Thermal Protection Applications Research Articles

Study of ZnO‐coated Modified Hollow Microsphere Insulation Coated Fabrics

AbstractIn this study, new ZnO/TEMs composites were prepared using the electrostatic gravitational method, which combines the high reflectivity of ZnO with the low thermal conductivity of TEMs to create materials with excellent thermal insulation and heat preservation properties. The initial test results indicate that the ZnO‐coated TEMs are effective in blocking thermal radiation from sunlight, with thermal conductivity of 0.0523 W/m ⋅ K for the ZnO/TEMs microsphere coating. In addition, the internal and external temperature difference of ZnO/TEM‐C 1200 is 7 °C lower than that of cotton fabric under an optical power of 350 mW/cm2. Moreover, the ZnO/TEM‐C 1200 has a UPF value of up to 1894 and a total solar reflectance of 81.40 % in the 200–2500 nm wavelength range. These findings demonstrate the potential of ZnO/TEMs composites for use in thermal insulation and UV protection applications.

Delamination analysis of a ductile phase-toughened environmental barrier coating for oxygen-rich turbopumps

The turbine in an oxygen-rich turbopump subjects materials to high-pressure gaseous oxygen environments, where the risk of metal fires presents a potentially catastrophic failure mode. A candidate approach for mitigating particle impact ignition, one key metal ignition mechanism, is to coat metallic components with an inert ceramic environmental barrier coating; however, such coatings are susceptible to delamination during the rapid thermal transients upon engine startup and shutdown. Here, we investigate the delamination risk of a ductile phase-toughened composite environmental barrier coating under a nominal flight cycle of a reusable boost-stage rocket engine. The coating of present interest comprises a borate-based glass-ceramic matrix reinforced with Ni and is applied as an aqueous slurry that bonds to the substrate upon firing. We first varied the Ni content in the coating and characterized its structure, finding that the Ni reinforcement sinters to the substrate and percolates through the brittle glass-ceramic when the Ni volume fraction exceeds 0.3, in excellent agreement with percolation theory. We also experimentally assessed the thermomechanical properties of the coating and used these measurements to compute its energy release rate under the thermal transients expected in service. Our analysis shows that thermal stresses and energy release rates are greatest during engine startup and shutdown, with energy release rates on the order of 100 J/m2 for a 100-μm thick coating on an IN718 substrate. Our analysis then highlights strategies for reducing the energy release rate, which include tailoring the thermal expansion coefficient to balance transient vs. steady-state thermal stresses and using active heating to promote film boiling upon exposure to cryogenic liquid oxygen, thus mitigating the severity of cold shocks. Most importantly with respect to materials design, we predict that interpenetrating composite coatings with Ni concentrations greater than 0.3 exhibit enhanced toughness via crack bridging, allowing them to resist delamination under even the most aggressive operating conditions. These results highlight the potential of high-toughness metal/ceramic interpenetrating composite coatings in thermal and environmental protection applications where extreme thermal transients delaminate conventional monolithic ceramic coatings.

Medium and high-entropy transition mental disilicides with improved infrared emissivity for thermal protection applications

