Ceramic foam-fiber composite materials, methods for their manufacture, and uses thereof

Abstract

Ceramic foam-fiber composite materials, methods for producing ceramic foam-fiber composite materials, and uses of ceramic foam-fiber composite materials. Ceramic foam-fiber composite materials may be produced by contacting one or more fibers; one or more ceramic precursors; one or more pore-forming gas-forming additives (one or more inert gas generators); one or more catalysts; and, optionally, one or more additives, where the contact results in the formation of an inert gas, forming a ceramic foam-fiber composite material. Ceramic foam-fiber composite materials may include a plurality of fibers, where at least some or all of the fibers individually comprise ceramic foam disposed on at least some or all of the fiber surfaces. Ceramic foam-fiber composite materials may exhibit one or more or all of thermal stability, mechanical strength, and soundproofing / acoustic insulation properties. Ceramic foam-fiber composite materials can be used as building materials.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. Provisional Application No. 62 / 959,907, filed January 11, 2020, the disclosure of which is incorporated herein by reference.

[0002] Statement Regarding Federally Sponsored Research This invention was made with government support under Contract No. DE-EE0008675 awarded by the U.S. Department of Energy. The government has certain rights in this invention. Background of the Disclosure

[0003] Flexible, high-temperature, and lightweight insulating materials are widely used in thermal management and protection systems and space exploration. Ceramic aerogels offer promise for high-temperature insulation, but they lack mechanical flexibility, while fibrous materials with desirable mechanical elasticity offer only moderate insulation.

[0004] High-temperature insulation materials (ceramic foams, mineral wool, and aerogels) are important for thermal management and protection systems. Ceramic aerogels, composed of pearl-necklace-like nanoparticles, are one of the emerging insulating materials characterized by low density, high porosity, chemical inertness, and high specific surface area. However, their insufficient structural continuity leads to mechanical brittleness and defect sensitivity, limiting their application in high-temperature flexible insulation. Fibrous insulation materials promise mechanical flexibility, mild high-temperature insulation, and flame retardancy, but do not meet the requirements for thermal stability and material reliability. To meet the rapidly evolving needs for flexible insulation under extreme conditions (e.g., high temperatures), it is important to design insulating materials that combine high-temperature thermal radiation, conductivity, and convective resistance while maintaining mechanical flexibility and light weight.

[0005] The thermal conductivity and mechanical properties of insulating materials can be controlled by their nanoscale structure. Materials with low density, nanoporous structures (<68 nm), and radiation-absorbing elements can reduce conduction in solids, reduce conduction and convection in air, and slow thermal radiation, respectively, providing excellent super-insulation performance in high-temperature environments. Previously, all-ceramic insulating fiber composites were prepared to exhibit compressive elasticity and anisotropic room-temperature thermal conductivity due to the multilayer assembly of aerogel-fiber composites. Desired room-temperature insulation performance results primarily from reduced thermal convection and conduction of solid and gas components in the aerogel-fiber composite. However, achieving flexible high-temperature insulation performance remains a challenging task. Summary of the Invention

[0006] In one aspect, the present disclosure provides a method for producing a ceramic foam-fiber composite. The composite has a ceramic foam disposed on at least a portion of the individual fibers of the composite. The ceramic foam may be a silica aerogel. The method is based on the in-situ generation of a pore-forming gas and the reaction of precursors, which may be in a closed environment (e.g., at pressures above ambient pressure) or may be carried out in the presence of fibers. The ceramic foam or ceramic foam-fiber composite may be formed under hydrothermal conditions.

[0007] In various embodiments, a method for forming a ceramic foam-fiber composite (e.g., a silica aerogel-fiber composite) includes contacting (e.g., in a reaction mixture, which may be in a closed environment, or a sealed container) one or more types of a plurality of fibers; one or more ceramic precursors; one or more pore-forming gas-forming additives (one or more inert gas generants); one or more catalysts; and, optionally, one or more additives, wherein the contacting results in the formation of an inert gas (e.g., carbon dioxide) and a plurality of fibers, each fiber having a ceramic foam layer disposed on at least a portion of the fiber. The ceramic foam may be formed under hydrothermal conditions. The ceramic foam-fiber composite may be subjected to ambient pressure drying (APD). After formation of the ceramic foam-fiber composite, the composite may be sintered. In various examples, the method further includes post-ceramic foam formation modification of at least a portion of the ceramic foam surface of the ceramic foam composite.

[0008] The ceramic foam material may be a composite material (e.g., a composite ceramic foam) that may include a polymer material in some or all of the pores of the ceramic foam (sometimes called a hybrid composite or hybrid ceramic foam).

[0009] Forming the ceramic foam may include a thermal annealing step, which may occur after the ceramic foam is formed, washed, dried, etc.

[0010] The methods of the present disclosure may further include forming a composite sheet. In various examples, the composite sheet is made by forming a mixture, which may be referred to as a pulp mixture, and may be a reaction mixture, where the ceramic aerogel-fiber composite is formed after the composite is formed, including one or more ceramic foam composite materials and water, mixed, spread on a large mesh screen, and removing the water to form a wet sheet.

[0011] In one aspect, the present disclosure provides a ceramic foam-fiber composite material. The ceramic foam-fiber composite material comprises a plurality of fibers, wherein at least some or all of the fibers individually comprise a ceramic foam disposed on at least some or all of the surface of the fiber. The ceramic foam of the ceramic foam composite material may be a ceramic foam film. The film may be continuous or may be formed from a plurality of particles. The ceramic foam may be referred to as a ceramic aerogel. The ceramic foam may be a silica aerogel. Non-limiting examples of ceramic foams are provided herein. A ceramic foam material (e.g., a ceramic foam composite material) comprises a ceramic foam. The ceramic foam comprises a matrix of a ceramic material. The ceramic foam may be produced by the method of the present disclosure.

[0012] The ceramic foam may be in the form of a layer, which may be continuous or discontinuous.

[0013] The ceramic foam of the ceramic foam-fiber composite is porous and exhibits a hierarchical graded pore structure. The ceramic foam of the ceramic foam-fiber composite may be a composite material (e.g., a composite ceramic foam).

[0014] The ceramic foam composite may be in the form of a sheet. The ceramic foam of the ceramic foam composite may be infiltrated (interpenetrated) into a matrix formed from a plurality of fibers.

[0015] In some aspects, the present disclosure provides uses of the ceramic foam-fiber composite materials of the present disclosure. The ceramic foam-fiber composite materials can be used in a variety of applications. The ceramic foam-fiber composite materials can be or provide superinsulation. In one example, the ceramic foam-fiber composite materials are used as insulating materials (e.g., building materials or acoustic insulation materials). In one example, the ceramic foam-fiber composite materials are used as templates or support substrates for coating with other functional materials, such as composite materials in applications such as catalysis, membranes, separations, etc. [Brief explanation of the drawings]

[0016] For a fuller understanding of the nature and objects of the present disclosure, reference should be made to the following detailed description taken in conjunction with the accompanying figures.

[0017] Figure 1 shows a schematic illustration of the synthesis of fiber-silica aerogel paper via (A) the silica precursor approach and (B) the silica aerogel approach.

[0018] Figure 2 shows (A) EcoTouch (登録商標) PINK (登録商標) Fiberglass TM (B) Optical image of paper taken with Unifrax. Dimensions: 30 x 30 x 0.3 cm. (登録商標) Optical image of paper using C-08. Dimensions: 30 x 30 x 2.7 cm.

[0019] Figure 3 shows the structural characterization of fiber-silica aerogel paper. (a) XRD patterns of silica aerogel, fiber aerogel paper mat with heat treatment (400 °C), and fiber aerogel paper mat without heat treatment (400 °C). (b) Typical TEM image of silica aerogel. The inset shows the diffraction pattern indicating an amorphous structure. (c) Out-of-plane SEM image of fiber-aerogel paper from the precursor approach. (d) Out-of-plane SEM image of fiber-aerogel paper from the aerogel approach. (e) In-plane SEM image of the fiber-aerogel layer stack. (f) Out-of-plane contact angle of the fiber-aerogel paper after coating, (g) In-plane contact angle. The inset shows water absorption before and after coating.

[0020] Figure 4(A) shows the gel and Unifrax (登録商標) SEM image (high resolution, approximately 5 microns) showing intercalation between E-08 and the gel. (B) EcoTouch (登録商標) PINK (登録商標) Fiberglass TM SEM image showing intercalation between

[0021] FIG. 5 shows the relationship between thermal conductivity (tested under ASTM C518 standard) and reaction time of gel (SDS).

[0022] Figure 6 shows the mechanical properties of fiber-aerogel paper. (a) Multiple uniaxial compression in the out-of-plane direction of 41 wt% fiber-aerogel paper with recoverable strain after sintering at 400 °C. (b) 100-cycle fatigue test at 50% compressive strain. (c) Young's modulus (Young's modulus), strength, and relative height during 100 compression cycles. (d) Strength vs. sintering temperature T for 41 wt% fiber-aerogel paper. (e) Compressive strength vs. fiber concentration and density vs. fiber concentration. (f) In-plane compressive stress vs. strain curve of 41 wt% fiber-aerogel paper.

[0023] Figure 7 shows the thermal properties of the fiber-aerogel paper mat. (a) Thermal conductivity and R-value vs. fiber concentration. (b) Thermal conductivity and R-value vs. sintering temperature. (c) In-plane thermal conductivity of a 41 wt% fiber paper mat vs. sintering temperature. (d) Thermal conductivity measured by humidity cycling in 60% and 80% humidity environments.

[0024] Figure 8(a) shows the sound insulation performance of different fiber-aerogel papers with 15 wt%, 41 wt%, and 82 wt% fiber under sound frequencies (audible frequencies) from 500 Hz to 3000 Hz. (b) Sound insulation performance of fiber-aerogel papers under a frequency of 2000 Hz. (c) Sound insulation performance plot of sound intensity at 500 Hz, 800 Hz, 2000 Hz, and 3000 Hz.

[0025] FIG. 9 shows an example of the disclosed R2R process combined with in situ APD to produce low-cost silica aerogel.

[0026] FIG. 10 shows a scanning electron microscope (SEM) image of an example of a silica aerogel of the present disclosure.

[0027] FIG. 11 shows an SEM image of an example of a silica aerogel of the present disclosure.

[0028] FIG. 12 shows an EDX image of an example of a silica aerogel of the present disclosure.

[0029] FIG. 13 shows an EDX image of an example of a silica aerogel of the present disclosure.

[0030] FIG. 14 shows a thermal image of an example of a silica aerogel produced using the method described in Example 1.

[0031] FIG. 15 shows an image of an example of a silica aerogel produced using the method described in Example 2 being heated, demonstrating the flame retardant properties of the silica aerogel.

[0032] FIG. 16 shows an image of an example of a silica aerogel of the present disclosure and an image of a carbon material-coated silica aerogel of the present disclosure.

[0033] Figure 17 shows images of example silica aerogels prepared using the method described in Example 2. (A) is a white silica aerogel prepared using TEOS as the silica precursor. (B) is a transparent silica aerogel prepared using MTMS as the silica precursor. (C) and (D) are images of the white silica aerogel (B) that was heat-treated under different conditions. The heat treatment was performed in a tubular furnace.

[0034] Figure 18 shows thermal conductivity data for an example of a silica aerogel produced using the method described in Example 2 (and TEOS as the silica precursor). The equation used for thermal resistance is q = P / A * d / ΔT, where P / A is recorded by the FluxTap, d is the thickness of the sample, and ΔT is calculated by subtracting the measurements of the two temperature sensors.

[0035] Figure 19 shows an SEM image of an example of a white silica aerogel produced using the method described in Example 2 (and TEOS as the silica precursor). The image shows a porous structure on the surface of the white silica aerogel.

[0036] Figure 20 shows an SEM image of an example of a white silica aerogel produced using the method described in Example 2 (and TEOS as the silica precursor). The image shows the porous structure on the side of the white silica aerogel.

[0037] Figure 21 shows an SEM image of an example of a white silica aerogel produced using the method described in Example 2 (and TEOS as the silica precursor). The image shows a porous structure on the surface of the white silica aerogel.

[0038] Figure 22 shows an SEM image of an example of a white silica aerogel produced using the method described in Example 2 (and TEOS as the silica precursor). The image shows the porous structure on the surface of the white silica aerogel. The pore structure includes small and large pores.

[0039] FIG. 23 shows an SEM image of an example of a white silica aerogel produced using the method described in Example 2 (and TEOS as the silica precursor).

[0040] Figure 24 shows an SEM image of an example of a transparent silica aerogel produced using the method described in Example 2 (and MTMS as the silica precursor). The image shows a porous structure on the surface of the white silica aerogel.

[0041] Figure 25 shows an SEM image of an example of a white silica aerogel produced using the method described in Example 2 (and TEOS as the silica precursor) and heated at 400°C for 3 hours. The image shows a porous structure on the surface of the white silica aerogel.

[0042] FIG. 26 shows images illustrating mechanical testing of silica aerogel samples of the present disclosure.

[0043] Figure 27 shows mechanical testing data for an example of a white silica aerogel produced using the method described in Example 2 (and TEOS as the silica precursor). This material has a Young's modulus of 7.6054 MPa.

[0044] Figure 28 shows porosity data obtained using a pycnometer for an example of a white silica aerogel produced using the method described in Example 2 (and TEOS as the silica precursor). This material has a porosity of 89.587%.

[0045] Figure 29 shows porosity data obtained using a pycnometer for an example of a transparent silica aerogel produced using the method described in Example 2 (and MTMS as the silica precursor). This material has a porosity of 83.925%.

[0046] FIG. 30 shows an example image of a white silica aerogel produced using the method described in Example 2 (and TEOS as the silica precursor) heated to 2000° C., demonstrating the flame retardant properties of the silica aerogel.

[0047] [Figure 31] (a) Schematic diagram of the three-step synthesis process of silica PGAero. Step 1: CTAB-assisted micelle formation in aqueous urea solution. Step 2: Hydrolysis of TEOS at the interface of CTAB micelles. Step 3: Decomposition of urea with the release of NH3 and CO2. (b) Optical image of a typical silica foam with a diameter of 6 cm. (c) 0.6 cm thick polished silica PGAero sample. (d) Typical SEM image of silica PGAero showing a sharp pore gradient. The inset shows the increasing average pore size from bottom to top. (e)(f) High-resolution SEM images showing large pores (e) and small pores (f), corresponding to the top and bottom areas of Figure 31d, respectively. (g)(h) g) Low-resolution and h) high-resolution TEM images of particles in the silica network of PGAero.

[0048] [Figure 32] SEM images of silica PGAero at (a) 48 h and (b) 72 h reaction times. The inset shows the corresponding size distribution of the pores. (c) Thermal conductivity of silica PGAero synthesized by different reaction times.

[0049] [Figure 33] (a)–(f) SEM images of silica PGAero synthesized by varying the amount of precursor (referred to as PGAero-1, 5, 6, 7, 8, and 9, respectively). (g) The thermal conductivity of a series of PGAero depends on the average pore size and porosity.

[0050] [Figure 34] (a) Mechanical properties of silica PGAero before and after annealing at 400 °C. The inset shows SEM images before (top) and after (bottom) annealing. (b) Schematic diagram showing the heat and sound reduction due to the gradient structure of silica PGAero. (c) The sound-proofing performance of silica PGAero is compared with polyurethane, Kevlar, and two ceramic fiber blankets from Unifrax (ceramic fiber 1: PC-Max 2000i, ceramic fiber 2: Saffil Alumina) under sound frequencies from 500 Hz to 1800 Hz. (d) Sound insulation performance of silica PGAero and standard polystyrene foam under a frequency of 2000 Hz. (e) Sound insulation performance plot of sound intensity and sound insulation coefficient at frequencies of 500 Hz, 800 Hz, and 2000 Hz.

