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NiCo2O4/CNT nanocomposite films were fabricated by in-situ growing ultrafine NiCo2O4 nanoparticles on acid-modified carbon nanotube (CNT) films. The effects of CNT-film pretreatment were investigated thoroughly by various characterization outfits including Fourier Transform Infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, RTS-9 four-point probes resistivity measurement system, X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and CHI660D electrochemical workstation. These results suggested that carbon nanotubes were uniformly wrapped by NiCo2O4 nanoparticles forming a hierarchical core-shell structure. And the crystallinity, conductivity of the CNTs and detail structure (both morphology and size) of the NiCo2O4 nanoparticles varied with prolonged acid treatment time which resulted in increased functional groups and defects on CNT films and further affected the electrochemical properties. The composite film composed of the CNT film pretreated by mixed acid for 12 h exhibited excellent electrochemical properties: 828 F/g at 1 A/g and 656 F/g at 20 A/g, and maintained over 99 % of its capacitance after 3000 cycles of charge/discharge at 5 A/g. Acid treatment for either too long or too short is detrimental to the electrochemical properties of the composite films. Such work should be of fundamental importance for tailoring electrochemical properties by elaborate design of acid treatment on CNTs. [ABSTRACT FROM AUTHOR]

Continuous carbon nanotube (CNT) networks were formed in Cf/SiC composites via freeze-drying method. Composites were fabricated by precursor infiltration and pyrolysis (PIP) process afterwards. The different distribution morphologies of CNTs in the preforms originating from the different CNT contents were analyzed while the influence of the distribution of CNTs was discussed in detail. Compared to composites without CNTs, the interfacial shear strength (ILSS) and the flexural strength of Cf/1%CNTs/SiC were increased by 31% and 27%, respectively, but the values of Cf/2.5%CNTs/SiC decreased as a result of lots of defects caused by excess CNTs. With the analysis of ILSS, the flexural strengths, and the fracture morphologies, CNTs effectively improved the weak interfacial strength between T700SC carbon fibers and SiC matrix. [ABSTRACT FROM AUTHOR]

Carbon/carbon( C/ C) composites were bonded with a phosphate adhesive prepared from H3 PO4 (orthophosphoric acid) and Al( OH)3 as the matrix and Si and Cu O as the inorganic fillers. The mechanical properties were tested at room temperature after the bonded specimens were treated from RT to 1500°C. The results showed that the addition of Cu O could greatly improve the adhesive's mechanical properties due to the formation of Cun Si (copper silicides). The shear strength of bonded specimens could be up to 8.2 MPa without heat treatment and remain above 2 MPa within the whole heat-treatment temperature range. [ABSTRACT FROM AUTHOR]

ABSTRACT Silicon oxycarbide (SiOC) fibers with different chemical compositions were successfully fabricated by electrospinning a mixture of polyvinylpyrrolidone (PVP) and commercially available polymethylsilsesquioxane (MK) or polymethylphenylsilsesquioxane (H44) preceramic polymers, followed by cross-linking and pyrolysis at 1000°C in Argon. The influence of the processing procedure (solvent selection, cross-linking catalyst and additives) on the morphology of the produced fibers was investigated. For the MK/isopropanol system, the introduction of 20 vol% N,N-dimethylformamide (DMF) enabled to decrease the diameter of the as-spun fibers from 2.72 ± 0.12 μm to 1.65 ± 0.09 μm. For the H44/DMF systems, beads-free fibers were obtained by adding 50 vol% choloroform. After pyrolysis, the resultant SiOC fibers derived from MK and H44 resins possessed uniform morphology, with an average diameter of 0.97 ± 0.07 μm and 1.07 ± 0.08 μm, respectively. Due to their different chemical compositions, the MK-derived and H44-derived SiOC ceramic fibers could find different potential applications. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 39836. [ABSTRACT FROM AUTHOR]