• The medium and high-entropy transition mental disilicides present significantly reduced electrical conductivities. • The medium and high-entropy transition mental disilicides are promoting infrared emissivity materials for thermal protection applications. • The mechanism for the reduced thermal conductivity and high infrared emissivity are disclosed. Transition metal disilicides are widely used as heating elements and infrared emission coatings. However, the limited intrinsic infrared emissivity and high thermal conductivity are the main limitations to their applications as infrared emission coatings in the thermal protection system. To cope with these problems, four medium and high-entropy transition metal disilicides, i.e., (V 0.25 Ta 0.25 Mo 0.25 W 0.25 )Si 2 (ME-1), (Nb 0.25 Ta 0.25 Mo 0.25 W 0.25 )Si 2 (ME-2), (V 0.2 Nb 0.2 Ta 0.2 Mo 0.2 W 0.2 )Si 2 (HE-1), and (Cr 0.2 Nb 0.2 Ta 0.2 Mo 0.2 W 0.2 )Si 2 (HE-2), were designed and synthesized by spark plasma sintering method using transition metal binary disilicides as precursors. The introduction of multi-elements into transition metal disilicides not only improved the infrared emissivity but also reduced the electrical and thermal conductivity. Among them, (Cr 0.2 Nb 0.2 Ta 0.2 Mo 0.2 W 0.2 )Si 2 (HE-2) had the lowest electrical conductivity of 3789 S cm –1 , which is over one order of magnitude lower than that of MoSi 2 (50000 S cm –1 ), and total infrared emissivity of 0.42 at room temperature, which is nearly double of that of TaSi 2 . Benefiting from low electrical conductivity and phonon scattering due to lattice distortion, the medium and high-entropy transition metal disilicides also demonstrated a significant decline in thermal conductivity compared to their binary counterparts. Of all samples, HE-2 exhibited the lowest thermal conductivity of 6.4 W m − − 1 K − − 1 . The high-entropy transition metal disilicides also present excellent oxidation resistance at high temperatures. The improved infrared emissivity, reduced thermal conductivity, excellent oxidation resistance, and lower densities of these medium and high-entropy transition metal disilicides portend that they are promising as infrared emission coating materials for applications in thermal protection systems.

FDM-3D printing LLDPE/BN@GNPs composites with double network structures for high-efficiency thermal conductivity and electromagnetic interference shielding

Towards the high-frequency and miniaturization of modern electronic devices, the multi-functional materials with high-efficiency thermal management and electromagnetic interference shielding performance are urgently demanded. The contributions in materials are mostly focused on a single function, and difficult to meet the requirement of the precision device with complicated structures. Herein, linear low-density polyethylene (LLDPE)/boron nitride (BN)@graphene nanoplatelets (GNPs) composite parts with double network structures were designed and realized by combining ball-milling strategy and fused deposition modeling (FDM) 3D printing technology. The FDM-3D printed parts could exhibit a thermal conductivity of 3.11 W/(m·K) along the printing direction at 3.51 vol% GNPs loading, achieving an improvement of ∼2.88 and ∼8.33 times over that of flat printing parts and pure LLDPE, respectively. The long-range aligned network along the printing direction is formed due to the shear extrusion effect during FDM-3D printing. Also, FDM-3D printing is applied to print heat sinks with excellent thermal conductive property in vertical direction. Furthermore, the ball milling process could enable the GNPs to form thermal and electrical conductivity pathways in LLDPE/BN composites. The printed parts accordingly exhibit good electromagnetic shielding performance (27.8 dB) and electrical conductivity (12.5 S/m). This study not only enriches the strategy for preparation of multifunctional FDM 3D printed parts, but also paves the way for further applications in advanced thermal management and protection against electromagnetic irradiation.

Optimal Nb5+ doping for enhanced optical reflectivity and improved thermophysical properties of La0.9Sr0.1Ti1−xNbxO3+δ

AbstractThermal protection materials with high optical reflectivity, low thermal conductivity, and good high‐temperature stability are required for the development of laser technologies and the protection of the critical equipment components. Herein, we synthesize a novel thermal protective material, La0.9Sr0.1Ti1−xNbxO3+δ (LSTN; x = 0.1, 0.125, 0.15), with different Nb5+‐ion contents using solid‐state sintering. Phase structure analysis demonstrates that LSTN (x = 0.1, 0.125, 0.15) presents a single‐phase monoclinic structure with a uniform element distribution. In particular, the LSTN0.125 ceramic exhibits ultrahigh optical reflectivity (96%, 2300 nm) and excellent thermophysical properties, such as a high thermal expansion coefficient (10.3 × 10−6 K−1, 1000°C), an ultralow thermal conductivity (0.408 W (m K)−1, 300°C), and excellent high‐temperature stability. Aberration‐corrected scanning transmission electron microscopy reveals that the disordered substitution of Nb5+ ions induces numerous lattice distortions and mass fluctuations, which decrease the thermal conductivity, and makes difference in the relative refractive indices of atomic layers causing the high reflectivity of the material. These remarkable properties render the LSTN0.125 ceramic as an ideal alternative for near‐infrared thermal protection applications.

