High-temperature Insulation Research Articles

Ceramic Microsphere Aerogels by Curled Precursor Molecular Chain: Antishrinkage, Thermal Insulation and Multiscale Simulations.

Ceramic aerogels prepared by the route of polymer-derived ceramics (PDCs) have been of significant attention in high-temperature insulation. However, the application of ceramic aerogels was seriously confined due to the structural damage and shrinkage cracking of ceramic precursors during pyrolysis. In this investigation, precursor ceramic microsphere aerogels with outstanding antishrinkage properties were prepared by storing strain in curled molecular chains and using polysilazane (PSZ) as the precursor. Meanwhile, precursor ceramic microsphere aerogels with different curled molecular chain structures were prepared by modulating solvent interactions and cross-linked structures. Different curled molecular chain structures were formed, and the impact on the antishrinkage properties of precursor aerogels was analyzed. The shrinkage resistance, thermal insulation, and mechanical properties of the prepared aerogels were tested and compared. Furthermore, the mechanism of the impact of different curled molecular chain structures on thermal insulation and mechanical properties was investigated through multiscale simulations combined with fractal theory. The thermal and stress transfer at the interfaces of different microsphere skeleton structures and the mechanisms were investigated. An idea for solving the problem of pyrolytic shrinkage in the preparation of ceramic aerogels was provided in this investigation. In addition, insights into the influence of the microsphere skeleton structure on the thermal and mechanical properties of ceramic aerogels were provided.

High-Temperature SHS Heat Insulators Based on Pre-Activated Mineral Raw Materials

In this paper, the results of the technological combustion of SHS heat insulators based on mineral origins are presented. It is shown that after mechanochemical treatment of minerals—diatomite—the kinetic characteristics of the combustion process change, providing targeted formation of the phase composition, structure, and properties of the SHS composite. A positive effect of using various modifiers during the MCT of diatomite—the activation of the combustion process—was established. The selection of modifiers provides an increase in the strength of the synthesized SHS composites as a result of the formation of aluminate compounds in the synthesis products, and a decrease in thermal conductivity to 0.157 W/m*K due to the formation of the ultraporous structure of the samples.

Preparation and Properties of Flexible Phenolic Silicone Hybrid Aerogels for Thermal Insulation

In order to prepare flexible thermal protection aerogel materials, using dimethyldimethoxysilane (DMDMS) and methyltrimethoxysilane (MTMS) as co-precursors, isocyanate-propyltrimethoxysilane (CFS-006) was added to the co-precursor as a coupling agent, and resorcinol and formaldehyde were added to the sol solution to prepare a phenolic silicone hybrid aerogel (FAS) by the sol–gel method. The prepared FAS aerogel had no phase separation problem, the density was only 0.118 g/cm3, the hydrophobic angle reached 155.3°, and it had certain flexibility. It could be compressed to 70% and still be restored to its original state. The FAS aerogel also had a low thermal conductivity of 0.0318 W/(m·K) and good high temperature insulation. The introduction of phenolic groups improved thermal stability; Tmax increased to 643.7 °C, and the residual carbon rate was 24.5%. This work has positive significance for the future combination of aerogels and textiles in the preparation of firefighting protective clothing.

Research on thermal insulation performance and application simulation of high-temperature vacuum insulation panel

Research on thermal insulation performance and application simulation of high-temperature vacuum insulation panel

“Cocktail-like” double-layered polyimide/alumina composite aerogels via side-direction freezing method as designable high-temperature thermal insulations

The extremely low thermal conductivity, low density, and high-temperature stability of polyimide (PI) aerogels are promising candidates for thermal insulation applications. In this work, the layered PI/Al2O3 composite aerogels (PACAs) were developed, inspired by the biomimetic idea of a “cocktail” layered structure to enhance the service temperature of PI. By exploiting the density difference between the water-soluble polyimide acid (PAA) solution and Al2O3 slurry, we successfully fabricated PACAs with a macro-scale layered structure through side-direction freezing and thermal imidization processes. The PACAs exhibit significant anisotropic structural characteristics, with pore channels presenting a honeycomb structure in the Z-direction, effectively suppressing heat transfer along this direction. Both PI and Al2O3 aerogels demonstrate anisotropic properties in different directions, with the PI aerogel achieving excellent thermal insulation with a thermal conductivity of 0.0197 W/(m·K) along the Z-direction. By adjusting the relative thickness of the PI and Al2O3 layers, optimal thermal insulation performances were achieved at temperatures of 300 °C, 600 °C, and 900 °C. These results showcase the innovative advantages of the layered structure in enhancing thermal insulation while leveraging the low thermal conductivity of PI and the high-temperature tolerance of Al2O3.

