Nitrogen-enriched hierarchically porous carbons (HPCs) were synthesized from a novel nitrile-functionalized benzoxazine based on benzoxazine chemistry using a soft-templating method and a potassium ...hydroxide (KOH) chemical activation method and used as electrode materials for supercapacitors. The textural and chemical properties could be easily tuned by adding a soft template and changing the activation temperature. The introduction of the soft-templating agent (surfactant F127) resulted in the formation of mesopores, which facilitated fast ionic diffusion and reduced the internal resistance. The micropores of HPCs were extensively developed by KOH activation to provide large electrochemical double-layer capacitance. As the activation temperature increased from 600 to 800 °C, the specific surface area of nitrogen-enriched carbons increased dramatically, micropores were enlarged, and more meso/macropores were developed, but the nitrogen and oxygen content decreased, which affected the electrochemical performance. The sample HPC-800 activated at 800 °C possesses a high specific surface area (1555.4 m2 g–1), high oxygen (10.61 wt %) and nitrogen (3.64 wt %) contents, a hierarchical pore structure, a high graphitization degree, and good electrical conductivity. It shows great pseudocapacitance and the largest specific capacitance of 641.6 F g–1 at a current density of 1 A g–1 in a 6 mol L–1 KOH aqueous electrolyte when measured in a three-electrode system. Furthermore, the HPC-800 electrode exhibits excellent rate capability (443.0 F g–1 remained at 40 A g–1) and good cycling stability (94.3% capacitance retention over 5000 cycles).
Carbonaceous materials have been accepted as a promising family of anode materials for lithium‐ion batteries (LIBs) owing to optimal overall performance. Among various emerging carbonaceous anode ...materials, hard carbons have recently gained significant attention for high‐energy LIBs. The most attractive features of hard carbons are the enriched microcrystalline structure, which not only benefits the uptake of more Li+ ions but also facilitates the Li+ ions intercalation and deintercalation. However, the booming application of hard carbons is significantly slowed by the low initial Coulombic efficiency, large initial irreversible capacity, and voltage hysteresis. Many efforts have been devoted to address these challenges toward practical applications. This paper focuses on an up‐to‐date overview of hard carbons, with an emphasis on the lithium storage fundamentals and material classification of hard carbons as well as present challenges and potential solutions. The future prospects and perspectives on hard carbons to enable practical application in next‐generation batteries are also highlighted.
Hard carbons with high reversible capacity, excellent rate capacity, superior cycling stability, and low working potential, are better positioned to be chosen as the next‐generation advanced anode materials compared to soft carbons and graphite. Herein a comprehensive analysis of classification, formation, microstructure, and lithium storage fundamentals of hard carbons is provided, which is expected to be very attractive for the energy material communities.
A novel biomass-based carbon material was successfully prepared from black locust by KOH chemical activation in combination with surface modification by heat treatment with ammonia solution for ...enhancing CO2 adsorption. The textural and surface characteristics of the prepared activated carbons were analyzed with N2 adsorption isotherms, scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), elemental analysis, and X-ray photoelectron spectroscopy (XPS). The results show that the modified activated carbon possesses a high surface area of 2511 m2/g, a large micropore volume of 1.16 cm3/g, and a high nitrogen content of 7.21 wt %. The adsorption behavior of CO2 onto all activated carbon samples was experimentally evaluated by a volumetric method at three different adsorption temperatures of 0, 25, and 50 °C under atmospheric pressure (1 bar). High CO2 uptakes of 7.19 and 5.05 mmol/g at 0 and 25 °C were achieved for the sample AC-KOH-N due to its well-developed micropore structure and abundant basic nitrogen-containing functionalities. The thermodynamic parameters indicate that both physical adsorption and chemical adsorption mechanisms for CO2 adsorption coexist in the sample AC-KOH-N. The sample AC-KOH-N also shows a good selectivity for CO2/N2 and fast adsorption kinetics that be easily regenerated with superior cyclic stability after multiple cycles. These results suggest that the obtained biomass-based activated carbon is promising for CO2 capture.
