Extreme High-temperature Environments Research Articles

The long-lasting maintenance of the pore structure achieves the stability of lithium metal batteries

The separator is considered critical to the safety and performance of lithium metal batteries (LMBs), however, the separator structure fails under high temperature conditions due to damage resulting in decreased mechanical strength, which causes short-circuiting of the battery. This paper describes a novel process to prepare stable and uniform dispersions of aramid nanofibers (ANFs) by bottom-up low-temperature polymerization, and then crosslink the ANFs with N2 plasma-treated polypropylene (PP) separator through capping isocyanate crosslinkers. The composite separator not only has excellent mechanical properties with hardness and modulus of elasticity up to 0.35 and 2.26 GPa, which is three times higher than the PP separator, but also has high-temperature thermal stability, the size maintenance rate reaches 99.8 % at 200 °C. Meanwhile, real-time monitoring of the pore size at different temperatures by synchrotron radiation small-angle X-ray scattering (SR-SAXS) showed that the pore radius of gyration was kept at 8.81 nm and the size change rate was only 22.8 % at 200 °C, which demonstrated that the composite separator had an outstanding ability to maintain the pore structure to ensure the stability of the ionic transport channel. Therefore, the crosslinked composite separator has greater potential for improving the performance and safety of LMBs in extreme high-temperature environments.

Process optimization and tribological behavior of Ti-48Al-2Cr-2Nb prepared by selective electron beam melting

Selective electron beam melting (SEBM) technology was utilized to fabricate TiAl alloys which possess low density and excellent high-temperature performance, to achieve lightweight design of automotive engines. The forming process of Ti-48Al-2Cr-2Nb was systematically optimized, and found that the microstructure of TiAl formed by SEBM consisted of a layer of alternating γ-band structure and duplex-like structure. As the energy density increases, grain coarsening, proportion increasing of high angle grain boundaries, and anisotropy strengthening occur successively. The forming quality of TiAl reaches its peak at an energy density of 22.5 J/mm3, at which point its mechanical properties and wear resistance also perform the best. Subsequently, in-depth friction experiments at high and room temperatures were conducted, and it was found that at room temperature, as the load increased, the friction coefficient of the samples decreased and the wear rate increased. In addition, the friction coefficient decreases from 0.54 to 0.44, while the wear rate increases from 19.90×10−5 mm3/(N·m) to 25.97×10−5 mm3/(N·m). At this point, abrasive and adhesive wear were the main wear mechanism. Under high temperature conditions, the wear mechanism of the substrate is mainly abrasive wear, adhesive wear, and oxidative wear. And the friction coefficient decreases from 0.69 to 0.49. At lower temperatures, the detached debris was filled and solidified on the wear marks under the action of the friction ring, forming a hardened layer called “enamel”, which can alleviate the negative effects of wear. Under the influence of extreme high temperature environment, the unworn surface forms a light blue oxide film due to rapid oxidation, known as the “burning blue” phenomenon. Along with the high-temperature oxidation phenomenon confirmed by EDS, the oxide layer is more prone to peeling off and forming debris. In addition, melting softening occurs inside the annular wear scar, which increases the amount of deformation under external force, ultimately leading to a significant increase in wear.

Microstructurally resolved electrochemical evolution of mechanical- and irradiation-induced damage in nuclear alloys

There is a need for high-throughput, scale-relevant, and direct electrochemical analysis to understand the corrosion behavior and sensitivity of nuclear materials that are exposed to extreme (high pressure, temperature, and radiation exposure) environments. We demonstrate the multi-scale, multi-modal application of scanning electrochemical cell microscopy (SECCM) to electrochemically profile corrosion alterations in nuclear alloys in a microstructurally resolved manner. Particularly, we identify that both mechanically deformed and irradiated microstructures show reduced charge-transfer resistance that leads to accelerated oxidation. We highlight that the effects of mechanical deformation and irradiation are synergistic, and may in fact, superimpose each other, with implications including general-, galvanic-, and/or irradiation-activated stress-corrosion cracking. Taken together, we highlight the ability of non-destructive, electrochemical interrogations to ascertain how microstructural alterations result in changes in the corrosion tendency of a nuclear alloy: knowledge which has implications to rank, qualify and examine alloys for use in nuclear construction applications.