[0051] FIG. 35 shows (a) large scale and (b) enlarged SEM images of the PGAero-2 sample.

[0052] FIG. 36 shows the change in porosity with reaction time.

[0053] FIG. 37 shows the details of the preparation of samples PGAero-1 and PGAero-5 to 10.

[0054] [Figure 38] (a) to (g) show the average pore size distributions of samples PGAero-1, PGAero-5 to PGAero-10.

[0055] [Figure 39] (a)(b) shows photographs of the mechanical test.

[0056] [Figure 40] (a) Stress-strain curve of the initial specimen PGAero-1 under 6 lbs. (b) Stress-strain curve of the initial specimen compressed to failure. (c) Stress-strain curve of the specimen annealed at 400°C under 20 lbf.

[0057] FIG. 41 shows a photograph of the sample annealed at 1000° C. for 24 hours.

[0058] FIG. 42 shows the difference in acoustic intensity between the blank, expanded polystyrene, and silica PGAero at frequencies from 20 Hz to 5000 Hz.

[0059] Figure 43 shows the difference in acoustic intensity at 500 Hz (a) and 800 Hz (b).

[0060] FIG. 44 shows humidity aging cycle measurements of silica foam under 60% and 80% humidity.

[0061] FIG. 45 is a schematic diagram showing the change in opaque and transparent phases as surfactant concentration increases. (a) For the surfactant CTAB, the opaque phase becomes more prevalent with increasing CTAB concentration because the hydrophilic particles dominate in the precursor. (b) For the surfactant SDS, the clear phase becomes more prevalent as the concentration of SDS increases, since hydrophobic particles dominate in the precursor. (c) As the concentration of SDS increases, the micelle formation of SDS changes. The micelle formation becomes more organized, and each micelle particle becomes smaller as the concentration of SDS increases.

[0062] [Figure 46] (a) Optical image of the gel portion. (b)(c) SEM and TEM show the microstructure of the gel part. (d) The density and porosity of the gel changed depending on the concentration of SDS. (e) BET results of the gel portion. (f) Relationship between thermal conductivity and average pore size and density.

[0063] [Figure 47] (a)(b)(c) SEM images show the structure of the white area changing from open to closed pores. (d) Optical image of the white area. (e) Density and porosity change with SDS concentration. (f) Relationship between thermal conductivity, density, and average pore size.

[0064] [Figure 48] (a) The strain-stress curve shows high mechanical strength, which decreased with increasing SDS concentration. (b) Young's modulus decreased with increasing density due to increasing SDS concentration. (c) Optical images of the 3.33% SDS sample before and after the mechanical compression test.

[0065] [Figure 49] (a) Sound insulation performance of different concentrations of SDS under high sound frequencies from 3000 Hz to 8500 Hz. (b) Sound insulation performance of different concentrations of SDS under a sound frequency of 500 Hz. (c) Sound insulation performance of different concentrations of SDS under 800 Hz sound frequency.

[0066] Figure 50 shows the preparation and structure of the HT-Aero composite material. (a) Fabrication scheme of hot-pressed aerogel-fiber composite paper. The inset shows a highly flexible composite paper sheet. The scale bar indicates 5 cm. (b) TEM image of ceramic fibers bonded with a silica aerogel network (scale bar indicates 100 nm). The inset is a zoomed TEM image of the silica aerogel layer bonded onto the fiber surface (scale bar indicates 10 nm). (c) FTIR spectra of different samples. (d) Water absorption. The inset shows the superhydrophobic performance of the in situ coating on the paper sheet (water contact angle 145°). (e) Comparison of thermal conductivity and density of this study and other reported insulation materials.

[0067] FIG. 51 shows the room temperature and high temperature thermal performance of the hot-compressed HT-Aero composites. (a) Thermal conductivity of composites vs. hot pressing temperature and thermal conductivity vs. fiber concentration. (b) Thermal conductivity vs. density of composites with different aerogel concentrations after hot compression at a temperature of 150 °C. (c) Flame retardancy of the thermocompressed composite. The scale bar indicates 2 cm. (d) Candle soot scheme. (e) Thermocompressed composite sheet with candle soot and its superhydrophobic performance (water contact angle 152°) demonstrated. The scale bar indicates 2 cm. (f) SEM image of the porous carbon coating on the composite paper sheet. The inset shows the enlarged microstructure of the porous carbon. (g) Top surface temperature vs. bottom heating temperature of a thermo-compressed composite paper sheet with and without carbon soot. The inset is a FLIR image of the composite paper sheet with candle soot, demonstrating the high temperature resistance provided by the porous carbon coating. (h) Thermal conductivity vs. temperature for high temperature insulation of composite paper sheets.

[0068] Figure 52 shows the sound insulation properties of the hot-compressed HT-Aero composite. (a) (Top) Cross-sectional SEM image of the composite without thermal compression, and (bottom) cross-sectional SEM image of the composite with thermal compression, in which the fiber-aerogel is tightly packed. (b) Acoustic strength of blank, 30, 45, and 72 wt% thermo-compressed composite paper sheets under frequencies ranging from 500 to 3000 Hz. (c) Acoustic strength of blank, 30, 45, and 72 wt% thermo-compressed composite paper sheets under a frequency of 3000 Hz. (d) Acoustic intensity vs. frequency of various sheets and their sound insulation coefficients.

[0069] Figure 53 shows the mechanical performance of hot-compressed HT-Aero composites. (a) Demonstration of the uniaxial tensile process of a composite sheet (scale bar 2 cm). Fracture occurs at the middle of the sample. Stress vs. strain curves of hot-compressed composites with different densities at (b) 30 wt%, (c) 45 wt%, and (d) 72 wt% ceramic fibers. (e) Illustration of the mechanical mechanism of aerogel fiber composites under tensile stress. (f) Maximum strength vs. density of samples with different concentrations of fibers.

[0070] [Figure 54] (a) BET analysis of silica aerogel, where the N adsorption-desorption isotherm shows an H1-type hysteresis loop, suggesting the mesoporous nature of the silica aerogel. The insert is a TEM image of the silica aerogel network. (b) SEM image of the thermal compression-induced in-plane fiber-aerogel composite, where the silica aerogel is bonded to the fiber.

[0071] [Figure 55] (a) Thermal conductivity vs. density of 20, 30, and 57 wt% HT-Aero composites. For different fiber concentrations, there is an optimal thermal insulation performance with tunable density. (b) Thermal conductivity of the HT-Aero composite with and without the candle soot coating. The porous carbon coating further improves the thermal insulation performance. Temperature measurement setup and IR images of (c) the HT-Aero composite without coating and (d) the HT-Aero composite with candle soot coating (under different heating temperatures). From the IR images, it can be seen that the temperature of the hotplate increases from 95°C to 174°C, and the temperature distribution on the top surface is very uniform in the center, with much lower values. The data are summarized in Figure 51.

[0072] [Figure 56] (a) Flame retardancy of HT-Aero with alcohol flame. (b) Flame retardancy of HT-Aero with hydrogen flame, and (c) Corresponding SEM image showing the undamaged microstructure.

[0073] [Figure 57] (a) SEM image of candle soot carbon network. (b) Magnified SEM image of the porous carbon network formed by candle soot.

[0074] Figure 58 shows the sound insulation data of 30, 45, and 72 wt% HT-Aero composites and blank reference under sound frequencies of (a) 500 Hz and (b) 2000 Hz.

[0075] [Figure 59] (a) Stress vs. strain curves of HT-Aero with 45 wt% fiber compressed at different temperatures. As the temperature increases, the maximum stress of HT-Aero increases due to the enhanced interfacial bonding between the fiber and aerogel. (b) Comparison of tensile stress curves of HT-Aero with 20 and 45 wt% fiber. (c) Tensile stress vs. strain curves of HT-Aero with 35 wt% fiber having different densities. (e) Yield strength vs. density of HT-Aero with different fiber concentrations. The power scaling relationship ranges from 1 to 2.6. DETAILED DESCRIPTION OF THE INVENTION

[0076] Although the claimed subject matter is described with reference to particular embodiments and examples, other embodiments and examples, including embodiments and examples that do not provide all of the advantages and features described herein, are also within the scope of this disclosure. Various structural, logical, and process step changes can be made without departing from the scope of this disclosure.

[0077] Ranges of values are disclosed herein. The ranges have lower and upper limits. Unless otherwise specified, the ranges include all values up to the minimum value (either the lower or upper limit) and ranges that lie between the values in the stated range.

[0078] As used herein, unless otherwise specified, the term "group" refers to a chemical entity having one end or two or more ends that can be covalently bonded to another chemical species. The term "group" includes radicals. Examples of groups include, but are not limited to, the following: [ka] As used herein, unless otherwise specified, the term "alkyl" refers to a branched or unbranched saturated hydrocarbon group. Examples of alkyl groups include, but are not limited to, methyl, ethyl, propyl, butyl, isopropyl, tert-butyl, and the like. For example, an alkyl group is a C1-C6 alkyl group (e.g., a C1, C2, C3, C4, C5, or C6 alkyl group). An alkyl group can be unsubstituted or substituted with one or more substituents. Examples of substituents include, but are not limited to, halogens (-F, -Cl, -Br, and -I), aliphatic groups (e.g., alkyl, alkenyl, and alkynyl groups), aryl groups, alkoxide groups, carboxylate groups, carboxylic acids, ether groups, and the like, and any combination thereof.

[0079] As used herein, unless otherwise specified, the term "alkoxy" refers to an -OR group, where R is an alkyl group, as defined herein. Examples of alkoxy groups include, but are not limited to, methoxy, ethoxy, n-propoxy, i-propoxy, n-butoxy, i-butoxy, s-butoxy, and the like. In one embodiment, an alkoxy group comprises a C1-C6 alkyl group (e.g., a C1, C2, C3, C4, C5, or C6 alkyl group).

[0080] The present disclosure provides ceramic foam-fiber composite materials. The present disclosure also provides methods for making ceramic foam-fiber composite materials and uses of ceramic foam-fiber composite materials.

[0081] The present disclosure provides, in various examples, the use of sol-gel chemistry (e.g., silica aerogel chemistry) combined with ambient pressure drying (which may be in situ ambient pressure drying). The present methods can replace current supercritical extraction processes, i.e., complex processes using low surface tension organic solvents and high-pressure supercritical drying, by using ambient pressure, e.g., drying with in situ generated pore-supporting gas bubbles (e.g., carbon dioxide, ammonia, etc.). The processes described herein can significantly reduce one or more of the energy input, time, and cost for producing ceramic foams (e.g., silica aerogels) with, for example, controlled porosity and / or pore sizes less than 60 nm.

[0082] In one aspect, the present disclosure provides a method for producing a ceramic foam-fiber composite. The composite has a ceramic foam disposed within at least some of the individual fibers of the composite. The ceramic foam may be referred to as a ceramic aerogel or a ceramic aerogel-like foam (e.g., a silica aerogel-like foam). The ceramic foam may be a silica aerogel. The method is based on the in situ generation of a pore-forming gas and the reaction of precursors, which may be carried out in a sealed environment (e.g., a reaction at a pressure greater than ambient pressure) or in the presence of fibers. The ceramic foam or ceramic foam-fiber composite may be formed under hydrothermal conditions. In one example, the method does not include the use of any supercritical gas species. Non-limiting examples of the method are provided herein.

[0083] In various embodiments, a method for forming a ceramic foam-fiber composite (e.g., a silica aerogel-fiber composite) includes contacting (e.g., in a reaction mixture, which may be in a closed environment, or a closed environment, which may be a sealed container) one or more types of fibers; one or more ceramic precursors; one or more pore-forming gas-forming additives (one or more inert gas generants); one or more catalysts; and, optionally, one or more additives, wherein the contacting results in the formation of an inert gas (e.g., carbon dioxide) and a plurality of fibers, each fiber having a ceramic foam layer disposed on at least a portion of the fiber. The ceramic foam may be formed under hydrothermal conditions. The reactants (e.g., fibers, ceramic precursor(s), pore-forming gas-forming additive(s), catalyst(s); and optional additive(s)) may be added / contacted in any order. The reactants may be contacted in a single container. The ceramic foam-fiber composite may be subjected to ambient pressure drying (APD).

[0084] The reaction can be carried out in a sealed environment. The reaction can be carried out in a sealed container or mold. As an illustrative, non-limiting example, the reaction is carried out in an autoclave. The pressure in the container can be autogenous (e.g., resulting from the closed nature of the container and the state of the reactants), or the pressure can be increased externally, for example, by pressurizing the sealed container to a desired pressure (e.g., 1 to 100 psi, including all 0.1 psi values and ranges therebetween). The container can be pressurized by the addition of exogenous gas(es) (e.g., inert gases, such as argon, nitrogen, etc., and any combination thereof).

[0085] In one example, a method for forming a ceramic foam-fiber composite (e.g., a silica aerogel-fiber composite) includes contacting (e.g., in a reaction mixture) a plurality of fibers; a ceramic precursor(s) (e.g., silica precursor) selected from TEOS, MTMS, water glass / sodium silicate, and any combination thereof (e.g., 57 mL of TEOS or MTMS, or a 1:3 to 3:1 mixture of TEOS:MTMS); urea (e.g., 33.33 g) as a pore-forming gas-forming additive (inert gas generant); acetic acid (which may be in the form of an aqueous solution (e.g., 100 mL of a 1 mmol / L solution)) as a catalyst; and CTAB or SDS (e.g., 3.33 g) as a surfactant additive, wherein the contacting results in the formation of an inert gas (e.g., carbon dioxide, ammonia, etc.), and the ceramic foam-fiber composite (e.g., a silica aerogel-fiber composite) is formed. In various examples, one or more or all of the values in this example are varied by up to and including 5%, or by up to and including 10%. In various examples, one or more additional additives are contacted (e.g., included in the reaction mixture).

[0086] Various ceramic precursors can be used. The precursor may be a sol-gel precursor. Suitable sol-gel precursors are known in the art. Non-limiting examples of precursors include silica precursors, alumina precursors, transition metal oxide precursors, and any combination thereof. In various examples, the silica precursor(s) are selected from tetraalkoxysilanes (e.g., TMOS, TEOS, etc.) (e.g., C1-C5 alkoxytetraalkoxysilanes), alkyltrialkoxysilanes (e.g., methyltrimethoxysilane (MTMS)) (e.g., C1-C5 alkyl, C1-C5 alkoxyalkyltrialkoxysilanes), sodium metasilicate (e.g., water glass), and any combination thereof. In various examples, the alumina precursor(s) are selected from aluminum alkoxides (e.g., C1-C6 aluminum alkoxides), alumatorane, tris(alumatranyloxy-i-propyl)amine, etc., and any combination thereof. In various examples, the transition metal oxide precursor(s) are selected from transition metal alkoxides and the like (e.g., transition metal alkoxides having the formula M(OR)x, where M is a transition metal (e.g., Al, Ti (e.g., titanium(IV)-iso-propoxide, etc.), Zr, W, Cr, Mo, etc.), R is an alkyl group, and x is, for example, 1, 2, 3, 4, or 5). The transition metal can be present in various oxidation states (e.g., + 1. + 2. + 3. + 4, or + 5).

[0087] In one example, water glass is used as a silica precursor (alone or in combination with one or more additional silica precursors). Water glass is also called sodium silicate or soluble glass. In one example, water glass is a substance containing sodium oxide (NaO) and silica (e.g., silicon dioxide, SiO, etc.) that forms a glassy solid.