The mullite ceramic/fiber brick system was bonded by two kinds of phosphate adhesives. The specimens were treated from 200 to 1400°C. The mechanical properties were tested at room temperature and at high temperature, and the relevant bonding mechanism was also discussed. The results show that the addition of silicon can greatly improve the adhesive's mechanical properties. The room-temperature shear strength of the component bonded by adhesive with the silicon calcined at 800°C can reach 6.58 MPa. The shear strength of the adhesive with silicon tested at 800°C can reach 0.42 MPa. [ABSTRACT FROM AUTHOR]

Thermal protection has always been an important issue in the energy, environment and aerospace fields. Porous ceramics produced by the particle-stabilized foaming method have become a competitive material for thermal protection because of their low density and low thermal conductivity. However, the study of porous ceramics for composite systems using particle-stabilized foaming method was relatively rare. Here, silica-alumina composite porous ceramics were prepared by particle-stabilized foaming method, which was achieved by tailoring the surface charges of silica and alumina through adjustment of the pH. Porous ceramics exhibited porosity as high as 97.49% and thermal conductivity (25 °C) as low as 0.063 W m−1 K−1. The compressive strength of porous ceramics sintered at 1500 °C with a solid content of 30 wt% could reach 0.765 MPa. Based on the light weight and excellent thermal insulation properties, the composite porous ceramic could be used as a potential thermal insulation material in the spacecraft industry. [ABSTRACT FROM AUTHOR]

High emissivity coatings on hypersonic vehicle surfaces dissipate heat by emitting thermal radiation. While the difficulty of increasing emissivity limits the performance of coatings to improve heat-dissipation of the thermal insulation felt. Herein, a novel high-reflectivity and high-emissivity integrated double-layer coating was developed to enhance the thermal insulation performance of the alumina fiber fabric. The coating comprised of TiO 2 @SiO 2 (T@S) as reflective agent and ZrO 2 /SiC w (ZSC) as emittance agents, was applied on the surface of alumina fiber fabric (AFF). The reflecting effect of radiation heat from the high reflective agent enhanced the thermal insulation properties of the double-layer coating. In the wavelength range of 0.4–2.5 μm, the average emissivity of the ZSC coating was 0.83 and the average reflectivity of the T@S coating was 0.63. With continuous heating at 1400 °C for 10 min with a butane torch, the temperature on the backside of the T@S–ZSC-coated AFF remained relatively stable at 225 °C, which is notably decreased by 80 °C compared to that of the single-layer ZSC-coated AFF. The tensile strength of AFF with T@S–ZSC coating reached 35 MPa after being heat treated at 1200 °C. Moreover, the bonding strength between the coating and the AFF substrate was measured to be 0.15 MPa. The double-layer coating with high emissivity and reflectivity, along with a flexible AFF substrate, offers a promising solution for addressing the challenging of surface heat-dissipation in hypersonic vehicles. [ABSTRACT FROM AUTHOR]

Integration of thermal insulation and electromagnetic wave absorption was crucial in stealth technology and hypersonic vehicles but challenging. Herein, silicon carbide nanofibers were synthesized by in situ chemical vapor deposition within a carbon foam skeleton to form a wave absorbing and heat insulating integrated composite aerogel with a hierarchical porous structure. The unique hierarchical porous structure provided an excellent platform for the absorption of electromagnetic waves, achieving a minimum reflection loss (RL min) of −51.46 dB at 17.20 GHz. Meanwhile, the C/SiC nanofiber aerogel maintained a low density of 0.013 g/cm3, an ultra-low thermal conductivity of 0.030 W/(m⋅K) and a high thermal stability up to 1000 °C. Furthermore, to enhance the electromagnetic wave (EMW) absorption property of the aerogel, polypyrrole (PPy) was coated on the surface of C/SiC nanofiber aerogel by facile impregnation and chemical polymerization. The multiple conductor-semiconductor-conductor structure of C/SiC-PPy composite aerogel leads to various EMW loss mechanisms and excellent impedance match, resulting in an outstanding EMW absorption performance, with a RL min of −60.31 dB at 2.96 GHz. [ABSTRACT FROM AUTHOR]

