Thermal Protection Materials Research Articles

ZrO2f-coated Cf hybrid fibrous reinforcements and properties of their reinforced ceramicizable phenolic resin matrix composites

Carbon fiber-reinforced ceramicizable phenolic resin matrix composites have been widely used in the field of thermal protection materials. In this paper, the ZrO2f-coated Cf (ZrO2f/Cf) hybrid fibrous reinforcements were designed to improve oxidation resistance of carbon fiber and ceramicizable composites reinforced by ZrO2f/Cf hybrid fibrous reinforcements were prepared to investigated oxidation resistance and mechanical properties of the composites at high temperature. The results show that ZrO2f/Cf hybrid fibrous reinforcements have good thermal stability and high oxidation resistance, and its ceramicizable composites have good bending strength at high temperature. Weight loss rate of the composites is only 21 %, and bending strength can be as high as 39 MPa when ablation time was 12 min at 1400 °C.

An Experimental Study on the Ablation Properties of Carbon/Carbon Composites Using Thermal Plasma

The ablation properties of two carbon/carbon (C/C) composites currently considered as thermal protection materials for radioisotope thermoelectric generators (RTGs) were investigated using a plasma wind tunnel with a heat flux between the range of 2–4 MW/m2. The ablation properties were identified through an analysis of erosion rates and microstructures after testing. During ablation, erosion reactions of the matrix were faster than those of fibers and pores, and the defects and cracks between the fibers and matrix grew. The fibers eroded from their outer surface and ablation led to the formation of sharp tapered tips. Lower density C/C composites appeared to lose more matrix than higher density C/C composites. The erosion rate increased with heat flux. The ablation properties were compared with the test results using a vacuum plasma spray (VPS) facility and an E-beam facility. It was shown that both thermochemical and thermomechanical erosion occurred via oxygen in the plasma flow, and a rapid high-pressure heat stream occurred in tests using the plasma wind tunnel while only thermal ablation occurred in tests using the VPS and E-beam facilities.

Effect of ablation at the inlet of submerged nozzle on discharge characteristics

The effect of ablation on the discharge characteristics of solid rocket engines with submerged nozzles is examined. State-of-the-art computational fluid dynamics software package ANSYS Fluent is employed for simulation. The ablation is considered from the standpoint of the effect caused by uniform blowing of degradation products on the boundary layer developing over the entrance length of the submerged nozzle. Different masses of injected substance are considered. The impact of injection on velocity profiles is estimated. The discharge coefficient is affected by the non-isothermal boundary layer when degraded thermal protection material is injected and chemical reactions are neglected. The effect of injection on the profiles of velocity and temperature, and hence, on discharge characteristics is revealed.

Spectral emissivity inversion of quartz composite ceramics under hypersonic airflow collision

In this paper, the radiation spectra of quartz composite ceramic thermal protective materials in a pneumatic environment were measured in a plasma arc wind tunnel experiment. Spectral emissivities and material temperature at varying airflow speeds were calculated based on the algorithm of slow variation properties of emissivity. The inversion results show that the spectral emissivity reaches its maximum at a maximum airflow velocity of Mach 10. Emissivity uncertainty caused by the spectral measurement was analyzed. Relative error was determined by comparing real and calculated emissivities from Standard blackbody radiation spectrums at 2298 K in the wavelength range of 420–900 nm and 1573 K for 1200–2400 nm. Results obtained by the algorithm of slow variation properties for emissivity show that the maximum relative error in 420–900 nm is 3.3% and the average relative error is 2.7%; the maximum relative error for 1400–2400 nm is 4.1% and the average relative error is 2.1%. This provides a new method for the study of material emissivity under hypersonic flow collision aerodynamic heating conditions.

