FIELD OF THE INVENTION

The present invention generally relates to monomer formulations suitable for making preceramic polymers, which can be converted into ceramic matrix composites and other ceramic structures.

BACKGROUND OF THE INVENTION

Ceramic matrix composite (CMC) materials overcome many disadvantages of conventional ceramics, such as brittle failure, low fracture toughness, and limited thermal shock resistance. Applications of ceramic matrix composites include those requiring reliability at high temperatures (beyond the capability of metals or polymers) and resistance to corrosion and wear.

There is also high commercial demand for additively manufactured (3D-printed) ceramics in fields including industrial filtration (molten metal filters, flow separators); metal processing (casting molds/blanks); implantable dental and medical devices; and semiconductor processing. Additive manufacturing of ceramic materials is also of interest for propulsion components, thermal protection systems, porous burners, microelectromechanical systems, and electronic device packaging, for example.

No mature method for 3D printing ceramic matrix composites exists. Currently, CMC materials are limited to manual lay-up, molding, or thermoforming. There are also known techniques for sintering ceramic particles or using ceramic particles printed in a binder, both of which typically produce porous ceramics which have lower strength than the parent material. Ceramic structures are typically sintered as compacted porous materials, severely limiting the manufacturable geometries.

Formulations have been described for creating ceramic materials, which can be printed (additively manufactured) with various methods such as stereolithography techniques and laser sintering. These are typically unreinforced ceramics that do not contain a second phase and suffer from low fracture toughness. These methods are described in Zocca et al., “Additive Manufacturing of Ceramics: Issues, Potentialities, and Opportunities”,J. Am. Ceram. Soc.,98 [7] 1983-2001 (2015).

In addition, formulations which can create 1D or 2D ceramics, or very small 3D structures, have been described. See U.S. Pat. No. 4,816,497 issued Mar. 28, 1989 to Lutz et al.; U.S. Pat. No. 5,698,485 issued Dec. 16, 1997 to Bruck et al.; U.S. Pat. No. 6,573,020 issued Jun. 3, 2003 to Hanemann et al.; U.S. Pat. No. 7,582,685 issued Sep. 1, 2009 to Arney et al.; and U.S. Patent App. Pub. No. US2006/0069176A1 published Mar. 30, 2006 to Bowman et al.

In comparison with metals and polymers, ceramics are difficult to process, particularly into complex shapes. Because they cannot be cast or machined easily, ceramics are typically consolidated from powders by sintering or deposited in thin films. Flaws, such as porosity and inhomogeneity introduced during processing, govern the strength because the flaws initiate cracks, and—in contrast to metals—brittle ceramics have little ability to resist fracture. This processing challenge has limited the ability to take advantage of ceramics' impressive properties, including high-temperature capability, environmental resistance, and high strength. Recent advances in additive manufacturing have led to a multitude of different techniques, but all additive manufacturing techniques developed for ceramic materials only process unreinforced ceramics and not ceramic matrix composites. Only a few of the commercially available three-dimensional (3D) printing systems offer printing of ceramics, either by selective curing of a photosensitive resin that contains ceramic particles, selective deposition of a liquid binder agent onto ceramic particles (binder jetting), or selective fusion of a powder bed with a laser. All these techniques are limited by slow fabrication rates, and in many cases, a time-consuming binder removal process. By starting with powders that need to be consolidated to a dense part, it is an almost insurmountable challenge to add reinforcement and create ceramic matrix composites without fusing or reacting the matrix and the second phase, losing reinforcing capability. Furthermore, many additive processes introduce large thermal gradients that tend to cause cracks in ceramics. Pores, cracks, and inhomogeneities are often responsible for the low strength and poor reliability of additively manufactured ceramic parts.

