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Stable, superfast and self-healing fluid coating with active corrosion resistance
No full textFluid material can recover from damage rapidly with no demand of external triggering in contrast with the traditional self-healing material which presents low healing efficiency and demands external triggering, such as heat, light, moisture, electricity, etc. However, due to its low viscosity, fluid material is easy to flow away from the surface and thus it is difficult to form a stable coating on the surface to provide practical corrosion resistance to the substrate. Herein, a stable and superfast self-healing coating on steel substrate has been obtained by incorporating carbon nanotube (CNT) into the fluid matrix of epoxy resin (EP) or silicone oil (OIL). To further achieve the active corrosion resistance, 1H, 1H, 2H, 2H- perfluorooctyltriethoxysilane (PTES) which can react with the water inside the coating is added. The coating possesses superfast (tens of seconds) self-healing properties against millimeter-scale scratch repeatedly and excellent corrosion resistance in the aqueous solution of HCl (1 M) and NaOH (1 M). In-situ self-healing and electrochemical behavior in scanning vibrating electrode technique (SVET) measurement indicate the fluid coating possesses infinite self-healing capacity theoretically. Due to its excellent durability and infinite self-healing capacity with short responding time, the optimized fluid coating can be a smart corrosion barrier coating for metals
Self-powered ultraviolet photodiode based on lateral polarity structure GaN films
No full textIn this work, we report on a self-powered ultraviolet photodiode realized using lateral polarity structure (LPS) GaN films. The opposite nature of the polarization charge yields different barrier heights at the standard Ni/Au Schottky contact interface of N-polar and III-polar GaN films. As a result, a natural nonzero built-in potential is obtained in the LPS GaN photodiode, which showed photoresponsivity even at 0 V applied bias. The self-powered mechanism inside such an LPS GaN photodiode is discussed in detail by a combination of simulation prediction and experimental validation. Furthermore, a variation in the doping concentration of the adjacent III- and N-polar GaN domain is shown to improve the photoresponsivity compared to the conventional III-polar photodiode. Thus, this work validates that the LPS GaN photodiode is a promising candidate to realize self-powered operation and a general design rule for the photodiode with in-plane built-in potential
Hidden Charge Order in an Iron Oxide Square-Lattice Compound
No full textSince the discovery of charge disproportionation in the FeO2 square-lattice compound Sr3Fe2O7 by Mossbauer spectroscopy more than fifty years ago, the spatial ordering pattern of the disproportionated charges has remained hidden to conventional diffraction probes, despite numerous x-ray and neutron scattering studies. We have used neutron Larmor diffraction and Fe K-edge resonant x-ray scattering to demonstrate checkerboard charge order in the FeO2 planes that vanishes at a sharp second-order phase transition upon heating above 332 K. Stacking disorder of the checkerboard pattern due to frustrated interlayer interactions broadens the corresponding superstructure reflections and greatly reduces their amplitude, thus explaining the difficulty of detecting them by conventional probes. We discuss the implications of these findings for research on hidden order in other materials
Analysis of coumarin in food and plant tissue without extraction based on voltammetry of microparticles
No full textThe detection of coumarins in real samples often requires a complex extraction process, which makes the analytical technique unable to meet the actual detection needs. In this work, we proposed a novel analytical technique based on the electrochemical reduction behavior of coumarins. This technique does not require complex pretreatment of the real sample, such as extraction and filtration. The sample particles were directly immobilized on the surface of the electrode after co-mixing with graphene. After a simple pre-reduction process, the amount of coumarin in the real sample can be evaluated by voltammetry. We have analyzed the feasibility of this technique by using cakes, fruits and different organ tissues of Glehnia littoralis. The results showed that this new analytical technique successfully achieved the rapid detection of coumarin content in real samples. The amount of coumarin in apples was 0.045 mg/g. The amount of coumarin in the roots, leaves and fruits of Glehnia littoralis was 0.037 mg/g, 0.011 mg/g and 0.079 mg/g, respectively
Helium-induced damage in U3Si5 by first-principles studies
No full textUranium silicide U3Si5 has been explored as an advanced nuclear fuel component for light water reactor to enhance the accident tolerance. In this paper, in order to understand the fuel performance of U3Si5, the primary point defects, secondary point defects, and the dissolution of He gas were studied by first-principles methods. Compared with U atoms and another type of Si-2 atoms, Si-1 atoms far from intrinsic Si vacancies are more likely to form point defects, implying that Si vacancies are prone to form separate single vacancies rather than vacancy clusters in the initial stage. From the calculated anti-site defect energies, it can be predicted that non-stoichiometric U-rich phase of U3Si5 are more likely to be formed than Si-rich phase, which are consistent with the chemical analysis of experimentally sintered Si-lean U3Si5 sample. It can be found that a single He atom favors residence in the interstitial site in the U layer directly above/below the intrinsic vacancy. It can also be seen that Vac-U, Vac-Si-1, and Vac-Si-2 vacancies can energetically accommodate up to 4, 0, and 3 He atoms, respectively. The formation of secondary vacancy defects is strongly dependent on the helium concentration. The current results show that the He-filled vacancy can promote the formation of adjacent secondary vacancy, leading to the formation of gas bubbles. This work may provide theoretical insights into the He irradiation-induced damage in U3Si5 as well as provide valuable clues for improving the design of the UN-U3Si5 composite fuel
Hyperbranched flame retardant to simultaneously improve the fire-safety, toughness and glass transition temperature of epoxy resin