Fibers crystallize and become brittle at high temperatures for a long time, so the surface coating must maintain long-lasting emission performance, which requires superior antioxidant properties of the high-emissivity fillers. To improve the radiation performance of the coating and the tensile strength of the fiber fabric, a double-layer coating with high emissivity was prepared on the surface of flexible aluminum silicate fiber fabric (ASFF) using MoSi2 and SiC as emissive agents. The incorporation of borosilicate glass into the outer coating during high-temperature oxidation of ZrB2 results in superior encapsulation of emitter particles, effectively filling the pores of the coating and significantly reducing the oxidation rate of MoSi2 and SiC. Furthermore, the addition of an intermediate ZrO2 layer enhances the fiber bundle's toughness. The obtained double-coated ASFF exhibits an exceptionally high tensile strength of 57.6 MPa and a high bond strength of 156.2 kPa. After being subjected to a 3 h heating process, the emissivity exhibits a minimal decrease of only 0.032, while still maintaining a high value above 0.9. The thermal insulation composites, consisting of a flexible ASFF matrix and a ZrB2-modified double-layer coating, exhibit significant potential for broad applications in the field of thermal protection. [ABSTRACT FROM AUTHOR]

Mullite fiber felt is a promising material that may fulfill the demands of advanced flexible external thermal insulation blankets. However, research on the fabrication and performance of mullite fiber felt with high-temperature resistance and thermal stability is still lacking. In this work, mullite fibers were selected as raw materials for the fabrication of mullite fibrous porous materials with a three-dimensional net structure. Said materials' high-temperature resistance and thermal stability were investigated by assessing the effects of various heat treatment temperatures (1100 °C, 1300 °C, and 1500 °C) on the phase composition, microstructure, and performance of their products. When the heat treatment temperature was below 1300 °C, both the phase compositions and microstructures of products exhibited stability. The compressive rebound rate of the product before and after 1100 °C reached 92.9% and 84.5%, respectively. The backside temperature of the as-prepared products was 361.6 °C when tested at 1500 °C for 4000 s. The as-prepared mullite fibrous porous materials demonstrated excellent high-temperature resistance, thermal stability, thermal insulation performance, and compressive rebound capacity, thereby indicating the great potential of the as-prepared mullite fibrous porous materials in the form of mullite fiber felt within advanced flexible external thermal insulation blankets. [ABSTRACT FROM AUTHOR]

Ensuring a consistently high-strength connection in superalloy components of space shuttles from 25 to 1200 °C is essential yet challenging. To achieve the objective, we developed an adhesive using silicon-boron modified phenolic resin (Si-BPF) as the matrix and inorganic fillers as additives. The continuous Si– O –Si– O –B– O –B skeleton endowed the Si-BPF with excellent thermal stability. In addition, the inorganic fillers inhibited the thermal decomposition of Si-BPF. The generation of low-melting-point glass phases compensated for the defects in the adhesive. Therefore, within the "300–600 °C weak strength interval", the synergistic effect of Si-BPF and inorganic additives increased the adhesive strength to 17.26 MPa. The formation of intermetallic compounds and the ceramization of the adhesive resulted in a gradual increase in the bonding strength of the composite adhesive with increasing temperature, reaching 34.23 MPa after 1200 °C. The adhesive enabled high-strength bonding for superalloys throughout the wide temperature range, enhancing the application of superalloy components in space shuttles. [ABSTRACT FROM AUTHOR]

