Thermal Protection Materials Research Articles

Nano-TiO2 coated needle carbon fiber reinforced phenolic aerogel composite with low density, excellent heat-insulating and infrared radiation shielding performance

High-performance thermal protection materials (TPMs) for spacecraft are becoming current research hotspots. Lightweight polymer-based ablators are considered to be the most promising candidates for TPMs due to their excellent designability and versatility. In this study, a unique nano-TiO2 coated needled carbon fiber felt/phenolic resin aerogel composite (TiCF/PR) is reported. Wherein the anatase nano-TiO2 was in-situ coated on the surface of carbon fibers uniformly through the sol-gel and calcination method, then, the phenolic resin aerogel was in-situ synthesized in the nano-TiO2 coated needled carbon fiber felt (TiCF) preform through vacuum impregnation and solvothermal method. The as-prepared aerogel composite possesses a low density (0.30–0.32 g/cm3), low thermal conductivity (0.034 and 0.312 W/(m K) in the z and xy directions), and excellent thermal stability with 13.86% residual weight at 1300 °C in air. It is worthwhile to note that the TiCF/PR composite exhibits excellent antioxidant ablation and infrared (IR) radiation shielding properties in a high-temperature heating environment. With an oxygen-acetylene blaze heating of 1.5 MW/m2 for 150 s, the linear ablation rates decreased by 13.4%, and the backside temperature reduced from 322.3 to 179.1 °C compared to that of the sample without nano-TiO2 coating. The experimental and theoretical analysis showed that the present TiCF/PR nanocomposite has competitive and potential application prospects in the field of future TPMs.

The solid solution and microstructural evolution of WC doped Hf-Ta-C powders by induction plasma spheroidization

Hf-Ta-C ultra-high temperature ceramics are one of the important candidates for future thermal protective materials due to their high melting point. WC was doped by induction plasma spheroidization (IPS) into Hf-Ta-C to improve the microstructure, thermodynamic properties, and solid solubility. The doped WC is mainly enriched at grain boundaries, which is conducive to the formation of Hf-Ta-W-C solid solution and promotes density of the particle during IPS process. Thus, compared with the undoped WC ceramic, the spheroidization rate, fluidity and apparent density of the WC doped powder are significantly improved. Moreover, based on the melting and the solidification process of the Hf-Ta-W-C solid solution, the microstructure evolution of the particle is explored and summarized. Due to the inhomogeneity of the particle size, the microstructure of IPS-treated powder presents three different spherical particles: loose structure with a rough surface, dense structure with cellular surface and soccer ball surface.

Experimental research on online monitoring of high temperature and high speed airflow ablation of quartz ceramic thermal protection structure using guided wave

Thermal protection structure (TPS) plays a key role in protecting hypersonic flight vehicles from harsh service environment and has been widely used. As a common ablative thermal protection material, quartz ceramic TPS realizes thermal insulation by generating ablation during the reentry phases. The structural state of quartz ceramic TPS therefore is of great importance to the service performance and safety of hypersonic flight vehicles, and shows an urgent need for structural health monitoring (SHM). However, the monitoring of real ablation of quartz ceramic structure is barely considered in the current study, let alone online monitoring under harsh service environment, which brings a great challenge to the implementation of reliable ablation monitoring. Aiming at online ablation monitoring of quartz ceramic structure, this paper performs experimental research by taking advantage of guided wave (GW)-based monitoring method. An ablation experiment and monitoring system is built to generate real ablation under high temperature and high speed airflow and perform GW monitoring. The maximal temperature of the system can reach about 2100 °C. The feasibility of ablation monitoring is verified by analyzing ablation-induced influence on GW signals. Gaussian mixture model (GMM) is adopted to combine with GW method to suppress the high temperature variation caused by uncertainty influence on GW signals during the ablation process, so that reliable monitoring of ablation can be realized. Experimental results show that online monitoring of ablation propagation of quartz ceramic structure under high temperature variation is achieved, which can be further used for ablation quantification evaluation.