Ablation resistant C/C-HfC-ZrC-TaC-SiC composites prepared by reactive melt infiltration

Ultra-high temperature ceramics (UHTCs) modified C/C composites for extreme high-temperature environments are fascinating, the rapid introduction of UHTCs and structural temperature resistance are essential for the long-term service. Herein, C/C-HfC-ZrC-TaC-SiC composites with continuous ceramic-rich layers were designed and prepared to improve the ablation resistance. HZT441 (HfC:ZrC:TaC = 4:4:1) sample exhibited pseudo-plastic fracture with a flexural strength of 195.27 ± 11.11 MPa. After 80 s of oxyacetylene ablation (4.2 MW/m2), the mass and linear growth rates were 0.10 mg/s and 1.02 μm/s. This is attributed to the dense oxide layer, including (Hf,Zr)6Ta2O17, (Hf,Zr)O2 and SiO2, which effectively inhibits oxygen intrusion and carbon fiber damage. In addition, the thermal response behavior and stress distribution of ceramic-rich layers to C/C composites were investigated, which is contributed to provide a theoretical basis for the material design of thermal protection systems in extreme high-temperature environments.

Designed fabrication of lightweight SiC(Hf, rGO) bulk composites derived from Hafnium-modified precursors for hypersonic vehicle components

Demand for SiC-based polymer-derived ceramics (PDCs) employed as hypersonic vehicle components with light weight, high strength, excellent high-temperature/ablation resistance is increasingly urgent. Herein, bulk SiC(Hf, rGO) nanocomposite PDCs were fabricated via re-pyrolyzing ball-milling blends of unique SiC(Hf, rGO)p/polyhafniumcarbosilane-vinyltriethoxysilane-graphene oxide (PHVG). Highly cross-linked PHVG can effectively optimize compact formability and improve ceramic yield. In-situ formed HfO2 embedded in ceramic network toughens microstructure, while interfacial HfOSi increases structure disorder to improve high-temperature properties. As demonstrated, SiC(Hf, rGO) modified by 3 wt.% Hf and re-pyrolyzed at 1300 °C possess good mechanical performances including hardness (5.83 GPa), fracture toughness (4.29 MPa·m1/2), compressive strength (181.83 MPa) and flexural strength (46.55 MPa). More interestingly, self-healing HfO2(HfSiO4)/SiO2 protective layer emerging during 20 min surface ablation test at 1300 °C, timely covers defects and avoids destructive structure, thus retains stable structure and mechanical properties of specimens. Such nanocomposites can promote uses in thermal protection systems (TPS) for hypersonic vehicles against extreme high-temperature environments.

Research on the heat–humidity coupling transfer model of the CRTS Ⅱ type track slab and its characteristics

After operation for more than 10 years, CRTSⅡtype track slab structures have developed interlayer diseases in continuous extreme high-temperature environments, which are dominated by track slab-CA mortar layer cracking. To reveal the formation mechanism of track slab-CA mortar layer cracking under complicated operation conditions, a heat–humidity coupling transfer model, which is utilized to analyze track slab deformation, was developed. Furthermore, to enhance the precision of the model, we investigated the variation law that regulates relevant parameters of concrete materials with respect to temperature and humidity. Moreover, a testing apparatus was established to validate the accuracy of the transfer model under natural conditions. The analysis revealed that the maximum temperature error in the track slab was 3.33 K, and that the maximum error of relative humidity (RH) was 6.04 %. The distribution characteristics of temperature and humidity fields in the track slab during 10 consecutive rainless days under different seasonal climates in a hot-summer and cold-winter zone (Hangzhou) in China were calculated and analyzed using COMSOL Multiphysics® software. The results indicated that in the distribution of the summer temperature field, the maximum negative temperature gradient could attain -48.67 K/m, and that the maximum positive temperature gradient could attain 76.37 K/m. Moreover, RH values at 10 mm, 20 mm, 30 mm, and 40 mm decreased by 30.85 %, 15.51 %, 9.17 %, and 5.9 %, respectively. In a year, a higher track slab temperature, a greater temperature fluctuation range, and more apparent positive and negative temperature gradients were observed during summer, and the influencing depth of water also attained the maximum value during summer.

