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Epoxy resin with excellent ultraviolet resistance and mechanical properties derived from renewable camphoric acid
No full textGenerally, high-performance epoxy resins, which are derived from aromatic compounds have two major disadvantages of yellowing and brittleness, and thus it presently remains a challenge for the facile synthesis of epoxy resin with excellent ultraviolet resistance and superior strength and toughness. Herein, a novel bio-based epoxy resin diglycidyl ester of camphoric acid (DGECA) was synthesized from the renewable camphoric acid via an efficient and scalable route. The chemical structure of DGECA was carefully characterized by Fourier transform infrared (FT-IR), nuclear magnetic resonance (NMR), and mass spectrometry before being cured with methylhexahydrophthalic anhydride (MHHPA). Compared with the cured diglycidyl ether of bisphenol A (DGEBA)/MHHPA, the cured DGECA/MHHPA system achieved 11.5%, 16.7%, and 109.4% increment in flexural strength (126 MPa vs. 113 MPa), modulus (2.8 GPa vs. 2.4 GPa), and impact strength (6.7 kJ/m(2) vs. 3.2 kJ/m(2)), respectively. Moreover, cured DGECA exhibited extremely lower ultraviolet absorption (0.038A) and better ultraviolet resistance than that of cured DGEBA. This work provides a new strategy to synthesize epoxy resin with excellent ultraviolet resistance and high toughness by using the unique structure of renewable feedstock
Lithium doped nickel oxide nanocrystals with a tuned electronic structure for oxygen evolution reaction
No full textThe electronic structure of catalysts influences the electrocatalytic behavior. Herein, the electronic structure of NiO nanocrystals is modified by doping with a small amount of Li+. The Li+ doped NiO nanocrystals show much better OER activity than pristine NiO and LiNiO2, which is a result of tuned Fermi levels, stronger hybridization between Ni 3d and O 2p, and narrowed energy band gap. This work provides a facile strategy to regulate NiO electronic energy bands to promote OER performance
Nuclear phylotranscriptomics and phylogenomics support numerous polyploidization events and hypotheses for the evolution of rhizobial nitrogen-fixing symbiosis in Fabaceae
No full textFabaceae are the third largest angiosperm family, with 765 genera and similar to 19 500 species. They are important both economically and ecologically, and global Fabaceae crops are intensively studied in part for their nitrogen-fixing ability. However, resolution of the intrasubfamilial Fabaceae phylogeny and divergence times has remained elusive, precluding a reconstruction of the evolutionary history of symbiotic nitrogen fixation in Fabaceae. Here, we report a highly resolved phylogeny using >1500 nuclear genes from newly sequenced transcriptomes and genomes of 391 species, along with other datasets, for a total of 463 legumes spanning all 6 subfamilies and 333 of 765 genera. The subfamilies are maximally supported as monophyletic. The clade comprising subfamilies Cercidoideae and Detarioideae is sister to the remaining legumes, and Duparquetioideae and Dialioideae are successive sisters to the clade of Papilionoideae and Caesalpinioideae. Molecular clock estimation revealed an early radiation of subfamilies near the K/Pg boundary, marked by mass extinction, and subsequent divergence of most tribe-level clades within similar to 15 million years. Phylogenomic analyses of thousands of gene families support 28 proposed putative whole-genome duplication/whole-genome triplication events across Fabaceae, including those at the ancestors of Fabaceae and five of the subfamilies, and further analyses supported the Fabaceae ancestral polyploidy. The evolution of rhizobial nitrogen-fixing nodulation in Fabaceae was probed by ancestral character reconstruction and phylogenetic analyses of related gene families and the results support the hypotheses of one or two switch(es) to rhizobial nodulation followed by multiple losses. Collectively, these results provide a foundation for further morphological and functional evolutionary analyses across Fabaceae
Mesoporous titanium niobium nitrides supported Pt nanoparticles for highly selective and sensitive formaldehyde sensing