Development of active heat-protective materials for information-measuring devices and systems experiencing thermal loads in emergency situations

The article deals with the problem of creating a t-protective coating for information-measuring devices and systems for various purposes exposed to external high-temperature exposure in emergency situations related to fire. As a solution to the problem, it is proposed to use thermal-protective materials containing active additives that provide a thermal-protective effect that promotes the refraction of heat flows aimed at heating the protected object. The heat-shielding effect is provided by an endothermic reaction that occurs in the material when the decomposition temperature of the selected component is reached. It should be noted that the temperature at which the reaction with heat absorption should occur should be lower than the temperature of the lesion of the protected object. In this case, the heat flows passing through the layer of heat-shielding material will be refracted, since heat will be spent on the decomposition of the endothermic filler. The heating of the material will be carried out due to the matrix of the material and decomposition products. Based on the tasks that require the use of a heat-protective material, the amount of endothermic filler is determined. Accordingly, with an increase in the time interval during which it is necessary to eliminate the fire, the content of endothermic filler also increases. The use of thermal-protective material is relevant for emergency flight data recorders, since in the event of a plane crash, a fire is likely to occur, which can lead to the loss of information necessary to determine the causes of an emergency.

Large-Scale Fabrication of High-Performing Single-Crystal SiC Nanowire Sponges Using Natural Loofah

This study presents large-scale fabrication of single-crystal SiC nanowire (SiCnw) sponges through a carbothermal reduction approach using agricultural residue loofah, which is believed to be a perfect alternative to traditional petrochemical materials as the carbon source in industrial fabrication of SiC nanowires, without additional chemical C sources or catalysts. The single-crystal ultralong SiCnw are observed to have diverse morphologies with diameters of 50–400 nm, which possess a significant anisotropic and hierarchical microstructure with planar-aligned bamboo joints. A roughly 2 nm thick amorphous SiO2 layer is identified wrapping the crystalline 3C-SiC. The underlying vapor–solid mechanism is systematically investigated via thermodynamic calculations on the formation and interactions of SiO, CO, and SiC. Noteworthily, the fabricated loofah-based SiCnw sponge exhibits prominent high-temperature performance after thermal insulation tests of alcohol lamp flame and butane blowtorch flame, which is attributed to the stacking faults, SiO2 layer, SiC/SiO2 interface of the nanowires, and the overlength pathway in the porous aerogel–sponge domain synergetically acting as a phonon barrier to enhance phonon scattering, prolong phonon diffusion, and eventually reduce solid thermal conductivity in the sponge architecture. Our current work has great potential to be applied in the eco-friendly industrial preparation of high-performing SiCnw as thermal protection materials in harsh environments.

Nanoindentation deformation and fracture mechanisms of SiC/SiO2 thermally oxidized in plasma wind tunnel

Mechanical strain and delamination of surface oxide from substrate are important mechanisms leading to failure of thermal protection systems in hypersonic vehicles. In this work, the deformation and fracture mechanisms of a thermally oxidized SiC/SiO2, formed by dynamic oxidations inside a plasma wind tunnel, are studied by nanoindentation experiments and finite element modeling. The results show an amorphous and uniform SiO2 formation on β-SiC at 1200∼1400 °C in the plasma flow (pressure ≈6.5 kPa), after long-term single/repeated oxidations. In the plasma environment the passive oxidation of SiC is slow, as a result the as-formed SiO2 is very thin. The SiO2 thickness is only ≈680 nm after 8 × 500 s dynamic oxidation. SiC/SiO2 exhibits a strong depth dependent indentation behavior, and at a critical indentation depth, delamination of SiO2 oxide scale is triggered. Finite element modeling helps decouple the effects of SiC substrate, residual thermal stress and interfacial delamination on the nanoindentation response of SiC/SiO2. The results evidence that delamination has a negligible effect on the nanoindentation response, and the main contributions are the SiC substrate and residual thermal stress. This work may forward the fundamental understanding of deformation and fracture mechanisms of oxide scales on thermal protection materials in response to localized loading conditions.