No full textIt is highly desired yet very challenging to overcome the flammability and brittleness of epoxy resin without compromising its glass transition temperature (T-g). Herein, an epoxy-terminated hyperbranched flame retardant (EHBFR) was designed and synthesized from 9, 10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO), and renewable protocatechualdehyde as well as guaiacol. When the synthesized EHBFR was taken to modify diglycidyl ether of bisphenol A (DGEBA), it is found that the incorporation of EHBFR remarkably improved its fire safety, endowing it with a UL-94 V-0 rating and a limiting oxygen index (LOI) of 33.0 vol%. Meanwhile, the notched impact strength of modified DGEBA at 25 and -196 degrees C (quenched by liquid nitrogen) exhibited significant increment by 135% (from 3.39 to 7.97 KJ/m(2)) and 114% (from 2.34 to 5.01 KJ/m(2)), respectively. Moreover, the T-g of modified epoxy resin did not show any decrease, and even increased from 172 to 194 degrees C when the content of EHBFR was 10 wt%, due to the synergistic effect of rigid DOPO-containing groups and high crosslink density. This work offers an efficient strategy for constructing high-performance epoxy thermosets with excellent flame retardancy, superior toughness and strength, as well as elevated T-g
A review on the tensile behavior of fiber-reinforced polymer composites under varying strain rates and temperatures
No full textThe fiber-reinforced polymer (FRP) composites are currently widely used in infrastructure construction, and the study on the dynamic performance and temperature sensitivity is still under investigation. Understanding the effects of strain rate and temperature on the tensile behaviour of FRP composites is vital to design the composite structures under harsh conditions (earthquake, explosion, or impact). Therefore, this study comprehensively reviews tensile performance of FRP composites under several strain rates (quasi-static, low, intermediate, and high) and temperatures. The tensile strength of FRP composites depends on the strain rates, temperatures, and coupling effect. The failure patterns of FRP materials are also reviewed at different strain rates and temperatures and found that fiber cracking and fiber pullout become dominant at low and high strain rates, respectively, which can help gain insight into failure mechanisums of FRP composites. (c) 2021 Elsevier Ltd. All rights reserved
Density Functional Theory Study of Influence of Oxide Thickness and Surface Alloying on Cl Migration within alpha-Al2O3
No full textInsertion and migration of chlorine atoms (Cl) in alpha-Al2O3 were studied by density functional theory calculations focusing on the influence of oxide thickness and doping by Mg, Cu and Si. Work function, electronic band gap, and insertion energy were calculated to explore thermodynamics of Cl migration. Partial density of state (PDOS) calculations revealed the role of dopants in the electronic character of metal-O and Al-Cl bonds. Work function data showed the effect of Cl insertion into the oxide film on the corrosion resistance. Cl can locate at an O vacancy (V-O) with a large exothermic insertion energy, independent of oxide thickness, but can only locate at superficial Al vacancy (V-Al) exothermically. The energy barrier for Cl migration via neighboring V-O increases with oxide thickness, and is 2 similar to 2.5 eV for thicker oxides. Cl insertion causes a work function reduction exceeding 2 eV, implying a decreased corrosion resistance. The inhibition of Cl migration by Si-doping can be explained by a more intense hybridization peak of Si-O over Al-O in the PDOS profile, while the reduction of energy barrier by Mg-/Cu-doping probably is due to the deviation of metal-s state from the Fermi energy, thus facilitating Cl movement within the oxide
Characterization of ta-C film on micro arc oxidation coated titanium alloy in simulated seawater
No full textThe harsh marine environment puts forward higher performance requirements for titanium alloy parts, and it is urgent to develop advanced surface protection technology. In this paper, micro arc oxidation (MAO)/tetrahedral amorphous carbon (ta-C) composite coatings were fabricated via MAO processing and filtered cathodic vacuum arc (FCVA) system on TC4 titanium alloy. The surface morphologies, tribological properties and corrosion resistance in simulated seawater of the coatings were investigated. The results showed that, compared with the monolayer of MAO coating or ta-C film, the MAO/ta-C composite coating still showed porous characteristics and had an improved bonding force. Due to compact oxide ceramic coating of MAO coating and self-lubrication of taC film, the MAO/ta-C composite coating had the lowest friction coefficient (0.13) and width of wear scar (356.84 um) in all samples. The lowest corrosion current density (8.321 x 10-9 A/cm2) and highest corrosion potential (-0.012 V) in the simulated seawater solution confirmed the most effective corrosion protection provided by the MAO/ta-C coating. These research results could provide important support for promoting the application of titanium
Early sex determination of Ginkgo biloba based on the differences in the electrocatalytic performance of extracted peroxidase
No full textGinkgo biloba is a dioecious plant. Male ginkgoes are mainly used in landscaping, while females are mainly used for fruit production. However, sex identification of ginkgo is a difficult task, especially at the seedling stage. In this work, we present for the first time the use of electrochemical techniques for the identification of ginkgo sex based on the differences in peroxides within male and female ginkgos. Graphene was used to concentrate peroxides in ginkgo extract, thereby improving electrochemical signal sensitivity. The electrochemical reduction of hydrogen peroxide catalyzed by peroxidase was used as a prob for sex determination in ginkgo. This electrochemical identification technique can be used not only for the analysis of adult ginkgo, but also successfully for the analysis of tissue culture seedlings and live seedlings. This electrochemical sensor has excellent discrimination ability due to the difference in peroxidase content in the leaves and petiole of ginkgo of different sexes. This electrochemical sensor allows for a rapid identification of the sex of ginkgo and has a very strong potential for field analysis. (c) 2021 Elsevier B.V. All rights reserved