Improving ablation properties of ceramifiable vitreous silica fabric reinforced boron phenolic resin composites via an incorporation of MoSi2

ABSTRACT Various thermal protective ablative materials (TPAM) have been extensively studied. However, there are few reports on the thermal stability, the ablation properties and ceramisation of vitreous silica fabric reinforced boron phenolic resin composites with an incorporation of MoSi2 (VMBPR) and their bending strength after ablation. At this work, the above performances of the composites were characterised and analysed. Results reveal that the addition of MoSi2 decreases the graphitisation temperature of glass carbon of BPR pyrolysis, promoting the formation of a more ordered structure of the glassy carbon during pyrolysis. Furthermore, compared with the composites without MoSi2 (VBPR), the linear and the mass ablation rate of VMBPR composites decrease by about 94.46% and 39.09%, and its room temperature bending strength after static ablation at 1400°C for 20 min is more than twice that of the fused fibre aggregation formed by VBPR composites. This is attributed to the ceramisation reaction of VMBPR composites at high temperature.

Evaluation method and key factor analysis for thermal protection performance of multifunctional integrated ablative materials

AbstractThe thermal protection materials of hypersonic aircrafts in near space are subjected to extremely serious aerothermodynamic environment under long heating time, higher enthalpy, larger heat accumulation, and so forth. Proposing new concepts of materials and accurate evaluation of their performance take the dominant roles in developing high‐efficiency thermal protection materials under this severe environment. By introducing the concepts of gradient and fiber hybridization, this study proposes a multifunctional integrated ablative material scheme to replace heritage ones in order to improve the heat insulation, ablation resistant, and weight reduction capacities. Meanwhile, a thermal‐fluid‐ablative coupling mathematical model taking the manufacturing processing parameters reflecting the gradient and fiber hybridization into consideration is established. Furthermore, the sensitivity analysis for the manufacturing processing parameters is carried out. A simulation tool is developed based on writing FORTRAN codes to solve the multi‐field coupling model numerically. The results that the model and code are effective in analyzing the material's performance and the key manufacturing processing parameters influencing on the thermal protection performance of multifunctional integrated ablative material are pointed out. This work helps to design new thermal protection materials for hypersonic vehicles under extreme aerothermodynamic environments.Highlights New scheme of multifunctional integrated ablative material is proposed. Developed multi‐field coupling thermal protection model for new material is established. A bridge between material responses and manufacture processing parameters is built. Key factors influencing on material performance are pointed out by sensitivity analysis.

Design of a novel all-carbon multi-layer structure with excellent thermal protection performance based on carbon/carbon composites and carbon foam

In order to obtain high-performance thermal protection materials, a novel all-carbon triple-layer structure was designed by orderly combining high thermal conductivity carbon/carbon composites (HTC-C/C), polyacrylonitrile-based carbon fiber reinforced composites (PAN-C/C) and carbon foam. During exposure to the oxyacetylene torch, compared with the multi-layer structure made of PAN-C/C and carbon foam, the maximum surface temperature of the triple-layer structure was lowered from 2348 °C to 2215 °C, and the mass ablation rate was reduced by 90.0%, attributed to the excellent heat-dissipation performance and the higher anti-oxidation property of HTC-C/C. When compared with the multi-layer structure composed of HTC-C/C and PAN-C/C, the back surface temperature of the triple-layer structure is further decreased by 700 °C, proving the effective thermal insulation of carbon foam; meanwhile, by isolating the air structure of the intermediate layer made of PAN-C/C was protected from oxidation.

Numerical analysis of ablative behavior of silicone resin coated carbon fabric

Purpose The purpose of this paper is to study the ablative behavior of the silicone resin-coated carbon fabric (coated fabric) that will swell significantly during ablation. Design/methodology/approach The ablation experiments of three coated fabrics were conducted by quartz lamp radiant. Based on the experimental analysis, a numerical model was proposed for the coated fabrics to study the ablative process in term of the energy balance, mass conservation and thermal decomposition equations. Findings Results showed that the average relative errors between the simulated temperatures and experimental values of back surfaces of coated fabric 1, 2 and 3 were 10.01, 7.53 and 7.32%, respectively. The average density of silicone resin of coated fabric 1 was reduced by 47.96%, and the closer the distance from the heated surface was, the more the density decreased. The thermal conductivity and specific heat capacity of silicone resin of coated fabric 1 increased with time. Before 50 s, each decomposition rate curve showed an inflection point, at which the silicone resin decomposed most intensely. Research limitations/implications Based on experimental observations, the ablative behavior of the material with fixed expansion layer was simulated. In the further research, the moving expansion layer could be considered. Originality/value This paper provides the theoretical basis to evaluate the effectiveness of thermal protection materials that will swell during ablation.