Transition of catalytic recombination pathways on silica-based thermal protection materials at different temperatures using reactive molecular dynamics method

Silica-based ceramic material is one of the most competitive options of thermal protection material. However, catalytic reaction mechanism of gaseous atoms on it is complex and confusing. To model catalytic recombination of dissociated oxygen atoms accurately in prediction of chemical non-equilibrium flow and aerodynamic heating, the reactive molecular dynamics method was adopted to simulate gas–surface interaction on the interface, and a series of post-processing methods were constructed to analyze recombination pathways of atomic oxygen on α-quartz. It was found that there are four types of adsorbates on α-quartz surface and five pathways to produce recombined oxygen molecules. Recombination pathways would change from Eley–Rideal recombination-dominated to molecule desorption-dominated with increase in temperature. Information extracted by current post-processing methods explains how and why the recombination coefficient changes with temperature. The post-processing methods can be further applied in analysis of catalytic recombination on other thermal protection materials.

BAYESIAN IDENTIFICATION OF PYROLYSIS MODEL PARAMETERS FOR THERMAL PROTECTION MATERIALS USING AN ADAPTIVE GRADIENT-INFORMED SAMPLING ALGORITHM WITH APPLICATION TO A MARS ATMOSPHERIC ENTRY

For space missions involving atmospheric entry, a thermal protection system is essential to shield the spacecraft and its payload from the severe aerothermal loads. Carbon/phenolic composite materials have gained renewed interest to serve as ablative thermal protection materials (TPMs). New experimental data relevant to the pyrolytic decomposition of the phenolic resin used in such carbon/phenolic composite TPMs have recently been published in the literature. In this paper, we infer from these new experimental data an uncertainty-quantified pyrolysis model. We adopt a Bayesian probabilistic approach to account for uncertainties in the model identification. We use an approximate likelihood function involving a weighted distance between the model predictions and the time-dependent experimental data. To sample from the posterior, we use a gradient-informed Markov chain Monte Carlo method, namely, a method based on an Ito stochastic differential equation, with an adaptive selection of the numerical parameters. To select the decomposition mechanisms to be represented in the pyrolysis model, we proceed by progressively increasing the complexity of the pyrolysis model until a satisfactory fit to the data is ultimately obtained. The pyrolysis model thus obtained involves six reactions and has 48 parameters. We demonstrate the use of the identified pyrolysis model in a numerical simulation of heat-shield surface recession in a Martian entry.

Simulation of flow field infrared radiation over reentry vehicle with ablation of carbon-based thermal protection material

Simulation of flow field infrared radiation over reentry vehicle with ablation of carbon-based thermal protection material

Effect of carbon black powder content on thermal, physical, and mechanical properties of carbon fabric reinforced phenolic composite

Using heat-resistant fiber-reinforced phenolic composite materials (carbon fiber, glass fiber, etc.) to protect the rocket motor from high temperature has confirmed its superiority thanks to its thermal insulation and high-temperature resistance. The improvement of thermal protection properties of materials to diversify the thermal protection material family is a growing trend. Accordingly, this paper focuses on determining the influence of the percentage of carbon nano powder (0-14%) on the thermal, physical and mechanical properties of carbon fiber/phenolic matrix composite (CPC) in order to find out the extent of reasonable proportion of carbon powder to improve thermal protection. The results indicated that the addition of carbon powder with a content of about 6–10% significantly improved the thermal protection efficiency of CPC materials. The determined thermophysical parameters are the basis for calculating and designing of solid rocket motor heat insulation layer.

Low thermal conductivity of dense (TiZrHfVNbTa)Cxhigh-entropy carbides by tailoring carbon stoichiometry

Transition metal carbides are promising candidates for thermal protection materials due to their high melting points and excellent mechanical properties. However, the relatively high thermal conductivity is still a major obstacle to its application in an ultra-high-temperature insulation system. In this work, the low thermal conductivity of dense (TiZrHfVNbTa)C_<i>x</i> (<i>x</i> = 0.6–1) high-entropy carbides has been realized by adjusting the carbon stoichiometry. The thermal conductivity gradually decreases from 10.6 W·m⁻¹·K⁻¹ at room temperature to 6.4 W·m⁻¹·K⁻¹ with carbon vacancies increasing. Due to enhanced scattering of phonons and electrons by the carbon vacancies, nearly full-dense (97.9%) (TiZrHfVNbTa)C_0.6 possesses low thermal conductivity of 6.4 W·m⁻¹·K⁻¹, thermal diffusivity of 2.3 mm²·s⁻¹, as well as electrical resistivity of 165.5 μΩ·cm. The thermal conductivity of (TiZrHfVNbTa)C_0.6 is lower than that of other quaternary and quinary high-entropy carbide ceramics, even if taking the difference of porosity into account in some cases, which is mainly attributed to compositional complexity and carbon vacancies. This provides a promising route to reduce the thermal conductivity of high-entropy carbides by increasing the number of metallic elements and carbon vacancies.

