding process uses isopentane to remove the first polymer component from the green body part and the thermal debinding process heats the green body part to 700 °C to remove the second polymer component from the green body part, andwherein the ceramic powder component is 20 vol% to 60 vol%, alternatively 35 vol% to 45 vol% or 38 vol% to 42 vol%, relative to a total vol% of the formulation.

23. A method to manufacture a ceramic body preform, the method comprising the steps of:preparing a formulation including a first resin component and a ceramic powder component;forming a slurry from the formulation;providing the slurry to a mold;DB1 / 156716277.1 35PATENT Atty. Dkt. No.: 102085-5048-WOcuring the slurry in the mold to form a green body part; and pyrolyzing the green body part to form the ceramic body preform, wherein the first resin component is a pre-ceramic polymer or a carbon-forming resin,wherein the ceramic powder component is silicon carbide, carbon black, or a refractory material, andwherein the ceramic body preform has an average backfill flow rate equal to and greater than 0.25 Torr per second, alternatively in a range of 0.25 to 2.00 or 0.50 to 1.50 Torr per second.

24. The method according to claim 23, further comprising sintering the ceramic body preform to form a sintered ceramic body preform,wherein the sintered ceramic body preform has a microstructure including interparticle necking of the ceramic powder component and a plurality of pores.

25. The method according to claim 23 or 24, wherein the ceramic powder component is 20 vol% to 60 vol%, alternatively 35 vol% to 45 vol% or 38 vol% to 42 vol%, relative to a total vol% of the formulation.

26. The method as in any one of claims 23-25, wherein the pre-ceramic polymer is selected from the group consisting of carbosilanes, silazanes, and siloxanes.DB1 / 156716277.1 36PATENT Atty. Dkt. No.: 102085-5048-WO27. The method as in any one of claims 23-25, wherein the pre-ceramic polymer is selected from the group consisting of hafnium carbide, silicon carbide, and zirconium carbide.

28. The method as in any one of claims 23-27, wherein the carbon-forming resin is selected from the group consisting of phenolic resin, anthracene, and naphtha.

29. The method as in any one of claims 23-27, wherein the first resin component has a pyrolytic yield of 1-100 wt%, alternatively 10-70 wt%, relative to an amount of the first resin component in the formulation.

30. The method according to claim 29, wherein the ceramic body preform has a microstructure including the ceramic powder component in a matrix of char formed from the first resin component.

31. The method as in any one of claims 23-30, wherein the ceramic powder component includes silicon carbide.

32. The method as in any one of claims 23-30, wherein the ceramic powder component includes carbon black.DB1 / 156716277.1 37PATENT Atty. Dkt. No.: 102085-5048-WO33. The method as in any one of claims 23-30, wherein the ceramic powder component includes a refractory material and the refractory material is selected from the group consisting of tungsten-alloys, titanium-alloys, molybdenum-alloys, and zirconium-alloys.

34. The method as in any one of claims 23-30, wherein the ceramic powder component includes a refractory material and the refractory material is zirconium carbide or zirconium metal.

35. A ceramic body preform manufactured by the method as in any one of claims 23- 34.

36. The ceramic body preform according to claim 35, wherein the ceramic body preform is for a fuel element.

37. A method to manufacture a ceramic body preform, the method comprising the steps of:preparing a formulation including a polymeric binder, a ceramic powder component, and a carrier fluid;forming a slurry from the formulation;creating a granulated flowable powder from the slurry;providing the granulated flowable powder to a mold;isostatically pressing the mold to form a green body part from the granulated flowable powder; andDB1 / 156716277.1 38PATENT Atty. Dkt. No.: 102085-5048-WOpyrolyzing the green body part to form the ceramic body preform, wherein the ceramic powder component includes silicon carbide, carbon black, or a refractory material, andwherein the ceramic body preform has an average backfill flow rate equal to or greater than 0.25 Torr per second, alternatively in a range of 0.25 to 2.00 or 0.50 to 1.50 Torr per second.

38. The method according to claim 37, wherein the formulation includes one or more selected from the group consisting of a pore former, a plasticizer, and a dispersant.

39. The method according to claim 38, wherein the pore former is selected from the group consisting of graphite, nylon, polyacrylate, andwherein the pore former is 1 vol% to 25 vol% relative to a total vol% of the formulation.

40. The method as in any one of claims 37-39, wherein the ceramic powder component is 20 vol% to 60 vol%, alternatively 35 vol% to 45 vol% or 38 vol% to 42 vol%, relative to a total vol% of the formulation.

41. The method as in any one of claims 37-40, wherein the polymeric binder is selected from the group consisting of polyvinyl acetate, acrylic emulsion, methocellulose, hydroxypropyl methocellulose, and polyvinyl alcohol.DB1 / 156716277.1 39PATENT Atty. Dkt. No.: 102085-5048-WO42. The method according to claim 40 or 41 , wherein the ceramic powder component includes silicon carbide, and wherein the ceramic powder component is 20 vol% to 60 vol% relative to a total vol% of the formulation.

43. The method according to claim 40 or 41 , wherein the ceramic powder component includes carbon black, and wherein the ceramic powder component is 20 vol% to 60 vol% relative to a total vol% of the formulation.

44. The method according to claim 40 or 41 , wherein the ceramic powder component includes a refractory material and the refractory material is selected from the group consisting of tungsten-alloys, titanium-alloys, molybdenum-alloys, and zirconium-alloys, andwherein the ceramic powder component is 20 vol% to 60 vol% relative to a total vol% of the formulation.

45. A ceramic body preform manufactured by the method as in any one of claims 37- 44.

46. The ceramic body preform according to claim 45, wherein the ceramic body preform is for a fuel element.DB1 / 156716277.1 40