A Hierarchical Mesoporous Insulation Ceramic

Achieving Remarkable Specific Mechanical Strength and Energy Absorption Capacity in SiC Nanowire Networks through Graded Structural Design

Lightweight porous ceramics with a unique combination of superior mechanical strength and damage tolerance are in significant demand in many fields such as energy absorption, aerospace vehicles, and chemical engineering; however, it is difficult to meet these mechanical requirements with conventional porous ceramics. Here, we report a graded structure design strategy to fabricate porous ceramic nanowire networks that simultaneously possess excellent mechanical strength and energy absorption capacity. Our optimized graded nanowire networks show a compressive strength of up to 35.6 MPa at a low density of 540 mg·cm-3, giving rise to a high specific compressive strength of 65.7 kN·m·kg-1 and a high energy absorption capacity of 17.1 kJ·kg-1, owing to a homogeneous distribution of stress upon loading. These values are top performance compared to other porous ceramics, giving our materials significant potential in various engineering fields.

Electricity Harvesting from Water Evaporation on Hierarchical Pore Gradient Silica Aerogel-Based Generators

In this study, the electric energy harvesting capability of the hierarchical pore gradient silica aerogel (HPSA) is demonstrated due to its unique porous structure and inherent hydroxyl groups on the surface. Taking advantage of the positively charged surface of unwashed HPSA credited by the preparation strategy, poly(4-styrene sulfonic acid) (PSS) can be spontaneously adsorbed onto unwashed HPSA and shows gradient distribution due to the pore-gradient structure of HPSA. By virtue of the gradient distribution and the stronger ionization of PSS, PSS-modified HPSA (PSS-HPSA) shows enhanced electricity generation performance from natural water evaporation with an average output voltage of 0.77 V on an individual device. The water evaporation-induced electricity property of PSS-HPSA can be maintained in the presence of a low concentration of salt. The desirable salt resistance capability benefits from the unique 3D hierarchical porous structure of HPSA which ensures rapid water replenishment so as to effectively avoid the salt accumulation. The HPSA-based devices with the advantages of unique porous structure, easy functionalization, good physicochemical stability, good salt resistance capability, and eco-friendliness show great potential as water evaporation-induced electricity generators.

Ultrastrong and High Thermal Insulating Porous High-Entropy Ceramics up to 2000 °C

High mechanical load-carrying capability and thermal insulating performance are crucial to thermal-insulation materials under extreme conditions. However, these features are often difficult to achieve simultaneously in conventional porous ceramics. Here, for the first time, it is reported a multiscale structure design and fast fabrication of 9-cation porous high-entropy diboride ceramics via an ultrafast high-temperature synthesis technique that can lead to exceptional mechanical load-bearing capability and high thermal insulation performance. With the construction of multiscale structures involving ultrafine pores at the microscale, high-quality interfaces between building blocks at the nanoscale, and severe lattice distortion at the atomic scale, the materials with an ≈50% porosity exhibit an ultrahigh compressive strength of up to ≈337 MPa at room temperature and a thermal conductivity as low as ≈0.76 W m-1 K-1. More importantly, they demonstrate exceptional thermal stability, with merely ≈2.4% volume shrinkage after 2000 °C annealing. They also show an ultrahigh compressive strength of ≈690 MPa up to 2000 °C, displaying a ductile compressive behavior. The excellent mechanical and thermal insulating properties offer an attractive material for reliable thermal insulation under extreme conditions.

Bioinspired Super Thermal Insulating, Strong and Low Carbon Cement Aerogel for Building Envelope

The energy crisis has arisen as the most pressing concern and top priority for policymakers, with buildings accounting for over 40% of global energy consumption. Currently, single-function envelopes cannot satisfy energy efficiency for next-generation buildings. Designing buildings with high mechanical robustness, thermal insulation properties, and more functionalities has attracted worldwide attention. Further optimization based on bioinspired design and material efficiency improvement has been adopted as effective approaches to achieve satisfactory performance. Herein, inspired by the strong and porous cuttlefish bone, a cement aerogel through self-assembly of calcium aluminum silicate hydrate nanoparticles (C-A-S-H, a major component in cement) in a polymeric solution as a building envelop is developed. The as-synthesized cement aerogel demonstrates ultrahigh mechanical performance in terms of stiffness (315.65 MPa) and toughness (14.68 MJ m^-3 ). Specifically, the highly porous microstructure with multiscale pores inside the cement aerogel greatly inhibits heat transfer, therefore achieving ultralow thermal conductivity (0.025 W m^-1 K^-1 ). Additionally, the inorganic C-A-S-H nanoparticles in cement aerogel form a barrier against fire for good fire retardancy (limit oxygen index, LOI ≈ 46.26%, UL94-V0). The versatile cement aerogel featuring high mechanical robustness, remarkable thermal insulation, light weight, and fire retardancy is a promising candidate for practical building applications.