Simulation research on thermal protection performance of firefighting robots and design of protection system

In response to manufacturing strategy demand, fire accidents in petroleum, chemical, forestry, and high-rise buildings are on the rise. Although the firefighting robot can replace fire rescue workers who come into the dangerous rescue site, electronic devices’ thermal failure problem caused by high temperatures in the whole electronic equipment problem is bigger. The proportion of electronic device thermal failure has a significant impact on the normal operation of electronic equipment. How to dissipate heat quickly and avoid local high temperatures becomes a key problem. Most domestic and foreign scholars only study the influence of thermal protection materials themselves on robot protection systems, and few study the influence of heat insulation materials and heat dissipation materials on robot protection systems through appropriate structure combinations. Therefore, the establishment of comprehensive high-temperature fire situations on the fire protection robot automatic detection of smoke concentration and temperature of heat insulation material and heat dissipation material composition of folded tensile structure and liquid nitrogen cooling system thermal protection model of robot thermal protection performance research is of great significance, at the same time through COMSOL Multiphysics software to simulate the proposed model, Select the best heat dissipation materials and heat insulation materials, protect the internal electronic components in the fire accident sustained high temperature, can adjust the temperature as soon as possible, make it adapt to the change of temperature field, for the rescue process to gain 2~15 minutes time duration.

Simulation and Application of a New Multiphase Flow Ablation Test System for Thermal Protection Materials Based on Liquid Rocket Engine

Internal flow field ablation is an important issue in thermal protection materials for rocket engines and hypersonic vehicles. In this paper, a new multiphase flow ablation test system, with an Al2O3 particle delivery device based on an oxygen-kerosene liquid rocket engine, is designed and manufactured. A general variable-precision modular system simulation method is proposed to analyze the dynamic characteristics of the system. In addition, a unique internal flow field ablation test was performed on the 4D C/C composite simulating the working conditions of the SRM. The results show that the system can provide a wide temperature range (756~3565 K) and pressure range (0.2~4.2 MPa). The multi-disciplinary dynamic variable-precision system simulation method is helpful for more accurate design and test analysis, and the maximum error is less than 5%. The ablation tests show that the line ablation rate of the C/C composite nozzle at 3380 K and 1 MPa is 0.053 mm/s, verifying the combined effect of thermochemical and mechanical ablation. The ablation environment is controllable, which provides an effective way for the ablation test of thermal protection materials. In addition, the variable-precision dynamic simulation method has important reference value for the system design related to liquid rocket engine.

Elucidating the role of preferential oxidation during ablation: Insights on the design and optimization of multicomponent ultra-high temperature ceramics

Multicomponent ultra-high temperature ceramics (UHTCs) are promising candidates for thermal protection materials (TPMs) used in aerospace field. However, finding out desirable compositions from an enormous number of possible compositions remains challenging. Here, through elucidating the role of preferential oxidation in ablation behavior of multicomponent UHTCs via the thermodynamic analysis and experimental verification, the correlation between the composition and ablation performance of multicomponent UHTCs was revealed from the aspect of thermodynamics. We found that the metal components in UHTCs can be thermodynamically divided into preferentially oxidized component (denoted as MP), which builds up a skeleton in oxide layer, and laggingly oxidized component (denoted as ML), which fills the oxide skeleton. Meanwhile, a thermodynamically driven gradient in the concentration of MP and ML forms in the oxide layer. Based on these findings, a strategy for pre-evaluating the ablation performance of multicomponent UHTCs was developed, which provides a preliminary basis for the composition design of multicomponent UHTCs.