Ablation resistance and high-temperature insulation capacity of TiB2-B4C modified Al-coated carbon fibre/boron phenolic resin ceramizable composites

The inherent susceptibility to oxidation limits the application of carbon fibre/phenolic resin composites (CF/Ph) in the thermal protection of hypersonic vehicle engines. Herein, TiB2-B4C modified Al-coated carbon fibre/boron phenolic resin ceramizable composites were fabricated. The optimal ceramizable composite (T30C10) exhibited excellent ablation resistance and high-temperature insulation capacity at a linear ablation rate and bottom-surface temperature of -0.00768 mm/s and 129.8 °C, respectively. Oxygen consumption and inhibition, carbon fixation, and self-healing effects contributed to the excellent ablation resistance, and the effects of the Al coatings and carbothermal reduction reactions led to excellent high-temperature insulation capacities.

Synergic process of molybdenum recovery and ceramic preparation for clean and efficient utilization of industrial leaching residues

Ammonia-leaching residues of roasted molybdenite concentrates are intractable wastes and are mostly stockpiled in factories. Common treatments suffer from low Mo recovery and secondary pollution. This study has developed a synergistic process involving a single-step roasting with the addition of Al2O3 and MoO3 to recover Mo and simultaneously prepare porous refractories from the residues containing 5.6% Mo. The Mo separation efficiency, ceramic properties, and thermal behaviors—including chemical reactions, melting transformations, ceramic structure evolutions, and Mo species migrations—were comprehensively investigated. It was found that the addition of Al2O3 facilitated CaMoO4 decomposition to release volatile MoO3, thus promoting Mo recovery. The mullite started to form at about 900 °C, grew into whiskers, and further into interconnected clusters, under the catalytic effect of liquid MoO3 and the sintering effect of glassy melt. Liquid MoO3 was scattered on the outer surface of whisker clusters, achieving a high separation efficiency of over 98% after roasting at 1300 °C for 150 min. Meanwhile, a ceramic with a high porosity of 64.2% and a high compressive strength of 21.2 MPa was obtained, exhibiting promise for serving as a high-temperature insulation refractory. Overall, this study presents a novel approach for both the profound recovery of Mo and the value-added utilization of gangue minerals derived from CaMoO4-bearing wastes.

Predicting effective thermal conductivity of HGM composite using ML

Data-driven materials research can be used as an effective tool to supplement conventional approaches in designing new materials. Hollow glass microsphere (HGM) composites are widely used for high-temperature thermal insulation applications, and their synthesis is traditionally done by varying parameters of the constituents on a trial-and-error basis. In this work, a prediction tool based on a supervised machine learning (ML) model is developed to predict the effective thermal conductivity (ETC) of an HGM composite by tailoring the composition and parameters of the constituents to reduce the time and cost involved. A comprehensive database containing the various input features is generated from previous experimental investigations conducted on various HGM composites. ML models, namely random forest regression (RF), K-nearest neighbor (KNN), support vector regression (SVR), and artificial neural network (ANN), are used to predict the ETC of HGM composites. Feature importance analysis showed that the matrix material’s thermal conductivity and the composite’s bulk density have the highest impact on the ETC of the HGM composite, followed by porosity and average microsphere size. ANN emerged as the best model to predict HGM composite ETC with the lowest root mean square error and highest R2 value for predictions. Moreover, a systematic approach for key feature selection using ANN shows that adding or omitting additional features beyond an optimal combination degrades the model’s predictive accuracy.

A novel Yb2SiO5 ceramic aerogel with excellent thermal stability for high-temperature thermal insulation

To investigate the potential of rare earth oxide structural ceramics for high-temperature insulation applications, we introduced aerogel structures into Yb2SiO5 ceramics. In this study, the pure Yb2SiO5 ceramic aerogels were successfully prepared by calcination using formamide as a gelling agent, the sol-gel method, and the CO2 supercritical drying method. The results indicate that the Yb2SiO5 ceramic aerogel exhibits exceptional structural and phase stability at a temperature of 1400 °C. In addition, we have developed Yb2SiO5 ceramic aerogel composites reinforced with aluminosilicate fiber cotton, which exhibit low density (228.77 kg m−3) and low thermal conductivity (0.038 W m−1 K−1 at 25 °C, 0.102 W m−1 K−1 at 1000 °C). The back temperature of the 10 mm thick composites is only 285 °C after exposure to a butane blowtorch flame at 1300 °C for 600 s. This demonstrates its excellent high-temperature insulation performance. This work can provide a basis for further design and preparation of oxide ceramic high-temperature thermal protection materials with controllable morphology and properties.