This study is carried out to investigate the material removal characteristics in elliptical ultrasonic assisted grinding (EUAG) of monocrystal sapphire using single diamond abrasive grain. The ...scratching experiments are performed to develop a fundamental understanding of the ductile–brittle transition mechanism during EUAG of monocrystal sapphire. An elliptical ultrasonic vibrator attached with a sapphire substrate was set up on a multi-axis CNC controlled machining center equipped with a single point diamond tool. The vibrator was constructed by bonding a piezoelectric ceramic device (PZT) having two separated electrodes on a metal elastic body, and an elliptical ultrasonic vibration was generated on the end-face of the metal elastic body when two phases of alternating current (AC) voltages with a phase difference are applied to their respective electrodes on PZT. In scratching experiments, the effects of ultrasonic vibration on the critical depth of cut ac for the ductile–brittle transition region and the material removal ratio, i.e., the ratio of the removed material volume to the machined groove volume, fab, are investigated by the examination of the scratching groove surfaces with SEM and AFM. The obtained results show that the critical depth of cut in EUAG is much larger than that in conventional grinding without vibration (CG), and even the bigger vibration amplitude leads to a greater improvement. Although the values of fab in the ductile–brittle transition region in both EUAG and CG are less than 1, that in EUAG is bigger than that in CG. Furthermore, as the vibration amplitude increases, the value of fab is increased to eventually be close to 1. These show that it is prone to achieve a ductile mode grinding in greater vibration amplitude. It was also found that in the process there are two kinds of material removal modes, i.e., continuous cutting and discontinuous cutting modes, which are determined by the relationship between values of vibration amplitude and depth of cut. This study validates that the elliptical ultrasonic assisted grinding method is highly effective in ductile mode machining of hard and brittle materials.
•Elliptical ultrasonic assisted scratching experiments are performed.•The critical depth of cut is significantly increased by using ultrasonic vibration.•Material removal ratio in EUAG is increased in ductile–brittle transition region.•It is prone to achieve ductile region with greater vibration amplitude in EUAG.•The continuous and discontinuous cutting modes occur in EUAG.
In this paper, we attempts to investigate cutting mechanisms in high-speed cutting of Al6061/SiCp/15p composites using a semi-phenomenologically based damage model in the equivalent homogeneous ...material (EHM) framework. By combining macroscale EHM modeling and underlying microscale physical mechanisms, a feasible semi-phenomenological plastic model is proposed for prediction of cutting forces and chip morphology during high-speed turning Al6061/SiCp/15p composites. This model incorporates the modified Weibull weakest-link effect to represent the strain-based damage evolution in large deformations. This proposed semi-phenomenological constitutive model is implemented by compiling material subroutines into cutting finite element (FE) codes. The effects of the critical shear stresses on chip formation that depend on the tool-chip frictional coefficient are accounted for in the cutting FE model. The chip formation mechanism affecting material removal behaviors during high-speed turning is further investigated. The capabilities of the proposed constitutive model are evaluated by comparing cutting forces and chip morphologies between experiments and simulations at different cutting speeds associated with strain rates. The EHM-based and microstructure-based models are further compared in both computational efficiency and accuracy. The simulation results show that the developed semi-phenomenological constitutive formalism and cutting model are promising and efficient tools for further investigation of dynamic mechanical and cutting behaviors of particle-reinforced composites with different volume fraction and particle size.
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•Strengthening mechanisms of dispersion of SWCNTs in an aluminum matrix using MD.•MD simulations make use of a RVE accounts for geometrical constraints using PBCs.•A critical CNT ...length exists beyond which significant enhancement of AMC develops.•Fracture behavior of Al/CNT composite is mainly governed by morphology of CNTs.
