Thermal superinsulation,arising from nanoporous aerogels with pore sizes<70 nm,involves ultralow heat conduction with a thermal conductivity lower than that of stationary air(24 mW m^(−1)K^(−1)).However,the inheren...Thermal superinsulation,arising from nanoporous aerogels with pore sizes<70 nm,involves ultralow heat conduction with a thermal conductivity lower than that of stationary air(24 mW m^(−1)K^(−1)).However,the inherently weak necklace connection mechanism between building units and the confined deformation space within nanopores result in the intrinsic brittleness of these materials.Additionally,improvements in their mechanical flexibility typically result in compromised thermal insulation performance.To address this limitation,we herein report a core–sheath structure design of La_(2)Y_(0.4)TiZr_(2)O_(9.6)ceramic aerogel(CSCA)featuring a nanofibrous core framework for flexible deformation and a nanoporous aerogel sheath for thermal superinsulation.The resulting aerogel demonstrates remarkable mechanical flexibility with a compressive strain of up to 80%,a fracture strain of up to 21.9%and a bending strain of up to 100%,as well as thermal superinsulation with a conductivity of 21.96 mW m^(−1)K^(−1)at 26℃and remains stable at working temperatures exceeding 1300℃.Ultimately,proposed CSCA constitutes a fundamentally new approach in structure design to resolving the formidable mechanical–thermal tradeoff of aerogels,and it offers promising material configuration for further advancements in thermal superinsulation.展开更多
Porous SiC ceramics(PSCs)are promising lightweight and efficient thermal insulators that can evade infrared detection by reducing the surface temperature of the protected object,which plays a crucial role in the devel...Porous SiC ceramics(PSCs)are promising lightweight and efficient thermal insulators that can evade infrared detection by reducing the surface temperature of the protected object,which plays a crucial role in the development of new military equipment.However,the controllable synthesis of PSCs with both hierarchical pore structure and thermal/mechanical stability remains challenging.In this work,such PSCs were prepared by a facile foam-gelcasting/solid-state reaction method,using silicon powders and glucose-derived carbon as starting materials.The favorable dispersibility and wettability of hydrophilic carbon microspheres and the in-situ formed SiC guarantee the highly porous structure(92.8%porosity),comparable bulk density(0.20 g·cm^(-3))and reasonable mechanical property of the product.The designed PSCs performed outstanding high-temperature performance,especially thermal insulation in both oxidizing and inert atmospheres.More importantly,the composite architecture of PSCs and low emissivity layer(Al foil)exhibited desirable infrared stealth property(at a temperature up to 1100℃),significantly extending the operating temperature range of thermal camouflage material.The unique combination of excellent properties would make PSCs a potential candidate material for future thermal protection and infrared stealth applications in an extreme environment.展开更多
Hybrid aerogels have been prepared by freeze-drying technique after mixing water dispersions of cellulose microfibers or cellulose nanofibers and silica(SiO2)of type SBA-15(2D-hexagonal).The prepared composites were c...Hybrid aerogels have been prepared by freeze-drying technique after mixing water dispersions of cellulose microfibers or cellulose nanofibers and silica(SiO2)of type SBA-15(2D-hexagonal).The prepared composites were characterized by different analysis techniques such as SEM,hot-filament,DMA,etc.These composites are compared to those previously prepared using nanozeolites(NZs)as mineral charge.The morphology studied by SEM indicated that both systems have different structures,i.e.,individual fibers for cellulose microfibers WP-based aerogels and films for nanofibrillated cellulose NFC-based ones....These differences seem to be driven by the charge of the particles,their aspect ratio and concentrations.These hybrid materials exhibit tunable thermal conductivity and mechanical properties.The thermal conductivity values range between^18 to 28 mW.m^-1.K^-1 and confirm the superinsulation ability of these fibrous aerogels.Synergism on the thermal insulation properties and mechanical properties was shown by adjunction of mineral particles to both cellulose-based aerogels by reaching pore size lower than 100 nm.It significantly reduces the thermal conductivity of the hybrid aerogels as predicted by Knudsen et al.Furthermore,the addition of mineral fillers to aerogels based on cellulose microfibers induced a significant increase in stiffness.展开更多
基金supported by the National Natural Science Foundation of China(52322803)the Key Program of National Natural Science Foundation of China(52192661)the National Key Research and Development Program of China(2022YFC3005800).