ZrB2-Based "Brick-and-Mortar" Composites Achieving the Synergy of Superior Damage Tolerance and Ablation Resistance.

The intrinsic brittleness and poor damage tolerance of ultrahigh-temperature ceramics are the key obstacles to their engineering applications as nonablative thermal protection materials. Biomimetic layered or "brick-and-mortar" hybrid composites composed of alternative strong/weak interfaces exhibit excellent strength and high toughness; however, the commonly used interfacial materials are weak and have poor thermal stability and ablation resistance, which strictly limit their use in high-temperature and oxidative environments. In this work, ZrB2-based "brick-and-mortar" hybrid ceramics were constructed with a hierarchical biomimetic design to improve the fracture resistance and damage tolerance. ZrB2-20vol %SiC ceramics containing 30 vol % reduced graphene oxide nanosheets were used as the weak interface to increase crack growth resistance without destroying the excellent ablation resistance. Finally, the ZrB2-based "brick-and-mortar" composites achieve the synergy of superior damage tolerance and ablation resistance.

On experimental determination of the catalycity coefficient of heat-proof thermal protection materials

This paper reviews the developed and tested algorithm of experimental determination of the catalycity coefficient of heat-proof thermal protection materials and determines the conditions which should be followed during the simulation process at high-temperature gas-dynamic testbeds within the experiment.

Multicomponent Pyrolysis Model for Thermogravimetric Analysis of Phenolic Ablators and Lignocellulosic Biomass

A multicomponent kinetic mechanism has been developed for the pyrolysis at low heating rate of carbon/phenolic thermal protection material and a wood species. An experimental campaign has been carried out using thermogravimetric analysis to study the mass loss under different conditions of crucible (with or without a lid) and heating rate for both materials. Using a pierced lid to cover the crucible during pyrolysis promotes char production compared with the case of open crucible. Kinetic parameters were then extracted from the experiments by an optimization approach using an in-house-developed kinetic identification code. The parameters recovered for the two applications allow to reproduce accurately the mass loss evolution.

Effects of Ca2+-Sr2+ doping on the infrared emissivity of LaCrO3

LaCrO3 shows excellent thermal stability and good emissivity, and can be used as a potential thermal protection material for hypersonic vehicle. In this study, LaCrO3 and Ca2+-Sr2+ doped LaCrO3 were prepared by solid state reaction at 1400 °C for 2 h. The microstructures of the samples and effects of Ca2+-Sr2+ doping on the infrared emissivity of LaCrO3 were studied by XRD, XPS, FT-IR, and UV–VIS–NIR spectrophotometer. The results show that after doping Ca2+ and Sr2+ ions, the infrared emissivity of all samples has significantly improved at 2.5–10 μm, from 0.61 (minimum value) to above 0.90. In the range of 10–14 μm, the emissivity of pure LaCrO3 and La0.8CaxSr0.2-xCrO3 samples shows a similar trend and all remains above 0.97. Therefore, doping Ca2+ and Sr2+ can significantly increase the emissivity of LaCrO3 at 2.5–10 μm, which makes it have a wider application prospect in the field of high temperature thermal protection.

