Temperature Thermal Insulation Research Articles

Enhanced thermal performance of CeYSZ coating on Ni-based high temperature alloy with a unique Y-doped Al2O3 barrier layer via cathodic plasma electrolytic deposition

Cathodic plasma electrolytic deposition (CPED) has shown considerable potential in producing high-performance thermal barrier coatings (TBCs) for components operating in extreme thermal environments, such as gas turbines and aviation engines. However, the dendritic and porous structures greatly limited the use of CPED-coatings in some harsh environments. In this study, one Y-doped Al2O3 (Y/A) barrier layer was prefabricated before the deposition of CeO2 and Y2O3 stabilized ZrO2 (CeYSZ) thermal barrier coating using CPED. The results suggested that the prefabricated Y/A barrier layer can attenuate the plasma bombardment and promote the uniform discharge, resulting in the formation of a thinner gas film layer on the cathode surface, which significantly avoided the course dendritic defects and improved the density of the CeYSZ coating from 6.788 g/cm³ to 6.978 g/cm³. Consequently, the thermal insulation temperature of Y/A-CeYSZ coatings exceeded that of CeYSZ coatings by a factor of 1.3, and the thermal cycling performance at 1300 °C demonstrated a 52.5% improvement. This study provided a valuable method for the development of novel CPED TBCs.

Preparation and thermal cycling performance of Ce-doped YSZ thermal barrier coatings by a novel cathode plasma electrolytic deposition

The preparation and realization of highly reliable thermal barrier coatings (TBCs) on the internal surface of complex cavities is a bottleneck problem. Traditional coating methods are difficult to deposit and fulfil service requirements. In this study, a novel structure of YSZ and Ce-doped YSZ (CeYSZ) TBCs was prepared by a newly cathode plasma electrolytic deposition (CPED) technology. The results suggested that both the CPED-YSZ and CPED-CeYSZ coatings exhibited porous cross-linked dendritic structures. Because Ce doping significantly improved the phase stability of tetragonal structure and enhanced thermal insulation temperature during a burner-rig test at 1300 °C, resulting in a threefold increase in the thermal cycling life of the CPED-CeYSZ coating compared to the CPED-YSZ coating. This work provided a new strategy for tailoring multiple rare-earth principal components of high-performance TBCs and depositing them on the inner surface of complex cavities with high aspect ratios.

Study on the thermal insulation property of lanthanum–cerium oxide coatings

Functional fillers with low thermal conductivity and high near-infrared reflectance play a vital role in high temperature thermal insulation coatings and make an outstanding contribution to achieving efficient comprehensive thermal insulation. In this work, the thermal insulation and bonding properties of lanthanum–cerium oxide (LCO) coatings were regulated by composition design. The effects of the La/Ce mole ratio on phase composition, the thermal conductivity and near-infrared reflectivity of LCO coatings were investigated systematically. The results showed that coating with a La/Ce mole ratio of 1:1 possess the excellent thermal insulation properties (ΔT ≈ 115°C) due to the formation of a LCO solid solution and a lanthanum phosphate mesophase with low thermal conductivity and high near-infrared reflectivity. In addition, the mortise and tenon structure was formed between the coating and the substrate, which led to the remarkable bonding properties. The LCO coating offers excellent thermal insulation properties and broad application prospects in the fields of high temperature and energy conservation.

Phase transformation inhibition and improved thermo-mechanical properties of rare earth niobates for thermal barrier coatings