Preceramic polymers are a class of polymers which allow, via a thermal treatment, a conversion of a polymer part to a ceramic material. Typically, these preceramic polymers contain silicon (Si) in the molecular backbone, with the resulting material containing Si. There are a wide variety of known preceramic polymers. Examples include polysilazanes, borazine-modified hydridopolysilazanes, polysilanes, polycarbosilanes, silicone resins, polyvinylborazine, polyborazylene, and decaborane-based polymers. These preceramic polymers have been used to form specific polymer-based structures that can be subsequently heat-treated (pyrolyzed or sintered) to create near net-shape ceramic structures.

A stereolithography technique provides a method to build a 3D polymer microstructure in a layer-by-layer process. This process usually involves a platform (e.g., substrate) that is lowered into a photomonomer bath in discrete steps. At each layer, a laser is used to scan over the area of the photomonomer that is to be cured (i.e., polymerized) for that particular layer. Once the layer is cured, the platform is lowered by a specific amount, determined by the processing parameters and desired feature/surface resolution, and the process is repeated until the complete 3D structure is created. One example of such a stereolithography technique is disclosed in U.S. Pat. No. 4,575,330 issued Mar. 11, 1986 to Hull et al.

Modifications to the above-described stereolithography technique have been developed to improve the polymer resolution by using laser optics and special resin formulations. Also, modifications have been made to decrease the fabrication time of the 3D polymer structure by using a dynamic pattern generator to cure an entire layer at once. One example of such a modification is disclosed in Bertsch et al., “Microstereo-lithography: A Review,”Materials Research Society Symposium Proceedings, Vol. 758, 2003. Another advancement to the standard stereolithography technique includes a two-photon polymerization process, as disclosed in Sun et al., “Two-Photon Polymerization And 3D Lithographic Microfabrication,”Advances in Polymer Science,Vol. 170, 169-273, 2004.

There exists a need for creating ceramic parts of various sizes through 3D printing, for engineering and other applications. Lower-cost structures that are lightweight, strong, and stiff, but can withstand a high-temperature oxidizing environment, are sought. There is a desire for a method of direct 3D printing of ceramics reinforced with particles, whiskers, or fibers, also known as ceramic matrix composite structures.

SUMMARY OF THE INVENTION

The present invention addresses the aforementioned needs in the art, as will now be summarized and then further described in detail below.

Some variations provide a 3D-printing composition comprising:(a) from about 10 vol % to about 99 vol % of one or more preceramic, UV-curable, silicon-containing monomers in a liquid phase; and(b) from about 1 vol % to about 70 vol % of solid-phase fillers, wherein the solid-phase fillers may be selected from the group consisting of SiOC, SiCN, SiC, SiCBN, SiOCN, SiAlON, Si3N4, SiO2, silicate glasses, Al2O3, ZrO2, TiO2, carbon, TiC, ZrC, HfC, Y3Al5O12, B4C, BN, TiN, ZrN, AlN, and combinations thereof.

In some embodiments, the preceramic, UV-curable, silicon-containing monomers are selected from the group consisting of silazanes, siloxanes, silanes, carbosilanes, and combinations, analogues, or derivatives thereof.

In some embodiments, the solid-phase fillers are in the form of fibers, whiskers, nanotubes, nanorods, flat platelets, microparticles with average diameter from 1 micron to 100 microns, nanoparticles with average diameter from 1 nanometer to 1000 nanometers, or combinations thereof.

In certain embodiments, the solid-phase fillers are in the form of fibers with average length from 1 micron to 100 microns and with average diameter that is less than 10% of the average length, and wherein the solid-phase fillers are selected from the subgroup consisting of Si3N4, Al2O3, SiO2, BN, Y3Al5O12, ZrO2, and combinations thereof.

In certain embodiments, the solid-phase fillers are coated with an interfacial coating that includes a material such as (but not limited to) BN, C, AlN, or combinations thereof. That is, solid-phase fillers may be in the form of particles, whiskers, fibers, or other particles, in which surfaces are coated with an interfacial coating.