Development of polyetherimide composites for use as 3D printed thermal protection material

As additive manufacturing (AM) increasingly gains commercial and academic interest, government agencies, such as NASA Johnson Space Center, seek to produce thermal protection systems using AM methods, such as fused filament fabrication (FFF). The purpose of this study is to develop a suitable polyetherimide (ULTEM™ 1010) nanocomposite with enhanced ablation and thermal properties while maintaining compatibility with commercially available FFF machines. Eleven formulations were compounded using the twin-screw extruder with varying amounts of nanoclay, glass bubbles, and flame-retardant additives. All formulations were characterized via multiple instruments to be down-selected to four candidates for aerothermal testing. After discovering specific characteristics of some formulations, aerothermal test models were 3D printed for four formulations. Enhanced thermal properties among the composite formulations were demonstrated. Aerothermal testing also displayed promising results. In addition to experimental data, microstructural analyses were performed.

Preparation and characterization of phthalonitrile resin within hyperbranched structure

In this article, a kind of polyester-type phthalonitrile cyano resin (2,2-bis (((3-((4-(3,4-dicyanophenoxy) benzoyl)oxy)-2-(hydroxymethyl)-2-methylpropanoyl)oxy)methyl) propane-1,3-diyl)bis(oxy)) bis (2-(hydroxymethyl)-2-methyl-3-oxopropane-3, 1-diyl) bis (4-(3,4-dicyanophenoxy) benzoate (hbppn)) with branched structure was introduced. The molecular structure and relative molecular mass of hbppn were characterized by nuclear magnetic resonance, Fourier transform infrared spectroscopy, and the matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF). The results showed that the synthesized HBPPN contained both polyester and hyperbranched structures. The thermal and rheological properties of HBPPN were characterized by differential scanning calorimetry and rheometer, and the results showed that HBPPN would be cured at about 322°C and the viscosity of the resin showed good processability. The results of dynamic mechanical analysis and thermogravimetric analysis showed that the synthesized resin had good heat resistance. The glass transition temperature was above 329°C, the residual weight ( C y) at 900°C was as high as 66.2% in the nitrogen atmosphere, and the temperature at which the resin lost 5 wt% of heat in air atmosphere was about 423.3°C. The synthesized HBPPN had good comprehensive properties, which could be applied to high-temperature resistant and thermal protection materials.

Nano-silica modified phenolic resin film: manufacturing and properties

Abstract Nano-silica modified phenolic resin film is prepared using different mass fractions of nano-silica by liquid composites molding (LCM). The effects of nano-silica on the rheology and curing of phenolic resin are studied by rheometer and differential scanning calorimeter (DSC). The results show that the viscosity of nano-silica modified phenolic resin decreases with the increase of temperature, and the viscosity is lowest between 70°C and 90°C. The appropriate resin film infusion (RFI) process is investigated, and the stepped curing process system is established. In addition, the microstructures of modified phenolic film and composites are tested by scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS). Nano-silica can be uniformly dispersed in phenolic resin when the amount of nano-silica added is ≤ 4%. And the mechanical properties of nano-silica modified phenolic composites are tested by universal material testing machine. The optimum nano-silica mass loading for the improvement of mechanical properties is found. This work provides an effective way to prepare the modified phenolic resin film suitable for resin film infusion (RFI) processes, and it maybe become a backbone of thermal protection material in aerospace.

Experimental Studies of the Scatter in Heat-Shielding Characteristics of a Rubber-Like Heat Shield

The scatter in heat-shielding characteristics of a material used as a heat shield of high-temperature units, in particular, solid propellant rockets, considerably affects the design thickness and weight of the heat shield, and, hence, the efficiency and reliability of the unit. Based on the results obtained during high-temperature bench tests, the data scatter is shown to depend considerably on the method used to calculate the depth of heating and/or the depth of thermal destruction. Analysis of the experimental data yielded estimates of the scatter in the heat-shielding characteristics of a rubber-like thermal-protection material.

