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Carbon Fibers with Low Cost and Uniform Disordered Structure Derived from Lignin/Polyacrylonitrile Composite Precursors
No full textLignin/polyacrylonitrile (PAN) composite precursors and PAN precursors were prepared by wet spinning and then converted into carbon fibers together under different carbonization temperatures. The microscopic morphology, mechanical properties and microstructure of the carbon fibers were studied. All the carbon fibers had dense structure without any visible macrovoids. Carbon fibers with tensile strength of 2.1 GPa and tensile modulus of 224 GPa were obtained from the lignin/PAN composite precursor by carbonizing at 1200 degrees C. Interestingly, the lignin/PAN-based carbon fibers had a unique uniform disordered carbon structure. They were expected to be applied in the fields of electrothermal conversion and thermal insulation, besides composites
Fluorescence detection of malachite green in fish tissue using red emissive Se,N,Cl-doped carbon dots
No full textFacile detection of malachite green (MG), a toxic dye, in aquaculture is urgently demanded for environment and food safety. Herein, we design a novel fluorescent probe, namely red emissive Se,N,Cl-doped carbon dots (CDs), to accurately determinate MG. CDs are prepared by hydrothermal treatment of selenourea and o-phenylene-diamine in HCl solution. This material exhibits excitation-independent dual emissions at 625 and 679 nm, with a high quantum yield of 23.6%. A selective and sensitive fluorescent sensor toward MG is established based on inner filter effect, because both the excitation and emission light of CDs can be strongly absorbed by MG. The fluorescence quenching of CDs is linear to the MG concentration over the range of 0.07-2.50 mu M with a low detection limit of 21 nM. Trace-level analysis of MG in fish tissue is successfully explored, demonstrating the great potential of the proposed sensor for MG monitoring in aquatic products
Competitive Solvation-Induced Concurrent Protection on the Anode and Cathode toward a 400 Wh kg(-1) Lithium Metal Battery
No full textThe unstable electrode/electrolyte interface is one of the key obstacles for practical Ah-level Li metal batteries, but an efficient approach that can construct a stable interface on both a cathode and an anode simultaneously is lacking. Herein, on the basis of a strategy for regulating electrolyte solvation chemistry, fluoroether as a destabilizer is introduced to disturb the Li+ solvation sheath and weaken the interaction between Li+ and carbonyl of carbonate-based solvents, which renders recrystallization of LiPO2F2 from the electrolyte for concurrent surface protection on both the anode and the cathode. Decomposition of LiPO2F2 forms Li3PO4 and LiF, which rebuild the electrode/electrolyte interface and prevent oxidation of carbonate solvent under a high voltage of 4.6 V. Using this strategy, the Li symmetrical cell can sustain 10 mAh cm(-2) Li stripping/plating for 1000 h; a 3.62 Ah pouch cell of Li/Li-rich layered oxide with a N/P ratio of 2.0 and an electrolyte injection ratio of 2.49 g/Ah exhibit an ultrahigh energy density of 430 Wh kg(-1) and an extended lifespan
MOF-Derived Zinc-Doped Ruthenium Oxide Hollow Nanorods as Highly Active and Stable Electrocatalysts for Oxygen Evolution in Acidic Media
No full textIt is highly desirable but challenging to develop active and stable electrocatalysts for oxygen evolution reaction (OER) in acid media. Heteroatom incorporation is an effective strategy of defect engineering for optimizing the intrinsic electrocatalytic activities. In this research, zinc-doped ruthenium oxide (Zn-doped RuO2) nanorods were prepared by using the facile two-step method. It is found that the OER activity of Zn-doped RuO2 catalysts can be readily controlled by varying the amount of Zn dopants. The Zn-doped RuO2 catalyst with 6.4 at.% displays the best electrocatalytic activity with a low overpotential of 206 mV at 10 mA cm(-2), a Tafel slope of 49 mV dec(-1) and a long-term chronopotentiometry test at 10 mA cm(-2) for 30 h towards OER in 0.5 M H2SO4 solution. The enhanced OER performance may be attributed to the defective structures caused by Zn doping and the ultrasmall size of the RuO2 nanocrystals
Theoretical and experimental study on hybrid laser and shaped tube electrochemical machining (Laser-STEM) process
No full textLaser and electrochemical machining (LECM) is extensively researched due to its high efficiency and good surface quality. Laser and shaped tube electrochemical machining (Laser-STEM) is a novel hybrid process, in which both the laser beam and electrolyte jet are guided to the machining zone through the inner hole of a specially designed tubular electrode. This process could be utilized to process small holes with a larger depth and a higher controlled precision, compared with the existing LECM processes. In Laser-STEM, the direct laser processing and the enhanced electrochemical machining (ECM) rate allow the high-efficiency material removal. ECM that is synchronously occurred in the side gap guarantees the high surface quality of the processed small holes. Through the total internal reflection of the laser beam in the inner hole of the tubular electrode, the laser energy is transmitted to the machining zone in high efficiency, and the laser energy has been confined in the inner hole exit area. Theoretical and experimental results showed that the electric current density in the machining zone for ECM could be increased by the assistance of a laser, which enhances the material removal rate of ECM. With the self-developed experimental setup, microcavities with a depth of 2 mm and small holes with a depth of 5 mm have been fabricated. A comparison of the effects of various machining parameters shows that the machining precision and material removal rate were improved by 60.7% and 122.7%, respectively. Both the machining precision and the material removal rate could be increased by using higher laser power. The mechanisms of machining precision improvement by adopting laser to STEM were explored, considering the generation of the passivating layer in the machining zone. Laser-STEM was also adopted to fabricating three-dimensional structures such as groove and channel