At least some of the solid-phase fillers may be chemically bonded to the silicon-containing monomers. At least some of the solid-phase fillers may contain a surface treatment that increases the compatibility, solubility, and/or bonding reactivity of the solid-phase fillers with the silicon-containing monomers. For example, the solid-phase fillers may contain one or more surface-functional groups selected from the group consisting of silane, methoxy silane, ethoxy silane, vinyl, ethynyl, vinyl ether, vinyl ester, vinyl amide, vinyl triazine, vinyl isocyanurate, acrylate, methacrylate, diene, triene, mercapto, thiol, oxirane, oxetane, and combinations, analogues, or derivatives thereof.

In some embodiments, the composition further comprises a reactive or non-reactive surfactant and/or a reactive or non-reactive wetting agent.

At least some of the solid-phase fillers may be coated with a UV-reflective material, such as a UV-reflective material selected from the group consisting of Al, Ni, Sn, Ag, Rh, Au, and combinations or alloys thereof.

At least some of the solid-phase fillers may be coated with a protective material that inhibits degradation of the solid-phase fillers during high-temperature pyrolysis.

At least some of the solid-phase fillers may be coated with a sacrificial material that selectively degrades, thereby inhibiting degradation of the solid-phase fillers during high-temperature pyrolysis.

Other variations of the invention provide a 3D-printing composition comprising:(a) from about 10 vol % to about 99 vol % of one or more preceramic monomers in a liquid phase; and(b) from about 1 vol % to about 70 vol % of solid-phase fillers, wherein the solid-phase fillers contain one or more surface-functional groups selected from the group consisting of silane, methoxy silane, ethoxy silane, vinyl, ethynyl, vinyl ether, vinyl ester, vinyl amide, vinyl triazine, vinyl isocyanurate, acrylate, methacrylate, diene, triene, mercapto, thiol, oxirane, oxetane, and combinations, analogues, or derivatives thereof.

In some embodiments, the preceramic monomers are UV-curable monomers selected from the group consisting of silazanes, siloxanes, silanes, and combinations, analogues, or derivatives thereof.

In some embodiments, the preceramic monomers are non-UV-curable monomers, wherein the surface-functional groups react with the preceramic monomers when exposed to UV radiation.

The solid-phase fillers may be selected from the group consisting of SiOC, SiCN, SiC, SiCBN, SiOCN, SiAlON, Si3N4, SiO2, silicate glasses, Al2O3, ZrO2, TiO2, carbon, TiC, ZrC, HfC, Y3Al5O12, B4C, BN, TiN, ZrN, AlN, and combinations thereof.

In certain embodiments, at least some of the surface-functional groups are attached to silane compounds that are in turn attached to the solid-phase fillers.

In some embodiments, the surface-functional groups, when exposed to UV radiation or visible light, react with the preceramic monomers.

The solid-phase fillers may be in the form of fibers, whiskers, nanotubes, nanorods, flat platelets, microparticles with average diameter from 1 micron to 100 microns, nanoparticles with average diameter from 1 nanometer to 1000 nanometers, or combinations thereof. Alternatively, or additionally, the solid-phase fillers may be in the form of fibers with average length from 1 micron to 100 microns and with average diameter that is less than 10% of the average length, wherein the solid-phase fillers are selected from the subgroup consisting of Si3N4, Al2O3, SiO2, BN, Y3Al5O12, ZrO2, and combinations thereof.

In some embodiments, least some of the solid-phase fillers are coated with a protective material that inhibits degradation of the solid-phase fillers during high-temperature pyrolysis, wherein the protective material is disposed between the surface-functional groups and the surface of the solid-phase fillers.

In some embodiments, at least some of the solid-phase fillers are coated with a sacrificial material that selectively degrades, thereby inhibiting degradation of the solid-phase fillers during high-temperature pyrolysis, wherein the sacrificial material is disposed between the surface-functional groups and the surface of the solid-phase fillers.

In certain embodiments, the solid-phase fillers are in the form of fibers with average length from 1 micron to 100 microns and with average diameter that is less than 10% of the average length, wherein the solid-phase fillers are coated with an interfacial coating selected from BN, C, AlN, or combinations thereof, and wherein the interfacial coating is disposed between the surface-functional groups and the surface of the solid-phase fillers.

