Super Thermal Insulation Research Articles

Thermal stability investigations of different aerogel insulation materials at elevated temperature

Super thermal insulation materials with low thermal conductivities, such as aerogels and vacuum insulation panels, are increasingly pushing conventional thermal insulations out of the market. Super insulation materials such as aerogels can be used easily on both vehicles and buildings. Nowadays, their usage by pipes transporting hot medium is also widespread. In these environments where elevated temperatures (100–250 °C) are applied, it is a basic requirement that they should keep their excellent thermal insulating capability. In this study, a comprehensive examination performed on two new silica-aerogel type insulations is presented. We investigated the change in the thermal performance of different types of aerogel insulations (Slentex and Pyrogel) after thermal annealing, ageing them at 150 and 250 °C temperatures for 1 day. After these thermal treatments, their thermal parameters such as thermal conductivities and specific heat capacities were measured. We revealed that both the thermal conductivity and the specific heat capacity for the Pyrogel changed considerably after annealing, while for Slentex the thermal conductivity remained constant and the specific heat capacity changed. To understand these changes we executed calorimetry tests and microscopic inspections with different methods. These experiments were completed with X-ray diffractometry to analyze the possible structural changes in the samples. From an application point of view, we consider the importance of these results, since they predict the lifetime of the used insulating material during their industrial use.

Chemically bonded multi-nanolayer inorganic aerogel with a record-low thermal conductivity in a vacuum.

Inorganic aerogels have exhibited many superior characteristics with extensive applications, but are still plagued by a nearly century-old tradeoff between their mechanical and thermal properties. When reducing thermal conductivity by ultralow density, inorganic aerogels generally suffer from large fragility due to their brittle nature or weak joint crosslinking, while enhancing the mechanical robustness by material design and structural engineering, they easily sacrifice thermal insulation and stability. Here, we report a chemically bonded multi-nanolayer design and synthesis of a graphene/amorphous boron nitride aerogel to address this typical tradeoff to further enhance mechanical and thermal properties. Attributed to the chemically bonded interface and coupled toughening effect, our aerogels display a low density of 0.8mg cm-3 with ultrahigh flexibility (elastic compressive strain up to 99% and bending strain up to 90%), and exceptional thermostability (strength degradation <3% after sharp thermal shocks), as well as the lowest thermal conductivities in a vacuum (only 1.57mW m-1 K-1 at room temperature and 10.39mW m-1 K-1 at 500°C) among solid materials to date. This unique combination of mechanical and thermal properties offers an attractive material system for thermal superinsulation at extreme conditions.

Mechanically Robust Nanoporous Polyimide/Silica Aerogels for Thermal Superinsulation of Aircraft

Polyimide aerogels (PIAs) are thermally insulating materials that possess various advantages, such as exceptionally high temperature resistance and low thermal conductivity, which make them great potential candidate materials to be applied in the area of thermal protection. However, under harsh mechanical stresses, the macro- and microscopic structural stability of PIAs may be compromised due to shrinkage/collapse, leading to performance degradation. Herein, we propose a homogeneous organic/inorganic hybrid formation strategy for constructing nanoporous polyimide/silica aerogels (PIAs-A) with exceptional mechanical strength and ultralow thermal conductivity. The results obtained indicate that PIAs-A have an optimal three-dimensional nanoporous network structure with a pore size distribution mainly within the range of 10–20 nm. Monitoring the temperature evolution of the material’s cold surface showed that it remained at a low temperature of 37.5 °C even when the material was placed against a hot surface of 150 °C. The residual mechanical strengths of the aerogels remained at a superior level (with strength degradation being less than 9%) after exposure to ultralow and high-temperature atmospheres. Furthermore, compressive stress values at 3% strain exceeded previously reported values for PIAs by 625 and 733% at −50 and 100 °C, respectively. Meanwhile, our aerogels displayed flame resistance even when exposed to a heat source of approximately 1200 °C, possessed favorable hydrophobic properties, and maintained dimensional stability up to 504 °C. The robust mechanical and thermal insulation properties of PIAs-A make them a promising substitute material for thermal superinsulation in aircraft.

