Ceramic foams, methods for their manufacture and uses thereof

Abstract

Ceramic foams are provided. The ceramic foams can have a graded pore gradient. The ceramic foams can be silica aerogels. The ceramic foams can be prepared by reacting one or more precursors in the presence of an inert gas produced by a pore-forming gas forming additive. The ceramic foams can be used as insulation materials.

Description

[0001] Cross-reference of related applications

[0002] This application claims the benefits of U.S. Provisional Application No. 62 / 791,778, filed January 12, 2019, and U.S. Provisional Application No. 62 / 861,892, filed June 14, 2019, the disclosures of which are incorporated herein by reference in their entirety. Background Technology

[0003] The search for lightweight yet high-strength ultra-insulation (thermal and acoustic insulation) is key to energy-efficient buildings and many other industries, while low-cost manufacturing with scalability is essential for large-scale, practical, and energy-efficient applications.

[0004] HVAC (Heating, Ventilation, and Air Conditioning) in buildings accounts for 40% of global energy consumption. HVAC in existing and future buildings can be improved by installing enhanced insulation, thereby reducing CO2 emissions. An economical way to reduce building heat loss is to install thicker layers of insulation material. However, this takes up more space, thus reducing living space. Silica aerogel achieves the same insulation performance with only half the thickness of conventionally installed insulation. Silica aerogel exhibits the lowest known thermal conductivity of a solid at ambient temperature, pressure, and relative humidity, approximately 0.015 W / m·K. This low thermal conductivity is due to a combination of its low density and the porosity created during manufacturing. In the construction industry, space saving is one of the most important reasons for using high-performance insulation materials, particularly for building renovations and the construction of thin facade insulation, side enclosures, and roof balconies. The main drawback of large-scale use of silica aerogel as a standard insulation material in buildings is its production cost.

[0005] Superbaric materials require tightly regulated heat transfer. In this context, silica aerogels are among the most effective insulating materials, achieving thermal conductivity even lower than that of still air. The superbaric properties of ceramic aerogels result from the geometry of the porous material, including high pore volume, optimized pore size, and porous solid walls with boundaries and defects. The confined heat conduction within the gas pores and the low solids fraction heat dissipation pathways due to phonon scattering contribute to their excellent insulating performance. Despite their superbaric properties, large-scale applications of silica aerogels are limited by their costly and time-consuming manufacturing process via supercritical drying (avoiding capillary-induced structural degradation during the drying process). Furthermore, the poor mechanical stability of aerogels hinders their monolithic applications. While additives such as carbon nanowires and polymer fibers are used to blend with aerogels to improve mechanical stability, achieving mechanical strength without compromising insulating properties remains quite challenging.

[0006] Inspired by the human skin structure, aerogel-based foams with a gradient of pore size have recently attracted interest due to their asymmetric structure, which not only provides excellent insulation properties but also offers a basis for developing new functionalities. In addition, this aerogel-based foam with a gradient of pore structure shows good prospects in optimizing the mechanical properties of dense materials or porous materials with uniform pore size. Gradient-pore polylactic acid foams with the same porosity have about 20% higher sound absorption capacity than uniform foams. Controlled hollow nano / microstructures of silica foams with tunable void fraction, pore size, and mass density play a role in the development of super-insulating materials.

[0007] Lightweight aerogel materials are ideal for thermal / heat insulation. However, their low mechanical integrity and high manufacturing cost hinder their development for large-scale adoption of energy-saving building insulation materials. In addition, it can be important to obtain better sound and heat resistance properties for thermal management.

[0008] Since silica aerogels have a very large surface-to-volume ratio (about 2 x 10 9 m -1 ) and specific surface area (about 900 m 2 / g), the internal surface chemical processes play an important role in their thermal and chemical properties. The surface produced by conventional supercritical drying is simply covered with hydroxyl groups (-OH) (~ 5 -OH / nm 2 ) with strong hydrogen bonding ability (hydrophilic). Therefore, it absorbs moisture from humid air, thereby increasing its mass by 20%. In addition, the condensation of moisture within the nanoscale pores exerts a strong enough capillary force to break the silica skeleton and collapse the aerogel as a whole. In addition, at relatively high temperatures, the radiation component of the thermal conductivity of silica aerogels is significant.

[0009] Silica aerogels are typically prepared by a sol-gel process combined with supercritical extraction to maintain structural integrity and high porosity. Conventional aerogel preparation by supercritical extraction has many limitations, including high energy consumption, large environmental footprint, long processing times, and high material costs. However, the complex processing and high pressures involved in supercritical drying limit its scalability for large-scale production of building insulation. The most common method of aerogel synthesis involves extraction of the liquid from the gel by critical point drying using a low surface tension supercritical fluid, such as CO2 or CH4. However, supercritical extraction requires expensive high-pressure equipment and is a hazardous and time-consuming process. Alternative methods include organic solvent sublimation, which is difficult to scale up due to the energy-intensive requirements of high vacuum and cryogenic drying. Conventional ambient pressure drying processes, as a lower energy alternative, replace the original solvent used for gel formation with low surface tension organic solvents, such as hexane, heptane, and octane. Additionally, it often results in the production of hydrochloric acid, which further requires organic solvents for removal. Thus, the current APD method remains a time-consuming and expensive process due to the use of large amounts of organic solvents. All of these limit large-scale aerogel production for building insulation. According to the 2014 Allied market research report, the rapid growth of the aerogel market indicates people’s interest in silica aerogel insulation materials (18.5 USD / ft 2 - inch): In 2004, the sales of aerogel insulation materials were about 25 million USD, but by 2013, it had increased to 500 million USD (expected to reach 1,927 million USD in 2021). However, the main drawback of large-scale use of silica aerogels as a standard insulation material in buildings is their high production cost. Therefore, current aerogel production is mainly used for industrial applications, such as pipe insulation.

[0010] A new method of insulation material (e.g., gradient-structured insulation material) with ideal mechanical integrity and low cost is desirable, particularly for scalable manufacturing of insulation material (e.g., gradient-structured insulation material). SUMMARY

[0011] In the present disclosure, in various examples, a scalable ceramic aerogel (e.g., a pore gradient ceramic aerogel, which can be referred to as a ceramic foam, PGAeros) is designed and synthesized. In-situ bubble formation further facilitates the low-cost manufacturing of PGAeros to support the pore gradient. PGAeros can exhibit robust mechanical and thermal stability (e.g., 0.040 W m -1 K -1and compressive strength of 100.56 MPa). For example, the full ceramic monolith properties of PGAeros can exhibit robust sound and fire insulation performance. The ceramic aerogel material can be manufactured at scale to demonstrate utility in thermal insulation applications, for example, with desirable thermal management, mechanical strength, low mass density, and sound and fire insulation performance.

[0012] In an aspect, the present disclosure provides a method of making a ceramic foam. The ceramic foam can be referred to as a ceramic aerogel or a ceramic aerogel-like foam (e.g., a silica aerogel-like foam). The ceramic foam can be a silica aerogel. The silica aerogel can be a silica aerogel thin film. The method is based on an in-situ production of a pore-forming gas reaction. The reaction can be performed in a sealed environment (e.g., the reaction can be performed at a pressure greater than ambient pressure). The ceramic foam can 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.

[0013] In various examples, a method for forming a ceramic foam: contacting (e.g., the contacting can be performed in a sealed environment such as a sealed container) one or more ceramic precursors (e.g., one or more silica 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, wherein the contacting results in the formation of an inert gas (e.g., carbon dioxide), and the formation of a ceramic foam (e.g., a silica aerogel). The ceramic foam (e.g., a silica aerogel) can be formed under hydrothermal conditions. The reactants (ceramic precursors, pore-forming gas forming additives, catalysts, and optional additives) can be added / contacted in any order. The reactants can be contacted in a single vessel. The ceramic foam (e.g., a silica aerogel) so formed can be subjected to ambient pressure drying (APD). In various examples, the method further includes post-foam formation modification of at least a portion of a surface of the ceramic foam (e.g., a silica aerogel). Advanced surface modification (e.g., trimethylchlorosilane treatment and / or carbon coating) can be used to build capillary action and superhydrophobicity. The method can be a continuous (e.g., roll-to-roll) method.

[0014] In an aspect, the present disclosure provides a ceramic foam. The ceramic foam can be a ceramic foam film. The ceramic foam can be referred to as a ceramic aerogel. The ceramic foam can be a silica aerogel. The silica aerogel can be a silica aerogel film. Non-limiting examples of ceramic foams are provided herein. Ceramic foam materials (e.g., ceramic foam composites) include ceramic foams. The ceramic foams comprise a matrix of ceramic material. The ceramic foams can be prepared by the methods of the present disclosure. The ceramic foams (e.g., silica aerogels) can have various forms. For example, the ceramic foams (e.g., silica aerogels) are monolithic pieces. In another example, the ceramic foams (e.g., silica aerogels) are thin films. The ceramic foams (e.g., silica aerogels) can be free-standing thin films or disposed on a substrate. The ceramic foams (e.g., silica aerogels) can be infiltrated into a substrate. The ceramic foams can be porous and exhibit a hierarchical gradient pore structure. The ceramic matrix of the ceramic foams can be mesoporous. The ceramic foam materials can be composites (e.g., composite ceramic foams, e.g., composite silica aerogels). The composites can include a polymeric material in some or all of the pores of the ceramic foams (which can be referred to as hybrid composites or hybrid ceramic foams). The ceramic foams can have desirable sound propagation / insulation / sound deadening properties. In one example, the ceramic foams are used as insulating materials (e.g., building materials and / or sound insulation materials). In various examples, the ceramic foams are used as a template or support substrate in catalyst, membrane, separation, etc. applications for coating other functional materials as composites. BRIEF DESCRIPTION OF DRAWINGS

[0015] For a more complete understanding of the nature and content of the application, reference should be made to the following detailed description taken in connection with the accompanying drawings in which:

[0016] Figure 1 An example showing the R2R process of the present disclosure in combination with in-situ APD manufacturing of low cost silica aerogels is shown.

[0017] Figure 2 Scanning electron microscope (SEM) images of an example of a silica aerogel of the present disclosure are shown.

[0018] Figure 3 SEM images of an example of a silica aerogel of the present disclosure are shown.

[0019] Figure 4 EDX images of an example of a silica aerogel of the present disclosure are shown.

[0020] Figure 5 EDX images of an example of a silica aerogel of the present disclosure are shown.

[0021] Figure 6 Thermal images of an example of a silica aerogel produced using the method described in Example 1 are shown.

[0022] Figure 7 Images showing examples of silica aerogels produced using the method described in Example 2, which were heated to demonstrate the flame retardant properties of the silica aerogels.

[0023] Figure 8 Images showing examples of silica aerogels of the present disclosure and images of carbon material coated silica aerogels of the present disclosure.

[0024] Figure 9 Images showing examples of silica aerogels produced using the method described in Example 2 (A is a white silica aerogel produced using TEOS as the silica precursor, B is a transparent silica aerogel produced using MTMS as the silica precursor) and images of white silica aerogels heat treated under different conditions (B, which is transparent) (C, 400 °C, 3 hours and D, 600 °C, 6 hours). Heat treatment was performed in a tube furnace.