Lightweight and Strong Ceramic Network with Exceptional Damage Tolerance

Lightweight materials such as porous ceramics have attracted increasing attention for applications in energy conservation, aerospace and automobile industries. However, porous ceramics are usually weak and brittle; in particular, tiny defects could cause catastrophic failure, which affects their reliability and limits the potential use greatly. Here we report a SiC/SiO2 nanowire network constructed from numerous well-bonded SiC nanowires coated by a biphasic structure consisting of amorphous SiO2 and nanocrystal SiC. The as-obtained SiC/SiO2 nanowire network is lightweight (360 ± 10 mg cm-3), mechanically strong (compressive strength of 16 MPa), and damage-tolerant. The high strength of the network is attributed to the biphasic mixed structure of the binding coating which can restrict the deformation of nanowires upon compression. The lightweight and strong SiC/SiO2 nanowire network shows potential for engineering applications in harsh environments.

Preparation of Aerogel-like Silica Foam with the Hollow-Sphere-Based 3D Network Skeleton by the Cast-in Situ Method and Ambient Pressure Drying

Silica aerogels have incomparable advantages among thermal insulation materials because of their ultralow density and thermal conductivity, but cumbersome production processes, high cost, and low mechanical stability limit their practical application. In this study, a novel aqueous process to prepare lightweight aerogel-like silica foams (ASFoams) through the cast-in situ method and ambient pressure drying was proposed with multiblock polyurethane surfactant as the vesicle template. ASFoams possess a unique loose stacking morphology of the silica hollow sphere with a 3D network structure as the skeleton, which endues ASFoams with a low density of 0.059 g/cm³, low thermal conductivity of 36.1 mW·k^-1·m^-1, and pretty good mechanical properties. These properties make ASFoams a promising option for thermal insulation in industrial, aerospace, and other extreme environmental conditions. In addition, the micromorphology of ASFoams can be adjusted by changing the reaction conditions, which may provide a facile method for the preparation of a silica aerogel-like foam with adjustable microstructure.

Transparent thermal insulation ceramic aerogel materials for solar thermal conversion

Thermal management in energy-efficient solar thermal energy conversion and transparent windows requires advanced materials with low thermal conductivity and high transparency, such as transparent silica aerogel materials. However, the large scatter domains in porous silica materials would deteriorate their optical transparency. Herein, we report transparent silica aerogels by controlling hydrolyzation and meanwhile silylation modification to enhance the integrity of the microstructure under ambient pressure drying. The transparent silica aerogel materials show a broad-spectrum transparency of 70% from 400 nm and 800 nm, showing promising applications in transparent windows and solar thermal energy conversion systems. The scalability for transparent windows could be achieved with a composite material by incorporating transparent polymeric materials. The solar receiver coupled with a transparent silica aerogel could reach 122 °C within 12 min at a solar irradiance of 1 Sun, ∼200% higher than that in the ambient atmosphere. The engineered structure of the transparent porous silica backbone provides a pathway for solar thermal systems and transparent window applications.

Additive Manufacturing of Resilient SiC Nanowire Aerogels

Resilient ceramic aerogels are emerging as a fascinating material that features light weight, low thermal conductivity, and recoverable compressibility, promising widespread prospects in the fields of heat insulation, catalysis, filtration, and aerospace exploration. However, the construction of the resilient ceramic aerogels with rational designed multiscale architectures aiming for tunable physical and mechanical performances remains a major challenge. Here, 3D constructed resilient SiC nanowire aerogels possessing programmed geometries and engineered mechanical properties are created via additive manufacturing. The Young's modulus of the fabricated SiC nanowire aerogel lattices are tuned systematically from 0.012 MPa to 5.800 MPa spanning over 2 orders of magnitude. More importantly, the customized lightweight and resilient SiC nanowire aerogels show a low thermal conductivity (0.046 W m^-1 K^-1). The present work provides another approach to the design and rapid fabrication of resilient ceramic aerogels toward flexible thermal management devices, lightweight engineered structures, and other potential applications.