Triple-shape memory polybenzoxazine resins and their composites

Shape memory polymer (SMP) as a new type of smart material can be programmed into a temporary shape by external excitation. Benzoxazine is a novel thermosetting resin with excellent heat resistance, high glass transition temperature (Tg) and mechanical properties. Here, triple-shape memory polybenzoxazines with high Tg were obtained by copolymerization of phenol/polyetheramine with phenol/furanamine benzoxazines. Electrically driven composites were prepared using multi-walled carbon nanotubes, and the SMP electrically driven function was achieved by forming a complete and continuous conductive permeable network inside the composites, shape recovery can be completed in 15 s at 60v. Furthermore, at high temperatures the carbon residue rate is increased to 45 % at 800 °C, demonstrating the high performance of electrically driven shape memory polymer composites. The realization of the triple and electrically induced shape memory properties of shape memory polybenzoxazines broadens the way for their application in extreme high-temperature environments in aerospace and aviation.

Phase stability, mechanical and thermodynamic properties of (Hf, Zr, Ta, M)B2 (M= Nb, Ti, Cr, W) quaternary high-entropy diboride ceramics via first-principles calculations

As the high-entropy design concept applied to the diboride ceramic system, high-entropy diboride ceramics with a wide range of composition control, is expected to become a new high-performance material for extreme high-temperature environments. Herein, the effects of four transition metal elements (Nb, Ti, Cr, W) on the phase stability and properties of (Hf, Zr, Ta)B2-based high-entropy diboride ceramics are systematically investigated via the first-principles calculations. All components were identified as thermodynamically, mechanically and dynamically stable from enthalpy of formation, elastic and phonon spectrum calculations. Among these, compared with the (Hf, Zr, Ta)B2 ceramics, the addition of Nb and Ti on the metal sublattice is beneficial to improve the mechanical properties of ceramics, including Young's modulus, hardness and fracture toughness, while the introduction of Cr and W weakens the strength of covalently and ionic bonds inside the material, reducing its mechanical properties. The predicted thermophysical properties show that the high-entropy diboride ceramics containing Nb and Ti have better high-temperature comprehensive performance, including higher Debye temperature, thermal conductivity and lower thermal expansion characteristics, which is conducive to the application in extreme high-temperature environments. This research will provide important guidance for the design and development of new high-performance high-entropy diboride ceramics.

Renewable resource-derived elastomer vitrimer and its sustainable manufacturing and application in extreme environmental conditions

The development of biomass (e.g., lignin, cellulose or vegetable oil)-based reversibly dynamic covalent cross-linked elastomer vitrimer materials is a novel approach to address issues related to the recycling of waste cross-linked elastomer material. The primary questions discussed are about how to design chemically recycled biomass-derived cross-linked elastomer vitrimer materials, what are the potential challenges in sustainable manufacturing of cross-linked renewable resources derived elastomer vitrimer materials, and what are their potential advanced applications under extreme environmental conditions, such as extreme low or high temperature and irradiated environments.

Multi-Scale Structural Design and Advanced Materials for Thermal Barrier Coatings with High Thermal Insulation: A Review

Thermal barrier coatings (TBCs) are a fundamental technology used in high-temperature applications to protect superalloy substrate components. However, extreme high-temperature environments present many challenges for TBCs, such as the degradation of their thermal and mechanical properties. Hence, highly insulating, long-life TBCs must be developed to meet higher industrial efficiency. This paper reviews the main factors influencing the thermal insulation performance of TBCs, such as material, coating thickness, and structure. The heat transfer mechanism of the coating is summarized, and the degradation mechanism of the thermal insulation is analyzed from the perspective of the coating structure. Finally, the recent advances in improving the thermal insulation and lifetime of coatings are reviewed in terms of advanced materials and structural design, which will benefit advanced TBCs in future engineering applications and provide guidance for the next generation of high thermal insulating TBCs.