[0025] Figure 10 Thermal conductivity data for examples of silica aerogels 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 / AT, where P / A is recorded by FluxTap, d is the sample thickness, and AT is calculated by subtraction of the two temperature sensor readings.

[0026] Figure 11 SEM images showing examples of white silica aerogels produced using the method described in Example 2 (and TEOS as the silica precursor). The images show the porous structure on the surface of the white silica aerogel.

[0027] Figure 12 SEM images showing examples of white silica aerogels produced using the method described in Example 2 (and TEOS as the silica precursor). The images show the porous structure on the side surface of the white silica aerogel.

[0028] Figure 13 SEM images showing examples of white silica aerogels produced using the method described in Example 2 (and TEOS as the silica precursor). The images show the porous structure on the surface of the white silica aerogel.

[0029] Figure 14 SEM images showing examples of white silica aerogels produced using the method described in Example 2 (and TEOS as the silica precursor). The images show the porous structure on the surface of the white silica aerogel. The porous structure contains smaller pores and larger pores.

[0030] Figure 15An SEM image of a white silica aerogel example produced using the method described in Example 2 (and TEOS as the silica precursor) is shown.

[0031] Figure 16 An SEM image of a transparent silica aerogel example produced using the method described in Example 2 (and MTMS as the silica precursor) is shown. The image shows the porous structure on the surface of the white silica aerogel.

[0032] Figure 17 An SEM image of a white silica aerogel example produced using the method described in Example 2 (and TEOS as the silica precursor) and heated at 400°C for 3 hours is shown. The image shows the porous structure on the surface of the white silica aerogel.

[0033] Figure 18 An image showing the mechanical testing of a silica aerogel sample of the application is shown.

[0034] Figure 19 Mechanical testing data for a white silica aerogel example produced using the method described in Example 2 (and TEOS as the silica precursor) is shown. The Young's modulus of this material was 7.6054 MPa.

[0035] Figure 20 Porosity data for a white silica aerogel example produced using the method described in Example 2 (and TEOS as the silica precursor) obtained using a pycnometer is shown. The porosity of this material was 89.587%.

[0036] Figure 21 Porosity data for a transparent silica aerogel example produced using the method described in Example 2 (and MTMS as the silica precursor) obtained using a pycnometer is shown. The porosity of this material was 83.925%.

[0037] Figure 22 An image of a white silica aerogel example produced using the method described in Example 2 (and TEOS as the silica precursor) is shown, heated to 2000°C to demonstrate the fire resistant properties of the silica aerogel.

[0038] Figure 23a) Schematic representation of the synthesis process of silica PGAeros, which comprises the following three steps: 1. CTAB-assisted micelle formation in aqueous urea solution, 2. TEOS hydrolysis at the CTAB micelle interface, 3. Urea decomposition and release of NH3 and CO2; b) Optical image of a typical silica foam with a diameter of 6 cm; c) Polished silica PGAero sample with a thickness of 0.6 cm; d) Typical SEM image of silica PGAeros, showing the presence of a clear pore gradient, the inset shows the increasing average pore diameter from the bottom to the top; e, f) High resolution SEM images, where e) corresponds to the top and f) to the bottom region in d); g) Low resolution TEM image and high resolution TEM image of a particle from the PGAeros silica network. Figure 23

[0039] Figure 24 SEM images of silica PGAeros are shown and the reaction time is a) 48 h (hours); and b) 72 hours, the inset shows the corresponding size distribution of the pores; c) Thermal conductivity of silica PGAeros synthesized at different reaction times.

[0040] Figure 25 SEM images of silica PGAeros synthesized by varying the amount of precursor (referred to as PGAero-1, 5, 6, 7, 8 and 9, respectively) are shown; g) Thermal conductivity of the PGAeros series, depending on the average pore diameter and porosity.

[0041] Figure 26 Mechanical properties of silica PGAero before and after annealing treatment at 400 °C are shown, the inset shows SEM images before (top) and after (bottom) annealing; b) Schematic representation showing the reduced heat and sound through the gradient structure of silica PGAero; c) Soundproofing performance of silica PGAero compared to polyurethane, Kevlar and two different types of ceramic fiber mats from Unifrax (Ceramic fiber 1: PC Max 2000i, Ceramic fiber 2: Saffil alumina) at acoustic frequencies from 500 Hz to 1800 Hz; d) Soundproofing performance of silica PGAero and reference sample polystyrene foam at a frequency of 2000 Hz; e) Soundproofing performance plot of sound intensity and sound reduction coefficient at frequencies of 500 Hz, 800 Hz and 2000 Hz.

[0042] Figure 27 Large scale SEM images and magnified SEM images of the PGAero-2 sample are shown.

[0043] Figure 28 Variation of porosity with reaction time is shown.

[0044] ​Figure 29 Tuning details of samples PGAero-1, PGAero-5-10 are shown.

[0045] Figure 30 Average pore size distribution of a-g) samples PGAero-1, PGAero-5- PGAero-10 are shown.

[0046] Figure 31 Photos of a, b) mechanical testing are shown.

[0047] Figure 32 a) Stress strain curve of original sample PGAero-1 at 6 lbs; b) Stress strain curve of original sample compressed to failure; c) Stress strain curve of 400°C annealed sample at 20 lbs are shown.

[0048] Figure 33 Photos of samples annealed at 1000°C for 24 hours are shown.

[0049] Figure 34 Sound intensity difference of blank, polystyrene foam and silica PGAero at 20 Hz to 5000 Hz frequency is shown.

[0050] Figure 35 Sound intensity difference at 500 Hz and 800 Hz is shown.

[0051] Figure 36 Humidity aging cycle measurements of 60% and 80% of silica foam are shown.

[0052] Figure 37 Schematic diagrams showing changes in opaque and transparent phases with increasing surfactant concentration are shown. a) For surfactant CTAB, as the hydrophilic particles are in the majority in the precursor, the opaque phase gradually increases with increasing CTAB concentration; b) For surfactant SDS, as the hydrophobic particles are in the majority in the precursor, the transparent phase gradually increases with increasing SDS concentration; c) The micelle formation of SDS changes with increasing SDS concentration. The formation of micelles becomes more ordered and the individual micellar particles become smaller with increasing SDS concentration.

[0053] Figure 38 a) Optical image of the gel fraction; b, c) SEM and TEM show the microstructure of the gel fraction; d) Changes in gel fraction density and porosity with SDS concentration; e) Thermal conductivity as a function of average pore size and density; f) BET results showing the gel fraction are shown.

[0054] Figure 39a, b, c) SEM images showing the structure of the white part changes from open to closed cells; d) Optical image of the white part; e) Density and porosity as a function of SDS concentration. f) Thermal conductivity as a function of density, average pore size.

[0055] Figure 40 a) Strain stress curves showing high mechanical strength, which decreases with increasing SDS concentration; b) Young's modulus decreases with increasing density due to increasing SDS concentration; c) Optical images of 3.33% SDS sample before and after mechanical compression test.

[0056] Figure 41 a) Sound insulation performance of different concentrations of SDS at high acoustic frequencies from 3000 Hz to 8500 Hz; b) Sound insulation performance of different concentrations of SDS at 500 Hz acoustic frequency; c) Sound insulation performance of different concentrations of SDS at 800 Hz acoustic frequency.

[0057] DETAILED DESCRIPTION OF THE DISCLOSURE

[0058] Although the claimed subject matter will be described in terms of certain embodiments and examples, other embodiments and examples (including embodiments and examples that do not provide all of the benefits and features set forth herein) are also within the scope of the claims. Various structural, logic, and process steps can be performed in a different order, or omitted, without departing from the scope of the claims.

[0059] Ranges of values are disclosed herein. These ranges are given as a smallest minimum value and a largest maximum value. Unless otherwise stated, the range includes all values between the minimum and maximum values, in increments of the smallest minimum or maximum value.

[0060] As used herein, unless otherwise indicated, the term “group” refers to a chemical entity that can be covalently bonded to one end or two or more ends of other chemical species. Examples of groups include, but are not limited to:

[0061]

[0062] The term “group” includes radicals.

[0063] As used herein, unless otherwise indicated, the term “alkyl” refers to branched or unbranched saturated hydrocarbon groups. 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 C1 to C5 (e.g., C1 alkyl, C2 alkyl, C3 alkyl, C4 alkyl, or C5 alkyl). An alkyl group can be unsubstituted or substituted with one or more substituents. Examples of substituents include, but are not limited to: halogen (-F, -Cl, -Br, and -I), aliphatic groups (e.g., alkyl, alkenyl, and alkynyl), aryl, alkoxy, carboxylate groups, carboxylic acids, ether groups, and the like, as well as combinations thereof.

[0064] As used herein, unless otherwise indicated, the term "alkoxy" refers to a -OR group, wherein R is an alkyl group as defined herein. Alkoxy groups include, but are not limited to, methoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy, isobutoxy, sec-butoxy, and the like. In an example, alkoxy groups include C1-C5 alkyl groups.

[0065] The present disclosure provides a ceramic foam. The present disclosure also provides a method of making a ceramic foam and uses of the ceramic foam.

[0066] In the present disclosure, in various examples, scalable ceramic aerogels (e.g., pore- gradient ceramic aerogels, which can be referred to as ceramic foams), monoliths (e.g., PGAeros) are designed and synthesized. In-situ bubble formation facilitates low-cost manufacturing of PGAeros, which can support a pore gradient. PGAeros can exhibit robust mechanical and thermal stability (e.g., 0.040 W m -1 K -1 , and compressive strength of 100.56 MPa). For example, the integral ceramic monolith properties of PGAeros can exhibit robust sound and fire insulation performance. The scalable manufacturing of this ceramic aerogel material demonstrates can be used for thermal insulation applications, for example, with one or more of ideal thermal management, mechanical strength, low mass density, sound insulation, and fire resistance performance.

[0067] In various examples, the present disclosure provides ceramic aerogel chemistry processes related to reactions in a sealed environment (e.g., reactions under reaction conditions higher than ambient pressure) and in-situ ambient pressure drying. The method can produce a ceramic aerogel with a graded pore gradient.

[0068] In various examples, the present disclosure also provides surface modification of the ceramic foam. The surface modification described herein can provide a ceramic foam material with capillary action and reduced radiative component of thermal conductivity: for example, supercritical drying-induced hydroxyl (-OH) groups (~5 OH / nm 2 ) are replaced with methyl (-CH3) and / or carbon material coatings to reduce capillary pressure and energy radiative transport. In various examples, the surface modification is a moisture-resistant and / or fire-resistant surface modification. The surface modification can form a fractal superhydrophobic network. In one example, nanocrystal deposition on a silicon oxide framework results in smaller pore diameters, stronger mechanical integrity, higher moisture resistance and fire resistance, and lower thermal conductivity.