Synergistic performance enhancement of lead-acid battery packs at low- and high-temperature conditions using flexible phase change material sheets

Thermal management of lead-acid batteries includes heat dissipation at high-temperature conditions (similar to other batteries) and thermal insulation at low-temperature conditions due to significant performance deterioration. To address this trader-off, this work proposes a thermal management solution based on flexible phase change materials (PCMs) with moderate thermal conductivity and other favourable properties including high specific heat capacity and high latent heat. A novel type of flexible PCM sheets is prepared with paraffin, olefin block copolymers (OBC) and expanded graphite using the co-melting method. The flexible PCM sheets are attached to a common type of lead-acid battery packs (12 Ah, dimensions of 151 × 98 × 97 mm) and thermal management performance is experimentally investigated at –10 °C and 40 °C as low- and high-temperature conditions, respectively, along with 25 °C as a baseline case for comparison purposes. Thermal properties of the battery packs such as temperature regulation and electric properties including charge/discharge capacities and rates are studied synchronously based on a standard high-performance battery detection facility. The results indicate that at –10 °C condition, the PCM sheet enhances thermal insulation of the battery pack and significantly promotes the service temperature during the charging processes. Compared with a benchmark pack attached with an encapsulated sheet, the charge and discharge capacities of the PCM-attached pack are improved by 3.7% and 5.9%, respectively. At 40 °C condition, phase transition of the PCM sheet restrains the temperature rise of the battery pack, with a maximum temperature decrease of 4.2 °C during the charging processes relative to the benchmark pack, and the temperature of the PCM-attached pack is maintained below 45 °C across 60% of the overall charge period. The overcharge and overdischarge have also been alleviated by 3.2% and 2.8%, respectively, and thus the running stability and service lifespan can be improved. The proposed PCM sheets with preferable thermal properties demonstrate potential to promote performance of lead-acid battery packs and such components are also expected to improve heat dissipation and thermal insulation in similar applications including building energy saving, thermal management of electronic chips and thermal regulation of electronic devices.

Preparation and Properties of Lightweight Aggregates from Discarded Al2O3-ZrO2-C Refractories.

Refractory materials are an important pillar for the stable development of the high-temperature industry. A large amount of waste refractories needs to be further disposed of every year, so it is of great significance to carry out research on the recycling of used refractories. In this work, lightweight composite aggregate was prepared by using discarded Al2O3-ZrO2-C refractories as the main raw material, and the performance of the prepared lightweight aggregate was improved by adjusting the calcination temperature and introducing light calcined magnesia additives. The results showed that the cold compressive strength and thermal shock resistance of the lightweight aggregates were significantly improved with increasing calcination temperature. Moreover, the introduction of light calcined magnesia can effectively improve the apparent porosity, cold compressive strength, and thermal shock resistance of the prepared lightweight aggregates at the calcination temperature of 1400 °C. Consequently, this work provides a useful reference for the resource utilization of used refractories, while the prepared lightweight aggregates are expected to be applied in the field of high-temperature insulation.

Design of High-Temperature Packaging Insulation for Power Modules Using Grafted Nanostructured Silicone Elastomer Composites

Design of High-Temperature Packaging Insulation for Power Modules Using Grafted Nanostructured Silicone Elastomer Composites

Design and fabrication of metal spherical conformal thin film multisensor for high-temperature environment

Conformal thin-film sensors enable precise monitoring of the operating conditions of components in extreme environments. However, the development of these sensors encounters major challenges, especially in uniformly applying multiple film layers on complex metallic surfaces and accurately capturing diverse operational parameters. This work reports a multi-sensor design and multi-layer additive manufacturing process targeting spherical metallic substrates. The proposed high-temperature dip-coating and self-leveling fabrication process achieves high-temperature thin-film coatings with excellent uniformity, high-temperature electrical insulation, and adhesion properties. The fabricated Ag/Pt thin film thermocouple arrays and a heat flux sensor exhibit a maximum temperature resistance of up to 960 °C, with thermoelectric potential outputs and high-temperature resistance closely mirroring those of wire-based Ag/Pt thermocouples. Harsh environmental testing was conducted using high-power lasers and a flame gun. The results show that the array of thin-film conformal thermocouples more accurately reflected temperature changes at different points on a spherical surface. The heat flux sensors achieve responses within 95 ms and withstand environments with heat fluxes over 1.2 MW/m2. The proposed multi-sensor design and fabrication method offers promising monitoring applications in harsh environments, including aerospace and nuclear power.