文摘Thermal superinsulation,arising from nanoporous aerogels with pore sizes<70 nm,involves ultralow heat conduction with a thermal conductivity lower than that of stationary air(24 mW m^(−1)K^(−1)).However,the inherently weak necklace connection mechanism between building units and the confined deformation space within nanopores result in the intrinsic brittleness of these materials.Additionally,improvements in their mechanical flexibility typically result in compromised thermal insulation performance.To address this limitation,we herein report a core–sheath structure design of La_(2)Y_(0.4)TiZr_(2)O_(9.6)ceramic aerogel(CSCA)featuring a nanofibrous core framework for flexible deformation and a nanoporous aerogel sheath for thermal superinsulation.The resulting aerogel demonstrates remarkable mechanical flexibility with a compressive strain of up to 80%,a fracture strain of up to 21.9%and a bending strain of up to 100%,as well as thermal superinsulation with a conductivity of 21.96 mW m^(−1)K^(−1)at 26℃and remains stable at working temperatures exceeding 1300℃.Ultimately,proposed CSCA constitutes a fundamentally new approach in structure design to resolving the formidable mechanical–thermal tradeoff of aerogels,and it offers promising material configuration for further advancements in thermal superinsulation.
基金financially supported by the National Natural Science Foundation of China (Nos.52072274,52272021 and 52232022)。
文摘Porous SiC ceramics(PSCs)are promising lightweight and efficient thermal insulators that can evade infrared detection by reducing the surface temperature of the protected object,which plays a crucial role in the development of new military equipment.However,the controllable synthesis of PSCs with both hierarchical pore structure and thermal/mechanical stability remains challenging.In this work,such PSCs were prepared by a facile foam-gelcasting/solid-state reaction method,using silicon powders and glucose-derived carbon as starting materials.The favorable dispersibility and wettability of hydrophilic carbon microspheres and the in-situ formed SiC guarantee the highly porous structure(92.8%porosity),comparable bulk density(0.20 g·cm^(-3))and reasonable mechanical property of the product.The designed PSCs performed outstanding high-temperature performance,especially thermal insulation in both oxidizing and inert atmospheres.More importantly,the composite architecture of PSCs and low emissivity layer(Al foil)exhibited desirable infrared stealth property(at a temperature up to 1100℃),significantly extending the operating temperature range of thermal camouflage material.The unique combination of excellent properties would make PSCs a potential candidate material for future thermal protection and infrared stealth applications in an extreme environment.
文摘Hybrid aerogels have been prepared by freeze-drying technique after mixing water dispersions of cellulose microfibers or cellulose nanofibers and silica(SiO2)of type SBA-15(2D-hexagonal).The prepared composites were characterized by different analysis techniques such as SEM,hot-filament,DMA,etc.These composites are compared to those previously prepared using nanozeolites(NZs)as mineral charge.The morphology studied by SEM indicated that both systems have different structures,i.e.,individual fibers for cellulose microfibers WP-based aerogels and films for nanofibrillated cellulose NFC-based ones....These differences seem to be driven by the charge of the particles,their aspect ratio and concentrations.These hybrid materials exhibit tunable thermal conductivity and mechanical properties.The thermal conductivity values range between^18 to 28 mW.m^-1.K^-1 and confirm the superinsulation ability of these fibrous aerogels.Synergism on the thermal insulation properties and mechanical properties was shown by adjunction of mineral particles to both cellulose-based aerogels by reaching pore size lower than 100 nm.It significantly reduces the thermal conductivity of the hybrid aerogels as predicted by Knudsen et al.Furthermore,the addition of mineral fillers to aerogels based on cellulose microfibers induced a significant increase in stiffness.