Some embodiments provide a ceramic matrix composite comprising a pyrolyzed form of a 3D-printed, UV-cured composition(s) as described above.

Other variations provide a method of making a ceramic matrix composite, the method comprising:(i) obtaining a 3D-printing composition;(ii) 3D-printing and polymerizing the 3D-printing composition to generate a preceramic polymer; and(iii) thermally treating the preceramic polymer to produce a ceramic matrix composite,wherein the 3D-printing composition comprises:(a) from about 10 vol % to about 99.9 vol % of one or more preceramic, UV-curable, silicon-containing monomers; and(b) from about 1 vol % to about 70 vol % of solid-phase fillers, wherein the solid-phase fillers are selected from the group consisting of SiOC, SiO2, SiCN, SiC, SiCBN, SiOCN, SiAlON, Si3N4, SiO2, silicate glasses, Al2O3, ZrO2, TiO2, carbon, TiC, ZrC, HfC, Y3Al5O12, B4C, BN, TiN, ZrN, AlN, and combinations thereof.

Other variations provide a method of making a ceramic matrix composite, the method comprising:(i) obtaining a 3D-printing composition;(ii) 3D-printing and polymerizing the 3D-printing composition to generate a preceramic polymer; and(iii) thermally treating the preceramic polymer to produce a ceramic matrix composite,wherein the 3D-printing composition comprises:(a) from about 10 vol % to about 99.9 vol % of one or more preceramic monomers; and(b) from about 1 vol % to about 70 vol % of solid-phase fillers, wherein the solid-phase fillers contain one or more surface-functional groups selected from the group consisting of silane, vinyl, ethynyl, vinyl ether, vinyl ester, vinyl amide, vinyl triazine, vinyl isocyanurate, acrylate, methacrylate, diene, triene, and combinations, analogues, or derivatives thereof.

In other variations of the present invention, a preceramic monomer formulation is provided for 3D-printing and (typically UV-initiated) cationic polymerization, the monomer formulation comprising:(a) a monomer molecule containing (i) non-carbon atoms, such as (but not limited to) atoms selected from the group consisting of Si, B, Al, Ti, Zn, P, S, Ge, and combinations thereof, and (ii) two or more functional groups selected from the group consisting of aliphatic ether, cyclic ether, vinyl ether, epoxide, cycloaliphatic epoxide, oxetane, and combinations, analogues, or derivatives thereof;(b) a cationic photoinitiator or photoacid generator that may (in some embodiments) generate a Brønsted acid when exposed to light; and(c) a 3D-printing resolution agent selected from the group consisting of UV or visible-light absorbers, fluorescent molecules, optical brighteners, and combinations thereof.

The formulation may contain more than one type of the monomer molecule. In some embodiments, at least 10% or at least 40% (on an atom basis) of the non-carbon atoms is Si.

In some embodiments, the cationic photoinitiator or photoacid generator is present in a concentration from about 0.001 wt % to about 10 wt % in the formulation. The formulation may include a photoacid generator that cleaves when exposed to light to generate a Brønsted acid. The formulation may alternatively or additionally include an ionic photoacid generator or a non-ionic photoacid generator.

In some embodiments, the formulation comprises or further comprises a thermal cationic initiator.

In some embodiments, the formulation comprises a cationic photoinitiator that is active at a first wavelength, as well as a radiation-trigger Brønsted acid generator that is active at a second wavelength substantially different from the first wavelength (i.e., the cationic photoinitiator active wavelength).

The 3D-printing resolution agent may be present in a concentration from about 0.001 wt % to about 10 wt % in the formulation. The 3D-printing resolution agent may be selected from the group consisting of 2-(2-hydroxyphenyl)-benzotriazole, 2-hydroxyphenyl-benzophenones, 2-hydroxyphenyl-s-triazines, thiophenediyl)bis(5-tert-butylbenzoxazole), 2,2′-(1,2-ethenediyl)bis(4,1-phenylene)bisbenzoxazole, and combinations thereof.