Molecular dynamics simulation of glass transition and thermal stability of novel silicone elastomer and its nanocomposites

Existing silicone elastomers (SR) are difficult to serve properly in extreme high and low temperature environments. Herein, through molecular dynamics (MD) simulations, a novel SR with wide temperature resistance range was designed using silicon-oxygen bonds (-Si-O-) to construct the backbone and side chains of polymer chains. Firstly, we investigated the cold and heat resistance of SR with various grafting density and side chain length. Three different approaches were utilized to estimate the glass transition temperature ( T g ) of SR, i.e., by calculating the volume, non-bonding energy, and conformational transitions rate of the torsion angle ( K T ). Also, the rate of change of mean square displacement (MSD) versus temperature was used to characterize the thermal decomposition temperature ( T d ) of this designed material. The results demonstrated that when the grafting density is high and the length of side chain is moderate, the elastomer has the best extreme temperature resistance, with T g and T d reaching below -140℃ and above 420℃ respectively. Then, SR pyrolysis was investigated by Reactive Force Field (ReaxFF) MD simulations. The dominant final products were CH 4 , H 2 , C 2 H 4 and siloxane. Finally, the introduction of SiO 2 nanoparticles improves the cold and heat resistance of the composite, with T g reaching about -150℃ and T d reaching above 450℃. In addition, the heterogeneous distribution of molecular chain conformational transitions demonstrated that the introduction of more nanoparticles resulted in the chain segments have more space for rotation, leading to decrease in T g . Arrhenius parameters were extracted through pyrolysis simulations, illustrating that the SiO 2 nanoparticles improves the thermal stability of nanocomposites. In general, our work could provide rational guidelines for the design and fabrication of novel polymeric materials with a wide temperature resistance range. • Silicon-oxygen bonds are used to build the backbone and side chains of polymer chains. • The rate of change of MSD versus temperature is employed to estimate the T d . • Novel silicone elastomer pyrolysis is investigated by ReaxFF-MD simulations. • The temperature resistance range of SR/SiO 2 nanocomposites is about -150℃ to 450℃.

Effects of extreme high temperature environment on photosynthetic characteristics of ‘Junzao’ and ‘Fucuimi’

Effects of extreme high temperature environment on photosynthetic characteristics of ‘Junzao’ and ‘Fucuimi’

A novel deep earth observation-oriented methods for enhancing magnetometry sensor stability

The existing magnetic sensors are sensitive to temperature and are prone to temperature drift, which makes it difficult to guarantee detection accuracy when working continuously at high temperatures downhole for long periods of time. Moreover, the confined space underground greatly affects the installation and working of equipment. To this end, this paper proposes a method to enhance the stability of magnetic measurements in deep wells. Firstly, the fact that the stability of the magnetic sensor is subject to temperature is verified at four temperatures; then, the effect of the proposed method on the stability of the magnetic sensor at four temperatures of 120 °C, 150 °C, 180 °C and 210 °C is demonstrated through simulations and experiments; subsequently, the long-term stability of the method is confirmed by ageing tests in the extreme high temperature environment; finally, field experiments are conducted to reaffirm the effectiveness and engineering feasibility of the method.