Waterjet-assisted Laser Scanning Machining of Large Depth Microgrooves and Microholes with High Efficiency
No full textTo address the issues of recast layer and heat affected zone (HAZ) in laser processing in the air, a new waterjet-assisted laser scanning machining (WALSM) was adopted. Laser processing experiments were conducted on DD6 single crystal (SC) superalloy plate to study the effects of various parameters on the microgroove and microhole machining quality, efficiency and taper angle. Results show that WALSM process can eliminate the recast layer, decrease the taper angle, and reduce the HAZ thickness with no microcracks. Orthogonal analysis shows that the waterjet velocity and pulse frequency are the most significant factors affecting the efficiency of WALSM. To further improve the machining efficiency of WALSM in a larger depth, a hybrid laser processing and WALSM process were proposed for drilling large depth holes with high machining efficiency, high accuracy and good surface quality. The hybrid machining process holds great potential in drilling shaped cooling holes on the turbine blades in the aviation industry
Design and analysis of a novel AFPM with counter-rotation dual rotors based on non-linear magnetic circuit model
No full textThis paper presents a nonlinear iterative magnetic equivalent circuit (MEC) model for a novel counter-rotation dualrotor axial flux permanent magnet synchronous machine (CRDR-AFPMSM). The proposed machine mainly consists of two rotors with opposite rotation directions, two sets of concentrated windings and a stator core sandwiched in between the two rotors. The model takes into account of the nonlinear characteristics of the saturable permeance in the stator core, and the permeance matrix is updated by an iterative procedure to accurately illustrate its nonlinear feature. The air gap flux density, back electromotive force (EMF) and torque are predicted by the model. Based on the nonlinear model, the thickness of the stator yoke is determined. All of the results obtained by the proposed model match with finite element analysis (FEA) results closely, thus the validity of the proposed MEC model is verified
Coercivity and microstructure of sintered Nd-Fe-B magnets diffused with Pr-Co, Pr-Al, and Pr-Co-Al alloys
No full textThe commercial 42M Nd-Fe-B magnet was treated by grain boundary diffusion (GBD) with Pr70Co30 (PC), Pr70Al30 (PA) and Pr70Co15Al15 (PCA) alloys, respectively. The mechanism of coercivity enhancement in the GBD magnets was investigated. The coercivity was enhanced from 1.63 T to 2.15 T in the PCA GBD magnet, higher than the 1.81 T of the PC GBD magnet and the 2.01 T of the PA GBD magnet. This indicates that the joint addition of Co and Al in the diffusion source can further improve the coercivity. Microstructural investigations show that the coercivity enhancement is mainly attributed to the exchange-decoupling of the GB phases. In the PCA GBD magnet, the wider thin GB phases can be formed and the thin GB phases can still be observed at the diffusion depth of 1500 mu m due to the combined action of Co and Al. At the same time, the formation of the Pr-rich shell can also be observed, which is helpful for the coercivity enhancement
Multifunctional Polyhedral Oligomeric Silsesquioxane (POSS) Based Hybrid Porous Materials for CO2 Uptake and Iodine Adsorption
No full textIn this study, two different types of hybrid porous organic polymers (POPs), polyhedral oligomeric silsesquioxane tetraphenylpyrazine (POSS-TPP) and tetraphenylethene (POSS-TPE), were successfully synthesized through the Friedel-Crafts polymerization of tetraphenylpyrazine (TPP) and tetraphenylethene (TPE), respectively, with octavinylsilsesquioxane (OVS) as node building blocks, in the presence of anhydrous FeCl3 as a catalyst and 1,2-dichloroethane at 60 degrees C. Based on N-2 adsorption and thermogravimetric analyses, the resulting hybrid porous materials displayed high surface areas (270 m(2)/g for POSS-TPP and 741 m(2)/g for POSS-TPE) and outstanding thermal stabilities. Furthermore, as-prepared POSS-TPP exhibited a high carbon dioxide capacity (1.63 mmol/g at 298 K and 2.88 mmol/g at 273 K) with an excellent high adsorption capacity for iodine, reaching up to 363 mg/g, compared with the POSS-TPE (309 mg/g)
A novel modification to boron-doped diamond electrode for enhanced, selective detection of dopamine in human serum
No full textIn this work, we proposed a novel modification technique to immobilize nanoparticles by the nanopores on a boron-doped diamond surface, preventing the aggregation of nanoparticles physically and improving the stability of nanoparticles layer by the anchoring effect. All the exposed surfaces of a bare boron-doped diamond were etched into nanoporous form and larger electrochemically active surface area was obtained on the porous boron-doped diamond electrode. The carbon black nanoparticles modified porous boron-doped diamond electrode showed good selectivity to separate the oxidation potential of three molecules, but led to an extra increase in the peak current of dopamine (DA). The carbon black/Nafion modified porous diamond electrode effectively suppress the oxidation current of ascorbic acid (AA), enhancing the sensitivity of DA. The dual layer treatment enables a wide linear range, 0.1-100 mu M and a low limit of detection, 54 nM for DA detection, which is almost unaffected by the excess AA and uric acid (UA). At last, real sample tests of the carbon black/Nafion modified porous diamond electrode was validated by applying to the detection of DA in human serum and dopamine hydrochloride injection, which were found to be promising at our preliminary experiments. Additionally, the fabricated carbon black/Nafion modified porous diamond electrode also demonstrated good stability and long-term functionality. (C) 2020 Elsevier Ltd. All rights reserved