Superelastic Carbon Aerogels: An Emerging Material for Advanced Thermal Protection in Extreme Environments

AbstractCarbon aerogels (CAs) are desirable for thermal protection in aerospace because of their lightweight and high‐temperature insulation characteristic; however, their intrinsic brittleness and flaw sensitivity easily trigger catastrophic failure when resisting high‐frequency thermal shocks or complex mechanical stresses. Compression is the predominant load applied on aerogels by aerodynamic pressure and pre‐tightening force; therefore, the structural elasticity and exceptional capability to keep thermal performance under impact stress are crucial in deciding the actual availability of aerogels. This review presents the recent progress in newly resilient CAs for thermal protection, focusing on reliable structural stability, thermal stability, and thermal superinsulation property. The influence law of microstructures on heat transfer behaviors is first investigated, followed by construction strategies for adiabatic CAs, emphasizing the recoverable deformability resulting from increased continuity of building blocks from 0D nanoparticles to 1D nanofibers/nanotubes and then to 2D nanosheets. Moreover, the optimization of thermal stability in high‐temperature aerobic environments and thermal insulation performance are discussed. Finally, it raises current challenges and further opportunities for CAs toward better properties and brighter prospects.

Ultrasound and H2O assisted scCO2 foaming technology for preparation of PS/PMMA composite foams with ultra-lightweight and super thermal-insulation

Porous polymer with lower density is more favorable for practical thermal insulation. In this work, a judicious combination of mechanical mixing and supercritical carbon dioxide foaming was applied to prepare ultra-lightweight polymer microcellular foam. The polymer foaming behavior is improved by adding water and ultrasound as an external energy source. The presence of water greatly increases the efficiency of ultrasound propagation, resulting in an almost two-fold increase in expansion ratio of foams. With the assistance of water and ultrasonic irradiation, the prepared foams have a 79-fold foaming expansion ratio and an average thermal conductivity as low as 26.79 mW/mK. The ultrasound also affects the process of foaming in both the saturation and release stage, but is more effective in the release stage than in the saturation stage. Consequently, this study provides a novel, facile, versatile, green approach for the preparation of microcellular polymers with ultra-lightweight and super thermal insulation.

Ultralight elastic Al2O3 nanorod-graphene aerogel for pressure sensing and thermal superinsulation.

Novel nanorod aerogels have gained tremendous attention owing to their unique structure. However, the intrinsic brittleness of ceramics still severely limits their further functionalization and application. Here, based on the self-assembly between one-dimensional (1D) Al2O3 nanorods and two-dimensional (2D) graphene sheets, lamellar binary Al2O3 nanorod-graphene aerogels (ANGAs) were prepared by the bidirectional freeze-drying technique. Thanks to the synergistic effect of rigid Al2O3 nanorods and high specific extinction coefficient elastic graphene, the ANGAs not only exhibit robust structure and variable resistance under pressure, but also possess superior thermal insulation properties compared to pure Al2O3 nanorod aerogels. Therefore, a series of fascinating features such as ultra-low density (3.13-8.26 mg cm-3), enhanced compressive strength (6 times higher than graphene aerogel), excellent pressure sensing durability (500 cycles at 40% strain) and ultra-low thermal conductivity (0.0196 W m-1 K-1 at 25 °C and 0.0702 W m-1 K-1 at 1000 °C) are integrated in ANGAs. The present work provides fresh insight into the fabrication of ultralight thermal superinsulating aerogels and the functionalization of ceramic aerogels.

Facile synthesis of super-thermal insulating polyimide aerogel-like films.

Thermal superinsulation materials play a key role in reducing energy consumption. In this article, flexible polyimide aerogel-like films are developed by a facile non-solvent-induced phase separation combined with ambient drying method. The pore structure and insulation properties are well controlled by changing the compositions of the coagulation bath. Polyimide films with macro-nano hierarchical pore structure and uniform nanopores are prepared by adjusting the content of water and alcohol as the non-solvent. The relationship between the insulation performance and textured structure of polyimide was studied. After optimization, the produced film achieved a low thermal conductivity of 0.019 W⋅m-1·K-1 but good tensile strength of 89.6 MPa, compared favorably with literature results. Hence, this article demonstrates that application of the facile phase inversion method to prepare porous polymers can be expanded from desalination or gas separation fields to insulation for energy-saving purposes.