(Invited, Digital Presentation) The Challenges of Overcoming Defects in GaN Hemts for Operation in Extreme Environments

GaN high electron mobility transistors (HEMTs) are known to contain a high density of crystal defects. The material properties of GaN such as high breakdown voltage, carrier mobility, critical electric field strength, and higher thermal conductivity than Si, make it an ideal candidate material for use in power switches in extreme environments. In high power environments (>1.5kV), vertical GaN device geometry is emerging as an effective technique to improve performance, but the more mature lateral GaN HEMT technology is being consistently improved upon to increase breakdown voltage and overall performance in the high-power regime. In high temperature environments, GaNs wide bandgap helps in preventing unwanted thermal generation of carriers, but devices also experience increased gate-leakage current and ohmic contact resistance degradation at high temperatures. The role of defects in these limiting factors of GaN HEMT performance in extreme high power and high temperature environments is reviewed.

Evaluation of discharging performance of molten salt/ceramic foam composite phase change material in a shell-and-tube latent heat thermal energy storage unit

Molten salts are widely used energy storage media in integrated solar power systems, however, due to their high corrosivity and the extreme high-temperature environment, many current methods of heat transfer enhancement do not apply. Herein, we proposed to use ceramic foam to enhance the discharging performance of molten salt to efficiently supply heat for power generation. The ceramic foam was prepared and its corrosion resistance was confirmed experimentally. The discharging performance in a shell-and-tube latent heat thermal energy storage unit was numerically studied. It is found that compared to the configuration without enhancement, the solidification time of the ceramic foam-enhanced unit is shortened by up to 52.0%. The unit with the upper foam insert shows better discharging performance than the one with the lower foam insert. Different foam filling height is also considered and results indicate that the thermal energy release rate always increases with the foam filling height and that of the fully foam-inserted unit is 118.1% higher than that of the none foam-inserted unit. For the first time, the discharging performance of ceramic foam-enhanced molten salt is quantitatively evaluated. This study provides guidance on designing thermal energy storage sub-system with excellent heat supply performance for solar power generation.

Experimental Study and Numerical Analysis of Structural Performance of CRTS II Slab Track under Extreme High Temperature

A ballastless track is susceptible to damage and even failure of structural components under the long-term effects of extremely high temperatures. In this paper, considering the influence of different constraint boundaries, a 1 : 4 scaled model of a ballastless track-bridge structural system was produced and placed in a large-sized environmental chamber. The thermal performance of the track structure was studied by carrying out temperature loading tests at extreme temperatures. In combination with the scaled-down model test data, a 3D nonlinear finite element model was established to investigate the damage evolution of broad-narrow joints under temperature gradient loading. The results are shown as follows: (1) the cement asphalt (CA) mortar layer has a hysteretic effect on the vertical temperature transfer. The most unfavorable structural part is between the track slab and the CA mortar layer of the track structure. (2) The constraint conditions accelerate the rate of temperature transfer, creating disturbances to the internal stresses of the track structure and amplifying the internal stresses induced by the environmental temperature increase. (3) Temperature and longitudinal stresses in the track’s structural layers are highly correlated. There is a significant quadratic regression between internal temperature and structural stresses in different extreme high-temperature environments. (4) As the temperature gradient load increases, the damage occurs at the junction of the broad-narrow joint and tends to expand towards the ends, which has little effect on the compression damage of the broad-narrow joint but significantly increases the tension damage. The research could provide useful guidance for the scientific operation and maintenance of the ballastless track in extreme high-temperature environments.

Preparation of NaF Microcapsules for High-Temperature Thermal Storage.

A novel NaF phase change microcapsule with a carbon shell (NaF@C microcapsule) was prepared by a simple approach. The carbon shell was synthesized by carbonization of a resole-type phenolic resin shell, which was encapsulated onto the surface of NaF particles by a simple phase separation process induced by tetraethoxysilane. Scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, differential scanning calorimetry (DSC), and thermogravimetric analysis were used to characterize the morphology, composition, crystal phase, and thermal properties of the microcapsules. The size of the NaF@C microcapsule was 3–5 μm with a core–shell structure. DSC results showed that the melting point of the prepared NaF@C microcapsule was 988 °C, and the enthalpy value was 192 J/g. The prepared NaF@C microcapsules retained the powder morphology after 30 times of heat treatment at 1100 °C, with no NaF leakage detected, and the micromorphology remained stable, presenting good thermal stability. The NaF@C microcapsules can be used in the fields of thermal protection and thermal management in extreme high-temperature environments such as aerospace and solar energy.