Rare earth niobate Re3NbO7 (Re=Rare earth element) possesses ultra-low thermal conductivity for application as thermal barrier coatings (TBCs). However, Re3NbO7 with large rare earth ion radius (ReLa, Nd, Sm) exhibits both low temperature phase transition and poor facture toughness which is detrimental to the durability of the coatings. In this work, an effective method was proposed to solve those problems by doping. Considering the low-temperature phase transition at about 340K, La3NbO7 is selected as representative material. In order to suppress phase transition, Y3+ with relatively smaller ionic radius is used as a doped ion, and (La1-xYx)3NbO7 (x = 0.0,0.1,0.3,0.5) were prepared and investigated. It is shown that, low temperature phase transition of La3NbO7 is effectively suppressed due to Y3+ doped. Facture toughness is increased significantly from 0.5 to 2.3 MPa m1/2 with the increase of doping concentration. Furthermore, the Vickers hardness is also improved by doping. Considering the phase stability and ultra-low thermal conductivity, (La1-xYx)3NbO7 solid solution (x = 0.5) maybe promising candidates for high temperature thermal insulation materials such as TBCs, thermoelectric materials, etc.

Advancements in Thermal Insulation through Ceramic Micro-Nanofiber Materials.

Ceramic fibers have the advantages of high temperature resistance, light weight, favorable chemical stability and superior mechanical vibration resistance, which make them widely used in aerospace, energy, metallurgy, construction, personal protection and other thermal protection fields. Further refinement of the diameter of conventional ceramic fibers to microns or nanometers could further improve their thermal insulation performance and realize the transition from brittleness to flexibility. Processing traditional two-dimensional (2D) ceramic fiber membranes into three-dimensional (3D) ceramic fiber aerogels could further increase porosity, reduce bulk density, and reduce solid heat conduction, thereby improving thermal insulation performance and expanding application areas. Here, a comprehensive review of the newly emerging 2D ceramic micro-nanofiber membranes and 3D ceramic micro-nanofiber aerogels is demonstrated, starting from the presentation of the thermal insulation mechanism of ceramic fibers, followed by the summary of 2D ceramic micro-nanofiber membranes according to different types, and then the generalization of the construction strategies for 3D ceramic micro-nanofiber aerogels. Finally, the current challenges, possible solutions, and future prospects of ceramic micro-nanofiber materials are comprehensively discussed. We anticipate that this review could provide some valuable insights for the future development of ceramic micro-nanofiber materials for high temperature thermal insulation.

PS/PPO foam with excellent comprehensive properties prepared by integrated foaming and sintering strategy with microwave-assisted

Expanded polystyrene (EPS) foam, as the earliest and most common foam part, holds the largest market share in the bead foam industry. However, its poor mechanical and thermal performance significantly hinders its widespread application. Introducing high-performance polymer polyphenylene oxide (PPO), which is well-compatible, can markedly enhance the properties of polystyrene (PS). Nevertheless, the elevated processing temperature poses a challenge for sintering the beads of PS/PPO. In this study, we propose a microwave-assisted polymer integrated foaming and sintering strategy (IFS strategy). Benefiting from the selective heating properties of microwaves, PS/PPO bead foams after rapid depressurization foaming can be sintered into robust foam parts in an extremely short time, with the simultaneous expulsion of microwave absorbers. The compressive performance of PPO-enhanced PS foam is improved by 155 % compared to PS foam and 707 % compared to expanded polystyrene (EPS). Additionally, the foam also has excellent temperature resistance (over 140 °C), flame retardancy, and thermal insulation (thermal conductivity of about 40 mW/m·K). This approach provides a feasible pathway for the green, efficient, safe, energy-saving, and sustainable preparation of high-temperature processing and high-performance polymer bead foam parts.

High Temperature Thermal Insulation Ceramic Aerogels Fabricated from ZrC Nanofibers Welded with Carbon Nanoparticles

High Temperature Thermal Insulation Ceramic Aerogels Fabricated from ZrC Nanofibers Welded with Carbon Nanoparticles

Ionic-physical–chemical triple cross-linked all-biomass-based aerogel for thermal insulation applications