[0088] Combinations of ceramic precursors may also be used. For example, binary, ternary, and higher order mixed oxide ceramic foams can be produced using mixtures of precursors. As an illustrative example, mixed oxide ceramic foams, such as those having a compositional formula corresponding to a desired ratio of AlO to TiO, can be produced using a combination of one or more AlO sol-gel precursors (e.g., aluminum alkoxides (e.g., C1-C6 aluminum alkoxides), alumatran, tris(alumatranyloxy-i-propyl)amine, etc., or any combination thereof) with a TiO sol-gel precursor (e.g., titanium(IV)-iso-propoxide, etc.). One skilled in the art will understand that ceramic foams having a desired compositional formula can be formed by selection of the appropriate ceramic precursor(s) and / or relative amounts of precursors.

[0089] After formation of the ceramic foam-fiber composite, the composite can be sintered. For example, the ceramic foam can be sintered at a temperature of 200-800°C (e.g., 350-450°C or about 400°C; including all 0.1°C values and ranges therebetween). The ceramic foam can be sintered in air and / or at ambient pressure (e.g., 1 atm). While not intending to be bound by any particular theory, it is believed that sintering can improve the properties of the ceramic foam. This improvement may result from carbonization of residual organic residues, if present.

[0090] The ceramic foam (e.g., silica aerogel) network (e.g., Si, Al, transition metal(s), or combinations thereof-oxygen network) of the ceramic foam-composite material may be formed in the presence of a pore-forming gas. The pore-forming gas may be generated in the presence of the ceramic foam (e.g., silica) precursor and, optionally, the fiber (e.g., the pore-forming gas is generated during silica network formation). In one example, substantially all network formation is completed in the presence of the pore-forming gas. Substantially all network formation means that no additional processing is required to form the ceramic foam (e.g., silica aerogel) network. In various examples, 50% or more, 60% or more, 70% or more, or 80% or more of the ceramic foam precursor(s) (e.g., silica precursor(s)) react in the presence of the pore-forming gas.

[0091] In various examples, the method further includes post-ceramic foam modification of at least a portion of the ceramic foam surface of the ceramic foam composite. One example of a post-ceramic foam modification is the formation of a layer of a carbon-containing material on at least a portion of the surface (e.g., all of the surface, or all of the ceramic foam surface). The carbon-containing material may provide a superhydrophobic (ultra-water-repellent) outer surface. For example, a carbon soot coating may be formed by burning a candle under the ceramic foam sample to allow the soot coating to form, or by post-thermal annealing.

[0092] Advanced surface modifications (including trimethylchlorosilane treatment and carbon coating) can be used to engineer capillary action and superhydrophobicity. Surface modification may involve replacing at least a portion of the hydroxyl groups on the silica gel surface with methyl groups, resulting in the formation of (CH3)3-Si-Si-O-, followed by a continuous carbon coating. These modification processes are expected to control pore size and surface chemistry to achieve desired thermal insulation performance and durability.

[0093] For example, trimethylchlorosilane ((CH3)3SiCl) can be combined with a continuous carbon coating to achieve the goals of methyl group formation and surface modification with a nanocrystalline carbon coating, reducing both capillary and radiative transport modes of heat transfer at higher temperatures. Surface-modified silica will result in smaller pore sizes, stronger mechanical integrity, higher moisture and fire resistance, and lower thermal conductivity.

[0094] Another example of post-formation modification of the ceramic foam includes decorating or coating at least a portion of the surface or all of the surface of the ceramic foam with nanoparticles.

[0095] In various examples, the method further includes using a silica aerogel that has been modified after aerogel formation. One example of a silica aerogel that has been modified after aerogel formation is a silica aerogel that includes a layer of a carbon-containing material on at least a portion of its surface (e.g., all of its surface, or all of the surface of the aerogel). The carbon-containing material can provide a superhydrophobic exterior surface. For example, a carbon soot coating can be formed by burning a candle under the silica aerogel sample to allow the soot coating to occur, or by post-thermal annealing.

[0096] The ceramic foam precursor can be formed from / using ceramic foam particles. The ceramic foam particles can be preformed. In various examples, the ceramic foam composite is formed by contacting a ceramic foam powder (e.g., a powder having an average particle size of 50 nm and an average pore size of 5 nm) with a plurality of fibers (e.g., creating a powder-fiber mixture slurry or pulp in water). This results in the formation of a plurality of fibers, each fiber having a ceramic foam layer disposed on at least a portion of the fiber.

[0097] The ceramic foam powder may be formed from a preformed ceramic foam. The ceramic foam may be used in its as-synthesized state. The preformed ceramic foam may be mechanically processed (e.g., using a grinding process) to form the ceramic foam powder.

[0098] Ceramic foams can also be referred to as ceramic aerogels. Ceramic foams can be silica aerogels. Non-limiting examples of ceramic foams are provided herein. Ceramic foam materials (e.g., ceramic foam composites) include ceramic foams. Ceramic foams include a matrix of ceramic material. Ceramic foams can be produced by the methods described herein.

[0099] The ceramic foam may be an oxide. Non-limiting examples of oxides include silicon oxides (e.g., silica), aluminum oxides (e.g., alumina), transition metal oxides, and the like, and any combination thereof. The ceramic foam may be stoichiometric or non-stoichiometric.

[0100] The ceramic foam may be a mixture of oxides. The ceramic foam may be based on binary oxides, ternary oxides, or higher oxides. Non-limiting illustrative examples of ceramic foams include aluminosilicate foams, aluminotitanate foams, and the like.

[0101] In one example, the ceramic foam and / or ceramic foam material does not have fluorine atoms (e.g., fluorine atoms detectable by conventional methods known in the art), which may be fluorine atoms bonded to silicon atoms (e.g., -Si-F).

[0102] The ceramic foam can have a variety of forms, for example, the ceramic foam can be a monolith, a film, or a powder.

[0103] Ceramic foams are porous and exhibit a hierarchical gradient pore structure. Ceramic foams can be described as including a hierarchical hollow structure with an interior of micropores (also called macropores) (e.g., voids in a ceramic matrix) and mesopores within a shell (e.g., matrix). At least some or all of the pores may be interconnected. The pores may be mesopores and / or macropores. The pores may be mesopores as defined by IUPAC.

[0104] The pores (which may be micropores or macropores, but not mesopores of the ceramic matrix) of the ceramic foam can have a variety of sizes. For example, the size (e.g., average size, and / or 90%, 95%, 99%, 99.9%, or 100%) of the pores may be between 500 microns and 1 micron (including all 0.1 micron values and ranges therebetween). The size may be at least one dimension (e.g., diameter) as measured in a plane parallel to the axis of the pore. For example, the pores may have a size (e.g., at least one dimension (e.g., diameter) measured in a plane parallel to the axis of the pore and / or at least one dimension (e.g., height) measured in a plane perpendicular to the axis of the pore) between 500 microns and 1 micron (e.g., 200 microns and 10 microns, 200 microns and 1 micron, or 100 microns and 1 micron). The size of the pores generally decreases or increases along a direction moving from a first surface of the ceramic foam to a second surface opposite the first surface. The gradient may be a linear gradient or a non-linear gradient.

[0105] The ceramic matrix of the ceramic foam may be mesoporous (e.g., including mesopores, which may be mesopores as defined by IUPAC). For example, the ceramic matrix may include a plurality of pores having a diameter of 2 nm to 100 nm (e.g., 2 nm to 60 nm, 10 nm to 60 nm, or 10 nm to 100 nm) (including 0.1 nm values and ranges therebetween). For example, the ceramic matrix may include a plurality of pores having an average diameter of 2.5 nm to 30 nm (e.g., 2.5 nm to 10 nm or 15 nm to 30 nm) (including 0.1 nm values and ranges therebetween). The pore size distribution may be bimodal. For example, the ceramic matrix has a plurality of pores with an average diameter of 2 nm to 100 nm (e.g., 2 nm to 60 nm, 10 nm to 60 nm, or 10 nm to 100 nm) (which may be multimodal, e.g., bimodal) and a plurality of pores with an average diameter of 2.5 nm to 30 nm (e.g., 2.5 nm to 10 nm, or 15 nm to 30 nm).

[0106] The pore size and / or pore size distribution of the ceramic foam and / or ceramic matrix can be determined using methods known in the art, for example, the pore size and / or pore size distribution can be determined using BET analysis.

[0107] The ceramic foam can have desirable properties, such as a Young's modulus of 2 to 100 MPa (e.g., 2 to 8 MPa), including all integer MPa values and ranges therebetween.

[0108] The ceramic foam may be a porous silica aerogel. For example, the silica aerogel has a plurality of pores with diameters of 2 nm to 100 nm (e.g., 2 nm to 60 nm, 10 nm to 60 nm, or 10 nm to 100 nm) (including values and ranges of 0.1 nm therebetween). For example, the silica aerogel has a plurality of pores with an average diameter of 2.5 nm to 30 nm (e.g., 2.5 nm to 10 nm or 15 nm to 30 nm) (including values and ranges of 0.1 nm therebetween). The pore size distribution may be bimodal. For example, the silica aerogel has a plurality of pores with an average diameter of 2 nm to 100 nm (e.g., 2 nm to 60 nm, 10 nm to 60 nm, or 10 nm to 100 nm) (which may be multimodal, e.g., bimodal) and a plurality of pores with an average diameter of 2.5 nm to 30 nm (e.g., 2.5 nm to 10 nm or 15 nm to 30 nm). The pore size and / or pore size distribution can be determined using methods known in the art, for example, the pore size and / or pore size distribution can be determined using BET analysis.

[0109] The ceramic foam material may be a composite material (e.g., a composite ceramic foam). The composite material may contain a polymer material in some or all of the pores of the ceramic foam (which may be referred to as a hybrid composite or hybrid ceramic foam). The polymer may be formed by in situ polymerization within the ceramic foam. Additionally or alternatively, the composite material may contain a carbon coating on the ceramic foam (also referred to as a ceramic-carbon aerogel). For example, a ceramic foam (e.g., a ceramic foam monolith or ceramic foam film) may be at least partially (or completely) coated with a carbon material.

[0110] In various examples, a method for forming a ceramic foam includes contacting (e.g., in a reaction mixture, which may be in a closed environment or a sealed container) one or more ceramic precursors; one or more pore-forming gas-forming additives (one or more inert gas-generating agents); one or more catalysts; and, optionally, one or more additives, wherein the contacting results in the formation of an inert gas (e.g., carbon dioxide) and the formation of a ceramic foam (e.g., silica aerogel). The ceramic foam may be formed under hydrothermal conditions. The reactants (e.g., ceramic precursor(s), pore-forming gas-forming additive(s), catalyst(s); and optional additive(s)) can be added / contacted in any order. The reactants may be contacted in a single container.

[0111] The reaction can be carried out in a sealed environment. The reaction can be carried out in a sealed container or mold. As an illustrative, non-limiting example, the reaction is carried out in an autoclave. The pressure in the container can be autogenous (e.g., resulting from the closed nature of the container and the state of the reactants), or the pressure can be increased externally, for example, by pressurizing the sealed container to a desired pressure (e.g., 1 to 100 psi, including all 0.1 psi values and ranges therebetween). The container can be pressurized by the addition of an exogenous gas (e.g., an inert gas, such as argon, nitrogen, etc., and any combination thereof).

[0112] In one example, a method for forming a ceramic foam (e.g., a silica aerogel-like foam) includes contacting (e.g., in a reaction mixture) in a sealed vessel silica precursor(s) consisting of TEOS, MTMS, water glass, or any combination thereof (e.g., 57 mL of TEOS or MTMS, or a 1:3 to 3:1 mixture of TEOS:MTMS); urea (e.g., 33.33 g) as a pore-forming gas-forming additive (inert gas generant); acetic acid (which may be in the form of an aqueous solution (e.g., 100 mL of a 1 mmol / L solution)) as a catalyst; and CTAB (e.g., 3.33 g) as an additive, wherein the contacting results in the formation of an inert gas (e.g., carbon dioxide, ammonia, etc.) and the formation of a silica aerogel-like foam. In various examples, one or more or all of the values in this example are varied by up to and including 5% or by up to and including 10%. In various examples, one or more additional additives are contacted (e.g., included in the reaction mixture).

[0113] Various ceramic precursors can be used. The precursor may be a sol-gel precursor. Suitable sol-gel precursors are known in the art. Non-limiting examples of precursors include silica precursors, alumina precursors, transition metal oxide precursors, and any combination thereof. In various examples, the silica precursor(s) are selected from tetraalkoxysilanes (e.g., TMOS, TEOS, etc.) (e.g., C1-C5 alkoxytetraalkoxysilanes), alkyltrialkoxysilanes (e.g., methyltrimethoxysilane (MTMS)) (e.g., C1-C5 alkyl, C1-C5 alkoxyalkyltrialkoxysilanes), sodium metasilicate (e.g., water glass), and any combination thereof. In various examples, the alumina precursor(s) are selected from aluminum alkoxides (e.g., C1-C6 aluminum alkoxides), alumatorane, tris(alumatranyloxy-i-propyl)amine, etc., and any combination thereof. In various examples, the transition metal oxide precursor(s) are selected from transition metal alkoxides and the like (e.g., transition metal alkoxides having the formula M(OR)x, where M is a transition metal (e.g., Al, Ti (e.g., titanium(IV)-iso-propoxide, etc.), Zr, W, Cr, Mo, etc.), R is an alkyl group, and x is, for example, 1, 2, 3, 4, or 5). The transition metal can be present in various oxidation states (e.g., + 1. + 2. + 3. + 4, or + 5).

[0114] In one example, water glass is used as a silica precursor (alone or in combination with one or more additional silica precursors). Water glass is also called sodium silicate or soluble glass. In one example, water glass is a substance containing sodium oxide (NaO) and silica (e.g., silicon dioxide, SiO, etc.) that forms a glassy solid.

[0115] Combinations of ceramic precursors may also be used. For example, binary, ternary, and higher order mixed oxide ceramic foams can be produced using mixtures of precursors. As an illustrative example, mixed oxide ceramic foams, such as those having a compositional formula corresponding to a desired ratio of AlO to TiO, can be produced using a combination of one or more AlO sol-gel precursors (e.g., aluminum alkoxides (e.g., C1-C6 aluminum alkoxides), alumatran, or tris(alumatranyloxy-i-propyl)amine, and any combination thereof) with a TiO sol-gel precursor (e.g., titanium(IV)-iso-propoxide, and the like). One skilled in the art will understand that ceramic foams having a desired compositional formula can be formed by selection of the appropriate ceramic precursor(s) and / or relative amounts of precursors.

[0116] After formation of the ceramic foam, the ceramic foam can be sintered. For example, the ceramic foam can be sintered at a temperature of 200-800°C (e.g., 350-450°C or about 400°C; including all 0.1°C values and ranges therebetween). The ceramic foam can be sintered in air and / or at ambient pressure (e.g., 1 atm). While not intending to be bound by any particular theory, it is believed that sintering can improve the properties of the ceramic foam. This improvement may result from carbonization of residual organic residues, if present.

[0117] In various examples, the method further includes post-formation modification of at least a portion of the surface of the ceramic foam. One example of post-formation modification of the ceramic foam is the formation of a layer of a carbon-containing material on at least a portion of the surface (e.g., all of the surface, or all of the surface of the ceramic foam). The carbon-containing material may provide a superhydrophobic outer surface. For example, a carbon soot coating may be formed by burning a candle under the ceramic foam sample to allow the soot coating to form, or by post-thermal annealing.