[0069] In one example, it is contemplated that the combination of ceramic foam (e.g., silica aerogel) chemistry, in-situ ambient pressure drying, and roll-to-roll (R2R) manufacturing can provide a continuous, low-cost manufacturing (about 90% reduction), high R-value, and high durability ceramic foam (e.g., silica aerogel-based) building insulation material. Thus, for example, it is contemplated that the combined silica aerogel chemistry, in-situ ambient pressure drying, and roll-to-roll (R2R) manufacturing can be used for continuous manufacturing of a low-cost (about 90% reduction), high R-value, and high durability silica aerogel building insulation material. It is believed that existing manufacturing processes can be retrofitted to enable low-cost, continuous production (e.g., rapid prototyping) of ceramic foam (e.g., silica aerogel-based foam) sheets while maintaining the desirable thermal insulation properties of silica aerogels. Thus, it is believed that existing R2R manufacturing processes can be retrofitted to enable low-cost, continuous production (e.g., rapid prototyping) of silica aerogel sheets while maintaining the desirable thermal insulation properties of silica aerogels. For example, a method of producing a low-cost silica aerogel insulation material is shown in FIG. 1. Figure 1 ) The method combines the following operations: 1) R2R manufacturing, which can improve production efficiency; 2) in-situ ambient pressure drying (APD), which can control aerogel cost; and 3) surface modification to improve R-value and durability.

[0070] In the present disclosure, in various examples, a silica aerogel chemistry is combined with in-situ ambient pressure drying. These methods can replace the existing supercritical extraction step (a complex process that employs low surface tension organic solvents and high pressure supercritical drying) by using ambient pressure (e.g., drying by using in-situ generated pore-supporting gas bubbles (e.g., carbon dioxide, ammonia, etc.)). For example, the methods described herein can significantly reduce one or more or all of energy input, time, and cost to produce a silica aerogel, e.g., a silica aerogel having a controlled porosity and a pore size of less than 60 nm.

[0071] For example, R2R rapid prototyping manufacturing of a low-cost water-based APD silica aerogel followed by continuous surface modification is contemplated to enable smaller pore sizes (<60 nm to minimize the gaseous component of thermal conductivity), enhanced durability (mechanical strength, moisture resistance, and fire resistance), and increased infrared radiation absorption (to minimize the radiative component of thermal conductivity). The benefit of using R2R manufacturing of an aqueous gel is that continuous operation under ambient conditions can enable a scalable, low-cost, durable, and rapid prototyping of insulation material synthesis and installation.

[0072] In various embodiments, the present disclosure provides the following features: 1) low cost and scalable aqueous aerogel synthesis (using, for example, tetraethoxysilane, CTAB, and urea to produce silica aerogels) and in-situ pore support enabling APD to significantly reduce energy, time, and cost of silica aerogel production; 2) surface modification to control pore size, reduce capillary action, suppress radiative heat transfer, and meet durability requirements (regarding fire, structural, moisture, and acoustic mode degradation); and 3) low cost and robust installation enabled by R2R continuous manufacturing for rapid prototyping, enabling simpler installation.

[0073] In various examples, the present disclosure provides a method of producing aerogel materials that can avoid expensive chemical processing steps and can avoid any supercritical extraction process in case of fragile materials. The instant method is based on in-situ APD of silica aerogels enabled by addition of, for example, sodium bicarbonate, which generates in-situ pore-supporting carbon dioxide to significantly reduce energy, time, and cost of silica aerogel production.

[0074] The method can utilize near room temperature and ambient pressure processing to reduce the cost of synthesis of silica aerogels. Rapid prototyping of shape and size customized aerogel products enabled by R2R manufacturing can further reduce installation costs. For example, incorporation of elemental carbon in silica aerogels can effectively suppress radiative heat transfer. For example, additional C addition to aerogels to reduce thermal conductivity from 0.016 to 0.0135 W / mK at ambient pressure.

[0075] In an aspect, the present disclosure provides a method of making a ceramic foam. The ceramic foam can be referred to as a ceramic aerogel or a ceramic aerogel-like foam (e.g., a silica aerogel-like foam). The ceramic foam can be a silica aerogel. The silica aerogel can be a silica aerogel thin film. The method is based on an in-situ pore-forming gas reaction. The reaction can be performed in a sealed environment (e.g., the reaction can be performed at a pressure greater than ambient pressure). The ceramic foam can 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.

[0076] In various examples, a method for forming a ceramic foam: contacting (e.g., can be a reaction mixture in a sealed environment, which can be a sealed vessel) 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, wherein the contacting results in the formation of an inert gas (e.g., carbon dioxide) and a ceramic foam. The ceramic foam can be formed under hydrothermal conditions. The reactants (ceramic precursors, pore-forming gas-forming additives, catalysts, and optional additives) can be added or contacted in any order. The reactants can be contacted in a single vessel.

[0077] In various examples, a method for forming a silica aerogel includes: contacting (e.g., as a reaction mixture) one or more silica 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, wherein the contacting results in the formation of an inert gas (e.g., carbon dioxide) and a silica aerogel. The silica aerogel can be formed under hydrothermal conditions. The reactants (silica precursors, pore-forming gas-forming additives, catalysts, and optional additives) can be added / contacted in any order. The reactants can be contacted in a single vessel.

[0078] The reaction can be performed in a sealed environment. The reaction can be performed in a sealed vessel or a sealed mold. As an illustrative, non-limiting example, the reaction is performed in an autoclave. The pressure in the vessel can be autogenic (e.g., resulting from the closed nature of the vessel and the state of the reactants) or the pressure can be increased from the outside, e.g., by pressurizing the sealed vessel to the desired pressure (e.g., 1 to 100 psi, including all values in increments of 0.1 psi therebetween and ranges therebetween). The vessel can be pressurized by the addition of an exogenous gas (e.g., an inert gas, such as argon, nitrogen, etc., and combinations thereof).

[0079] 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 container: TEOS, MTMS, or a combination of silica precursors (e.g., 57 mL TEOS or MTMS or TEOS:MTMS = 1 :3 to 3: 1 mixture); urea (e.g., 33.33 g) as a pore forming gas forming additive (inert gas generator); acetic acid as a catalyst, which can be in the form of an aqueous solution (e.g., 100 mL of a 1 mmol / L solution); and CTAB or SDS (e.g., 3.33 g) surfactant additive, wherein the contacting results in formation of an inert gas (e.g., carbon dioxide, ammonia, etc.) and a silica aerogel-like foam. In various examples, one or more or all of the values in this example vary by up to 5% (inclusive), or up to 10% (inclusive). In various examples, one or more additional additives are contacted (e.g., included in the reaction mixture).

[0080] In one example, a method for forming a silica aerogel includes contacting (e.g., in a reaction mixture) TEOS, MTMS, or a combination of silica precursors (e.g., 57 mL TEOS or MTMS or TEOS:MTMS = 1 :3 to 3: 1 mixture); urea (e.g., 33.33 g) as a pore forming gas forming additive (inert gas generator); acetic acid as a catalyst, which can be in the form of an aqueous solution (e.g., 100 mL of a 1 mmol / L solution); and CTAB (e.g., 3.33 g) as an additive, wherein the contacting results in formation of an inert gas (e.g., carbon dioxide, ammonia, etc.) and a silica aerogel. In various examples, one or more or all of the values in this example vary by up to 5% (inclusive), or up to 10% (inclusive). In various examples, one or more additional additives are contacted (e.g., included in the reaction mixture).

[0081] Various ceramic precursors are used. The precursor can 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 combinations thereof. In various examples, silica precursors are 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 alkoxyalkyltrialkoxysilanes), sodium metasilicate (e.g., water glass), alkyl groups, and combinations thereof. In various examples, alumina precursors are selected from: aluminum alkoxides (e.g., C1 to C6 aluminum alkoxides), tris(β-hydroxy)ethylamine condensed aluminum hydroxide (alumatrane), or tris(alumatranyloxy-i-propyl)amine, etc., and combinations thereof. In various examples, the transition metal oxide precursor is selected from: transition metal alkoxides (e.g., those having the formula M(OR)). x Transition metal alkoxides, wherein M is a transition metal (e.g., Al, Ti (e.g., titanium(IV)-isopropoxide, etc.), Zr, W, Cr, Mo, etc.), and each R is an alkyl group, and x is, for example, 1, 2, 3, 4, or 5, etc. Transition metals can have various oxidation states (e.g., + 1. + 2. + 3. + 4 or + 5).

[0082] In one example, water glass can be used as a silica precursor (e.g., alone or in combination with one or more other silica precursors). Water glass is also known as sodium silicate or soluble glass. In one example, water glass is a material containing sodium oxide (Na₂O) and silica (e.g., silicon dioxide, SiO₂, etc.) that forms a glassy solid.

[0083] Combinations of ceramic precursors can be used. For example, binary, ternary, and higher-order ordered mixed oxide ceramic foams can be prepared using precursor mixtures. As an illustrative example, mixed oxide ceramic foams, such as those with a nominal composition corresponding to the desired ratio of Al2O3 to TiO2, can be prepared using a combination of one or more Al2O3 sol-gel precursors (e.g., tris(β-hydroxy)ethylamine condensed aluminum hydroxide, tris(aluminatricyclooxyisopropyl)amine, or combinations thereof) and TiO2 sol-gel precursors (e.g., titanium(IV) isopropoxide, etc.). Those skilled in the art will understand that ceramic foams with the desired nominal composition can be formed by selecting appropriate ceramic precursors and / or relative amounts of the precursors.

[0084] After the ceramic foam is formed, the ceramic foam can be sintered. For example, the ceramic foam is sintered at a temperature of 200 °C to 800 °C (e.g., 350 °C to 450 °C, or about 400 °C) (including all values in between that are 0.1 °C apart and ranges in between). The ceramic foam can be sintered under air and / or ambient pressure (e.g., 1 atm). Without being bound to any particular theory, it is believed that sintering can improve the properties of the ceramic foam. The improvement can result from carbonization of residual organic residues, if present.

[0085] In various examples, the method further includes post-formation modification of at least a portion of a surface of the ceramic foam (e.g., silica aerogel). One example of post-formation modification of the ceramic foam is forming a layer of carbon-containing material on at least a portion of a surface of the ceramic foam (e.g., all of one surface, or all of all surfaces, of the ceramic foam). The carbon-containing material can provide a superhydrophobic outer surface. For example, a carbon soot coating is formed by burning a candle underneath a sample of the ceramic foam to achieve a carbon soot coating or by post-thermal annealing.

[0086] Advanced surface modification, including trimethylchlorosilane treatment and carbon coating, can be used to build capillary action and superhydrophobicity. This is achieved by replacing surface hydroxyl groups with methyl groups through the formation of (CH3)3-Si-Si-O≡ on the silica gel surface, followed by a continuous carbon material coating. These modification steps control the pore size and surface chemistry to achieve the desired thermal insulation performance and durability.