Aerogels, as a unique porous material, are expected to be used as insulation materials to solve the global environmental and energy crisis. Using chitosan, citric acid, pectin and phytic acid as raw materials, an all-biomass-based aerogel with high modulus was prepared by the triple strategy of ionic, physical and chemical cross-linking through directional freezing technique. Based on this three-dimensional network, the aerogel exhibited excellent compressive modulus (24.89 ± 1.76 MPa) over a wide temperature range and thermal insulation properties. In the presence of chitosan, citric acid and phytic acid, the aerogel obtained excellent fire safety (LOI value up to 31.2%) and antibacterial properties (antibacterial activity against Staphylococcus aureus and Escherichia coli reached 81.98% and 67.43%). In addition, the modified aerogel exhibited excellent hydrophobicity (hydrophobic angle of 146°) and oil–water separation properties. More importantly, the aerogel exhibited a biodegradation rate of up to 40.31% for 35 days due to its all-biomass nature. This work provides a green and sustainable strategy for the production of highly environmentally friendly thermal insulation materials with high strength, flame retardant, antibacterial and hydrophobic properties.

Fire-resistant and thermal insulation performance of SiC nanofiber batt fabricated from cotton fiber batt

The cotton fiber batt is one of the most commonly used thermal insulator in our lives at room temperature because of its flexible and porous structure. The SiC nanofibers have excellent mechanical, physical, and chemical properties such as high mechanical strength and modulus, low density, high-temperature resistance, which is a promising material for high temperature structural materials or thermal insulator. In this work, a flexible SiC nanofiber batt was fabricated from the cotton fiber batt by sol-gel carbothermal reduction reaction. The fluffy carbonized porous cotton batt was used as a template for the fabrication of sponge-liked SiC nanofiber batt composed of single crystalline β-SiC fibers. It exhibits good compressive flexibility, ultra-high porosity (a specific surface area was 30.90 m²/g), excellent high-temperature stability (ranging from −196 °C in liquid nitrogen to 1300 °C under the flame of butane blowtorch) and low thermal conductivity (0.02 W/(m·K) at room temperature). The SiC nanofiber batt, which has low density, excellent high-temperature resistance and oxidation resistance, is a promising material for high-temperature structural materials or thermal insulators under extreme conditions. The facile fabrication method of SiC nanofiber batt from common cotton batt provides a novel technique for economic industrial production of high temperature thermal insulation material.

Fabrication of thermally resistant and mechanically flexible polyimide foams with anisotropic pore structures for thermal insulation and irradiation tolerance applications

Flexible polyimide foams (PIFs) demonstrate a great potential for applications in the fields of thermal insulation, flame retardancy and irradiation tolerance. In this work, mechanically flexible PIFs with anisotropic pore structure were prepared by adopting the copolymerization strategy and microwave-assisted foaming process. The copolymerization reaction was conducted to synthesize polyester ammonium salt (PEAS) precursors using 3,3′,4,4′-benzophenone tetracarboxylic acid dianhydride (BTDA) as dianhydride, 4,4′-diaminodiphenyl ether (ODA) and 4,4′-diaminodiphenyl sulfone (DDS) as the copolymerized diamines; afterwards, PEAS powders with particle sizes ranging from 100 to 300 μm were obtained by drying, crushing and sieving treatments, which were used as the feedstock for “bottom-up” microwave-assisted foaming and thermal imidization process, thereby leading to the formation of PIFs with regular three-dimensional near-spherical pores in vertical direction (parallel to the pore growth direction) and the aligned ellipsoidal strip-like pore structure in horizontal direction. The directional growth of foam pores resulted in anisotropic mechanical flexibility and thermal insulation performance. Moreover, PIFs possessed excellent thermal stability and flame retardancy with the initial thermal degradation temperature higher than 545 °C and limited oxygen index up to 58.8%. The PIFs exhibited exceptional thermal insulation performance with thermal conductivity values ranging from 0.0276 to 0.0517 W/(m·K) between 25 and 300 °C. Additionally, the PIFs demonstrated excellent irradiation tolerance, with the mechanical and thermal stability retention rate being above 96% after the irradiation experiment (radiation dosage: 1.15 × 105 Gy) using 60Co source. Thus, lightweight PIFs with superior high temperature thermal insulation performance, flame retardancy and irradiation tolerance were successfully prepared, which showed potential applications in aerospace, medical and nuclear power sectors.