Biomimetic, hierarchical-ordered cellulose nanoclaw hybrid aerogel with high strength and thermal insulation

High-performance thermally insulating nanocellulose-based aerogels with robust mechanical properties is highly desirable for energy-saving and thermal protection applications. However, the large-scale applications of traditional nanocellulose aerogels are still limited by their brittleness nature and rigorous processes. Herein, an effective biomimetic hybrid strategy for high strength and thermal insulated nanocellulose-based aerogel with hierarchical-ordered microstructure is designed and fabricated. The novel cellulose nanoclaws-based aerogels extracted from corncob are hybridized by nanosized silica aerogel layer in situ and have an intensified H-bonding crosslinked network after ambient-drying and hotpress treatment, endowing excellent mechanical properties (16–58 MPa) as well as scalable potential for structure materials. Benefitting from the synergistic effect of the tailored hierarchical-ordered microstructure, the resulting hybrid aerogels also possess high specific surface area (30–630 m2 g−1), low thermal conductivity (0.021 W m−1 K−1), and outstanding flame retardant. This hybrid strategy provides an avenue to produce thermal-insulated and mechanically robust materials.

(AlCrMg)x(PO4)y/MgO composite: A new thermal protection and insulation material up to 2400 °C

A (AlCrMg)x(PO4)y/MgO composite(APMC) was prepared based on the acid–base reaction between MgO and chromium aluminum phosphate solution for thermal protection and insulation applications at ultrahigh-temperatures up to 2400 °C. The compositions, formation mechanisms, microstructure, mechanical properties, thermal conductivity and ablation resistance of the composite were systematically investigated. The results show that the (AlCrMg)x(PO4)y/MgO composite can be consolidated in different shapes at room temperature. The compressive strength of the as-prepared porous composites is higher than 20 MPa due to the macromolecular network structure, and it can be further improved to 42 MPa via thermal treatment. After ablation by an oxyacetylene flame at 2400 ± 70 °C for 60 s, the mass and line ablation rates of the composite were 0.0195 g/s and 0.43 × 10−3 mm/s, respectively, which are comparable to those of ultrahigh-temperature ceramics. The excellent ablation resistance can be attributed to the in situ formation of a dense protective layer composed of spinel MgCr2O4 and MgO phases. Interestingly, during ablation at 2400 °C the back-side temperature of the 15 mm-thick sample was lower than 130 °C, suggesting outstanding thermal insulation performance. The temperature gradient leads to the formation of a gradated porous structure which reduces the overall thermal conductivity of the composite.

A comparative study of different oxidation states of raw materials on the properties of a novel medium-entropy Co2.77Mn1.71Fe1.10Zn0.42O8 thermistor materials

In recent years, high entropy oxides (HEOs) have aroused extensive attention due to their potential applications in catalysis, energy storage and thermal protection. However, as an emerging material, the synthesis, properties and applications of HEOs have yet to be further developed. Herein, we reported a novel non-equiatomic medium-entropy Co2.77Mn1.71Fe1.10Zn0.42O8 oxides for temperature sensing applications by using the different oxidation states of cobalt and iron as raw materials. Results indicate that the prepared multi-component samples present a pure spinel phase, highly dense microstructure, and typical negative temperature coefficient characteristics. Our results also suggest that the different oxidization states of cobalt and iron of raw materials induce obvious influences on resistivity and aging stability. In particular, the medium-entropy oxides can exhibit excellent superior aging stability (the resistance drift ≤0.2% after accelerated aging in 125 °C for 600 h) by a suitable selection of the starting oxides. This work will provide new material design strategies for sensors or other electronic devices and guidance on the raw material selection from laboratory research to industrial production processes.