[0087] For example, trimethylchlorosilane ((CH3)3SiCl) in combination with a continuous carbon material coating can meet the goals of surface modification by forming a methyl and nanocrystalline carbon coating to reduce capillary action and radiative transfer mode heat transfer at higher temperatures. The surface modified silica will result in smaller pore size, stronger mechanical integrity, higher moisture and fire resistance, and lower thermal conductivity.

[0088] As another example of post-formation modification of the ceramic foam, it includes painting or coating at least a portion of a surface or all of the surfaces of the ceramic foam with nanoparticle.

[0089] The method can be a continuous method. For example, the method is a roll-to-roll continuous manufacturing method. R2R is capable of forming near-net shape manufacturing and size customized ceramic foams on, for example, low cost and high thermal insulation inorganic paper substrate carriers.

[0090] Using roll-to-roll continuous manufacturing, it is contemplated to use, for example, tetraethoxysilane or waterglass silica gel precursors and R2R manufacturing processes that are capable of forming near-net shape manufacturing and size customized ceramic foams on, for example, inorganic ceramic fiber paper substrate carriers (Unifrax’s Nextel® paper substrate carrier ) to be formed at low cost, resulting in a desirable cost of the silica aerogel material.

[0091] The methods of the present disclosure can include a thermal annealing step. The thermal annealing step can be performed after the ceramic foam (e.g., silica aerogel) is formed, washed, dried, etc. For example, the thermal annealing is the last step in the preparation of the ceramic foam (e.g., silica aerogel). In various examples, the thermal annealing is performed at 300 °C to 600 °C, including all integer °C values therebetween and ranges therebetween, and can be performed for different lengths of time (e.g., 1 hour to 6 hours, including all integer minute values therebetween and ranges therebetween).

[0092] The ceramic network (e.g., silica network, alumina network, aluminosilicate network, transition metal oxide network, or combinations thereof) of the ceramic aerogel can be referred to as a ceramic matrix, can include ceramic nanoparticles (e.g., silica nanoparticles) (e.g., 20 to 200 nm in size (e.g., 150 to 200 nm or about 200 nm), which can be a maximum or minimum dimension size, including all integer nanometer values therebetween and ranges therebetween; or 20 to 200 nm in average size (e.g., 150 to 200 nm or about 200 nm), which can be an average size of a maximum or minimum dimension, including all integer nanometer values therebetween and ranges therebetween) can be formed in the presence of a pore-forming gas. The ceramic nanoparticles can have a narrow size distribution, and 90% or more, 95% or more, 99% or more, or all of the ceramic nanoparticles have a size and / or average size of 20 to 200 nm (e.g., 150 to 200 or about 200 nm), including all integer nanometer values therebetween and ranges therebetween. The pore-forming gas can be produced in the presence of a ceramic precursor (e.g., the pore-forming gas is produced during the formation of the silica network). In one example, substantially all of the ceramic matrix formation (e.g., silica matrix) is completed in the presence of the pore-forming gas. Substantially all of the ceramic matrix formation means that no additional processing is needed to form the ceramic matrix (e.g., silica matrix) of the ceramic foam (e.g., silica aerogel). In various examples, 50% or more, 60% or more, 70% or more, 80% or more of the silica precursor is reacted in the presence of the pore-forming gas.

[0093] In an aspect, the present disclosure provides a ceramic foam. The ceramic foam can be a ceramic foam film. The ceramic foam can be referred to as a ceramic aerogel. The ceramic foam can be a silica aerogel. The silica aerogel can be a silica aerogel film. Non-limiting examples of ceramic foams are provided herein. Ceramic foam materials (e.g., ceramic foam composites) include the ceramic foams. The ceramic foams include a matrix of a ceramic material. The ceramic foams can be prepared by the methods of the present disclosure.

[0094] The ceramic foam can be an oxide. Non-limiting examples of oxides include: oxides of silicon (e.g., silicon oxide), aluminum oxide (alumina), transition metal oxides, and the like, and combinations thereof. The ceramic foam can be stoichiometric or non-stoichiometric.

[0095] The ceramic foam can be a mixture of oxides. The ceramic foam can be a binary oxide, a ternary oxide, or a more multi-component oxide system. Non-limiting illustrative examples of ceramic foams include: aluminosilicate foams, titania-alumina foams, and the like.

[0096] In an example, the ceramic foam and / or the ceramic foam material does not have any fluorine atoms (e.g., detectable by any conventional method known in the art). The fluorine atoms can be fluorine atoms bonded to silicon atoms (e.g., -Si-F).

[0097] The ceramic foam (e.g., silicon oxide aerogel) can have various forms. For example, the ceramic foam (e.g., silicon oxide aerogel) is a monolith. In another example, the ceramic foam (e.g., silicon oxide aerogel) is a thin film. The ceramic foam (e.g., silicon oxide aerogel) thin film can be a free-standing thin film or disposed on a substrate. The ceramic foam (e.g., silicon oxide aerogel) thin film can be infiltrated into the substrate.

[0098] The ceramic foam is porous and can exhibit a hierarchical pore gradient structure. The ceramic foam can be described as including hierarchical hollow structures with micropores (which can be referred to as macropores) as the interior (e.g., voids in the ceramic matrix) and mesopores within the shell (e.g., the matrix). At least some or all of the pores can be interconnected. The pores can be mesopores and / or macropores. The pores can be mesopores as defined by IUPAC.

[0099] The pores of the ceramic foam can be referred to as micropores or macropores and not mesopores of the ceramic matrix, which can have various sizes. For example, the size (e.g., average size and / or 90%, 95%, 99%, 99.9%, or 100%) of the pores is 500 micrometers to 1 micrometer, including all values and ranges therebetween in increments of 0.1 micrometers. The size can be at least one dimension (e.g., diameter) as measured in a plane parallel to the pore axis. For example, the size of the pores (e.g., at least one dimension (e.g., diameter) as measured in a plane parallel to the pore axis and / or at least one dimension (e.g., height) as measured in a plane perpendicular to the pore axis) is 500 micrometers to 1 micrometer (e.g., 200 micrometers to 10 micrometers, 200 micrometers to 1 micrometer, or 100 micrometers to 1 micrometer). The size of the pores decreases or increases generally along a dimension moving from a first surface of the ceramic foam to a second surface opposite the first surface. The gradient can be a linear gradient or a non-linear gradient.

[0100] The ceramic matrix of the ceramic foam can be mesoporous (e.g., include mesopores, which can be mesopores as defined by IUPAC). For example, the ceramic matrix has 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 therebetween and ranges therebetween. For example, the ceramic matrix has 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 therebetween and ranges therebetween. The pore size distribution can be multimodal, e.g., bimodal. For example, the ceramic matrix has a plurality of pores having 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 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).

[0101] 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 is determined using BET analysis.

[0102] The silica aerogel is porous. For example, the silica aerogel has 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 therebetween and ranges therebetween. For example, the silica aerogel has 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 therebetween and ranges therebetween. The particle size distribution can be bimodal. For example, the silica aerogel has a plurality of pores having 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 can be bimodal) and 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). 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 is determined using BET analysis.

[0103] The ceramic foam material can be a composite material (e.g., a composite ceramic foam, e.g., a composite silica aerogel). The composite material can include a polymeric material in some or all of the pores of the ceramic foam (which can be referred to as a hybrid composite material or a hybrid ceramic foam). The polymer can be formed by in-situ polymerization in the ceramic foam. Additionally or alternatively, the composite material can include a carbon coating on the ceramic foam, which can be referred to as a ceramic-carbon aerogel. For example, the ceramic foam (e.g., a ceramic foam monolith or a ceramic foam film) is at least partially (or entirely) coated with a carbon material.

[0104] The silica aerogel material can be a composite material (which can be referred to as a silica-carbon aerogel) including a silica aerogel (e.g., a silica aerogel monolith or a silica aerogel film) at least partially (or entirely) coated with a carbon material.

[0105] The building insulation material can include a ceramic foam (e.g., a silica aerogel) of the present disclosure (e.g., a ceramic foam, e.g., a silica aerogel) made by the method of the present invention.

[0106] Table 1: Cost, thermal insulation, and mechanical properties of silica-carbon aerogels

[0107]

[0108] 4 https: / / www.saylor.org / site / wp-content / uploads / 2011 / 04 / Thermal_conductivity.pdf

[0109] It is expected that the method of the present disclosure will provide a low cost building insulation material. It is expected that the method of the present disclosure will provide inexpensive mass production and installation of high R-value building insulation materials (ceramic foams, e.g., silica aerogels) that can impact a wide range of building envelope applications, e.g., roofs and walls of existing buildings and future buildings. For example, by replacing supercritical dried ceramic foams (e.g., silica aerogels) with the ceramic foams (e.g., silica aerogels) of the present disclosure in building insulation applications, it is expected that the cost of building insulation materials will be reduced by 50% or more. The cost is expected to be reduced by 90% or more relative to current technology by 2028 (Source: McKinsey & Company, Building a better grid, July 2018). In addition, the building energy efficiency of the insulating material having the ceramic foam of the present disclosure is expected to be at least 45%. The insulating material having the ceramic foam of the present disclosure can have an R-value and thermal conductivity at room temperature comparable to commercially available ceramic foams. However, the insulating material having the ceramic foam of the present disclosure (e.g., silica aerogel) can have an increased R-value at high temperatures (e.g., relative to commercially available ceramic, and can significantly reduce the cost per unit). The complex processing involved in the preparation of ceramic foams by conventional high-pressure supercritical drying processes and volatile organic solvents make the cost of using such ceramic foams prohibitive for building insulating material manufacturers.

[0110] The building insulating material can be a thermal insulating sheet. The thermal insulating sheet can be used for commercial or residential applications. The thermal insulating sheet can be formed using a R2R production method. The thermal insulating sheet can be used for existing building retrofit. In various examples, the thermal insulating sheet comprising the ceramic foam of the present disclosure (e.g., silica aerogel) is an R15 / inch thermal insulating sheet, which can have a thermal conductivity of 0.01 W / mK or less.

[0111] In an example, the ceramic foam (e.g., silica aerogel) is formed using TEOS and is white. In another example, the ceramic foam (e.g., silica aerogel) is formed using MTMS and desirably exhibits transparency. For example, the ceramic foam (e.g., silica aerogel) formed using MTMS exhibits a visible wavelength (e.g., 400-800 nm light wavelength, e.g., 530 nm) transmittance of 85% or more, 90% or more, 95% or more, or 98% or more (e.g., measured at a sample thickness of 2-3 mm, e.g., 2.7 mm). In another example, the ceramic foam (e.g., silica aerogel) is formed using TEOS and MTMS and has one or more white domains and one or more transparent domains (e.g., exhibits a visible wavelength (e.g., 400-800 nm light wavelength) transmittance of 90% or more, 95% or more, or 98% or more).

[0112] In an example, the ceramic foam or ceramic foam material (e.g., silica aerogel or silica aerogel material) does not comprise any extrinsic material (e.g., any detectable extrinsic material, which can be detected by conventional methods known in the art). Extrinsic materials include, but are not limited to, materials used to form the building material from the silica material (e.g., ceramic foam material). Non-limiting examples of extrinsic materials include adhesives (polymeric adhesives), polymers, and the like.