[0118] Advanced surface modifications (including trimethylchlorosilane treatment and carbon coating) can be used to engineer capillary action and superhydrophobicity. This involves replacing surface hydroxyl groups with methyl groups on the silica gel surface through the formation of (CH3)3-Si-Si-O-, followed by subsequent carbon coating. These modification processes control pore size and surface chemistry to achieve the desired thermal insulation performance and durability.

[0119] For example, trimethylchlorosilane ((CH3)3SiCl) can be combined with a continuous carbon coating to achieve the goals of methyl group formation and surface modification with a nanocrystalline carbon coating, reducing both capillary and radiative transport modes of heat transfer at higher temperatures. Surface-modified silica will result in smaller pore sizes, stronger mechanical integrity, greater water and fire resistance, and lower thermal conductivity.

[0120] Another example of post-formation modification of the ceramic foam includes decorating or coating at least a portion of the surface or all of the surface of the ceramic foam with nanoparticles.

[0121] Forming the ceramic foam can include a thermal annealing step. The thermal annealing step can be performed after the ceramic foam is formed, washed, dried, etc. For example, the thermal annealing can be the final step in manufacturing the ceramic foam. In various examples, the thermal annealing can be performed at temperatures between 300°C and 600°C (including all integer degrees Celsius values and ranges therebetween) for various times (e.g., 1 hour to 6 hours (including all integer minutes values and ranges therebetween)).

[0122] The ceramic network (e.g., silica network, alumina network, aluminosilicate network, transition metal oxide network, or any combination thereof), which may also be referred to as a ceramic matrix, may include ceramic nanoparticles (e.g., silica nanoparticles) of a ceramic aerogel that may be formed in the presence of a pore-forming gas. The ceramic nanoparticles may have a size (which may be a maximum dimension or a minimum dimension) of, for example, 20 to 200 nm (e.g., 150 to 200 or about 200 nm) (including all integer nm values and ranges therebetween), or an average size (which may be an average maximum dimension or an average minimum dimension) of 20 to 200 nm (e.g., 150 to 200 or about 200 nm) (including all integer nm values and ranges therebetween). The ceramic nanoparticles may have a narrow size distribution, with 90% or more, 95% or more, 99% or more, or all of the ceramic nanoparticles having a size and / or average size of 20 to 200 nm (e.g., 150 to 200 or about 200 nm) (including all integer nm values and ranges therebetween). The pore-forming gas may be generated in the presence of the ceramic precursor (e.g., the pore-forming gas is generated during silica network formation). In one example, substantially all of the ceramic matrix formation is completed in the presence of the pore-forming gas. Substantially all of the ceramic matrix formation means that no additional processing is required to form the ceramic matrix of the ceramic foam. In various embodiments, 50% or more, 60% or more, 70% or more, or 80% or more of the silica precursor reacts in the presence of the pore-forming gas.

[0123] In one example, the ceramic foam is formed using TEOS and is white. In another example, the ceramic foam is formed using MTMS and exhibits desirable transparency. For example, a ceramic foam formed using MTMS exhibits a transmittance of 85% or more, 90% or more, 95% or more, or 98% or more of visible light wavelengths (e.g., light wavelengths of 400-800 nm, such as 530 nm) (e.g., when measured with a sample thickness of 2-3 mm (e.g., 2.7 mm)). In yet another example, a ceramic foam formed using TEOS and MTMS has one or more white regions and one or more transparent regions (e.g., exhibiting a transmittance of 90% or more, 95% or more, or 98% or more of visible light wavelengths (e.g., light wavelengths of 400-800 nm)).

[0124] In one example, the ceramic foam or ceramic foam material does not include any exogenous materials (e.g., any detectable exogenous materials that may be detected by conventional methods known in the art). Exogenous materials include, but are not limited to, materials used in forming building materials from silica materials (e.g., ceramic foam materials). Non-limiting examples of exogenous materials include binders (e.g., polymeric binders), polymers, etc.

[0125] Various fibers can be used to form ceramic-foam composites. Without intending to be bound by any particular theory, it is believed that the fibers provide mechanical flexibility and reinforcement for the deformability and compressibility of silica aerogel-fiber composites. The fibers may be solid and / or hollow. The fibers may be fibers used in the textile industry. Fibers having a silica aerogel layer disposed on at least a portion of the fiber can be referred to as silica aerogel composites. Combinations of structurally and / or compositionally different fibers may also be used. Non-limiting examples of fibers include ceramic fibers, polymers (e.g., nylon, polyaramid, cellulose, etc.), and combinations thereof. The fibers may be present in the form of a substrate (e.g., a textile). Fibers of various sizes can be used. For example, at least some or all of the fibers have a width (e.g., diameter), which may range from 100 nm to 15 microns (including all 0.1 nm values and ranges therebetween), and a length (e.g., longest dimension), which may range from 100 microns to 10 cm (including all 0.1 micron values and ranges therebetween). Suitable examples of fibers are known in the art and can be obtained commercially or produced by methods known in the art.

[0126] Various amounts of fiber can be used (e.g., in the reaction mixture). In various examples, the amount of fiber used (e.g., in the reaction mixture) corresponds to 10 to 90 wt. % (based on the total weight of the ceramic foam-fiber composite), based on 90%, 95%, 99%, or 100% conversion of the ceramic precursor(s) (e.g., silica precursor), including all 0.1 wt. % values and ranges therebetween (e.g., provided). In various examples, the amount of fiber used (e.g., in the reaction mixture) corresponds to 30 to 50 wt. %, 35 to 45 wt. %, or about 40 wt. % (based on the total weight of the ceramic foam-fiber composite), based on 90%, 95%, 99%, or 100% conversion of the ceramic precursor(s) (e.g., silica precursor).

[0127] The methods of the present disclosure can include a thermal annealing step, which may be an ambient pressure drying step. The thermal annealing step may be performed after the ceramic foam-fiber composite (e.g., silica aerogel-fiber composite) has been formed, washed, dried, etc. For example, thermal annealing is the final step in manufacturing a ceramic foam-fiber composite (e.g., silica aerogel-fiber composite). In various examples, thermal annealing is performed at 300°C to 600°C (including all integer values and ranges of degrees Celsius therebetween), for various times (e.g., 1 hour to 6 hours (including all integer values and ranges of minutes therebetween)), and optionally at ambient pressure (e.g., the pressure during thermal annealing is not changed from ambient pressure).

[0128] The ceramic foam-fiber composite may be used to form a sheet. The ceramic foam-fiber composite or fibers may be disposed in a ceramic foam matrix. A composite sheet comprises multiple ceramic foam-fiber composites. The sheet may be in the form of a mat or a paper sponge. The sheet may have a variety of thicknesses. In various examples, the sheet has a thickness of 1 mm to 100 mm (including all values and ranges of 0.1 mm therebetween). The composite sheet may be formed by methods known in the art (e.g., papermaking methods, etc.).

[0129] The methods of the present disclosure may further include forming a composite sheet. In various examples, the composite sheet is made by forming a mixture, which may be referred to as a pulp mixture and may be a reaction mixture, where the ceramic aerogel-fiber composite is formed after the composite is formed, including one or more ceramic foam-composite materials and water, mixing, spreading on a large mesh screen, and removing the water to form a wet sheet. The wet sheet can then be annealed (e.g., overnight at 60°C), and the paper sheet can be dried. In various examples, no additives or binders are used in the sheet manufacturing process. This approach provides a simple, low-cost method for forming composite sheets and is capable of scalable production.

[0130] The method can be a continuous method. For example, the method is a roll-to-roll (R2R) continuous manufacturing method. R2R allows for near-net-shape manufacturing and dimensional customization of ceramic foam formations, for example, on a low-cost, highly insulating inorganic paper substrate support.

[0131] Using roll-to-roll continuous manufacturing, aerogel-based insulation materials with improved R-values are expected to be formed at low cost, for example, by using tetraethoxysilane or water-glass silica aerogel precursors to mix with inorganic ceramic or fiberglass fiber carriers, allowing for customization of shape and size through the roll-to-roll manufacturing process (e.g., inorganic ceramic fiber paper substrate carriers (Fiberfrax, Unifrax)). (登録商標) )) is expected to lead to favorable material costs for silica aerogel.

[0132] In one aspect, the present disclosure provides a ceramic foam-fiber composite material. The ceramic foam-fiber composite material comprises a plurality of fibers, wherein at least some or all of the fibers individually comprise a ceramic foam disposed on at least some or all of the surface of the fiber. The ceramic foam of the ceramic foam composite material may be a ceramic foam film. The film may be continuous or may be formed from a plurality of particles. The ceramic foam may be referred to as a ceramic aerogel. The ceramic foam may be a silica aerogel. Non-limiting examples of ceramic foams are provided herein. A ceramic foam material (e.g., a ceramic foam composite material) comprises a ceramic foam. The ceramic foam comprises a matrix of a ceramic material. The ceramic foam may be produced by the method of the present disclosure.

[0133] Ceramic foam-fiber composites can have varying amounts of fiber. In various examples, the amount of fiber in the ceramic foam-fiber composite is 10-90 wt. % (based on the total weight of the ceramic foam-fiber composite), including all values and ranges up to 0.1 wt. % therebetween. In various examples, the amount of fiber in the ceramic foam-fiber composite is 30-50 wt. % or 35-45 wt. % or about 40 wt. % (based on the total weight of the ceramic foam-fiber composite).

[0134] The fibers of the ceramic foam-fiber composite can have ceramic foam disposed on at least a portion of the fiber surface (e.g., 10 to 100%, including all 0.1% values and ranges therebetween). In various examples, for example, when the composite is formed in situ, 70% or more, 80% or more, 90% or more, 95% or more, 99% or more of the surface (which may be the interior and / or exterior surfaces of the fibers) has ceramic foam disposed thereon. In various examples, for example, when ceramic foam powder is used to form the in situ formed composite, 10% or more, 20% or more, 30% or more, 40% or more, 50% or more, 60% or more, 70% or more, or 80% or more of the surface (which may be the interior and / or exterior surfaces of the fibers) has ceramic foam disposed thereon.

[0135] The ceramic foam may be in the form of a layer. The layer may have a thickness of 10 mm to 10 microns (including all values and ranges of 0.1 mm therebetween). The layer may be continuous or discontinuous.

[0136] The ceramic foam may be in the form of a plurality of particles, which may have a size (e.g., longest dimension, such as diameter) or average size (e.g., average longest dimension, such as average diameter) of 20 nm to 100 nm (including all 0.1 nm values and ranges therebetween).

[0137] The ceramic foam of the ceramic foam-fiber composite may be an oxide. Non-limiting examples of oxides include silicon oxides (e.g., silica), aluminum oxides (e.g., alumina), transition metal oxides, and the like, and any combination thereof. The ceramic foam may be stoichiometric or non-stoichiometric.

[0138] The ceramic foam of the ceramic foam-fiber composite may be a mixture of oxides. The ceramic foam may be based on binary oxides, ternary oxides, or higher oxides. Non-limiting illustrative examples of ceramic foams include aluminosilicate foams, aluminotitanate foams, and the like.

[0139] In one example, the ceramic foam and / or ceramic foam material of the ceramic foam-fiber composite does not have fluorine atoms (e.g., fluorine atoms detectable by conventional methods known in the art), which may be fluorine atoms bonded to silicon atoms (e.g., -Si-F).

[0140] The ceramic foam of the ceramic foam-fiber composite is porous and exhibits a hierarchical gradient pore structure. The ceramic foam may be described as comprising a hierarchical hollow structure with an interior of micropores (also called macropores) (e.g., voids in a ceramic matrix) and mesopores within a shell (e.g., matrix). At least some or all of the pores may be interconnected. The pores may be mesopores and / or macropores. The pores may be mesopores as defined by IUPAC.

[0141] The pores (which may be referred to as micropores or macropores, not mesopores of the ceramic matrix) of the ceramic foam-fiber composite can have a variety of sizes. For example, the size (e.g., average size and / or 90%, 95%, 99%, 99.9%, or 100%) of the pores can be between 500 microns and 1 micron (including all 0.1 micron values and ranges therebetween). The size can be at least one dimension (e.g., diameter) as measured in a plane parallel to the axis of the pore. For example, the pores can have a size (e.g., at least one dimension (e.g., diameter) measured in a plane parallel to the axis of the pore and / or at least one dimension (e.g., height) measured in a plane perpendicular to the axis of the pore) between 500 microns and 1 micron (e.g., 200 microns and 10 microns, 200 microns and 1 micron, or 100 microns and 1 micron). The pore size generally decreases or increases along a direction moving from a first surface of the ceramic foam to a second surface opposite the first surface, and the gradient can be linear or non-linear.

[0142] The ceramic matrix of the ceramic foam of the ceramic foam-fiber composite may be mesoporous (e.g., including mesopores, which may be mesopores as defined by IUPAC). For example, the ceramic matrix includes a plurality of pores having a diameter of 2 nm to 100 nm (e.g., 2 nm to 60 nm, 10 nm to 60 nm, or 10 nm to 100 nm), including values and ranges of 0.1 nm therebetween. For example, the ceramic matrix includes a plurality of pores having an average diameter of 2.5 nm to 30 nm (e.g., 2.5 nm to 10 nm or 15 nm to 30 nm), including values and ranges of 0.1 nm therebetween. The pore size distribution may be bimodal. For example, the ceramic matrix has a plurality of pores (which may be multimodal, e.g., bimodal) with an average diameter of 2 nm to 100 nm (e.g., 2 nm to 60 nm, 10 nm to 60 nm, or 10 nm to 100 nm) and a plurality of pores with an average diameter of 2.5 nm to 30 nm (e.g., 2.5 nm to 10 nm, or 15 nm to 30 nm).

[0143] The silica aerogel of the ceramic foam-fiber composite is porous. For example, the silica aerogel has a plurality of pores with diameters ranging from 2 nm to 100 nm (e.g., 2 nm to 60 nm, 10 nm to 60 nm, or 10 nm to 100 nm), including values and ranges of 0.1 nm therebetween. For example, the silica aerogel has a plurality of pores with an average diameter ranging from 2.5 nm to 30 nm (e.g., 2.5 nm to 10 nm or 15 nm to 30 nm), including values and ranges of 0.1 nm therebetween. The pore size distribution may be bimodal. For example, silica aerogels have a plurality of pores with average diameters of 2 nm to 100 nm (e.g., 2 nm to 60 nm, 10 nm to 60 nm, or 10 nm to 100 nm) (which may be multimodal, e.g., bimodal), and a plurality of pores with average diameters of 2.5 nm to 30 nm (e.g., 2.5 nm to 10 nm, or 15 nm to 30 nm). The pore size and / or pore size distribution can be determined using methods known in the art. For example, the pore size and / or pore size distribution can be determined using BET analysis.

[0144] The pore size and / or pore size distribution of the ceramic foam and / or ceramic matrix of the ceramic foam-fiber composite can be determined using methods known in the art, for example, the pore size and / or pore size distribution can be determined using BET analysis.

[0145] The ceramic foam of the ceramic foam-fiber composite may be a composite material (e.g., a composite ceramic foam). The composite material may include a polymer material in some or all of the pores of the ceramic foam (sometimes referred to as a hybrid composite or hybrid ceramic foam). The polymer may be formed by in situ polymerization in the ceramic foam. Additionally or alternatively, the composite material may include a carbon coating on the ceramic foam (sometimes referred to as a ceramic-carbon aerogel). For example, the ceramic foam (e.g., a ceramic foam monolith or ceramic foam film) may be at least partially (or completely) coated with a carbon material.

[0146] The ceramic foam-composite may be in the form of a sheet. The ceramic foam of the ceramic foam-composite may be infiltrated into a substrate formed from a plurality of fibers.