No full textA proton exchange membrane fuel cell (PEMFC) gas sensor is a promising and novel gas sensing device. However, the poor sensitivity and strong cross sensitivity of commercial carbon-supported-platinum (Pt/C) remain obstacles to its utilization. Here, we demonstrate that the issue can be addressed using mesoporous titanium niobium nitrides (Ti0.75Nb0.25N) synthesized using a solid-solid phase separation process. Pt nanoparticles supported on ternary transition metal nitrides enable the strong metal support interaction (SMSI), which changes the surface electronic structure and catalytic activity of the electrode material. Compared with the Pt/C-sensor, the selectivity of the Pt/Ti0.75Nb0.25N-based sensor to formaldehyde (HCHO) is significantly higher, while the response to other gases is effectively inhibited. In mixed gas tests, HCHO sensing of the Pt/Ti0.75Nb0.25N-sensor is still not affected (within 3.5% of the standard deviation limit). Furthermore, the Pt/Ti0.75Nb0.25N-sensor exhibits a much higher sensitivity (0.208 mu A per ppm) toward HCHO when compared to the Pt/C-sensor (0.058 mu A per ppm). The Pt/Ti0.75Nb0.25N-sensor also exhibits extraordinary long-term stability due to its electrochemical stability and SMSI of the electrode material. This work hence points to the design and development of a new sensing electrode system, which offers a combination of high selectivity and sensitivity when used in fuel-cell gas sensors
In-situ growing amorphous carbon film with attractive mechanical and tribological adaptability on PEEK via continuous plasma-induced process
No full textThe a-C:H films with plasma-induced in-situ transition layer were fabricated on Polyether ether ketone (PEEK) substrates by continuous acetylene plasma treatment, using plasma-enhanced chemical vapor deposition (PECVD) method. Microstructure, chemical bonding state, mechanical and tribological properties of the asfabricated a-C:H and Cr/a-C:H films were systematically investigated. Based on these, a self-consistent in-situ growth mechanism is discussed in detail. Results show that the a-C:H films with plasma-induced in-situ transition layer endows the treated PEEK substrates high hardness, toughness and adhesion strength. In addition, the interaction of in-situ transition layer and amorphous enhanced phase show better load-bearing capacity in the scratch and tribological test. The failure mechanism of scratch test is proposed and wear mechanisms in vacuum, air and seawater environment are analyzed. Importantly, this novel plasma-induced in-situ transition layer structure is a further development of the concept of gradient coatings in its application to polymers
Carbon-emcoating architecture boosts lithium storage of Nb2O5
No full textIntercalation transition metal oxides (ITMO) have attracted great attention as lithium-ion battery negative electrodes due to high operation safety, high capacity and rapid ion intercalation. However, the intrinsic low electron conductivity plagues the lifetime and cell performance of the ITMO negative electrode. Here we design a new carbon-emcoating architecture through single CO2 activation treatment as demonstrated by the Nb2O5/C nanohybrid. Triple structure engineering of the carbon-emcoating Nb2O5/C nanohybrid is achieved in terms of porosity, composition, and crystallographic phase. The carbon-embedding Nb2O5/C nanohybrids show superior cycling and rate performance compared with the conventional carbon coating, with reversible capacity of 387 mA h g(-1) at 0.2 C and 92% of capacity retained after 500 cycles at 1 C. Differential electrochemical mass spectrometry (DEMS) indicates that the carbon emcoated Nb2O5 nanohybrids present less gas evolution than commercial lithium titanate oxide during cycling. The unique carbon-emcoating technique can be universally applied to other ITMO negative electrodes to achieve high electrochemical performance
Tunable cell structure and mechanism in porous thermoplastic polyurethane micro-film fabricated by a diffusion-restricted physical foaming process