[0113] The ceramic foam (e.g., silica aerogel) can have desirable properties. For example, the ceramic foam (e.g., silica aerogel) can have a Young's modulus of 2 to 100 MPa (e.g., 2 to 8 MPa), including all integer MPa values therebetween and ranges therebetween.

[0114] The ceramic foam can have desirable sound propagation / sound insulation / sound deadening properties. In various examples, the ceramic foam has at least 10%, at least 15%, at least 20%, or at least 25% improvement in sound insulation (e.g., increase in sound reduction coefficient) in one or more, substantially all, or all frequencies from 500 to 2000 Hz relative to another material (e.g., an organic polymer foam, such as a PS foam, a PU foam, etc., or a ceramic fiber, etc.) of a given thickness. In another example, a silica aerogel-like foam (e.g., Silica PGAeros) having a thickness of 0.014 m has better sound insulation performance than a reference sample of PS foam at different frequencies of 500 Hz, 800 Hz, and 2000 Hz, showing a noise reduction of 10.9%, 12.0%, and 28.4%, respectively.

[0115] In an example, the silica aerogel and / or the silica aerogel material does not have any fluorine atoms (e.g., detectable by any conventional method known in the art). The fluorine atom can be a fluorine atom bonded to a silicon atom (e.g., -Si-F).

[0116] In an aspect, the present disclosure provides uses of the ceramic foam of the present disclosure. The ceramic foam can be used in various applications. The ceramic foam can be or provide a super insulating material. For example, the material can have a thermal conductivity of 0.01 W / mK or less.

[0117] In an example, the ceramic foam is used as an insulating material (e.g., a building material or a sound insulating material). The insulating material can exhibit desirable thermal management and / or sound insulation properties.

[0118] In an example, the ceramic foam is used as a template or support substrate in catalyst, membrane, separation, etc. applications for coating other functional materials as a composite material.

[0119] The steps of the methods described in the various embodiments and examples disclosed herein are sufficient to carry out the methods of the present disclosure. Thus, in an example, the method consists essentially of a combination of the steps of the methods disclosed herein. In another example, the method consists of these steps.

[0120] The following statements provide examples of the ceramic foam of the present disclosure, the methods of making the ceramic foam, and the uses of the ceramic foam:

[0121] Statement 1. A method for forming a ceramic foam (e.g., a hierarchical pore gradient ceramic foam) (e.g., a silica aerogel), the method comprising: contacting (e.g., in a reaction mixture) in a sealed environment (e.g., a sealed reaction vessel):

[0122] a ceramic precursor (e.g., a silica precursor) (e.g., one or more ceramic precursors) (e.g., a silica precursor); a pore-forming gas forming additive (an inert gas generator) (e.g., one or more pore-forming gas forming additives); a catalyst (one or more catalysts); and optionally an additive (e.g., 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 hierarchical pore gradient ceramic foam (e.g., a silica aerogel) is formed. For example, the hierarchical pore gradient ceramic foam is a thin film or a monolith. The method can comprise a sintering step, wherein the hierarchical pore gradient ceramic foam is sintered.

[0123] Statement 2. The method of Statement 1, wherein the contacting is performed at an initial pressure of 1-100 psi (e.g., the reaction vessel is pressurized to 1-100 psi, including all values of 0.1 psi difference therebetween and ranges therebetween) before the one or more ceramic precursors and / or the one or more pore-forming gas forming additives and / or the one or more additives (if present) react in mass (e.g., 5%, 1%, or 0.1% of the reaction occurs).

[0124] Statement 3. The method of Statement 1 or 2, wherein the one or more ceramic precursors are selected from the group consisting of a silica precursor, an alumina precursor, a transition metal oxide precursor, and combinations thereof.

[0125] Statement 4. The method of Statement 3, wherein the silica precursor is selected from the group consisting of: a tetraalkoxysilane (e.g., TMOS, TEOS, etc.) (e.g., a C1-C5 alkoxy tetraalkoxysilane), an alkyltrialkoxysilane (e.g., methyltrimethoxysilane (MTMS), etc.) (e.g., a C1-C5 alkyl, C1-C5 alkoxy alkyltrialkoxysilane), sodium metasilicate (e.g., water glass), alkyls, and combinations thereof.

[0126] Statement 5. The method of Statement 3 or 4, wherein the alumina precursor is selected from the group consisting of: an aluminum alkoxide (e.g., a C1 to C6 aluminum alkoxide), a tris(beta-hydroxy)ethylamine condensate aluminum hydroxide (alumatrane), or a tris(heteroaluminum tricyclic oxyisopropyl)amine (tris(alumatranyloxy-i-propyl)amine), etc., and combinations thereof.

[0127] Statement 6. The method of Statement 3 or 4, wherein the transition metal oxide precursor is selected from the group consisting of: a transition metal alkoxide (e.g., a transition metal alkoxide having the formula M(OR) x wherein M is a transition metal (e.g., Al, Ti (e.g., titanium (IV)-isopropoxide, etc.), Zr, W, Cr, Mo, etc.), and each R is independently an alkyl group, and x is 1, 2, 3, 4, or 5), etc. The transition metal can have various oxidation states (e.g., + 1, + 2, + 3, + 4, or + 5).

[0128] Statement 7. The method of any of the preceding Statements, wherein the one or more catalysts is a basic catalyst (e.g., ammonia, ammonium fluoride, ammonium hydroxide, urea, cetyltrimethylammonium bromide, etc., and combinations thereof).

[0129] Statement 8. The method of any of Statements 1-6, wherein the catalyst is an acidic catalyst (e.g., a protic acid (e.g., acetic acid, etc.), a hydrogen halide acid, etc., and combinations thereof).

[0130] Statement 9. The method of any of the preceding Statements, wherein the one or more pore-forming gas forming additives (inert gas generators) is selected from the group consisting of: sodium bicarbonate, urea, and combinations thereof (e.g., wherein the pore-forming gas forming additives (inert gas generators) provide a subcritical amount (e.g., pressure) of inert gas). The pore-forming gas (inert gas) can be carbon dioxide and / or nitrogen and / or ammonia.

[0131] Statement 10. The method of any of the preceding Statements, wherein the one or more additives is selected from the group consisting of a surfactant (e.g., cetyltrimethylammonium bromide (CTAB)), urea, and combinations thereof. The surfactant can aid in pore formation. The surfactant can also provide surface functionalization.

[0132] Statement 11. The method of any of the preceding Statements, wherein the one or more ceramic precursors (e.g., silica precursors), the one or more pore-forming gas forming additives (inert gas generators), and optionally the one or more additives are contacted prior to contacting the catalyst with the one or more ceramic precursors (e.g., silica precursors), the one or more pore-forming gas forming additives (inert gas generators), and optionally the one or more additives.

[0133] Statement 12. The method of any of the preceding Statements, wherein the contacting comprises mixing one or more ceramic precursors (e.g., silica precursors) that are disposed (e.g., dissolved) in water, a solvent (e.g., an alcohol, e.g., ethanol), or a combination thereof; one or more pore-forming gas forming additives (inert gas generators) that are disposed (e.g., dissolved) in water; one or more catalysts that are disposed (e.g., dissolved) in water. The ceramic precursors, inert gas generators, catalysts, and optional additives can be combined in any order. In an example, the catalyst is the last component added.

[0134] Statement 13. The method of any of the preceding Statements, wherein the one or more ceramic precursors (e.g., silica precursors) are present at 2 to 10 wt% each (based on the total weight of the ceramic precursors (e.g., silica precursors), catalysts, pore-forming gas forming additives, and additives (if present)).

[0135] Statement 14. The method of any of the preceding Statements, wherein the one or more pore-forming gas forming additives are present at 0.4 to 2 wt% (based on the total weight of the ceramic precursors (e.g., silica precursors), catalysts, pore-forming gas forming additives, and additives (if present)). For example, the weight ratio of ceramic precursors (e.g., silica precursors) to pore-forming gas forming additives (inert gas generators) is at least 5 times greater.

[0136] Statement 15. The method of any of the preceding Statements, wherein the one or more catalysts are present at 1 to 2 wt% (based on the total weight of the ceramic precursors (e.g., silica precursors), catalysts, pore-forming gas forming additives, and additives (if present)).

[0137] Statement 16. The method of any of the preceding Statements, wherein the one or more additives are present at 200 to 1000 wt% (based on the total weight of the ceramic precursors (e.g., silica precursors), catalysts, pore-forming gas forming additives). For example, the weight of the additives is 2 times to 10 times the weight of the ceramic precursors. For example, the amount of the one or more additives is 10 times the weight of the silica precursors, catalysts, pore-forming gas forming additives (based on the total weight of the silica precursors, catalysts, pore-forming gas forming additives).

[0138] Statement 17. The method of any of the preceding Statements, wherein the ratio of ceramic precursors (e.g., silica precursors): pore-forming gas forming additives: catalysts: additives is 5: 1: 1: 50. In various examples, one or more of these values can float by 10% or 20%.

[0139] Statement 18. The method of any of the preceding statements, wherein the contacting is performed at a temperature of from room temperature (e.g., 18-23 °C) to 70 °C, and / or for a period of from 1 minute to 96 hours (e.g., 1 hour to 24 hours).

[0140] Statement 19. The method of any of the preceding statements, further comprising exchanging a substance (e.g., removing a solvent) from the ceramic foam (e.g., silica aerogel).

[0141] Statement 20. The method of any of the preceding statements, further comprising washing the ceramic foam (e.g., silica aerogel). The washing step can be an exchange step, wherein unwanted materials (e.g., solvents, unreacted ceramic (e.g., silica) reaction components, etc.) are removed. In various examples, 90% or more, 95% or more, 99% or more, or all observable undesirable materials are removed from the thin film.

[0142] Statement 21. The method of Statement 20, wherein the washing comprises contacting the ceramic foam (e.g., silica aerogel) with an aqueous solution (e.g., an aqueous alcohol solution).

[0143] Statement 22. The method of any of the preceding statements, further comprising washing the ceramic foam (e.g., silica precursor) with an alcohol (e.g., ethanol) and / or drying the ceramic foam (e.g., silica precursor). For example, the ceramic foam (e.g., silica aerogel) is subjected to a temperature of from room temperature (e.g., 18-23 °C) to 100 °C (e.g., 30-60 °C), for example, (e.g., the ceramic foam (e.g., ceramic foam) is heated to) where the (or heating) can be performed under ambient conditions. For example, the hydrophobic coating is compatible with the ceramic foam structure (e.g., silica aerogel structure).

[0144] Statement 23. The method of any of the preceding statements, further comprising forming a layer (e.g., thin film) of a hydrophobic carbon-containing material disposed on at least a portion or all of a surface of the ceramic foam (e.g., silica aerogel). In one example, the ceramic foam (e.g., silica aerogel) is contacted with a silane (e.g., trialkylhalosilane, such as trimethylchlorosilane (TMCS)), a carbon material (e.g., carbon soot), or a combination thereof.