In this paper, the strengthening and the deformation mechanisms associated with the aligned dispersion of single-walled carbon nanotubes (CNTs) in an aluminum matrix composite (AMC) are investigated at the atomic level. Our molecular dynamics (MD) simulations make use of a representative volume element (RVE) that accounts for geometrical constraints that manifest themselves in periodic boundary conditions (PBCs) of AMCs possessing nearly perfect crystalline structure. The tensile properties characterization of AMCs reinforced by aligned CNTs of different length and diameter was studied using the RVE concept. Our work reveals that there exists a critical CNT length beyond which the addition of a small amount of CNTs led to a significant enhancement in stiffness and strength of AMCs. It further reveals that the elasticity and strength enhancement is proportional to CNT diameter. The atomistic results are compared with those predicted by the well-known rule of mixture (ROM) technique and reveal that the ROM can provide a reasonable estimate of properties provided that the CNT length was comparable to a certain critical length. In addition, the AMCs reinforced by armchair CNTs show better enhancement in the mechanical behavior of reinforced matrix than those strengthened by zigzag CNTs. It further reveals that the fracture behavior of Al/CNT composite is mainly governed by size characteristics of CNTs.
A three-dimension (3D) finite element (FE) end milling model with equivalent homogenous material (EHM) model, which was drawn from the quasi-static and SHPB (Split Hopkinson pressure bar) tests, has ...been developed by using ABAQUS/Explicit in order to describe the machining process of SiC
p
/Al6063/30P composites. The model is verified by milling experiments and it is found that the predicted milling forces at different combinations of feed rate and rotation speed are consistent with those in milling experiments, and the prediction error of the peak value of
F
y
and
F
x
can be controlled within 20%. Moreover, the general shapes of the predicted chips are very similar to the experimental ones, but the application of EHM material model leading to the limitation of the simulated chip morphology such as cracks on chip contact surface and free surface caused by the existence of hard SiC particles cannot be described. Hence, further microstructure-level 3D FEM model which can reveal the interactions between particles and matrix and their effect on the chip formation mechanism of SiC
p
/Al6063composites becomes very necessary.
An investigation is carried out to analyze and quantify the wear mechanisms of resin-bonded diamond wheel in Elliptical Ultrasonic Assisted Grinding (EUAG) of monocrystal sapphire. The EUAG is a new ...grinding method proposed by the present authors in which an elliptical ultrasonic vibration is imposed on the workpiece by using an elliptical ultrasonic vibrator. In this paper, a series of grinding experiments under the presence/absence of ultrasonic vibration assistance are performed. The grinding forces and work-surface roughness are measured, and the wheel surface is examined too. The experimental results indicate that during grinding, the steady process region performed in EUAG is longer than that in Conventional Grinding (CG) by 20%, meaning that the grinding wheel has a longer sharp cutting period in EUAG. It is validated that the main wear mechanisms in EUAG is micro-fracture and cleavage of abrasive grains, which has a positive effect on the better grinding performance, such as lower grinding forces, force ratio
F
n
/
F
t
, wheel loading, and smoother work-surface. This study demonstrates that the improved grinding performance of diamond wheel can be realized by using EUAG method.
Juvenile onset open-angle glaucoma (JOAG) affects patients before 40 years of age, causing high intraocular pressure and severe optic nerve damage. To expand the mutation spectrum of the causative ...genes in JOAG, with a view to identify novel disease-causing mutations, we investigated MYOC, OPTN, NTF4, WDR36 and CYP1B1 in a cohort of 67 unrelated Chinese JOAG patients. Whole exome sequencing was used to identify possible pathogenic mutations, which were further excluded in normal controls. After sequencing and the use of a database pipeline, as well as predictive assessment filtering, we identified a total of six mutations in three genes, MYOC, OPTN and CYP1B1. Among them, 2 heterozygous mutations in MYOC (c. 1109C > T, p. (P370L); c. 1150G > C, p. (D384H)), 2 heterozygous mutations in OPTN (c. 985A > G, p.(R329G); c. 1481T > G, p. (L494W)) and 2 homozygous mutations in CYP1B1 (c. 1412T > G, p.(I471S); c. 1169G > A, p.(R390H)) were identified as potentially causative mutations. No mutation was detected in NTF4 or WDR36. Our results enrich the mutation spectra and frequencies of MYOC, OPTN and CYP1B1 in JOAG among the Chinese population. Further studies are needed to address the pathogenicity of each of the mutations detected in this study.
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