carbon fiber-reinforced silicon carbide composites (c/Sic) are widely used in lightweight aerospace structures for thermal protection due to its excellent mechanical properties. The low interfacial shear strength of t...
详细信息
carbon fiber-reinforced silicon carbide composites (c/Sic) are widely used in lightweight aerospace structures for thermal protection due to its excellent mechanical properties. The low interfacial shear strength of the composites decreases its performance and limits its application. To investigate the shearing performance of c/Siccomposite, interlaminar shear and in-plane shear tests were conducted. Real-time X-ray micro-computed tomography (XcT) non-destructive testing technology is an effective method for damage analysis of composite materials. The damage mechanisms of 2D plain weave c/Siccomposites prepared by chemical vapor infiltration process under interlaminar shear loading are investigated using the combination of XcT and acoustic emission detection system. The in-situ XcT results reveal the damage visualization mechanisms of the composites and the damage evolution process including matrix damage, interfacial debonding and fiber fracture. The failure mechanisms and morphology of the shear effect for 2D plain weave c/Sic were analysed.
c/c-Zrccomposites are promising thermal structural materials for aerospace applications. However, until now, the reported c/c-Zrccomposites exhibited a porous matrix and weaker mechanical properties. In this study, ...
详细信息
c/c-Zrccomposites are promising thermal structural materials for aerospace applications. However, until now, the reported c/c-Zrccomposites exhibited a porous matrix and weaker mechanical properties. In this study, the matrices of c/c-Zrccomposites were modified by slurry infiltration in order to improve density and properties. Different slurry powders such as Sic, Zrc, and ZrB2 were used to densify the c/c-Zrccomposites. After slurry infiltration, the loose c-Zrc matrix was connected to a dense matrix, and some ceramic powders settled on the surface of the composites. The density of the composites increased from 1.94 to 2.42 +/- 0.06 g cm-3, while the porosity decreased from 39.4 +/- 4.4% to 10.3 +/- 1.9% after infiltration with various slurries. The ablation and mechanical properties of the c/c-Zrccomposites improved significantly by matrix modification. The flexural strength of the composites increased from 116 to 269 +/- 21 MPa after slurry infiltration. Furthermore, the ablation properties of c/c-Zrccomposites infiltrated with the ZrB2 slurry showed the lowest linear rate (24.7 mu m s-1) and mass recession rate (7.5 mg s-1).
A rapid method was developed to fabricate c/c-Zrc-Sic-cuxSiy composites with low open porosity by precursor infiltration and pyrolysis combining with pressure assisted reactive melt infiltration. Dominant phases of Zr...
详细信息
A rapid method was developed to fabricate c/c-Zrc-Sic-cuxSiy composites with low open porosity by precursor infiltration and pyrolysis combining with pressure assisted reactive melt infiltration. Dominant phases of Zrc and Sic with scattered cuxSiy inclusions were present in continuous infiltrated matrix, in which the dimension of submicron Zrc particles displayed gradient change. At ablation test, the heat absorbing effect of cuxSiy-phase and formation of protective ZrO2-SiO2 cover enhanced the ablative property of composites for short-time ablation, causing ablation rates of 30 s ablation reached 1.7 +/- 0.1 mu m/s and 1.3 +/- 0.1 mg/s, respectively. As ablation time extends to 60 s, the massive consumption of Si-phase damaged the integrity of surface oxide cover, but the partial melted ZrO2 improved the viscosity and self-healing ability of ZrO2-SiO2 mixture, protecting substrate from further erosion. Thus, ablation rates were increased and decreased to 3.8 +/- 0.2 mu m/s and 1.2 +/- 0.1 mg/s, respectively.
The low carbon-to-nitrogen (c/N) ratio in wastewater will inhibit pollutant removal, and more seriously, it will cause an increment of nitrous oxide (N2O) emissions of constructed wetlands (cWs). Raising the c/N ratio...