[0147] The insulating material may include a ceramic foam-composite material of the present disclosure (e.g., a ceramic foam-composite material made by a method of the present disclosure). The insulating material may be thermally insulating (thermally insulating), acoustically insulating (soundproofing), or both.

[0148] The methods or ceramic-foam composites of the present disclosure are expected to provide low-cost building insulation materials that may include one or more ceramic fiber composites of the present disclosure and / or one or more ceramic fiber composites made by the methods of the present disclosure.

[0149] The methods of the present disclosure are expected to provide inexpensive, large-scale production and installation of high R-value architectural insulation materials (ceramic foam-composites) that can impact a wide range of building envelope applications, such as roofs and walls in existing buildings and future construction. For example, supercritically dried ceramic foams (e.g., Spaceloft (登録商標) Replacing conventional ceramic foams (e.g., July 2018) with the ceramic foams of the present disclosure is expected to result in cost savings of 90% or more over current technology. Additionally, the building energy efficiency of insulation based on the ceramic foams of the present disclosure is expected to be at least 45%. At room temperature, insulation based on the ceramic foams of the present disclosure may have R-values and thermal conductivities comparable to commercially available ceramic foams. However, insulation using the ceramic foams of the present disclosure may have increased R-values at elevated temperatures (e.g., compared to commercially available ceramic foams) and may significantly reduce unit costs. The complex processing and volatile organic solvents involved in producing ceramic foams by conventional high-pressure supercritical drying make their use cost-prohibitive for building insulation manufacturers.

[0150] The building insulation material may be a thermal insulation sheet. The thermal insulation sheet may be used in commercial or residential applications. The thermal insulation sheet may also be formed using a roll-to-roll manufacturing method. The thermal insulation sheet may be used to retrofit existing buildings. In various examples, the thermal insulation sheet including the ceramic foam of the present disclosure is a R15 / inch thermal insulation sheet that may have a thermal conductivity of 0.01 W / mK or less.

[0151] In one example, the ceramic foam-composite material does not include any exogenous materials (e.g., any detectable exogenous materials that can be detected by conventional methods known in the art). Exogenous materials include, but are not limited to, materials used in forming building materials from silica materials (e.g., ceramic foam materials). Non-limiting examples of exogenous materials include binders (e.g., polymeric binders), polymers, etc.

[0152] Ceramic foam composites can have desirable sound transmission / insulation / insulation properties. In various examples, the ceramic foam has an improvement in sound insulation (e.g., an increased sound insulation coefficient) of at least 10%, at least 15%, at least 20%, or at least 25% over another material of a given thickness (e.g., organic polymer foam such as PS foam or PU foam, or ceramic fiber) at one or more, substantially all, or all frequencies between 500 and 2,000 Hz. In another example, a silica aerogel-like foam (e.g., silica PGAero) having a thickness of 0.014 m exhibits better sound insulation performance than a reference PS foam at frequencies of 500 Hz, 800 Hz, and 2,000 Hz, exhibiting noise reductions of 10.9%, 12.0%, and 28.4%, respectively.

[0153] In one aspect, the present disclosure provides uses of the ceramic foam-fiber composite material of the present disclosure. The ceramic foam-fiber composite material can be used in a variety of applications. The ceramic foam-fiber composite material may be or provide superinsulation. For example, the material has a thermal conductivity of 0.01 W / mK or less.

[0154] In one example, ceramic foam-fiber composites are used as insulating materials (e.g., building materials or acoustic insulation materials), which may exhibit desirable thermal management and / or acoustic insulation properties.

[0155] In one example, ceramic foam-fiber composites are used as composite materials in applications such as catalysis, membranes, and separations, as templates or support substrates for coating with other functional materials.

[0156] The method steps described in the various embodiments and examples disclosed herein are sufficient to carry out the methods of the present disclosure. Thus, in one example, a method consists essentially of a combination of the method steps disclosed herein. In another example, a method consists solely of such steps.

[0157] The following statements describe various examples of ceramic foam-fiber composite materials and methods of making ceramic foam-fiber composite materials: Statement 1. 1. A method for forming a ceramic foam-fiber composite (which may include a fiber-hierarchical pore-gradient ceramic foam or silica aerogel), comprising: The method includes contacting (e.g., in a reaction mixture, which may also be in a closed environment, such as a sealed reaction vessel) one or more fibers; one or more ceramic precursors; one or more pore-forming gas-forming additives (one or more inert gas generants); one or more catalysts; and, optionally, one or more additives, wherein the contacting results in the formation of an inert gas (e.g., carbon dioxide, nitrogen, or a combination thereof) and a ceramic foam-fiber composite (e.g., a plurality of fibers are formed, each fiber having a ceramic foam layer disposed on at least a portion of the fiber). The ceramic foam may be a hierarchical pore-gradient ceramic foam. The method may also include a sintering step, in which the ceramic foam-fiber composite is sintered. Statement 2. 10. The method of claim 1, wherein the contacting is carried out at an initial pressure of 1 to 100 psi (e.g., pressurizing the reaction vessel to 1 to 100 psi) (including all 0.1 psi values and ranges therebetween) before substantial reaction (e.g., 5%, 1%, or 0.1% reaction) of the one or more ceramic precursors and / or one or more pore-forming gas-forming additives and / or one or more additives, if present, occurs. Statement 3. 3. The method of claim 1 or 2, wherein the one or more ceramic precursors are selected from silica precursors, alumina precursors, transition metal oxide precursors, and any combination thereof. Statement 4. 4. The method of claim 3, wherein the silica precursor(s) is selected from tetraalkoxysilanes (e.g., TMOS, TEOS, etc.) (e.g., C1-C5 alkoxytetraalkoxysilanes), alkyltrialkoxysilanes (e.g., methyltrimethoxysilane (MTMS)), etc. (e.g., C1-C5 alkyl, C1-C5 alkoxy alkyltrialkoxysilanes), sodium metasilicate (e.g., water glass), alkyls, and any combination thereof. Statement 5. 5. The method of claim 3 or 4, wherein the alumina precursor(s) is selected from aluminum alkoxide (e.g., C1-C6 aluminum alkoxide), alumatoran, or tris(alumatranyloxy-i-propyl)amine, and the like, and any combination thereof. Statement 6. The transition metal oxide precursor(s) may be a transition metal alkoxide (e.g., a metal oxide having the formula M(OR) x wherein M is a transition metal (e.g., Al, Ti (e.g., titanium(IV)-iso-propoxide, etc.), Zr, W, Cr, Mo, etc.), R is an alkyl group, and x is 1, 2, 3, 4, or 5). The method of claim 3 or 4, wherein the transition metal is in various oxidation states (e.g., + 1. + 2. + 3. + 4. + 5). Statement 7. The method of any one of the preceding statements, wherein the catalyst is a base catalyst (e.g., ammonia, ammonium fluoride, ammonium hydroxide, urea, cetyltrimethylammonium bromide, and the like, and any combination thereof). Statement 8. 7. The method of any one of statements 1 to 6, wherein the catalyst is an acid catalyst (e.g., a protonic acid (e.g., acetic acid, etc.), a hydrohalic acid, etc., and any combination thereof). Statement 9. The method of any one of the preceding statements, wherein the pore-forming gas-forming additive (inert gas generator) is selected from sodium bicarbonate, urea, and any combination thereof (e.g., the pore-forming gas-forming additive (inert gas generator) provides a subcritical amount (e.g., pressure) of inert gas). The pore-forming gas (inert gas) may be carbon dioxide and / or nitrogen and / or ammonia. Statement 10. The method of any one of the preceding statements, wherein the one or more additives are selected from a surfactant (e.g., cetyltrimethylammonium bromide (CTAB)), urea, and combinations thereof. The surfactant may aid in pore formation. The surfactant may also provide surface functionalization. Statement 11. The method of any one of the preceding statements, wherein the one or more ceramic precursors (e.g., silica precursors), one or more pore-forming gas-forming additives, and optionally one or more additives are contacted, and then the catalyst is contacted with the one or more ceramic precursors (e.g., silica precursors), one or more pore-forming gas-forming additives, and optionally one or more additives. Statement 12. The method of any one of the preceding statements, wherein the contacting comprises mixing one or more fibers; one or more ceramic precursors, which may be disposed (e.g., dissolved) in water, a solvent (e.g., an alcohol, such as ethanol), or any combination thereof; one or more pore-forming gas-forming additives (one or more inert gas generators), which may be disposed (e.g., dissolved) in water; and a catalyst, which may be disposed (e.g., dissolved) in water. The ceramic precursor(s), pore-forming gas-forming additive(s) (inert gas generator(s)), catalyst(s), and optional additive(s) can be combined in any order. In one example, the catalyst(s) or fibers are the last components added. Statement 13. The method of any one of the preceding statements, wherein the one or more ceramic precursors are present in an amount of 2 to 10 wt. % (each in the case of more than one) (based on the total weight of the one or more ceramic precursors, one or more catalysts, one or more inert gas generating agents, and one or more additives, if present). Statement 14. The method of any one of the preceding statements, wherein the one or more inert gas generating agents are present at 0.4 to 2 wt. % (based on the total weight of the one or more ceramic precursors, one or more catalysts, one or more inert gas generating agents, and one or more additives, if present). For example, the one or more ceramic precursors are at least 5 times the weight of the one or more pore-forming gas-forming additives (one or more inert gas generating agents). Statement 15. The method of any one of the preceding statements, wherein the catalyst is present at 1 to 2 wt. % (based on the total weight of the one or more ceramic precursors, the one or more catalysts, the one or more inert gas generating agents, and the one or more additives, if present). Statement 16. The method of any one of the preceding statements, wherein the one or more additives are present in an amount of 200 to 1000 wt. % (based on the total weight of the one or more ceramic precursors, one or more catalysts, and one or more inert gas generating agents), including all 0.1 wt. % values and ranges therebetween. For example, the additive(s) are present in an amount 2 to 10 times greater by weight than the ceramic precursor(s). For example, the one or more additives are present in an amount 10 times greater by weight than the one or more silica precursors, one or more catalysts, and one or more inert gas generating agents (based on the total weight of the one or more silica precursors, one or more catalysts, and one or more inert gas generating agents). Statement 17. The method of any one of the preceding statements, wherein the ratio of one or more ceramic precursors:one or more inert gas generating agents / pore-forming gas-forming additives:one or more catalysts:one or more additives is 5:1:1:50 (e.g., one or more ceramic precursors:one or more inert gas generating agents / pore-forming gas-forming additives:one or more catalysts=5:1:10). In various embodiments, one or more of these values are within 10% or 20% of each other. Statement 18. The method of any one of the preceding statements, wherein the contacting is carried out at a temperature between room temperature (e.g., 18-23°C) and 70°C, and / or for a time between 1 minute and 96 hours. Statement 19. The method of any one of the preceding statements, further comprising exchanging (e.g., removing) the solvent(s) from the ceramic foam-fiber composite. Statement 20. The method of any one of the preceding statements, further comprising washing the ceramic foam-fiber composite. The washing step may be an exchange step in which undesired materials (e.g., solvent(s), unreacted ceramic reaction components, etc.) are removed. In various embodiments, 90% or more, 95% or more, 99% or more, or all observable undesired materials are removed from the film. Statement 21. 21. The method of claim 20, wherein the washing comprises contacting the ceramic foam-fiber composite with an aqueous solution (e.g., an alcohol-water solution). Statement 22. The method of any one of the preceding statements, further comprising washing the ceramic foam-fiber composite with alcohol (e.g., ethanol) and / or drying the ceramic foam-fiber composite (e.g., APD). For example, subjecting the ceramic foam-fiber composite (e.g., heating the ceramic foam-fiber composite) to a temperature between room temperature (e.g., 18-23°C) and 100°C (e.g., 30-60°C), where the treatment (or heating) may be under ambient conditions (e.g., ambient pressure conditions, such as about 1 atm). For example, hydrophobic coatings are compatible with ceramic foam structures. Statement 23. The method of any one of the preceding statements, further comprising forming a layer (e.g., a film) of a hydrophobic carbon-containing material disposed on at least a portion or all of a surface of the ceramic foam. In one example, the ceramic foam (e.g., silica aerogel) is contacted with a silane (e.g., a trialkylhalosilane such as trimethylchlorosilane (TMCS)), a carbon material (e.g., carbon soot), or any combination thereof. Statement 24. The method of any one of the preceding statements, wherein the fibers are solid fibers or hollow fibers. Statement 25. The method of any one of the preceding statements, wherein the fiber is a textile. Statement 26. The method of any one of the preceding statements, wherein the fibers are ceramic fibers, polymers (e.g., polymer fibers), or a combination thereof. Statement 27. The method of any one of the preceding statements, further comprising decorating or coating at least a portion or all of a surface (e.g., an exterior surface) of the ceramic foam body. Statement 28. 28. The method of claim 27, wherein the ceramic foam is decorated or coated with a substance (e.g., nanoparticles, which may be metal oxide nanoparticles) (e.g., iron oxide nanoparticles, which may be magnetic nanoparticles). For example, the ceramic foam is decorated or coated using an in situ reaction by impregnating the foam with a substance (e.g., a nanoparticle precursor, which may be a metal oxide nanoparticle precursor) followed by solid-state sintering at 200-1000°C (including all integer °C values and ranges therebetween). Statement 29. 29. The method of claim 28, wherein the nanoparticles are formed by impregnating a ceramic foam with nanoparticle precursors (e.g., CuCl2, FeCl3, etc., and combinations thereof), and the nanoparticles are formed by reaction of the nanoparticle precursors (e.g., heating the impregnated ceramic foam to form the nanoparticles) to form a nanocomposite. Statement 30. A ceramic foam-fiber composite material of the present disclosure (e.g., a ceramic foam-fiber composite material comprising a plurality of fibers and a ceramic foam) (e.g., a ceramic foam-fiber composite material formed from the method of any one of the preceding statements). Statement 31. 31. The ceramic foam-fiber composite of claim 30, wherein the ceramic foam of the composite is silica aerogel. Statement 32. 32. The ceramic foam-fiber composite of claim 30 or 31, wherein the ceramic foam is disposed on at least a portion of the surface of at least some (or all) of the fibers of the composite. Statement 33. The ceramic foam-fiber composite material of any one of statements 30-32, wherein the ceramic foam of the composite material has a hierarchical pore gradient. At least some or all of the pores may be interconnected. The size of the pores (e.g., macropores) generally decreases or increases along the lateral direction moving from a first surface of the ceramic foam to a second surface opposite the first surface. The gradient may be a linear gradient. The ceramic foam may contain mesopores and / or macropores. The mesopores may be mesopores as defined by IUPAC. Statement 34. 34. The ceramic foam-fiber composite of any one of claims 30-33, wherein the ceramic foam comprises a ceramic matrix. The ceramic matrix may be formed from ceramic nanoparticles. The ceramic matrix may be mesoporous. Statement 35. 35. The ceramic foam-fiber composite material of any one of statements 30-34, wherein the ceramic foam comprises pores (e.g., macropores) having a size (e.g., at least one dimension (e.g., diameter) measured in a plane parallel to the pore axis and / or at least one dimension (e.g., height) measured in a plane perpendicular to the pore axis) of 500 microns to 1 micron (e.g., 200 microns to 1 micron, or 100 microns to 1 micron). Statement 36. 36. The ceramic foam-fiber composite of any one of statements 30-35, wherein the ceramic foam is silica aerogel-like and transparent. Statement 37. The ceramic foam is 90-99% air (e.g., at least 90%, at least 95%, or at least 98% air), highly porous (<100 nm), and has a low density (~0.003 g / cm 3 37. The ceramic foam-fiber composite of any one of statements 30-36, having a high thermal conductivity (typically ∼0.017 W / mK). Statement 38. The ceramic foam-fiber composite material of any one of statements 30 to 37, wherein the ceramic foam includes a layer of a carbon-containing material disposed on at least a portion or all of the surface (e.g., outer surface) of the ceramic foam. For example, the thickness (e.g., a dimension perpendicular to the surface of the ceramic foam) is 10 nm or less (e.g., 0.1 to 10 nm). Non-limiting examples of the carbon-containing material include carbon soot, alkylsilane groups, and additive (e.g., surfactant) residues (which may be produced by thermal annealing). The layer may be continuous and / or conformal and / or may have a desirable low number of defects (e.g., no observable defects, which may be visually observable). The layer may be a molecular layer (e.g., a molecular layer of groups that may be hydrophobic groups). This layer can provide a hydrophobic outer surface. The carbon material (e.g., carbon soot) layer may be formed by combustion of a carbon source. Statement 39. 39. The ceramic foam-fiber composite material of any one of statements 30 to 38, wherein the ceramic foam further comprises nanoparticles disposed on at least a portion of the surface of the ceramic foam. Statement 40. The ceramic foam-fiber composite of any one of statements 30-39, wherein the ceramic foam-fiber composite is a monolith, a free-standing film, or a film disposed on at least a portion or all of a substrate. In one example, the ceramic foam-fiber composite is a free-standing film (e.g., a sheet). In one example, the film does not include a binder (e.g., a polymeric binder). Examples of binders (e.g., polymeric binders) for ceramic foams (e.g., silica aerogel materials) are known in the art. Statement 41. 41. The ceramic film-fiber composite of claim 40, wherein the film has a thickness of 1 / 4 inch to 2 inches. Statement 42. 42. The ceramic foam-fiber composite of claim 40 or 41, wherein a film is disposed on at least a portion of a surface of a substrate (e.g., aluminum foil, insulating paper, fiber, etc.). Statement 43. 43. The ceramic foam-fiber composite of any one of statements 30-42, wherein the ceramic foam-fiber composite exhibits one or more or all of the following: Thermal stability (e.g., thermal stability up to at least 2000°C) Mechanical strength (e.g., mechanical strength of at least 100 MPa) ·Soundproofing and acoustic insulation properties. Statement 44. 44. The ceramic foam-fiber composite material of any one of statements 30 to 43, wherein each fiber of the plurality of fibers is a solid fiber or a hollow fiber. Statement 45. 45. The ceramic foam-fiber composite material of any one of statements 30 to 44, wherein at least some or all of the plurality of fibers are textiles. Statement 46. 46. The ceramic foam-fiber composite material of any one of statements 30 to 45, wherein each fiber of the plurality of fibers is a ceramic fiber or a polymer. Statement 47. 47. The ceramic foam-fiber composite of any one of statements 30 to 46, wherein the amount of fiber is 10 to 90 wt. % (based on the total weight of the ceramic foam-fiber composite).

