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Design of novel NiSiAlY alloys in marine salt-spray environment: Part II. Al-Ni-Si-Y thermodynamic dataset
No full textThe NiSiAlY material is a promising candidate to replace NiCrAlY, which can withstand the harsh salt-spray conditions in marine environment. To efficiently design novel NiSiAlY alloys, this work establishes a thermodynamic dataset of the Al-Ni-Si-Y quaternary system using the CALPHAD (CALculation of PHAse Diagrams) approach. We employ this database to calculate and predict the phase constitutions and solidification behaviors of different NiSiAlY alloys concerning the content variations of Al and Si. We have further proposed the selection of the NiSiAlY alloys for serving in marine salt-spray environment with three constraints: (i) outstanding mechanical property; (ii) good high-temperature anti-oxidation; (iii) excellent corrosion resistance. This results in a compositional range of the NiSiAlY alloys with 1 wt% < w(Si) < 5 wt%, 11 wt% < w(Al) < 20 wt% and w(Y) =1 wt%, which corresponds the L1(2) +bcc_B2+Ni5Y ternary phase region at temperatures ranging from similar to 500 to similar to 1000 degrees C. Our predictions are validated by key experiments, suggesting that the model-based description of the Al-Ni-Si-Y system can serve as a guidance to design the novel NiSiAlY alloys in resisting harsh salt-spray environment.(C) 2021 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology
A composite surface configuration towards improving cycling stability of Li-rich layered oxide materials
No full textLi-rich layered oxides are promising positive electrode candidates for next-generation high-energy Li-ion batteries. However, they suffer from a severe gas release issue and side reaction-induced surface degradation resulting in significant capacity fade and voltage decay. Herein, this work proposes a composite surface configuration by coordinating the three different structures from Nb/Al surface doping, surface oxygen vacancies and Al2O3 layer via solution coating. A comprehensive characterization provided persuasive evidence that the composite surface configuration not only mitigates oxygen release but also regulates Li+ ion extraction/insertion during cycling. Due to the reduced side reaction and promoted surface stability, a decent specific discharge capacity of about 270 mA h g(-1) at 0.1C between 2.0 and 4.6 V vs. Li+/Li was achieved with 57.0% capacity preservation after 1000 cycles at 1C. Most importantly, a 20 A h pouch cell fabricated with this surface-modified positive electrode and an SGC/Gr-negative electrode delivered 345 W h kg(-1) in specific energy and retained 77.9% of it at 0.2C after 340 cycles
Constructing a three-dimensional nano-crystalline diamond network within polymer composites for enhanced thermal conductivity
No full textIn order to meet the requirement of thermal performance with the rapid development of high-performance electronic devices, constructing a three-dimensional thermal transport skeleton is an effective method for enhancing the thermal conductivity of polymer composites. In this work, a three-dimensional porous diamond framework was prepared by depositing nano-crystalline diamond on alumina foam which was impregnated with epoxy to obtain a nano-crystalline diamond@alumina foam/epoxy composite. The epoxy composite with nano-crystalline diamond@alumina foam demonstrated a thermal conductivity of 2.21 W m(-1) K-1, which was increased by 1063% in comparison with pure epoxy. The thermal conductivity of the epoxy composite measured under various conditions and heat transport applications demonstrates that it possesses excellent thermal transportation and stability properties. This work provides a new idea to significantly enhance the thermal transportation properties of epoxy composites in the application of advanced packaging materials
Facile synthesis of hemiacetal ester-based dynamic covalent polymer networks combining fast reprocessability and high performance
No full textDynamic covalent polymer networks (DCPNs) can address the recycle or reuse issue of thermosets due to their network rearrangement from the dynamic bond exchange. However, developing DCPNs combining fast reprocessability and high performance through a facile and green method is still a huge challenge. Herein, a facile and green method (in situ polymerization and dynamic cross-linking (ISPDC)) was utilized to produce hemiacetal ester-based DCPNs which exhibited fast reprocessability and high performance. No solvent and no purification were required, and the facile synthesis process also showed readily regulated performance for the DCPNs. The obtained DCPNs could be continuously reprocessed by extrusion as well as compression remolding; meanwhile their solvent resistance, thermo-physical and mechanical properties are excellent on account of their high cross-link density. The small-molecule model reactions and theoretical calculation demonstrated that hemiacetal ester exchange follows a dissociative mechanism without or with an extra carboxyl group. This work studied DCPNs which showed great potential to be efficiently recycled via reprocessing and scaled up. It tallies with sustainable development and contributes to carbon neutrality
Taxonomic notes on the genus Dumasia (Fabaceae)
No full textThe phylogenetic relationships between species of the genus Dumasia have been revealed by previous studies. However, some taxonomic problems still remain to be resolved. In this article, we recognize 10 species of Dumasia. We re-circumscribe D. yunnanensis Y. T. Wei & S. K. Lee, promote D. nitida var. kurziana Predeep & M. P. Nayar as a distinct species, and synonymize D. hunanica Y. K. Yang, L. H. Liu & J. K. Wu with D. hirsuta Craib. D. prazeri Predeep & M. P. Nayar is here confirmed as a newly recorded species for China, and D. zhangjiajieensis Y. K. Yang, L. H. Liu & J. K. Wu, a distinct species with winged peduncles which was overlooked in previous studies, is also reported here. We provided detailed descriptions, expanded distributions, habitat and phenological information, conservation status, and taxonomic notes for these five species. An updated key to the genus is also provided