In some embodiments, the formulation further comprises a UV sensitizer that forms an excited state under UV light absorption.

In preferred embodiments, the formulation further comprises from about 0.1 vol % or about 1 vol % to about 70 vol % of solid-phase fillers.

Other variations provide a preceramic monomer formulation for 3D-printing and (typically UV-initiated) free-radical polymerization, the monomer formulation comprising:(a) a monomer molecule containing (i) non-carbon atoms that are optionally selected from the group consisting of Si, B, Al, Ti, Zn, P, S, Ge, N, O, and combinations thereof, and (ii) two or more C═X double bonds, two or more C≡X triple bonds, or at least one C═X double bond and at least one C≡X triple bond, wherein X is selected from C, S, N, O, or a combination thereof;(b) a photoinitiator that generates free radicals when exposed to light;(c) a free-radical inhibitor; and(d) a 3D-printing resolution agent selected from the group consisting of UV absorbers, fluorescent molecules, optical brighteners, and combinations thereof.

In some embodiments, at least one of the C═X double bonds or the C≡X triple bonds is located at a terminal position of the monomer molecule.

The monomer molecule may include two or more functional groups selected from the group consisting of vinyl, ethynyl, vinyl ether, vinyl ester, vinyl amide, vinyl triazine, vinyl isocyanurate, acrylate, methacrylate, diene, triene, and combinations, analogues, or derivatives thereof. Alternatively, or additionally, the monomer molecule may contain an alkyl group, an ester group, an amine group, a hydroxyl group, or a combination thereof.

In some embodiments, the non-carbon atoms are selected from the group consisting of Si, B, Al, Ti, Zn, P, S, Ge, and combinations thereof. In these or other embodiments, X is selected from C, S, or a combination thereof.

In some embodiments, at least 10 wt % of the monomer molecule is inorganic. In some embodiments, at least 10% (on an atom basis) of the non-carbon atoms is Si.

In some embodiments, the photoinitiator is present in a concentration from about 0.001 wt % to about 10 wt % in the formulation. In certain embodiments, the photoinitiator generates free radicals by intramolecular bond cleavage or intermolecular hydrogen abstraction when exposed to light having a wavelength from about 200 nm to about 500 nm. The photoinitiator may be selected from the group consisting of 2,2-dimethoxy-2-phenylacetophenone, 2-hydroxy-2-methylpropiophenone, camphorquinone, bis(2,4,6-trimethylbenzoyl)-phenylphosphineoxide, benzophenone, benzoyl peroxide, and combinations thereof.

In some embodiments, the formulation further comprises a thermal free-radical initiator, such as one selected from the group consisting of benzoyl peroxide, dicumyl peroxide, 2,2′-azobisisobutyronitrile, and combinations thereof, for example.

In certain embodiments, the formulation further includes a radiation-trigger free-radical initiator active at a wavelength substantially different from the photoinitiator active wavelength (i.e. the primary 3D-printing wavelength).

The free-radical inhibitor may present in a concentration from about 0.001 wt % to about 10 wt % in the formulation. The free-radical inhibitor may be selected from the group consisting of hydroquinone, methylhydroquinone, ethylhydroquinone, methoxyhydroquinone, ethoxyhydroquinone, monomethylether hydroquinone, propylhydroquinone, propoxyhydroquinone, tert-butylhydroquinone, n-butylhydroquinone, and combinations thereof, for example.

The 3D-printing resolution agent may be present in a concentration from about 0.001 wt % to about 10 wt % in the formulation. The 3D-printing resolution agent may be selected from the group consisting of 2-(2-hydroxyphenyl)-benzotriazole, 2-hydroxyphenyl-benzophenones, 2-hydroxyphenyl-s-triazines, thiophenediyl)bis(5-tert-butylbenzoxazole), 2,2′-(1,2-ethenediyl)bis(4,1-phenylene)bisbenzoxazole, and combinations thereof.

Preferred formulations herein further include about 1 vol % to about 70 vol % of solid-phase fillers.