Effect of γ-radiation on silica aerogel and composite material for thermal insulation applications in nuclear power pipeline

SiO2 aerogel and its composite materials are considered as promising high-temperature thermal insulation materials due to their high porosity, low density and low thermal conductivity. However, a major obstacle for their application in nuclear power systems is the currently insufficient mechanism of the radiation effect. This study therefore aimed to investigated the changes in the microstructure, hydrophobic properties and thermal insulation properties of aerogel and ultrafine glass fiber reinforced aerogel composite (uGF/SiO2 aerogel) before and after γ-radiation, and explore the mechanism of the γ-radiation effect of aerogel materials. With an increase in cumulative radiation dose, the microstructure of aerogel suffered significant radiation damage, causing a gradual increase in crystallinity and thermal conductivity. When the cumulative dose reached 1700 kGy, the nanoparticles in the aerogel agglomerated and crystallized significantly, leading to an approximately 30 % increase in thermal conductivity. Notably, at the radiation of 1700 kGy, the uGF/SiO2 aerogel exhibited excellent structure stability, with a thermal conductivity of 31.60 mW/m·K, which was 3.27 % higher than that of unirradiated sample. This indicated the uGF/SiO2 aerogel exhibited excellent thermal performance and thermal stability even after γ-radiation. The study on the radiation effect of aerogel materials offers valuable insights for the composition optimization of aerogel used in nuclear power applications.

Thermally stable low-shrinkage monolithic SiC aerogels for heat insulation

In recent years, SiC aerogels have attracted considerable research interest owing to their excellent high-temperature resistance. It is crucial to research and improve the thermal stability of SiC aerogels under long and multiple heat treatments. Herein, we develop a series of monolithic SiC aerogels with a density of 0.23–0.28 g cm−3, low-thermal linear shrinkage of 21%–27 %, and high compressive strength of 0.38–0.60 MPa by designing a novel core–net structure. The resulting aerogels exhibit excellent thermal insulation thermostability and high-temperature reusability. Thermal conductivities of 0.0455–0.0678 W K−1 m−1 and 0.0934–0.1313 W K−1 m−1 were achieved at 40 °C and 900 °C, respectively. Following three consecutive heat treatments using a butane spray gun for 2000 s, the macromorphology exhibited no change, and the backside temperature was 230 °C. The results demonstrate an effective solution to reuse aerogels as long-lasting high-temperature insulation materials.

Realization of ultra-high temperature stability and excellent electrical properties in LTO-based ceramics via A/B-site co-doing

La2Ti2O7 (LTO) ceramics, ideal for ultra-high temperature applications with a Curie temperature near 1460 °C, were previously limited by a low piezoelectric coefficient (d33) of 1.5 pC/N. In this work, the incorporation of Bi3+ and V5+ dopants have been employed to augment the piezoelectric properties of LTO. An enhanced d33 ∼ 4.0 pC/N is achieved in La1.91Bi0.09Ti1.97V0.03O7 (LBTV9) ceramics, while maintaining an ultra-high Curie temperature of 1437 °C. This improvement is attributed to local heterogeneity in the lattice structure induced by the doping. LBTV9 ceramics also exhibit excellent high-temperature stability and insulation properties, maintaining a d33 at 4.0 pC/N after annealing at 1000 °C for 48 h and stabilizing at 4.2 pC/N across temperatures from 200 °C to 1600 °C, with a DC resistivity of 1.7 × 106 Ω·cm at 1000 °C. These enhancements make LBTV9 ceramics suitable for extreme condition applications, thus unlocking new possibilities for their use in ultra-high temperature piezoelectric devices.

Elevating high-temperature insulation performance of silica aerogels enabled by innovative surface-structured opacifiers

Silica aerogel, recognized as an exceptional material for thermal insulation, has gained considerable attention in thermal protection. However, its inherent infrared transparency compromises its insulating performance at high temperatures. To address this limitation, incorporating micron-sized opacifier particles has emerged as a crucial strategy. This study introduces a novel opacifier particle, distinguished by surface protrusions inspired by the ’structural absorption’ mechanism, and assesses its extinction capabilities. Then, a thorough analysis was conducted to understand how the shape, volume, and numbers of these surface protrusions influence the radiative heat transfer properties of silica aerogels. The findings reveal that the presence of protrusions on the opacifier surface significantly enhances its extinction capacity, consequently reducing the radiative thermal conductivity of silica aerogels. Notably, cylindrical protrusions demonstrate the most effective extinction properties compared to spherical protrusions and rectangular protrusions. Additionally, for opacifier particles with cylindrical protrusions, there exists an optimal number of 12 protrusions that minimize the radiative thermal conductivity of the aerogel. At 1300 K, the radiative thermal conductivity of the silica aerogel doped with opacifiers featuring 12 protrusions is 22.6 % lower than that of the silica aerogel doped with opacifiers lacking protrusions. Moreover, it was observed that maintaining a constant diameter of cylindrical protrusions while increasing their height diminishes the radiative thermal conductivity of silica aerogel. However, the effect on the radiative thermal conductivity becomes less significant beyond a certain protrusion height. The outcomes of this study provide significant insights into the innovation of opacifiers.