No full textIn this study, porous thermoplastic polyurethane (TPU) micro-films were fabricated using a novel diffusion restricted foaming technology. TPU film with thickness of 40?50 ?m was sandwiched between two polyimide (PI) films by hot compression. Porous TPU films with tunable cell morphology were obtained by manipulating interface bonding force, gas solubility, and driving force for cell growth. The sandwiched PI films could act as a gas barrier film to trigger the enhanced interface cell nucleation, resulting in skin-free cellular TPU film and oriented internal microcellular structure. The possible mechanism of microvoid-assisted interfacial cell nucleation and the preferential cell growth along the thickness direction was proposed with aim to explain the cell morphology and their evolution
Large solubility of silicon in an incongruent nitride: The case of reactively magnetron co-sputtered W-Si-N coatings
No full textHere we examine the equilibrium solubility of silicon in a nitride matrix with a relatively low bond ionicity (i.e., the incongruent W2N). By reactively magnetron co-sputtering under a kinetically unconstrained growth condition, we systematically increased the amount of silicon in W-Si-N coatings, and investigated in detail the composition, chemical bonding, phases, and microstructure through a combination of energy-dispersive x-ray spectrometry, x-ray photoelectron spectroscopy, x-ray diffractometry, scanning electron microscopy, and transmission electron microscopy. Up to a 12 at.% Si content was dissolved in the W2N matrix; the well-crystallized NaCl-structured W-Si-N solid solution exhibited an uninterrupted fibrous growth structure through the whole thickness (similar to 4 mu m). Beyond this critical solubility, the coatings turned into nanocomposites in which some silicon nitride was segregated as a second phase and interrupted the vertical growth of nanocolumns. The large solubility was rationalized in terms of the electrochemical affinity between silicon nitride and the incongruent W2N. This finding highlights the importance of thermodynamic aspects in developing novel nanocomposite structures
Achieving High Thermoelectric Performance of n-Type Bi2Te2.79Se0.21 Sintered Materials by Hot-Stacked Deformation
No full textBismuth telluride has been the only commercial thermoelectric candidate, but the n-type sintered material lags well behind the p-type one in the zT value, which severely limits the further development of thermoelectrics. Here, we report a promising technique named hot-stacked deformation to effectively improve the thermoelectric properties of n-type Bi2Te2.79Se0.21 + 0.067 wt % BiCl3 materials based on zone-melting ingots. It is found that a high grain alignment is maintained during the plastic deformation and the carrier concentration is properly optimized owing to the donor-like effect, leading to an enhanced power factor. Moreover, the lattice thermal conductivity is obviously suppressed due to the emerged phonon scattering centers of dense grain boundaries and dislocations. These effects synergistically yield a maximum zT value of 1.38 and an average zT(ave) of 1.18 between 300 and 500 K in the hot-stacked deformed sample, which is approximately 42% higher than those of the zone-melting ingots
A Review on Disturbance Analysis and Suppression for Permanent Magnet Linear Synchronous Motor
No full textIn high-end testing and manufacturing equipment, a trend exists whereby the traditional servo feed system with a ball screw and rotary motor will gradually be replaced by a direct drive system. The precision motion system driven by a permanent magnet linear synchronous motor (PMLSM) offers several advantages, including high speed, high acceleration, and high positioning accuracy. However, the operating precision of the feed device will be affected by the PMLSM robustness to nonlinear and uncertain disturbances, such as cogging force, friction, thermal effects, residual vibration, and load disturbance. The aim of this paper was to provide a survey on disturbance analysis and suppression approaches to improve the dynamic performance of PMLSM motion systems. First, the origin and inhibition methods of thrust ripple and friction are presented. Second, the mechanisms, modeling approaches, and mitigation measures of thermal effects are introduced. Additionally, the residual vibration characteristics and suppression methods are discussed. Finally, disturbance observers of periodic and aperiodic loads are introduced. These suppression methods from structural design and control compensation are then discussed in order to improve the dynamic response and steady-state accuracy of PMLSM