Ultrahigh-Strength Porous Ceramic Composites via a Simple Directional Solidification Process

Porous ceramics possess great application potential in various fields. However, the contradiction between their pores and their strength have significantly hampered their applications. In this study, we present a simple directional solidification process that relies on its in situ pore forming mechanism to fabricate Al₂O₃/Y₃Al₅O₁₂/ZrO₂ porous eutectic ceramic composites with a highly dense and nanostructured eutectic skeleton matrix and a lotus-type porous structure. The flexural strength of this porous ceramic composite with a porosity of 34% is 497 MPa at ambient temperature, which is a new record of the strength of all current porous ceramics. This strength can remain at 324 MPa when the temperature increases up to 1773 K because of its refined lamellar structure and strong bonding interface. We demonstrate an interesting application of the directional solidification in efficiently preparing the ultrahigh-strength porous ceramic with high purity. The findings will open a window to the strength of porous ceramics.

Facile Method for Preparing Hierarchical Al2O3-Glass Foam Ceramics with Superior Thermal Insulating Property

Porous ceramics are good candidates for thermal-insulating materials. Glass is a low-cost material that possesses low intrinsic thermal conductivity of less than 10 W·m^-1·K^-1. However, the mechanical strength of a homogeneous glass material is fairly low. We, in this work, have fabricated Al₂O₃-hollow glass sphere (HGS) foam ceramics with a facile particle-stabilized foaming method. The obtained foam ceramic presents a hierarchical microstructure that is rare to be seen elsewhere using this foaming technique. The foaming system contains two types of particles having opposite charges, and the particle-stabilized foaming mechanism is hence discussed. The optimal sample possesses a porosity above 94% with a thermal conductivity as low as 0.0244 W/m·K, which reaches the level of superinsulating materials. The compressive strengths of the foam ceramics range from 0.07 to 0.83 MPa. The effective medium theory model is used to calculate the thermal conductivities as reference. The deviation of the theoretical values from the experimental ones are derived from the effect of the hierarchical microstructure of the foams. The results of this work may deepen one's understanding and pave new ways for the particle-stabilized foaming technique. The unique microstructure of the ceramic may also shed some light on fabricating superior thermal-insulating ceramic materials.

Three-Dimensional-Printed Silica Aerogels for Thermal Insulation by Directly Writing Temperature-Induced Solidifiable Inks

Silica aerogels are attractive materials for various applications due to their exceptional performances and open porous structure. Especially in thermal management, silica aerogels with low thermal conductivity need to be processed into customized structures and shapes for accurate installation on protected parts, which plays an important role in high-efficiency insulation. However, traditional subtractive manufacturing of silica aerogels with complex geometric architectures and high-precision shapes has remained challenging since the intrinsic ceramic brittleness of silica aerogels. Comparatively, additive manufacturing (3D printing) provides an alternative route to obtain custom-designed silica aerogels. Herein, we demonstrate a thermal-solidifying 3D printing strategy to fabricate silica aerogels with complex architectures via directly writing a temperature-induced solidifiable silica ink in an ambient environment. The solidification of silica inks is facilely realized, coupling with the continuous ammonia catalysis by the thermolysis of urea. Based on our proposed thermal-solidifying 3D printing strategy, printed objects show excellent shape retention and have a capacity to subsequently undergo the processes of in situ hydrophobic modification, solvent replacement, and supercritical drying. 3D-printed silica aerogels with hydrophobic modification show a super-high water contact angle of 157°. Benefiting from the low density (0.25 g·cm^-3) and mesoporous silica network, optimized 3D-printed specimens with a high specific surface area of 272 m²·g^-1 possess a low thermal conductivity of 32.43 mW·m^-1·K^-1. These outstanding performances of 3D-printed silica aerogels are comparable to those of traditional aerogels. More importantly, the thermal-solidifying 3D printing strategy brings hope to the custom design and industrial production of silica aerogel insulation materials.

Experimental and CFD Investigation on the Application for Aerogel Insulation in Buildings

Reducing building energy consumption is a significant challenge and is one of the most important research areas worldwide. Insulation will help to keep the building’s desired temperature by reducing the heat flow. Additionally, proper insulation can provide an extended period of comfort, leading to reduced building energy requirements. Encapsulated air is the major aspect of most thermal insulation materials. Low thermal conductivity is a good characteristic of thermal insulation materials. Aerogel has low thermal conductivity, so it is suitable for glazing and insulation purposes. This research paper investigates the effectiveness of aerogel as an insulation material in buildings by incorporating a translucent aerogel-glazing system in the window and aerogel insulation in the wall of a building. Experimental investigation of a 10 mm thick aerogel blanket surrounded box was conducted to assess its performance. Additionally, a CFD simulation was conducted, and the results of temperature degradation for the wall showed good agreement with experimental results. Additionally, the CFD simulation of temperature decay was compared between the aerogel-glazed window and argon-glazed window. It was found that the aerogel-glazed window has slower temperature decay compared to the argon-glazed window. The results showed that integrating aerogel in the glazing system and wall insulation in a building has the potential to reduce the building’s energy consumption. Moreover, a numeric simulation was conducted, and showed that the building’s annual energy consumption is reduced by 6% with the use of aerogel insulation compared to fiberglass.