Thermal/vibration joint experimental investigation on lightweight ceramic insulating material for hypersonic vehicles in extremely high-temperature environment up to 1500 °C

Conducting a ground thermal/vibration joint test of thermal protection materials in extremely high-temperature environments is important for the safety and reliability design of hypersonic vehicles. This study establishes a joint high-temperature and vibration environment and attempts to solve the problem of accurately measuring and controlling the surface temperature of lightweight porous insulating materials under strong vibrations. By employing a water-cooled insulation device to protect the expensive vibration excitation equipment, a joint heat/vibration test of lightweight thermal protection materials for hypersonic vehicles in a high-temperature environment of 1500 °C is conducted. The fracture morphology and cracked section properties of the non-metallic insulating ceramic fibreboard are obtained. The material is subsequently improved based on test results, such as apparent and microscopic changes in the material and changes in the internal binder before and after the test. After a simulation test, the material demonstrated that it satisfied the usage requirements. The thermal/vibration joint test system and test results under an extremely high-temperature environment of 1500 °C provide important support for evaluating the anti-vibration capability, determining the thermal insulation effect, and improving the material properties of thermal protection materials for long-range hypersonic vehicles.

The effect of fibre content on properties of ceramifiable composites

ABSTRACTWith the development of rocket and aerospace technology in recent decades, people have put forward higher requirements on the heat resistance and ablation performance of thermal protection materials. In this paper, zirconia fibre hybrid alumina fibre/boron phenolic (ZA/BPF) ceramifiable composites, based on ceramic fillers of MgO, Al2O3, SiC and mica-modified boron phenolic resin matrix, were prepared with different hybrid fibre contents (5, 10, 15, 20, 25, 30 wt-%) by hot compression moulding. The result shows that fibre contents have little effect on the ablation resistance of composite materials which all have a low linear ablation rate below 0. 01 mm s−1. When the fiber content is 25%, the ZA/BPF composite reaches the highest bending strength 48. 86 MPa and 15. 57 MPa before and after sintering respectively. It is showed by the SEM results that too high and too low fibre content would both lead to poor bonding between resin and fibre interfaces.

Competitive kinetic model for the pyrolysis of the Phenolic Impregnated Carbon Ablator

Carbon/phenolic ablators are successfully used as thermal protection material for spacecraft. Nevertheless, their complex thermal degradation is not yet fully understood, and current pyrolysis models do not reproduce important features of available experimental results. Accurate and robust thermal degradation models are required to optimize design margin policy. We investigate whether the competitive kinetic schemes commonly used to model biomass pyrolysis are appropriate to describe the thermal degradation of carbon/phenolic composites. In this paper, we apply competitive pyrolysis mechanisms for the thermal degradation of the carbon/phenolic ablator PICA. Model parameters are then calibrated using a robust two-step methodology: first deterministic optimization is used to obtain the best estimation of the calibration parameters based on the experimental data, then a stochastic Bayesian inference is performed to explore plausible set of solutions taking into account the experimental uncertainties. The proposed calibrated model provides an accurate description of the pyrolysis process at different heating rates. The model shows great flexibility and robustness at a similar computational cost as the traditional devolatilization models. This opens the possibility for more complex mechanisms when more experimental data becomes available.

Heat Transfer and Ablation Prediction of Carbon/Carbon Composites in a Hypersonic Environment Using Fluid-Thermal-Ablation Multiphysical Coupling

Carbon/carbon composites are usually used as a thermal protection material in the nose cap and leading edge of hypersonic vehicles. In order to predict the thermal and ablation response of a carbon/carbon model in a hypersonic aerothermal environment, a multiphysical coupling model is established taking into account thermochemical nonequilibrium of a flow field, heat transfer, and ablation of a material. A mesh movement algorithm is implemented to track the ablation recession. The flow field distribution and ablation recession are studied. The results show that the fluid-thermal-ablation coupling model can effectively predict the thermal and ablation response of the material. The temperature and heat flux in the stationary region of the carbon/carbon model change significantly with time. As time goes on, the wall temperature increases and the heat flux decreases. The ablation in the stagnation area is more serious than in the lateral area. The shape of the material changes, and the radius of the leading edge increases after ablation. The fluid-thermal-ablation coupling model can be used to provide reference for the design of a thermal protection system.