[0158] The following examples are presented to illustrate the present disclosure and are not intended to be limiting in any regard.

[0159] [Example 1] This example provides an example of a ceramic foam-fiber composite material of the present disclosure, a method for making the composite material, and a description of the use of the composite material.

[0160] The following fibers were used: 1. Pure Fiber (登録商標) Owens Corning (R-13, fiber diameter approximately 10 μm) (登録商標) EcoTouch (登録商標) PINK (登録商標) Fiberglass TM Insulation 2. Unifrax (登録商標) E-class and C-class fibers (fiber diameter approximately 0.8 μm)

[0161] Fiber-aerogel paper manufacturing:

[0162] Preparation of silica aerogel precursor using water glass : First, prepare a gas-forming solution (Solution A). Add 0.3 mol / L CTAB (VWR) to 3 mol / L urea (Sigma-Aldrich) and dissolve in distilled water to a volume of 100 mL (in a beaker). Stir for 3 hours until a clear solution forms. Next, prepare Solution B. Dilute 11 mL of reagent-grade sodium silicate solution (Sigma-Aldrich) with water in a 1:4 volume ratio, then add 2 mol / L HCl to the sodium silicate solution until it begins to become translucent. Immediately, add Solution A to Solution B and stir for 10 minutes to thoroughly mix them to form a silica aerogel precursor (considered one piece of precursor).

[0163] Commercially available fibers were added to 1000 mL of DI water and stirred for 3 minutes to homogenously disperse the fibers. Then, a certain amount of the silica precursor prepared in section 1.1 was added. The ratio is listed in Table 1. First, a wet fiber-precursor paper mat was prepared by vacuum filtration of a mixed solution of Unifrax E08 fibers and silica aerogel precursor. The top and bottom of the wet paper mat were then covered with two sheets of stiff paper, sealed in a Zip plastic bag, and placed in an oven at 60 °C for two days, during which time the precursor reacted with the fibers and strengthened the bond between the final aerogel and the fibers. A flexible fiber-aerogel paper mat was successfully prepared after being covered with two sheets of thick stiff paper and slowly dried in an oven for two days. Various fiber concentrations were adjusted by the ratio of the fiber weight to the amount of silica precursor. Details are listed in Table 1. Scaling up can be achieved by adjusting the amounts of fiber and precursor.

[0164] [Table 1]

[0165] Preparation of silica aerogel from water glass: The silica precursor solution prepared above was transferred into a plastic bottle and tightly sealed. The container was then placed in an oven preheated to 60°C for 3 days. After this step, the sample powder was transferred from the container to distilled water preheated to 60°C (for 2 days). During this washing process, the water was exchanged several times to remove ammonia and excess CTAB. In this method, the commercially available fiber and the prepared silica aerogel were simply mixed together (without any further reaction). The wet paper mat obtained by vacuum filtration was directly dried in an oven for 1-2 days with a thick, hard paper cover.

[0166] Preparation of silica gel with tetraethyl orthosilicate: 3 mol / L urea (Sigma-Aldrich), 0.3 mol / L CTAB / SDS, cetyltrimethylammonium bromide (VWR), and 1 mmol acetic acid (EMD Millipore Corporation) were added and dissolved in distilled water to a total volume of 100 mL (in a beaker). The solution was stirred for 3 hours until it became completely clear. 1.4 mol / L tetraethyl orthosilicate (TEOS, Sigma-Aldrich) was then added to the solution. Stirring was continued for 10 minutes, and the solution turned homogeneous and translucent. The solution was then transferred to an aluminum container and tightly sealed. The container was placed in an oven (preheated to 60°C) for 4 days to allow gelation. After this gelation process, the sample (gel) was removed from the container and placed in a container filled with distilled water preheated to 60°C for 2 days. During this washing process, the water was replaced several times until the supernatant water became clear and all ammonia was removed. The sample (gel) was then stored in a sealed container for further application. The blender was set to a constant speed and a certain amount of DI water was blended into the container. The chopped fiber was gradually added and blended for 1 minute (Unifrax (登録商標) for E-class and C-class fibers), 3 minutes (Owens Corning (登録商標) EcoTouch (登録商標) PINK (登録商標) Fiberglass TM (In the case of 1000-12000), the fibers were blended. After the fibers were uniformly dispersed in water, the previously prepared gel was added to the mixture and blended for 1 minute. After the solution became homogeneous, the solution was poured into a sealed caster (with a fine grid sheet in the center), and a large amount of water was sucked out using a vacuum pump, forming a paper on the grid in the center of the caster. Then, immediately after the paper was made, it was placed in a preheated oven at 60°C for 24 hours for drying purposes.

[0167] Thermal, mechanical and acoustic characterization: 1. Customized thermal conductivity measurements were performed according to the ASTM C518 standard thermal conductivity procedure. The commercially available insulation materials were calibrated against a polystyrene standard using a heat flux sensor purchased from Fluxtaq. 2. Acoustic testing - A customized sound box equipped with internal sound insulation and a sound detector purchased from Kasuntest was used to test various fiber-aerogel paper mats at different frequencies generated by a sound source. 3. Mechanical Testing - Both the original fiber-aerogel paper mat and the sintered mat samples were subjected to compression testing under different loads at multiple cycle times. 4. The humidity aging cycle test measures the thermal conductivity of the sample. The sample is placed in each humidity environment for 5 hours, dried in a preheated oven for another 5 hours, and the cycle is repeated.

[0168] [Example 2] This example provides a description of the preparation and characterization of silica aerogel materials of the present disclosure.

[0169] One gram of sodium bicarbonate was mixed with 7.08 ml of DI water. 4.59 ml of tetraethyl orthosilicate (TEOS) and 22.34 ml of pure ethanol were added. 1 ml of catalyst was also added to speed up gel formation. The catalyst was a mixture of 1.457 ml of ammonium hydroxide (28%), 0.1 g of ammonium fluoride, and 4.35 ml of DI water. After 3 minutes, the gel was washed with DI water and then added to 500 ml of pure ethanol and immersed in it, stirring for 24 hours. After immersion, the ethanol was removed. Next, 10 ml of TMCS (98%) was added dropwise to the solution. Pure ethanol was also added. Continuous CO2 evolution was observed over the next 24 hours. Finally, the gel was dried in ethanol at 60°C in an ambient atmosphere for 24 hours to obtain the aerogel product.

[0170] [Example 3] This example provides a description of the preparation and characterization of silica aerogel materials of the present disclosure.

[0171] 3.3 g of cetyltrimethylammonium bromide (CTAB) and 33.3 g of urea were dissolved in an aqueous acetic acid solution (1 mM, 100 mL) followed by stirring for 20 minutes. Next, 56.7 mL of tetraethyl orthosilicate (TEOS) was added. The solution was vigorously stirred for 30 minutes to form a uniform foam emulsion, which was sealed and then transferred to a preheated oven at 60 °C for reaction for 2 days. The as-prepared aerogel was washed with water and dried at room temperature. The resulting aerogel had a low density (approximately 0.15 g / cm). 3 ) and has good thermal insulation properties.

[0172] [Example 4] This example provides a description of the silica aerogel material of the present disclosure and its characterization.

[0173] Samples were prepared by carrying out the reaction on a substrate (Unifrax paper) in contact with the reaction mixture, which can be referred to as in-situ infiltration. SEM, energy dispersive X-ray spectroscopy (EDX), and thermal images were obtained (Figures 10-14).

[0174] [Example 5] This example provides a description of the preparation and characterization of silica aerogel materials of the present disclosure.

[0175] Trimethylchlorosilane (TMCS):(CH3)3SiCl was used for surface modification of silica gel, producing HCl as a by-product, which reacted spontaneously with sodium bicarbonate to generate pore-supported carbon dioxide in situ. The carbon dioxide formed was trapped in the wet silica gel, and the resulting pressure in the bubbles counteracted capillary pressure, which prevented pore shrinkage and collapse during the ambient pressure drying process. The silica gel precursors used were aqueous tetraethoxysilane (TEOS, Si(OC2H5)4) and sodium bicarbonate (NaHCO3), and trimethylchlorosilane (used for surface modification).

[0176] Low-cost production of aerogel insulating materials is expected through in situ APD and R2R fabrication. Well-formulated gels may be R2R deposited onto inorganic paper substrate carriers. Central to the production of aerogel materials using R2R fabrication is the formation of a gel precursor that is robust to printing. The rheological behavior of silica gel plays a key role for continuous deposition in the R2R process, which requires a non-Newtonian liquid with shear-thinning behavior. The Weber number (We) and Ohnesorge (Oh) number (or reciprocal Z) were used to predict whether stable deposition would be achieved:

number

[0177] The pore size distribution of silica aerogels was investigated using nitrogen physisorption with fitting by the Brunauer-Emmett-Teller technique. The N adsorption-desorption isotherm plots of silica aerogels showed the presence of hierarchical pores and a relatively sharp pore size distribution (major pore size <60 nm).

[0178] Mechanical properties are important for constructing silica aerogels. Honeycomb aerogel structures were fabricated to study the stress-strain curve. The compressive strength, σ, can be seen from the following equation: * is the total density of the sample, ρ * is strongly influenced by.

number

[0179] Thermal insulation performance is an important evaluation criterion for silica aerogel. The thermal insulation ability of 3D fabricated silica aerogel was investigated. Thermography analysis showed that silica aerogel functions as an excellent thermal insulator. The thermal insulation property of silica aerogel varies with its thickness. The effective thermal conductivity can be calculated according to the effective medium percolation theory.

number

[0180] This example provides a description of the preparation and characterization of the ceramic foam material of the present disclosure.

[0181] Pore-gradient silica aerogel-like foam monoliths (PGAero) with controlled hierarchical hollow structures and gradient pore sizes were designed and synthesized by hydrolysis of tetraethyl orthosilicate (TEOS) in the presence of acetic acid, urea, and cetrimonium bromide (CTAB). In situ foam formation from the thermal decomposition of CTAB micellar networks and urea leads to the formation of hierarchical pores and pore gradients in PGAero, respectively. The as-synthesized silica insulation material exhibits excellent thermal insulation, sound insulation, and fire resistance performance with thermal conductivity as low as 0.040 W / mK and high mechanical integrity with a compressive strength of 100.56 MPa, which allows for further molding and customization for desired shapes and structures. Acoustic performance was also tested at different frequencies, demonstrating better sound insulation properties than the reference insulation foam (28.3% or 22.3 dB sound reduction at 2000 Hz / 15 mm thickness).

[0182] Results and Discussion The scheme in Figure 31a illustrates the formation of hierarchical hollow silica PGAero, achieved by a facile one-pot synthesis. The surfactant CTAB is used to form micelles in a mixed solution of TEOS and water. Hydrolysis of TEOS proceeds on the as-formed micelle shell, which acts as a template to guide the formation of the silica shell. The addition of urea promotes the polymerization of silicon alkoxide by increasing the solution pH, while its thermal hydrolysis to ammonia (NH3) and carbon dioxide (CO2) can act as an in situ foaming agent. The as-formed silica PGAero floats on the water surface due to its low mass density. The continuous decomposition of urea and the subsequent release of in situ carbon dioxide and ammonia bubbles creates high pressure at the top of the reaction chamber, which leads to a top-to-bottom foaming process that creates a pore gradient in the PGAero. Figure 31b shows a typical photograph of the as-formed opaque silica PGAero, which can be cut and polished to desired shapes for further study (as shown in Figure 31c). The pore gradient can be easily observed from the scanning electron microscope (SEM) image (Figure 31d), which shows an increase in average pore size from top to bottom, where the pore size depends on the reaction conditions, such as chemical concentration, reaction temperature, and time (discussed in the following section). The average pore size of PGAero from the bottom to the top region was calculated, showing an increase from 33.3 μm to 174.8 μm with a TEOS:CTAB:urea ratio of 27.8:1:60.7 (inset in Figure 31d). High-resolution SEM images of PGAero in the large-pore and small-pore regions are shown in Figures 31e and 31f, respectively. Furthermore, the as-synthesized silica PGAero had a porosity of 94.1% and a porosity of 0.128 g / cm by pycnometer. 3The PGAero solid network is constructed by nanoscale silica particles, which was further characterized by transmission electron microscopy (TEM). As shown in Figures 31g and 31h, numerous micropores were clearly observed within each particle, likely due to the templating effect of CTAB molecules. Therefore, due to the hierarchical hollow structure with gradient macroscale pores and mesopores within the silica network, silica PGAero with high porosity and low density was obtained. The as-synthesized silica PGAero with limited gas thermal conductivity and high phonon scattering is expected to provide high insulating performance.