详细信息
The low carbon-to-nitrogen (c/N) ratio in wastewater will inhibit pollutant removal, and more seriously, it will cause an increment of nitrous oxide (N2O) emissions of constructed wetlands (cWs). Raising the c/N ratio of wastewater is an effective way to solve this problem, while it may cause secondary pollution and is costly. Assembling plant diversity promotes N removal, while the effects of plant diversity and increasing c/N ratio on global warming potential (GWP) combined by N2O and methane (cH4) are lack of comparison. In this study, 108 cW microcosms were established to explore the effects of increasing the c/N ratio from 1 to 5 and assembling plant diversity on N removal and GHG emissions. Results showed that when the c/N ratio was 1, (1) increasing species richness reduced N2O and cH4 emissions then reduced the GWP by 70%;(2) the presence of Arundo donax in microcosms reduced GWP by 72%;(3) an A. donax x Tradescantia fluminensis x Reineckia carnea mixture resulted in a high N removal and decreased the GWP per g N removal by 92% with a cost increment of 0.05 USD per m(3) wastewater treated;and (4) as the c/N ratio increasing to 5, the GWP per g N removal of monocultures was reduced by 96%, but the cost increased by at least 0.29 USD per m(3) wastewater treated. In summary, configuring plant diversity in cWs is an efficient, clean, and cost-effective measure to treat wastewater with a low c/N ratio.
In order to further improve the ablative resistance of c/c-Zrc-Siccomposites, YF3 modified c/c-Zrc-Siccom-posites were prepared by molten salt assisted reactive melt infiltration, and the infiltration mechanism and ...
详细信息
In order to further improve the ablative resistance of c/c-Zrc-Siccomposites, YF3 modified c/c-Zrc-Siccom-posites were prepared by molten salt assisted reactive melt infiltration, and the infiltration mechanism and ablative behavior of the composites were discussed. After fluorination, diffusion, adsorption and reaction of yttrium in ionic melt generated by K2ZrF6, YF3 was generated inside c/c-Zrc-Siccomposites, which effectively seals the existing pores and cracks in c/c-Zrc-Sic material. YF3 modified c/c-Zrc-Siccomposites can form yttrium oxide stabilized zirconia during the ablation process, and improve the ablation stability of the oxide layer compared with c/c-Zrc-Siccomposites, the mass ablation rate and linear ablation rate of YF3 modified c/c-Zrc-Siccomposites are reduced by 42.61% and 90.14% respectively.
To investigate the ablation mechanism of the mullite modified c/c-Sic-Hfccomposites prepared by precursor infiltration pyrolysis, a 60 s single ablation and 30 s x 3 cyclic ablations were carried out at heat fluxes o...
详细信息
To investigate the ablation mechanism of the mullite modified c/c-Sic-Hfccomposites prepared by precursor infiltration pyrolysis, a 60 s single ablation and 30 s x 3 cyclic ablations were carried out at heat fluxes of 2.38 and 4.18 MW/m2, respectively. Results showed that the ablation temperatures played a vital role in the ablation process. Under the lower heat flux condition, the single ablation behavior was mainly influenced by the escape of gaseous oxidation products and slight airflow erosion, while cyclic ablation was influenced primarily by the stresses induced by crystallization transformation during the heating-cooling process. Under the higher heat flux condition, HfSiO4 was gradually generated at the interface between HfO2 and SiO2, which stabilized the crystallization of HfO2. The ablation behavior under higher heat flux was mainly influenced by thermal-induced stresses and mechanical forces of high-velocity airflow.
The synthesis of cuO/c nanocomposites was fabricated using an uncomplicated and eco-friendly method by cyperus rotundus (c. rotundus) leaf extract. The formation of nanocomposites and their size were optimized with va...
详细信息
The synthesis of cuO/c nanocomposites was fabricated using an uncomplicated and eco-friendly method by cyperus rotundus (c. rotundus) leaf extract. The formation of nanocomposites and their size were optimized with various factors, such as operational parameters, viz. exposure time, temperature, and concentration of the precursor, by response surface methodology (RSM). The effects of the synthesis of cuO/c nanocomposite samples and their characterization by various analytical techniques such as UV, XRD, XPS, EDX, SEM, and TEM have been reviewed and confirmed. The XRD patterns revealed that the biosynthesized cuO/c sample exhibited a monoclinic and crystalline structure. Moreover, the elements available in nanocomposites were determined as cu 2p, O 1 s, and c1s using XPS analysis. The TEM pictures reveal the morphology of the nanocomposites as spherical in form, with an average size of 30 nm. Additionally, synthesized cuO/c nanocomposites were examined for toxic effects on the mortality of two-winged insect larvae, and they were absolutely found to be extremely active and considerably kill larvae. The molecular docking study found that the nanocomposites were able to bind to the target protein with high affinity, which suggests that they are likely to be effective larvicidal agents. Our existing analysis findings can open up a replacement void for the larvicidal analysis exploiting biosynthesized nanocomposites.