Proton Donor-Regulated Mechanically Robust Aramid Nanofiber Aerogel Membranes for High-Temperature Thermal Insulation

High-performance thermal insulators are urgently desired for energy-saving and thermal protection applications. However, the creation of such materials with synchronously ultralow thermal conductivity, lightweight, and mechanically robust properties still faces enormous challenges. Herein, a proton donor-regulated assembly strategy is presented to construct asymmetric aramid nanofiber (ANF) aerogel membranes with a dense skin layer and a high-porous nanofibrous body part. The asymmetric structure originates from the otherness of the structural restoration of deprotonated ANFs and the resulting ANF assembly due to the diversity of available proton concentrations. Befitting from the synergistic effect of the distinct architectures, the resulting aerogel membranes exhibit excellent overall performance in terms of a low thermal conductivity of 0.031 W·m-1·K-1, a low density of 19.2 mg·cm-3, a high porosity of 99.53%, a high tensile strength of 11.8 MPa (16.5 times enhanced), high heat resistance (>500 °C), and high flame retardancy. Furthermore, a blade-scraping process is further proposed to fabricate the aerogel membrane in a continuous and scalable manner, as it is believed to have potential applications in civil and military fields.

The water uptake, thermal and mechanical properties, and aging resistance to thermo‐oxidation of phenylboronic acid‐modified benzoxazine‐glass fiber composites

AbstractPolybenzoxazines, also known as Benzoxazine (Bz) is one kind of high‐performance thermoset polymers. It manifests several advantages when used for thermal protection applications, such as thermal and dimensional stabilities, low rate of moisture absorption and near zero volatility in curing process. However, benzoxazine shows its drawbacks in terms of curing temperature, char yield at elevated temperature, and resin toughness. Thus, modification of Bz matrix would be essential in order to improve these unfavorable properties. In this study, a facile synthesis of phenylboronic acid‐modified (PBA) benzoxazine (PBz) and glass fibers (GF) composites with varied PBA ratios were prepared. Briefly, GF fabrics were impregnated with each of Bz or PBz/acetone solution and baked to form B‐staged prepregs. Then, the prepregs were stacked, molded and cured in a hot‐pressing machine to form composites. The present study shows the 10 wt% PBA modified‐Bz/GF composite is the optimal formulation as it exhibits minimal water uptake, enhanced char yield, decent thermomechanical stability in terms of glass transition temperature, exceptional interlaminar shear strength (ILSS) and highest flexural strength. Moreover, the PBz 10/GF composite subject to thermo‐oxidative aging still maintains good levels of shear and flexural properties for potential service as thermal protection layer.

High strength, high toughness, low thermal conductivity, and appropriate expansion capacity of hybrid organic/inorganic nanocomposites used for thermal protection

A thermal protection material (TPM) was prepared using Al 2 O 3 -phosphate, expanded aluminosilicate, and phenolics through compression molding and the gradient heating reaction technique, and the effect of the high-temperature treatment on the properties of the composites were investigated. Scanning electron microscopy, X-ray diffraction, and Fourier transform infrared spectroscopy were used to analyze the structures and compositions of the composites. After the high-temperature treatment, the composites exhibited increased porosity, decreased density, and generated SiC particles with high strength and temperature resistance. The prepared composites have high compressive strength and compression deformation ability of the bending point. Thermogravimetric analysis, coefficient of thermal conductivity measurements, and expansion analysis were carried out to evaluate the thermal properties of the composites, and the effects of the preparation conditions on the thermal properties of the composites were investigated. The results showed that the prepared composites exhibited complete morphology, excellent high-temperature resistance, high compressive strength and toughness, and low thermal conductivity before and after the high-temperature treatment at 1000 °C, and hence showed great potential for future thermal protection applications.

Principles, design, structure and properties of ceramics for microwave absorption or transmission at high-temperatures

ABSTRACT The multifunctional metastable SiBOCN system ceramics (including SiBN, SiCN, SiON, SiBC, SiBCN, SiBON, SiBOCN, etc.) are a new type of advanced structure–function integrated materials with unique structure and adjustable dielectric properties for high-temperature applications in thermal protection, communications, precise guidance, and microwave-absorption stealthy. These metastable materials generally require the rational co-design of multiscale structure and chemical composition to achieve desirable dielectric properties which induce interaction with incident electromagnetic wave. Herein, this review presents the latest development of metastable SiBOCN system ceramics, with the intent of summarising key findings, uncovering major trends and providing guidance for future efforts. Major themes in this assessment focus on the main processing routes, basic mechanisms for microwave transmission and absorption, scientific basis for material selection in specific background, principles for multiscale structure design and chemistry optimisation, tunable microwave transparent or absorbing properties, and future challenges and prospects in this active research filed.