[0183] To understand and control the pore gradient formation in PGAero, a series of experiments was designed to synthesize PGAero with shorter reaction times of 24, 48, and 72 hours (designated PGAero-2, PGAero-3, and PGAero-4, respectively). Compared with the initial sample with a pore gradient (designated PGAero-1) synthesized by a 96-hour reaction time, the 24-hour silica PGAero has a uniform pore size of 27.5 μm with a standard deviation of 9.4 μm (Figures 35a and 35b). Increasing the reaction time to 48 hours gradually leads to the formation of gradient pores in PGAero, resulting in a larger pore deviation, as shown in Figure 32a. Increasing the reaction time to 72 hours results in a broader pore size range of 15 μm to 300 μm, with a much larger deviation of 85.3 μm (Figure 32b). The porosity of the silica PGAero remained at approximately 80% and decreased slightly with increasing reaction time due to the continued growth of silica (Figure 36). The porosity gradient and the decrease in porosity with increasing pore size exhibit competing effects on the insulating performance. The decrease in porosity of the synthesized silica PGAero (from 24 to 48 hours) primarily results in an increase in thermal conductivity from 0.049 W / mK to 0.060 W / mK. Meanwhile, the porosity gradient with increasing pore size dominates the insulating performance, leading to a lower thermal conductivity of 0.054 W / mK. Further increasing the reaction time results in the formation of silica PGAero with the lowest thermal conductivity of 0.040 W / mK (Figure 32c).

[0184] By adjusting the reaction conditions and their correlation with the thermal conductivity of PGAero, the average pore size and porosity were investigated (Figure 37). Typical SEM cross-sectional images of silica PGAero are shown in Figures 33a-33f. The average pore size of each sample was calculated by counting over 100 pores via SEM images, as shown in Figures 38a-g. Increasing the TEOS concentration from 1.4 mol / L (average pore size 138.3 μm, porosity 94.1%) for the PGAero-1 sample to 2.1 mol / L and 2.8 mol / L, corresponding to PGAero-5 and PGAero-6, resulted in average pore sizes of 85.0 μm and 68.4 μm, respectively, and porosities of 89% and 88% (33a-33c). Increasing the TEOS concentration reduces the average pore size and porosity, resulting in a densified silica PGAero, which results in higher thermal conductivity from 0.040 W / mK to 0.049 W / mK (PGAero-5) and 0.055 W / mK (PGAero-6). The increase in thermal conductivity is primarily due to increased solid-state heat transport through the high-component silica network. The CTAB concentration primarily determines the pore size of the silica PGAero, where a lower CTAB content results in a smaller average pore size for PGAero (PGAero-7), as shown in Figures 33a and 33d. Urea addition acts as a mineralization chemical and an in situ cell blowing agent; therefore, increasing urea addition can result in larger pore size and lower mass density. As shown in Figures 33f and 33g, the pore size of the as-formed silica PGAero significantly increased from 38.65 μm to 110.39 μm when the urea concentration was changed from 1.5 mol / L (PGAero-8) to 4.5 mol / L (PGAero-9). The thermal insulation performance was highly correlated with the pore size and porosity of the silica PGAero. Figure 33g shows the thermal conductivity of different silica PGAeros depending on the pore size and porosity. Larger pore size and higher porosity resulted in lower thermal conductivity of the PGAeros. The lowest thermal conductivity of 0.040 W / mK could be achieved by the silica PGAero synthesized with a TEOS:CTAB:urea ratio of 27.8:1:60.7.

[0185] The mechanical stability of silica aerogels is key to their large-scale commercial applications. It has been reported that gradient pore structures offer significant advantages for optimizing mechanical performance. Silica PGAero with pore gradients synthesized as monolithic forms possesses high mechanical strength, which was characterized by uniaxial compression tests (Figure 39). The stress-strain curve of silica PGAero-1 shows high mechanical strength with a high Young's modulus of 81.33 MPa, which can be further increased to 100.56 MPa by post-annealing at 400°C for 2 h (Figures 34a and 40a-c). The inset in Figure 34a shows SEM images of silica PGAero before (top) and after (bottom) annealing. The robust pore structure confers good mechanical integrity to silica PGAero. The silica PGAero before and after annealing have thermal conductivities of 0.040 W / mK and 0.044 W / mK, respectively. The annealing process improves the mechanical properties without compromising the insulating performance. Importantly, the mechanically robust foam can maintain a low thermal conductivity of 0.060 W / mK after long-term annealing at 1000°C for 24 hours (Figure 41). The high degree of mechanical robustness and thermal stability makes the synthetic silica PGAero highly promising for the increasing demands on insulating materials applied in extreme environments.

[0186] Acoustic insulation plays an important role in superinsulation applications. As shown in Figure 34b, both sound waves and heat were significantly reduced by the silica PGAero with a pore gradient structure. The acoustic intensity detected through no sample (blank control), the silica PGAero, and polystyrene standards is plotted as shown in Figure 42. Additionally, several commonly used commercial soundproofing materials, such as polyurethane, Kevlar, and two types of ceramic fiber blankets, are plotted. The silica PGAero exhibits low detected acoustic intensity across the entire frequency range (500 Hz to 1800 Hz), demonstrating far superior soundproofing performance compared to all commonly used commercial soundproofing materials shown in Figure 34c. The 0.014 m thick silica PGAero exhibits better soundproofing performance compared to standard PS foam, showing 10.9%, 12.0%, and 28.4% noise reduction at different frequencies of 500 Hz, 800 Hz, and 2000 Hz, respectively (Figures 34e, 43a, and 43b). This is especially true at a sound frequency of 2000 Hz (Figure 34d). To calibrate the thickness-independent sound insulation performance, the sound insulation coefficient was defined by dividing the noise reduction by the sample thickness. The sound insulation coefficients of the silica PGAero were 2.7, 2.0, and 18.2 times higher than those of the standard sample at 500 Hz, 800 Hz, and 2000 Hz, respectively. In addition to the mechanical and acoustic sound insulation properties, the moisture absorption performance of the silica PGAero was investigated in a humid environment. Two PGAero samples with initial thermal conductivities of 0.045 W / mK and 0.052 W / mK were selected for moisture absorption experiments under 60% and 80% humidity, respectively. High humidity conditions result in an increase in thermal conductivity, which can be recovered after drying at 60°C (Figure 44). Cyclic experiments show that the thermal conductivity of the PGAero can return to its initial point with less than a 16% loss.

[0187] We have developed a lightweight silica PGAero with high porosity and a large pore gradient for thermal and acoustic superinsulation. Micelle-mediated growth of silica and a gas-foaming process using urea thermal hydrolysis both result in pore generation and gradient formation. The unique pore structure and well-designed monolithic shape with ceramic properties provide this PGAero with excellent thermal insulation and fire resistance over a wide temperature range (thermal conductivity as low as 0.040 W / mK and high mechanical integrity with a compressive strength of 100.56 MPa). This silica PGAero also exhibits better sound insulation properties at various frequencies, achieving a sound reduction of 28.3% or 22.3 dB at a 15 mm thickness at a frequency of 2,000 Hz (higher than standard insulation foam). Its stability in humid environments has also proven reliable over the long term. Materials with high thermal and acoustic insulation performance while maintaining thermal conductivity are considered suitable for next-generation construction materials and other applications.

[0188] Materials and Experiments Experimental: Preparation: 3 mol / L urea (Sigma-Aldrich), 0.3 mol / L CTAB (VWR), and 1 mmol acetic acid (EMD Millipore Corporation) were dissolved in distilled water and placed in a beaker to make 100 mL. The solution was stirred for 3 hours until it became a clear liquid. 1.4 mol / L TEOS (Sigma-Aldrich) was then added to the solution. After stirring for 10 minutes, the solution turned homogeneously translucent. The solution was then transferred to a plastic bottle and tightly sealed. The container was then placed in a preheated oven at 60°C for 4 days. After this gelation process, the sample was removed from the container and transferred to distilled water preheated at 60°C for 2 days. During this washing process, the water was replaced several times until the supernatant water became clear and all ammonia was removed. Immediately after the washing process was completed, the sample was placed in a preheated oven at 60°C for 2 days for drying purposes.

[0189] Characterization: The thermal conductivity measurement platform was customized according to the ASTM C518 standard thermal conductivity procedure. Heat flux sensors were purchased from Fluxtaq and calibrated with standard polystyrene commercial insulation.

[0190] Acoustic testing, a customised sound box for home use (with internal sound insulation and an echo detector purchased from Kasuntest). Samples of different thicknesses are tested under different frequencies generated by a sound source.

[0191] A pycnometer test uses helium gas to infiltrate a porous sample in a chamber to obtain the volume of the solid portion of the sample. If the solid portion of the sample is known, the porosity of a silica foam sample can be calculated.

[0192] Mechanical Testing: Both the original silica foam samples and the bulk samples after thermal synthesis at 400°C were compression tested under different loads and multiple cycle times.

[0193] The humidity aging cycle test measures the thermal conductivity of a sample by exposing it to various humidity conditions for 24 hours, drying it in a preheated oven for another 24 hours, and then repeating the cycle.

[0194] [Example 7] This example provides a description of the preparation and characterization of the ceramic foam material of the present disclosure.

[0195] Experimental Method: 3 mol / L urea (Sigma-Aldrich), 0.3 mol / L CTAB (cetyltrimethylammonium bromide) (VWR) / SDS (sodium dodecyl sulfate) (Sigma-Aldrich), and 1 mmol acetic acid (EMD Millipore Corporation) were dissolved in distilled water and placed in a beaker to make a 100 mL solution. The solution was stirred for 3 hours until it became completely clear. 1.4 mol / L TEOS (Sigma-Aldrich) was then added to the solution. After stirring for 10 minutes, the solution turned homogeneously translucent. The solution was then transferred to an aluminum container and tightly sealed. The container was then placed in a preheated oven at 60 °C for 4 days. After this gelation process, the sample (monolith and gel) was removed from the container and transferred to a container filled with distilled water preheated to 60 °C for 2 days. During this washing process, the water was replaced several times until the supernatant water became clear and all ammonia was removed. The sample (gel) was then stored in a sealed container for further application, see Figures 45-49.

[0196] [Example 8] This example provides a description of the preparation and characterization of the ceramic foam material of the present disclosure.

[0197] Described here is a flexible, high-temperature, superhydrophobic ceramic insulating nanocomposite, in which the engineered nanostructure, radiative insulating coating, and interfacial cross-linking between ceramic fibers and aerogel are critical for its high-temperature insulation. The lightweight, flexible aerogel nanocomposite can be fabricated with a thermal conductivity of 0.1 g / cm. 3 It exhibits a density of 1.0, high temperature resistance exceeding 500°C, fire resistance with a thermal conductivity of 0.023 W / mK, and superhydrophobicity with a water contact angle of 152°. Its mechanical resilience and high-temperature thermal insulation, along with its acoustic performance, shed light on the possibility of producing low-cost, flexible aerogels with scalability for high-temperature insulation applications.

[0198] All-ceramic high-temperature insulating nanocomposites via compression molding (HT-Aero) are described, constructing flexible aerogel and nanofiber networks by adjusting the microstructure density and in situ crosslinking between aerogel and fibers. Compression molding, previously applied to construct bulk materials, is here used to strengthen the interfacial bonding between aerogel and fibers at high temperatures and control the pressure-dependent density and crosslinking reaction of HT-Aero nanocomposites. Furthermore, a superhydrophobic carbon porous coating could further reduce high-temperature thermal radiation. Benefiting from its hierarchical structure framework, the as-prepared superhydrophobic nanocomposite exhibited a thermal conductivity of 0.1 g / cm. 3 The material exhibits a flyweight density of 1.04 mm, heat resistance exceeding 500°C, and fire resistance with a low thermal conductivity of 0.023 W / mK, indicating that it can be understood as a promising candidate for next-generation high-temperature insulation materials in extreme environments.

[0199] Results and Discussion Figure 50a shows a fabrication scheme for flexible ceramic aerogel-fiber nanocomposite sheets with controllable density and crosslinked networks via thermal compression. The inset shows a large, flexible, thermally compressed composite sheet with lateral dimensions exceeding 20 cm. The silica pre-aerogel precursor is a mixture of sodium dodecyl sulfate (SDS) surfactant micelles, the in-situ foaming agent urea, sodium silicate (water glass), and hydrogen chloride solution. Urea can promote the polymerization of silicon alkoxide, while its decomposition into carbon dioxide and ammonia bubbles acts as an in-situ foaming agent and supports pore formation during ambient pressure drying. During thermal compression, further hydrolysis and condensation of the silica aerogel occur, while the applied load compresses the nanocomposite to a controllable density, and heat treatment strengthens the interfacial bonding between the silica aerogel and ceramic fibers. The porous silica aerogel network and ceramic fibers can be observed by transmission electron microscopy (Figure 50b), and the inset shows the interface between the aerogel and fiber network. To confirm the cross-linking-induced interfacial bonding, Fourier transform infrared spectroscopy (FTIR) is performed on the silica aerogel, ceramic fiber, and aerogel-fiber nanocomposite (Figure 50c). The FTIR spectra of these materials show a peak at 1,100 cm -1 From 1,000cm -1 The SiO2 molecules share the same absorption region up to 797.5 cm, which are prominent peaks corresponding to the asymmetric and symmetric modes of silicon dioxide. -1 is associated with the symmetric Si-O-Si stretching or vibrational mode of the ring structure. -1 Nearby peaks and 3,447cm -1 The broad absorption bands around 1,374 cm originate from Si-OH groups, but these peaks become weaker in the hot-compressed composites when the temperature exceeds 150 °C. High temperatures enhance the in situ crosslinking reaction, so that the peaks around 1,374 cm appear in the FTIR spectra of the composites after hot-compression. -1 , 2,881 cm -1 , 2,978cm -1 , and 3,654 cm -1New peaks were observed around ≈ ...

[0200] The thermal conductivity k of an insulating material can be expressed as follows:

number

[0201] Figure 51b shows the thermal conductivity vs. density of composite paper sheets with fiber concentrations of 35, 40, 45, and 72 wt% after hot compression treatment at 150°C, while the others are shown in Figure 55a. As the applied compression force increases, the density increases, while the thermal conductivity decreases to an optimum value and then increases. For the HT-Aero composite with a fiber concentration of 45 wt%, the density is 0.27 g / cm. 3 to 0.295 g / cm 3As the density increases, the thermal conductivity decreases to 0.023 W / mK. This may be due to the heat transport pathway consisting of nanoporous silica aerogel and ceramic fiber structure. However, as the density increases further (>0.295 g / cm), 3 ), the porous network is damaged by compression, and solid-state contact dominates the heat transport pathway, resulting in a reduction in thermal insulation performance. The flame-retardant performance of the ceramic composite paper sheet is evident from the fact that the back surface remains intact even when the front surface is exposed to a hydrogen flame (Figures 51c and 56), suggesting potential high-temperature thermal insulation applications.