Heat transfer characteristics and compatibility of molten salt/ceramic porous composite phase change material

Molten salts are popular energy storage materials for medium- and high-temperature thermal energy storage. However, current methods for heat transfer enhancement do not apply due to the high corrosivity of molten salts and extreme high-temperature environment. Herein, porous silicon carbide (SiC) ceramic and solar salt are formed into a composite phase change material (PCM). The ceramic skeleton is fabricated to an open-cell structure with high porosity and a large pore configuration. The SiC ceramic is wetted by the solar salt, so that the impregnation of salt into ceramic achieves a high loading at atmospheric pressure. The result of visual inspection shows that the temperature distribution in the composite PCM is more uniform compared with pure solar salt. The maximum temperature difference is reduced from 148 ℃ to 130 ℃ and the overall phase change rate is increased by up to 42.9 %. The SiC ceramics show excellent corrosion resistance during the cycles of thermal charging and discharging as compared to copper and aluminium which are the widely used thermal promoters for low-temperature PCMs. The results obtained from reactive molecular dynamics (MD) simulation are consistent with the corrosion behaviours of SiC ceramic in solar salt from aspects of physical dissolution, chemical reaction, and thermal stress failure. The composite PCM has advantages of simple preparation, low cost, and easy maintenance, therefore it has a great potential for large-scale applications.

Printed electronics for extreme high temperature environments

There is a rapidly growing interest in the development of electronic microsystems that can maintain functionality in high temperature environments, particularly in power generation and aircraft engines where the operating temperatures can exceed 500 °C. The current work presents a major advancement toward development of additively printed electronics made for high temperature applications. Here, the electronic system is represented by gold-based electrical structures that have been printed on 3D printed ceramic substrates. The substrate is alumina-based with a purity level of 99.8% and was fabricated through photopolymerization digital light processing (DLP). An aerosol jet printing technique that can deposit an ink stream down to 10 µm was utilized to fabricate gold-based electronic structures. The gold ink printability and its adhesion to the ceramic substrate were assessed. Furthermore, the microwave dielectric constant and loss tangent of the alumina substrate were extracted through measurements of the scattering parameters of transmission lines up to 750 °C. A 3D printed conformal broadband antenna was successfully fabricated and tested at temperatures up to 850 °C. The printed gold structures showed excellent stability and adhesion after aging at temperatures up to 750 °C. The substrate dielectric constant slightly increased for temperatures up to 450 °C and significantly increased for temperatures between 450 °C and 750 °C. It was found that the dielectric loss increased as the temperature increased. This work presents an entirely additive manufacturing-based approach to fabricate electronic components including substrates, interconnects, and RF elements for high temperature applications.

Gas-Phase Preparation of Silyl Cyanide (SiH3CN) via a Radical Substitution Mechanism.

The silyl cyanide (SiH3CN) molecule, the simplest representative of a fully saturated silacyanide, was prepared in the gas phase under single-collision conditions via a radical substitution mechanism. The chemical dynamics were direct and revealed a pronounced backward scattering as a consequence of a transition state with a pentacoordinated silicon atom and almost colinear geometry of the attacking cyano radical and leaving hydrogen. Compared to the isovalent cyano (CN)-methane (CH4) system, the CN-SiH4 system dramatically reduces the energy of the transition state to silyl cyanide by nearly 100 kJ mol-1, which reveals a profound effect on the chemical bonding and reaction mechanism. In extreme high-temperature environments including circumstellar envelopes of IRC +10216, this versatile radical substitution mechanism may synthesize organosilicon molecules via reactions of silane with doublet radicals. Overall, this study provides rare insights into the exotic reaction mechanisms of main-group XIV elements in extreme environments and affords deeper insights into fundamental molecular mass growth processes involving silicon in our universe.