Research on Trajectory Optimization of Multilateral Thin Metal Rubber Automatic Laying Based on Virtual Fabrication Technology
No full textHerein, an in-depth exploration of the trajectory optimization process of multilateral thin metal rubber (MT-MR) in laying to build a virtual fabrication model that reflects the morphology and macro-properties of material is done. According to the MT-MR automatic blank laying process, which is based on the iteration mechanism of a local coordinate system in global space, and dynamically coupling with the Rodrigues rotation matrix, a parametric curve model under 3D random trajectory is constructed. Based on the evaluation of the background grid projection method, the optimization of the blank forming path of MT-MR is discussed in depth using the improved multi-objective genetic algorithm, and a MT-MR complex network structure model based on the path optimization laying process is constructed. The structure and performance optimization of MT-MR is further verified by combining virtual fabrication technology and experimental means. The results show that compared with MT-MR with traditional experience-based trajectory laying, the component with automatic trajectory laying optimization based on an improved genetic algorithm has a more uniform and compact wire turn structure. Therefore, an in-depth discussion of the optimization of the MT-MR automatic laying trajectory with a special configuration is presented and some theoretical guidance for the application of this material laying process is provided
The Effects of Forming CeFe2 on Phase Structure and Magnetic Properties in Ce-Rich Nd-Ce-Fe-B Permanent Magnetic Materials
No full textThe decomposition of the Nd-Ce-Fe-B phase to form CeFe2 has been usually believed to have an important positive effect on the magnetic properties of Nd-Ce-Fe-B permanent magnetic materials. In this work, a new decomposition process of the Nd-Ce-Fe-B phase on the formation of the CeFe2 phase was observed to play a negative role in its magnetic properties. It is demonstrated that the Nd-Ce-Fe-B phase decomposes into non-magnetic CeFe2, accompanied by the precipitation of Fe soft-phase. The kinks usually occurring in the demagnetization curves of Ce-rich Nd-Ce-Fe-B magnets have been determined to be related to the Fe soft-phase. Instead of using CeFe2 as a grain-boundary phase, another Ce-Cu boundary phase has been explored to efficiently improve the coercivity of Ce-rich Nd-Ce-Fe-B magnets, provided that the Ce-Cu boundary phase has an appropriate Ce to Cu ratio. The present results contribute to the mechanism comprehension and high-performance design of Nd-Ce-Fe-B permanent magnetic materials.</p
Polarization-Insensitive Broadband THz Absorber Based on Circular Graphene Patches
No full textA polarization-insensitive broadband terahertz absorber based on single-layer graphene metasurface has been designed and simulated, in which the graphene metasurface is composed of isolated circular patches. After simulation and optimization, the absorption bandwidth of this absorber with more than 90% absorptance is up to 2 THz. The simulation results demonstrate that the broadband absorption can be achieved by combining the localized surface plasmon (LSP) resonances on the graphene patches and the resonances caused by the coupling between them. The absorption bandwidth can be changed by changing the chemical potential of graphene and the structural parameters. Due to the symmetrical configuration, the proposed absorber is completely insensitive to polarization and have the characteristics of wide angle oblique incidence that they can achieve broadband absorption with 70% absorptance in the range of incident angle from 0 & DEG; to 50 & DEG; for both TE and TM polarized waves. The flexible and simple design, polarization insensitive, wide-angle incident, broadband and high absorption properties make it possible for our proposed absorber to have promising applications in terahertz detection, imaging and cloaking objects.</p
Nickel-Catalyzed Reductive Cross-Coupling of Alkyl Bromides and Chlorosilanes
No full textA novel nickel-catalyzed highly selective reductive cross-coupling of alkyl bromides and chlorosilanes to construct the C-Si bond has been developed. Under benign reaction conditions, a series of structurally interesting organosilanes can be accessed without Ni-catalyzed isomerization. The utility of this chemistry is illustrated by further transformations of the product. Moreover, the radical mechanism of the reaction is illustrated by control experiments
Selective oxidation of thermoelectric TiNiSn
No full textMultiscale modelling, involving thermodynamic assessment and molecular dynamics based on density functional theory, was employed to unravel oxidation mechanisms pertinent to half-Heusler TiNiSn (space group F-43 m), in particular counterintuitive Ni inertness. O-2 molecules dissociate and chemisorb onto TiNiSn(0 0 1) and TiNiSn (110), which is followed by ingress of O. Both Ti and Sn egress, while Ni is less mobile. Such diffusion processes yield point defects (vacancies and interstitials) and give rise to Ti and Sn binary oxide formation, while Ni is inert, which may be corelated to its relatively low mobility. Based on the Mulliken analysis and thermodynamics at 900 K, the Ti oxide formation sequence is suggested to be Ti2O3 -> Ti3O5 -> TiO2 -> TiO. These data explain the experimental observations on the Ni inertness during oxidation of TiNiSn