[0145] Statement 24. The method of any of the preceding statements, comprising forming a thin film from the ceramic foam (e.g., silica aerogel).

[0146] Statement 25. The method of Statement 24, wherein the thin film is formed on a substrate. For example, at least a portion of the ceramic foam (e.g., silica aerogel-like foam or silica aerogel) is formed in a reaction that is conducted on a substrate. Non-limiting examples of substrates include paper, metal (e.g., aluminum, possibly aluminum foil, thermal insulation paper substrate, fiber, etc.)

[0147] Statement 26. The method of Statement 24 or 25, wherein the forming is a continuous process (e.g., a continuous roll-to-roll process).

[0148] Statement 27. The method of Statement 24 or 25, wherein the forming is by doctor blading, drop casting, or additive manufacturing (e.g., 3D printing) and / or the like.

[0149] Statement 28. The method of Statement 24 or 25, wherein the thin film is formed by spray coating of a reaction mixture in a gelled (e.g., uncured) form, the reaction mixture comprising one or more ceramic precursors, one or more pore-forming gas-forming additives, one or more catalysts, and optionally one or more additives. For example, the gelled form reaction mixture has a viscosity of 85 to 1000 cP. Optionally, compressed air can be added to the gel to enhance flowability.

[0150] Statement 29. The method of any one of Statements 1-23, the method comprising impregnating a substrate with a ceramic foam (e.g., silica aerogel-like foam or silica aerogel). The porous substrate can be impregnated and incubated in a silica sol or gel solution for 1 hour to 24 hours. The composite material can then be dried under ambient conditions or low temperature thermal drying (300 K to 355 K) to form the impregnated substrate.

[0151] Statement 30. The method of any one of the preceding Statements, further comprising painting or coating at least a portion of a surface (e.g., an outer surface) of the ceramic foam.

[0152] Statement 31. The method of Statement 30, wherein the ceramic foam is painted or coated with a material (e.g., one or more nanoparticles, possibly metal oxide nanoparticles) (e.g., iron oxide nanoparticles, which can be magnetic nanoparticles). For example, the ceramic foam can be painted or coated using an in situ reaction by impregnating the foam with the material (e.g., nanoparticle precursors, which can be metal oxide nanoparticle precursors) and subsequently performing solid state sintering at 200 °C to 1000 °C (including all integer °C values therebetween and ranges therebetween).

[0153] Statement 32. The method of statement 31, wherein the nanoparticles are formed by impregnating the ceramic foam with nanoparticle precursors (e.g., CuCl2, FeCl3, etc., and combinations thereof) and the nanoparticles are formed from a reaction of the nanoparticle precursors (e.g., heating the impregnated ceramic foam to form the nanoparticles), and form a nanocomposite.

[0154] Statement 33. A silica aerogel formed by the method of any of the preceding claims.

[0155] Statement 34. A ceramic foam (e.g., formed by the method of any of the preceding claims) having (e.g., comprising) pores and a graded pore gradient. At least some or all of the pores can be interconnected. The pore (e.g., macropore) size decreases or increases roughly along a dimension moving from a first surface of the ceramic foam to a second surface opposite the first surface. The gradient can be a linear gradient. The ceramic foam can comprise mesopores and / or macropores. The mesopores can be IUPAC-defined mesopores.

[0156] Statement 35. The ceramic foam of statement 34, wherein the ceramic foam comprises a ceramic matrix. The ceramic matrix can be formed from ceramic nanoparticles. The ceramic matrix can be mesoporous.

[0157] Statement 36. The ceramic foam of statement 35, wherein the ceramic foam comprises pores 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).

[0158] Statement 37. The ceramic foam of any of statements 34-36, wherein the ceramic foam is a silica aerogel class, or is a silica aerogel, and is transparent.

[0159] Statement 38. The ceramic foam (e.g., silica aerogel) of any of statements 34-37, wherein the ceramic foam has one, more, or all of the following characteristics: (e.g., the silica aerogel) has 90-99% air (e.g., at least 90%, at least 95%, or at least 98% air), ideal porosity (<100 nm), ideal density (~0.003 g / cm 3 ), and ideal thermal conductivity (typically about 0.017 W / mK).

[0160] Statement 39. The ceramic foam (e.g., silica aerogel) of any of statements 34-38, wherein the ceramic foam (e.g., silica aerogel) includes a layer of carbon-containing material disposed on at least a portion or all of a surface (e.g., an outer surface) of the ceramic foam. For example, wherein 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 carbon-containing materials include carbon soot, alkylsilane groups, additive (e.g., surfactant) residue (which can be produced by thermal annealing). The layer can be a continuous layer and / or a conformal layer and / or can have desirably low number of defects (e.g., no observable, which can be defects that are visually observable). The layer can be a molecular layer (e.g., of groups, which can be hydrophobic groups). The layer can provide a hydrophobic outer surface. The layer of carbon material (e.g., carbon soot) can be formed by burning a carbon source.

[0161] Statement 40. The ceramic foam of any of statements 34-39, wherein the ceramic foam further includes nanoparticles disposed on at least a portion of a surface of the ceramic foam.

[0162] Statement 41. The ceramic foam of any of statements 34-39, wherein the ceramic foam is a monolithic piece, a free-standing film, or a film disposed on at least a portion of a substrate or on an entirety of a substrate. In an example, the ceramic foam is a free-standing film (e.g., a sheet). In an example, the film is free of adhesive (e.g., polymeric adhesive). Adhesives (e.g., polymeric adhesives) for ceramic foams (e.g., silica aerogel materials) are known in the art.

[0163] Statement 42. The ceramic film (e.g., silica aerogel) of statement 41, wherein the film has a thickness of 1 / 4 inch to 2 inches.

[0164] Statement 43. The ceramic foam (e.g., silica aerogel) of statement 41 or 42, wherein the film is disposed on at least a portion of a surface of a substrate (e.g., aluminum foil, thermal insulation paper, fiber, etc.).

[0165] Statement 44. A substrate impregnated with a ceramic foam formed by the method of any of statements 25-29, wherein the impregnated substrate has a desirably porosity (e.g., greater than 100 nm) and / or a desirably conductivity (e.g., about 0.017 W / mK, or 0.017 W / mK or less).

[0166] Statement 45. The ceramic foam of any of statements 34-42, wherein the ceramic foam exhibits one or more or all of the following characteristics:

[0167] • Thermal stability (e.g., thermal stability of at least 2000 °C)

[0168] • Mechanical strength (e.g., mechanical strength of at least 100 MPa)

[0169] • Sound / insulation properties

[0170] Statement 46. A silica aerogel formed by the method of any one of Statements 1-32 or a ceramic foam (e.g., silica aerogel) of any one of Statements 34-45. In one example, the silica aerogel thin film is a free-standing thin film (e.g., sheet). In one example, the thin film is free of a binder (e.g., polymeric binder). Binders (e.g., polymeric binders) for silica aerogel materials are known in the art.

[0171] Statement 47. A silica aerogel impregnated substrate formed by the method of Statement 28, wherein the impregnated substrate has desirable porosity (< 100 nm) and desirable conductivity (about 0.017 W / mK).

[0172] The following examples are provided to illustrate the present disclosure. These examples are not intended to limit anything.

[0173] Example 1

[0174] This example provides a description of making and characterizing the silica aerogel materials of the present disclosure.

[0175] 1 g of sodium bicarbonate was mixed with 7.08 ml of deionized water. 4.59 ml of tetraethyl orthosilicate (TEOS) and 22.34 ml of pure ethanol were added. Also added was 1 ml of catalyst to speed up gel formation. The catalyst was a mixture of 1.457 ml of ammonium hydroxide (28%), 0.1 gram of ammonium fluoride, and 4.35 ml of deionized water. After 3 minutes (minute = minute), the gel was washed with deionized water and then soaked with 500 ml of pure ethanol for 24 hours (hour = hour) with stirring. After soaking, the ethanol was removed. Then 10 ml of TMC (98%) was added dropwise to the solution. Also added was pure ethanol. The CO2 evolution was observed continuously over the next 24 hours. Finally, the gel was dried with ethanol in a surrounding environment of 60 °C for 24 hours to get the aerogel product.

[0176] Example 2

[0177] This example provides a description of making and characterizing the silica aerogel materials of the present disclosure.

[0178] 3.3 g of cetyltrimethylammonium bromide (CTAB) and 33.3 g of urea were dissolved in an aqueous solution of acetic acid (1 mM, 100 mL) followed by stirring for 20 minutes. Then, 56.7 mL of tetraethyl orthosilicate (TEOS) was added. The solution was stirred vigorously for 30 minutes to form a uniform bubble emulsion, which was sealed and then transferred to a preheated oven at 60 °C for 2 days of reaction. The prepared aerogel was washed with water and dried at room temperature. The obtained aerogel had a small density (about 0.15 g / cm3) and good thermal insulation (thermal insulation). 3 ) and good thermal insulation (thermal insulation).

[0179] Example 3

[0180] This example provides a description of the silica aerogel material of the present disclosure and its characterization.

[0181] The samples were prepared by contacting the substrate (Unifrax paper) with the reaction mixture to react. This can be referred to as in-situ infiltration. SEM; energy dispersive X-ray spectroscopy (EDX); and thermal imaging Figures 2-6 ) were obtained.

[0182] Example 4

[0183] This example provides a description of the method of preparing the silica aerogel material of the present disclosure and its characterization.

[0184] Trimethylchlorosilane (TMCS) ((CH3)3SiCl) was used for surface modification of the silica gel, producing HCl as a byproduct, which spontaneously reacts with sodium bicarbonate, thus creating pores in situ supported by carbon dioxide. The formed carbon dioxide is trapped in the wet silica gel, the pressure in the produced bubbles being opposite to the capillary pressure, thus preventing the shrinkage and collapse of the pores during the atmospheric drying step. The silica gel precursor used was aqueous tetraethoxysilane (TEOS, Si(OC2H5)4) and sodium bicarbonate (NaHCO3), and trimethylchlorosilane was used for surface modification.

[0185] Low cost production of aerogel insulation materials is expected to be achieved with in situ APD and R2R manufacturing. The properly specified gel can be R2R deposited on an inorganic paper substrate carrier. The core of using R2R manufacturing of aerogel materials is the formulation of the gel precursor that is very robust in printing. The rheological behavior of the silica gel plays a crucial role in the continuous deposition in the R2R process, which requires a non-Newtonian liquid with shear thinning behavior. The Weber number (We) and Ohnesorge number (Oh) (or inverse Z) are used to predict whether stable deposition is achieved: We = p v^2 d / and Z = 1 / Oh = p d s / m, where v is the fluid velocity, d is the nozzle diameter, s is the surface tension, and m is the viscosity. A Brookfield viscometer is employed to measure the gel viscosity. The surface tension is measured by capillary rise, g = 1 / 2 r h p, where r is the capillary radius, h is the fluid height, and p is the fluid density.