Bioinspired SiC aerogels for super thermal insulation and adsorption with super-elasticity over 100,000 times compressions

Silicon carbide (SiC) aerogels with high porosity and excellent thermal stability are a promising thermal insulation and adsorption material. However, the poor mechanical properties of SiC aerogels greatly limit its practical application. Herein, inspired by flexible palm bark, for the first time, we report a novel method called “bioinspired link assembly” (BLA) to fabricate bioinspired SiC aerogels (BSA) with significant layered structure. The layered structure and elastic links are in situ constructed in bioinspired link assembly process. The BLA method optimizes structure of the BSA by regulate monolayer dimensions. Owing to the elastic links between the layered structures, the BSA can be bent 180°. Moreover, the BSA shows super-elasticity (elastic deformation up to 70 %) and fatigue resistance (100000 compressions). Benefiting from layered structure, the BSA exhibits an ultralow thermal conductivity (0.027 W m−1 K−1). In addition, BSA shows excellent absorption capacities (weight gain about 44 ∼ 72 times) for organic solvents. Therefore, the excellent comprehensive properties make BSA have broad application prospects in the fields of high temperature thermal insulation and oil pollution treatment.

Get the light & keep the warmth - A highly insulating, translucent aerogel glass brick for building envelopes

Silica aerogels are thermal superinsulation materials that have found increasing application in the building sector in the last ten to fifteen years. While the most common material types are opaque insulating blankets and renders, in its monolithic form silica aerogel can be almost transparent, allowing for composite translucent insulating building system.Here, we developed and characterized a novel modular, translucent and thermally insulating building component based on silica aerogel granules, the aerogel glass brick. Both thermal and mechanical properties were tested and the former were compared to a 3D simulation of the heat transfer through the brick. The glass brick has a measured thermal conductivity of 53 mW/(m·K), corresponding well to the simulation results of 51 mW/(m·K), and a compressive strength of almost 45 MPa. This makes the glass brick the insulating brick with the highest insulation performance reported in literature or available on the market, and at the same time adds the feature of light transmission.The aerogel glass brick is suitable when the requirements combine daylighting, glare protection and the need to protect privacy, e.g. offices, libraries, museums; an analysis of the materials costs indicates that the insulating glass brick can be competitive in such applications. The glass brick provides architecture with new design opportunities to increase daylight inside buildings.

Carbon layer encapsulation strategy for designing multifunctional core-shell nanorod aerogels as high-temperature thermal superinsulators

Aerogels have been considered as attractive candidates for spacecraft thermal protection systems. However, constructing lightweight aerogels with better mechanical strength, higher temperature resistance and lower high-temperature thermal conductivity, whether based on nanoparticles or nanofibers, is still a great challenge. Moreover, to avoid performance degradation caused by moisture absorption, insulating aerogels usually suffer from complex post-processing to obtain superhydrophobicity, which also cannot be guaranteed once the surface breaks down. Herein, a carbon layer encapsulation (CLE) strategy is proposed to resolve the above-mentioned conundrums in a simple way. Thanks to the collaboration of structural design and theoretical simulations, the tailored Al2O3-carbon core–shell nanorod aerogels demonstrate excellent comprehensive properties of low density (as low as 0.086 g·cm−3), outstanding stiffness (a specific compressive strength of 69.83 kN·m·kg−1), bionic abrasion-durable superhydrophobicity (WCA 156° after 1000 abrasion cycles), ultra-high thermal stability (over 1500 °C in argon and over 1400 °C in air) and high-temperature thermal superinsulating performance (0.065 W·m−1·K−1 at 1200 ℃). The synergy of ultrafine Al2O3 nanorods and carbon layers with suitable thickness not only forms a robust lotus leaf-like structure, but also enables the obtained aerogels to exhibit much superior thermal insulation properties than reported Al2O3-based aerogels. The significant increase in temperature resistance induced by lattice distortion is also an interesting phenomenon that has been investigated in detail. This novel strategy provides a fresh perspective for the preparation of multifunctional thermal high-temperature superinsulators applicable to spacecraft thermal protection systems.