Si3N4 Nanofibrous Aerogel with In Situ Growth of SiOx Coating and Nanowires for Oil/Water Separation and Thermal Insulation

Nanofibrous aerogels constructed by ceramic fiber components (CNFAs) feature lightweight, compressibility, and high-temperature resistance, which are superior to brittle ceramic aerogels assembled from nanoparticles. Up to now, in order to obtain CNFAs with stable framework and multifunctionality such as hydrophobicity and gas absorption, it is necessary to perform binding and surface modification processes, respectively. However, the microstructure as well as properties of CNFAs are deteriorated by the direct addition of binders and modifiers. To tackle these problems, we introduced a unique low-temperature (100 °C) chemical vapor deposition method (LTCVD) to achieve the cross-linking and hydrophobization of Si₃N₄ CNFA in only one step. More importantly, during the LTCVD process, SiO_x coatings and nanowire arrays were in situ formed via vapor-solid (VS) and vapor-liquid-solid (VLS) mechanisms on the surface and intersection of Si₃N₄ nanofibers, which cemented the aerogel framework, endowed it with hydrophobicity, and improved its oxidation resistance at high temperature. Compared to most of its counterparts, the Si₃N₄/SiO_x CNFA exhibited better mechanical properties, higher capability of oil/water separation (33-76 g·g^-1), lower thermal conductivity (0.0157 W/m·K^-1), and superior structural stability in a wide temperature range of -196-1200 °C. This work not only presents an excellent Si₃N₄/SiO_x CNFA for the first time but also provides fresh insights for the exquisite preparation strategy of CNFAs.

Transparent thermal insulation silica aerogels

Silica aerogels have received much attention due to their unique nanoporous networks, which consist of nanoscale connective silica particles and high-volume nanoscale pores. This lightweight superinsulation solid materials are synthesized by a 'sol-gel' process involving precursor preparation, gelation, aging and drying. By controlling their synthesis and processing, silica aerogels demonstrate good thermal and acoustic insulation, mechanical strength and optical transparency. In recent years, incorporating transparent and thermal insulation silica aerogels in energy-saving windows is of great interest for both scientific and technological applications. This review introduces the basic principles of thermal and optical properties of silica aerogels and highlights their tunability via synthetic and processing control. In addition, the use of silica aerogels in transparent thermal insulation windows is discussed.

Magnetically hard ferrite nanoparticles synthesized through aerogel nanoreactor

Magnetic ferrite materials have been extensively studied for a range of technological applications, such as magnetic motors, recording media, and millimetre-wave devices. In this context, the nanosized epsilon phase of Fe₂O₃ (ϵ-Fe₂O₃) attracts significant attention due to its high coercive field at room temperature. Here, we report the in-situ aerogel nanoreactor growth of magnetic ϵ-Fe₂O₃ nanoparticles, exhibiting a coercive field (H_c) of 4000 Oe. We show that the control of nanoreactor plays an important role in the growth of ϵ-Fe₂O₃ nanoparticles. The findings provide a versatile reaction pathway for the growth of magnetically hard ferrite nanoparticles.

An All-Ceramic, Anisotropic, and Flexible Aerogel Insulation Material

To exploit the high-temperature superinsulation potential of anisotropic thermal management materials, the incorporation of ceramic aerogel into the aligned structural networks is indispensable. However, the long-standing obstacle to exploring ultralight superinsulation ceramic aerogels is the inaccessibility of its mechanical elasticity, stability, and anisotropic thermal insulation. In this study, we report a recoverable, flexible ceramic fiber-aerogel composite with anisotropic lamellar structure, where the interfacial cross-linking between ceramic fiber and aerogel is important in its superinsulation performance. The resulting ultralight aerogel composite exhibits a density of 0.05 g/cm³, large strain recovery (over 50%), and low thermal conductivity (0.0224 W m^-1 K^-1), while its hydrophobicity is achieved by in situ trichlorosilane coating with the water contact angle of 135°. The hygroscopic tests of such aerogel composites demonstrate a reversible thermal insulation. The mechanical elasticity and stability of the anisotropic composites, with its soundproof performance, shed light on the low-cost superelastic aerogel manufacturing with scalability for energy saving building applications.