Radiative Transfer in Discretely Homogenous Media with the Zonal Monte Carlo Method

The zonal Monte Carlo method is generalized for applications to radiative heat transfer in multidimensional absorbing and isotropic scattering media with different homogenous optical properties in discrete regions. As an example of application, the scattering of a collimated energy beam through an absorbing and isotropic scattering medium to disjoint receiving surfaces is analyzed. The multidimensional distribution of the scattered energy for different extinction coefficients, scattering albedos, and geometrical configurations is generated. Numerical data are used to assess the effectiveness of using scattering materials for thermal protection. Some insights on the design of laser scattering experiments to determine the optical properties of scattering materials by numerical inversion are identified.

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.

Preparation and Properties of Three-dimensional Graphene-based Multifunctional Thermal Control Coating

According to the requirements of spacecraft light alloy materials for thermal control, anti-static and corrosion protection, based on the synthesized three-dimensional graphene functional filler, a multifunctional thermal control coating with high emissivity, anti-static and anti-corrosion properties was prepared on magnesium alloy materials. By testing the coating properties, the hemispherical emissivity was 0.91,volume resistivity was 104Ωm and neutral salt spray corrosion resistance was more than 800 hours.

Preparation and Properties of Three-dimensional Graphene-based Multifunctional Thermal Control Coating

According to the requirements of spacecraft light alloy materials for thermal control, anti-static and corrosion protection, based on the synthesized three-dimensional graphene functional filler, a multifunctional thermal control coating with high emissivity, anti-static and anti-corrosion properties was prepared on magnesium alloy materials. By testing the coating properties, the hemispherical emissivity was 0.91,volume resistivity was 104Ωm and neutral salt spray corrosion resistance was more than 800 hours.

Improving the Heat and Ablation Resistance of Silicone Rubber Composites by Incorporating Hollow Microspheres.

For thermal protection materials (TPMs) which are used to protect space vehicles from extreme thermomechanical environments, the thermal conductivity of the original material and the char layer that has formed during ablation plays a significant role in determining the ablation performance. In order to investigate this, in this study, we introduced glass hollow microspheres (GHMs), phenolic hollow microspheres (PHMs), and acrylonitrile-methyl methacrylate copolymer hollow microspheres (AMHMs) into silicone rubber (SR), and the ablation performance of these composites was systematically studied. The thermogravimetric results showed that the residue yield of the SR composites was increased with the incorporation of the hollow microspheres. Compared to the SR composites without the hollow microspheres, the residue weight values under 800 °C (R800) of the SR composites with the 30 parts of fumed silica per hundred of the SR (phr) addition of GHMs, PHMs, and AMHMs were increased from 10.11% to 21.70%, 18.31%, and 20.83%, respectively. The ablation tests showed that the addition of the AMHMs enhanced the ablation performance of the SR composites because the linear ablation rates and the backplane temperature were clearly decreased when compared to the SR composites without the hollow microspheres. This work provides an effective and potential method for preparing thermal protection materials with an improved ablation performance.

2.5D quartz fabric reinforced nanoporous phenolic composites with weakened heat transfer and optimized mechanical properties

Phenolic-based composites are the most promising ablative thermal protection materials for space applications, but optimizing their thermal insulation performance while maintaining high strength remains extremely challenging. Herein, phenolic-based composites with co-optimized thermal insulation and mechanical properties are prepared via 2.5D quartz fabric reinforcing nanoporous phenolic. The pore size of phenolic matrix is efficiently refined to ∼35 nm by adjusting resin concentration, enabling composites to exhibit high density but low thermal conductivity by enhancing Knudsen diffusion. Finite element analysis shows that low braiding angle of 2.5D fabric can further weakening heat transfer of composites due to anisotropic thermal conductivity of fiber yarns. In-situ X-ray micro-CT results indicate that 2.5D fabrics can reinforce composites through interwoven yarns, and straighter weft yarns result in higher strength along weft direction than that along warp direction. Compared with dense quartz/phenolic composite, the resulting composites exhibit 16.5% lower density (1.32 g/cm3), 58.8% lower thermal conductivity (0.21 W/(m·K), ≥372.7% higher tensile strength (≥182.0 ± 9.6 MPa) and comparable ablation resistance. The present results will further advance the application of phenolic-based composites in more extreme re-entry environments.