[0202] Regarding high-temperature insulation performance, the porous carbon network via candle soot coating could enhance radiative insulation. Candle soot technology has been successfully applied to insulating window materials to resist solar radiation. The scheme of the candle soot coating process is shown in Figure 51d. HT-Aero composite sheets are treated over a candle flame, and incomplete combustion of carbon nanoparticles deposits on the surface of the composite paper sheet. Figure 51e demonstrates the uniform carbon coating on the surface of the thermocompressed composite material by candle soot, which exhibits superhydrophobic performance with a water contact angle of 152°, consistent with what is known in the art. The candle soot-coated porous carbon network with pore sizes of approximately several hundred nanometers in Figures 51f and 57 may reduce thermal radiation in high-temperature environments. Figure 51g compares the top surface temperature T vs. heating temperature curves of composite sheets with and without carbon soot. As the heating surface temperature increases from 25°C to ~430°C, both top surface temperatures increase linearly with ~80% thermal resistance, while the coated HT-Aero sample has a lower temperature curve (~7% lower than the sample without the carbon coating). The inset shows an IR image of the sample heated at 174°C, while the top surface temperature is 60.7°C, qualitatively demonstrating the high-temperature resistance of the carbon-coated HT-Aero ceramic composite paper sheet. The associated temperature changes of the HT-Aero ceramic composite with and without the candle soot coating, as observed by the IR camera, are shown in Figure 55. The thermal insulation performance of the HT-Aero composite at high temperatures (100–900°C) is also investigated. Figure 51h compares the thermal conductivity vs. average temperature of the hot-compressed composite (12.7 mm thick) with and without the carbon coating, showing a linear temperature dependence compared to the parabolic relationship of the pure ceramic aerogel. This is caused by the enhanced interfacial bonding between the aerogel and the fibers in the hot-compressed HT-Aero composite. By depositing the heat-radiation-resistant carbon network, the thermal conductivity at 300 °C decreased to 0.075 W / mK (from 0.09 W / mK for the sample without the carbon coating), suggesting that the porous carbon network improves thermal insulation at high temperatures.The inset shows the corresponding HT-Aero heated surface temperature vs. bottom measured temperature curve with the candle soot coating, demonstrating the excellent thermal resistance of the HT-Aero sample (12.7 mm thick) heated to the hot surface from 100 °C to 900 °C during high-temperature thermal conductivity measurements.

[0203] Acoustic insulation is another important feature of flexible ceramic nanocomposite sheets, and its soundproofing is achieved through the effective reflection and absorption of sound waves. The aerogel and nanofiber structures can effectively reflect sound waves and increase airflow resistivity, reducing sound transmission. The cross-sectional SEM image (top) of the aerogel-fiber composite in Figure 52a shows the fiber layer stack structure with large gaps created by vacuum filtration during paper sheet production, where thermal convection and conduction by gas components are prominent. After thermal compression, the ceramic fiber-aerogel layers were densely packed, as shown in the SEM image (bottom) of Figure 52a. This induced dense microstructure could enhance soundproofing performance. Figure 52b shows the soundproofing performance of HT-Aero composite sheets with different fiber concentrations (30, 45, and 72 wt%) and a blank sheet as a baseline. Compared to the blank reference, the HT-Aero sheet exhibits superior soundproofing performance at sound frequencies between 500 and 3,000 Hz. The 45 wt% composite sheet exhibits optimal, low detected acoustic intensity across the entire frequency range. This may be due to the synergistic effect between the crosslinked aerogel and nanofibers, consistent with its excellent thermal insulation performance. Comparing the acoustic intensity vs. time curves of the different samples at a frequency of 3,000 Hz (Figure 52c) indicates the optimal sound insulation performance of the sample containing 45 wt% fibers, which is consistent with its thermal conductivity performance. The sound insulation performance at 800, 1,000, and 3,000 Hz is shown in Figure 52d. In particular, the noise reduction of the 45 wt% nanofiber sheet is 15.3%, 30.0%, and 37.4% at frequencies of 800, 1,000, and 3,000 Hz, respectively, compared to the blank reference. The sound insulation coefficient of the sample containing 45 wt% fiber is 10 times, 1.8 times, and 1.3 times that of the sample containing 72 wt% fiber at 800, 1,000, and 3,000 Hz, respectively.

[0204] Hot-compressed HT-Aero composite sheets with different densities and fiber concentrations have different mechanical responses, which are very important for flexible thermal insulation applications under external forces. Uniaxial tensile tests were conducted to investigate the mechanical performance of flexible HT-Aero ceramic composite paper sheets (Figure 53a). The stress-strain curves for specimens with 30 wt%, 45 wt%, and 72 wt% fiber are plotted in Figures 53b–d. Typically, as strain increases, the stress first increases linearly, followed by yielding (shortly after the stress drops), and finally, when the stress reaches a maximum value, the specimen begins to fracture. For specimens with different densities in Figures 53b–d, the stress curves become higher under the same strain as the density increases. For the hot-compressed HT-Aero composite with 30 wt% fiber (Figure 53b), the density of 0.118 g / cm3 is 0.118 g / cm3. 3 to 0.163 g / cm 3 As the density increases, the maximum strength increases from 0.048 MPa to 0.22 MPa, and for the HT-Aero sample with 72 wt% fiber (Figure 53d) in a similar density range, the maximum strength increases from 0.047 MPa to 0.13 MPa. The lower maximum strength is due to the lower amount of interfacial bonding between the aerogel and the fiber. The HT-Aero sample with 45 wt% fiber has a maximum strength of 0.272 g / cm. 3 ~0.356g / cm 3Because of the relatively high density of the aerogel (Figure 53c), its maximum tensile strength is large, suggesting its robustness. On the other hand, as the fiber concentration increases to 30, 45, and 72 wt% (Figures 53b-d and 59), the maximum yield strength (i.e., first stress drop) of each sample decreases from 0.17 MPa to 0.075 MPa and 0.048 MPa, respectively, indicating that a higher fraction of interfacial bonding between the aerogel and the fibers contributes significantly to the superior yield strength. A tensile failure mechanism, resulting from the fiber-aerogel network structure, is proposed in Figure 53e, in which sliding occurs between fiber-fiber connections under tensile stress and a stick-sliding mechanism for the fiber-aerogel connections. The initial linearly increasing stress is due to the small applied force (insufficient to pull the fibers and slide them past their contact points), and the reversible bending behavior of the fiber network dominates this stage. When the stress reaches the yield strength value, sliding occurs between the fibers. The load drop observed in the stress-strain curves results from the sticking-sliding mechanism of the fiber-aerogel adhesive connections. The bonded fiber-aerogel connections may be stress concentration locations where stress is released after sliding occurs. Furthermore, the failure behavior of HT-Aero in tension was different from that in compression. Tensile stress can cause tear-like failure, while compressive stress can lead to progressive crushing. Upon reaching the maximum stress, a fracture crack initiates in the HT-Aero and propagates throughout the specimen, while the stress gradually decreases. Figure 53f shows the maximum strength vs. density (ρ) of specimens with 30, 35, 45, and 72 wt% fiber, and the scaling relationship is shown as σ~ρ. n (n is 2.56 to 4.71). The larger the n value, the stronger the density-dependent fracture strength, which is governed by the interfacially bonded fiber-aerogel structure.

[0205] In summary, all-ceramic flexible, high-temperature insulating nanocomposites are described. A flexible aerogel and nanofiber bonded network is constructed through thermal compression by adjusting the microstructure density and in situ crosslinking between the aerogel and the fibers. The application of high temperature and applied load strengthens the crosslinked interfacial interactions between the nanofibers and silica aerogel, allowing for control of the microstructure's porosity and density. This approach allows for the in situ construction of an elastic bonded structure during the process. Furthermore, low thermal emissivity can provide high-temperature insulating performance through the nanoporous carbon coating on the nanocomposite. Meanwhile, benefiting from the hierarchical structure framework of the ceramic aerogel composite, the as-prepared superhydrophobic nanocomposite exhibited a thermal conductivity of 0.1 g / cm. 3 The material exhibits a flyweight density of 1.04 mm, heat resistance exceeding 500°C, and fire resistance with a low thermal conductivity of 0.023 W / mK, indicating that it can be understood as a promising candidate for next-generation high-temperature insulation materials in extreme environments.

[0206] method Thermally compressed paper sheets via silica aerogel precursor 0.3 mol of urea (Sigma-Aldrich) and 2.0 g of sodium dodecyl sulfate (SDS(VWR)) were dissolved in 100 mL of distilled water in a beaker and stirred for 3 hours until a clear solution was obtained. Next, 11 mL of reagent-grade sodium silicate solution (Sigma-Aldrich) was added, followed by 2 mol / L HCl until the solution became translucent. Commercially available ceramic fibers were added to the solution and kept in an oven at 60 °C for 2 hours for further gelation. 1000 mL of DI water was then added and stirred for 3 minutes to uniformly disperse the fibers. The wet composite was then prepared by vacuum filtration of the mixed solution containing ceramic fibers and silica preaerogel. The wet paper sheet was then covered on both sides with aluminum foil and placed in a hot press. The composite was then compressed at a specific elevated temperature for 1 hour. The temperatures examined in this study were 60 °C, 100 °C, 150 °C, and 200 °C, respectively. All hot-pressed composite samples were kept in an oven (under 60°C) to dry completely. Different fiber concentrations were adjusted by changing the ratio of fiber weight to silica precursor amount.

[0207] Structural characterization The microstructure of the studied samples was characterized using a Carl Zeiss AURIGA scanning electron microscope (SEM) and a JEOL 2010 high-resolution transmission electron microscope (HRTEM). Fourier transform infrared (FTIR) spectra were acquired in attenuated total reflectance mode (ATR-FTIR spectroscopy) using a Bruker VERTEX 70 on a ZnSe substrate, with atmospheric correction performed during the measurements. BET analysis was performed on a Tristar II 3020 (Micromeritics Corp., Atlanta, GA). Specific surface area (SSA) and pore size distribution were evaluated using low-temperature nitrogen adsorption / desorption isotherm measurements. Pure aerogels were degassed at 300 °C for 1 h before analysis. Surface areas were calculated using the Brunauer-Emmett-Teller (BET) theory using isothermal adsorption data at P / P0 values between 0.05 and 0.30. Water contact angles were measured using an Ossila contact angle goniometer. Infrared (IR) images of the 6 mm thick composite material (~4 layers of composite sheet) on the hotplate were taken by a Fotric 225 Pro thermal camera.

[0208] Thermal Characterization The thermal conductivity of the composite sheets was measured using a Thermtest HFM-100 in accordance with the ASTM C518 standard. Calibration was performed before each measurement against a standard reference material (NIST SRM 1450d) with a thermal conductivity of 0.0325 W / mK. The thickness of the composite material was automatically measured by the HFM-100. Measurements began with the upper and lower plates fixed at 30°C and 40°C, respectively, and the thermal conductivity was determined at a constant heat flux. Extruded polystyrene boards of different thicknesses, ranging from 1 mm to 25 mm, were used for thermal conductivity measurement calibration. Thermal conductivity measurements on small samples also followed the ASTM C518 standard procedure. A reference commercial polystyrene insulation was used to calibrate the Fluxteq flux sensor. The temperatures of the upper and lower plates were recorded with a steady heat flux through the sample, and then the thermal conductivity values were calculated. High-temperature thermal conductivity measurements followed the ASTM C892 standard procedure.

[0209] Mechanical property evaluation The mechanical properties of the composites were investigated using an MTS universal testing machine.

[0210] Although the present disclosure has been described with reference to one or more particular embodiments and / or examples, it will be understood that other embodiments and / or examples of the present disclosure may be made without departing from the scope of the present disclosure.

Claims

1. A method for producing a silica aerogel-fiber composite, comprising: fiber; Silica precursor; a pore-forming gas-forming additive; wherein said pore-forming gas-forming additive comprises urea a catalyst; and surfactants wherein said contacting results in the formation of an inert gas and a silica aerogel-fiber composite; A method wherein said inert gas is formed by reaction of said pore-forming gas-forming additive with said catalyst.

2. the contacting is carried out at an initial pressure of 1 to 100 psi; and / or 10. The method of claim 1, wherein the contacting is carried out at a temperature from room temperature to 70°C and / or for a time from 1 minute to 96 hours.

3. contacting the silica precursor, the pore-forming gas-forming additive, and the surfactant, and then contacting the catalyst with the silica precursor, the pore-forming gas-forming additive, and the surfactant; and / or The method of claim 1 , wherein said contacting comprises mixing said fibers; said silica precursor; said pore-forming gas-forming additive; and said catalyst.

4. The method of claim 1, wherein the silica precursor is selected from tetraalkoxysilanes, alkyltrialkoxysilanes, sodium metasilicate, and any combination thereof.

5. the catalyst is a base catalyst selected from ammonia, ammonium fluoride, ammonium hydroxide, and combinations thereof, or an acid catalyst selected from a protonic acid, a hydrohalic acid, and any combinations thereof; and / or The method of claim 1 , wherein the fibers are solid or hollow fibers.

6. the silica precursor is present at 2 to 10 wt. % (based on the total weight of the silica precursor, the catalyst, the pore-forming gas-forming additive, and the surfactant); and / or 10. The method of claim 1, wherein the pore-forming gas-forming additive is present at 0.4 to 2 wt. % (based on the total weight of the silica precursor, the catalyst, the pore-forming gas-forming additive, and the surfactant).

7. the catalyst is present at 1 to 2 wt. % (based on the total weight of the silica precursor, the catalyst, the pore-forming gas-forming additive, and the surfactant); and / or the surfactant is present at 200 to 1000 wt. % (based on the total weight of the silica precursor, the catalyst, and the pore-forming gas-forming additive); and / or 10. The method of claim 1, wherein the ratio of said silica precursor: said pore-forming gas-forming additive: said catalyst is 5:1:

10.

8. removing the solvent from the silica aerogel-fiber composite; and / or washing the silica aerogel-fiber composite, wherein the washing comprises contacting the silica aerogel-fiber composite with an aqueous solution; and / or Washing the silica aerogel-fiber composite with alcohol and / or drying the silica aerogel-fiber composite. The method of claim 1 further comprising:

9. 10. The method of claim 1, further comprising forming a layer of a hydrophobic carbon-containing material disposed on at least a portion of a surface of the silica aerogel.

10. 10. The method of claim 1, further comprising decorating or coating at least a portion of the surface of the silica aerogel, wherein the silica aerogel is decorated or coated with a substance.

11. 10. The method of claim 1, wherein the silica aerogel-fiber composite further comprises a plurality of nanoparticles formed by impregnating the silica aerogel with nanoparticle precursors and reacting the nanoparticle precursors to form a nanocomposite.

12. A silica aerogel-fiber composite material produced by the method of any one of claims 1 to 11, comprising: at least a portion of the pores in the silica aerogel are interconnected; A silica aerogel-fiber composite having a pore gradient structure in which the size of the pores decreases or increases along a direction moving from a first surface of the silica aerogel-fiber composite to a second surface opposite the first surface.

13. The composite material, wherein the silica aerogel is disposed on at least a portion of the surface of at least a portion of the fibers of the composite material; and / or 13. The silica aerogel-fiber composite of claim 12, wherein the silica aerogel is a plurality of particles.

14. 13. The silica aerogel-fiber composite of claim 12, wherein the silica aerogel comprises a silica matrix.

15. 13. The silica aerogel-fiber composite of claim 12, wherein the silica aerogel comprises pores having a size between 500 microns and 1 micron.

16. the silica aerogel is transparent, and / or 13. The silica aerogel-fiber composite of claim 12, wherein the silica aerogel comprises a layer of a carbon-containing material disposed on at least a portion of a surface of the silica aerogel.

17. At least a portion of the fibers are are solid or hollow fibers, and / or is a textile, and / or 13. The silica aerogel-fiber composite of claim 12, which is a ceramic fiber or a polymer.

18. The silica aerogel-fiber composite of claim 12, wherein the silica aerogel-fiber composite comprises 10 to 90 weight percent fibers.

19. 13. The silica aerogel-fiber composite of claim 12, wherein the silica aerogel further comprises nanoparticles disposed on at least a portion of a surface of the silica aerogel.

20. 13. The silica aerogel-fiber composite of claim 12, wherein the silica aerogel-fiber composite is a monolith, a free-standing film, or a film disposed on at least some or all of a substrate, wherein the free-standing film or the disposed film has a thickness of between ¼ inch and 2 inches.

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