Thermal-responsive, super-strong, ultrathin firewalls for quenching thermal runaway in high-energy battery modules

Cascaded thermal runaway (TR) propagation is the utmost safety issue for large-format lithium-ion battery (LIB) modules because of the high risk of system fires or explosions. However, quenching TR without side effects still remains a challenge. Herein, we delivered an ultrathin smart firewall concept for avoiding the TR propagation in a LIB module. We demonstrate that the firewalls have thermally-triggered switchable thermal physical properties because of the synergistic effect of non-flammable phase change materials (NFPCM) and flexible silica nanofiber mats. Under TR condition, the firewalls give rise to multiple functions simultaneously, including cooling, fire extinguishing and thermal insulation. Consequently, the TR propagation between fully charged 50 Ah LIBs, with a transient thermal shock of up to 53 kW, is successfully suppressed by 1-mm-thick smart firewalls, yielding a maximum cell-to-cell temperature gap of 512 °C. The smart firewall design provides a reliable approach to quench TR propagation in large-format LIBs, which can also be suitable for other dynamically adaptive thermal-protection applications for oil tanks, space exploration, and firefighting equipment.

Evaluation and design methods for high‐efficiency charring composite under complex coupling mechanisms in both material and boundary layer

AbstractWith the development of hypersonic vehicles, reentry vehicles are facing a more severe aerothermodynamic heating environment. It is necessary to design high‐efficiency charring composite used as the heat shield in the thermal protection system (TPS) of reentry vehicles. By taking the material responses (volume‐surface coupled ablation), exothermic gas‐phase reactions of pyrolysis gases in the boundary layer and the flow behavior of chemical nonequilibrium inflow coupling ablative mechanism into consideration, a developed thermal/fluid/chemical/ablation coupling model with the key influencing factor on thermal protection performance of charring composites is built to evaluate the material responses and the chemical responses in boundary layer near its surface. Based on this model, the key factor (fiber volume fraction) influencing on the thermal protection performance is analyzed by using a coupling numerical calculation strategy. By designing the distribution of this parameter along the thickness of the material, a gradient design for charring composite is given. The numerical results indicate that the gradient charring composite can control the temperature distribution and the amount of surface ablation recession. This study will be a guidance for the design of charring composites for thermal protection application in reentry vehicles in a quantitative and efficient manner.

Low density, three-dimensionally interconnected carbon nanotube/silicon carbide nanocomposites for thermal protection applications

Synthesis of silicon carbide (SiC) nanostructures and their composites has been a topic of interest for the scientific community due to the unique properties that can be obtained with nanoscale features. Herein, we report the scalable fabrication of anisotropic and low density, carbon nanotube/SiC (CNT/SiC) core-shell structures synthesized via chemical vapor infiltration (CVI) of silicon on aligned CNT foams followed by heat treatment at 1350 °C. Structures made of CNT/SiC nanotube networks with a thickness of 1 cm and length of 9 cm were prepared in the present work. Upon the removal of the CNT foam via calcination of the hybrid nanocomposite in air, a free-standing mechanically robust three-dimensional network of pure SiC nanotubes was left behind. The density of the synthesized CNT/SiC is the lowest reported for any C/SiC structure. Furthermore, the CNT/SiC hybrid nano-architecture demonstrated superb heat resistance and stability in ultrahigh temperature environment.