Preparation and thermal insulation performance of Al2O3[sbnd]Y2O3[sbnd]SiO2 ternary composite aerogels with high specific surface area and low density

Against the background of global energy shortages and the need for long-term flight safety of aerospace vehicles, traditional silica aerogels have the problems of insufficient temperature resistance and poor thermal insulation at high-temperatures, and are no longer able to meet the demand. In this study, a series of monolithic Al2O3Y2O3SiO2 ternary aerogels were successfully synthesized via synchronous sol–gel and ethanol supercritical drying. Both the prepared aerogels and the calcined samples at 1000 °C exhibited a complete three-dimensional network structure and a high specific surface area (up to 675.7 m2/g and 214.4 m2/g), which was attributed to the supporting effect of the Al2O3 component on the overall skeleton and the inhibiting effect of the Y2O3 component on the crystal transformation. Mullite fiber reinforced Al2O3Y2O3SiO2 aerogel composites were synthesized by vacuum impregnation using mullite fiber felt as a matrix. The prepared sample exhibit very low thermal conductivity (as low as 0.079 W⋅m−1·K−1 at 1000 °C). In summary, the good structural stability and high temperature thermal insulation performance make Al2O3Y2O3SiO2 ternary aerogel have the potential of efficient service in more application scenarios. This study provides a product optimization reference idea for the thermal insulation material industry.

Preparation and characterization of novel lightweight Y2Si2O7 fibrous porous ceramics for high temperature thermal insulation

Fibrous porous ceramics play a vital role in the field of thermal protection systems. In this work, novel lightweight Y2Si2O7 fibrous porous ceramics were successfully prepared based on Y2Si2O7 fibrous membranes by molding method. The effects of mechanical dispersion speed and heat treatment temperature on the properties of Y2Si2O7 fibrous porous ceramics were characterized. The results revealed that benefiting from the appropriate fiber length, the ceramics had a better performance at a mechanical dispersion speed of 4000 revolutions per minute. The density, shrinkage, and compressive strength of the ceramics increased, but the porosity decreased slightly with the increasing heat treatment temperature. The prepared Y2Si2O7 fibrous porous ceramics exhibited favorable properties like low density (0.37 g/cm3), high porosity (90.56%), good high-temperature resistance (∼1350 °C), and low thermal conductivity (∼0.12 W m−1 K−1 at 27 °C, ∼0.566 W m−1 K−1 at 1000 °C). These properties indicate that Y2Si2O7 fibrous porous ceramics could be a promising candidate as thermal insulation materials in high-temperature environments.

Chitosan based aerogel fibers for piezoelectric and moisture electric energy harvesting

Taking advantages of renewable resourced materials in the preparation of multifunctional aerogel fibers which integrate thermal insulation, piezoelectric and moisture electric generation could be a promising way of relieving pressure on both energy loss and generation. A series of chitosan-konjac glucomannan (CS-KGM) aerogel fibers was obtained by means of wet-spinning method followed by freeze-drying. The CS-KGM aerogel fibers with submicron porous morphology exhibit excellent thermal insulation performance. Single layer of CS-KGM aerogel fiber with only a thickness of 0.6 mm shows a thermal insulation temperature difference of 23 °C. A stable piezoelectric output voltage of 0.35 V can be generated from a single CS-KGM aerogel fiber during a 500 press-release cycle attributing to the intrinsic piezoelectricity of CS and the porous structure. Single aerogel fibers were coated with multi-walled carbon nanotubes as a way to prepare conductive aerogels. Meanwhile, the moisture electric output voltage can be as high as 160 mV and last for >8 h at 60% relative humidity for CS-KGM single aerogel fiber assisted by a thin layer of carbon nanotube coating. Overall, CS-KGM aerogel fibers prepared in this work has good compatibility and potential applications in thermal management and energy harvesting from low density resource, which provides a new strategy for the preparation of sustainable and multifunctional wearable materials.