The Applications of silica aerogel are limited due to its brittleness and low strength. As a result, it is essential to strengthen and toughen it. Organic nanofibers are one of the preferred reinforcement materials. In this work, we designed and fabricated flexible and compressible nanostructure-assembled aramid nanofiber/silica composites aerogel (ANF/SiO2 aerogel) to improve the mechanical strength and flexibility of silica aerogel without compromising thermal insulation properties. The aramid nanofiber/silica composite aerogels were prepared by immersing the aramid nanofiber wet gel into the silica sol for a certain period of time followed by freeze drying without solvent replacement. The surface modifier 3-aminopropyltriethoxysilane (APTES) was used as a coupling agent to form chemical linkage between the ANF fiber and silica gel. It was observed that APTES can effectively drive the silica sol to infuse into ANF hydrogel, promoting the assembly of silica gel onto the fiber surface and a uniform distribution in the network of ANF. The compressive resilience, thermal stability, and thermal insulation properties of the composite aerogels were evaluated by inducing the silica aerogel into the ANF network to form a protective layer on the fiber and change the pore structure in the ANF network. [ABSTRACT FROM AUTHOR]

Ceramic fiber thread is one of the key components in flexible external thermal insulation blankets, and it has been applied in various fields as a flexible ceramic fibrous material with excellent deformability and high-temperature resistance. However, ceramic fiber threads are often subjected to reciprocating friction motion at specific bending angles, making them highly susceptible to abrade and fracture. Enhancing the abrasion resistance performance of ceramic fiber threads under bending conditions is the future trend and remains a significant challenge. Hence, we design and construct a novel polyurethane-modified coating on the ceramic fiber threads to improve their abrasion resistance performance. The effects of the types and concentrations of modifiers on the microstructure, abrasion resistance property, and tensile property of ceramic fiber threads are systematically investigated. The ceramic fiber threads, after modification with hexamethylene diisocyanate waterborne polyurethane (HDI-WPU) with a concentration of 3%, exhibit excellent abrasion resistance properties. The number of friction cycles at fracture of the modified ceramic fiber thread is more than three times, and the tensile strength is more than one and a half times, that of the original ceramic fiber thread, demonstrating the great potential of the HDI-WPU modifier for enhancing the abrasion resistance performance of ceramic fiber threads. [ABSTRACT FROM AUTHOR]

Mullite fiber-based porous ceramics is one of the most commonly used high-temperature insulation materials. However, how to further reduce the thermal conductivity and improve the strength of such materials has been a challenge in the field of high-temperature insulation. In this paper, mullite micro/nano fiber-based porous ceramic was prepared by introducing mullite nanofibers into mullite microfiber-based porous ceramics and the effect of microfiber/nanofiber weight ratio on the samples properties were characterized and analyzed. Results showed that the compressive strength and high-temperature thermal insulation properties of the porous ceramics increased significantly with an increase in the nanofiber content. For the porous ceramics with similar density (about 0.50 g/cm3), the compressive strength of the sample with a microfibers/nanofibers weight ratio of 1:2 was 1.43 MPa, which was much higher than that of the porous ceramics prepared with only microfibers (0.26 MPa). Meanwhile, the backside thermal equilibrium temperature of the sample with a microfiber/nanofiber weight ratio of 1:2 at 900 °C environment was 355.8 °C, which was much lower than that of the porous ceramic prepared with only microfibers (476.5 °C). In addition, in order to investigate the temperature resistance of mullite micro/nano fiber-based porous ceramics, the sintering temperatures was increased from 1400 °C to 1500 °C. Results shows that the high-temperature thermal insulation performance of mullite micro/nano fiber-based porous ceramics with high mullite nanofiber content decays more seriously. The back-temperature test showed that the thermal equilibrium temperature of the samples with a mullite micron/nanofiber weight ratio of 1:1 in 900 °C environment increased rapidly from 386.3 °C to 454.2 °C when the sintering temperature was increased from 1400 °C to 1500 °C. The preparation of mullite micro/nanofiber-based porous ceramics provides a new strategy to improve the performance of fiber-based porous ceramics. [ABSTRACT FROM AUTHOR]