DFT analysis of elastic and optoelectronic properties of Cs2NaXCl6 (X=In, La, Sc, Y) double perovskite compounds

This study employs first-principles Density Functional Theory (DFT) to investigate the structural, electronic, and optical properties of double perovskites Cs2NaXCl6 (X = In, La, Sc, and Y) compounds. By applying various functionals (GGA-PBE, GGA-PBEsol, HSE06, and mBJ), we ensure an accurate and thorough description of their electronic structures and other physical properties. Our analysis reveals excellent mechanical, thermodynamic, and dynamical stability of Cs2NaXCl6 compounds. Band gap calculations employing mBJ and HSE06 functionals reveal wide direct band gaps ranging from 4.1 to 6.4 eV, with notable contributions from Cl-p states near the valence band maximum. Furthermore, electron density analysis highlights a mixed covalent-ionic bonding nature, predominantly ionic. Additionally, the optical conductivity and absorption spectra peaks extend beyond the visible region, indicating potential applications in ultraviolet (UV) technologies. Finally, thermal conductivity analyses exhibit a significant reduction with increasing temperature, suggesting promising applications in high-temperature thermal insulation.

Double-Phase-Networking Polyimide Hybrid Aerogel with Exceptional Dimensional Stability for Superior Thermal Protection System.

Polyimide aerogels have been extensively used in thermal protection domain because they possess a combination of intrinsic characteristics of aerogels and unique features of polyimide. However, polyimide aerogels still suffer significant thermally induced shrinkage at temperatures above 200 °C, restricting their application at high temperature. Here, a novel "double-phase-networking" strategy is proposed for fabricating a lightweight and mechanically robust polyimide hybrid aerogel by forming silica-zirconia-phase networking skeletons, which possess exceptional dimensional stability in high-temperature environments and superior thermal insulation. The rational mechanism responsible for the formation of double-phase-networking aerogel is further explained, generally attributing to chemical crosslinking reactions and supramolecular hydrogen bond interactions derived from the main chains of polyimide and silane/zirconia precursor/sol. The as-prepared aerogels exhibit excellent high-temperature (270 °C) dimensional stability (5.09% ± 0.16%), anti-thermal-shock properties, and low thermal conductivity. Moreover, the hydrophobic treatment provides aerogels high water resistance with water contact angle of 136.9°, further suggestive of low moisture content of 3.6% after exposure to 70 °C and 85% relative humidity for 64h. The proposed solution for significantly enhancing high-temperature dimensional stability and thermal insulation provides a great supporting foundation for fabricating high-performance organic aerogels as thermal protection materials in aerospace.

Low-density, large-sized SiCnw/SiOC composite aerogels with excellent thermal insulation, microwave absorption, and thermostability

Polymer-derived ceramic aerogels are promising materials for thermal insulation and microwave absorption in harsh environments because their microstructures can be controlled at the molecular level. Silicon oxycarbide (SiOC) aerogels are considered as potential high-temperature electromagnetic wave (EMW) absorbers, but their application range is limited by complex preparation process and unsatisfactory microwave-absorption performance. This paper reports a new SiC nanowire/SiOC composite aerogel (SCA) synthesized through the sol–gel process, environmental pressure drying, and high-temperature treatment. The SCA performance is adjusted by controlling the ratio of SiC nanowires, obtaining low thermal conductivities (0.04–0.042 W m−1 K−1) and excellent mechanical properties (4.37–5.45 MPa). Increasing the SiC nanowire content gradually increases the EMW absorption capacity of SCA. The optimal reflection loss is −53.64 dB and the effective absorption bandwidth is 3.88 GHz, substantially higher than that of SiOC aerogels. This high performance is mainly attributable to the appropriate impedance matching characteristics and strong polarization loss ability. Moreover, the performance of the composite aerogels was retained after long-term treatment in an air environment at 800 °C. SCA also exhibits excellent high-temperature insulation and flame retardancy. Owing to its light weight, strong microwave-absorption ability, good thermal insulation performance, and oxidation resistance, SCA is a highly promising alternative material for use in extreme environments.