Vacuum insulation arrays as damage-resilient thermal superinsulation materials for energy saving

<h2>Summary</h2> The building sector, where heating and cooling are the major energy consumers, contributes significantly to global greenhouse gas emissions. Large energy savings can be achieved if buildings are thermally insulated from the environment. Existing high-thermal insulation materials, such as aerogels and vacuum insulation panels, are vulnerable to mechanical forces and damage, making their installation a significant challenge and compromising their long-term performance. Here, we report a vacuum insulation array (VIA) design that combines mechanical robustness and ultrahigh thermal-insulation performance, with local vacuum cells that are hermetically sealed and separated from each other. This design allows the material to be punctured, cut, or reassembled, with a long-term thermal conductivity of less than 0.007 W/m-K even after puncture damage. Our insulation material can potentially realize a 20%–40% reduction in the annual energy use for the existing building-space heating and cooling with only 2 cm of added thickness.

Ultralight, super thermal insulation, and fire-resistant cellular cement fabricated with Janus nanoparticle stabilized ultra-stable aqueous foam

Bubble-templated advanced cellular materials with ultralight and superior thermal insulation properties have shown great potential in energy-saving related applications. However, insufficient bubble stability severely limits the generation of such highly porous structures. Herein, we present an efficient method to produce ultra-stable aqueous foams by combing the amphiphilic Janus nanoparticle (Janus-SiO2) with the surface-active polymer (hydroxypropyl methylcellulose). The life of aqueous foams is dramatically increased from 4 h to over 5 days with 5 wt% Janus-SiO2 concentration. The dense adsorbed layer formed by the efficient adsorption of Janus-SiO2 on the bubble film is the main factor for the outstanding foam stability. Owing to the greatly enhanced foam stability, we successfully produce ultralight cellular cement with hierarchical cellular structures and a density as low as 80 kg/m3. The ultralight cellular cement exhibits superior mechanical strength, robust fire resistance and excellent thermal insulation with a thermal conductivity as low as 0.038 W·m−1·K−1. This work provides a practical approach for fabricating various advanced porous materials that employ bubbles as templates.

Preparation and characterization of novel nano‐Al2O3/SiO2‐based composites for energy‐saving

AbstractNano‐porous super thermal insulation composites are an important component in refractory and play a key role in energy‐saving. In this work, we adopt dry preparation technology and high‐temperature sintering and use nano‐Al2O3 and nano‐SiO2 as the main materials to prepare nano‐Al2O3/SiO2‐based composites for a range of performance characterization. According to this study, the as‐prepared nano‐Al2O3/SiO2‐based composites exhibited a high porosity (77.4%–89.6%) and a low thermal conductivity (.06–.134 W/(m k) at 200–800°C). The most striking finding of this study was the nanostructure that was successfully constructed in nano‐Al2O3/SiO2‐based composites and exhibited a well hierarchical aperture distribution. The as‐prepared nano‐Al2O3/SiO2‐based composites could be widely applied in energy‐saving and heat preservation applications.

Exploring Mechanical Properties of SiO2 Elastic Micro-Nano Ceramic Fibres Aerogels

With the development of hypersonic vehicles and the military, SiO2 elastic nano-fibre ceramic aerogel becomes a preferred and potential material due to its ultralight, thermal superinsulation, and superelasticity properties. Compared with traditional ceramic materials which are brittle and easily degraded, SiO2 elastic nano-fibre aerogel shows up with its outstanding characteristics under extreme conditions. Facing a major demand in the national strategy of thermal insulation materials, this study will keep an eye on these growing and famous novel materials. Summarizing current studies and research at home and abroad. And explaining the evolution from traditional SiO2 aerogels to elastic aerogels to new SiO2 nano-fibre aerogels with flexible elastic bonds. Finally, providing regulation factors that can be improved and employed in future experiments. Giving prospects and focus for future research.

Implementing an Air Suction Effect Induction Strategy to Create Super Thermally Insulating and Superelastic SiC Aerogels.

Silicon carbide (SiC) aerogels are promising thermal insulators that are lightweight and possess high thermal stability. However, their application is hindered by their brittleness. Herein, an air suction effect induction (ASEI) strategy is proposed to fabricate a super thermally insulating SiC aerogel (STISA). The ASEI strategy exploits the air suction effect to subtly regulate the directional flow of the SiO gas, which can induce directional growth and assembly of SiC nanowires to form a directional lamellar structure. The sintering time is significantly reduced by >90%.Significant improvements in the compression and elasticity performance of the STISA are achieved upon the formation of a directional lamellar structure through the ASEI strategy. Moreover, the lamellar structure endows the STISA with an ultralow thermal conductivity of 0.019 W m-1 K-1 . The ASEI strategy paves the way for structural design of advanced ceramic aerogels for super thermal insulation.