Synergistic regulation of temperature resistance and thermal insulation performance of zirconia-based ceramic fibers

Synergistic regulation of temperature resistance and thermal insulation performance of zirconia-based ceramic fibers

Aggregation-induced microfilaments enabled cotton cellulose aerogels with highly compressive and fatigue resistance, greatly thermal insulation and fireproofing

Green and sustainable cellulose aerogels have attracted extensive attention, but are severely limited by unsatisfied elasticity, fatigue resistance as well as fire hazard for functional applications. Herein, we proposed a novel and feasible strategy to fabricate highly elastic, thermal insulating and fireproof phytic acid/cellulose (PA/CE) aerogel via constructing microfilament substructure derived from PA-induced aggregation and assembly of cellulose chains. Benefiting from the interconnected fibrous cellular walls integrating with abundant microfilaments, the resultant PA/CE aerogels demonstrated excellent compressibility and resilience with recovery rate of 91.26% after 100 compressive cycles at 50% strain. With the hierarchical porous structure, PA/CE aerogels exhibited low thermal conductivity of 0.0340–0.0352 W/m·K, could maintain its structural integrity and high temperature thermal insulation after heat treatment for 30 min at 400 ℃. Moreover, the integration of PA enabled aerogel high fireproofing with limiting oxygen index (LOI) of 42.6% and UL-94 V-0 rating. The peak of heat release rate (PHRR) and total heat release (THR) of PA/CE aerogels were 79.97 kW/m2 and 1.75 MJ/m2, reduction by 43.0% and 46.5% compared with cellulose aerogels. Thus, the elastic cellulose aerogels proposed by this strategy provide an insight and feasibility for high performance and multifunctional applications.

Layered Inorganic Silicate Aerogel Pillared by Nanoclusters for High Temperature Thermal Insulation.

Layered inorganic material, with large-area interlayer surface and interface, provides an essential material platform for constructing new configuration of functional materials. Herein, a layered material pillared with nanoclusters realizing high temperature thermal insulation performance is demonstrated for the first time. Specifically, systematic synchrotron radiation spectroscopy and finite element calculation analysis show that ZrOx nanoclusters served as "pillars" to effectively produce porous structures with enough boundary defect while maintaining the layered structure, thereby significantly reducing solid state thermal conductivity (≈0.32Wm-1 K-1 , 298-573K). Moreover, the layered inorganic silicate material assembled aerogel also exhibits superior thermal insulation performance from room temperature (0.034Wm-1 K-1 , 298K, air conditions) to high temperature (0.187Wm-1 K-1 , 1073K, air conditions) and largely enhanced compressive strength (42kPa at 80% compression), which is the best layered material-based aerogel that has achieved synergistic improvement in thermal and mechanical performance so far. Layered inorganic silicate aerogel pillared by nanoclusters will pave a new avenue for the design of advanced thermal insulation materials under extreme conditions.

Lightweight and large-scale rGO reinforced SiBCN aerogels with hierarchical cellular structures exposed to high-temperature environments

SiBCN ceramic aerogel is an ideal potential candidate for ultra-high temperature thermal insulation due to its unique microscopic pore structure combined with the excellent thermal stability of SiBCN ceramic. Here, reduced graphene oxide (rGO) modified SiBCN aerogels (rGO/SiBCN) were prepared through solvothermal, freeze-casting and pyrolysis, and the dimension of the aerogel is up to Φ130 mm × 28 mm. The density of the rGO/SiBCN aerogel is as low as 0.024 g/cm3 and the microstructural regulation is achieved by controlling the rGO content in the aerogel. The hierarchical cellular structure endows the aerogel with a high specific surface area (148.6 m2/g) and low thermal conductivity (0.057 W m−1 K−1). The 10 mm-thick sample exhibits excellent thermal insulation and ablation resistance, as evidenced by its ability to reduce the temperature from ∼1100 °C to ∼180 °C under the intense heat of a butane flame. Moreover, benefiting from the ultrahigh-temperature stability of SiBCN, the rGO/SiBCN aerogel exhibits good thermal stability up to 1200 °C in argon and short-oxidation resistance at 800 °C in air. Therefore, the rGO/SiBCN aerogel with superior overall performance could expand its practical application in high-temperature thermal insulation under extreme environments.