Some embodiments provide a ceramic structure comprising a pyrolyzed form of a 3D-printed, UV-cured composition as described.

Other variations provide a method of making a ceramic structure, the method comprising:(i) obtaining a preceramic monomer formulation;(ii) 3D-printing and polymerizing the preceramic resin formulation to generate a preceramic polymer; and(iii) thermally treating the preceramic polymer to produce a ceramic structure,wherein the preceramic resin formulation comprises:(a) a monomer molecule containing (i) non-carbon atoms selected from the group consisting of Si, B, Al, Ti, Zn, P, S, Ge, and combinations thereof, and (ii) two or more functional groups selected from the group consisting of aliphatic ethers, cyclic ether, vinyl ether, epoxide, cycloaliphatic epoxide, oxetane, and combinations, analogues, or derivatives thereof;(b) a cationic photoinitiator or photoacid generator that may generate a Brønsted acid when exposed to light; and(c) a 3D-printing resolution agent selected from the group consisting of UV absorbers, fluorescent molecules, optical brighteners, and combinations thereof.

Other variations provide a method of making a ceramic structure, the method comprising:(i) obtaining a preceramic monomer formulation;(ii) 3D-printing and polymerizing the preceramic resin formulation to generate a preceramic polymer; and(iii) thermally treating the preceramic polymer to produce a ceramic structure,wherein the preceramic resin formulation comprises:(a) a monomer molecule containing (i) non-carbon atoms selected from the group consisting of Si, B, Al, Ti, Zn, P, S, Ge, N, O, and combinations thereof, and (ii) two or more C═X double bonds, two or more C≡X triple bonds, or at least one C═X double bond and at least one C≡X triple bond, wherein X is selected from C, S, N, O, or a combination thereof;(b) a photoinitiator that generates free radicals when exposed to light;(c) a free-radical inhibitor; and(d) a 3D-printing resolution agent selected from the group consisting of UV absorbers, fluorescent molecules, optical brighteners, and combinations thereof.

Still other variations of the present invention provide a 3D-printing composition comprising:(a) from about 10 vol % to about 99 vol % of one or more preceramic, UV-curable monomers (typically in a liquid phase); and(b) from about 1 vol % or about 1 vol % to about 70 vol % of solid-phase functional additives, wherein the functional additives have at least one average dimension from about 5 nanometers to about 50 microns, and wherein the functional additives are characterized in that when heated, the functional additives are reactive with the monomers to cause an increase in volume of the composition.

In some embodiments, when the functional additives are heated, they are reactive with the monomers. In these or other embodiments, the functional additives are characterized in that when heated under a heating atmosphere, the functional additives are reactive with one or more gases (e.g., O2and/or N2) contained in the heating atmosphere.

In some embodiments, the preceramic, UV-curable monomers are selected from unsaturated ethers, vinyls, acrylates, methacrylates, cyclic ethers (epoxies or oxetanes), thiols, or a combination thereof. In other embodiments, the preceramic, UV-curable monomers are selected from silazanes, siloxanes, silanes, carbosilanes, or a combination thereof.

In some embodiments, the preceramic, UV-curable monomers contain (i) non-carbon atoms selected from the group consisting of Si, B, Al, Ti, Zn, P, S, Ge, and combinations thereof, and (ii) two or more functional groups selected from the group consisting of aliphatic ethers, cyclic ether, vinyl ether, epoxide, cycloaliphatic epoxide, oxetane, and combinations, analogues, or derivatives thereof.

In some embodiments, the preceramic, UV-curable monomers contain (i) non-carbon atoms selected from the group consisting of Si, B, Al, Ti, Zn, P, S, Ge, N, O, and combinations thereof, and (ii) two or more C═X double bonds, two or more C≡X triple bonds, or at least one C═X double bond and at least one C≡X triple bond, wherein X is selected from C, S, N, O, or a combination thereof.