Polyimide Aerogel Fibers with Controllable Porous Microstructure for Super-Thermal Insulation Under Extreme Environments

Polyimide Aerogel Fibers with Controllable Porous Microstructure for Super-Thermal Insulation Under Extreme Environments

All-Ceramic and Elastic Aerogels with Nanofibrous-Granular Binary Synergistic Structure for Thermal Superinsulation.

High-performance thermally insulating ceramic materials with robust mechanical properties, high-temperature resistance, and excellent thermal insulation characteristics are highly desirable for thermal management systems under extreme conditions. However, the large-scale application of traditional ceramic granular aerogels is still limited by their brittleness and stiff nature, while ceramic fibrous aerogels often display high thermal conductivity. To meet the above requirements, in this study, ceramic nanofibrous-granular composite aerogels with lamellar multiarch cellular structure and leaf-like fibrous-granular binary networks are designed and fabricated. The resulting composite aerogels possess ultralow weight, superelasticity with recoverable compression strain up to 80%, and large mechanical strength. Furthermore, excellent fatigue resistance with 1.2% plastic deformation after 1000 cyclic compressions, temperature-invariant dynamic mechanical stability from -100 to 500 °C, and an operational temperature range from -196 to 1100 °C are successfully achieved in the proposed composites. The nanosized silica granular aerogels are assembled into a leaf-like shape and wrapped around the fibrous cell walls, endowing low thermal conductivity (0.024 W m-1 K-1) as well as favorable high-temperature thermal superinsulation properties. Benefiting from the favorable compatibility, the present strategy for nanofiber-granular composite ceramic aerogels provides a dominant route to produce thermally insulated and mechanically robust composite cellular materials for use in harsh environments.

Ultralight, Super Thermal Insulation, and Fire-Resistant Cellular Cement Templated by Janus Nanoparticle Stabilized Ultra-Stable Wet Foam

Ultralight, Super Thermal Insulation, and Fire-Resistant Cellular Cement Templated by Janus Nanoparticle Stabilized Ultra-Stable Wet Foam

Application of Nanoporous Super Thermal Insulation Material in the Prevention and Control of Thermal Hazards in Deep Mining of Metal Mines

As an important energy material, mineral resources have an important role in the rapid growth of the national economy. In recent years, with the enhancement of mining strength and the improvement of mechanized production level, the depth of mining has also increased year by year. Therefore, the number of heat hazards in deep mine mining has increased year by year, and the problem of heat loss in deep mines has become increasingly prominent, which has seriously affected the safe and efficient production of mines. In this paper, the application of nanoporous super insulation materials in the prevention of thermal damage in deep mining of metal mines is studied, and the related theories of nanoporous super insulation materials and the prevention of thermal damage in deep mining of metal mines are understood on the basis of literature data. Nanoporous thermal insulation materials refer to thermal insulation materials with pore diameters in the nanometer range. This material can effectively prevent the collision of gas molecules and prevent the heat conduction of the gas. Then, the application experiment of nanoporous super thermal insulation materials in the prevention and control of heat damage in deep mining of metal mines is carried out. Through experiments, it is concluded that the room temperature thermal conductivity of the experimental material decreases with the increase of the addition of SiO2 aerogel, and the downward trend is linear, and when the heat source temperature is 200°C, the coating surface temperature of the thermal insulation material (excluding aerogel) is 100°C, and the thermal insulation temperature difference is 100°C, while when the coating surface temperature of the aerogel thermal insulation coating is only 60°C, the thermal insulation temperature difference is 140°C. From these data, it can be seen that the thermal insulation performance of nanoporous super thermal insulation materials is better, which verifies the feasibility of its application in the prevention of heat damage in metal mine mining.

Organosilica Nanotubes for Thermal Insulation

Super-thermal insulation materials have important applications in the field of building insulation. The construction of one-dimensional nanotube thermal insulation materials is expected to further reduce their thermal conductivity. Organosilica nanotubes are fabricated using an in situ interfacial sol–gel reaction at the inverse-emulsion interface. Compared with the preparation method of silica aerogel, this one-pot sol–gel method is facile and can be carried out at room temperature. The nanotube morphologies and gelation process can be controlled. Because of their hierarchical porous structures, the as-formed nanotube materials have high thermal insulation properties, which are below that of air.