In situ one-step construction of monolithic silica aerogel-based composite phase change materials for thermal protection

Currently, numerous studies are devoted to the pursuit of thermal conductivity enhancement of phase change materials (PCMs). On the contrary, few researches are reported to reduce the thermal conductivity of PCMs. Generally, the PCMs with reduced thermal conductivity have great potential in thermal protection application. Herein, we propose a novel in situ one-step strategy to facilely prepare monolithic silica aerogel-based composite PCMs. The silica aerogels possess low thermal conductivity and are used to encapsulate PCMs to prepare composite PCMs, such as polyethylene glycol (PEG) or octadecanol. Compare with PEG2000@silica aerogel, the resulting monolithic octadecanol@silica aerogel have low thermal conductivity (0.12 W m−1 K−1), high latent heat (127.73 J/g), large compressive strength (11 MPa), good hydrophobicity (contact angle 124°) and superior thermal cycling stability. This monolithic silica aerogel-based composite PCMs could prolong heat preservation duration due to the synergistic effect between low thermal conductivity and high latent heat of composite PCMs, showing potential promise for direct application to the thermal insulation and thermal protection device. More importantly, this in situ one-step synthesis strategy is universal for different types of PCMs.

Silica–Phenolic Nanocomposite Ablatives for Thermal Protection Application

A novel class of ablative materials using phenolic resin, silica fabric, and nano-zirconium dioxide is being developed as a potential alternative for use in high-heat-flux thermal protection applications. Four new silica–phenolic ablatives have been fabricated using tandem nanocomposite formulations. Each of the tandem composites consist of nano-zirconium dioxide with small amounts of one of the following additives: multiwalled carbon nanotubes, nano-graphene platelets, alumina nanofibers, and nano-boron carbide. Materials have been fabricated, characterized, and compared using thermal and microanalysis. Thermogravimetric analysis and microscale combustion calorimetry were used to compare char yield, thermal stability, and flammability properties. Oxy-acetylene test bed aerothermal ablation testing was used to evaluate the composites under a high heat flux of environment. Data analysis on recession rate, mass loss rate, backside heat-soaked temperature, surface temperature, and materials surface behavior were collected and used as a comparison tool to rank ablation performance of candidate materials. After testing of the candidates, it was determined that the nanocomposite containing nano-boron carbide in tandem with nano-zirconium dioxide was the best-performing candidate, demonstrating superior ablation properties, such as mass loss, recession rate, and insulative properties.

Numerical Simulation of the Solar Spectral Properties of Filled Polyvinyl Chloride Plastisols

Notable efforts have been done to describe the propagation of a solar radiation in a heterogeneous medium containing particles. In the latter case, it is necessary to use the radiative transfer equation (RTE) that describes the propagation of radiations in participating media. Herein, the RTE was solved by using the four-flux method coupled with the T-matrix approach for the determination of effective scattering and absorption coefficients. Consequently, it was possible to understand and to predict the interaction of light with polyvinyl chloride (PVC) plastisol–based films containing fillers such as alumina, nacre, titanium dioxide, and glass beads. It was shown that the theoretical reflectance and transmittance spectra of the filled PVC plastisol film in the visible and the near-infrared regions are quite close to the experimental ones. The effect of the film thickness, the particle diameter, and the filler concentration on the reflectance and the transmittance of filled PVC plastisol film was investigated, and it was demonstrated that the filler could be well adapted for thermal protection applications.

Advanced Materials for Heat Energy Transfer, Conversion, Storage and Utilization

Advanced Materials for Heat Energy Transfer, Conversion, Storage and Utilization

Composites of silica aerogels with organics: a review of synthesis and mechanical properties

Aerogels are considered as outstanding future materials owing to their wide surface area and three-dimensional network of silica particles, low density, low-thermal conductivity, high porosity, and low dielectric property. Their outstanding characteristics represent excellent potential applications in thermal insulation systems, aeronautical domains, environmental clean-up and protection, as heat storage devices, transparent windows, thickening agents in paints, etc. Among these applications, thermal insulating materials can play a vital role in living systems and for saving energy in various domestic and industrial processes. However, native silica aerogels are fragile and sensitive to relatively low pressures, which limit their application. More robust aerogels with higher strength and stiffness can be obtained by compounding silica networks with organoalkoxysilanes, polymers or using porous scaffolds as supports. This paper presents a review on the approaches for mechanical reinforcing methods for silica aerogels and recent achievements toward improving the strength of native silica aerogels. In addition, various characteristics derived from composite aerogels are analyzed synthetically.