The functional additives may be selected from the group consisting of scandium, yttrium, titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, manganese, iron, cobalt, nickel, zinc, boron, aluminum, gallium, silicon, germanium, phosphorus, and combinations, alloys, oxides, carbides, or nitrides thereof. In these or other embodiments, the functional additives may be selected from the group consisting of titanium silicide, chromium silicide, magnesium silicide, zirconium silicide, molybdenum silicide, and combinations or silicates thereof. In certain embodiments, the functional additives are selected from the group consisting of aluminum, titanium, zirconium, titanium silicide, chromium silicide, magnesium silicide, zirconium silicide, and combinations thereof.

Other variations provide a method of making a ceramic structure, the method comprising:(i) obtaining a 3D-printing composition comprising (a) from about 10 vol % to about 99 vol % of one or more preceramic, UV-curable monomers; and (b) from about 1 vol % to about 70 vol % of solid-phase functional additives, wherein the functional additives have at least one average dimension from about 5 nanometers to about 50 microns, and wherein the functional additives are characterized in that when heated, the functional additives are reactive with the monomers to cause an increase in volume of the composition;(ii) 3D-printing and polymerizing the 3D-printing composition to generate a preceramic polymer; and(iii) thermally treating the preceramic polymer to produce a ceramic structure, wherein during the thermally treating, the functional additives react with the monomers to cause an increase in volume, or reduce volumetric shrinkage, of the ceramic structure compared to a ceramic structure that does not contain the functional additives.

Other variations provide a 3D-printing composition comprising:(a) from about 10 vol % to about 99 vol % of one or more preceramic, UV-curable monomers, wherein at least some of the preceramic, UV-curable monomers contain thiol groups; and(b) from about 1 vol % to about 70 vol % of solid-phase functional additives, wherein the functional additives have at least one average dimension from about 5 nanometers to about 50 microns, and wherein the functional additives are characterized in that when heated, the functional additives reactively bind with sulfur contained in the thiol groups of the monomers.

The functional additives may be selected from the group consisting of scandium, yttrium, titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, manganese, iron, cobalt, nickel, zinc, boron, aluminum, gallium, silicon, germanium, phosphorus, and combinations, alloys, oxides, carbides, or nitrides thereof. In certain embodiments, the functional additives are selected from the group consisting of titanium, zirconium, hafnium, silicon, aluminum, chromium, niobium, chromium silicide, titanium silicide, and combinations thereof.

A ceramic structure is provided, comprising a pyrolyzed form of a 3D-printed, UV-cured composition as disclosed. In some embodiments, the ceramic structure contains sulfur in a concentration from about 0.01 wt % to about 30 wt % on an elemental sulfur basis. For example, the ceramic structure may contain sulfur in a concentration from about 0.1 wt % to about 10 wt % on an elemental sulfur basis.

Other variations provide a method of making a ceramic structure, the method comprising:(i) obtaining a 3D-printing composition comprising (a) from about 10 vol % to about 99 vol % of one or more preceramic, UV-curable monomers, wherein at least some of the preceramic, UV-curable monomers contain thiol groups; and (b) from about 1 vol % to about 70 vol % of solid-phase functional additives, wherein the functional additives have at least one average dimension from about 5 nanometers to about 50 microns, and wherein the functional additives are characterized in that when heated, the functional additives reactively bind with sulfur contained in the thiol groups of the monomers;(ii) 3D-printing and polymerizing the 3D-printing composition to generate a preceramic polymer; and(iii) thermally treating the preceramic polymer to produce a ceramic structure, wherein during the thermally treating, the functional additives reactively bind with the sulfur contained in the thiol groups.

Other variations provide a 3D-printing composition comprising:(a) from about 10 vol % to about 99 vol % of one or more preceramic, UV-curable monomers, preferably in a liquid phase; and(b) from about 1 vol % to about 70 vol % of solid-phase functional additives, wherein the functional additives have at least one average dimension from about 5 nanometers to about 50 microns, and wherein the functional additives are characterized in that when heated, the functional additives catalyze nucleation and/or crystallization associated with conversion of the monomers into a solid ceramic phase.