[0186] Nitrogen physisorption is fitted with the Brunauer-Emmett-Teller technique to explore the pore distribution of the silica aerogel. The N2 adsorption-desorption isotherm plot of the silica aerogel indicates the presence of hierarchical porosity and a relatively sharp pore distribution (mainly < 60 nm).

[0187] Mechanical properties are very important for building the silica aerogel. To study the stress-strain curve, a honeycomb-like aerogel structure is fabricated. The compressive strength s* is strongly affected by the total density p* of the sample, as shown in the equation s^ / s_(ts,strut) = C (p^ / p_strut) c, where s^ is the compressive strength, s_(ts,strut) is the compressive strength of the struts that make up the honeycomb. Therefore, the compressive strength of the aerogel is a function of the porosity, thickness, and length. The thickness is customized by R2R printing. The porosity can be adjusted by the gel concentration and shrinkage.

[0188] Thermal insulation performance is a measure of the silica aerogel. The thermal insulation capability of the 3D fabricated silica aerogel is studied. Thermal imaging analysis shows that the silica aerogel works as a thermal insulator. The thermal insulation of the silica aerogel depends on its thickness. The effective thermal conductivity can be calculated according to the effective medium impregnation theory, l_eff = 1 / 4{[l_p(3v_p - 1) + l_s(3v_s - 1)] + [(l_p(3v_p - 1) + l_s(3v_s - 1))2 + 8 l_p l_s]1 / 2}, where l_s and l_p are the conductivities of the solid and the pores, respectively, and v_s, v_p are their volume fractions. In this case, the thermal conductivity of the thermal silica aerogel can be estimated to be 0.016 W / mK.

[0189] SEM and other test data are shown in Figures 7-22.

[0190] Example 5

[0191] This example provides a description of the preparation of the ceramic foam materials of the present disclosure and their characterization.

[0192] Porous gradient silica aerogel monoliths (PGAeros) were designed and synthesized with hierarchical hollow structures and gradient porosity controlled by hydrolysis of tetraethyl orthosilicate (TEOS) in the presence of acetic acid, urea, and cetyltrimethylammonium bromide (CTAB). CTAB micellar networks and in-situ gas bubbles generated by thermal decomposition of urea guided the formation of hierarchical porosity and porosity gradient in PGAeros, respectively. The synthesized silica insulator has excellent thermal insulation, sound insulation, and fire resistance properties, and a thermal conductivity as low as 0.040 W m -1 K -1 and mechanical integrity with compressive strength of 100.56 MPa, which can be further shaped and tailored for desired shapes and geometries. Sound performance was also tested at different frequencies, showing superior sound insulation performance over the reference sample insulation foam (28.3% noise reduction, or 22.3 db at 2000 Hz frequency, 15 mm thickness).

[0193] Results and Discussion: Figure 23 The scheme in a shows the formation of hierarchical hollow structured silica PGAeros achieved through a facile one-pot synthesis. Surfactant CTAB was used to form micelles in the mixed solution of TEOS and water. TEOS hydrolysis was carried out on the shell of the formed micelles, which served as a template leading to the formation of silica shell. The addition of urea accelerated the condensation of silanols by increasing the solution pH, while it can act as an in-situ foaming agent due to its thermal hydrolysis into ammonia (NH3) and carbon dioxide (CO2). The formed silica PGAeros floated on the water surface due to its low mass density. The continuous decomposition of urea and the subsequent in-situ release of carbon dioxide and ammonia bubbles formed high pressure in the upper part of the reaction chamber, leading to a foaming process from top to bottom, resulting in a pore gradient in PGAeros. Figure 23 b shows a typical photo of the grown opaque silica PGAeros, which can be cut and polished into desired shapes for further studies (such as Figure 23 c shows). The pore gradient can be easily observed from the scanning electron microscope (SEM) images ( Figure 23 d) showing an increase in average pore size from top to bottom, where the pore size depends on the reaction conditions, such as chemical concentrations, reaction temperature, and time (these will be discussed in the following sections). The average pore size of PGAeros was calculated from the bottom to the top region, showing an increase from 33.3 pm to 174.8 pm when the ratio of TEOS:CTAB:urea = 27.8:1:60.7 Figure 23(Illustration in d). High-resolution SEM images of the PGAeros region for large and small apertures are shown in Figures d. Figure 23 As shown in e and 23f. Furthermore, the synthesized silica PGAeros had a porosity of 94.1% as determined by a hydrometer, and a low density of 0.128 g / cm³. -3 The solid-state network of PGAeros consists of nano-sized silica particles and was further characterized by transmission electron microscopy (TEM). Figure 23 As shown in g and h, numerous micropores are clearly observed in each particle due to the template effect of the CTAB molecules. Therefore, due to the hierarchical hollow structure of gradient large-scale pores and mesopores within the silica network, silica PGAeros with high porosity and low density is obtained. It can be expected that the synthesized silica PGAeros will have confined gas thermal conductivity and high phonon scattering, resulting in high insulation performance.

[0194] To understand and control the formation of the pore gradient in PGAeros, a series of experiments were designed to synthesize PGAeros with reaction times of 24 hours, 48 ​​hours, and 72 hours (named PGAero-2, PGAero-3, and PGAero-4, respectively). Compared with the original sample with a pore gradient synthesized through a 96-hour reaction time (referred to as PGAero-1), the silica PGAeros synthesized through 24 hours exhibited a uniform pore size of 27.5 μm and a standard deviation of 9.4 μm. Figure 27 (a, b) As the reaction time increases to 48 hours, a gradient pore structure gradually forms in the PGAeros, leading to a larger pore deviation, such as... Figure 24 As shown in figure a, when the reaction time is increased to 72 hours, the pore size range of PGAeros shows a wide range from 15 μm to 300 μm, with a larger deviation of 85.3 μm. Figure 24 b). The porosity of the silicon oxide PGAeros remained around 80%, and due to the continuous growth of silicon oxide, the porosity decreased slightly with increasing reaction time. Figure 28 As pore size increases and porosity decreases, the pore gradient exhibits a competitive effect on insulation performance. The decrease in porosity of PGAeros silica synthesized over 24 to 48 hours primarily leads to a decrease in thermal conductivity from 0.049 W / m². -1 K -1 Increased to 0.060W m -1 K -1 Meanwhile, as the pore size increases, the pore gradient determines the insulation performance, resulting in 0.054 W / m². -1 K -1 The low thermal conductivity of silicon oxide PGAero. Further increases in reaction time resulted in a thermal conductivity of 0.040 W / m². -1 K -1The lowest thermal conductivity ( Figure 24 c).

[0195] The average pore size and porosity were investigated by tuning the reaction conditions and their correlation with the thermal conductivity of PGAeros. Figure 29 Typical SEM cross-sectional images of silicon oxide PGAeros are shown below. Figure 25 As shown in a-25f. Figure 30 As shown in ag, the average pore size of each sample was calculated by counting more than 100 pores using SEM images. The TEOS concentration was 1.4 mol L⁻¹ for the PGAero-1 sample (average pore size 138.3 μm, porosity 94.1%). -1 Increase to 2.1 mol L for PGAero-5 and PGAero-6. -1 and 2.8 mol L -1 This resulted in an increase in average pore size of 85.0 μm and 68.4 μm, and a porosity of 89% and 88%, respectively. Figure 25 (ac). Increased TEOS concentration reduced the average pore size and porosity, resulting in highly dense silica PGAeros with a thermal conductivity increasing from 0.040 W / m². - 1 K -1 Increased to 0.049W m -1 K -1 (PGAero-5) and 0.055W m -1 K -1 (PGAero-6). The increase in thermal conductivity is primarily due to increased solid-state heat transport through the high-concentration silica network. The concentration of CTAB initially determines the pore size of the silica PGAeros, where, by comparison... Figure 25 For α and 25d (PGAero-7), the less CTAB component, the smaller the average pore size of PGAeros. Urea is used as a mineralizing chemical and an in-situ foaming agent; therefore, increasing urea addition can lead to larger pore sizes and lower mass density. For example... Figure 25 As shown in f and 25g, urea was transferred from 1.5 mol L... -1 (PGAero-8) changed to 4.5 mol L -1 When using (PGAero-9), the pore size of the formed silicon oxide PGAeros can be significantly increased from 38.65 μm to 110.39 μm. The thermal insulation performance is highly correlated with the pore size and porosity of the silicon oxide PGAeros. Figure 25 g shows the thermal conductivity of different silica PGAeros, which depends on pore size and porosity. Large pore size and high porosity result in lower thermal conductivity of PGAeros. 0.040 W / m -1 K -1The lowest thermal conductivity of silica aerogels can be achieved by TEOS:CTAB:urea = 27.8:1:60.7 synthesized silica PGAero.

[0196] The mechanical stability of silica aerogels is a key for their large-scale commercial applications. The gradient pore structure has great advantages in optimizing the mechanical properties. Silica PGAero synthesized in monolithic form with a pore gradient has high mechanical strength, which is characterized by uniaxial compression tests Figure 31 ). 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 Figure 26 a and 32a-C) after annealing at 400 °C for 2 h. Figure 26 The inset of a shows the SEM images of silica PGAero before (top) and after (bottom) annealing. The robust pore structure enables the silica PGAero to have good mechanical integrity. The thermal conductivities of the silica PGAero before and after annealing are 0.040 W m -1 K -1 and 0.044 W m -1 K -1 , respectively. The annealing treatment improves the mechanical properties without affecting the insulation performance. Importantly, the mechanically robust foam can maintain a low thermal conductivity of 0.060 W m -1 K -1 after long-term annealing at 1000 °C for 24 h, as shown in Figure 33 . With the increasing demand for insulation materials in extreme environments, the high mechanical robustness and thermal stability make the synthesized silica PGAero show good prospects.

[0197] Sound insulation for soundproofing plays an important role in super-insulation applications. Silica PGAero with a pore gradient structure can significantly reduce sound waves and heat, as shown in Figure 26 b. The sound intensity measured by silica PGAero and polystyrene reference without any sample (blank) is shown in Figure 34 . In addition, a variety of commonly used commercial soundproofing materials are such as polyurethane, aramid (Kevlar), and two types of ceramic fiber blanket. Silica PGAero shows low detected sound intensity in the entire frequency range (500 Hz to 1800 Hz), indicating much better soundproofing performance compared to all commonly used commercial soundproofing materials as shown in Figure 26 c. Silica PGAero with a thickness of 0.014 m has better soundproofing performance compared to the reference PS foam at different frequencies of 500 Hz, 800 Hz, and 2000 Hz, showing noise reduction of 10.9%, 12.0%, and 28.4%, respectively.Figure 26 e, 35a, b). Especially at an acoustic frequency of 2000 Hz, Figure 26 d) To calibrate the sound insulation performance independent of the thickness, we defined the sound insulation coefficient by dividing the noise reduction by the sample thickness. The sound insulation coefficient of the silica PGAeros was 2.7, 2.0, and 18.2 times higher than that of the reference sample at 500 Hz, 800 Hz, and 2000 Hz, respectively. In addition to the mechanical and acoustic sound insulation performance, the moisture uptake performance of the silica PGAeros was investigated under humid conditions. The initial thermal conductivity was 0.045 W m - 1 K -1 and 0.052 W m -1 K -1 Two PGAeros with an initial porosity of 0.45 and 0.52 were subjected to moisture uptake experiments at 60% and 80% humidity. The high humidity conditions led to an increase in thermal conductivity, which could be recovered after drying at 60 °C Figure 36 ). The cyclic experiments showed that the thermal conductivity of the PGAeros could be recovered to the initial point with a loss of less than 16%.