Multilayered mullite ceramics with anisotropic properties

Anisotropic layered porous ceramics are crucial to satisfy the demand for devices with directional functions. However, challenges, such as complicated preparation processes and difficulties in regulating the oriented structure, severely limit their application. Here, multilayered mullite ceramics (MLMCs) with specific porosities and strongly anisotropy properties, were prepared by designing porous thin-layered units and an interlayer layout, in combination with a simple gel-casting. Benefiting from the suitable slurry properties, the samples did not show obvious defects, and a perfect bonding was observed between the layers. The optimized MLMCs exhibited a porosity of 65.12%, the differences in compressive and flexural strengths of 14 (±0.7) and 5 (±0.2) MPa in different pressure directions respectively, and the anisotropy factor of thermal conductivity up to 0.98, as well as exhibited good high temperature thermal insulation properties. Ultimately, the MLMCs formed transverse heat conductor and longitudinal heat insulation heat-transfer patterns, with promising applications in thermal insulation.

Investigation of the heat transfer through down clothing with quilting structure

Down clothing is commonly adopted as cold protective clothing to maintain human thermal comfort. However, its surface temperature distribution, heat transmission and thermal insulation are still not fully understood due to the complex heat and mass transfer caused by the quilting structure and varying mass density. In this work, we comprehensively explored the thermal behavior of down clothing with quilting structures. Objective tests were carried out by the thermal manikin and infrared thermal imager in a climate room at a fixed temperature of 10 ± 1 °C and relative humidity of 40 ± 5%. Four different down clothing were examined to investigate the effect of down lattice structure and mass density on heat flux, surface temperature distribution and thermal resistance. The results revealed a distinct valley in the surface temperature along the down lattice due to the quilting structure. A space-averaged method to estimate the thermal insulation of down clothing would neglect variation among different local positions. Besides, the thermal insulation performance significantly improved with the higher down mass density. Because the average clothing thickness as well as the thickness near quilting position both increased, resulting in an additional reduction of heat dissipation. Furthermore, the surface convective and radiative heat exchange decreased with the higher down mass density as a result of lower surface temperature. The lowest comfort temperature for clothing with various down mass density under activity level 2 met and 4 met was also estimated. The results can help to improve the design of down clothing's thermal performance and enhance human comfort in cold environments.

High thermal insulation and high strength SiBCN@SiC double network ceramic composite aerogel

Silicon carbide (SiC) fiber materials prepared by precursor conversion method have attracted extensive attention in recent years due to their excellent high temperature resistance and thermal insulation properties. Herein, a novel SiBCN/SiC dual network ceramic composite aerogel with the three-dimensional (3D) porous SiC fiber network obtained by direct electrospinning as the first network and SiBCN aerogel as the second network was prepared by combining electrospinning with sol-gel technology and supercritical drying technology. The microstructure, phase composition, pore size distribution, compressive resistance, thermal insulation and related mechanisms of the 3D SiC fiber network and composite aerogel at different heat treatment temperatures were investigated in detail. The results show that the constructed double-network structure can make up for the heat transfer problem of a single SiC fiber network and further reduce its thermal conductivity, so that the prepared composite aerogel exhibits a lower thermal conductivity (∼0.0316 W m−1 K−1). In addition, the unique double network structure endows the composite aerogel with excellent compressive properties (2.56–2.89 MPa).