Carbon fiber (CF) reinforced SiBCN composites were generally considered as key candidates for thermal protection under severe aerodynamic heating in aerospace due to their excellent high-temperature properties, but they were also faced with challenges in stably monitoring the structural integrity of themselves under extreme conditions. Herein, with the introduction of SiC coating, multifunctional CF-SiC/SiBCN composites were fabricated which integrated functions of the thermal protection and the structural health monitoring. Compared to the untreated CF/SiBCN composites, the stability of sensing of CF-SiC/SiBCN composites was greatly improved and the sensitivity of CF-SiC/SiBCN composites maintained at a high level with a gauge factor of 652.65. Furthermore, additional researches revealed that the CF-SiC/SiBCN composites enjoyed a high compressive strength (155.33 MPa), a light weight (1.07–1.61 g/cm3), and a relatively low thermal conductivity (4.02 W/(m·K)), which showed a potentiality of CF-SiC/SiBCN composites to be applied as multifunctional structural components in thermal protection systems. [ABSTRACT FROM AUTHOR]

The mechanical behaviors of single mullite fiber and binder/mullite fiber interface were experimentally investigated. The growth of the mullite grains of the fiber with the increasing calcination temperature greatly affected the tensile and compression strengths of the mullite fibers. As the calcination temperature went up from 1000 °C to 1500 °C, the average tensile strength decreased from 0.954 GPa to 0.191 GPa, and the Weibull modulus decreased from 5.1 to 1.8. The compressive strength was 50–60% of the average tensile strength under the same calcination temperature. The bonding strength of the binder/fiber interface increased with the increase of the calcination temperature. The mechanical properties and fracture mechanism of the mullite fiber-based porous ceramics with different binder contents were comprehensively analyzed based on the mechanical behavior of the single mullite fiber and the binder/fiber interface. [ABSTRACT FROM AUTHOR]

To prepare a coating with a high emissivity and low solar absorption ratio on the surface of aluminum silicate fiber cloth, the sol-gel method was used with silica sol as a binder. In this study, the effects of two white fillers, titanium oxide and zirconia, on the substrate and radiation properties of coatings were compared after heat treatment at 800–1200 °C. The ZrO 2 -based coating had good stability after heat treatment at 800–1200 °C, and maintained its white color, exhibiting solar absorption ratio of approximately 0.14 and emissivity of 0.84. ZrO 2 -based coatings prevented harmful cracking, as observed for the TiO 2 -based coatings after heat treatment, because of the ZrO 2 phase transformation. The ZrO 2 -based coating did not have strong bonding with the substrate, and the substrate strength was improved by maintaining a weak bonding interface. Compared with the TiO 2 -based coatings, which exhibit reduced substrate strength above 1000 °C, the ZrO 2 -based coating was more suitable for the surface of flexible fiber cloths as a temperature-resistant coating with good development prospects. [ABSTRACT FROM AUTHOR]

To improve the oxidation inhibition of TaSi 2 -based high-emissivity coatings at high temperatures, TaSi 2 –SiC coating modified by SiB 6 was prepared on the surface of alumina fibre fabrics. The effects of the SiB 6 content on the surface appearance and emissivity of the coating were investigated, and the mechanical properties of the coated fabrics were compared. When the SiB 6 content in the coating was 2.5%, the borosilicate glass liquid phase generated by SiB 6 oxidation effectively prevented the oxidation of TaSi 2. The bond strength between the coatings and fibre fabric was 207 kPa after calcination at 1200 °C, which was 39% higher than that of the coated fabric without SiB 6. The emissivity of the TaSi 2 –SiC coating, modified by a SiB 6 content of 2.5%, reached above 0.92 after calcination at 1200 °C for 5 h. Therefore, the TaSi 2 –SiC high-emissivity coating modified by SiB 6 has good application prospects in the field of thermal protection. [ABSTRACT FROM AUTHOR]