In some embodiments, the preceramic, UV-curable monomers are selected from unsaturated ethers, vinyls, acrylates, methacrylates, cyclic ethers (epoxies or oxetanes), thiols, or a combination thereof. In other embodiments, the preceramic, UV-curable monomers are selected from silazanes, siloxanes, silanes, or a combination thereof.

The preceramic, UV-curable monomers may contain (i) non-carbon atoms selected from the group consisting of Si, B, Al, Ti, Zn, P, S, Ge, and combinations thereof, and (ii) two or more functional groups selected from the group consisting of aliphatic ethers, cyclic ether, vinyl ether, epoxide, cycloaliphatic epoxide, oxetane, and combinations, analogues, or derivatives thereof.

In some embodiments, the preceramic, UV-curable monomers contain (i) non-carbon atoms selected from the group consisting of Si, B, Al, Ti, Zn, P, S, Ge, N, O, and combinations thereof, and (ii) two or more C═X double bonds, two or more C≡X triple bonds, or at least one C═X double bond and at least one C≡X triple bond, wherein X is selected from C, S, N, O, or a combination thereof.

In certain embodiments, the preceramic, UV-curable monomers consist of or contain carbosilanes, wherein the functional additives consist of or contain silicon carbide (optionally as β-SiC).

In certain embodiments, the preceramic, UV-curable monomers consist of or contain silazanes and/or polysesquiazanes, wherein the functional additives consist of or contain silicon nitride (optionally as α-Si3N4and/or β-Si3N4) and/or contain silicon carbide (optionally as β-SiC), or a combination thereof.

A ceramic structure is provided, comprising a pyrolyzed form of a 3D-printed, UV-cured composition as disclosed.

Other variations provide a method of making a ceramic structure, the method comprising:(i) obtaining a 3D-printing composition comprising (a) from about 10 vol % to about 99 vol % of one or more preceramic, UV-curable monomers; and (b) from about 1 vol % to about 70 vol % of solid-phase functional additives, wherein the functional additives have at least one average dimension from about 5 nanometers to about 50 microns, and wherein the functional additives are characterized in that when heated, the functional additives catalyze nucleation and/or crystallization associated with conversion of the monomers into a solid ceramic phase;(ii) 3D-printing and polymerizing the 3D-printing composition to generate a preceramic polymer; and(iii) thermally treating the preceramic polymer to produce a ceramic structure, wherein during the thermally treating, the functional additives catalyze nucleation and/or crystallization of a solid ceramic phase in the ceramic structure.

In various embodiments of the invention, the functional additives are in the form of fibers, whiskers, nanotubes, nanorods, flat platelets, microparticles with average diameter from 1 micron to 100 microns, nanoparticles with average diameter from 1 nanometer to 1000 nanometers, or combinations thereof. In certain embodiments, the functional additives are in the form of fibers with average length from 1 micron to 100 microns and with average diameter that is less than 10% of the average length.

In various embodiments, the functional additives are coated with one or more compounds or chemical groups that polymerize or crosslink the monomer when exposed to UV radiation and/or heat. The compounds or chemical groups may be selected from the group consisting of unsaturated ethers, vinyls, acrylates, methacrylates, cyclic ethers (epoxies or oxetanes), and combinations thereof.

In various embodiments, the functional additives are covalently bonded to one or more compounds or chemical groups selected from the group consisting of unsaturated ethers, vinyls, acrylates, methacrylates, cyclic ethers, epoxies, oxetanes, amines, hydroxyls, isocyanates, hydrides, thiols, and combinations thereof.

In various embodiments, at least some of the functional additives contain a surface treatment that increases the compatibility, solubility, and/or bonding reactivity of the functional additives with the monomers. For example, at least some of the functional additives may be surface-treated with silane compounds.

In various embodiments, the composition further comprises a reactive or non-reactive surfactant and/or a reactive or non-reactive wetting agent.

In various embodiments, the functional additives are at least partially transparent to UV light. Alternatively, or additionally, the functional additives may be at least partially reflective of UV light.