[0198] A lightweight silica PGAeros with an ideal porosity and an ideal pore gradient was developed for thermal and acoustic superinsulation. The micellar-mediated silica growth and the gas foaming process due to the thermal hydrolysis of urea together led to the pore generation and the gradient formation. The well-designed bulk geometry with the unique pore structure and ceramic properties provided the PGAeros with outstanding thermal insulation and fire resistance properties with a thermal conductivity as low as 0.040 W m -1 K -1 and a high mechanical integrity with a compressive strength of 100.56 MPa over a wide temperature range and a thermal conductivity as low as 0.040 W m -1 K -1 and a high mechanical integrity with a compressive strength of 100.56 MPa. The silica PGAeros also showed better sound insulation properties at different frequencies and a noise reduction of 28.3% or 22.3 db higher than the reference insulation foam at a frequency of 2000 Hz with a thickness of 15 mm. The stability under humid conditions was also proven to be long-term reliable. Materials with high thermal insulation and sound insulation properties while maintaining the thermal conductivity are expected to be applicable for next-generation building materials and other applications.

[0199] Materials and experiments. Experiment: Preparation: dissolved 3 mol L -1 g urea (Sigma-Aldrich), 0.3 mol L -1 CTAB (VWR), 1 mmol acetic acid (EMD Millipore), and added distilled water to 100 ml, stirred in a beaker for 3 hours until a completely transparent solution was formed. Then, 1.4 mol L -1TEOS (Sigma-Aldrich) was added to the solution. Stirring was continued for 10 minutes and the solution became homogenous translucent. The solution was then transferred to a plastic bottle and the container was tightly sealed. The container was then placed in an oven preheated to 60 °C for 4 days. After the gelation process, the sample was removed from the container and placed in distilled water preheated to 60 °C for two days. During this washing process, the water was changed several times until the supernatant was clear and all ammonia was removed. Immediately after the washing step was completed, the sample was placed in a preheated oven at 60 °C for two days for drying purposes.

[0200] Characterization: Thermal conductivity measurement home customized followed the ASTM C518 standard thermal conductivity procedure. A heat flux sensor was used purchased from Fluxtaq and calibrated using a reference sample of polystyrene commercial insulation.

[0201] Acoustic test, home customized sound box with built-in sound insulation material and sound detector purchased from Kasuntest. Samples of different thickness were tested at different frequencies generated by the sound source.

[0202] Pycnometer test used helium to penetrate the porous sample in the chamber to obtain the volume of the solid part of the sample. After knowing the solid part of the sample, we can calculate the porosity of the silica foam sample.

[0203] Compression test and mechanical test at different loads and multiple cycle times (including original silica foam sample and bulk sample after 400 °C thermal synthesis).

[0204] Moisture aging cycle test measured the thermal conductivity of the sample. The sample was placed in each humidity environment for 24 hours and dried in a preheated oven for another 24 hours, then the cycle was repeated.

[0205] Example 6

[0206] This example provides a description of the preparation of the ceramic foam material of the present disclosure and its characterization.

[0207] Experimental method: 3 mol L -1 g urea (Sigma-Aldrich), 0.3 mol L -1 CTAB (cetyltrimethylammonium bromide) (VWR) / SDS (sodium dodecyl sulfate (Sigma-Aldrich)), 1 mmol acetic acid (EMD Millipore), and distilled water was added to 100 ml, stirred in a beaker for 3 hours until the solution became completely transparent. Then, 1.4 mol L -1TEOS (Sigma-Aldrich) was added to the solution. Stirring was continued for 10 minutes and the solution became homogenous translucent. The solution was then transferred to an aluminum container and the container was tightly sealed. The container was then placed in an oven preheated to 60 °C for 4 days. After this gelation process, the sample (monolith and gel) was removed from the container and placed in a container preheated to 60 °C filled with distilled water for two days. During this washing process, the water was changed several times until the supernatant was clear and all ammonia was removed. The sample (gel) was then stored in a sealed container for further applications.

[0208] Figure 37 A schematic of the ceramic foam manufacturing process is shown. Figures 38-41 Various characterizations of the ceramic foam examples prepared in the examples are shown.

[0209] While the present disclosure has been described with respect to one or more particular embodiments and / or implementations, it will be apparent to those of ordinary skill in the art that many modifications, e.g., adaptations, changes, substitutions, and / or alterations, can be made to the present disclosure without departing from the scope of the present disclosure.

Claims

1. A method for forming a ceramic aerogel, the method comprising: contacting: a ceramic precursor; a pore-forming gas-forming additive selected from the group consisting of: urea and sodium bicarbonate in combination; a catalyst; a solvent; and optionally, a surfactant, wherein the contacting results in the formation of an inert gas and a ceramic aerogel having a pore gradient structure. The ceramic precursor is selected from the group consisting of a silicon oxide precursor, an aluminum oxide precursor, a transition metal oxide precursor, and combinations thereof.

2. The method of claim 1, wherein, The silicon oxide precursor is selected from the group consisting of: a tetraalkoxysilane, an alkyltrialkoxysilane, sodium metasilicate, and combinations thereof; 3. The method of claim 2, wherein, wherein the aluminum oxide precursor is selected from the group consisting of: an aluminum alkoxide, a tris(beta-hydroxy)ethylamine condensed aluminum hydroxide, or a tris(heteroaluminum tricyclopentadienyl oxyisopropyl) amine, and combinations thereof; and / or wherein the transition metal oxide precursor is selected from a transition metal alkoxide. The silicon oxide precursor is selected from the group consisting of: tetramethyl orthosilicate, tetraethyl orthosilicate, methyltrimethoxysilane, sodium metasilicate, and combinations thereof.

4. The method of claim 3, wherein, The catalyst is a basic catalyst selected from the group consisting of: ammonia, ammonium fluoride, ammonium hydroxide, and combinations thereof.

5. The method of claim 3, wherein, The transition metal oxide precursor is selected from the group consisting of: a transition metal alkoxide having the formula M(OR)x x wherein M is a transition metal selected from the group consisting of Ti, Zr, W, Cr, Mo, R is an alkyl group, and x is selected from 1, 2, 3, 4, or 5.

6. The method of claim 1, wherein, 7. The method of claim 1, The catalyst is an acidic catalyst selected from the group consisting of: a protic acid, a hydrogen halide acid, and combinations thereof. wherein The catalyst is a protic acid.

8. The method of claim 7, wherein, The surfactant is selected from the group consisting of: hexadecyltrimethylammonium bromide and sodium dodecyl sulfate.

9. The method of claim 1, wherein, The contacting includes mixing the ceramic precursor, which can be formulated in the solvent; the pore-forming gas-forming additive, which can be configured in water; the catalyst, which can be formulated in water; or 10. The method of claim 1, wherein, wherein the contacting is performed at a temperature ranging from room temperature to 70 °C, and / or for a period of time ranging from 1 minute to 96 hours. The ceramic precursor is present in an amount ranging from 2 to 10 wt.%, based on the total weight of the ceramic precursor, the catalyst, the pore-forming gas-forming additive, and the surfactant; The pore-forming gas-forming additive is present in an amount ranging from 0.4 to 2 wt.%, based on the total weight of the ceramic precursor, the catalyst, the pore-forming gas-forming additive, and the surfactant; 11. The method of claim 1, wherein, The catalyst is present in an amount ranging from 1 to 2 wt.%, based on the total weight of the ceramic precursor, the catalyst, the pore-forming gas-forming additive, and the surfactant; The surfactant is present in an amount ranging from 200 to 1000 wt.%, based on the total weight of the ceramic precursor, the catalyst, the pore-forming gas-forming additive; or The ratio of the ceramic precursor: the pore-forming gas-forming additive: the catalyst: the surfactant is 5: 1: 1:

50.

12. The method of claim 1, further comprising: exchanging a substance from the ceramic aerogel; washing the ceramic aerogel and drying the ceramic aerogel. The washing includes contacting the ceramic aerogel with an aqueous solution.

14. The method of claim 1, further comprising:

13. The method of claim 12, wherein, forming a layer of a hydrophobic carbon-containing material disposed on at least a portion of a surface of the ceramic aerogel; ​ ​ A thin film is formed from a ceramic aerogel, the thin film is formed on a substrate, the formation is a continuous process, the formation is by doctor blading, slip casting or additive manufacturing, or, the thin film is formed by spray coating of a reaction mixture in gelation form, the reaction mixture includes a ceramic precursor, a pore forming gas forming additive, a catalyst and a surfactant; Impregnating a substrate with a ceramic aerogel; or At least a portion of the surface of the ceramic aerogel is painted or coated, the ceramic aerogel is painted or coated with a material, the material is nanoparticles, the nanoparticles are formed by impregnating the ceramic aerogel with nanoparticle precursors, and a nanocomposite is formed.

15. A ceramic aerogel formed by the method of any one of claims 1-14, comprising a ceramic matrix and pores, wherein, At least a portion of the pores are interconnected, and the pores of the ceramic aerogel have a hierarchical pore gradient.

16. The ceramic aerogel of claim 15, wherein, The pore size decreases or increases along a dimension moving from a first surface of the ceramic aerogel to a second surface opposite the first surface.

17. The ceramic aerogel of claim 15, wherein, The ceramic aerogel is silica aerogel based, and is transparent.

18. The ceramic aerogel of claim 15, wherein, The pore size is 500 microns to 1 micron.

19. The ceramic aerogel of claim 15, wherein, 90 - 99% of the ceramic aerogel is air; The ceramic aerogel has a porosity of less than 100 nm; The density of the ceramic aerogel is 0.003 g / cm 3 ; or The ceramic aerogel has a thermal conductivity of 0.017 W / mK.

20. The ceramic aerogel of claim 15, wherein, The ceramic aerogel includes a layer of carbon-containing material disposed on at least a portion of the surface of the ceramic aerogel.

21. The ceramic aerogel of claim 15, wherein, The ceramic aerogel further includes nanoparticles disposed on at least a portion of the surface of the ceramic aerogel.

22. The ceramic aerogel of claim 15, wherein, The ceramic aerogel is a monolith, a free-standing thin film, or a thin film disposed on at least a portion of a substrate, the thin film has a thickness of 1 / 4 inch to 2 inches, or, the thin film is disposed on at least a portion of a surface of a substrate.

23. The ceramic aerogel of claim 15, wherein, The ceramic aerogel exhibits the following properties: Thermal stability of at least 2000 °C; Mechanical strength of at least 100 MPa; or Soundproofing / sound isolation properties.

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