In order to maintain the strength of flexible substrate while applying the oxidation resistance dense glass coating, a scale structure coating on aluminum silicate fiber cloth was prepared with fused silica powder and silica sol as the binder and MoSi 2 as the emissive agent. The scale structure of the coating with large cracks along the braided grain and small random cracks on the fiber bundles allowed the fiber cloth to retain its flexible properties. Due to the block effect of dense SiO 2 glass phase on oxygen diffusion, the mass loss was only 0.35% after oxidation at 800 °C for 24 h while the average normal emissivity (2–14 μm) remained about 0.88. The MoSi 2 -silicon glass coating could avoid the generation of excessively strong interface with the substrate and improve the tensile strength of the sample to 140.52 MPa. [ABSTRACT FROM AUTHOR]

As a critical structure of thermal protection systems, flexible fibre insulation felts are widely used on the leeward surface of spacecrafts. To enhance the thermal resistance of flexible fibre felts, SiC w -ZrO 2 coatings with different SiC whisker (SiC w) contents were fabricated on the surface of a high-silica-fibre fabric (HSFF) by employing a sol-gel method combined with a spraying route. The introduction of SiC w having a length of 10–50 μm effectively improved the coating integrity. After calcination at 1000 °C for 1 h, the SiC w -ZrO 2 coating containing 8 wt% SiC w did not damage the tensile strength and flexibility of the fibre fabric, and the interfacial bonding strength between the coating and HSFF reached 0.40 MPa, benefitting from the whisker toughening mechanism. The SiC w -ZrO 2 coating with a high emissivity of 0.96 in the 2–14 μm wavelength range reduced the surface temperature of the flexible insulation felt by approximately 300 °C when a butane torch was applied at above 1300 °C. [ABSTRACT FROM AUTHOR]

How to improve the strength of fibrous porous ceramics dramatically under the premise of no sacrificing its low density and thermal conductivity has remained a challenge in the high-temperature thermal insulation field. In this paper, a new kind of high-strength mullite fiber-based ceramics composed of interlocked porous mullite fibers was prepared by nanoemulsion electrospinning and dry pressing method. Results show that as to the porous ceramics with the same density (∼ 0.8 g/cm3), the three-dimensional skeleton structure composed of porous mullite fibers was much denser than that composed of solid mullite fibers. Therefore, porous mullite fiber-based ceramics exhibited a higher compressive strength (5.53 MPa) than that of solid mullite fiber-based ceramics (3.21 MPa). In addition, porous mullite fiber-based ceramics exhibited a superior high-temperature heat insulation property because the porous structure in fibers could reduce the radiant heat conduction. This work provides new insight into the development of high-temperature thermal insulators. [ABSTRACT FROM AUTHOR]

Porous alumina microspheres have attracted significant attention owing to their high mechanical strength and excellent chemical and thermal stability. The emulsion method is considered as a simple and controllable method for the preparation of inorganic microspheres. However, preparing alumina microspheres with the emulsion method is challenging because the emulsification of the precursor is inhibited by the rapid hydrolysis of aluminum alkoxide. Herein, we report a new emulsion method for the preparation of high-porosity alumina microspheres using a combination of ionic and non-ionic surfactants; in this method, the compound surfactants act as a template agent to guide aluminum alkoxide to form a lamellar structure through self-assembly. The decomposition of the templating agent and transformation of the alumina crystal at a high temperature result in structural collapse and formation of lamellar pores. Compound surfactants increased the spheroidization rate of the emulsion from 47% to 63% after hydrolysis, whereas the particle size was decreased by almost half. Additionally, the morphology and porosity of the alumina microspheres were changed. With increasing anionic surfactant content, the porosity increased initially and then decreased. The porosity of the alumina microspheres reached a maximum value of 76% at the 1:1 mass ratio of the non-ionic to anionic surfactants. Heat treatment was found to change the size of lamellar pores, with the pore diameter reaching maximum value at 1300 °C. The compound surfactants also increased the compressive stress and specific surface area of the porous alumina microspheres. [ABSTRACT FROM AUTHOR]