Aimed to enhance the high-temperature service performance of c/Siccomposites in high-speed aircraft thermal protection system, in this article, pitch-based carbon fibers were used to construct high thermal conductive...
详细信息
Aimed to enhance the high-temperature service performance of c/Siccomposites in high-speed aircraft thermal protection system, in this article, pitch-based carbon fibers were used to construct high thermal conductive channels to improve the heat transfer capability of c/Siccomposites. The results revealed that the as-prepared composites equipped with 4.7 times higher thermal conductivity than that of conventional c/Siccomposites. The oxyacetylene flame ablation test confirmed that the constructed high thermal conductive channels, which quickly conducted the heat flow from the ablation center area to other areas is the main reason of as-prepared composites exhibiting a very impressive ablation resistance property. Briefly, the ablation temperature of the as-prepared composite surfaces considerably dropped by about 300 & DEG;ccompared with conventional c/Siccomposites, while the linear ablation rate and mass ablation rate of the composites are 1.27 & mu;m/s and 0.61 mg/s respectively, which is superior to many recent reports, demonstrating that this article provides a simple but highly effective measure to improve the ablation resistance property of c/Siccomposites.
In order to enhance ablation resistance of c/ccomposites, Zr1-xHfxc and Sic were intro-duced into c/ccomposites, and ablation behavior of the composites was studied. In the composites (cHZS), Hfc and Zrc produced a ...
详细信息
In order to enhance ablation resistance of c/ccomposites, Zr1-xHfxc and Sic were intro-duced into c/ccomposites, and ablation behavior of the composites was studied. In the composites (cHZS), Hfc and Zrc produced a solid solution, and solid solubility of Hfc in Zrc was 0.4, which indicated that the solid solution was defined to be Zr0.6Hf0.4c. compared with c/c-Zrc-Siccomposites (cZS), cHZS possessed a better ablation resistance. During ablation of cHZS, Zr0.6Hf0.4c is oxidized to produce HfO2 and ZrO2, and HfO2 particles played a pinning effect, which fixed molten oxide coating. Moreover, due to low cTE of HfO2 and decreasing content of ZrO2, there was a smaller thermal stress and its distribu-tion area on cHZS ablation surface, thus thermal stress corrosion was weakened to strengthen integrity of oxide coating. In this case, a complete and continuous HfO2-ZrO2 coating was formed on cHZS surface, which could resist oxygen diffusion and reduce oxidation rate of the composites.& cOPY;2023 The Authors. Published by Elsevier B.V. This is an open access article under the cc BY-Nc-ND license (http://***/licenses/by-nc-nd/4.0/).
The transition-metal-catalyzed intramolecular hydroarylation of alkenes has been recognized as a straightforward approach for the construction of 3,3-disubstituted 2,3-dihydrobenzofurans. The reactions mainly rely on ...
详细信息
The transition-metal-catalyzed intramolecular hydroarylation of alkenes has been recognized as a straightforward approach for the construction of 3,3-disubstituted 2,3-dihydrobenzofurans. The reactions mainly rely on the reductive Heck reaction of aryl halides or the direct c-H bond activation of arenes bearing a directing group. This work realizes the Rh-catalyzed intramolecular hydroarylation of olefin-tethered benzocyclobutenols via c-c bond activation, which offers an alternative approach to 3,3-disubstituted 2,3-dihydrobenzofurans bearing a 4-beta-keto moiety. The methodology features 100% atom economy and pH-and redox-neutral conditions, and is applicable to the late-stage functionalization of complex molecules. The asymmetric variant has also been achieved with excellent enantioselectivities.
暂无评论